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The lowermost Late Permian coal seam (C4 Coal) in the Tongzi Coalfield offers an opportunity to investigate the influence of terrigenous detrital materials from the Qianbei Upland on the mineralogical and geochemical patterns of the C4 Coal. The minerals are mainly dominated by pyrite and, to a lesser extent, tobelite, kaolinite, and calcite, along with traces of Al-oxyhydroxide minerals. The various degrees of marine influence may have resulted in the variation in the amount of Fe-sulfides (e.g., pyrite) and elements having Fe-sulfides affinity. Furthermore, the abundant Fe ions involved in the formation of Fe-sulfides were most likely derived from the claystone on the Qianbei Upland. The tobelite identified in the C4 Coal probably originated from the interaction between pre-existing kaolinite and NH4+ from NH3 released from the thermally affected organic matter at least shortly after the highly volatile bituminous stage under NH4+-rich and K+-poor conditions. The terrigenous detrital materials were derived from two possible sediment-region sources-the Qianbei Upland and Kangdian Upland-which is different from Late Permian coals in Western Guizhou Province. The claystone on the Qianbei Upland may have served as parent rock, as indicated by the presence of the Al-oxyhydroxide minerals as well as low SiO2/Al2O3 ratio (0.66 on average) and low quartz content. Meanwhile, the detrital materials from the Kangdian Upland most likely originated from the erosion of the felsic rocks at the uppermost part of the Kangdian Upland, as evidenced by the high Al2O3/TiO2 ratio (36.0 on average) and the strongly negative Eu anomaly (0.61 on average). [ABSTRACT FROM AUTHOR]

The abnormal enrichment of the REY (rare earth elements and yttrium)-Zr (Hf)-Nb (Ta) assemblage in Late Permian coals occurring in some coalfields in SW China has been extensively investigated, but the geological controlling factors of this assemblage are still under debate. This study reports on the mineralogical and geochemical features of coals and noncoal rocks collected from the Yudai and Jinqi coal mines within the Qiandongbei Coalfield in Guizhou Province to elucidate the geological controls on the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons. The studied coals show rather consistent clay mineral assemblage of kaolinite, together with varying amounts of quartz, gypsum, pyrite, and calcite. Notably, the coals are anomalously enriched in REY, Nb, Ta, Zr, and Hf and enriched in other incompatible elements (e.g., Ga, Th, and U). Phosphates (e.g., florencite) and, to a lesser extent, zircon are the primary carriers of REY. Zirconium and Hf are mainly incorporated into zircon and then anatase, the latter of which is a predominant carrier of Nb and Ta. The detrital materials originate from a mixture of the erupted felsic volcanic ash resembling a peralkaline rhyolite composition and the eroded materials of Emeishan Large Igneous Province (ELIP) basalts. The studied coals owe their highly enhanced concentrations of the REY-Zr (Hf)-Nb (Ta) assemblage to the input of felsic volcanic ash, wherein the highly acidic aqueous solutions allowed these elements to become mobile and be redistributed. Both geological processes governed the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons. The highly acidic solutions were possibly derived from the oxidation of peat bogs and volcanism-related acidic rain. The concentrations of REY, Zr, and Nb in the coal ashes exceed their corresponding cut-off grades; thus, these coals can be considered highly promising raw material sources for the REY-Zr (Hf)-Nb (Ta) assemblage. • The studied coals are significantly enriched in REY-Zr (Hf)-Nb (Ta) assemblage. • Detrital materials are derived from a mixture of felsic volcanic ash and eroded mafic materials. • The joint influence of highly acidic solutions and volcanism governs the REY-Zr (Hf)-Nb (Ta) enrichment horizons. • The volcanic ash erupted into peat bogs is geochemically similar to the peralkaline rhyolite. [ABSTRACT FROM AUTHOR]