R e– O s Geochronology on Molybdenites from the D onggebi M o Deposit in the Eastern T ianshan of the C entral A sia O rogenic B elt and its Geological Significance

TheDonggebiMo deposit is located in the eastern section of theEasternTianshanOrogenicBelt,CentralAsiaOrogenicBelt. Rhenium and osmium isotopes of molybdenites from theDonggebi porphyryMo deposit have been used to determine the timing of mineralization and the source of osmium and, by inference, ore metals. Molybdenite was collected mainly from a granite porphyry stock, which is characterized by moderate to strong silicification. Rhenium concentrations in molybdenite samples are between 10 and 63 μg g−1. Analysis of eight molybdenite samples yields an isochron age of 234.3 ± 1.6 Ma (2σ) with an initial187Os of 0.04 ± 0.45 (MSWD= 0.25). The data support the hypothesis that a significant part of the metals and magmas have a mixed (crust + mantle) origin. Based on the geological history and spatial‐temporal distribution of the granitoids, it is proposed that theMo deposits in the eastern part of theEastTianshanOrogenicBelt were related to a post‐collision extensional setting in theEarlyMesozoic.