Peat-accumulation models affected by the transgression-regression: a case study of mineralogy and geochemistry of the Permo-Carboniferous coals in the Lingshi Deposit, Qinshui Basin, China

Mineralogy and geochemistry of Nos.1, 9 and 10 coals in the Lingshi Deposit, Qinshui Basin, China, are investigated in this paper, using industrial analysis, total sulfur and forms of sulfur analyses, optical microscope, scanning electron microscope equipped with energy dispersive X-ray spectrometer, X-ray powder diffraction, X-ray fluorescence, and inductively coupled plasma-mass spectrometers. The results show that the minerals in coals are mainly kaolinite, nacrite, dickite, palygorskite, calcite, pyrite, anatase, dolomite, siderite and barite. Kaolinite of terrigenous origin is commonly discovered in No. 1 coal, which results in a high concentration of SiO2 (up to 6.81%) and Al2O3 (up to 8.42%); In the process of coalification, kaolinite could be converted into dickite and nacrite in Nos. 9 and 10 coal; Pyrite, the host of W, Tl, and As, and palygorskite in Nos. 9 and 10 coals are formed under the influence of the transgression. Besides, Nos. 9 and 10 coals, affected by transgression, are similar in the element contents and distribution patterns with positive delta Y-N anomalies (up to 1.44). However, No. 1 coal, normalized by No. 10 coal, is characterized by high concentration coefficients of Co, Ni, Sb, Li, Be, Sc, V, Cu, Ga, Rb, Cs, Ba, Pb and Th (2 < CC < 10), and these elements are derived from clay minerals of terrigenous origin, which means that Permo-Carboniferous coals in the Lingshi Deposit show the evolution of a regressive process in general.