Rhenium‐Osmium Isotope Constraints on the Origin of the Tianyu Cu‐Ni Deposit in the East Tianshan Orogenic Belt, Xinjiang, NW China

AbstractThe Tianyu Cu‐Ni sulfide deposit occurs in the north margin of the Central Tianshan Arc in East Tianshan orogenic belt, Xinjiang, NW China. The intrusions consist of gabbro, peridotite, and olivine pyroxenite. The peridotite and pyroxenite are the main host rock for the Cu‐Ni ores. Rhenium and osmium isotopic analyses of Ni‐ and Cu‐bearing sulfide minerals from the deposit have been used to determine the source of osmium, and by inference, the sources of ore metals. Sulfide ore samples have Os and Re concentrations varying in the ranges 1.85 to 4.58 ppb and 93.56 to 146.00 ppb, respectively. An initial 187Os/188Os ratio ranges from 0.86 to 1.23 for the ores and the γOs values from 592 to 2227. Osmium isotopic data suggest that the Tianyu intrusion and associated Cu‐Ni mineralization has derived from crustal‐contaminated mantle melts. The intrusions early show island‐arc geochemical signatures, which indicate that the Hulu mafic–ultramafic intrusions, along with the Cu‐Ni deposit, formed as a result of subduction of oceanic crust in the Early Permian.