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International audience; The Bou Jaber ore deposit is one of the numerous diapir-related Pb–Zn–F–Ba deposits of the Dome Zone in Northern Tunisia. Its location is controlled by the regional NE-SW Tajerouine Fault.Ore minerals are hosted in the Late Aptian limestones (Serdj Formation) as open space filling and stratabound replacement bodies. According to Bouhlel et al. (2016), the poly-phase mineralization resulted from the successive activity of three mineral systems, a Pb–Zn, then a barite, and eventually a fluorite deposition system. The latter, from the Late Miocene, is demonstrated in the present study.The fluorite system is characterized by the involvement of oil in the hydrothermal fluids. This oil was produced in the local environment of the deposit from the thermal maturation of the Albian Fahdene black shale source-rock at temperature range of~140 °C–~100 °C. Two brines were involved in the fluorite hydrothermal system. The first one (L1) is a Ca-rich brine (≥20 wt % bulk salinity), with Na/Ca ≤ 0.18, which is thought to have long resided in the basement, before its transfer into the Jurassic reservoir (Upper Nara Formation) and its eventual mobilization at the time of ore deposition. The second brine (L2), less saline (≤14 wt % bulk salinity) is more sodic, with Na/Ca up to 0.53, and represents unmodified brine originated from the nearby Triassic salt. The L1 brine was F-bearing, whereas the L2 brine was associated with oil. Fluorite deposition occurred at the estimated shallow depth of 1.7 km from cooling of the L1 brine due to the first isobaric cooling from ~160 °C to 135 °C under sub-lithostatic conditions (36 MPa). This stage is followed by mixing with the newly incoming L2 brines (transporting oil) along a sub-isochoric decompression path (down to the hydrostatic pressure at 17 MPa) and continuously cooling from 135 °C to 125 °C. The cooling and mixing caused fluorite deposition after which a transient heat advection episode (up to 145 °C) caused late calcite deposition prior to the end of hydrothermal circulation.

International audience; This study is the first synthesis of chemical composition and stable isotopes values for the Kerguelen archipelago waters. The stable isotope values for rainfall and river waters in the Kerguelen archipelago allow a calculation of the Local Meteoric Water Line (δD rainfall = 8.43 x δ18O rainfall + 11) and a summer runoff line (δD river drainage = 7.45 x δ18O river drainage + 6). Surface waters with low- ion concentrations, chlorine facies and stable isotope values infiltrate through fractures and lava flows recharging deeper groundwaters. Thermal groundwater with low- (7 to 50 °C) and high- (50 to 100 °C) temperatures emerges in different localities in the volcanic archipelago. The low-temperature thermal waters might represent a mixture of high-temperature water with rainfall, thermal gradient changes or shallower infiltration compared to that for high-temperature thermal waters. The Rallier du Baty and Val Travers areas contain geothermal fluids with high-temperature springs, fumaroles and a large water flow. In the Rallier du Baty, the major ion chemistry and O, H, C and S stable isotope ratio of low (7 to 50 °C) temperature spring waters in Rallier du Baty area demonstrate a geothermal-system recharged by meteoric water (δD H2O liquid = 7.0 x δ18O H2O liquid + 0.5) rather than sea water. The chemical and isotopic compositions of elevated temperature spring waters (50 to 100 °C) have a long and complex history of meteoric water interacting with cooling magmas (δD H2O liquid = 1.78 x δ18O H2O liquid – 23). Surficial precipitation of aragonite, kaolinite, pyrite, native sulfur attest to a long livied geothermal system. A temperature of the geothermal reservoir has been estimated between 193 and 259 °C by cation geothermometry. The combination of minerals observed, major ion composition of water with thermodynamic modeling and stable isotope data suggest a geothermal system with a series of water/rock interactions from 50 to 250 °C. The conductive cooling of rising of H2O−CO2-rich fluids have produced a H2O−CO2 phase separation with the precipitation of secondary minerals.

