The 109 porphyry Cu deposit in the western Tianshan orogenic belt, NW China: An example of Cu mineralization in a reduced magmatic-hydrothermal system in an extensional setting

Ore Geology Reviews 112 (2019) 102989

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The 109 porphyry Cu deposit in the western Tianshan orogenic belt, NW China: An example of Cu mineralization in a reduced magmatichydrothermal system in an extensional setting ⁎

Rui Liua,b,c, , Genwen Chenb,

T

⁎

a

Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China c Southern Laboratory of Ocean Science and Engineering (Guangdong Zhuhai), Zhuhai 519000, China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Reduced ore system fO2 Extensional tectonic setting Sulfur degassing

The 109 porphyry Cu deposit in the western Tianshan orogenic belt, NW China, is hosted in albite porphyry. The albite porphyry is metaluminous to peraluminous and alkaline in terms of composition, and has an affinity of Atype granite, and is considered to have formed in an extensional tectonic setting. Zircon grains from the albite porphyry yielded a weighted mean 238U/206Pb age of 300 ± 4 Ma (95% confidence) by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The age can be considered to be the crystallization age of the 109 albite porphyry. The zircon grains have Ce4+/Ce3+ ranging from 10.8 to 50.5. The ore minerals mainly include chalcopyrite, bornite and chalcocite, and the absence of magnetite, hematite and sulfates. The oxygen fugacity (fO2) was estimated to be below the quartz-fayalite-magnetite (QFM) + 2 buffer using the Ti-inzircon thermometer. We therefore assumed that the 109 Cu deposit formed in a reduced magmatic-hydrothermal system, which is similar to the coeval Cu deposits elsewhere in the western Tianshan orogenic belt, indicating that they may have the same the reduced ore system is likely attribute to an extensional tectonic setting during the late Carboniferous in the western Tianshan orogenic belt. Sulfides in the ores display quench texture or exsolution texture. The rim of each sulfide grains always have δ34S higher than the cores, which is attributed to a fast decrease of temperature and degassing of sulfur from ore-forming fluid. The sulfur degassing may lead to the progressive increase of the fO2 of the ore-forming fluids. The ore-forming fluids with high fO2 can contain more sulfur leading to the formation of the 109 Cu deposits

1. Introduction Porphyry Cu deposits are considered to be closely related to oxidized porphyries with S6+ in the system (Ishihara, 1977; Burnham and Ohmoto, 1980; Blevin and Chappell, 1992). The oxygen fugacity (fO2) of oxidized porphyry Cu deposits varies from the hematite-magnetite (HM) to nickel-nickel oxide (NNO) oxygen buffers in the temperatures associated with mineralization (Burnham and Ohmoto, 1980). In the classic model, the ore body is associated with oxidized I-type granitoids, and contains large amounts of primary magnetite, hematite, and sulfates (Burnham and Ohmoto, 1980). However, the fO2 of ore-forming fluids in many porphyry Cu (Mo–Au) systems is less than or equal to the QFM buffer (Rowins, 2000). These systems are associated with I-type, ilmenite-bearing granitoids, and contain abundant hypogene pyrrhotite, lack of primary hematite and sulfate minerals, e.g., the

Paleogene North Fork Cu–Au deposit in the Cascades, Washington, and the Baogutu porphyry Cu deposit in the Junggar Basin, Xinjiang (Smithson, 2004; Shen et al., 2010a,b; Cao et al., 2014). It is unclear the mechanism that lead to the formation of such the reduced porphyry Cu deposits (Wu et al., 2015). The Awulale metallogenic belt is located in the western Tianshan orogenic belt. Numerous late Paleozoic large-scaled marine volcanic iron deposits occur in the eastern part of the Awulale metallogenic belt. (Zhang et al., 2014a,b), and extensive late Paleozoic porphyry-style mineralization that has similar feature of the reduced porphyry Cu occurs in the western part of the belt (Wang et al., 2006; Liu et al., 2017; Liu et al., 2018). The 109 porphyry Cu deposit is a typical example in the western Awulale metallogenic belt that can be used to decipher the mechanism of Cu mineralization in a reduced ore-forming system.

⁎ Corresponding authors at: Guangdong Provincial Key Lab of Geodynamics and Geohazards, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China (R. Liu). E-mail addresses: [email protected] (R. Liu), [email protected] (G. Chen).

https://doi.org/10.1016/j.oregeorev.2019.102989 Received 8 June 2018; Received in revised form 21 June 2019; Accepted 24 June 2019 Available online 27 June 2019 0169-1368/ © 2019 Elsevier B.V. All rights reserved.

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Fig. 1. (a) Tectonic location of the western Tianshan in the CAOB; (b) Sketch map of the western Tianshan (modified from Gao et al., 2009).

developed; the axis of the Carboniferous folds are mainly E-W-trending, and there are many N-E and N-W-trending compressional and torsional faults in this area. In the Permian, the E-W-trending tectonic belt is transformed by the N-E and N-W-trending tectonic belts, resulting in the formation of many folds, faults and dome structures. Affected by the regional structure, the direction of the long axis of rocks in this region are mainly parallel to the structure direction. These structures control the distribution of the intrusive porphyries and associated mineral deposits in this region; the Changuoer iron deposit is controlled by NW, NWW, NE fractures (Zhang et al., 2014b), and the porphyry Cu ore bodies in the western Awulale metallogenic belt mainly occur besides these structures (Zhang et al., 2012).

In this study, we investigated the age, geology, geochemistry and petrology of the ore-bearing intrusion of the 109 porphyry Cu deposit in the western Tianshan orogenic belt. A combination of mineral assemblages and trace elements in zircon was applied to quantify the oxidation state of the magmas. We propose the presence of reduced magmas and ore-forming fluids resulting from an extensional tectonic setting during the late Carboniferous in this region, and highlight the increasing fO2 during the deposition of sulfides in reduced ore-forming system.

2. Geological setting The Awulale metallogenic belt is part of the western Tianshan orogenic belt, and is located in the southwestern part of the Central Asian Orogenic Belt (Fig. 1a). It is bounded by the Junggar Plate in the north, by the Kazakhstan-Yili Plate in the west and by the Tarim Plate in the south (Fig. 1b). The eastern part of the Awulale metallogenic belt consists of late Carboniferous sequence, including the Dahalajunshan Formation, Akeshake Formation and Yishenjilike Formation. The Dahalajunshan Formation is composed of a suite of volcanic-sedimentary rocks, consisting of rhyolite, trachyte, trachyandesite and ignimbrite. The Akeshake Formation is composed of purple-colored tuff, andesite, volcanic breccia, silty shale, grayish-green limestone, and grayish-green marl. The Yishenjilike Formation is dominated by felsic volcanic rocks (rhyolite) and minorbasalts, which are intruded by a quartz syenite porphyry. The western part of the Awulale metallogenic belt comprises the late Carboniferous to Permian (260–320 Ma) sequences, including the Yishenjilike Formation, Wulang Formation, Taerdetao Formation, Xiaoshansayi Formation, Hamisite Formation, Tamuqisayi and Basiergan Formation. The Wulang Formations is composed of continental intermediate-mafic and felsic volcanic rocks, including andesite, dacite, rhyolite, olivine basalt, felsite, volcanic breccia, ignimbrite and tuff. The Taerdetao Formation consists of bimodal volcanic rocks, including basalt and rhyolite. The Xiaoshansayi Formation is mainly composed of purplish red and gray thick-bedded conglomerate, pebbly sandstone, sandstone, siltstone, and mudstone. The Hamisite Formation is a suit of volcano-sedimentary rocks, including conglomerate, pebbly sandstone and sandstone in the lower part and basalt and rhyolite in the upper part. The Tamuqisayi Formation mainly consists of red and gray thickbedded conglomerate, sandstone, siltstone, and mudstone. The Basiergan Formation mainly consists of red thick-bedded conglomerate and sandstone. Intermediate to felsic pluton (296–306 Ma) are widely distributed in the western Awulale metallogenic belt (Fig. 2a). Folds, faults and dome structures are well developed in the Awulale metallogenic belt. E-W-trending tectonic belt is the earliest in this area, which is formed in the late Early Paleozoic to early Late Paleozoic. In the middle Late Paleozoic, the E-W-trending tectonic belt is well

