Re-Os Geochronology of Porphyry Molybdenum Deposit in South Segment of Da Hinggan Mountains,Northeast China

The ages for porphyry Mo deposits in south segment of Da Hinggan Mountains,Northeast China,are not well known.Five molybdenite samples from the Aolunhua(奥伦花) porphyry Mo deposit,five molybdenite samples from the Yangchang(羊场) porphyry-quartz vein Mo deposit and two molybdenite samples from the Banlashan(半拉山) porphyry Mo deposit were selected for Re-Os dating.Three deposits are spatial-temporally associated with the granite porphyry stock.Re-Os isochron age of 131.2±1.9 Ma was obtained for the Aolunhua porphyry Mo deposit.The Yangchang Mo deposit provides isochron age of 138.5±4.5 Ma for two groups of molybdenite(within porphyry ore and within quartz vein).The Banlashan porphyry Mo deposit provides model ages of 140.5±2.4 and 143±2.2 Ma.All of these Re-Os ages are consistent presumed Yanshanian ages for granite intrusions,formed in crust thinning setting in Cretaceous in North China.