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(Hf)–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 δEu showed a well-pronounced negative anomaly and that of δCe 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, bastnäsite, 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 bastnäsite and xenotime; and rare-scattered elements (Ge, Se, Cd, In, and Te) are hosted in sulfide minerals (pyrite).

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Four coal samples from the Huoshaopu Mine and six coal samples from the Jinjia Mine, Liupanshui Coalfield, China were collected and analyzed, focusing on their petrological and organic geochemical features. The microscopic results show that the vitrinite random reflectance (R o ) of all samples is 0.97%, which is classified as high-volatile A bituminous coal. The maceral groups are dominated by vitrinite followed by inertinite. The low ratios (0.07-0.42) of saturated to aromatic hydrocarbons indicate a terrestrial plant input for the coals. Gas chromatography and gas chromatography/mass spectrometry were employed to analyze the composition of organic matter in the samples. The gas chromatography chromatograms of saturates display a monomodal outline of n-alkanes with a predominance of short chains. The odd-even preference values around 1 reflect the thermal maturity of the coals. Based on the different pristine/phytane ratios and dibenzofuran contents, we infer a relatively weak oxic coal-forming environment for Huoshaopu coals and a relatively anoxic environment for Jinjia coals. Among the aromatics, thermodynamically stable compounds, including 2-methylnaphthalene, 2,6 + 2,7-dimethylnaphthalenes, 3 and 4-methylbiphenyls, 4,4 0 -dimethylbiphenyl, methylphenanthrene, 2 and 3-methyldibenzofurans, were the dominant isomers in the respective homologs. The occurrence of dibenzothiophenes and benzonaphthothiophenes may confirm the paralic depositional environment of Late Permian coals from the Huoshaopu and Jinjia mines.

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Compositional characteristics of maceral and extractable organic matter (EOM) of the No. 10 coal from the Yueliangtian mine, Guizhou, Southwestern China, were analyzed by optical microscopy, gas chromatography (GC), and gas chromatography-mass spectrometry (GC-MS). The depositional conditions, thermodynamic effect, type and maturity of organic matter, and possible health hazards were evaluated. The random vitrinite reflectance (R o ) is 1.01%, and the macerals are dominated by collodetrinite, inertodetrinite, collotelinite, and fusinite. The coal seam is a terrestrial sedimentary environment of the lower delta plain through the analysis of coal facies. Additionally, the extracted yield of EOM is 1.01%. The low ratio of saturated to aromatic fraction and the distribution of n-alkanes indicate that the coal-forming plants are primarily terrestrial higher plants. Typical isoprenoid biomarker parameters, including pristane/phytane (Pr/ Ph), Pr/n-C 17 , and Ph/n-C 18 , reflect a weak oxidizing environment of coal. The hopanoid biomarkers, odd−even predominance index (OEP), and carbon preference index (CPI) reveal that the organic matter was mature. More than one hundred polycyclic aromatic compounds (PACs) were eluted and identified, and the phenanthrenes and naphthalenes account for a higher proportion. Thermodynamic stabilities play an essential role in the conversion of molecular structures, which support the relatively high contents of 2-methylnaphthalene, 2-and 3-methylphenanthrenes, and 2,6-and 2,7-dimethylphenanthrenes compared to their respective isomers. The oxygen-containing and sulfur-containing aromatic compounds also indicate the weak oxidization of the coal-formation environment, which is consistent with the results of isoprenoid biomarkers. Because of the carcinogenicity and mutagenicity of PACs, the distribution and toxic equivalency of PACs are briefly summarized.