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

Abstract

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 °C) and salinity (12.2–17.8 wt% NaCl equiv.), and are CH4-rich. They have δ18OH2O = 9.5–10.8 ‰ and δDH2O = −93.4 to −80.8 ‰. 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 °C) and salinity (2.1–10.7 wt% NaCl equiv.), and CO2– and CH4-bearing. They have δ18OH2O = 3.3–5.2 ‰ and δDH2O = − 95.4 to − 89.6 ‰. 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.