Journal of African Earth Sciences最新文献

{"title":"Growth anatomical anomalies in Cenomanian echinoids of the Bellezma-Batna Mountains (NE Algeria)","authors":"Benmansour Sana ,&nbsp;Benmessaouda Hadil ,&nbsp;Drifi Naima","doi":"10.1016/j.jafrearsci.2025.105560","DOIUrl":"10.1016/j.jafrearsci.2025.105560","url":null,"abstract":"<div><div>This article reports cases of growth anatomical anomalies in two echinoid species, <em>Macraster douvillei</em> (Gauthier) and <em>Mecaster pseudofourneli</em> (Péron and Gauthier), from the Cenomanian deposits of the Bellezma-Batna mountains (northeastern Algeria). Such a topic is first reported in Algeria ever. The large collection (400 specimens) made it possible to distinguish several types of these rare pathologies, each one being illustrated by explanatory drawings. Three types of deformation directly concerning the pentamery, are presented. They are most often resulting from an additional growth zone (6 ambulacra), a complete tetramery represented by a missing growth zone (4 ambulacra) and constrictions or strangulation of the ambulacres. Abnormalities can develop in the rudiment as soon as the larva enters metamorphosis, or shortly afterwards in juvenile broods. They may alter the plate arrangement and the general shape of the test or, on the contrary, result in local deformations, influencing the arrangement or shape of the ambulacra, etc. These malformations resulted from either intrinsic (genetic) or extrinsic (ambiental) conditions.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105560"},"PeriodicalIF":2.2,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143347923","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":"Numerical terrain analysis of fluvial-marine watersheds on the Isle of Santiago, Cape Verde, based on satellite imagery, ground-truthing and landform indices - A preparatory study in search of Nb -Ta - REE deposits related to hotspot islands","authors":"Harald G. Dill ,&nbsp;Andrei Buzatu ,&nbsp;Sorin-Ionut Balaban ,&nbsp;Dominik Schmitt ,&nbsp;Ulrich Heimhofer ,&nbsp;Astrid Techmer","doi":"10.1016/j.jafrearsci.2025.105548","DOIUrl":"10.1016/j.jafrearsci.2025.105548","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Numerical terrain analysis constitutes the missing link between the classical descriptive geomorphology and geomorphometry providing landform indices by means of which issues in applied and genetic geosciences can be solved. This method is fully satellite-based and supplemented by ground-truthing dealing with the interior parts of the positive landforms and the inter-landform sediments.&lt;/div&gt;&lt;div&gt;This approach can successfully be taken prevalently for immature modern landscapes, exemplified by Cenozoic volcanic hotspot islands such as Santiago, the main island of the Cape Verde Archipelago, where four lithofacies types could be delineated. Corresponding to the scale of observation, a tripartite subdivision is achieved in numerical terrain analysis (1st order regional, 2nd order local, 3rd order outcrop scale).&lt;/div&gt;&lt;div&gt;The first order indices allow for a tripartite compartmentalization of the volcanic island into the presumed paleosurface of all volcanic summits within a certain altitude (“Gipfelflur”), the volcanic pediment and the coastal zone. Among the second order indices, the VaSlAn&lt;sub&gt;alti&lt;/sub&gt; index (Variation of Slope Angle altitude) giving the variation of slope angle as function of altitude is an excellent environmental marker. Its correlation coefficients provide a measure for the homogeneity of volcanogenic, mass wasting, fluvial, and coastal landform series. Among the third order indices, the QuantGrav&lt;sub&gt;situ&lt;/sub&gt; index (Quantification Gravel situmetry) lends much support to the afore-mentioned environmental markers. It is a meticulous measure of the modality, sharpness and fan width of the orientation of clasts with their data, illustrated in semicircle rose diagrams. It is used to fine-tune volcaniclastic deposits at outcrop scale. The compositional quantification encompasses mineralogy, biosedimentology and isotope geochemistry (δ&lt;sup&gt;13&lt;/sup&gt;C, δ&lt;sup&gt;18&lt;/sup&gt;O) as well as &lt;sup&gt;14&lt;/sup&gt;C-dating.&lt;/div&gt;&lt;div&gt;The compositional study of the terrain analysis reveals on the biosedimentological part a low-relief coral accumulation with an impoverished fauna of Caribbean affinity. On the mineralogical part, the two strings heavy and light minerals unravel different processes. The heavy minerals accumulated in the fluvial-marine sediments of the coastal region point to magmatic host rocks from basaltic andesites to picrobasalt and basanite. Zeolites among the light minerals are indicative of a meteoric to low-temperature hydrothermal alteration confined to the lithofacies types C and D.