Les granites à métaux rares ont une faible valeur économique mais sont souvent exploités pour leurs minéraux industriels. L’objectif de ce travail est d’évaluer la potentialité de certains résidus issus de la production de kaolin de St Austell (Angleterre) pour la récupération de métaux critiques (CRMs) comme les Terre Rares légères (LREE), le niobium (Nb), le tungstène (W) et l’étain (Sn) via le développement d’un procédé de récupération des CRMs. L’étude des résidus miniers montre que les CRM sont concentrés dans le résidu micacé avec des teneurs en LREE allant jusqu’à 170 ppm avec 40 à 60% des CRMs distribués dans ce résidu. Un procédé de traitement de ce résidu a été développé incluant des étapes de concentration par gravité et flottation. Les teneurs en LREE permettent la récupération d’environ 60% des LREE avec des teneurs de 1,6 % et 0,5% LREE respectivement dans le concentré de gravité et flottation / Rare metals granites have always been considered of poor economic value due to their low metal grades but, when altered, they are often exploited for their industrial minerals. This work address the recovery of critical metals (CRMs) including Light Rare Earth Elements (LREE) and rare metals (Sn, Nb, W) from St Austell (UK) kaolin residues though the development of a beneficiation process. Results shows that CRMs are pre-concentrated in the micaceous residue stream with LREE grades of 170 ppm, which account from 40% to 60% of the mass of CRM entering the plant. Analysis of this residue streams shows a high variability of CRM grades and suggest a cut-off grades for some of them. A combined gravity/flotation process have been developed for this residue which allow to recover up to 60% LREE with LREE grade of 1.6 to 0.5% for the gravity and flotation concentrate respectively

Le tungstène (W) fait partie des « ressources minérales critiques » définies par la Commission Européenne en terme d’approvisionnement pour de nombreuses applications technologiques. Le Massif Central Français (MCF), localisé dans la partie interne de la Chaîne Varisque Européenne, possède un potentiel économique significatif en W (>45 kt WO3) essentiellement sous forme de minéralisations disséminées dans des granites spécialisés ou associées à des systèmes filoniens hydrothermaux péri-granitiques à quartz-wolframite±cassiterite. Le but de cette thèse est (i) de caractériser les sources des fluides et des métaux impliquées dans la formation des minéralisations à W et (ii) de dater ces événements métallogéniques afin de les relier avec l’évolution orogénique de la Chaîne Varisque et notamment avec les événements métamorphiques et magmatiques fini-carbonifères. Ce travail est basé sur l’étude de plusieurs gisements hydrothermaux à W±Sn dans le MCF dans une approche multidisciplinaire combinant pétrographie et minéralogie détaillée, géochimie minérale et isotopique, géochimie en roche totale des granites et roches métamorphiques, géochronologie et étude des inclusions fluides. Les datations U-Pb des wolframites montrent que les minéralisations à W résultent d’événements hydrothermaux distincts sur une période d’au moins 40 Ma, correspondant à trois épisodes géodynamiques majeurs affectant la Chaine Varisque : (i) des minéralisations viséo-namuriennes (333-327 Ma) contemporaines de la compression syn-orogénique et de la mise en place des complexes leucogranitiques peralumineux à 335-325 Ma; (ii) des minéralisations namuro-westphaliennes (315-310 Ma) associées au jeu complexe de conditions compressives et extensives dans les zones internes de la Chaîne Varisque qui caractérise la fin du Carbonifère; (iii) des minéralisations stéphano-permiennes (298-274 Ma) mises en place en contexte post-collisionnel. L’analyse in situ des éléments mineurs et traces dans la wolframite a révélé l’existence de différents types de signatures géochimiques régionales, qui montrent de nombreuses similarités avec celles de granites évolués riches en métaux rares. L’étude détaillée du gisement de Puy-les-Vignes, exemple exceptionnel de minéralisation hydrothermale à W associée à un pipe bréchique, a permis de démontrer la superposition d’un stade à Nb-Ta sur la paragenèse primaire à W, interprété comme la contribution d’un fluide magmatique issu d’une coupole granitique à métaux rares. Ce résultat apparait similaire avec ceux déjà obtenus dans le cas du gisement de W d’Echassières, où le stockwerk à quartz-wolframite de La