Mafic Microgranular Enclaves (MMEs) within granitoids are commonly interpreted as indicators of coexisting mafic magma that were derived from the mantle, which can offer valuable insights into the origins and evolution of primary mafic magmas. In this article, we investigate the petrography and bulk-rock major and trace elements geochemistry of quartz monzonite, the hosted MMEs, and the associated pink granite, from the Bougaffer pluton in the eastern Saghro Inlier. This study aims to clarify the petrogenetic processes that formed the MMEs and their granitoid host rocks. The MMEs are characterized by a microgranular texture and occur as ellipsoidal, angular and rounded shape, ranging in size from 2 to 80 cm, with sharp boundaries. They share the same mineral content as their host rocks though in distinct proportions, and are classified as monzonite and monzodiorite with high-K calc-alkaline to shoshonitic composition. The MMEs show lower SiO2 contents and higher TiO2, CaO, MgO, Fe2O3t, and Al2O3 contents compared to their host granitoids. The MMEs and their host granitoid display several similarities, including the same mineralogy and similar total-rock compositions, suggesting a genetic relationship. The MMEs are most likely cumulates formed during the initial phase of the same magmatic system that produced the Bougaffer quartz monzonite. A two stages model is proposed, involving rapid solidification within the cogenetic host granitoid magma at the chamber boundaries, leading to the formation of crystal accumulations at the bottom of the magma chamber as cumulates. These cumulates were later fragmented and disturbed due to subsequent magma recharge and the convection induced within the magma chamber.
{"title":"Geochemistry and petrogenesis of mafic microgranular enclaves (MMEs) in the bougaffer granitoid, Saghro inlier, eastern anti-atlas belt, Morocco","authors":"Omar Outaaoui , Ezzoura Errami , Kadio Aka Donald Koua , Abdellatif Jouhari , Saber Salmi , Abdelmalek ouadjou , Nasser Ennih","doi":"10.1016/j.jafrearsci.2024.105528","DOIUrl":"10.1016/j.jafrearsci.2024.105528","url":null,"abstract":"<div><div>Mafic Microgranular Enclaves (MMEs) within granitoids are commonly interpreted as indicators of coexisting mafic magma that were derived from the mantle, which can offer valuable insights into the origins and evolution of primary mafic magmas. In this article, we investigate the petrography and bulk-rock major and trace elements geochemistry of quartz monzonite, the hosted MMEs, and the associated pink granite, from the Bougaffer pluton in the eastern Saghro Inlier. This study aims to clarify the petrogenetic processes that formed the MMEs and their granitoid host rocks. The MMEs are characterized by a microgranular texture and occur as ellipsoidal, angular and rounded shape, ranging in size from 2 to 80 cm, with sharp boundaries. They share the same mineral content as their host rocks though in distinct proportions, and are classified as monzonite and monzodiorite with high-K calc-alkaline to shoshonitic composition. The MMEs show lower SiO<sub>2</sub> contents and higher TiO<sub>2</sub>, CaO, MgO, Fe<sub>2</sub>O<sub>3</sub>t, and Al<sub>2</sub>O<sub>3</sub> contents compared to their host granitoids. The MMEs and their host granitoid display several similarities, including the same mineralogy and similar total-rock compositions, suggesting a genetic relationship. The MMEs are most likely cumulates formed during the initial phase of the same magmatic system that produced the Bougaffer quartz monzonite. A two stages model is proposed, involving rapid solidification within the cogenetic host granitoid magma at the chamber boundaries, leading to the formation of crystal accumulations at the bottom of the magma chamber as cumulates. These cumulates were later fragmented and disturbed due to subsequent magma recharge and the convection induced within the magma chamber.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105528"},"PeriodicalIF":2.2,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152735","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-28DOI: 10.1016/j.jafrearsci.2024.105532
Fahad Abubakar , Ismail Ahmad Abir , Abdulrasheed Adamu Hassan
<div><div>In a recent report by the Nigerian Geological Survey Agency, new minerals, including gold, lepidolite, and tantalite, were discovered in the western part of Kogi State. If found in sufficient quantities, these commercially valuable minerals have the potential to drive technological advancement, create jobs, and promote economic growth, which are crucial for the sustainable development of Nigeria. This study aims to delineate these occurrences, extensions, and other potential mineralisation zones using integrated high-resolution airborne magnetic and gamma-ray spectrometry geophysical datasets aided by the Analytical Hierarchy Process (AHP) and weighted overlay analysis (WOA). The AHP and WOA algorithms were employed based on expert opinions and the accuracy of each signal enhancement technique to delineate the mineralisation potential of the study area (using the IMOs as control). Centre for Exploration Targeting (CET) grid analysis, analytic signal (Asig), and Euler deconvolution were used to enhance the magnetic datasets, while radiometric ratios and ternary images were utilised for the radiometric datasets. The Asig categorises the magnetic amplitude into low (<0.023 nT/m), intermediate (0.023–0.105 nT/m), and high (>0.105 nT/m). It reveals magneto-structures and intrusive zones, which are potential targets for mineralisation. WNW-ESE and NE-SW are the dominant fault trends, with the IMOs being more consistent with NE-SW faults. The estimated depth of potential mineralisation zones ranges from 20.87 to 87.34 m. The ternary image and radiometric ratio maps (K/Th and Th/K) indicate that the mineralisation zones have undergone advanced weathering, resulting in potassium leaching and thorium enrichment. Asig, lineament density, and the Th/K ratio map were integrated to assess the mineralisation potential. Employing the ArcGIS weighted overlay tool and AHP evaluation, the mineralisation potential of Kogi West was classified as high, intermediate, or low. 90% of the IMOs fall within the high class, while 10% are in the intermediate category. The high-potential zones should be prioritised for further exploration and exploitation. The high correspondence indicates the effectiveness of the integrated geophysical approach in identifying regions with favourable geological conditions for mineralisation. However, while the study provides a promising framework for targeting potential mineral deposits, future exploration activities should consider the following implications to improve the reliability and applicability of the results: validation with ground-truthing, incorporating other geophysical methods (such as electrical, gravity, and electromagnetic surveys), and acknowledgement of eventualities that high potential mineralisation zones not been economically viable, may be due to poor mineral grade or volume. These endeavours and acknowledgements will refine the current understanding of the high-potential mineralisation zones and expand t
