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Ore Geology Reviews 60 (2014) 76–96
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Ore Geology Reviews

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Epithermal Au and polymetallic mineralization in the Tulasu Basin,

western Tianshan, NW China: Potential for the discovery of porphyry
Cu\Au deposits
Xiaobo Zhao a, Chunji Xue a,⁎, Guoxiang Chi b, Honggang Wang a, Tianjiao Qi a
a
State Key Laboratory of Geological Processes and Mineral Resources, Faculty of the Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
b
Department of Geology, University of Regina, S4S 0A2 Regina, Canada
a r t i c l e i n f o a b s t r a c t
Article history: The Tulasu basin is an important epithermal Au mineralization district in western Tianshan in northwestern
Received 3 July 2013 China. Geochemical and geochronological studies of the volcanic host rocks (the Dahalajunshan Formation)
Received in revised form 11 December 2013 and associated intrusive rocks, particularly the enrichment of large-ion lithophile elements and depletion of
Accepted 23 December 2013
high field strength elements, suggest that the Tulasu basin was located in a magmatic-arc setting from Late-
Available online 14 January 2014
Devonian to Early-Carboniferous, associated with the southward subduction of the North Tianshan Ocean be-
Keywords:
neath the Kazakhstan–Yili plate. Geologic and geochemical characteristics of the Au\Cu–polymetallic deposits
Porphyry-epithermal mineralization in the Tulasu basin suggest that the mineralization is related to the Late-Devonian to Early-Carboniferous arc
Au\Cu–polymetallic mineralization magmatism, and is mainly of epithermal nature, including both the adularia–sericite type (Axi, Tawuerbieke
Late Paleozoic and Tabei) and alunite–kaolinite or acid–sulfate type (Jingxi–Yelmend and Tieliekesayi). However, some
Tulasu basin evidence of porphyry-type mineralization has also been found, including the presence of mineralized porphyry
Western Tianshan enclaves in volcanic rocks hosting the Tawuerbieke Au prospect, and the development of porphyry-style Cu
Xinjiang mineralization overprinted by vein-type mineralization at Kexiaxi. Considering the magmatic-arc setting that
NW China
is favorable for both epithermal and porphyry types of mineralization, and the development of such mineraliza-
tion systems in other parts of western Tianshan and the Altaid Belt (e.g., Uzbekistan, Kazakhstan and Kyrgyzstan),
we suggest that major porphyry Cu\Au deposits may have been developed in the Tulasu basin, probably beneath
or adjacent to known epithermal Au mineralization.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction Au\Cu–Zn deposit (Waters et al., 2011). Similar mineralization systems

are also well documented at Tombulilato, northern Indonesia (Perelló,
The Western Tianshan Orogen, which extends from Uzbekistan, 1994), and at Ladolam, Lihir island, northeastern Papua New Guinea
through southeastern Kazakhstan, Kyrgyzstan and northern Tajikistan, (Müller et al., 2002).
to Xinjiang in northwestern China, is situated along the southwestern Several large porphyry-skarn-epithermal Au\Cu–polymetallic
margin of the Central Asian Orogenic Belt (Fig. 1a). It formed from mul- mineralization systems have been recognized in western Tianshan.
tiple subduction–collision and amalgamation events in the Paleo-Asian The Almalyk ore district in eastern Uzbekistan hosts five major
Ocean during the late Paleozoic, in an island-arc environment similar to porphyry Cu\Au deposits, one large skarn Zn–Pb deposit and twenty-
the present-day southwestern Pacific (Charvet et al., 2011; Gao et al., one epithermal Au deposits within an area of ~ 150 km2 (Golovanov
2009; Khain et al., 2003; Safonova et al., 2011; Xiao et al., 2010, 2013), et al., 2005; Shayakubov et al., 1999). A world class porphyry-
where porphyry-skarn-epithermal Au\Cu–polymetallic mineralization epithermal Au metallogenic system has also been recognized at
systems are well developed, with the porphyry Cu\Au deposits occur- Taldybulak Levoberezhny in northern Kyrgyzstan (Djenchuraeva et al.,
ring beneath or adjacent to epithermal Au deposits (Andrew, 1995; 2008). Major epithermal Au deposits have been discovered in the
Cooke et al., 2005; Sillitoe, 1973, 1989). For example, the Lepanto–Far Chinese part of western Tianshan, but no significant porphyry Cu
Southeast Au\Cu district in northern Luzon, Philippines, contains mineralization has been reported so far.
both porphyry and epithermal styles of mineralization (Arribas, 1995; The Tulasu basin, located in western Tianshan, Xinjiang (Fig. 1) is
Chang et al., 2011), and the neighboring Baguio district hosts important well endowed with epithermal Au deposits, including the large Axi
Au\Cu–polymetallic systems including two major porphyry Au\Cu and Jingxi–Yelmend deposits. Previous stream sediment surveys in the
deposits, three large epithermal Au–Ag deposits and one large skarn Tulasu basin demonstrated enrichment of Au but dispersion and deple-
tion of Cu in this area (FGTXBGMR, 2005). As a result, exploration activ-
⁎ Corresponding author. Tel.: +86 10 82321895; fax: +86 10 82322175. ities have been focused on Au deposits and little attention has been paid
E-mail address: chunji.xue@cugb.edu.cn (C. Xue). to copper. In this contribution, based on a systematic investigation of
0169-1368/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.oregeorev.2013.12.018
X. Zhao et al. / Ore Geology Reviews 60 (2014) 76–96 77
Fig. 1. a) Tectonic map of the Central Asian Orogenic Belt (modified from Gao et al., 2009); b) Geological map of the Western Tianshan Orogen (modified from Qian et al., 2009); and c)
Geological and mineral resources map of the Tulasu basin (modified from FGTXBGMR, 1990).
mineralization styles and alteration types in the Tulasu basin, together Junggar terrane by the ‘North Tianshan Suture’ in the north (Fig. 1b),
with new geochronological and geochemical data for the magmatic respectively. In the Anrakhai range of southern Kazakhstan, Archean
rocks in the region, we propose that the porphyry-epithermal mineral- granitic gneisses have a U\Pb sensitive high-resolution ion microprobe
ization systems developed in the western section of western Tianshan (SHRIMP) zircon age of 2791 ± 24 Ma and the Paleoproterozoic granitic
are also present in the eastern (or Chinese) section. The implications gneisses have U\Pb SHRIMP zircon ages of 2187.0 ± 0.5 Ma and
of this new mineralization model for exploration are discussed. 1789.0 ± 0.6 Ma (Kröner et al., 2007). These Precambrian basement
rocks were unconformably covered by Cambrian–Early Ordovician oce-
2. Regional geological setting anic island-arc complexes and Middle Ordovician continental volcanic
rocks (Mikolaichuk et al., 1997). In the Yili block of northern Xinjiang,
The Tulasu basin is part of an amalgamated island-arc belt resulting Precambrian rocks are widely exposed, including the Paleoproterozoic
from the southward subduction of the North Tianshan Ocean beneath Wenquan Group, Mesoproterozoic Haerdaban Group, Tekesi Group
the northern margin of the Kazakhstan–Yili plate (An and Zhu, 2008; and Kusongmuqieke Group, and Neoproterozoic Kaiertasi Group
Tang et al., 2009; Wang et al., 2006, 2007), and occurring along and Kekesu Group (XBGMR, 1993). Paleoproterozoic amphibolite and
the northeast margin of the Kazakhstan–Yili plate (Fig. 1b). The gneisses of the Wenquan Group have a Sm\Nd isochron age of
Kazakhstan–Yili plate is separated from the Central Tianshan plate by 1727 Ma (Hu et al., 1994). Precambrian granitic gneisses with a second-
the ‘Nikolaev Line–North Nalati Suture’ in the south and from the ary ion mass spectroscopy (SIMS) zircon U\Pb age of 1609 ± 40 Ma (Li
78 X. Zhao et al. / Ore Geology Reviews 60 (2014) 76–96
Fig. 2. A sketch of the stratigraphic column of the Tulasu basin.