Bosse est recoupé par le granite à métaux rares de Beauvoir. De même, des aplites et pegmatites à métaux rares impactant les minéralisations à W±Sn ont été mises en évidence à Puy-les-Vignes et à St-Mélany. L’analyse par LA-ICPMS des inclusions fluides du granite de Beauvoir et du stockwerk de la Bosse a permis de caractériser la composition chimique des fluides primaires exsolvés lors de la transition magmatique-hydrothermale et de montrer leurs concentrations très élevées (102-103 ppm) en métaux rares (Sn, W, Nb) et la plus grande mobilité hydrothermale du Nb par rapport à celle du Ta. L’analyse minéralogique et géochimique de minéraux marqueurs des circulations fluides, tels que la tourmaline et les oxydes de titane, apporte de nouvelles évidences sur l’importance du rôle joué par les fluides métamorphiques régionaux précoces pour la mise en place des minéralisations à W-Sn. Enfin, cette thèse apporte des mises au point de développement méthodologique pour l’analyse multi-élémentaire des inclusions fluides et de la wolframite par LA-ICPMS. / Tungsten (W) is part of the “critical mineral resources” as defined by the European Commission in terms of supply for several technological applications. The French Massif Central (FMC), located in the internal part of the European Variscan belt, is the host for a significant economic potential in W (>45 kt WO3), mainly as disseminated mineralization in specialized granites or associated with peri-granitic quartz-wolframite±cassiterite hydrothermal vein systems. The aim of this thesis is (i) to characterize the fluids and metals sources involved in the genesis of W mineralization and (ii) to date these metallogenic events in the framework of the orogenic evolution of the Variscan belt, especially in link with the late-Carboniferous metamorphic and magmatic events. This work is based on the study of several W±Sn hydrothermal deposits in the FMC using a multidisciplinary approach combining petrography and detailed mineralogy, mineral and isotope geochemistry, whole-rock geochemistry of granites and metamorphic rocks, geochronology and fluid inclusions study. U-Pb dating of wolframite show that the W mineralization formed during several distinct hydrothermal events in a period of at least 40 Ma, corresponding to three major geodynamic episodes affecting the Variscan belt: (i) Visean-Namurian (333-327 Ma) mineralization coeval with the syn-orogenic compression and the emplacement of peraluminous leucogranitic complexes at 335-325 Ma; (ii) Namurian-Westphalian (315-310 Ma) mineralization associated with a complicated setting characterized by coeval compressive and extensive conditions in the internal zones of the Variscan belt, typical of the late-Carboniferous; (iii) Stephanian-Permian (298-274 Ma) mineralization emplaced in post-collisional context. In situ analysis of minor and trace elements in wolframite showed the existence of different types of regional geochemical signatures, which share several similarities with those from rare-metal-rich evolved granites. The detailed study of the Puy-les-Vignes deposit, an exceptional case of hydrothermal W mineralization associated with a breccia pipe, allowed to demonstrate the superposition of a Nb-Ta stage on the primary W paragenesis, which is interpreted as the contribution of a magmatic fluid derived from a rare-metal granitic cupola. This result appears similar with those already obtained in the Echassières W deposit, where the La Bosse quartz-wolframite stockwork is cut by the Beauvoir rare-metal granite. Similarly, rare-metal aplites and pegmatites overprinting W±Sn mineralization have been shown in the Puy-les-Vignes and St-Mélany deposit. LA-ICPMS analysis of fluid inclusions from the Beauvoir granite and the La Bosse stockwork allowed to characterize the chemical composition of the primary fluids exsolved during the magmatic-hydrothermal transition and to show their very high concentrations (102-103 ppm) in rare-metals (Sn, W, Nb), and the higher hydrothermal mobility of Nb compared to Ta. Mineralogical and geochemical analyses of minerals markers of fluid circulations, such as tourmaline and titanium oxides, bring new evidences of the important role played by the early regional metamorphic fluids in the emplacement of W-Sn mineralization. Finally, this thesis gives new methodological developments for the multi-element analysis of fluid inclusions and wolframite by LA-ICPMS.

