20 research outputs found
The Bou Dahar Jurassic carbonate-hosted PbâZnâBa deposits (Oriental High Atlas, Morocco): Fluid-inclusion and CâOâSâPb isotope studies
The Bou Dahar PbâZnâBa (±Sr) is hosted in the Lower and Middle Liassic carbonate platform in the oriental High Atlas of Morocco. The paragenetic sequence includes quartzâpyriteâmelnicoviteâsphaleriteâgalenaâ calciteâbarite ± fluoriteâ ± celestite. Fluid-inclusion studies were conducted on sphalerite (early mineralizing stage) and barite, and celestite (late mineralizing stage). These studies reveal two end-member fluids, a hot (~143 °C) and saline fluid (~23 wt.% NaCl eq.) and a cooler (b50 °C) and diluted fluid (~5 wt.% NaCl eq.). Based on fluid-inclusion and CâOâS isotope studies, a conclusion is reached that the Bou Dahar ore deposits were formed by the mixing of two fluid â a diluted, SO2â4-rich fluid, and an 18O-enriched basinal brine that carried Pb, Zn, and Ba. The sulfur required for the precipitation of sulfides was generated by the thermochemical sulfate reduction of dissolved sulfate (SO24â) of the Mesozoic seawaters, and delivered to the site of ore deposition. The sulfur of sulfate minerals was derived directly from these dissolved SO24. The Pb isotope compositions are homogenous with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios ranging from 18.124 to 18.183, 15.630 to 15.634, and 38.325 to 38.440 respectively. This Pb isotope composition is indicative of an upper crust and orogene reservoirs as the source of lead and other metals. The emplacement of mineralization occurred during the Eoceneâ Miocene Alpine orogeny, and tectonic burial and compression were the driving forces behind the circulation of the orogenic-brines. These ore-forming fluids migrated, along thrusting regional EâW and NEâSW deep-seated faults, to the confined carbonate-Liassic reservoir
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Composition chimique, fréquence et distribution des minéraux de la série barytine-célestite dans les gisements de fluorine de Hammam Jédidi et Hammam Zriba-Jébel Guébli (Tunisie nord-orientale)
Mineralogical investigations of barium and strontium sulfates of fluorite deposits in North-Eastern Tunisia (Hammam Jédidi and Hammam Zriba-Jébel Guébli deposits) show :
â the presence of different facies of these sulfates : massive lamellar, massive saccharoĂŻd, massive microfibrous, fibrous-lamellar, tabular and spherolitic ;
â the existence of a series of solid solutions ranging from barite to celestite, passing by strontian barites and barian celestite, however, the absence of strontian barites between 30 % and 50 % SrSO4 is to be noted ;
â strontian barites and barian celestites more abondant than pure barite or pure celestite ;
â the different relationship between minerals of the considered series and the crystallization facies ;
â a relationship between the SrSO4 contents in the barite-celestite series and the morphology of the mineralized ore body ; barite constitutes the main part of vein fillings ; strontian barites and barian celestites are found in stratoĂŻd bodies, and karsts, the strontium-rich minerals (barian celestite) occur near the Triassic evaporites ; celestite appears in the pockets or in the late fractures.
These mineral concentrations result from substitution phenomena and from fracture and karst fillings. The formation temperatures range from 150 to 200°C.L'étude minéralogique des sulfates de baryum et de strontium des gisements de fluorine de la Tunisie nord-orientale (gisements de Hammam Jédidi et Hammam Zriba-Jébel Guébli), a mis en évidence :
â la prĂ©sence de diffĂ©rents faciĂšs de sulfates : massif lamellaire ou saccharoĂŻde, massif microfibreux, fibrolamellaire, tabulaire et sphĂ©rolitique ;
â l'existence d'une sĂ©rie de solutions solides allant de la barytine Ă la cĂ©lestite en passant par des barytines strontianifĂšres et des cĂ©lestites baryfĂšres avec toutefois l'absence des termes intermĂ©diaires entre 30 % et 50 % de SrSO4 ;
â des minĂ©raux de compositions intermĂ©diaires plus abondants que les termes extrĂȘmes, barytine ou cĂ©lestite ;
â une correspondance entre les diffĂ©rentes phases de cette sĂ©rie et les faciĂšs de cristallisation ;
â une relation entre la composition des sulfates et la morphologie du corps minĂ©ralisĂ© : les termes les plus riches en baryum se trouvent dans des fractures prĂ©coces et constituent ainsi l'essentiel des remplissages filoniens ; les termes intermĂ©diaires sont observĂ©s dans les amas stratoĂŻdes et les karsts ; les termes les plus riches en strontium Ă©tant au voisinage des Ă©vaporites du Trias ; enfin, la cĂ©lestite apparaĂźt dans les poches ou les fractures tardives.
