Zircon U-Pb and Molybdenite Re-Os Dating of Gangjiang Porphyry Cu-Mo Deposit in Nimu Ore Belt, Southern Tibet, China and Its Geological Significance

In order to determine the ages of magmatism and mineralization, and thus to disentangle the complicated magmatic evolution and the relationship between magmatic process and copper-molybdenum mineralization, the authors carried out a study of LA-ICP-MS zircon U-Pb dating of monzonite granite porphyry, granodiorite porphyry, quartz-mica diorite porphyrite in Gangjiang porphyry Cu-Mo deposit, corresponding with zircon U-Pb ages of 16.6 +/- 0.3Ma, 16.1 +/- 0.2Ma, and 14.4 +/- 0.4Ma. Meanwhile, twelve molybdenite samples separated from quartz sulfides veins in Gangjiang copper orebodies were used for Re-Os dating; the model ages obtained range from 13.24 +/- 0.20Ma to 13.55 +/- 0.22Ma, with weighted average 13.4 +/- 0.1Ma and isochron age 13.6 +/- 1.6Ma. To combine our study results, field geological survey and previous research data, it is proposed that the intrusion sequence is ore-bearing monzonite granite porphyry. granodiorite porphyry -> rhyolite porphyry (depth named as quartz-mica diorite porphyrite), the porphyry intrusion occurred range from 16.6Ma to 14.4Ma, and the mineralization age of Gangjiang porphyry Cu-Mo deposit is about 13.4Ma, so the porphyritic granodiorite could responsible for the mineralization and related alteration. Diagenesis and mineralization is a continuous process of magmatic evolution. Gangjiang porphyry Cu-Mo deposit was formed in post-collisional extension setting of India-Asia continental collision orogenic belt during the Miocene.