A boulder find of the lithium-mineral spodumene in Bergby, Sweden in 2007 subsequently led to the discovery of an LCT-type granitic pegmatite system. Since then, exploration and research have been conducted on the LCT pegmatites to expand the knowledge of lithium mineralisations. Using optical microscopy, SEM-EDS and powder X-ray diffraction, a granitic to aplitic sample from Bergby has been studied, focused on its mineralogy, chemistry, and tentative paragenesis. The results conclude that the sample is from a highly fractionated unit which can be categorised as a petalite-bearing granite to aplite unit of the pegmatite, as petalite is the primary lithium mineral within the sample. The sample exhibits signs of at least one stage of late hydrothermal activity, which has led to the (partial) alteration of primary minerals. The majority of these minerals display signs of alteration and/or replacement, and two different alteration products have been identified with a probable origin being the primary petalite.The last fluid has been active synchronous or immediately subsequent to brittle deformation. This study was conducted as a part of the ULiBS project, which aims to further the knowledge of the Swedish lithium pegmatites with the Bergby system as a case study. / Ett blockfynd av litiummineralet spodumen i Bergby, Sverige år 2007 ledde till upptäckten av ett granitiskt pegmatitsystem av LCT-typ. Sedan dess har prospektering och forskning bedrivits på LCT-pegmatiterna för att utöka kunskapen om litiummineraliseringar. Med hjälp av optisk mineralogi, SEM-EDS och pulverröntgendiffraktion har ett granitiskt till aplitiskt prov från Bergby studerats, med fokus på dess mineralogi, kemi och tentativa paragenes. Resultaten visar att provet är från en högfraktionerad enhet som kan kategoriseras som en petalitförande granit- till aplitenhet inom pegmatiten, då petalit är det primära litiummineralet inom provet. Provet uppvisar tecken på minst en fas av sen hydrotermal omvandling, vilket har lett till (partiell) omvandling av primära mineral. Majoriteten av dessa mineral uppvisar tecken av omvandling och/eller ersättning, och två olika omvandlingsprodukter har identifierats med den primära petaliten som troligt ursprung. Den sista fluiden har varit aktiv i systemet synkront eller omedelbart efter spröd deformation. Denna studie genomfördes som en del av ULiBS-projektet, vars syfte är att öka kunskapen om de svenska litiumpegmatiterna med Bergbysystemet som fallstudie.

Secondary generation biofuels such as cellulosic biofuels rely on large portions of cellulosic bioresources, which may include forests, perennial grasses, wood and agricultural residues. Switchgrass is one promising feedstock for biofuel production. In the present study, thesis work focused on the chemical and structural profiles and hydrothermal pretreatment of switchgrass. Four populations of switchgrass were investigated for their chemical properties among populations and morphological portions, including the compositions of lignin and carbohydrates, extractives content, higher heating value (HHV), and syringyl:guaiacyl (S:G) ratio. The results demonstrate similar chemical profiles and lignin structure among the four populations of switchgrass. Morphological fractions of switchgrass including leaves, internodes, and nodes differ significantly in chemical profiles and S:G ratios of lignin. The structure of isolated cellulose from switchgrass SW9 is similar between leaves and internodes. The structure of isolated lignin from leaves and internodes of switchgrass SW9 differs in S:G ratio and molecular weight. Hydrothermal pretreatment of leaves and internodes indicates that a similar chemical composition and chemical structure for pretreated leaves and internodes. The degree of polymerization (DP) for cellulose of the pretreated internodes is 23.4% greater than that of the pretreated leaves. The accessibility of pretreated leaves measured by Simons' Staining technique is greater than that of pretreated internodes. Pretreated leaves have a 32.5-33.8% greater cellulose-to-glucose conversion yield than do pretreated internodes.

The Pozzolane Rosse ignimbrite [PR] (457±4 ka) in the Alban Hills Volcanic District, Rome, Italy was exposed ~ 40 ka prior to a subsequent volcanic event which coverd it entirely. XRF, XRD, and clay separation results from PR samples from INGV and CA1 boreholes and Castel di Leva quarry show evidence of paleopedogenesis. All locations display loss of base cations, loss of K is consistent with XRD datat showing dissolution or alteration of leucite to analcime. Accumulation of Al and high L.O.I. support XRD evidence of 1:1 clay species at upper depth. Data suggest alteration extent can be determined by geochemistry. Hydrothermal alteration is assessed from geochemistry showing significant leaching of major and trace elements, primary mineralogy loss and iron sulfide and sulfate mineral development. Deep samples of PR may show groundwater influenced alteration with the presence of expandable 2:1 clays, zeolites, and possible mixing with the underlying Vallerano Lava.

