Pub Date : 2025-07-22DOI: 10.1016/j.coal.2025.104846
Emine Cicioglu Sutcu
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.
{"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}
Pub Date : 2025-07-10DOI: 10.1016/j.coal.2025.104843
Alexander Zdravkov , Achim Bechtel , Ksenija Stojanović , Doris Groβ , Johannes Weitz , Ivan Kojić , Reinhard F. Sachsenhofer , David Misch , Dragana Životić
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.
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.
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.
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.
{"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 , Achim Bechtel , Ksenija Stojanović , Doris Groβ , Johannes Weitz , Ivan Kojić , Reinhard F. Sachsenhofer , David Misch , 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}
Pub Date : 2025-07-07DOI: 10.1016/j.coal.2025.104845
Hongbiao Wang , Daming Niu , Zhisheng Luan , Hongliang Dang , Xinyu Pan , Pingchang Sun
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 > 0.9998). By integrating kinetic parameters with burial and thermal histories, we reconstructed hydrocarbon evolution pathways in the Minhe Basin. Simulations indicate that in-situ 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.
{"title":"Kinetic characteristics of secondary hydrocarbon generation from oil shale and coal at different maturation stages: Insights from open-system pyrolysis","authors":"Hongbiao Wang , Daming Niu , Zhisheng Luan , Hongliang Dang , Xinyu Pan , 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 (R<sup>2</sup> > 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}
Pub Date : 2025-07-07DOI: 10.1016/j.coal.2025.104844
Juan Sebastian Gomez-Neita , Ana Maria Pimentel Mizusaki , Taís Freitas da Silva , Sandra Rocio Manosalva-Sanchez , Jorge Eliecer Mariño-Martínez , David Enrique Vega Porras , Simone Patricia Aranha da Paz
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.
{"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 , Ana Maria Pimentel Mizusaki , Taís Freitas da Silva , Sandra Rocio Manosalva-Sanchez , Jorge Eliecer Mariño-Martínez , David Enrique Vega Porras , 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 (CH<sub>2</sub>/CH<sub>3</sub>), 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, CH<sub>2</sub>/CH<sub>3</sub> 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 (CH<sub>2</sub>/CH<sub>3</sub>). 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}
Pub Date : 2025-07-04DOI: 10.1016/j.coal.2025.104842
Angeles G. Borrego
{"title":"Editorial of the special issue: 75th ICCP meeting: Organic petrology research and applications for the 21st Century","authors":"Angeles G. Borrego","doi":"10.1016/j.coal.2025.104842","DOIUrl":"10.1016/j.coal.2025.104842","url":null,"abstract":"","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104842"},"PeriodicalIF":5.7,"publicationDate":"2025-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144621942","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 : 2025-07-03DOI: 10.1016/j.coal.2025.104831
Monica Sahoo , James C. Hower , Ganesh Chalavadi
The increasing demand and utilization of rare earth elements (REE or REY, if yttrium is included) in numerous sectors have led to the consideration of secondary resources for their recovery. The worldwide research has been focused on coal beds that may have potential recovery of REE or REY. Despite India's extensive coal reserves, the complex geochemistry of REE in its coalfields remains underexplored, with only a few basins being investigated. This paper reviews existing literature on the enrichment types, modes of occurrence, and anomalies of REE in Indian coal measures. Key findings indicate the presence of REY-bearing minerals such as xenotime, rhabdophane, mixed layer smectite/illite, etc., in Gondwana and Paleogene coals along with a high fractionation of LREE (light REE). Coals from Satupalli, Hura, Meghalaya, and Jharia show strong potential for the REY extraction. The Upper Continental Crust (UCC)-normalized REE patterns of the coal deposits illustrate variations in their distribution types. Satupalli coals exhibit an heavy-type distribution, Hura coals display light- and medium-type distribution patterns, Sohagpur coals show light-type pattern, while Assam coals have an heavy-type distribution pattern. The modes of occurrence of the REE in Indian coals are primarily influenced by the input of detrital minerals in erosional areas. The Paleogene coals have experienced marine-influenced environments; however, few of them exhibit distinctive depositional settings as well. Limited coal samples from Meghalaya and Raniganj show substantial REE enrichment. This study highlights the dissimilar characteristics in REE distribution patterns across India's coalfields, each with disparate geological settings, which need supplementary research work to establish their precise modes of occurrence and incorporation mechanisms into the peat depositional environment.
