Petrographic, geochemical and carbon isotopic determinations were conducted on five samples from four seams within the Late Cretaceous-Paleocene of the Guaduas Formation in Colombia. The individual ...coal seams are thin, ranging from 0.59 to 1.2 m, and occur over a 157 m interval. The average weighted ash yield is 13.7% (dry basis), although one sample presented values >35%. Vitrinite reflectance increases from 1.33% in the stratigraphically uppermost seam (La Cuarta) to 1.44% in the lower most coal seam (Cisquera), indicating their rank to be medium volatile bituminous.
The studied sequence of the Guaduas Formation represents a peat environment influenced by shifting depositional settings, particularly in relation to the proximity of marine/brackish water environments as indicated by Sr/Ba values, sulfur, pyrite, δ13C and the proportion of telinite. A decrease in inertinite indicates that the peat mires were becoming relatively ‘wetter’ stratigraphically upwards. This trend, unlike that of Sr/Ba and telinite, may be driven by climatic shifts rather than only changes in depositional environment.
Both trace and rare earth elements, plus yttrium (REY) are related to the inorganic fraction of the coal. All rare earth elements are depleted relative to average worldwide hard coals (for trace elements) and average upper continental crust (for REY) with the notable exception of Li and Sb for the high ash yield sample (the La Cuarta lower coal seam). The abundance of some REY elements (i.e. Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) may be more influenced by the presence of illite rather than just the quantity of total ash yield. Based on the relationship between SiO2 and Nb/Y, the provenance of the inorganics changed from a rhyolitic source at the lowest seam (Cisquera) to a dacite source in the middle layer (El Tesoro) to an andesite source in the stratigraphically uppermost seams (La Gemela and La Cuarta).
Display omitted
•Low inertinite at the top seam may indicate wetter conditions and/or less fire than the lower seams•Strong correlation between Sr/Ba, %telinite and δ13C may be related to the relative proximity to marine/brackish water environments•Both trace elements and REY are depleted relative to world averages but vary directly with ash yield•The upper most seam studied (La Cuarta) demarcates a change from mostly terrestrially influenced to more marine/brackish water influenced environments•The ultimate source of the inorganics changed from rhyolitic to dacite to andesite from the bottom most coal to the top most in this study.
Critical elements in coal have attracted much attention in recent years as some coals and coal combustion products may provide an alternative source of these. This paper provides mineralogical and ...geochemical data on the No. 4 coal seam, the major minable coal from the Eastern Surface Mine, Ningwu Coalfield, Shanxi Province, northern China. It also discusses the provenance of mineral matter, the origin of aluminum minerals (boehmite), carbonates (calcite and ankerite) and phosphates (goyazite) and the potential economic significance of critical elements (e.g., Al, Nb, Ta, Zr, Hf, and Ga). Mineralogically, the studied coal samples are characterized by high kaolinite (64.7% on average, low-temperature ash basis) and boehmite (24.1%) contents, followed by carbonates (calcite, ankerite, siderite, and dolomite), titanium oxides (anatase and rutile), goyazite, quartz, and apatite. In comparison with average values for Chinese coals, the studied coal samples are characterized by high Al2O3 contents (mean 11.82% on a whole-coal basis and mean 49.49% on an ash basis). Compared with world hard coals, the No. 4 Coal is enriched in Ga, Se, Zr, Nb, La, Ce, Hf, Ta and Pb. In addition to Al, critical elements including Nb, Ta, Zr, Hf, and Ga in this coal have an economic significance. The Al2O3/TiO2 vs. Nb/TiO2, Al2O3/TiO2 vs. Zr/TiO2, Zr vs. Nb, Hf vs. Ta, and REY distribution patterns (REY, rare earth elements plus Y), indicate that the provenance of mineral matter (e.g., boehmite and critical elements Nb, Ta, Zr, Hf and Ga) in the No. 4 Coal is a number of sediment-source regions including the Neoarchean granites of the Yinshan Oldland, and the Paleoproterozoic granites and Benxi Formation bauxites (Late Carboniferous, to the northeast of the coal basin) of the northern Trans North China Orogen. Carbonate minerals (calcite and ankerite) are of epigenetic origin while the phosphate mineral (goyazite) was syngenetically deposited in the peat swamp during a period of a low water table.
