Pub Date : 2026-01-05DOI: 10.1016/j.coal.2026.104937
Sanki Biswas, Nicola J. Wagner, Ndivhuho Nendouvhada, Ofentse M. Moroeng
<div><div>Permian coal samples from five major coalfields in Botswana—Lechana, South Orapa, Morupule, Takatokwane, and Tuli—were systematically characterized using coal petrography (maceral and mineral composition, microlithotype, and vitrinite reflectance) and geochemical analyses (inherent moisture, volatile matter, ash, and fixed carbon contents, total sulphur (TS), and gross calorific value (GCV)) to assess coal quality and enable the consideration of the depositional environments at the time of coal formation in these coalfields. Lechana and Morupule coals are inertinite-rich (avg. 54.5 and 84.4 vol.%, respectively; mmf basis), indicative of oxidizing conditions, whereas South Orapa, Takatokwane, and Tuli coals are vitrinite-dominated (avg. 78.1, 67.3, and 82.5 vol.%, respectively), reflecting deposition under oxygen-depleted (oxygen-lean), waterlogged peat-forming environments. Vitrinite reflectance indicates medium-rank D-C bituminous coals at Lechana, Morupule, and Tuli; low-rank sub-bituminous coals with localized medium-rank intervals at South Orapa; and a broader range of reflectance readings obtained for the Takatokwane samples, likely influenced by igneous intrusions and tectonic control. Elevated ash contents in all samples reflect detrital input of silicates and epigenetic mineralization of carbonates and sulphides, overall impacting the calorific value. The TS contents, up to 4.5 wt.% in some samples, will require selective mining and/or beneficiation prior to use in industrial applications. Selected samples, notably from Morupule Coalfield, might have potential to meet thermal power specifications, and certain studied coal samples (no. 12106, 12110, 12111, 1287, 1298, and 1471) from different coalfields shows potential for synthetic fuel production. Therefore, further detailed and systematic investigations are recommended.</div><div>Microlithotype and maceral analyses enable the elucidation of palaeomire depositional conditions. The peat-producing plants in the Lechana Coalfield accumulated in palaeomires evolving from lacustrine–deltaic to fluvial and back to lacustrine facies conditions. The occurrence of clay minerals, individual quartz grains, sporinite, and inertodetrinite highlights water table fluctuations, sediment influx, and periodic oxidation. The Morupule coal samples, dominated by durite and inertite, reveal more stable lacustrine deposition interrupted by episodic flooding, oxidation, and palaeowildfire events. The association of inertodetrinite, semifusinite, fusinite, and detrital clay infillings within cell lumens provides further evidence of episodic fluvial incursions into the mire. In contrast, the Takatokwane, South Orapa, and Tuli coals are vitrite and clarite rich, consistent with fluvial peat mire formation under waterlogged, oxygen-depleted (oxygen-lean) conditions. Variations in mineral and sulphur content further highlight localized geochemical controls. A regional gradient from fluvial to deltaic–lacus
{"title":"Organic petrology of coals from Botswana: Evidence of variations in depositional environments","authors":"Sanki Biswas, Nicola J. Wagner, Ndivhuho Nendouvhada, Ofentse M. Moroeng","doi":"10.1016/j.coal.2026.104937","DOIUrl":"10.1016/j.coal.2026.104937","url":null,"abstract":"<div><div>Permian coal samples from five major coalfields in Botswana—Lechana, South Orapa, Morupule, Takatokwane, and Tuli—were systematically characterized using coal petrography (maceral and mineral composition, microlithotype, and vitrinite reflectance) and geochemical analyses (inherent moisture, volatile matter, ash, and fixed carbon contents, total sulphur (TS), and gross calorific value (GCV)) to assess coal quality and enable the consideration of the depositional environments at the time of coal formation in these coalfields. Lechana and Morupule coals are inertinite-rich (avg. 54.5 and 84.4 vol.%, respectively; mmf basis), indicative of oxidizing conditions, whereas South Orapa, Takatokwane, and Tuli coals are vitrinite-dominated (avg. 78.1, 67.3, and 82.5 vol.%, respectively), reflecting deposition under oxygen-depleted (oxygen-lean), waterlogged peat-forming environments. Vitrinite reflectance indicates medium-rank D-C bituminous coals at Lechana, Morupule, and Tuli; low-rank sub-bituminous coals with localized medium-rank intervals at South Orapa; and a broader range of reflectance readings obtained for the Takatokwane samples, likely influenced by igneous intrusions and tectonic control. Elevated ash contents in all samples reflect detrital input of silicates and epigenetic mineralization of carbonates and sulphides, overall impacting the calorific value. The TS contents, up to 4.5 wt.% in some samples, will require selective mining and/or beneficiation prior to use in industrial applications. Selected samples, notably from Morupule Coalfield, might have potential to meet thermal power specifications, and certain studied coal samples (no. 12106, 12110, 12111, 1287, 1298, and 1471) from different coalfields shows potential for synthetic fuel production. Therefore, further detailed and systematic investigations are recommended.</div><div>Microlithotype and maceral analyses enable the elucidation of palaeomire depositional conditions. The peat-producing plants in the Lechana Coalfield accumulated in palaeomires evolving from lacustrine–deltaic to fluvial and back to lacustrine facies conditions. The occurrence of clay minerals, individual quartz grains, sporinite, and inertodetrinite highlights water table fluctuations, sediment influx, and periodic oxidation. The Morupule coal samples, dominated by durite and inertite, reveal more stable lacustrine deposition interrupted by episodic flooding, oxidation, and palaeowildfire events. The association of inertodetrinite, semifusinite, fusinite, and detrital clay infillings within cell lumens provides further evidence of episodic fluvial incursions into the mire. In contrast, the Takatokwane, South Orapa, and Tuli coals are vitrite and clarite rich, consistent with fluvial peat mire formation under waterlogged, oxygen-depleted (oxygen-lean) conditions. Variations in mineral and sulphur content further highlight localized geochemical controls. A regional gradient from fluvial to deltaic–lacus","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"314 ","pages":"Article 104937"},"PeriodicalIF":5.7,"publicationDate":"2026-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145903478","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2026-01-02DOI: 10.1016/j.coal.2026.104936
