Oxidation Rims Research Articles

Influence of thermal intrusion on the Alum Shale from south central Sweden

This study investigates the geochemical and petrological characteristics of solid bitumen in the DBH15/73 core from the Furongian (upper Cambrian) and Miaolingian (middle Cambrian) Alum Shale in Billingen, south central Sweden. At Billingen a > 30 m thick Permian diabase (dolerite sill) intruded approximately 100 m above the Alum Shale that promoting the formation of solid bitumen in the uppermost half of the Alum Shale due to enhanced heat flow. The bitumen has been classified into bituminite/diagenetic solid bitumen (DSB), initial-oil solid bitumen (IOSB), and primary-oil solid bitumen (POSB) based on their genesis, morphology and random solid bitumen reflectance (BRo). The Miaolingian shale, constituting the lower part of the Alum Shale, is immature and contains solely bituminite and DSB, with measured BRo ranging from 0.40% to 0.48%. In contrast, the Furongian shale exhibits enrichment in IOSB and POSB and range from marginally mature to peak oil generation with towards the top of the section. Characteristics of uneven heating is seen in the IOSB (BRo: 0.97–1.08%) including oxidation rims and abnormally high maturity surrounding fractures. The POSB (BRo: 0.63–2.01%) is present not only in the Alum Shale but also in the overlying Ordovician Latorp limestone and the underlying Kakeled Limestone Bed, and shows flow structures which is further evidence for migration. The abundance of POSB and IOSB is determined through maceral point counting, revealing POSB as the dominant bitumen type (1.54–7.13 vol%), while IOSB constitutes the minority (0.05–0.31 vol%) within the Furongian shale. This distribution suggests rapid thermal evolution of organic matter within the oil generation window. Additionally, a reduction in free hydrocarbons (Rock-Eval S1), potential hydrocarbons (Rock-Eval S2), and unexpectedly low Tmax was observed in the Furongian shale. Results indicate that hydrocarbon generation resulting from thermal intrusion contributes to the relatively low S2. Migration of POSB and generated oil to adjacent layers leads to the loss of S1, while the reduced Tmax may be attributed to high uranium content which weakens carbon chain bond energy. These anomalies result in an underestimation when evaluating thermal maturity and kerogen type conversion based on Rock Eval data alone.

Weathering alterations of coal mining wastes geochemistry, petrography, and mineralogy, a case study from the Janina and Marcel Coal Mines, Upper Silesian Coal Basin (Poland)

Weathering-caused alterations in coal mining waste geochemistry, petrography, and mineralogy occurring in the known time span of 1998–2018 in the temperate climate of Poland were investigated. A series of coal mining waste rocks representing two parts of the Upper Silesian Coal Basin (USCB), differing in coalification stage, i.e., corresponding to sub-bituminous and bituminous coals, have been selected to find how the level of organic matter conditionates the weathering. Differences in organic matter content, petrographic composition, rock mineralogy and inorganic geochemistry were also taken into account. Whereas organic petrography, including vitrinite reflectance values, do not show significant weathering signs, apart from irregular cracks and, in very rare cases, paler in color oxidation rims, organic geochemistry has been affected due to low-temperature secondary processes, including increased oxygen index values, particularly in less mature coal mining wastes. Biomarker distribution has been changed to the largest extent, with partial removal of n-alkanes possibly due to biodegradation of organic matter and water-washing of lighter polycyclic aromatic hydrocarbons, including alkyl naphthalenes. Organic matter of lower maturity in coal mining wastes from the USCB eastern part, as more reactive, showed a higher level of secondary transformations. Minerals formed during weathering due to time and storage on dumps were mainly oxidation products of iron sulphides: goethite and jarosite; however, most of the minerals have not been altered. Thus, despite physical changes in coal mining wastes, such as increased brittleness, decreasing fragment size and surface color change, there are only limited changes in inorganic chemistry and mineralogy. This indicates that low-temperature processes do not favour the inorganic elements release to the environment and points out that measures to prevent self-heating within the dumps are the most vital part of post-mining activity leading to the best scenario - slow low-temperature weathering of coal mining wastes.

