Résumé: Rare earth element (REE) enrichment in Algerian phosphorites has been evoked recently by a number of authors and are considered among the richest Paleocene-Eocene phosphorites worldwide. The Bled El Hadba deposit belongs to the giant Djebel Onk phosphorite complex in northeast Algeria. The deposit was subject to many geological studies that were focused on P2O5 contents for commercial purposes. The upper Thanetian phosphorite layer is about 30 m thick, and subdivided into three sub-layers (lower, main and upper sub-layer), based on P2O5 contents, where the main sub-layer is considered to be the richest. Despite this, few detailed geochemical investigations were carried out on this deposit thus far. In this work, major, trace and REE analyses were conducted on phosphate particles (pellets, coprolites and glauconites) using ‘in situ’ LA-ICP MS, and on whole-rock samples using XRF technique. The results show that the main sub-layer displays the highest whole-rock P2O5 contents, varying between 19.65 and 21.32 wt% compared to the lower (10.47–16.87 wt%) and upper (9.43–13.87 wt%) sub-layers. Among the phosphate particles, glauconites display the lowest P2O5 contents in the three sub-layers (17.45–19.35 wt%) compared to pellets (21.14–24.33 wt%) and coprolites (21.75–24.12 wt%), and largely the highest Al2O3, SiO2, MgO and Fe2O3(t). Glauconites also show higher ΣREE contents (764–2050 ppm) compared to pellets (221–910 ppm) and coprolites (214–909 ppm). Within the glauconite particles, the ΣREE, along with Al2O3, SiO2, MgO, and Fe2O3(t) contents, increase from core to the rim, whereas P2O5 contents decrease, which suggests that glauconitization postdates phosphatization processes. Also, the glauconitization process increase from the lower to the upper sub-layer; this is shown by the positive correlations between Al2O3 contents and those of MgO and SiO2 in one hand, and negative correlations between Al2O3 and P2O5 on the other hand. Ce, Eu, Y anomalies, along with La/Nd ratios and Nd contents, all point towards phosphatization under oxic conditions as a result of warm water upwelling, whereas glauconitization started under more reduced (suboxic) conditions; i.e., during early diagenesis, the peak of REE uptake from porewater, and under slow sedimentation rates. Despite their relatively low P2O5 concentrations, the ΣREE contents of the Bled El Hadba phosphate particles record the highest concentrations in all Algerian and north African phosphorites. The main sub-layer is considered to be the most glauconite-rich phosphorite in Algeria. Therefore, more extensive REE analyses are recommended to better evaluate its economic potential in terms of critical raw materials.

Résumé: The use of natural catalysts in various processes, including the electro-Fenton (EF) process, is a topic of interest in current research and development. Natural catalysts are being explored as potential alternatives to conventional catalysts due to their advantages such as sustainability, low-cost, and environmental compatibility. It is worth noting that the application of natural catalysts in the EF process is an active area of ongoing research, and their full-scale implementation may still require further development and optimization. That is why in our work, we chose to use hematite and pyrite as natural catalysts in the degradation of the black azo dye Eriochrome Black T (EBT) by EF process. Color and chemical oxygen demand (COD) removal efficiencies were compared with those obtained with the conventional catalyst (FeSO4). The pyrite-EF process followed a pseudo-second-order and was found to be more efficient than the hematite-EF process due to the self-adjustment of its pH, it gave slightly lower color (90.30%) and COD (89.20%) removal rates than those obtained with the conventional catalyst (93.05% and 92.06%) after 60 min of treatment. The morphology, chemical composition and crystal structure of hematite and pyrite samples were identified by scanning electron microscopy, X-ray fluorescence and X-ray diffraction analyses. Furthermore, the study of some operating parameters effects allowed determining the optimal conditions for treatment of the Eriochrome Black T solution: 0.03 g·L–1 (pyrite dose), 8 × 10–3 M (supporting electrolyte concentration) and 15 mA·cm–2 (current density). The pyrite-EF process showed similar behavior to that of FeSO4-EF with a low energy consumption. Therefore, EBT can be efficiently removed electrochemically using natural pyrite as an eco-friendly catalyst.

