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This paper investigates the mineralogy and geochemistry of four coal beds (WJB-6, WJB-7, FHS-23 and FHS-27 Coals) of the Late Permian in the Zhina Coalfield, western Guizhou Province, China. The investigated coals reach the semianthracite -anthracite coal rank and have super-low to low ash yields. The sulfur contents vary considerably through coal sections and are mostly in the range of medium-high sulfur coal. The mineral assemblage present in the FHS-23 and FHS-27 Coals is mainly made up of pyrite and rectorite; the WJB-6 and WJB-7 Coals have different mineralogy, with kaolinite and rectorite dominant in the former as well as quartz and rectorite in the latter. These coals contain high concentrations of Nb and Ta, but Li is only enriched in the WJB-6 Coal. Rectorite and anatase in these coals are important hosting phases of Nb and Ta while kaolinite, and to a lesser extent chamosite in the WJB-6 Coal, are dominant carriers for the elevated Li concentration. The terrigenous material input, the marine influence and the effect of circulating hydrothermal solution are the pivotal geological factors causing geochemical anomalies in coals investigated. The high-sulfur coals were subjected to an enhanced marine influence in the depositional environment, as well as to a higher terrigenous influx, when compared with the medium-sulfur and low-sulfur coals, resulting in higher concentrations of S-Fe-As-Mo-U-Hg in the former coals than in the latter ones. The anomalous enrichment of Nb and Ta in these coals, as well as of Li in the WJB-6 Coal, is the result of the contributions from ascending hydrothermal solutions, although source rocks (e.g., high-Ti basalt) may provide relatively high background abundances of Nb, Ta and Li. [ABSTRACT FROM AUTHOR]

Abstract: The Yimin Ge-coal deposit, located in the Yimin coalfield, Inner Mongolia, is the third largest Ge-rich coal deposit in China just after the Lincang and Wulantuga Ge-coal deposits. Based on the coal and non-coal samples recently collected from the Wumuchang coal mining district in the Yimin Ge-coal deposit, this paper reports some new data on the mineralogical and geochemical characteristics of the Yimin high-Ge coals, and provides some new evidence for the possible mode of Ge enrichment in the Yimin coals. Mineralogical analyses were performed by means of Powder X-ray diffraction (XRD). Major and trace element concentrations were determined by inductively coupled plasma atomic-emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Element affinities were determined by Pearson's correlation analysis. The studied coals fall within the coal rank between sub-bituminous A and high volatile bituminous C, with relatively high moisture content, high volatile matter yield and low to medium ash yield. Quartz and kaolinite are the main mineral matters in the Yimin coals, with small amounts of pyrite and traces of microcline. Common pyrite and As-bearing pyrite occurring in the Yimin coals show an epigenetic origin. The epigenetic precipitation of kaolinite, quartz and As-rich pyrite (with Ge, and other trace elements) in the Yimin coal fractures may be caused by activities of both hydrothermal and low temperature fluids. Compared to common Chinese and worldwide coals, the Yimin coals are markedly enriched in Ge (43mg/kg), As (155mg/kg), and W (9.84mg/kg) and slightly enriched in Pb (22mg/kg) and Hg (0.24mg/kg). Most of the elements (e.g. Al, K, Sc, Ti, V, Cu, Ga, Sn, Th and REEs) in the studied coals present an aluminosilicate affinity as deduced from their obvious positive correlation with Al and ash yields. High correlation coefficients of As and Hg with Fe and S indicate a sulfide affinity of these elements in the Yimin coals. Germanium, B, Mo, and W in the studied coals show an organic affinity and a partial sulfur affinity as deduced from their negative correlation with Al and positive correlation with S, respectively. The preliminary and possible model for Ge enrichment in the Yimin Ge-coal deposit was that Ge was carried by hydrothermal fluids and then these fluids were incorporated in the water existing in the upper porous conglomerates and percolate in the top of the coal seam, where Ge was trapped by organic matter and finally enriched in an early diagenetic stage (humification–gelification). [Copyright &y& Elsevier]

