The differences of element geochemical characteristics of the main coal seams in the Ningdong coalfield, Ordos Basin

In this study, we investigate the vertical variation of the geochemical characteristics of the Jurassic coal in the Ningdong coalfield, Ordos Basin. The major and trace element compositions (including rare earth elements) of three of the main coal seams were determined using optical microscopy, X-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, and scanning electron microscopy with energy dispersive X-ray. The results indicate that the three coal seams have similar properties with low-ash yields (ash yield < 10%) and low-sulfur contents (total sulfur < 1%), and the maceral composition of the three coal seams is generally dominated by inertinite (> 50% on average). The geochemical characteristics of the three coal seams vary. Mn is enriched in the three coal seams, but their degrees of enrichment differ. The degree of Sr and Ba enrichment gradually increases from coal 18 (85 mu g/g for Sr and 80 mu g/g for Ba) to coal 6 (230 mu g/g for Sr and 421 mu g/g for Ba) and then to coal 4-2 (1667.06 mu g/g for Sr and 741.69 mu g/g for Ba). In addition, the Sr and Ba occurrence of the three coals differs. The REE contents and distribution patterns of the three seams reflects a stable source supply during sedimentation. The variation in the sedimentary environment of the coal seams is the main factor controlling the differences in their geochemical characteristics.