3. The 109 porphyry Cu deposit Numerous Fe-Cu (Au) polymetallic deposits occur in the Awulale FeCu metallogenetic belt (Zhang et al., 2014b). In the western part of Awulale metallogenic belt, volcanic-subvolcanic hydrothermal Cu deposits are related to Permian terrestrial intermediate to basic volcanic rocks, such as the Nulasai and Kezikezang deposits, whereas, porphyry copper deposits are hosted in the Late Paleozoic intermediate to acidic intrusive rocks, such as the Yinulasai, Qiongbulake, Qunjisayi, Qunji, 109 and Heishantou deposits (Zhang et al., 2012; Zhao et al., 2012a,b; Liu et al., 2018). The 109 porphyry Cu deposit is hosted in an albite porphyritic pluton (Fig. 2a). The pluton is irregular in shape about 1000 m long and 300 m wide. It emplaced the Wulang Formations composed of bimodal volcanic rocks (Fig. 2b). The rocks of the pluton display porphyritic texture (Fig. 3). The phenocrysts include euhedral albite (40 vol%) and subhedral quartz (20 vol%). Albite crystals have Ab contents of 97.2–99.8 (Table 1), and 200–800 μm in size. They usually occur as twin structure. The matrix shows cryptocrystalline textures and is Siand K-rich in composition (Table 1). Hydrous minerals (e.g., amphibole or biotite) are absent in the rocks. The rocks are relatively fresh with weak potassic alteration. The ore reserves of the 109 porphyry Cu deposit are 0.7–0.8 million tons Cu with average Cu grade of 0.8% Cu (Fig. 4). There are three Cu orebodies in the deposit (Figs. 2 and 4), two of which are crops out (Fig. 2) and one is underground (Fig. 4). The Cu orebodies are plate- or lenticular-like, with length varying from 100 to 500 m, and thickness from 20 to 50 m. Major ore types are disseminated ore and vein-like ore (Fig. 5a, b). The ore minerals mainly include chalcopyrite, bornite, and chalcocite in both disseminated and vein-like ores. Sulfides occur as aggregates or disseminated grains, typically showing metasomatic and exsolution textures (Fig. 5c). Chalcopyrite exsolution is developed in bornite. Bornite usually replaced chalcocite. The crystallization sequence revealed by the textural relationship is chalcopyrite 2

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Fig. 2. (a) Sketch map of the tectonics and magmatic rocks in the western Auwulale metallogenic belt (modified from Li et al., 2013); (b) Geological map of the 109 porphyry Cu deposit (modified from Zhao et al., 2012a,b). Note: the ages in Fig. 2a are from: Li et al. (2015) and Author’s unpublished data.

Fig. 3. Microphotographs of the 109 albite porphyry, showing porphyritic texture with euhedral albite phenocrysts, subhedral quartz and a cryptocrystalline matrix. (a) perpendicular polarized light; (b) reflected polarized light. Ab: Albite; Q: Quartz. 3

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Preliminary analyses were carried out using an electron microprobe analyser (EMPA) (JEOL JXA-8230) at the Key Laboratory of Mineralogy and Metallogeny, Chinese Academy of Sciences, to study the chemical composition of the phenocrysts and matrix. Peak calibration on each element was carried out using reference materials. The beam current was 20 nA with an accelerating voltage of 20 kV. Spot size was 1 μm. The following 9 elements and standards were used for measurements: Si (plagioclase), Al (plagioclase), Ca (plagioclase), K (potassium feldspar), Na (albite), Fe (garnet), Mn (garnet), Ti (rutile) and P (apatite).

Table 1 Chemical composition of phenocryst of the 109 albite porphyry (wt. %). Samples

1092-1

1092-2

1092-3

1092-5

1092-6

matrix

SiO2 TiO2 Al2O3 FeO MgO MnO CaO Na2O K2O P2O5 Total Si Ti Al Fe2+ Mg Mn Ca Na K P TOTAL An Ab Or

68.26 0.00 19.90 0.06 0.00 0.02 0.09 11.66 0.03 0.00 100.02 11.93 0.00 4.10 0.01 0.00 0.00 0.02 3.95 0.01 0.00 20.00 0.43 99.81 0.04

68.71 0.00 19.93 0.03 0.00 0.03 0.09 11.67 0.04 0.00 100.50 11.94 0.00 4.08 0.00 0.00 0.00 0.02 3.93 0.01 0.00 19.99 0.40 99.78 0.04

69.57 0.00 19.89 0.06 0.01 0.02 0.06 10.11 0.05 0.00 99.77 12.08 0.00 4.07 0.01 0.00 0.00 0.01 3.41 0.01 0.00 19.59 0.33 99.69 0.05

67.96 0.00 20.39 0.11 0.03 0.01 0.12 8.61 0.37 0.00 97.60 12.03 0.00 4.25 0.02 0.00 0.00 0.02 2.95 0.08 0.00 19.36 0.76 97.18 0.43

68.73 0.01 19.98 0.03 0.00 0.01 0.13 10.94 0.03 0.00 99.84 11.98 0.00 4.10 0.00 0.00 0.00 0.02 3.70 0.01 0.00 19.82 0.64 99.84 0.03

64.77 0.01 17.83 0.44 0.02 0.00 0.02 0.22 16.10 0.00 99.40

4.2. Zircon U-Pb dating and trace elements Zircon separation was carried out using conventional density and magnetic separation techniques to concentrate the non-magnetic heavy fractions. Representative zircon grains were then handpicked under a binocular microscope and mounted in epoxy mounts. Grains were then polished to nearly half-section to expose their internal structures. All mounted zircon grains were studied petrographically with transmitted and reflected light microscopy, as well as by cathodoluminescence (CL) imaging to reveal their internal structures. Most grains are transparent euhedral crystals ranging in size from 50 to 100 mm (Fig. 6). Zircon morphology and internal structures were imaged using a JEOL JXA8100 Superprobe at the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIG CAS). These images were used as guides during laser-ablation inductively-coupled plasma-mass spectrometry (LA-ICP-MS) analysis. In-situ U-Pb dating analysis of zircon was undertaken at the State Key Laboratory of Isotope Geochemistry, GIG CAS. LA-CP-MS zircon U-Pb dating and trace element analyses were synchronously conducted on an Agilent 7500 ICP-MS equipped with a 193 nm laser. Laser ablation was operated at a constant energy of 80 mJ, with a repetition rate of 8 Hz and a spot diameter of 31 μm. The zircon Temora standard was used for external standardization, and the Qinghu standard and NIST SRM 610 glass were used to optimise the machine. Repeated analyses of the standard zircon yielded a 206Pb/238U age of 416.9 ± 2.8 Ma for Temora (MSWD = 0.1, n = 22) and 160.6 ± 2.0 Ma for Qinghu (MSWD = 1.4, n = 9), which were in good agreement with the recommended Temora 206Pb/238U age of 416.8 ± 1.1 (Liu et al., 2010) and Qinghu 206Pb/238U age of 159.5 ± 0.2 Ma (Li et al., 2012). The operating conditions for the laser ablation system and the ICP-MS instrument, and the data reduction techniques follow (Li et al., 2012). Concordia diagrams and weighted mean calculations were constructed using the Isoplot/Ex program 3.0 (Ludwig, 2000). 4.3. Whole-rock major and trace elements Major and minor element geochemical analyses were undertaken at ALS Mineral/ALS Chemex (Guangzhou) Co Ltd. at Guangzhou, China. Major oxide concentrations were measured by XRF spectrometer. Fused glass disks with Lithium Borate were used and the analytical precisions were better than ± 0.01%, estimated from repeated analyses of the standards GSR-2 and GSR-3. Trace element concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). Analyses of USGS rock standards (BCR-2, BHVO-1 and AGV-1) indicate precision and accuracy better than ± 5% for trace elements.

Fig. 4. Cross-section of the 109 porphyry Cu deposit, showing the porphyry intruded into the bimodal volcanic rocks and ore body hosting in the albite porphyry.

(chalcopyrite-bornite solid solution) → bornite → chalcocite. The veinlike ores are mainly composed of sulfides (Fig. 5d) with minor quartz and calcite.

4.4. Sulfides sulfur isotope (34S) composition In-situ sulfur isotope analyses of chalcopyrite and bornite were performed using a NuPlasma HR multicollector ICP-MS at the Geological Survey of Finland in Espoo together with a Photon Machine Analyte G2 laser microprobe. Samples were ablated in He gas (gas flows = 0.4 and 0.11/min) within a HelEx ablation cell (Müller et al., 2009). Sulfur isotopes were analysed at medium resolution. During the ablation, the data were collected in static mode (34S). Samples of chalcopyrite and bornite were ablated at a spatial resolution of 25 µm,

4. Analytical methods 4.1. Chemical composition of phenocrysts and matrix Ore samples from the 109 porphyry Cu deposit were observed under a microscope, and the minerals were determined based on their texture. 4

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Fig. 5. Ore types and microphotographs of ore minerals. (a) disseminated ores; (b) vein-like ores with weak potassic alteration; (c) ore minerals in disseminated ores including chalcopyrite, bornite and chalcocite and exsolution texture showing exsolution chalcopyrite in bornite and exsolution bornite in chalcocite. (d) ore minerals in veined-like ores with full of sulfides. Cpy: chalcopyrite, Bo: bortnie, Cc: chalcocite.

combustion. All sulfur isotope compositions are expressed in standard delta notation as per mil (‰) deviations from the Canyon Diablo Troilite (CDT), with an analytical error of ± 0.2‰.

