Les circulations de fluides aux interfaces entres les socles cristallins et leur couvertures sédimentaires sont des événements majeurs de transferts élémentaires dans la croûte. Dans de nombreux contextes, des fluides de bassins peuvent pénétrer dans les socles de faible perméabilité, interagir avec eux, y lessiver des métaux, et donner lieu à des concentrations métalliques, notamment en Pb, Zn, Cu, Ag et U. Les gisements d’uranium de type discordance du bassin d’âge protérozoïque de l’Athabasca (Canada), sont des témoins essentiels de ce type de circulations de fluides, et sont des objets modèles pour comprendre les mécanismes et les conséquences de tels événements. Les inclusions fluides permettent d’échantillonner et d’analyser directement les paléofluides. Malgré les difficultés d’analyse, ces objets de taille micrométriques apportent des informations importantes sur les propriétés des fluides. Les techniques d’analyse disponibles (microthermométrie, LA-ICP-MS, écrasement-lessivage, écrasement sous vide) permettent de reconstituer la température, la pression, la composition chimique détaillée des fluides, dont les teneurs en métaux, ainsi que la composition isotopique de l’hydrogène de l’eau, du chlore et du carbone du CO2 dissous. De plus, l’analyse de la composition isotopique de l’oxygène et du carbone des minéraux dans lesquels sont piégées les inclusions fluides apporte des informations complémentaires sur la température des fluides et les interactions fluides-roches. Cette approche a été utilisée sur six gisements d’uranium du Bassin de l’Athabasca, et a permis d’apporter les résultats suivants, potentiellement généralisables à l’ensemble du bassin. (1) Deux saumures, une calcique et une sodique ont circulé et se sont mélangées à la base du bassin et dans le socle au cours de la formation des gisements à environ 150 ± 30°C. (2) Ces deux saumures ont transporté de l’uranium, dont les concentrations exceptionnelles et très hétérogènes (entre 0.2 et 600 ppm) indiquent qu’il a été lessivé dans le socle. (3) Ces saumures ont une origine commune et se sont formées essentiellement par évaporation en surface de l’eau de mer, et mélange avec des fluides issus de la dissolution de minéraux évaporitiques. (4) La saumure calcique s’est formée par interaction entre la saumure sodique et les roches du socle. (5) Les interactions des saumures avec les minéraux et le graphite du socle, la radiolyse de l’eau, et la synthèse de bitumes ont contrôlé la composition isotopique en oxygène, hydrogène et carbone de ces saumures. / Fluid circulations between crystalline basements and their sedimentary covers are major events for element transfer in the crust. In numerous settings, basinal fluids penetrate the low-permeability basement, interact with basement lithologies, leach metals, leading to metal concentrations, notably Pb, Zn, Cu, Ag and U. Unconformity-related uranium deposits from the Proterozoic Athabasca Basin (Canada) are crucial witnesses and useful tools for the understanding of mechanisms and consequences of such fluid events. Fluid inclusions allow us to directly sample and analyze paleofluids. Despite analytical difficulties, these micrometer size objects provide key information on fluid properties. Available analytical techniques (microthermometry, LA-ICP-MS, crush-leach, in-vacuo crushing) provide reconstruction of temperature, pressure, detailed fluid chemistry, including metal concentrations, as well as isotopic composition of water hydrogen, chlorine and of dissolved CO2 carbon. In addition, analysis of isotopic composition of oxygen and carbon from minerals in which fluid inclusions are trapped provide supplementary information on fluid temperatures and fluid-rock interactions. This approach was used on six uranium deposits from the Athabasca Basin and provided the following results, which can be potentially generalized to the entire basin. (1) Two brines, a calcium-rich brine and a sodium-rich brine have circulated and mixed at the base of the basin and in the basement at the time of formation of uranium deposits, at temperature close to 150 ± 30°C. (2) Both brines have transported uranium, whose exceptional and highly heterogeneous concentrations (0.2 to 600 ppm) indicate that it was leached in the basement. (3) Both brines share a common origin and were formed mainly by surface evaporation of seawater and mixing with fluids originating from dissolution of evaporitic minerals. (4) The calcium-rich brine was formed by interaction between the sodium-rich brine and basement lithologies. (5) Interaction with basement minerals and graphite, water radiolysis, and bitumen synthesis were the main controls on the oxygen, hydrogen and carbon isotopic composition of brines.

