Session 7
Understanding ore systems though
precise geochronology, isotope tracing
and microgeochemistry
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Chapter 7-1
7-1
Origin of titanomagnetite-ilmenite mineralization,
Arsentyev gabbro-syenite massif, Transbaikalia, Russia
Roza Badmatsyrenova, Dmitriy Orsoev
Geological Institute SD RAS, Ulan-Ude, Russia
Abstract. The study of endogenic titanomagnetite-ilmenite ores are
of interest as they present a number of petrologic problems. One
such problem is determining their genetic connection with alkalimafic and mafic complexes and associated phosphorus enrichment.
The Arsentyev gabbro-syenite massif is representative of these systems and provides an ideal situation in which a detailed study allows further understanding of interrelated magmatic and ore-formation processes. It is shown that an oxide-ore liquid separated
from a parental silicate melt during early stages of subalkaline mafic magma crystallization.
Keywords. Liquid immiscibility, geochemistry, ore mineralization
1
Introduction
Titanomagnetite-ilmenite ores sourced from various deposits are considered as a premier source of commercial
iron and vanadium. Select deposits additionally contain
significant titanium enrichment providing a mineral
source for titanium production. Currently ores from large
tonnage, high grade deposits are now mined from
Bushveld (the South Africa Republic), Lac-Tio (Canada),
Panzhihuan (China), Kachkanar (Russia). Ore occurrences
are known in the Urals, Kareliya, East Sayan, Transbaikalia,
and Far East. The Arsentyev gabbro-syenite massif with
titanomagnetite-ilmenite mineralization is representative
of this association. Understanding iron ore deposit genesis
is problematic, with particular difficulties in rectifying
magmatic titanomagnetite-ilmenite deposits formation, yet
a comprehensive understanding is essential for exploration.
Therefore, studies identifying genetic processes occupies a
special place in the analysis of ore genesis in magmatic systems. In addition to fundamental understanding, the study
of already known of ore complexes is necessary for development of prospecting criteria and interpretations of results, which may form the basis for rating production
feasability of titanomagnetite-ilmenate ores.
2
and have the geochemical signature of alkaline basalts.
Two intrusive phases, each of them being followed by formation of dike complexes, form the Arsentyev massif
(Fig. 1b). The first phase consists of a stratified series pyroxenites, olivine and kersutite gabbros, gabbros, anorthosites and syenite. The second phase includes the
rocks of the syenite series.
The titanomagnetite-ilmenite mineralization is confined to the stratified gabbro-anorthosite series. This mineralization is subdivided into syngenetic and epigenetic
by morphological features and degree of localization. The
widespread syngenetic mineralization is represented by
disseminated and net-textured ores while the restricted
epigenetic mineralization is represented by massive ores.
As a rule, disseminated ores are confined to apatite-free
and apatite ore gabbros and pyroxenites with 10 to 25
vol.% ore minerals. Ore gabbros are advanced among most
differentiated intrusive region, where they alternate with
leucogabbro (up to anorthosite) and gabbro.
The thickness of orebodies are highly variable but prevail as ventricular and vein ore. The massive ores are usually contained within area associated with disseminated
and net-textured ores and are related to protomagmatic
fracturing. The contact between ore bodies with host
gabbroids are tectonic as a rule.
Geological setting and structure
The Arsentyev massif is located at the central part of the
Monostoy ridge west of the Arsentyevka village (Fig. 1a).
The massif outcrops over a 20 km2 area.
The Arsentyev massif is defined by intrusions of syenite-pyroxenite-gabbro with a high titanium ultramafic-mafic association (Badmatsyrenova et al. 2004). These
intrusions are related to rift-like structures of various ages
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Roza Badmatsyrenova · Dmitriy Orsoev
3
Mineral composition and geochemistry
The disseminated ores are divided into titanomagnetiteilmenie ore and apatite-titanomagnetite-ilmenite ore with
apatite contents of 10-15 wt.%. Apatite-titanomagnetiteilmenite ores have a subordinate value. Magnetite and ilmenite are the main ore minerals. They are intimately
associated, forming xenomorphic aggregates interstial to
silicate minerals and always crystallizing after the silicates. The grains size varies from 0.04 to 3 mm. They also
occur as small inclusions in pyroxene, kersutite and plagioclase but in insignificant amounts. The separate grains
of magnetite and ilmenite display variable degrees of isomorphism depending on their quantitative ratio. Both
“homogeneous” magnetite having roughly a pure iron
composition and titaniferous magnetite with dissolution
structures are observed. Ilmenite also has variable composition based on the concentration of Fe3 +.
In addition to ore minerals and apatite, the ores contain varying amounts of olivine, pyroxene and plagioclase. Amphibole and biotite are also present. Sulphides
and spinel are present but economically insignificant compared to the apatite-titanomagnetite-ilmenite ores. The
apatite-bearing ores have significantly more sulphides and
spinel compared to the massive and disseminated irontitanium ores.
The mineral composition of massive ores is rather restricted. The ore is dominated (70-90 vol.%) by aggregates of magnetite, titanomagnetite and ilmenite. Magnetite is the dominant ore mineral with a half to a third
as much ilmenite. The grains of ore minerals are larger,
up to 5 mm, in massive ores compared with disseminated
ore minerals. Separate, fine-grained pyrite, pyrrhotite,
chalcopyrite, marcasite and pentlandite are present in the
ores at insignificant amounts. The constant presence of
apatite at insignificant amounts and increased contents
of spinel (up 10-30%) are characteristic of the massive
ores. Kersutite is also present.
Titanomagnetite from the massive ore contains 6.48
wt.% TiO2 and is seen as thin intergrowths of magnetite,
ilmenite, spinel and ulvöspinel(?). Trellised or reticulated
titanomagnetite from ore gabbros contain appreciablly
less TiO2 (0.18-0.91 wt.%). Finally, titanomagnetite from
host gabbros contains only TiO2 (0.06-0.08 wt.%).
The concentration of TiO2 in ilmenite forming lamellar inclusion in titanomagnetite found in disseminated
ore is 48.68 wt.% while concentration of TiO2 in massive
ore is 53.31 wt.%. Spinel in disseminated ores contain 0.1
to 0.3 wt.% TiO2, whereas spinel from massive ores forming tear-shaped structures of immiscibility in magnetite
contains TiO2 up 4.94 wt.% and in ilmenite in massive
ore contains 0.96 wt.% TiO2. Manganese concentration
in ilmenite is 0.52 to 1.57 wt.%. Mn in magnetite is 0.07
to 0.19 wt.%. The magnesium contents in magnetite-bear-
ing ore much more exceeds (up to 1.57 wt.%) contents in
ore gabbro and gabbro (0.08 wt.%). Mg concentrates in
lamella of ilmenite in massive ores are 7.94 wt.%. The
aluminium in magnetite in massive ores contains up to
1.73 wt.%. The maximum contents Al in rocks are 0.11
wt.%. Ilmenite is aluminum-poor (0.06 wt.% Al2O3). Dissolution structures in massive ores are present with Al2O3
up to 5.55 wt.%. Aluminium in titanomagnetite is associated with spinel intergrowths.
Amphibole (TiO2 up to 6 wt.%) is identified as an accessory mineral in ores. Large kersutite crystals are distinctly brown colour and pleochroic suggesting greater
Fe and Ti content. Analyzed amphibole have the high contents Al2O3, Ti and alkalis in comparison with gabbro from
other units.
Biotite in massive ore is FeO deficient with proportionaly
more MgO, TiO2, Na2O than in dissiminated ores.
Clinopyroxene composition directly correlates to plagioclase composition. The most magnesian pyroxene (MgO
14.56 wt.%) is associated with the most basic plagioclase
(An40). The pyroxene Mg# changes from 80 to 74 %.
Fayalite olivine is enriched with increasing ore abundances. Nickel contents correlate with the olivine.
Apatite is often the only mineral in mafic rocks that
yield information about volatile composition. Fluorapatite is found in gabbros and ores of the Arsentyev massif.
The fluorine contents in ores (1 to 2 wt.%) is noticeably
less than in gabbro (2 to 3.5 wt.%). High fluorine and
phosphorus concentrations in connection with increased
alkalinity of the primary basalt magma facilitates volatile immiscibility and support ore cluster formation. REE
concentrations in apatite from gabbro have typical for
basalt distribution: the relative concentration of lanthanides increases from HREE to LREE, the degree of division is marginal (La/Yb = 21-36), and a negative Europium anomoly is evident. Conversely, apatite from ores
does not have a negative Europium anomoly. The new
data does not contradict immiscibility of titanomagnetiteilmenite ores and apatite formation.
The geochemical data suggest an iron-bearing silicate
melt of large anion trivalent iron complexes (Fe2O42 -)
formed after oxidation by interaction with alkaline oxide
components and water. The predominance of oxidic iron
in magnetite points to an oxidizing environment. It is probable that the formation of anion complexes Fe2O42- instead of cation of bivalent iron facilitates initiation of
immiscibility in the melt system resulting in an ore-forming and a silicate liquid.
4
Conclusions
Microprobe analysis shows that magnetite, ilmenite, amphibole and biotite of the massive ores are significantly
richer in TiO2, Al2O3, MgO and Na2O than the minerals
Close
Chapter 7-1 · Origin of titanomagnetite-ilmenite mineralization, Arsentyev gabbro-syenite massif, Transbaikalia, Russia
of the disseminated ores. The massive ores are characterized by high V (1400 to 1600 ppm), Zn (200 to 500 ppm),
and Cr (21 to 36 ppm) concentrations and low concentrations of Sr (60 to 210 ppm), Co (73 to 112 ppm) and
P2O5 (0.06 to 0.21 ppm) compared to the disseminated
ores that have very high concentrations of the main components (TiO2, Fe2O3 and FeO). Variations in ore compositions are illustrated on the ratio plots of petrogenic and
trace elements. A later independent formation of the massive ores is indicated by significantly lower values of Cr/
V and Ni/Co ratios than in the disseminated ores if using
these ratios as indicators of ore formation stages. Using
classification based on chemical composition, the ores of
the Arsentyev massif belong to the iron-titanium-vanadium type.
The study of distribution of noble metals has shown
that the ores have platinum enrichment: Pt contents of
massive ores are up to 6.3 ppb and Ag contents up to 2.8
ppm while Pt contents of disseminated one are < 2 ppb
and Ag 1 ppm.
727
Conditions favorable for phosphorus induced liquid
immiscibility can be expected in silicate-salt melts
(Krigman, Krot 1991), or immiscibility may be induced
by another component, possibly ferrous iron complexes.
For example, it is possible to form gabbroid complexes
associated with apatite-ilmenite and titanomagnetite
mineralization, which, in opinion of some researchers
(McBirney, Nakamura 1974, Marakushev 1987), is connected to immiscibility decomposition of the parental melt
into a salic and a femic melt, where the latter representing an ore magma with the contents P2O5 7 to 8%.
Two genetic ore types in the Arsentyev massif are allocated: the first type, massive titanomagnetite-ilmenite
ores, are of immiscibility genesis while the second type,
ore gabbro, formed in result of crystallization differentiation of a basalt magma.
Acknowledgements
This work was supported by the Russian Foundation for
Basic Research (grant No 05-05-97246), Russia President
grant for leading science school No Sh-2284.2003.5, Russian Science Support Foundation.
References
Badmatsyrenova RA, Orsoev DA (2004) Computer simulation of
titanomagnetite-ilmenite mineralization formation, Arsentyev
massif, Transbaikalia, Russia. In: Proc. of the Interim IAGOD Conference, Vladivostok, Russia, 1-20 September, 2004, pp. 407-410
Krigman LD, Krot TV (1991) Stable phosphate-aluminosilicate liquation in magmetic melts Geokhimia. 11: 1548-1561 (in Russian)
Marakushev AA (1987) Geology and mineralogy of the anorthosite
associations. Vladivostok, p.17 (in Russian)
McBirney A.K., Nakamura Y (1974) Ann. Report Director geophys.
Lab. Washington, 348 pp
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Chapter 7-2
7-2
Direct dating of ore minerals: A feasibility study of
the Pb-Pb isotope step-leaching technique
K. Bassano, J. Hergt, R. Maas, J. Woodhead
pmd*CRC, School of Earth Sciences, The University of Melbourne, Australia
Abstract. Pb-Pb step-leaching (PbSL) is a digestion technique based
on sequential acid treatment of a mineral resulting in the selective
recovery of radiogenic and common Pb components from the crystal
lattice, making single-phase Pb-Pb dating possible. Developed originally by R. Frei and colleagues at Bern, the technique was recently
applied to Proterozoic garnets to test the reliability of PbSL as a
dating tool in multiply deformed terranes (Tonelli 2002).
This study builds on previous observations and tests the reliability of PbSL in directly dating ore minerals such as sulfides (chalcopyrite, pyrite, pyrrhotite/pentlandite) and oxides (magnetite),
thereby obtaining the timing of mineralisation from a phase that is
unambiguously linked to the ore-forming process. This is based on
the often surprisingly high U contents (relative to what might be
anticipated), yielding rather higher than expected initial U/Pb ratios in several types of low-Pb sulfides. The technique is applied to
well-constrained samples from a number of predominately Australian mineral deposits covering a range of mineralization types.
Keywords. Pb-Pb, step-leaching, ore minerals, direct dating
1
Introduction
The mechanism of Pb isotope unmixing in step-leaching
was examined by Frei et al. (1997) who proposed two main
processes; the surface/crystallographic site dependent hydrolysis of metal cations, and the progressive remobilisation
of radiogenic Pb from the leached gel-like structure. Different rates of these processes during progressive leaching
results in an effective separation of common and radiogenic Pb, producing generally linear unmixing arrays with
age significance in the 206Pb/204Pb vs 207Pb/204Pb diagram.
Benefits of PbSL over bulk U-Pb and Pb-Pb techniques
include the ability to:
– detect sub-microscopic U-rich inclusions using the
distinct variations in 208Pb/206Pb (i.e. time-integrated
Th/U) between host mineral and inclusions such as
zircon or monazite
– date a wide range of minerals with low-U; minerals
generally thought to be unfavourable for conventional
U/Pb dating
– obtain ‘single’-mineral isochron ages without the need
for analysing associated minerals to produce isotopic
dispersion on isochrons
Although previous authors (eg Collerson et al. 2002)
have obtained age estimates on (mixed) ore minerals using PbSL prior to this study, further investigation is re-
quired into the circumstances in which this technique may/
may not be reliably applied.
2
Discussion
In this study the technique has been applied to well-constrained samples from a number of Australian ore deposits, including the analysis of chalcopyrite and magnetite from Broken Hill (BHT), Mt Isa, Ernest Henry (IOCG)
and Osborne (IOCG). Magnetite and pentlandite/pyrrhotite from the Merensky Reef in the Bushveld Complex have
also been studied.
Studies of chalcopyrite from Copper Blow (Broken Hill)
yielded promising results. Lead isotope ratios obtained,
particularly in the second leach step, indicate the presence of radiogenic Pb with 206Pb/204Pb ratios ranging up
to ~57. As chalcopyrite at Copper Blow occurs with
torbernite (U-rich), typical grains were interrogated using the SEM to confirm that the Pb compositions reflect
those of the chalcopyrite and not inclusions. Results for
magnetite from the same deposit display greater spread
in the 206Pb/204Pb (~23 to 183). The age estimates obtained
from these co-genetic minerals are the same (magnetite:
1094±89Ma; MSWD=250; chalcopyrite: 1071±210;
MSWD=213), to within error, although the uncertainties
are quite large. Unlike the 206Pb/204Pb and 207Pb/204Pb ratios of these samples, 208Pb/204Pb displays very little variation, retaining values typical of common lead (~37 to 38).
This indicates that the mineralising fluid from which these
phases grew carried U but not Th into the system.
Both chalcopyrite and magnetite were also analysed
from the Osborne deposit. The chalcopyrite displays radiogenic values (206Pb/204Pb ~20 to 48) that generate an
age estimate of 1252±190Ma.
Preliminary studies at Ernest Henry indicate the
samples are also highly radiogenic. Chalcopyrite shows a
large spread in 206Pb/204Pb (~18 to 257) generating an age
estimate of 1590±17Ma (MSWD=1). The variation in
206Pb/204Pb ratios displayed by the associated magnetite
is even greater (~214 to 965) although the scatter is considerable. These data yield a poorly constrained age of
1044±450Ma because, although the range in ratios is considerable, ‘gaps’ in the array contribute to the large errors
obtained as the isochrons become dominated by one or two
points. Further analyses of these samples with varied leaching protocols produced consistently scattered data sets.
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K. Bassano · J. Hergt · R. Maas · J. Woodhead
In order to determine if the technique is producing
the ‘correct’ age estimates, three samples from the
Merensky Reef in the Bushveld Complex, South Africa
(two magnetites and one mixed pyrrhotite /pentlandite
sulfide) where analysed. Samples from this orthomagmatic
deposit were selected due to the generally widely excepted
age of the Bushveld Complex ore system. The resulting
leach steps from each of these samples displayed little or
practically no spread in 206Pb/204Pb and 207Pb/204Pb. The
majority of the age estimates generated from this data
fall within error of the “known” age of the Merensky Reef,
however the uncertainties are large, most likely due to
the minor data spread.
3
Evaluation of the leaching process
ICPMS trace element analyses of the study samples have
been undertaken in order to examine possible causes for
the apparently variable success of this technique. First,
the U and Pb contents of bulk-separates will clearly influence how much radiogenic ingrowth can occur relative to the common Pb component, and hence how great
the spread in the Pb isotope ratios may be during stepleaching. How this varies between particular ore deposit
types is a central question of this study. Another important question is to determine the factors that control the
retention or mobility of different elements (particularly
Pb, but also how this behaves relative to other trace elements). The acid leaching mechanism cannot be the same
as that determined in the step-leaching experiments of
silicates (where Si-O bonds are broken during hydrolysis
reactions). The assessment of trace element mobility is
conducted via analysis of the leachates from different leach
steps, and comparisons between these and data for bulkseparates. Finally, the extent to which variations in the
initial Pb isotope composition within samples has influenced the scatter in isochrons will be explored. This involves the analysis of numerous separate aliquots of material to check for levels of heterogeneity in their Pb isotope compositions.
Acknowledgements
The authors would like to thank the many members of
the pmd*CRC who have provided us with the well-constrained materials required for this study.
References
Collerson KD, Kamber BS, Schoenberg R (2002) Applications of accurate, high-precision Pb isotope ratio measurements by multicollector ICP-MS. Chem Geol 188: 65-83
Frei R, Villa IM, Nagler ThF, Kramers JD, Przybylowicz WJ, Prozesky
VM, Hofmann BA, Kamber BS (1997) Single mineral dating by
the Pb-Pb step leaching method: Assessing the mechanisms.
Geochim Cosmochim Acta 61: 393-414
Tonelli M (2002) An evaluation of Pb step leaching geochronology
as applied to high-grade metamorphic terranes. PhD Thesis,
University of Melbourne (unpubl)
Close
Chapter 7-3
7-3
Rutiles in eclogite from the Sulu UHPM Terrane:
A preliminary study
Chen Zhenyu, Chen Yuchuan, Wang Denghong, Xu Jue, Zhou Jianxiong
Institute of Mineral Resources, Chinese Academy of Geological Science, Beijing, 100037, China
Abstract. In recent years more than 40 rutile-bearing eclogite ore bodies
have been discovered among the thousands of eclogite bodies in
the Sulu Utra-High Pressure Metamorphic (UHPM) terrene. Rock- and
ore-cores obtained by the Chinese Continental Scientific Drilling
(CCSD) Project revealed the presence of several hundred meters of
rutile-bearing eclogites. This paper presents a preliminary petrographic, trace element, and Pb isotope study of rutile ores in eclogite.
Rutiles occur as inclusions, intergranular infillings, remnant replacements, and hydrothermal infillings in the host rocks. The ore minerals
define four stages of rutile mineralization and metamorphic evolution in the eclogites. Electron microprobe (EMP) trace element analysis
of three rutile specimens show that different occurrences of eclogite
also have different trace element compositions in rutile. These compositional differences may reflect different source rocks for the
eclogites. Peak metamorphic temperatures were calculated using the
Zr geothermometer in rutile. The Pb isotopic compositions of rutile
obtained by step-fuse analysis of single grains of rutile did not fall on
one growth line, but show similar variation between different samples.
This implies that the Pb isotopic compositions of rutile may have been
disturbed during its growth. This variation could be used to trace the
growth history of the rutile, and further to trace the process of continental subduction- exhumation.
Keywords. Rutile, eclogite, petrography, trace elements, Pb isotope,
Sulu UHPM terrene
1
Introduction
The Sulu ultra-high pressure metamorphic (UHPM) terrene
is the product of the Triassic collision involving the north
China and Yangtze cratons. There are thousands of eclogite
bodies of different size and occurrence in the UHPM belt
in the Sulu terrene, and more than 40 rutile-bearing eclogite
ore bodies have been recently discovered. The total reserves
of rutile ore amount to several million tons (Huang J P., et
al. 2003). The main hole of the Chinese Continental Scientific Drilling (CCSD) project is located at Maobei, Donghai,
in the southern part of the Sulu UHPM terrene (a simplified geological map is showed in Fig. 1). Drilling to 5100m
at this locality has recently completed. Rock- and ore-cores
obtained by the CCSD revealed rutile-bearing eclogites
amounting to several hundred meters (Xu et al. 2004).
The rutile deposit in the Sulu UHPM terrene is a typical eclogite-type rutile deposit. To assess the relationship
between UHPM and the mineralization of rutile in
eclogite, we have conducted a preliminary study on the
rutile from the main hole of the CCSD. In this study we
focus on the different rutile occurrences, petrography,
trace element composition and Pb isotopic composition.
2
Petrography of rutile and titanium minerals in
eclogite
The rutile ore bodies mainly occur in massive eclogites,
as strips and lenses. Rutile-bearing eclogites have at least
three different occurrences: (1) xenoliths in ultra-mafic
serpentines, e.g. in Xugou and Jiangzhuang; (2) lenses in
marbles e.g. in Yanmachang and Banzhuang; (3) metamorphosed intrusive complex rocks in Donghai. The
eclogites show variable mineral assemblages and chemical compositions, and indicate diverse origins for their
protoliths (Zhang et al. 2004). The observation and documentation of both the rock- and ore-cores obtained by
CCSD reveal that the major titanium mineral phases of
economic interest are rutile and titano-magnetite. The
most important ore-bearing rock types are normal rutile
eclogite, quartz eclogite associated with phengite-rutile
eclogite and kyanite-rutile eclogite. The modal content
of rutile in eclogite is 2%~5% (vol.) and is as high as
8%~10% (vol.) (Xu et al. 2004).
Detailed petrographic investigation reveals that rutile
in eclogite mostly occurs in four types: (1) as inclusions
in garnets, omphacites or zircons, which may have crystallized during prograde metamorphism (coesite or its
pseudomorph can be found coexisting with rutile in the
same garnet, omphacite or zircon host); (2) as intergranular infilling grains between garnets and omphacites. In
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Chen Zhenyu · Chen Yuchuan · Wang Denghong · Xu Jue · Zhou Jianxiong
this stage, metamorphism reached its peak conditions,
and rutile crystallized simultaneously with eclogite-face
minerals such as garnets and omphacites. This is the main
crystallization stage of rutile; (3) as replacement remnant,
at the amphibolite-face retrograde metamorphism stage.
Garnets and omphacites are altered to hornblende and
plagioclase. Rutlie is also partly altered to ilmenite or
titanite; (4) as hydrothermal infilling forms. Rutile fills in
the cleavages and cracks as veins, strings or megacrysts.
This rutile occurrence may have crystallized at the
greenschist-facies metamorphic stage. At this time, hydrothermal fluids extracted components of mineralization from wall rocks and deposited them in cleavages and
cracks in the rocks. On the other hand, the early rutile
phase is partly or totally altered to ilmenite or titanite. As
for the above-mentioned four occurrences, the second one
is the most abundant, and accounts for about 90% of the
gross rutile ore reserves. Rutile and titano-magnetite that
were altered to ilmenite and titanite during retrogressive
metamorphism led to a drop in grade of the titanium
mineralization.
content of these elements, averaging 615ppm, 324ppm,
3457ppm and 3333ppm for Cr, Nb, Fe and V respectively.
In the Nb-Cr diagram defined by Zack, et al. (2004b),
protoliths of these three eclogites all plot in the “mafic
rocks” field. Temperature calculated from Zr content
in rutile showed that the peak temperature of metamorphism for these eclogites was 550~575o for Qinglongshan, 565~615 o for Banzhuang and ~716 o for
Machang. These temperature values are comparable with
those calculated by the cation-exchange geothermometer
of host minerals.
4
3
Pb isotopic composition of rutile
Trace elements in rutile
Rutile has long been considered to be an important carrier of high field strength elements (HFSE; Zr, Nb, Mo,
Sn, Sb, Hf, Ta, W). It also plays a key role in subduction
zones by retaining HFSE in the restite/residuum during
dehydration and melting reactions. Recent studies by
Zack et al. (2002, 2004a, 2004b) show that the trace elements in rutile can give us more information than just
the dominant control of HFSE in eclogite. For example,
the Nb, Cr content in rutile can be used to distinguish
different protoliths of rutile-bearing eclogites. Additionally, the Zr content in rutile is temperature dependent
and can be used as a geothermometer in rutile. In this
study, we used a JXA-8800R electron microprobe to determine the trace element composition of rutiles in
eclogites from Machang, Qinglongshan and Banzhuang.
The Machang and Qinglongshan samples occur in metamorphosed intrusive complex rocks, and the Banzhuang
samples occur as lenses in marbles. Particular operating
conditions were used to obtain low detection limit (20kV,
100nA and 100~300s counting time, which resulted in a
detection limit of elements of interest in the 20~30ppm
range). Analytical results (Table 1) show that rutiles in
eclogite from Machang have the lowest content of Cr and
Nb, averaging ~89ppm and mostly below the detection
limit. However, these rutiles also have the highest Fe and
V content, averaging 5390ppm and 3853ppm respectively.
Rutiles in eclogite from Banzhuang show the highest Cr
and Nb content, averaging ~1574ppm and ~385ppm respectively; but they also show the lowest Fe and V content, averaging 2602ppm and 2114ppm respectively.
Rutiles in eclogite from Qinglongshan have moderate
To obtain the U-Pb age of rutile in eclogite from the Sulu
UHPM terrene, we selected three rutile specimens for UPb isotope analysis by the step-fuse method. Unfortunately,
we could not obtain a correct age because of the very low
content of radiogenic Pb isotopes in rutile. But, to our
surprise, the Pb isotopic compositions (206Pb/204Pb, 207Pb/
204Pb, 208Pb/204Pb) obtained from a series of step-fuse
analyses of a single grain from its shell to its core can not
be plotted on one growth line. This means that Pb isotopic ratios can not be attributed to in-situ Pb growth. Franz
et al. (2001) found a similar phenomenon when they tried
to determine the U-Pb age of a rutile specimen in an
eclogite-facies quartz vein within a metabasalt in South
Dabieshan. In their case, one 4-cm-long single crystal was
divided into 3 small fragments, and each fragment was
analyzed. The isotopic variability among these fragments
was too large to be attributable to in situ Pb growth, and
patterns on the 206Pb/204Pb-207Pb/204Pb and 206Pb/204Pb208Pb/204Pb are incompatible with secondary addition or
removal of Pb (Franz et al. 2001) . The rutile in the quartz
vein may have been crystallized in the retrograde fluid,
so they considered the initial Pb composition of this specimen to be isotopically heterogeneous, which implies that
the Pb in the fluid is isotoptically variable during rutile
crystallization. In our case, the Pb isotopic compositions
of these three specimens have shown abrupt variations
at a certain middle step and at the final step of fuse analysis
in a similar way. This implies that these three rutile specimens have similar Pb growth history. The two abrupt
variations indicate that Pb isotopic compositions of rutile
were disturbed twice during its crystallization. These disturbances may reflect the variation of geologic settings
Close
Chapter 7-3 · Rutiles in eclogite from the Sulu UHPM Terrane: A preliminary study
during rutile growth, which can be used to infer continental subduction-exhumation processes. This suggests
to us that the variation of Pb isotopic composition in rutile
by step-fuse analysis may be used to trace the growth
history of the rutile, and further to trace the process of
continental subduction- exhumation. Although this is a
preliminary discussion and needs further study and more
evidence to support it, this approach has shown great
potential in the study of the geodynamics of subduction
zones.
5
Conclusions
The rutile deposit in the Sulu terrene is genetically related to the UHPM. Rutile is mainly mineralized during
eclogite-facies metamorphism. The alteration by retrogressive metamorphism leads to a drop in grade of the
titanium mineralization.
EMP was used to obtain trace element composition
of different occurrences of rutile in eclogites. These analyses show variations in Nb, Cr, Fe and V content between
each occurrence, which may be used to infer the protolith
of these eclogites. Temperatures calculated from the Zr
geothermometer in rutile are comparable with the results from other methods. This implies that the Zr
geothermometer in rutile is a feasible and effective
method for calculating peak metamorphic temperatures.
Pb isotopic compositions obtained from step-fuse
analysis of single grains of rutile may be potential tracers of rutile growth history. If so, this analytical technique could play an important role in furthering the understanding of continental subduction- exhumation processes.
733
Acknowledgements
This study is supported by the Major State Basic Research
Development Program (2003CB716501). We thank Parham
Gardner for her critical reviews, which improved this paper significantly.
References
Franz L, Romer RL, Klemd R, Schmid R, Oberhansli R, Wagner T, Dong
S (2001) Eclogite-facies quartz veins within metabasites of the Dabie
Shan (eastern China): Pressuretemperature-time- deformation path,
composition of the fluid phase and fluid flow during exhumation of
high-pressure rocks. Contrib Mineral Petrol 141: 322-346
Huang JP, Ma DS, Liu C, Wang CL (2003) Character and origin of
rutile deposit in eclogite in Xiaojiao, Xinyi, Jiangsu province.
Geoscience 17: 435-443
Xu J, Chen YC, Wang DH, Yu JJ, Li CJ, Fu XJ, Chen ZY (2004) Titanium
mineralization in the ultrahigh-pressure metamorphic rocks
from Chinese Continental Scientific Drilling 100~2000m main
hole. Acta Petrologica Sinica 20: 119-126
Yang JJ, Jahn BM. (2000) Deep subduction of mantle-derived garnet
peridotites from the Su-Lu UHP metamorphic terrane in China.
J. metamorphic Geol., 18: 167-180
Zack T, von Eynatten H, Kronz A (2004b) Rutile geochemistry and
its potential use in quantitative provenance studies. Sediment
Geol. 171: 37-58
Zack, T, Kronz, A, Foley S., River T (2002) Trace element abundances
in rutiles from eclogites and associated garnet mica schists. Chem.
Geol. 184: 97-122
Zack, T, Moraes, R, Kronz A (2004a) Temperature dependence of Zr
in rutile: empirical calibration of a rutile thermometer. Contr.
Min. Petrol. 148: 471- 488
Zhang ZM, Xu ZQ, Liu FL, Shen K, Yang JS, Li TF, Chen SZ (2004)
Geochemistry of eclogites from the main hole (100~2050m) of
the Chinese Continental Scientific Drilling Project. Acta
Petrologica Sinica 20: 27-42
Close
Close
Chapter 7-4
7-4
A non-magmatic component in fluids of South
American Fe oxide-Cu-Au deposits inferred from
δ 37Cl, 87Sr/86Sri and Cl/Br
M. Chiaradia1, D. Banks, R. Cliff
School of Earth Sciences, University of Leeds, Leeds LS2 9JT, U.K.
1
Present address: Department of Mineralogy, University of Geneva, 1205-Geneva, Switzerland
R. Marschik
Department of Earth and Environmental Sciences, Ludwig-Maximilians University, 80333-München, Germany
A. de Haller
Department of Mineralogy, University of Geneva, 1205-Geneva, Switzerland
Abstract. The magmatic versus basinal brine origin of the hypersaline fluids associated with iron oxide-copper-gold (IOCG) deposits
is controversial. In this study we present and discuss the first stable
chlorine and strontium isotope data, combined with Cl/Br ratios, of
inclusion fluids of South American IOCG deposits. The isotopic and
elemental signatures of South American IOCG deposits suggest either mixing of juvenile magmatic fluids with up to several tens wt.%
of crustal brines or magmatic fluids leaching up to few wt.% of
evaporite.
Keywords. Iron oxide Cu-Au deposit, chlorine isotope, strontium isotope, fluid inclusion, Andes
range between 3 and 7‰ (Magenheim et al. 1995) whereas
crustal chlorine has δ37Cl values around 0‰ (Eggenkamp
et al. 1995). In principle, therefore, chlorine isotopes are
able to discriminate between heavy mantle- and light
crust-derived chlorine. Additionally, since IOCG deposits constitute an end-member of a continuum with magnetite-apatite (Kiruna-type) deposits (Hitzman 2000),
combined investigations of these two mineralization types
increase our understanding of the origin of their hypersaline fluids resulting in improved exploration strategies.
2
1
Introduction
Iron oxide-copper-gold (IOCG) deposits represent a hydrothermal mineralization style characterized by abundant magnetite and/or hematite, variable amounts of Cusulfides, pyrite, gold and REE, and intense and voluminous sodic ± calcic and potassic alteration (Hitzman et
al. 1992). These deposits form at shallow to mid-crustal
levels within cratonic or continental margin settings
(Hitzman et al. 1992), and although they usually occur
within magmatic rocks, they are not always clearly related to igneous activity. The most controversial aspect
of IOCG deposits is the origin of their hypersaline fluids
as either (i) fluids exsolved from magmas (e.g., Pollard
2002), or (ii) basinal brines heated by nearby intrusions
(e.g., Barton and Johnson 1996).
We report the first stable chlorine and strontium isotope data, as well as Cl/Br ratios, for inclusion fluids of
four IOCG deposits and one magnetite-apatite deposit
from South America. Chlorine is the dominant metal
ligand in IOCG hypersaline fluids and behaves conservatively during fluid-rock interaction. Therefore, chlorine
isotopic compositions, combined with strontium isotopes
and Cl/Br ratios, may provide tighter constraints, compared to O and S stable isotope data, on the origin of
IOGC fluids. The mean mantle δ37Cl value is 4.7‰ with a
Ore deposits investigated, samples and
techniques
The investigated deposits belong to the Carajás Mineral
Province (CMP), Brazil, and to the Peruvian and Chilean
Andes (Fig. 1). The CMP consists of a Late Archean volcano-sedimentary sequence deposited upon high-grade
tonalitic and trondhjemitic gneisses of the southern part
of the Central Brazilian Shield. The region is subsequently
intruded by 2.56-2.76 Ga alkaline and calc-alkaline granites and by 1.8-1.9 Ga anorogenic granites (Machado et
al. 1991). Either a continental rift (Olszewski et al. 1986)
or a subduction-related arc (Dardenne et al. 1988)
geodynamic setting is suggested. Investigated CMP mineralization includes the Archean to Early Proterozoic
Sossego and Gameleira deposits.
The Cretaceous IOCG deposits of Candelaria (Chile),
and Raul-Condestable (Peru) and the magnetite-apatite
deposit of El Romeral (Chile) occur in the Andean Cordillera of Peru and Chile in extensional to transpressional
arc settings (e.g. Sillitoe 2003).
Geological, mineralogical, and stable isotope data (mostly
O, S) indicate dominantly magmatic fluids formed Gameleira
(Lindenmayer et al. 2001) and El Romeral, whereas mixed
magmatic and non-magmatic fluids characterize Sossego
(Marschik et al. 2003) Candelaria (Marschik and Fontboté
2001) and Raul-Condestable (de Haller et al. 2002).
Close
736
M. Chiaradia · D. Banks · R. Cliff · R. Marschik · A. de Haller
Selected fragments of quartz representing the primary
ore stages at Raul-Condestable, Candelaria, Gameleira, and
Sossego, apatite from El Romeral, as well as two calcites
from the late ore stage at Sossego were sampled and
crushed. The inclusion fluids were analyzed for stable
chlorine and strontium isotope compositions by thermal
ionization mass spectrometry (TIMS) and for Cl- and Brconcentrations by ion chromatography at the School of
Earth Sciences (University of Leeds, U.K.).
3
Sources of chlorine and strontium in inclusion
fluids
Chlorine isotope compositions and Cl/Br ratios of hydrothermal fluids of South American IOCG and magnetiteapatite deposits plot along two distinct arrays (Figure 2),
allowing discrimination between magmatic fluid-dominated deposits (Gameleira and El Romeral) and deposits
with mixed magmatic and non-magmatic fluids (Sossego,
Candelaria, Raul) consistent with previous geochemical
studies. We interpret the two trends defined by fluids of
the magmatic fluid-dominated (Gameleira, El Romeral)
and mixed fluid (Candelaria, Raul-Condestable, Sossego)
deposits as the result of mixing between a common
mantle-derived magmatic fluid and two distinct crustal
sources of chlorine both with near 0‰ δ37Cl values but
with different Cl/Br values (Fig. 2).
The trend defined by the magmatic fluids of Gameleira
and El Romeral integrated with data from the magmatic
fluids of the Capitan and SW-England plutons (Banks et
al. 2000: Figure 2) is shifted to high Cl/Br values suggesting that chlorine is a mixture between mantle and halitederived chlorine, probably resulting from variable magmatic interaction with evaporites. A non-magmatic component at El Romeral is supported by the significantly
more radiogenic strontium isotopic composition (87Sr/
86Sr = 0.7065) of the fluid compared to that of the associi
ated magmatic rocks (87Sr/86Sri ~ 0.703-0.704). The Sr isotope data addtionally suggest evaporite assimilation by
high-temperature exsolved magmatic fluids rather than
evaporite assimilation by the magma itself is responsible
for the observed Cl and Sr isotope systematics of the inclusion fluid at El Romeral.
We have calculated that assimilation of 2 to 9 wt.%
halite by a mantle-derived magmatic fluid could cause
the shift to the near 0‰ δ37Cl values and high Cl/Br ratios observed in the Gameleira, El Romeral and Capitan
pluton fluids. The existence of evaporites in the host sequences of El Romeral (Chile) and Capitan pluton
(Mexico) yields geological support to the above scenario.
However, there is no evidence for evaporites in the CMP.
As a result a fluid souce with ~0‰ δ37Cl and high Cl/Br
ratios such as a hypersaline crustal brine may explain the
data of Gameleira.
The other IOCG deposits investigated (Sossego,
Candelaria, Raul-Condestable) define a linear array in the
Close
Chapter 7-4 · A non-magmatic component in fluids of South American Fe oxide-Cu-Au deposits inferred from δ37Cl, 87Sr/86Sri and Cl/Br
Cl/Br-δ37Cl space that may result from mixing of the
mantle-derived magmatic-hydrothermal fluid with a
crustal brine characterized by Cl/Br ratios significantly
lower than evaporites but higher than seawater (Figure 2).
The fact that all these IOCG deposits plot along a common mixing line (despite the large compositional field of
crustal brines) is intriguing and appears to indicate that
the mantle-derived magmatic fluid has interacted with a
crustal brine characterized by virtually identical Cl/Br
ratios despite the different ages and geographic locations
of the deposits. The presence of a non-magmatic fluid
component in these IOCG deposits is again supported by
strontium isotope compositions of the inclusion fluids,
which are significantly more radiogenic ( 87Sr/ 86Sr i
= 0.7053-0.7056 at Candelaria and 0.7051-0.7062 at RaulCondestable) than those of the associated magmatic rocks
(87Sr/86Sri = 0.7031 at Candelaria and 0.7042 at RaulCondestable). In addition, at Candelaria-Punta del Cobre
chalcopyrite, secondary biotite, ore-related calcite and
anhydrite also have 87Sr/86Sri (0.7043-0.7063) higher than
the magmatic rocks (R. Marschik, unpublished data). Calculated chlorine contributions from the crustal brine range
between 50 and 95% assuming δ 37 Cl mantle = 4.7‰
(Magenheim et al., 1995) and a δ37Clbrine = -0.4‰. However, due to the ten- to hundred-fold higher chlorine content of crustal brines compared to (non-boiled) magmatic
fluids, these figures correspond to 4 and 30 wt.% crustal
brine contribution.
The above calculations are highly sensitive to assumptions about Cl and Br concentrations in brines and magmatic fluids, to the poorly constrained δ37Cl composition
of the mantle-derived magmatic fluid and crustal brines,
and to the relatively large analytical uncertainty of δ37Cl
values (±0.2‰), yet they clearly indicate the presence of
a measurable non-magmatic, crustal Cl (and Sr) component in fluids of IOCG deposits.
4
Conclusions
Chlorine and strontium isotope data combined with Cl/
Br ratios indicate that ore fluids in the investigated IOCG
and magnetite-apatite deposits result from variable mixing of mantle-derived magmatic-hydrothermal fluids with
crustal brines or evaporites. The Gameleira IOCG deposit
and the El Romeral magnetite-apatite deposit formed by
magmatic-hydrothermal fluids leaching evaporites from
the host sequence or by mixing with crustal brines characterized by high Cl/BR ratios. Fluids of these deposits
preserve a pristine magmatic O and S isotope signatures,
yet minimal interactions with evaporites (e.g., 2-9 wt.%)
are sufficient to produce the observed evaporite-type Cl
and Sr isotope signatures as well as Cl/Br ratios.
In contrast, the IOCG deposits of Candelaria, RaulCondestable and Sossego formed by the mixing of magmatic-hydrothermal fluids with up to a few tens percent
737
of crustal brine (4-30 wt.%). The significant contribution
of crustal brines in these deposits is suggested by Cl and
Sr isotope data as well as by Cl/Br ratios. The results are
consistent with mixed magmatic and non-magmatic hydrothermal fluid signatures inferred from other isotope
systems (oxygen, sulfur). Chlorine isotope data combined
with Cl/Br ratios and strontium isotope compositions
suggest a measurable contribution of crustal brines and/
or evaporites to the ore fluids in IOCG and magnetiteapatite deposits of South America. This conclusion may
help to refine strategies for IOCG deposit exploration in
South America.
Acknowledgements
We thank Rolf Romer (GFZ, Potsdam) and Holly Stein,
Aaron Zimmerman, and Parham Gardner (AIRIE Program, Colorado State University, U.S.A.) for their comments that helped to improve an earlier version of the
manuscript.
References
Banks DA, Green R, Cliff RA, Yardley BWD (2000) Chlorine isotopes
in fluid inclusions: determination of the origins of salinity in
magmatic fluids. Geochim Cosmochim Acta 64: 1785-1789
Barton MD, Johnson DA (1996) Evaporitic-source model for igneousrelated Fe oxide-(REE-Cu-Au-U) mineralization. Geology 24:259-262
Dardenne MA, Ferreira Filho CF, Meirelles MR (1988) The role of
shoshonitic and calc-alkaline suites in the tectonic evolution of
the Carajás district, Brazil. J South Amer Earth Sci 1: 363-372
de Haller A, Zúñiga Alvarado J, Corfu F, Fontboté L (2002) The iron
oxide-Cu-Au deposit of Raul-Condestable, Mala, Lima, Peru. In:
Sociedad Geologica del Peru (ed) Conf Abst Vol XI Congr Peruano
Geol, Lima: p. 80
Eastoe CJ, Long A, Land LS, Kyle JR (2001) Stable chlorine isotopes
in halite and brine from the Gulf Coast Basin: brine genesis and
evolution. Chem Geol 176: 343-360
Eggenkamp HGM, Kreulen R, van Groos FK (1995) Chlorine stable
isotope fractionation in evaporites Geochim Cosmochim Acta
59: 5169-5175
Hitzman MW (2000) Iron oxide-Cu-Au deposits: what, where, when,
and why? In: Porter TM (ed) Hydrothermal iron oxide-coppergold and related deposits: a global perspective, vol 1. PGC Publishing, Adelaide, Australia, p 9-25
Hitzman MW, Oreskes N, Einaudi MT (1992) Geological characteristics and tectonic setting of Proterozoic iron oxide (Cu-U-AuREE) deposits. Precamb Res 58: 241-287
Johnson LH, Burgess R, Turner G, Milledge HJ, Harris JW (2000)
Noble gas and halogen geochemistry of mantle fluids: comparison of African and Canadian diamonds. Geochim Cosmochim
Acta 64: 717-732
Lindenmayer ZG, Pimentel MM, Ronchi LH, Althoff FJ, Laux JH,
Araújo JC, Fleck A, Bortowski DC, Nowatzki AC (2001) Geologia
do depósito de Cu-Au do Gameleira, Serra dos Carajás, Pará. In:
Jost H, Brod JA, Queiroz ET (eds) Caracterização de depósitos
auriferous brasileiros. ADIMB-DNPM, Brasília, p. 79-139
Machado N, Lindenmayer Z, Krogh TE, Lindenmayer D (1991) U-Pb
geochronology of Archean magmatism and basement reactivation in the Carajás area, Amazon shield, Brazil. Precambrian Res
49: 239-354
Close
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M. Chiaradia · D. Banks · R. Cliff · R. Marschik · A. de Haller
Magenheim AJ, Spivack AJ, Michael PJ, Gieskes JM (1995) Chlorine
stable isotope composition of the oceanic crust: implications for
Earth’s distribution of chlorine. Earth Planet Sci Lett 131: 427-432
Marschik R, Fontboté L (2001) The Candelaria-Punta del Cobre iron
oxide Cu-Au(-Zn-Ag) deposits, Chile. Econ Geol 96: 1799-1826
Marschik R, Spangenberg JE, Leveille RA, de Almeida AJ (2003) The
Sossego iron oxide-Cu-Au deposit, Carajás, Brazil. In: Eliopoulos
D et al (eds) Mineral Exploration and Sustainable Development
v 1. Millpress, Rotterdam, p. 331-334
Olszewski WJ, Wirth KR, Gibbs AK, Gaudette HE (1989) The age,
origin and tectonics of the Grão-Pará Group and associated rocks,
Serra dos Carajás, Brazil. Precambrian Res 42: 229-254
Pollard PJ (2002) Evidence of a magmatic fluid and metal source for
Fe-oxide Cu-Au mineralisation. In: Porter TM (ed) Hydrothermal iron oxide copper-gold and related deposits – A global perspective v 1. PGC Publishing, Linden Park, Australia: 27-41
Sillitoe RH (2003) Iron oxide-copper-gold deposits: An Andean View.
Mineral Deposita 38: 787-812
Close
Chapter 7-5
7-5
Origin of hydrothermal ore-forming processes in the
Dapingzhang polymetallic copper deposit in the
Lanping- Simao Basin, Yunnan Province
Dai Baozhang, Jiang Shaoyong
State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, 210093,
China
Liao Qilin
Jiangsu Geological Survey Institute, Nanjing, 210018, China
Abstract. The newly discovered Dapingzhang polymetallic copper
deposit in the Lanping-Simao Basin is hosted in volcanic rocks. The
orebodies include an upper stratiform and lentiform massive sulfide orebody, and a lower vein type and disseminated sulfide
orebody. The Rb-Sr isotopes of quartz fluid-inclusions in the vein
type orebody yield an isochron age of 118 ±12 Ma. Fluid-inclusion
analysis shows that the ore-forming fluid is of low to middle salinity (2.0-8.0 wt%NaCl), and of low to middle temperature (90~200oC).
The δ34S values of pyrite and chalcopyrite minerals in this deposit
concentrate at about 0‰. Our modeling and water/rock ratio calculations using available hydrogen-oxygen isotope data suggests
an evolved meteoric water origin for the ore-forming fluids, instead
of mixture of seawater and magmatic fluids. The Pb isotope composition indicates radiogenic Pb sources, and suggests Pb from sedimentary rocks and mantle-derived volcanic rocks in the basin both
contribute to this deposit. In conclusion, the Dapingzhang deposit
shares many similar geochemical characteristics with vein type copper deposits in the Lanping-Simao Basin. These data support the
conclusion that the Dapingzhang polymetallic copper deposit is a
hydrothermal deposit formed during Yanshanian period, not a massive sulfide deposit of submarine-exhalative-sedimentary origin as
proposed by previous researchers.
Keywords. Isotope geochemistry, quartz fluid inclusion, Rb-Sr isochron age, Yanshanian period, hydrothermal deposit
1
Introduction
2
Rb-Sr isochron age
Determining the age of mineralization is essential for
understanding any deposit. In this study, mineralization
was dated using Rb-Sr analysis of fluid inclusions. The
Rb-Sr isotopic compositions of fluid inclusions in 8 selected quartz samples were analyzed. The data were then
plotted using the ISOPLOT program with λ ( 87 Rb)
1.42x1011/a. The input error was 87Rb/86Sr = 0.5%. The 6
samples from the vein type and disseminated sulfide
orebody yield an isochron age of 118 ±12Ma, MSWD =
0.46. Previous isotope dating (Zhong et al. 2000) shows
that the age of the host rock is 500~530 Ma. The ages of a
variety of intrusions in this area are between 300 Ma and
150 Ma, which indicate that the Dapingzhang deposit
formed after these local intrusions.
Two samples from the massive orebody evidently depart from the isochron and show higher 87Sr/86Sr values
(Fig. 1). This could be caused by increased contribution
from materials with higher 87Sr/86Sr values (e.g., sediments
in the basin). This could be because the massive orebody
is relatively shallower than the vein type deposits. The
limited sample number in this case (2) prevents the possibility of obtaining an age for the massive orebody. Some
The Dapingzhang polymetallic copper deposit is an important recent discovery in Lanping-Simao Basin. It is
composed of an upper stratiform and lentiform massive
sulfide orebody, and a lower vein type and dissiminated
sulfide orebody. Previous researchers have identified it
as a massive sulfide deposit with submarine- exhalativesedimentary origin (Li 2000; Li et al. 2000; Li and Zhuang
2000; Li and Zhang 2001; Zhong et al. 2000). In this paper,
new results of fluid inclusion, sulfur isotope and mineralization age are taken into account. The data lead to a
different perspective on ore-forming process, which is also
consistent with previous data. The Dapingzahng deposit
was formed by extensive interaction between meteoric
water (or brine) and host rocks. This is similar to the
oreforming process identified in the vein type deposits
in Lanping-Simao Basin.
Close
740
Dai Baozhang · Jiang Shaoyong · Liao Qilin
direct dating methods such as Re-Os isotope analysis of
metal sulfides (Jiang et al., 2000) should be adopted in
further research. The reliable age of 120 Ma for the vein
type and disseminated sulfide orebody indicates that this
deposit mainly formed in Yanshanian period.
concentrate at about 0‰, implying that sulfur in this deposit is mainly mantle-derived. Sulfur with such characteristics can either come directly from volcano exhalative,
or can be leached from volcanic rocks. For the
Dapingzhang deposit, the latter is more reasonable.
3
4.2 Hydrogen-oxygen isotopes
Fluid inclusions
In this study, quartz and calcite minerals from variety of
samples were carefully selected for fluid inclusion analysis
in order to acquire information about the composition
of ore-forming fluids. The results show that the range of
homogeneous temperatures is 90~200 o C (mainly
from130oC to 160oC), and the salinity of the ore-forming fluid varies from 2.0 to 8.0 wt%NaCl. These results
are relatively lower in temperature and salinity than previous data; however this could be due to the fact that
these samples originate from shallower depths than those
from previous studies.
As shown in Figure 2, the ore-forming fluid of Dapingzhang deposit is similar to that of the vein type deposit
series in Lanping-Simao Basin composed by Jinman,
Shuixie and Bailongchang.
On the other hand, temperature of ore-forming fluids in massive sulfide deposits mainly ranges from 200oC
to 350 o C, which is much higher than that of the
Dapingzhang deposit.
4
To determine the origin and evolution of the ore-forming fluid, available hydrogen and oxygen isotope data (Li
and Zhuang 2000; Zhong et al. 2000) are compiled (δ18OH2O
values of -2.5 to +2.9‰, and δD values of –84 to –59‰
for the ore-forming fluids) and further analyzed. The calculation of water/rock interaction is taken in this study
with the δD and δ18OH2O values of meteoric water are 120‰ and -16‰ (Liu et al., 2000) and the δD and δ18OH2O
values of volcanic rocks are -65‰ and 8‰ (Shen 1997).
Figure 4 shows that the available hydrogen and oxygen
data are consistent with the two evolution curves at 150oC
Isotope research
4.1 Sulfur isotopes
Chalcopyrites and pyrites from variety of samples were
selected in this study for sulfur isotope analysis. Both the
results in this study and previous studies (Li et al. 2000;
Zhong et al. 2000) indicate that δ34S values of all sulfides
Close
Chapter 7-5 · Origin of hydrothermal ore-forming processes in the Dapingzhang polymetallic copper deposit in the Lanping- Simao Basin, Yunnan Province
741
2. The ore-forming fluid is similar to that of the vein type
deposit series, with low to middle salinity and low to
middle temperature. Hydrogen-oxygen isotope data
indicate an evolved meteoric water origin for the fluid.
3. Sulfur and lead isotope data imply that the host volcanic rocks are the main source for sulfur and oreforming metals.
4. It is most likely that mineralization of the Dapingzhang
deposit is similar to that of the vein type deposit series in Lanping-Simao Basin. The Dapingzhang
polymetallic copper deposit is a hydrothermal deposit.
References
and 250oC, respectively. Thus, it is most likely that the oreforming fluid is extensively evolved meteoric water.
4.3 Lead isotopes
Available lead isotope data are plotted onto the Zartman
Pb isotope diagram. Lead in this deposit is relatively rich
in radiogenic Pb. Fig. 5 shows that host-rock samples lay
on the orogen curve, while orebody samples lie between
the orogen curve and the mantle curve, implying some
contribution from a magmatic source. It is likely that host
rocks supply most of the ore-forming metal to both the
vein type deposit series and the Dapingzhang copper
polymetallic deposit.
5
Conclusions
Combining the new results in this study and the available
data of previous researchers, we acquire some essential
perspectives on the Dapingzhang copper polymetallic
deposit:
1. The fluid-inclusion Rb-Sr isotopes of quartz in the
vein-type orebody yield an isochron age of 118 ±12
Ma. This indicates that the orebody was formed in late
Yanshanian period.
Jiang S, Yang J, Zhao K (2000) Re-Os isotope tracer and dating methods in ore deposits research. Journal of Nanjing University (Natural Sciences) 36(6): 669~677
Li F (2000) Volcanic-exhalative-sedimentary ore- forming model of
Dapingzhang Cu-polymetal deposit, western Yunnan. Bulletin of
Mineralogy, Petrology and Geochemistry 19(4): 296~297
Li F, Zhang F (2001) Volcanic-exhalative- sedimentary genesis of
Dapingzhang Cu-polymetal deposit, western Yunnan. Geology
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Li F, Zhuang F (2000) Fluid inclusion characteristics and its
metallogenic significance of the Dapingzhang Cu-polymetal deposit in Simao, western Yunnan. Geotectonica et Metallogenia
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Li F, Zhuang F, Yang H (2000) Fluid inclusions analysis of
Dapingzhang Cu-polymetal deposit, western Yunnan. Acta
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Liu J-J, Li C-Y, Pan J-Y (2000) Isotopic Geochemistry of copper deposits in sandstone and shale of Lanping-Simao basin, western
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Ohmoto H, Skinner BJ (1983) The Kuroko and related volcaogenic
massive sulfide deposit. Economic Geology (Monograph) (5): 604
Shen W (1997) Textbook on isotopic geology. Atomic energy publishing house, Beijing.
Wu N (2003) Geochemistry of the vein-type copper deposits in
Lanping-Simao Basin, Yunnan Province, China. Paper for master’s
degree of Department of Earth Sciences, Nanjing University
Wu N (2003) Lead and sulfur isotope geochemistry and the ore
sources of the vein-type copper deposits in Lanping-Simao Basin, Yunnan Province. Acta Petrologica Sinica 19(4): 799~807
Zhong H, Hu R-Z, Ye Z-J (1999) Isotopic chronology of the spiliteceratophyre formation in Dapingzhang, Yunnan Province and its
geologic significance. Science in China (D) 29(5): 407~412
Zhong H, Hu R-Z, Ye Z-J (2000) Sulfur, lead, hydrogen and oxygen
isotopic geochemistry of the Dapingzhang copper- polymetallic
deposit, Yunnan Province. Geochemica 29(2): 136~142
Close
Close
Chapter 7-6
7-6
Stable isotope geochemistry of the gold-sulfide
mineralized zone of the Kottapalle block of the
Ramagiri greenstone belt, Dharwar Craton, South India
M. Deb, K. Bheemalingeswara
Department of Geology, University of Delhi, Delhi 110007, India
Abstract. The Neo-Archean Ramagiri-Penakacherla belt is located
in the eastern Dharwar craton of South India. It hosts auriferous
quartz bodies in altered mafic and felsic volcanic rocks, intimately
interlayered and co-folded with carbon phyllites. The sequence is
metamorphosed to low greenschist facies. Pervasive quartz-carbonate alteration is a conspicuous feature in the gold-sulfide mineralized zone of the Kottapalle block of this greenstone belt.
The carbonate compositions spread along the dolomite-ankerite or calcite-ankerite join. The host volcanics are of tholeiitic basalt, andesitic and dacitic compositions representing a probable
island-arc setting. The majority of carbonaceous samples fall in
the range of – 20 and – 28 per mil δ13Corg (PDB), suggesting a
biogenic derivation of the reduced carbon and a sedimentary origin of the strata. Carbonate δ13C (PDB) have median values of -2.4
per mil and mean of – 4.0 per mil. δ34S (CDT) values of pyrite and
pyrrhotite cluster around +2 per mil. Primary fluid inclusions, rich
in CO 2 with subordinate CH 4 , as observed in preliminary
microthermometric studies, demonstrate the pervasive presence
of a CO2-rich hydrothermal fluid responsible for the extensive carbonation of the auriferous host rocks.
Absence of any sedimentary carbonate strata in the sequence,
and the stable-isotope data support the role of mantle-derived
fluids in producing the quartz-carbonate alteration. The δ13C values of carbonates indicate that the hydrothermal fluid did not
have any significant interaction with the reduced carbon in the
ore zone. The sulphur isotope data points to the mantle-source of
sulphur in the ore-bearing hydrotherms.
Keywords. Shear gold, quartz-carbonate alteration, Dharwar craton, stable-isotope geochemistry
1
Introduction
The Ramagiri-Penakacherla belt is one of a series of auriferous greenstone belts in the eastern Dharwar craton
of South India. This belt, considered to be of Neo-Archean
age (2746+ 64 Ma; Zachariah et al. 1995) is located in the
Anantapur district of Andhra Pradesh. The belt forms a
Y-shaped outcrop of prominently mafic volcanic rocks,
which are surrounded on all sides by the Peninsular
Gneiss. The litho-units present in the area (Ghosh et al.
