In situ LA-ICP-MS analyses of muscovite: Constraints on granite-type Li mineralization in northwestern Jiangxi, South China

Giant granite-type lithium (Li) deposits in northern Jiangxi province (South China), such as the Shiziling-Baishuidong (1.1Mt @ 0.3 wt% Li2O) and Yichun #414 (0.6 Mt @ 0.39 wt% Li2O), are tectonically located in the Jiangnan Orogen. The concentration and enrichment mechanism of rare metals (incl. Li) in northern Jiangxi is still unclear. Mica is widely distributed in this Li-ore type and is closely ore-related. Therefore, we used mica geochemistry to determine the mineralization process and mechanism of the Shiziling-Baishuidong and Yichun #414 deposits. At Shiziling-Baishuidong, lithium mineralization is concentrated along the intrusive endocontact of Early Cretaceous highly-fractionated S-type muscovite granite. Early albite and muscovite (with Li-rich mica) alterations, and late greisen (muscovite and quartz) alterations are common in the ShizilingBaishuidong and Yichun #414 deposits. The hydrothermal and magmatic muscovite is mostly lepidolite and zinnwaldite, respectively. At Yichun, the biotite- or two-mica granite may have altered by F- and Na-rich magmatic-hydrothermal fluids, leaching the Li-Nb-Ta-W for the subsequent mineralization in the muscovitization and greisenization stages. The re-equilibrated muscovite (M2r), a metasomatic(altered) equilibrated muscovite in the altered granite, has the lowest Li (663 ppm), Nb (15.2 ppm), Ta (16.7 ppm), and W (6.12 ppm) contents. At both Shiziling-Baishuidong and Yichun, the magmatic muscovite has the highest Nb/Ta (mostly > 8) but lower Li/Rb (mostly 1.5), whereas the hydrothermal muscovite has the lowest Nb/Ta (mostly similar to 4) but higher Li/Rb (mostly > 1.5). The re-equilibrated muscovite has Nb/Ta = 4 to 8 and a wide Li/Rb range (0.1 to 2.0). When lithium was precipitated, the re-equilibrated and hydrothermal muscovite mineralogy and chemistry show that hydrothermal alteration was essential in the granite-type Li ore formation at Shiziling-Baishuidong.