The Petrogenesis And Metallogenetic Model Of Qianlishan Tin-tungsten Bearing Granite In Hunan, China

The21st Century is a key period for rapid economic development in China, thus demand on the metal resources, especially on the Non-ferrous metals is rising sharply. The A-type granite belt along the NE directional Chenzhou-linwu fault in Nanling is closely related with tin-tungsten deposit. The Qianlishan igneous rock in Bingzhou, Hunan is typical of those many tin-tungsten deposits.Therefore, knowledge of the petrogenesis and ore-forming mechanism of Qianlishan granite helps to shed light on the tin-tungsten deposit-related granite evolution and metal enrichment process in Nanling.Qianlishan granite complex is controlled by5times of magmatic activities, forming the biotite granite, granite porphyry as well as mafic dikes such as diabase in chronological order. Qianlishan granite is rich in Si, Fe and alkalis while poor in Ca and Mg. It shows enrichment of Rb, Th, U, Zr, Hf and Ga, and depletions of Sr and Ba in chemical geology, which is correspond to the typical A-type granite. Moreover, it has relatively high Fe-index values, making it the ferroan granite defined by Frost et al.(2011).Chemical geological data shows that the Qianlishan complex is peraluminous alkali-calcic ferroan granite with enrichment of Si, Fe and depletion of Mg, which is generated by low-degree partial melting of crust source region, and it’s also a typical A-type granite. The biotite granite which is the main body of Qianlishan granite is formed at an average temperature of718℃with a pressure of0.7～1.0GPa, showing the characteristics of the granite that generated in the lowest melting point. Qianlishan granite is generated in the extensional background after thrust in the late stage of Yanshan movement in east China, which leads to the underplating of mantle derived magma and the following partial melting of crust.The magma chamber provides energy and materials continuously for the Qianlishan area through the large-scale deep fault, and promotes the partial melting of the crust to generate granite magma. The multiply magmatic fluids supply the metal elements continuously in Qianlishan, and the Fluorine in the fluid phase is an agent that can increase the solubility of metals significantly, and decrease the crystallizing temperature as well as prolong the mineralization time.Although deuteric intrusive granite porphyry is mainly form Pb-Zn deposits instead of W-Sn mineralization, the late stage emplacement of granite porphyry and mafic dikes provide an essential heating source for the earlier ore forming fluids to keep high chemical activity.