{"title":"Kogi west geophysical mineralisation appraisal using Analytical Hierarchy Process (AHP)","authors":"Fahad Abubakar , Ismail Ahmad Abir , Abdulrasheed Adamu Hassan","doi":"10.1016/j.jafrearsci.2024.105532","DOIUrl":"10.1016/j.jafrearsci.2024.105532","url":null,"abstract":"<div><div>In a recent report by the Nigerian Geological Survey Agency, new minerals, including gold, lepidolite, and tantalite, were discovered in the western part of Kogi State. If found in sufficient quantities, these commercially valuable minerals have the potential to drive technological advancement, create jobs, and promote economic growth, which are crucial for the sustainable development of Nigeria. This study aims to delineate these occurrences, extensions, and other potential mineralisation zones using integrated high-resolution airborne magnetic and gamma-ray spectrometry geophysical datasets aided by the Analytical Hierarchy Process (AHP) and weighted overlay analysis (WOA). The AHP and WOA algorithms were employed based on expert opinions and the accuracy of each signal enhancement technique to delineate the mineralisation potential of the study area (using the IMOs as control). Centre for Exploration Targeting (CET) grid analysis, analytic signal (Asig), and Euler deconvolution were used to enhance the magnetic datasets, while radiometric ratios and ternary images were utilised for the radiometric datasets. The Asig categorises the magnetic amplitude into low (<0.023 nT/m), intermediate (0.023–0.105 nT/m), and high (>0.105 nT/m). It reveals magneto-structures and intrusive zones, which are potential targets for mineralisation. WNW-ESE and NE-SW are the dominant fault trends, with the IMOs being more consistent with NE-SW faults. The estimated depth of potential mineralisation zones ranges from 20.87 to 87.34 m. The ternary image and radiometric ratio maps (K/Th and Th/K) indicate that the mineralisation zones have undergone advanced weathering, resulting in potassium leaching and thorium enrichment. Asig, lineament density, and the Th/K ratio map were integrated to assess the mineralisation potential. Employing the ArcGIS weighted overlay tool and AHP evaluation, the mineralisation potential of Kogi West was classified as high, intermediate, or low. 90% of the IMOs fall within the high class, while 10% are in the intermediate category. The high-potential zones should be prioritised for further exploration and exploitation. The high correspondence indicates the effectiveness of the integrated geophysical approach in identifying regions with favourable geological conditions for mineralisation. However, while the study provides a promising framework for targeting potential mineral deposits, future exploration activities should consider the following implications to improve the reliability and applicability of the results: validation with ground-truthing, incorporating other geophysical methods (such as electrical, gravity, and electromagnetic surveys), and acknowledgement of eventualities that high potential mineralisation zones not been economically viable, may be due to poor mineral grade or volume. These endeavours and acknowledgements will refine the current understanding of the high-potential mineralisation zones and expand t","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105532"},"PeriodicalIF":2.2,"publicationDate":"2024-12-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171380","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-27DOI: 10.1016/j.jafrearsci.2024.105530
Mohamed Th S. Heikal , Mokhles K. Azer , Mohamed S. Kamar , Mohamed O. Ibrahim , Mohamed Abd El Monsef
Nuweibi Albite Granite (NAG, 1.3 km2 as total area) is considered one of the well-known highly evolved, rare metals-bearing pluton in the Egyptian Nubian Shield. The Nuweibi area constitutes ophiolite assemblage (metagabbros, serpentinites and related talc-carbonates), tuffaceous metasediments with their associated hornfelse, granodiorite-tonalite and post-tectonic albite granite, the latter is cross cutting by aplite and basaltic dykes. The present work focuses on the geochemical characteristic of NAG, using new data of whole-rock geochemistry and mineral chemistry to address-out approach on its origin, geodynamic evolution and genetic relation with the Ta-Nb mineralization. The main (Ta, Nb)-bearing minerals include; tantalite, columbite, wodginite and calciomicrolite. The geochemical analyses revealed that, the studied NAG has peraluminous, within-plate, post-collisional, A-type characters. It exhibits an enrichment of Na2O (up to 6.56 wt%) reflecting the alkaline affinity (σ up to 6.19), closing to alkaline trend of an extensional regime. The REEs tetrad effect is well pronounced with negative Eu anomaly, which is most remarkable toward the closing of magma at the late magmatic stage of fractionation. The analytical criteria support the evolution of NAG through highly evolved magmatic fractionation (in major) and later metasomatic replacement (in minor). The abundance of rare metals such as (Ta, Nb), suggests the strong influence of fluorine and aqueous fluid system in the residual melt. With respect to the magmatic origin of NAG through advanced degree of fractionation, a complex set of geological processes including crust-mantle mixing, partial melting and fluid flux-volatiles interaction (i.e. metasomatism) have been involved during the geodynamic evolution.
