Session 13
Metallogeny of the Au-Ag-Se-Te
mineralized systems
(IAGOD +IGCP-486 sponsored)
Close
Close
Chapter 13-1
13-1
Zonation of Au, Ag, Se and Te in orebodies from the
Kochbulak gold-telluride deposit (Uzbekistan)
Umid K. Aripov
National University of Uzbekistan, Tashkent
Abstract. This research deals with the Kochbulak Au deposit, which
is considered unique because of the mineralogical diversity of tellurides and selenides. The deposit is currently under exploitation.
The mineralogy and geochemistry of this deposit have been well
investigated by many previous researchers and it is recognized as a
reference deposit for the gold-telluride genetic type. The aim of
this work has been to investigate the tendency of vertical zonation
of Au, Ag, Te, Se distribution in different orebodies and to explain
zonation trends. The question of Au, Ag, Te, Se zonal distribution in
Au deposits bears great importance in solving genetic problems
and developing the criteria of search and evaluation.
Keywords. Kochbulak, gold deposit, Uzbekistan, tellurium, selenium,
distribution
1
Four main stages of ore formation have been delineated in the deposit (Kovalenker et al. 1997): 1) pre-productive alteration stage; 2) early productive stage - goldpyrite-quartz; 3) main productive stage - gold-sulphosaltstellurides; 4) post-productive - carbonate-barite-quartz.
Many different types of texture are recognisable in the
ores; bedding, ribbon-banding, tectonic and hydrothermal breccias, cockade, crustified, colloform, spongy, etc.
Mineralization of economic grade can only be determined by sampling, as strict geological boundaries are
lacking. Gold-silver ore formations are concentrated in
quartz-dominant veins, tubular pipe-like orebodies and
vein metasomatites.
Introduction
3
Tellurium and selenium may be abundant in some Au
deposits. They occur within different sulphide minerals,
as well as discrete telluride and selenide minerals. In tellurium-enriched ores containing galena, arsenopyrite,
sulphosalts, bismuth and several other minerals, the concentrations of these elements may be in the hundreds of g/
t, but in parts of a deposit characterized by widespread
micro-inclusions of telluride minerals, contents may be
much higher. Nevertheless, despite such high concentrations, the total amounts of Se and Te is rarely so large,
and the elements themselves have only minor economic
significance.
The question of the zonal distribution of Au, Ag, Se, Te
in ore bodies of gold deposits bears great importance for
solving aspects of ore genetic, as well as for exploration
and exploitation.
This study addresses the distribution of Au, Ag, Se and
Te within a distinct type of epithermal Au-telluride
epithermal deposits in Uzbekistan, using the results of a
sampling programme of the Kochbulak deposit.
2
Geology
The Kochbulak deposit is situated in the tectonic collage of
the Western Tien-Shan, within the Kuramin zone of the
Beltau-Kuramin volcano-plutonic-belt. It is located in the
central part of the Kochbulak volcano-tectonic depression,
composed of volcanic and volcano-sedimentary rocks of
Upper Paleozoic age. The ore bodies, of which there are
three types, are positioned in andesite-dacite porphyrites,
in zones of faulting and deformation (Islamov et al. 1999).
Morphology and composition of orebodies
The orebodies within the deposit can be divided into two
morphological types:
Type 1: linear elongated gently- and steeply-dipping
orebodies, represented by veins and mineralized zones
developed in the Central area of the deposit.
Type 2: tubular, pipe-like bodies which are filled with
brecciated, hydrothermally altered rocks with quartzsulphide cement. The pipes are up to 400 m in vertical
extent, and as much as 100m in diameter, changing into
a single vein at depth.
The most widespread ore minerals are the sulphides (pyrite, sphalerite, galena, bismuthinite, chalcopyrite, etc), sulphosalts (goldfieldite, freibergite, tetrahedite), tellurids of gold,
silver, bismuth and several other elements. Most ores have
moderate sulphide contents, up to 30%. The main economic
components of the deposit are Au and Ag, but Cu, Bi, Te and
Se are also valuable by-products. Gold occurs preferentially
in native form, chiefly as thinly dispersed, dust-like grains,
up to 700 µm in size, rarely larger, as well as in tellurides and
sulphosalts (15-25% of total gold) and sulphides (1-5%). Gold
fineness ranges from .326 to 1.000; the average is 880.
Dissolution of quartz containing finely-dispersed gold
accumulation in HF from the tubular orebodies has been
carried out. A fine crystalline powder was obtained, consisting of tiny crystals and grains of gold and crystals of pyrite.
The size of the gold grains ranges from 1 to 700 µm.
The compositions of the gold grains have been studied
using a Jeol Superprobe 8800R microprobe (Table 1).
Close
1380
Umid K. Aripov
4
Distribution of Au, Ag, Se and Te
The distributions of Au, Ag, Se, Te have been studied in
two orebodies of each type. The average concentration of
elements has been calculated using 25-30 representative
analyses from each level.
The two orebody types (linear elongated and tubular
ore bodies) were delineated based on their morphological
characteristics. The linear elongated ores are represented
by two structural types: gently pitching orebodies (10-40°)
and intersecting steeply-dipping (more than 45°) orebodies.
Steeply-dipping orebodies. Analysis of steeply-dipping
linear orebodies showed that they have a well-defined
zonality, expressed by the fact that the average content of
Au, Ag, Te, Se increase with depth. Gold fineness also increases with depth (Fig. 3).
At the intersections of gently-pitching bodies with the
steeply-dipping veins, the relationships of the ore elements
change. The average content of Ag sharply increases, and
the content of Te and Se decreases (Fig. 4).
Gently pitching ore bodies. In the gently pitching
orebodies, the average content of Au, Ag, Se and Te do
not change significantly with depth. The fineness of gold
also does not change (Fig. 5).
Close
Chapter 13-1 · Zonation of Au, Ag, Se and Te in orebodies from the Kochbulak gold-telluride deposit (Uzbekistan)
1381
Tubular orebodies. In the upper horizons of the tubular orebodies, high average content of Au and Ag may be
seen. With depth, the average content of Au, Ag, Se, Te
decreases. The gold fineness also markedly decreases with
depth (Fig. 6).
5
Conclusions
1. The following trends have been identified in patterns of
Au, Ag, Te and Se distribution. In the steeply-dipping
veins, Au, Ag, Se, Te increases with depth. In gently pitching bodies their content doesn’t change much. In the tubular ore bodies, all elements have a maximum concentration at upper levels and decrease with depth.
2. Within the studied horizons of the deposit the common tendency is for Au, Ag, Te and Se to occur together, suggesting that they were deposited synchronously.
3. As a result of our research, it was found that, in the
tubular bodies, finely-dispersed gold may occur in two
forms: as tiny crystals and as grains with irregular or
amorphous morphology.
References
Aripov UK, Dunin-Barkovckay EA (2004) Gold- tellurium deposits
formation conditions, mineralogical features. 32nd International
Geological Congress, Florence, Italy., Abstract 54-32, CD-ROM
Islamov F, Kremenetsky A, Minzer E, Koneev R (1999) The
Kochbulak-Kairagach ore field. In: T Shayakubov, F Islamov, A
Kremenetsky, R Seltmann, Eds., Excursion guidebook; Au, Ag,
and Cu deposits of Uzbekistan. GeoForschungs Zentrum
Potsdam: 91-106
Kovalenker VA, Safonov YG, Naumov VB, Rusinov VL (1997) The
epithermal gold-telluride Kochbulak deposit (Uzbekistan).
Geology of Ore Deposits 39 (2): 107-128
Close
Close
Chapter 13-2
13-2
Bismuth tellurides as gold scavengers
Cristiana L. Ciobanu1,2, Nigel. J. Cook3, Allan Pring1,2
of Earth and Environmental Sciences, University of Adelaide, S.A., 5005, Australia
2 Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, S.A. 5000 Australia
3 Geology Section, Natural History Museum, University of Oslo, Boks 1172 Blindern, 0318 Oslo, Norway
1 Department
Abstract. Bi-Te melts have potential as Au scavengers in different
types of gold deposits. Using phase equilibria, we define ‘melt-(precipitation) windows’ within which the Bi-Te scavenging mechanism
can operate. Predicted assemblages correlate well with those in
natural samples and can be applied in other cases to explain the
distribution of telluride minerals in Au deposits.
their implied involvement in the formation of Au-telluride
deposits, other than those in which only tellurides of Au
and Au-Ag are present. Maldonite is not a telluride but should
be consid-ered alongside Bi-tellurides when Au-concentrating mechanisms via Bi-Te melts are discussed.
Keywords. Bismuth tellurides, gold scavenger, melt precipitates,
epithermal, skarn, orogenic gold
2
1
Introduction
Telluride minerals are commonly abundant in Au deposits
of various types and ages. When highly concentrated
throughout, or in limited parts of a deposit, Au-(Ag)-tellurides may themselves constitute an economic ore (Cook
and Ciobanu, this volume). Bismuth-tellurides, on the other
hand, are not themselves, exploitable minerals, but may be
an important part of the Au association. Maldonite (Au2Bi)
and unnamed Au5BiS4 are the only known Au-Bi compounds
and may attain exploitable concentrations within certain
deposits; there are no Bi-Te-Au compounds as such.
In many cases the occurrence of Au together with Bitellurides is as droplets or droplet-derived patches hosted
within common ore minerals (Ciobanu and Cook 2002).
Such morphologies are highly indicative of precipitation
in a molten state. Indeed, droplets of sulphide-Au-Bimaldonite in annealed samples from Challenger (S. Australia) showed quenched textures that support their origin as polymetallic melts formed during metamorphism
of a pre-existing ore (Tomkins and Mavrogenes 2002).
The hypothesis that metals precipitated above their melting points (as melts) from fluids can extract Au from those
fluids was proven experimentally for native Bi (Douglas et
al. 2000). Using hydrothermal fluids undersaturated in Au
for the experiments, this mechanism was shown to be a
more efficient alternative in extracting Au from a fluid than
precipitation upon saturation, i.e. a proper ‘scavenger’ for
Au. Once precipitated, Bi melt remains mobile and will continue to attract Au until crystallisation is complete.
We discuss the potential that Bi-Te melts have as Au scavengers in relevant templates of Au-mineralisation. This in
turn allows us to define a ‘melt-(precipitation) window’ that
can be used to explain and understand distribution of tellurides in Au deposits. Such an approach emphasizes the
importance of Bi-tellurides as Au pathfinders, as much as
Bismuth tellurides
Bi-tellurides represent a group of chalcogenides with
modular structures. They form a polytypoid series with
general formula mBi2.nBi2Te3, in which individual members are characterised by distinct stacking sequences of
two types of layer, the 2-atom ‘BiBi’ layer and the 5-atom
‘TeBiTeBiTe’ layer (Imamov and Semiletov 1971). Bisulphotellurides and selenides are structurally related
compounds that have similar configuration, but Te is partially or totally replaced by S and/or Se in the 5-atom layer.
Currently recognised mineral species can be grouped in
several isoseries (Cook et al. in press).
Close
1384
Cristiana L. Ciobanu · Nigel. J. Cook · Allan Pring
2.3 Application to natural samples
2.1 Bi-Te phase diagram
In the simple Bi-Te diagram (Fig. 1a), telluro-bismuthite has
the highest thermal stability (588ºC; Okamoto and Tanner
1990). The eutectic on the Bi-side (266ºC) is close to the m.p.
of native Bi (271ºC), and the eutectic on the Te-side (413ºC)
is close to the m.p. of native Te (450ºC). Although structural formulae were derived for a larger number of synthetic compounds in the Bi-Te series (Fig. 1a), there are only
a limited number of tellurides defined (Cook et al. in press).
2.2 Gold incorporation in Bi- and Bi-Te-melts
The only eutectic on the binary Au-Bi phase diagram indicates that liquid Bi can incorporate as much as 17 at.% Au
and will crystallise as Bi+maldonite at 241ºC (Fig. 2a,
Table 1); beyond the solubility capacity of any fluid at any
temperature. The potential of melts to dissolve Au is even
higher for Bi-Te melts (10-37 at.% Au) - see eutectics in the
Au-Bi-Te system (Table 1).
When present in natural samples, eutectic associations
(Figs. 1, 2, 4b) provide minimum formation temperatures
for the respective Bi-Te±Au assemblages. It is rare,
however, that the droplets consist only of tellurides;
in most cases, they also include sulphotellurides and/or
Bi-sulphosalts (Fig. 3). Maldonite (Figs. 3a, b) or Au
(Figs. 3c, d) is included within one or the other mineral
components, proving that Bi- and Bi-Te-(S) melts can
scavenge Au in each of the respective Au-bearing systems, not only at eutectic composition. Collectively, droplet chemistry (Fig. 3) represents a compositional range
close to the eutectic on the Bi-rich side of the Bi-Te system. Similar associations are reported from many Au
skarns (Meinert 2000).
Even though virtually all intermediate compositions
between Bi and Te can be stabilised by structural modulation in Bi-tellurides (sulpho-tellurides, -selenides),
the chemistry of telluride droplets that are paragenetically related covers a certain range of intermediate
compositions on either Bi- or Te-rich sides of the BiTe(Se,S) and/or Bi-Te(Se,S)-Au systems. Based on theoretical considerations (Afifi et al. 1988) and observation of speciation in Bi-telluride associations found
in deposits spanning the metamorphic and magmatic
to hydrothermal spectrum, the ratio Bi/Te+Se+S (RBi/Te)
is found to be relevant for oxidizing/ reducing conditions in fS 2-fO 2 space (Ciobanu and Cook 2002).
Tsumoite (BiTe) spans both reduced environments
(Po,Mt) characterised by Bi-tellurides with RBi/Te>1, native Bi and maldonite, and oxidized environments
(Py,Hm) including Bi-tellurides with RBi/Te<1, Au-Ag-tellurides and native Te.
Close
Chapter 13-2 · Bismuth tellurides as gold scavengers
1385
and (2) insolubility of metal complexes in the fluid at the
respective temperature. The latter is, in turn, controlled by
chemistry of the fluid, e.g. sulphidation/oxidation (fS2/fO2)
and redox (Ph/Eh) characteristics of the fluid.
3.3 Epithermal deposits
3
Application of melt hypotheses
3.1 Au-concentration by partial melting
Frost et al. (2002) pointed to the fact that a number of
chalcophile elements form low-melting point sulphides
(LMCE) and thus will assist partial melting of a sulphide
ore if this undergoes metamorphism at temperatures
above the m.p. of available LMCE in the system. Of relevance here is the fact that both Bi and Te are included
within the LMCE group. The importance of partial melting of a pre-existing ore via LMCE is that such melts will
act as scavengers for Au, a metal that otherwise has a high
melting point (Fig. 2a), e.g. Challenger deposit (Tomkins
and Mavrogenes 2002).
Emphasising the importance of LMCE melts in concentrating Au is the formation of telluride-rich high-grade
ore (including bonanza ore Au, ~200 g/t) in tectonically
controlled pipes at Kochbulak, Uzbekistan (Stenina et al.
2003). Native Au is associated with Au-(Ag)-tellurides
(calaverite, AuTe2; sylvanite, (Au,Ag)2Te4, petzite, Ag3AuTe2;
hessite Ag2Te), Bi-tellurides (tellurobismuthite, tetradymite), altaite, PbTe). Evidence for incorporation of Au and
Ag in melts during partial melting of sulphosalts (fahlore,
bismuthinite) and sulphides from preexisting epithermal
ore is seen in a series of emulsion-like textures displayed
between Au and various combinations of tellurides and
sulphosalts/ sulphides. Especially relevant to melt involvement are the telluride droplets within tetrahedrite,
Tet88Ten11 (Fig. 4a), highly reminiscent of liquid magmatic
ores formed by immiscibility between sulphide and silicate melts. An estimated melt temperature of >400ºC is
based on the two eutectics recorded within telluride associations (Figs. 1c, 4b).
3.2 The melt-precipitation window: Au extraction from
hydrothermal fluids
Fractionation of melts from a fluid (precipitation of metals
above the solvus curve) is controlled by two factors: (1)
temperature above m.p. (Tmelt) along the liquid/solid curve,
The stability of native Te broadly covers the pyrite field
in fS2/fO2 space with a solubility minimum close to the
Mt/Hm buffer at 300ºC (McPhail 1995). This explains the
presence of native Te in many epithermal deposits since
there is a significant overlap between the above conditions and those considered for fluids that form this type
of ore (Cooke and Simmons 2000). However, most
epithermal Au ores in the Pacific Rim lack Bi-tellurides;
Te+Au-(Ag)-telluride signature is instead prominent. This
is because the minimum temp-erature of the melt window is at least 413ºC (Fig. 1a), even though the chemistry
of epithermal fluids is otherwise suited for formation of
melts in the tellurobismuthite-Te range. Consequently, Auscavenging from fluids by formation of Bi-Te melts (with
Te>Bi) is likely to happen in epithermal systems only if
T> 400ºC is reached (some HS systems; Cooke and
Simmons 2000). In LS epithermal systems formed at lower
T (<300ºC), other precipitation mechanisms, e.g. condensation of Te vapor(s), followed by reaction with Au-Agbearing fluids, is invoked to explain the presence of Au(Ag)-tellurides+Te (Acupan, Phillipines; Cooke and
McPhail 2001). Temperatures >400ºC can nonetheless be
attained in LS epithermal systems at the porphyry to
epithermal transition if this is triggered early in the porphyry evolution by active strike-slip tectonics (some deposits in Apuseni Mts., Romania). The association of Bitellurides (RBi/Te <1), typical for deeper parts of kin-veins,
opened onto an immature porphyry root at Larga (Cook
and Ciobanu 2004), is evidence for Au-scavenging. Porphyry and epithermal Cu deposits (both HS & LS) in the
Banatitic Belt (SE Europe, Late Cretaceous) include Auenriched ores with Bi-telluride signature (RBi/Te<1; tetradymite, telluro-bismuthite) ± Te ± Au-(Ag)-tellurides)
that are formed by similar mechanisms, at T=400ºC and
at the Mt/Py± Hm buffer ( Ciobanu et al. 2003).
3.4 Skarn and orogenic Au
In contrast to native Te, the stability of native Bi covers
Po-Mt fields in fS2/fO2 space (Skirrow and Walshe 2002).
Partitioning of liquid Bi (melt) was obtained experimentally from fluid at fS2 below the Po/Py buffer and temperatures above the m.p. of Bi (271ºC) (Douglas et al. 2000).
Importantly, Au was also partitioned from fluid into liquid Bi, proving the point that destabilisation of soluble
metal complexes at T above the solvus curve can induce
precipitation irrespective of their saturation at the time.
Close
1386
Cristiana L. Ciobanu · Nigel. J. Cook · Allan Pring
Minimum T for the Bi-Te melt window is 266ºC on the Bi
side (Fig. 1a) and 241ºC for Bi-Au melts (Fig. 2a). Although
such temperatures are in the epithermal range, associations
of native Bi, maldonite and tellurides (RBi/Te>1) require more
reducing conditions than those considered for epithermal
systems. Such reducing conditions are met in skarns during sulphidation at the Mt/Po buffer (e.g. droplets in Figs. 2b,
3 are found only in Mt replaced by Po in Baisoara Fe skarn)
or reducing reactions at the Hm/Mt buffer (Fe skarn at Ocna
de Fier, Romania; Ciobanu et al. 2003). The templates of
many Au skarns (Meinert 2000) and orogenic Au (e.g.
Maiskoe, Ukraine; Cook et al. 2002) replicate the experiments of Douglas et al. (2000) below the Po/Py buffer.
Two distinct Bi-telluride associations, (1) Au+ Bitellurides (RBi/Te>1)+Bi±maldonite; (2) Au+Bi-tellurides
(RBi/Te<1)±Te±Au-(Ag)-tellurides, are often seen in skarns
and orogenic Au, either separately or together (Ciobanu et
al. 2003, 2004; Mudrovska et al. 2004). The type association
will reflect the reducing (1) or oxidizing (2) character of
sulphidation reactions, e.g. at redox fronts, often the case of
interaction between orogenic Au fluids and BIF, or during
retrograde stages in skarns. Bi-tellurides are hence excellent pathfinders for Au in such deposits, where they are
abundant.
References
Afifi AM, Kelly WC, Essene EJ (1988) Phase relations among tellurides, sulfides, and oxides. Econ Geol 83: 377-394, 395-404
Ciobanu CL, Cook NJ (2002) Tellurides, selenides (and Bi-sulphosalts)
in gold deposits. 11th IAGOD Symp-Geocongress, CD vol, Geol
Surv Namibia
Ciobanu CL, Cook NJ, Bogdanov K, Kiss O, Vuckovic B (2003) Gold
enrichment in deposits of the Banatitic Magmatic and Metallogenetic Belt, SE Europe. In: Mineral Exploration and Sustainable
Development. Millpress, 1153-1156
Ciobanu CL, Cook NJ, Sundblad K, Kojonen K (2004) Tellurides
and selenides in Au ores from the Fennoscandian Shield: A status report. 32nd IGC, Florence, Italy, CD-ROM Abstr vol, part 1,
54-12, 274
Cook NJ, Ciobanu CL (2004) Bismuth tellurides and sulphosalts from
the Larga hydrothermal system, Metaliferi Mts., Romania. Mineral Mag 68: 301-321
Cook NJ, Ciobanu CL, Nechaev SV, Mudrovska IV (2002) Genetic
constraints from Bi-mineral associations in the Maiskoe Au-deposit, Ukrainian Shield. Metallogeny of Precambrian Shields,
Ukraine. Abstr. Vol.: 46-48
Cook NJ, Ciobanu CL, Wagner T, Stanley CJ (in press) Minerals of
the system (Pb)-Bi-Te-Se-S related to the tetradymite archetype.
Can Mineral
Cooke DR, McPhail DC (2001) Epithermal Au-Ag-Te mineralization,
Acupan, Baguio District, Philippines; numerical simulations of
mineral deposition. Econ Geol 96: 109-131
Cooke DR, Simmons SF (2000) Characteristics and genesis of
epithermal gold deposits. Rev Econ Geol 13: 221-244.
Douglas N, Mavrogenes J, Hack A, England R (2000) The liquid bismuth collector model: an alternative gold deposition mechanism.
AGC Abstr. vol. 59: 135
Frost BR, Mavrogenes JA, Tomkins AG (2002) Partial melting of sulfide deposits during medium- and high-grade metamorphism.
Can Mineral 40: 1-18
Gather B, Blachnik R (1974) The gold-bismuth-tellurium system. Z
Metallkunde 65: 653-656
Imamov RM, Semiletov SA (1971) The crystal structure of the phases
in the systems Bi-Se, Bi-Te, and Sb-Te. Sov Phys – Crystallogr 15:
845-850
McPhail DC (1995) Thermodynamic properties of aqueous tellurium species between 25oC and 350oC. Geochim Cosmochim Acta
59: 851-866
Meinert LD (2000) Gold in skarns related to epizonal intrusions. Rev
Econ Geol 13: 347-375
Mudrovska I, Ciobanu CL, Cook NJ, Merkushin I, Sukach V, Lysenko
A, Bobrov A (2004) Bi-tellurides and orogenic gold: Examples
from the Ukrainian Shield. 32nd IGC, Florence, Italy, CD-ROM
Abstr vol, part 1, 54-29, 277
Okamoto K, Masaalski TB (1983) Au-Bi (gold-bismuth). Binary Alloy Phase Diagrams. Vol. I. ASM Intl: 238-240
Close
Chapter 13-3
13-3
Tellurides in Au deposits: Implications for modelling
Nigel J. Cook
Geology Section, Natural History Museum, University of Oslo, Boks 1172 Blindern, 0318 Oslo, Norway
Cristiana L. Ciobanu
Department of Earth and Environmental Sciences, University of Adelaide, S.A., 5005, Australia
Abstract. We use the distribution of tellurides in the main types of Audeposit (spanning the magmatic-hydrothermal and metamorphic
spectrum) to comment upon Au-telluride and Au-Bi-telluride types
of deposit. By emphasizing this distinction, the genetic links between
Bi-tellurides and Au are recognised to be as important as those between Au-tellurides and gold in deposit formation. A general scheme
for telluride deposition via gas condensation is attractive to explain
features of mineralising systems that experienced sustained boiling,
but tectonically-driven hydrothermal systems could be as efficient
in making a Au-telluride deposit. Depending on temperatures, scavenging of Au by Bi(Te) melts, or partial melting of a pre-existing ore,
may offer alternatives to generate telluride-rich gold ores.
Keywords. Gold-telluride deposits, distribution, genetic models, deposit types
1
Introduction
IGCP project 486 addresses both the fundamental character of Au-(Ag)-Te deposits from a geological, mineralogical
and geochemical perspective, and also the petrogenetic value
of tellurides. One goal of IGCP-486 is realising a database
in which telluride occurrences are summarised.
In this contribution, we make a first attempt at an inventory of Au deposits in which tellurides are present. These
include Au-telluride deposits sensu strictu, in which a significant part of the gold is present as Au(Ag)-tellurides, as
well as deposits, districts and belts in which Au(Ag)-tellurides are present as accessories and may contribute to the
overall balance of gold in the ore. In addition, we address
Au-deposits with sparse or absent Au(Ag)-tellurides, but
with variable amounts of other tellurides (of Bi, Pb, Hg etc.),
associated with the gold. The number of Au-telluride deposits sensu strictu is relatively small within the whole population, and appear largely restricted to the epithermal type.
We point to the implication that the strong genetic link between Au and other tellurides, especially of Bi, has for defining a Au-telluride deposit. Cooke and McPhail (2001)
proposed a formational model in which Te vapour condensation follows sustained boiling. We discuss several other
deposits, with the purpose of identifying alternative mechanisms for generating Au-telluride deposits.
2
Telluride distribution in gold deposits
Jensen and Barton (2000) reviewed a number of
epithermal Au-Te systems associated with alkaline
magmatism, some of which grade downwards into por-
phyry-type Cu(Au) deposits. These include classic Au-Te
districts such as Cripple Creek, Emperor, Porgera, Ladolam
and the Montana Au-Ag telluride belt (Table 1). Commenting on the association of tellurides with alkaline
magmatism, they emphasize that melting of Te-rich sediments may be key sources for the mantle-sourced alkaline magmas in subduction settings.
An association between alkaline magmatism and telluride-bearing epithermal mineralization has often been
assumed (e.g. Richards 1995; see also discussion of ‘aberrant deposits’ by Sillitoe 2002), but may have been overstated. Well-studied examples of telluride-enriched
epithermal mineralization in calc-alkaline volcanic rocks
include the Baguio District, Phillipines (Cooke and
McPhail 2001) and Cretaceous-Quaternary deposits of
Japan (Shikazono et al. 1990). Telluride enrichment has
been noted in a number of high-sulphidation deposits,
also in calc-alkaline volcanics, e.g. Pueblo Viejo, Lepanto
or Furtei (Sardinia; Fadda et al. this volume). Nevertheless, Au-tellurides are rarely of major economic importance in such deposits.
The 900 km2 Golden Quadrilateral (GQ), Romania, has
historically produced as much as 2000 t Au. The 64 (dominantly epithermal vein) deposits are associated with Neogene calc-alkaline volcanics. Mineable amounts of Au-tellurides were restricted to the Sacarîmb deposit and small,
dominantly upper parts of some others (Fata Baii, Baia
de Aries, Stanija, Botes), but the presence of tellurides in
at least 20 deposits (Cook and Ciobanu 2004b; unpubl.
data) emphasizes the consistent telluride signature of the
province. Moreover, tellurides are recognised in different
deposit types, including those spanning the porphyryepithermal transition, as well as late veins in breccia deposits (Rosia Montana). Tellurides composed >50% of the
32 t Au exploited from Sacarîmb, and occurred throughout the 600m vertical extent of the deposit (Cook and
Ciobanu 2004b and references therein).
The Tien Shan represents a similar case, with telluride-bearing deposits hosted by calc-alkaline volcanics
of Paleozoic age. Deposits of the Kurama Belt, Uzbekistan
(Kochbulak, Kairagach etc.) are examples. As well as
contradicting the alkaline-telluride association, Kochbulak, like Sacarîmb, is anomalous in other ways, as shown
below.
The 1,400 km long calc-alkaline Late Cretaceous
Banatitic Belt, SE Europe, contains 60 Cu-dominant de-
Close
1388
Nigel J. Cook · Cristiana L. Ciobanu
posits, including epithermal ores alongside porphyry and
skarn deposits. The belt has a consistent telluride-signature, with tellurides closely associated with Au in all deposit types. Here, however, it is Bi-tellurides that accompany the gold; Au(Ag)-tellurides are rare (Ciobanu et al.
2003). A telluride mineral signature is also reported from
Cu-Au deposits in the adjacent Tertiary calc-alkalineshoshonitic Rhodope Province. Here too, tellurides occur throughout deposits of the porphyry-epithermal continuum (Voudouris and Alfieris 2004).
Although they acknowledge alternative opinions about
the genesis of several deposits/districts covered in their
study, Thompson and Newberry (2000) discuss intrusion-related Au deposits, stressing that ‘many intrusionhosted and intrusion-proximal gold deposits display a
consistent and striking Au-Bi-Te-As… association’. Citing examples ranging from the Bohemian Massif (Europe) to the Tintina Belt (Alaska) and the Altai and Tien
Shan (Central Asia), these authors claim Te is always
anomalous, but generally lower than either Au or Bi. Jurassic-Cretaceous low-sulphidation epithermal deposits
of East China around the margins of the North China
and Yangtze cratons (Dongping; >100t @ 5-9 g/t Au;
Guilaizhuang 45t @ 2-6 g/t Au; Mao et al. 2003) are telluride-bearing. Epithermal models have also been proposed
for these deposits, emphasizing the often controversial
classification of intrusion-related Au deposits.
Gold skarns have the same Au-Bi-Te signature. (Meinert
2000) describes maldonite and native bismuth and a predominance of S-poor or S-absent tellurides of bismuth
(hedleyite, joséite-B) as part of Au ores; Au-tellurides
(calaverite) are rare to absent.
Enrichment in tellurides is noted among other types
of deposit, at least locally. Among VMS deposits, for example, both the Iberian Pyrite Belt and the Urals province display telluride enrichment. In the IPB, Bi-tellurides
are considered pathfinders for Au-Cu-rich stringer zones
beneath massive ores (Marcoux et al. 1996).
