Mineralogy, geochemistry and fluid inclusions of the Qinglong Sb-(Au) deposit, Youjiang basin (Guizhou, SW China)

摘要

Graphical abstractDisplay OmittedHighlights?New Au mineralization in the Qinglong Sb deposit (SW China) is reported.?Ore-forming fluids were of mixed H2O-NaCl-hydrocarbon?±?CO2aqueous fluids.?Sulfur in the ore-forming fluids was dominantly magmatic-derived.?Fluid mixing is a key factor for the extensive stibnite precipitation.?Stibnite precipitation destabilized the AuHS0complexes and caused Au precipitation.AbstractThe Qinglong deposit is a newly-characterized, large Sb-(Au) deposit in the Youjiang basin (Guizhou, SW China). Four mineralization stages are identified (i.e., pre-ore, early-ore, late-ore and post-ore) in this study based on crosscutting relationships. Our study shows that the Qinglong Sb mineralization (early-ore stage) was dominated by quartz-stibnite?±?fluorite, whilst the Sb-Au mineralization (late-ore stage) comprises quartz-stibnite?±?pyrite. Electron Probe Microanalysis (EPMA) indicates that the Au is present as Au1+in the arsenian pyrite. Besides, our new fluid inclusion data from fluorite, stibnite and quartz show that the Sb-Au-rich hydrothermal fluids were derived from the mixing fluids consisting of H2O, NaCl, hydrocarbon and minor CO2. In the early-ore stage, the ore-forming fluids are characterized by medium to low temperatures (161–294?°C, mean: 220?°C), medium to low salinities (0.35–13.18?wt% NaCl equiv.), low pH, and the presence of hydrocarbons and CO2. In comparison, the late-ore stage ore-forming fluids are featured by low temperatures (113–255?°C, mean: 175?°C), low salinities (0.18–6.30?wt% NaCl equiv.) and nearly neutral pH. The δ34S∑Svalues (?2.8 to 2.3‰) of the ore-forming fluids suggest that the sulfur at Qinglong was dominantly magmatic-derived. From the early-ore to late-ore stage, the ore-forming fluid temperature and oxygen fugacity (fO2) decrease but the pH increases (from acidic to neutral). Such physicochemical transition may have significantly decreased the Sb solubility from 10?s to 100?s of ppm to 0.001?ppm. Therefore, we propose that fluid mixing was the main process that substantially reduced the fluid temperature and oxygen fugacity, which effectively lowered the Sb solubility and led to abundant stibnite precipitation.