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Article

Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations

by
Shu-Min Chen
1,
Yu-Xuan Zhou
2,*,
Bin Li
2,
Jin-Hong Wu
1,
Hong-Tao Zhao
2,
Zhi-Ming Zhang
1 and
Hao Zeng
1
1
Changsha Natural Resources Comprehensive Survey Centre, China Geological Survey, Changsha 410600, China
2
Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Ministry of Education), School of Geosciences and Info-Physics, Central South University, Changsha 410083, China
*
Author to whom correspondence should be addressed.
Minerals 2022, 12(7), 867; https://doi.org/10.3390/min12070867
Submission received: 24 April 2022 / Revised: 30 June 2022 / Accepted: 2 July 2022 / Published: 8 July 2022
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Abstract

:
The Chaxi gold deposit is located in the southwestern Hunan Province (South China). Extremely high-grade (up to 3 × 105 g/t, avg. 5.3 g/t) Au mineralization is developed in quartz-sulfide veins controlled by WNW- and NNE-trending faults. The sulfide/sulfosalt assemblage is dominated by pyrite, chalcopyrite, and galena, with minor tetrahedrite and chalcocite. The alteration includes beresitization and carbonation. Based on the vein crosscutting relationship and mineral assemblages, the hydrothermal period comprises three stages: (1) pre-ore quartz-pyrite, (2) syn-ore quartz-ankerite-native gold-sulfide-sulfosalts, and (3) post-ore quartz-calcite-pyrite alteration. The Au occurrence is dominated by native gold, with minor native Au nanoparticles (inside sulfides) as indicated by EPMA. Fluid inclusions (FIs) in the ore-related quartz yielded homogenization temperatures and salinities of 139.6–267.1 °C and 2.7–17.6 wt.% NaClequiv (Stage I), 137.5–387.2 °C and 2.7–19.9 wt.% NaClequiv (Stage II), and 139.7–330.5 °C and 3.1–21.4 wt.% NaClequiv (Stage III). Such varying and high FI salinities can be attributed to fluid boiling. The calculated δ18OH2O values are of 2.40–5.63‰, and the fluid inclusion δD values for quartz are of −71.73 to −49.8‰. The auriferous sulfide δ34S values (6.26–19.33‰) overlap with those of the Chang’an formation (16.31–21.66‰) and Banxi Group metamorphic rocks. The auriferous sulfides have 206Pb/204Pb = 16.7215–17.2281, 207Pb/204Pb = 15.4413–15.6177, and 208Pb/204Pb = 36.9731–38.7232, distinct from those of the wallrocks. The analyzed pyrites yield Co/Ni ratio > 1 (0.539–77.000, avg. 10.559). The isotope (H, O, S, Pb) signatures coupled with EPMA results indicate that the ore-forming fluids were derived from the magmatic fluid and mixed with meteoric water, and the Pb was originated from the mantle. The ore sulfur was likely leached from the Neoproterozoic meta-clastic rocks. The Chaxi gold mineralization shares many geological and geochemical similarities with (albeit also with minor differences) typical orogenic gold deposits, and is best classified as broad sense orogenic deposit, as proposed for many other gold deposits in the Jiangnan Orogen.

1. Introduction

The Jiangnan Orogen Belt (JOB) is one of the two lode Au-Sb-W metallogenic belts in the world, and over 250 gold-polymetallic occurrences have been reported in it, with a total Au resource of over 970 tonnes (t) [1,2,3,4,5,6]. As a Precambrian terrane extending northeastward for 1500 km, the JOB is a collision zone between the Yangtze and Cathaysia blocks, which formed the South China Block [7,8,9]. Gold deposits in the JOB are mostly hosted by the Neoproterozoic metasedimentary rocks, located near the NE-trending faults, Caledonian and Indosinian intrusions, and controlled by NE-trending major and WNW-trending secondary faults [10,11]. Various metallogenic models have been proposed for these Au deposits, including SEDEX, orogenic, epithermal, magmatic-hydrothermal [2,10,11,12,13,14,15,16,17,18,19]. A key controversy is about the ore-fluid source, which has been variably attributed to evolving seawater, low-grade metamorphic sediments, meteoric fluid, magmatic fluid or mixing fluid [10,12,20,21,22,23]. Meanwhile, the ore-metal source was widely interpreted to be the Neoproterozoic strata and magmatic intrusions [13,14,24,25]. In sum, the genesis of the deposits in the JOB is an international hotspot.
The newly explored Chaxi gold deposit is located in the southwestern JOB, hosts an ore reserve of 117,668 t, and is characterized by its extremely high-grade honeycomb gold @ 2.4–3 × 105 g/t (mean 5.3 g/t). In the Chaxi deposit, the gold occurs mainly as native gold in quartz veins, and the sulfide assemblage lacks arsenopyrite, which is common in typical orogenic gold deposits. This raises a question of whether the formation of Chaxi represents a new type of gold deposit in JOB or is similar to other gold deposits in JOB. Previous H-O isotope studies on the Chaxi gold deposit favored a metamorphic origin for the ore fluids, with magmatic-hydrothermal fluid overprint and late meteoric water mixing [26]. However, the ore-fluid nature, ore-material source, and the metallogenic mechanism are still poorly constrained. Meanwhile, compared with other areas of Jiangnan orogen, the research of gold deposits in southwest orogen is obviously insufficient, which hampers the exploration work of this ore district.
In this study, we report new data from electron probe microanalysis (EPMA), fluid inclusion microthermometry and H-O-S-Pb isotopes on the Chaxi gold ores, in order to characterize the fluid nature and metal source.

