Coupled fluid-rock interaction and fluid cooling triggered orogenic Au-Sb mineralization in the Zaorendao deposit, China

Lode Au-Sb deposits in metamorphic terranes represent significant and economically valuable global sources of gold and antimony. A close spatial relationship between intrusion and lode Au-Sb deposits is commonly observed. Nonetheless, considerable debate remains regarding the existence of a genetic link between magmatic-hydrothermal systems and Au-Sb mineralization. The Zaorendao Au-Sb deposit, hosted by the Triassic granitoid in the West Qinling Orogen, is characterized by disseminated gold mineralization and vein-type antimony mineralization. The orebodies within Triassic quartz diorite are structurally controlled by NW-trending brittle faults and comprise two distinct mineralization styles: (1) early-stage invisible gold hosted in pyrite and arsenopyrite disseminated throughout altered quartz diorite nearby faults, and (2) later-stage fault-controlled quartz veins containing stibnite mineralization. Petrological and geochronological analyses indicated that gold and antimony mineralization occurred contemporaneously at 233±5.8 Ma and 231.5±5.7 Ma, respectively, approximately 15 Ma later than the ore-hosting quartz diorite. Arsenopyrite thermometer indicated that early disseminated mineralization occurred at approximately 380 ℃, while the sphalerite GGIMFis thermometer suggested that late-stage stibnite precipitated at around 260℃. The δ³⁴S values of arsenopyrite and pyrite in the disseminated ore range from -19.4‰ to -3.9‰ and -12.1‰ to -6.2‰, respectively. In the vein-type ore, the δ³⁴S values of stibnite and sphalerite range from -19.5‰ to -6.5‰ and -18.0‰ to -7.4‰, respectively. These sulfur isotope compositions differ from those of magmatic-hydrothermal deposits but closely resemble the isotopic signature of diagenetic pyrite in Triassic slates (-25.2 to -20.1‰). All evidence supports hypothesis that the Zaorendao deposit represents an orogenic Au-Sb deposit associated with the Late Triassic tectonic collision orogeny in the West Qinling Orogen. Gold, antimony and sulfur were sourced from deep-seated Triassic sedimentary rocks during regional metamorphism. Gold deposition was primarily controlled by fluid-rock interaction coupled with a decrease in sulfur fugacity, whereas stibnite precipitation was induced by fluid cooling.