Characteristics of ore-forming fluids and metallogenic mechanism of the Daheishan porphyry Mo deposit in Yongji area, Jilin province

The Daheishan Mo deposit is located in the south segment of the Xiao Hinggan Mountains-Zhangguangcai Mountains metallogenic belt. Ore bodies are mainly hosted in granodiorite and granodiorite porphyry. Fluid inclusions in ore-bearing quartz veins can be classified into aqueous two-phase(W-type)and daughter mineral-bearing multiphase(S-type) occasional containing CO2 inclusion. Fluid inclusions formed in the early stage are W-type, S-type and a small amount of containing CO2 inclusions, and the homogenization temperature of this type of inclusion change from 208°C to 443°C, salinities from 2.9% to 49.8% NaCl equivalent and the density from 0.5 g·cm-3 to 1.2g·cm-3; The quartz-molybdenite veins from the main ore-forming stage contain W-type and S-type inclusions with homogenization temperatures from 197°C to 398°C, salinities from 1.6% to 43.9% NaCl equivalent and density from 0.5 g·cm-3 to 1.1 g·cm-3. The daughter minerals in fluid inclusions from the main ore-forming stage include salt daughter mineral and metallic sulfide daughter mineral. Fluid inclusions of the late stage are major W-type inclusions, with homogenization temperatures from 171°C to 301°C, salinities from 1.6% to 19.8% NaCl equivalent and the density from 0.6 g·cm-3 to 0.9 g·cm-3. Fluid boiling in the main stage is evidenced by the co-existence of different types of fluid inclusions with similar homogenization temperatures. The pressures of fluid inclusions formed in main stage change from 30 MPa to 100 MPa, corresponding to depths of about 4 km.The fluid boiling in the early ore-forming stage and fluid miscibility in late stage played very important roles in the precipitation of metal sulfides.