The geochemistry, U-Pb and Re-Os geochronology, and Hf isotopic constraints on the genesis of the Huangjiagou Mo deposit and related granite in the Dabie region, Hubei Province, China

In recent years, a number of Mo deposits have been discovered in the Dabie region of the Qinling-Dabie orogenic belt. These deposits have a genetic relationship with Late Jurassic to Early Cretaceous granites. In this study, we present a geochemical and geochronologic study on the recently found Huangjiagou Mo deposit, which is the first Mo deposit found in Hubei Province from the Dabie region. The Huangjiagou deposit is currently under exploration, and a middle-sized Mo deposit with 100,000t of proven Mo metal reserves has already been reached. Mo mineralization mainly occurs as small quartz-molybdenite veins and disseminations within the country rocks next to the Huangjiagou granite. Re-Os isotope dating of molybdenites from the ore veins yields an age of 137.0±8.1Ma, which is consistent with the LA-ICP-MS zircon U-Pb age of the Huangjiagou granite (137.6±1.6Ma), suggesting a coeval and causative relation between the granite and mineralization. Geochemical analysis indicates that the Huangjiagou granite is high-K calc-alkalic to shoshonitic and weakly peraluminous with relatively low Mg contents. The rocks are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs). The (La/Yb)N ratios vary from 24.39 to 40.37, and no significant Eu anomalies occur for these samples. The rocks also show enrichment in large ion lithophile elements (LILEs, e.g., Pb, Ba) and depletion in high-field-strength elements (HFSEs, e.g., Nb, Ti). The Hf isotopic compositions of zircons from the granite indicate εHf(t) variations from −17.3 to −22.1 (average −19.8±0.5) with two-stage model ages (TDM2) from 2.26 to 2.56Ga (average 2.42Ga). These geochemical and isotopic features imply that the Huangjiagou granite was likely derived from partial melting of a thickened lower crust that mainly contained garnet and clinopyroxene without feldspar. The abundance of Re in the molybdenites also indicates that the Mo may be derived from the thickened crust with possible minor mantle material mixing. Considering all of the available data for the Mo deposits and related granites in the entire Dabie region, the Mesozoic Mo mineralization can be divided into two stages. The early-stage Mo mineralization (>130Ma) is mainly related to granites that resulted from partial melting of the thickened lower crust (including eclogite) with few mantle components added, whereas the late-stage Mo mineralization (<130Ma) is related predominantly to continental crust melts, as eclogite had already been removed at ca. 130Ma in the region.