Further Studies of Ore-Forming Fluid Sources of Bangpu Molybdenum-Copper Polymetallic Deposit, Tibet

Abstract

Bangpu molybdenum-copper polymetallic deposit is located in the eastern section of the Gangdese Porphyry Copper Belt of Tibet. It is a typical large porphyry molybdenum copper polymetallic deposit. The isotope study of fluid inclusions H and O in the quartz (calcite) of various mineralization stages shows that, the ore-forming fluid comes mainly from meteoric hydrothermal caused by atmospheric precipitation, which has consistency with ore-forming fluid sources of Gangdese Porphyry Copper Belt. The Mo-Cu phase with low δD value (-140.5 ~ -104.0 ) suggests a large-scale magmatic degassing. The alteration and mineralization have been caused precisely by the degassing, and the obvious O isotope drift occurred being accompanied by alteration-mineralization, so that the fluid has a low δ18O (vary from 5.50 to 9.0 ). The statistical research indicates that, the massive magmatic degassing occurred in Gangdese Porphyry Copper Belt, and was gradually increased from east to west, suggesting the direct impact of the magmatic degassing on the formation of the porphyry copper-gold deposit and molybdenum copper deposit: the stronger the magmatic degassing, the more easily to form the molybdenum-based porphyry deposit, otherwise it will be formed the deposits dominated by Cu and Au.