International Journal of Coal Geology最新文献

{"title":"Understanding coalbed gas distribution from longwall mining: Geochemical and isotopic approach","authors":"Yaroslav Bezyk ,&nbsp;Dawid Szurgacz ,&nbsp;Dariusz Strąpoć ,&nbsp;Magdalena Misz-Kennan ,&nbsp;Monika J. Fabiańska ,&nbsp;Ewa Szram ,&nbsp;Łukasz Kruszewski ,&nbsp;Miroslaw Zimnoch ,&nbsp;Jarosław Nęcki ,&nbsp;Izabela Sówka ,&nbsp;Tomasz Kowalski ,&nbsp;Carina van der Veen ,&nbsp;Thomas Röckmann ,&nbsp;Maciej Górka","doi":"10.1016/j.coal.2025.104859","DOIUrl":"10.1016/j.coal.2025.104859","url":null,"abstract":"<div><div>Coalbed methane plays a critical role in both energy resource potential and environmental and mine safety strategies. Despite much research has been done on coalbed gas origin, the combined effects of coal maturity, gas migration processes, and mine ventilation in an active mining environment are still not fully understood. This study combined molecular and stable carbon and hydrogen isotope analyses of coalbed gases collected along the longwall coal face during the early and final stages of operation, with petrographic and geochemical characteristics of freshly mined coal from the Upper Silesian Coal Basin, Poland. Complementary organic petrography and biomarker analysis performed on freshly mined coal revealed that the vitrinite-rich bituminous coal is at peak oil-window maturity. Gas composition from a borehole in the coal seam indicated methane as the dominant component (up to 87 %), with contributions from carbon dioxide (up to 2.3 %) and lower amounts (0.1–1.5 %) of heavier hydrocarbons (C₂ − C₆). Heterocyclic species of sulfur (thiophene) and nitrogen (pyridine), chlorinated (1,2-DCE) compounds, oxygen-bearing organic gases (acetic acid), dimethyl sulfide (DMS), and some portion of ortho-cresol, tetrahydrofuran, formaldehyde, and cumene tracers were also found in the complex gas mixtures from the borehole.</div><div>Isotopic data of methane in the examined longwall coal face averaged at −48.1 ± 0.7 ‰ for δ¹³C and − 192.1 ± 7.1 ‰ for δ²H and coal maturity vitrinite reflectance at 0.75 ± 0.02 %. These molecular and isotopic coalbed gas data implied a thermogenic origin of the coalbed methane, with fingerprints of biodegradation in thermogenic system. Slightly depleted isotope values from the borehole under examination (δ¹³C: −50.9 ± 0.2 ‰ and δ²H: −194.2 ± 2.8 ‰) suggested the presence of free gas stored in the coal fractures. Spatial variations in gas composition and isotopic shifts across the longwall panel were found to be driven by ventilating airflow supplied to the working face. Isotope alteration along airflow path from main- to tailgate entries emphasized the influence of secondary processes, such as desorption and diffusion. Preferential loss of isotopically light ¹²CH₄ molecules, especially at gas accumulation zones (tailgate), aligns with findings from laboratory desorption experiment on successively crushed coal samples. In contrast, less systematic δ²H-CH₄ patterns under active mining reflected the combined effects of gas mixing, site-specific conditions, and parameters of coal mine operations.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104859"},"PeriodicalIF":5.7,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144780412","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":"CBM enrichment mechanisms in the Southern Qinshui Basin: A synergistic role of tectonic-lithological-hydrodynamic coupling","authors":"Xiaoxiao Sun ,&nbsp;Hui Wang ,&nbsp;Fengfeng Du ,&nbsp;Yanbin Yao ,&nbsp;Dameng Liu ,&nbsp;Zhong Liu","doi":"10.1016/j.coal.2025.104861","DOIUrl":"10.1016/j.coal.2025.104861","url":null,"abstract":"<div><div>The Qinshui Basin is renowned for its thick, laterally extensive coal seams, high thermal maturity, and significant coalbed methane (CBM) potential. However, reservoir heterogeneity resulting from multi-stage tectonic activity leads to pronounced variability in CBM enrichment, posing challenges for efficient development. This study examines the influence of individual and coupled tectonic, roof–floor lithological, and hydrodynamic factors on CBM accumulation in the southern Qinshui Basin, using seismic data, well logs, and gas content analysis. Four distinct CBM enrichment models are identified from north to south: in shallow seams, atmospheric precipitation-driven groundwater recharge, coupled with anticlinal structures, controls the spatial distribution of gas; with increasing burial depth, reduced groundwater mobility and improved roof–floor sealing shift the dominant control from hydrodynamic to lithological factors; in structural slope zones, gas enrichment is governed by the coupling of nose structure and hydrodynamic sealing; In fault-dominated areas, gas migration along faults and the sealing capacity of fault zones are the primary controls. These findings provide a scientific basis for optimizing CBM exploration and development in geologically complex basins.