{"title":"Geochemical perspectives of the rare earth elements and yttrium in some Permian and Paleogene coals of India: A review","authors":"Monica Sahoo , James C. Hower , Ganesh Chalavadi","doi":"10.1016/j.coal.2025.104831","DOIUrl":"10.1016/j.coal.2025.104831","url":null,"abstract":"<div><div>The increasing demand and utilization of rare earth elements (REE or REY, if yttrium is included) in numerous sectors have led to the consideration of secondary resources for their recovery. The worldwide research has been focused on coal beds that may have potential recovery of REE or REY. Despite India's extensive coal reserves, the complex geochemistry of REE in its coalfields remains underexplored, with only a few basins being investigated. This paper reviews existing literature on the enrichment types, modes of occurrence, and anomalies of REE in Indian coal measures. Key findings indicate the presence of REY-bearing minerals such as xenotime, rhabdophane, mixed layer smectite/illite, etc., in Gondwana and Paleogene coals along with a high fractionation of LREE (light REE). Coals from Satupalli, Hura, Meghalaya, and Jharia show strong potential for the REY extraction. The Upper Continental Crust (UCC)-normalized REE patterns of the coal deposits illustrate variations in their distribution types. Satupalli coals exhibit an heavy-type distribution, Hura coals display light- and medium-type distribution patterns, Sohagpur coals show light-type pattern, while Assam coals have an heavy-type distribution pattern. The modes of occurrence of the REE in Indian coals are primarily influenced by the input of detrital minerals in erosional areas. The Paleogene coals have experienced marine-influenced environments; however, few of them exhibit distinctive depositional settings as well. Limited coal samples from Meghalaya and Raniganj show substantial REE enrichment. This study highlights the dissimilar characteristics in REE distribution patterns across India's coalfields, each with disparate geological settings, which need supplementary research work to establish their precise modes of occurrence and incorporation mechanisms into the peat depositional environment.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104831"},"PeriodicalIF":5.6,"publicationDate":"2025-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144596541","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 : 2025-06-28DOI: 10.1016/j.coal.2025.104833
Zhenyu Xu , Xiaomei Wang , Fan Deng , Xingxing Guo , Yuxuan Han , Ke Sheng , Yuanhe Mu , Qin Yang
As the promising critical metal elements in coal, rare earth elements and yttrium (REY) can occur in minerals or complex with organic matter. Some differences have been observed in the modes of occurrence of REY in coals with different ranks, which raises interesting questions on their variation characteristic and mechanism during complex coalification. In this study, the modes of occurrence of REY and organic structure characteristics in bituminous coals with different ranks from the Hedong Coalfield are investigated. The sequential chemical extraction procedure shows that REY mainly remain in the residue in the low-rank bituminous coals and display an increasing total leaching rate as vitrinite reflectance increases. While in the high-rank bituminous coals, REY are dominated by HCl-leachable and residual phases. These results demonstrate that organic matter is the dominant carrier of REY in the low-rank bituminous coals. While in the high-rank bituminous coals, REY predominantly associate with phosphates and organic matter, indicating a gradual transformation from organic to mineral forms during coalification. Fourier Transform infrared (FTIR) spectroscopy experiments have found that the peak areas of most oxygenated functional groups are negatively correlated with vitrinite reflectance. In comparison to other functional groups, the content of phenolic group (Ar-OH) displays a strong positive correlation with the proportion of residual REY in the sequential chemical extraction experiment. This indicates that Ar-OH probably serves as the dominant organic binding site of REY during coalification. The loss of organic binding sites during coalification may result in the gradual decline of the proportion of organic-bound REY. Meanwhile, some REY released from these binding sites probably form authigenic minerals, leading to the higher proportion of mineral-associated forms of REY in the high-rank bituminous coals.
