Seam Section Research Articles

In-situ inorganic analysis of coal seams using a hand-held field-portable XRF Analyser

The major inorganic elements in cores of coal and associated non-coal materials, ranging up to 7.6 m in length, as well as in large, naturally-broken coal blocks, have been measured using a hand-held, field-portable energy-dispersive X-ray fluorescence (fp-XRF) analyser, to evaluate the potential of such technology in quality assessment of coal seams for exploration and mine geology programs. Calibration against a suite of independently-analysed coals was used to provide element-specific user factors, which were incorporated into the individual fp-XRF analyses to obtain data on the percentages of Si, Al, K, Ca, Fe, Ti and S, and in some cases Mg and P, at each measurement point. With the exception of (total) S, these values were then recalculated as percentages of the relevant oxides, and combined to provide an estimate of the expected ash yield from the materials concerned. Profiles were prepared illustrating the variation in the different components through seam sections in three different drill cores, based on measurement of points at a 10 mm spacing. Samples of selected core intervals were analysed by conventional techniques, and the ash yield, total sulphur and individual oxide percentages compared to those indicated for the same intervals by the fp-XRF data. Although difficulties were encountered due to precipitated salts and anomalous element concentrations on or near some core surfaces, the results have shown a general level of agreement for the different coal and non-coal materials involved. While the accuracy is not as high as that from conventional methods, the fp-XRF data allow the materials in cores and exposed coal faces to be categorised to an extent that is of value for many research and industry applications.

Depositional environments of the Jurassic Maghara main coal seam in north central Sinai, Egypt

Twenty-eight channel samples with a cumulative thickness of about 4 m collected from three sections of the Maghara main coal seam in the middle Jurassic Safa Formation have been studied for their lithotype and maceral compositions to reconstruct the character of peat swamp, its hydrological regime and the predominating type of vegetation. Lithotype composition is a combination of dully lithotypes with duroclarain (19% of total cumulative thickness), clarodurain (15%), black durain (15%), and shaly coal (15%) and bright lithotypes represented by clarain (23%), vitrain (12%) and a small proportion of wild fire-generated fusain (1%). Maceral analyses revealed the dominance of vitrinite (70.6% on average), followed by liptinite (25.2%) and inertinite (8.1%). Mineral matter content is ∼9% on average and consists of clay, quartz and pyrite concentrate mostly at the base and the roof of the seam. Dominantly vitrinite composition of coal and extremely low fire- and oxidation-borne inertinite content, together with high Gelification Indices imply predomination of waterlogged anoxic conditions in the precursing mire with water tables mostly above the peat surface throughout most of the time during peat swamp formation. Increases in collotelinite contents and Tissue Preservation Index up the section, followed by a reversal trend in upper third of the coal section, further accompanied by a reversal trend in collodetrinite, liptodetrinite, alginite, sporinite and clay contents records a transition from dominately limnotelmatic and limnic at the lower part to dominately limnotelmatic with increase telmatic condition achieved in the middle part of coal. At the upper part of coal seam an opposite trend marks the return to limnic and limnotelmatic conditions in the final phases of peat swamp history and its subsequent inundation. The proportion of arborescent (mostly coniferous) and herbaceous vegetation varied throughout the section of the coal with tendency of increasing density of arborescent vegetation to the middle part of the coal seam section. The intercalation of coal in shallow marine strata implies that peat swamp precursor formed in a coastal setting, probably on delta plain or lagoon. Its formation was controlled by water table changes driven by sea level fluctuations that created an accommodation space necessary for preservation of peat.

Rockburst hazard assessment based on seismic tomography and analytical modelling - a case study

In accordance with the formal regulations currently in force in Poland, the criteria for rockburst hazard assessment with respect to coal deposits include the records of seismic events and their impacts, de-stressing of the entire seam or its parts and expert opinions of mine operation engineers. Effectiveness of the de-stressing can be verified by geophysical test data whilst the expert opinions are mostly based on mathematical modelling using specialist software or dedicated simulation algorithms. This study collates and synthesises the results of tests carried out in a seam section in a colliery within the Upper Silesia Coal Basin, obtained by the outlined methods. Geophysical survey results are interpreted basing on seismic tomography procedures utilising the geo-tomography techniques for velocity field reconstruction in data processing. For comparison, the stress state modelling data are provided, based on conventional engineering solutions applicable to mechanics of deformable media. The actual assessment of the rockburst threat level is based on observations of distributions of the longitudinal wave velocity in relation to the actual value of the vertical component of stress concentration within the coal seam.