Thesis (doctoral)--University of Tartu, 2006. / Vita. Includes bibliographical references. Also available on the Internet.

La formation des planètes a laissé derrière elle des matériaux dont la nature primordiale a été préservée. Ces astéroïdes primitifs de la ceinture principale sont aujourd'hui échantillonnés par la diversité de météorites chondritiques dans nos collections qui nous permettent d'étudier les premiers instants du Système Solaire. Cependant, beaucoup d'entre elles présentent des traces d'altération hydrothermale qui ont modifié leur minéralogie, et ainsi occulté ces informations primordiales. Ce processus de modification de la roche via l'interaction avec un fluide a été grandement étudié au cours des dernières décennies, notamment dans les chondrites carbonées de type CM, dont la minéralogie témoigne de plusieurs épisodes d'altération dans différents degrés d'intensité. Comprendre l'évolution de l'eau ainsi que l'influence de ce processus sur la matière organique dans ces astéroïdes est essentiel du fait de leur éventuelle contribution à l'origine de la vie sur Terre. Afin de mieux contraindre les conditions géochimique et chronologique dans lesquelles est survenu ce processus, les travaux de cette thèse ont été focalisés sur les chondrites de type CM et les phases secondaires qu'ils contiennent. Des mesures in situ des isotopes de l'oxygène dans les carbonates des CM nous ont permis de développer une méthode d'estimation de leurs températures de précipitation. Nos résultats indiquent une gamme de températures bien plus étendue que celles estimées auparavant, s'étalant de -50 à environ 300 °C avec une température moyenne de 113 +/- 54°C (2σ). Afin d'approfondir notre étude des conditions géochimiques de l'altération nous avons conduit une étude détaillée de la chondrite de Boriskino. La texture atypique de cette chondrite, due à ses nombreux clastes aux frontières nettes et aux degrés d'altération variables, nous a permis d'explorer l'hypothèse d'un lien entre les processus à l'origine de la formation des brèches et l'altération hydrothermale. L'utilisation de notre nouvelle méthode sur les carbonates de cette chondrite a mis en évidence un rôle secondaire de la température dans l'intensité du processus d'altération. De plus, nos travaux suggèrent que les épisodes d'altération sont antérieurs à la formation du corps-parent final et que la quantité de glace initialement accrétée peut être le facteur dominant de l'efficacité du processus d'altération. Néanmoins cette hypothèse ne prend pas en compte l'influence que peut avoir la durée d'exposition de la roche au fluide. Afin de tester cette dernière hypothèse, notre dernier projet devait permettre d'estimer l'âge des carbonates dans des CM présentant différents degrés d'altération. La datation de ces objets repose sur la décroissance radioactive du radioisotope 53Mn en 53Cr. Cependant, l'absence de standards de carbonates adéquats pour ces mesures nous a conduit dans un premier temps à les synthétiser. Pour ce faire nous avons abordé le problème en nous éloignant des méthodes traditionnelles de précipitation de carbonates sur substrat ayant conduit à des minéraux très hétérogènes, et nous avons effectué nos synthèses à haute pression et haute température grâce à une presse piston-cylindre. / Chondrites are leftover solids from the evolution of the solar protoplanetary disk that enable for its primordial conditions to be studied. However, many chondrites have seen their mineralogy modified by the circulation of fluids during hydrothermal alteration events, thereby blurring the primordial informations retained in it. CM carbonaceous chondrites have been extensively studied, mainly because of the various episodes and extent of hydrothermal alteration they exhibit. The understanding of the evolution of water and the influence of alteration on organic matter in those asteroids is essential as they might be the source of life on Earth. In order to better understand the geochemical conditions and the chronology of this process in carbonaceous asteroids, we focused this project on CM chondrites and the secondary phases they contain. We developped a methodology to estimate the precipitation temperatures of carbonates in CM chondrites relying only on in situ measurements of their O-isotopic composition. Our results yield precipitation temperatures in a larger range than what has previsouly been estimated, i.e. from -50 to approximatively 300°C with an average temperature of 113 +/- 54°C (2σ). To further our study of the geochemical conditions of hydrothermal alteration we extensively studied the CM of Boriskino. The peculiar texture of this meteorite, due to its numerous clasts with sharp boundaries and their various degrees of aqueous alteration, enable to investigate the reccurent question of a genetic link between brecciation and aqueous alteration. Using the same methodology as in our first project we concluded that temperatures in which the process took place could not account for the various extent of aqueous alteration that we observe. In addition, Our work suggest that aqueous alteration in this chondrite was discontinuous and preceeded brecciationand that instead the initial quantity of accreted ice could be the controlling parameter of aqueous alteration. However, this study neglect the contribution of the duration of exposure of the rock to the fluid to the extent of aqueous alteration. Therefore, our last project was to determine the age of carbonates in several CM chondrites of various degrees of aqueous alteration. The datation of these minerals in chondrites relies on the radiochronometer 53Mn-53Cr. However, the lack of a suitable carbonate standard for these SIMS analyses pushed us to synthetize carbonates with the adequat cristallinity and chemical composition first. To do so, we experimentated at high pressure and high temperature using a piston-cylinder apparatus.