{"title":"Modes of occurrence of rare earth elements and yttrium in bituminous coals with different ranks from the Hedong Coalfield, northern China","authors":"Zhenyu Xu , Xiaomei Wang , Fan Deng , Xingxing Guo , Yuxuan Han , Ke Sheng , Yuanhe Mu , Qin Yang","doi":"10.1016/j.coal.2025.104833","DOIUrl":"10.1016/j.coal.2025.104833","url":null,"abstract":"<div><div>As the promising critical metal elements in coal, rare earth elements and yttrium (REY) can occur in minerals or complex with organic matter. Some differences have been observed in the modes of occurrence of REY in coals with different ranks, which raises interesting questions on their variation characteristic and mechanism during complex coalification. In this study, the modes of occurrence of REY and organic structure characteristics in bituminous coals with different ranks from the Hedong Coalfield are investigated. The sequential chemical extraction procedure shows that REY mainly remain in the residue in the low-rank bituminous coals and display an increasing total leaching rate as vitrinite reflectance increases. While in the high-rank bituminous coals, REY are dominated by HCl-leachable and residual phases. These results demonstrate that organic matter is the dominant carrier of REY in the low-rank bituminous coals. While in the high-rank bituminous coals, REY predominantly associate with phosphates and organic matter, indicating a gradual transformation from organic to mineral forms during coalification. Fourier Transform infrared (FTIR) spectroscopy experiments have found that the peak areas of most oxygenated functional groups are negatively correlated with vitrinite reflectance. In comparison to other functional groups, the content of phenolic group (Ar-OH) displays a strong positive correlation with the proportion of residual REY in the sequential chemical extraction experiment. This indicates that Ar-OH probably serves as the dominant organic binding site of REY during coalification. The loss of organic binding sites during coalification may result in the gradual decline of the proportion of organic-bound REY. Meanwhile, some REY released from these binding sites probably form authigenic minerals, leading to the higher proportion of mineral-associated forms of REY in the high-rank bituminous coals.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104833"},"PeriodicalIF":5.6,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144515584","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 : 2025-06-27DOI: 10.1016/j.coal.2025.104832
Søren B. Nielsen, Oskar Hagelskjær, Hamed Sanei
Thermal maturity assessment in sedimentary basins often relies on thermal indicators of varying quality and sensitivity, frequently available in an uneven distribution across wells. To improve interpretative reliability and reduce the influence of local statistical variability, we apply a joint inversion approach to thermal maturity data from three wells situated in contrasting geological settings. One well, Aars-1, located in the Danish Basin of the eastern North Sea, is constrained by high-quality data including present-day temperature, vitrinite reflectance (VRo), red-to-green (R/G) fluorescence quotients, and apatite fission track (AFT) ages. The other two wells, from the northwestern Black Sea Basin, contain VRo and R/G data but lack temperature and AFT records.
All wells contribute to constraining a kinetic model for the R/G quotient and the thermal evolutiuon of the Black Sea wells. The resulting models yield predicted present-day bottom hole temperatures of approximately 100 °C at 4000 m depth, consistent with values from independent studies in the region. The thermal immaturity of the Black Sea wells is attributed to low background heat flow and high sedimentation rates. In the immature to early mature maturity window, a linear relationship is established between VRo and R/G, described by the equation: VRo = 1.3239 × R/G – 0.2352, valid within the calibration range of 0.43 < R/G < 0.73 and 0.33 < VRo < 0.73. Based on this relationship, the previously reported VRo discontinuities at the base of the Black Sea wells are likely artefactual.
This study demonstrates the value of combining independent thermal indicators across multiple wells and depositional settings. The approach enhances the robustness of thermal history reconstructions and offers a practical framework for evaluating relative heat flow and maturity in basins with incomplete or uneven datasets. Particularly, the R/G quotient, derived from autochthonous alginite deposited within the basin, is less affected by transport-related degradation than VRo and may offer a more representative measure of in-place thermal maturity, particularly in high-sedimentation environments.