•The coal investigated is highly enriched in boehmite (24.1% on average, ash basis).•Elements Al, Nb, Ta, Zr, Hf, and Ga in the coal have an economic significance.•Mineral matter in the coal was dominantly derived from the Precambrian granites.•The boehmite was largely derived from the bauxite of the Benxi Formation.
Boehmite-rich coal of Pennsylvanian age was discovered earlier at the Heidaigou Surface Mine, Jungar Coalfield, Inner Mongolia, China. This paper reports new results on 29 bench samples of the no. 6 ...coal from a drill core from the adjacent Haerwusu Surface Mine, and provides new insights into the origin of the minerals and elements present. The results show that the proportion of inertinite in the no. 6 coal is higher than in other Late Paleozoic coals in northern China. Based on mineral proportions (boehmite to kaolinite ratio) and major element concentrations in the coal benches of the drill core, the no. 6 coal may be divided into five sections (I to V). Major minerals in Sections I and V are kaolinite. Sections II and IV are mainly kaolinite with a trace of boehmite, and Section III is high in boehmite. The boehmite is derived from bauxite in the weathered surface (Benxi Formation) in the sediment-source region. The no. 6 coal is rich in Al
2O
3 (8.89%), TiO
2 (0.47%), Li (116 μg/g), F (286 μg/g), Ga (18 μg/g), Se (6.1 μg/g), Sr (350 μg/g), Zr (268 μg/g), REEs (172 μg/g), Pb (30 μg/g), and Th (17 μg/g). The elements are classified into five associations by cluster analysis, i.e. Groups A, B, C, D, and E. Group A (ash–SiO
2–Al
2O
3–Na
2O–Li) and Group B (REE–Sc–In–Y–K
2O–Rb–Zr–Hf–Cs–U–P
2O
5–Sr–Ba–Ge) are strongly correlated with ash yield and mainly have an inorganic affinity. The elements that are negatively or less strongly correlated with ash yield (with exceptions of Fe
2O
3, Be, V, and Ni) are grouped in the remaining three associations: Group C, Se–Pb–Hg–Th–TiO
2–Bi–Nb–Ta–Cd–Sn; Group D, Co–Mo–Tl–Be–Ni–Sb–MgO–Re–Ga–W–Zn–V–Cr–F–Cu; and Group E, S–As–CaO–MnO–Fe
2O
3. Aluminum is mainly distributed in boehmite, followed by kaolinite. The high correlation coefficients of the Li–ash, Li–Al
2O
3, and Li–SiO
2 pairs indicate that Li is related to the aluminosilicates in the coal. The boehmite-rich coal is high in gallium and F, which occur in boehmite and the organic matter. Selenium and Pb are mainly in epigenetic clausthalite fillings in fractures. The abundant rare earth elements in the coal benches were supplied from two sources: the bauxite on the weathered surface of the Benxi Formation and from adjacent partings by groundwater leaching during diagenesis. The light rare earth elements (LREEs) are more easily leached from the partings and incorporated into the organic matter than the heavy REEs, leading to a higher ratio of LREEs to HREEs in the coal benches than in the overlying partings.
Some previous studies have investigated the enrichment origin of Sb and Cs in coal, but strong supportive evidence for the sources of the two elements in coal is still absent. The main aims of this ...study were to provide a better understanding of the geochemical and mineralogical characteristics of the Palaeogene No. 5 Coal from the Zhoujing coal mine, Baise Coalfield, Guangxi Province, southwestern China. The No. 5 Coal has a low rank (0.44% Ro,max; 46.96% volatile matter content), an average ash yield 19.37%, and a medium sulfur content (1.23% on average). The main minerals in the No. 5 Coal are kaolinite, illite, quartz, and pyrite. Bassanite (2CaSO4•(H2O)) was identified in the low-temperature ashes in varying proportions (2.7% - 37.6%). The mineralogy of the non-coal samples (partings, roof and floor strata) is similar to that of the coals but chlorite is additionally present and pyrite is largely absent in these non-coal samples. The modes of calcite occurrence in the partings indicates a terrigenous origin for this phase.