Au(Ag) tellurides are known in Archaean orogenic gold
deposits (Hagemann and Cassidy 2000). Exceptional enrichment in Au- and Au-Ag tellurides is seen in some deposits, including the giant Golden Mile deposit, western
Australia (Shackleton et al. 2003), the largest single lode
gold system in the world, in which 20-25% of the gold is
accounted for by tellurides. Other deposits in the Yilgarn
Craton (e.g. Marymia; Vielreicher et al. 2002) contain Birather than Au-Ag-tellurides. Gold and Au-Ag tellurides
are generally less abundant in Proterozoic and Phanerozoic orogenic Au deposits, but may be of local importance
in parts of individual deposits (e.g. Ashanti; Bowell et al.
1990; Omai; Voicu et al. 1999; Tauern Window; Paar et al.
2004). Hemlo, Ont. is a special case, as it contains rare
Au(Ag) tellurides, but Bi is absent (Tomkins et al. 2004).
A Bi-Te enriched signature is common to many orogenic gold systems. Bi-tellurides may be prominent and
commonly paragenetically associated with gold. Recent
surveys of orogenic gold deposits in the Fennoscandian
and Ukrainian Shields (Ciobanu et al. 2004b; Mudrovska
et al. 2004), for example, indicate that varying amounts of
tellurides have been reported from nearly half, and the
majority of deposits, respectively, irrespective of age or
setting. Moreover, other types of shield-hosted deposits
(e.g. metamorphosed epithermal gold or VMS) may share
the Au-Bi-Te signature evident in the orogenic deposits.
Close
Chapter 13-3 · Tellurides in Au deposits: Implications for modelling
2.1 Gold-bismuth-telluride deposits
As indicated above, a close association of gold with Bitellurides is seen throughout many Au-deposits, other than
epithermal. The implied genetic link between Bi-tellurides and Au means that such deposits should be considered alongside Au-telluride deposits sensu stricto as a distinct type. However, the role that Bi-tellurides play in gold
extraction has only begun to be evaluated. In terms of
elemental abundance, however, many deposits show AuBi, Au-Te or Bi-Te associations, i.e. with one of the three
elements absent or low. The tetradymite-dominant
Dashuigou Bi-Te deposit (Mao et al. 1995), in which Au is
a by-product, can be considered as a close-to-end-member example of the Bi-Te association. Deposits such as
Tennant Creek, (Skirrow and Walshe 2002) and Challenger
(Tomkins and Mavrogenes 2002) - in loose terms, Te free
end-members of a Au-Bi-Te deposit spectrum, are representative of the Au-Bi association.
3
Gold-telluride deposit models
Cooke and McPhail (2001) modelled epithermal Au-AgTe mineralization at Acupan, Philippines. From their numerical simulation of mineral deposition, they concluded
that multistage boiling would account for bulk gold ore
deposition, although other mechanisms have contributed
in some ways. Of interest to us is that simulation suggested that tellurium precipitated by vapour condensation into lower temperature precious metal bearing waters. Such a mechanism efficiently explains zoning of the
Acupan system, with Au-telluride ore at the upper part
and rich gold ore, without tellurides, underneath. The key
to this zonation model is Te separation into the vapour
phase during the boiling that caused deposition of the
gold-only mineralization. The model is reinforced by thermodynamic data suggesting Te should be in the vapour
rather than as complexes. Cooke and McPhail (2001) go
on to argue that such a zonation model applies to
epithermal systems that underwent multistage boiling.
The Fata Baii–Larga porphyry-epithermal system, GQ,
Romania, however, features gold and tellurides distributed across the 1 km vertical extent of the system, although Au-/Au-Ag tellurides dominate at upper levels, and
Bi-tellurides at depth, with free gold in both associations
(Cook and Ciobanu 2004a). A marked sulphidation event,
in which Po+Lö is converted to Py+Asp in the presence
of Au and Bi-tellurides, is recorded in the deeper part of
the veins above an (immature) porphyry root. Sulphidation, induced by rapid opening of kin veins prior to maturity of the porphyry system, may have been an important factor in destabilising metal complexes in the fluid.
Au scavenging by Bi-Te melt precipitates (Ciobanu et al.
2005) would be activated given the temperatures >400ºC
(Cook and Ciobanu 2004a).
1389
The Sacarîmb deposit, in the same province, however,
has no evidence of T>300ºC and also no substantial evidence for boiling. The veins, with characteristic pinch-andswell features, represent strike-slip meshes. Observations
of textures among telluride assemblages (Ciobanu et al.
2004a) indicate that micro-shearing was coincident with
telluride deposition. The deposit also stands out from other
epithermal Au-telluride deposits, in that nagyágite, a S-bearing Au-telluride, [Pb(Pb,Sb)S2] (Au,Te), is the dominant Au
phase in the system, commonly associated with Pb-As or
Pb-Sb sulphosalts. A shift from Sb- to As-rich fluids is indicated by changes in mineral assemblages and Sb/As partitioning within nagyagite-bournonite pairs. The position of
the deposit, at the intersection of different fault systems,
was optimal for development of sustained fluid throttling,
probably the main mechanism of Au deposition at Sacarîmb.
Tectonically-driven gold-telluride deposition has
strong analogies in orogenic gold deposits. Periodic release of gas due to throttling has been put forward as
instrumental in formation of the Golden Mile deposit
(Shackleton et al. 2003).
Textures among Au- and Bi-tellurides in high-grade
ore pipes (200 g/t) at fault intersections in the Kochbulak
deposit also indicate the role of active tectonics. Here,
however, they also support a model of enrichment in gold
and tellurides by partial melting of a pre-existing ore
(Ciobanu et al. 2005), even if other workers (e.g. Kovalenker
et al. 1997) favour an explosive hydrothermal breccia
model to explain the same features.
Acknowledgement
Discussion with participants in IGCP project 486 is gratefully appreciated.
References
Bowell RJ, Foster RP, Stanley CJ (1990) Telluride mineralization at
Ashanti gold mine, Ghana. Mineral Mag 54: 617-627
Ciobanu CL, Cook NJ, Bogdanov K, Kiss O, Vuckovic B (2003) Gold
enrichment in deposits of the Banatitic Magmatic and Metallogenetic Belt, SE Europe. In: Mineral Exploration and Sustainable
Development. Millpress: 1153-1156
Ciobanu CL, Cook NJ, Damian G, Damian F, Buia G (2004a) Telluride
and sulphosalt associations at Sacsrîmb. IAGOD Guidebook Series 12: 145-186
Ciobanu CL, Cook NJ, Pring A (2005) Bismuth tellurides as gold scavengers (this volume)
Ciobanu, C.L., Cook, N.J., Sundblad, K. and Kojonen, K. (2004b) Tellurides and selenides in Au ores from the Fennoscandian Shield: A
status report. 32nd IGC, Florence, Italy, CD-ROM Abstr vol, part 1,
54-12: 274
Cook NJ, Ciobanu CL (2004a) Bismuth tellurides and sulphosalts
from the Larga hydrothermal system, Metaliferi Mts., Romania:
Paragenesis and genetic significance. Mineral Mag 68: 301-321
Cook NJ, Ciobanu CL (2004b) Au-Ag-telluride Deposits of the Golden
Quadrilateral, Apuseni Mts., Romania. IAGOD Guidebook Series
12: 266
Close
1390
Nigel J. Cook · Cristiana L. Ciobanu
Cooke DR, McPhail DC (2001) Epithermal Au-Ag-Te mineralization,
Acupan, Baguio Philippines; numerical simulations of mineral
deposition. Econ Geol 96: 109-131
Fadda S., Fiori M., Grillo SM, Matzuzzi C (2005) The polymetallic
assemblages with precious metal tellurides and sulphosalts from
the Furtei epithermal gold deposit, Sardinia, Italy: paragenesis
and genetic significance. (this volume)
Hagemann SG, Cassidy KF (2000) Archean orogenic lode gold deposits. Rev Econ Geol 13: 9-68
Jensen EP, Barton MD (2000) Gold deposits related to alkaline
magmatism. Rev Econ Geol 13: 279-314
Kelley KD, Romberger SB, Beaty DW, Pontius JA, Snee LW, Stein HJ,
Thompson TB (1998) Geochemical and geochronological constraints on the genesis of Au-Te deposits at Cripple Creek, CO.
Econ Geol 93: 981-1012.
Kovalenker VA, Safonov YG, Naumov VB, Rusinov VL (1997) The
epithermal gold-telluride Kochbulak deposit (Uzbekistan). Geol
Ore Deposits 39: 107-128
Mao JW, Chen YC, Wang PA (1995) Geology and geochemistry of the
Dashuigou deposit, western Sichuan, China. Int Geol Rev 37:526-546
Mao JW, Li YQ, Goldfarb RJ, He Y (2003) Fluid Inclusion of the
Dongping telluride gold deposit, Hebei province: implication of
the contribution of mantle-derived fluids to metallogenesis. Econ
Geol 98: 517-534
Marcoux E, Moëlo Y, Leistel JM (1996) Bismuth and cobalt minerals:
indicators of stringer zones to massive-sulfide deposits, South
Iberian Pyrite Belt. Miner Deposita 31: 1-26
Meinert LD (2000) Gold in skarns related to epizonal intrusions. Rev
Econ Geol 13: 347-375
Müller D, Kaminski K, Uhlig S, Graupner T, Herzig PM, Hunt S (2002)
The transition from porphyry- to epithermal-style gold mineralization at Ladolam, Lihir Island, PNG: a reconnaissance study.
Mineral Deposita 36: 61-74
Mudrovska I, Ciobanu CL, Cook NJ, Merkushin I, Sukach V, Lysenko
A, Bobrov A (2004) Bi-tellurides and orogenic gold: Examples
from the Ukrainian Shield. 32nd IGC, Florence, Italy, CD-ROM
Abstr vol, part 1, 54-29: 277
Paar W, Topa D, Robl K, Amann G (2004) Tellurides related to gold
mineralization of Salzburg Province, Austria. 32nd IGC, Florence,
Italy, CD-ROM Abstr vol, part 1, 54-2: 273
Pals DW, Spry PG (2003) Telluride mineralogy of the low-sulfidation
epithermal Emperor gold deposit, Vatukoula, Fiji. Mineral Petrol
79: 285-307
Richards JR (1995) Alkalic-type epithermal gold deposits-A review:
In Thompson, JFH (Ed), Magmas, Fluids, and Ore Deposits. MAC
Short Course 23: 367-400
Richards JP, Kerrich R (1993) The Porgera gold mine, Papua New
Guinea: Magmatic, hydrothermal to epithermal evolution of an
alkalic-type precious metal deposit. Econ Geol 88: 755-781
Shackleton JM, Spry PG, Bateman R (2003) Telluride mineralogy of
the Golden Mile Deposit, Kalgoorlie, Western Australia. Can Mineral 41: 1503-1524
Shikazono N, Nakata M, Shimizu M (1990) Geochemical mineralogic and geologic characteristics of Se- and Te-bearing
epithermal gold deposits in Japan. Mining Geol 40: 337-352
Sillitoe RH (2002) Some metallogenic features of gold and copper
deposits related to alkaline rocks and consequences for exploration. Mineral Deposita 37: 4-13
Skirrow RG, Walshe JL (2002) Reduced and oxidised Au-Cu-Bi iron
oxide deposits of the Tennant Creek Inlier, Australia: An integrated geologic and chemical model. Econ Geol 97: 1167-1202
Spry PG, Foster F, Truckle JS, Chadwick TH (1997) The mineralogy
of the Golden Sunlight gold-silver, telluride deposit, Whitehall,
Montana, USA. Mineral Petrol 59: 143-164
Thompson JFH, Newberry RJ (2000) Gold deposits related to reduced
granitic intrusions. Rev Econ Geol 13: 377-400
Tomkins AG, Mavrogenes JA (2002) Mobilization of gold as a
polymetallic melt during pelite anatexis at the Challenger deposit, South Australia: A metamorphosed Archean gold deposit.
Econ Geol 97: 1249-1271
Tomkins AG, Pattison DRM, Zaleski E (2004) The Hemlo gold deposit, Ontario: An example of melting and mobilization of a precious metal-sulfosalt assemblage during amphibolite facies metamorphism and deformation. Econ Geol 99: 1063-1084
Close
Chapter 13-4
13-4
New occurrences of gold-porphyry type ores in the
southeast of East Sayan (Russia)
B.B. Damdinov
Geological Institute SB RAS, Ulan-Ude, Russia
Abstract. In this paper, we discuss ore occurrences in the Tissa and
Sarhoi river basins, East Sayan, Russia. These deposits are associated with small granitoid intrusions of island arc type. The ores occur as quartz veins, as well as veinlet-impregnated and disseminated
ores, in which gold-telluride associations are widespread. The geological and mineralogical characteristics allow the deposits to be
interpreted as gold-porphyry types of deposit.
Keywords. East Sayan, granitoid intrusions, gold, tellurides, gold-porphyry type
1
Introduction
The SE part of East Sayan has been known for gold deposits for a long period of time. Quartz-vein (Pionerskoe,
Granitnoe, Dinamitnoe, etc.) and gold-sulfide polygenic
deposits and occurrences (Zun-Kholba, Zun-Ospa, etc.)
are located in the region (Mironov and Zhmodik 1999).
However, understanding of gold-porphyry style deposits
has been limited, until now, to the Tainskoe gold deposit
(Mironov et al. 2001).
It is known that volcano-plutonic associations within
island arc complexes host Au-Cu porphyry-type deposits. These deposits consist of disseminated, veinlet-impregnated and veinlet ores that are confined to small
plagiogranite and granodiorite intrusions with porphyry
structures (Kryvtsov et al. 1986).
We have investigated two gold ore occurrences in the
Tissa river basin: Horingolskoe and Sagangolskoe (Fig. 1).
Geological prospecting is currently being carried out in
these areas.
2
seminated pyrite ores in relatively weakly altered
plagiogranites, in which grain size of sulfide disseminations attains 1-1.5 cm, are noted.
Granitoids are represented by porphyry-like biotite
plagiogranites that have undergone different styles of alteration. Sericitization, epidotization and carbonatization
of plagioclase, chloritization and muscovitization of biotite and the appearance of pyrite are observed as alteration types. The most altered varieties (called beresites
or quartz-sericite metasomatites) have a quartz-carbonate-sericite composition with pyrite contents up to 5 wt.%.
Carbonates are represented by ferrodolomite, calcite and
ankerite. Rocks defined as listwaenites differ by their high
carbonate and chlorite contents. These are quartz – chlorite - carbonate, quartz – muscovite -carbonate and quartz
– chlorite – muscovite - carbonate rocks with impregnations of pyrite (up to 5 vol.%). Relics of plagioclase relics
are locally present. The carbonates in the listwaenites are
ankerite and ferrodolomite.
Except for the granitoid intrusions, gold mineralization is also revealed within volcanic rocks of the Sarhoi
series. The orebodies consist of zones of sulfidization, 3050 m in thickness. The sulfidized volcanites are altered to
Geological setting
The region features volcanic rocks of island arc affiliation,
consisting of rhyolites, dacites and andesites (Sarhoi Series
R3) (Fig. 1). These are intruded by small granitoid bodies
of the Sarhoi (S3-D1), Urik (PR3) and Horingol (V-a1) complexes. In addition to these rocks, outcrops of gabbropyroxenite massif, as well as crystalline schists of the
Bilinskaya suite are present within the area.
The gold mineralization is mainly confined to porphyry-like plagiogranites and diorite dikes. Gently-dipping low-sulfide quartz veins with altered margins are
developed along zones of mylonitisation and constitute
the main orebodies. Beside the quartz veins, zones of
quartz impregnation and beresitization, as well as dis-
Close
1392
B.B. Damdinov
quartz-sericite rocks with impregnations of pyrite (up to
10 vol.%), albite and relicts of epidote.
Four ore types: (1) low-sulfide quartz veins with altered margins, (2) zones of quartz veinlets (veinlet ores),
(3) impregnated sulfide ores in granites and (4) impregnated sulfide ores in volcanic rocks have been established
in these deposits. Mineralogical characteristics of the four
types are shown below.
3
Ore mineralogy
Quartz veins are 1–2 m in thickness. The quartz is milky,
crystalline and drusoid. Mineralization occurs as isolated
small nests and impregnations of pyrite, chalcopyrite and
rare chalcocite. The altered rocks surrounding the vein
(beresites) contain dense disseminations of pyrite that
disappear away from quartz veins. A SEM study of polished sections and ore concentrates have revealed cinnabar, pyrrhotite inclusions in pyrite, as well as telluride
minerals [tellurobismuthite (Bi2Te3), hessite (AgTe2),
petzite (Ag3AuTe2)], native gold with rare argentite inclusions, together with the main ore minerals. Gold and
Ag contents in the vein ores reach 52.6 and 20.8, g/t, respectively (assay analyses of trench samples).
Veinlet ores represent areas in which the thin quartz veins
thicken into a network of veinlets, accompanied by relatively high sulfide content (mainly pyrite). The altered vein
margins join together, forming zones of beresites and
beresitized granites up to 30 m thick. Pyrite is the dominant ore mineral; galena, bismuthinite and chalcocite occur sporadically. Tellurobismutite (Bi2Te3), altaite (PbTe),
hessite (AgTe2), petzite (Ag3AuTe2), calaverite (AuTe2) are
observed among the tellurides. Significant amounts of native gold grains, locally with argentite inclusions are present.
Gold and Ag contents in veinlet ores achieve 26.8 and 37.8 g/
t, respectively.
Impregnation ores are located within the relatively
weakly-altered coarse-grained plagio-granites that are composed by the grains of sericitized plagioclase, quartz and
muscovite. The size of the impregnation pockets reaches
1–1.5 cm. The main ore mineral is pyrite; galena, chalcocite
and native gold are present in minor amounts. Tellurides
include petzite (Ag3AuTe2) and hessite (AgTe2). Gold and
Ag contents in the impregnated ores are 7.4 and 13.1 g/t,
respectively.
The sulfidized volcanites compose the extensive zones
that are up to 50 m thick within the weakly-altered effusive rocks. Impregnations of pyrite make up 5-10 of the
rock by volume; grain size is typically <0.5 mm. Other
ore minerals are chalcopyrite, galena, molybdenite, rutile,
native gold and tellurides [tellurobismuthite (Bi2Te3),
altaite (PbTe) and melonite (NiTe2)]. Individual grains of
uraninite are also observed. The gold content in the
sulfidized volcanic rocks is 2.2 g/t.
Thus, all the studied ore types are characterized by a
common set of ore minerals. The predominant mineral
is pyrite; chalcopyrite, galena, chalcocite, cinnabar, molybdenite, rutile and pyrrhotite are persistently present
in smaller amounts. Tellurides compose discrete grains
(up to 50 µm), inclusions within pyrite (up to 10 µm)
and intergrowths with native gold and other tellurides.
Native gold has middle to high purity (.820-.999), without impurities. The gold grains have isometric or rounded
(as inclusions) shape. Size varies from sub-10 µm to hundreds of µm. Some gold grains are porous and interstices
are filled by aggregates of oxidized pyrite. As a result,
admixtures of Fe, O and S (to 5-6 wt.%) are measured in
these grains. The absence of native silver or electrum is
characteristic; silver minerals are represented only by
hessite and rare argentite, which occurs as inclusions in
gold. It should be noted that the Au distribution is irregular and that the Ag content is less than the detection
limit (<1 ppm; atom-absorption and assay analyses) in
the majority of samples.
Two ore mineral associations can be distinguished
from the ratios of ore minerals: an early gold-pyrite
association, and a late gold-telluride association. It is
suggested that formation of the gold-pyrite association
is closely related to the relatively high-temperature
process of granite (and effusive rock) beresitisation at
340-460°C. The formation of Au-bearing pyrite occurs
during this process. As a result, gold with Fe, S, and O
impurities appears in the ores. The low-temperature
gold-telluride association appears later. Pure native gold,
often in intergrowths with telluride minerals, forms
during this stage. Based on the Au-Ag-Te mineral stability diagram of Bortnikov et al. (1988), the gold-telluride association is interpreted to form at 150-280°C.
Comparable temperatures were obtained for gold-telluride-polymetallic association in the Tainskoe deposit,
using thermobarometric-geochemical data (Mironov et
al. 2001).
4
Conclusions
The studied deposits are characterized by a number of
features typical of Au-(Cu)-porphyry type deposits:
1. The ores are confined to small porphyry granitoid intrusions of island-arc type;
2. Widespread veinlet and sulfide-impregnation ores
along with a quartz veins;
3. All types of ore share similar structural features and
secondary alteration character of the wallrock;
4. The presence of a gold-telluride association throughout the ores;
5. Similar to gold-porphyry type deposits temperature
conditions of ore formation.
Close
Chapter 13-4 · New occurrences of gold-porphyry type ores in the southeast of East Sayan (Russia)
Considering the low Cu and Mo contents (less than
0.03 and 0.001 wt.%, respectively), the deposits can be
classified as gold-porphyry type. It is known that goldporphyry types of deposit commonly have significant reserves (Krivtsov et al. 1986). This fact is encouraging for
future exploration and discovery of large gold deposits
in the area.
Acknowledgements
Investigations were supported by Russian Fund of Basic
Research grant 03-05-64857.
1393
References
Bortnikov NS, Cramer H, Genkin AD, Krapiva LYa, Santa-Krus M
(1988) Gold and silver telluride parageneses in Florencia gold
deposit (Republic Cuba). Geology of Ore Deposits 2: 49-61
Kryvtsov AI, Migatchev IF, Popov VS (1986) Copper-Porphyry Deposits of the World. Moscow. Nedra, 236 pp.
Mironov AG, Zhmodik SM (1999) Gold deposits in the Urik-Kitoy
metallogenic zone (East Sayan, Russia). Geology of Ore Deposits
41: 54-69
Mironov AG, Zhmodik SM, Ochirov YuC, Borovikov AA, Popov VD
(2001) The Tainskoe gold deposit (East Sayan, Russia) is a rare
type of gold-porphyry formation. Geology of Ore Deposits 43:
395-413
Close
Close
Chapter 13-5
13-5
Polymetallic assemblages with precious metal tellurides
and sulfosalts from the Furtei epithermal Au deposit,
Sardinia, Italy: Paragenesis and genetic significance
S. Fadda1, M. Fiori1, S.M. Grillo2, C. Matzuzzi1
Istituto di Geologia Ambientale e Geoingegneria del CNR, Cagliari, Italy
2
Dipartimento di Geoingegneria e Tecnologie Ambientali, Università di Cagliari, Italy
1
Abstract. Ore bodies of the Furtei epithermal gold deposit, W Sardinia,
are highly enriched in telluride minerals. The association of hessite,
stützite, sylvanite, petzite, coloradoite, altaite, with native tellurium
indicates direct magmatic inputs to the mineralizing solutions: a
transition of this magmatic hydrothermal system from porphyry to
high sulfidation epithermal mineralization environments is envisaged. Sulfidation states of telluride bearing ore fluids fluctuated
between IS and HS conditions within the same mineralization, with
telluride minerals related to both HS and IS assemblages. On the
basis of available corroborative electron microprobe data on the
telluride-rich parts of drillcore samples, the relationship between
mineral assemblages and sulfidation states of fluids is assessed.
Keywords. Sardinia, porphyry, epithermal, tellurides, sulfidation state
1
Introduction
Telluride minerals may be important in epithermal precious metal ores. The occurrence, distribution and composition of a number of Te-bearing minerals and
sulphosalts, as well as their mutual relationships offer
potential for deciphering the physicochemical conditions
of ore formation because they are valuable indicators of
changes in temperature and sulfidation state (Cook and
Ciobanu 2002). Reported tellurides include those of Ag,
Au, Bi, Cu, Fe, Hg, Ni and Pb. Paragenetic relationships
involving tellurides, gold and native tellurium are difficult to study due to extensive replacement, annealing and/
or phase decomposition on cooling; their deposition is
traditionally restricted to one or two stages that always
follow initial deposition of sulfides, pyrite, chalcopyrite,
sphalerite, galena (Afifi et al. 1988b). Epithermal Au-(Ag)
deposits may be broadly grouped into high-sulfidation
(HS) and low-sulfidation (LS) types, based on the
sulfidation state of their primary sulfide assemblage. In
all reported occurrences, gold or electrum is deposited
either with, or following tellurides, but not before the telluride-bearing stage. Recently Einaudi et al. (2003) discussed the relationship between porphyry Cu deposits,
associated base metal veins and epithermal deposits in
respect to sulfidation state of ore fluids, and suggested
that Au deposition in HS epithermal deposits occurs at
intermediate sulfidation (IS) conditions.
In Sardinia (Italy), tertiary porphyry- and epithermal
style ore deposits (Fiori et al. 2003) host telluride ore minerals as major gold carriers. Highly acidic fluids form
advanced argillic alteration halos and/or silicic lithocaps
over porphyry systems which may host subsequent HS
mineralization introduced by higher-pH, moderate- to
low-salinity fluids. The aim of this work is to investigate
the connection between the acid sulfate type gold deposit
at Furtei and a porphyry- style shallow intrusion located
beneath the zone of most intense hydrothermal alteration
(Meloni 1994). The Te-rich paragenetic assemblages in the
Au-Ag-Te-bearing ores with telluride-dominant mineralogy are examined to investigate the timing of precious metal
introduction at different vertical levels in the system, and
the sulfidation states of the hydrothermal fluids.
2
Tertiary calc-alkaline magmatism in Sardinia
The calc-alkaline magmatism in Sardinia appears to be
related to extension associated with the eastwards drift
of the Sardinian-Corsican Massif and the establishment
of a Benioff zone east of the island. The resulted magmatic rocks include volcanics and subvolcanics of intermediate to acid composition. The ore forming events are
associated with the hydrothermal activity that affected
most of the volcano-sedimentary sequences during or
immediately after volcanism and before deposition of
unaltered Miocene sediments. The epithermal deposits
include precious and base-metal ores, mainly of low
sulfidation type, e.g. Osilo. Among the precious-metal
occurrences, the Furtei Au deposit is the only example of
HS mineralization in Sardinia. It is typically acid-sulfate
in style with the mineralized bodies of S. Miali-Is Concas,
Sa Perrima and a small, economically unimportant but
mineralogically interesting, gold showing, located near
Bruncu sa Casa. These bodies are located within a relatively small area (1.5 km2), south of the town of Furtei.
In terms of shape, the orebodies are pipe-like and have
vertical extents exceeding 200-300 m and extend horizontally from a few tens to a hundred meters. Under the
surficial oxidized zone of supergene nature, the primary
sulfide zone is largely hosted by diatreme breccia and
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S. Fadda · M. Fiori · S.M. Grillo · C. Matzuzzi
characterized by a vertical zoning of the mineral assemblage, dominated by pyrite-enargite-luzonite-gold at
higher levels, whereas in the deep zone tetrahedritess,
minor base metal sulfides and Te-rich minerals are present,
especially in the deeper parts of the orebodies. Gold mostly
occurs as high-fineness native metal and in some tellurides (Fiori and Grillo 2001).
Table 1 shows the three main ore mineral assemblages.
Pyrite is ubiquitous and may, in places, be abundant - up
to 20 vol%. In the near-surface environment, the oxidation of sulfide minerals is controlled by the present topographic surface and might extend in fractures down to
60 m from the surface: here the ore mineral assemblage
only includes free gold plus associated oxide minerals.
Supergene alteration grades downward into primary sulfide zones. The As-sulfosalt assemblage grades into the
telluride assemblage with increasing depth. In the deeper
parts of the system the paragenesis evolves into a Te- and
Sb- rich assemblage with the presence of increasing tetrahedrite and Te-rich tetrahedrite up to goldfieldite,
calaverite and krennerite, sometimes associated with native Te. Native Au in drillcore samples always appears as
blebs in enargite. It is ubiquitous and fairly pure, with a
maximum Ag content around 6%. Current evidence indicates continuity of ore grade over a vertical span of at
least 300 m, suggesting underlying reserves of higher gold
grades, recoverable grades of Cu and possibly also Te.
3
alization at Furtei may be associated with a porphyry system with a fluid of magmatic derivation circulating at
deeper level followed by the mixing of the high-temperature magmatic hypersaline brine with cooler low-salinity meteoric water at shallow depth. The epithermal mineralization of Furtei can be divided into two stages postdating the silicic, and much of the advanced argillic alteration and was characterized by a distinct zoning with
depth: the HS-state sulfosalts, enargite and luzonite are
the principal Cu minerals in the orebody and occur at
shallow level with abundant euhedral pyrite and gold. At
depth tennantite-tetrahedrite, chalcopyrite, stannite, Au,
Ag-tellurides (including coloradoite, petzite, hessite) and
Bi- minerals are present. Garbarino et al. (1991a, b) also
reported the presence of Te-tetrahedrite, native Te, calaverite
or krennerite in some deep core samples from the deeper
sulfide assemblage. Deposition of sulfide-gold mineralization at shallow depth occurred under comparatively high
fS2, whereas deep assemblages where characterized by lower
fS2 (Ruggeri et al. 1997). Gold mineralization is associated
with tennantite and chalcopyrite which partially replaces
enargite, luzonite appearing paragenetically later. Minerals
are found in cavities and fractures of vuggy and massive
silica and form fine disseminations.
4
Discussion
Systematic, detailed microanalytical (EPMA) and highmagnification SEM investigations of the mineralogy of
the telluride-rich segments of drill cores from the
orebodies of the mine were carried out in order to investigate the relative sulfidation states of hydrothermal fluids which introduced the telluride assemblages (Table 2a,
b). Ruggeri et al. (1992) estimated fS2 and fTe2 for formation of Is Concas deep mineral assemblages:
log fS2 = -14.0 to –10.0 log fTe2= -13.0 to –9.0
Sulfidation state during ore deposition
A relatively shallow intrusion may have provided the heat
needed to drive fluid circulation and to induce phreatic
and phreatomagmatic phenomena. Geophysical evidence
for the presence of such an intrusion at 1 to 1.5 km present
depth is reported by Meloni (1994). Volumes of high temperature fluids were rapidly flushed upwards from the
already emplaced porphyry into a ready network of fractures, breccias and channelways. Fluid inclusion data
(Ruggieri et al. 1997) are similar to those found in many
porphyry Cu deposits, including Calabona in NW Sardinia
(Frezzotti et al. 1992) suggesting that epithermal miner-
Close
Chapter 13-5 · Polymetallic assemblages with precious metal tellurides and sulfosalts from the Furtei epithermal Au deposit, Sardinia, Italy
The construction of fS2-fTe2 diagrams at 100°C and
300°C (Afifi et al. 1988b) has shown that the topologies of
these diagrams are essentially constant with changing
temperature making these diagrams useful for comparison of telluride assemblages in low-temperature (<350°C)
hydrothermal deposits.