2. Geological Background

2.1. Regional Geology

The early Neoproterozoic Yangtze-Cathaysia collision may have developed the NE-trending Xuefeng uplift belt, which is also part of the JOB (Figure 1a). The Xuefeng belt has undergone multiphase tectonic movement [27,28]. Local Neoproterozoic metamorphic rocks were in unconformable contact with the Sinian-Nanhua series, which is suggested to be related to the Nanhua rifting event [29]. The Caledonian Orogeny likely generated many NW-WNW-trending structures, including slaty cleavage, folds, kink bands, and thrust faults [30]. During the Indosinian (Triassic)-Yanshanian (Jurassic) Orogeny, the Paleo-Tethys closure, the Indochina-South China collision, and the Paleo-Pacific subduction and slab rollback likely caused the widespread late Mesozoic I-S-type granites, and formed the regional NE-NNE-trending tectonic patterns and large-scale W, Sn, Bi, Mo, Co, Au and Ag mineralization at ca. 177–170 Ma [12,25,31,32,33,34,35].
Southwestern Hunan Province, located in the western-central Xuefeng belt (Figure 1b), is part of the Yangtze-Cathaysia collision zone. The region is dominated by sub-greenschist-facies metamorphic clastic successions of the Neoproterozoic Lengjiaxi and Banxi groups, the Middle Neoproterozoic Nanhua continental deposits, and Paleozoic and Mesozoic-Tertiary sedimentary rocks [36,37,38]. The Lengjiaxi Group contains low-grade meta-turbidites, including sandy/silty slate, sandstone and greywacke, and is in angular unconformable contact with the overlying Banxi Group conglomerate, sandstone, slate-phyllite, and intermediate-felsic tuffs [36]. The Banxi Group comprises the lower Madiyi formation and the upper Wuqiangxi formation: The Madiyi formation contains a series of sandy conglomerate, feldspathic sandstone, and carbonaceous/sericite silty slate, whilst the Wuqiangxi formation comprises mainly feldspathic-quartz sandstone and carbonaceous slate [6]. The Banxi Group is in unconformable contact with the Nanhua series, which comprises (from base to top) the Chang’an, Fulu and Nantuo formations, including volcaniclastic rocks, tillite, limestone and carbonaceous shale [6].
Neoproterozoic magmatic rocks are exposed widely across the study region, generating NNE-/NE-trending ultramafic-mafic dikes that intruded the Banxi Group. Numerous gold deposits have been discovered in southwestern Hunan, with the majority hosted in the Jiajiantian formation (Banxi Group), sub-greenschist-facies meta-marine volcanic/clastic rocks. These gold deposits including the Mobin, Shenxi, and Taojinchong. Recent studies show that the Chang’an formation is also an important ore host in this area [39], for instance for the Chaxi gold deposit.
Minerals 12 00867 g001 550
Figure 1. (a) Location map of the Xuefeng uplift belt and Jiangnan Orogen (modified from [40]); (b) Geological map of the Xuefeng uplift belt, showing the distributions of regional structures, strata, granites, and Au/Au-Sb/Sb deposits. Abbreviations: NCB, North China Block. Abbreviations for regional faults: ALF, Anhua-Liping; AXF, Anhua-Xupu; CPF, Changsha-Pingjiang Fault; DYF, Dayong Fault; JSF, Jiangshan-Shaoxing Fault; LHF, Liling-Hengdong Fault; TCF, Taojiang-Chengbu Fault; XHF, Xinning-Huitang Fault; XJF, Xupu-Jingxian (modified from [41]).
Figure 1. (a) Location map of the Xuefeng uplift belt and Jiangnan Orogen (modified from [40]); (b) Geological map of the Xuefeng uplift belt, showing the distributions of regional structures, strata, granites, and Au/Au-Sb/Sb deposits. Abbreviations: NCB, North China Block. Abbreviations for regional faults: ALF, Anhua-Liping; AXF, Anhua-Xupu; CPF, Changsha-Pingjiang Fault; DYF, Dayong Fault; JSF, Jiangshan-Shaoxing Fault; LHF, Liling-Hengdong Fault; TCF, Taojiang-Chengbu Fault; XHF, Xinning-Huitang Fault; XJF, Xupu-Jingxian (modified from [41]).
Minerals 12 00867 g001

2.2. Deposit Geology

Outcropping stratigraphic units at Chaxi include the Neoproterozoic Chang’an, Fulu and Nantuo formations, and Quaternary sediments (Figure 2). The Chang’an formation is dominated by metamorphosed gray, medium-fine-grained lithic arkose and gravel-bearing quartz graywacke interbedded with laminated sericite slate and chloritoid-calcite-sericite phyllite. The Fulu formation consists of Mn-bearing carbonaceous slate interlayered with Mn-bearing dolomite, metamorphosed feldspathic-quartz graywacke, and silty slate. The Nantuo formation comprises grayish-green, very-thick-bedded sandy pelitic conglomerate, metamorphosed gravel-bearing graywacke, slate, and minor siliceous limestone interbeds.
Two sets of faults are documented at Chaxi, i.e., the NNE- and WNW-trending ones (Figure 2): The WNW-trending faults host gold-bearing veins and dip SSW, with slickenside developed on the fault gouge, with length of 10–300 m. The NNE-trending faults crosscut the regional Anhua-Liping trans-crustal fault (>100 km long) and are the main migration channel for the ore-forming fluids at Chaxi. Minor structures, such as secondary parallel faults and folds, are well-developed along the main faults. Late faults (S-/SE-dipping) cut the NNE-trending faults. Both sets of faults are commonly filled with quartz veins. The NNE-trending veins cut the WNW-trending veins, and feature composite veining (SE-dipping at 55–89°). The WNW-trending quartz veins can be further divided into conjugate steep (SW-dipping at 52–89°) and shallow (NNE-dipping at 8–24°) dipping ones.
There are no exposed plutons at Chaxi, and the closest exposed intrusion is located ~60 km (and some mafic dykes ~30 km) to the southeast. These mafic dykes intruded the Duoyitang formation (Banxi Group).
In southern Chaxi, gold is produced as honeycomb/nuggets in the WNW-trending quartz veins at/near the intersection of the NNE- and WNW-trending faults, but the mineralization is not extended into the metagreywacke wallrocks (Figure 3). In contrast, only rare native gold is present in the NNE-trending quartz veins at northern Chaxi. Recent exploration revealed that Au mineralization is mainly distributed at ca. 540–390 m above sea level (asl), with minor gold present at depth.
Metallic sulfides include dominantly pyrite, chalcopyrite, and galena, with minor tetrahedrite, chalcocite, cosalite and native gold (Figure 4 and Figure 5). Sulfides are commonly altered to form hematite, lepidocrocite, goethite, and covellite. Native gold is assigned in the form of visible gold of mainly honeycomb-shaped (Figure 4), nugget (Figure 3), and irregular coarse-grained (size: 50 μm–3 mm; Figure 4). Minor fine-grained electrum is hosted in the sulfides. Non-metallic minerals include primarily quartz, ankerite, calcite, dolomite, and chlorite.
Ore-related wallrock alterations include mainly pyrite and discoloration alteration halos, with local chlorite, carbonate, siderite, and ankerite. Dolomite alteration commonly occurs as fault gouge-infill and veinlet-infill in quartz veins and wallrocks. Extensive beresitization occurred in the pre-ore metamorphic stage.
According to the vein crosscutting relationship and mineral assemblages, two periods and three paragenetic stages are recognized at Chaxi (Figure 3, Figure 4, Figure 5, Figure 6 and Supplementary Table S1). Hydrothermal period: (I) early fractured quartz stage with pyrite but no Au mineralization. The NNE-trending faults were filled by early milky, pale purplish-red quartz veins (10–100 cm wide). Stage I pyrite is coarse-grained (size: 3–15 mm) cubic and occurs in metagreywackes along quartz vein margin (Figure 3e and Figure 5c); (II) main-ore quartz-ankerite-native gold- polymetallic sulfide-sulfosalt stage, with a quartz + pyrite + chalcopyrite + galena + tetrahedrite + chalcocite ± electrum ± enargite ± bornite ± bournonite ± tetradymite ± bursaite ± aleksite ± electrum ± enargite assemblage (Figure 3b,f and Figure 5a,b,d,f–i). The native gold is associated with galena-pyrite-tetrahedrite and hosted in quartz-ankerite veins (Figure 3a,c, Figure 4d,f, and Figure 5e); (III) post-ore quartz-calcite-pyrite stage. Stage III quartz veins are cut by Fe-bearing dolomite-calcite veinlets. Cubic pyrite patches are commonly developed along the quartz vein margin (Figure 4e) Supergene period, which developed mainly limonite, and minor covellite (Figure 3d).

