International Journal of Coal Geology最新文献

{"title":"Confocal laser-scanning microscopy (CLSM)-based thermal maturity of Tasmanites and progress in standardization of fluorescence microspectrometry","authors":"Jolanta Kus ,&nbsp;Paul C. Hackley","doi":"10.1016/j.coal.2025.104885","DOIUrl":"10.1016/j.coal.2025.104885","url":null,"abstract":"<div><div>Evaluation of thermal maturity in vitrinite-free or vitrinite-deficient sediments via fluorescence microspectrometry can provide relevant information related to petroleum exploration and thermal history assessment. However, variation in spectral fluorescence properties of alginite macerals with increasing thermal maturity is largely underexplored. Here, authors of this study have applied confocal laser-scanning microscopy (CLSM) in conjunction with fluorescence microspectrometry to a maturity series of marine Upper Devonian <em>Tasmanites</em> algae from the Ohio Shale (Huron Member) and a single sample from the Marcellus Formation of the Appalachian Basin. Spectral fluorescence properties of <em>Tasmanites</em> were evaluated in relation to orientation, measurement location, and the number of measurements per sample, and were compared to published literature. Emission spectra of <em>Tasmanites</em> from continuous wave laser excitation (405 nm) were acquired from sections perpendicular and parallel to bedding and at different positions within individual <em>Tasmanites</em> bodies. The results showed a progressive red-shift in emission maxima (λ_max) in a large sample sized maturity series (<em>N</em> = 19), e.g., 493 to 578 nm for the perpendicular section at middle position. Further, blue-shifted apex and mineral-adjacent positions within sections perpendicular to bedding were observed, with the latter being reported here for the first time. While blue-shift at apex positions can be attributed to mechanical deformation-induced reorientation of photoselected fluorophores, the blue-shifted mineral-adjacent positions could result from strain loading and development of a plastic deformation region at the mineral contact zone with <em>Tasmanites</em>. A decrease in standard deviation with increasing number of measured emission maxima is well-observed, and 15 to 20 individual measurements per sample appears sufficient for low standard deviation and coefficient of variance. CLSM-derived thermal maturity parameters indicated that a moderate positive correlation of red/green quotient (Q_650/500; R² = 0.67) with solid bitumen reflectance (BR_o in %) exists. For reproducible results, the determination of λ_max and Q_650/500 should be conducted exclusively in the middle position at perpendicular and parallel sections of the polished whole-rock pellets, where the lowest standard deviation in measurement was observed. These results strengthen the suitability and relevance of the CLSM technique in thermal maturity studies of dispersed organic matter (DOM) and contribute to the standardization of fluorescence microspectrometry methods in organic petrology investigation.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104885"},"PeriodicalIF":5.7,"publicationDate":"2025-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145267327","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}

{"title":"Petrolographic characteristics of graphitic carbon in coal-based graphite: Implications for the applicability of reflectance","authors":"Jiuqing Li ,&nbsp;Yong Qin ,&nbsp;Jian Shen ,&nbsp;Yilin Chen ,&nbsp;Geng Li ,&nbsp;Peipei Zhu","doi":"10.1016/j.coal.2025.104884","DOIUrl":"10.1016/j.coal.2025.104884","url":null,"abstract":"<div><div>Coal-based graphite deposits developed in Lutang, Hunan Province, China, provide an opportunity to investigate the petrographic characteristics of graphitic carbon. Optical microscopy and microphotometry were employed to observe the morphology, microstructure, occurrence and reflectance of graphitic carbon and thus classify its type. The results indicated that the evolutionary stage of the coal-based graphite reached the semi-graphite to graphite phase, and five types of graphitic carbon, namely, matrix graphite, granular graphite, needle graphite, flake graphite and pyrolytic carbon, were identified. The maximum reflectances of different types of graphitic carbon vary, indicating a differential evolutionary stage. However, the bireflectance progressively