Ahmed Mansour , Lamia A. Abdelhalim , Wei Hengye , Thomas Gentzis , Sameh S. Tahoun , Daniel Campos
The middle-late Permian was an interval with global paleoenvironmental and paleoeceanographic instabilities, including the end-Guadalupian or the Guadlupian-Lopingian major extinction event. It was controlled by massive eruptions of the Emeishan Large Igneous Province (LIP) in South China, leading to the release of significant quantities of greenhouse gases and toxic elements into the ocean-atmosphere ecosystem. Here, the middle-upper Permian strata at the Xibeixiang section and well Daye 1 (DY1) from the western and northern depression of the Sichuan Basin were analyzed for palynological data, total organic carbon (TOC), Rock-Eval pyrolysis, and organic petrography. The identified palynomorphs are dominated by significantly high concentrations of acritarch, mainly of Leiosphaeridia and Lophosphaeridium, along with moderate to low abundances of prasinophytes, mainly Dictyotidium with some Cymatiosphaera. These palynomorphs reflect deposition of the Gufeng and Wujiaping formations in a shallow marine shelf environment characterized by low-energy and reducing conditions, consistent with occasional occurrences of foraminiferal test linings, pollen, and spores. Elevated levels of phytoclasts and sparse spores and pollen in the Gufeng Formation reinforce high terrestrial influx, compared to low phytoclasts and absence of terrestrial palynomorphs in the Wujiaping Formation, which indicated low-energy, distal depositional conditions associated with subsidence of the Guangwang-Kaijiang–Liangping Trough. Source rock evaluation revealed fair to excellent organic matter richness in the Gufeng Formation, compared to poor to very good richness in the Wujiaping Formation. However, both formations exhibited poor present-day hydrocarbon generation potential of Type III–IV kerogen, with most samples have reached the dry gas stage. The back-calculated (original) S2o and HIo values revealed good to excellent generative potential and Type II to mixed Type II/III kerogen. In the study region, the eruption of the Emeishan LIP resulted in high rates of greenhouse outgasing and isotopically light carbon resulting in global perturbations in the carbon cycle, elevated organic carbon export, and the development of anoxic-euxinic conditions as evidenced from framboidal pyrite size and redox-sensitive elements. Additionally, it controlled a spike in heat flow patterns throughout the Sichuan Basin and thus expedited the thermal evolution of organic matter. As a consequence, the Permian source rocks in the Sichuan Basin entered the peak oil window in the Early Triassic, while they reached the dry gas window by the Jurassic.
{"title":"The Emeishan large igneous province (middle-late Permian) and implications for source rock development in South China (Sichuan Basin)","authors":"Ahmed Mansour , Lamia A. Abdelhalim , Wei Hengye , Thomas Gentzis , Sameh S. Tahoun , Daniel Campos","doi":"10.1016/j.coal.2026.104936","DOIUrl":"10.1016/j.coal.2026.104936","url":null,"abstract":"<div><div>The middle-late Permian was an interval with global paleoenvironmental and paleoeceanographic instabilities, including the end-Guadalupian or the Guadlupian-Lopingian major extinction event. It was controlled by massive eruptions of the Emeishan Large Igneous Province (LIP) in South China, leading to the release of significant quantities of greenhouse gases and toxic elements into the ocean-atmosphere ecosystem. Here, the middle-upper Permian strata at the Xibeixiang section and well Daye 1 (DY1) from the western and northern depression of the Sichuan Basin were analyzed for palynological data, total organic carbon (TOC), Rock-Eval pyrolysis, and organic petrography. The identified palynomorphs are dominated by significantly high concentrations of acritarch, mainly of <em>Leiosphaeridia</em> and <em>Lophosphaeridium</em>, along with moderate to low abundances of prasinophytes, mainly <em>Dictyotidium</em> with some <em>Cymatiosphaera</em>. These palynomorphs reflect deposition of the Gufeng and Wujiaping formations in a shallow marine shelf environment characterized by low-energy and reducing conditions, consistent with occasional occurrences of foraminiferal test linings, pollen, and spores. Elevated levels of phytoclasts and sparse spores and pollen in the Gufeng Formation reinforce high terrestrial influx, compared to low phytoclasts and absence of terrestrial palynomorphs in the Wujiaping Formation, which indicated low-energy, distal depositional conditions associated with subsidence of the Guangwang-Kaijiang–Liangping Trough. Source rock evaluation revealed fair to excellent organic matter richness in the Gufeng Formation, compared to poor to very good richness in the Wujiaping Formation. However, both formations exhibited poor present-day hydrocarbon generation potential of Type III–IV kerogen, with most samples have reached the dry gas stage. The back-calculated (original) S<sub>2</sub>o and HIo values revealed good to excellent generative potential and Type II to mixed Type II/III kerogen. In the study region, the eruption of the Emeishan LIP resulted in high rates of greenhouse outgasing and isotopically light carbon resulting in global perturbations in the carbon cycle, elevated organic carbon export, and the development of anoxic-euxinic conditions as evidenced from framboidal pyrite size and redox-sensitive elements. Additionally, it controlled a spike in heat flow patterns throughout the Sichuan Basin and thus expedited the thermal evolution of organic matter. As a consequence, the Permian source rocks in the Sichuan Basin entered the peak oil window in the Early Triassic, while they reached the dry gas window by the Jurassic.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"314 ","pages":"Article 104936"},"PeriodicalIF":5.7,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145893887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-25DOI: 10.1016/j.coal.2025.104935
Grzegorz P. Lis , Tomasz Topór , Maria Mastalerz