O Granito Desemborque, um corpo de forma, aproximadamente, circular, situado no sul do Estado de São Paulo, tem área aflorante de 50 km2 e é representado por um biotita sienogranito. O caráter peraluminoso com teores significativos de K2O e Na2O, juntamente com o baixo conteúdo de CaO, altas razões Fe/Mg, elevados valores de SiO2 e de elementos traços como Zr, Nb e Y, atestam a afinidade alcalina do granito que pode ser classificado como do tipo A. Os teores de Y refletem a presença de fases acessórias como parisita de Ce, itrofluorita e monazita. Columbita, zircão rico em háfnio e cassiterita presentes na associação de minerais acessórios do Granito Desemborque foram analisados semiquantitativamente (teores em peso) por MEV-EDS. Com isso foi possível discriminar duas fases evolutivas para a geração de alguns dos minerais de metais raros associados ao corpo; uma francamente magmática (com subfases granítica e pegmatítica) e uma fase hidrotermal. A columbita (teor médio de Nb2O5 de 66,2% e 6,5% de Ta2O5) é nitidamente gerada na fase magmática sendo que na subfase granítica ela tem presença ubíqua e caráter disseminado. O zircão, por sua vez, ocorre nas duas subfases magmática, sendo que na subfase granítica ele teria um caráter mais tardio. O teor médio das análises foi de 9,3% de HfO2, classificando-o como um zircão rico em háfnio. Na fase hidrotermal, é que se desenrolariam os processos de enriquecimento em Hf desse mineral. A cassiterita, os minerais de REE e boa parte dos minerais radioativos têm a sua formação restrita a fase hidrotermal. Dentre as classificações propostas para granitos mineralizados, o Granito Desemborque se aproxima do tipo peralcalino mineralizado a metais raros com tendência a formar depósitos ou ocorrências de Nb e ETR. Os senões seriam o fato desse corpo não ser peralcalino (ele é peraluminosso) e dos potenciais minerais de Y e ETR só terem sido registrados como inclusões minerais hospedadas nos grãos de cassiterita (ítriocolumbita) e de zircão (xenotímio). A falta de concentrações minerais econômicas de Nb-Hf-Sn associadas ao Granito Desemborque pode ser imputada ao caráter anídrico do magma (tipo-A) e a falta ou limitação do fraturamento hidráulico. A ausência de concentrações minerais econômicas em virtude da remoção erosiva da zona de cúpula não se encontra de acordo com os resultados prospectivos encontrados, pois, a presença da cromita nas amostras de leito ativo coletadas nas drenagens estabelecidas bem no cerne do corpo granítico indica a preservação de restos de pendentes de teto da rocha encaixante (ortognaisses com boudins de rochas ultrabásicas). / The Desemborque Granite, a body almost of circular shape, placed in the southernmost part of São Paulo State, has an area of ca. 50 km2. and it is represented by a sienogranite biotite. Its peraluminous features with significant contents of K2O and Na2O, together with low CaO contents, high Fe/Mg ratios, elevated values of SiO2 and trace elements as Zr, Nb and Y, assure the granite alcaline affinity that can be classified as type A. The Y numbers reflect the presence of acessory phases as parasite de Ce, yttrofluorite and monazite. Columbite, zircon rich in hafnium and cassiterite presented in the association of accessory minerals of the Granite Desemborque were semiquantitatively analysed(values in weight) by MEV-EDS. Because of this it was possible to detail the two evolutional phases for the generation of some minerals of rare metals associated to the body; one fairly magmatic (with granitic sub-phases and pegmatitic) and an hidrotermal phase. Columbite (Nb2O5 mean value 66,2% and 6,5% Ta2O5) is clearly generated in magmatic phase and in the granitric sub-phase it has ubiquitous presence and disseminated character. Zircon, in its turn, occurs in the two magmatic sub-phases, and in the granitic sub-phase it would have a later character. The mean value of the analysis was of 9,3% for HfO2, classifying it as a zircon rich in hafnium. In the hidrotermal phase, the enrichment proccesses are developed in Hf of this mineral. Cassiterite, the REE minerals and a large number of radiactive mineral have their formation restricted to the hidrotermal phase. Amongst the proposed classification for the mineralized granites, the Granite Desemborque has an peralkalkine mineralized approach to rare metals with a wide tendency to create deposits or Nb and REE occurences. The opposition could be the fact that this body is not peralkaline (it is peraluminous) and the Y and REE mineral potentials only have been recorded in the hosted mineral inclusions in the cassiterite grains (yttrocolumbite) and of zircon (xenotímio). The lack of profitable Nb-Hf-Sn mineral concentrations associated to the Granite Desemborque can be magma anhydrous character (type-A) and the lack or limitation of the hydraulic fracturing. The absence of profitable mineral concentrations because of the erosive removal of the apical zone is not in agreement with the prospective results found, once the presence of chromite in the samples of the active stream bed collected at the draining which is established exactly in the basis of the granite body indicates the preservation of remaints roof pendant the wall rocks (ortognaisses with boudins of ultrabasic rocks).

