In situ geochemical investigations of pyrite constraining Au-Sb mineralization in the Jienagepu deposit, southern Tibet, China

• Pyrite contains high contents of Co, Ni, Cu, As, Sb and Pb, with Au existing as solid solution. • Mesozoic slate strata were the main sulfur source. • The ore-forming fluids are dominated by meteoric and characterized by low temperature and salinity. • The Miocene Au-Sb mineralization in southern Tibet represents a geothermal fluid metallogenic system. The Jienagepu Au-Sb deposit, recently identified in the eastern Tethyan Himalayan Sequence (THS), southern Tibet, shows considerable resource potential in this Sb-Au metallogenic domain. Although numerous local Sb-Au ore bodies hosted in Mesozoic weakly metamorphosed slate have been identified and investigated, the sources of regional Sb and Au resources and the properties of the ore-forming fluids in this unique orogenic setting remain highly controversial. To address these issues, in situ trace element and sulfur isotope analyses were performed on pyrite from the gold-base metal sulfides mineralization stage (II) of the Jienagepu deposit. Trace element analyses indicate that pyrite contains high concentrations of Ni, Cu, As, and Sb, whereas the concentrations of Zn, Se, and Ag are relatively low. Except for minor Sb-(Ni/As)-bearing inclusions, most trace elements, including gold, are hosted within pyrite as solid solutions. The newly obtained in situ sulfur isotope data for pyrite (δ 34 S = 5.0‰-8.0‰; average = 6.2‰), in comparison with regional S isotopic reservoirs, suggest that the slate strata were the main sulfur source. In situ geochemical results for pyrite further indicate that the Jienagepu ore-forming fluids were mainly meteoric with a minor magmatic water, and were characterized by low temperature (<300 °C) and low salinity (<9 wt% NaCl equiv). Combined with previous studies, we propose that, in a Miocene post-collisional extensional setting, meteoric-dominated geothermal fluids, driven by heat from coeval felsic magmatism, circulated at shallow levels, leaching ore-forming elements from the slate strata and then migrating along N-S-trending faults, ultimately forming the giant Sb-Au resources of southern Tibet. This study provides important insights for understanding the Sb-Au enrichment in post-collisional settings and for guiding regional Sb-Au ore exploration.