Organic matter (OM) quantity, type, and thermal maturity are fundamental parameters in the evaluation of unconventional shale reservoirs. While numerous prior studies have addressed the chemical evolution of OM, detailed petrographic analyses tracing evolution of maceral composition across a full maturity range are less common, especially for pre-Devonian shale formations. This study examines maceral composition in 93 Lower Silurian shale samples from the Baltic Basin, Poland, spanning a maturity range from immature to overmature (0.50–4.19 % VRE). The results show a systematic evolution of maceral composition with increasing thermal maturity. Immature samples are dominated by macerals of the liptinite group, with bituminite being the most common maceral in the majority of the samples. The exception are organic-lean samples, where alginite and liptodetrinite dominate, possibly due to preferential degradation of bituminite. With increasing maturity, these primary macerals progressively convert to secondary solid bitumen, which becomes the dominant OM component above 0.8 % VRE. The study identifies distinct populations of solid bitumen, including diagenetic, initial-oil, primary-oil, and late-oil varieties, often coexisting, which complicates the use of solid bitumen reflectance as a robust maturity indicator. Graptolites, present in most samples, do not show significant morphological change across maturity but serve as a reliable maturity indicator. The maceral composition, characterized by an abundance of liptinite macerals at lower maturity, indicates that the formation had significant hydrocarbon potential, and that its OM quality is not responsible for the current low gas content. This research provides a quantitative model for OM transformation in a pre-Devonian source rock, bridging the gap between geochemical and petrographic studies and providing a crucial reference for interpreting ancient marine shales.
{"title":"Evolution of maceral composition with thermal maturation of kerogen type II: Example from Silurian marine shales, Baltic Basin","authors":"Grzegorz P. Lis , Tomasz Topór , Maria Mastalerz","doi":"10.1016/j.coal.2025.104935","DOIUrl":"10.1016/j.coal.2025.104935","url":null,"abstract":"<div><div>Organic matter (OM) quantity, type, and thermal maturity are fundamental parameters in the evaluation of unconventional shale reservoirs. While numerous prior studies have addressed the chemical evolution of OM, detailed petrographic analyses tracing evolution of maceral composition across a full maturity range are less common, especially for pre-Devonian shale formations. This study examines maceral composition in 93 Lower Silurian shale samples from the Baltic Basin, Poland, spanning a maturity range from immature to overmature (0.50–4.19 % VRE). The results show a systematic evolution of maceral composition with increasing thermal maturity. Immature samples are dominated by macerals of the liptinite group, with bituminite being the most common maceral in the majority of the samples. The exception are organic-lean samples, where alginite and liptodetrinite dominate, possibly due to preferential degradation of bituminite. With increasing maturity, these primary macerals progressively convert to secondary solid bitumen, which becomes the dominant OM component above 0.8 % VRE. The study identifies distinct populations of solid bitumen, including diagenetic, initial-oil, primary-oil, and late-oil varieties, often coexisting, which complicates the use of solid bitumen reflectance as a robust maturity indicator. Graptolites, present in most samples, do not show significant morphological change across maturity but serve as a reliable maturity indicator. The maceral composition, characterized by an abundance of liptinite macerals at lower maturity, indicates that the formation had significant hydrocarbon potential, and that its OM quality is not responsible for the current low gas content. This research provides a quantitative model for OM transformation in a pre-Devonian source rock, bridging the gap between geochemical and petrographic studies and providing a crucial reference for interpreting ancient marine shales.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"314 ","pages":"Article 104935"},"PeriodicalIF":5.7,"publicationDate":"2025-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145845305","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-21DOI: 10.1016/j.coal.2025.104927
James C. Hower , Susan M. Rimmer , Darrell N. Taulbee , Debora Berti , Robert B. Finkelman , David French , Ian T. Graham , Harold H. Schobert , Lei Zhao , Shifeng Dai
The high volatile A bituminous Pennsylvanian (Duckmantian substage) Blue Gem coal, southeastern Kentucky, provides an opportunity to examine the concentration of minor elements in high-vitrinite, low-ash specific gravity fractions of the basal and middle lithotypes and the whole coal. For this study, the distributions of Ge and Ni are emphasized. While previous studies have suggested that Ge may be in an organic association, at least at ranks lower than the high volatile bituminous coal in this study, the studies generally relied upon indirect methods. Nickel, an element with known hyperaccumulation tendencies, is not correlated with the ash yield in the +90 %-vitrinite specific gravity fractions. Among the +90 %-vitrinite samples, Ni, Ge, and vitrinite decrease and Fe concentration increases with a decrease in density. While the absence of a correlation between element concentration and ash content might be an indirect indicator of an organic association, a previous transmission electron microscopy study demonstrated that Ni and Ge were present in a NiSn mineral, with the Ge possibly substituting for Sn. The association of Ge with minerals in high volatile bituminous coal does not necessarily imply that the peat through the low-rank precursors of that coal did not have organic associations. The functional groups responsible for binding inorganics in low-rank coals are lost in the metamorphic passage to bituminous coal and the previously organic elements may be incorporated into clays or other minerals, precipitated as oxides, or lost to the coal system. In the case of the Blue Gem coal, one factor in the coal metamorphism was the flow of hydrothermal brines coincident with the emplacement of the Pine Mountain thrust sheet. New elements introduced to the coal, at the time at a lower rank than the present high volatile A bituminous, could have interacted with elements in organic association, resulting in an episode of mineralization.