The commonly observed dominant telluride mineral
assemblages stable at the deep levels of Furtei ore bodies allows a narrow domain to be constrained in fTe2-fS2
space (Fig. 1). Because Te solubilities are predicted to
be low in auriferous chloride waters (Cooke et al.
2001), deposition of tellurides and native tellurium in
IS/LS environments may result from condensation of
magmatically-derived H2Te(g) and Te2(g) into deep-level
chloride waters. Such magmatic input into the hydrothermal system is later than the input of sulfur, since
telluride deposition is always preceded by that of sulfides. The fugacity of Te2 is very important and is controlled by the supply of this element from the source,
and also locally controlled by reactions between the fluid
and rock minerals or changes in fluid chemistry. Whether
gold occurs in the native form, in petzite or in sylvanite
is influenced by variations of this parameter. The relative stabilities of hessite and calaverite depend on the
initial tellurium concentration and Ag:Au ratio in the
water. However minor amounts of Te can dissolve into
chloride waters and could precipitate into lower temperature surficial acid sulfate waters by cooling or fluid mixing producing geochemical anomalies only or Te-rich
mineralizations.
Study of the mineral assemblages in the Furtei ore
bodies demonstrates that introduction of gold in HS ores
1397
is related to IS assemblages (Voudouris et al. 2004), indicating an evolution from an IS towards HS environment. This implies that HS-style epithermal mineral assemblages may be precipitated from Au-bearing LS/IS
waters with a distinct vertical zonation of electrum and
tellurides. In fact, the deeper part of the ore is characterized by tetrahedritesss, Te-rich minerals, including precious metal tellurides, Te-tetrahedrite and native tellurium evolving in shallow level to enargite-luzonite, CuFe-sulfides and native gold.
The ore minerals also indicate that a part of gold introduction (in native form and in sulfosalts) has taken
place contemporaneously with deposition of the HS assemblage, thus suggesting a genetic link between the two
sulfidation states in the same ore deposition environment. In conclusion, there is a strong suggestion that the
magmatic-hydrothermal system at Furtei underwent an
evolution from an earlier IS porphyry-style mineralization, to IS-HS mineralizations in porphyry related, base
metal- and epithermal precious metal veins. Tellurium
was introduced by both HS and IS solutions in a succession of phases of progressively lower Te content until
the establishment of the observed paragenesis. The initial increase in fTe2 from the magmatic source led to saturation, with the appearance of native Te and di-tellurides
(sylvanite, calaverite, krennerite), followed in turn by
altaite, coloradoite, hessite, petzite and finally gold with
gradual decreasing fTe2 values. Continuing systematic
optical identifications and micro-analytical investigations
of drillcore samples, aim to estimate under which
sulfidation state the bulk of the Au deposition took place
within the zoned epithermal system.
Close
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S. Fadda · M. Fiori · S.M. Grillo · C. Matzuzzi
Acknowledgements
We thank the Sardinia Gold Mining Company for the help
provided during the current study. The research has been
also supported by the Istituto di Geologia Ambientale e
Geoingegneria – CNR, Cagliari.
References
Afifi AM, Kelly WC, Essene EJ (1988b) Phase relations among tellurides, sulfides, and oxides: II. Applications to telluride bearing ore
deposits. Econ Geol 83: 395-404
Cook NJ, Ciobanu CL (2002) Tellurides: more than mineralogical curiosities, but also markers of fS2-fO2 evolution in zoned hydrothermal systems. IMA, 18th General Meeting, Edinburg, Programme
with Abstracts: 283
Cooke DR, McPhail DC (2001) Epithermal Au-Ag-Te mineralization,
Acupan, Baguio District, Philippines: numerical simulations of
mineral deposition. Econ Geol 96: 109-131
Einaudi MT, Hedenquist JW, Inan EE (2003) Sulfidation state of hydrothermal fluids: the porphyry-epithermal transition and beyond.
In: Simmons SF, Graham IJ, (eds), Volcanic, geothermal and oreforming fluids: Rulers and whitnesses of processes within the Earth.
SEG-Geochem Soc Special Publication 10: 285-313
Fiori M, Grillo SM (2001) The Furtei high-sulfidation epithermal gold
deposit (Sardinia, Italy): mineral assemblage and its evolution. In:
A Piestrzynski et al. (eds), Mineral Deposits at the beginning of
the 21st Century, Swets & Zeitlinger: 739-742
Fiori M, Granitzo F, Grillo SM, Simeone R (2003) Porphyry and
epithermal systems near Siliqua, Sardinia, Italy. In: DG
Eliopoulos et al. (eds), Mineral Exploration and Sustainable
Development, Millpress: 267-270
Frezzotti ML, Ghezzo C, Stefanini B (1992) The Calabona intrusive
complex (Sardinia Italy): Evidence for porphyry copper system.
Economic Geology 87: 425-436
Garbarino C, Grillo SM, Melis F, Pretti S, Uras I (1991a) Epitermalismo Terziario a metalli preziosi in Sardegna. Esempi di
alcune paragenesi. Plinius 6: 174-175
Garbarino C. Grillo SM, Marcello A, Pretti S, Uras I, Fiori, M (1991b)
First data on Tertiary epithermal occurrences in Sardinia,
Italy. In: Ladeira EA, ed. Proc. Brazil ’91, Balkema, Rotterdam:
143-150
Meloni P (1994) Metodologie di prospezione geomineraria e
geofisica di mineralizzazioni sepolte tipo porphyry copper. Studio del settore di Serrenti-Furtei (Sardegna Meridionale):
Unpubl. PhD thesis, University of Cagliari (english abstract in
Plinius 13: 145-148)
Ruggieri G, Lattanzi P, Luxoro S, Dessì R, Benvenuti M, Tanelli G
(1997) Geology, Mineralogy, and Fluid Inclusion Data of the
Furtei High-Sulfidation Gold Deposit, Sardinia, Italy. Economic
Geology 92: 1-19
Vouduris P, Alfieris D, Fiori M, Grillo SM (2004) Te-Rich MagmaticHydrothermal System in Northeastern Greece and Sardinia: a
comparative study of ore mineralogy and sulfidation state. In:
Metallogeny of the Pacific NorthWest: Tectonics, Magmatism
and Metallogeny of active continental margins. IAGOD Conference Vladivostok/Russia: 572-575
Close
Chapter 13-6
13-6
Ore-forming fluids in gold-telluride deposits in the
Pingyi area, western Shandong, China
Huabin Hu1,2, Jingwen Mao2, Shuyin Niu1, Fengmei Chai2, Yongfeng Li2, Mengwen Li2
of Resources, Shijiazhuang University of Economics, Shijiazhuang 050031, China
1 College
2
China University of Geosciences, Beijing 100083, China
Abstract. The Au-telluride district of the Pingyi area, western
Shandong, mainly comprises the Guilaizhuang and Lifanggou gold
deposits. The former is hosted in cryptoexplosive breccia of the
Tongshi complex with a zircon SHRIMP U-Pb weighted mean age
of 175.7±3.8 Ma. The latter occurs in dolomitic limestone, micrite
and dolomite of the Early Cambrian Zhushadong Formation. Fluid
inclusion studies indicate that the inclusions of both Au telluride
deposits are both of vapor-liquid two-phase NaCl-H2O type. Homogenization temperatures of the fluid inclusions vary from 103
to 250ºC, and the ice melting temperatures range from –2.5 to –
13.5 ºC, corresponding to a salinity range of 4.65 to 17.26 wt.% NaCl
equiv. The δ34S values of pyrite associated with gold mineralization
exhibit a narrow range of –0.71 to 2.99‰, implying that the sulfur
was probably derived from the mantle or magma. The δ18OSMOW
values of vein quartz and calcite range from 11.5 to 21.5‰, corresponding to the δ18Ofluid values of –1.13 to 10.9‰, and the δD values of the fluid inclusions between –70 and –48‰. The isotope
data suggest that the ore-forming fluids of the two gold deposits
were derived from the mantle, and mixed with meteoric water at
shallow levels. Pressure release and boiling of the fluids played an
important role in the ore-forming processes of the two deposits.
nantly composed of amphibolite and biotite granulitite,
with minor TTG gneisses, which suffered from mediumto low-grade metamorphism. The cover rocks comprise
the Neoproterozoic and its overlying strata, lithologically
including carbonate rocks and clastic rocks (Shen et al.
1998; Yu 2001; Hu et al. 2004).
The most important structure at the eastern margin
of the western Shandong is the Tan-Lu fault zone, which
extends NNE more than 330 km in Shandong province
(Yan et al. 1996; Niu et al. 2004). Faults in western Shandong
occur in concentric ring and radial forms and are subsidiary structures of the Tan-Lu fault zone.
In western Shandong Mesozoic-Cenozoic mantle- derived magmatic rocks, including intrusive rocks, potassium- rich volcanic rocks and lamprophyre dikes, are
widely distributed. The Mesozoic intrusive rocks are widespread but relatively small in size (Xu et al. 2000; Niu et
al. 2001; Qiu et al. 2001; Yin et al. 2001).
Keywords. Au telluride-deposit, fluid inclusion, stable isotope, western Shandong
3
Geology of gold deposits
3.1 Stratigraphy, structure and magmatism of gold districts
1
Introduction
The western Shandong (Luxi) region is located on the
southeastern edge of the North China craton and separated by the Tanlu fault from the Jiaodong gold province,
the largest gold producing area in China. The Guilaizhuang
gold deposit, with 35 tonnes of gold reserves, was discovered by the No.2 Geological Party of Shandong Province
in the Pingyi area in 1988. The Guilaizhuang gold deposit
and Lifanggou gold deposits, with total gold reserves of
45 tonnes, constitute the main part of the gold deposits
found in western Shandong. On the basis of detailed field
investigations, this paper discusses the characteristics of
fluid inclusions and H and O stable isotopes of the
Guilaizhuang and Mofanggou gold deposits.
2
Regional geological setting
The strata of the Luxi region consists of basement and
cover strata. The basement rocks are composed by the
Neoarchean Taishan Group-complex and trondhjemitetonalite- granodiorite suite (TTG) and Paleoproterozoic
orogenic granites. The Taishan Group-complex is domi-
The strata exposed in the ore districts include the basement and cover deposits. The former consists of biotite
granulite and gneissic granodiorite of the Taishan Groupcomplex, mainly distributed in the southwestern part and
also exposed in small amount in the central part of the
area. The covers exposed extensively are Cambrian-Ordovician carbonate rocks, including dolomitic limestone,
dolomite, micrite, thin-bedded pelitic dolomite, thin-platy
limestone, argillaceous limestone and oolitic limestone
with yellowish green shale. The Jurassic Santai Formation is distributed sporadically in the northeastern part
of the ore district and unconformably overlies Ordovician dolostone. It is composed of purple sandstone and
conglomerate. Cretaceous andesitic pyroclastic rocks are
exposed in the northeastern part of the ore district (Fig. 1).
Fault structures of the ore district faults fall into three
main groups: N-S-trending, NW-trending and EW-trending. The N-S-trending Yangan fault, a regional normal fault,
15-50m in width, crosscuts the Tongshi magmatic complex and Paleozoic carbonate. NW- and EW-trending faults
occur at the periphery of the Tongshi magmatic complex
and cut Cambrian- Ordovician sedimentary rocks. The
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Huabin Hu · Jingwen Mao · Shuyin Niu · Fengmei Chai · Yongfeng Li · Mengwen Li
Lifanggou and Mofanggou gold deposits are controlled
by secondary NW- trending normal faults, whereas the
Guilaizhuang gold deposit is controlled by an EW-trending fault.
The Mesozoic Tongshi complex is closely associated
with gold mineralization. The complex, irregular in shape
with an outcrop area of ~30 km2, was emplaced into Precambrian crystalline basement rocks and Cambrian and
Ordovician strata. It is predominantly composed of medium- to fine-grained diorite (porphyry) and pyroxene
(hornblende)-bearing monzosyenite porphyry. The
samples for zircon SHRIMP U-Pb dating from porphyritic fine-grained diorite of the Tongshi complex were
collected from Xifengshan. Single-zircon SHRIMP 206Pb/
238U ages of ten analytical spots range from 167.9 to 183
Ma, with a weighted mean age of 175.7±3.8 Ma, which is
interpreted as the crystallization age of the Tongshi magmatic complex.
normal fault. Inside the fault zone, orebody no. 1 is largest, contributing 98% of the total ore reserves of the
Guilaizhuang gold deposit. It has a controlled length of
550 m, a thickness of 3.3–10.1 m (mean 6.8 m), and a dip
width of >650 m. Drilling has revealed that the ore vein
pinches and swells and branches and converges. Gold
grade ranges from 3.42 to 26.37 g/t, with a mean of 6.8 g/
t and a maximum of 457.4 g/t (Lin et al. 1997).
The orebodies of the Guilaizhuang gold deposit are
lithologically composed of cryptoexplosive breccia, which
consists of diorite porphyry and monzosyenite porphyry
from the Tongshi complex and minor clasts of CambrianOrdovician dolostone. Gold minerals mainly include native gold, electrum and calaverite, with minor petzite,
altaite, melonite, and native tellurium (Lin et al. 1997).
The fine-nesses of native gold and electrum are .979 and
.719, respectively, on average.
3.3 Lifanggou and Mofanggou gold deposits
3.2 Guilaizhuang gold deposit
The Guilaizhuang gold orebodies, hosted in CambrianOrdovician dolomite, are controlled by an E-W-trending
The Lifanggou and Mofanggou gold deposits occur as bedlike bodies in dolomitic limestone, micrite and dolostone
in the Early Cambrian Zhushadong Formation. The
Close
Chapter 13-6 · Ore-forming fluids in gold-telluride deposits in the Pingyi area, western Shandong, China
orebodies are about 20–30 m from the unconformity between Cambrian carbonate rocks and Neoarchean biotite
leptite or Paleoproterozoic monzogranite. This unconformity
is actually a dominant detachment formed during Mesozoic uplift of the crust in western Shandong. The Lifanggou
ore bed is generally from 3 to 10 m in thickness, and is
controlled by NW-trending secondary detachment faults,
whereas the Mofanggou gold bed, dipping 325°–350° at
8–20°, in the Early Cambrian Zhushadong Formation is
ca. 280 m long and 1.0–8.0 m thick.
The gold grade of the Lifanggou gold deposit ranges
from 2.19 to 7.24 g/t, with a mean of 4.9g/t, and the gold
grade of the Mofanggou gold deposit from 1.09 to 25.21 g/
t, with a mean of 11.54g/t.
The homogenization temperatures of the fluid inclusions in alteration minerals from the Mofanggou gold
deposit also range from 120 to 260ºC and cluster between
120 and 190ºC. In addition, some inclusions in quartz were
measured and the homogenization temperatures obtained
range from 300 to 450ºC. The ice-melting temperatures
range from –3.5 to –11.5ºC and show a bimodal pattern
with two temperature peaks from –3.5 to –4.5ºC and from
–7.5 to -10ºC. The salinity estimated from the ice-melting point data of two-phase inclusions range from 5.41 to
15.47 wt.% NaCl equiv., with a peak between 11.7 and
13.18 wt.% NaCl equiv. The fluid densities range from
0.649 to 1.03 g/cm3.
5
4
Fluid inclusion studies
4.1 Samples and analytical methods
Samples for fluid inclusion studies were collected from
the Lifanggou, Mofanggou and Guilaizhuang gold deposits. Six samples were taken from Lifanggou, five from
Mofanggou and six from Guilaizhuang.
Microthermometric measurements were carried out
on a Linkam THMSG 600 programmable heatingfreezing stage (–196 to +600ºC) at the Laboratory of the
Faculty of Geosciences and Mineral Resources, China
University of Geosciences, Beijing. The heating rate
was 0.1 to 1 ºC/min below 10 ºC, whereas the heating
rates were about 3 to 5ºC/min at 10 to 31ºC, with a
reproducibility of ± 0.1ºC. The heating rate was 5 and
10ºC/min at higher temperatures (>100ºC), with a reproducibility of ± 2ºC.
4.2 Microthermometric results
The homogenization temperatures of fluid inclusions in
the Guilaizhuang gold deposit are between 110 and 310°C.
The ice-melting temperatures vary from –2.5 to –10.3ºC,
at a peak of –2.5 to –6.5°C. The salinities determined from
the ice-melting point of the fluid inclusions range from
4.65 to 17.26 wt.% NaCl equiv (Bodnar 1992). We obtained
corresponding fluid densities between 0.643 and 1.027 g/
cm3 by consulting the table of Liu and Shen (1999) according to the homogeni-zation temperatures and salinities of the aqueous fluid inclusions.
The homogenization temperatures of fluid inclusions
in the Lifanggou gold deposit mainly range from 103 to
220°C. Some data from quartz range from 300 to 450°C.
The ice-melting temperatures vary from –2.5 to –9.3ºC
and cluster at -8 to -9.3ºC, and the corresponding salinities of the aqueous inclusions range from 4.65 to 13.18
wt.% NaCl equiv. and mainly from 11.7 to 13.18 wt.% NaCl
equiv. (Bodnar 1992). We obtained corresponding fluid
densities in the range from 0.5 to 1.019 g/cm3.
1401
Stable isotope studies
δ34S values of pyrite from silicified and carbonatized
monzodiorite porphyry, igneous breccia and mineralized
dolostone of the Guilaizhuang and Mofanggou gold deposits range from -0.71 to 2.99‰ (Lin et al. 1997), close
to those of the mantle sulfur, suggesting a mantle or
magma source of sulfur in the ores. In the Guilaizhuang
gold deposit, the five δD and δ18O values of five calcite
samples range from –48 to –61‰ with a mean of –54‰
and from 11.5 to 17.7‰ with a mean of 15.9‰ respectively; and the δ18O value of one quartz sample is 19.3‰.
In the Lifanggou gold deposit, the δD and δ18O values of
five calcite samples vary from –63 to –70‰ with a mean
of –66‰ and from 18.4 to 21.2‰ with a mean of 19.9‰
respectively; the δ18O values of one calcite sample from
the Mofanggou gold deposit is 21.5‰.
The mean homogenization temperatures of 150.2 and
181°C were obtained by averaging homogenization temperatures of 63 inclusions in calcite from the Guilaizhuang
gold deposit and 30 inclusions in calcite from the
Lifanggou gold deposit. Using the calcite-water isotope
fractionation equation 1000 lna=2.78x106 T -2 –2.89 (O’Neil
et al. 1969), the δ18O values of the mineralizing fluids are
calculated, ranging from -1.13 to 10.9‰. According to the
mean homogenization temperatures in quartz, using the
quartz-water isotope fractionation equation 1000 lna
=3.42x106 T -2 - 2.86 (Zhang 1989), the δ18O values of the
mineralizing fluids were calculated to be 6.3‰ for the
Guilaizhuang gold deposit.
Therefore, the sulfur, hydrogen and oxygen isotopic
compositions from deposits of this area have signatures suggesting mixing of formational water and deepseated magmatic fluids, suggesting that the ore-forming
fluids were derived from complex sources. Although
the Guilaizhuang and Mofanggou gold deposits are hosted in different strata, the fluid inclusion data described
suggests that the metallogenic mechanisms are consistent. Mineralization is related to decompressional
boiling of fluids and mixing of deeply circulating meteoric water.
Close
1402
Huabin Hu · Jingwen Mao · Shuyin Niu · Fengmei Chai · Yongfeng Li · Mengwen Li
Acknowledgements
This study was supported by the State Development and
Planning Programs for Basic Researches in Key Areas of
China (No. 1999043211) and the National Natural Science
Foundation of China (No. 40272088).
References
Bodnar R (1992) The system H2O-NaCl. PACROFI IV, Program and
Abstracts: 108–111
Hu H, Niu S, Mao J, Zhang Z, Wang Y (2004) The Mesozoic mantlebranch structure and related gold deposits in western Shandong,
Mineral deposits 23: 115–122 (in Chinese with English abstract)
Lin J, Tan D, Yu X, Li B, Li Y, Xu W (1997) Genesis of Guilaizhuang
gold deposit of western Shandong. Jinan: Shandong Science and
Technology press, 160 (in Chinese with English abstract)
Liu B, Shen K (1999) Thermodynamics of fluid inclusions. Beijing:
Geological Publishing House, 290 (in Chinese with English abstract)
Niu M, Zhu G, Song C (2001) Mesozoic volcanic activities and deep
processes in the Tanlu fault zone. Journal of Hefei University of
Technology 24 (2): 147-153(in Chinese with English abstract)
Niu S, Hu H, Mao J, Sun A, Xu, C, Hou Q (2004) Structure in western
Shandong and its genetic mechanism. Geology in China 31 (1):
34-39(in Chinese with English abstract).
O’Neil J, Taylor H (1969) Oxygen isotope fractionation in divalent
metal carbonates. Journal of Chemical Physics, 51: 5547-5558
Qiu J, Xu X, Luo Q (2001) Potash-rich volcanic rocks and
lamprophyres in western Shandong province: 40Ar-39Ar dating
and source tracing. Chinese Science Bulletin 46 (18): 1500-1508
Shen Y, Zeng Q, Liu T, Xie H, Li G (1998) Discussion of the types and
ore exploring direction of Shandong gold deposits. Gold Science
and Technology 6 (3): 1-5 (in Chinese with English abstract)
Xu W, Wang D, Wang S (2000) pTtc model of Mesozoic and Cenozoic
volcanisms and lithospheric evolution in eastern China. Journal
of Changchun University of Science and Technology 30 (4): 329335(in Chinese)
Yan S, Wang G, Shao Z, Meng X (1996) Extensional tectonic model of
crustal elevation in western Shandong. Acta Geologica Sinica 70
(1): 1-11 (in Chinese)
Yu X (2001) Ore-forming series and model of Tongshi Gold field in
Pingyi, Shandong province. Geology of Shandong 17 (3-4): 5964 (in Chinese with English abstract)
Zhang L (1989) Petrogenetic and minerogenetic theories and prospecting. Beijing: Beijing Technological University Press, 267 (in
Chinese)
Close
Chapter 13-7
13-7
Au-Ag-Se-Te mineral and geochemical systems in
black shale-hosted deposits (Uzbekistan)
Rustam I. Koneev, Arpay H. Turesebekov, Evgeniy N. Ignatikov
National University of Uzbekistan, Tashkent, Uzbekistan
B.B. Vasilevsky, R.R. Rakhimov
State Committee of the Republic of Uzbekistan on Geology and Mineral Resources, Tashkent, Uzbekistan
Abstract. The Republic of Uzbekistan is among the leading gold mining nations in the world. In terms of explored gold reserves, the
country ranks fourth in the world; current annual production ranks
8th or 9th. Deposits of the western part of the Kyzyl-Kum area are
the most economically important in the country. Among these are
the largest deposits such as Muruntau, Myutenbai, Daugyztau,
Kokpatas, as well as others. The primary goals of our research were
to study the role, distribution characteristics and mineralogical occurrence of Te and Se in gold and silver ores; prove the importance
of those elements for the formation of the deposits in the black
shales; and also to show the wide occurrence of Te and Se in ores at
the sub-microscopic level.
Keywords. Gold deposits, black shales, Uzbekistan, Muruntau,
Myutenbai, Vysokovoltnoe, Kosmanachi, tellurides, selenides
1
Geological location of deposits
All gold deposits of Uzbekistan are located within the thick
Beltau-Kurama volcano-plutonic belt (BKVPB). This belt
stretches from Kyzyl-Kum in the west of the Republic to the
Chatkal-Kurama Mountains in the east. Gold deposits tend
to be clustered: e.g. Kyzyl-Kum, Nurata, Kurama (Fig. 1). The
BKVPB was formed due to subduction of the oceanic crust
of Turkistan paleobasin under the northern KazakhstanKyrgyz microcontinent. Clustering of ore deposits occurred
due to intersection of the BKVPB with transform sub-meridional faults. The deposits are located within coaly shales,
sedimentary and carbonate rocks. Formation of the deposits is considered connected to the presence of deep intrusions (e.g. Ahmedov 2001). The host rocks have undergone
such processes as propylitization, beresitization and
argillization. The age of the main stage of ore formation in
all deposits of the BKVPB is Upper Carboniferous to Permian (e.g. Dalimov et al. 2004).
2
Mineralogical and geochemical types
Traditionally, for geological and exploitation purposes, the
gold deposits of Uzbekistan have been divided into goldquartz and gold-sulphide types. Within the largest black
shale hosted deposit, Muruntau, 85% of the gold occurs
within gold-scheelite mineralization. The general idea of
previous research was that mineral composition of the ores
is simple, and that Au, W and As determine their geochemistry (Ahmedov 2001). The most recent studies have shown
that all gold ore deposits of the BKVPB, irrespective of type
of host rocks, consist of defined sets of geochemical parageneses from early to late: Au-W/Au-As/Au-Te/Au-Ag/Au-Sb/
Au-Hg. In the giant deposits, with limited levels of erosion
these series will be more widespread. The economic
resource(s) of the deposit are generally determined by only
two, rarely three, parageneses.
The importance of the late parageneses increases from
west to east, but the richest gold-bearing parageneses in
all deposits are the Au-As, Au-Te and Au-Ag associations.
The common mineral components in all types of ore are
pyrite, arseno-pyrite, scheelite, pyrrhotite, sphalerite, chalcopyrite, galena, sulphosalts and molybdenite.
3
Ore geochemistry and trace mineralogy
Our research was conducted using the ICP MS Elan-DRS,
Jeol Superprobe -8800R and JSM methods. The methodology of research is based on the main principles of microand nanomineralogy outlined by Koneev (2001, 2004). It is
commonly thought that Te and Se are characteristic elements of epithermal Au-Ag deposits in volcanogenic regions.
This is very true in the Kurama District, in which economic
resources are largely defined by: (1) Ag-Au-Te parageneses
with Au, Ag, Sb, Hg, Pb, selenides and tellurides, Bi, and
high grade gold; (2) Au-Ag-Se paragenesis with alloys,
sulphides, sulphosalts, selenides Ag, electrum and kustelite.
The earliest of these is the Au-As paragenesis, with pyrite,
arsenopyrite and invisible gold (Koneev et al. 2004; Koneev
2004). These studies had shown that, in terms of their Te
and Se contents, the ores of deposits in the Kyzylkum region are only slightly less inferior to those of the Kurama
District (Table 1). There are two main groups of the deposits: I - Au:Ag > 1 (Muruntau, Myutenbai), II - Au:Ag < 1 (Vysokovoltnoe, Kosmanachi). In accordance with the series of
intensity of element accumulation in ores (relative concentration factors with respect to Clark values), alongside Au
and Ag, the leading elements are Te, Bi, As, Sb and Se.
Studies of trace mineralogy (Table 2) show that the associations and parageneses which determine the economic value
of the black shale hosted deposits are: 1) Au-As paragenesis
with arsenopyrite, pyrite, Ni- and Co-minerals and finely-dispersed gold; 2) Au-As, or associated with, tellurides and selenides, Bi-minerals, maldonite, and high grade gold; 3) Au-Ag
Close
1404
Rustam I. Koneev · Arpay H. Turesebekov · Evgeniy N. Ignatikov · B.B. Vasilevsky · R.R. Rakhimov
Close
Chapter 13-7 · Au-Ag-Se-Te mineral and geochemical systems in black shale-hosted deposits (Uzbekistan)
with microscopic silver, electrum and kustelite. The Au-Sb
and Au-Hg mineral associations are of negligible importance.
4
Conclusions
1. In the black shale-hosted gold deposits, as in the epithermal deposits, Te and Se, together with Bi, As and Sb,
determine the geochemistry and mineralogy of gold and
silver.
2. The main form of segregation of gold, tellurides and
selenides is micro- and submicro-scopic. Gold minerals are segregated into arseno-pyrite, pyrite and quartzscheelite metasomatites.
3. Tellurides and selenides, native bismuth, maldonite and
high-grade gold are developed in the deposits hosted
within black shales. At high temperature, Bi “takes
away” Te from Au and Ag. Part of gold is formed during the decay of maldonite. Selenides Bi and Ag are
indicators of poor erodibility of deposits.
4. The studied ores are complex, allowing possible byproduct extraction of platinum-group elements, Bi, Se,
Te, Mo, Re, Os and W.
1405
References
Ahmedov NA, editor (2001) Ore deposits of Uzbekistan. Tashkent:
661
Dalimov T, Koneev R, Ganiev I (2004) Beltau-Kurama volcanic-plutonic belt and metallogeny of Uzbekistan. Abstract, 32nd International Geological Conference, Florence, Italy, CD-ROM, part
2: 996
Koneev R (2001) Micromineralogy-mineralogy of the XXI Century.
Episodes 2001 (1): 8
Koneev R (2003) Systematization of gold ore deposits of Uzbekistan
on the basis of micromineral paragenesises. Ores and Metals 2:
320-28
Koneev R (2004) Natural nanotechnology in mineral geochemistry systems. Abstract, 32nd International Geological Conference,
Florence, Italy, CD-ROM, part 1: 331
Koneev R (2004) Gold-epithermal mineralization of Kurama
volcanogenic area (Uzbekistan). IAGOD Guidebook Series 12
(NJ Cook, CL Ciobanu, eds): 236-237
Koneev R, Cook N, Ciobanu C (2004) Tellurides and selenides in
ore deposits of the Kurama metallogenic zone (Uzbekistan). 32nd
JGC-Florence. Abstracts part 1273
Vasilevsky BB, Koneev RI, Rustamov AI (2004) New data on the
real composition of gold ores in the Muruntau deposit. Ores
and Metals: 67-79
Close
Close
Chapter 13-8
13-8
The relationship between Carbonaceous chert and
selenium enrichment in the Yutangba selenium
deposit, China
J. Liu, H. Xie, J. Wang
State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083,
and Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, China University of
Geosciences, Beijing 100083, China
C. Feng, G. Zhou
Open Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002,
China
Z. Li
Wuxi Research Institute of Experimental Geology, SINOPEC, Wuxi 214151, China
Abstract. The Yutangba Se deposit is a rare high-Se deposit and is
well known for its high contents of up to 8590 ppm Se. The rocks
hosting the ore are dominated by widespread cherts. Selenium
enrichment is clearly controlled by both stratigraphic position and
lithological character. The closer the rocks are to cherts of the
Maokou Formation, the more Se they contain, but lithological character plays a role in Se-enrichment in cases where the stratigraphic
horizons are close to one another. Large amounts of discrete Sebearing minerals have been found in Se-ores from the Yutangba
deposit, e.g., achavalite, klockmannite, chalcomenite, krutaite,
eskebornite, as well as a variety of forms of native selenium. The
extensive discovery of Se minerals in the deposit is of great significance for expanding known selenium reserves and meeting global
demand for selenium.