&lt;/div&gt;&lt;div&gt;The coastal zone shows a characteristic quadripartite subdivision. It is the reference terrain for any inter-island comparison regarding volcanogenic islands. And it is the starting level for a more detailed characterization of the volcanic island's upper slope. LFS A1 (Landform Series) is characteristic of a curvilinear-rectilinear cliff coast sculped by a strong marine wave action with subordinate subaerial - submarine point sour","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"227 ","pages":"Article 105548"},"PeriodicalIF":2.2,"publicationDate":"2025-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143696708","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":"Mineralogy and geochemistry of the middle to upper jurassic sargelu, naokelekan, and barsarin formations from northeastern Iraq: Implications for paleoenvironmental, provenance, and tectonic setting proxies","authors":"Rebwar H. Rasool ,&nbsp;Sarmad A. Ali ,&nbsp;Ali I. Al-Juboury ,&nbsp;Nasir Alarifi ,&nbsp;Fadhil A. Lawa ,&nbsp;Harry Rowe ,&nbsp;Giovanni Zanoni ,&nbsp;David L. Dettman","doi":"10.1016/j.jafrearsci.2025.105559","DOIUrl":"10.1016/j.jafrearsci.2025.105559","url":null,"abstract":"<div><div>This study investigates the mineralogical and geochemical characteristics of the middle-upper Jurassic Sargelu, Naokelekan, and Barsarin formations in the Sargelu area, northeastern Iraq. The study aims to interpret the provenance, tectonic setting, paleoclimate, and paleoweathering processes that shaped these formations using X-ray diffraction, X-ray fluorescence, and stable isotopes of carbon and oxygen. The findings provided valuable insights into the geological history and environmental conditions of the region during the Jurassic period. XRD analysis revealed that the clay minerals in the shale samples primarily consist of illite, kaolinite, and mixed-layer illite-smectite. Geochemical analysis of major and trace elements, along with clay mineralogy and stable oxygen and carbon isotopic data, indicate that arid to semi-arid and semi-humid climatic conditions prevailed during the deposition of the Jurassic formations. The shales from the Sargelu, Naokelekan, and Barsarin formations were derived from a felsic igneous source, as evidenced by multiple multidimensional diagram plots and a bivariate plot of SiO₂ vs log (K₂O/Na₂O). Variations in oxygen and carbon isotopes, along with trace element data, suggested that the Sargelu Formation was deposited in a saline marine environment, the Naokelekan Formation in a saline marine to freshwater environment, and the Barsarin Formation in a highly saline, brackish-to-freshwater environment. Paleoredox and paleoproductivity proxies indicated deposition under anoxic to suboxic conditions, with particularly high productivity observed in the Naokelekan Formation.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105559"},"PeriodicalIF":2.2,"publicationDate":"2025-01-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143350008","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":"Ecological differences in upper Pliensbachian (Early Jurassic) reef communities determined by environmental conditions in carbonate settings","authors":"Travis Stone ,&nbsp;Rowan Martindale ,&nbsp;Stéphane Bodin ,&nbsp;Bernard Lathuilière ,&nbsp;François-Nicolas Krencker ,&nbsp;Tanner Fonville ,&nbsp;Lahcen Kabiri","doi":"10.1016/j.jafrearsci.2025.105547","DOIUrl":"10.1016/j.jafrearsci.2025.105547","url":null,"abstract":"<div><div>Reef communities changed dramatically during the Early Jurassic as they recovered from the End-Triassic Mass Extinction. The Atlas Rift Zone in Morocco provided expansive shallow water substrate, which allowed a variety of reef communities to develop, such as lithiotid bivalves that established themselves as new and prolific reef builders alongside corals, microbialites, and sponges in the Sinemurian and Pliensbachian stages. To better understand the dynamics between these reef builders and their environments, a detailed facies analysis of upper Pliensbachian reefs and a quantitative analysis of their composition was undertaken. We describe two distinct environmentally controlled reef types in the Central High Atlas Mountains. Lithiotid bivalves dominated reef construction in lagoonal environments and, together with phaceloid corals, commonly built bioherms and biostromes that ranged from 1 to 2 m tall and up to several hundred meters wide. Meanwhile, on the platform edge, microbialites, corals, and sponges constructed patch reefs up to 7 m tall and 20 m wide. These two reef types share common facies, as many of the same reef inhabitants, and some framework builders, grew in both environments. Despite the facies overlap, the communities in these two environmental settings are distinct, which is likely a result of environmental controls on the dominant reef framework builders. Moderately turbid waters and soft substrate in lagoons were ideal conditions for lithiotids but excluded many corals, sponges, and microbialites. Conversely, the clear, oligotrophic waters at the platform edge allowed photosynthetic and photosymbiotic organisms to thrive (e.g., coral and microbial reefs), while firmer substrate and higher wave energy may have prevented lithiotids from establishing dense populations.