Geology, fluid inclusions, and geochemistry of the Zhazixi Sb–W deposit, Hunan, South China

Accepted Manuscript Geology, fluid inclusions, and geochemistry of the Zhazixi Sb–W deposit, Hunan, South China Guo-Ping Zeng, Yong-Jun Gong, Xin-Lu Hu, Suo-Fei Xiong PII: DOI: Reference:

S0169-1368(16)30462-0 http://dx.doi.org/10.1016/j.oregeorev.2017.08.001 OREGEO 2298

To appear in:

Ore Geology Reviews

Received Date: Revised Date: Accepted Date:

2 August 2016 26 July 2017 1 August 2017

Please cite this article as: G-P. Zeng, Y-J. Gong, X-L. Hu, S-F. Xiong, Geology, fluid inclusions, and geochemistry of the Zhazixi Sb–W deposit, Hunan, South China, Ore Geology Reviews (2017), doi: http://dx.doi.org/10.1016/ j.oregeorev.2017.08.001

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Geology, fluid inclusions, and geochemistry of the Zhazixi Sb–W deposit, Hunan, South China Guo-Ping Zenga, Yong-Jun Gonga, *, Xin-Lu Hua, Suo-Fei Xionga, b a b

Faculty of Earth Resources, China University of Geosciences, Wuhan, 430074, PR China Collaborative Innovation Center for Exploration of Strategic Mineral Resources, Wuhan, 430047,

PR China

Abstract The Zhazixi Sb–W deposit in the Xuefeng uplift, South China, exhibits a unique metal association of W and Sb, where the W orebodies are hosted by interlayer fractures and the Sb orebodies are contained within NW-trending faults. This study proposes that the W and Sb mineralization took place in two separate periods. The mineral paragenesis of the W mineralization reveals a mass of quartz, scheelite and minor calcite. The mineral assamblage of the Sb mineralization developed after W mineralization and consists of predominantly quartz and stibnite, and small amounts of native Sb, berthierite, chalcostibnite, pyrite, and chalcopyrite. Fluid inclusions in quartz and coexisting scheelite are dominated by two-phase, liquid-rich, aqueous inclusions at room temperature. Microthermometric studies suggest that ore-forming fluids for W mineralization are characterized by moderate temperatures (170–270 °C), low salinity (3–7 wt.% NaCl equiv.), low density (0.75–0.95 g/cm3), and moderate to high pressure (57.2–99.7 MPa) and these fluids experienced a cooling and dilution evolution during W mineralization. Ore-forming fluids for Sb mineralization are epithermal types with low temperatures (150–230 °C), low salinity (4–6 wt. % NaCl equiv.), moderate density (0.82–0.94 g/cm3), and high pressure (42.2–122.5 MPa) and

these fluids display an evident decline in homogenization temperature during Sb mineralization. Laser Raman analyses of the vapor phase indicate that the ore-forming fluids for both W and Sb mineralization contain a small amount of CO2. The ore-forming fluids for Sb mineralization are identified as predominantly originating from the continental crust, as suggested by the low

3

He values

(0.009×10-12 cc.STP/g) and 3He/4He ratios (0.002–0.056 Ra) as well as high values (1.93×10 -9 cc.STP/g) and

40

36

Ar

Ar/36Ar ratios (909.5–2279.7). The source of S is

identified to be the Neoproterozoic Wuqiangxi Formation, as traced by the δ34SV-CDT values of stibnite (3.1–9.4‰). The (15.456–15.681), and

208

Pb/204Pb (37.643–40.222),

207

Pb/204Pb

206

Pb/204Pb (17.093–20.042) ratios suggest a mixture of lower

crustal and supracrustal Pb sources. It is thus concluded that the ore genesis of the Zhazixi Sb–W deposit is related to the intracontinental orogeny during the early Mesozoic. Fluid mixing is considered to be the critical mechanism involved in W mineralization, whereas a fluid cooling process is responsible for Sb mineralization. Furthermore, the absence of Au is attributed to the low Σas content in Sb-mineralizing fluids.

Keywords: Zhazixi Sb–W deposits; Fluid inclusions; S–Pb–He–Ar isotopes; Ore genesis; South China

* Corresponding author at: 388, Lumo Road, Hongshan District, China University of Geosciences, 430074, Wuhan, PR, China. Tel.: +86 18802786531. E-mail address: [email protected] (Y.-J. Gong)

1. Introduction

Most Sb-bearing deposits worldwide occur as monometallic Sb deposits (Akçay, 2006; Fan et al., 2004a; Wu, 1993) or Au–Sb deposits (Brogi and Fulignati, 2012; Dill et al., 1995; Dill, 1998; Hinsberg et al., 2003; Neiva et al., 2008), with a small number of sulfphoantimonites-base metal deposits, which are well known in the Dachang deposit in South China (Fan et al., 2004b). Numerous studies have been conducted on the geologic, mineralogic, geochemical, and metallogenic features of the Sb-bearing deposits (Dill, 1985; Hagemann and Lüders, 2003; Obolensky et al., 2009; Yang et al., 2009; Zaw et al., 2007). In addition, many Sb-bearing deposits have a unique element association of Sb–W±(Au) in areas such as Western Thailand (Dill et al., 2008), Spain (Arribas and Gumiel, 1984), Western Carpathians (Chovan et al., 1999), Russia (Afanas'eva et al., 1994; Prokof'yev et al., 1993; Prokof'yev et al., 1995), Guatemala (Guillemette and Williams-Jones, 1993), Central Turkey (Akçay, 1994; Akçay et al., 1995), and South China (Gu et al., 2012; He et al., 1996; Peng and Frei, 2004; Murao et al., 1999; Yang and Blum, 1999). Akçay (1994), Dill et al. (2008) and Prokof'yev et al. (1995) proposed that scheelite and Sb-bearing minerals precipitated from different hydrothermal stages and that epithermal Sb mineralization overprinted mesothermal W mineral assemblages. However, studies from China have typically focused on Sb and ignored W mineralization and the relationship between Sb and W. In addition, some studies have determined that Sb and W precipitated in a single metallogenic process (Chen, 2012; Gu et al., 2007; Peng et al., 2003a, 2003b), even though approximately 100

Sb–W±(Au) ore deposits and occurrences have been found in South China (Yang and Blum, 1999). The Zhazixi Sb–W deposit in the Xuefeng uplift, South China, is marked by the Sb mineralization of its lode and its large-sized fracture-filled W mineralization (Peng et al., 2008, 2010; Wang et al., 2012). This deposit contains proven resources of 25.07×104 tonnes of Sb and 13,401 tonnes of WO3 with average grades of 9.46% Sb and 0.824% WO3. In this paper, we determine that two separate metallogenic processes were involved in the occurrences of Sb and W and provide a comprehensive account of the geology, fluid inclusions, and isotopic geochemistry of both Sb and W mineralization.