1970) are:
– Dolerite dyke
– Ultrabasic rocks
– Pyroclastics
–
–
–
–
–
–
–
–
Light and dark phyllites
Greenstones with chert layers
Quartz-chlorite schists
Quartzite
Banded Iron Formation
Hornblende schist
Metagabbro
Granitic rocks, massive and banded
The light grey phyllite consists essentially of carbonate and chlorite, with minor amounts of sericite and
quartz. The dark grey phyllite on the other hand has chlorite as the dominant phase over carbonates. Auriferous
quartz bodies of different types and generations occur
in this part of the sequence (shown in italics above) in
the form of reefs, pods and veinlets along the pervasive
foliation.
In the Kottapalle block of the Ramagiri ore zone (Fig. 1)
the altered volcanics are intimately interlayered and cofolded with carbon phyllite. In the auriferous zone these
rocks contain sulfide minerals such as, pyrite, chalcopyrite, pyrrhotite, sphalerite and minor arsenopyrite..The
metamorphic mineral assemblage indicates that the grade
of metamorphism has attained low green schist facies.
Pervasive quartz-carbonate alteration is a conspicuous geological feature noted in the gold-sulfide mineralized zone in the Kottapalle block. It has affected both
the felsic and mafic volcanic units of the greenstone belt.
The carbonates co-exist as grains, bands and patches with
the carbonaceous matter in the carbon phyllites. Thus,
carbon, either as graphitic carbon or as carbonate is invariably associated with the Au-sulfide mineralization.
This first stable isotope study in this belt was conducted to ascertain the source of carbon and sulfur in
the ore-host rock association. This work would also provide useful insight into the oregenetic process and environment of ore emplacement. Towards this end, three
bore holes drilled by the Geological Survey of India in
the Kottapalle block (cf. Fig. 1) were logged and sampled
systematically and subjected to XRD, XRF, CHNS (elemental), EPMA analyses and stable isotope mass spectrometry.
Close
744
M. Deb · K. Bheemalingeswara
2
Results
2.1 Petrology and geochemistry
Based on discriminant diagrams, using their major and
trace element abundances, the mafic and felsic volcanics
in the host sequences were found to be of tholeiitic basalt, andesite and dacite compositions. In tectonic discriminant diagrams, the Kottapalle metabasalts plot in
the IAB field, suggesting the possibility of subductionrelated volcanism in an island arc setting in the Archean
Dharwar craton (cf. Zachariah et al. 1997). The volcanic
rocks have been so severely altered and metamorphosed
that the two main protoliths, tholeiitic basalt and dacite,
can hardly be distinguished petrographically. Both the
volcanics have turned into fine grained chlorite-sericite
schists, the only distinction being the fine grained quartzofeldspathic matrix in the felsic compositions. These schists
have been described as light and dark phyllites in field
parlance.
Carbonate grains in three samples of metabasalt and
felsic volcanics were investigated through XRD, CL and
EPMA (JEOL JXA 8600 superprobe) analyses. All carbonate grains analysed contain manganese as a minor component, with MnO content ranging from nil to 0.9 wt.%.
Their compositional characteristics, in terms of the three
major components, CaO, MgO and FeO, are presented in
Figure 2. Coarse quartz-carbonate veins and lenses occur in contact with finely schistose carbonaceous and carbonate interlayerings in sericite-quartz schists (RG49/11).
Compositions of carbonates in them showed the predominance of ankerite over dolomite molecule along the dolomite-ankerite join. Coarse brownish carbonates in lenses
and bands in another section (RG47/1) within sericitechlorite-quartz schist showed a trend of increasing dolomitic and calcitic molecules. This section showed excellent microstructural relationships, with the schistosity
transected by tightly folded late quartz veinlets. In yet
another section (RG47/18) brownish pre- to syntectonic
carbonate-quartz-sulfide lenses show compositions along
the calcite-ankerite join. In this section, two types of carbonates are observed. The late carbonates, identified under CL, are clearly more calcitic. They are located along
the grain boundaries of earlier carbonate grains. Fe-rich
carbonates, as noted in this study, are typically related to
gold mineralization in greenstone belts the world over.
Total carbon content of 48 analyzed samples from the
ore zone rocks ranged from 7.3 to 0.27 wt.%, with a mean
of 3.11 wt.% (std. dev. 1sigma = 1.67%). Corg content mea-
Close
Chapter 7-6 · Stable isotope geochemistry of the gold-sulfide mineralized zone of the Kottapalle block of the Ramagiri greenstone belt, Dharwar craton
745
δ18O (SMOW) per mil of 21 carbonates from Kottapalle
ore zone (Fig. 4) show spread of δ13C values from 0 to 9.2 per mil with a mean of – 4.0 and a median of – 2.4 per
mil. δ18O values range from 26.0 to 12.5 per mil. One
pure calcite from a late veinlet had an unusual composition of -9.2 per mil δ13C and -11.2 δ18O. While only one
sample showed sea water-derived carbonate δ13C value
near zero, the majority clustered between – 1.5 and – 2.7
per mil. A few values were spread between – 3.9 and - 6.2
per mil while 2 samples gave values around – 9 per mil.
Limited sulfur isotope analyses of 8 monomineralic pyrite and 1 pyrrhotite separates gave a range of δ34S (CDT)
between +2.8 and -1.7 per mil, with the majority clustering around +2 per mil (Fig. 5).
3
sured in 15 samples ranged from 5.8 wt.% to nil, while
Ccarb, estimated as the difference between Ctotal and Corg
in 15 samples, ranged between 5.9 wt.% to nil.
2.2 Stable isotope composition
Twenty one analyses of δ13Corg in three carbonaceous
samples (Fig. 3) ranged between – 14.2 and – 32.4 per
mil (PDB), with the majority of samples falling in the range
of – 20 and – 28 per mil. These values suggest a biogenic
source for the carbon, and thus, a sedimentary origin for
the carbonaceous strata. Values heavier than – 20 per mil
probably reflect partial equilibration with co-existing carbonates or thermal maturation to heavier values by liberation of CH4. δ13CCarb-graphite of 11.6 and 13.8 per mil in
co-existing carbonate and reduced carbon suggest an
equilibration temperature of about 300 to 225oC (cf.
Oberthür et al. 1996). A plot of δ13C (PDB) per mil against
Discussion and conclusion
For shear- or fault-controlled Archean epigenetic goldquartz deposits, controversy prevails regarding the source
of the ore components and fluids. There are two end-member genetic hypotheses - one metamorphic and the other
magmatic - which continue to compete. Since most deposits of this type show pervasive carbonate alteration and sulfide association, determination of the source of carbon and
sulfur in the ore zone can lend significant support to either
of the two hypotheses. Extensive quartz-carbonate alteration of the host volcanics, absence of any sedimentary carbonate strata in the sequence and presence of primary fluid
inclusions rich in CO2 with subordinate CH4, as observed
in preliminary microthermometric studies, demonstrate the
pervasive presence of a CO2-rich hydrothermal fluid. This
type of fluid is necessary for carbonation of the auriferous host rocks in the Kottapalle block of the Ramagiri
greenstone belt. The variation in the composition of the
carbonates, noted above, may be attributed to episodic
fluctuations in the temperature and composition of the
fluids in the structural conduits (cf. Mumin et al. 1996).
The median δ13C of -2.4 per mil composition of the carbonates is too negative to have been derived from metamorphically remobilized CO2 from sea water-derived carbonate. This median value of ore zone carbonates and
their spread upto -6.2 per mil conforms closely to the range
Close
746
M. Deb · K. Bheemalingeswara
of -2.0 to -6.0 recorded by Groves et al. (1988) for faultcontrolled regional carbonation involving CO2 of magmatic or mantle origin. The median value is also close to
the -3.1 ± 1.3 per mil δ13C value of undoubted magmatically-derived carbonates found in association with molybdenite mineralization in a granodiorite intrusion in
Canada (Burrows et al. 1986). Direct involvement of mantle
fluids in the ore-bearing hydrotherm is envisaged instead
of reworking of mantle-derived carbonates into metamorphic fluids, as an alternative process of ore formation.
This is supported by the limited variation in the δ13C values of carbonates and the near-zero (+2 per mil) mantle
signature in the associated sulfides. Absence of strongly
negative (> -10 per mil) δ13C values in the carbonates
also imply that the hydrothermal fluid did not have any
significant interaction with reduced carbon.
Acknowledgements
This study was made possible by the kind permission
granted by the Deputy Director General (Southern Region), Geological Survey of India for the logging and collection of bore hole samples. The help received in the field
from senior geologist, K.N.Reddy is gratefully acknowledged. The EPMA, CL, XRD and Mass spectrometry were
carried out during a revisit of the first author (MD) to
the Geochemisches Institut, Göttingen, Germany with an
Alexander von Humboldt Foundation fellowship. He is
grateful to Prof. J.Hoefs for extending all laboratory fa-
cilities at Göttingen. Thanks are also due to Dr. Andreas
Hoppe, Director, Landesamt fur Bodenforschung, Wiesbaden, for help in generating the XRF data. This study
was supported by a research grant (ESS/CA/A5-11/95)
from the Department of Science & Technology, Govt. of
India, to the first author.
References
Burrows DR, Wood PC, Spooner ETC (1986) Carbon isotope evidence
for a magmatic origin for Archean gold-quartz vein ore deposits. Nature 321 851-854
Ghosh DB, Sastry BBK, Rao AJ, Rahim AA (1970) Ore environment
and ore genesis in Ramagiri Gold Field, Andhra Pradesh, India.
Econ. Geol. 65 801-814
Groves DI, Golding SD, Rock NMS, Barley ME, McNaughton NJ (1988)
Archean carbon reservoirs and their relevance to the fluid source
for gold deposits. Nature 331: 254-257
Mumin AH, Fleet ME, Longstaffe FJ (1996) Evolution of hydrothermal fluids in the Ashanti gold belt, Ghana: stable isotope geochemistry of carbonates, graphite and quartz. Econ. Geol. 91: 135-148
Oberthür T, Schmidt Mumm A, Vetter U, Simon K, Amanor, JA
(1996) Gold mineralization in the Ashanti belt of Ghana: genetic constraints of the stable isotope geochemistry. Econ. Geol.
91: 289-301
Zachariah JK, Hanson GN, Rajamani V (1995) Postcrystallisation
disturbance in the neodymium and lead isotope systems of
metabasalts from the Ramagiri schist belt, southern India.
Geochimica et Cosmochimica Acta 59: 3189-3203
Zachariah JK, Rajamani V, Hanson, GN (1997) Petrogenesis and
source characteristics of metatholeiites from the Archean
Ramagiri schist belt, eastern part of Dharwar craton, India.
Contrib. Mineral. Petrol. 129: pp. 87-104
Close
Chapter 7-7
7-7
Isotope systematics of ore-bearing granites and host
rocks of the Orlovka-Spokoinoe mining district,
eastern Transbaikalia, Russia
A. Dolgopolova, R. Seltmann, C. Stanley
Natural History Museum, Dept. Mineralogy, CERCAMS, Cromwell Road, London SW7 5BD, UK
D. Weiss
Imperial College, London, Prince Consort Road, London SW7 2BP, UK
B. Kober
Institute of Environmental Geochemistry, Im Neuenheimer Feld 234, D-69120 Heidelberg, Germany
W. Siebel
Dept. of Earth Sciences, Eberhard-Karls-University, Wilhelmstr. 56, D-72074 Tübingen, Germany
Abstract. Pb, Rb and Sr isotope data are reported for the Khangilay,
Orlovka and Spokoinoe granite massifs and their host rocks in the
Orlovka-Spokoinoe mining district, Eastern Transbaikalia, Russia. Pb
isotope analyses indicate a common Pb source for all three granite
massifs reflecting a homogenous source melt from which all magmatic members evolved. Pb isotope systematics identify two possible scenarios for the source of Li-F granites: 1) a crust-mantle source
where a mixture of MORB and continental-derived material were
brought together in an orogenic environment; and 2) a type II enriched mantle source where subducted continental material could
have been strongly implicated in volcanic suites. New Rb-Sr isotope
age data yield a 143.8±4.2 Ma age for barren granites of the Orlovka
and Khangilay massifs.
mantle interaction in the development of granitoid
magmatism, the genetic relationship between the three
massifs and similarities and differences among them may
be identified. Rb-Sr isotopes provide additional insights into
the age of granites from the Orlovka-Spokoinoe mining site.
Keywords. Pb Rb Sr isotope systematics, ore-bearing granite, Eastern Transbaikalia
1
Introduction
The rare-metal granite-related Orlovka tantalum deposit
and the Spokoinoe tungsten vein quartz-greisen deposit
are located in Eastern Transbaikalia 140 km and 148 km SE
of Chita, respectively. Both deposits are hosted by the
Khangilay granite pluton and are believed to be its satellites (Fig. 1) (Badanina et al. 2004; Beskin et al. 1994;
Kovalenko et al. 1999; Syritso et al. 2001). In recent years,
the evolution of rare-metal granites, their formational stages,
and their relation to intraplate magmatism have been studied. Specifically, Rb-Sr and Sm-Nd isotopic systems were
used to reveal the source(s) of rare-metal granite melts from
the study area, and the results indicate that sources were
likely to be either crustal, mantle or combined crustal-mantle
(Kostitsyn 2001; Kovalenko et al. 1999, 2002, 2003; Yarmolyuk
et al. 2001, 2003). Our study uses Pb isotopes for the granites of the Orlovka, Spokoinoe, and Khangilay massifs and
their host rocks with the goal to study the evolutionary
trends and features of the Khangilay pluton and the Orlovka
and Spokoinoe deposits (barren versus mineralized granites, ores, host rocks). By examining fluid-rock and crust-
Close
748
A. Dolgopolova · R. Seltmann · C. Stanley · D. Weiss · B. Kober · W. Siebel
2
Geological setting
The Orlovka-Spokoinoe mining district belongs to the
Central Asian Orogenic Belt (CAOB) (Jahn et al. 2000) or
Transbaikal-Mongolian orogenic collage where multiple
oroclinally bent magmatic arcs separated by accretionary complexes and ophiolitic sutures are located between
the major cratons. Rare-metal Li-F enriched granites and
pegmatites are widespread as products of continental
crustal growth and associated intraplate magmatism. The
Khangilay pluton is located in the central portion of the
Paleozoic Aginskaya microplate, which is made up of predominantly sandstone and shales (Beskin et al. 1994; Syritso
et al. 2001). The granitoids of the pluton cut Proterozoic to
Carboniferous shales and volcanics, a Triassic terrigenous
and volcano-sedimentary sequence, and gabbro-diorite,
granodiorite, and lamprophyre bodies (Kovalenko et al.
1999). The microplate was intruded by granite plutons, the
largest of which is 24 km by 22 km in dimension at a depth
of 500-2500 m based on gravimetric data.
It is exposed at the surface as three separate granitic
(Khangilay, Spokoinoe and Orlovka) massifs. The
Khangilay granite massif is composed of biotite granite
and biotite-muscovite granites. The Orlovka satellite is a
highly differentiated Ta-(Nb-Sn-) bearing intrusion of
lithionite-amazonite-albite granite. The Spokoinoe body is
a muscovite-albite granite with W (Sn, Be) mineralization.
To assess magma–host-rock interactions of the Khangilay-Orlovka intrusions within the regional geochemical
framework, greisenized Spokoinoe granites and a representative suite of host rocks (volcanics, hornfelses, metasediments, gabbro-diorite) were included in the study.
3
Results and discussion
The mixing diagram (Fig. 2) shows a strong relationship
between the barren parental granites of the Khangilay
pluton and the ore-bearing granites of the Orlovka and
Spokoinoe massifs. They all plot within a single linear
array. Despite a wide range of Pb isotope compositions
within each granite body, they do not differ significantly
among all three granite massifs (Dolgopolova et al. 2004).
It hints at fractionation from a homogenous (or homogenized) source melt with uniform initial 206Pb/204Pb and
207Pb/204Pb ratios. The overall data trend demonstrates a
simple mixing of the uniform Pb composition with different radiogenic components in the rocks and a strong
relation of the barren parental rocks to the ore-bearing
rocks. Lead isotope signatures of the host rocks are more
scattered than those of the granite rocks and are off the
granite’s mixing line.
The Orlovka ore-bearing amazonite granites, with the
highest Pb concentration, were used to identify the initial Pb isotopic signature subsequently transferred to the
ore-bearing rocks. The high Pb concentrations, up to 190
ppm, found in ore-bearing amazonite granites minimize
the effects of fluid-wall rock interaction and associated
perturbation to Pb systematics. The amazonite granites
are characterized by the lowest rate of radiogenic Pb accumulation because of their very low 238U/204Pb (µaverage
= 1.3). The calculated initial values for these “least sensitive” ore-bearing granites are very similar and their averages are: 206Pb/204Pb = 18.41 ± 0.02; 207Pb/204Pb = 15.56 ±
0.006; and 208Pb/204Pb = 38.3 ± 0.03 (Dolgopolova et al.
2004). Pb isotope compositions were also determined in
two separate grains of K-feldspar from the ore-bearing
amazonite granite of the Orlovka Ta-Nb deposit. Pb isotope analyses and U-Pb isotope dilution measurements
were carried out for blue-green cores and white feldspar
rims. Differences between core and rim Pb isotopic compositions are negligible within the limits of statistical significance. The averages of measured initial Pb isotope
compositions of feldspars are shown in Table 1.
The average values of initial Pb isotope composition
of ore-bearing granites were calculated previously to assess sources of the granitic magmas and were in the range
of: 206Pb/204Pb = 18.49 ± 0.05; 207Pb/204Pb = 15.57 ± 0.01
and 208Pb/204Pb = 38.23 ± 0.06 (Dolgopolova et al. 2004).
Our new data on Pb isotope compositions of K-feldspar
(Table 1) show very good agreement with the calculated
Close
Chapter 7-7 · Isotope systematics of ore-bearing granites and host rocks of the Orlovka-Spokoinoe mining district, eastern Transbaikalia, Russia
749
0.0012 (Fig. 4). The data for barren biotite-muscovite granites are in excellent agreement with published data of the
Orlovka-Spokoinoe granites, where the determined age
of granites was 142.9 ± 1.8 Ma at initial 87Sr/86Sr of 0.706
± 5 (Kovalenko et al. 1999).
5
initial Pb isotopic composition of the Orlovka granite
pluton.
Pb isotope systematics show the presence of a mantle
signature transferred during the formation of the studied granites (Figure 3). A mantle-derived component is
in a transitional field between mid-ocean ridge basalt
(MORB) and type II enriched mantle (EM II) (Zartman
and Doe 1981) but closer to the latter. There is a mixture
of different epochs presented on Figure 3. The mantle arrays indicate present-day mantle Pb isotopes while granite data reflects “frozen” Jurassic Pb isotope compositions.
If the mantle arrays are traced back to a Jurassic age with
less radiogenic EM II and MORB sources than the plotted arrays, they would slightly shift to the lower left part
of the plot and indicate EM II input.
Therefore, Pb isotopic data suggest two possible sources
contributed to the formation of the studied granites: 1) a
crust-mantle source where a mixture of MORB and upper crustal-derived material were brought together in an
orogenic environment; and 2) type II enriched mantle
source where subducted continental material could have
been strongly implicated in several island-arc volcanic
suites and the corresponding isotopic signatures, thus
reflecting a strong similarity of EM II with upper continental crust or continentally derived sediment.
4
New Rb-Sr age data
Seven samples of barren and ore-bearing granites of
Khangilay and Orlovka massifs were analyzed for Rb and
Sr isotope compositions. Analyses of four samples from
the barren granites yield a whole rock isochron age of
143.8 ± 4.2 Ma with an initial 87Sr/86Sr ratio of 0.7065 ±
Regional evidence for the proposed model
Evidence from Sr, Nd and O isotope investigations
(Kovalenko et al. 1999, 2002, 2003; Yarmolyuk et al. 2003)
is consistent with our lead isotope data reaffirming the
two possible common sources for granitic magmas of the
Orlovka-Spokoinoe mining district. However, there is no
unequivocal data implicating either a mixed upper crustmantle source or a type II enriched mantle source.
Regional studies of Transbaikalian granitoids incorporating geochemical, geophysical and geodynamic data
indicate both crustal and mantle inputs triggering granitic melt generation of all petrochemical series (Jahn et
al. 2000; Kovalenko et al. 1996; Litvinovsky et al. 2002).
The isotopic heterogeneity of these granites was predetermined by the isotopic heterogeneity of their sources
(Kovalenko et al. 1996). Blocks of consolidated preRiphean crust were overthrust during the accretionary
collision of the foldbelts onto the younger crustal complexes of within-block oceanic basins contributing to an
anomalous crustal thickness. The Riphean-aged crust in
Caledonian structures most likely reflects the same average composition of a mixed source (basites + pelites) of
the granitoid magmas; the source formed at 450-500 Ma.
The isotopic evolution of this source resulted in εNd(T) ~
0 of the mixed source by 100-200 Ma. Some of the young
(~120 Ma) granites show evidence of assimilation of preRiphean crust (Kovalenko et al. 1996). Some metaluminous
and peralkaline syenite-granite suites and closely associated comendites of Transbaikalia constrain A-type granitoid magma generation emplaced at ca. 280 Ma as a result of fractional crystallization of syenite magmas. Alkali-rich silicic magma formed at an estimated depth of
50-60 km far exceeding the normal crust thickness. The
Sr-Nd isotope data advocate the main role of mantle-de-
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A. Dolgopolova · R. Seltmann · C. Stanley · D. Weiss · B. Kober · W. Siebel
rived material in the source region from which the alkali-rich syenitic and granitic magmas were produced
(Litvinovsky et al. 2002). Also, widespread Transbaikalian
alkali monzodiorite-syenite series are explained by fractional crystallization from tephritic magma intrusions at
ca. 130 Ma. In contrast to calc-alkaline granite batholiths
generated during continental crustal growths, subalkaline
granites of Transbaikalia are often accompanied by basalt-trachyte-pantellerite-alkaline granite associations
marking rift structures of intraplate “hotspots” (Kovalenko
et al. 1996). The related Li-F and alkaline granites represent A-type granites with high heat production. Sr, Nd
and O isotope investigations of late Oligocene–Holocene
volcanics from the adjacent area of the Southern Baikal
region (Yarmolyuk et al., 2003) show that the isotopic signature of the magma source is a mixture of moderately
depleted mantle and enriched mantle reservoirs of types
I and II enriched mantle (EM I and EM II). EM II source
has been reported to be one of the mantle sources contributing to the formation of Early Mesozoic rocks of the
Mongolia-Transbaikalia magmatic area and has been listed
among mantle sources for the CAOB as a whole (Kovalenko
et al. 2002). The published data on Sr and Nd isotopes for
the Orlovka massif with the values of initial 87Sr/86Sr of
0.706 ± 0.005 and εNd = 0.1 (Kovalenko et al. 1999) also
favor EM II mantle input. Data hints at the possibility
that an EM II source controlled intraplate activity in Eastern Transbaikalia during late Mesozoic times including
formation of the Orlovka and Spokoinoe deposits.
6
Conclusions
Pb isotope data of crustal rocks and ore deposits of the
Orlovka-Spokoinoe mining district complement the existing Nd and Rb-Sr data for this region. Our results indicate
that the three granite massifs have uniform Pb isotope compositions and show a strong genetic relationship between
the barren biotite-muscovite granites of Khangilay and the
Spokoinoe and Orlovka ore-bearing granites suggesting a
common source for the three massifs. Pb isotope data also
confirm that the Khangilay pluton can be considered as the
parental intrusion for its hosted mineralized apical intrusions. Pb isotope systematics outline two possible scenarios
for the source of granitic melts: a mixed upper crust-mantle
source, and a type II enriched mantle source.
New Rb-Sr isotope data confirms the age of 143.8±4.2
Ma for biotite and biotite-muscovite granites of the
Khangilay and Orlovka massifs.
Acknowledgements
The authors would like to thank Russian colleagues who
participated in the INTAS 97-0721 project for inspiring
discussions, assistance in field sampling and analytical
support. Continuous assistance of the EMMA laboratory
at the Natural History Museum London and of Barry Coles
(Imperial College London) with the analytical part of the
project is acknowledged. This is a contribution to the IGCP
Project #473 “GIS Metallogeny of Central Asia”.
Close
Chapter 7-8
7-8
Syn-metamorphic dates for tourmaline formation
around Mount Isa, north-west Queensland, Australia
Robert J. Duncan, Andy R. Wilde
pmd*CRC, School of Geoscience, Monash University, Melbourne, VIC 3800, Australia
Roland Mass, Katherine Bassano
pmd*CRC, School of Earth Sciences, Melbourne University, Melbourne, VIC 3010, Australia
Abstract. Pb stepwise leaching of tourmaline from the Palaeoproterozoic Western Fold Belt of the Mount Isa Inlier yield dates of 1559±17
Ma, 1577±52 Ma and 1480±90 Ma. Structural, petrological and textural data suggest that 1559±17 Ma is the best estimate for peak
metamorphism in the area. Estimates of Pb closure temperature
and comparison with peak metamorphic temperatures indicate that
this age represents tourmaline crystallisation. These dates represent syn-metamorphic fluid flow and indicate metal mobility during the Isan Orogeny. A result of this event is regional-scale silicification that has the same relative timing as extensive silica deposition in the rocks that now host the Cu orebodies at Mount Isa.
Keywords. Mount Isa, metamorphism, tourmaline, hydrothermal fluid
flow, Pb stepwise leaching
1
Introduction
To further constrain the timing of the Isan Orogeny in
the Western Fold Belt of the Mount Isa Inlier we applied
the Pb step-leaching (PbSL) technique to tourmaline. PbSL
involves sequential acid leaching of low-U minerals to
generate Pb-Pb isochrons for old (>400 Ma) rocks (Frei
and Kamber 1995). The tourmaline samples dated here
can be demonstrated to have formed under, or close to,
peak metamorphic conditions using structural, petrographical and geochemical evidence.
As tourmaline is generally considered metasomatic in
origin, this work not only allows an improved understanding of the timing of peak metamorphism, but also new
insights into the nature of fluid flow associated with compressional deformation. The timing and nature of this
hydrothermal event has potential implications for the Cu
mineralisation at Mount Isa.
2
Previous work
The polydeformed mid- to late Proterozoic Mount Isa Inlier in north-west Queensland was tectonically active between 1900 and 1500 Ma (Blake and Stewart 1992). The
most intense period of deformation is considered to be
largely synchronous with peak high temperature-low pressure metamorphism that resulted from crustal shortening during the Isan Orogeny from 1590 to 1500 Ma
(Connors and Page 1995; O’Dea et al. 1997).
Previous attempts to date peak metamorphism have
focused on U-Pb analysis of zircon and monazite (Connors
and Page 1995; Hand and Rubatto 2002), but their relationship to metamorphic reactions and structural features
is ambiguous (e.g. Roberts and Finger 1997). Published
Ar-Ar biotite dates (Perkins et al. 1999) are likely to represent cooling ages past the closure temperature. Table 1
summarises the current age estimates of peak metamorphism on single mineral phases.
3
Tourmaline occurrence, petrography and
geochemistry
Tourmaline-rich lithologies are abundant in areas around
Mount Isa. Tourmaline is especially prevalent in the Eastern Creek Volcanics (ECV) west of the Mount Isa fault. In
this area it occurs in quartz-K feldspar-mica-apatite
pegmatites around the contact of the Sybella Batholith
and apparently stratabound, but not stratiform,
tourmalinites (representative of extensive silicification).
Minor tourmaline occurrences have been identified in
the ECV to the east of Mount Isa. The three samples selected for dating are from within a 25 km radius of Mount
Isa and are in close proximity to small mineral occurrences (Fig. 1).
Tourmaline has been identified as an accessory phase
in the silica dolomite alteration halo to the Cu orebodies
at Mount Isa (Mathias and Clark 1975). The silicification
at the mine is considered to have occurred prior to Cu
mineralisation, synchronous with D2 or D3 deformation
(Swager 1985; Wilde et al. this volume) during the peak
of deformation. The orebody tourmaline is dravitic in
Close
752
Robert J. Duncan · Andy R. Wilde · Roland Mass · Katherine Bassano
composition and is concentrated in the Paroo Fault in
the footwall of the Cu orebodies (W. Perkins and J. Knights
pers. comm. 2004).
Tourmaline from close to the King Cu deposit is
stratabound, but not stratiform within quartzite and
psammopelitic units of the Myally subgroup. Tourmaline
growth overprints the S2 fabric, defined by biotite and
sillimanite, and is deformed by D3 NNW-trending shear
zones and NNW gently plunging meso-scale folds (Fig. 2a).
The sample consists of zoned glomerocrysts and coarsegrained strained quartz, along with minor amounts of
titanite, sphalerite and Fe-Ti oxides.
Adjacent to the Eldorado U deposit (hosted by the ECV)
is a quartz-tourmaline-K feldspar-mica pegmatite. The pegmatite is parallel to the S2 fabric and is boudinaged by D3
structures. Tourmaline in the pegmatite selvages defines a
steeply plunging mineral lineation (L2) and pseudomorphs cordierite poikiloblasts in the wall rock (Fig. 2b). Primary fluid inclusions within tourmaline from this sample
contain up to 436 ppm U (Duncan and Wilde 2004).
At Anderson’s Lode (a small U deposit hosted by the
ECV) a quartz-fibrous tourmaline vein is deformed by
D3 shearing. Host rock tourmaline is overprinted by a biotite-chlorite metamorphic matrix (Fig. 2c). These relationships suggest that tourmaline crystallisation was early
to syn-metamorphic and pre-D3 in timing. Paragenetically associated with the quartz-tourmaline vein are minor amounts of pyrite and chalcopyrite.
Electron-microprobe analyses demonstrate the transitional Fe-Mg composition of all the tourmaline samples.
Tourmaline from Anderson’s Lode is schorlitic, whilst
samples from Eldorado and King are dravitic. Trace element analysis by laser ablation ICP-MS reveals that the
tourmalines are relatively enriched in light rare earth elements with variable Eu and Ce anomalies, indicative of
crystallisation from a metamorphic fluid (cf. Jiang et al.
2004).
4
Pb stepwise leaching
PbSL was carried out at the University of Melbourne. The
main advantage of PbSL over bulk U-Pb dating is the ability to chemically separate Pb from U-rich and U-poor
domains within the samples, thus generating Pb isotopic
dispersion from a single mineral separate. 208Pb/206Pb systematics can be used to recognise, and discard if necessary, results from leach steps dominated by unequilibrated
impurities with distinct Th/U ratios, such as zircon and
monazite.
Tourmaline concentrates (200 to 400 µm) were produced by conventional dense medium separation and
purified by hand-picking. After removal of surficial Pb
contamination with distilled water, samples weighing 80
to 100 mg were sequentially leached with 1.5 N HCl-2N
HBr mix, 1N and 8N
Close
Chapter 7-8 · Syn-metamorphic dates for tourmaline formation around Mount Isa, north-west Queensland, Australia
HBr, 7N and 15N HNO3 and 48% HF on a hot plate at
~100oC for periods of five minutes to 120 hours. Pb from
each leach step was extracted using a single pass over 0.1
ml columns of EICHROMTM Sr resin following the method
of Thériault and Davies (1999). Pb isotopic ratios were
determined by multi-collector ICP-MS (Woodhead 2002).
753
Pb-Pb isochrons parameters and ages were calculated
using ISOPLOT (Ludwig 2003). External 2sigma m
(±0.03%) or internal (2sigmam) errors (whichever is
greater) and error correlations derived from these uncertainties were used as input errors for the isochron calculations. No blank corrections were applied.
Tourmaline from Anderson’s Lode yielded five leach
steps, with a range in 206Pb/204Pb of 17.2 to 72.9. A regression of all five leach steps identifies some scatter (MSWD
77), but a relatively precise Pb-Pb isochron age of 1559±17
Ma (Fig. 3a).
Seven leach steps derived from the tourmaline at
Eldorado gave a range in 206Pb/204Pb from 19.9 to 67.2,
regression of all the data indicates a excessive amount of
scatter (MSWD >6000). Inspection of the 208Pb/206Pb data
shows that three leach steps are affected by Pb from Thrich micro-inclusions. Omission of these points results
in a four-point age of 1577±52 Ma (MSWD 46; Fig. 3b).
The five leach spectra of the tourmaline from King
yield the narrowest range in 206Pb/204Pb (16.4 to 35.3).
After the removal of one step with anomalously high 208Pb/
206
Pb (i.e., Pb derived from Th-rich inclusions), this short
data array produce an imprecise age of 1488±90 Ma
(MSWD 16; Fig. 3c).
5
Interpretation of ages
Estimates of Pb closure temperatures in tourmaline for
compositions similar to these samples were calculated
according to the method outlined by Dahl (1997) and range
from 580 oC to 630 oC. The Anderson’s Lode area is
characterised by low to mid-greenschist facies rocks, so
the 1557 Ma date reflects tourmaline formation. Around
Eldorado peak metamorphic temperatures are estimated
at 540oC to 640oC (Rubenach 1992) and at King temperatures of ~600oC are likely to have been encountered during peak metamorphism (Connors 1992). At these two
locations the ages and associated large errors may represent a period of elevated heat flow, when the ambient geothermal gradient was above the Pb closure temperature
and Pb could diffuse easily. The may explain the range of
U-Pb zircon dates (Table 1; 1565 to 1480 Ma from one
sample in Connors and Page (1995)).
Comparing age data derived from Pb-Pb dating of tourmalines with other metamorphic dates it is clear that between ~1575 and ~1530 Ma the Western Fold Belt around
Mount Isa was undergoing high-temperature/low-pressure
peak metamorphism. This metamorphic window reflects
the prolonged duration of tectonic shortening during the
Isan Orogeny. It appears that regional tourmalinisation resulted from prolonged hydrothermal activity related to this
compressional deformation. The best estimate of peak metamorphism is now ca. 1557±17 Ma.
The occurrence of tourmaline with small Cu and U
deposits and paragenetic relationships with minor
Close
754
Robert J. Duncan · Andy R. Wilde · Roland Mass · Katherine Bassano
sulphides suggests that during hydrothermal fluid movement driven by metamorphism, metals of economic interest were mobile. The regional spatial and temporal association of tourmalinisation with silicification indicates
that the silica-rich halo around the Cu orebodies may have
formed at a similar time.
Acknowledgements
The PbSL routines are based largely on unpublished experiments by M Tonelli, J Hergt and J Woodhead (Univ.
of Melbourne). The work reported is part the pmd*CRC
with support from Xstrata Copper. Thanks to R. Romer
for reviewing this abstract.
References
Blake DH, Stewart AJ (1992) Stratigraphic and tectonic framework,
Mount Isa Inlier. In: Stewart AJ, Blake DH (eds) Detailed studies
of the Mount Isa Inlier. Aust Geol Surv Organ Bull 243: pp 1-11
Connors KA (1992) Tectonothermal evolution of the Mount Novit
Ranges, Mount Isa Inlier, Australia. PhD Thesis, Monash University
Connors KA, Page RW (1995) Relationships between magmatism,
metamorphism and deformation in the western Mount Isa Inlier, Australia. Precambr Res 71: 131-153
Dahl PS (1997) A crystal-chemical basis for Pb retention and fissiontrack annealing systematics in U-bearing minerals, with implication for geochronology. Earth Planet Sci Lett 150: 277-290
Duncan RJ, Wilde AR (2004) Tourmaline at Mount Isa, Australia: a
tracer of metal-rich hydrothermal fluid flow. In: Muhling J et
al. (eds) SEG 2004: Predictive Mineral Discovery Under Cover,
Perth, Western Australia; Extended Abstracts, Centre for Global Metallogeny, The University of Western Australia Publication 33: 413
Frei R, Kamber BS (1995) Single mineral Pb-Pb dating. Earth Planet
Sci Lett 129: 261-268
Hand M, Rubatto D (2002) The scale of the thermal problem in the
Mt. Isa Inlier. In: Preiss VP (ed) Geoscience 2002: Expanding
Horizons. Abstracts of the 16th Australian Geological Convention, Adelaide, SA, Australia 67: 173
Jiang SY, Yu JM, Lu JJ (2004) Trace and rare-earth element geochemistry in tourmaline and cassiterite from the Yunlong tin deposit,
Yunnan, China: implications for migmatic-hydrothermal fluid
evolution and ore genesis. Chem Geol 209: 193-213
Ludwig KR (2003) User’s Manual for Isoplot 3.00: A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center
Spec Publ 4, California, p 70
Mathias BV, Clark GJ (1975) Mount Isa copper and silver-lead-zinc
ore bodies; Isa and Hilton mines. In: Knight CL (ed) Economic
Geology of Australia and Papua New Guinea. Aust Inst Mining
Metall, pp 351-371
O’Dea MG, Lister GS, MacCready T, Betts PG, Oliver NHS, Pound KS,
Huang W, Valenta RK (1997) Geodynamic evolution of the Proterozoic Mount Isa terrain. In: Burg JP, Ford M (eds) Orogeny
through time. Geol Soc Spec Publ 121: 99-122
Perkins C, Heinrich CA, Wyborn LAI (1999) 40Ar/39Ar geochronology of copper mineralization and regional alteration, Mount Isa,
Australia Econ Geol 94: 23-36
Roberts MP, Finger F (1997) Do U-Pb zircon ages from granulites
reflect peak metamorphic conditions? Geology 25: 319-322
Rubenach MJ (1992) Proterozoic low-pressure/high-temperature metamorphism and an anticlockwise P-T-t path for the Hazeldene area,
Mount Isa Inlier, Queensland, Australia. J Meta Geol 10: 333-346
Swager CP (1985) Syndeformational carbonate-replacement model for
the copper mineralization at Mount Isa, Northwest Queensland; a
microstructural study. Econ Geol 80: 107-125
Thériault RJ, Davies WJ (1999) Rapid extraction of Sr and Pb by ionspecific chromatography for thermal ionisation mass spectrometry analysis. In Radiogenic age and isotopic studies, report 12,
Geol Surv Can Current Research 1999-F: 9-12
Wilde AR, Gregory MJ, Duncan RJ, Gessner K, Kühn M, Jones P (2005)
Geochemical process model for the Mt Isa Cu-Co-Ag deposits,
this volume
Woodhead JD (2002) A simple method for obtaining highly accurate Pb isotope data by MC-ICP-MS. J Anal Atom Spec 17: 1-6
Close
Chapter 7-9
7-9
Potassic alteration and veining and the age of copper
emplacement at Mount Isa, Australia
Melissa J. Gregory, Andy R. Wilde, Bruce F. Schaefer, Reid R. Keays
pmd*CRC, School of Geoscience, Monash University, Melbourne, VIC 3800, Australia
Abstract. Preliminary 187Re/188Os dating of whole rocks and sulphide
separates from the Mount Isa copper orebody has generated an
isochron age of 1367 ± 80 Ma (MSWD = 49; n = 6). This age is approximately 150 myr younger than published biotite 40Ar/39Ar ages
previously assumed to date the copper-forming event at ca. 1523
Ma. These older ages are from rocks in which biotite is likely to be
metamorphic rather than hydrothermal in origin. Unambiguous
potassic alteration related to copper formation is characterised by
biotite replacement of metabasalt (brownstones) and potassium
feldspar replacement of meta-tuffs. Previous 40Ar/39Ar dating of biotite from brownstone yields 1352 Ma to 1385 Ma ages, while 87Rb/
86
Sr dating of potassium feldspar altered tuffs gives 1323 Ma. Muscovite from the Buck Quartz Fault, considered a conduit for copper
mineralising fluids, yields an 40Ar/39Ar age of 1324 Ma. We suggest
that these ages more accurately reflect the age of copper emplacement, whereas the older 40Ar/39Ar ages more likely relate to cooling from peak metamorphism.
Keywords. Mount Isa, Re-Os, potassic alteration
1
Introduction
The Mount Isa copper deposit contains over 13 million
tonnes of copper at 3.3 wt.%, and is hosted within the
Proterozoic Urquhart Shale (Perkins 1990). Textural evidence suggests that chalcopyrite-pyrrhotite mineralisation
occurred late in the tectonic history of the Mount Isa Inlier (Perkins 1984; Swager 1985; Valenta 1994; Waring
1990). The absolute age of copper mineralisation, however, is poorly defined. In this paper we discuss the available radiometric data and their significance. Most published data are from potassic phases, such as biotite, muscovite and potassium feldspar so it is necessary to review
evidence for the relationship of such phases to copper
deposition.
2
Metamorphic biotite
2.1 Eastern Creek Volcanics
The Eastern Creek Volcanics below and to the east of the
Mount Isa copper deposit have undergone lower
greenschist facies metamorphism. Stable assemblages in
the metabasalts include chlorite, albite, actinolite, epidote,
calcite, titanomagnetite, magnetite, sphene and biotite.
Biotite and chlorite define a metamorphic foliation in
some areas.
2.2 Urquhart Shale
Biotite is a common phase in metasedimentary rocks of
the Mount Isa Group, including the Urquhart Shale. It
defines the peak metamorphic foliation, and ranges in
composition from Fe-rich to more magnesian phlogopite,
depending on the host rock composition.
Biotite is rare in the intense silica-dolomite alteration
associated with economic copper mineralisation, but distinctive biotite-magnetite-stilpnomelane bearing rocks
occur in close proximity to Pb-Zn ore (Fig. 1). Swager et
al. (1987) interpret these zones to be the result of the interaction of the copper mineralising fluid with pre-existing iron-rich metasomatic rocks in the Urquhart Shale.
Conversely, Waring (1990) suggests that these zones were
the result of greenschist facies metamorphism. He notes
that the biotite-magnetite-stilpnomelane assemblage is
cut by dolomite veins considered to be contemporaneous
with copper emplacement.
3
Absolute age of metamorphism
The absolute age of the peak (maximum temperature and
pressure) of regional metamorphism is poorly constrained. Biotite from the Eastern Creek Volcanics 14.5
km east of the mine, gave 40Ar/39Ar ages of 1534 ± 4 Ma
and 1524 ±3 to 1554 ± 2 Ma (Perkins et al. 1999). These
ages were interpreted to reflect hydrothermal activity at
the end of regional metamorphism at 1534 Ma. This date
is consistent with the SHRIMP U-Pb zircon ages of 1532
± 7 Ma by Connors and Page (1995) and the whole rock
87Rb/86Sr ages of 1544 ± 12 Ma from Page and Bell (1986).
U/Pb monazite dating by Hand and Rubatto (2002)
suggests that peak metamorphism is older at ca. 1575 Ma.
This older age is supported by new metamorphic tourmaline dates of 1559 ± 17 Ma and 1577 ± 52 Ma using PbPb step leaching (Duncan et al. this volume).
4
Potassic alteration
4.1 Urquhart Shale
There are over 60 potassium-rich layers within the
Urquhart Shale throughout the Mount Isa mine sequence
(Croxford 1964). These layers are typically less than 5 cm
Close
756
Melissa J. Gregory · Andy R. Wilde · Bruce F. Schaefer · Reid R. Keays
thick, and characterised by an unusual pale gray colour.
Croxford (1964) interpreted these layers as tuffs, based
on the rare presence of glass shards. The tuffs consist of
microcline (after adularia), quartz, rutile, hematite, sericite
and carbonate. Perkins (1997), however, found that only
the tuffs in the mine area were potassium-rich, suggesting a hydrothermal origin for potassium.
4.2 Eastern Creek Volcanics
Detailed logging of drillcore at the northern end of the
Mount Isa copper deposit (mine section 38,000 mN) has
defined a zone of potassium-rich alteration within the
Eastern Creek Volcanics, below copper mineralisation in
the Urquhart Shale (Fig. 1). This zone, which is dominated
by biotite, has previously been called brownstone and has
been reported in many deep drillholes that have inter-
sected the Eastern Creek Volcanics below the Mount Isa
copper deposit (e.g. Hannan et al. 1993).
This biotite-rich alteration parallels the Paroo Fault
(Fig. 1) and is thicker (up to 70m) where copper
mineralisation overlies the fault. In thin section, the biotite-dominated rocks have a groundmass of chlorite, albite and ilmenite that is overprinted by a fine network of
biotite veinlets. Undeformed biotite also pseudomorphs
weakly foliated chlorite.
4.3 Potassium feldspar veining
Away from biotite-rich zones, potassium-rich veins are
observed in the metabasalts of the Eastern Creek Volcanics.
These veins are dominated by potassium feldspar, calcite, quartz and chalcopyrite and are commonly 2 to 5
mm thick. Typically the veins are zoned with potassium
feldspar lining the metabasalt contact and calcite with
lesser quartz in the core. Chalcopyrite is intergrown with
the potassium feldspar. The vein boundaries are sharp
and cross cut the peak metamorphic foliation found within
the metabasalts.
5
Absolute age of ore formation
Preliminary 187Re/188Os isotopic analyses of whole rocks
and sulphide separates from the Mount Isa copper orebody
define an imprecise isochron age of 1367 ± 80 Ma (Fig. 2).
87Rb/86Sr dating of potassic altered tuff horizons from
the mine area define isochron ages from 1341 ± 21 Ma to
1474 ± 202 Ma (Farquharson and Richards 1975; Page
Close
Chapter 7-9 · Potassic alteration and veining and the age of copper emplacement at Mount Isa, Australia
1981). A significantly more precise age is achieved by combining the two data sets (as all samples are from the same
lithology and area) to give an age of 1323 ± 12 Ma (Gregory et al. 2004). A radiogenic initial ratio of 0.7418 ±
0.0061 suggests isotopic resetting may have occurred at
this time (Farquharson and Richards 1975; Gregory et al.
2004; Page 1981).
Perkins et al. (1999) reported numerous 40Ar/39Ar dates
for biotite and muscovite from the Urquhart Shale and
the Eastern Creek Volcanics (Table 1). Biotite and phlogopite from stilpnomelane-magnetite zones gave 40Ar/39Ar
ages of 1523 ± 3 Ma and 1516 ± 3 Ma, from which 1523
Ma was interpreted as the most likely date of copper ore
deposition (Perkins et al. 1999).
Perkins et al. (1999) also dated biotite separates from
brownstones within the Eastern Creek Volcanics adjacent
to the copper deposit. 40Ar/39Ar dating of these separates
gave distinct plateau ages at 1352 ± 3 Ma and 1385 ± 3
Ma, which was interpreted as the age of late stage fluid
flow.
Muscovite from the Buck Quartz Fault, interpreted to
be the inflow zone for the copper bearing fluids (Waring
1990), gave an 40Ar/39Ar age of 1324 ± 2 Ma, also interpreted as due to minor late stage fluid flow (Perkins et al.
1999).
6
Discussion and conclusions
Biotite and phlogopite are virtually absent from intensely
altered and mineralised rocks which form the Mount Isa
copper deposit but there is a close spatial relationship
between biotite-rich alteration below the Paroo Fault and
copper mineralisation above the fault. The biotite overprints the metamorphic foliation and the spatial relationships and timing supports the idea of hydrothermal fluid
757
flow along the fault, as suggested by Hannan et al. (1993)
and Heinrich et al. (1995).
Chalcopyrite-bearing potassium feldspar veins overprint
the metamorphic foliation and therefore have the same relative timing as the biotite-rich alteration and the copper ore.
The presence of both biotite-rich alteration below the Paroo
Fault and potassium feldspar-rich veins demonstrates the
presence of a potassium and copper-rich fluid. This fluid
post-dates regional metamorphism and is spatially associated with the Mount Isa copper deposit.
A number of isotopic dating techniques suggest that
the peak of metamorphism at Mount Isa occurred prior
to 1532 Ma and possibly prior to 1575 Ma. Emplacement
of the Mount Isa copper deposit, based on numerous studies, clearly postdates the metamorphic peak. The absolute age of copper emplacement however, and particularly the gap between the conclusion of metamorphism
and ore formation has been poorly defined.
Our re-evaluation of published 40Ar/39Ar and 87Rb/86Sr
data on potassic hydrothermal alteration, together with
our preliminary 187Re/188Os dating of sulphide ore suggest that copper mineralisation was emplaced between
1300 Ma and 1400 Ma, at least 130 million years after the
metamorphic peak.
An alternative interpretation may be that the terrain
remained above the closure temperature for these systems for several hundred million years after the peak of
metamorphism.
We suggest that the ca. 1523 Ma age of Perkins et al.
(1999), previously assumed to be the date of copper ore
formation, instead dates cooling from the metamorphic
peak. The maximum temperature of ore formation is suggested to be between 300 and 350°C (Heinrich et al. 1989;
Heinrich et al. 1995), and may not have exceeded the Ar
closure temperature range of the metamorphic biotite.
Therefore, there is significantly more evidence to support a ca. 1350 Ma age for copper mineralisation compared with the previously accepted ca. 1523 Ma age. This
has implications for the genetic models proposed for the
formation of the Mount Isa copper deposit.
Acknowledgements
Work reported here was conducted as part of the
pmd*CRC with support from Xstrata Copper.
References
Connors KA, Page RW (1995) Relationships between magmatism,
metamorphism and deformation in the western Mount Isa Inlier, Australia. Precambr Res 71:131-153
Croxford NJW (1964) Origin and significance of volcanic potashrich rocks from Mount Isa. Inst. Min. & Met. Tr. 74:33-43
Duncan RJ, Wilde AR, Maas R, Bassano K (2005) Syn-metamorphic
dates for tourmaline formation around Mount Isa, North-west
Queensland, Australia, this volume
Close
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Melissa J. Gregory · Andy R. Wilde · Bruce F. Schaefer · Reid R. Keays
Farquharson RB, Richards JR (1975) Isotopic remobilization in the
Mount Isa tuff beds. Chem Geol 16:73-88
Gregory MJ, Wilde AR, Keays RR, Schaefer BF (2004) Preliminary ReOs dating of the Mount Isa copper ores, Northwest Queensland.
Barnicoat AC, Korsch RJ (eds) Predictive Mineral Discovery Cooperative Research Centre – Extended Abstracts, Geoscience Australia Record 2004/09, pp 79
Hand M, Rubatto D (2002) The scale of the thermal problem in the
Mt Isa Inlier. In: Preiss VP (ed) Geoscience 2002: Expanding Horizons, 16th Australian Geological Convention, Adelaide, South
Australia, pp 173
Hannan KW, Golding SD, Herbert HK, Krouse HR (1993) Contrasting alteration assemblages in metabasites from Mount Isa,
Queensland; implications for copper ore genesis. Econ Geol
88:1135-1175
Heinrich CA, Andrew AS, Wilkins RWT, Patterson DJ (1989) A fluid
inclusion and stable isotope study of synmetamorphic copper
ore formation at Mount Isa, Australia. Econ Geol 84:529-550
Heinrich CA, Bain JHC, Mernagh TP, Wyborn LAI, Andrew AS, Waring CL (1995) Fluid and mass transfer during metabasalt alteration and copper mineralization at Mount Isa, Australia. Econ
Geol 90:705-730
Page RW (1981) Depositional ages of the stratiform base metal deposits at Mount Isa and McArthur River, Australia, based on U-Pb
zircon dating of concordant tuff horizons. Econ Geol 76:648-658
Page RW, Bell TH (1986) Isotopic and structural responses of granite to successive deformation and metamorphism. Journal of
Geology 94:365-379
Perkins C, Heinrich CA, Wyborn LAI (1999) 40Ar/39Ar geochronology of copper mineralization and regional alteration, Mount Isa,
Australia. Econ Geol 94:23-36
Perkins WG (1984) Mount Isa silica dolomite and copper orebodies;
the result of a syntectonic hydrothermal alteration system. Econ
Geol 79:601-637
Perkins WG (1990) Mount Isa copper orebodies. In: Hughes FE (ed)
Geology of the mineral deposits of Australia and Papua New
Guinea. Aust Inst Mining Metall, pp 935-941
Perkins WG (1997) Mount Isa lead-zinc orebodies; replacement lodes
in a zoned syndeformational copper-lead-zinc system? Ore Geol
Rev 12:61-111
Swager CP (1985) Syndeformational carbonate-replacement model for
the copper mineralization at Mount Isa, Northwest Queensland; a
microstructural study. Econ Geol 80:107-125
Swager CP, Perkins WG, Knights JG (1987) Stratabound phyllosilicate
zones associated with syntectonic copper orebodies at Mt. Isa,
Queensland. Aust J Earth Sci 34:463-476
Valenta R (1994) Syntectonic discordant copper mineralization in
the Hilton Mine, Mount Isa. Econ Geol 89:1031-1052
Waring CL (1990) The Genesis of the Mount Isa Copper Orebodies.
PhD, Monash University
Close
Chapter 7-10
7-10
Contact metamorphism at the manganese deposits of
the Noda-Tamagawa Mine, northeast Japan: Insight
from oxygen isotope data of manganese minerals
Ken-ichiro Hayashi
Doctoral Program in Earth Evolution Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba,
Tsukuba 305-8572, Japan
Abstract. Manganese ores of the Noda-Tamagawa mine are metamorphosed equivalents of bedded-type sedimentary manganese
deposits. The ore lenses are typically zoned with a central
pyrochroite-hausmannite zone, outer tephroite zone, and outermost
rhodonite zone closest to the wall rock chert. The δ18O (VSMOW)
values of 65 tephroite, 32 rhodonite and eight quartz samples from
the manganese ores and chert are in the ranges of 9.9–20.0‰, 11.7–
20.3‰ and 23.0–23.9‰, respectively. The overall order of 18O-enrichment corresponds to the order of equilibrium fractionation
among these minerals. However, the temperatures calculated from
quartz-rhodonite and rhodonite-tephroite pairs from neighboring
ore zones do not give temperatures consistent with those estimated
from the mineral assemblages in the wall rocks. These data suggest
that equilibrium was not established among neighboring mineral
pairs, H2O, and CO2 during metamorphism. The fluid/rock ratios
during metamorphism were very low (<< 1).
Keywords. Manganese deposit, oxygen isotope, contact metamorphism, metamorphic fluid
1
Introduction
Manganese ores of the Noda-Tamagawa mine are highly
metamorphosed and folded. This metamorphism makes
it difficult to obtain information on the primary features
of the deposits, such as the original mineralogy, chemical composition, and environment of deposition. Despite
these difficulties, the deposit is interpreted to be the metamorphosed equivalent of bedded-type sedimentary manganese deposits. The main objective of this study is to
elucidate the origin and metamorphic history of the manganese ores at Noda-Tamagawa using the δ18O relationships among various metamorphic Mn-bearing silicate
minerals. These data constrain the temperatures of metamorphism, fluid/rock ratios, and composition of the metamorphic fluids.
2
Geology of the Noda-Tamagawa mine
The manganese deposits of the Noda-Tamagawa mine are
situated in the northeastern part of a roof pendant of the
granodiorite body. The roof pendant is ca. 8 km (N-S) x
12 km (E-W) in area, and is comprised of the Jurassic
Formation. In the vicinity of the Noda-Tamagawa mine,
these rocks have been hornfelsed due to the thermal meta-
morphism by the granodiorite. Sillimanite, andalusite, and
cordierite are present in some pelitic hornfels near the
manganese ore bodies.
As a result of the thermal metamorphism, a distinct
zoning of manganese minerals developed in each ore lens,
on a scale of 2 to 5 m. Pyrochroite (Mn(OH) 2) and
hausmannite (Mn3O4) typically occupy the central part
of the ore lens (0 to 1 m in thickness), surrounded by a
tephroite (Mn2SiO4) ore, and an outer rhodonite (MnSiO3)
ore.
The major Mn-bearing minerals in the NodaTamagawa mine can be represented in the MnO-SiO2Al2O3 system. The principal zoning sequence in the ore
lenses of the Noda-Tamagawa mine corresponds to a trend
of decreasing MnO content (and increasing SiO2 content)
toward the wall rocks. Bulk chemical compositions of the
manganese ores change along the MnO-SiO2 join from
near the MnO apex for pyrochroite-hausmannite ore in
the central part of the bed to rhodonite near the wall rock.
3
Oxygen isotope study
Mineral grains were hand picked from thick sections of
~0.5 mm under a binocular microscope. Since most ore
samples of this study are monomineralic in nature, the
purities of mineral separates were better than 95 %.
Extraction of oxygen from quartz, rhodonite and
tephroite was carried out using a CO2-laser and BrF5 by a
fluorination method similar to that described by Hayashi
et al. (2001). The reproducibility of the δ18O values was
better than ±0.2 ‰.
4
Results and discussion
The δ18O values of quartz samples from 3 localities of the
mine have a narrow range from 23.0 to 23.9 ‰. Quartz
from thin quartz layers in rhodonite ore has essentially
the same δ18O value as quartz in the wall rock chert. Thirtytwo samples of rhodonite from rhodonite ore have δ18O
values that range from 11.7 to 20.3 ‰; 65 samples of
tephroite from tephroite ore and have values from 9.9 to
20.1 ‰. The order of 18O enrichment is generally quartz
> rhodonite > tephroite, which corresponds to the ex-
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760
Ken-ichiro Hayashi
pected order of enrichment for isotopic equilibrium between minerals. Reversals in the order of 18O enrichment
(i.e., nonequilibrium relationships) was observed for some
rhodonite and tephroite pairs that were collected from
zones separated by a distance of less than 1 m.
The δ18O values for the series of samples from ore stope
L13S78 do not show a symmetrical pattern from the wall
rocks toward the center of the ore lens. In general, the
δ18O values of both rhodonite and tephroite are higher in
the footwall of the ore zone than those in the hanging
wall.
Because the manganese ores in the Noda-Tamagawa
mine are generally monomineralic on a hand specimen
scale, truly coexisting mineral pairs are difficult to obtain. However, if the Mn-silicates and oxides were both
formed from MnCO3 and SiO2 (i.e., the most probable
primary mineral assemblage of the Mn ores before
metamorphism) in conditions accompanying a large
amount of metamorphic fluid, isotopic equilibrium may
be expected among minerals in samples up to a few meters
apart.
Isotopic equilibrium temperatures were calculated for
mineral pairs in the neighboring zones within individual
ore lenses (Fig. 1). Except for one very high temperature,
three quartz-rhodonite and four rhodonite-tephroite pairs
give temperatures between 545°C and 145°C. These temperatures are much lower than the estimated metamorphic temperatures and suggest that the minerals did not
equilibrate at peak temperature. The presence of sillimanite, although it is rare in the pelitic hornfelses near the
manganese ore bodies suggests that the peak metamorphic temperature was near the stability limits for andalusite and sillimanite (ca. 600°C at P= 2kb).
