Résumé: Phosphorite exploitation poses environmental risks due to potentially hazardous elements (PHEs). This study investigates their distribution, fractionation, and origin in Algeria’s sedimentary deposits. Whole-rock (n = 16), grain size fractions (n = 15), and phosphate particles (n = 32) were analyzed using petrographic, SEM-EDS, ICPMS, and LA-ICP-MS techniques. Robust Principal Component Analysis (Robust PCA) and environmental indices, including enrichment factors (EF) and potential ecological risk index (PERI), were applied. Samples contains carbonate-fluorapatite (CFA) with minor carbonate and silica, while SEM-EDS occasionally detects sulfide inclusions in P-particle pores. Chemical analysis reveals high CaO and P2O5 (up to 45 and 38 wt%, respectively),along with elevated Sr (516–2597 mg/kg), Zn (106–609 mg/kg), Cr (199–348 mg/kg), Cd (0.5–143 mg/kg), and U (11–126 mg/kg). According to Robust PCA, CFA hosts, through substitutions, U, Sr, Y, V, Cr, Pb, Cd, Cu, and Zn, while the matrix retains Nb, Rb, Ta, Hf, Zr, Li, Cs, Mo, As, and Th, via adsorption. Fine fractions and glauconite show enhanced PHEs, with peak enrichment at the Paleocene-Eocene transition. Environmental assessments reveal extreme risks, particularly from Cd and U, necessitating selective mining to mitigate contamination in PHE-enriched layers, along with appropriate waste management.

Résumé: Phosphorite exploitation poses environmental risks due to potentially hazardous elements (PHEs). This study investigates their distribution, fractionation, and origin in Algeria’s sedimentary deposits. Whole-rock (n = 16), grain size fractions (n = 15), and phosphate particles (n = 32) were analyzed using petrographic, SEM-EDS, ICPMS, and LA-ICP-MS techniques. Robust Principal Component Analysis (Robust PCA) and environmental indices, including enrichment factors (EF) and potential ecological risk index (PERI), were applied. Samples contains carbonate-fluorapatite (CFA) with minor carbonate and silica, while SEM-EDS occasionally detects sulfide inclusions in P-particle pores. Chemical analysis reveals high CaO and P2O5 (up to 45 and 38 wt%, respectively),along with elevated Sr (516–2597 mg/kg), Zn (106–609 mg/kg), Cr (199–348 mg/kg), Cd (0.5–143 mg/kg), and U (11–126 mg/kg). According to Robust PCA, CFA hosts, through substitutions, U, Sr, Y, V, Cr, Pb, Cd, Cu, and Zn, while the matrix retains Nb, Rb, Ta, Hf, Zr, Li, Cs, Mo, As, and Th, via adsorption. Fine fractions and glauconite show enhanced PHEs, with peak enrichment at the Paleocene-Eocene transition. Environmental assessments reveal extreme risks, particularly from Cd and U, necessitating selective mining to mitigate contamination in PHE-enriched layers, along with appropriate waste management.