Nenhuma / A Província Uranífera de Lagoa Real (PULR) constitui a melhor conhecida e a mais importante ocorrência de urânio atualmente no Brasil. Abrange uma área de 1200 Km2 e está localizada na região centro-sul do Estado da Bahia. Na PULR, são conhecidas 34 áreas mineralizadas em urânio, distribuídas aproximadamente ao longo de uma faixa orientada N-S com cerca de 30 km de comprimento por 5 km de largura. No extremo norte da região, situa-se a Jazida Cachoeira, única jazida de urânio em fase de produção no Brasil e na América Latina, atualmente sendo lavrada a céu aberto. A jazida apresenta uma extensão de 420 metros na direção noroeste e uma largura de aproximadamente 250 metros. Nessa jazida foram individualizados três corpos principais de minério. As amostras utilizadas neste estudo foram coletadas no corpo 3 da jazida. A mineralização uranífera na PULR está associada às rochas ricas em albita denominadas albititos que são rochas constituídas de plagioclásio, de composição albita a albita-oligoclásio, em porcentagem volumétrica estimada igual ou superior a 70%. Ocorrem ainda, como minerais essenciais: piroxênio, granada, anfibólio e biotita. Os minerais acessórios mais freqüentes são: titanita, apatita, zircão, allanita, magnetita e hematita. Carbonato e fluorita também podem ser observados. O objetivo do trabalho é o detalhamento da caracterização mineralógica e cristaloquímica dos albititos mineralizados e não mineralizados da Jazida Cachoeira, procurando-se pesquisar possíveis diferenças entre eles. Os principais minerais constituintes dos albititos desta jazida foram, portanto, estudados aplicando-se as seguintes técnicas: Difratometria de raios X, Espectroscopia vibracional de absorção no infravermelho, Análise Térmica, Microssonda Eletrônica, além de microscopia óptica convencional. Além desses minerais, foram também estudados microclina (variedade amazonita), natroapofilita, wollastonita e minerais secundários de urânio observados na mesma Jazida (autunita e tyuyamunita). Durante a primeira etapa dos estudos foram realizadas as observações mesoscópicas e microscópicas das amostras. A seguir, foi efetuada a separação mineralógica dos minerais em função de suas características magnéticas e densimétricas, visando-se obter minerais limpos e puros. Esses foram, a seguir, preparados de acordo com a técnica a ser empregada. As técnicas analíticas utilizadas permitiram o entendimento da cristaloquímica dos minerais, obtendo-se resultados confiáveis a partir de pequenas quantidades de material (cerca de 10 mg). Além da identificação dos minerais e da determinação da sua composição, foram também obtidas informações sobre a presença de água nos minerais. A presença de wollastonita (CaSiO3) indica condições de formação sob elevadas pressões litostáticas, sem as quais haveria a liberação de CO2 para a atmosfera. A transformação do U6+ presente na uranila em U4+ incorporado na uraninita implica na oxidação do Fe2+ para Fe3+ que se incorpora na estrutura cristalina de vários minerais da paragênese da uraninita (granada, magnetita, aegirina-augita). Se estas transformações estiverem associadas a zonas de cisalhamento, essas poderão ser reativadas ao longo do tempo geológico. Isto revela que as rochas encaixantes das faixas mineralizadas da PULR são mais antigas que a mineralização e que as futuras prospecções de urânio devem se localizar nas faixas de cisalhamento. O trabalho permitiu a descrição de tyuyamunita pela primeira vez no âmbito da PULR. / The Lagoa Real uranium province is presently by far the most important and best known uranium occurrence in Brazil. With an area of 1,200 Km2 it is located in centralsouthern part of Bahia State. The 34 deposits or prospects are distributed within a N-S 30 x 5 Km area. The Cachoeira open pit mine is in the northern part of the province and is the sole uranium mine in production in Brazil and South America as well. The mine has an area of 420 x 250 m stretching in northwestern direction. Three main mineralized orebodies have been identified. The samples studied were all collected in the orebody #3. The uranium mineralization is hosted by albitites, a rock with over 70% of albite and/or oligoclase. Pyroxene, garnet, amphibole, and biotite are the other essential minerals. Titanite, apatite, zircon, allanite, magnetite, and hematite are the accessory minerals besides carbonate and fluorite. The mineralogical and crystallochemical features of the main albitites minerals were investigated, looking for possible differences and characteristics between uraniferous and barren rocks. The following analytical techniques were applied during the work: X ray diffraction, Infrared spectroscopy, thermal analysis, microprobe and also optical microscopy. Besides albitites minerals, microcline (amazonite), natroapophyllite, wollastonite and oxidized uranium mineral (autunite and tyuyamunite) were also studied. This is also the first description of tyuyamunite in the Lagoa Real uranium province. All these minerals are from the Cachoeira open pit mine. The studying process started with mesoscopic and microscopic (thin sections) observations. Next, clean and pure fractions of each mineral were obtained using magnetic and/or bromoform separation . Using tiny amounts of each mineral (~10mg) the analytical methods used permitted the determination not only of their composition, including the water content, but the comprehension of crystallochemical characteristics as well. The presence of wollastonite indicates high hydrostatic pressure conditions which prevents the CO2 liberation to the atmosphere. The reduction process of U6+ to U4+ leading to the uraninite deposition occurs simultaneously with the oxidation of Fe2+ to Fe3+ which is incorporated in the crystalline structure of garnet, hematite, and aegirine-augite. As these transformations seem to be related to shear zones, it may indicate an epigenetic model for the U mineralization. The mineral tyuyamunite was described for the first time in the PULR.

