Zircon U-Pb Ages of the Granodioritic Porphyry in the Laba Molybdenum Deposit,Yunnan,SW China and Its Geological Implication

The Geza island-arc is a well-known mineralization concentration area,part of the Sanjiang Domain at the east margin of the Tibetan Plateau.In recent years,several Late Yanshanian granitic intrusions and associated deposits have been found in this region,the largest one of which in the Shangri–La region is the Laba molybdenum deposit.Previous studies suggested that the timing of the Laba mineralization is 85 ± 2 Ma.However,the ages of the granodioritic porphyry remain unknown.In this study,LA-ICP-MS U-Pb dating of zircons from three samples of the molybdenite-bearing granodioritic porphyry has been conducted with resulting dates of 85.00 ± 0.23 Ma(MSWD = 0.58),85.28 ± 0.28 Ma(MSWD = 1.12),and 84.83 ± 0.26 Ma(MSWD = 0.79),respectively,indicating that these granodioritic porphyries formed in the Late Yanshanian around ~85 Ma.Combined with the geological features of the mineralization,the Laba deposit is spatially,temporally,and probably genetically associated with the granodioritic porphyries.In addition,the ages of the Laba deposits are consistent with the other Late Yanshanian intrusions and mineralization,suggesting that the mineralization was probably generated under an intra-plate extensional environment during the Late Cretaceous.