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105547"},"PeriodicalIF":2.2,"publicationDate":"2025-01-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171379","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":"Lithostratigraphy of the Katangan supergroup in the Kalindi-Kipushi area at the DRC-Zambia border and its relationship to lithostratigraphic successions in other portions of the central African copperbelt","authors":"Helen C. Twigg,&nbsp;Murray W. Hitzman","doi":"10.1016/j.jafrearsci.2025.105545","DOIUrl":"10.1016/j.jafrearsci.2025.105545","url":null,"abstract":"<div><div>This study describes the lithostratigraphy of the Katangan Supergroup from the Kansuki Formation of the Roan Group to the Kanianga Formation of the Kundelungu Group in the Southern Congolese Copperbelt (CCB) in the area south of the Kipushi mine. The study utilises information from diamond drill holes as well as information on the lateral extent of lithostratigraphic units from a new map of the area constructed from both geophysical and geochemical data. A lithofacies analysis approach is used to better understand depositional environments and controls on sedimentation. Facies variability and unconformities in the study area are related to active rifting and eustatic controls during deposition of the Mwashya and Muombe subgroups and a combination of thermal subsidence, salt withdrawal, and global eustatic controls during deposition of the Bunkeya and Gombela subgroups. Comparisons of the study area with areas to the north suggest they were separated by a structural high present from at least the time of deposition of the upper Mwashya Subgroup. The study area appears to exhibit deeper water facies than those of the comparable sequence present in the Zambian Copperbelt.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105545"},"PeriodicalIF":2.2,"publicationDate":"2025-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100087","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":"Characterization and evolution of a retrograding-prograding deltaic system, NE Sirte Basin, north-central Libya — Sequence stratigraphic architecture and controlling factors","authors":"Muneer Abdalla ,&nbsp;Husamaldeen Zubi ,&nbsp;Abdalla Abdelnabi","doi":"10.1016/j.jafrearsci.2025.105558","DOIUrl":"10.1016/j.jafrearsci.2025.105558","url":null,"abstract":"<div><div>This study presents the first deltaic system interpreted from three-dimensional seismic and wireline log data in the Sirte Basin, the largest sedimentary basin in Libya and most producing petroliferous basin in Africa. The research focuses on examining the internal sedimentary configuration and sequence stratigraphic architecture of an Oligocene deltaic system in the northeastern part of the Sirte Basin. Three major log facies were defined on the basis of wireline log responses: sandstone, siltstone, and shale. The deltaic system was subdivided into three sedimentary facies based on interpreted log facies and their vertical stacking patterns, seismic geometries, and position along the depositional profile. Those facies are distributary channel, delta front, and prodelta. Three major synchronous and regional stratigraphic surfaces were delineated, encompassing the whole study focus and extend beyond the boundaries of the 3D seismic survey. The deltaic system forms a third-order depositional sequence that is bounded by two unconformable sequence boundaries from below and above. It consists of two system tracts separated by a maximum flooding surface: a transgressive systems tract at the base capped by a regressive systems tract. The deltaic sequence is further subdivided into eleven fourth-order sequences. The development of the deltaic system was mainly controlled by sea-level changes and sediment influx. The deltaic system retreated to the south due to a rise in sea level, reduction in sediment input, with a minor contribution of subsidence resulting from sediment loading. While the progradation occurred as a result of increasing sediment influx that exceeded the creation rate of accommodation space. Additionally, the study provides insights onto the sedimentary and sequence stratigraphic structure, depositional mechanisms, and development of deltaic systems during a stable, post-rift stage of a sedimentary basin.