2. Regional geology

The Zhazixi Sb ore belt containing the Zhazixi Sb–W deposit is located in the central part of the Xuefeng uplift, which lies between the Yangtze and Cathaysia blocks in South China. The Xuefeng uplift trends to the northeast in its southwestern part and is orientated to the east in its northeastern part (Fig. 1a) (HBGMR, 1988). The Mesoproterozoic Lengjiaxi Group and the Neoproterozoic Banxi Group constitute the basement of the Xuefeng uplift (Liu, et al., 2015; Wang et al., 2014; Yao et al., 2014). The Grenville orogeny took place between ~1000 Ma and ~800Ma generated the regional tectonic framework and deformed the Proterozoic rocks extensively and metamorphosed them into sub-greenschist facies (Bai et al, 2011; Li et al., 2008; Li et al., 2009; Qiu, et al., 2000; Wu et al., 2006; Zhai, 2013). Lines of

evidence regarding its magmatism, structures, metamorphic deformation, and paleomagnetism suggest that the Xuefeng uplift was involved in multiple tectonic movements (Chen et al., 2001; Otofuji et al., 1998; Shu, 2012), including the early Paleozoic and Mesozoic intracontinental orogeny (Ren, 1990; Shu et al., 2008). The lithologies of the Zhazixi Sb ore belt are predominantly of the Neoproterozoic to Paleozoic in age (Fig. 1b). The Neoproterozoic Madiyi and Wuqiangxi Formations are the oldest units exposed in the belt. The Madiyi Formation has a thickness greater than 1.3 km and features green and red low-grade metamorphic slates. Above the Madiyi Formation, the Wuqiangxi Formation is composed of 2.4-km-thick sub-greenschist facies metamorphic detrital and pyroclastic rocks, which can be subdivided into two lithological parts (He et al., 1996). However, the moraine-breccia of Ediacaran and the black shale and carbonate of the Paleozoic are discordant on the Wuqiangxi Formation. The NE-trending F1 and F2 faults are the most important ore-controlling structures of the Zhazixi ore belt. The NE-trending faults spread 65–100 km along the strike and dip steeply toward the southeast. Fault zones are 2–50 m wide and filled by wall rock lenses and mylonite with widespread silicification and sericitization. Secondary NE-, NW-, and EW-trending faults are also common in the ore belt, whereas a few NE-trending insignificant folds occur in the Ediacaran or Paleozoic rocks. Magmatic intrusions are scarce in this region and are represented by minor lamprophyre dykes in the hanging wall of the F1 fault. Sb±W deposits are widespread throughout the Zhazixi ore belt. Most of these

deposits are hosted in the metamorphic clastic rocks of the Wuqiangxi Formation (e.g., Zhazixi Sb–W and Tongxin Sb deposits; Bao et al., 1998), although a few Sb±W deposits occur in the Ediacaran moraine-breccia and Paleozoic black shale (e.g., the Zengjiaxi Sb–W and Songxi Sb deposits; Xie et al., 2015). Silicification and sericitization are the hydrothermal alterations that spatially and genetically related to mineralization in this belt. Their mineralized zones are dominated by lenticular orebodies. Scheelite and stibnite are the dominant ore minerals. The Sm–Nd isochron age of scheelite (227.3±6.2 Ma, Wang et al., 2012) has been interpreted to be the metallogenic age of these Sb±W deposits.

3. Deposit geology

The Wuqiangxi Formation is the most important ore-bearing lithological unit in the Zhazixi Sb–W deposit. The lower part of the formation is composed of sandstone, greywacke, and quartz sandstone, and the upper part consists of tuff, tuffaceous sandstone, slate, and thick-bedded sandstone, which serve as the major wall rocks for the W and Sb orebodies. The Wuqiangxi Formation forms a monoclinic fold with a steady attitude, striking to NE and dipping toward SE with dips of 41°–48°. The moraine-breccia of Ediacaran and black shale of the Cambrian are separated from the Wuqiangxi Formation by faults and are located both on the hanging and foot walls. The Zhazixi Sb–W deposit is dominated by interlayer fractures and NW-trending faults (Fig. 2). The former are composed of slip interfaces along the boundary between the thick-bedded sandstone and tuff and the secondary joint fissures in the

thick-bedded sandstone. The latter consist of the F3 fault and its secondary faults on the hanging wall. The F3 fault extends for about 2.6 km along 295° and dips toward the northeast with dip ranges between 52°–80°. Horizontal and vertical sinistrally reverse-movements with 80-meter displacements are present on the F3 fault, and stibnite is also developed within it. Secondary faults are generally NW trending and converge in the deep part of the F3 fault. In addition, the interlayer fractures are evidently crosscut by the NW-trending faults, suggesting that the interlayer fractures predate the NW-trending faults (Figs. 2 and 3). It is considered that these structures may have been triggered by the early Mesozoic orogeny.

4. Mineralization

W and Sb mineralization in the Zhazixi deposit are controlled by different structures, and each display different mineralization features. The W orebodies are restricted to the interlayer fractures and are predominantly composed of scheelite + quartz veins. In contrast, the Sb orebodies are hosted by the NW-trending faults and mainly consist of quartz + stibnite veins.

4.1. W mineralization

To date, 11 economic W orebodies have been discovered above the −160 m level within a 10–250 m wide zone on the hanging wall of the F3 fault. The W orebodies mainly occur as lenses and are usually parallel to the wall rocks with striking 20°–58°

NE and dipping 57°–69° SE. The W orebodies are generally 30–200-m long along the strike and spread obliquely to a depth of 320 m along the plunge. Scheelite + quartz veins are hosted by the slip interfaces and the joint fissures (Fig. 4a–4c). Some angular wall rock breccias were also discovered in W orebodies (Fig. 4d). The W orebodies in the Zhazixi Sb–W deposit are offset by the NW-trending Sb mineralization (Figs. 2 and 3). Scheelite is the only ore mineral within W mineralization. Gangue minerals include massive quartz, minor chlorite, and calcite. Hydrothermal alteration is well-developed and characterized by intensive silicification with minor chloritization and carbonate alteration. Silification has resulted in quartz veins or stockworks, and subhedral or anhedral quartz grains coexisting with scheelite in scheelite + quartz veins (Figs. 4e–4g). Chloritization developed in the boundary between the scheelite + quartz veins and wall rocks (Fig. 4h). Evidence of carbonate alteration is rarely visible on hand specimens, but coarse-grained euhedral or subhedral calcite grains coexisting with scheelite and quartz are evident with microscope analysis (Fig. 4i).