3. Analytical Methods

3.1. Fluid Inclusions

Microthermometric measurements were performed at the Central Laboratory of the Tianjin Geological Survey Center, China Geological Survey, using a Linkam MDSG 600 programmable heating–freezing stage with temperature range of −196 to + 600 °C. The general heating–freezing rate is 0.01–150 °C/min with an accuracy within 0.1 °C.
The compositions of individual FIs were determined on a Renishaw inVia Laser Raman spectrometer, with 532 nm wavelength and 44 mW power. The spectral range was 100 to 4500 cm−1 and the measured spectrum time during the analysis was 10 s. The beam spot diameter was 1 μm.

3.2. H-O-S-Pb Isotope Analysis

The H-O-S isotope analyses were conducted at the Beijing Createch Testing Technology Co. Ltd. (Beijing, China). Oxygen and hydrogen isotopes were measured with the bromine pentafluoride method [43], using a Thermo ScientificTM 253 PlusTm and Flash EA elemental analyzer (Thermo Electric Cooling America, TECA, Chicago, IL, USA). Water was reduced to H2 through a uranium metal-bearing tube, and then H2 was transported to the mass spectrometer. The results are presented in per mile (‰) relative to the different SMOW standards, and the analytical precision was ± 1‰ for δD and ± 0.2‰ for δ18O.
The sulfur isotope ratios are reported as δ34S relative to the Canon Diablo Troilite (CDT). The sulfide reference materials IAEA-S3, GBW04414, and GBW04415 were used as the standards, and the analytical precision was better than ± 0.2‰.
Lead isotope analyses were conducted on a Triton Mass Spectrometer (TIMS) at the Central Laboratory of the Tianjin Center, China Geological Survey. About 100 mg of the samples were dissolved at 150 °C in a mixture of 2.5 mL HF, 0.5 mL HNO3, and 0.15 mL HClO4 in PFA beakers. The dissolved samples were dried, and were then digested with 2 mL of 3M HNO3 in preparation for ion exchange chromatography. The results are corrected by the Pb standard NBS981. Errors were quantitatively propagated across all calculations and recorded at 2σ level.

3.3. EPMA

Electron probe microanalysis (EPMA) was conducted on the sulfide chemical compositions at the Laboratory of the Tianjin Center, China Geological Survey, using a SHIMADZU-1600 electron microprobe and an EDAX-GENESIS energy disperse spectroscopy. The spot analysis conditions included 15 kV accelerating voltage, 20 nA probe current, 1 μm beam, and ZAF correction procedure for data reduction. Elements were standardized using SPI Supplies sulfide, gold and silver specimens, and silicate specimens, then acquired using the following analyzing crystals: LIF for As Kα, Se Kα, Au Kα, Pb Kα, Ag Kα, Te Kα, Fe Kα, Co Kα, Ni Kα, Cu Kα, Zn Kα, and Mo Kα. Counting time was 100 s for As Lα, Se Lα, Co Kα, Ni Kα, Cu Kα, and Zn Kα, and 20 s (10 s in two spectrometers) for Fe Kα. Background times were determined by peak time divided by two due to both sides of the peak being accumulative measured. Detection limits are below 0.01 wt.%.

4. Results

4.1. Fluid Inclusions

4.1.1. Petrography and Fluid Inclusions

Petrography shows that FIs are widely developed in stage I to III quartz (Figure 7). Two types of FIs are identified based on their petrographic characteristics and components at room temperature, i.e., CO2 inclusions (C-type) are present in Stage II, and aqueous inclusions (W-type) in stage I to III. The C-type inclusions contain three phases (liquid H2O, liquid CO2, and vapor CO2) at room temperature (Figure 7a). These FIs are oval, elongated or irregular and 2–10 μm (mostly 2–6 μm, up to 15 μm). The gas–liquid ratios of C-type inclusions are 5%–35% (mostly 8%–16%), and they homogenized to liquid when heated. C-type FIs occur as isolated, randomly aligned inclusions or clusters. The W-type inclusions contain one (pure liquid) or two (liquid and vapor) phases at room temperature, and are generally oval, elongated or irregular and 2–8 μm (mostly 2–5 μm, up to 12 μm) in size. The vapor proportion of these inclusions varies from 5 to 30 vol%. The FIs homogenized to liquid phase when heated. The W-type FIs occur as isolated inclusions in stage I, II and III, and often show parallel distribution of pseudo-secondary inclusions in stage II.

4.1.2. Microthermometric Data

The microthermometric measurement included determining Tmice and Thtotal values to calculate the fluid salinity. Freezing experiments were first performed to avoid FI decrepitation. The FIs salinity was estimated using CO2–clathrate melting temperatures, by assuming a simple NaCl–H2O–CO2 system [44]. The microthermometric and salinity data were summarized in Table 1 and illustrated in Figure 8. These data clearly show a link between the mineral assemblages, physicochemical conditions, and hydrothermal stages.
Stage I quartz crystals contain W-type FIs, which homogenized to liquid at Thtotal = 139.6–267.1 °C (avg. 189.7 °C, peak at 150–170 °C), with Tmice = −13.8 to −1.6 °C (avg. −8.4 °C). The salinity is 2.7–17.6 wt.% NaClequiv., corresponding to density of 0.81–1.04 g/cm3.
Stage II quartz crystals have W- and C-type FIs. C-type FIs homogenized to liquid at Thtotal = 151.3–387.2 °C (avg. 229.1 °C, peak at 150–170 °C), with Tmice = −16.6 to −2.1 °C (avg. −11.7 °C). The salinity is 3.6–19.9 wt.% NaClequiv., corresponding to density of 0.85–1.06 g/cm3 (avg. 0.99 g/cm3). W-type FIs homogenized to liquid at Thtotal = 137.5–327.0 °C (avg. 188.8 °C, peak 150–170 °C). The Tmice = −14.9 to −1.6 °C (avg. −6.3 °C). The salinity is 2.7–18.5 wt.% NaClequiv., corresponding to density of 0.81–1.05 g/cm3.
Stage III quartz crystals have W-type FIs, which homogenized to liquid at Thtotal = 139.7–330.5 °C (avg. 188.5 °C, peak at 150–170 °C), with Tmice = −18.6 to −1.8 °C (avg. −7.2 °C). The salinity is 3.1–21.4 wt.% NaClequiv., corresponding to density of 0.80–1.07 g/cm3.