Coal Facies Characteristics and Coal Formation Mechanism of No. 38 Coal Seam in Cuipingshan Coal Mine

No. 38 coal seam is the main coal seam in Cuipingshan Coal Mine. In order to reveal its coal-forming mechanism, the microlithologic types of No. 38 coal seam in Cuipingshan Coal Mine are analyzed by using modern testing methods such as sequence stratigraphy, coal petrology and geochemistry. We find that the maceral of No. 38 coal seam is mainly vitrinite, the average content is respectively 57.28%, the vitrinite is mainly telinite and desmocollinite, and the microlithotypes is semi-bright coal. The coal facies of the No. 38 coal seam include tidal flat-tidal channel wet forest swamp facies, shoreland lacustrine wet forest swamp facies and barrier island-lagoon low swamp facies. The formation background of coal seam is an environment of shoreland lacustrine facies, barrier island~lagoonfacies and tidal flat-tidal channel swamp facies, etc., which are sea-land transitional facies. The shoreland lacustrine wet forest swamp facies and barrier island-lagoon low swamp facies are the main coal facies types of the No. 38 coal facies in the region of interest and are distributed throughout the whole coal seam section. This indicates that it always predominated in the evolutionary process of swamp. The tidal flat-tidal channel wet forest swamp facies also accounted for a certain proportion in the formation process of coal seam, and constitutes periodic cycle structure with the shoreland lacustrine wet forest swamp facies and barrier island-lagoon low swamp facies. Generally the coal formation mechanism of No. 38 coal seam is a regressive swamp development process, and its coal formation environment is tidal flat-tidal channel swamp and shoreland lacustrine swamp. Besides, the development process of peat swamp is influenced by the frequent advance and retreat of secondary seawater.

Geochemistry of Mercury in the Permian Tectonically Deformed Coals from Peigou Mine, Xinmi Coalfield, China

AbstractAs the mercury emitted from coal combustion can lead to serious environmental issues, researchers pay more attention to the content, distribution and occurrence of mercury in coal. In this paper, the content, distribution, and occurrence of mercury in the Permian tectonically deformed coals from Peigou Mine, Xinmi coalfield, Henan Province were investigated. A total of 18 bench samples were taken from No.2‐1 coals seam in Peigou Mine, including 15 coal bench samples, two roofs and one floor. The mercury concentration, mineral composition, and main inorganic element content of 18 samples were determined by DMA‐80 direct mercury analyzer, XRD, and XRF respectively. The results show that the mercury content ranges from 0.047 ppm to 0.643 ppm, with an average of 0.244 ppm. Though the coal seam has turned into typical tectonically deformed coal by the strong tectonic destruction and plastic deformation, the vertical distribution of mercury has remarkable heterogeneity in coal seam section. By the analysis of correlation between mercury and the main inorganic elements and the mineral composition in coal, we infer that majority of mercury mainly relates to pyrite or kaolinite.

Meso- and microporosity of the subbituminous kM2 coal seam (Soma, Turkey) and its relationship with coal characteristics

This study focuses on meso- and microporosity of the subbituminous kM2 coal seam and its relation to coal characteristics. The coal seam is being mined in an underground coal mine at the Eynez sector in the Soma Basin (Western Turkey). The analysed coal samples are characterized by low moisture (avg. 8.2%, on air-dry basis) and total S content (avg. 1.5%, on dry basis), and moderate ash yield (avg. 26.1%, on dry basis). The predominant maceral group is huminite, in which telohuminite is the dominant maceral subgroup (up to 57.1vol.%, on whole-coal basis), whereas liptinite and inertinite maceral groups occur in low but variable proportions. Mineralogically, the samples are composed of quartz, clay minerals (kaolinite and illite), carbonates, pyrite, and rarely feldspars and gypsum. Statistical and SEM-EDX analyses indicate that the majority of elements have inorganic affinity, particularly the aluminosilicate minerals. The specific surface area and volume of mesopores, and average mesopore size determined by low pressure N2 adsorption, range widely throughout the studied seam section. Micropore characteristics, analysed by low-pressure CO2 adsorption, demonstrate that micropores are abundant, and specific surface area and volume of micropores vary widely. Surface area and volume of mesopores are slightly higher in the lower part of the seam, whereas the opposite was observed for surface area and volume of microspores. These trends may imply that hydrostatic pressure has little impact upon mesopore characteristics, although increased ash yields in the lower part of the seam suggest that minerals are the major contributor of coal mesopores. Furthermore, total C contents and huminite macerals, particularly telohuminite, display positive correlations with micropore characteristics. Thus, the variations in the microporosity are mainly correlated with the proportion of organic matter (macerals) in the analysed samples. The contents of aluminosilicate-affiliated elements display moderate to strong positive correlations with surface area and volume of mesopores, and total S and B contents display weak positive correlations with surface area and volume of micropores. The element B likely precipitated from porewater or intra-seam solutions during coalification and was absorbed by macerals having abundant microporosity. The abundance of micropores along with frequent disseminated pyrite crystals within the reactive macerals (telohuminite group) and higher total S contents in the upper parts of the seam could increase the risk of self-heating. Therefore, care should be taken to use caution when mining the upper part of the seam.