Ces concentrations minérales sont le résultat de phénomÚnes de substitutions et de remplissages de poches et de fractures à des températures de mise en place de l'ordre de 150 à 200 °C.Bouhlel Salah. Composition chimique, fréquence et distribution des minéraux de la série barytine-célestite dans les gisements de fluorine de Hammam Jédidi et Hammam Zriba-Jébel Guébli (Tunisie nord-orientale). In: Bulletin de Minéralogie, volume 108, 3-4, 1985. Minéralogie dans les Sciences de la Terre et l'Industrie - Hommage à François Permingeat
Stretching of hydrocarbon fluid inclusions in fluorite at 200 and 400 bars confining pressure. Application to low pressure geobarometry
Intrakarstic fluorite samples from Djebel Guebli (Tunisia) contain spherical primary yellow oil inclusions with detectable amounts of H2O, CH4 and CO2. After overheating above homogenization temperature at one bar pressure, decrepitation of inclusions is observed which is related to abrupt gas loss with simultaneous injection of oil droplets into microcracks. This process is not operative under elevated confining pressures (200 and 400 bars), but stretching occurs instead. From a comparison between temperatures of onset of stretching for oil and water inclusions of similar volumes, an oil isochore slope of about 0.3 °C/bar is proposed for geobarometric applications under low-pressure conditions.Les fluorines intrakarstiques de Djebel Guebli (Tunisie) renferment des inclusions aqueuses et des inclusions primaires sphériques d'hydrocarbures liquides jaunes associés à des quantités détectables d'H2O, CH4, et CO2. Sous pression atmosphérique, aprÚs surchauffe au-dessus de leur température d'homogénéisation, on observe leur décrépitation par explosion, avec injection d'hydrocarbures liquides dans les fractures et dégazage simultané. Ce phénomÚne ne se produit plus sous pressions de confinement élevées (200 et 400 bars), pour lesquelles on observe une déformation de caractÚre plastique sans perte de matiÚre qui se traduit par une augmentation de volume comparable à celle observée dans les inclusions aqueuses (stretching).