4.1.3. Laser Raman Analysis

The analysis was performed to constrain the representative FI compositions (Figure 9). The results suggest that H2O (characteristic peak 3310–3610 cm−1) is the main volatile in Stage I to III W-type FIs, whilst CO2 (characteristic peak 1387 cm−1) and H2O are the main volatiles in Stage II C-type FIs. Minor N2 (characteristic peak 2328–2332 cm−1) is also present.

4.2. H-O-S-Pb Isotopes

The quartz H-O isotope compositions were listed in Table 2 and illustrated in Figure 10. The δ18OV-SMOW and δDV-SMOW values of the different quartz generations are 15.36–17.11‰ and −71.73 to −49.80‰, respectively. According to the average FI homogenization temperature obtained from this study (Table 1), the fluid δ18OH2O values can be estimated by the following formula [45]:
1000ln αQuartz − H2O = 3.38 × 106/T2 − 3.4.
The 12 sulfide, 4 wallrocks and 1 fault gouge samples have δ34SV-CDT of 6.26–18.61‰ (avg. 14.70‰), 16.31–21.66‰ (avg. 19.28‰) and −5.35‰, respectively (Table 3; Figure 11a,b). The six pyrite samples have δ34S = 15.95–18.61‰ (avg. 17.00‰), higher than those of galena (6.26–6.67‰, avg. 6.46‰) and chalcopyrite (11.77–11.83‰, avg. 11.80‰).
Seven samples of three sulfides (pyrite, galena, and chalcopyrite) minerals, five wallrocks and two fault gouge samples have 206Pb/204Pb = 16.7215–18.4466, 207Pb/204Pb = 15.3877–15.5879, and 208Pb/204Pb = 36.0358–38.3225 (Table 4). The sulfides and wallrocks (contain fault gouge samples) have µ values of 9.37–9.52 (avg. 9.44) and 9.25–9.44 (avg. 9.38), ω values of 38.55-39.86 (avg. 38.90) and 31.88-39.12 (avg. 36.60), respectively. The dataset obtained in this study and the Pb isotope composition of sulfides and wallrocks from other orogenic gold deposits in the JOB are summarized in Supplementary Table S2 and illustrated in Figure 12a,b.

4.3. EPMA Pyrite Compositions

Fifty-two EPMA analyses were conducted on the pyrites. The EPMA results are listed in Table 5 and shown in Figure 13. The pyrites were selected from the stage I and II. Sample CX21-16 contains lead (6.54 wt.%), which is probably galena inclusion. Gold contents in most sulfides are above the EPMA detection limit (0.01 wt.%). The analyzed sulfides have Co/Ni > 1 (0.539–77.000, avg. 10.559; Figure 13a), consistent with a magmatic/volcano origin [57]. Most pyrites have the Au/As molar ratio of >0.02, above the solubility limit in pyrite (Figure 13b), suggesting the presence of Au0 nano-particles [58].

5. Discussion

5.1. Evolution of Ore-Forming Fluids

The Chaxi gold deposit is characterized by having multiphase hydrothermal activities. The widespread W-type and C-type inclusions in quartz show that the ore fluid belongs to the CO2-H2O-NaCl system. The three-phase (liquid, vapor, and gas) C-type inclusions are only present in stage II, accounting for ~10% of the total inclusions. This implies a close link between CO2 and Au mineralization [59]. Carbonic acid (H2CO3) can buffer the pH of the mineralizing fluid and facilitate the migration of Au complexes [59].
From the FI homogenization temperature and salinity obtained, fluid properties between the three stages are broadly similar. Laser Raman analysis shows that the FI gas-phase composition at Chaxi contains a certain amount of CO2, and the presence of CO2 implies that the liquid phase of the ore fluid also contains a certain amount of CO2. This may have caused the lower freezing point, corresponding to a higher-than-actual salinity calculated by the H2O-NaCl system [60]. Analysis results show that the temperature of inclusions in different phases does not change much in a vertical range of 1–2 km, which is similar to that of lode gold deposits [61].
Fluid boiling is an important gold precipitation mechanism for many gold deposits [38,62,63,64]. Petrography and microthermometry on FIs of the Chaxi deposit reveal that ore-fluid boiling may have been the gold precipitation mechanism, because (1) varying gas–liquid ratios in the C-type FIs show different homogenization modes (V→L vs. L→V), despite a limited homogenization temperature range; and (2) despite the salinity variations between most FIs in the different quartz generations, a negative homogenization temperature vs. salinity correlation is observed (Figure 8).

5.2. Source of Ore-Forming Fluids and Materials

5.2.1. Ore Fluid Source

The Chaxi quartz samples have a narrow δ18O range (15.36–17.11‰), indicating that the quartz may have precipitated from a homogeneous fluid source. The δ18O values are similar to those recorded from Archean to Cenozoic orogenic gold deposits (δ18O = 12–22‰) [65]. In addition, the ore-fluid δD values at Chaxi (−71.73 to −49.80‰; Table 2) fall inside the orogenic gold mineralization range (δD = −20 to −80‰) [66].
The calculated δ18OH2O values (2.35–4.10‰) of our samples are comparable to those of gold deposits from southwestern Hunan (δ18OH2O = −0.4 to 9.0‰; Xu et al., 2017 [16]). In the δD vs. δ18OH2O plot (Figure 10), data from all stages overlap and fall adjacent to the primary magmatic water box, and between the magmatic, metamorphic and meteoric water fields. This could mean that the ore-forming fluids were sourced from magmatic water and mixed with meteoric water. The high Co/Ni ratio of pre-/syn-ore pyrites also implies a magmatic genesis (explained by Figure 13a). Therefore, we proposed that the initial source of the ore-forming fluids was magmatic water, with later meteoric water involvement.