International audience; The Palaeoproterozoic Bled M’Dena ring complex (BRC) dated at 2.01 Ga (Rb–Sr isochron) situated in the eastern part of the Yetti–Eglab junction-zone, belongs to the Aftout orogenic province, intruding the Aftout granite (2.07 Ga). It exhibits a centripetal evolution from gabbro to granodiorite. The western part of the Bled M’Dena ring complex is dominated by volcanic rocks varying in composition from basalt, trachyandesite, andesite, dacite to rhyolite. Andesite constitutes the major volcanic type in the Bled M’Dena ring complex. Chemistry of these rocks suggest two distinct magmatic trends: A transitional-tholeiitic suite localised at the outer part of the ring complex, and a high-K calc-alkaline suite situated within the inner ring structure. Basic volcanics exhibit flat primitive REE patterns with insignificant Eu anomalies, suggesting that they probably represent a parental basaltic melt from which the Bled M’Dena complex evolved, (Eu/Eu∗ = 2.06–4.07). The europium anomaly did not vary significantly, as it evolved progressively through the volcanic series by differentiation and feldspar accumulation.It is proposed that a primitive basic magma from the mantle was contaminated by Eburnian crust (2.2–2.0 Ga). Thus the transitional-tholeiitic volcanic rocks, dominant in the region have developed a high-K calc-alkaline suite. Their source is melted shortly after its generation when the lithosphere was still hot, which restricts high-K calc-alkaline magmatism mainly to post-collisional settings. This has been linked to large movement along mega-shear zones (Yetti–Eglab junction) due to subduction of oceanic basins in a post collisional setting.

International audience; Structure- and tectonic-related gas migration into Ordovician sandstone reservoirs and its impact on diagenesis history were reconstructed in two fields in the Sbaa Basin, in SW Algeria. This was accomplished by petrographical observations, fluid inclusion microthermometry and stable isotope geochemistry on quartz, dickite and carbonate cements and veins. Two successive phases of quartz cementation (CQ1 and CQ2) occurred in the reservoirs. Two- phase aqueous inclusions show an increase in temperatures and salinities from the first CQ1 diagenetic phase toward CQ2 in both fields. Microthermometric data on gas inclusions in quartz veins reveal the presence of an average of 92 ± 5 mole% of CH4 considering a CH4-CO2 system, which is similar to the present-day gas composition in the reservoirs. The presence of primary methane inclusions in early quartz overgrowths and in quartz and calcite veins suggests that hydrocarbon migration into the reservoir occurred synchronically with early quartz cementation in the sandstones located near the contact with the Silurian gas source rock at 100-140°C during the Late Carboniferous period and the late Hercynian episode fracturing at temperatures between 117 and 185°C, which increased in the NW-direction of the basin. During the fracture filling, three main types of fluids were identified with different salinities and formation temperatures. A supplementary phase of higher fluid temperature (up to 226°C) recorded in late quartz, and calcite veins is related to a Jurassic thermal event. The occurrence of dickite cements close to the Silurian base near the main fault areas in both fields is mainly correlated with the sandstones where the early gas was charged. It implies that dickite precipitation is related to acidic influx. Late carbonate cements and veins (calcite - siderite - ankerite and strontianite) occurred at the same depths resulting from the same groundwater precipitation. The absence o

The rocks of the earth's surface are constantly exposed to the action of natural agents such as water, temperature variations, atmospheric gases and the action of living beings. Among the action of living beings, in the urban centers highlight the anthropogenic, which often ends up by degrading natural resources. In this context, understanding the processes of transformation of the rocks, you can understand the genesis and evolution of soils, and improve methods for their recovery. This study was conducted in a profile altered granitic rock located in the urban area of Porto Alegre, where eight samples were collected representing different levels, from rock to soil. The samples were analyzed by X-ray diffraction, by the powder method on whole rock and in the fraction, As rochas da superfície terrestre estão permanentemente expostas à ação de agentes naturais, como a água, as variações de temperatura, os gases atmosféricos e a ação dos seres vivos. Dentre a ação dos seres vivos, nos centros urbanos destaca-se a ação antrópica, que por vezes acaba por degradar os recursos naturais. Nesse contexto, entender os processos de transformação das rochas, para que se possa compreender a gênese e evolução dos solos, e assim, aperfeiçoar métodos para sua recuperação, torna-se imprescindível. Este estudo foi desenvolvido em um perfil de alteração de rocha granítica localizado na área urbana de Porto Alegre, onde foram coletadas oito amostras representativas dos diferentes níveis, da rocha ao solo. As amostras foram analisadas por difratometria de raios X (DRX), pelo método do pó na rocha total e na fração < 4 μm. A composição química foi determinada por fluorescência de raios X (FRX). Fragmentos das amostras foram observados no microscópio eletrônico de varredura (elétrons secundários) e no microscópio ótico. Os estudos mineralógicos e petrográficos mostraram a existência de pequena variação composicional vertical no perfil, essencialmente composto por quartzo, feldspato alcalino e caolinita, identificados em todos os horizontes, e ilita/biotita identificadas nos horizontes saprolíticos. As análises através de imagens de elétrons secundários permitiram identificar ainda a presença de haloisita. A exsudação de ferro pelas lamelas da biotita observada no microscópio óptico marca o início da alteração supergênica no granito. Os dados de FRX mostram que a escolha do elemento imóvel de referência para verificar a existência ou não de enriquecimento dos elementos ao longo do perfil é muito importante, pois neste trabalho verificou-se que o alumínio tem um comportamento móvel, provavelmente associado às condições de acidez do solo.

