Separation of Au and Sb mineralization in the Qukulekedong intrusion-related deposit, East Kunlun Orogen (NW China): Evidence from fluid inclusions, H-O isotopes, and quartz geochemistry

Separation of Au and Sb mineralization from different hydrothermal stages is a common phenomenon in many Au-Sb deposits, but its cause remains enigmatic. The Qukulekedong intrusion-related Au-Sb deposit in the East Kunlun Orogen has undergone four hydrothermal stages: (1) barren quartz vein, (2) quartz vein with disseminated arsenopyrite-pyrite alteration halo, (3) stibnite-quartz +/- native gold vein, and (4) calcite-quartz vein. Stages 2 and 3 formed disseminated Au and vein-type Sb +/- Au ore, respectively. Here, internal texture and trace elements in quartz, fluid inclusions (Fls) microthermometry, and H-O isotopes were analyzed to unravel the separation mechanism of the Au and Sb +/- Au mineralization at Qukulekedong. Stage 2 quartz has euhedral growth zones with elevated Ti-Al-Li-K-Sb and varying As contents. Stage 2 FIs have medium homogenization temperature (203-307 degrees C) and salinity (12.2-17.8 wt% NaCl equiv.), and are CH4-rich. They have delta 18OH2O = 9.5-10.8 %o and delta DH2O =-93.4 to-80.8 %o. In contrast, stage 3 quartz has lower Ti-Al-Li-K and varying Sb contents. Stage 3 FIs show phase separation (coexistence of V-, L-and V-L-type FIs), and are of lower temperature (141-164 degrees C) and salinity (2.1-10.7 wt% NaCl equiv.), and CO2- and CH4-bearing. They have delta 18OH2O = 3.3-5.2 %o and delta DH2O = -95.4 to -89.6 %o. Considering that the disseminated Au ore is Sb-rich and its pyrite has fine stibnite inclusions, we suggest that the disseminated Au and vein-type Sb +/- Au mineralization shared a common Au-and Sb-rich initial magmatic fluids. The disseminated Au mineralization may have formed by fluid-rock interactions. Meanwhile, the vein-type Sb +/- Au mineralization was likely caused by the phase separation and cooling led by dilational activities and meteoric water injection.