Journal of African Earth Sciences最新文献

{"title":"Petrogenetic relationships between Paleoproterozoic granitoids and rare-element pegmatites from Dibilo (Liptako, West Niger, West African Craton)","authors":"Sofiyane Abdourahamane Attourabi ,&nbsp;Marieke Van Lichtervelde ,&nbsp;Mallam Mamane Hallarou ,&nbsp;Yacouba Ahmed ,&nbsp;Mahamane Moustapha Sanda Chékaraou ,&nbsp;Amadou Abdourhamane Toure","doi":"10.1016/j.jafrearsci.2024.105440","DOIUrl":"10.1016/j.jafrearsci.2024.105440","url":null,"abstract":"<div><div>The rare-element pegmatites of Dibilo form intrusions in a tonalitic gneiss of the Paleoproterozoic Téra-Ayorou pluton about 4 km from the contact zone with the Diagorou-Darbani greenstone belt, in the Nigerien Liptako (NE portion of the Man Ridge of the West African Craton). The general objective of the present study is to determine the petrogenetic relationships between the granitoids and the Dibilo pegmatites through a multidisciplinary approach combining petrology, geochemistry, structural geology and metallogeny. Two generations of granitoids have been distinguished at Dibilo. A first generation of metaluminous to weakly peraluminous granitoids (tonalitic gneiss, metadiorite and two-mica granitic gneiss) constitute a calc-alkaline series. Trace element geochemical signatures suggest that these granitoids were emplaced in an island arc and subduction zone context. A second generation of granitoids (leucogranites), encompassing two-mica, muscovite and two-mica-garnet granites, are peraluminous and calc-alkaline. These leucogranites are fertile, i.e., rich in incompatible elements, with Li concentrations attaining 250 ppm in the richest. A model of partial melting shows that they could derive from the partial melting of Li-rich metadiorite, which is itself highly enriched in lithium (150 ppm). One sample of migmatite has Li contents of 300 ppm, which evidences the fertile nature of the tonalitic-dioritic-granitic gneiss complex.</div><div>Three types of pegmatite have been identified at Dibilo: sterile pegmatites (type I), peraluminous and poorly evolved; Nb-Ta pegmatites (type II-a) and Nb-Ta, Mo pegmatites (type II-b), moderately evolved, peraluminous, respectively mineralized with columbite-group minerals (type II-a) and columbite-group minerals and Mo-bearing sulfide (type II-b); and highly evolved, peraluminous Li and Nb-Ta pegmatites (type III) mineralized with spodumene and columbite-group minerals. The type I barren pegmatites share similarities with the leucogranites and could also originate from the partial melting of the dioritic gneiss. The highly evolved type II-a, type II-b and type III pegmatites correspond to the residual liquids resulting from the fractional crystallization of leucogranites. Therefore, we propose that the Dibilo rare-element pegmatites derive from both fractional crystallization and partial melting processes within the tonalitic-dioritic-granitic complex.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105440"},"PeriodicalIF":2.2,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420655","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}

{"title":"Physico-thermal and geochemical behavior and alteration of the Au indicator gangue hydrothermal quartz at the Kubi Gold ore deposits","authors":"Gabriel K. Nzulu,&nbsp;Lina Rogström,&nbsp;Jun Lu,&nbsp;Hans Högberg,&nbsp;Per Eklund,&nbsp;Lars Hultman,&nbsp;Martin Magnuson","doi":"10.1016/j.jafrearsci.2024.105439","DOIUrl":"10.1016/j.jafrearsci.2024.105439","url":null,"abstract":"<div><div>Altered and gangue quartz in hydrothermal veins from the Kubi Gold deposit in Dunkwa on Offin in the central region of Ghana are investigated for possible Au-associated indicator minerals and to provide the understanding and increase the knowledge of the mineral hosting and alteration processes in quartz. X-ray diffraction, air annealing furnace, differential scanning calorimetry, energy dispersive X-ray spectroscopy, and transmission electron microscopy have been applied on different quartz types outcropping from surface and bedrocks at the Kubi Gold Mining to reveal the material properties at different temperatures. From the diffraction results of the fresh and annealed quartz samples, we find that the samples contain indicator and the impurity minerals iron disulfide, biotite, titanium oxide, and magnetite. These minerals, under oxidation process between 574 and 1400 °C temperatures experienced hematite alterations and a transformation from α-quartz to β-quartz and further to cristobalite as observed from the calorimetry scans for hydrothermally exposed materials. The energy dispersive spectroscopy revealed elemental components of Fe, S, Mg, K, Al, Ti, Na, Si, O, and Ca contained in the samples, and these are attributed to the impurity phase minerals observed in the diffraction. The findings also suggest that during the hydrothermal flow regime, impurity minerals and metals can be trapped by voids and faults. Under favorable temperature conditions, the trapped minerals can be altered to change color at different depositional stages by oxidation and reduction processes leading to hematite alteration which is a useful indicator minerals in mineral exploration.