Re-Os Isotopic Dating of Molybdenite of Pingdi Molybdenum Deposits in Wuyishan, Fujian Province and Its Geological Significance

Pingdi molybdenum deposit was attributed to medium-high hydrotherm type deposits, occurring in layer-joints of K-feldspar granite of Chenwulou unite of Late Jurassic and the north-south faults developed within Chenwulou magmatic body and the contact between Chenwulou magmatic body and lower Proterozoic Dajinshan formation. The ore mineralizations are of silified alteration type (quartz vein type), pyrite sericite quartz rock type, granite type and structural breccia type. Ore structures are of veinlet, disseminated, breccia, small vein. The ores mainly have medium and coarse-medium fine grain platy texture, and minor molybdenites are thick tabular and bent banding. Molybdenite is the only ore mineral in this molybdenum deposit. We collected molybdenites with different occurrences and elevations from different ore bodies of Pingdi molybnum deposits for Re-Os isotopic dating. The isochron age of (102.9±1.8) Ma(MSWD=2.1), and the model age of (107.4±3.3) Ma (MSWD=16) were obtained. This results indicated the multi-stages mineralization with three types of molybdenite such as fine veins in rock of K-feldspar granite, thick veins in "bedding joint" of K-feldspar granite and in breccia silicified rocks controlled by fractures, which were formed in different metallogenic phases,(111.20±1.7) Ma-(111.60±1.6) Ma, (105.60±1.6) Ma-(107.40±1.6) Ma and (103.70±1.7) Ma,the mineralization periods during late stage of early cretaceous. This isotopic data provided the new geochemical evidences for Mesozoic tectonic magma evolution and guided regional ore-exploration of Pucheng-Ningde NW tectonic belt of Southeast coast of Fujian Province.