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Metal stable isotopes (e.g., Zn, Cd, and Cu) have been used to track metal sources in different types of hydrothermal systems. However, metal isotopic variations in sulphides could be triggered by various factors such as mineral precipitation and fluid mixing. Thus, tracking the metal sources of hydrothermal systems is still a big challenge for metal isotopes. In this study, we investigated the Cd isotopic systematics of sphalerite from the Nayongzhi Zn–Pb deposit, which is a Mississippi Valley‐type (MVT) deposit in the Sichuan–Yunnan–Guizhou mineralization province (SYGMP). We reinterpreted the published S isotope data for the SYGMP and found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. As such, a model that involves mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction (TSR) can explain the ore formation in the Nayongzhi deposit. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing, and thus the Cd isotopic variations of sphalerite were inherited from the source rocks. The large range of Zn/Cd ratios and uniform Cd isotopic compositions of the sulphides are similar to those of igneous rocks but different from those of sedimentary rocks, indicating that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Our results reaffirm that metal stable isotopes, particularly Cd isotope compositions of sphalerite, are powerful geochemical tracers for investigating the formation mechanisms of ore deposits. Plain Language Summary: Metal stable isotopes, particularly Cd isotopes, have been widely used in investigating the metal sources, fluid evolution, and formation mechanisms of ore deposits. Here, we studied the Cd isotopic compositions of sphalerite from the Nayongzhi Zn–Pb deposit in the Sichuan–Yunnan–Guizhou mineralization province. The range of δ114/110CdNIST‐3108 value is smaller in the Nayongzhi deposit (−0.16–0.21‰), but the published S isotopic composition has significant variation (11.8–33.0‰). We found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. Thus, a mineralization model of the Nayongzhi deposit has been proposed, which involves the mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing. Therefore, the Cd isotopic variations of sphalerite were inherited from the source rocks. Combining the Zn/Cd ratios and Cd isotopic composition characteristics of the sulphides, igneous rocks, and sedimentary rocks, it is indicated that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Key Points: S isotopic variations caused by Rayleigh fractionation between sulphide and reduced S; Cd isotopic variations inherited from source rocksZn/Cd ratios and Cd isotopic compositions reveal that Zn and Cd were dominantly derived from basement rocksThe Nayongzhi deposit was formed by mixing between metal‐rich and reduced sulfur ore‐forming fluids [ABSTRACT FROM AUTHOR]

The Sichuan–Yunnan–Guizhou (SYG) metallogenic province of southwest China is one of the most important Zn–Pb ore zones in China, with ~ 200 Mt Zn–Pb ores at mean grades of 10 wt.% Zn and 5 wt.% Pb. The source and mechanism of the regional Zn–Pb mineralization remain controversial despite many investigations that have been conducted. The Wusihe Zn–Pb deposit is a representative large-scale Zn–Pb deposit in the northern SYG, which mainly occurs in the Dengying Formation and yields Zn–Pb resources of ~ 3.7 Mt. In this paper, Zn and S isotopes, and Fe and Cd contents of sphalerite from the Wusihe deposit were investigated in an attempt to constrain the controls on Zn and S isotopic variations, the potential sources of ore-forming components, and the possible mineralization mechanisms. Both the δ66Zn and δ34S values in sphalerite from the Wusihe deposit increase systematically from the bottom to the top of the strata-bound orebodies. Such spatial evolution in δ66Zn and δ34S values of sphalerite can be attributed to isotopic Rayleigh fractionation during sphalerite precipitation with temperature variations. The strong correlations between the Zn–S isotopic compositions and Fe–Cd concentrations in sphalerite suggest that their variations were dominated by a similar mechanism. However, the Rayleigh fractionation mechanism cannot explain the spatial variations of Fe and Cd concentrations of sphalerite in this deposit. It is noted that the bottom and top sphalerites from the strata-bound orebodies document contrasting Zn and S isotopic compositions which correspond to the Zn and S isotopic characteristics of basement rocks and host rocks, respectively. Therefore, the mixing of two-source fluids with distinct Zn–S isotopic signatures was responsible for the spatial variations of Zn–S isotopic compositions of sphalerite from the Wusihe deposit. The fluids from basement rocks are characterized by relatively lighter Zn (~ 0.2 ‰) and S (~ 5 ‰) isotopic compositions while the fluids from host rocks are marked by relatively heavier Zn (~ 0.6 ‰) and S (~ 15 ‰) isotopic compositions. [ABSTRACT FROM AUTHOR]