Résumé: The In Ezzane region, located in eastern Algerian Sahara, close to Libya – Niger border, is marked by late Pliocene and Pleistocene volcanism and by a remarkable group of circular structures, 4–9 km in diameter, situated on a basement composed of Tassili Cambrian-Ordovician sandstones. Both manifestations are imbricated and can only be subcontemporaneous. In this study, first, we date and characterize the volcanism and second, we try to constrain the origin of the circular structures that were visited just before the region closed for security reasons. Two basaltic lavas were dated at 2.01 ± 0.05 Ma (Gelasian) and at 1.49 ± 0.03 Ma (Calabrian) by K-Ar method. Petrographic investigations show that most volcanic rocks are basanites composed of olivine and Al-Ti diopside phenocrysts with xenocrystic mantle olivine and orthopyroxene. Temperatures of eruptions (1200–1300 ◦C) and of primary picritic magma (1500–1600 ◦C, i.e. a depth of 120–150 km), along with major and trace elements, and Sr-Nd isotopes all point to an asthenospheric source along the western lithospheric margin of the Murzuq craton (Murzuq volcanic province). The In Ezzane counter-relief circular structures are nested and NNW-SSE aligned, with each structure being truncated by the next one to the south-south-east. Up to 500 m outside circular structures, Tassili sandstones are reddened, dissected by intense fractures that are filled with fine-grained brown material and newly formed acicular white quartz, and often show white, cm-size, vesicles. The rims of the circular structures are composed of densely brecciated sandstones with dark veins, whereas the central parts are crosscut by a loose network of dyke-like dark veins. Microscopic observations, SEM imagery, SEM-EDS determinations and laser-ICP-MS chemical analyses of hydrothermal breccia components point to large masses of fluids having moved rapidly at shallow depths and having induced hydrofracturing of the heated sandstones with the generation of veins composed mostly of iron oxide. The viability of various processes that may have induced these large circular structures, i.e. tectonic reliefs, igneous and associated hydrothermal phenomena, meteorite impact craters, are discussed and favour sandstone karst features.

Résumé: The Algerian phosphorites, deposited during the Paleocene-Eocene, are part of the Tethyan phosphogenesis along the southern paleo-Tethys margin. Located primarily in the Tebessa region, these deposits hold reserves exceeding 2 billion metric tons. Recent interest has grown due to their enrichment in rare earth elements plus yttrium (REY). While previous studies have examined whole-rock and grain-size fractions, the fine-grained matrix (<45 μm) remains poorly explored. This study provides the first mineralogical and geochemical characterization of this fraction to assess its economic potential and paleoenvironmental significance. Twenty-two fine-fraction samples from four Tebessa localities were separated using humid grain-size classification. Mineralogical analysis was supported by X-Ray Powder Diffraction (XRD), whereas geochemical analyses were carried out using inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). The XRD results show that the phosphorite fine-grained matrix is composed of calcite, dolomite, carbonate fluorapatite, glauconite, quartz, chlorite, and gypsum. Notably, glauconite occurs in higher amounts in southern deposits (Kef Essenoun), suggesting intensified glauconitization process. Geochemically, the fine fraction contains an average of 12.48 wt% P2O5, with REY concentrations ranging from 55 to 863 ppm. REY contents increase southward, with REEs ranging between 68 and 678 ppm (avg. 416 ± 198 ppm) and Y varies from 9 to 187 ppm (avg. 125 ± 56 ppm). The higher REY content is partly linked to glauconite phase abundance. Normalized REY contents indicate seawater-like patterns in the northern deposits, whereas the southern deposits show middle REE (MREE) enrichment patterns. High (La/Yb)N ratios in the glauconite-rich samples suggest earlydiagenetic adsorption under slow sedimentation rate and sub-reduced conditions. An enhanced glauconitization process occurred in the southern basin at the Paleocene–Eocene boundary, which is marked by global thermal event. These findings suggest that the fine-grained matrix, typically considered as waste during the treatment of raw phosphorites, holds economic potential due to its high REY content, presenting a promising resource for future exploitation.

