Geochemical characteristics and their implications on mineralization of biotite from the Maodeng Mo-Bi-Sn-Cu deposit, southern Great Xing’an Range, China

The Maodeng Mo-Bi-Sn-Cu deposit lies in the southern part of the Great Xing’an Range. In this deposit, the ore-associated Alubaogeshan complex has been identified, which consists of porphyritic monzogranite (PMG), granite porphyry (GP), and alkali feldspar granite (AFG). This research provides the major-trace element concentrations in biotites from the three granite subtypes, with the intention of uncovering the petrogenetic relationships among different lithologies. The biotites in the Alubaogeshan complex have a magmatic origin. As the granitic subtypes change from PMG and GP, to AFG, they vary from alkaline anorogenic to peraluminous types. Simultaneously, the biotites exhibit a diverse array of compositions, spanning from lepidomelane to protolithionite-zinnwaldite. The total aluminum content and the Fe/(Fe + Mg) values in biotites rise gradually from PMG to GP and then to AFG, indicating a progressive degree of magmatic evolution. The trend of increasing magmatic differentiation from PMG to AFG is manifested by the decline in K/Rb and Nb/Ta ratios and the increase in contents of Rb, Cs, Sn, W and Li in biotites. From PMG to GP and then to AFG, a decrease in IV(F) value and an increase in IV(Cl) value in biotite suggest that a high-degree fractional crystallization resulted in F enrichment, and fluid exsolution caused Cl depletion in the residual melt. From PMG to AFG, Nb/Ta ratios of biotite drop from 12.8 to 33.5 to 2.76–3.66. This study indicates that fractional crystallization of biotite, as well as intense interaction of melt and fluid, is the main factor causing the decrease in biotite Nb/Ta ratios in the Alubaogeshan complex. The highly fractional crystallization, intense exsolution of Cl-bearing fluid, and enrichment of the F element in the ore-related granite may exert a crucial role in mineralization in the Maodeng deposit.