A Jazida do Engenho (anomalia 09) está situada ao norte da Província Uranífera de Lagoa Real. A mineralização está associada aos albititos, rochas constituídas de plagioclásio, de composição albita a albita-oligoclásio, em porcentagem volumétrica igual ou superior a 70%. Também ocorrem epidositos mineralizados. Os minerais essenciais do albitito são piroxênio, granada, albita, anfibólio, e biotita. Neste trabalho foi estudada, por inclusões fluidas, boa parte dos minerais (piroxênio, granada, plagioclásio, titanita, epidoto) que constituem a seqüência mineralógica associada à mineralizações uraníferas dos albititos desta jazida. Os fluidos associados a piroxênio, granada e epidoto, aquo-salinos, primários e sem fases carbônicas apresentam características semelhantes, com leves variações. Todos apresentam média a alta salinidade (de 14 a 18% equivalente em peso de NaCl), onde os maiores valores correspondem ao piroxênio e os menores à granadas e epidotos. Os fluidos associados ao metassomatismo sódico, que gerou o plagioclásio albítico nos albititos, embora sejam aquo-salinos e sem fases carbônicas, apresentam salinidades muito inferiores às observadas no piroxênio, granada e epidoto, sugerindo processo de diluição bem mais intensos. Desta maneira, os fluidos da anomalia 09 apresentam uma diluição no sentido das fases minerais mais recentes. Os resultados sugerem que os processos de fomação do piroxênio ocorreram sob condições de pressão equivalente a 3,5 kbar que corresponde a profundidades de aproximadamente 10 km. Entretanto, a dilatação observada nas IF da albita durante o aquecimento, originaram uma dispersão nas medidas de Th, tornando pouco confiáveis os cálculos de pressão para esse mineral. A microscopia de IF em plagioclásios dos gnaisses (encaixantes dos albititos) sugere que, provavelmente, haveria fluidos carbônicos primários associados a esses minerais. Os fluidos com CO2 que aparecem nos gnaisses talvez também estejam presentes nos albititos, provavelmente como fluidos tardios ou intergranulares. Esta suposição baseia-se no fato de ter sido encontrado (durante os estudos de esmagamento nos albititos) indícios da presença de gases carbônicos. Estas tendências sugerem a ocorrência de duas etapas de albitização no setor de Lagoa Real: um associado a fluido composto por H2O + CO2 + sais (na encaixante gnáissica) e outro (no albitito) formado por uma fase aquo-salina. Os dados obtidos neste trabalho sugerem que, provavelmente, o Brasiliano foi um evento térmico sem um fluido predominante associado, pelo menos no setor de Lagoa Real. Do contrário, esse fluido deveria estar presente nos minerais da paragênese mineral. Finalmente, os dados obtidos na Jazida do Engenho permitiram verificar a ocorrência de um quadro de fluidos que apresentam variações composicionais em, pelo menos, três estágios diferentes: Piroxênio magmático → Px metamórfico associado a urânio → albita (poligonizada) associada a urânio, faltando posicionar o fluido associado à albita precoce. / The Engenho deposit (anomaly 09) is south-eastern from Cachoeira Mine (anomaly 13), in the northern part of the Province. The uranium mineralization is associated to albitites (over 70% of albite/oligoclase). Epidosites with uranium may also occur. The albitite main minerals are pyroxene, garnet, albite/oligoclase feldspar, amphibole and biotite. Pyroxene, garnet, plagioclase, titanite and epidote are the minerals associated to the uranium mineralization. The fluids related to pyroxene, garnet and epidote are aqueous-saline, primary and with no carbonic phases and are constant, with small variations. They all present medium to high salinity (14 to 18wt% NaCl eq.), the higher values being related to pyroxene and the lower ones related to garnet and epidote. The fluids associated to albite/oligoclase, although aquo-saline and with no carbonic phases, show salinities much lower than in pyroxene, garnet and epidote, suggesting a intense dilution process indicating dilution toward the later minerals phases. The data suggest the pyroxene formation process occurring under a 3,5 kbar pressure condition which corresponds to approximately 10km depth. The dispersion on Th in albites, due probably to the overheating and non elastic increase in volume, precluded a reliable pressure calculation. The IFs microscopy in plagioclase gneiss (albitites host-rocks) suggests the probability of primary carbonic fluids associated to these minerals. The fluids with CO2 showed in the gneiss maybe also be present in the albitites, probably as late or intergranular fluids. This assumption is based on the fact that signs of carbonic gases were shown during crushing tests. These tendencies suggest the occurrence of two albitization phases in this Lagoa Real area: one associated to a fluid composed by H2O + CO2 + salts (in the gneiss host) and another (in the albitite) formed by an aqueous-saline phase. The data indicate the Brasiliano event as a thermal event without a predominant fluid associated, at least in this Lagoa Real area. Otherwise, the presence of this fluid should be present in the mineral paragenesis. Finally, the data from the Engenho deposit indicate the occurrence of fluids showing compositional variations in, at least, three different stages: magmatic pyroxene → metamorphic pyroxene associated to uranium → albite (recristalized) associated to uranium. The place of the aqueous-carbonic fluid associated to previous albite is still unknown.