Table 1
Major (wt.%) and trace element (ppm) data for igneous rocks in the Tawuerbieke area, Tulasu basin.
No. T-1 T-2 T-3 T-4 T-5 T-6 T-7 T-10 T-11 T-12 T-13 T-14 T-15
Rocks Andesite Granitic porphyry
Major elements (wt.%)

SiO2 50.46 47.69 52.32 49.92 47.98 48.03 50.13 75.36 75.27 77.11 75.85 77.15 73.5
Al2O3 13.45 14.95 13.99 14.32 13.36 16.83 16.36 12.78 13.05 12.35 12.94 12.24 14.36
T
Fe2O3 6.91 8.04 8.20 7.33 8.12 7.69 7.24 1.21 1.07 0.66 0.83 0.41 0.79
MgO 5.86 5.32 6.20 5.85 5.83 4.47 4.97 0.19 0.11 0.11 0.11 0.09 0.37
CaO 8.56 9.03 6.08 7.39 12.38 7.58 6.82 0.28 0.21 0.18 0.2 0.12 0.51
Na2O 2.65 3.02 1.67 2.51 1.98 2.35 1.96 4.19 3.41 2.86 3.03 1.39 2.74
K2O 0.83 1.07 0.75 1.31 0.48 2.71 2.25 4.46 5.55 5.58 5.72 7.66 5.73
MnO 0.12 0.13 0.12 0.11 0.11 0.12 0.11 0.007 0.009 0.015 0.008 0.007 0.008
TiO2 0.71 0.77 0.73 0.74 0.76 0.81 0.80 0.24 0.24 0.22 0.22 0.22 0.25
P2O5 0.09 0.09 0.10 0.10 0.13 0.13 0.12 0.024 0.037 0.032 0.035 0.028 0.029
LOI 10.34 9.83 9.76 10.40 8.84 9.24 9.18 1.12 0.91 0.74 0.92 0.53 1.59
Trace elements (ppm)

Rb 25.7 51.0 29.0 27.2 22.3 26.5 25.7 155.0 184.0 166.0 165.0 252.0 197.0
Ba 216 296 210 145 132 163 150 715 827 806 701 898 839
Th 4.94 4.77 4.90 3.04 2.81 3.31 3.02 8.99 9.35 8.43 8.05 8.97 9.30
U 1.35 1.22 1.30 1.04 1.03 1.06 0.98 2.43 3.34 2.42 2.51 2.65 2.86
Nb 8.55 8.77 8.62 3.42 3.27 3.46 3.37 16.50 17.10 16.80 15.30 16.70 17.70
Ta 0.66 0.67 0.71 0.41 0.37 0.37 0.35 1.46 1.56 1.41 1.38 1.40 1.59
Sr 452 472 436 282 269 259 283 177 186 136 131 139 159
Zr 267 147 254 216 202 238 209 174 187 159 144 153 168
Hf 7.29 4.52 6.64 5.17 4.80 5.78 5.46 4.56 4.95 4.27 3.91 4.06 4.74
Y 31.9 25.8 30.9 30.3 27.8 32.5 30.6 11.2 12.1 10.5 9.8 10.4 12.8
La 20.2 19.6 19.8 11.1 9.8 12.0 11.0 28.6 30.4 27.4 25.0 28.5 30.3
Ce 41.0 39.7 40.3 23.8 22.2 26.5 24.1 49.2 51.9 45.5 44.9 48.3 50.1
Pr 5.00 4.80 5.01 3.18 2.76 3.31 3.07 4.96 5.14 4.54 4.19 4.74 5.03
Nd 21.0 18.9 20.6 12.9 13.4 15.1 13.5 16.6 17.9 15.2 14.1 16.0 16.8
Sm 4.41 4.17 4.72 3.60 3.19 3.46 3.61 2.42 3.00 2.21 2.05 2.49 2.57
Eu 1.24 1.01 1.14 1.12 1.02 1.11 1.07 0.67 0.63 0.57 0.55 0.57 0.62
Gd 4.40 3.90 4.56 3.42 3.15 3.96 3.64 1.91 2.12 1.87 1.44 1.87 1.90
Tb 1.00 0.79 0.95 0.79 0.78 0.89 0.83 0.37 0.37 0.29 0.26 0.37 0.33
Dy 5.45 4.55 5.30 5.22 4.84 5.60 5.13 1.86 2.23 1.73 1.47 1.81 2.07
Ho 1.24 0.91 1.21 1.07 1.09 1.10 1.12 0.36 0.39 0.32 0.35 0.34 0.42
Er 3.25 2.45 3.08 3.08 3.12 3.47 3.11 1.17 1.30 1.16 1.03 1.11 1.39
Tm 0.49 0.40 0.50 0.49 0.45 0.55 0.51 0.20 0.23 0.22 0.19 0.21 0.25
Yb 3.36 2.52 3.24 3.32 3.14 3.62 3.69 1.39 1.55 1.39 1.19 1.37 1.77
Lu 0.54 0.35 0.56 0.56 0.49 0.52 0.54 0.23 0.23 0.22 0.24 0.25 0.27
Note: Fe2OT3 refers to total iron, LOI = loss on ignition.
et al., 2009) and a thermal ionization mass spectrometer (TIMS) U\Pb (Han et al., 2010), suggesting that the closure of the North Tianshan
zircon age of 798 Ma (Chen et al., 1999) were discovered in western Ocean and the subsequent collision between the Kazakhstan–Yili plate
Awulale and eastern Sailimu, respectively. The Precambrian basement is and Junggar terrane ended before 316 Ma in the Late Carboniferous.
unconformably overlain by Cambrian–Early Ordovician epicontinental
siliciclastic and carbonate rocks (Gao et al., 1998), followed by Silurian 3. Analytical methods
volcanic rocks formed in a subaqueous volcanic island-arc setting (Zuo
et al., 2008). The lower Paleozoic strata were unconformably overlain Major and trace element compositions were analyzed at the Analyt-
by a Devonian molasse succession, Lower Carboniferous continental/ ical Laboratory of the Beijing Research Institute of Uranium Geology
marine island-arc volcanic rocks, Upper Carboniferous shore to shallow (ALBRIUG). Major element analyses were done by X-ray fluorescence
marine siliciclastic and carbonate rocks, Lower Permian continental spectrometry (Philips PW2404) on fused glass beads. The analytical
bimodal volcanic rocks, and an Upper Permian molasse succession in precision is generally better than 5%. Loss on ignition was measured
the Bole and Awulale areas. by gravimetry after heating the samples to 1100 °C. Trace element
The Bayingou and Lucaogou ophiolitic mélanges occurring along the compositions were analyzed by Inductively-coupled plasma-mass
northern edge of the Kazakhstan–Yili plate are widely accepted to be spectrometry (Finnigan-MAT Element I) after complete dissolution in
the obducted remnants of the North Tianshan Ocean crust (Fig. 1b). distilled HF + HNO3 in Teflon vessels. The analytical uncertainties are
The North Tianshan Ocean may have been opened as early as Late less than 7%, estimated from repeated analyses of two Chinese National
Cambrian (Long et al., 2011), and ocean spreading likely continued at standards (GBW 07106 and GBW 07312).
least until the Carboniferous, as indicated by SHRIMP zircon U\Pb Zircon grains were hand-picked under a binocular microscope after
ages of 325 ± 7 Ma and 344 ± 3 Ma from cumulate gabbro and conventional heavy liquid and magnetic separation techniques. The
plagiogranite, respectively, of the Bayingou ophiolite complex (Xu internal structures of the zircon grains were examined with reflected
et al., 2006). Siliciclastic rocks from the Bayingou mélange yielded and transmitted light microscopy, and cathodoluminescence imaging,
Late Devonian Famennian conodonts including Palmatolepis sp. and at the Institute of Geology, Chinese Academy of Geological Sciences
Polygnathus sp. and Early Carboniferous radiolarians of Ceratoikicum (CAGS), to select suitable spots for U\Pb analyses. Zircon U\Pb isotopic
sp. (Xiao et al., 1992). Late Devonian to Early Carboniferous island-arc dating was performed by the SHRIMP II ion microprobe at the Beijing
magmatism in the northern Yili block is related to the southward subduc- SHRIMP center, CAGS, following the analytical procedures of Williams
tion of the North Tianshan Ocean (Long et al., 2008; Wang et al., 2006, (1998) and Wan et al. (2010). Five scans through the mass stations
2007). The undeformed Sikeshu pluton, which crosscuts the Bayingou were made for each age determination. Standards for elemental abun-
ophiolitic mélanges, has a SHRIMP zircon U\Pb age of 316 ± 3 Ma dance and calibration of 206Pb/238U, respectively, were SL13 and TEM
Table. 2
SHRIMP U\Pb data for zircons from igneous rocks in the Tawuerbieke area, Tulasu basin.
Spots U Th Th/U Isotope composition Age (Ma)

