The Yuchiling Mo deposit, Songxian County, Henan Province, is a large porphyry deposit recently discovered in the famous East Qinling Mo belt. It is spatially associated with a biotite monzogranite porphyry intruding into the Heyu multistage granite batholith. Ore-bodies are lentiform or stratiform occurring in the porphyry which was universally mineralized. The ores are characterized by disseminated multistage stockworks of quartz +/- potassic feldspar +/- epidote, quartz-fluorite +/- calcite, fluorite and quartz-sulfide including quartz-pyrite, quartz-molybdenite, quartz-polymetallic sulfides. Paragenesis and crosscutting relationship of the stockworks suggest the ore-forming process includes the early, middle and late stages, accompanied by characteristic wall-rock alterations of silicification-potassic feldspathization-epidotization, silicification-sericitization-chloritization-sulfidization, and low-temperature carbonation-fluoritization, respectively. In the vein quartz, four types of fluid inclusions are distinguished from aqueous water (W-type), pure CO2 (PC-type), H2O-CO2 (C-type) and daughter mineral-bearing (S-type). The early-stage barren quartz veins trapped the initial high-salinity (30.1 wt% similar to 54.1 wt% NaCl eqv.) H2O-CO2-NaCl ore-fluids at temperatures of 280 similar to 420 degrees C with the pressure up to 194MPa, corresponding to depth of < 6.8 km. Due to the high CO2 content and low sulfur fugacity, little sulfide precipitated in the early-stage fluid process. The quartz-pyrite-molybdenite veins formed where high temperature, CO2-rich fluids ascended to depth of ca 5.6km and cooled to ca 400 degrees C, due to fluid boiling and CO2-escape. Further fluid ascending resulted in intense boiling and formation of quartz-molybdenite or molybdenite stockworks whose fluid inclusions yield homogenization temperature of 280 similar to 380 degrees C and pressure of up to 137MPa, corresponding to depth of up to 4.8km. Quartz-polymetallic sulfide veins progressively formed at lower temperature and shallower depth, i.e. 200 similar to 340 degrees C and 0 8 similar to 4.3km, The late-stage barren quartz veins contain only aqueous fluid inclusions with homogenization temperatures between 130 and 200 degrees C. Fluid inclusions are rare in the latest quartz-fluorite calcite and fluorite veins. The results above show that fluid-system forming intracontinental intrusion-related hypothermal deposit; are likely characterized by high salinity and high CO2 content. Considering regional tectonic evolution, we conclude that the Heyu granite batholith where Yuchiling deposit located formed during a rapid uplift of a thickened orogenic crust. The erosion thickness is estimated to be less than 7km and erosion rate is less than 0.05mm/a since 144Ma which is interpreted as the formation age of the Yuchiling deposit.