Coal characteristics, palynology, and palaeoenvironmental interpretation of the Yeniköy coal of Late Oligocene age in the Thrace Basin (NW Turkey)

The Yeniköy coal field is located in a narrow area between the Black Sea coast and the Istranca (Standrja) Mountain in the Thrace Basin. The aims of this study are to characterize coal petrographical, mineralogical, palynological, geochemical, and sedimentological properties of the Yeniköy coal deposit and to reconstruct palaeoenvironmental conditions during peat accumulation. A total of 9 coal samples collected from the coal seam section are almost entirely composed of xylite-rich lithotype, and are characterized by low ash yield (7.9–21.1%, average 13.6%; on dry basis) and high total S contents (1.0–3.7%, average 2.2%; on dry basis). The macroscopic features, maceral composition, and coal facies suggest that the peat was accumulated under mesotrophic anoxic conditions, and the peat-forming vegetation consisted mainly of arboreal species (e.g. Cupressaceae, Ulmus, Carya, Zelkova, Alnus, Pterocarya and Quercus). The low HI values of the analysed samples are presumably related to presence of xylite-rich lithotype rather than the dominance of herbaceous plant and/or low preservation of organic matter in the palaeomire. Even though, relatively B-enrichments, high total S contents, and weak anomalies of some REY (e.g. Y, Ce, and Gd) in the analysed samples could refer possible sea water influence into palaeomire in the study area during Late Oligocene; the sedimentological and palynological (freshwater algaes: Pediastrum, Spirogyra, and Mougeotia) data that indicate the palaeomire was located within a delta plain environment where small freshwater lakes and/or ponds developed. The statistical analysis and SEM-EDX data show the vast majority of elements in the analysed coal samples have inorganic affinity. The major elements Al, K, and enriched elements like B, V, Cr, Hg, and U seem to be affiliated with aluminosilicate minerals, whereas Fe, Ni, and As have probably sulphide affinity. The detrital presences of apatite crystals as detected by SEM-EDX analysis indicate that REY have mainly phosphate affinity in the analysed samples. Vertical distributions of the elements and ash yields suggest that the detrital input ratio was changeable and controlled some elemental enrichment during peat accumulation. These variations could be related to development of and fluvial conditions in the study area which interrupted peat-accumulation several times during Late Oligocene.

The use of coal cuttings from underground boreholes to determine gas content of coal with direct desorption method

In underground coal mining operations, gas content in a coal seam is used to assess the risk of coal and gas outbursts. A broadly standard procedure has been adopted to estimate the gas content with coal core in the coal mining industry. In soft or friable or geologically complex sections of coal seams, it has proven to be extremely troublesome in taking coal cores as cores can be severely fragmented or sometimes it is simply impossible to core with conventional coring methods due to poor borehole stability, leaving coal cuttings from boreholes as the only practical alternative for sampling. When coal core is replaced with coal cuttings, concerns have been raised about the validity and accuracy of the procedure used for gas content determination with coal core, in particular with respect to the sampling method of coal cuttings and gas content calculation due to faster initial gas desorption rates of coal cuttings. The standard procedure for gas content determination with coal core has been modified to determine gas content of coal with coal cuttings from underground boreholes. This paper describes the modified method and presents and discusses the results when it was trialed in a soft coal seam at Huainan, China.