(ppm) (ppm) 207 207 206 207 207
Pb/ ±% Pb/ ±% Pb/ ±% Pb/ 1σ Pb/ 1σ
206 235 238 235 206
Pb U U U Pb
TWE-20 (andesite)
1.1 586 367 0.65 0.054 1.5 0.429 2.5 0.058 2.1 361.5 ±7.2 368 ±33
2.1 225 224 1.03 0.056 2.2 0.453 3.5 0.059 2.8 367.3 ±9.9 453 ±49
3.1 179 98 0.57 0.052 4.1 0.405 4.6 0.057 2.2 355.6 ±7.6 278 ±93
4.1 146 62 0.44 0.055 3.5 0.426 4.1 0.056 2.2 352.9 ±7.7 410 ±78
5.1 157 68 0.45 0.053 4.5 0.417 5.0 0.057 2.2 357.1 ±7.7 334 ±100
6.1 316 394 1.29 0.052 3.2 0.422 3.8 0.059 2.1 366.5 ±7.6 299 ±73
7.1 152 65 0.44 0.050 4.7 0.401 5.2 0.058 2.2 363.5 ±7.9 204 ±110
8.1 158 114 0.75 0.051 3.0 0.411 3.7 0.059 2.2 368.8 ±7.9 221 ±69
9.1 313 209 0.69 0.051 2.5 0.408 3.2 0.058 2.1 365.9 ±7.5 223 ±57
10.1 111 44 0.41 0.055 4.0 0.452 4.6 0.060 2.3 372.5 ±8.3 416 ±89
11.1 254 124 0.50 0.050 3.5 0.395 4.1 0.057 2.1 358.0 ±7.4 205 ±81
12.1 138 60 0.45 0.053 4.6 0.415 5.4 0.057 2.8 356.1 ±9.8 331 ±110
13.1 159 88 0.57 0.051 4.1 0.391 4.6 0.056 2.2 349.2 ±7.5 240 ±94
14.1 141 53 0.39 0.051 4.3 0.407 4.9 0.058 2.2 362.0 ±7.8 244 ±100
15.1 183 95 0.54 0.055 2.8 0.436 3.5 0.057 2.2 358.1 ±7.5 424 ±62
16.1 163 112 0.71 0.055 2.5 0.439 3.4 0.058 2.2 365.4 ±7.9 395 ±56
17.1 182 76 0.43 0.051 3.5 0.406 4.2 0.057 2.2 360.0 ±7.7 255 ±81
18.1 139 63 0.47 0.052 4.2 0.414 4.8 0.057 2.4 358.7 ±8.5 304 ±95
19.1 541 520 0.99 0.055 1.9 0.437 2.8 0.058 2.0 364.2 ±7.2 391 ±42
20.1 401 442 1.14 0.053 3.2 0.408 3.8 0.056 2.1 351.6 ±7.1 317 ±72
TWE-8 (granitic porphyry)

1.1 209 295 1.46 0.053 2.8 0.410 3.0 0.056 1.1 353.9 ±3.7 314 ±64
2.1 726 344 0.49 0.057 2.7 0.426 2.8 0.054 0.9 337.7 ±2.9 506 ±59
3.1 117 92 0.81 0.051 8.5 0.396 8.6 0.056 1.3 351.2 ±4.4 254 ±200
4.1 296 156 0.55 0.056 1.5 0.594 1.8 0.077 1.0 478.4 ±4.4 449 ±33
5.1 608 262 0.45 0.055 1.3 0.433 1.6 0.057 0.9 360.2 ±3.2 398 ±30
6.1 291 151 0.54 0.052 2.8 0.411 2.9 0.057 1.0 357.9 ±3.4 296 ±63
7.1 441 211 0.49 0.052 1.9 0.408 2.1 0.057 0.9 357.1 ±3.2 284 ±43
8.1 642 304 0.49 0.054 2.2 0.411 2.4 0.055 0.9 346.7 ±3.0 369 ±50
9.1 609 344 0.58 0.054 2.0 0.427 2.3 0.058 1.1 361.6 ±3.9 355 ±44
10.1 341 374 1.13 0.054 3.1 0.423 3.3 0.057 1.0 357.8 ±3.4 362 ±70
11.1 231 143 0.64 0.055 3.4 0.424 4.0 0.056 2.0 353.8 ±6.7 392 ±77
12.1 354 480 1.40 0.057 2.3 0.417 2.7 0.053 1.4 331.1 ±4.5 507 ±51
13.1 162 174 1.11 0.053 4.3 0.410 4.5 0.056 1.1 353.4 ±3.9 321 ±98
Notes: Errors are 1σ; Common Pb corrected using measured 204Pb.
(Williams, 1998). Uncertainties for individual analyses are quoted at 1σ The basement consists of neritic carbonate and siliciclastic rocks of
and for weighted mean ages at 2σ (with 95% confidence level). The age the Mesoproterozoic Kusongmuqieke Group (Fig. 2). The lower Paleo-
calculation and plotting of concordia diagrams was performed using zoic strata include, from lowest to uppermost, tuffaceous and calcareous
SQUID 1.0 and ISOPLOT software of Ludwig (2003). siltstone of the Middle Ordovician Nailenggeledaban Formation,
Sulfur isotopic compositions of sulfides were analyzed with an carbonate and minor siliciclastic rocks of the Upper Ordovician
MAT-251 mass spectrometer at ALBRIUG using the SO2 method as de- Hudukedaban Formation, limestone with intercalated andesite of the
scribed by Robinson and Kusakabe (1975). Analytical precision for Lower Silurian Qianzilike Formation, carbonate interlayered with
δ34S is better than ± 0.2‰, and results are reported in standard per siliciclastic rocks of the Lower Silurian Nilekehe Formation, and
mil (‰) notation relative to the Vienna Canyon Diablo Troilite (VCDT) biocalcarenite and tuff of the Middle Silurian Jifuke Formation. The
standard. upper Paleozoic strata include, from bottom to top, quartz sandstone
Isotopic data are reported in standard per mil (‰) notation relative of the Upper Devonian Tulasu Formation, volcanic and volcaniclastic
to the Vienna Standard Mean Water (VSMOW) for oxygen and rocks of the Lower Carboniferous Dahalajunshan Formation and con-
hydrogen. glomerate and calcareous sandstone of the Lower Carboniferous
Aqialehe Formation (Fig. 2).
4. Geology, igneous geochemistry and geochronology of the The Dahalajunshan Formation, widely exposed in western Tianshan,
Tulasu basin comprises volcanic rocks of andesite, dacite, rhyolite and basaltic andes-
ite, as well as volcaniclastic rocks including volcanic breccia, volcanic
4.1. Geology of the Tulasu basin agglomerate and ignimbrite (Fig. 1c) with a total thickness of up to
1067–1515 m (XBGMR, 1993). The Dahalajunshan Formation is
The Tulasu basin is separated from the Yili basin by the North Yili subdivided into five lithologic members including, from bottom to top,
basin fault in the southwest and from the Keguerqin terrane by the the Conglomeratic, Acidic Tuff, Lower Andesite, Volcaniclastic, and
South Keguqinshan fault in the north (Fig. 1c). The Tulasu basin consists Upper Andesite members (XBGMR, 1993).
of Paleozoic volcanic and sedimentary rocks overlying Proterozoic Intrusive rocks are rare within the Tulasu basin (Fig. 1c). Granitic
metamorphic basement rocks. The basin formed in a passive continental porphyries that intrude andesites of the Dahalajunshan Formation are
margin setting during the early Paleozoic, and then evolved into an ac- exposed in the Tawuerbieke area (Fig. 2). Middle Hercynian intrusions
tive continental margin due to the southward subduction of the North cut limestone of the Neoproterozoic Kaiertasi Group and glacial deposits
Tianshan Ocean. This change of tectonic setting is marked by an uncon- of the Sinian Kailaketi Group in the Kexiaxi area. Various intrusions
formity between upper and lower Paleozoic strata (Figs. 1c and 2). including hornblende-bearing gabbro, quartz-diorite, micro-diorite,
Fig. 3. Petrochemical and concordia diagrams for andesite of the Dahalajunshan Formation in the Tawuerbieke area, Tulasu basin. The primitive mantle and chondrite values are from Sun
and McDonough (1989); the Th–Hf/3–Ta discrimination diagram is from Wood et al. (1979).
granodiorite, tonalite and diorite porphyry are distributed along the 2008; Long et al., 2008; Wang et al., 2006, 2007; Xia et al., 2011; Xiao
northern margin of the Tulasu basin (Fig. 1c). In the northeastern part et al., 2005; Zhai et al., 2006, 2009), only very few studies have been un-
of the Tulasu basin, late Hercynian intrusions of quartz-monzonite and dertaken on the Tawuerbieke area (Tang et al., 2009). Hence, in this
quartz-monzodiorite cut intermediate–felsic volcanic rocks of the study, eight andesite samples were collected from outcrops at the
Upper Carboniferous Dongtujin Formation (Fig. 1c). Tawuerbieke Au prospect for detailed geochemical and geochronologi-
cal studies.
4.2. Geochemistry and geochronology of the upper Paleozoic volcanic rocks Seven of these samples were selected for whole-rock geochemical
analyses, and the eighth sample (TWE–20) was used for dating. The
The upper Paleozoic volcanic rocks in the Tulasu basin have been analytical results are listed in Tables 1 and 2. Volcanic rocks of the
considered by some researchers to have formed in extensional environ- Dahalajunshan Formation in the Tulasu basin are mainly andesite.
ments, either in an intracontinental rift system (Che et al., 1996; Xia Andesite samples from the Tawuerbieke area show broadly similar
et al., 2004) or related to a mantle plume (Xia et al., 2008, 2012), and trace and rare-earth element (REE) compositions as andesite, rhyolite
by others as in a convergent, continental arc setting (An and Zhu, and basaltic andesite rocks from other parts of the basin (Fig. 3a, b).
2008; Gao et al., 1998; Tang et al., 2009; Wang et al., 2006, 2007; Xia These samples are characterized by a pronounced enrichment of
et al., 2011). Different dates of volcanic eruption have been obtained large-ion lithophile elements and a depletion of Nb, Ta, P and Ti
by different authors. The andesite from the topmost Upper Andesite (Fig. 3a). On the chondrite-normalized REE plot, all the samples display
Member of the Dahalajunshan Formation in eastern Tawuerbieke has slightly enriched LREE, flat HREE and a subtle negative Eu anomaly (Eu/
yielded a LA–ICP–MS zircon U\Pb date of 347.2 ± 1.6 Ma (Tang et al., Eu⁎ = 0.69–0.85) (Fig. 3b). These geochemical characteristics are con-
2009), whereas the quartz-andesite from the same member in the sistent with typical island-arc magmas (Innocenti et al., 2005; Wilson,
neighboring Axi area has a SHRIMP zircon U\Pb date of 363.2 ± 1989). The volcanic rocks of the Dahalajunshan Formation plot within
5.7 Ma (Zhai et al., 2006). A SHRIMP U\Pb date of 386.4 ± 9.3 Ma has the calc-alkaline basalts (CAB) field (Fig. 3c) in the Th–Hf–Ta diagram
been obtained for zircons from rhyolite in the Lower Andesite Member (Wood et al., 1979), also consistent with a volcanic island-arc setting.
of the Dahalajunshan Formation in the Jingxi–Yelmend ore deposit (An Twenty SHRIMP analyses spots of zircon from an andesite sample
and Zhu, 2008). These different dates need to be resolved using addi- (TWE–20) yield an average U\Pb concordant age of 361 ± 4 Ma
tional geochemical and geochronological data. (MSWD = 0.61) (Fig. 3d). This age, together with those reported in pre-
Compared to the Axi and Jingxi–Yelmend areas in the Tulasu basin, vious studies (ca. 347–386 Ma; An and Zhu, 2008; Tang et al., 2009; Zhai
which have been studied by numerous researchers (An and Zhu, et al., 2006) from other parts of the Tulasu basin, suggests that the calc-
Fig. 4. Petrochemical and concordia diagrams for granitic porphyries in the Tawuerbieke area, Tulasu basin. The primitive mantle and chondrite values are from Sun and McDonough
(1989); the Y + Nb–Rb discrimination diagram is from Pearce et al. (1984).
alkaline island-arc magmatic eruption in the Tulasu basin mainly took diagram (Pearce et al., 1984), all the samples consistently plot on the
place from Late Devonian to the Early Carboniferous. volcanic arc granite (VAG) field (Fig. 4c). These geochemical character-
istics are similar to those that have been reported in the Kexiaxi area of
4.3. Geochemistry and geochronology of the upper Paleozoic intrusive rocks the Tulasu basin (Fig. 4a, b).
With the exception of two discordant grains (spots 2.1 and 12.1) and
Compared to the upper Paleozoic volcanic rocks, relatively little at- one concordant grain (spot 4.1) giving a 206Pb/238U age of 478.4 ±
tention has been paid to the upper Paleozoic intrusive rocks in terms 4.4 Ma, the remaining ten analyses of zircon grains from the granitic
of their geochemistry, geochronology and tectonic setting. SHRIMP porphyries sample (TWE–8) yield a weighted mean 206Pb/238U age of
zircon U\Pb ages of 368.4 ± 5.2 Ma and 354.2 ± 4.1 Ma were obtained 355.4 ± 4.0 Ma (Fig. 4d).
from micro-diorite and tonalite of the composite Kexiaxi pluton, which In summary, both the volcanic rocks and intrusions of Late-Devonian
is considered to have formed in a continental-arc setting (Wu et al., to Early-Carboniferous ages in the Tulasu basin have island-arc calc-
2011). In this study, we selected seven unaltered samples of granitic alkaline characteristics (Foley and Wheller, 1990; Wilson, 1989). They
porphyries from the Tawuerbieke prospect for geochemical and geo- are defined by similar patterns on primitive mantle-normalized spider
chronological studies, using the same techniques as for the andesite diagrams and chondrite-normalized REE diagrams (Figs. 3 and 4),
samples. Six granitic porphyries samples were selected for whole-rock with relative enrichment of Th (2.81–4.94 ppm for andesite, 8.05–
geochemical analyses, and the seventh sample (TWE–8) was used for 9.35 ppm for granitic porphyry) and U (0.98–1.35 ppm for andesite,
dating. The analytical results are presented in Tables 1 and 2. 2.42–3.34 ppm for granitic porphyry), high (La/Yb)N values (2.1–5.5
The granitic porphyry samples are highly evolved (SiO 2 = for andesite, 7.0–10.4 for granitic porphyry), and depletion of Nb
73.5–77.15%), rich in total alkalis (Na2O + K2O = 8.44–9.05%), and (3.27–8.77 ppm for andesite, 15.30–17.70 ppm for granitic porphyry),
poor in CaO (0.12–0.51%). They fall into the high potassic calc-alkaline Ta (0.35–0.71 ppm for andesite, 1.38–1.59 ppm for granitic porphyry),
series with the Rittmann Index between 2.1 and 2.5, and are weakly and Ti (TiO2 = 0.71–0.81 wt.% for andesite, 0.22–0.25 wt.% for granitic
peraluminous with A/CNK values from 1.33 to 1.60. All the samples porphyry). These geochemical data suggest that the igneous rocks
show negative anomalies of Nb, Ta, Sr, Ti on the primitive mantle- in the Tulasu basin, including both the volcanic and intrusive rocks,
normalized trace element spider diagram (Fig. 4a), and slight LREE en- were possibly generated from a common calc-alkaline parental
richment, flat HREE, and a slightly negative Eu anomaly on a chondrite- magma chamber in an island-arc setting during the southward
normalized REE diagram (Fig. 4b) that are similar to those of island-arc subduction of the North Tianshan ocean plate beneath the Kazakhstan–
magma (Foley and Wheller, 1990). In the (Y + Nb)–Rb discrimination Yili Plate.
5. Au\Cu–polymetallic mineralization in the Tulasu basin
An and Zhu (2008),

