Fluid inclusions and stable isotope characteristics of the Chalukou porphyry Mo deposit in Heilongjiang Province

Abstract：The superlarge Chalukou porphyry Mo deposit, located in northern Da Hinggan Mountains, is the biggest Mo deposit in Northeast China. Its ore bodies are mainly hosted in the intermediate-acid complex and Jurassic volcanic sedimentary rocks, of which granite porphyry, quartz porphyry and fine grained granite are closely associated with Mo mineralization. Three types of fluid inclusions are distinguished based on petrographic and microthemometric criteria, namely liquid-rich two-phase, gas-rich two-phase and daughter mineral-bearing multiphase fluid inclusions. Fluid inclusions in quartz phenocrysts of granite porphyry are mainly liquid-rich two-phase, gas-rich two-phase and daughter mineral-bearing multiphase fluid inclusions, their homogenization temperatures vary from 230 to 440℃ and from 470 to 510℃, and salinities vary from 0.7％ to 53.7％ NaCl eqv and from 6.2％ to 61.3％ NaCl eqv, respectively. Fluid inclusions of the ore-forming early stage K-feldspar-quartz-magnetite vein are mainly composed of liquid-rich two-phase, gas-rich two-phase and daughter mineral-bearing multiphase fluid inclusions, and their homogenization temperatures and salinities vary from 320°C to 440°C and from 4.2% to 52.3% NaCl eqv, respectively. Fluid inclusions of the ore-forming middle stage quartz-molybdenite vein and breccia are mainly composed of liquid-rich two-phase, gas-rich two-phase and daughter mineral-bearing multiphase fluid inclusions, and their homogenization temperatures and salinities vary from 260°C to 410°C and from 0.4% to 52.3% NaCl eqv, respectively. Fluid inclusions of the ore-forming late stage quartz-fluorite-galena-sphalerite vein are mainly liquid-rich two-phase fluid inclusions, and their homogenization temperatures and salinities vary from 170°C to 320°C and from 0.5% to 11.1% NaCl eqv, respectively. The ore-forming fluid of the Chalukou deposit is characterized by high temperature, high salinity and high oxygen fugacity, roughly belonging to the H2O-NaCl±CO2 system enriched in F. The δ18OW values of the ore-forming fluid vary from -4.5‰ to 3.2‰, and δDW values vary from -138‰ to -122‰, indicating that the ore-forming fluid was derived mainly from magmatic fluid mixed with meteoric water. The δ34S values of metallic sulfides range from -1.9‰ to +3.6‰, with an average of +1.6‰, suggesting that the ore-forming materials came mainly from deep magma. The multi-stage boiling action of the ore-forming fluid seems to have been the dominant factor for metallic sulfide deposition.