Physicochemical Properties of Fe-Bearing Phases from Commercial Colombian Coal Ash

High amounts of coal combustion products, such as fly ash and bottom ash, are generated every year; however, only 64% are used, which means that a significant part is landfilled despite containing valuable materials such as ferrospheres, which may be used as catalysts, substituting critical raw materials (e.g., platinoids). In commercial coals, pyrite contents are reduced as a pre-combustion S-emissions control measure, so low amounts of ferrospheres are expected in the respective ashes. However, given the large amounts of ash being generated from these coals, it may provide a reliable source of catalysts, with ferrospheres being easily recovered via magnetic separation. Several studies have been conducted regarding these morphotypes; however, there is a lack of investigation considering the ash derived from highly beneficiated coals and the variations with location and time. In this study, bottom ash, economizer grits, and fly ash samples from a Portuguese power plant burning Colombian commercial coal were fractionated using ferrite (Fe-MC fraction) and Nd (Nd-MC fraction) magnets, and a multi-technique approach was used to assess their properties (magnetic parameters, particle size distribution, mineralogy, particle morphology, microtexture, and chemical composition). The Fe-MC presented higher Fe concentrations (up to 44 wt.% Fe2O4) than the Nd-MC (up to 7 wt.% Fe2O4). Once it was a sequential process, Nd magnets essentially collected Fe-bearing aluminosilicate glass, and Fe-bearing minerals were residual when compared to the Fe-MC, where magnetite, magnesioferrite, hematite, and maghemite accounted for up to 30 wt.%. Among the Fe-MC, the sample collected from electrostatic precipitator fly ash (ESP FA), despite having a lower yield, presented higher Fe concentrations than the ones from bottom ash and economizer grits, which was related to the mode of occurrence of Fe-bearing phases: in the Fe-MC from ESP FA, discrete ferrospheres predominated, while in the remaining Fe-bearing phases, they were often embedded in aluminosilicate glass. All Fe-MC samples showed an increase of Fe-substituting elements (e.g., Mn and Ni) and their concentration tended to increase with decreasing particle size along with Fe. The integrated study of cross-sections enabled the identification of oxidation rims, martitization aspects, and the co-existence of hematite and magnesioferrite.

Miocene coals in the Hanoi Trough, onshore northern Vietnam: Depositional environment, vegetation, maturity, and source rock quality

The Hanoi Trough in northern Vietnam forms the landward extension of the large Song Hong Basin in the South China Sea. Several gas and condensate discoveries have been made in the offshore part while exploration in the Hanoi Trough has been less successful. Encountered hydrocarbons suggest a terrigenous source rock, the most likely candidate being Miocene coals. The composition of these is poorly documented in the public domain, but in the Hanoi Trough with a thinner Cenozoic succession numerous Miocene coal beds have been penetrated by several wells. The current study examines by organic petrography, geochemistry, and sedimentology the depositional environment, paleo-vegetation, thermal maturity and source rock potential of Miocene coal samples from two about 1000 m fully cored wells in the Hanoi Trough. The sedimentological facies, dinoflagellate cyst content and pyrite nodules suggest the coals were formed in coastal mires, in particular the younger section, testifying to an overall relative sea-level rise in the Miocene. This is supported by abundant framboidal pyrite and high TS contents in the coals. Dominance of huminite in all samples suggests water-logged mire conditions while abundant funginite and high concentrations of hopanes indicate high bacterial and fungal activity. Reduced fluorescence, oxidation rims, and elevated reflectance of resinite in a sample with concentrations of liptinite composed of resinite, cutinite, suberinite, sporinite and liptodetrinite might suggest the liptinite-enrichment was the result of degradational removal of less resistant organic matter. Biomarkers indicate the mire vegetation consisted of gymnosperms related to Podocapaceae or Cupressaceae, and perhaps Pinaceae. Presence of angiosperms is indicated by oleanane and aromatic oleananes, lupanes and ursanes. An unknown diterpane derived from Araucaria nemorosa (conifer in the Araucariaceae family) and/or Araucaria cunninghamii (pine) may be the first occurrence in a geological sample. The coals are of lignite to sub-bituminous A rank and are thermally immature with regard to hydrocarbon generation. They are today not at maximum burial depth due to c. 480–1450 m of Miocene uplift before reburial in Plio-Pleistocene time. HImax values around 200 mg HC/g TOC reveal the coals primarily are gas-prone, but exsudatinite in cleats in huminite and cell lumens in funginite is evidence for in situ generation from labile macerals. Oil droplets in cleats/cracks suggest migration of liquid hydrocarbons from deeper buried source rocks and are indicative of a working petroleum system in the Hanoi Trough.