5.2.2. Ore-Material Source

Field and microscopic observations suggest that ore minerals at Chaxi are predominantly sulfides (pyrite, chalcopyrite, and galena, chalcocite and enargite), whereas sulfates are absent (Figure 3, Figure 4 and Figure 5). Thus, the sulfur isotope compositions of sulfides should approximate those of the hydrothermal fluids at Chaxi [67].
The Chaxi sulfide samples have significantly higher δ34S values (6.67–18.61‰, avg. 14.70‰; Figure 11a) than the published δ34S data for most orogenic gold deposits in the JOB, e.g., Huangjindong (−12.9 to −3.4‰) [12], Wangu (−11.6 to −8.0‰) [12], Yanlinsi (−4.3 to −0.2‰) [12], but overlap with those of the wallrocks and sedimentary pyrites, e.g., the Chang’an (16.31–21.66‰) and Wuqiangxi formation (4.5–23.3‰; Figure 11b) [17,20]. Compared to the Yuhengtang and Gutaishan, the Chaxi is higher than the magma-hydrothermal syn-ore δ34S values (0–5.3‰, −3.7–+2.1‰), and overlaps with the sedimentary pre-ore δ34S values (15.6–25.8‰, 7.0–23.3‰). These overlaps can be an indication that the sulfur was extracted from the wallrocks (e.g., Chang’an Formation and Wuqiangxi Formation) by deep-sourced hydrothermal fluid. The results are consistent with the interpreted sulfur source (i.e., from wallrocks) for most gold deposits in southwestern Hunan, e.g., the Mobin and Wulipai deposits (Supplementary Table S3) [12].
Lead isotopes of ore sulfides are generally used to constrain the ore-material source [6,68]. Both galena and pyrite can be used to estimate the initial Pb isotope composition for lode-gold systems [69,70]. The Pb isotopic range of co-existing sulfide minerals in the same ore assemblages can be used to estimate the initial fluid Pb composition, with the least radiogenic composition generally considered to be more reliable [69]. For our samples, the Pb isotopes from galena sample CX2022 are the least radiogenic (206Pb/204Pb = 16.7215, 207Pb/204Pb = 15.4413, and 208Pb/204Pb = 36.9731), which could represent the initial Pb isotope composition of the Chaxi ore-forming fluids.
As shown in Figure 12, the Chaxi ore sulfides show limited range in radiogenic Pb isotopes with positive 206Pb/204Pb vs. 208Pb/204Pb correlation, indicating mixing between a high radiogenic and a low radiogenic end-member [70]. In the 206Pb/204Pb vs. 207Pb/204Pb and 208Pb/204Pb vs. 207Pb/204Pb diagrams, the lead isotopes of sulfides are distinct from those of wall rocks (Neoproterozoic strata and NNE-trending fault gouge), but overlapped with those of the WNW-trending fault gouge. This reveals a possible deep hydrothermal origin controlled by WNW-trending fault (rather than wallrock-derived), and that tectonism dominated metallogenic process. The samples plot between the mantle and orogene evolution curves, and close to the mantle curve (Figure 12a,b), is characterized by a mixed source of lower crust and mantle. Furthermore, the relatively low μ values (9.37–9.52) and high ω values (38.55–39.86) indicate lower crust source [71,72]. We suggest that the ore metals of Chaxi were mainly mantle-originated, with involvement of lower crust materials, which was then ascended along the WNW-trending fault system.

5.3. Genesis of the Chaxi Gold Deposit

Concerning the gold metallogenesis in the JOB, previous studies have classified the deposits in the JOB as SEDEX [73], orogenic [3,38,64,74], magmatic-hydrothermal [16,17,18,19].
The conjugate parallel-cut-layers shear deformation system at Chaxi is significantly different from the SEDEX. Both the ore fluid and metals dominantly derived from magmatism (Figure 10 and Figure 12) resemble the Gutaishan and Yuhengtang deposits in the JOB [16,19]. Nevertheless, geological observations show that the Chaxi gold ore lacks evidence of magmatic-hydrothermal ore genesis, including biotite and K-feldspar alteration, late magmatic gold-bearing pegmatite/aplite/granite dike outcrops or drill cores [75,76]. This makes it questionable whether the Chaxi is intrusion-related/magmatic-hydrothermal.
General features of the Chaxi gold ores resemble typical orogenic gold deposits, including the Precambrian low-grade metamorphic rock ore-host, shear zone structural control, medium-/low-temperature mineral assemblage (Py-Ccp-Chl), CO2 contained, and low-salinity fluid. Since the ore-forming fluids are magmatic sources, this indicates that Chaxi gold ore is not a typical orogenic gold deposit. The high pyrite Co/Ni ratio and Pb isotopes suggest that the contribution of mantle and lower crust for the ore-forming material (Figure 12 and Figure 13a) and that the Chaxi ore sulfur was likely leached from the Neoproterozoic strata (e.g., Chang’an and Wuqiangxi Formation) by deep-sourced hydrothermal fluids, which also differs from typical orogenic gold deposits. Hence, we suggest the Chaxi deposit would fit into a category of broad sense orogenic gold deposits mentioned by Goldfarb and Mao [77,78].

6. Conclusions

(1)
The Chaxi alteration and gold mineralization comprises three stages, i.e., quartz-pyrite, quartz-native gold-polymetallic sulfides, and quartz-carbonate-pyrite alteration.
(2)
Fluid inclusions Raman spectra and microthermometry reveal a medium-/low- temperature, low salinity CO2-H2O-NaCl fluid system. Fluid boiling may have triggered gold precipitation.
(3)
H-O-S-Pb isotope compositions coupled with EPMA results suggest that the Chaxi gold ore fluids were sourced from the magmatic fluid with meteoric water input, and the sulfur was from the Chang’an and Wuqiangxi formation (Banxi Group). The Chaxi gold metallogenic system is of hybrid origin and controlled by the WNW-trending shear fault.
(4)
The Chaxi gold ore resembles typical orogenic gold deposits, given magmatic sources, is best classified as a broad sense orogenic gold deposit.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/min12070867/s1, Table S1. EMPA data of sulfides/sulfosalts in the Chaxi gold deposit; Table S2. Lead isotopic data of typical gold deposits, host rocks and associated intrusions in the Xuefeng uplift belt; Table S3. Sulfur isotope compositions of sulfides from typical gold deposits and Precambrian strata in the Xuefeng uplift belt.

Author Contributions

Conceptualization, S.-M.C., Y.-X.Z. and B.L.; methodology, S.-M.C.; software, S.-M.C.; validation, Y.-X.Z. and B.L.; formal analysis, S.-M.C. and Y.-X.Z.; investigation, S.-M.C., H.Z. and Z.-M.Z.; resources, S.-M.C., Z.-M.Z. and H.-T.Z.; data curation, S.-M.C., H.Z. and J.-H.W.; writing—original draft preparation, S.-M.C., Y.-X.Z. and H.-T.Z.; writing—review and editing, S.-M.C., Y.-X.Z. and B.L.; visualization, S.-M.C. and J.-H.W.; supervision, Y.-X.Z. and B.L.; project administration, S.-M.C.; funding acquisition, H.-T.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by China Geological Survey, grant number DD20208007 and ZD20220308.

Data Availability Statement

Not applicable.