Compared with average values for world low-rank coals, the No. 5 Coal is distinctively enriched in Sb (29.12 μg/g), Cs (9.71 μg/g), and U (15.61 μg/g). Compared with the average values for world clays, the parting and host rock samples have normal concentrations for most trace elements, with an exception of higher Sb (9.93 μg/g). The elevated Sb and Cs in the coal were derived from the detrital material shedding from the exposed middle Triassic strata, which host notable Au and Sb deposits in the surrounding region. The REY (rare earth elements and Y) distribution patterns for the coal benches, partings, roof and floor strata are generally characterized by enrichment in medium REY and positive Gd anomalies, both of which were due to acidic waters circulating within the coal basin. The mineral compositions and their association indicate that the depositional environment was weakly acidic at the early stage of peat accumulation and then changed to neutral or weakly alkaline in the later stage.
•The coal investigated is distinctively enriched in Sb (29.12 μg/g) and Cs (9.71 μg/g).•Sb and Cs in the coal were derived from the terrigenous middle Triassic strata hosting Au and Sb deposits.•The medium REY enrichment and positive Gd anomalies were due to the acidic waters circulating within the coal basin.•The depositional environment was acidic at the early stage of peat accumulation.•The depositional environment was changed to neutral or weakly alkaline in the later stage of peat accumulation.
This paper describes numerous siderite occurrences from Nb-Zr-REY-Ga-enriched beds of tuffaceous mudstone from the Yujingshan borehole, eastern Yunnan, southwestern China. The mineral phases in the ...samples were identified and characterized through macroscopic observation, XRD (X-ray diffraction) analysis, optical microscopy, and FE-SEM (field emission-scanning electron microscopy). The results show that the siderite occurs in the drill core from depths of 664.07 to 729.21 m, where its content varies from 15.1 to 65.7%, 31.3% on average. Modes of occurrence of authigenic siderite include irregular banded or massive aggregates, discrete fine particles, oolitic aggregates, and double or multi-ring ellipsoid-shaped or rhombohedral aggregates. The mineralogical association with quartz, anatase, ilmenite, chromite, and zircon with sharp-edged outlines, high-temperature cracks and/or corroded embayments, and REE-bearing minerals and geochemical characteristics such as Al2O3/TiO2 between 3 and 8, less commonly 8–23.77, indicate that abundant siderite was produced by hydrothermal alteration of airborne volcaniclastic materials. The δ13CPDB, δ18OPDB, and δ18OSMOW values of siderite in the argillized tuff range from −12.56 to −1.32‰, −8.98 to −5.88‰, and 21.60 to 24.80‰, respectively. In the δ13CPDB-δ18OSMOW diagram, plots of the studied siderite are distributed between the fields of marine carbonate rocks, sedimentary organic matter, and carbonates of hydrothermal ores. Some siderite from the upper part of the studied borehole is isotopically close to REY carbonates from the Abramovka lignite deposit, Far Eastern Russia, which precipitated from evolved basinal waters mixed with CO2 from a mantle source. In summary, this indicates a hybrid origin for the studied siderite including carbonate dissolution, dehydroxylation of sedimentary organic matter, and hydrothermal activity. Furthermore, the paleosalinity (Z) and paleotemperature (T) of the ore-forming fluids were calculated based on the age-corrected stable carbon and oxygen isotopic data in the samples. The Z values range from 96.65 to 121.5‰, suggesting the formation of siderite under brackish-water conditions. The T values vary from 19.47 to 47.12 °C, with some sharp fluctuations that may be due to ash falls and/or hydrothermal injections. Overall, our data support the model for critical-metal Nb(Ta)-Zr(Hf)-REY-Ga enrichment in tuffaceous deposits of southwest China including a combination of volcanic activity and terrestrial organic-rich sedimentation under warm and humid conditions, followed by low-temperature alteration evolved from acidic leaching, which is responsible for the Nb-Zr-REY-Ga enrichment, and, subsequently, formation of authigenic siderite with associated quartz, sulfide minerals, and phosphate minerals under reducing neutral/weakly alkaline conditions.
•Abundant siderite is documented in the clay-altered tuffaceous horizons.•Fe was primarily derived from airborne pyroclastics.•C and O were sourced from carbonate, organic matter, and hydrotherm.•C-O isotopes show that siderite was affected by seawater and hot fluids.•A genetic model of siderite in Nb-Zr-REY-Ga deposits has been proposed.