O Distrito Mineiro de Artigas, no Uruguai, compreende uma das maiores jazidas de ametista e ágata de que se tem conhecimento e é comparável às jazidas da região do Alto Uruguai, próximas ao município de Ametista do Sul, Brasil. A mineralização ocorre em geodos parcialmente preenchidos por ágata, quartzo incolor, ametista e ± calcita, que ocorrem nesta seqüência, da borda para o centro das cavidades. As rochas hospedeiras da mineralização são basaltos andesíticos da Formação Arapey, equivalente à Formação Serra Geral, no Brasil. Na área de estudo ocorre uma seqüência de seis derrames, de composição entre basalto e andesito. As estruturas de resfriamento são dos tipos I e II, que diferem pela ausência e presença de disjunção colunar, respectivamente, na porção interna do derrame. Destes seis derrames dois são do tipo I (maciço na zona central) e portadores de minério. Com base em observações de campo de estruturas rúpteis associadas às zonas mineralizadas, foi elaborado um modelo epigenético para a mineralização de ametista em geodos em basalto. Neste modelo, os geodos são formados após a solidificação da lava, por deformação ou dissolução do basalto, depois de alterado para argilominerais do grupo da esmectita pela interação com fluidos hidrotermais. O preenchimento ocorre após a abertura e pelo mesmo fluido que abriu a cavidade. O fluido é meteórico, de baixa salinidade e tem composição próxima a de água pura. A temperatura do fluido é < 200°C, com base na mineralogia de alteração da rocha hospedeira. A temperatura de cristalização dos minerais no interior dos geodos não ultrapassa 70°C. Esta temperatura foi calculada com base nos coeficientes de partição do oxigênio entre quartzo e água e entre calcita e água para um fluido com assinatura isotópica de T18O de -5 ‰. A intensa alteração hidrotermal nas rochas portadoras do minério e nos derrames, no âmbito do Distrito Mineiro de Artigas, corrobora para eventos epigenéticos relacionados com a mineralização. Isótopos de T34S nas encaixantes do minério indicam percolação de fluido em grande escala, e assinatura isotópica compatível com as unidades sedimentares subjacentes ao pacote vulcânico. A integração dos dados obtidos sugere que os geodos de ametista foram formados após a solidificação da lava e os minerais que preenchem os geodos cristalizadados por um fluido de origem meteórica. / The Artigas Mining District, in Uruguay, is a world-class amethyst deposit, and is comparable with those in Alto Uruguai region, Brazil (Ametista do Sul). The mineralization occurs as geodes partially filled by agate, colorless quartz and amethyst, ± calcite, which occur in this sequence from the rim to the inner part of the cavities. The host rocks are andesitic basalts from the Arapey Formation. The study area comprises a sequence of six lava flows, including basaltic to andesitic composition. The cooling structure of the flows is type I and type II; those are differentiated by the inner part of the flow. Type II has columnar joints, whereas type I is massive. Two out of six flows are mineralized and structured as type I flows. Based on field observations of brittle failures associated with the geode zone, an epigenetic model is elaborated for the mineralization of amethyst in geodes hosted by basalts. In this model, the geodes are formed after the flow solidifies. The cavities are formed by deformation or dissolution, after the basalt was altered to clay minerals (smectite group) by hydrothermal fluids. The filling occurred after the cavity was formed by the same fluid. The fluid is close to pure water in composition, of meteoric origin, with low salinity. The temperature is <200°C, based on alteration mineralogy in the host rock. The crystallization temperature is <70°C. The temperature is calculated based on fractionation coefficient of oxygen isotopes between quartz and water and between calcite and water. The value of T18O of the mineralized fluid is assumed to be -5 ‰. The intensive alteration in the host rocks and in lava flows within the mining district, favors the epigenetic hypothesis related to the mineralization processes. T34S isotopes on the host rock, agree with large scale hydrothermal fluid percolation. The data obtained suggest that the amethyst geodes were formed after the lava solidified and was filled by meteoric hydrothermal fluids.

