Enrichment of Li–Ga–Zr–Hf and Se–Mo–Cr–V–As–Pb Assemblages in the No. 11 Superhigh Organic Sulfur Coal from the Sangshuping Coal Mine, Weibei Coalfield, Shaanxi, North China

Abstract

Superhigh organic sulfur(SHOS) coals have currently attracted great attention due to their typical depositional environments and formation history as well as their great negative impact on the ecosystem. This study investigated the geochemistry of the No. 11coalof the Late Carboniferous Taiyuan Formation from the Sangshuping coalmine, Hancheng miningarea, Weibei coalfield, Shaanxi, North China. The No. 11 coal is a high-sulfur coal with a large proportion of organic sulfur content (3.7 to 5.5%, avg. 4.4%) and belongs to typical SHOS coal. The high sulfur content in the Sangshuping coal mine has been mainly caused by the combined influences of seawater and hydrothermal fluids. The SHOS in No. 11 coal was formed in the Fe-poor and S-rich high-marine influenced occlusive environment. During the late coalification stage, a high proportion of pyritic sulfur was formed due to sufficient Fe supply from the Fe–S-rich epigenetic hydrothermal fluids. The No. 11 SHOS coal is enriched in Li–Ga–Zr–Hf and Se–Mo–Cr–V–As–Pb element assemblages. The sediment provenance of the Sangshuping coal mine is predominantly felsic–intermediate rocks from both the Yinshan and Qinling Oldland. However, the elevated concentrations of critical elements (Li, Ga, Zr, and Hf) in the No. 11 coal are primarily inherited from the Yinshan Oldland. The enrichment of the Se–Mo–Cr–V–As–Pb assemblage in No. 11 coal can be ascribed to the influence of both seawater and epigenetic hydrothermal activity.

Geological Controls on Mineralogical Characteristic Differences of Coals from the Main Coal Fields in Shaanxi, North China

“…21.3-35.2%, on an ash basis), with minor and different proportions of quartz, tobelite, dolomite, pyrite, siderite, ankerite, and anatase in different coal mines (Table 2). Furthermore, svanbergite, chalcopyrite, galenite, and apatite, although below the detection limit of XRD analysis, were also identified in these coals by SEM-EDS analysis, as accessory phases [6,55].…”

“…1.8-4.6%), belonging to medium-to high-sulfur coal [52]. The analyzed coal samples from the Sangshuping coal mine of the Weibei coal field are typical superhigh-organic-sulfur (SHOS) coals, with a high proportion of organic sulfur content [6]. The early Permian coal seams in the Shanxi Formation from both the Weibei and Shanbei C-P coalfields are classified as low-sulfur coals.…”

“…Tobelite is ubiquitously present in coals from the Weibei C-P coal field [6,55]. As previously mentioned, tobelite is a high-temperature hydrothermal indicator, usually occurring in high-rank coals, and has also been found present in several Permo-Carboniferous coals in China [60][61][62].…”

“…According to the geological age and the geographic distribution, there are dominantly five important coalfields in Shaanxi Province, comprising two Permo-Carboniferous (Weibei and Shanbei), one Triassic (Shanbei), and two Jurassic (Huanglong and Shanbei) coalfields (Figure 1). Due to the different tectonic evolution stages and deposition conditions, mineralogical and geochemical characteristics of coals vary remarkably among these coal fields [2][3][4][5][6][7]. The composition, abundance, distribution, and modes of occurrence of minerals in coals may provide significant geologic information on coal depositional conditions, coalbearing sequence formation, regional geological history, and associated diagenetic and epigenetic processes affecting coal formation [8][9][10][11][12][13][14][15][16][17][18][19].…”

“…Several studies have been conducted on the elemental and mineralogical characteristics of coal seams in the Ordos Basin, with special emphasis on the geochemical characteristics of hazardous elements (S, As, Hg, and Se) [2,3,[29][30][31][32], and potential critical elements (Ga, Li, Ge, Nb, Zr, and REY) in coals from several coal basins in the Ordos Basin [4,6,7,[33][34][35][36][37]. However, as important carriers of critical elements, the geological controls on distribution, occurrence, and origin of minerals in coal are still not clear.…”