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105439"},"PeriodicalIF":2.2,"publicationDate":"2024-10-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420656","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}

{"title":"Paleoenvironmental conditions across the Coniacian-Santonian in the Kometan Formation, northeastern Iraq: Insights from planktonic foraminifera distribution, mineralogy and geochemistry","authors":"Mohammed A. Sulaiman ,&nbsp;Ali I. Al-Juboury ,&nbsp;Majid M. Al Mutwali ,&nbsp;Irfan Sh Asaad ,&nbsp;David L. Dettman ,&nbsp;Nasir Alarifi ,&nbsp;Fathy Abdalla ,&nbsp;Giovanni Zanoni ,&nbsp;Harry Rowe","doi":"10.1016/j.jafrearsci.2024.105437","DOIUrl":"10.1016/j.jafrearsci.2024.105437","url":null,"abstract":"<div><div>The paleoenvironmental conditions during the Coniacian-Santonian interval within the Kometan Formation in northeastern Iraq have been analyzed through the distribution of depth-related planktonic foraminifera in the carbonate rocks (limestone and marly limestone) of the Kometan Formation using standard washing method for soft samples and thin section method for hard samples supported by mineralogical investigations, geochemical analysis and stable isotopic δ¹³C and δ¹⁸O data. The findings indicate that saline marine waters and a hot, dry to semi-arid climate with low to medium oxygen conditions were conducive to deposition, which was characterized by high organic productivity due to marine transgression. The study revealed that the distribution of shallow water forms (SWF) of globular-shaped foraminifera, compared to deep water forms (DWF) of keeled-shaped genera, along with δ¹³C data from the late Turonian-early Campanian succession, indicated a relatively low sea level throughout the Late Turonian period. The water level began to rise in the early Coniacian, continuing gradually until the late Coniacian, when a noticeable increase in sea level was observed. This elevated sea level persisted through the early and late Santonian periods, before starting to drop. A slight marine transgression was noted at the beginning of the early Campanian period, followed by a significant drop in sea level. During the late Turonian, a subtropical climate prevailed. Temperature increased during the early to middle Coniacian, decreased slightly at the beginning of the late Coniacian, and then rose again at the end of the late Coniacian, indicating a shift from tropical to subtropical climatic conditions. Similar hot climatic conditions persisted in a tropical-subtropical climate during the early to late Santonian and early Campanian, with a relative temperature drop near the end of the early Campanian. No evidence of an oceanic anoxic event (OAE3) was found in the Kometan Formation during the late Coniacian–early Santonian period. The hypothesized event, based on biostratigraphy, facies analysis, stable isotopes, geochemical evidence, and field study, was limited to demonstrating an increase in the ratio of keeled chamber planktonic foraminifera compared to globular chamber ones. This ratio increase of the keeled chamber types is believed to result from a deepening sedimentary environment due to rising sea levels, creating organic matter-rich beds with high productivity and relatively low oxygen conditions during the Coniacian-Santonian boundary.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105437"},"PeriodicalIF":2.2,"publicationDate":"2024-09-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420461","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}