4.2. Sb mineralization

Sb mineralization strikes 290°–330° NWW, dips 55°–88° NE to NNE and exhibits reversed horse-tail structures in a representative cross section (Fig. 3). Whereas the Sb orebodies are sparse, thin and widely spaced in the shallow part, they are dense, thick and narrowly spaced in the deep part. The Sb orebodies all converge toward the deep site of the F3 fault. Lateral Sb orebodies are also arranged regularly

and are intense near the F3 fault but become weaker at a distance from the fault (Fig. 3). The F3 fault is also mineralized with stibnite, suggesting its role as a conduit for Sb-bearing fluids. The No.1 Sb orebody is the largest of its kind in the ore district. It is 80–235 m along the strike, 818 m along the plunge and 0.12 to 2.96 m thick. The Sb grade spans from 0.25% to 44.27%, with an average of 11.07%. Some Sb orebodies are generally confined by compressive structural planes (Fig. 5a) and the internal wall rocks have been transformed into lenses, confirming that a compressive tectonic activity preceded Sb mineralization. However, fragments of the wall rock lenses have been cut by the stibnite + quartz stockwork, indicating an extensional regime during Sb mineralization (Fig. 5b). Mineralized zones are dominated by stibnite, with a small amount of native Sb, berthierite, chalcostibnite, pyrite, and chalcopyrite (Figs. 5j–5l). Gangue minerals primarily contain quartz and minor rutile. Rutile is disseminated in the wall rocks without any obvious relationship to the stibnite-bearing quartz veins. Their formation occurring either in relation to the hydrothermal circulation that preceded the Sb metallogenic period or simultaneously with Sb mineralization. Hydrothermal alteration is characterized by silicification with trace amounts of sulfidation.

Silification

is

evident

as

quartz

veins

or

stockworks

and

euhedral–subhedral quartz grains coexisting with stibnite in quartz + stibnite veins (Figs. 5c and 5f). Sulfidation occur as disseminated pyrite and chalcopyrite in wall rocks and Sb orebodies (Figs. 5g–5i).

4.3. Mineral paragenesis

Based on the mineral assemblages and crosscutting relationships of mineralizing veins (Figs. 4 and 5), the ore-forming process in the Zhazixi Sb –W deposit can be divided into two periods: a W mineralizing period and a Sb mineralizing period, both of which experienced two stages of ore formation. Given that, the entire mineralization process can be subdivided into four stages (Fig. 6). Stage I (quartz + scheelite stage) is characterized by massive quartz accompanied by a small number of subhedral–anhedral scheelite grains, where the quartz occurs as coarse, subhedral–anhedral grains. Stage II (scheelite + quartz + calcite stage) primarily consists of abundant subhedral or anhedral scheelite and a small quantity of coarse-grained subhedral or anhedral quartz and calcite (Fig. 4i). Stage III (quartz + stibnite stage) is dominated by massive quartz with minor stibnite and fine-grained anhedral pyrite (Fig.5c). Stibnite at this stage occurs occasionally as acicular crystals within quartz veins (Fig. 5f). Stage IV (stibnite + quartz stage) is marked by massive stibnite and trace amounts of quartz with minor disseminated fine-grained anhedral pyrite, chalcopyrite, native Sb, chalcostibnite, and berthierite. Polysynthetic twins of stibnite can be observed under a microscope. Chalcopyrite occurs as fine, anhedral grains and is replaced by stibnite (Fig. 5i). Native antimony is irregular in shape and replaces stibnite (Figs. 5i and 5j). Chalcostibnite associated with stibnite occurs as laths and can replace scheelite of stage II (Fig. 5k). Berthierite appears as isolated grains in the quartz grains of stage II (Fig. 5l).

5. Samples and analytical methods

All samples were collected from underground exposures of the Zhazixi Sb –W deposit (Fig. 3). To characterize the mineralogy, textures, and mineral paragenesis of these samples, polished blocks and thin sections were examined by reflected and transmitted light microscopy. The fluid inclusions in scheelite and quartz that coexists with scheelite and stibnite were examined. Microthermometric measurements were performed in the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences using a Linkam THMSG 600 programmable heating-freezing stage mounted on a Leica microscope. The uncertainty of the temperature measurements in this study was approximately ±0.2 °C below 50 °C and ±2 °C above 100 °C and a heating rate of 0.1 °C/min was adopted to approach the ice-melting and homogenization temperatures. The compositions of the selected fluid inclusions were determined using laser Raman spectroscopy at the State Key Laboratory of Geological Process and Mineral Resources of China University of Geosciences, Wuhan. Stibnite grains were collected from stage IV stibnite + quartz veins and crushed down to a 40–60 mesh size. Mineral separates were handpicked to a purity of more than 99% using a binocular microscope. He and Ar isotopic compositions of four stibnite samples were measured using a Noblesse mass spectrometer at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS), Beijing, based

on the detailed analytical procedure described by He et al. (2011) and Zhu et al. (2013). The stibnite crystals were crushed in vacuum in a one-step process at about 2000 psi to extract the noble gases. Line blanks were run before the samples. Helium blanks were negligible (3He blank <3×10-17 ccSTP) and Ar blanks were in only trace quantity (40Ar blank <4×10-11 ccSTP), within about 0.1% of the signals. The standard air obtained by reducing the pressure and purifying the air was measured, and the ratios of 3He/4He and

40

Ar/36Ar were 1.4×10-6 and 295.5, respectively. Aliquots of

about 5×10 -10 ccSTP 40Ar and from 3×10 -7 to 3×10 -8 ccSTP 4He were introduced to the mass spectrometer and measured. The uncertainty of the average 3He/4 He ratio was better than 5%. The data was corrected for blanks and calibrated using air shots and helium standards. Seven stibnite samples were selected for S and Pb isotopic studies. The S and Pb isotopic compositions were measured at the Geological Analysis Laboratory in the Beijing Research Institute of Uranium Geology, China, using the analytical procedures described by Wang et al. (2013) and Yang et al. (2012). S isotopic compositions were analyzed on a MAT 251E gas mass spectrometer by using Cu2O to oxidize the stibnite. An in-run analytical precision of ±0.2‰ was calibrated using regular analyses of internal δ34S standards. Pb isotopic ratios were determined on a MAT 261 mass spectrometer. Stibnite samples were dissolved using 14.0 N ultrapure HNO3 and then dried and transformed into chloride using 12.0 N ultrapure HCl. Pb was separated and purified using anion exchange resin. The measured ratios (2σ) of 208

Pb/206Pb,

207

Pb/206Pb, and

207

Pb/206Pb obtained from running the international

standard NBS981 were 2.16736±0.00066, 0.91488±0.00028, and 16.9386±0.0131, respectively.

