Search

International audience; The Djebel El Hamra Pb-Zn-Ba-Sr (Hg) deposits in northern Tunisia are hosted in a post-nappe anticline with a core of a Triassicevaporite diapir affected by the NE–SW-trending Ghardimaou-Cap Serrat lineament. Three stages of mineralization occurred inthe Triassic dolostone: stages I and II caused alternating deposition of sulfate (Ba, Sr) and sulfide (sphalerite, galena) minerals;stage III formed late-stage calcite-marcasite-cinnabar. Zebra textures record the syntectonic transition from compression toextension in the Late Tortonian-Messinian interval. Two fluid end-members were involved in sulfate deposition: one lowsalinity(L1, ~3 wt% eq. NaCl) fluid, probably from a meteoric origin, and a Na-Ca-Cl brine (L2, ~22 wt% eq. NaCl) solutionwhich originated from the Triassic diapiric source. A third end-member fluid (L3) with long residence time in the basement wasalso involved in the Pb-Zn deposition. The δ34S values froma cluster of sulfates around +16‰, show a Triassic evaporate source.The sulfur in sphalerite resulted from bacterial sulfate reduction (BSR); however, crystallization in a closed system resulted in arange of δ34S between +1.6 and +26.5‰. The δ34S values in galena (−28.4 to +8.2‰) are consistent with a BSR and thermochemicalsulfate reduction (TSR) origin of the sulfur. Secondary ion mass spectrometry (SIMS) lead isotope data in galena(207Pb/204Pb: 15.595 to 16.193, 206Pb/204Pb: 18.673 to 18.939, 208Pb/204Pb: 38.330 to 40.572) point to local contributions(sedimentary and Cenozoic magmatic rocks) to the main source from the Precambrian basement. Ore deposition occurred at adepth of about 2 km at temperatures between 80 and 250 °C. A shallow magmatic heat source was the cause of these thermalfluctuations.

We investigate the potential use in traditional ceramics of several clays collected in the Numidian Flysch Formation (Upper Oligocene) at Tabarka, and Sejnane; Northern part of Tunisia). The valorisation of these adopts the technique of dry process, which requires a mixture of powdered clay with 7% water. This allows rapid drying of uncooked tiles. The tiles are fired at four different temperatures (1000 °C, 1050 °C, 1100 °C and 1150 °C) in order to optimize technological parameters such as shrinkage, water absorption and flexural strength. The obtained tiles show acceptable drying and firing shrinkage (not exceeding 3%), and bending strength (between 13 and 16 N/mm2) which are close to the required standards (EN ISO 10545–4, 15N/mm2 for wall tiles). The absorption ranges from 10 to 20%, which classifies these products in group BIII according to the international standards (ISO 13006 and EN ISO 10545–3). Variation of shrinkage and water absorption with the firing temperature reveals that optimal range is 1125–1150 °C for the Tabarka samples, whereas the Sejnane products might be fired at lower values (~1025 °C). The Tabarka fired pieces exhibit strong brightness. These results suggest that these latter clays could be used for white products such as sanitary ware formulations while those from Sejnane ones are more appropriated for colored (red) applications. The X-ray diffraction on the fired tiles powders shows the formation of quartz which is initially present in the crude clays, and mullite that is present at all firing temperatures. Moreover, the presence of mullite due to the richness of Al2O3 in Tabarka clays could support their refractory properties.

Relationship between salt domes and base metal mineralization is widely recognized across many salt-bearing basins (e.g., US Gulf Coast, Southern Europe and North Africa). In the northern Tunisian Atlas, the Mississippi Valley-type Fej El Adoum lead-zinc deposit represents one of these salt-related ore deposits . It consists of a combination of stratabound, veins, stockworks and cavity filling ore bodies , hosted by dolostone and limestone units, formed along the transition between Triassic evaporites and Cretaceous limestone. In the aim to better understand the concealed complex geological structures across the area, new-acquired detailed gravity data, constrained with field investigation and drill hole data were analyzed. Particularly, edge source detection techniques such as vertical gradient, total horizontal gradient and theta angle map were applied to outline structural contacts related to subsurface density variations. The main detected lineaments are in N–S, E-W and NW-SE directions. The N–S direction represents the deepest and most important lineament in direct contact with the evaporitic Triassic, while the transverse E-W direction is related to dextral strike-slip faults that subdivide the area into blocks. These major deeper lineaments have controlled the growth of the Triassic salt dome mainly during the Albo-Aptian as revealed by pinch outs of these series in direction of the crest of the structure. The detected lineaments seem to play a significant role in: (1) providing favorable pathways for the migration and ascent of mineralized fluids and (2) creating open space filling mainly at the interferences of N–S and E-W trending faults present at the contact between Triassic evaporitic unit and Cretaceous limestone. Our results suggest further reserves mainly in the E-W Ain Said occurrence and West of the Dar N'Hal closed mine. Our study also revealed the importance of structural study in the understanding of complex structures such as highly deformed salt dome cap rocks such as the Fej El Adoum diapiric structure.