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104861"},"PeriodicalIF":5.7,"publicationDate":"2025-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144766729","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":"Characteristics of pre- and syn-rift sequences in the central Gulf of Suez: Implications for hydrocarbon generation and paleoenvironment","authors":"Moataz El-Shafeiy ,&nbsp;Thomas Gentzis ,&nbsp;Ismail A. Hussein ,&nbsp;Dina Hamdy","doi":"10.1016/j.coal.2025.104850","DOIUrl":"10.1016/j.coal.2025.104850","url":null,"abstract":"<div><div>The October sub-basin is one of the largest oil fields in Egypt, situated within the central Gulf of Suez petroleum province. Four wells were studied to investigate the petroleum system using integrated geochemical and petrographic techniques. This gives valuable information on the source rock potentialities, which may help in new hydrocarbon discoveries in the October sub-basin. Organic-rich pre-rift (Late Cretaceous-Eocene) and syn-rift (early-middle Miocene) sequences were analyzed for TOC, Rock-Eval pyrolysis, vitrinite reflectance (R_o%), and lipid biomarkers. 1D basin models were built to assess hydrocarbon generation timing and remaining potential. This analysis provides valuable insights into source rocks characteristics, including quantity, quality, thermal maturity, and paleoenvironmental implications. Pre-rift strata show fair-very good organic richness, while syn-rift strata demonstrate poor-good organic richness. Pyrolysis shows that the NW wells predominantly contain Type III dispersed organic matter and organic petrography shows the presence of vitrinite in the form of collotelinite and collodetrinite) in both sequences. The same analysis also shows that the SE wells contain Type II-III and II kerogen while organic petrography shows the presence of dispersed liptinitic organic matter (e.g., telalginite, lamalginite, sporinite, liptodetrinite) and also low inertinite content. This indicates a greater marine organic matter input, which is also supported by biomarker data, with the latter suggesting low-oxygen conditions in the SE parts of the sub-basin. Pre-rift source rocks range from immature to the upper oil/wet gas window (R_o% of 0.50–1.35 % in the NW wells, 0.41–0.82 % in the SE wells), but mostly within the oil window. The NW wells show higher thermal maturity, particularly in well NO124–1, likely due to elevated geothermal gradients from rift-related Oligocene-Miocene igneous activity. As expected, syn-rift strata are immature or in the early oil window (R_o % 0.37–0.61 % in the NW, 0.36–0.61 % in the SE). Thermal maturity modeling indicates that pre-rift strata are effective source rocks entered the early oil window ∼20–15 Ma, earlier onset in the NW wells. Present-day pre-rift transformation ratios are higher in the NW (60–88 %) than in the SE (17–35 %) wells, suggesting greater remaining hydrocarbon generation potential in the SE region.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104850"},"PeriodicalIF":5.7,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144757945","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":"Sedimentology and geochemistry of the Upper Permian Longtan and Dalong formations in the Lianyuan Sag, Xiangzhong Depression, South China: Implications for paleoclimate, provenance, tectonic setting, and organic matter accumulation","authors":"Zhongrui Wu ,&nbsp;Ralf Littke ,&nbsp;Shuo Qin ,&nbsp;Yahao Huang ,&nbsp;Sheng He ,&nbsp;Yaohui Xu ,&nbsp;Yan Liu ,&nbsp;Xiao Chen ,&nbsp;Kaiming Wang","doi":"10.1016/j.coal.2025.104849","DOIUrl":"10.1016/j.coal.2025.104849","url":null,"abstract":"<div><div>The organic-rich shales in the Upper Permian Longtan Formation (LF) and Dalong Formation (DF) are important hydrocarbon source rocks and have become key targets for shale gas exploration in the Yangtze area, South China. To investigate the provenance, tectonic setting, paleoenvironmental conditions, and mechanisms of organic matter (OM) accumulation, this study presents an integrated petrological and geochemical study of a continuously cored well in the Xiangzhong Depression, South China. The LF was deposited in marine–continental transitional facies under a hot and humid climate with intense chemical weathering. OM is predominantly terrigenous-derived, consisting mainly of vitrinite and inertinite. Multiple geochemical proxies, together with pyrite framboid analyses, suggest that oxic, brackish water conditions, low paleoproductivity, and a high influx of terrestrial material prevailed during the deposition of the LF. In contrast, the DF comprises fully marine sediments, reflecting a depositional setting influenced by a rapid sea-level rise and progressive climatic aridification. These changes resulted in a saline, anoxic water column with enhanced primary productivity and reduced weathering intensity. The relationships between total organic carbon (TOC) content and geochemical indicators suggest that paleoclimate and terrigenous influx are the dominant factors controlling the OM accumulation in the LF, whereas upwelling-induced high productivity was the dominant factor driving OM enrichment in the DF. This study provides a comprehensive dataset on the LF and DF, which exhibit markedly different depositional environments, and aims to address the gap in the evaluation of Permian shale gas potential in the Middle Yangtze region.