Geochemistry Characteristics and Paleoenvironmental Significance of Trace Elements in Coal and Coal Gangue in the Yangcheng Mining Area, Qinshui Basin

The geochemical characteristics of trace elements in Carboniferous-Permian coal and gangue in the Yangcheng mining area in Qinshui Basin, a large Carboniferous-Permian coalfield in China, were studied by inductively coupled plasma mass spectrometry (ICP-MS), and their geological significance was discussed. The results show that the content of trace elements in late Paleozoic coal in the Yangcheng mining area is depleted, except for slight enrichment of Li. Except for Li, Co, and Mo, the content of trace elements in the gangue was higher than that in the coal. The content of rare earth elements in gangue (324.28 μg/g) is much higher than that in coal (66.22 μg/g). The rare earth elements (REY) content in the coal in the Shanxi Formation (93.88 μg/g) is slightly higher than that in the Taiyuan Formation (66.19 μg/g). The mean values of δEu and δCe are 0.71 and 0.94, respectively. Except for the YIC3-1 curve of the Shanxi Formation, which is obviously convex and shows a positive Eu anomaly, the REY distribution patterns of the remaining samples are similar, showing the characteristics of light rare earth elements (LREY) enrichment and heavy rare earth elements (HREY) depletion. The Carboniferous-Permian coal-forming environment in the Yangcheng mining area is in an anoxic-reducing, warm, humid, and brackish water sedimentary environment. The paleosalinity and paleotemperature of the Shanxi coal formation are higher than those of the Taiyuan Formation, which is more inclined to be a reducing environment. The provenance of Carboniferous-Permian coal in the Yangcheng mining area is mainly derived from acidic sedimentary rocks of the upper crust of the post-Archaean, mixed with a small amount of granite, alkaline basalt, and oceanic tholeiite. The tectonic setting of the provenance is mainly an active continental margin related to a continental island arc mixed with an oceanic island arc and a passive continental margin tectonic setting.