The Chalukou giant Mo deposit in the Heilongjiang Province, northeastern China, is a porphyry deposit hosted in an intermediate-felsic complex surrounded by Mesozoic volcano-sedimentary rocks. The mineralization process is composed of four stages, including quartz + K-feldspar (Stage I), quartz + molybdenite (Stage II), pyrite + chalcopyrite + quartz ± other sulphides (Stage III) and carbonate ± fluorite ± quartz (Stage IV). The mineralization is generally associated with intense K-feldspar-, fluorite-, phyllic-and propylitic alteration. Primary fluid inclusions (FIs) in quartz include four compositional types, i.e. pure carbonic (PC-type), aqueous-carbonic (C-type), daughter mineral-bearing (S-type) and aqueous (W-type) inclusions. Halite, sylvite and hematite are recognized as the daughter minerals in Stage I S-type FIs, whereas molybdenite and chalcopyrite occur as daughter minerals in Stage II S-type FIs. High-salinity and high pressure (>220 MPa) FIs exist in Stage I quartz veins, characterized by homogenization through halite dissolution at temperatures of 324 to 517°C. The paucity of coexisting vapour-rich FIs with similar homogenization temperatures at this stage indicates that the initial S-type inclusions have directly exsolved from the magma rather than boiling off of a low-salinity vapour. Stage I quartz has captured the C-and W-type FIs, which have totally homogenized at 270-530°C with salinities of 1.6-17.0 wt.% NaCl equiv. At Stage II, the coexistence of all FI types were only observed at pressures of 150-218 MPa and temperatures of 352-375°C, with two salinity clusters of 0.9-16.6 wt.% NaCl equiv. and 37-56 wt.% NaCl equiv. Stage III quartz contains W-type FIs with homogenization temperatures of 158-365°C, salinities of 0.5-9.0 wt.% NaCl equiv., and minimum pressures of 12-116 MPa; whilst Stage IV fluorite or calcite only contains W-type FIs with homogenization temperatures of 121-287°C, salinities of 0.5-5.3 wt.% NaCl equiv., and minimum pressures of 10-98 MPa. The estimated trapping pressure from Stages II to III suggests an alternating lithostatic-hydrostatic fluid-system caused by fluid boiling. Ore fluids at the Chalukou Mo deposit may have been evolved from a CO 2 -rich, high-salinity, and high-oxygen fugacity (fO 2 ) magma system, to a CO 2 -poor, low-salinity, and low-fO 2 epithermal system. Two key points may have contributed to the formation of the Chalukou giant Mo deposit: The magmatic origin and fluid boiling that has resulted in decompression and rapid precipitation of metals.
