Fluid geochemistry of the Daxigou gold deposit in Fengning, Hebei Province

Abstract：The experimental results of fluid inclusion microthermometry, material constituents, H-O isotopes and ore-forming fluids in the Daxigou gold deposit suggest that there exist three types of fluid inclusions in the ore deposit, namely gas inclusions (V type), gas-liquid inclusions (V-L type) and liquid inclusions (L type). Fluid inclusions occur in vein quartz, with their homogenization temperature, salinity, fluid density and ore-forming depth being 175～275℃, 2%～7%, 0.804～0.959g/cm3 and 1.01～2.24 km respectively. The gases in fluid inclusions are chiefly composed of H2O and CO2. As for liquid composition, the cations are mainly Na+ and subordinately Ca2+ and K+, and the anions are mainly comprised of SO2-4 and Cl- with minor amounts of F-. The δ18O H2O values of quartz from the ore-forming fluids range from 2.1‰ to 5.8‰, and δD values from -87‰～-103.67‰, indicating a mixed source of magmatic water and atmospheric precipitation. The gas fugacity determinations show that Au was transported in the form of complex compound Au（HS）2- in the ore-forming fluids. In addition, the mixing process and the hydrothermal alteration contributed to gold deposition and concentration.