Dissertations / Theses on the topic 'Guide de prospection'

L’existence de fluides géologiques riches en hydrogène (H2) doit nécessairement faire l’objet de travaux d’exploration afin de statuer sur le potentiel énergétique de cette éventuelle ressource décarbonée. Depuis plus d’un siècle de nombreuses exhalations naturelles d’H2 ont été mis en évidence. Or à ce jour il n’existe aucun guide d’exploration basé sur une méthodologie et sur des indicateurs robustes. La détection d’occurrence gazeuse en surface correspond bien évidemment à l’approche la plus efficace et la plus rapide à mettre en œuvre pour identifier des flux. Il n’en reste pas moins qu’un flux ne constitue pas une ressource pour autant, puisqu’à ce jour, l’homme n’exploite que les stocks de ressources énergétiques fossiles. Il sera donc important de développer un guide d’exploration non pas orienté uniquement sur une problématique de surface, mais aussi sur des considérations géologiques profondes intégrant le système hydrogène dans son entier de la source au piège ou à la fuite dans l’atmosphère.Au cours de ce travail de thèse nous proposons d’utiliser le cadre géologique du piémont nord Pyrénéen pour élaborer un guide d’exploration. La compilation des données bibliographiques a révélé un contexte prometteur pour un système H2 du fait d’un lien entre sources profondes, chemins de migration crustale, dynamique de circulation de fluides, et pièges sédimentaires. En effet le nord-ouest des Pyrénées et plus particulièrement le Bassin Mauléon est caractérisé par la présence i) d’un corps mantellique (&lt;10 km) où les conditions pression-température sont favorables à la serpentinisation ; ii) d’accidents structuraux majeurs tels que le Chevauchement Frontal Nord Pyrénéens (CFNP) constituant des drains collecteurs de grande ampleur, iii) des gradients hydrauliques, conjugués à des gradients de température et de pressions qui permettent la mise en mouvement des fluides ; iv) des formations sédimentaires imperméables ou de couvertures comme les évaporites ou les argiles consitutant des pièges pour accumuler l’H2.Suite à cette étude préalable, nous avons mis en place une campagne d’analyses des gaz du sol (H2, CO2, 222Rn, O2, CH4) à l’échelle régionales. Cette campagne d’analyse réalisée sur plus de 7500 km2 a très vite permis de mettre en évidence une zone à très fortes anomalies en H2, CO2, et 222Rn sur le pourtour du Bassin de Mauléon. Cette découverte nous a permis de resserrer rapidement le maillage de prospection sur la partie nord du bassin de Mauléon. Une campagne d’analyses géochimiques et géophysiques a été réalisée à Sauveterre-de-Béarn afin de déterminer l’origine et le parcours des gaz à l’origine de cette anomalie. Sur la base de l'analyse des gaz du sol et des levés électromagnétiques, nous avons confirmé l'existence d'une faille drainant les fluides profonds. De plus, l’étude des données historiques des forages entrepris dans la région il y a plus de 50 ans, conjugué à une mise en perspective des dernières connaissances géologiques et géophysiques de la région, nous a permis de mettre en évidence des zones où l’H2 pourrait s’accumuler.Enfin une partie expérimentale de broyage de quartz et de roches de la région a été menée afin d’explorer de nouveaux mécanismes de production d’H2 le long des failles. Nous avons mis en évidence une très forte influence du rapport eau/roche (W/R) et du pH sur la production d’H2. Ces découvertes apportent un éclairage nouveau sur les mécanismes mécano-radicalaires de production d’H2 où la spéciation des sites des surface des minéraux sont des paramètres clés contrôlant la production d’H2. Nous révélons pour la première fois que le broyage du quartz en présence de solutions carbonatés induit la formation d’espèces carboxylates (formate, acétate, oxalate). En plus de produire de l’H2, les mécanismes mécano-radicalaires permettent donc de produire des espèces réduites du carbones pouvant constituer une source d’énergie pour les écosystèmes microbiens lithotrophe de subsurface<br>The existence of geological fluids rich in hydrogen (H2) rise the question about the energy potential of this carbon-free resource. For more than a century and throughout