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104849"},"PeriodicalIF":5.7,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144749815","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 mapping and distribution patterns of critical elements resources in Chinese coal-bearing strata","authors":"Ruiwen Yan ,&nbsp;Jun Zhu ,&nbsp;Qingyi Cao ,&nbsp;Gang Lin ,&nbsp;Xiang Li ,&nbsp;Furui Xi","doi":"10.1016/j.coal.2025.104848","DOIUrl":"10.1016/j.coal.2025.104848","url":null,"abstract":"<div><div>Critical elements in coal have attracted global attention in recent years due to a substantial increase in demand driven by economic development and defense security needs. Understanding their geochemical distribution patterns is crucial for the future strategic management and effective utilization of these metals. As the world's largest coal-producing country which has a complex condition of coal formation, China provides an ideal natural laboratory for studying the geochemical characteristics of critical elements in coal. This work collected a large dataset on critical elements, including U (<em>n</em> = 1461), Ga (<em>n</em> = 1556), Ge (<em>n</em> = 1210), V (n = 1461), Zr (<em>n</em> = 1199), and Li (<em>n</em> = 1122) from Chinese coal using multi-analysis methods to understand their spatial distribution patterns. With these data, we have: (1) updated the average contents of critical elements (U, Ga, Ge, V, Zr, and Li) in Chinese coals, which showed a more enriched Ga, V, Zr, and Li level compared with the global average; (2) generated a set of geochemical distribution maps for these elements in Chinese coals and coal ashes, targeting key potential areas for their exploration within China's coal-bearing regions based on development and utilization grades. With these important geochemical data, this work provides critical information for studying geochemical characteristics of the trace elements in coal, offering a valuable reference for prospecting and utilizing critical elements in coal.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104848"},"PeriodicalIF":5.7,"publicationDate":"2025-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144771242","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":"Industrial and mining impacts on the organic matter of soils in a protected area of the Central Portuguese Coast: A petrographic and geochemical approach","authors":"Fernando Michels ,&nbsp;Joana Ribeiro ,&nbsp;Maria Helena Henriques ,&nbsp;Ádám Nádudvari ,&nbsp;Magdalena Misz-Kennan ,&nbsp;Monika J. Fabiańska","doi":"10.1016/j.coal.2025.104847","DOIUrl":"10.1016/j.coal.2025.104847","url":null,"abstract":"<div><div>Long-term industrial operations fueled by coal and oil have the potential to significantly impact surrounding ecosystems, particularly in the past when environmental regulations were less stringent. In this study, organic contamination was investigated in soils surrounding a former industrial complex and coal mining area on the Portuguese Atlantic coastline, active from the 19th century through the early 21st century. This area is currently included in the Natural Monument of Cabo Mondego, which highlights concerns regarding its environmental quality. Surface soil samples were investigated through a multi-technique approach using organic petrography, an uncommon yet powerful tool that provides unequivocal evidence of contaminants, and geochemical methods to identify sources of fossil fuel-derived contaminants. Results indicate that most of the samples exceed national reference levels for priority polycyclic aromatic hydrocarbons (PAH), with the highest concentrations found in the samples located up to 500 m from the former industrial facilities. These findings suggest that emissions from the industrial complex are the primary source of organic contamination in the area. Elevated levels of PAH (recognized environmental pollutants and human carcinogens) associated with contaminant combustion-derived organic particles (coke and char) raise environmental concerns. The presence of both local and imported coal particles in soil, along with the disposal of coal residues in the area, highlights contamination linked to historical coal handling and transport. The detection of charcoal particles in soil reflects the influence of regional wildfires that occurred in recent decades. These findings contribute to understanding the environmental vulnerabilities of the Cabo Mondego Natural Monument.