Evolution of the Au-Sb-W mineralization system: Evidence from geochronology, mineralogy, fluid inclusions, and H-O-S isotopes of the Xingfengshan and Xiangxi deposits, Jiangnan Orogenic Belt, South China

The Jiangnan Orogenic Belt in South China hosts numerous world-class Au-Sb-W deposits, with different mineralization styles, including Au-W and Au-Sb. Yet the genetic link and fluid evolution processes among these mineralization types and their genetic association with magmatic processes remain poorly constrained. This study integrates field observations, 40Ar/39Ar geochronology, fluid inclusion, and H-O-S isotope analyses of the Xingfengshan Au-W and Xiangxi Au-Sb deposits in the central in situ orogenic belt to document the fluid evolution and their genetic association with magmatism. Results show that sheeted quartz vein Au-W mineralization at Xingfengshan occurred at 212.9–204.6 Ma, while Au-Sb mineralization at Xiangxi formed at 207.3–203.1 Ma, both coeval with the adjacent Late Triassic Baimashan reduced granitic complex (218.0–204.5 Ma). Fluid inclusion data reveal a transition in ore-forming fluids from medium–high temperature, medium–low salinity H2O-NaCl ± CO2 ± CH4 systems (221–420 °C, 1.2–8.5 wt% NaCl eqv) at Xingfengshan to lower-temperature H2O-NaCl-CO2 systems (232–335 °C, 0.2–8.8 wt% NaCl eqv) at Xiangxi. Hydrogen and oxygen isotope compositions (δD = −103.6‰ to −50.1‰ and δ18O = 6.6‰ to 12.1‰ for the Xingfengshan Au-W deposit; δD = −59.6‰ to −51.9‰ and δ18O = 7.5‰ to 8.9‰ for the Xiangxi Au-Sb deposit) indicate a major contribution from magmatic fluids for both mineralization types, with only a minor amount of meteoric fluid involved. Sulfur isotope compositions show that the dominant magmatic fluid signature was buffered by fluid-rock interaction, as the high-temperature Xingfengshan deposit has negative δ34S values (−11.4‰ to −0.6‰), whereas the Xiangxi deposit shows near-zero δ34S values (−3.9‰ to 1.1‰). The systematic spatial-temporal and geochemical changes from the high-temperature Au-W to lower-temperature Au-Sb mineralization record an evolving magmatic-hydrothermal system and provide robust evidence for a unified magmatic-hydrothermal origin of the diverse Au-Sb-W mineralization in the Jiangnan Orogenic Belt.