{"title":"Petrogenesis and geodynamic model for (Ta, Nb)-fertilized Nuweibi albite granite, Egyptian Nubian Shield: Juvenile crust-mantle mixing and metasomatic enhancement","authors":"Mohamed Th S. Heikal , Mokhles K. Azer , Mohamed S. Kamar , Mohamed O. Ibrahim , Mohamed Abd El Monsef","doi":"10.1016/j.jafrearsci.2024.105530","DOIUrl":"10.1016/j.jafrearsci.2024.105530","url":null,"abstract":"<div><div>Nuweibi Albite Granite (NAG, 1.3 km<sup>2</sup> as total area) is considered one of the well-known highly evolved, rare metals-bearing pluton in the Egyptian Nubian Shield. The Nuweibi area constitutes ophiolite assemblage (metagabbros, serpentinites and related talc-carbonates), tuffaceous metasediments with their associated hornfelse, granodiorite-tonalite and post-tectonic albite granite, the latter is cross cutting by aplite and basaltic dykes. The present work focuses on the geochemical characteristic of NAG, using new data of whole-rock geochemistry and mineral chemistry to address-out approach on its origin, geodynamic evolution and genetic relation with the Ta-Nb mineralization. The main (Ta, Nb)-bearing minerals include; tantalite, columbite, wodginite and calciomicrolite. The geochemical analyses revealed that, the studied NAG has peraluminous, within-plate, post-collisional, A-type characters. It exhibits an enrichment of Na<sub>2</sub>O (up to 6.56 wt%) reflecting the alkaline affinity (σ up to 6.19), closing to alkaline trend of an extensional regime. The REEs tetrad effect is well pronounced with negative Eu anomaly, which is most remarkable toward the closing of magma at the late magmatic stage of fractionation. The analytical criteria support the evolution of NAG through highly evolved magmatic fractionation (in major) and later metasomatic replacement (in minor). The abundance of rare metals such as (Ta, Nb), suggests the strong influence of fluorine and aqueous fluid system in the residual melt. With respect to the magmatic origin of NAG through advanced degree of fractionation, a complex set of geological processes including crust-mantle mixing, partial melting and fluid flux-volatiles interaction (i.e. metasomatism) have been involved during the geodynamic evolution.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105530"},"PeriodicalIF":2.2,"publicationDate":"2024-12-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153413","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-25DOI: 10.1016/j.jafrearsci.2024.105529
Asmaa F. El-Moghazy, Nader A.A. Edress
Crystal Mountain (also called Gebel Crystal) is a famous karst feature in the Western Desert of Egypt. It is a huge, unroofed cave composed of chalky limestone that constitutes the host rock of the Upper Cretaceous Khoman Formation. The cave filling consists of alternating irregular strata composed of calcareous coal horizons with complex sinkholes, detrital material, calcite crystals, and red sandstones. These coal horizons have attracted the attention of many scientists to explain the depositional environment, coal types, and ash minerals. However, there are no recent studies about the detailed paleoenvironmental conditions of these coal horizons. Accordingly, different calcareous coal horizons from the Gebel Crystal were examined to determine the paleoenvironment of the deposits. Coal samples were subjected to mineralogy and organic geochemistry to determine the nature, origin and density of the vegetation cover paleoenvironment. In addition, analyses of major and trace elements of the studied coal samples were performed to determine the different paleoenvironmental conditions of the deposits, such as paleoclimate, paleosalinity, organic matter origin, and paleo-redox conditions. The results reveal that the calcareous coal is a very low-grade coal (average ash content 40.96 wt%) with a low-rank lignite type (soft brown coal), which belongs to the ortho-lignite and/or lignite A and B facies. Type III kerogen was observed to be the main precursor of the humic peat, lignite, and sub-bituminous coal, and organic matter maturation suggests immature diagenesis stage. The immature diagenesis stage is consistent with the concept that excludes a hydrothermal solution for the formation of calcite in the coal samples. The dominance of inertinite (49.2%) and liptinite (32.4%) over huminite (18.3%) as macerals indicates that the desiccation phase took place in the mire prior to final preservation. Paleoenvironmental indices such as tissue preservation index (TPI), gelification index (GI), vegetation index (VI), ground water index (GWI) and facies diagrams suggest the dominance of marsh vegetation in the limno-telmatic, rheotrophic mire system. Piedmont alluvial plain and back-barrier with freshwater supply are inferred as the depositional sites for the studied calcareous coal formation. The mineralogical composition of the coal horizons consists of carbonate (calcite and manganocalcite), quartz, and evaporite (halite and anhydrite) minerals. The results of the paleoenvironmental indicators (e.g., Sr/Ba, Rb/K2O, Sr/Cu, V/(V + Ni), V/Cr, Ni/Co, V/Ni, Co/Ni, sulfur, and C-value) reveal that freshwater conditions were dominant during the deposition of the coal horizons. The prevailing paleoclimate was an arid climate, which was responsible for the formation of the evaporite minerals. The organic matter originated from terrestrial sources of plant material, and the coal horizons were deposited under suboxic redox conditions.
