Re-Os DATING OF MOLYBDENITE FROM LALA Fe-Oxide-Cu-Au-Mo-REE DEPOSIT, SOUTHWEST CHINA: IMPLICATIONS FOR ORE GENESIS

The recentl works suggest that Lala deposit, located in Sichuan Province of China, is a typical FeOxideCuAuMoREE deposit (Wang et al, 2002). Lala deposit is situated in the western margin of Yangtze block. The host rock of the deposit is named He Kou Group. He Kou Group is composed of quartz albitite, garnetbiotite schist, magnetite quartzite, quartz schist, hornblende schist and minor marble. The protolith of the quartz albitite, garnetbiotite schist, magnetite quartzite are spilite, keratophyre, and keratophyre volcaniclastic rock, with subsidiary cogenetic intrusive rocks.The Lala deposit appears to have the forms of lens and vein. The deposit strike east northeast and dip at approximatel 30° to south. The mineralization are also accompanied by high P concentrations, and anomalous, but erratic, F, U, Th, Nb and Ta. It was reported that the deposit was formed by the magmatic hydrothermal fluids secreted from a gabbro sill, at ~800 Ma. In this paper, direct dating of molybdenite from the deposit using the ReOs method has been done. Four ReOs ages range between 928±1 Ma and 1005±1 Ma. These ages are interpreted as the age of Cu and Mo mineralization. This age is much older than the emplacement ages for the main intrusive suites. The age is consistent with the age of the metamorphism of He Kou Group, which is 969±52 Ma of the whole rock Rb-Sr dating of muscovite schist (Li et al.1988). We suggest that Cu and Mo mineralization is genetically linked to the metamorphic hydrothermal fluid processes at ~1000 Ma thereby precluding the ~800 Ma gabbro as the source for mineralizing fluids.