Keywords. Selenium enrichment, carbonaceous chert, Yutangba,
China
1
lntroduction
The crustal abundance of Se is a thousand times lower
than that of S, but larger than that of Te (Liu et al. 1987;
Simon et al. 1997). Se and S are very similar in crystal
chemistry and in some geochemical properties, e.g., ionic
radius (S2- 0.184 nm, Se2- 0.191 nm), lattice energy coefficient (S2- 1.15, Se2- 1.10), ionic potential (S2- -1.09eV, Se2- 1.05 eV) (Liu et al. 1987). Moreover, Se, unlike Te, is a
strongly chalcophile element; it is easy for Se to replace S
in sulfides, but difficult to form selenides. The occurrence
of selenides has been reported in 4 major types of hydrothermal deposits: ‘telethermal’ selenide vein-type deposits, unconformity-related deposits, sandstone-hosted uranium deposits and epithermal Au-Ag deposits in subaerial
volcanic environments (Simon and Essene 1996; Simon
et al. 1997). However, it has been found that Se is considerably enriched in black shales in China (Zheng et al. 1992;
Li 1995; Liu et al. 2000). Among them, the Yutangba Se
deposit in western Hubei is the most typical example demonstrating Se enrichment. This ore deposit is easy to explore and exploit, and belongs to the sedimentary-reworked- type of strata-bound ore deposits. The discovery of this deposit has added a new type to the list of Se
deposits. Detailed studies of the ore-forming environment
and metallogenic characteristics of the Yutangba Se deposit are of great significance in exploration for other
ore deposits of the same type.
2
Geological characteristics
The Yutangba mining district is located in the NE segment of the Upper Yangtze platform of the southwestern
Hubei paraplatform, where the most outstanding structures are NNE- and NE-extending folds and faults, with
evidence of multi-stage tectonic activity. Sedimentary
rocks are widespread; Cambrian, Ordovician, Silurian,
Devonian, Carboniferous, Permian and Triassic strata are
all exposed in the mine area (Song 1989).
The mining district can be divided into three deposits: Majingao, the Yutangba and Xiaba. The Yutangba
orebody is more than 1700 m long, and the bed hosting
the ore shows an undulated relief along strike, with
interlayer slip and distortion appearing along plunge, and
three groups of NNE-, NE- and NW-trending joints (Fig. 1).
The Yutangba Se deposit is hosted in carbonaceous
cherts in the lower part of the Lower Maokou Formation.
The overlying strata are coal-bearing series of the Permian WujiaPing Formation (P2w), in parallel unconformable contact with the ore-hosting bed. The underlying
strata are limestones of the Maokou Formation (P1m1), in
conformable contact with the ore-hosting bed (Song 1989).
The Se-rich bed is generally a suite of black, thin-bedded, carbonaceous cherts, which are typically stratiform,
Close
1408
J. Liu · H. Xie · J. Wang · C. Feng · G. Zhou · Z. Li
with horizontal bedding and laminated structures. The
ore horizon can be further divided into three parts: the
lower and middle parts are composed of carbonaceous
cherts and Si-bearing carbonaceous shales, which occur
as rhythmic layers, but the micro-fine rhythmic layers and
semi-dark sapropelic coal layers in the middle part contain abundant carbonaceous material. In the rhythmic
layers, the cherts are usually 3-11 cm thick, whereas the
shales are 2-8 cm in thickness.
The late Early Permian black carbonaceous chert series represents the ore-hosting bed within the mining district. This is restricted to a specific sedimentary interval,
i.e., a black carbonaceous chert, which is interpreted as
having been formed in an algal bog environment in the
shallow part of the carbonate-platform sea basin. The selenium orebodies are intimately related to this suite of
carbonaceous cherts, a so-caled ‘petrographic zone’ (Wang
and Li 1996).
Three major types of selenium ores can be distinguished: carbonaceous chert-type, siliceous- carbonaceous
shale-type, and semi-dark sapropelic coal-type. The selenium ores are relatively simple in mineral composition,
with quartz, chalcedony, carbonaceous material and hydrous mica as the major minerals, and pyrite, hematite
and Se-bearing pyrite as minor minerals (Song 1989).
In the study of minerals in this region, the authors
found that there are large amounts of native selenium, as
well as selenium minerals such as achavalite, krutaite,
eskebornite, klockmannite, chalcomenite and berzelianite.
These minerals were mostly formed during sedimentation and diagenesis. Later hydrothermal reworking processes promoted re-distribution and re-organization of
the ore-forming materials, or caused selenium to be transport and re-concentrated.
3
Origin of the Se-bearing cherts
Chert is the main host rock for ore in the Yutangba deposit. All geological and geochemical characteristics of
the cherts suggest that they are products of biochemical
and submarine exhalative sedimentation. The following
main features are documented. (1) In the late Paleozoic
periods, there were several syngenetic faults that
transected the crust of this area (Shuanghe Basin) and
provided conduits for hydrothermal activity. Crustal extension along these faults resulted in the formation of a
series of depressions and uplift within the basin. (2) There
are many synsedimentary-syndiagenetic and diagenetic
deformation fabrics in the ores, host-rocks (cherts) and
pyrite, such as lamination, convoluted bedding, slump
textures and diagenetic cracks. They indicate the occurrence of synsedimentary faulting which assisted the exhalation. (3) The ore-bearing cherts are characterized
by bedded, massive, pseudo-brecciated and nodule structures. The rhythmic layered cherts generally vary from 3
to 11 cm in thickness. (4) Because of the only small difference between ores and host rocks (cherts), orebodies
are often congruent with the bedding, and can only be
contoured by chemical analysis. (5) Host elements are
simple and concentrated in the cherts. Besides SiO2 (average up to 87.30%), only Al2O3 and organic carbon reach
or are more than 1%. The ratios of Al/(Al+Fe+Mn) in all
chert samples are lower than 0.53 . In the Fe/Ti vs. Al/
(Al+Fe+Mn) diagram and the Al-Fe-Mn triangle diagram,
the chert samples fall into the hydrothermal field. (6)
REE (rare-earth elements) are characterized by a low
content (15.2-80.6 ppm), negative Ce anomaly and positive Eu anomaly and a gradually increasing NASC-normalized value with increasing atomic number of REE,
Close
Chapter 13-8 · The relationship between Carbonaceous chert and selenium enrichment in the Yutangba selenium deposit, China
concordant with that seen in modern hydrothermal sediments. (7) The δ18O values of the cherts range from 22.7
to 27.3‰, and the δ30Si range from 0.7 to 1.1‰, similar
to that of biochemical sedimentary silica with the involvement of some hydrothermal materials. This data
suggests that the cherts are characterized not only by a
biochemical but also by hydrothermal origin.
hydrolysis, speeding up release of Se from the rock, resulting in low contents of Se in the rock. All this goes to
show that the closer to the chert segment is to the Maokou
Formation, the higher the contents of Se will be in the
rock. However, where ore horizons are close to one another, Se contents are strictly controlled by lithological
character.
4
5
Geochemical characteristics
The occurrence of selenium
4.1 Selenium abundance in rocks and ores
5.1 Selenides and Se-bearing minerals
The results of the analysis of Se content in 120 representative rock samples showed that Se enrichment is strictly
sedimentary strata-bound. With the exception of the
Maokou Formation limestones, the samples with Se contents exceeding 80ppm were all cherts from the Lower
Permian Maokou Formation (Table l).
On the basis of available data, the following Se-bearing
minerals are recognized: Se-bearing pyrite, klockmannite
(CuSe), chalcomenite (CuSeO3·2H2O), krutaite (CuSe2)
(Yao et al. 2001), eskebornite (CuFeSe2), achavalite (FeSe),
native selenium (Se) and an unnamed Fe-Cu-selenide
(Song 1989). Samples of native selenium can be classified into three groups in accordance with their visible
morphology: slaty, prismatic and allotriomorphic-granular. Electron microprobe analyses of all three categories
indicate that they are relatively pure (Se >97%).
4.2 Abnormal distribution of selenium
As can be seen from Table 1, the contents of Se follow
the descending order limestone < chert < carbonaceous
chert, in direct proportion to the contents of SiO2. Sample
00S-l3 is a carbonaceous chert sample, but the Se content is only 21.1 ppm, much lower than those in other
rocks of the same lithological character. A possible explanation is that this sample, as seen in hand specimen,
is easy to break, underwent weathering, thereby increasing the surface area of the rock, favoring oxidation and
1409
5.2 Adsorption
In the region studied, the contents of organic matter are
relatively high either in the ores themselves, or in the wall
rocks, and are positively correlated with the contents of
Se (Table 1). This demonstrates that a portion of selenium
has been adsorbed on the surface of organic matter.
Close
1410
J. Liu · H. Xie · J. Wang · C. Feng · G. Zhou · Z. Li
6
Conclusions
Up until now, economic accumulations of selenides are restricted to a few types of ore deposits. The Yutangba Se
deposit is characterized by a high Se-enrichment, the extensive occurrence of native selenium, independent selenide
minerals and Se-bearing minerals, reflecting specific oreforming conditions. Selenium enrichment is intimately tied
to the carbonaceous cherts which are characterized by biochemical and submarine exhalative sedimentation. Rational utilization of these high-selenium resources and extraction of selenium from highly pure native selenium are of
great significance in meeting growing demand for selenium
on a global scale, as well as improving the metallurgical
and recovery technologies for selenium production.
Acknowledgements
This project is supported by the National Natural Science
Foundation of China (No. 40273026, 40234051, and 40434011).
References
Li Y (1995) New advances in the study of associated elements in
Lower Cambrian black shale of northwestern of Hunan. Mineral Deposits 14: 346-354 (in Chinese with English abstract)
Liu J, Zheng M, Liu J, Su W (2000) Geochemistry of the La’erma
and Qiongmo Au-Se deposits in the westem Qinling Mountains,
China. Ore Geology Reviews 17: 91-l l l
Liu Y, Cao L, Wang H, Chu T, Zhang J (1987) Element Geochemistry. Beijing: Geological Publishing House, 244-257 (in
Chinese)
Simon G, Essene EJ (1996) Phase relation among selenides, sulfides, tellurides, and oxides: I. Thermodynamic data and calculated equilibria. Economic Geology 91: 1183-1208
Simon G, Kesler SE, Essene EJ (1997) Phase relation among
selenides, sulfides, tellurides, and oxides: II. Application
to selenide-bearing ore deposits. Economic Geology 92:
468-484
Song C (1989) A brief description of the Yutangba sedimentary type selenium mineralized area in southwestern
Hubei. Mineral Deposits 8: 83-89 (in Chinese with English
abstract)
Wang H, Li J (1996) Geological characteristic of Shuanghe selenium ore deposit in Enshi, Hubei Province. Hubei Geology 10:
10-21 (in Chinese with English abstract)
Yao L, Gao Z, Yang Z, Long H (2001) The study on the existing forms
of selenium in Yutangba independent selenium deposit by electron-microprobe analysis. Acta Minerologica Sinica 2l: 49-5l (in
Chinese with English abstract)
Yao L, Gao Z, Yang Z, Long H (2002) Origin of seleniferous cherts
in Yutangba independent selenium deposit, southwest Enshi,
Hubei Province. Science in China (series D) 45: 741-754
Zheng B, Hong Y, Zhao W (1992) Selenium-rich silicalite and local
selenium poisoning in western Huhei Province. Chinese Science Bulletin 37: 1027-l029 (in Chinese with English abstract)
Close
Chapter 13-9
13-9
A sedex-type stibnite-only deposit in the giant
metallogenic Sb belt, South China
J.M. Liu, J. Ye
Institute of Geology and Geophysics, Chinese Academy of Sciences, 100101 Beijing, China
Abstract. There are many known examples of sedex-type Pb-Zn ore
deposits. However, stibnite-only ores of sedex-type have not previously been reported. The Maxiong stibnite deposit in South China
represents a superb insight into ore formation in the Devonian period. The conduit system (filled by quartz and stibnite) and the overlying exhalative ores (in the form of laminated quartz-stibnite deposits) have been perfectly preserved by the subsequent rapid deposition of sand and mud. Isotopic studies reveal the Sb-only fluids
involved in formation of the deposit were probably sourced within
underlying metamorphic-sedimentary basement rocks.
Keywords. Stibnite ore, hydrothermal exhalation, Sb-only basement
brines, pervasive fluid conduits, South China
1
Introduction
A large number of sedex-type Pb-Zn ore deposits are
known (Russell et al. 1981; Goodfellow et al. 1994). However, stibnite-only ores of sedex origin remain unknown
up until now. This paper presents, for the first time, a
case study on a sedex-type stibnite-only deposit, the
Maxiong deposit, in the well-known giant Sb metallogenic
belt of South China, from where more than 50% of world
Sb mine production currently derives. In the Maxiong Sb
deposit, stibnite-only ores, with beautiful quartz/stibnite/sandstone lamination and well-preserved perva-sive
fluid-conduit veins, are hosted within Devonian sand- and
mudstones on the divergent continental margin of the
Yangtze Craton (Fig. 1a). It is, however, worth mentioning that the Maxiong deposit is still regarded as typical
epigenetic hydrothermal vein-type mineralization in connection with Mesozoic magmatism, even though there is
no magmatic pluton in the vicinity.
2
Except for the so-called Permian Emeishan basalt and
its related high-level basic sills, there are no other magmatic intrusive rocks in an area tens of km around
Maxiong. The Devonian rocks were folded and tilted, but
neither metamorphosed nor strongly faulted.
Two ore types, the major concordant stratiform layer
and the subordinate crosscutting ore veins underlying the
layer ore, are very distinctive in the Maxiong deposit
(Fig. 2). The major ore layer, with a thickness of 0.2-3.5 m
and a stretching length over 1400 m, is hosted in the lowest part of the Devonian sequence with a distance of several to tens of meters to the underlying unconformity
(Fig. 1). It consists of intercalated beds/laminae of white
quartz, dark-gray stibnite and black sandstone (Fig. 2),
fully concordant with the Devonian host lithology. Quartz
and subordinate dolomite are almost the only gangue
minerals and stibnite the only sulfide in both ore types,
except that the intercalated black sand similar to the Devonian hostrock contains quartz clasts, clay minerals, pyrite and organic matter. The sand laminae are usually fine
Geological features
The Maxiong deposit features a straightforward geological setting, simple ore features and only limited post-formational modification. It hence provides a well-preserved
‘natural laboratory’ of ancient submarine exhalation of
Sb-only fluids. In the Maxiong deposit, the host rock (Lower
Devonian dark sand- and mudstone, rich in organic matter and pyrite), and unconformably overlying Cambrian
dolostone (Figs. 1b, c), represents the lowest part of the
Devonian-Triassic deposition of a rift basin (Youjiang
Basin) in the southern margin of the Yangtze Craton (Liu
et al. 2002).
Close
1412
J.M. Liu · J. Ye
cordantly along the depression surface. Downward, these
veins become stockwork and go through the unconformity
into the Cambrian dolostone where evident silicification
occurs, probably due to higher temperature in that depth
and stronger chemical activity of the dolostone. According to evidence from present drillholes and mine adits,
they extend downwards at least 100 m.
There are two types of upward-invading veins according to the features of their upper portions and the relationship between the veins and upper contact with the
bands of stibnite. 1) Chimney veins had apparently played
the role of fluid conduits between the stratiform major
layer and the deep fluid source, analogous to the necks
of volcanoes connecting the lava flow on the surface to
the deep magma chamber in a volcanic plumbing system. 2) Intrusive veins which had apparently failed to
reach the seafloor and stopped halfway, just like an igneous intrusion. The laminae cut by veins were often
warped upward, implying a upward flowing of fluids
along the veins while the laminae were not yet totally
solidified.
(with a thickness of 0.5-3 mm), while the beds of quartz
and stibnite can be over 40 cm thick. The beautiful concordant bedding/lamination of the major ore layer (Fig. 2),
together with soft-sediment deform-ation (small-scale
isoclinal folding) and limited wallrock alteration, suggests
a submarine hydrothermal sedimentation origin of the
major layer from a local brine pool.
Repetition of the laminae reflects multi-stage exhalation of ore-forming fluids, and the inter-calation of sandstone apparently represents intermission of brine exhalation. Earlier quartz/stibnite beds are often distorted,
indicating strong sudden upflowing of later fluids that
disturbed the quiet depositional environment as indicated
by the fine successive lamination. However, strong brecciation was rarely observed in the major ore layer, implying an effusive way of fluid exhalation rather than an explosive one.
3
Fluid conduits
The most interesting discovery in the Maxiong deposit is
the numerous quartz-stibnite veins and their relationship
to the beds of the stratiform ore layer. These discordant
veins (1-20 cm thick) only occur in the footwall of the
major layer. They invade the major ore layer from its footwall upward, but do not cut through it. Instead, they stop
somewhere inside the major layer and then are overlain
by new laminae (Fig. 2), which clearly manifests the character of growth faults within sedimentary basins. These
small-scale growth faults, parallel to one another, are highangle normal faults with a relatively thick deposition on
their hanging-wall that had slid down several to tens of
cm. Growth fault-related depressions are often observed
where the hydrothermal depositional laminae run con-
4
Geochemical evidence
Homogenization temperatures of fluid inclusions in quartz
range between 185-314°C, with an average around 250°C.
Composition analysis of inclusion fluids of quartz by
means of quadrupole MS indicates that the fluids are
mainly composed of H2O and CO2. These CO2 and H2O
were separated and purified by using three cooling traps
and then analyzed for its carbon and hydrogen isotopes
with Finnigan MAT 252. Obtained δDSMOW values of H2O
and δ13CPDB values of CO2 are ~-63‰ (n=5) and ~-9‰
(n=4) in average, respectively. Six quartz samples give
remarkably heavy δ18OSMOW values of 18.6—23.8‰ (aver.
21‰), requiring a H2O with ~11.5‰ δ18OSMOW value according to isotope frac-tionation equation at 250°C
(Clayton et al. 1972). Twelve dolomite samples show
δ13CPDB and δ18OSMOW values of -6.9 to -9.7‰ (average 8.2‰) and 14.6 to 18.9‰ (average 17.6‰), respectively.
According to isotope fractionation equations at 250°C
(Sheppard and Schwartz 1970; Zheng et al. 1997), these
values require an ore-forming fluid with ~+10‰
δ18O(H2O)SMOW value and ~-7.2‰ δ13C(CO2)PDB value, respectively. These strongly support the above-obtained isotopic data of quartz and inclusion fluids in quartz. Although CO2 with -7.2 to -9‰ δ13CPDB values might be
sourced from the atmosphere or from basement brines/
metamorphic fluids contaminated by organic carbon to
varying degrees, but H2O with 10 to 11.5‰ δ18OSMOW values and ~-63‰ δDSMOW value is only comparable with
basement brines/ metamorphic fluids with relatively
strong water-rock interaction (Hoefs 1997).
According to data from this study and those of previous workers (Yang et al. 2000; Huang et al. 2001), Paleo-
Close
Chapter 13-9 · A sedex-type stibnite-only deposit in the giant metallogenic Sb belt, South China
zoic carbonate rocks around the Maxiong area are characterized by 87Sr/86Sr ratios between 0.70589 and 0.71070,
inconsistent with the global values of Paleozoic carbonate rocks. Seven samples of dolomite in ores with Sr/Rb
ratios>100 give 87Sr/86Sr ratios between 0.71962 and
0.72755, much higher than the 87Sr/86Sr ratios of the Phanerozoic seawater (<0.7120) (Denison et al. 1998). This again
implies a fluid source of basement brine/metamorphic fluid
with a large proportion of radiogenic 87Sr.
5
Discussion
There are numerous reports on modern/ancient submarine hydrothermal venting, but such a well-preserved track
of fluid exhalative system as the Maxiong deposit has never
been reported before. It provides a unique ‘Natural Laboratory’ for studying submarine exhalation. The following
new aspects can be inferred from this study.
Instead of a centralized fluid conduit in the form of
alteration breccia/stockwork pipe associated with largescale faults, as usually described in the literatures of sedex
ores (Russell et al. 1981; Goodfellow et al. 1994), the
Maxiong deposit provides a new alternative model of conduit systems characterized by numerous small-scale
growth faults parallel to each other that are dispersed
across a relatively large space and might be active in various stages of the exhalative process. This new model may
be called as pervasive exhalation.
Ore-forming fluids of sedex-type deposits are often
regarded as derived from the underlying compacting sediment pile (Russell et al. 1981; Goodfellow et al. 1994; Lowell
1991). This, however, could not be true for the Maxiong
deposit, because the underlying Devonian sand/mudstone
(between the major ore layer and the unconformity) is
too thin (less than 200 m). Similar to the Maxiong deposit, it is well known in South China that Devonian rocks
just tens of meters above the same major unconformity
variety of Pb, Zn, Sn and Sb ores (sedex-type or otherwise). Since there is no igneous rock of Devonian age
around the Maxiong area, magma-derived fluids are impossible. The ore-forming fluids thus might have come
from the underlying continental basement in response
to the onset of extensional tectonism during basin opening in the Youjiang region. The basement of the Youjiang
basin is comprised of Proterozoic-Lower Paleozoic sedimentary-volcanic rocks with greenschist facies metamorphism in the lower part grading upward into non-metamorphic rocks. Accordingly, the ore-forming fluids might
be 1) basement brines from the underlying Early Paleozoic sediments, and 2) metamorphic fluids from the Proterozoic metamorphic rocks, as suggested by the isotopic
study. As mentioned above, these Sb deposits in South
China were, and still are, regarded as typical epigenetic
hydrothermal vein-type mineralization associated with
Mesozoic magmatism.
1413
82.6% of the world Sb mine production in the year
2000 came from China (USGS 2001), the majority from
the giant Sb metallogenic belt in South China (Fig. 1a),
where many famous stibnite-only deposits occur in sediments of Proterozoic-Triassic age, particularly in Devonian rocks (Liu et al. 1998). They often show sedex features, just like the Maxiong deposit, indicating that antimony could be an important metal of submarine
exhalative mineralization in continental crust too, alongside Pb, Zn and Ag. In the Maxiong area, although several
stibnite occurrences have been discovered, no ores of other
metals were found, like many other stibnite-only deposits in the giant Sb belt, implying that Sb-only ore-forming fluids were very active over a long-time period and a
vast space. It is really amazing that such Sb-only hydrothermal fluids with very little other metals could ever occur!
Antimony is a so-called double-incompatible element
(Jochum and Hofman 1992) that tends to be enriched in
the Earth’s core and crust, and depleted in the mantle.
Antimony abundance increases with increasing crustal
maturity (Sims et al. 1990). In the giant Sb belt of South
China, sedimentary-metasedimentary rocks of all ages
show abnormally high Sb abundance and host stibnite
ores (Liu et al. 1998). It seems that the giant Sb belt of
South China might be a product of long-term crustal evolution, characterized by multi-stage recycling of Sb-only
fluids. The Maxiong Sb deposit provides a high-resolution view of an ancient submarine exhalation system on
continental crust, and yields insights into source and migration of Sb-only fluids in response to the onset of extensional tectonism during continental crust evolution.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant No.40372054). We thank
LCh Xiang, X Yang, XL. Chu, P Kong, WG Huo, J Tan, HP
Zhu, BD Li, FS Zhang, RF Zhang, JH Xu and MG Zhai for
their helps and profitable discussions.
References
Clayton RN, O’Neil JR, Mayeda TK, Newton, RC (1972) Oxygen isotope exchange between quartz and water. Journal of Geophysical
Research B77: 3057-3067
Denison RE, Koepnick RB, Burke WH, Hetherington EA (1998) Construction of the Cambrian and Ordovician seawater 87Sr/86Sr.
Chemical Geology 152: 325-340
Goodfellow WD, Lydon JW, Turner R (1994) Geology and genesis of
stratiform sediment-hosted (SEDEX) Zn-Pb-Ag sulphide deposits. Geological Association of Cananda Special Paper 40: 201-252
Hoefs J (1997) Stable Isotope Geochemistry. Springer, Heidelberg
Huang SJ, Shi H, Zhang M (2001) Strontium isotope evolution and
global sea level changes of Carboniferous and Permian carbonates, Upper Yangtze Platform. Acta Sedimentlogica Sinica 19: 481487 (in Chinese with English abstract)
Close
1414
J.M. Liu · J. Ye
Jochum KP, Hofmann AW (1992) Sn und Sb im Erdmantel und
ihre Bedeutung fuer die Entwicklungsgeschichte des Erdkerns. Bericht der Deutschen Mineralogischen Gesellschaft
4-1: 1-135
Liu JM, Gu XX, Liu JJ, Zheng MH (1998) Giant metallogenic Sb belt
in South China and its constraints: Acta Geophysica Sinica 41
Suppl: 206-215 (in Chinese with English abstract)
Liu JM, Ye J, Ying HL, Liu JJ, Zheng MH, Gu XX (2002) Sedimenthosted micro-disseminated gold mineralization constrained by
basin paleo-topographic highs in the Youjiang basin, South
China. Journal of Asian Earth Sciences 20: 517-533
Lowell RP (1991) Modelling continental and submarine hydrothermal systems. Reviews of Geophysics 29: 457-476
Russell MJ, Solomon M, Walshe JL (1981) The genesis of sedimenthosted, exhalative zinc + lead deposits. Mineralium Deposita
16: 113-127
Sheppard SMF, Schwartz HP (1970) Fractionation of carbon and
oxygen isotopes and magnesium between coexisting metamorphic calcite and dolomite. Contributions to Mineralogy and Petrology 26: 161-198
Sims KWW, Newsom HE, Gladney ES (1990) Chemical fractionation
during formation of the Earth’s core and continental crust: Clues
from As, Sb. W, and Mo. In: Newsom HE, Jones JH (eds) Origin of
the Earth. Oxford University Press, New York: 291-317
United States Geological Survey (2001) Antimony. In: Mineral Commodity Summaries: 20-21
Yang JD, Zhan JM, Tao XC, Wang ZZh (2000) Strontium and carbon
isotope calibration of the terminal Proterozoic. Geological Journal China University 6: 532-545 (in Chinese with English abstract)
Zheng YF, Zhou GT, Gong B (1997) Theoretical study of oxygen isotope fractionation in carbonate minerals. Geological Journal
China University 3: 241-255 (in Chinese with English abstract)
Close
Chapter 13-10
13-10
The telluride mineralization event(s) within the
late-variscan gold deposits in the western Sudetes
(NE part of the Bohemian massif, SW Poland)
S.Z. Mikulski
Polish Geological Institute, 4 Rakowiecka St., 00-975 Warsaw, Poland
Abstract. In the Western Sudetes, Bi- and Ag-tellurides have been
described from arsenic-polymetallic gold deposits. Crystallization
of tellurides occurred in at least in two separate events of ore crystallization at a temperature range from 300 to 200°C. The first event,
dominated by Bi-tellurides, was connected with metasomatic processes in the contact zones of post-tectonic calc-alkaline granites.
The second event, with Ag-tellurides, was connected with epithermal
low sulphidation processes associated with post-orogenic regional
extension and uplift. Bi and Te played a significant role as scavengers of non-refractory gold.
Keywords. Tellurides, gold deposits, W Sudetes, SW Poland, Bohemian
Massif, Variscides
1
Introduction
To date in the Western Sudetes of Poland, telluride mineralization have been recognized in Late-Variscan goldbearing arsenic-polymetallic deposits and occurrences
(vide Lis and Sylwestrzak 1986; Mikulski 1998, 1999;
Parafiniuk and Domanska 2002). These deposits were the
subject of gold, silver and base metals exploration since
medieval time. None of them is, however, currently under exploitation They are sited within regional shear zones,
in second-order tectonic structures, or occur in the contact zones of metamorphosed Palaeozoic sedimentaryvolcanic rocks and late-, to post-tectonic Upper Carboniferous, calc-alkaline and alkaline igneous rocks. The crystalline basement of the Western Sudetes unit is considered as a continuation of the Saxothuringian Zone of the
European Variscides.
2
ated with base-metal sulphides suggest a temperature range
of 350 to 250°C at pressures of 1.2 to 0.8 kbar and moderate
salinity (13 ± 3 wt% NaCl equiv., whereas quartz from the
Au-Ag-Bi-Te stage indicates 290-190°C and fluids with salinities of 12-15 wt% NaCl equiv. Similar crystallization temperatures of about 300°C for cogenetic base metal sulphides
couples have been also estimated on the basis of the fractionation of sulphur isotopes (Mikulski 2004). Tellurium
minerals appear in the paragenesis with bismuth minerals
(native bismuth, bismuthinite - Bi2S3, maldonite - Au2Bi),
non-refractory gold (electrum), Ag-Pb-Bi sulphosalts, magnetite and gangue of carbonates and fine-crystalline quartz
(Mikulski 1999). Tellurium minerals occur as multi-component inclusions (up to 100 µm in size) within arsenopyrite, as fine-scale replacements (up to 200 µm in size) of the
arsenopyrite-chalcopyrite aggregates, and intergrowths with
associated minerals. According to the microanalytical investigation, the main tellurium mineral at Radzimowice
deposit is hessite (Ag2Te). It may forms intergrowths with
members of different phases from the rucklidgeite
(PbBi2Te4), volynskite (AgBiTe2), and altaite (PbTe) series
that are in close association with Ag-Pb-Bi sulphosalts such
Tellurides at the Radzimowice deposit
At the Radzimowice Au-As-Cu deposit, auriferous mineralization occurs in sheeted quartz veins representing the
hydrothermal transition between porphyry and epithermal
type (Mikulski 2005). The Au-Ag-Bi-Te-Pb-S mineral assemblages followed in two major stages. The first stage of
mesothermal character consists of strongly brecciated
quartz-Fe-As sulphides, and crystallized at temperatures
from 535 to 345°C (arsenopyrite geothermometer). The later
stages have low-sulphidation epithermal character with
base-metal sulphides, non-refractory gold, tellurides and
carbonates. Fluid inclusion data on quartz veinlets associ-
Close
1416
S.Z. Mikulski
as gustavite (AgPbBi3S6), other phases in the lillianite homologous series (Fig. 2) and other Bi-sulphosalts which have
chemical compositions between those of pavonite (AgBi3S5)
and galena with inclination to matildite (AgBiS2) (Mikulski
2004).
3
Tellurides at the Bardo Slaskie prospect
Bi-tellurides in association with gold and other ore minerals were found in ellipsoid-like form concretions of
boudinage character in the old rock fall materials unburied in 1997 by flowed of the Nysa Klodzka River (Mikulski
1998). Ore mineralization was described as of a contact
metasomatic type. However, the precise position and geometry of ores and gold reserves are not yet defined.
