Study of fluid inclusion characteristic and genetic type of the Huachanggou gold deposit, West Qinling Orogen

The Huachanggou gold deposit, Shaanxi Province, is located in the southern edge of Mianlue suture zone of the West Qinling Orogen. It is controlled by a ductile-brittle shear zone and hosted in the Devonian spilite, tuffaceous sericitized phyllite and limestone. The crosscutting relationships and mineral replacement suggest that the ore forming process includes the early, middle and late stages. In the quartz of Huachanggou gold deposit, four types of fluid inclusions (FIs) are identified as CO2-H2O, pure CO2 H2O-solution and daughter mineral-bearing. The early-stage quartz contains primary pure CO2 and CO2-H2O with homogenization temperatures clustering 320 similar to 360 degrees C and the salinity of 0.43% similar to 5.14% NaCleqv. Vapor bubbles are composed of CO2 + H2O +/- N-2 +/- CH4 +/- H2S. The middle-stage quartz trapped all the four types of FIs, the H2O-solution FIs account for the majority. Most of CO2-H2O and the H2O-solution FIs homogenized betwwen 240 similar to 320 degrees C, and with the salinities 0.43% similar to 11.19% NaCleqv. Fluid inclusions in late-stage quartz are H2O-solution with low homogenization temperatures (118 similar to 228 degrees C) and low salinities (0.18% similar to 6.59% NaCleqv). Minimum trapping pressures estimated from CO2-H2O inclusions are 70 similar to 195MPa for middle stages, suggesting that gold mineralization occurred at the depths of 5 similar to 7km. In general, the ore fluids in the early and middle stages are characterized by meso- to hypothennal, CO2-rich and low salinity, which are considered as the nature of metamorphic fluids, whereas the late-stage fluids are low temperature, low salinity and CO2-poor. Fluid immiscibility caused gold precipitation in the middle-stage. The ore-forming fluid-system of the Huachanggou gold deposit is same to the orogenic-type. The Huachanggou gold deposit is a mesozonal to epizonal orogenic gold deposit.