Magmatic-hydrothermal ore deposits are formed in association with aqueous fluids that exsolve from hydrous silicate melts during ascent and crystallization. These fluids are invariably trapped as inclusions in vein-filling minerals associated with hydrothermal fluid flow, and their composition may be modeled based on the H₂O-NaCl system. Thus, if we know the pressure-volume-temperature-composition (PVTX) properties of H₂O-NaCl solutions, it is possible to interpret the PTX trapping conditions, which is important for understanding the processes leading to the generation of the hydrothermal system and ore mineralization. High salinity (> 26 wt. % NaCl) fluid inclusions contain liquid, vapor, and halite at room temperature, and are common in magmatic-hydrothermal ore deposits. These inclusions homogenize in one of three ways: A) halite disappearance (Tmhalite) followed by liquid-vapor homogenization (ThL-V), B) simultaneous ThL-V and Tmhalite, or C) ThL-V followed by Tmhalite. The PVTX properties of H₂O-NaCl solutions three phase (L+V+H) and liquid-vapor (L+V) phase boundaries are well constrained, allowing researchers to interpret the minimum trapping pressure of inclusion types A and B. However, data that describe the pressure at Tmhalite for inclusion type C are limited to a composition of 40 wt. % NaCl. To resolve this problem, the synthetic fluid inclusion technique was used to determine the relationship between homogenization temperature and minimum trapping pressure for inclusions that homogenize by mode C. These results allow researchers to interpret the minimum trapping pressure of these inclusions, and by extension the depth at which the inclusions formed. The temporal and spatial distribution of fluid inclusions formed in associated with porphyry copper mineralization has been predicted using a computer model. A simple geologic model of an epizonal intrusion was developed based on a Burnham-style model for porphyry systems and thermal models of the evolution of epizonal intrusions. The phase stability fields and fluid inclusion characteristics at any location and time were predicted based on PVTX properties of H₂O-NaCl solutions. These results provide vectors towards the center of a magmatic-hydrothermal system that allow explorationists to use fluid inclusion petrography to predict position with the overall porphyry environment when other indicators of position are absent. / Ph. D.

Volatiles are a fundamental component of the Magmatic-Hydrothermal model of platinum group element (PGE) ore deposition for PGE deposits in layered mafic intrusions such as Bushveld and Stillwater. Volatiles have the potential to complex with PGEs in silicate melts and hydrothermal fluids, increasing PGE solubility; in order to assess the models of PGE ore deposition reliable estimates on the solubilities in the various magmatic phases must be known. However, experimental studies on the solubility and partitioning behaviour of PGEs in mafic magmatic-hydrothermal systems under relevant conditions are sparse, and the data that do exist produce conflicting results and new or adapted experimental methods must be applied to investigate these systems. Experimental results are presented here, investigating the effect of volatiles (i.e. H2O, Cl and CO2) on Pt and Ir solubility in a haplobasaltic melt and fluid-melt partitioning of Pt between an aqueous fluid and a haplobasaltic melt under magmatic conditions using a sealed-capsule technique. Also included are the details of the development of a novel experimental technique to observe fluid-melt partitioning in mafic systems and application of the method to the fluid-melt partition of Pt. Solubility experiments were conducted to assess the effect of volatiles on Pt and Ir solubility in a haplobasaltic melt of dry diopside-anorthite eutectic composition at 1523K and 0.2GPa. Synthetic glass powder of an anhydrous, 1-atm eutectic, diopside-anorthite (An42-Di58) haplobasalt composition was sealed in a platinum or platinum-iridium alloy capsule and was allowed to equilibrate with the noble metal capsule and a source of volatiles (i.e. H2O, H2O-Cl or H2O-CO2) at experimental conditions. All experiments were run in an internally-heated pressure vessel equipped with a rapid quench device, with oxygen fugacity controlled by the water activity and intrinsic hydrogen fugacity of the autoclave (MnO-Mn3O4). The resultant crystal- and bubble-free run product glasses were analyzed using a combination of laser ablation ICP-MS and bulk solution isotope-dilution ICP-MS to determine equilibrium solubilities of Pt and Ir and investigate the formation and contribution of micronuggets to overall bulk determined concentrations. In water-bearing experiments, it was determined that water content did not have an intrinsic effect on Pt or Ir solubility for water contents between 0.9 wt. % and 4.4 wt. % (saturation). Water content controlled the oxygen fugacity of the experiment and the resulting variations in oxygen fugacity, and the corresponding solubilities of Pt and Ir, indicate that over geologically relevant conditions both Pt and Ir are dissolved primarily in the 2+ valence state. Pt data suggest minor influence of Pt4+ at higher oxygen fugacities; however, there is no evidence of higher valence states for Ir. The ability of the sealed capsule technique to produce micronugget-free run product glasses in water-only experiments, allowed the solubility of Pt to be determined in hydrous haplobasalt at lower oxygen fugacities (and concentrations) then was previously observed. Pt and Ir solubility can be represented as a function of oxygen fugacity (bars) by the following equations: [Pt](ppb)= 1389(fO-sub-2)+7531(fO-sub-2)^(1/2) [Ir](ppb)=17140(fO-sub-2)^(1/2) In Cl-bearing experiments, experimental products from short run duration (<96hrs) experiments contained numerous micronuggets, preventing accurate determination of platinum and iridium solubility. Longer run duration experiments showed decreasing amounts of micronuggets, allowing accurate determination of solubility; results indicate that under the conditions studied chlorine has no discernable effect on Pt solubility in the silicate melt from 0.6 to 2.75 wt. % Cl (saturation). Over the same conditions, a systematic increase in Ir solubility is found with increasing Cl content; however, the