The δ18O values for H2O and CO2 in equilibrium with
quartz, rhodonite and tephroite at the calculated temperatures are variable, 7.6 to 18.4 ‰ for H2O and 16.7 to 33.6
‰ for CO2. These data suggest that the equilibrium was
not established among neighboring mineral pairs, H2O,
and CO2 during the metamorphism. At high fluid/rock
ratios, isotopic equilibrium between the neighboring (but
non-coexisting) minerals would be expected. Therefore,
our data suggest that the fluid/rock ratios during metamorphism were very low (<< 1) or that fluids with different isotopic compositions were present. A comparison of
δ18O values between the manganese silicate minerals of
this study and calc-silicate minerals from skarn deposits
provides constraints on the nature of metamorphism and
the origin of the isotopic composition of the Mn-minerals. As the skarn minerals were probably equilibrated with
magmatic or meteoric water (e.g. El Rhazi and Hayashi
2002), the relatively narrow range of δ18O values of the
skarn minerals was probably controlled by the δ18O values of skarn-forming water. In contrast, the wide range
of δ18O values for the manganese minerals in this study
suggests that their isotopic compositions mainly reflect
the precursor minerals. The contribution of 18O-depleted
fluids during metamorphism was not important.
References
El Rhazi M, Hayashi K (2002) Mineralogy, geochemistry, and age
constraints on the Beni Bou Ifrour skarn type magnetite deposit,
northeastern Morocco. Resource Geology 52: 25-39
Hayashi K, Maruyama T, Satoh H (2001) Precipitation of gold in a
low-sulfidation epithermal gold deposit: insights from a submillimeter-scale oxygen isotope analysis of vein quarts. Economic
Geology, 96: 211-216
Close
Chapter 7-11
7-11
Isotopic geochemistry of Mesozoic igneous rocks and
mineralization of Shanmen silver deposit in Yi-Su Basin,
Jilin Province
Huang Wenbin
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, and Chinese Geological Library,
Beijing 100083, China
Shen Haoche
JIlin University, Changchun Jilin, 130021, China
Fen Lin
Research Institute, China Water Northeastern Investigation Design and Research Co. Ltd., Changchun, 130021, China
Abstract. The present study focuses on isotopic geochemistry of the
Mesozoic igneous rocks and the Shanmen silver deposit in Yi-Su basin.
Petrochemistry, isotopic geochemistry and isotopic geochronology are
used to explore the relationship between regional magmatic activity
and the formation of the ore deposit. In this study, we explore the isotopic geochemistry in the deposit and the surrounding igneous rocks
by studying Rb, Sr, Pb, S, H and D isotopes. This helps us to discern the
source of the economic minerals and the metallogenetic mechanism
responsible for the formation of the Shanmen silver deposit.
Keywords. Igneous rock, isotopic geochemistry, silver deposit, source
of ore material
1
Introduction
The Yi-Su basin is located in the fold zone of the TianShanXinan orogenic belt, where two deep parallel faults known
as the Yi-Su fracture zones, are oriented 45~50°E and extend to the base of the lithosphere. The strata from the
Paleozoic group to the Cenozoic group lie along the side
of the basin. Metamorphosed igneous rocks that have
experienced alteration and compressional deformation,
outcrop around the outer edge of the basin. Many economic deposits have been discovered in this region, including iron, copper, gold, silver, and coal, fluorite deposits. These deposits are controlled by fractures and show
an intimate relationship with Mesozoic igneous rocks.
The Shanmen silver deposit is located in the Yi-Su basin. In this paper, we present a detailed study of isotopic
geochemistry of the Mesozoic igneous rocks and the sliver
ore in order to determine the relationship between magmatic activity and mineralization.
2
Isotopic geochemistry and formation of igneous
rocks
2.1 Petrochemistry
A variety of igneous rocks from the Herynian to Himalayan can be found in the Yi-Su basin.Neutral and acidic
magmatic rocks comprise about 70% of the igneous rocks.
The petrochemical composition of neutral and acidic igneous rocks shows that the younger rocks are relatively
richer in Si and alkali elements. As rocks get older, Na2O
content, and especially K2O content gradually rise. With
the evolution of magma from neutral to the acidic-alkali,
the petrochemical composition of the rocks shows a range
in SiO2 content from 51.0% to 78.9%. Alkalinity ranges
from Na2O>K2O to K2O<Na2O. Initial 87Sr/86Sr ratios vary
from 0.74 to 0.70. These geochemical characteristics indicate that the netural and acidic magma was derived from
the deep earth.
2.2 Genesis of igneous rocks
2.2.1 Mantle–derived (M-Type) igneous rocks
Mantle-derived igneous rocks occur sparsely in this region, with the exception of large scaleHimalayan alkali
basalts which are found along the Yi-Su deep fault. The
87Sr/86Sr ratio determined for olivine inclusions in basalt
is 0.738. Because the geologic age of these basalts is relatively young, the 87Rb content is fairly low. The half-life of
87Rb is 48.8 b.y.. We suggest that the 0.738 may represent
the initial 87Sr/86Sr ratio in the basalt. This indicates that
the basaltic magma was derived from the upper mantle.
2.2.2 Mantle-crust mixed (MC-type) igneous rocks
The rocks derived from both mantle and crustal materials are controlled by a basement rift, which lies in the
topographically lower region of the basin. Most of the
neutral-acidic and acidic igneous rocks occur in this locality. The initial 87Sr/86Sr ratio in these rocks ranges from
0.705 to 0.710. The δ18O value in the quartz varies from
7.8‰ to 8.5‰. The Rb/Sr ratio ranges from 0.6 to 0.4.
SiO2 content varies form 57% to 72%, whereas Na2O>K2O,
Al2O3/Na2O+CaO+K2O = 1, and f ’ (ω%) varies from 0.1
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762
Huang Wenbin · Shen Haoche · Fen Lin
to 0.4. These characteristics can be used to identify igneous rocks derived from both crustal and mantle material
in the relative deeper earth.
2.2.3 Crustal-derived (C-Type) igneous rocks
Crustal-derived igneous rocks are mainly located in the
folded region of the basin, and are controlled by regional
fracture zones and folds. In this locality, the crust is thick.
The initial 87Sr/86Sr ratio of these igneous rocks ranges from
0.716 to 0.720. The δ18O value in the quartz is l0‰, and the
Rb/Sr ratio is high. The rocks are rich in Si and K, and poor
in Ca. SiO2 content varies from 74% to 98% K2O>Na2O, f’
(ω%) varies from 0.4~0.7. These characteristics can be used
to identify rocks derived from crustal materials.
3
Isotopic and geochemical features of the silver
deposit
3.1 Regional geology
The Shanmen silver deposit is located along the western
margin in the Jihei fold system of the TianShan-Xinan orogenic belts. The main strata are the Cambrian-Ordovician
Baoan group and the Middle Ordovician Huangyingtun
group. The latter has undergone silicification, sericitization
and carbonatization. Igneous rocks outcrop in the uplifted area, which intrudes along deep fractures, mainly
consisting of monzogranite, biotite granite, and quartz
diorite (Fig. 1). The Indosin Kaodaozi diorite, Wuolong
hornblende pyroxenite and Yanshanian granites display
a close relationship with the silver deposit. The Kandaozi
pluton, which controls the distribution of the main ore
body, is located near the upper section of the silver deposit, and overlaps the Huangyintun group. The Wuolong
pluton, which forms the base of the ore body, lies on the
eastern edge of the Kaodaozi pluton. It has a skewed contact with the main fracture, and forms the wall rock for
the deposit. The silver deposit is 10 km long, 1~2 km wide,
and is distinctly controlled by NE-NNE factures. These
fractures divide the deposit into 5 ore blocks from south
to north: the Zhangjiatun block, the Longwang block, the
Wuolon block, the Gudong block and the Yingpan block.
The Wuolong block contains the majority of the ore reserves, which occur in marbles and meta-siltstones from
the middle-upper Huangyingtun group. The ore minerals are mainly silver (50%), galena, sphalerite, secondly
pyrite and chalcopyrite.
3.2 Petrography and petrochemistry of the mine region
The Kaodaozi pluton is the host rock for the main ore body.
It consists mainly of diorite, with lesser quartz diorite and
quartz monzonite. The petrochemical composition is as
follows: K2O/Na2O<1, Al/K+Na+2Ca<1, [Fe2O3+FeO+1/
2(MgO+Ca)] is 11.65, (Si+Na+K)/Fe2++Fe3++Mg) is 6.03,
(Cao+Na2O+K2O/(Al2O3+CaO+Na2O) is 1.70, and the coefficient of consolidation is 24.37. The main accessory minerals are titanite, apatite and barringerite.
The geochemistry of the rock is as follows: the 207Pb/
204Pb ratios vary from 15.56 to 15.64, the 206Pb/204Pb ratios from 18.32 to 18.35, the 208Pb/204Pb ratios from 38.24
to 38.47, respectively. The initial 87Sr/86Sr ratio is 0.70544.
The δEu values range from 0.92 to 1.02. The LRee/HRee is
5.93. Therefore, we suggest the Kaodaozi diorite is likely
derived from the mantle-crust melting. Whole rock UTh-Pb dating, measured by MS, produces an age of 193.3
Ma. Pb-Pb dating of zircon in the quartz diorite produces
an age of 187.8 Ma.
The Wuolong pluton forms the base of the ore body,
and is the wall rock for the deposit. It consists mainly of
adamellite, with lesser granite and moyite. The petrochemical composition is as follows: K2O/Na2O>1, Al/
K+Na+2Ca>1, SiO2 content is 73.4%. The main accessory
minerals are zircon, apatite and magnetite.
The geochemistry of the rock is as follows: the 207Pb/
204Pb ratios vary from 15.58 to 15.61, the 206Pb/204Pb ratios
from 18.56 to 18.61, the 208Pb/204Pb ratios from 38.71 to 38.85,
respectively. The initial 87Sr/86Sr ratio is 0.7158. The δEu
value is 0.45. Therefore, we suggest the Wuolong pluton is
likely derived from mantle-crust melting. U-Th-Pb dating
for zircon, measured by MS, produces an age of 150Ma.
Whole rock K-Ar dating produces an age of 158 Ma.
Close
Chapter 7-11 · Isotopic geochemistry of Mesozoic igneous rocks and mineralization of Shanmen silver deposit in Yi-Su Basin, Jilin Province
3.3 Isotopic and geochemical evidence of genesis of the
Shanmen silver deposit
A histogram is plotted for the 22 ore samples. The results
show that the 208Pb/204Pb ratio shows normal distribution with a single population except one. This indicates
that Pb isotopes come from a distinct parental material,
and that the source of mineralization is separate.
The model age, computed by a Doe single-stage model
using Pb isotopes, is a negative age. This reveals that Pb
isotopic values within the ore zone are similar to isotopic
values expected from Pb derived from the upper mantle
The model age computed by the Stacey two-stage formula
is 180 Ma. This model age, which represents the age of
the formation of the silver deposit, is close to the age of
formation of Kaodaozi and Wuolong plutons. Moreover,
the Pb isotopic composition in the ore is the same as the
Pb isotopic composition of the two plutons, but differs
from the stratum of Hangyintong group. Therefore, the
source of Pb isotopes in the ore has an intimate relationship with magmatic activity.
The Pb isotopic composition in galena ore may be compared with Pb isotopic composition in the rocks which
763
come from the modern mantle or the crust, in order to
discern the source of minerals for the younger deposits
(Y. W. Cheng, 1983). Fig. 2, Fig. 3 illustrate that Pb isotopic
composition of the galena is between the Pb composition of the tholeiite found at mid-oceanic ridges (representing the upper mantle), and the Pb composition of island-arc magmas found along the western coast of the
Pacific Ocean. The results reveal that the mineral material is derived from the deep earth, and formed from a
magma composed of mixed upper mantle and crust. We
compare the Pb isotopic composition in the galena in the
Shanmen deposit with the Phanerozoic metal deposits in
China. The Pb isotopic composition in the metal deposits, which are related to the Mesozoic lava or granodiorite in China is as follows (Cheng 1984): the Pb composition is steady, The 207Pb/204Pb ratios vary from 15.3 to
15.6, and the 206Pb/204Pb ratios >17.5. In the Shanmen silver deposit, the 206Pb/204Pb ratios vary from 18.017 to
18.149, whereas the 207Pb/204Pb ratios vary from 15.418 to
15.525. Therefore, we suggest the minaeralization may be
related to the intrusion of the granodiorite.
We measured the δ34S values in galena, sphalerite and
pyrite in the ore bodies, wall rocks, and local strata.
(Table 1). The δ34S data is as follows: the variation of the
δ34S values is narrow, the δ34S values are low in the ore
bodies and the wall rocks, This is similar to the δ34S values in meteorites. The δ34S values are negative in the stratum. The average δ34S values in pyrite are -1.37‰. This is
within the range of δ34S values in meteorites. These results indicate that the mineral material is derived from
the deep earth.
The δ34S values from different ore bodies show a normal distribution. Most of them cluster around -2.0‰. The
δ34S values in the ore minerals are as follows: δ34S (FeS) >
δ34S(ZnS) > δ34S(PbS). This agrees with the equilibrium
conditions for sulfur isotopes in hydrothermal systems.
Therefore, these minerals are paragenetic. Thermometry
of sphalerite galena shows that the metallogenic temperature was between 160 to 300oC.
Close
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Huang Wenbin · Shen Haoche · Fen Lin
The δ18OH2O values in quartz show that mineralized
fluids consisted of magmatic water in the early stages,
and meteoric waters mixed with magmatic waters during the later stages. The δD values range from -92% to 106%. Thereby, we suggest the silver deposit was formed
in the same hydrothermal system.
4
Conclusions
The genesis of the igneous rocks in the study region falls
into two groups: crustal-derived igneous rocks, and
mantle-crustal mixed igneous rocks. These two groups
of igneous rocks have distinct differences in petrochemistry, mineral assemblage, and geologic environment of
formation.
On the basis of detailed study of geology and isotopic
geochemistry of Rb, Sr, Pb, S, H, and O in both ore and wall
rock, we suggest the silver deposit is a mesothermal ore
deposit, and the mineral material is derived form the mixed
upper mantle and crust. The metallogenesis of Shanmen
silver deposit has an intimate relationship with magamatic
activity. The origin of mineral material and mineralizing
fluids is complex. Magmatic activity is the metallogenetic
mechanism of formation for this silver deposit.
References
Amstrong BL, Hales WH (1977) Rb-Sr and K-Ar geochemistry of
Mesozoic grantic rock and their isotopic composition. Ball, Geol.
Soc. Am 88
Cheng YW, Zhu BQ (1984) The feature of isotopic composition of
ore lead and genesis. Geochemica 3: 35-45
Hu X, Xu C, Niu S (1990) Evolution of the early Paleozoic continental margin in northern margin of the North China Platform.
Beijing: Peking University Publishing House, 6-34
Li L, Zheng YF, Zhou JB (2001) Dynamic model for isotope Pb evolution in the Continental Crust of China. Acta Petrologica Sinica
1:63-67
Liang YH, Zheng, XS, Zhang S (1996) The discussion on the
relation between the magmatite and the silver deposit and
exploration of the mechanism of the formation of the silver
deposit in Sipin. Songliao Journal (Nature Science Edition) 1:
41-45
Liu, JQ (1987) Geochronology Study of Cenozoicin Lava in North
East China. Acta Petrologica Sinica 4: 21-31
Taylor SR, Mclennan SM (1985) The continental crust: Its composition and evolution. Oxford: Blackwell, 67-96.
Wang FK (1994) Analysis on metallogenetic conditions of the
Shanmen Silver Deposit in Sipin, Jilin Povice. Jilin Geology 3:
9-16
Wang FK (1997) A new understanding of the Mesozoic intrusive
rock genesis and relationship with metallogeny in the Shanmen
Silver Deposit, Sipin Area. Jilin Geology 3: 9-26
Close
Chapter 7-12
7-12
Platinum group elements as useful genetic tracers for the
origin of polymetallic Ni-Mo-PGE-Au sulfide ores in Lower
Cambrian black shales, Yangtze Platform, South China
S.-Y. Jiang, Y.-Q. Chen, H.-F. Ling, J.-H. Yang, H.-Z. Feng
State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, China
Abstract. The polymetallic Ni-Mo-PGE-Au sulfide ores occur in the
Lowermost Cambrian Niutitang Formation of a thick black shale
sequence in Yangtze Platform of South China. The origin for this
special type of sulfide ore has been hotly debated. Three genetic
models have been proposed: (1) extraterrestrial impact origin (Fan
et al. 1984); (2) submarine hydrothermal exhalative origin (Coveney
et al., 1992; Lott et al. 1999; Steiner et al. 2001); (3) seawater scavenging origin (Mao et al. 2002). In this paper, we discuss the origin
for this special type of sulfide ore based on platinum group element geochemistry. We suggest that the chondrite-normalized PGE
patterns of the sulfide ores show some distinctive difference from
the seawater pattern and may indicate a submarine hydrothermal
input for the metal enrichments in the sulfide ore. We defined a
new parameter, namely Pt anomaly (Pt/Pt*), and found that the Pt
anomaly in the polymetallic Ni-Mo-PGE-Au sulfide ores is similar to
those ancient and modern sea-floor massive sulfide deposits. Other
platinum group element pairs, such as Pt/Pd, Ir/Pd, and Au/Pd ratios of the Ni-Mo sulfide ores also share some similarity with those
of ancient and modern submarine massive sulfide deposits. In conclusion, we support the submarine hydrothermal exhalative origin
for the sulfide ores, and suggest that this is a new type of sediment-hosted submarine hydrothermal exhalative sulfide deposits.
Keywords. PGE, sulfide ore, black shale, Lower Cambrian, South China
1
Introduction
The polymetallic Ni-Mo-PGE-Au sulfide ores occur in the
Lowermost Cambrian Niutitang Formation of a thick black
shale sequence on the Yangtze Platform of South China,
which extend over 1600 kilometers length along a NE
trending belt. Although this type of polymetallic Ni-MoPGE-Au mineralization has been known for more than
30 years, its origin has long been debated (Fan et al. 1984;
Coveney et al. 1992; Horan et al. 1994; Lott et al. 1999;
Steiner et al. 2001; Mao et al. 2002; Coveney 2003; Lehmann
et al. 2003). Our study in recent years suggest that the
occurrence of PGE and other metal anomalies and mineralizations in black shales may belong to a special class
of sedimentary-exhalative sulfide deposits that can potentially provide economically significant PGE and other
metal resources in the future.
2
Geological setting
In South China, the polymetallic enrichment bed in the
Lowermost Cambrian Niutitang Formation accounts for
extreme enrichments of a large spectrum of metals, such
as Mo, Ni, Se, Re, Os, As, Hg, Sb, Ag, Au, Pt, and Pd, with
up to 106 to 109 fold enrichment relative to seawater values. Although this belt extends over 1600 km, economically minable ores occur mostly within the provinces of
Guizhou and Hunan, with the most famous deposits being Huangjiawan near Zuuyi (Guizhou province) and
Dayong near Zhangjiajie (Hunan province).
Steiner et al. (2001) suggested that the linear trend of
the Ni-Mo sulfide ore occurrence in South China may relate to structural controls by a major deep fault zone in
the transitional area between the Neoproterozoic back
arc basin and the platform. Lott et al. (1999) found footwall hydrothermal quartz-sulfide stockworks for the sulfide deposit, which may represent submarine hydrothermal venting systems. Mao et al. (2002) reported a Re-Os
age for the Ni-Mo sulfide ores of 541 ± 16 Ma. Chen et al.
(2003) also obtained a similar age using the Pb-Pb dating
technique for the host black shales (531 ± 24 Ma).
The major ore minerals are vaesite, bravoite, jordisite,
and MOCs; and minor ore minerals include arsenopyrite, chalcopyrite, covellite, sphalerite, millerite,
polydymite, gersdorffite, sulvanite, pentlandite, tennantite,
tiemannite, violarite, and native gold. Gangue components
consist of organic debris, siliceous rock, carbonate, clay,
and phosphorite.
3
Platinum group element geochemistry
The Platinum group element and their chondrite-normalized patterns are very useful indicators for the origin of
ore deposits including those within black shales and submarine hydrothermal exhalative massive sulfide deposits (e.g., Coveney et al. 1992; Pasava 1993; Pan and Xie
2001; Pasava et al. 2004).
3.1 The Ir anomaly
The polymetallic Ni-Mo-PGE-Au sulfide ores in South
China were first reported by Fan et al. (1973) and were
regarded as an entirely new type of sulfide ore, which
contains up to several percent of Ni, Mo, As, together with
substantial amounts of PGE and Au. In 1984, Fan et al.
(1984) found high Ir values for these polymetallic Ni-Mo-
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S.-Y. Jiang · Y.-Q. Chen · H.-F. Ling · J.-H. Yang · H.-Z. Feng
PGE-Au sulfide ores, and consequently they suggested a
meteorite impact model for the origin of these ores. However, this model was doubted and discarded by Conveney
et al. (1992) who found that the Ir contents are actually
relatively low (<0.02-2 ppb, average 1.7 ppb) compared
with other PGEs (up to 700 ppb Pt and 1255 ppb Pd).
Hence, Conveney et al. (1992) concluded that an extraterrestrial source seems unlikely for the Chinese polymetallic
Ni-Mo-PGE-Au sulfide ores.
3.2 The Pt anomaly (Pt/Pt*)
Jiang et al. (2003) proposed a new PGE parameter of Pt
anomaly (Pt/Pt*), which can be used as a sensitive genetic tracer. By analogy with the Eu anomaly in chondrite-normalized REE patterns, a Pt anomaly can be defined using the following equation:
where the PtN, RhN, and PdN are the chondrite-normalized
values of the samples. The Pt/Pt* values are generally larger
than 1 (positive Pt anamaly) for most crustal sources. In
contrast, the mantle-derived sources display negative Pt
anomaly with Pt/Pt* close to or less than 1. We found that
the Pt/Pt* values for the host rocks of phosphorites, siliceous shales, and black shales in South China are significantly larger than 1, but the Pt/Pt* values for the Ni-Mo
sulfide ores are close to 1, overlapping the values for Kuroko
VMS-type sulfide ores. This similarity may imply a similar
submarine hydrothermal origin for the Chinese Ni-Mo sulfide ores. This hypothesis supports other studies that favor
a hydrothermal origin for the Chinese polymetallic Ni-MoPGE-Au sulfide ores (Murowchick et al. 1994; Li and Gao
1996; Lott et al. 1999; Steiner et al. 2001).
(0.1-3.3) and the ancient massive sulfide ores (0.4-1.0), although the range in these deposits seems to be smaller. The
Fe-Mn crusts, which scavenged PGEs from seawater, also
show large Pt/Pd ratios ranging from 6 to 272, whereas Au/
Pd ratios show even larger variations.
Hence, we suggest that a simple comparison of these
noble metal ratios to those of seawater is by no means an
adequate way to prove or disprove their derivation. Instead, we suggest that the correlations between the noble
metal ratio pairs are more useful to differentiate hydrothermal origin from seawater origin. The comparison of
Chinese Ni-Mo sulfide ores with submarine hydrothermal exhalative sulfide ores and Fe-Mn nodules and crusts
in Pt/Pd vs Pt/Pt*, Pt/Pd vs. Ir/Pd, Au/Ir vs. Au/Pd diagrams demonstrate the similarity between the Chinese
Ni-Mo sulfide ores with Kuroko VMS-type sulfide ores
and modern sea-floor metalliferous sediments and sulfides, but a distinct contrast to Fe-Mn nodules and crusts.
Taken together, we suggest that the Chinese Ni-Mo ores
are likely to have a similar hydrothermal origin to modern and ancient sea-floor massive sulfide deposits.
4
Conclusions
The ore genesis for the Chinese polymetallic Ni-Mo-PGEAu ores within the Lowermost Cambrian Niutitang Formation has been hotly debated. The increasing amount of
data from field geology, fluid inclusions, geochemistry (trace,
rare earth elements, and platinum group elements), and
isotopes support a formation of these deposits via submarine hydrothermal venting systems, in an anoxic environment where abundant organic matter promotes extreme
enrichment of redox-sensitive metals. According to our
systematic PGE investigation, we propose a genetic model
for the submarine hydrothermal ore-forming process, and
suggest this is a new type of sediment-host Sedex deposits.
3.3 Platinum group element ratios
Acknowledgements
The Platinum group element ratios are diagonastic tools
to trace ore genesis. Lehmann et al. (2003) suggested that
the Chinese Ni-Mo sulfide ores have Pt/Pd and Au/Pd ratios around 1, quite close to seawater ratios (Pt/Pd= 0.8,
Au/Pd=0.3), but are different from the Serra Pelada AuPd-Pt deposit of northern Brazil and the Rammelsberg
deposit of Germany (Au>Pd>Pt).
However, we found that the Pt/Pd ratios of magmatic
Ni-Cu sulfide deposits are also commonly close to 1 (Barnes
et al. 1985; Brugmann et al. 1989). In fact, the Pt/Pd ratio for
the Chinese Ni-Mo ores and their host rocks, as well as for
many modern and ancient sea-floor massive-sulfide deposits
and Fe-Mn crusts show a relative large variation. We found
that the Pt/Pd ratios of the Chinese Ni-Mo sulfide ores (0.320) are similar to their host rocks (0.5-14), and are also
comparable to the modern sea-floor metalliferous sediments
This research was supported by China National Science
Foundation grants (40221301, 40372059, 40172041). Profs.
Zhu Maoyan, Zhang Junming, and Wu Xianhe are thanked
for their very helpful assistance in field work and for critical discussion. This is a contribution to the Sino-German
joint project of Biological and Geological Processes of the
Cambrian Explosion.
References
Barnes SJ, Naldrett AJ, Gorton MP (1985) The origin of fractionation
of platinium-group elements in terrestrial magmas. Chem Geol
53: 303-323
Brugmann GB, Naldrett AJ, MacDonald AJ (1989) Magma mixing
and constitutional zone refining in the Lac des Iles Complex,
Ontario: Genesis of platinum-group element mineralization. Econ
Geol 84: 1557-1573
Close
Chapter 7-12 · Platinum group elements as useful genetic tracers for the origin of polymetallic Ni-Mo-PGE-Au sulfide ores in Lower Cambrian black shales
Chen Y-Q, Jiang S-Y, Ling H-F, Feng H-Z, Yang J-H, Chen J-H (2003)
Pb-Pb isotope dating of black shales from the Lower Cambrian
Niutitang Formation, Guizhou Province, South China. Progr Nat
Sci 13: 771-776
Coveney RM Jr (2003) Re-Os dating of polymetallic Ni-Mo-PGE-Au
mineralization in Lower Cambrian black shales of South China and
its geological significance-A discussion. Econ Geol 98(3): 661-662
Coveney RM Jr, Murowchick JB, Grauch RI, Michael D, Glascock D,
Denison JD (1992) Gold and platinum in shales with evidence
against extraterrestrial sources of metals. Chem Geol 99:
101-114
Fan D, Yang R, Huang Z (1984) The Lower Cambrian black shales
series and the iridium anomaly in south China. Development in
Geoscience, Inter Geol Congr, 27th, Moscow, 1984, Beijing, Science Press, 215-224
Fan D, Yang X, Wang Y, Chen N (1973) Petrological and geochemical
characteristics of a nickel-molybdenum-multe-element-bearing
Lower Cambrian black shale from a certain district in south
China. Geochim 3:143-163
Horan MF, Morgan JW, Grauch RI, Coveney RM Jr, Murowchick JB,
Hul-bert LJ (1994) Rhenium and osmium isotopes in black shales
and Ni-Mo-PGE-rich sulfide layers, Yukon Territory, Canada, and
Hunan and Guizhou Provinces, China. Geochim Cosmochim Acta
58: 257-265
Jiang S-Y, Yang J-H, Ling H-F, Feng H-Z, Chen Y-Q, Chen J-H (2003)
Re-Os isotopes and PGE geochemistry of black shales and inter-
767
calated Ni-Mo polymetallic sulfide bed from the Lower Cambrian
Niutitang Formation, South China. Progr Nat Sci 13: 788-794
Lehmann B, Mao J, Li S, Zhang G, Zeng M (2003) Re-Os dating of
polymetallic Ni-Mo-PGE -Au mineralization in Lower Cambrian
black shales of South China and its geological significance-A reply. Econ Geol 98(3): 663-665
Li S, Gao Z (1996) Siliceous rocks of hydrothermal origin in the Lower
Cambrian black rock series of South China. Acta Mineral Sinica
16: 416-422
Lott DA, Coveney RM Jr, Murowchick JB (1999) Sedimentary exhalative
nickel-molybdenum ores in South China. Econ Geol 94: 1051-1066
Mao J, Lehmann B, Du A, Zhang G, Ma D, Wang Y, Zeng M, and Kerrich
R (2002) Re-Os dating of polymetallic Ni-Mo-PGE-Au mineralization in Lower Cambrian black shales of South China and its
geologic significance. Econ Geol 97: 1051-1061
Murowchick JB, Coveney RM Jr, Grauch RI, Eldridge CS, and Shelton
KL (1994) Cyclic variations of sulfur isotopes in Cambrian
stratabound Ni-Mo-(PGE-Au) ores of southern China. Geochim
Cosmochim Acta 58: 1813-1823
Pasava J (1993) Anoxic sediments- an important environment for
PGE: An overview. Ore Geol Rev 8: 425-445
Steiner M, Willis E, Erdtmann BD, Zhao YL, and Yang RD (2001) Submarine-hydrothermal exhalative ore layers in black shales from
South China and associated fossils- insights into a Lower Cambrian facies and bio-evolution. Palaeogeo Palaeoclim Palaeoeco
169: 165-191
Close
Close
Chapter 7-13
7-13
Chemical and mineralogical characteristics of tourmaline
in pegmatites from Vavdos, Chalkidiki peninsula, N Greece
M.D. Laskou
Department of Geology and Geoenvironment, Section of Mineralogy and Petrology, Athens University, Greece
Abstract. Pegmatite veins crosscutting dunites and serpentinites
of the ophiolitic complex of the Vavdos (Gioldaki and Loukoviti),
northern Greece contain tourmalines with a wide variation in
size and composition. Pegmatite veins mainly consist of quartz
crystals, microcline, albite, perthitised-feldspars. The accessory
minerals include mostly coarse to medium grained zoned tourmaline, and lesser amounts of sericite (only occasionally biotite).
There are also trace amounts of some rare earth element minerals, such as morazite, xenotime and minerals of the bastnaesite
group (epigenetic products of monazite). The pegmatite veins host
also fine-grained tourmalile, which shows an orientation parallel
to the schistosity of the rock. They are composed of quartz, low-T
albite and K-feldspars. Hydroxy apatite, chlorite, Nb-bearing REE
minerals (koragoite), garnet, zircon and talc are also present in
lesser amounts.
Keywords. Tourmaline, quartz, pegmatites, Chalkidiki Greece
1
Introduction
Pegmatites occur in veins crosscutting dunites and serpentinites of the ophiolitic complex of Vavdos in the western part of the Chalkidiki peninsula, N. Greece (Fig. 1).
The Vavdos ophiolitic complex forms an elongate faultbounded body within the Circum-Rhodope Belt. It is one
of several similar complexes of Middle to Upper Jurassic age, extending in NW-SE direction, from north-east
of Thessaloniki to Sithonia (Kockel et al. 1977; Musallam
and Jung, 1986). It consists of dunite, websterite, olivine
clinopyroxenite, gabbroic rocks and serpentinite. It also
hosts a major deposit of cryptocrystalline magnesite
(Dabitzias 1980).
Pegmatites crosscutting the ultramafic sequence of the
Vavdos ophiolite complex contain tourmaline dispersed
throughout the whole tourmaline mass (Kassoli-Fournaraki 1990).
The present study focuses on two particular occurrences of tourmaline within the unit. These occurrences
have coarse, medium and also fine-grained tourmaline
hosted in pegmatite. The description of the mineral assemblages and their composition are given.
2
Analytical methods
The phase mineral analyses were carried out using SEM
JEOL JSM-5600 combined with an Oxford Link ISIS Series 300 EDX (University of Athens). ZAF corrections were
applied using SEMQuant™ software. Accelerating voltage and beam current were kept at 20.0 kV and 0.5 nA,
respectively.
3
Mineralogical characteristics
Pegmatites from the area of Vavdos (Gioldaki and
Loukoviti) have a thickness ranging from 0.5 to 3m, and
are characterized by a medium- to coarse-grained texture (Fig. 2). The coarse and medium grained pegmatite
veins mainly consist of quartz crystals, microcline, albite,
and perthitised-feldspars. The accessory minerals include
coarse-grained, medium to fine-grained and the mostly
zoned tourmaline, plus small quantities of sericite and
rarely biotite. Lesser amounts of rare earth element minerals are also present (morazite, xenotime and minerals
of the bastnaesite group, which are epigenetic products
of monazite). Tourmaline occurs in sub to euhedral crystals. Optical zoning in coarse-grained tourmaline is well
pronounced, with core color ranging from greenish-blue
to brown, while rims range from green brown to olive-
Close
770
M.D. Laskou
Hydroxyapatite, chlorite, Nb-bearing REE minerals
(koragoite), garnet, zircon and talc are present in lesser
amounts.
Tourmaline is visible in hand specimens and in thin
section, and is identified as green grains with fine brown
rims. The fine-grained tourmaline associated with quartz
and microcline occurs along shear zones within the host
pegmatite, which seem to have formed by re-crystallization during a subsequent event
4
Mineral chemistry
Tourmalines from the area of Vavdos show wide compositional variation, in particular in the SiO 2 (33.9438.93wt%), Al2O3 (34.55-39.92wt%), FeO (3.78-12.29wt%),
TiO2 (0.00-3.33wt%), NaO (0.00-1.51wt%), MgO (0.006.14wt%) and MnO (0.00-1.8wt%).
The range of the FeO/(FeO+MgO+MnO) and Fe/
(Fe+Mg) ratios are generally comparable to those given
in granitic systems (Deer et al. 1986). The majority of tourmaline cores fall in the schorl field. Tourmaline rims are
depleted in FeO and enriched in Al203 in Table 2 only.
All tourmaline cores data are plotted in two areas: the
field 2 [Li-poor granitoids and their associated pegmatites
and aplites] and the field 3 [Fe3+-rich quartz-tourmaline
rocks (hydrothermally altered granites)] (Fig. 5).
green. Tourmaline of medium size exhibits green-pale
cores and olive-green rims. The textural association of
tourmaline and quartz (Fig. 2) indicate that these two
minerals are genetically related.
Fine grained tourmalines in pegmatite veins occur
in crystals with a wide range in grain size, from
250-500 µm to 1000-1500 µm. (Fig. 3). These pegmatites
are composed of quartz, low-T albite, K-feldspars
and tourmaline.
5
Concluding remarks
Although much more research is required to establish the
origin of the Vavdos tourmalines, their textural, mineralogical and chemical characteristics suggest a multistage
genesis. Changes in the chemical composition of tourmalines and associated minerals are probably the result
of epigenetic processes.
Close
Chapter 7-13 · Chemical and mineralogical characteristics of tourmaline in pegmatites from Vavdos, Chalkidiki peninsula, N Greece
771
Close
772
M.D. Laskou
References
Dabitzias S (1980) Petrology and genesis of the Vavdos cryptocrystalline magnesite deposits, Chalkidiki Peninsula, Northern
Greece. Econ Geol 75:1138-1151
Deer WA, Howie RA, Zussman J (1986) Rock-forming minerals:
volum 1B, Disilicates and ring silicates: London, Longman Scientific and Technical, 629p
Henry DJ, Guidotti CV (1985) Tourmaline as a petrogenetic indicator mineral: an example from the staurolite-grade metapelites of
NW Maine. Am. Mineral. 70, 1-15.
Kassoli-Fournaraki A (1990) Chemical varuations in tourmalines
from pegmatite occurrences in Chalkidiki Peninsula, Northern
Greece. Scheiz Mineral Petrogr Mitt 70: 55-65
Kockel F, Mollat H, Walther HW (1977) Erlauterung zur geologischen
Karte der Chalkidiki und angrenzender Gibiete 1:100000,
Nordgriechenland. 119 S, Hanover
Mussalam K, Jung D (1986) Petrology and geotectonic significance
of salic rocks preceding ophiolites in the eastern Vardar Zone,
Greece. Tscher Min Petr Mitt 35:217-242
Close
Chapter 7-14
7-14
Geochemical characteristics of He-Ar and Pb isotopes
in the Dajiangping pyrite deposit, western
Guangdong, South China
Kuang Li, Kai Hu, Shaoyong Jiang, Shiming Song
State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, 210093, China
Abstract. He-Ar isotopes were measured from fluid inclusions in six
samples of the Dajiangping pyrite orebody III and orebody IV., The
3
He/4He values range from 0.13 to 2.55Ra, and the 40Ar/36Ar values
range from 348 to 443. These data indicate that mantle-derived fluids contributed to the ore-forming fluids. This study suggests that
the hot fluids from the deep mantle intruded into the ore body
along a thrust fault, and hydrothermed the orebody. This caused
differentiation of the orebody resulting in the formation of the
banded orebody III and the massive orebody IV. Pb isotopes from
the ore and wall rocks were also measured in this study. 206Pb/204Pb
values range from 18.075 to 18.292, 207Pb/204Pb values range from
15.654 to 15.737, and 208Pb/204Pb values range from 38.401 to 38.781.
These ratios indicate that orebody III is very similar to the wall rock,
whereas orebody IV has lower Pb/Pb ratios than wall rock. The data
support the interpretation that mantle fluid intruded into the entrapping Pre-Sinian basement migmatite, causing lower Pb isotope
ratios in orebody IV.
Keywords. He-Ar isotope, Pb isotope, Crust fluid, Mantle fluid, Thrust
fault
1
Introduction
The Dajiangping pyrite deposit lies in the northeastern
part of the of Yunkai ridge, south China. It is a unique
ultra-large pyrite deposit in the south of Sinian (period)
layer (Chen and Chen 1998). The ore genesis model for
the Dajiangping deposit has long been in dispute, and
the major debate focuses on whether the orebodies formed
during hydrothermal sedimentation reform, by a vapourliquid superimposition event (Zhang et al. 1992, 1993,
1994), or whether formation was the product of
hydrothemal sedimentation (Chang and Chang 1998).
Noble gases, especially helium and argon have distinct
isotopic compositions in the crust and mantle. Due to
this characteristic, He and Ar isotopes have been widely
applied in tracing the origins and water-rock interactions
of contemporary crustal fluids. Recently, these isotope
systematics have also been successfully applied to the study
of the origin of ancient ore-forming fluids and mineralization (Turner and Stuart 1992; Turner et al 1993; Burnard
et al. 1994; Hu 1997; Zhao et al. 2002; Sun and Wang 2003;
Zheng et al. 2003). In this note, we report He and Ar isotopic data for the Dajiangping ore deposit first time, and
discuss the origin and evolution of the hydrothermal fluid.
2
Sampling and analytical methods
He and Ar isotope were measured in fluid inclusions from
six pyrites in the Dajiangping Deposit. These samples were
collected from orebody III, orebody IV, CK36 core and
wall rock. The samples were dispersed to 0.1~0.2mm grain
size, through dressing by both magnetic separation and
heavy-liquid separation, then the pyrites were selected
by stereomicroscope.
The He and Ar isotope compositions were analyzed in
the Open Laboratory for Isotope Geology at the Institute
of Mineral Deposits at the Chinese Academy of Geological Sciences. All samples were cleaned for 20 min in ultra-sonic bath using acetone and then dried. The samples
were heated under vacuum at 120oC for 24 h to remove
absorbed atmospheric gases. They were crushed to extract inclusion-trapped noble gases. The released gases
were purified four times through two titanium sponge
pumps, a Zr-Al pump and an active-carbon cooling trap
filled with liquid nitrogen.
Active gases were frozen and completely absorbed.
Then comparatively pure He and Ne were introduced into
the analyzing system. He and Ne were purified further to
remove traces of impure gases such as H2. and Ar using a
titanium sublimation pump filled with liquid nitrogen.
He isotopes were analyzed by mass spectrometer. Finally
Ar was released at -78oC and Ar isotopes were then analyzed. The instrument used in this study is an MI 120l IG
noble gas mass spectrometer. The 3He values were measured by an electronic multiplier detector. 4He was measured by a Faraday cup. The resolutions are 1200 for the
electronic multiplier detector, and 760 for the Faraday cup.
The standard gas air is atmospheric air with a 3He/4He
ratio of l.4x10-6.
3
He-Ar isotope analysis and discussion
The results of helium and argon isotope data are given in
table 1. As shown in table 1, the fluid inclusions from pyrite have 3He/4He ratios of 0.18~3.55x10-6(0.13~2.55Ra).
The values of 40Ar/36Ar ratios show slight variation between 348~443, which is higher than Air-saturated water’s
40
Ar/36Ar ratios of 295.5.
Close
774
Kuang Li · Kai Hu · Shaoyong Jiang · Shiming Song
Three possible noble gas sources exist in hydrothermal fluids (Burnard et al. 1999): (1)Air-saturated water
(ASW), including meteoric water and seawater. This is
characterized by atmospheric He and Ar isotopic compositions, i.e. 3He/4He=1.4 × 10–6 = 1Ra, 40Ar/36Ar=295.5.
(2) Radiogenic He and Ar accumulated in the crust. In
this source, the 3He/4He ratio varies from 0.01 to 0.05 Ra,
and the 40Ar/36Ar ratio usually higher than 295.5. (3)
Mantle-derived volatiles. These are characterized by high
3
He with a well-defined 3He/4He ratio of 6–9 Ra. The 40Ar/
36Ar ratio varies widely, and are usually higher than 400.
By comparing the isotopic composition of the sample to
the isotopic compositions of the three possible sources
of noble gases, we can determine the origin of the noble
gases in hydrothermal fluids.
As shown in the plot of 3He/4He vs. 40Ar/36Ar ratios
(Fig. 1), the data fall among three sources district, which
indicates that the hydrothermal fluid did not originate
from the single source, and instead may be a product of
crust-mantle mixture. There are two orebody IV samples,
two orebody IV samples, one CK36 drill core sample
(depth 133 m), and one wall sample of all the six samples.
We find that the ore-forming fluids of orebody IV fall in
between mantle-derived fluids and ASW. In contrast, the
others lie lower on the graph; the CK-36 and DP-11 even
lie between ASW and crust fluids.
We can make use of the 3He/4He ratios to Figure out
the mantle fluids (Rm) ratio and the crustal fluids (Rc)
ratio of the ore-forming fluids. By following formula[13],
we can Figure out the helium from mantle fluids:
Helium from mantle fluids = [(R–Rc)/(Rm–Rc)] (1)
The Rm, Rc and R represent the 3He/4He ratios of
mantle fluids, crust fluids and the samples. Rm=6~9 Ra,
Rc=0.01~0.05 Ra. According to formula (1), the six
samples’ helium content from mantle fluids declines from
orebody IV, orebody to wall rock, indicating that the degree of mantle fluids participating in the ore-forming
processes was decreasing. The reason for this may be that
the ore deposit’s formation passed through a few different stages. Zhu and Meng (1999) found that the
Dajiangping pyrite deposit was located on the thrust
slip fault of a nappe structure in the western Guangdong. The deposit was controlled by both a large overturned fold; which has an axial plane to the southeast; and a secondary rotational fault. We can find
out the tectonic characteristics from Figure 2. It is conjectured that after the orebodies underwent the hydrothemal sedimentaion event, thrust faults formed by intensive crustal tectonic movement, which pushed the
Sinian layer onto limestone of Devonian and Carboniferous.
Then mantle fluids rose with the intensive tectonic
movement. Finally the hydrotherm from deep mantle
fluids entered into, and transformed the orebodies
along the fault. Therefore, the characteristics of noble
gas isotope signature changed systematically during formation, as shown in Figure 1. At the same time the
hydrotherm transformed the shape of orebodies, and
caused differentiation resulting in the formation of the
banded pyrite ore (orebody III) and the massive pyrite
ore (orebody IV).
Close
Chapter 7-14 · Geochemical characteristics of He-Ar and Pb isotopes in the Dajiangping pyrite deposit, western Guangdong, South China
4
775
Pb isotope geochemical characteristics
Lead isotopes are a powerful tool to trace the origin of
metal deposits. We also measured lead isotope of 11
samples including orebody III, orebody IV, and wall rock.
The data in Figure 3 also incorporate Pb isotope data of
Yunkai ridge area magmatic rock and basement migmatite
in Pre-Sinian period, as well as other Pb isotope data from
pyrites. The lead isotope data from the pyrites differs from
the lead isotope data from the magmatic rocks. This indicates that the ore deposit must not be the product of
igneous magmatism. It also shows that the lead isotope
compositions of minerals and wall rocks are mainly consistent.
Although the lead isotope compositions of the two ore
types partially overlap, the massive orebody has lower
Pb isotopic values than the banded orebody. It is possible
that the lead from mantle fluid had been added to the
orebody. Therefore, the Pb isotope characteristics of the
Dajiangping pyrite deposit strengthen our conclusion that
the orebody IV was formed by late mantle fluid, which
migrated along a thrust fault and altered the original shape
of the orebody.
ment rocks, and eventually formed the mixing hydrotherm.
Then, the fluid burst out of sea floor from growth faults
and formed stratiform deposits in the reducing environment. The formation of the thrust fault was initiated by
teconic movement at the spot of ore deposits. Later, the deep
mantle hydrotherm entered into, and reformed the
orebodies. Though no new element was added in, the
hydrotherm changed the orebody shape and differentiated
the deposit into two distinct members: the banded orebody
III and the massive orebody IV.
Acknowledgements
This work was supported by the Youth Excellent-Group
Program No.40221301 and No.40172035 in the National
Science Foundation of China.
References
5
Conclusions
The ore-forming fluid of pyrites in Dajiangping orebodies
mainly consists of air-saturated water (seawater), which
leached lithospheric ore-forming material. The original
R/Ra ratio of Helium Isotope was less than 1, but after
the deposit was altered by the late mantle fluid, the R/Ra
ratio rose by about 50 points.
We conclude that in the Sinian layer, the air-saturated
water (seawater) was cyclically heated in the growth faults,
absorbed by the ore-forming matter of the crustal base-
Burnard PG, Hu RZ, Turner G (1999) Mantle, crustal and atmosphere
noble gases in Ailaoshan, yun-nan Province, China. Geochimica
et Cosmochimica Acta, 63,pp. 1595-1604
Burnard PG, Stuart F, Turner G (1994) C-He-Ar variations with in a
dunite nodule as a function of fluid inclusion morphology. Earth
Planet Sci.Lett,128: 243-258
Chen D, Chen Q (1998) Characteristics of the hydrothermal sedimentation of the Dajiangping super-large pyrite deposit in Yunfu,
Guangdong. Geochimica 27: 12-19
Chen DF (1998) Pb and Nd Isotopes of the dajiangping Pyrite deposit, Guangdong Province, and its metallic ore source. Mineral
deposits: 215-222
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Kuang Li · Kai Hu · Shaoyong Jiang · Shiming Song
Hu R (1997) Geochemistry of He, Ar isotopes in ore forming fluids.
Bulletin of Mineralogy, Petrology and Geochemistry 16: 120-124
Li X, Mao J (2004) Helium and Argon Isotope Systematics in Fluid
Inclusion of the Gold Deposits along the Daduhe River, Sichuan
Province, Southwestern China. Acta Geologica Sinica 78: 203-210
Sun X, Wang M (2003) He-Ar isotopic systematics of fluid inclusions
in pyrites from PGE-polymetallic deposits in lower Cambrian
black rock series, southern China. Geological Journal of China
Universities 9: 661-666
Turner G, Burnard PB, Ford JL (1993) Tracing fluid sources and interaction. Phil Trans R Soc Lond A 344: 127-140
Turner G, Stuart F (1992) Helium/heatratios and deposition temperatures of sulfides from the ocean floor. Nature 357: 581~583
Zeng Z, Qin YS (2003) He, Ne and Ar isotope compositions of fluid
inclusions in massive sulfides from the Jade hydrothermal field,
Okinawa Trough. Acta Oceanolog 25: 36-42
Zhang B, Zhang Q, Pan J (1994) Trace element characteristics and
their geological significance of Dajiangping pyrite deposit, western Guangdong. Geology and Prospecting 30: 66-71
Zhang Q, Zhang B, Cao Y (1993) Preliminary discussion on sulfur
and lead isotope compositions of the Dajiangping pyrite deposit
in western Guangdong province. Acta Geologica Sinica, 67(3), pp.
232-242
Zhang Q, Zhang B, Pan J (1992) Silicalite characteristics and rareearth element model of Dajiangping pyrite deposit in western
Guangdong province. Chinese Science Bulletin 37: 1588-1592
Zhao K, Jiang S, Xiao H (2002) Origin of ore-forming fluids of the
Dachang Sn-polymetallic ore deposit: Evidence from helium isotopes. Chinese Science Bulletin 47: 1041-1045
Zu D, Meng X (1999) Primary study on the western Guangdong nappe
structure in the hercynian and indo-Chinese epoch. Journal of
geomechanics 5: 51-58
Close
Chapter 7-15
7-15
Precise Re-Os dating of molybdenite from the east
Qinling molybdenum belt in central China and its
geodynamic implications
Yong-Feng Li, Jing-Wen Mao, Feng-Jun Bai, Bao-Jian Guo
Faculty of Geosciences and Resources, China University of Geosciences, Beijing 100083, China
Zhi-Guang Wang
Bureau of Geology and Mineral Resources for Nonferrous Metals, Henan Province, 107 Zhongyuandong Road, Zhengzhou
450052, Henan, China
Abstract. Located in central China on the southern margin of the
North China craton, the East Qinling molybdenum belt is one of
the important large molybdenum belts in China. This study provides reliable Re-Os isotopic dating results for the metallogenetic
epoch of four deposits by inductively coupled plasma mass spectrometry (ICP-MS), with analytical errors of Re and Os between 0.110.4% (2sigma). The results show that the Re-Os model ages are
141.8±2.1Ma for the Nannihu deposit, 145.4 ±2.0 to 144.5 ±2.2 Ma
(averaging 145.0 ±2.2 Ma) for the Sandaozhuang deposit, 145.8±2.1
to 143.8±2.1 Ma (averaging 144.8 ±2.1 Ma) for the Shangfanggou
deposit, and 133.1±1.9 to 131.6±2.0 Ma (averaging 132.4±2.0 Ma)
for the Leimengou deposit. According to these ages, combined with
the results of previous work in the molybdenum belt, it is suggested
that the age of the molybdenite deposits in the East Qinling molybdenum belt is mainly ~140 Ma. These deposits are the product
of transformation from the N-S to the nearly E-W tectonic regime
in eastern China. Except for the Huanglongpu Mo deposit, which
originated at ~220 Ma, the deposits appear to have geodynamically
formed in the extensional stage of the post-collisional orogeny between the North China craton and the Yangtze craton.
Keywords. Mo deposit, Re-Os dating, geodynamics, East Qinling, China
1
phyry Mo (Fe) deposit and Leimengou porphyry Mo deposit. These results, combined with the results of previous work in the Mo belt, provide further insight into the
geodynamic setting for the formation of these ore deposits.
2
Geological setting
Located on the southern margin of the North China craton, The East Qinling belt is used to be a part of the North
China craton (Fig. 1). Recently, it has also been described
as a component part of the northern margin of the Qinling
orogen because of its involvement in the Qinling
intracontinental orogenic movement during the MesoCenozoic, accompanied by intense magmatic activities
dominated by acid magma (Jurassic to Cretaceous), as
the Wuzhangshan batholith, the Haoping, Heyu and
Huashan batholiths. Concomitantly with the intrusion of
the above-mentioned large granite bodies, a number of
small, hypabyssal to near-surface granite porphyries (such
lntroduction
The East Qinling molybdenum belt contains the most
important large molybdenum deposits in China. This belt
is the second largest molybdenum belt in the world subsequent to the Climax-Henderson porphyry molybdenum
belt. The molybdenum deposits occur along a tectonic
lineament of trending nearly east-west. They are mostly
concentrated in a region extending from the JinduichengHuanglongpu area, south to the Shaanxi, eastward to the
Nannihu area in Luanchuan County and the Leimengou
area in Songxian County, western Henan. There are a total of more than 30 superlarge, large and intermediate
molybdenum polymetallic ore deposits in the belt, which
contribute 52 percent of the total identified Mo reserves
in China (Zhang et al. 2001). Stein et al. (1997) have reported the Re-Os ages for the Jinduicheng-Huanglongpu
area. This study provides the reliable Re-Os isotopic dating results for the other two clusters, including four large
deposits: the Nannihu porphyry Mo (W) deposit,
Sandaozhuang skarn Mo (W) deposit, Shangfanggou por-
Close
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Yong-Feng Li · Jing-Wen Mao · Feng-Jun Bai · Bao-Jian Guo · Zhi-Guang Wang
as the Leimengou granite porphyry) and their genetically
related cryptoexplosive breccias, were emplaced. They
form a NW-trending tectonomagmtic belt in the region
and provide the source of ore materials for molybdenum
polymetallic mineralization. The Qinling molybdenum belt
may be approximately divided into three molybdenum clusters. The first cluster is found in the JinduichengHuanglongpu area (Huang et al. 1984), and can be described
as a mineralization cluster. The second cluster, is located in
the Nannihu-Sandaozhuang area about 75 km ESE of the
Jinduicheng-Huanglongpu area, and consists of porphyry
skarn-type Mo-W mineralization,. The third cluster is located in the Leimengou area, and includes the Leimengou
porphyry type Mo deposit and the Huangshuian Mo-Pb
deposit, which occurs in carbonatite veins.
According to the geological characteristics, ore element assemblage, ore genesis, mode of occurrence and
metallogenic mechanisms of the ore deposits, the
molybdenum deposits in the Qinling belt may be classified into three distinctly different groups; porphyry
type, skarn-porphyry type and hydrothermal carbonate
vein type.
3
Previous dating
In the East Qinling molybdenum belt, there have been
numerous attempts to date molybdenum mineralization.
For many years the mineralization ages in this area were
indirectly estimated by using the ages of mineralizationrelated granites, alteration minerals or by dating accessory minerals and nearby plutonic rocks. The development of new dating techniques, such as Re-Os dating of
molybdenite, has allowed for direct dating of mineralization., In the past several years, Re-Os analyses of molybdenite from the East Qinling belt have been performed
by Huang et al. (1994, 1996) and Stein et al. (1997). These
data are summarized in Table 1.
4
Samples and analytical methods
A total of eight ore samples were collected from the East
Qinling Mo deposits for Re-Os dating in this study. One
of them came from the Nannihu deposit, three from the
Sandaozhuang deposit, two from the Shangfanggou deposit, and two from the Leimengou deposit. The samples
were carefully identified under the binocular microscope
and then molybdenite separates were picked out by hand.
The separates were fresh, non-oxidized and pollution-free.
Samples were sealed in tubes and dissolved, following the
Carius tube digestion technique (Mao et al. 2003b). The
Re and Os isotopic compositions were determined by using the ICP-MS (VG PQ-EXCELL). In this study, the average blanks for the Carius tube procedure as described
above are ca.10 pg for Re and ca.1 pg for Os.
Close
Chapter 7-15 · Precise Re-Os dating of molybdenite from the east Qinling molybdenum belt in central China and its geodynamic implications
5
Results
Common Os was not detected in the eight samples of
molybdenite Table2.shows the isotopic components of the
samples. The decay constant used for 187Re of 1.666×1011 -1
yr , which has an uncertainty of about ±1.02%. The results show that the Re-Os model ages are 141.8±2.1 Ma
for the Nannihu deposit, 145.4 ±2.0 to 144.5 ±2.2 Ma (averaging 145.0 ±2.2 Ma) for the Sandaozhuang deposit,
145.8±2.1 to 143.8±2.1 Ma (averaging 144.8 ±2.1 Ma) for
the Shangfanggou deposit, and 133.1±1.9 to 131.6±2.0 Ma
(averaging 132.4±2.0 Ma) for the Leimengou deposit.
6
Metallogenic environment and geodynamical
setting
The North China craton had been in a stage of steady
development from the Cambrian until the Early Triassic.
The isotopic age data suggest the following: the Yangtze
craton collided and converged with the North China craton at about 218 to 238 Ma (Li et al. 1989), This was followed by an intracontinental orogeny, which ended in the
Jurassic (Chen and Fu 1992). During the late Jurassic and
early Cretaceous, the regional tectonic regime in the whole
of eastern China began to change. The main stress field
began to shift from N-S to nearly E-W, signaling the beginning of the Pacific tectonic evolution stage (Ren 1991).
During this stage the southern margin of the North China
craton, including the East Qinling area, transformed into
the extensional tectonic environment. The IndosinianYanshanian magmatic activity corroborates the features
of the tectonic evolution in this period.
First, in the Middle-Late Jurassic mafic magma rose and
intruded along tenso-shear steep-dipping fractures, forming diabase dikes or dike swarms in the area. Later, widespread acid magmatic activity formed large granite
batholiths and numerous granite porphyry stocks and dikes.
During the Early Cretaceous, large amounts of intermediate-acid magma were erupted along the Sanmenxia-Lushan
deep fault, forming volcanic basins at Tianhu of Songxian
779
County, Jiudian of Ruyang County and other areas (Wang
et al. 1997). Magmatism intensified, and the magma evolved
successively from the alkaline through subalkaline to calcalkaline compositions. This suggests a change in the character of the magamitic activity during that period. The
fact that more than 80% of Mesozoic intrusive rocks occurred in the Early Cretaceous indicates that the transition
of the tectonic regime began at the turn of the JurassicCretaceous. The Re-Os isotope model ages obtained in this
study are between 145.8±2.1 and 131.6±2.0Ma. It can be
concluded that the East Qinling metallogenic molybdenum
belts originated during this great transition of the tectonic
regime in eastern China. This time period belongs to the
second phase of large-scale metallogenesis in East China
during the Mesozoic (Mao et al. 2000; 2003b).
Acknowledgements
This study was supported by the National Natural Science Foundation of China (grant 40434011) and the State
Development and Planning Program for Basic Researches
in Key Areas of China (grant 1999043211).
References
Chen Y, Fu S (1992) Mineralization of gold deposits in Henan, China.
