Abstract Understanding the factors that control the co-precipitation of Sb and Au is critical for guiding exploration in epizonal orogenic systems. Stibnite is a common ore mineral that is closely associated with the Au mineralization in such systems, serving as an ideal mineral target for micro-analytical studies to better constrain the hydrothermal controls of coupled Au-Sb deposition. This study focuses on the newly-discovered, large Qukulekedong orogenic Au-Sb deposit in the westernmost East Kunlun orogenic belt. Antimony mineralization predominantly occurs as quartz-stibnite veins in the deposit. Two generations of stibnite mineralization were identified, including (1) early quartz-stibnite (Sbn1) veins with abundant inclusions of visible Au, andorite, jamesonite and sphalerite, and (2) late quartz-stibnite (Sbn2) stockwork. Comparable in-situ S and Pb isotope compositions of both generations of stibnite suggest a common fluid and metal source. However, Se concentrations from both stibnite generations vary significantly, with Sbn1 containing 310 to 580 ppm Se, which is about one order of magnitude higher than in Sbn2 (Se 50 ppm). The high Se contents in Sbn1 are related to increasing ∑Se/S ratios and decreasing fS2 in the hydrothermal fluids due to accompanied sulfide precipitation. This ultimately led to the strong Au enrichment associated with Sbn1, which is controlled by two mechanisms that are not mutually exclusive, including (1) the fS2-driven destabilization of Au-HS complexes and (2) the substitution of Se2- for S2- in Sbn1 that may have induced lattice distortions and defects enhancing the Au adsorption potential. These processes highlight the critical role of Se in stibnite as a pathfinder towards high-grade Au-Sb mineralization, offering new insights into the geochemical mechanisms that control the formation of epizonal orogenic Au-Sb deposits.
Liu et al. (Thu,) studied this question.