{"title":"Aspects of Germanium and Nickel accumulation in low-ash coal: Examples from the Blue Gem coal, eastern Kentucky, USA","authors":"James C. Hower , Susan M. Rimmer , Darrell N. Taulbee , Debora Berti , Robert B. Finkelman , David French , Ian T. Graham , Harold H. Schobert , Lei Zhao , Shifeng Dai","doi":"10.1016/j.coal.2025.104927","DOIUrl":"10.1016/j.coal.2025.104927","url":null,"abstract":"<div><div>The high volatile A bituminous Pennsylvanian (Duckmantian substage) Blue Gem coal, southeastern Kentucky, provides an opportunity to examine the concentration of minor elements in high-vitrinite, low-ash specific gravity fractions of the basal and middle lithotypes and the whole coal. For this study, the distributions of Ge and Ni are emphasized. While previous studies have suggested that Ge may be in an organic association, at least at ranks lower than the high volatile bituminous coal in this study, the studies generally relied upon indirect methods. Nickel, an element with known hyperaccumulation tendencies, is not correlated with the ash yield in the +90 %-vitrinite specific gravity fractions. Among the +90 %-vitrinite samples, Ni, Ge, and vitrinite decrease and Fe concentration increases with a decrease in density. While the absence of a correlation between element concentration and ash content might be an indirect indicator of an organic association, a previous transmission electron microscopy study demonstrated that Ni and Ge were present in a NiSn mineral, with the Ge possibly substituting for Sn. The association of Ge with minerals in high volatile bituminous coal does not necessarily imply that the peat through the low-rank precursors of that coal did not have organic associations. The functional groups responsible for binding inorganics in low-rank coals are lost in the metamorphic passage to bituminous coal and the previously organic elements may be incorporated into clays or other minerals, precipitated as oxides, or lost to the coal system. In the case of the Blue Gem coal, one factor in the coal metamorphism was the flow of hydrothermal brines coincident with the emplacement of the Pine Mountain thrust sheet. New elements introduced to the coal, at the time at a lower rank than the present high volatile A bituminous, could have interacted with elements in organic association, resulting in an episode of mineralization.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"314 ","pages":"Article 104927"},"PeriodicalIF":5.7,"publicationDate":"2025-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145796308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-18DOI: 10.1016/j.coal.2025.104924
Fritz-Lukas Stoepke , Ralf Littke , Alexander Wheeler , Hitoshi Hasegawa , Niiden Ichinnorov , Ulrich Heimhofer
Lignites from the Mongolian Khukhteeg Formation bear exceptionally well-preserved plant macro- and mesofossils, providing important insights into the evolution and composition of peat forming flora in inner-continental paleo-Asia during the late Early Cretaceous. Numerous paleobotanical studies deal with fossil plant material from the Tevshiin Govi site, a small-scale open-cast lignite mine located in the Choir-Nyalga Basin of central Mongolia. However, information on the peat depositional environment of the Tevshiin Govi site is limited. In order to reconstruct the conditions during peat formation, coal petrology and palynology, complemented by geochemical measurements (TOC, TS, δ13Corg), was applied across a ∼ 35 m thick lignite-rich succession. Maceral composition is dominated by huminite with few samples being rich in inertinite and/or mineral matter. Calculated maceral indices indicate a topogenous mire setting. Variability of the GWIAC indicates regular flooding of the peat. The stratigraphic trend in δ13Corg covaries with fusinite content, suggesting short-lived events such as peat fires affecting the δ13Corg signature. Palynological observations show a strong dominance of pollen produced by Cupressaceae and Pinaceae, which is in accordance with the meso- and macrofossil findings. No angiosperm pollen was observed. Based on diverse spore genera, a high diversity of herbaceous plants is suggested, which contrasts with previous reconstructions. Overall, the Tevshiin Govi site reveals a paleoenvironment that was mainly forested. Trees were dominated by conifers with an understory of pteridophytes (mainly ferns). The depositional setting was strongly influenced by fluvial processes. During phases of peat formation, the swamp was either covered by water or regularly flooded.
