Petrogenesis of the Bao'anzhai granite and associated Mo mineralization, western Dabie orogen, east-central China: Constraints from zircon U-Pb and molybdenite Re-Os dating, whole-rock geochemistry, and Sr-Nd-Pb-Hf isotopes

Recently, many Mo deposits genetically related to emplacement of Early Cretaceous granites have been found in the Dabie-Qinling belt. A typical intrusion that combines magmatism and metallogenesis, the Bao'anzhai granite, yields a zircon U-238-Pb-206 age of 123.2 +/- 1.1Ma and a molybdenite Re-Os isochron age of 122.5 +/- 2.7Ma. This granite is characterized by high silica and alkali, but low Mg, Fe, and Ca. It is enriched with light rare earth elements (REEs) and large-ion lithophile elements (LILEs, Rb, K, Th, U) but depleted of heavy REEs, high field strength elements (HFSEs, Nb, Ta, Ti, and Y), and Sr. This high-K granite has medium initial Sr-87/Sr-86 ratios (0.706518-0.707116) and low initial Pb isotopic ratios [(Pb-206/Pb-204)(i), 16.423-16.699; (Pb-207/Pb-204)(i), 15.285-15.345; (Pb-208/Pb-204)(i), 37.335-37.633], and is characterized by low E-Nd(t) and E-Hf(t) values (-14.92 to-14.22 and-21.67 to-19.19, respectively). These data indicate that this pluton is a high-K calc-alkaline fractionated I-type granitite. It was generated by partial melting of the Yangtze lower crust, which is probably similar to Neoproterozoic TTG-like magmatic rocks at the north Yangtze Block under a non-thickened lower crust environment (<35km). The ores also have low radiogenic Pb isotopes (Pb-206/Pb-204, 16.592-17.674; Pb-207/Pb-204, 15.300-15.476; Pb-208/Pb-204, 37.419-37.911) and low Re content in molybdenite (5.693-10.970ppm), suggesting a crustal magmatic source for the metallogenic minerals in the Mo deposit.