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: This study investigates the first stable S-, O- and C-isotopes data on the Beleleita scheelite skarn deposit to assess the origin of the mineralising fluids involved in the formation of the skarn and related W-As-Bi-(Au) mineralisation. Two skarn bodies are embedded within the Neoproterozoic gneisses, south of the Edough metamorphic complex, NE Algeria. They show subparallel, discontinuous slabs (F1 and F2) approximately 700 m long and 10 m wide, striking NE–SW. The slabs were cross-cut by bore-hole drilling at a depth of 130 m during ORGM (Office de Recherche Géologique et Minière) mining exploration in the 1980s. Textural observations reveal two main cycles. Cycle I displays early classical zoned skarn assemblage, including clinopyroxene, garnet, plagioclase, pyrite, pyrrhotite, and chalcopyrite. Cycle II shows late lithiniferous and fluorinated skarn assemblage that corresponds to greisenised secant skarns, with fluorite, scheelite, lollingite, allanite, zinnwaldite series, sphene, wolframite, arsenopyrite, native bismuth, and quartz. Stable O-isotope analyses were carried out on both whole-rock samples and clinopyroxene, quartz, and garnet mineral separates, whereas C- and O-isotope analyses were conducted on gangue calcite. S-isotopes were carried out on sulphides (pyrite, chalcopyrite, lollingite and pyrrhotite). All the results display relatively narrow ranges (δ18OSMOW varying from +8.4 to +9.9‰; δ13CPDB ranging between -6.9 to -4.2‰ and δ34SCDT between -0.3to +5.3‰), indicating a homogeneous source of fluids with significantmagmatic signatures that contribute to skarn formation and ore deposition.Accordingly, the involved mineralising fluids most likely originated from theI-type magmatic event that prevailed during Burdigalian times in theEdough massif, similar to many other ore deposits in the area. Moreover,previous fluid inclusion studies carried out on fluorite, scheelite, and quartz of Cycle II show that the ores were deposited from hot (Th = 500°-520°C), highly saline magmatic fluids under low pressure (0.5–0.6 kb), and this complies well with the present stable isotope data.

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: The Algerian sedimentary phosphorites of marine origin are located mainly in the Tébessa region, which is part of the Eastern Saharan Atlas. These phosphorites are hosted by Paleocene-Eocene series and crop out in two main sedimentary areas: the northern sites (Djebel El Kouif, Djebel Dyr and Djebel Tazbant) and the southern sites, which include the Djebel Onk commercial world-class ore deposits that are represented in this study by the Kef Essenoun sector. This study reports a detailed investigation of these phosphorites at a regional scale and is aimed to characterizing the evolution of their depositional environments. Field and laboratory works consist of a systematic sampling of outcrops, petrographical (OM and SEM-EDS), mineralogical (XRPD) and chemical (major, trace and rare earth elements by ICP-MS) analyses associated with a PCA statistical treatment. The timewise evolution of the depositional environments was constrained based on rare earth elements (REE) and selected redox sensitive element proxies, such as Ce, Eu, Y, Mn, U and V. The results show that the phosphorites have a granular fabric with variable grain sizes. The grains can contain micro-remains and impurities related to their origin, which was most often fecal pellets. Carbonate fluor-apatite is the main mineral phase in these phosphorites, where P2O5 contents show large variations between different outcrops (average from 18.39 to 30.16 wt%). A marked evolution of depositional environments is observed in their vertical trends from sub-reduced and sub-oxic in the lower beds to rather oxic conditions in the upper layers. This evolution shows a significant shift along the sedimentary profiles reflecting more open connection to Tethyan seawater towards younging trend. These results contrast remarkable changes of depositional conditions during Paleocene–Eocene transition.

Résumé: Les roches ignées du massif d’El Aouana font partie de la chaîne magmatique miocène des Maghrébides qui s’étend du nord de la Tunisie jusqu’au Maroc. Ces roches sont composées de faciès volcaniques (andésites et dacites) et subvolcaniques (microdiorites et microgranodiorites), qui ont été mis en place au sein des flyschs crétacés, oligo-miocènes et sédiments miocènes post-nappes. Les andésites sont composées de phénocristaux de plagioclase, d’amphibole et de pyroxène dans une mésostase microlithique. Les dacites sont plus riches en plagioclase avec de rare minéraux ferromagnésiens souvent altérés. Les microdiorites et microgranodiorites sont généralement à hornblende verte, plagioclase, pyroxène et rare biotite dans une mésostase microcristalline. Les résultats géochimiques montrent que ces roches sont calco-alcalines avec une affinité type-I et elles présentent un enrichissement en éléments à grand rayon ionique (LILE) et éléments de terres rares légers (LREE) par rap¬port aux éléments à champs électrostatique élevé (HFSE) et aux éléments de terres rares lourds (HREE). Les anomalies négatives en Nb, P et Ti témoignent d’un magma de zones de subduction. Les observations de terrains, les données pétrographiques et géochimiques montrent que les granitoïdes miocènes d’El Aouana ont été mis en place dans un environnement post-collisionnel. Ces roches sont similaires aux granitoïdes métalumineux, post-collisionnels de l’Algérie du nord, considérés comme dérivés d’une source mantellique métasomatisée suite au processus de ‘slab break-off’ sous la marge nord-africaine.