Beijing: Seismological Press: 1-146 (in Chinese)
Huang D, Du A, Wu C, Liu L, Sun Y, Zhou X, (1996) Metallochronology
of Mo(-Cu) deposits in the North China plateform: Re-Os age of
molybdenite and its geological significance. Mineral Deposits 15:
365-373
Huang D, Wu C, Du A, He H (1994) Re-Os isotope ages of molybdenum deposits and in East Qinling their geological significance.
Mineral Deposits 13; 221-230 (in Chinese with English abstract)
Li S, Hart SR, Zheng S (1989) The collision time of North China plate
and South China plate: evidence from Sm-Nd ages. Scientia
Sinica(B):19: 312-319 (in Chinese)
Li Y, Mao J, Guo B (2004) Re-Os dating of molybdenite from the
Nannihu Mo(W) orefield in the east Qinling and Its Geodynamic
significance. Acta Geologica Sinica 78: 463-470
Mao J, Wang Z (2000) A preliminary study on time limits and
geodynamic setting of large-scale metallogeny in East China.
Mineral Deposits 19:289-296 (in Chinese with English abstract)
Close
780
Yong-Feng Li · Jing-Wen Mao · Feng-Jun Bai · Bao-Jian Guo · Zhi-Guang Wang
Mao J, Yang J, Qu W, Du A, Wang Z, Han C (2003b) Re-Os age of CuNi ores from the Huangshandong Cu-Ni sulfide deposit in the
east Tianshan Mountains and its implication for geodynamic
process. Acta Geol Sinica 77: 220-226.
Mao J, Zhang Z, Yu J, Wang Y, Niu B (2003a) The geodynamics setting
of Mesozoic large-scale mineralization in North China: the revelation from accurate timing of metal deposits. Science in China
(series D) 33:289-299
Ren J (1991) A discussion on the basic features of the lithosphere
tectonics in Chinese continents. Regional Geology of China 2:
289-293 (in Chinese with English abstract)
Stein HJ, Markey RJ, Morgan JW, Du A, Sun Y (1997) Highly precise
and accurate Re-Os ages for molybdenite from the east Qinling
molybdenum belt, Shaannxi Province, China. Economic Geology
92:827-835
Wang Z, Cui B, Xu M (1997) The tectonic evolution and mineralization in the south margin of North China block. Beijing: Metallurgical Industry Press. pp1-296 (in Chinese)
Zhang Z, Zhu B, Chang X, Qiang L, Wen M (2001) Petrogenetic
metallogenetic background and time space relationship of the
East Qinling molybdenum ore belt, China. Geological journal of
China University 7(3):307-315(in Chinese with English abstract)
Close
Chapter 7-16
7-16
Studies on the genesis of adjacent Changkeng goldand Fuwang silver-deposits, Guangdong Province, China
Hua-Ying Liang, Ping Xia, Xiu-Zhang Wang
Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry and South China Sea Institute of Oceanology, Chinese Academy of Sciences, 510640 Guangzhou, China
Heng-Xiang Yu
Guilin Institute of Technology, Guilin 541004, China
Abstract. The Changkeng Au- and Fuwang Ag-deposits represent
an economically significant and distinct member of the Au–Ag deposit association in China. The two deposits are immediately adjacent, but the Au- and Ag-orebodies separated from each other.
Changkeng is hosted in brecciated cherts and jasperoidal quartz
and is characterized by disseminated ore minerals. Fuwang, hosted
in the Lower Carboniferous Zimenqiao group bioclastic limestone,
has vein and veinlet mineralization associated with alteration comprised of quartz, carbonate, sericite, and sulfides. The Changkeng
gold and Fuwang silver deposits overlap in homogenous temperature and salinity of fluid inclusions. The δDH2O, δ18OH2O, δ13CCO2 and
3
He/4He values of the fluid inclusions suggest the ore fluids of the
Changkeng Au-ore come from the meteoric water and the ore fluids of the Fuwang Ag-ore are derived from mixing of magmatic
water and meteoric water. The Changkeng gold- and the Fuwang
silver deposits show different Pb isotope signatures, suggesting different sources of ore-forming material. Rb-Sr isochron age (68 ± 6
Ma) and 40Ar-39Ar age (64.3 ± 0.1 Ma) of the ore-related quartz veins
from the Ag-deposit indicate that the Fuwang deposit formed during the Cenozoic Himalayan tectono-magmatic event. The adjacent
Changkeng and Fuwang deposits could, however, represent a single
evolved hydrothermal system. The deposits are alternatively the
product of the superposition of two different geological events. Our
work indicates that the Pacific Coastal Volcanic Belt in the South
China Fold Belt has greater potential for Himalayan precious metal
mineralization than previous realized.
gold deposit is hosted in brecciated siliceous rocks on the
top of rocks of the Zimenqiao Group bioclastic limestone
and is characterized by disseminated mineralization. Ore
minerals in the gold deposit include disseminated anhedral
pyrite, native gold, stibnite, realgar, and orpiment. Gangue
minerals include quartz, illite, dickite, calcite, less fluorite,
and barite (Du et al. 1993). The silver content in the gold
orebodies is low (generally <11 ppm).
The Fuwang silver deposit is hosted in Early Carboniferous Zimenqiao bioclastic limestone along the contact
fault zones between the limestone and the overlying
Changkeng gold-hosting siliceous rocks. The Fuwang silver is characterized by vein and veinlet mineralization
with zones of silicification. The main sulphide minerals
are sphalerite and galena, with lesser pyrite and rare arsenopyrite, chalcopyrite, and bornite. The deposit is poor
in gold (< 0.2 ppm). The crosscutting relationship indicates that the gold deposit is older than the silver deposit.
Keywords. Himalayan, gold, silver, Guangdong, ore genesis
1
Geological setting
The adjacent Changkeng gold- and Fuwang silver-deposits
are located along the southwestern rim of the Shanshui
basin (Fig. 1). Sedimentary rocks in the region range from
Proterozoic to Cenozoic.(Bureau of Geology and Mineral
Resource of Guangdong Province 1985; Du et al. 1993).
Eocene volcanic and sedimentary rocks are widespread
(Tang 1987) and a small Tertiary volcanic rocks hostedsilver deposit was discovered (Fig. 1).
The adjacent Changkeng gold- and Fuwang silver- deposits differ in their geologic characteristics, stratigraphic
position, and metal contents, but are both located at the
same locality (Fig. 1), The Changkeng gold orebodies are
present in the upper part of the stratigraphic section (Du
et al. 1993). The Fuwang silver orebodies are located in the
lower parts of the stratigraphic section. The gold and silver
ore bodies are separated from each other. The Changkeng
Close
782
Hua-Ying Liang · Ping Xia · Xiu-Zhang Wang · Heng-Xiang Yu
2
Genesis of the gold-hosting siliceous rocks
Genesis of the gold-hosting siliceous rocks has been debated extensively. Du et al. (1993) argues that the goldhosting siliceous rocks are jasperoid quartz formed from
limestone. However, Xia et al. (1996) suggest that these
rocks are syngenetic chert. Gold-hosting silicious rocks
consist of thin-bedded and laminated, massive, and brecciated black material. Some radiolaria, which suggest an
age of between Carboniferous and Permian, are present
in some of the laminated and massive siliceous material.
This suggests that some parts of the gold-hosting siliceous laminated and massive material is radiolarian chert.
The limestone-siltstone contacts are common sites of deep
burial diagenetic silicification. Some of the massive zones
contain framboidal pyrite, and therefore may have formed
by diagenetic processes as diagenetic chert. The Changkeng gold ore is hosted mainly in the breccia. Thus, the
gold-bearing breccias imply that the gold was introduced
after the diagenetic silicification. The gold-hosting rocks,
therefore, formed by multistage silicification that at least
includes syngenetic-, diagenetic-, and hydrothermal- silicification. The hydrothermal silicification is related to
gold deposition. The syngenetic silicification and the diagenetic silicification have high background abundances
of gold and may indicate that a pre-existing enriched of
gold in the stratigraphic section contributed to the Changkeng gold deposit, similar to processes suggested for the
Meikle and neighboring Carlin-type deposits of Nevada
(Emsbo et al. 2003).
3
Geochemical studies of the adjacent Changkeng
gold and Fuwang silver deposits
3.2 Pb Isotopes of the adjacent Changkeng gold- and
Fuwang silver- deposits
The adjacent Changkeng gold- and Fuwang silver- deposits show different lead isotopic signatures. The
Changkeng gold deposit has Pb isotope ratios (206Pb/204Pb:
18.580-19.251, 207Pb/204Pb: 15.672-15.801, 208Pb/204Pb:
38.700-39.104) similar to those (206Pb/204Pb: 18.578-19.433,
207Pb/204Pb: 15.640-15.775, 208Pb/204Pb: 38.925-39.920) of
its host rocks and different from those (206Pb/204Pb: 18.82018.891, 207Pb/204Pb: 15.848-15.914, 208Pb/204Pb: 39.57939.786) of the Fuwang silver deposit. The Pb in the gold
deposit is derived from the local sources. The Pb isotope
composition of the Fuwang silver deposit is similar to
those of the Neoproterozoic metamorphic basement of
the western Guangdong region (Zhang et al. 1993), suggesting that the Pb of the Fuwang silver deposit is derived from the Neoproterozoic metamorphic basement.
3.3
40Ar/39Ar age and Rb-Sr isochron age of mineralized
quartz veins
The mineralized quartz sample from the Fuwang silver
deposit yields 40Ar/39Ar a plateau age of 64.3 ± 0.1 Ma
and isochron age of 64.0 ± 0.1 Ma with an initial 40Ar/36
ratio of 294.5 ± 0.4. The Rb and Sr isotopic data obtained
from six samples define an Rb-Sr isochron, with an age
of 68 ± 6 Ma, MSWD = 4.14. Quartz 40Ar/39Ar age s and
Rb-Sr isochron age are concordant within error, and correspond to the Himalayan tectono-magmatic event (Himalayan is a period <90 Ma; Wang and Mo 1995).
4
Origin of Changkeng gold and Fuwang silver
deposits
3.1 Geochemistry of the ore-forming fluid
The gold and silver deposits overlap in homogenization
temperature, in the ranging 210 ± 80 °C and 230 ± 50 °C,
respectively. Salinities of the fluid inclusion from the gold
and silver deposits are also overlap, ranging from 1.6
- 7.3 wt % and 1.6 - 2.6 wt % equiv. NaCl, respectively.
The adjacent Changkeng gold- and Fuwang silver- deposits are different in δDH2O, δ18OH2O, δ13CCO2 and 3He/4He
isotope composition (Guo et al. 1996; Sun et al. 1999). The
δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions from the Changkeng gold deposit range from –80
to -30 ‰, -7.8 to –3.0 ‰, -16.6 to -17.0 ‰ and 0.0100 to
0.0054 Ra, respectively. The δDH2O, δ18OH2O, δ13C CO2 and
3He/4He values of fluid inclusions from the Fuwang silver
deposit range from –59 to -45 ‰, -0.9 to 4.1 ‰, -6.7 to –0.6
‰ and 0.5930 to 0.8357 Ra, respectively. The δDH2O, δ18OH2O,
δ13CCO2 and 3He/4He values of the fluid inclusions suggest
the ore fluids of the Changkeng gold ore come from the
meteoric water and the ore fluids of the Fuwang silver ore
come from mixing of magmatic water and meteoric water.
The Changkeng gold deposit is hosted in siliceous rocks
and limestone and shows similar mineralization and mineral associations to many Carlin-type deposits (Hofstra
and Cline 2000; Hu et al. 2002; Peters et al. 2002).
Age evidence suggests that the Fuwang silver deposit
bear a genetic relation to the Himalayan magmatic event
in the Shanshui Basin. Given the close temporal and broad
spatial association of the silver deposit with Early Tertiary magmatism, the D, O, C, and He isotope data are
consistent with ore fluids that consisted of a mixture of
deeply sourced magmatic and local meteoric water.
The most plausible explanation is to ascribe these combined mineralized ages and isotopic results for the Fuwang
silver deposit to the Himalayan tectono-magmatic event. The
presence of disseminated gold in brecciated siliceous rocks
along with epigenetic quartz, orpiment, realgar, and stibnite,
together with meteoric D, O, C, and He isotopic values and
fluid inclusion salinity and temperature data that overlap those
from Fuwang silver deposit, suggests that the gold was deposited by an epigenetic meteoric hydrothermal system.
Close
Chapter 7-16 · Studies on the genesis of adjacent Changkeng gold- and Fuwang silver-deposits, Guangdong Province, China
The adjacent Changkeng gold- and Fuwang silver-deposits could represent a single evolved hydrothermal system where the ore fluids deposited gold at first in the brecciated silicification, and then mixed with the magmatic water
and deposited silver in the fracture zone in the limestone.
Alternatively, the second ore genetic model is that the adjacent Changkeng gold- and Fuwang silver-deposits may have
resulted from the superposition of different geological
events. Given the close proximity of the two deposits and
the overlap of fluid inclusions salinities and temperatures,
the adjacent Changkeng gold and Fuwang silver deposits
were most likely formed by the first model.
Early Tertiary isotopic ages from the Fuwang silver deposit and the nearby Xiqiaoshan Tertiary volcanic rockhosted silver deposit suggest that the South China Fold
Belt underwent a Himalayan event of precious metal mineralization.
Acknowledgements
The work was supported by the the NSFC (No.49872035,
40472049), and the important project of CAS (No. KZCXZSW-117 and No. GIGCX-03-04).
References
Bureau of Geology and Mineral Resource of Guangdong province
(1985) Regional geology of Guangdong province. Geol Pub House,
Beijing, China, 1-350 (in Chinese)
Du JE, Ma CH, Zhang GH (1993) Mineralization characteristics of
the Changkeng gold-silver deposit, Guangdong province. Guangdong Geology 8: 1-8. (in Chinese with English abstract)
783
Emsbo P, Hofstra AH, Lauha EA, Griffin GL, Hutchinson RW (2003)
Origin of high-grade gold ore, source of ore fluid components,
and genesis of the Meikle and Neighboring Carlin-type deposits, Northern Carlin trend, Nevada, Econ Geol 98: 1069-1105
Guo XS, Du JE (1996) Study on the fluid inclusions and geochemistry of the Changkeng Gold-Silver deposit. Min Res Geol 10: 187193. (in Chinese with English abstract)
Hofstra A H, Cline JS (2000) Characteristics and models for Carlintype gold deposits, Rev Econ Geol 13: 163-220.
Hu RZ, Su WC, Bi XW, Tu GZ, Hofstra AH (2002) Geology and
geochemistry of Carlin-type gold deposits in China. Miner Depos
37: 378-392
Peters SG, Huang JZ, Jing CG (2002) Introduction to and classification of sedimentary rock-hosted Gold deposits in P.R. China. In:
Peters S.G. (ed), Geology, geochemistry, and geophysics of sedimentary rock-hosted gold deposits in P. R. China. Open-File Rep
02-131, versi 1.0: 1-60
Sun XM, Norman DI, Sun K, Chen BH (1999) Characteristics and
source of ore-forming fluids of Changkeng Gold-Silver deposits
in middle Guangdong province, evidences from N2-Ar-He. Scie
China (Series D) 29: 240-246 (in Chinese)
Tu GZ (2000) The super-large deposits in China. Vol. 1. Scie China
Press, Beijing, pp. 3-9 (in Chinese)
Wang HZ, Mo XX (1995) An outline of the tectonic evolution of China.
Episodes 8: 6-16
Xia P, Zhang H, Wang XZ, Chen JP (1996) Geology-geochemistry and
genesis of chert from Changkeng Au-Ag deposit, west Guangdong
province, China. Geochemica 25: 129-139 (In Chinese with English abstract)
Zhang Q, Zhang BG, Pang JY, Cao YB, Hong DH (1993) The isotope
signature and source rocks of Chadong Silver-Gold deposit. Mineral Deposits 12: 349-355 (in Chinese with English abstract)
Zhang WH, Lu WJ, Jiao YQ, Li ST (2000) Composition and source
study of ore-forming fluid in the Changkeng gold-silver deposits, Guangdong province, China. Acta Petrol Sinica 16: 521-527
(in Chinese with English abstract)
Close
Close
Chapter 7-17
7-17
Fluid inclusion and stable isotope geochemistry of the
Ernest Henry Fe oxide-Cu-Au deposit, Queensland, Australia
Geordie Mark1, Patrick J. Williams, Nick H.S. Oliver
School of Earth Sciences, James Cook University, Townsville 4811, Australia
1 Current address: School of Geosciences, Monash University, Melbourne 3168, Australia
Chris Ryan
CSIRO Exploration and Mining, School of Geosciences, Monash University, Melbourne 3168, Australia
Terry Mernagh
Geoscience Australia, GPO Box 378, Canberra 2601, Australia
Abstract. Ernest Henry is an iron oxide-copper-gold deposit characterized by magnetite>>hematite, chalcopyrite as the only significant
hypogene copper mineral. It occurs within a large, zoned, medium to
high temperature alteration system. Pre- to synmineralization quartz
contains three broad populations of fluid inclusions. Type 1 (L-VH±nS) inclusions decrepitate or homogenise at 200-500° C, have
salinities of 32-55 wt% NaClequiv, display chemical variations that
parallel the paragenetic sequence of alteration, and have variable
Br/Cl mostly less than magmatic brines. Type 2 (L-V) inclusions
homogenise at temperatures of 120-350°C have salinities up to 20
wt% NaClequiv and inferred to contain CaCl2. Type 3 L-rich CO2 inclusions were entrapped at 130-370MPa. dD and dO of pre- to
synmineralisation fluids are estimated to have been -23 to -66 and
8 to 11 per mil respectively. dS in main ore pyrite and chalcopyrite
is -1.6 to +5.4 per mil. The data are compatible with a substantial
magmatic contribution to Ernest Henry fluids but also suggest the
system was complex and involved fluids and other components
with different sources. Ernest Henry is distinguished from the giant
Olympic Dam deposit by evidence for high temperature/salinity
fluids and for no major involvement of surficial waters during mineralization.
Keywords. Ernest Henry, copper, gold, fluid inclusions, stable isotopes
1
Introduction
The sources of ore fluids and mechanisms of mineralization in iron oxide-copper-gold (IOCG) deposits are poorlyunderstood and could differ amongst the geologically
diverse members of the group (e.g. Barton and Johnson
2004). Ernest Henry is the largest known magnetite-dominated IOCG deposit in Australia (Mark et al., in press; cf.
Williams and Pollard 2003). In contrast to the giant hematite-rich Olympic Dam deposit in South Australia, it is
characterized by complex high temperature alteration
zoning and has chalcopyrite as the only significant copper mineral (Mark et al. in press; cf. Reeve et al. 1990).
This paper reports on fluid inclusion and stable isotope
studies that were undertaken to characterize Ernest Henry
ore fluids. It is the first fluid inclusion study to have been
attempted at the deposit where such work is challenging
because of the low abundance of quartz compared to most
other hydrothermal deposits and a general tendency for
fluid inclusions to be small and difficult to work with.
New stable isotope data augment earlier work by
Twyerould (1997) and include the first reported δD data
for the deposit.
2
Geological context
Ernest Henry is the largest of several magnetite bearing
IOCG deposits in the Cloncurry mining district, which
encompasses the eastern part of the Proterozoic Mount
Isa inlier in northwest Queensland, along with its extensions beneath shallow cover in the surrounding area (Williams and Pollard 2003). Late Palaeoproterozoic
supracrustal rocks and early ca 1.74 and 1.66 Ga intrusions were deformed and metamorphosed at greenschist
to amphibolite facies between 1.58 and 1.50 Ga and extensively intruded by granitoids from 1.55 to around 1.50
Ga (Page and Sun, 1998; Williams and Pollard, 2003). The
Ernest Henry deposit is hosted in a sequence of metamorphosed, predominantly intermediate volcanic rocks
and is spatially-associated with bodies of ca 1.66 Ga diorite. U-Pb dating of titanite from pre-ore alteration assemblages suggests that the Ernest Henry hydrothermal
system was broadly contemporaneous with the later (1.551.50) granitoids, examples of which are present within 15
km of the ore deposit (Mark et al. in press). Proterozoic
basement near Ernest Henry is obscured by Mesozoic to
recent cover. However, extensive drilling around the deposit has demonstrated there is a very large volume of
altered rocks that extends for at least several kilometres
in all directions near the current erosion level (Mark et
al. in press).
3
Paragenesis of alteration and mineralization
Twyerould (1997) and Mark et al. (in press) documented
the time-space evolution of the Ernest Henry hydrothermal system. Distal stage 1 alteration produced secondary
albitic plagioclase and calc-silicates and was similar to
regional-scale sodic-calcic metasomatism elsewhere in the
Close
786
Geordie Mark · Patrick J. Williams · Nick H.S. Oliver · Chris Ryan · Terry Mernagh
district (De Jong and Williams 1994). It is preserved with
variable overprints by younger alteration at distances of
1-3 km from the orebody. Stage 2 formed a potassic-iron(manganese) association represented predominantly by
biotite, magnetite, K feldspar, almandine-spessartine garnet and quartz rich veins. Stage 2 alteration is preserved
around the periphery of the mine and along NE-trending structures extending away from it. Stage 3 potassic
alteration was pervasive in the immediate vicinity of the
orebody where the rocks were replaced by hematitestained and variably barian K-feldspar. Stage 3 altered
rocks were selectively affected by Stage 4 which formed a
SE-plunging breccia lens up to 300m thick in which magnetite, sulphides and a very complex association of other
minerals form the matrix to K-feldspar-dominated clasts.
Stage 5 calcite-dominated veins are predominantly localized near the footwall contact of the ore lens.
4
Sampling and methods
Samples were obtained from drill cores where the geological context and paragenetic setting was well known
from detailed logging undertaken as part of general geological description of the deposit and the surrounding
altered rocks (Mark et al. in press). The fluid inclusion
study focussed on interpreted primary inclusions hosted
by quartz from paragenetic stages 2, 3 and 4 (i.e. pre- to
synmineralization). The inclusions were investigated by
conventional and electron microscopy, subjected to
microthermometric experiments, and selected examples
were analyzed by Laser Raman spectrometry and proton
induced X-ray excitation (PIXE) analysis (cf. Ryan et al.
2001). Hand-picked separates were prepared of minerals
from stages 1-5 and analyzed using conventional methods as appropriate for δD in biotite and amphibole (n=10,
SUERRC, East Kilbride, Scotland), δ13C and δ18O in carbonates (n=36, Monash University), δ18O in silicates and
magnetite (n=42, Monash University) and δ 34 S in
sulphides (n= 32, University of Tasmania).
5
Fluid inclusion types and geochemistry
Quartz-hosted fluid inclusions from stages 2 to 4 can be
classified into three broad groups (Fig. 1). Type 1 (L-VH±nS) inclusions contain liquid, a small H2O vapour
bubble (<10% of total volume) and a halite solid at room
temperature. Most have additional solids in a variety of
assemblages containing one or more of ferropyrosmalite,
sylvite, Fe-chloride, magnetite, hematite, calcite and
kutnahorite (CaMn(CO3)2). Brown ice forms on freezing
and low first melting temperatures indicate the presence
of Ca and other divalent metals. A small proportion of
Type 1 inclusions decrepitate without homogenising on
heating while the remainder homogenise by halite or
ferropyrosmalite dissolution at temperatures between 200
and 520°C (65% > 300°C). Salinities estimated from halite dissolution temperatures are 32-55 wt% NaClequiv. Type
2 (L-V) inclusions occur in both primary and secondary
Close
Chapter 7-17 · Fluid inclusion and stable isotope geochemistry of the Ernest Henry Fe oxide-Cu-Au deposit, Queensland, Australia
settings (i.e. some of them represent the youngest fluid
type). At room temperature they contain liquid and an
H2O vapour bubble which occupies up to 25% of the volume of the inclusion. They homogenise at temperatures
of 120-350°C. Type 2 inclusions form brown ice on freezing and are deduced to be CaCl2-bearing. Salinities range
up to 20 wt% NaClequiv. Type 3 inclusions are dominated
by CO2 and are liquid-rich (>90%) at room temperature.
Some contain a small proportion of liquid H2O and/or a
nahcolite (NaHCO3) solid. Their densities suggest entrapment at pressures of 130-370 MPa during stages 2 to 4.
PIXE studies were undertaken on populations of single
fluid inclusions from stages 2, 3 and 4 (total analyses =
40). The results are quantitative at an accuracy of around
±50% for Cl, K, Ca, Mn, Fe, Cu, Zn, As, Br, Rb, Sr, Ba and
Pb. Accuracy for many interelement ratios is far better
than this as the main sources of error have similar effects
on all elements. Analytical detection limits were mostly
in the range 30-300 ppm. Type 1 inclusions display systematic stage to stage variation. All are distinguished by
high Mn:Fe ratios (mostly > 1) compared to complex brine
inclusions from other Cloncurry Fe oxide Cu-Au deposits such as Osborne, Starra and Eloise (Williams et al. 1999;
2001). Stage 3 (K feldspar-related) Type 1 inclusions have
lower (Mn+Fe)/K than those from stages 2 and 4 (magnetite/biotite/garnet-related). With the exception of one
outlying result, Br/Cl ratios in Type 1 inclusions are less
than 0.0013 and in some cases in which Br was undetected must be less than 0.0005. Cu was only detected in Type
1 inclusions at concentrations of 30-200ppm. Analyses of
the eight analyzed ore stage Type 1 inclusions have previously been reported by Mark et al. (2005). These are
distinguished by the highest K/Ca ratios and absolute
concentrations of Ba (mean 2.8 wt%), Zn (mean 4800
ppm), As (mean 590 ppm), and Pb (mean 2300 ppm) but
all had estimated Cu below 120 ppm.
6
Stable isotope results
δD values are -80 to -88 per mil in three stage 1 amphiboles, -85 and -91 per mil in two stage 2 biotites, - 69 to -95
in four stage 4 biotites, and -72 in a stage 5 amphibole.
Allowing for the likely fractionations this suggests that
the fluids in the Ernest Henry system had δD of -23 to 66 per mil Mean δ18O values (per mil) are: Stage 1, amphibole = 5.8, calcite = 15.7; Stage 2, biotite = 6.4, calcite
= 12.5, K feldspar = 11.3, magnetite = 4.6, quartz = 10.7;
Stage 3, biotite = 5.7, calcite = 12.5, K feldspar = 9.0, magnetite = quartz = 11.8; Stage 4, biotite = 6.2, calcite = 12.6,
K feldspar = 10.1, magnetite = 3.1, quartz = 11.7; Stage 5,
amphibole = 10.5, calcite = 14.9. In conjunction with data
from Twyerould (1997) these results suggest that fluid δ18O
remained in the range 8-11 per mil in the time period
represented by stages 1-4. The data for carbonate-rich stage
5 are consistent with an influence from metamorphosed
787
carbonates either involving an external fluid with higher
δ18O of 13-16 per mil that had equilibrated with such rocks
or from their presence in the protoliths of the highly deformed rocks in the footwall of the deposit where the carbonate veining is localized.
Mean δ13C values (per mil) in calcite are; Stage 1, -2.4;
Stage 2, -4.2; Stage 3, -3.5; Stage 4 -3.0; Stage 5, -2.1. 34S
ranged from - 0.5 to +5.4 per mil (mean 2.2) in ore stage
chalcopyrite and from -1.6 to +4.8 (mean 1.6) in ore stage
pyrite. The two common sulphide minerals are not preserved in isotopic equilibrium.
7
Discussion
The pre- to synmineralization (Stages 2-4) mineral
parageneses at Ernest Henry that distinguish the system
from from regionally sodic-calcic altered rocks are deduced to have formed in a hydrothermal system dominated by compositionally complex fluids. Type 3 (high
density CO2) inclusions may have formed by unmixing
from aqueous brine phase. The Type 1 and 2 inclusions
imply that at least two fundamentally different types of
aqueous brine were present echoing the situation that
has been found in other Cloncurry district Cu-Au deposits (e.g. Williams et al. 2001). High salinity brines are
most likely to have cotransported Cu and Au in the system though ore-stage Type 1 inclusions studied by PIXE
have much lower Cu concentrations than were found at
the much smaller Starra Au-Cu deposit (Williams et al.
2001). They do however high concentrations of Zn, Pb
and Ba compared both to premineralization Type 1 inclusions and the relatively Cu-rich brines from Starra.
This suggests ore deposition was associated with the influx of a distinct mineralizing brine and although the
studied Type 1 inclusions could indicate that the ore was
deposited by efficient Cu precipitation from a very large
mass of fluid a more plausible explanation maybe that
the analyzed inclusions represent a “spent” fluid after
chalcopyrite precipitation (cf. Mark et al. 2005). Assuming that fluid Br/Cl ratios would have been essentially
insensitive to fluid-rock interactions, then the variable
measured values in Type 1 inclusions imply they derived
their salinity from more than one source and including
a component with Br/Cl similar to evaporitic halite. The
rocks near Ernest Henry have evidently undergone extensive fluid-rock interactions at elevated temperatures.
The O-H stable isotopic data are consistent with substantial magmatic contributions of these elements during the main presyn mineralization stages but given that
immediate host rocks are igneous, cannot be taken to
demonstrate an exclusively magmatic fluid source. Compared to Olympic Dam, Ernest Henry seems to have
formed from relatively high temperature and salinity fluids without a significant contribution from surfice waters (cf. Oreskes and Einaudi 1992).
Close
788
Geordie Mark · Patrick J. Williams · Nick H.S. Oliver · Chris Ryan · Terry Mernagh
Acknowledgements
This research was supported by the Australian Research
Council, Ernest Henry Mining and MIM Exploration. The
project was planned and executed in collaboration with
Richard Crookes and Rick Valenta.
References
Barton MD, Johnson DA (2004) Footprints of Fe-oxide(-Cu-Au) systems. SEG 2004: Predictive Mineral Discovery Under Cover. Centre for Global Metallogeny, The University of Western Australia, Special Publication 33: 112-116
De Jong G, Williams PJ (1995) Giant metasomatic system formed
during exhumation of mid crustal Proterozoic rocks in the vicinity of the Cloncurry Fault, NW Queensland: Australian Journal of Earth Sciences 42: 281-290
Mark G, Oliver NHS, Williams PJ (in press) Mineralogical and
chemical evolution of the Ernest Henry Fe oxide-Cu-Au ore
system, Cloncurry district, northwest Queensland, Australia:
Mineralium Deposita
Mark G, Wilde AR, Oliver NHS, Williams PJ (2005) Predicting alteration patterns in the outflow zones of hydrothermal ore systems: a case study using the “spent” fluids from the Ernest Henry
Fe-oxide-Cu-Au deposit: Journal of Geochemical Exploration
85: 31–46
Oreskes N, Einaudi MT (1992) Origin of hydrothermal fluids at Olympic Dam: preliminary results from fluid inclusions and stable isotopes: Economic Geology 87: 64-90
Page RW, Sun S-S (1998) Aspects of geochronology and crustal evolution in the Eastern Fold Belt, Mt Isa Inlier: Australian Journal
of Earth Sciences 45: 343-361
Reeve JS, Cross KC, Smith RN, Oreskes N (1990) Olympic Dam copper-uranium-gold-silver deposit: Australasian Institute of Mining and Metallurgy Monograph 14:1009-1035
Ryan CG, McInnes BM, Williams PJ, Guoyi Dong, Tin Tin Win, Yeats
CJ (2001) Imaging fluid inclusion content using the new CSIROGEMOC nuclear microprobe: Instruments and Methods in Physics Research B 181: 570-577
Twyerould SC (1997) The geology and genesis of the Ernest Henry
Fe-Cu-Au deposit, NW Queensland, Australia: Unpublished PhD
thesis, University of Oregon. 494pp
Williams PJ, Dong Guoyi, Pollard PJ, Perring C, Ryan CG Mernagh
TP (1999) Fluid inclusion geochemistry of Cloncurry (Fe)-CuAu deposits: In: Stanley CJ et al. (eds) Mineral Deposits: Processes
to Processing. Balkema, Rotterdam, pp 111-114
Williams PJ, Guoyi Dong, Ryan CG, Pollard PJ, Rotherham, JF,
Mernagh TP, Chapman LH (2001) Geochemistry of high salinity
fluid inclusions from the Starra (Fe)-Cu-Au deposit, Cloncurry
district, Queensland: Economic Geology 96: 875-883
Williams PJ, Pollard PJ (2003) Australian Proterozoic iron oxide-CuAu deposits: An overview with new metallogenic and exploration data from the Cloncurry district, northwest Queensland.
Exploration and Mining Geology 10: 191-213
Close
Chapter 7-18
7-18
The Re-Os age for molybdenite from the Variscan
Strzegom-Sobótka massif, SW Poland
Stanislaw Z. Mikulski
Department of Economic Geology, Polish Geological Institute, 4 Rakowiecka St., 00-975 Warsaw, Poland
Holly J. Stein
AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482 USA
Norges Geologiske Undersøkelse, Leiv Eirikssons vei 39, 7491 Trondheim, Norway
Abstract. Molybdenites from quartz veins in a late Variscan granite
from the Fore-Sudetic block in southwest Poland yield ages of 309
to 304 Ma with the Re-Os method. The ages of the molybdenites
reflect post-magmatic hydrothermal activity associated with
leucogranite porphyry (aplogranite) related to regional uplift and
shear deformation during Westphalian time within this part of the
Saxothuringian zone of the European Variscan belt.
Keywords. Molybdenite, Re-Os, Strzegom-Sobótka granites, ForeSudetic block, SW Poland, Bohemian Massif
1
Introduction
Re-Os dating of molybdenite has been successfully employed to date magmatic and metamorphic pulses within
orogenic cycles (Bingen and Stein 2003; Requia et al. 2003).
Magmatism associated with deformation and hydrothermal activity in regional scale shear zones has also been
dated using molybdenite geochronology (Stein et al., in
press). In northern Sweden, over 100 m.y. of Svecofennian
orogenic history is recorded in molybdenite, both within
magmatic and metamorphic assemblages, and low Re
concentrations are attributed to molybdenite derived by
local biotite breakdown (Stein, in press).
In the northeastern part of the Bohemian massif that
constitutes the Saxothuringian zone of the European
Variscan belt, exposed crystalline rocks in the Western
Sudetes continue under the Cenozoic cover across the
Sudetic Marginal fault into the Fore-Sudetic block to the
Odra Fault Zone, which defines the northeastern boundary of the massif. During the Carboniferous and early
Permian, a major post-orogenic episode of granitic
magmatism and coeval volcanism occurred. Most of the
granites in this region are generally late to post-tectonic
I-type and S-type intrusions with a span of Rb-Sr ages
from ~330 to 280 Ma (Pin et al. 1989; Duthou et al 1991;
Oberc-Dziedzic et al. 1996; Kennan et al. 1999).
2
for the SSG range from 0.703 to 0.707 (Kennan et al. 1999).
However, for some of petrographic variants this ratio is
as high as 0.708-0.709 probably due to crustal contamination (Pin et al. 1989). The Strzegom-Sobótka granites
are calcic to calc-alkaline in character (Oberc-Dziedzic
et al. 1999). Using the Pearce et al. (1984) classification
scheme, the SSG are within the late orogenic to syn-collisional granite groups.
Numerous faults divide the SSGM into an elevated
western part and downthrown middle and eastern parts.
The SSGM contains three petrographic varieties
(Majerowicz 1972; Maciejewski and Morawski 1975;
Puziewicz 1985, 1990):
1. equigranular to porphyritic monzonite granite
(Kostrza type, western SSGM),
2. equigranular biotite granodiorite (Chwalków type,
central and eastern SSGM),
3. equigranular two-mica monzonite granite (eastern
SSGM).
The Strzegom-Sobótka granitoid Massif
The Strzegom-Sobótka granites (SSG) are classified as Itype granites, based on their generally low A/CNK (commonly less than 1.1). The 87Sr/86Sr initial ratios determined
Close
790
Stanislaw Z. Mikulski · Holly J. Stein
3
The granite intrusion has two phases. A younger phase
is represented by Kostrza-type granite and leucogranite
from the Paszowice quarry. Rb-Sr ages for two-mica granite from the SSGM provide an age of ca. 330-325 Ma (±
22 Ma), whereas some of monzogranites have a reported
age of ca. 290 Ma (Pin et al. 1989). Based on Rb-Sr wholerock isochron ages, Kennan et al. (1999) suggest that posttectonic Carboniferous granites in the Western Sudetes,
including some of the Strzegom-Sobótka massif, were
emplaced over a short time interval at ~328 Ma and derived from a source with similar 87Sr/86Sr initial ratios.
The present U/Pb dating of monazite and xenotime from
two-mica granites of SSGM yielded ages of 309.1 ± 0.8
Ma and 306.4 ± 0.8 Ma, respectively and indicate for the
younger emplacement of the two-mica granites during
the late Westphalian (Turniak and Bröcker 2002). The
relation of the leucogranite porphyry (aplogranite) from
the Paszowice quarry to the entire SSGM is not well understood (Pendias and Walenczak 1956; Majerowicz
1972).
Molybdenite mineralization from the Paszowice
quarry
In the NW part of the Strzegom-Sobótka granitoid massif (SSGM), numerous occurrences of molybdenite mineralization have been documented (Pendias and
Walenczak 1956; Salacinski 1978). Among other localities, Mo mineralization is found in the abandoned
aplogranite quarry near the Paszowice village (Fig. 1).
Here, mineralization occurs in a system of gray quartz
veinlets up to 2 cm thick that cut fine-grained leucogranite
porphyry (aplogranite). The veins are oriented at 290300° and dip steeply to the NE. The ore veinlets are cut by
massive but barren milky quartz veinlets striking 240°.
Molybdenite is a major sulfide present in veinlets forming either monomineral concentrations or may occur in
paragenetic association with other sulfides (chalcopyrite,
pyrite) native bismuth, or rarely with oxides such as wolframite and cassiterite (Pendias and Walenczak 1956;
Salacinski 1973). The ore mineralization is accompanied
by feldspathization, albitization, silicification, sericitization
and chloritization. The deposit has a moderate to high
temperature hydrothermal origin based on ore paragenesis (Salacinski 1978). According to fluid inclusion studies of sulfide-bearing quartz veinlets the deposit has been
classified as mesothermal based on temperatures and
pressures of 361-236°C and ~0.9 MPa, respectively (Ilnicki
1998). Ore-bearing quartz veinlets have also been found
in three oriented prospecting holes drilled in 1957 in the
surrounding area (Chilinska, unpublished). The average
content of Mo is 0.34 wt% and of Cu 0.13 wt%. Existing
data from these boreholes and from the surface geochemical prospecting led to the classification of the mineralization as Mo-Cu stockwork type (Kanasiewicz and
Mikulski 1989). Two zones of quartz vein Mo-Cu mineralization are now identified, extending to 100 m below
the surface (Fig. 2). They occupy shear zones oriented NWSW and dipping 70-80° NE. The shear zones range from
about 2 to 5 m in thickness.
4
Sample description for Re-Os data
Two molybdenite samples for Re-Os dating were collected
from the lowest level in the central part of the quarry
within the Strzegom-Sobótka granitoid massif. Molybdenite in quartz veins represents the main stage of mineralization. Euhedral molybdenite was selected from finecrystalline gray quartz veins (up to 2 cm thick) cutting
fine-grained leucogranite porphyry (aplogranite). Some
crystals form rosette aggregates 3-5 mm in diameter. The
length of single molybdenite flakes is usually <1 mm with
a width of ~0.1 mm. Larger molybdenite crystals are
curved and overgrown by chalcopyrite or pyrite, or they
may contain fine-grained chalcopyrite and pyrite grains
Close
Chapter 7-18 · The Re-Os age for molybdenite from the Variscan Strzegom-Sobótka massif, SW Poland
intergrown within molybdenite crystal cleavage, indicating an intimate temporal relationship. Albite crystals may
be found within quartz veinlets, but more commonly albite together with chlorite (after biotite) is found marginal to the quartz veins.
5
Methods and results
Re-Os dating of molybdenite is described in Stein et al.
(2001). We present the results of high precision Re-Os age
determinations for two molybdenite samples using procedures and techniques outlined in Markey et al. (2003).
A mixed double Os spike was used (185Re, 188Os-190Os).
The samples have low Re contents, all < 1 ppm, and the
resulting ages range from 309 to 304 Ma. A replicate of
sample #3, is provided in MDID-315. Sample weights
ranged from 41 to 73 mg.
6
Discussion
Re-Os dating of molybdenites from the Paszowice quarry
from the western part of the Strzegom-Sobótka granitoids
massif yields ages from 309 to 304 Ma. Their markedly
low Re concentrations (<1 ppm) are consistent with a
derivation related to metamorphic processes (Stein, in
press). The Mo mineralization clearly postdates emplacement of leucogranite porphyry (aplogranite), but is considered as either (1) related to post-magmatic processes
associated with the emplacement of evolved and Mo-specialized leucogranite magma (Kanasiewicz and Mikulski
1989), or (2) related to metamorphic processes and the
development of shear zones. Field relationships permit
an interpretation whereby the Paszowice leucogranite and
mineralized quartz veins were emplaced during shear
deformation in late Variscan time. Re-Os dating of molybdenite provides an age for this deformation of about
310-305 Ma. Thus, the Mo mineralization formed during
791
uplift of the Variscan orogen. The unidirectional NW-SE
strike of the ore veinlets at the Paszowice quarry and the
vein-hosted Mo zones recognized by boreholes are similar to the direction of the Marginal Sudetic fault, which
was also active during the Upper Carboniferous
(Zelazniewicz et al. 1997).
Mo mineralization of similar type and age (307 ± 3
Ma) has been reported from the southern margin of the
Variscan orogen (Langthaler et al. 2004) and similarly,
but slightly younger Re-Os ages from Sardinia are also
latest Variscan (289 ± 1 Ma; Boni et al. 2003). In Sardinia,
at least two ages of leucogranites are recognized, with
only the younger one displaying Mo mineralization and
the older (~310-300 Ma) being barren (Boni et al. 2003).
The molybdenite Re-Os ages from the SSGM also coincide with a sharp increase in the rate of uplift in the Massif Central (310-305 Ma; Bouchot et al. 2000) that consitute
the western part of European Variscides.
Acknowledgements
The analytical work was supported by the National Committee Scientific Research, Grant 5 T12B 001 22. Special
thanks goes to Dr. S. Ilnicki for providing one of molybdenite samples.
References
Bingen B, Stein HJ (2003) Molybdenite Re-Os dating of biotite dehydration melting in the Rogaland high-temperature granulites, S
Norway. Earth and Planet Scientific Letter 208: 181-195
Boni M, Stein HJ, Zimmerman A, Villa IM (2003) Re-Os age for molybdenite from SW Sardinia (Italy): A comparison with Ar/Ar
dating of Variscan granitoids. In: Eliopoulos et al (eds), Mineral
Exploration and Sustainable Development: pp 247-250. Millpress,
Rotterdam
Bouchot V, Milesi JP Ledru P (2000) Crustal scale hydrothermal
Paleofield and related Au, Sb, W orogenic deposits at 310-305 Ma
(Massif Central). SGA News 10: 6-10
Duthou JL, Couturie JP Mierzejewski MP, Pin C (1991) Next dating
of granite sample from the Karkonosze Mountains using Rb-Sr
total rock isochrones method. Przeglad Geologiczny 39:75-79
Ilnicki S (1998) Conditions of hydrothermal alterations in aplite from
Paszowice (Strzegom-Sobótka massif). Mineralogia Polonica 29:
29-42
Kanasiewicz J, Mikulski SZ (1989) On the occurrence possibility of
the molybdenium deposit of Cu-Mo formation on the Strzegom
granites massif. Przeglad Geologiczny 37: 129-133
Kennan PS, Dziedzic H, Lorenc MW Mierzejewski MP (1999) A review of Rb-Sr isotope patterns in the Carbo-niferous granitoids
of the Sudetes in Poland. Geologia Sudetica 32: 49-53
Kural S, Morawski T (1968) Strzegom-Sobótka granitic massif.
Biuletyn Instytutu Geologicznego 227: 33-85
Langthaler KJ, Raith JG, Cornell DH, Stein HJ, Melcher F (2004)
Molybdenum mineralization at Alpeiner Scharte, Tyrol (Austria):
results of in-situ U-Pb zircon and Re-Os molybdenite dating.
Mineralogy and Petrology 82: 33-64
Maciejewski S, Morawski T (1975) Petrographic diversity of granites of the Strzegom massif. Kwartalnik Geologiczny 19: 47-65
Close
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Stanislaw Z. Mikulski · Holly J. Stein
Majerowicz A (1972) The Strzegom-Sobótka granite massif. Geologia
Sudetica 6: 7-96
Markey R, Hannah JL, Morgan JW, Stein HJ (2003) A double spike
for osmium analysis of highly radiogenic samples. Chemical
Geology 200: 395-406
Oberc-Dziedzic T, Zelazniewicz A, Cwojdzinski S (1999) Granitoids
of the Odra Fault Zone: late- to post-orogenic Variscan intrusions, SW Poland. Geologia Sudetica 32: 55-71
Pearce JA, Harris NB, Tindle AG (1984) Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic rocks.
Journal Petrology 25: 956–983
Pendias H, Walenczak Z (1956) Signs of mineralization in the NW part
of Strzegom Massif. Biuletyn Instytutu Geologicznego 227: 209-228
Pin C, Puziewicz J, Duthou JL (1989) Ages and origins of a composite granitic massif in the Variscan belt: a Rb-Sr study of the
Strzegom-Sobótka Massif. Neues Jahrbuch Mineralogische
Abhandlungen 160: 71-82
Puziewicz J (1985) Origin of chemical, structural and textural variations in aplites from Strzegom granite (Poland). Neues Jahrbuch
Mineralogische Abhandlungen 153: 19-31
Puziewicz, J., 1990. Strzegom-Sobotka granitic massif (SW Poland). Summary of recent studies. Archiwum Mineralogiczne 45: 135-154
Requia K, Stein HJ, Fontboté L, Chiaradia M (2003) Re-Os and Pb-Pb
geochronology of the Archean Salobo iron oxide copper-gold
deposit, Northern Brazil. Mineralium Deposita 38: 727-738
Salacinski R (1973) Ore mineralization in granite at Paszowice. Acta
Geologica Polonica 23: 587-596
Salacinski R (1978) Ore mineralization and its origin in the granitoids of the Strzegom massif. Biuletyn Instytutu Geologicznego
308: 41-90
Smoliar MI, Walker RJ, Morgan JW (1996) Re-Os ages of group II1,
IIIA, IVA and IVB iron meteorites. Science 271: 117-133
Stein HJ, Hannah JL, Zimmerman A, Markey R, Sarkar SC, Pal AB,
in press, A 2.5 Ga porphyry Cu-Mo-Au deposit at Malanjkhand,
central India: implications for Late Archean continental assembly. Precambrian Research.
Stein HJ, in press, Low-rhenium molybdenite by metamorphism:
recognition, sampling, genesis, economics, and regional implications based on examples from northern Sweden. Lithos.
Stein HJ, Markey RJ, Morgan JW, Hannah JL, Scherstén A (2001)
The remarkable Re-Os chronometer in molybdenite: how and
why it works. Terra Nova 13: 479-486
Turniak K, Bröcker M (2002) Age of the two-mica granite from the
Strzegom Massif: new data from U/Pb monazite and xenotime study. Mineralogical Society of Poland Special Papers 20:
211-213
Zelazniewicz A, Cwojdzinski S, England P, Zientara P (1997) Variscides in the Sudetes and the reworked Cadomian orogen: evidence from the GB-2A seismic reflection profiling in southwestern Poland. Geological Quarterly 41 (3): 289-308
Close
Chapter 7-19
7-19
Re-Os ages for auriferous sulfides from the gold
deposits in the Kaczawa Mountains (SW Poland)
Stanislaw Z. Mikulski
Department of Economic Geology, Polish Geological Institute, 4 Rakowiecka St., 00-975 Warsaw, Poland
Richard J. Markey1, Holly J. Stein1, 2
1
AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482 USA
2 Norges Geologiske Undersøkelse, Leiv Eirikssons vei 39, 7491 Trondheim, Norway
Abstract. A Re-Os six-point isochron age of 317 ± 17 Ma has been
obtained for auriferous sulfides from sheeted quartz-veins representing the first stage of ore precipitation at the Radzimowice AuAs-Cu deposit. The age uncertainty is dominated by the fact that
sulfides contain very little common Os. Extremely low Re concentrations for gold-bearing sulfides from another gold district, KleczaRadomice, permitted dating of only one Co-arsenopyrite sample
G-4 from Klecza – analyzed as a Low Level Highly Radiogenic (LLHR)
sample. A precise age of 316.6 ± 0.4 Ma was obtained. Re-Os ages
indicate gold mineralization in Late Namurian time associated with
post-collisional extension and regional uplift in a continental arc
setting. Opening of deep-seated structures, marked also by the presence of lamprophyre dykes, may have allowed for the migration of
post-magmatic mineralizing fluids from various magmatic sources
at about 317 Ma.
Keywords. Gold, Re-Os, low level and highly radiogenic sulfides (LLHR),
Kaczawa Mountains, SW Poland, Bohemian Massif
1
Introduction
The Re-Os method has been successfully applied to molybdenite and can be similarly applied to other sulfides
with much lower concentrations of Re and Os, provided
the Re/Os ratio is very high. These sulfides have been
named LLHR (low level highly radiogenic), as their Os
isotopic composition mimics molybdenite (Stein et al.
2000). LLHR sulfides are samples whose 187Os dominates
the total Os. They are common in some hydrothermal
environments, and may be particularly common in small
crustally-derived deposits (Stein et al. 2000). The first
Re-Os isotopic ages for LLHR sulfides closely associated
with Au mineralization were reported from Bendigo, Australia (Arne et al. 2001). Recently, the giant Muruntau Au
deposit was successfully dated using LLHR samples of
arsenopyrite (Morelli et al. 2004). Analysis of samples
with extremely low-level Os contents is dominated by
Os contributions from procedural blanks (Markey et al.
2003). Subtraction of blank contributions in such cases
may result in significant adjustments to the 187Os/188Os
ratio, with a commensurate increase in the uncertainties of both the isotopic composition and the concentration of Os in the samples.
2
Geological setting
In the northwestern part of the Bohemian Massif, i.e., the
Western Sudetes that constitute the eastern fragment of
the Saxothuringian Zone of the European Variscides, several abandoned small and medium size gold-bearing arsenic-polymetallic deposits are found (Manecki 1965;
Paulo and Salamon 1974; Mikulski 2001). Among them,
there is still a high potential for exploration in vein deposits in Radzimowice and the Klecza-Radomice gold ore
district (KROD) in the Kaczawa Mountains. In these deposits the major gold, silver, and arsenic production came
from the sheeted quartz-sulfide veins, and vein arrays in
folded flysch-like sediments deformed and metamorphosed to lower greenschist facies during Upper Devonian-Lower Carboniferous. At the Radzimowice and
Klecza deposits the most important ore minerals are refractory gold-bearing Co-arsenopyrite and pyrite. This
stage of mineralization underwent strong cataclasis and
was later overprinted by base metal sulfides and non-refractory gold associated with quartz and carbonates. The
Radzimowice auriferous ore mineralization is considered
transitional between a porphyry and epithermal type
around the Upper Carboniferous composite Zelezniak
porphyry intrusion of subalkaline to alkaline igneous
rocks formed in a post-collisional arc setting (Mikulski
2005). The genesis of gold mineralization at the KleczaRadomice ore district was commonly assumed to be a
hydrothermal type connected with Variscan KarkonoszeJizera granites. Recently auriferous mineralization is classified as orogenic type (Mikulski 2003).
3
Sample description for Re-Os data
The auriferous sulfide samples for Re-Os dating were collected from the old mining wastes and underground workings of the Luis shaft in the northern part of the
Radzimowice Au-As-Cu deposit and from the old mining
wastes of the Klecza Northern Ore Field of the KROD.
Auriferous sulfide mineralization occurs as massive or
semi-massive ores in quartz veins that have been brecci-
Close
794
Stanislaw Z. Mikulski · Richard J. Markey · Holly J. Stein
ated and cemented by a younger generation of quartzcarbonate and base metal sulfides with non-refractory
gold. For Re-Os measurements we selected medium-, and
fine-grained (0.5 to 3 mm) euhedral Co-arsenopyrite,
pyrite and chalcopyrite non-fractured crystals. Arsenopyrite crystals from Radzimowice display compositional
variability in their As contents (34.8 to 37.4 at.%) and high
admixtures of cobalt (up to 6.4 at.%) and refractory gold.
Refractory gold (ca. 70 ppm) appears as sub-microscopic
inclusions within Co-bearing arsenopyrite and is less
abundant in pyrite. Arsenopyrite from Klecza has arsenic
contents between 31.5 and 33.4 at.% and a cobalt admixture from 0.1 to 0.9 at.%.
4
Methods and results
Re and 187Os concentrations in selected sulfides were determined at AIRIE, Colorado State University, using procedures and techniques outlined in Stein et al. (2000) and
Markey et al. (2003). Analyses of auriferous Co-arsenopyrites from the Radzimowice Au-As-Cu deposit yield Re
concentrations of 0.13-3.5 ppb with total Os in the very
low ppt range (Table 1). Nearly all analyzed auriferous
sulfide samples from the KROD were characterized by
extremely low Re concentrations (near blank level), so
age information based on those samples, with the exception of one, is not possible. Co-arsenopyrite sample G-4
from Klecza – analyzed as a LLHR sample – gave an age
316.6 ± 0.4 Ma assuming an initial 187Os/188Os ratio of 0.2
(Table 1). The LLHR arsenopyrite from Radzimowice with
the highest Re content (run LL-99) yields a Re-Os model
age of 317 Ma that is fairly insensitive to the assumed
187Os/188Os
initial ratio (187Re/188Os > 105). A four-point
isochron based on auriferous Co-arsenopyrites yields a
Re-Os age of 314 ± 31 Ma (initial ratio = 0.8 ± 2.2, MSWD
= 2.1). However, the large uncertainties for two Co-arsenopyrite analyses (LL-28, 29) resulting from extremely
low Os contents, precludes a precise age. We note that there
Close
Chapter 7-19 · Re-Os ages for auriferous sulfides from the gold deposits in the Kaczawa Mountains (SW Poland)
is general agreement between model ages for these
samples when an Os initial ratio of 0.2 is used. We support our arsenopyrite analyses by additional analyses of
a pyrite and chalcopyrite sample from the Radzimowice
deposit. These sulfides also contained low to very low ppt
level Re and Os (Table 1). Collectively, all sulfide analyses
from Radzimowice provide a six-point isochron with a
Re-Os age of 317 ± 17 Ma (Fig. 2). The six-point isochron
has a reduced uncertainty compared to the four-point isochron based only on Co-arsenopyrite samples. The still
relatively large uncertainty is due to the very low Os concentrations of most of the samples (<5 ppt total Os in all
cases but one). Within uncertainty, the Re-Os isochron
age overlaps with a much more precise model age of 316.6
± 0.4 Ma for Co-arsenopyrite sample G-4 (run MDID350) from the Klecza deposit.
5
Discussion
According to 40Ar/39Ar data presented by Marheine et al.
(2002), in the Western Sudetes, host rock schists of Ordovician-Lower Carboniferous represent shaly flysch-type
sediments that were recrystallized during regional uplift-related greenschist metamorphism in the Viséan at
344-333 Ma and the upper limit of the Variscan
tectonometamorphic and magmatic activity was dated
at 314-312 Ma (Namurian / Westphalian boundary). ReOs data suggest that refractory gold- sulfide mineralization in the Kaczawa Mountains postdates regional metamorphism of host rocks and orogenic deformation. Refractory gold mineralization is related to Late-Namurian
tectonometamorphic and magmatic processes. At the
Radzimowice Au-As-Cu deposit, the schist unit was intruded by the Zelezniak Intrusion (ZI) (Mikulski 2005).
Gold-bearing sulfide veins cut dacite porphyries and postdate lamprophyre dykes, but are spatially associated with
the dykes. SHRIMP ages for zircons from the fine-grained
rhyolite are similar to zircon ages from the mediumgrained microgranites of ZI, and indicate that the main
795
magmatic event was restricted to the Late Namurian
(weighted mean 206Pb/238U at 316.7 ± 1.2 Ma; Muszynski
et al. 2002). The Re-Os age of ca. 317 Ma for arsenopyrite
sample LL-99 in the context of SHRIMP ages from ZI support an association between post-orogenic felsic
magmatism and auriferous Co-arsenopyrite mineralization. This is further supported by the six point 317 ± 17
Ma Re-Os isochron age. The spatial association of quartzsulfide veins with lamprophyre dykes implicates them in
the ore-forming process, and suggests they are also of
similar age. Genesis of the gold mineralization in Klecza,
like other Au deposits and occurrences in the KROD, is
suggested to be of orogenic type (Mikulski 2003). The
KROD deposit is located in the Intra Sudetic Fault zone
that separates two different terranes (Aleksandrowski et
al. 1997). At KROD there is no evidence for a direct magmatic origin for hydrothermal fluids responsible for the
gold mineralization, despite the widely held belief that
mineralization is related to the Karkonosze-Jizera granites located ca. 10 km to the south. Re-Os data for auriferous Co-arsenopyrite from Klecza (316.6 ± 0.4 Ma), the
first stage of refractory gold mineralization, may be slightly
younger than the porphyritic granites of the KarkonoszeJzera pluton dated at 325-330 Ma by the Rb-Sr method
(Duthou et al. 1991) or date at 320 ± 2 Ma by 40Ar/39Ar on
biotite (Marheine et al. 2002). Au mineralization is most
likely associated with lamprophyre dykes dated at 314 ±
6 Ma 40Ar/39Ar (Marheine et al. 2002) or with aplitic granites date at 310 ± 5 Ma by Rb-Sr (Duthou et al. 1991).
Summarizing, our Re-Os results indicate that one of
the major Late Namurian post-orogenic extension episodes and regional uplift in the Kaczawa Mountains took
place ca. 317 Ma. Deep-seated structures allowed mineralizing fluids, mostly likely associated with magmatic
sources, to migrate upwards, forming auriferous sulfide
mineralization. The age of auriferous mineralization (ca.
317 Ma) recognized in the Kaczawa Mountains is not coeval with gold events described from the Central Bohemian province (ca. 338 Ma; Bouchot et al. 2001; or at 344
± 2.8 Ma by Re-Os method on molybdenite by Zachariáš
et al. 2001) and Massif Central (310-305 Ma; Bouchot et
al. 2000).
Acknowledgements
The analytical work was supported by NCSR, Grant no. 5
T12B 001 22.
References
Aleksandrowski P, Kryza R, Mazur S, Zaba J (1997) Kinematics data
on major Variscan strike-slip faults and shear zones in Sudetes.