Nenhuma / Diversos trabalhos na literatura têm utilizado análises de U-Th-Pb obtidas por microssonda eletrônica para a datação química de episódios de fechamento do sistema U-Th-Pb em minerais. Tais episódios podem ser de natureza metamórfica, termal, intempérica ou ainda estar ligados a processos de fissão natural. Diferentes minerais de urânio e/ou tório contendo chumbo radiogênico têm sido analisados com esse propósito. Na região de Lagoa Real (BA) situa-se a única mina de urânio em atividade na América Latina, controlada pela INB (Indústrias Nucleares do Brasil). Os albititos, rochas portadoras de urânio exploradas nessa mina, guardam diversos minerais portadores de urânio e/ou tório tais como uraninita, titanita, zircão, epidoto, allanita-Ce, uranofana e autunita. Ao longo do tempo, diferentes episódios geológicos afetaram heterogeneamente esses minerais. Nesta dissertação foram investigados titanita e zircão com teores variáveis de urânio e chumbo, através da datação química U-Th-Pb em microssonda eletrônica. Os dados obtidos para a titanita indicaram várias idades: 2052 80 Ma, idade aparente interpretada como a idade da cristalização magmática, bem como 1701 57 Ma, 1488 64 Ma, 1298 69 Ma, 1108 78 Ma e 978 58 Ma, idades aparentes interpretadas como resposta aos eventos hidrotermais sofridos pelo mineral. Os dados obtidos para o zircão não foram conclusivos. Além desses minerais, foram datadas uranofanas ricas em ferro e chumbo radiogênico que revelaram também cinco idades aparentes diferentes, muito próximas às mencionadas para a titanita. Essas uranofanas confirmam as múltiplas mobilizações de urânio e chumbo ao longo do Proterozóico, ocorridas durante os referidos eventos hidrotermais. Datações em allanita-Ce mostraram cinco idades aparentes. Por essas idades estarem acima da idade da Terra, elas permitem sugerir que o Pb mobilizado durante os eventos hidrotermais (em número de cinco, indicados pela titanita) estaria sendo sucessivamente incorporado na allanita-Ce e que esse mineral já existiria, pelo menos em parte, concomitantemente com a titanita. Os dados obtidos em epidoto mostraram uma única idade aparente, também acima da idade da Terra, que parece indicar incorporação de chumbo em um único evento, provavelmente o Brasiliano, apontando para sua formação mais tardia na rocha. Essa idade anômala, apesar de não indicar um momento geológico real, aponta para um episódio de incorporação de chumbo pelo epidoto. As uraninitas, principalmente aquelas associadas ao epidoto, apontaram uma idade aparente de 489,3 7,0 Ma, indicativa da influência do evento Brasiliano na região de Lagoa Real. O panorama geocronológico apresentado questiona modelos metassomáticos precedentes para os albititos de Lagoa Real e a mineralização de urânio. Juntamente com recentes dados U-Pb por LA-ICP-MS da literatura, as idades aparentes dos minerais dos albititos sugerem a cristalização do protólito, um sienito sódico uranífero, há aproximadamente 2,0 Ga. Subseqüente metamorfismo há 1,9 Ga parece ter ocorrido durante os estados finais da orogênese orosiriana, quando uma primeira geração de uraninitas foi formada. Múltiplas mobilizações de urânio e chumbo promovidas por cinco eventos hidrotermais (em torno 1,7 Ga, 1,5 Ga, 1,3 Ga, 1,1 Ga e 1,0 Ga) foram detectadas em tais rochas. Como já dito, uma provável geração de um segundo grupo de uraninitas e/ou reinício da contagem do tempo pelo relógio U-Pb de uraninitas mais antigas durante um segundo evento orogênico, por volta de 0,5 Ga (Brasiliano), também ocorreram. A uranofana e a autunita apresentaram idades aparentes de 26,7 Ma e 10,9 Ma, respectivamente, indicativas do intemperismo recente. / Different works in literature have used U-Th-Pb electron microprobe analyses for the chemical dating of U-Th-Pb system closing episodes in minerals. These episodes could have either metamorphic, thermal, and weathering nature or could be related to natural fission processes. Different thorium and uranium-bearing minerals which contain radiogenic lead have been analyzed for this purpose. At the region of Lagoa Real (BA) is located the only active uranium mine in Latin America, controlled by INB (Nuclear Industries of Brazil). The albitites, uraniferous rocks explored in this mine, preserve a lot of thorium and/or uraniumbearing minerals like uraninite, titanite, zircon, epidote, allanite-Ce, uranophane, and autunite. Different geologic episodes should have affected these minerals along time. At this dissertation, zircon and titanite with different uranium and lead contents have been examined by U-Th-Pb electron microprobe dating. The data acquired for zircon had not been conclusive. The data obtained for titanite indicated some ages: 2052 80 Ma, interpreted as the magmatic crystallization apparent age as well as 1701 57 Ma, 1488 64 Ma, 1298 69 Ma, 1108 78 Ma and the 978 58 Ma, interpreted as response to hydrothermal events. In addition to these minerals, Fe and Pb rich uranophanes had been dated, which shown five different ages, close to the ones mentioned for titanite. These uranophanes are the record of multiple lead and uranium mobilizations during Proterozoic, which took place throughout hydrothermal events. Allanite-Ce presented five ages which are older than earths age. They suggest that the Pb mobilized during the hydrothermal events (in number of five, indicated by the titanite) was successively incorporated in the allanite-Ce structure and that this mineral already would exist, at least in part, concomitantly with titanite. The epidote data had shown only one very old anomalous age, which may indicate lead incorporation in only one event, probably the Brasiliano. Uraninites, mainly those related to epidotes, indicated na apparent age of 489.3 7.0 Ma, which shows the Brasiliano event action over Lagoa Real region. The geochronological scenario presented questions previous metasomatic models for Lagoa Real albitites and uranium mineralization. Along with recent LA-ICP-MS U-Pb data from literature, the apparent mineral ages suggest an uraniferous sodic syenitic protolith cristallization 2.0 Ga ago. A 1.9 Ga subsequent metamorphism took place during final moments of the orosirian orogenesis, when a first uraninite group was generated. Uranium and lead multiple mobilizations yielded by five hydrothermal events (ca 1.7 Ga, 1.5 Ga, 1.3 Ga, 1.1 Ga, and 1.0 Ga) were detected in albitites. As metioned, another uraninite group and/or reset of older uraninite U-Pb system during Brasiliano event also took place. Ordinary uranophane and autunite had presented 26,7 Ma and 10,9 Ma ages respectively, indicative of recent weathering.