Minerals and elements in coal are derived from the processes associated with peat accumulation and rank advance, as well as possibly a range of epigenetic processes, and thus can provide information ...on the depositional conditions and geologic history of coal beds and coal-bearing sequences, as well as perhaps on regional tectonics. This paper investigates the petrology, mineralogy, and geochemistry of anthracites and their host rocks (partings, roof, and floor strata) from two coal deposits (Hongmao and Luocheng) in Guangxi Province, southern China. Samples collected from these deposits were analyzed using optical microscopy, scanning electron microscopy plus energy-dispersive X-ray spectrometry, low-temperature ashing, X-ray diffraction, X-ray fluorescence spectrometry, and quadrupole-based inductively coupled plasma mass spectrometry.
The anthracites from the two deposits are medium- to high-sulfur coals. The rare earth elements in the Luocheng anthracites are characterized by distinct positive Eu anomalies and medium- and heavy-REE enrichment types. The minerals in the Hongmao anthracites are characterized by the occurrence of K-illite, paragonite, and ammonian illite, which, however, are absent in the Luocheng anthracites. The paragonite, ammonian illite, and chlorite resulted from the alteration of pre-existing kaolinite by hot solutions containing Na+, NH4+, and Fe2+ respectively. The partings in the Luocheng anthracite seams contain pyrophyllite that was formed by reactions between kaolinite and quartz during injection of high-temperature solutions. The mineralogical and geochemical characteristics of the anthracites in the two deposits indicate that the coals were subjected to high-temperature (>250 °C) solutions that also elevated the coal rank to anthracite grade. The assemblage of K-illite-paragonite-NH4-illite in the coals of the Hongmao deposit was formed under greater hydrothermal but less tectonic influence compared to the Luocheng deposit; by contrast, the pyrophyllite-illite-chlorite assemblage of the Luocheng deposit reflects a greater tectonic but lesser hydrothermal influence.
•Rare earth elements in the anthracites have distinct positive Eu anomalies and medium- and heavy-REE enrichment types.•The minerals in the anthracites are characterized by the occurrence of K-illite, paragonite, and ammonian illite.•Paragonite and ammonian illite resulted from the alteration of kaolinite by hot solutions containing Na+ and NH4+.•Pyrophyllite in partings of coalbed formed by reactions between kaolinite and quartz during injection of high-T solutions.•The mineralogical and geochemical characteristics of the anthracites indicate the injection of high-T (>250 °C) solutions.
We present multi-element data on the super-high-organic-sulfur (SHOS; 5.19 % on average) coals of Late Permian age from Guiding, in Guizhou Province, China. The coals, formed on restricted carbonate ...platforms, are all highly enriched in S, U, Se, Mo, Re, V, and Cr, and, to a lesser extent, Ni and Cd. Although the Guiding coals were subjected to seawater influence, boron is very low and mainly occurs in tourmaline and mixed-layer illite/smectite. Uranium, Mo, and V in the coal are mainly associated with the organic matter. In addition, a small proportion of the U occurs in coffinite and brannerite. The major carrier of Se is pyrite rather than marcasite. Rhenium probably occurs in secondary sulfate and carbonate minerals. The U-bearing coal deposits have the following characteristics: the formation age is limited to Late Permian; concentrations of sulfur and rare metals (U, Se, Mo, Re, V, and in some cases, rare earth elements and Y) are highly elevated; the U-bearing coal beds are intercalated with marine carbonate rocks; organic sulfur and rare metals are uniformly distributed within the coal seams; and the combustion products (e.g., fly and bottom ash) derived from the coal deposits may have potential economic significance for rare metals: U, Se, Mo, Re, V, rare earth elements, and Y.
Determination of the geochemical and mineralogical characteristics of coal can provide useful information on the geological setting and evolution of coal basins and assist in identifying factors that ...control the distribution of the minerals and elements of interest. The Late Permian coals of southwestern China have received much attention because some of these coals are usually considered to be potential sources of some critical metals and have high concentrations of potentially toxic elements.
