Noble gas isotopic constrains on mineralization of the Jinchuan Cu-Ni-PGE sulfide deposit, West China
金川Cu-Ni-PGE硫化物矿床成矿过程稀有气体同位素组成示踪

Noble gases are recognized as being exceptional tracers of volatile sources during mineralization. He, Ne and Ar abundances and isotopic compositions from 23 silicate and sulfide separates in the Jinchuan Cu-Ni-PGE sulfide deposit, West China, have been investigated by melting extraction MM5400 mass spectrometer. The results show that 3He/4He ratios in silicate minerals (av. 0.239Ra) are slightly lower than those in sulfide (av. 0.456Ra), and decrease from olivine (av. 0.291Ra), orthopyroxene (av. 0.215Ra) to clinopyroxene (av. 0.174Ra). 20Ne/22Ne and 21Ne/22Ne ratios are plotted into the ranges between MORB line and continental crust line. 3He/4He and 40Ar/36Ar of olivine (Olv) and orthopyroxene (Opx) deducted by radiogenic He* and Ne* are close to the He and Ar isotopic ranges of subcontinental lithosphere mantle (SCLM). He, Ne and Ar isotopic compositions suggested that SCLM, continental crust (CC) and air saturated water (ASW) three end-members were involved into ore-forming magma of the Jinchuan Cu-Ni-PGE sulfide deposit. The segregation of immiscible sulfide liquid from magma took place at the early stage of magma evolution. The primary ore-forming magma had been formed by partial melting of SCLM, and undergone two stages of evolution. It had been assimilated possibly with wall rock which resulted in the sulfur supersaturating in silicate magma and segregation of immiscible sulfide melt and formed a mixed component (MC) with SCLM and continental crust (CC) signatures. The mixed component (MC) emplaced into upper chamber and mixed with a high proportion of deep circulatory ASW which induced sulfur supersaturating of ore-forming magma and in-situ formed the disseminated ore in upper magma chamber.