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

: 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 su ﬃ cient 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.


Introduction
The Weibei Carboniferous-Permian coalfield is a very important coal resource base in Shaanxi, North China [1]. Several researchers have studied the mineralogical and geochemical characteristics of the Weibei coal, and several critical metals, including Ga, Li, Nb, and Zr, have been found enriched in the Weibei coalfield, making Weibei coal a potential source for recovery of critical metals. Wang

Sampling and Analytical Methods
Thirteen bench samples were systematically taken along the underground coal faces of the No. 11 coal seam(the Taiyuan Formation) in the Sangshuping coalmine, Hancheng mining district, following the Chinese Standard Method GB482-2008 [32], including one roof sample (numbered as SSP11-R), one floor sample (SSP11-F), two parting samples(SSP11-P1 and SSP11-P2, respectively), and nine coal bench samples (SSP11-1 to SSP11-9 from top to bottom, Figure 2C). In order to fully elaborate the characteristics and possible genesis of the No. 11 SHOS coals through a comparative study,12 samples were simultaneously taken from the No.3 coal seam (the Shanxi Formation), including one roof sample (SSP3-R) and 11 coal bench samples (SSP3-1 to SSP3-11 from top to bottom, Figure 2B). The lower portion and floor of the No. 3 coal seam were not accessed for safety reasons. All the samples were crushed and milled to 1 mm for vitrinite reflectance determination and were continuously milled until they were passed through an 80-mesh sieve and a 200-mesh sieve for proximate analysis and geochemical and mineralogical analyses, respectively. To determine the moisture content, high-temperature ash (HTA) yield, and volatile matter yield, proximate analysis was performed following the ASTM Standards D3173-11 (2011), D3174-12 (2018), and D3175-18 (2018), respectively [33][34][35]. The contents of total sulfur and forms of sulfur were analyzed following the ASTM Standards D4239-18a (2018) and D2492-02 (2012), respectively [36,37]. Vitrinite reflectance was measured according to the ASTM Standard D2798-20 (2020) [38].

Sampling and Analytical Methods
Thirteen bench samples were systematically taken along the underground coal faces of the No. 11 coal seam(the Taiyuan Formation) in the Sangshuping coalmine, Hancheng mining district, following the Chinese Standard Method GB482-2008 [32], including one roof sample (numbered as SSP11-R), one floor sample (SSP11-F), two parting samples(SSP11-P1 and SSP11-P2, respectively), and nine coal bench samples (SSP11-1 to SSP11-9 from top to bottom, Figure 2C). In order to fully elaborate the characteristics and possible genesis of the No. 11 SHOS coals through a comparative study,12 samples were simultaneously taken from the No.3 coal seam (the Shanxi Formation), including one roof sample (SSP3-R) and 11 coal bench samples (SSP3-1 to SSP3-11 from top to bottom, Figure 2B). The lower portion and floor of the No. 3 coal seam were not accessed for safety reasons. All the samples were crushed and milled to 1 mm for vitrinite reflectance determination and were continuously milled until they were passed through an 80-mesh sieve and a 200-mesh sieve for proximate analysis and geochemical and mineralogical analyses, respectively.
To identify the mineral phases in the studied bulk coals and noncoal rocks, mineralogical analysis was conducted using powder X-ray diffraction (XRD) with a Bruker D8 A25diffractometer and monochromatic Cu Kα radiation at 2 theta range of 4-60 • , step size of 0.19 • , and counting time of 0.1 s/step. An internal reference method was used to semiquantify the mineral contents [39]. The morphology and modes of occurrence of minerals were observed by a field emission scanning electron microscope (FE-SEM) coupled with an energy dispersive X-ray spectrometer (EDX).
Prior to determination of major and trace element concentration, samples were acid-digested according to a two-step digestion method (firstly with HNO 3 and secondly with HF-HNO3-HClO4 mixture). This was fully described by Querol et al. (1997) and proposed to keep any volatile elements of the bulk samples in solution [40]. Subsequently, the resulting solutions were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) for major and trace element concentrations, respectively. Blank samples and South African coal reference material (SARM-19) were analyzed following the same procedure to subtract blanks and check the analytical precision.