Acknowledgments

Thanks to the two anonymous reviewers for their comments.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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Figure 2. Simplified geological map of Chaxi Au deposit. Modified from unpublished data from [42].
Figure 2. Simplified geological map of Chaxi Au deposit. Modified from unpublished data from [42].
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Minerals 12 00867 g003 550
Figure 3. Photographs of the different quartz vein generations at Chaxi: (a,b) Gold, galena, tetrahedrite, chalcopyrite, chalcocite, bournonite and tetradymite in Stage II WNW-trending quartz vein; (c) Stage II NNE-trending quartz-pyrite-gold vein; (d) Limonite, covellite, calcite, and dolomite in Stage III NNE-trending quartz vein; (e) Cubic coarse-grained pyrite along Stage I quartz vein margin; (f) Chalcopyrite, tetrahedrite, and chalcocite in Stage II WNW-trending quartz vein. Ttr-Tetrahedrite; Gn-Galena; Ccp-Chalcopyrite; Cc-Chalcocite; Bnn-Bournonite; Ttd-Tetradymite; Py-Pyrite; Cv-Covellite; Cal-Calcite; Dol-Dolomite-; Lmn-Limonite; Au-Gold.
Figure 3. Photographs of the different quartz vein generations at Chaxi: (a,b) Gold, galena, tetrahedrite, chalcopyrite, chalcocite, bournonite and tetradymite in Stage II WNW-trending quartz vein; (c) Stage II NNE-trending quartz-pyrite-gold vein; (d) Limonite, covellite, calcite, and dolomite in Stage III NNE-trending quartz vein; (e) Cubic coarse-grained pyrite along Stage I quartz vein margin; (f) Chalcopyrite, tetrahedrite, and chalcocite in Stage II WNW-trending quartz vein. Ttr-Tetrahedrite; Gn-Galena; Ccp-Chalcopyrite; Cc-Chalcocite; Bnn-Bournonite; Ttd-Tetradymite; Py-Pyrite; Cv-Covellite; Cal-Calcite; Dol-Dolomite-; Lmn-Limonite; Au-Gold.
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Minerals 12 00867 g004 550
Figure 4. Photographs of the different generations of quartz veins and minerals from the Chaxi deposit: (a) Normal fault cut Stage II WNW-trending quartz veins; (b) Stage I and III NNE-trending quartz veins. The latter cut Stage II WNW-trending quartz vein; (c) Conjugate Stage II quartz veins; (d) Stage II auriferous quartz vein outcrop; (e) Stage III NNE-trending quartz vein cut Stage II quartz vein; (f) Stage II galena and auriferous quartz vein; (g) Intercutting Stage II quartz veins.
Figure 4. Photographs of the different generations of quartz veins and minerals from the Chaxi deposit: (a) Normal fault cut Stage II WNW-trending quartz veins; (b) Stage I and III NNE-trending quartz veins. The latter cut Stage II WNW-trending quartz vein; (c) Conjugate Stage II quartz veins; (d) Stage II auriferous quartz vein outcrop; (e) Stage III NNE-trending quartz vein cut Stage II quartz vein; (f) Stage II galena and auriferous quartz vein; (g) Intercutting Stage II quartz veins.
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Figure 5. Reflected light and backscattered electron (BSE) images of ore minerals from Chaxi: (a) Tetrahedrite and chalcopyrite inside bournonite; (b) Tetrahedrite, aleksite, tetradymite inside chalcopyrite; (c) Chalcopyrite inside cubic pyrite; (d) Chalcocite and galena formed after tetradymite; (e) Gold cut by quartz veinlet; (f) Bursaite inside chalcopyrite; (g) Tetradymite and aleksite formed after tetrahedrite and sinnerite; (h) Tetrahedrite and galena inside chalcocite; (i) Electrum and sinnerite inside tetrahedrite, and formed after chalcopyrite. Abbreviations: Ttr-Tetrahedrite; Ccp-Chalcopyrite; Bnn-Bournonite; Alk-Aleksite; Ttd-Tetradymite; Rt-rutile; Py-Pyrite; Qz-Quartz; Gn-Galena; Cc-Chalcocite; Au-Gold; Ank-Ankerite; Bst-Bursaite; Sin-Sinnerite; Alk-Aleksite; Et-electrum. EPMA data of sulfides/sulfosalts is in Supplementary Table S1.
Figure 5. Reflected light and backscattered electron (BSE) images of ore minerals from Chaxi: (a) Tetrahedrite and chalcopyrite inside bournonite; (b) Tetrahedrite, aleksite, tetradymite inside chalcopyrite; (c) Chalcopyrite inside cubic pyrite; (d) Chalcocite and galena formed after tetradymite; (e) Gold cut by quartz veinlet; (f) Bursaite inside chalcopyrite; (g) Tetradymite and aleksite formed after tetrahedrite and sinnerite; (h) Tetrahedrite and galena inside chalcocite; (i) Electrum and sinnerite inside tetrahedrite, and formed after chalcopyrite. Abbreviations: Ttr-Tetrahedrite; Ccp-Chalcopyrite; Bnn-Bournonite; Alk-Aleksite; Ttd-Tetradymite; Rt-rutile; Py-Pyrite; Qz-Quartz; Gn-Galena; Cc-Chalcocite; Au-Gold; Ank-Ankerite; Bst-Bursaite; Sin-Sinnerite; Alk-Aleksite; Et-electrum. EPMA data of sulfides/sulfosalts is in Supplementary Table S1.
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Figure 6. Mineral paragenetic sequence for the Chaxi gold deposit. EPMA data of sulfides/sulfosalts is in Supplementary Table S1.
Figure 6. Mineral paragenetic sequence for the Chaxi gold deposit. EPMA data of sulfides/sulfosalts is in Supplementary Table S1.
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Minerals 12 00867 g007 550
Figure 7. Photos showing the fluid inclusion features in the different quartz generations from Chaxi: (a) Stage II C-type and W-type FIs; (b,c) Stage II W-type FIs; (d–f) Stage III W-type FIs. Abbreviations: LCO2-CO2 liquid phase, LH2O-H2O liquid phase, VCO2-CO2 vapor phase, VH2O-H2O vapor phase.
Figure 7. Photos showing the fluid inclusion features in the different quartz generations from Chaxi: (a) Stage II C-type and W-type FIs; (b,c) Stage II W-type FIs; (d–f) Stage III W-type FIs. Abbreviations: LCO2-CO2 liquid phase, LH2O-H2O liquid phase, VCO2-CO2 vapor phase, VH2O-H2O vapor phase.
