REE geochemistry and petrogenesis and mineralization of the Yanshanian mineralized granites in the southern Hunan polymetallic deposit concentration region

Abstract：Yanshanian mineralized granites in southern Hunan may be divided into three types, which have different REE geochemical features, distribution patterns and characteristics of compositional variations, showing distinct differences in petrogenesis and mineralization. (1) The total REE of MC-type granites is lowest, 225×10-6 on average; the average La/Yb ratio is 17, the average LREE/HREE ratio is 5.4, and δEu is 1.67, all of which are highest. Chondrite-normalized REE patterns are nearly straight lines inclined to the right. The total REE of C-type granites is highest, 353×10-6 on average; the average La/Yb ratio is 4.3, the average LREE/HREE ratio is 1.5, and δEu is 1.67, all of which are lowest. The REE distribution patterns are seagull wing-shaped. CM-type granites are intermediate between MC- and CM-type granites. The distribution patterns of the early-stage CM-type granites incline to the right, while those of the late-stage ones are seagull wing-shaped. (2)With increasing acidity, the ΣREE and REE concentrations increase from MC-type through CM-type to C-type mineralized granites and from the east to late stage of the same type of granite. However, LREE show somewhat depleted slightly and HREE enriched; the δEu, La/Yb and LREE/HREE show significantly antithetic relationships with SiO2；and HREE display a reversed trend of evolution and differentiation with magma evolution. (3)The REE of the late-stage CM-type and C-type granites are remarkably differentiated. The deep Eu troughs of the REE patterns indicate a significant fractional crystallization of CM- and C-type granitic magma, which caused HREE to be enriched and Sn, W, Nb and Pb to be concentrated to form ore deposits. (4)Mineralized granites show features of crust- and mantle-derived melt mixing granites rich in volatiles such as F and Cl, and their formation was related to crust-mantle magma mixing; whereas the magmatic evolution of the late-stage CM-type granites and C-type granites might also involve fractional crystallization.