{"title":"Geochemical evaluation of calcareous coal horizons, Gebel Crystal, Western Desert, Egypt: Paleoenvironmental implications","authors":"Asmaa F. El-Moghazy, Nader A.A. Edress","doi":"10.1016/j.jafrearsci.2024.105529","DOIUrl":"10.1016/j.jafrearsci.2024.105529","url":null,"abstract":"<div><div>Crystal Mountain (also called Gebel Crystal) is a famous karst feature in the Western Desert of Egypt. It is a huge, unroofed cave composed of chalky limestone that constitutes the host rock of the Upper Cretaceous Khoman Formation. The cave filling consists of alternating irregular strata composed of calcareous coal horizons with complex sinkholes, detrital material, calcite crystals, and red sandstones. These coal horizons have attracted the attention of many scientists to explain the depositional environment, coal types, and ash minerals. However, there are no recent studies about the detailed paleoenvironmental conditions of these coal horizons. Accordingly, different calcareous coal horizons from the Gebel Crystal were examined to determine the paleoenvironment of the deposits. Coal samples were subjected to mineralogy and organic geochemistry to determine the nature, origin and density of the vegetation cover paleoenvironment. In addition, analyses of major and trace elements of the studied coal samples were performed to determine the different paleoenvironmental conditions of the deposits, such as paleoclimate, paleosalinity, organic matter origin, and paleo-redox conditions. The results reveal that the calcareous coal is a very low-grade coal (average ash content 40.96 wt%) with a low-rank lignite type (soft brown coal), which belongs to the ortho-lignite and/or lignite A and B facies. Type III kerogen was observed to be the main precursor of the humic peat, lignite, and sub-bituminous coal, and organic matter maturation suggests immature diagenesis stage. The immature diagenesis stage is consistent with the concept that excludes a hydrothermal solution for the formation of calcite in the coal samples. The dominance of inertinite (49.2%) and liptinite (32.4%) over huminite (18.3%) as macerals indicates that the desiccation phase took place in the mire prior to final preservation. Paleoenvironmental indices such as tissue preservation index (TPI), gelification index (GI), vegetation index (VI), ground water index (GWI) and facies diagrams suggest the dominance of marsh vegetation in the limno-telmatic, rheotrophic mire system. Piedmont alluvial plain and back-barrier with freshwater supply are inferred as the depositional sites for the studied calcareous coal formation. The mineralogical composition of the coal horizons consists of carbonate (calcite and manganocalcite), quartz, and evaporite (halite and anhydrite) minerals. The results of the paleoenvironmental indicators (e.g., Sr/Ba, Rb/K<sub>2</sub>O, Sr/Cu, V/(V + Ni), V/Cr, Ni/Co, V/Ni, Co/Ni, sulfur, and C-value) reveal that freshwater conditions were dominant during the deposition of the coal horizons. The prevailing paleoclimate was an arid climate, which was responsible for the formation of the evaporite minerals. The organic matter originated from terrestrial sources of plant material, and the coal horizons were deposited under suboxic redox conditions.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105529"},"PeriodicalIF":2.2,"publicationDate":"2024-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153353","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The offshore region of East Africa has undergone extensive geological evolution since the Permian period, characterized by two stages of rifting phases followed by a subsequent stage of passive margin development. The stratigraphic record in this area is comprehensive, indicating the formation of multiple series of source rocks. Recent discoveries have identified over 200 trillion cubic feet of natural gas in the Ruvuma Basin, in addition to a modest quantity of light crude oil found onshore in Mozambique. However, the precise origins of hydrocarbons in this region remain unclear. In this study, the paleo-position restoration technique for oil and gas fields was utilized to reconstruct the paleo-positions of key wells and reservoirs during critical periods of source rock development. Three significant Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) wells drilled in the offshore region of East Africa were selected for source rock assessment. The geochemical data obtained from these wells were systematically analyzed, resulting in the creation of continuous geochemical profiles that elucidate the characteristics of the thick, high-quality, oil-prone marine source rocks formed in the southern offshore region of East Africa during the Upper Jurassic to Lower Cretaceous periods. These source rocks exhibit high total organic carbon (TOC) and hydrogen index (HI) values, indicating a robust capacity for hydrocarbon generation. They are widely distributed and predominantly consist of oil-prone Type II1-II2 kerogen. The sequence of source rocks with elevated TOC exceeds 115 m in thickness. Carbon isotope data from methane and ethane in natural gas samples suggest that the hydrocarbons in the onshore and southern offshore areas of East Africa are derived from these Upper Jurassic to Lower Cretaceous marine source rocks, thereby indirectly indicating significant exploration potential for these source rocks. Based on seismic sections, a hydrocarbon accumulation model has been developed for the southern offshore region of East Africa. This model comprises multiple series of source rocks that provide sufficient hydrocarbon supply, effective source-reservoir-seal assemblages, and near-source hydrocarbon migration and accumulation. The findings of this study enhance confidence in hydrocarbon exploration within the study area and further delineate potential areas and directions for future exploration efforts.