The iron mine of Tamra (Nefza District, NW Tunisia) is a 50 m thick Upper Mio-Pliocene sedimentary series impregnated by Fe-Mn oxides associated with white clay lenses with high halloysite and kaolinite content. This mineralization results from i) synsedimentary weathering/pedogenesis, and ii) mixing surface water and regional hydrothermal fluids. The oxygen and hydrogen isotope composition of halloysite-kaolinite and goethite-hematite is examined in order to provide new insights into the ore formation. This study concludes that halloysite-kaolinite was not equilibrated only with meteoric fluids: the δ18O values have a range towards high values that are not consistent with weathering conditions for their formation and/or during their subsequent alteration. The δD and δ18O values of goethite lead to the same conclusion. The stable isotope compositions could be related to fluid-rock interaction with the underlying marls (and/or skarns), providing relatively high δ18O values to the fluids responsible for the white clay formation. This model also shows that the Pb-isotope compositions of halloysite-kaolinite are explained by a felsic and a carbonated end-member, similar to other ore deposits (IOCG and Sedex) of the vicinity. Several factors should be considered for the precipitation of halloysite-kaolinite and/or destabilization of primary clays in the Tamra ore, i.e. mixing of deep hot saline fluids, related to a thermally driven circulation, and meteoric waters. This hydrothermal contribution postdates the main synsedimentary weathering/pedogenetic Fe-enrichment and may be related to late Fe, Mn, Pb, Zn and As inputs of the Fe-Mn oxides., SCOPUS: ar.j, info:eu-repo/semantics/published

The Oued Belif 48 and Koudiat El Halfa 5 borehole samples have been analysed in order to reveal the mineralogical composition of the Triassic successions and their burial history within the geological evolution of the Tethysian southern margin. Oued Belif 48 borehole belongs to Nefza district which is a part of the “Nappe zone” (Tellian unit, north-western Tunisia). Koudiat El Halfa 5 borehole crosses the Koudiat El Halfa diapir (north–west of the north–south axis, Central Atlas). In this paper, the burial degree of evaporitic Triassic samples was determined by the “illite crystallinity” index and by the evolution of the other phyllosilicates, essentially chlorite, talc and illite/chlorite and illite/smectite mixed layers. The studied samples of the two boreholes are characterized by the presence of abundant clay minerals. The