{"title":"Relationship between vitrinite reflectance, fluoresence red/green quotients, apatite fission tracks and temperature by joint inversion of three wells","authors":"Søren B. Nielsen, Oskar Hagelskjær, Hamed Sanei","doi":"10.1016/j.coal.2025.104832","DOIUrl":"10.1016/j.coal.2025.104832","url":null,"abstract":"<div><div>Thermal maturity assessment in sedimentary basins often relies on thermal indicators of varying quality and sensitivity, frequently available in an uneven distribution across wells. To improve interpretative reliability and reduce the influence of local statistical variability, we apply a joint inversion approach to thermal maturity data from three wells situated in contrasting geological settings. One well, Aars-1, located in the Danish Basin of the eastern North Sea, is constrained by high-quality data including present-day temperature, vitrinite reflectance (VRo), red-to-green (R/G) fluorescence quotients, and apatite fission track (AFT) ages. The other two wells, from the northwestern Black Sea Basin, contain VRo and R/G data but lack temperature and AFT records.</div><div>All wells contribute to constraining a kinetic model for the R/G quotient and the thermal evolutiuon of the Black Sea wells. The resulting models yield predicted present-day bottom hole temperatures of approximately 100 °C at 4000 m depth, consistent with values from independent studies in the region. The thermal immaturity of the Black Sea wells is attributed to low background heat flow and high sedimentation rates. In the immature to early mature maturity window, a linear relationship is established between VRo and R/G, described by the equation: VRo = 1.3239 × R/G – 0.2352, valid within the calibration range of 0.43 < R/G < 0.73 and 0.33 < VRo < 0.73. Based on this relationship, the previously reported VRo discontinuities at the base of the Black Sea wells are likely artefactual.</div><div>This study demonstrates the value of combining independent thermal indicators across multiple wells and depositional settings. The approach enhances the robustness of thermal history reconstructions and offers a practical framework for evaluating relative heat flow and maturity in basins with incomplete or uneven datasets. Particularly, the R/G quotient, derived from autochthonous alginite deposited within the basin, is less affected by transport-related degradation than VRo and may offer a more representative measure of in-place thermal maturity, particularly in high-sedimentation environments.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"308 ","pages":"Article 104832"},"PeriodicalIF":5.6,"publicationDate":"2025-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144515591","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 : 2025-06-25DOI: 10.1016/j.coal.2025.104827
Rongbin Yang , Qingyong Luo , Jiapeng Wu , Qixiang Huang , Man Lu , Wenxin Hu , Dandan Wang , Zhengyu Chen , Jinqi Qiao
Continental hypersaline lacustrine basins constitute critical repositories of unconventional shale oil resources, often hosting source rocks with primary exploration value. The hydrocarbon generation potential and organic matter accumulation within the Qianjiang Formation of Jianghan Basin, however, remain elucidated inadequately. This study targets the third member of the Qianjiang Formation (Eq3) through systematic analysis of dolomitic shale sequences from the QYP1 directional well in Qianjiang Depression. A comprehensive analytical approach is employed, integrating programmed open-system pyrolysis, major and trace element geochemistry, biomarker analysis, and organic petrology. The multidisciplinary framework is utilized to evaluate sediment provenance, organic matter supply, paleoenvironmental reconstruction (including paleoclimate, redox condition, and paleosalinity) during the Eq3 depositional period, and the thermal maturity of organic matter. Based on these influencing factors, the hydrocarbon generation potential and organic matter enrichment model for source rocks of the Eq3 interval are assessed.
