The Re-Os isotope system of the Xiongcun porphyry copper-gold deposit, Tibet

Abstract：Re-Os dating of molybdenite is an efficient means to restrict the time of mineralization. The age of mineralization of the Xiongcun porphyry copper-gold deposit is confined between 171 Ma and 175 Ma based on this study and other data available. No.Ⅰ ore body of the Xiongcun deposit was affected by later magmtic thermal event. Molybdenite contains trace K-Si silicate enriched in Re. As a result of this event, the Re content of molybdenite is one to four times higher than that of molybdenite in No.Ⅱ ore body and No. Ⅲ ore body, and the age of molybdenite in No.Ⅰ ore body is younger than the real age. The authors also compared the Re content of molybdenite between this deposit and other porphyry-skarn deposits within this belt and found that the content of Re shows systematic variation. The Re content of the Xiongcun porphyry copper-gold deposit is one order of magnitude high than that of Miocene porphyry deposits and two order of magnitude higher than Paleocene to Eocene porphyry-skarn deposits. The Re variation is related to the source of metal, the content of molybdenum, the composition of magma and the physical/chemical condition of magmatic-hydrothermal solution.