Fluid evolution of the Yaochong porphyry Mo deposit, Xinxian County, Henan Province, China.

The Yaochong porphyry Mo deposit in Xinxian County, Henan Province, China, is located in the Dabie orogenic belt Mo mineralization formed in continental collision settings. The hydrothermal ore-forming process can be divided into the early, middle and late stages, characterized by mineral assemblages of quartz + potassic feldspar +/- pyrite +/- magnetite, quartz +/- potassic feldspar + molybdenum +/- other sulfides and quartz +/- calcite +/- fluorite, respectively. There are four fluid compositional types determined in hydrothermal quartz and fluorite from early to late: pure CO2, CO2-H2O, aqueous and solid-bearing fluid inclusions (FIs). The early-stage quartz contains three of the four types FIs other than the aqueous type. The middle-stage quartz has CO2-H2O, aqueous and solid-bearing FIs, without pure CO2 FIs. In the late stage, a small amount of CO2-H2O FIs can be observed in quartz of barren quartz veins, while in quartz-carbonate-(fluorite) veins, only the aqueous FIs are present. Fluid inclusions in the early-stage quartz are homogenized at temperatures of 277 similar to 380 degrees C, clustering at 300 similar to 360 degrees C, with salinities mainly ranging from 3.0% to 10.3% NaCleqv. Fluid inclusions in the middle stage quartz yield homogenization temperatures of 185 degrees C to 351 degrees C, with most between 260 degrees C and 320 degrees C, and salinities of 2.4% to 9.3% NaCleqv. Fluid inclusions in the late stage are totally homogenized at temperatures of 139 similar to 245 degrees C, yielding salinities of 0.7% similar to 6.3% NaCleqv. The estimated pressures decrease from a span of 47 similar to 131MPa in the early stage, to a range of 26 similar to 118MPa in the middle stage, corresponding to a change in depths from 4.7km to 2. 6 similar to 4.2km. We conclude that the initial fluids forming the Yaochong deposit is high temperature, high salinity and CO2-rich, and predict that the deeper exploration is potential for ore prospecting.