Résumé: The Khenchela massif, northeast Algeria, belongs to the eastern Saharan Atlas that extends northeasterly from the Aures Chain, through the Mellegue mountains, to the Tunisian Atlas. This massif is characterized by sandstone and marl outcrops of the Lower Cretaceous that are overlain by limestone and marl of the Upper Cretaceous. The anticline structure was subjected to several NW–SE to WNW-ESE-directed major normal faults that split the massif into a number of mega-blocs. Triassic evaporitic lithologies crop out as diapirs at the northeastern and southwestern parts of the anticline. The Ain Mimoun region, located on the northern flank of the Khenchela anticline, is composed of Albian-Aptian sediments that host the barite veins of the so-called ‘Mizab barite deposit’. This deposit, which is currently exploited, consists of a dozen main veins composed mainly of barite with quartz, calcite, ankerite and rare base-metal sulphide mineralisation (galena, sphalerite, tennantite and chalcopyrite). The host sedimentary rocks were subjected to severe silicification and dolomitisation processes. Barite shows a number of aspects: banded, massive and stockwork; in all cases, barite shows tabular crystals of several millimeters in size. Microthermometric measurements carried out on primary two-phase fluid inclusions in barite crystals (barite I and barite II) and gangue quartz gave homogenization temperatures between 155 and 225 °C and salinities of 17.6 to 25.9% NaCl eq. The data show at least three types of mixing fluids that deposited the sulphate-sulphide mineralisation. δ34S values of barite are between + 17.9 and + 27.6‰ and the δ34S values of the associated sulphides vary between − 9.2 and + 3.0‰. These data indicate that the most likely source of sulphur is the sulphates (gypsum) of the Triassic evaporitic formation (δ34S ranging between + 11.5 and + 13.4‰). Thermochemical sulphate reduction is the most probable process by which H2S was produced, although relatively large negative δ34S values point to a possible minor contribution from the biogenic sulphate reduction process. Carbon and oxygen isotopic compositions of gangue carbonates (calcite and ankerite) and oxygen of gangue quartz indicate a common source of the mineralising fluid. Calculated δ18Ofluid from quartz oxygen isotope data varies between + 6 and + 12‰, indicating deep-seated brines with minor contribution from a surface water component. The relatively hot and saline fluids have most likely migrated upward in several pulses during the Triassic halokinesis and compressive/distensive Atlassic (Eocene) and Alpine (Miocene) tectonic phases. The Mizab barite deposit exhibits geological, fluid inclusion and isotopic features similar to those of the peridiapiric mineralisation of northeastern Algeria and Tunisia. Guelma. Infiltration and runoff contribute to pollution, and the highest infiltration rate is generally observed in areas of agricultural and industrial activities. Pollution of the aquifers in this area is of concern. Mountains, such as the Edough and Gelaat Bou Sbaa, contribute high runoff that carries pollutants towards the groundwater.

Résumé: Rare earth elements and yttrium (REY) have gained greater attention for being largely used in various high-tech applications and green energies. Recently, supply shortage and high demand on REY led to target secondary resources such as phosphorites. Algerian sedimentary phosphorites, which are located mainly in the T´ebessa region, Eastern Saharan Atlas, are relatively enriched in REY according to recent whole-rock analyses. The aim of this study is to explore variation of REY contents and other geochemical features with respect to particle size fractions. In addition, the economic significance of the P-deposits was assessed using new indicators, such as the outlook coefficient of REY composition (Coutl) and the percentage of critical element in total ΣREY (REYdef). Three friable whole-rock samples from two P-deposits (Djebel El Kouif and Kef Essenoun) were sieved and retained fractions (f) of <45 μm, 45–125 μm, 125–250 μm, 250–500 μm and >500 μm were analyzed for their major and REY contents using ICP-MS techniques. Principal Component Analysis (PCA) was applied on centred log-transformation (clr) data, which are adapted to such compositional dataset, as well as Variance Analysis (one-way ANOVA) technique. The results show that the samples yield P2O5 grades ranging from 20 to 36 wt% and total REY contents in selected 15 samples vary in the considered grain size fractions as follows: f<45μm = 325 ppm–719 ppm; f45–125μm = 309 ppm–893 ppm; f125–250μm = 314 ppm–1029 ppm, f250–500μm = 354 ppm–809 ppm, f>500μm = 308 ppm–652 ppm. The one-way ANOVA reveals that there is no significant difference of REY concentrations between the grain size fractions. However, the REY grades strongly based on both the studied deposits and the stratigraphic position of the hosting samples (p-value ≤ 0.01); this is also confirmed by PCA. REY geochemical signatures (normalized REY distribution patterns and Ce, Eu, and Y anomalies) are similar in the grain size fractions from the same hosting samples indicating synchronized evolution of all rock components, where REY distribution is mostly controlled by the depositional environment, irrespective of grain size in the rock. The Coutl coefficient shows values between 1.89 and 6.85 and REYdef varies from 47.44 % to 64.90 %. However, the upper sub-layer of Kef Essenoun phosphorites that yielded the lowest ΣREY contents, shows markedly the highest Coutl (6.61–6.85) and REYdef (64.31–64.90), pointing to more promising source for extracting individual critical REY elements, even in low P-grade phosphorite ores.