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105558"},"PeriodicalIF":2.2,"publicationDate":"2025-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100090","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":"Petrogenesis of basalt and associated silicic rocks from upper Omo valley volcanic section, southwestern Ethiopia","authors":"Getnet Assefa ,&nbsp;Demise Tadessa ,&nbsp;Negedie Abrha ,&nbsp;Geremu Fufa ,&nbsp;Andualem Getaw","doi":"10.1016/j.jafrearsci.2025.105546","DOIUrl":"10.1016/j.jafrearsci.2025.105546","url":null,"abstract":"<div><div>Field, petrography, major and trace element analyses of mafic and silicic rocks from upper Omo valley volcanic section, Southwestern Ethiopia are presented to determine petrogenetic evolution. The analyzed rocks belong to the basaltic and rhyolitic suites within the sub-alkaline group and these suites are linked via fractional crystallization as evidenced by occurrence of intermediate rocks (basaltic andesite and andesite rocks). Plagioclase, pyroxene, and Fe–Ti oxide minerals are the prominent phenocryst in basaltic rocks, while alkali feldspar phenocrysts are abundant in rhyolitic rocks. Major element correlations indicate fractional crystallization played a significant role in the evolution of the upper Omo volcanic rocks. The rhyolitic rocks show general enrichment of light rare earth element (LREE) and depletion of heavy rare earth element (HREE), strong negative anomalies in Sr, P and Ti, and low Ba/Nb, La/Nb,and Th/Nb ratios indicate that they were formed through low-pressure fractionation of basaltic lava derived from the depleted mantle with unremarkable crustal input. Correspondingly, REE abundances and incompatible trace element (e.g., Zr/Nb, Nb/Y ratios as well as plots of Nb/Yb vs. Th/Yb) suggest that rhyolite rocks were derived from basalt magma source which resemble ocean island basalt (OIB)-like magma. The source area features and the similarity of melting conditions suggest that the ascent and development of mantle diapirs is the key to elucidate the volcanic activity in the upper Omo valley volcanic section. The geochemical features of the volcanic rocks found in the upper Omo valley volcanic section are similar to those found in the northwest Ethiopian plateaus (such as LT and HT1-type basalt, Lima Limo and Wegel Tena rhyolitic ignimbrite). However, the crustal materials involvement in the genesis of LT-type basalt and Lima Limo rhyolite, Northwestern Ethiopian plateau were determined (Pik et al., 1998, 1999; Ayalew and Yirgu, 2003).</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105546"},"PeriodicalIF":2.2,"publicationDate":"2025-01-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171378","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":"Groundwater recharge zone mapping in a coastal mediterranean aquifer applying fuzzy and analytical hierarchy process and frequency ratio: A case study of northeast Tunisia","authors":"Amal Kouaied ,&nbsp;Mohamed Haythem Msaddek ,&nbsp;Adel Zghibi ,&nbsp;Aziza Barrek ,&nbsp;Séverin Pistre ,&nbsp;Ismail Chenini","doi":"10.1016/j.jafrearsci.2025.105537","DOIUrl":"10.1016/j.jafrearsci.2025.105537","url":null,"abstract":"<div><div>Global water stress, driven by demographic growth, climate change, industrialization, and agricultural development, is exacerbated by excessive groundwater extraction, depleting aquifer storage. Groundwater recharge is crucial for ensuring water sustainability and preserving coastal water resources. This study assess aquifer suitability zones of the Aoussja Ghar El Melh coastal region in Tunisia using geographic information techniques (GIS), and three numerical methods: Fuzzy Logic, Analytical Hierarchical Process (AHP) and Frequency ratio (FR) method. The aim is to delineate significant groundwater recharge areas. The findings reveal three distinct recharge capacity classes. Fuzzy Logic indicated that a approximately 72 % of the study area, characterized by lithological features like sandstone alluvium and sandy marly soils in central plains, is suitable for groundwater potential zones (GWPZ). In contrast, the AHP indicates about 79% of the area, while FR model indicates 48%. These variations are influenced by the region's lithological and hydrogeological characteristics. Validation against 22 well locations show AHP as the most accurate (AUC = 91%), followed by Fuzzy Logic (AUC = 86 %) and the FR model (AUC = 70%). The application of the Fersi equation shows a strong correlation and spatial distribution similar to the AHP approach. This study concludes that while the Fuzzy Logic and FR models are valid for identifying GWPZ, they are less effective than AHP method, which provides refined recommendations for selecting recharge sites. Environment risks such as groundwater contamination and salinization in agricultural areas highlight the need for land resources management. The final map serves as a guideline for planning aquifer recharge projects and emphasizes the necessity of regulations and pumping limits to prevent overexploitation and saltwater intrusion. This preliminary assessment underscores the importance of implementing protective measures and recharge programs.