observed increase is within the analytical variation/error and is therefore not conclusive. If there is an effect of Cl on PGE solubility the effect is minor resulting in increased Ir solubilities of 60% at chlorine saturation. However, the abundance of micronuggets in short run duration experiments, which decreases in abundance with time and increases with Cl-content, offers compelling evidence that Cl-bearing fluids have the capacity to transport significant amounts of Pt and Ir under magmatic conditions. It is suggested that platinum and iridium dissolved within the Cl-bearing fluid are left behind as the fluid dissolves into the melt during the heating stages of the experiment, leaving small amounts of Pt and Ir along the former particle boundaries. With increasing run duration, the metal migrates back to the capsule walls decreasing the amount of micronuggets contained within the glass. Estimates based on this model, using mass-balance calculations on the excess amount of Pt and Ir in the run product glasses (i.e. above equilibrium solubility) in short duration experiments, indicate estimated Pt and Ir concentrations in the Cl-bearing fluid ranging from tens to a few hundred ppm, versus ppb levels in the melt. Respective apparent (equilibrium has not been established) partition coefficients (D,fluid-melt) of 1x10^3 to 4x10^3 and 300-1100 were determined for Pt and Ir in Cl-bearing fluids; suggesting that Cl-bearing fluids can be highly efficient at enriching and transporting PGE in mafic magmatic-hydrothermal ore-forming systems. Platinum solubility was also determined as a function of CO2 content in a hydrous haplobasalt at controlled oxygen fugacity. Using the same sealed capsule techniques and melt composition as for H2O and Cl, a hydrous haplobasaltic melt was allowed to equilibrate with the platinum capsule and a CO2-source (CaCO3 or silver oxalate) at 1523 K and 0.2 GPa. Experiments were conducted with a water content of approximately 1 wt. %, fixing the log oxygen fugacity (bars) between -5.3 and -6.1 (log NNO = -6.95 @ 1573 K and 0.2 GPa). Carbon dioxide contents in the run product glasses ranged from 800-2500 ppm; and over these conditions, CO2 was found to have a negligible effect on Pt solubility in the silicate melt. Analogous to the Cl-bearing experiments, bulk concentrations of Pt in CO2-bearing experiments increased with increasing CO2 content due to micronugget formation. Apparent Pt concentrations in the H2O-CO2 fluid phase, prior to fluid dissolution, were calculated to be 1.6 to 42 ppm, resulting in apparent partition coefficients(D,fluid-melt) of 1.5 x 10^2 to 4.2 x 10^3, increasing with increasing mol CO2:H2O up to approximately 0.15, after which increasing CO2 content does not further increase partitioning. As well, a novel technique was developed and applied to assess the partitioning of Pt between an aqueous fluid and a hydrous diopside-anorthite melt under magmatic conditions. Building upon the sealed-capsule technique utilized for solubility studies, a method was developed by adding a seed crystal to the capsule along with a silicate melt and fluid. By generating conditions favourable to crystal growth, and growing the crystal from the fluid, it is possible to entrap fluid inclusions in the growing crystal, allowing direct sampling of the fluid phase at the conditions of the experiment. Using a diopside seed crystal with the diopside-anorthite eutectic melt, it was possible to control diopside crystallization by controlling the temperature, thus allowing control of the crystallization and fluid inclusion entrapment conditions. Subsequent laser ablation ICP-MS analysis of the fluid inclusions allowed fluid–melt partition coefficients of Pt to be determined. Synthetic glass powder of an anhydrous, 1-atm eutectic, diopside-anorthite (An42¬Di58) haplobasalt composition (with ppm levels of Ba, Cs, Sr and Rb added as internal standards), water and a diopside seed crystal were sealed in a platinum capsule and were allowed to equilibrate at experimental conditions. Water was added in amounts to maintain a free fluid phase throughout the experiment, and the diopside crystal was separated from the melt. All experiments were run in an internally heated pressure vessel equipped with a rapid-quench device, with oxygen fugacity controlled by the water activity and intrinsic hydrogen fugacity of the autoclave (MnO-Mn3O4). Experiments were allowed to equilibrate (6-48 hrs) at experimental conditions (i.e. 1498K, 0.2 GPa, fluid+melt+diopside stable) before temperature was dropped (i.e. to 1483K) to induce crystallization. Crystals were allowed to grow for a period of 18-61 hours, prior to rapid isobaric quenching to 293K at the conclusion of the experiment. Experimental run products were a crystal- and bubble-free glass and the diopside seed crystal with a fluid-inclusion-bearing overgrowth. Analysis of fluid inclusions provides initial solubility estimates of Pt in a H2O fluid phase at 1488 K and 0.2 GPa at or near ppm levels and fluid melt partition coefficients ranging from 2 – 48. This indicates substantial metal enrichment in the fluid phase in the absence of major ligands such as carbonate or chlorine. The results of this study indicate that the volatiles studied (i.e. H2O, CO2, and Cl) do not have a significant effect on Pt and Ir solubility in a haplobasaltic melt at magmatic conditions. These results suggest that complexing of Pt and Ir by OH, Cl, and carbonate species in a haplobasaltic melt is insignificant and the presence of these volatiles will not result in significantly increased PGE contents over their dry counterparts, as has been suggested. Preliminary evidence of minor Cl-complexing of Ir is presented; however, resulting in only a slight increase (<100%) in Ir solubility at Cl-saturation. Significant partitioning of Pt and Ir into a fluid phase at magmatic conditions has been demonstrated; with estimates of fluid-haplobasaltic melt partition coefficients increasing from 1x10^1 for pure water to up to an apparent 4x10^3 with the addition of Cl or CO2 to the system. This result indicates complexing of Pt and Ir with OH< HxCOy≤ Cl. Using these estimates, Cl- or CO2-bearing magmatic fluids can be highly efficient at enriching and transporting platinum group elements (PGEs) in mafic magmatic-hydrothermal ore-forming systems.

