The end-Permian mass extinction (EPME) is sudden, but prior to which, the ecological resilience has diminished. The Late Permian is an important geologic period for coal formation associated with ...extensive volcanic activities in South China and adjacent regions. Here we present a systematic analysis of organic carbon and mercury isotopes as well as elemental geochemistry and mineralogy of a coal-bearing section from the Lianying Coalfield in Yunnan Province, South China. The data show that organic carbon δ13C values are negatively shifted by −25.22‰ to −25.99‰ in pyroclastic tonstein partings, which are near-synchronous with the negative Eu anomaly (0.48–0.52), significant Hg enrichment (130–352 ppb) and near-zero Δ199Hg (−0.08–0.07‰). These C and Hg isotope anomalies and associated geochemical signatures, which are manifested by characteristic Al2O3/TiO2, Zr/TiO2, and Nb/Yb ratios, are likely caused by subduction or collision-related volcanism. Our study provides evidence for the occurrences of volcanism before the advent of EPME, which played a significant role in stressing the environment and consequently diminishing the ecological resilience in the latest Permian.
Volcanic ashes in coal and coal-bearing sequences typically occur as persistent bands within coal seams (generally as tonsteins, but in a few cases as bentonites, K-bentonites, or as clay-free ...partings), as an intimate mixture with organic matter, as host rocks (such as roof and floor strata), or as thick layers in coal-bearing strata that are stratigraphically separated from coal seams, including those of thick, laterally persistent tuffs, and in the broader sense fragmental clay rocks and flint clays. Altered volcanic ashes have been found in numerous coals with rank ranging from lignite through various bituminous coals to anthracite, as well as in all the continents where coal beds are present.
The main primary minerals in volcanic ash that survive post-depositional alteration include high-temperature quartz, plagioclase, sanidine, zircon, apatite, monazite, micas, rutile, and anatase. Alteration of volcanic glass and less stable primary minerals may result in the formation of kaolinite, smectite, illite, mixed-layer I/S and, in some cases, chlorite and zeolites. In addition to mineralogical and petrographic characteristics, identification of the parent magma type is commonly based on relatively immobile elements rather than the total alkali-silica contents, which are often affected by post-depositional alteration. Four types of volcanic ashes have been identified in coal and coal-bearing sequences, namely felsic, mafic, intermediate, and alkali. Altered mafic volcanic ashes are characteristically enriched in Sc, V, Cr, Co, and Ni; have positive Eu anomalies; and are of a medium-REE enrichment type. Altered alkali volcanic ashes are unique in their significant high concentrations of rare metals such as Nb, Ta, Zr, Hf, REE, and Ga, and are characterized by distinct negative Eu anomalies. Compared with altered alkali volcanic ashes, felsic tonsteins have relatively lower REE concentrations and less pronounced negative Eu anomalies, but a greater fractionation between light and heavy REEs. The compositional variation of different types of altered volcanic ashes is attributed to the tectonic framework and geodynamic controls.
Volcanic ashes in coal may serve as chronostratigraphic markers to identify and correlate coal seams, and can also be used for radiometric age determination. The ashes may have provided terrigenous materials that served as substrates for peat development; and may have terminated peat accumulation if volcanic ash in large quantities fell into the peat swamp; they can also be used to indicate the geodynamic processes of coal formation; and perhaps explain mass extinction events. Admixed volcanic ash may lower the quality of the coal if not removed in the preparation plant. From a practical viewpoint, alkali volcanic ashes may be significantly enriched in rare earth elements, Y, Nb, Ta, Zr, Hf, and Ga, which have potential economic significance. This paper reviews the distribution, geochemical and mineralogical compositions, and the significance and applications of volcanic ashes in coal and coal-bearing sequences.
► There are many coal deposits worldwide with high content Ge, Ga, Se, Li, and REY. ► The rare metals are concentrated both coals and host- and basement-rocks. ► Genesis of the metal accumulations ...and their mode of occurrence may be different. ► Recovery of the metals from coal deposits is new way for clean energy development.
This paper presents data on widespread abnormal accumulations in coal deposits of some rare metal(loid)s (Ge, Ga, Se, Li and REE+Y), which play a key role in energy-efficient technologies and alternative power development. It is shown that enrichment of these metal(loid)s may occur in coal seams in host- and basement-rocks of coal basins at comparable concentrations to those in conventional ores. Genesis of high concentrations of the rare metal(loid)s and their modes of occurrence in coal basins are reviewed. Moreover, utilization prospects of these metal(loid)s as byproduct coal deposits are evaluated. The extraction of these metal(loid) resources during coal exploitation and utilization would not only increase beneficial use of coal deposits themselves but also promote humanity’s further movement on the “green road”.
