Rb-Sr geochronology of single gold-bearing pyrite grains from the Katbasu gold deposit in the South Tianshan, China and its geological significance

    Rb-Sr geochronology of single gold-bearing pyrite grains from the Katbasu gold deposit in the South Tianshan, China and its geological significance Leilei Dong, Bo Wan, Weizhong Yang, Chen Deng, Zhenyu Chen, Lei Yang, Keda Cai, Wenjiao Xiao PII: DOI: Reference:

S0169-1368(16)30104-4 doi: 10.1016/j.oregeorev.2016.10.030 OREGEO 1993

To appear in:

Ore Geology Reviews

Received date: Revised date: Accepted date:

1 March 2016 20 October 2016 21 October 2016

Please cite this article as: Dong, Leilei, Wan, Bo, Yang, Weizhong, Deng, Chen, Chen, Zhenyu, Yang, Lei, Cai, Keda, Xiao, Wenjiao, Rb-Sr geochronology of single gold-bearing pyrite grains from the Katbasu gold deposit in the South Tianshan, China and its geological significance, Ore Geology Reviews (2016), doi: 10.1016/j.oregeorev.2016.10.030

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Rb-Sr geochronology of single gold-bearing pyrite grains from the

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geological significance

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Katbasu gold deposit in the South Tianshan, China and its

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Leilei Dong a, b, Bo Wan a, b, c*, Weizhong Yangd, Chen Deng a, b,

a

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Zhenyu Chen a, b, Lei Yang a, b, Keda Caie, Wenjiao Xiaoa, b, c, e State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics,

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Graduate University of Chinese Academy of Sciences, Beijing 100049, China

No.1 Geological Survey Party, Xinjiang Bureau of Geology and Mineral Exploration

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d

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CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China

and Mining, Urumqi 830011, China

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c

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Chinese Academy of Sciences, Beijing 100029, China

Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China

* Corresponding author. E-mail: [email protected]; Tel: +86-10-8299-8154; Fax: +86-10-6201-0846

Revised ms. submit to Ore Geology Reviews

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Abstract

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The newly discovered Katbasu gold deposit in the South Tianshan region has a gold reserve of 76 tonnes at an average grade of 3.84 g/t. It is the first large gold deposit in the

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central segment of the South Tianshan. Gold mineralization is hosted within granite, and is associated with potassic, phyllic and chloritic alteration. Gold-bearing pyrite occurs as

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disseminations in the host rock and as quartz-sulfide veins cross-cutting the potassic and

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phyllic alteration assemblage. Rubidium (Rb) - strontium (Sr) analyses on sericite within five individual pyrite grains from a phyllic alteration sample yield an isochron age of 322.5 ± 6.8

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Ma (MSWD= 3.2). The host granite has a SIMS U-Pb zircon age of 351.4 ± 1.1 Ma

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(MSWD=0.13). The Rb-Sr isochron age represents the mineralizing age of the Katbasu gold deposit, which significantly postdates the ore-hosting granite but is consistent with the age of

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regional porphyry type mineralization at ~320 Ma in the South Tianshan. Discovery of the Katbasu gold deposits indicates huge potential for gold exploration in the central segment of the South Tianshan as it is geologically similar to the western and eastern segments of the South Tianshan, which both host many world-class gold deposits. Key words: West Tianshan, Au deposit, Late Carboniferous, Rb-Sr, pyrite

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ACCEPTED MANUSCRIPT 1. Introduction Gold (Au) deposits commonly occur in orogenic belts (Kerrich et al., 2000). The orogenic,

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porphyry and epithermal-type Au deposits are the most important mineral systems (Groves et al., 1998; Sillitoe and Hedenquist, 2003), which have contributed approximately 32%, 9% and

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8% of global Au production, respectively (Singer, 1995; Frimmel, 2008; Sillitoe, 2010). Among the different types of orogenic belts, accretionary orogenic belts are the most

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well-endowed Au provinces with prominent examples including the Alaskan, North American

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Cordillera, Andes, New Zealand, Papua New Guinea-Irian Jaya island, and Philippine in the Circum-Pacific regions at the present day (Sillitoe, 2008). The Central Asian Orogenic belt is

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the best-preserved fossil accretionary orogenic system and is also the Paleozoic analogy to the

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present Circum-Pacific (Schulmann and Paterson, 2011). It is the world’s most important Paleozoic Au province (Yakubchuk et al., 2005; Goldfarb et al., 2014).

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The Tianshan is located in the southern part of the Central Asian Orogenic Belt (Gao et al., 1998; Windley et al., 2007) and it hosts several world-class Au deposits (Table 1), including the Muruntau orogenic gold deposit (5246t Au), the Almalyk porphyry gold deposit (2800t Au), and the Kochbulak epithermal gold deposit (340t Au) (Yakubchuk et al., 2005). All these Au deposits are scattered along the southern margin of the Tianshan (South Tianshan), but are clustered in the western and eastern segments of the South Tianshan (Fig. 1). These Au deposits are products of the prolonged subduction of the Paleo-Asian Ocean. However, the central segment of the South Tianshan contain very few known Au deposits of any kind. Many comparative studies indicate that the South Tianshan is a continuous geological terrane that extends from Uzbekistan, through Tajikistan and Kyrgyzstan, to the Xinjiang province of

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ACCEPTED MANUSCRIPT China (Wang et al., 2011; Xiao et al., 2013; Klemd et al., 2015). Therefore, the central segment of the South Tianshan has long been regarded as a promising target for Au prospecting. The

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discovery of the Katbasu Au deposit in 2008 was a breakthrough for Au exploration in the central segment of the South Tianshan, (Yang et al., 2014). Currently, the Katbasu deposit has

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76 tonnes of gold and that reserve will increase with more detailed exploration in the near future (Yang et al., 2014).

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The Katbasu is a blind deposit covered by thick Cenozoic sediments, which explains why it

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was discovered only recently. The timing of mineralization is critical for understanding ore deposits in the regional geological context (Stein et al., 2001). Zhang et al. (2015) considered

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Katbasu to be an orogenic Au deposit, mainly because that the Re-Os age of pyrite (310.9 ±

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4.2Ma) is significantly younger than the LA-ICP-MS U-Pb zircon age of the granite (345 ± 2.6 Ma) (Feng et al., 2014); whereas the 40Ar-39Ar age of sericite in the altered granite was reported

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to be ~269 Ma (Gao et al., 2015). Neither the ore geology, nor the age of mineralization of the Katbasu gold deposit is well described or constrained. Geological relationship between the ores and the host rocks suggest that the emplacement ages of the magmatic rocks can only put a limited constraint on the maximum timing of gold mineralization, and the precise age of the sulfides still needs to be obtained by other methods. There are many indirect methods of constraining the ore forming age, with the prerequisite that the datable mineral is coeval with the ore minerals (Wan et al., 2012). Mineral Rb-Sr dating is a traditional method, which has been successfully applied on sphalerite (Nakai et al., 1990), pyrite (Li et al., 2008) and chalcopyrite (Wan et al., 2009). At the Katbasu deposit, pyrite is closely relaed to the alteration minerals such as sericite. The most important characteristic of sericite is their large variation of

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ACCEPTED MANUSCRIPT Rb/Sr ratios, which has been shown to be optimal for Rb-Sr isochron. In this study, we report Rb-Sr dating results of the sericite included in single gold-bearing

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pyrite grains of a gold-hosting pyrite-sericite-quartz vein. Furthermore, we report a SIMS zircon U-Pb ages for the same sample and other country rocks. Major and trace elements of the

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granite, rhyolite and granodiorite are also analyzed to better understand the attributes of the country rocks. Integrating the geological observation with our new data, and comparing with

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the Au mineralization regionally, we propose that the Katbasu may be related to a felsic

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intrusion and a possible porphyry type Au deposit of the Late Carboniferous period.

