Lead Isotopes as Tracers of Metal Sources and Timing of the Carbonate-Hosted Pb-Zn Deposits in the Nappes Zone, Northern Tunisia

The polymetallic deposits in the Nappes zone, Northern Tunisia occur in the contact between Triassic-Miocene/Eocene carbonate rocks and in the Upper Cretaceous limestones. They can be divided into two groups: one is Pb-Zn mineralization with Hg and As in fractures with local intrusions of Neogene volcanics (e.g., Fej Hassene, Oued Maden), and the second is stratabound and karst Pb-Zn mineralization with arsenic and antimony hosted in the continental Neogene strata or situated immediately below them (Aïn Allega, Sidi Embarek, Jebel Hallouf-Sidi Bou Aouane, Bazina, Jalta and Jebel Ghozlane). Pb-isotopic compositions of galenas display a homogeneous Pb isotope signature. Generally, Pb isotope ratios on ores from the Jalta, Jebel Ghozlane, Jebel Hallouf, Oued Maden and Fedj Hassene plot between samples of the Late Miocene igneous rocks and the sedimentary country rocks of the Nefza area and between the upper crust and orogen curves. This intermediate position may imply potential mixing between end-member sources. Because the Pb-Zn mineralization is fault-controlled and spatially associated with the post-nappe Miocene series and the calculated model age is about 10.86 Ma, one is led to argue that the mineralization in the Nappes zone deposits occurred during the last paroxysmal phase of the Alpine folding (i.e., Miocene age)

Un risque d'origine anthropique : la contamination chronique par les métaux lourds à proximité d'anciens sites miniers. Le cas de la mine (plomb, zinc, cadmium) de Jebel Ressas (Tunisie nord-orientale)

L'analyse des risques en relation avec l'environnement s'intéresse surtout aux catastrophes naturelles telles que les éruptions volcaniques, les inondations, les séismes. Or, la société actuelle étant fortement marquée par le développement industriel et technologique, les risques d'origine anthropique deviennent de plus en plus prégnants.L'objectif de l'étude entreprise est de proposer une nouvelle méthode d'évaluation et de cartographie du risque de contamination métallique sur et autour d'un ancien site minier situé à proximité de la ville de Tunis. Ce type de risque que les sociologues dénomment " risques diffus " (Beck, 1992 ; Peretti-Watel, 2000), appelle une approche interdisciplinaire couvrant un large spectre depuis la géochimie jusqu'aux données sociétales afin d'intégrer les données quantitatives et qualitatives dans un même modèle. Les résultats préliminaires exposés dans cet article ont été obtenus en adoptant une démarche d'analyse du risque basée sur le couplage entre une analyse de l'intensité de l'aléa et de l'estimation du degré de vulnérabilité des enjeux, adaptés à une contamination chronique d'un écosystème

Etude gitologique et conditions de formation des gisements de fluorine (Pb, Zn, Ba) du Jebel Zaghouan (J. Stah et Sidi Taya) et du Jebel Oust (Tunisie nord-orientale)

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Effect of submarine morphology on environment quality: Case of Monastir bay (Easter Tunisia)

International audienceThe Monastir Bay is characterized by high organic pollution (up to 6% TOC), along the coastal zone and significant eutrophication. Such degradation seems to be strongly related to both characteristics of the supplied water which is rich in organic particles and the submarine morphology showing a flat extending between Khniss and Lamta and a series of shoals and sand bars between Ras Dimass and Kuriates Islands. Results of the hydrodynamics modeling have shown that the submarine morphology of the bay is responsible for the transformation of the waves coming from the open sea (N, E, SE) to the coastal zone, where reduced energy contributes to the concentration of pollution. Wave modeling has also shown that such concentration prevails in low-depth (0 to -3m depth) areas where both surf and breaking zones are almost absent. This case illustrates an example of the Mediterranean coasts vulnerability to pollution under moderate energy conditions

Geochemical Assessment and Mobility of Undesired Elements in the Sludge of the Phosphate Industry of Gafsa-Metlaoui Basin, (Southern Tunisia)

The raw phosphates in the Gafsa-Metlaoui phosphate basin are valorized by wet processes that are performed in the laundries of the Gafsa Phosphates Company (CPG, Gafsa, Tunisia) to reach market grades (>28% P2O5). This enrichment process allows the increase of P2O5 content by the elimination of the coarse (>2 mm) and fine (<71 µm) fractions. Mineralogical analysis has shown that all the investigated materials (raw phosphate, marketable phosphate, coarse waste, and fine waste) from the laundries of M’Dhilla-Zone L and Redeyef are both composed of carbonate fluorapatite, carbonates, quartz, gypsum, clays, and clinoptilolite. Chemical analysis shows that Cr, Cd, Zn, Pb, and U are concentrated in the fine wastes and associated with the clay–phosphate fraction. The rare earth elements are more concentrated in both raw and marketable phosphates. Drilling and sludge-water analysis, along with leaching tests conducted on the fine wastes, showed that, due to phosphate industry, cadmium, fluorine, and sulfate contributing to the pollution of water resources in the region, pollution is more conspicuous at M’Dhilla

Phosphoric acid purification sludge: Potential in heavy metals and rare earth elements