Coal Characteristics
The No. 11 and No. 3 coal were both characterized by low moisture contents (avg. 1.0 and 1.2%, respectively, air dry basis), low to medium HTA yield (avg. 14.8 and 12.1%, respectively, dry basis), and low volatile matter yields (avg. 16.3 and 16.2%, respectively, dry and ash-free basis, Supplementary  Table S1). Furthermore, the vitrinite reflectance of No.11 and No.3 coal samples were 1.5 and 1.4% on average, respectively (Table S1), indicating that both11 and No.3 coal are within the rank of low-volatile bituminous [41]. The relatively higher HTA yields of No. 11 coals (avg. 14.8% db) than No. 3 coals (avg.12.1% db) indicate higher terrigenous detrital supply during the formation of No. 11 coal with respect to No. 3 coal.
In comparison, SiO 2 (avg. 24 [43]. Except for CaO, the proportion of the other major element oxides were generally higher in the roofs/floors/partings than in bothNo.11and No.3 coals, which can be attributed to higher mineral content in the roofs/floors/partings than in the coal seams (Table S4) and is indicative of higher detrital input during formation of noncoal rocks. It is worth nothing that the values of SiO 2 /Al 2 O 3 (1.1and 1.0 for No. 11 and No. 3 coals, respectively) were lower than both the average for Chinese coals (1.42) and the theoretical value of kaolinite (1.18), which may be due to extremely low quartz content in the coals (Table S4).
Apart from Li, concentrations of most other trace elements were also significantly higher in the roof of No. 3 coal compared to the No. 3coal seam ( Figure 5). Vertical variation of Li, Ga, Zr, Nb, and LREY in the No. 3 coal was also similar to that of kaolinite, while elevated Pb had similar variation to S and Fe ( Figure 5). Note that the high arsenic contents in the roof of the No. 11 coal (CC of 4.9) and the floor of the No. 3 coal (CC of 3.3) may pose a serious threat to the ecosystem, which should arouse attention.
The average concentration of rare earth elements and yttrium (REY) were81 and 93 µg/g in No. 11 and No. 3 coal, respectively, which is higher than the average for world hard coals (68.6 µg/g) [44] but lower than that for common Chinese coals (136 µg/g) [42]. Considering the closer nature of coal to the upper continental crust (UCC), the REY concentrations in the coal were normalized to values for the UCC in the present research [45,46]. The UCC-normalized REY enrichment pattern of the No. 11 and No. 3 coals were predominantly the MREY type [47] (Figure 6), while those of the roof/parting/floor of the No. 11 and No. 3 coal seams were characterized by the LREY type ( Figure 6).     The average concentration of rare earth elements and yttrium (REY) were81 and 93 μg/g in No. 11 and No. 3 coal, respectively, which is higher than the average for world hard coals (68.6 μg/g) [44] but lower than that for common Chinese coals (136 μg/g) [42]. Considering the closer nature of coal to the upper continental crust (UCC), the REY concentrations in the coal were normalized to values for the UCC in the present research [45,46]. The UCC-normalized REY enrichment pattern of the No. 11 and No. 3 coals were predominantly the MREY type [47] (Figure 6), while those of the roof/parting/floor of the No. 11 and No. 3 coal seams were characterized by the LREY type ( Figure  6).

Modes of Occurrence of Elements
The following different modes of occurrence of elements in the studied coals were identified based on statistical analysis through Pearson's correlations.

Aluminosilicate Affinities
As illustrated in Figures 7 and 8, the elevated elements (Li-Ga-Zr-Hf assemblage) and several other trace elements, including Be, B, Sc, Cu, Nb, Ta, W, Bi, Th, and LREY, in the No. 11 coal as well as elevated Li and V, Cr, As, Ga, Zr, Nb, Ta, Hf, Th, U, and LREY in the No. 3 coal were all highly correlated with HTA yield (r = 0.67-0.94) and Al2O3content (r = 0.64-0.97) on a whole-coal basis, representing dominant aluminosilicate affinities. Furthermore, as aforementioned, the concentrations of these elements showed similar vertical distribution to kaolinite (Figures 4 and 5), indicating their possible occurrence in aluminosilicate minerals in the studied coals.

Modes of Occurrence of Elements
The following different modes of occurrence of elements in the studied coals were identified based on statistical analysis through Pearson's correlations.