2.1 Geological background

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2. Geological settings

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The Central Asian Orogenic belt (CAOB) (Jahn, 2004) or Altaids (Sengör et al., 1993) is

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situated among the Siberia, East Europe, Karakum-Tarim and North China craton (Fig. 1 inset). It has a prolonged history of subduction, accretion and collision of island arcs, oceanic plateaus, and micro-continents from 1250 to 250 Ma (e.g. Xiao et al., 2015). Its complex evolutional history makes the CAOB to be one of the most important metallogenic provinces in the world (Chen et al., 2011; Mao et al., 2013). The CAOB broadly grew southward (present coordinates), so its southern region documents the youngest parts of growth history as evidenced in the Tianshan range (Fig. 1) where the geological history has been well described (Gao et al., 1998). The core of Tianshan is a ribbon-continent often called the Ili-Central Tianshan micro-continent. The Junggar Ocean subducted beneath the micro-continent from the north since ~ 540 Ma, building an accretionary system along the northern margin of the

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ACCEPTED MANUSCRIPT micro-continent. In contrast, an Andean-type arc and a huge accretionary complex on the southern margin of the micro-continent was constructed by the northward subduction of the

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South Tianshan Ocean from the south since 460 Ma (Gao et al., 1998). Accordingly, from north to south, the Tianshan orogenic collage is chiefly subdivided into the three tectonic units: The

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North Tianshan Accretionary complex, the Ili-Central Tianshan micro-continent, and the South Tianshan Accretionary complex (Fig.1). The North Tianshan Accretionary complex is

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separated from the Ili-Central Tianshan by the North Tianshan Fault (Fig.1), dominated by

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Ordovician to Devonian-Carboniferous volcanic rocks, turbidites, basalts, cherts, and ultramafic rocks. The Ili-Central Tianshan micro-continent is situated between the North and

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South Tianshan Faults (Fig. 1) and is dominated by Precambrian basement rocks, intermediate

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to felsic magmatic rocks. The Paleozoic volcanic rocks expose mainly on the northern and southern margin of the Ili-Central Tianshan micro-continent. The South Tianshan arc is located

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on the southern margin, and there is no clear boundary between the Ili-Central Tianshan micro-continent and the South Tianshan arc. The South Tianshan Accretionary complex is separated by the South Tianshan Fault from the South Tianshan arc in the north (Fig.1). It is mainly composed of Paleozoic limestones and clastic rocks (Gao et al., 1998). Many ophiolitic mélanges with ages of 440-420 Ma, ~390 Ma, and ~330 Ma are exposed in the South Tianshan accretionary complex (e.g., Han et al., 2011; Wang et al., 2011; Jiang et al., 2014). One of the ophiolites with an LA-ICP-MS zircon U-Pb age of 332 ± 7 Ma is located 200 km to the southeast of Katbasu (Jiang et al., 2014). These ophiolitic mélanges are direct, robust evidence for the existence of ocean subduction. Extensive eclogite/blueschist with peak metamorphic ages of 315 ± 5 Ma in the accretionary complex (Hegner et al., 2010) are interpreted to be

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ACCEPTED MANUSCRIPT fragments of sea mounts (Gao and Klemd, 2003), suggesting that oceanic subduction was still

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active during this time (Xiao et al., 2013).

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2.2 Deposit geology

The Katbasu Au deposit is located about 30 km southwest of Xinyuan County at the north

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of the South Tianshan Fault (Fig. 1). It was discovered by the No.1 Party of the Geological

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Survey of Xinjiang Bureau of Geology and Mineral Exploration and Mining in 2008 (Yang et al. 2014). The elevation of the mine site is about 3000 m above the sea level and the gold ore is

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a blind target below thick Cenozoic sediments (Fig. 2A). Continuous drill-holes exploration

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makes it possible to understand the variation of the orebodies and their relationship with the alteration of the country rocks. The orebodies are hosted by the 345.5 Ma granite (Fig. 2B) and

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occur mainly in the form of thick plates or lenses dipping to the south, with the angle of dip

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angle varying between 20° and 70° (Fig. 2C). In general, the thickness of the orebody ranges from several meters to tens of meters, extending about 2 km along strike. Gold ore plates with grade above 0.6g/t stretch east to west within a single encapsulated orebody (>0.3g/t). The relatively higher grade ores present in the central part of the orebody (Au > 0.6g/t), and gold ores with grade of >1.8g/t contribute to approximately half of the total Au reserve. The maximum gold grade exceeds 300g/t. There is no correlation between sulfide content and grade from the center to periphery. The Au reserve was confirmed to be of 76 tonnes with an averaged grade of 3.84g/t in 2015. The average grade of the copper is of 0.65% with a Cu resource of only 46000 tonnes (Yang et al., 2014). Early Carboniferous intrusions including granodiorite, diorite, and granite, are well exposed in the mine. A few Silurian limestones occurring as xenoliths in the middle of the 7

ACCEPTED MANUSCRIPT granite, represent the oldest rocks within the mine. Skarn can be recognized locally at the north boundary between granodiorite and limestone. There is no gold mineralization in the skarn,

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though pure pyrite veins and massive sulfides (mainly pyrite) are frequently recognized. Several fine-grained diorite veins without mineralization occur in the equigranular granite

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pluton. These diorite dikes strike NE, with lengths less than 100m and the width of several meters. They are commonly situated in the central part of the orebody beneath the surface and

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are located southwest of the major orebody subaerially. Granite is the most common outcrop

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and the dominant host rock for gold orebodies, while small portions of ore occur within granodiorite with relatively low gold contents in comparison with those in granite. In the

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northwest of the mine area, the dominant rock is rhyolite of the Early Carboniferous

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Dahalajunshan Formation (Zhu et al., 2005). The granite body is a calc-alkaline I type monzogranite with a mineral assemblage of plagioclase (~35%), potassium feldspar (~40%),

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quartz (15%-20%), and minor biotite (<5%). Accessory minerals such as apatite and zircon sporadically occur in the granite and hydrothermal veins. LA-ICP-MS U-Pb dating of zircons from granite near the mine yielded an age of 345.5 ± 2.6 Ma (Feng et al., 2014). Both the Early Carboniferous Dahalajunshan Formation and the 345 Ma granite have similar geochemical characteristics with magmatic rocks formed from the subduction zone (Zhu et al., 2005; Feng et al., 2014).

2.3 Alteration style, paragenetic sequence and associated mineralization Potassic, phyllic and chloritic alterations are recognized from ores in the mine. These alterations do not extend across the rhyolite (Fig.2); this has been confirmed by drilling (Yang et al., 2014). The intensive potassic alteration is best represented by plagioclase replacement by 8

ACCEPTED MANUSCRIPT orthoclase, sometimes accompanied by biotite alteration (Fig. 3A). This type of alteration is only identified in adits or drill holes beneath the surface, and may primarily appear in the

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central orebody (Fig. 2D). Both disseminated type and vein type ores occur in the potassic alteration assemblages. Phyllic alteration is as widespread as the potassic alteration. The

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altered rock is mainly composed of quartz, sericite and pyrite with either minor residue K-feldspar or the K-feldspar has been totally replaced by quartz and sericite (Fig. 3B; 3C; 3D).

