Session 12
Geodynamics and metallogeny of
the Altaid Orogen (IAGOD +IGCP-473)
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Chapter 12-1
12-1
Geology, petrology and geochemistry of the Baishiquan
Cu-Ni-bearing mafic-ultramafic intrusions in Xinjiang,
NW China
F. Chai, Z. Zhang, J.-W. Mao
State Key laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
L. Dong
Xinjiang Bureau of Geology and Mineral Resources, Urumqi, Xinjiang 830000, China
H. Wu, X. Mo
No.6 Geological Team of Xinjiang Bureau of Geology and Mineral Resources, Hami, Xinjiang 830065, China
Abstract. The Baishiquan mafic-ultramafic intrusions associated with
magmatic Cu-Ni-PGE sulfide deposit are located in the Central
Tianshan Block in northern Xinjiang, NW China. They are composed
of olivine pyroxenite, pyroxene peridotite, troctolite, hornblendite,
gabbro and diorite. A SHRIMP U-Pb zircon age yields 286 Ma. Their
geochemical characteristics indicate that the parental magma was
high-magnesium tholeiitic, and contaminated by a small amount
of subducted-related components. Sulfides had saturated and segregated from silicate magmas before emplacement. The magma
source contamination combined with the crystal fractionation resulted in the Cu-Ni-PGE mineralization.
Keywords. Petrology, geochemistry, Cu-Ni deposit, mafic-ultramafic
intrusion, Xinjiang, NW China
1
Introduction
The Baishiquan mafic-ultramafic intrusion, 94°55’–95°01’ E
and 41°55’ – 41°59’ N, is located about 170 km southeast of
Hami city, east of Xinjiang, NW China (Fig. l). About 20 intrusions have been recognized by local Chinese geological team
in this area. They are tectonically situated along the junction
of Tarim Block and Central-Tianshan Block. They intruded
the middle-Proterozonic metasedimentary sequences composed of schists, gneisses and marbles (Fig. 1). Cu-Ni-(PGE)
mineralization occurred in some of these intrusions.
Dating of igneous zircon grains separated from a diorite in the intrusions yield a 286 Ma by SHRIMP method
(Li Huaqing, personal communication 2004). However,
detailed petrological and geochemical studies have not
been performed. In this paper, we discuss their petrogenesis via their petrological and geochemical data, and
provide some clues of Cu-Ni ore genesis.
2
Petrology and mineralogy
2.1 Petrography
The Baishiquan intrusion is composed mainly of olivine
pyroxenite, pyroxene peridotite, troctolite, hornblendite
and gabbro.
Olivine pyroxenite generally contains 35-55% pyroxene, 20-30% olivine, altered hornblende with minor sulfide and chromite. Most pyroxenes were altered by magnesium hornblende and chlorite. Olivine crystals range
from 1 to 1.5 mm in size, and were usually altered by serpentine in their margins and enclosed by orthopyroxene.
Greenish brown hornblende account for less than 5% in
volume and occurs as epitaxial overgrowths superposed
on pyroxene and olivine.
Troctolite consists of 30-40 percents of modal cumulus olivine and 45-50 percents of modal plagioclase and
interstitial minerals. Olivine occurs as elliplical grains of
1-3 mm in diameter. Most of olivine grains were partly
serpentinized along their cleavages. Plagioclase varies
from 1 to 5 mm in length, and they are randomly distributed, with interstitial other minerals. Larger plagioclase
crystals enclose euhedral olivine, and the rims of the enclosed olivine grains have a direct contact with secondary magnesium hornblende. Many cleavages at the rim
of olivine grains enclosed by plagioclase are commonly
observed. Intercumulus minerals include hornblende, biotite, ilmenite and trace sulfide. In general, these interstitial minerals account for less than 25 modal%.
Peridotite is the main rock type hosting Cu-Ni-(PGE)
ores. It consists of about 60% medium-grained olivine,
pyroxene, hornblende, biotite, plagioclose and sulphide
minerals. It exhibits cumulate texture and can be divided
into harzburgite and iherzolite according to the content
of orthopyroxene and clinopyroxene. Most samples are
highly serpentinized and exhibit a characteristic net texture in which they released magnetite along grain boundaries and cracks. Irregular remnant olivine kernels occur
in a network of serpentine. Olivine is normally rounded
and enclosed by orthopyroxene or clinopyroxene
oikocrysts, and pyroxene, plogioclase are enclosed by
hornblende. Olivine crystals have usually reaction rims
of orthopyroxene.
Hornblendite consisted mainly of 70% hornblende, 1520% plagioclase and less than 5% pyroxene and opaque
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F. Chai · Z. Zhang · J.-W. Mao · L. Dong · H. Wu · X. Mo
minerals. Euhedral six-sided hornblende crystals usually
assemble to form a synneusis texture. Poikilitic textures
are common, their anhedral and fine embayed plagioclases are enclosed by hornblende. Larger plagioclases
occur in interstitial textures and usually are cut by sericite
veinlets.
Gabbro generally includes 30% pyroxene, 40-50%
plagioclas, green hornblende, brown biotite and apatite,
spinel, chromite as well. Poikilitic texture can be observed
in large hornblende crystals which include numerous inclusions of pyroxene, plagioclase, apatite and opaque oxide. Pyroxene shows conversion to green hornblende in
some cases. Plagioclase crystals are often replaced by
granular saussurite and fine-grained clay minerals.
2.2 Mineralogy
The Baishiquan mafic-ultramafic rocks are mainly composed of olivine, orthopyroxene, clinopyroxene, hornblende and biotite, plagioclase. Electronic microprobe
analyses were performed at Chinese Academy of Geological Sciences (CAGS). A total of 91 crystals were analyzed. All collected samples contain unaltered crystals
or altered remnants. All minerals were determined with
an accelerating voltage of 15KV and a beam current and
counting time for major elements of 20 nA and 20s, respectively.
The analyzed olivine crystals have homogeneous composition from core to rim and different grains have slightly
different compositions in the same specimen. Fo contents
of olivine range from 78 to 85, which is much lower than
those of olivines in most abyssal peridotite (average
Fo=90.8, Dick and Bullen 1984). Fo contents of different
olivine grains depend on their lithologic types. The olivine compositions of Baishuiquan intrusions overlap those
of the magmatic sulfide Cu-Ni deposits in the world.
Based on their composition, the pyroxene can be named
as bronzite, endiopside, hypersthene and diopside.
Orthopyroxenes of different rocks have heterogenous FeO,
Al2O3 contents, but their CaO contents are homogeneous.
The FeO contents are the highest in peridotite (En=8183), and lowest in hornblende-gabbro (En=48.5). Their
Al2O3 contents of orthopyroxenes (0.36-2.1%) are much
lower than those in abyssal peridotite (2.1-5.0%) (Dick
and Natland 1996). Clinopyroxene have no significant
variations in composition except for Al2O3 contents ranging from 0.28-5.03% in the same specimen. Al2O3 contents in pyroxene are sensitive to the partial melting degree of mantle, decreasing systematically with increasing
depletion of peridotites (Dick and Natland 1996; Zhou et
al. 2004).
The plagioclases show a continuous change for CaO
contents in different rocks, ranging from 95.7 to 44.6. The
An contents of the enclosed plagioclase are higher than
of interstitial plagioclase. In addition, the reverse zonal
texture is common in plagioclase, indicating that the sequence of fractionation and the addition of adventitious
materials would have had a great influence on the composition of plagioclase.
3
Geochemistry
Major oxide abundances were determined by X-ray fluorescence spectrometry (XRF) techniques, and REE and
trace elements were determined by inductively coupled
plasma mass spectrometry (ICP-MS) at CAGS.
Close
Chapter 12-1 · Geology, petrology and geochemistry of the Baishiquan Cu-Ni-bearing mafic-ultramafic intrusions in Xinjiang, NW China
1295
The primitive mantle-normalized trace element diagrams exhibit variable abundances of elements, and all
rocks show very distinctive positive U, Th, Sr anomalies
and negative Nb, Ta, Zr anomalies, which indicate crustal
contamination either in the mantle sources or during
magma ascent en route to the magma chamber (Fig. 3).
4
3.1 Major elements
These rocks have a range of SiO2 (wt.%) between 37.89
and 50.71, and the MgO (wt.%) content varies from 10 to
28.38. Mg# values (Mg/(Mg+Fe) atomic ratio) vary from
0.71 to 0.78. The AFM diagram indicates that these magmas belong to tholeiite series.
3.2 Rare earth elements and trace elements
The samples have variable REE contents, but all of them
have similar chondrite-nomalized REE patterns (Fig. 2).
They are uniformly enriched in LREE relative to HREE,
with (La/Yb)N and (La/SmN) ratios 2.1-5.3 and 1.2-2.5,
respectively, and flat HREE chondrite-normalized patterns
with (Gd/Yb)N=1.0-1.7 as well. Most of samples have negative Eu anomalies (Eu/Eu*=0.78-0.96), which may be attributed to fractionation of plagioclase, but one sample
displays slightly positive Eu anomaly (Eu/Eu*=1.1-1.3),
which can be ascribed to accumulation of plagioclase.
Discussion
The maximum magnesian olivine composition in these intrusions is Fo=85, and the melts equilibrated with the olivine MgO/FeOT should have 0.9423 by a molar Mg-Fe distribution coefficient (Kd=(Fe/Mg) Ol /(Fe/Mg) magma ) of
0.3 ± 0.03 (Roeder and Emslie, 1970). The MgO/FeOT in these
intrusions are much higher than 0.9423, which indicates
that these rocks cannot represent primitive magma but involved magmas based on the data of our analysis. The highly
compatible elements such as Cr, Co, Ni are depleted, which
indicates that olivine, orthopyroxene and chromite fractionate from primitive magma. In addition, the presence of hornblende and biotite indicates a moisture-laden parent magma.
We estimate that the parent magmas of these intrusions
were likely to be high magnesium picritic.
All of the rocks are enriched in large-ion lithophile
elements (LILE) and LREE, negative Nb, Zr anomalies,
which suggests that the parent magma were contaminated.
We do not know exactly its isotopic characteristics; however, we speculate that is a good candidate as the major
contaminant is not the upper crust but subducted-related
components. The La/Sm ratios varying between 1.4 and
4.7 are less than 5, and Nb/La ratios<1. They indicate that
the contaminants are not likely upper-crustal materials,
but subduction-related components (Lassiter and Depaolo
1997; Thirlwall et al. 1994). In addition, hornblende and
biotite is observed in almost all thin sections, which demonstrate subduction event is reasonable because subducted-related magmas are usually enriched in hydrous
minerals. Furthermore, the high contents of Zr, Hf, Nb in
country rocks do not have any contribution to negative
anomalies in these elements of mafic-ultramafic rocks.
In addition, the oxygen isotopic compositions of these
rocks (in preparation) range from 2.5 to 6.0, also suggestive of mantle-derived magmas (Ripley et al. 1999).
The Cu/Pd ratios (in preparation) are higher than 6500
(primitive mantle value) in most rocks, which suggests
sulfide-saturated environment. The positive correlation
between Cu and Cu/Zr ratios of these intrusions indicate
that sulfide liquid segregated from the silicate melts before emplacement (Song et al. 2003).
5
Conclusions
The parental magmas of the Baishiquan mafic-ultramafic
rocks had a high-magnesium composition and the magma
source was contaminated by subducted-related components.
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F. Chai · Z. Zhang · J.-W. Mao · L. Dong · H. Wu · X. Mo
These magmas are not contaminated by upper-crustal materials and country rocks during ascent or within magma
chamber, and sulfide had saturated and segregated from
silicate magmas before emplacement. We propose the
magma source contamination and fractionation play an
important role for Cu-Ni-PGE mineralization in this area.
References
Dick HJB, Natland JH (1996) Late stage melt evolution and transport in the shallow mantle beneath the East Pacific Rise: Deep
Sea Drilling Project. Initial Reports 147: 103-134
Dick HJB, Bullen T (1984) Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas. Contributions to Mineralogy and Petrology 86: 54-76
Lassiter J, Depaolo DL (1997) Plume/lithosphere interaction in the
generation of continental and oceanic flood basalt: chemical and
isotope constraints. In: Mahoney J, ed. Large Igneous Provinces:
Continental, Oceanic, and Planetary Flood Volcanism. Geophysical Monography 100, Amercian Geophysical Union: 335-355
Ripley E, Park YR, Li C, Naldrett A.J (1999) Sulfur and oxygen isotopic evidence of country rock contamination in the Voisey’s Bay
Ni-Cu-Co deposit, Labrador, Canada. Lithos 47:53-68
Roeder PL, Emslie RF (1970) Olivine-liquid equilibrium. Contributions to Mineralogy and Petrology 29: 275-289
Song X, Zhou MF, Cao ZM, Sun M, Wang Y. L (2003). Ni-Cu-(PGE)
magmatic sulfide deposits in Yangliuping area, Permian
Emeishan igneous province, SW China. Mineralium Depoaita
38: 831-834
Sun S, McDonough WF (1989) Chemical and isotopic systematics
of oceanic basalts: implications for mantle composition and
processes. In: Saunders A D, Norry M J (ed.).M gmatism in the
ocean basins. Geological Society Special Publication No.42:
313-345
Thirlwall MF, Smith TE, Graham A.M (1994) High field strength
element anomalies in arc lavas: Source or process? Journal of
Petrology 35: 819- 838
Zhou M, Robinson PT, Malpas J, Edwards SJ, Qi L (1992) Ree
and PGE Geochemical constraints on the Formation of Dunites in the Luobusa Ophiolite, Southern Tibet. Journal of Petrology: 1-25
Close
Chapter 12-2
12-2
Discovery of picrite and related iron–copper–gold
mineralization in North Junggar, Xinjiang, China
Yuchuan Chen
Chinese Academy of Geological Sicences(CAGS), Beijing 100037, China
Dequan Liu, Ruhong Zhou, Yanling Tang
Bureau of Geology and Mineral Resources in Xinjiang, Wulumuqi 830000, China
Denghong Wang, Lijuan Ying
Institute of Mineral Resources, CAGS, Beijing 100037, China
Ting Liang
Chang’an Univercity, Xi’an 710054, China
Abstract. Picrite has been discovered recently in the Qiaoxiahala–
Laoshankou region in the north Junggar tectonic zone, Xinjiang,
China. Picritic basalt, basalt-porphyrite, diabase, latite, trachyte, tuff
and carbonate rocks constitute the ocean-floor picrite suite. This
suite contains more than 6 cycles, and its total thickness is more
than 1780m. Picrite includes three types: olivine picrite, olivine–pyroxene picrite and pyroxene picrite. As a whole, picrite is low in silicon, aluminium, titanium, and alkalis, but high in magnesium: SiO2
39.9~46.78%; MgO 16.4~36.67%; Na2O+K 2O 0.17~1.47%, TiO 2
0.28~0.62%. The gross of its rare earth elements (REE) is less than
45ppm, with slight light REE enrichment and a low positive Eu
anomaly. Trace elements such as Li, Be, U, Rb, Sr, Ba, V, F, Bi, Pb, are
noticeably enriched, whereas Ni, Cr, Co and S are extremely depleted.
This suggests that they have been differentiated to certain degree
and contaminated by upper crustal compositions. The contents of
platinum group elements (PGE) are similar to those of other picrites
in the world, with Pt/Pd<1 and low contents of Os and Ir. Iron–copper–gold mineralization occurring at the top of the third cycle, between the tuff and carbonate rocks, is the stratoid magnetitization–
chalcopyritization in the multiple layered skarns. Ores near the surface are dominated by magnetite, with chalcoprite–pyrite associated with native gold dominating at depth. Ores are intensely disseminated to partially massive.
Keywords. Picrite, geochemistry, platinum group elements (PGE), iron–
copper ore deposit, Qiaoxiahala, Laoshankou, north Junggar, Xinjiang
1
Introduction
Through work in 2003~2004, a suite of picritic rocks was
identified in Qiaoxiahala–Laoshankou, the southeast of
Fuyun, Xinjiang. The Qiaoxiahala iron–copper–gold ore
deposit also occurs there.
2
(Lower Devonian Series), and bimodal volcanic rocks of
the Tuoranggekuduke group (Lower Devonian Series). The
picrite-bearing rocks in north Junggar can be divided into
two suits of middle Devonian: in the north, it is a picritic
rock suite with middle Devonian below and boninites of
the Yunduhala group above; in the south (Zalate–Jiabosa’er
region), the rock suite is composed of bimodal volcanic
rocks of the Beitashan group (D2) below and normal calcalkalic basic–intermediate–acidic volcanic rocks of the
Yunduhala group above. Distinct rock types in the north
and south point to different tectonic settings: the north
represents an the ocean-floor setting, while the south is
near the continental margin. However, both in the north
and south, the rock suite of middle Devonian Series
formed from during the convergent stage, which indicates
that the middle Devonian Period was a time for the tectonic zone to switch from extension to convergence.
The strata of the Kaxiwen Group (upper Devonian Series) are volcanic clastic–normal clastic sediments of littoral–shallow sea facies interlayered by continental facies
and resulted from deposition during the late transitional
crust stage. It is represented by oceanic–continental clastic
rocks and more alkalic volcanic rocks of lower the Carboniferous Series belonging to the deposit at the end convergent stage. In the Ha’erjiawu group (upper Carboniferous
Series), it is locally the small intracontinental basin conglomerate, sandy conglomerate with dacite and tuff, belonging to the products during the consolidation of the new
continental crust. During the Permian Period intraplate
stage, local the mollase deposits of intracontinental river–
lake facies were formed.
Geological setting
3
The picritic rocks occur in the north Junggar tectonic zone,
Xinjiang. Its basal strata are carbonate rocks of upper
Ordovician, belonging to passive epicontinental shallow
deposits of the transitional crust during extension. Overlying these are volcanic clastic rocks – sedimentary clastic rocks of oceanic-continental facies of Kaxiwen group
Picritic rocks
In the Qiaoxiahala region, the picrite–trachyte formation
consists of picrite, diabase, basalt, olivine trachyandesite,
latite, trachyte and their volcanic clastic rocks and rare
limestone. The outcrop of this rock suite is 1~4km wide
and more than 60km along a north–northwest strike, con-
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Yuchuan Chen · Dequan Liu · Ruhong Zhou · Yanling Tang · Denghong Wang · Lijuan Ying · Ting Liang
tacting with the northern–southern strata by faults. By
measuring and logging three profile sections, the geologic section was shown to comprise six cycles at most,
with a total thickness of at least 918~1779m (roof and
base unexposed).
Lavas (including picrite, basalt-porphyrite etc.) are
dominant in the lower cycle, while in the upper cycle, the
latite–trachyte–tuff–carbonate rocks dominate. The thickness of a single cycle is 100~400m. An integrated cycle
includes: lower picrite, occasional diabase; middle andesitic basalt-porphyrite–picritic basalt–basalt–latite and
upper tuff–limestone–trachyte. In the east, Laoshankou
region, the cycle usually begins from the picrite and ends
by the volcanic breccia. While in the west (Qiaoxiahala
region), the cycle commonly lacks picrite and diabase,
beginning from andesitic basalt-porphyrite and ending
by carbonate rocks.
In the whole rock series, volcanic rocks (including
subvolcanic rocks, like diabase) make up 95.82%, with
limestones 4.18%.
In the volcanic rock series, the ratio of lavas to volcanic clastic rocks is 59.78 to 40.22, which shows lavas
are dominant. The percents of the compositions in
lavas are 25.49% ultrabasic rocks (picrite), 43.61% basic
rocks (diabase, basalt and trachybasalt), 0.52% intermediate rocks (olivine trachyandesite) and 30.37% acidic
rocks (latite, trachyte), which suggests that it is a bimodal volcanic rock formation because of the rare intermediate compositions.The dust tuffs are the dominant
volcanic clastic rocks, while volcanic breccias are rare.
The ratios of volcanic breccia, breccia tuff and dust
tuff are 17.37 to 14.77 to 67.88.The only nonvolcanic component is limestone, directly above the picrite and tuff.
There are no clastic rocks.The above features illustrate
that the deposit setting is within an ocean–floor region
off the continental margin, similar to the present Pacific
intraplate.
4
Petrology of picrite and its geochemical
signatures
Picrites in north Junggar, Xinjiang, are bedded lavas,
whose single bed is 20-200m thick. The directly associated rocks are basalt, basaltic tuff, and a few picritic volcanic breccias. In hand specimen picrite is deep green to
dark green, and masses of pyroxene phenocrysts can be
observed. olivine phenocrysts are rare because the
majority of the rocks have been altered. It presents a
dosemic texture under the microscope, and the phenocrysts, olivine and augite are 40~80% voluminally, with
grain sizes of 1~4mm. The groundmass has a crystallitic to hyalopilitic texture, which has been replaced by
the extremely fine uralite aggregate due to the intense
alteration. The olivine phenocrysts with integrated
sharply angular hexagonal shape have been largely replaced by epidosite–actinolite–chlorite or carbonate aggregates, and locally fibrous serpentine aggregates. Augite phenocrysts with the octagon section and integrated
short columnar shape, mainly hav not been altered, but
are partially chloritized along inner cracks of pyroxene.
The accessory minerals of picrite include magnetite and
few chromite.
According to the mineral components and petrochemical compositions, picrite in north Junggar can be
divided into three types: olivine picrite, olivine–pyroxene picrite, and pyroxene picrite with corresponding
phenocrystal components: olivine, olivine–pyroxene, and
pyroxene. Pyroxene in all picrites belongs to augite, with
En: Es: Wo= 30~59: 9~26: 30~34, while it is calcium-rich
salite in picritic basalt, with En: Es: Wo= 36~40: 11~13:
Close
Chapter 12-2 · Discovery of picrite and related iron–copper–gold mineralization in North Junggar, Xinjiang, China
5
49~51.The petrochemical compositions of picrite are
shown by No.1~3 in Table 1. As a whole, it is low in silicon, aluminium, titanium, and alkali, but high in magnesium. Compared with picrite in Gujarat, Deccan plateau, India (No.8~10 in Table 1), its MgO content is higher,
Al2O3 lower and alkali higher slightly.
On a alkali–Si diagram, the evolution of the rock series evolves from picrite, then trachy-basalt–olivine
trachyandesite, to trachyte, rather different from the common evolution of the calc-alkalic volcanic rocks. It is similar to oceanic island basalt series.
Compared with the average composition of the upper mantle, trace elements such as Li, Be, U, Rb, Sr, Ba, V,
F, Bi and Pb, are enriched, while Ni, Cr, Co and S are
depleted, indicating that it has been differentiated to a
certain degree, and contaminated by the compositions
from the upper crust. Compared with MORB, the incompatible elements are enriched slightly, approaching the
OIB of mantle plume (Fig. 1). On the Ti/Y–Nd/Y diagram,
it lies at the top of MORB, near the basalt region of oceanic intraplate. The contents of Cr, Co and Ni in picrite
are: 422~1267ppm, 62.9~70.9ppm, and 394~571ppm,
higher than the common basalt, indicating that it has
the features of the partly melting matter from the upper
mantle. The characteristic contents of REE of picrite in
north Junggar, Xinjiang, are REE= 32.29~41.28ppm, Eu
= 0.92~1.31, (La/Yb)N=2.06~3.57. It indicates that REE
concentrations are low, with positive Eu anomalies and
slight light REE enrichment. The picrite is distinct from
MORB, but similar to basalt related to mantle plumes.
The parallel curve group from olivine picrite to pyroxene picrite suggests that they are the products of the same
source while the distinct differentiated degrees. The similar partition pattern of andesitic basalt-porphyrite and
pyroxene picrite shows that they are at the same level.
The partition pattern of REE of latite and trachyte is
similar to that of picrite and basalt, and only light REE
of latite and trachyte is enriched slightly. The Pt/Pd ratio of picrite in north Junggar is less than 1. Compared
with Hawaiian picrite, Ru is higher, while Os and Ir much
lower; compared with picrite in Gujarat, India, Pd is similar, Pt lower and Ir much lower.
1299
Iron–copper–gold mineralization of the picritic
rock suite in north Junggar, Xinjiang
Gold–copper–magnetite mineralization occurred along
the whole length of 60km of the picrite rock series in
north Junggar, Xinjiang. Qiaoxiahala iron–copper ore
deposit is located at the western part, Qiaoxiahala.
The stratoid magnetite in the Qiaoxiahala ore deposit
occurred at the top of the third cycle of the picritic rock
series, between tuff and limestone beds, along the bed,
commonly with one industrial orebody among multiple
beds. A single orebody usually is 0.5~11m thick and
10~270m long.
The host rocks of the ores are mainly skarnized
tuffs. The roof and bottom are skarnized tuff, limestone, trachyte, basalt etc. The alterations near the
orebody are characterized by skarnization–epidositization (clinozoisitization) –pyritization–magnetitization–tourmalinization, with chloritization–carbonatization (including minor sericiti-zation–silicification)
towards the margins followed by epidositization–
uralitization–biotitization and stacked carbonatization–chloritization. The stratified skarnization is distributed only near the orebody, 10m wide at most. Tourmalinization only occurred in the roof of the orebody. The
alterations mentioned above have the features of the
exhalative volcanism.
On the surface of the orebody, massive and partly intensely disseminated magnetite ore dominates, with rare
disseminated chalcopyrite. Banded chalcopyrite in the
magnetite ore increased with depth (20~50m below surface) and grades into chalcopyrite ore as the dominant
sulfide with a sharp recduction of the magnetite. The
majority of the chalcopyrite ores are intensely disseminated to partially massive. Commonly, ores contain gold,
whose mineralization scale is wider than iron–copper
ores, and outside of the orebody, the gold content gradually decreases.
Gold, being fine native gold, commonly occurs in the
sulfides: the average gold content in chalcopyrite is
230ppm, bornite 395ppm and pyrite 158ppm. Ore grade:
the content of total Fe(TFe) in magnetite ores is up to
57.8%, often between 30~40%. In ores, the copper content is 0.2~2.97% and gold 0.03~0.65ppm. In some Cubearing magnetite ores, the cobalt content is 0.018~0.05%,
and molybdenum 0.026~0.04%.
The native types of ores are banded (massive) magnetite, massive Cu-bearing magnetite, disseminated
magnetite, disseminated copper ore and massive copper ore. The industrial types include low grade magnetite ores with Fe content of 20~45%, high grade ores
with Fe>45%, Cu-bearing mixed magnetite ores, low
grade copper ores (Cu 0.2~1.0%) and high grade copper
ores (Cu >1%).
Close
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Yuchuan Chen · Dequan Liu · Ruhong Zhou · Yanling Tang · Denghong Wang · Lijuan Ying · Ting Liang
The main ore minerals include magnetite and chalcopyrite, while its minor compositions are pyrite, pyrrhotite, hematite, limonite, specularite, bornite, chalcocite,
molybdenite, covellite, pentlandite, malachite, azurite,
chalcanthite, jarosite etc. Gangue minerals include quartz,
calcite, plagioclase, chlorite, epidote, actinolite, garnet, and
rare K-feldspar, tremolite, diopside, muscovite and
sericite.The discovery of picrite in north Junggar is the first
time in Xinjiang, China. Its significance can be outlined as:
Until now, it is the first time to discover picritic rock suite
of Palaeozoic occurring in the orogenic belt;
The picritic rock suite formed during the extensional
stage in the middle Devonian in the north Junggar orogenic belt, indicating the special characteristics of the
geotectonic setting for north Junggar.
Iron–copper–gold mineralization with industrial significance occurs in the picritic rock suite of north Junggar,
Xinjiang, representing a new type of ore deposit that
plays an important role in metallogy, ore-searching and
assessment.
The fact that picritic rocks distributed widely in north
Junggar, Xinjiang, provides a new clue for prospecting
PGE deposit in future.
Close
Chapter 12-3
12-3
Lead sources in ore deposits and magmatic rocks of
the Tien Shan and Chinese Altay
M. Chiaradia
School of Earth Sciences, University of Leeds, Leeds LS2 9JT, U.K.
Present address: Department of Mineralogy, University of Geneva, Geneva 1205, Switzerland
D. Konopelko
Geological Faculty, St. Petersburg State University, St. Petersburg 199034, Russia
R. Seltmann
Natural History Museum, CERCAMS, London SW7 5BD, U.K.
R. Cliff
School of Earth Sciences, University of Leeds, Leeds LS2 9JT, U.K.
Abstract. The Altaid orogen consists of Paleozoic subduction-accretion complexes and magmatic arcs as well as narrow Precambrian
basement slivers which were accreted, consolidated and then deformed during Paleozoic collisions and subsequent Alpine-Himalayan
deformations between the East European craton in the West, the Siberian craton in the East, and the Alai-Tarim and Karakum
microcontinents in the South. The Altaids are the site of abundant
plutonism and host some of the largest gold deposits in the world,
especially of the orogenic gold type. Over 100 new lead isotope data
show that each one of the Altaid domains investigated is characterized by distinct lead isotope signatures and that there is an W-E Pb
isotope gradient suggesting a progressive transition from a continental crust environment in the west (Western Tien Shan) to an almost 100% juvenile (mantle-derived) crust environment in the east
(Chinese Altay). Our data indicate also the locally extensive presence
of old continental crust at the base of the Tien Shan east of the TalasFarghona fault but not west of it. The lead isotope signatures of the
ore deposits follow closely those of the magmatic and basement rocks
of the host domains suggesting that no unique reservoir has been
responsible for the gold concentration in this orogen.
1
Introduction
The Altaid orogen hosts abundant plutons and some of
the largest gold deposits in the world, especially of the
orogenic gold type (e.g. Yakubchuk et al. 2002).
In this study we present over 100 new lead isotope data
on magmatic and metamorphic rocks as well as ore deposits of the southern part of the Altaids, including the
domains of Southern, Middle and Northern Tien Shan,
and Chinese Altay. Our data cover a WSW-ENE transect
about 2000 km long and 300 km wide from the Kyzylkum
desert of Uzbekistan in the west to the Chinese Altay of
Xinjiang in the east (Fig. 1).
2
West, the Siberian craton in the East, and the Alai-Tarim
and Karakum microcontinents in the South (Sengör et
al. 1993). Much of the Altaid orogenic collage was formed
by the accretion of allochthonous fragments, including
giant subduction-accretion complexes, island arcs,
ophiolites, and continental blocks, between the Late Proterozoic and the Early Mesozoic along a major subduction zone (Sengör et al. 1993).
The Tien Shan is composed of three major structural
units or terranes (Fig. 2): (1) the Northern Tien Shan (NTS),
the deformed margin of the Palaeo-Kazakhstan continent;
(2) the Middle Tien Shan (MTS), a Late Palaeozoic volcanoplutonic arc; and (3) the Southern Tien Shan (STS), an intensely deformed fold and thrust belt formed after the final closure of the Palaeo-Turkestan ocean.
The Altaid orogen is characterized by conspicuous
volumes of intrusions, which are directly or indirectly
associated with gold mineralization. Magmatism and associated mineralization in the Altaid orogen occurred in
relation to subduction, intra-continental rifting, collision,
and post-collisional extension and spanned a time range
between 500 and 120 Ma.
Geological setting, magmatism and
mineralization
The Altaid orogenic collage includes several orogens
(Mongol-Okhotsk, Altay, Kazakhstania, Tien Shan and
Urals) formed between the East European craton in the
Close
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M. Chiaradia · D. Konopelko · R. Seltmann · R. Cliff
Jahn et al. (2000) estimated that the mantle component in most granitoids of the Altaids ranges between 70
and 100%. However, some granitoids also display negative εNd(T) values suggesting crustal contamination.
Crustal contamination of granitoids coincides with their
emplacement within or in proximity to Precambrian
blocks which are characterized by εNd(T) values typical
of old crustal rocks (Hu et al. 2000).
3
Results and discussion
Rocks and ore deposits of the different geotectonic domains plot in separate isotope fields. The differences are
best seen in the uranogenic plot where ore deposits of
the geotectonic domains investigated (STS-W, MTS-W,
MTS-E, NTS-E, Yili block, Chinese Altay: see legend of
Figure 2 for explanations of the acronyms) plot within
distinct intervals of 207Pb/204Pb values (Fig. 2). Magmatic
rocks, metasediments and orogenic Au-deposits of the
STS-W have 207Pb-enriched, upper crustal signatures compatible with derivation from a continental crust characterized by elevated µ values (µ ~ 10.3 in the model of
Stacey and Kramers 1975). Therefore, lead isotope data
for STS-W rocks and ore deposits indicate that Late Paleozoic syncollisional magmatism has largely recycled
continental crust materials and that ore fluids which were
associated with this magmatism have leached lead (and
by inference other metals) from basement rocks characterized by high µ values. Ore deposit signatures only partly
overlap those of the STS-W intrusive rocks associated with
them, suggesting that lead in these deposits is not entirely of magmatic origin. The variable signatures within
these deposits also suggest that they are derived from a
non-homogenized mixture of at least two sources.
In contrast, the signatures of epithermal and porphyryCu deposits of the MTS-W reflect derivation of lead from
a homogeneous reservoir, which could be the continental arc magmas with which these deposits are associated.
This interpretation is consistent with 87Sr/86Sri data on
magmatic rocks of the Valerianov-Beltau-Kurama arc that,
ranging between 0.7061 and 0.7075 (Solomovich 1997),
indicate mixed mantle and crustal sources typical of a
continental arc setting.
Ores, magmatic rocks and metasediments of the MTSE and NTS-E plot along a linear trend in the uranogenic
plot (Fig. 2) lying just below the orogen curve of Zartman
and Doe (1981) and corresponding to an apparent age of
380±120 Ma, which, within the large error, coincides with
the age of mineralization and magmatism. The post-collisional magmatism and associated ore deposits of the
MTS-E and NTS-E (Makmal, Boordu, Taldybulak, Kumtor,
Aktyuz), plot in a narrow field. The only exceptions are
Boordu and Taldybulak (NTS-E II), which plot at significantly higher 207Pb/204Pb values than the associated magmatic rocks and than all other ores of the MTS-E and
NTS-E I and fall within the STS-W field (Fig. 2). Their
elevated 207Pb/204Pb compositions can only be explained
by lead leached from basement rocks characterized by
high µ values, similar to those of the STS-W.
The 207Pb/204Pb values of magmatic arc rocks and associated mineral deposits of the MTS-E and NTS-E I are
slightly lower than those of the MTS-W and are accompanied by higher 208Pb/204Pb values which might indicate
a larger contribution from old metamorphosed (lower
crust-type) basement rocks.
The Chinese Altay ore deposits have low 207Pb/204Pb
values suggesting a dominant mantle contribution (Fig. 2).
Compared with orogenic-Au deposits of the STS-W, the
MTS-E (Kumtor) and Chinese Altay (Saidu) orogenic gold
deposits are characterized not only by lower 207Pb/204Pb
values, but also by highly homogeneous signatures within
each deposit (Fig. 2). This implies either a better fluid
homogenization at Kumtor and Saidu or hydrothermal
leaching of rocks characterized by homogeneous Pb isotope compositions compared to those of the STS-W.
The Pb isotope signatures of the magmatic rocks of
the northern margin of the Tarim microcontinent (STSE), different from those of the STS-W and MNTS-E, are
Close
Chapter 12-3 · Lead sources in ore deposits and magmatic rocks of the Tien Shan and Chinese Altay
1303
characterized by a steep trend in the uranogenic plot,
which suggests mixing between upper crust and a less
radiogenic Pb-source. Their thorogenic lead enrichment
with respect to analogues in the STS-W and MNTS-E suggests a significant contribution from old metamorphosed
rocks with lower crust-type isotopic compositions.