{"title":"Confirmation and significance of high quality and oil prone source rocks in the southeast African offshore","authors":"Zhaoming Wang, Zhixin Wen, Chengpeng Song, Ruiyin Chen, Zhengjun He, Xiaobing Liu, Tianyu Ji, Yanyan Chen","doi":"10.1016/j.jafrearsci.2024.105531","DOIUrl":"10.1016/j.jafrearsci.2024.105531","url":null,"abstract":"<div><div>The offshore region of East Africa has undergone extensive geological evolution since the Permian period, characterized by two stages of rifting phases followed by a subsequent stage of passive margin development. The stratigraphic record in this area is comprehensive, indicating the formation of multiple series of source rocks. Recent discoveries have identified over 200 trillion cubic feet of natural gas in the Ruvuma Basin, in addition to a modest quantity of light crude oil found onshore in Mozambique. However, the precise origins of hydrocarbons in this region remain unclear. In this study, the paleo-position restoration technique for oil and gas fields was utilized to reconstruct the paleo-positions of key wells and reservoirs during critical periods of source rock development. Three significant Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) wells drilled in the offshore region of East Africa were selected for source rock assessment. The geochemical data obtained from these wells were systematically analyzed, resulting in the creation of continuous geochemical profiles that elucidate the characteristics of the thick, high-quality, oil-prone marine source rocks formed in the southern offshore region of East Africa during the Upper Jurassic to Lower Cretaceous periods. These source rocks exhibit high total organic carbon (TOC) and hydrogen index (HI) values, indicating a robust capacity for hydrocarbon generation. They are widely distributed and predominantly consist of oil-prone Type II1-II2 kerogen. The sequence of source rocks with elevated TOC exceeds 115 m in thickness. Carbon isotope data from methane and ethane in natural gas samples suggest that the hydrocarbons in the onshore and southern offshore areas of East Africa are derived from these Upper Jurassic to Lower Cretaceous marine source rocks, thereby indirectly indicating significant exploration potential for these source rocks. Based on seismic sections, a hydrocarbon accumulation model has been developed for the southern offshore region of East Africa. This model comprises multiple series of source rocks that provide sufficient hydrocarbon supply, effective source-reservoir-seal assemblages, and near-source hydrocarbon migration and accumulation. The findings of this study enhance confidence in hydrocarbon exploration within the study area and further delineate potential areas and directions for future exploration efforts.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105531"},"PeriodicalIF":2.2,"publicationDate":"2024-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-24DOI: 10.1016/j.jafrearsci.2024.105520
Mounir El-Azabi , Mohamed Boukhary , George Henry , Walid Kassab
Larger benthic foraminifera (LBF) experienced rapid evolution during the Paleogene, reaching a widespread distribution in both northern and southern Tethys during the Eocene Epoch. Paleobiogeographic insights regarding their migration patterns were facilitated by this distribution. To date, there have been no investigations of LBF in the eastern Maadi-Sukhna region. In the middle Eocene succession of the El-Ramliya-Akheider block in this region, the taxonomic identification of Nummulites and larger porcelaneous foraminifera is examined in detail for this work. N. praegizehensis and N. praediscorbinus were identified, along with six larger agglutinated and porcelaneous foraminiferal species (Dictyoconus egyptiensis, Idalina cuvilleri, Rhabdorites malatyanesis, Pseudolacazina schwagerinoides, Somalina danieli). These taxa are associated with the three standard Shallow Benthic Zones (SBZ) of the Mokattam and Observatory formations. The top of the middle Lutetian SBZ 14 was characterized by a significant unconformity between the Mokattam and Observatory formations. The Nummulites gizehensis group, which started at the plateau of the Giza pyramids and expanded throughout northern Africa and the Arabian Peninsula, was shown to have dispersed, according to a new paleobiogeographic map. Due to the physical barrier of the Galala Mountains, the N. gizehensis group migrated southward in Egypt during the middle-late Lutetian stage, dispersing more quickly in the north Western Desert than the north Eastern Desert and Sinai.