Mineralogical and geochemical analyses were carried-out on the Late Permian coals from the Kulishu and Sijichun mines of the Zhijin-Nayong Coalfield, Western Guizhou, China. The diagram of Al2O3/TiO2-Nb/Yb shows that the sediment source of the Kulishu and Sijichun coals is dominantly the Emeishan magmatic province with a smaller contribution from a Neoproterozoic metamorphic-granite complex, both of which are the two major components of the Kangdian Upland. The sediment source of the roof and floor rocks is dominantly basaltic volcanics in the Emeishan large igneous province (ELIP), while the partings were probably derived from eruptions of the Emeishan felsic-alkaline magmas and a mixture of ashes derived from a distal volcanic arc. Highly elevated total sulfur contents (dominated by pyritic and organic sulfur), abundant framboidal pyrite, as well as disseminated fine-grained pyrite provide evidence for input of seawater during the peat and coal formation. Paragonite mineralization with enrichment of Li, Nb (Ta), Zr (Hf), REY and Pb in the Sijichun coals and partings of the Kulishu coal are attributed to the intrusion of alkaline magma. The pyrite, quartz, albite, anatase and gypsum occurring as veins-, cleat-fillings and separate well-crystallized aggregates of epigenetic origin in the studied coals are indicative of the influence of hydrothermal fluids from a magmatic source.
Stone coal in China: a review Dai, Shifeng; Zheng, Xue; Wang, Xibo ...
International geology review,
04/2018, Letnik:
60, Številka:
5-6
Journal Article
Recenzirano
Stone coal is defined as a combustible, low-heat value, high-rank black shale of early Paleozoic (in a few cases, Permian) age, widely distributed in southern China. Attention has been focused on ...stone coals because (1) they can be used as fuel energy (for power plants and daily use in some villages) mainly in southern China; (2) they are enriched in critical elements and are currently industrially (economic extraction of V) and agriculturally (such as Se) utilized or have such a great potential (e.g. Au, platinum group elements, Mo, and Ni); (3) they are the sources for some toxic elements that have caused environmental pollution (e.g. SO
2
emission during their combustion) and endemic diseases such as selenoisis and fluorosis; and (4) they can provide useful information for geological events and regional geological setting (e.g. hydrothermal activities). This article reviews stone coal's definition; occurrence and distribution; petrologic properties, mineralogy, and geochemistry; adverse impacts on environment and human health; and by-products of critical elements as well as major challenges remaining from point of view of determining element enrichment mechanisms, utilization of critical elements, and control of toxic elements released during stone coal utilization.
Silicic and alkali intra-seam tonsteins were discovered earlier in southwestern China. This paper reports new data on the geochemical and mineralogical compositions of tonsteins from the Songzao ...Coalfield, Chongqing, southwestern China, and provides new insights into the origin and distribution of the minerals and elements present. Three types of tonsteins (silicic, mafic, and alkali) were identified based on their lateral correlation over a large coalfield area and the overall similarity of corresponding mineralogical and chemical compositions. The clay minerals in most tonsteins of different sources and the mafic tuffs in the lower portion of the late Permian are dominated by kaolinite or are mainly composed of mixed layers of illite and smectite. The silicic tonsteins contain high quartz while the mafic tonsteins and mafic tuffs have high contents of anatase. All the tonsteins and tuffs contain pyrite, attributed to the seawater influences. The mafic tonsteins and tuffs have higher pyrite contents, probably due to the higher Fe derived from mafic volcanic ashes. The mafic tonsteins and tuffs are enriched in Sc, V, Cr, Co, and Ni, similar to the normal clay sediments in the southwestern China, indicating similar sources. The alkali tonsteins are characterized by high contents of Nb, Ta, Zr, Hf, REEs (rare earth elements), and Ga. The TiO
2/Al
2O
3 values are 0.02-0.08 for alkali, <
0.02 for silicic, and >
0.10 for mafic tonsteins and mafic tuffs, indicating different magma sources. Mafic tuffs and alkali tonsteins are enriched in rare earth elements, and silicic tonsteins contain a lowest REE but have the highest fractionation between light REE and heavy REE. Tonsteins and tuffs may be at the periphery of the Emeishan Large Igneous Province and probably resulted from a waning activity of the plume. They were probably derived from different mantle sources that were underwent not only low-degree partial melting but also fluid fractionation and contamination by lithospheric mantle. Their source magmas had an alkali-basalt composition and were similar to that of ocean island basalt.
►Three types of tonsteins (silicic, mafic, and alkali) were identified in coal. ►Mafic tonsteins are high in Sc, V, Cr, Co, and Ni. > Nb, Ta, Zr, Hf, REE, and Ga are enriched in alkali tonsteins. ►The source magmas of tonsteins had an alkali-basalt composition.
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