# The Metallogeny of the Tieling Cu-Mo Porphyry Deposit in Eastern Tianshan, NW China: New Insights from Zircon U-Pb, Fluid Inclusion, and H-O-S Stable Isotope Analyses

Authors: Ping Li; Ting Liang; Fan Huang; Tongyang Zhao; Zhixin Zhu; Yong Li; Jing Feng; Lei He
Journal: Geofluids
 (2021)

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## Abstract

The eastern Tianshan metallogenic belt is an important molybdenum resource base in Xinjiang and is characterized by large-scale porphyry Mo deposits formed during the Triassic. The Tieling Cu-Mo porphyry deposit, which is situated in the western part of the eastern Tianshan metallogenic belt, was recently recognized as being related to Carboniferous granite porphyry. Three stages of hydrothermal mineralization were identified, including quartz+K-feldspar+pyrite±molybdenite±magnetite (stage I), quartz+molybdenite+pyrite+chalcopyrite (stage II), and quartz+pyrite±molybdenite±epidote (stage III). Fluid inclusion petrography and microthermometry analyses indicate the presence of gas-liquid inclusions with a H2O-NaCl composition. The ore-forming fluids have a characteristic temperature ranging from 157 to 262°C under stage II and 135 to 173°C under stage III, which correspond to salinities of 7.2-17.2 wt% NaCl equiv. and 5.9 to 9.6 wt% NaCl equiv., respectively. The hydrogen and oxygen isotope data indicate that the ore-forming fluids of the Tieling deposit were originally derived from magmatic hydrothermal fluids and then mixed with meteoric water. The sulfur isotope compositions indicate that the ore-forming materials were mainly derived from the Late Carboniferous felsic magma. Furthermore, zircon U-Pb analysis of ore-bearing granite porphyry yields a concordant age of 298.4±0.7Ma, indicating that the Tieling Cu-Mo deposit formed during the Late Carboniferous and differed from that processed under pre-Early Carboniferous and Triassic mineralization in the eastern Tianshan metallogenic belt. These results also indicate that the Tieling porphyry deposit was formed in the transition condition between subduction-related accretion and postcollisional orogeny, and it should be given more attention in prospect evaluations.


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## Body

## 1. Introduction

Porphyry deposits, as one of the most important types of Cu-Mo-Au deposits, have attracted extensive interest from the geologic community [1, 2]. Subduction-related magmatic arcs are considered to be closely related to porphyry deposits worldwide, especially that of porphyry Cu-Mo in the Circum-Pacific metallogenic belt [3–5]. Recent studies of metallogenic systems in China have shown that a postcollisional setting is favourable for the development of porphyry deposits [6–10], especially for porphyry Mo-only or Mo-dominated polymetallic deposits in the Dabie orogen [11–13].The postcollision-type porphyry Mo deposits in eastern Tianshan are found within a Triassic formation [14, 15], and the subduction-type porphyry Cu-Mo deposits are characterized by a formation preceding the Early Carboniferous [16, 17]. However, the Tieling Cu-Mo deposit, which was discovered by the Xinjiang Geological Survey Academy during a geochemical element anomaly survey, may be closely related to Late Carboniferous magmatism [18]. As an unexploited blind mineral system, the geological characteristics and metallogenic processes supporting its formation are still unclear. In this contribution, we first report new data, including the zircon U-Pb isotopic age of ore-bearing granite porphyry rocks, fluid inclusions, and H-O-S isotopes, to constrain the age of mineralization, determine the origin of the ore-forming fluids and material, and establish a metallogenic model of the Tieling deposit, which will be beneficial to enhance metallogenic theory and provide insights for the exploration of porphyry Cu-Mo mineralization in eastern Tianshan.


## 2. Geological Background

The Central Asian Orogenic Belt (CAOB), surrounded by North China, Tarim, European, and Siberian cratons (Figure1(a)), is a typical accretionary orogenic belt [19, 20], which resulted from collision between the Siberian and Tarim plates (Figure 1(a)) that progressively closed eastwards from the Late Carboniferous to Early Triassic [21, 22]. Eastern Tianshan, located at the southern margin of the CAOB, is an important mineral resource base in China (Figure 1(b)). Many notable deposits have occurred, including the Huangtupo and Xiaorequanzi VMS Cu-(Zn) [23, 24], Tuwu and Yandong porphyry Cu [16], Baishan and Donggebi porphyry Mo [21, 25], Huangshan and Tulaergen magmatic sulfide Ni-Cu [26, 27], Kangguer and Shiyingtan orogenic Au [28], and Yamansu volcanic Fe [29] deposits.Figure 1
(a) Simplified map of the CAOB; (b) tectonic framework and representative deposits in northern Xinjiang; (c) simplified geological map of the eastern Tianshan showing the distribution of representative deposits (modified from Wang et al. [16]). 1: Asikaerte; 2: Suoerkuduke; 3: Yulekenhalasu; 4: Suyunhe; 5: Baogutu; 6: Hongyuan; 7: Dabate; 8: Kekesai; 9: Lailisigaoer; 10: Kendenggaoer; 11: Donggebi; 12: Baishan.
(a)(b)(c)Eastern Tianshan, as an important part of the CAOB, has been subdivided into four tectonic units from north to south, namely, the Dananhu–Tousuquan island arc, the Kanggur–Huangshan shear zone, the Aqishan–Yamansu belt, and the Central Tianshan massif, with a series of approximately east-west-trending faults defining the boundaries, including the Dacaotan, Kanggur, Yamansu, and Aqikekuduke faults (Figure1(c)). The Dananhu–Tousuquan belt comprises Ordovician to Carboniferous volcanic and intrusive rocks that host a series of large porphyry Cu-(Mo) deposits, such as the Yudai [30], Tuwu, Yandong, Linglong [31], Chihu [32], Fuxing [33, 34], Yuhai [17], and Sanchakou deposits [35]. The Kanggur–Huangshan shear zone, located between the Yamansu and Kanggur faults, contains a set of tectonic slices, disordered strata, and intrusive rocks. Most strata-originating rocks with strong deformation and metamorphism host gold deposits in the west, including the Kangguer, Matoutan, and Shiyingtan deposits [28]. Most mafic-ultramafic rocks in the east host nickel-copper deposits, such as Huangshan, Huangshandong, Huangshannan, Hulu, and Tulargen deposits [26, 27]. Most notably, the Baishan and Donggebi superlarge porphyry Mo deposits formed in the Triassic are also found in the Kanggur–Huangshan shear zone [25, 36]. The Aqishan–Yamansu belt, located between the Aqikekuduke and Yamansu faults, consists of lavas, volcaniclastic rocks, and terrigenous clastic sedimentary rocks interbedded with bioclastic limestones. Carboniferous granitic intrusions are widely distributed and intrusively bedded by diabase walls [37]. A series of iron deposits related to volcanism have been recognized in this belt, including the Hongyuntan, Bailingshan, Duotoushan, Heijianshan, Chilongfeng, and Yamansu deposits [18, 29, 38, 39]. The Central Tianshan massif, bounded by the Aqikekuduke fault in the north, is an ancient block composed of calc-alkaline basaltic to andesitic volcanic and volcaniclastic rocks, slightly altered granites and granodiorites, and Precambrian basement rocks [34]. In addition to iron and nickel-copper deposits, there is also a skarn-type tungsten-molybdenum deposit (Xiaobaishitou, Li et al. [40]) in the eastern part of the belt.