{"title":"New implications for regional biostratigraphy and paleobiogeography of larger benthic foraminifera in the Lutetian-Bartonian succession of the el-Ramliya-Akheider block, north Eastern Desert, Egypt","authors":"Mounir El-Azabi , Mohamed Boukhary , George Henry , Walid Kassab","doi":"10.1016/j.jafrearsci.2024.105520","DOIUrl":"10.1016/j.jafrearsci.2024.105520","url":null,"abstract":"<div><div>Larger benthic foraminifera (LBF) experienced rapid evolution during the Paleogene, reaching a widespread distribution in both northern and southern Tethys during the Eocene Epoch. Paleobiogeographic insights regarding their migration patterns were facilitated by this distribution. To date, there have been no investigations of LBF in the eastern Maadi-Sukhna region. In the middle Eocene succession of the El-Ramliya-Akheider block in this region, the taxonomic identification of <em>Nummulites</em> and larger porcelaneous foraminifera is examined in detail for this work. <em>N. praegizehensis</em> and <em>N. praediscorbinus</em> were identified, along with six larger agglutinated and porcelaneous foraminiferal species (<em>Dictyoconus egyptiensis, Idalina cuvilleri, Rhabdorites malatyanesis, Pseudolacazina schwagerinoides, Somalina danieli</em>). These taxa are associated with the three standard Shallow Benthic Zones (SBZ) of the Mokattam and Observatory formations. The top of the middle Lutetian SBZ 14 was characterized by a significant unconformity between the Mokattam and Observatory formations. The <em>Nummulites gizehensis</em> group, which started at the plateau of the Giza pyramids and expanded throughout northern Africa and the Arabian Peninsula, was shown to have dispersed, according to a new paleobiogeographic map. Due to the physical barrier of the Galala Mountains, the <em>N. gizehensis group</em> migrated southward in Egypt during the middle-late Lutetian stage, dispersing more quickly in the north Western Desert than the north Eastern Desert and Sinai.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105520"},"PeriodicalIF":2.2,"publicationDate":"2024-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153354","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-21DOI: 10.1016/j.jafrearsci.2024.105522
M.A.I. Ari , M.E. Nton , M. Harouna
The Termit Basin, a Cretaceous-Paleogene rift in southeastern Niger, and other rift basins of the West and Central African Rift System are widely studied using traditional oil-oil correlation methods. These methods face challenges in subjectivity, large dataset processing, and distinguishing geochemically similar oils due to multiple source rocks and geological complexity.
This research aims to improve the understanding of crude oil types, sources, depositional environments, and thermal maturity stages of oil organic precursors by examining their molecular compositions. It also seeks to identify the most suitable biomarkers for oil-oil correlation studies. Gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and chemometric methods were used in this study.
Crude oil samples were classified as paraffinic-naphthenic, aromatic-intermediate, and aromatic-asphaltene oils. Statistical analyses identified steranes and terpanes as the most suitable biomarkers for oil-oil correlation studies, with three distinct oil groups. Thermal maturity indicators suggest that the precursor organic materials were in the early to mid-maturity stages.
These findings reveal the potential of extending the oil-oil correlation studies in the Termit Basin and other rift basins of the WCARS to enhance understanding of source rocks contributing to proven hydrocarbons, reservoir connectivity, and hydrocarbon migration pathways.
{"title":"Biomarker geochemistry and oil-oil correlation from reservoir unit oils of the Sokor-1 Formation, Fana low uplift, Termit Basin, southeastern Niger","authors":"M.A.I. Ari , M.E. Nton , M. Harouna","doi":"10.1016/j.jafrearsci.2024.105522","DOIUrl":"10.1016/j.jafrearsci.2024.105522","url":null,"abstract":"<div><div>The Termit Basin, a Cretaceous-Paleogene rift in southeastern Niger, and other rift basins of the West and Central African Rift System are widely studied using traditional oil-oil correlation methods. These methods face challenges in subjectivity, large dataset processing, and distinguishing geochemically similar oils due to multiple source rocks and geological complexity.</div><div>This research aims to improve the understanding of crude oil types, sources, depositional environments, and thermal maturity stages of oil organic precursors by examining their molecular compositions. It also seeks to identify the most suitable biomarkers for oil-oil correlation studies. Gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and chemometric methods were used in this study.</div><div>Crude oil samples were classified as paraffinic-naphthenic, aromatic-intermediate, and aromatic-asphaltene oils. Statistical analyses identified steranes and terpanes as the most suitable biomarkers for oil-oil correlation studies, with three distinct oil groups. Thermal maturity indicators suggest that the precursor organic materials were in the early to mid-maturity stages.</div><div>These findings reveal the potential of extending the oil-oil correlation studies in the Termit Basin and other rift basins of the WCARS to enhance understanding of source rocks contributing to proven hydrocarbons, reservoir connectivity, and hydrocarbon migration pathways.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105522"},"PeriodicalIF":2.2,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153356","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The geothermal aquifer complex investigated in this study comprises a component of the eastern geothermal reservoir of Northern Algeria that is located close to the Algerian−Tunisian border. Seven thermal and two cold water springs were sampled in the framework of this study. The area hosts the region's second hottest spring discharging at a temperature of 67 °C. The thermal waters are carbogaseous type and are dominated by a Na−HCO3 composition. Isotopic analyses of deuterium and oxygen-18 confirm their meteoric origin. Radiogenic strontium isotopes (87Sr/86Sr up to 0.710841) suggest interactions with a silicate basement, probably composed of granodiorites and micaschists. Interaction with the Triassic evaporites results in a total dissolved solids (TDS) concentration of up to 1773 mg L−1. The thermal waters emerging through the faults have a temperature ranging between 36 and 67 °C. These waters mix with cooler waters during their ascent. The use of various chemical geothermometers yielded a maximum reservoir temperature of 78–162 °C for the Bouhadjar region. Using the average regional geothermal gradient (43.5 °C·km−1) and the aforementioned temperature interval, an estimated depth range of 1793–3731 m was computed for the geothermal water reservoir. All the thermal waters are found oversaturated with respect to kaolinite and K−mica reflecting the dissolution of granodiorites and muscovite-rich micaschists. High PCO2 levels (0.07–1.07 atm) suggest the existence of a thermo-decarbonation reaction taking place in the tectonic collision zone. This highlights the important role played by major geological structures occurring in such a geothermal system.