increases through the sequence of needle graphite, pyrolytic carbon and flake graphite, reflecting enhanced structural ordering of basic structural units. In terms of their particle size and reflectance characteristics, granular graphite, needle graphite, pyrolytic carbon, and flake graphite exhibit phanerocrystalline structures, whereas matrix graphite belongs to the cryptocrystalline graphite category. Three primary mechanisms for the origin and formation of graphitic carbon were proposed: in situ solid-phase transformation, liquid-phase crystallization, and vapor-phase deposition. Flake graphite serves as the ideal material for measuring reflectance in coal-based graphite, with its reflectance value acting as an indicator of evolutionary maturity.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104884"},"PeriodicalIF":5.7,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155171","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}

{"title":"The organic petrology of graptolites in sections parallel and perpendicular to the bedding: Implication for thermal maturity evaluation","authors":"Jin Wu ,&nbsp;Qingyong Luo ,&nbsp;Ningning Zhong ,&nbsp;Fariborz Goodarzi ,&nbsp;Yang Bai ,&nbsp;Václav Suchý ,&nbsp;Meijun Li ,&nbsp;Lipeng Yao ,&nbsp;Imran Khan ,&nbsp;Ye Zhang ,&nbsp;Haoran Wang ,&nbsp;Haixu Liu ,&nbsp;Yinghang Tang","doi":"10.1016/j.coal.2025.104883","DOIUrl":"10.1016/j.coal.2025.104883","url":null,"abstract":"<div><div>Graptolites are widely presented in the Ordovician–Silurian Wufeng–Longmaxi Formations and other Lower Paleozoic marine shales throughout the world, and their reflectance is regarded as an effective index for the thermal maturity assessment of the graptolite-bearing shales devoid of vitrinite. Graptolites display distinct optically biaxial features, and the optical characteristics and reflectance of graptolites reveal significant differences depending on orientation of respective graptolite fragments relative to the bedding planes. However, specific studies on these optical discrepancies remains limited, resulting in confusion and/or substantial errors in thermal maturity assessment of graptolite-bearing shales. In this study, the organic petrological method was employed to compare the optical characteristics of graptolites in sections parallel and perpendicular to the bedding. Graptolites and in-source solid bitumen (SB) are the dominant organic components in the Alum and Wufeng–Longmaxi graptolite-bearing shales, and the liptinites are only detected in low maturity samples. In the studied sediments, both non-granular and granular graptolites were identified in abundance, but non-granular graptolites, which exhibit higher reflectance and stronger anisotropy than granular graptolites, were the predominant species. The intense positive correlations between the mean random reflectance (GR_o) and true maximum reflectance (R_max) and bireflectance of non-granular graptolites indicate their increasing anisotropy with maturation. R_max values in sections parallel to the bedding are slightly lower than or equal to those in sections perpendicular to the bedding, and the mean maximum reflectance (<span><math><mover><mi>R</mi><mo>¯</mo></mover></math></span>_max), the intermediate reflectance (R_int), and bireflectance are lower than those in sections perpendicular to the bedding. GR_o values in sections parallel to the bedding display a strong positive correlation with GR_o in sections perpendicular to the bedding, and the former are higher than the latter. GR_o exhibits stronger positive correlations with R_max, <span><math><mover><mi>R</mi><mo>¯</mo></mover></math></span>_max, and bireflectance in sections perpendicular to the bedding than those in sections parallel to the bedding, revealing the stronger anisotropy of non-granular graptolites in sections perpendicular to the bedding. According to the reflectance discrepancies of non-granular graptolites in sections parallel and perpendicular to the bedding, several equivalent equations are proposed to evaluate the thermal maturity of Ordovician–Silurian graptolites-bearing sediments.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104883"},"PeriodicalIF":5.7,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096990","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}