Chen et al. (2012)
Xiao et al. (2005),

Zhai et al. (2006),
Sha et al. (2005),
Wu et al. (2011)
QMDCY (2009)
Jia et al. (2001)
JMCX (2009)
References The Tulasu basin is one of the most important Au districts in Xinjiang
province. In addition to the large Axi and Jingxi–Yelmend Au deposits,
several small Au prospects have been found at Tawuerbieke,
Qiabukanzhuota, Kuangou, Tulasu, and southwestern Tulasu. The main
geologic and geochemical features of these deposits are listed in
1.2–32.5 g/t
Cu 0.2–1.3%
0.9–4.5 g/t
Table 3 and discussed below.
Zn 6.03%
Pb 2.82%
3–8 g/t
Grade
5.1. Axi Au deposit

Size
70 t
50 t
P
P
The Axi Au deposit is located in the central part of the Tulasu basin
(Fig. 1c), approximately 30 km northwest of Yining City, and it repre-
Chalcedony, quartz, sericite,
sents the largest epithermal Au deposit in the Xinjiang province. The

resource is currently estimated to be 12.6 Mt at an average grade of
5.57 g/t Au, for 70 t of Au (Chen et al., 2012). The main strata exposed
Quartz, gypsum,
kaolinite, barite,
calcite, adularia,
Gangue mineral
Quartz, sericite,
Calcite, sericite,
quartz, chlorite
calcite, chlorite
Quartz, dickite,
at Axi are intermediate and felsic lavas with related pyroclastic rocks
pyrophyllite
assemblage
of the Upper Andesite Member of the Dahalajunshan Formation, includ-

calcite
ing andesites, dacites, rhyolites, tuffs, and volcanic breccias. Agglomer-

ate, conglomerate and sandstone of the Lower Carboniferous Aqialehe
Formation unconformably cover the Dahalajunshan Formation in the
pyrrhotite, molybdenite
northeastern part of the deposit (Fig. 5). The Axi maar-diatreme with
ring structures and radial features are well developed in the area, and
Pyrite, marcasite,
the maar-diatreme is characterized by a typical oval shape aeromagnet-

galena, pyrite,
Pyrite, galena,
Pyrite, native
arsenopyrite,
arsenopyrite,
Chalcopyrite,
chalcopyrite
Ore mineral
assemblage
Au, copper
ic anomaly with 2.6 km long and 2.4 km wide (Dong and Sha, 2005).
Sphalerite
native Au
electrum,
This circular structure and related ring and radial faults represent the
pyrite,
major loci of the Axi Au veins and neighboring Tabei Pb–Zn and
Tawuerbieke Au mineralization (Fig. 5a). The largest orebody of Axi,
Pyrite, sericite, carbonate,
Hydrothermal alteration
the NS-trending No. 1 vein, extends up to 1000 m along strike, has a

thickness of 11–15 m, and extends downdip to about 400 m (Fig. 5b).
dickite, kaolinite,
The Au grades range from 2 to 16 g/t, with an average of 5.57 g/t

sericite, chlorite,
(FGTXBGMR, 1992).
Silicification,
Silicification,
Silicification,
Silicification,
silicification
The Au mineralization can be divided into four stages, each charac-

chlorite,
chlorite,
sericite,
chlorite
sericite
pyrite,
terized by different mineral assemblages in the veins, including 1)

illite
light grey–white quartz and/or chalcedony veins (Fig. 6a), 2) smoky–

grey quartz and chalcedony veins (Fig. 6b), 3) quartz–sulfide veins
of 60 m, and 6.3 m
Length, thickness
(Fig. 6c), and 4) quartz–carbonate veins (Fig. 6d). Hydrothermal alter-

Average length
Main characteristics of Au\Cu–polymetallic deposits and prospects in the Tulasu basin, western Tianshan.
ation shows a clear zonation, changing outward from the center of the
30–1400 m;
in thickness
50–210 m;
60–300 m;
of orebody
20–200 m
11–15 m
quartz veins, and grading from a zone of silicification through a zone

1000 m;
1–4.8 m
3–45 m
of phyllic alteration into a zone with propylitic alteration (Fig. 5b).