Evaluation of arsenic mineralogy and geochemistry in gold mine-impacted matrices: Speciation, transformation, and potential associated risks

The risk of arsenic (As) contamination from gold mining is a long-term environmental concern for mines worldwide. Researchers have mainly focused on As contamination induced by tailings, however, less attention has been paid mineralogically to differentiate the fate of As among different As-bearing matrices. This paper presents a detailed study of the mineralogical and morphological features of three typical As-bearing matrices (waste rock, ores, and tailings) using bulk chemical, microscopic and spectroscopic analyses, and reveals the geochemical behavior of As in those matrices. Results from mineral composition identified by RoqSCAN revealed that the matrices were dominated by quartz, k-feldspar, albite, muscovite, and clay minerals, with subordinate ankerite, chlorite, smectite, hematite, arsenopyrite, pyrrhotite, apatite, pyrite, halite, and calcite. The sequential extraction scheme indicated that As in waste rock, ores and tailings was mainly hosted in arsenopyrite. Microscopic analysis observed that waste rock was significantly different from the ores and tailings in terms of mineralogical and morphological characteristics. For waste rock, from arsenopyrite to hematite, As content decreased from 46.12 wt% to 3.54 wt%. However, arsenopyrite presented as unweathered euhedral crystals or slight fragmentation in ores and tailings and a narrower oxidation rims than that of waste rock. The leaching test of SPLP showed that the highest As leaching was found in waste rock (0.246 mg/L) which was significantly higher than those in ores (0.080 mg/L) and tailings (0.148 mg/L). The As in waste rock displayed weaker geochemical stability than in ores and tailings, as supported by mineralogy analysis. Health risk assessment suggested waste rock had a higher health risk for both adults and children compared with ores and tailings. These findings reaffirm that understanding of As fate among different source materials is paramount for securing humans from As hazards. More must be done to decelerate the continuous oxidation of waste rock, thus mitigating As release into nature.

Development of an argillic horizon in polygenetic paleosols in the Marília Formation (Maastrichtian), Brazil: Precautions for paleoenvironmental interpretation

A study of paleosols with argillic horizons found in the Marília Formation associated with Maastrichtian in the Cretaceous is presented herein. This study aims to investigate the polygenetic processes involved in argillic horizon formation under paleoclimatic conditions from arid to semiarid in the Brazilian Cretaceous and considers morphological soil attributes, such as evidence of cementation, macromorphological data (horizons, matrix color, structure, clay coatings, nodules, and bioturbations), micromorphological data (coarse/fine patterns, b-fabric, clay coatings, infillings, and nodules), and water table oscillation. Seven representative profiles of paleosols were selected in the São Paulo state, Brazil, and soil samples of lithified paleosols were collected to determine their macromorphological–micromorphological and chemical properties. Clay illuviation, carbonate accumulation, and gleization were dominant processes in the paleosols. Clay illuviation was identified from clay coatings along grain and ped surfaces. Carbonates occurred as nodules and rhizoliths and as coatings on peds. Red mottles, gray rhizohaloes with red oxidation rims, oxidic nodules, an iron-depleted matrix, and iron oxide depletion hypocoatings confirmed gleization. The argillic horizon polygenesis in the Marília Formation is usually interpreted as evidence of high-moisture events under arid/semiarid climates or climate change toward moister conditions than arid/semiarid. Thus, argillic horizon paleosols in the sedimentary records of the Marília Formation are not necessarily reliquial characteristics of wet paleoenvironments but are associated with changes in dominant granulometry, types of macroaggregates–microaggregates, carbonate accumulation in horizons, and/or water table oscillation. Thus, the presence of Bt horizons does not necessarily imply wet conditions with changes in the depositional system, as proposed by some authors.

Speciation and mobility of antimony and arsenic in a highly contaminated freshwater system and the influence of extreme drought conditions

Environmental context Toxicity and mobility of antimony and arsenic in aqueous systems are largely determined by their speciation and redox chemistry. In a highly contaminated freshwater system, one antimony species (dissolved SbV) dominated, while dissolved arsenic was more responsive to environmental conditions. Arsenic (as AsV) increased significantly during a drought period; this increase in As mobility presents a threat for first flush events and water contamination in a changing climate. Abstract Aqueous and solid-state antimony (Sb) and arsenic (As) speciation is assessed in an Australian freshwater system contaminated by mining of primary sulfide minerals. The study aims to understand metalloid transformation and mobilisation in the system, and coincides with a severe drought providing the opportunity to examine the influence of extreme low-flow conditions. X-ray absorption spectra identified only SbV in <2 mm sediments, despite boulder size stibnite evident in the creek. Roméite-group minerals were detected by X-ray diffraction in oxidation rims of creek-bed stibnite, which potentially limit the contribution of dissolved SbIII to the waterway. Arsenic in <2 mm sediments was dominated by AsV (17–91 %) and orpiment (16–93 %), while the co-occurrence of AsIII (11–36 %) with orpiment suggests that primary As minerals are an important ongoing source of AsIII to the system. Dissolved metalloids (<45 µm filtered) dominated total water column concentrations and comprised mainly pentavalent species. Arsenic(III) was however identified in most water samples (up to 6.6 µg L−1), while dissolved SbIII was only detected in one sample (3.4 µg L−1) collected during the drought period. Dissolved AsV increased significantly in samples collected in low-flow conditions, considered a result of reductive dissolution of sediment Fe-oxyhydroxide host phases, but a similar increase in dissolved Sb was not observed. This study highlights a greater risk from As in this system, and the likelihood of increased As mobility under the warmer and drier environmental conditions predicted with climate change, especially during first-flush events.