International audience; Pas de résumé

The area of Camaquã Mines is part of the camaquã basin, which has NE-NW directions and is filled out by silliciclastics sediments interbedded with volcanic rocks. Chlorite is the most abundant clay mineral in the area and appears in high amount in the halos of hydrothermal alteration present in the host's mineralization rocks. This work consists on the chlorite's petrologic, chemical and structural characterization, supplying important information on different processes and formation conditions of the hydrothermal environment. The following procedures were made: optical petrography, X-ray diffraction, difractograms modeling through the Reynolds Newmod© program, and scanning electron microscopy ( secondary electrons and microanalysis - EDS) in representative samples of the different identified hydrothermal alteration zones. Chlorites are present under three different tendencies: Chlorite I takes place with a pervasive aspect over the matrix rocks located near the mineralized veins; it is classified as Fe-chlinoclore, presents fraction ˂1 µm predominance of plytype IIb and a Mg2+ enrichment in the fraction of ˂10 µm predominance of polytype Ib (90°) and Fetotal enrichment. Chlorite II occurs as veins filling out small fractures; it is classified as Chamosite and presents structural polytype IIb. Chlorite III occurs altering detrital minerals; it is classified as Mg-chamosite. The variation on the amount of Fe of the chlorites generated over the hydrothermal processes ( Chlorite I ˂10 µm and Chlorite II) indicates the occurrence of at least two pulses in the process of the hydrothermal alteration: one is responsible for the great matrix and clasts alternation and the other one for the generation of the late veins. The variation in the amount of Fetotal of the two different responsible fluids for the crystallization of the chlorites is was quite more enriched in iron than the early fluid that crystallized Chlorite I ˂10 µm., A região das Minas do Camaquã é a parte constituinte da Bacia do Camaquã, a qual possui direção NE-NW e é preenchida por sedimentos siliciclásticos intercalados com rochas vulcânicas. A clorita é o argilomineral mais abundante da área, ocorrendo em grande quantidade nos halos de alteração hidrotermal presentes nas rochas encaixantes nas mineralizações na Mina Uruguai. Este trabalho consiste na caracterização petrológica, química e estrutural das cloritas, que fornece importante informações sobre diferentes processos e condições de formação do ambiente hidrotermal. Para isso se realizou petrografia óptica, difratometria de raios X, modelamento dos difratogramas através do programa Reynolds Newmod © e microscopia eletrônica de varredura (elétrons secundários e micro-análises por EDS) em amostras representativas de diferentes zonas de alteração hidrotermal identificadas. As cloritas se apresentam com três diferentes tendências: a Clorita I ocorre com aspecto pervasivo sobre matriz das rochas localizadas próximos aos filões mineralizados; é classificada como Fe-clinocloro, apresenta na fração ˂1 µm predominância do politipo IIb e um enriquecimento em Mg2+ e na fração ˂10 µm predominância do politipo Ib (90°) e enriquecimento em Fetotal . A Clorita II ocorre com veios preenchendo pequenas fraturas; é classificada como Chamosita e apresenta politipo estrutural IIb. A Clorita III ocorre alterando minerais detríticos sendo classificada como Mg-Chamosita. A variação na quantidade de ferro das cloritas geradas por processos hidrotermais ( Clorita I ˂10 µm e Clorita II) fornece indícios da ocorrência de pelo menos dois pulsos no processo de alteração hidrotermal: um responsável pela intensa alteração da matriz e dos clastos das rochas e outro responsável pela geração de veios tardios. A variação na quantidade Fetotal dos dois diferentes fluidos responsáveis pela cristalização das cloritas fica evidenciada pela associação de co-genecidade da Clorita II com a hematita, mostrando que o fluido final foi muito mais enriquecido em ferro que o fluido precoce cristalizou a Clorita I ˂10 µm.