the world, numerous natural H2 seepages have been discovered. However, to date there is no exploration approach based on robust methodologies and pathfinders. The detection of H2 seepages at the surface is known to be the most ecient and straight forward approach to identify H2 flows. However, a gas flow does not necessarily constitute a resource, since to date, mankind only exploit reservoirs of fossil energy resources. Therefore, it is important to develop an exploration guide that is not only focusing on surface gas monitoring, but also considering a deep geological approach integrating the entire hydrogen system from source to trap or leakage into the atmosphere. Here, we propose to use the geological framework of the North Pyrenean foothills as a case study to develop this exploration guide. A literature review of the area revealed a promising geological setting for a H2 system due to a strong link between putative deep H2 sources, crustal-scale migration pathways, fluid circulation dynamics, and sedimentary traps. Indeed, the northwestern Pyrenees and particularly the Maul´eon Basin is characterised by the presence of i) an ultramafic mantle body located less than 10 km depth and under pressure-temperature conditions favourable to serpentinisation ; ii) major faults such as the North Pyrenean Frontal Thrust (NPFT) constituting large-scale flow convergence and drainage, iii) hydraulic gradients due to the presence of strong reliefs, combined with temperature and pressure gradients that trigger fluids ; iv) impermeable sedimentary formations or caprocks such as evaporites or claystones overlying porous reservoir rocks that can constitute traps for accumulating H2.Following this preliminary geological survey, we set up a soil gas exploration campaign (H2, CO2, 222Rn, O2, CH4) at the regional scale. These field measurments, carried out over more than 7,500 km2, revealed several hotspots with very high H2, CO2 and 222Rn concentrations anomalies around the Maul´eon Basin. This discovery allowed us to refine the mesh of the prospecting grid to the northern part of the Maul´eon Basin around the locality of Sauveterre-de-Béarn. Geochemical and geophysical measurements were carried out at Sauveterre-de-B´earn to determine the source and migration path of the gases at the origin of this anomaly. Based on soil gas analysis and electromagnetic surveys, we confirmed the existence of a fault draining deep fluids. In addition, the study of historical data from drilling carried out in the region more than fifty years ago, combined with the latest geological and geophysical knowledge of the region, enabled us to highlight zones where H2 could accumulate.Finally, an experimental part of comminution of quartz and rocks from the region was carried out in order to explore the reaction mechanisms of H2 production in active fault zones. We reveal the very strong influence of the water/rock ratio (W/R) and pH on H2 production. These findings shed new light on the mechano-radical mechanisms of H2 production where the efficiency of grinding as well as the speciation of mineral surface sites are key parameters controlling H2 production. We reveal for the first time that grinding of quartz in the presence of carbonate solutions induces the formation of carboxylate species (formate, acetate, oxalate). In addition to producing H2, the mechano-radical mechanisms thus allow the production of reduced carbon species that can constitute an energy source for subsurface lithotrophic microbial ecosystems

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>Conselho Nacional de Desenvolvimento Científico e Tecnológico<br>A região de Itutinga foi alvo de estudos prospectivos por parte da empresa BP mineração na década de 80, onde foram encontradas mineralizações em lentes de sulfetos metálicos (Zn-Cu-Ag-Fe) associados a rochas komatiíticas peridotíticas e basaltos toleíticos (anfibolitos) do greenstone belts, nas proximidades da fazenda São Jerônimo, enquadrando-se em um depósito do tipo VMS. A partir destas informações encontradas na literatura propôs-se estudar a estaurolita, a magnetita e a ilmenita para, a partir da determinação do seu conteúdo em zinco, indicar a