Antimony mobility during the early stages of stibnite weathering in tailings at the Beaver Brook Sb deposit, Newfoundland

The aqueous speciation and mineralogy of antimony (Sb) in waters and tailings at Beaver Brook antimony deposit have been analyzed to understand Sb mobility during the initial stages of stibnite (Sb2S3) weathering in a near-surface environment. Dissolution of stibnite in oxidizing conditions releases Sb in drainage water and Sb is incorporated into the mineral structures of several secondary minerals. The most abundant Sb host in Beaver Brook tailings is primary stibnite, which dissolves, releasing Sb(III) to the pore water which rapidly oxidizes to Sb(V). The maximum concentration of Sb in tailings pore water is 26.4 mg/L and only 0.9% is in the form of Sb(III). In all surface water, Sb concentration ranges from 0.01 to 26.1 mg/L (average 9.4 mg/L) and is mostly present in its Sb(V) form (98.9–99.2% of total Sb). The secondary minerals containing Sb formed in tailings impoundment include tripuhyite-like Sb–Fe oxides (FeSbO4) where Sb is an important part of their structure, with variable Fe/Sb ratios and Sb concentrations of up to 37.8% by weight (average of 21.7%). These are important Sb host phases in the top 30 cm of tailings. Iron oxides enriched in Sb, such as goethite (FeOOH), where Sb (average of 3.9% by weight) is adsorbed or incorporated in the structure are common but represent less than 1.3% of the total mass of Sb. The elevated Mg concentrations in tailing ponds and pore water promote the precipitation of brandholzite (Mg[Sb(OH)6]2·6H2O) (in association with gypsum) during dry periods, which is easily dissolved during rainy periods. Brandholzite dissolution may significantly contribute to the concentration of dissolved Sb, together with stibnite dissolution, whereas Sb–Fe oxides are stable in the neutral pH, oxidized surface environment. Arsenic (As) accompanies Sb in all media but its behavior differs from that of Sb. The source of As is arsenopyrite, which decomposes more slowly than stibnite. This may be due to the formation of oxidation rims on arsenopyrite grains composed of Fe, As, S, Sb, and Ca which slow the dissolution, whereas no rims are seen on stibnite. Also, despite similar As and Sb concentration in bulk tailings, the concentration of Sb in drainage water is higher than that of As. In pore water, As(III) is the dominant oxidation state of As suggesting that the oxidation of dissolved As is slower than that of Sb.

Development of a petrographic technique to assess the spontaneous combustion susceptibility of Indian coals

ABSTRACTPetrographic studies are commonly used to categorize the potential utilization of coals. Eleven coal samples from the Jharia coalfield (JCF), India, were studied using petrographic techniques to investigate maceral content, reflectance, and textural characteristics. Multiple test samples of each coal were slowly oxidized under controlled laboratory conditions from an ambient temperature of 30°c to 300°c to investigate the morphology of oxidized coals. The petrographic characterization of coals before and after oxidation showed significant changes in both morphology and vitrinite reflectance. The oxidation of coal particles produced three predominant textural changes: particles with homogeneous change of reflectance (HCv), particles with oxidation rims (ORv), and particles with no changes were observed (Uv), respectively. These textural characteristics were used to indicate how particles had interacted with oxygen at low temperatures during the early stages of oxidation. The morphological classification developed provides an alternative method to confirm the susceptibility of a coal to spontaneous combustion. Conventional thermal parameters such as crossing point temperature (CPT) were unable to identify the coals prone to spontaneous combustion. However, certain petrographic parameters could be combined with CPT values to provide a much more accurate measure for susceptibility to spontaneous combustion.