6. Results

6.1. Fluid inclusion petrography

To understand the physico-chemical nature of the ore-forming fluids responsible for W and Sb mineralization, representative samples of scheelite and quartz coexisting with scheelite and stibnite were selected for fluid inclusion analysis. Primary, pseudosecondary, and secondary fluid inclusions were identified using the criteria proposed by Roedder (1984). Primary inclusions occur as inclusion assemblages, or in random isolation. Pseudosecondary inclusions have a linear distribution in crystal, whereas secondary inclusions occurring as trails penetrating the crystal boundary are present. Compared to pseudosecondary and secondary inclusions, there are small quantities of primary inclusions in the samples from the Zhazixi Sb–W deposit. Only those recognized as primary fluid inclusions were selected for the Raman spectroscopic and microthermometric analyses in this study. Primary inclusions in the samples from the four mineralizing stages mainly occur as two-phase liquid-rich aqueous inclusions at room temperature (25 °C), while vapor-rich, vapor-pure, and liquid-pure aqueous inclusions are rare in the Zhazixi Sb–W deposit. The two-phase liquid-rich fluid inclusions share similar petrographic features in the four mineralization stages. They

have diameters of 2–13 µm and are usually irregular, tubular, or rounded rectangle forms. The boundaries of the fluid inclusions are relatively clear in quartz but black in scheelite (Fig. 7), and vapor bubbles range from 5–25% percent of total volume without any obvious variation between different mineralization stages.

6.2. Raman spectroscopy

To study the vapor phase compositions of ore-forming fluids, Raman spectroscopic analyses of fluid inclusions in quartz related to W and Sb mineralization were conducted, respectively. The vapor bubbles of fluid inclusions in quartz I show a weak signal of CO2 (Fig. 8a), whereas that in the quartz III present a significant peak of CO2 (Fig. 8b). These results suggest that the W metallogenic fluids in this deposit contain rare CO2, whereas the Sb metallogenic fluids possess only a small amount of CO2.

6.3. Microthermometry

6.3.1. Homogenization temperature and salinity Of the four mineralization stages in the study, homogenization temperature (Th) and final ice-melting temperature (Tm-ice) were measured only on the two-phase liquid-rich aqueous inclusions recognized as primary inclusions in quartz and scheelite. Salinities were calculated from the final ice-melting temperatures (Tm-ice) using the revised equation of Bodnar (1993) (Table 1).

All primary fluid inclusions of the four generations were homogenized to a liquid phase during the heating process. The fluid inclusions in quartz I were homogenized at temperatures ranging from 209.2 °C to 298.2 °C. They present a tower-type distribution mostly ranging within 230 °C to 270 °C and Tm-ice values vary from −5.8 °C to −3.2 °C, which correspond to salinities of 5.26–8.95wt.% NaCl equiv., with most salinities at around 6–7 wt.% NaCl equiv. (Figs. 9a and 9b). The fluid inclusions in quartz II became homogenized at temperatures ranging between 161.7 °C and 257.3 °C, with a mode range of 170–210 °C. The transformational salinities varied from 2.90–7.45 wt.% NaCl equiv. (concentrated within 3–5 wt.% NaCl equiv.), according to the final ice-melting temperature of −4.7 °C to −1.7 °C. Homogenization temperatures of the fluid inclusions in scheelite ranged from 204.2 °C to 305.9 °C (concentrating within 230–250 °C). The fluid inclusions yield final ice-melting temperatures of −4.0 °C to −1.4 °C. Calculated salinities are 2.41–6.54 wt. % NaCl equiv., with mode values between 4 and 6 wt.% NaCl equiv. (Figs. 9a and 9b). The fluid inclusions in quartz III homogenized within a temperature range of 146.5–279.0 °C, mostly falling between 190 °C and 230 °C. Their salinities are 2.57–7.17 wt.% NaCl equiv., with the majority changing from 4 to 6 wt.% NaCl equiv., calculated by the Tm-ice values of −4.5 oC to −1.5 oC (Figs. 9c and 9d) The total homogenization temperatures of the two-phase liquid-rich aqueous inclusions in quartz IV vary within the range of 132.5 °C to 261.0 °C, and most fall

within the range of 150 °C and 190 °C. The final ice-melting temperature values vary from −4.4 °C to −1.4 °C. The corresponding salinities are 2.41–7.17 wt.% NaCl equiv., mostly in a range of 4–6 wt.% NaCl equiv. (Figs. 9c and 9d).

6.3.2. Ore-forming fluids density, pressure and depth The homogenization temperatures and salinities of liquid-rich aqueous inclusions were utilized to calculate the densities of ore-forming fluids using the FLINCOR software proposed by Brown (1989). This was because there was an absence of multiphase daughter-minerals containing inclusions and three-phase CO2-rich inclusions. The estimated densities of the fluid inclusions in quartz I range from 0.85 g/cm3 to 0.91 g/cm3. Most densities of the fluid inclusions in scheelite and coexisting quartz II range between 0.75–0.90 g/cm3 (mostly higher than 0.80 g/cm3) and 0.82–0.95 g/cm3 (mostly higher than 0.90 g/cm3), respectively. The fluid inclusions in the quartz III present densities between 0.82 g/cm3 and 0.94 g/cm3. The fluid inclusions of quartz IV have densities in the range of 0.86 g/cm3 to 0.94 g/cm3, and most densities are higher than 0.90 g/cm3. Isochores were constructed based on temperature and pressure parameters acquired using the FLINCOR software (Zhang and Frantz, 1987). As no independent geothermobarometer was available to determine the trapping temperatures, we selected isochores with the maximum densities to reach the trapping pressures. The maximum values of mode range of homogenization temperatures from the four metallogenic stages were selected to estimate ore-forming pressures (Fig. 10). The

plot shows that quartz I formed under a pressure of 99.7 MPa; the forming pressure of quartz II was less than 83.6 MPa, and that of coexisting scheelite dropped to 57.2 MPa. In addition, quartz III precipitated at around 122.5 MPa, whereas the forming pressure of quartz IV declined to 42.2 MPa. Since mineral assemblages of W and Sb mineralization occur predominantly as veins, the mineralization depths are estimated based on overlying hydrostatic pressure. Results suggest that the formation depth of quartz I was around 10.17 km; quartz II formed at a depth of around 8.53 km, whereas the coexisting scheelite precipitated at a relative shallower depth of 5.84 km. Quartz III crystallized at a deeper site of about 12.50 km and was then uplifted to 4.31 km to form quartz IV. The Sb mineralized over a larger range of depths than the W mineralization, which is consistent with the occurrences of the Sb and W orebodies in the Zhazixi Sb–W deposit.

