Enrichment and metallogenic prospect of lithium in the coal of Ceshui Formation from the Toushi open-pit mine, Hunan Province

The mineralogical and geochemical characteristics of elements in coal from the Lower Carboniferous Ceshui Formation at the Toushi open-pit mine in the Lianshao coalfield, Hunan Province, were investigated using a suite of analytical techniques: X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), inductively coupled plasma-mass spectrometer (ICP-MS), and high-resolution transmission electron microscope (HR-TEM). The Ceshui Formation bitumite from the Toushi mine is characterized by medium-high ash yield and low volatile matter content. The dominant minerals present arc kaolinite, tobelite, and calcite, followed by quartz, anatase, ankerite, microcline, siderite, and illite, with trace amounts of pyrite. Li is obviously enriched in this coal compared to global averages, with a concentration coefficient of 15. 6. This enrichment exhibits a distinct spatial correlation, with concentration increasing towards the roof and floor of the coal seam. HR-TEM observation, coupled with the strong positive correlation between Li concentration and ash yield, Al2O3and K2O content, suggest that Li is mainly hosted in aluminosilicate minerals, such as kaolinite and Li-bearing chlorite. The elevated Li concentration in the coal is attributed to the felsic nature of the parent rocks in the source regions, as well as the presence of granitic intrusions peripheral to the basin. During peat accumulation, Li migrated from these sediment sources into the peat swamp. Subsequent leaching processes, facilitated by the intermittent influx of seawater and magmatic hydrothermal fluids, further concentrated Li in the coal scam. The Li concentration in the Toushi coal seams approaches industrial recovery grade. Especially in the floor and adjacent coal seams, Li has a promising metallogenic potential. © 2024 Geological Society of China. All rights reserved.