Mineralogy and elemental geochemistry of Permo-Carboniferous Li-enriched coal in the southern Ordos Basin, China: Implications for modes of occurrence, controlling factors and sources of Li in coal

Abstract

As the decisive element promoting the battery industry and a raw material in aerospace Al-Li alloys, the demand for Li is increasing daily. At present, the exploitation and utilization of lithium resources mainly originates from brine (salt lake) deposits and pegmatite deposits. Emerging sediment hosts, including coal-hosted Li deposits, provide a potential source of lithium resources. Based on proximate analyses, including X-ray diffraction analysis (XRD), energy dispersive X-ray spectroscopy (SEM-EDX), X-ray fluorescence spectroscopy (XRF), and inductively coupled plasma mass spectrometry (ICP-MS), the petrological, mineralogical and geochemical characteristics were determined in Permo-Carboniferous Li-enriched coal and Jurassic coal in the southern margin of the Ordos Basin. The results show that Li concentrations in Permo-Carboniferous coal seams range from 16.2 μg/g to 521 μg/g. The maximum Li concentrations occur in parting samples of the Permo-Carboniferous coal seam and are as high as 1822 μg/g. The correlation coefficient of Li with other mineralogical and geochemical parameters shows that clay minerals are the main carriers of Li in coal seams. The discovery of high-temperature minerals (pyroclastic quartz and zircon) and vermicular kaolinite with good crystalline form provide direct evidence for the contribution of volcanic ash to coal. The enrichment of lithium in coal-measure strata is dominated by a Li-enriched source, sealing layer and enrichment place. Li originated from felsic volcanic ash, was captured by clay minerals, sealed in by the coal seam, and preferentially enriched in the coal seam parting. The coal seam itself can also cause some aluminosilicate minerals to be enriched in Li by ionic isomorphism.