International audience

Les roches volcanogéniques de la Mine de Seival appartiennent à la Formation Hilário du Bassin de Camaquã, d’âge Néoprotérozoique. Cette zone contient six mines inactives avec diverses zones de prospection du cuivre et de l’argent. Les minéralisations semblent associées à un contrôle structural en régime cassant. La compréhension des transformations chimiques liées à l’hydrothermalisme et associées aux paléo-contraintes est assez méconnue dans la région. L'étude présentée fut basée sur l'obtention de mesures structurales pour comprendre les contraintes et leur cinématique dans la région, associée aux transformations chimiques des minéraux des phases magmatiques et hydrothermales de haute et basse températures. Fractures et les minéralisations montrent une direction principale N40-60°E/70-88°NW souvent associées à des veines de calcite. Les structures profondes de direction NW-SE et NE-SW étaient liées aux filons volcaniques, aux circulations de fluides hydrothermaux et aux minéralisations associées. Une modélisation thermodynamique utilisant les différentes phases minérales (magmatiques et hydrothermales) a permis d’estimer les températures de haute (tardi-magmatique) et basse (altération hydrothermale). L’albitisation (650 à 250°C) s’est produite en association avec une chloritisation (312 à 120°C). La déstabilisation des sulfures primaires (pyrite et chalcopyrite) dans les sulfures riches en cuivre (bornite-chalcocite) était associée à des interstratifiés de chlorite/smectite à des températures d'environ 250 à 50°C. Ces mêmes interstratifiés chlorite/smectite indiquent des zones riches en cuivre. Les événements plus tardifs (

