Geological characteristics and molybdenite Re-Os isotopic dating of Shiyaogou porphyry molybdenum deposit in the East Qinling

The Shiyaogou deposit is a large molybdenum deposit lately discovered in the East Qinling molybdenum belt. Emplaced along the intersection of the EW-trending Machaoying fault and the NE-trending Jiaoyuan fault,the Shiyaogou deposit has a proven reserve of more than 100,000 tonnes Mo,averaging grade of 0.068%. Mineralization of the deposit consists of quartz-molybdenite veinlets and stockworks which occur in the altered granite porphyry and Proterozoic Xionger Group. Hydrothermal alteration is well developed and is composed of potassic feldspar alteration,silicification,sericitization,and pyritization,typical of porphyry Mo deposits. Five molybdenite-bearing samples of different mineralizing types were selected for precise Re-Os dating,and the results yield Re-Os model ages between 131.3±2.4~134.3±2.6Ma and an isochron age of 135.2±1.8 Ma. The Re contents of molybdenite are (8.242±0.116~30.24±0.24) ×10-6,indicating that they were mainly derived from the lower crust. The age of the Shiyaogou molybdenum deposit is consistent with that of the Yuchiling and Leimengou Mo deposits in the East Qinling molybdenum belt,indicating that porphyry Mo mineralization was driven by the Early Cretaceous lithospheric extension in East China.