The Dahongliutan two-mica granite is considered as parental rock to the adjacent pegmatite-type lithium deposits such as Bailongshan.To constrain the magmatic-hydrothermal evolution of granite and associated pegmatites,we selected the penetrative minerals,mica and tourmaline,from two-mica granite and pegmatite with different degrees of mineralization,for backscattering observation(BSE)and electron probe microanalysis(EPMA).In the two-mica granite(Ms1)and muscovite-microcline pegmatite(Ms2),the muscovite is homogeneous,with limited chemical variations.In muscovite-albite-spodumene pegmatite,the muscovite(Ms3)incorporates much higher Li(Li2O up to 4.68%)and F(up to 6.47%)in comparison to Ms1 and Ms2.There are additional Li-bearing phengite,zinnwaldite and lepidolite that have replaced muscovite.Tourmalines from two-mica granite(Tur1)and muscovite-microcline pegmatite(Tur2)belong to alkaline schorl,while those from spodumene pegmatite(Tur3)are alkaline elbaite.Compared to alkaline schorl,alkaline elbaite is enriched in SiO2,Al2O3,Li2O,but depleted in TiO2,MgO and CaO.The textural and compositional features of mica and tourmaline reveal that the two-mica granite and muscovite-microcline pegmatite were formed by magmatic process,without lithium mineralization.By contrast,muscovite-albite-spodumene pegmatite was formed during the magmatic-hydrothermal transition,where lithium was significantly enriched,and numerous lithium-rich minerals such as spodumene,lithium-rich polysilicon muscovite,Li-bearing phengite,zinnwaldite,lepidolite and elbaite,were precipitated.Accordingly,we propose that the magmatic-hydrothermal transition is of great significance for lithium mineralization.In pegmatite-type deposits,the presence of elbaite and lepidolite indicates high degree of magmatic evolution.
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