Geochemistry of Late Permian coals from the Yueliangtian coal deposit, Guizhou: Evidence of sediment source and evaluation on critical elements

Abstract

The enrichment of rare, scattered, rare earth, and noble elements, such as Li, Ga, Ge, rare earth elements and yttrium (REY), platinum group elements (PGE), Au, and Ag, have been discovered in the Late Permian coals from southwestern China. With the gradual depletion of traditional ore deposits, the geochemistry and resource utilization of critical metals in coals have received considerable attention. The geochemistry of associated elements in the Late Permian coals from the No. 10 coal profile of the Yueliangtian (YLT) underground mine, Liupanshui coalfield in Guizhou, were investigated to reveal the sediment source of inorganic components, as well as utilization prospects and controlling factors of critical metals. Silver and Pb were slightly enriched in the Yueliangtian coals, while Be, Rb, Sr, Mo, Cs, Ba, Tl, Bi, and U were significantly lower than that of world hard coals. The concentrations of total REY and individual elements in the Yueliangtian coals were similar to those of world hard coals. The minerals kaolinite, pyrite, calcite, and quartz predominated in coals, with trace amounts of anatase, gypsum, and apatite. High anatase proportion was identified in the floor and roof rock samples. Based on the Al₂O₃/TiO₂ and Zr/TiO₂ versus Nb/Y ratios, elemental assemblages, REY distribution, and paleogeography, the sediment source of mineral matter in the Yueliangtian coals dominated by felsic-intermediate rocks that from a distal volcanic arc or orogens was inferred. The terrigenous debris in the roof and floor rocks primarily originated from the high-Ti basalt of the Emeishan Large Igneous Province (ELIP). The relatively low elemental concentrations in these coals were primarily determined by their sediment sources. Although most critical metals in this coal were not enriched, the concentration of REY in coal ash was high enough to be considered as a potential resource for REY recovery given the extremely low ash yields of this coal.

Keywords: Coal; Critical metal elements; Geochemistry; Minerals; Sediment source; Southwestern China.