6.4. Noble gas isotopes

Stibnite samples selected in this study for noble gas isotopic analyses are euhedral grains without subsequent deformation. All the selected stibnite have a spatial association with quartz in stibnite + quartz veins. Thus, the fluids extracted from these veins reflect the primary Sb-mineralizing fluids. The noble gas isotopic compositions of fluid inclusions in stibnite (Table 2) show that 4He and

40

Ar are the dominant isotopes of He and Ar, with concentrations

varying from 2.2×10-7 to 9.0×10-7 ccSTP/g and from 17.5×10 -7 to 33.6×10-7 ccSTP/g, respectively. 3He and

36

Ar are predominantly primordial and are predominantly

derived from the deep earth interior. 3He and

36

Ar of stibnite samples range from

0.002×10-12 to 0.016×10 -12 ccSTP/g and from 1.47×10 -9 to 1.93×10-9 ccSTP/g, respectively. The 3 He/4 He ratios were from 0.002 to 0.056 Ra (Ra = 1.01 × 10−6 for air), and 40Ar/36Ar ratios were 909.5–2279.7 (Table 2).

6.5. S and Pb isotopes

The δ34SV-CDT values of stibnite ranged from 3.1‰ to 9.4‰ (average of 5.2‰) (Table 3). The δ34SV-CDT values reported by previous studies (Bao and Bao 1991, and Bao et al., 1998) were 4.7‰ to 10.4‰, and are thus roughly consistent with the values obtained in this study. Pb isotopic data of stibnite (Table 3) show that the 206

208

Pb/204Pb,

207

Pb/204Pb, and

Pb/204Pb ratios were 37.643–40.222 (mean of 38.544), 15.456–15.681 (average of

15.549), and 17.093–20.042 (mean of 18.098), respectively.

7. Discussion

7.1. Nature of ore-forming fluids

7.1.1. Nature of W-forming fluids Based on structural characteristics and mineral paragenesis, it is evident that ore-forming stages I and II are associated with W mineralization. In this study, primary fluid inclusions in scheelite and coexisting quartz I and II were selected to conduct a study on the nature of W ore-forming fluids. Results show that most of the

fluid inclusions in quartz I have homogenization temperatures ranging 230–270 °C, and those in quartz II and coexisting scheelite range from 170–210 °C and 230–250 °C, respectively. Their salinities are generally less than 8.95 wt. % NaCl equiv., and decrease gradually from 6–7 wt.% NaCl equiv. to 3–6 wt.% NaCl equiv. The estimated densities of ore-forming fluids are also relatively low, with values ranging from 0.75 g/cm3 to 0.95 g/cm3. The pressures of the ore-forming fluids decrease from 99.7 MPa to 57.2 MPa during W mineralization as shown in the P–T plot,. In addition, Raman spectroscopic analysis indicates that the ore-forming fluids for W mineralization contain rare CO2. Overall, the ore-forming fluids responsible for W mineralization are characterized by moderate temperature, low salinity, low density, and medium to high pressure, with obvious declining evolutions in both homogenization temperature and salinity from stage I to stage II.

7.1.2. Nature of Sb-forming fluids Ore-forming stages III and IV are responsible for Sb mineralization. In this study, the nature of Sb mineralization fluids was identified through microthermometric studies of primary fluid inclusions in quartz III and IV associated with stibnite. Homogenization temperatures ranged from 190 °C to 230 °C in quartz III and varied between 150 °C and 190 °C in quartz IV, exhibiting epithermal-hydrothermal features throughout the Sb mineralization process. The mineral assemblages of berthierite, stibnite, and native Sb in the Zhazixi deposit are also indicative of epithermal mineralization fluids, which are consistent with antimony±gold quartz veins in

northern Portugal (Neiva et al., 2008). The calculated salinities and densities for Sb mineralization fluids were 4–6 wt. % NaCl equiv. and 0.82–0.94 g/cm3, respectively, with the estimated fluid pressures dropping from 122.5 MPa in stage III to 42.2 MPa in stage IV. Raman spectroscopic analyses also suggest that the fluids responsible for Sb mineralization contain a small amount of CO2. In summary, the Sb ore-forming fluids present epithermal hydrothermal features with low salinity, moderate density, high pressure, and a decreasing process only in the homogenization temperature. It is also considered that the fluids for Sb mineralization are cooler than those for W mineralization.

7.2. Sources of ore-forming fluids

The noble gas isotopes in the ore-forming fluids are likely to be a combination of primary and secondary noble gases. As such, the noble gas components and their concentrations could be good tracers of ore-forming fluids when secondary noble gases have been removed (Zhang et al., 2013).

7.2.1. Secondary noble gases The secondary noble gases in the measured fluids are considered to be generated by four kinds of mechanisms in relation to either cosmogenic nuclides, air-derived contamination, in situ radiogenic ingrowths of U, Th, and K after the formation of stibnite, or noble gases associated with subsequent regional metamorphism or hydrothermal alteration (Li et al., 2005; Wei et al., 2010; Wu et al., 2007; Zhang et al.,

2011). Cosmogenic nuclides and air-derived contamination are negligible with respect to the stibnite collected from underground exposures in the Zhazixi Sb–W deposit and to noble gases extracted by stepwise heating (Li et al., 2003; Zhang et al., 2013; Zhu and Peng, 2015). In addition, the absence of visible daughter U, Th, and K bearing silicates in fluid inclusions suggests that the 4He and

40

Ar injected by in situ

radiogenic ingrowths of U, Th and K may be insignificant. Furthermore, noble gases associated with subsequent regional metamorphism or alteration can also be ignored because regional metamorphism mainly occurred during the Neoproterozoic and the stibnite samples selected for the noble gas isotopic analyses are in the form of euhedral crystals without any obvious subsequent deformation or alteration. As many studies indicate that the helium diffusion is extremely slow in sulfide (e.g., pyrite, chalcopyrite, stibnite, and galena) (Baptiste and Fouquet, 1996; Burnard et al., 1999; Zhang et al., 2011), the mass fraction of helium is also likely to be negligible (Li et al., 2005). Accordingly, the measured results of noble gas isotopes in this study can be used to truly represent the primary components and concentrations of ore-forming fluids, which will then enable an evaluation of the possible sources of these fluids.