{"title":"Paleoenvironmental reconstruction based on Early Cretaceous lignite deposits from Central Mongolia (Tevshiin Govi mine)","authors":"Fritz-Lukas Stoepke , Ralf Littke , Alexander Wheeler , Hitoshi Hasegawa , Niiden Ichinnorov , Ulrich Heimhofer","doi":"10.1016/j.coal.2025.104924","DOIUrl":"10.1016/j.coal.2025.104924","url":null,"abstract":"<div><div>Lignites from the Mongolian Khukhteeg Formation bear exceptionally well-preserved plant macro- and mesofossils, providing important insights into the evolution and composition of peat forming flora in inner-continental paleo-Asia during the late Early Cretaceous. Numerous paleobotanical studies deal with fossil plant material from the Tevshiin Govi site, a small-scale open-cast lignite mine located in the Choir-Nyalga Basin of central Mongolia. However, information on the peat depositional environment of the Tevshiin Govi site is limited. In order to reconstruct the conditions during peat formation, coal petrology and palynology, complemented by geochemical measurements (TOC, TS, δ<sup>13</sup>C<sub>org</sub>), was applied across a ∼ 35 m thick lignite-rich succession. Maceral composition is dominated by huminite with few samples being rich in inertinite and/or mineral matter. Calculated maceral indices indicate a topogenous mire setting. Variability of the GWI<sub>AC</sub> indicates regular flooding of the peat. The stratigraphic trend in δ<sup>13</sup>C<sub>org</sub> covaries with fusinite content, suggesting short-lived events such as peat fires affecting the δ<sup>13</sup>C<sub>org</sub> signature. Palynological observations show a strong dominance of pollen produced by Cupressaceae and Pinaceae, which is in accordance with the meso- and macrofossil findings. No angiosperm pollen was observed. Based on diverse spore genera, a high diversity of herbaceous plants is suggested, which contrasts with previous reconstructions. Overall, the Tevshiin Govi site reveals a paleoenvironment that was mainly forested. Trees were dominated by conifers with an understory of pteridophytes (mainly ferns). The depositional setting was strongly influenced by fluvial processes. During phases of peat formation, the swamp was either covered by water or regularly flooded.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"314 ","pages":"Article 104924"},"PeriodicalIF":5.7,"publicationDate":"2025-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145785693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-14DOI: 10.1016/j.coal.2025.104926
Sławomira Pusz , Anna Hercog , Karolina Olszowska
Anthracites, due to their highly ordered internal structure, are chemically quite inert and thus difficult to process. However, for various applications of anthracites, including as precursors of carbon materials with specific properties, improving their processability is often necessary. For this purpose, various pretreatments are used, among which oxidation methods are of great importance. This work aimed to study the influence of oxidation using three different methods (in concentrated HNO3, in air at 420 °C, in plasma oxygen) on optical properties and morphology of three anthracites of increasing rank (VIC < MO < DON) from the Lower Silesian Coal Basin and Upper Silesian Coal Basin (Poland) and from Donbass (Ukraine), respectively. Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), Raman spectroscopy, and light microscopy (imaging and reflectance measurement) allow for following the changes in morphology and optical properties of anthracites after oxidation. In the case of the highest rank DON anthracite, its morphology and optical properties remained almost unchanged following oxidation by all the methods used, except for the narrow oxidation zone created by HNO3. In the case of lower rank anthracites, MO and VIC, their morphology and optical properties changed significantly under oxidation in HNO3 and air, but remained unchanged after plasma oxidation. The extent and intensity of the oxidation process were stronger for VIC anthracite than for MO.
Ultimately, it was shown that the level of anthracite oxidation in HNO3 and thermal oxidation with air strongly depends on the rank of the anthracite. The nature of the changes in morphology and reflectance parameters also suggests that the liquid agent, HNO3, acts more intensively but also more closely at the surface of anthracite grains, as it has a lower ability to penetrate deeper into the grains than air. The oxidation level under the influence of oxygen plasma was similar for all anthracites, regardless of their rank.
Optical properties are very sensitive indicators, which can reveal even very subtle structural changes in anthracites during oxidation, invisible to other research methods. The nature and intensity of changes of optical properties illustrate the extent and level of anthracites' oxidation and can be a useful complement to the results obtained using other research methods for determining anthracites' structural transformations. Due to the growing interest in using anthracite as a potential source of new carbon materials, thorough knowledge of their structural changes resulting from various technological processes, including oxidation, seems to be important from a scientific as well as technological point of view.
