Descussion on the mechanism of seperation of copper and molybdenum in jima porphyry deposit system, Tibet

With the highest exploration and the first large-scale exploitation, Jiama copper polymetallic deposits is a supper-large skarn-porphyry deposit, located at the middle-eastern section of gangdise in Tibet. In this paper, taking the typical phenomenon copper upside and molybdenum underside of hornfels- and porphyry-orebodies from Jiama deposit as the starting point, the differences of ore forming fluids among physical and chemical conditions and the migrating behavior of trace elements in the copper and molybdenum mineralization stages have been discussed in virtue of microthermometry, laser Raman testing, synchrotron radiation X-ray fluorescence analysis (SR-XRF) and other researching methods. The results of fluid inclusions microthermometry show that the temperature of ore-forming fluid in the copper mineralization stage (roughly 235 ∼ 451 °C, mainly between 340 and 380°C) is overall greater than that in the molybdenum stage (roughly 213-500°C, mainly between 310 and 360°C), sharing the similar salinity that is less than 18% NaCleqv and more than 30% NaCleqv, and lack of the transition zone, which explained ore-forming fluids had experienced boiling. And the results of Raman microprobe show that the oxidizability of ore-forming fluids in the copper mineralization stage is a little stronger than that in the molybdenum mineralization stage, while the reducibility is reverse. Synchrotron radiation X-ray fluorescence analysis of single fluid inclusion indicates that Cu, Au, Fe, Mn, S, As and other elements are mainly and widely distributed in the gas phase, while the residual Mo is mainly concentrated in the liquid phase. Thus it can be concluded the main controlling factors leading to copper earlier and molybdenum later and copper upside and molybdenum underside of hornfels- and porphyry-orebodies in the Jiama deposit are the physical and chemical properties of copper and molybdenum, the natures of ore-bearing magma, and their emplacing sequence and depth, along with the different redox and the ulfur content of ore-forming fluids released after that.