Discovery of Late Triassic mineralization in the Gangdese Metallogenic Belt, Tibet: The Banduo Pb-Zn deposit, Somdo area

The newly discovered Banduo Pb-Zn deposit in the Somdo area of Tibet is hosted by a Late Triassic granodiorite. A combination of zircon U-Pb dating, Hf isotopic compositions, sulfide Rb-Sr dating, and whole-rock chemistry was used to determine the age of the mineralization and characterize the metallogenesis of the posit. The weighted-mean U-Pb ages of zircon from the granodiorite (203.8 +/- 1.7 Ma, MSWD = 206.1 +/- 0.4 Ma, MSWD = 0.098) and the weighted-mean Rb-Sr isochron age of sulfides from the mineralization (202.7 +/- 2.3 Ma; MSWD = 1.3) suggest that the timing of mineralization was close to that granodiorite crystallization during the Late Triassic. The average (Sr-87/Sr-86)i value of 0.71026 implies that ore-forming metals were sourced from a mixture of mantle and crustal material. The weakly altered granodiorite of the deposit is characterized by SiO2 = 66.78-67.85 wt%, K2O = 2.57-3.37 wt%, Al2O3 = 13.53-15.15 and Mg# = 45.5-51.3. It is enriched in LREEs and LILEs and depleted in HREEs and HFSEs, and it exhibits negative Eu anomaly. The granodiorite has positive and negative epsilon Hf(t) values (-2.5 to 1.7) and crustal ages (TC DM) of 1.14-1.40 Ga. Hf isotopic analyses and whole-rock geochemistry indicate that the Late Triassic granodiorite was likely sourced from of a mixture of mantle and ancient lower-crust material that had undergone variable degrees of fractional crystallization. Based on regional data, the Banduo deposit is the oldest deposit in the Gangdese belt and likely formed as a result of the northward subduction of the Neo-Tethys Ocean. The metallogenic epoch indicates that deposits related to the northward subduction of the Neo-Tethys oceanic crust exist in this area. The Late Triassic age of granitoid-hosted mineralization provides additional prospects exploration in the Gangdese Metallogenic Belt.