7.2.2. Sources of primary noble gases The primary noble gas components in ore-forming fluids can be obtained from three main sources: air-saturated (i.e., meteoric and marine water) fluids (ASF),

mantle, and continental crust (CC) (Burnard et al., 1999; Wei et al., 2010). Results show that the 3 He values and 3He/4He ratios (0.009×10 -12 cc.STP/g, 0.002–0.056 Ra) in stibnite samples from the Zhazixi Sb–W deposit are much lower than those of mid-ocean ride basalt (MORB) (0.0266×10-9 cc.STP/g, 7–9 Ra) (Burnard et al., 1999; Ozima and Podosek, 2002) and the upper mantle (0.174×10-9 cc.STP/g, 6–7 Ra) (Burnard et al., 1999; O'Nions and Tolstikhin, 1994), but are rather similar to those of the continental crust (with 3He/4He ratios of 0.02Ra ) (Ballentine and Burnard, 2002; Zhang et al., 2013). Overall, measured helium isotopic data show an obvious continental crust source signal (Fig. 11). The paucity of magmatic rocks in the mineralized area also eliminates any possible contribution from magmatic sources to the ore-forming fluids responsible for Sb mineralization. 3

He/4 He ratios from samples Z3254 (0.006) and Z3258 (0.002) are lower than

those of the CC. An alternative explanation for this feature may be a locally high concentration of radiogenic 4 He, which would result in low 3He/4 He ratios. However, the 3He/4He ratios from samples Z32517 (0.038) and Z3709 (0.056) are higher than those of the CC, implying the possibility of mixing with traces of the ASF. To calculate the proportion of 4He derived from the ASF, the 3He/4 He ratio of atmospheric sources of fluids was used. XASF can be used to provide a minimum estimation of the proportion of the ASF, even though most geological fluids of meteoric or marine origin contain slightly higher 4 He values and lower 3He/4He ratios than the ASF. The conventional formula utilized is as follows: XASF=[(3He/4He)−( 3He/4He)CC]/[ (3He/4He) ASF−( 3He/4He)CC].

Results suggest that 1.8−3.7% of ASF-derived helium (XASF) was added to these stibnite samples and that most of the helium was probably inherited from the CC. The

36

Ar concentration in the stibnite samples was 1.93×10-9 cc.STP/g, which is

obviously higher than that in MORB (0.074×10-9 cc.STP/g) (Burnard et al., 1999; Ozima and Podosek, 2002) or the upper mantle (0.27×10 -9 cc.STP/g) (Burnard et al., 1999; O'Nions and Tolstikhin, 1994). In addition, the

40

Ar/36Ar ratios (909.5–2279.7)

of the stibnite samples are higher than the atmospheric ratio (295.5) and represent a significant excess proportion of

40

Ar. Argon isotopic data thus indicate a mantle or

crustal origin. Therefore, by integrating these results with observations of geologic features, it is considered that the CC (the Meso-Neoproterozoic rocks or underlying basement) is more likely than the mantle to be the origin (Fairmaid et al., 2011; Kendrick et al., 2002).

7.2.3. Source of fluids for W mineralization Nd and Sr isotopic compositions of scheelite from the Zhazixi Sb–W deposit have been previously discussed by Peng et al. (2008). The initial Nd isotopic compositions of scheelite can be classified into two groups, which range from −10.2 to −14.7 and from −3.79 to +0.01, respectively. An alternative source of the ore-forming fluids for W mineralization could be related to the Neoproterozoic sedimentary rocks, or the clastic rocks of underlying crystalline basement, and the mafic-ultramafic rocks in the Mesoproterozoic Lengjiaxi Group. The

87

Sr/86Sr ratios

of scheelite are relatively homogeneous (0.7304–0.7329) and also agree with the

results from the Meso-Neoproterozoic rocks, indicating an injection of components of the Meso-Neoproterozoic rocks into the ore-forming fluids for W mineralization.

7.3. Source of S and Pb

The sulfides in the Zhazixi Sb–W deposit are dominated by stibnite, and therefore, the S isotopic composition of stibnite can be interpreted as representing the bulk S isotopic composition of the ore-forming fluids. The δ34SV-CDT values of stibnite varied from 3.1‰ to 9.4‰, with an average of 5.2‰ (Fig. 12); these are obviously higher than the average values of magmatic sources (mainly –3 to 3‰ δ34S) and the deep mantle (about 0‰) (Ohmoto and Rye, 1979). In addition, no intrusive rocks have been discovered in the Zhazixi Sb–W deposit. Both the S isotopic data and geologic features exclude any contribution from magmatic and mantle sources. The δ34SV-CDT values of stibnite are consistent with those of the Neoproterozoic Wuqiangxi Formation along the Xuefeng uplift (Chen, 2012), indicating that S in the Zhazixi Sb–W deposit may be derived from the Neoproterozoic lithological units. This also seems to be a plausible explanation with respect to the noble gas and Nd–Sr isotopic data. 207

Pb/204Pb vs.

206

Pb/204Pb and

208

Pb/204Pb vs.

206

Pb/204Pb diagrams are used to

discriminate the sources of Pb in the Zhazixi Sb–W deposit. According to the 207

Pb/204Pb vs.

206

Pb/204Pb diagram, most stibnite samples plot in the lower crustal

field adjacent to the orogenic field, although two samples plot around the supracrustal field (Fig. 13a). The

208

Pb/204Pb vs.

206

Pb/204Pb (Fig. 13b) diagram shows similar

features to those of

207

Pb/204Pb vs.

206

Pb/204Pb, except that Z32517 sample plots

outside the diagram. Zartman and Doe (1981) suggest that the Pb of an orogenic belt source could be a mixture of lower crustal and the supracrustal sources. The results in this study reveal that Pb of the Zhazixi Sb–W deposit may be derived from a Pb source that was mixed by lower crustal and supracrustal sources (e.g., the Meso-Neoproterozoic rocks) during the early Paleozoic or Mesozoic intracontinental orogeny.

7.4. Implications for ore genesis

Based on a combination of geologic and mineralization features, the nature of ore-forming fluids, and isotopic data, this study proposes that Sb and W mineralization occurred during two separate periods. It is also considered that the superposition of these two types of mineralization in the Zhazixi Sb–W deposit may be related to the early Mesozoic intracontinental orogeny. Considering the paucity of magmatic rocks, the primary ore-forming fluids for W mineralization are suggested to be metamorphic fluids produced during the intracontinental orogeny. Initial Nd isotope values (–14.7 to –10.2 and –3.79 to +0.01) and homogeneous

87

Sr/86Sr ratios (0.7304–0.7329) of scheelite indicate that

components from the Meso-Neoproterozoic rocks were injected. Metamorphic fluids with moderate temperature (170–270 °C), low salinity (3–7 wt.% NaCl equiv.), low density (0.75–0.95 g/cm3), and high pressure (57.2–99.7 MPa) extracted W from the Meso-Neoproterozoic rocks. W was then primarily transported as HWO-4 , H10[WO]2-,

or H18[WO4]6- in the slightly oxidized CO2-containing ore-forming fluids. According to depth estimations, the ore-forming fluids decreased at a depth from 10.17 km to around 5.84 km with the mineralization progress. Microthermometric analysis results suggest that the ore fluids experienced an obvious decline both in homogenization temperatures and salinities from stage I to stage II (Fig. 14a), which may be attributed to mixing with shallow H2O–NaCl fluids. This fluid mixing may be related to the transformation of the regional tectonic regime and could be the critical mechanism leading to precipitation of scheelite and quartz in the interlayer fractures. The geologic features, low 3He/4He ratios (0.002–0.056 Ra), and high