Impact of underground coal fire on coal petrographic properties of high volatile bituminous coals: A case study from coal fire zone No. 3.2 in the Wuda Coalfield, Inner Mongolia Autonomous Region, North China

The Wuda Coalfield located in the Inner Mongolia Autonomous Region, North China is known as one of China's major source of prime coking coals and a site of well-researched and well-documented underground coal fires. The underground coal fire at the coal fire zone No. 3.2 is situated in the active coal mine of Suhai-Tu, located in the north westerly part of the Wuda Coalfield.The present paper investigates the impact of the underground coal fire on the coal seam No. 10 by application of coal petrographic methods, including detailed characteristic of macerals and other coal components, maceral analysis, microstructural analysis, and vitrinite reflectances performed on (1) coal grains lacking impurities, microfractures, dark oxidation rims, (2) on dark-rimmed vitrinite, as well as (3) on low-temperature semi-coke. The investigated coal seam No. 10 represents a high volatile A bituminous coal and is dominated by vitrinite, followed by inertinite with minor amounts of liptinite and by non-isotropic low-temperature semi-coke. The microstructure of the oxidatively and thermally altered coals is represented by (1) extensive non-tectonic microfissures and non-tectonic microfractures i.e., shrinkage microfractures, leading to defragmentation of coal grains, (2) dark oxidation rims observed at grain margins, non-tectonic microfissures and microfractures, and by (3) devolatilisation micropores. Random vitrinite reflectances measured in (1) coal grains lacking impurities, microfractures, and dark oxidation rims, and in (2) dark-rimmed vitrinite at non-tectonic microfissures and fractures reveal significant lateral variations. The presence of low-temperature semi-coke and its marked lower reflectance values are indicative of thermal alteration induced by the underground coal fire in the coal fire zone No. 3.2. The results obtained from the performed analyses of organic matter point to both low-temperature oxidation and low-temperature-pyrolysis processes. The applied coal petrological approach revealed characteristic changes to the coal's microstructure, its petrographic composition, as well as to optical properties induced by the underground coal fire.

Geochemistry of arsenic in low sulfide-high carbonate coal waste rock, Elk Valley, British Columbia, Canada.

This study investigated the geochemistry of arsenic (As) in low sulfide-high carbonate coal waste rock of the Elk Valley, British Columbia, Canada. Its abundance and mineralogical associations in waste rock of different placement periods were determined in addition to its mobilization into porewater and rock-drain effluent. The mean (5.34mg/kg; 95% confidence interval: 4.95-5.73mg/kg) As concentration in the waste rock was typical of sedimentary rock. Electron microprobe and As K-edge X-ray absorption near-edge spectroscopic analyses showed the As is predominantly associated with primary pyrites in both source and freshly blasted waste rock. However, in aged waste rock the As is associated with both primary pyrites and secondary Fe oxyhydroxides. Oxidation of pyrite in waste rock dumps was reflected by the presence of high concentrations of SO42- in porewater and oxidation rims of Fe oxyhydroxides around pyrite grains. Acid released from pyrite oxidation to Fe oxyhydroxides is neutralized by carbonate mineral dissolution that buffers the pH in the waste rock to circumneutral values. Adsorption of As onto secondary Fe oxyhydroxides provides an internal geochemical control on As release during pyrite oxidation and porewater flushing from the dump, resulting in the low As concentrations observed in porewater (median: 9.91μg/L) and rock-drain effluent (median: 0.31μg/L). Secondary Fe oxyhydroxides act as a long-term sink for As under present day hydrologic settings in waste rock dumps in the Elk Valley.

The effect of bacterial degradation on bituminite reflectance

Within bituminite particles, high reflectance oxidation rims (HROR) were observed in close proximity to framboidal pyrites. Through examining a maceral with the framboidal pyrite physically removed, a high number of reflectance measurements were made covering the entire surface of the maceral. Additional measurements were taken in the form of transects across the maceral, allowing an examination of the relationship between reflectance and distance from the bacterial sulfate reduction (BSR) zone. A baseline reflectance value of approximately 0.50%Ro was measured, with peak values of approximately 0.75%Ro measured adjacent to the pyrite. This large variability in bituminite reflectance (BRo) was not induced via thermal catagenesis; however, it could be accounted for by a diagenetic process. This process involves labile organic matter (OM) entering a BSR zone. In this zone, anaerobic bacteria reduces dissolved sulfate to oxidize OM. This process results in the formation of bacterially-derived framboidal pyrite in close proximity to HROR in bituminite macerals. Although there has been a previous report of elevated BRo associated with biogenic gas in the regional scale, there was no microscopic evidence of such occurrence reported. This study examines low reflectance bituminite particles with embedded framboidal pyrite and associated HROR.Examination of the measured transects yielded a very rapid drop in reflectance a few micrometers away from the BSR zone. This study demonstrates a bacterial process that causes elevation of BRo on a micrometer scale and leads to a positively skewed, highly variable BRo population. We also demonstrate the magnitude of variation that can be expected when measuring BRo which could result in significant overestimation of thermal maturity.