Toxic elements arsenic and selenium in coal are of great concern mainly because of their adverse effects on human health during coal combustion. This paper describes the concentration determination ...of As and Se in coal and coal combustion products (CCPs), performed by collision/reaction cell technology (CCT) of inductively coupled plasma mass spectrometry (ICP-MS; collectively ICP-CCT-MS) after closed vessel microwave digestion. The reagents for 50-mg coal sample digestion are 2-ml 40% (v/v) HF and 5-ml 65% (v/v) HNO3 but for the CCP samples, the reagents include 5-ml 40% HF and 2-ml 65% HNO3. To significantly diminish the argon-based interferences at mass to charge ratios (m/z) 75 (40Ar35Cl) and 78 (40Ar38Ar), a helium and hydrogen mixture was used in the optimized hexapole collision cell. The results showed that CCT technology can effectively diminish the spectral interferences of the Ar-based polyatomic ions 40Ar35Cl and 40Ar38Ar to 75As and 78Se, respectively. The method detection limit of As and Se is 0.024 and 0.095μg/l, respectively, and their linearity of the calibration curves in the range 0–100μg/l has a determination coefficient r2>0.9999. The determination of As and Se in NIST standard reference materials of coal and fly ash samples showed that ICP-CCT-MS plus closed vessel microwave digestion is a reliable method for concentration determination of the two elements in coal and CCPs.
This paper reports the mineralogical and geochemical compositions of the Late Permian C2 and C3 coals (both medium volatile bituminous coal) from the Xinde Mine, near Xuanwei in eastern Yunnan, which ...is located close to the area with the highest female lung cancer mortality in China. The two coals are characterized by high ash yields and low sulfur contents. Three factors, including sediment-source region, multi-stage volcanic ash generation, and multi-stage hydrothermal fluid injections, were responsible for variations in the geochemical and mineralogical compositions of the Xinde coals.
Trace elements, including V, Sc, Co, Ni, Cu, Zn, Se, Zr, Nb, Hf, and Ta, are enriched in the coals and were mainly derived from the sediment-source Kangdian Upland region. Major minerals in the samples of coal, roof, floor and non-coal sediment partings include quartz, kaolinite, and chamosite, as well as interstratified illite/smectite and anatase. Chamosite in the coal was derived from reactions between kaolinite and Fe–Mg-rich hydrothermal fluids. However, chamosite in the roof strata was directly precipitated from Fe–Mg-rich hydrothermal fluids or was derived from the alteration of precursor minerals (e.g., biotite) by hydrothermal fluids. Quartz in some samples is very high, especially in the roof strata of the C2 and C3 coal. Such high quartz, along with minor minerals including pyrite, chalcopyrite, sphalerite, calcite, celestite, vanadinite, barite, clausthalite and silicorhabdophane, were derived from multi-stage hydrothermal fluids.
The floors of both the C2 and C3 coal seams are fully-argillized fine-grained tuffaceous claystone and the immediate roof of the C2 coal is argillized coarse-grained tuff. The original materials of the floors and roofs of these coal seams were high-Ti alkali basaltic volcanic ashes, as indicated by high TiO2, Nb, and siderophile elements, and the distribution patterns of rare earth elements.
Two intra-seam tonstein layers in the C3 coal were identified based on their lateral persistence, mineralogical mode of occurrence and composition, as well as their elemental composition. The tonsteins are dominated by kaolinite, with minor quartz and possibly mixed-layer illite/smectite. Both tonsteins were derived from dacitic magma. The ratios of Nb/Ta, Zr/Hf, and U/Th are much lower in tonsteins than in the adjacent coal benches, which is attributed to the hydrothermal leaching.
•Most elevated elements in Xinde Coals were derived from Kangdian Upland.•Chamosite and quartz in the coal are mainly of hydrothermal origin.•The roof and floor of the coal are argillized high-Ti alkali basaltic volcanic ashes.•Two intra-seam tonsteins were derived from dacitic magma.
This paper reports the geochemical and mineralogical compositions of the Late Permian No. 25 Coal (semi-anthracite) and its host rocks (roof and floor strata) from the Guxu (Gulin–Xuyong) Coalfield, ...Sichuan Province, China. The coal is characterized by medium-sulfur content (average 2.73%) and has an average ash yield of 20.95%. In contrast to other Late Permian coals from southwestern China that are enriched in Sc, V, Cr, Co, Ni, and Cu, the No. 25 coal does not contain an abundance of these transition elements but is rich in lithophile elements Be, Y, Nb, Zr, Hf, and U. The elevated concentrations of trace elements in the No. 25 Coal were probably derived from the felsic–intermediate rocks at the top of the Emeishan basalt sequence, rather than from the Emeishan mafic basalts.