{"title":"Geochemical and petrological characteristics coupled with stable isotope of the Permian Gondwana coals from Tatapani–Ramkola Coalfield, Son–Mahanadi Basin, India: Insights for paleodepositional and paleoclimate conditions","authors":"Neeraj Kumar Upadhayay ,&nbsp;Amiya Shankar Naik ,&nbsp;Shweta Rai ,&nbsp;Prakash K. Singh ,&nbsp;Alok Kumar ,&nbsp;Afikah Rahim ,&nbsp;Mohammed Hail Hakimi ,&nbsp;Govind Kumar ,&nbsp;Pramod Kumar Rajak","doi":"10.1016/j.coal.2025.104882","DOIUrl":"10.1016/j.coal.2025.104882","url":null,"abstract":"<div><div>This study aimed to investigate the quality and rank of the Tatapani-Ramkola coal and decipher the paleoclimate and depositional conditions during coal formation, explicitly focusing on vegetation sources, detrital contributions, and paleomire conditions. The studied coals exhibit a moisture between 4.0 % and 12.8 % and a volatile matter yield in the range of 28.8–49.5 wt% (dry ash–free basis), classifying them as subbituminous–A to bituminous in rank. This finding is supported by the vitrinite reflectance (VRo) values between 0.5 and 0.7 %. Maceral compositions reveal the dominance of vitrinite (average 47.8–62.4 %) followed by inertinite (average 13.0–29.9 %) and liptinite (average 8.5–13.1 %). This finding of the maceral characteristics together with the mineral composition (primarily clay, carbonate, and sulfide), show that the Tatapani–Ramkola coals were formed under mildly oxic–to–anoxic conditions in limno–telmatic to telmatic paleomires and contributions from forest and herbaceous vegetation. Geochemical isotope indicators, such as δ¹³C (−24.149 ± 0.825 ‰) and δ¹⁵N (+2.710 ± 0.344 ‰), suggest that the coals formed from C3 land plants under warm and humid climate conditions. Major oxide ratios indicate a moderate to high degree of chemical weathering in the source area, further confirming the prevailing warm and humid climate during the peat accumulation. The detrital/authigenic index (DAI) suggests significant detrital influence and authigenic sediment formation in the Tatapani–Ramkola coals. This study provides critical insights into the depositional history and paleoclimate of the Tatapani–Ramkola Basin, contributing to a deeper understanding of Permian coal formation processes.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104882"},"PeriodicalIF":5.7,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096989","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}

{"title":"CO2 sorption induced mechanical response of Beetaloo shale","authors":"Umar Farooq ,&nbsp;Klaus Regenauer-Lieb ,&nbsp;Abolfazl Hashemi ,&nbsp;Linan Su ,&nbsp;Hamid Roshan","doi":"10.1016/j.coal.2025.104881","DOIUrl":"10.1016/j.coal.2025.104881","url":null,"abstract":"<div><div>Understanding the mechanical response of organic-rich shales to CO₂ adsorption is critical for optimising CO₂ sequestration and enhanced gas recovery operations. However, these responses are often highly complex and demand a thorough understanding of the underlying sorptive poromechanical mechanisms involved. This study examines the sorptive poromechanical response of Beetaloo shale to CO₂ adsorption under varying confining stress and pore pressure conditions, with a focus on quantifying strength reduction mechanisms. Through controlled triaxial compression experiments, the effects of CO₂ exposure on shale strength with varying pore pressures under different confining stresses were analysed. A theoretical model was then developed and experimentally validated to predict the peak strength of shale with CO₂ adsorption integrating triaxial response with Langmuir adsorption mechanics. The experimental results showed a strong linear relationship between confining stress and both peak strength and elastic modulus, within the range of confining stress tested (up to 25 MPa). It was also revealed that while variations in adsorption across different confining stress levels were relatively small for low gas pressures, this difference became more pronounced at higher pore pressures. In addition, it was observed that the shale strength reduction due to gas adsorption under lower confining stresses follows a near-linear trend with increasing gas saturation. However, under higher confinement (e.g., 25 MPa), the relationship becomes nonlinear, with a more pronounced drop in strength occurring at the early stages of gas adsorption. Moreover, the developed model aligned well with experimental data across all tested conditions, offering a practical tool for predicting mechanical alterations in CO₂ saturated formations. The findings of this study enhance our understanding of coupled poromechanical-sorption effects in shale rocks and provide critical insights for optimising CO₂ injection strategies, ensuring formation integrity, and improving long-term sequestration security in shale carbon sequestration.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104881"},"PeriodicalIF":5.7,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145096894","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}