Le District Minier de Lavras do Sul (Au-Cu ± Pb, Zn, Ag) e la Mina du Seival est associée à une altération hydrothermale et de minéralisation hébergé par des séquences volcaniques-sédimentaires et et des intrusions plutoniques Néoprotérozoïques. Le système plutôno-volcanique de Lavras do Sul est liée à l'évolution de la Bacia do Camaquã. Cette bassin avec l'âge Ordovicien - Ediacaran est situé dans la partie centrale de Rio Grande do Sul - Sud du Brésil. La séquence volcano-sédimentaire accumulée dans la Bacia do Camaquã est liée aux des activités plutoniques (Lavras do Sul et Caçapava do Sul et volcano-magmatique (Formação Hilário) dans un contexte tectonique post-collisionnel. L'activité plutonique et volcanique produit métamorphisme de contact et de la circulation des fluides épithermaux avec des dépôts métalliques. Les études avec l’isotopes stables (C-O-S) dans les sulfure, sulfates et les gangue favoriser la détermination de la source, température, interaction fluide / rock associé au processus de dépôt de minerai. L'altération hydrothermale, la distribution des métaux et le dépôt subséquent de minerai par des processus épithermal ont été rapportés dans cette région dans des études datant du début du siècle. Les associations de minéraux de haute et basse sulfuration ont été associés à l'évolution d'un système magmatique post-collisionnel. Cette étude se concentre sur la région de la Mina do Seival (MS) situé dans la partie nord-est de la ville de Lavras do Sul qui est hébergé par la formation de roches vulcanogênique de la Formação Hilário. Ces mines de Cu étaient importants au cours de la première moitié du XXème siècle, et l'exploitation minière ajoutés résultats scientifiques dans plusieurs études d'expression régionale. La MS comprend un certain nombre de petits dépôts de 0,6 à 2,5% en poids de Cu et jusqu'à 70 ppm de Ag confinés dans la succession volcanogênica Hilário. La minéralisation est principalement sous la forme de bornite, chalcocite, covellite et minéraux supergènes, par exemple l'abondance de malachite. Il est principalement contrôlé par des fractures et des failles avec NE dans les roches extrusives et sousvolcanique. Le minerai riche em cuivre se propage habituellement ou remplir de petites cavités et fractures formant des halos d'altération. Les minéralisations sont associées à gangue carbonate, barytine et minéraux argileux dans les alteration argílique et propilítique. O Distrito Mineiro de Lavras do Sul (Au-Cu ± Pb, Zn, Ag) e a Mina do Seival estão associado a alteração hidrotermal e mineralizações hospedadas por seqüências vulcano-sedimentares Neoproterozóicas e intrusões ígneas. O sistema plutôno-vulcânico de Lavras do Sul esta intimamente associado a evolução da Bacia do Camaquã. Esta bacia de idade Ordoviciana - Ediacarana está localizada na parte central do Rio Grande do Sul, no sul do Brasil. A seqüência vulcano-sedimentar acumulada na Bacia de Camaquã está relacionada a: i) atividades plutônicas - Lavras do Sul e Caçapava do Sul; ii) vulcâno-magmáticas na Formação Hilário. Ambas ocorrem em um contexto tectônico pós-colisional. As atividades plutônicas e vulcânicas produziram metamorfismo de contato e circulação de fluidos epitermais com depósitos metálicos. Os estudos com isótopos estáveis (C-O-S) em sulfetos, sulfatos e ganga auxiliam na determinação de fonte, temperatura e interação fluido / rocha associado ao processo de deposição do minério. A alteração hidrotermal, a distribuição de metais e a conseqüente deposição de minério por processos epitermais já foram relatadas nesta região em trabalhos que datam do início do século. As associações de minerais de alta e baixa sulfetação têm sido associadas a evolução de um sistema magmático-tectônico pós-colisional. Este estudo concentra-se na região da Mina do Seival (MS), localizada na porção NE da cidade de Lavras do Sul que é hospedada por rochas vulcanogênicas da Formação Hilário. Estas minas foram importantes minas de Cu na região durante a primeira metade do século XX, e a exploração mineral adicionou resultados científicos em vários estudos de expressão regional. A MS compreende um conjunto de pequenos depósitos com 0,6 a 2,5% em peso de Cu e até 70 ppm de Ag confinados na sucessão volcanogênica Hilário. A mineralização é principalmente na forma de bornita, calcocite, covelita e em fases supergênicas posteriores, como exemplo a abundância de malaquita. É predominantemente controlada por fraturas e falhas com direção NE nas rochas extrusivas e sub-vulcânicas. O minério rico em cobre é geralmente disseminado ou preenche pequenas cavidades e fraturas formando halos de alteração. As mineralizações estão associadas a uma ganga de carbonato, barita e minerais argilosos, na forma de alterações argílica e propilítica. The Lavras do Sul Mining District (Au-Cu ± Pb, Zn, Ag) and Seival Mine is associated to hydrothermal alteration and mineralization hosted by Neoproterozoic volcano-sedimentary sequences and igneous intrusions. The plutono-volcanic system of Lavras do Sul is closely associated with the evolution of the Camaquã Basin. This Ordovician - Ediacaran basin is located in the central part of Rio Grande do Sul, in southern Brazil. The accumulated volcano-sedimentary sequence in the Camaquã Basin is related to: i) plutonic activities - Lavras do Sul and Caçapava do Sul and; ii) volcano-magmatic in the Hilario Formation. Both of them occur in a postcollision tectonic context. The plutonic and volcanic activities produced contact metamorphism and circulation of epithermal fluids with metallic deposits. The stable isotopes studies (C-O-S) of sulfides, sulphates and gangue assist the determination of source, temperature, fluid / rock interaction associated with the ore deposition process. The hydrothermal alteration, the distribution of metals and the consequent deposition of ore by epithermal processes have already been reported in this region in works that date from the beginning of the century. The associations of high and low sulfidation minerals have been associated with the evolution of a post-collision magmatic-tectonic system. This study focuses on the Seival Mine (MS) region, located in the NE portion of Lavras do Sul city which is hosted by volcanogenic rocks of the Hilário Formation. These mines were important Cu mines in the region during the first half of the twentieth century, and mineral exploration added scientific results in regional studies. The MS comprises a set of small deposits with 0.6 to 2.5% by weight of Cu and up to 70 ppm of Ag confined in the Hilário Formation volcanogenic sequence. The mineralization is mainly in the form of bornite, chalcocite, covellite and in later supergenic phases, as an example the abundance of malachite. It is predominantly controlled by fractures and faults with NE direction in the extrusive and sub-volcanic rocks. Copper-rich ore is usually disseminated or fills small cavities and fractures forming alteration halos. The mineralizations are associated to a gangue of carbonate, barite and clay minerals, within argilic and propilithic alterations.