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Figure 8. Homogenization temperature (Th) vs. salinity plot of stage I to III fluid inclusions at Chaxi.
Figure 8. Homogenization temperature (Th) vs. salinity plot of stage I to III fluid inclusions at Chaxi.
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Figure 9. Representative Raman spectra and transmitted light photographs of fluid inclusions from Chaxi: (a) Stage II C-type and W-type FIs; (b) Stage III W-type FIs.
Figure 9. Representative Raman spectra and transmitted light photographs of fluid inclusions from Chaxi: (a) Stage II C-type and W-type FIs; (b) Stage III W-type FIs.
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Minerals 12 00867 g010 550
Figure 10. δD vs. calculated δ18OH2O of the Chaxi gold ore fluids. Metamorphic and magmatic water data field are from [46].
Figure 10. δD vs. calculated δ18OH2O of the Chaxi gold ore fluids. Metamorphic and magmatic water data field are from [46].
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Minerals 12 00867 g011 550
Figure 11. (a) δ34S histogram for sulfides from the Chaxi gold deposit; (b) Comparison of δ34S values of Chaxi Au deposit with typical Au(-Sb) deposits in the Xuefeng belt, Precambrian strata, and other rock types [16,17,20,22,40,41,47,48,49,50,51,52,53,54,55].
Figure 11. (a) δ34S histogram for sulfides from the Chaxi gold deposit; (b) Comparison of δ34S values of Chaxi Au deposit with typical Au(-Sb) deposits in the Xuefeng belt, Precambrian strata, and other rock types [16,17,20,22,40,41,47,48,49,50,51,52,53,54,55].
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Figure 12. (a) 207Pb/204Pb vs. 206Pb/204Pb and (b) 208Pb/204Pb vs. 206Pb/204Pb plots for sulfides, wall rocks and fault gouge from the Chaxi gold deposit. Plumbotectonic framework is from [56]. Data of Precambrian strata are from [50].
Figure 12. (a) 207Pb/204Pb vs. 206Pb/204Pb and (b) 208Pb/204Pb vs. 206Pb/204Pb plots for sulfides, wall rocks and fault gouge from the Chaxi gold deposit. Plumbotectonic framework is from [56]. Data of Precambrian strata are from [50].
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Figure 13. (a) Ni vs. Co and (b) Au vs. As plots of the different-stage pyrites from Chaxi.
Figure 13. (a) Ni vs. Co and (b) Au vs. As plots of the different-stage pyrites from Chaxi.
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Table
Table 1. Microthermometric data of fluid inclusions in the Chaxi gold deposit.
Table 1. Microthermometric data of fluid inclusions in the Chaxi gold deposit.
StageFl TypeTmice
(°C)		Average
(°C)		Thtot
(°C)		Average
(°C)		Salinity
(wt.% NaClequiv)		Average
(wt.% NaClequiv)		Density
(g/cm3)		Average
(g/cm3)		Pressure
(MPa)		Average
(MPa)
stage IW−13.8 to −1.6−8.4 139.6 to 267.1189.72.7 to 17.611.80.81 to 1.040.95 0.46 to 4.862.02
stage IIC−16.6 to −2.1−11.7151.0 to 387.2229.13.6 to 19.915.0 0.85 to 1.060.99 0.42 to 11.752.16
W−14.9 to −1.6−6.3137.5 to 327.0188.8 2.7 to 18.59.20.81 to 1.050.95 0.44 to 4.381.27
stage IIIW−18.6 to −1.8−7.2 139.7 to 330.5188.53.1 to 21.410.30.80 to 1.070.950.44 to 5.401.43
Table
Table 2. Oxygen and hydrogen isotopic data of quartz in the Chaxi gold deposit.
Table 2. Oxygen and hydrogen isotopic data of quartz in the Chaxi gold deposit.
SampleMineralStageOccurrenceδDV-SMOW‰δ18OV-SMOW‰Temperatureδ18OH2O
CX2003-1-3quartzIIshallow vein, strike WNW, bearing galena and chalcopyrite−49.816.96187.84.45
CX2006quartzIIsteep vein, strike WNW, thickness of 20 cm−56.617.02187.84.52
CX2010quartzIIIsteep vein, strike ENE, thickness of 0.3–1.5 cm, rich in gold, galena and irregular fine-grained pyrite−61.515.50187.82.99
CX2015quartzIIshallow vein, strike WNW, thickness of 8–12 cm, bearing cubic pyrites−62.316.96187.84.45
CX2016quartzIIsteep vein, strike WNW, thickness of 8–12 cm, bearing cubic pyrites−62.915.36187.82.85
CX2022quartzIIshallow vein, strike WNW−54.017.11203.55.63
CX2026-1-2quartzIsteep vein, strike ENE, thickness of 8–12 cm−53.116.72186.84.14
CX-6quartzIIshallow vein, strike WNW−53.7515.44180.42.40
CX-17quartzIsteep vein, strike ENE, bearing irregular shape fine-grained pyrites−61.4515.62187.83.11
CX-18quartzIIshallow vein, strike WNW−71.7316.44169.32.58
Table
Table 3. Sulfur isotopic compositions of sulfides, wallrocks and fault gouge in the Chaxi gold deposit.
Table 3. Sulfur isotopic compositions of sulfides, wallrocks and fault gouge in the Chaxi gold deposit.
SampleMineralStageOccurrenceδ34SV-CDT‰
CX2008-1pyriteIIIsteep quartz veins, strike ENE, thickness of 0.3–1.5 cm, rich in visible gold, galena and irregular shape fine-grained pyrite18.55
CX2008-2pyrite17.50
CX2009-1pyriteIIIsteep quartz veins, strike ENE, thickness of 0.3–1.5 cm, rich in visible gold, galena and irregular shape fine-grained pyrite19.33
CX2009-2pyrite18.61
CX2010-1pyriteIIIsteep quartz vein, strike ENE, thickness of 0.3–1.5 cm, rich in visible gold, galena and irregular shape fine-grained pyrite17.74
CX2010-2pyrite17.12
CX2011-1pyriteIcubic pyrites in meta-greywacke15.11
CX2011-2pyrite16.38
CX2016-1pyriteIcubic pyrites in meta-greywacke18.59
CX2016-2pyrite15.95
CX2022-1galenaIISulfides-gold-bearing WNW-striking quartz veins6.26
CX2022-2galena6.67
CX-17-1chalcopyriteIISulfides-electrum-bearing WNW-striking quartz veins 9.78
CX-17-2chalcopyrite11.77
CX2004meta-graywacke 18.20