## 3. Geology of the Tieling Ore District

The Tieling Cu-Mo deposit is situated southwest of the Bailingshan intrusion in the Aqishan–Yamansu arc belt (Figure1(c)). The lithostratigraphic unit in the ore district is dominated by the Late Carboniferous Tugutubulake Formation, which consists of tuffaceous dacitic lava with an age of 324 Ma [41]. The intrusive rocks at Tieling mainly include granite porphyry, monzogranite, and granodiorite, with minor gabbroic and dioritic dikes (Figure 2). The monzogranite and granodiorite of the Bailingshan complex were emplaced early into the strata at 317–307 Ma [41], and the gabbroic and dioritic dikes were both emplaced in the Late Carboniferous (311 to 315 Ma, Long et al. [37]). The concealed granite porphyry, as an important ore-bearing rock, was emplaced into the granodiorite (Figure 3). The granite porphyry is characterized by a medium- or fine-grained porphyritic texture (Figure 4(a)) and mainly consists of K-feldspar (65%) and quartz (30%), with minor accessory minerals such as molybdenite, zircon, apatite, pyrite, and magnetite. The phenocryst content is approximately 15% and mainly includes K-feldspar with a particle size of approximately 0.5 mm (Figure 4(b)). Muscovite is distributed among the K-feldspar and quartz aggregates in sheet form (Figure 4(c)).Figure 2
Simplified geological map of the Tieling Cu-Mo deposit (modified from Geological Survey Academy of Xinjiang, 2008).Figure 3
The geological section along the no. 9 exploration line on the map with lithologies and orebodies.Figure 4
Characteristics of the rocks and ore minerals of the Tieling Cu-Mo deposit. (a) Disseminated molybdenite and pyrite in granite porphyry; (b) porphyritic texture of granite porphyry; (c) porphyritic texture of granite porphyry; (d) molybdenite in quartz vein; (e) molybdenite and pyrite coexisting in quartz vein and epidote fills in fissures; (f) veinlet molybdenite in granite porphyry; (g) molybdenite in quartz vein; (h) fascicular molybdenite in quartz vein; (i) molybdenite and chalcopyrite coexisting with quartz. Qz: quartz; Kf: K-feldspar; Ep: epidote; Bi: biotite; Mo: molybdenite; Py: pyrite; Ccp: chalcopyrite.
(a)(b)(c)(d)(e)(f)(g)(h)(i)The iron orebodies in the NE direction on the surface, which were regarded as target ores, are mainly distributed in the northeastern ore district (Figure2). Newly identified molybdenum mineralization is only found in the deep part of granite porphyry, forming a combination of “upper iron and lower copper-molybdenum” with the previously mined iron ores. The iron ores are composed of magnetite, haematite, and pyrite [42]. The metal sulfide minerals of Cu-Mo mineralization mainly include molybdenite, chalcopyrite, and pyrite, with disseminated, massive, and vein structures, while gangue minerals mainly include K-feldspar, quartz, epidote, and chlorite. Molybdenite occurs as coarse-grained clusters in quartz veins (Figures 4(d) and 4(e)) and as a disseminated mineral (Figure 4(a)) and veinlets in granite porphyry (Figure 4(f)). Molybdenite either exists as independent aggregates (Figures 4(d), 4(g), and 4(h)) or is associated with chalcopyrite and pyrite (Figures 4(e) and 4(i)). Wallrock alteration includes silicification, argillization, sericitization, chloritization, epidotization, and biotitization. Silicification and potassic feldspar are closely related to molybdenum mineralization. The alteration of the surrounding rock shows spatial zonation. From the granite porphyry to the surrounding rock, the alteration varies from a potassium silicate zone to a sericitization zone and finally a propylitization zone.Based on field and microscopic observation of the mineralogy and the textural and paragenetic relationships of various hydrothermal minerals, three paragenetic stages of mineralization were identified in the Tieling deposit (Figure5). These sequences are quartz+K-feldspar+pyrite+molybdenite±magnetite (stage I), quartz+molybdenite+pyrite+chalcopyrite (stage II), and quartz+pyrite+epidote±molybdenite±chlorite (stage III).Figure 5
Paragenetic sequence of the Tieling Cu-Mo deposit.


## 4. Sampling and Analytical Methods

### 4.1. Zircon U-Pb Isotopes

The zircon U-Pb isotope samples were collected from bearing molybdenite granite porphyry at a depth of 188 m in drill hole no. ZK9-2. Zircon grains were separated using heavy liquid and magnetic techniques, hand-picked under a binocular microscope, and mounted in epoxy resin. The internal texture of the zircons (including zoning, structures, and fractures) was characterized via cathodoluminescence (CL) imaging using a CAMECA electron microprobe at Yujin Technology Co., Ltd. U-Pb isotope analysis was performed at the State Key Laboratory of Mineral Deposits Research, Nanjing University, using an Agilent 7500a laser ablation system coupled with an iCAP RQ ICP-MS. The analytical spot size, laser frequency, and energy density were 32 mm, 5 Hz, and 6.5 J/cm2, respectively. The analytical drift of the U-Th-Pb isotopic ratios was corrected using linear interpolation (with time) for every twelve analyses based on the signal variations of the zircon standard GJ1. Weighted mean age calculations and concordia diagrams were processed using ISOPLOT software [43].


### 4.2. Fluid Inclusion Microthermometry and Laser Raman Spectroscopy

The mineral assemblage and its paragenetic sequence were observed in the field and under the microscope for dividing three metallogenic stages. However, due to the low degree of exploration, we did not collect representative stage I samples for fluid inclusion study. Therefore, five samples comprising quartz veins of the stage II and stage III were selected, of which samples 20TL-3-78, 20TL-3-80, 20TL-3-83, and 20TL-3-87 were collected at depths of 78 m, 80 m, 83 m, and 87 m in drill hole no. ZK9-3, respectively. Sample 20TL-2-167 was collected at a depth of 167 m in drill hole no. ZK9-2.Fluid inclusion analyses were carried out at the Laboratory of Mineralization and Dynamics, Chang’an University, Xi’an, China, using the fluid inclusion assemblage (FIA). Microthermometric measurements were conducted using a Linkam THMSG 600 heating-freezing stage mounted on a Leica DMR microscope. The estimated accuracies of the freezing and heating measurements were ±0.1°C from -100°C to 25°C, ±1°C from 25°C to 400°C, and ±2°C above 400°C. Heating and freezing rates were generally 0.2-5°C/min and were reduced to 0.2°C/min near the temperatures of phase change. The salinity of aqueous fluid inclusions was estimated using equations for the NaCl-H2O system provided by Bodnar [44]. The density of the ore-forming fluid was estimated using data provided by Liu and Shen [45]. Volatile components of representative fluid inclusions were identified using a HORIBA HR Evolution 800 mm laser Raman spectrometer at the same institution. The laser wavelength was 532 nm, and the single spectrum collection time was 2 s. The Raman shift ranged from 100 cm-1 to 4000 cm-1. The spectrum resolution was ±2 cm-1 with a beam size of 1 μm. The instrumental setting was kept constant during all analyses.


### 4.3. H-O-S Isotopic Systematics

Five quartz samples from stage II and stage III were analysed for O (quartz) and H (water from fluid inclusions) isotopes. Their acquisition location corresponds to that of the fluid inclusions. Seven pyrite samples and one chalcopyrite sample were analysed for S isotopes. Of these, samples 20TL-1-160 and 20TL-1-166 of stage I were collected from 160 m and 166 m drilling cores underground in drill hole no. ZK9-1, respectively. Samples 20TL-3-78, 20TL-3-87, 20TL-2-26, and 20TL-5-54 of stage II were collected from 78 m, 87 m, 26 m, and 54 m drilling cores underground in drill hole nos. ZK9-3, ZK9-2, and ZK9-5, respectively. Sample 20TL-2-167 was collected from a 167 m drilling core underground in drill hole no. ZK9-2. Samples 20TL-3-83 of stage III were collected from an 83 m drilling core underground in drill hole no. ZK9-3.TheδD values of water from fluid inclusions and the δ18O values of their host minerals were measured at the Beijing Research Institute of Uranium Geology, China. The water contained in the fluid inclusions of the host minerals was released via thermal decrepitation at 400°C and then collected, frozen, and purified. Then, using reductive zinc, we replaced and released the hydrogen in the water to perform mass spectrometry. The analytical precision of the δD values was within ±2‰ (1σ) and that of the δ18O values was within ±0.2‰ (2σ). The δ18O values in quartz water (αquartz water) were calculated from the δ18Oquartz values of the analysed quartz by using the fractionation equation 1000Inαquartzwater=3.38×106T−2−3.40, where T is the temperature in Kelvin [46], and the average corrected temperature of fluid inclusion was used to calculate the δ18Owater value.We separated the pyrite and chalcopyrite samples from the disseminations, veins, and crumb ores for sulfur isotope analysis. Sulfur isotopic analyses were carried out on a MAT253 mass spectrometer at the Beijing Research Institute of Uranium Geology, China. Seven pyrite samples and one chalcopyrite sample were converted to SO2 under high-temperature vacuum conditions. The δ34S values were measured on a DELTA V plus gas isotope mass spectrometer. Sulfur isotope values are reported in per mil relative following the Vienna Canyon Diablo Troilite (V-CDT) standard, and the analytical uncertainty was within ±0.2‰ for δ34S. The equilibrium temperature of sulfur isotopes was calculated from symbiotic sulfides by using the fractionation equation 1000InαPy−Ccp=0.45×106/T−2, where T is the temperature in Kelvin [47].