Geol Magazine 134: 727-739
Arne DC, Bierlein FP, Morgan JW, Stein HJ (2001) Re-Os dating of
sulfides associated with gold mineralization in Victoria, Australia. Economic Geology 96: 1455-1459
Close
796
Stanislaw Z. Mikulski · Richard J. Markey · Holly J. Stein
Bouchot V, Faure M, Feybesse JL, Correira P, Zachariáš J (2001)
Variscan orogenic Au district related to a regional Visean detachment in the Central Bohemian province. In: Eliopoulos et al (eds)
Mineral Exploration and Sustainable Development. Millpress, pp
747-750
Bouchot V, Milesi JP Ledru P (2000) Crustal scale hydro-thermal
Palaeofield and related Au, Sb, W orogenic deposits at 310-305
Ma (Massif Central). SGA News 10: 6-10
Duthou JL, Couturie JP, Mierzejewski MP, Pin C (1991) Rb/Sr whole
rock samples isochrones method of the age determination of the
Karkonosze granite (in Polish). Przeglad Geologiczny 32: 75-79
Manecki A (1965) Petrographic-mineralogical studies of the
polymetallic veins from Wojcieszow vicinities (Lower Silesia).
Prace Mineralogiczne PAN, 47 (2): pp 65
Marheine D, Kachlik V, Maluski H, Patocka F, Zelazniewicz A (2002)
The 40Ar/39Ar ages from the West Sudetes (NE Bohemian Massif): constraints on the Variscan polyphase tectonothermal development. In: Winchester JA, Pharaoh TC, Verniers J (eds)
Palaeozoic Amalgamation of Central Europe. Geological Society
of London Special Publication 201: 133-155
Markey R, Hannah JL, Morgan JW, Stein HJ (2003) A double spike
for osmium analysis of highly radiogenic samples. Chemical
Geology 200: 395-406
Mikulski SZ (2001) Late-Hercynian gold-bearing arsenic-polymetallic
mineralization in Saxothuringian zone in the Polish Sudetes, NE
Bohemian Massif. In: Piestrzynski et al (eds), Mineral Deposits
at the Beginning of the 21st century. Balkema, pp 787-790
Mikulski SZ (2003) Orogenic quartz-sulfide-gold veins from the
Klecza-Radomice ore district in the Kaczawa Mountains (Western Sudetes) – NE part of Bohemian Massif. In: Eliopoulos et al
(eds), Mineral Exploration and Sustainable Development,
Millpress, pp 787-790
Mikulski SZ (2005) Geological, mineralogical and geochemical characteristics of the Radzimowice Au-As-Cu deposit from the Kaczawa
Mts. (Western Sudetes, Poland) - an example of the transition of
porphyry and epithermal style. Mineralium Deposita 39: 904-920
Morelli, R, Creaser, RA, Seltmann, R (2004) The age of gold mineralization at the Muruntau Au deposit, Uzbekistan, from Re-Os arsenopyrite geochronology. Geological Society America Abstracts
with Programs 36 (5): 444
Muszynski A, Machowiak K, Kryza R, Armstrong R (2002) SHRIMP
U-Pb zircon geochronology of the Zelezniak rhyolite intrusion,
Sudetes – preliminary results. Mineral Society of Poland – Special Papers 19: 156-158
Paulo A, Salamon W (1974) Contribution to the knowledge of the
Stara Gora deposit. Kwartalnik Geol 18: 266-276
Stein HJ, Morgan JW, Scheresten A (2000) Re-Os of low level highly
radiogenic (LLHR) sulfides: The Harnas gold deposit, southwest
Sweden, records continental-scale tectonic events. Economic Geology 95: 1657-1671
Zachariáš J, Pertold Z, Pudilová M, Zák K, Pertoldová J, Stein H,
Markey R (2001) Geology and genesis of Variscan porphyry-style
gold mineralization, Petráčkova hora deposit, Bohemian Massif,
Czech Republic. Mineralium Deposita 36: 517-541
Close
Chapter 7-20
7-20
Dating of gold occurrences in the Sayan-Baikal Fold
Belt, Southern Siberia, Russia
A.G. Mironov
Geological Institute of SB RAS, Sakhyanova 6a, Ulan-Ude, 670047, Russia
H. Stein, A. Zimmerman
AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80512-1482 USA
S.M. Zhmodik
Institute of Geology UIGGM SB RAS, Koptyuga 3, Novosibirsk, 630090, Russia
Abstract. The complex geologic history of the Tain gold-porphyry
deposit in the Sayan-Baikal Fold Belt (South Siberia) makes direct
age determinations problematic. Timing of porphyry gold mineralization, magmatism, and hydrothermal alteration are constrained
to an interval of 670-280 Ma based on dating of the host granodiorites, altered rocks, and ores by the Rb-Sr, Ar-Ar, and Re-Os techniques, respectively.
Keywords. Sayan-Baikal Fold Belt, gold-porphyry deposit, dating, ArAr, Rb-Sr, Re-Os techniques
1
Introduction
The gold-bearing Sayan-Baikal Fold Belt is known for its
important ore reserves. Both quartz lode deposits (Pioneer, Granite, Dynamite, Irokinda, etc.) and gold-sulfide
polymetallic deposits, along with sub-economic ore occurrences (Zun-Kholba, Zun-Ospin, etc.), are located in
the Belt (Mironov and Zhmodik 1999). Only recently, new
types of gold mineralization such as those at Tain,
Konevinskoye, and Kharalginskoye have been discovered.
The Tain deposit is of particular significance as it appears genetically different from previously studied deposits in the region and has unique geolocial features.
The Tain gold deposit lies in the central Ospin-Kitoi
massif of ultrabasic rocks comprising the ophiolitic Ilchir
plate. Regionally, the Gargan Craton consists of ArcheanProterozoic volcanogenic-sedimentary strata, ophiolite sequences of the Neo-Proterozoic age, and granitoids of the
Sumsunur (PZ1-2) and Samsal (PZ2-3) sequences. The
Ospin-Kitoi ultrabasic massif is defined by the convergence of ophiolite outcrops from north to south in the
eastern Gargan Craton. The massif is suggested to be a
single unit later dissected by erosion associated with uplift of the Gargan Craton and preserved along its periphery (Belichenko et al. 1988).
2
Gold deposit description
The Tain deposit is localized in 300 m by 700 m granodiorites and plagiogranites stocks that crosscut local
serpentinites and serpentinized harzburgites (Fig. 1). The
massif hosting gold mineralization is shaped like two attached lenses. The inner massif is composed of the grey
mid- to fine-grained diorites and quartz diorites (granodiorites) that are variably altered and deformed. The marginal areas of the massif are variably enriched in yet to
identified carbonaceous matter. The carbonaceous matter is commonly encountered as fine dust in quartz, along
zone planes, or as dust-like spotted disseminations in plagioclase. The carbonaceous matter is also observed in the
cross-cutting microfractures, occasionally associated with
epidote-clinozoisite. The granulated aggregates of albite
replacing calcic plagioclase are also pigmented by dustlike carbonaceous matter (Mironov et al. 2001).
The beresitized rocks and beresites (mineral association of quartz, sericite, pyrite, and calcite) are the dominant rock type in the massif. They are greenish-grey fineand medium-grained rocks composed of sericitized plagioclase, quartz, sericite, calcite, chlorite, sulfides (pyrrhotite predominates), leucoxene, apatite, and zircon.
Quartz is characterized by two varieties, i.e., pressed, fractured grains (quartz 1) and almost undeformed aggregates (quartz 2). Sulfides are represented by impregnations (0.1-1.5mm) of pyrrhotite. Pyrite is associated with
quartz 2, iron hydroxides, and calcite or chlorite. The low
SiO2 concentrations, higher concentrations of MgO and
CaO and dominantly more Na2O than K2O are characteristic of beresitized rocks.
In the southern part of the massif, accompanying and
hosting gold mineralization are medium to dark grey, variably grain-sized, porphyritic plagiogranites. They have an
irregularly grained texture of quartz and plagioclase aggregates 0.2-5mm in size and porphyry-like quartz impregnations with traces of deformational cataclasite. Muscovite
is developed along fractures in plagioclase and locally
intense alteration results in completely replaced plagioclase. Calcite (up to 1-2 wt.%), sulfides (to 3-5 wt.%),
sericite, biotite, sphene, rutile, apatite, and carbonaceous
matter (0.1-0.5 wt.%). The carbonaceous matter gives the
dark grey colour to the rock and is best developed on altered plagioclase, infilling of microfractures in quartz grains,
and along fractures intersecting mineral aggregates.
Close
798
A.G. Mironov · H. Stein · A. Zimmerman · S.M. Zhmodik
Geochemically all the varieties of the stock granitoids
have low Th and U concentrations, moderate Ba and Sr
concentrations with Sr prevailing in the unaltered or
weakly altered rocks, and sharp increase of Ba concentrations in muscovitized and dyke formations. The precious metal contents significantly vary, reaching maximum in the muscovitized and carbonatized rocks.
Three types of orebodies: (1) quartz-veined low sulfide
bodies, (2) quartz-muscovite-pyrrhotite ores and (3) veinlet-impregnated ores are identified at the Tain deposit.
Quartz veined low sulfide bodies occur as 0.3 to 1.5 m
thick bodies observable for 230 m along strike. The quartz
veins are characterized by the carbonaceous matter-induced dark gray color and intensive boudinage structures
with a clear tectonic orientation. Quartz grains within
the boudins elongate by unidirectional fracturing and
dislocation with equigranular grains showing pressureinduced dissolution-reprecipitation. In some locations
brittle deformation is seen as cataclasis and brecciation
of host granitoids.. Muscovite, chlorite, biotite, amphibole and iron hydroxides (1-3 wt.%) are locally developed
in microfractures.
The major ore minerals (0.1-10 wt.%) occur as nest-like
features (1-8cm across) of pyrite, pyrrhotite, galena,
sphalerite and chalcopyrite. These minerals also occur as
fine impregnations. Rare ore minerals hessite, wehrlite,
argentite, native gold and silver are associated with netlike features as well.
Quartz-muscovite-pyrrhotite ores are differientiated by
high sulfide contents, mainly pyrrhotite, comprising up
to 70% of the total rock, hosted in light grey and white
quartz muscovite granitoids. The vein-like bodies are up
to 0.6 m thick in the quarry walls, hardly accessible, and
dominantly studied from rockfall in talus piles.
In contrast to the quartz veins, this type of ore is characterized by lighter colored quartz without carbonaceous
matter, high precious metal contents between 150 to 200
ppm Au and 300 to 450 ppm Ag, and a peculiar paragenesis of gold and sulfide minerals. Hexagonal pyrrhotite is
the dominant sulfide mineral comprising 95-98 vol.% of
ore minerals. Chalcopyrite (0.1-3 vol.%) occurs as thread
veinlets and impregnations at the contact between massive pyrrhotite ores and quartz-muscovite aggregates.
Pyrite, cobaltite, sphalerite, galena, kustelite, and native
gold occur in subordinate amounts. Cobaltite (CoAsS) is
always seen as impregnations of small (0.01-0.09mm) crystals in pyrrhotite. The important peculiarity of this ore
type is the partitioning of Au and Ag into kustelite rather
than other Au and Ag minerals. Kustelite forms isometric
grains 0.01-0.06mm in size that localize at the contact of
pyrrhotite with chalcopyrite and quartz.
Ores of veined-impregnated type are found within the
dark grey carbonatized, muscovitized and cataclased porphyry-like plagiogranites. The ore consists of quartz veinlets 0.5-3 cm thick and a few meters long with impregnations (0.1-5 mm) of pyrrhotite and chalcopyrite (0.5-5
vol.%) and noticably subordinate pyrite, sphalerite and
galena. The plagiogranite host rocks are five to thirty
meters thick and 100’s of meters long zones made of
quartz-sericite-muscotite rocks with variable amounts of
calcite, sulfides, and carbonaceous matter. Mineralogical
analysis of this ore type identify native gold, silver, argentite, and Ag-bearing bornite. Gold is present as two
distinctly different morphologies. The first is represented
by middle and large native gold particles (0.1-0.3 mm and
0.7-1.0 mm, respectively) of bright yellow color and
cloddy-laminar shape with high purity (915-965). The
second variety is composed by small and middle (0.010.3 mm) gold particles of low purity (429-323) and
kustelite.
Molybdenite is found as flakes and little nests in both
dark grey quartz and beresite ores. In the veinlets of dark
grey quartz, molybdenite is found together with gold and,
in beresite ore, it is found as “dry” veinlets along fractures.
The Tain gold deposit has a number of features that
are atypical of East Sayan hydrothermal deposits. The
veinlet-impregnated type of ore mineralization in porphyry-like granitoids are dominant here unlike the Pioneer, Barun-Kholba, Granite, and other lode deposits. The
presence of carbonaceous material, predominance of pyrrhotite among sulfides, that of kustelite among gold minerals, and of methane in the gas phase are peculular as
well. In our view, it is interpreted that the Tain deposit
formed in different conditions and due to the magmatism
of another type.
Close
Chapter 7-20 · Dating of gold occurrences in the Sayan-Baikal Fold Belt, Southern Siberia, Russia
The granitoids of the Tain stock belong to the granitoids
of the island arc type based on geochemical data. Although
variable in absolute composition, the stocks generally
corresponds to the island arc granites according to the
main indices (for example, Nb-Y, Rb-(Nb+Y) ratios) in
discrimination plots. Predominance of Sr and Ba and low
contents of U and Th are typical of unaltered varieties.
Ba, Cu, and Zn concentrations increase in the beresitized
and carbonatized granodiorites and granites. The maximum contents of Ba (1100-1600 ppm) have been found
in the carbonatized dykes of granite-porphyries. Co and
Ni predominance as well as low concentrations of U (1.33.2 ppm) and Th (0.4-3.9 ppm) are also characteristic of
the granite porphyries. Analyzed rare earth elements form
a trend similar to the REE trend of granitiods from the
Amur-Alyaska island arc system. Some decrease of their
contents is observed in ores at their enrichment in quartz
and pyrrhotite.
The massif rocks are intensly tectonized by subhorizonal
faulting. Small, spotted occurences of plagiogranites, diorites and dacite-porphyries are known in other areas of
the ophiolite cover (Ekhe-Shigns, Borto-Gol rivers, etc.).
All this testifies to the fact that the Tain stock granitoids
and analogous rocks formed in the island arc stage suffered deformation during the subsequent collision and
obduction. In contrast, the granitoids of the Sumsunur
and other younger sequences (PZ2-3) are clearly syn- and
postcollisional.
3
Dating results
The study of absolute age in rocks and ores of the Tain
deposit shows significant variations in obtained data. A
Rb-Sr isochron indicates 670±19 Ma and 87Sr/86Sr
=0.7120±0.0010 on the altered porphyry-like granites and
muscovite. Two Ar-Ar ages of 435±9 Ma (samples Th–330
and Th–331) and 280±4.1 Ma (Th–329) were obtained
from amphiboles taken from the Tain massif diorite. Those
ages are likely to indicate the later metamorphism and
hydrothermal alteration of rocks.
The question arises which process is associated with
and/or reponsible for gold mineralization. The answer
may be obtained from Re-Os data on molybdenite associated with gold mineralization. A sample of molybdenite as a rosette-like inclusion in a veinlet (6mm thick) of
dark grey quartz (TN-1) and a sample of molybdenite
from a “dry” veinlet (molybdenite powdery coating on
the fracture surface 0.5-1.5mm thick) (sample TN-2) were
selected.
799
TN-1 was taken from a single molybdenite bleb in an
0.8 cm vein of dark gray quartz, of the variety associated
with Au mineralization. Although the rock is quite weathered and Fe stained, the vein and molybdenite are moderately fresh. The rock appears to be a fine-grained granitoid that is highly altered, including silicification and a
vuggy nature due to leaching of mm scale feldspar. This
molybdenite-bearing vein yielded a Re-Os age of about
550 Ma, but additional molybdenite separates will be taken
and dated to confirm this result.
TN-2 is also a fine-grained granitoid with mm scale
euhedral crystals of feldspar with diffuse margins due to
silicification. The rock is also sericitized. Fe-oxide staining is locally prevalent. Molybdenite occurs in abundance
along a surface that appears to be the margin of an irregular, not planar, vein. The Re-Os age is about 860 Ma,
but additional mineral separates are necessary to affirm
geologic accuracy of this somewhat weathered occurrence.
Thus, the gold mineralization in the massif has the
age that is close to the island arc and island arc type granitoid formation (800-600 Ma). The Tain gold deposit contains the mineralization formed by reducing fluids and
has obvious features typical of gold porphyry deposits.
Its specific features are caused by granitoid emplacement
in an area of ultrabasites and black shales that are enriched in carbonaceous matter of both biogenic and
mantle nature. It is likely the earliest gold mineralization
in the region in the massif of island arc granitoids that
were subsequently subjected to obduction within the
ophiolite cover and accompaning turbidite and craton
terranes (Bogatikov and Tsvetkov 1988).
Acknowledgements
The work has been carried out with the grant support of
the leading research schools No -2208.2003.5 and RFBR
grant 03-05-65162.
References
Belichenko VG, Butov YuP, Dobretsov NL (1988) Geology and metamorphism of the East Sayan. Novosibirsk, Nauka.
Bogatikov OA, Tsvetkov AA (1988) Magmatic evolution of island arcs.
Moscow, Nauka.
Mironov AG, Zhmodik SM (1999) Gold deposits of the Urik-Kitoi
metallogenic zone (East Sayan, Russia). Geology of ore deposits.
V. 41, N1, 54-69
Mironov AG, Zhmodik SM, Ochirov YuCh, Borovikov AA, Popov VD
(2001) The Tain gold deposit (East Sayan, Russia) is rare type of
gold-porphyry formation. Geology of ore deposits. N5, 395–413
Close
Close
Chapter 7-21
7-21
Jurassic magmatism and Au-Ag mineralization
in the Deseado Massif (Patagonia Argentina):
Lead and sulfur isotopic studies
P. Moreira, R.R. Fernández, I.A. Schalamuk, R.O. Etcheverry
Instituto de Recursos Minerales (INREMI), Universidad Nacional de La Plata, CICBA, Argentina
A.P. Rolando
Pará-Iso Laboratory, Instituto de Geociencias, Universidade Federal do Pará, Belém, Brazil
Abstract. Lead isotope analyses of volcanic rocks and hydrothermal
minerals and sulfide isotope analyses of sulfurs from Au-Ag La
Josefina prospect (Deseado Massif geological province, Argentina)
are reported. Lead isotope ratios for sphalerite and pyrite have mean
values of 18.48, 15.69 and 38.61 for 206Pb/204Pb, 207Pb/204Pb and
208Pb/204Pb, respectively, and are similar to Pb isotope ratios for the
Jurassic volcanic rocks of Bajo Pobre and Chon Aike Formations.
δ34S ‰ values of sphalerite, pyrite and galena cluster between 1.3
and 3.8 ‰, suggesting that the sulfur at La Josefina was primarily
of magmatic origin. These results are interpreted to indicate that
the Jurassic volcanic rocks are closely related with low sulfidation
Au-Ag occurrences.
Keywords. Pb isotopes, S isotopes, epithermal deposits, Jurassic volcanism, Patagonia Argentina
1
Introduction
The Deseado Massif (DM) is located in the southern
Argentinean Patagonia (Fig. 1). In this region, the most
important unit is a volcanic complex of upper to middle
Jurassic age with bimodal features marked by andesitic
and rhyolitic magmas that conform the Bajo Pobre and
Chon Aike Formations, respectively. These units crop out
over more than half the area of a wide plateau. The
geochemical analyses of the Jurassic volcanism show a
calc-alkaline magmatism with a volcanic arc affinity.
These volcanic rocks are related to the early history of
the Gondwana break-up and were deposited in the backarc Patagonian Andes during a long period (187 to 144
My) of extension (Riley et al. 2000). The geotectonic environment of Patagonia in the Jurassic times was characterized by very slow subduction in the Pacific margin of
Gondwana (Ramos 1988). Pankhurst et al. (2000) support
the idea that the volcanic rocks were probably generated
by a variety of mechanism, among which the melting of
pre-existing continental crust was a dominant process.
These volcanic rocks host the Au-Ag veins of Cerro
Vanguardia, the principal ore deposit currently in production, and also host the Ag-ore shoot worked in the Marta
Mine, as well as some other important prospects like
Manantial Espejo, Huevos Verdes-Cerro Saavedra-El Pluma,
El Dorado-Monserrat, Cerro Negro and La Josefina. Most
of these prospects (Schalamuk et al. 1997) correspond to
the low sulfidation epithermal type of deposits. The last
prospect, currently under exploration, is located in the central part of the DM and the mineralization is represented
by Au-Ag bearing vein systems (up to 300 g Au/t).
The objective of this paper is to present the lead and
sulfur isotopic data from samples of hydrothermal sulfides and volcanic rocks obtained at the La Josefina prospect.
There are few isotopic studies of the DM, only two lead
isotope data for the Jurassic volcanic rocks are indicated
by Kay and Gorring (1999) and five lead isotope measurements on galena from several ore deposits of the DM
were showed by Schalamuk et al. (1997). Theses analyses
show isotopic values between 18.48-18.72, 15.73-15.95 and
38.70-39.53 for 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb,
respectively.
Isotope sulfur ratios carried out in samples from AuAg epitermal prospects (Cerro Vanguardia, Manantial
Espejo, El Dorado-Monserrat and Cerro León) in the DM,
were reported by Echavarría (1997), Schalamuk et al.
(1998) and Jovic et al. (2004). The δ34S values range between –2.8 and 4.2 ‰, indicating a magmatic source for
the sulfur.
2
La Josefina geology
The La Josefina prospect (Fig. 1) includes lower Paleozoic low grade metamorphic muscovitic schists,
metavolcanic and calk-silicate rocks with minor magnetitic levels and tourmalinites of La Modesta Formation (Moreira et al. 2005).
The Bajo Pobre and Chon Aike Formations represent
the Jurassic volcanic rocks. The Bajo Pobre Formation,
mainly andesitic-dacitic rocks, include porphyritic and
aphanitic flows partially self-brecciated, porphyries, sills
that intrude the low angle dip schist of the La Modesta
Formation, and ring-dikes surrounding rhyolitic domes.
The Chon Aike Formation cover approximately a 60 % of
the area. The lower member outcrop on the west part,
and consists of crystal-rich quartz-feldspar-biotite welded
ignimbrite with some flatten pumice-rich levels that was
dated at 153.2 ±3.6 My (K/Ar on biotite; Arribas et al.
Close
802
P. Moreira · R.R. Fernández · I.A. Schalamuk · R.O. Etcheverry · A.P. Rolando
1996). On the eastern part dominate a welded pumicerich, crystal-poor welded ignimbrite whose lower levels
carrying 5-20 cm crystal-rich-ignimbrite lithic fragments,
whereas in the upper levels these lithics are smaller and
sporadic. A rhyolitic dome-complex outcrops on 10 km2
in the north-northwest of the area and some smaller rhyolitic domes extend to the northwest, both with slowly
propylitic, pyritic and argillic patch of hydrothermal alteration. These domes intruded the Paleozoic metamorphic rocks (La Modesta Formation).
Paleogene and neogene basaltic flows cover the Jurassic volcanic rocks.
3
La Josefina Au-Ag epithermal ocurrences
The mineralization at the La Josefina prospect consists
of system of low sulphidation epithermal veins and veinlets filled mainly by quartz and chalcedony with minor
adularia, barite and platy calcite. The primary assemblages
are composed by native gold, electrum, specularite and
pyrite, arsenopyrite, galena with freibergite inclusions,
sphalerite, chalcopyrite and bornite and a supergenic association consist in limonites, chalcocite-covelite, cerusiteanglesite and malachite.
These occurrences are distributed in a curved belt about
N-S 12 km long and between 500 and 1200 m wide. The
age of the mineralization is not well constrained; a Rb-Sr
errorchron gave an age of 156 ± 2 My (Fernández et al.
1999). The veins are spatially associated with superficial
epithermal occurrences, like hydrothermal eruption breccias, silica sinter terraces, geyserites, carbonate stromatolitic deposits, and steam heated blankets, mainly to the
north of the prospect.
4
Samples and results
4.1 Samples
The samples collected for the lead isotopic study of the
La Josefina prospect consisted in intermediate-acid Jurassic volcanic rock from Bajo Pobre and Chon Aike Formation (feldspar separates) and hydrothermal minerals
from veins (pyrite and sphalerite). The isotopic Pb composition were determinate on 13 samples in the Pará-Iso
Laboratory, Instituto de Geociencias, Universidade Federal do Pará, Belém, Brazil.
Seven sulfide paragenetic samples, including separates
of pyrite (3), sphalerite (3), and galena (1), were analyzed
for their sulfur isotope composition. Analyses were carried out at the Stable Isotopic Service from Salamanca
University (Spain). The results are given as δ34S ‰ values relative to the CDT standard.
4.2 Results
The analyses of Pb in samples from La Josefina prospect
are summarized in the Table 1 and plotted in the Zartman
and Doe (1981) diagrams (Fig. 2).
The volcanic Jurassic samples have an average ratios
of 206Pb/204Pb= 18.44, 207Pb/204Pb= 15.65 and 208Pb/204Pb=
38.50 and the elongate trends in the general cluster indicate mainly an orogenic model fit, suggesting variable
mixing of lead from different sources, mainly model upper crust and to a lesser extent model mantle and lower
crust reservoirs.
The Pb isotopic compositions of pyrite and sphalerite
from La Josefina are near 206Pb/204Pb= 18.48, 207Pb/204Pb=
Close
Chapter 7-21 · Jurassic magmatism and Au-Ag mineralization in the Deseado Massif (Patagonia Argentina): Lead and sulfur isotopic studies
15.69 and 208Pb/204Pb= 38.61. The lead isotope composition of these sulfides are in general slightly more radiogenic than the volcanic host rocks.
The analyses of δ34S ‰ are summarized in the Table 2.
Sulfur samples in La Josefina show δ34Smineral values between 1.3 and 3.8 ‰. The δ34S high value for sphalerite
(13.1 ‰) demonstrate an overall increase. This could be
explained by changes of the hydrothermal fluid pH produced by the interaction with the volcanic rocks.
803
Lead isotopes obtained from galena samples by
Schalamuk et al. (1997) although have slightly higher values, do not show significant differences from the samples
studied here. The δ34S results in La Josefina are similar to
those in several ore deposits in the DM.
Based on these features, there is a genetic link between
the DM low sulfidation epithermal deposits and the bimodal magmatism of the Bajo Pobre and Chon Aike Formation.
Acknowledgements
The authors are grateful to the Agencia Nacional de
Promoción Científica y Tecnológica (FONCyT) and the
Santa Cruz state mining company (FOMICRUZ S.E.) for
the support and close cooperation during this research.
References
5
Conclusions
δ34S
The
values of pyrite, sphalerite and galena indicate that their sulfur was derived from a magmatic
sulfur source with scarce supergene activity. Pb isotope
ratios of pyrite and sphalerite, are most similar to those
of the volcanic rocks and suggest that they are the likely
source.
The correspondence of both sets of values with the
orogenic growth curve of Zartman and Doe (1981) suggests further that varied sources contributed to the lead
of the magma.
Arribas Jr A, Schalamuk I, de Barrio R, Fernández R, Itaya T (1996)
Edades Radimétricas de Mineralizaciones Epitermales Auríferas
del Macizo del Deseado, Provincia de Santa Cruz, Argentina. In:
XXXIX Congresso Brasileiro de Geología, pp 254-257
Echavarría LE (1997) Estudio geológico-minero del área El DoradoMonserrat, Departamento Magallanes, provincia de Santa Cruz.
Tesis Doctoral Facultad de Ciencias Naturales y Museo,
Universidad Nacional de La Plata. Unpublished
Fernández R, Echeveste H, Tassinari C, Schalamuk I (1999) Rb-Sr
age of the La Josefina ephitermal mineralization and its relation
with host volcanic rocks. Macizo del Deseado, Santa Cruz Province, Argentina. In: 2º Simposio Sudamericano de Geología
Isotópica, pp 462-465
Close
804
P. Moreira · R.R. Fernández · I.A. Schalamuk · R.O. Etcheverry · A.P. Rolando
Jovic SM, Guido D, Tiberi P, Schalamuk I (2004) Cerro Leon, una variación del modelo epitermal de baja sulfuración del Macizo del Deseado. In: VII Congreso de Mineralogía y Metalogenia, pp 225-230
Kay SM, Gorring ML (1999) Evolution of the Patagonian Mantle:
evidence from isotopic studies of Tertiary to recent plateau lavas.
II South American Symposium on Isotope Geology, pp 556-565
Moreira P, González P, Fernández R, Echeveste H, Schalamuk I,
Etcheverry R (2005) El basamento de bajo grado de las Estancias
La Modesta y La Josefina, Macizo del Deseado, Provincia de Santa
Cruz. Revista de la Asociación Geológica Argentina 60-1
Pankhurst RJ, Riley TR, Fanning CM, Kelley SR (2000) Episodic silicic volcanism in Patagonia and the Antarctic Peninsula: chronology of magmatism associated with the break-up of Gondwana.
J Petrol 41: 605-625
Ramos V. (1988) Late Proterizoic-Early Paleozoic of South America.
A collisional history. Episodes, 11:168-175
Riley T, Leat P, Pankhurst R, Harris C (2000) Origin of large volume
rhyolitic volcanism in Antartic Peninsula and Patagonia by crustal
melting. J Petrol 42: 1043-1065
Schalamuk I, Echeveste H, Etcheverry RO, Ametrano S (1998)
Metalogénesis del yacimiento “Manantial Espejo”,Macizo del
Deseado, provincia de Santa Cruz. In: Academia Nacional de
Ciencias Exactas, Físicas y Naturales, Anales 50: 217-236
Schalamuk I, Zubia M, Genini A, Fernández R (1997) Jurassic
epithermal Au-Ag deposits of Patagonia, Argentina. Ore Geol Rev
12: 173-186
Zartman RE, Doe BR (1981) Plumbotectonic-the model. Tectonophys
75: 135-162
Close
Chapter 7-22
7-22
Re-Os ages for molybdenite from the Tepeoba
breccia-centered Cu-Mo-Au deposit, western Turkey:
Brecciation-triggered mineralization
Hiroyasu Murakami
Institute for Geo-resources and Environment, Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba 305-8567, Japan
Yasushi Watanabe
Institute for Geo-resources and Environment, Geological Survey of Japan, AIST, 1-1-1 Higashi, Tsukuba 305-8567, Japan
Holly Stein
AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, CO 80523-1482 USA, and
Norges Geologiske Undersøkelse, Leiv Erikssons vei 39, 7491 Trondheim, Norway
Abstract. The Tepeoba breccia-centered Cu-Mo-Au deposit is associated with the Miocene Eybek granodiorite complex in western
Turkey. The ages for molybdenite samples in the hydrothermal breccia and two molybdenite samples in veins surrounding breccia, one
in metasedimentary rocks and one in the granodiorite, were dated
by the Re-Os method using a double Os spike. Re-Os ages of molybdenite are 25.03 ± 0.14 and 25.11 ± 0.14 Ma for the veins and
25.62 ± 0.09 Ma for the breccia-hosted sample. These results indicate that the hydrothermal breccia in the Tepeoba deposit formed
prior to the vein formation. We conclude, based on the Re-Os ages,
that hydrothermal activity at Tepeoba lasted at least half a million
years.
Keywords. Re-Os, 188Os-190Os double spike, hydrothermal breccia, CuMo-Au deposit, Turkey
1
Introduction
Re-Os dating of molybdenite (MoS2) is an effective tool
for directly dating mineralization. Notably, molybdenite
posses the unique property of accommodating Re at the
ppm level, while incorporating essentially no initial (common) Os, thus providing a suitable single mineral chronometer utilizing the 187Re-187Os method (Stein et al. 2001).
The 188Os-190Os double spike may be essential for young
or low Re molybdenites (Markey et al. 2003). This method
can precisely determine and correct for common Os and
mass fractionation. The method thus provides a precise
mineralization age associated with formation of molybdenite even in young samples with low Re contents.
In this study, we report three Re-Os ages of molybdenite, dated by the double Os spike method, in the
Tepeoba Cu-Mo-Au deposit in western Turkey. We discuss duration of mineralization and the spatial and temporal evolution of the Tepeoba hydrothermal system.
2
Geologic background
Western Turkey is comprised of Permo-Triassic metamorphic and sedimentary rocks (Fig. 1A). A series of intru-
sions was emplaced into these basement rocks during the
Oligocene and Early Miocene period. A ~24 Ma rapidly
exhumed high-grade metamorphic core complex in the
Kazdað mountain range was uplifted from ~14 km to ~7
km along a thick shear zone (Okay and Satir 2000). The
Eybek granodiorite is situated on eastern margin of the
Edremit graben bounded by ENE-WSW trending highangle normal faults. The granodiorite is a typical calcalkaline, I-type, magnetite-series. Granite body with Stype and ilmenite-series signatures occurs locally along
the margin of the granodiorite body (Fig. 1B). A two-component mixing pattern of strontium isotope values suggests the “granite” formed by mixing between the granodiorite and the host meta-sedimentary rocks. Early to
Middle Miocene volcanic and sedimentary rocks overlie
the basement rocks.
3
Tepeoba breccia-centered Cu-Mo-Au deposit
The Tepeoba deposit was discovered in 2002, by diamond
drilling conducted by the General Directorate of Mineral
Research and Exploration of Turkey. A drill hole shows
the upper 100 m with an average grade of 0.5 % Cu and
~1 g/t Au, with the upper 53 m at 1 % Cu, and 0.05 % Mo.
The deposit occurs along and above the south granite body,
located at the southern margin of the Miocene Eybek granodiorite complex. This deposit is hosted by metamorphic and sedimentary rocks of Permo-Triassic age, metamorphosed to andalusite-biotite schist due to the contact metamorphism by the granodiorite. The deposit consists of semicylindrical hydrothermal breccia 200 m wide,
and extends for 800 m southwards with a maximum thickness of 100 m (Fig. 1B). This hydrothermal breccia includes fragments of surrounding rocks (e.g., andalusitebiotite schist and granite) except granodiorite in a matrix mainly of phlogopite. The ratio of granite fragments
to andalusite-biotite schist fragments is greater nearer to
the granite. The breccia ore is composed of chalcopyrite
Close
806
Hiroyasu Murakami · Yasushi Watanabe · Holly Stein
and phlogopite with accessory molybdenite, pyrite, calcite, quartz, tourmaline, sphalerite, and electrum. In the
hydrothermal breccia, post-brecciation hydrothermal activity is limited to thin quartz veining.
It has been proposed that the Tepeoba deposit has been
tilted almost 90° with its top to the south due to Miocene
normal faulting, resulting in full exposure of hydrothermal alteration zones associated with the granodioritegranite complex on the present surface (Murakami et al,
2004). We suggest that alteration and mineralization at
Tepeoba resemble types seen at porphyry-style Cu-Mo
deposits. The alteration sequence in order of increasing
proximity to mineralized breccia is a propylitic zone,
muscovite zone, and K-silicate zone. The propylitic and
muscovite zones are characterized by the presence of small
amounts of chlorite and pyrite, and the presence of muscovite partly replacing biotite and quartz-calcite-molybdenite veins, respectively. These alteration zones surround
the breccia dominated by K-silicate alteration, depicted
by phlogopite with disseminated chalcopyrite and molybdenite. K-Ar ages for phlogopite in the matrix of the
mineralized breccia are 23.8 ±1.2 and 23.8 ±1.4 Ma (hereafter, all ages are shown with two sigma uncertainty), and
K-Ar ages for muscovite surrounding the breccia are 22.8
±1.4, and 24.6 ±1.4 Ma. Ages of the intrusions have also
been dated by K-Ar. Biotite in the granodiorite is dated at
20.3 ±1.0 and 21.4 ±1.2 Ma. K-feldspar in the granite is
older at 34.7±2.0 Ma. Integration of stable isotope data,
together with geologic relations and fluid inclusion data
indicate that boiling, high-salinity fluids were responsible
for the K-silicate and muscovite alteration and Cu-Mo-
Au mineralization is related to the granodiorite intrusion
and subsequent brecciation (Murakami et al. 2004).
4
Samples and analytical procedures of Re-Os
dating
The three molybdenite samples used for Re-Os dating are
(A) molybdenite cementing a matrix of a granite-fragment rich hydrothermal breccia, with phlogopite, quartz
and chalcopyrite, (B) molybdenite in a hydrothermal calcite-quartz vein in andalusite-biotite schist, and (C) molybdenite in a vein containing chlorite (after igneous biotite) found along cracks in the granodiorite (Fig. 1B).
Molybdenite was extracted from these samples in a
targeted, occurrence-specific manner using a diamondtipped, slow-speed drill (Stein et al. 2003). Chemical procedures follow Markey et al. (2003). Isotopic compositions
were determined using NTIMS on two NBS spectrometers at AIRIE. Age is calculated by applying the equation
187
Os=187Re (eλt-1), where λ is the decay constant for 187Re
and t is the age. The 187Re decay constant used is 1.666 ·
10-11 yr-1 with an uncertainty of 0.31%. During this study,
blanks were Re = 4.77 ± 0.04 pg, total Os = 4.09 ± 0.02 pg,
and 187Os/188Os = 0.229 ± 0.002 pg.
5
Relationship between granodiorite and
hydrothermal alteration
Re-Os and K-Ar ages for hydrothermal minerals, granodiorite and granite from the Tepeoba Cu-Mo-Au deposit
are summarized in Figure 2.
Close
Chapter 7-22 · Re-Os ages for molybdenite from the Tepeoba breccia-centered Cu-Mo-Au deposit, western Turkey: Brecciation-triggered mineralization
Re-Os dates are consistently older than all K-Ar dates.
The Re-Os system has been shown to remain closed at the
scale of the molybdenite phase even through high-grade
ductile deformation and metamorphism of a porphyry system (Stein et al. 2004b). On the contrary, the temperatures
where minerals begin to lose radiogenic argon are of 300 ±
50 ºC, 350 ± 50 ºC, and the interval ranging from 400 to
470ºC, for biotite, muscovite, and phlogopite, respectively
(Dodson and McClelland-Brown 1985). Additionally, K-Ar
dates in a contact metamorphic aureole generally reflect
cooling ages for the associated intrusion. A pluton showing
a close temporal and spatial association with the Eybek granodiorite has a Rb-Sr age of 25 ± 0.4 Ma (Yilmaz and Karacik
2001 and references therein), which is close to the Re-Os
molybdenite ages. Therefore, K-Ar ages for biotite in the
granodiorite should correspond to final cooling of the granodiorite, and that of hydrothermal minerals rejuvenated
due to contact metamorphism.
During cooling of the granodiorite, contact metamorphism may cause continuous loss of radiogenic argon from
hydrothermal minerals, because the youngest age of granodiorite is accord with that of hydrothermal muscovite.
The K-Ar age of the hydrothermal phlogopites is somewhat older than that of muscovite, which is consistent
with the observation that phlogopite commonly retains
its radiogenic argon better than muscovite at higher temperature (Dodson and McClelland-Brown 1985).
6
Style of Tepeoba mineralization relative to
porphyry copper
807
Re-Os ages for molybdenites yield a time-span from
25.62 ± 0.09 to 25.03 ± 0.14 Ma, a period > 0.5 m.y., slightly
longer than 0.3 m.y. estimates for the Far Southeast porphyry deposit (Arriibas et al. 1995) and 0.16 m.y. for the
Batu Hijau porphyry deposit (Garwin 2002). Recent ReOs dating indicates that some porphyry Cu-Mo deposits
have longer mineralization periods (e.g. Los Pelambres,
El Teniente, Stein et al. 2004a). Dilles et al. (2004) interpreted extended mineralization at Butte to overprint of
multiple mineralization events.
There is no syn- or post-hydrothermal activity except
a single stage of mineralized breccia at the Tepeoba deposit with a lack of significant veining in the hydrothermal breccia body. Molybdenite of ca. 25.03 Ma also coexists with low-temperature assemblages compare to those
in the breccia. These occurrences suggest that the 0.5
m.y.mineralization period of Tepeoba is more likely to
represent an extended mineralization event such as pro
and retro-grade alteration in skarn type deposit, rather
than possible multiple mineralization events.
We have determined formation pressure for the granodiorite using plagioclase-hornblende geobarometry.
The crystallization pressure is estimated at ~2 kbar. According to geobarometry, if rock density is 2.7 g/cm3, depth
of crystallization of the Eybek granodiorite is considered
to be ~7.5 km, which is consistent with depth estimates
for surrounding metasedimentary rocks (Okay and Satir
2000). Such a deeper depth relative to many other porphyry copper deposits (ca. 1-4 km) may utilize a more
static regime for skarn formation (e.g. controlled by diffusion rate rather than infiltration), and to limit hydrothermal activity accompanying mineralization in the vicinity of hydrothermal source without disturbance such
as meteoric water circulation. This may be supported by
the presence of small-scale skarn type Cu-Fe deposits
which are sporadically distributed in and around the
Eybek granodiorite at almost the same depth as the
Tepeoba deposit.
Although a period of hydrothermal activity at the
Tepeoba deposit related to the granodiorite and subsequent brecciation is consistent with the time interval for
common porphyry-style deposits, there is a huge difference in the scale between these types. This is interpreted
that volume and scale of mineralization of intrusion-related style should be controlled by number of cycles of
hydrothermal alteration linked to magmatic fluid derived
from intramineral intrusion (e.g., giant Cu-Mo porphyry
deposits in Chilean Andes).
Acknowledgements
For porphyry-style Cu deposits, hydrothermal breccia generally forms at the close of major hydrothermal activity,
although there are exceptions (e.g. Sillitoe 1985). Based on
Re-Os dating results, mineralized hydrothermal breccia at
the Tepeoba deposit formed prior to the vein formation.
We are grateful to Dr R Sari and Mr S Küçükefe of the
General Directorate of Mineral Research and Exploration
of Turkey for helping a field survey and providing geologic data of the Tepeoba deposit.
Close
808
Hiroyasu Murakami · Yasushi Watanabe · Holly Stein
References
Arribas AJr, Hedenquist JW, Itaya T, Okada T, Concepción RA, Garcia,
JSJr (1995) Contemporaneous formation of adjacent porphyry
and epithermal Cu-Au deposits over 300 ka in northern Luzon,
Philippines. Geology 23: 337-340.
Dilles JH, Stein H.J, Martin MW (2004) Re-Os and U-Pb ages for the
duration of the giant Butte, Montana, porphyry Cu-Mo and Cordilleran base metal lode ore deposit. IAVCEI general assembly
Pucón, Chile
Dodson MH, McClelland-Brown E (1985) Isotopic and paleomagnetic evidence for rates of cooling, uplift and erosion. Geol Soc
Mem 10: 315-325
Garwin S (2002) The Geologic Setting of Intrusion-Related Hydrothermal Systems near the Batu Hijau Porphyry Copper-Gold Deposit, Sumbawa, Indonesia, Global Exploration 2002: Integrated
Methods for Discovery, Colorado, USA. Soc Econ Geol 9: 333-366
Markey R, Hannah JL, Morgan1 JW, Stein HJ (2003) A double spike
for osmium analysis of highly radiogenic samples. Chemi Geol
200: 395-406
Murakami H, Watanabe Y, Sari R, Küçükefe S (2004) Newly discovered
Tepeoba breccia-centered Cu-Mo-Au deposit in western Turkey:
(electronic, session 1c) IAVCEI general assembly Pucón, Chile
Okay A, Satir M (2000) Coeval plutonism and metamorphism in a
latest Oligocene metamorphic core complex in northwest Turkey. Geol Mag 137: 495-516
Sillitoe RH (1985) Ore-Related Breccias in Volcanoplutonic Arcs. Econ
Geol 80: 1467-1514
Stein HJ, Cannell J, Cooke D, Sillitoe R, Perelló J (2004a) Metalliferous moments inside the lifespan of porphyry-style Cu-Au-Mo
deposits: (electronic, session 12a) IAVCEI General Assembly,
Pucón, Chile
Stein HJ, Hannah JL, Zimmerman A, Markey R, Sarkar SC, Pal AB
(2004b) A 2.5 Ga porphyry Cu-Mo-Au deposit at Malanjkhand,
central India: implications for Late Archean continental assembly. Precambr Res 134: 189-226
Stein HJ, Markey, RJ, Morgan JW, Hannah JL, Scherstén, A (2001)
The remarkable Re-Os chronometer in molybdenite: how and
why it works. Terra Nova 13: 479-486
Stein HJ, Scherstén, A, Hannah, JL, Markey R (2003) Sub-grain scale
decoupling of Re and 187Os and assessment of laser ablation ICPMS spot dating in molybdenite. Geochim Cosmochim Acta 67:
3673-3686
Yilmaz Y, Karacik Z (2001) Geology of the northern side of the Gulf
of Edrem it and its tectonic significance for the development of
the Aegean grabens. Geodin Acta 14: 31-43
Close
Chapter 7-23
7-23
U-Pb SHRIMP dating of zircon from quartz veins
at the Yangshan gold deposit: Evidence for multiple
magmatic-hydrothermal events
Qi Jinzhong, Li Li, Yuan Shisong, Liu Zhijie
Gold Geological Institute of China Armed Police Force, Langfang 065000, China
Abstract. The Yangshan gold deposit is a fine-grained disseminated
gold deposit located in south Gansu province. The metallogenic age
was determined by cathodoluminescence imaging and U-Pb SHRIMP
techniques. Zircons associated with quartz veins containing finegrained disseminated gold ore have typical magmatic features including pillar idiomorphism, rhythmic zoning, and Th/U ratio of 0.5
to 1.5. Average 206Pb/238U ages of 197.6 ±1.7 Ma, 126.9±3.2 Ma, and
51.2±1.3 Ma define three primary zircon populations. The former age
correlates to K-Ar ages (189.4±7.2 Ma mean) for plagiogranite dikes,
while the later two ages suggest buried Cretaceous and Tertiary
intrusives in or near the ore field. The Yangshan gold deposit is genetically related to the three magmatic-hydrothermal events.
Keywords. Disseminated gold, zircon, quartz vein, SHRIMP dating,
Gansu
1
Introduction
The recently discovered found Yangshan gold deposit, located in south Gansu province, China, is a large deposit
containing fine-grained disseminated gold. Four discovered ore blocks occur in metamorphosed Devonian sandstone, phyllite and limestone. The ore belt is primarily
controlled by the Anchanghe- Guanyinba fault as well as
small secondary faults. Locally, plagiogranite dikes lie along
the fault, and gold mineralization is concentrated in the contact zone between the dikes and the Devonian phyllite. The
orebodies, roughly sigmoidal in plane and tabular in profile, are hosted in pyritized, arsenopyritized, sericitized and
argillized phyllite and plagiogranite. Late-stage pyrite-quartz
veinlets crosscut the orebodies. Native gold, mainly electrum, is found as microscopic to sub-microscopic (<3µm)
inclusions in pyrite and arsenopyrite.
Previous K-Ar and 39Ar-40Ar dating of the deposit give
early Jurassic ages for the plagiogranite dikes, which were
spatially associated with the mineralization (Qi 2003). In
order to refine the metallogenic age of the Yangshan gold
deposit, zircons from quartz veinlets are analyzed using
cathodoluminescence images (CL) combined with
SHRIMP U-Pb dating.
2
Sample description and experimental method
Sample YM is from 305# gold vein in the Caopingliang
adit while sample AB from 314# gold vein in the Anba
adit. Both samples are from pyrite-quartz veinlets host-
ing fine-grained disseminated gold ore. The quartz veinlets (often 1 to 2 cm wide) occur in the contact zone between the plagiogranite dikes and the Devonian phyllite.
The samples consist mainly of quartz (95 wt.%) with subordinate sericite and clay minerals (4 wt.%), minor arsenopyrite and pyrite (1 wt.%), and rare electrum.
Representative zircon grains from the samples were
selected under microscope. The grains together with a
slice of standard zircon SL13 and grains of standard zircon TEM from Australia State University were mounted
in epoxy, ground, and polished to expose the interior.
Cathodoluminescence (CL) images were made on the zircons prior to analyses at the electronic probe laboratory
of Institute of Mineral Deposits, CAGS. U, Th, Pb isotopic
compositions of zircons were analyzed on a SHRIMP II
at the ion probe center of Geological Institute, CAGS.
Analyses followed the established methods of Composton
et al (1992) and Williams et al (1998). Programs SQUID
1.02 and ISOPLOT were utilized for data processing. Reported uncertainties for U/Pb ratios are at the 1σ level.
Common Pb is corrected from measured 204Pb. Weighted
mean ages are quoted at the 95% confidence level.
3
Result of SHRIMP dating
Fourteen analyses were made on zircon grains from
sample YM representing fine-grained disseminated ore.
Three age groups are defined and shown in the U-Pb
concordia diagram (Fig. 1). The first group consists of
three analyses giving 206Pb/238U ages of 195.4 to 200.9 Ma.
These zircons are prismatic with concentric zoning (Fig. 3)
suggesting a magmatic genesis (Yang 2002; Wu 2002). The
second group consists of six analyses yielding 206Pb/238U
ages between 121.8 and 137.0 Ma with a 128.2±5.5 Ma
mean. These oscillatory zoned zircons are also prismatic
(Fig. 3) and regarded as magmatic. The third group consists of four analyses giving 206Pb/238U ages between 48.1
and 51.7 Ma (50.0±3.0 Ma mean). These zircons are also
prismatic with clear oscillatory zoning and are interpreted
as magmatic (Fig. 3). The remaining analyses are scattered in the diagram.
Zircon samples YM-13 and YM-15 are short prisms
with concentric zoning yielding 206Pb/238U ages of 1069±22
Ma and 809±17 Ma, respectively. They likely represent
Close
810
Qi Jinzhong · Li Li · Yuan Shisong · Liu Zhijie
4
captured zircons from late Proterozoic intrusives. Analysis on zircon YM-12 gives an 206Pb/238U age of 375±11 Ma
and might be captured from the Devonian strata.
16 zircons from sample AB representing the quartz
veinlet of fine-grained disseminated ore were analyzed.
These zircons are small and their common lead concentrations are slightly high. One analysis with significantly
high common lead content was rejected. Two age groups
were obtained as shown in the U-Pb concordia diagram
(Fig. 2). The first group consists of five analyses giving
206Pb/238U ages between 121.4 and 130.2 Ma (125.3±4.9
Ma mean). These zircons are interpreted to be magmatic
from their prismatic morphology and oscillatory zoning
(Fig. 4). The second group consists of eight analyses which
yield 206Pb/238U ages of 49.8 to 55.3 Ma (51.7±1.6 Ma in
average). These concentrically zoned zircons are also
primsatic (Fig. 4) and regarded as magmatic zircons.
Geological significance of the SHRIMP age and
discussion
With high U-Pb isotope closure temperature of 700 to
750°C (Harrison et al. 1987; Tilton et al. 1991) and a strong
resistence to thermal disturbance (Meger et al. 1997), zircon is widely used to constrain the timing of geological
events. Although it has been proposed that “hydrothermal zircon” may form at lower temperatures (Corfu et al.
1984; Claoue-long et al. 1990), published ages of “hydrothermal zircons” from quartz veins in some gold deposits are very close to the ages of their host rocks, so whether
“hydrothermal zircon” do exist in quartz veins is suspicious (Luo et al. 2000). The relatively low temperature of
the hydrothermal fluid (150 to 250oC, Qi et al. 2003) at
Yangshan could hardly result in the formation of “hydrothermal zircon”. Furthermore, among the 30 analyses, only
3 zircons have Th/U ratios close to or less than 0.1, indicating that typical metamorphic zircons are not well-developed in the district (Gebauer et al, 1985; Yang J S et al.
2002). Therefore, zircons from the quartz veins in the district should be the ones captured during hydrothermal
activity. The zircons may be captured from intrusives (including intrusives in the source area and those near the
path of the hydrothermal fluid flow) and those captured
from strata (mainly from older rocks that supplied source
material to the Devonian strata).
Three analyses on zircons from sample YM constitute
the first group age, giving the 206Pb/238U ages between 195.4
and 200.9 Ma. Having short prism form with concentric
zoning and Th/U ratios of 0.44 to 0.87, these are regarded
as Jurassic igneous zircons. As the age is consistent with the
whole rock K-Ar ages of five plagiogranite samples in the
gold field (171 to 209 Ma, Qi et al. 2003), these zircons may
be captured from the plagiogranite dikes. Furthermore, the
age coincides with the 39Ar-40Ar plateau age of 195.40±1.05
Ma of the quartz veinlet (Qi et al. 2003), suggesting that the
intrusion of the plagiogranite dikes is responsible for hydrothermal activity in the district.
Cretaceous and Tertiary zircon groups were detected
in samples YM and AB. Analyses revealed eleven Cretaceous zircons yielding an average 206Pb/ 238U age of
126.9±3.2 Ma and twelve Tertiary zircons give an average
206Pb/238U age of 51.2±1.3 Ma. These zircons are prismatic
with concentric oscillatory zoning and dominant Th/U
ratios between 0.5 and 1.5 indicating their magmatic genesis. These zircons could not be captured from the nearby
strata as no Cretaceous or younger strata is found in the
district. Furthermore, no intrusives other than the Jurassic plagiogranite are found related to the ore belt suggesting these zircons are captured from buried Cretaceous
and Tertiary intrusives. Consequently, after the intrusion
of plagiogranite dikes, two major magmatic events occurred in early Cretaceous and in early Tertiary, with a
later ore fluid capturing the zircons from the intrusives.
Close
Chapter 7-23 · U-Pb SHRIMP dating of zircon from quartz veins at the Yangshan gold deposit: Evidence for multiple magmatic-hydrothermal events
Therefore, the gold field was influenced by three magmatic and associated hydrothermal events.
Comparing Yangshan magmatic-hydrothermal events
with the magmatic events in western Qinling, we can see
that the early Jurassic hydrothermal epoch coincides with
one fastigium of felsic intrusions in western Qinling (190Ma
to 220Ma, Zhang et al. 1994), while the early Cretaceous
hydrothermal epoch corresponds to another fastigium of
granite activities in western Qinling (120Ma to 150Ma, Du
et al. 1998). These two epochs were also considered to be
the fastigiums of gold mineralization in China (Zhai et al.
2002; Mao et al. 2002). The early Tertiary magmatic-hydrothermal epoch is consistent with the major metallogenic
age of gold deposits in southwestern China (Chen et al. 2001),
and the magmatic-hydrothermal activity may be linked to
811
the continental-continental collision of the penetrating Indian plate and Eurasian plate. The gold mineralization at
Yangshan may be directly linked to multiple, localized magmatic-hydrothermal events in the district and major magmatic-tectonic events in the region.
5
Conclusion
1. Zircons from quartz veinlets associated with ore are
dominantly prismatic with concentric oscillatory zoning and Th/U ratios of 0.5 to 1.5 indicating a magmatic
genesis.
2. The magmatic zircons with 206Pb/238U ages of 195.4 to
200.9 Ma in quartz veinlet sample YM are captured
from the early Jurassic plagiogranite intrusives.
Close
812
Qi Jinzhong · Li Li · Yuan Shisong · Liu Zhijie
3. The two zircon groups with average 206Pb/238U ages of
126.9±3.2 Ma and 51.2±1.3 Ma in quartz veinlets are captured from buried Cretaceous and Tertiary intrusives,
respectively. The early Jurassic, early Cretaceous, and
early Tertiary magmatic-hydrothermal events affected
Yangshan gold field and the deposit was genetically related to the three magmatic-hydrothermal events.
References
Chen YC, Wang DH (2001) Study of Himalayan endogenic mineralization. Bejing: Seismic Publishing House. 1-138 (in Chinese with
English abstract)
Claoue-long J, King RW, Kerrich R (1990) Archean hydrothermal zircon in the Abitibi greenstone belt: constrains on the timing of
gold mineralization. Earth Planet Sci. Letters 98:109-128.
Composton W, Williams IS, Kirschvink JL, Zhang Z, Ma G (1992) Zircon U-Pb ages for the Early Cambrian time scale. Journal of the
Geological Society London 149:171-184.
Corfu F, Ayres LD (1984) U-Pb age and genetic significance of heterogeneous zircon populations in rocks from the Favourable Lake
area, Northwestern Ontario. Contrib Mineral Petrol 88: 86-101
Du ZT, Wu GG (1998) Study on tectonic systems and gold
metallogenic tectono-dynamics in the region of west Qinling.
Bejing: Geological Publishing House. 1-145 (in Chinese with English abstract)
Gebauer D, Lappin MA, Grunenfelder M (1985) The age and origin
of same Norwegian eclogite: A U-Pb zircon and REE study.
Chemical Geology 52: 227-248
Harrison TM, Aleinkoff JN, Compston W (1987) Observation and
controls on the occurrence of inherited zircon in concord-type
granitoids, New Hampshire. Geochem Cosmochim Acta5 1:
2549-2568
Luo ZK, Miao LC, Guan K (2000) Discussion on the metallogenetic
epoch of gold deposit on north fringe of North China platform,
Gold Geology 6: 70-75 (in Chinese with English abstract)
Mao JW, Qiu YM, Goldfarb RJ, Zhang Z, Garwin S, Fengshou R
(2002) Geology, distribution, and classification of gold deposits in the western Qinling belt, central China, Mineralium Deposita 37:352-377
Mezger K, Krogstad E J (1997) Interpretation of discordant U-Pb
zircon ages: An evaluation. J. Metamorphic Geol. 15:127-140
Qi JZ, Yuan SS, Li L, Sun B, Guo JH (2003) Geological and geochemical study of yangshan gold deposit, gansu province. Mineral Deposits. 22:24-31 (in Chinese with English abstract)
Tilton GR, Schreyer W, Schertl HP (1991) Pb-Sr-Nd isotopic behavior of deeply subducted crustal rocks from the Dora Maira massif, Western Alps, Italy-II: what is the age of the ultra-high pressure metamorphism? Contrib. Mineral. Petrol, 108:22-33
Williams I S. (1998) U-Th-Pb Geochronology by Ion Microprobe, in
McKibben MA, Shanks III WC and Ridley WI (eds), Applications
of microanalytical techniques to understanding mineraling processes. Reviews in Economic Geology 7:1-35.
