Molybdenite Re-Os Precise Dating for Molybdenite from Cu-Au-Mo Deposits in the Middle-Lower Reaches of Yangtze River Belt and Its Implications for Mineralization

The Middle-Lower Yangtze River metallogenic belt is an important corridor for Cu-Au-Mo-Fe deposits in East China. Because there are porphyry-skarn Cu-Au-Mo deposits, and stratabound Cu-Au-Mo deposits, their origin have been strongly controversial for a long time. We obtained eleven molybdenite samples from five skarn-porphyry Cu-Au-Mo deposits and the other five samples from the Datuanshan stratabound Cu-Au-Mo deposit for Re-Os dating. The total 16 samples are dated with ICP-MS method and 9 of them are dated by NTIMS. The results from the two methods of ICP-MS and NTIMS are almost concordant each other. Re-Os model ages of 16 molybdenite range from 134. 7±2. 3 to 143. 7±1. 6Ma (2σ) in which the model ages of the five samples from the Datuanshan deposit are quite close, varying from ?38. 0±3. 2 to 140. 8±2. 0 Ma, averaging 139. 3±2. 6 Ma, their corresponding isochron is 139. l±2. 7 Ma with initial Os value of 0. 7±8.1 (MSDW =0. 29). These data definitely reflect the porphyry-skarn-Cu-Au-Fe-Mo deposits and the stratabound skarn Cu-Au-Mo deposits share the same forming ages and are the products of a same metallogenic system. They all occurred at the time of the transition stage of geodynamic regimes i. e. from the main compression regime in north-south direction to quickly significant extension in EW-direction.