## 4.1. Zircon U-Pb Isotopes

The zircon U-Pb isotope samples were collected from bearing molybdenite granite porphyry at a depth of 188 m in drill hole no. ZK9-2. Zircon grains were separated using heavy liquid and magnetic techniques, hand-picked under a binocular microscope, and mounted in epoxy resin. The internal texture of the zircons (including zoning, structures, and fractures) was characterized via cathodoluminescence (CL) imaging using a CAMECA electron microprobe at Yujin Technology Co., Ltd. U-Pb isotope analysis was performed at the State Key Laboratory of Mineral Deposits Research, Nanjing University, using an Agilent 7500a laser ablation system coupled with an iCAP RQ ICP-MS. The analytical spot size, laser frequency, and energy density were 32 mm, 5 Hz, and 6.5 J/cm2, respectively. The analytical drift of the U-Th-Pb isotopic ratios was corrected using linear interpolation (with time) for every twelve analyses based on the signal variations of the zircon standard GJ1. Weighted mean age calculations and concordia diagrams were processed using ISOPLOT software [43].


## 4.2. Fluid Inclusion Microthermometry and Laser Raman Spectroscopy

The mineral assemblage and its paragenetic sequence were observed in the field and under the microscope for dividing three metallogenic stages. However, due to the low degree of exploration, we did not collect representative stage I samples for fluid inclusion study. Therefore, five samples comprising quartz veins of the stage II and stage III were selected, of which samples 20TL-3-78, 20TL-3-80, 20TL-3-83, and 20TL-3-87 were collected at depths of 78 m, 80 m, 83 m, and 87 m in drill hole no. ZK9-3, respectively. Sample 20TL-2-167 was collected at a depth of 167 m in drill hole no. ZK9-2.Fluid inclusion analyses were carried out at the Laboratory of Mineralization and Dynamics, Chang’an University, Xi’an, China, using the fluid inclusion assemblage (FIA). Microthermometric measurements were conducted using a Linkam THMSG 600 heating-freezing stage mounted on a Leica DMR microscope. The estimated accuracies of the freezing and heating measurements were ±0.1°C from -100°C to 25°C, ±1°C from 25°C to 400°C, and ±2°C above 400°C. Heating and freezing rates were generally 0.2-5°C/min and were reduced to 0.2°C/min near the temperatures of phase change. The salinity of aqueous fluid inclusions was estimated using equations for the NaCl-H2O system provided by Bodnar [44]. The density of the ore-forming fluid was estimated using data provided by Liu and Shen [45]. Volatile components of representative fluid inclusions were identified using a HORIBA HR Evolution 800 mm laser Raman spectrometer at the same institution. The laser wavelength was 532 nm, and the single spectrum collection time was 2 s. The Raman shift ranged from 100 cm-1 to 4000 cm-1. The spectrum resolution was ±2 cm-1 with a beam size of 1 μm. The instrumental setting was kept constant during all analyses.


## 4.3. H-O-S Isotopic Systematics

Five quartz samples from stage II and stage III were analysed for O (quartz) and H (water from fluid inclusions) isotopes. Their acquisition location corresponds to that of the fluid inclusions. Seven pyrite samples and one chalcopyrite sample were analysed for S isotopes. Of these, samples 20TL-1-160 and 20TL-1-166 of stage I were collected from 160 m and 166 m drilling cores underground in drill hole no. ZK9-1, respectively. Samples 20TL-3-78, 20TL-3-87, 20TL-2-26, and 20TL-5-54 of stage II were collected from 78 m, 87 m, 26 m, and 54 m drilling cores underground in drill hole nos. ZK9-3, ZK9-2, and ZK9-5, respectively. Sample 20TL-2-167 was collected from a 167 m drilling core underground in drill hole no. ZK9-2. Samples 20TL-3-83 of stage III were collected from an 83 m drilling core underground in drill hole no. ZK9-3.TheδD values of water from fluid inclusions and the δ18O values of their host minerals were measured at the Beijing Research Institute of Uranium Geology, China. The water contained in the fluid inclusions of the host minerals was released via thermal decrepitation at 400°C and then collected, frozen, and purified. Then, using reductive zinc, we replaced and released the hydrogen in the water to perform mass spectrometry. The analytical precision of the δD values was within ±2‰ (1σ) and that of the δ18O values was within ±0.2‰ (2σ). The δ18O values in quartz water (αquartz water) were calculated from the δ18Oquartz values of the analysed quartz by using the fractionation equation 1000Inαquartzwater=3.38×106T−2−3.40, where T is the temperature in Kelvin [46], and the average corrected temperature of fluid inclusion was used to calculate the δ18Owater value.We separated the pyrite and chalcopyrite samples from the disseminations, veins, and crumb ores for sulfur isotope analysis. Sulfur isotopic analyses were carried out on a MAT253 mass spectrometer at the Beijing Research Institute of Uranium Geology, China. Seven pyrite samples and one chalcopyrite sample were converted to SO2 under high-temperature vacuum conditions. The δ34S values were measured on a DELTA V plus gas isotope mass spectrometer. Sulfur isotope values are reported in per mil relative following the Vienna Canyon Diablo Troilite (V-CDT) standard, and the analytical uncertainty was within ±0.2‰ for δ34S. The equilibrium temperature of sulfur isotopes was calculated from symbiotic sulfides by using the fractionation equation 1000InαPy−Ccp=0.45×106/T−2, where T is the temperature in Kelvin [47].


## 5. Results

### 5.1. Zircon U-Pb Isotopes

The granite porphyry (TL1) was dated by zircon U-Pb analysis. LA-ICP-MS zircon U-Pb dating results are summarized in Table1, and representative CL images of zircon grains from these rocks are shown in Figure 6. All the analysed zircons are prismatic, euhedral, and colourless, and most of them show oscillatory zoning patterns, which imply a magmatic origin. The analysed zircons have variable U (37-433 ppm) and Th (164-547 ppm) contents, with Th/U ratios ranging from 0.22 to 0.81 (mainly >0.1). Twenty-four zircon grains from the granite porphyry samples define a narrow range with 206Pb/238U ages of 296 to 298 Ma, yielding a concordant age of 298.4±0.7Ma (MSWD=28; Figure 7(a)), with a weighted mean age of 297.0±1.6Ma (MSWD=0.027; Figure 7(b)).Table 1
LA-ICP-MS U-Pb data of zircon grains from granite porphyry of the Tieling deposit.
SpotTh (ppm)U (ppm)Th/U207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238URatio1σRatio1σRatio1σAge (Ma)1σAge (Ma)1σAge (Ma)1σTL1-11252900.430.053080.000970.345010.006620.047150.000603324230152974TL1-21142670.430.051420.000960.334750.006540.047230.000602604429352974TL1-32404300.560.052410.000920.339540.006310.046990.00060303412975296TL1-41313140.420.052400.000940.339530.006450.047000.00060303422975296TL1-53254450.730.052520.000920.340240.006310.046990.00060308412975296TL1-61202860.420.052280.000970.340710.006610.047270.000602984329852984TL1-71182830.420.053360.001060.347090.007150.047180.000613444630352974TL1-8872220.390.053260.001030.347010.007030.047260.000613404530252984TL1-94335430.800.053520.000890.347040.006240.047030.00061351383025296TL1-101693510.480.053210.000850.346630.006060.047250.000613383730252984TL1-111233110.400.054530.000930.355560.006540.047290.000613933930952984TL1-12741970.380.053340.001050.346910.007210.047180.000623434630252974TL1-131603330.480.054450.000970.354220.006750.047190.000623904130852974TL1-142865470.520.053750.000800.349480.005760.047160.000613613430442974TL1-151903680.520.054970.000890.357430.006310.047160.000614113731052974TL1-161152770.420.055240.000940.358900.006590.047130.000614223931152974TL1-17711980.360.053040.001040.345570.007180.047260.000633314630152984TL1-18762100.360.051920.000970.337910.006730.047210.000632824429652974TL1-19551640.340.053300.001690.346120.009860.047090.000653427330272974TL1-20721790.400.053860.001130.349900.007730.047120.000633654830562974TL1-21902290.390.052640.001010.342780.007020.047230.000633134529952974TL1-221122420.460.054490.001050.354440.007230.047180.000633914430852974TL1-231794170.430.054910.000860.357300.006160.047200.000624093631052974TL1-241543900.390.052250.000850.338680.006010.047020.00062296382965296Figure 6
Cathodoluminescence (CL) images of representative zircons from granite porphyry in the Tieling deposit.Figure 7
The U-Pb concordant diagram and the weighted average age of zircons from granite porphyry in the Tieling deposit.
(a)(b)