4
Geodynamic implications
Despite different origins and ages, ore deposits and magmas belonging to a specific geotectonic domain of the
Altaids have similar Pb isotope signatures suggesting that
basement lithologies had a significant control on the isotopic compositions of both magmatism and hydrothermal activity at the regional scale.
One of the most intriguing features of our data is the
systematic longitudinal variation of Pb isotope compositions of ore deposits and magmatic rocks that can be better
viewed through the variations of the uranogenic and
thorogenic components (Fig. 3). Figure 3 shows a systematic decrease of the uranogenic Pb component from W to
E, which suggests an eastward increasing mantle or lower
crust lead contribution. The magmatic rocks and ores of
the STS-W, which have a consistently high uranogenic Pb
component, have in contrast a variable thorogenic Pb component (Fig. 3).
The thorogenic Pb component shows that the low
uranogenic Pb component in the central domains of the
NTS-E, MTS-E and STS-E is due to Pb contribution from
lower crust-type rocks (Fig. 3). It also shows that magmatic rocks and ores of the Boordu-Taldybulak district
display an anomalously low thorogenic component compared to all other magmatic rocks and ores of the MTS-E
and NTS-E (Fig. 3), which reflects mantle lead input as
supported by their low uranogenic Pb component (Fig. 3).
In contrast, the low thorogenic component of the Boordu
and Taldybulak deposits reflects mobilization of upper
crustal lead characterized by high µ values as supported
by the high uranogenic Pb component of these ore deposits (Fig. 3).Finally, the low uranogenic Pb in the Yili
block and Chinese Altay can only be related to a significant mantle lead input as shown by the consistently low
thorogenic Pb component (Figs. 3a and b).
In summary, our data indicate a dominantly juvenile
crust east of 80°E and a dominantly continental crust west
of 80°E in the investigated transect. West of 80°E both
upper and lower crust-type rocks are present and interact with mantle-derived magmas and fluids. The impact
of lower crust-type rocks on the isotopic compositions
of magmas and ores is widespread in the NTS-E, MTS-E
and STS-E domains whereas it is only local in the STS-W.
Proterozoic to Archean rocks are known to occur in the
NTS-E, MTS-E and STS-E thus explaining the thorogenic
Pb-rich signatures of rocks and ores in these domains
(e.g. Jenchuraeva 2001; Kiselev and Maksumova 2001). In
contrast, Pre-Cambrian slivers are rare in the STS-W
(Brookfield 2000) thus explaining the dominant upper
crustal signature (with no lower crust-type component)
in most of the ores and all the magmatic rocks of the
STS-W. The only exception is represented by the orogenic
gold deposits of Muruntau, Amantaitau and Daugyztau
whose thorogenic Pb component suggests leaching of old
metamorphosed rocks, perhaps representing a hidden
sliver.
5
Conclusions
New Pb isotope data of crustal rocks and ore deposits of
the Southern Altaids allow us to complement existing Nd
and Sr data on crustal rocks of Central Asia. Our results
indicate that ore deposits and crustal rocks have similar
Pb isotope compositions within each one of the different
geotectonic domains of the Southern Altaids. Additionally, the investigated domains differ for their Pb isotope
signatures providing support to their identity as separate pieces of the Altaid orogenic collage. Geotectonic
domains are characterized by a systematic decrease of
Close
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M. Chiaradia · D. Konopelko · R. Seltmann · R. Cliff
the uranogenic Pb component from west to east suggesting an increasing contribution from the lower crust in
the NTS-E, MTS-E and STS-E and from a primitive mantle
in the Chinese Altay. This is in agreement with geodynamic
reconstructions that interpret the Chinese Altay as the
result of accretion of giant subduction complexes, island
arcs and mantle-sourced magmatism and with the occurrence of Proterozoic and Archean rock slivers in the
NTS-E, MTS-E and STS-E. It also supports the participation of old lower crust-type continental fragments in the
formation of the orogenic collage (see also Hu et al. 2000).
Major orogenic (plus other type) gold deposits occur
in several Altaids domains (i.e. STS-W, MTS-E, Chinese
Altay) and are characterized by different isotopic compositions and systematics. Following the general westeast isotopic gradient mentioned above, orogenic gold
deposits of the STS-W are characterized by crustal Pb
isotope signatures typical of rocks with high-µ(±ω) values, those of the MTS-E (e.g. Kumtor) are characterized
by a significant input of lower crust-type lead and those
of the Chinese Altay display a dominant mantle contribution. Therefore, there seems to be no preferential source
of metals for these deposits, but rather a control in the
form of the type of lithologies that are leached by hydrothermal fluids (e.g. schists), position of the hydrothermal system within the orogen, and its association with
magmatism (see also Yakubchuk et al. 2002).
Acknowledgements
Boris Belyatsky is thanked for fruitful discussions and
partial provision of complementary sample material. This
is a contribution to the IGCP Project #473 “GIS Metallogeny
of Central Asia”.
References
Brookfield ME (2000) Geological development and Phanerozoic
crustal accretion in the western segment of the southern Tien
Shan (Kyrgyzstan, Uzbekistan and Tajikistan). Tectonophysics
328: 1-14
Hu A, Jahn BM, Zhang G, Chen Y, Zhang Q (2000) Crustal evolution
and Phanerozoic crustal growth in northern Xinjiang: Nd isotopic evidence. Part I. Isotopic characterization of basement rocks.
Tectonophysics 326: 15-51
Jahn BM, Wu F, Chen B (2000) Massive granitoid generation in Central Asia: Nd isotope evidence and implication for continental
growth in the Phaneorozoic. Episodes 23: 82-92
Close
Chapter 12-4
12-4
Distribution of gold in the Paleozoic sedimentary
strata of the Kyrgyz range (northern Tien-Shan)
A.V. Djenchuraeva, D.D. Djenchuraev
State Agency on Geology and Mineral Resources of Kyrgyz Republic, Erkindik Avenue, 2, 720300 Bishkek, Kyrgyzstan
A.D. Gonchar
Institute of Mineral Resources of Uzbek Republic, Tashkent, Uzbekistan
Abstract. New data on goldspectrometry were obtained from
samples selected in the measured sections. These sections were
constructed on different strata of the Paleozoic while conducting
large-scale geological survey of the Kyrgyz Range (eastern part).
Some 16 sections through the 10 stratigraphic divisions of the Paleozoic were constructed and 618 samples were selected and
analysed for spectrogoldmetry. Analysis shows that practically all
samples contain increased gold content. Red-colour psephitic sediments of the Shamsi molassa, where the buried placers of gold developed seem to be more prospective. Study of this problem is required in special investigations.
Keywords. Spectrogoldmetry, Paleozoic sedimentary strata, frequency
of gold
1
Black-shale formations are another genetic type of gold
mineralization in Central Asia (Shein 1984). The Paleozoic sedimentary strata are composed by products of
washout of more ancient sediments. They often contain
diverse ore components, including gold.
We have fulfilled the goldmetric sampling of the Paleozoic sedimentary formations of the Kyrgyz Range (eastern part). Samples were selected from all rock types and
stratigraphic divisions. Spectrogoldmetric analysis was
carried out in Spectral Laboratory of State Agency of
Kyrgyz Republic. The data presented below (Table. 1) make
it possible to determine concentration and nature of gold
distribution in Paleozoic sedimentary formations of the
studied area.
Introduction
2
Identification and study of conditions of formation and regularities of location of mineral deposits in space and time is
the main purpose of geological investigations. Two principal factors such as historic-geological features of the region and geochemical peculiarities of different kinds of
commercial minerals are the base for these constructions.
Gold has been discovered in all rocks of diverse rock
associations and different age. According to Shcherbakov
(1931), its average content (in g/t) is: 0.0032 (in granites),
0.0094 (in ultrabasites), 0.0036 (in shales and sandstones)
and 0.0032 in limestones. Apparently, periods of minimum and maximum accumulation of this element took
place attached to distribution of gold in the lithosphere.
Solution of
the problem on establishment of gold increased concentrations has significant scientific and practical meaning. According to published literature, the Late Hercynian
period (Late Carboniferous – Early Permian) is the most
productive period in Central Asia.
The endogenic gold-bearing mineralization of these
periods is of hydrothermal origin, and it is genetically
linked with intrusive rocks of granitic type and extrusive
rocks of intermediate and acid composition. Gold mineralization of endogenic origin is mainly distributed in
zones of intensive silicification and quartz-veined formation. Gold-bearing metasomatites are developed among
terrigenous formations of volcanic rocks and granodiorites, and less frequently in carbonate rocks o (Babaev 1977).
Gold distribution in the stratigraphic units
The Cambrian sediments (Arsin Formation) are the oldest rocks in the Kyrgyz Range. Sandstones and tuff-sandstones of the formation (the Koshokbulak, KoshokbulakI and II sections) contain from <0.005 to 0.2 g/t gold according to data from 74 samples (64 of them are empty).
Average content of gold in the first section is 0.027 g/t.
Sediments of this formation are without prospects on goldbearing mineralization on account to high volume of
empty samples. Isolated 0.2 g/t content (the KoshokbulakII section) are connected, most likely, with occasional hit
of ore grains into the sample.
The Ordovician sediments were studied in the TyundyukI section (left bank of the River Tyundyuk) and are represented by sandstones intercalated by sandy-shaly bench in
the upper part of the section. These rocks were derived from
sediments of an underwater delta. 46 samples were selected
and 27 of these contain from <0.005 to 0.03 g/t gold concentration (average content is 0.009 g/t).
In the Ichke-II section (left side of the Ichke gully),
the Middle-Upper Ordovician sandy-shaly) sediments
were sampled in tectonic block. Gold content is 0.0050.2 g/t. In 39 samples, the average content is 0.019 g/t.
Undifferentiated Middle Ordovician sediments
(Shyrgyi Formation) were sampled in the Chetyndy-II
section (right side of the Chetyndy gully). Of 25 samples
selected 22 samples contain from <0.005 (5 samples) to
0.4 (2 samples) g/t gold. One sample contains 0.009 g/t,
Close
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A.V. Djenchuraeva · D.D. Djenchuraev · A.D. Gonchar
one sample – 0.012 g/t, two samples contain 0.03 g/t and
two samples contain 0.04 and 0.05 g/t gold. Lithologically
this section is distinguished from the similar section parts
of this unit by shaly composition. A conglomerate bench
is developed only in the upper part. Apparently, the
Chetyndy-II section occurs in an apical part of small intrusive body and is the cause of increased gold content in
this section. Contained sediments noticeably are metamorphosed and pierced by system of quartz-reefs. One
of them is stretched across the strike of the strata for hundred metres and has 1.0-1.5 m thickness in swells. Quartz
is white, fusible, with inclusion of ore minerals lending
brown-yellow colour to it. Certain part of samples of these
veins has shown gold content from 0.04 to 0.4 g/t.
In the uppermost part of interfluve Chaktash-Northern Kerkebes (the Chak-Tash section), the sedimentaryextrusive Ordovician complexes were studied and sampled.
21 samples were selected, but gold was found only in 12
samples. Gold content is from <0.005 to 0.009 g/t.
Middle Devonian sediments (Tuyukjar Formation)
were sampled in the Komorchek-I and Akbulak sections,
and 11 samples were selected from each of them. In
the Komorchek section, 0.005 g/t gold was found only
in 1 sample. In the Akbulak section, 0.009 g/t of gold
was found in 3 samples. On left bank of the River Tuyukjar
(Tuyukjar section), the formation is represented by
sandstones with lenses of siltstones and gravel inclusions. In the upper part, beds of sandy limestones and
extrusive rocks are developed. The major part of samples with gold is located in the bottom part of the section. Gold content is from <0.005 to 0.015 g/t (mainly,
0.02-0.05 g/t). Low gold concentrations (from <0.005 to
0.012 g/t) were found in the Taldybulak-I section (left
divide of the Chetyndy stream head), although here the
formation is represented by conglomerate strata and
sandstones in the upper part.
The Upper Devonian – Lower Carboniferous sediments
(Torsu Formation) were studied in the Muztor, Muztor-I,
Taldybulak, Kyzyl-Moinok, Tyundyuk, Tyundyuk-II and
Karabulak sections. 26 samples were selected in the Muztor
section, but gold was established only in 9 samples. Gold
concentration is from 0.005 to 0.03 g/t. Average content is
0.01 g/t. Similar low average gold content is allocated in
other sections: interfluve Taldybulak-Tyundyuk – 0.012 g/
t, Anshi-Tyundyuk – 0.009 g/t, Karabulak – 0.009 g/t. Only
in the Muztor section (the River Tyundyuk), average content is 0.023 g/t in 11 samples (maximum content is 0.15 g/
t in one sample).
On the left bank of the Kurgan-Ashu stream, near the
Sagyschan-Shony Mountain, these units were described
in the Kurgan-Ashu section. This section has a binary
structure. The lower part is represented by sandstones
with conglomerate interbeds, and the upper part by conglomerates. Gold is only associated with the lower band.
15 samples were selected and in 3 samples, the content is
from 0.005 to 0.09 g/t.
The conditionally Visean sediments were described in
the Kyzylompul-II section, on left bank of the River Chu
(northern slope of the Kyzyl-Ompul Mountains). In lowthick carbonate series with terrigenous admixture, gold
was determined only in a few samples with 0.005 g/t content. Only in one sample (7/3), content is 0.012 g/t. In the
Kyzylompul section (left bank of the River Chu), the conditionally Visean sediments are represented by effusivesedimentary complex with dense quartz-reefs. In effusive rocks, gold is absent. In effusive-sedimentary sediments, it is 0.3-0.4 g/t (6/5 and 6/6 samples).
Close
Chapter 12-4 · Distribution of gold in the Paleozoic sedimentary strata of the Kyrgyz range (northern Tien-Shan)
The Visean – Bashkirian sediments (Shamsi Formation) were described in many sections, because in the studied region, these sediments (molassa formation) have a
widespread distribution. This formation is generally represented by psephites (sandstones, siltstones with
interbeds and bands of coarse-sandstones and conglomerates). The relationship of red-colour molassa formation with gold-bearing mineralization is well-known
(Kazakevich 1972). However, in the studied sections, average gold content does not exceed 0.007-0.003 g/t and in
many samples content is <0.005 g/t.
In the Bailamtal-II section (left divide of the River
Bailamtal), gold content is 0.4 g/t (sample number 15).
This sample was selected from a sandstone bed developed among conglomerates. In this section, a few samples
had shown content from 0.009 to 0.09 g/t.
171 samples were selected from the (Tuyuk-I) section
of this formation (left bank of the River Tuyuk). Gold
was discovered in 127 samples and ranges from 0.005 to
0.04 g/t. Gold content is 0.12-0.5 g/t in a few samples in
the uppermost part of the formation.
32 samples were selected in the Komorchek-I section
(left bank of the River Komorchek) and gold was deter-
1307
mined in 24 samples. Gold content varied from 0.005 to
0.012 g/t. In spite of monotonous structure of the sandyshaly section, the highest concentrations are connected
with the lower part of the section (bands 1-47), where
gold content varied from 0.02 to 0.07 g/t. Sediments in
the upper part of the section (bands 48-76) contain gold
concentrations of 0.04–0.07 g/t in individual samples.
The nature of gold distribution in sediments from the
Shamsi (molassa) Formation has shown that in lower parts
of the section (coarse sandstones and conglomerates), an
increased content is connected with more coarse-grained
varieties. A reverse dependence was noticed in the upper
part of the section (siltstones and sandstones). This regularity was observed in the Tuyuk-II section (left bank of
the River Tuyuk). Total 37 samples were selected and gold
was determined in 22 samples. The content is from <0.003
to 0.049 g/t (0.012 g/t content is numerous).
The Lower Carboniferous Minteki Formation is a facial analogue of the short-time and local marine cycle
sedimentation.
In the Kegety-II section (right bank of the River Kegety)
the formation is represented by sandy-shaly interbedding,
interbeds of effusive rocks and individual beds of lime-
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A.V. Djenchuraeva · D.D. Djenchuraev · A.D. Gonchar
stones at the top. Some 36 samples were selected and only
6 samples of them were empty. In the remaining 30 samples,
gold content is 0.005-0.04 g/t (often 0.05-0.09 g/t). The maximum content (0.2 g/t) was noted in 12/6 sample. Possibly,
gold concentration in the formation is connected with
extrusive rocks. But it is also possible that gold was introduced from the washed-out land by deltaic streams, because, on the whole, sediments of the Minteki Formation
are concerned facially to these environments.
The Lower–Middle Carboniferous Kegety Formation
was sampled in the Kegety-II section, where it occurs conformably on the Minteki formation, and it is overlapped
by the Janbulak formation of Middle Carboniferous. The
formation id represented by sandy-shaly strata with dense
beds of effusive rocks (bands 77-98). Possibly, this fact is
the cause of gold concentration as from <0.005 to 0.09 g/
t (average content is 0.005-0.009 g/t).
The Middle Carboniferous Janbulak Formation is characterized by not numerous number of samples (bands
99-106 of the Sagyschanshony-I section). The formation
is composed by extrusive rocks, but gold content is <0.0050.005g/t and only one sample (11/96) has 0.04 g/t content.
The Middle – Upper Carboniferous Ortok Formation
is represented by sandy-shaly interbedding with development of claystones at the top of sections. At the left
divide of the River Bailamtal (the Bailamtal section, bands
49-76), gold content is from 0.005 to 0.02 g/t (sample 3/44).
In the Kokadyr-I section (the River Kokadyr), the formation was sampled more closely. 47 samples were selected,
but gold was determined in 27 samples. Content is from
0.005 to 0.03 g/t. Average content is 0.009 g/t.
Low gold concentrations were obserbed in the IchkeII section (the River Ichke): from <0.005 to 0.007 g/t. 54
samples were selected, but only 10 of them contain gold.
In the Tyundyuk-III section (the River Tyundyuk), low
and rare gold concentrations were observed as well.
Another gold content was established in the Ichke-I
section (the River Ichke). In this section, 54 samples were
selected, and in 37 samples gold was determined with
0.005-0.007 g/t content. This deflection is connected with
the possible presence of land washes (kaolinite, quartzy
sandstones and grainstones) in the section developing on
the adjoining Kyrgyz-Kazakh continent.
The Permian sediments (Ashukoltor Formation) are
widespread products of extrusive activity (Bogdetsky and
Nekrasov 1983), which actively developed at the end of
Hercynian across the whole Tien-Shan. Only in the
Baialmtal-II section (left divide of the River Baialmtal),
gold content is 0.005 g/t in a few samples. Maximum content is 0.04 g/t (sample number 3/33).
3
Conclusions
On the basis of the above review on the gold distribution
in the studied sections of the Paleozoic sedimentary formations of the Kyrgyz Range (eastern part), it is possible
to draw a preliminary conclusion about increased gold
concentrations in all Paleozoic sediments. Red psephite
sediments of the Shamsi molassa are especially prospective, where the buried placers of gold can be developed.
Study of this result is required for detailed investigations.
The volume of spectral analysis in the studied sections
is not enough for statistical interpretations and geochemical inclusions, because on technical account (absence of
standards), and several elements (strontium, barium etc.)
that were not determined. But according to these elements,
methods of calculation of correlated coefficients using in
the time of paleogeographic reconstructions exist. According to the data of semi-quantitative spectral analysis obtained by now, in many samples concentrations of iron,
aluminium, titanium exceeding Clarkes by 2-3 times were
observed. The majority of the trace elements do not their
Clarkes with the exception of a number of effusive rock
samples from Ashukoltor volkanic complex that is typical for this type of rocks.
Reference
Babaev KL (1977) Some questions of gold metallogeny of Middle
Asia. In: Geology and relationships of location of the Tien-Shan
endogenic ore formations (gold), Vol.1, Tashkent, Uzbekistan,
SAIGIMS: 23-25
Close
Chapter 12-5
12-5
Geodynamics and metallogeny of active continental
margins of the Kyrgyz Tien Shan
R.D. Djenchuraeva
Institute of Geology, National Academy of Sciences, pr. Erkindik 30, Bishkek, Kyrgyz Republic
Abstract. This paper focuses on the Late Riphean – Paleozoic stage
that in the Kyrgyz Tien Shan is the most productive period in terms
of ore mineralization. During the Riphean–Vendian stage, development of riftogenic structures resulted in ocean formation. Ensimatic
island arcs and backarc basins rose in Cambrian – Early Ordovician
time; ensialic island arcs formed in Middle Ordovician. Closure of
the oceanic and backarc basins, accretion of continental blocks and
formation of Kyrgyz-Kazakh microcontinent (KKM) took place during Late Ordovician – Silurian time. The KKM was bordered by subduction zones on both sides. Two marginal continental volcanic arcs
(north – Aral-Kendyktas and south - Beltau-Kurama) were superimposed on a mosaic of various geodynamic complexes stacked in
the course of collision. The evolution of the Aral-Kendyktas volcanic arc in the Northern Tien Shan was accompanied by ore mineralization of porphyry type. The Beltau-Kurama volcanic belt in the
Middle Tien Shan is characterized by the volcanic-plutonic associations with porphyry Cu, Mo-Cu, Au-Cu, skarn-base-metal, and silver-base-metal mineralization.
The interior of the continent, the Middle Tien Shan back-arc magmatic belt appeared beyond the Beltau-Kurama marginal continental volcanic arc. The close spatial connection of the complex Au-CuMo-W ore mineralization is defined by homo-dromic multiphase complexes of the Middle Carboniferous age. Complex polygenic ore systems with a wide spectrum of ore forming elements in various quantities are characteristic of this belt. The Tarim microcontinent closely
approached the subduction zone at the southern margin of KKM, so
that the Late Carboniferous and Early Permian were characterized
by a continent-continent collision. Intraplate stage (P2-T1) is characterized by the emplacement of acidic and alkaline intrusions in the
whole Tien Shan region. In addition to the mentioned intrusions, in
the South Tien Shan, emplacement of carbonatites and rapakivi granites occurred. The formation of quartz-gold, rare-metallic, and REE is
associated with this stage.
Keywords. Island arcs, active continental margin, backarc magmatic
belt, ore deposits
1
Introduction
The reconstruction of the geodynamic evolution of the
Tien Shan overlapping-fold formation permits a re-assessment of existing structural units and their metallogeny
during the Late Pre-Cambrian – Paleozoic period. Formation of various types of ore deposits and their spatial
location relative to plate boundaries is closely associated
with the history of the regional geodynamic development.
Polygenic and polychronic ore deposits are typical for the
Tien Shan region and were formed as result of long-lasting processes and under various geodynamic environments. Thus, the primary accumulation of disperse ore
mineralization occurred in Pre-Cambrian time in
riftogenic conditions in the Au-W-pyrite Kumtor deposit.
But the principal stage of the re-accumulation and additional in-depth supply of these ore elements was conditioned
by subduction processes in Middle Carboniferous time. In
the Middle Tien Shan, multiphase granitoid complexes developed during this period. Au-W-Cu ore mineralization is
associated with the named intrusion complexes.
The polygenic gold deposit Makmal (Middle Tien
Shan) formed on the contact of intrusions that exhibit
different ages. Diorites intruded in active continental
margin environment (C 2), and leucocratic granites
emplaced in collision stage (C3-P1) during the period of
the Turkestan paleo-ocean closure.
2
Pre-Cambrian geodynamic history
The present structure of Tien Shan is a collage of separate blocks contiguous along the ancient sutures that are
characterized by different geodynamic complexes. Continental and oceanic rifts, passive and active continental
margins, island-arcs systems, and collision zones are recognized in the geological history of the Tien Shan. Autochthonous and allochthonous inliers of Pre-Riphean
basement occur within younger geodynamic complexes,
see Maksumova (1996), Bakirov et al. (1999), Seltmann et
al. (2001), Maksumova and Djenchuraeva (2003).
The major structural units of the Tien Shan are Northern, Middle, Southern Tien Shan, and Talas-Karatau block,
and the metallogeny differences of which were defined
by the history of the development of these blocks.
The composition and structure of AR-PR1 basement
of the Northern and Middle Tien Shan are similar providing evidence for their past unity (Bakirov and
Maksumova 2001).
The rifting in the marginal part of Eastern Gondwana
in the Early and Middle Riphean resulted in the eruption
of acid volcanics (Greater Naryn Group, 850±50 Ma) in
the Middle Tien Shan and the formation of bimodal volcanic series in the Northern Tien Shan. Riftogenic structures were subsequently sealed by a thick pile of acid
metavolcanics and subsidiary sandstones, slates, and overlying carbonate rocks. The arching and following formation of extended linear rifts with an active bimodal volcanism gave way to the gradual subsidence and destructions of the Eastern Gondwana margin in Late Riphean
(720±20 Ma). Rocks of this stage are enriched in Au, Pb,
Close
1310
R.D. Djenchuraeva
Ag, Zn, Mo, Bi, Cu, and Pt relative to the respective Clarke
values, see Jenchuraeva and Maksumova (1994).
Volcanism waned in the Vendian when the argillaceoussiliceous, carbonaceous, carbonate rocks, and iron formations hosted in carbonaceous shale were deposited.
Disseminated Au-W-Te-pyrite mineralization and hematite-magnetite ore were related to black shales in the Jetym
basin. The primary enrichment of black shales in ore elements within an intracontinental rift was caused by the
influence of magmatism expressed as flows and dikes of
subalkali basalt.
3
Early Paleozoic subduction and porphyry goldcopper deposits
In the Cambrian, rift opening reached a maximum, and
in this time was formed Ishim-Naryn branch of Paleoasian
ocean. The subduction of paleooceanic structures gave
rise to the formation of Cambrian-Ordovician ensimatic
and Middle Ordovician ensi-alic island arcs in the Northern Tien Shan (Fig. 1).
Then the Middle Ordovician subduction was completed
by a collision of island arcs with the continent of the Northern Tien Shan and their abduction on the continental
margin. The early collision was accompanied by emplacement of granodiorite, monzodiorite, diorite intrusions,
and by numerous porphyry gold-copper deposits
(Taldybulak, Uzunbulak, Andash, Almaly, etc.). The
stockwork and disseminated mineralization is localized
in breccia pipes and in zonal altered rocks. The U-Pb zircon age yielded 440±8Ma for the monzonite and
monzodiorite porphyries, and ore mineralization - 400Ma.
The isotopic composition of sulphide sulphur (δ34) varies from +0.52 to -2.00‰, see Jenchuraeva and
Maksumova (1993) and Jenchuraeva (1997).
The large Jerooy gold deposit is related to post-abduction granitoids. Host rocks are monzodiorite and diorite
(O2). Ore bodies – gold-bearing quartz veins, stockwork
zones are accompanied by the quartz-feldspar altered
rocks, phyllic, argillic alterations, and zones of
silicifications. Vertical extensions of ore bodies are up to
900m. Resources of the main ore zone estimated about
75t of gold with a grade of 6.26g/t. Major ore mineral is
native gold, minor – silver, tellurium, bismuth and others. Quartz-bismuthite-tetradymite-gold is the major productive mineral assemblage (Jenchuraeva and Oakes
2001). The Ishim-Naryn basin was completed by closure.
The following collision and related emplacement of granitic batholiths in the late Ordovician and Silurian built
up a new large Kyrgyz-Kazakh microcontinent (KKM).
Collision granites with related gold mineralization are
represented by small ore deposits and occurrences (Aubearing skarn and zones of mineralization). During this
period, thick overthrust sheets were formed, which later
became favorable structures for ore mineralization.
4
Devonian-Carboniferous active continental margin
In Early Devonian time spreading in the Turkestan
paleoocean was resumed that predetermined the origination of marginal continental volcanic belt. The interaction of the collage-structure of KKM with DjungarBalkhash in the north (in modern coordinates) and the
Turkestan paleoocean in the south resulted in the formation of the marginal-continental volcanic arcs.
In the Northern Tien Shan Devonian magmatic belt
superimposed the Ordovician island arc complexes during the stage of active continental margin. Gold-copper
porphyry deposits originated within the marginal continental magmatic arc, controlled by thrust-fault zones, related to monzonite and metasomatic zones. The
Taldybulak Levoberzhny gold-copper deposit can be considered as a model. Principal ore-controlling structures
at the deposit are represented by three shear and thrustfault zones, with total thickness 700m and accompanied
by a tectonic mélange, injected by intrusions of
monzodiorite and which undergone metasomatic alteration. There are fuchsite-bearing quartz-carbonate rocks,
quartz-carbonate-sericite rocks, potassic, and phyllic and
quartz-tourmaline alteration. The ore bodies are represented by gently dipping sheet like and steep columnar.
The lode is controlled by monzodiorite porphyry and breccia pipes. Resources of the main ore zone are estimated
at about 80t of gold with a grade of 5.5g/t.
In the Middle Tien Shan the Beltau-Kurama volcanicplutonic belt started to evolve during Middle Carboniferous as an expression of subduction of the Turkestan
paleooceanic crust beneath the southern margin of the
KKM with a thick (up to 5-6 km), succession of volcanic
and volcanogenic-terrigenous sediments. Porphyry cop-
Close
Chapter 12-5 · Geodynamics and metallogeny of active continental margins of the Kyrgyz Tien Shan
per, molybdenum-copper, gold copper, skarn base-metal
deposits and occurrences are known in that volcanic belt.
At the same time the backarc magmatic belt of the
Middle Tien Shan appeared behind the Beltau-Kurama
zone (see Jenchuraeva 1996, 1998). This belt extends in
latitudinal direction along the Nikolaev suture zone and
is characterized by multiphase intrusions, belonging to
latite geochemical type. Formation of such ore mineralization as gold-tungsten-telluride-pyrite (Kumtor), goldtungsten-skarn-skarnoid deposits (Kumbel, Kashka,
Kensu), copper-tungsten-molybdenum with some fragments of porphyry copper systems (Molo-Sarychat), and
gold-tungsten (Donarcha and Djerkulak in Kazakhstan)
is connected with multiphase complex of Middle Tien
Shan (see Jenchuraeva et al. 2001).
Intrusive rocks are enriched in K, Ba, Sr, and accessory
magnetite. The initial Sr87/Sr86 of 0.7061-0.7075 corresponds
to the mantle and crustal sources (Solomovich 1997).
The super-large gold-tungsten-pyrite deposit Kumtor is
placed in this belt. The Kumtor gold deposit is localized
close to Nikolaev Tectonic Line (suture) of regional importance. The Kumtor ore field is hosted in a Vendian carbonaceous flyschoid sequence and overlying rocks of Cambrian,
Ordovician and Paleogene-Neogene age (Nikonorov 1993).
5
Late Paleozoic collision and intraplate stage
By the Late Carboniferous, the Tarim microcontinent closely
approached the subduction zone at the southern margin of
KKM, so that the Late Carboniferous and Early Permian
were characterized by a continent – continent collision.
Complex gold mineralization in the Middle Tien Shan was
formed at contacts with Middle Carboniferous intrusions
and Permian leucogranite (Makmal, Uzunbulak, and
Chaetkisay).
In the Northern Tien Shan several ore deposits (Aktyuz
- Mo, Zr, Pb, Sn, Ag; Kutessai II – REE; Kuperlisai - REETh; Kolesai – Be) are located in the Precambrian gneiss
and crystalline schists intruded by a variety of Permian
intrusive rocks including monzodiorite, syenite, subalkali
leucogranite, granophyre, and dikes (Kim et al. 2001).
Subalkali leucogranite pluton is wedge-shaped in plan and
plunges beneath the metamorphic rocks. The roof of this
fault-controlled intrusion is characterized by ridges and
deep troughs. The ridges are crowned by local cupolas
and explosion pipes are composed of brecciated schists
injected by granophyres that host ore mineralization. Intrusive rocks are widely affected by postmagmatic alteration including the early stages of replacement by potassic feldspar, albite, and biotite and late stages of
sericitization, chloritization, and silicification. About 10
Mt of REE ore with a grade up to 0.3% TR2O3 is retained
for open-pit and 8 Mt are designed for underground mining (Aktiuz). The Kutessai II is currently being mined by
open-pit.The REE reserves are estimated as 88,000 t REE
1311
with a grade of 0.39%; 2.6 t Ta (0.012%); 7.3 t Nb (0.037%);
56,000 t Zr (0.6%); 6,325 t Th (0.029%); 48,500 t Pb (2.21%).
Late Permian-Early Triassic time was completed by
intraplate processes related to the Paleotethys closure. In
Southern Tien Shan two different complexes of rapakivi
granites exist. The metallogeny of both complexes is extremely variable (Jenchuraeva and Maliukova 2000).
The older Jangart Complex is spatially in juxtaposition of two different basement blocks: the Tarim
microcontinent (southern block) and the foldbelt of the
Southern Tien Shan (northern block). The sequence of
emplacement was as follows: biotite-hornblende granite
→ granosyenite → syenite → nepheline syenite →
carbonatites. The REE mineralization is associated with
carbonatites characterized by low Nb/Ta ratio (Sarysai).
The younger Akshiirak Complex, which is represented
by discordant sheet like intrusions in fault zones cutting
the Precambrian basement, reveals another succession of
intrusive phases: granodiorite, monzodiorite, quartz syenite → amphibole-biotite rapakivi granite → biotite
granite and leucogranite. Gold-sulphide-quartz mineralization is represented by zones of thrust in rapakivi granite
of the main intrusive phase (Jangart, Togolok). Tin mineralization is hosted in greisen associated with hastingsite
leucogranite. The intraplate processes are related to widespread rifting. The system of narrow grabens was filled
with subalkali basalt and andesite. Mercury (Khaidarkan),
antimony-mercury (Kadamjai), gold-antimony (Tereksay)
mineraliza-tion is known as deposits of jasperoid type.
The ore is localized in the silicified shattered marble being confined to interformational detachments. Recently,
this type of deposit took on great economic significance.
The gold-antimony deposit Tereksay is hosted by Lower
Proterozoic schists folded into anticline. The ore bodies
mainly concentrated in a series of zones of interstratal
thrust and fractures filled by quartz-sulphide material.
The gold-polysulphide, gold-antimonite, gold-quartz-pyrite and gold-pyrite-arsenopyrite ores are distinguishable
in the deposit. Reserves and resources of gold have been
proved at 80 tons with an average gold content of 7.4 g/t.
6
Conclusions
The long and complex evolution of ore mineralization
connected with various geodynamic environments of Tien
Shan. The spatial superimposition of geodynamic complexes stipulate formation of complex (polygenic and
polychronic) ore mineralization.
Acknowledgements
Many thanks are expressed to R. Seltmann (CERCAMS,
NHM London) for correcting and completing the English
version of the paper. This paper is a contribution to the
IGCP-473 project on “GIS Metallogeny of Central Asia”.
Close
Close
Chapter 12-6
12-6
Granitoids and related mineralization of Mongolia:
Petrochemistry and mineral deposits GIS
O. Gerel, S. Amar-Amgalan, S. Oyungerel, S. Myagmarsuren
Dept. of Geology and Mineralogy, Mongolian University of Science & Technology, Ulaanbaatar, P.O. 46, Box 520, Mongolia
D. Kirwin
Ivanhoe Mines Ltd., Mongolia
R. Armstrong, R. Herrington, R. Seltmann
Natural History Museum, Dept. of Mineralogy, CERCAMS, London SW7 5BD, U.K.
Abstract. Granitoids occupy the main part of Mongolia’s territory
forming elongated Phanerozoic accreted belts. The major deposits
and occurrences in Mongolia are associated with granitoids and
their interpretation plays key role for mineral deposit assessment.