Résumé: The Sidi El Hemissi region, Souk-Ahras, is part of the Tellian Atlas where the Triassic sediments tectonically outcrop under the Tellian nappes of the Maghrebide chain. Mafic rocks, mainly gabbros and dolerites, called Bophites,^ are interbedded as a ~200 × 30-m lenticular body within the Triassic gypsum-rich formation. These rocks show granular, microgranular, and microlithic textures and are composed of plagioclase, amphibole, pyroxene, and scarce olivine crystals. Albitization is the main alteration process, though chloritization, calcitization, and epidotization of ferromagnesian minerals can also be occasionally observed. The major, trace, and rare earth element studies show that these mafic rocks display relatively low P2O5 (less than 0.2 wt%) and moderate to low TiO2 contents (less than 2 wt%) and exhibit low-Ti continental tholeiitic basalt affinity. They are enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) compared with high field strength elements (HFSE) and heavy rare earth elements (HREE). This, along with the observed weak Nb and Ce anomalies and the low-Ti contents, suggests an enriched mantle source for the generation of the magma, which likely underwent crustal contamination before emplacement within the Triassic sediments. The petrological and geochemical features of the Sidi El Hemissi ophites show many similarities with the basaltic rocks emplaced during the Late Triassic–Early Jurassic times, now cropping out in north-western Africa, south-western Europe, northeastern, and south-eastern America. This large magmatic activity is believed to be related to the continental rifting associated with the early stages of the Pangea breakup.

Résumé: The Oued Amizour granitoids of North Africa were studied in order to assess the role of magma processes in the formation of the large Zn-deposit in the region. Access to material from a ∼800m drillhole cutting the entire igneous succession greatly facilitated the investigation. The rocks reveal, from the top to the bottom, two distinct lithologies: volcanic, mainly pyroclastic rocks and sub-volcanic microgranitic –plutonic granodioritic rocks. Both lithologies were subject to hydrothermal alteration. The boundary between the two lithologies is marked by a massive, ∼10m thick anhydrite layer. The geochemistry of these rocks shows that they are intermediate to felsic in composition and exhibit high-K to shoshonitic calc-alkaline features with I-type signature. The negative Eu, Sr and Nb anomalies and the high LILE and LREE enrichment observed in the whole igneous suite indicate that the various volcanic and plutonic rocks are genetically related. The granitoids are considered to have formed under post-collisional geotectonic regime during the Miocene, similar to those described in the Alpine Belt of northern Africa. The main sulphide mineralisation is dominated by sphalerite with rare marcasite, melnikovite, galena and minor but ubiquitous pyrite. The sphalerite ore body of about 20–30m thick is hosted by hydrothermally altered andesite breccias and volcanic tuff, between the anhydrite layer at the base and the volcanic pile at the top. Replacement, colloform and open space filling are the main ore texture patterns which indicate hydrothermal processes throughout successive percolation phases. δ34S of sulphides (sphalerite, pyrite and chalcopyrite) vary between −7.2‰ and +4.5‰ (n=22 ; mean=−1.3‰), suggesting that magmatic fluids have played a major role in the formation of the Oued Amizour Zn-deposit. However, δ34S of sulphates (anhydrite and gypsum) which are isotopically heavier ranging between +13.2‰ and +20.6‰(n=10; mean=+16.3‰), likely reflect mixing between Miocene seawater sulphate and magmatic sulphur. Fluid inclusion microthermometric measurements on anhydrite and gangue calcite yield a mean temperature of ∼200 °C and salinity between 22.3 and 26.6% eq. NaCl. Calcite δ18OV-SMOW varies between +11.2 and +20.2‰ (n=12, mean=+16.7‰) and δ13CV-PDB varies between −3.7 and −11.0‰(mean=−7.8‰). These results confirm the magmatic origin of the mineralising fluids, with a marked contribution of seawater, for precipitation of the Oued Amizour Zn mineralisation. Low δ13CV-PDB could, however,be attributed to the contribution of carbon from unconsolidated mudstones and/or magmatic carbon. The observed data on the Oued Amizour Zn deposit show that the mineralisation is part of VHMS group with a Kuroko-type signature.

