Occurrence state and metallogenic process of Li in granitic aplite-type Li deposits in the western Jiangxi: Constraints from data of mica mineralogy and Li isotope

The Early Cretaceous Ganfang granite complex, located in the western Jiangxi, is one of the most important rare metal related granites in South China. A large amount of lithium resources has been newly discovered and explored within this granite complex. The granitic aplite dikes, widely distributed in the area around the Ganfang granite complex, are characterized with high Li2O grade, fine particles, and strong alteration with fluorination. However, researches of the occurrence state and mineralization process of Li within granitic aplite dikes are very limited. In this paper, taking the typical granitic aplite-type Tongan and Dongshang Li deposits as research objects, the mica mineralogical study and Li isotope analysis of whole-rock samples are undertaken in order to explore the lithium occurrence state and mineralization process of these two deposits. The results show that micas within these two deposits are dominated by lepidolite, with minor zinnwaldite and Li-rich muscovite. Generally, micas have an overall evolution trend from Li-rich muscovite to zinnwaldite, and to lepidolite. With the increase of magmatic evolution, contents of F, Rb2O, Cs2O, MnO, and Li2O of micas are gradually increased, indicating that elements including Li F, Rb, Cs are gradually enriched in micas in the magmatic evolution process. Meanwhile, there is obvious fractionation of Li isotopes with the δ 7Li values of bulk samples of aplite ranging from –5.57‰ ± 0.28‰ to –0.75‰ ± 0.19‰, suggesting that a large amount of magmatic-hydrothermal fluids was exsolved from the magma in the late stage of magmatic evolution. The high δ 7Li values of bulk rock samples of the granitic aplite are resulted from the feature of 7Li which is tended to be partitioned in the fluid phase. Therefore, it is believed that the Li enrichment and mineralization in the granitic aplite are closely related to the high degree crystalization diffrentiation of magma and the exsolution of magmatic-hydrothermal fluids from the magma.