Although Zn–Pb deposits are one of the most important Cd reservoirs in the earth, few studies have focused on the Cd isotopic fractionation in Zn–Pb hydrothermal systems. This study investigates the causes and consequences of cadmium and sulfur isotope fractionation in a large hydrothermal system at the Tianbaoshan Zn–Pb–Cd deposit from the Sichuan–Yunnan–Guizhou (SYG) metallogenic province, SW China. Moderate variations in Cd and S isotope compositions have been measured in sphalerite cover a distance of about 78 m. Sphalerite has δ 114/110 Cd values ranging from 0.01 to 0.57‰, and sulfides (sphalerite, galena and chalcopyrite) have δ 34 S CDT values ranging from 0.2 to 5.0‰. Although δ 34 S CDT and δ 114/110 Cd values in sphalerites have no regular spatial variations, the δ 34 S CDT values in galena and calculated ore-forming fluid temperatures decreased from 2.1 to 0.2‰ and from about 290 to 130 °C, respectively, from the bottom to the top of the deposit. Heavy Cd isotopes are enriched in early precipitated sphalerite in contrast to previous studies. We suggest that Cd isotopic compositions in ore-forming fluids are heterogeneous, which result in heavy Cd isotope enrichment in early precipitated sphalerite. In comparison with other Zn–Pb deposits in the SYG area, the Tianbaoshan deposit has moderate Cd contents and small isotope fractionation, suggesting differences in origin to other Zn–Pb deposits in the SYG province. In the Tianbaoshan deposit, the calculated δ 34 S∑ S-fluids value is 4.2‰, which is not only higher than the mantle-derived magmatic sulfur (0 ± 3‰), but also quite lower than those of Ediacaran marine sulfates (about 30 to 35‰). Thus, we suggest that reduced sulfur of ore-forming fluids in the deposit was mainly derived from the leaching of the basement, which contains large amount of volcanic or intrusive rocks. Based upon a combination of Cd and S isotopic systems, the Tianbaoshan deposit has different geochemical characteristics from typical Zn–Pb deposits (e.g., the Huize deposit) in SYG area, indicating the unique origin of this deposit. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cu++In3+↔Zn2++Fe2+ is the most plausible indium substitution mechanism for ZnS in polymetallic vein along the western Jiangnan Orogen. • Zn and Cd isotopic data suggest ore-forming fluids were derived from magmatic-hydrothermal systems. • Hydrothermal fluids of polymetallic vein deposit mightderive from the fractionation of Zn, Cd, Cu, In and Sn in the Guangxi Orogeny related to granitic magma. Polymetallic veins of Zn-Pb (Cu) deposits containing elevated levels of indium are hosted within the upper part of the Banxi Group in the western Jiangnan Orogen. The indium in the polymetallic vein deposits is hosted within sphalerite and chalcopyrite. Cu++In3+↔Zn2++Fe2+ is the most plausible indium substitution mechanism for ZnS in these deposits. Hydrothermal fluids were enriched in Cu, In, Co, Mn and Fe in the later mineralization stage. Ores, sphalerite and dolomite minerals displayed analogous Ce and Eu anomalies, and Zn/Cd ratios, while being noticeably different from its host rocks, that provided its mineralized metals were not derived from its host rock. Despite the Zn and Cd isotopic variations in sphalerite being relatively narrow (δ66Zn JMC = +0.01‰–+0.28‰; δ114Cd Spex = −0.14‰–+0.11‰), they display increase during mineralization and are negatively correlated to Cd concentrations; the Rayleigh distillation might be the fractionation mechanism. Zn/Cd ratios and Zn-Cd isotopic variations suggest the magmatic-hydrothermal origin of the polymetallic vein-type deposits. These hydrothermal fluids might derive from the fractionation of Zn, Cd, Cu, In and Sn in the granitic magma. This is triggered by crust thickening and the detachment of the lower crust along the Jiangnan Orogen during the intracontinental orogenic events of the Guangxi orogeny. This period of granitic magmatism might be another important indium mineralization episode in South China. [ABSTRACT FROM AUTHOR]

