Abstract

Igneous intrusions significantly modify the distribution and mobility of elements in coal. In order to explore the influence of igneous intrusions on the elements in coals, the No. 2-2 coal seam of the Shanxi Formation of Juji Coal Mine was selected as the research focus. The No. 2-2 coal was investigated using X-ray fluorescence spectrometry and a high-resolution inductively coupled plasma mass spectrometer. The results show that the volatile gases accompanying the igneous intrusion, together with CO2 generated by reaction between the intrusion and the coal seam, led to marginally higher MnO and MgO in the thermally altered coals compared to unaltered coal, and also promoted reprecipitation of carbonate and silicate minerals, which increased loss on ignition. The content of P2O5 initially rises with increasing distance from the intrusion, indicating that contact metamorphism can lead to a depletion of major elements in thermally altered coals. Meanwhile, the igneous intrusion caused reprecipitation of silicate minerals, but the high temperatures from the intrusion pyrolyzed some of these minerals, resulting in Li, Sb, and U contents that increase with distance from the intrusion. In contrast, Ge, Mo, Ba, Eu, and Pb, together with hydrothermal fluids, entered the thermally metamorphosed coal via fractures and migrated downward, gradually accumulating within it; their contents therefore decrease with increasing distance. Additionally, the intrusion and associated hydrothermal fluids also induced positive Eu, Gd, and Y anomalies and negative Ce anomalies in the thermally altered coals, whereas intermediate-felsic source rocks and oxidizing conditions produced negative Eu, positive Ce, and weakly negative Y anomalies in coals farther from the intrusion. Contact metamorphism results in a significant element depletion, exerting negative effects. Conversely, hydrothermal fluids and fluids from the host rocks promote the redistribution and enrichment of elements in coal, producing positive effects. Overall, the negative effects outweigh the positive ones.

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