Geochemical characteristics of the Late Permian coals from the Yueliangtian Coalfield, western Guizhou, southwestern China

Abstract

This paper investigated geochemical characteristics of the Late Permian No. 6 upper (YLT6U) and No. 6 lower (YLT6L) coals from the Yueliangtian Coalfield, Guizhou, southwestern (SW) China, using x-ray fluorescence spectrometry, inductively coupled plasma mass spectrometry, field emission-scanning electron microscopy plus an energy-dispersive x-ray spectrometry, and optical microscopy. The YLT6U coal is slightly enriched in Se and W. The YLT6L coal is enriched in elements Hg, As, Tl, Co, Cu, Se, Mo, and Cd. Different with other Late Permian coals from SW China, the Yueliangtian coals are depleted in Sc, V, Cr, Ni, and Zn. The enrichment patterns of rare earth elements and yttrium (REY, or REE if Y is not included) in the benches of the Yueliangtian coal are characterized by heavy-REY enrichment and, to a lesser extent, light- and medium-enrichment types. Germanium in the YLT6U coal is mainly organic-associated and relatively enriched in the middle portion of the coal seam. It is due to Ge adsorption by organic matter during the input of Ge-rich solution into peat swamp of the YLT6U coal. Boron in the Yueliangtian coal mainly occurs in clay minerals and is derived from terrigenous materials rather than marine influence. Owing to the parting leaching by circulated hydrothermal solutions, the Nb/Ta, U/Th, Yb/La, and Zr/Hf ratios are higher in the coal benches relative to their corresponding overlying partings. The parent rocks of the sediment-source region for the Yueliangtian coal are not only the mafic basalts but also the felsic-intermediate rocks in the upper portion of the Kangdian Upland.