Abstract

The Baishan Mo–Re deposit is located in the eastern section of the eastern Tianshan orogenic belt, NW China. The deposit has a grade of 0.06% Mo and a high content of rhenium of 1.4 g/t. Rhenium and osmium isotopes in sulfide minerals from the Baishan deposit are used to determine the age of mineralization. Rhenium concentrations in molybdenite samples are between 74 and 250 μg/g. Analysis of eight molybdenite samples yields an isochron age of 224.8±4.5 Ma (2σ). Pyrite samples have rhenium and osmium concentrations varying in the range 33.4–330.6 ng/g and 0.08–0.81 ng/g, respectively. Isotope data on seven pyrite samples yield an isochron age of 225±12 Ma (2σ) on the 187Re/188Os versus 187Os/188Os plot and an age of 233±14 Ma (2σ) on the 187Os versus 187Re correlation diagram. The ages of molybdenite and pyrite are consistent within the analytical errors. Combined with field observations, the data indicate that Mo–Re mineralization in the Baishan deposit is produced by a magmatic-hydrothermal event in an intracontinental extensional setting after late Paleozoic orogeny. The initial 187Os/188Os ratio of pyrite is 0.3±0.07. The δ34S values of molybdenite vary from +0.5 to +3.6‰. Both data indicate that mineralization is derived mainly from a mantle source.

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