The GIS database and compilation is being constructed in
MapInfo 6.5 and contains a digitally compiled thematic maps linked
to Geologic map of Mongolia, Tectonic map of Mongolia and Mineral Deposit map of Mongolia at 1:1,000,000 scale. The major layers
are: Granitoid distribution map at the scale of 1:500,000 and
1:200,000 with topography and major tectonic units, major towns,
roads, railroads, likes and rivers. Database contains tables with description of plutons and complexes, which includes area, host rocks,
age, and contact metamorphism, petrographic description of major phases of granitoid plutons and complexes, dikes, postmagmatic
alteration.
Geochronological data and major trace and isotopic data of each
pluton are shown in separate tables. The GIS compilation provides
maps of large regions showing granitoid belts. Granitoid interpretation includes chemical classification, tectonic discrimination,
magma source, origin of granitoids and evolution of granitic
magmatism trough the time. Also location of major mineral deposits and mineralization associated with accreted belts and interpretation of this relation will be done. An example of maps and interpretation is demonstrated for the Southeast Mongolia. Output of
project will be: Granitoid magmatism map on the scale of 1:500,000.
Keywords. Granitoids, GIS, database, mineralization
1
Introduction
Granitoids occupy about 30% of the Mongolia’s territory
forming elongated Phanerozoic accreted belts. Coppermolybdenum, copper-gold, tin-tungsten major deposits
and occurrences in Mongolia are associated with
granitoids and petrological interpretation of accreted belts
plays a key role for mineral resource assessment.
The major goal of three years project “Granitic
magmatism, continental crust evolution and metallogeny
of Mongolia: a GIS based synthesis on a modern
geodynamic background (2003-2005)” sponsored by
Ivanhoe Mines Mongolia is to summarize and to interpret granitoid magmatism based on the new tectonic
model for understanding origin and evolution of granitic
magma and intrusive rock related mineralization for ter-
ritory of Mongolia and to create a new GIS based petrological database for granitoids and associated volcanics.
2
Methods
The GIS database and compilation is being constructed
in MapInfo 6.5 and contains a digitally compiled thematic
maps linked to Geologic map of Mongolia, Tectonic map
of Mongolia and Mineral Deposit map of Mongolia at the
scale of 1:1 000 000, Terrane map of Mongolia (Badarch
et al. 2002). The major product is the Granitoid distribution map at the scale of 1:500 000 and 1:200 000 with topography and major tectonic units and major towns, roads,
railroads, lakes and rivers. Additional products include:
the granitoid distribution related to different terranes and
structural zones; (c) pluton and complexes description;
(d) chemistry of different plutons. Description contains:
ID, name, code, list, complex, tectonic zone, terrane and
area occupied by different plutons, era, age, stage and rock
content. For rock classification Q-ANOR normative diagram was used (Streckeisen and LeMaitre 1979) and KSiO 2 for additional classification of calc-alkaline
granitoids.
The further interpretation includes mol. Al 2O 3 /
(CaO+Na2O+K2O) vs. SiO2 diagram (Chappel and White
1992) for distinguishing Al2O3 saturation index, magnetite and ilmenite series (Ishihara 1981) and also series of
tectonic discrimination diagrams based on major element
data after Maniar and Picolli (1989) and R1-R2 (Batchelor
and Bowden 1985) diagrams. Tectonic discrimination
Y+Nb vs. Rb plots after Pearce at al. (1984) and spider
diagrams are used only if data are available.
Database contains tables with description of plutons
and complexes, which includes host rocks, age, contact
metamorphism of host rocks, petrographic description
of major phases of granitoid plutons and complexes, dikes,
postmagmatic alteration. Geochronological data and
major, trace and isotopic data of each pluton are also
shown in separate tables. The GIS compilation provides
maps of large regions showing granitoid belts.
Close
1314
O. Gerel · S. Amar-Amgalan · S. Oyungerel · S. Myagmarsuren · D. Kirwin · R. Armstrong · R. Herrington · R. Seltmann
3
Interpretation
Granitoid interpretation includes chemical classification,
tectonic discrimination, magma source, origin of
granitoids and evolution of granitic magmatism trough
the time. Also location of major mineral deposits and
mineralization associated with accreted belts and interpretation of this relation is done.
Examples of map and interpretation are demonstrated
for the southeast Mongolia Interpretation is shown on
example of the late Paleozoic and Mesozoic complexes
distributed there.
Tectonically granitoids occur in the Nuhetdavaa zone
(Tectonic of Mongolia 1974) or back arc terrane, which forms
a narrow northwest trending belt near the Mongolia-China
border of eastern Mongolia (Badarch et al. 2002). The terrane is composed of Neoproterozoic gneiss, schists, quartzite, stromatolitic marble, Cambrian sandstone, siltstone,
minor conglomerate, olistostrome, Ordovician-Silurian
sandstone, siltstone, phyllite, minor conglomerate, coral limestone. Devonian basalt, andesite, volcaniclastic rocks and
minor coral limestone overlain by early Carboniferous shallow marine sedimentary rocks.
There are Carboniferous, Permian and Triassic-early
Jurassic granitoids. Granitoids in this terrane include a
number of complexes: late Carboniferous Nukhetdavaa,
early Permian South Mongol, late Triassic-early Jurassic
Eguzer and mid-late Jurassic Sharhad. Late Carboniferous magmatism dated by K-Ar method of 288-315 Ma,
333-310 Ma (Geology of Mongolia 1973) consists of mafic to felsic rocks in composition and form plutons ranging in size from 44 km2 to 1700 km2. Plutons are localized along significant faults of northeast direction (Fig. 1).
Composition of calc-alkaline K-rich rocks (Figs. 2a, b)
range from gabbro, gabbrodiorite to leucogranite, most
common are granodiorite and granites of main phase.
Granitoids are related to I-type series, and are metaluminous to peraluminous. Both, the oxidized, magnetite series and reduced, ilmenite series rocks are common
(Fig. 2). Cu and Au mineralization is associated with Carboniferous granitoids (Fig. 1).
Early Permian (South Mongol Complex) magmatism
in this terrane is restricted to uppermost southeast part
of the Nukhetdavaa terrane. It consists of felsic unfoliated
plutonic rocks associated with volcanics of same age. Plutonic rocks have granitic composition with granite and
syenite dikes. They form small bodies from 38 to 157 km2
in dimensions. Granites are composed of K-feldspar, plagioclase, quartz and biotite with accessory magnetite, fluorite, zircon, titanite. Geochemically are medium-K,
Close
Chapter 12-6 · Granitoids and related mineralization of Mongolia: Petrochemistry and mineral deposits GIS
peralkaline and peraluminous (Figs. 2, 3). Tin and molybdenum mineralization is associated with this highly
evolved magmatism.
Late Triassic-early Jurassic magmatism (Eguzer Complex) is represented by granites, which form small simple
plutons from 22 km2 to 360 km2 and composite large bodies up to 1123 km2. It composed of two phase granites. The
firstone is represented by porphyritic biotite granite and
the second one by K-feldspar granite and leucogranite. Also
two mica and tourmaline granites are present. Granites are
1315
plotted in area of syncollisional field and are dominated by
felsic metaluminous to peraluminous (Fig. 2c) calc-alkaline, oxidized mainly magnetite series, but some of them
are ilmenite series (Fig. 3) granites with low primary oxidation states. W-Sn mineralization is associated with these
granites.
R1-R2 diagram shows that many of evolved granites
were formed in collisional and post-collisional condition
(Fig. 4). Carboniferous granitoids are orogenic and later
stages show accretion which is very characteristic for
Phanerozoic granitoids in Mongolia.
Granites of mid-late Jurassic Sharhad Complex form
small plutons about first few km2 up to 12 km2. They
consist of medium- to coarse-grained granite and K-feldspar granite (Fig. 2). Many of intrusions are small bodies
controlled by faults. Jurassic intrusions are slightly
peraluminous, high K rocks (Fig. 2), mainly oxidized
magnetite type. W-Mo-Sn mineralization is mainly associated with granites.
Close
1316
O. Gerel · S. Amar-Amgalan · S. Oyungerel · S. Myagmarsuren · D. Kirwin · R. Armstrong · R. Herrington · R. Seltmann
4
Conclusions
The Nuhetdavaa terrain contains a variety of igneous
rocks of various composition and ages from middle Paleozoic to Mesozoic and from mafic to felsic, and variety
of deposits either hosted by, or spatially associated with
igneous rocks. The tectonic environment responsible for
this wide variety of rocks and ores can be explained by
a series of different tectonic events, representing cycles
of subduction, collision and extension. The different
magmatic complexes have variable ages and are associated with specific ore types. The age and associated metallogeny is not yet fully understood and is a topic for future study.
Magmatism is critical for production of mineralized
fluids. Hydrothermal fluids flow was a product of subduction-related tectonism and terrane accretion. Igneous rocks range from I-type to peraluminous and alkaline relatively reduced rocks. Igneous rocks range from
I-type to peraluminous and alkaline relatively reduced
rocks.
References
Badarch G, Cunningham WD, Windly BF (2002) A new subdivision
for Mongolia: implications for the Phanerozoic crustal growth of
Central Asia. Journal of Asian Earth Sciences 21: 87-110
Batchelor RA, Bowden P (1985) Petrogenic interpretation of granitoid rock
series using multicationic parameters. Chemical Geology 48: 43-55
Chappel BW, White AJR (1974) Two contrasting granite types. Pacific
Geol. 8: 173-174
Classification and nomenclature of magmatic rocks (1981) M. Nedra:
160 (in Russian)
Geology of Mongolia (1973) M. Nedra 2: 751 (in Russian)
Ishihara S (1981) The granitoid series and mineralization. Econ. Geol.
75th Ann.Vol. 458-484
Maniar PD, Picolli PM (1989) Tectonic discrimination of granitoids.
Geol. Soc. Amer. Bull. 101: 635-643
Rollinson HR (1993) Using geochemical data: evolution, presentation,
interpretation, Longman: 352
Pearce JA, Harris NB, Tindle AG (1984) Trace element discrimination
diagrams for the tectonic interpretation of granitic rocks. J Petrol
25:956-983
Streckeisen A, Le Maitre RW (1979) A chemical approximation to the
modal QAPF classification of igneous rocks. Neues Jahrb. Mineral.
Abh. 136: 169-206
Tectonics of Mongolia (1974) (ed. Yanshin AL). M Nauka 284 (in Russian)
Close
Chapter 12-7
12-7
Mass transfer during alteration and Au precipitation at
Muruntau: Alteration behaviour of different rock types
T. Graupner
Institute of Mineralogy, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
U. Kempe
Institute of Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, 09599 Freiberg, Germany
V.J. Wall
Taylor Wall and Associates, Ground Level, 67 St. Pauls Terrace, Spring Hill, 4004, Australia
R. Seltmann
CERCAMS, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
S. Köhler
Centrum Baustoffe und Materialprüfung, TU München, Baumbachstraße 7, 81245 München, Germany
V. Shatov
VSEGEI, 74, Sredniy Pr, St Petersburg, 199106, Russia
Abstract. Results from petrographic microscopy, scanning electron
microscopy (SEM), and Rietveld analysis indicate intense hydrothermal alteration processes for those pelitic and psammopelitic
metasedimentary rocks of the Variegated Besapan, which occur
within the Muruntau ore field. However, whereas significant input
of ore-bearing hydrothermal fluids into the psammopelitic rock
types and strong transfer of components from the fluid to these
rocks is indicated by mass transfer calculations, these calculations
yield a significantly smaller transfer of components to the rocks for
pelitic rock types. Alteration reactions in the psammopelitic rock
types at Muruntau are strongly controlled by the infiltration of orebearing hydrothermal fluids. The variable alteration behaviour has
significantly contributed to an accumulation of higher contents of
gold in the psammopelitic rocks, compared to the pelitic rocks.
Keywords. Mass transfer calculation, fluid flow, metasomatic alteration, pelitic, psammopelitic rocks
1
Introduction
The economic gold mineralization at the Muruntau gold
deposit (Central Kyzylkum desert, Uzbekistan) is mainly
hosted by the psammopelitic rock types of the Lower
Palaeozoic Variegated Besapan package (e.g. Berger et al.
1994). Detailed investigations of Russian and Uzbek geologists as well as the field work carried out in this study,
have demonstrated that, compared to the pelitic metasedimentary rocks, the psammitic-psammopelitic Variegated
Besapan packages at Muruntau are characterized by (i)
higher densities of dilatant fracturing, (ii) more intensely
developed high-temperature microcline alteration along
the vein margins, as well as (iii) significantly increased
Au concentrations (e.g. Kremenetsky et al. 1990; Wall et
al. 2004). However, the different alteration behaviour of
both rock types as well as the link between alteration and
circulation of hydrothermal fluids it is not well under-
stood at present. This study presents preliminary results
of mass transfer calculations for hydrothermally altered
rocks of both types from the Muruntau deposit.
2
Types of hydrothermal alteration
A number of overlying prograde and retrograde stages
of alteration were identified in this study using petrographic microscopy, SEM and Rietveld analysis. The early,
high-temperature stage includes amphibole-pyroxene-,
biotite- and microcline-bearing assemblages (cf. Arifulov
1976; Uspenskiy and Aleshin 1993; Kempe et al. 2002),
whereas the medium-temperature stages are characterized by albite-, carbonate-apatite-, chlorite- and sericitedominated alteration assemblages (e.g. several authors in
Shayakubov et al. 1998). However, most samples are influenced by more than one alteration process and, therefore, it is rather difficult to identify the specific samples,
which clearly show the characteristics of a single alteration stage.
3
Standard samples
Standard samples for the mass transfer calculations have
average values of three (pelitic) and six (psammopelitic)
least altered metasedimentary rocks from the Variegated
Besapan package (e.g. from drill core of the SG 10 borehole, which is located SE of Muruntau). A comparison of
the major element data with analytical results of Arifulov
(in Shayakubov et al. 1998; see Fig. 1a-b) shows that the
standard samples can be used as representative of the
purely low-grade altered metasediments of the Variegated
Besapan suite (essentially no hydrothermal alteration
present).
Close
1318
T. Graupner · U. Kempe · V.J. Wall · R. Seltmann · S. Köhler · V. Shatov
ning electron microprobe work or from the geochemistry data. Furthermore, immobility of Th, Nb and Ga is
indicated for some of the samples; however, this may be
an effect of the different overlying processes of hydrothermal alteration. Pelitic rock types never show immobile behaviour of components other than the HREE during late alteration.
5
Mass transfer calculations
A preliminary evaluation of the data from mass transfer
calculations can be summarized in the following points:
4
Immobile elements during hydrothermal
alteration
Identification of immobile rock components was carried
out using the isocon method. The immobile elements generate a straight line of slope (isocon; Grant 1986) in the
altered rock vs least altered rock diagram. Whereas the
mobile/immobile behaviour of the components was tested
in logarithmic isocon diagrams, only non-logarithmic diagrams are shown here for better illustration (Fig. 2a-d).
During early, high-temperature alteration, immobile
components include the HREE (Tb, Dy, Ho, Er, Tm, Yb,
Lu), Th, Nb, Ga, TiO2 and partly Al2O3U and MgO. Al2O3U
and MgO seem to be immobile in psammitic rocks, but
show some mobility in pelitic rocks.
The number of immobile components significantly
decreases during subsequent, medium-temperature hydrothermal alteration. So far, the authors have no indication of significant mobility of the HREE either from scan-
1. a typical feature for all altered rock samples is the loss
in SiO2; the values range from –4 to –25 g/ 100 g
protolith for the high-temperature alteration.
2. For psammopelitic rocks Al2O3 is immobile during
high-temperature alteration (Fig. 2a). The data indicate, however, a moderate transfer of Al2O3 from the
rock to the fluid for pelitic rocks. Medium-temperature alteration is characterized by a mostly strong
transfer of Al2O3 from the rocks to the hydrothermal
fluid (not for sample 98-25). This transfer is more intense for the pelitic (up to -10.6 g/ 100 g protolith) than
for the psammopelitic rocks.
3. Fe2O3t and MgO show a similar behaviour during alteration. There is a correlation between the calculated
mass transfers for both components for pelitic
(r2=0.966) and also for psammopelitic rocks (r2=0.645).
A strong transfer of Fe2O3t and of MgO from the fluid
to the rock during high-temperature alteration was
observed for some of the psammopelitic samples (up
to 4.3 g/100 g protolith; e.g. Fig. 2a). The other
psammopelitic rocks show insignificant changes in
both components during early alteration. Pelitic rocks
show losses of MgO and mostly also losses of Fe2O3t
from the rock. During late alteration, Fe2O3t is extremely mobile in pelitic rocks (e.g. Fig. 2d). The
psammopelitic rocks show only small losses or gains
in both components during late alteration (Fig. 2c).
4. For psammopelitic rocks there is always a significant
transfer of K2O from the fluid to the rock during early
alteration (mostly > 2 g/100 g protolith; Fig. 2a). In contrast, only very small gains between 0.4 and 0.9 g/100 g
protolith were calculated for pelitic rock types (Fig. 2b).
Hydrothermal microcline is only partly formed due
to addional K2O input from the fluid to the rock; the other
part of the microcline formed at the expense of metamorphic orthoclase according to the Rietveld data. During albitization, carbonatization and chloritization there
is always a transfer of K2O from the rock to the fluid
(Fig. 2d). This is independent of the protolith type. The
location of the K2O value close to the immobility line in
Fig. 2c represents a summary effect of overlying highand medium-temperature alteration for this sample.
Close
Chapter 12-7 · Mass transfer during alteration and Au precipitation at Muruntau: Alteration behaviour of different rock types
1319
5. During the high-temperature alteration stage, there
was in general a transfer of Na2O from the rock to the
fluid independent of the protolith type (Fig. 2a). For
the medium-temperature alteration the calculated
mass transfers vary considerably for the individual
samples. Psammopelitic rocks with a significant transfer of Na2O from the fluid to the rock have high albite
contents, whereas those rocks without significant Na2O
gain are characterized by low albite contents. In contrast, pelitic rock samples containing rather high albite contents may also show transfer of Na2O from the
rock to the fluid.
6. For the psammopelitic rock types a negative correlation between the calculated mass transfers for Fe2O3t
and Na2O (r2=0.599) was found. In contrast, there is
no trend observable for the pelitic rock types.
7. There is a positive trend between the calculated mass
transfers for Fe2O3t and S. This indicates that Fe is
mostly incorporated into sulfides.
8. Rather similar mass transfers were calculated for W
for most of the psammopelitic and pelitic rocks
(Fig. 2a-d). However, the highest calculated values commonly occurred in pelitic meta-sedimentary rocks. No
differences were observed between rocks mainly affected by high- and by medium-temperature alteration.
9. The calculated mass transfer for Au is much higher for
high-temperature altered rocks than for the mediumtemperature altered metasediments. During high-temperature alteration, a much stronger transfer of Au
from the hydrothermal fluid to the rock was in general
observable for psammopelitic rocks (up to 7.5 g/1000
kg protolith) when compared to pelitic rocks (up to ~
2 g/1000 kg protolith). However, high Au values were
found for two pelitic samples with very high microcline contents (Rietveld analysis).
6
Discussion and conclusions
1. Hydrothermally altered pelitic rocks at Muruntau contain significantly higher amounts of biotite and microcline compared to the altered psammopelitic rocks
(Rietveld data). This clearly indicates more intense
hydrothermal alteration reactions in the pelitic than
in the latter rocks. However, the mass transfer calculations confirm a significantly smaller transfer of components from a fluid into the pelitic, compared to the
psammopelitic, rock types. Therefore, alteration reactions in the more psammitic rock types at Muruntau
are clearly initiated and more definitely controlled by
the infiltration of ore-bearing hydrothermal fluids,
compared to the pelitic rock types. This also resulted
in an accumulation of higher contents of gold in the
psammopelitic rock types.
Variable slopes of the trend lines in the Au vs. Na/K
diagrams for both rock types confirms the above dis-
Close
1320
T. Graupner · U. Kempe · V.J. Wall · R. Seltmann · S. Köhler · V. Shatov
cussion. Psammopelitic Au-rich, microcline-altered
rocks have low molar Na/K-ratios of ~ 0.1 (Kempe et
al. 2002). Using a ratio of ~ 2.5 for the least altered rocks,
this results in a rather flat trend line in the diagram. In
contrast, pelitic microcline- and biotite-rich rocks,
which are also Au-enriched (> 1 ppm), have much
higher molar Na/K-ratios of ~ 0.5. Connected with the
ratio of ~ 0.8-0.9 for the least altered rocks, the slope
of the trend line is much steeper than for the
psammopelitic rocks.
This alteration behaviour is also supported by Au vs.
MgO diagrams for both rock types. Whereas increased
Au contents correlate with increased MgO contents for
psammopelitic rocks, pelitic rock types show almost
unchanged MgO contents for low and high Au samples.
2. At least parts of the quartz in the hydrothermal ore
veins at Muruntau may be derived from hydrothermal
alteration processes in the wall rocks.
3. During strong albitization of psammopelitic rock
types, Fe2O3t is transferred from the metasedimentary
rocks into the hydrothermal fluid. Consequently, some
of the late sulfides in the veins are interpreted to be
directly related to wall rock alteration.
Acknowledgements
We thank NGMK (N.I. Kuchersky, S.B. Inosemzev, V.
Yantsen), the State Committee on Geology and Mineral
Resources, IMR (N.A. Akhmedov, B.A. Isakhodjaev, I.M.
Golovanov) and Placer Dome International (G. Hall) for
facilitating this study. This paper is a contribution to the
IGCP-473 project “GIS Metallogeny of Central Asia”.
References
Arifulov TK (1976) Mineralogy and genesis of veinlet zones with
gold-sulfide mineralization in the Kyzylkum. Uzbekskii Geol.
Zhurnal 5: 54-61 (in Russian)
Berger BR, Drew LJ, Goldfarb RJ, Snee LW (1994) An epoch of gold
riches: The late Paleozoic in Uzbekistan, Central Asia. SEG Newsletter 16: 1-11
Grant JA (1986) The isocon diagram – A simple solution to Gresens
equation for metasomatic alteration. Economic Geology 81:
1976-1982
Kempe U, Graupner T, Belyatsky B, Köhler S, Wolf D, Kremenetsky
AA (2002) Wall rock alteration in the giant Muruntau Au deposit
(Uzbekistan): new constraints on the genesis of Au mineralisation:
In: Proc. of Geocongress 2002, Windhoek, Namibia, 3 (on CD)
Kremenetsky AA, Lapidus AV, Skryabin VJ (1990) Geological and
geochemical methods of deep prognosis for minerals, based on
superdeep drilling data. Nauka, Moscow, 224 (in Russian)
Shayakubov T, Golovanov IM, Sakirov AT, Isak-hodjaev BA (1998)
The gold deposit Muruntau. FAN, Tashkent, 539 (in Russian)
Uspenskiy YI, Aleshin AP (1993) Patterns of scheelite mineralization in the Muruntau gold deposit, Uzbekistan. International
Geology Rev. 35: 320-342
Wall VJ, Graupner T, Yantsen V, Seltmann R, Hall GC (2004) Muruntau,
Uzbekistan: a giant thermal aureole gold (TAG) system. In: SEG
2004 ‘Predictive Mineral Discovery Under Cover, Extended Abstracts’. Muhling J. et al. (eds.) UWA Publ. 33, Perth: 199-203
Close
Chapter 12-8
12-8
The Bainaimiao Cu deposit in Inner Mongolia, China:
A possible orogenic-type Cu deposit
Wen-Bo Li, Yan-Jing Chen, Yong Lai
Department of Geology, Peking University, Beijing 100871, and Institute of Geochemistry, Chinese Academy of Sciences,
Guiyang 50002, China
Abstract. The Bainaimiao Cu deposit, Inner Mongolia, occurs in the
Central Asia Orogen, where most gold deposits have been considered previously to be of the orogenic-type. Previous studies also
considered the Bainaimiao Cu deposit to be of volcanogenic or
porphyry-type. However, available geochemical data and our field
observation do not support these views. Instead, they suggest
Bainaimiao to be an orogenic-type Cu deposit.
Keywords. Bainaimiao Cu deposit, Inner Mongolia, orogenic-type Cu
deposit, Central Asia Orogen
1
Introduction
The Bainaimiao Cu-Au deposit, Inner Mongolia, is located
at 112°33'00'’E and 42°43'00'’N. It occurs in the northern
Yin Shan area of the Central Asia Orogen. The deposit was
discovered in 1959 and prospected by 1985. 0.51 Mt Cu with
average grade of 0.8%, 19.1 t Au with grades from <1 to
16 g/t, 181 t Ag and 4 600 t Mo have been produced from an
area of about 25 km2. More than 100 orebodies have been
found in this area and 12 of them are economically exploitable, making this deposit a large Cu-Au system in China.
The genesis of the Bainaimiao Cu-Au system is debatable. Previous studies proposed four genetic models such
as: (1) Cu was enriched in the accumulation and metamorphism of the host-rocks in Neoproterozoic and Early Paleozoic, and then in the emplacement of granite porphyry
(Li and Wu 1987); (2) submarine exhalation accompanied
with volcanism (Nie et al. 1993; Xiao et al. 2000); (3) the
northern and southern portions of the ore system were
porphyry- and volcanogenic types, respectively (Nie et al.
1994); and (4) a porphyry Cu-Au system (Huang et al. 2001;
Nie et al. 2004). Based on field investigation and synthesis
of available geochemical data, we suggest this deposit to be
an orogenic-type Cu-Au system in this paper.
2
Regional and ore geology
Situated at the northern margin of the North China plate,
the Bainaimiao deposit is hosted in the Bainaimiao Group
which is underlain by the Baiyinduxi Group, and overlain by the middle Silurian, middle to upper Carboniferous and lower Permian (in ascending sequence). The
Bainaimiao Group is mainly a greenstone-facies metamorphosed volcanic sequence with an zircon U-Pb age
of 1130 ± 16 Ma. The NW-dipping Bainaimiao fault, strik-
ing 20 km, was repeatedly activated and controlled the
developing of the ore-system. Intrusions in the orefield
are plagiogranite and granite porphyry yielding a whole
rock Sm-Nd age of 440 ± 40 Ma.
12 exploitable orebodies were numbered from 2 to 13
Nos. 2 to 7 and Nos. 10 and 11 orebodies constitute the
southern ore-belt, and the other 4 orebodies constitute the
northern ore-belt. Orebodies of the northern ore-belt are
hosted in mineralized granodiorite porphyry and/or its
contact zones with the Bainaimiao Group, the others in the
Bainaimiao Group. Spatial relationships and the ore-metallic association encouraged geologists to interpret it to be
of porphyry-type or other intrusion-related genetic type.
However, the geological map and exploration profiles show
that all the orebodies are hosted in schists instead of porphyry. Occurrences of orebodies are controlled by faults,
especially by shear zones. All the orebodies are vein-like in
shape and occur en-echelon along a fault. Most orebodies
are NW- to NWW-trending and S-dipping with angles
around 55°, similar to the Bainaimiao fault.
Orebodies are generally restricted to the brittle-ductile
transitions. Metallic minerals are represented mainly by
pyrite, chalcopyrite, pyrrhotite, sphalerite, galena, bornite,
molybdenite, magnetite and native gold. Gangue minerals
are quartz, sericite, biotite, chlorite, epidote, and calcite. Silicification, sericitization, chloritization, epidotization and
carbonation can be observed. Ore structures and vein intersecting shows a three-stage metallogenic processes
(Fig. 1), i.e. from E-stage quartz-pyrite assemblage, through
to M-stage polymetallic sulfides stocks, and to L-stage carbonate veinlets. This is identical to those of orogenic-type
lode gold and or silver deposits (Chen et al. 2004).
3
Isotope geochemistry
89 values of δ34S for sulfide samples range from –6.5‰ to
+1.9‰, suggesting a magmatc sulfur source (Nie et al., 1993).
The 206Pb/204Pb ratios of 18 sulfide samples range from
17.866 to 18.486, with an average value of 18.170; 207Pb/204Pb
ratios range is 15.482-15.626, with an average of 15.549; and
208Pb/204Pb ratios range is 37.296-38.343, with average of
37.904 (Nie et al. 1993, 1994). These values plot between the
evolution lines for the mantle and upper crust, with the
majority of samples occurring between mantle and orogen
lines (Fig. 2). One granite porphyry sample from the north-
Close
1322
Wen-Bo Li · Yan-Jing Chen · Yong Lai
4
Discussion
Although the Bainaimiao Cu-Au deposit was proposed
to be porphyry-, volcanogenic, or volcanic-related
exhalative types, but no powerful geological or geochemical data can support these interpretations. In other words,
occurrence of ore bodies, ore textures and structures,
mineralogical associations and their generations, as well
as some available geochemical data, suggest this to be more
similar to orogenic type ore systems.
References
ern ore-belt yields ratios of 206Pb/204Pb=17.807, 207Pb/204Pb
=15.566, and 208Pb/204Pb=37.943. Two green-schist samples
have 206Pb/204Pb ratio of 17.854 and17.895, 207Pb/204Pb
ratio of 15.519 and 15.531, and 208Pb/204Pb ratio of 38.155
and 38.160 (Nie et al. 1993). The 206Pb/204Pb, 207Pb/204Pb and
208Pb/204Pb ratios of a plagiogranite sample are 18.462, 15.508
and 38.094, respectively (Li et al. 2003). These data suggest
that ore metals were possibly sourced from two or more of
the above geologic units.
Seven pairs of δ13C (-8.9~-3.2 per mil) and δ18O (5.8~7.4
per mil) for calcite samples are in the range of the primary
carbonatite (δ13CPDB=-4~-8 per mil and δ18OSMOW=6 ~ 10
per mill). This indicates that the mantle or magmatic rocks
contributed much to the Bainaimiao ore system. Five detected δD for FIs in quartz separates range from –118 to –
91 per mil. Five calculated δ18Owater values from δ18OQ, in
terms of 1000 lnαquartz-water=3.05 × 106T-2-2.09, suggest that
of the ore-fluids might range from 1.5 to 3.4 per mil. These
five pairs of D-O isotopes do not give any concluding information but an input of meteoric water, which is a general
feature of orogenic-type ore systems during L-stage (Chen
and Pirajno 2005; Pirajno and Chen 2005; see this volume).
Chen YJ, Pirajno F, Sui YH (2004) 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
Huang CK, Bai Y, Zhu YS (2001) Copper deposits of China. Beijing:
Geological Publishing House (in Chinese)
Li DX, Wu GG (1987) Tectono-geochemistry of superimposed mineralization in the Bainaimiao ore field, Nei Mongol (Inner
Mongolia). Acta Geologica Sinica 1: 32-45 (in Chinese with English abstract)
Li JW, Wang CX, Hou WR (2003) Mineralization of gold deposits in
the Bainaimiao area, Inner Mongolia. Geoscience 17(3): 275-280
(in Chinese with English abstract)
Nie FJ, Pei RF, Wu LS (1993) Magmatic activity and metallogeny of
the Bainaimiao district, Inner Mongolia, People’s Republic of
China. Beijing: Beijing Science and Technology Press (in Chinese)
Nie FJ, Pei R F, Wu LS (1994) Nd, Sr and Pb isotopic study of copper
(gold) and gold deposit in Bainaimiao area, Inner Mongolia. Mineral Deposits 13(4): 331-344 (in Chinese with English abstract)
Nie FJ, Jiang SH, Zhang Y (2004) Geological features and origin of
porphyry copper deposits in China-Mongolia border region and
its neighboring areas. Mineral Deposits 23(2): 176-189 (in Chinese with English abstract)
Xiao RG, Peng RM, Wang MJ (2000) Analysis of major metallogenic
systems in western section, northern margin of North China Platform. Earth Science-Journal of China University of Geosciences
25(4): 362-368 (in Chinese with English abstract)
Close
Chapter 12-9
12-9
Zonation of polymetallic, rare-earth, molybdenum,
zirconium, beryllium and tantalum-niobium mineralization
in the Ak-Tyuz ore deposits (Northern Tien Shan)
N. Malyukova
Kyrgyz-Russian Slavic University; 44 Kievskaiya ul., Bishkek, Kyrgyz Republic
V. Kim, R. Tulyaev
Kyrgyz Mining University, 215 Chuy pr., Bishkek, Kyrgyz Republic
Abstract. Polymetallic -rare-earth - rare-metal mineralization in the
Ak-Tyuz ore field is associated paragenetically with subalkaline
leucocratic granites, but genetically with their postmagmatic activity. At Kuperlisai, where granites are exposed, localizations of
pegmatites occur. These contain orangites, albitite deposits of thorium, beryllium and REE greisen deposits. Within close proximity of
these granites (500-700m) formations of high-temperature
plutogenic, hydrothermal deposits of columbium-thorium-zirconium-rare-earth mineralization occur. Further away from the granites (3-5 km) there are formations of middle-low-temperature hydrothermal ore bodies with polymetallic and gold-bearing mineralization.
Keywords. Zoning, mineralization, genetically different types,
polymetallic, rare-earth, rare-metal mineralization
1
Introduction
The Ak-Tyuz ore deposits are located in the Ak-TyuzMuyunkumo-Naratsky Middle terrain of Pre-Cambrian
stabilization, and which contains Archaean and Early-Proterozoic formations (Fig. 1). The gneiss, gneiss-migmatites,
mica schists, marble with lenticular bodies of amphibolites and eclogites have a radiogenic age of 2.8 Ga (AkTyuz suite). The meta-volcanics turned into chlorite-epidote-actinolite schists (Kuperlisay suite) at 1.6-1.7 Ga
(Bakirov and Korolev 1979), and were associated with regressive metamorphism.
Metarocks of the baesement are intruded by magmatic
formations during three tectonic magmatic cycles: PrePaleozoic, Caledonian and Hercynian.
The specifics of the geological development of the different structural zones called for an investigation into its
magmatic activity. Pre-Paleozoic and Caledonian magmatic formations with island arc affinity developed in a
marginal trough. The intrusive bodies are characterized
by granodiorite and granite composition, form large laccoliths and stocks.
During Hercynian tectono-magmatic reactivation, intrusions were emplaced into the Middle terrain along the
north-eastern Ak-Tyuz zone: gabbro-diorite and monzonite (phase 1), syenite-diorite (phase 2), subalkaline
leucocratic granite (phase 3) and granophyres, aplite-like
granites and granite-porphyries (phase 4).
From a metallogenic point of view, the most significant ones are the Kuperlisaysky fissure leucogranite with
an absolute age of 260 Ma, and “blind” stock-like bodies
of granophyres with absolute ages of 215-225 Ma. The
granitic body has a wedge-shaped form, becoming more
narrow in a north-eastern direction. According to structural data from drilling, the granite intrusion settled to
the north-east at an angle of 16° into green amphibole
schist and gneiss. The roof of the subalkaline leucogranite
massif is characterized by the presence of a number of
blind domes, positioned mainly in pipe-like bodies of
brecciated green amphibole schist. The latter have been
intruded by the stock-like bodies of granophyres.
The group of polymetallic rare-metal and rare-earth
Ak-Tyuz deposits are spatially linked to the areas of
subalkaline leucocratic granites and granophyres, and
genetically connected to postmagmatic activity (Kim et
al. 2001). In the Ak-Tyuz deposits a specific regularity is
observed and described further below.
