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Galai H.,Institute National Of Recherche Et Danalyse Physico Chimiques
Arabian Journal of Chemistry | Year: 2014

The mineralogy of the Tunisian phosphatic series of the Jebel Oum El Khacheb deposit which belongs to the Gafsa-Metlaoui basin, located in the South of Tunisia, was studied. Chemical and mineralogical characterization of eight representative samples (2. mm-70. μm) were undertaken by X-ray diffraction, thermal analysis TG/DTA, Carbon and Sulfur analyzer and Atomic Absorption Spectroscopy. It was revealed that each phosphatic layer contains various silicates and carbonates. The X-ray diffraction results were supported by the Rietveld method to confirm the presence of certain minor phases (calcite, dolomite, bassanite and anorthoclase). The precision and accuracy of the quantitative-phase analysis, using the Rietveld method as a routine tool for process control, were highlighted. © 2014 The Authors.


Jemmali N.,Institute National Of Recherche Et Danalyse Physico Chimiques | Jemmali N.,Tunis el Manar University | Souissi F.,Institute National Of Recherche Et Danalyse Physico Chimiques | Villa I.M.,University of Bern | And 2 more authors.
Ore Geology Reviews | Year: 2011

The Jalta and Jebel Ghozlane ore deposits are located in the extreme North of Tunisia, within the Nappe zone. The mineralization of Jalta, hosted in Triassic dolostones and the overlying Mio-Pliocene conglomerates, consists of abundant galena, barite, and cerussite with accessory sphalerite, pyrite, and jordanite. At Jebel Ghozlane, large Pb-Zn concentrations occur in the Triassic dolostones and Eocene limestones. The mineral association consists of galena, sphalerite, barite, and celestite and their oxidation products (cerussite, smithsonite, and anglesite). Lead isotope ratios in galena from both districts are relatively homogeneous (206Pb/204Pb=18.702-18.823, 207Pb/204Pb=15.665-15.677, 208Pb/204Pb=38.725-38.875). The δ34S values for sulfates from both areas (+12.2 to +16.2‰ at Jalta and +14.3 to +19.4‰ at Jebel Ghozlane) are compatible with a derivation of sulfur from marine sulfates, possibly sourced from the Triassic evaporites. The δ34S values of the sulfides have a range between -10 and +12.5‰ at Jalta, and between -9.1 and +22.1‰ at Jebel Ghozlane. The large range of values suggests reduction of the sulfate by bacterial and/or thermochemical reduction of sulfate to sulfur. The high δ34S values of sulfides require closed-system reduction processes. The isotopically light carbon in late calcites (-6.3 to -2.5‰) and authigenic dolomite (-17.6‰) suggests an organic source of at least some of the carbon in these samples, whereas the similarity of the δ18O values between calcite (+24.8‰) and the authigenic dolomite (+24.7‰) of Jalta and their respective host rocks reflects oxygen isotope buffering of the mineralizing fluids by the host rock carbonates. The secondary calcite isotope compositions of Jalta are compatible with a hydrothermal fluid circulation at approximately 100 to 200°C, but temperatures as low as 50°C may be indicated by the late calcite of Jebel Ghozlane (δ18O of +35.9‰). Given the geological events related to the Alpine orogeny in the Nappe zone (nappe emplacement, bimodal volcanism, and reactivation of major faults, such as Ghardimaou-Cap Serrat) and the Neogene age of the host rocks in several localities, a Late-Miocene age is proposed for the Pb-Zn ore deposits considered in this study. Remobilization of deep-seated primary deposits in the Paleozoic sequence is the most probable source for metals in both localities considered in this study and probably in the Nappe zone as a whole. © 2011 Elsevier B.V.


Jemmali N.,Institute National Of Recherche Et Danalyse Physico Chimiques | Souissi F.,Institute National Of Recherche Et Danalyse Physico Chimiques | Souissi F.,Tunis el Manar University | Carranza E.J.M.,James Cook University | Bouabdellah M.,Laboratory of Mineral Deposits
Journal of Geochemical Exploration | Year: 2013

The Oued Maden, Jebel Hallouf and Fedj Hassene Pb-Zn (Ba-Sr-F-Fe-Hg) hydrothermal ore deposits are located in the Nappe zone of Northern Tunisia. These ore deposits occur as epigenetic veins, karst and stockwork fillings in Upper Cretaceous limestones. The ore mineralogy consists mainly of galena and sphalerite, accompanied by minor amounts of jordanite, pyrite, chalcopyrite, orpiment, realgar, and other sulfosalts. Sulfur isotope data from sphalerite and galena indicate that the reduced sulfur was derived through thermochemical and/or bacterial reduction of dissolved sulfate resulting in metal precipitation. Lead isotope ratios and corresponding calculated age models indicate that the Pb in galenas has been derived from a homogenous crustal source during Upper Miocene time. © 2013 Elsevier B.V.