Wu CL, Jone W, Yang JS, Li HB (2002) margin of Qilian mountains:
evidence from zircon SHRIMP age of the Aolaoshan granite, Acta
Geologica Sinica, 76(1): 118-125
Yang JS, Xu ZQ, Wu CL, Liu FL, Shi RD, Wooden J, Maruyama S (2002)
SHRIMP U-Pb dating on coesite bearing zircon: Evidence for
Indosinian ultrahigh-pressure metamorphism in Su-Lu, East
China, Acta Geologica Sinica, 76(3): 354-372 (in Chinese with
English abstract)
Zhai YS, Miao LC, Xiang YC, Deng J, Wang JP (2002) Preliminary
discussion on ore-forming system in greenstone belt-type of
north China Craton. Earth Science-Journal of China University
of Geosciences. 27: 522-529 (in Chinese with English abstract).
Zhang BR, Gao S, Luo TC (1994) Lithosphere structure of Qinba area
and metallogenic geochemistry. Wuhan: Publishing House of China
University of Geosciences. 1-446 (in Chinese with English abstract)
Close
Chapter 7-24
7-24
87Sr/86Sr, 3He/4He, REE and stable isotope (δ
δ 34S, δ 18O)
δ
δ
constraints on the hydrothermal fluid evolution of
the PACMANUS system, Manus Basin
Stephen Roberts
School of Ocean and Earth Science, Southampton Oceanography Centre, University of Southampton, Southampton, SO14
3ZH, UK
Wolfgang Bach
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
Adrian Boyce
Scottish Universities Environmental Research Centre, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride,
G70 0QF, UK
Ray Burgess
Department of Earth Sciences, University of Manchester, Manchester, M13 9PL, UK
Abstract. δ34S, 87Sr/86Sr, δ18O, REE and 3He/4He analyses of anhydrite
from the PACMANUS hydrothermal system suggest a complex interplay between hydrothermal fluid, magmatic fluid, and seawater during alteration and mineralization. These new data significantly expand the subsurface data on seafloor hydrothermal systems and may
begin to explain the earliest processes of multistage mineralization
and alteration history that typify ancient massive sulfide systems.
Keywords. Hydrothermal vents, sulfides, anhydrite, isotopes
1
The 87Sr/86Sr and δ34S data for anhydrite from Snowcap
(Site 1188) and Roman Ruins (Site 1189) suggest contrasting fluid evolution and flow regimes.
The rare-earth element (REE) contents of anhydrite
from PACMANUS show extreme variability, in terms of
both absolute concentrations (e.g., 0.08–28.3 ppm Nd) and
pattern shape (LaN/SmN=0.08–3.78, SmN/YbN=0.48–23.1,
Introduction
Ocean Drilling Program Leg 193 investigated two sites of
hydrothermal activity along the crest of the Pual Ridge
in the eastern Manus Basin. A site of low-temperature
diffuse venting, Snowcap (Site 1188), and a high-temperature black smoker site, Roman Ruins (Site 1189), were
drilled to depths of 386 and 206 meters below sea floor,
respectively (Binns et al. 2002; Roberts et al. 2003; Bach et
al. 2003; Vanko et al. 2004). Although the two sites are
<1000 m apart, the geochemical signatures of anhydrite
recovered at both sites are very different. Measured anhydrite 87Sr/86Sr ratios vary between 0.7050 and 0.7086;
the most radiogenic values occur just beneath the variably altered dacitic cap at both sites (Fig. 1).
At Snowcap (Site 1188) there is a clear trend downhole
to less radiogenic 87Sr/86Sr values, from 0.7086 beneath
the dacite cap to values of 0.7060 at ~100 mbsf, and these
low values are broadly maintained to the base of the hole.
The measured anhydrite δ34S values vary between
18.1‰ and 22.5‰. For Snowcap, most of the values are
less than 21.0‰ and trend significantly toward lower values downhole. In contrast, anhydrite δ34S values at Roman Ruins are mostly equal to or greater than the seawater value and show no obvious downhole trends.
Close
814
Stephen Roberts · Wolfgang Bach · Adrian Boyce · Ray Burgess
Eu/Eu*=0.59–6.1). The range of REE patterns in anhydrite includes enrichments in the middle and heavy REEs
and variable Eu anomalies (Fig. 2a,b). The REE patterns
of anhydrite from hole 1188 differ markedly from those
of anhydrite recovered during ODP Leg 158 from the TAG
hydrothermal system at the Mid-Atlantic Ridge, which
display uniform LREE-enriched patterns, in contrast the
1189 data are more comparable.
The anhydrite and sulfides from both sites show
variable 3He/4He ratios with R/Ra in the range 0.29-6.91
(R/Ra Seawater = 1.05) (Fig. 3). The data show correlations with depth, δ34S and 87Sr/86Sr data. Oxygen
isotope data for the anhydrite are relatively uniform,
δ18O varies between 8 and 10‰, and show no downhole
correlation.
2
Discussion
The Snowcap data are consistent with higher sulfate concentrations of the hydrothermal end-member fluid. If
the sulfate concentration is increased because of magmatic SO2 disproportionation and dissociation, it would
predict a lower fluid pH. This is consistent with the dominance of pyrophyllite at Snowcap and secondary feldspar at Roman Ruins.
Furthermore, Bach et al. (2003) have suggested that
the range of REE patterns in the anhydrites from Snowcap
reflects the waxing and waning input of magmatic
volatiles (HF, SO2) and variable complexation of REEs in
the fluids. Taken together, these observations strongly
suggest a magmatic contribution to the hydrothermal
system drilled at Snowcap. In contrast, Roman Ruins data
are characterized by 87Sr/86Sr ratios of ~0.7065, with significant intrasample variation, and δ34S ratios that are at
seawater or slightly elevated values. The 87Sr/86Sr and S
isotope data show no systematic downhole trends and
are very similar to data reported for anhydrites recovered during the TAG drilling, ODP Leg 158 and are consistent with the mixing of a low-sulfate hydrothermal fluid
and seawater.
Close
δ 34S, δ 18O) constraints on the hydrothermal fluid evolution of the PACMANUS system, Manus Basin
Chapter 7-24 · 87Sr/86Sr, 3He/4He, REE and stable isotope (δ
815
Overall, the data suggest a complex interplay among
hydrothermal fluid, magmatic fluid, and seawater during alteration and mineralization of the PACMANUS
system.
References
Bach W, Roberts S, Vanko DA, Binns RA, Yeats CJ, Craddock PR,
Humphris SE (2003) Controls of fluid chemistry and complexation on rare earth element contents of anhydrite from the
PACMANUS subseafloor hydrothermal system, Manus Basin,
Papua New Guinea. Mineralium Depos, 38: 916-935
Binns RA, Barriga FJAS, Miller DJ (2002) Proc. ODP, Init. Repts., 193
[CD-ROM]. Available from: Ocean Drilling Program, Texas A&M
University, College Station TX 77845-9547, USA
Roberts S, Bach W, Binns RA, Vanko DA, Yeats CJ, Teagle DAH,
Blacklock K, Blusztajn J.S, Boyce AJ, Cooper MJ, Holland N,
McDonald B (2003) Contrasting evolution of hydrothermal fluids in the PACMANUS system, Manus Basin: The Sr and S isotope evidence. Geology 31: 805-808
Vanko DA, Bach W, Roberts S, Yeats CJ, Scott SD (2004) Fluid inclusion evidence for subsurface phase separation and variable fluid
mixing regimes beneath the deep-sea PACMANUS hydrothermal filed, Manus Basin back arc rift, Papua New Guinea. J Geophys
Res 109: B03201-03214
Close
Close
Chapter 7-25
7-25
U-Pb dating of micro-inclusions: The age of the
Ehrenfriedersdorf tin deposit (Erzgebirge, Germany)
R.L. Romer, R. Thomas
GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany
Abstract. Multiple reworking of ore deposits may disturb geochronologic systems and eventually render incorrect ages for ore deposition or different stages of ore formation. Micro-inclusions may
beprotected from later disturbances by their host mineral and, thus,
yield reliable age information. Major problems in dating micro-inclusions include their genetic connection with various stages of
ore formation and technical aspects, such as loss of daughter isotopes by α-recoil and the initial isotopic composition of the daughter element. The problem of daughter-loss from a high-µ microinclusion (µ = 238U/204Pb)by α-recoil can be avoided by analyzing
the inclusion together with its low-µ host. The philosophy behind
the presented analytical approach is to “trade” radiogenic composition of the daughter element (i.e., high 206Pb/204Pb, 207Pb/204Pb, and
208
Pb/204Pb) against closed-system behavior. This approach is demonstrated for <10 microns small uraninite inclusions in darkmica
from Ehrenfriederdorf, Erzgebirge, Saxony. Our data demonstrate
that micro-inclusions may yield precise and accurate age data for
early ore forming processes.
Keywords. Micro-inclusions, U-Pb dating, Ehrenfriederdorf, tin deposits
1
Introduction
Precise and accurate dating of many kinds of ore deposits is problematic because later hydrothermal and tectonic
overprint (resulting in the repeated redistribution of elements or the introduction of various metals at different
time) may disturb geochronometers that are genetically
and texturally related to early stages of deposit formation. For instance, U deposits in the Aue-Niederschlema
district (Erzgebirge, Saxony) yield ages of c. 280-270 Ma,
190 Ma, 120 Ma, 80 Ma, and 30 Ma (Förster 1996), the
oldest age related with the introduction of U into the deposit, the younger ages reflecting redistribution of U in
conjunction with multiple tectonic reactivation of the
Gera-Jachymov zone, along which numerous U deposits
occur.
Many of the ambiguities and complexities arising from
the redistribution of the ore metals during multiple overprint and alteration can be avoided by (i) dating the economically interesting minerals, which is possible for minerals of the columbite-tantalitetapiolite series (e.g. Romer
and Wright 1992; Romer and Smeds 1996), molybdenite
(e.g. Stein et al. 1998, 2001; Stein and Bingen 2002), and
U-minerals (e.g. Ludwig and Simmons 1991; Förster 1996),
(ii) by dating minerals that have formed cogenetically with
the economically interesting minerals, which for skarn
ores may involve titanite, vesuvianite, and garnet (e.g.,
Romer 1992; Romer and Soler 1995) and for hydrothermal vein deposits may involve gangue minerals such as
white mica or quartz (e.g. Franzke et al. 1996; Romer and
Linnemann 2004), and (iii) by dating fluid inclusions in
economically interesting minerals or associated gangue
minerals (e.g. Glodny 1997; Pettke and Diamond 2000).
In this paper, we demonstrate that U-Pb dating of microinclusions is technically possible and yields accurate results as long as precautions are taken (i) to avoid microminerals along grain-boundaries and fractures and (ii)
to sample in a way that compensates for recoil-related
open-system behavior in the U-Pb system.
2
Advantages and disadvantages of the use of
micro-inclusions in mineral dating
Dating micro-inclusions entirely enclosed in other minerals has the advantage that the host prevents interaction
of the micro-inclusion with later fluids. The host-mineral represents a container that makes the geochronologic
system of the inclusion behave as a closed system even
for inclusions (e.g., uraninite) that are known to react
readily with fluids. The host mineral, however, should
neither react with the inclusion nor incorporate those elements that define the geochronologic system of the inclusion. Otherwise there may be exchange of the geochronologically relevant element between host and inclusion. The
major problem in the use of micro-inclusions for dating
originates from ambiguities in the genetic connection between inclusion and host and the representativity of the
inclusion.
3
Requirements on micro-inclusions to be suitable
for dating
There are basically three requirements that must be fulfilled for micro-inclusions to become potentially attractive for dating attempts: (i) closed system, (ii) strong
daughter-to-parent (D/P) fractionation, and (iii) high P
contents.
i. Closed system behavior requires that neither the P nor
the D element is lost from the inclusion. Major processes for possible daughter loss include diffusion and
recoil, both of which are more likely to become more
important for smaller grain size. Loss by diffusion de-
Close
818
R.L. Romer · R. Thomas
pends not only on temperature, the diffusion constant
of the considered element, the cooling history of the
sample, and the distance to the grain surface, but also
on the transport of the lost ions away from the grain
surface. If a host that does not accept ions lost from
the inclusion, these ions will concentrate at the contact between the two minerals and prevent additional
loss from the inclusion. An example for an inclusion
that remained a closed system to high temperature
has been presented by Kühn et al. (2000). They showed
that biotite in Sveconorwegian granulite-facies garnet recorded this older event rather than the Caledonian eclogite facies overprint. α-recoil refers to the
displacement of the daughter isotope due to the emission of an α-particle (Fig. 1). The daughter nucleus
typically is displaced by some 20 to 30 nm (e.g., Matzke
1982). At the contact between a high-µ phase and a
low-µ phase, the loss of daughter isotopes from the
high-µ phase is more important than the addition of
daughter isotopes. Thus, the high-µ phase eventually
shows a deficit in daughter isotopes and the low-µ
phase shows an excess (cf. Ludwig 1978; Mattinson et
al. 1996; Romer 2001, 2003). This effect becomes more
important, the smaller the high-µ phase (cf. Romer
2003). Because of α-recoil, isolated small high-µ inclusions are beyond doubt open systems showing a
daughter deficit. The same inclusion and its immediate host in combination, however, may represent a
closed system as the daughter isotopes lost from the
inclusion are collected in the host. This behavior is
shown in Figure 1. Note that the isolated inclusion
would fall below the concordia and the separated host
would fall above the concordia.
ii. High P/D values result with time in highly radiogenic
D-element compositions, which makes uncertainties
about the initial composition of D irrelevant for the
age calculation and allows to constrain the slope of an
isochron more closely, i.e., to deduce more precise ages.
High P/D are restricted to element-pairs of contrasting
geochemical behavior, such as Rb-Sr, U-Pb, and Th-Pb
and to mineral phases that strongly prefer P over D.
iii. Analytical uncertainties originating from counting statistics depend on signal intensity. To obtain small uncertainties, the signal has to be strong, i.e., many ions
have to be available for counting. For small inclusions
to yield high signal intensities, the content of D has to
be high, which is a function of time and P. Thus, for an
optimal analytical result, P has to be high.
Only few phases fulfill above three requirements. For
the U-Th-Pb systems, minerals that have high P/D and
high P contents include xenotime, monazite, and uraninite;
for the Rb-Sr system, the requirements may be fulfilled
by micas and Rb-rich phases. To obtain a closed system,
the inclusions should be analyzed together with their host.
Thus, the host should yield very low or no contributions
of P and D to the bulk sample.
4
High-µ inclusions (monazite, xenotime, and
uraninite)
Because of alpha-recoil, micro-inclusions are notoriously
open systems. Separating inclusions results in too young
apparent 206Pb/238U ages as there is a deficit in radiogenic Pb. Drilling the inclusions together with a rim of
their host directly from thin sections solves the problem. (i) Recoiled daughter isotopes are collected by the
host. (ii) U-rich and Th-rich minerals are readily recognized by their pleochroitic haloes (Fig. 2) and can be iden-
Close
Chapter 7-25 · U-Pb dating of micro-inclusions: The age of the Ehrenfriedersdorf tin deposit (Erzgebirge, Germany)
tified by micro-Raman. For sampling, special care should
be taken to collect only inclusions that are entirely enclosed in the host. Outcropping inclusions always show
a deficit in radiogenic Pb. (iii) The radius of pleochroitic
haloes is more than 100 times larger than the distance
of recoil displacement of U-daughters. Thus, drilling
samples that include the entire pleochroitic halo must
yield closed systems. In thoroughly altered or multiply
overprinted rocks, inclusions that are protected by their
host mineral from interaction with late fluids may represent the only datable minerals from the early evolution of the altered rock.
5
Uraninite inclusions in mica from the
Ehrenfriederdorf tin deposit
Extensive high-temperature Sn-mineralizations that form
skarns, pegmatites, greisen, and pneumatolyitc- hydrothermal vein deposits are closely associated with Late
Variscan granites in the Ehrenfriedersdorf-Geyer area (cf.
Oelsner 1952). The granite is dominated by quartz, alkali-feldspar, plagioclase (<An12), and up to 5 vol-% mica.
Accessory minerals include topaz, cassiterite, zircon,
monazite, xenotime, uraninite, apatite, tourmaline, and
Sn-rich pyrrhotite. Melt inclusions in topaz prove that this
mineral is magmatic and did not form during pneumatolytic or hydrothermal overprinting. High Sn contents (up
to 800 ppm) in melt inclusions in quartz demonstrate that
819
the granite is closely related with the formation of the Sn
deposits in the marginal greisen and skarns (Thomas et al.
2003). The radioactive elements U and Th are predominantly hosted in tiny crystals of zircon, uraninite, monazite, and less common xenotime that are readily recognized
as they show distinctive pleochroitic haloes in mica
(Fig. 2). The small crystal size of the radioactive minerals and the distinctive pleochroitic haloes are typical for
most late Variscan granites of the Ehrenfriedersdorf-Geyer
district.
We analyzed three uraninite inclusions that gave
concordant data (filled symbols, Fig. 3). The best age
estimate, obtained from the weighted mean of the
206Pb/238U ages, is 323.9±3.5 Ma (2sigma). It falls within
the expectation range for these post-kinematic granites,
which is defined by 40Ar/39Ar ages of intruded metamorphic rocks and the age of tectonically comparable
granites from Fichtelgebirge, Oberpfalz, and the Bavarian Forrest (e.g., Werner and Lippolt 2000; Siebel et al.
2003). The age also agrees well with chemical ages obtained on uraninite, monazite, and xenotime from numerous geochemically corresponding granites of the
Erzgebirge (Förster et al. 1999). Thus, our data demonstrate that complete dissolution of inclusion and host
yields concordant data that give accurate age constraints.
Data from samples with incompletely dissolved monazite and xenotime (open symbols, Fig. 3) show an excess
of radiogenic Pb that represents Pb implanted by α-recoil into the host.
Close
820
R.L. Romer · R. Thomas
References
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Aue-Niederschlema (Erzgebirge). Dissertation, Universität
Giessen Förster H-J, Tischendorf G, Trumbull RB, Gottesmann B
(1999) Late-collisional granites in the Variscan Erzgebirge, Germany. J Petrol 40: 1613-1645
Franzke HJ, Ahrend H, Kurz S, Wemmer K (1996) K-Ar Datierungen von
Illiten aus Kataklasiten der Flossbergstörung im südöstlichen Thüringer Wald und ihre geologische Interpretation. Z geol Wiss 24:441-456
Glodny J (1997) Der Einfluß von Deformation und fl uidinduzierter
Diaphthorese auf radioaktive Zerfallssysteme in Kristallingesteinen. Dissertation, Universität Münster Kühn A, Glodny J, Iden K,
Austrheim H (2000) retention of Precambrian Rb/Sr phlogopite
ages through Caledonian eclogite facies metamorphism, Bergen
Arc Complex, WNorway. Lithos 51: 305-330
Ludwig KR (1978) Uranium-Daughter Migration and U/Pb Isotope
Apparent Ages of Uranium Ores, Shirley, Basin, Wyoming. Econ Geol
73: 29-49
Ludwig KR, Simmons KR (1991) U-Pb dating of uranium ores in
collapse-breccia pipes, Grand Canyon region. In: Pagel M, Leroy
JL (eds) Source, transport and deposition of metals. A.A. Balkema,
Rotterdam, pp 405-408
Mattinson JM, Gaubard CM, Parkinson DL, McLelland WC (1996)
U-Pb reverse discordance in zircons: the role of fi ne-scale oscillatory zoning and sub-microscopic transport of Pb. Am Geophys
Union Geophys Monogr 95: 355-370
Matzke H (1982) Radiation damage in crystalline insulators, oxides
and ceramic nuclear fuels. Rad Effects 64: 3-33
Nasdala L,Wenzel M,Vavra G, Irmer G,Wenzel T, Kober B (2001) Metamictisation of natural zircon: Accumulation versus thermal annealing of
radioactivity-induced damage. Contrib Mineral Petrol 141: 125-144
Oelsner O (1952) Die pegmatitisch-pneumatolytischen Lagerstätten
des Erzgebirges mit Ausnahme der Kontaktlagerstätten. Freib
Forschh 9: 80 pp
Pettke T, Diamond LW (2000) Rb-Sr Dating of Sphalerite based on fl
uid inclusion-host mineral isochrons: A clarifi -cation of why it
works. Econ Geol 91: 951-956
Romer RL (1992) Vesuvianite — a new tool for the U-Pb dating of
skarn ore deposits. Mineral Petrol 46: 331-341
Romer RL (2001) Isotopically heterogeneous initial Pb and continuous 222Rn loss in fossils: The U-Pb systematics of Brachiosaurus
brancai. Geochim Cosmochim Acta 65: 4201-4213
Romer RL (2003) Alpha-recoil in U-Pb geochronology: effective
sample size matters. Contrib Mineral Petrol 145: 481-491
Romer RL, Linnemann U (2004) U-Pb dating the Schlottwitz agate-amethyst vein (Erzgebirge, Saxony). Eur J Mineral 16
(Beiheft 1): 116
Romer RL, Smeds S-A (1996) U-Pb columbite ages of pegmatites
from Sveconorwegian terranes in southwestern Sweden.
Precambr Res 76: 15-30
Romer RL, Soler A (1995) U-Pb age and lead isotopic characterization of Au-bearing skarn related to the Andorra granite (central
Pyrenees, Spain). Mineral Deposita 30: 374-383
Romer RL, Wright JE (1992) U-Pb dating of columbites: a geochronologic tool to date magmatism, metamorphism, nand ore deposits. Geochim Cosmochim Acta 56: 2137-2142
Siebel W, Chen F, Satir M (2003) Late-Variscan magmatism revisited: new implications form Pb-evaporation zircon ages on the
emplacement of redwitzites and granites in NE Bavaria. Int J Earth
Sci 92: 36-53
Stein HJ, Bingen B (2002) 1.05-1.01 Ga Svenconorwegian metamorphism and deformation of the supracrustal sequence at Saesvatn,
South Norway: Re-Os dating of Cu-Mo Mineral occurances. In:
Blundell DJ, Neubauer F, von Quadt A (eds) The timing and location of major ore deposits in an evolving orogen. Geol Soc London Spec Publ 204: 319-335
Stein HJ, Markey RJ, Morgan JW, Hannah JL, Schersten A (2001) The
remakable Re-Os chronometer in molybdenite: how and why it
works. Terra Nova 13: 479-486
Close
Chapter 7-26
7-26
U-Pb data of Au-Pd-Pt-bearing quartz-hematite veins,
Quadrilátero Ferrífero, Minas Gerais, Brazil
R.L. Romer, V. Lüders
GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany
D.A. Banks
School of Earth Sciences, University of Leeds, Leeds, LS2 9JT, UK
J. Schneider
Inst. Geowissenschaften und Lithosphärenforschung, Universität Gießen, 35390 Gießen, Germany
Abstract. Fluid inclusions hosted in specular hematite from auriferous (jacutinga) and barren veins in the Quadrilátero Ferrífero either contain fluid inclusions assemblages of high-temperature
aqueouscarbonic and multiphase high-salinity, high-temperature
aqueous inclusions or multiphase aqueous fluid inclusions showing narrow ranges of salinity and homogenization temperatures.
Fluid inclusions in quartz and hematite are characterized by uniform Na/K ratios and considerable SO4 contents indicating similar
formation conditions and perhaps fluid origin from a common
source. The formation of specular hematite veins may be related to
retrograde metamorphic fluids being released during the Brazilian
orogenic cycle (600-700 Ma). The Pb isotopic characteristics of all
jacutinga-type samples is readily reconciliated in a simple model
that (i) involves different Palaeoproterozoic or Archaean source
lithologies for lead and gold and that (ii) possibly reflects contrasting depths of fluid percolation during the Braziliano orogeny and
(iii) heterogeneous Au distribution in the greenstone source.
Keywords. Fluid inclusions, U-Pb, jacutinga, Au-Pd-Pt, Minas Gerais
1
Introduction
2
Results
Fluid inclusions have been studied in specular hematite
from two auriferous jacutinga-style mineralization and
two barren hematite veins using infrared microscopy.
Hematite from barren veins of the Fábrica and Córrego
do Feijão iron ore mines contain only one compositional
type of fluid inclusions. These are aqueous inclusions with
a vapour bubble and with more than 90% having one or
more solid phases. Hematite-hosted fluid inclusions from
the jacutinga style mineralization of Gongo Soco are similar to those of barren veins. Hematite from jacutinga-style
mineralization at Itabira contain two compositional types
of fluid inclusions, (i) aqueous carbonic inclusions, and
(ii) multiphase aqueous inclusions with at least one solid
phase. Both types of inclusions occur together in isolated
clusters or as isolated fluid inclusion pairs within individual samples.
Two-phase and multiphase aqueous inclusions with
solid phases in specular hematite from jacutinga veins of
Palladian gold mineralization is unusual worldwide and
only Brazilian occurrences are of economic importance.
In the Quadrilátero Ferrífero of Minas Gerais, which includes Paleoproterozoic clastic and chemical sedimentary
sequences (Minas Supergroup) underlain by an Archean
greenstone belt (Riodas Velhas Supergroup) and granitegneiss terrains (Fig. 1), the auriferous portions of itabirites
have traditionally been denoted as jacutinga. This peculiar
mineralization occurs as Au-Pd-Pt-bearing quartzspecular
hematite veins crosscutting the metamorphosed host
itabirites. The gold is coarse-grained and commonly black
(ouro preto) due to coatings of Pd-O species and Feoxyhydroxide. A number of jacutinga-style gold deposits
were worked in the 18 th and 19 th centuries in the
Quadrilátero Ferrífero. Openpit iron ore mining-operations have exposed sections of jacutinga mineralization.
Gold is currently an intermittent by-product of iron ore
mining at Gongo Soco (several tens of kg Au per year)
and Itabira, where gold production amounted to about
600 kg Au per year in 2000.
Close
822
R.L. Romer · V. Lüders · D.A. Banks · J. Schneider
the Gongo Soco mine as well as from barren veins show
narrow ranges of salinity between 7.2–11.7 wt.% NaCl
equiv. and homogenization temperatures between 148 and
229°C (Fig. 2). Fluid inclusions in specular hematite from
the Itabira area are comparatively more complicated. The
ice melting temperatures of multiphase aqueous inclusions cover a wide range between -26.1 and -10.7°C (Fig. 2).
The majority of the homogenization temperatures of
multiphase aqueous inclusions range between 317 and
365°C (Fig. 2). In contrast, aqueous carbonic inclusions
have considerably higher total homogenization temperatures when compared with multiphase aqueous inclusions
and higher ice melting temperatures (Fig. 2). Crush-leach
analyses on samples of quartz and hematite show that Cl
and SO4 are the major anions in the fluid inclusions. The
fluids are dominated by Na and show significant but variable amounts of K and Ca, and lesser amounts of Mg and
Li. The low Cl/Br and Na/Br ratios of the analyzed inclusions are indicative of halite dissolution and reprecipitation
by a halite saturated fluid. During dissolution and
reprecipitation, Br is excluded from halite and enriched
in the fluid, just as during halite precipitation from seawater. The salinity of the fluid inclusions, however, is below halite saturation and indicates dilution after they have
gained Br by interaction with halite. The Na/K ratios of
the analysed fluids fall into the narrow range (mean
4.5±2.2). The Na/K ratios in brines are likely to be controlled by equilibrium reactions with alkali feldspars and
muscovite. Therefore, the elevated K and Li concentration in the fluids are likely to derive from water-rock interaction between the ore-forming fluids and granites and/
or gneisses of the crystalline basement.
3
U-Pb systematics of hematite and gold
3.1 Hematite
The Pb isotope data of the hematite samples scatter widely
in the 206Pb/204Pb – 207Pb/204Pb, 206Pb/204Pb–208Pb/204Pb,
and 206Pb/204Pb–238U/204Pb diagrams (Fig. 3a-c). The data
do not define isochrons. Although the scatter among
samples from individual deposits is smaller than for the
entire data set, there is significant excess scatter, which
may originate from (i) initial isotopic heterogeneity within
single deposits and contrasting Pb composition in different deposits, (ii) addition of isotopically distinct Pb at
some time after formation of the deposits, and (iii) fractionation between U and Pb (modification of the 238U/
204Pb ratio) during a later event. Furthermore, there may
have been some redistribution of radiogenic Pb between
hematite host and fluid inclusions by recoil. These potential non-idealities make the derivation of a precise age
impossible. Nonetheless, the Pb isotope systematics of the
fluid-free hematite samples imposes several constraints
on the evolution of the hematite deposits. (1) The data
fall in a triangular area in the 206Pb/204Pb–207Pb/204Pb diagram (shaded area, Fig. 3a), which may reflect a heterogeneous source or a poly-stage evolution of the hematite
veins. The steepest 207Pb/206Pb trend corresponds to a
mixing line of Pb that evolved from ca. 2.7 Ga to 1.9-2.0
Ga. Since the sampled jacutinga–style veins are hosted
by Palaeoproterozoic itabirite-type iron deposits, variations along the 2.7-1.9 Ga trend possibly reflects derivation of Pb from an isotopically heterogeneous source during the Palaeoproterozoic formation of the iron deposits.
(2) In the 206Pb/ 204Pb– 238U/ 204Pb isochron diagram
(Fig. 3c), most data scatter about a linear trend, whose
slope corresponds to an age of c. 635 Ma. This age has no
strict geochronological meaning as the requirements for
an isochron (common initial, single stage evolution) are
not met. There are numerous samples that fall above this
Palaeozoic reference line, which either implies that these
samples had a more radiogenic initial Pb isotopic composition (dashed line, Fig. 3c) or that they record an older
age. (3) Hematite from each deposit shows a relatively
narrow range in 208Pb/204Pb, but shows distinct differences
between deposits (Fig. 3b). (4) The initial Pb isotopic composition of all deposits is characterized by 207Pb/204Pb
values, which implies that the initial Pb of the hematite
deposits was dominantly derived from an old crust.
3.2 Gold
The Pb isotopic composition of gold flitters from jacutinga
veins at Gongo Socco align along the steep trend in the
206
Pb/204Pb–207Pb/204Pb diagram (Fig. 3a) with some
samples being displaced to the right of this trend. In situ
Pb growth (shift to the right) was insignificant for most
Close
Chapter 7-26 · U-Pb data of Au-Pd-Pt-bearing quartz-hematite veins, Quadrilátero Ferrífero, Minas Gerais, Brazil
823
samples. The Pb from the gold samples is distinctive by
its higher 207Pb/204Pb and lower 208Pb/204Pb values (at comparable 206Pb/204Pb) than the hematite samples (Figs. 3a
and 3b), the itabirites, or the wall-rocks. This implies that
trace Pb in gold may have been derived from a different
source than the iron. Hematite from the barren deposit
Córrego do Feijão is in its 208Pb/204Pb signature closest to
the host-rocks and the itabirite deposits, whereas hematite from the Au-bearing jacutinga-style veins have 208Pb/
204
Pb values that are closer to the signature of Au.
4
Discussion
Specular hematite ores from barren veins and Au-Pd-Ptbearing jacutinga–style mineralization at Gongo Soco
were deposited from fluids that show narrow ranges of
salinity and homogenization temperatures. This may be
due to similar formation conditions or fluid origin from
a common source, although the barren veins do not contain Au, Pd, and Pd. Crush-leach analyses demonstrate Cl
and SO4 to be the major anions in the ore-forming fluids.
The high sulfate concentrations of the analyzed fluids may
also be derived by leaching of evaporites (gypsum). The
formation of schistose high-grade specular hematite veins
at Itabira can be related to acid Cl-SO4-CO2 retrograde
metamorphism fluids that interacted intensively with crystalline rocks. The absence of CO2 in hematite-hosted inclusions from veins in the low-strain domain may be attributed to carbonate precipitation or conversion of CO2
to bicarbonate due to cooling during fluid migration from
the highto low-strain domain. A Brasiliano age can be
derived from the 238U/204Pb–206Pb/204Pb diagram (Fig. 3c)
where specular hematite samples from the Itabira district and fluid inclusions therein fairly plot on or close to
the reference line for 635 Ma. The least radiogenic Pb isotopic composition from the investigated region was measured on galena from stratiform gold deposits in the Archaean Rio das Velhas Supergroup. Starting from such a
composition and lasting until the Transamazonian orogeny in situ Pb growth would yield values that fall on the
red array in Fig. 3. Samples with low µ values would have
evolved less from their starting composition, whereas
samples with high µ values would have evolved to more
radiogenic composition. There may be a lithologic control on the µ values, which higher values in more evolved
felsic units than in mafic units. Depending on source regions for the itabirite-type iron deposits in the
Palaeoproterozoic clastic-chemical sediments of the Minas
Supergroup, different deposits may have a constrasting
Pb isotopic composition. Undisturbed in situ Pb growth
in itabitirite-type iron deposits until the present would
result in Pb isotopic compositions that fall between the
1.83 Ga reference line of Olivo et al. (1996) and the Archaean-to-Transamazonian Pb trend (Fig. 3). As the Pb
isotopic composition of most samples falls to the right of
Close
824
R.L. Romer · V. Lüders · D.A. Banks · J. Schneider
the 1.83 Ga reference line, lead evolution to highly radiogenic compositions occurred mainly after the Braziliano
orogeny (see also Fig. 3c). The scatter of the data in the
206Pb/204Pb vs. 238U/204Pb diagram either may reflect several events, most prominantly a Braziliano and a
Transamazonian event (Fig. 3c) or it may reflect that the
initial Pb isotopic compositions of some deposits was
highly radiogenic at the time of the Braziliano orogeny
(dashed line in Fig. 3c).
The Pb isotopic composition of trace Pb in gold generally has lower 208Pb/204Pb values than the hematite
samples. Furthermore, this trace Pb plots above the 1.83
Ga reference line and above the hematite field (Fig. 3).
The contrasting Pb isotopic composition between hematite and gold in the jacutinga-style veins possibly suggests that hematite incorporated significant amount of
locally derived material and that the veins in part even
may contain hematite grains originating from the older
wallrock. The relation of the trace Pb from gold is compatible with a derivation from an Archaean source rock
that is characterized by high 238U/204Pb values and relatively low 232Th/204Pb values. In this context, Archaean
source does not only refer to the Archaean basement, but
also to its cover of Palaeoproterozoic clastic sediments
that were derived from the Archaean basement. The relation of the trace Pb from gold is incompatible with a derivation from the same source as the Pb in the itabirites or
from the itabirites itself. If the Archaean felsic basement
is the source of the trace Pb in gold, the same source could
also be the source of U, which eventually gave rise to radiogenic Pb isotopic compositions in hematite. This source
may also have had controlling influence on the homoge-
neous Na/K ratios in hematite-hosted fluid inclusions. A
felsic Archean basement, however, could not provide Au
and Pd. Instead, these two elements may be derived from
the Archaean supracrustal rocks that include voluminous
units of mafic volcanic rocks. Since the Pb contents in
felsic rocks are much higher than in mafic and ultramafic rocks, the Pb isotopic composition reflects the signature of the felsic basement rather than the mafic units.
Thus, the fluid that transported Au and Pb into the
jacutinga–style veins may carry the Pb isotopic signature of a source rock that does not correspond to the
source of Au and Pd. This explanation allows the fluid to
acquire its Pb isotopic signature either in the felsic basement below the greenstone unit or in the Palaeoproterozoic clastic sediments between the Archaean basement
and the units hosting the itabirite-type iron deposits. The
occurrence of Au (and Pd), however, is controlled by the
distribution of Au-bearing mafic to ultramafic
supracrustal rocks in the Archaean basement. Thus, there
may be a spatial correspondance between stratiform Archaean and jacutinga-type Braziliano gold deposits. Au
in both deposits would have been mobilized from the
same source rocks.
The formation of the jacutinga–style veins during the
Brazilian orogenic cycle explains both the homogeneous
nature of the fluids with respect to dissolved major components, e.g., Na/K, Cl/Br ratios, high-SO4 content, and
the heterogeneous character of the fluids with respect to
CO2 content and trace (Au, Pd, Pb, and U) constituents,
as differences in proportions of major components reflect contrasting evolution histories of the fluid in terms
of unmixing and cooling.
Close
Chapter 7-27
7-27
Constraints on the source and evolution of mineralising
fluids in the Norrbotten Fe oxide-Cu-Au province, Sweden
Martin Smith
School of the Environment, University of Brighton, Brighton, BN2 4GJ, U.K.
Sarah A. Gleeson
University of Alberta, Edmonton T6G 2E, Canada
Abstract. Norrbotten County, Sweden, is well known for the iron oxide-apatite deposits of the Kiruna and Malmberget areas. These are
spatially associated with iron oxide Cu (± Au) deposits and a genetic link between the two has been suggested as a part of the
IOCG spectrum of deposits. Here, we report the results of a fluid
inclusion microthermometry and bulk crush leach halogen and
chlorine stable isotope study, carried out to test that hypothesis.
Quartz veins from late stage veins from Fe oxide-apatite deposits
and Cu-(Au) deposits contain hypersaline brine inclusions, with a
salinity range of 32 to 38wt. % NaCl eq. in Fe-oxide bodies, and of
38 to 47wt % NaCl eq. in Cu-Au deposits. In Cu-(Au) deposits these
are sometimes accompanied by CO2-rich inclusions.
The Cl/Br ratio of the fluid inclusion leachates is consistent with
magmatic fluid compositions, and ranges between 859 and 9597,
with no distinction between the Fe-oxide samples and the Cu-mineralizing brines. δ37Cl(SMOW) values range from –0.99 to –5.63‰. The data
are far removed from both mantle (δ37Cl = +4.7‰) and crustal (δ37Cl
= 0‰) values and must represent fractionation of the isotopes during the mineralizing process. We suggest this fractionation occurred
during the formation of Cl-rich mineral phases commonly found associated with the deposits e.g. scapolite, biotite and amphibole.
Keywords. Fluid inclusions, halogens, IOCG, chlorine isotopes
1
Introduction
The original classification of iron oxide-copper-gold type
deposits by Hitzman et al. (1992) postulated a link between Fe oxide-apatite deposits (‘Kiruna-type’) and the
IOCG deposits themselves. Northern Norrbotten County,
Sweden, is well known for the Kirunavaara deposit, and
also hosts several Cu-(Au) deposits (Bergman et al., 2001).
However, magnetite-apatite bodies and epigenetic Cu-Au
bodies formed in the range 1900-1860Ma (Romer et al.,
1994; Billstrom and Martinsson, 2000), but with the CuAu systems potentially post-dating the Fe oxide-apatite
bodies. Younger deposits still (~1800-1750Ma) are associated with regional scale shear zones. All these deposits
show similar alteration types and association with regional
sodic alteration (Frietsch, 1997), and have been suggested
to belong to the IOCG group. A knowledge of fluid source
in all three deposit types is therefore of value for
metallogenetic models, and will help to define any common mineralising processes related to episodic metamorphism or magmatism. As a part of the EU-RDF Georange
program we have investigated the fluid sources for quartz
veins from the late stage of Fe oxide-apatite ore forma-
tion and from a range of Cu-(Au) deposits and prospects
using a bulk crush leach technique to analyse for cation,
anion, and chlorine isotope composition within the inclusion fluids.
2
Sample sites
The geology of the Norrbotten area consists of a Palaeoproterozoic supracrustal sequence overlying Archaean basement, which was deformed and intruded by grantoids during the Svecofennian orogeny (1.96-1.85Ga). The Palaeoproterozoic sequence within the area studied is broadly separated into the Greenstone Group metabasic rocks, and the
overlying Porphyry Group, which consists of intermediate
to acid volcanics and intercalated sediments. Within Fe oxide-apatite bodies, quartz veins cross-cut both the ore itself, and altered footwall rocks. Samples of this kind were
collected from the magnetite-hematite-apatite bodies of the
Kiruna area and from the Valkommen deposit, which forms
a part of Malmberget Fe oxide-apatite body.
Samples from Cu-(Au) deposits where collected from
sites hosted in the Greenstone and Porphyry Group
volcanics at Pahtohavare (Lindblom et al. 1996), Kallosalmi
and Gruvberget, and from younger deposits associated
with the Nautanen Deformation Zone (Fig. 1).
Close
826
Martin Smith · Sarah A. Gleeson
3
Techniques
Samples were initially characterised petrographically and
microthermometrically using a Linkam TMS600 heatingfreezing stage at the University of Brighton. Samples were
then crushed and hand picked to provide approximately
5g of pure quartz for crush leach analysis. Samples were
electrolytically cleaned prior to crushing, and the leachates
analysed for Na, Li and K using atomic absorption spectroscopy, for other cations using ICP-MS, and for halogens, sulphate and phosphate using ion chromatography
at the University of Alberta. Chlorine isotope analyses
were carried out on the leachates using gas source mass
spectrometry at Environment Canada, Saskatoon.
4
Results
4.1 Microthermometry
Late stage quartz veins cutting Fe-oxide apatite bodies or
their wall rocks contain a consistent fluid population
across the area (salinity 30-40 wt. % NaCl eq.; Th=100150°C). Fluids associated with quartz veins from Cu-(Au)
deposits and prospects, range from much higher salinities (around 50-60 wt % NaCl eq.) to those comparable
with the late stage veins associated with the Fe-oxide bodies. Two veins from the Gruvberget body contain lower
salinity, Ca-rich inclusions, which probably represent a
post-ore fluid.
The inclusion assemblage from deposits associated with
the NDZ is more complex, with coexisting Lw+Sh+V,
Lw+Lc+V and Lc+V inclusions. In some instances these
are preserved along the same secondary fluid inclusion
trails. Lw+Sh+V inclusions from the Valkommen body,
and from some veins at Nautanen show similar salinities
and homogenisation temperatures to those from the Feoxide and Cu-Au deposits already discussed. At Nautanen
complex inclusion assemblages are hosted on secondary
trails. These are indicative of phase separation. Salinities
vary from ~12-18 wt. % NaCl eq. for Lw+Lc+V inclusions
to ~29wt % NaCl eq. for halite bearing inclusions. Total
homogenisation temperatures for Lw+Lc+V inclusions
are typically around 250-300°C, whilst partial L-V
homogenisation for halite bearing inclusions is around
100-120°C. At both Nautanen and Ferrum a further assemblage of Ca-rich brines is observed similar to those
observed in some veins at Gruvberget. Many of the observations made here are in agreement with previous work
by Broman and Martinsson (2000).
4.2 Halogen chemistry
Log Br/Cl ratios within leachates from these fluids (Fig. 2)
range from approximately –2.5 to -3.7, with two exceptional analyses at –2.3 and –4.4. The majority of analyses
fall in the range –2.8 to –3.5 with no distinction between
Fe-oxide related and Cu-related brines. These data are
compared with a selection of previous data from Yardley
et al. (2000) in Figure 2. They are most comparable to S.W.
England granite related fluids, and are clearly distinct from
fluids associated with the Capitan Pluton, New Mexico
and Columbian Emerald deposits. This is significant as
these are both interpreted as deriving their salinity either from magmatic interaction with evaporites, or from
metamorphism of evaporites. Our data are therefore consistent with magmatic sources for mineralising fluids in
Norrbotten, and not with a meta-evaporitic source. The
more Br enriched samples are lower salinity fluids from
the NDZ, and possibly indicate interaction of a magmatic
fluid with the surrounding metasediments.
4.3 Chlorine isotopes
The chorine isotopic composition of leachates from vein
quartz samples from Fe oxide-apatite bodies, and from
epigenetic Cu-Au deposits ranges in δ37Cl relative to standard mean ocean chlorine (SMOC) from -5.63 to -0.99‰.
These data are compared with previous data from inclu-
Close
Chapter 7-27 · Constraints on the source and evolution of mineralising fluids in the Norrbotten Fe oxide-Cu-Au province, Sweden
sion fluids, natural porewaters and rocks and minerals
in Figure 3. Norrbotten inclusion fluids are consistently
enriched in 35Cl relative to all previously analysed fluid
inclusions, most rocks and minerals and most natural
porewater samples. The only comparable data are from
subduction zone porewaters sampled in the Barbados
and Nankai accretionary prisms (Ransom et al. 1995).
Luders et al. (2002) showed that submarine hydrothermal fluids could be enriched in 37Cl by extraction of 35Cl
into a vapour phase during boiling, and consequently a
condensate from a low density fluid or vapour could show
low δ37Cl values.
However, the high salinity of these fluids would seem
to preclude their origin as a condensate. Equally 35Cl enriched fluids can be formed by the evapo-concentration
of seawater and precipitation of halite (Eastoe et al. 1998),
but such fluid have not yet been reported with the low
δ37Cl values seen here. The most likely explanation for
the Cl isotope data is the preferential extraction of 37Cl
into silicate mineral phases (in this case scapolite, biotite
827
and amphibole) results in a passive enrichment of hydrothermal fluids in 35Cl. Chlorine isotope analyses of silicate minerals are relatively limited at the present time,
but those available from biotites in the Stillwater complex (Boudreau et al. 1997), Porphyry Cu related biotites
(Arcuri and Brimhall 2003) show uniformly positive δ37Cl
values. Experimental data from. Pan and Dong (2003) show
that Br/Cl ratios of marialitic scapolite closely reflect the
halogen composition of co-existing fluids, and hence this
process would not be expected to affect the Br/Cl signature of hydrothermal fluids.
5
Discussion and conclusions
The data presented here are consistent with a magmatic
fluid source for Porphyry and Greenstone Group hosted
Cu-(Au) mineralization in Norrbotten, and for late stage
fluids associated with Fe oxide-apatite bodies. The
microthermometric data do not, however, indicate that
directly comparable fluids were involved in the formation of the Fe oxide- apatite bodies and the Cu-(Au) mineralization. The displacement of δ37Cl values to lower values in the epigenetic Cu-(Au) mineralising fluids may reflect extensive water rock interaction and Na-Cl metasomatism during this stage of the regions evolution.
Fluids associated with younger, shear zone hosted deposits are also potentially magmatic, although the inclusion of several fluid inclusion populations reflects the
modification over an extended period and possibly the
input of metamorphic fluids. Temporal constraints indicate that the highly saline ore fluids present in all deposits must have been generated during several magmatic
events, with the additional input of non-magmatic fluids
into the younger, shear zone hosted deposits at Nautanen.
Previous workers have suggested that meta-evaporites
may have played a role in generating the highly saline
brines and regional sodic alteration in Norrbotten
(Frietsch et al. 1997). We find no evidence to support this
idea. Halite typically shows heavy δ37Cl values relative to
the fluid from which it precipitates, so halite dissolution
is unlikely to form strongly 37Cl depleted fluids. We have
not yet, however, analysed samples containing a significant proportion of the Ca-rich brine, and this may preserve such a signature (Wanhainen et al. 2003).
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Martin Smith · Sarah A. Gleeson
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Geology 25 791-794
Broman C, Martinsson O (2000) Fluid inclusions in epigenetic FeCu-Au ores in northern Norrbotten. In: L..T research report
2000:06. 2nd GEODE Fennoscandian Shield field workshop on
Palaeoproterozoic and Archaen greenstone belts and VMS districts in the Fennoscandian Shield.
Eastoe CJ, Long A, Kinaith LP (1998) Stable chlorine isotopes in the
Palo Duro Basin, Texas: Evidence for preservation of Permian
evporite brines. Geochim Cosmochim Acta 63: 1375-1382
Frietsch R, Tuisku P, Martinsson O, Perdahl JA (1997) Early proterozoic
Cu-(Au) and Fe ore deposits associated with regional Na-Cl metasomatism in northern Fennoscandia. Ore Geol Rev 12: 1-34
Hitzman MW, Oreskes N, Einaudi MT (1992) Geological characteristics and tectonic setting of proterozoic iron-oxide (Cu-U-AuREE) deposits. Precambr Res 58: 241-287
Lindblom S, Broman C, Martinsson O (1996) Magmatic-hydrothermal fluids in the Pahtohavare Cu-Au deposit in greenstone at
Kiruna, Sweden. Mineralium Depos 31: 307-318
Luders V, Banks DA, Halbach P (2002) Extreme Cl/Br and δ37Cl isotope fractionation in fluids of modern submarine hydrothermal
systems. Mineralium Depos 37: 765-771
Pan Y, Dong P (2003) Bromine in scapolite-group minerals and sodalite: XRF microprobe analysis, exchange experiments, and application to skarn deposits. Can Mineral 41: 529-540
Ransom B, Spivack AJ, Kastner M (1995) Stable Cl isotopes in subduction-zone pore waters - implications for fluid-rock reactions
and the cycling of chlorine. Geology 23:715-718
Romer RL, Martinsson O, Perdahl JA (1994) Geochronology of the
Kiruna iron ores and hydrothermal alterations. Econ Geol,
89:1249-1261
Yardley BWD, Banks DA, Barnicoat AC (2000) The chemistry of
crustal brines: tracking their origins. In: TM Porter (ed) Hydrothermal iron oxide copper-gold and related deposits: A global
perspective. Austral Min Found, Adelaide, pp. 61-70.
Close
Chapter 7-28
7-28
LA-ICPMS U-Pb dating of titanite: New constraints
on multistage geological evolution of the Norrbotten
mining district, Sweden
Martin Smith, Craig Storey
School of the Environment, University of Brighton, Brighton, BN2 4GJ, U.K.
Teresa Jeffries
Department of Mineralogy, The Natural History Museum, London, SW7 5BD, U.K
Abstract. Established techniques for the laser ablation ICP-MS UPb analysis of zircon have been developed for application to common Pb bearing phases, including titanite and allanite. A novel
common Pb correction procedure has been developed for deriving mineral ages, and has been tested using well characterised
samples. This technique has been applied to samples from the
mining district of Norrbotten, Sweden, with the aim of constraining the timing of iron oxide-copper-gold (IOCG) mineralization in
relation to the formation of Fe-oxide-apatite deposits and the regional geological evolution. Titanites from three of the Fe oxide
apatite deposits studied show complex multistage growth textures implying a prolonged metasomatic history. Cores from these
samples show ages in the range 2070 to 2000 Ma before present,
indicating that the age of the host supracrustal sequence in
Norrbotten may be significantly older than previously thought.
The rims of these crystals, which show distinct trace element
signatures to the cores, as well as unequivocally metasomatic
titanites and allanites from other areas give ages in the range
~1875-1820Ma. These ages probably indicate the time of primary
mineralization of both the late stages of Fe oxide and Cu-Au types.
Younger ages in the range ~1790-1700Ma are interpreted to relate to subsequent metamorphism of the deposits, and
remobilisation of sulphide mineralization along long lived, regional
scale structures.
2
Technique
In this study we have extended established U-Pb techniques
by LA-ICPMS (quadrupole) to titanite and allanite. Titanite
and other common U hosting minerals readily incorporate
up to ppm levels of (common)Pb into their lattice alongside U and Th during crystallisation, making the necessity
for common Pb correction paramount. In this study we have
used both a mathematical based 207Pb-correction, and the
far more robust TIMS-style correction. The TIMS-style correction is based upon measurement of the stable 204Pb isotope to assess the amount of common Pb in the analysis.
This requires an independent measurement or estimate of
the common Pb composition to be corrected for. We have
made measurements of common Pb composition by utilising
in line gold traps to reduce interferances on the 204Pb peak
from mercury stable isotopes. In samples with low analytical signal intensity we combine this approach with a novel
appraoch based on 3 dimensional U-Pb concrodia.
3
Sites investigated
Keywords. U-Pb, geochronology, titanite, Norrbotten, Kiruna, IOCG
1
Introduction
Northern Norrbotten County, Sweden, is well known as a
region of Fe oxide-apatite mineralization, and also hosts
a range of copper-gold deposits (Bergman et al. 2001).
These deposits have been proposed to be related as a part
of the iron oxide-copper-gold (IOCG) spectrum of deposits. A more detailed understanding of this relationship will be of great use to defining ore genetic and exploration models in terms of both the relationship of CuAu mineralization to Fe oxide mineralization, and the relationship of both mineralization types to the regional
geological evolution. As a part of the EU-RDF Georange
program we have investigated this relationship via the
development of a novel U-Pb geochronological technique,
which allows the use of in situ laser ablation ICP-MS for
analysis of titanite and other common lead-bearing phases
within polished thick sections.
The geology of the Norrbotten area consists of a
Palaeoproterozoic supracrustal sequence overlying Archaean basement, which has subsequently been deformed
and intruded by grantoids during the Svecofennian orogeny (1.96-1.85Ga). The Palaeoproterozoic sequence within
the area studied is broadly separated into the Greenstone
Group metabasic rocks, and the overlying Porphyry Group,
which consists of intermediate to acid volcanics and intercalated sediments.
For the purpose of this study we have examined material from both Fe oxide-apatite and copper deposits
(Bergman et al. 2001) including titanite intergrown with
magnetite from deformed vesicle fills within the sodically
altered footwall trachyandesites at Luossavaara, and
titanite hosted in quartz-carbonate veins cutting magnetite cemented brecciated metavolcanics in the footwall of
the Kirunavaara magnetite-apatite body. Within the
Kiruna area samples were also analysed from Cu-(Au)
deposits and prospects at Rakkurijarvi (Porphyry Group
hosted) and Kallosalmi (Greenstone Group hosted). We
Close
830
Martin Smith · Craig Storey · Teresa Jeffries
have also analysed samples from the Gruvberget Cu deposit, developed in the footwall to a magnetite-hematiteapatite body, again hosted by intermediate metavolcanics.
The third area studied was around Malmberget to the
south of Kiruna. The Malmberget body itself is an Fe oxideapatite body exposed in a large fold structure. It is interpreted to be a metamorphosed Kiruna type deposit. Samples
where taken from the hanging wall of the Valkommen ore
body. To the east of the Malmberget body both the supracrustal sequences and the Svecofennian granitoids are cut
by a regional scale shear system (the Nautanen Deformation Zone). This hosts the working Cu-(Au) mine at Aitik,
and a historically worked prospect at Nautanen.
4
Results of geochronological studies
A number of samples show complex multistage growth
(Fig. 1). Samples from Luossavaara, Gruvberget, and
Malmberget show core ages in the range 2073-2028 Ma. All
these bodies are Fe-oxide (and sometimes copper) deposits hosted in Porphyry group metavolcanics, supposedly of
Svecofennian age. The BSE light rims of most of these
Close
Chapter 7-28 · LA-ICPMS U-Pb dating of titanite: New constraints on multistage geological evolution of the Norrbotten mining district, Sweden
titanites give ages in the range 1920 to 1826 Ma. LA-ICPMS
trace element analyses from corresponding sites in the same
grains show a clear distinction between core and rim analyses (Fig. 2). The younger, rim zones are strongly LREE enriched relative to the core zones. These patterns are comparable to the composition of unequivocally metasomatic
titanites from other deposits. The rim zones are volumetrically the most significant parts of the crystals. The ages
obtained from these zones are reflected in previous TIMS
data from Norbotten titanite which analysed bulk crystals.
The range of ages from the alteration surrounding Fe-oxide and Cu-deposits is previously unreported from the Porphyry Group and the deposits which it hosts. These data
suggest a minimum age of the Porphyry group of between
~2070-2028 Ma, significantly older than currently thought.
Analyses of titanites from regional alteration (Nunasvaara)
and the alteration surrounding Fe-oxide and Cu-Au deposits
hosted by the Porphyry Group range from 1902+/-8 Ma
(Nunasvaara) to 1758+/-18 Ma (Tjarrajäkka). The data in
the range of 1920-1826 Ma correspond to the time range
of the Svecofennian metamorphism, and the main intrusive activity in the area. Our data are consistent with
831
either metamorphic growth of titanite during this period or metasomatic growth of titanite during hydrothermal activity. The youngest ages so far encountered
are from the Valkommen body, with titanite at 1708±20
Ma, and apatite at 1584±12 Ma. The very young age recorded in apatite from Valkommen is related to the lower
closure temperature of apatite relative to either titanite
or zircon. We suggest that these ages record subsequent
metamorphism of the deposits in question.
Data from deposits hosted by, or associated with, the
NDZ range from 1826+/-15 Ma to 1756+/-20 Ma. Two
samples from the Nautanen deposit gave ages of 1810+/21 Ma and 1756+/-20 Ma respectively. These data indicate a prolonged history of deformation and fluid flow
along the NDZ, probably involving multiple episodes of
ore deposition and remobilisation. The REE patterns of
these titanites are LREE depleted; indicating different
chemical conditions of titanite formation in the NDZ compared to other Cu-(Au) deposits. This may be related to
contrasting fluid chemistry, or may reflect ore-forming
processes, particularly the co-precipitation of allanite and
LREE enriched epidote.
Close
832
Martin Smith · Craig Storey · Teresa Jeffries
5
Discussion and conclusions
The data presented here are generally in agreement with
previous data on mineral deposits within the Norrbotten
region. The Kirunavaara and Luossavaara mineralization
has previously been dated at 1888+/-6 Ma between 1876+/
-9 Ma by Billstrom and Martinsson (2000), who reported
U-Pb titanite ages for Cu-Au mineralization in the ranges
1880-1860Ma and 1800-1750Ma. These ages are also in broad
agreement with our data; however, a number of deposits in
the younger group in their study gave ages in the older group
in this study. This is likely to represent a difference in the
scale of sampling, and suggests that the age heterogeneity
seen in these deposits is the result of metamorphic
remobilisation of ore in the period 1800-1750Ma. In complex zoned grains we interpret the data from the cores as
indicating the timing of initial metamorphism (and a minimum age for magmatism), and data from the rims as indicating the timing of metasomatic fluid flow associated with
mineralization.
Previous constraints on the age of the Porphyry group
come from U-Pb dating of zircon (Welin 1987; Skiöld and
Cliff 1984). Our new data now suggest these ages may represent recrystallisation of zircon during a later metamorphic/metasomatic event. In summary, the data from titanite
cores suggest that Porphyry and Porphyrite group volcanism occurred significantly earlier than previously thought.
This has significant implications for the timing of rifting
and subduction during the early tectonic evolution of the
Fennoscandian shield. It may also have implications for
correlation of Norrbotten stratigraphy with that of the
Skellefte district (Bergman et al. 2001). The timing of Fe
oxide and Cu-Au deposit formation corresponds to that of
the Svecofennian metamorphism, and the intrusion of the
Haparanda and Perthite-monzonite suite granitoids. A second stage of mineralisation, or metamorphism of previously formed deposits occurred in association with the
younger stage of metamorphism. This possibly accompanied movements on the Nautanen Deformation Zone.