2
Kuperlisay deposit
The Kuperlisay ore deposit is located in the western part
of Ak – Tyus ore field, where the subalkaline leucocratic
granites form small (5 × 3 m) outcrops of pegmatite with
orangite, as well as albitite and greisen deposits of thorium, beryllium and rare earth. The latter are located directly in the zone of granites in metamorphic rocks. Preliminary exploration held on these sites was appraised
positively (Kim et al. 2000). Only beryllium mineralization has been without appraisal, and is localized in the
albite pipe of the Kuperlisay.
3
Kutessai – II deposit
On the north-eastern side of the subalkaline leucocratic
granites mass, about 2 - 2.5 km from the Kuperlisay deposit, the Kutessai-II deposit is situated. It is a blind intrusion-related hydrothermal deposit localized in metasomatically transformed stock-like bodies of granophyres.
In 1958, detailed exploration of this deposit was completed,
and resources of rare-earth and other metals counted and
Close
1324
N. Malyukova · V. Kim · R. Tulyaev
confirmed by the USSR GKZ (state commission on resources). Th deposit was mined by open-pit from 1962 to
1992. Annual ore processing in Ak-Tyuz ore mill was about
300 thousand tones.
In the Kutessay-II deposit, the following zoning of ore
mineralization distribution was recognised (Kim et al.
2000). Apical parts and hanging side of stock-like ore
bodies set by silicificated rocks of second quartzite type
are characterized by predominant development of
polymetallic mineralization with fluoride of rare-earth
(yttrofluorite and fluorite) and malacon. A distribution
of polymetallic mineralization inside of silicificated rocks
is controlled by linear structures of the north-eastern
stretch (Nevsky et al. 1974).
The polymetallic ores are sharply decreasing with
depth. It is reasoned that the zones of silicificated rocks
(of secondary quartzite type), with which the polymetallic
mineralization is genetically and spatially connected are
thinning out at depth. In the Kutessay-II deposit, the main
resources of lead are concentrated in these rocks (48.5
thousand tones with average lead content 2.58%).
In the upper horizons of the deposit quartz-chlorite
biotite and quartz-chlorite metasomatites are widespread.
These are localized in the peripheral parts of stock-like
ore body and on its upper horizons. Its formation took
place in postmagmatic stage due to green amphibole schist
and granophyres as a result of intensive pneumatolytic
and hydrothermal processes.
Microscopically, the quartz- chlorite biotite rocks are
characterized by lepidogranoblastic structural and massive texture, and composed mainly by the grassy-green,
small-grained biotite (20-80%), chlorite (10-60%), quartz
(5-40%), orthoclase (3-25%) and ore minerals (up to 34%). Among the latter the most common ones are monazite, xenotime, yttrobastnasite, yttroparisite, malacon,
molybdenite, cyrtolite, ferritorite, galena, blende, pyrite
and chalcopyrite.
In comparison with the other metasomatic rocks
quartz-peach biotite and quartz-chlorite ores contain more
phosphate, carbonate and fluorinecarbonate of rare earth.
Therefore these ores are the main host of rare-earth mineralization which concentrate in the arched and ringshaped zones, controlled by the structural elements. Maximum accumulation of rare-earth mineralization is observed in the marginal zones, located directly on the contact of stock-like bodies of granophyres with green amphibole or breccia schists. In the northern stock-like body
(horizon 2353 m) parts with maximum concentration of
rare-earth minerals are concentrated in the central and
the north-eastern parts of it in the upper horizons of the
central stock-like ore body, the highest rare-earth zones
are located in the southern and eastern peripheral parts
of tubular breccia bodies of schists.
Different zones, composed by the minerals of rare-earth
stage are getting wider and flatter with depth. This is explained by the observation that at depth areas of the
quartz- chlorite biotite and quartz-sericitic metasomatites,
with which rare-earth mineralization are connected spatially and genetically, and increase significantly. This is
linked to that in the lower horizons of the deposit, the
greisen process is widely developed, and that is why fluorides, phosphates, carbonates and fluorinecarbonates are
substituted by the rare-earth silicates containing less number of the latter ones.
Close
Chapter 12-9 · Zonation of polymetallic, rare-earth, molybdenum, zirconium, beryllium and tantalum-niobium mineralization in the Ak-Tyuz ore deposits
To the horizon 2353 m all granophyric bodies are replaced by quartz-sericitic metasomatites, located ring-like,
formed on granophyres as a result of pneumatolito-hydrothermal metasomatism.
Macroscopic quartz-sericitic formations represent
massive small-grained rocks of gray-pink, in some parts
of brown colors. It is mainly composed by sericites (5055%), quartz (40-45%), chlorite (5-7%) and ore minerals
(in average up to 1.5-2%). An average presence of rare
earths sum in the metasomatites is 0.30% and ZrO2 0.56%.
In the distribution of ore minerals the following regularity is observed: on the areas of sericite development, the
main mass of cyrtolite, columbite, ferritorite and tinstone
is located. Although in the zones of biotite, chlorite - monazite, yttrobastnasite, yttroparisite and molybdenite these
ore minerals are found in the form of small grains, of
irregular configuration or punctual inclusions.
The sericite is gradually replacced by muscovite towards the lower ore horizon, and the amount of the latter
increases from 5-8% to 80-85%. Then, rock suits change
to greisen quartz-muscovite phases.
In close association with aggregate of muscovite it
is possible to see fluorite, cyrtolite, tantalo-niobates,
tinstone, ferritorite, silicates of rare-earth (tscheffkinite,
cerite) and rarely fluorinecarbonates of rare-earth.
The average content of rare-earth sum in the quartzmuscovite metasomatites is 0.169% and ZrO2 0,61%.
Generally, the ores of lower ore zone are perspective for
extraction of zirconium and hafnium and at the same
time of - tantalo - niobates, tin, thorium and rare-earth
mineralization.
Thus, in the deposit Kutessay-II, the following vertical
(from top to bottom) and horizontal (from the center of
stock-like ore body to the periphery) zoning in ore mineralization disposal is observed:
in the above-ore zone – beryllium mineralization;
in the upper-ore zone – polymetallic mineralization
with peach (yttrofluorite, fluocerite) of rare-earth and
malacon, and also phosphate, carbonate and fluorinecarbonate rare-earth mineralization with molybdenum;
in the middle-ore zone – thorium- -rare-earth with tinstone;
in the lower-ore zone – thorium- zirconium with
tantalo-niobates and silicates of rare-earth.
There are 4 stages of ore mineralization in the deposit:
1.
2.
3.
4.
beryllium;
polymetallic;
rare-earth;
columbium-thorium-zirconium.
Temperature of formation ranges from 200°C to 400°C.
4
1325
Kalesay Deposit
The deposit is located 800m to the north-east of KutessayII. At the north-eastern side of the Kutessay open pit, the
south-western wing of the Kalesay deposit is exposed,
resources of which are 12 thousand tones of metal (Mineral and raw material bas 1998).
This deposit is located in the above-ore zone and localized in the linear feldspar stockworks with phenacites
and fluorites, lying down in the green amphibole schists
of Kuperlisay suite. Nowadays there are 2 ore zones – the
Northern and Southern, divided by the Ak-Tyuz anticline,
the kernel of which is composed by the gneiss of Ak-Tyuz
suite.
The beryllium mineralization is controlled by the slim
(first mm-2.5 cm) albite-fluorite- phenacite veins. System of veins composes in the schists of linear stockworks
zone:
The northern stockwork has a length of 800 m and
contains 253 ore veins.
The southern zone has a length of 1600 m and 700 ore
veins have been documented. Among the beryllium minerals besides phenacite, representing the main ore value,
there are also genthelvine, geltbertrandite, bavenite,
baverite, beryl and mialarite.
Concentration of beryllium mineralization in the
above-ore zone is explained by that it is connected with
high migration ability of beryl in the form of volatile complex compounds with peach (Na[BeF3], etc.) (Ginzburg
et al. 1974).
5
Ak-Tyuz deposit
This deposit is located 5 km to the north-east from the
Kuperlisay deposit and represents a blind granophyric
stock which has been exposed by excavation at a depth
of 33m. An apical part of the stock was completely composed by the silicificated rocks of second quartzite type,
where were rich polymetallic ore with average presence
of lead at about 17%. The resources, confirmed by GKZ
were 150 thousand tones of lead. In the contact of granophyres with the breccia green amphibole schists a lowpgrade (3-5 m) zone of the quartz- chlorite biotite and
quartz- chlorite metasomatites has been noted. The
silicificated rocks of the deposit lens out gradually in
the 4th horizon, and the number of quart-chlorite
metasomatites grows sharply with the content of rareearth, molybdenite and cassiterite. The silicificated rocks
with polymetallic mineralization almost completely
lenses out to the horizon 2353 m, which is why the AkTyuz deposit was abandoned in 1959, although more than
15 million tones of the quartz- chlorite biotite and quartzchlorite ores with the industrial content of rare-earth
(1% TR2O3), zirconium, thorium, molybdenite, and tin
remained.
Close
1326
N. Malyukova · V. Kim · R. Tulyaev
6
Conclusions
The following zonation of different genetic types of ore
deposits, spatially connected to the subalkaline leucocratic
granites is observed in the Ak-Tyuz ore field:
In the Kuperlisay, where granites are exposed pegmatites
with orangite, albitite deposits of thorium, beryllium and
greisen deposits with rare-earth are localized.
In Kutessay-II, located 350-400 m from the leucocratic
granites, high-temperature plutogene deposits of niobiumthorium-zirconium, rare-earth and polymetallic mineralization formed in the granophyres. These are lower-ore zone
greisen formations with tantalo-niobium and ferritoritetinstone-cyrtolite mineralization with silicates of rare-earth.
More diatlly from the granites ore deposits, low to middle
temperature hydrothermal ore bodies with polymetallic and
gold-ore mineralization formed.
The beryllium mineralization is localized in the aboveore zone.
References
Bakirov, Korolev (1982) The age of ancient rocks in Tien Shan. In:
Izv. Akad. Nauk SSSR, Ser.Geol., 1979, #7: 144-146
Ginzburg A, Zabolotnaya N, Shaskaya V, Getmanskaya T, Kupriyanova
I, Novikova M (1974) Zoning of the hydrothermal beryllium deposits, In: “Nauka” Publishing House, Moscow: 267-275
Kim V, Ashirova Z, Malyukova N, Shamgunov K, Shamshiev O,
Ysakov A (2000) Development of mineral resource of rare-earth,
some rare and noble metals in the Kyrgyz Republic, VIMS, Vol.
1, Moscow: 86-91
Kim V, Malyukova N, Raimbault L (2001) The Ak-Tyuz rare-metal
ore field. In: Geodynamics and Gold Deposits in the Kyrgyz
Tien Shan. In: IGCP 373 International Field Conference, Bishkek
and Kyrgyz Tien Shan, Kyrgyz Republic, 16-25 August, 2001,
IAGOD Guidebook Series V.9: Natural History Museum London: 115-124
Nevsky V, Turovsky S, Kozlova P, Kim V, Turchinskiy V (1974)
Samples of hypogene zoning and mineralization in rare-metalpolymetallic deposit. In: “Nauka”, Moscow: 239-266
Mineral and raw materials base of the Kyrgyz Republic at the threshold of transfer to the market economy. Bishkek (1998), 211
Close
Chapter 12-10
12-10
Eight stages of major ore deposits in northern Xinjiang,
NW-China: Clues and constraints on the tectonic
evolution and continental growth of central Asia
Kezhang Qin, Wenjiao Xiao, Lianchang Zhang, Xingwang Xu, Jie Hao, Shu Sun, Jiliang Li
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029,
China
Richard M. Tosdal
MDRU, University of British Columbia, Vancouver BC V6T 1Z4, Canada
Abstract. Major Cu, Ni, Cr, Au, Pb, Zn, Fe, W, Sn and rare metal deposits
of northern Xinjiang (China) formed during eight tectonic stages,
based on their plate tectonic setting. These stages are (1) Precambrian stable continental, (2) Neoproterozoic rift stage, (3) formation
of oceans, (4) Silurian-early Carboniferous subduction, (5) Devonian
and Carboniferous back-arc, intra-arc extension, (6) late Carboniferous to early Permian collision, (7) Permian post-collision extension, and (8) Triassic inter-continental rift stage. Different ore deposits correspond to each evolution stage, and their formation, and
associated magmatic and volcanic sedimentary sequences place
important constraints on the development of a tectonic framework
for the continental growth of Central Asia Orogenic Belt.
Keywords. Ore deposit association, temporal-spatial distribution, plate
tectonic cycle, Xinjiang
1
Introduction
Central Asia is an excellent natural laboratory for analysis of accretionary tectonics, crustal growth and associated metallogeneses (Sengor et al. 1993; John et al. 2000;
Qin 2000; Xiao et al. 2004). One of the major lithotectonic
belts of the region is the arcuate Central Asia Orogenic
Belt (CAOB) that crosses northern Xinjiang. The CAOB
is a Paleozoic mosaic of structurally bounded blocks (Xiao
et al. 1992) characterized by belts of ophiolites, peralkaline
intrusions, mafic-ultramafic complexes, and ductile-shear
zones. Mesozoic-Cenozoic extension has broken the Paleozoic and Precambrian rocks into basins and ranges.
Within CAOB, major Cu, Ni, Cr, Au, Pb, Zn, Fe, W, Sn
and rare metal deposits of northern Xinjiang are divided
into 8 stages, based on their geodynamic setting (see below). We review this metallogenic evolution within the
context of the tectonic evolution, and propose that the
Late Carboniferous-Permian is the most important
metallogenic epoch. This epoch also corresponded to a
significant period of crustal growth in Xinjiang and elsewhere in the CAOB.
2
Geology and metallogeny in northern Xinjiang
The Tianshan Mountains, Junggar basin and Altay Mountains of north Xinjiang (an area of 550,000 km2) in north-
west China are located along the southern margin of the
oroclinally folded CAOB (Yakubchuk et al. 2002; Mao et.
al. eds 2003). The CAOB is a vast region of Phanerozoic
juvenile crustal growth on the south side of the Siberian
craton (Shatov et al. 1996; Heinhorst et al. 2000; Hu et al.
2000). The accretionary, Cordilleran-type orogen was
formed from a series of allochthonous terranes, which
include turbidite sequences, oceanic arcs, and fragments
of Proterozoic microcontinent blocks. North Xinjiang is
characterized by tectonic elements of an active margin
that include ophiolite belts, accretionary arcs, peralkaline
intrusive belts, post-tectonic mafic-ultramafic complexes,
and ductile-shear zones (Tu 1993; He et al. 1994; Qin 2000).
Ophiolites mainly surround the Junggar basin and are
typically of Lower to Middle Paleozoic age (Wang et al.
2003). Abundant oil and gas occur in basins in northern
Xinjiang, and important Cu, Au, Ni, Cr, Fe, and rare metal
resources are known in the orogenic belts. The recent discovery of the large Tuwu-Yandong porphyry Cu deposits
in the northern Tianshan Mountains (Wang et al. 2001)
and Baogutu porphyry Cu-Au deposit in western Junggar
as well as Halasu porphyry Cu-Au in northeastern Junggar
are of major economic significant to Xinjiang.
Silurian to Carboniferous accretion in the Altay and
Tianshan was marked by intermittent terrane collision,
complex reversals of and jumps in subduction loci and
polarity, and the stranding of devolatilizing slabs that
extensively metasomatised the underlying sublithospheric
mantle. In Tianshan the major collisional events were Late
Carboniferous to Early Permian (300-290 Ma). Carboniferous to Permian magmatism included emplacement of
Cu- and Au-rich, high-K, relatively oxidized, calc-alkaline to alkaline intrusions (Qin 2000; Heinhorst et al. 2000).
Most mesothermal gold deposits were formed in association with widespread syn- and post-tectonic, relatively
reduced magmatism in Late Carboniferous and Permian,
with the causative melts intruding and interacting with
thicker reduced crustal sequences. The widespread presence of lamprophyre and diabase dikes and shoshonitic
stocks within some metalliferous fore-arc accretionary
complexes indicates that major fault zones tapped fertile
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Kezhang Qin · Wenjiao Xiao · Lianchang Zhang · Xingwang Xu · Jie Hao · Shu Sun · Jiliang Li · Richard M. Tosdal
mantle melts during late collisional episodes (Li 1989; Hu
et al. 2000). Significantly, the late Paleozoic orogen evolved
into a transtensional regime during Permian, leading to
basin development (e.g. the Jungger, and Tu-Ha basins)
and preservation of widespread greenschist facies rocks
with mesothermal gold deposits and areas of little erosion with epithermal vein and porphyry copper districts.
Highly mineralized Devonian and Early Carboniferous
accreted island arcs in the eastern and western Tianshan
(Qin et al. 1999; Qin 2000) extend to the west into adjacent Kazakhstan (Heinhorst et al. 2000; Mao et al. 2003).
3
Division of ore deposit association into eight
tectonic stages in northern Xinjiang
The eight tectonic stages are: (1) Precambrian stable continental, (2) Neoproterozoic rift stage, (3) formation of
oceans, (4) Silurian-early Carboniferous subduction, (5)
Devonian and Carboniferous back-arc, intra-arc extension, (6) late Carboniferous to early Permian collision,
(7) Permian post-collision extension, and (8) Triassic inter-continental rifting. The major ore deposits are summarized in the following section.
3.1 Ore deposit association in Precambrian stable
continental stage
The continental blocks of northern Xinjiang along the
north margin of Tarim Craton and Yili block consists of
Pre-Sinian strata and intrusions, whereas the cover sequences consist of strata of Sinian to Ordovician. Metasedimentary rock-hosted iron deposits and sedimentary rockhosted phosphorous deposits of middle to late Proterozoic age were formed along the stable Precambrian craton margin. The main ore deposits include:
1. Alkalic ultramafic and carbonatite-hosted superlarge
vermiculite-apatite-rare earth element deposit as
Qieganbulake;
2. Mafic-ultramafic hosted Cu-Ni sulfide deposit, such as
the Xingdi ore district;
3. Proterozoic metamorphosed sedimentary ore deposits including Fe deposits, (Tianhu,Yuxi and Shalong),
and Cu deposits (Namasayi Cu deposits at Bole,), and
apatite deposits, (Akesai and Akesala deposits at Jinghe,
and Jianshanzi deposit at Hami);
4. Sedimentary P, V, U, Mn, Co, Ag deposits such as
Keguqing P deposit, Pintaishan P and V deposits, and
Qieganbulake V-Ag deposit.
3.2 Primary-rift stage
Continental rifting since the Sinian (Neoproterozoic) was
accompanied by the formation of small manganese oxide deposits such as Dashui and additional sedimentary
phosphorous and iron deposits such as Kuluoketage of
Sinian and Cambrian.
3.3 Spreading oceanic stage
Continental rifting formed the Junggar Ocean in the
north, the Tianshan Ocean in the south (Harke-Liuhuangshan Ocean), as well as the Qimantage-western Kunlun
aulacogen. Middle Paleozoic seafloor spreading in the
Junggar ocean led to development of small Cyprus-type
VMS copper deposits of Silurian (e.g. Kekenaike Cu deposit) that were later obducted as parts of ophiolite sequences within the northern Tianshan. Elsewhere in the
oceanic basins, podiform chromite in metaperidotite associated with ophiolite suites is found in the Mayila Hills.
Sartouhai at Mayila is a medium-sized deposit and is
the second largest Cr mine in China. Serpentinized, ultramafic-hosted asbestos, talc and magnesite deposits,
such as the large, Tonghuashan talc deposit with associated Cu-Co-Zn-Ni mineralization at Tuokeshun also
formed at this time.
3.4 Subduction-accretion stage
Early subduction-accretion events led to development of
a calc-alkalic magmatic arc and associated deposits. Included are early Carboniferous porphyry Cu deposits, such
as the Tuwu-Yandong deposits in eastern Tianshan, the
Lailisigaor porphyry Cu-Mo, and the Lamasu skarn-porphyry Cu deposit at Boluhoulu in the western Tianshan,
and epithermal Au deposits, such as the giant Axi LS
epithermal Au deposit in western Tianshan. Subaerial,
volcanic-hosted, Fe deposits such as the large LaomaohuBeishan mine in eastern Junggar, and the contact- metamorphosed Alatage and Shuangjingzi Fe deposits adjacent to calc-alkalic granite in the eastern Tianshan were
also formed in the Carboniferous.
3.5 Back-arc, intra-arc extension stage
A back-arc basin formed in the Devonian in north Junggar
and in the Carboniferous in north Tianshan. Cu-Zn and
Fe-Cu VMS as well as magnesite and dolomite deposits
formed at this time.
1. Metamorphosed sedimentary-rock host Fe deposits such
as the large Wutonggou, Pargang and Heiheijiangzi deposits in the eastern Tianshan;
2. The large Mengku Fe deposit formed in the Devonian
back-arc basin in Altay, whereas the Yamansu, Aqishan
and Chilongfeng Fe deposits formed in the Carboniferous Yamansu back-arc basin in the eastern Tianshan;
3. VMS deposits, such as the Ashele Cu-Zn-Au and the
Keketale Pb-Zn deposits were formed in the Devonian
back-arc basin along the south margin of Altay.
Close
Chapter 12-10 · Eight stages of major ore deposits in northern Xinjiang, NW-China: Clues and constraints on the tectonic evolution and continental growth
3.6 Collision orogenic stage
Ore formation in collisional settings can be divided into
late Silurian-early Devonian, late Devonian and late Carboniferous stages. Further terrane collision led to formation of mesothermal gold deposits of Late Carboniferous
to Early Permian age.
1. Middle to late Silurian andalusite and gem deposits
formed in metamorphosed pelitic rocks in the Heiyingshan-Liushugou high-T low-P metamorphic terrane.
2. Late Silurian to Early Devonian corundum deposit,
mainly distributed in the north side of Heiyingshan
fracture of SW-Tianshan, is hosted in metamorphosed
clastic-carbonate rocks.
3. The late Paleozoic large Nasunka glucine-bearing aquamarine and Ayoubulake muscovite deposit associated
with granitic pegmatite.
4. Carboniferous migmatitic pegmatite-hosted rare metallic and jewel-jade deposit such as the world-class
Keketouhai and Kelumute Li-Be-Nb-Ta deposits in
Altay Mountains.
5. Ductile-shear zone-hosted mesothermal gold deposits, such as the Carboniferous Duolanasayi and
Tuokusibayi Au deposit in south Altay, and Saritale
large Au deposit in Central Tianshan, and large
Kanggur-Matoutan Au-Cu-Pb-Zn deposits in eastern
Tianshan.
3.7 Post-collision extensional stage
During the latest Carboniferous, the collapsed oceans and
marginal seas were accreted, uplifted, and underwent regional extension in the Permian. The early Permian is
the most important stage for Au, Fe, and Cu-Ni mineralization in Xinjiang. Numerous deposits were formed during this stage, including:
1. Magmatic hydrothermal Au deposits, such as the
Xifengshan Au deposit in east Tianshan and the
Sartouhai Au in west Junggar;
2. The large Shiyingtan LS- epithermal Au deposit in east
Tianshan;
3. Mafic-ultramafic rock-hosted Cu-Ni deposits in north
Xinjiang. Examples include the Kelatongke Cu-Ni mine
in the southern Altay, the Qingbulake Cu-Ni deposit in
the western Tianshan, and the Huangshan-XiangshanTulargen Cu-Ni-Co belt in the eastern Tianshan;
4. Alkalic gabboro and syenite-hosted V-Ti-Fe-REE magnetite at Weiya deposit;
5. Large Permian magnetite-type deposits hosted in
subvolcanic mafic rocks in the east Tianshan;
6. Bimodal volcanic-hosted Fe-Cu deposits in intra-continental rift such as Nileke Permian copper belt in the
western Tianshan;
1329
7. The late Carboniferous to Permian nepheline-syenitealkalic pegmatite and carbonatite-hosted rare metallic
deposit (Heiyingshan-Yenanlike Nb-Ta-Zr-Y-Yb-Ce-sodalite-phlogopite deposit in southwest Tianshan);
8. Alkalic granite-hosted Kamusite and Beilekudouke Sn
deposit in east Junggar;
9. The large Sawayardun Au deposit hosted in weakly
metamorphosed carbonaceous clastic-hosted Au deposits in an eastern extension of the same tectonic belt
hosting the giant Muruntau Au deposit;
10.Sedimentary rock-hosted Chahansala Hg-Sb-Au deposit thought to be related to nearby volcanic rocks.
3.8 Inter-continental stage
Inter-continental extension in the northern Xinjiang, began in the Triassic and was accompanied by eruption and
emplacement of crustally derived magmas. The large,
Baishan porphyry Mo deposit of Climax type was formed
in the Late Triassic or Early Jurassic (Li et al. 2004; Zhang
et al. 2005). Resources of oil-gas, coal, uranium, bentonite, gypsum and mica were formed in the basins also in
the Mesozoic.
4
Implications of temporal-spatial record
of metallogeneses in north Xinjiang to
paleo-tectonic settings and evolution of CAOB
Ore deposits, particularly large and giant ore deposits,
reflect the geologic, tectonic, and petrologic evolution of
a terrane. Conversely, the metallogeny of the region can
be utilized to gain some insights into plate tectonic environment of that region. Based on the distribution of ore
deposits, we infer major convergent tectonics in the late
Silurian-early Devonian, late Devonian and late Carboniferous-Early Permian. Epithermal gold deposits surround
the Junggar basin, and show a spatial and temporal association with porphyry Cu deposits (Tosdal and Richards
2001). The epithermal Au deposits in northern Xinjiang
were formed in the late Paleozoic (ca. 340-240 Ma) (Li et
al. 1998; Zhang et al. 2004), and are well preserved in little
eroded arc settings. The arcuate distribution of epithermal
Au and porphyry Cu deposits also suggested that the Paleozoic Junggar basement was oceanic (Qin et al. 2002).
Some metamorphosed ore deposits such as andalusite,
corundum and asbestos deposits formed in the late Silurian-early Devonian, with muscovite and rare metals
deposits formed in the late Devonian. The third convergent and collision stage is the most metallogenetically
important as major Au, Cu-Ni-Co, V-Ti-Fe, Li-Be-Nb-Ta
deposits formed in north Xinjiang. Furthermore, the character of ore deposits indicates three episodes of rifting
and/or ocean formation. The oldest major oceanic spreading was in the Sinian to Ordovician. A second stage involved back-arc spreading in early to middle Devonian.
Close
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Kezhang Qin · Wenjiao Xiao · Lianchang Zhang · Xingwang Xu · Jie Hao · Shu Sun · Jiliang Li · Richard M. Tosdal
This episode was a major metallogenic stage with many
large VMS and Fe deposits. The third stage involved backarc and intra-arc spreading and resulted in only small
VMS and Sedex deposits. The multiple accretionary arcs,
multiple back-arc or intra-arc basins, multiple ophiolite
zones, multiple magmatic belts, and multiple ductile shear
zones, and corresponding mineral deposits around
Junggar ocean suggest that the geodynamic setting of
Xinjiang in the Paleozoic resembles modern Southeast
Asia and Southwest Pacific Ocean (Qin et al. 1999; Qin
2000). This Late Paleozoic (400-250 Ma) time is the most
important metallogenetic episode in Xinjiang (Li et al.
1998; Qin et al. 2003), with many deposits localized in the
transitional stage from collisional to extensional settings.
Within this time frame the late Carboniferous-Permian
is the most important metallogenic epoch, and is also a
significant period of crustal growth in the Altay and
Tianshan and elsewhere in the Central-Asia Orogenic Belt.
Acknowledgements
This research was financially supported by CAS knowledge innovation project (KZCX3-SW-137) and NSFC
project (40072078).
References
Carroll AR, Liang Y, Graham SA, Xiao X, Hendrix MS, Chu J, and
McKnight CL (1990) Junggar basin, northwestern China: trapped
Late Paleozoic ocean: Tectonophysics 181: 1-14
Goldfarb RJ, Groves DI and Gardoll S (2001) Mesothermal gold
and geologic time: a global synthesis. Ore Geology Reviews 18:
1-75
Close
Chapter 12-11
12-11
GIS package on mineral deposits database and
thematic maps of Central Eurasia
R. Seltmann
Natural History Museum, CERCAMS, London SW7 5BD, U.K.
V. Shatov, G. Guriev
All-Russian Geological Research Institute (VSEGEI), St. Petersburg, Russia
A. Yakubchuk, A. Dolgopolova
c/o Natural History Museum, CERCAMS, London SW7 5BD, U.K.
Abstract. The GIS (Geographic Information System) Central Asia is composed of spatially referenced geographical, geological, geophysical,
geochemical and mineral deposit thematic layers, and their respective attribute data. It is issued to establish insights in the regions mineral potential and its past and future mining activities. Subsequently,
the information system is further exploited to derive new rules between the different attribute information in their relation to mineral
deposit information and the special distribution of the deposits.
Keywords. GIS, metallogeny, Central Asia, mineral deposits database,
thematic layers
1
Introduction
The ArcView 3.2 and MapInfo 6.0 (7.0) GIS Package: Mineral Deposits Database and Thematic Maps of Central Asia,
1.5 Million Scale is a product of the Centre for Russian and
Central Asian Mineral Studies (CERCAMS), Department of
Mineralogy, Natural History Museum (NHM), London. Technical support was provided by a group of scientists from St.
Petersburg and Moscow, Russia. The GIS package was produced under the IGCP Project 473 «GIS metallogeny of Central Asia» and the International Association on the Genesis
of Ore Deposits (IAGOD). Cooperation, scientific contributions and logistical support from the IGCP-473 teams and
project participants from Kazakhstan, Uzbekistan, Kyrgyzstan,
Tajikistan, Russia, China, Mongolia, USA, Canada, Japan, India, Albania, Austria, Czech Republic, Finland, France, Germany, Israel, the Netherlands, Norway, Poland, Slovakia, Spain,
Switzerland, Turkey, UK and others is appreciated.
The GIS package provides a regional-scale (1.5 million) overview of the geology, metallogeny, magnetic and
gravimetric geophysical data together with a digital topographic base map for the territory of the four Central
Asian countries: Kazakhstan, Kyrgyzstan, Uzbekistan and
Tajikistan. This product is intended as a reference tool to
support a broad spectrum of applications by geoscientists, managers, planners, and developers. Using the GIS
software users can display and analyze the data and also
prepare customized maps for specific applications.
The data in the GIS package are available either in the
form of an ArcView project or in MapInfo format, which
consists of five thematic maps: (1) topographic base map,
(2) geologic map, (3) mineral deposits map, (4) anomalous
magnetic field map and (5) gravimetric map. Attribute data
on specific mineral deposits are included as linked txt. files.
All the coverages in the GIS package were produced in
ArcInfo v. 8.2 format and saved in the ArcView (MapInfo)
project as shape files with identical boundaries and stored
in real geographic coordinates.
In all project Views the above-mentioned thematic
maps are presented in Equidistant Conic projection
(Krasovsky spheroid) with Central Meridian of 69 degrees
East and reference latitude of 46 degrees North. Standard
parallels are as follows: 39.3 and 52.7 degrees North, respectively. Map Coordinates: 46 - 88 degrees East, 37 - 56
degrees North.
2
Geologic thematic map
This part of the GIS contains a 1.5 million scale vector geologic map of Central Asian countries (Kazakhstan, Kyrgyzstan, Uzbekistan and Tajikistan except Turkmenis-tan) produced on the basis of the new GEOLOGICAL MAP OF CENTRAL ASIA, scale 1:1 500 000 compiled for IGCP-473 by N.
Afonichev & N. Vlasov (St. Petersburg, 2002) (Fig. 1).
The geologic thematic map consists of several layers.
The base geologic layer shows sedimentary, volcanic, intrusive and metamorphic rocks on the present day surface.
Sedimentary and stratified volcanic units are colored in
accordance with common Russian standards for stratigraphic units. The age of the stratified sedimentary and
volcanic units as well as metamorphic formations is indicated by special indices. The composition of volcanic units
is shown by means of special lithology symbols. Intrusive
rocks are colored based upon their composition whereas
the age of intrusive bodies is indicated both by special indices like stratified units and by color density. The main
tectonic contacts, faults, thrusts and explosion pipes are included as separate sub-layers.
The geologic thematic map layer consists of two views
“MAP-view” and “Legend-view”, two layouts -”MAP-print”
and “Legend-print”.
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R. Seltmann · V. Shatov · G. Guriev · A. Yakubchuk · A. Dolgopolova
The Map-view includes the following 7 specific themes
(thematic sub-layers): (1) geology -polygons with color,
(2) lithology - polygons with hatching and symbols, (3)
geological contacts and facial contacts, (4) faults, thrusts
and tectonic contacts bordering salt cupolas, (5) explosion pipes, (6) auto-labels of geologic indices for printing,
(7) direct lines for geologic indices for printing (Fig. 2). The
Legend-view comprises the following 4 specific themes (thematic sub-layers): (1) legend to intrusive rocks, (2) legend
to stratified formations, (3) legend to lithology of volcanics,
(4) legend to genetic type of Quaternary sediments.
Topographic vector base map, consisting only of “MAPview,” includes the following several themes (thematic sublayers) accompanied by respective attributive tables: (1)
water drainage system, (2) lakes and islands, (3) highways, (4) railways, (5) elevation numbers, (6) towns, cities, and settlements, (7) topographic network, (8) state
borders, (9) frame of the study area.
3
Metallogenic thematic map
This part of the GIS contains the metallogenic thematic
map of Central Asia showing the distribution of mineral
deposits positioned on the geologic vector map at 1.5
million scale. All materials to be used during the
metallogenic thematic map layer compilation had official, legal and public domain status.
The metallogenic thematic map consists of several sublayers. The metallogenic background is prepared and visualized as symbols of mineral deposits positioned on
the geological map and classified in the following legend: the symbol shape denotes the mineral deposit type,
the symbol size indicates a rank of mineralization, and
the mineral commodity is shown by the color of the symbol (Fig. 3).
All mineral deposits shown on the map are subdivided
into the following 22 mineral commodity types: (1) Molybdenum, (2) Tungsten, (3) Tin, (4) Uranium, (5) Rare
metals (Ta+Nb+REE+Be+Zr+Li), (6) Boron, (7) Copper,
(8) Base-metals, (9) Gold + Silver, (10) Antimony + Mercury, (11) Bismuth, (12) Iron + Manganese, (13) Titanium,
(14) Vanadium, (15) Chromium, (16) Platinum Group Elements, (17) Nickel + Cobalt, (18) Phosphorite, (19)
Alunite, (20) Diamond, (21) Fluorite, and (22) Bauxite.
Ore mineralization on the map is ranked as large, medium, small deposits.
The genetic classification includes the following 23 mineral deposit types: (1) Placer/paleoplacer, (2) Sedimentary
stratiform, (3) Residually enriched, (4) Metamorphosed
stratiform, (5) SEDEX, (6) VHMS, (7) Stratabound clastichosted, (8) Sandstone-hosted uranium (roll subtype), (9)
Stratabound carbonate-hosted, (10) Sediment-hosted disseminated shear zone-relate, (11) Ultramafic/mafic-hosted
disseminated shear zone-related, (12) North-Kazakhstantype uranium (U-Mo and U-P subtypes), (13) Volcanic-associated epithermal vein/stockwork, (14) Basalt/andesitehosted native copper, (15) Gabbro/granitoid-related
mesothermal vein/stockwork, (16) Porphyry, (17) Graniterelated hypothermal vein/stockwork, (18) Skarn, (19)
Peralkaline rock-associated, (20) Granitic pegmatite-hosted,
(21) Carbonatite-associated, (22) Eclogite-hosted diamond,
(23) Ultramafic/mafic intrusion-hosted, (24) Unclassified.