Gold-bearing sulphide mineralization (5-10 g/t Au)
occurred as quartz-carbonates lode/vein (?) within a tectonic zone of WNW-ESE direction that separates Upper
Devonian-Lower Carboniferous flysch sedimentary rocks
of the Bardo Structure from the Upper Carboniferous
Graniec-Bardo tonalite and granodiorite apophyses in the
NW part of the Klodzko-Zloty Stok Massif (KZM) (Fig. 3).
The KZM is an I-type intrusion formed during the
Asturian phase of the Variscan orogeny in the Eastern
part of the Western Sudetes.
The KZM consists of metaluminous, calc-alkaline igneous rocks of cafemic association with subsequent mag-
matic activity that formed dykes of melanocratic and
leucocratic rocks and quartz veins. In the Eastern metamorphic cover of the KZM, there occurs the famous skarnlike Au-As deposit of Zloty Stok (Reichenstein). At the
Bardo Slaskie prospect, ore minerals are represented
mainly by arsenopyrite, pyrite and titanite, and less frequently by base metal sulphides, stibnite and marcasite.
The sulphides are intergrown with quartz, calcite and
chlorite.
Arsenopyrite geothermometry indicates arseno-pyrite
crystallization temperature in the range from 450 to 350°C
along the pyrrhotite + loellingite - arsenopyrite buffer.
However, a constant admixture of Co within arsenopyrite from (0.6 to 2.9 atom.%) limits such thermometry.
The sulphur isotope composition of arsenopyrite ranges
from -1.48 to 1.04‰ and suggests a magmatic source.
Arsenopyrite commonly contains mono-, or polymineral
inclusion from 5 to 100 µm in size. Inclusions consist of
pyrrhotite, base metal sulphides, native gold, electrum, native bismuth, bismuthinite, hedleyite (Bi2Te), tellurobismuthite (Bi2Te3), pilsenite (Bi4Te3), joseite B? (Bi4STe)3,
rucklidgeite (Bi,Pb)3Te4, and Bi-sulphosalts (Fig. 4).
4
Tellurium distribution in auriferous sulphide ore
The distributions of tellurium and other metallic elements
within the gold-bearing polymetallic ores from the LateVariscan deposits in the Western Sudetes were determined
by use of ICP-MS and gold of GF-AAS methods. The content of Te within auriferous ores varies significantly between deposits. The highest average contents of Te: 44.1
Close
Chapter 13-10 · The telluride mineralization event(s) within the late-variscan gold deposits in the western Sudetes (NE part of the Bohemian massif, SW Poland)
ppm (n=12; range from <1 to 149 ppm) was found in
samples from the Radzimowice deposit (black dots in
Fig. 5). The ratio of gold to tellurium varies from 3:1 to
1:16 (geometric average 1:2.2). In the Au-richest samples
(>100 g/t), the Au:Te ratio is 1:1.3. In the Radzimowice
deposit, Te has a very strong positive correlation with Au,
Bi, Co, Ag and S (r = 0.90-0.71), a strong correlation with
Sc, Fe, Mo, and Se (r = 0.54-0.47), a week positive correlation with Cd, Cu, Ca and Zn (r = 0.38-0.26), and a negative correlation with most of the REE, and with Pb, As
and Sb (r = −0.40).
The lack of Te−Bi−Au correlation with As−Pb indicates
that Ag-tellurides postdate precipitation of high-temperature arsenic minerals and galena. The tellurides event
was also not related to the early potassic alteration event,
but instead to the carbonatization episode.
Average Te contents within auriferous ores from the
Zloty Stok, Czarnów, and Klecza-Radomice deposits are
at least a one order lower than those of the Radzimowice
deposit, except for the Bardo prospect, where the Te content is ~50 ppm.
5
Discussion and conclusion
In the auriferous As-polymetallic deposits in the Western Sudetes, the appearance of Bi- and Ag-tellurides after initial deposition of As- and base metal sulphides reflects an increase in the ratio of fTe2/fS2 at temperatures
about 300°C degrees due to input of H2Te from a magmatic source (Fig. 6). At the Bardo prospect, Bi-tellurides
dominate, but at Radzimowice, Ag-tellurides prevail, even
though Bi-minerals are also present. At the Bardo Slaskie
prospect, the presence of numerous inclusions of various
1417
mineral phases in arsenopyrite indicates crystallization
of Bi-tellurides associated with non-refractory gold during the crystallization of arsenopyrite.
The increase in fTe2 allowed for formation of the following minerals: bismuth → hedleyite → tellurobismuthite. Tellurobismuthite is the Te-rich end member of the
homologous series of bismuth tellurides that includes
hedleyite. These minerals are stable from below 150°C to
their melting points, which range from 312°C for hedleyite
to 588°C for tellurobismuthite (Afifi et al. 1988). The maximum temperature of bismuth stability is 271°C, and a
minimum temperature for presence of bismuthinite and
pyrrhotite is 235°C (vide Afifi et al. 1988). At the Radzimowice deposit, the presence of the Ag- and Bi-tellurides
in paragenetic association with gold and sulphotellurides
and Ag,Bi,Pb sulphosalts minerals and carbonates indicates that those minerals crystallized at close to neutral
conditions at temperatures <371°C (melting point of
maldonite) and probably <250°C (Cabri 1965 in Afifi et
al. 1988). Tellurium has a high positive correlation with
Co, Au, and Ag and positive correlation with Se, Cu, Zn,
Bi, Fe, S and Sc. Arsenic, which usually has a strong posi-
Close
1418
S.Z. Mikulski
tive correlation with Au in the considered deposits does
not display a correlation with Te, except at Zloty Stok and
Bardo.
It also indicates that Bi and Te have a significant importance as scavengers of non-refractory gold in the arsenic–polymetallic gold deposits in the Sudetes. The results presented here for the Te mineralization, in conjunction with other data from the Czech side of the Bohemian Massif (Litochleb and Srein 1994), indicates a wide
distribution of Te-bearing minerals in this part of the
Variscan belt.
Acknowledgements
The analytical work was supported by the NCSR, Grant
5T12B00122.
References
Afifi AM, Kelly WC, Essene EJ (1988) Phase relations among tellurides, sulphides, and oxides: I. Thermochemical data and calculated equilibrium. II. Applications to telluride-bearing ore deposits. Economic Geology 83: 377–404
Cook NJ, Ciobanu C (2004a) Bismuth tellurides and sulphosalts from
the Larga hydrothermal system, Metaliferi Mts., Romania:
Paragenesis and genetic significance. Mineralogical Magazine 68:
301-321
Cook NJ, Ciobanu C (2004b) Telluride metallogeny in the ‘Golden Quadrilateral’ and beyond: Quo vadis? In: Cook NJ, Ciobanu CL (eds.),
Gold-Silver-Telluride deposits of the Golden Quadrilateral, South
Apuseni Mts., Romania. IAGOD Guidebook Series 12: 203-211
Emerle-Tubielewicz H (1979) Detailed Geological map of the Sudetes
– Klodzko sheet. Wydawnictwa Geologiczne, Warszawa
Litochleb J, Srein V (1994) Minerály bismutu a telluru z lozisek a
vyskytu zlata v Ceské Republice. Bull min-petr odd. NM v Praze 2:
89-103
Lis J, Sylwestrzak H (1986) Mineraly Dolnego Slaska: pp 643.
Wydawnictwa Geologiczne Warszawa.
Mikulski SZ (1998) The Au-bearing ore mineralization from Bardo
Slaskie (Sudetes, SW Poland). Przeglad Geologiczny 46: 1261-1267
Mikulski SZ (1999) Gold from Radzimowice deposit (Kaczawa Mountains. Sudetes) – a new geochemical and mineralogical data.
Przeglad Geologiczny 47: 999-1005
Mikulski SZ (2004) Te-Bi-Au-Ag-Pb-S mineral assemblages within the
Late-Hercynian polymetallic deposits in the Western Sudetes (Poland). In: Cook NJ, Ciobanu CL (eds.), Gold-Silver-Telluride deposits of the Golden Quadrilateral, South Apuseni Mts., Romania.
IAGOD Guidebook Series 12: 242-244
Mikulski SZ (2005) Geological, mineralogical and geochemical characteristics of the Radzimowice Au-As-Cu deposit from the Kaczawa
Mts. (SW Poland) - an example of the transition of porphyry and
epithermal style. Mineralium Deposita 39: 904-920
Parafiniuk J, Domanska J (2002) Bismuth minerals from Redziny (Rudawy Janowickie, SW Poland). Mineralogia Polonica 33(2): 3-14
Paulo A, Salamon W (1974) Contribution to the knowledge of a
polymetallic deposit at Stara Góra. Kwartalnik Geologiczny 18 (2):
266–276
Close
Chapter 13-11
13-11
Occurrence and paragenesis of tellurium in mineral
deposits of Argentina
W.H. Paar, H. Putz, D. Topa
Department of GGM, Division of Mineralogy and Material Science, University, Hellbrunnerstr. 34, A-5020 Salzburg, Austria
M.K. de Brodtkorb
Consejo Nacional de Investigaciones Científicas y Técnicas, University of Buenos Aires, Paso 258-9A, 1640 Martinez, Argentina
R.J. Sureda
Cátedra de Mineralogia, Facultad de Ciencias Naturales, Universidad Nacional, 4400 Salta, Argentina
Abstract. The occurrence of Te-bearing species in different deposit
types of Argentina is reviewed. Tellurides with Au and/or Ag are
especially abundant in epithermal environments of the high-and
low-sulphidation states whereas those with Ag and Sn may prevail
in Ag-Sn deposits. In very few cases (La Mejicana, Famatina; Farallón
Negro) Au- and/or Ag-bearing tellurides contribute to the grade of
these elements in the ore and thus are of economic importance. A
great part of the deposits which contain tellurides is structurally
controlled and genetically related with the Miocene to Pliocene
volcanism.
Keywords. Tellurides, Argentina, epithermal, mesothermal, high-, intermediate-, low-sulphidation
1
Introduction
Tellurium-bearing minerals are widely distributed but
rarely abundant constituents in polymetallic and precious
metal-containing ore deposits of Argentina. A compilation of the occurrences was recently provided by
Brodtkorb (2002).
Au-bearing tellurides (sylvanite, krennerite, calaverite
and petzite) may significantly contribute to the grade of
gold in the ore. Ag tellurides (hessite, stützite) are more
common whereas tellurides with PGE (merenskyite) or
with Ag and Sn (Te-canfieldite) are rare. From a genetic
point of view tellurides (and native tellurium) may occur
in the following depositional environments of Argentina:
(1) Epithermal high-sulphidation, (2) epithermal lowsulphidation, (3) epithermal intermediate sulphidation,
(4) mesothermal low-sulphidation, and (5) others. Using
this classification, a condensed review of the more interesting occurrences is given below.
2
Polymetallic and precious metal-bearing mineralization
is genetically related to silicic to intermediate magmatism
of Lower to Middle Pliocene age. Three different styles of
mineralization can be distinguished all of which contain
tellurides:
(1) Cu-Mo porphyries, (2) epithermal high-sulphidation
and (3) epithermal intermediate sulphidation (Schalamuk
and Logan 1994,Losada-Calderon and McPhail 1996).
Striking similarities in detailed tellurium mineralogy (sylvanite, goldfieldite) between the last porphyry vein stage
(stage V of Losada-Calderon and McPhail 1996) and
epithermal veins can be recognized. The epithermal mineralization is well documented from the La Mejicana mining district. Two vein systems, San Pedro and Upulungus,
contain a three-stage mineralization which is accompanied by typical high-sulphidation alteration assemblages.
Tellurides are widely distributed in the veins and have
economic significance because they contain gold and/or
silver. A detailed study of samples from the Upulungus
vein (dump of Banco de Nación) revealed the presence of
intergrown Au- and/or Ag-tellurides (Fig. 1), character-
Environments of Te-bearing mineralization
2.1 Epithermal high-sulphidation
Nevados del Famatina. This district is located within the
Famatinian Ranges in the Central Andean Cordillera of
the province of La Rioja, and covers an area of 35 km².
Close
1420
W.H. Paar · H. Putz · D. Topa · M.K. de Brodtkorb · R.J. Sureda
istically embedded in goldfieldite and associated with
pyrite, tennantite, enargite, members of the luzonitefamatinite series, colusite and chalcopyrite (Paar et al.
1998).
Capillitas. This district is located in the province of
Catamarca, and is part of the Farallón Negro Complex
(Sasso and Clark 1998). The veins are hosted in intrusive
and volcaniclastic rocks of Miocene and granite of Paleozoic age. Six different stages of mineralization are identified during which very complex Cu-Pb-Zn-Fe-As-SbAu-Ag ores were formed (Márquez-Zavalía and Craig
2004). Important minor elements are W-Sn-Bi-Te and (in
traces) Ge-Tl-In and Cd. Only recently, two different Gebearing assemblages were encountered and investigated
in detail (Putz and Paar 2002; Paar et al. 2004). Te-bearing minerals are frequently detected but only in small
and isolated grains. The tellurium mineralogy is characterized by the presence of various Au- and/or Ag-bearing
tellurides, melonite, tetradymite, (?) volynskite and
goldfieldite. They are accompanied by hübnerite, pyrite,
chalcopyrite, Bi- and Sn-minerals; gangue is quartz. Native gold is a common associate.
Fátima. This location is a small prospect which is situated in the Organullo mining district, province of Salta.
This district is dominated by vein-type deposits which
are hosted within low-grade metamorphic siliciclastic
rocks of the Precambrian to Lower Cambrian Puncoviscana Formation. A genetic relationship between mineralization and dacitic volcanics of Miocene to Upper Pliocene age is assumed. At Fátima a small vein was
exposed yielding a typical epithermal and high-sulphidation assemblage with tellurides (Paar et al. 2000a).
2.2 Epithermal low-sulphidation
Farallón Negro. This mine is situated in the equally-named
complex of Catamarca and exploits subparallel veins
within Miocene andesite breccias which were affected by
a quartz-sericite alteration. The Au-Ag-base metal sulfide veins are associated with a Mn-oxide supergene assemblage (crypto-melane, pyrolusite, manganite). Gold
and silver in the ores can be related to native gold,
nagyagite (the only telluride), polybasite and acanthite.
The gangues are Mn-(Ca)carbonates and quartz (Sasso
and Clark 1998; Schalamuk and Nicolli 1975).
Macizo del Deseado. This Au-Ag district is located in the
province of Santa Cruz, and more than 21 different prospects are scattered over an area of 60,000 km². Cerro
Vanguardia and Manantial Espejo are economically the
most important targets. The mineralization is dominantly
vein-type and locally associated with brecciation,
stockworks and disseminations. The host rocks are
volcanics of Jurassic age and have suffered hydrothermal
alteration typical for this environment. Gold and silver
are bound to native gold, uytenbogaardite, freibergite,
pyrargyrite and acanthite. The only telluride at two locations (Cerro Vanguardia, La Manchuria) is petzite which
occurs sparingly but closely associated with native gold
(Schalamuk et al. 1999).
2.3 Epithermal intermediate sulphidation
Cerro Negro. This important mining district is located in
the Famatina Range (cf. 2.1) and characterized by a complex Pb-Ag-Zn (Cu-Ni-Co-Te-Sb) mineralization
(Schalamuk and Logan 1994). The vein-type mineralization of the La Viuda and Peregrina mines is accompanied by intense silicification and sericitic alteration. Numerous mineral species have been determined, amongst
them Ag-Sb and Ag-As sulfosalts, argyrodite, acanthite,
native silver, Co-Ni arsenides, base metal sulfides and,
rarely, Te-bearing minerals such as native tellurium, altaite
and an unnamed compound of Pb, As, Sb and Te.
Ángela. Ángela denotes a group of Au- and Ag-bearing
vein-type deposits which are located in the Los
Manantiales mining district, department of Gastre, province of Chubut (Arizmendi et al. 1996). The veins of “Grupo
Ángela” have a total extension of 1400 m along strike. The
mineralization is emplaced into Late Jurassic andesitic to
dacitic rocks of age, which were affected by phyllic and
argillic alteration near, and propylitization further away
from, the veins. Mineralization is composed of pyrite,
sphalerite, chalcopyrite, galena, hematite and quartz. Native gold, electrum and native silver are associated with
various sulphosalts (wittichenite, aikinite, miharaite) and
Close
Chapter 13-11 · Occurrence and paragenesis of tellurium in mineral deposits of Argentina
1421
and show a complex Au, Bi, Fe, Cu, Sn, Sb, As, Zn, Pb, Ag,
Te paragenesis (Sureda 1991). The first stage comprises
the formation of abundant pyrite, cassiterite and members of the stannite-kesterite series. Te-canfieldite may
occur at this stage in association with abundant matildite
and Ag-Pb-Bi sulfosalts (benjaminite, schirmerite).
The mineralizing process continued with a second stage
during which Bi sulfosalts (bismuthinite, aikinite, emplectitechalcostibite series, hodrushite) crystallized, followed by
tetrahedrite-tennantite (locally Bi-enriched), enargite,
luzonite-famatinite, Sn-bearing species (mohite, kuramite),
traces of kawazulite and native gold. Tetradymite occurs as
tiny grains in the fahlore matrix (Fig. 3). The final stage is
typified by minor amounts of bornite (with exsolved chalcopyrite) and Sn-bearing species (mawsonite, vinciennite,
stannoidite). Supergene minerals are digenite and covellite.
2.5 Others
the new mineral species ángelaite. Tellurium minerals
(native tellurium, cervelleite) are trace constituents.
2.4 Mesothermal low-sulphidation
Pirquitas. This mine is situated 135 km W of Abra Pampa,
province of Jujuy, and was intensively exploited for silver
and tin. Alluvial deposits of these metals are also known.
Pirquitas is a typical Ag-Sn deposit within a Ag-Sn belt
which extends from Bolivia into Argentina. The vein system is hosted by Ordovician metapelites and sandstones,
and occurs in an area of 1.5 x 2 km. The major veins
attain a thickness of almost 2 m and are associated with
a more stockwork type of mineralization. The alteration
comprises weak sericitization and pyritization. Argillic
alteration and silicification is dominant in the vicinity of
the veins. Alunite is found in higher levels of the system,
where an epithermal environment of the high-sulphidation
state may be assumed (Sillitoe et al. 1998). The mineralization is polymetallic and very complex, and was precipitated in several stages (Malvicini 1978; Paar et al. 1996,
2000b). The common minerals (pyrite, arsenopyrite, cassiterite) are frequently associated with galena, sphalerite,
wurtzite, Ag-(Pb)-Sb and Ag-Pb-Bi sulfosalts. Members
of the stannite series (stannite-kesterite, hocartite,
pirquitasite) and Pb-(Fe)-Sn-Sb(As) sulfosalts (franckeite,
cylindrite, suredaite) are common within the Oploca vein
(Paar et al. 2000b). Te-bearing species are tetradymite and
Te-canfieldite which are locally abundant and frequently
intergrown with Bi sulfosalts (bismuthinite, pavonite,
benjaminite) (Fig. 2).
Julio Verne. This is one of the two important deposits in
the Organullo mining district, province of Salta (cf. 2.1).
Two major veins with a maximum thickness of 0.8 m were
exploited. Three stages of mineralization can be discerned
Several other mineral deposits, genetically different from
those briefly reviewed in the preceding chapters, may contain Te-bearing minerals. Examples are:
Los Águilas. This Cu-Ni deposit is located in the province of San Luis. It is hosted by mafic to ultramafic rocks.
Melonite, tellurobismuthite and the PGM merenskyite
occur in traces.
Las Asperezas. This is one of several ocurrences with selenide mineralization in the Sierra de Cacho, province of
La Rioja. Merenskyite (Paar et al. 2004) is closely associated with selenide minerals, such as umangite, klockmannite
and eucairite.
San Martín. This deposit is situated in the province of
Rio Negro. The single vein contains a complex Sn-W-BiAg-Sb-Te mineralization. Te-bearing minerals are hessite
and cervelleite, which are embedded in galena and associated with Ag-wittichenite, chalcopyrite and sphalerite.
3
Conclusions
Te-bearing minerals and mineral assemblages are widely
distributed in ore deposits of Argentina. Most of them
belong to the epithermal and/or mesothermal environment and may be of the high-, intermediate or lowsulphidation state. In most deposits tellurides are rare
constituents but can contribute to better understand the
conditions of ore genesis. Only exceptionally are tellurides of economic importance and contribute to the grade
of precious metals (Au, Ag) in the ore. The majority of
the polymetallic deposits which contain tellurides are
structurally controlled and show genetic affinities with
the Miocene to Pliocene volcanism.
Close
1422
W.H. Paar · H. Putz · D. Topa · M.K. de Brodtkorb · R.J. Sureda
Acknowledgements
The support of the Austrian Science Foundation (FWF)
through grants P11987 and 13974 to the first author is
gratefully acknowledged.
References
Arizmendi A, Brodtkorb MK de, Bernhardt HJ (1996) Paragenesis
mineral de la mina Ángela, Gastre, Prov.del Chubut. III Reunión
de Mineralogía y Metalogenía 5: 1-7
Brodtkorb MK de (2002) Las especies minerales de la República Argentina. Brodtkorb MKde (ed). Asociación Mineralogica Argentina, Tomo I
Losada-Calderon AJ, McPhail DC (1996) Porphyry and highsulfidation epithermal mineralization in the Nevados del
Famatina mining district, Argentina. In: Camus F, Sillitoe RH,
Petersen R (eds.) Andean copper deposits: new discoveries, mineralization, styles and metallogeny. SEG Spec.Publ 5: 91-118
Malvicini L (1978) Las vetas de estaño y plata de mina Pirquitas
(Pircas) prov. de Jujuy, República Argentina. Asociación de
Mineralogia, Petrografia y Sedimentologia, Rev. 9 (1-2): 1-26
Márquez-Zavalía F, Craig JR (2004) Tellurium and precious-metal
ore minerals at Mina Capillitas, Northwestern Argentina.
N.Jb.Miner.Mh. 4: 176-192
Paar WH, Roberts AC, Berlepsch P, Armbruster T, Topa D, Zagler G
(2004) Putzite, (Cu4.7Ag3.3)∑8GeS6, a new mineral species from
Capillitas, Catamarca, Argentina: Description and crystal structure. Can Mineral 42: 1335-1347
Paar WH, Sureda RJ, Topa D, Brodtkorb MKde (2000a) Los telururos
de oro y plata, krennerita, petzita y silvanita, del prospecto Fátima,
distrito minero Organullo, Provincia de Salta. Mineralogía y
Metalogenía 2000. Schalamuk I, Brodtkorb MKde, Etcheverry R
(eds), INREMI, Publicación 6: 369-373
Paar WH, Miletich R, Topa D, Criddle AJ, Brodtkorb MKde,
Amthauer G, Tippelt G (2000b) Suredaite, PbSnS3, a new mineral species, from the Pirquitas Ag-Sn deposit, NW-Argentina:
Mineralogy and crystal structure. Amer Mineral 85: 1066-1075
Paar WH, Brodtkorb MKde, Topa D (1998) Los telururos de oro y
plata de la mina la Mejicana, provincia de la Rioja, Argentina.
IV Reunión de Mineralogía y Metalogenía, MINMET´98EDIUNS: 207-211
Paar WH, Brodtkorb MKde, Topa D, Sureda RJ (1996) Caracterización mineralógica y química de algunas especies
metalíferas del yacimiento Pirquitas, Provincia de Jujuy,
República Argentina. Parte I. XIII Congreso Geológico
Argentino y III Congreso de Exploracíon de Hidrocarburos,
Actas III: 141-158
Putz H, Paar WH, Sureda RJ, Roberts AC (2002) Germanium mineralization at Capillitas, Catamarca Province, Argentina. IMA
18th Gen. Meeting Abstr.: 265
Sasso AM, Clark AH (1998) The Farallón Negro Group, Northwest
Argentina: Magmatic, hydrothermal and tectonic evolution and
implications for Cu-Au metallo-geny in the Andean back-arc.
SEG Newsletter 34: 7-18
Schalamuk IB, Barrio REde, Zubia MA, Genini A, Echeveste H (1991)
Provincia auroargentífera del Deseado, Santa Cruz. In
Zappettini O (ed) Recursos Minerales de la República Argentina. Instituto de Geología y Recursos Minerales SEGEMAR,
Anales 35: 1177-1188
Schalamuk IB, Logan MAV (1994) Polymetallic Ag-Te-bearing
paragenesis of the Cerro Negro district, Famatina Range, La
Rioja, Argentina. Can Mineral 32: 667-679
Schalamuk IB, Nicolli H (1975) Hallazgo de nagyágita en Farallón
Negro, prov. de Catamarca, Rep.Argentina. Rev de la Asociación
Geológica Argentina 30(4): 384-387
Sillitoe RH, Steele GB, Thompson JFH, Lang JR (1998) Advanced
argillic lithocaps in the Bolivian tin-silver belt. Mineral. Deposita 33: 539-54
Close
Chapter 13-12
13-12
Genesis and geochemistry feature of carbonaceous
siliceous rocks in Shuanghe Se-deposit, Enshi, Hubei
province, China
Qian Handong, Zheng Xiang, Wu Xuemei
Department of Earth Sciences, State Key Laboratory for Mineral Deposits Research, Nanjing University, Nanjing 210093,
China
Abstract. This paper discusses genetic features of the Shuanghe Se
deposit, which occurs in the carbonaceous siliceous rocks of the
Permian Gufeng Formation. Our study is based on a series of samples
investigated for their petrochemical and geochemical characteristics. The results show that the distribution of Se in the seleniferous
layer is proportional to the amount of basic pyroclastic rocks in the
stratigraphic sequence, and that the source of selenium is related
to eruption or weathering of the Emei Mountains basalt in SW China.
The process of enrichment and ore- formation occurred through
hydrothermal dissol- ution, oxidized leaching, transfer and filtration
as selenium complexes. Selenium minerals were deposited in favorable structure positions or absorbed by organic materials.
Keywords. Selenium deposit, geochemistry, genesis, Shuanghe, Hubei
province, China
1
Geology
Shuanghe village is located about 81 km SE of Enshi City
in southwestern Hubei province. The selenium deposit is
located in the northeastern part of the Upper Yangtze
Platformal fold belt of the Yangtze Paraplatform. The seleniferous layer, tens of km in length, is controlled by the
Shuanghe synclinal structure and is closely related to rifts
or syngenetic deep faulting and palaeoweathering horizons (Fig. 1). The strata in this area are well exposed and
include Ordovician, Silurian, Devonian, Carboniferous,
Permian and Triassic units (Yu Renyu 1993). The Middle
Permian Gufeng Formation, mainly composed of bedded
carbonaceous siliceous rocks and shales, is the host rock
of the Shuanghe Se deposit. The mineralized area can be
divided into 7 mine areas: Yutangba, Guanyinge, Miaowan,
Tudiya, Majingao, Gongshanwan, and Qiaoping. Of these
mines, only Yutangba has been reported in previous studies. The Se-bearing layers occur within the carbonaceous
siliceous rocks and change in thickness. The lens-shaped
orebodies delimited by the mines occur above the watertable. A series of selenide minerals have been reported
within the Se-rich carbonaceous siliceous rocks in the
Yutangba Mine, including native selenium (Zhu Jianming
2001), krutaite (CuSe2), klockmannite (CuSe), naumannite
(Ag2Se), mandarinoite [Fe2(SeO3)3·6H2O] (Belkin et al.
2003), and chalcomenite [Cu(SeO3)·2H2O].
2
Features of petro- and geochemistry
The ore-bearing carbonaceous siliceous rocks are characterized by bedded, laminated, massive and pseudo-brecciated structures. Table 1 gives the chemical composition of
the Se-rich carbonaceous siliceous rocks in the Middle Permian Gufeng Formation from Shuanghe. The results (17
samples were analyzed) show that they are mainly composed of SiO2, but that the silica content varies from
38.54~82.00% (mean 61.16%). The content of MnO is, on
average, less than 0.0021%. Average contents of Al2O3, TiO2
K2O and MgO are 7.39, 0.31, 1.22 and 0.86, respectively - i.e.
relatively higher than typical biogenetic siliceous rocks, and
also differing from hydrothermal siliceous rocks. Ratios of
the main oxides, SiO2/Al2O3, SiO2/MgO, SiO2/(K2O+ Na2O),
and the projection of the carbonaceous siliceous rocks of
Shuanhe in SiO2- (Na2O+K2O), SiO2-MgO, Al2O3-SiO2, TiO2Al2O3, Fe2O3-MgO- K2O, (Na2O+K2O)-Al2O3, SiO2 and
Al2O3×10- (Fe2O3+MnO)x10 diagrams, all fall within the
field of volcanosedimentary and hydrothermal sedimentary cherts. The compositions are compared with those of
different genetic types of siliceous rocks in the world in
Table 2. The petrochemical characteristics suggest the carbonaceous siliceous rocks in Shuanghe are not typical siliceous rocks and that their characteristics are instead similar to the volcano-sedimentary rocks.
3
Geochemical features
The carbonaceous siliceous rocks are enriched in numerous trace elements, including Se, Te, Mo V, Ag, Sb, Cr, U
etc., and are, in particular, characterized by the element
association of Se-Te-Mo. The dispersive elements Se and
Te are abnormally enriched, with average values of 674.66
and 2.08 ppm, respectively, i.e. 7641 and 1551 times the
crustal abundances), respectively (Li Tong 1992). The content of Se in the carbonaceous siliceous rocks of Shuanghe
has been reported to be a maximum of 8390 ppm (Song
Chengzu 1989); analyses of our 35 samples gave a maximum of 3670 ppm.
The Se mineralization is concentrated in the three
mines of Yutangba, Miaowan and Tudiya. In addition, Mo
Close
1424
Qian Handong · Zheng Xiang · Wu Xuemei
and V are also sufficiently abundant to be produced as
by-products. Other trace elements are relatively poor or
depleted, such as Mn, Sr, Ba.
Rare-earth elements are characterized by a low total
contents that range between 52.43 and 177.60 ppm; distribution patterns show a relatively steep profile (Fig. 2),
with a clear negative Ce anomaly. The value of äCe is
0.61 ppm on average (Fig. 2).
4
Discussion
All the geological, petrochemical and geochemical characteristics suggest that the genesis of the carbonaceous
siliceous rocks of the Shuanghe Se deposit relates to Permian volcano- sedimentary activity - either eruption or
weathering of basalts of Emei Mountain. In the meantime, deep-sourced hydrothermal solutions are consid-
Close
Chapter 13-12 · Genesis and geochemistry feature of carbonaceous siliceous rocks in Shuanghe Se-deposit, Enshi, Hubei province, China
ered to have been suitable “solvents” for Se. We conclude
that Se was largely derived from volcanic detrital sediment and hydrothermal siliceous rocks.