{"title":"Sequence stratigraphic architecture and depositional evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate successions, N Cyrenaica Promontory, NE Libya – Interplay of tectonics and eustasy","authors":"Muneer Abdalla,&nbsp;Salah Hassan,&nbsp;Akram Zafir,&nbsp;Abdlsaid Ibrahem,&nbsp;Ahmad Issa","doi":"10.1016/j.jafrearsci.2024.105438","DOIUrl":"10.1016/j.jafrearsci.2024.105438","url":null,"abstract":"<div><div>The interactions of tectonics and eustasy on the stratigraphic architectural evolution of the early Eocene-early Miocene Al Jabal Al Akhdar carbonate sedimentary successions were evaluated. This evaluation was achieved through detailed analyses of microfacies, depositional interpretation, and sequence stratigraphic framework of five measured sections located within the Al Jabal Al Akhdar Uplift, northeast Libya. The study interval was subdivided into distinct microfacies based on lithological changes, grain size and components, sedimentary texture and structures, fossil contents, color, and vertical stacking pattern. Six major depositional settings were delineated: restricted lagoon, open marine lagoon, platform margin and shoals, platform-margin reefs, foreslope, and middle to lower slope. Four third-order unconformity-bounded depositional sequences were identified based on vertical and lateral facies distribution, variations in fossil contents, and diagenetic features. Each sequence is composed of a transgressive-regressive interval, except for the younger sequence, which only contains a transgressive unit. Four evolutionary stages are recognized: initiation, growth, high-relief platform, and subaerial exposure. Subsidence resulting from tectonism and sediment loading, coupled with rising sea-level, created the accommodation space for the sedimentation of the studied carbonates. Repeated eustatic sea-level fluctuations controlled the internal stratigraphic heterogeneity and sequence development. Tectonic uplift caused a major sea-level retreat, resulting in the emersion of the carbonate sequences. The pre-existing Mesozoic and Paleocene sequences that underwent major uplift during the Late Cretaceous-early Eocene formed a shallow-water positive-antecedent topography for the formation of the carbonate sediments. This study establishes a carbonate sequence stratigraphic hierarchy of different cyclic sedimentation orders and improves our knowledge of sedimentary and stratigraphic architectural evolution and depositional mechanisms of carbonate platforms in an inverted basin setting. This knowledge can aid in predicting the distribution of lithofacies and depositional systems of economic importance.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105438"},"PeriodicalIF":2.2,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142357128","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}

{"title":"Tectonic evolution and structural geology of the Jurassic succession in the Zubair oil field, southern Iraq","authors":"Aymen Adil Lazim ,&nbsp;Amna M. Handhal ,&nbsp;Fraidoon Najm Rashid","doi":"10.1016/j.jafrearsci.2024.105436","DOIUrl":"10.1016/j.jafrearsci.2024.105436","url":null,"abstract":"<div><div>This study investigates the structural style and tectonic evolution of Jurassic succession in southern Iraq, within the Zubair oil field, which are crucial for charging oil to the Cretaceous reservoirs, utilized 3-D seismic reflection data to explore its complex geological history. The field is located in the Mesopotamian plain on the northeast Arabian Plate in southern Iraq. Four folds recognized: Hammar, Shuaiba, Rafdyia, and Safwan, each shaped by specific geodynamic processes. Hammar, Shuaiba, and Safwan are characterized as salt-related folds, influenced by salt tectonics. Rafdyia is identified as a compression-related fold formed due to the convergence of the Arabian and Eurasian plates. Forty-seven faults were identified, with diversity patterns and spatial distributions suggesting a tectonic history marked by three distinct phases: extensional tectonics, extensional with concurrent salt activity, and plate convergence. These phases have created a series of graben structures that, along with the identified folds, highlight the role of three primary tectonic processes: basement tectonics, salt dynamics, and plate interactions in shaping the structural style of the Zubair oil field during the Jurassic time.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105436"},"PeriodicalIF":2.2,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142433492","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}