Petrographic characterization of coals as a tool to detect spontaneous combustion potential

Textural features of 25 worldwide coals were studied after slow oxidation processing (0.5°Cmin−1 from 20 to 250°C in air) using oil immersion microscopy and image analysis techniques. The characterization of samples, before and after oxidation, showed important changes in vitrinite reflectance with high reactive coals, which also related to their intrinsic self-oxidation potential. The morphology of the coal particles was also altered after the oxidation, to produce at least six different morphotypes. Particles with ‘homogeneous change of reflectance’ and particles with ‘oxidation rims’ were predominant in the samples studied, which related to boundary reactive conditions (kinetic and diffusion control of the reaction respectively). These textural characteristics indicate how particles interacted with oxygen at low temperatures, which could be used to predict the most probable pathway during the early stages of oxidation which could then lead to a spontaneous combustion event. The magnitude of the reflectance change and the morphological characteristics of samples studied were also related to the reactivity properties, providing an additional source of information to identify coals prone to spontaneous combustion.

Chemical composition of weathering products in neutral and acidic mine tailings from stibnite exploitation in Slovakia

* �Correspondingauthor Here we describe the chemical composition of the weathering products at two abandoned stibnite deposits, Dubrava and Poproc in Slovakia. The tailings at Dubrava are circumneutral (pH 7-8), richer in Sb than As and rich in carbonates. The tailings at Poproc are acidic (pH 3-5), the Sb/As ratio is usually close to 1, carbonates are missing, and the tailings have elevated Pb contents. The most common sulphide at both sites was pyrite (FeS 2 ), less frequently stibnite (Sb 2 S 3 ) and arsenopyrite (FeAsS); minor berthierite (FeSb 2 S 4 ) was found only at Poproc. At both sites, sandy layers of the tailings contain the weathering products; the clayey portions are sterile. The most frequent secondary phases in the Dubrava impoundments are oxidation rims on pyrite and arsenopyrite, with relics of the primary sulphides commonly preserved. At Poproc, the primary sulphides were completely oxidized and decomposed. A common feature of the oxidation rims on all primary sulphides is their enrichment with respect to elements rather rare in the primary phase, an effect which is most apparent in the outermost portions of the rims. Rims around arsenopyrite may be enriched in Sb, around pyrite in As and Sb, and around stibnite in Pb. Antimony is usually incorporated into Sb-Fe, Fe-Sb, Sb, or Sb-Ca oxides, with the Sb/(Sb + Fe) ratio varying from 0 to 1. Arsenic behaves differently in comparison with Sb in that the highest As/(As + Fe) ratio on a wt. % basis is 0.41, as observed in weathering rims on arsenopyrite, the only primary sulphide with a substantial As content. Our results show that the nature of the weathering products is controlled by the primary mineralogy and the ability of the aqueous solutions to transport As, Sb, Ca, Fe, and Pb. There is no indication that the final products would be chemically or mineralogically different if weathering reached the terminal stages at the two studied sites.