International audience; Ain Allega and El Aguiba are among the largest barite-celestite deposits attributed to the Triassic period in Tunisia. They are located in the flysch zone on the eastern edge of the Triassic diapir of Jebel Hamra. The ore body consists of dolomite intensely brecciated and surrounded by marls, clay, gypsum and dolomite which forms the hanging wall of the deposit, and rimmed by Paleocene marls. The ore the surface structure, which in turn controls the mechanism of adsorption and incorporation of minor and trace elements into the growing crystal. For a solid solution, the transitional supersaturation for different growth mechanisms can be significantly different for the two end members. One of the most interesting and intriguing phenomena observed in natural crystals of the (Ba, Sr) SO4 solid solution from this study area is the development of compositional oscillatory zoning, consisting of alternating Ba-rich and Sr-rich layers. The sulfur isotope analyses show significant variability for barite and celestite (from 16.2 to 23 ‰). These values are interpreted as the result of the mixing of two sulfur end-members in the mineralizing fluids, corresponding to thermochemical sulfate reduction of Messinian seawater, together with Triassic sulfate, as sulfur sources. Fluid inclusion studies of celestite show that the BaSO4-SrSO4 solid-solution in both deposits was precipitated from hot saline solution (Th=190±20°C; 16.37 wt. % NaCl equivalent in Ain Allega and 8.2 wt. % NaCl equivalent in El Aguiba). Consequently, the precipitation could be from mixing of basinal brines with magmatic-meteoric fluid. minerals show a cap-rock type mineralization with various forms and types, in particular impregnation in dolomite, breccia cement, replacement of carbonate caprock and open space-filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are barite, celestite, calcite, dolomite and quartz .The ore minerals are hosted by the Triassic carbonate rocks, which show hydrothermal alteration, dissolution and brecciation. The study of barite-celestite solid-solution shows a bimodal distribution in which the composition is not continuous. Some intermediate compositions are missing; 20-80% SrSO4 for El Aguiba ore deposit and 50-70% SrSO4 for the Ain Allega ore deposit. X-ray diffraction peaks in the BaSO4-SrSO4 series display considerable broadening at intermediate compositions. The unit cell volume varies from 346.97 Å3 in barite (100% BaSO4) to 308.29 Å3 in celestite (100% SrSO4). This variation in cell parameters is attributed to the degree of substitution of barium by strontium since there is less variation between ionic radii of these elements. Consequently, these substitutions caused variation in morphologies, position and d-spacing of peaks (200, 011, 113, 312,122, 112, and 111). Some barite crystals have small-scale, strontium compositional banding which suggests that the crystals responded to regular fluctuations in physiochemical conditions during deposition. The degree of supersaturation in Ba2+ and Sr2+ controls the growth mechanism and consequently

Le présent travail visait à déterminer l'impact de rejets de deux mines de fer et de phosphates sur la qualité physicochimique de l'eau d'un système aquifère alluvial (nord-ouest de la Tunisie). Des échantillons de terrils, de sols ainsi que de l'eau de puits captant la nappe ont été prélevés et analysés. Les résultats d'analyses des échantillons de terrils ont montré que cette matrice renferme des concentrations remarquables en métaux lourds (essentiellement le Cd, Cr, Pb et Zn). Ces éléments métalliques ont été également détectés à des concentrations non négligeables dans la fraction fine des sols situés en aval des rejets miniers, suite à son transport éolien et hydrique. En ce qui concerne les eaux de la nappe, il s'avère que le transport des métaux issus des terrils est totalement atténué par les éléments constituant le sous-sol. Ces eaux, de bonne qualité géochimique, sont toutefois assez contaminées en nitrates dû aux pratiques agricoles intenses et à l'absence de systèmes d'assainissement urbains., The aims of this work were to determine the impacts of releases from two iron and phosphate mines (North West Tunisia) on the physico-chemical water composition of the related alluvial aquifer system. Samples from tailings, soil and water wells were collected and analyzed. The analytical results of tailing samples showed that this matrix contains high concentrations of heavy metals (mainly Cd, Cr, Pb and Zn). These metals were also detected at significant levels in the fine soil fraction downstream from the mine waste discharge due to transport by wind and water. The heavy metal concentrations in groundwater showed that the metal transport from the tailings is completely attenuated by the soil constituents. Overall, the physic-chemical quality of the groundwater is good, except for nitrates, which are present at relatively high concentrations due to intensive agricultural practices and the absence of urban wastewater treatment plants.

White clayey geomaterials were collected from northeast of the Nefza region (northern Tunisia). These deposits belong to the Mio-Pliocene molassic basins (basin of Tamra-Sidi Dris, Boukhchiba) and Oligocene Numidien in the area of El Aouinet. Analysis by X-ray diffraction showed associations of halloysite and kaolinite (Tamra), kaolinite and illite (Aouinet zone) and mixed layers, kaolinite and feldspars (Boukhchiba zone). Semi-industrial processed bricks showed promising characteristics and were visibly free of defects. Ceramic tiles had a bending strength that met the required standards but water absorption was somewhat high. So, to achieve higher quality, optimisation needs to be carried out in the formulation of batches or in the processing conditions. Finally, the incorporation in whitish sanitary-ware glaze formulations generated smooth coating layers that showed the required strong brightness and were free of defects.

