Geochemical Characteristics of Rare-Metal, Rare-Scattered, and Rare-Earth Elements and Minerals in the Late Permian Coals from the Moxinpo Mine, Chongqing, China

The rare-metal, rare-scattered (dispersed), and rare-earth elements (TREs) and minerals of the K2 coal from the Moxinpo mine, Chongqing, were analyzed using inductively coupled plasma mass spectrometry and scanning electron microscopy (SEM) with energy-dispersive X-ray spectrometry, respectively. In addition, three-fold geochemical classification of TREs (Li-Be-Rb(Cs)-Sr-Ge-Se-Tl, Zr(HO-Nb(Ta)-Ga(In)-Te-Re-Cd, and REY-Sc) was used to determine the vertical distribution. Compared to world bituminous coals, the K2 coal is enriched in Li, Be, Zr, Nb, Hf, Ta, Ga, Se, Cd, In, Te, Re, Sc, and REY elements (except Eu and Tm), especially in Zr, Nb, Ta, Se, Re, and Sc (>5 times). Compared with the upper continental crust, the K2 coal is enriched with REY, and the fractionation of individual light-REY is higher than that of heavy-REY except for few cases. The value of delta Eu showed a well-pronounced negative anomaly and that of delta Ce showed a slightly negative anomaly, which indicate that the K2 coal-seam was intermittently affected by seawater. Minerals in the K2 coal are mainly represented by kaolinite, pyrite, and quartz, while rutile, bastnasite, and xenotime were observed under SEM. The migration, enrichment, and occurrence of TREs in coal are determined by many factors, such as terrigenous rocks, coal-forming microfacies, and paleo vegetation. The correlation analysis showed that rare-metal and rare-earth elements in K2 coal mainly occur in aluminosilicate minerals due to their high correlation coefficients with SiO2 and Al2O3; traces of rare-earth elements mainly occur in bastnasite and xenotime; and rare-scattered elements (Ge, Se, Cd, In, and Te) are hosted in sulfide minerals (pyrite).