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Pyrite in this alteration assemblage is abundant with quartz and sericite (Fig. 3E). This type of

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alteration is the most common type in the Katbasu deposit, and generally outcrops southwest of the orebody. Chloritic alteration assemblages are represented by chlorite – sericite ± calcite in

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granite (Fig. 3F; 3G; 3H), associated with few sulfides.

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The alteration sequences of the Katbasu are summarized and presented in Fig. 4. They are roughly divided into three main stages of potassic, phyllic and chloritic, respectively.

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a) The alteration assemblage of potassic stage is characterized by pervasive K-feldspar replacement (Fig. 3A), accompanied by patches of magnetite occurrences inside the adit, and traces of biotite, quartz, albite, and impregnated pyrite. The hydrothermal orthoclase generally formed along the cleavage of plagioclase or at the grain margin. Biotite appears as light brown in thin section with minor presence of fine-grained euhedral pyrite. Such an alteration type is rarely observed in orogenic type gold deposit (Groves et al., 1998). b) The second stage is exemplified by pervasive sericite and quartz replacement with gold mineralization. The abundant quartz and sericite in the phyllic alteration zone present either as extensive/total replacement of country rock by quartz and sericite

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ACCEPTED MANUSCRIPT (pyrite) or is characterized by stock-work veining (Fig. 3B). The relatively weak alteration zone is represented by weak sericite replacement of plagioclase. The

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recognizable veining is further subdivided into two sub-styles of quartz dominated Qtz-Ser-Py vein (Fig. 3C) and sericite dominated Ser-Py±Qtz veins (Fig. 3D). The

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major distinction between them is the abundance of gangue minerals and the gold grade. The Qtz-Ser-Py veins are enriched with quartz and native gold particles,

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though contain less sericite in comparison with the Ser-Py±Qtz veins. Pyrites in

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the Qtz-Ser-Py veins incorporate more mineral enclaves, such as sericite, chalcopyrite, and quartz (Fig. 3E). The anhydrite mainly occurs together with

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sericite in the form of veinlet. Disseminated ores are coarse-grained pyrites. Ore

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veinlets are in the Qtz-Ser-Py veins or Ser-Py-Qtz veins. Most of the Au is probably present as nano-scale particles or as invisible Au in the pyrite lattice

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(Yang et al., 2014), similar to most of the other Au deposits in the world (Hough et al., 2008). Tiny native Au grains are present within pyrite and quartz grains (Fig. 3C). Native gold grains exclusively appear in the Qtz-Ser-Py veins, and reach up to 100μm in size. The major stage of mineralization is accompanied by this phyllic alteration (pyrite-quartz-sericite), where the pyrite and sericite formed simultaneously (Fig. 3D, E), and both of them are associated with quartz and native gold particles in the same hydrothermal vein.

c) Chloritization is accompanied by magnetite, and they appear in the form of pseudomorphs of biotite in granite or amphibole within the granodiorite. Chloritization and impregnated calcite are commonly encountered in pale-green

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ACCEPTED MANUSCRIPT granite. Calcite also occurs as form of calcite-pyrite veins in localities adjacent to the main orebody. The pyrite present in these veins is euhedral and gold free.

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Epidote is not as widespread as chlorite but is also a common mineral phase. It is sometimes accompanied by patches of chlorite and euhedral magnetite in chloritic

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alteration zones.

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3. Analytical method and Results

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3.1 Analytical method

Major and trace elements were determined by X-ray fluorescence spectrometry using

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AXIOS Minerals at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS). Trace element concentrations were analyzed by inductively coupled plasma mass

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spectrometry (ICP-MS) at the IGGCAS.

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Five pyrite grains weighing 8 to 24 mg were extracted from the gold bearing Qtz-Ser-Py vein from sample no. KB48. KB48 is a phyllic-altered granite cut by a Qtz-Ser-Py vein that was sampled from the main orebody in the adit. Small pyrite grains were selected to avoid contamination from other minerals. Backscatter scanning microscopy of pyrite grains was performed under LEO 1450VP SEM at IGGCAS. Abundant inclusions of quartz and sericite (Fig. 3E) were detected by the INCA ENERGY 300 X-ray Energy Dispersive Spectrometer (EDS) system equipped with the SEM. Gold bearing pyrite was subjected to element mapping to determine whether it was affected by deformation or fluid disturbance by the energy dispersive detector X-MAXN80 equipped with the Nova NanoSEM 450 at IGGCAS. After being washed ultrasonically by alcohol and Millipore water, mineral grains were shifted into

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ACCEPTED MANUSCRIPT Teflon® vessels. Pyrite grains were dissolved using 0.3 ml 3N HNO3 and 0.1 ml HF at 80 °C. Separation and purification of Rb and Sr were performed according to the procedure of Li et al.

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(2012) in Teflon® mini-columns filled with about 0.1 ml Sr-spec® resin. The Rb-Sr isotopic analysis was carried out on a Triton Plus thermal ionization mass spectrometry at IGGCAS,

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operating in positive ionization mode with a 10 kV acceleration voltage and 10 11 for the Faraday cups. This instrument was equipped with nine Faraday collectors. A double Re

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filament geometry was used to obtain Sr+. The specific procedures and working conditions are

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referred to in Li et al. (2012).

Zircons for U-Pb dating were separated from the crushed granite (KB48), granodiorite

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(KB56), and rhyolite (KB33). KB48 is the same sample used for Rb-Sr geochronology. KB56,

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sampled from south of the orebody, is a weakly altered granodiorite within which the plagioclase is partially replaced by K-feldspar. It is mainly composed of amphibole,

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plagioclase and minor biotite. KB33 is a rhyolite that was sampled from the north side of the ore district. The zircons were mounted in epoxy together with the zircon standard Qinghu (Li et al., 2013). Transmitted, reflected light and cathodoluminescence images were captured to acquire information about the inner structure, surface characteristics and cathodoluminescent textures of the zircons respectively. The U, Th and Pb isotope analysis was conducted with the Cameca IMS 1280 large-radius SIMS at IGGCAS. The spot size of 20×30 µm was used. Analytical methods and procedures are detailed in Li et al. (2009). Data processing was done using ISOPLOT 3.00 (Ludwig, 2001).

3.2 Results The SiO2 content of granite is between 70-75%, with high Na + K concentration 12

ACCEPTED MANUSCRIPT (Supplementary Table 1). A primitive mantle normalized spider diagram (Fig. 5A) displays negative anomalies for Nb, Ta and Sr. Light REEs are enriched but heavy REEs are depleted,

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with La/Yb ratios ranging from 12.38 to 19.79. Europium shows a negative anomaly. These granites are characterized by low Sr/Y ratio and Y content and they show arc affinity when

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plotted on a Sr/Y-Y diagram (Fig. 5B). The rhyolite and granodiorite share similar characteristics with the granite in terms of trace elements and REE patterns. The rhyolite is

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more depleted in Sr and Eu, while the granodiorite shows a weak Eu anomaly.