5. Results 5.1. Composition of phenocrysts and matrix of albite porphyry The phenocrysts mainly contain Si, Al, and Na, with minor Ti, Fe, Mg, Mn, Ca and P (Table 1). The phenocrysts have An contents of 0.33–0.76 and Or contents of 0.03–0.43, and Ab contents of 97.2–99.8. The matrix mainly contains Si and K (Table 1).

5.2. Whole-rock compositions of albit porphyry The samples from the 109 albite porphyritic pluton contain SiO2 (61.4–76.2 wt%), Na2O (2.65–6.60 wt%), total alkalis (5.16–7.02 wt%) and low MgO (0.03–0.57 wt%), P2O5 (0.04–0.08 wt%) and CaO (0.23–1.49 wt%) (Table 2). In the SiO2-AR diagram, samples are plotted in the alkaline to peralkaline field (Fig. 7a). These samples have A/CNK ratios ranging from 0.84 to 1.18, belonging to metaluminous to peraluminous granitoids (Fig. 7b). Samples display enriched light rare earth elements (REE) and heavy REE patterns on a chondrite-normalized REE plot, with negative Eu anomalies (Fig. 8a). On the primitive mantle-normalized trace element patterns, there are negative Ba, Sr, Nb and Ta anomalies and positive Zr and Hf anomalies (Fig. 8b). On a (N2O + K2O)/CaO vs Zr + Nb + Ce + Y diagram, all samples plot in the A-type granite field (Fig. 9), indicating that the 109 albite porphyry has an A-type granite geochemical affinity. This finding is consistent with the high amount of alkaline feldspar occurring in this porphyry and high total alkali content.

Fig. 6. Typical CL images of zircons from the 109 albite porphyry.

using a fluence of 2.7 J/cm2 at 5 Hz, depending on sensitivity. The total S signal obtained for samples was typically 2 V. Under these conditions, after a 20 s baseline, 30–40 s of ablation was needed to obtain an internal precision of 34S/32S≤ ± 0.00005 (1 SE). Two in-house samples standards have been used for external standard bracketing and quality control of analyses. Those standards have been measured by gas mass spectrometry. For a δ34S CDT (‰) value of −0.7 ± 0.5‰, we have found an average value of −0.7 ± 0.6‰ (2 s, n = 17). Chalcocite sulfur isotope analyses were conducted at Beijing Research Institute of Uranium Geology. Chalcocite was combined with an excess of Cu2O, and analysed using a Finnigan MAT 251 gas source mass spectrometer fitted with an elemental analyser for on-line sample 5

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Table 2 Major (wt. %) and trace elements (ppm) of the 109 albite porphyry. Samples

109-01

109-02

109-03

109-04

109-06

109-07

109-08

109-09

109-10

SiO2 TiO2 Al2O3 TFe2O3 Fe2O3 FeO MgO MnO CaO Na2O K2O P2O5 LOI ∑ Na2O + K2O (Na2O + K2O)/CaO A/CNK A/NK F Cl Li Be Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Nb Mo Cd In Sb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ta W Tl Pb Bi Th U Zr Hf Zr + Nb + Ce + Y

71.22 0.55 11.42 2.26 0.08 1.48 0.63 0.08 0.44 3.77 2.48 0.083 1.44 93.67 10.41 23.66 1.18 1.29 315 111 15.50 1.31 11.30 21.80 2.00 3.04 1.00 30,784 43.30 9.70 108.00 90.40 41.00 10.30 7.89 0.10 0.08 0.64 1.77 558.00 14.70 30.30 4.40 18.30 4.70 0.70 4.20 0.80 5.30 1.10 3.40 0.60 4.00 0.70 0.80 1.00 0.22 11.60 0.68 13.40 9.09 389.00 15.60 470.60

72.10 0.50 12.13 2.21 0.13 1.42 0.03 0.16 0.61 6.60 0.13 0.076 1.83 95.71 11.41 18.70 1.00 1.10 267 164 1.31 0.54 8.20 15.60 37.40 1.46 2.82 15,305 7.90 11.60 26.90 29.00 52.30 9.20 4.08 0.10 0.02 0.85 0.18 80.00 43.10 80.50 10.40 42.70 8.40 1.10 7.60 1.30 7.60 1.50 4.30 0.80 4.80 0.80 0.70 1.09 0.02 4.02 0.38 4.94 0.75 352.00 11.60 494.00

74.28 0.54 11.32 1.07 0.17 0.58 0.16 0.03 0.83 6.04 0.37 0.076 1.76 96.16 12.41 14.95 0.96 1.10 315 134 4.90 0.84 11.40 14.50 1.80 0.80 0.20 12,696 4.60 11.60 26.90 48.50 43.60 10.50 3.26 0.00 0.04 0.45 1.07 70.00 28.00 57.80 7.20 30.40 6.60 0.90 5.90 1.10 6.90 1.40 4.30 0.80 5.00 0.90 0.90 0.64 0.05 2.31 0.12 7.19 1.34 360.00 11.40 471.90

60.14 0.54 11.32 4.29 0.58 2.42 0.26 0.10 0.36 5.31 0.43 0.064 1.31 82.83 13.41 37.25 1.15 1.23 233 87.2 2.58 0.60 14.00 20.90 18.50 1.76 1.45 113,221 16.30 < 2.0 26.90 34.90 17.10 9.50 26.30 0.29 0.03 0.37 0.50 315.00 10.40 24.10 3.20 13.10 3.30 0.40 3.20 0.70 5.00 1.10 3.40 0.60 4.00 0.70 0.70 0.69 0.07 48.00 0.11 3.44 1.05 171.00 34.00 221.70

70.37 0.39 10.06 2.99 0.17 1.92 0.08 0.19 0.23 5.10 0.06 0.039 2.42 91.03 14.41 62.65 1.13 1.19 179 185 6.46 0.42 10.30 17.50 43.90 1.52 2.66 60,524 13.70 < 2.0 26.90 29.90 28.30 6.80 11.50 0.10 0.03 0.59 0.12 169.00 5.70 12.90 1.70 8.00 2.20 0.30 2.30 0.50 3.90 1.00 3.10 0.60 3.70 0.70 0.50 1.22 0.03 24.75 1.50 3.43 0.97 206.00 23.40 254.00

76.22 0.41 11.31 1.65 0.05 1.10 0.03 0.18 1.49 6.50 0.13 0.071 1.41 98.90 15.41 10.34 0.84 1.04 223 172 5.68 0.60 5.50 18.80 41.80 2.47 3.70 206 3.70 10.20 26.90 30.60 40.50 10.40 9.06 0.05 0.01 0.88 0.52 33.00 51.10 92.80 12.00 49.10 9.20 1.10 7.90 1.20 6.90 1.40 4.20 0.80 5.00 0.90 0.70 0.71 0.04 1.73 0.70 6.01 1.33 290.00 8.30 433.70

66.42 0.56 13.10 2.94 0.42 1.64 0.19 0.16 0.60 6.30 0.28 0.084 1.19 90.94 16.41 27.35 1.11 1.23 243 101 2.83 0.92 14.60 24.90 15.60 1.44 1.54 65,394 12.60 < 2.0 26.90 50.30 37.40 9.70 27.50 0.13 0.07 0.57 0.25 185.00 13.60 28.20 4.20 18.40 4.70 0.60 4.60 1.00 7.00 1.50 4.80 0.90 5.70 1.00 0.80 0.94 0.07 26.30 0.87 5.67 2.27 266.00 24.50 341.30

61.39 0.52 11.44 5.54 0.47 3.40 0.57 0.22 0.78 2.65 4.37 0.075 1.97 87.86 17.41 22.32 1.09 1.26 301 110 9.13 0.66 12.60 23.30 15.00 3.40 1.90 78,611 44.10 < 2.0 123.00 45.90 26.50 9.90 20.30 0.16 0.06 0.49 1.25 1017.00 9.10 22.50 3.40 15.70 4.10 0.40 3.90 0.80 5.10 1.10 3.40 0.60 3.90 0.70 0.70 1.00 0.31 33.50 2.00 11.80 4.29 253.00 27.90 311.90

70.88 0.45 10.59 2.42 0.23 1.46 0.03 0.12 0.31 6.30 0.07 0.056 1.16 91.66 18.41 59.39 0.96 1.01 204 138 5.29 0.36 10.40 17.60 30.20 1.01 1.63 44,697 6.30 2.10 26.90 33.00 39.90 7.60 7.19 0.00 0.02 0.43 0.11 150.00 9.40 19.80 2.70 12.00 3.10 0.40 3.20 0.70 4.80 1.10 3.50 0.70 4.30 0.80 0.60 0.68 0.02 18.40 1.49 4.77 0.92 282.00 18.60 349.30

Note: A/CNK = Al2O3/(CaO + Na2O + K2O); A/NK = Al2O3/(Na2O + K2O).

albite porphyry were undertaken. All analyses yielded concordant Pb/238U ages ranging from 285 to 310 Ma (Table 3) and a weighted mean 206Pb/238U age of 300 ± 4 Ma (2σ; n = 11) with a MSWD value of 1.5 (Fig. 10).