Résumé: The present day architecture of the Western Mediterranean mainly results from the interplay of different lithospheric plates and the Cenozoic consumption of various branches of the Alpine Tethys and Neo-Tethys Oceans. Identifying relics of these oceanic domains in the peri-Mediterranean belts enables pinpointing the earliest stages of this evolutionary framework. In NE Algeria, the Kef Lakhal Complex (Edough Massif) is composed of amphibolites and meta-gabbros metamorphosed under amphibolite facies conditions and thrust onto the northern African margin during earliest Miocene. Geochemical analyses reveal that amphibolites and metagabbros have major and trace element signatures characteristic of tholeiitic basalts and gabbros and display N-MORB (La/SmN = 0.7–0.9) to E-MORB (La/SmN = 1.1–1.2) affinities. Enrichments in U and alkalis (Cs, Rb) and high 87Sr/86Sri ratios on bulk rocks and minerals (up to 0.70856) are typical of seawater alteration and indicate that the Kef Lakhal Complex represents a piece of altered oceanic crust. Parental magmas were derived from a Depleted Mantle source (WR εNdi = 8.2–9.9 and εHfi = 10.4–14.4) that preserved some canonical MORB ratios (Ti/Eu=5700–7600 and Y/Ho=27.4–29.0), butwhichwas contaminated by a component akin to recycled oceanic crust and associated sediments (Ce/Pb = 10.5–22.2; 206Pb/204Pbi = 18.41–18.74; 207Pb/204Pbi = 15.49–15.59; 208Pb/204Pbi=37.73–38.37). The sedimentary component is consistent with a volcaniclastic origin and substantiates an intra-oceanic setting. The geochemical characteristics of the Kef Lakhal rocks are comparable to present day (Mariana,WPacific Ocean) or fossil (Xigaze, SE Tibet) fore-arc oceanic crust. An overview of the Western Mediterranean geodynamic indicates that the most likely period for initiating formation of a fore-arc corresponds either to the Early/Late Cretaceous or to the Middle Eocene. 40Ar/39Ar dating on amphibole further indicate that after thrusting onto the African margin, the Kef Lakhal Complex cooled down to c.550 °C at 18.14 ± 0.27 Ma (2σ).

Résumé: The In Allarene mafic-ultramafic complex is located at the southern part of the In Ouzzal terrane and was known as the unique Pan-African mafic-ultramafic intrusion in this terrane. The complex shows a ring-shaped intrusion of about 20 km2 and concentric structures. Petrological observations and mineralogical analyses show that the core of the intrusion is composed of harzburgites and dunites surrounded by lherzolites, whereas the outer part consists of fine- to coarse-grained gabbros that are crosscut by dolerite dykes. The mineralogy and geochemistry of these rocks show that they are mainly cumulates, but some gabbros and dolerites have characteristics indicating that they correspond to magmatic liquids or they have trapped a variable amount of magmatic liquid. They correspond to the least magnesian and the most alkaline-rich gabbros and dolerites. The geochemistry of the gabbros and dolerites is very similar to the mafic-ultramafic complexes linked to arc zones and they exhibit all the features of the subduction zones magmatism as showing in the N-MORB normalization, with LILE enrichment relatively to HFSE, and Nb-Ta and Ti negative anomalies. The chemical compositions of clinopyroxene and spinel support this hypothesis. This is also the case for all geodynamic setting discrimination diagrams, both those using major elements and trace elements. Several of these diagrams also show that the studied rocks can be distinguished from intracontinental plate tholeiites, which can be very close geochemically to continental arc tholeiites. These results support the hypothesis of the existence of an arc-type metasomatized mantle under the In Ouzzal terrane during Pan-African orogeny.

Résumé: L’important développement industriel dans la région de Berrahal (Nord-Est de l’Algérie) s’est traduit par un accroissement des rejets concentrés en métaux lourds considérés comme toxiques pour la faune et la flore, induisant une dégradation de l’environnement et de la qualité des eaux des aquifères. L’analyse statistique des données acquises a permis d’élaborer le schéma de transfert des polluants et d’identifier les principaux facteurs responsables de l’acquisition du contenu physico-chimique des eaux. Les résultats obtenus montrent que les milieux récepteurs (les habitants, le lac Fetzara et la nappe phréatique) seront touchés par les différents rejets de la zone industrielle. L’infiltration des eaux des rejets constitue par conséquent, une menace pour les populations et la faune environnante. Par ailleurs, les eaux souterraines présentent également un risque potentiel particulièrement pour l'écosystème du lac Fetzara et pour les captages d’eau (AEP, irrigation et alimentation du bétail).