Three types of Au ore are documented, including the quartz vein type,
altered rock type and breccia type. The quartz veins occur in various
Orebody shape
types, and are commonly associated with silicification. The alteration

Lenticular,
Lenticular,
Lenticular,
Vein-like,
lenticular
Flat vein,
vein-like
vein-like
bed–like
is most pronounced on the top and bottom of the respective orebodies,

banded
including silicification, and sericite and chlorite alteration of andesite of

the Dahalajunshan Formation (Fig. 6e). The breccia ores are mainly
SN-trending faults
NS-trending faults
developed at structural intersections and contains fragments of both

WNW-trending
Volcanic edifice
Ore-controlling
NNW- and NS-

trending faults
NNE-, NE- and
the veins and altered andesites that are cemented by hydrothermal

and related
quartz–sulfide (Fig. 6f).

structure
The Au ores are characterized by crustiform texture (Fig. 6g) and

faults
faults
drusy cavity (Fig. 6h), showing open-space filling. Ore minerals are
mainly pyrite, arsenopyrite and electrum with minor native Au, sphaler-
D3–C1 hornblende-bearing
ite, chalcopyrite and galena. Gangue minerals are quartz, chalcedony,

conglomerate and tuff,
C1 tuff, Dahalajunshan
sericite, calcite, adularia and laumontite. Adularia is sparsely distributed

gabbro, micro-diorite
C1 andesite and tuff
Abbreviations: P—prospect; Fm.—Formation.

Dahalajunshan Fm.
Dahalajunshan Fm.
Dahalajunshan Fm.
clastic rocks of the
in the quartz veins (Zhai et al., 2009).

diorite porphyrite
C1 andesite and
The δ34S values of pyrite from the auriferous quartz veins vary from
and C1 granitic
quartz-diorite,
C1 polymictic
granodiorite,
−4.0 to 3.1‰ (Table 4) with a peak value of −0.5‰ (Zhai et al., 2006).
Host rocks
porphyry
The homogenisation temperatures of fluid inclusions in the auriferous

Fm.
quartz veins range from 120 to 240 °C (average 190 °C), and the salin-
ities vary from 0.7 to 3.1 wt.% NaCl equiv. (average 2.2 wt.% NaCl
equiv.) (Zhai et al., 2009). The δD values of fluid-inclusion water in au-
riferous quartz veins range from -115.2 to − 98.0‰, together with a
Axi Au deposit
Jingxi–Yelmed
Au prospect
Tawuerbieke
Au deposit
Tabei Zn–Pb
δ18Owater value of − 3.3 to 0.4‰ calculated from δ18Oquartz values of

Ore deposit
prospect
prospect
Kexiaxi Cu
11.1 to 13.3‰ and the fluid-inclusion homogenization temperatures

Table 3
(Table 5), suggesting that the ore-forming fluids were dominated by

meteoric waters (EARCXGMRB, 1992; Sha et al., 2005; Zhai et al., 2009).
Fig. 5. Geological map (a) and cross section of the A–A′ prospecting line (b) of the Axi–Tawuerbieke area (modified from Dong and Sha, 2005; FGTXBGMR, 1992; Zhao et al., 2012).
5.2. Tabei Zn–Pb prospect northward-dipping monoclinal structure, cut by a NNE-trending re-
verse fault that controls the large No. 1 mineralized zone. Mineralization
The Tabei Zn–Pb prospect is located about 0.5 km south of Axi occurs within a 10–40 m wide alteration zone in the hanging wall of the
(Figs. 1c and 5a), and represents the only Zn–Pb deposit in the Tulasu fault (Fig. 7).
basin. It occurs in the southwestern part of the Axi volcanic edifice. The mineralization is hosted by tuffs of the Dahalajunshan Forma-
The strata exposed in the Tabei area are mainly volcanic agglomerate, tion (Fig. 7). It has an average length of 60 m, an average thickness of
volcanic breccia, tuff, andesite and dacite of the Dahalajunshan Forma- 6.3 m, and average grades of 2.82% Pb and 6.03% Zn (QMDCY, 2009).
tion (Fig. 5a). The volcanic clasts decrease in size gradually from Axi The mineralization can be divided into three types: 1) breccia
(coarse) to Tabei (fine). The strata of the Tabei prospect occur in a (Fig. 8a), 2) massive (Fig. 8b), and 3) banded (Fig. 8c, d). Ore minerals
Fig. 6. Field photos showing various types of ore in the Axi Au deposit. (a) Stage I light gray to white quartz-chalcedony veins and stage II smoky gray quartz-chalcedony veins; (b) stage II
smoky-gray quartz-chalcedony veinlets; (c) stage III quartz-sulfide veins crosscutting stage II smoke-gray quartz-chalcedony veinlets; (d) stage IV quartz-carbonate veins crosscutting
stage II smoke-gray quartz-chalcedony veinlets; (e) altered andesite ores; (f) breccia ores; (g) crustiform texture of Au ores; and (h) drusy cavity in auriferous quartz.
are mainly sphalerite and galena with minor chalcopyrite and pyrite, mineralization and occurs both in the hanging wall and footwall of the
and the gangue minerals include quartz, calcite, kaolinite and gyp- mineralized zone.
sum (Fig. 8). Vug-filling drusy quartz and chalcopyrite are common The δ34S values of four galena samples span a narrow range from 2.1
(Fig. 8b). to 2.6‰ (Table 4), with an average of 2.3‰.
Wall rock alteration includes chlorite and sericite alteration, and
silicification. The chlorite alteration is characterized by selectively per- 5.3. Tawuerbieke Au prospect
vasive replacement of mafic minerals and volcanic glass by chlorite.
Sericite alteration is well developed throughout the entire alteration The Tawuerbieke Au prospect is situated about 1 km southwest of
zone, and it is strongest near the main mineralization shoot. Silicifica- Axi (Figs. 1c and 5a). The rock types in the area mainly consist of andes-
tion is the principle alteration that is directly associated with Zn–Pb ite and andesitic pyroclastic rocks of the Dahalajunshan Formation with
Table 4 associated with pervasive alteration that includes pyrite, sericite,