Volatiles are a fundamental component of the Magmatic-Hydrothermal model of platinum group element (PGE) ore deposition for PGE deposits in layered mafic intrusions such as Bushveld and Stillwater. Volatiles have the potential to complex with PGEs in silicate melts and hydrothermal fluids, increasing PGE solubility; in order to assess the models of PGE ore deposition reliable estimates on the solubilities in the various magmatic phases must be known. However, experimental studies on the solubility and partitioning behaviour of PGEs in mafic magmatic-hydrothermal systems under relevant conditions are sparse, and the data that do exist produce conflicting results and new or adapted experimental methods must be applied to investigate these systems. Experimental results are presented here, investigating the effect of volatiles (i.e. H2O, Cl and CO2) on Pt and Ir solubility in a haplobasaltic melt and fluid-melt partitioning of Pt between an aqueous fluid and a haplobasaltic melt under magmatic conditions using a sealed-capsule technique. Also included are the details of the development of a novel experimental technique to observe fluid-melt partitioning in mafic systems and application of the method to the fluid-melt partition of Pt. Solubility experiments were conducted to assess the effect of volatiles on Pt and Ir solubility in a haplobasaltic melt of dry diopside-anorthite eutectic composition at 1523K and 0.2GPa. Synthetic glass powder of an anhydrous, 1-atm eutectic, diopside-anorthite (An42-Di58) haplobasalt composition was sealed in a platinum or platinum-iridium alloy capsule and was allowed to equilibrate with the noble metal capsule and a source of volatiles (i.e. H2O, H2O-Cl or H2O-CO2) at experimental conditions. All experiments were run in an internally-heated pressure vessel equipped with a rapid quench device, with oxygen fugacity controlled by the water activity and intrinsic hydrogen fugacity of the autoclave (MnO-Mn3O4). The resultant crystal- and bubble-free run product glasses were analyzed using a combination of laser ablation ICP-MS and bulk solution isotope-dilution ICP-MS to determine equilibrium solubilities of Pt and Ir and investigate the formation and contribution of micronuggets to overall bulk determined concentrations. In water-bearing experiments, it was determined that water content did not have an intrinsic effect on Pt or Ir solubility for water contents between 0.9 wt. % and 4.4 wt. % (saturation). Water content controlled the oxygen fugacity of the experiment and the resulting variations in oxygen fugacity, and the corresponding solubilities of Pt and Ir, indicate that over geologically relevant conditions both Pt and Ir are dissolved primarily in the 2+ valence state. Pt data suggest minor influence of Pt4+ at higher oxygen fugacities; however, there is no evidence of higher valence states for Ir. The ability of the sealed capsule technique to produce micronugget-free run product glasses in water-only experiments, allowed the solubility of Pt to be determined in hydrous haplobasalt at lower oxygen fugacities (and concentrations) then was previously observed. Pt and Ir solubility can be represented as a function of oxygen fugacity (bars) by the following equations: [Pt](ppb)= 1389(fO-sub-2)+7531(fO-sub-2)^(1/2) [Ir](ppb)=17140(fO-sub-2)^(1/2) In Cl-bearing experiments, experimental products from short run duration (<96hrs) experiments contained numerous micronuggets, preventing accurate determination of platinum and iridium solubility. Longer run duration experiments showed decreasing amounts of micronuggets, allowing accurate determination of solubility; results indicate that under the conditions studied chlorine has no discernable effect on Pt solubility in the silicate melt from 0.6 to 2.75 wt. % Cl (saturation). Over the same conditions, a systematic increase in Ir solubility is found with increasing Cl content; however, the observed increase is within the analytical variation/error and is therefore not conclusive. If there is an effect of Cl on PGE solubility the effect is minor resulting in increased Ir solubilities of 60% at chlorine saturation. However, the abundance of micronuggets in short run duration experiments, which decreases in abundance with time and increases with Cl-content, offers compelling evidence that Cl-bearing fluids have the capacity to transport significant amounts of Pt and Ir under magmatic conditions. It is suggested that platinum and iridium dissolved within the Cl-bearing fluid are left behind as the fluid dissolves into the melt during the heating stages of the experiment, leaving small amounts of Pt and Ir along the former particle boundaries. With increasing run duration, the metal migrates back to the capsule walls decreasing the amount of micronuggets contained within the glass. Estimates based on this model, using mass-balance calculations on the excess amount of Pt and Ir in the run product glasses (i.e. above equilibrium solubility) in short duration experiments, indicate estimated Pt and Ir concentrations in the Cl-bearing fluid ranging from tens to a few hundred ppm, versus ppb levels