5.3. Zircon U-Pb ages

206

Zircon grains from the 109 albite porphyry are generally transparent, euhedral or subhedral with a range in length to width ratios of 1.2–1.5, and they contain oscillatory magmatic zoning indicative of a magmatic genesis. A total of 11 analyses of zircon grains in the 109 6

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Fig. 7. Major element diagrams of the 109 albite porphyry. (a) Total alkalis vs. silica diagram; (b) A/NK vs. A/CNK diagram.

5.4. Zircon trace elements The zircon grains from the 109 albite porphyry have enriched HREEs relative to LREEs, with positive Ce anomalies and negative Eu anomalies (Fig. 11), having patterns similar to that of magmatic zircon grains in igneous rocks (Hoskin and Schaltegger, 2003). The zircon grains from the 109 albite porphyry have Ce4+/Ce3+ ratios ranging from 10.8 to 50.5 with an average of 27.2 (n = 11) (Table 4). The Ti-inzircon temperature varies from 772 to 838 °C (average 794, n = 11) (Table 4). 5.5. Sulfur isotopic composition of sulfides in the ores Sulfides from all of the samples have δ34S values ranging from 1.4‰ to 4.5‰, with an average of 2.4‰ (Table 5). Chalcopyrite, bornite and chalcocite have δ34S ranging from 2.2‰ to 3.0‰, 1.4‰ to 2.7‰ and 2.9‰ to 4.5‰, respectively (Table 5). The chalcopyrite and bornite grains have δ34S increasing from core to rim (Fig. 12).

Fig. 9. Geochemical discrimination diagram for plutons in the western Awulale metallogenic belt (modified after Whalen et al., 1987).

magmatic origin. In addition, no (F, Li, Cl)-bearing minerals, such as topaz or lepidolite are found within this porphyry, which are common in metasomatic processes (e.g., Beauvoir albite granite, Cuney et al., 1992; Eurjako granite, Haapala, 1997). Zircons are sensitive to the circulation of Na-rich fluids, and preserved oscillatory zoning (Fig. 6). However, zircon grains were dissolved in the contact with Na-rich fluids, forming spongy textures with mosaic zoning and pervasive recrystallization (Rubatto et al., 2008). The the chemical index of alteration (CIA = molecular [A12O3/ (Al2O3 + CaO + Na2O + K2O)] × 100) of the 109 albite porphyry vary from 45.5 to 54.0, indicating the rocks are quite fresh (Nesbitt and Young, 1982). Weak alteration occurr in the magmatic-hydrothermal stage or hydrothermal stage (Fig. 5b), which is related to the major oreforming stage, nothing to do with rock-forming. In addition, the albite porphyry is enriched in LREEs, different from the depletion of LREE for

6. Discussion 6.1. Magmatic origin of the 109 albite porphyry The Na enrichment of granitic porphyry could be attributed to reworked A-type granite by post-magmatic metasomatic processes (e.g., Kaur et al., 2006), either by pervasive infiltration of high Na/(Na + K) fluid (Cerny, 1991) or by late-stage magmatic fluid exsolution (e.g., Chaudhri et al., 2003; Haapala, 1997). The magmatic albite porphyry is different from the metasomatized one in terms of texture and chemical composition. The 109 albite porphyry displays a porphyritic texture (Fig. 3), which is usually formed by rapid magmatic upwelling. The albite crystals also show corrosion texture along the contact with latestage minerals or the matrix (Fig. 3), indicating that the albite has a

Fig. 8. Chondrite-normalized REE pattern (a) and primitive mantle-normalized trace element spider diagram (b) of the 109 albite porphyry. Average chondrite and primitive mantle normalizing values are from Sun and McDonough (1989). 7

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Table 3 Zircon U-Pb dating results of the 109 albite porphyry. Samples

Th(ppm)

U(ppm)

Th/U

Isotopic ratios 207

10903-01 10903-02 10903-03 10903-04 10903-05 10903-06 10903-07 10903-08 10903-09 10903-10 10903-11

81.92 111.78 62.48 226.14 71.59 61.24 243.98 361.18 145.60 56.74 64.18

85.91 107.75 75.27 189.65 92.66 64.46 204.73 284.11 131.29 74.15 81.17

0.95 1.04 0.83 1.19 0.77 0.95 1.19 1.27 1.11 0.77 0.79

206

Pb/

0.0543 0.0525 0.0516 0.0629 0.0570 0.0564 0.0568 0.0566 0.0522 0.0651 0.0581

Pb

Apparent ages (Ma) 1σ

207

235

0.0026 0.0019 0.0025 0.0019 0.0021 0.0023 0.0015 0.0025 0.0018 0.0026 0.0025

0.3477 0.3491 0.3268 0.4073 0.3775 0.3732 0.3805 0.3447 0.3204 0.4329 0.3761

Pb/

U

1σ

206

0.0157 0.0124 0.0146 0.0114 0.0141 0.0151 0.0102 0.0178 0.0102 0.0178 0.0167

0.0473 0.0484 0.0464 0.0472 0.0484 0.0483 0.0485 0.0449 0.0449 0.0485 0.0472

Pb/

238

U

1σ

207

Pb/206Pb

1σ

207

Pb/235U

0.0008 0.0008 0.0008 0.0006 0.0008 0.0008 0.0006 0.0013 0.0005 0.0007 0.0007

383 306 333 706 500 478 483 476 300 777 600

107 77 111 63 81 95 53 98 81 81 94

303 304 287 347 325 322 327 301 282 365 324

1σ

206

Pb/238U

12 9 11 8 10 11 8 13 8 13 12

298 305 293 297 305 304 305 283 283 305 298

1σ 5 5 5 3 5 5 4 8 3 4 4

Fig. 10. Concordia diagrams of LA-ICP-MS zircon U–Pb analyses for the 109 albite porphyry.

than those from the ore-bearing porphyry in Chile porphyry Cu deposit, but are consistent with those in ore-barren porphyries (Fig. 13a). In addition, the logƒO2 can be calculated through the Ti-in-zircon thermometer, and the Ti-in-zircon thermometer of this porphyry range from 743 to 828 °C, being calculated by the trace elements in zircon range from −25.68 to −9.24 (Table 4). In the plot of T versus logƒO2 chart, most samples plot below the fayalite-magnetite-quartz (FMQ) buffer curve (Fig. 13b), which is the oxygen buffer of oxidized porphyry at the temperatures associated with mineralization (Sun et al., 2015). These features indicate that the 109 albite porphyry and ore-forming hydrothermal alteration are formed from reduced magma system. 6.2. Tectonic setting of the western Awulale metallogenic belt in late Carboniferous Fig. 11. Chondrite-normalized REE pattern of zicorns in the 109 albite porphyry. Average chondrite normalizing values are from Sun and McDonough (1989).