Bore holes were drilled in the Senonian limestone of the Hedils-Jalta area (northern Tunisia) in order to determine their potential as an aquifer. Structural, tectonic and hydrogeologic data compilation shows the discrimination of productive and not productive zones. Differential hydraulic productivity was recognised with four distinct productive geological zones separated by a sterile corridor trending NW–SE. The structure consists of two compressional dihedrons, limited by two conjugate strike-slip faults, trending NNE–SSW and nearly E–W. The reduction of the (1) potential reservoir, (2) the low hydraulic productivity of the central band, (3) the torsion of the fold axis in eccentric arcs on both sides of the compressive relay and (4) the differential hydrogeological zonation are all related to the distribution of stress in the interference zone between conjugate strike-slip faults and to the reorientation of the stress field in their vicinity. This study constitutes a main database in establishing strategies for groundwater exploration in the similar zones.

The Debadib-Ben Gasseur anticlinal structure, situated between El Kef and the Algero-Tunisian border, belongs to one of the main diapiric, alignments of the oriental Maghreb. It constitutes an elliptic form oriented NE-SW. The heart is occupied by Triassic residual evaporites containing basaltic volcanites which seem to indicate an extensional setting during the Triassic period. The contact between the saliferous bodies and surrounding Cretaceous-Tertiary age rocks is locally underlined by conglomerates including reworked Triassic blocks and glauconite, suggesting a sedimentary contact. Biostratigraphic and sub-surface data could indicate, in terms of model reconstitution, an extrusive system with numerous phases starting in the Aptian and acting until the Tertiary period. However, tectonic events are clearly expressed during the Miocene.

In northwestern Tunisia, a paleomagnetic study was carried out on Albian levels, objects of controversy. They are considered to be either overturned strata on the limb of diapirs, or in their upright position as the floor of a salt glacier. After correction for the apparent dip, the polarity of the primary magnetization is always reversed, and the magnetization directions are relatively scattered. The Earth's magnetic field was always of normal polarity during the Albian, so that these levels are overturned. The scattering of the magnetization direction points out moreover that the tilting occurred around axes of various orientations. All these observations show that the evaporitic bodies were emplaced in diapirs, and that the notion of a salt glacier interbedded within the Albian sediments has to be given up.

The Ain Allega ore deposit represents one of the most significant Pb-Zn Sr-Ba deposits of the flysch zone in northern Tunisia. The total quantity of sulphide produced is 22,700 metric tons, with 13,300 t of galena and 9,400 t of sphalerite. It is located on the eastern edge of the Triassic diapir of the Jebel Hamra. The main ore minerals include sphalerite, galena, pyrite and marcasite, and gangue minerals including dolomite, calcite, celestite, quartz and barite. The mineralization hosted by carbonate rocks, shows some evidence of dissolution and brecciation characteristic of cap-rock formation. The fluid inclusion study from the celestite suggests that the primary and secondary monophase liquid (L) inclusions are most abundant compared to the other types. The microthermometric analyses of two-phase primary inclusions display homogenization temperatures ranging from 136 to 208°C (average of 180°C) and salinities ranging from 11.34 to 24.38 equivalent weight % NaCl (average of 16.4). The calculated density, pressure and depth are 0.965 g/cm3, 18 bars and 80 m, respectively. The hydrothermal fluid resulted from mixing of basinal brines and magmatic-meteoric solutions. Geological, mineralogical and thermometric data indicate that the Ain Allega ore deposit results of a mixing of basinal fluids (Mississippi valley type deposit) and hydrothermal fluids related to a shallow intrusion.

La formation a anhydrite du diapir de Sakiet Sidi Youssef contient aux environs de Sakiet Koucha des mineraux a Cu, Sb, Ag, Hg, au sein des minerais de type BPG habituels des formations corticales des diapirs de Tunisie septentrionale. L'association minerale comprend: pyrite, cuivres gris, chalcopyrite, bournonite, blende, galene, et un amalgame Ag-Hg. La composition des cuivres gris est tres variable, du pole tetraedrite au pole freibergite. La composition de l'amalgame argentifere est de stoechiometrie peu courante (Ag 0,71 Hg 0,26). Cette relative richesse en Ag est un caractere deja mis en evidence dans les concentrations du dome de Hockley en Gulf Coast, ce qui suggere qu'il s'agit d'une caracteristique propre a ce type de gisement lie aux diapirs. Par ailleurs, le rapprochement entre la presence de mercure dans le minerais, et l'existence au Nord du gisement d'un district a cinabre lie au volcanisme neogene, suggere que les phenomenes magmatiques recents ont pu avoir une influence dans cette region pourtant plus meridionale.