无烟煤由于其高度有序的内部结构，在化学上是相当惰性的，因此很难加工。然而，对于无烟煤的各种应用，包括作为具有特定性质的碳材料的前体，改进其可加工性通常是必要的。为此，使用了各种预处理方法，其中氧化法是非常重要的。本研究旨在研究三种不同氧化方法（浓HNO3、420 °C空气和等离子体氧）对三种不同等级无烟煤（VIC <； MO <； DON）光学性质和形态的影响，这些无烟煤分别来自波兰的下西里西亚煤盆地和上西里西亚煤盆地以及乌克兰的顿巴斯。扫描电子显微镜（SEM）、能量色散x射线光谱仪（EDS）、拉曼光谱和光学显微镜（成像和反射率测量）可以跟踪无烟煤氧化后形貌和光学性质的变化。对于最高等级的DON无烟煤，除了HNO3产生狭窄的氧化区外，其形貌和光学性质在所有使用的氧化方法中几乎没有变化。低阶无烟煤MO和VIC在HNO3和空气中氧化后形貌和光学性质发生显著变化，但在等离子体氧化后基本保持不变。VIC无烟煤的氧化程度和氧化强度均大于MO无烟煤。
{"title":"Changes in optical properties and morphology of anthracites oxidized under different conditions: In HNO3, air and plasma oxygen","authors":"Sławomira Pusz , Anna Hercog , Karolina Olszowska","doi":"10.1016/j.coal.2025.104926","DOIUrl":"10.1016/j.coal.2025.104926","url":null,"abstract":"<div><div>Anthracites, due to their highly ordered internal structure, are chemically quite inert and thus difficult to process. However, for various applications of anthracites, including as precursors of carbon materials with specific properties, improving their processability is often necessary. For this purpose, various pretreatments are used, among which oxidation methods are of great importance. This work aimed to study the influence of oxidation using three different methods (in concentrated HNO<sub>3</sub>, in air at 420 °C, in plasma oxygen) on optical properties and morphology of three anthracites of increasing rank (VIC < MO < DON) from the Lower Silesian Coal Basin and Upper Silesian Coal Basin (Poland) and from Donbass (Ukraine), respectively. Scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), Raman spectroscopy, and light microscopy (imaging and reflectance measurement) allow for following the changes in morphology and optical properties of anthracites after oxidation. In the case of the highest rank DON anthracite, its morphology and optical properties remained almost unchanged following oxidation by all the methods used, except for the narrow oxidation zone created by HNO<sub>3</sub>. In the case of lower rank anthracites, MO and VIC, their morphology and optical properties changed significantly under oxidation in HNO<sub>3</sub> and air, but remained unchanged after plasma oxidation. The extent and intensity of the oxidation process were stronger for VIC anthracite than for MO.</div><div>Ultimately, it was shown that the level of anthracite oxidation in HNO<sub>3</sub> and thermal oxidation with air strongly depends on the rank of the anthracite. The nature of the changes in morphology and reflectance parameters also suggests that the liquid agent, HNO<sub>3</sub>, acts more intensively but also more closely at the surface of anthracite grains, as it has a lower ability to penetrate deeper into the grains than air. The oxidation level under the influence of oxygen plasma was similar for all anthracites, regardless of their rank.</div><div>Optical properties are very sensitive indicators, which can reveal even very subtle structural changes in anthracites during oxidation, invisible to other research methods. The nature and intensity of changes of optical properties illustrate the extent and level of anthracites' oxidation and can be a useful complement to the results obtained using other research methods for determining anthracites' structural transformations. Due to the growing interest in using anthracite as a potential source of new carbon materials, thorough knowledge of their structural changes resulting from various technological processes, including oxidation, seems to be important from a scientific as well as technological point of view.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"313 ","pages":"Article 104926"},"PeriodicalIF":5.7,"publicationDate":"2025-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145753508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-11DOI: 10.1016/j.coal.2025.104925
K. Alami Sounni , M. Camps-Arbestain , J. Kaal , C.J. Tighe , M.M. Titirici , G. Siavalas
Carbon removal permanence refers to the duration over which carbon remains securely stored across various reservoirs without re-entering the atmosphere. Random reflectance (Ro) has been proposed as a proxy for assessing carbon permanence in biochar. In this study, Ro was measured for 25 plant-derived biochars and compared with (i) the molar H/C ratio, (ii) Raman spectroscopy parameters, and (iii) pyrolysis-GC–MS fingerprints. Four of the biochars showed bimodal Ro distributions, indicating two distinct reflectance populations. A strong relationship was found between mean Ro and H/C (r2 = 0.88). Biochars with H/C ≤ 0.40 had mean Ro ≥ 2.3 %, with ≥83 % of the 500 measurement points per sample exceeding 2 % (IBRo2), except one bimodal sample. This sample, despite mean Ro of 3.72 %, and H/C of 0.37, had only 65 % of measurements > IBRo2. Based on the fraction > IBRo2, the biochars were grouped as: Class 1: < 50 %; Class 2: 50–80 %; Class 3: ≥ 80 %. For unimodal biochars, these classes corresponded to mean Ro < 2.0 %, 2.0–2.3 %, and ≥ 2.3 %, and H/C ≥ 0.45, 0.40–0.45, and ≤ 0.40, respectively. Among Raman parameters, saddle intensity effectively distinguished the classes. Mean Ro inversely related to analytical pyrolysis yield (r2 = 0.72). Chemical markers (methoxyphenols and (alkyl)phenols) helped explain transitions between classes. The strong correspondence between mean Ro and H/C in unimodal biochars suggests either proxy may suffice in most cases. However, the fraction > IBRo2 becomes critical for polymodal, Class 2, non-plant feedstock biochars, or when required by certification registries.