{"title":"Unraveling hiatuses in black shales: Mechanisms and implications from the Lower Silurian Longmaxi Formation, South China","authors":"Yichen Liu ,&nbsp;Benzhong Xian ,&nbsp;Qianran Wu ,&nbsp;Zhiyong Lu ,&nbsp;Haocheng Shi ,&nbsp;Mingjin Wu ,&nbsp;Zhiyun Yu ,&nbsp;Lin Zhao ,&nbsp;Junyang Geng ,&nbsp;Haiying Chen","doi":"10.1016/j.coal.2025.104869","DOIUrl":"10.1016/j.coal.2025.104869","url":null,"abstract":"<div><div>Fine-grained successions, traditionally interpreted as continuous archives, contain cryptic hiatuses that are critical for evaluating stratigraphic completeness and paleoenvironmental evolution but remain difficult to resolve, especially in deep-water black shales. This study identifies six hiatuses (H1–H6) in the Lower Silurian Longmaxi Formation through integrated sedimentology, cyclostratigraphy, geochemistry, and Evolutive Spectral Analysis (ESA). A 405 kyr eccentricity-tuned astronomical timescale combined with sedimentary noise modeling yields a third-order relative sea-level (RSL) curve, demonstrating controls from both glacio-eustasy and the Kwangsian Orogeny. Our results demonstrate that hiatuses H1–H4 and H6 align with RSL falls, as evidenced by erosion, oxidation, and enhanced bottom-current/gravity-flow activity under cooler climates. Conversely, H5 formed during a warmer highstand, characterized by intense bioturbation and sediment starvation, indicating a non-depositional hiatus. We propose a classification scheme linking ESA spectral features (spectral bifurcation/shifts) with sedimentary attributes, defining seven hiatus types. The Results highlight sea-level fall-driven bottom-current and gravity-flow erosion as the primary hiatus-forming mechanism in deep-water settings. Third-order RSL fluctuations generate major erosional and non-depositional hiatuses (million-year scale), whereas higher-frequency fluctuations induce more subtle and cryptic hiatuses. These surfaces serve as key sequence boundaries, refining sequence stratigraphic frameworks in fine-grained systems. The integrated approach provides a robust methodology for recognizing hiatuses and advances understanding of sedimentary dynamics in deep-water successions.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104869"},"PeriodicalIF":5.7,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020450","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}

{"title":"Pliensbachian (Early Jurassic) deep-time peatland evolution in Northwest China driven by climate change","authors":"Lusheng Yin ,&nbsp;Minfang Yang ,&nbsp;Jing Lu ,&nbsp;Xiaoxuan Wu ,&nbsp;Xue Peng ,&nbsp;Wanqing Wang ,&nbsp;Maoyin Tang ,&nbsp;Kai Zhou ,&nbsp;Peixin Zhang ,&nbsp;Longyi Shao ,&nbsp;David P.G. Bond ,&nbsp;Jason Hilton","doi":"10.1016/j.coal.2025.104871","DOIUrl":"10.1016/j.coal.2025.104871","url":null,"abstract":"<div><div>As peat deposits represent significant terrestrial carbon sinks, the processes of peatland initiation, evolution and termination are important components of the global carbon cycle. Research on recent peatlands leaves many questions unanswered concerning peatland evolution and the driving mechanisms for changes in peat forming environments in deep-time. Using a combination of sedimentology, coal petrology and palynology, this study investigates coal seams #B, #C and #D from the Pliensbachian (Early Jurassic) Qaidam Basin in China to elucidate the evolution of mire types and vegetation in their precursor peats, and to evaluate paleoenvironmental conditions during peat formation. Based on ash yield, total sulfur contents and coal maceral proxies, coals #B and #C record rheotrophic swamp forest mires that gradually transitioned to ombrotrophic bog forest mire conditions. Coal #D has a more complex