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"309 ","pages":"Article 104847"},"PeriodicalIF":5.6,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144714490","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":"Enrichment of Ni-Zn-Cd-Mo-V in the Şırnak asphaltites, Türkiye: The effects of organic matter, sedimentary processes, and hydrothermal fluids on element concentrations and occurrences","authors":"Emine Cicioglu Sutcu","doi":"10.1016/j.coal.2025.104846","DOIUrl":"10.1016/j.coal.2025.104846","url":null,"abstract":"<div><div>There are numerous asphaltite veins in southeastern Anatolia, Turkey. The Avgamasya, Anılmış, Harbul, Silip, and Üçkardeşler veins, which are the focus of this study, are enriched in elements such as As, Cd, Mo, Ni, Sb (except in Harbul), U, V, Zn, and Hg. Commonly detected minerals across all samples include dolomite, calcite, apatite, pyrite, sphalerite, alkali feldspar, quartz, illite, and iron oxides. Additionally, smectite, barite, celestine, ilmenite, galena, hematite, rutile, and strontianite were also observed. The mineral matter present can be both syngenetic and epigenetic. The microcrystalline minerals present within solid bitumen may have precipitated from supersaturated fluids during the maturation of hydrocarbons. In contrast, epigenetic minerals may have originated from hydrothermal fluids after the solid bitumen was formed or may have been incorporated from the surrounding host rocks during the hydrocarbon migration process. Organisms in the shelf environment likely played a crucial role in the enrichment of these elements. Sedimentary and diagenetic processes, sediment pore waters, and hydrothermal fluids may have significantly contributed to the formation of minerals that host these enriched elements. Solid bitumen, iron oxides, pyrite, and sphalerite can serve as major carriers of these enriched elements. Meanwhile, lithophile elements such as Sr, Ba, and Na are typically found in minerals like barite, strontianite, celestine, calcite, apatite, and fossil shells.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104846"},"PeriodicalIF":5.6,"publicationDate":"2025-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144703088","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":"Petrological and organic geochemical insights into the peat-forming environmental settings during the deposition of the early Oligocene Pirin coal deposit, SW Bulgaria","authors":"Alexander Zdravkov ,&nbsp;Achim Bechtel ,&nbsp;Ksenija Stojanović ,&nbsp;Doris Groβ ,&nbsp;Johannes Weitz ,&nbsp;Ivan Kojić ,&nbsp;Reinhard F. Sachsenhofer ,&nbsp;David Misch ,&nbsp;Dragana Životić","doi":"10.1016/j.coal.2025.104843","DOIUrl":"10.1016/j.coal.2025.104843","url":null,"abstract":"<div><div>The up to 30-m-thick Brezhani coal seam in the Pirin deposit (SW Bulgaria) is the only coal of early Oligocene age on the territory of Bulgaria, providing important insights into peat-forming environments during that period. The coal seam was investigated using organic petrography, bulk organic geochemistry and biomarker analysis.</div><div>Coal is predominantly composed of detrovitrinite with subordinate collotelinite and abundant corpogelinite. Liptinite macerals are mostly represented by alginite and suberinite, and locally resinite. The coal commonly contains semi-inertinized (oxidized) root tissues without apparent thermal influence. The low- to moderate tissue preservation indicates predominant contribution from plants with low preservation potential. Rare resin-impregnated woody tissues argue for peat accumulation within a sparsely forested shrub-dominated mire. Biomarker proxies indicate a contribution from mixed vegetational communities, composed of flowering plants and bald cypresses. A contribution of aquatic macrophytes is also evident.</div><div>Variable ash yields and sulfur contents indicate changeable water supply and pH conditions. However, high sulfur contents and ash yields in a large number of the samples denote organic matter accumulation within a topogenous mesotrophic marginal limno-telmatic mire. Plant material accumulated at or very close to the water surface in a predominantly water-logged environment, indicated by strong gelification. The initial oxidizing conditions were quickly shifted to reductive settings due to flooding of the peat surface with possible seasonal dynamics.</div><div>Low maturity of the organic matter and limited hydrocarbon generation potential are evident from the low vitrinite reflectance (avg. Ro = 0.52 %), biomarker parameters and Rock-Eval data.