Lithium resources in coal-bearing strata: Occurrence, mineralization, and resource potential

As an important strategic metal resource, lithium has been a hot spot in the exploration field in recent years. Lithium deposits occur primarily in brines, pegmatites, and clays. The research on strategic metal deposits in coal and coal-bearing sequences has also made a lot of progress in recent years. Some coal-hosted metal (such as Ge, Ga, Al, U, REE, Nb, and Zr) deposits have been found. Lithium in coal has not been regarded as an important metal for exploration and utilization for a long time in the past, and it has only received more attention since 2008. When the concentration of lithium in coal exceeds a certain grade, it can form coal-hosted lithium deposits, which are classified as sedimentary lithium deposits. In recent years, several cases of lithium enrichment in coal have been reported. However, lithium has a low atomic number, along with its low concentration in coal, and various modes of occurrence, which makes it one of the most difficult elements to be studied in coal. Based on the authors' previous research and the data published by previous researchers, it is proposed that when the Li2O content in coal-bearing strata reaches 0.08%(on high-temperature ash basis), it can be considered that the grade of the coal-hosted lithium deposit in the coal-bearing strata has been reached. The coal-hosted lithium deposits discovered so far in China mainly occur in the Carboniferous-Permian strata of North China, while a small number occur in Southern China. Coals that are mostly enriched in Li (Li2O in high-temperature ash≥0.2%) include the late Carboniferous coal of the Jincheng coalfield, Shanxi Province, the late carboniferous coal from the Guanbanwusu mine in the Jungar coalfield, and the late Triassic coal from the Caotang Mine, Chongqing. The most important carrier of Li in these three deposits are cookeite and/or lithium-bearing chlorite. These three coal-hosted lithium deposits are all caused by hydrothermal fluid activities. Coal-hosted lithium deposits are often associated with strategic metals such as Ga and REE, which are expected to be co-exploited and comprehensively utilized. © 2022, Editorial Office of Journal of China Coal Society. All right reserved.