Résumé: Les métabasites de Sidi Mohammed, localisées sur le flanc NE du massif cristallophyllien de l’Edough, forment un affleurement métrique au sein de formations ultramafiques (péridotites). La composition minéralogique de ces métabasites consiste en minéraux progrades (pyroxènes avec environ 20% de jadéite et grenats de type almandin) et en minéraux rétrogrades (amphiboles représentées principalement par de l'hornblende édénitique et de l'hornblende pargasitique) et des plagioclases (An27 - 36) interstitiels. Les diagrammes discriminants en éléments majeurs et en traces montrent que les métabasites ont un caractère tholeiitique. L’allure relativement plate des spectres des terres rares normalisés au Manteau Primitif ainsi que les fortes teneurs en Cr et Ni indiquent une similitude avec les basaltes océaniques mis en place dans un bassin arrière arc.

Résumé: La décharge publique de la ville de Tiaret, située à 150 km au Sud-Ouest de Mostaganem (Algérie occidentale), repose sur des formations marno-calcaires à porosité de fissures facilitant la pollution des réserves en eaux souterraines. Le terrain, en faible pente, favorise le déplacement des polluants. Les lixiviats s’écoulent à partir de la décharge en entraînant une dégradation de la qualité des eaux souterraines. Les analyses effectuées sur des échantillons d'eau prélevée de trois piézomètres montrent des concentrations importantes en chrome, zinc, plomb, confirmant ainsi la forte dégradation des eaux souterraines. Pour connaître le degré de pollution engendrée par cette décharge, les résultats obtenus ont été comparés à ceux d’autres décharges. Il apparaît que la décharge, d’exploitation ancienne, n’est pas encore stabilisée avec une phase acide de dégradation anaérobie en cours. Les analyses bactériologiques effectuées sur les eaux souterraines indiquent une contamination micro biologique.

Résumé: L’étude pétrographique et sédimentologique de l’Albien d’Ain Mimoun (anticlinal de Khenchela), montre que les formations de l’Aptien terminal datées Clansayésien; représentent un cycle sédimentaire incomplet. Ce dernier se termine par une phase d’émersion et se sépare du premier cycle sédimentaire de l’Albien par un niveau de sédiments de plage marquant le début d’une transgression. La lacune stratigraphique de l’Albien inférieur est bien soulignée par la présence d’une inconformité entre les deux cycles. Le découpage séquentiel et l’évolution des cortèges sédimentaires de la série étudiée, mettent en évidence 5 séquences de 4ème ordre niveau scalaire. Les grès littoraux puisnéritiques et les argiles marneuses bien exprimés au début, sont progressivement relayés par des calcaires au milieu de la série étudiée, et réapparaissent à son sommet pour traduire la phase d’émersion fini-albienne précédant la transgression Cénomano-turonienne. Les ensembles d’association de faciès suggèrent un mode de dépôt en interaction entre les environnements de dépôt d’une plate forme silico-clastique et ceux d’une plate-forme carbonatée. Mots clés: Albien, émersion, transgression, cycle sédimentaire, Ain Mimoun, Algérie

Résumé: La structure originale de la rgion d'tude avait attir l'attention des premiers auteurs (Durozoy, 1948; Flandrin, 1959). Ainsi, Chria, d'une altitude moyenne de 1100 m‚tres et grƒce „ ses ressources karstiques, reprsente un vritable chƒteau d'eau pour Tbessa situe plus bas „ 800 m‚tres d'altitude. Le plateau de Chria se caractrise donc par des aquif‚res assez importants pour toute la rgion. De forts dbits y sont prlevs pour l'alimentation d'autres agglomrations et projets situs hors du bassin. Ce dernier prsente une srie stratigraphique connue sur plus de 1000 m‚tres, avec des possibilits hydrauliques certaines (Chaffai, 1983). Les formations marines, c'est-„-dire le Trias, le Crtac et l'Eoc‚ne, occupent 80% de la sdimentation; les 20% restant correspondent au remplissage Mio-Plio-Quaternaire.

