Fluid inclusion study of the Saishitang Cu deposit in Qinghai

Abstract：The fluid inclusions in the Saishitang Cu deposit can be classified into liquid-rich two-phase, gas-rich two-phase and daughter mineral-bearing polyphase types. According to studies of petrography, microthermometry and laser Raman spectrographic analyses of fluid inclusions in garnet and diopside from skarn and sulflde-rich quartz veins, the fluid inclusion homogenization temperatures and salinities of the early skarn stage vary in the range of 436℃-562℃ and 34 %-45%wt%NaCl eqv. respectively, indicating that the fluid is dominated by magmatic water characterized by high temperature and high salinity; the fluid inclusion homogenization temperatures and salinities of the retrogressive metamorphic stage vary in the range of 322℃-419℃ and 15%-39%wt%NaCl eqv. Respectively; the fluid inclusion homogenization temperatures and salinities of the sulfide stage vary in the range of 235℃-366℃ and 5%~36%wt%NaCl eqv. respectively. Laser Raman spectrogtaphic analyses show that the gas phase components of fluid inclusions are mainly composed of CH4, H2S, CO2 and H2O, and the ore-forming fluids belong to the NaCl-H2O-CH4-H2S-CO2 system. The boiling event of ore-forming fluid occurred at temperatures of 290℃~360℃, resulting in the formation of massive metal sulfides. The fluid boiling was favorable for the formation of the Saishitang Cu deposit.