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105537"},"PeriodicalIF":2.2,"publicationDate":"2025-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143100089","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":"Implementation of machine learning predictive models for targeting gold prospectivity mapping in part of the Ilesha schist belt, southwestern Nigeria","authors":"Ajibola Richard Faruwa ,&nbsp;Jing Ba ,&nbsp;Wei Qian ,&nbsp;Uti Ikitsombika Markus ,&nbsp;Imane Bachri","doi":"10.1016/j.jafrearsci.2025.105543","DOIUrl":"10.1016/j.jafrearsci.2025.105543","url":null,"abstract":"<div><div>This research leverages innovative machine learning techniques, including artificial neural networks(ANN), support vector machines(SVM), random forests(RF), and Naïve Bayes(NB), to construct a predictive model for gold deposits in part of the Ilesha schist belt. Thirteen predictor maps were used from geophysical, remote sensing, and geological datasets highlighting essential processes in ore formation, such as source characteristics, transport mechanisms, and chemical deposition. Together with 35 gold deposits and non-deposit locations, these datasets were employed to train and test the machine learning models using 10-fold cross-validation techniques. Performance was evaluated with confusion matrices, statistical metrics, and receiver operating characteristic (ROC) curves. All models achieved high predictive accuracy: RF at 98.94%, ANN at 97.80%, SVM at 93.65%, and NB at 90.48%. Key localization factors include magnetic lineament density, structural complexity, SRTM lineament density, analytical signals, and Bouguer gravity anomalies. Using the trained models, prospectivity maps were created, highlighting areas of very-high, high, moderate, and low potential for further research. The Prediction-Area for all the models exceeded 78%, confirming their effectiveness in identifying significant gold deposits in the area. Euler deconvolution suggests geological influences from sill/dyke structures, with magnetic source depths from &lt;-12.96 m to &gt; - 801.67 m and from &lt; −30.82 m to &gt; -1053.94m for structural indices (SI) of 0.5 and 1, respectively while spectral analysis indicates depths of 100m to 1.1 km for shallow sources. A strong correlation exists between gold prospectivity and magnetic sources below 300 m, especially near the Iwaraja/Ifewara fault and lithological boundaries. This study highlights the effectiveness of machine learning models in gold exploration and suggests avenues for future research in similar geological contexts.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"225 ","pages":"Article 105543"},"PeriodicalIF":2.2,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143419527","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":"Genesis of the Hamash gold deposit, eastern desert, Egypt: Inferences from new studies on mineral chemistry and fluid inclusions","authors":"Islam.A. Dourgham ,&nbsp;Safwat S. Gabr ,&nbsp;Lin-Fei Qiu ,&nbsp;Masoud A. Omar ,&nbsp;Fatma Deshesh","doi":"10.1016/j.jafrearsci.2025.105544","DOIUrl":"10.1016/j.jafrearsci.2025.105544","url":null,"abstract":"<div><div>In the South-Eastern desert of Egypt, where gold mineralization is hosted by granites, the Hamash gold deposit is recognized as one of the pharaoh's mines. In this study, the present authors aimed to study the paragenesis of sulfide minerals and the genesis of the related gold deposit based on field observation, ore mineralogy, electron probe analysis, and fluid inclusion data. The result was that the granitoid rocks of the Hamash area, composed mainly of granite and granodiorite, covered the center and southern portions of the study area and intruded into the metavolcanics. The Hamash gold deposit is hosted by intensely deformed granitic rocks that are dissected by numerous gold-bearing sulfide-quartz veins. The abundant ore minerals include pyrite, sphalerite, galena, and chalcopyrite (±tetrahedrite and ±gold disseminations), which occur in crosscutting quartz veins. Gold is associated with sulfides in quartz veins and alteration zones. The results of electron probe microanalysis (EMPA) reveal three varieties of pyrite with low As content (Py1 and Py2) and high As content (Py3) that were replaced by galena ± gold. Gold occurs either as clusters of tiny gold grains included in pyrite or as streak-like small inclusions within goethite. The new microthermometric and laser Raman spectroscopy studies indicate that the gold-bearing quartz veins are characterized by two types of fluid inclusions: H₂O-NaCl and H₂O-CO₂-NaCl. The lithostatic and hydrostatic pressure gradients in the isochores of the two types of fluid inclusions indicate fluid entrapment and gold deposition at temperatures between 235 °C and 270 °C at pressures ranging from 1.6 kbar to 2.7 kbar with low to moderate salinity of ∼2–7 eq. mass % NaCl of aqueous-carbonic fluid during the transition from lithostatic to hydrostatic conditions. Based on all the author's observations and conditions of ore formation, we suggest that the Hamash gold deposit is related to porphyry-type and epithermal sulfide deposits.</div></div>","PeriodicalId":14874,"journal":{"name":"Journal of African Earth Sciences","volume":"224 ","pages":"Article 105544"},"PeriodicalIF":2.2,"publicationDate":"2025-01-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143171382","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}