### 5.2. Fluid Inclusions

Based on phase characteristics at room temperature, phase transitions during heating and cooling, and the results of laser Raman spectroscopy, fluid inclusions in the Tieling deposit mainly include liquid-rich inclusions (WL type). Fluid inclusions occurring as isolated inclusions, random distributions, or clusters are interpreted as primary features at various stages (Figure8). Each cluster or group of fluid inclusions along growth zones was considered to represent an FIA. Fluid inclusions occurring in linear arrays along fractures or grain boundaries were considered to be secondary fluid inclusions, which were not analysed by microthermometry because they formed later with respect to mineralization. The inclusions are ovular, polygonal, and irregular, with diameters in the range of 3-18 μm, mainly 5-10 μm, and contain gas bubbles that account for 10-40% of the total volume. These inclusions homogenize to the liquid phase when heated.Figure 8
Photomicrographs of representative fluid inclusions in quartz crystals from the Tieling Cu-Mo deposit: (a) liquid-rich inclusions in quartz of stage II; (b) liquid-rich inclusions in quartz of stage II; (c) liquid-rich inclusions in quartz of stage II; (d) liquid-rich inclusions in quartz of stage II; (e) liquid-rich inclusions in quartz of stage III; and (f) morphology of liquid-rich inclusions in quartz at different temperatures. LH2O: liquid-phase H2O; VH2O: vapor-phase H2O.
(a)(b)(c)(d)(e)(f)The microthermometric results and fluid inclusion parameters are shown in Table2. For the fluid inclusions in quartz of stage II, the final ice melting temperatures of WL-type fluid inclusions range from -13.8 to -4.5°C (with an average of -9.1°C), with corresponding salinities of 7.2 to 17.2 wt% NaCl equiv. (with an average of 12.9 wt% NaCl equiv.). The homogenization temperatures of fluid inclusions range from 157 to 262°C (with an average of 193.1°C), and the fluid densities are 0.897 to 1.025 g/cm3. For the fluid inclusions in quartz (samples 20TL-3-83) of stage III, the final ice melting temperature of WL-type fluid inclusions is -6.3 to -3.6°C (with an average of -5.0°C), the salinity is 5.9 to 9.6 wt% NaCl equiv. (with an average of 7.9 wt% NaCl equiv.), the homogenization temperatures of fluid inclusions range from 135 to 173°C (with an average of 154.2°C), and the fluid densities are 0.959 to 0.995 g/cm3. Previous studies indicate that the emplacement depths for porphyry deposits are generally around 3-5 km [48]. Due to lack of pressure data for this deposit, we used the lithostatic pressure at 5 km to calculate the entrapment temperatures of the analysed fluid inclusions. The fluid lithostatic pressure of the Tieling deposit can be estimated to be 1350 bar. Then, the average ore-forming temperatures of stage II and stage III were corrected to range from 268°C to 225°C (Figure 9).Table 2
Microthermometry data and relative parameters of fluid inclusions in the Tieling deposit.
Sample no.LocationMineralTypeSize(μm)V (%)No.Tmice (°C)Th (°C)Tc (°C)Salinity (% NaCl equiv.)Density (g/cm3)Quartz of stage II20TL-3-78ZK9-3/78 mQuartz+pyriteWL5-1410-6028-13.2 to -6.7182 to 262251 to 35510.1 to 17.20.897 to 1.01320TL-3-80ZK9-3/80 mQuartz+pyrite+chalcopyriteWL6-1510-4516-12.8 to -7.2157 to 242224 to 32810.7 to 16.80.934 to 1.02520TL-3-87ZK9-3/87 mQuartz+pyrite+molybdeniteWL5-1510-4023-13.8 to -4.5168 to 222237 to 3017.2 to 17.10.922 to 1.01920TL-2-167ZK9-2/167 mQuartz+molybdeniteWL6-1210-4021-12.8 to -6.1165 to 250232 to 3409.3 to 16.80.906 to 0.999Quartz of stage III20TL-3-83ZK9-3/83 mQuartzWL3-810-2021-6.3 to -3.6135 to 173201 to 2465.9 to 9.60.959 to 0.995Tmice: final melting temperature of ice; Th: total homogenization temperature; Tc: corrected temperature; V: percentage of bubble volume.Figure 9
Histograms of homogenization temperatures and salinities of fluid inclusions in the Tieling Cu-Mo deposit.Th: total homogenization temperature.We conducted a laser Raman spectroscopic speak scan of the gas-phase components in the fluid inclusions of quartz from the Tieling deposit. The results of representative laser Raman spectroscopic analyses are shown in Figure10. The primary gas component of WL-type fluid inclusions in quartz veins is mainly H2O.Figure 10
Laser Raman spectra of vapor-phase composition of WG-type fluid inclusions of the Tieling Cu-Mo deposit.


### 5.3. H-O-S Isotopes

The hydrogen and oxygen isotope data of the host minerals and water from fluid inclusions are summarized in Table3. The δDH2O(V-SMOW) values of quartz in four samples from stage II range from −79.5‰ to −63.3‰, the δ18OQ(V-SMOW) values of quartz range from 8.8‰ to 9.5‰, and the calculated δ18OH2O(V-SMOW) values of quartz range from 0.5‰ to 1.3‰. The δDH2O(V-SMOW) value of quartz in one sample from stage III is −67.6‰, the δ18OQ(V-SMOW) value is 9.1‰, and the calculated δ18OH2O(V-SMOW) value is 1.1‰.Table 3
Hydrogen, oxygen, and sulfur isotopic compositions of the Tieling Cu-Mo deposit.
Sample no.LocationStageMineralδ18OQ (‰)Tc (°C)δDH2O (‰)δ18OH2O (‰)δ34SCDT (‰)20TL-1-160ZK9-1/160 mStage IPyrite-0.820TL-1-166ZK9-1/166 mStage IPyrite-1.120TL-3-78ZK9-3/78 mStage IIQuartz8.9282-63.91.3Pyrite0.220TL-3-80ZK9-3/80 mStage IIQuartz9.5249-63.30.520TL-3-87ZK9-3/87 mStage IIQuartz8.8266-67.70.6Pyrite1.320TL-2-26ZK9-2/26 mStage IIPyrite1.420TL-2-167ZK9-2/167 mStage IIQuartz9.3267-79.51.120TL-5-54ZK9-5/54 mStage IIPyrite-1.620TL-3-83ZK9-3/83 mStage IIIQuartz9.1225-67.6-1.1Pyrite1.4Chalcopyrite-0.1D443/2Stage IPyrite-1.5D434/1Stage IPyrrhotite0.5D436/1Stage IPyrrhotite0.1Sulfur isotopic analysis on the Tieling deposit yielded pyrite and chalcopyrite. The sulfur isotopic compositions of seven pyrite samples and one chalcopyrite sample were analysed, and the corresponding measuredδ34SV-CDT values of minerals are listed in Table 3. The eight δ34SV-CDT values of the samples vary narrowly from −1.6‰ to 1.4‰. The sulfur isotopic compositions of the disseminations, veins, and crumb ores are symmetrical and cluster near zero. The equilibrium temperature of symbiotic sulfides between the pyrite and chalcopyrite crystals was 275°C.


## 5.1. Zircon U-Pb Isotopes

The granite porphyry (TL1) was dated by zircon U-Pb analysis. LA-ICP-MS zircon U-Pb dating results are summarized in Table1, and representative CL images of zircon grains from these rocks are shown in Figure 6. All the analysed zircons are prismatic, euhedral, and colourless, and most of them show oscillatory zoning patterns, which imply a magmatic origin. The analysed zircons have variable U (37-433 ppm) and Th (164-547 ppm) contents, with Th/U ratios ranging from 0.22 to 0.81 (mainly >0.1). Twenty-four zircon grains from the granite porphyry samples define a narrow range with 206Pb/238U ages of 296 to 298 Ma, yielding a concordant age of 298.4±0.7Ma (MSWD=28; Figure 7(a)), with a weighted mean age of 297.0±1.6Ma (MSWD=0.027; Figure 7(b)).Table 1
LA-ICP-MS U-Pb data of zircon grains from granite porphyry of the Tieling deposit.
SpotTh (ppm)U (ppm)Th/U207Pb/206Pb207Pb/235U206Pb/238U207Pb/206Pb207Pb/235U206Pb/238URatio1σRatio1σRatio1σAge (Ma)1σAge (Ma)1σAge (Ma)1σTL1-11252900.430.053080.000970.345010.006620.047150.000603324230152974TL1-21142670.430.051420.000960.334750.006540.047230.000602604429352974TL1-32404300.560.052410.000920.339540.006310.046990.00060303412975296TL1-41313140.420.052400.000940.339530.006450.047000.00060303422975296TL1-53254450.730.052520.000920.340240.006310.046990.00060308412975296TL1-61202860.420.052280.000970.340710.006610.047270.000602984329852984TL1-71182830.420.053360.001060.347090.007150.047180.000613444630352974TL1-8872220.390.053260.001030.347010.007030.047260.000613404530252984TL1-94335430.800.053520.000890.347040.006240.047030.00061351383025296TL1-101693510.480.053210.000850.346630.006060.047250.000613383730252984TL1-111233110.400.054530.000930.355560.006540.047290.000613933930952984TL1-12741970.380.053340.001050.346910.007210.047180.000623434630252974TL1-131603330.480.054450.000970.354220.006750.047190.000623904130852974TL1-142865470.520.053750.000800.349480.005760.047160.000613613430442974TL1-151903680.520.054970.000890.357430.006310.047160.000614113731052974TL1-161152770.420.055240.000940.358900.006590.047130.000614223931152974TL1-17711980.360.053040.001040.345570.007180.047260.000633314630152984TL1-18762100.360.051920.000970.337910.006730.047210.000632824429652974TL1-19551640.340.053300.001690.346120.009860.047090.000653427330272974TL1-20721790.400.053860.001130.349900.007730.047120.000633654830562974TL1-21902290.390.052640.001010.342780.007020.047230.000633134529952974TL1-221122420.460.054490.001050.354440.007230.047180.000633914430852974TL1-231794170.430.054910.000860.357300.006160.047200.000624093631052974TL1-241543900.390.052250.000850.338680.006010.047020.00062296382965296Figure 6
Cathodoluminescence (CL) images of representative zircons from granite porphyry in the Tieling deposit.Figure 7
The U-Pb concordant diagram and the weighted average age of zircons from granite porphyry in the Tieling deposit.
(a)(b)