Application of organic petrology and geochemistry to coal waste studies

Coal wastes produced during mining activities are commonly deposited in nearby dumps. These wastes mostly composed of minerals and variable amounts (usually 20–30%) of organic matter start to weather immediately after deposition. Oxidation of the organic matter can lead to self heating and self combustion as a result of organic and mineral matter transformations. The degree of alteration depends on the properties of the wastes, i.e., the maceral and microlithotype composition of the organic matter and its rank. Alteration of wastes also depends on the heating history, i.e., the rate of heating, final heating temperature, duration of heating, and the degree of air access. Although air is probably necessary to initiate and drive the heating processes, these usually take place under relatively oxygen depleted conditions. With slow heating, color of organic matter particles changes, irregular cracks and oxidation rims develop around edges and cracks, and bitumen is expelled. As a result, massive and detritic isotropic and strongly altered organic matter forms. On the other hand, higher heating rates cause the formation of devolatilization pores, oxidation rims around these pores and along cracks, vitrinite-bands-mantling particles, and bitumen expulsions. Organic compounds generated from the wastes include n -alkanes, iso -alkanes, alkylcyclohexanes, acyclic isoprenoids, mainly pristane, phytane and, in some cases, farnesane, sesquiterpanes, tri- and tetracyclic diterpanes, tri- and pentacyclic triterpanes, and steranes, polycyclic aromatic hydrocarbons (mostly with two- to five rings, rarely six rings), and phenols. The compounds formed change during the heating history. The fact that phenols are found in dumps where heating has not yet been completed, but are absent in those where heating ceased previously suggests the presence of water washing. The organic compounds formed may migrate within the dumps. However, when they migrate out of the dumps, they become a hazard to environment. This paper is a review on transformations of organic matter (both maceral composition and reflectance and chemical composition) in coal wastes deposited in coal waste dumps. Immediately after deposition the wastes are exposed to weathering conditions and sometimes undergo self heating processes. ► Oxidation, pyrolysis, and hydropyrolysis dominate in self heating coal waste dumps. ► Various forms of macerals alterations reflect the conditions within dumps. ► Generated chemical compounds migrate within dumps. ► Heating history and properties of organic matter play key role in its alterations.

Thermal alterations of organic matter in coal wastes from Upper Silesia, Poland

Thermal alterations of organic matter in coal wastes from Upper Silesia, PolandSelf-heating and self-combustion are currently taking place in some coal waste dumps in the Upper Silesian Coal Basin, Poland, e.g. the dumps at Rymer Cones, Starzykowiec, and the Marcel Coal Mine, all in the Rybnik area. These dumps are of similar age and self-heating and combustion have been occurring in all three for many years. The tools of organic petrography (maceral composition, rank, etc.), gas chromatography-mass spectrometry, and proximate and ultimate analysis are used to investigate the wastes.Organic matter occurs in quantities up to 85 vol.%, typically a few to several vol.%, in the wastes. All three maceral groups (vitrinite, liptinite, and inertinite) are present as unaltered and variously-altered constituents associated with newly-formed petrographic components (bitumen expulsions, pyrolytic carbon). The predominant maceral group is vitrinite with alterations reflected in the presence of irregular cracks, oxidation rims and, rarely, devolatilisation pores. In altered wastes, paler grey-vitrinite and/or coke dominates. The lack of plasticity, the presence of paler-coloured particles, isotropic massive coke, dispersed coked organic matter, and expulsions of bitumens all indicate that heating was slow and extended over a long time. Macerals belonging to other groups are present in unaltered

Tales from a distant swamp: Petrological and paleobotanical clues for the origin of the sand coal lithotype (Mississippian, Valley Fields, Virginia)

Abstract Tournasian (Mississippian) Price Formation semianthracites ( R max = 2.40%) in the Valley Fields of southwestern Virginia contain a lithotype described in an early-20th-century report as a “sand” coal. The Center for Applied Energy Research inherited a collection of coals containing sand coal specimens, making it possible to study the lithotype from the long-closed mines. The sand coal consists of rounded quartz sand and maceral assemblages (secretinite, corpogelinite, and rounded collotelinite) along with banded collotelinite, vitrodetrinite, and inertodetrinite assemblages. The association of rounded macerals and similar-size quartz grains suggests transport. Oxidation rims surrounding the rounded collotelinite provides further evidence for transport. Due to the semianthracite rank, palynology could not be performed. Stratigraphic evidence indicates that the Lepidodendropsis flora would have been the dominant mire vegetation. Pteridosperms in this assemblage could have contributed resin rodlets, subsequently metamorphosed to collogelinite or secretinite. While a resin rodlet origin is an intriguing possibility for the origin of the rounded macerals (at least some of the rounded maceral, the rounded collotelinite clearly has a different origin), we cannot definitively prove this origin.

Organic components in thermally altered coal waste: Preliminary petrographic and geochemical investigations