{"title":"Mesozoic clastic provenance during post-rift evolution of the Essaouira Agadir Basin, Northern Morocco","authors":"Emmanuel Roquette ,&nbsp;Aude Duval-Arnould ,&nbsp;Orrin Bryers ,&nbsp;Stefan Schröder ,&nbsp;Tim Luber ,&nbsp;Ian Millar ,&nbsp;Rémi Charton ,&nbsp;Luc Bulot ,&nbsp;Jonathan Redfern","doi":"10.1016/j.jafrearsci.2024.105429","DOIUrl":"10.1016/j.jafrearsci.2024.105429","url":null,"abstract":"<div><div>This study combines several provenance tools, analysis of published structural and geodynamic data, integrated with Low-Temperature Thermochronology (LTT) and time-Temperature Modelling (tTM) to reconstruct the evolution of source-to-sink systems feeding the Essaouira-Agadir Basin (EAB) during the Jurassic (Toarcian, Bathonian, and Kimmeridgian) and Lower Cretaceous (Hauterivian and Barremian).</div><div>LTT and tTM define timing and rate of subsidence and exhumation of the hinterland and allows modelling of the predicted age and lithology of eroding rock units from the most-likely source locations through time. Extrapolation of predicted surface geology allows recognition of the lithology of sedimentary overburden in the hinterland, much of which has been subsequently eroded and is not preserved in the modern surfical geological record.</div><div>Heavy mineral, petrography and detrital zircon data analysis was carried out on fluvial and shallow marine sandstones sampled from Jurassic and Cretaceous sections across in the EAB. The results document changing sediment source terrains through time. In the Early and Middle Jurassic, the heavy mineral and detrital zircon signature correlates with a Palaeozoic source, suggesting provenance was dominantly from erosion of Cambrian and Ordovician sandstone in the Central and Western Anti-Atlas. From the Late Jurassic to Early Cretaceous, the heavy mineral and zircon signatures have a strong affinity with Triassic sediments. This indicates a provenance switch to the exhuming West Moroccan Arch (MAM and Western Meseta), interpreted to have been largely covered by Triassic continental red beds at the time.</div><div>The results help in predicting sediment delivery offshore, into the deep-water basin, where sandstones are a target for hydrocarbon exploration. Defining timing of input, location and composition helps to de-risk exploration. All the intervals examined contained discrete fluvial systems entering in the EAB, suggesting multiple periods of clastic delivery. Results suggest the Middle Jurassic and Hauterivian and Barremian intervals offer the optimum time for delivery of coarse clastics to the shelf margin, and potentially into the deep basin. The source to sink maps developed in this study further characterize these systems, their provenance and timing.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105429"},"PeriodicalIF":2.2,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420463","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Application of petrography, geochemistry and palynology of the mid-Ordovician – Pennsylvanian sediments of Tabenken in the investigation of Palaeo-environmental alterations of the Oku massif, North West Cameroon","authors":"Abimnui Norine Wendi ,&nbsp;Njilah Isaac Konfor ,&nbsp;Yongue Fouateu Rose ,&nbsp;Bruno Ndicho Nfor","doi":"10.1016/j.jafrearsci.2024.105428","DOIUrl":"10.1016/j.jafrearsci.2024.105428","url":null,"abstract":"<div><div>This study is effected on the volcano-sedimentary terrain of Tabenken on the Oku massif. Here is a region predominantly underlain by a granitoid basement of Precambrian age (600 ma), overlain in most parts by alkali basalts, andesites, trachytes and rhyolites. Between the basement and volcanics is sandwiched a discontinuous sequence of sedimentary lithofacies composed of conglomerates, sandstones, claystones, siltstones and patches of coal raising the question of the palaeoenvironment. Petrographic analyses, major and trace element geochemistry and palynological analyses were conducted on samples of sediments. Palynological constituents found include amorphous organic matter, phytoclasts, opaque material and palynomorphs consisting of spores with no pollen grains. The presence of cuticles is environmental indicator for delta sediments while abundance of amorphous organic matter (AOM) suggests deposition in a reducing environment. Petrographic studies reveal two cycles of deposition; L1 and L2 separated by Cenozoic outpours. U/Th ratios for the analyzed samples range from 0.3, 0.06, 0.00 to 0.2 and fall within the range of sediments formed in oxidizing environments. This contrasts evidence from AOM hence suggests sediment input cut across climatic and environmental alterations over a long period of time. Sr/Ba ratios range from 0.08 to 0.25 with an average of 0.18 reflecting fresh water environment; while Rb/Sr ratios range from 0.2, 0.29, 0.33 and 0.45 being low and suggests sediments deposited under warm climatic conditions. Diagram of Roser and Korsch, 1986 reveals deposition in a passive margin while Al₂O₃/TiO₂ and Th/Co ratios support sediment input of principally felsic origin with little input from mafic sources.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105428"},"PeriodicalIF":2.2,"publicationDate":"2024-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142420462","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}