## 5.2. Fluid Inclusions

Based on phase characteristics at room temperature, phase transitions during heating and cooling, and the results of laser Raman spectroscopy, fluid inclusions in the Tieling deposit mainly include liquid-rich inclusions (WL type). Fluid inclusions occurring as isolated inclusions, random distributions, or clusters are interpreted as primary features at various stages (Figure8). Each cluster or group of fluid inclusions along growth zones was considered to represent an FIA. Fluid inclusions occurring in linear arrays along fractures or grain boundaries were considered to be secondary fluid inclusions, which were not analysed by microthermometry because they formed later with respect to mineralization. The inclusions are ovular, polygonal, and irregular, with diameters in the range of 3-18 μm, mainly 5-10 μm, and contain gas bubbles that account for 10-40% of the total volume. These inclusions homogenize to the liquid phase when heated.Figure 8
Photomicrographs of representative fluid inclusions in quartz crystals from the Tieling Cu-Mo deposit: (a) liquid-rich inclusions in quartz of stage II; (b) liquid-rich inclusions in quartz of stage II; (c) liquid-rich inclusions in quartz of stage II; (d) liquid-rich inclusions in quartz of stage II; (e) liquid-rich inclusions in quartz of stage III; and (f) morphology of liquid-rich inclusions in quartz at different temperatures. LH2O: liquid-phase H2O; VH2O: vapor-phase H2O.
(a)(b)(c)(d)(e)(f)The microthermometric results and fluid inclusion parameters are shown in Table2. For the fluid inclusions in quartz of stage II, the final ice melting temperatures of WL-type fluid inclusions range from -13.8 to -4.5°C (with an average of -9.1°C), with corresponding salinities of 7.2 to 17.2 wt% NaCl equiv. (with an average of 12.9 wt% NaCl equiv.). The homogenization temperatures of fluid inclusions range from 157 to 262°C (with an average of 193.1°C), and the fluid densities are 0.897 to 1.025 g/cm3. For the fluid inclusions in quartz (samples 20TL-3-83) of stage III, the final ice melting temperature of WL-type fluid inclusions is -6.3 to -3.6°C (with an average of -5.0°C), the salinity is 5.9 to 9.6 wt% NaCl equiv. (with an average of 7.9 wt% NaCl equiv.), the homogenization temperatures of fluid inclusions range from 135 to 173°C (with an average of 154.2°C), and the fluid densities are 0.959 to 0.995 g/cm3. Previous studies indicate that the emplacement depths for porphyry deposits are generally around 3-5 km [48]. Due to lack of pressure data for this deposit, we used the lithostatic pressure at 5 km to calculate the entrapment temperatures of the analysed fluid inclusions. The fluid lithostatic pressure of the Tieling deposit can be estimated to be 1350 bar. Then, the average ore-forming temperatures of stage II and stage III were corrected to range from 268°C to 225°C (Figure 9).Table 2
Microthermometry data and relative parameters of fluid inclusions in the Tieling deposit.
Sample no.LocationMineralTypeSize(μm)V (%)No.Tmice (°C)Th (°C)Tc (°C)Salinity (% NaCl equiv.)Density (g/cm3)Quartz of stage II20TL-3-78ZK9-3/78 mQuartz+pyriteWL5-1410-6028-13.2 to -6.7182 to 262251 to 35510.1 to 17.20.897 to 1.01320TL-3-80ZK9-3/80 mQuartz+pyrite+chalcopyriteWL6-1510-4516-12.8 to -7.2157 to 242224 to 32810.7 to 16.80.934 to 1.02520TL-3-87ZK9-3/87 mQuartz+pyrite+molybdeniteWL5-1510-4023-13.8 to -4.5168 to 222237 to 3017.2 to 17.10.922 to 1.01920TL-2-167ZK9-2/167 mQuartz+molybdeniteWL6-1210-4021-12.8 to -6.1165 to 250232 to 3409.3 to 16.80.906 to 0.999Quartz of stage III20TL-3-83ZK9-3/83 mQuartzWL3-810-2021-6.3 to -3.6135 to 173201 to 2465.9 to 9.60.959 to 0.995Tmice: final melting temperature of ice; Th: total homogenization temperature; Tc: corrected temperature; V: percentage of bubble volume.Figure 9
Histograms of homogenization temperatures and salinities of fluid inclusions in the Tieling Cu-Mo deposit.Th: total homogenization temperature.We conducted a laser Raman spectroscopic speak scan of the gas-phase components in the fluid inclusions of quartz from the Tieling deposit. The results of representative laser Raman spectroscopic analyses are shown in Figure10. The primary gas component of WL-type fluid inclusions in quartz veins is mainly H2O.Figure 10
Laser Raman spectra of vapor-phase composition of WG-type fluid inclusions of the Tieling Cu-Mo deposit.


## 5.3. H-O-S Isotopes

The hydrogen and oxygen isotope data of the host minerals and water from fluid inclusions are summarized in Table3. The δDH2O(V-SMOW) values of quartz in four samples from stage II range from −79.5‰ to −63.3‰, the δ18OQ(V-SMOW) values of quartz range from 8.8‰ to 9.5‰, and the calculated δ18OH2O(V-SMOW) values of quartz range from 0.5‰ to 1.3‰. The δDH2O(V-SMOW) value of quartz in one sample from stage III is −67.6‰, the δ18OQ(V-SMOW) value is 9.1‰, and the calculated δ18OH2O(V-SMOW) value is 1.1‰.Table 3
Hydrogen, oxygen, and sulfur isotopic compositions of the Tieling Cu-Mo deposit.
Sample no.LocationStageMineralδ18OQ (‰)Tc (°C)δDH2O (‰)δ18OH2O (‰)δ34SCDT (‰)20TL-1-160ZK9-1/160 mStage IPyrite-0.820TL-1-166ZK9-1/166 mStage IPyrite-1.120TL-3-78ZK9-3/78 mStage IIQuartz8.9282-63.91.3Pyrite0.220TL-3-80ZK9-3/80 mStage IIQuartz9.5249-63.30.520TL-3-87ZK9-3/87 mStage IIQuartz8.8266-67.70.6Pyrite1.320TL-2-26ZK9-2/26 mStage IIPyrite1.420TL-2-167ZK9-2/167 mStage IIQuartz9.3267-79.51.120TL-5-54ZK9-5/54 mStage IIPyrite-1.620TL-3-83ZK9-3/83 mStage IIIQuartz9.1225-67.6-1.1Pyrite1.4Chalcopyrite-0.1D443/2Stage IPyrite-1.5D434/1Stage IPyrrhotite0.5D436/1Stage IPyrrhotite0.1Sulfur isotopic analysis on the Tieling deposit yielded pyrite and chalcopyrite. The sulfur isotopic compositions of seven pyrite samples and one chalcopyrite sample were analysed, and the corresponding measuredδ34SV-CDT values of minerals are listed in Table 3. The eight δ34SV-CDT values of the samples vary narrowly from −1.6‰ to 1.4‰. The sulfur isotopic compositions of the disseminations, veins, and crumb ores are symmetrical and cluster near zero. The equilibrium temperature of symbiotic sulfides between the pyrite and chalcopyrite crystals was 275°C.


