Genetic link between gold mineralization and porphyry magmatism in the Baogutu district, West Junggar, NW China: Constraints from Re-Os and S isotopes in sulphide

Baogutu is a large gold deposit (4 Mt @ 5.5 g/t Au) in West Junggar, NW China. We conducted a Re-Os geochronological study on seven pyrite samples from auriferous quartz-pyrite veins, which yielded a Re-Os isochron age of 312 +/- 11 Ma (2 sigma). This age defines the timing of gold mineralization, and overlaps the emplacement age of diorite to granodiorite porphyry stocks (319-310 Ma) in the Baogutu district. The Os initial ratio of 0.46 +/- 0.21 (2 sigma) suggests a mix of components from both mantle and continental crust in the ore-forming system, which is similar to the proposed magma source of porphyry stocks. The delta S-34 values of sulphide minerals vary in a narrow range from +0.1 to -3.3 parts per thousand, indicating that the sulphur is likely of igneous origin. Our data suggest that the Baogutu gold mineralization is probably genetically linked to the regional diorite to granodiorite magmatism. The new data provide important constraints for an evolving genetic model of the Baogutu gold deposit.