{"title":"Heavy metals in the surface sediments of Farwa Lagoon, NW Libya: Assessment and correlation with other Mediterranean lagoons","authors":"Sherif M. El Baz ,&nbsp;Ahmed Al Furjany ,&nbsp;Fouzi Dahan","doi":"10.1016/j.jafrearsci.2024.105435","DOIUrl":"10.1016/j.jafrearsci.2024.105435","url":null,"abstract":"<div><div>The present study aims to evaluate the heavy metal pollution in the Farwa Lagoon, which is one of the most important coastal lagoons in NW Libya. The concentrations of six heavy metals (Fe, Zn, Pb, Ni, Cu, Cd) are measured in the surface sediment of the lagoon. Moreover, the contamination indices, including contamination factor, degree of contamination, pollution load index, geo-accumulation index, enrichment factor, risk factor, and potential ecological risk index, are applied. The results indicate that, Fe has the highest concentration, followed by Zn, Pb, Ni, Cu and Cd. The distribution patterns of metals reflect that the levels of Fe, Cu and Zn increase in the central part of the lagoon, whereas Cd and Pb increase in the central and western parts. In addition, the values of contamination factor reflect that the examined sites are moderately contaminated with Pb and Zn, whereas they are very highly contaminated with Cd. These findings lead to very high degree of contamination. Moreover, pollution load index reflects that the Farwa Lagoon is polluted. Finally, the study area is very highly ecological risk with Cd. The concentration of metals in the Farwa Lagoon is correlated with those from other regions in the Mediterranean region, such as Egypt, Algeria, Tunisia, Italy, France, and Turkey. The comparison reflects that the Farwa Lagoon has the highest concentrations of Cd and Zn.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105435"},"PeriodicalIF":2.2,"publicationDate":"2024-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142322391","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}

{"title":"A review of the geological setting and economic potential of uranium occurrences in the proterozoic part of the Reguibat Shield of the west African Craton, in northern Mauritania","authors":"Salem-Vall Brahim ,&nbsp;M. Cuney ,&nbsp;Akinade Shadrach Olatunji ,&nbsp;Sid’Ahmed Sidi Reyoug ,&nbsp;Ahmed Hamoud","doi":"10.1016/j.jafrearsci.2024.105434","DOIUrl":"10.1016/j.jafrearsci.2024.105434","url":null,"abstract":"<div><div>Uranium mineralisation is formed in a wide range of geological settings, including deep magmatic to surficial conditions, and ranges in age from Archean to recent. The success of exploration planning and the choice of efficient extraction methods in an environmentally sustainable manner depend clearly on the understanding of the uranium genesis model and the detailed knowledge of the mineralogy of the deposit.</div><div>Mauritania hosts eighty known uranium occurrences, mainly located in the oriental part of the Reguibat Shield. Some of these occurrences have been evaluated with the publication of estimated resources, and even exploratory mining works have been performed on some of them. However, the detailed genetic conditions prevailing for the genesis of most of these occurrences remain poorly studied. Exploration reports indicate that uranium mineralisation in the Reguibat Shield mainly occurs as high temperature deposits hosted by shear zones in granites (hydrothermal Na-metasomatic deposits) and low temperature deposits hosted by calcretes (Calcrete deposits), which form more than 70% of these occurrences.</div><div>This paper focuses on the dominant uranium mineralisation systems (uraniferous calcretes and Na-metasomatite) of the oriental part of the Reguibat Shield and, to a lesser extent, other types of uranium deposits. Na-metasomatites are mainly originating from Neobirimian granite and basic rocks and occur through hydrothermal fluids, inducing regional metasomatism along NNW–SSE trending shear zones. While uraniferous calcretes in the area are found as subsurface layers covering a Proterozoic basement made of granitoid and associated gabbro-diorite massifs intersected by a network of mafic dykes. The uraniferous calcretes result from the weathering of the Neobirimian (Paleoproterozoic) granitic basement. Carbonate and uranium minerals (carnotite and tyuyamunite) crystallize as cementation materials within the granite arena. Two types of Neobirimian granites have been identified: the first one being an orientated coarse-grained porphyritic brown to pink granite, while the second one is a porphyritic grey medium-grained granite, whose mineralogy is mostly made up of plagioclase, K-feldspar, quartz, and chloritized biotite, while magnetite, apatite, titanite, zircon, uranothorite, and monazite are the accessory minerals.