## 6. Discussion

### 6.1. Sources of Hydrothermal Fluid and Sulfur

#### 6.1.1. Sources of Hydrothermal Fluid

The fluid inclusions show that the ore-forming fluid has the characteristics of a relatively medium-low temperature, medium-high salinity, and medium-high density and represents a NaCl-H2O system. The average corrected mineralization temperatures of stage II and stage III range from 268°C to 225°C, which is consistent with the equilibrium temperature of sulfur isotopes (275°C) and indicates that the corrected mineralization temperature is within the acceptable error range. The δ18O values of quartz in the Tieling deposit range from 8.8‰ to 9.5‰, with an average value of 9.1‰ (Table 2), which is consistent with those of crustal remelting granite (10.0–12.0‰ [49]), indicating that the formation of hydrothermal quartz was associated with Carboniferous felsic intrusive rocks and was derived from magmatic fluids. The δD values of the fluids in the Tieling deposit mostly range from −79.5‰ to −63.3‰ (Table 3) and approach those of magmatic water and meteoric water [50, 51]. The H-O isotope data of stages II and III plot between the primary magmatic water field and the meteoric water line (Figure 11), which is similar to other deposits in the same metallogenic belt [25, 52–57], indicating that the ore-forming fluids of the Tieling Cu-Mo deposit were derived from Carboniferous magmatic hydrothermal fluids and then mixed with meteoric water.Figure 11
δDfluid vs. δ18Ofluid values from various stages in the Tieling Cu-Mo deposit. Fields for magmatic and metamorphic water are from Taylor [50] and Sheppard [51]. The data of previous studies were referenced from Zhang et al. [54], Zhang et al. [25], Liu et al. [55], Wang et al. [56], and Li et al. [57].


#### 6.1.2. Sources of Sulfur

The sulfide assemblage in the Tieling deposit is dominated by molybdenite and pyrite with minor chalcopyrite, and no sulfate minerals have been detected. Therefore, the hydrothermal system during the ore-forming process in the Tieling deposit was dominated by H2S. Molybdenite, pyrite, and chalcopyrite were formed under low-fO2 and low-pH conditions [58]. According to Table 3, the average δ34SV-CDT value for the seven pyrite samples collected from the Tieling deposit is 0.1‰, and the δ34SV-CDT value for one chalcopyrite sample is -0.1‰. The basic sequence is consistent with the δ34S enrichment condition of δ34SPy>δ34SCcp at isotopic equilibrium, indicating that the mineral S isotopes had reached equilibrium [59]. Therefore, the S isotopic compositions of pyrite are close to the total S isotopic compositions of the hydrothermal system and can be used to trace S sources. The overall range of the δ34SV-CDT values of sulfides in the Tieling deposit is narrow, indicating that the S sources of sulfides deposited in the ore-forming hydrothermal fluids were undiversified. The δ34SV-CDT values are consistent with those of felsic magma [60] and other representative deposits related to magmatism [14, 16, 25, 39, 54, 56, 61, 62], indicating that the sulfur in the Tieling deposit was mainly derived from Late Carboniferous felsic magma (Figure 12).Figure 12
δ34SV-CDT values of ore-forming fluids at Tieling and other major deposits in eastern Tianshan. Sulfur isotopic compositions of global seawater in the Late Carboniferous were modified after Holser [63]. Sulfur isotopic compositions of representative deposits were modified after Han et al. [14], Wang et al. [16], Zhang et al. [25], Sun et al. [39], Zhang et al. [54], Wang et al. [56], Dai et al. [61], and Zhao et al. [62].


### 6.2. Mineralization Age and Ore-Forming Process

In the early Paleozoic, porphyry Cu-Mo-Au deposits formed under the northward subduction of the Kanggur ocean basin, such as Sanchakou [64], Sanchakouxi [35], and Yudai [30]. During the Early Carboniferous, porphyry Cu-Mo deposits in the northern Kanggur belt, such as Yuhai and Tuwu [65, 66], formed under the north-south bidirectional subduction of the Kanggur ocean basin. At the same time, a series of iron ores related to magmatism were formed in the southern Kanggur belt, including those of the Bailingshan [67], Hongyuntan [39], and Duotoushan [68]. The ductile shear gold deposits were formed in Late Carboniferous [69], followed by abundant magmatic sulfide Cu-Ni under the postcollisional extensional environment of the Early Permian [70, 71]. After approximately ca. 240 Ma, porphyry Mo deposits related to Triassic granite porphyry in a postcollisional environment were formed, including the Baishan and Donggebi deposits [72, 73]. The zircon U-Pb age from ore-bearing granite porphyry yields a concordant age of 298.4±0.7Ma, which is consistent with the molybdenite Re-Os isochron age (299.0 ± 7.7 Ma, in publishing). The chronology data of the two groups within error indicate that the Tieling Cu-Mo deposit was decidedly formed during the Late Carboniferous.Previous studies have shown that the iron orebodies taking tabular or lensoid shapes of the Tieling deposit were hosted in monzogranite and granodiorite along fractures [42]. The formation of the iron orebodies was considered related to the Bailingshan complex generated by the southward subduction of the Kanggur oceanic plate beneath the Yili–Central Tianshan block during 324 to 303 Ma [42, 67], and Cu-Mo mineralization was supposed to have formed later than Fe mineralization. Therefore, the mineralization process of the Tieling deposit has been described as two distinct metallogenic periods, including Fe and Cu-Mo periods. The iron orebodies related to volcanic rocks were formed first in the strata during the subduction stage of the early Late Carboniferous [42]. With the emplacement of the Bailingshan complex, iron orebodies were formed in monzogranite and granodiorite and partially in the contact zone with skarnization (Figure 13(a)). Magnetite was found in the later basic dikes [37]. At the end of the Late Carboniferous, the hydrothermal fluids released from the ore-bearing granite porphyry in the late crystallization stage were mixed with meteoric water, resulting in precipitation mineralization in favourable structural positions (Figure 13(b)).Figure 13
The metallogenic model of the Tieling copper-molybdenite deposit: (a) iron mineralization period in the early Late Carboniferous; (b) copper-molybdenum mineralization at the end of the Late Carboniferous.
(a)(b)


### 6.3. Geological Significance

The Mo deposits mainly include (W-/Be-) Mo and Cu-Mo types in northern Xinjiang on the southwestern margin of the CAOB (Table4). The (W-/Be-) Mo-type deposits were formed in the Triassic period resulting from postcollisional orogeny and mainly distributed in Altay [74, 75] and eastern Tianshan [14, 25, 76, 77]. The (W-/Be-) Mo-type deposits distributed in West Junggar formed in the transition condition [78–80]. In addition, the Cu-Mo-type deposits formed before the Carboniferous were widely distributed in the northern region of Xinjiang [78–82]. All of them, including Suoerkuduke, Xilekuduke, Yulekenhalasu, and Mengxi in East Junggar [78, 79, 82–85]; Baogutu in West Junggar [86]; Dabate, Lailisigaoer, and Kendenggaoer in West Tianshan [87–91]; and Tuwu-Yandong, Yuhai, and Sanchakou in East Tianshan [17, 64–66], were related to subduction-related accretion orogeny. Notably, Mo mineralization in the eastern Tianshan was concentrated in the Triassic and before the Early Carboniferous, with the (W-/Be-) Mo type related to collisional orogeny and the Cu-Mo type related to subduction-related accretion orogeny (Figure 14). However, no significant Cu-Mo deposits were found in the transitional time between the Triassic and Early Carboniferous in eastern Tianshan. Perhaps more attention should be given to prospecting because there are abundant contemporaneous Cu-Mo deposits in West Junggar [86], East Junggar [79, 82], and West Tianshan [88, 89, 91, 92].Table 4
Molybdenite Re-Os isochron ages of Mo deposits in northern Xinjiang, NW China.
No.DepositTypeMetalSizeMethodAge (Ma)ReferenceAltay1AsikaertePorphyryBe, MoLargeMolybdenite Re-Os218.6±1.3228.7±7.1Wang et al. [74]Liu et al. [75]East Junggar2SuoerkudukeSkarnCu, MoMediumMolybdenite Re-Os317.1±7.6305±7Liu and Liu [82]Wan et al. [84]3XilekudukePorphyryCu, MoMediumMolybdenite Re-Os327.1±2.9Long et al. [81]4YulekenhalasuPorphyryCu, MoMediumMolybdenite Re-Os331.5±4.8357.3±5.2376.9±2.2Xiang et al. [85]Xue et al. [86]5MengxiPorphyryCu, MoMolybdenite Re-Os411.6±3.2Qu et al. [87]West Junggar6SuyunhePorphyryMoGiantMolybdenite Re-Os294.4±1.7Zhong et al. [78]7BaogutuPorphyryCu, MoLargeMolybdenite Re-Os310±3.6Song et al. [89]8HongyuanPorphyryMoMolybdenite Re-Os294.6±4.6314.3±1.9Li [79]Yan et al. [80]West Tianshan9DabatePorphyryCu, MoSmallMolybdenite Re-Os300.3±2.1301±20Li [92]Zhang et al. [91]10LailisigaoerPorphyryCu, MoSmallMolybdenite Re-Os379.9±8.3359±8Zhu et al. [90]Li et al. [93]11KendenggaoerSkarnCu, MoSmallMolybdenite Re-Os313.9±2.5Jia [88]East Tianshan12Tuwu-YandongPorphyryCu, MoLargeMolybdenite Re-Os323±2343±26Rui et al. [65]Zhang et al. [66]13DonggebiPorphyryMoGiantMolybdenite Re-Os233.2±2.2231.1±1.5231.9±6.5234.3±1.6Wu et al. [72]Tu et al. [94]Wu et al. [76]Han et al. [14]14KumutageSkarnMoMolybdenite Re-Os319.1±4.5Zhang et al. [95]15YuhaiPorphyryCu, MoSmallMolybdenite Re-Os355.7±2.4Wang et al. [17]16SanchakouPorphyryCu, MoMolybdenite Re-Os416±6.4358±6.2Lin et al. [64]Liao and Lv [35]17XiaobaishitouSkarnW, MoMolybdenite Re-Os239.7±3.6251.4±3.6251.1±1.6Deng et al. [96]Li et al. [57]18BaishanPorphyryMoGiantMolybdenite Re-Os224.8±4.5227±4.3223.2±2.7Zhang et al. [25]Zhang et al. [73]Tu et al. [15]19TielingPorphyryCu-MoMolybdenite Re-OsZircon U-Pb299.0±7.7298.4±0.7UnpublishedThis studyFigure 14
Re-Os isotopic ages from the Mo deposits in northern Xinjiang, NW China.


