Evidence for multiple sources for inorganic components in the Tucheng coal deposit, western Guizhou, China and the lack of critical-elements

Highlights

• The two coals in Tucheng deposit are not rich in Sc-V-Cr-Co-Ni-Cu-Zn-Se.

• Mineral matter in the coals were derived from volcanic arc and/or distal orogens.

• Mineral matter in the host rocks were supplied by the high-Ti Emeishan basalts.

• The two tonsteins originated from the final activity of the Emeishan plume.

• Critical elements in the samples are economically unpromising.

Abstract

Terrigenous materials from sediment-source regions are important controls on the types and concentrations of inorganic components in coal. The Kangdian Upland (dominated by the Emeishan basalts) is the dominant terrigenous supplier for most of the Late Permian coals, as well as for their associated host rocks (roof and floor strata) in southwestern China. The high volatile bituminous coals (Nos. 3 and 6 coals) are the two major minable coal seams in the Tucheng coal deposit in southwestern China. Unlike most Late Permian coals in this region that are characterized by elevated concentrations of the element assemblage Sc-V-Cr-Co-Ni-Cu-Zn-Se, these two coals are not enriched in this assemblage although Se is slightly concentrated.

The mineralogical (e.g., relatively abundant quartz and mixed-layer illite/smectite) and elemental distribution patterns (e.g., spider diagrams of rare earth elements, discrimination diagrams of Al₂O₃-TiO₂ and Zr/TiO₂-Nb/Y, and elemental assemblages) indicate that the inorganic components in the two coal seams were mainly derived from unidentified volcanic arc and/or distal orogens, while the clastic components in the roof and floor strata of the two coal seams were mainly supplied by the high-Ti Emeishan basalts. The two partings in the two coal seams, identified as tonsteins, were probably derived from the final (rejuvenated) activity of the Emeishan plume. Critical elements in the two coals and associated non-coal horizons (partings, roof and floor strata) are economically unpromising, indicating that prospecting for Late Permian coal-hosted critical metal ore deposits in the vicinity of the Emeishan plume in southwestern China, should not be focused on coals with inorganic components derived mostly from distal volcanic arcs and orogens and high-Ti Emeishan basalts, and a minor contribution of volcanic ashes resulting from the final rejuvenated activity of the Emeishan plume.