Acknowledgements
We are grateful to the National Natural Science Foundation of China (No.40272025) for financial supports.
References
Adachi M, Yamamoto K, Suigiski R (1986) Hydrothermal chert and
associated siliceous rocks from the Northern Pacific: Their geological significance as indication of ocean ridge activity. Sedimentary Geology 47: 125-148
Belkin HE, Zheng BS, Zhu JM (2003) First occurrence of mandarinoite
in China. Acta Geological Sinica 77(2): 169-172
Feng CX, Liu JJ, Liu S (2002) The Geochemistry and Genesis of Siliceous Rocks of Selenium Diggings in Yutangba. Acta Sedimentologica Sinica 20 (4): 727-732 (in Chinese with English abstract)
1425
Han F, Hutchinson RW (1989) Evidence for exhalative origin for
rocks and ores of the Dachang tin polymetallic field: the orebearing formation and hydrothermal exhalative sedimentary
rocks. Mineral Deposits 8 (2): 25-40 (in Chinese with English
abstract)
He B, Xu YG, Xiao L (2003) Generation and Spatial Distribution of
the Emeishan Large Igneous Province: New Evidence from Stratigraphic Records. Acta Geologica Sinica, 77 (2): 194-202 (in Chinese with English abstract)
Li T (1992) The Statistical Characteristics of the Abundance of
Chemical Elements in the Earth’s Crust. Geology and Prospecting 28 (10): 1-7 (in Chinese with English abstract)
Marchig V (1982) Some geochemical indiction for determination
between diagenetic hydrothermal metalliferous sediments. Marine Geology 50 (3): 241-256
Pollock SG (1987) Chert formation in an Ordovician volcanic arc.
Journal of Sedimentary Petrology 57: 75-87
Rona PA (1978) Criteria for recognition of hydrothermal mineral
deposits in ocean crust. Economic Geology 73: 135-160
Song CZ (1989) A brief Description of the Yutangba Sedimentary Type Selenium Mineralized Area in Southwestern Hubei.
Mineral Deposits 8 (3): 83-89 (in Chinese with English abstract)
Sugisaki R (1984) Relation between chemical composition and sedimentation rate of Pacific ocean-floor sediments deposited since
the middle Cretaceous: Basic evidence for chemical constrains
on depositional environments of ancient sediments. Journal of
Geology 92: 235-259
Wen HJ, Qiu YZ (2002) Geology and Geochemistry of Se-Bearing
Formation in Central China. International Geology Review 44
(2): 164-178
Yamamoto K (1987) Geochemical characteristics and depositional
environments of cherts and associated rocks In the Franciscan
and Shimanto terranes. Sedimentary Geology 52: 65-108
Yao LB, Gao ZM, Yang ZS (2002) Origin of Seleniferous Cherts in
Yutangba Se Deposit, Southwest Enshi, Hubei Province. Science
in China (Series D) 45 (8): 741-754
Yu RY (1993) Preliminary analysis of the Geological Characteristics and Origin of The Shuanghe Selenium Ore beds, Hubei. Hubei Geology 7 (1): 50-56 (in Chinese with English abstract)
Zhu JM, Zheng BS (2000) Some new forms of native selenium and
their genetic investigation. Acta Mineralogica Sinica 20 (4): 337341 (in Chinese)
Close
Close
Chapter 13-13
13-13
Progress in developing Te-Xe dating of ore minerals
H.V. Thomas, R.A.D. Pattrick, J.D. Gilmour
School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Manchester M13 9PL, U.K.
Abstract. 130Xe accumulates in telluride minerals due to β-decay of
130
Te and 131Xe can be produced from 130Te by neutron capture.
Thus Xe isotopic analysis of irradiated tellurium-rich minerals allows a xenon closure age to be determined. We show that the technique can be applied to sub-milligram samples of tellurium, and
report data from ore deposits in Wales, Colorado and Uzbekistan.
Native tellurium from the Good Hope mine, Colorado, is highly reproducible and shows promise as a monitor of the irradiation. The
130Te half-life is constrained to be no more than (1.41 ± 0.16) x 1021
yr by data from Kochbulak, Uzbekistan. Clogau and Good Hope data
suggest closure ages of 358 ± 47 and 564 ± 73 Ma, the latter in
contrast to a reported Pb-Pb age of 1.30 Ga. Errors are dominated
by uncertainty in the accepted Kochbulak age and are not inherent in the technique.
Keywords. Age dating, ore deposits, noble gases
1
Introduction
Tellurium bearing minerals are widespread in ore deposits. In epithermal and mesothermal Au-(Ag-) bearing telluride deposits they can represent the major economic
phases, and can also be found in a variety of other deposit types. While tellurides are not typically common
minerals, they are present in trace quantities in a substantial fraction of ore deposits. In contrast to conventional methods which date deposits indirectly through
wall rock or alteration products, β-decay of 130Te to 130Xe
has the potential to give a direct age of ore deposition.
2
Principles of Te-Xe dating
The Te-Xe dating technique relies on determining the ratio between the 130Xe decay product and its parent 130Te
(Kirsten et al. 1968). We subject samples to a low-fluence
neutron irradiation which produces 131Te from 130Te, 131Xe
is then produced by beta decay via 131I. Subsequent xenon isotopic analysis determines both parent and daughter
isotope, provided the 130Te to 131Xe conversion can be calibrated. This approach greatly extends the sample range
since the stoichiometry of the mineral under analysis need
not be well established and separation from gangue minerals is not necessary.
In Ar-Ar and I-Xe dating, which also rely on n-capture for parent element determination, calibration is provided using a well-characterised sample of known age,
typically Shallowater enstatite for I-Xe ( Brazzle et al. 1999).
We propose a similar approach if a suitable sample can
be identified and calibrated. This will avoid direct reliance on varying geochemical estimates of the 130Te half
life. However, use of reactor-produced 131Xe* (excess 131Xe
over an air 131Xe/132Xe ratio of 0.789) for tellurium determination requires quantification of the effect of 131Xe*
production from the background neutron flux experienced
by the sample over geological time production
3
Methodology
This project employs the University of Manches-ter’s unique
resonance ionization mass spectrometer RELAX (Refrigerator Enhanced Laser Analyser for Xenon) for xenon isotopic analysis, which has an ionization lifetimes close to
120 seconds and a 130Xe blank of a few hundred atoms
(Gilmour et al. 1994; Crowther et al. 2005). Samples are
analysed by laser step heating, so that the consistency of
the ratio 130Xe*/130Te can be examined for signs of thermal
resetting or inherited “parentless” 130Xe*. Thus several analyses are required from each sample, each analysis yielding a
few thousand atoms of 130Xe. For comparison, current estimates of the 130Te half life (8 x 1020 years: Manuel 1991;
Meshik et al. 2002) correspond to a production rate of ~1000
atoms (mgTe Ma)-1. Sample sizes are constrained to a maximum of a few mg in most common tellurides by the requirement to avoid self-shielding during the irradiation (this
would make 131Xe*/Te inconsistent through the sample volume). Typically samples of ~1 mg are used here.
Samples were irradiated at the Imperial College Research Reactor, Ascot, with a nominal thermal fluence of
1013ncm-2. Samples are wrapped in aluminium foil for the
irradiation and not unwrapped before analysis. A free
decay period of 100 days after irradiation (equal to 10
half lives) allows complete production of 131Xe*.
4
Deposits and samples
We report analyses of samples from the Clogau gold mines,
Kochbulak and Good Hope.
The Clogau Gold Mines are situated in the Clogau formation which is part of the Dolgellau Gold-belt in Harlech
district, North Wales. Here, gold mineralization is present
in a series of quartz-sulfide veins where they cut graphitic
units of the Mawddach Group. Telluride deposition is
thought to have been a late-stage process, taking place
after the main stage of quartz veining and after the gold
mineralization deposition (Naden 1988). The most likely
method of deposit formation is thought to be due to dewatering of the underlying Cambrian sediments and
volcaniclastics during uplift, with the result that result-
Close
1428
H.V. Thomas · R.A.D. Pattrick · J.D. Gilmour
tellurides. The deposit was mined out during the 19th Century Gold Rush. K-Ar dating suggests the age of this deposit is 1.30Ga (Kirsten et al. 1968). The samples analysed
were native tellurium provided by A. Meshik.
5
ing auriferous fluid interacted with the slates to precipitate gold-rich quartz (Sheppherd and Allen 1985). The
age of this deposit has been reported as early Devonian,
coeval with Acadian deformation, but this is probably a
time of resetting with the actual time of deposition much
earlier, Tremadoc to Arenig (510-476.1 Ma) (Mason et al.
1999). Samples of telluro-bismuthite (provided by the
National Museum and Gallery, Cardiff, courtesy of J. Mason) in quartz veining were analysed – telluride was
scraped off the rock surface with a scalpel and was not
well separated from gangue.
Kochbulak is an epithermal gold-telluride mineral deposit, situated in the Kurama Range of the Tien Shan
Mountains, Uzbekistan. The deposit contains an exotic
assemblage of minerals and features three types of ore
formation: high- and low-angle veining and ore-bearing
pipe breccia. The ore was deposited during the orogenic
uplift associated with sub-aerial volcanism and granitoid
emplacement in the region (Kovalenker et al. 1997). The
age of this deposit is geologically constrained to be between the C3 and P1 Epochs i.e. 317.5 ± 41.5 Ma
(Kovalenker et al. 1997). The sample used was native tellurium provided by A. Meshik.
Good Hope is a volcanic hosted massive sulfide deposit situated in the Vulcan District of Gunnison County,
Colorado. It is believed to have formed from hydrothermal circulation associated with mid-ocean ridge volcanism, the main ore-bearing minerals being gold and silver
Natural production of 131Xe*
In Figure 1 we show results from analyses of unirradiated
samples from Kochbulak (two samples) and Good Hope
(one sample). The correlation betwe-en 131Xe* and 130Xe*
demonstrates that 131Xe* has been produced from the
natural neutron flux experienced by the sample and will
contribute to the 131Xe* determined from irradiated
samples. The extent to which this presents a problem depends on the fraction of total 131Xe* in an irradiated
sample that was present before irradiation (discussed
below). This ratio is clearly sample dependent, but in Figure 2 we examine the correlation between 131Xe* and
129
Xe*. Since both these isotopes are produced by neutron capture reactions on tellurium isotopes, less sample
dependence is expected and observed. Remaining variations between samples might arise due to variations in
the subterranean neutron energy spectrum, production
of 129Xe* by reactions with cosmic ray muons (Takagi et
al. 1974), and by delayed production of 129Xe* since the
half life of its precursor 129I is 16 Ma. This isotope is effectively not produced from 129I after reactor irradiation
and so can be used in irradiated samples to monitor natural neutron production of 131Xe*.
Close
Chapter 13-13 · Progress in developing Te-Xe dating of ore minerals
6
1429
Irradiated samples
Data from two irradiations are reported here and illustrate
the use of Good Hope tellurium as a monitor. In Ascot 2,
three samples from Good Hope were irradiated (D, E, F).
Reactor produced 131Xe* proved to account for 97% of the
total excess 131Xe – natural 131Xe* is thus neglected hereafter though a correction based on 129Xe* might be made if
required. Total 131Xe* contents were determined for Good
Hope samples D and E (one release from sample F was lost
so no gas total is available) using a monoisotopic 128Xe spike
of 1.2 x 105 atoms. This led to 131Xe*/130Te = 5.66 x 1011 for
the Ascot 2 irradiation and 130Xe*/130Te = 3.2 x 1012 for the
Good Hope sample. This allows 131Xe*/130Te for the Ascot 1
irradiation, in which a sample of Kochbulak and Clogau
were included, to be determined from 130Xe*/131Xe* observed
in the Good Hope sample (B) included in this irradiation.
Data from both irradiations can thus be converted to 130Te/
130Xe and plotted on common graphs (Fig. 3, 4, 5). Good
Hope and Kochbulak yield consistent isochrons while there
is evidence of disturbance in the Clogau samples.
7
Discussion
The consistent 130Xe*/Te ratio revealed by the Kochbulak and Good Hope samples is strong evidence that chronological information is present. Both partial resetting
Close
1430
H.V. Thomas · R.A.D. Pattrick · J.D. Gilmour
and inheritance of 130Xe from a previous generation
of mineralization would disturb the system. As always,
the process responsible for setting or resetting the chronometer needs careful consideration. Furthermore,
precise determination of absolute ages must await the
interacting constraints that will become available once a
larger sample suite has been analysed. This work is underway.
However, working on the assumption that a telluride
sample cannot be older than the accepted age of the deposits under consideration, the most stringent constraint
is provided by the Kochbulak data, which correspond to
a half life shorter than 1.09 x 1021 Yr. Adopting the age
range of Kochbulak we deduce a 130Te half life of (1.25 ±
0.16) x 1021 Yr. This in turn suggests closure of the telluride samples from Clogau and Good Hope, Colorado at
358 ± 47 Ma and 564 ± 73 Ma, respectively. The errors
involved derive ultimately from uncertainty in the
Kochbulak formation age and are not inherent in the
technique. As more samples are analysed the half life
will be better constrained – errors approaching the limit
on the isotope ratio measurements (<1%) should be
achievable.
At the present state of development, natural production of 131Xe* is not an important source of inaccuracy. A
reasonable correlation exists between 129Xe* and 131Xe*
in the small suite of samples analysed to date, suggesting
that monitoring 129Xe* will allow correction for this effect should it become necessary.
References
Allen PM, Jackson AA (1985) Geology of the Country around Harlech.
BGS, HMSO, 111
Brazzle RH, Pravdivtseva OV, Meshik AP, Hohenberg CM (1999) Verification and interpretation of the I-Xe chronometer. Geochim.
Cosmochim. Acta 63: 739–760
Crowther SA, Mohapatra RK, Turner G, Blagburn DJ, Gilmour JD
(2005) Characteristics and applications of RELAX, an ultrasensitive,
resonance ionization mass spectrometer for Xenon. Lunar and
Planetary Science XXXVI (1723)
Gilmour JD, Lyon IC, Johnston WA, Turner G (1994) RELAX: An
ultrasensitive, resonance ionization mass spectrometer for xenon.
Rev. Sci. Inst. 65: 617-625
Kirsten T, Shaeffer OA, Norton E, Stoenner RW (1968) Experimental evidence for the double-beta decay of 130Te. Phys. Rev. Lett. 20: 1300-1303
Kovalenker VA, Safonov YG, Naumov VB, Rusinov VL (1997) The
Kochbulak epithermal gold-telluride deposit, Uzbekistan. Geology
of Ore Deposits 39: 107
Manuel OK (1991) Geochemical measurements of double-beta decay.
J. Phys. G. Nucl. Part. Phys. 17: 221-229
Mason JS, Fitches WR, Bevins RE (1999) Evidence of a pre-tectonic
origin for the auriferous vein-type mineralization of the Dolgellau
gold Belt, North Wales. Trans., Inst. Min. Metall. B108: 45-42
Meshik AP, Hohenberg CM, Pravdivtseva OV, Bernatowicz TJ (2002)
Double Beta Decay of Tellurium-130: Current Status. Lunar and
Planetary Science XXXIII: 1342
Naden J (1988) Gold mineralization in the British Caledonides with special reference to the Dolgellau Gold-Belt, North Wales and the Southern Uplands, Scotland. Unpubl. Ph.D. Thesis. University of Aston,
Birmingham
Sheppherd TJ, Allen PM (1985) Metallogenesis in the Harlech Dome:
a fluid inclusion interpretation. Mineral. Deposita, 20: 159-168
Takagi J, Hampel W, Kirsten T (1974) Cosmic-ray muon-induced 129I
in tellurium ores. Earth Planet. Sci. Lett. 24: 141-150
Close
Chapter 13-14
13-14
Gold – telluride ore mineralisation in the Chatkal-Kurama
region: The case of the Samarchuk deposit
Akromiddin Z. Umarov
National University of Uzbekistan. Tashkent, Uzbekistan
Abstract. Mineral associations of gold, tellurides and associated
sulphides and sulphosalts are described from the Samarchuk deposit in the Kizilalmasay orefield, Chatkal-Kurama region of
Uzbekistan. The breccia- and vein- deposit has many characteristics of typical Au-telluride deposits.
2
Keywords. Samarchuk, Uzbekistan, Chumauk, Shavaz-Dukent
1. Pre-ore alteration. The association consists of quartz,
sericite, carbonate, pyrite and other minerals.
2. Quartz-gold-pyrite. The association makes up the bulk
of the ore volume in the Kizilalmasay orefield. The ore
generally contains low sulphide contents. Gold is not
abundant, and is thinly-dispersed within As-bearing
pyrite. The association also includes ankerite. Fine acicular arsenopyrite and native gold occur; marcasite is
a rare component.
3. Quartz-carbonate-electrum-polysulphide-sele-nide
mineralization, in which a large number of silver minerals were formed: native silver, frei-bergite, sulphides,
sulphosalts and selenides. The carbonate in the association is ankerite; chalcopyrite, galena, sphalerite, and
pyrite are also present. This association is particularly
widely developed in the Central deposit, occurring
within veins, 10-15 cm in thickness, commonly as nests
within minerals of the previous associations. Deposition of the association is often preceded by brecciation of earlier-formed minerals, with the formation of
quartz breccia. Observations show that ore minerals
form the rims around the rock fragments and are distinguished by a dark colour. This association contains
a greater amount of sulphides than the previous ones.
4. Quartz-(carbonate)-gold-telluride-polymetallic ore. The
association has a moderate to high sulphide content, but
the main feature is the widespread presence of tellurides
of Au, Ag, Bi, Sb etc., as well as the presence of Sn-mineralization. Unlike association (3), the selenides include Segalena, Se-volynskite, kawazulite etc. Generally, it contains low-moderate-sulphide contents, with significant
amount of galena, sphalerite, chalcopyrite, and sulphosalts, as well as cassiterite and scheelite. The peculiar feature of the association is the isolation of ore minerals as
colloform-ribboned aggregates by explosive breccia, a
very typical for gold-telluride deposits. This association
is mainly developed at Samarchuk and Chumauk, and is
locally developed in Central.
5. Quartz-carbonate-chalcopyrite (with bismuth). Carbonate is mostly siderite. Minerals include native bis-
1
Introduction
The Samarchuk deposit lies within the Kizilalmasay
orefield, and is located on the right bank of the Angren
River in the south-western part of the Chatkal Rdge. Deposits of the orefied include Kizilalma (Central),
Samarchuk, Chumauk, and Mezhdu-Rechge (between the
rivers). Much data has been accumulated on the gold deposits within the orefield, but precise estimates of grade
and tonnage have yet to be definitely established.
Geologically the orefield lies within the boundaries of
Shawaz-Dukent graben within the Chatkal-Kurama
metallogenic zone. The Chatkal-Kurama region experienced extensive magmatic activity between the Ordovician - Silurian to the Early Cretaceous and contains a diverse range of ore deposits (Cu-Mo, Au-Te, Au-Ag, Pb-Zn
etc.). One of the reasons for this is the formation, in the
Upper Palaeozoic (Early Permian) of a mantle plume. The
entire Chatkal-Kurama region is considered to be a
‘hotspot’ (Dalimov et al. 2004).
The Samarchuk deposit lies at the southern flank of
the Karabausky fault, which marks the division between
the basement and volcanogenic cover (Middle-Late Carboniferous dacite-andesite). The deposit consists of a body
of intensively silicified deformed and brecciated rocks. It
is accompanied by felsite dikes and explosive breccias.
Felsic dikes are developed in the hanging- and footwall
of the vein, sometimes overlapping the vein itself Minorto moderate sulphide mineralization is developed among
the breccias. A distinctive feature of the geological structure of Samarchuk deposit is the absence of metamorphic schists. Volcanic rocks occur widely, in particular, a
subvolcanic body of trachydacite porphyry associated with
the ‘Gold vein’ which in fact extends up to Chumauk.
The emphasis of the present paper is to give an accurate definition of the mineral associations which compose the economic orebodies.
Ore mineral associations
Koneev (2001) defined six mineral associations in the
Kizilalmasay orefield.
Close
1432
Akromiddin Z. Umarov
muth, bismuthinite, wittichenite, Co-bearing pyrite,
sphalerite, galena and gold. In the Central deposit, the
association occurs in the form of narrow siderite-chalcopyrite veins in the selvages of mineralization zones.
It is more fully developed in the Chumauk deposit and
in the Katranga prospect (Shavazsay).
6. Quartz-barite and quartz-calcite. Barite veins with galena and chalcopyrite, and quartz-calcite calcite streaks
belong to the post-ore stage and are widespread in the
area. None of them carry gold.
3
Gold mineralogy
The thinly-dispersed gold and its compounds, primarily
with tellurium, are seen in the veins of the area. Gold is
the main commercially valuable mineral in the deposits.
According to Badalova et al. (1976), gold in the
Kizilalmasay orefield is very fine, and occurs as plates,
lump-shaped masses and irregular grains with dendritelike and amoeboid forms. Among crystalline gold,
cuboctahedral and cubic morphological types predominate. Gold fineness is given as .662 for Kizilalmasay, .817
for Chumauk, .666 for Samarchuk. According to
Sulejmanov (1970), the average for Samarchuk is .730.
Earlier studies have given the average gold fineness in
the Kizilalmasay deposit as 687.
We investigated the native gold of the Samarchuk deposit, showing that the gold is high-grade, from .700 to
.960. Impurities include Te, Bi, Se, As, Zn, Pt and Hg. Our
investigation also addressed the internal heterogeneity
and structural features of the fine-grained gold. Analyses
were made on a JEOL MS-46 electron microprobe.
An early generation of sub-µm scale thinly-dispersed
gold is supposed to be present in the quartz-pyrite association, based on neutron-activation and fire assay analyses. The gold may be present as invisible gold in the pyrite.
The forms of gold observed within interstitial cracks
in quartz are diverse. Crystalline gold may occur, and some
have a block-like structure. When occurring within
sulphides and sulphosalts, gold occurs as xenomorphic
or rounded grains.
4
Discussion
Based on its geological features and ore structures, the
Samarchuk deposit is considered to be a typical representative of the gold-telluride type of deposit. It has the
potential to become a leading economic ore deposit among
those in the Chatkal-Kuraminsk region. The following
evidence supports this interpretation:
The deposit is linked to explosive brecciation: a characteristic geological feature of Au-telluride deposits.
Typomorphic features of the main ore minerals.
High fineness of gold.
Colloform segregations of pyrite, typically with pentagonal dodecaedron morphology, and impurities of
Co, As, Cu, Au, Ag and Te.
The Au:Ag ratio >10; Se:Te <1.
Close
Chapter 13-14 · Gold – telluride ore mineralisation in the Chatkal-Kurama region: The case of the Samarchuk deposit
Sulphosalts, including Bi-Zn-bearing tennantite, with
Se and Te impurities.
High contents of Cd, Fe, Mn, Se and Sn in sphalerite.
High contents of Te, Se, Sb, more rarely Bi, Pt and Pd,
in galena.
The presence of Au, Te, Se and Co in chalcopyrite.
The most economically significant mineral association
in the Samarchuk deposit is the quartz-carbonate goldselenide-telluride polymetallic association. The intensity
of elements participating in formation of economic ores
in the deposit can be expressed as follows: Au-Te-Bi-SeAg-Pb-Sb-Cu-As-Zn-W-Mo-Co-Ni-Sn. In the ores, the elements show mainly, chalcophile properties, and occur
as tellurides, simple and complex sulphides, sulpho-selenides and sulphosalts. Gold is typically present in the
form of alloys of the Au-Ag series.
Among the geochemical indicators most useful in exploration are analyses of concentrates rather than bulk
samples. The most direct indicators of the presence of
gold-telluride ore are higher concentrations of Te, Se, Bi.
Gold, silver and the geochemically associated elements
Te, Se, As, Sb and Bi occur dominantly as ‘microminerals’
1433
and form natural microparageneses consisting of, and
associated with tellurides, sulphoselenides and sulphosalts.
The form in which the individual elements occur varies due to zoning and the presence of discrete microparageneses that correspond to specific settings within the
deposits. This fact enables us not only to formulate a common model for the deposits in the area, but also to correlate levels of erosion, temperatures of ore formation etc.
within the orefield.
The results and conclusions of our research enable us
to expand the prospectivity of the Kizilalmasay orefield
not only due to the searches of the main economic types
of Au-Ag ore (e.g. Central), but also exploration for goldtelluride mineralization of Samarchuk type.
References
Badalova RP, Suleimanov MO, Rafikov NF (1976) Produktive Mineral Associations of Kizilalmasay Ore Field. VMO
Dalimov T, Koneev R, Ganiev J (2004) Beltau-Kurama volcanic-plutonic belt and metallogeny of Uzbekistan. 32nd JGC-Florence,
Abstract volume CD-ROM 2: 996
Koneev R (2001) Micromineralogy-mineralogy of the XXI Century.
Episodes 8 (1)
Close
Close
Chapter 13-15
13-15
Mineralogy of the high-sulfidation Cu-Sb-Te
Mavrokoryfi prospect (western Thrace, Greece)
Panagiotis Voudouris
Department of Mineralogy–Petrology, Faculty of Geology, University of Athens, Panepistimioupolis 15784 Athens, Greece
Abstract. The high-sulfidation Mavrokoryfi prospect is located in
the Petrota graben, a tectonic depression filled with calc-alkaline
and shoshonic volcanic rocks of Oligocene age. Mineralization was
introduced following a brecciation event of preore silicification,
and is hosted within veins of massive silicification enveloped by
alunitic advanced argillic alteration. Ore consists of pyrite, marcasite, famatinite, tetrahedrite (up to 15.5 wt% Ag), goldfieldite (up
to 29.3 wt% Te) and traces of chalcopyrite. Al-phosphate-sulfate
minerals, together with normal alunites, occur in both advanced
argillic alteration and as gangue minerals, and are characterized
by unusual Pb-enrichment (up to 24.7 wt% PbO in hinsdalites).
Mavrokoryfi goldfieldite is among the purest in the world, with
up to 3.7 apfu Te.
Keywords. Western Thrace, Mavrokoryfi, high-sulfidation, APS minerals, goldfieldite
andesite flows, volcanic breccias and hyaloclastites are
overlain by the Perama sandstones (Lescuyer et al. 2003).
In the western part of the graben, subaerial pyroclastics,
tuffs, rhyolite domes and dacite flows dominate. Two main
fault systems, trending NNE and NW, caused by sinistral
strike slip reactivation of submeridian basement faults,
accompanied by NW tension gashes and synchronous
hydrothermal activity, are recognized in the area (Lescuyer
et al. 2003). On the southwest (about 8km), the rocks of
the Circum Rhodope belt are intruded by a Tertiary intrusive complex composed of monzonite-monzogabbro
and a microgranite porphyry, the later hosting a porphyry
Cu-Mo mineralization (Melfos et al. 2002).
3
1
The high-sulfidation Mavrokoryfi prospect (Fig. 1) in
western Thrace/NE Greece (Voudouris and Skarpelis 1998;
Skarpelis et al. 1999) is one of several magmatic-hydrothermal deposits genetically related to the Tertiary postcollisional orogenic magmatic activity that affected the
southeastern Balkan region during the Oligocene-Miocene.
Magmatic activity is characterized by the development of
calc-alkaline to shoshonitic volcano-plutonic arcs in NE
Greece and the Aegean region (Innocenti et al. 1984;
Christofides et al. 2003). Mavrokoryfi shares many common features with the deeper parts of the adjacent highsulfidation Perama Hill gold deposit (Lescuyer et al. 2003),
but also displays an unusual ore and gangue mineralogy
not previously reported from other high-sulfidation deposits
in Greece - and to our knowledge - worldwide.
2
Mineralization and alteration
Introduction
Regional geology
Mavrokoryfi is located in the central part of the Petrota
graben, a major tectonic depression within Mesozoic
metamorphic rocks of the Circum-Rhodope zone
(Papadopoulos 1982). The graben is mainly covered by
Oligocene calc-alkaline and shoshonitic volcanic and
subvolcanic rocks. Petrographic and geochemical studies of magmatic rocks from the Petrota graben were carried out by Frass et al. (1990) and Arikas and Voudouris
(1998). In the NE part of the graben, where the
Mavrokoryfi prospect is located, subaqueous pyroxene
Precious metal mineralization occurs within brecciated veins
of black massive silicification (<2m thick), underlying a
wedge shaped zone of opaline silica. The host rocks are
calc-alkaline two-pyroxene volcanic breccias. The silicification is enveloped by advanced argillic alteration, grading
outwards to argillic (quartz+kaolinite+smectite+ pyrite)
and intermediate argillic (smectite+ kaolinite+pyrite) alteration. Silicification comprises microcrystalline quartz,
opal-CT, alunite, and abundant pyrite and marcasite. The
advanced argillic zone contains variable amounts of
quartz, Al-phosphate-sulfate minerals (APS), alunite, kaolinite and pyrite, occurring as pseudomorphs of phenocrysts and also disseminated in the matrix.
The ore minerals were introduced after formation of
the high-sulfidation silicic alteration and occur as the
matrix of the breccia fragments within the veins. They
consist of pyrite, marcasite, famatinite, tetrahedrite,
goldfieldite and minor chalcopyrite (Fig. 2). Very minor
pyrrhotite occurs as small inclusions in pyrite. Paragenetic data indicate initial deposition of pyrrhotite, followed by pyrite, tetrahedrite and then by famatinite,
goldfieldite and traces of chalcopyrite. Galena is totally
absent as are any other sulfides and sulfosalts containing
lead. Gangue minerals include quartz, alunite and kaolinite. Alunite accompanying the vein-type mineralization
occurs as rhomboedral crystals displaying pseudocubic
habit. The mineralization is characterized by elevated Au
(<1.5 ppm) and Ag (<162 ppm) grades (Voudouris and
Skarpelis 1998; Skarpelis et al. 1999).
Close
1436
Panagiotis Voudouris
5
4
Ore mineralogy
Electron microprobe analyses of selected ore minerals are
presented in Table 1. They were carried out at the Department of Mineralogy and Petrology, University of
Hamburg, using a Cameca-SX-100 wavelength-dispersive
electron microprobe.