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Au-Fe-S mapping of the gold-bearing pyrite show that the distribution of Fe and S are homogenous (Fig. 6), and such textures indicate the pyrite was not altered or overprinted by

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later hydrothermal events. Five pyrite grains from a pyrite-sericite veinlet in the phyllic altered

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granite (KB48) yielded an Rb-Sr isochron age of 322.5 ± 6.8 Ma (n = 5, MSWD = 3.2，Fig. 7A and Table 2). Rb contents of the five pyrite grains range from 0.281 to 1.789 ppm. Sr

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contents range from 0.219 to 6.492 ppm. 87Rb/86Sr ratios range from 0.5005 to 5.6312. Sr/86Sr values range from 0.709286 to 0.732682. Initial 87Sr/86Sr ratio was calculated to be

0.70695 ± 0.00015. Standard solution NIST-NBS987 was used and gave a mean87Sr/86Sr value of 0.710255 ± 0.000010. Nineteen analyses of zircons from the same sample gave a concordia U-Pb age of 351.4 ± 1.1 Ma (n = 19, MSWD = 0.13, 1σ, Fig. 7B, Table 3), with a weighted mean 206Pb/238U age of 351.7 ± 2.4 Ma. U and Th contents in these zircons both range from ~250ppm to 1300ppm, with Th/U ratios in each zircon ranging from 0.8 to 2.0. The zircon age is interpreted to be the emplacement age of the granite. Fourteen zircons analysis from the granodiorite (sample KB56) gave a concordia age of 355.7 ± 2.7 Ma (n = 14, MSWD = 1.01, 1σ, Fig. 7C, Table 3), with a weighted mean 206Pb/238U ages of 356.2 ± 3.7 Ma (MSWD = 1.4).

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ACCEPTED MANUSCRIPT The U contents of KB56 are all below 1000ppm, while Th contents are scattered within the range of 100~1500ppm. Th/U ratios fall into the range of 1~2. The rhyolite (sample KB33)

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from northwest of the mine area yielded a concordia age of 335.7 ± 1.3 Ma (n = 12, MSWD = 1.3; Fig. 7D), with a weighted mean 206Pb/238U age of 335.0 ± 2.8 Ma. U and Th contents from

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these zircons range from 270 to 1060, with Th/U ratios of 0.58~1.80.

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4. Discussion

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4.1 Timing of mineralization

Five grains of pyrite with sericite inclusions yielded an Rb-Sr isochron age of 322.5 ± 6.8

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Ma (MSWD=3.2, Fig. 7A). The age is of a high quality due to its small error and relatively low MSWD. The high precision of the age can be attributed to a single stage of sericite inclusion

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formation in pyrite. Many pyrites occur as inclusions in sericite (Fig. 3D), while sericite and

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Au granules also occur as inclusions in the pyrite (Fig. 3E, F). Such relationship between pyrite and sericite indicates that they formed simultaneously. Gold formed together with pyrite and sericite. Therefore, the Rb-Sr isochron of sericite (322.5 ± 6.8Ma) represents the mineralization age of the Katbasu deposit. Zhang et al. (2015) reported a pyrite Re-Os isochron age of 310.9 ± 4.2 Ma of the Katebasu deposit, which is younger than our Rb-Sr result. However, it still supports the formation of the Katebasu deposit in the Late Carboniferous. According to field observations, the main ore stage must postdate the host rock (Fig. 3B, sample KB48). The SIMS U-Pb zircon age of this sample is of 351.4 ± 1.1 Ma, and Feng et al. (2014) has reported a LA-ICP-MS U-Pb zircon age of 345 ± 2.6 Ma for a granite sample near the mine site. Although the granodiorite (KB56) in this study shows a slightly older age than

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ACCEPTED MANUSCRIPT that of the granite, they emplaced almost simultaneously. Our geochronological data are therefore coherent with the observed geological relationships. They all indicate that the granite

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and granodiorite were emplaced contemporaneously at ~350-355 Ma, significantly prior to gold mineralization (323-310 Ma). The fresh rhyolite at the northwestern portion of the mine

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was formed at ~335 Ma. It is slightly older than the gold mineralization and cannot be responsible for the mineralization.

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The Tianshan is one of the most important Au provinces in the world, therefore many of

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the Au deposits within the region have been described in detail, including their formation ages (e.g., Rui et al., 2002; Yakubchuk et al., 2005; Goldfarb et al., 2014). There are many different

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types of Au deposits formed in different times during the Late Paleozoic. A few Au deposits,

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such as the Andash and Taldy Bulak deposits formed in the early Ordovician (Jenchuraeva, 2001; Yakubchuk et al., 2005). In contrast, most of the deposits, including the majority of the

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largest Au deposits, formed in the Late Paleozoic (Table 1). The formation ages of porphyry Au or Au-Cu deposit vary in the range of ~330 - 315 Ma (e.g., Rui et al., 2002; Liu et al., 2003; Seltmann et al., 2011), but are clustered around ca. 323 Ma (Fig. 8A). The volcanic arc at the Southern margin of the Ili-Central Tianshan block was being formed during the late Carboniferous, coeval with the formation of these giant porphyry ore deposits. These substantial amounts of magmatism favor the magmatic-hydrothermal activities that ultimately lead to porphyry ore formation (e.g., Almalyk, Tuwu-Yandong). However, the orogenic type Au deposits formed from ca. 300 to 280 Ma, systematically younger than porphyry deposits (e.g., Mao et al., 2004; Morelli et al., 2007; Zhang et al., 2008), mostly peaking at around 288 Ma.

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ACCEPTED MANUSCRIPT 4.2 Geological significance of new geochronological data from the Katbasu Au deposit As mentioned above, the Tianshan hosts numerous world-class Au deposits with various

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genetic types. The most famous are the Muruntau orogenic type, Almalyk porphyry type, and Kochbulak epithermal-type deposits (Yakubchuk et al., 2005). The key features of these three

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types of gold deposits are listed in Table 4 (Lang and Baker, 2001; Groves et al., 2003; Sillitoe

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and Thompson, 1998; Sillitoe, 2008; Thompson et al., 1999). The Katbasu Au deposit is located in the South Tianshan Arc (Fig. 1), and its hosting rocks are hydrothermally altered but

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undeformed granite. Xue et al. (2014) suggested that the Katbasu deposit is an orogenic-type Au deposit. Zhang et al. (2015) conducted fluid inclusion study and concluded that the

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homogenization temperature of the main ore stage is 270~390ºC, with moderate salinity

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(7-16% NaCl eq.) and presence of CO2. Together with the Re-Os age of pyrite, they inferred that the Katbasu is an orogenic gold deposit that formed during collision between the Tarim

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block and the Ili-Central Tianshan micro-continent. However, the salinity and homogenization temperature should not be the diagnostic criteria (Sillitoe and Thompson, 1998). Moderate to low homogenization temperature and salinity are also present in porphyry gold deposits, such as ore related fluid inclusions of Verde in the Maricunga Belt, Northern Chile (with homogenization temperature from 220 to 350ºC and salinities 3.4 to 34 wt. percent NaCl equiv., Muntean and Einaudi, 2000). Also, the presence of CO2 in fluid inclusions should not be diagnostic of the type of gold system (Sillitoe and Thompson, 1998), because CO2 may be magmatic in origin (e.g. Fort Knox gold deposit of Alaska). Furthermore, the most important feature for an orogenic Au deposit is its consistent association with a deformed metamorphic terrane, as it is a product of metamorphic devolatilization during the orogeny (Groves et al.,