O Brasil possui atualmente a sétima maior reserva de urânio do mundo. A Província Uranífera de Lagoa Real (PULR) está localizada na região centro-sul do estado da Bahia. Ao longo de uma estrutura helicoidal, com orientação norte-sul, de aproximadamente 33 km de extensão, estão concentradas mais de 30 anomalias de urânio. A anomalia 03 (AN03), denominada Lagoa da Rabicha, está localizada na região centro-sul dessa estrutura e foi descoberta e mapeada pela NUCLEBRÁS (Empresas Nucleares Brasileiras), na década de 80. A Mina da Cachoeira (AN13), localizada na região norte da PULR, é atualmente a única jazida de urânio em fase de produção no Brasil e na América do Sul. Tendo em vista o crescimento da demanda energética no Brasil e no mundo, estudos e pesquisas petrogenéticas aplicadas ao estudo de jazidas de urânio são relevantes tanto para que se possa aumentar seu potencial de prospecção quanto para auxiliar na possível descoberta de futuras ocorrências. Nos últimos anos, análises de inclusões fluidas (IF) vêm sendo amplamente utilizadas no estudo da gênese das jazidas de urânio da PULR e ainda assim existem dúvidas sobre a metalogênese das mineralizações uraníferas. Nesse contexto este trabalho teve como principal objetivo estudar os minerais e fluidos associados a um setor representativo dos albititos uraníferos (rochas portadoras de mineralização uranífera) e rochas encaixantes gnáissicas da Jazida Lagoa da Rabicha. Dessa forma, procurou-se elaborar um quadro geral dos fluidos encontrados nesse setor, estabelecendo uma comparação com estudos realizados por diversos autores em outros setores de Lagoa Real, tentando-se mostrar a evolução das soluções, ao tempo que ocorria a precipitação de uraninita. As metodologias de trabalho utilizadas foram petrografia, a microssonda eletrônica (ME), a ablação a laser (LA-ICP-MS) e os estudos de inclusões fluidas (IF). Foram estudados os fluidos presentes no piroxênio, granada e plagioclásio, constituintes da sequência mineralógica dessa jazida. O fluido mais antigo foi encontrado no piroxênio aegirina-augita, de composição aquo-salina (sem fases carbônicas) contendo Ca, Fe e Mg, salinidades de 9-13 wt% NaCl e temperatura de homogeneização entre 220 e 290 C. Concomitantemente ocorreu uma remobilização e precipitação de uraninita. Essa remobilização e precipitação de urânio também foi registrada nas granadas, originadas a partir de fluidos aquo-salinos com Na, Mg, Sr, Ba e Pb, sob condições de temperatura e salinidade próximas as do piroxênio. Nas amostras estudadas não foi encontrado o piroxênio diopsídico precoce (magmático), com fluidos aquo-salinos [H2O + Na, Rb, Ba (16%wt NaCl)], estudado por Chaves et al (2007) na Jazida da Cachoeira (Anomalia 13, norte de Lagoa Real). Isto provavelmente é consequência de que a intensidade do metamorfismo no setor da Rabicha foi maior do que na Cachoeira, preservando assim muito pouco da textura magmática pré-existente. Salienta-se que é notória a ocorrência de uma diluição dos fluidos, presentes nos minerais piroxênio e granada, quando se observa as jazidas no sentido N→S (AN13→AN09→AN03). Também foi verificado que o volume de anfibólios aumenta no centro e norte de Lagoa Real. A precipitação do plagioclásio (que forma a estrutura dos albititos) ocorreu posteriormente, a partir de um fluido bem menos salino, provavelmente com pouco ou nenhum CO2 associado. Uma remobilização e precipitação de urânio também esta associada a esta fase. Nas amostras estudadas não foram encontrados carbonatos. Portanto, não foi possível cruzar dados com dados preliminares obtidos por Fuzikawa (1982) em fluidos primários de carbonatos, que evidenciaram a presença de soluções aquo-carbônicas (H2O + CO2 +CH4), que sugerem condições redutoras para essa fase evolutiva. O estudo de inclusões fluidas nas encaixantes gnáissicas dos albititos foi focado nos plagioclásios, com o intuito de comparar as soluções associadas ao metassomatismo sódico que teria afetado corpos mineralizados e rochas hospedeiras. Nos gnaisses foi registrada a presença de fluidos aquo-carbônicos precoces de salinidade intermediária, associados aos plagioclásios precoces. Entretanto, as soluções que precipitaram os plagioclásios tardios eram de composição aquo-salina de baixa salinidade, equivalentes aquelas encontradas nos plagioclásios dos albititos. Fluidos tardios aquo-carbônicos foram encontrados em alguns cristais de quartzo da matriz gnáissica. A presença de CO2 foi verificada sistematicamente no quartzo de veios formados tardiamente, que cortam gnaisses e albititos, revelando condições oxidantes para os últimos estágios de precipitação mineral no setor da Rabicha. Sobre a presença de fluidos em todas as fases minerais estudadas os dados apresentados demonstram que o Evento Brasiliano não obliterou os fluidos pré-existentes. Entretanto, com exceção do plagioclásio precoce do gnaisse encaixante dos albititos, os fluidos aquo-carbônicos não são facilmente encontrados nos minerais precoces da paragênese. Isso pode ser explicado pelo fato de esse fluido ser anterior ao evento de deformação Brasiliano. Durante esse evento as inclusões contendo o CO2 dos minerais precoces poderiam ter crepitado devido à diferença de pressão, restando poucas evidências deste fluido nas rochas. Isto, aliado ao fato de não se ter encontrado um fluido característico associado ao Brasiliano, sugere que este evento deformacional deve ter sido predominantemente térmico, uma vez que fluidos anteriores ao evento foram preservados. / Brazil has now the seventh largest uranium reserve in the world. The Lagoa Real Uranium Province (PULR) is located in central-south region of Bahia State. Along a helical structure, north-south oriented, with approximately 33 km long, there are 34 known uranium mineralized areas. In its central-south portion is located anomaly 03 (AN03), named Lagoa da Rabicha, discovered and mapped by NUCLEBRÁS (Brazilian Nuclear Enterprises), in the 80s. The Cachoeira Mine (AN13), located in northern PULR, is currently the only uranium mine in production in Brazil and even in South America. Nowadays it is observed a growth in energy demand in Brazil and also worldwide and studies and research applied to the petrogenetic uranium deposits are relevant both to be able to increase their potential for exploration and to assist in the possible future occurrences discovery. In recent years, fluid inclusions analysis (FI) have been widely used to study the genesis of uranium deposits in PULR and even thought there are still doubts about the uranium mineralization metallogenesis at Lagoa Real. Therefore, this work aimed to study the minerals and fluids associated with Lagoa da Rabicha albitites uraniferous and gneissic host rocks. In this way it was prepared an overview of the fluids found in this sector, establishing a comparison with several authors studies in this and