{"title":"Assessment and integration of different methodologies for the characterisation of carbon aromaticity and structure in biochar","authors":"K. Alami Sounni , M. Camps-Arbestain , J. Kaal , C.J. Tighe , M.M. Titirici , G. Siavalas","doi":"10.1016/j.coal.2025.104925","DOIUrl":"10.1016/j.coal.2025.104925","url":null,"abstract":"<div><div>Carbon removal permanence refers to the duration over which carbon remains securely stored across various reservoirs without re-entering the atmosphere. Random reflectance (R<sub>o</sub>) has been proposed as a proxy for assessing carbon permanence in biochar. In this study, R<sub>o</sub> was measured for 25 plant-derived biochars and compared with (i) the molar H/C ratio, (ii) Raman spectroscopy parameters, and (iii) pyrolysis-GC–MS fingerprints. Four of the biochars showed bimodal R<sub>o</sub> distributions, indicating two distinct reflectance populations. A strong relationship was found between mean R<sub>o</sub> and H/C (r<sup>2</sup> = 0.88). Biochars with H/C ≤ 0.40 had mean R<sub>o</sub> ≥ 2.3 %, with ≥83 % of the 500 measurement points per sample exceeding 2 % (IBR<sub>o</sub>2), except one bimodal sample. This sample, despite mean R<sub>o</sub> of 3.72 %, and H/C of 0.37, had only 65 % of measurements > IBR<sub>o</sub>2. Based on the fraction > IBR<sub>o</sub>2, the biochars were grouped as: Class 1: < 50 %; Class 2: 50–80 %; Class 3: ≥ 80 %. For unimodal biochars, these classes corresponded to mean R<sub>o</sub> < 2.0 %, 2.0–2.3 %, and ≥ 2.3 %, and H/C ≥ 0.45, 0.40–0.45, and ≤ 0.40, respectively. Among Raman parameters, saddle intensity effectively distinguished the classes. Mean R<sub>o</sub> inversely related to analytical pyrolysis yield (r<sup>2</sup> = 0.72). Chemical markers (methoxyphenols and (alkyl)phenols) helped explain transitions between classes. The strong correspondence between mean R<sub>o</sub> and H/C in unimodal biochars suggests either proxy may suffice in most cases. However, the fraction > IBR<sub>o</sub>2 becomes critical for polymodal, Class 2, non-plant feedstock biochars, or when required by certification registries.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"313 ","pages":"Article 104925"},"PeriodicalIF":5.7,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145732129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-05DOI: 10.1016/j.coal.2025.104921
Richard Bryan Magalhaes Santos , Karen Soares Augusto , Sidnei Paciornik , Marcos Henrique de Pinho Maurício , Tiago de Souza Mota , Bruno Conceição do Nascimento , Italo de Oliveira Matias , Lauro Tiago Souza Santos , Leandra Costa Lages , Gil Marcio Avelino Silva , André Luiz Durante Spigolon
Determining the degree of maturation and thermal evolution in kerogen is vital to the hydrocarbons industry. This study evaluates the thermal maturation of source rock sections in sedimentary basins. Its determination makes it possible to estimate whether a sample from a given depth in an oil well falls within the window of oil or natural gas generation or remains immature. The Spore Coloration Index (SCI) can indicate the maturation of oil- and gas-prone material. The objective of this study is to automate this analysis, thereby achieving significant improvements in time efficiency and reliability. Traditionally, an operator visually identifies the presence of sporomorphs in slides using an optical microscope. When they encounter a sporomorph, the operator visually compares it with standard reference slides. The standard consists of 19 slides of spores of different degrees of maturity, ranging from the lightest to the darkest, from 1.0 to 10.0, in increments of 0.5. Comparison with the standard allows the operator to estimate the Spore Coloration Index (SCI) of a sporomorph. Various tests corroborated the literature's indication that the red channel best correlates with the thermal maturation index. A linear relationship was obtained between the average intensity of the red channel and the SCI (correlation coefficient R2 = 0.97). Images of samples from various wells at different depths were acquired under conditions similar to those standardized for organopalynological slides. Deep Learning-based systems were trained to identify sporomorphs in the images. With the help of an expert operator, the objects were manually outlined in the images to create a reference database. This database was separated into a training set and a validation set, allowing the network to learn and then have its performance evaluated (accuracy ≈ 86 %). The captured images feed the system, which identifies the presence of sporomorphs, measures the SCI value of each one, and generates a histogram of SCI distribution for each case, allowing, for the first time, the direct calculation of the SCI without the need for visual analysis.
{"title":"A deep learning system for sporomorph identification and Spore Coloration Index (SCI) calculation for evaluating source rocks' thermal maturity","authors":"Richard Bryan Magalhaes Santos , Karen Soares Augusto , Sidnei Paciornik , Marcos Henrique de Pinho Maurício , Tiago de Souza Mota , Bruno Conceição do Nascimento , Italo de Oliveira Matias , Lauro Tiago Souza Santos , Leandra Costa Lages , Gil Marcio Avelino Silva , André Luiz Durante Spigolon","doi":"10.1016/j.coal.2025.104921","DOIUrl":"10.1016/j.coal.2025.104921","url":null,"abstract":"<div><div>Determining the degree of maturation and thermal evolution in kerogen is vital to the hydrocarbons industry. This study evaluates the thermal maturation of source rock sections in sedimentary basins. Its determination makes it possible to estimate whether a sample from a given depth in an oil well falls within the window of oil or natural gas generation or remains immature. The Spore Coloration Index (SCI) can indicate the maturation of oil- and gas-prone material. The objective of this study is to automate this analysis, thereby achieving significant improvements in time efficiency and reliability. Traditionally, an operator visually identifies the presence of sporomorphs in slides using an optical microscope. When they encounter a sporomorph, the operator visually compares it with standard reference slides. The standard consists of 19 slides of spores of different degrees of maturity, ranging from the lightest to the darkest, from 1.0 to 10.0, in increments of 0.5. Comparison with the standard allows the operator to estimate the Spore Coloration Index (SCI) of a sporomorph. Various tests corroborated the literature's indication that the red channel best correlates with the thermal maturation index. A linear relationship was obtained between the average intensity of the red channel and the SCI (correlation coefficient R<sup>2</sup> = 0.97). Images of samples from various wells at different depths were acquired under conditions similar to those standardized for organopalynological slides. Deep Learning-based systems were trained to identify sporomorphs in the images. With the help of an expert operator, the objects were manually outlined in the images to create a reference database. This database was separated into a training set and a validation set, allowing the network to learn and then have its performance evaluated (accuracy ≈ 86 %). The captured images feed the system, which identifies the presence of sporomorphs, measures the SCI value of each one, and generates a histogram of SCI distribution for each case, allowing, for the first time, the direct calculation of the SCI without the need for visual analysis.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"313 ","pages":"Article 104921"},"PeriodicalIF":5.7,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145689426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-04DOI: 10.1016/j.coal.2025.104922
Yaroslav Bezyk , Dawid Szurgacz , Maciej Górka , Dariusz Strąpoć , Łukasz Kruszewski , Przemysław Wachniew , Jarosław Nęcki , Miroslaw Zimnoch , Izabela Sówka , Magdalena Modelska , Wojciech Wołkowicz , Carina van der Veen , Thomas Röckmann
Methane release into mine workings and the atmosphere poses a serious environmental and safety risks. This study examines the composition and stable isotope geochemistry of coalbed methane in a hard coal mine of the Upper Silesian Coal Basin (Poland), with emphasis on gas migration pathways from the coal seam through mine workings and ventilation shaft to the atmosphere. Methane concentrations decrease progressively with distance from the active excavation zone toward the exhaust shaft. In addition to CH4 and CO2, the coalbed gas contained notable amounts of nitrogen heterocyclic compounds, sulfur-bearing species, and chlorinated gases, depending on the sampling location and temporal window.