Résumé: Rare earth element (REE) analyses are reported on glauconite-bearing phosphorites from northeastern Algeria. These rocks of Paleocene-Eocene age are located in the Eastern part of the Saharan Atlas, where two localities were investigated: the Djebel El Kouif in the north and the Kef Essenoun in the south. The latter belongs to the world-class Djebel Onk mining deposit. Petrographic examination indicates that phosphorite from the main layer of the Kef Essenoun deposit has a significant abundance in glauconite grains, while their occurrence in the Djebel El Kouif is restricted to the basal levels. In both deposits, glauconite grains are richer in REEs than other coexisting particles (pellets, coprolites, enameloid and dentine of marine fish teeth), but the glauconites of the Kef Essenoun deposit exhibit significantly higher REE concentration (min=654 ppm, max=1760 ppm, average=1146 ppm) than those of Djebel El Kouif deposit (min=543 ppm, max=623 ppm, average=584 ppm). The whole-rock REE concentrations also show substantial differences between the two deposits and the REE enrichment in the Kef Essenoun main sub-layer is more likely the result of the high glauconite content. PAAS normalized-REE patterns of the glauconite grains display similar patterns between the northern and southern localities with weak negative Ce anomalies and slight middle REE enrichments. On the other hand, the pellets and whole phosphorite grains from the northern deposit indicate a REE source from oxicsuboxic seawater, whereas those from the Kef Essenoun deposit exhibit slight middle REE enriched patterns with weak negative Ce anomaly suggesting a different environment of deposition (i.e. a tendency to reduced conditions). These geochemical results along with previous petrographic studies confirm the allochthonous character of the main phosphorite sub-layer in Kef Essenoun, where winnowing, transport and re-deposition of previously deposited phosphorites resulted in high accumulation and formation of glauconite grains. The glauconitization process of fecal pellets happened in two stages and was controlled by semi-confined microenvironments. This can explain the abundance of glauconite grains in the phosphorites from Kef Essenoun deposit and their restricted occurrence in the basal levels of the Djebel El Kouif outcrop.

Résumé: At the southern margin of the Tethys, the Es Souabaa area recorded traces of Oceanic Anoxic Event 2 (OAE2) around the Cenomanian-Turonian boundary (C/Tb). The dark, laminated, filament- and pyrite-bearing limestones represent the typical facies of this event. In terms of sedimentary environment, these features reflect a transgressive drowning that had induced hypoxia in these sedimentary environments. Such conditions favored the deposition and preservation of organic matter of marine origin, the distribution of which was controlled by paleogeography and halokinetic tectonics at that period. The OAE2 reached a climax between the last upper Cenomanian occurrence of Rotalipora cushmani and the lower Turonian occurrence of Whiteinella praehelvetica. Positive shift of the δ13C excursion along with relatively high total organic carbon (TOC) contents during OAE2 both indicate palaeo-environmental modifications enhanced by a significant change in primary marine productivity. Meanwhile, negative δ18O peaks in carbonates reflect increasing temperatures. Comparison of the data from this study with those from the neighboring Kalaat Senan section (Tunisia) suggests close similarities of events, although OAE2 is much more enhanced in Algeria.

