Geological factors controlling variations in the mineralogical and elemental compositions of Late Permian coals from the Zhijin-Nayong Coalfield, western Guizhou, China

Determination of the geochemical and mineralogical characteristics of coal can provide useful information on the geological setting and evolution of coal basins and assist in identifying factors that control the distribution of the minerals and elements of interest. The Late Permian coals of southwestern China have received much attention because some of these coals are usually considered to be potential sources of some critical metals and have high concentrations of potentially toxic elements. Mineralogical and geochemical analyses were carried-out on the Late Permian coals from the Kulishu and Sijichun mines of the Zhijin-Nayong Coalfield, Western Guizhou, China. The diagram of Al₂O₃/TiO₂-Nb/Yb shows that the sediment source of the Kulishu and Sijichun coals is dominantly the Emeishan magmatic province with a smaller contribution from a Neoproterozoic metamorphic-granite complex, both of which are the two major components of the Kangdian Upland. The sediment source of the roof and floor rocks is dominantly basaltic volcanics in the Emeishan large igneous province (ELIP), while the partings were probably derived from eruptions of the Emeishan felsic-alkaline magmas and a mixture of ashes derived from a distal volcanic arc. Highly elevated total sulfur contents (dominated by pyritic and organic sulfur), abundant framboidal pyrite, as well as disseminated fine-grained pyrite provide evidence for input of seawater during the peat and coal formation. Paragonite mineralization with enrichment of Li, Nb (Ta), Zr (Hf), REY and Pb in the Sijichun coals and partings of the Kulishu coal are attributed to the intrusion of alkaline magma. The pyrite, quartz, albite, anatase and gypsum occurring as veins-, cleat-fillings and separate well-crystallized aggregates of epigenetic origin in the studied coals are indicative of the influence of hydrothermal fluids from a magmatic source.