Distribution of As, Hg and other trace elements in different size and density fractions of the Reshuihe high-sulfur coal, Yunnan Province, China

A Lopingian coal from the Reshuihe Mine in southwestern China contains high pyritic sulfur (5.2%) and trace elements including As (10.8μg/g), Hg (0.81μg/g), V (98.9μg/g), Co (15.7μg/g), Cu (47.5μg/g), Se (4.8μg/g) and Th (7.2μg/g). The variation of trace elements in coal samples of different size and density were investigated. The results showed that the vertical variation of As and Hg through the seam section is the result of hydrothermal activity. Arsenic and Hg are highly concentrated in coal layers far from the parting, roof and floor in vertical section. For example, the highest concentrations of As (44.3μg/g) and Hg (2.8μg/g) occur in ply 6, which is 40-cm vertically away from partings. Elements As, Hg, Co, Ni, Se, Sb and Tl occur mainly in pyrite; Be, F, Cs, Th and U are evenly distributed in clay minerals and organic components; V and Cr mainly occur in the organic portions of the coal. The As and Hg content generally increases with greater particle size and density, with content in the light fractions as low as 1.1 and 0.14μg/g, respectively, and as high as 75.8 and 3.8μg/g, respectively, in heavy fractions. Co, Ni, Se, Sb and Tl exhibit similar density dependence. Vanadium and Cr are more concentrated in lower-density fractions.The genetic type and mode of occurrence of elements in coal both exert a great impact on their removability; epigenetic and coarse minerals may be readily liberated by gravity separation. Elements associated with pyrite (e.g., As, Hg, Co, Ni, Cu, Se, Sb and Tl) demonstrate high removability; F, Th, U, V and Cr, which mainly occur in clay minerals and/or organic components of the coal, show a relatively low removability. Trace elements in particle size fractions 6–13mm and <0.5mm are most easily removed by gravity separation. In order to fully remove toxic elements from coal, it is suggested fractions with particle sizes of 3–6mm and 0.5–3mm be reduced in size to <0.5mm prior to gravity separation.

Geochemistry of Trace Elements in Coals from the Yueliangtian Mine, Western Guizhou, China: Abundances, Modes of Occurrence, and Potential Industrial Utilization

This paper reports the geochemical compositions of coals and non-coal samples from a complete seam section in the Late Permian Longtan Formation from the Yueliangtian mine, western Guizhou, southwestern China. The abundances, modes of occurrence, and origin of elements and minerals in the Yueliangtian coal were investigated using optical microscopy, scanning electron microscopy with an energy dispersive X-ray spectrometer, X-ray powder diffraction, X-ray fluorescence spectrometry, and inductively coupled plasma mass spectrometry. The host rocks (roof and floor) and one parting sample of the coal seam have high TiO2 contents, which is in accordance with the high TiO2 content in the Emeishan basalt from the Kangdian Upland. The coal bench samples are rich in SiO2 (14.52%, whole-coal basis) compared with the average for the common Chinese coals, and the high SiO2 present in this study is consistent with the abundant quartz, which was mainly precipitated from siliceous solutions produced by weathering of the ...

Assessment of aldosterone synthase (CYP11B2), mineralocorticoid receptor expression and markers of fetal cardiac gene reprogramming in rats exposed to fine particles

A Lopingian coal from the Reshuihe Mine in southwestern China contains high pyritic sulfur (5.2%) and trace elements including As (10.8 μg/g), Hg (0.81 μg/g), V (98.9 μg/g), Co (15.7 μg/g), Cu (47.5 μg/g), Se (4.8 μg/g) and Th (7.2 μg/g). The variation of trace elements in coal samples of different size and density were investigated. The results showed that the vertical variation of As and Hg through the seam section is the result of hydrothermal activity. Arsenic and Hg are highly concentrated in coal layers far from the parting, roof and floor in vertical section. For example, the highest concentrations of As (44.3 μg/g) and Hg (2.8 μg/g) occur in ply 6, which is 40-cm vertically away from partings. Elements As, Hg, Co, Ni, Se, Sb and Tl occur mainly in pyrite; Be, F, Cs, Th and U are evenly distributed in clay minerals and organic components; V and Cr mainly occur in the organic portions of the coal. The As and Hg content generally increases with greater particle size and density, with content in the light fractions as low as 1.1 and 0.14 μg/g, respectively, and as high as 75.8 and 3.8 μg/g, respectively, in heavy fractions. Co, Ni, Se, Sb and Tl exhibit similar density dependence. Vanadium and Cr are more concentrated in lower-density fractions.The genetic type and mode of occurrence of elements in coal both exert a great impact on their removability; epigenetic and coarse minerals may be readily liberated by gravity separation. Elements associated with pyrite (e.g., As, Hg, Co, Ni, Cu, Se, Sb and Tl) demonstrate high removability; F, Th, U, V and Cr, which mainly occur in clay minerals and/or organic components of the coal, show a relatively low removability. Trace elements in particle size fractions 6–13 mm and < 0.5 mm are most easily removed by gravity separation. In order to fully remove toxic elements from coal, it is suggested fractions with particle sizes of 3–6 mm and 0.5–3 mm be reduced in size to < 0.5 mm prior to gravity separation.

