Re-Os dating of molybdenite from the Hongshan Cu-Mo deposit in Northwest Yunnan and its implications for mineralization

The Hongshan Cu-Mo deposit is located in the Geza volcanic magmatic arc which lies on the southern part of the Yidun island arc in Sanjiang Tethyan area. The mineralization is dominated by skarn Cu, accompanying with granite porphyry Cu-Mo in deep. Re-Os isotopic dating technique on molybdenites collected from the skarn and porphyry type ores in the Hongshan Cu-Mo deposit have been applied to confirm the age of mineralization. The Re-Os dating of five molybdenite samples from skarn-type ore yields a Re-Os model age ranging from 77.90Ma to 80.05Ma, with an average of 79.32±0.87Ma and the isochron age of 80.0±1.8Ma. The Re-Os model age of the one molybdenite sample from porphyry-type ore is 80.71Ma. The ore-forming ages both skarn and porphyry type ores are identical within error. The Re content of molybdenites in Hongshan Cu-Mo deposit is (4.074±0.035)×10-6 ～ (94.21±0.75)×10-6, suggesting that the ore-forming material is mainly originated from crust and a little from mantle. The rock-forming and ore-forming ages of Hongshan Cu-Mo deposit and other polymetallic deposits occurred in Late Yanshanian are consistent. It is indicated that these deposits are formed under the same geodynamics background of late post-orogenic extension after Yanshanian arc-continental collision orogeny. The polymetallic mineralization in ～80Ma of Geza volcanic magmatic arc shows bright future for further prospecting.