The 109 albite porphyry has an affinity of A-type granite (Fig. 9) and was dated to be 300 ± 4 Ma. Other porphyries in this area, such as the Qunji Pluton and the Qunjisayi Pluton, have similar geochemical compositions and ages (Fig. 9), indiating that they may have formed in similar tectonic setting during the late Carboniferous. Typical A-type magmatism is commonly related to extensional settings (Dall’Agnol et al., 2012 and references therein). The Mosizaote Pluton has a typical adakitic geochemical affinity and the age of this pluton is 296 Ma (our unpublished data). It is considered to have formed in an extensional setting (Zhao et al., 2004, 2006). Xia et al. (2004) proposed that the Paleozoic ocean basin, which is now the Tianshan area, had already closed in the Carboniferous (316 ± 3 Ma), and the Tianshan orogenic belt entered a post-collision (extensional) stage. The Wulang Formations encroached by the 109 albite porphyry are bimodal volcanic rocks, indicating that the western Tianshan was in an extensional environment in the late Paleozoic (Chen et al., 2015). The red continental molasse formation widely occurred in the Yili Basin during the early Permian, also indicating that the Yili Basin entered an extensional stage before the early Permian (Chen

the porphyry formed by post-magmatic metasomatism (Higgins et al., 1986; Mackenzie et al., 1988). 6.2 Reduced magmas and hydrothermal alteration forming the 109 porphyry Cu deposit Oxidized minerals (magnetite and hematite) are absent in the 109 porphyry Cu deposit and the ore system shows reduced mineral paragenesis. Typical oxidized porphyries contain chalcopyrite, pyrite and bornite in equilibrium with primary hematite and anhydrite (Richards, 1990; Rowins, 2000; Seedorff et al., 2005; Streck and Dilles, 1998). Neither anhydrite nor hematite is present at the 109 albite porphyry, and the low contents of sulfides is indicative of a relatively reducing ore-forming fluid. Ce4+ has higher partition coefficient in zircon than Ce3+, so that Ce4+/Ce3+ is thus a sensitive and robust indicator of magmatic oxidation state (Ballard et al., 2002; Liang et al., 2006; Trail et al., 2011, 2012; Sun et al., 2015). Ce4+/Ce3+ of zircon grains from the 109 albite porphyry range from 16.2 to 55.0, which are much lower 8

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Table 4 Major (wt. %) and trace elements (ppm) of zircons in the 109 albite porphyry. Samples

10903-1

10903-2

10903-3

10903-4

10903-5

10903-6

10903-7

10903-8

10903-9

10903-10

10903-11

ZrO2 Ti Y Nb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Th Eu/Eu* Ce4+/Ce3+ log(ƒO2) (zircon) TTi

52.68 27.42 1141.90 0.98 0.33 11.64 0.29 3.55 5.21 1.25 26.19 8.69 102.80 39.39 176.70 37.10 338.50 71.74 6902.91 0.38 81.92 0.27 21.98 −15.45 838.21

54.74 17.61 1072.06 1.16 0.09 12.92 0.13 2.68 4.86 1.06 24.12 8.12 95.45 36.86 166.79 35.22 321.85 68.90 7253.29 0.49 111.78 0.25 27.24 −13.10 793.37

53.16 15.22 1071.24 0.80 0.04 9.98 0.21 3.05 5.03 1.25 24.39 8.15 96.21 36.77 166.14 34.59 317.74 67.59 7105.70 0.37 62.48 0.31 16.00 −14.04 779.38

53.01 14.60 1439.07 2.57 40.36 123.48 13.51 67.23 22.22 3.43 48.51 13.36 139.54 50.39 218.58 45.05 405.84 82.48 7541.66 0.78 226.14 0.27 50.49 −25.68 775.44

53.26 17.85 967.47 1.30 9.10 30.30 2.57 12.12 5.61 1.09 21.07 6.78 82.17 32.33 152.22 32.90 310.59 68.75 6696.10 0.53 71.59 0.28 19.03 −24.14 794.69

56.01 25.56 982.96 1.06 0.02 10.96 0.13 2.04 3.93 1.66 21.01 7.11 84.50 33.71 156.52 33.17 306.57 66.72 6607.17 0.39 61.24 0.45 34.42 −9.24 830.84

53.24 17.19 1892.44 2.55 70.32 182.84 19.73 85.61 23.82 2.38 53.81 15.64 172.98 64.93 293.32 60.58 550.56 115.45 6846.11 0.76 243.98 0.20 29.62 −25.23 790.99

53.47 14.05 2761.51 3.62 0.89 45.52 1.95 21.04 20.28 3.14 82.34 25.43 279.02 99.52 416.25 83.12 717.89 141.01 6892.74 0.75 361.18 0.20 10.81 −18.80 771.86

53.39 17.89 1282.42 1.72 0.46 17.79 0.53 4.87 5.48 1.32 27.29 9.21 111.72 43.45 201.41 43.25 397.59 85.13 6881.66 0.62 145.60 0.27 36.77 −17.54 794.90

54.44 16.36 943.87 1.05 0.10 10.21 0.28 3.09 4.28 1.14 20.51 6.90 81.71 32.43 148.66 32.06 299.36 65.56 6867.45 0.46 56.74 0.31 26.60 −16.00 786.25

53.28 14.96 975.73 1.08 0.12 10.72 0.25 3.13 4.41 1.16 21.90 7.26 85.16 33.19 151.97 32.75 308.43 66.47 6736.22 0.44 64.18 0.29 26.60 −16.30 777.71

Note: (Ce4+/Ce3+)Zircon = (Cemelt − CeZircon/Dce(III))/(CeZircon/Dce(IV) − Cemelt), where, Cemelt and CeZircon represent the concentrations of Ce in whole rock and zircon, respectively, and Dce(III) and Dce(IV) are the zircon-melt distribution coefficients for Ce(IV), respectively. The Dce(III) and Dce(IV) values can be estimated on the basis of crystal chemical constraints on trace-element partitioning (Ballard et al., 2002). ln(Ce/Ce*)D = (0.1156 ± 0.0050) × ln(ƒO2) + (13860 ± 708)/T − 6.125 ± 0.484. Eu anomalies are calculated by EuN/(SmN × GdN)1/2, where element abundances are normalized (N) to chondrite values from McDonough and Sun (1995). Table 5 Sulfur isotope compositions of sulfides in the 109 albite porphyry. Samples

Sulfide

Location

δ34S‰

1510905-CPY1 1510905-CPY2 1510905-CPY3 1510905-CPY4 1510905-CPY5 1510905-CPY6 10906-Bo1 10906-Bo2 10906-Bo3 10906-Bo4 10906-Bo5 10906-Bo6 10906-Bo7 10906-Bo8 10906-Bo9 10906-Bo10 10906-Bo11 10906-Bo12 10906-Bo13 10906-Bo14 10906-Bo15 10906-Bo16 10906-Bo17 10,913 10,914 10,915

chalcopyrite chalcopyrite chalcopyrite chalcopyrite chalcopyrite chalcopyrite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite bornite chalcocite chalcocite chalcocite

– rim rim core rim rim core rim – – – core rim core rim – rim core core rim – core rim

2.5 3.0 2.6 2.2 2.4 2.4 2.3 2.5 2.4 2.4 2.9 1.7 2.1 2.2 2.7 2.1 2.1 2.0 1.9 2.5 2.0 1.4 1.7 4.5 2.9 2.9

CDT

2σ 0.19 0.22 0.20 0.18 0.20 0.19 0.24 0.22 0.22 0.22 0.18 0.21 0.25 0.22 0.24 0.22 0.24 0.23 0.24 0.25 0.22 0.22 0.23

Fig. 12. Within-grain sulfur isotopic variations of sulfide in the 109 porphyry Cu deposit, showing the rims of sulfide having higher δ34S values than the respective cores.

mineralization occur in the western Awulale metallogenic belt, such as the Qunji, the Qunjisayi, the Yuntoushan, and the Mosizote plutons. These plutons have identical alteration and ore assemblages (chalcopyrite-bornite-chalcocite) and lack primary hematite and sulfate minerals. Most of the Ce4+/Ce3+ ratios of zircons from these plutons are < 200 (7.75–218) and most of their ƒO2 values are lower than ΔFMQ + 2 (Fig. 13). These characteristics indicate that reduced ore systems widely occurred in the western Awulale metallogenic belt. The oxidation state of magma is related to its tectonic setting (Wood et al., 1990); such as MORB has an average logƒO2 of about −0.9 relative to the FMQ buffer, the peridotite xenoliths from zones of continental extension exhibiting a logƒO2 of approximately −2.5 relative to FMQ. Magmas from regions of recent or active subduction have a high ƒO2 (logƒO2 greater than FMQ), and the redox state of magmas is related to the origin of the magmas (Carmichael, 1990). In summary, the

Note: – Represents that the data is from a small single grain (< 50 μm) that can only ablate one spot.

et al., 2015). These porphyries in this region are therefore considered to have formed in an extensional setting. 6.3. Genesis of reduced ore system in the western Tianshan orogenic belt Several

late

Paleozoic

porphyritic

plutons

associated

with 9

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Fig. 13. Diagram of Eu/Eu* vs. Ce4+/Ce3+ in zircons (a) and Ti-in-zircon thermometer (T) vs logƒO2 for the 109 albite porphyry. Note: the data in Fig. 9a are from: Ballard et al., 2002, Li et al. (2015) and Author’s unpublished data. The data in Fig. 9b are from: Li et al. (2015) and Author’s unpublished data.

