Ore fluid geochemistry of gold polymetallic deposits in the Fengtai ore district, Qinling Mountains

Abstract： Take for example the Baguamiao gold deposit and Bafangshan-Erlihe lead-zinc deposit, a comparative study has been conducted of the characteristics of ore-forming fluids of gold and lead-zinc deposits in the Fentai ore district, Qinling Mountains. Study indicates the following： the gas phase composition in fluid inclusions of all deposits in the district is of CO2-N2-CO-CH4-H2 type, but in comparison with lead-zinc deposits the CH4 value in different mineralization stages of the Baguamiao gold deposit is notably high, while its f o2 and f s2 values are low； for the liquid phase composition, except the values of Ca2+/Mg2+ and Eh which are lower than those in lead-zinc deposits, the values of Na+/K+, Cl-, F- and pH in the main metallogenic epoch of the Baguamiao gold deposit are all higher than those in lead-zinc deposits, and the ore-forming fluids in the main metallogenic epochs of both types of deposit are mesosaline but the salinity of the gold deposit is markedly higher than that of the lead-zinc deposits；δD and δ18O in fluids indicate that the water in ore-forming fluids of the lead-zinc deposits is mainly connate water, while most of the water in ore-forming fluids of the Baguamiao gold deposit is magmatic water or connate water heated by magma, whose metallogenic relation is closely related to magmatic hydrothermal fluids.