Abstract: The Zhundong coalfield is a very large coal deposit, currently under exploration, and promises to be an important coal mining resource in Western China. The coal reserves amount to 164Gt. At Xiheishan and Wucaiwan, the coal-bearing units are the Badaowan (Lower Jurassic) and, especially, the Xishanyao formations (Middle Jurassic). These contain from one to 31 coal seams (one to 10 workable coals reaching the rank of high volatile A bituminous) with an accumulated workable coal thickness of 20–87m. These recently explored coal reserves are of a high quality and are characterized by low ash, aluminum, iron, sulfur, and trace element contents. The minerals present in this coal are mainly quartz, kaolinite, siderite, and pyrite. The trace element contents in both Xiheishan and Wucaiwan coals are much lower when compared with the usual concentration ranges present in Chinese coals, with the exception of Ba and Sr. Thus, Ba contents in Xiheishan coal are higher than Swaine''s worldwide concentration range. A large number of elements have mainly aluminosilicate affinity, and occur in clay and other detrital coal minerals. Ca and Mn have mainly carbonate affinity; Fe and S have mainly sulphide affinity in Wuchaiwan coal. In Xiheishan, Fe, Mn and Mg have mainly carbonate affinity (siderite), and probably, B, Co, Ni and S have an organic affinity. Thus, the Zhundong coalfield contains coal with a very high quality and very low levels of impurities. The very low ash yields, S, Fe, and trace element contents may be attributed to the sedimentological setting, with intensive peat bog aggradation in a very shallow lake environment with a low detrital supply. The very low sulfur content, the relatively high Ba-sulfate (barite) content and the high siderite occurrence in Xiheishan coal (in contrast to the pyrite occurrence in Wucaiwan coal) may be attributed to the rapid aggradation of peat with the consequent oxidation and leaching of minerals, elements, and degradation of organic components. Under this scenario, sulfate is trapped by the continuous precipitation and accumulation of barium sulfate (very low soluble). [Copyright &y& Elsevier]

Abstract: The geological and geochemical controls of the Ge distribution in the Cretaceous Wulantuga high-Germanium coal deposit in the Shengli coal field, Inner Mongolia are investigated. This paper focuses mainly on the spatial distribution of the Ge contents in coal. The high-Ge coals mainly occur in three splits of the #6 coal in the southwestern part of the Shengli coal field. Mean germanium contents in the coal range from 32 to 820 μg/g, with a mean value of 137 μg/g, on a bulk coal basis (mean of 939 coal samples from 75 boreholes in the #6 coal seam) in an area of 2.2 km2. The highest Ge content occurs SW of #6 coal seam, close to the margins of the coal basin, decreasing with a fan-shaped trend towards NW, the direction of the coal basin. There is an negative correlation between the mean Ge content and the thickness of the coal seam. Different distribution patterns of Ge content were found in vertical profiles. High Ge concentrations may occur in the middle parts of coal seams, at the bottom and/or the top of thick coal seams and inconspicuous variation. A major organic affinity was determined for Ge, with a special enriched in the banded bright and semibright coal. The high-Ge coals and the coalified wood in the sandstone overlaying the #6-1 coal highly enriched in Ge, As, Sb, W, Cs, Tl, Be, and Hg. The Late Jurassic silicified volcanic rocks in the NW of the Ge coal deposit relatively high enriched in Ge, Ga, Sb, As, Cs, Be, Ge and Hg. The correlation coefficients among the elements enriched showed marked variations at close sites in this deposit, suggesting a possible diagenetic origin of the geochemical anomaly. The main Ge anomaly was attributed to early Cretaceous hydrothermal fluids circulating through the fault systems and porous volcanic rocs, probably from the subjacent granitoid rocks. The fault systems, the porous coarse clastic rocks overlying coal seam and the lithotype of coal played an important role in the transport and trapping of Ge. A main diagenetic origin (overlapping a slight synsedimentary accumulation) is deduced for the Ge anomaly. [Copyright &y& Elsevier]

