The Metallogenisis Of Tulaergen And Baixintan Cu-Ni Sulfide Deposits,China:Constraints From The Petrogeochemistry And Volatile Compositions

Many large scale Cu-Ni sulfide deposits occur along the East Tianshan maficultramafic complex belt in the Central Asian Orogenic Belt. The sulfide orebody occur in the hornblende peridotite and olivine pyroxenolite at the upper part of Kulaergen Cu-Ni sulfide deposit in the eastern part of the East Tianshan maficultramafic complex belt, whereas sulfide orebody occur in the lherzolite at the lower part of Baixintan Cu-Ni sulfide deposit newly discoved in the western part of this belt. Hence, a comparative study of petrology, volatiles and carbon isotopes have been carried out in the Tulaergen and Baixintan mafic-ultramafic intrusions, which provide new insight into the origin of the volatiles, the source characteristics, the condition and process of volatiles during magma evolution, and the mechanism for sulfur saturation. The most important conclusions from this study are summarized below.1.The volatiles in Tulaergen and Baixintan Cu-Ni sulfide deposit are mainly released at the medium temperature interval. CO₂ relaesed from hornblende peridotite and lherzolite in Tulaergen intrusion and CH₄ relaesed from olivine pyroxenite in Baixintan intrusion have two releasing peaks during heating.2. The volatiles of Tulaergen and Bainxintan intrusions are dominated by H₂ O, and the H₂ O contents are 5400.41 mm³/g and 11183.18mm³/g on average, respectively. Excluding H₂ O, other major volatiles are H₂, CO₂, O₂, N₂, H₂ S, CH₄ and C₂H₆, and the contents of these volatiles are 547.3 mm³/g in Tulaergen and 533.67mm³/g in Baixintan. The release of SO₂ at 800-1200 oC interval in Tulaergen intrusion may be caused by the decomposition of sulfide.3. The ?13C value of CO₂ range from-22.62‰ to-8.52‰, and the ?13C values of CH₄ and C₂H₆ vary from-42.15‰ to-32.19‰ and from-26.25‰ to-20.59‰, respectively. The carbon isotopic data of methane homologue show a normal distribution pattern with the increase of the carbon number. Generally, Tulaergen samples have heavier ?13C values than Baixintan samples.4. The main mechanism of sulfur saturation for Tulaergen deposit are the cooling of magma, fractional crystallization, and the addition of external materials. Whereas there is no addition of external sulfur in Baixintan deposit.5. Tulaergen and Baixintan Cu-Ni sulfide deposits are formed in arc environment related to subduction, and they are both have undergone mantle material contaminated with crustal materials by metasomatism during subduction, whereas the degree of crustal contamination is higher in Baixintan intrusion.