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104843"},"PeriodicalIF":5.6,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621965","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":"Kinetic characteristics of secondary hydrocarbon generation from oil shale and coal at different maturation stages: Insights from open-system pyrolysis","authors":"Hongbiao Wang ,&nbsp;Daming Niu ,&nbsp;Zhisheng Luan ,&nbsp;Hongliang Dang ,&nbsp;Xinyu Pan ,&nbsp;Pingchang Sun","doi":"10.1016/j.coal.2025.104845","DOIUrl":"10.1016/j.coal.2025.104845","url":null,"abstract":"<div><div>Understanding secondary hydrocarbon generation from organic matter is critical for assessing source rock potential in thermally complex basins. This study investigates the hydrocarbon generation kinetics of immature to low-maturity kerogen types (Type I, II, III) using open-system pyrolysis experiments on oil shale and coal samples from the Minhe and Meihe Basins, China. Results show that Type I kerogen exhibits a narrow hydrocarbon generation window and rapid depletion of generative potential, whereas Types II and III display broader, more gradual trends. Activation energy increases with thermal maturity, and interruptions during active generation raise the energy threshold for reactivation. A parallel first-order reaction model accurately simulates generation rates (R² &gt; 0.9998). By integrating kinetic parameters with burial and thermal histories, we reconstructed hydrocarbon evolution pathways in the Minhe Basin. Simulations indicate that <em>in-situ</em> conversion of shallow oil shale at a heating rate of 0.35 °C/day over 881 days yields maximum hydrocarbon output with minimal energy consumption. These insights provide a theoretical foundation for both conventional reservoir prediction and unconventional resource development.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104845"},"PeriodicalIF":5.6,"publicationDate":"2025-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144596540","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":"FTIR spectral signatures of Cretaceous-Paleogene sub-bituminous and bituminous coal: Insights into molecular structure evolution during coalification in the Eastern Cordillera Basin, Colombian Andes","authors":"Juan Sebastian Gomez-Neita ,&nbsp;Ana Maria Pimentel Mizusaki ,&nbsp;Taís Freitas da Silva ,&nbsp;Sandra Rocio Manosalva-Sanchez ,&nbsp;Jorge Eliecer Mariño-Martínez ,&nbsp;David Enrique Vega Porras ,&nbsp;Simone Patricia Aranha da Paz","doi":"10.1016/j.coal.2025.104844","DOIUrl":"10.1016/j.coal.2025.104844","url":null,"abstract":"<div><div>The coalification process and maceral composition influence the molecular structure of the organic matter, yet their precise effects remain a significant challenge in coal geology studies. This investigation focused on sub-bituminous and bituminous coal from the Cretaceous-Paleogene Guaduas Formation in the Colombian Andes, concurrently creating an extensive database of FTIR spectral signatures with 118 samples. Analytical techniques employed in this study included Fourier Transform Infrared spectroscopy in the mid-Infrared Region (FTIR-MIR) using the KBr pellet method, micro-FTIR spectroscopy, and X-ray diffraction (XRD). Molecular structural parameters, such as Aromaticity (AR1 and AR2), Degree of Condensation (DOC1 and DOC2), methylene-to-methyl ratio (CH₂/CH₃), and Factor A, were determined. The random vitrinite reflectance (VRr%) of the studied samples ranged from 0.46 % to 1.65 %, indicating the occurrence of sub-bituminous and bituminous coals. The results revealed AR1 ranging from 0.026 to 0.182, AR2 from 0.208 to 1.282, DOC1 from 0.048 to 0.244, DOC2 from 0.373 to 1.797, CH₂/CH₃ from 2.444 to 6.430, and Factor A from 0.559 to 0.701. The prominent inorganic peaks in the FTIR spectra corroborated with the coal mineralogy, kaolinite and quartz, which are dominant, with minor occurrences of siderite, pyrite, and iron oxides. Micro-FTIR data indicated higher aromaticity and condensation in macerals of the inertinite group compared to vitrinite and liptinite groups. The correlation of structural parameters showed an increase in condensation and aromaticity with higher VRr% (or increased coal rank). The aromaticity and condensation increased with depth, suggesting that burial affected the rank of the Guaduas Formation coal. Coal with a higher inertinite content showed higher aromaticity/condensation and shorter aliphatic chain length (CH₂/CH₃). The FTIR spectra of the analyzed dataset reveal that coalification was the dominant factor that affected the organic molecular structure of coal in the Eastern Cordillera Basin. It was found that maceral composition is also crucial in explaining the variations in molecular structural parameters observed in isorank coals. In this sense, liptinite-rich coal was enriched in aliphatic components, whereas vitrinite and inertinite-rich coals were enriched in aromatic compounds, exhibiting gas-prone characteristics.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104844"},"PeriodicalIF":5.6,"publicationDate":"2025-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621964","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}