U-Pb zircon LA-ICP-MS age of the Yaguila molybdenum-bearing intrusion in Tibet and its geological significance

Abstract：There exist a large number of large and medium-sized lead-zinc deposits as well as a large-sized molybdenum deposit in Nyainqentanglha region of eastern Gangdise. The former deposits are considered to be products of Eocene mineralization，whereas the latter deposit is regarded as a Paleocene porphyry deposit. In the process of the evaluation of the Yaguila ore deposit, which is the largest lead-zinc deposit in the Gangdise metallogenic belt，the authors found that lead-zinc mineralization is closely related to the quartz porphyry body, and that a large-sized molybdenum vein occurs inside the intrusion body. U-Pb isotopic ages and trace element content of zircon crystals from the intrusion were measured by using LA-ICP-MS techniques. About 90% of the zircons have relatively high Th/U ratios and clear oscillatory zoning，indicating that they are of igneous origin. The acquired 206Pb/238U weighed average ages of LA-ICP-MS zircon U-Pb isotopes are 65.8±1.3 Ma (MSWD =3.0) and 68.6±1.7 Ma(MSWD=1.8), indicating that the quartz porphyry body was formed in the late Cretaceous period. Based on field investigation and an analysis of trace elements content of the quartz porphyry in combination with the Re-Os ages of the molybdenum vein obtained by previous researchers, the authors point out that both molybdenum and lead-zinc mineralizations are associated with the quartz porphyry, but Yaguila′s molybdenum was formed earlier than Sharang′s. It is concluded that not only lead-zinc mineralization but also molybdenum mineralization occurred in late Cretaceous in Nyainqentanglha region.