{"title":"Hydrogeochemical and isotopic characterization of the El-Tarf geothermal aquifer (Algerian−Tunisian border): Implications of the regional geodynamic structure and the water−rock interactions","authors":"Hana Nouali , Yasmina Bouroubi-Ouadfel , Adnane Souffi Moulla , Halim Mutlu , Orlando Vaselli , Haythem Dinar , Abdelkader Khiari","doi":"10.1016/j.jafrearsci.2024.105523","DOIUrl":"10.1016/j.jafrearsci.2024.105523","url":null,"abstract":"<div><div>The geothermal aquifer complex investigated in this study comprises a component of the eastern geothermal reservoir of Northern Algeria that is located close to the Algerian−Tunisian border. Seven thermal and two cold water springs were sampled in the framework of this study. The area hosts the region's second hottest spring discharging at a temperature of 67 °C. The thermal waters are carbogaseous type and are dominated by a Na−HCO<sub>3</sub> composition. Isotopic analyses of deuterium and oxygen-18 confirm their meteoric origin. Radiogenic strontium isotopes (<sup>87</sup>Sr/<sup>86</sup>Sr up to 0.710841) suggest interactions with a silicate basement, probably composed of granodiorites and micaschists. Interaction with the Triassic evaporites results in a total dissolved solids (TDS) concentration of up to 1773 mg L<sup>−1</sup>. The thermal waters emerging through the faults have a temperature ranging between 36 and 67 °C. These waters mix with cooler waters during their ascent. The use of various chemical geothermometers yielded a maximum reservoir temperature of 78–162 °C for the Bouhadjar region. Using the average regional geothermal gradient (43.5 °C·km<sup>−1</sup>) and the aforementioned temperature interval, an estimated depth range of 1793–3731 m was computed for the geothermal water reservoir. All the thermal waters are found oversaturated with respect to kaolinite and K−mica reflecting the dissolution of granodiorites and muscovite-rich micaschists. High P<sub><em>CO2</em></sub> levels (0.07–1.07 atm) suggest the existence of a thermo-decarbonation reaction taking place in the tectonic collision zone. This highlights the important role played by major geological structures occurring in such a geothermal system.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105523"},"PeriodicalIF":2.2,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143152737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-21DOI: 10.1016/j.jafrearsci.2024.105519
Adel A. Surour , Mostafa M. El Desouky , Mariam M. Ismail , Raneem Abo Aissa , Hamada Zaghloul
Gold-bearing rocks in Um Araka area, south Eastern Desert of Egypt, comprise mineralized quartz veins and wall-rock alterations. Gold mineralized rocks are confined to post-collisional granite that intrudes a variety of island-arc association dominated by amphibolite, mafic schist and marble bands. The paper aims to assess environmental hazards related to extensive artisanal mining, extraction of gold, leaching by poisonous cyanides and the haphazard storage of mine wastes. The latter comprise heaps of dump rocks and tailings. Energy-dispersive X-ray spectroscopy (EDS) coupled with scanning electron microscopy (SEM) confirms the ore paragenesis revealed from the petrographic study. Beside gold, the gold-bearing quartz veins and alteration zones have considerable amounts of sulphides such as pyrite and arsenopyrite, in addition to lesser amounts of galena. Gold-rich samples collected from the excavated pits and shafts show enrichment in an electrum alloy consisting of 71.7 wt% Au and 15.2 wt% Ag, which is washed out totally if subjected to cyanidation. Upon cyanidation, Cl is greatly eliminated from 29,200 ppm to 2300 ppm whereas S is slightly lowered from 33,200 ppm to 27,500 ppm. Trace elements as pollutants in the investigated tailings are distinguished into base metals (Zn, Pb Cu & Ni), and rare-metals (Mo & Nb). The paper emphasizes the need for sustainable mining practices and environmental management to mitigate the random impacts artisanal mining for gold. Data materialized here categorize hazards into the use of cyanide, high concentrations of some heavy metals and appreciable U & Th. It is recommended to use safer alternatives for cyanide (e.g., thiourea CH4N2S) to ensure clean environment and sustainable mining of the known and unexplored gold resources in the south Eastern Desert of Egypt.
