Controlling factors on enrichment of critical element cesium in Paleogene coals from the Baise Basin

Under specific geological conditions, strategic metal elements can be enriched in coal and subsequently form strategic metal ore deposits in coal-bearing strata. The research of strategic metal elements in coal-bearing strata is the main direction and frontier issue of coal geology. The input of terrigenous materials is one of the main factors affecting the enrichment of strategic metal elements in coal. X-ray diffraction analyzer (XRD), Scanning Electron Microscope equipped with an energy-dispersive X-ray spectrometer (SEM-EDS), Inductively Coupled Plasma Mass Spectrometer (ICP-MS), X-ray fluorescence spectrometry (XRF) and other instruments were used to analyze the composition of minerals and elements in the Palaeogene coal from the Baise Basin, Guangxi Province. The influence of sediment-source region on enrichment of critical element cesium in Paleogene coals from the Baise Basin is discussed based on the study of mineralogy and element geochemistry of these coal seams from under Baigang section of Nadu Formation in the Baise Basin. The minerals in Paleogene coal in the Baise Basin are mainly illite, kaolinite and quartz, which mainly come from the weathering products of Triassic clastic rocks around the basin; the percentage of clay minerals in western part of the Baise basin is higher than eastern part. Carbonate mineral calcite was detected only in Zhoujing No.4 coal seam and No.5 coal seam in the eastern part of the Baise Basin. Compared with the average values for world low-rank coals, rubidium (Rb), antimony (Sb) and cesium (Cs) are enriched in the Palaeogene coal from the Baise Basin; The coal seams in the western part of Baise basin are enriched in elements Rb and CS, while the coal seams in the eastern part of the Baise Basin are enriched in elements Sb, Cs and U. The enrichment of Cs in the current study occurs not only in coal but also in the non-coal samples, and the content of Cs in the non-coal is higher than that in coal. The correlation analysis show that Cs is predominantly associated with clay minerals, which were most likely derived from the terrigenous source region surrounding Baise basin, indicating that sedimentary source rocks are potential source of anomalous Cs. The mineral composition and enrichment characteristics of trace elements in different coal seams in Baise basin are different, which may be related to the difference sedimentary sources and sedimentary environment. © 2022, Editorial Office of Journal of China Coal Society. All right reserved.