Résumé: Karst aquifers receive increasing attention in Mediterranean countries as they provide large supplies water used for drinkable and irrigation purposes as well as for electricity production. In Teboursouk basin, Northwestern Tunisia, characterized by a typical karst landscape, the water hosted in the carbonates aquifers provides large parts of water supply for drinkable water and agriculture purposes. Groundwater circulation in karst aquifers is characterized by short residence time and low water-rock interaction caused by high karstification processes in the study area. Ion exchange process, rock dissolution and rainfall infiltration are the principal factors of water mineralization and spatial distribution of groundwater chemistry. The present work attempted to study karstic groundwater in Teboursouk region using hydrochemistry and stable isotopes (d18O and d2H) tools. Karst aquifers have good water quality with low salinity levels expressed by TDS values largely below 1.5 g/l with Ca-SO4-Cl water type prevailing in the study area. The aquifers have been recharged by rainfall originating from a mixture of Atlantic and Mediterranean vapor masses.

Résumé: Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U–Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzedin situ provide a U–Pb age of 32.4 ±3.3Mainterpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740–810°C, most likely during HP retrograde metamorphism. U–Pb analyses provide a significantly younger age of 20.7 ±2.3Maattributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica–Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.

Résumé: The ultramafic rocks of the Collo region in northeastern Algeria crop out as “stratified” masses that cut across older metamorphic formations of the Petite Kabylie basement. Based on petrological compositions and mineralogical observations, these rocks are mainly peridotites and serpentinites. The peridotites are identified as lherzolites, but dunites may occur rarely. The lherzolites are composed of olivine, orthopyroxene, clinopyroxene and chromian spinel. Their chemical composition shows high MgO (34.4-7.5 wt%), Cr (0.14-0.27 wt%), Ni (0.14-0.26 wt%) and Co (34-133 ppm) contents and low CaO and Al2O3 concentrations (0.02-2.2 wt% and 0.5 to 2.8 wt%, respectively). The chromite, which represents approximately 1-3% of the rock, is ubiquitous and shows two different generations: primary millimetric euhedral crystals and secondary fine xenomorphic grains and interstitial aggregates. The primary chromites are alumino-ferro-magnesian crystals that show high Al2O3 (25.77%-27.36%) and MgO (10.70%-13.36%). Cr# (100*Cr/(Al ‏ Cr)) ranges from 45 to 48, and Mg# (100*Mg/(Mg ‏ Fe2‏)) from 49 to 59. The secondary interstitial grains are iron-rich chromites. They show low Al2O3 (4.67%-9.54%) and MgO (4.60%-4.65%). Cr# is relatively high (77-88), whereasMg# shows relatively low values, ranging from 22 to 25. Primary chromite and whole-rock chemistry show that the Collo ultramafic rocks belong to Alpinetype peridotites that were emplaced within an orogenic setting. The oxygen isotopic composition of both peridotites and chromites is consistent with their derivation from a mantle source (18O ranges from ‏3.0 to ‏5.9‰). Low 18O values (<‏4.4‰) are recorded in serpentinites and are attributed to the effect of serpentinization processes through high-temperature metasomatic fluids. Magnesite-bearing serpentinites show the lowest 18O values. These are interpreted as the result of surface water input.

Résumé: In the Saharan Atlas (NE Algeria), the Triassic evaporitic formation was brought to the surface through the thick Cretaceous and Tertiary sedimentary cover as diapirs due to the effect of Atlasic tectonic events. The diapir piercing began in the Jurassic and has continued through present day. Many outcrops of several square kilometres are distributed in a large area (approximately 80 km wide) that extends northeasterly over 300 km towards Tunisia. The diapiric evaporitic formation is often accompanied by the emplacement of Pb-Zn-Ba-F mineralization. The Mesloula massif is an example of these deposits. Fluid inclusion and sulphur, carbon and oxygen isotope studies were carried out on Pb-Zn-Ba mineralization and associated gangue carbonates. Gypsum of the Triassic formation was also analysed for its sulphur isotope composition to show the role of evaporates in the generation of this typical peridiapiric deposit. Gypsum from the Triassic formation showed a narrow range of 34SVCDT values, ranging from ‏14.6 to ‏15.5‰ (n = 8). This range is comparable to that of Triassic seawater sulphates. Sulphide minerals yielded 34SVCDT values between 0 and ‏ 11.7‰ (n = 15), indicating that sulphide sulphur was likely derived from Triassic sulphates through thermochemical sulphate reduction (TSR) because fluid inclusion microthermometric measurements yielded a mean temperature of 150°C. Residual sulphate in such a system would have been enriched in 34S; this is reflected in the barite 34SVCDT values, which range from ‏21.1 to ‏33.5‰ (n = 5). The 13CVPDB values of calcite minerals, ranging from ‏2.1 to ‏6.3‰ (n = 4), indicate an inorganic carbon origin, likely from the host carbonate rocks. 18OVSMOW values were between ‏21.9 and ‏ 24.9‰, indicating that the most likely source of mineralizing fluids was formation water.