in the melt. Respective apparent (equilibrium has not been established) partition coefficients (D,fluid-melt) of 1x10^3 to 4x10^3 and 300-1100 were determined for Pt and Ir in Cl-bearing fluids; suggesting that Cl-bearing fluids can be highly efficient at enriching and transporting PGE in mafic magmatic-hydrothermal ore-forming systems. Platinum solubility was also determined as a function of CO2 content in a hydrous haplobasalt at controlled oxygen fugacity. Using the same sealed capsule techniques and melt composition as for H2O and Cl, a hydrous haplobasaltic melt was allowed to equilibrate with the platinum capsule and a CO2-source (CaCO3 or silver oxalate) at 1523 K and 0.2 GPa. Experiments were conducted with a water content of approximately 1 wt. %, fixing the log oxygen fugacity (bars) between -5.3 and -6.1 (log NNO = -6.95 @ 1573 K and 0.2 GPa). Carbon dioxide contents in the run product glasses ranged from 800-2500 ppm; and over these conditions, CO2 was found to have a negligible effect on Pt solubility in the silicate melt. Analogous to the Cl-bearing experiments, bulk concentrations of Pt in CO2-bearing experiments increased with increasing CO2 content due to micronugget formation. Apparent Pt concentrations in the H2O-CO2 fluid phase, prior to fluid dissolution, were calculated to be 1.6 to 42 ppm, resulting in apparent partition coefficients(D,fluid-melt) of 1.5 x 10^2 to 4.2 x 10^3, increasing with increasing mol CO2:H2O up to approximately 0.15, after which increasing CO2 content does not further increase partitioning. As well, a novel technique was developed and applied to assess the partitioning of Pt between an aqueous fluid and a hydrous diopside-anorthite melt under magmatic conditions. Building upon the sealed-capsule technique utilized for solubility studies, a method was developed by adding a seed crystal to the capsule along with a silicate melt and fluid. By generating conditions favourable to crystal growth, and growing the crystal from the fluid, it is possible to entrap fluid inclusions in the growing crystal, allowing direct sampling of the fluid phase at the conditions of the experiment. Using a diopside seed crystal with the diopside-anorthite eutectic melt, it was possible to control diopside crystallization by controlling the temperature, thus allowing control of the crystallization and fluid inclusion entrapment conditions. Subsequent laser ablation ICP-MS analysis of the fluid inclusions allowed fluid–melt partition coefficients of Pt to be determined. Synthetic glass powder of an anhydrous, 1-atm eutectic, diopside-anorthite (An42¬Di58) haplobasalt composition (with ppm levels of Ba, Cs, Sr and Rb added as internal standards), water and a diopside seed crystal were sealed in a platinum capsule and were allowed to equilibrate at experimental conditions. Water was added in amounts to maintain a free fluid phase throughout the experiment, and the diopside crystal was separated from the melt. All experiments were run in an internally heated pressure vessel equipped with a rapid-quench device, with oxygen fugacity controlled by the water activity and intrinsic hydrogen fugacity of the autoclave (MnO-Mn3O4). Experiments were allowed to equilibrate (6-48 hrs) at experimental conditions (i.e. 1498K, 0.2 GPa, fluid+melt+diopside stable) before temperature was dropped (i.e. to 1483K) to induce crystallization. Crystals were allowed to grow for a period of 18-61 hours, prior to rapid isobaric quenching to 293K at the conclusion of the experiment. Experimental run products were a crystal- and bubble-free glass and the diopside seed crystal with a fluid-inclusion-bearing overgrowth. Analysis of fluid inclusions provides initial solubility estimates of Pt in a H2O fluid phase at 1488 K and 0.2 GPa at or near ppm levels and fluid melt partition coefficients ranging from 2 – 48. This indicates substantial metal enrichment in the fluid phase in the absence of major ligands such as carbonate or chlorine. The results of this study indicate that the volatiles studied (i.e. H2O, CO2, and Cl) do not have a significant effect on Pt and Ir solubility in a haplobasaltic melt at magmatic conditions. These results suggest that complexing of Pt and Ir by OH, Cl, and carbonate species in a haplobasaltic melt is insignificant and the presence of these volatiles will not result in significantly increased PGE contents over their dry counterparts, as has been suggested. Preliminary evidence of minor Cl-complexing of Ir is presented; however, resulting in only a slight increase (<100%) in Ir solubility at Cl-saturation. Significant partitioning of Pt and Ir into a fluid phase at magmatic conditions has been demonstrated; with estimates of fluid-haplobasaltic melt partition coefficients increasing from 1x10^1 for pure water to up to an apparent 4x10^3 with the addition of Cl or CO2 to the system. This result indicates complexing of Pt and Ir with OH< HxCOy≤ Cl. Using these estimates, Cl- or CO2-bearing magmatic fluids can be highly efficient at enriching and transporting platinum group elements (PGEs) in mafic magmatic-hydrothermal ore-forming systems.