others Lagoa Real anomalies, trying to show the solutions evolution, at the same time that happened the uraninite precipitation. Petrography, electronic microprobe, laser ablation (LA-ICP-MS) and fluid inclusion studies were the applied methodologies. The fluids inclusions assemblages present in pyroxene, garnet and plagioclase, the main mineralogical constituents, were studied. The older fluid was found in aegirine-augite pyroxene and had aquo-saline composition (without carbonic phases) with Ca, Fe and Mg, 9-13 wt% NaCl salinities and homogenization temperatures between 220 and 290 C. Concomitantly, occurred a uraninite remobilization and precipitation. This uranium remobilization and precipitation was also registered in garnets, formed from aquo-salines fluids with Na, Mg, Sr, Ba and Pb, under temperatures and salinities conditions close to those of pyroxene. In the studied samples it was not found the precocious diopsidic pyroxene (magmatic), with aquo-salines fluids [H2O + Na, Rb, Ba (16%wt NaCl)], studies by Chaves et al (2007) in Cachoeira Mine (Anomaly 13, north of Lagoa Real). This is probably a consequence of a more intense metamorphism in the Rabicha sector when compared to Cachoeira Mine region, preserving very little the pre-existing magmatic texture. It is worthy to note that occurs a dilution of the fluids present in pyroxene and garnet, when the uranium occurrences are observed in the N→S direction (AN13→AN09→AN03). It was also observed that the amphibole volume increases in the center and north portion of Lagoa Real. The plagioclase precipitation (which forms the albitite structure) occurred lately from a less saline fluid, probably with little or no associated CO2. One uranium remobilization and precipitation is also associated to this phase. In the studied samples carbonate was not found. It was not possible to compare data with some preliminary data from Fuzikawa (1982) in primary fluids from carbonate, where the presence of aquo-carbonic solutions (H2O + CO2 +CH4) suggest reducing conditions for this evolutionary phase. The fluid inclusion studies in albitites host rocks were focused in plagioclase, in order to compare the solutions associated to the sodium metassomatism that would have affected the mineralized bodies and host rocks. In the gneisses it was registered the presence of precocious aquo-carbonic fluids with intermediate salinities, associated do precocious plagioclases. However, the solutions that precipitate the late plagioclase had aquo-saline composition with low salinity, similar to those found in plagioclase from albitites. Late aquo-carbonic fluids were found in some quartz grains in the gneissic matrix. The CO2 occurrence was systematically verified in lately formed quartz veins that cut gneisses and albitites, showing oxidizing conditions for the last mineral precipitation stages in the Rabicha sector. About the presence of fluids in all the studied mineral phases, the shown data demonstrate that the Brasiliano Event (Pan African Event) had not obliterated the pre-existing fluids. However, with exception to early plagioclase from gneiss albitite host rock, the aquo-carbonic fluids are not easily found in precocious minerals. This might be explained by the fact that this fluid is previous to the Brasiliano deformation event. During this event the inclusions containing the CO2 from the precocious minerals may have crepitated due to the pressure difference, remaining little evidence of this fluid in the rocks. This observation, associated to the fact that no characteristic fluid was found related to Brasiliano, suggest that this deformation event must have been predominantly thermal, since previous fluids were preserved.

Les principales cibles d'exploration pour les gisements d’uranium de type discordance du bassin d’Athabasca (Canada) sont les structures graphiteuses du socle. Toutes ces structures ne sont pourtant pas fertiles et elles présentent des histoires plus ou moins complexes de circulations fluides successives. Cette thèse propose de déconvoluer les caractéristiques propres à chaque évènement de circulations fluides par une étude multidisciplinaire focalisée sur l’exemple de l’environnement proche du gisement de Cigar Lake. Au cours de l’exhumation tardi-orogénique du socle, la formation de failles ductile-cassantes associées à une circulation intense de fluides à C-O-H-N a permis des enrichissements en graphite et une première évolution pétrophysique des zones endommagées. Ces structures du socle particulièrement fragilisées par la déformation cassante fini-Hudsonienne ont pu être réactivées après dépôt du bassin et devenir des lieux favorables à la convection de saumures sédimentaires. La circulation de saumures sodiques dans le socle a favorisé des interactions fluides-roches à l’origine de la solubilisation de l’uranium, d’altérations K-Mg et d’évolution de composition du fluide vers un pôle plus calcique de plus forte salinité. Enfin une méthodologie d’analyse intégrée des compositions élémentaires majeures, traces et isotopiques U-Pb-O sur oxydes d’uranium est proposée, permettant de déconvoluer les effets des évènements fluides ultérieurs sur la minéralisation primaire. Cinq évènements ont ainsi contribué aux caractéristiques actuelles du gisement de Cigar Lake : Un évènement primaire de circulation de saumures à 1290-1380 Ma, à l’origine de l’ensemble du stock d’uranium ; un événement de circulations fluides à ca. 900 Ma à l’échelle régionale qui n’est pas associé à une reprécipitation d’uranium mais a brechifié et perturbé la chimie des oxydes primaires ; deux évènements tardifs de circulations fluides à ca. 340 et 220 Ma qui ont significativement remobilisé le stock primaire d’uranium. Enfin un dernier épisode récent de circulation d’eaux météoriques est à nouveau à l’origine d’un changement de chimie des oxydes antérieurs et d’une remise à zéro des systèmes isotopiques / The main exploration targets for unconformity-related U deposits of the Athabasca Basin are the graphite-rich structures in the basement. But these are not necessarily fertile. They show distinct features expressing specific events of fluid circulations. This study aims, through a multidisciplinary approach, at unravelling the complex history of fluid flow events recorded in the vicinity of the Cigar Lake deposit. During the basement uplift, at the end of the Trans-Hudson Orogeny, the formation of ductile-brittle shear zones associated to the circulation of C-O-H-N fluids led to hydrothermal graphite enrichments and a petrophysical evolution of damages zones. These graphite-rich shear zones that were specifically weakened by the ante-Athabasca brittle reactivation have been reactivated once more after basin deposition allowing the formation of a developed damage zone especially favorable for sedimentary brine convection. Circulations of NaCl-rich