The floor strata of the No. 25 Coal can be divided into two sub-sections. The upper sub-section of the sequence immediately below the No. 25 Coal consists of material with a felsic–intermediate composition probably derived from terrigenous sources and the lower sub-section is composed of mafic tuff. The terrigenous mineral matter in the No. 25 coal appears to have the same sediment-source region as the upper sub-section of the floor strata, based on their similar geochemical compositions. The roof strata of the No. 25 Coal are more quartzose, and were probably derived from a different sediment-source region. The mineral matter in the coal is dominated by kaolinite and, to a lesser extent, calcite and pyrite; the roof and floor strata each have quite different mineralogy, with kaolinite dominant in the latter and illite, kaolinite and quartz in the former; pyrite contents are variable both in the coal and in the host rocks. The floor strata and the coal have been affected by hydrothermal solutions, leading to the enrichment of rare earth elements and yttrium (REY), Nb, Ta, Zr, Hf, and U. The REY in the coal and floor strata, as well as the Nb, Ta, Zr, Hf, and U in the floor strata, represent potentially economic rare metal resources.
•Lithophile elements Be, Y, Nb, Zr, Hf, and U are enriched in the Guxu coal.•The terrigenous-source rocks for the coal are mainly of felsic–intermediate composition.•The lower part of the floor strata are a mafic tuff.•The terrigenous-source region for the upper part of the floor rock has a felsic–intermediate composition.•The coal and the floor strata are potential sources of rare metals.
Europium (Eu) in coal, coal combustion residues (e.g., fly ash), and sedimentary rocks in coal-bearing sequences has attracted much attention in recent years mainly because of its world-wide demand ...and use as a geochemical indicator of geological setting for coal deposit studies. This paper presents a method for accurately measuring the concentration of Eu in coal, fly ash, and sedimentary rocks by quadrupole-based inductively coupled plasma mass spectrometry (ICP-MS), plus the use of closed-vessel microwave digestion and a cation exchange resin. To significantly diminish the inference of Ba-based polyatomic ions (137Ba16O, 136Ba17O, 135Ba18O, and 134Ba18OH) on 153Eu in coal, fly ash, and sedimentary rock samples, a Bio-Rad AG50W-x8 cation exchange resin was used to separate Ba from digested solutions of solid samples. The AG50W-x8 cation exchange resin can effectively separate the barium from digested solutions and thus could diminish the inference of Ba on Eu. The determination of Ba and Eu in the National Institute of Standards Technology (NIST) standard references of coal and fly ash samples showed that the use of the AG50W-x8 cation exchange resin combined with quadrupole-based ICP-MS analysis can provide a reliable method for the accurate determination of Eu concentrations in coal and coal-related samples. The method detection limits for Ba and Eu are 0.030 μg/l and 0.006 μg/l, respectively, and the determination coefficient of their calibration curves (linearity range 0–100 μg/l) is >0.9999. A Ba/Eu value of 1000 in the samples is proposed for judging the interference of Ba on Eu. If Ba/Eu > 1000, then Ba in coal, fly ash, and sedimentary rocks significantly interferes with Eu and this interference then needs to be considered when interpreting the analytical results and their significance.
•Barium would interfere Eu using quadrupole-based ICP-MS for coal and coal-related materials.•The AG50W-x8 cation exchange resin can effectively separate the barium from Eu from digested solutions.•A method for accurately determining Eu concentrations was designed.•A Ba/Eu value of 1000 in the samples is proposed for judging the interference of Ba on Eu.
The Late Permian coals from the Huayingshan Coalfield of southwestern China are significantly enriched in Zr (695μg/g), Nb (75.9μg/g), Se (6.99μg/g), Hf (10.1μg/g), and rare earth elements and Y ...(1423μg/g). Previous studies showed that the sediment-source region for these coals was the Kangdian Upland, which was formed at an early stage of the late Permian Period. The source rocks have a basalt composition, and those studies attributed the enrichment of the above high field strength elements (HFSEs) to derivation from the Kangdian Upland.