Distribution of mineral species in different coal seams of Talcher coalfield and its transformation behavior at varying temperatures

Mineral phase characterization and thorough understanding of its transformation behavior during combustion are imperative to know the potential utilization of coal in the thermal industries. The primary objective of this work is to analyze the quality of Indian Coals and obtain their mineral species-specific information at different depths. The samples were obtained from Talcher Coalfield, Odisha, India. Coal from four seam sections in the Talcher coalfield, India are mainly high ash coal (>50 %) and volatile matter deceases along with the seam depth. XRD results show that the major mineral phases present in the coal are quartz and kaolinite. Siderite, illite, and anatase were found in minor quantities. It has been observed that the clay minerals (kaolinite, silimanite, illite) decompose at higher temperature and traces of dolomite, mullite, hematite etc. are formed during the process of combustion. Among the four seams (M2, M12, M24 and M43) studied, ash of M43 has high Al2O3%, TiO2% and K2O% content and low SiO2%, CaO% and MgO% content. High acid-to-base ratios contributed to high ash fusion temperatures (IDT > 1500 °C) and low slagging potential of the coals studied. Relatively low fouling index (<0.3) was estimated for all the coal seams studied. Furthermore, thermodynamic modeling software, FactSage, have been used to envision the mineral phase transformations that take place between 800 and 1500 °C during coal combustion.

Thermomechanical analysis of the formation of hot cracks in remote laser welded aluminium fillet welds

Remote laser welding of high strength aluminum alloys is still a field of extensive research due to the hot cracking phenomena. Recent research activities have been focused on center-line hot cracks in welds that are located close to the edge of the material. To avoid this type of crack from occurring, a fillet weld joint design could be utilized. However, within the fillet welds there are still transverse hot cracks present on a microscopic scale. This paper presents a thermomechanical analysis of the formation of transverse hot cracks in EN AW-6082 alloy fillet welds. In order to calculate the local deformation near the mush zone, a welding simulation based on the finite element method was created. The simulation was able to depict different settings for the welding speed, laser power, beam position, protruding length of the lower sheet, and the sheet thickness. For this purpose, an automated method for heat source calibration was developed based on image processing of polish of cross sections of different weld seams. As a result, it was possible to investigate the influencing factors on the formation of local strain and strain rate during the hot crack sensitive temperature range. It was found that the welding speed and laser power significantly increased the strain rate, but had no effect on the strain. In addition, it was determined that the position of the laser beam caused a major difference in the formation of strain and strain rate if weld seams changed from partial penetration to full penetration. Full penetration welds had lower strain and strain rate. The protruding length of the lower sheet and the sheet thickness had a minor impact on strain and strain rate. By linking the computerized results of strain and strain rate with data obtained from experiments on the hot crack susceptibility, a hot cracking criteria based on strain rate was found.

Geochemistry of major and trace elements in Permian coal: with an emphasis on No. 8 coal seam of Zhuji coal mine, Huainan Coalfield, China

A better understanding on geochemistry of elements in coal has both environmental and geological implications. In this study, 53 coal samples were collected from No. 8 coal seam of the Zhuji coal mine, Huainan Coalfield. The concentrations of 49 elements, ash yield, and total organic compound (TOC), as well as mineralogical phases in coal were determined. As compared with Chinese, the USA, and world coals, Si, K, Se, Cd, Sn, Sb, and W in studied coal seam are higher, whereas Zn, As, and Lu are lower. The enrichment factor and concentration coefficient show that Se, Cd, Sn, Sb, and W are preferably enriched in studied coals. The enrichment of Se and Cd is probably attributed to their higher proportions of organic forms. Most major and trace elements tend to concentrate in either the upper or lower sections of coal seams, which suggest that depositional micro-environment was important in controlling elements migration and enrichment. The correlation analysis of elements with ash yield shows that the behavior of elements in coal follows the periodic change of metallic activity. The modes of occurrence of major and trace elements are elaborated by statistical methods. Silicon is mainly in form of montmorillonite or presents as free quartz. Iron is associated with chlorite, siderite, lepidocrocite, and other iron-bearing minerals. Ti shows obviously organic association. Three groups of elements are divided in accordance with the cluster dendrogram: Group 1 (Sc–HREE–Be–Y–V–Co–Cu–P–Sr–B–Sn–Se–Bi–TOC–S–Ba–As), Group 2 (LREE–Zn–Al–Mn–Li–Na–Th–Cr–Fe–Mg) and Group 3 (Ca–Mo–Si–W–Ad–Ti–Pb–K). Many trace elements, including Li, Sc, V, Cr, Zn, Sr, La, Ce, Nd, Sm, Eu, Gd, Tb, Lu, Pb, Bi, and Th, correlate positively with Al, suggesting their occurrence mainly in clay such as kaolinite and chlorite. REE in the studied coalfield was primarily supplied by terrestrial clastics coming from North China Coal Basin. The differentiation of LREE and HREE is probably attributable to their different physicochemical characterisitcs and specific paleo-sedimentary environment. Various indexes (e.g., B content, Ash Index, C-value) and the existence of certain minerals suggest a reducing and anoxic sedimentary environment of coal swamp with a stable supply of terrigenous detrital materials in a moist environment. The origins of enriched elements are primarily derived from the source rock, sedimentary environment, and thermally contact metamorphism or possibly magmatic–hydrothermal fluids.