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ACCEPTED MANUSCRIPT 1998; Phillips and Powell, 2010). However, even the rhyolite (335.7Ma) that is slightly older than the Au mineralization (322.5) show no signs of deformation and metamorphism. It is

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difficult to imagine metamorphic fluids can travel distance from at least greenschist zone to none metamorphic zone and keep the hydrothermal fluid with an ore forming temperature like

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270-390ºC as proposed by Zhang et al. (2015) from fluid inclusion data. The ‘Intrusion related gold deposit’ proposed by Sillitoe and Thompson (1998). Thompson

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et al. (1999) and Lang and Baker (2001) summarized several important features common to

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this deposit type: a) temporal and spatial association with intrusions of intermediate to felsic composition; b) carbonic hydrothermal fluids; c) a metal assemblage that variably combines

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gold with elevated Bi, W, As, Mo, Te, and/or Sb with low concentrations of base metals; d) low

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sulfide content with a reduced ore mineral assemblage (arsenopyrite, pyrrhotite, and pyrite which lacks magnetite or hematite); e) commonly restricted and weak hydrothermal alteration;

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f) a tectonic setting inboard of known or inferred convergent plate boundaries; g) a location in magmatic provinces best or formerly known for tungsten and/or tin deposits. However, 1) the Katbasu is hosted by granitic intrusion but has no temporal association with granite; 2) it contains chalcopyrite and correlate with Cu but not Bi, Te, W; 3) the sulfides at Katbasu deposit have few reduced ore assemblages (arsenopyrite and pyrrhotite), whereas the magnetite is frequently observed; 4) Katbasu is located on the south Tianshan volcanic arc. The limited geological evidence indicates that the deposit developed potassic, phyllic, and chloritic alteration assemblages (Fig. 3A-C). The ores are of disseminated and vein types, being limited in areas with intensive potassic and phyllic alterations. These features are very similar to the alteration patterns of classic porphyry deposits (Lowell and Guilbert, 1970;

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ACCEPTED MANUSCRIPT Sillitoe, 2010), and it is less common to observe the potassic alteration in orogenic type Au deposit (Groves et al., 1998). These alteration features are also similar to the gold deposits at

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the Jiaodong Peninsula, but the metal assemblages and known tectonic position of Katbasu are different from those in Jiaodong (Li et al., 2013; Li et al., 2015). There are some orogenic gold

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deposits hosted by plutonic rocks (e.g., Yilgarn Craton in West Australia, Cassidy et al., 1998), these deposits are inevitably located in the granitoid-greenstone terranes. Typical porphyry

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type Cu/Au deposit normally form in Andean-type margins (Sillitoe, 2010). With respective to

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the formation age of the Katbasu Au deposit (~323 Ma), the South Tianshan was still an Andean type margin constructed by the northward subduction of the South Tianshan Ocean

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beneath the Ili-Central Tianshan micro-continent (e.g., Gao et al., 1998; Charvet et al., 2011;

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Xiao et al., 2013). The most robust evidence for this is that the 332 ± 7 Ma ophiolite is located 200 km away to the southeast of the Katbasu (Jiang et al., 2014), indicating that an ocean still

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existed until then. High pressure eclogite with seamount oceanic crust (Gao and Klemd, 2003) have a peak metamorphic age of late Carboniferous, which is constrained by a Sm-Nd isochron of ~320 Ma of garnet with clinopyroxene and a

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Ar/39Ar cooling age of 316 ± 3 Ma of

phengite from these eclogite (Hegner et al., 2010). The eclogites must have been exhumed very quickly to the surface in order to be preserved. The peak metamorphic age of the eclogite indicates that a oceanic subduction was still active from 320 to 316 Ma (e.g. Xiao et al., 2015). Thus, the Katbasu gold deposit (~323 Ma) formed in a subduction environment. The age of the Katbasu Au deposit is similar to those of the porphyry type deposits in the South Tianshan, such as the Almalyk porphyry type (315 Ma) in the western segment of the South Tianshan, and the Tuwu porphyry type in the eastern segment of the South Tianshan (322.7 Ma) (Fig. 8B).

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ACCEPTED MANUSCRIPT The Katbasu Au deposits in the central segment of the South Tianshan with this new age of 323 Ma strongly suggests that the central segment of the South Tianshan is no different from the

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west segment in Uzbekistan, Tajikistan and Kyrgyzstan, and the eastern segment of East Xinjiang, China. The scarcity of ore deposits in this region is due to the low exploration level,

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and therefore this region deserves more detailed investigation. It is worth noting that giant orogenic Au deposits, such as the Muruntau (287.5 Ma) located in the Southern Tianshan

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accretionary complex (Fig.1), are temporally younger than the porphyry type (Fig.8). Such

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contrasting age populations may indicate regional tectonic transformation. Porphyry mineral systems prefer to form in a thick crust, which is indicated by high Sr/Y ratios (Chiaradia, 2014).

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The relatively low Sr/Y ratios of granites and granodiorite in Katbasu (Fig. 5B, Supplementary

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Table 1) may indicate that the south Tianshan arc was immature or was not thick enough at ~350 Ma (or even at ~335 Ma) to produce magmas of high Sr/Y ratios (Chiaradia, 2014). Until

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the late Carboniferous, the arc was built thick enough to form high Sr/Y granites in the Tuwu-Yandong area (Zhang et al., 2006); many porphyry deposits formed during this time. Orogenic ore deposits are normally related with compressional-transpressional regimes (Goldfarb et al., 2001; Wan et al., 2017). Extensive regional strike-slip faults were active in the Early Permian (see. Xiao et al., 2015 and reference therein). An oblique convergence can trigger devotilization of the lower crust and circulate fluid to deposit gold in regional strike-slip faults. Therefore, there might be an important regional tectonic transformation from convergence to oblique convergence during the Latest Carboniferous to Early Permian.

5. Conclusions Rb-Sr isotopic analyses by TIMS on five individual pyrite grains (8 to 24 mg) yielded an 19

ACCEPTED MANUSCRIPT isochron age of 322.5 ± 6.8 Ma (MSWD=3.2). The age dated pyrites contain sericite inclusions, while sericite grains also commonly include small pyrite crystals in the phyllic alteration

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sample. The inter-included relationship between pyrite and sericite indicate that these two types of mineral formed coevally. Because the Au is coeval with the pyrite, the Rb-Sr isochron

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of 322.5 ± 6.8 Ma represent the mineralizing age of the Katbasu deposit, which is consistent with the regional porphyry type mineralizing epoch at 323 Ma in the South Tianshan. As to the

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emplacing ages of magmas in the mine area, magmatic zircons from granite were dated by

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SIMS yielding a concordia age of 351.4 ± 1.1 Ma (MSWD = 0.13), with a weighted mean age of 351.7 ± 2.4 Ma. Zircons from granodiorite give a concordia age of 355.7 ± 2.7 Ma (n = 14,

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MSWD = 1.01), with a weighted mean age of 356.2 ± 3.7 Ma (n = 14, MSWD = 1.4). These

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granodiorite ages are highly consistent with that of the granite. In addition, zircons from the rhyolite that sited far from the orebody yielded a concordia age of 335.7 ± 1.3 Ma, with a

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weighted mean age of 335.0 ± 2.8 Ma (n = 12, MSWD = 0.48). All magmatic activities observed in the mine are temporally not responsible for the ore forming processes. Detailed work is required to find the ore causative intrusion. Limited geological evidence supports the idea that the Katbasu Au deposit may be related to an intrusion beneath the mine area and probably a porphyry (or magmatic hydrothermal) type Au deposit.