Sulfur isotope compositions of Au\Cu–polymetallic deposits and prospects in the Tulasu carbonate, chlorite, epidote and quartz. This type of mineralization is
basin.
overprinted by late-stage auriferous quartz veins that form the high-
Sample no. Sample δ34S(‰) Source grade mineralization (Fig. 9c, d).
Axi The ore minerals are mainly auriferous pyrite and native Au.
04A-2/8a Pyrite 0.1 A Euhedral–subhedral Au-bearing pyrite is disseminated in both mineral-
04A-2/9a Pyrite −0.1 ization types. Native Au is commonly found in oxidized quartz veins on
04A-2/10a Pyrite −0.1
the surface (Fig. 9d). Comb texture and drusy cavity are common in the
04A-3/a Pyrite −0.2
04A-4/8a Pyrite 1.4 veins (Fig. 9f). Gangue minerals include calcite, quartz and sericite.
04A-8/a Pyrite −4.0 Some sulfide-mineralized enclaves of monzonite porphyry (Fig. 10a)
04A-1450/8a Pyrite −1.2 and fine-grained diorite (Fig. 10b) were recorded in andesite from the
04A-1450/12a Pyrite 1.2 western Tawuerbieke area (Zhao et al., 2012). These enclaves have
04A-1450/16a Pyrite −0.3
rounded to subangular shapes, and they are randomly distributed with-
04A-1450/24a Pyrite −0.4
04A-1450/28a Pyrite −3.2 in the andesite (Fig. 10a, b). Native Au occurs as isolated inclusions or
04A-2 Sulfide-bearing quartz 3.1 along microfractures within pyrite that is disseminated in the enclaves
04A-2/13 Sulfide-bearing quartz −2.2 (Fig. 10c, d). Native Cu was found in basaltic andesite cores from drill
Tawuerbieke hole ZK28-1 (Fig. 10e, f), resulting in elevated copper grades of
C1 Pyrite 3.6 This paper 0.21–0.35% (XIECBMG, 2010).
C4 Pyrite 4.2 A total of 16 pyrite samples from Au mineralization of the
C6 Pyrite 2.5
Tawuerbieke prospect were selected for sulfur isotope analyses. The
C7 Pyrite 3.1
C8 Pyrite 2.9
δ34S values exhibit a relatively narrow range from 0.6 to 4.2‰
C9 Pyrite 2.7 (Table 4), with a peak value of 2.2‰. Homogenisation temperatures of
C10 Pyrite 2.8 fluid inclusions from quartz veins of the main stage range from 100 to
C11 Pyrite 1.4 250 °C (average of 130 °C), and the salinities vary from 0.6 to 2.1 wt.%
C12 Pyrite 2.5
NaCl equiv. (1.1 wt.% NaCl equiv.) (Jia et al., 2001). The δ18Owater values
C13 Pyrite 1.7
C14 Pyrite 2.5 were calculated to be − 1.6 to − 0.2‰, based on δ18Oquartz values of
XT4–1 Pyrite 1.4 10.3–10.7‰ and an average fluid-inclusion homogenization tempera-
XT4–2 Pyrite 1.6 ture of 130 °C, and the δD values range from −98 to −101‰ (Table 5).
XT4–3 Pyrite 0.7
XT4–4 Pyrite 0.6
XT4–5 Pyrite 1.3
5.4. Jingxi–Yelmend Au deposit
Jingxi–Yelmend
The Jingxi–Yelmend Au deposit is located about 8 km northwest of
TUD03-162 Pyrite 5.1 B
TUD06-17 Pyrite 6.8
Axi (Fig. 1c) and has an estimated resource of 52.6 Mt at an average
TUD03-252 Pyrite 8.1 Au grade of 0.95 g/t, for 50 t of Au (JMCX, 2009). The geology in the
GM04 Pyrite 6.9 C area consists of limestones of the Hudukedaban Formation that are
GM05 Pyrite 2.2 unconformably overlain by volcanic and pyroclastic rocks of the
GM14 Realgar −7.0
Dahalajunshan Formation. Minor andesitic porphyry and acidic dikes
GM15 Stibnite 3.0
GM16-A Realgar 5.8 occur in the center of the deposit (Fig. 11).
GM16-B Realgar 5.7 Gold mineralization in the Jingxi–Yelmend deposit is hosted by con-
GM35 Pyrite −12.0 glomerate, tuff and tuffaceous sandstone. The orebodies are controlled
GM36 Pyrite −12.7 by the intersections of the NNW- and nearly NS-trending faults, and
GM37 Pyrite −4.3
GM38 Pyrite −0.6
have various shapes, including veins, pods, and stratiform bodies. The
GM39 Pyrite −0.6 veins obliquely cut across the bedding of the host rocks, whereas the
GM13 Barite 16.0 pods and stratiform orebodies are concordant with the strata. The
GM22 Barite 17.4 orebodies are typically 60 to 300 m long, 20 to 200 m thick, and have
09-JX-02 Barite 16.6
an average grade of 0.9 g/t Au, with a maximum grade of 46.8 g/t
Tabei (JMCX, 2009).
GM16-B Realgar 5.7 This paper Three mineralization stages have been identified (An and Zhu,
GM35 Pyrite −12.0
2010): 1) an early silicification and sericite alteration stage that precip-
GM36 Pyrite −12.7
GM37 Pyrite −4.3 itated a large amount of quartz, sericite and pyrite in the host rocks; 2) a
brecciation and silicification stage, and 3) a calcite–barite stage that is
Data sources: (A) Zhai et al. (2006); (B) Xiao et al. (2001); (C) Zhu et al. (2011).
characterized by abundant coarse-grained calcite-barite veins. The sec-
ond stage is the main mineralization stage and can be further divided
into two substages: the substage-I hydrothermal breccias are composed
of altered host rock fragments (first stage) cemented by smoky–grey
minor limestone of the Middle Ordovician Nailenggeledaban Formation. quartz and pyrite (Fig. 12a), and the substage-II hydrothermal breccias
Hercynian dikes of granitic porphyry and diorite occur in the central and are composed of altered rock fragments (first stage) and breccias
west part of the area (Fig. 5a). formed during substage-I that are cemented by fine-grained quartz,
Gold mineralization is hosted by andesite, tuff, volcanic breccia and pyrite, and arsenopyrite (Fig. 12b).
granitic porphyries (Fig. 5a). The mineralized shoots occur as discontin- Hydrothermal mineralization in the Jingxi–Yelmend area extends
uous veins and lenses that are controlled by NNW- and nearly NS- over more than 4 km2, and shows a distinct alteration zonation from
trending faults, preferentially at their intersections. The size of the pervasive silicification in the core that grades outwards through
veins varies, but they are typically 30–1400 m long and 3–45 m thick, advanced argillic alteration into moderate argillic alteration in the
with Au grades ranging from 1.22 to 32.5 g/t (XIECBMG, 2010). periphery (Xiao et al., 2005). The bulk of mineralization is hosted by
The mineralization can be divided into two types and stages. The the first two alteration zones (Fig. 12d). The zone with silicification is
early-stage, low-grade, fracture-controlled type of mineralization is characterized by the development of vuggy quartz and chalcedony
Table. 5
Hydrogen and oxygen isotope composition of ore-forming fluids associated with epithermal gold deposits and prospects in the Tulasu basin.
Sample no. Analyzed sample Temperature(°C) δDwater (‰) δ18Oquartz (‰) δ18Owater (‰) Soures
Axi
901 T6-S04† Auriferous quartz 190 −101.0 13.1 0.2 A
901 T6-S06† Auriferous quartz 190 −115.0 12.2 −0.6
901 T6-S03† Auriferous quartz 190 −110.0 12.4 −0.4
SAI8-3 Auriferous quartz 150 −106.3 12.2 −3.3 B
SAI6-7 Auriferous quartz 150 −113.6 13.2 −2.3
Auriferous quartz 150 −103.9 11.6 −3.9
901 T6-06 Auriferous quartz 150 −101.4 13.1 −2.3
901 T6-03 Auriferous quartz 150 −115.2 12.2 −3.3
Auriferous quartz 150 −109.8 12.4 −3.1
04A-2/8 Auriferous quartz 190 −98.0 12.8 -0.1 C
04A-2/9 Auriferous quartz 190 −102.0 12.1 −0.8
04A-2/10 Auriferous quartz 190 −110.0 12.9 0.0
04A-3 Auriferous quartz 190 −108.0 11.1 −1.8
04A-8 Auriferous quartz 190 −112.0 12.3 −0.6
Tawuerbieke
TW-1 Auriferous quartz 130 −101.4 10.3 −0.2 D
TW-9 Auriferous quartz 130 −98.2 10.7 −1.6
Jingxi–Yelmend
2–47 Auriferous quartz 223 −75 18.5 4.2 E
2–47 Auriferous quartz 235 −77 17.2 4.5
δOwater value were calculated using the fractionation equations of Clayton et al. (1972).
Data sources: (A) EARCXGMRB (1992); (B) Sha et al. (2005); (C) Zhai et al. (2009); (D) Jia et al. (2001); (E) Xiao et al. (2005).
(Fig. 12e), the advanced argillic alteration zone by abundant kaolinite, The δ34S values of pyrite, realgar, and stibnite in the Au ores of the
dickite (Fig. 12f), and alunite and pyrophyllite (Xiao et al., 2005), and Jingxi–Yelmend deposit vary from −12.7 to 8.1‰, and those of barite
the intermediate argillization zone by smectite with minor kaolinite. from 16.0 to 17.4‰ (Xiao et al., 2005; Zhu et al., 2011) (Table 4). The hy-
drothermal sulfur is considered to be mixture of seawater and igneous
sulfur. Homogenisation temperatures of fluid inclusions from vuggy
quartz range from 198 to 275 °C (average 240 °C), and salinities range
from 0.7 to 5.0 wt.% NaCl equiv. (average 2.8 wt.% NaCl equiv.) (Xiao
et al., 2005). The δDwater in auriferous quartz ranges from − 89 to
− 68‰, and the δ18Owater values were calculated to be 4.1 to 5.8‰
using δ18Oquartz values of 17.2–21.6‰ and the fluid-inclusion homogeni-
zation temperatures (Table 5).
5.5. Kexiaxi Cu prospect
The Kexiaxi Cu prospect is located 15 km northeast of the Axi Au de-