International audienceThe present study was carried out to show the potential in heavy metals (HM) and the rare earth elements (REE) which presents the residues of phosphoric-acid(PA) purification. Three different cadmiferous solid residues (according to the nature of the purification process of the PA: BG, BC and BS) were collected from an industrial site located in the south of Tunisia. The mineralogical study showed the predominance of anhydrite, accompanied by quartz, malladrite; calcium sulfate hemihydrate and fluorapophyllite. The microanalysis showed (i) the association of cadmium and zinc, (ii) as well as the presence of associated REEs. The chemical analysis showed that (i) the calcium sulfate concentrations are majority in samples BS, BG and BC (44, 34 and 44%, respectively), (ii) significant concentrations of phosphoric acid (28, 18 and 21% P2O5, respectively), (iii) the HM: Cd, Zn, Cr, Ni, V, Cu, Pb, Co, Mo, Mn and U have proportion in the order of 0.1%. The concentrations of Cd, Zn and Cr are respectively in the order of: 230, 149 and 189 mg/kg for BS, 346, 243 and 153 mg/kg for BG and 183, 129 and 440 mg/kg for BC and (iv) the REEs: La, Ce, Nd, Eu, Y et Yb present considerable mass percentages able to reach 0.2%. A series of extraction tests was led on the cadmiferous sludges to evaluate the rates of HM (Cd, Zn) and REE dissolution, using two solvents (deionized water (DW) and aqueous sodium based alkaline metal solution). The results showed that the dissolution rates of Cd and Zn are respectively in the order of (12–29% and 41–45% for DW; 67–86% and 83–93% for Na2SO4 solution). The extractability of HM and REE is strongly influenced by pH, solvent nature and mineral load in the cadmiferous sludges. The water-soluble metals represent a significant mobile fraction, making the toxic elements more sensitive to mobilization processes, such as leaching and erosion. Whereas, the metals extractable by the Na2SO4 solution represent a very important exchangeable and “co-crystallization” fraction, which reflects the bioavailability of these metals

Mobility of Potentially Toxic Elements (Pb, Zn, Cd, As, Sb) in Agricultural Carbonated Soils Contaminated by Mine Tailings (Northern Tunisia): A New Kinetic Leaching Approach with Organic Acids

International audienc

Heavy metals distribution and mobility in flotation tailings and agricultural soils near the abandoned Pb-Zn district oF Jebel Hallouf-Sidi Bouaouane (NW Tunisia)

International audienceMineralogical and geochemical analyses of the environmental components in the vicinity of the abandoned mines of Jebel Hallouf-Sidi Bouaouane have shown that large volumes of flotation tailings are made of base metal sufides (galena, sphalerite, pyrite, marcasite) accompanied with lesser amounts of sulfosalts (jordanite, tennantite) and associated to a carbonated (calcite) and clayey (kaolinite, illite) matrix. Strong heavy metals (Pb, Zn and Cd) concentrations are recorded in soil and flotation tailings. Their concentrations in the flotation tailings are around 9250 mg.kg-1, 8200 mg.kg-1 and 66.5 mg.kg -1, respectively. Their mean concentrations in the soils surrounding the aforementioned mine wastes, are 39,720 mg.kg-1, 9030 mg.kg-1 and 86 mg.kg-1, respectively. Erosion by wind and running waters (heavy rain and flood periods) are considered as important mechanism in carrying these toxic elements to flood areas, and especially to soils lying on the eastern side of Jebel Hallouf Mountain. The statistical analyses of geochemical data relative to mine wastes and soils display a relationship between heavy metals and clay. Another relation is established between these metals and iron oxides. In soil, the µltivariate statistical approach [principal component analysis (PCA)] has shown two contamination origins: the mining wastes and rock dumps (F1xF2 diagram). Heavy metals concentrations in batch solutions of the contaminated soil samples varied between 36.6 µ g.l-1 and 51.2 51.2 µ g.l-1 for Pb, 543 µ g.l-1 and 3600 µ g.l-1 for Zn and 0.2 µ g.l-1 and 2.5 µ g.l-1 for Cd, while for the flotation tailings the concentrations varied between 16.9 µ g.l-1 and 483 µ g.l-1, 63 µ g.l-1 and 3240 µ g.l-1, and 2 µ g.l-1 and 9.8 µ g.l-1 for the same elements respectively. Concentrations of the same order are measured in meteoric water samples taken at the top of the flotation tailing piles essentially for Zn (145 µ g.l-1 to 1933 µ g.l-1) and Cd (4.6 1.µ g1-1 to 34.6 µ g.l-1). These results express the high mobility of heavy metals as to exceed the environmental norms especially for Pb in the contaminated soils as well as Pb and Cd in the flotation tailings leaching solution

Sequence stratigraphy, palaeoenvironments and tectonics at the Cenomanian-Turonian boundary : tilted bloc of Jabal Chemsi, northern part of southern Tunisia

Abdallah Hassen, Sassi Sassi, Souissi Fouad, Meister Christian. Sequence stratigraphy, palaeoenvironments and tectonics at the Cenomanian-Turonian boundary : tilted bloc of Jabal Chemsi, northern part of southern Tunisia. In: Documents des Laboratoires de Géologie, Lyon, n°156, 2002. STRATI 2002. 3ème congrès français de stratigraphie. Lyon, 8-10 juillet 2002. p. 15