The metallogenic thematic map layer consists of two
views “MAP-view” and “Legend-view”, and two layouts ”MAP-print” and “Legend-print”.
The Map-view comprises the following 4 specific mineral deposits themes (thematic sub-layers): (1) narrow
white strip around of mineral deposit symbol (for better
Close
Chapter 12-11 · GIS package on mineral deposits database and thematic maps of Central Eurasia
1333
Activating any of the specific mineral deposits themes
and clicking “Hotlink” on any symbol on the map displays a box with the text description of the selected mineral deposit (see example in Table 1).
5
symbol visualization on the map), (2) mineral commodities (symbol with single color), (3) combined mineral
commodities (symbol with double color), (4) mineral
deposit type (symbol shape).
4
Mineral deposits database
The mineral deposits database includes information on 1692
mineral deposits shown on the geologic thematic map layer.
The characteristics of each mineral deposit in the database
contain information on its location (latitude and longitude,
country and administrative region), mineral deposit type,
major and minor mineral commodity, deposit size, geology, tectonic setting, age of host rocks and wallrock alteration, mineral composition of ore, orebody size and morphology, tonnage of ores and metal grades, references list,
date of discovery etc. Nevertheless, at the moment the database includes 608 full descriptions of mineral deposit
(mainly of large and medium size) whereas the rest of the
deposits from the database have a short description including deposit name, location (latitude and longitude), mineral deposit type, major and minor mineral commodity,
and mineral deposit size.
The attribute table, linked to specific mineral deposits
themes, consists of the following columns: (1) ID -identification number, (2) L_code - numeral code of mineral
deposit (it is a unique code of the mineral deposit in the
database), (3) Gen_code - numeral code of mineral deposit type, (4) Ore_code -numeral code of single and combined mineral commodities, (5) Size - numeral code of
mineral deposits size, (6) Lat latitude, (7) Long longitude,
(8) Name name of mineral deposit, (9) Main_ore major
commodity, (9) Accomp_ore minor commodity, (10)
Info_txt - reference to txt. file with mineral deposit description linked to the attribute table, (11) Info_bmp reference to bmp.file with local geologic map view, (12)
Full_inf reference to text.file with available full description of the mineral deposit.
Anomalous magnetic field thematic map
This part of the GIS package contains a 5 million scale
(source map resolution) vector thematic map of anomalous magnetic field (DT)a of Central Asia produced on
the basis of corresponding fragment of the Map of anomalous magnetic field (DT)a of Russia, former USSR territory and adjacent water areas, Epoch 1964.5 (middle 1965),
scale 1:5 000 000, Editor-in-Chief: T. P. Litvinova. St. Petersburg: VSEGEI, 2000. The latter was compiled on the
basis of materials obtained during the airborne magnetic
investigations at 1:200 000 and 1:1 000 000 scales carried
out in the 90s, and the map of normal magnetic field reduced to the epoch 1964.5.
Anomalous magnetic field thematic map consists of
two sub-layers: isolines and polygons colored in accordance with accepted worldwide standards for airborne
magnetic maps. Red color denotes negative values of
anomalous magnetic field on the map, whereas blue color
denotes positive values of anomalous magnetic field. Variations of anomalous magnetic field intensity are shown
on the map by color density. The following ranges of
anomalous magnetic field (DT)a intensity are utilized on
the map (in nT): < -500, -500, -300, -100, 0, +100, +300,
+500, +1000, > +1000.
6
Gravimetric thematic map
This part of the GIS package contains a 2.5 million scale
vector thematic map of gravimetric field of Central Asia
produced on the basis of corresponding fragments of the
Gravimetric map of the USSR, scale 1:2 500 000, intensity
(mgal), Bouguer reduction, reduced for the relief (r = 200
km), Helmert normal formula of 1901-1909, system of
the 1971, Eds. P. P. Stepanov & M. A. Yanushevich, Moscow: VNIIgeofizika and NPO Neftegeofizika, 1990. The
latter was compiled on the basis of materials obtained
during the gravimetric investigations, at 1:200 000 and
1:1 000 000 scales, carried out in the 1980s.
The gravimetric thematic map consists of two sub-layers: isolines and polygons colored in accordance with accepted worldwide standards for gravimetric maps. Green/
blue colors denote negative values of the gravimetric field
on the map whereas yellow/brown colors denote positive
values of the gravimetric field. Variations of gravimetric
field intensity are shown on the map by color density.
The following ranges of gravimetric field intensity are
utilized on the map (in mgal): < -450, -450, -425, -400, 375, -350, -325, -300, -275, -250, -225, -200, -175, -150, -125,
-100, -75, -50, -25, 0, +25, +50, +75, +100, +125, > +125.
Close
1334
R. Seltmann · V. Shatov · G. Guriev · A. Yakubchuk · A. Dolgopolova
Acknowledgements
This paper is a contribution to the IGCP-473 project on
“GIS Metallogeny of Central Asia”. Input of the many
project participants, ranging from individuals to institutions, and sponsorship mainly of IUGS-UNESCO
through its IGCP programme are highly appreciated. Irina
Gurieva, Valentina Belova and Kiril Mazurkevich of AllRussian Geological Research Institute (VSEGEI), St. Petersburg, Russia are especially thanked for the technical
support.
Contact information on the GIS package
The GIS Central Asia package is a product of the IGCP473 project (2002-2006). The GIS Central Asia can be obtained from the Natural History Museum, Department of
Mineralogy, CERCAMS (Centre for Russian and Central
Asian Mineral Studies), Cromwell Road, London SW7 5BD,
UK. Phone: +44 207 942-5042, Fax: +44 207 942-6012, Email: R.Seltmann@nhm.ac.uk, http://www.nhm.ac.uk/
mineralogy/cercams/index.htm
References
Afonichev N, Vlasov N (Eds.) (2002) Geological map of Central Asia,
scale 1: 1,500,000. St. Petersburg
Litvinova TP (Chief Editor) (2000) Map of anomalous magnetic field
(DT)a of Russia, former USSR territory and adjacent water areas, Epoch 1964.5 (middle 1965), scale 1:5,000,000. VSEGEI, St.
Petersburg
Stepanov PP, Yanushevich MA (Eds.) (1990) Gravimetric map of the
USSR, scale 1:2 500 000 intensity (mgal), Bouguer reduction, reduced for the relief (r = 200 km), Helmert normal formula of
1901-1909, system of the 1971. VNIIgeofizika and NPO Neftegeofizika, Moscow
Close
Chapter 12-12
12-12
Rare-earth element and noble gas studies of
Kuoerzhenkuola gold field, Xinjiang, China:
A mantle connection for mineralization
P. Shen, Y. Shen, T. Liu, G. Li, Q. Zeng
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Abstract. The Kuoerzhenkuola gold field is the most important one
in the Sawuer gold belt, in north Xinjiang. Rare-earth element studies reveal that the ore-forming fluids of two deposits were derived mainly from the mantle, with a minor component originating from another source. Helium isotope studies of fluid inclusions
in pyrites indicate 3He/4He ratios of 0.64 Ra to 4.25 Ra for the
Kuoerzhenkuola and 1.16 Ra to 5.08 Ra with two exceptions of
8.18 Ra and 9.48 Ra for the Buerkesidai. The data suggest that the
helium of the ore-forming fluids is mainly a mantle helium and
partially participation of meteoric water in the mineralization process, with the combined consideration of 40Ar/36Ar ratios. Based
on these, we propose that the genesis of the two gold deposits is
identical, being volcanogenic late-stage hydrothermal.
Keywords. Rare element, noble gas isotopes, metallogenic time,
Kuoerzhenkuola, Buerkesidai
1
Introduction
2
Deposit geology
The Sawuer gold belt is located in the transition belt between the Siberian plate and the Kazakhstan-Junggar plate,
the west section of the Sawur-Armantai island arc in the
south margin of the Siberia plate.
The regional strata of the study area include Sawuer
Formation of middle Devonian, Taerbahatai Formation
of upper Devonian, Heishantou Formation of Lower Carboniferous and Kalagang Formation of lower Permian.
The EW to NEE-trending deep faults are well developed
(Fig. 1). A series of EW-trending subsidiary faults of
Sawuer fault are main controlling faults.
The outcropping strata in the Kuoerzhenkuola field
are mainly Taerbahatai Formation and Heishantou Formation. For the first time, the authors have mapped the
volcanic lithofacies and structure and argue that a vol-
The Kuoerzhenkuola and Buerkesidai gold deposits are
the most important occurrences in the Sawur gold belt
located in the north-western margin of the Zhunggar
Basin, Xinjiang. The genesis of the two ore deposits has
been strongly debated and various models proposed. Most
researchers have inferred that the two gold deposits are
hosted in different strata and are of different genesis (Yin
et al. 2004; Wang et al. 2004; Guo et al. 1997; Li et al. 2000;
He et al. 1994).
The Kuoerzhenkuola epithermal gold deposit is hosted
in the Devonian Sawuershan group and gold formed by
near-surface hot spring activity.
The Buerkesidai gold deposit is hosted in the Heishantou group of Carboniferous age and can be classified into fractured and altered rock gold controlled by
host rocks and regional faults.
This paper examines rare-earth elements and noble
gases in pyrites with the aim to constrain sources of
ore fluids at Kuoerzhenkuola and Buerkesidai gold deposits, and to determine the geneses of the two important gold deposits. It is particularly of significance
to the genesis of volcanic-hosted ore deposits, deep
metallogenic precitions and exploration, both at the
two deposits and, by inference that these formed at the
same ore-forming condition throughout much of northern Xinjiang.
Close
1336
P. Shen · Y. Shen · T. Liu · G. Li · Q. Zeng
canic centre existed in the study area. We have divided
the volcanic-magmatic activity into six lithofacies (Fig. 1),
and propose the volcanic rocks in the two deposits were
formed in the same volcanic activityand may belong to
the same period. It deserves mentioning that the interbed
of carbonaceous siltstone occurs in near-surface andesite and andesitic lava breccia in the Buerkesidai has not
been discovered in the Kuoerzhenkuola deposit. The results suggest that the wall-rock in the two deposits belong to the same strata (Heishantou Formation). In addition, the andesites with Rb/Sr isochron age of 343 ± 22 Ma
(Kuoerzhenkuola) and 347 Ma (Buerkesidai) respectively,
belong to Early Carboniferous period.
The ring and radiating fracture system of the volcanic
centre are well developed in the study area, which is superimposed by the WE-trending faults. The fracture system constrains the pathway for transportation of goldbearing fluids and controls the distribution of orebodies
in the gold field. Mineralization is marked by altered wall
rocks, which occur along above-mentioned arc-shape fault
zones. Among these, orebody No. 1 and No. 2 are the largest ones (Fig. 1B, 1C). Individual ore-bearing veins are
commonly a few ten to a few hundred meters long, 0.5 to
5 m wide, and extend down dip for 300-700 m.
3
Rare-earth element geochemistry
The geochemistry of rare-earth elements (REE) has been
widely used to develop models of metallogenesis for various types of hydrothermal ore deposits (Campbell et al.
1984; Fryer and Taylor 1987; Plimer et al. 1991; Lottermoser
1992). Pyrite is a particularly suitable mineral for such
studies because it precipitates from hydrothermal oreforming systems simultaneously with the gold mineralization (Shen et al. 2004a). It is likely that pyrite records
and preserves primary information of rare-earth element
geochemistry of the ore-forming fluids.
The pyrites were sampled from orebody no. 1 in
Kuoerzhenkuola and Buerkesidai respectively. Moreover,
we analyzed whole rock samples from the Heishantou
Formation volcanic rocks to discriminate the relationship between mineralization and those rocks. The composition of volcanic rocks is basaltic to andesitic. The REE
compositions of pyrites and rocks were determined on a
ICP-MS in the Isotope Laboratory, Institute of Geology
and Geophysics, CAS. The analytic precision is typically
better than 5% for REE based on the reproducibility of
standards during the run.
Samples from the Kuoerzhenkuola deposit have average-high total REE contents (Σ REE; 21.4x10-6 to 81.9x106) and display light REE (LREE)- enriched and heavy REE
(HREE)-depleted patterns (Fig. 2a) with LREE/HREE=6.411.1, (La/Yb)N=4.8-11.6, (La/Sm)N = 4.3-8.7 and (Gd/Yb)N
= 1.3-3.1 accompanied by negative Eu anomalies with Eu/
Eu* = 0.2-0.6. Similarly, samples from the Buerkesidai
deposit have similar Σ REE abundances (27.6 × 10 -683.8 × 10-6) and show right slop REE patterns (Fig. 2b) with
LREE/HREE=3.5-3.8, (La/Yb)N=2.0-2.5, (La/Sm)N =2.53.5, (Gd/Yb)N = 0.9-1.4. They display negative Eu anomalies with Eu/Eu* = 0.2-0.3. All pyrites from the two deposits have no evident Ce anomalies (Ce/ Ce* = 0.94–
1.02 for Kuoerzhenkuola, 0.95–1.04 for Buerkesidai). Overall, all pyrites show the same variations in the absolute
REE abundances and in the chondrite-normalized patterns, indicating that the source of fluids from the two
deposits is the same.
All rocks have high Σ REE abundances (77.3 × 10-6–
122.7 × 10-6) and display LREE-enriched and HREE-flat
patterns (Fig. 2) with (La/Yb)N, (La/Sm)N and (Gd/Yb)N
ratios of 3.1-8.1, 2.14-3.8, and 0.9-1.4, respectively. They
display evident negative Eu anomalies with Eu/Eu* = 0.20.32 and evident positive Ce anomalies (Ce/Ce* = 2.963.53). The host rock REE patterns remain roughly the same
with all pyrites in this area, implying that both ore-forming fluids and hosted volcanic rocks were derived from
the same source (i.e., upper mantle).
Some authors have concluded that REE are immobile
during hydrothermal processes (Bence and Taylor 1985;
Maclean 1988), but there is also evidence that Eu and LREE
preferentially fractionate into hydrothermal fluids (Plimer
et al. 1991; Slack et al. 1993; Slack 1996). Results indicate
Close
Chapter 12-12 · Rare-earth element and noble gas studies of Kuoerzhenkuola gold field, Xinjiang, China: A mantle connection for mineralization
that HREE are largely unaffected by hydrothermal processes (Jing et al.,2004). If the HREE contents in the oreforming fluids change during hydrothermal processes, it
may imply the different sources of hydrothermal fluids.
The pyrites from the two gold deposits display lower
Σ REE contents (including LREE and HREE) than the host
volcanic rocks in the area. The results indicate that HREE
contents in pyrites are changed except for LREE. The REE
systems of ore-forming fluids, therefore, may be affected
by the different sources of hydrothermal fluids, that is, a
certain amount of other sources fluids is involved in oreforming fluids except for volcanic late stage fluids during
hydrothermal processes. As mentioned above, the
orebodies in the two deposits occur in the fracture system of volcanic centre superposed by the regional fault,
implying that the ore-forming setting may be a “semiopen system”. In this situation, the hydrothermal fluids
derived from the other different sources may be input
the ore-forming fluids. Considering the geological conditions during ore-formation, it is likely that a certain
amount of water was involved the in ore-forming fluids
system except for volcanic late stage fluids. If minor water with low REE content was drawn into the ore-forming
system during hydrothermal processes, the Σ REE contents of the ore-forming fluids could be lower, but the
REE patterns of ore-forming would remain the same.
4
Noble gas isotopes of fluid inclusions
As suggested by Ozima and Podosek (1983), isotopes of
noble gases, particularly He and Ar may be valuable discriminators between fluids of mantle verses crustal versus meteoric origins. Helium isotope composition have
been extensively used as extremely sensitive tracers, given
that depleted upper mantle 3He/4He ratios of 6 to 9 Ra
(Ra=atmospheric ratio) and deep mantle plume-derived
ratios of 9-32 Ra are very distinct from both the atmospheric
ratio (1.0) and ratios of shallow crustal (0.01-0.05 Ra) hydrothermal fluids (Stuart et al. 1995; Harrison et al. 1999;
Trieloff et al. 2000; Matsumoto et al. 2002; Finlay et al. 2003).
Pyrite is known to be a suitable trap for noble gases
(Stuart et al. 1994; Baptiste and Fouquet 1996; Burnard
et al. 1999) because it retains helium over geologic periods in contrast to quartz and feldspar (Hu et al. 1997;
Kendrick et al. 2002). We have chosen 13 samples from
orebodies 1 in Kuoerzhenkuola and Buerkesidai respectively (Shen et al. 2004b) for study of noble gas isotopes
in the trapped inclusion fluids. In this study we selected
another 5 samples. Isotopic compositions were measured
on MI-1201IG inert gas mass spectrometer at the Isotope
Laboratory, Institute of Mineral Resources, Chinese Academy of Geological Sciences.
The helium and argon isotope compositions were analyzed by bulk extraction of fluids using the invacuo crushing method. The related studies (Burnard et al. 1999;
1337
Matsumoto et al. 2001) show that if selecting the crushing extraction technique, most of radiogenic helium and
argon are retentive in the lattice location of U, Th and K,
this method can reduce the effects from in situ-produce
radiogenic isotopes and adsorbed atmospheric gases overcoming problems due to the low blank. The analytical
precision was 1%.
Previous researchers found that post-entrapment processes of ancient fluids formed in Yanshan and Himalayan periods did not modify greatly He and Ar primordial isotope compositions (Simmons et al. 1987; Hu et al.
1998; Stuart et al. 1995) after being trapped. The authors
assessed post-mineralization modifications to these isotopes of 13 pyrites of 334Ma age and argued that these
processes have negligible effect on He and Ar primordial
isotope compositions (Shen et al., 2004b). In this study
we reached the same conclusion by calculating 6 pyrites.
The results show that He and Ar isotopes can be used to
trace origins of ore-forming fluids formed in the
Hercynian period.
The 3He/4He ratios of fluid inclusions in pyrites from
Kuoerzhenkuola gold deposit range from 0.64 Ra to 4.25
Ra, all significantly higher than crustal value (0.01-0.05Ra)
and close to the mantle typical value (6-9Ra). 3He/4He ratios of fluid inclusions from samples of Buerkesidai gold
deposits range from 1.16 Ra to 5.08 Ra, being close to
mantle 3He/4He ratios, except that two samples have values up to 8.18 Ra and 9.48 Ra, which are consistent with
the mid-ocean ridge basalt (MORB) 3He/4He ratio. Ore
fluids in both main orebodies in the Kuoerzhenkuola deposit and Buerkesidai deposit are markedly enriched in
3He relative to typical crustal values. Their 3He/4He ratio
is at least 13 to 149 times, at most is 65 to 745 times higher
than that of fluids typical of a crustal origin, which requires helium input from a mantle source into the ore
fluids.
The REE data mentioned above imply that the sources
of ore-forming fluids have a mainly magmatic source. The
Close
1338
P. Shen · Y. Shen · T. Liu · G. Li · Q. Zeng
noble gas data allow us to further evaluate and discriminate these possible fluid sources. As shown by the results
of helium isotope analyses, the ore fluids in the two deposits must contain a mantle component. Assuming pure
mantle helium to have a value of 8 Ra (Tolstikhin 1978),
fluid inclusions in pyrite from Kuoerzhenkuola would
contain approximately 8% to 53% mantle helium, whereas
the proportion in Buerkesidai would be 14% to 64%. However, as was suggested by Kendrick et al. (2001), these values are probably minimum estimates for the original fluids because crustal contamination and magmatic aging
may lower the Ra value for mantle melts.
The 3He/4He and 40Ar/36Ar ratios of fluid inclusions in
pyrite from the deposits are between mantle- and meteoric
water-derived fluid ratios, being considerably higher than
helium produced in the continental crust (Fig. 3). The result indicates some participation of meteoric water, rather
than crust fluids in the mineralization process. It is importantly that a way can be found to estimate the presence of
significant amounts of mantle helium in the ore-forming
fluids and identify meteoric water-derived fluid.
5
Genesis of the two deposits
REE of pyrites and noble gas isotopic studies show that
the ore-forming fluids of in the two deposits derived from
the same source, that is, mainly from the mantle, and partially from meteoric water. Moreover, we adopted the ArAr isochron method of dating fluid inclusions in quartz
to determine the age of ores that are 332.05 Ma - 332.59
Ma in Kuoerzhenkuola and 335.53–336.78 Ma in
Buerkesidai, respectively. The results indicate that the ages
of the two deposits are agreeable and similar to those of
the host rocks (343-347Ma), indicating both of deposits
and host rocks are formed by the same geological event,
namely volcanic activity.
Based on these results, it is not difficult to propose that
the genesis of the two gold deposits is identical, being
volcanogenic late-stage hydrothermal.
References
Lottermoser BG (1992) Rare earth elements and hydrothermal ore
formation processes. Ore Geol. Rev. 7: 25- 41
Boynton WV (1984) Geochemistry of the rare earth elements: meteorite studies. In: Henderson, P. (Ed.), Rare Earth Element
Geochemistry. Elsevier 63- 114
Ozima M, Podosek FA (1983) Rare Gas Geochemistry, Cambridge:
Cambridge Univ. Press 276
Finlay M, Solveigh LE, Godfrey J (2003) High 3He/4He ratios in
picrictic basalts from Bsffin Island and the role of a mixed reservoir in mantle plumes. Nature 424: 57-59
Trieloff M, Kunz J, Clague DA (2000) The nature of pristine noble
gases in mantle plumes. Science 288: 1036-1038
Poreda R, Craig H (1989) Helium isotope ratios in circum- Pacific
volcanic arcs. Nature 338: 473-478
Turner G, Stuart F (1992) Helium/heat ratios and deposition temperatures of sulfides from the ocean floor. Nature 357: 581-583
Shen P, Shen Y, Zeng Q et al. (2004b) Helium and argon isotope trace
in ore-forming fluid of Sawuer gold belt in Xinjiang, China. Chinese Science Bulletin 49(13): 1408-1414
Close
Chapter 12-13
12-13
Genesis of volcanic-hosted gold deposits in
West Junggar, NW China
Y. Shen, P. Shen, T. Liu, G. Li, Q. Zeng
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Abstract. Volcanic rocks and a series of volanic-hosted gold deposits are well-developed in West Junggar, which comprises the Sawuer
gold belt in the north and the Hatu gold belt in the centre-south. A
volcanic centre existed in the two gold belts, with volcanic lithofacies
and fracture systems of volcanic association controlling the formation and distribution of orebodies. Isotopic studies including D, O
and S reveal that the ore-forming fluids of three deposits derived
mainly from magmatic water, partially from meteoric water; and
sulfur derived from mantle beneath the island arc and back-arc. 40Ar39Ar dating constrains the metallogenic time of the deposits which
is close to the age of the hosting rocks. These formed via volcanic
activity in the Sawur and Hatu gold belts. Based on these results,
with combined consideration of the tectonic setting and geological features, it is possible to propose that the genesis of the gold
deposits in west Junggar is volcanogenic late-stage hydrothermal.
Keywords. Hosting volcanic lithofacies, stable isotopes, metallogenic
time, gold deposits, west Junggar
1
Introduction
The suite of intermediate-basic volcanic lava, pyroclastic
rocks and sedimentary rocks of Devonian-Carboniferous
is well-developed in the west Junggar. Calc-alkaline volcanic
rock series formed in island arc localities in the north of
the west Junggar, whereas tholeiite series formed in back
arc setting in the centre-south of west Junggar. Many gold
deposits and about 70 gold occurrences are distributed in
the above-mentioned volcanic rocks, and comprise the
Sawuer gold belt in the north and the Hatu gold belt in the
centre-south (Shen et al. 1993, 2001). As a result, the west
Junggar has become one of the largest gold centres in the
region. The Kuoerzhenkuola gold field including
Kuoerzhenkuola the gold deposit and Buerkesidai gold deposit, and the Hatu gold field including Hatu gold deposit
are the most important gold fields in the west Junggar.
This paper mainly studies volcanic lithofacies and isotopic characteristics of gold deposits hosted in volcanic
rocks in the west Junggar. In addition, ore-forming ages
of those gold deposits were determined using Ar-Ar isochron methods. As a result, the genesis of those gold deposits in the west Junggar has been identified.
2
leozoic island arc and back-arc adjoining the Siberian plate
in the north and the Tarim plate in the south. The Sawuer
gold belt is situated in the west section of the SawurArmantai island arc (Fig. 1). The Hatu gold belt is located
in the middle section of the back-arc basin (Fig. 1).
The regional stratae of the Sawuer gold belt include
Sawuer Formation of middle Devonian, Taerbahatai Formation of upper Devonian, and Heishantou Formation
of lower Carboniferous, which are characterized by typical island arc assemblage. The regional stratae of the Hatu
gold belt are simply the Tailegula Formation and Baogutu
Formation of Lower Carboniferous, which belong to typical back-arc basin assemblage.
The EW to NEE-trending deep faults are well developed in the Sawuer gold belt, including the Sawuer arcshape fault and the Kalataolegai fault. A series of EWtrending subsidiary faults of the regional Sawuer fault are
the main controlling faults, such as Buerkesidai fault and
Kuoerzhenkuola fault. The NE 50° striking Dalabute fault
is the main fault in the Hatu gold belt. The well-developed subsidiary faults of the Dalabute fault, such Anqi
fault and Hatu fault control the distribution of gold deposits in the Hatu gold belt. Frequent magmatic activities are characteristic of massive invasion of late Hercynian
intermediate-acid intrusive.
Geological setting
The west Junggar is located in the middle section of the
Kazakhstan-Junggar plate, which comprises a typical Pa-
Close
1340
Y. Shen · P. Shen · T. Liu · G. Li · Q. Zeng
3
Hosting volcanic lithofacies and mineralization
Outcropping strata in the Kuoerzhenkuola gold field in
the Sawuer gold belt are Taerbahatai Formation of Upper
Devonian and Heishantou Formation of Lower Carboniferous. For the first time, the authors have mapped the volcanic lithofacies and structure within regional 50 km2, examined 247 thin sections selected from surface exposures
and drill core of 9 medium-deep drill holes. Based on these
results, we argue that a volcanic centre existed in the study
area, and divided the volcanic-magmatic activity into six
lithofacies, including crater explosive phase (andesitic lava
breccia), crater overflow phase (andesite), nearly crater explosive phase (andesitic tuff breccia and andesitic tuff),
nearly crater overflow phase (andesite), crater sedimentary
phase (tuffite) and dacitic cryptoexplosion breccia. The
volcanic rocks in the two deposits are formed during the
same volcanic activity and may belong to the same period
(Heishantou Formation of lower Carboniferous). The
hosting volcanic lithofacies include crater overflow phase
(andesite), nearly crater explosive phase (andesitic tuff)
and minor carbonaceous siltstone formed in intermittent
period of eruption.
The fracture system of the volcanic centre is well developed in the Kuoerzhenkuola gold field, which is superimposed by the WE-trending faults. The superimposed
fracture system constraints the pathway for transportation of gold-bearing fluids and controls the distribution
of the orebodies (arc-shape) in the gold field. Mineralization is marked by altered wall rocks, which occur along
above-mentioned arc-shape fault zones. Individual orebearing veins are commonly a few ten to a few hundred
meters long, 0.5 to 5 m wide, and extend downdip 500700 m.
The authors investigated the volcanic lithofacies and
structure of the Hatu deposit and believe that a volcanic
apparatus existed in the Hatu area. We divided the volcanic-magmatic activity into three lithofacies, including
neck phase (diabase), crater overflow-eruption phase (basalt and basaltic tuff), crater explosive phase (basaltic lava
breccia) and crater sedimentary phase (tuffite) and minor tuffaceous siltstone. The orebodies occur in all types
of volcanic lithofacies, such as neck phase, crater overflow-eruption phase and crater explosive phase. The hosting rocks are basaltic lava breccia, basalt, basaltic tuff,
tuffite and diabase.
The fracture system of the volcanic centre is also well
developed in the Hatu deposit, which has been overprinted
by the NEE-trending Anqi fault. Mineralization is marked
by auriferous quartz veins, which occur along above-mentioned arc-shape fault zones. Individual ore-bearing veins
are commonly a few ten to a few hundred meters long,
0.5 to 4 m wide, and extend downdip 500 m. The distribution of ore bodies is featured by being deep buried or
at depth, being blind and dipping to the west.
4
Stable isotopes
4.1 Hydrogen and oxygen isotopes
The O and H isotope compositions of hydrothermal minerals in ore deposits help to trace the origin(s) of the hydrothermal water. In this study, we sample the typical quartz
in ores of main stages from Kuoerzhenkuola deposit,
Buerkesidai deposit and Hatu deposit, respectively.
The δ18O values of the mineralizing fluids in main oreforming stage range from 1.8‰ to 3.2‰ (Kuoerzhenkuola)
and from 4.9‰ to 5.6‰ (Buerkesidai), the δD values range
from -84‰ to -89‰ (Kuoerzhenkuola) and from -97‰ to
-98‰ (Buerkesidai) in Sawuer gold belt. Similarly, the δ18O
values of the ore-forming fluids range from 6.0‰ to 11.7‰,
the δD values range from -86‰~-111‰ in Hatu deposit
of Hatu gold belt. These data are slightly less than those
of magmatic water (Ohmoto et al., 1986). On a δD vs. δ18O
diagram (Fig. 2), the δD and δ18O values of the main mineralizing stage plot low-left outside of metamorphic and
magmatic water boxes.
Based on these results, ore-forming fluids in west
Junggar are not typical magmatic waters instead represent a mixture of meteoric water and magmatic hydrothermal solutions.
Taylor (1974) suggested that the “δ18O shift” resulted
from the equilibrium exchange of oxygen isotopes between meteoritic water and wall rock or mixing of different original waters. In west Junggar, the δ18O values of
the hosting intermediate volcanic rocks (andesite and
basalt) range from 5.5‰ to 7.4‰, and agree with the δ18O
values of meteoritic water (5.5‰~9.5‰, Ohmoto et al.
1986). When the ore-forming fluids enter the volcanic
rocks, as a result, the exchange reaction of δ18O cause no
significant change in ore-forming fluids. It is common
that volcanic rock mass develops the hydrothermal cycle
system of groundwater in the near-surface, particularly
in the volcanic rocks with well developed fractures
(Roedder 1984). Therefore, the authors consider that the
mixing of meteoric water may be the main reason of the
“δ18O shift” in the ore-forming fluids.
Because there is a strong fractionation of H isotopes
during early magma degassing (Taylor, 1986), the lateformed hydroxyl-bearing igneous minerals represent the
isotopic composition of a degassed melt rather than that
of the initial magmatic water (Fig. 2; open arrows; Jeffrey
1994). It is not difficult to extrapolate that hydrothermal
minerals formed in volcanogenic late-stage may show
lighter H-isotope composition than the degassed melt. This
may result in the lower δD values of quartz in the three
deposits than that of the initial magmatic water in andesites and basalts in west Junggar. Besides, δD of Mesozoic
meteoric water in the region is -90‰ (Zhang et al. 1995),
which may be one of the factors causing the lower δD
values of quartzes in the three deposits.
Close
Chapter 12-13 · Genesis of volcanic-hosted gold deposits in West Junggar, NW China
5
4.2 Sulfur isotopes
In Sawuer gold belt, 17 δ34S values from the Kuoerzhenkuola
deposit range from 0.32‰ to 2.44‰ with average of 0.92‰,
9 δ34S values from Buerkesidai vary from 0.44‰ to 2.85‰,
averaging 1.85‰. In Hatu gold belt, 32 δ34S values from
the Hatu deposit range from -0.1‰ to 2.7‰ with average of 1.2‰.
The values of δ34S of deposited pyrite are assumed to
represent that of total S of the ore-forming fluid (Ohmoto
1972; Ohmoto and Rye 1979). Therefore, we obtain δ34S
of the hydrothermal fluid system in the three deposits.
These data show a very narrow range and close to zero
values, and similar to that of the meteorite, reflecting that
the sulfur in ore-forming fluids is derived from
unfractionated mantle sulfur (Hoefs 1987).
4.3 The ages of ore formation and volcanic rocks
We carried out 40Ar-39Ar age dating on fluid inclusions in
quartz in the ore bodies from the Sawur gold belt and the
Hatu gold belt, west Junggar. The ages of the Ar-Ar dating show the ages of the deposits of 332.05 ± 2.02 Ma
~332.59 ± 0.51 Ma in the Kuoerzhenkuola deposit that
agree with Rb/Sr isochron age of 341± 30 Ma in quartz
by Li (2000), 335.53 ± 0.32 Ma~336.78 ± 0.50 Ma in
Buerkesidai deposit, and 308.6Ma~341.6Ma in Hatu, respectively, indicating that the ages of the three deposits
are agreeable, and belong to early Carboniferous.
The andesites, with Rb/Sr isochron age of 343 ± 22 Ma
(Kuoerzhenkuola) (Liu et al. 2003) and 347 Ma (Buerkesidai)
(He et al. 1994) respectively. Besides that, the basalt in the
Hatu gold deposit belong to Early Carboniferous period.
Therefore, the metallogenic times of the three deposits
are close to those of the hosting rocks formed by volcanic activity of the Sawur gold belt and the Hatu gold belt
in west Junggar.
1341
Proposed mineralization model
The Sawuer gold belt and Hatu gold belt in west Junggar
are located in the island arc and back-arc tectonic regime,
respectively, and both of them belong to covergent plate
margins. Sawkins (1990) believe that this is the tectonic
setting where most magma-related hydrothermal ore deposits are concentrated. Experimental and modeling studies have shown that magmas contribute components such
as the water, metals and ligands to hydrothermal fluids
(Sillitoe 1989; Hedenquist and Lowenstern 1994). Furthermore, the flux of metals measured from some erupting
volcanoes indicates that, given sufficient time and a concentration mechanism, degassing magmas can exsolve
sufficient metals to create an ore deposit (Jeffrey 1994).
For example, White Island, New Zealand is an arc-related
volcano with an associated hydrothermal system that has
been active for at least the past 10,000 yr. The long-term
Cu flux is 110 t/yr (with > 350 kg/yr Au). The volcanism
is active well in west Junggar (including arc and backarc), therefore, a potential magmatic fluid phase has developed and is likely to contribute to the Au–Cu mineralization during eruption and crystallization of the andesitic and basaltic melts.
The O- and H-isotope compositions of quartzes in three
gold deposits constraint the sources of the water of the
ore-forming fluids, which derived mainly from magmatic
hydrothermal solutions experienced early degassing and
incorporated by meteoric water. The S-isotope compositions of pyrites from the three gold deposits in west
Junggar suggest that the bulk of the S was derived from
unfractionated mantle sulfur. Besides, the 3He/4He ratios
of fluid inclusions in pyrite from the Sawuer gold belt
identify that the helium was derived mainly from mantle
helium (Shen et al. 2004). The ages of the Ar-Ar dating
show that the metallogenic time of the three deposits are
close to that of the volcanic rocks in west Junggar. Those
results indicate that a potential magmatic fluid phase including metals has developed during island arc and backarc volcanic activity and are likely to contribute to the Au
mineralization. The three gold deposits occur in volcanic
centres, where the distribution of orebodies are controlled
by the volcanic lithosfacies and fracture system of volcanic centres. The vertical extension of the ore bodies is
more intensive than their horizontal extension, which is
typical for volcanic-hosted gold deposits.