brines in the basement led to brine-rock interactions, and subsequent uptake of uranium and other metals from the basement rocks. The latter have subsequently undergone strong K-Mg alteration whereas the NaCl dominated brines evolved toward a CaCl2-dominated composition with higher salinities. Finally, this thesis sets out an integrated methodology allowing to decipher the complex superimposed geochemical signatures of distinct fluid flow events on the primary uranium oxides. Five fluid flow events contributed to the present day state of the Cigar Lake deposit: a primary event of brine circulation occurred at 1290-1380 Ma and is at the origin of the main U stock; a second basin-scale event of fluid flow occurred at ca. 900 Ma, it brecciated and strongly disturbed the deposit; two later events of fluid flow strongly remobilized the deposit at ca. 340 and 220 Ma and greatly contributed to the actual state of the deposit. Finally a last, rather recent event of fluid flow was at the origin of strong chemical changes in the uranium oxides compositions and strong isotopic resetting

Les granites peralumineux sont les acteurs principaux de la différentiation de la croûte continentale et représentent un enjeu sociétal important car ils sont associés à de nombreux gisements métallifères. Dans la chaîne hercynienne européenne, la majorité des gisements hydrothermaux d'uranium (filons ou épisyenites) sont associés à des leucogranites peralumineux d'âge tardi-carbonifère. Ainsi dans le Massif armoricain, 20000 t d'uranium (U) (~20% de la production historique française), ont été extraites des gisements associés aux leucogranites de Mortagne, Pontivy et Guérande. L'objectif de ce travail est de mieux comprendre le cycle de l'uranium dans la chaîne hercynienne armoricaine depuis la source des leucogranites, leur évolution et leur mise en place dans la croûte supérieure jusqu'à leur lessivage par des fluides, la formation des gisements puis leur exhumation en sub-surface. Dans ce but, des données pétro-géochimiques, géochronologiques et thermochronologiques ont été obtenues sur les leucogranites de Guérande, Pontivy et leurs gisements d'uranium associés. Les leucogranites de Guérande et de Pontivy se sont mis en place, respectivement, à ca. 310 Ma dans une zone de déformation extensive dans le domaine interne de la chaîne et ca. 315 Ma dans le domaine externe le long du cisaillement sud armoricain (CSA), une faille décrochante d'échelle lithosphérique. Les deux leucogranites sont issus d'un faible taux de fusion partielle de métasédiments détritiques et d'orthogneiss peralumineux, la fusion de ces derniers ayant vraisemblablement joué un rôle majeur dans la richesse en uranium des leucogranites. La fusion de la croûte continentale dans la zone interne de la chaîne a été induite par l'extension tardi-orogénique alors que la fusion de la croûte mais aussi du manteau dans la zone externe était probablement contrôlée par une déformation décrochante diffuse. La cristallisation d'oxydes d'uranium magmatiques dans les facies les plus évolués des leucogranites au moment de leur mise en place a été vraisemblablement rendue possible grâce à l'action combinée de la cristallisation fractionnée et d'une activité magmatique-hydrothermale diffuse. De ca. 300 Ma à 270 Ma, une activité tectonique fragile le long du CSA et des détachements a permis l'infiltration de fluides météoriques oxydants en profondeur induisant la mise en solution des oxydes d'uranium des leucogranites. Ensuite, les fluides ont précipité leur U dans des failles ou des fentes de tension à proximité du contact avec des lithologies sédimentaires avec un caractère réducteur variable. Les leucogranites étaient toujours en profondeur à des températures supérieures à 120°C au moment de la formation des gisements et leur exhumation en sub-surface n'est pas enregistrée avant le Trias ou le Jurassique. Ce modèle métallogénique n'est probablement pas exclusif au Massif armoricain car la période de formation des gisements d'U dans la région entre 300 et 270 Ma est la même que dans l'ensemble de la chaîne hercynienne européenne. / Peraluminous leucogranites are the principal actors for the differentiation of the continental crust and play an important economic role because they are commonly associated with significant metalliferous deposits. Most hydrothermal uranium (U) deposits (vein or episyenite types) from the European Hercynian belt are spatially associated with Carboniferous peraluminous leucogranites and in the French Armorican Massif (western part of the European Hercynian belt) 20000 t of U (~20 % of the French production) were extracted from the deposits associated with the Mortagne, Pontivy and Guérande leucogranites. The objective of this work is to improve our knowledge about the U cycle in the Armorican Hercynian Belt from the leucogranites sources, their evolution and emplacement in the upper crust to U leaching, deposit formation and leucogranites exhumation at the subsurface level. For that purpose, petro-geochemical, geochronological and thermochronological data were obtained on the Guérande and Pontivy leucogranites as well as their spatially associated U deposits. The Guérande leucogranite was emplaced ca. 310 Ma ago in an extensional deformation zone in the internal domain of the belt whereas the Pontivy leucogranite was emplaced ca. 315 Ma ago in the external domain along the South Armorican Shear Zone (SASZ), a lithospheric scale wrench fault. Both leucogranites were formed by a low degree of partial melting of detrital metasediments and peraluminous orthogneisses; the fusion of the latter probably played a major role in the generation of U rich leucogranites. Partial melting of the crust in the internal zone of the belt was triggered by late orogenic extension whereas partial melting of the crust but also the mantle in the external zone was likely controlled by pervasive wrenching. The crystallization of magmatic uranium oxides in the most evolved leucogranitic facies was induced by fractional crystallization and probably enhanced by magmatic-hydrothermal processes. From ca. 300 to 270 Ma, a fragile tectonic activity along detachments and the SASZ, allowed for the infiltration at depth of meteoric oxidizing fluids, able to dissolve magmatic uranium oxides in the leucogranites. These fluids have then precipitated their U in faults or tension gashes close to the contact with sediments having a variable reducing character. The leucogranites were at depth above 120°c during the formation of U deposits and the exhumation of these intrusions did not occur before the Trias or the Jurassic. The proposed metallogenic model is likely not exclusive to the Armorican Massif as the timing of U deposits formation in the region from ca. 300 to 270 Ma is similar to the main U mineralizing event in the whole European Hercynian belt.

