Minerals and Enrichment of W, Rb, and Cs in Late Permian Coal from Meitian Mine, Meitian Coalfield, Southern China by Magmatic Hydrothermal Fluids

Abstract

We report on the effects of magmatic hydrothermal fluids on the mineralogical and geochemical compositions of 12U and 12L Coals from the Meitian Mine in the Meitian Coalfield, southern China. The minerals in 12U Coal are predominantly chlorite, quartz, and calcite, while the minerals in 12L Coal consist mainly of illite, quartz, chlorite, kaolinite, and mixed-layer illite/smectite (I/S). The vesicle- and fracture-filling illite, chlorite, I/S, pyrite, and fluorite, cleat- and fracture-filling carbonate minerals (i.e., calcite, and dolomite), and cleat-filling tremolite, diopside, and talc have epigenetic hydrothermal origins. Tremolite, diopside, and talc were probably formed from the reaction between dolomite and Si-rich magmatic hydrothermal fluids. Elevated Pb–Zn–Sn–Cd assemblages are characteristic for the 12U Coal, while 12L Coal is enriched in W, Rb, Cs, Th, V, Zn, and Zr, most notably W, Rb, and Cs. REY (Rare Earth Elements and Yttrium) plots for almost all coals, partings and host rocks are similar, showing an M-type REY distribution, Gd-maximum, positive Y anomalies, and negative Ce anomalies, suggesting acid hydrothermal circulation in the coal-bearing strata. Rubidium and cesium in the coal is clearly associated with K-rich clay minerals (illite + I/S), and to a lesser extent with silicate minerals that were precipitated from hydrothermal solutions. W in the coals mainly occurs in the inorganic constituents of illite and pyrite, especially illite. Enrichment of W, Rb, and Cs in the coal and host rocks is genetically associated with magmatic hydrothermal fluids. Specifically, magmatic hydrothermal fluids of relatively high temperatures that are rich in volatile matter can extract abundant W, Rb, and Cs from granitic melts. The enrichment of these rare metals in the coal is mainly related to illitization. Our study results suggest that, for coal intruded by magmatic rocks, the type of hydrothermal alteration may greatly influence the enrichment of elements.

Rare-Earth Element Phase Associations in Four West Virginia Coal Samples

“…Additional support for a fluid-based influence in the Fayette sample includes the relatively high W concentrations measured during pXRF, which range from undetectable to 99 ppm (Table 3). The published literature suggests that high W concentrations in coal are more likely to be supplied by aqueous solutions rather than by terrigenous sources [51][52][53]. Further, SEM-EDS revealed gold and platinum-group element mineralization in organic matter pore spaces and coal fractures, which could have been introduced by groundwater or hydrothermal fluids [54,55].…”

Distribution, modes of occurrence, and main factors influencing lead enrichment in Chinese coals

“…Epigenetic lead-rich minerals derived from hydrothermal fluids in coals include pyrite, ankerite, and clays. Hydrothermal pyrite, which can form during the early stages of coal formation and interact with basinal brines and hydrothermal fluids during burial, may be the main carrier of lead (Diehl et al 2012;Xiao et al 2018). Lead ion is reported to be transported into coal seams through hydrothermal fluids (Guo et al 1994).…”