porphyry was formed in 310 Ma (Li et al., 2014), which is the time of the transition from subduction-related orogeny to collision orogeny (Wu et al., 2016). Therefore, the ore-bearing porphyry in the Baogutu porphyry Cu deposit can have higher water content than porphyries formed in extensional settings do, but have lower zircon Ce4+/Ce3+ ratios than porphyries formed by deep subduction in the eastern Pacific do. Furthermore, Wu et al. (2016) found that in the western Tianshan orogenic belt, mineralization mainly occurs as porphyry Cu deposits associated with oxidized porphyries in the period from the Devonian to middle Carboniferous (320–440 Ma) under subduction conditions. After the middle Carboniferous, the Paleozoic oceanic subduction was in closure and mineralization mainly occurred as porphyry W, Mo and Sn deposits, which are associated with reduced porphyries. These findings also demonstrate that magmas formed under post-collision (extensional setting) conditions may have the lower ƒO2 than those formed in subduction zones do. Overall, the transformation of the tectonic setting from subduction to post-collision (extensional setting) in the western Tianshan orogenic belt may be the main reason why many reduced porphyry Cu deposits occur in this area.

reduced ore systems in the western Awulale metallogenic belt formed in an extensional setting. In regions of extension, H2O in magma is less than that in a subduction zone because subduction can generate much more H2O from hydrous minerals (Grove et al., 2015). Liu et al. (2017) have proposed that the parental magma of the Qunji albite porphyry is “dry”. As H2O acts as an efficient oxidizing agent in magmas and the mantle (Wood et al., 1990; Brandon and Draper, 1996; Parkinson and Arculus, 1999), the magma that is lack of H2O may have lower ƒO2 in an extensional setting than that enriched H2O does in a subduction zone (Chen et al., 2019). In addition, both S and Fe, important oxidizing agents in the formation of ore-forming porphyry Cu deposits, are low in content (Ague and Brimhall). Therefore, fewer oxidizing agent in the magma can induce the ƒO2 to increase. In general, there are many sedimentary strata with organic substances occurring in the extensional setting. These strata contain highly reduced sediments or metasediments. The local-scale formation of granite may be contaminated with graphitic pelite or, in some case, granite may directly be fused with this reducing politic wall rock (Ague and Brimhall, 1988). Therefore, granite formed in extensional setting may have low ƒO2. Therefore, the western Awulale metallogenic belt can widely occur in reduced ore systems in the late Paleozoic. Besides, this finding could also explain why large scale porphyry-skarn Cu deposit occurs in the westernmost of the Awulale metallogenic belt, such as the Lamasu porphyry-skarn Cu deposit. These deposits are usually formed at 390 Ma (Zhang et al., 2008). In this stage, the paleo-Asian Ocean Plate entered into the early collision orogenic phase. Therefore, the ore-forming porphyries in the Lamasu Cu deposit may contain more H2O than these formed at the late Paleozoic do. In addition, there is another example of a reduced porphyry Cu deposit in the western Tianshan orogenic belt: the Baogutu porphyry Cu deposit (Cao et al., 2014). Oxidized minerals (magnetite, hematite and anhydrite) are also absent in this porphyry Cu deposit (Shen et al., 2010a,b; Cao et al., 2014). The zircon Ce4+/Ce3+ ratios in the Baogutu ore-bearing porphyries range from 28 to 110 (Shen et al., 2015), which are similar to that of the porphyry Cu deposit in our study and lower than that of the porphyry Cu deposit in Chile. However, the mineral assemblages and hydrothermal alteration of the Baogutu porphyry Cu deposit are different from those of the porphyry Cu porphyry in our study. In the Baogutu porphyry Cu porphyry, hydrous minerals, such as amphibole and biotite, are very common. Hydrothermal alterations in the Baogutu Cu porphyry are also very common, including silicate alteration, potassic alteration and propylitic alteration. The characteristics of mineral assemblages and hydrothermal alteration in the Baogutu Cu porphyry indicate that the water content in the ore-bearing porphyry is higher than that in the 109 porphyry Cu deposit. We think that these differences can be attributed to the different geologic settings where the ore-bearing porphyries formed. The Baogutu ore-bearing

6.4. Cu mineralization in a reduced ore system Copper is a chalcophilic element that is strongly controlled by the behaviour and speciation of sulfur (Sun et al., 2015). Therefore, sulfur is of important in forming porphyry Cu deposits. In addition, the speciation of sulfur is different with different magmas and fluid oxygen fugacities, e.g., sulfur occurs as SO42− at ΔFMQ + 2 (Jugo, 2009; Jugo et al., 2005, 2010) and occurs as S2− at the ƒO2 lower than the FMQ buffer. Different speciation of sulfur have different solubility in magmas and fluids, e.g., the estimated S content at sulfide saturation ranges from 1500 ppm (S predominantly occurring as S2− at ΔFMQ + 0.4) to 4500 ppm (S predominant occurring as SO42− at ΔFMQ + 1.7) (Jugo, 2009). Therefore, the ore-forming fluid may have higher ƒO2 to form an economic Cu deposit. In an oxidized ore system, the ƒO2 of an oreforming fluid is mainly elevated by the oxidation of ferrous Fe and reduction of sulfate, which lowers the pH (Sun et al., 2014). However, the number of reduced ore systems is so small that the mechanism of ƒO2 elevation of ore-forming fluid in this system is still unknown. Previous studies have reported that degassing of reduced volatile species (e.g., H2, H2S and CH4) can elevate the ƒO2 of system (Ballhaus, 1993; Lee et al., 2005). In addition, Smith et al. (2012) have proposed that sulfur degassing occurred in reduced ore system form the Catface porphyry Cu (Mo-Au) deposit. Therefore, sulfur degassing may be the main factor that increases the ƒO2 of ore-forming fluids in reduced ore systems. When an ore system undergoes degassing, crystallization conditions abruptly change to generate a quench texture of sulfide (Gomide et al., 10

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2013). Exsolution is a common quench texture (Fig. 5c) in the 109 porphyry Cu deposit and are interpreted as the result of rapid temperature decrease in the ore-forming fluid related to sulfur degassing. In addition, the cores and rims of single sulfide grains could not achieve isotopic equilibrium, also indicating that sulfur degassing occurred in the ore-forming fluid. Zheng (1990) has shown that under oxidizing conditions (ƒO2 > ΔFMQ), sulfur degassing drives the residual system towards higher δ34S, whereas sulfur degassing under reducing conditions (ƒO2 < ΔFMQ) drives the residual system towards lower δ34S values. In this study, the within-grain δ34S variation show that the rims of sulfides always have higher δ34S than the cores (Fig. 12), consistent with the degassing under oxidized condition (ΔFMQ + 2 > ƒO2 > ΔFMQ), indicating that the ƒO2 of ore-forming fluids increased during sulfide deposition. As the ƒO2 increases, the content of sulfur and metals (Cu, Fe) in ore-forming fluids is increased to form an economic Cu deposit. Thus, sulfur degassing resulted by the rapid temperature decrease may have an important role in Cu mineralization in reduced ore systems.