Acknowledgments This study was supported by National Basic Research Program of China (2014CB448000) and National Science Foundation of China (41390445, 41672085). B.W. thanks the generosity of the Youth Innovation Promotion Association CAS (2013047). We thank Luo, Q. and Xing, L. for the guide in the ore field. We appreciate Li, C.F for his assistance in Rb-Sr isotopic analysis, 20

ACCEPTED MANUSCRIPT Tang, G.Q. and Ling, X.X for their assistance in SIMS analysis, and Gillespie, J.A. and Gerger, D. for language improvement. Critical comments of two anonymous reviewers and Franco

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Pirajno greatly improve the paper.

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Figure captions:

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Fig. 1. Geological map of the Tianshan region. Locations of giant or large ore Au (Cu) deposits,

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high-pressure metamorphic rocks and ophiolite mélanges and section A-A’ in Fig. 2 in the South Tianshan region are marked. Modified after Xiao et al. (2013). Detailed information

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of the ore deposits is listed in Table 1.

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Fig. 2. A) Overview of Katbasu gold deposit. B) Simplified geological map of the Katbasu deposit. C) Geological cross sections of A-A’ modified from Zhang et al. (2015). D)

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Alteration zonation outlined mainly based on drill holes along A-A’ section. Fig. 3. Photographs of alteration and mineralization at the Katbasu gold deposit. A) Potassic alteration of granite mainly composed of orthoclase and hydrothermal biotite. The biotite is overprinted by chlorite locally. B) Phyllic alteration, and the granite is replaced by quartzes along with some sericite that cannot be observed on hand specimen. Pyrite-gold-quartz vein cut through phyllic altered granite. C) Ores of quartz-sericite-pyrite vein from Fig. 3B. Note that native gold grains ca.100um in diameter occur in pyrite and smaller ones scattered in pyrite and quartz. D) Sericite-pyrite-quartz vein shows some pyrite occurred as inclusion in sericite. E) BSE images of pyrite grains from Fig. 3B and Energy Dispersive Spectrometry used for mineral identification. F) Potassic alteration overprinted by chloritization,

30

ACCEPTED MANUSCRIPT accompanied by sericite and magnetite. G) Chloritic altered granite. H) Pyrite-calcite vein

RI P

Ccp-chalcopyrite, Mag-magnetite, Kfs-K-feldspar, Cal-calcite.

T

developed in the country rock. Abbreviations: Py-pyrite, Ser-sericite, Qtz-quartz, Au-gold,

Fig. 4. Alteration and mineralization sequence of mineral assemblages in the Katbasu gold

SC

deposit. Sericite bearing pyrite for Rb-Sr dating is labeled with a red triangle. Fig. 5. A) Primitive Mantle normalized spider diagram for granite in Katbasu. Primitive Mantle

NU

values are from Sun and McDonough (1989). B) Sr/Y verse Y diagram of granite. Data of

MA

Tuwu from Zhang et al. (2006)

Fig. 6. BSE image and Au-Fe-S mapping of the gold bearing pyrite.

ED

Fig. 7. A) Rb–Sr isochron age of pyrite samples from Fig. 3B; B) SIMS U-Pb concordia age of

PT

granite (KB48). C) SIMS U-Pb concordia age of granodiorite (KB56). D) SIMS U-Pb concordia age of rhyolite (KB33).

AC CE

Fig. 8. A) Histogram of ages of mineralization of porphyry Au (Cu) deposits and orogenic Au deposits in the South Tianshan; Cartoon shows porphyry (B) and orogenic (C) gold deposits formed during the Late Paleozoic and associated tectonic locations. Ages of deposits used for calculation are listed in Table 1.

31

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

32

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

33

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

34

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

35

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

36

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

37

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

38

AC CE

PT

ED

MA

NU

SC

RI P

T

ACCEPTED MANUSCRIPT

39

ACCEPTED MANUSCRIPT Table 1. A compilation of gold (copper) ore deposits in South Tianshan. Name Ore type Age Method Tectonic Country (Ma) location orogenic

287.5 ±

Re-Os

South Tianshan

1.7

Accretionary complex

orogenic

260-270

——

South Tianshan

Uzbekistan

Accretionary complex orogenic

286

Re-Os

South Tianshan

SC

Zarmitan

Morelli et al. (2007)

RI P

Amantaitau

Uzbekistan

T

Muruntau

Reference

Uzbekistan

Accretionary

Yakubchuk et al. (2005) Goldfarb et al. (2014)

complex orogenic

299

——

South Tianshan

NU

Jilau

Tajikistan

Accretionary

Mao et al. (2004)

complex

orogenic

288.4 ± 0.6

orogenic

Taldybulak

orogenic

AC CE

Daugyztau

Kokpatas

orogenic

206-213

PT

Sawayaerdun

282 ± 5

orogenic

orogenic

Rb-Sr

——

South Tianshan

Kyrgyzstan

Accretionary

Mao et al. (2004)

complex South Tianshan

China

Accretionary

ED

Kanggur

Ar-Ar

MA

Kumtor

Zhang et al. (2008)

complex

Rb-Sr

South Tianshan

China

Accretionary

Liu et al. (2007)

complex ——

South Tianshan

Uzbekistan

Accretionary

Goldfarb et al. (2014)

complex ——

——

South Tianshan

Uzbekistan

Accretionary

Seltmann et al. (2014)

complex ——

——

South Tianshan

Levoberezhny

Kyrgyzstan

Accretionary

Goldfarb et al. (2014)

complex Karakol

orogenic

——

——

South Tianshan

Kyrgyzstan

Accretionary

Goldfarb et al. (2014)

complex Terakkan

orogenic

——

——

South Tianshan

Kyrgyzstan

Accretionary

Goldfarb et al. (2014)

complex Chapchaea

orogenic

——

——

South Tianshan

Kyrgyzstan

Accretionary

Goldfarb et al. (2014)

complex Matoutan

orogenic

——

——

South Tianshan Accretionary 40

China

Mao et al. (2004)

ACCEPTED MANUSCRIPT complex Kochbulak

epithermal

290-280

——

South Tianshan

Uzbekistan

Arc Taldy Bulak

porphyry

475-455

——

al. (2005)

South Tianshan

Kyrgyzstan

porphyry

440 ± 8 315± 1

U-Pb on

South Tianshan

zircon

Arc

——

South Tianshan Arc

porphyry

322.7 ±

Re-Os

South Tianshan

SC

Yandong

2.3 Tuwu

porphyry

Kyrgyzstan

RI P

Almalyk

porphyry

Uzbekistan China

Arc Re-Os

South Tianshan South Tianshan

zircon

Arc

Rb-Sr

PT

ED

6.8

NU

322.5 ±

U-Pb on

MA

Porphyry？

322 ± 3

AC CE

Katbasu

porphyry

41

South Tianshan Arc

Jenchuraeva (2001) Seltmann et al. (2014) Rui et al. (2002)

China

Arc

Chihu

Yakubchuk et al. (2005)

T

Arc Andash

Yakubchuk et

Rui et al. (2002)

China

Liu et al. (2003)

China

This study

ACCEPTED MANUSCRIPT Table 2 TIMS Analysis of 5 Pyrite Grains from Sample KB48. Sr [ppm] 3.017 6.492 0.946 2.521 0.219

87

Rb/86Sr 0.8454 0.5005 5.6312 1.5616 3.7565

NU MA ED PT AC CE 42

87

Sr/86Sr 0.710769 0.709286 0.732682 0.714106 0.72432 0.710255

T

Rb [ppm] 0.894 1.108 1.789 1.339 0.281

RI P

Weight (g) 0.0240 0.0126 0.0218 0.0125 0.0080

SC

Sample No. Grain 1 Grain 2 Grain 3 Grain 4 Grain 5 NIST-NBS987

Error (2s) 0.000020 0.000026 0.000014 0.000018 0.000020 0.000010

ACCEPTED MANUSCRIPT Table 3. SIMS U-Pb analytical data of granite, granodiorite and rhyolite in the ore district. Pb

235

/ U

± σ

206

Pb

238

/ U

±

ρ

207

Pb

206

σ

/ P

207

±

Pb

206

σ

σ

/ P

b

±

b Age

Granit KB48 0.40

1.