Major and Trace Element Geochemistry of Coals and Intra-Seam Claystones from the Songzao Coalfield, SW China

Silicic, mafic and alkali intra-seam tonsteins have been known from SW China for a number of years. This paper reports on the geochemical compositions of coals and tonsteins from three seam sections of the Songzao Coalfield, SW China, and evaluates the geological factors responsible for the chemical characteristics of the coal seams, with emphasis on the influence from different types of volcanic ashes. The roof and floor samples of the Songzao coal seams mostly have high TiO2 contents, consistent with a high TiO2 content in the detrital sediment input from the source region, namely mafic basalts from the Kangdian Upland on the western margin of the coal basin. The coals from the Songzao Coalfield generally have high ash yields and are highly enriched in trace elements including Nb, Ta, Zr, Hf, rare earth elements (REE), Y, Hg and Se; some variation occurs among different seam sections due to input of geochemically different volcanic ash materials. The geochemistry of the Songzao coals has also been affected by the adjacent tonstein/K-bentonite bands. The relatively immobile elements that are enriched in the altered volcanic ashes also tend to be enriched in the adjacent coal plies, possibly due to leaching by groundwaters. The coals near the alkali tonstein bands in the Tonghua and Yuyang sections of the Songzao Coalfield are mostly high in Nb, Ta, Zr, Hf, Th, U, REE and Y. Coal samples overlying the mafic K-bentonite in the Tonghua section are high in V, Cr, Zn and Cu. The Datong coal, which has neither visible tonstein layers nor obvious volcanogenic minerals, has high TiO2, V, Cr, Ni, Cu and Zn concentrations in the intervals between the coal plies affected by mafic and alkaline volcanic ashes. This is consistent with the suggestion that a common source material was supplied to the coal basin, derived from the erosion of mafic basaltic rocks of the Kangdian Upland. Although the Songzao coal is generally a high-sulfur coal, most of the chalcophile trace elements show either poor or negative correlations with total iron sulfide contents. The absence of traditional pyrite-metal associations may reflect wide variations in the concentrations of these elements in individual pyrite/marcasite components, or simply poor retention of these elements in the pyrite/marcasite of the relevant coals.

The geochemistry and mineralogy of high-S coals, with examples mainly from the East Pennines Coalfield in Yorkshire and Nottinghamshire, UK: an overview