Cao, M.J., Qin, K.Z., Li, G.M., Jin, L.Y., Evans, N.J., Yang, X.R., 2014. Baogutu: an example of reduced porphyry Cu deposit in western Junggar. Ore. Geol. Rev. 56, 159–180. Carmichael, I.S.E., 1990. The redox states of basic and silicic magmas: a reflexion of their source regions. Contrib. Mineral. Petr. 106 (2), 129–141. Cerny, P., 1991. Rare-element granitic pegmatites. Part I: anatomy and internal evolution of pegmatite deposits. Geosci. Can. 18 (2), 49–67. Chaudhri, N., Kaur, P., Okrusch, M., Schimrosczyk, A., 2003. Characterisation of the dabla granitoids, north khetri copper belt, Rajasthan, India: evidence of bimodal anorogenic felsic magmatism. Gondwana. Res. 6 (4), 879–895. Chen, G.W., Deng, T., Liu, R., Xia, H., Liu, Q., 2015. Geochemistry of bimodal volcanic rocks in Permian Taerdetao Formation in Awulale area of western Tianshan, Xinjiang. Acta Petrol. Sin. 31 (1), 105–118 (in Chinese with English abstract). Chen, G.W., Yang, J.X., Liu, R., 2019. Potassic alkaline granitoid magmatism in the northern margin of the Tarim Craton: first evidence of a back-arc extensional environment. Geol. J. 1–15. Cuney, M., Marignac, C., Weisbrod, A., 1992. The Beauvoir topaz-lepidolite albite granite (Massif Central, France); the disseminated magmatic Sn-Li-Ta-Nb-Be mineralization. Econ. Geol. 87 (7), 1766–1794. Dall'Agnol, R., Frost, C.D., Rämö, O.T., 2012. IGCP Project 510 “A-type granites and related rocks through Time”: project vita, results, and contribution to granite research. Lithos 151 (1–2), 1–16. Gao, J., Long, L., Klemd, R., Qian, Q., Liu, D., Xiong, X., Su, W., Liu, W., Wang, Y., Yang, F., 2009. Tectonic evolution of the South Tianshan orogen and adjacent regions, NW China: geochemical and age constraints of granitoid rocks. Int. J. Earth. Sci. 98 (6), 1221–1238. Gomide, C.S., Brod, J.A., Junqueira-Brod, T.C., Buhn, B.M., Santos, R.V., Barbosa, E.S.R., Cordeiro, P.F.O., Palmieri, M., Grasso, C.B., Torres, M.G., 2013. Sulfur isotopes from Brazilian alkaline carbonatite complexes. Chem. Geol. 341 (11), 38–49. Grove, T.L., Till, C.B., Krawczynski, M.J., 2015. The role of H2O in subduction zone magmatism. Annu. Rev. Earth Plant. Sci. 40 (1), 413–439. Haapala, I., 1997. Magmatic and postmagmatic processes in tin-mineralized granites: topaz-bearing leucogranite in the Eurajoki Rapakivi granite stock, Finland. J. Petrol. 38 (12), 1645–1659. Higgins, N.C., Turner, N.J., Black, L.P., 1986. The petrogenesis of an I-type volcanicplutonic suite: the St. Marys Porphyrite, Tasmania. Contrib. Mineral. Petr. 92 (2), 248–259. Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and igneous and metamorphic petrogenesis. Rev. Mineral. Geochem. 53 (1), 27–62. Ishihara, S., 1977. The Magnetite-series and Ilmenite-series granitic rocks. Min. Geol. 27, 293–305. Jugo, P.J., 2009. Sulfur content at sulfide saturation in oxidized magmas. Geology 37 (5), 415–418. Jugo, P.J., Luth, R.W., Richards, J.P., 2005. Experimental data on the speciation of sulfur as a function of oxygen fugacity in basaltic melts. Geochim. Cosmochim. Acta 69 (2), 497–503. Jugo, P.J., Wilke, M., Botcharnikov, R.E., 2010. Sulfur K-edge XANES analysis of natural and synthetic basaltic glasses: implications for S speciation and S content as function of oxygen fugacity. Geochim. Cosmochim. Acta 74 (20), 5926–5938. Kaur, P., Chaudhri, N., Okrusch, M., Koepke, J., 2006. Palaeoproterozoic A-type felsic magmatism in the Khetri Copper Belt, Rajasthan, northwestern India: petrologic and tectonic implications. Mineral. Petr. 87 (1), 81–122. Lee, C.A., Leeman, W.P., Canil, D., Zhengxue, A.L.I., 2005. Similar V/Sc systematics in MORB and Arc basalts: implications for the oxygen fugacities of their mantle source regions. J. Petrol. 46 (11), 2313–2336. Li, G.M., Cao, M.J., Qin, K.Z., Evans, N.J., Mcinnes, B.I.A., Liu, Y.S., 2014. Thermaltectonic history of the baogutu porphyry Cu deposit, West Junggar as constrained from zircon U-Pb, biotite Ar/Ar and zircon/apatite (U–Th)/He dating. J. Asian Earth. Sci. 79 (5), 741–758. Li, H., Ling, M.X., Li, C.Y., Zhang, H., Ding, X., Yang, X.Y., Fan, W.M., Li, Y.L., Sun, W.D., 2012. A-type granite belts of two chemical subgroups in central eastern China: indication of ridge subduction. Lithos 150 (1), 26–36. Li, N.B., Niu, H.C., Qiang, S., Jiang, Y.H., Zeng, L.J., Yang, W.B., Pei, Z.J., 2013. Zircon UPb geochronology and geochemistry of post-collisional granitic porphyry from Yuantoushan, Nileke, Xinjiang. Acta Petrol. Sin. 29 (10), 3402–3412 (in Chinese with English abstract). Li, N.B., Niu, H.C., Shan, Q., Yang, W.B., 2015. Two episodes of late paleozoic A-type magmatism in the Qunjisayi area, western Tianshan: petrogenesis and tectonic implications. J. Asian Earth Sci. 113 (1), 238–253. Liang, H.Y., Campbell, I.H., Allen, C., Sun, W.D., Liu, C.Q., Yu, H.X., Xie, Y.W., Zhang, Y.Q., 2006. Zircon Ce4+/Ce3+ ratios and ages for Yulong ore-bearing porphyries in eastern Tibet. Miner. Depos. 41 (2), 152–159. Liu, R., Wang, L.X., Chen, G.W., 2017. Genesis, geological significance and metallogentic potentiality of A-type granites in the Awulale area of the western Tianshan, Xinjiang. Acta Petrol. Sin. 33 (6), 1741–1754 (in Chinese with English abstract). Liu, R., Chen, G.W., 2018. Characteristics of rare earth elements, Zr, and Hf in Orebearing porphyries from the Western Awulale Metallogenic Belt, Northwestern China and their application in determining metal fertility of granitic magma. Resour. Geol. 69 (2), 1–18. Liu, Y.S., Gao, S., Hu, Z., Gao, C., Zong, K., Wang, D., 2010. Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China orogen: U-Pb Dating, Hf Isotopes and trace elements in zircons from Mantle Xenoliths. J. Petrol. 51 (1–2), 392–399. Ludwig, K.R., 2000. Users Manual for ISOPLOT/EX, version 2. A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication, Berkeley. Mackenzie, D.E., Black, L.P., Sun, S.S., 1988. Origin of alkali-feldspar granites: an

7. Conclusions The 300 ± 4 Ma 109 albite porphyry is metaluminous to peraluminous and alkaline in composition, and has an affinity of A-type granite, forming in an extensional setting. The rocks contain reduced sulfides and lack oxidized minerals are absent. The Ce4+/Ce3+ of zircon is < 200. The ƒO2 of the porphyry is lower than the FMQ buffer. Reduced ore systems in the western Awulale metallogenic belt formed in extensional settings. The magmas from these systems have H2O, S and Fe lower than those in subduction zones, and therefore have lower magmatic ƒO2. Rapid decrease of temperature could be responsible for sulfur degassing, which resulted in the increase of ƒO2 of the ore-forming fluid, recorded by the quench texture and within-grain sulfur isotopic variation in sulfide. Sulfur degassing may be an important factor for Cu mineralization in reduced ore systems. Acknowledgements This study was financially support by the National 305 Project (2011BAB06B02-03) the Deep Resources Exploration and Mining, a Special Project in the Framework of National Key R & D Program of China (2017YFC0602302). We thank a number of technical staff for assistance during this study. We are also grateful to Drs. Changming Xing and Bo Wei for their help. Comments and suggestions from the journal’s anonymous reviewers and associate editor Jingwen Mao greatly improved the quality of the manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.oregeorev.2019.102989. References Ague, J.J., Brimhall, G.H., 1988. Regional variations in bulk chemistry, mineralogy, and the compositions of mafic and accessory minerals in the batholiths of California. Geol. Soc. Am. Bull. 100 (6), 891–911. Ballard, J.R., Palin, M.J., Campbell, I.H., 2002. Relative oxidation states of magmas inferred from Ce(IV)/Ce(III) in zircon: application to porphyry copper deposits of northern Chile. Contrib. Mineral. Petr. 144 (3), 347–364. Ballhaus, C., 1993. Redox states of lithospheric and asthenospheric upper mantle. Contrib. Mineral. Petr. 114 (3), 331–348. Blevin, P.L., Chappell, B.W., 1992. The role of magma sources, oxidation states and fractionation in determining the granite metallogeny of eastern Australia. Earth. Env. Sci. Trans. R. Soc. 83 (1–2), 305–316. Brandon, A.D., Draper, D.S., 1996. Constraints on the origin of the oxidation state of mantle overlying subduction zones: an example from Simcoe, Washington, USA. Geochim. Cosmochim. Acta 60 (10), 1739–1749. Burnham, C.W., Ohmoto, H., 1980. Late-stage processes of felsic magmatism. Min. Geol. 8, 1–11.

