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The Chehugou Mo-Cu deposit, located 56 km west of Chifeng, NE China, is hosted by Triassic granite porphyry. Molybdenite-chalcopyrite mineralization of the deposit mainly occurs as veinlets in stockwork ore and dissemination in breccia ore, and two ore-bearing quartz veins crop out to the south of the granite porphyry stock. Based on crosscutting relationships and mineral paragenesis, three hydrothermal stages are identified: (i) quartz-pyrite-molybdenite Ϯ chalcopyrite stage; (ii) pyrite-quartz Ϯ sphalerite stage; and (iii) quartz-calcite Ϯ pyrite Ϯ fluorite stage. Three types of fluid inclusions in the stockwork and breccia ore are recognized: LV, two-phase aqueous inclusions (liquid-rich); LVS, three-phase liquid, vapor, and salt daughter crystal inclusions; and VL, two-phase aqueous inclusions (gas-rich). LV and LVS fluid inclusions are recognized in vein ore. Microthermometric investigation of the three types of fluid inclusions in hydrothermal quartz from the stockwork, breccia, and vein ores shows salinities from 1.57 to 66.75 wt% NaCl equivalents, with homogenization temperatures varying from 114°C to 550°C. The temperature changed from 282-550°C, 220-318°C to 114-243°C from the first stage to the third stage. The homogenization temperatures and salinity of the LV, LVS and VL inclusions are 114-442°C and 1.57-14.25 wt% NaCl equivalent, 301-550°C and 31.01-66.75 wt% NaCl equivalent, 286-420°C and 4.65-11.1 wt% NaCl equivalent, respectively. The VL inclusions coexist with the LV and LVS, which homogenize at the similar temperature. The above evidence shows that fluid-boiling occurred in the ore-forming stage. d

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