Early Cretaceous A-type granites and Mo mineralization, Aershan area, eastern Inner Mongolia, Northeast China: geochemical and isotopic constraints

The Jiazishan porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. To better understand the link between mineralization and host igneous rocks, we studied samples from underground workings and report new SHRIMP II zircon U-Pb and Re-Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Seven molybdenite samples yield a Re-Os isochron weighted mean age of 135.4 +/- 2.1 Ma, whereas the porphyry granite samples yield crystallization ages of 139 +/- 1.5 Ma (Jiazishan deposit) and 133 +/- 1 Ma (Taolaituo deposit). The U-Pb and Re-Os ages are similar, suggesting that the mineralization is genetically related to Early Cretaceous porphyry emplacement. Re contents of the molybdenite range from 21.74 ppm to 52.08 ppm, with an average of 35.92 ppm, whereas delta S-34 values of the sulphide vary from 1.3% to 4.2%. The ores have Pb-206/Pb-204, Pb-207/Pb-204, and Pb-208/Pb-204 ratios of 18.178-18.385, 15.503-15.613, and 37.979-38.382, respectively. We also obtained a weighted mean U-Pb zircon age of 294.2 +/- 2.1 Ma for the oldest granite in Jiazishan area. All granites are A-type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Jiazishan deposit occurred contemporaneously with Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in Northeast China.