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105434"},"PeriodicalIF":2.2,"publicationDate":"2024-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142312199","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}

{"title":"The Ain Dibba and Ain Kissa phosphorites, Tebessa (NE Algeria): REE depletion versus shallow, open depositional environment during the Paleocene-Eocene phosphogenesis in North Africa","authors":"Ibtissam Diab ,&nbsp;Rabah Laouar ,&nbsp;Delphine Bosch ,&nbsp;Ali Tlili ,&nbsp;Amor Degaichia ,&nbsp;Olivier Bruguier ,&nbsp;Mourad Zaabat ,&nbsp;Salah Bouhlel ,&nbsp;Rabah Kechiched","doi":"10.1016/j.jafrearsci.2024.105433","DOIUrl":"10.1016/j.jafrearsci.2024.105433","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The Ain Dibba and Ain Kissa phosphorites, located north of Tebessa town, NE Algeria, belong to the Upper Cretaceous-Paleocene-Eocene Afro-Arabian phosphatic province that extends from Morrocco to the Middle East. These two phosphorite showings, which were partly exploited at the beginning of the 20th century, were deposited during the Late Paleocene (Thanetian) times on the northern basin of the Kasserine Paleo-Island. Although they are not yet economically very important, the present petrological and geochemical study contribute highly to the knowledge of their critical trace and REE contents as well as the understanding of their paleo-depositional environment. Petrographic and XRD data show that these phosphorites are mainly composed of pellets, coprolites, bioclasts and rare glauconite, gypsum, quartz grains and zeolites. These constituents are cemented by calcareous, siliceous or rarely clayey matrix. The pellets and coprolites are composed mainly of cryptocrystalline carbonate fluor-apatite (CFA). The XRF and ICP-MS chemical analyses of these phosphorites, show they are not as rich as those from Kef Essenoun and Bled El Hadba southern basin, neither in P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; nor in REE contents. P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; concentrations range from 14.16 to 26.57 wt% (average = 20.24 ± 4.33 wt%, n = 15), with only one sample having 31.89 wt% P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;, whereas ΣREE contents range from 171 to 344 ppm (average = 252 ± 69 ppm, n = 9) and, therefore, considered as moderately REE-enriched phosphorites. Ce anomaly values display a decrease from the lower to the upper phosphorite sub-layers (from −0.57 down to −0.72), suggesting an increase from relatively sub-oxic to more oxic conditions. The Eu anomalies range from 0.89 to 1.35 for Ain Dibba and from 0.93 to 1.35 for Ain Kissa phosphorites. The highest Ce/Ce∗ and lowest Eu/Eu∗ anomalies are recorded in the lower layers, often enriched in both REE and glauconite contents, whereas the lowest Ce/Ce∗ and highest Eu/Eu∗ anomalies, reflecting more oxic conditions, are characteristics of the glauconite-free and REE-poor upper layers. The gradual timewise transition from relatively sub-oxic to oxic conditions (from the lower to the upper layers) is also recorded in the redox-sensitive (Cr, Ni, V, U) trace element data. This implies that during early diagenesis, the sedimentary environment became slightly reduced, which enabled intensive uptake of both REE and some trace element (e.g., Cr, V, Ni, U) mainly from pore-water through substitution and adsorption mechanisms onto apatite and glauconite minerals. This is noticed especially in the lower phosphorite layers of both Ain Dibba and Ain Kissa deposits. In a larger scale, the Ain Dibba and Ain Kissa phosphorites show lower REE contents, lower Ce and Eu anomalies, and lower redox-sensitive trace element contents than those of the southern (Kef Essenoun and Bled El Hadba) and eastern (Tunisian) basins of the Kasserine paleo-Is","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"220 ","pages":"Article 105433"},"PeriodicalIF":2.2,"publicationDate":"2024-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142322394","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}