evolution, initially forming under the ombrotrophic bog forest mire conditions that characterized coal #C before transitioning to a rheotrophic mire with initially fen and then wet swamp forest conditions. Finally, coal #D records a reversion to ombrotrophic mire conditions dominated by bog forest. Palynological assemblages and the ratios of hygrophytic (H) to xerophytic (X) plants reveal a remarkable change in peat-forming vegetation and paleoclimate. Coals #B and #C are dominated by woody gymnosperms, while deposition of the precursor peats of coal #D gradually evolved into a mix of woody and herbaceous plants. This floristic transition coincided with intensified climatic oscillations, establishing cyclic dry-wet conditions during the later stages of coal #D deposition. Our results reveal that during the Pliensbachian in the Qaidam Basin, climate forcing on peatland environments was manifested primarily through changes in precipitation and water availability brought on by intensification of seasonality. Peatland evolution was a multi-phase process of changing mire types and an overall vegetation succession from woody to herbaceous and woody plants.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104871"},"PeriodicalIF":5.7,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145005080","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}

{"title":"Enhancing coal seam gas recovery through greenzyme-induced relative permeability optimisation: Helium-driven core flooding experiments and field-scale production simulations","authors":"Wen Xi ,&nbsp;Kunning Tang ,&nbsp;Ying Da Wang ,&nbsp;Yu Jing ,&nbsp;Joan Esterle ,&nbsp;Klaus Regenauer-Lieb ,&nbsp;Lucas Evangelista ,&nbsp;Ryan T. Armstrong ,&nbsp;Peyman Mostaghimi","doi":"10.1016/j.coal.2025.104866","DOIUrl":"10.1016/j.coal.2025.104866","url":null,"abstract":"<div><div>Coal seam gas (CSG) is an unconventional gas resource in the global energy supply. A key factor in predicting and evaluating methane production in coalbeds is coal relative permeability. This study explores the effects of an enzyme-based surfactant, GreenZyme (GZ), on coal relative permeability through drainage unsteady-state core flooding experiments. Initial measurements of interfacial tension (IFT) between helium and GZ solutions at various concentrations demonstrate a decrease in IFT from approximately 70 <span><math><mi>mN/m</mi></math></span> to 45 <span><math><mi>mN/m</mi></math></span> as GZ concentration increases, with 1.2 wt% identified as the critical concentration for solution preparation. Helium was employed as a substitute for methane to eliminate sorption effects and focus on liquid–gas phase interactions. The relative permeability curves for gas and water were derived using the Johnson–Bossler–Naumann (JBN) method. The results show that GZ improves the displacement of water by approximately 5%, with relative permeability curves for both water and gas moving leftward and upward in the presence of GZ. This enhancement is attributed to the reduction in IFT between the water and gas phases. To assess the impact at the field scale, an Eclipse-developed CSG production model incorporating experimental data was developed. Simulation results show that while the gas production rate based on the original relative permeability curves is initially higher during the first 0.28 years, the rate for the GZ-enhanced case surpasses it for the remainder of the production period. These findings provide valuable insights into the influence of GZ on coal relative permeability and demonstrate its potential to enhance CSG recovery at the field scale.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104866"},"PeriodicalIF":5.7,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145020449","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}