The petrographic and geochemical composition of coal wastes exposed to fire in the minestone dump of Piekary Ślą1skie town (Upper Silesia, Poland) was investigated using samples collected at various distances from a recent fire site. The question as to whether geochemical biomarker maturity parameters could be applied to assess thermal changes in organic matter caused by waste dump fires, was examined using the data obtained. Geochemical parameters were correlated with observed petrographic changes in the organic matter caused by oxidation and heating. Petrographic analyses included the determination of maceral group contents (vitrinite, liptinite and inertinite), mineral matter and coke contents, and reflectance measurements on organic matter. All results were supported by proximate and ultimate analyses. Geochemical analysis included ultrasonic solvent extraction of bitumen followed by gas chromatography–mass spectrometry (GC–MS) of the extracts. In petrographic terms, the influence of heating was seen in reflectance variations and as oxidation rims, cracks, pores and coke development. Some zoned oxidation rims may be interpreted as re-heating episodes. In terms of chemical fingerprints, less thermally-stable compounds such as lighter n-alkanes, cyclic isoprenoids, methyl- and dimethylnaphthalenes, methyphenanthrenes and five-ring polycyclic aromatic hydrocarbons were destroyed or evaporated in the most fire-affected material. The presence/absence of particular compound groups was used to assess heating temperatures. Biomarker parameters of thermal maturity were used to assess alterations in organic matter around the waste dump fires, especially those indices and ratios with higher maturity ranges, e.g. (3-methylbiphenyl + 4-methylbiphenyl)/dibenzofurane and Σdimethylbiphenyls/Σmethyldibenzofuranes.

Petrography and geochemical affinities of Spitsbergen Paleocene coals, Norway

The petrography and geochemistry of the two main Paleocene coal seams mined at Spitsbergen have been investigated through detailed analyses of more than 350 samples across the coalfield. The results are used for seam identification during exploration, for production planning and for quality assurance. Geochemical compositions of duplicate samples were determined by Proton Induced X-ray Emission (PIXE) and by conventional techniques. Every dataset provides comparable qualitative results. Statistical evaluation of analytical results indicates that the distribution of three element-groups, (S + Fe), (Ca + Sr) and (Si + Al + Ti) describes nearly all variations within the dataset qualitatively. Electron microprobe investigations of fusinite identified some cells containing strontium and phosphorous, whereas other cells contain calcium, magnesium and iron. In contrast, mineral grains containing an association of phosphorous, calcium and strontium were also identified. The lower Svea seam, close to the Cretaceous/Tertiary boundary exhibits high lateral variability in thickness and maceral composition whereas the Longyear seam, 20 to 40 m above, has a more consistent lateral and vertical development. The Longyear seam contains about 80% by volume of the maceral group vitrinite which is dominated by detrovitrinite. In contrast, the Svea seam contains only 40% to 50% vitrinite and 35–50% inertinite. We interpret this to reflect that the early Paleogene topography gradually developed from laterally discontinuous mires of ombrogenous nature towards more widespread topogenous mires. Coarse grains and fragments of high reflecting fusinite with oxidation rims together with splinters of highly reflecting inertodetrinite are seen as expression of temporarily oxygen rich, arid, peat conditions and are correlated to the inorganic constituents of the coal. Random vitrinite reflectance of the Svea seam is 0.94% and the Longyear seam is 0.71%. This steep reflectance gradient is probably due to the lower seam having acted as an insulation layer for the heat flow from below. The vitrinite reflectance within the Longyear seam varies from 0.76% at the base to 0.62% at the top. This could be due to suppressed reflectance from impregnation by bitumen, which is supported by the occurrences of cleats filled with exsudatinite. Oil expulsions were observed on polished sections of coal and host rocks of both seams. GC–MS analyses proved that the oil is coal derived. As the total liptnite of the seam is < 3% this may require further investigations.

English

At the active tailings impoundment Caren (surface 22 km 2 ) from the porphyry copper mine El Teniente, Chile, initial steps of primary mineral alteration and geochemical changes after deposition were studied. The tailings contained up to 3 vol% sulfides (mainly pyrite). At five points in the tailings impoundment, water samples up to a depth of 4 m were taken from piezometer. Preliminary data showed that the water, which was entering the tailings impoundment as an alkaline (pH 9.21) tailings slurry, changed to neutral (pH 7.41) conditions at the discharge of clear water from a decantation lake into a natural river system. The discharged clear water contained Cu up to 80g/L, Zn up to 180 g/L, Mg up to 30 mg/L, Mo up to 0.35 mg/L and sulfate (up to 1400 mg/L) indicating the liberation of metals from the very early stage of sulfide oxidation. Initial water and mineralogical data indicated a 2-layer structure of the tailings: (1) the first layer (0 m -1 m depth) was dominated by the alkaline pH of the fresh tailings but with lower pH at the surface and higher pH at 1 m depth. Incipient pyrite alteration was observed at the surface already two weeks after deposition; pyrite grains also in the youngest layers showed small oxidation rims. This process seemed to lower the pH at the surface of the tailings impoundment. New tailings deposition renewed in a 4-weeks rhythm the alkaline conditions at the surface. (2) In the second layer (1 m to 4 m depth) the pH decreased down to near-neutral environment, possibly due to neutralisation of the bases by the tailings.