• The limited Zn isotopic fractionation between sphalerite and original fluid could be attributed to the striking decrease in the temperature of the incoming fluid. • Zinc and sulfur were derived respectively from basement rocks and host rocks, suggesting the mixing of Zn-bearing and S-bearing fluid in the Maozu deposit. • The integrally lower Zn isotopic compositions of sphalerite may indicate that the Maozu deposit is closer to the regional Zn-bearing fluid center. The Sichuan-Yunnan-Guizhou (SYG) metallogenic province, southwestern Yangtze Block, is one of the most important Zn-Pb repositories in China, with more than 200 million tons (Mt) of Zn-Pb ores. The source regions for the regional Zn-Pb mineralization in the SYG are still controversial, mostly in regard to the Emeishan flood basalts, basement rocks and host rocks. The Maozu Zn-Pb deposit is geographically close to the SYG center, which could also indicate that it is closer to the regional Zn-bearing fluid center than those deposits along the SYG margin. However, the origin of the ore-forming Zn in the Maozu deposit has not been constrained until now. In this study, the Zn and S isotopic compositions and Fe and Cd concentrations of the sphalerite from the Maozu deposit are investigated to evaluate the Zn isotopic fractionation during sphalerite precipitation, the source regions of the ore-forming zinc and sulfur, and the center of the regional Zn-bearing fluid system. It is suggested that the Zn isotopic fractionation between the sphalerite and original fluid during sphalerite precipitation could be limited due to the striking decrease in the temperature of the incoming fluid. The Zn isotopic variation of the sphalerite from four mining levels in the Maozu deposit is really small (−0.06 to +0.23‰), which could be attributed to heterogeneous Zn isotopic compositions in original incoming fluid rather than Zn isotopic fractionation during sphalerite deposition. As such, in the Maozu deposit, the Zn isotopic compositions of original hydrothermal fluid could approximately be represented by the Zn isotopic signals documented in sphalerite (−0.06 to +0.23‰). We found that the Zn isotopic signatures of incoming fluid are largely overlapped with those of the basement rocks (+0.10 to +0.34‰), signifying that the ore-forming Zn could be predominantly sourced from the basement rocks. However, in the Maozu deposit, the ore-forming sulfur is most likely derived from the sulfur-bearing evaporates hosted in the country rocks via thermochemical sulfate reduction (TSR). The contrasting sources of ore-forming zinc and sulfur suggest the mixing of Zn-bearing fluid from the basement rocks and sulfur-bearing fluid from the host rocks, which could be responsible for the sharp decrease in the temperature of the incoming fluid in the Maozu deposit. Combined with the results of previous studies, the integrally lower Zn isotopic compositions of sphalerite in the Maozu deposit compared to those deposits along the SYG margin may demonstrate that the Maozu deposit is closer to the regional Zn-bearing fluid center. If this is the case, Zn isotopes could be an effective proxy to trace the Zn source of Zn-enriched ore deposits and to identify the regional Zn-bearing fluid center of Zn-enriched metallogenic provinces. [ABSTRACT FROM AUTHOR]

[Display omitted] • The source and evolution of ore-forming fluids are characterized using lithium and chlorine isotopes. • Magmatic source of ore-forming fluids plays a critical role in the mineralizing systems of the Luziyuan Zn-Pb-Fe-(Cu) deposit. • The increase of δ 7 Li values in the ore-forming fluids during retrograde skarn alteration is the results of Rayleigh fractionation in a closed system. The sources and temporal evolution of fluids related to distal skarn mineralization strongly influence the minerals that form, but remain poorly understood. In this study, we use the lithium and chlorine isotopic compositions of fluid-inclusion leachates (FIL) to elucidate the nature and evolution of fluids that formed the Luziyuan distal skarn Zn–Pb–Fe–(Cu) deposit, China. The δ7Li values of prograde skarn stage rhodonite FIL (+5.37‰–+7.31‰) are similar to those of typical magmatic fluid. The δ7Li values (+11.69‰–+12.54‰) of actinolite FIL are higher than those of rhodonite FIL; this is attributed to Rayleigh fractionation within a closed magmatic–hydrothermal system. It is inferred that up to 70% of fluid-borne Li is sequestered by hydrous minerals during retrograde skarn alteration, consistent with conclusions drawn from previous studies of fluid-inclusions. The δ7Li values of galena FIL (+9.78‰–+13.19‰), black sphalerite FIL (+11.62‰), and reddish-brown sphalerite (+10.44‰–+11.66‰) overlap with those of actinolite FIL, indicating that phase separation occurred during Zn–Pb mineralization at the Luziyuan deposit. The low δ7Li values of light-yellow sphalerite FIL (+6.75‰) and calcite FIL (+3.95‰–+6.49‰) record external fluid input, probably meteoric water. The positive δ37Cl values of rhodonite FIL (+1.82‰–+1.83‰) are consistent with those of magmatic fluids. However, the δ37Cl values of actinolite FIL (+0.49‰) are lower than those of rhodonite FIL, indicating that FIL within hydrous minerals might not record fluid sources reliably. [ABSTRACT FROM AUTHOR]