O Distrito Mineiro de Artigas, no Uruguai, compreende uma das maiores jazidas de ametista e ágata de que se tem conhecimento e é comparável às jazidas da região do Alto Uruguai, próximas ao município de Ametista do Sul, Brasil. A mineralização ocorre em geodos parcialmente preenchidos por ágata, quartzo incolor, ametista e ± calcita, que ocorrem nesta seqüência, da borda para o centro das cavidades. As rochas hospedeiras da mineralização são basaltos andesíticos da Formação Arapey, equivalente à Formação Serra Geral, no Brasil. Na área de estudo ocorre uma seqüência de seis derrames, de composição entre basalto e andesito. As estruturas de resfriamento são dos tipos I e II, que diferem pela ausência e presença de disjunção colunar, respectivamente, na porção interna do derrame. Destes seis derrames dois são do tipo I (maciço na zona central) e portadores de minério. Com base em observações de campo de estruturas rúpteis associadas às zonas mineralizadas, foi elaborado um modelo epigenético para a mineralização de ametista em geodos em basalto. Neste modelo, os geodos são formados após a solidificação da lava, por deformação ou dissolução do basalto, depois de alterado para argilominerais do grupo da esmectita pela interação com fluidos hidrotermais. O preenchimento ocorre após a abertura e pelo mesmo fluido que abriu a cavidade. O fluido é meteórico, de baixa salinidade e tem composição próxima a de água pura. A temperatura do fluido é < 200°C, com base na mineralogia de alteração da rocha hospedeira. A temperatura de cristalização dos minerais no interior dos geodos não ultrapassa 70°C. Esta temperatura foi calculada com base nos coeficientes de partição do oxigênio entre quartzo e água e entre calcita e água para um fluido com assinatura isotópica de T18O de -5 ‰. A intensa alteração hidrotermal nas rochas portadoras do minério e nos derrames, no âmbito do Distrito Mineiro de Artigas, corrobora para eventos epigenéticos relacionados com a mineralização. Isótopos de T34S nas encaixantes do minério indicam percolação de fluido em grande escala, e assinatura isotópica compatível com as unidades sedimentares subjacentes ao pacote vulcânico. A integração dos dados obtidos sugere que os geodos de ametista foram formados após a solidificação da lava e os minerais que preenchem os geodos cristalizadados por um fluido de origem meteórica. / The Artigas Mining District, in Uruguay, is a world-class amethyst deposit, and is comparable with those in Alto Uruguai region, Brazil (Ametista do Sul). The mineralization occurs as geodes partially filled by agate, colorless quartz and amethyst, ± calcite, which occur in this sequence from the rim to the inner part of the cavities. The host rocks are andesitic basalts from the Arapey Formation. The study area comprises a sequence of six lava flows, including basaltic to andesitic composition. The cooling structure of the flows is type I and type II; those are differentiated by the inner part of the flow. Type II has columnar joints, whereas type I is massive. Two out of six flows are mineralized and structured as type I flows. Based on field observations of brittle failures associated with the geode zone, an epigenetic model is elaborated for the mineralization of amethyst in geodes hosted by basalts. In this model, the geodes are formed after the flow solidifies. The cavities are formed by deformation or dissolution, after the basalt was altered to clay minerals (smectite group) by hydrothermal fluids. The filling occurred after the cavity was formed by the same fluid. The fluid is close to pure water in composition, of meteoric origin, with low salinity. The temperature is <200°C, based on alteration mineralogy in the host rock. The crystallization temperature is <70°C. The temperature is calculated based on fractionation coefficient of oxygen isotopes between quartz and water and between calcite and water. The value of T18O of the mineralized fluid is assumed to be -5 ‰. The intensive alteration in the host rocks and in lava flows within the mining district, favors the epigenetic hypothesis related to the mineralization processes. T34S isotopes on the host rock, agree with large scale hydrothermal fluid percolation. The data obtained suggest that the amethyst geodes were formed after the lava solidified and was filled by meteoric hydrothermal fluids.

