Compositions and microthermometry of fluid inclusions of Chalukou porphyry Mo deposit from Great Xing'an Range: implications for ore genesis

The Chalukou Mo deposit lies in the northern Great Xing'an Range, in which veinlet and breccia dominate mineralization. The whole hydrothermal ore-forming processes involve the following four stages: I. quartz-potash feldspar stage; II. quartz-molybdenite stage; III. quartz-polymetallic sulfide stage; IV. quartz-fluorite-calcite stage. The petrographic and laser Raman spectroscopy study show that the melt-fluid inclusions in quartz phenocryst contain component of oligoclase and albite, indicating they directly exsolved from primary magma. Halite, sylvite, hematite, and gypsum are recognized as daughter minerals in S-type inclusions of granite porphyry, suggesting high oxygen fugacity. The stageIquartz captures (L+V)-type, C-type, and S-type (contain halite, sylvite, hematite, and anhydrite daughter minerals) fluid inclusions. The stage II quartz captures (L+V)-type, C-type, and S-type (contain halite, sylvite, chalcopyrite, and molybdenite daughter minerals) fluid inclusions, in addition, V-type and S-type fluid inclusions are coexistent. In the stage III, there are (L+V)-type and S-type with calcite as daughter minerals. Stage IV develops (L+V)-type and L-type fluid inclusions. Microthermometric data show the homogenization temperatures (530°C→120°C) and salinities (66.7% NaCl equiv→1.2% NaCl equiv) decrease gradually. The gas components have a certain amount of CO2 in every stage, and the liquid components in fluid inclusions have Na+, K+, Ca2+, Cl-, and SO42-, and small amount of F-. The initial fluids are high oxygen fugacity and salinity NaCl-H2O-CO2 fluid system with abundant CO2. The homogenization temperatures, salinities, lgfO2, and CO2 content tend to fall from the early to late stage. The decline of homogenization temperatures, salinities, and CO2 content as well as sericitization greatly hinder the depositing of metallogenic elements.