Aluminosilicate Affinities
As illustrated in Figures 7 and 8

Sulfide Affinities
Unlike V, Cr, and As in the No. 3 coal, which had an aluminosilicate affinity, elevated V, Cr, and As as well as Co, Rb, Sr, Cs, Ba, Tl, and Pb in the No. 11 coals were remarkably correlated with

Sulfide Affinities
Unlike V, Cr, and As in the No. 3 coal, which had an aluminosilicate affinity, elevated V, Cr, and As as well as Co, Rb, Sr, Cs, Ba, Tl, and Pb in the No. 11 coals were remarkably correlated with total sulfur (r = 0.72-0.92), pyritic sulfur (r = 0.76-0.99), and iron (r = 0.76-0.98) content (Figures 7  and 8). Furthermore, each of these elements presented higher correlation coefficients with pyritic sulfur than total sulfur, suggesting that these elements primarily occur with sulfide (e.g., pyrite) in the studied coals.

Carbonate Affinities
Manganese in the studied coals was obviously correlated with Fe (r = 0.41-0.79) and Ca (r = 0.70-0.81), indicating a major carbonate affinity (Figures 7 and 8). The carbonate affinity of Mn is common in coals and has been found in several other coals [50][51][52][53].

Sediment Provenance
A number of studies have been conducted to investigate the sediment source for strata of North China block and the Ordos basin [54][55][56][57].
In the current research, Al2O3/TiO2 ratios of the No.    However, compositions of the source and structural setting of provenance in the north and south are different, which is in accordance with the varying trend from oceanic island arc to passive continental margin. The north provenance is mainly derived from plate subduction zones and is related to the tectonic setting of active and passive continental margin until Middle-Late Paleozoic. The source for the northern basin has affinities to Archeozoic and Proterozoic metamorphotic rocks, such as granitic gneiss, diorite gneiss, adamellite, metamorphotic litharenite, and phyllite [56]. According to the China National Administration of Coal Geology (CNACG; 1997), the sediment However, compositions of the source and structural setting of provenance in the north and south are different, which is in accordance with the varying trend from oceanic island arc to passive continental margin. The north provenance is mainly derived from plate subduction zones and is related to the tectonic setting of active and passive continental margin until Middle-Late Paleozoic. The source for the northern basin has affinities to Archeozoic and Proterozoic metamorphotic rocks, such as granitic gneiss, diorite gneiss, adamellite, metamorphotic litharenite, and phyllite [56]. According to the China National Administration of Coal Geology (CNACG; 1997), the sediment source for the North China block is mainly from the Yinshan Oldland during the Late Paleozoic (Figure 1) [64]. However, the Weibei coalfieldis situated on the southwestern edge of North China, where the sediment source for the Late Paleozoic strata is controversial. The source for the southern basin has been deeply affected by passive continental margin, and its chemical composition is consistent with those of metamorphic rocks and granites of the Archean-Proterozoic Taihua Group, Qinlin Group, and Kuanping Group, with high SiO 2 and K 2 O/Na 2 O > 1 [56,65]. It is supposed that during the Late Paleozoic, the sediment source for the southcentral part of the North China block and the Ordos basin was controlled by detrital supplies from both the Yinshan tectonic belt to the north and the Central China Orogenic Belt (including Qinling, Dabie, Qilian, and Kunlun Mountain Ranges) to the south [66,67]. Nonetheless, it is still debatable when the provenance in the south started to supply detrital sediments to the Ordos basin. The northern margin where terrigenous input from the southern provenance terminated is also in question [55,57,68].
The provenance from the Yinshan Oldland has the characteristics of abundant feldspar and mica but few quartz contents, which is markedly different from the abundant quartz and lithoclast contents of the Qinling Oldland [65]. With respect to the REY distribution, the sediment source from the North Qinling Orogenic Belt does not present obvious differentiation [55,69,70] or a weak LREY enrichment in the Qilian-Qinling Oldland [65], while that from the Yinshan Oldland is characterized by a distinct light rare earth element (LREE) enrichment [71]. The studied coals did not show distinct REY differentiation with a slight MREY enrichment (Figure 7), indicating that the coals may have been supplied by terrigenous detritus from the Qilian-Qinling Oldland to a certain extent. In comparison, the noncoal samples presented similar REY distribution to the Haerwusu and Heidaigou coals with a slight LREY enrichment and UCC-normalized negative Eu anomaly. In addition, the enrichment of Li-Ga-Zr-Pb-Th trace element assemblages in the No. 11 coal also matched with the Haerwusu and Heidaigou coals, which was originally ascribed to the influence of the sediment source from Yinshan Oldland [48]. Furthermore, K 2 O/Na 2 O ratios of the No. 11 coals and most of the No. 3 coals was higher than 1, but the SiO 2 and quartz content was not as high as in the Qinling Oldland. Overall, it can be inferred that provenance from both the northern Yinshan Oldland and the southern Qilian-Qinling Oldland of the studied area had a combined influence during the formation process of No. 11 and No. 3 coals in the Sangshuping coal mine.

