矿床地球化学国家重点实验室知识库

Mesozoic granitic intrusions are widely distributed in the Nanling region, South China, Yanshanian granites are closely connected with the formation of tungsten deposits. The Xihuashan granite is a typical representative of tungsten‐bearing granite. The Xihuashan granite consists mainly of medium‐grained porphyritic biotite granite, medium‐grained biotite granite and fine‐grained two‐mica granite, which correspond to LA‐ICP‐MS zircon U‐Pb ages of 155.5±0.4 Ma, 153.0±0.6 Ma and 152.8±0.9 Ma, respectively. Rocks from the Xihuashan mining area displays high SiO₂ (73.85% to 76.49%) and Na₂O+K₂O contents (8.09% to 9.43%), belonging to high‐K calc‐alkaline series. They are metaluminous to weakly peraluminous with A/CNK values ranging from 0.96 to 1.06. All granites in this study area are rich in Rb, Th, U and Pb, and depleted in Ba, Sr, P, Ti, Nb and Eu, especially depleted in medium‐grained biotite granite and fine‐grained two‐mica granite. The medium‐grained porphyritic biotite granites usually have high LREE concentrations, whereas medium‐grained biotite granite and fine‐grained two‐mica granite displays high HREE contents. Our geochemical data reveal that the studied rocks are highly fractionated I‐type granite. The magma underwent strong magma differentiation with decreasing temperature and increasing oxygen fugacity, which may explain the formation of three types of distinct granites. Variations of Rb, Sr and Ba concentrations in different type granites were controlled by fractional crystallization of biotite and feldspar. Fractional crystallization of monazite, allanite and apatite resulted in LREE changes in granite, and formation of garnet mainly caused HREE changes. Granites from the Xihuashan mining area have relatively high ε_Nd( t ) values (–9.77 to –11.46), indicating that they were probably generated by partial melting of underlying Proterozoic metasedimentary rocks with minor addition of juvenile crust or mantle‐derived magmas.