Zircon U-Pb and Molybdenite Re-Os Ages of the Lakange Porphyry Cu-Mo Deposit, Gangdese Porphyry Copper Belt, Southern Tibet, China

The Lakange porphyry Cu-Mo deposit within the Gangdese metallogenic belt of Tibet is located in the southern-central part of the eastern Lhasa block, in the Tibetan Tethyan tectonic domain. This deposit is one of the largest identified by a joint Qinghai-Tibetan Plateau geological survey project undertaken in recent years. Here, we present the results of the systematic logging of drillholes and provide new petrological, zircon U-Pb age, and molybdenite Re-Os age data for the deposit. The ore-bearing porphyritic granodiorite contains elevated concentrations of silica and alkali elements but low concentrations of MgO and CaO. It is metaluminous to weakly peraluminous and has A/CNK values of 0.90-1.01. The samples contain low total REE concentrations and show light REE/heavy REE (LREE/HREE) ratios of 17.51-19.77 and (La/Yb)(N) values of 29.65-41.05. The intrusion is enriched in the large-ion lithophile elements (LILE) and depleted in the HREE and high field-strength elements (HFSE). The ore-bearing porphyritic granodiorite yielded a Miocene zircon U-Pb crystallization age of 13.58 +/- 0.42 Ma, whereas the mineralization within the Lakange deposit yielded Miocene molybdenite Re-Os ages of 13.20 +/- 0.20 and 13.64 +/- 0.21, with a weighted mean of 13.38 +/- 0.15 Ma and an isochron age of 13.12 +/- 0.44 Ma. This indicates that the crystallization and mineralization of the Lakange porphyry were contemporaneous. The ore-bearing porphyritic granodiorite yielded zircon epsilon Hf(t) values between -3.99 and 4.49 (mean, -0.14) and two-stage model ages between 1349 and 808 Myr (mean, 1103 Myr). The molybdenite within the deposit contains 343.6-835.7 ppm Re (mean, 557.8 ppm). These data indicate that the mineralized porphyritic granodiorite within the Lakange deposit is adakitic and formed from parental magmas derived mainly from juvenile crustal material that partly mixed with older continental crust during the evolution of the magmas. The Lakange porphyry Cu-Mo deposit and numerous associated porphyry-skarn deposits in the eastern Gangdese porphyry copper belt (17-13 Ma) formed in an extensional tectonic setting during the India-Asia continental collision.