RE OS ISOTOPIC DATAING OF THE XIANGSHAN DEPOSIT, EAST TIANSHAN, NW CHINA

Abstract

The Xiangshan Cu-Ni deposit is located in the eastern part of the East Tianshan orogenic belt, northwestern China. Rhenium and osmium isotopic analyses of Ni-and Cu-bearing pentlandite from the deposit have been used to determine the timing of mineralization, the source of osmium, and, by inference, the source of ore metals. Pentlandite samples have osmium and rhenium concentrations varying in the ranges of 39. 61 - 110. 60 ppb, and 0.437 - 3.763 ppb, respectively. Analyses of these data yield a seven-point isochron with an age of 298±7.1 Ma. The age implies that the Cu-Ni sulfide deposit and other related magmatic deposits in the same area formed between the latest Carboniferous and Early Permian extension in the East Tianshan. An initial 187Os/188Os ratio of 0.682±0.32(MSWD = 9.4) and the δ34S of - 0.84‰ to + 2.40‰ for the ores, suggests a magmatic source for the ores, with the melts being dominated by mantle contributions. The data also indicate that the Xiangshan Ni-Cu deposit, like many other silver, iron, copper, gold, and nickel deposits within East Tianshan, is related to a large-scale extensional process.