Tetrahedrite is present as inclusions in famatinite
(Fig. 2b). It contains appreciable Ag (1.4 to 15.5 wt% Ag),
substituting for Cu, as well as Hg (up to 3.1 wt%), substituting for Fe and Zn. It is almost pure tetrahedrite with
As contents in the range between 5 and 5.6 wt%. Small
amounts of Bi (up to 0.11 wt%), and Au (0.37 wt%) could
be attributed to mineral impurities.
Goldfieldite, ideally Cu10Te4S13, contains Te >2 apfu, which
in respect to the relationship Te/(Te+As+Sb+Bi) > 0.5 resulted in calculation of the structural formula on the basis
of 29-4[Te/ (Te+As+Sb+Bi)-0.5] apfu according to Trudu
and Knittel (1998). The Te content ranges between 24.7 and
29.3 wt% (Table 1), corresponding to 3.2-3.7 apfu Te, exceeding the maximum of 3.5 apfu reported from natural
goldfieldites by Trudu and Knittel (1998). Antimony, and to
a lesser extent As, substitutes for Te. Silver, substituting for
Cu (max. 0.4 apfu), is compatible with a maximum concentration of precious metal in goldfieldite rarely >0.5 apfu
(Trudu and Knittel 1998). The 0.28 wt% Au in one analysis
could be bound within the crustal structure, or alternatively
the product of sub-microscopic inclusions of native gold.
Famatinite, with small amounts of As (up to 5.11 wt%),
substituting for Sb, and Ag (<0.7 wt%), substituting for Cu,
also shows elevated contents in Au (up to 0.34 wt% Au).
APS mineralogy
Combined EMPA and SEM data indicates that three types
of the alunite group minerals are present in the Mavrokoryfi
prospect (Table 2, Fig. 3): APS minerals occur as cores
rimmed by K-Na-rich alunites within the advanced argillic
alteration and pseudocubic K-Na-rich gangue alunites associated with sulfides and sulfosalts in the mineralization.
The cores are Ca-Sr-Ba-Pb-rich phosphates-sulfates and
represent solid solutions between members of the alunite,
woodhouseite and crandallite group minerals (Table 2): they
consist of Pb-rich alunites (No. 5), K-rich hinsdalite (No. 6),
Ba-rich swanbergite-woodhouseite (No. 3) and K-rich
woodhouseite-swanbergite (No. 4). The rims are K- alunites
rich in Ca-Pb (No. 2). Concerning the pseudocubic alunites,
these are K-Natroalunites (No. 1). The X-ray element maps
(Fig. 3) best demonstrates the presence of Ba-rich
swanbergite-woodhouseite cores, rimmed by K-Na-alunites
in two large crystals from the alunitic wallrock alteration.
Lead displays a rather abnormal distribution, but is rather
enriched in the cores of the largest crystals (hinsdalite).
6
Discussion and conclusions
In Mavrokoryfi, both the pre-ore wallrock alteration and
subsequent introduction of ore took place by infiltration of
acid and sulfate rich fluids, probably in a transitional shallow submarine to subaerial environment. This mineralization is in many aspects similar to other Thracian magmatic–
hydrothermal deposits, such as the neighbouring Perama
Hill deposit (Lescuyer et al. 2003) and the St Demetrios
and Viper deposits in Sappes area (Michael et al. 1995;
Shawh and Constantinides 2001).
Mavrokoryfi differs significantly from the above deposits because of the presence of unusual Pb-rich APS
minerals, and by the very Te-rich goldfieldites.
Lead-bearing sulfides and sulfosalts are absent in the
exposed mineralization so it remains enigmatic why the
APS minerals are extremely enriched in Pb (XRF analyses in alunitized wallrocks indicated up to 1.5 wt% Pb).
The presence of APS mineral cores within normal alunites
and the absence of pyrophyllite and diaspore from the
Close
Chapter 13-15 · Mineralogy of the high-sulfidation Cu-Sb-Te Mavrokoryfi prospect (western Thrace, Greece)
mineralization suggest a decline of temperatures from
below 250ºC to about 200ºC, and a trend towards more
oxidized and acid-sulfate solutions from core to rim
(Watanabe and Hedenquist 2001). Pseudocubic alunites
that accompany mineralization are also hypogene and
similar to magmatic-hydrothermal pseudocubic alunites
from Bulgaria as described by Lerouge et al. (2003).
Mineralization took place following a brecciation event
within the silicic and advanced argillic alteration zone,
1437
at a temperature of above 180ºC, as this is considered to
be the lower limit of stability of goldfieldite (Kalbskopf
1974). Ore deposition took place by hydrothermal fluids
of high-sulfidation state close to the tetrahedrite/
famatinite boundary in accordance to statement of
Kovalenker and Rusinov (1986) that the formation of
goldfieldite requires oxidizing conditions and high sulfur activity. The Te concentrations in goldfieldite are not
only the highest among other goldfieldites from the
northern Greek area (20.51 wt% from Pefka prospect,
Dimou et al. 1994), but probable the richest in the world
(Trudu and Knitel 1998).
Due to the absence of any chronological data for the
alteration minerals, there is uncertainty about a connection between specific magma type and Te-enrichment in
the mineralization. The high-K calc-alkaline and
shoshonitic volcanics in the Graben of Petrota and their
equivalent subvolcanic bodies emplaced at greater depths
could be possible sources for Te-enrichment in the fluids
as proposed by Jensen and Barton (2000).
Close
1438
Panagiotis Voudouris
References
Arikas K, Voudouris P (1998) Hydrothermal alterations and mineralizations of magmatic rocks in the southern Rhodope Massiv.
Acta Vulcanologica 10: 353-365
Christofides G, Pecskay Z, Eleftheriadis G, Soldatos T, Koroneos A
(2004) Tertiary Evros volcanic rocks, Thrace, Northeastern
Greece: Petrology, K/Ar geochronology and volcanism evolution.
Geologica Carpathica 55: 397-409
Dimou Å, Michael Ê, Serment R (1994) Mineralogical composition of
the epithermal–polymetallic mineraliza-tion at Pefka area, Rhodope
district. Bulletin, Geological Society of Greece 30: 533-550 (in Greek)
Frass A, Hegewald S, Kloos RM, Tesch Ch, Arikas K (1990) Geology of
the Graben of Petrota (Thrace, NE Greece). Geol Rhodopica 2: 50-63
Innocenti F, Kolios N, Manetti O, Mazzuoli R, Peccerilo G, Rita F, Villari
L (1984) Evolution and geodynamic significance of the Tertiary
orogenic volcanism in northeastern Greece. Bulletin of Volcanology 47: 25-37
Jensen EP, Barton MD (2000) Gold deposits related to alkaline
magmatism. Reviews in Economic Geology 13: 279-314
Kalbskopf R (1974) Synthese und Kristallstructur von Cu12-x Te4S13,
dem Tellur-Endglieder der Fahlerze. Tschermaks Mineralogische
Petrographische Mitteilungen 21: 1-10
Kovalenker VA, Rusinov VL (1986) Goldfieldite: chemical composition, paragenesis and formation conditions. Mineral Zhurnal 8:
57-70 (in Russian)
Lerouge C, Bailly L, Flehoc C, Petrunov R, Kunov A, Georgieva S,
Velinov I, Hikov A (2003) Preliminary results of a mineralogical
and stable isotope study of alunite in Bulgaria-Constraints on its
origin. In: DG Eliopoulos et al. (eds) Mineral Exploration and
Sustainable Development, Millpress, Rotterdam: 495-498
Lescuyer JL, Bailly L, Cassard D, Lips ALW, Piantone P, McAlister M
(2003) Sediment-hosted gold in south-eastern Europe: the
epithermal deposit of Perama, Thrace, Greece. In: DG Eliopoulos
et al. (eds). Mineral Exploration and Sustainable Development,
Millpress, Rotterdam: 499-502
Melfos V, Vavelidis M, Christofides G, Seidel E (2002). Origin
and evolution of the Tertiary Maronia porphyry copper-molybdenum deposit, Thrace, Greece. Mineralium Deposita 37:
648-668
Michael C, Perdikatsis V, Dimou E, Marantos I (1995) Hydrothermal
alteration and ore deposition of precious metal deposit of Agios
Demitrios, Konos area, Northern Greece. Geological Society of
Greece, Special Publication 4: 778-782
Papadopoulos P (1982) Geological map of Greece. Maronia sheet,
scale 1:50000, I.G.M.E, Athens
Skarpelis N, Voudouris P, Arikas K (1999) Exploration for epithermal
gold in SW Thrace, Greece: New target areas. In: Stanley et al.
(eds). Mineral deposits: Processes to Processing, Balkema,
Rotterdam: 589-592
Shawh AJ, Constantinides DC (2001) The Sapes gold project. Bulletin, Geological Society of Greece XXXIV/3: 1073-1080
Trudu AG, Knittel U (1998) Crystallography, mineral chemistry and
chemical nomenclature of goldfieldite, the tellurian member of
the tetrahedrite solid-solution series. Canadian Mineralogist 36:
1115-1137
Voudouris P, Skarpelis N (1998) Epithermal gold-silver mineralizations at Perama (Thrace) and Lemnos island. Bull Geol Soc Greece
XXXII/3: 125-135
Watanabe Y, Hedenquist JW (2001) Mineralogical and stable isotope
zonation at the surface over the El Salvador porphyry copper
deposit, Chile. Economic Geology 96: 1775-1797
Close
Chapter 13-16
13-16
Synthetic palladium tellurides, their structures and
mineralogical significance
A. Vymazalová, P. Ondrus, M. Drábek
Czech Geological Survey, Geologicka 6, 152 00 Prague 5, Czech Republic
Abstract. Phases of the Pd-Te system have been synthesized. The
existence of Pd20Te7, Pd9Te4 Pd3Te2, PdTe, and PdTe2 at 400°C,
and Pd8Te3 at 800°C was confirmed. The structures of Pd20Te7,
Pd9Te4, Pd3Te2, and unit cell parameters of PdTe and PdTe2 were
refined by the Rietveld method. The crystal structure data of Pd8Te3
are newly refined in hexagonal space group P 6/mmm, a =
25.9398(3), c = 7.9742(1) Å.
The crystal structures of synthetic Pd9Te4, Pd20Te7,
Pd3Te2 and “Pd7Te3” were refined from X-ray powder diffraction data by the Rietveld method. Results of the refinement for Pd-Te phases are given in Tables 1 and 2.
Keywords. Palladium, tellurium, Rietveld method, crystal structure
refinement
According to Okamoto (1992), the identification of the
most Pd-rich telluride is ambiguous. Kim (1986) reported
the homogeneity range of Pd17Te4 from 18.7 to 19.4
atomic% of Te, Chattopadhyay et al. (1986) reported the
“β” phase with composition in the range 17.6 to 18.8
atomic% Te and Ipser and Schuster 1986 determined the
homogeneity range between 16 and 24 atomic% of Te.
On the other hand, Gronvold and Rost (1956) observed
single-phase “Pd4Te”, and Khar’kin et al. (1968) determined the structure of “Pd4Te”, which was Pd-deficient
(>20 at.% Te).
Our experiments performed on the “Pd17Te4” phase
resulted in an intermetallic alloy; a good quality X-ray
diffraction pattern was not possible to obtain within this
study. Chemical analyses of this alloy showed to be a mixture of native Pd and the phase of composition Pd20Te7.
The obtained mixture (exp. conditions: 52 hrs at 1300ºC
and 652 hrs at 600ºC) could have been a product of an
uncompleted reaction. Further studies are needed.
1
Introduction
The following phases of the Pd-Te system have been described as minerals: native elements Pd and Te, PdTe –
kotulskite, PdTe2 – merenskyite, Pd3-xTe – keithconnite and
Pd9Te4 – telluropalladinite. Furthermore, Elvy et al. (1998)
described two unnamed palladium tellurides with the compositions Pd8Te3 and Pd20Te7. Nine binary phases are known
from the Pd-Te system: Pd17Te4 (?), high temperature Pd3Te
(stability range 785 to 727°C), Pd20Te7, Pd8Te3, Pd7Te3, Pd9Te4,
Pd3Te2, PdTe and PdTe2 (Kim et al. 1990; Okamoto 1992).
In view of some controversies on the stability of Pd
tellurides, and missing crystal structure data, we initiated experiments to confirm stability and structures of
these tellurides.
2
Pd17Te4
Techniques and methods
Pd20Te7
Pd-Te phases were synthesized using the evacuated silicatube method and DTA techniques (Kullerud 1971). High
purity tellurium (99.999%) and palladium (99.999%) were
used as starting materials.
The powder diffraction data were collected using a
Phillips X´Pert MP diffractometer using Cu Kα radiation
and with a setting of 40kV and 40mA. Obtained data were
evaluated by using X-ray powder diffraction software
BEDE ZDS – System version 4.00 (Ondrus 2000). The crystal structure and unit cell parameters were refined by the
Rietveld method (Rietveld 1969) using the FULLPROF
program (Rodriguez-Carvajal 2001).
3
Discussion and results
The recent experiments within the Pd-Te system confirm
the stability of five binary phases at 400°C: Pd20Te7, Pd9Te4,
Pd3Te2, PdTe and PdTe2.
The existence of rhombohedral Pd20Te7 was reported by
Wopersnow and Schubert (1977), Bhan and Kudielka
(1978), Chattopadhyay et al. (1986), Ipser and Schuster
(1986), and Kim (1986). Pd20Te7 exists in two modifications; the high-temperature form is not quenchable. The
“Pd3Te” in Medvedeva et al. (1961) should be Pd20Te7 (Bhan
and Kudielka 1978), and the “Pd3Te” found by Gronvold
and Rost (1956) was actually Pd20Te7, according to XRD
data (Kim 1986).
Our research confirmed the existence and crystal
structure data of Wopersnow and Schubert (1977). The
Pd20Te7 is rhombohedral, isotypic to Pd20Sb7, with space
group R 3 (Table 2). Elvy et al. (1998) described
Pd20(Te,Bi)7 from Broken Hill, N.S.W., with optical properties in accord of those described by Kim et al. (1990)
for synthetic Pd20Te7. Unfortunately X-ray data are not
available in Elvy‘s work.
Close
1440
A. Vymazalová · P. Ondrus · M. Drábek
Pd9Te4
Pd9Te4 exhibits two modifications; the high temperature
form is most likely unquenchable. Pd9Te4 melts incongruently at 610ºC (Chattopadhyay et al. 1986), or according to Ipser and Schuster (1986) and Kim (1986), at 605ºC.
At 472ºC (Chattopadhyay et al. 1986; Okamoto 1992), the
high temperature modification transforms to low-temperature, monoclinic Pd9Te4. The structure of Pd9Te4
synthesised in this study at 400ºC corresponds with the
phase described by Matkovic and Schubert (1978) and
was refined in the monoclinic space group P 21/c (see
Tables 1 and 2). The phase “Pd2Te” reported in Medvedeva
et al. (1961) is most likely Pd9Te4 (Okamoto 1992).
The tentative monoclinic Pd7Te3 phase, stable below
470°C, was suggested by Kim (1986). According to our
experiments, the phase of chemical composition Pd7Te3
forms a narrow solid solution of Pd9Te4. The structure of
“Pd7Te3” (Pd9.1Te3.9) was refined in the monoclinic space
group P 21/c (Table 1 and 2). The phases “Pd2.5Te” (Ipser
and Schuster 1986), “d” (Chattopadhyay et al. 1986), and
“Pd5Te2” (Gronvold and Rost 1956, Medvedeva et al. 1961)
are probably a part of Pd9Te4 solid solution.
Pd8Te3
The existence of Pd8Te3 was suggested in Cabri (1981) from
Stillwater Complex, Montana. According to Kim (1986),
Close
Chapter 13-16 · Synthetic palladium tellurides, their structures and mineralogical significance
Pd8Te3 quenched from 800°C is orthorhombic. X-ray powder diffraction pattern of Pd8Te3 synthesized in this study at
800°C is not in agreement with that given in Kim (1986). The
crystal structure was refined in the hexagonal P 6/mmm space
group (Table 1). The run, of the same composition, quenched
at 400°C showed to be a mixture of Pd20Te7 and solid solution of Pd9Te4. The synthetic Pd8Te3 is metastable below 500°C.
This is in an agreement with predicted thermal stability limits for Pd8Te3 (Chattopadhyay et al. 1986; Ipser and Schuster
1986). Nevertheless, Elvy et al. (1998) described the phases
Pd8(Te,Bi)3 and Pd8(Te,Hg)3 from Broken Hill, N.S.W. Likewise, Grokhovskaya et al. (1992) reported (Pd,Pt,Ag)8 (Te,Bi)3
from the Lukkulaisvaara Pluton, Russia. It is most likely that
Bi (Hg) content in Pd8Te3 stabilizes the high temperature
hexagonal phase at lower temperatures.
1441
Pd3Te2
Khar’kin et al. (1968) and Okamoto (1992) reported Pd3Te2
as orthorhombic with space group P 2221. Matkovic and
Schubert (1977) determined the crystal structure of Pd3Te2
to be orthorhombic, with space group A mam. The structure of Pd3Te2 synthesized in this study was refined by
the Rietveld method, in the orthorhombic space group A
mam (Table 1 and 2).
PdTe and PdTe2
The studied crystal structures data of PdTe and PdTe2
are in a good agreement with previous studies (Thomassen
1929; Groeneveld Meijer 1955; Gronvold and Rost 1956;
Close
1442
A. Vymazalová · P. Ondrus · M. Drábek
Furuseth et al. 1956; Kim 1986). Atoms of PdTe, similarly
as in PdTe2, are in special positions, and therefore only
unit cell parameters were refined (Table 1).
4
Conclusions
The following phases were reinvestigated in the course of
this study: Pd 17Te 4, Pd 20Te 7, Pd 8Te 3, Pd 7Te 3, Pd 9Te 4
(telluropalladinite), Pd3Te2, PdTe (kotulskite) and PdTe2
(merenskyite). Analogues of the synthetic phases Pd20Te7
and Pd3Te2 could be found in association with known Pd
tellurides, among others, in mafic-ultramafic rocks. The high
temperature Pd8Te3 stabilized by another element (Bi, Hg)
could be expected in nature too. The study of synthetic PdTe phases provided useful data concerning the crystal structures of phases that could be expected in nature.
Acknowledgements
This is a contribution to IGCP 486 “Au-Ag telluride selenide deposits”.
References
Bhan S, Kudielka H (1978) Ordered bcc- Phases at High Temperatures in Alloys of Transition Metals and B - Subgroup Elements.
Z. Metallkd 69: 333-336
Cabri LJ (1981) The Platinum-Group Minerals. In: L.J. Cabri, Platinum Group Elements: Mineralogy, Geology, Recovery. CIM Special Volume 23: 83-150
Elvy SB, Gray ND, McAndrew J, Williams PA, French DR (1998) Unnamed
Palladium Telluride Minerals from Broken Hill, New South Wales J
and Proceedings of the Royal Society of New South Wales 131: 85-93
Furuseth S, Selte K, Kjekshus A (1956) Redetermined Crystal Structures of NiTe2, PdTe2, PtS2, PtSe2, and PtTe2. Acta Chem, Scand.
19(1): 257-258.
Groeneveld Meijer WOJ (1955) Synthesis, Structures, and Properties of Platinum Metal Tellurides. Am. Min 40: 646-657
Grokhovskaya TI, Distler VV, Klynnin SF, Zakharov AA., Laputina IP
(1992) Low-sulphide platinum group mineralization of the
Lukkulaisvaana pluton, northen Karelia. Geol Rudn Mestorozhdeniy 2: 32-50 (in Russian)
Gronvold F, Rost E (1956) On the Suphides, Selenides and Tellurides
of Palladium. Acta Chem Scand 10(10): 1620-1634
Chattopadhyay G, Bhatt YJ, Khera SK (1986) Phase Diagram of the
Pd-Te System. J Less-Common Metals 123: 251-266
Ipser H, Schuster W (1986) Transition-Metal-Chalcogen Systems. X:
The Pd-Te Phase Diagram. J Less-Common Metals 125: 183-195
Khar’kin VS, Imanov RM, Semileto SA (1968) Phases in the Pd-Te
System. Izv.Akad.Nauk SSSR, Neorg.Mater 4(10): 1801-1802 (in
Russian)
Kim WS (1986) Two New Synthetic Phases, Pd17Te4 and Pd7Te3 and
New Phase Relations of the Pd-Te System. J Geol Soc Korea 22(2):
146-160
Kim WS, Chao GY, Cabri LJ (1990) Phase relations in the Pd-Te system. J Less-Common Metals 162: 61-74
Kullerud G (1971) Experimental Techniques in Dry Sulfide Research.
In: Ulmer GC, ed, Research Techniques for High Pressure and
High Temperature, Spinger-Verlag, New York: 288-315
Matkovic P, Schubert K (1977) Kristallstrtuktur von Pd3Te2. J LessCommon Metals 52: 217-220.
Matkovic P, Schubert K (1978) Kristallstrtuktur von Pd9Te4. J LessCommon Metals 58: 39-46
Medvedeva ZS, Klochko MA, Kuznetsov VG, Andreeva NS (1961)
Equilibrium Diagram of the Palladium-Tellurium System. Zh.
Neorg.Khim 6(7): 1737-1739 (in Russian)
Okamoto H (1992) The Pd-Te System (Palladium - Tellurium). J Phase
Equilibria 13(1): 73-78
Ondrus P (2000) ZDS – software for analysis of X-ray powder diffraction patterns. ZDS Systems Inc., Prague
Rietveld HM (1969) A profile refinement method for nuclear and
magnetic structures. J. Appl. Cryst 2: 65 - 71
Rodríguez-Carvajal J (2001) FullProf.2k. Rietveld Profile Matching
& Integrated Intensities Refinement of X-ray and/or Neutron Data
(powder and/or single crystal). Laboratoire Léon Brillouin. ftp://
charybde.saclay.cea.fr/pub/divers/fullp
Thomassen L (1929) Crystal Structures of some binary alloys of Platinum metal. Z. Phys. Chem. B 2(5-6): 349-379 (in German)
Wopersnow W, Schubert K (1977) Kristallstrtuktur von Pd20Sb7 und
Pd20Te7. J Less-Common Metals 51: 35-44
Close
Chapter 13-17
13-17
Bulong quartz-barite vein-type gold deposit in the
Xinjiang Uygur autonomous region, China
Fuquan Yang, Jingwen Mao, Caishang Zhao, Yitian Wang
Institute of Mineral Resources, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, Beijing 100037, China
Abstract. The Bulong gold deposit, located in Akqi County, Southwest
Tianshan, China, is hosted in Upper Devonian fine-grained clastic rocks.
Gold mineralization is controlled by a series of gently- dipping fracture zones. The δ34S values of pyrite range from 14.6 to 19.2‰ and
those of barite from 35.0 to 39.6‰, indicating that the sulfur was
probably derived from the surrounding sedimentary rocks. The 3He/
4He ratios of fluid inclusions in pyrite are 0.24–0.82 R/Ra, the 40Ar/
36
Ar ratios vary from 338 to 471, and the 40Ar/4He ratios range from
0.015 to 0.412, indicating that the ore fluids of the Bulong gold deposit were mainly derived from the crust. The δ13CPDB values of fluid
inclusions in vein quartz define a narrow range of –4.6 to –1.4‰. The
δ18Ofluid values of 6.7 to 14.7‰, and δD values of fluid inclusions of
between –70 and –55‰. The combined isotopic data imply that the
ore-forming fluids of the Bulong gold deposit were mainly derived
from basinal fluids, with some minor contributions from magmatic
fluids and meteoric water.
Keywords. Quartz-barite vein-type gold mineralisation, stable isotopes, Bulong deposit, China
1
Introduction
The Bulong gold deposit was discovered in the early 1990’s
and represents a distinct style of gold mineralization that
is characterized by a quartz-barite vein association (Yang
et al. 2004). The Bulong gold deposit has not been studied
in detail previously. Zheng et al. (1996) carried out a preliminary geochemical study of the host rocks of the Bulong
gold deposit. On the basis of several rare earth element,
trace element, and stable isotope analyses, Zheng et al. (1996)
inferred that ore-forming materials were derived from the
host rocks. Yang and Wu (1999) studied the geological characteristics and physico-chemical conditions of the Bulong
gold deposit, and proposed that the deposit displays characteristics of hypabyssal, medium- temperature metallogenesis. Zhao et al. (2002) obtained Rb-Sr isochron age of
258±15Ma from fluid inclusions in auriferous quartz vein.
This paper mainly addresses the geological and S, C, O,
H, He and Ar isotopic characteristics of the unusual Bulong
quartz-barite vein-hosted gold deposit. Our studies have
played a significant role in characterizing deposit type and
understanding ore-forming processes of the Bulong deposit.
2
Deposit geology
2.1 Stratigraphy
The strata exposed in the Bulong ore district belong to the
Upper Devonian Yimugantawu Formation and Kiziltag For-
mation, and the Upper Carboniferous Kangkelin Formation (Fig. 1). The Yimugantawu Formation is represented
by a suite of siltstone and fine sandstone. The quartz-barite
compound veins are dominantly hosted within the Yimugantawu Formation, overlain by the Kiziltag Formation, which
is a sequence of phyllitized sandstone and siltstone and locally intercalated with sandstone- conglomerate. A large
barite vein and most large quartz veins are hosted in this
formation. The Kangkelin Formation is a sequence of limestone, locally intercalated with sandstone, siltstone and shale.
2.2 Tectonic characteristics and magmatic activity
The ore district is located in the northwestern limb of the
Aerbaqieke box anticline. The first-order Karateki fault is main
regional fault. The ore veins are controlled by a series of the
NE-trending, gently tilted fractured zones, but a large barite
vein and large quartz veins in the ore district are controlled
by a series of steeply dipping faults. No magmatic rocks are
exposed in the ore district, except for a few Permian diabase
dykes in the western part of the ore district and its surroundings. Two Variscan intermediate-acid porphyries occur in
about 6 km NE and SE of the area (Wang 2001).
2.3 Ore veins
More than 20 veins and cataclastic alteration zones have
been recognized in the Bulong ore district (Fig. 1). These
veins can be divided into large quartz veins, large barite
veins and quartz-barite compound veins. Among them is
the No. I vein, a large barite vein that occurs in a fracture
zone. The vein trends NNE and intersects the strata at a
high angle, and its average gold grade is 0.45 g/t. Nos. II, III
and IV ore veins are gold-bearing quartz-barite compound
veins. These range in length from 230 to 660 m and are up
to 1 m thick. They are dominantly pure barite veins, quartz
veins, quartz-barite veins and some calcite-quartz -barite
veins. In vertical section, we can see pure barite veins in the
middle and quartz veins or barite-quartz veins in the lower
and upper parts of the compound veins. The gold orebodies
mainly occur as quartz veins and quartz-barite veins. The
average gold grade is 1.6–18.0 g/t.
Veins nos. VIII–XI and XVII–XXI are large quartz veins,
0.8–5.0 m in thickness, and obviously striking obliquely
to the strike of the strata; they dip steeply at angles of
more than 60°. The gold grade is low (<0.5 g/t).
Close
1444
Fuquan Yang · Jingwen Mao · Caishang Zhao · Yitian Wang
2.4 Mineralization stages and wallrock alteration
On the basis of field evidence and petrographic analysis,
four stages of vein emplacement and hydrothermal mineralization can be distinguished: (1) an early quartz stage,
characterized by the occurrence of massive quartz veins;
(2) a barite vein stage; (3) a barite-quartz stage; this represents the main stage of gold mineralization in the Bulong
deposit and is characterized by the formation of laminated quartz veins, barite-quartz veins and locally occurring calcite-barite-quartz veins in quartz-barite veins; and
(4) a late-stage ankerite -calcite veinlet stage.
Ore minerals in ores account for <1% of the ore. The
dominant ore minerals are pyrite, siderite and native gold.
Gangue minerals are mainly barite and quartz; calcite and
ankerite are less abundant and sericite, chlorite, and feldspar just occur sparely.
Types of wallrock alteration include silicification,
pyritization, sideritization, sericitization, chloriti zation,
calcitization and ankeritization; silicification and
pyritization are closely associated with the gold mineralization.
3
Isotope geochemistry
The δ34S values of pyrite range from 14.6 to 19.2‰ with a
mean of 17.6‰. The δ34S values of barite show narrow
range and vary from 35.0 to 39.6‰ with a mean of 37.3‰.
The 3He/4He ratios of fluid inclusions in pyrite are 0.24–
0.82 R/Ra, 40Ar/36Ar ratios are 338–471 and 40Ar /4He ratios are 0.015–0.222 with a mean of 0.153, except for one
sample which gives 0.412.
The δ13CPDB values of fluid inclusions in quartz vary
between –4.6 and –1.4‰, averaging of –3.6‰.
The δ 18O SMOW values of quartz are characterized
by high enrichment of 18O and range from 17.2 to
21.1‰. Using the quartz-water fractionation equation
1000 lna = 3.38x106 T–2 – 3.40 (Clayton et al. 1972) and
the average homogenization temperature of fluids inclusions in quartz in the same stage of the same sample,
the δ18O values of the mineralizing fluids are calculated to be 6.7–14.7‰. The δD values of fluids vary from
–70 to –55‰.
4
Discussion and conclusions
Both the presence of barite as well as the association of
barite + pyrite within the ore assemblage imply that the
deposit formed under conditions of high oxygen fugacity. This implies that the δ34S value of barite is equivalent
to or slightly higher than the total δ34S values of the hydrothermal fluids (Zheng and Chen 2000). In the Bulong
gold deposit the total δ34S values of the hydrothermal fluids
range from 3 5 to 40‰, which are notably higher than
those (~25‰) of Devonian marine sulphate, indicating
that the sulphur was derived from the strata and related
to the reduction of sulfate.
The 3He/4He ratios of fluid inclusions in pyrite are
0.24–0.82 R/Ra, which are ten times higher than that of
the crust (0.01–0.05 R/Ra) (Stuart et al. 1995) but 10–30
times lower than that of the mantle (6–9 R/Ra). The
40Ar/36Ar ratios of ore-forming fluids in the Bulong are
slightly higher than those of the atmosphere (40Ar/
36Ar=295.5). The 40Ar /4He ratios of mantle fluids are
0.69±0.006 and the average value of the crust is ~ 0.2
(Stuart et al. 1995). 40Ar/4He ratios of ore fluids in the
Bulong gold deposit are similar to the value of the crust.
The diagram of 3He/4He (R/Ra) vs. 40Ar/36 of fluids in py-
Close
Chapter 13-17 · Bulong quartz-barite vein-type gold deposit in the Xinjiang Uygur autonomous region, China
rite shows that the data points of the Bulong gold deposit
are close to the field of the crustal fluid component, again
indicating that the ore fluids were mainly derived from
the crust.