40

Ar/36Ar

ratios (909.5–2279.7) jointly suggest that the metamorphic fluids responsible for Sb mineralization were generated from the CC (e.g., the Meso-Neoproterozoic rocks or underlying basement). The δ34SV-CDT values (3.1–9.4‰) and Pb isotopic data suggest that S and Pb were most likely sourced from the Meso-Neoproterozoic rocks. Sb can carried as Sb(OH)3(aq) or Sb2S2 (OH)02 in oxidized and weakly acid ore-forming fluids. Based on thermodynamic results, it is considered that the epithermal ore-forming fluids (150–230 °C) with low salinity (4–6 wt.% NaCl equiv.), moderate density (0.82–0.94 g/cm3), and high pressure (42.2–122.5 MPa) ascended from 12.50 km to 4.31 km underground along the NW-trending F3 fault and dispersed into the secondary faults on the hanging wall. During this process, the temperatures of the Sb-bearing ore-forming fluids gradually declined from stage III to stage IV, suggesting that the deposition of antimoniferous minerals and quartz was triggered by a cooling mechanism (Fig. 14b). These types of scenarios were also common in

Western Europe (Neiva et al., 2008; Wagner and Cook, 2000; Wagner and Boyce, 2003), the Moretons Harbour area, Canada (Kay and Strong, 1983), and China (An and Zhu, 2010). An and Zhu (2010) and Williams-Jones and Normand (1997) suggest that Sb and Au could potentially be carried in relatively alkaline and slightly reducing fluids, and the co-precipitation of native gold and antimoniferous minerals is favored by the acidification and/or decrease of fO2. This hypothesis has been verified by the Woxi Sb–W–Au deposit in the Xuefeng uplift (Murao et al., 1999). However, no Au mineralization was detected in the Zhazixi Sb–W deposit; this absence can be interpreted as being related to either over-oxidized Sb mineralization fluids (i.e., in the field of SO2-4 ), which would be in contradiction to the presence of similar fO2 in these two deposits, or to the low Σas, which would restrict the metal carrying capacity. The latter hypothesis is consistent with the low Σas content in the Zhazixi deposit (He et al., 1996). The occurrence of native Sb in the Zhazixi deposit also indicates a low S fugacity (Williams-Jones and Normand, 1997).

8. Conclusions

(1) The Zhazixi Sb–W deposit is a typical representative Sb–W±(Au) deposit in the Xuefeng uplift, South China. The W and Sb orebodies are hosted by interlayer fractures and NW-trending faults, respectively, and the mineral assemblages and hydrothermal alterations associated with W and Sb mineralization are obviously different.

(2) W and Sb mineralization took place in two separate periods: W mineralization is composed of a large amount of quartz, scheelite, and minor calcite; while Sb mineralization developed after W, and contains massive quartz and stibnite, with small amounts of native Sb, berthierite, chalcostibnite, pyrite, and chalcopyrite. (3) The ore-forming fluids for W mineralization experienced an evolution of cooling and dilution and contain rare CO2 with moderate temperature, low salinity, low density, and moderate–high pressure. However, the ore-forming fluids for Sb mineralization underwent a cooling process, contain a small amount of CO2, and exhibit an epithermal features with low salinity, moderate density, and medium–high pressure. (4) Components from the Meso-Neoproterozoic rocks were injected into W mineralization fluids, whereas Sb-bearing fluids originate from the CC. It is deduced that S was probably sourced from the Wuqiangxi Formation, whereas Pb was derived from a mixture of crustal and supracrustal sources (e.g., the Meso-Neoproterozoic rocks). (5) The ore genesis of the Zhazixi Sb–W deposit may be related to the intracontinental orogeny in the early Mesozoic. Fluid mixing is considered to be the critical mechanism involved in W mineralization, whereas fluid cooling could be responsible for Sb mineralization. The absence of Au can be interpreted by the low Σas content in the Sb-bearing fluids.

Acknowledgments

This research is financially supported by the geological survey project from China Geological Survey (Grant No. 12120113094200 and No. 12120115036201) and the Natural Science Foundation of China (Grant No. 41602070). The geologists and miners of the Anhua Zhazixi Antimony Mining Co. Ltd are acknowledged for their help during field work. Dr. Diwei Luo, Mr. Hang Li, and Mr. Wei Wang are also thanked for their assistance in laboratory research. Constructive reviews from Prof. M. Akçay and another anonymous reviewer significantly improved this paper. We also deeply appreciate the comments from the Editor-in-chief Prof. Franco Pirajno, Guest Editors Prof. M. Santosh and Prof. Liqiang Yang.

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Captions of Figures and Tables Fig. 1. (a) Tectonic outline of South China displaying the location of the Xuefeng uplift and the study area (Modified after Zhai, 2013); (b) geological sketch of Zhazixi Sb ore belt showing the location of the Zhazixi W–Sb deposit (Modified after HBGMR, 2010). Fig. 2. Geological map of the Zhazixi Sb–W ore deposit (Modified after HBGMR, 2010). Fig. 3. No. 0 cross section showing the structure patterns and mineralization styles of the Zhazixi Sb–W deposit (Modified after HBGMR, 2010). Fig. 4. Characteristic of W mineralization in the Zhazixi Sb–W deposit. (a) Interlayer fractures. Slip interfaces control bedding-parallel banded orebodies, and secondary fractures hold stringer veins. (b) Quartz + scheelite veins in the slip interfaces. Scheelite presents blue light under fluoreescence. (c) Quartz + scheelite stringer veins in thick sandstone. Scheelite presents blue light under fluoreescence. (d) Angular wall rock breccias appear in the W orebodies. Scheelite coexists with stibnite in a single vein. (e) Silification. Scheelite + quartz vein. (f) Silification. Scheelite vein crosscuts early quartz vein in sandstone. (g) Silification alteration. Quartz + scheelite vein. (h) Chloritization. Chlorite in the wall of banded quartz-scheelite veins. (i) Carbonation. Coarse-grained, enhedral or subhedral calcite coexisting with scheelite and quartz under microscope. Mineral abbreviations: Sch=scheelite, Qz=quartz, Stb=stibnite, Chl= Chlorite, Cal=calcite.