Résumé: This study deals with the preliminary data of rare earth elements (REE) obtained on northeastern Algerian phosphorites from the Tébessa region. These phosphorites are located in two different basins: the northern basin represented by Dj. El Kouif, Dj. Dyr and Tazbant showings and the southern basin with the giant Dj. Onk phosphate deposit. The host sedimentary formation is Late Paleocene to Early Eocene. Twenty-six (26) samples from the four (4) localities were collected and analyzed for their REE contents using the ICP-MS technique. Phosphates from the southern basin (Dj. Onk deposit) show ΣREE contents ranging from 174.41 and 906.39 ppm (average ΣREE = 623.01 ppm), while the northern phosphorites have lower ΣREE contents (from 125.45 to 472.44 ppm; average = 265.57 ppm). PAAS-normalized REE patterns and binary Box plot of (Sm/Pr)N vs (Sm/Yb)N show HREE enrichments for samples from the northern localities while most samples from the southern basin are HREE depleted. Normalized (La/Yb)N vs (La/Sm)N plot shows that (La/Sm)N ratios of all samples are similar to those of modern seawater (from 0.83 to 1.55). However, the (La/Yb)N ratios of the two basins are significantly higher (from 0.67 to 1.18), which indicates an early diagenesis. The Ce/Ce* vs Pr/Pr* diagram shows that the observed Ce anomaly was not affected by diagenesis and more likely represents a proxy for redox conditions. The obtained results substantiate that the northern phosphorites were formed in more oxic environment with more pronounced negative Ce anomalies, whereas the southern phosphorites have lower Ce anomalies. Northern phosphorites are different from those from the south probably because the northern basin was more connected to an open sea as did the Sra Ouartan basin in northern Tunisia. These results have also been confirmed by statistical method studies, such as factorial discriminate analysis.

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 Algerian-Tunisian phosphorites, from Paleocene-Eocene, were mainly deposited around “Kasserine Island” into three main basins as a result of the large Tethyan phosphogenesis. This chapter reviews the main characteristics of the most representative phosphorite deposits with the aim of comparing their lithostratigraphy, petrography, mineralogy, and geochemical features (major and trace elements, and isotopes), in order to summarize the current state of knowledge of their depositional environments. The phosphorites while sharing similar characteristics in terms of lithology and petrography, also show significant variations in thickness and vertical configuration mostly related to the depth of local basins and depositional facies. Phosphorites are often made up of a complex carbonate fluorapatite (CFA) mineral phase that arises from a microbial-driven phosphatization process of former particles (pellets, coprolites, and bioclasts). The mineral exo-gangue is mainly represented by dolomite, calcite, quartz, gypsum, heulandite-clinoptilolite, and Opal-CT in addition to some accessory minerals. P2O5 contents range from 17.97 wt% to 35.00 wt% (median = 26.5 ± 3.59 wt%), and consequently the values of other oxides fluctuate in different phosphorites facies. Contents of trace elements and rare earth elements (REE) vary significantly through the deposits (e.g. ~0.8 ppm < Cd > ~172 ppm; ~101 ppm < Cr > ~374 ppm; ~2 ppm < Cu > ~44 ppm; ~16 ppm < U > ~126 ppm; ~125 ppm < ΣREE > ~1018 ppm). REE + Y-geochemistry shows that the northern deposits formed under oxic conditions, while the eastern and southern deposits formed in sub-reduced to sub-oxic environments. There, a little detrital input and slight paleoproductivity occurred, as revealed by detrital and paleoproductivity geochemical proxies. This realm, associated with the δ13C, δ18O, and 7Sr/86Sr isotopic records, contrasts with the occurrence of the Paleocene Eocene Thermal Maximum (PETM) global warming event during the phosphorite formation.