The abnormal enrichment of the REY (rare earth elements and yttrium)-Zr (Hf)-Nb (Ta) assemblage in Late Permian coals occurring in some coalfields in SW China has been extensively investigated, but the geological controlling factors of this assemblage are still under debate. This study reports on the mineralogical and geochemical features of coals and noncoal rocks collected from the Yudai and Jinqi coal mines within the Qiandongbei Coalfield in Guizhou Province to elucidate the geological controls on the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons. The studied coals show rather consistent clay mineral assemblage of kaolinite, together with varying amounts of quartz, gypsum, pyrite, and calcite. Notably, the coals are anomalously enriched in REY, Nb, Ta, Zr, and Hf and enriched in other incompatible elements (e.g., Ga, Th, and U). Phosphates (e.g., florencite) and, to a lesser extent, zircon are the primary carriers of REY. Zirconium and Hf are mainly incorporated into zircon and then anatase, the latter of which is a predominant carrier of Nb and Ta. The detrital materials originate from a mixture of the erupted felsic volcanic ash resembling a peralkaline rhyolite composition and the eroded materials of Emeishan Large Igneous Province (ELIP) basalts. The studied coals owe their highly enhanced concentrations of the REY-Zr (Hf)-Nb (Ta) assemblage to the input of felsic volcanic ash, wherein the highly acidic aqueous solutions allowed these elements to become mobile and be redistributed. Both geological processes governed the distribution of REY-Zr (Hf)-Nb (Ta) enrichment horizons. The highly acidic solutions were possibly derived from the oxidation of peat bogs and volcanism-related acidic rain. The concentrations of REY, Zr, and Nb in the coal ashes exceed their corresponding cut-off grades; thus, these coals can be considered highly promising raw material sources for the REY-Zr (Hf)-Nb (Ta) assemblage. • The studied coals are significantly enriched in REY-Zr (Hf)-Nb (Ta) assemblage. • Detrital materials are derived from a mixture of felsic volcanic ash and eroded mafic materials. • The joint influence of highly acidic solutions and volcanism governs the REY-Zr (Hf)-Nb (Ta) enrichment horizons. • The volcanic ash erupted into peat bogs is geochemically similar to the peralkaline rhyolite. [ABSTRACT FROM AUTHOR]

[Display omitted] • The late Triassic coals from, Northeastern Vietnam were formed in limnic sedimentary environment. • Coals from the Coc Sau open-pit mine in Cam Pha Coalfield are promising economic source of critical elements (Rb and Cs). • High enriched Rb and Cs in the Coc Sau coals most likely occur in K-rich clay minerals, e.g., muscovite. • Rb and Cs enrichment are originated from terrigenous influx from felsic-intermediate sediment provenance. The current study investigates the mineralogical and geochemical characteristics of the Late Triassic coals from the Coc Sau open-pit mine, Cam Pha Coalfield (Quang Ninh Province, Northeastern Vietnam) using Powder X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), inductively coupled plasma atomic-emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Coals from Coc Sau open-pit mine are characterized by medium ash yield (avg. 29.7%), low sulfur content (avg. 0.17%), and low moisture content (avg. 1.8%). The volatile matter content (avg. 8.4%) indicates a semianthracite rank. The crystalline phases identified in Coc Sau coals and host rocks (roof, floor, parting) are primarily quartz, kaolinite and muscovite, with small proportions of ankerite, clinochlore, anatase, calcite, and tobelite. Illite, pyrite, and siderite were occasionally detected in individual samples. In addition, several minerals below the XRD detection limit, such as barite, apatite, zircon, xenotime, and florencite were observed by SEM. The low sulfur concentrations, low Sr/Ba ratio and relatively high ash yield of these coals indicate a continental lake basin