Fig. 5. Characteristics of Sb in the Zhazixi Sb–W deposit. (a) Sb orebodies. Sb orebodies were limited between two compressive structural planes, and the wall rocks were transformed into structural lens. (b) Stibnite + quartz veins. Structural lens were broken into fragments and then cemented by stibnite + quartz stockwork. (c) Stibnite-quartz vein. Stibnite vein crosscut stibnite + quartz vein. (d) stibnite stockwork. (e) Wall rock breccias in stibnite vein. f. Silification. acicular stibnite in the wall of quartz aggregate. (g) Sulfidation. Disseminated pyrite in massive stibnite. (h) Anhedral pyrite in quartz aggregate. (i) Chalcopyrite. Fine-grained, anhedral chalcopyrite replaced by stibnite. (j) Native Sb. Occurs as isolated minerals in stibnite. (k) Chalcostibnite occurs as lath shaped and appears to replace scheelite. (l) Berthierite appears as isolated grains in the quartz aggregates. Mineral abbreviations: Stb= stibnite, Sch=scheelite, Qz=quartz, Py= pyrite, Ccp= chalcopyrite, Sb=native antimony, Cs= chalcostibnite, Ber=berthierite. Fig. 6. Mineral paragenesis for the Zhazixi Sb–W deposit. Fig. 7. Photographs of hand specimen samples and photomicrographs of representative fluid inclusion at room temperature from four different mineralization stages in the Zhazixi Sb–W deposit. (a) quartz vein from stage I; (b) and (c) show the two-phase liquid-rich aqueous inclusions in quartz I; (d) scheelite + quartz vein from stage II; (e) two-phase liquid-rich aqueous inclusions in quartz II; (f) two-phase liquid-rich aqueous inclusions in scheelite coexisted with quartz II; (g) quartz+ stibnite from stage III; (h) and (i) indicate the two-phase liquid-rich aqueous inclusions in quartz III; (j) stibnite-quartz vein from stage IV; (k) and (l) present the

two-phase liquid-rich aqueous inclusions in quartz IV. Abbreviations for minerals: Stb=stibnite; Qz=quartz; Sch=scheelite. Fig. 8. Representative Raman spectra of fluid inclusions in the Zhazixi Sb–W deposit (a) shows that the vapor phase are mainly of CO2 in quartz I; (b) indicates that the vapor phase in quartz III contains some CO2. Fig. 9. Histograms of homogenization temperatures and salinities of fluid inclusions in quartz and scheelite related to W mineralization (a–b), and fluid inclusions from quartz that coexists with stibnite (c–d). Fig. 10. P-T plots to estimate the bulk fluid isochores for aqueous inclusions in the Zhazixi deposit. Fig. 11. 3He vs. 4He plot of fluid inclusions-trapped in stibnite from the Zhazixi Sb–W deposit. Fig. 12. S isotopic data scatter diagram of stibnite from the Zhazixi Sb–W deposit. Fig. 13. Pb isotope compositions (207Pb/204Pb versus versus

206

206

Pb/204Pb and

208

Pb/204Pb

Pb/204Pb) of samples from the Zhazixi deposit plotted in the tectonic

environment discrimination diagrams of Zartman and Doe (1981). The dotted lines show the concentration areas for the corresponding Pb sources. Fig. 14. Th–Salinity plot of type I fluid inclusions showing the evolution of ore-forming fluids that are responsible for W (a) and Sb (b) mineralization respectively, in the Zhazixi W-Sb deposit.

Table 1 Summary of the microthermometric data of the fluid inclusions from the

Zhazixi W-Sb deposit. Table 2 He and Ar isotope ratios in stibnite from the Zhazixi deposit. Errors quoted are at the 1σ confidence level. F4He values reflect enrichment 4 He in the

fluid

relative

to

air;

F4He=(4He/36Ar)sample/(4He/36Ar)air,

where

(4He/36Ar)air=0.1655 (Kendrick et al., 2001). Locations of samples are the same with table 2 and 3. Table 3 S and Pb isotope composition of stibnite from the Zhazixi deposit and slate of the Wuqiangxi Formation.

Table 1

Volume of Stage

Mineral

Th( →L) (℃)

Tm-ice (℃)

Salinity

D (g/cm3)

209.2– 298.2

-5.8 to

5.26–8.95

0.847–0.907

(19)

-3.2(11)

(11)

(11)

161.7– 257.3

-4.7 to

2.90–7.45

0.843–0.949

(31)

-1.7(20)

(20)

(20)

204.2– 305.9

-1.4 to

2.41–6.54

0.746–0.902

(59)

-4.0(48)

(48)

(48)

146.5– 279.0

-4.5 to

2.57–7.17

0.817–0.936

(78)

-1.5(48)

(48)

(48)

132.5– 261.0

-4.4 to

2.41–7.17

0.857–0.938

(48)

-1.4(24)

(24)

(24)

P (MPa)

vapor

I

20%–25% Quartz

~99.7

5%– 20% Quartz

II

~83.6

5%– 25% Scheelite

III

IV

~57.2

5%– 25% Quartz

~122.5

5%– 15% Quartz

~42.2

Table 2

3

He(E-12

4

He(E-7

3

He/4He

40

Ar(E-7

36

Ar(E-9 40

Ar/36Ar

F4He

Sample

ccSTP/g)

ccSTP/g)

（Ra）

ccSTP /g)

ccSTP/g)

Z3254

0.003

4.8

0.006±0.001

28.3

1.92

1469.9±10.3

1512.0

Z3258

0.002

9

0.002±0.001

17.8

1.60

1117.2±7.7

3411.0

Z32517

0.009

2.2

0.038±0.007

33.6

1.47

2279.7±16.3

921.1

Z3709

0.002

2.9

0.056±0.007

17.5

1.93

909.5±6.2

905.4

Table 3

Stand Sam

Mineral

δ34SV-

208

Pb/2

Location

Stand 207

Pb/2

ard ple

/rock

CDT

04

Z11

110m level

03

No.43 Sb orebody

Z11

in -115m level

56

No.5 Sb orebody in

Z32

325m level

54

No.13 Sb orebody

Z32

in 325m level

56

No.16 Sb orebody

Z32

in 325m level

58

vein type ores in

Z37

370m level

09

Massive ores in

Z32

Com ard

04

Pb

error No.9 Sb orebody in

Pb/2

ard 04

Pb

Stand 206

Pb

error

ment error

stibnite

5.3

37.643

0.003

15.481

0.001

17.116

0.001

stibnite

6.5

37.743

0.007

15.456

0.003

17.093

0.004

stibnite

4.6

38.446

0.004

15.508

0.002

17.504

0.002 this

stibnite

9.6

37.851

0.007

15.494

0.003

17.379

0.003

stibnite

4.2

38.179

0.017

15.552

0.007

17.894

0.008

stibnite

3.3

39.722

0.008

15.668

0.003

19.659

0.004

stibnite

3.1

40.222

0.008

15.681

0.003

20.042

0.004

study

325m level

517 BWslate

39.028

15.465

17.528

slate

37.897

15.460

17.507

slate

39.455

15.526

18.338

1 BW10 BWWuqiangxi

12

Formation

BW-

Liu and Zhu, slate

39.163

15.524

18.318 1994

18 BWslate

41.640

15.592

18.986

slate

41.421

15.553

18.506

20 BW23

Graphical abstract