Geochemical results reveal a strong link between gas migration and isotopic variability in the underground environment. Zones of methane accumulation, commonly associated with bends in return airways, showed enrichment in 13C, consistent with diffusive fractionation. Variations in CH4 and corresponding isotope effects during coal transport indicate multiple gas origins within the coal seam. Isotope signatures point to predominantly thermogenic CH4 at the active mining level, whereas 13C-depleted methane at the exploited and flooded levels suggests secondary microbial generation. The microbial contribution is likely promoted by infiltrating meteoric waters supplying nutrients for methanogenic archaea, as supported by δ2H, δ18O signatures of mine water, and measurable tritium activity. The absence of enriched δ13C values in CO2 and dissolved inorganic carbon (DIC) further implies mixed thermogenic-microbial gas origin in abandoned mine workings.
These findings highlight the combined influence of mining operations, diffusion-desorption processes, microbial activity, and gas mixing on the molecular and isotope composition of coalbed gases transported toward the exhaust shaft. Moreover, isotopic data from downwind emission plumes demonstrate the value of integrating underground measurements with atmospheric observations to trace and quantify methane emissions from coal mining operations.
{"title":"Isotope and chemical alteration of coalbed gases during migration from underground coal mine into the atmosphere","authors":"Yaroslav Bezyk , Dawid Szurgacz , Maciej Górka , Dariusz Strąpoć , Łukasz Kruszewski , Przemysław Wachniew , Jarosław Nęcki , Miroslaw Zimnoch , Izabela Sówka , Magdalena Modelska , Wojciech Wołkowicz , Carina van der Veen , Thomas Röckmann","doi":"10.1016/j.coal.2025.104922","DOIUrl":"10.1016/j.coal.2025.104922","url":null,"abstract":"<div><div>Methane release into mine workings and the atmosphere poses a serious environmental and safety risks. This study examines the composition and stable isotope geochemistry of coalbed methane in a hard coal mine of the Upper Silesian Coal Basin (Poland), with emphasis on gas migration pathways from the coal seam through mine workings and ventilation shaft to the atmosphere. Methane concentrations decrease progressively with distance from the active excavation zone toward the exhaust shaft. In addition to CH<sub>4</sub> and CO<sub>2</sub>, the coalbed gas contained notable amounts of nitrogen heterocyclic compounds, sulfur-bearing species, and chlorinated gases, depending on the sampling location and temporal window.</div><div>Geochemical results reveal a strong link between gas migration and isotopic variability in the underground environment. Zones of methane accumulation, commonly associated with bends in return airways, showed enrichment in <sup>13</sup>C, consistent with diffusive fractionation. Variations in CH<sub>4</sub> and corresponding isotope effects during coal transport indicate multiple gas origins within the coal seam. Isotope signatures point to predominantly thermogenic CH<sub>4</sub> at the active mining level, whereas <sup>13</sup>C-depleted methane at the exploited and flooded levels suggests secondary microbial generation. The microbial contribution is likely promoted by infiltrating meteoric waters supplying nutrients for methanogenic archaea, as supported by δ<sup>2</sup>H, δ<sup>18</sup>O signatures of mine water, and measurable tritium activity. The absence of enriched δ<sup>13</sup>C values in CO<sub>2</sub> and dissolved inorganic carbon (DIC) further implies mixed thermogenic-microbial gas origin in abandoned mine workings.</div><div>These findings highlight the combined influence of mining operations, diffusion-desorption processes, microbial activity, and gas mixing on the molecular and isotope composition of coalbed gases transported toward the exhaust shaft. Moreover, isotopic data from downwind emission plumes demonstrate the value of integrating underground measurements with atmospheric observations to trace and quantify methane emissions from coal mining operations.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"313 ","pages":"Article 104922"},"PeriodicalIF":5.7,"publicationDate":"2025-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145689431","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：