References
Bergman S, Kübler L, Martinsson O (2001) Description of regional
geological and geophysical maps of northern Norrbotten county
(east of the Caledonian orogen). Sveriges geologiska undersökning
Ba 56
Billstrom K, Martinsson O (2000) Links between epigenetic Cu-Au
mineralisations and magmatism/deformation in the Norrbotten
county, Sweden. In L.U. T. research report 2000:06. 2nd GEODE Fennoscandian Shield field workshop on Palaeoproterozoic and Archaen
greenstone belts and VMS districts in the Fennoscandian Shield
Romer RL (1996) What is the significance of lead isotope data from
stilbite, a low temperature natural ion exchanger? The 22nd Nordic Geological Winter Meeting, Turku, Åbo, Abstracts, 172
Romer RL, Martinsson O, Perdahl JA (1994) Geochronology of the
Kiruna iron ores and hydrothermal alterations. Economic Geology 89: 1249-1261
Skiöld T, Cliff RA (1984) Sm-Nd and U-Pb dating of Early
Protoerozoic mafic-felsic volcanism in northernmost Sweden.
Precambrian Research 26: 1-1
Welin E (1987) The depositional evolution of the Svecofennian
supracrustal sequence in Finland and Sweden. Precambrian Research 35: 95-113
Close
Chapter 7-29
7-29
Metamorphic to magmatic transition captured at the
Myszków Mo-W deposit, southern Poland
H.J. Stein
AIRIE Program, Department of Geosciences, Colorado State University, USA, and
Norges Geologiske Undersøkelse, Trondheim, Norway
M. Markowiak, S.Z. Mikulski
Polish Geological Institute, Sosnowiec and Warszawa, Poland
Abstract. Millimetre scale drilling of paragenetic ally-specific sulphide
occurrences represented by ten Myszków molybdenite samples
provides a temporal framework for this Mo-W deposit, associated
with the transcontinental Hamburg-Kraków tectonic zone. With replicates (second mineral separates) for two samples, a total of twelve
Re-Os model ages pin high temperature molybdenite-scheelite(chalcopyrite) mineralization to a narrow time window, from 300 ±
1 to 296 ± 1 Ma (2-sigma). Published 40Ar/39Ar ages (305-290 Ma)
for potassium feldspar, white mica, and biotite do not precisely pin
the timing of mineralization, but provide information on the regional cooling history. Alteration is characterized by local metasomatism of hosting Vendian to Cambrian metamorphic rocks, and
spatial patterns for Mo-W-(Cu) mineralization support a relationship between metasomatism and mineralization. Dehydration melting of middle crust was followed by local intrusion of magmas along
structurally vulnerable zones. Melting of hosting metaclastic sequences influenced local metallic assemblages and provided the
magmatic apophyses and crustal enclaves associated with much
of the Myszków mineralization. Even though local stockwork may
be found, the overall architecture of the Myszków deposit does not
support a calc-alkaline porphyry-style deposit, and this interpretation should be reconsidered. We attribute Myszków mineralization
to unroofing of the Variscan orogen, rapid late Variscan uplift, and
exhumation melting.
Keywords. Re-Os, molybdenite, Mo-W deposit, metasomatism,
Myszków, Poland
1
Introduction
Late Variscan (~300 Ma) Mo-W mineralization at
Myszków has been classified as a calc-alkaline porphyrytype deposit situated in a poorly defined belt of magmatic rocks in south-central Poland (Podemski et al. 2004;
Markowiak et al. 2001). Features defining of calc-alkaline
porphyry-style mineralization, however, are conspicuously
absent, not the least an intrusion centered brittle-planar
stockwork and attendant alteration types.
Re-Os data for molybdenites have provided key information on the timing and genesis of a broad spectrum of
deposits, in particular, metamorphically-derived deposits versus classic Cu-Mo-Au porphyry-style mineralization (e.g. Stein, in press). The former tend to be small in
size, of erratic but locally high-grade, and display widely
dispersed rather than focussed ore zones. They are associated with moderate-low ppm to sub-ppm levels of Re.
In contrast, true porphyry systems have high to very high
Re contents (hundreds to thousands of ppm) associated
with main stage molybdenites, and are the product of a
vertically and laterally communicative magmatic-hydrothermal system that moved from deep to shallow crustal
levels, over a period of several million years, importantly,
without venting. With these characteristics in mind, we
apply Re-Os dating of molybdenite through the paragenetic history of Myszków to document the timing and
duration for its formation and to improve our understanding of this unusual deposit.
2
Geologic setting
The Myszków deposit is situated along the NE margin
of the NW-trending Kraków-Lubliniec tectonic zone, a
segment of the transcontinental Hamburg-Kraków tectonic zone. In southern Poland, the tectonic history of
this zone is poorly known but strike-slip movement appears to be an important component. Mafic to felsic
magmatism with granodiorite prevailing is common
along the 15 km segment of the Kraków-Lubliniec tectonic zone that includes the Myszków Mo-W region.
Magmatic rocks are hosted by intensely folded, predominantly fine-grained Vendian to Cambrian clastic units
at regional greenschist facies. Upper amphibolite-granulite facies (metasomatic) is locally present in the vicinity of magmatic rocks. A NW-trending granodiorite body
with subvolcanic dacite and rhyolite porphyry dikes intruded the metasedimentary rocks, and contact relations
vary from sharp to ill-defined. The overall character of
the Myszków granodiorite is one of a moderately flattop intrusion extending over tens of kilometres, and dissected by normal faults (Fig. 1). Interfingering and foliation parallel magmatic units intersected in drill holes
in the vicinity of the granodiorite are interpreted as apophyses to the granodiorite body (Podemski et al. 2001).
Associated alteration is described both as metasomatic
and hydrothermal vein type, with significant K-feldspar,
silica, sericite, and carbonate. While potassic alteration
is prevalent, secondary biotite, magnetite, and significant pyrite are conspicuously sparse. Some alteration
assemblages have been described as greisen-like at
Myszków.
Close
834
H.J. Stein · M. Markowiak · S.Z. Mikulski
Three periods of mineralization are defined at
Myszków: Early Skarn (Period I), Main Hydrothermal
(Period II), and Late Post-Ore (Period III). The first two
are molybdenite-bearing. Within Period I, early skarn
consists of magnetite-sulfide mineralization. Within Period II, different stages of ore deposition are proposed
(Stage 1, feldspar-molybdenite veins with biotite; Stage 2,
quartz-feldspar pegmatite veins; Stage 3, quartz-molybdenite stockwork with scheelite; Stage 4, black quartz veins
with microsulfide; Stage 5, quartz polymetallic veins without molybdenite and late brecciated quartz veins with
sulfide. The Period-Stage classification (Þlósarz 1985, 1993)
was used for our molybdenite samples (Table 1), and is
summarized in Podemski et al. (2001).
4
The Myszków deposit, outlined by 35 boreholes from
1985 to 1993, is estimated to contain 800 million tons of
ore at 0.15% Cu, 0.05% Mo, and 0.04% W and continues
to at least 1250m depth (Podemski et al. 2001). Several
similar deposits were also discovered in this region. Significantly, Cu mineralization (chalcopyrite) bears little
spatial relation to W and Mo mineralization (scheelite
and molybdenite). And, W and Mo also exhibit differences. In general, W (and Mo) are associated with magmatic rocks, whereas Cu and to some extent Mo, are associated with contact regions between granodiorite and
metaclastic host units. Molybdenite is generally associated with quartz veins and patches in pink (potassic) granodiorite, but these ill-defined and scattered veins do not
constitute stockwork in the classical sense. Also, the richest ore body is contained in an enclave of metaclastic host
rock within the upper portion of the granodiorite (Chaffee
et al. 1997), rather than exhibiting an intrusion-wide association to the granodiorite. Myszków mineralization and
paragenesis have been described in detail by Piekarski
(1982, 1995) and Þlósarz (1985, 1993), including vein, pegmatitic, metasomatic, disseminated, and skarn varieties
(see Podemski et al. 2001).
3
Molybdenite samples dated
This Re-Os study utilizes different ore occurrences to determine the relative timing of ore-forming environments
at Myszków. Even at the hand-specimen scale, molybdenite
was drilled from occurrence-specific sites, a critical step
for successful age determinations in complex metamorphic settings (Stein in press). Replicate ages for two
samples were acquired from new mineral separates exploiting the same occurrence. This is an indisputable test
for age accuracy.
Re-Os analytical results
Twelve Re-Os ages representing paragenetically defined
Myszków molybdenites provide a remarkably narrow age
range, 300 ± 1 to 296 ± 1 Ma (2-sigma). Re concentrations are moderate, ranging from an about 40 to 74 ppm.
The lower value (40 ppm) is an estimate of the true Re
concentration as up to 95% dilution of the molybdenite
separate by quartz was unavoidable during drilling of
some samples. Such samples consist of very fine-grained
grey streaks of molybdenite in quartz (see footnote,
Table 1). This does not affect the age calculation, as diluting quartz contains essentially no Re and Os. Four samples
with abundant and coarser crystalline molybdenite suggest that ~70 ppm Re was common to the fluids forming
quartz-molybdenite veins.
Notably, the Re values reported in Podemski et al.
(2001), 0.07 to 0.17% (700 to 1700 ppm), bear no resemblance to our Re values determined by isotope dilution. It
is highly unlikely that both data sets can be correct for a
single deposit.
5
Discussion and conclusions
The moderate and fairly consistent Re levels (about 40 to
75 ppm) for Myszków molybdenites do not support a subduction-related porphyry-style origin (Stein et al. 2001).
A better fit would be a moderately local derivation utilizing a crustal reservoir with fairly consistent Re, rather
than one dependent on batch additions of material from
different reservoirs, mixing, and system wide fluid separation (porphyry model). At Myszków, development of
local veins, stockwork, and pegmatite likely depended on
local separation and volatile enhancement of hydrothermal fluids that were not far-travelled.
Re-Os ages have a very tight range (300-296 Ma) and
40Ar/39Ar ages (305-290 Ma) overlap the molybdenite age
range but should be interpreted as recording the cooling
history at the sampled localities for the minerals dated
Close
Chapter 7-29 · Metamorphic to magmatic transition captured at the Myszków Mo-W deposit, southern Poland
(potassium feldspar, biotite, white mica). Argon geochronology should not be used to define ages of high temperature Mo-W-Cu mineralization (Stein et al. 2001). General agreement between Re-Os and 40Ar/39Ar ages suggests that the region cooled very quickly, and has not seen
any further thermal activity.
Mineralogy (e.g. lack of abundant chalcopyritee, fluorite, and Au), lack of an intrusion-centered relationship
for mineralization, lack of correlation between Cu and
Mo, the abundance of W, lack of planar-brittle vein styles,
and lack of classic porphyry-style alteration collectively
do not support a Mo-W calc alkaline intrusion-related,
porphyry model (Podemski et al. 2001).
Re-Os ages and the preserved regional greenschist facies character of host rocks with local high temperature
contact metamorphism suggest rapid uplift with structurally favourable but localized discontinuities serving as
focussing sites for intrusion. This was accompanied by
local and brief in situ melting and metasomatism. As a
result, erratic mineralization of variable grade covers a
large region. This includes the Myszków deposit and other
prospects in the Kraków-Lubliniec tectonic zone. Small
perturbations in pressure permitted local formation of
thick (cm scale) “stockwork” veins but true and abundant stockwork never formed system wide as defines classic Cu-Mo-Au-W porphyry-style mineralization. Furthermore, there is no evidence for a regional tectonic envi-
835
ronment conducive to classic porphyry-style mineralization, as at ~300 Ma the Variscan orogeny is not characterized by subduction. We suggest that the Myszków Mo-W
deposit is the product of exhumation melting associated
with rapid unroofing of the Variscan orogen.
Acknowledgements
Re-Os analytical work was carried out by AIRIE graduate students A Zimmerman and N Loeppke, and supported
by NSF EAR-0087483. Salary support for HJS was provided by Edward Warner.
References
Chaffee MA, Eppinger RG, Lasón K, Mlósarz J, Podemski M (1999) A
geological, alteration, and geochemical model of the Myszków
porphyry Cu-Mo deposit, southern Poland, in Papunen (ed).
Mineral Deposits, Balkema, Rotterdam, 851-854
Markey RJ, Hannah JL, Morgan JW, Stein HJ (2003) A double spike
for osmium analysis of highly radiogenic samples. Chemical
Geology 200: 395-406
Markowiak M, Þlósarz J, Lasón K, Podemski M, Karwowski L, Chaffee
MA (2001) Palaeozoic porphyry molybdenum-tungsten mineralization in the Myszków area, southern Poland, in Piestrzynski
et al. (eds). Mineral Deposits at the Beginning of the 21st Century, Swets & Zeitlinger Publishers Lisse, 445-448
Piekarski K (1982) Molybdenum schists in the vicinities of Myszków
(Eng Sum). Prz Geol 30(7): 335-340
Close
836
H.J. Stein · M. Markowiak · S.Z. Mikulski
Piekarski K (1995) Geologic setting and ore mineralisation characteristics of the Myszków area (Poland). Geol Quart 39(1): 31-42
Podemski M (editor), BuÝa Z, Chaffee MA, Cießla E, Eppinger R, Habryn
R, Karwowski L, Lason K, Markiewicz J, Markowiak M, Snee LW,
Þlósarz J, Truszel M, Wybraniec S, Zaba J (2001) Palaeozoic porphyry molybdenum-tungsten deposit in the Myszków area, southern Poland. Polish Geological Institute Special Papers 6: 1-87
Þlósarz J (1985) Stages and zonality of ore mineralization in
Palaeozoic rocks of the environs of Myszków. Ann Soc Geol Pol
53(1-4): 267-288
Þlósarz J (1993) The main paragenetic stages for molybdenum
mineralisation in the Palaeozoic rocks of the Myszków area and
their importance to the formation of the ore deposits of that area
(Eng Sum). Pol Tow Mineral Pr Spec 3: 123-128
Stein HJ (in press) Low-rhenium molybdenite by metamorphism in
northern Sweden: recognition, genesis, and global implications.
Lithos.
Stein HJ, Markey RJ, Morgan JW, Hannah JL, Scherstén A (2001) The
remarkable Re-Os chronometer in molybdenite: how and why it
works. Terra Nova 13(6): 479-486
Close
Chapter 7-30
7-30
New K-Ar, 87Sr/86Sr, REE, and XRF data for Tertiary
volcanic rocks in the Sasa-Toranica ore district,
Macedonia
G. Tasev, T. Serafimovski, P. Lazarov
Department of Mineral Deposits, Faculty of Mining and Geology, Goce Delcev 89, 2000 Stip, Macedonina
Abstract. The latest K-Ar, 87Sr/86Sr, and REE data for samples from
Sasa-Toranica ore district are presented. Whole rock XRF analyses
confirm host rock composition as dacites, quartz-latites, trachyandesites and rhyolites. K-Ar absolute ages range from 31 to 14 Ma confirming Oligocene-Miocene age as previously determined by relative methods. 87Sr/86Sr ratios (0.70954 to 0.71126) suggest material
is sourced from the contact zone between the lower crust and upper mantle where contamination of primary melt occured. New REE
data including negative Eu anomalies along with previously determined La/Yb ratios ranging from 13.3 to 43.0 (Serafimovski 1990)
confirm inferred material source. These new data reconfirm previous results, provide insight into the Tertiary magmatic history of
the district, and suggest the exact origin of the material that produced the Tertiary magmatic rocks.
Keywords. Sasa, Toranica, volcanic rocks, age, origin, contamination,
Tertiary
1
Introduction
Tertiary volcanic rocks in the Osogovo-Besna Kobila (SasaToranica ore district) area regionally strike NW-SE for
100 km on both sides of Macedonia-Bulgaria border. Volcanic rocks in the area occur as ~50 m thick elongate
dykes oriented roughly east-west (260o). From the Osogovo
Mountain to the Besna Kobila Mountain (Osogovo-LukeKaramanica), volcanic rocks are present as pyroclastics
(Deve Bair), volcanic domes, dykes, necks and veins. Volcanic rocks at the Osogovo-Besna Kobila mountains cut
the Paleozoic and Riphean-Cambrian metamorphic and
igneous rocks and overlie Upper Eocene sedimentary sequences. The volcanics are mainly dacitic tuffs (Deve Bair),
dacites, quartzlatites, rhyolites, trachyandezites, andesitelatites and occasionally lamprophyre veins (Sasa and
Toranica localities).
2
Methodology
After detailed sampling and preparation at the Faculty of
Mining and Geology in Stip, samples were sent to the
Geological Department, University of Padova, Italy for
whole rock XRF analysis, Actlabs in Canada for ICP-MS
and INAA REE analysis, the Geology Department, Royal
Holloway University of London, U.K. for TIMS 87Sr/86Sr
ratios, and the Geological Institute in Budapest, Hungary
for K-Ar dating.
3
Results and discussion
The new K-Ar, Sr isotope, REE, and whole rock XRF data
from Sasa-Toranica host rocks provide insight into the
composition, timing, and sources of volcanic activity in
the region.
Dacites in the Luke-Kiselica area occur from the
Karamanica mountain to the southeast at the Osogovo
mountain (Serafimovski and Alexandrov 1995). The
dacites contain plagioclase (37% An), small amount of
orthoclase, quartz, biotite and amphibole phenocrysts.
Their matrix is holocrystaline to hypocrystaline with
glassy domains. Apatite, sphene and zircon were identified as accessory minerals; while sericite, chlorite, kaolinite,
carbonate and metallic minerals are present as secondary minerals.
Quartzlatites are found near the springs of Lucka River
and Kuprina Padina as dykes and at Samar and
Karamanica as dykes and volcanic flows (Samar and
Crcorija) over the volcano-sedimentary rocks. They are
characterized by a porphyritic coarse grained texture with
sanidine and plagioclase (35-40% An) phenocrysts, with
secondary amphibole and augite phenocrysts. Sphene and
zircon are accessory minerals. These rocks also contain
metallic secondary minerals.
Hialoandesites appear as necks and lava flows over the
Upper Pliocene sediments at Gradeska Mountain. These
rocks are porphyry-vitrophyric with phenocrysts of plagioclase (37% An), biotite, amphibole and augite; apatite
and zircon occur as accessory minerals.
Hypoabyssal and subvolcanic dacites and quartzlatites
dominate the Sasa-Toranica zone (Osogovo). All the
dacites and quartzlatites in the Sasa-Toranica zone experienced hydrothermal alteration. Dacites are
holocrystalline with ~ 30% phenocrystals of andesine
(5-16%), quartz (2-3%) and smal amount of orthoclase
and coloured minerals (13-20%), mainly replaced by epidote, chlorite and carbonates. Hydrothermal alteration
of andesites result in various new mineral assemblages.
Illitization, seritization and propylitization dominante
andesite alteration. Apatite, zircon, sphene and magnetite are present as accesory minerals, while pyrite, chalcopyrite, sphalerite and galena represent economic mineralization.
Close
838
G. Tasev · T. Serafimovski · P. Lazarov
Quartzlaties are the most common rocks in the zone
mentioned above. They occur as elongated dykes a few
kilometers in length. These rocks are characterized by
large phenocrysts of sanidine, andezine and femic minerals biotite, amphibole and rarely augite. Sanidine crystals are fresh and quite large (up to 5-6 cm). Quartzlatites
were intensively hydrothermaly altered.
Transition rocks from quartzlatites to rhyolites are
found at a few locations at Osogovo Mountain. Rocks with
increased SiO2 content occur near the Sekirica Tower close
to the Macedonian-Bulgarian state border. These rocks
were intensly propylitized and hydrothermaly altered.
The volcanic rocks from the Kozja River and Svinja
River (Sasa Mine area) are dominantly dacites and
quartzlatites. The volcanic rocks from this area are intensly
propylitized and hydrothermaly altered. In addtion to
previously mentioned secondary minerals, these rocks also
contain ore minerals including pyrite, galena, sphalerite,
sometimes chalcopyrite and occasionally traces of
ceruzite, anglezite and malachite.Trachyandesites occur
as small bodies at subvolcanic-volcanic levels in the SasaToranica zone and its western borders. They are characterized by porphyry structure (fine grained porphyry)
and crystalized microlitic or microtrachytic matrix.
Phenocrystals of large, around 2 to 3 mm, andezine,
sanidine, biotite, augite and hornblende are present. Apatite, sphene, and zircon occurs as accessory minerals. In
comparison to the quartzlatites, the trachyandesites are
characterized by lower SiO2 concentrations. Similar rocks
were identified in Pecovska Maala on the Osogovo Mountain on the Bulgarian side of the Bulgaria-Macedonian
border.
Lamprophyres occur as small dykes near Sredno Brdo
and Toranica. They are dark grey to brown rocks with a
fine-grained porphyrtic texture and glassy matrix. Pyroxene, amphibole and biotite pheocrysts are identified.
Accessory minerals are apatite, sphene and zircon.
Data obtained after geochemical analyses were entered
into the computer software IGPET 2000 and Microsoft
Excel; results are displayed in Table 1.
Use of IGPET 2000 software facilitated determination
of rock types by the Total Alkali Silica (TAS) classification scheme, their classification under the calk-alkaline
or tholeiitic series of rocks (Fig. 1, 2), and subsequent interpretations based on the classifications.
Graphical view of those determinations is presented
in Figure 1.
TAS classification indicate that the rocks of interest
mostly plot in the areas that define dacites, trachydacites,
trachyandesites and rhyolites. All analyzed rocks plot in
the area of calk-alkali series. Selected samples were analyzed for rare earth element (REE) concentrations. The
analyses were performed at the Active Labs, Canada. REE
concentration data for four samples are presented in
Table 2 and plotted in a chondrite-normalized spider diagram in Figure 2.
From the spider diagram (Fig. 2) it can be seen that
the rare earth elements in the Sasa-Toranica ore region
have a decreasing trend. Comparing the left and right side
of the diagram suggests there is a decrease in heavy rare
earth elements, HREE with an atomic number higher than
63 (Eu), in comparison with light rare earth elements,
LREE with an atomic number lower than 63 (Eu). The
trend is typical as the product of fractionation of light
Close
Chapter 7-30 · New K-Ar, 87Sr/86Sr, REE, and XRF data for Tertiary volcanic rocks in the Sasa-Toranica ore district, Macedonia
rare earth elements and their increase in comparison to
the chondritic values. Fractionation occurred as a direct
consequence of partial melting, which according to the
angle of the line in the diagram was not of high intensity.
Looking at the middle part of the diagram the value
of Eu is slightly and negatively displaced from the “ideal”
linear line between Sm and Gd defining a distinct negative Eu anomaly. A chondrite normalized, geometric mean
calculation of the Eu anomaly is shown in Table 3.
From the table it can be seen that Eu anomaly values
are in range from 0.727669702 up to 0.828905716, and all
are less than 1, which implies a negative Eu anomaly
(Rollinson 1992). Eu anomalies are controled by presence
839
of feldspars. Eu2+ is compatible in plagioclase and K-feldspar, in contrast to the Eu3+ which is incompatible. Thus
the removal of feldspar from a felsic melt by crystal fractionation or the partial melting of a rock in which feldspar is retained in the source will result in a negative Eu
anomaly in the melt.
Accordingly, the data for Eu in analyzed samples and
its negative anomaly it can be concluded that Eu has been
removed from the melt as a compatible Eu2+, by the processes of crystal fractionation or partial melting.
With the analyses of strontium isotopes (Table 4) was
performed to construct a general model of formation for
rock complexes at the Osogovo Mountain (Sasa-Toranica
ore field). Strontium isotope analyses of rock samples from
the volcanic rocks from the Sasa-Toranica ore field results in strontium ratios that range from 0.70954 up to
0.71125. The results suggest the magma forming Neogene
magmatic complexes at the Osogovo Mountain is a product of primary magmatic melt originating from the border zone between upper mantle and continental crust
where mixing and contamination of primary magma occurred.
The new data complies with previous 87Sr/86Sr data for
Upper Tertiary calk-alkaline complexes formed in the
Serb-Macedonian metallogenic province. 87Sr/86Sr ratios
Close
840
G. Tasev · T. Serafimovski · P. Lazarov
tration distribution of elements show that the magmatic
rocks originated from one magmatic chamber but during different time intervals producing different rock types.
K-Ar isotopic age data give Tertiary magmatic ages in
the study area. Results of this study are shown in Table 5.
The range of ages (Oligocene-Miocene) confirms the
age determined by the relative methods.
4
Conclusion
This study of the volcanic rocks in the Sasa-Toranica ore
region identified the distinct and uniform chemical composition of these rocks. The rocks are characterized as
dacites, trachydacites, trachyandesites and rhyolites based
on the TAS scheme. New K-Ar ages range from 31.16 ±
1.40 to 14.0 ± 3.0 Ma confirming Oligocene-Miocene ages.
Strontium isotope ratios and REE analyses identify magmatic material originated from the contact zone between
the upper mantle and lower continental crust where certain contamination of primary melts occurred.
References
of samples from Kozuf Mountain range from 0.7088 to
0.7090 and those for volcanic rocks from the Rogozna
range between 0.7074 and 0.7085 (Serafimovski 1990).
Osogovo Tertiary igneous rocks are characterized by
interesting distributions of Pb, Ba, Sr, Rb, Li, Cs and Be.
Compared to Clark standard values Pb, Ba, Sr and Be are
enriched while Li, Rb and Cs are similar to Clark standard values. Also, in magmatic processes it was noticed
trend of increasing Li, Pb, Cs, Be, Rb and Ba concentrations going from fine-grained porphyry quartzlatites to
coarse-grained porphyry quartzlatites (Serafimovski
1993a; Serafimovski et al. 2003). Tendencies in concen-
Rollinson H (1992) Using Geochemistry Data: evaluation, presentation, interpretation. pp. 352. Prentice Hall, an imprint of Pearson
Education, Harlow, England.
Serafimovski T (1990) Metallogeny of the Lece-Halkidiki zone. Doctoral thesis, Faculty of Mining and Geology, Stip, p. 390 (in
Macedonian)
Serafimovski T (1993a) Structural - Metalogenic features of the LeceHalkidiki zone: Types of Mineral Deposit and Distribution. Faculty of Mining and Geology. Stip, Special Issue N. 2, 325 p, Stip.
Serafimovski T, Aleksandrov M (1995) Lead-zinc deposits and occurrences in the Republic of Macedonia. Faculty of Mining and
Geology, Stip, Special Issue 4, p. 387 (in Macedonian)
Serafimovski T, Jelenkovic R, Tasev G (2003) Geodynamic Evolution
and Metallogeny in the Southern Parts of the Balkan Peninsula.
Geodynamics and Ore Deposit Evolution of the Alpine-BalkanCarpathian-Dinaride Province. Final GEODE-ABCD Workshop.
Programme and Abstracts. pp. 50. Seggauberg, Austria.
Serafimovski T, Jelenkovic R, Tasev G, Lazarov P (2003) Mineral
Deposits Related to Tertiary Magmatism in the Southern Part
of the Balkan Peninsula. Geologica Macedonica, Volume 17, pp.
19-23, Stip.
Tasev G (2003) Polymetalic mineralizations related to the Tertiary
magmatism in the Republic of Macedonia. Faculty of Mining and
Geology, Stip. Master thesis, p. 176. (in Macedonian)
Close
Chapter 7-31
7-31
Sources of rhenium and osmium enrichment in
fumaroles, sulphide sublimates and volcanic rocks
from the Kudriavy volcano
Svetlana G. Tessalina, Françoise Capmas, Jean-Louis Birck, Claude-Jean Allègre
Laboratoire de Geochimie et Cosmochimie, Institute de Physique du Globe, 4 pl. Jussieu, 75252 Paris, France
Marina A. Yudovskaya, Vadim V. Distler, Ilya V. Chaplygin
Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), RAS, Moscow, Russia
Abstract. Rhenium loss through magma degassing could be partly
balanced by rhenium enrichment in fumarolic magmatic gases and
Re-bearing precipitates, as may be the case for the Kudriavy volcano associated with an active subduction zone. The relatively
unradiogenic 187Os/188Os isotope ratios (0.122 up to 0.152) and high
Os contents (averaging 0.6 ppb) of fumarolic gas condensates imply that significant Re and Os are remobilised from depleted MORB
mantle. Involvement of a Re-rich component is evident from high
Re concentrations in high-temperature gas condensates, ranging
from 7 to 200 ppb. Indeed, Re-rich Os-poor components such as
organic-rich subducted sediments and volcanic rocks do not significantly shift the isotopic composition of fumarolic products. The
relatively radiogenic composition of the dacite-andesite-basaltic arc
volcanics (187Os/188Os ratio up to 0.58), however, could result from
significant Os (and Re) input from subducted sediments.
Keywords. Re-Os, subduction zone, rheniite, Kurile Islands, Kudriavy
loor sediments are almost completely subducted beneath
Kurile Island arc (Von Huene and Scholl 1991). The lower
part of the sedimentary section consists of the Cretaceous
chert (120 to 92 Ma) of carbonate composition with abundant siliceous organisms. The radiolarian and diatom ooze
accumulated during the middle to late Miocene (14 to 5
Ma) represents the upper part of the sedimentary section (Bailey 1993).
The Kudriavy volcano has been passively degassing at
500-940° C, as recorded in fumarole activity for the last
100 years. The unique occurrence of rhenium disulphide
(rheniite ReS2) has been discovered around high-temperature fumaroles on the Kudriavy volcano, together with
elevated PGE contents.
3
1
Subduction zones are major sites of continental crust formation and elemental recycling between the mantle and
crust. The great difference between Re contents in degassed subaerially deposited arc volcanics (~0.19 ppt,
Lassiter 2003) and in melt inclusions from undegassed
primary arc volcanics (~2 ppb, Sun et al. 2003) requires
Re loss during magma degassing. Substantial Re loss from
arcs can be partly balanced by high Re contents in magmatic gases and the presence of pure Re sublimates in
arc systems (Korzhinsky et al. 1994), as reported for the
Kudriavy volcano, above an active subduction zone in the
Kurile Islands. The Re-Os systematics should provide
important information on the source of Re-rich magmatic
volatiles and sulphide precipitates with regard to contributions from the mantle, crust, subducting slab, and seawater, because of compatible Os and slightly incompatible Re behaviour.
2
Sample description and analytical methods
Introduction
Tectonic setting of the Kudriavy volcano
The Kurile Islands are the result of Pacific plate subduction beneath the Eurasian plate. Subducted Pacific plate
comprises oceanic crust (MORB), oceanic lithospheric
mantle and associated sediments. The 400 m-thick seaf-
In order to understand mechanisms for rhenium and osmium enrichment, we undertook integrated studies of
fumarolic gases, sulphide sublimates and volcanic rocks
at Kudriavy. The sulphide sublimates are represented by
molybdenite (MoS2), rheniite (ReS2) and Pb-Bi sulphosalt.
The suite of volcanic rocks ranges from basaltic to dacitic
in composition. Two fractions of fumarolic gas condensates were analysed: = 0.2 mm (Fraction 1) and bulk fumaroles condensates (Fraction 2). Re and Os concentrations and Os isotopic compositions was determined by
negative thermal ionisation mass spectrometry (NTIMS)
on a Finnigan MAT 262 at the IPGP. Analytical procedure
has been described previously (Birck et al. 1997).
4
Re-Os isotope systematics
The Re contents in Kudriavy volcano rocks range from
3.5 to 17 ppb (Fig. 1) averaging 7 ppb, which is about 20
times higher than the estimated average Re abundance
for arc lavas (0.3 ppb) and 3 times higher than for melt
inclusions from primitive arc lavas, southern Pacific (Sun
et al. 2003). The Os contents (ave. 11 ppt.) are similar to
those of MORB (Roy-Barman and Allègre 1994). The 187Os/
188Os ratios vary from 0.205 in basalt to 0.588 in dacite
with an average of 0.385. This range of Os isotopic com-
Close
842
Svetlana G. Tessalina · Françoise Capmas · Jean-Louis Birck · Claude-Jean Allègre · Marina A. Yudovskaya · Vadim V. Distler · Ilya V. Chaplygin
position in volcanic rocks could be explained by mixing
of an unradiogenic MORB-type reservoir with more radiogenic components. Our mass balance calculations are
based on the following parameters (Table 1).
The unradiogenic MORB-type component could represent Os-poor oceanic crust. The Os contribution from
high-Os depleted mantle is limited to 10% in basalts and
almost negligible in felsic volcanic rocks formation. Fluid–
saturated sedimentary slab from the subduction zone can
be considered as the more radiogenic end-member. Thus,
the relatively radiogenic Os signatures for Kudriavy volcanic rocks could be explained by significant Os and Re
input (up to 50 %) from slab-derived fluids and melts contaminated by more radiogenic (0.29 to 0.64 for 187Os/188Os)
organic-rich sediments from the subducting Pacific plate
(Peucker-Ehrenbrink et al. 1995) (Fig. 2) .
Previous studies of fumarolic gases using H, He and C
isotopic systematics (Taran et al. 1995; Fischer et al. 1998)
showed that the subducted slab and mantle wedge were the
main sources for fluids in the Kudriavy volcanic system.
The Re-Os contents and isotope composition of gas condensates vary significantly depending on the method of
analytical sampling. Fractions = 0.2 mm (Fraction 1) are
characterised by high Re and Os contents (average values
are 85 ppb and 0.6 ppb, respectively) and unradiogenic 187Os/
188Os compositions (0.122 to 0.152). In contrast, bulk condensates (Fraction 2) are characterised by lower Re and Os
concentrations (~0.4 ppb Re and 2-37 ppt Os) and slightly
more radiogenic Os isotope compositions (0.12 to 0.45),
similar to those of the hosting volcanic rocks. This difference can be explained by chemical procedure (incomplete digestion of Fraction 2 due to the absorption of Re
and Os complexes by coarse sulphur particles coagulated
during acid decomposition), or by the presence of rocks
particles in a Fraction 2. Thus, the data obtained for Fraction 1 can be considered as representative of bulk gas
condensate composition. The relatively unradiogenic
187Os/188Os ratios (0.122 to 0.152) and high Os contents
(averaging 0.6 ppb) for fumarolic gas condensates imply
that a significant part of Re and Os was remobilised from
depleted MORB mantle (Table 1). Involvement of a Rerich component is evident from high Re concentrations
in gas condensates, ranging from 7 to 200 ppb. But this
radiogenic, Re-rich and Os-poor component, possibly
organic-rich subducted sediments (up to 20%) and volcanic rocks (up to 20%), does not significantly shift the
Os isotopic composition of fumarolic products.
Rheniite is highly radiogenic due to its high Re content
(74.5 wt.% Re). Repeated analyses of two rheniite samples
provide model ages of 79±11 yr, which agree with the known
100 year period of fumarolic activity. The initial 187Os/188Os
ratio is not well defined (0.32±0.15), but appears to be higher
than ratios associated with gas condensates. The Pb-Bi
sulphosalts have much lower Re contents (~250 ppb) and
relatively unradiogenic osmium isotopic compositions
(0.125 to 0.176), similar to that of gas condensates.
5
Conditions of Re enrichment
Experimental work has shown that rhenium can be mobilized by high-temperature, saline, and sulphide-poor
hydrothermal solutions (Xiong and Wood 1999). According to these experimental data, Re concentrations at 510°C
in 0.5 m KCl solution are about 8 x 10-6moles/kg H2O (~1
ppm). Thus, Re could be easily remobilised from the host
rocks and sediments by high temperature (700-940°C)
Close
Chapter 7-31 · Sources of rhenium and osmium enrichment in fumaroles, sulphide sublimates and volcanic rocks from the Kudriavy volcano
fumarolic gases with 0.5 mol% of Cl (Taran et al. 1995).
On the other hand, Re and Os enrichment in fumarolic
gases could depend on melt-vapor fractionation processes.
Deposition of Re-bearing sulphide could be induced by
subaerial conditions, which exclude the possibility for
dissolution of Re-complexes in water.
6
Importance for Re resources
Until now, molybdenite-bearing Cu-porphyry deposits
have been the primary source of Re. High Re concentrations in molybdenite from Cu-porphyry environments
have been attributed to mantle involvement in a subduction setting (Stein et al. 2003; Zimmerman et al. 2003)
The occurrence of high levels of rhenium in gases and
sulphides from the Kudriavy volcano may represent a new
and unexplored resource for Re. The Re resources of
Kudriavy volcano are still under considerations.
References
Bailey JC (1993) Geochemical history of sediments in the northwestern Pacific Ocean. Geochem. J 27: 71-92
Birk JL, Roy-Barman M, Capmas F (1997) Re-Os isotopic measurements at the femtomole level in natural samples. Geostandards
newsletter 20: 19-27
Fischer TP, Giggenbach WF, Sano Y, Williams SN (1998) Fluxes and
sources of volatiles discharged from Kudriavy, a subduction zone
volcano, Kurile Islands. Earth Planet Sci Lett 160: 81-96
Korzhinsky MA, Tkachenko SI, Shmulovich KI, Taran YA, Steinberg
GS (1994) Discovery of a pure rhenium mineral at Kudriavy Volcano. Nature 369: 51-52
843
Lassiter JC (2003) Rhenium volatility in subaeral lavas: constraints
from subaeral and submarine portions of the HSDP-2 Mauna
Kea drillcore. Earth Planet. Sci. Lett. 214: 311-325
Peucker-Ehrenbrink B, Ravizza G, Hofmann AW (1995) The marine
187Os/188Os record of the past 80 million years. Earth Planet Sci
Lett 130: 155-167
Roy-Barman M, Allègre CJ (1994) 187Os/186Os ratios of mid-ocean
ridge basalts and abyssal peridotites. Geochim Cosmochim Acta
58: 5043-5054
Stein H, Scherstén A, Hannah J, Markey R (2003) Sub-grain scale
decoupling of Re and 187Os and assessment of laser ablation ICPMS spot dating in molybdenite Geochim Cosmochim Acta 67:
3673-3686
Sun W, Benett VC, Eggins S, Kamenetsky VS, Arculus R (2003) Enhanced mantle-to-crust rhenium transfer in undegassed arc
magmas. Nature 422: 294-297
Taran YuA, Hedenquist JW, Korzhinsky MA, Tkachenko SI,
Shmulovich KI (1995) Geochemistry of magmatic gases from
Kudriavy volcano, Iturup, Kuril Islands. Geochim Cosmochim
Acta 59: 1749-1761
Von Huene R, Scholl DW (1991) Observations at convergent margins concerning sediment subduction, subduction erosion, and
the growth of continental crust. Reviews in Geophysics 29: 279316
Widom E, Kepezhinskas P, Defant M (2003) The nature of metasomatism in the sub-arc mantle wedge: evidence from Re-Os isotopes in Kamchatka peridotite xenoliths. Chemical Geology 196:
283-306
Xiong Y, Wood SA (1999) Experimental determination of the solubility of ReO2 and the dominant oxidation state of rhenium in
hydrothermal solutions. Chem Geol 158: 245-256
Zimmerman A, Stein H, Markey R, Fanger L, Heinrich C, von Quadt
A, Peytcheva I (2003) Re-Os ages for the Elatsite Cu-Au deposit,
Srednogorie zone, Bulgaria: in Eliopoulos, D.G. et al. (eds), Mineral Exploration and Sustainable Development, Millpress,
Rotterdam: 1253-1256
Close
Close
Chapter 7-32
7-32
Muluozhai REE deposit in Sichuan Province, China:
Stable isotope data and their implications on the
dynamics of mineralization
Shihong Tian, Zengqian Hou, Tiping Ding
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China, and Key Laboratory on
Isotope Geology, Ministry of Land and Resources, Beijing 100037, China
Yuling Xie
Civil & Environmental Engineering School, Beijing University of Science and Technology, Beijing 100083, China
Zhongxin Yuan, Ge Bai, Tianren Zou
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
Abstract. The Muluozhai REE deposit, located about 60 km to the
southwest of the Mianning County, Sichuan Province, is the third
largest light REE deposit in Sichuan. The Muluozhai REE deposit is
tectonically located on the northern Jinpingshan Mountains, a Cenozoic intracontinental orogenic belt in southwestern China. The authors analyzed the essential ores from two tunnels for their carbon,
hydrogen, oxygen, and sulfur isotopic compositions of the mineralizing fluid. The δ13CV-PDB values of fluid from fluid inclusions of the
quartz and fluorite vary from - 2.5 to - 9.0 per mil, which show characteristics of mantle-derived carbon. The δDV-SMOW values of fluid
from fluid inclusions of the calcite, quartz, fluorite, and bastnaesite
range from - 63 to - 87 per mil, which are characteristics of mantlederived hydrogen. The δ34SV-CDT values of barite and galena vary in
a narrow range of + 0.1 to + 2.2 per mil and - 8.6 to - 9.3 per mil,
respectively, showing the isotopic characteristics of mantle-derived
sulfur. The δ13CV-PDB values and the δ18OV-SMOW values of calcite range
from - 6.6 to - 6.8 per mil and from + 8.4 to + 9.1 per mil, respectively, which are fallen into the range of the “primary carbonatites”,
showing the carbon and oxygen in the ores of the Muluozhai ore
veins were mainly derived from depths. The stable isotopic data
suggest a mantle source for the rare earth elements mineralization
and a dynamic process involving mantle materials and tectonics.
Keywords. Rare earth element deposit, stable isotopes, mantle source,
mineralization dynamics, Muluozhai in Sichuan Province
1
Introduction
The Muluozhai REE deposit (28°22’ N Lat. and 101°50’ E
Long.), located about 60 km to the southwest of the
Mianning County, Sichuan Province, is the third largest
light REE deposit in Sichuan. Along with other REE deposits in the Panzhihua-Xichang area, it forms one of the
three major REE deposit producing regions in China. Although known since the 1960s, it has not attracted nearly
as much interest as the Maoniuping and the Daluchao
REE-deposits in the Panxi REE ore belt, and, therefore,
only little research has been performed concerning its
geological characteristics, geochemistry, isotopic
geochemistry, mineralogy, and fluid inclusions. Because
it is an important part of the Panxi REE ore-forming belt
and is situated at the eastern margin of the Tibetan Plateau, it is necessary to understand regional metallogenic
rules and the collision between the Indian plate and the
Eurasia plate. In this paper, we present systematic studies
on the characteristics of S, C, O, and H isotopes of the
ores to ascertain the sources of the mineralizing fluids
and the dynamic process related to the mineralization.
2
Geologic setting and REE mineralization
The Muluozhai REE deposit is tectonically located on the
northwest margin of the Panxi (Panzhihua-Xichang) rift
zone at the western side of the Yangtze Platform (Fig. 1).
According to Luo et al. (1985), the Panxi rift zone formed
on the Yangtze platform starting in the early Paleozoic.
Deposition continued during the late Paleozoic into the
Mesozoic and ended in the early Cenozoic with the beginning of the Himalayan Orogeny. The Panxi rift was
bordered by the Ganluo-Xiaojiang Fault to the east and
Qinghe-Chenghai Fault to the west. It extends north-south
for over 300 km and reaches a width of about 100 km.
Large amounts of alkali-rich ultramafic, basic, and intermediate-acid rocks with a great deal of REE were intruded
or erupted in the Panxi rift zone and its neighboring areas. In the region, the Devonian, Permian, Triassic and
Jurassic strata are distributed scatteredly because of the
destruction of the developed igneous rocks. The latter
are distributed extensively in the region and the main
rocks are Indosinian quartz diorite, granite, and
Yanshanian alkali-feldspar granite.
On the basis of orebody distribution, three kinds of
ores have been identified: (i) massive fluorite-bastnaesite,
(ii) impregnated, and (iii) banded. The ore minerals are
mainly bastnaesite, whereas the gangue minerals include
fluorite, barite, calcite, feldspar, quartz, mica and aegirineaugite. The textures and structures are allotriomorphic
inequigranular, tabular, subhedral, and massive, banded,
respectively. The wall-rock alteration is characterized by
Close
846
Shihong Tian · Zengqian Hou · Tiping Ding · Yuling Xie · Zhongxin Yuan · Ge Bai · Tianren Zou
clusions in quartz and fluorite was released by the decrepitation method and collected in sample tube at liquid N2 temperature. All SO2, CO2, and H2 were analyzed
using a Finnigan MAT 251 mass spectrometer at the Key
Laboratory on Isotope Geology, Ministry of Land and
Resources. Analytical reproducibility in this study is ±
0.2 per mil for C, O, and S isotopes, and ± 2 per mil for H
isotope.
3.2 Results
contact metamorphism and hydrothermal alteration,
which includes sericitization, pyritization, baritization, and
carbonatization.
3
Stable isotope analysis
3.1 Experiments
Sulfur, carbon, oxygen, and hydrogen isotopes of mineral
separates from the Muluozhai deposit have been analyzed.
SO2 was prepared from the samples for sulfur isotope
analysis with the method of Robinson and Kusakabe
(1975). For oxygen and carbon isotope analysis, calcite
was reacted with phosphoric acid at 25° (McCrea 1950)
to release CO2. The δ18OV-PDB values of calcite samples
were directly obtained from the δ18O values of their CO2
against the CO2 of PDB. For converting the δ18OV-PDB to
δ18OV-SMOW, the equation by Friedman and O’Neil (1977)
was used, δ18OV-SMOW = 1.03086 · δ18OV-PDB + 30.86. For
analysis of hydrogen isotopes, the water in fluid inclusion was released by the decrepitation method. Then, the
water was reacted with Zn at 400° to produce H2 (Coleman
et al. 1982), which was collected in a sample tube with
activated charcoal at liquid N2 temperature. For the analysis of carbon isotopes from the fluid, the CO2 in fluid in-
Sulfur isotope analyses have been done on 3 barite and 3
galena samples. The δ34SV-CDT values vary in a narrow
range of + 0.1 to + 2.2 per mil with an average of + 0.8
per mil for the barite, and - 8.6 to - 9.3 per mil with an
average of - 9.0 per mil for the galena, respectively. According to the theory by Ohmoto (1972), the δ34SV-CDT
values of ore-forming fluid in the Muluozhai deposit vary
from - 9.0 to + 0.8. On account of barite more than galena, the δ34SV-CDT values of ore-forming fluid is more than
0 per mil, but less than + 2.2 per mil, which shows the
isotopic characteristics of mantle-derived sulfur (Lu 1986).
Five calcite samples were analyzed for their carbon and
oxygen isotopes. The δ13CV-PDB values and the δ18OV-SMOW
values range from - 6.6 to - 6.8 per mil with an average of
- 6.7 per mil and from + 8.4 to + 9.1 per mil with an
average of + 8.7 per mil, respectively. These values fall
into the range of “primary carbonatites”, showing that
carbon and oxygen in the ores of the Muluozhai deposit
were mainly derived from the mantle (Keller and Hoefs
1995).
Carbon isotope analyses of fluid from fluid inclusions
were made on 2 quartz and 5 fluorite samples. The δ13CVPDB values range from - 2.5 to - 3.6 per mil for quartz with
an average of - 3.1 per mil and - 5.5 to - 9.0 per mil for
fluorite with an average of - 7.1 per mil. Quartz and fluorite samples show narrow ranges in δ13CV-PDB values, which
are close to the estimated value of mantle carbon (Pineau
and Methez 1990).
Hydrogen isotope analyses of fluid from fluid inclusions have been done on 2 quartz, 5 fluorite, 5 calcite, and
5 bastnaesite samples. The δDV-SMOW values range from 69 to - 76 per mil for the quartz with an average of - 73
per mil, - 73 to - 87 per mil for the fluorite with an average of - 81 per mil, - 70 to - 82 per mil for the calcite with
an average of - 76, and - 63 to - 86 per mil for the bastnaesite
with an average of - 71 per mil. All minerals show a narrow range in δDV-SMOW values that fall close to the estimated value (-60 to -80 per mil) of mantle hydrogen (Mao
and Li 2004).
4
Discussion and conclusions
REE mineralizations in rift belts are characterized by
multiphase and multistage processes. Mineralizing types
Close
Chapter 7-32 · Muluozhai REE deposit in Sichuan Province, China: Stable isotope data and their implications on the dynamics of mineralization
vary through time. Correspondingly, geological, mineralogical, petrological, and geochemical features differ also.
For example, in the Liaodong rift belt, REE mineralizations in pegmatites and migmatites formed during an early
stage of rift formation, REE-Fe-rich formation of metamorphism volcano-sedimentary rocks during the midstage of rift formation, and REE-U-rich aegirine and
aegirine-nepheline syenites are related to the postrift evolution (Chen 1984). In the Bayan Obo rift belt, Inner
Mongolia, the famous Bayan Obo Fe-Nb-REE ore deposit
formed during the Proterozoic, in the evolved rift (Bai
1996) and REE-rich hydrothermal vein and skarn deposits formed during the Caledonian and Hercynian. These
late mineralizations reworked the Proterozoic mineralizations (Yuan et al. 1992). The REE mineralizations of
the Panxi rift belt are also characterized by multiphase
and multistage processes.
REE-rich nordmarkites, alkali granites, syenite porphyries, and albitites. formed during the Hercynian-Indosinian
epoch in the developed stage of the Panxi rift, which were
mostly associated with alkaline and basic bedded rocks in
the region. Affected by the collision between the Indian plate
and the Eurasia plate, the rift closed during the Himalayan
epoch and changed into an intracontinental orogenic belt,
i.e. the Jinpingshan Orogen (Fig. 1), which was formed during Cenozoic and became the eastern margin of the Tibetan Plateau (Burchfiel et al. 1995).
The Muluozhai REE deposit is located in the transitional zone between the Panxi rift and the LongmenshanJinpingshan orogenic zone, where the Yangtze plate penetrated as a wedge into the crust at Longmenshan, resulting in a Moho dislocation, thereby inducing partial melting of the mantle materials (Xu et al. 1999). This tectonic
environment may have caused intensive faulting and
magmatism, possible metamorphic dehydration and upwelling of mantle fluids along the deep faults in the western margin of the Yangtze. The fluids that were responsible for the formation of the Muluozhai REE deposit have
S, C, O, and H isotopes similar to mantle or mantle-derived rocks.
Acknowledgements
This work was supported by grants from the State Science and Technology Commission (contract No.
2002CG412610 and G1999043211) and China Natural Sciences Foundation (Grant No. 40425014). We thank Luo
Yaonan of Sichuan Bureau of Geology and Mineral Resources and Pu Guangping, Yu Bo and other engineers of
the No. 109 Geological Team during our field investigation. We are grateful to Professor Wang Denghong and
847
Professor Chen Wenming at the Institute of Mineral Resources, CAGS, for their constructive suggestion. We also
thank Professor Wan Defang, Senior Engineer Li Jincheng,
Senior Engineer Bai Ruimei, and Engineer Luo Xurong
at the Key Laboratory on Isotope Geology, Ministry of
Land and Resources, for their performance of analyses.
References
Bai G, Yuan ZX, Wu CY (1996) Geotectonic setting of the Bayan Obo
deposit, Inner Mongolia. Acta Geosci Sinica 17 (supl): 1-8 (in
Chinese with English abstract)
Burchfiel BC, Chen, ZL, Liu, YP, Royden LN (1995) Tectonics of the
Longmen Shan and adjacent regions, central China. Intern Geol
Rev 37: 661-735
Chen RD (1984) A Proterozoic rift basin-Liaodong rift. Liaoding
Dizhi 2: 125-133 (in Chinese with English abstract)
Coleman ML, Sheppard TJ, Durham JJ, Rouse JE, Moore GR (1982)
Reduction of water with zinc for hydrogen isotope analysis. Anal
Chem 54: 993-995
Friedman I, O’Neil JR (1977) Compilation of stable isotope fractionation fraction factors of geochemical interest. In: Fleischer
M (ed) Data of geochemistry. Sixth Edition. Geol Surv Profl Pap
US P. 117
Keller J, Hoefs J (1995) Stable isotope characteristics of recent
natrocarbonatites from Oldoinyo Lengai. In: Bell K (ed)
Carbonatites volcanism: Oldoinyo Lengai and Petrogenesis of
Natrocarbonatites. LAVCEI Proceeding in Volcanology. LAVCEI,
113-123
Lu CW (1986) Stable Isotopic geochemistry. Chengdu Univ Technol,
Publ House, Chengdu, pp. 40-43 (in Chinese)
Luo YN (1985) Panzhihua-Xichang paleo-rift zone, Southwest of
Sichuan. In: Zhang YX (ed) Contribution to Panzhihua-Xichang
rift, China. Geol Publ House, Beijing, pp. 1-25 (in Chinese with
English abstract)
Mao JW, Li XF (2004) Mantle-derived fluids in relation to ore-forming and oil-forming process. Mineral Deposits 23: 520-532 (in
Chinese with English abstract)
McCrea JM (1950) On the isotope chemistry of carbonates and a
paleotemperature scale. J Chem Phys 18: 849-857
Ohmoto H (1972) Systematics of sulfur and carbon isotopes in hydrothermal ore deposits. Econ Geol 67: 551-578
Pineau F, Methez EA (1990) Carbon isotopes in xenoliths from the
Hualalai volcano, Hawaii, and the generation of isotopic variability. Geochim Cosmochim Acta 54: 2117-2127
Robinson BW, Kusakabe M (1975) Quantitative preparation of sulphur dioxide for 34S/32S analyses from sulphides by combustion
with cuprous oxide. Anal Chem 47: 1179
Wang DH, Yang JM, Yan SH, Xu J, Chen YC, Pu GP, Luo YN (2001) A
special orogenic-type rare earth element deposit in Maoniuping,
Sichuan, China: Geology and Geochemistry. Resource Geol 15:
177-188
Xu ZQ, Yang JS, Jiang M, et al., (1999) Continental subduction and
uplifting of the orogenic belts at the margin of the Qinghai-Tibet Plateau. Earth Sci Front 6: 139-150 (in Chinese with English
abstract)
Yuan ZX, Bai G, Wu CY, Zhang ZQ, Ye XJ (1992) Geological features
and genesis of the Bayan Obo REE ore deposit, Inner Mongolia,
China. Appl Geochem 7: 429-442
Close
Close
Chapter 7-33
7-33
Stable isotope composition of the Dalucao rare earth
deposit in western Sichuan
Wan Defang, Tian Sihong
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
Luo Mei
Chengdu University of Technology, Chengdu 610059, Sichun China
Jiang Shaoyong
Department of Earth Sciences, Nanjing University, Nanjing 210093, Jiangsu, China
Abstract. Ore-forming solutions and the origin of mineralizing material in the Dalucao rare earth deposit were studied by means of H,
O, C, and Si isotope analyses. The δ13C of the bastnasite range narrowly from -8.1‰ to-8.0‰, while the δD values range from -89‰
to -79‰. The quartz δ30Si of the orebody is -0.3‰, and the δD and
δ18O of the quartz-fluid inclusion range from -87‰ to +6.0‰, respectively. The δD and δ18O values of the fluorite-fluid inclusion in
the ore body are -99‰ to -11.6‰, respectively. The study shows
that the compositions of hydrogen and oxygen isotopes in oreforming fluid of Dalucao rare earth deposit lie in the region between magmatic water and meteoric water. Therefore the ore-forming fluid was mixed from magmatic and meteoric water. The carbon isotopic features suggest that carbon of the bastnasite was
from the mantle, carbon of fluorite-fluid inclusions in the ore body
was from a mixture carbon source, and carbon of quartz-fluid inclusions was from the mantle.
Keywords. Stable isotope composition, quartz-fluid inclusion, fluorite-fluid inclusion, rare earth deposit, Dalucao
1
Introduction
The Dalucao rare earth ore deposit, one of the largest
rare earth ore deposits of China, is located 20 km southwest from Dechang county town, Sichuan Province. It covers an area of about 3 km2. Tectonically, the deposit is
situated in the middle part of the Panxi rift belt, a famous epicontinental rift in the western border of the
Yangtze platform.
Rare earth ore bodies of Dalucao rare earth ore deposit are mainly hosted in the aegirine-augite syenite,
bordering to quartz diorite, and are related to hydrothermal activations associated with the quart diorite. Geological and geochemical features demonstrate that the
deposit is a hydrothermal deposit that formed at medium
to low temperature. Based on the C, H, O, and Si isotopes
and in the context of the regional geology and tectonics
of the Panxi rift, it is further suggested that the source
rocks of the ore-bearing aegirine-augite syenite are probably early-formed alkali-rich rocks of the Hercynian epoch that are present at depth. The ore-bearing aegirineaugite syenite was mostly formed by remelting, ascend-
ing, and emplacement of the source rocks under the activation of mantle plume and tectonic mobilization in the
Himalaya period.
2
Geological survey of Dalucao rare earth deposit
Dalucao rare earth ore deposit is located in the middle
part of the Panxi rift belt, which is a famous epicontinental rift in the western border of the Yangtze platform. The
distributive strata of the deposit are mainly Previndean
system, Vindean-Cambrian system and Jurassic system
(Fig. 1). Previndean strata are mainly composed of Yanbian
formation strata of Huili group, Vindean-Cambrian strata
are consisted of Guanyinyan formation and Dengying
formation, and Jurassic system is made up of Baiguowan
group and Yimen formation.
The deposit is situated in part between Shuenhe
syncline and Xincun syncline, located at intersections
with the Dalucao (F1), Nanmuhe (F7)and Xincun syncline, located at intersections with the Dalucao (F1),
Nanmuhe (F7) and Zhangmenzha (F6) faults. The regional structural framework was mainly made up of
SN-striking, NW-striking and NE-striking faults. The
ore body is cut through by Dalucao fault (F1), and affected by the fault.
Outcropping magmatic rocks in the mineral district include quartz diorites of the Jinning epoch, alkali granites of the Indo-Chinese epoch, aegirine-augite syenites, and syenites of the Himalaya epoch. The
Daluxiang quartz diorite (853Ma) is emplaced into the
Presinian Huili group and is covered by the Jurassic
Baiguowan formation. Rare earth ore bodies are hosted
in the 64.9 Ma old aegirine-augite –syenite, which is
emplaced in Daluxiang quartz diorite. The major ore
body is lens-shaped and shows net-veining and mineralization of structural fissures in the aegirine-augite syenite. The major mineral assemblage in the ore
is made up of bastnasite, celestobarite, barytocelestite,
aegirine-augite, fluorite, calcite, quartz, mica, minor
sulphide, and rare earth titanite.
Close
850
Wan Defang · Tian Sihong · Luo Mei · Jiang Shaoyong
3
Geochemistry of stable isotopes
3.1 Signature of silicon and oxygen isotopic compositions
We measured the silicon and oxygen isotope compositions of many wall rock and quartz samples from the rare
earth ore body in order to elucidate the origin and the
evolution of ore-forming fluid in the deposit. Table 1 shows
the Si and O isotope compositions of the deposit. Quartz
δ18O in quartz diorite has values around 9.1‰ to 9.3‰,
and the quartz diorite δ18O is +7.1‰.
It is suggested that the quartz diorite belongs the granitoid (Talor 1968). The quartz δ30Si in quartz diorite is
0.0‰, hornblende -0.2‰ and the quartz diorite δ30Si
0.1‰, which is close to the granitoid average.