The δ13CPDB values of fluid inclusions in quartz fall
between those of magmatic carbon (δ13CPDB= -8 to -5‰;
Faure 1986) and the marine carbonate field (δ13CPDB= -1
to +2‰; Keith and Weber 1964). In the δ 13CPDB vs.
δ18OSMOW diagram, the data of quartz are distributed on
the lower-left side of the field of marine carbonates and
slightly shift to the igneous carbonatite field, indicating
that carbon was derived from marine carbonates.
The δ18O values of the ore-forming fluids range from
6.7 to 14.7‰. Four samples analyzed fall in the range of
magmatic water (5.5–9.5‰) defined by Ohmoto (1986).
In the δD vs. δ18Ofluid diagram, four data points plot within
or just adjacent to the magmatic water field and the other
ten samples plot within the formation water below the
metamorphic water, indicating that the ore fluids of the
Bulong gold deposit were mainly derived from the basinal fluids and mixed with a small amount of magmatic
fluids and meteoric water.
Acknowledgements
This work was granted by the Major State Basic Research
Program of the People’s Republic of China (No. 2001CB
409807), and Geological Survey of China (200413000026).
1445
References
Clayton RN, O’Neil JR, Mayeda TK (1972) Oxygen isotope exchange
between quartz and water. Journal of Geophysical Research 77:
3057-3067
Faure G (1986) Principles of Isotope Geology, 2. ed. New York: Wiley, 589
Keith ML, Weber JN (1964) Carbon and oxygen isotopic composition
of selected limestones and fossils. Geochimica et Cosmochimica
Acta 28: 1787-1816
Stuart FM, Burnard PG, Taylor RP, Turner G (1995) Resolving mantle
and crustal contribution to ancient hydrothermal fluids: He-Ar
isotopes in fluid inclusions from Dae Hwa W-Mo mineralisation,
South Korea. Geochimica et Cosmochimica Acta 59: 4663-4673
Wang WP (2001) Characteristics of aeromagnetic field and metallogenic
prognosis of Wuqia–Keping area, southwestern part of Tianshan.
Uranium Geology 17: 162-167 (in Chinese with English abstract)
Yang FQ, Wang YT, Mao JW (2004) The Bulong gold deposit - a quartzbarite vein type gold deposit in Xinjiang: geological characteristics and S, He and Ar isotopic compositions. Acta Geologica Sinica
(English Edition) 78: 404-416
Yang FQ, Wu H (1999) Geological characteristics and genesis of Bulong
gold deposit in Xinjiang Bulletin of the 562 Comprehensive Geological Party, Chinese Academy of Geological Science No.14: 60-68
(in Chinese with English abstract)
Zhao RF, Yang JG, Wang MC, Yao WG (2002) The study of metallogenic
geologic setting and prospecting potential evaluation in Southwestern Tianshan mountains. Northwestern Geology 35: 101-121
(in Chinese with English abstract)
Zheng MH, Liu JJ, Long XR (1996) Ore-forming geological conditions
and target study of Muruntau-type gold deposit in southern Tianshan Mountains, Xinjiang. Unpublished Report: 29-42 (in Chinese)
Zheng YF, Chen JF (2000) Stable isotope geochemistry. Beijing: Science Press, 218-247 (in Chinese)
Close
Close
Chapter 13-18
13-18
Ore geology and fluid-system of the Yindonggou Ag
deposit, Henan: Implications for genetic type
Zhang Jing
Open Laboratory of Orogenic and Crustal Evolution, Peking University, Beijing 100871, and China University of Geosciences, Beijing 100083, China
Chen Yan-jing
Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, and Department of Geology, Peking University,
Beijing 100871, China
Abstract. The Yindonggou silver deposit is a fault-controlled lode
deposit and occurs in the Erlangping Terrane, northern East Qinling
Orogen. The ore is classified into quartz-vein and alteration rock
types. Wall-rock alteration is dominantly expressed as silicification,
sericitization, carbonation, and chloritization, as well as pyritization
and polymetallic sulfidization. The deposit was formed by a
mesothermal (270~370°C), CO 2-rich, low density and dilute
(<11.4wt%NaCl.eqv) fluid-system. From the early to late stage of hydrothermal ore-forming process, the depth of ore formation became slightly shallower and the fluid inclusion capture pressure
changed from lithostatic to hydrostatic as the system turned open.
This indicates that metallogenesis occurred in a tectonic setting
which underwent change from orogenic compression to extension.
The above information shows that the ore-forming fluid-system and
geological characteristics of the Yindonggou deposit are similar to
those of the orogenic gold deposit, which leads us to suggest that
it represents a typical orogenic silver deposit.
Keywords. Yindonggou silver deposit, orogenic Ag deposit, fluid inclusion, East Qinling Orogen, Henan province
1
Introduction
Application of plate tectonics has resulted in much
progress in the study of ore deposits, such as the development of tectonic models for porphyry copper and
epithermal gold systems in the Circum-Pacific rim (Sillitoe
1972, 1989), and for collisional orogeny, metallogeny and
fluid flow (Chen et al. 2004a; Pirajno and Chen 2005; this
volume), and the definition of a new concept for orogenictype gold deposit (Groves et al. 1998).
The spatial distribution and metallogenetic epochs of
orogenic gold deposits are discussed in detail elsewhere
(Kerrich et al. 2000; Goldfarb et al. 2001). Orogenic-type
fluid systems have been summarized to be rich in CO2
and low in salinity (Kerrich et al. 2000; Hagemann and
Cassidy 2000; Bierlein and Maher 2001; Fan et al. 2003) characteristics which have become used to identify orogenic fluid systems. However, whether there are orogenictype deposits of other metals, such as Ag, Cu and Hg-Sb,
remains an open issue.
The Yindonggou silver (polymetallic) deposit in
Neixing county, Henan Province has a resource of ca 3,000
t Ag. The deposit is ranked as a large silver deposit and
was discovered in 1999. Our studies in regional geology,
ore geology and geochemistry show that it is similar to
orogenic-type Au systems. In this paper, we report the
research results and argue that it is an orogenic-type Ag
deposit.
2
Ore geology
The Yindonggou silver (polymetallic) deposit occurs in
the Erlangping Terrane, northern East Qinling Orogen
(Fig. 1A). It is a typical lode deposit. Orebodies are hosted
in altered fault-zones subsidiary to the Zhu-Xia fault that
separates the Erlangping and Central Qinling terranes.
The Erlangping Terrane is characterized by the Erlangping
Group of Neoproterozoic-Early Paleozoic, comprising of
various types of schists. The terrane was intruded by
multistage granitoids with isotope ages from 800 Ma to
100 Ma (Hu et al. 1988; Chen and Fu 1992) (Fig. 1). The
Ag-bearing lodes and quartz veins emplaced into the
Erlangping.Group and an Indosinian granite with a 40Ar/
39Ar plateau age of 225 Ma. Sericite of the altered wallrock
yields a 40Ar/39Ar plateau age of 169.27±1.08 Ma (Zhang
2004).
The Yindonggou deposit includes eight ore-bearing
lodes/veins (Fig. 1B), numbered from Y1 to Y8. From the
orebodies to wallrock, mineral associations change from
Ag-bearing quartz veins (0.2~1.2 m thick), through a Agbearing pyrite-sericite-quartz assemblage, to weakly mineralized altered wallrock, and to weakly altered Ag-poor
wallrock. This shows an obvious lateral zonation. However, no vertical zonation can be observed. Quartz-vein
and altered rock are two types of ore which are mined.
Ore textures include disseminated, massive and breccia
types. The main ore minerals are native sliver, argentite,
tetrahedrite-freibergite, galena, sphalerite, pyrite, copper
pyrite, etc. The main gangue minerals are quartz, sericite,
chlorite, calcite, etc. The Ag-bearing minerals are
freibergite, argentite and native silver. Sliver contents in
ores range from 50 g/t to 6477 g/t. The average grades of
Au, Pb and Zn are 4.65~10.47g/t, 0.58~3.63% and 0.76~
4.93%, respectively (Henan Geological Survey of Nonferrous Metals 2001).
Close
1448
Zhang Jing · Chen Yan-jing
According to the paragenetic sequences of minerals, ore
petrography, and crosscutting relationships of veins and
veinlets, the ore-forming process can be divided into three
stages, i.e. the early (E), middle (M) and late (L) stages, which
are characterized by pyrite/arsenopyrite-bearing quartzveins, polymetallic sulfide stockworks and carbonate-quartz
veinlets, respectively. Silver, Au, Pb and Zn are enriched in
minerals of the M-stage, and poor in those of the E- or Lstages, indicating that the ore-forming elements were mainly
precipitated and enriched in M-stage hydrothermal process. This is also a common character of orogenic-type gold
deposits (Chen et al. 2003, 2004b; Li et al. 2004).
The E-stage quartz and pyrite crystals were structurally deformed and broken, and replaced and/or filled by
minerals of the M- and/or L-stages, indicating a compressive or shearing tectonic setting. The M-stage polymetallic
sulfide stockworks usually filled up the crevices, locally
co-axial, of the E-stage quartz-veins or altered wallrocks.
They were not deformed and brecciated, suggesting a tectonic setting of shearing relaxation. The comb structure
is characteristic of the L-stage quartz/calcite veinlets,
strongly demonstrating the extensional tectonic setting
during this stage. Therefore, it can be interpreted that the
hydrothermal metallogenesis was coeval with a tectonic
transition from compression to extension.
3
Fluid inclusion study
Quartz- and carbonate-crystals of the Yindonggou deposit
contain abundant fluid inclusions – these are from <2 to
>20 µm in size. Three populations of fluid inclusions can
be identified: CO2-rich or pure CO2 (A-type), CO2-bearing fluid (B-type) and fluid-only (C-type). Most A- and
B-types inclusions occur in the E- and M-stages quartz
crystals, while C-type inclusions often occur in the L-stage
minerals. Using laser-Raman spectra (LRS) analysis, methane could be recognized in aqueous CO2 and gaseous CO2
of the B-type fluid inclusions.
The microthermometric data and, accordingly, the calculated values of salinity, density and capture pressure
for different type fluid inclusions of different stage minerals allow us to interpret the following genetic information:
1. All the total homogenization temperatures (ThTOT) are
distributed in three ranges of 370~350, 330~310 and
290~270°C, respectively, which generally agree with the
three-stage metallogenic process discussed above. This
suggests the Yindonggou silver deposit is of meso-thermal class.
2. The CO2 homogeneous temperatures (ThCO2) of the
E-stage A-type inclusions are lower than 31°C, consistent with the LRS results that indicate that a few fluid
inclusions contain methane.
3. The melt temperatures of CO2 clathrate (Tmclath) of
B-type inclusions range from 3~9 °C. The calculated salinities of the E-, M- and L-stage fluids are
7.31~9.69 w t% NaCl.eqv , with an average of 8.56
wt%NaCl.eqv, 4.87~9.08 wt%NaCl.eqv, with an average of
7.09 wt%NaCl.eqv, and 2.03~10.87 wt%NaCl.eqv, with an
Close
Chapter 13-18 · Ore geology and fluid-system of the Yindonggou Ag deposit, Henan: Implications for genetic type
4.
5.
6.
7.
8.
4
average of 6.16 wt%NaCl.eqv, respectively. On the whole,
the salinities of the Yindonggou ore-forming fluid-system were low and decreased gradually from the early
to late stage.
The fluid densities are low (0.56~1.08g/cm3), which is
similar to those of orogenic-type gold systems. The
data show no obvious differences between the different stages.
The values of ThTOT, density, pressure of C-type inclusions are lower than those of B-type. Considering that
the C-type inclusions are dominant in L-stage samples,
we believe that C- and B-type inclusions represent fluids of different origins. The C-type inclusions were
probably sourced from meteoric water.
The secondary inclusions, with salinity of 1.74
wt%NaCl.eq and density of 0.93g/cm3, are of C-type. The
calculated capture pressure is about 0.6 MPa, corresponding to a hydrostatic depth of about 600 m. This
suggests that the postore meteoric water circulation
occurred at very shallow depths.
In a M-stage sample (YDG15), gas inclusions (V/
(V+L)>50%) closely coexist with liquid inclusion (V/
(V+L)<50%) and were homogeneous to gas phase at
Th=320.0°C, and liquid phase at Th=310.3~322.9°C, respectively. This, combined with the fact that B- and Ctype inclusions coexisted and were totally homogeneous
at temperatures of 312.6~339.8 and 291.2~322.9°C, respectively, shows that the fluid-system had boiled during the M-stage. Fluid boiling probably caused rapid
precipitation of ore metals; thereafter the fluid-system
became open and hydrostatic.
From E-stage to L-stage, the capture pressure of fluid
inclusions decreased from 280~320 MPa, through
250~277 MPa, to 90~92 MPa. Their corresponding
lithostatic depths (rock density assumed to be 3 t/m3)
decreased from 10.0~11.4 km, through 8.9~9.9 km,
and to 3.2~3.3 km (L-stage hydrostatic depth is about
9.0~9.2 km). Hence the ore-forming process should
be coeval with a rapid crustal uplift event, i.e. mountain-building or orogenesis.
Discussion
The regional geology, ore geology and fluid-system of the
Yindonggou Ag deposit are coincident with the characteristics of orogenic gold deposit summarized by previous studies (Groves et al. 1998). The metallogenesis occurred in a tectonic setting which underwent change from
compression to extension and coeval with orogenic uplifting. The Yindonggou Ag deposit is thus interpreted as
a typical case of an orogenic-type Ag deposit formed in a
continental collision regime.
1449
Acknowledgements
This work was financially supported by the NSFC (Nos.
40425006, 49972035, 40352003), the Hundred Young Scientists Program of CAS, and the Trans-Century Teacher
Program of the EMC. Prof. Fan Hong-rui, Zhu He-ping
and Wei Qi-ying and Dr. Chen Hua-yong are thanked for
helping laboratory research.
References
Bierlein FP, Maher S (2001) Orogenic disseminated gold in Phanerozoic
fold belts - examples from Victoria, Australia and elsewhere. Ore
Geology Reviews 18: 113-148
Chen YJ, Fu SG (1992) Gold Mineralization in West Henan, Beijing: China.
Seismological Press, 1-234 (in Chinese)
Chen YJ, Pirajno F, Sui YH (2004a) Isotope geochemistry of the Tieluping
silver deposit, Henan, China: A case study of orogenic silver deposits and related tectonic setting. Mineralium Deposita 39: 560-575
Chen YJ, Li J, Pirajno F, Lin ZJ, Wang HH (2004b) Hydrothermal metalogeny of the Shanggong gold deposit, East Qinling: studies on ore
geology and fluid inclusion geochemistry. Journal of Mineralogy
and Petrology 24 (3): 1-12 (in Chinese)
Chen YJ, Sui YH, Pirajno F (2003). Exclusive evidences for CMF model
and a case of orogenic silver deposits: Isotope geochemistry of the
Tieluping silver deposit, east Qinling orogen. Acta Petrologica Sinica
19: 551-568 (in Chinese)
Fan HR, Zhai MG, Xie YH (2003) Ore-forming fluids associated with
granite-hosted gold mineralization at the Sanshandao deposit,
Jiaodong gold province, China. Mineralium Deposita 38: 739-750
Goldfarb RJ, Groves DI, Gardoll S (2001) Orogenic gold and geologic
time: a global synthesis. Ore Geology Reviews 18: 1-75
Groves DI, Goldfarb RJ, Gebre-Mariam M, Hagemann SG, Robert F
(1998) Orogenic gold deposits: a proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geology Reviews 13: 7-27
Hagemann SG, Cassidy KF (2000) Archean orogenic lode gold deposits.
Reviews in Economic Geology 13: 9-68
Henan Geological Survey of Nonferrous Metals (2001) The Plan for AgCu-Pb Exploration in Neixiang-Nanzhao Region, Henan Province.
Unpublished, Zhengzhou, 43 (in Chinese)
Hu SX, Lin QL, Chen ZM, Li SM (1988). Geology and Metallogeny of the
Collision Belt between the North and the South China Plates. Nanjing
Univ Press, Nanjing, 558 (in Chinese)
Kerrich R, Goldfarb R, Groves D, Garwin S, Jia YF (2000) The characteristics, origins and geodynamic settings of supergiant gold metal-logenic
provinces. Science in China Series D 43 (supp.):1-68
Li, J, Chen YJ, Liu YX (2004) Typomorphic characteristics of pyrite from
the lode gold deposits in North China Craton: implications for fluid
mineralization. Journal of Mineralogy and Petrology 24 (3): 93-102
(in Chinese)
Pirajno F, Chen YJ (2005) Hydrothermal ore systems associated with
the extensional collapse of collision orogens. Extended Abstract,
SGA-2005, Beijing (this volume)
Sillitoe RH (1972) A plate tectonic model for the origin of porphyry
copper deposits. Economic Geology 67: 184-197
Sillitoe RH (1989) Gold deposits in western Pacific island arcs: the magmatic connection. Economic Geology Monograph 6: 274-291
Zhang J (2004) Case and Comparative Studies on the Typical SilverGold Deposits in East Qinling-Tongbai Mountains. Unpublished
Ph.D. Thesis, Peking University, 139 (in Chinese)
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Close
Chapter 13-19
13-19
Au-Te deposits associated with alkali-rich igneous
rocks in China
Zhao Zhenhua, Zhang Peihua, Xiong Xiaolin, Wang Qiang
Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
Abstract. Four Au-Te or Au(Te) deposits are discussed with respect
to their geological and geochemical characteristics. All of them are
rich in tellurides but low in sulfide contents. The Dongping Au(Te)
deposit was formed by interaction between fluids derived from an
alkaline syenite magma and hydrothermal origin. The Guilaizhuang
Au-Ag (Te) deposit is a quartz-fluorite-adularia type epithermal
deposit associated with high-K and shoshonitic series igneous rocks.
The Dashuigou deposit may be a seldom giant tellurium–dominant
Te(Au) deposit and is possibly related to the Ermeishan basaltic Large
Igneous Province. The Detiangou Au-Te-Ag deposit is a hydrothermal deposit, controlled by ductile shear zone.
Keywords. Au-Te deposits, alkaline igneous rocks, Dongping,
Guilaizhuang, Dashuigou, Detiangou, China
1
Introduction
In China, a number of large Au-Te or Te(Au) deposits are
directly or indirectly related with alkali-rich igneous rocks.
These include Dongping and Guilaizhuang, and in particular, the new type of superlarge Te(Au) deposit,
Dashuigou, related to alkaline or subalkaline basalts. These
alkali-rich igneous rocks are widespread, generally occurring in groups or zones within plates or close to plate
margins and associated with deep crustal faults. In China,
fifteen alkali-rich igneous rock belts, each extending several hundreds or even thousands of km in length, have
been recognized. The Au-Te or Te(Au) deposits discussed
in this paper occur within some of these belts (Fig. 1).
2
The Shuiquangou alkaline syenite complex is an elongated batholith with a E-W length of 55 km and a N-S
width of 5-8 km. Alkali feldspar syenite, quartz alkali feldspar syenite, pyroxene- hornblende syenite and hornblende monzonite constitute the syenite-monzonite
batholith. These rocks are chemically characterized by
lower SiO2 (57-65%), and high alkali contents (K2O+Na2O:
8.4-14.8%), commonly with K2O=Na2O. SHRIMP zircon
U-Pb dating gives 390±6Ma (Luo et al. 2001); 40Ar/39Ar
on hornblende gives 327.4±9Ma for the Shuiquangou alkaline complex.
The ore bodies can be classified into three types: quartz
veins, quartz veins with associated potassium-altered rocks
and potassium- and silica-altered rocks. Orebodies nos. I
and 70 are very rich in Te (Fig. 2). A very strong positive
correlation between contents of Au and Te has been recognized (y=0.98). The telluride mineralization becomes stronger from the top to deeper levels within the orebody. In the
alteration zones, the telluride mineralization shows a positive correlation with the intensity of alteration.
More than 14 Te-bearing minerals have been identified; they are mainly tellurides of Au, Ag, Pb and Bi
(calaverite, petzite, altaite, hessite, native tellurium,
tellurobismuthite, krennerite) or oxysalts of tellurium.
These minerals can be divided into three series: Au-Te,
Ag-Te and Au-Ag-Te. A new tellurium, mineral-zincospiroffite (Zn2Te3O8), was discovered by us (Zhang et al.
Dongping Au(Te) deposit
The Dongping Au (Te) deposit, situated in Chongli County,
is located at the northern margin of the North China Craton, within the Yan-Liao alkali-rich igneous rock belt. The
deposit is hosted by the Shuiquangou alkaline syenite
complex. Archean and early Proterozoic rocks, metamorphosed at amphibolite- and granulite-facies, are widely
distributed in the district of the deposit. The ShangyiChongli-Chicheng E-W-trending deep- seated fault occurs to the north, and a series of NE-trending faults are
located in the vicinity of the deposit. More than 30 gold
deposits and occurrences are hosted by the Shuiquangou
alkaline syenite complex. The Dongping Au(Te) deposit
is the largest and most representative among these (Song
et al. 1996).
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1452
Zhao Zhenhua · Zhang Peihua · Xiong Xiaolin · Wang Qiang
3
2004). The mineral forms by secondary co-oxidation of
calaverite.
Four metallogenetic stages can be distinguished: Kfeldspar-quartz stage; quartz-pyrite stage; quartz- polymetallic sulfide stage and pyrite-carbonate the stage. Telluride mineralization occurred mainly in second and third
stages. The main minerali- zation temperatures are 230390, 230-320 and 140-200°C, based on homogenization
temperatures of fluid inclusions in quartz. Salinities are
0.06-11.9 wt% NaCl. Laser Raman spectroscopy demonstrated that Na, K, Ca, Cl, SO4 and volatiles (CO2, N2, H2)
are very rich in these inclusions.
The δ34S values for 25 pyrite, 15 galena, 4 sphalerite
and 3 chalcopyrite samples range from –13,44 to +0.5‰,
with δ34Sch =δ34Spy>δ34Ssph>δ34Sga indicating the equilibrium of S-isotope compositions in mineralization processes. Based on the Ohmoto model the total S isotopic
compositions (δ34S) were estimated to be +1.85‰.
Pb-isotopic compositions for 11 samples of galena, 3
K-feldspars, and 1 pyrite sample are: 206Pb/204Pb 16.9717.75; 207Pb/204Pb 15.15-15.70; 208Pb/204Pb 36.48-37.95.
From analysis of inclusions of quartz, the δ18OH2O and
δDH2O values are –1.7 to +5.53 and –66.5 to 117.3‰, respectively. 3He/4He ratios for inclusions of pyrites in
orebody no.1 are 2.1-5.2 Ra, and 0.3-0.8 Ra in orebody
no. 70 (Mao et al. 2003). The physical and chemical features of the Te-mineralization are shown in Table 1.
Numerous mineralization ages have been attained by
isotopic dating. K-Ar K-feldspar ages are 148-157 Ma; 40Ar/
39Ar ages are 157±0.9 Ma, 173±5 Ma and 177±5 Ma, respectively. 40Ar/39Ar dating of micas gave 150 Ma.
According to the above geological and geochemical characteristics, we consider that mineralization of Dongping
Au(Te) deposit relates to an alkaline igneous complex and
was formed by a mixture of two fluids, of hypogene and
hypabyssal-hydrothermal origin, respectively.
Guilaizhuang Au-Ag (Te) deposit
The Guilaizhuang Au-Ag (Te) deposit, PingyiCounty,
Shandong Province is located in the easternpart of the
North China craton and Tan-lu alkali-rich deposits and
prospects around the Tongshi alkali-rich subvolcanic complex. In the mine area, Archean granitic gneisses, Paleozoic carbonates and Jurassic clastic rocks outcrop. The
Tongshi alkaline complex hosts the Guilaizhuang AuAg(Te) deposit. This consists of high-K calc-alkaline and
shoshonitic igneous rocks (monzonite-diorite porphyries,
monzonite-syenite porphyries). SiO2 contents in the
monzonitic diorite porphyry are 60-64%, (K2O+Na2O) is
7-11%, usually with Na2O-2.0 ≥ K2O (Le Bas 1986). The
SiO2 contents of the monzonite- syenite porphyry are 5264%, (K2O+Na2O) is 8-13%, and K2O=Na2O. A hornblende
40Ar/39Ar age of 189.8±0.2 Ma was given by Lin et al. (1996).
Four types of mineralization can be recognized as follows: cryptoexplosion breccia, porphyry, skarn and veins
in limestones. Four mineralization stages were recognized:
biotitization stage (biotite, apatite, pyrite and magnetite);
quartz-pyrite stage (quartz, fluorite, adularia, sericite, calcite, pyrite, chalco-pyrite); polymetallic sulfide stage
(sericite, hydro- muscovite, quartz, chalcedony, opal, fluorite, adularia, calcite) and gold-telluride stage (native gold
and tellurides of Au, Ag, Pb etc). Biotitization, silification,
sericitization and argillization are the main types of alteration; the last two are the most strongly associated with
mineralization. Au and Ag tellurides (calaverite, hessite,
petzite and beszmer- tovite) and other tellurides, such as
altaite, melonite and coloradoite, as well as native tellurium, were formed in the late stage of the main
metallogenetic event. Homogenization temperatures of
fluid inclusions in quartz from the main mineralization
stage are 180-250°C; δD values are –68.9 to 148.0‰ and
δ18O values are 9.92 to 17.74‰, indicating mixing of magmatic with meteoritic water. Nine pyrite samples gave δ34S
values of -0.24 to +2.99‰ (Lin et al. 1996). Based on the
above, the Guilaizhuang deposit can be classified as a
quartz-fluorite-adularia type epithermal Au-Ag(Te) deposit associated with high-K and shoshonitic series igneous rocks.
4
Dashuigou Te(Au) deposit
The Dashuigou Te(Au) deposit, Shimian County, Sichuan
Province, is located in the western margin of the Yangtze
craton and within the Panxi alkali-rich igneous rock belt.
It may be a rare – or even unique - giant tellurium-dominant deposit in the world. Precambrian granitoids, metamorphosed acid volcanic rocks, marble and sandy slate
make up the basement. Devonian, Permian and Triassic
cover rocks were metamorphosed to form sandy slate,
phyllite, schist and marble. Magmatic activity was mainly
late Paleozoic and Mesozoic, such as Permian basalts, Tri-
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Chapter 13-19 · Au-Te deposits associated with alkali-rich igneous rocks in China
assic mafic metavolcanic rocks and Cretaceous aegirineamphibole syenite. The ore deposits are located in the
middle part of NNW-trending Luding-Mianning ductile
shear belt. The Wanbahe dome is the main structure in
the vicinity of the deposit.
Permian metabasalts intercalated between marbles are
the host rocks of the telluride mineralization. The contents
of SiO2 and Na2O in the metabasalts are 45.38-46.63% and
1.50-2.53%, respectively, and the K2O/ Na2O ratios range
from 0.04 to 0.18, corresponding to alkaline or sub- alkaline series. The telluride orebodies occur in a group of NNEstriking parallel veins within the metabasalts. Three types
of ores comprise the tellurium ore bodies. These are: massive, nearly gangue-free ore; disseminated pyrrhotite-dolomite- telluride ore and disseminated dolomite-telluride
ore. Six tellurides are recognized: tetradymite, tsumoite,
joseite, tellurobismuthite, calaverite, stützite, plus native tellurium. Of these, tsumoite and tetradymite are the main
ore minerals. The tenor of Te is usually 0.2-10% in main
ore bodies and sometimes can reach up to 34.58%. The contents of Au, Ag, Se and Cu are 280, 148-260, 100-110 ppm
and 0.10-1.23%, respectively. In 1993, the reserves of elemental Te in a part of the deposit were assessed to be 1000 tons
(Chen et al. 1996). Sulphur and Pb isotope compositions
are listed in Table 2. Homogenization temperatures of fluid
inclusions in quartz and dolomites are 186-289°C. The δDH2O
of fluid inclusions in quartz, dolomite and pyrrhotite are 68.7 to -41.6‰ (average -56.13‰), and δ18OH2O are -2.12 to
11.64‰ (Tu et al. 2003), indicating that the ore forming
fluids are mainly from a magmatic source. The δ13C and
δ18O of dolomites are –5.8±0.3 and 11.70±1.23‰, respectively. According to the relationship of log ƒTe2-T, the
ƒTe2 are 10-6.1x105 Pa-10-15.2x105 Pa in the magmatic hydrothermal and the underground water hydrothermal mineralization epochs.
1453
The Dashuigou Te(Au) deposit is considered to relate
to the Ermeishan basalts, which are interpreted as products of a Permian large igneous province- related mantle
plume (Chen et al. 1996). A meso- and hypothermal genetic model was also proposed by Luo et al. (1996).
5
Detiangou Au-Te-Ag deposit
The Detiangou Au-Te-Ag deposit is located in the margin of North China craton, not far from Beijing, within
the Yan-Liao alkali-rich igneous rock belt. Archean biotite-amphibole-plagioclase gneiss and plagioclase amphibolite are the main host rocks. Several tens of veins of
alkali-rich porphyry, such as monzonitic porphyry, quartzmonzonitic porphy- ry and syenitic porphyry, are widely
distributed in the vicinity of the ore deposit.
Silicification, sericitization and carbonatization are the
main types of alteration associated with the mineralization. The contents of Te in the quartz veins and altered rocks
are 175-392 and 9.5-10.3 ppm, respectively. Ore minerals
consist of three series: Pb-S-Te, Ag-Bi-Te and Au-Ag-S-Te.
These minerals were crystallized in three mineralization
stages: the first is composed of altaite, galena, petzite, hessite, hedleyite, volynskite and native gold; the second is composed of sylvanite, stützite+/- native tellurium and the last
one: native tellurium +/- sylvanite +/- stützite. Among these,
altaite is the main ore mineral. Based on the association of
altaite with native gold, without calaverite, ƒTe2 values are
10-11.2 Pa-10-15.1 Pa from a diagram of ƒTe2-ƒS2. At the highest homogenization temperature 390°C of liquid inclusions,
native tellurium crystallized and the value of ƒTe2 can be
up 10-4.5 (Cui and Qi 1996).
Genetically, the Detiangou Au-Te-Ag deposit is a hydrothermal deposit with small- scale reserves and is controlled by ductile shear zone.
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Zhao Zhenhua · Zhang Peihua · Xiong Xiaolin · Wang Qiang
Acknowledgements
This work was supported by the National Climbing Program of China (No.95-yu-25) and the National Natural
Science Foundation of China (40373017).
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