Significant contribution of seawater infiltration and hydrothermal activity on lithium enrichment in the Ceshui Formation coal of the LianShao Coalfield, Hunan Province, South China

The Ceshui Formation is one of the most important coal-bearing formation of the Lower Carboniferous in China, especially in South China. This study investigates the mineralogical and geochemical characteristics of the Lower Carboniferous Ceshui Formation coal from the studied area, Lianshao Coalfield, Hunan Province, with special emphasis on significant lithium enrichment in the studied area. The Ceshui Formation bituminous from the Toushi open-pit mine is characterized by medium-low ash yield, low volatile matter yield and low sulfur content. Minerals occurring in the coal are mainly composed of kaolinite, tobelite and calcite, followed by quartz, anatase, ankerite, microcline, siderite and illite, with a trace amount of pyrite. Compared with the average values in worldwide coals, Li is significantly enriched in the Ceshui Formation coals in the studied area, occurring mainly in kaolinite and secondarily in chlorite. The closer to the roof and floor, the higher the concentration of Li. The concentration of Li 2 O in coal ashes exceeds the Extraction Standard for Li 2 O in coal-bearing strata, presenting a promising metallogenic potential. The enrichment of Li in the Toushi coals is primarily derived from the supply of terrigenous sediment provenance and strongly influenced by its interaction with infiltrated seawater and hydrothermal fluids. The sediment provenance of the terrigenous clastic was derived from the Li-rich granite in the Xuefeng Oldland to the northeast of Lianshao coalfield. The Ceshui Formation coal in the studied area was formed in a marine-influenced transitional sedimentary environment, and Li from Li-rich granitic debris was more readily enriched in coal seams during slow sea regressive process. The infiltration of hydrothermal fluids and interaction with Li-bearing terrestrial material further promoted Li enrichment in the Toushi coals.