## 6.1. Sources of Hydrothermal Fluid and Sulfur

### 6.1.1. Sources of Hydrothermal Fluid

The fluid inclusions show that the ore-forming fluid has the characteristics of a relatively medium-low temperature, medium-high salinity, and medium-high density and represents a NaCl-H2O system. The average corrected mineralization temperatures of stage II and stage III range from 268°C to 225°C, which is consistent with the equilibrium temperature of sulfur isotopes (275°C) and indicates that the corrected mineralization temperature is within the acceptable error range. The δ18O values of quartz in the Tieling deposit range from 8.8‰ to 9.5‰, with an average value of 9.1‰ (Table 2), which is consistent with those of crustal remelting granite (10.0–12.0‰ [49]), indicating that the formation of hydrothermal quartz was associated with Carboniferous felsic intrusive rocks and was derived from magmatic fluids. The δD values of the fluids in the Tieling deposit mostly range from −79.5‰ to −63.3‰ (Table 3) and approach those of magmatic water and meteoric water [50, 51]. The H-O isotope data of stages II and III plot between the primary magmatic water field and the meteoric water line (Figure 11), which is similar to other deposits in the same metallogenic belt [25, 52–57], indicating that the ore-forming fluids of the Tieling Cu-Mo deposit were derived from Carboniferous magmatic hydrothermal fluids and then mixed with meteoric water.Figure 11
δDfluid vs. δ18Ofluid values from various stages in the Tieling Cu-Mo deposit. Fields for magmatic and metamorphic water are from Taylor [50] and Sheppard [51]. The data of previous studies were referenced from Zhang et al. [54], Zhang et al. [25], Liu et al. [55], Wang et al. [56], and Li et al. [57].


### 6.1.2. Sources of Sulfur

The sulfide assemblage in the Tieling deposit is dominated by molybdenite and pyrite with minor chalcopyrite, and no sulfate minerals have been detected. Therefore, the hydrothermal system during the ore-forming process in the Tieling deposit was dominated by H2S. Molybdenite, pyrite, and chalcopyrite were formed under low-fO2 and low-pH conditions [58]. According to Table 3, the average δ34SV-CDT value for the seven pyrite samples collected from the Tieling deposit is 0.1‰, and the δ34SV-CDT value for one chalcopyrite sample is -0.1‰. The basic sequence is consistent with the δ34S enrichment condition of δ34SPy>δ34SCcp at isotopic equilibrium, indicating that the mineral S isotopes had reached equilibrium [59]. Therefore, the S isotopic compositions of pyrite are close to the total S isotopic compositions of the hydrothermal system and can be used to trace S sources. The overall range of the δ34SV-CDT values of sulfides in the Tieling deposit is narrow, indicating that the S sources of sulfides deposited in the ore-forming hydrothermal fluids were undiversified. The δ34SV-CDT values are consistent with those of felsic magma [60] and other representative deposits related to magmatism [14, 16, 25, 39, 54, 56, 61, 62], indicating that the sulfur in the Tieling deposit was mainly derived from Late Carboniferous felsic magma (Figure 12).Figure 12
δ34SV-CDT values of ore-forming fluids at Tieling and other major deposits in eastern Tianshan. Sulfur isotopic compositions of global seawater in the Late Carboniferous were modified after Holser [63]. Sulfur isotopic compositions of representative deposits were modified after Han et al. [14], Wang et al. [16], Zhang et al. [25], Sun et al. [39], Zhang et al. [54], Wang et al. [56], Dai et al. [61], and Zhao et al. [62].


## 6.1.1. Sources of Hydrothermal Fluid

The fluid inclusions show that the ore-forming fluid has the characteristics of a relatively medium-low temperature, medium-high salinity, and medium-high density and represents a NaCl-H2O system. The average corrected mineralization temperatures of stage II and stage III range from 268°C to 225°C, which is consistent with the equilibrium temperature of sulfur isotopes (275°C) and indicates that the corrected mineralization temperature is within the acceptable error range. The δ18O values of quartz in the Tieling deposit range from 8.8‰ to 9.5‰, with an average value of 9.1‰ (Table 2), which is consistent with those of crustal remelting granite (10.0–12.0‰ [49]), indicating that the formation of hydrothermal quartz was associated with Carboniferous felsic intrusive rocks and was derived from magmatic fluids. The δD values of the fluids in the Tieling deposit mostly range from −79.5‰ to −63.3‰ (Table 3) and approach those of magmatic water and meteoric water [50, 51]. The H-O isotope data of stages II and III plot between the primary magmatic water field and the meteoric water line (Figure 11), which is similar to other deposits in the same metallogenic belt [25, 52–57], indicating that the ore-forming fluids of the Tieling Cu-Mo deposit were derived from Carboniferous magmatic hydrothermal fluids and then mixed with meteoric water.Figure 11
δDfluid vs. δ18Ofluid values from various stages in the Tieling Cu-Mo deposit. Fields for magmatic and metamorphic water are from Taylor [50] and Sheppard [51]. The data of previous studies were referenced from Zhang et al. [54], Zhang et al. [25], Liu et al. [55], Wang et al. [56], and Li et al. [57].


## 6.1.2. Sources of Sulfur

The sulfide assemblage in the Tieling deposit is dominated by molybdenite and pyrite with minor chalcopyrite, and no sulfate minerals have been detected. Therefore, the hydrothermal system during the ore-forming process in the Tieling deposit was dominated by H2S. Molybdenite, pyrite, and chalcopyrite were formed under low-fO2 and low-pH conditions [58]. According to Table 3, the average δ34SV-CDT value for the seven pyrite samples collected from the Tieling deposit is 0.1‰, and the δ34SV-CDT value for one chalcopyrite sample is -0.1‰. The basic sequence is consistent with the δ34S enrichment condition of δ34SPy>δ34SCcp at isotopic equilibrium, indicating that the mineral S isotopes had reached equilibrium [59]. Therefore, the S isotopic compositions of pyrite are close to the total S isotopic compositions of the hydrothermal system and can be used to trace S sources. The overall range of the δ34SV-CDT values of sulfides in the Tieling deposit is narrow, indicating that the S sources of sulfides deposited in the ore-forming hydrothermal fluids were undiversified. The δ34SV-CDT values are consistent with those of felsic magma [60] and other representative deposits related to magmatism [14, 16, 25, 39, 54, 56, 61, 62], indicating that the sulfur in the Tieling deposit was mainly derived from Late Carboniferous felsic magma (Figure 12).Figure 12
δ34SV-CDT values of ore-forming fluids at Tieling and other major deposits in eastern Tianshan. Sulfur isotopic compositions of global seawater in the Late Carboniferous were modified after Holser [63]. Sulfur isotopic compositions of representative deposits were modified after Han et al. [14], Wang et al. [16], Zhang et al. [25], Sun et al. [39], Zhang et al. [54], Wang et al. [56], Dai et al. [61], and Zhao et al. [62].