Dans cette thèse, nous développons le modèle phénoménologique optimisé de lessivage chimique in situ (ISL) de l'uranium par l'injection d'acide sulfurique, en prenant en compte la précipitation des espèces non-solubles telles que le gypse, qui réduisent la récupération de l'uranium. Le modèle proposé décrit le transport de masse avec des réactions chimiques hétérogènes entre le liquide et les roches solides, qui mènent à la dissolution des oxydes d'uranium et à la récupération de l'uranium sous forme liquide. Ce modèle comprend à la fois des réactions utiles, qui décrivent la dissolution de divers types d'oxydes d'uranium, et les réactions néfastes qui conduisent à la précipitation des sédiments solides (gypse), dont les flocons couvrent la surface de canaux poreux et réduisent l'efficacité des réactions utiles. Parmi les résultats qualitatifs, nous avons révélé l'existence d'un taux critique de sédimentation de gypse, en dessous duquel la récupération ultime de l'uranium est complète. En revanche, elle tend à une valeur limite inférieure à 100% lorsque le taux de sédimentation est supérieur à la valeur critique. Ce taux de récupération limite dépend de divers paramètres du processus. La théorie et la méthodologie développées dans ce travail peuvent être facilement étendues et appliquées aux autres types de minerais qui sont récupérés par la méthode de lessivage in situ, et autres types de solvant / In the present thesis we develop the optimized phenomenological model of in-situ chemical leaching (ISL) of uranium by the injection of sulfuric acid, with special account for the precipitation of non-soluble species as gypsum, which reduces the uranium recovery. The suggested model describes the mass transport with heterogeneous chemical reactions between liquid and solid rocks, leading to dissolve uranium oxides and recover uranium in liquid form. It includes both useful reactions, describing the dissolution of various kinds of uranium oxides, and detrimental reactions, leading to the precipitation of solid sediments (gypsum), whose flakes cover the surface of porous channels and reduce the efficiency of useful reactions. Among the qualitative results we revealed the existence of a critical rate of gypsum sedimentation, below which the ultimate uranium recovery is complete. In contrast, it tends to a limit value lower than 100% when the sedimentation rate is higher than the critical value. This limit recovery depends on various parameters of the process. The theory and the methodology developed in this work can be easily extended and applied on other type of ores that are recovered by in-situ leaching method and other types of solvents

Les gisements d’U de type discordance sont associés à des circulations de saumures chlorurées acides et caractérisés par des tonnages et concentrations exceptionnels ce qui amènent à s’interroger sur les processus de transport et de dépôt de l’U contribuant à leur genèse. Cette thèse est donc dédiée à des études expérimentales de la spéciation de l’U6+ et sa précipitation en UO2 par réduction en U4+ en condition hydrothermale. Concernant le transport de l’U, l’étude de la spéciation de l’U6+ dans ces fluides chlorurés (T ≤ 350°C) est réalisée par spectroscopie Raman et XAS. Les résultats montrant la coexistence de plusieurs complexes d’uranyle chlorurés UO2Cln2-n (n=0-5) dont certaines constantes de complexation sont proposées. Ainsi, la complexation de l’uranyle par les chlorures explique la forte capacité de transport en U6+ par les saumures chlorurées acides, condition nécessaire à la formation de gisements de fort tonnage. Pour le dépôt de l’U, les cinétiques de réduction de l’U6+ en U4+ par H2, CH4, Fe2+ et C-graphite sont mesurées et paramétrées en fonction de la température, de la chlorinité, du pH et de la concentration en réducteur. H2, CH4 et le C-graphite sont être très efficaces, contrairement au Fe2+. Le caractère mobile des gaz réducteurs explique en partie les minéralisations massives et focalisées observées dans ces gisements. Enfin des coefficients de partage UO2/fluide d’éléments en traces, dont certaines ETR, sont mesurés, ouvrant de nouvelles perspectives quant à (i) la compréhension de la signature des ETR caractéristiques de chaque type de gisement d’U, et (ii) la composition des fluides à l’origine des minéralisations uranifères / Circulations of acidic chloride brines are associated with unconformity-related uranium (URU) deposits. The spectacular high grade combined with the large tonnage of these deposits is at the origin of the key questions concerning the geological processes responsible for U transport and precipitation. The aim of this work is to performed experimental studies of U6+ speciation and its reduction to U4+ subsequently precipitation to UO2 under hydrothermal condition. About U transport, the study of U6+ speciation in acidic brines at high temperature is performed by Raman spectroscopy and XAS, showing the coexistence of several uranyl chloride complexes UO2Cln2-n (n=0-5). From this study, complexation constants are proposed. The strong capability of chloride to complex uranyl is at the origin of the transport of U6+ at high concentration in acidic chloride brines. Concerning U precipitation, the reactivity of four potential reductants under conditions relevant for URU deposits genesis is investigated: H2, CH4, Fe2+ and the C-graphite. The kinetics of reduction reaction is measured as a function of temperature, salinity, pH and concentration of reductant. H2, CH4, and the C-graphite are very efficient while Fe2+ is not able to reduce U6+ in same conditions. These mobile and efficient gaseous reductant could be at the origin of the extremely focus and massive character of ore in URU deposits. Finally, first partition coefficients UO2/fluid of trace elements are obtained. This last part opens-up new perspectives on (i) REE signatures interpretation for a given type of U deposit (ii) and reconstruction of mineralizing fluids composition