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.

Le gisement de Tocantinzinho est situé sur la province aurifère de Tapajós et est le plus grand gisement d'or de la province, avec 53,9 tonnes d'or estimées. Sa formation commence par un magmatisme granodioritique autour de 2005 Ma, suivi d'un magmatisme granitique. Le granite Tocantinzinho est composé de deux faciès principaux (syenogranite - 1996± 2Ma; monzogranite 1989±1 Ma), des corps d’aplite et de pegmatite, qui suggère un magmatisme enrichie en fluide et mis en place à faible profondeur. Intrusifs dans ces roches, des dykes d'andésite (1998±8Ma) ont des fragments de granite et des mélanges entre les 2 magmas suggèrent un magmatisme à la fois continu et polyphasé. Il est proposé que les premiers dykes d’andésite se sont mis en place alors que le granite n’était pas entièrement cristallisé (mingling) et les derniers lors des stades de déformation à l’état solide du granite. Utilisant la courbe de refroidissement, un âge minimum de 1975 Ma a été estimé pour l’andésite. Les taux de refroidissement des roches plutoniques varient de 3,6 à 14,7°C/Ma, avec une moyenne de 7,5°C/Ma, suggérant que les processus d'exhumation verticale sont faibles. La géométrie allongée du granite ainsi que la tectonique syn-magmatique de l'andésite corroborent la prédominance des mouvements horizontaux. L’affinité calc-alcaline fortement potassique et des anomalies en niobium définissent deux configurations possibles pour le cadre géotectonique: arc continental de type Andin ou Post-collisionnel. Compte tenue la relation génétique entre magmatisme, cisaillement décrochant et les faibles taux de refroidissement, l’environnement post-collisionnel est plus probable. Cela ensemble avec les âges nous permettent de comparer ces roches avec celles de la Suite Intrusive Creporizão (1997-1957Ma). La dacite (1992 ± 2 Ma) recoupe les autres roches, cependant, la signature géochimique comparable aux roches anorogéniques suggère qu’elle appartient à une série magmatique distinct. La zone minéralisée est limitée par deux failles majeures senestres de direction N100°-130E°. Le granite Tocantinzinho et les roches hypo-volcaniques déformées sont dans ce couloir, altérées par de fluides hydrothermaux et minéralisées pendant deux phases tectoniques distinctes. La première est caractérisée par des brèches et des microfractures remplies par muscovite (1864±5Ma) et pyrite, associées à de faibles teneur d’or (<1,5ppm) restreintes au granite. La deuxième phase a été contrôlée par le cisaillement décrochant senestre normal générant des fentes de tension et des brèches remplies par quartz, chlorite, calcite, albite, rutile, pyrite, galène, sphalérite, chalcopyrite et or. La teneur en or peut atteindre jusqu'à 70 ppm dans les veines riches en sulfures. Ces structures de remplissage syntectonique sont parallèles entre elles et orientées N30-60°E. Deux hypothèses ont été proposées pour expliquer la genèse du gisement: la première considère une relation génétique entre magmatisme et minéralisation au moins pour le premier stage de minéralisation selon un modèle porphyrique et la seconde alternative considère une réactivation des failles préexistantes par une tectonique transtensive liée au magmatisme Maloquinha (ca. 1880Ma) pour les deux stades minéralisateurs. Les deux phases dans les deux hypothèses, ont été classées comme des minéralisations de type magmato-hydrothermale qui pourraient être classées soit comme des systèmes d'or liés à l'intrusion. De nouveaux travaux sur le terrain et en laboratoire seraient nécessaires pour identifier et caractériser la nature et la source des fluides hydrothermaux, pour dater la minéralisation et mieux comprendre le rôle des roches hypo-volcaniques. Toutefois, les premiers résultats, et notamment le rôle fondamental du contrôle tectonique pour la minéralisation sont très significatifs et peuvent aider de manière conséquente à l'établissement des programmes d'exploration et d'exploitation futurs. / The Tocantinzinho deposit is located on the Tapajós Gold Province and is the largest gold deposit within Province, with 53,9 tons of gold. Its formation begins with a granodioritic magmatism around 2005Ma, followed by a granitic magmatism 10 Ma latter. The Tocantinzinho granite is composed by two main facies, syenogranite (1996±2Ma) and monzogranite (1989±1Ma), and by aplite and pegmatite bodies, suggesting a fluid-rich magmatism at shallow depth. Andesite dikes (1998±8Ma) are intrusive in both rocks. Sharp fragments of those rocks along contacts and minor mingling with granitic magma suggest a multiphase magmatism at distinct timing. The first dikes have intruded within granite when it was crystalizing, thus a minimum age of 1975Ma was estimated. Cooling rates of plutonic rocks vary from 3.6 to 14.7°C/Ma, with an average of 7.5°C/Ma, suggesting vertical exhumation processes were minor. The elongated geometry of granite along with sin-magmatic strike-slip tectonics of andesite corroborate the predominance of horizontal movements. Geochemical analysis show high-K calk-alkaline affinity and niobium anomaly indicator of two possible geotectonic settings for these rocks: Andean-type continental arc or