Geochemistry of Trace Elements in Coals from the Yueliangtian Mine, Western Guizhou, China: Abundances, Modes of Occurrence, and Potential Industrial Utilization

This paper reports the geochemical compositions of coals and non-coal samples from a complete seam section in the Late Permian Longtan Formation from the Yueliangtian mine, western Guizhou, southwestern China. The abundances, modes of occurrence, and origin of elements and minerals in the Yueliangtian coal were investigated using optical microscopy, scanning electron microscopy with an energy dispersive X-ray spectrometer, X-ray powder diffraction, X-ray fluorescence spectrometry, and inductively coupled plasma mass spectrometry. The host rocks (roof and floor) and one parting sample of the coal seam have high TiO2 contents, which is in accordance with the high TiO2 content in the Emeishan basalt from the Kangdian Upland. The coal bench samples are rich in SiO2 (14.52%, whole-coal basis) compared with the average for the common Chinese coals, and the high SiO2 present in this study is consistent with the abundant quartz, which was mainly precipitated from siliceous solutions produced by weathering of the Emeishan basalt. Compared to the average values for world hard coals, the coal bench samples are enriched in V (77.0 μg/g), Cu (41.9 μg/g), Se (4.77 μg/g), Zr (93.8 μg/g), Hg (0.375 μg/g), and Pb (21.4 μg/g). In contrast to many other Permian coals from southwestern China, the transition elements, including Cr, Co, Ni, and Zn, are not enriched in the coal bench samples, possibly due to the input of the terrigenous materials with felsic and felsic-intermediate rock compositions. The highfield strength elements are relatively enriched not only in the parting samples but also in the adjacent coal bench samples, indicating that the partings were subjected to leaching by groundwater during the diagenetic process. Elements in coal, including B, Cr, Co, Zn, and Ni, are mainly associated with clay minerals, while As, Se, Sb, and Pb mainly occur in sulfide minerals (pyrite and marcasite). An intra-seam volcanic ash-derived tonstein layer identified in the coal is characterized by strong negative Eu anomaly in the Upper Continental Crust-normalized rare earth elements and Y distribution pattern, indicating the input of felsic or felsic-intermediate terrigenous materials.