The Chemical Compositions Of Volatiles And Its Ore-genesis Implications In Jinchuan Cu-Ni Sulfide Deposit, West China

Magmatic Cu-Ni sulfide deposit is the main ore-forming type of copper, nickel, platinum group elements (PGE) resources, and Jinchuan Cu-Ni sulfide deposit is the third largest Ni-Cu sulfide deposit in the world. The volatiles trapped in the magmatic Cu-Ni sulfide deposit not only record the composition of volatiles in primary magma and also show the forming condition of mineralization process. In present paper, the stepwise heating mass spectromety method is used to determine chemical compositions of volatiles in constitute minerals from lherzolite, pyroxenite and sulfide ores in the Jinchuan Cu-Ni-PGE sulfide deposit. The following understanding has been obtained:1. The volatiles in constitute minerals from Jinchuan Cu-Ni sulfide deposit are released at the temperature interval of 200-500,500-800 and 800-1200℃; The volatiles (deducting H2O) are composed mainly of CO2, H2, N2+CO, SO2 and H2S, with the minor CH4, O2, Ar, C2H6 and C3H8 etc. The chemical compositions of volatiles vary between silicate minerals and ores, the pyroxene's volatiles composed mainly of CO2 and H2 and display the highest content, olivine's volatiles composed mainly of CO2 and H2S, the metal sulfide's volatiles composed of CO2 and CH4 except sulfur-bearing volatile speciation, and exhibit the lowest amount of volatiles.2. The volatiles released at high temperature interval (800-1200℃) composed mainly of CO2 and SO2; the volatiles at mid-temperature interval (500-800℃) show largest volatile amount, and composed mainly of CO2 and H2, secondary by SO2 and H2S; the volatiles at low temperature interval (200-500℃) composed mainly of CO2 and H2O with lower SO2.3. The volatiles released at the concentration peak (500-800℃) are mainly of CO2, H2S and H2, etc. The high-density CO2 in the mantle plays an important role in moving the main ore-forming elements. And the oxidation volatile of CO2 can also reduce the solubility of sulfur in ore-forming magma, which could prompt sulfide segregate massively, and prompt large deposits formate. Magmatic hydrothermal volatiles are mainly of oxidizing volatiles.