A partir des tempĂ©ratures de "stretching", dĂ©terminĂ©es pour des inclusions de volumes comparables contenant respectivement des hydrocarbures liquides et contenant des solutions aqueuses, on propose une pente d'environ 0,3 °C/bar pour les isochores des hydrocarbures Ă©tudiĂ©s. On discute l'utilisation gĂ©obaromĂ©trique de ce rĂ©sultat dans le domaine des faibles pressions.Guilhaumou Nicole, Touray Jean-Claude, Bouhlel Salah. Stretching of hydrocarbon fluid inclusions in fluorite at 200 and 400 bars confining pressure. Application to low pressure geobarometry. In: Bulletin de MinĂ©ralogie, volume 111, 3-4, 1988. Inclusions fluides. IXth symposium on fluid inclusions. University of Oporto â May 1987
Fluid inclusion microthermometry and rare earth element distribution in the celestites of the Jebel Doghra ore deposit (Dome Zone, northern Tunisia): towards a new genetic model
International audienceThe celestite ore of Jebel Doghra Occurs as stratabound deposits within the cap-rock of a diapiric structure of Triassic salt-rocks. The celestite deposits result mainly from the late diagenetic to epigenetic replacement of the carbonated host-rocks giving rise to a dolomite-celestite "banded ore". Celestite is locally observed within fractures. This Study proposes a new genetic model based on fluid inclusion (F1) microthermometry and REE geochemistry. FI show that celestite, Occurring either as stratabound bodies or locies, was deposited from a highly saline (20.7 +/- 1.3 wt% NaCl equivalents) and warm (174 +/- 3 degrees C) basinal fluid, which contains hydrocarbon droplets and CO2. The geochemistry of the REE shows that the deposition of celestite is clue to the mixing between a deep-sourced fluid which has acquired high Sr concentrations by leaching feldspar-rich series in depth and a sulfate-rich solution associated with the Triassic evaporites
Origin of the Tala Hamza Igneous Rocks-Hosted Zinc-Lead Deposit, NE Algeria
The Miocene igneous rocks that host the Tala Hamza ZnâPb 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
The Sidi El Hemissi Triassic âophitesâ (Souk Ahras, NE Algeria): petrology, geochemistry, and petrogenesis
International audienceThe 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 âophites,â are interbedded as a ~â200âĂâ30-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 TriassicâEarly Jurassic times, now cropping out in north-western Africa, south-western Europe, north-eastern, 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
C-O stable isotopes geochemistry of Tunisian nonsulfide zinc deposits: A first look
A preliminary CâO stable isotopes geochemical characterization of several nonsulfide Zn-Pb Tunisian deposits has been carried out, in order to evidence the possible differences in their genesis. Nonsulfide ores were sampled from the following deposits: Ain Allegua, Jebel Ben Amara, Jebel Hallouf (Nappe Zone), Djebba, Bou Grine, Bou Jaber, Fedj el Adoum, Slata Fer (Diapir Zone), Jebel Ressas, Jebel Azreg, Mecella (North South Axis Zone), Jebel Trozza, Sekarna (Graben Zone). After mineralogical investigation of selected specimens, the CâO stable isotopic study was carried out on smithsonite, hydrozincite, cerussite and calcite. The data have shown that all the carbonate generations in the oxidized zones of Ain Allegua and Jebel Ben Amara (Nappe Zone), Bou Jaber, Bou Grine and Fedj el Adoum (Diapir Zone), Mecella and Jebel Azreg (North South Zone) have a supergene origin, whereas the carbonates sampled at Sekarna (Graben Zone) (and in limited part also at Bou Jaber) precipitated from thermal waters at moderately high temperature. Most weathering processes that controlled the supergene alteration of the Zn-Pb sulfide deposits in Tunisia had probably started in the middle to late Miocene interval and at the beginning of the Pliocene, both periods corresponding to two distinct tectonic pulses that produced the exhumation of sulfide ores, but the alteration and formation of oxidized minerals could have also continued through the Quaternary. The isotopic characteristics associated with the weathering processes in the sampled localities were controlled by the different locations of the sulfide protores within the tectonic and climatic zones of Tunisia during the late Tertiary and Quaternary
Origin of the Mizab barite vein-type deposit, Ain Mimoun (NE Algeria): evidence from fluid inclusion and S-, O- and C-stable isotope studies
The Khenchela massif, northeast Algeria, belongs to the eastern Saharan Atlas that extends northeasterly from the AurĂšs 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 NWâSE 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 âMizab barite depositâ. 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. ÎŽ34S values of barite are betweenâ+â17.9 andâ+â27.6â° and the ÎŽ34S values of the associated sulphides vary betweenâââ9.2 andâ+â3.0â°. These data indicate that the most likely source of sulphur is the sulphates (gypsum) of the Triassic evaporitic formation (ÎŽ34S ranging betweenâ+â11.5 andâ+â13.4â°). Thermochemical sulphate reduction is the most probable process by which H2S was produced, although relatively large negative ÎŽ34S 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 ÎŽ18Ofluid from quartz oxygen isotope data varies betweenâ+â6 andâ+â12â°, 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