1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China;
3. The 8th Geological Team of Non-ferrous Exploration Bureau of Geology and Mineral Resources, Xining 810000, China

Xintian polymetallic deposit is a hydrothermal vein type Cu-Mo deposit. Analysis on Re-Os isotopic dating for the molybdenite from this deposit is undertaken to determine metallogenic epoch and dynamics setting of the deposit. Re-Os isotopic dating for the molybdenite yields model ages ranging from 123.9±1.9 Ma to 124.7±1.8 Ma, with a weighted mean age of 123.4±0.81 Ma, and an isochron age of 127±16 Ma, MSWD=0.25, indicating that the metallization was at late Yanshanian. The content of Re in molybdenite is (330.1±4.0-367.9±3.1)×10^-6, which demonstrates mantle derived metallogenic sources. Integrating the regional tectonic evolution and the metallogenic characteristics of other contemporaneous Cu-Mo deposits in the region, it is suggested that the Cu-Mo mineralization of this deposit occurred in an active epicontinental environment under lithospheric extension resulted from the subduction of the Izanagi plate to the Paleo-Asia continental margin at late Yanshanian. The Mantle wedge was partially melted with large amount of metallogenic elements dissolved in it. Under the favorable conditions of crust-mantle interaction, large-scale magmatic activity turns out to be the important mechanism of the mineralization of many Cu-Mo deposits in the Xiaoxingan Range-Zhangguangcai Mountain metallogenic belt, including the Xintian Cu-Mo polymetallic deposit.