Factors controlling geochemical and mineralogical compositions of coals preserved within marine carbonate successions: A case study from the Heshan Coalfield, southern China

• Published in: International journal of coal geology Vol. 109-110; pp. 77 - 100
• Main Authors: Dai, Shifeng, Zhang, Weiguo, Seredin, Vladimir V., Ward, Colin R., Hower, James C., Song, Weijiao, Wang, Xibo, Li, Xiao, Zhao, Lixin, Kang, Huan, Zheng, Licai, Wang, Peipei, Zhou, Dao
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2013
• Subjects: Heshan of southern China; Hydrothermal fluids; Late Permian coal; Minerals in coal; Trace elements in coal; Hydrothermal fluids; Heshan of southern China; Trace elements in coal; Minerals in coal; Late Permian coal
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2013.02.003

The Late Permian coals in the Heshan Coalfield of southern China are preserved within marine carbonate successions and characterized by super-high organic sulfur (5.13–10.82%). Minerals identified in the coals include quartz, kaolinite, illite, mixed layer illite/smectite, albite, pyrite, marcasite, calcite, and dolomite, along with trace amounts of smectite, fluorite, strontianite, REY-bearing carbonate minerals, jarosite, and water-bearing Fe-oxysulfate. The coals are very rich in trace elements including F (up to 3362μg/g), V (up to 270μg/g), Se (up to 24.4μg/g), Mo (up to 142μg/g), U (up to 111μg/g), and, to a lesser extent, Sr, Y, Zr, Nb, Cd, Cs, heavy rare earth elements, Hf, Ta, W, Hg, and Th. Previous studies attributed the high organic sulfur and elevated trace elements to the seawater influence or the formation of soil horizons before the accumulation of peat in the basin. However, mineralogical and geochemical data presented in this study have shown that the sediment-source region and multi-stage hydrothermal fluids are the dominant influences on the mineralogical composition and elevated trace elements in the coal, although seawater influence also contributed to the composition of the mineral matter. For example, a large proportion of the quartz and clay minerals, as well as almost all the albite, in both the coal benches and the parting mudstones were derived from detrital materials of terrigenous origin in the Yunkai Upland. High concentrations of lithophile trace elements were also derived from the sediment source region. Minerals including fluorite, calcite, dolomite, strontianite, and REY-bearing carbonate minerals were derived from multi-stage hydrothermal activities. High concentrations of V, Mo, and U that occur through the coal seam sections were probably derived from hydrothermal solutions during peat accumulation or at the early diagenetic stages. The hydrothermal fluids also corroded the syngenetically-formed minerals (quartz, albite, and pyrite) and caused re-distribution of lithophile elements from partings to the underlying coal benches, resulting in higher key element ratios (Yb/La, Nb/Ta, and Zr/Hf) and more abundant heavy rare earth elements in the coal benches than in the immediately overlying partings. ► The super-high organic sulfur coals were preserved in marine carbonate successions. ► Quartz, albite and clay minerals were mainly derived from sediment-source region. ► Fluorite and carbonate minerals were derived from hydrothermal activities. ► The elevated organic S, V, Mo, and U were mainly from hydrothermal solutions. ► Hydrothermal solutions corroded the early-formed quartz, albite, and pyrite.