post-collisional one. Considering the genetic relationship between magmatism, strike-slip faults, and low cooling rates, a post-collisional setting is more likely. The geochemical signature, ages and style of tectonism allow us to compare those rocks with the ones from Creporizão Intrusive Suite (1997-1957Ma). Dacite dikes (1992±2Ma) cut across all other rocks, but the temporal relationship among them remains misunderstood, due to the geochemical signature similar to the anorogenic rocks, suggesting it belongs to a distinct and latter magmatic series. Indeed, the dated zircons were probably inherited from host rocks. The mineralized area is restricted to a domain constrained by two major sinistral strike-slip N100°-130E°E faults that comprises the Tocantinzinho granite and sub-volcanic rocks, which were hydrothermally altered, brittle deformed and mineralized during two phases. The first one is characterized by breccias and microfractures infilled with muscovite (1864±5Ma) and pyrite, which contains low gold grades and are restricted to the Tocantinzinho granite. The second phase was controlled by strike-slip and normal tectonics generating tension gashes veins and pull apart breccias infilled with quartz, chlorite, calcite, albite, rutile, pyrite, galena, sphalerite, chalcopyrite, and gold. The gold grade can reach up to 70 ppm in some sulfide-rich veins. These structures are parallel and mainly trends N30-60°E, showing textures and orientated minerals typical of syn-tectonic infilling. Based on petrographical features and argon ages two hypothesis were proposed for the ore genesis: the first one consider a genetic relationship between magmatism and ore fluids for first mineralization stage and the second hypothesis consider a reactivation of pre-existing faults by an extensional tectonism related to the Maloquinha Intrusive Suite magmatism (ca.1880Ma) for this phase. The second mineralization phase is considered as formed as consequence of tectonic reactivation at ca. 1880Ma, in both hypothesis. Both phases in both hypothesis were classified as magmatic-hydrothermal ore mineralization and might be classified as intrusion-related gold systems. However, new field works are important in order to identify and characterize the nature and source of hydrothermal fluids, as well as ore dating and new geochemical and geochronological data of sub-volcanic rocks are imperative to better understand the genesis and evolution of the Tocantinzinho gold deposit. Such results, strongly linked to the fact that the tectonic control seem significant, may help for future exploration and exploitation programs.

Le Granite Passa Três est situé à l'Est de l'Etat du Paraná, au Sud du Brésil, et est allongé selon une direction NNE-SSW. Sa mise en place se fait au cœur des metapélites mesoprotérozoïques du Groupe Açungui (Province Mantiqueira). La minéralisation d’or du Granite Passa Três est composée par des veines de quartz contenant des quantités variables de fluorite, sulfures et carbonates. Les objectifs principaux de ce travail de thèse sont : de comprendre le modèle de formation du système de veines minéralisées en prenant en compte les relations entre magmatisme, hydrothermalisme, déformation et minéralogie à la fois dans l’espace et dans le temps ; la caractérisation de la nature, de la source et des conditions de dépôt des fluides ; et la caractérisation du modèle métallogénique de ce gisement singulier. Pour arriver à ces objectifs, les méthodes utilisées seront, en sus de la géologie structurale et de terrain : la pétrographie, la géochronologie U-Pb (LA-ICP-MS) sur zircon et 40Ar-39Ar sur muscovite, la microscopie électronique à balayage (MEB), la microsonde électronique, la fluorescence X (XFR), l’analyse isotopique du soufre (δ34S) et l’analyse microthermométrique et RAMAN des inclusions fluides. Les données structurales ont montré la coexistence de deux systèmes principaux de filons minéralisés, l’un N-S et l’autre E-W, avec des pendages de 60-75°W et 45-70°S, respectivement. Les deux systèmes sont interprétés comme contemporains et conjugués. Les corps minéralisés forment des géométries sigmoïdales qui résultent de l’ouverture en pull-aparts résultant de mouvements en faille normale le long de plans de glissement à faible pendage. Le fort pendage des structures minéralisées s’explique par l’enveloppe globale formée par la succession des pull-aparts. Quatre étapes minéralogiques sont à l’origine de la formation du système minéralisé : phase 1 [qtz 1 + fl], phase 2a [qtz 2 + py 2a ± or ± cpy ± aik ± fl ± sph ± musc], phase 2b [qtz 2 + py 2b + or + cpy + aik + ank ± sph ± fl ± musc] et phase 3 [qtz 3 + ank + calc + molyb ± aik ± musc ± fl]. L’or se trouve dans la forme d’or invisible et d’or natif dans des fractures qui affectent les pyrites des phases 2a et b, systématiquement associé avec la chalcopyrite et l’aikinite. L’altération associée à la minéralisation inclue des assemblages composés par muscovite/quartz/pyrite (altération du type greisen) et séricite/carbonate/clinochlore (altération phyllique). Les valeurs δ34S des pyrites (de -0.1‰ à 1.1‰) indiquant que le soufre du dépôt peut être d’origine magmatique. Cette hypothèse est en accord avec