posit (Fig. 1c). The geology exposed in the area is dominated by Protero-
zoic metamorphic basement, consisting of carbonate and siliciclastic
rocks of the Neoproterozoic Kaiertasi Group and siliciclastic and glacial
deposits of the Sinian Kailaketi Group (Fig. 13a).
The basement rocks were intruded by Late-Devonian hornblende-
bearing gabbro, which was in turn intruded by quartz-diorite in the
southern part of the area. Late-Devonian micro-diorite occurs in the
northern part of the area, and Early-Carboniferous granodiorite–tonalite
intrusions as well as dioritic porphyry dikes are developed in the
western part (Fig. 13a). NE- and ENE-trending faults are closely related
to the mineralization and are crosscut by WNW-trending faults.
Hydrothermal alteration is well developed in both the intrusions
and the host rocks, mainly consisting of potassic alteration, silicification,
and epidote, chlorite, sericite, and carbonate alteration. Potassic alter-
Fig. 7. A cross section along the B–B′ prospecting line (see Fig. 5 for location) of the Tabei ation is characterized by fine-grained K-feldspar and hydrothermal
Zn–Pb prospect (modified from QMDCY, 2009). botite in granodiorite–tonalite intrusions. Silicification is marked by
Fig. 8. Photographs showing the main types and characteristics of ores in the Tabei Zn\Pb prospect. (a) Sphalerite breccia ore; (b) massive sphalerite–galena ore with local chalcopyrite
associated with drusy quartz; (c) banded galena associated with gypsum and kaolinite; and (d) banded sphalerite–galena with quartz and kaolinite.
quartz ± pyrite ± chalcopyrite veinlets (Fig. 14c, e, g) as well as Tieliekesayi area consists of the Dahalajunshan Formation and the
replacement of the host rocks by quartz. Strongly silicified rocks have Upper Ordovician Hudukedaban Formation (Fig. 15). The Dahalajunshan
lost all primary textures (Fig. 14h). Silicification is widespread through- Formation includes rhyolitic crystal tuff and pelitic siltstone of the Acid
out the prospect, and shows a close spatial relationship with Cu miner- Tuff Member, intermediate to acid volcanic rocks of the Lower Andesite
alization (Fig. 14). Epidote alteration in fine-grained diorite is broadly Member, and the Hudukedaban Formation consists of sandstone and
coeval with silicification, and is related to Mo mineralization at depth limestone.
(Fig. 14f). Sericite, chlorite, and carbonate alteration affect all the intru- The kaolinite–dickite mineralization is mainly developed in rhyolitic
sions in Kexiaxi pervasively, with sericite preferentially replacing crystal tuffs of the Dahalajunshan Formation. The contact between the
plagioclase and chlorite and carbonates replacing mafic minerals re- kaolinite–dickite alteration zone and the wall rock is gradational over
placement. Copper mineralization is mainly hosted by the fine-grained less than 1 m (Fig. 16a), and a 5–10 m thick silicified cap is developed
diorite. The mineralized zone has an average length of 400 m, a thick- above the kaolinite–dickite alteration zone. The kaolinite–dickite alter-
ness of 100–400 m, a down-dip extension of 400 m, and Cu grades ation zone has a lenticular form, trends NW–SW, and is 220–270 m
range from 0.5 to 0.8% (Wu et al., 2011). long and 40–60 m wide (Fig. 15). The kaolinite–dickite altered rocks
The supergene zone of the Kexiaxi Cu prospect is up to 50 m thick, are pale yellow to grey in color with a greasy luster (Fig. 16b), and
with the copper mineralization occurring in cracks of fine-grained they show a slight transparency when soaked with water. The XRD
diorite and granodiorite as malachite and covellite (Fig. 14a). The analyses indicate that the clay minerals are dickite, kaolinite, pyrophyl-
primary mineralization is vein-type near the surface and this changes lite, with minor ralstonite and anhydrite.
to veinlet–disseminated at depth. The veins consist of quartz, chalcopy-
rite and pyrite (Fig. 14b), and are controlled by fracture zones in
hornblende-bearing gabbro and fine-grained diorite. The veins are 6. Discussion and conclusions
generally 50 to 210 m long with an average thickness of 1 to 4.8 m,
and the Cu grades vary from 0.21 to 1.37% (Wu et al., 2011). The The radiometric ages of the volcanic and intrusive rocks that host the
veinlet–disseminated mineralization is mainly developed in fine- Au and copper mineralization in the Tulasu basin range from 346 Ma to
grained diorite (Fig. 14b, d) and granodiorite (Fig. 14e) at depth. The 386 Ma (Table 6). The geochemical characteristics of the volcanic rocks,
ore minerals mainly consist of chalcopyrite and pyrite (Fig. 14d, e) with especially their enrichment in large-ion lithophile elements and LREE,
minor molybdenite and pyrrhotite. Chalcopyrite and pyrite occur as and their depletion in high-field strength elements, indicate a magmatic
1–10 mm wide veinlets (Fig. 14d, e, g, h) or as disseminations arc environment. The similarities in geochemical characteristics be-
(Fig. 14e), and molybdenite occurs as patches or scattered specks, togeth- tween the coeval intrusive rocks and volcanic rocks suggest that they
er with quartz and epidote, in cracks of the granodiorite (Fig. 14f). The were formed from common magmatic sources. This interpretation is
veinlet-disseminated mineralization is overprinted by the vein-type min- consistent with the regional tectonic framework in which the Tulasu
eralization that is accompanied by intense silicification (Fig. 14h). basin was located above the southward subduction zone of North
Tianshan Ocean beneath the Kazakhstan–Yili plate from Late Devonian
5.6. Tieliekesayi kaolinite–dickite prospect to Early Carboniferous (Gao et al., 1998; Xiao et al., 1992), one of multi-
ple subduction zones of different polarity developed during the closure
The Tieliekesayi kaolinite–dickite prospect is situated about 1.5 km of the Paleo-Asian Ocean (Charvet et al., 2011; Khain et al., 2003; Qin
to the southwest of the Tawuerbieke area (Fig. 1c). The geology in the et al., 2002; Safonova et al., 2011; Xiao et al., 2010, 2013).
Fig. 9. Main ore types and their structures in the Tawuerbieke Au prospect. (a) Mineralized granitic porphyry ore with silicification and chlorite and pyrite alteration; (b) gold-mineralized
andesite with silicification and chlorite and pyrite alteration; (c) auriferous calcite vein; (d) native gold in quartz vein; (e) late-stage calcite vein crosscutting quartz-sulfide veins; and (f)
comb texture and drusy cavity in gold-bearing quartz vein.
A range of 339 to 289 Ma mineralization ages of the Au\Cu– Tawuerbieke Au prospect and the Tabei Zn–Pb prospect fall in a narrow
polymetallic deposits in the Tulasu basin has been reported by Li et al. range from 0.6 to 4.2‰, with an average of 1.4‰ (Fig. 17), indicating
(1998) using the Rb\Sr and Ar\Ar methods of fluid inclusions in aurif- that the sulfur was mainly derived from an igneous source. The δ34S
erous quartz. However, these data are generally considered unreliable values of sulfides from the Jingxi–Yelmend Au deposit, however, exhibit
due to the interference of secondary inclusions (Hart et al., 2003; Liu a wide range from −12.7 to 8.1‰ (Xiao et al., 2001; Zhu et al., 2011),
et al., 1998; Yao and Zheng, 2001). Based on the observation that suggesting that sulfur was derived from a mixture of seawater and igne-
the mineralized and altered rocks of the Dahalajunshan Formation ous sulfur. The δD and δ18Owater values of fluid inclusions in quartz from
are unconformably overlain by the Aqialehe Formation (Figs. 1c, 2 the ores indicate that the ore-forming fluids were slightly (Jingxi–
and 5) which contains Visean Siphonodendron sp., Caninia sp. and Yelmend) to significantly (Axi and Tawuerbieke) depleted in 2H and 18O
Gigatoproductus sp. of fossils (FGTXBGMR, 1990), the timing of (Fig. 18), suggesting different degrees of involvement of meteoric water.
Au\Cu–polymetallic mineralization in the Tulasu basin may be The fluid inclusion data of Axi (homogenisation temperature:
constrained between the end of the Late Devonian to the end of the 120–240 °C; Salinities: 0.7–3.1 wt.% NaCl equiv.), Tawuerbieke (homoge-
Visean in the Early Carboniferous. It is therefore inferred that the nisation temperature: 100–250 °C; Salinities: 0.6–2.1 wt.% NaCl equiv.),
Au\Cu–polymetallic mineralization in the Tulasu basin is related to and Jingxi–Yelmend (homogenisation temperature: 198–275 °C; Salin-
the Late Devonian–Early Carboniferous arc magmatism. ities: 0.7–5.0 wt.% NaCl equiv.) indicate that the mineralizing fluids have
The geologic and geochemical characteristics of the Au and Cu de- relatively low temperatures and low salinities. These geochemical charac-
posits in the Tulasu basin are typical for epithermal Au and porphyry teristics suggest that the Au and Cu mineralization in the Tulasu basin is
Cu\Au systems. The δ34S values of sulfides in the Axi Au deposit, the mainly of epithermal nature. The development of adularia and/or calcite
Fig. 10. Photographs and photomicrographs showing mineralized porphyry enclaves in volcanic rocks and native copper in volcanic rocks at the Tawuerbieke Au prospect. (a) Round mon-
zonite porphyry enclave with a sharp boundary with the host andesite; (b) round fine-grained diorite enclave with a sharp boundary with the host andesite; (c) pyrite with native gold
along its edge in a monzonite porphyry enclave, reflected light; (d) coarse-grained euhedral pyrite and native gold in fine-grained diorite enclave, reflected light; (e) native copper in ba-
saltic andesite from ZK28-1 drill hole; (f) dendritic native copper in the matrix of basaltic andesite, reflected light; Abbreviations (after Whitney and Evans, 2010): Au—native gold; Py—
pyrite; Cu—native copper.
in the alteration mineral assemblages in the Axi Au deposit, the decrease in the proportion of magmatic components in the ore-
Tawuerbieke Au prospect, and the Tabei Zn–Pb prospect suggests that forming fluids, as well as temperatures and salinities (Arribas, 1995;
these mineralizations are of the adularia-sericite type, with Axi and Hedenquist et al., 1998; Lefort et al., 2011; Pudack et al., 2009;
Tawuerbieke representing shallower veins, and Tabei representing Richards, 2011; Sillitoe, 2010). Therefore, in a magmatic-arc environ-
deeper mineralization. This inference is also supported by the present ment such as western Tianshan in the Late-Devonian to Early-
elevation of the three mineralization zones, with 1450 m for Tabei, and Carboniferous time, both epithermal and porphyry deposits may be
1600 m for Axi, and 1800 m for Tawuerbieke (Fig. 19). Whereas the devel- developed. Indeed, five very large porphyry Cu\Au, one large skarn
opment of advanced argillic alteration in the Jingxi–Yelmend Au deposit Zn–Pb and 21 epithermal Au deposits have been found in the Almalyk
and the Tieliekesayi kaolinite–dickite prospect appears to indicate an ore district in western Tianshan in Uzbekistan, forming a world-class
acid-sulfate affiliation (Hayba et al., 1985; Heald et al., 1987). These inter- porphyry-skarn-epithermal Au\Cu–polymetallic system (Golovanov
pretations are consistent with the subduction-related tectonomagmatic et al., 2005). A very large porphyry-epithermal Au\Cu–polymetallic
environment, which favors the formation of porphyry as well as system has also been recognized in northern Tianshan, Kyrghyzstan
epithermal deposits (Hedenquist et al., 1998; Richards, 2011; Sillitoe, (Djenchuraeva et al., 2008). It is therefore inferred that the Tulasu
1973, 2010). basin in the eastern part of western Tianshan, which hosts several
Epithermal Au deposits are commonly developed above or laterally major epithermal Au deposits, may contain buried porphyry Cu\Au
offset from porphyry systems, with a gradual upward and outward deposits that have not been discovered yet.
Fig. 11. Geologic map (a) and a cross section (b) of the Jingxi–Yelmend Au deposit (modified from JMCX, 2009).
Fig. 12. Photographs showing various mineralization and alteration features of the Jingxi–Yelmend Au deposit. (a) Stage II—substage I hydrothermal breccias with altered host-rock frag-
ments; (b) Stage II—substage II hydrothermal breccias containing fragments formed in substage I; (c) coarse-grained calcite–barite veins; (d) silicification and advanced argillic alteration
associated with the Yelmend orebody; (e) vuggy quartz and chalcedony in the Yelmend orebody; (f) dickite and kaolinite in the advanced argillic alteration zone of the Yelmend orebody;
Abbreviations (after Whitney and Evans, 2010): Qz—quartz.
Fig. 13. Geologic map (a) and a cross section along the A–A′ prospecting line (b) of the Kexiaxi Cu prospect (modified from Wu et al., 2011).
Some evidence of porphyry-type mineralization has been found in Support Program of China (No. 2011BAB06B02), the Chinese Geological
the Tulasu basin. In the Kexiaxi Cu prospect, early-stage veinlet–dissem- Survey Program (121211220926), and the Xinjiang Key Laboratory for
inated mineralization is overprinted by vein-type mineralization, and Geodynamic Processes and Metallogenic Prognosis of the Central
the mineralization shows a gradual change from Cu to Cu–Mo with Asian Orogenic Belt Project (No. XJDX1102-2012-06). We are grateful
depth (Wu et al., 2011). We infer the presence of a large porphyry Cu to Daniel Müller, an anonymous reviewer, and Associate Editor Jeffrey
deposit at Kexiaxi (Fig. 19). The presence of mineralized enclaves of Mauk for insightful comments and suggestions. We would like to
monzonite porphyry in andesite that hosts the Tawuerbieke Au pros- thank Professor David T. A. Symons for comments on an early version
pect suggests that there may be a hidden porphyry Cu\Au system of the manuscript.
beneath the epithermal prospect. Native copper occurs in basaltic an-
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Table 6
Geochronological data of igneous rocks with magmatic arc characteristics in the Tulasu basin.
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Fig. 18. Hydrogen and oxygen isotope compositions of ore-forming fluids of epithermal Au
Fig. 17. Sulfur isotope compositions of sulfides for Au-polymetallic deposits and prospects deposits and prospects in the Tulasu basin (reference fields from Hedenquist and
in the Tulasu basin. Data for Tawuerbieke and Tabei are from this paper; Data for Axi are Lowenstern, 1994). Data for Axi are from Zhai et al. (2009) and Sha et al. (2005); Data
from Zhai et al. (2006); Data for Jingxi–Yelmend are from Xiao et al. (2001) and Zhu for Jingxi–Yelmend are from Xiao et al. (2005); Data for Tawuerbieke are from Jia et al.
et al. (2011). (2001).
Fig. 19. Schematic model of porphyry and epithermal mineralization in the Tulasu basin.
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Ore Geology Reviews 60 (2014) 76–96

