Mineralogy, fluid inclusion petrography, and stable isotope geochemistry of Pb–Zn–Ag veins at the Shizhuyuan deposit, Hunan Province, southeastern China

Abstract

The Shizhuyuan polymetallic deposit is located in the central part of the Nanling region, southeastern China, and consists of proximal W–Sn–Mo–Bi skarns and greisens and distal Pb–Zn–Ag veins. The sulfides and sulfosalts in the distal veins formed in three distinct stages: (1) an early stage of pyrite and arsenopyrite, (2) a middle stage of sphalerite and chalcopyrite, and (3) a late stage of galena, Ag-, Sn-, and Bi-bearing sulfides and sulfosalts, and pyrrhotite. Combined sulfide and sulfosalt geothermometry and fluid inclusion analyses indicate that the early stage of mineralization occurred at a temperature of ~400 °C and involved boiling under hydrostatic pressure (~200 bar), with the temperature of the system dropping during the late stage to ~200 °C. Laser Raman analysis indicates that the fluid inclusions within the studied minerals are dominated by H2O, although some contain carbonate solids and CH4 gas. Vein-hosted sulfides have δ34S values of 3.8–6.3‰ that are interpreted as indicative of a magmatic source of sulfur. The mineralization process can be summarized as follows: an aqueous fluid exsolved on final crystallization of the Qianlishan pluton, ascended along fracture zones, cooled to <400 °C, and boiled under hydrostatic conditions, and with decreasing temperature and sulfur fugacity, sulfide and sulfosalt minerals precipitated successively from the Ag–Cu–Zn–Fe–Pb–Sb–As–S-bearing fluid system.