Genesis of Re-rich Molybdenite in the Baishan Mo deposit,Eastern Tianshan,Xinjiang, Northwest China

The Baishan molybdenum deposit is located in the central part of the Eastern Tianshan-Beishan tectonic belt, NW China. The deposit is hosted in early Carboniferous Gandun Formation biotite-rich hornfels and is genetically related to unexposed granodiorite porphyry beneath the orebodies. The molybdenite occurs in three different types from early to late stage: Molybdenite - Fe-Cu-sulfides - K-feldspar - quartz veins (Group 1); Molybdenite - Fe-Cu-sulfides - quartz veins (Group 2); and disseminated molybdenite in the wall rock (Group 3). Rhenium concentrations in the molybdenite grains range from 108 to 277 ppm in Group 1, 69–121 ppm in Group 2 and 46–135 ppm in Group 3. The Re concentrations of molybdenite in the Baishan Mo deposit decrease from early to late and from the center to periphery, and molybdenite types vary from the 2H₁ poly-type in Groups 1 and 2 to the 2H₁ + 3R2H₁ poly-type in Group 3, based on X-ray diffraction results. The Re-enriched molybdenite probably formed from an oxidized magmatic fluid that separated from a highly oxidized and H₂O- and volatile-enriched adakitic intrusion generated in the lower crust.