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)

Isotope geochemistry of Mississippi Valley Type strataboundF-Ba-(Pb-Zn) ores of Hammam Zriba (Province of Zaghouan, NETunisia).

Peer reviewed journal article. Geology, 2017.Abstract available in PDF file

Geochemistry Of Triassic Carbonates: Exploration Guide To Pb-zn Mineralization In North Tunisia

The Triassic carbonate rocks in Northern Tunisia (Nappes, Domes, Jurassic Mountains zones), consist of massive carbonates, clays and gypsum with authigenic minerals. These are associated with several Pb-Zn deposits and occurrences. At Jebel Ichkeul, Bechateur and Oum Edeboua, these Triassic carbonates exhibit enrichment in Pb (0.32 to 228ppm), Zn (17 to 261ppm), Cd (5 to 6ppm) and Co (0.3 to 89.5ppm), with respect to their average contents in crustal carbonates. The enrichment is more pronounced at Oum Edeboua (near the ore zone). Permeability is one of the most effective factors of dispersion of metallic trace elements, causing the development of geochemical halos. The genetic relationship of the Triassic carbonate rocks with the ore deposits was controlled by diapirism and tectonic movements, which favored mineralization along the Triassic-cover contact as well as the remobilization of metals from the mineralized rocks. Analysis of metallic trace elements in Triassic rocks provides clues to the presence of possible mineral deposits. These could be effectively used for both geochemical interpretation and mineral exploration. Carbon and O-isotope data (- 9.3 parts per thousand<C-13<+3 parts per thousand; +21.9<O-18<+31 parts per thousand) suggest that the Triassic carbonates of all study areas have marine carbonates as their origin; some of them show significantly lower O-18 values indicating some exchange with hydrothermal fluids. Calcites associated with mineralization at Oum Edeboua have C-13 of -6.2 parts per thousand to -8.22 parts per thousand and O-18 of +24.88 parts per thousand to +25 parts per thousand. The C-isotope compositions of these calcites are C-13 depleted, indicating an organic origin.66433535

Geochemistry of Triassic carbonates: exploration guide to Pb–Zn mineralization in North Tunisia

The Triassic carbonate rocks in Northern Tunisia (Nappes, Domes, Jurassic Mountains zones), consist of massive carbonates, clays and gypsum with authigenic minerals. These are associated with several Pb–Zn deposits and occurrences. At Jebel Ichkeul, Bechateur and Oum Edeboua, these Triassic carbonates exhibit enrichment in Pb (0.32 to 228 ppm), Zn (17 to 261 ppm), Cd (5 to 6 ppm) and Co (0.3 to 89.5 ppm), with respect to their average contents in crustal carbonates. The enrichment is more pronounced at Oum Edeboua (near the ore zone). Permeability is one of the most effective factors of dispersion of metallic trace elements, causing the development of geochemical halos. The genetic relationship of the Triassic carbonate rocks with the ore deposits was controlled by diapirism and tectonic movements, which favored mineralization along the Triassic-cover contact as well as the remobilization of metals from the mineralized rocks. Analysis of metallic trace elements in Triassic rocks provides clues to the presence of possible mineral deposits. These could be effectively used for both geochemical interpretation and mineral exploration. Carbon and O-isotope data (– 9.3‰ < δ13C < +3‰; +21.9 < δ18O < +31‰) suggest that the Triassic carbonates of all study areas have marine carbonates as their origin; some of them show significantly lower δ18O values indicating some exchange with hydrothermal fluids. Calcites associated with mineralization at Oum Edeboua have δ13C of –6.2‰ to –8.22‰ and δ18O of +24.88‰ to +25‰. The C-isotope compositions of these calcites are 13C depleted, indicating an organic origin

The ore genesis of the Jebel Mecella and Sidi Taya F–Ba (Zn–Pb) Mississippi Valley-type deposits, Fluorite Zaghouan Province, NE Tunisia, in relation to Alpine orogeny: constraints from geological, sulfur, and lead isotope studies