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the oxidation state of magmas. Geochim. Cosmochim. Acta 97 (15), 70–87. Wang, Z.L., Mao, J.W., Zhang, Z.H., Zuo, G.C., Wang, L.S., 2006. Geology, time-space distribution and metallogenic geodynamic evolution of porphyry copper (molybdenum) deposits in the Tianshan Mountains. Acta Geol. Sin. 7, 942–955 (in Chinese with English abstract). Whalen, J.B., Currie, K.L., Chappell, B.W., 1987. A-type granites: geochemical characteristics, discrimination and petrogenesis. Contrib. Mineral. Petr. 95 (4), 407–419. Wood, B.J., Bryndzia, L.T., Johnson, K.E., 1990. Mantle oxidation state and its relationship to tectonic environment and fluid speciation. Science 248 (4953), 337–345. Wu, C., Liu, Y., Cao, M.J., Hong, T., Xu, X.W., Dong, L.H., 2015. Characteristics and formation mechanism of reduced porphyry Cu and Mo-Cu deposits. Acta Petrol. Sin. 31 (2), 617–638 (in Chinese with English abstract). Wu, Y.S., Chen, Y.J., Zhou, K.F., 2016. Mo deposits in Northwest China: geology, geochemistry, geochronology and tectonic setting. Ore. Geol. Rev. 81, 641–671. Xia, L.Q., Xu, X.Y., Xia, Z.C., Li, X.M., Ma, Z.P., Wang, L.S., 2004. Petrogenesis of Carboniferous rift-related volcanic rocks in the Tianshan, northwestern China. Geol. Soc. Am. Bull. 116 (3), 419–433. Zhang, Z.C., Hou, T., Santosh, M., Li, H.M., Zhang, Z.H., Song, X.Y., Wang, M., 2014a. Spatio-temporal distribution and tectonic settings of the major iron deposits in China: an overview. Ore. Geol. Rev. 57, 247–263. Zhang, Z.H., Hong, W., Jiang, Z.S., Duan, S.G., Li, F.M., Shi, F.P., 2014b. Geological characteristics and metallogenesis of iron deposits in western Tianshan, China. Ore. Geol. Rev. 57, 425–440. Zhang, Z.H., Hong, W., Jiang, Z.S., Duan, S.G., Xu, L.G., Li, F.M., Guo, X.C., Zhao, Z.G., 2012. Geological characteristics and zircon U-Pb dating of volcanic rocks from the Beizhan iron deposit in western Tianshan Mountains, Xinjiang, NW China. Acta Petrol. Sin. 86 (3), 737–747. Zhang, Z.H., Wang, Z.L., Wang, L.S., Zuo, G.C., 2008. Metallogenic epoch and ore-forming environment of the Lamasu skarn-porphyritic Cu-Zn deposit, western Tianshan, Xinjiang, NW China. Acta Petrol. Sin. 82 (4), 731–740 (in Chinese with English abstract). Zhao, J., Zhang, Z.H., Zhang, H., Liu, M., Zhu, W.N., 2012a. Fluid inclusion and stable isotope studies of the Qiongbulake copper deposit in western Awulale Mountain, Xinjiang. Geol. China 39 (5), 1345–1358 (in Chinese with English abstract). Zhao, J., Zhang, Z.H., Liu, M., Zhang, H., Zhu, W.N., 2012b. Carbon, oxygen, sulfur and lead isotope constraints on the ore source and metallogenesis of copper deposits in western Awulale Mountain metallogenic belt, Xinjiang. Mineral Depos. 31 (5), 999–1013 (in Chinese with English abstract). Zhao, Z.H., Wang, Q., Xiong, X., Zhang, H.X., Niu, H.C., Xu, J.F., Bai, Z.H., Qiao, Y.L., 2006. Two types of adakites in north Xinjiang, China. Acta Petrol. Sin. 22 (5), 1249–1265 (in Chinese with English abstract). Zhao, Z.H., Xiong, X.L., Wang, Q., Bai, Z.H., Mei, H.J., 2004. A case study on porphyry Cu deposit related with adakitic quartz albite porphyry in Mosizaote, Western Tianshan, Xinjiang, China. Acta Petrol. Sin. 20 (2), 249–258 (in Chinese with English abstract). Zheng, Y.F., 1990. Sulfur isotope fractionation in magmatic systems: models of Rayleigh distillation and selective flux. Acta Geochim. 9 (1), 27–45.

example from the Poimena Granite, northeastern Tasmania, Australia. Geochim. Cosmochim. Acta 52 (10), 2507–2524. Mcdonough, W.F., Sun, S.S., 1995. The composition of the earth. Chem. Geol. Chem. Geol. 120 (3–4), 223–253. Müller, W., Shelley, M., Miller, P., Broude, S., 2009. Initial performance metrics of a new custom-designed ArF excimer LA-ICPMS system coupled to a two-volume laser-ablation cell. J. Anal. Atom. Spectrom. 24 (2), 209–214. Nesbitt, H.W., Young, G.M., 1982. Early proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature 299 (5885), 715–717. Parkinson, I.J., Arculus, R.J., 1999. The redox state of subduction zones: insights from arc-peridotites. Chem. Geol. 160 (2), 409–423. Richards, J.P., 1990. Petrology and geochemistry of alkalic intrusives at the Porgera gold deposit, Papua New Guinea. J. Geochem. Explor. 35 (1–3), 141–199. Rowins, S.M., 2000. Reduced porphyry copper-gold deposits: a new variation on an old theme. Geology 28 (6), 491. Rubatto, D., Muntener, O., Barnhoorn, A., Gregory, C., 2008. Dissolution-reprecipitation of zircon at low-temperature, high-pressure conditions (Lanzo Massif, Italy). Am. Mineral. 93 (10), 1519–1529. Seedorff, E., Dilles, J.H., Proffett, J.M., Einaudi, M.T., Zurcher, L., Stavast, W.J.A., Johnson, D.A., Barton, M.D., 2005. Porphyry deposits: characteristics and origin of hypogene features. Econ. Geol. 251–298. Shen, P., Hattori, K., Pan, H., Jackson, S., Seitmuratova, E., 2015. Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry cu deposits in the central asian orogenic belt. Econ. Geol. 110 (7), 1861–1878. Shen, P., Shen, Y., Wang, J., Zhu, H., Wang, L., Meng, L., 2010a. Methane-rich fluid evolution of the Baogutu porphyry Cu–Mo–Au deposit, Xinjiang, NW China. Chem. Geol. 275 (1–2), 78–98. Shen, P., Shen, Y.C., Pan, H.D., Wang, J.B., Zhang, R., Zhang, Y.X., 2010b. Baogutu porphyry Cu-Mo-Au deposit, west junggar, Northwest China: petrology, alteration, and mineralization. Econ. Geol. 105 (5), 947–970. Smith, C.M., Canil, D., Rowins, S.M., Friedman, R., 2012. Reduced granitic magmas in an arc setting: the Catface porphyry Cu–Mo deposit of the Paleogene Cascade Arc. Lithos 154 (1), 361–373. Smithson, D.M., 2004. Late Eocene tectono-magmatic evolution and genesis of reduced porphyry copper-gold mineralization at the North Fork deposit, west central Cascade Range, Washington, U.S.A. Streck, M.J., Dilles, J.H., 1998. Sulfur evolution of oxidized arc magmas as recorded in apatite from a porphyry copper batholith. Geology 26 (6), 523–526. Sun, S., McDonough, W., 1989. Chemical and isotopic systematics of ocean basalts: implications for mantle composition and processes, in Magmatism in the Ocean Basins. Geol. Soc. Lon. Spec. Publ. 42 (1), 313–345. Sun, W.D., Huang, R.F., Li, H., Hu, Y.B., Zhang, C.C., Sun, S.J., Zhang, L., Ding, X., Li, C.Y., Zartman, R., Ling, M.X., 2015. Porphyry deposits and oxidized magmas. Ore. Geol. Rev. 65, 97–131. Sun, W.D., Huang, R.F., Liang, H.Y., Ling, M.X., Li, C.Y., Ding, X., Zhang, H., Yang, X.Y., Ireland, T., Fan, W.M., 2014. Magnetite-hematite, oxygen fugacity, adakite and porphyry copper deposits: reply to Richards. Geochim. Cosmochim. Acta 126 (1), 646–649. Trail, D., Watson, E.B., Tailby, N.D., 2011. The oxidation state of Hadean magmas and implications for early Earth's atmosphere. Nature 480 (7375), 79–82. Trail, D., Watson, E.B., Tailby, N.D., 2012. Ce and Eu anomalies in zircon as proxies for

Further reading Wedepohl, E.B.H., 1978. Handbook of geochemistry, vol 2/5B Springer.

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