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

The D onggebi M o deposit is located in the eastern section of the E astern T ianshan O rogenic B elt, C entral A sia O rogenic B elt. Rhenium and osmium isotopes of molybdenites from the D onggebi porphyry M o 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 initial 187 O s 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 the M o deposits in the eastern part of the E ast T ianshan O rogenic B elt were related to a post‐collision extensional setting in the E arly M esozoic.