Jebel Mecella and Sidi Taya F–(Ba–Pb–Zn) deposits are located within the Fluorite Zaghouan Province (NE Tunisia). The mineralization occurs along the unconformity surface between the Jurassic limestones and Upper Cretaceous rocks. The mineralization consists mainly of fluorite, barite, sphalerite, and galena. The δ³⁴S values of barite at Jebel Mecella (14.8–15.4‰) and at Sidi Taya (21.6–22.2‰) closely match those of the Triassic evaporites and Messinian seawater, respectively. The range of δ³⁴S values of galena and sphalerite in both deposits (−6.9 to +2.4‰) suggests the involvement of thermochemical sulfate reduction and possibly organically-bound sulfur in the generation of sulfur. Lead isotope data with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.893–18.903, 15.684–15.699, and 38.850–38.880, respectively suggests a single homogeneous source reservoir of Paleozoic age and/or the homogenization of the Paleozoic–Cretaceous multireservoir-derived fluids along their long migration paths to the loci of deposition during the Alpine orogeny

Geochemistry of triassic carbonates: exploration guide to Pb-Zn mineralization in north tunisia

The Triassic carbonate rocks in Northern Tunisia (Nappes, Domes, Jurassic Mountains zones), consist of massive carbonates, clays and gypsum with authigenic minerals. These are associated with several Pb–Zn deposits and occurrences. At Jebel Ichkeul, Bechateur and Oum Edeboua, these Triassic carbonates exhibit enrichment in Pb (0.32 to 228 ppm), Zn (17 to 261 ppm), Cd (5 to 6 ppm) and Co (0.3 to 89.5 ppm), with respect to their average contents in crustal carbonates. The enrichment is more pronounced at Oum Edeboua (near the ore zone). Permeability is one of the most effective factors of dispersion of metallic trace elements, causing the development of geochemical halos. The genetic relationship of the Triassic carbonate rocks with the ore deposits was controlled by diapirism and tectonic movements, which favored mineralization along the Triassic‐cover contact as well as the remobilization of metals from the mineralized rocks. Analysis of metallic trace elements in Triassic rocks provides clues to the presence of possible mineral deposits. These could be effectively used for both geochemical interpretation and mineral exploration. Carbon and O‐isotope data (– 9.3‰ < δ13C < +3‰; +21.9 < δ18O < +31‰) suggest that the Triassic carbonates of all study areas have marine carbonates as their origin; some of them show significantly lower δ18O values indicating some exchange with hydrothermal fluids. Calcites associated with mineralization at Oum Edeboua have δ13C of –6.2‰ to –8.22‰ and δ18O of +24.88‰ to +25‰. The C‐isotope compositions of these calcites are 13C depleted, indicating an organic origin.66433535

Lead and sulfur isotope constraints on the genesis of the polymetallic mineralization at Oued Maden, Jebel Hallouf and Fedj Hassene carbonate-hosted Pb–Zn (As–Cu–Hg–Sb) deposits, Northern Tunisia

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

Sulfur and lead isotopes of Guern Halfaya and Bou Grine deposits (Domes zone, northern Tunisia): implications for sources of metals and timing of mineralization

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

Metal sources and timing of Pb-Zn deposits associated to salt dome cap rocks in northwest Tunisia: evidence from isotope (Pb,S) geochemistry

The Pb-Zn ore deposits in the Oum Edeboua and Bou Grine areas (northern Tunisia) are hosted mainly by limestones in the contact zone between Triassic and Upper Cretaceous strata and by Upper Cretaceous limestones. The deposits occur as lenticular, stratiform, vein, dissemination and stockwork ore bodies consisting of sphalerite, galena, pyrite, chalcopyrite and sulfosalt (grey copper). Barite and calcite dominate the gangue.The ^34S of barite and celestite (12.7–15.0‰) at the Oum Edeboua (Guern Halfaya area) mine are consistent with the reduction of sulfates from Triassic evaporites within the study area (12.8<^34S<14.0‰). The ^34S values in base-metal sulfides from both study areas (2.6–9.5‰)\ud and the presence of bacterial relics suggest involvement of bacterially-mediated sulfate reduction in the mineralizations. Pb isotope data are homogeneous with\ud ^206Pb/^204Pb, ^207Pb/^204Pb and ^208Pb/^204Pb ratios of 18.723–\ud 18.783, 15.667–15.685 and 38.806–38.889, respectively, which suggests a single source reservoir of Pb in the upper crust. The syn-diagenetic mineralization (F2) in the Bahloul Formation and the calculated ages from the Pb isotopic data suggest an Upper Cretaceous age for thePb-Zn deposits in the Oum Edeboua and Bou Grine mines

Geochemical constraints on the genesis of the Pb–Zn deposit of Jalta (northern Tunisia): implications for timing of mineralization, sources of metals and relationship to the Neogene volcanism

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