sedimentary environment with a relatively strong supply of terrigenous detritus. Quartz, kaolinite, and muscovite were most likely derived from the terrigenous source region surrounding the basin, and the other minerals are mainly of authigenic origin. Relative to worldwide coals, the Coc Sau coals and host rocks are highly enriched in Rb and Cs, which can be a potential source for Rb and Cs recovery during coal utilization and combustion. Rubidium and Cs enriched in the coals are positively correlated with Al and K, indicating that they most likely occur in potassium-rich clay minerals (e.g., muscovite), and originate from weathered felsic terrigenous detritus. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Upper Triassic coal from the Nui Hong open-pit mine is high-organic-sulfur coal. • The Nui Hong coal is promising economic source for strategic metal recovery. • Highly elevated Cs in coal most likely occurs in K-rich tobelite and illite. • Elevated Mo, Sb, U, Ge, and Tl are mainly associated with organic matter in coal. • Enrichment of strategic metals in Nui Hong coal is due to hydrothermal activities. Research on coal-hosted strategic metal ore deposits is an important subject in coal geology and mineral deposit worldwide. However, the related geological characteristics of coals from Vietnam have seldom been investigated, let alone the strategic metals in coals. This paper investigates the mineralogical and geochemical characteristics of the Upper Triassic coal from the Nui Hong open-pit mine, Thai Nguyen Coalfield, NE Vietnam, with emphasis on the enrichment of strategic metals in coal. The Nui Hong coal is low-volatile bituminous with high sulfur organic content. Minerals in the Nui Hong coal is predominantly composed of authigenic quartz, tobelite, pyrite, and calcite, with a small proportion of sphalerite, gypsum and fluorapatite in some coal bench samples. Mo-U-V-Se and Ge-W-Sb-Cs-Tl(-U) strategic metal element assemblages along with As-P toxic element association is significantly enriched in the Nui Hong coal, pointing to a significant economic benefit for Cs, Mo, U, and Ge recovery from the Nui Hong coal. The Ge enrichment in the Nui Hong coal provides a new perspective on prospecting of coal-hosted Ge deposit in high-rank coal. Cesium mostly occurs in K-rich aluminosilicate minerals (tobelite and/or illite), while Mo, Sb, U, Ge, and Tl are predominantly associated with organic matter in the Nui Hong coal. Multistage hydrothermal activities occurring in the marine-influenced S-rich, Fe-poor and clastic-starved anoxic-euxinic coal-forming environment are responsible for the significant enrichment of strategic metal elements in the upper Triassic coals from the Nui Hong open-pit mine, Thai Nguyen Province. [ABSTRACT FROM AUTHOR]

This paper represents the first integrated research on the mineralogical, geochemical and stable isotope characteristics of the Upper Triassic high‑sulfur coals from the Khanh Hoa open-pit mine, Thai Nguyen Coalfield, NE Vietnam. Formed in a marine-influenced carbonate succession, the Khanh Hoa coal is characterized by medium ash yield, low volatile matter yield, and high sulfur content. Minerals in the Khanh Hoa coal are predominantly composed of authigenic calcite in the upper portion; and pyrite, quartz, with minor amounts of tobelite ([(NH 4), K] (Si, Al) 4 Al 2 O 10 (OH) 2), gypsum in the middle and lower portions. The high‑sulfur Khanh Hoa coal is enriched in an As-Mo-Sb-U-Cs-P assemblage, which presents both an organic and inorganic mode of occurrence, and is largely ascribed to hydrothermal fluids. The δ 13C values of the Khanh Hoa coal range from −24.77‰ to −22.80‰ (avg. −23.33‰), reflecting a change in sedimentation pattern (from transgressive to high stand system upwards). The δ 15N values of the Khanh Hoa coal range from 2.41‰ to 3.73‰ (avg. 3.30‰), possibly resulted from influenced by seawater influence and a redox environment. The mineralogical, geochemical and isotopic characteristics reflected that the high‑sulfur Khanh Hoa coal was formed/preserved in marine-influenced anoxic environment, with low detrital input, and strong activities of multi-stage hydrothermal solutions. [ABSTRACT FROM AUTHOR]