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.

Résumé: The Miocene igneous activity in northeastern Algeria is believed to be responsible for the emplacement of many base-metal deposits, mainly Pb-Zn, Cu. Examples of these are those of Oued Amizour region. The igneous rocks that host the giant Tala Hamza Zn deposit in this area are made up of two distinct lithologies: volcanic rocks and subvolcanic-plutonic rocks, both of which have undergone intense hydrothermal alteration. The boundary between the two rock types is marked by a 10 m-thick layer of massive anhydrite. Field observations and petrological studies carried out on core samples from a borehole of approximately 800 m deep, show the following lithologies, from top to bottom: pyroclastic rocks, andesites, porphyritic pyroclastic rocks, vesicular andesites, microgranites, tuffs and lava flows, volcanic breccias and highly altered andesites, metasomatised granodiorites and, finally, massive granodiorites. The chemical composition of these rocks ranges from intermediate to acidic magmas. These magmas show high K calc-alkaline to shoshonitic character with an I-type affinity, characteristics of orogenic zones. The main sulphide mineralization is dominated by Zn sulphides, mainly sphalerite and schalenblende, with rare marcasite, melnikovite, galena and minor but ubiquitous pyrite. The sphalerite orebody is approximately 20 to 30 m thick and lies between the anhydrite layer and the volcanic pile, in a hydrothermally altered brecciated andesite. Replacement textures, pseudomorphism, collomorphic texture and open space infill are the main textures of the mineralisation, indicating hydrothermal processes through successive percolation phases. A detailed metallogenic study of the Tala Hamza sector (Oued Amizour) shows that the emplacement of the main Zn orebody and associated Pb and Fe sulphides was accompanied by hydrothermal alteration: intense argillitisation, calcitisation, chloritisation, kaolinitisation and sericitisation. These types of alteration, together with fluid inclusion and stable isotope (S, O, C) data, are consistent with the ‘Volcanic-Hosted Massive Sulfides’ (VHMS) model, with a ‘Kuroko-type’ signature. Keywords: Tertiary magmatism, Zinc deposit, Hydrothermal alteration, Stable isotopes, Oued Amizour.

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 and Kef Essenoun deposits are examples of these phosphorites that belong to the giant Djebel Onk complex in northeast Algeria. Their geological and geochemical studies were mainly focused on P2O5 contents for commercial purposes. The upper Thanetian phosphorite layer in both deposits is 30 m thick, and is subdivided into three sub-layers (lower, main (middle) and upper sub-layer), based on P2O5 contents, the richest being the main sub-layer. In our recent studies on theses phosphorates, major, trace and REE analyses, were mainly conducted on phosphate particles (pellets, coprolites and glauconites) using ‘in situ’ LA-ICP MS technique. The results show that the main sub-layer displays the highest whole-rock P2O5 contents (up to 35 wt%; average 28 wt%) compared to the lower and upper sub-layers. Among the phosphate particles at Bled El Hadba, 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 the highest REE contents (up to 2050 ppm) compared to pellets (221-910 ppm) and coprolites (214-909 ppm). Within the glauconite particles, the REE, 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. 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 (sub-oxic) conditions; i.e., during early diagenesis, the peak of REE uptake from porewater, and under slow sedimentation rates. The REE contents of the Bled El Hadba phosphate particles record the highest contents in all North African phosphorites. The main sub-layer is the most glauconite-rich phosphorite. Therefore, more extensive REE analyses are recommended to better evaluate its economic potential in terms of critical raw materials. Keywords: Phosphorites particles, REE, Glauconitization, Phosphatization, Djebel Onk.