Noble Gas Isotopic Tracing Systematics Of Ore-Genesis Of Jinchuan Cu-Ni Sulfide Deposit, China

Jinchuan Cu-Ni sulfide deposit is the third largest Cu-Nil sulfide deposit in the world. The sulfide segregation is important process in large scale sulfide deposit formation, but the main cause of sulfide saturation and segregation is still unclear. In present study the excellent trcer noble gas abundances and isotopic compositions have been employed to reveal fluid sources, magmatic evolution and sulfide segregation in Jinchuan Cu-Ni sulfide deposit.The main conclusions as following.1. He, Ne and Ar elemental abundances in silicate minerals are higher than in sulfide of Jinchuan deposit.3He/4He ratios in silicate minerals and sulfide is between 0.16 and 0.81Ra; the rang of 20Ne/22Ne ratios is 9.00-11.37; 21Ne/22Ne ratios are between 0.027 and 0.044; the rang of 40Ar/36Ar ratios is 377.30-43202.40.2. Jinchuan Cu-Ni sulfide deposit has following characteristics:lower 3He/4He ratios; 20Ne/22Ne and 21Ne/22Ne are plotted into the range between MORB line and continental crust line; He, Ne and Ar isotope compositions are from mantle, crust and Air, and proportion of crust and Air are higher.3.3He/4He ratios are very low in both silicate minerals(especially olivine) and sulfide, moreover gradually decrease from olivine, clinopyroxene to orthopyroxene, which suggested that high proportion of contaminated crustal and atmospheric component could be deep circulatory fluids which had been added into ore-forming magma chamber at early stage of olivine crystallization and last during magmatic fractionation crystallization.4. Radiogenic He* and Ne* contributions are negligible in olivine minerals and sulfide, which can reflect the original characters of ore-forming magma and sulfide magma.3He/4He ratios (average 0.46Ra) in sulfide are higher than in silicate minerals (average 0.24Ra). According to Ar isotope deducted radioactive 40Ar*, proportion of Air compositions in sulfide (average3.95%) are obvious lower than in silicate minerals(average 54.91%). The segregation of immiscible sulfide liquid from magma took place at the early stages of magma evolution.