Over a number of years, coals have been analysed in the geochemical laboratories of the University of Sheffield. Much of this work has been published and this paper presents an overview and, in some cases, a reinterpretation of the data. Most of the coal samples were obtained from seam sections in the Yorkshire and Nottinghamshire coalfields (now included in the East Pennines Coalfield), and from the Parkgate Coal in particular. Sulphur variations are essentially due to pyrite. In individual plies of the seam, lateral variation in total sulphur is thought to be due to the availability of sulphate at the time of deposition. Access of sulphate into the coal swamp environment can be directly related to river channels, many of which are known to have been long-lived features. The pyrite is of concern because of S emissions, but in addition it is the location in the coal for Hg, Tl, Pb, As and Se, all of which are of major environmental concern. Concentrations were determined by direct and indirect methods. The most common of the latter methods is statistical, and some of the potential problems are reviewed. Also contained within pyrite, but not exclusively so, are Cd, Ni and Sb. Trace element concentrations from different pyrite samples are similar, strongly suggesting a common source. Comparable trace element enrichment patterns for coals and marine shales provide evidence of a seawater origin. The chloride concentration in the coals is high and can also be linked to seawater. The two elements, S and Cl, differ in that Cl is conservative, is not involved in diagenetic reactions and is retained in the coal in residual pore fluids. Illite and kaolinite are the main clay minerals present, with subsidiary chlorite and mixed-layer illite-smectite. In most coals, the clay minerals are dominantly detrital, but in low ash coals, kaolinite of diagenetic origin can be detected. In some samples from the Barnsley Coal, the source of this kaolinite, based on the trace element geochemistry, is dispersed volcanic ash (basaltic). It is also highly likely that organic matter contributes small amounts of Si and Al in the coal, and phytoliths are one potential source. However, the detrital sediment is a major contributor to the major and trace element geochemistry of the coals. Trace elements with a dominantly detrital origin are Rb, Cs, Cr, Ga, Th, Nb and Li. Trace elements are also associated with the organic matter to a greater or lesser extent. Germanium is mainly associated with organic matter, but V is also present in the clays. These elements are mainly contained in vitrinite, although Ge concentrations are more variable, suggesting some mobility during diagenesis. This is borne out by Ge, V and Be showing enrichment at the margins of the the Parkgate Coal, following ‘Zilbermints Law’. Mobility during diagenesis is also demonstrated by the mineral infill of the cleat (joints). Stages of cleat mineralization have been recognized and related to diagenetic stages in siliciclastic sequences. Although there is evidence of element mobility after deposition in the coals, this is not thought to be related to the mineralizing fluids in the Pennine Orefields.

Failure probability analysis of coal crushing induced by uncertainty of influential parameters under condition of in-situ reservoir

The uncertainties of some key influence factors on coal crushing, such as rock strength, pore pressure and magnitude and orientation of three principal stresses, can lead to the uncertainty of coal crushing and make it very difficult to predict coal crushing under the condition of in-situ reservoir. To account for the uncertainty involved in coal crushing, a deterministic prediction model of coal crushing under the condition of in-situ reservoir was established based on Hoek-Brown criterion. Through this model, key influence factors on coal crushing were selected as random variables and the corresponding probability density functions were determined by combining experiment data and Latin Hypercube method. Then, to analyze the uncertainty of coal crushing, the first-order second-moment method and the presented model were combined to address the failure probability involved in coal crushing analysis. Using the presented method, the failure probabilities of coal crushing were analyzed for WS5-5 well in Ningwu basin, China, and the relations between failure probability and the influence factors were furthermore discussed. The results show that the failure probabilities of WS5-5 CBM well vary from 0.6 to 1.0; moreover, for the coal seam section at depth of 784.3–785 m, the failure probabilities are equal to 1, which fit well with experiment results; the failure probability of coal crushing presents nonlinear growth relationships with the increase of principal stress difference and the decrease of uniaxial compressive strength.

Mineralogy and major-element geochemistry of the lower Permian Greta Seam, Sydney Basin, Australia

The mineralogy of the high-volatile bituminous coals and associated strata from the Greta seam, Sydney Basin, Australia, has been evaluated in this study. Although the seam is not immediately overlain by marine strata, percolation of marine water into the original peat bed is indicated by the petrological, mineralogical and geochemical characteristics, which resemble those of coals with marine roof strata. The upper and lower sections of the seam have contrasting mineralogy. Pyrite typically comprises 40 to 56 wt% of the mineral assemblage in the marine-influenced upper part of the seam section. The lower part contains much less pyrite (typically <5 wt%, organic-free basis), and also relatively abundant dawsonite (up to 14 wt%, organic-free basis). The minerals within most coal plies are largely of authigenic origin. These include pyrite, siderite, clay minerals (mainly kaolinite and Na-rich mixed-layer illite/smectite), and quartz, most of which have a relatively early, syngenetic origin. Minor Ti-bearing minerals, anatase or rutile, and phosphate minerals, fluorapatite and goyazite, were probably also formed during early diagenesis. Other minerals have features that indicate late-stage precipitation. These include abundant cleat- and fracture-filling dawsonite, which may be the result of reactions between earlier-precipitated kaolinite and Na2CO3- or NaHCO3-bearing fluids. Minor albite may also be epigenetic, possibly precipitated from the same Ca–Al bearing fluids that formed the dawsonite. The most abundant detrital minerals in the Greta coals are quartz, poorly ordered kaolinite, illite and mixed-layer illite/smectite (I/S). These occur mainly in the floor, roof and other epiclastic horizons of the seam, reflecting periods of greater clastic influx into those parts of the original peat-forming environment. Detrital minerals are rare in the coals away from the epiclastic horizons, probably owing to almost complete sediment bypassing in the depositional system. Alternatively, any detrital minerals that were originally present may have been leached from the peat bed by diagenetic or post-diagenetic processes.