• δ 114/110Cd values were determined for sulfides of the Zhugongtang Zn–Pb deposit, China. • Metals of the deposit were derived from a mixture of basement and sedimentary rocks. • Metal concentrations in deposits of the SYGMP were likely controlled by source rocks. The Sichuan–Yunnan–Guizhou metallogenic province (SYGMP) includes > 400 Zn − Pb deposits and prospects, eight of which are large-scale deposits with large reserves of critical metals such as Cd and Ge, including the Huize Zn − Pb − Cd − Ge and Daliangzi Zn–Pb–Ge–Cd deposits. The newly discovered Zhugongtang Zn − Pb deposit is a super-large deposit with Zn–Pb reserves of > 3 Mt. Its geochemical features are similar to those of the Huize deposit, with similar sulfide δ34S values and concentrations of critical elements in sphalerite (e.g., Cd and Ge). However, the two deposits have different host strata, and it remains unclear as to whether they have similar oregenesis. In this study, δ 114/110Cd values and major- and trace-element compositions of sphalerites collected from a drill-core and tunnels of the Zhugongtang deposit were determined in an investigation of metal sources. Drill-core samples were impure and exhibited strong correlation (R2 = 0.89) between Zn and Cd contents. For samples from mining tunnels, the Cd and Fe contents of selected sphalerites were positively correlated, especially yellow sphalerites (R2 = 0.76). Cadmium is likely hosted in sphalerite by the substitution mechanism of (Fe2+, Cd2+) ↔ Zn2+. The δ 114/110Cd values of all samples ranged from − 0.43 ‰ to 0.06 ‰. Based on Zn/Cd ratios, and excluding geochemical processes that may have caused the variable Cd isotopic compositions, we suggest that the metal sources of the deposit were derived from the mixing of sedimentary and basement rocks. This model is supported by the strong relationship between the δ 114/110Cd and 1/Cd values of sphalerites from 11 typical Zn–Pb deposits in the SYGMP (R2 = 0.81). The quantification of metal contributions of source rocks indicates that deposits derived mainly from sedimentary rocks generally have relatively low sphalerite Ge contents and small Ge reserves, whereas those derived mainly from basement rocks have higher Ge contents and larger Ge reserves. This study provides a new model for explaining the enrichment of critical metals in Zn–Pb deposits of the SYGMP, thus extending the applications of Cd isotopes in hydrothermal systems. [ABSTRACT FROM AUTHOR]

• Determined Ge isotopic compositions in sphalerite in the Fule deposit. • Performance of δ 74/70Ge and Ge contents in sphalerite decline linearly in sphalerite. • Ge contents of sphalerite may be controlled by the temperature of the ore-forming fluid. • Performance of δ 114/110Cd and δ 74/70Ge decline linearly during sphalerite precipitation. • Rayleigh process control Ge and Cd isotope variations in sphalerite. The Sichuan–Yunnan–Guizhou metallogenic province in southwest China is one of the most important low-temperature metallogenic domains in the country, and more than 400 Pb–Zn deposits and/or mineralization points are located in this area. The Fule deposit is better known that the other Pb–Zn deposits in the region because it is extremely highly enriched with dispersed elements, including Ge, Ga, and Cd. Based on information obtained from our previous studies, the contents of Ge and its isotopic compositions in sphalerite are investigated herein. Results show that the Ge content ranges from 60 ppm to 141.5 ppm, and δ 74/70Ge values vary from −6.57‰ to 0.97‰. In this respect, −6.57‰ is the most negative Ge isotope composition value reported in any sphalerite or seafloor sulfides to date. The Cd and Ge contents in sphalerite have a good negative relationship, and it is suggested that the mechanisms of Cd and Zn substitution are responsible for the low incorporation of Ge and relate to the high Cd content (up to 3%) of the sphalerite. In addition, there is a good positive correlation between the Ge contents and δ34S values, which was likely triggered by variations of fluid temperature. In the same hand specimen, light Ge isotope is more likely to be enriched in dark sphalerite rather than light sphalerite, similarly to Cd isotope distribution in dark and light-colored sphalerite. In addition, Cd and Ge isotope compositions, measured in an ore profile from SBFL22 to SBFL26, show a good positive relationship, suggesting that the fractionation mechanisms between Cd and Ge isotopes may be similar and they were controlled by kinetic fractionation during sphalerite precipitation. Based upon previous limited studies, we conclude that Ge in the Fule deposit is derived from mixing sources and sediment is likely the dominant one. [ABSTRACT FROM AUTHOR]