Major element geochemistry and genesis of Yanshanian mineralized granites in the polymetallic deposit concentration region, southern Hunan

Abstract：There are three types of Yanshanian mineralized granite distributed in Hunan. Major element geochemical analyses show the following：(1) Mineralized granites have a higher ratio of K2O/Na2O and display the features of the high-K, calc-alkaline shoshonite series. (2)The MC-type and early CM-type granites are poor in Si and alkalis (K+Na) and rich in Ca, Mg and Fe with a lower aluminum index (A/KNC) and a lower alkalinity ratio of KN/A, which indicates that those granites have the same characteristics as magnesian and ferruginous, para-aluminous, high-K calc-alkaline rocks, such as I-type granite. The lC-type and late CM-type granites are relatively rich in Si and alkalis and poor in Ca and Mg, belonging to the ferruginous, slightly peraluminous-peraluminous shoshonite series. Their ratios of FeOT/MgO are notably higher than those of I- and M-type granites and their higher FeOT values indicate that these granites are apparently distinguished from highly differentiated I-type granites, but generally, they show the features of S-type granites. (3)The higher percentages of F and Cl in mineralized granites indicate that the magma of Yanshanian mineralized granites evolved toward the peraluminous or peralkaline one. The increase in concentrations of the HFSE in the late-stage magma led to mineralization of multiple metals such as Cu, Pb, Zn and Sb in the early-stage MC- and CM-type granites and large-scale mineralization of Sn, W, Pb, Zn, Nb, Ta and LREE in the late-stage aluminous C-type and CM-type granites. (4)The formation of the mineralized granites is related with crust-mantle magma intermingling. The magma generating the MC-type and early-stage CM-type granites was sourced from magma intermingling, while the magmatic evolution of C-type and late-stage CM-type granites might also involve fractional crystallization.