By virtue of the results of geological and geochemical
studies, it is not difficult to conclude that there are necessary origin relations between the mineralization and their
host volcanic rocks. Therefore, we propose that the Kuoerzhenkuola deposit, Buerkesidai deposit in Sawuer gold belt
and Hatu deposit in Hatu gold belt posses the same genesis, and belong to volcanogenic late-stage hydrothermal
gold deposits. The drilling carried out in 2004 have confirmed the law and genesis of the deposits mentioned above.
Close
1342
Y. Shen · P. Shen · T. Liu · G. Li · Q. Zeng
Based on the above study, the mineralization model of
volcanogenic late-stage hydrothermal gold deposits can
be inferred as follows. The gold deposits are located in
strong tectonic and volcanic regime, such as convergent
plate margins. The magmatic fluid including metals and
ligand condensed gradually and formed the ore-forming
fluids during eruption and crystallization of volcanic melts,
which migrated to the near-surface through fissure channels of the volcanic centre, mixed with the infiltration
meteoric water, and deposited in available spaces. This
model is particularly significant to identify the genesis
of volcanic-hosted ore deposits, deep metallogenic predictions and exploration, both for gold deposits of the
west Junggar and, by inference, those formed at the same
ore-forming condition throughout much of northern
Xinjiang.
References
He BC, Tan KR, Wu QH (1994) Ages and Sr, Nd isotopic evidences of
mantle source magmatate in the Bu’s gold deposit, Jimunai county,
Northern Xinjiang (in Chinese). Geotectonica et Metallogenia.
18(3): 219-228
Hedenquist JW, Jacob BL (1994) The role of magmas in the formation of hydrothermal ore deposits. Nature 370 (18): 519-527
Hedenquist JW, Lowenstern JB (1994) The role of magmas in the
formation of hydrothermal lore deposits. Nature 370: 519-527
Hoefs J (1987) Stable Isotope Geochemistry. 3rd ed. Spring, Berlin:1–250
Li HQ, Cheng FW, Cai H (2000) Study on chronology of the Buerkesidai
gold deposit in northwestern margin of the Jungger basin(in Chinese). Geology and Mineral Resources of South China 4: 15-18
Liu GR, Long ZM, Chen QZ (2003) The formation age and geochemical characteristics of volcanic rock of Kuoerzhenkuolas gold mine
in Xinjiang(in Chinese). Xinjiang Geology 21(2): 177-180
Close
Chapter 12-14
12-14
Metallogenic characteristics of the Central Asia-type
orogenic zone in West China
Sun Baosheng, Wang Cheng, Zhang Jian
College of Rescource and Environment, Xinjiang University Urumqi, 830008 China
Abstract. The Altai-Tianshan-Kunlun mountains are situated in the
Eurasia hinterland, and represent the largest exposed districts of
a Paleozoic orogenic zone in the world. In recent years, research
has suggested that the Central Asian metallogenic province has
significant potential for mineral resources. The Central Asia
metallogenic province has diverse Paleozoic metallization and
particular metallogenic characteristics, which are distinguished
from the Circum Pacific metallogenic province and the Tethys
metallogenic province.
Keywords. Central Asian-type orogenic zone, metallogenesis, West
China
1
Introduction
Central Asia in this paper includes the mountain area of
Russian Altai, Western Mongolia, Northern and Western
Xinjiang, Central and Eastern Kazakhstan, Kirghizstan,
Tadzhikstan, Eastern Uzbekistan and Northeastern Afghanistan; together, these regions occupy about 3.6×106 km2.
This paper introduces regional metallogenic conditions
and regularities of some large to super-large precious
metal and nonferrous metal ore deposits, makes a comparison between regional tectonic and crustal evolution,
infrastructure of Xinjiang and Central Asia, points out
their metallogenic characteristics, and analyses the prospect of looking for large to super-large metallic ore deposits in some areas of Xinjiang.
3
Ore deposits formed during three large cycles: Precambrian, Caledonian and Variscan. The Variscan cycle is the
most important because of the many kinds of mineral
deposit types in it, whereas the other two cycles resulted
in just two kinds of mineral deposits: gold and iron, with
some copper, lead and zinc also recorded in some areas.
Devonian and Carboniferous are the most important
metallogenic periods for copper, lead, zinc and tin. Furthermore, mercury and antimony formed in the Permian
and gold formed in late Proterozoic era, late Ordovician
– early Silurian and late Carboniferous.
4
Main development stages and evolution of
geology and tectonics in Central Asia
According to a revised tectonic framework, the main development stage of geological tectonics in Central Asia
can be divided as follows:
A phase of nuclear area formation which ended by the
late Archaean (>3000~2600Ma).
A phase of primary platform formation that ended in
the early Proterozoic era (2600~1800Ma).
A phase of platform formation during the Proterozoic
(1800~800Ma).
A phase of continental marginal develop-ment and
ancient continental formation until the Permian
(800~250Ma).
A phase of continental interior development since the
Triassic.
Polycycle, polystage and polygene style of
mineralization in Central Asia
Large ore deposits appeared in different cycles and stages
from Pre-Cambrian to Variscan. In addition, many of them
went through several stages. In this area, polymetallic
mineralization occurred many times in late Proterozoic
and Caledonian cycles, made the high copper, lead and
zinc contents in the crust, and provided many metal
sources for Variscan cycle of mineralization. Therefore,
this is the major reason that large ore deposits such as
copper, lead, zinc were formed mainly in Variscan cycle.
5
2
Mineralization cycle and metallogenic period
The main characteristics of the Central Asian
metallogenic province
The Central Asian metallogenic province has several characteristics:
1. It is situated in the joint part between the Siberian and
Gondwana cratons. Some Paleozoic accretionary zones
and some microplates such as Kazakhstan-Junggar, Tarim,
Qaidam, which are localized between the Paleozoic accretionary zones, are composed of complicated tectonic province. Since the Mesozoic era, Circum Pacific subduction
and Indian plate subduction has had little influence on
the tectonic evolution of Central Asia, thus maintaining
its geological integrity and metallogenic characteristics.
2. The metallogenic era in the Central Asian province is
mainly late Paleozoic. However, in the Circum Pacific
zone and the Tethys zone, the metallogenic era is mainly
Cenozoic.
Close
1344
Sun Baosheng · Wang Cheng · Zhang Jian
3. The metallization in the Central Asia metallogenic
province has distinct characteristics. It extensively exhibits gold deposits in siliciclastic rock (Muruntautype) and strata-bound Sb-Hg deposits in clastic and
carbonate rock (the Central Asia Southern Tianshan
zone), whereas this metallization in the Circum Pacific
zone and Tethys zone is rare.
Furthermore, the Central Asian metallogenic province in the Paleozoic orogenic zone developed magmatic Cu-Ni deposits in the mafic and ultramafic rocks,
rare metal deposits in the granitic pegmatites, REE
deposits in the high-alkaline granite rocks, which composed suchsuper-large mineral deposits as Keketuohai,
Aerhalei, and Keqibulake. In other areas of the world,
these deposit types are mainly developed in Precambrian craton settings.
Porphyry copper deposits and continental volcanic gold deposits in the Central Asian metallogenic
province are of economic significance and their
metallogenic era is mainly Paleozoic, whereas in the
Circum Pacific zone and the Tethys zone, the peak era
for the formation of these deposits is Mesozoic and
Cenozoic.
4. The space-time distribution of the Central Asian
large metallogenic district is mainly related to the
accretionary zone of the continental margin (convergental zone), intracontinental tectonic rock zone,
intracontinental craton or continental margin rift,
craton and continental margin transition zone and
intracontinental uplift margin sediment. The superlarge deposits definitely have selectivity, limitation and the limited time to the metallogenic type as
follows:
– Continental volcanic type: A’xi gold deposits;
– Black shale system: Swayardon gold deposits;
– Porphyry type: Eastern Tianshan;
– Tectonic alteration rock type: Kanggurtage.
5. The formation and distribution of the Cen-tral Asian
large metallogenic district are controlled by the system of Basin-Mountain transformation. The spatial
distribution of large deposits is controlled by the Central Asian large linear tectonic obviously.
6. The statistic to the current inadequate infor-mation
shows that the Central Asian metallogenic province has
great potential for mineral resources:
– Gold deposits: there are 26 known super-large deposits with reserves of 13,842 tons.
– Copper deposits: 10 super-large deposits are known,
with reserves of 85.56 million tons.
– Rare metal deposits: Central Asia is an important
producer of rare metal deposits globally. Among
the super-large deposits in this area are Keketuohai,
Xingdoukuti, and Pasishuta.
– Pb-Zn deposits: the reserves of Pb and Zn in the
Central Asia are considerable.
6
Mineralization regularities of main metal
minerals in Xinjiang
All industrial ore deposits were formed during the
Variscan cycle except for some iron ore deposits that
formed in Pre-Cambrian.
The majority of ore deposits are distributed in Saysan,
Northeastern-Junggur, southern-Mongolia Variscan fold
system and neighboring inner and outer tectonic units.
Copper, lead, zinc and iron ore deposits of volcanic – sedimentary type are widespread in the inner zone and form
large deposits; within the outer tectonic zone are the A’xi
gold deposit, the largest one among Xinjiang, and the
Keketuohai rare metal deposit.
Concealed basement faults have important effect on controlling the distribution of ore deposits (or ore fields). Large
ore deposits are dominantly located near the intersection
of basement faults, or of basement faults with crustal faults.
South-North direction faults have special importance in
controlling large gold and copper deposits.
Mineralization settings can be divided into five types
according to the industrial degree of major known metal
ore deposits: geosyncline setting of the early stage of
Variscan cycle; tectonic-magmatic activiation setting of
Variscan cycle; postorogenic rift setting of Variscan cycle;
orogenic setting of Variscan cycle; Pre-Baikal crystalline
basement.
7
The main minerogenetic prospect provinces in
northern Xinjiang
We need to use the geological characters, mineralization
circumstances and mineralization regularities of some
famous ore deposits in Central Asia for reference purposes as well as considering potential of Xinjiang for predicting new deposits of precious metals and nonferrous
metals and specifically concentrating on looking for large
mineral deposits in Northern Xinjiang.
1. Altai minerogenetic prospect province of rare metal,
gold, copper (nickel), iron, lead and zinc.
2. The Southern margin of the Turfan-Hami basin and
the Kanggurtage-Huangshan minerogenetic prospect
province of iron, copper (nickel), gold, rare metal.
3. Boluohuolo-Awulale minerogenetic prospect province
of gold, lead, zinc, iron and copper
4. Hark moutain minerogenetic prospect province of
gold, copper (nickel) and tin.
5. Sawayarton minerogenetic prospect province of gold.
In the above five minerogenetic prospect provinces, the
main direction of attack on looking for large ore deposit
is as following: Altai and Asele copper-zinc deposit,
Duolanasyi-Tuokuzbayi gold deposit, Nuortkumasu gold,
lead, zinc, tin deposit, Halum-Qinhe lithium deposit;
Close
Chapter 12-14 · Metallogenic characteristics of the Central Asia-type orogenic zone in West China
Kanggurtage-Huangshan, Kanggurtage gold deposit, specifically the area with relatively wide distribution of LowerMiddle Carboniferous and well developed ductile shear
belt; Boluhulo-Awulale, Early-Carboniferous large volcanic
basin and well developed volcanic frame around A’xi gold
deposit, Sarim Lake which lies in the border of China and
Kazakhstan, Precambrian copper, lead, zinc deposit of
strata-bound; Hark, Kumtor-type gold deposit of Precambrian in Nalati fault belt of Middle Tianshan, Muruntautype gold deposit and Hark tin deposit in OrdovicianSilurian carbonaceous formation and tectonic development area; Sawayarton, Sawayarton gold deposit and
Muruntau-type gold deposit in Ordovician-Silurian carbonaceous rock and tectonic development area from the
outer of Sawayarton to Hark Mountain.
8
Conclusions
The Central Asian orogens are characterized by a mosaic
structure of several late Paleozoic suture zones and multiple Pre-Cambrian blocks, coupling Mesozoic-Cenozoic
orogens and the basins. It is different not only from the
Alpine –Himalayan orogens, which formed via the collision of large continents, but also from the Andean mountains which resulted from subduction of an oceanic plate
beneath a large continental plate. The Central Asian
orogens represent a distinct type of orogenesis featured
by the amalgamation of multiple blocks such as Ili, Junggar
and Hami. The Hercynian orogenesis resulted in largescale mineralization in the Central Asia orogenic area.
This indicates that Xinjiang in China may play a more
important role for China with new mineral resources in
the twenty–first century. Porphyry copper deposits,
epithermal gold deposits and massive sulfide polymetallic
deposits have been found in the Central Asian orogens,
e.g. the Kangguer gold deposits belt in Tianshan, the Qrqs
gold deposits, gold deposits in Altai (including five large
gold deposits).
The carbonaceous strata-bound type gold deposits
represented by the Muruntau deposits in Western
Tianshan and the Sawayarton in South Tianshan are the
most important gold reserves in Central Asia, and are of
1345
great economic significance in the Central Asian orogens.
However, the mineralization pattern and the metallogenic
mechanism of this type of gold deposits, as well as the
exploration direction are still unclear. The metallogenesis
during Central Asia orogenesis is a key to the development of continent geodynamics and regional metallogens.
Acknowledgements
This research was sponsored by the National Nature
Science Foundation of China (No. 49862002), 973 Program (No. 2001CB409809) and Xinjiang program (No.
XJEDU2004107).
References
Chen YJ (2000) Progress in the study of central Asia-type orogenesis-metallogenesis in Northwest China. Geological Journal of
China Universities 6(1): 17-22
Feng J, Wang QM (2001) Geochemical Characteristics and appraise
indicator of Ashele Cu-Zn deposits in Xinjiang. Xinjiang Geology 19(3): 124-179
Mao JW, Hua RM, Li XB (1999) A preliminary study of large-scale
metallogenesis and large clusters of mineral deposits. Mineral
Deposits 18(4): 292-299
Rui ZY, Liu YL, Wang LS, Wang YT (2002) The Eastern Tianshan porphyry copper belt in Xinjiang and its tectonic framework. Acta
Geologica Sinica 76(1): 63-94
Shi YS, Lu HF, Jia D, Chen CX, Cai DS, Wu SM (1996) Origin and
evolution of tectonics in central Asia. Geological Journal of Universities 2(2): 134-145
Sillitoe RH (1997) Characteristics and controls of the largest porphyry Cu-Au and epithermal Au deposits in the Circum-Pacific
region. Australian Jour. of Earth Sciences 44: 373-388
Teng YG, Zhang CJ, Ni SJ (1999) Elemental geochemical marks of
ore-forming fluid activities in A’xi gold deposits. Xinjiang Geology 14(2): 30-42
Tu GZ (1999) On the Central Asia metallogenic Province. Scientia
Geologica Sinica 34(4): 397-404
Wei HM, Wu WK, Xue CJ (1999) Metallogenic series and their formation and evolution in Western Tianshan, Xinjiang. Acta
Geologica Sinica 73(3): 219-230
Yang YQ, Fang JZ, Chen LH (2000) Comprehensive information ore
–searching model and metallogenic prediction for Cu-Ni ore in
Altay, Xinjiang. Journal of Changchun University of Science and
Technology 30(2): 158-160
Close
Close
Chapter 12-15
12-15
Strike-slip fault controls on mineralization in the
Kanggurtag gold belt in the Eastern Tianshan, Xinjiang,
NW China
Y.T. Wang, J.W. Mao
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China
W. Chen
Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China
J.M. Yang, Z.L. Wang, F.Q. Yang
Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China
Abstract. The Kanggurtag gold belt is located in the eastern Tianshan
Late Paleozoic orogenic belt, where three types of gold deposit are
developed on the south margin of an east-west-trending ductile shear
zone. From a tectonic point of view, we suggest that gold mineralization is dominantly controlled by post-collisional dextral strike-slip
faults, and gold resources are the product of the same metallogenetic
event in the Late Carboniferous-Early Permian. The spatial distribution of different types of gold deposits is restricted to different strain
distribution along the shear zone. This proposed structural model
has important implications for further exploration in this belt.
Keywords. Tectonic control, strike-slip fault, post-collisional, mineralization, Kanggurtag gold belt, eastern Tianshan
1
Introduction
The eastern Tianshan is located in east Xinjiang, NW China,
where a number of gold deposits and occurrences have been
found since the end of the 1980s. Most of the gold deposits
are distributed within an east-west-trending, 120 km long
shear zone, making up the Kanggurtag gold belt, which is
expected to be a promising gold province with a great gold
potential in Xinjiang. From a tectonic point of view, we suggest a structural model of gold mineralization based on the
available data and previous work in an attempt to understand the metallogenic mechanism more comprehensively
and help further exploration in this area.
2
1994), Aqishan-Yamansu island arc, and Early Paleozoic
Central Tianshan massif.
The Tuwu-Harlike island arc comprises a Lower Carboniferous suite. The outcropping strata in the Qiugemingtashi-Huangshan belt are Carboniferous rocks composed
of turbidite greywacke with features of gravity flows, dark
gray tuff, lithic sandstone, and siliceous rocks, which have
undergone strong deformation to form a huge ductile shear
zone, where most of gold deposits are developed. The Lower
Carboniferous suite crops out in the Aqishan-Yamansu island arc. The Central Tianshan massif is mainly composed
of Mesoproterozoic strata.
Volcanic rocks and intrusive rocks are well developed
to form the east-west-trending magmatic rock belt in the
eastern Tianhsan. The volcanic rocks consist of basalt,
basaltic andesite, andesite, rhyolite, and pyroclastic rocks,
and the island arc-type calc-alkali volcanic rocks are much
better developed. The intrusive rocks are exposed extensively as batholiths, stocks, and dikes, and Variscan granitoid bodies are the dominant intrusions (Fig. 1), which
are closely related to gold mineralization.
Geological setting
Located in the central part of the eastern Tianshan, the
Kanggurtag gold belt is tectonically a Late Paleozoic orogenic belt resulting from convergence and collision of the
Tarim plate in the south and the Kazakhstan-Junggar plate
in the north. Three major nearly east-west-trending faults
outline the tectonic framework (Fig. 1) and divide the eastern Tianshan into four tectonic units. From north to south,
these are the Tuwu-Harlike island arc, QiugemingtashiHuangshan trench (Ji et al. 1997) or restricted oceanic basin which closed in the Late Carboniferous (Zhou et al.
Close
1348
Y.T. Wang · J.W. Mao · W. Chen · J.M. Yang · Z.L. Wang · F.Q. Yang
3
Nature of gold mineralization
Three types of shear zone-hosted, epithermal and intrusion-related gold deposits are developed in the eastern
Tianshan, which are mainly distributed on the south margin of the Qiugemingtashi-Huangshan ductile shear zone.
The shear zone-hosted deposits mainly include Kanggur,
Matoutan, Hongshi, Dadonggou, etc.; Shiyingtan is the
only epithermal deposit; Xifengshan and Xiaojianshan
occurrences are of intrusion-related type (Fig. 1).
The shear zone-hosted gold deposit, located in the central part of the belt, contains the most important gold
resource in this area. In the Kanggur gold district, the
strong deformation belts and weak deformation areas
make up the structural framework. Several ENE-trending brittle-ductile shear belts, the second-order faults of
the Yamansu-Kushui fault, host the orebodies. The shear
system controls the attitude, shape, size and distribution
of the orebodies (Wang et al. 2003). The isotopic compositions (Zhang et al. 2003; Wang et al. 2004) indicate that
ore-forming fluids originated from the deep-seated source.
In the light of development of the synkinematic granitoids
in the Yamansu-Kushui fault belt, it appears that the
magmatism is related to shear melting, which can also
produce dynamometamorphic fluids.
The Shiyingtan gold deposit, located in the western
part of the gold belt (Fig. 1), is an adularia-sericite
epithermal deposit (Ji et al. 1999). The host rocks are
andesitic-dacitic rocks and volcanic breccia and their
subvolcanic equivalents. There a Permian volcanic edifice in the vicinity of Shiyingtan and orebodies are basically subjected to the dual control of the fracture system
of the volcanic edifices and regional faults, mainly developing along a set of tensile faults. The ore is of low sulfide
type, which fills in the fissures within the microcrystalline quartz veins. H and O isotope data (Ji et al. 1999)
show that the ore-forming fluids are dominantly meteoric water.
The intrusion-related gold deposits (occurrences) are
developed in the east part of the belt. The orebodies, sulfide-bearing quartz veins, are mainly controlled by a set
of tensile fractures, and the host rocks are mostly granitic rocks. The gold occurrence is small in size, but high
in gold grade with an average of 10-15 g/t. The gold mineralization is related to the magmatic hydrothermal system (Ji et al. 1997; Mao et al. 2002).
4
Discussion
Microthermometric measurements and H and O isotopic compositions of fluid inclusions show that from the
intrusion-related type through shear zone-hosted type
to epithermal type, the temperature, depth, and salinity
of gold deposits decrease, and that the ore-forming fluids change gradually from dominantly magmatic (and
metamorphic) hydrothermal fluids to fluids with a significant meteoric water component (Ji et al, 1997; Mao et
al. 2002; Zhang et al. 2003; Wang et al. 2004). Sulfur isotope study shows that the sulfur in the gold metallogenic
system was mainly derived from the mantle or the great
depth of the Earth (Ji et al. 1994; Zhang et al. 2003). The
isotope geochronology study (Ji et al. 1997; Li et al. 1998;
Zhang et al. 2003) indicates that the ages of gold deposits
cluster between 290 and 250 Ma.
The previous work shows that the final collision between the Tarim plate and the Junggar plate occurred in
the Late Carboniferous (Ma et al. 1993; Ji et al. 1994; Qin
et al. 2000; Rui et al. 2002). The QiugemingtashiHuangshan belt experienced compressional deformation
in the early collisional stage and superposed deformation of late collisional and post-collisional dextral strikeslip faulting (Ma et al. 1993; Wang et al. 2002). The N-S
compressional regime disappeared after 276 Ma and the
dextral strike-slip movement occurred during 276-239 Ma
(Wang et al. 2002). Strain measurements indicate that the
amount of shear displacement is about 75-100 km (Li
1995; Yang et al. 1998). The ore-forming ages are consistent with the time of strike-slip movement, implying that
the gold mineralization in the belt is dominantly controlled
by post-collisional dextral strike-slip faults, which also
control the emplacement of voluminous granitic magma.
The strike-slip shear movement along the irregularly
curved fault can lead to convergence or divergence around
the bend, depending on the sense of motion and sense of
curvature (Woodcock and Fischer 1986). Concerning the
Yamansu-Kushui fault, the south margin of the Qiugemingtashi-Huangshan ductile shear zone, two bends occur at
Shiyingtan and Xifengshan (Fig. 1), and they are all the
releasing bends for the dextral strike-slip movement. The
deformation at the releasing bend can create sites of dilation for magmatism and hydrothermal fluid circulation.
Therefore, the epithermal and intrusion-related gold deposits developed in the extensional regime along the shear
system. As for the Kanggur and Matoutan deposits, where
the fault plane is more linear, shear deformation dominantly developed during the strike-slip movement, resulting in the formation of the shear zone-hosted gold resources.
5
Conclusions
In summary, the gold mineralization in the Kanggurtag
gold belt is dominantly controlled by post-collisional dextral strike-slip faulting and all the gold resources are the
product of the same metallogenic event in the Late Carboniferous-Early Permian. The spatial distribution of different types of gold resources is restricted to the different strain distribution along the strike of the shear zone.
The releasing bend site of the shear zone, where the second-order extensional structure develops, is favorable for
Close
Chapter 12-15 · Strike-slip fault controls on mineralization in the Kanggurtag gold belt in the Eastern Tianshan, Xinjiang, NW China
the epithermal and intrusion-related gold resources, and
the linear site, where the simple shear regime develops, is
favorable for the shear zone-hosted gold resource. This
proposed structural model of gold mineralization has
important implications for further exploration in this area.
Acknowledgements
This study was financially supported by projects of the
Major State Basic Research Program (2001CB409807 and
G1999043216).
References
Ji JS, Tao HX, Zeng ZR (1994) Geology and mineralization of the
Kangurtag gold belt in Eastern Tianshan. Beijing: Geological
Publishing House: 1-20
Ji JS, Xue CJ, Zeng ZR (1997) Studies on the Kanggurtag gold
belt in Eastern Tianshan, Xinjiang. Geological Review, 43:
69-77
Li HQ, Xie CF, Chang HL (1998) Study on metallogenetic chronology of nonferrous and precious metallic ore deposits in
north Xinjiang, China. Beijing: Geological Publishing House,
1-244
Li XF (1995) Deformation feature and evolution of the Kanggurtag ductile shear zone in east Xinjiang. Paper Collection
of the 3rd Symposium on Geology and Mineral Resources in
Tianshan, Xinjiang: 96-101
Ma RS, Wang CY, Ye SF (1993) Tectonic framework and crust
evolution of Eastern Tianshan. Nanjing: Nanjing University
Press, 1-202
1349
Mao JW, Yang JM, Wang ZL, Han CM, Ma TL (2002) Geological setting and metallogenic process of the copper-gold mineralization
in the East Tianshan. Internal Scientific Report: 1-289
Qin KZ (2000) Metallogenesis in Relation to Central-Asia Style Orogeny in the North Xinjiang. Institute of Geology and Geophysics,
Chinese Academy of Sciences, Postdoctoral Research Report
Rui ZY, Goldfarb RJ, Qiu Y (2002) Paleozoic-early Mesozoic gold deposits of the Xinjiang Autonomous Region, northwest China.
Mineral Deposita 37: 393-418
Wang YT, Mao JW, Wang ZL, Li HQ, Yang JM (2003) The Kanggur
and Matoutan gold deposits, eastern Tianshan, Xinjiang. In Mao
J W, Goldfarb R, Seltmann R, Wang D H, Xiao W J, Hart C. Eds.
Tectonic Evolution and Metallogeny of the Chinese Altay and
Tianshan. Natural History Museum, London: 217-282
Wang Y, Li JY, Li WQ (2002) 40Ar-39Ar chronological evidence of dextral shear and tectonic evolution of the eastern Tianshan orogenic belt. Xinjiang Geol 20: 315-320
Wang ZL, Jiang N, Wang YT, Mao JW, Yang JM (2004) Genesis of
Kanggur gold deposit in eastern Tianshan orogenic belt, NW
China: fluid inclusion and oxygen and hydrogen isotope constraints. Resource Geol 54: 177-185
Woodcock NH, Fischer M (1986) Strike-slip duplexes. J. of Structural Geology, 8: 725-735
Yang XK, Zhang LC, Ji JS (1998) Deformation characters of the
Qiumingtashi-Huangshan ductile shear zone in Eastern
Tianshan. J. of Xi’an Engineering University 20: 11-18
Zhang LC, Shen YC, Ji JS (2003) Characteristics and genesis of
Kanggur gold deposit in the eastern Tianshan mountains, NW
China: evidence from geology, isotope distribution and chronology. Ore Geol Rev 23: 71-90
Zhou JY, Mao YS, Huang ZX (1994) Volcano geology of the ancient
continental margin in Eastern Tianshan. Chengdu: Press of
Chengdu Science and Technology University: 1-280
Close
Close
Chapter 12-16
12-16
Lithochemical factors for paragenetic Cu-Ni sulfide
and vanadium-titanomagnetite deposits: A case
study from the Xiangshanxi deposit, Xinjiang, China
Wang Yuwang, Wang Jingbin, Wang Lijuan
Beijing Institute of Geology for Mineral Resources, Beijing 100012, China
Abstract. The Xiangshanxi deposit is a CNS and VTM paragenetic
deposit. Lithochemical indices and parameters of the hosting mafic-ultramafic rocks such as alkalinity (or alkaline contents), femic
ratio (FeO*/MgO) or mafic index (m/f ), magmatic acidity (αsi), calcalkaline enrichment index (calk/m), and oxygen and sulfur fugacity
all exhibit dualism and transitional feature of typical CNS deposits
and VTM deposits.
Keywords. Mafic-ultramafic rocks, copper-nickel sulfide, vanadic
titianomagnetite, transitional feature, Xiangshanxi
1
Introduction
Both copper-nickel sulfide (CNS) deposits and vanadic
titianomagnetite (VTM) deposits are related to mafic-ultramafic rocks and belong to the orthomagmatic mineral deposits bearing similar mineralization mechanism
(Wilemes 1989; Tang 1993, 1998). However, their host
mafic-ultramafic rocks can be clearly distinguished as
follows: CNS deposits are commonly hosted either in a
small rockmass (most CNS deposits in China, usually less
than 1.5km2) or in concentric ring complexes (most overseas CNS deposits), and the host rocks are characterized
by tholeiite to calc-alkalic series and ferruginous maficultramafic rocks with mafic index (m/f ratio) of 2.0 to 6.5
(Wu 1963). VTM deposits often occur in large layered intrusions, and the host rocks are characterized by alkali
basalt series and high-ferruginous mafic rocks with less
than 0.5 m/f ratio. Both CNS and VTM deposits can occur in one and/or adjacent tectonic zone as in case of
Bushveld deposit in South Africa and Panzhihua-Xichang
deposit in China, but they rarely coexist on one deposit.
The Xiangshanxi deposit in the Hami area of Xinjiang,
China, is an unusual case of CNS and VTM paragenetic
deposits. The main purpose of this paper is to identify
special conditions for the paragenetic deposits. The
geochemistry of host rocks will be studied in this paper,
which attempts to analyze the coexisting conditions of
the Xiangshanxi CNS-VTM deposits.
2
Outline of geology and deposits
The Xiangshanxi ore deposit is situated in the east section
of the Kangguertage orogenic belt of East Tianshan Mts.
The East Tianshan area, located in the south margin of the
Paleo-asiatic ocean (Junggar-Kazakhstan terranes), is a converged area of the Siberian plate and the Tarim plate.
The Xiangshanxi rockmass is 4250 m long and 100870 m wide with acreage of 1600 m2. Intruding volcanic
pyroclastic rocks of Lower Carboniferous Yamansu Formation, the rockmass tends towards NE direction in
lentoid shape on the surface (Fig. 1). It is mostly composed of mafic-ultramafic rocks in three intrusive stages:
gabbro types including green and gray hornblende gabbro, gray hornblende gabbro, and gray medium-grained
gabbro in the first stage, lentoid ultramafic rocks including pyrolite, Cpx-pyrolite (clinopyroxene pyrolite),
lherzolite in the second stage, and Ti-Fe mineralized gabbro (VTM orebody) in the third stage.The CNS ore bodies have lengths of more than 100 m and average thicknesses of 2.38-5.52 m with the average grades 0.34%-0.58%
of copper and 0.32%-0.55% of nickel. All deposits occur
in green-gray hornblende gabbro and/or altered gabbro
in vein or lentoid form. The CNS ores mainly exhibit disseminated structure with minor massive, veinlet, network
vein and bead-structures, and mainly euhedral-subhedral
granular and sideronitic textures. Ore minerals are dominantly pyrrhotite, pentlandite, and chalcopyrite with minor violarite, pyrite, and cubanite. Gangue minerals including pyroxene, basic plagioclase, hornblende, chlorite, and
minor epidote, sericite, calcite and quartz, are in accord with
the magmatic minerals in host gabbro. Based on the above
descriptions, it is suggested that the CNS mineralization
owes to be magmatic liquation. The VTM ore bodies have
lengths of 400-1000 m, thickness of 1-15 m and elongation
of 100-250 m with the average grades 5%-8.38% of TiO2,
8.95%-19.09% of TFe and 0.08%-0.28% of V2O5, and all are
hosted by Ti-Fe mineralized gabbros that intrude in green
and gray hornblende gabbro in vein, lentoid, and bedded
form. The VTM ore dominantly exhibits disseminated and
mottled structure, and euhedral-subhedral granular texture
with minor sideronitic, eutectic, emulsion, and metasomatic
relict textures. Ore minerals are dominantly composed of
titanomagnetite, ilmenite and magnetite, with minor hematite, siderite, pyrite, chalcopyrite, sphalerite and pyrrhotite. Gangue minerals are also in accord with the magmatic
minerals in host gabbro. It is suggested that the TVM mineralization formed during late magmatic crystallization-differentiation (Qin 2003).
Close
1352
Wang Yuwang · Wang Jingbin · Wang Lijuan
3
Characteristics of igneous rocks of the
Xiangshanxi deposit
3.1 Rhythmic layering structure
In contrast to stratified rockmasses occurring in most
VTM deposits, the Xiangshanxi hosting rockmass did
not produce macrocosmic stratiform segregation, however, rhythmic layering or rhythmic banding structure
has been observed in the Xiangshanxi district. Two
rhythmite types have been identified as follows: one is
composed of tint CNS-bearing epidotization hornblende
anorthosite rhythmite and dark CNS-bearing olivine
gabbro rhythmite; the other is composed of gabbro-diorite rhythmite and coarse transitioning to fine-grained
altered olivine gabbro rhythmite. The former probably
contributed to autochthonous fractional crystallization
evidenced by the equal-thickness rhythmite or inched
rhythmic structure (Hess 1960), the latter have yielded
crystal gravitational settling (Naslund and McBirney
1996). It is well known that mafic-ultramafic complexes
related to CNS deposits are generally concentric ring
complexes, small stocks or dykes, rather than stratified
rock masses. However, the VTM deposit is characterized
by a hosting layered mafic-ultramafic complex. The structures of rocks and rockmass in the Xiangshanxi district
suggest that it is the transitional characteristics of the
hosting rockmass of the CNS deposit and VTM deposit.
In other words, this structure of rock and rockmass might
be a favorable factor for the paragenesis of CNS and VTM
deposit.
3.2 Lithochemistry
More than 500 silicate chemical data have been collected
from typical CNS deposits and VTM deposits of China
and have been recalculated and plotted on lithogeochemical diagrams (Fig. 2).
The mafic-ultramafic rocks related to VTM deposits
are dominantly alkalic, titanium-rich rock types and belong to ferruginous or high-ferruginous alkalic to calcalkalic series. Contrarily, mafic-ultramafic rocks related
to most CNS deposits except for that in the East Tianshan
area are mainly alkali-low and titanium-poor rock types
and ferruginous tholeiite to calc-alkalic series.
With the similar SiO2 contents, the alkaline contents
and femic ratio of the Xiangshanxi rocks range between
that of typical CNS deposits and VTM deposits (Fig. 2).
Host rocks from the Xiangshanxi district show a transitional feature of VTM and CNS deposit. The TiO2 contents vary in a wide range, the higher values may correspond to or higher than that in VTM deposits and the
lower ones may be corresponding to or lower than that in
CNS deposits. Likewise, the alkaline contents (Na2O+K2O
wt%), femic ratio (FeO*/MgO) or mafic index (m/f), magmatic acidity (αsi) and calc-alkaline enrichment index
(calk/m) exhibit the similar variation.
It worth to notice that host rock from those deposits
from the same tectono-metallogenic belt (called as East
Tianshan Cu-Ni metallogenic belt) as the Xiangshanxi,
yielded similar lithogeochemical parameters including
alkalinity, FeO and TiO2 contents and FeO*/MgO or m/f
ratios to that of the Xiangshanxi deposit, which distinctly
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Chapter 12-16 · Lithochemical factors for paragenetic Cu-Ni sulfide and vanadium-titanomagnetite deposits: A case study from the Xiangshanxi deposit, Xinjiang, China
1353
differs from that of other Cu-Ni mineral districts such as
Jinchuan and Hongqiling (China) and Norilsk (Russia).
This indicates that there exist favorable rock conditions
to form paragenetic CNS-VTM deposit not only in the
Xiangshanxi deposit but also in other districts of the East
Tianshan area.