O Distrito Mineiro de Artigas, no Uruguai, compreende uma das maiores jazidas de ametista e ágata de que se tem conhecimento e é comparável às jazidas da região do Alto Uruguai, próximas ao município de Ametista do Sul, Brasil. A mineralização ocorre em geodos parcialmente preenchidos por ágata, quartzo incolor, ametista e ± calcita, que ocorrem nesta seqüência, da borda para o centro das cavidades. As rochas hospedeiras da mineralização são basaltos andesíticos da Formação Arapey, equivalente à Formação Serra Geral, no Brasil. Na área de estudo ocorre uma seqüência de seis derrames, de composição entre basalto e andesito. As estruturas de resfriamento são dos tipos I e II, que diferem pela ausência e presença de disjunção colunar, respectivamente, na porção interna do derrame. Destes seis derrames dois são do tipo I (maciço na zona central) e portadores de minério. Com base em observações de campo de estruturas rúpteis associadas às zonas mineralizadas, foi elaborado um modelo epigenético para a mineralização de ametista em geodos em basalto. Neste modelo, os geodos são formados após a solidificação da lava, por deformação ou dissolução do basalto, depois de alterado para argilominerais do grupo da esmectita pela interação com fluidos hidrotermais. O preenchimento ocorre após a abertura e pelo mesmo fluido que abriu a cavidade. O fluido é meteórico, de baixa salinidade e tem composição próxima a de água pura. A temperatura do fluido é < 200°C, com base na mineralogia de alteração da rocha hospedeira. A temperatura de cristalização dos minerais no interior dos geodos não ultrapassa 70°C. Esta temperatura foi calculada com base nos coeficientes de partição do oxigênio entre quartzo e água e entre calcita e água para um fluido com assinatura isotópica de T18O de -5 ‰. A intensa alteração hidrotermal nas rochas portadoras do minério e nos derrames, no âmbito do Distrito Mineiro de Artigas, corrobora para eventos epigenéticos relacionados com a mineralização. Isótopos de T34S nas encaixantes do minério indicam percolação de fluido em grande escala, e assinatura isotópica compatível com as unidades sedimentares subjacentes ao pacote vulcânico. A integração dos dados obtidos sugere que os geodos de ametista foram formados após a solidificação da lava e os minerais que preenchem os geodos cristalizadados por um fluido de origem meteórica. / The Artigas Mining District, in Uruguay, is a world-class amethyst deposit, and is comparable with those in Alto Uruguai region, Brazil (Ametista do Sul). The mineralization occurs as geodes partially filled by agate, colorless quartz and amethyst, ± calcite, which occur in this sequence from the rim to the inner part of the cavities. The host rocks are andesitic basalts from the Arapey Formation. The study area comprises a sequence of six lava flows, including basaltic to andesitic composition. The cooling structure of the flows is type I and type II; those are differentiated by the inner part of the flow. Type II has columnar joints, whereas type I is massive. Two out of six flows are mineralized and structured as type I flows. Based on field observations of brittle failures associated with the geode zone, an epigenetic model is elaborated for the mineralization of amethyst in geodes hosted by basalts. In this model, the geodes are formed after the flow solidifies. The cavities are formed by deformation or dissolution, after the basalt was altered to clay minerals (smectite group) by hydrothermal fluids. The filling occurred after the cavity was formed by the same fluid. The fluid is close to pure water in composition, of meteoric origin, with low salinity. The temperature is <200°C, based on alteration mineralogy in the host rock. The crystallization temperature is <70°C. The temperature is calculated based on fractionation coefficient of oxygen isotopes between quartz and water and between calcite and water. The value of T18O of the mineralized fluid is assumed to be -5 ‰. The intensive alteration in the host rocks and in lava flows within the mining district, favors the epigenetic hypothesis related to the mineralization processes. T34S isotopes on the host rock, agree with large scale hydrothermal fluid percolation. The data obtained suggest that the amethyst geodes were formed after the lava solidified and was filled by meteoric hydrothermal fluids.