Jemmali N.,Institute National Of Recherche Et Danalyse Physico Chimiques | Jemmali N.,Tunis el Manar University | Souissi F.,Institute National Of Recherche Et Danalyse Physico Chimiques | Souissi F.,Tunis el Manar University | And 2 more authors.
Ore Geology Reviews | Year: 2013

The Pb-Zn ore deposits in the Guern Halfaya and Bou Grine areas (northern Tunisia) are hosted mainly by dolostones in the contact zone between Triassic and Upper Cretaceous strata and by Upper Cretaceous limestones. The deposits occur as lenticular, stratiform, vein, disseminations and stockwork ore bodies consisting of sphalerite, galena, pyrite, chalcopyrite and sulfosalt (gray copper). Barite and celestite dominate the gangue, with lesser calcite. The δ34S values of barite and celestite (12.7-15.0‰) at the Oum Edeboua mine are consistent with the reduction of sulfates in Triassic evaporites within the study area (12.8<δ34S<14.0‰). The δ34S values in base-metal sulfides from both study areas (2.6-9.5‰) and the presence of bacterial relics suggest involvement of bacterially-mediated sulfate reduction in the mineralization. The present Pb isotope data are homogeneous with 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.723-18.783, 15.667-15.685 and 38.806-38.889, respectively, which suggest a single source reservoir of Pb at depth in the upper crust. The syn-diagenetic mineralization in the Bahloul Formation and the calculated age from the Pb isotopic data suggest an Upper Cretaceous age for the Pb-Zn deposits in the Guern Halfaya and Bou Grine areas. During this period, NE-SW to ENE-WSW trending regional extensional tectonic structures likely favored migration of mineralizing fluids and eventual deposition at Guern Halfaya and Bou Grine. © 2012 Elsevier B.V.


Jemmali N.,Institute National Of Recherche Et Danalyse Physico Chimiques | Souissi F.,Institute National Of Recherche Et Danalyse Physico Chimiques | Souissi F.,Tunis el Manar University | Carranza E.J.M.,James Cook University | And 2 more authors.
Chemie der Erde - Geochemistry | Year: 2014

The occurrence of Pb-Zn deposits of Jalta district (northern Tunisia) as open space fillings and cements and breccia in the contact zones between Triassic dolostones and Miocene conglomerates along or near major faults provides evidence of the relationship between the mineralization and tectonic processes. Pb isotopes in galena from the deposits yielded average 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.821, 15.676 and 38.837, respectively, implying a well-mixed multi-source upper crustal reservoir of metals. Magmatism and compressional tectonism during the Alpine orogeny favored Pb-Zn mineralization in the Jalta district. The enrichment in Pb, Zn, Cd and Co of the Triassic carbonates and enrichments in Pb, Zn and Cd in Triassic clayey shales is associated with hydrothermal alteration around faults. Alunite in the deposit has δ34S values (-2.5 to -1.5‰ VCDT), which could have been formed at and above the water table in a kind of steam-heated environment, where fluids containing H2S mixed with fluids containing K and Al. The H2S could have been produced by TSR of sulfates at high temperature at depth and then leaked upward through deep-seated faults, whereas the K and Al could have been acid-leached from Miocene volcanic rocks. © 2014 Elsevier GmbH.


Jemmali N.,Institute National Of Recherche Et Danalyse Physico Chimiques | Jemmali N.,Tunis el Manar University | Souissi F.,Institute National Of Recherche Et Danalyse Physico Chimiques | Souissi F.,Tunis el Manar University | And 2 more authors.
Resource Geology | Year: 2013

The Pb-Zn deposit at Jebel Ghozlane, in the Nappe zone (northern Tunisia), is hosted by Triassic dolostones and Eocene limestones and is located along faults and a thrust-sheet boundary. The sulfide mineralization of the deposit consists mainly of galena and sphalerite and occurs as vein, stockwork, breccia, dissemination and replacement ores. Three hydrothermal stages are involved in the formation of the ores: stage I is dominated by celestite-barite, hydrothermal dolomite DII, colloform sphalerite, and galena I; stage II consist of galena II; and stage III contains calcite. Galena in the deposit yielded average 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.705, 15.667 and 38.734, respectively, suggesting a single upper crustal source reservoir for metals. Trace element data indicate the presence of Zn- and As-free galena and As-rich galena (with 0.2-0.5% As). Sphalerite contains 0.4% As, 0.7-0.9% Cd and 0.1-1.5% Fe. Microthermometric analysis of fluid inclusions in celestite shows that the deposit formed from fluids composed of heterogeneous mixtures of saline (19.5 ± 1 wt% NaCl eq.) aqueous solutions sourced from basinal brines, and gaseous CO2-rich phases bearing low amounts of CH4, N2 and/or H2S, at temperatures of 172 ± 5°C. © 2012 The Authors; Resource Geology © 2012 The Society of Resource Geology.

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