CX2005carbonaceous slate 21.66
CX2009cinerous sandy slate 20.95
CX2011-1meta-graywacke 16.31
CX2011-2meta-graywacke 16.42
CX2025NNE-trending fault gouge width ~15–25 cm −5.35
CX2027WNW-trending fault gouge 239°∠61°, purple, width ~20 cm, with sliding surface scratches-
Table
Table 4. Lead isotopic compositions for sulfides in Chaxi gold deposit.
Table 4. Lead isotopic compositions for sulfides in Chaxi gold deposit.
SampleSamples206Pb/204PbError (%) 1207Pb/204PbError (%)208Pb/204PbError (%)
CX2008pyrite17.0945 0.0004 15.4788 0.0003 37.3803 0.0007
CX2009pyrite17.2281 0.0010 15.5067 0.0010 37.5185 0.0035
CX2010pyrite16.8000 0.0006 15.4510 0.0007 37.0544 0.0018
CX2011pyrite16.9557 0.0007 15.4804 0.0006 37.3011 0.0016
CX2016pyrite17.0367 0.0013 15.4517 0.0015 37.3474 0.0048
CX2022galena16.7215 0.0067 15.4413 0.0074 36.9731 0.0180
CX-17chalcopyrite16.97340.000315.51410.000237.39190.0005
CX2004-1meta-graywacke17.85830.000415.53330.000637.99720.0045
CX2004-2meta-graywacke17.83080.001115.51880.000538.01500.0171
CX2005carbonaceous slate18.44660.001315.58790.000937.89940.0063
CX2009cinerous sandy slate17.62000.000815.51850.000737.91470.0066
CX2011meta-graywacke 17.76390.006615.53000.004838.32250.0133
CX2025NNE-trending fault gouge16.98310.001415.38770.001536.03580.0144
CX2027WNW-trending fault gouge17.0582 0.0006 15.4712 0.0006 37.3625 0.0008
1 Errors given at the 2σ level.
Table
Table 5. EPMA data of pyrites in the Chaxi gold deposit.
Table 5. EPMA data of pyrites in the Chaxi gold deposit.
Spot No.StageAsSeAuSPbAgTeFeCoNiCuZnMoSbBiMnTotal
Py CX2010
1Syn-ore0.14--52.98---44.890.06--0.030.36---98.47
20.16-0.0252.65--0.0245.680.040.02--0.46---99.04
30.180.01-53.61--0.0246.310.060.01-0.040.43---100.68
40.15-0.0254.32---46.580.05-0.07-0.410.02-0.01101.64
50.18-0.0154.82-0.02-47.040.040.08-0.080.40---102.67
60.19--54.32--0.0046.810.050.030.010.010.39--0.02101.85
80.16-0.0152.71---45.050.04-0.040.050.310.01--98.37
110.14--52.05---45.470.04-0.050.060.35--0.0198.17
130.170.020.0152.49--0.0145.490.030.01--0.46---98.68
140.16--51.05---46.180.060.01--0.58---98.14
Py CX21-11
10.230.020.0651.43-0.02-45.810.060.03-0.090.34---98.09
21.80-0.0250.55-0.010.0245.100.05---0.39--0.0197.93
30.20--52.05-0.050.0145.900.060.020.01-0.430.02--98.73
50.230.02-52.39---45.460.070.050.030.050.430.02--98.75
70.190.010.0252.28-0.00-47.010.100.050.010.100.410.01--100.18
80.25-0.0553.20-0.03-46.950.140.060.01-0.420.02--101.11
250.31--53.25--0.0247.300.04-0.070.080.410.01--101.49
260.13--53.47---47.350.06-0.050.030.44---101.52
270.22--52.35-0.02-47.880.08---0.410.02-0.01100.97
170.200.01-54.22-0.02-46.780.070.08--0.440.01--101.83
180.17-0.0153.66-0.020.0246.640.030.03--0.440.02--101.03
Py CX21-16
10.21--52.33-0.03-47.040.040.030.01-0.35---100.04
20.18--52.39-0.01-46.840.060.06-0.060.34---99.95
30.19-0.0151.95--0.0146.180.100.090.060.070.420.02-0.2599.32
50.19--52.03-0.010.0247.190.080.01--0.37---99.89
60.25--52.76-0.00-47.090.050.08-0.010.40---100.64
70.260.030.0147.876.54--42.910.160.100.050.070.180.01--98.19
9Syn-ore0.23-0.0253.26-0.02-47.880.030.03-0.040.37---101.89
100.350.020.0153.69-0.01-48.270.09--0.010.42---102.88
110.35-0.0351.45-0.010.0146.630.08---0.370.04-0.0198.99
120.510.020.0451.60-0.010.0146.930.060.04--0.44---99.65
130.52--51.90-0.02-46.350.090.02--0.47--0.0199.37
Py CX21-17
20.26-0.0152.28---47.210.170.060.060.030.360.01-0.01100.46
60.52--52.08-0.02-47.110.200.040.070.030.330.01-0.01100.41
100.39-0.0351.32-0.01-47.840.160.07--0.360.05--100.22
110.160.02-53.28-0.04-47.430.06---0.59---101.58
140.21--52.71-0.01-46.770.06---0.62---100.38
170.210.01-52.85---46.930.05---0.61---100.66
180.20--53.01-0.04-46.900.050.04-0.100.52---100.86
200.31-0.0651.33-0.01-46.880.06--0.010.68---99.34
210.31--51.87-0.03-46.910.020.04--0.61---99.80
Py BKS-2
2Pre-ore0.160.010.0252.42---46.600.050.01-0.020.370.01--99.66
30.14--52.53---47.070.060.050.02-0.350.01--100.24
40.18-0.0152.68---46.880.070.010.01-0.42---100.27
50.12-0.0352.40-0.01-46.390.350.04--0.350.02--99.71
70.150.02-52.74---45.800.050.03-0.050.60---99.50
80.21--52.90---45.830.060.05-0.020.57---99.79
800.15--51.43-0.02-46.880.07-0.020.020.41--0.0199.02
810.18--51.48-0.02-46.240.050.01--0.43--0.0198.42
820.20-0.0352.12---47.530.31-0.060.030.44---100.71
830.18-0.0753.28-0.01-46.930.070.01--0.37---100.92
850.14--51.27-0.020.0246.790.070.120.090.020.39---98.93
-: below the detection limits.
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Chen, S.-M.; Zhou, Y.-X.; Li, B.; Wu, J.-H.; Zhao, H.-T.; Zhang, Z.-M.; Zeng, H. Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations. Minerals 2022, 12, 867. https://doi.org/10.3390/min12070867

AMA Style

Chen S-M, Zhou Y-X, Li B, Wu J-H, Zhao H-T, Zhang Z-M, Zeng H. Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations. Minerals. 2022; 12(7):867. https://doi.org/10.3390/min12070867

Chicago/Turabian Style

Chen, Shu-Min, Yu-Xuan Zhou, Bin Li, Jin-Hong Wu, Hong-Tao Zhao, Zhi-Ming Zhang, and Hao Zeng. 2022. "Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations" Minerals 12, no. 7: 867. https://doi.org/10.3390/min12070867

APA Style

Chen, S.-M., Zhou, Y.-X., Li, B., Wu, J.-H., Zhao, H.-T., Zhang, Z.-M., & Zeng, H. (2022). Genesis of Chaxi Gold Deposit in Southwestern Hunan Province, Jiangnan Orogen (South China): Constraints from Fluid Inclusions, H-O-S-Pb Isotopes, and Pyrite Trace Element Concentrations. Minerals, 12(7), 867. https://doi.org/10.3390/min12070867

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