l’observation systématique, dans les parties supérieures du granite (sondage et niveaux supérieurs de la mine), de structures caractéristiques de transition magmatique-hydrothermale comme des systèmes aplo-pegmatitiques, des veines de quartz à bordure de K-feldspath, des concentrations de quartz de type stockscheider et des textures de solidification unilatérales (UST). Les résultats de géochronologie confirment cette hypothèse avec des âges U-Pb sur zircon (611.9±4.7 et 611.9±5.6 Ma pour le granite à grain moyen (GEM) et le microgranite (GEF) et 40Ar-39Ar sur muscovite (veines à bordure de K-feldspath : 612.9±2 à 608.8±2 Ma ; veines minéralisées : 611.7±2 à 608.8±2 Ma ; veines de quartz précoces : 608.4±2 Ma) très proches. Ces âges obtenus indiquent que la mise-en-place du granite, l’exsolution du fluide magmatique-hydrothermal et la formation des veines de quartz aurifères ont été réalisées pendant un écart de temps de 5 Ma, entre 613 et 608 Ma. La minéralisation (611 à 608 Ma) contemporaine de la cristallisation du granite (612 à 610 Ma), l’association de l’or avec des minéraux de bismuth (aikinite), la démonstration du contrôle structural sur la formation des veines et les évidences de transition magmatique-hydrothermale en domaine de coupole granitique montrent que le dépôt d’or du Granite Passa Três partage plusieurs similitudes avec les dépôts du type intrusion-related. / The Passa Três Granite is situated in southern Brazil (Paraná State) and presents a NNE-SSW elongated shape. This intrusion is emplaced within metapelites of the Mesoproterozoic Açungui Group (Ribeira Belt, Mantiqueira Province), between the N40E trending Morro Agudo and Lancinha faults. Gold mineralisation is composed of centimetric to metric quartz veins with fluorite, sulphides and carbonates. The main objectives of this work are i) to understand the model of formation of the mineralised veins systems taking into account the relationships between magmatism, hydrothermalism, deformation and mineralogy in space and time; ii) the characterization of the nature, source and emplacement conditions of the ore fluids; and iii) the characterization of a metallogenic model for this singular deposit. In order to reach these purposes, the methods to be applied include, beyond the structural geology and field works: petrography, U-Pb zircon (LA-ICP-MS) and 40Ar-39Ar muscovite geochronology, scanning electron microscopy (SEM), electron-microprobe analyses (EPMA), X-ray fluorescence (XRF), isotopic analysis of sulphur (δ34S), and microthermometric and Raman analysis of fluid inclusions. Structural data showed the coexistence of two major normal mineralised vein systems, one N-S and the other one E-W, with dips of 60-75ºW and 45-70ºS, respectively. Both systems are interpreted to be contemporaneous and conjugated. Orebodies form sigmoidal geometries that resulted of the opening of pull-aparts as a consequence of the normal movements along low-angle fault planes. High-angle dip of the global mineralised structures is explained by the succession of the pull-aparts. Four mineralogical stages resulted in the formation of the mineralised system: phase 1 [quartz 1 + fluorite], phase 2a [quartz 2 + pyrite 2a ± gold ± chalcopyrite ± aikinite ± fluorite ± sphalerite ± muscovite], phase 2b [quartz 2 + pyrite 2b + gold + chalcopyrite + aikinite + ankerite ± sphalerite ± fluorite ± muscovite] and phase 3 [quartz 3 + ankerite + calcite + molybdenite ± aikinite ± muscovite ± fluorite]. Gold occurs as invisible gold and as native grains within fractures that affect pyrite 2a and 2b, commonly associated with chalcopyrite and aikinite. Alteration related to the mineralisation includes muscovite/quartz/pyrite (greisen type alteration) and sericite/carbonato/clinochlore (phyllic alteration) assemblages. The δ34S values of pyrite crystals (from -0.1‰ to 1.1‰) indicate that the sulphur in this deposit may have a magmatic origin. This hypothesis agrees with the systematic observation, within the upper part of the granite (drill holes and superior levels of the mine), of structures typical of magmatic-hydrothermal transition such as aplite-pegmatite systems, quartz veins with K-feldspar border, quartz concentration of stockscheider type and unilateral solidification textures (UST). Geochronological data confirm this hypothesis with U-Pb zircon ages (611.9±4.7 and 611.9±5.6 Ma for medium grained granite facies (GEM) and microgranite (GEF), respectively) and 40Ar-39Ar muscovite dating (veins with K-feldspar border: 612.9±2 to 608.8±2 Ma; mineralised veins: 611.7±2 to 608.8±2 Ma; barren vein: 608.4±2 Ma), that are very close. These ages indicate that the granite emplacement, the magmatic-hydrothermal fluid release and the formation of gold-bearing quartz veins occur during a time lapse of approximately 5 Ma, between 613 and 608 Ma. The mineralisation (611 to 608 Ma) coeval to granite crystallization (612 to 610 Ma), the association of gold with Bi minerals (aikinite), the strong structural control for veins and magmatic-hydrothermal transition features at the roof of a small granitic intrusion suggest that the Passa Três gold deposit shares several similarities with intrusion-related gold deposits.