Results demonstrate that the organic-rich sediments of the Eq3 shales in the Qianjiang Depression exhibit exceptional hydrocarbon potential, qualifying as prime targets for shale oil exploration. Key characteristics include elevated total organic carbon (TOC), elevated S1 + S2 values, and superior hydrogen index (HI). Primary source of organic matter is attributed to saline lacustrine algae, as evidenced by a strong linear correlation between liptinite and TOC content and high proportion of lamalginite. The analyzed organic matter exhibits thermal maturity levels ranging from immature to low-mature level. Organic matter enrichment in these evaporative lacustrine source rocks is controlled by a combination of factors, including paleoclimate, sediment supply, organic matter sources, and depositional conditions. Paleoclimate reconstructions indicate that the Eq3 interval was deposited under cold and arid conditions, with low Ga/Rb, SiO2 and high K2O/Al2O3, Al2O3 + K2O + Na2O, accompanied by weak chemical weathering with minimal sediment recycling. Depositional environment demonstrates strongly reducing conditions and exceptional organic matter preservation, as indicated by low Pr/Ph ratios, exceptionally high Gamm/C30 (βα + αβ) hopane indices, rominent extended tricyclic terpanes ratios (ETR) and widespread pyrite occurrence. Elevated gammacerane, β-carotane content, along with high Sr/Ba, B/Ga and DBT/P radios, suggest high paleosalinity. Water column stratification further enhanced paleoproductivity and provided optimal conditions for organic matter preservation. Hydrocarbon-generating organic matter is predominantly derived from aquatic alga
{"title":"Hydrocarbon generation potential and organic carbon enrichment in evaporitic lacustrine source rocks from the Qianjiang Formation, Jianghan Basin (Central China): An integrated geochemical-petrological investigation","authors":"Rongbin Yang , Qingyong Luo , Jiapeng Wu , Qixiang Huang , Man Lu , Wenxin Hu , Dandan Wang , Zhengyu Chen , Jinqi Qiao","doi":"10.1016/j.coal.2025.104827","DOIUrl":"10.1016/j.coal.2025.104827","url":null,"abstract":"<div><div>Continental hypersaline lacustrine basins constitute critical repositories of unconventional shale oil resources, often hosting source rocks with primary exploration value. The hydrocarbon generation potential and organic matter accumulation within the Qianjiang Formation of Jianghan Basin, however, remain elucidated inadequately. This study targets the third member of the Qianjiang Formation (Eq<sup>3</sup>) through systematic analysis of dolomitic shale sequences from the QYP1 directional well in Qianjiang Depression. A comprehensive analytical approach is employed, integrating programmed open-system pyrolysis, major and trace element geochemistry, biomarker analysis, and organic petrology. The multidisciplinary framework is utilized to evaluate sediment provenance, organic matter supply, paleoenvironmental reconstruction (including paleoclimate, redox condition, and paleosalinity) during the Eq<sup>3</sup> depositional period, and the thermal maturity of organic matter. Based on these influencing factors, the hydrocarbon generation potential and organic matter enrichment model for source rocks of the Eq<sup>3</sup> interval are assessed.</div><div>Results demonstrate that the organic-rich sediments of the Eq<sup>3</sup> shales in the Qianjiang Depression exhibit exceptional hydrocarbon potential, qualifying as prime targets for shale oil exploration. Key characteristics include elevated total organic carbon (TOC), elevated S<sub>1</sub> + S<sub>2</sub> values, and superior hydrogen index (HI). Primary source of organic matter is attributed to saline lacustrine algae, as evidenced by a strong linear correlation between liptinite and TOC content and high proportion of lamalginite. The analyzed organic matter exhibits thermal maturity levels ranging from immature to low-mature level. Organic matter enrichment in these evaporative lacustrine source rocks is controlled by a combination of factors, including paleoclimate, sediment supply, organic matter sources, and depositional conditions. Paleoclimate reconstructions indicate that the Eq<sup>3</sup> interval was deposited under cold and arid conditions, with low Ga/Rb, SiO<sub>2</sub> and high K<sub>2</sub>O/Al<sub>2</sub>O<sub>3</sub>, Al<sub>2</sub>O<sub>3</sub> + K<sub>2</sub>O + Na<sub>2</sub>O, accompanied by weak chemical weathering with minimal sediment recycling. Depositional environment demonstrates strongly reducing conditions and exceptional organic matter preservation, as indicated by low Pr/Ph ratios, exceptionally high Gamm/C<sub>30</sub> (βα + αβ) hopane indices, rominent extended tricyclic terpanes ratios (ETR) and widespread pyrite occurrence. Elevated gammacerane, <em>β</em>-carotane content, along with high Sr/Ba, B/Ga and DBT/P radios, suggest high paleosalinity. Water column stratification further enhanced paleoproductivity and provided optimal conditions for organic matter preservation. Hydrocarbon-generating organic matter is predominantly derived from aquatic alga","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104827"},"PeriodicalIF":5.6,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144511107","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}
