Restricts Of Lithium On The Petrogenesis And Mineralization Of Granite

Lithium is a strategic critical metal,which is not only the research frontier of Geoscience,but also one of the scarce mineral resources of our country.In the magmatic stage,Li is mainly enriched and crystallized in granitic rocks.Due to its incompatibility and volatile properties,lithium has an important influence on the petrogenesis and mineralization of granite.In this paper,Laiziling and Jianfengling granites from the Xianghualing areas(South Hunan)were selected as our research objects.In this paper,based on field investigation and microsopic observation,the petrography,major-trace elements and mineralogy analyses of the granites were systematically studied by using electron microprobe analysis and LA-ICP-MS analysis,with the aim to reveal the influence of Li on vertical zoning of granite,and to discuss the restricts of Li on the mineralization of rare metals in the crystallization and differentiation processes of granite.The results are as follows:(1)During the crystallization differentiation of granitic magmas,from biotite granite to two-mica granite then to albite granite,as Li content increases gradually,the ratio of Zr/Hf,Nb/Ta and K/Rb decrease,thus the concentration of Li is closely related to highly differentiated evolution of granites.With the increasing content of Li in the granite melt,it lowers the melt viscosity,and increases the crystallization temperature range,resulted in the fully differentation of the granitic rocks and,in the vertical zonation of granite;(2)With the increasing Li content in granite,the contents of Nb and Ta also gradually increase.There is a positive correlation between Li contents and rare-metals contents in the granites.As the concentration of Li,Ta-and Nb-bearing minerals are gradually crystallized,suggested the synergistic mineralization among Li,Ta and Nb;(3)From biotite granite to two-mica granite then to albite granite,mica group minerals evolved from the biotite to the zinnwaldite,suggestive the trend of Li rich evolution of mica group minerals.With the crystallization of zinnwaldite,the contents of Nb,Ta and Sn and other rare metals in mica minerals decrease.The crystallizationof columbite,wolframite,cassiterite and other rare metal minerals leads to a decrease of Ta and Nb contents in late mica group minerals.(4)Although ther volatile components such as H2 O,F,etc.in the granite melt have a great impact on the properties and crystallization differentiation of the granitic magma,and restrict the petrogenesis and mineralization of the granite,they are insufficient to cause the vertical zonation of granitic rocks.