Contents lists available at ScienceDirect

Ore Geology Reviews

Epithermal Au and polymetallic mineralization in the Tulasu Basin,

1. Introduction Au\Cu–Zn deposit (Waters et al., 2011). Similar mineralization systems

Fig. 2. A sketch of the stratigraphic column of the Tulasu basin.

Rocks Andesite Granitic porphyry

Major elements (wt.%)

Trace elements (ppm)

Note: Fe2OT3 refers to total iron, LOI = loss on ignition.

Spots U Th Th/U Isotope composition Age (Ma)

TWE-8 (granitic porphyry)

Notes: Errors are 1σ; Common Pb corrected using measured 204Pb.

5. Au\Cu–polymetallic mineralization in the Tulasu basin

An and Zhu (2008),

Xiao et al. (2005),

5.1. Axi Au deposit

sents the largest epithermal Au deposit in the Xinjiang province. The

of the Upper Andesite Member of the Dahalajunshan Formation, includ-

ing andesites, dacites, rhyolites, tuffs, and volcanic breccias. Agglomer-

the maar-diatreme is characterized by a typical oval shape aeromagnet-

the NS-trending No. 1 vein, extends up to 1000 m along strike, has a

The Au grades range from 2 to 16 g/t, with an average of 5.57 g/t

The Au mineralization can be divided into four stages, each charac-

terized by different mineral assemblages in the veins, including 1)

light grey–white quartz and/or chalcedony veins (Fig. 6a), 2) smoky–

(Fig. 6c), and 4) quartz–carbonate veins (Fig. 6d). Hydrothermal alter-

quartz veins, and grading from a zone of siliciﬁcation through a zone

of phyllic alteration into a zone with propylitic alteration (Fig. 5b).

types, and are commonly associated with siliciﬁcation. The alteration

is most pronounced on the top and bottom of the respective orebodies,

including siliciﬁcation, and sericite and chlorite alteration of andesite of

developed at structural intersections and contains fragments of both

NNW- and NS-

NNE-, NE- and

the veins and altered andesites that are cemented by hydrothermal

quartz–sulﬁde (Fig. 6f).

The Au ores are characterized by crustiform texture (Fig. 6g) and

ite, chalcopyrite and galena. Gangue minerals are quartz, chalcedony,

sericite, calcite, adularia and laumontite. Adularia is sparsely distributed

Abbreviations: P—prospect; Fm.—Formation.

in the quartz veins (Zhai et al., 2009).

The homogenisation temperatures of ﬂuid inclusions in the auriferous

δ18Owater value of − 3.3 to 0.4‰ calculated from δ18Oquartz values of

11.1 to 13.3‰ and the ﬂuid-inclusion homogenization temperatures

(Table 5), suggesting that the ore-forming ﬂuids were dominated by

Table 4 associated with pervasive alteration that includes pyrite, sericite,

5.5. Kexiaxi Cu prospect

The Kexiaxi Cu prospect is located 15 km northeast of the Axi Au de-

Locations Igneous rocks Dating methods Age(Ma) References

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