Early Mesozoic granites and polymetallic mineralization in southeastern Yichun area, Xiao Hinggan Mountains

Abstract：The Late Triassic-Early Jurassic monzonitic granite in southern Yichun area of the Xiao Hinggan Mountains extensively has migmatitic MME-type fine-grained dark dioritic enclaves and plutonic intermediate-basic mafic dikes, characterized by crust-mantle mixture. In contrast, the syenitic-alkali feldspar granite is characterized by aluminian A2 type granite. Their petrographic, major and minor element and isotopic features show that their formation was related to underplating in an extension-collapse environment of the transition period from continental collision to post-collision after the closure of the palaeo-Asia Ocean. The similarity of the two types of granites in genesis, material source and metallogenic background also finds expression in their similarity of metallogenic series. The monzonitic granite assumes the Mo-Pb-Zn-Fe-Au-Ag metallogenic series, with Mo and Pb ore-forming processes being most intense, whereas syenitic- alkali feldspar assumes the Zn-Pb-Cu-Mo-W-Fe metallogenic series, characterized by weak and scattered mineralization. Their certain degrees of difference in metallogenic series might have to do with the somewhat different degrees of crust-mantle mixture. The difference of these Mesozoic granites in ore-forming features, ore deposit types, mineralization intensities and mineralization types indicates that this area still has great potential in search for polymetallic ore deposits.