Influence of Seawater
The No. 11 and No. 3 coal seams in the Sangshuping coal mine was characterized by high and low total sulfur content, respectively, indicating seawater influence during formation of the No. 11 coal seam, which is in accordance with the No. 11 coal formed in coastal plain environment as evidenced by the occurrence of interbedded argillaceous limestones [29]. Apart from sulfur, arsenic concentration was also high in the No. 11 coal, especially in the top of the coal seam, reflecting a strong transgression during the late coalification stage [72].
In addition, the influence of seawater was also reflected by negative Ce anomalies [73], with CeN/CeN* values of <0.5,~0.6-0.9, and~0.9-1.0 indicative of coals formed in oxic, suboxic, and anoxic marine waters, respectively [74]. Apart from SSP11-5 (CeN/CeN* of 0.77) and SSP11-6 (CeN/CeN* of 0.86), the CeN/CeN* values of most of the No. 11 coal samples were above 0.9, reflecting a dominant influence of anoxic marine water. By contrast, the average CeN/CeN* value in the noncoal samples was 0.89, indicating a relatively oxic environment and more input of terrigenous detritus with respect to the coal formation process.
In addition to different CeN/CeN* values, the varying degree of seawater influence and terrigenous material supply during peat accumulation was also evidenced by the various ash yields (Table S1) and Nb/Y ratios among coal and noncoal rocks [61]. Compared to the noncoal rocks, coal samples of the No. 11 coal seam presented relatively scattered Nb/Y ratios with a wider variation range (Figure 10), which is probably caused by stronger marine influence and less terrigenous input during the coal formation process.