Les gisements à Sn-W de type veine et greisen sont des systèmes magmatiques-hydrothermaux dont l’exploitation fournit une part importante de la production mondiale de tungstène et qui représentent également une source importante d’étain. La formation de ces gisements résulte d’un continuum de processus magmatiques et hydrothermaux et implique un transport efficace et la focalisation des fluides minéralisateurs. Cette étude vise àaméliorer la compréhension des processus hydrodynamiques et géologiques impliqués lors du transport et du dépôt de métaux conduisant à la formation de ces gisements. Nous avons réalisé une étude pluridisciplinaire combinant (i) travail de terrain (étude géologique et structurale), (ii) reconstruction des paléo-circulations hydrothermales via l’analyse texturale des bandes de croissance des tourmalines, (iii) détermination expérimentale des changements de perméabilité induits par la greisenisation et (iv) modélisation numérique des écoulements péri-granitiques prenant en compte l’évolution de la perméabilité dynamique lors des interactions fluide-roche. Cette méthodologie a été appliquée au cas du gisement W-Sn-(Cu) de Panasqueira, qui constitue un site de référence pour étudier les processus magmatiques e thydrothermaux conduisant à la formation de gisements à Sn-W de classe mondiale. Les résultats obtenus démontrent que l’expulsion des fluides magmatiques minéralisés a déclenché la greisenisation des parties apicales (coupoles etapex) de l’intrusion granitique, entraînant la création de porosité (~ 8,5%) qui améliore significativement la perméabilité(de 10-20 à 10-17 m²) au sein du greisen massif composant le toit de l’intrusion. Le développement de ce niveau perméable constitue un drain important favorisant l'expulsion et la focalisation des fluides magmatiques minéralisateurs exsolvés lors de la cristallisation du granite sous-jacent. Cette focalisation des décharges hydrothermales (i) améliore significativement le transport des métaux, et (ii) favorise l'établissement de conditions de pression de fluide élevées qui couplées aux contraintes régionales compressives causent l'ouverture des veines minéralisées au toit de l’intrusion.Cette étude souligne l’importance des rétrocontrôles entre perméabilité dynamique et altération hydrothermale. Ces derniers constituent des mécanismes majeurs permettant d’améliorer significativement la circulation des fluides minéralisateurs et donc la formation de gisements hydrothermaux de grandes tailles / The vein and greisen Sn-W deposits are magmatic-hydrothermal systems that provide an important part of theworld W production and represent an important source of Sn. The formation of these deposits involves continuum ofmagmatic-hydrothermal processes and implies the transfer and the focusing of a large amount of mineralizing fluids. Thisstudy aims to improve understanding of hydrodynamic and geological processes involved during the transport and thedeposition of metals leading to the formation of these deposits. We have performed a complete study combining (i) fieldworks (geological and structural studies), (ii) fluid flow reconstruction via the textural analysis of tourmaline growth bands,(iii) experimental determination of permeability changes during greisenization, and (iv) numerical modeling of peri-graniticfluid flow accounting for magmatic fluid production and dynamic permeability related to fluid-rock interactions. Thismethodology was applied in the case of the world-class W-Sn-(Cu) Panasqueira deposit, which represents a referencesite to study magmatic-hydrothermal processes leading to the formation of large vein and greisen deposit. Our resultsdemonstrate that the releasing and the expulsion of ore-bearing magmatic fluids triggered greisenization of the apicalpart of granite intrusion, which caused generation of porosity (~8.5%) and therefore a significant increase of permeability(from 10-20 to 10-17 m²) in massive greisen composing the granite’s roof. The development of this permeable pathwayconstitutes an important drain promoting the expulsion and the focusing of magmatic fluids produced during thecrystallization of the underlying granite. This enhancement of magmatic fluids expulsion (i) promotes significantly fluidflux and transfer of metals, and (ii) the establishment of high fluid pressure conditions, which coupled with the regionalcompressive crustal regime, triggered the opening of mineralized veins above the granite roof. Finally, this studyemphasizes that reactive hydrothermal fluids are able to generate their own pathways in initially impermeable rocks. Thisprocess represents an important mechanism to enhance fluid flow and promote the formation of large hydrothermaldeposits.