{"title":"The modes of occurrence, distribution and enrichment of critical raw materials (Ga, Sr, Zr and Ba) within coal discards of the Witbank Coalfield, South Africa","authors":"X. Nkwamza,&nbsp;N. Malumbazo","doi":"10.1016/j.coal.2025.104870","DOIUrl":"10.1016/j.coal.2025.104870","url":null,"abstract":"<div><div>Coal mineralogy and trace element composition provide vital insights into the geological coal formation processes, depositional environments, and potential resource valorization. However, there is limited knowledge and understanding of the geochemical and mineralogical composition of coal discards from the Witbank Coalfield. Thus, the coal discards remain underexplored, limiting effective management and future utilization strategies. To address this gap, this study investigates the occurrence, distribution and enrichment of CRMs within Permian coal discards of the Witbank Coalfield. An integrated suite of analytical techniques such as TGA, Bomb calorimeter, FTIR, XRD, TIMA, SEM-EDS, XRF and ICP-MS was utilized to determine the dominant mineral assemblages and trace elemental enrichments. Results revealed quartz and kaolinite as the principal minerals, with subordinate carbonate and sulfide phases introduced through diagenetic and hydrothermal processes. The coal discards were enriched in trace elements such as Ga, Sr, Zr and Ba. Ga was associated with kaolinite and organic matter, Sr and Ba predominantly occurred in barite, and Zr was hosted primarily in detrital zircon grains. Their spatial variability reflects depositional and diagenetic controls. Geochemical proxies, such as Sr/Ba and TiO₂/Al₂O₃ ratios, indicate freshwater depositional conditions influenced by volcanic ash input and post-depositional alteration. These findings enhanced the understanding of the geochemical cycling within coal discards, their mineralogical stability, and potential environmental implications. Furthermore, the presence of acid-neutralizing minerals supports the potential use of these coal discards in mitigating acid mine drainage, while the enriched CRMs highlight opportunities for sustainable resource recovery.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"310 ","pages":"Article 104870"},"PeriodicalIF":5.7,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144989494","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}

{"title":"Effect of temperature on coal maceral dissolution and matrix alteration during NaClO stimulation: Insights from microscopy and Micro-CT","authors":"Sen Yang ,&nbsp;Zhentao Li ,&nbsp;Joan Esterle ,&nbsp;Karen M. Steel","doi":"10.1016/j.coal.2025.104868","DOIUrl":"10.1016/j.coal.2025.104868","url":null,"abstract":"<div><div>Oxidant stimulation has emerged as a promising supplementary approach to enhance gas recovery from coal seams, targeting coal organic matter more directly than acid stimulation, which affects mineral components. However, the reactivity of different coal maceral subtypes to oxidants, particularly under reservoir conditions, remains poorly understood. In this study, sodium hypochlorite (NaClO) was used to investigate the maceral-specific reactivity and matrix alteration of bituminous coal samples from the Bowen Basin, Australia, under varying temperature conditions. Microscopic and Micro-CT analyses revealed that higher temperatures significantly enhanced maceral dissolution. The observed reactivity followed the order: semifusinite &gt; vitrinite &gt; fusinite, with collodetrinite within vitrinite displaying notably higher reactivity than collotelinite. These divergences should be ascribed to the differences in aromaticity, functional group composition, and pore structure. Micro-CT results revealed maceral-dependent dissolution depths, ranging from 300 to 500 μm for semifusinite, ∼100 μm for fusinite, and 50–150 μm for vitrinite bands. As a fine-grained heterogeneous host to telovitrinite macerals and other detrital components, coal matrix exhibited strong alteration in directional dependence, with significantly enhanced pore and fracture development along the horizontal (bedding plane) direction. At 60 °C, the reaction depth reached up to 850 μm, accompanied by substantial pore enlargement, particularly within the 30–50 μm range. Mixed maceral zones showed deeper reaction fronts than vitrinite-rich areas, emphasizing the influence of maceral heterogeneity on oxidant penetration. This study highlights that both maceral composition and bedding structure critically govern the extent, directionality, and effectiveness of oxidant-induced matrix alteration. These findings provide important insights into optimizing oxidant stimulation strategies for improved gas recovery in heterogeneous coal reservoirs.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104868"},"PeriodicalIF":5.7,"publicationDate":"2025-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144895538","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}