Influence of Hydrothermal Solutions
Previous research has demonstrated that occurrence of cleat-or fracture-infilling minerals in coals is also indicative of hydrothermal activities [15,22,75,76]. In the present study, calcite and gypsum were found occurring as fracture fillings, with pyrite or melanterite occasionally infilling the cleats or fractures in the calcite, which suggests an epigenetic origin in their formation (Figure 11a, b). The gypsum cross-cut the fracture-infilling calcite (Figure 11a), indicating that the precipitation of gypsum was later than that of calcite and followed by the crystallization of pyrite due to the influence of hydrothermal fluids penetrating the coal seam. Melanterite also occurred in the form of poreand cleat-infillings in the authigenic kaolinite particles (Figure 11c) and sometimes coexisted with pyrite (Figure 11d), which was crystallized from weathering and oxidation of pyrite in hydrothermal solutions. Furthermore, tobelite was also detected in the Sangshuping coals (Table S4), which is a typical hydrothermal mineral that has been found occurring in several Permo-Carboniferous coals in Chongqing [15], Inner Mongolia [77], and Shanxi [78]. Li et al. (2020) also reported that tobelite occurred in other coal mining districts of the Weibei coalfield [31]. The occurrence of tobelite in coals is attributed to the hydrothermal alteration of existing kaolinite in coals with NH 4 + from organic matter [75,79,80]. Apart from the mineralogical evidences, influence of hydrothermal activities was also indirectly confirmed by several geochemical evidences. Firstly, although the No. 11 coal was formed in a highly marine-influenced environment, concentration of SO 4 2− in paleo-seawater ranged from 5 to 27.6 mmol/kg in the Phanerozoic [81,82], which was not sufficient enough to generate that high sulfur content (8.4%) in coals. Therefore, in addition to the seawater influence, extremely high S contents in the No. 11 coals were also derived from hydrothermal fluids. Secondly, enrichment of V and Cr in coals is generally ascribed to the influence of hydrothermal activities [15]. Concentrations of As, V, Cr, Mo, and Pb are also high in the top of the No. 11 coal seam, and presents similar vertical distribution with S (Figure 4), which was largely caused by hydrothermal influence. Thirdly, despite of influence of marine depositional environment, high arcenic concentration in coals are also caused by hydrothermal activities [76,83]. Arsenic content is also high in the No. 3 coal formed in a continental environment, probably due to the influence of hydrothermal fluid. Furthermore, the No. 3 and No. 11 coal as well as the non-coal rocks from the Sangshuping mine are characterized by slightly positive Gd anomalies (Figure 7), which most probably caused by activities of hydrothermal fluids [45,60]. Enrichment of a V-Se-Mo-Re-U assemblage in the Late Permian SHOS coals formed in marine carbonate successions in southwestern China was ascribed to input of exfiltrational hydrothermal solutions [14,16]. Compared with these Late Permian SHOS coals, even if formed in marine environment and characterized by SHOS content as well, enrichment of a V-Se-Mo-Re-U assemblage was not found; instead, weak enrichment of a Mo-Se-V-Cr-As-Pb assemblage occurred in Late Carboniferous No. 11 coal of the Sangshuping mine ( Figure 4). Uranium was only slightly enriched in the noncoal rocks of the No. 11 coal and coals adjacent to them (Figure 4). Different vertical distributions of U and Mo from V, Cr, and As through the No. 11 coal section indicates that enrichment of these elements can be ascribed to different hydrothermal activities. Although there was no detection of any typical mineral phases related to volcanic ash in the current research, Wang et al. (2009) reported the occurrence of high-temperature quartz and zircon in Weibei coals, which confirmed the influence of felsic volcanic Energies 2020, 13, 6660 13 of 19 debris during the coal formation process [2]. Therefore, a most probable source of the hydrothermal solution can be derived from the volcanic/tectonic activity during accumulation of Late Carboniferous coals in the Weibei coalfield. Apart from the mineralogical evidences, influence of hydrothermal activities was also indirectly confirmed by several geochemical evidences. Firstly, although the No. 11 coal was formed in a highly marine-influenced environment, concentration of SO4 2− in paleo-seawater ranged from 5 to 27.6 mmol/kg in the Phanerozoic [81,82], which was not sufficient enough to generate that high sulfur content (8.4%) in coals. Therefore, in addition to the seawater influence, extremely high S contents in the No. 11 coals were also derived from hydrothermal fluids. Secondly, enrichment of V and Cr in coals is generally ascribed to the influence of hydrothermal activities [15]. Concentrations of As, V, Cr, Mo, and Pb are also high in the top of the No. 11 coal seam, and presents similar vertical distribution with S (Figure 4), which was largely caused by hydrothermal influence. Thirdly, despite of influence of marine depositional environment, high arcenic concentration in coals are also caused by hydrothermal activities [76,83]. Arsenic content is also high in the No. 3 coal formed in a continental environment, probably due to the influence of hydrothermal fluid. Furthermore, the No. 3 and No. 11 coal as well as the non-coal rocks from the Sangshuping mine are characterized by slightly positive Gd anomalies (Figure 7), which most probably caused by activities of hydrothermal fluids [45,60].
Enrichment of a V-Se-Mo-Re-U assemblage in the Late Permian SHOS coals formed in marine carbonate successions in southwestern China was ascribed to input of exfiltrational hydrothermal solutions [14,16]. Compared with these Late Permian SHOS coals, even if formed in marine environment and characterized by SHOS content as well, enrichment of a V-Se-Mo-Re-U assemblage was not found; instead, weak enrichment of a Mo-Se-V-Cr-As-Pb assemblage occurred in Late Carboniferous No. 11 coal of the Sangshuping mine ( Figure 4). Uranium was only

