Abstract
This work investigated the mineralogy and geochemistry of the No. 3 coal seam in Permian Shanxi Formation in Guotun Mine, Juye Coalfield, north China, in order to understand the genesis of the minerals and the enrichment of trace elements. Approaches used were optical microscopy and electron probe microanalysis for minerals, X-ray fluorescence analysis for major elements and inductively coupled plasma mass spectrometry analysis for trace elements. The coal is comprised of dominant kaolinite and calcite, the claystone is characteristic of major kaolinite, montmorillonite, and proportional illite, and the sandstone contains mainly quartz and chalcedony, and a relative amount of feldspar and kaolinite. These minerals were derived dominantly from the weathered source rocks with volcanic and granitic constituents in the pre-diagenetic period, and minor from the hydrothermal deposit in the epigenetic period. The claystone is relatively enriched in Li, Cs, Be, Nb, Mo, U, Th, V, In, Pb, Bi, and Se, which may probably be controlled by the source rocks and the specific sedimentary environment. The enriched trace elements are mostly associated with minerals. Li may probably occur in montmorillonite and illite, while In, Pb, Bi, and Se occur mainly in selenio-galena.
Highlights
The coal is comprised of dominant kaolinite and calcite; the claystone is characteristic of major kaolinite and montmorillonite, and proportional illite; and the sandstone contains mainly quartz and chalcedony and relative feldspar and kaolinite (Figure 2)
The source region of the Shanxi Formation is the orogenic belt at the northern margin of the North China Craton (Zhu and Mou, 1987) because the orogenic belt uplifting in the Early-Middle Devonian Epochs has made the terrain of the craton high in the north and low in the south (Figure 1) during the Carboniferous and Permian
The inheriting minerals derived from the source rocks with volcanic and granitic rocks and their weathering products are the major genesis of the minerals in the studied coal seam
Summary
The valuable elements in coal seams, such as Li, Ga, Ge, REEs, etc., have been a hot point in the field of coal geology recently for their high concentrations and utilization (Dai et al, 2014; Seredin and Finkelman, 2008; Sun et al, 2012, 2013; Zhao et al, 2017; Zhuang et al, 2006). Dai et al (2014) reviewed the geological origin, modes of occurrence, and evaluation methods of the coal-hosted rare metal deposits including Ge, Ga, U, Nb, and rare earth elements; Sun et al (2012, 2013) discovered Li deposits in the coal seams in the Inner Mongolia Autonomous Region and Shanxi Province in north China. Dai et al (2014) reviewed the geological origin, modes of occurrence, and evaluation methods of the coal-hosted rare metal deposits including Ge, Ga, U, Nb, and rare earth elements; Sun et al (2012, 2013) discovered Li deposits in the coal seams in the Inner Mongolia Autonomous Region and Shanxi Province in north China. Mineralogical and geochemical study is the key to clarify the distribution, origin, modes of occurrence, and evaluation of valuable elements in coal seam (Dai et al, 2012; Singh and Singh, 1995; Sun et al, 2010, 2012, 2013; Ward, 2002; Zhao et al, 2017). Though there is an amount of coalfield in north China, the coal seams studied in detail on mineralogy and geochemistry are still a few
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