Genesis of the Shuitoushan Pb–Zn deposit, Baoshan Block, Sanjiang region: Constraints from fluid inclusions and O, S, Pb isotopes

Abstract

The Shuitoushan Pb–Zn deposit, which is located in the southern Baoshan Block of Sanjiang region, SW China, forms an important part of the Luziyuan polymetallic ore field. The origin of ore‐forming fluids and the genesis of this deposit are rarely reported. In this study, we present the results of geological features, fluid‐inclusion and isotopic (O, S, Pb) analyses of the Shuitoushan deposit. The mineralization process of this deposit can be divided into three stages: pyrite‐quartz stage (Stage I), sphalerite‐galena‐chalcopyrite stage (Stage II), and chalcopyrite‐calcite stage (Stage III), with a relatively medium‐low temperature (their homogenization temperatures ranging from 261 to 340°C, 219 to 300°C, and 159 to 225°C, respectively) and low salinity (their salinities varying from 2.1 to 6.8 wt% NaCleqv., 1.2 to 4.9 wt% NaCleqv. and 0.7 to 3.85 wt% NaCleqv., respectively), as revealed by microthermometry study of three types of fluid inclusions, namely L‐type (liquid‐rich), V‐type (vapor‐rich), and PL‐type (pure liquid), distinguished in ore‐bearing quartz veins. The decline of δ18OH2O values (decreasing from 7.58‰ in early stage to 0.08‰ in late stage) of the mineralizing fluid indicates an initial magmatic water source of it, with a gradually increasing input of meteoric water during the process of evolution. The ore‐forming materials are likely to be mainly derived from the concealed intermediate‐acid intrusions and also wall rocks, as suggested by the δ34S values (4.1–12.2‰) and Pb isotope compositions (206Pb/204Pb = 18.325–18.448, 207Pb/204Pb = 15.806–15.944, 208Pb/204Pb = 38.822–39.439) of sulphides in ores. Above all, the Shuitoushan deposit can be classified as an epithermal Pb–Zn deposit. This study also indicates that the Pb–Zn polymetallic deposits in the Luziyuan ore field have similar ore‐forming fluids and materials sources, the distribution and mineralization process of which are controlled by the concealed intermediate‐acid intrusion at depth in Luziyuan, Wumulan, and Shuitoushan areas.