Geochemistry of Carboniferous–Permian Coal from the Wujiawan Mine, Datong Coalfield, Northern China: Modes of Occurrence, Origin of Valuable Trace Elements, and Potential Industrial Utilization

Abstract

This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and pyrite, as well as trace amounts of quartz and illite. The No. 5 coal is enriched in Li, Ga, high field strength elements (HFSEs), and rare earth elements and yttrium (REY) when compared with world hard coals. Of particular interest is the high average concentration of Li (67.66 μg/g), which is around seven times higher than the value for world hard coals. Lithium, Ga, and HFSEs have strong inorganic affinities, whereas REY have organic affinities. The main carrier of Li, Ga, and HFSEs is aluminosilicate minerals, while REY appear to occur with organophosphorus. These HFSEs are enriched, both in the parting and in the adjacent coal samples. This suggests that these elements are likely to leach out during the diagenetic process. The distribution patterns of REY, along with the ratio of Al2O3/TiO2 and the figure of Zr/TiO2 vs. Nb/Y are suggestive of their derivation from felsic parent material. In the northern and eastern part of the Datong coalfield, there are several regions where the Li content is higher than the mineable grade, in particular in the northern Datong coalfield where there is a mine with an Li content of 294.6 μg/g. This is significantly higher than the mineable grade. Therefore, there is a potential for financially viable recovery of Li in these coals of the Datong coalfield.

The Kaolinite Crystallinity and Influence Factors of Coal-Measure Kaolinite Rock from Datong Coalfield, China

“…The petrogenesis of kaolinite rocks is affected by their detrital or volcanic sedimentary origins, as well as their biological interactions and organic matter that promote the formation of clay minerals [5,6,11,18]. The crystallinity of the so-called "purple gangue" kaolinite found at Datong increases from a poorly ordered material with low crystallinity to a well-ordered material with high crystallinity upon increasing interaction with high-temperature geothermal fluids [18][19][20].…”

“…Earlier mineralogical and geochemical characterization of the coal-measure kaolinite from Datong indicated an acid plutonic (granitic) or volcanic (rhyolitic) precursor [2][3][4]20], with potential provenance from the Yinshan uplift orogenic belt to the north of NCC (Figure 1), which features shallow surface water with a weak oxidation condition diagenetic environment, formed by protolith in situ leaching and alteration [21,22]. The mineral crystallinity of kaolinite is associated with its microstructure, whereby aphanitic kaolinite reveals a higher crystallization index than clastic granular and worm-like kaolinite [23].…”

“…The mineral crystallinity of kaolinite is associated with its microstructure, whereby aphanitic kaolinite reveals a higher crystallization index than clastic granular and worm-like kaolinite [23]. In addition to the primary sedimentary and secondary weathered eluvial, the Datong kaolinite diagenesis is related to organic acid leaching in epigenesis diagenesis, kaolinite recrystallization, crystallinity and other factors [2][3][4]20,22].…”

Geochemical characteristics and the significance of two major coal‐bearing strata claystones from the Datong Coalfield (North China)

“…The Datong Coalfield is located in Shanxi Province, in the northern part of the North China Craton (Figure 1). The study area covers an area of approximately 1900 km 2 and lies between latitude 112 30 0 to 113 10 0 N and longitude 39 35 0 to 40 15 0 E. The geological structure of the Datong Coalfield is simple (Ma et al, 2020;Yuan et al, 2011).…”

“…The study area covers an area of approximately 1900 km 2 and lies between latitude 112°30′ to 113°10′N and longitude 39°35′ to 40°15′E. The geological structure of the Datong Coalfield is simple (Ma et al, 2020; Yuan et al, 2011). In this area, some northeast‐ and southeast‐trending anticlines and synclines exist and mainly normal faults are developed (Figure 1).…”