Distribution and origin of minerals in high-rank coals of the South Walker Creek area, Bowen Basin, Australia

The coals of the South Walker Creek area in the northern Bowen Basin, with a vitrinite reflectance (Rvmax) of 1.7 to 1.95%, are among the highest rank coals currently mined in Australia. X-ray diffraction studies have identified an unusual mineral variation through the vertical sequence, with kaolinite-rich assemblages typical of other Australian coals at the top and bottom of the seam section and an illite–chlorite assemblage resembling a metamorphic association in the middle. Calcite and ankerite are also abundant in parts of the vertical sequence. Diaspore is abundant in the middle section of the seam in some areas, and paragonite, dickite or nacrite occurs in some locations as well.The distribution of the non-carbonate mineral assemblages cross-cuts the seam stratigraphy, and appears to be primarily controlled by faults and other structural features. Integration of the mineral distribution with optical and electron microscope data on the coal and non-coal bands, chemical data from coal ash analysis, and information from X-ray micro-tomography, suggests that the illite–chlorite and diaspore-bearing assemblages resulted from hydrothermal effects associated with fluid migration through the middle part of the coal seam. This is further confirmed by the development of metamorphic textures in a tonstein band, also altered to illite and chlorite, in the illite-rich part of the seam section, in contrast to a tonstein with more normal sedimentary textures and a kaolinite composition in the kaolinite-rich upper part of the seam.Detailed studies of cleat mineralisation suggest that fluids rich in Ca, Mg and Al were introduced relatively early in the seam's post-depositional history, associated with heat flow sufficient to alter the minerals in the coal and tonstein in the affected part of the seam section. The relatively uniform vitrinite reflectance profile observed through the seam section may indicate that the coal was already of high rank before the fluids were introduced, or that any localised heat effects on the organic matter associated with the changes in clay mineralogy were overprinted by subsequent wider-ranging rank advance processes.

Factors controlling geochemical and mineralogical compositions of coals preserved within marine carbonate successions: A case study from the Heshan Coalfield, southern China

The Late Permian coals in the Heshan Coalfield of southern China are preserved within marine carbonate successions and characterized by super-high organic sulfur (5.13–10.82%). Minerals identified in the coals include quartz, kaolinite, illite, mixed layer illite/smectite, albite, pyrite, marcasite, calcite, and dolomite, along with trace amounts of smectite, fluorite, strontianite, REY-bearing carbonate minerals, jarosite, and water-bearing Fe-oxysulfate. The coals are very rich in trace elements including F (up to 3362μg/g), V (up to 270μg/g), Se (up to 24.4μg/g), Mo (up to 142μg/g), U (up to 111μg/g), and, to a lesser extent, Sr, Y, Zr, Nb, Cd, Cs, heavy rare earth elements, Hf, Ta, W, Hg, and Th.Previous studies attributed the high organic sulfur and elevated trace elements to the seawater influence or the formation of soil horizons before the accumulation of peat in the basin. However, mineralogical and geochemical data presented in this study have shown that the sediment-source region and multi-stage hydrothermal fluids are the dominant influences on the mineralogical composition and elevated trace elements in the coal, although seawater influence also contributed to the composition of the mineral matter.For example, a large proportion of the quartz and clay minerals, as well as almost all the albite, in both the coal benches and the parting mudstones were derived from detrital materials of terrigenous origin in the Yunkai Upland. High concentrations of lithophile trace elements were also derived from the sediment source region. Minerals including fluorite, calcite, dolomite, strontianite, and REY-bearing carbonate minerals were derived from multi-stage hydrothermal activities. High concentrations of V, Mo, and U that occur through the coal seam sections were probably derived from hydrothermal solutions during peat accumulation or at the early diagenetic stages. The hydrothermal fluids also corroded the syngenetically-formed minerals (quartz, albite, and pyrite) and caused re-distribution of lithophile elements from partings to the underlying coal benches, resulting in higher key element ratios (Yb/La, Nb/Ta, and Zr/Hf) and more abundant heavy rare earth elements in the coal benches than in the immediately overlying partings.