aplicabilidade destes três minerais como traçadores desses tipos de depósitos. Para isso foram coletadas amostras de sedimentos de corrente e concentrados de batéia na região próxima à ocorrência, no entorno da cidade de Itutinga, e também em uma região próxima a cidade de Itumirim, já que existem semelhanças litológicas entre as duas áreas. Os sedimentos de corrente, as frações magnéticas e as frações de 0,3A (separador eletromagnético Frantz) foram enviados para análises químicas por absorção atômica e ICP-OES. Os concentrados de batéia foram descritos, separando-se cristais de estaurolita de cada amostra coletada, e analisando-os em MEV-EDS para determinação da química mineral. Os resultados dos sedimentos de corrente apontaram que os pontos da fazenda São Jerônimo (ME-03, Itutinga 51,7 ppm de Zn) e o ponto do Ribeirão Santa Cruz, (ME-06, Itumirim 36,1 ppm de Zn) foram os que apresentaram melhores resultados, indicando anomalias em zinco nas duas áreas estudadas . As estaurolitas, retiradas dos concentrados de batéia de cada ponto estudado, foram divididas em três conjuntos, de acordo com os teores de ZnO encontrados: 1 - entre 2,96% e 3,25% de ZnO em peso; 2 - entre 2,03% e 2,76% de ZnO em peso; 3 - < 1,67% de ZnO em peso, sendo comparável com outras estaurolitas encontradas em diversos depósitos de Zn do mundo, como Dry River, Austrália e Palmeirópolis Goiás. Assim, as estaurolitas apresentam bons resultados como minerais indicadores na área estudada. Em relação as magnetitas e ilmenitas estudadas, o número de amostras coletadas no presente estudo foram muito pequenas para se ter informações conclusivas sobre o papel destes minerais como traçadores. Por outro lado, os resultados das análises químicas nos concentrados de ilmenita (até 856 ppm de Zn) e nos concentrados de magnetita (até 216 ppm de Zn), indicam a disponibilidade deste metal nas áreas estudadas. Assim, é possível se detectar a presença do zinco por dois meios: através de sedimentos de corrente, através de halos de dispersão química do elemento zinco, e através dos minerais resistatos (estaurolita zincífera, magnetita e ilmenita), a partir de uma dispersão clástica do grão.<br>The Itutinga region was studied for BP mineration in 80s , where they found sulphide mineralization in lenses (Zn-Cu-Ag-Fe) associated with komatiitic peridotite rocks and tholeitic basalts (amphibolites) of greenstone belts, near of Fazenda São Jerônimo. With this information in the literature the propose is study the staurolite, magnetite and ilmenite for indicating the applicability of these three minerals as tracers of these types of mineralization. For this, samples of stream sediment and panning concentrates in the region near the city of Itutinga, and also in a region near the city of Itumirim. The stream current, magnetic fractions and ilmenite fractions were sent to chemistry analyses (Atomic absorption and ICP-OES), and the panning concentrates were analyzed for the separating of staurolite crystals, and sent to SEM-EDS. The stream sediments results showed that the point of Fazenda São Jerônimo (ME-03, Itutinga 51,7 ppm of Zn) and the point of Ribeirão Santa Cruz (ME-06, Itumirim 36,1 ppm of Zn) were presented the best result. The staurolite of panning concentrates were divided into three groups according to levels of ZnO matched: 1 - between 2.96% and 3.25% by weight of ZnO, 2 - from 2, 03% and 2.76% by weight of ZnO, 3 - <1.67% ZnO by weight, comparable with other staurolite found in many zinc deposits in the world, such as Dry River, Australia and Palmeirópolis Goiás. Thus, the staurolite show good results as indicator minerals in the area. With respect to magnetite and ilmenite concentrates, the number of samples collected in both areas was too small to have conclusive information. On the other hand, the results of the chemical ilmenite (up to 856 ppm Zn) and magnetite (up to 216 ppm Zn), indicate the availability of this metal in the areas studied. Thus, it is possible to detect the presence of zinc by two means: through stream sediments through chemical dispersion halos of zinc, minerals and through resistive minerals (zincian staurolite, magnetite and ilmenite), from a crystal clastic dispersion.