Geochemical and mineralogical data presented in this study show that the dominant sediment-source regions for the coal and roof strata of the Huayingshan Coalfields are the Dabashan Uplift, Hannan Upland, and Leshan–Longnvsi Uplift. The highly-elevated concentrations of HFSEs in the coals are due to hydrothermal fluids. Three tonstein layers derived from alkali rhyolite were identified. These tonsteins are characterized by highly-enriched HFSEs and by strong negative Eu anomalies in the rare earth element distribution patterns.
The major carriers of the rare earth elements in the coal are rhabdophane and silicorhabdophane, the latter of which is also enriched in Zr. Zirconium, however, mainly occurs in zircon. Rhabdophane and silicorhabdophane in the coal are mainly distributed along the bedding planes and occur as cell-fillings. Zircon in the coal occurs as cell-fillings and is of authigenic origin. Anatase in the partings and coals contains Nb, and occurs as fracture-filling and colloidal forms. The modes of occurrence of the above minerals indicate that they were derived from hydrothermal fluids. Mercury and Se mainly occur in sulfide minerals (pyrite and marcasite).
•The dominant sediment-source region for the coal is not the Kangdian Upland.•The highly-elevated HFSEs contents in the coals are due to hydrothermal fluids.•Three tonstein layers derived from alkali rhyolite were identified•Rare earth elements mainly occur in rhabdophane and silicorhabdophane.•Zircon and anatase in the coals are mainly of authigenic origin.
The fly ashes derived from three giant coal-hosted Ge deposits, Lincang (Yunnan of southwestern China), Wulantuga (Inner Mongolia of northern China), and Spetzugli (Primorye, Russian Far East), are ...unique because they are highly enriched in elements, including up to (on an organic-free basis): 4.66% Ge, 2.12% As, 1.56% F, 1.22% Sb, 0.56% W, 0.56% Zn, 0.55% Pb, 0.13% Sn, 0.12% Ga, 0.056% Bi, 0.04% Be, 0.028% Cs, 0.017% Tl, and 0.016% Hg. These high element concentrations in the fly ashes are due both to their high levels in the raw coals from which they were derived and their high volatility during the coal combustion process.
Rare earth elements and yttrium (REY) were fractionated during coal combustion. They are more enriched in fly ashes than in slag from the respective coals. Maximum REY enrichment may occur either in fine-grained fly ash from baghouse filters or in coarse-grained fly ash from electrostatic precipitators. Cerium and Eu are more enriched in the fly ashes than other REY, and yttrium is relatively depleted in the fly ashes in comparison with the slag.
Three types of unburnt carbon can be identified in the fly ashes: (1) carbon with well-preserved initial maceral structures (fusinite and secretinite), (2) isotropic and anisotropic carbon, and (3) secondary fine-grained carbon. The last type of unburnt carbon is characterized by embedded fine-grained Ge-bearing and other mineral phases.
Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes. Other Ge-bearing mineral phases, however, were also identified, including glass, Ca ferrites, solid solutions of Ge in SiO2, and probably elemental Ge or Ge (Ge-W) carbide, as well as previously-unknown complex oxides including (Ge,As)Ox, (Ge,As,Sb)Ox, (Ge,As,W)Ox, and (Ge,W)Ox. Some portion of the Ge occurs as adsorbed species in different types of unburnt carbon (Types 1 and 2) in the ash particles.
•The Ge-rich fly ashes are highly enriched in Ge and toxic trace elements.•Three types of unburnt carbon can be identified in the fly ashes.•Rare earth elements and yttrium (REY) were fractionated during coal combustion.•Ge oxides (e.g., GeO2) are the major Ge carrier in the fly ashes.•Other Ge-bearing mineral phases in the fly ash were also identified.
This article addresses the fundamental difference between coal rank and coal type. While theoretically settled long ago as being different aspects of coal systems science, the two concepts are still ...often confounded. In recent years, this has resulted in the publication of several works stating that coal type changes with coal rank. Coal type refers solely to coals' depositional origin and the maceral–mineral admixture resulting from that origin. Coal types typically fall in to two categories: humic coals, developed from peat, and sapropelic coals, developed from organic mud. Either type may be allocthonous or autochthonous, and within types, further refinement of depositional environment can be made. Coal rank refers to the changes in geochemistry and resultant changes in reflectance caused by increasing thermal maturity of the coal. Thus, it provides an overprint of maturity on existing coal types. With proper techniques, such as use of crossed polars and etching, maceral forms can be differentiated even at high ranks, and the original coal type determined.
•Coal type & coal rank are fundamental aspects of coal systems science.•Coal type is a result of climate, topography & nutrient availability.•Coal rank is a function of thermal and pressure history.•Rank is an overprint on coal type, but does not change type.