L’objectif de cette thèse est de quantifier l’évolution de la surface réactive d’un silicate modèle (orthose) lors de son altération hydrothermale et estimer son impact sur la cinétique réactionnelle. L’étude porte sur : (1) l’influence de la présence de couverture de phases secondaires à même la surface de l’orthose, (2) l’impact de l’anisotropie de la structure cristalline de l’orthose et (3) l’effet de la formation de puits de corrosion en surface. Les résultats expérimentaux et numériques mettent en évidence que la vitesse de dissolution de l’orthose et son évolution au cours du temps dépendent essentiellement de sa morphologie.Certaines faces cristallines se dissolvent 10 fois plus rapidement que d’autres, entraînant une augmentation de la proportion de faces rapides au cours du processus et une élévation, jusqu’à un ordre de grandeur, de la vitesse de dissolution globale de l’orthose. Ces résultats ouvrent d’importantes pistes de réflexion sur la méthode adéquate pour rendre compte des cinétiques des interactions fluide/roche sur le terrain ainsi que sur la signification des lois de vitesse et des mécanismes réactionnels déterminés à partir d’expériences sur poudre. / This thesis aims at quantifying the reactive surface area evolution of dissolving K- feldspar, and evaluating the impact on the dissolution kinetics during its alteration in geothermal context. The study focuses on : (1) the influence of secondary coatings on the orthoclase surface, (2) the impact of the anisotropic crystalline structure of orthoclase and (3) the effect of etch pit formation on the mineral surface. Experimental and numerical results highlight that the orthoclase dissolution rate and its evolution over time mainly depends onits morphology. Some orthoclase faces dissolve 10 times faster than others, resulting in an increase of the surface proportion of rapid vs. slow dissolving faces during the process and the increase of up to an order of magnitude of the overall orthoclase dissolution rate. These results question the significance of rate laws and reaction mechanisms determined from powder experiments and the pave to new approaches for investigating mineral reactivity.

Les péridotites, roches du manteau terrestre, sont instables en présence d'eau et peuvent se transformer en un minéral hydraté la serpentine, qui a la capacité remarquable de générer de l'hydrogène H2; cette réaction s'appelle la serpentinisation. Au niveau des dorsales médio-océaniques, la circulation d'eau dans ces roches conduit à la formation de larges systèmes hydrothermaux. Ils montrent différentes conditions de température et de pH des fluides, bien qu'ils conduisent tous à la formation abiotique d'H2, de méthane CH4 et possiblement d'autres hydrocarbures légers.Cette thèse est dédiée à l'étude du rôle de la composition chimique du fluide hydrothermal sur la cinétique et les mécanismes de serpentinisation des roches ultrabasiques à différentes conditions de P-T. L'interaction entre l'olivine et/ou l'orthopyroxène a été analysée avec une solution aqueuse simulant une eau de mer enrichie en aluminium et/ou en ions bicarbonates, à différents pH. Une première série d'expériences a été réalisée à 200, 340 °C et 200 MPa en lp-DAC à l'ESRF en France. Elle a permis de quantifier les paramètres cinétiques de réaction, de déterminer un effet opposé de l'aluminium sur la cinétique de ces deux minéraux et l'accélération de la réaction en conditions alcalins. Autres expériences ont été réalisée à Pamb et 80 °C en flacons de verre. Elles ont conduit, pour la première fois, à la formation de serpentine ainsi qu'à la formation d'H2 et de CH4. Ces résultats montrent qu'une chimie plus complexe du fluide hydrothermal peut avoir un impact majeur sur la cinétique de la serpentinisation pour l'accélérer et la rendre plus accessible à une échelle de temps industrielle / Peridotites, Earth's mantle rocks, are unstable in the presence of water and can be transformed into a hydrated mineral, serpentine, which has the remarkable ability to generate hydrogen H2; this reaction is called serpentinization. At the mid-ocean ridges, the circulation of water in these rocks leads to the formation of large hydrothermal systems. They show great variability of temperature and fluids’pH conditions, although they all lead to the abiotic formation of H2, methane CH4 and eventually other light hydrocarbons. This PhD thesis is dedicated to the study of the chemical composition role of the hydrothermal fluid on the kinetics and mechanisms of serpentinization of ultramafic rocks to different conditions of P-T. The interaction between olivine and/or orthopyroxene was analyzed with an aqueous solution to simulate sea water which is rich in aluminum and/or bicarbonate ions, with different pH values. A first series of experiments was carried out at 200, 340 °C and 200 MPa in lp-DAC at the ESRF in France. It was used to quantify the kinetic parameters of the reaction, to determine an opposite effect of aluminum on the kinetics these two minerals and the acceleration of the reaction under alkaline conditions. Other experiments were performed in glass bottles at Pamb and 80 °C. They led, for the first time, to the formation of serpentine, as well as to the formation of H2 and CH4. These results show that the slightly more complex chemistry of the hydrothermal fluid can have a major impact on the kinetics of serpentinization to speed and make it more accessible to industrial time scale