Résumé: The Miocene igneous rocks that host the Tala Hamza Zn–Pb deposit are investigated in order to shed light on their petrogenesis and to provide a brief metallogenic description of associated sulphides mineralization. 800 m depth drill hole reveals from top to bottom the following succession: pyroclasitic rocks, andesite, volcanic tuff, microgranite, silicified tuff, kaolinized andesite cross-cut by aplite, metasomatized granodiorite and granodiorite. These rocks are composed of plagioclase, hornblende, biotite, alkali feldspar, sphene, apatite and zircon. Major elements geochemistry shows that these igneous rocks exhibit calc-alkaline, high K to shoshonitic, metaluminous to slightly peraluminous, I-type characters. Multi-elemental spectra, as well as chondrite-normalized rare earth spectra, show LILE and LREE enrichment relative to HFSE and HREE, respectively. The REE shows a slight negative anomaly in Eu. All these features indicate that the rocks originate from an igneous protolith, probably from a metasomatized mantle material that was contaminated by crustal material and emplaced in a post-collision context during the Miocene. Metallogenic study for both massive sulphides and stockworks reveals the presence of replacement textures, open-space-filling texture and pseudomorphism. These textural patterns, in addition to the presence of the anhydrite layer, are common in deposits of VHMS (volcanic-hosted massive sulphides) group formed in the submarine environment. They also indicate hydrothermal processes throughout two main stages: (1) an early stage in which disseminated pyrite and chalcopyrite hosted by metasomatized granodiorite were formed, and (2) a late-stage or mineralizing stage with the deposition of economic ore (mainly sphalerite and rare galena) along faults and fractures.

Résumé: Sited in Souk-Ahras, the Sidi El Hemissi region stands as part of the Tellian Atlas, where the Triassic formation tectonically outcrops under the Tellian nappes of the Maghrebide chain. Dubbed ‘ophites’, mafic rocks, mainly gabbros and dolerites are interbedded in 200-30 m lenticular body within the Triassic gypsum-rich formation. These rocks are composed of plagioclase, amphibole, pyroxene and scarce olivine crystals. Albitization represents the major alteration process, though chloritization, calcitization and epidotization of ferromagnesian minerals are also perceived. The geochemical observations prove to reveal that these mafic rocks exhibit medium- to low-Ti continental tholeiitic basalt affinity. They are enriched in LILE and LREE, as compared to HFSE and HREE, and display enriched-mid-ocean ridge basalt (E-MORB)-like incompatible element patterns in primitive mantlenormalized multi-element pattern. The weak Nb anomaly, along with the medium- to low-Ti contents, suggests possible interaction between an enriched mantle source-derived magma and lower crustal rocks. These chemical features display high similarities with those sited in the central Atlantic magmatic province (CAMP) of upper Triassic–lower Jurassic age. Hence, they turn out to be considered as highly linked to the western branch of the Alpine Tethys system, geologically and tectonically associated with the Central Atlantic Ocean opening.

Résumé: In this work, the physico-chemical and petrographic characterization of the Kef Essnoun phosphate ore deposit, Djbel Onk basin, were carried out by optical microscopy, X-ray diffraction and infrared spectroscopy. The microscopic observation conducted on the three raw phosphate layers (somital, main, basal) shows a variation in the petrographic composition from one layer to another, in terms of the amount of phosphatic elements compared to the cement. The phosphatic elements consist mainly of spherical to oval pellets, coprolites, pseudo-oolites and bioclasts in different sizes. The cement is composed of carbonates (dolomite and rarely calcite), amorphous silica and clays. The obtained structural results show the presence of francolite minerals, dolomite and calcite in small amounts. After sintering at different temperatures, allows us to conclude that it is possible to eliminate organic and carbonic matter, and formation of new compounds, such as calcium oxide and whitelockite. Infrared spectroscopy displays the nature of the functional groups that are present in the phosphate ore. These are phosphate groups, carbonate and hydroxyl groups. Finally, we can conclude that the present results highlight the quality of the Kef Essenoun to serve as valuable raw material for the production of bio-ceramic industrial products.

Résumé: The mineralizations presented in this paper are closely related to the “peri diapiric” zone in NE Algeria and are characterized by the occurrence of numerous Triassic diapers hosted mainly by different lithologies of the Cretaceous series. This series hosts numerous Pb-Zn, Ba-F, Fe and Cu mineralizations that were mined in the past. Siderite mines in this area (Ouenza in Algeria and Jerissa in Tunisia) are still operating. Mineralization occurs in swarms of steeply dipping veins and is usually accompanied by intense dolomitization and silicification, Fluid inclusion homogenization and freezing data, along with Na-Cl-Br leachates, permit the characterization of the mineralizing fluids. This data confirms that the mineralizations have formed during the Atlasic orogenic event. In the Na-Cl-Br diagram the composition of the mineralizing fluids lies well on the halite dissolution trend indicating that the fluids acquired their salinities by the dissolution of halite.