0.05

1.

0.8

0.052

0.

056

7

49

5

786

88

8

4

9

0.41

1.

0.05

1.

0.9

0.053

0.

094

6

6

5

263

19

5

0.41

1.

0.05

1.

243

5

58

5

7 0.41

1.

0.05

242

6

59

T h/ U

Age

Age

(p

(p

(Ma)

(Ma)

pm

pm

)

)

245

271

575

61

1. 5

AC CE

5

7

.

10

2

8

9

76

1

8

1

6

0.053

0.

329

54

5

354.6

1

350.

4.

4

0.

6

7

5

2 351.7

350

5

63

5

701

28

3

2

0

1.

0.05

1.

0.9

0.053

0.

357

5

51

5

627

14

4

3

9

1.

0.05

1.

0.9

0.053

0.

899

6

7

5

375

31

2

4

62

350.

4.

350.

5

557

3

6

8

5

.

18

1

9

8.

351.

4.

352.

5

101

6

3

7

9

.

9

662

981

9.

344.

4.

345.

5

7

2

6

6

.

782

137

1.

9

76 5

1

355.

4.

357.

5

5

2.

3

9

4

.

93

6

7

3

1

0.40

1.

0.05

1.

0.9

0.053

0.

766

5

48

5

670

94

4

1

3

368.7

8.

347.

4.

9

2

6

344

5

501

931

.

467

0.41

1.

0.05

1.

0.9

0.053

0.

804

7

64

6

532

73

4

4

1.

2

16 2

1

354.

5.

353.

5

5

1.

6

2

9

.

98

2

7

6

5

0.41

1.

0.05

1.

0.9

0.053

0.

434

5

62

5

763

51

3

2

1

1.

0.9

359.7

0.

108

1

350.5

7.

352

6

425

4.

352.

5

101

6

2

.

5

4 0.053

0. 3

1 341.9

1.

96

2 335

1.

1

3

0.41

893

1.

1

8

0.40

551

545

.

8 340.6

5

309

1.

.

335

0.05

344.

1

5

0.

1.

5.

1

8

0.053

0.42

342.

8.

5

0.9

336.9

1

3.

0.9

6 11

/ U

Th

6

1.

2 10

σ

σ

U

5

0.05

6 9

±

351.

1.

2 8

Pb

238

4.

0.41

9

7

/ U

206

349.

0.

7

7

6

0.053

7

1 5

0.9

PT

4

235

±

1

ED

2 3

4

323.8

MA

5

NU

e

2

Pb

SC

(Ma)

1

207

T

207

RI P

No.

844

895

364.7 43

1

357.

4.

356.

5

0. 88

2

0.

1.

1 414

500

1.

ACCEPTED MANUSCRIPT

7

0.05

1.

0.9

0.053

0.

494

6

77

6

645

44

3

7

16

17

81

5

1

7

1

701

52

3

1.

0.05

1.

0.9

0.053

0.

369

5

6

5

561

58

4

1.

0.05

1.

0.9

0.053

0.

505

5

62

5

683

59

3 9

0.41

1.

0.05

1.

0.9

0.053

0.

628

6

63

5

438

67

5

3

9

1.

0.05

1.

0.9

0.053

0.

332

6

62

5

243

38

6

4

0.05

1.

953

6

67

5

1.

0.05

26

6

62

diorite KB56

2

6

8

0.9

0.053

0.

331

65

5

1.

0.9

0.053

0.

5

454

28

AC CE

0.41

7

3

357.1

345.1

5

4

356.3

340.7

340.1

4 207

Pb

206

67

1

5

352.

4.

352.

5

7

5

6

3

.

/ P

Pb

206

σ

131

1.

3

65 4

1

353.

4.

352.

5

928

998

2

4

8

8

.

07

2

6

0.05

1.

0.9

0.053

0.

587

5

66

5

530

3

351.

4.

352.

5

106

136

1.

4

3

8

2

.

1

9

29

329

374

1.

1

355.

4.

355.

5

3

7

9

6

.

13

2

7

1

348.

4.

349.

5

4.

5

9

7

.

±

206

/ P

± σ

955

5

354

581

Pb

235

/ U

σ

Pb

238

/ U

±

64 U

Th

σ

h/

Age

Age

Age

(p

(p

(Ma)

(Ma)

(Ma)

pm

pm

)

)

777

109

1.

7

41

354.

5

4

0.

1

7

8

.

8

8

1.

0.9

0.053

0.

087

6

86

5

558

36

4

8

7

341.7

344.3

9 44

T U

4.

0.05

1.

2 207

353.

1.

0. 88

4

1

0.43

1.

1

b

1.

8

794

2

5 207

±

0.41

6

.

2

3

7

2

8.

1.

2

b

3

7

4

6

σ

5

8

26

/ U

5

.

219

σ

351.

3

5

/ U

4.

4

940

0.

351.

9

57

ρ

1

7

6

±

1

2.

943

Pb

97

5

0.

238

.

107

0.053

±

8

5

0.9

Pb

6

352.

1.

235

2

4.

0.05

206

5

350.

1. 6

5

1

0.40

207

347.

561

833

1.

4.

1

858

980

348.

0.

353.9

541

8.

3

0.41

1.

353.4

6

0.41

0.41

351

8

0.41

Grano

No.

.

5

6

1

5

54

1 19

1

5

PT

18

6

904

3

7

0.

0.

3

4

4

0.053

2

20

5

0.9 2

.

361.

1.

2

8

5.

0.05

5

9

359.

1.

347.4

MA

15

9

1

0.40

7

1. 3

1.

5 14

5

0.42

9 13

4

85

ED

12

507

T

2

5

RI P

69

SC

6

NU

253

2

3

1

363.

5.

366.

5

432

575

1.

1

8

1

9

.

33

6

2

ACCEPTED MANUSCRIPT 1.

0.05

1.

0.9

0.053

0.

161

6

73

5

418

38

2

3

.

38

4

2

3

5

1

7

71

5

895

51

1

4

350.6

357.

5

7

7.

8

1

7

.

32

8

4

3

3

1.

0.8

0.053

1.

785

8

53

5

304

52

0

2.

1

2

1

7

0.41

1.

0.05

1.

0.9

0.053

0.

912

5

68

5

682

53

4

4

3

1.

0.05

1.

0.9

0.053

0.

798

7

8

6

380

55

6

4

8

351.2

2

352.2

5.