3.3 Physical-chemical conditions
For the orthomagmatic mineral deposit, oxygen fugacity
(fo2) and sulfur fugacity (fs2) of ore-forming medium
(magma) are important physical-chemical conditions to
precipitate CNS or VTM deposits. It is possible that the
oxygen fugacity of the ore/rock-forming medium in the
VTM deposit is higher than that in the CNS deposit and
sulfur fugacity is opposite because the dominant ore minerals are respectively oxide and sulfide for the VTM and
CNS deposit.
Representative CNS deposits and VTM deposits of China
have been selected for comparisons with the Xiangshanxi
deposit. Firstly, crystallization temperature of plagioclase
is calculated based on the silicate composition of rocks (see
Qiu et al. 1991); secondly, crystallization pressure of the plagioclase is estimated according to a regression curve under
the liquid equilibrium crystallization of plagioclase and
magma established by Kudo and Weill (1970). Calculation
for oxygen fugacity of plagioclase equilibrium crystallization is taken from Mo’ (1984) formula.
Oxygen fugacity of VTM deposits show high values with
the lgfo2 in the range of -5.98 to -6.92. The lower limit of
oxygen fugacity (lgfo2) from CNS deposits disperses in the
range of -6.34 to -8.18 which are lower than that from VTM
deposits. Results of lgfo2 from the Xiangshanxi deposit range
on -8.68 to -7.43 which are close to the lower limit of oxygen fugacity from CNS deposits.
Sulfur fugacity of VTM deposit is quite low, e.g. the
lgfs2 value is only -19.54 in the Weiya VTM deposit of
East Tianshan, but it can reach to -2 to -11.2 in CNS deposits. Result of -9.8 of lgfs2 from the Xiangshanxi deposit is just between that of CNS and VTM deposits, which
presents a transitional value.
4
Discussion
The Xiangshanxi CNS-VTM composite deposit does not
occur in a stable craton but is situated in the Kangguertage
orogen. This characteristic could have resulted in an unstable tectonic setting for mineralization. There would have
been inadequate time for the original magma to completely
differentiate in such an environment. Thus, it is not unexpected that the acidity and physical-chemical parameters
of the host rocks exhibit dualism and transitional feature
under the condition. Moreover, the mafic-ultramafic rocks
from the East Tianshan metallogenic belt formed during
Close
1354
Wang Yuwang · Wang Jingbin · Wang Lijuan
the least tension period (Later Permian) of post-collisional
stage (Wang et al. 2004). Therefore, the magma was able to
penetrate several stratigraphic units during upward intrusion and can assimilate and contaminate various wallrock
types to be complication and homogenization, which also
induce to be transitional physical-chemical feature of
magma.
Acknowledgements
This work was supported by Major State Basic Research
Program of the People’s Republic of China (grant
2001CB409806) and the National Natural Science Foundation of China (grant 40273021).
References
5
Conclusions
Beside composite ore-forming elements (Cu-Ni-V-Ti-Fe)
in the Xiangshanxi deposit, the host rocks exhibit composite characteristic of an independent CNS deposit and VTM
deposit, i.e., coexisting of tholeiite series (gabbro, pyrolite,
and lherzolite) and alkali series (Ti-Fe mineralized gabbro). Lithochemical indices and parameters of the host rocks
such as alkalinity (or alkaline contents), femic ratio (FeO*/
MgO) or mafic index (m/f), magmatic acidity (asi), calcalkaline enrichment index (calk/m), and oxygen and sulfur fugacity in the Xiangshanxi deposit all exhibit dualism
and transitional features of typical CNS deposits and VTM
deposits. It is suggested that the controlling factor to form
the special composite CNS-VTM deposit could owe to its
tectonic setting, that is, anorogenic belt instead of a (margin of) craton.
Fu XM, Guo YS, Zhang MJ (1993) The features of chemical compositions of Huangshan mafic-ultramafic complex and their relations
to ore-bearing potential in Xinjiang. Journal of Lanzhou University (Natural Sciences) 29(3): 213-221
Hess HH (1960) Stillwater igneous complex, Montana: a quantitative mineralogical study. Mem. Geol. Soc. Am.
Kudo AM and Weill DF (1970) An igneous plagioclase thermometer.
Contrib. Miner. Petrol. (25): 52–65
Li CD, Mu JL, Zhu GQ (1996) Genesis and metallogenic Regularity of
Shallow-Rich Orebody of Huangshan Metallogenic Belt Hami,
Xinjiang. Chengdu: Chengdu Sci. & Tech. Univ. Press, 1-204
Mo XX (1996) Partial molar volume of oxide component in magma
and its lithological significance. Geoscience (1): 31-32
Mu JL (1996) On the characteristics and forming mechanism of the
rich and shallow-seated ores in the Huangshan copper-nickel
deposit Hami, Xinjiang. J. Mineral Petrol 16(1): 58-67
Naslund HR and McBirney AR (1997) Mechanisms of formation of
igneous layering. Richard GC ed. Layered Intrusions. Elsevier
Science: 1-43
Close
Chapter 12-17
12-17
Paleozoic reconstruction and tectonic evolution of
north Xinjiang, NW China: Implications for the lateral
growth of central Asia
Wen-Jiao Xiao, Chun-Ming Han
State Key Laboratory of Lithosphere Tectonic Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences,
P.O. Box 9825, Beijing 100029, China
Chao Yuan
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, China
Han-Lin Chen, Zi-Long Li
Faculty of Sciences, Zhejiang University, Hangzhou 310027, Zhejiang, China
Min Sun, Guo-Chun Zhao
Department of Earth Sciences, The University of Hong Kong, Hong Kong, China
Ke-Zhang Qin, Ji-Liang Li, Shu Sun
Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China
Abstract. The geology and tectonics of North Xinjiang can be divided into the Chinese Altay-East Junggar, West Junggar, and
Tianshan-Tarim domains, each of which is composed of Andeantype magmatic arc or island arc, accretionary wedge, and ophiolitic
slice, showing archipelago paleogeography. The Chinese Altay-East
Junggar domain was more closely located to the Angaran craton
(Siberia), while the Tianshan-Tarim domain was near the opposite
side of the early Paleozoic Paleoasian ocean. The West Junggar domain occupied an intermediate position near the Kazakhstan block
in the early Paleozoic Paleoasian basin. The Tianshan-Tarim and West
Junggar domains drifted northwards and approached the Chinese
Altay-East Junggar active margin of the Angaran craton in the late
Paleozoic. Subsequent amalgamation of these domains squeezed
the archipelago systems of these domains, leading to termination
of the Paleoasian ocean and formation of a complicated orogenic
collage between Angaran craton and the Tarim block by the late
Carboniferous or the early Permian. These multiple accretion processes significantly contributed to the lateral growth of Central Asia.
nism of the orogenesis as to whether there was a longlived, single subduction system (Rotarash et al. 1982;
Carroll et al. 1990; Sengör et al. 1993) or a collage of various terranes via different subduction systems (Coleman
1989, 1994; Mossakovsky et al. 1993; Buslov et al. 2001;
Windley et al. 2002; Badarch et al. 2002). The major debate centers on the time, nature and tectonic setting of
the various tectonostratigraphic units. This paper presents a new version of tectonic subdivision and a reconstruction and tectonic model for North Xinjiang in the
framework of southern Altaids.
The geology and tectonics of North Xinjiang can be
divided into the Chinese Altay-East Junggar, West Junggar,
and Tianshan-Tarim domains, roughly from N to S, which
are described in the following sections.
Keywords. North Xinjiang, Intra-oceanic subduction, ophiolite, accretion, Central Asia
2
1
Introduction
The North Xinjiang occupies a key tectonic position of
the Altaids (Sengör et al. 1993; Sengör and Natal’in 1996;
XNGMR 1993; Xiao et al. 2004a, 2004b) or Central Asian
Orogenic Belt (Mossakovskiy 1993; Jahn 2001; Dobretsov
2003), and its almost complete geological records and
excellent exposure of ophiolite, arc, and accretionary
wedge have made it a ideal natural laboratory to investigate subduction and accretion of juvenile material from
the Neoproterozoic through the Paleozoic (Sengör et al.
1993; Sengör and Natal’in 1996; Yin and Nie 1996; Jahn
2001). However, there is a strong debate about the mecha-
Chinese Altay-East Junggar
The Chinese Altay-East Junggar domain marks the site
where one branch of the Paleoasian ocean, the Junggar
ocean, was consumed (Sengör et al. 1993; Filippova et al.
2001).
Although different terranes in this region have been
distinguished (Li et al. 1990, 2003; Xiao et al. 1991; Windley
et al. 2002; Xiao et al. 2004a), they are all similar in that
all have an island arc/subduction zone with a brief southward younging (Li et al. 1990, 2003; O’Hara et al. 1997;
Niu et al. 1999; Xu et al. 2001; Xiao et al. 2004a). Based on
terrane analysis and zircon geochronology in the Chinese Altay region, Windley et al. (2002) concluded that
the Chinese Altay was a Cambro-Ordovician continental
magmatic arc. Similar SHRIMP zircon dates for the
Aermantai ophiolitic mélange (Jian et al. 2003) and com-
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Wen-Jiao Xiao · Chun-Ming Han · Chao Yuan · Han-Lin Chen · Zi-Long Li · Min Sun · Guo-Chun Zhao · Ke-Zhang Qin · Ji-Liang Li · Shu Sun
bined geology and geochemistry work (Jin et al. 2003;
Wang et al. 2003) all indicate that East Junggar was a
coeval island arc. However, ages as young as the Devonian have also obtained in the Aermantai and Kelameili
ophiolites (Jian et al. 2003), which points to a late stage
of subduction-accretion process (Liu et al. 1993; He et al.
1994).
Juxtaposition of these tectonic units indicate multiple
subduction-accretion systems amalga-mated by subsequent oblique convergence, including remnants of island
arc, subduction complexes, seamount and ophiolites, forming an enlarged Cordilleran-type margin by Mid-Carboniferous time (Xiao et al. 2004a).
3
West Junggar
The West Junggar domain comprise of various terranes
with island arc/ subduction origin (Coleman 1989; Feng
et al. 1989; Allen et al. 1989; Windley et al. 1990; Xiao et al.
1991; Zhang et al. 1993; Buckman and Aitchison 2001,
2004), but due to the severe Mesozoic-Cenozoic overprint
the terranes of the West Junggar domain are mostly
allochthonous (Allen et al. 1989, 1995), thus making its
geology much complicated than the East Junggar domain.
Another conspicuous character is that there are more
ophiolitic terranes than in the East Junggar domain (Allen
et al. 1989; Feng et al. 1989; Kwon et al. 1989; Zhang et al.
1993). These ophiolitic terranes are actually relicts of possible Ordovician-Silurian arc-related basins which acted
as basement or substrata of Devonian-Carboniferous arc
edifices (Wang et al. 2003; Xiao et al. 2004a). Based on
regional geology, radiolarian fossils and isotopic dating,
all terranes in the West Junggar were thought to be amalgamated by the end of Carboniferous (Allen et al. 1989;
Buckman and Aitchison 2004).
There has been a controversial issue concerning the
basement of Junggar Basin, which is located between the
West and East Junggar domains, and mostly covered by
Mesozoic-Cenozoic sediments. Based on geological,
geochemical, geochronological, and geophysical data, the
basement of the Junggar Basin may be mostly composed
of arcs and accretionary complexes or tapped oceanic crust
(Carroll et al. 1990; Hu et al. 2000; Chen and Jahn 2002,
2004), although different views such as continental basement exist.
4
Tianshan-Tarim
The Tianshan-Tarim domain is conveniently used to describe the southernmost tectonic domain of the Altaids,
which includes the Tianshan and Tarim sub-domains.
The Tianshan sub-domain comprises, from N to S, of
Northern, Central, and Southern Tianshan tectonic entities. The Northern Tianshan was assigned as an Ordovician-Silurian island arc with south-dipping subduction
at its northern side, and evolved into a possibly doublesubduction scenario in the Devonian and Carboniferous.
The Central Tianshan was an Andean-type arc during
most of its existence in the Paleoasian ocean history. The
Southern Tianshan was mainly an accretionary complex
including ophiolites, UHP and HP rocks (Xiao et al. 1991;
Gao et al. 1995, 2001; Zhang et al. 2002a, 2002b), island
arcs and accretionary wedges, which recorded the final
elimination of the Paleoasian ocean and the basic architecture in Central Asia in the Late Paleozoic (Windley et
al. 1990; Allen et al. 1993; Xiao et al. 2004a, 2004b).
The Tarim sub-domain was mainly a continental margin which remained passive during the Paleozoic. Some
of its Precambrian basement rocks had been thrust southward over its northern marginal sequences.
5
Reconstruction and tectonic model
The North Xinjiang orogenic collage, composed of various Paleozoic tectonic domains, provides one of the almost complete sections from the southern Angaran margin to the northern Tarim block. A summary of its tectonic evolution and reconstruction for this part of Central Asia is given as follows.
During the Early Paleozoic, the Chinese Altay-East
Junggar domain was more closely located to the Angaran
craton (Siberia), while the Tianshan-Tarim domain was
near the opposite side of the Paleoasian ocean. The West
Junggar domain occupied an intermediate position near
the Kazakhstan block in the early Paleozoic Paleoasian
basin. The Tianshan-Tarim and West Junggar domains
drifted northwards and approached the Chinese AltayEast Junggar active margin of the Angaran craton in the
late Paleozoic. Subsequent complicated amalgamation
processes of these domains squeezed the archipelago systems of these domains, leading to termination of the
Paleoasian ocean and formation of a complicated orogenic collage between Angaran craton and the Tarim block
by the late Carboniferous or the early Permian. These
multiple accretion processes significantly contributed to
the lateral growth of Central Asia.
From the summery presented here, we conclude that,
although with a general southward younging accretion,
there were multiple subduction systems existed in the long,
complicated evolution history of the Paleoasian ocean and
the formation of the Altaids. A number of the various
terranes were different parts of relicts of ancient subduction systems, mostly tectonically incorporated into accretionary complexes. Except from minor Precambrian
rocks in some Andean-type magmatic arcs, such as the
Chinese Altay and Central Tianshan, no significant old
continents had been involved into the orogenic processes
of the Altaids (Ma et al. 1997; Han et al. 1997; Qin et al.
1999; Qin 2000; Hu et al. 2000; Jahn 2001; Xiao et al. 2004a,
2004b; Zhang et al. 2004).
Close
Chapter 12-17 · Paleozoic reconstruction and tectonic evolution of north Xinjiang, NW China: Implications for the lateral growth of central Asia
The tectonic evolution and reconstruction of North
Xinjiang not only helps to reconcile the long-standing controversy of single Rotarash et al. 1982; Sengör et al. 1993)
versus complicated subduction polarities (Massakovsky et
al. 1993; Coleman 1989; Windley et al. 1990, 2002), but
also sheds lights on global reconstruction in the Paleozoic (Heubeck 2001; Yakubchuk et al. 2001; Torsvik and
Cocks 2004).
Acknowledgements
We thank Academicians Guang-Chi Tu, Xu-Chang Xiao,
and Ting-Dong Li, Professors Guo-Qi He, Fu-Chen Ma,
Ying-Jun Ma, Jing-Bin Wang, Jun Gao, Jin-Yi Li, Wei Liu,
Bao-Fu Han, Zhao-Jie Guo, Tao Wang, and Zheng-Le Chen
for discussion. We appreciate Professors B.F. Windley,
Reimar Seltmann and Jing-Wen Mao who helped us by
generously giving of their time and expertise. This study
was financially supported by the Chinese MOST
(2001CB409801, 96-915-07), the Chinese Academy of Sciences (KZCX2-SW-119-01), the Chinese NSF (40172080)
and the Hong Kong Research Grants Council (HKU7040/
04P). This is a contribution to IGCP 473 and 480.
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Close
Chapter 12-18
12-18
Fluid inclusions in gold mineralization in the Sarekoubu
area of the southern Altai Mountains, Xinjiang, China
J. Xu, Y. Xie, C. Zhong, X. Yuan
Department of Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China
R. Ding
Beijing Institute of Geology for Mineral Resources, Beijing 100012, China
Abstract. The Sarekoubu gold deposit occurs in Devonian metamorphic rocks at the southern margin of the Altai Mountains, Xinjiang,
China. The main mineralization stages are pyrite-quartz stage (II)
and polymetallic stage (III). Both the quartz debris in volcanics and
vein quartz contains abundant fluid inclusions, but they are very
different in types and compositions. Primary fluid inclusions in quartz
debris are mainly L-V type with th=255~270°C, and L-V-S type (They
are usually decrepitated from 248°C to higher than 335°C). SEM/
EDS analysis shows that many daughter minerals are calcic salts.
Fluid inclusions in vein quartz are different, and are dominated by L
CO2, LCO2-LH2O, and LH2O-LCO2 types; those in polymetallic stage are
more complex, probably with CO2-CH4 system fluid. The tm of solid
CO2 are -78.1~-61.9°C, and the thCO2 are -33.7~-17.7°C. Pure CO2 fluid
inclusions and CO2-rich fluid inclusions are widely developed in the
Sarekoubu gold deposit. δ13C of CO2 inclusions ranges from 10.725‰ to -21.151‰, which are similar to those from mantle minerals. CO2 fluids in the Sarekoubu gold deposit might originate from
degassing of upper mantle during late Hercynian collisional orogeny, or from the geochemical recycling of subducted materials
Keywords. Sarekoubu, Altai, daughter minerals, CO2 fluid inclusions
1
Introduction
The Sarekoubu gold deposit, located along the southern
margin of Altai in Xinjiang, occurs in the Keketale Aupolymetal mineralization belt. The Bazhai fault striking
310°–320° in the north restricts the southern Meizi volcanic-sedimentary basin, and the Abagong-Kurti fault, extending from the northwest of the Bazhai, restricts the
Kelang volcanic-sedimentary basin (Ding et al. 2001).
Strata in the belt are mainly middle-upper Proterozoic
and Devonian. The Sarekoubu gold deposit (320Ma; ArAr age) and Tiemierte Lead-Zinc deposit (369.5Ma; PbPb mode age) occur within the second lithological unit
of the lower Devonian upper Kangbutiebao Formation
(407Ma; zircon U-Pb age, Zhang et al. 2000). Lead-zinc
mineralization occurs in kiesel marble and manganeserich silicalite, while gold mineralization occurs in
lithofacies of chlorite biotite quartz schist and meta-tuff
west to lead-zinc mineralization.
A fluid inclusion study shows that pure CO2 fluid inclusions are dominated in quartz of main mineralization
stages at the Sarekoubu gold deposit, which are quite different from those in crystal detritus and early vein quartz.
The fluid inclusion characteristics obviously different from
those of many other hydrothermal gold deposits (Xu et
al. 1997; Jiang et al. 1999; Fan et al. 2000). CO2 fluid inclusions may play an important role in this new type of gold
mineralization.
2
Geology of the gold deposit
The Abagong and Keyingong faults control the southern
and northern borders of the Sarekoubu gold deposit, and
are boundaries of the Kangbutiebao Formation, middle
Devonian Altai Formation (D2a) and Silurian Kulumuti
Group respectively (Fig. 1). Echelon-like ore-bearing veins,
occurring as dextrorotation, intersect ore-controlling fault
in small angles. Gold-bearing veins were fractured frequently and filled by pyrite veinlets. The host rocks of
the Sarekoubu gold deposit were initially acid volcanic
rocks and volcaniclastic rocks, including crystal detritus
tuff and rhyolitic tuff. They are lithologically biotite quartz
schist, garnet hornblende biotite schist and tourmalin
biotite quartz schist. Wallrock alterations were developed,
including pyritization, silicification and carbonatization.
Five gold-bearing ore bodies have been exploited; these
are oriented 45°~55°∠65°~80°. Ore minerals are mainly
gold, electrum, pyrite, pyrrhotite, chalcopyrite, sphalerite and galena. Bismuth is commonly seen in the ore.
Gangue minerals are dominated by quartz, feldspar, garnet, carbonate, chlorite and clay minerals.
Gold mineralization in the Sarekoubu deposit includes
gold-bearing altered rocks and gold-bearing quartz veins.
Gold-bearing altered rocks are characterised by pyritedisseminated and silicified biotite-quartz schist and silicified rocks containing garnet, actinolite, and tremolite.
Gold-bearing quartz veins include pyrite-disseminated
saccharoidal quartz vein and stockworks in chlorite-biotite schist. Hydrothermal mineralization stages can be
distinguished as follows: (I) pyrite-disseminated and silicified stage; (II) pyrite-quartz vein stage, forming coarse
pyrite and disseminated pyrite in veins, cut by polymetallic
sulfides and fluorite; (III) polymetallic sulfide stage,
marked by chalcopyrite, sphalerite, galena, pyrrhotite and
bismuth. Stages I and II are the main gold mineralization
stages.
Close
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J. Xu · Y. Xie · C. Zhong · X. Yuan · R. Ding
3.2 Fluid inclusions in quartz veins
Fluid inclusions in vein quartz are dominated by pure
CO2 inclusions (L CO2) and CO2–rich inclusions (L CO2LH2O) (Fig. 3), which can be distinguished from those in
quartz detritus. Small amounts of aqueous inclusions (including LH2O-L CO2 and LH2O-VCO2) and CO2 gaseous inclusions also exist.
3
Fluid inclusion study
Fluid inclusions are commonly found in quartz, fluorite
and calcite of the Sarekoubu gold deposit. Quartz in wall
rocks and veins occurs as three types: 1) quartz crystal
detritus in tuff and biotite-quartz schist; 2) fine recrystal
quartz grains in groundmass; 3) vein quartz in mineralization stages, including stage II and stage III. Fluid inclusions are very small in recrystal quartz. Abundant fluid
inclusions occur both in quartz detritus and vein quartz,
but they have differences in types and components.
3.1 Fluid inclusions in quartz detritus
Quartz detritus is a residual mineral in the volcanic rocks.
Primary fluid inclusions in quartz debris are mainly L-V
type with th=255~270°C, and L-V-S type (They are usually decrepitated from 248°C to higher than 335°C). SEM/
EDS analysis shows that many daughter minerals are calcic salts and slaty potassic silicate, such as calcite, biotite
and potash feldspar (Fig. 2). These inclusions reflect that
fluids were rich in Ca and K during sea-floor extrusive
process in Late Devonian. Pure CO2 inclusions (L CO2) and
CO2–rich inclusions (LCO2-LH2O) arranged in tiny fractures of quartz detritus adjacent vein are also found. These
inclusions show the late hydrothermal event during gold
mineralization.
Pure CO2 inclusions (LCO2). They occur abundantly in the
Sarekoubu gold deposit, especially in pyrite-quartz stage
(II) and polymetallic sulfide stage (III), with sizes of several µm to several decades. There are two instances for
melting temperatures of frozen phases (Tm,CO2). The first
group is pure CO2 inclusions, Tm,CO2 of which equal -57°C~56°C; final homogenization temperatures (Th,CO2) vary
from +3°C to +20°C (exclusively homogenized to liquid
CO2 ), with 0.85~0.89g/m3 of densities. Laser Raman Microprobe analysis shows clear CO2 spectra peaks at Raman
shift 1384 cm-1 and 1278cm-1, and no CH4 or other spectra peak (SR15-7, SR15-5). The Tm,CO2 of the second group
are less than –57°C, even lower to -78.1~-61.9°C for those
in quartz of polymetallic sulfide stage, indicating some
other volatiles mixed in fluid, such as CH4 (Roedder, 1984).
Final homogenization of these inclusions may occur at
1.01~1.07g/cm3. Laser Raman Microprobe analysis shows
a distinct CH4 spectra peak at Raman shift 2911 cm-1 besides clear CO2 spectra peaks (SR21-14, 21-13). They are
typical CO2±(CH4) fluids.
CO2-rich inclusions (LCO2-LH2O). They are composed of
liquid CO2 phase and liquid H2O phase, with 50%~80%
of CO2/H2O volume ratios.
These inclusions occur occasionally in stages II and
III, associated with L CO2 inclusions, and are primary in
origin.
The cooling and homogenization characteristics of CO2
phases in CO2-rich inclusions are similar to pure CO2 inclusions. CO2 clathrate forms at low temperatures, with
+8.6~+10.5°C of melting temperatures. The final homogenization of these inclusions occurs at 254~276°C (homogenized to water phases), but most inclusions with high CO2/
H2O volume ratios may be decrepitated during heating.
Aqueous inclusions (LH2O-LCO2 and LH2O-VCO2). Primary
or pseudo-secondary aqueous inclusions are rarely found
in the Sarekoubu deposit. They have 60~80% of H2O/CO2
volume ratios, and are homogenized during 280~394.5°C
(to liquid water phases). The eutectic temperatures are
usually lower than -20.8°C, even lower to –47°C, showing
that K+, Ca2+ ions are contained in fluid. Secondary aqueous inclusions, which occur along the tiny fractures cutting quartz grains, have larger H2O/CO2 volume ratios
(>90%) and lower Th (113~188°C) similar to those in
quartz detritus.
Close
Chapter 12-18 · Fluid inclusions in gold mineralization in the Sarekoubu area of the southern Altai Mountains, Xinjiang, China
4
1361
Discussion
Mumm et al. (1997) reported that the gold mineralization of the Ashanti Belt, Ghana, formed from CO2-rich,
nearly water free (XCO2>0.8) hydrothermal system. They
suggested that these fluids (CO2>>H2O) represent a hitherto unrecognized category of ore forming fluids, because
either leaching of water from H2O-CO2 system after trapping of fluid, or a phase separation of an initially H2OCO2 fluid before trapping, can not explain abundant CO2
fluids on a regional scale.
CO2 fluids are abundant in the Sarekoubu gold deposit
but the lack of simultaneous aqueous inclusions makes it
is hard to argue that CO2 came from a phase separation
from initially H2O-CO2 fluid. Yin et al. (2004) suggested
that gold mineralization at the Sarekoubu is related to
prograde metamorphism resulting from rupture metamorphism, which is characterized by coarse metamorphic mineral grains, typical lower pressure and high temperature metamorphic minerals such as sillimanite and
andalusite. Retrograde alterations, such as sericitization
and propylitization are not developed, and indicating less
water in fluids. Further more, pure CO2 fluids have regional characters in the volcanic sedimentary basin. Initial study shows that there are abundant CO2 fluid inclusions in vein quartz of Tiemuerte Pb-Zn deposits, having
high CO2 densities, indicating a regional scale source for
high density CO2 fluids and CO2±(CH4) fluids. We analyzed mantle olivine (12 samples) from Hannuoba of Hebei
and Liuhe of Jiangsu, and obtained δ13C of CO2 fluids ranging from -17.4‰ to -27.3‰. Results of Chu et al. (1994),
Fan et al. (1996), and Yang et al. (2000) also show low 13C
Close
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J. Xu · Y. Xie · C. Zhong · X. Yuan · R. Ding
of mantle CO2 fluids. Carbon isotope analysis on the
Sarekoubu gold deposits shows that δ13C of CO2 fluid inclusions ranges from -10.725‰ to -21.151‰, which are
very similar to those in mantle minerals. In fact, since
light carbon (δ13C <-20‰) is also observed in kimberlite,
diamond, and carborundum, Deines (2002) suggested that
carbon isotope composition of 13C depletion (δ13C =-25‰)
is also important for mantle carbon. Hence, CO2 fluids in
the Sarekoubu gold deposit might originate from degassing of the upper mantle during late Hercynian collisional
orogenesis, or mixed with some water from country rocks
during ascending, or from the geochemical recycling of
subducted materials (Zheng et al. 2003).
Acknowledgements
We greatly appreciate the constructive and thoughtful
comments of Prof. H-R. Fan of IGG-CAS and Prof. P Ni of
Nanjing University. This work is supported by the National Science and Technology Development Program of
China (2003BA612A–06–09).
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Close
Chapter 12-19
12-19
SHRIMP zircon age of the Kaejiao intrusion in the
Sawuer region, Xinjiang
Yuan Feng, Zhou Taofa, Fan Yu, Tan Lugui, Yue Shucang
School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China
Abstract. The Kaejiao intrusion is mainly albite granite porphyry and
potassium feldspar granite porphyry. It was formed at the telophase
of Late Carboniferous confirmed by its SHRIMP U-Pb zircon age is
302.6 ± 7.6Ma (1σ). The intrusion is composed of partially alkali rocks,
whose REE distribution patterns are of the LREE enrichment type,
∆Eu value is low and Nd, Sr, Pb isotopes reflect characteristics of the
mantle source. The O isotopes of the intrusion are low for the isotope exchange with meteoric water. Diagenetic distinguishing shows
that it was formed in compressing structural setting of late orogenic period (post-collisional phase). Combined with existing studies
of A-type granites and Permian volcanic rocks, we believe that in
the telophase of Late Carboniferous, the Sawuer region is during
late post-collisional phase and west Zhungeer is later than east
Zhungeer in post-collisional structure evolution process.
Keywords. Granite, zircon, SHRIMP data, postcollisional, Sawuer region
1
Introduction
Sawuer region is located at the northern margin of the
Kazakstan-Zhungeer plate [1, 2] and belongs to the Sawuer
paleozoic island arc belt [3]. There are volcanic activities
in the Middle Devonian to Late Permian period. The Early
Permian Kalagang group volcanic rocks have characteristics of typical double peaking volcanic rocks. Intrusions
(mainly acid rocks) are widespread in the region (Fig. 1).
The Kaejiao intrusion is situated in the northeast part of
the study area, which intruded into the stratum of Carboniferous Jimunai group. The precise dating of intrusions in the study area will provide important evidence
to determine the process and the time of post-collisional
orogenic evolution. In this contribution we present a new
data on SHRIMP zircon age of the Kaejiao intrusion and
discuss its geological significance.
2
graphic texture and oriented distribution; ndividual crystals are 0.1-0.3 mm in length, with magnetite grains scattered throughout.
3
Geochemical characteristics
The K2O-SiO2 diagram shows that the intrusion belongs
to the high potassium series. The Σ REE contents of intrusion range from 86.3 × 10-6-215.61x10-6 and its average value is 146.72x10-6. The LREE/HREE ratios range from
6.65 to 10.88 with an average ratio of 8.16. Eu values range
from 0.66-0.96 and its average value is 0.75. The REE distribution patterns show LREE enrichment. The R1-R2
diagram shows that the intrusion was formed in late orogenic period. On Rb-Y+Nb diagram the intrusion is plotted in the domain of volcanic arc granite, reflecting that
it was formed in the compressing structure setting.
The (87Sr/86Sr)I, εSr(t), εNd(t), 206Pb/204Pb, 207Pb/204Pb
and 208Pb/204Pb values of intrusion are 0.70404, -1.56, 5.95,
17.863, 15.486, 37.799 respectively, reflecting the mantle
source characteristics. The low δ18O value (whole rock)
of 2.7 is the result of isotope exchange between intrusion
and meteoric water during magma chilling period.
Petrological characteristics
Lithologically, the intrusion comprises mainly porphyry,
including potassium feldspar granite porphyry, albite granite
porphyry, and granite-porphyry. Potassium feldspar granite porphyry, which has an incarnadine porphyritic structure distributes in the western part of intrusion. Its matrix
comprises a graphic texture and mass structure. Phenocrysts are represented by K-feldspar, with the matrix composed of alkali feldspar, quartz, and some magnetite. Potassium feldspar phenocrysts are hypidiomorphic-platy, 0.52.0 mm in length and 0.2-1 mm in width. Alkali feldspar
and quartz in the matrix are paragenetic as exhibited by
Close
1364
Yuan Feng · Zhou Taofa · Fan Yu · Tan Lugui · Yue Shucang
4
SHRIMP results
The U-Pb analyses were performed using the Sensitive
High-Resolution Ion Microprobe (SHRIMP-II) at the Chinese Academy of Geological Sciences in Beijing. Results
showed Th/U of all zircons from the Kaejiao intrusion
sample greater than 0.1, the age of 302.6±7.6 Ma (1 sigma)
representing the crystallization age of intrusion.
5
Discussion
The North of Xinjiang has a complete post-collisional
evolution history (from collision, post-collision to
intraplate), intense post-collisional structure-magma activity, large scale ore-forming process and well-preserved
conditions, so many researchers have paid attention to
this district [2, 3, 4]. The precise dating of post-collision
is a key aspect in the study of post-collisional structuremetallogenic processes. According to the definition of
Liegeois, Wang et al. (2005) suggest that the main collision period is Carboniferous to Permian in north of
Xinjiang.
In this study, the SHRIMP zircon age of the Kaejiao
intrusion is 302.6 ± 7.6Ma (telophase of late carboniferous). The partial alkali rocks were formed in late orogenic period compressing structure setting, corresponding to post-collisional evolution phase. Meanwhile, the
SHRIMP zircon age of the A2 type granite in the study
area (Qiaqihai intrusion: 290.7 ± 9.3Ma, Kuoyitasi intrusion: 297.9 ± 4.6Ma) and studies of typical volcanic rocks
of the early Permian Kalagang group indicate that in the
Sawuer region, the west Zhugeer post-collisional phase
ended in the early Permian and intraplate phase began.
By contrasting, the east Zhungeer Ulungur alkali
granite’s ages, Nd, Sr, Pb, O isotope and REE characteristics show that east Zhungeer underwent an extentional
period of post-collisional phase during the Late Carboniferous period, while the west Zhungeer Sawuer region
was still undergoing compression. Thus, it was formed
later than east Zhungeer in the post-collisional structure
evolution process.
6
Conclusions
SHRIMP U-Pb ages of zircon from the Kaejiao intrusion
give 302.6±7.6Ma (Late Carboniferous). Alkali rocks with
mantle source characteristics formed in a late orogenic structural setting, reflecting that in the Late Carboniferous the
Sawure region underwent a late post-collisional phase.
Compared to east Zhungeer, where the Late Carboniferous marked an extensional period of post-collisional
phase, the west Zhungeer Sawuer region was still undergoing compression in the Late Carboniferous period and
formed later than east Zhungeer in the post-collisional
structure evolution process.
Acknowledgements
We thank researcher Liu Dunyi and laboratory assistants
Shiyuruo, Songbiao, Wang Yanbin and Taohua for their
enthusiastic help in SHRIMP-II zircons U-Pb analyzing.
We thank Xinjiang “305” project office and Xinjiang Forth
geological team for their great help. We thank researchers Wang Jingbin, Gao Jun, Ma Yingjun, Wang Baolin and
WangYu for their instructive suggestion during the study.
We thank Mr. Yang Wenping and Helixin for their zealous help in the field. This research is supported by the
China National Key Basic Science Research project (Grant
No.2001CB409810-11) and Anhui Provincial Excellent
Youth Science and Technology Foundation (Grant
No.04045063).
References
He GQ, Li MS, Liu DQ (1994) Paleozoic crust evolution and ore-forming in Xinjiang, China. Hongkong: Hongkong education and culture publication house
He GQ, Liu DQ, Li MS (1995) Five phases pattern and ore-forming of
main orogenic belt crust evolution in Xinjiang. Xinjiang geology
13(2): 99-194
Liegeois JP, Navez J, Hertogen J (1998) Contrasting origin of postcollisional high-K calc-alkaline and shoshonitic versus alkaline
and peralkaline granitoids, the use of sliding normalization.
Lithos 45: 1-28
Liu JY, Yuan KR (1996) A discussion on the genesis and tectonic setting of alkali granites in the Ulungur alkali-rich granite belt,
Xinjiang. Geological Journal of China universities 2(3): 257-272
Liu W, Zhao ZH, Zhang FL (1999) H, O isotope constrain of mineralmeteoric water interaction of Tasigake alkali granite, Xinjiang.