Lithium Enrichment
As aforementioned, lithium was enriched in both No. 11 (CC = 9.3) and No. 3 (CC = 7.0) coals of the Sangshuping coal mine, Weibei coalfield. Lithium was also found to be enriched in No. 5 coal from Dongpo coal mine [3] and Jinhuashan and Dongdong coal mines in the Weibei coalfield [31]. Furthermore, lithium enrichment has also been found in some coalfields located in the north of the Ordos basin, such as coals from the Antaibo mine in the Ningwu coalfield [84] and from the Guanbanwusu, Heidaigou, Haerwusu, and Tianjiashipan coal mines in the Jungar coalfield [48,52,85].
As stated above, Li in the Sangshuping coals presented a dominant aluminosilicate affinity, most probably occurring in kaolinite. This is similar to the elevated Li in the Jungar coalfield, which was also found occurring with aluminosilicate minerals, such as kaolinite, chlorite and/or illite, boehmite, and svanbergite in coals [52,86]. It is believed that the YinshanOldland is enriched in Li and the detrital supply from Yinshan Oldland is the primary source for Li enrichment in the Junggar coalfield [84,85]. Furthermore, terrigenous materials from the Yinshan Oldland have, to large extent, served as the provenance for No. 11 and No. 3 coal-bearing sequences of the Sangshuping coal mine. Therefore, Li enrichment in the Sangshuping coal mine can probably be attributed to terrigenous sediment source from the Yinshan Oldland. Furthermore, the underlying bauxite of the Benxi formation is considered to be another source of Li due to its high Li content [84], which is raised and exposed to the surface during the sedimentation stage [86]. The detrital sediments from the weathered Yinshan Oldland and the exposed bauxite carry high concentration of Li and migrate to the coals by various fluids, e.g., meteoric waters, surface water, and seawater. Thereafter, Li is adsorbed or incorporated by a higher proportion of aluminosilicate minerals (including kaolinite or illite and muscovite) deposited in the coals [87][88][89].
The average content of Li 2 O in No. 11 and No. 3 coalswere 0.2 and 0.1%, respectively (on an ash basis), which is both below the cutoff grade for Li 2 O in traditional pegmatite-type Li deposits (0.4%). However, the average Li 2 O content in the coal ash of No. 11coal reached the marginal grade for Li 2 O in Be-Li-Ta-Nb ore deposits (0.2%) [90], indicating that coal ashes of the No. 11 coal are potential source material for Li recovery.

Genesis of High Organic Sulfur
Overall, total sulfur content showed a remarkable increasing trend in the upper section of the No. 11 coal seam and attained the highest value in the roof, such as Fe, V, Cr, and As ( Figure 5). This was caused by strong seawater transgression and additional hydrothermal activity during the late coalification stage, which did not pose a remarkable influence on element abundances in the lower section of the coal seam. Furthermore, unlike in the No. 5 medium-high sulfur coal in other coal mines of the Weibei coalfield [2,31], sulfur occurs primarily in organic sulfur form in No. 11 SHOS coal of the Sangshuping mine, with organicsulfur proportion >90% in most coal samples and relatively low proportion of pyritic sulfur (Table S1). This is mainly due to the limited Fe supply in the highly occlusive marine environment during the coal formation process; the abundant sulfur reacted with the organic matter in the peat swamp to form organic sulfur compounds [12]. Notably, the coal accumulation broke up due to the continuous strong transgression, and argillaceous limestone was eventually formed at the top of the No. 11 coal with an extremely high content of Fe and total sulfur as well as pyritic sulfur, probably due to sufficient Fe supply from the S-Fe-As-rich hydrothermal solution, which preferentially combined with sulfur to form pyrite.

Conclusions
The Late Carboniferous No. 11 coal of the Sangshuping mine in Hancheng mining district, Weibei coalfield, is characterized by superhigh organic sulfur content (avg. 4.53%), belonging to typical SHOS coal.
The SHOS No. 11 coal is enriched in Li-Ga-Zr-Hf and Mo-Se-V-Cr-As-Pb element assemblages. The former points to a dominant aluminosilicate affinity, and their enhancement can be ascribed to the sediment source region of the Yinshan Oldland, although terrigenous detritus from the Qinling Oldland also serves as the provenance to a certain extent. Due to the highly elevated concentrations of Li 2 O, coal ash of the No. 11 coal may be considered as a promising source for Li recovery. In contrast, the latter presents a high sulfide affinity. Similar to the high S content in coal, their enrichment can be ascribed to the influence of both seawater and epigenetic hydrothermal activity.
High sulfur content occurs primarily in the form of organic sulfur in the No. 11 coal but in a dominant pyritic form in the roof. This is ascribed to sulfur reacting with organic matter in the peat swamp to form organic sulfur because of the insufficient supply of Fe available in seawater during the coal formation process. However, due to a strong seawater transgression and hydrothermal activity during the late coalification stage, sufficient supply of Fe was available from the S-Fe-As-rich hydrothermal solution and preferentially reacted with sulfur to form pyritic sulfur.