346.

5

3

4

8

.

10

1

5

8.

355.

4.

356.

5

9

4

8

1

.

02

3

8

363.

5

3.

7

3

2

.

74

8

7

1.

0.05

1.

0.9

0.053

0.

1

355.

4.

355.

5

6

67

5

259

58

6

3.

2

9

5

.

2

9

2

9

1.

0.05

1.

0.8

0.053

0.

056

6

56

5

902

59

1.

0.05

413

6

74

1.

0.05

5

6

7.

3

7

3

290

6

3

5

1.

0.9

0.053

0.

5

707

68

3

4

9

AC CE

0.41

349.

5

1.

0.9

PT

0.42

0.053

0.

354.8

61

3.

1

7 357.5

1

5

359.

5

7

.

7

1

.

1

65

0

723

73

4

1.

5

4

9

1

0.

549

5

87

5

771

84

3

2

418

752

359.7

364.6

1

1. 8

755

100

1.

2

32

3

848

0.053

188

3 9

0.

4

5

1

6

0.053

0.9

1. 75

5

0.9

1.

331

.

351.

2.

0.05

84

6

4.

0.05

1.

1.

5

5

8

0.43

143

348.

351.

2. 1

359

5

8.

0.41

1.

3

1

7

353.7

780

471

1.

5.

884

270

836

1.

361.

0.41

0.41

813

126

1 6

353.3

114

1.

347.

NU

0.42

350.8

236

1.

5.

0.05

178

505

356.

1.

7

365

1

0.40

9

20

1

0.

422 18

9

0.053

4 17

2

0.8

9 14

2.

1.

4 13

5

0.05

4 12

5

1.

9 11

359.

0.42

2 10

4.

SC

9

357.

MA

8

1

RI P

2

345

T

0.42

ED

6

355

6.

354.

7

3

2

.

8 887

133

1.

1

5

119

1.

3

21

1

7.

367.

4.

367.

5

3

1

7

5

.

3

983

4

4

Rhyol ite KB33 1

0.39

1.

0.39

1.

0.8

0.052

0.

384

8

384

8

463

80

4

2

4 2

320.

2

339.

5

9

2.

2

2.

6

.

28

8

1

1

0

2.

0.39

2.

0.6

0.052

1.

090

2

090

2

576

85

8

3

8 3

2

0.39

320.2

3

322.

3

336.

4

102

7

8.

2

8.

9

.

6

2

6

0.38

1.

0.38

1.

0.9

0.053

0.

786

6

786

6

688

07

4

322.2

1

271

331.9

45

6

347

990

331.

9.

332.

5

0

9

0

9

.

0. 96

9

9.

1.

5 790

682

0. 86

ACCEPTED MANUSCRIPT

1.

0.38

1.

0.9

0.053

0.

942

6

942

6

522

16

1

9

4

1.

8

1.

7

.

97

9

1

0

1

0.

522

6

522

6

349

17

6

7

1

336.

1

5

3.

3

3.

9

3

0.38

1.

0.38

1.

0.9

0.053

0.

565

5

565

5

725

18

3

5

4

1.

0.38

1.

0.9

0.053

0.

881

5

881

5

593

21

4

6

9

4

0.39

1.

0.39

1.

0.9

0.053

0.

146

7

146

7

474

31

5

3

1

Pb

235

/ U

± σ

206

Pb

238

/ U

±

ρ

6

207

Pb

206

σ

336.6

/ P

342.0

±

0.38

1.

0.38

624

6

624

σ

/ P

10

11

0.053

0.

6

756

33

3

1

5

0.39

1.

0.9

0.053

0.

675

5

675

5

587

36

9

0

7

338.

1

332.

4

0.

0

0.

9

.

52

9

5

336.

8.

330.

4

6

1

4

.

970

110

1.

4

13

8

0

8 539

342.

1

334.

5

2.

0

2.

5

.

61

4

6

± σ

5 Pb

235

/ U

± σ

206

Pb

238

/ U

±

U

245

Th

σ

0.

T h/ U

Age

Age

(p

(p

(Ma)

(Ma)

(Ma)

pm

pm

)

)

8.

343.

8.

330.

5

105

187

1.

0

0

0

0

.

9

5

77

1

1

344.

1

338.

5

4

0.

1

0.

6

.

52

5

2

0

1

1.

0.39

1.

0.9

0.053

0.

835

5

835

5

644

39

4

6

3

344.1

0.

1

207

397

283

1

0.39

345.3

2

1.

0.39

1.

0.9

0.053

0.

154

6

154

6

334

54

1

3

351.8

528

719

275

345.

9.

339.

5

3

3

3

7

.

87

0

6

351.

1

333.

4

5

3.

8

3.

2

.

58

8

0

9

0

46

198

0.

1

0

340

630

0.

9.

1

0.39

1

83

Age

343.0

0.

.

5

1.

6

12

0.9

0.39

9

501

b

1.

AC CE

1

PT

9

Pb

206

598

1

8.

5

207

5

0.

5

3

0

ED

b

338.0

338.

773

1

1

6

0.38

207

336.3

T

0.053

1

796

RI P

0.9

3 No.

5

1.

6 8

333.

SC

7

1

0.39

335.8

3

335.

1.

5

0 1

0.39

6 6

0

0.38

1 5

1

MA

4

0

NU

0

0.

ACCEPTED MANUSCRIPT Table 4. Summary of major features of gold deposits.

Deformed

setting

margin

Structural

Compression

setting

transpression

continental

rocks

deposits

Inboard of known or inferred

convergent

to

Extensional

greenschist

facies

metavolcano-sedimentary

Felsic plutons + wall rocks

Reduced, subalkalic,

Associated

－－

intrusions

metaluminous, I- type

MA

intrusions

Typical proximal

Alkali

Sericite

feldspar,

sericitic

alterations

Sheeted

style

veins, saddle reefs

stockworks

Arsenopyrite,

Arsenopyrite,

PT

related

pyrite/pyrrhotite

minerals metal association Ore fluids

AC CE

Characteristic As, Te

Low-salinity, near-neutral, CO2 rich fluids

veins,

ED

Variable, vein arrays, large

ore

Porphyry stocks + wall

Potassic,

intermediate

Stockwork Magnetite,

+

molybdenite

Early carbonic fluids to

aqueous brines

pyrite,

chalcopyrite,

Bi, W, As, Mo, Te

47

porphyries

disseminated

pyrite/pyrrhotite

evolving

Mediate-felsic

argillic

Mineralization Typical

to

rocks

NU

rocks

extension

compression

to mainly

plate

boundaries Weak

structures

granulite facies,

Convergent

SC

host

deposits

late boundaries

Subgreenschist Typical

Porphyry gold (copper)

T

Tectonic

Intrusion-related gold

RI P

Orogenic gold deposits

later

Cu, Mo

Oxidized, high salinity fluids

ACCEPTED MANUSCRIPT

AC CE

PT

ED

MA

NU

SC

RI P

T

Graphical abstract

48

ACCEPTED MANUSCRIPT Highlights  The Katbasu is the first gold deposit in the Chinese South Tianshan.

RI P

T

 Potassic, phyllic and chloritic alteration develop successively at Katbasu.  The mineralization age of Katbasu is 322.5Ma.

AC CE

PT

ED

MA

NU

SC

 The Katbasu is probably a magmatic hydrothermal gold deposit

49