Science Bulletin 44(7): 704-710
Tu GC (1999) Primary study of central Asia metallogenic province.
Scientia geologica sinica 34(1): 397-404
Wang JB, Xu X (2005) Post collision structure evolution in north
Xinjing. Acta Geologica Sinica (in press)
Wang SG, Han BF, Hong DW (1994) Geochemistry and tectonic significance of alkali granites along Ulungur River, Xinjing. Scientia
geologica sinica 29(4): 373-383
Windley BF, Kroner A, Guo JH (2002) Neoproterozoic to Paleozoic
Geology of the Altai Orogen, NW China:New Zircon Age Data
and Tectonic Evolution. The Journal of Geology 110: 719-737
Zhao ZH, Wang ZG, Zou TR, A Masuda (1996) Study on petrogenesis of alkali rich intrusions of Ulungur, Xinjiang. Geochimica
25(3): 205-220
Close
Chapter 12-20
12-20
Sulfur, helium and argon isotopic features of gold deposits
in the Sawuershan region, Xinjiang, NW China
Qing-dong Zeng, Yuan-chao Shen, Ping Shen, Guang-ming Li, Tie-bing Liu
Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Abstract. Two gold deposits (Kuoerzhenkuola and Buerkesidai) have
been discovered, explored and mined in the Sawuershan district,
Xinjiang, NW China. Gold mineralization at Kuoerzhenkuola deposit
occurs within Carboniferous andesite and volcanic breccias. Gold
mineralization at Buerkesidai deposit occurs within Carboniferous
siltstones. δ34S‰ values of pyrite separates of ores and altered
andesite from Kuoerzhenkuola deposit variy from 0.25‰ to 1.3‰
and 1.5‰ to 2.44‰, respectively. δ34S‰ values of pyrite separates
of ores and altered albite porphyry from Buerkesidai deposit vary
from 0.44‰ to 0.84‰ and 1.1‰ to 2.81‰, respectively. He and Ar
isotope data from fluid inclusions in pyrites formed during mineralization stage of Kuoerzhenkuola and Buerkesidai gold deposits
show that the 40Ar/36Ar and 3He/4He ratios of fluid inclusions are
respectively in the range of 282-525 and 0.64-9.48 R/Ra, suggesting that mantle fluids may have played an important role in the
ore-forming processes. On the basis of S, He and Ar isotope data,
we conclude that the ore-forming materials may be derived from
the mantle and the ore-forming fluid may be a mixture of mantlederived fluid with the meteoric water.
Keywords. Isotopes, gold deposits, Sawuershan, Xinjiang
1
Introduction
hand specimens by conventional preparation techniques
including crushing, an oscillating, heavy liquid and magnetic separation. All mineral separates (pyrite) were further purified by hand-picking to at least 99% purity.
2.2 Analytical techniques
The samples for this study consist of pyrites formed during the ore-forming stage, which were taken from the
Kuoerzhenkuola and the Buerkesidai gold deposits. The
sulfur isotope compositions for the pyrites were determined
with a MAT251 mass spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Routine analytical precision for standard material was 0.01‰.
Helium and argon isotope analyses of fluid inclusions
in pyrites were determined with a MI1201IG inert gases
isotope mass spectrometer at the Chinese Academy of
Geological Sciences, with a resolution of 1200. 4He was
measured by a Faraday cup and 3He by an electronic multiplier with an amplification coefficient of 1×105. The analytical methods were described in detail by Li et al. (2002).
The Sawuershan district is located in north-western
Xinjiang, China, which is one of the most important gold
metallogenic zone in Xinjiang. Two gold deposits
(Kuoerzhenkuola and Buerkesidai) were identified (Fig. 1),
Some geological and geochemical data on these two gold
deposits have been published (Tan et al. 1996; Yin et al.
1996; Zhang 1998). Geologic features of the gold deposits
were described by Guo et al. (1997), Li (2002) and Li (2003).
The ore-forming chronology of the gold deposits was previously discussed by some authors (Cai et al. 2000; Liu et
al. 2003). Chen et al. (1995) and Li (1999) discussed the
regional geological setting and regional metallogenesis.
However, details of thye ore-forming processes of these
gold deposits, especially the source of ore-forming fluid
and material have not been reported. S, He and Ar isotopic data are reported in this paper with the aim to define
possible sources of gold and the ore-forming fluid.
2
Methods
2.1 Sampling
Samples of the Kuoerzhenkuola gold deposit were taken
from saps. Samples of the Buerkesidai gold deposit were
collected from ore stack. All minerals were separated from
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1366
Qing-dong Zeng · Yuan-chao Shen · Ping Shen · Guang-ming Li · Tie-bing Liu
All the analytic results are based on the atmosphere internationally used as standard, whose 3He/4He ratio is
1.40×10-6. All the results of helium are given in forms of
3He/4He ratio and R/Ra ratio, where R is the 3He/4He ratio of the sample and Ra is that of the air. The blank level
of 4He is 2×11-11cm3STP and the blanking 3He/4He ratio
is 1 ×10-6(Li et al. 2002). The analytical precision of the
standard gas is 1%.
3
Geologic features of the gold deposits
3.1 Kuoerzhenkuola gold deposit
The host rocks of the Kuoerzhenkuola deposit are composed mainly of Carboniferous andesite and volcanic breccia. Mafic porphyry dykes and stocks are widely exposed
in the mineralized area. The mafic intrusions are mainly
composed of diorite and diorite porphyrite. The main
NWW-trending Kuoerzhenkuola fault controls the distribution of the largest mineralization zone; it dips to south
with an angle of 65° to 80°. The main sources of gold ores
are No.1, 2, and 3 ore bodies. The No.1 ore body is the
largest one. It is 1700m long, 1.62 to 9.92m wide, with a
depth of 220 to 290m. It dips 65°to 80° towards the south.
The gold content ranges from 3.64 to 23.8g/t, with an average value of 10.72g/t. Each of these ore bodies is composed mainly of gold-bearing quartz-pyrite vein and disseminated-veinlet in altered rocks. The metallic minerals are mainly pyrite and pyrrhotite, with minor of chalcopyrite and sphalerite. The alteration minerals are quartz,
calcite, sericite, chlorite and epidote.
3.2 Buerkesidai gold deposit
The host rocks of the Buerkesidai deposit consist of Carboniferous andesite and siltstone. The WE-trending
Buerkesidai fault is the controlling ore fault. It dips 75° to
80° towards south. The Buerkesidai gold deposit is mainly
composed of No.1 and No.2 ore bodies. The NWW trending No.1 ore body is 720m long, 1.4 to 7.1m wide, with a
decline depth of 243m. The gold content ranges from 2.11
to 17.45g/t, with an average value of 6.17g/t. Each of the
ore bodies is composed of gold-bearing quartz veinlet
groups and altered rocks. The major metal minerals are
pyrite and arsenopyrite, with minor of chalcopyrite,
sphalerite and pyrrhotite. The alteration minerals are
quartz, calcite, sericite and chlorite.
4
Isotopes
4.1 Sulfur isotopes
Sulfur isotope data for 26 pyrite separates from two gold
deposits of the Sawuershan district are presented in Figure 2.
The δ34S‰ values of 17 pyrite samples from the
Kuoerzhenkuola deposit vary from 0.25‰ to 2.44‰, with
an average value of 0.93‰. The δ34S values of 9 pyrite
samples from the Buerkesidai deposit range from 0.44‰
to 2.85‰, with an average value of 1.85‰ (Fig. 2).
No significant variation in the δ34S values has been
observed in the two gold deposits. The sulfur isotope values of pyrites from two gold deposits are similar with
values of meteorolites, these values display sulfur have
features of mantle-derived sulfur, and the sulfur in mineralization fluid is mainly mantle-derived sulfur.
4.2 He-Ar isotopes
Many studies show that He-Ar isotopic analyse method
is one of the important methods which define the source
of ore-forming fluid (Kelly 1986; Stuart 1995; Burnard
1999; Hu et al. 1999). Analy-tical results of He and Ar isotopic compositions for 13 pyrite samples from fluid inclusions of the gold deposits are plotted in Figure 3.
Helium isotope ratios vary between 0.64 and 9.48
(Fig. 3). The atmosphere He contribution can be determined from the F4He values, defined as the 4He/36Ar of a
sample relative to the atmospheric 4He/36Ar value of
0.1655, such that a sample containing air will have an F
Close
Chapter 12-20 · Sulfur, helium and argon isotopic features of gold deposits in the Sawuershan region, Xinjiang, NW China
1367
values of the fluids in New Zealand island arc (295-700)
(Patterson et al. 1994). 40Ar/36Ar values higher than the
atmospheric ratio indicate the presence of a significant
proportion of 40Ar of mantle or crustal origin (Kendrick
et al. 2001).
5
Conclusions
1. Sulfur isotope compositions of gold deposits in the
Sawuershan district suggest that the sulfur in mineralization fluidis mainly derived from the mantle, and
reflect that ore-forming material may also have been
derived from the mantle.
2. He and Ar isotopic compositions of gold deposits in
the Sawuershan district suggest that the ore-forming
fluid may be a mixture of mantle-derived fluid with
the meteoric water, and the mantle fluid may be play
an important role in the ore-forming process.
value of 1 (Kendrick et al. 2001). The F4He values for the
pyrites of the gold deposits in Sawuershan region are
>1000 (1748-28470). This means that 4He is enriched by
more than 1000 times above the atmospheric concentration. The high F4He values are evidence that the fluids
contain negligible contributions of atmospheric He
(Kendrick et al. 2001).
The crust typically has an R/Ra value in the range 0.01
to 0.05, which is much lower than the mantle source fluid
with an R/Ra of 6 to 9 (Stuart et al. 1995). The 3He/4He
ratio of ore-forming fluid of the gold deposits in the
Sawuershan district is higher than the crustal ratio,
suggestingf that mantle fluids were involved in the
metallogenesis. Without mantle fluid, it would not be possible to form elevated 3He/4He ratios in ore-forming fluid.
According the binary mixing model (Kendrick et al.
2001), we calculated the proportion of mantle 4He using
a value of 6 Ra as representative of pure mantle helium
(Stuart et al. 1995; Simmons et al. 1987), a value of 0.01
Ra as representative of the crust helium, and the measured range in R/Ra of 0.64 to 4.25 of the Kuoerzhenkuola
gold deposit and 1.16 to 5.08 of the Buerkesidai gold deposit, gives the proportion of mantle helium as between
11 and 71% of Kuoerzhenkuola gold deposit, and 19 to
85% of the Buerkesidai gold deposit besides two
samples(mantle helium). It indicates that the helium in
ore-forming fluid of the gold deposits in Sawuershan district may be mainly mantle helium.
The measured 40Ar/36Ar composition of the ore-forming fluid of the Kuoerzhenkuola gold deposit ranges from
282 to 359, with an average value of 306.8, and slightly
higher the atmosphere composition (295.5) (Stuart et al.
1995). The 40Ar/36Ar values of the fluid inclusions in pyrites of the Buerkesidai gold deposit are between 312 and
525, and higher than the value of the atmosphere. These
40Ar/36Ar values of the ore-forming fluid are similar to
Acknowledgements
Authors thank the assistance we have received at all stages
of this study from our collaborators. This study was financed by the innovative project of Chinese Academy of
Sciences (KZCX3-SW-138, KZCX3-SW-137) and the important project of the National Science and Technology
(2001BA609A07-08).
References
Burnard PG, Hu R, Turner G (1999) Mantle, crustal and atmospheric
noble gases in Ailaoshan Gold deposits, Yunnan Province, China.
Geochimca et Cosmochimica Acta 63: 1595-1604
Cai H, Li HQ, Chen FW (2000) Study on chronology and origin of the
Kuoerzhenkuola gold deposit in northwestern margin of the
Junggar Basin. Geology and Mineral Resources of South China 4:
19-22
Chen YJ, Fu SG, Wu DH, Wu XD, Jing J (1995) The coupling of the gold
mineralization with the collisional orogenesis and the distribution of gold deposits, North Xinjiang. Gold Geology 1(3): 8-16
Guo DL, Li ZC, Tan KR (1997) Tectono-metallogenetic mechanism
for the Buerkesidai gold ore deposit. Geotectonica et Metallogenia
21(2): 162-166
Hu RZ, Bi XW, Turner G (1999) Helium and argon isotope geochemistry of ore-forming fluids on Ailaoshan gold belt. Science in
China (Series D) 29(4): 321-330
Kelly S, Turner G, Butterfeild AW (1986) The source and significance
of argon isotopes in fluid inclusions from areas of mineralization. Earth and Planetary Science Letters 79: 303-318
Kendrick MA, Burgess R, Pattrick RAD, Turner G (2001) Fluid inclusion noble gas and halogen evidence on the origin of Cu-Porphyry mineralizing fluids. Geochimica et cosmochimica Acta 65:
2651-2668
Li SM (2003) Geological features and origin discussion of the
Buerkesidai old deposit, Xinjiang. Xinjiang Non-ferrous Metals
2: 13-18 (in Chinese)
Li YH (2002) Geological features and metallogenetic mechanism of
the Kuoerzhenkuola gold deposit. Xinjiang Nonferrous Metal 1:
1-4 (in Chinese)
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Qing-dong Zeng · Yuan-chao Shen · Ping Shen · Guang-ming Li · Tie-bing Liu
Li ZC (1999) Two tectono-metallogenic types of Au deposits and their
metallogenic models in the southern Altai mountain. Geotectonica
et Metallogenia 23(1): 16-28
Liu GR, Long ZN, Chen QZ, Zhou G (2003) The formation age and
geochemical characteristics of the volcanic rock of Kuoerzhenkuola Gold Mine, Xinjiang. Xinjiang Geology 2: 177-180 (in Chinese with English abstract)
Patterson DB, Honda M, McDaugall I (1994) MORB-like, and crustalderived noble gas component in subduction-related samples. In:
Matsuda J-I, ed. Noble Gas Geochem. And Cosmochem Tokyo:
Terra Sci Publi Co: 147-158
Simmons SF, Sawkins FJ, Schlutter DJ (1987) Mantle derived
helium in two Peruvian hydrothermal ore deposits. Nature 329:
429-432
Stuart FM, Burnard PG, Taylor RP (1995) Resolving mantle and
crustal contributions to ancient hydrothermal fluids: He-Ar iso-
topes in fluid inclusions from Dae Hwa W-Mo mineralization,
South Korea. Geochimca et Cosmochimica Acta 59: 4663-4673
Tan KR, He BC, Pan CC, Guo DL, Wu QH (1996) Metallogenetic
process, type and model of gold deposits of Jimunai region,
north Xingjiang, China. Geotectonica et Metallogenia 1: 67-70
(in Chinese with English abstract)
Yin YQ, Chen DJ, An YC, Li JX, Fan Y, You ZF, Yang JR (1996) Characteristics of the Kuoerzhenkuola epithermal gold deposit in
Sawuershan, Xinjiang. Geological Exploration for Non-ferrous
Metals 5: 278-283 (in Chinese with English abstract)
Zhang JB (1998) Geological and geochemical features of the gold
deposit of Kuoerzhenkuola, Xinjiang. Mineral resources and
Geology 4: 267-270 (in Chinese with English abstract)
Zhou G, Qin JH, Wang X, Luan XD (1999) Formation time of
granitoids in Sawuer Mountains, Xinjiang. Acta Petrologica et
Mineralogica 3: 237-242 (in Chinese with English abstract)
Close
Chapter 12-21
12-21
Multiple mineralization in the eastern Tianshan mountains,
NW China: Evidence from isotope geochronology
L.-C. Zhang, K.-Z. Qin, W.-J. Xiao
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. BOX 9825,
Beijing 100029, China
Abstract. Based on geochronological data and the regional geological evolution, it is indicated that mineralization processes in
the eastern Tianshan are characterized by multiple stages. These
mineralization processes are related to an arc accretionary stage
(~360-320 Ma) with porphyry-type and volcanic sediment deposits,
a collision-post orogenic stage (~300-250 Ma) with orogen-type
deposits and magmatic copper-nickel ore deposits, and an intracontinental extension stage (~ 250-220 Ma) that gave rise to the
Jinwuozi gold deposit, Xiaobaishitou W-Mo deposit and Baishan
Mo-Re deposit.
Keywords. Geochronology, porphyry-type deposit, orogen-type deposit, multiple mineralization, east Tianshan
1
Introduction
The eastern Tianshan region has recently emerged as an
important metallogenic ore province in China. More than
ten large porphyry copper-molybdenum, orogenic gold,
magmatic copper-nickel and epithermal gold deposits
have been discovered in the eastern Tianshan orogen since
the late 1980s. The metallogenic epoch in the Tianshan
region was considered of late Paleozoic age. However,
Mesozoic ages of intrusions and mineralization in the
eastern Tianshan were repeatedly reported in recent years
(Chen et al. 1999; Zhang et al. 2004).
2
Geological setting
The east Tianshan mountains, a part of the Central Asian
Paleozoic collisional orogenic belt, have been studied by
many researchers (Windley et al. 1990; Allen et al. 1992 ,
1993; He et al. 1994; Qin et al. 2003; Xiao et al. 2004). The
main structures of the orogen are characterized by a series of approximately east-west-trending faults, including the regional-scale Kalamaili fault (Late Paleozoic suture), Kanggurtag fault, Kushui (or Yamansu) fault, and
Weiya fault (Fig. 1). Of these faults, the Kanggurtag fault,
expressed by mylonite, tectono-clastic rocks, tectonic
lenses and breccia, is an important structural zone along
which intense magmatic activity and associated mineralization took place. The Dananhu-Tousuquan Paleozoic island arc consisting mainly of Devonian to Carboniferous
volcanic-intrusive rocks and hosting most of the porphyry
copper deposits (e.g. Tuwu and Yandong) occurs to the north
of the Kanggurtag fault (Fig. 1). The Kanggurtag-Huangshan
Late Paleozoic arc-related basin consisting of Carboniferous sedimentary rocks, some Cu-Ni deposits associated
with mafic complexes (e.g. Huangshan and Huangshandong) and Cu-Mo (Re) deposits related to granite porphyry
(e.g. Baishan Mo-Re), are located between the Kanggurtag
and Kushui faults. The Carboniferous Aqishan-Yamansu
volcanic arc, and associated Au deposits (e.g. Shiyingtan
Au, Kanggur Au; Fig. 1), are located between the Kushui
and Weiya faults. The middle Tianshan block consisting of
Precambrian and early Paleozoic metamorphic rocks is located south of the Weiya fault.
Intrusive activity in the eastern Tianshan includes
granite, plagiogranite porphyry, tonalite, quartz porphyry,
dacite porphyry, and mafic-ultramafic bodies. They are
related to most of the gold-copper mineralizations.
3
Isotope geochronology data
The radiometric ages of some deposits in eastern
Tianshan (Table 1) were determined by several researchers (Li et al. 1998; Chen et al. 1999; Rui et al. 2002; Mao et
al. 2003; Qin et al. 2003; Zhang et al. 2003, 2004; Han et al.
2004). The available isotopic data show that these deposits were formed around 343-320, 290-250, and 250220 Ma, respectively.
Aside from Late Paleozoic intrusions, there are also
some Mesozoic granites reported recently in the eastern
Tianshan, such as the Weiya granite which has a SHRIMP
zircon age of 233 to 246 Ma (Gu et al. 2004, unpublished
data) and Ar-Ar age of 223-246 Ma (Li et al. 2002), the
Xiaobaishitou granite (located 20 km northeast of Weiya)
with a SHRIMP zircon age of 249 ± 3 Ma, and the Baishitou
granites (40 km northeast of Weiya) with a Rb-Sr isochron age of 209 ± 9.6 Ma (Gu et al. 2003).
4
Discussion and conclusions
4.1 Multiple mineralization in the eastern Tianshan
According to geochronological data and the regional geological evolution, we consider that mineralization processes in the eastern Tianshan were characterized by
multiple stages (Table 1):
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L.-C. Zhang · K.-Z. Qin · W.-J. Xiao
Arc accretionary stage (~360-320Ma): DananhuTousu-quan magmatic arc and associated porphyry-type
and volcanic sediment deposits were formed in accretionary stage of island arc. The former include TuwuYangdong Cu-Mo deposit with ore-forming age of 343320 Ma, and Chihu Cu ore-spot. The later is Xiaorequanzi
Cu-Zn deposit with a ore age of 339 Ma. Collision-post
orogenic stage (~300-250 Ma): The Kanggul gold deposit
is characterized by orogen-type deposit (Zhang et al.
2003). The main ore-forming stage is between 290 Ma
and 280 Ma. During the post orogenic-extensional stage,
the Huangshan ultramafic-mafic complexes were
emplaced and a number of large-scale magmatic copper-nickel ore deposits were formed in 280-270 Ma. Intra-continental extension stage (~250-220 Ma): Recent
studies indicate that the ages of the Jinwuozi gold deposit are 228 to 230 Ma (Chen et al. 1999), the Au-bearing quartz vein III of the Shiyingtan gold deposit is 244
± 9 Ma (Zhang et al. 2003), and the Xiaobaishitou W-Mo
deposit (20 km northeast of Weiya) is 248 Ma (Li et al.
2004, unpublished data). Zhang et al. (2004) reported recently Re-Os ages (225-224 Ma) of molybdenite and pyrite from the Baishan Mo-Re deposit in the eastern
Tianshan. Similarly, some ages of 245 to 211 Ma of metal
deposits in the western Tianshan were reported (Ye and
Ye 1999). These data indicate that the Indosinian period
is also an important mineralization epoch in the Tianshan
region.
4.2 Mineralization geodynamic processes
The plate margin and plate convergent zones are the most
important gold-copper mineralization regions. Various
styles of mineralization were formed in different tectonic
settings.
In the early Carboniferous, the Dananhu arc may have
generated magma intrusion, leading to formation of the
porphyry Cu deposits. From late Carboniferous to early
Permian, the formation of shear belt-type gold deposits
are associated with collisional events. Several magmatic
copper-nickel deposits are related to emplacement of
mafic-ultramafic complexes in post-orogenic stage. The
volcanic- or subvolcanic-hosted epithermal gold deposits,
such as the Xitan and Mazhuangshan gold deposits, are associated with extensional tectonics and volcanic activity in
post-tectonic period. In Early Mesozoic, the tectonic evolution of the east Tianshan is characterized by intra-continental extension with associated intrusion of granites and
volcanic hydrothermal activity (i.e. Jinwozi Au and Baishan
Mo-Re etc.). The ore-forming processes of the main gold
and copper deposits are correlative to processes active now
in the SW Pacific subduction system.
Close
Chapter 12-21 · Multiple mineralization in the eastern Tianshan mountains, NW China: Evidence from isotope geochronology
Acknowledgements
This study was financed by the Ministry of Science and
Technology of China (2001CB409805), and the Chinese
Academy of Sciences (KZCX3-SW-137).
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Gu LX, Guo XQ, Zhang ZZ, Wu CZ (2003) Geochemistry and petrogenesis of a multi-zoned high Rb and F granite in eastern
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220–226
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of major Au, Cu, Ni and Fe deposits and metallogenic evolution
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Rui ZY, Wang LS, Wang YT, Liu YL (2002) Discussion on metallogenic
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features and geodynamic significances of gold-copper deposits
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Int J Earth Sci 93: 224–240
Close
Chapter 12-22
12-22
Magmatic Cu-Ni sulfide deposits in northern Xinjiang,
China: A review
Z.-H. Zhang1, F.-M. Chai2, J.-W. Mao1,2, Z.-L. Wang1, D.-H. Wang1, Z.-C. Zhang2, J.-M. Yang1
of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
2China University of Geosciences, Beijing 100083, China
1Institute
Abstract. On the basis of previous studies, this paper provides a preliminary summary of recent research on mafic-ultramafic intrusions
and related magmatic Cu-Ni sulfide ore deposits in northern Xinjiang.
The authors argue that there is still a need to study some key problems concerning the origin and tectonic settings of these intrusions
and sulfide deposits.
Keywords. Mafic-ultramafic rocks, Cu-Ni sulfide deposit, Xinjiang
1
Introduction
Three main metallogenic belts of copper-nickel sulfide
have been discovered in the northern part of the Xinjiang
Autonomous Region since 1970’s, namely the Karatungk,
Huangshan-Jingerquan and Qingbulake belts. All Cu-Ni
deposits of these belts are related to mafic-ultramafic rock
belt. Although numerous studies have been carried out
and accumulated abundant data on these rocks and related ore deposits (e.g. Wang et al. 1987, 1991; Wang 1990;
Wang et al. 1992; Ni et al. 1994; Yang 1994; Wang et al.
2000; Zou et al. 2001; Mao et al. 2002; Zhang et al. 2003;
Han et al. 2004), there are still differing opinions on the
genesis and the tectonic environment of these deposits
and related rocks. In addition, limited by the analytical
accuracy of some dating methods, the ages of the Cu-Ni
sulfide ore deposits and related rocks vary across a rather
wide range. This paper provides a preliminary review of
the research on these ore deposits and points out some
key problems that require further study.
2
Characteristics of mafic-ultramafic intrusions in
Northern Xinjiang
Mafic-ultramafic rocks are developed widely in northern Xinjiang. For example, the Karatungk mafic-ultramafic
terrane located along the boundary between the north
margin of the Junggar basin and the south margin of the
Altay orogenic belt covers an area 200 km long and 10 to
20 km wide. Eight mafic-ultramafic intrusions such as
Xibodu, Wuertengsayi, Penteke, Yitieke and Karatungk are
distributed discontinuously from west to east along the
Irtysh fault zone. The Karatungk mafic intrusion hosts a
large Cu-Ni sulfide deposit. The Huangshan mafic-ultramafic terrane situated in the eastern Tianshan between
the Kangguertage fault and Kushui fault is ~270 km long
and 20 to 30 km wide. More than 30 intrusions have been
discovered in this area, and many of them are mineralized.
The Tudun, Huangshandong, Huangshan, Hongshigang,
Heishiliang and Mati intrusions host large Cu-Ni sulfide
deposits. In the Qingbulake terrane in the western Tianshan
there are ~10 intrusions, of which the Qingbulake, Sulu,
Qiong’awuzi and Qiaoletieke intrusions are associated with
Cu-Ni-sulfide- mineralization. Recently nickel orebodies of
commercial value have been found in the Baishiquan and
Pobei mafic-ultramafic terranes south of Hami.
The occurrence of these large Cu-Ni sulfide deposits
makes Xinjiang the second largest Ni resource province
next to Gansu in China (Wang 1990) and a region with
Cu-Ni sulfide ore deposit concentration that has great
potential for further exploration (Wang et al. 2002).
3
Origin of the intrusions and related ore deposits
Based on previous studies, we argue that the Hercynian
Cu-Ni sulfide deposits in northern Xinjiang have some
unique characteristics when compared with other Cu-Ni
sulfide deposits in China. For example, mineralization in
these intrusions is different from that in Jinchuan where
it only occurs in the Baijiazuizi intrusion (Tang and Li
1991). The nickel grade in these deposits is rather low,
with usually only 10 percent in the Jinchuan deposit.
Compared to typical mafic-ultramafic intrusions hosting Cu-Ni sulfide deposits, these intrusions are poor in
MgO and alkalis and rich in Al2O3 and SiO2. Although
intrusions and deposits in northern Xinjiang have similar characteristics, differences between them are also apparent. The contents of Cu, Ni, Co and PGE in the
Karatungk deposit are noticeably higher than those in
the Huangshan deposit (Wang et al. 2002).
Chen et al. (1995) and Li et al. (1998) proposed that mafic-ultramafic rocks of the Qingbulake and Karatungk terranes were derived from the depleted mantle. Whole-rock
oxygen isotope values of the intrusion No.1 of Karatungk
range from 5.47 to 11.21 per mil and increase with decreasing mafic composition. For the mafic-ultramafic rocks, the
initial 87Sr/86Sr ratios vary from 0.70330 to 0.70368 and the
initial 87Nd/86Nd ratio is 0.512561 with εNd=5.07 to 5.93.
For the ores, the initial 87Nd/86Nd is 0.512534 with εNd=5.09.
The mafic-ultramafic rocks of Karatungk, Huangshan,
Huangshandong and Huangshanxi show similar Rb and
Close
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Z.-H. Zhang · F.-M. Chai · J.-W. Mao · Z.-L. Wang · D.-H. Wang · Z.-C. Zhang · J.-M. Yang
Sr features to those of tholeiite from the mantle plume
and hot spots, which implies that these intrusions were
probably derived from the mantle plume (Wang et al.
2002). Generally, it is considered that the mantle plume is
close to the primitive mantle or depleted mantle, while midoceanic ridge basalt is derived from the depleted mantle
source, so relatively complex isotope characteristics may
be manifested in the area where the mantle plume overlaps. The Karatungk mafic-ultramafic intrusions exhibit
REE-enriched distribution characteristics, which might indicate that these intrusions were derived from the enriched
mantle. However, this is in contradiction to high Nd isotope values; so further study remains to be conducted.
There exist different views about the origin and tectonic environment of mafic-ultramafic intrusions in
northern Xinjiang. Feng et al. (1986) suggested that these
intrusions resulted from the ascent of mafic-ultramafic
magmas from the aulacogen produced by northward subduction of the Northern Tianshan. Wang et al. (1991) believed that the Early Carbonaceous Junggar trough closed
earlier than the Late Carbonaceous and that the
Karlatungk mafic-ultramafic terrane was emplaced after
the Carbonaceous. Li et al. (1991) proposed that maficultramafic rocks in Kalatungk and Huangshan were intruded after the eruption of volcanic rocks in the extensional environment of the transitional crust. Liu et al.
(1992) believed that mafic-ultramafic rocks in the
Karatungk and Huangshan terranes are intrusions thermally emplaced during the “extension period” of the
younger continental crust and formed at the site of crustal
weakness in the stress rebound stage after the end of the
orogenic movement and crustal consolidation.
Xiao et al. (1992) maintained that the northward subduction of the Junggar ocean resulted in lithospheric extension, upper mantle updoming and crustal thinning,
which brought about upwelling of asthenosphere below
the Yilianhabiga-Bogeda- Huangshan area. Ran and Xiao
(1994) advocated that magmatism at Karatungk occurred
in an environment of initial extension after the collision
between the Siberian and Junggar plates and so has the
features of island arc magmatism. Yang et al. (1994) suggested that all of the “magmatic Cu-Ni sulfide deposits
formed in the island-arc or back-arc extensional environment” during the post-orogenic extension stage. Liu
(1996) further demonstrated that this kind of island arc
is one part of the “Devonian North Junggar intra-arc arc”.
Mao et al. (2002, 2005) maintained that mafic-ultramafic
rocks in the Huangshan area formed in a post-collision
extensional environment. Zhang et al. (2003) believed that
the formation of the Karatungk intrusion was closely related to the extensional environment after the collision
between the Siberian and Junggar plates and that the
magma was derived from the depleted asthenospheric
mantle and underwent contamination with the crust in
the high-level magma chamber, thus causing immiscibility
of sulfide-rich ore magma and silicate-rich magma. From
above, it may be concluded that these mafic-ultramafic intrusions probably formed in an extension environment, but
the key of the problem lies in whether the extension occurred before or after the wholesale collision.
With regard to the origin of the Cu-Ni sulfide deposits
in northern Xinjiang, there are also some different views.
Wang et al. (1990) argued that the mineralization processes of these Cu-Ni sulfide deposits include magmatic
liquation, anatexis-injection, late ore magmatism and
pneumatolyto-hydrothermal activity.
Wang et al. (1991) contended that the formation of the
Karatungk Cu-Ni sulfide deposit progressed through the
deep-seated differentiation and in-situ differentiation stages.
Parat and Huang (1997) suggested that the three types
of orebody of the No.1 deposit at Karatungk resulted from
magmatic liquation, anatexis-injection and superimposition of hydrothermal processes respectively, with the
last two processes of mineralization being most closely
related to noble metals.
Zou et al. (2001) proposed that both the rock- and oreforming materials of the Karatungk ore district were derived from basaltic magma of the mantle. Wang et al. (2000,
2002) suggested that the formation of the Karatungk deposit is related to a mantle plume.
Chen et al. (1995) proposed that, after entering the intermediate magma chamber, the subalkaline tholeiitic
magma was stratified due to gravity differentiation, thus
forming rock bodies with different mafic compositions.
The stratified magma underwent multiple liquation and
crystallization differentiation, forming disseminated and
massive orebodies.
4
Available age data
Numerous data on the ages of rocks and ore deposits have
been obtained. The ages of the three above-mentioned
mineralized terranes (metallogenic belts) cluster around
the Late Paleozoic, but most ages of the ore deposits are
indirectly inferred from the ages of the intrusions dated
by the Sm-Nd, Rb-Sr and K-Ar methods. The ages yielded
by using these diverse dating methods have brought great
uncertainty in geological interpretation.
In the Karatungk area, intrusion No.1 has K-Ar ages
of 273.8 to 284 Ma (Lu et al. 1989; Wang et al. 1991), Rb-Sr
isochron ages of 285 to 317 Ma (Wang et al. 1991) and
Sm-Nd isochron ages of 281.4 to 297.7 Ma (Li et al. 1998).
Intrusion No.2 has K-Ar ages of 275.6 to 306.4 Ma and
Rb-Sr isochron ages of 296 to 308 Ma (Wang et al. 1991).
Intrusion No.3 has K-Ar ages of 229.1 to 306.4 Ma and
Rb-Sr isochron ages of 290 Ma (Wang et al. 1991). The
Sm-Nd isochron age of massive and disseminated ores
of deposit No. 1 of Karatungk is 281.4±12 Ma (Li et al.
1998). SHRIMP zircon U-Pb dating of diorite from No. 1
intrusion gives an age of 287±5 Ma (Han et al. 2004).
Close
Chapter 12-22 · Magmatic Cu-Ni sulfide deposits in northern Xinjiang, China: A review
Wang et al. (1987) obtained a K-Ar age range of 262.99
to 439.61 Ma for mafic-ultramafic rocks in the Huangshan
area. The Sm-Nd whole-rock isochron age for the
Huangshan ore-bearing complex is 308.9±10.7 Ma and
that for ores is 305.4±2.4 Ma (Li et al. 1998). Re-Os dating
of Cu-Ni sulfide ore presents one isochronological age of
288±20 Ma (Mao et al. 2002). The single zircon U-Pb age
for the Xiangshan amphibole gabbro is 285±1.2 Ma (Qin
2000). According to Ni et al. (1994), the Sm-Nd isochron
ages of the Qingbulake mafic-ultramafic intrusion range
from 313.5 to 324 Ma.
5
Some problems that require further study
Although a wealth of data on these terranes has been
gained from northern Xinjiang, some key problems have
not yet been resolved satisfactorily.
1. Did these intrusions form in an island arc, mid-oceanic ridge or post-collision environment? Why could
these mafic-ultramafic rocks be emplaced before or
after collision?
2. Were these magmatic rocks derived from the depleted
mantle or enriched mantle? And why do they display
different REE and isotope features?
3. To what degrees was the magmatic system contaminated with crustal materials? How did the interaction
of crust and mantle affect the ore-forming processes?
4. The rock- and ore-forming ages are highly varied. It is
very hard to evaluate the metallogenic environment
and geodynamic setting exactly.
Acknowledgements
This study was funded by the National Natural Science
Foundation of China (No. 40402012).
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