## 6.2. Mineralization Age and Ore-Forming Process

In the early Paleozoic, porphyry Cu-Mo-Au deposits formed under the northward subduction of the Kanggur ocean basin, such as Sanchakou [64], Sanchakouxi [35], and Yudai [30]. During the Early Carboniferous, porphyry Cu-Mo deposits in the northern Kanggur belt, such as Yuhai and Tuwu [65, 66], formed under the north-south bidirectional subduction of the Kanggur ocean basin. At the same time, a series of iron ores related to magmatism were formed in the southern Kanggur belt, including those of the Bailingshan [67], Hongyuntan [39], and Duotoushan [68]. The ductile shear gold deposits were formed in Late Carboniferous [69], followed by abundant magmatic sulfide Cu-Ni under the postcollisional extensional environment of the Early Permian [70, 71]. After approximately ca. 240 Ma, porphyry Mo deposits related to Triassic granite porphyry in a postcollisional environment were formed, including the Baishan and Donggebi deposits [72, 73]. The zircon U-Pb age from ore-bearing granite porphyry yields a concordant age of 298.4±0.7Ma, which is consistent with the molybdenite Re-Os isochron age (299.0 ± 7.7 Ma, in publishing). The chronology data of the two groups within error indicate that the Tieling Cu-Mo deposit was decidedly formed during the Late Carboniferous.Previous studies have shown that the iron orebodies taking tabular or lensoid shapes of the Tieling deposit were hosted in monzogranite and granodiorite along fractures [42]. The formation of the iron orebodies was considered related to the Bailingshan complex generated by the southward subduction of the Kanggur oceanic plate beneath the Yili–Central Tianshan block during 324 to 303 Ma [42, 67], and Cu-Mo mineralization was supposed to have formed later than Fe mineralization. Therefore, the mineralization process of the Tieling deposit has been described as two distinct metallogenic periods, including Fe and Cu-Mo periods. The iron orebodies related to volcanic rocks were formed first in the strata during the subduction stage of the early Late Carboniferous [42]. With the emplacement of the Bailingshan complex, iron orebodies were formed in monzogranite and granodiorite and partially in the contact zone with skarnization (Figure 13(a)). Magnetite was found in the later basic dikes [37]. At the end of the Late Carboniferous, the hydrothermal fluids released from the ore-bearing granite porphyry in the late crystallization stage were mixed with meteoric water, resulting in precipitation mineralization in favourable structural positions (Figure 13(b)).Figure 13
The metallogenic model of the Tieling copper-molybdenite deposit: (a) iron mineralization period in the early Late Carboniferous; (b) copper-molybdenum mineralization at the end of the Late Carboniferous.
(a)(b)


## 6.3. Geological Significance

The Mo deposits mainly include (W-/Be-) Mo and Cu-Mo types in northern Xinjiang on the southwestern margin of the CAOB (Table4). The (W-/Be-) Mo-type deposits were formed in the Triassic period resulting from postcollisional orogeny and mainly distributed in Altay [74, 75] and eastern Tianshan [14, 25, 76, 77]. The (W-/Be-) Mo-type deposits distributed in West Junggar formed in the transition condition [78–80]. In addition, the Cu-Mo-type deposits formed before the Carboniferous were widely distributed in the northern region of Xinjiang [78–82]. All of them, including Suoerkuduke, Xilekuduke, Yulekenhalasu, and Mengxi in East Junggar [78, 79, 82–85]; Baogutu in West Junggar [86]; Dabate, Lailisigaoer, and Kendenggaoer in West Tianshan [87–91]; and Tuwu-Yandong, Yuhai, and Sanchakou in East Tianshan [17, 64–66], were related to subduction-related accretion orogeny. Notably, Mo mineralization in the eastern Tianshan was concentrated in the Triassic and before the Early Carboniferous, with the (W-/Be-) Mo type related to collisional orogeny and the Cu-Mo type related to subduction-related accretion orogeny (Figure 14). However, no significant Cu-Mo deposits were found in the transitional time between the Triassic and Early Carboniferous in eastern Tianshan. Perhaps more attention should be given to prospecting because there are abundant contemporaneous Cu-Mo deposits in West Junggar [86], East Junggar [79, 82], and West Tianshan [88, 89, 91, 92].Table 4
Molybdenite Re-Os isochron ages of Mo deposits in northern Xinjiang, NW China.
No.DepositTypeMetalSizeMethodAge (Ma)ReferenceAltay1AsikaertePorphyryBe, MoLargeMolybdenite Re-Os218.6±1.3228.7±7.1Wang et al. [74]Liu et al. [75]East Junggar2SuoerkudukeSkarnCu, MoMediumMolybdenite Re-Os317.1±7.6305±7Liu and Liu [82]Wan et al. [84]3XilekudukePorphyryCu, MoMediumMolybdenite Re-Os327.1±2.9Long et al. [81]4YulekenhalasuPorphyryCu, MoMediumMolybdenite Re-Os331.5±4.8357.3±5.2376.9±2.2Xiang et al. [85]Xue et al. [86]5MengxiPorphyryCu, MoMolybdenite Re-Os411.6±3.2Qu et al. [87]West Junggar6SuyunhePorphyryMoGiantMolybdenite Re-Os294.4±1.7Zhong et al. [78]7BaogutuPorphyryCu, MoLargeMolybdenite Re-Os310±3.6Song et al. [89]8HongyuanPorphyryMoMolybdenite Re-Os294.6±4.6314.3±1.9Li [79]Yan et al. [80]West Tianshan9DabatePorphyryCu, MoSmallMolybdenite Re-Os300.3±2.1301±20Li [92]Zhang et al. [91]10LailisigaoerPorphyryCu, MoSmallMolybdenite Re-Os379.9±8.3359±8Zhu et al. [90]Li et al. [93]11KendenggaoerSkarnCu, MoSmallMolybdenite Re-Os313.9±2.5Jia [88]East Tianshan12Tuwu-YandongPorphyryCu, MoLargeMolybdenite Re-Os323±2343±26Rui et al. [65]Zhang et al. [66]13DonggebiPorphyryMoGiantMolybdenite Re-Os233.2±2.2231.1±1.5231.9±6.5234.3±1.6Wu et al. [72]Tu et al. [94]Wu et al. [76]Han et al. [14]14KumutageSkarnMoMolybdenite Re-Os319.1±4.5Zhang et al. [95]15YuhaiPorphyryCu, MoSmallMolybdenite Re-Os355.7±2.4Wang et al. [17]16SanchakouPorphyryCu, MoMolybdenite Re-Os416±6.4358±6.2Lin et al. [64]Liao and Lv [35]17XiaobaishitouSkarnW, MoMolybdenite Re-Os239.7±3.6251.4±3.6251.1±1.6Deng et al. [96]Li et al. [57]18BaishanPorphyryMoGiantMolybdenite Re-Os224.8±4.5227±4.3223.2±2.7Zhang et al. [25]Zhang et al. [73]Tu et al. [15]19TielingPorphyryCu-MoMolybdenite Re-OsZircon U-Pb299.0±7.7298.4±0.7UnpublishedThis studyFigure 14
Re-Os isotopic ages from the Mo deposits in northern Xinjiang, NW China.


## 7. Conclusions

(1)
The Tieling deposit is a porphyry system that exhibits three ore-forming stages, including quartz+K-feldspar+pyrite±molybdenite±magnetite (stage I), quartz+molybdenite+pyrite+chalcopyrite (stage II), and quartz+pyrite±molybdenite±epidote (stage III)(2)
The ore-forming fluids of the Tieling Cu-Mo deposit are characterized by medium-low temperatures (224 to 355°C in stage II and 201 to 246°C in stage III), medium-high salinities (7.2–17.2 wt% NaCl equiv. of stage II and 5.6 to 9.6 wt% NaCl equiv. of stage III), and a H2O-NaCl composition(3)
The H-O-S isotopes indicate that the ore-forming fluids were derived from a mixture of magmatic hydrothermal water and meteoric water and the ore-forming materials were derived from Late Carboniferous felsic magma(4)
The zircon U-Pb of ore-bearing granite porphyry yields a concordant age of298.4±0.7Ma, indicating that the Tieling Cu-Mo deposit was a rare metallogenic event in the Late Carboniferous of the eastern Tianshan, which should be given more attention for prospecting



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