Distribution of Trace Elements in Kaolinite from Li-Rich Coal, Mudstone, and Tonstein Revealed by LA-ICP-MS

Kaolinite is a common clay mineral in coal and can host various trace elements, including Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Ga, Rb, Cs, Sr, Ba, Zr, Hf, Nb, Ta, Bi, and Th. However, the distribution and potential association of these elements in kaolinite remain uncertain because previous studies mainly relied on indirect methods. This study integrates optical microscopy, SEM–EDS, and LA–ICP–MS to characterize trace-element distributions in different kaolinite-bearing domains (kaolinite types) from Carboniferous Li-rich coal, tonstein, and terrigenous mudstone of the Haerwusu Mine, Jungar Coalfield, Ordos Basin. Because an LA–ICP–MS spot may intersect associated mineral phases, the measured compositions are referred to as kaolinite-bearing domains rather than pure end-member kaolinite. Six domain types were analyzed: relatively pure detrital, K-bearing altered, Na-bearing altered, Al-rich altered, vermicular, and cryptocrystalline kaolinite-bearing domains. Li generally decreases in the order: K-bearing altered domain > cryptocrystalline domain in high-Sr/Ba-ratio tonstein > vermicular domain in high-Sr/Ba-ratio tonstein > Na-bearing altered domain > Al-rich altered domain > vermicular domain in low-Sr/Ba-ratio tonstein > cryptocrystalline domain in low-Sr/Ba-ratio tonstein. Ga is highest in Al-rich altered domains and shows a positive relationship with Al, followed by detrital domains. Nb and Ta are relatively enriched in Ti-rich vermicular domains in tonstein and co-vary with Ti, probably reflecting contributions from associated Ti-bearing phases such as anatase or rutile. Alkali and alkaline-earth elements (Li, Rb, Sr, Cs, and Ba) are relatively enriched in K-bearing altered domains and in domains from high-Sr/Ba-ratio, B-rich samples. These results reveal domain-scale heterogeneity in trace-element distributions and provide a useful reference for in situ characterization of clay minerals and silicate phases.