In the Elephant Game Reserve (EGR) in Mozambiquan Maputaland, several small peatlands have been developed between dunes. The aim of the study is to determine the peat-forming conditions and elucidate the evolution of the peatlands. Herbaceous vegetation (reeds and sedges) thrive on the surface of the mires. Fifty-five organic and inorganic samples were picked up from nine manually-retrieved cores up to 4.4 m deep, across several locations in the EGR. The maximum thickness of the organic sediments is 2.5 m. The determinations performed included proximate and ultimate analyses, pH and electrical Conductivity (eC) measurements, organic-petrography examination, as well as mineralogical and geochemical analyses applying X-ray diffraction and X-ray fluorescence spectrometry, respectively. The peat samples display ash yields between 10.1 and 46.8 % (on dry basis), sulphur content up to 8.9 % (db), pH and eC values from 2-7.3 and 142–2360 μS/cm, respectively. Quartz, K-feldspars and pyrite are the major minerals contained in peat; accordingly, silica is the major element with iron, aluminum, calcium and magnesium being minors. The maceral composition of peat reveals the predominance of the huminite group (57.6–78.6 vol%, on mineral matter-free basis), followed by inertinite (13.8–38.2 vol%) and liptinite (<9.6 vol%). The prevalence of the detrohuminite subgroup, particularly of attrinite, along with inertodetrinite, points to intense mechanical decomposition of the plant remains and periodical lowering of the local watertable with subsequent fires, during which the mire surface was exposed to oxidation. Overall, peat accumulation took place under rheo- to mesotrophic conditions.
{"title":"The evolution of interdunal peat-forming environments in the Maputaland coastal plain, Mozambique","authors":"Marios Panagiotis Chrysochos , Stavros Kalaitzidis , Mussa Achimo , Lopo Vasconcelos , Chrysoula Chrysakopoulou , Kimon Christanis","doi":"10.1016/j.coal.2025.104828","DOIUrl":"10.1016/j.coal.2025.104828","url":null,"abstract":"<div><div>In the Elephant Game Reserve (EGR) in Mozambiquan Maputaland, several small peatlands have been developed between dunes. The aim of the study is to determine the peat-forming conditions and elucidate the evolution of the peatlands. Herbaceous vegetation (reeds and sedges) thrive on the surface of the mires. Fifty-five organic and inorganic samples were picked up from nine manually-retrieved cores up to 4.4 m deep, across several locations in the EGR. The maximum thickness of the organic sediments is 2.5 m. The determinations performed included proximate and ultimate analyses, pH and electrical Conductivity (eC) measurements, organic-petrography examination, as well as mineralogical and geochemical analyses applying X-ray diffraction and X-ray fluorescence spectrometry, respectively. The peat samples display ash yields between 10.1 and 46.8 % (on dry basis), sulphur content up to 8.9 % (db), pH and eC values from 2-7.3 and 142–2360 μS/cm, respectively. Quartz, K-feldspars and pyrite are the major minerals contained in peat; accordingly, silica is the major element with iron, aluminum, calcium and magnesium being minors. The maceral composition of peat reveals the predominance of the huminite group (57.6–78.6 vol%, on mineral matter-free basis), followed by inertinite (13.8–38.2 vol%) and liptinite (<9.6 vol%). The prevalence of the detrohuminite subgroup, particularly of attrinite, along with inertodetrinite, points to intense mechanical decomposition of the plant remains and periodical lowering of the local watertable with subsequent fires, during which the mire surface was exposed to oxidation. Overall, peat accumulation took place under rheo- to mesotrophic conditions.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"307 ","pages":"Article 104828"},"PeriodicalIF":5.6,"publicationDate":"2025-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144513683","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}
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