{"title":"Gold mineralization and environmental impacts of artisanal mining in the Um Araka area, Egypt: Microanalyses and heavy metals assessment","authors":"Adel A. Surour , Mostafa M. El Desouky , Mariam M. Ismail , Raneem Abo Aissa , Hamada Zaghloul","doi":"10.1016/j.jafrearsci.2024.105519","DOIUrl":"10.1016/j.jafrearsci.2024.105519","url":null,"abstract":"<div><div>Gold-bearing rocks in Um Araka area, south Eastern Desert of Egypt, comprise mineralized quartz veins and wall-rock alterations. Gold mineralized rocks are confined to post-collisional granite that intrudes a variety of island-arc association dominated by amphibolite, mafic schist and marble bands. The paper aims to assess environmental hazards related to extensive artisanal mining, extraction of gold, leaching by poisonous cyanides and the haphazard storage of mine wastes. The latter comprise heaps of dump rocks and tailings. Energy-dispersive X-ray spectroscopy (EDS) coupled with scanning electron microscopy (SEM) confirms the ore paragenesis revealed from the petrographic study. Beside gold, the gold-bearing quartz veins and alteration zones have considerable amounts of sulphides such as pyrite and arsenopyrite, in addition to lesser amounts of galena. Gold-rich samples collected from the excavated pits and shafts show enrichment in an electrum alloy consisting of 71.7 wt% Au and 15.2 wt% Ag, which is washed out totally if subjected to cyanidation. Upon cyanidation, Cl is greatly eliminated from 29,200 ppm to 2300 ppm whereas S is slightly lowered from 33,200 ppm to 27,500 ppm. Trace elements as pollutants in the investigated tailings are distinguished into base metals (Zn, Pb Cu & Ni), and rare-metals (Mo & Nb). The paper emphasizes the need for sustainable mining practices and environmental management to mitigate the random impacts artisanal mining for gold. Data materialized here categorize hazards into the use of cyanide, high concentrations of some heavy metals and appreciable U & Th. It is recommended to use safer alternatives for cyanide (e.g., thiourea CH<sub>4</sub>N<sub>2</sub>S) to ensure clean environment and sustainable mining of the known and unexplored gold resources in the south Eastern Desert of Egypt.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105519"},"PeriodicalIF":2.2,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153357","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-21DOI: 10.1016/j.jafrearsci.2024.105525
Buyuk Ghorbani , Vahid Tavakoli , Hossain Rahimpour–Bonab , Navid Vahidimotlagh
This study investigates the organic characterization of three source rocks in the Abadan Plain (namely, Lower Cretaceous–Albian Kazhdumi, Lower Cretaceous–Neocomian Garau, and Middle Jurassic Sargelu formations), located in the western Zagros fold–and–thrust belt, southwest of Iran. A total of 82 source rock samples (33 from the Kazhdumi, 38 from the Garau, and 11 from the Sargelu) were analyzed using Rock–Eval pyrolysis and organic petrography to evaluate organic matter quantity, quality, and thermal maturity. The Kazhdumi source rock predominantly contains immature type II/III kerogens with macerals such as vitrinite, amorphinite, inertinite, alginite, cutinite, and solid bitumen. The Garau source rock primarily consists of moderately mature marine type II kerogen, with macerals including alginite, cutinite, and solid bitumen. The Sargelu source rock exhibits highly mature type II–S kerogen, dominated by late-oil solid bitumen and pyrobitumen macerals. Molecular analysis was performed on 26 source rock extracts and 58 crude oils from various reservoirs across the Abadan Plain. Using isoprenoids, triterpanes, steranes, and aromatic biomarkers, a thermal sequence of Kazhdumi < Garau < Sargelu or Kazhdumi < Sargelu < Garau was identified in source rock extracts, while crude oils followed Sarvak < Azadegan Sandstone < Gadvan < Fahliyan. Principal component and hierarchical cluster analyses revealed that crude oils align with the thermal maturity of their source rocks. Strong correlations were observed between the crude oils and Garau and Sargelu source rocks, distinctly separating from the Kazhdumi source rock, emphasizing their dominant role in the Abadan Plain's petroleum systems.
{"title":"Oil–oil and oil–source correlations in the Abadan Plain, SW Iran: Updated insights into middle Jurassic – Lower Cretaceous petroleum systems through biomarker analysis and chemometrics","authors":"Buyuk Ghorbani , Vahid Tavakoli , Hossain Rahimpour–Bonab , Navid Vahidimotlagh","doi":"10.1016/j.jafrearsci.2024.105525","DOIUrl":"10.1016/j.jafrearsci.2024.105525","url":null,"abstract":"<div><div>This study investigates the organic characterization of three source rocks in the Abadan Plain (namely, Lower Cretaceous–Albian Kazhdumi, Lower Cretaceous–Neocomian Garau, and Middle Jurassic Sargelu formations), located in the western Zagros fold–and–thrust belt, southwest of Iran. A total of 82 source rock samples (33 from the Kazhdumi, 38 from the Garau, and 11 from the Sargelu) were analyzed using Rock–Eval pyrolysis and organic petrography to evaluate organic matter quantity, quality, and thermal maturity. The Kazhdumi source rock predominantly contains immature type II/III kerogens with macerals such as vitrinite, amorphinite, inertinite, alginite, cutinite, and solid bitumen. The Garau source rock primarily consists of moderately mature marine type II kerogen, with macerals including alginite, cutinite, and solid bitumen. The Sargelu source rock exhibits highly mature type II–S kerogen, dominated by late-oil solid bitumen and pyrobitumen macerals. Molecular analysis was performed on 26 source rock extracts and 58 crude oils from various reservoirs across the Abadan Plain. Using isoprenoids, triterpanes, steranes, and aromatic biomarkers, a thermal sequence of Kazhdumi < Garau < Sargelu or Kazhdumi < Sargelu < Garau was identified in source rock extracts, while crude oils followed Sarvak < Azadegan Sandstone < Gadvan < Fahliyan. Principal component and hierarchical cluster analyses revealed that crude oils align with the thermal maturity of their source rocks. Strong correlations were observed between the crude oils and Garau and Sargelu source rocks, distinctly separating from the Kazhdumi source rock, emphasizing their dominant role in the Abadan Plain's petroleum systems.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"223 ","pages":"Article 105525"},"PeriodicalIF":2.2,"publicationDate":"2024-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143153355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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