The δ18O and δ30Si of quartz in the ore body are respectively +10.1‰ and -0.3‰, the δ18OH2O of fluid inclusions in quartz is 6.0‰, and bastnasite δ18O is from
+19.2‰ to +19.3‰.
3.2 Signature of H, O and C isotopic compositions
Table 2 displays H, O, and C isotope compositions of mineral-hosted fluid inclusions in the REE deposit.
The quartz δD in quartz diorite is -96‰ and the δ13CPDB
of its CO2 is -11.9‰.
δD and δ18OH2O of quartz in the ore body are respectively -87‰ and +6.0‰, the fluite inclusion δ13CPDB of
quartz in the ore body is -8.4‰, which show the H, C and
O isotope compositions of the magmatic water.
Close
Chapter 7-33 · Stable isotope composition of the Dalucao rare earth deposit in western Sichuan
Fluorite δD of in the ore body range from -119‰ to 83‰, averaging around -99‰. Its δ18OH2O range from 13.6‰ to -9.6‰, with an average of -11.6‰, indicating
that the ore-forming fluid is a mixed fluid of the magmatic water and the meteoric water.
The fluid inclusion δD of the bastnasite range from 89‰ to -79‰, showing that the ore-forming fluid is a
magmatic water. The bastnasite δ13CPDB is about -8.0‰,
indicating the characteristic of mantle carbon.
851
fluorites in the ore body was from a mixed carbon source,
and the fluid inclusion carbon of quartz was from mantle.
The rare earth partitioning of the bastnasite, the ore and
the alkali complex is all Ce>La>Nd, and Ce-rich, showing
the mantle features of the metallogenetic material in the rare
earth deposit. The 134Nd/144Nd of the rare earth deposit range
from 0.512297 to 0.512313, indicating that the rare earth
elements were mainly derived from the upper mantle.
4
Conclusions
3.3 Derivation of the metallogenetic material
In the graph of δ18O vs δD for ore-forming fluids (Fig. 2),
it is evident that the fluid-inclusion water in quartz belong to magmatic water, and the fluid-inclusion water in
fluorite belong to meteoric water, indicating that the oreforming fluid was a mixed fluid of the magmatic water
and the meteoric water.
According to the Si isotope compositions of the ore
body quartz and whole rock, it can help us infer that the
Si may be from a deep magmatic source area.
The carbon isotopic features suggest that carbon of the
bastnasite was from mantle, the fluid inclusion carbon of
The rare earth elements of Dalucao deposit are mainly from
the mantle. Si may also be from a deep magmatic source.
The ore-forming fluid was a mixture fluid of the magmatic
water and the meteoric water. The carbon of bastnasite was
deduced from the mantle and the carbon of the ore-forming fluid in bastnasites was from a mixture carbon source
area. It is further suggested that the source rocks of the orebearing aegirine-augite syenite are probably early-formed
alkali rich rocks in Triassic period or Carboniferous-Permian period. The ore-bearing aegirine-augite syenite was
mostly formed by remelting, ascending and emplacement
of the source rocks under the activation of mantle plume
Close
852
Wan Defang · Tian Sihong · Luo Mei · Jiang Shaoyong
References
and tectonic mobilization in the Tertiary-Quaternary period. C, H, O, and Si isotope compositions of the deposit
indicate that Dalucao rare earth deposit was a hydrothermal vein type deposit of the rich light rare earth element,
which was formed in the Tertiary-Quaternary period.
Clayton RN, O’Neil JR, Mayeda TK (1972) Oxygen isotope exchange
between quartz and water. J Geophys Res 77: 3057-3059
Ding T (1994) Silicon isotope geochemistry. Geol Pub House, Beijing,
23-30
Matsuhisa Y, Goldsmith JR, Clayton RN (1979) Oxygen isotopic fractionation in the systemquartz-albite-water. Geochim. Cosmochim
Acta 43: 1131-1140.
O’Neil JR, Taylor HP (1967) The oxygen isotope and cation exchange
chemistry of feldspars. Am Mineral 52: 1414-1418
Pu G (2001) REE mineralization evolution in Panxi rift and basic
metallogenic feature in Himalaya age. Study on the endogenetic
minerallization in Hymalaya age, China. China Seismol Press,
Beijing, 104-113 (in Chinese)
Shen W (1987) Geology of stable isotope. Atom Ener Pub House,
Beijing: 123-125 (in Chinese)
Tang L, Yang D, Liu S, Wang Z, Ye X, Chen Z (1985) The double structural feature of Panxi rift. The collected works of Panxi rift, China.
Geol Pub House Beijing: 72-84 (in Chinese)
Taylor HP (1968) 18O/16O ratios coexisting minerals in glancophanebearing metamorphic rock: Bull Geol Soc Am 79: 1727-1756
Yuan Z, Shi Z, Bai G, Wu C, Li X (1995) Mouniuping REE deposit,
Mianning County, Sichuan Province. China Seismol Press, Beijing:
103-105 (in Chinese)
Close
Chapter 7-34
7-34
Preliminary study on the Chinese continental
mineralization system
Wang Denghong
Institute of Mineral Resources, CAGS, Beijing, 100037, China
Chen Yuchuan
Chinese Academy of Geological Sciences (CAGS), Beijing, 100037, China
Abstract. China is enriched in mineral resources. How to systematically deduce the regularity of mineralization in order to serve for prospecting is the main purpose of this paper. The Chinese continental
mineralization system (CCMS) can be referred to as the whole group
of mineral deposits located in the present continent of China and
their genetically related geological factors. The CCMS consists of 214
minerogenic series of 11 geological periods from Early Archean to
Cenozoic, including at least 978 patterns of representative mineral
deposits.The CCMS is the final result of mineralization formed through
the whole evolution history of Chinese continental crust.
Keywords. Chinese continental mineralization system, minerogenic
series, metallogenic prognosis, evolution regularity
1
Introduction
After a long history of mining (at least 3000 years), especially large-scale geological exploration conducted since the
founding of the People’s Republic of China (1949), 171 kinds
of mineral resources have been discovered up to present.
Among these, 156 commodities have explored reserves, including 9 types of energy resource, 54 metallic minerals, 90
industrial minerals, plus groundwater, mineral water, and
carbon dioxide gas. The total value of potential reserves
places China third in the world. Various deposits are among
the richest in the world, including rare earths, W, Sn, Sb,
Mo, Bi, Be, coal, magnesite, barite, fluorite, talc, graphite,
bentonite, fireclay, asbestos, gypsum, wollastonite, diatomaceous earth, and building stone. On the other hand, the country is lacking oil, high-grade iron, Cr, Mn, Cu, PGE, potash
salt, and diamond. By now, about 200,000 localities of ore
deposits or mineral occurrences have been discovered.
Among these, 20,000 ore deposits have been investigated in
detail, including 90 super giant deposits (Fig. 1; Chen 1999).
However, little geological work has been done in the vast
western territory of China and for depths greater than 500
m, suggesting a great potential for further discoveries. Owing to the diversity of geological settings for mineralization in China, there is great potential for ore prospecting
(Guo, 1987; Chen 1999).
2
Concept of Chinese continental mineralization
system and related terms
In this paper, we refer the Chinese continental mineralization system (CCMS) as the whole group of mineral
deposits located in the present continental crust of China
and their genetically related geological factors. All mineral deposits located in the present continental crust of
China formed during the history of continent evolution.
The concept of CCMS contrasts with the term Chinese
oceanic mineralization system (COMS), both the CCMS
and the COMS compose the Chinese Mineralization System (CMS), while the CMS is part of the global mineralization system (GMS). The global mineralization system
can be divided into a series of sub-systems geographically. The GMS can be divided into sub-systems according to different classification systems, such as spatial subsystems, temporal sub-systems (Mesozoic mineralization
system, Cenozoic mineralization system and so on), and
genetically sub-systems (magmatic mineralization system,
sedimentary mineralization system and metamorphic
mineralization system). Thus, the CCMS is in fact a complex big system composed of different levels of sub-systems, which related to each other structurally, regularly,
inevitably and recognizably. By the study of CCMS, the
wholly, knowledge about mineralization can be concluded
systematically and sequentially, instead of individually,
fragmentally or randomly. In this paper, we will pay more
attention to the CCMS, because it’s forming history shows
an important aspect of the continental evolution history
of China and provides valuable clues and indispensable
examples for the understanding of global mineralization
system. The relationships among different deposits and
the relationships between mineralization and its geological
history and tectonic setting are very important for the
study of CCMS.
The present Chinese continental crust includes relative stable regions (paleo-plates or massif) and active belts
(suture zones and/or collision belts). There are three large
landmass or plates and four active belts in China (Fig. 2).
The three main landmass include: (1) the North China
landmass, which were formed after the Lvliang Movement
(1800 Ma) and includes a basement of Archean and/or
Lower Proterozoic metamorphic rocks; (2) the Tarlimu
landmass, formed after the Jinning Movement (1000 Ma)
and has a basement of pre-Sinian metamorphic rocks;
(3) the Yangtze landmass, also formed after the Jinning
Movement and its basement consists mainly of Proterozoic metamorphic rocks.
Close
854
Wang Denghong · Chen Yuchuan
The main active belts include: (1) the Tianshan- Xing’an
active belt, which consist with a series of fold belts and
micro-plates and formed after the Caledonian- Hercynian
movement; (2) the Kunlun-Qilianshan- Qinling active belt,
located between North China and South China and activated at different epochs of Jinning, Caledonian,
Hercynian, Indo-Chinese, Yanshanian and Himalayan; (3)
the Sichuan-Yunnan-Qinghai-Tibet active belt, which is
the most important active belt of Tethys- Himalayan in
the southwestern China; and (4) the western circum-Pacific active belt, mainly overprinted on the Paleozoic and
pre-Paleozoic tectonic belts in the eastern China and featured by strong activation of Mesozoic-Cenozoic volcanism-magmatism in East China, large-scale granitoid intrusion in the Nanling Region (Chen et al. 1989), NE-NNEtrending movement of blocks and rifting-magmatism in
the margin area of paleo-landmass.
3
Manifestation of the CCMS
Generally speaking, the CCMS is a natural system consisting of more than 200 thousand localities of ore deposits or mineral occurrences. Obviously, it is difficult to
reveal the nature and complexity of CCMS by single deposits, deposit types, mineralized belts, host rocks, or other
factors related to mineralization. In this paper, we apply
the terminology of minerogenic series to describe the
CCMS in brief. The concept of CCMS is different from
that of minerogenic series presented by Cheng et al. (1979,
1983), which groups a series of mineral deposits related
to each other genetically within a certain setting of geological environment and within a certain stage of geological history (Wang et al. 2002). However, because each
minerogenic series bases on the four most important factors (ore-forming age, tectonic setting, geologic event and
mineral assemblage and/or metal association), it is suitable to apply the nomenclature of minerogenic series to
construct the framework of CCMS. Generally speaking, we
have divided the CCMS into different sub-systems according to geological time, and each sub-system consist of secondly sub-system of mineralization based on geological
setting of the same geological time. Given a certain geological setting of a certain geological time, each minerogenic
series refers to a certain group of metals and/or mineral
resources and/or energy resources related to a certain geologic process. Thus, minerogenic series is the preferred and
integrant unit to make up of the CCMS. As a whole, the
CCMS consists of 214 minerogenic series of 11 geological
periods from Early Archean to Cenozoic, including at least
978 patterns of representative mineral deposits.
Close
Chapter 7-34 · Preliminary study on the Chinese continental mineralization system
4
Application significance of the CCMS
Because the CCMS can be build up by basic unit of
minerogenic series, minerogenic series and their relationship with the evolution history of China continental crust
then become the most important aspect of our present
research. As to each minerogenic series, all the mineral
deposits are grouped together genetically rather than randomly. For example, the Triassic sedimento-minerogenic
series of salt and coal deposits associated with marine
carbonaceous rocks and paralic clastic rocks within the
Sichuan basin, which is one of the above 214 minerogenic
series of the CCMS, consists of a series mineral deposits
including the gypsum deposits (named as Nongle-type)
and the celestite deposits (named as Chongqing-type)
hosted within the Jialingjiang Formation (T12j), including the polyhalite deposits (named as Quxian-type) within
the Jialingjiang Formation and the Leikoupo Formation
(T21l), including the halite deposits (named as Weixi-type)
within the Leikoupo Formation, and including the coal
deposits (named as Yongrong-type) within the Xujiahe
Formation (T32-3x). The evolution trend of mineral deposits from salt to coal gradually is in accordance with
the evolution history of the Sichuan basin changing from
oceanic to terrestrial facies at its waning stage. Such trend
855
of mineralization evolution can thus be deduced as a piece
of regularity for prospecting in the Sichuan basin and in
other similar basins further.
In a broad sense, in a geosyncline’s environment such
as the Northern marginal belt of the North China Platform of Proterozoic, the Kunlun- Qilianshan-Qinling belt
of Proterozoic-Paleozoic, the Altay tectonic belt of Paleozoic ,and the Tethys belt of Mesozoic, mineral deposits
usually change from base metal deposits of VHMS-type
formed at its early stage to rare metal deposits associated
with magmatism at its folding or mountain building stage,
and to gold deposits controlled by regional structures at
its late stage of structural adjustment within an actually
continental setting. Such trend is partly similar to that of
an Wilson cycle, but each minerogenic series is different
from each other because of its unique geological time of
ore-forming, tectonic environment, special association of
mineral resources and genetic relationship with other
geologic process. Thus, the study of CCMS also can provide a new approach for deduction the evolution history
of the Chinese continent crust.
In addition, the study of CCMS can contribute to
metallogenic prognosis. For instance, the number of
minerogenic series become more and more from Archean
to Proterozoic to Paleozoic to Mesozoic and to Cenozoic.
Close
856
Wang Denghong · Chen Yuchuan
However, the number of Yanshanian minerogenic series
shows a negative anomaly calculated on the same scale
of geological time, suggesting that there is still a good
potential for prospecting Yanshanian minerogenic series
in China. Recently, numerous new deposits of Mesozoic
age have been discovered both in northwestern China
(such as the Baishan Mo deposit in Xinjiang, dated
at 229±3Ma by a Re-Os isochron on molybdenite)
and in south-eastern China (such as the Taoxikeng wolframite deposit in south Jiangxi, the Baolun gold deposit
in Hainan). Some important deposits discovered earlier
have also been proved to be of Mesozoic age by systematic dating. For example, the famous rare metal deposit
hosted within the No.3 pegmatite-vein in Keketuohai
mine, North Xinjiang, yields 40Ar/39Ar isochron ages ranging from 177.9 Ma to 148 Ma (Wang et al. 2002). This
deposit has been recognized as a Hercynian deposit for
nearly a century.
5
Evolution of the CCMS
In general, the concept of CCMS can also be summarized as the systematic combination of all the minerogenic
series that formed during the whole evolution history
of the present continental crust in China. So, the CCMS
can be divided into Archean, Proterozoic, Paleozoic, Mesozoic, and Cenozoic sub-systems of mineralization as
follows:
1. Archean sub-systems occurred in nucleus of the Chinese
continental crust, dominated by BIF-type deposits,
VHMS-type Fe, Cu, Pb, and Zn deposits, gold, graphite,
and sillimanite deposits associated with metamorphic
rocks;
2. Proterozoic sub-systems occurred in the marginal rift
setting peripheral to the Archean Chinese continental
shield, also dominated by Fe, Cu, Ni, REE, Pb, Zn deposits related to magmatism and sedimentary process
and Au, B, P, magnesite, graphite, andalusite, and sillimanite deposits related to metamorphic process, and
featured by massive Cu-Ni deposits related to maficultramafic rocks;
3. Paleozoic sub-systems occurred in the main orogenic
belts around the Proterozoic Chinese continent, featured by more complex association of elements and/
or mineral resources than that of Proterozoic and by
typical plate tectonic environment;
4. Mesozoic-Cenozoic sub-systems occurred both around
and within the Paleozoic Chinese continent (Chen and
Wang 2001), featured by porphyry-type copper deposits, skarn-type Fe-Cu deposits, granite-related W, Sn,
Bi, Mo, REE, Rare metal, Pb, Zn, Sb, Ag, Au, Hg deposits, placer deposits, industrial mineral deposits formed
within weathering crust, energy resources formed
within continental basins and so on, with banded iron
formation and mafic-ultramafic massive Cu-Ni deposits disappearing (Wang et al. 2000).
Close
Chapter 7-35
7-35
Origin and evolution of Sn- and Cu-rich fluids in the
Dajing tin-polymetal deposit - evidence from
LA-ICP-MS analysis of individual fluid inclusions
Wang Lijuan, Wang Yuwang, Wang Jingbin
Beijing Institute of Geology for Mineral Resources, Beijing 100012, and Key Laboratory of Mineral Resources Institute of
Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
Zhu Heping
Key Laboratory of Mineral Resources Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029,
China
Günther Detlef
ETH, Swiss Federal Institute of Technology, 8092 Zürich, Switzerland
Abstract. LA-ICP-MS analysis of the composition of individual fluid
inclusions indicate that shallow-originated Sn-rich fluids and deeporiginated Cu-rich fluids mix at moderate to low temperature and
low salinity, eventually resulting in the formation of Cu and Sn mineralization in the Dajing deposit.
Keywords. Dajing, single inclusion, LA-ICP-MS anslysis, Cu-rich fluids,
Sn-rich fluids
The Dajing tin-polymetal deposit is located at the northern margin of North China Craton (Zhao and Zang 1997;
Wang et al. 2001). Quartz and fluorite are intergrown with
cassiterite and chalcopyrite. Chalcopyrite can be found
included in fluorite. Abundant fluid inclusions were found
in fluorite. They are large with a gas/liquid ratio of 10%.
Chalcopyrite crystals can be found in some fluid inclusions. It is deduced that these fluid inclusions with chalcopyrite crystals are trapped from Cu-rich fluids. Cassiterite can be found included in quartz. Fluid inclusions
in quartz are small in size and some are gas inclusions
with high gas/liquid ratios. Microthermometric data show
that the chalcopyrite-bearing fluid inclusions in chlorite have
low to moderate temperature and low to moderate salinity
whereas gas inclusions in quartz have moderate to high
temperature and low salinity. Therefore, it is inferred that
Cu-rich fluids are low to moderate temperature and low to
moderate salinity whereas the Sn-rich fluids are moderate
to high temperature and low salinity. The intergrowth of
Sn and Cu probably resulted from mixing of Cu-rich fluids
and Sn-rich fluids (Wang et al. 2000).
To further ascertain the origin and evolution of the
Sn-rich and Cu-rich fluids in the Dajing deposit, LA-ICPMS analyses on individual fluid inclusions with different
temperature, salinity, and occurrence in quartz and fluorite from the Sn-Cu orebodies were carried out at Swiss
Federal Institue of Technology, Switzerland in February,
2004. LA-ICP-MS is the most advanced analysis method
for the composition of single fluid inclusions. Most of
the reseach focused on fluids of high temperature and
high salinity (Audeat et al. 1998; Günther et al. 1998;
Günther and Heinrich 1999). Because some fluid inclusions in fluorite contain chalcopyrite crystals, we made
LA-ICP-MS analysis of individual fluid inclusions on them
and take their compositions as representative of the Curich fluids. Near the Dajing deposit, there is a tin deposit
named Huanggangliang, which belongs to the same tinmineralization belt as the Dajing deposit. Both deposits
have quite similar geological background (Li et al. 2001;
Wang et al. 2001). We analyzed the fluid inclusions in
quartz associated with cassiterite from the Dajing deposit
and primary fluid inclusions in fluorite from the
Huanggangliang deposit with LA-ICP-MS analysis. The
Close
858
Wang Lijuan · Wang Yuwang · Wang Jingbin · Zhu Heping · Günther Detlef
results are quite similar. Therefore, the LA-ICP-MS analytic results of individual fluid inclusions in quartz associated with cassiterite from the Dajing deposit were taken
as representative of the Sn-rich fluids.
Tables 1 and 2 are the LA-ICP-MS analytic results of individual Cu-rich and Sn-rich fluid inclusions, respectively.
Table 1 shows that the Cu-rich fluids have higher Cu
contents than Sn, have Sr contents one to several order of
magnitude higher than Rb, and are relatively richer in
Na than K. Table 2 shows that the Sn-rich fluids have higher
Sn contents than Cu, have Rb contents one to several oder
of mragnitude higher than Sr, and are relatively richer in
K than Na. Based on the compositions of representative
Cu-rich and Sn-rich fluids, we infer whether other fluid
inclusions with different occurrence, temperature and
salinity in quartz and fluorite belong to Cu-rich or Snrich fluids, and thereby trace the origin and evolution of
these fluids.
Cu-rich and Sn-rich fluid inclusions are listed in
Tables 3 and 4, respectively.
Figure 2 shows that both the Cu-rich and the Sn-rich
fluids have a similar evolutionary trend from high to low
temperature and the two kinds of fluids probably mix at
moderate temperature, resulting in mineralization.
The Sr and Rb concentrations in the fluids are important indicators for the fluid source. According to Zhao et
Close
Chapter 7-35 · Origin and evolution of Sn- and Cu-rich fluids in the Dajing tin-polymetal deposit - evidence from LA-ICP-MS analysis of individual fluid inclusions
859
shallow-originated Sn-rich fluids and the deep-originated Cu-rich fluids mix at the stage of moderate to low
temperature and low salinity and result in the formation of Cu and Sn mineralization in the Dajing deposit.
4. To our knowledge, there have been no reports about
LA-ICP-MS analysis on individual fluid inclusions with
such low temperature, low salinity and small size as in
the Dajing deposit. The results demonstrated that the
LA-ICP-MS analysis of individual fluid inclusions has
practical applications in studying ore-forming processes in polymetal ore deposits.
References
al (1997), Sr is enriched in the early stage of magma differentiation, whereas Rb is enriched in the late stage of
magma differentiation. Therefore, the ratio of Rb/Sr increases with magma differentiation, from an average of
about 0.5 at the early stage to above 10 at the late stage.
The Cu-rich fluid in the Dajing deposit are highly enriched in Sr, indicating that the fluids are derived from
the deep, whereas the Sn-rich fluids are enriched in Rb,
reflecting their derivation from the shallow.
Based on the analyses, several conclusions can be
reached:
1. The Cu-rich fluids have higher Cu contents than Sn,
higher Sr contents than Rb, and are relatively rich in
Na. The fluids are derived from a deep source and are
mainly trapped in fluorite.
2. The Sn-rich fluids have higher Sn contents than Cu,
higher Rb contents than Sr, and are relatively rich in K.
The fluids are shallowly derived and mainly trapped
in quartz.
3. Both the Cu-rich and Sn-rich fluids have an evolutionary trend from high temperature to low temperature. The
Audetat A, Günther D, Heinrich CA (1998) Formation of a magmatichydrothermal ore deposit: Insights with LA-ICP-MS analysis of
fluid inclusions. Science 279: 2091-2094
Günther D, Heinrich CA (1999) Enhanced sensitivity in laser ablation-ICP mass spectrometry using helium-argon mixtures as
aerosol carrier. J Anal Atom Spectrom 14: 1363-1368
Günther, D Audetat A, Frischknecht R, Heinrich CA (1998) Quantitative analysis of major, minor and trace elements in fluid inclusions using laser ablation-inductively couple plasma mass spectrometry. J Anal Atom Spectrom 13: 263-270
Li JW, Shimazaki H, Yoshihide S (2001) Skarns and genesis of the
Huanggang Fe-Sn deposit, Inner Mongolia, China Resource Geol
51: 359-376
Wang L, Wang J, Wang Y, Shimazaki H (2001) Ore-forming fluid and
metallization of the Huanggangliang skarn Fe-Sn deposit, Inner
Mongolia. Sci China (Series D) 44: 735-747
Wang L, Wang Y, Wang J, Jin X, Zhu H (2000) Metallogenetic fluid
study of tin and copper stage from Dajing deposit and its genetic
significance. Acta Petrol Sinica 16: 609-615 (in Chinese with English abstract)
Wang YW, Wang JB, Uemoto T, Wang LJ (2001) Geology and mineralization at Dajing tin-polymetallic ore deposit, Inner Mongolia,
China. Resource Geol 51: 307-320
Zhao Y, Zhang D (1997) Metallogeny and prospective evaluation of
copper-polymetallic deposits in the Da Hinggan Mountains and
its adjecent regions Seismo Press, Beijing: 125-144
Zhao Z (1997) The principle of trace elements geochemistry. Science Press 1-153 (in Chinese)
Close
Close
Chapter 7-36
7-36
Lead and zinc-rich fluid inclusions in Broken Hill-type
deposits: Fractionates from sulphide-rich melts or
consequences of exotic fluid infiltration?
Patrick J. Williams, Dong Guoyi
School of Earth Sciences and 1Predictive Mineral Discovery CRC, James Cook University, Townsville 4811, Australia
Bruce Yardley
School of Earth Sciences, University of Leeds, Leeds LS2 9JT, UK
Thomas Ullrich
Geology Department, The Australian National University, 0200 Canberra, Australia
Chris Ryan
CSIRO Exploration and Mining, School of Geosciences, Monash University, Melbourne 3168, Australia
Terry Mernagh
Geoscience Australia, GPO Box 378, Canberra 2601, Australia
Abstract. High salinity fluid inclusions (Th = 200-550° C) from the
Broken Hill and Cannington “Broken Hill-type” ore deposits in Australia have been analysed by PIXE and LA-ICP-MS. They have high
Pb (>1%) and Zn (>1000 ppm) and Pb/Zn ratios much higher than
those of the majority of crustal brines. Laser Raman studies reveal
the presence of methane and PIXE images show that Pb and Zn are
respectively concentrated in a Pb-K-Cl solid, and the liquid phase.
This indicates that the inclusions have very low total sulphur contents. The Pb/Zn ratios are similar to those of eutectic melts in the
Gn-Sp-Po system whereas Pb/Fe ratios are variable and lower than
those of such melts. If these brines originated by fractionation from
synmetamorphic sulphide-rich melts, then they must been greatly
modified prior to entrapment. An alternative origin involving lateto post-metamorphic interaction of externally-derived brines with
pre-existing sulphide accumulations should also be considered. In
either case, the unique brine chemistry would appear to relate to
the large amounts of sulphides in these systems.
New South Wales (2 pyroxene granulite) and Cannington
in NW Queensland (upper amphibolite). Along with just
a few other ore deposits worldwide these are referred to
as “Broken Hill-type” (BHt) deposits which are defined
more by their high grade metamorphic settings than any
consensus on their origin (e.g. Walters, 1998). It has recently emerged that very Pb- and Zn-rich aqueous fluid
inclusions occur in both large Australian BHt deposits
(Williams et al. 1999). In this paper we show that the chemistry of these brines is unlike any others previously known
and discuss the possible processes by which they may have
formed.
Keywords. Lead, zinc, fluid inclusions, Broken Hill-type deposits, PIXE,
LA-ICP-MS
1
Introduction
Yardley et al. (2003) used compiled natural brine and fluid
inclusion analyses to show that concentrations of many
metals vary systematically with temperature and salinity.
This was taken to indicate that rock buffering is a powerful control on other major chemical influences of solubility, such as pH, fO2 and sulphur abundance. Concentrations of elements such as Mn, Fe, Cu, Zn and Pb in
natural fluids can be predicted within about an order of
magnitude for known temperature and salinity and this
can be viewed as a limiting chemical framework for hydrothermal ore-forming processes
Large and very distinctive Pb-Zn-Ag ore deposits occur in partially melted metamorphic rocks at Broken Hill,
Close
862
Patrick J. Williams · Dong Guoyi · Bruce Yardley · Thomas Ullrich · Chris Ryan · Terry Mernagh
2
Petrography and microthermometry
A large variety of fluid inclusions have previously been
observed in the Broken Hill ore deposit but this have received little attention in the literature (Wilkins 1977; Spry
1978). The current study used rocks displaying evidence
of hydrothermal modification during the retrograde metamorphic history of the deposits. Sample 147001 from Broken Hill is a partly recrystallized quartz-rich rock from
Western A lode in which older “blue quartz” is overprinted
by late stage “white quartz” as described by Wilkins (1977).
Fluid inclusions, predominantly less than 15 microns in
diameter are very abundant as secondary trails in the older
quartz and belong to the same fracture association that
formed the white quartz. Sample 42170 from Cannington
is an example of a quartz vein associated with a form of
Fe- and Cl-rich hornblende alteration which is very common in the deposit (Chapman and Williams 1998). Fluid
inclusions are again abundant in secondary trails (Fig. 1)
and in this case can be very large (up to circa 100 microns).
In both samples, the vast majority of inclusions at room
temperature are composed of liquid, a small vapour bubble,
and number of solids. The latter have been investigated by
microprobe in opened inclusions, in PIXE images and (42170
only) by laser Raman probe and were consistently found to
include halite, pyrosmalite, and a Pb-K chloride.Some inclusions additionally contain sylvite and/or a Mn-rich carbonate mineral. Vapour bubbles were investigated by laser
Raman probe in 42170 only and were found to consist of
methane. The inclusions in 147001 homogenise by vapour
bubble disappearance at temperatures between 270 and 410°
C and have NaCl equivalent salinities between 30 and 40 wt
%. Those in 42170homogenise by pyrosmalite dissolution
at 400-450° C and have NaCl equivalent salinities between
30 and 40 wt %. In both samples the Pb-K-Cl phase dissolves at temperatures 100-200° below those of total
homogenisation.
3
lyzed by LA-ICP-MS owing to a lack of suitable external
standards, and (c) able to image the distribution of elements between the phases present in the inclusions at
room temperature. Coupled with microthermometric and
laser Raman gas phase data, the images throw light on
the likely abundance and speciation of the critical element sulphur which can not be determined at normal
geological abundance by either microanalytical technique.
PIXE analyses give a quantitative estimate of element abundances to an accuracy of ± circa 50 % though interelement
ratios are determined to a much better level of accuracy as
the main sources of error have similar effects on all elements. LA-ICP-MS data are determined as ratios and estimation of absolute concentrations depends on an independent internal standard such as the estimated abundance of
a component by PIXE or microthermometric salinity estimates (Heinrich et al. 2003). PIXE analysis can only be undertaken of shallow inclusions (typically < 20 microns).
Attempts to achieve controlled laserablation of shallow
inclusions were generally unsuccessful and the analyses
obtained by the two techniques were undertaken on different groups of inclusions.
Pb and Zn data from the three different laboratories
are very consistent (Fig. 2). The average concentrations
estimated by PIXE are 3150 ppm Zn, 36500 ppm Pb in
147001 and 4950 ppm Zn, 30300 ppm Pb in 42170 (ex-
Fluid inclusion geochemistry
In situ microanalysis of fluid inclusions is a new and rapidly developing field and to date there has been a general
lack of studies comparing results obtained using different techniques and in different laboratories. High salinity brine inclusions from Cannington and Broken Hill were
investigated using both proton induced X-ray excitation
(PIXE) analysis (method of Ryan et al. 2001), and laser
ablation inductively coupled plasma mass spectrometry
(LA-ICP-MS) using Excimer laser ablation systems (cf.
Heinrich et al. 2003) at the Australian National University and Leeds University. The PIXE method is (a) relatively insensitive to contamination from the host quartz
and any solid inclusions it contains, (b) able to provide
quantitative data for halogens (Cl, Br) that were not ana-
Close
Chapter 7-36 · Lead and zinc-rich fluid inclusions in Broken Hill-type deposits: Fractionates from sulphide-rich melts or consequences of exotic fluid infiltration?
cluding one outlying analysis with lower concentrations
- cf. Fig. 2). The PIXE images reveal that Zn is codistributed
with Ca and Br in the liquid phase of the inclusions at
room temperatures. Zn/Pb ratios determined by both techniques are all less than 1 and on average around an order
of magnitude below those of high temperature and high
salinity brines in the data set compiled by Yardley et al.
(2003). This reflects much higher concentrations of Pb in
the Broken Hill and Cannington inclusions than have been
measured in other natural high salinity fluids excepting
a single case where extreme Pb enrichment was deduced
to occurred in a fluid involved in retrograde hydration of
granulites (Svenson et al. 1999). Pb/Ag ratios measured
by LA-ICP-MS are between 640 and 1470 in sample 147001
and between 200 and 800 in sample 42170.
Br/Cl ratios determined by PIXE in sample 42170 are
in the range 0.0003 to 0.0016 which is distinctly lower
than seawater and magmatic brines as measured from
porphyry copper deposits (cf. Kendrick et al. 2003). The
PIXE investigation of sample 147001 was undertaken under conditions of comparatively poor instrumental performance and meaningful data were not obtained for Br
in this case.
4
Discussion
The studied fluid inclusions from Broken Hill and
Cannington have much higher Pb concentrations and Pb/
Zn ratios than fluid inclusions with similar salinities from
other geological settings suggesting that they result from
some process which is specific to this sort of ore deposit.
Mavrogenes et al. (2001) have shown that compositions
in the FeS-ZnS-PbS-Ag2S system would have been partially-molten under peak metamorphic conditions at Broken Hill (though it is not clear that this would also have
been the case at Cannington). One possible explanation
for the unusual fluid inclusions is that they represent aqueous phases that equilibrated with sulphide melts. If this
is the case then element abundances in the inclusions
should reflect their activity ratios in the melt. The FeSZnS-PbS eutectic as determined by Mavrogenes et al.
(2001) has Pb:Fe:Zn (by weight) approximating to 12:2.5:1
(Fig. 3) and all melts below 900° C have low ZnS compared to the other two components. High Pb/Zn ratios
are therefore to be expected in fluids equilbrated with
FeS-ZnS-PbS melts and the average ratios measured in
the fluid inclusions from samples 147001 and 42170 are
very similar to the ratio of the eutectic composition Furthermore, Mungall and Brenan (2003) established that Cl
has an affinity for Fe-Cu-Ni-S melts (due to similarities
with sulphur) and predicted that aqueous fluids evolved
from such melts should have low Br/Cl ratios (cf. the fluid
inclusions in 42170). This would be also expected to be a
feature of other sulphide melt systems. However, it is not
a diagnostic feature as low ratios could also reflect salin-
863
ity derived from evaporitic halite or its preserved signature in metamorphic rocks.
Other features of the fluid inclusions are less easily
reconciled with a relationship to sulphide melts. Thermometric results and paragenetic associations with
retrograde hydrous and Cl-bearing silicates suggest the
inclusions were trapped at temperatures several 100°s
below those of the metamorphic peaks in the two systems. At Cannington, metamorphic hornblendes did not
pass through their 40Ar-39Ar blocking temperatures until some 40 million years after the partial melting event
recorded in the gneissic host rocks (Pollard et al. 1997;
Giles and Nutman 2002). Aqueous fluids present at peak
conditions would have somehow had to have avoided
extraction by silicate melts and remained trapped in
the system throughout this period to have been preserved
in fluid inclusions. Fluids from both locations were
evidently strongly undersaturated in Pb and Zn when
trapped and must have very low reduced sulphur contents given the phase distribution of metals at room
temperature. Large chemical variations are present including those of Pb/Fe (all lower than eutectic melt; Fig. 3)
and Pb/Ag (different in the two samples) suggesting that
the fluids were involved in chemical reactions at the time
the inclusions were trapped. An alternative origin involving late- to postmetamorphic interaction of externallyderived brines with pre-existing sulphide accumulations
should also be considered. In this case the high Pb/Zn
ratio might reflect the higher solubility of galena compared to sphalerite in high temperature brines (Hemley
et al. 1992). In either case the unique chemistry would
appear to relate to the large concentrations of sulphides
in these systems.
Close
864
Patrick J. Williams · Dong Guoyi · Bruce Yardley · Thomas Ullrich · Chris Ryan · Terry Mernagh
Acknowledgements
This work was supported by AMIRA, the ARC and the
Predictive Mineral Discovery CRC.
References
Chapman LH, Williams PJ (1998) Evolution of pyroxene-pyroxenoid-garnet alteration at the Cannington Ag-Pb-Zn deposit,
Cloncurry district, Queensland, Australia: Econ Geol 93: 13901405
Giles D, Nutman AP (2002) SHRIMP U-Pb monazite dating of 16001580 Ma amphibolite facies metamorphism in the southeastern Mt Isa Block, Australia. Austr J Earth Sci 49: 455-465
Heinrich CA, Pettke T, Halter WE, Aigner-Torres M, Audétat A,
Günther D, Hattendorf B, Bleiner D, Guillong M, Horn I (2003)
Quantitative multi-element analysis of minerals, fluid and melt
inclusions by laser-ablation inductively-coupled plasma massspectrometry: Geochim Cosmochim Acta 67: 3473-3496
Hemley JJ, Cygan GL, Fein JB, Robinson GR, D’Angelo WM (1992)
Hydrothermal ore-forming processes in the light of studies in
rock-buffered systems: I, iron-copper-zinc-lead sulfide solubility relations: Econ Geol 87: 1-22
Kendrick MA, Burgess R, Pattrick RAD, Turner G (2001) Fluid inclusion noble gas and halogen evidence on the origin of Cuporphyry mineralising fluids: Geochim Cosmochim Acta 65:
2651-2668
Mavrogenes JA, Macintosh JW, Ellis DJ (2001) Partial melting of the
Broken Hill galena-sphalerite ore. Experimental studies in the
system PbS-FeS-ZnS-(Ag2S). Econ Geol 96: 205-210
Mungall JE, Brenan JM, (2003) Experimental evidence for the
chalcophile behavior of halogens. Can Mineral 41: 207-220
Pollard PJ, Perkins C (1997) 40Ar/39Ar geochronology of alteration
and Cu-Au-Co mineralization in the Cloncurry district, Mount
Isa Inlier. AMIRA P438 Cloncurry Base Metals and Gold Final
Report, Section 3, 40pp
Ryan CG, McInnes, BM, Williams PJ, Guoyi Dong, Tin Tin Win, Yeats CJ
(2001) Imaging fluid inclusion content using the new CSIROGEMOC nuclear microprobe. Instr Meth Physics Res B 181: 570-577
Spry PG (1978) The geochemistry of garnet-rich lithologies associated with the Broken Hill orebody, N.S.W., Australia. Unpubl MSc
thesis, University of Adelaide, 129pp
Svenson H, Jamtveit B, Yardley B, Engvik AK, Austrheim H, Broman C
(1999) Lead and bromine enrichment in eclogite-facies fluids: extreme
fractionation during lower-crustal hydration. Geology 27: 467-470
Walters SG (1998) Broken Hill-type deposits. AGSO J Austr Geol
Geophys 17: 229-237
Wilkins RWT (1977) Fluid inclusion assemblages of the stratiform Broken Hill ore deposit, New South Wales, Australia. Science 198: 185-187
Williams PJ, Dong Guoyi, Prendergast K, Pollard PJ, Ryan CG (1999)
Metasomatism and metal mobility in Broken Hill-type deposits.
In: Stanley CJ et al. (eds) Mineral Deposits: Processes to Processing. Balkema, Rotterdam, pp 999-1002
Yardley B, Bennett A, Banks D (2003) Controls on the chemical composition of crustal brines. J Geochem Expl 78/79: 133-135
Close
Chapter 7-37
7-37
Isotopic composition and source of lead in the
Jinding Zn-Pb Deposit, Yunnan, China
Zeng Rong, Zhao Shihua, Gao Yongbao, Li Yongqiang
Faculty of Earth Sciences and Territory Resources, Chang’an University, Xi’an, Shaanxi 710054, China
Abstract. The Jinding Zn-Pb deposit is the largest Zn-Pb deposit so
far discovered in China. To study the source of the mineralizing materials, we analyzed its lead isotopes. We found that the isotopic
composition of lead in coarse-grained and fine-grained galenite
crystals are very different. The ratio of lead isotopes in fine-grained
galenite is higher, and lead isotopes are distributed over the lead
development curve of the orogenic belt which is located in the range
of upper crustal lead. All these indicate that the lead of fine-grained
galenite comes mainly from stratigraphy. In contrast, the ratio of
lead isotopes in coarse-grained galenite is lower and lead isotopes
are distributed beneath the lead development curve of the orogenic belt, as well as in the upper mantle and lower crust.
Keywords. Lead isotope, composition, source, Jinding Pb-Zn deposit,
Yunnan, China
1
Previous research
The Jinding Zn-Pb deposit is one of the seventeen giant
Zn-Pb deposits in the world, with more than 10 million
tons of Zn+Pb reserves. It is also the largest Zn-Pb deposit so far discovered in China. The Jinding Zn-Pb deposit is sediment-hosted, however its genetic origin differs from other sediment-hosted Zn-Pb deposits such as
Mississippi Valley-type (MVT) deposits, Sedimentary
exhalative (Sedex) deposits and Sandstone-type (SST)
deposits. The Jinding Zn-Pb deposit may represent a new
type of sediment-hosted deposit. Geologists have been
studying the Jinding Zn-Pb deposit intensively since the
1980s, and during the twenty years of study there have been
many different opinions about the genesis of the lead ores.
Some think the lead in the ores comes mainly from the
deep mantle, with minor input from the crust (Zhao 1989).
Some argue that the lead in the ores is derived from the
mantle, but has been hybridized by lead from the crust (Zhou
and Zhou 1992). And others consider that the lead in the
ores is derived from the lower crust and is related to the
interaction between lead in the lower crust and in the
sedimentary rocks (Zhang and Shao 2002).
2
Geologic characteristics of the ore zone
The Jinding Zn-Pb deposit occurs in a Cenozoic dome
structure whose center is eroded. There are six ore blocks
(Beichang, Paomaping, Jiayashan, Xiponanchang,
Baicaoping and Fengzishan) surrounding the dome. The
slaty, veined, phacoidal and stratoid orebodies are dis-
tributed around the center of dome and tilt in towards
the deep dome. At the top of the dome the orebody is
thicker. Two stratigraphic systems are present in the
Jinding area, referred to as the autochthonous system and
the allochthonous system. The former refers to strata of
the Cretaceous Hutousi Formation (K2h) and the Paleocene Yunlong Formation (E1ya-E1yb). The allochthonous
system includes the Lower Cretaceous Jingxing Formation (K1j), Mid-Jurassic Huakaizuo Formation (J2h), the
Upper Triassic Maichuqing Formation (T3m) and the
Sanhedong Formation (T3s). The Zn-Pb ores are hosted
in the sandstones of the Lower Cretaceous Jingxing Formation (K1j) and the Upper Yunlong Formation (E1yb),
which are separated by a thrust-nappe structure (F2).
There are two distinct types of ores at the Jinding deposit, breccia-type ores and sandstone-type ores. The textures associated with the breccia-type ores include metasomatic and solutional texture, concentric zonal texture,
massive structure, brecciated structure and reticular vein
structure. These ores are hosted in the Upper Yunlong
Formation (E1yb), east of ore district. The sandstone-type
ores consist mainly of cementation texture and disseminated structure and are hosted in the middle and west of
the ore district.
3
Isotopic composition and source of lead
To study the source of the mineralizing materials of the
Jinding Zn-Pb deposit, we choose the homogeneous
galenite samples to do comparative study on lead isotopes
(Table 1). We find that the composition of lead isotopes
from coarse-grained and fine-grained galenite is different (Fig. 1): Fine-grained galenite 206Pb/204Pb 18.15~18.60,
207
Pb/ 204Pb 15.612~ 15.64, 208Pb/ 204Pb 38.287~ 38.66;
Coarse- grained galenite 206Pb/204Pb 18.03~19.21, 207Pb/
204Pb 15.252~15.55, 208Pb/204Pb 37.800~38.930. The ratio
of lead isotopes in fine-grained galenite is higher, and
lead isotopes are distributed over the lead development
curve of the orogenic belt which is located in the range of
upper crustal lead. All these indicate that the lead of finegrained galenite comes mainly from stratigraphy.
In contrast, the ratio of lead isotopes in coarse-grained
galenite is lower and lead isotopes are distributed beneath
the lead development curve of the orogenic belt, as well
as in the upper mantle and lower crust. The composition
of lead isotopes in three plagioclases crystals and garnets
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866
Zeng Rong · Zhao Shihua · Gao Yongbao · Li Yongqiang
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Chapter 7-37 · Isotopic composition and source of lead in the Jinding Zn-Pb Deposit, Yunnan, China
867
derived fluids rich in CO2 (jingdin and Chaoyang 1991).
The isotopes of He, Ne, Xe also indicate that there are
mantle components in the Jinding Zn-Pb deposit (Xue
and Chen 2003). These data are consistent with the lead
isotope data from coarse-grained galenite distributed in
the upper mantle. According to the data, we may conclude
that there are at least two metallogenic epochs in the
Jinding Zn-Pb deposit: (1) The epoch of fine-grained
galenite; (2) The epoch of coarse-grained galenite. The
source of the mineralizing materials is different between
the two epochs. The mineralizing materials of fine-grained
galenite come mainly from stratigraphy, while mineralizing materials of coarse-grained galenite come mainly
from the upper mantle and lower crust. The study on the
controlling factors of evolution of the Lanping-Simao
basin also indicates that the mineralization of the Jinding
Zn-Pb deposit involves the interaction between crust and
mantle (Yin and Fan 1990). All the data and analyses validate the theory of a multiperiod and multisource origin
for the Jinding Zn-Pb deposit.
References
derived from the enclosures of the lower crust in alkalic
rocks of western Yunnan is: 206Pb/204Pb 18.135~18.187,
207Pb/204Pb 15.335~15.388, 208Pb/204Pb 37.836~38.899.
These values are identical to the coarse-grained galenite
samples whose values are the lowest, so we can conclude
that coarse-grained galenite come from the lower crust.
The REE geochemical data indicate that the mineralizing
materials of the Jinding Zn-Pb deposit are mainly mantle-
Wang J, Li C (1991) REE geochemistry of the Jinding superlarge PbZn deposit Geochemica 19: 359~365
Xue C, Chen Y (2003) Geology and isotopic of Helium, Neon, Xeon
and Metallogenic age of the Jinding and Baiyangping Ore Deposits Northwest Yunnan, china. Science in China, Ser. D,
46:789~800
Yin H, Fan W (1990) Deep processes and mantle-crust compound
mineralization in the evolution of the Lanping-Simao MesozoicCenozoic Diwa Basin in Western Yunnan, China 4: 113~124
Zhang Q, Shao A (2002) Lead isotopic composition and lead soure
of polymetallic deposits in the Large Ore Assembly District in
the Langping Basin. Acta Mineralogica Sinica 22: 147~153
Zhao X (1989) stable isotope geochemistry of the Jinding lead-zinc
ore deposit, Yunnan, Science in the Earth–The Journal of Geology University of China 14: 495~501
Zhou W, Zhou Q (1992) A study on the isotopic composition of Pb
and Sinc in the Lanping Pb-Zn Deposit, Yunnan, Geochemica 2:
141~148
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Chapter 7-38
7-38
Geology and geochemistry of the Furong Tin Deposit,
Hunan Province, P. R. China
Zhao Kuidong, Jiang Shaoyong, Jiang Yaohui
State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, China
Abstract. Recently, a giant tin deposit, the Furong deposit, has been
discovered in the Qitianling granitoid, Hunan, South China. The tin
mineralization occurs as disseminated crystals or veins of cassiterite. The cassiderite is found in narrow envelopes of chlorite alteration within the granite. The Qitianling granite has distinctly different petrology and mineralogy from common S-type tin granites.
The oxygen and hydrogen isotope data indicate a dominant influence of surface-derived meteoric water associated with chlorite alteration. Variations in δ18O of fresh and altered granites are due to
continuous isotopic exchange reaction between hydrothermal fluids and granites at variable water/rock ratios. The sulfur isotope compositions of sulfides from the tin ores indicate that both the granite and the strata supported the sulfur for mineralization. The Pb
isotopic compositions of sulfides are same as those of feldspars from
the granite. Thus, Pb in the ores might come from the granite. Fractional crystallization of the magma and tin deposition directly from
exsolved magmatic-hydrothermal fluids may not be the major
mechanism for the tin mineralization in this deposit. Instead, we
suggest that interactions between fluids of meteoric origin and the
granite may contribute to the release and deposition of tin.
Keywords. Geochemistry, Furong tin deposit, Qitianling granite, South
China
1
Introduction
The Furong deposit is a newly discovered giant tin deposit in Hunan Province, P. R. China (Fig. 1). The tin reserve in this deposit has been estimated to be about
600,000 tons (Wei et al. 2002). Tin orebodies mainly occur as veins in the Qitianling granite, which lies in the
middle of the Nanling Granite Belt in South China. Previous workers mainly focused on the geology of this deposit (e.g. Wei et al. 2002; Huang et al. 2003; Wang et al.
2003; Mao et al. 2004). The main objectives of the present
study are to investigate the source of the ore-forming
materials, and to determine the origin and evolution of
the hydrothermal fluids and its relationship with the
Qitianling granite. We review the geology of the deposit
and present the geochemical and isotopic data of the granites and the ores. These data provide important insights
into the genetic model of this deposit.
2
Regional geology
The Qitianling granite and the Furong tin deposit lie in
the middle of the Nanling granitic magma intrusive belt,
South China. The belt is an important granitic intrusion
and metallic mineralization zone. The Nanling zone has
been suggested as one of the domains of the transition
from the Paleo-Asian to the Paleo-Pacific tectonic system (Shu and Zhou 2002). The Qitianling granite is ellipse shaped and is one of the largest stocks in the Nanling
Granite Belt with a total outcrop area of 520km2. Coutry
rocks intruded by the Qitianling granite are Permo-Carboniferous carbonates and Permo- Triassic sandy shales.
3
Geology of the Furong deposit
Most of the cassiterite ores occur as veins hosted by altered granites. There are about 40 cassiterite-bearing veins,
in which the No. 19 and the No. 10 veins contain 90% of
the tin reserve in the deposit. The main granite alterations
are chloritization, phyllic and potassic feldspar alteration,
in which chloritization is mostly associated with tin mineralization. Cassiterite occurs as disseminated mineralization in the altered granites. There are minor skarntype tin orebodies, which forms at the contact between
the granites and the country rocks. Other metallic minerals include scheelite, pyrite, chalcopyrite, sphalerite,
arsenopyrite, and rutile. An interesting fact is that cassiterite is generally precipitated together with rutile as
disseminations in chlorite. Chlorite has been used as a
useful exploration guide for tin mineralization in the
granites.
4
Petrology and mineralogy of the Qitianling
Granite
The Qitianling Granite is complex, with different intrusive phases (Zheng and Jia 2001). Tin mineralization
mainly occurs in the Furong phase. Geochemical characteristics of the granite are distinctly different from common S-type tin granites. The Furong phase is composed
of potassic feldspar (40%), plagioclase (24%), quartz (27%),
biotite (7%) and minor amphibole (2%). Accessory minerals are mainly magnetite, ilmenite, zircon, fluorite, apatite,
monazite, sphene. The granite is metaluminous with a ACNK
ratio (molar ratio of Al2O3/(CaO+K2O+Na2O)) of 0.88~1.05,
which is different from common strongly peraluminous tin
granites. The granite is alkaline-enriched and shows low
initial 87Sr/86Sr value (0.708), high εNd value (-5.1~-5.8)
and young Nd model ages, which suggests contribution
of mantle materials in granite genesis. Zircon SHRIMP
U-Pb dating gave a crystallization age of 157.1±1.2Ma.
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Zhao Kuidong · Jiang Shaoyong · Jiang Yaohui
5
Geochemical studies of the granite and the
deposit
5.1 Mineral chemistry
The main rock-forming minerals (amphibole, biotite, plagioclase and ore minerals such as cassiterite and rutile)
were analysed for chemical composition by electron microprobe (Zhao et al., 2004). The biotite is Fe-rich annite,
and has high Ti, Cl and Sn concentrations. The biotite
has high Fe3+/(Fe2++Fe3+) ratios and the oxygen fugacity
calculated by biotite compositions is above Ni-NiO (NNO),
and near the Fe2O3-Fe3O4 (MH). The amphiboles are
ferropargasite and ferro-edenite hornblende. The pressure of the granite, estimated by Al-in-hornblende barometer, is 3.6 ±0.9kbar. Amphibole- plagioclase thermometry and a semiquantitative hornblende thermometer yield a forming temperature of 750~820°C. The chlorite from the orebody has negligible K2O, Ti2O, F, and Cl,
but shows similar Fe/(Fe+Mg) ratios with amphibole and
biotite. Disseminated cassiterite is closely associated with
rutile in chlorite alteration veins and envelopes. The oreforming temperature is estimated to be 290~405°C from
chlorite geothermometry. The studied cassiterites are
nearly pure SnO2 (>98%). The concentrations of Nb2O5
and Ta2O5 in cassiterite are very low and almost negligible (Nb2O5+Ta2O5<0.1%).These values are distinctly
different from cassiterites found in granites or pegmatites,
but similar to cassiterite from epithermal or hydrothermal ore deposits.
5.2 REE geochemistry
REE contents of both fresh and altered granites are analyzed. Fresh granites show a LREE-enriched and large
negative Eu anomaly REE pattern. Altered granites have
a similar REE pattern to fresh granites. It suggested that
REEs were immobile during hydrothermal alteration of
granites in this case.
Most sulfides have very low REE contents and show
similar REE patterns with granites. Because REEs have
distinctly different ionic radii from those of base metal
elements, it is difficult for REEs to substitute into crystal
lattices of sulfides. Thus, it may be assumed that a major
part of REE content of sulfides comes from fluid inclusions in these minerals. REE patterns of sulfides may represent those of ore-forming fluids.
Fluorites coexisting with sulfides have relatively high
REE contents and show a different REE pattern. Fluorites
show a HREE-enriched pattern. Marchand et al. (1976)
studied the REE partition between fluorite and a solution of calcium chloride. The REE distribution coefficients
strongly favor fluorite, and those for the HREE are greater
than those for the LREE.
5.3 H-O isotopes
Cassiterites have δ18O values from -4.8‰ to 1‰. Chlorites from the ores have δ18O values from 0.5‰ to 2.5‰,
and δD values from -62‰ to -68‰. The estimated oxygen isotope compositions of the hydrothermal fluid from
Close
Chapter 7-38 · Geology and geochemistry of the Furong Tin Deposit, Hunan Province, P. R. China
cassiterites and chlorites vary from -2.0‰ to +3.8‰. The
values are lower than those of magmatic-hydrothermal
fluids, and are higher than those of Mesozoic meteoric
water (-8‰~-9‰) in the studied area. Involvement of
surface water of meteoric origin during mineralization
of the Qitianliang granite can be ascertained by the oxygen and hydrogen isotope data.
Oxygen isotopic compositions of fresh and altered
granites have also been measured. The fresh granite far
away from tin mineralization has the highest oxygen isotopic composition (+10.5‰). The fresh and slightly altered granites near the tin veins have lower δ18O values
from +6.0‰ to +10.0‰. The completely chloritized granites collected from the tin orebodies have the lowest oxygen isotopic composition (5.4‰~6.6‰). The oxygen isotopic variations of the whole rocks are the result of fluidrock interactions. The W/R ratios of completely chloritized
granites are estimated to be 0.3~0.5.
Pb diagram (Zartman et al. 1981). This suggests that Pb
is of crustal origin.
5.4 Sulfur isotopic data
Huang GF, Gong SQ, Jiang XW, Tan SX, Li CB, Liu DH (2003) Exploration on the ore-forming regularities of tin deposits in Qitianling
area, southern Hunan. Geological Bulletin of China 22: 445-451
Mao JW, Li XF, Lehmann B, Chen W, Lan XM, Wei SL (2004) 40Ar39
Ar dating of tin ores and related granite and its geodynamic
significance for rock and ore formation. Mineral Deposits 22: 164175
Marchand L, Joseph D, Touray JC, Treuil M (1976) Critères d’analyse
géochimique des gisements de fluorine basés sur l’étude de la
distribution des lanthanides- application au gîte de Maine (71Cordesse, France). Mineralium Deposita 11: 357-379
Shu LS, Zhou XM (2002) Late Mesozoic tectonism of Southeast China.
Geological Review 48:249-260
Wang DH, Chen YC, Li HQ, Chen ZH, Yu JJ, Lu YF, Li JY (2003)
Geochemical and geochemical features of the Furong tin deposit
in Hunan and their significance for mineral prospecting. Geological Bulletin of China 22: 50-56
Wei SL, Zeng QW, Xu YM (2002) Characteristics and ore prospects
of deposits in the Qitianling area, Hunan. Geology in China 29:
67-75
Zartman RE, Doe BR (1981) Plumbotectonics - the model.
Tectonophysics 75: 135-162
Zhao KD, Jiang SY, Jiang YH, Wang RC (2004) Mineral chemistry of
the Qitianling granitoid and the Furong tin ore deposit in Hunan
Province, South China: Implication for the genesis of granite and
related tin mineralization. Accepted by European Journal of Mineralogy
Zheng JJ, Jia BH (2001) Geological characteristics and related tinpolymetallic mineralization of the Qitianling granite complex in
southern Hunan Province. Geology and Mineral Resources of
South China 4: 50-57
Sulfur isotopic compositions of twelve sulfides were analyzed. The δ34S values of sulfides vary from -20.4‰ to
3.2‰. The sulfur isotopic compositions were divided into
two groups in the histogram plot. In one group, the sulfur isotopic compositions vary from -0.5‰ to +3.2‰.
Sulfur in this group might come from the granite. In the
other group, the sulfur isotopic compositions vary from 20.4‰ to -10‰. Sulfur in this group might come from
sulfides in strata.
5.5 Lead isotopic data
Thirteen sulfides from the ores and ten feldspars from the
Qitianling granite were analyzed for Pb isotopic composition. The Pb isotopic composition of both sulfides and
feldspars is relatively homogeneous. 206Pb/204Pb, 207Pb/204Pb
and 208Pb/204Pb ratios of sulfides are 18.615~18.898,
15.726~15.766 and 38.893~39.077, respectively. The Pb isotopic ratios of feldspars are 18.682~18.970, 15.747~15.774
and 39.030~39.183, respectively. The similarity in Pb isotopic composition in sulfides and feldspars indicates that
lead in sulfides might come from the Qitianling granite.
The lead isotope data of both sulfides and feldspars were
plotted on the upper crust Pb growth curve in a Zartman
6
871
Conclusions
Tin mineralization in the Furong tin deposit is related to
hydrothermal alteration of the Qitianling granite. The oreforming fluids might be derived from meteoric water. Both
the granite and the strata supported the sulfur for mineralization. Water-rock interaction might have released tin
and other metals (e.g. Pb and Ti) from the granite.
Acknowledgements
This work was supported by funding from China National
Science Foundation (40221301).
References
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