O Granito Desemborque, um corpo de forma, aproximadamente, circular, situado no sul do Estado de São Paulo, tem área aflorante de 50 km2 e é representado por um biotita sienogranito. O caráter peraluminoso com teores significativos de K2O e Na2O, juntamente com o baixo conteúdo de CaO, altas razões Fe/Mg, elevados valores de SiO2 e de elementos traços como Zr, Nb e Y, atestam a afinidade alcalina do granito que pode ser classificado como do tipo A. Os teores de Y refletem a presença de fases acessórias como parisita de Ce, itrofluorita e monazita. Columbita, zircão rico em háfnio e cassiterita presentes na associação de minerais acessórios do Granito Desemborque foram analisados semiquantitativamente (teores em peso) por MEV-EDS. Com isso foi possível discriminar duas fases evolutivas para a geração de alguns dos minerais de metais raros associados ao corpo; uma francamente magmática (com subfases granítica e pegmatítica) e uma fase hidrotermal. A columbita (teor médio de Nb2O5 de 66,2% e 6,5% de Ta2O5) é nitidamente gerada na fase magmática sendo que na subfase granítica ela tem presença ubíqua e caráter disseminado. O zircão, por sua vez, ocorre nas duas subfases magmática, sendo que na subfase granítica ele teria um caráter mais tardio. O teor médio das análises foi de 9,3% de HfO2, classificando-o como um zircão rico em háfnio. Na fase hidrotermal, é que se desenrolariam os processos de enriquecimento em Hf desse mineral. A cassiterita, os minerais de REE e boa parte dos minerais radioativos têm a sua formação restrita a fase hidrotermal. Dentre as classificações propostas para granitos mineralizados, o Granito Desemborque se aproxima do tipo peralcalino mineralizado a metais raros com tendência a formar depósitos ou ocorrências de Nb e ETR. Os senões seriam o fato desse corpo não ser peralcalino (ele é peraluminosso) e dos potenciais minerais de Y e ETR só terem sido registrados como inclusões minerais hospedadas nos grãos de cassiterita (ítriocolumbita) e de zircão (xenotímio). A falta de concentrações minerais econômicas de Nb-Hf-Sn associadas ao Granito Desemborque pode ser imputada ao caráter anídrico do magma (tipo-A) e a falta ou limitação do fraturamento hidráulico. A ausência de concentrações minerais econômicas em virtude da remoção erosiva da zona de cúpula não se encontra de acordo com os resultados prospectivos encontrados, pois, a presença da cromita nas amostras de leito ativo coletadas nas drenagens estabelecidas bem no cerne do corpo granítico indica a preservação de restos de pendentes de teto da rocha encaixante (ortognaisses com boudins de rochas ultrabásicas). / The Desemborque Granite, a body almost of circular shape, placed in the southernmost part of São Paulo State, has an area of ca. 50 km2. and it is represented by a sienogranite biotite. Its peraluminous features with significant contents of K2O and Na2O, together with low CaO contents, high Fe/Mg ratios, elevated values of SiO2 and trace elements as Zr, Nb and Y, assure the granite alcaline affinity that can be classified as type A. The Y numbers reflect the presence of acessory phases as parasite de Ce, yttrofluorite and monazite. Columbite, zircon rich in hafnium and cassiterite presented in the association of accessory minerals of the Granite Desemborque were semiquantitatively analysed(values in weight) by MEV-EDS. Because of this it was possible to detail the two evolutional phases for the generation of some minerals of rare metals associated to the body; one fairly magmatic (with granitic sub-phases and pegmatitic) and an hidrotermal phase. Columbite (Nb2O5 mean value 66,2% and 6,5% Ta2O5) is clearly generated in magmatic phase and in the granitric sub-phase it has ubiquitous presence and disseminated character. Zircon, in its turn, occurs in the two magmatic sub-phases, and in the granitic sub-phase it would have a later character. The mean value of the analysis was of 9,3% for HfO2, classifying it as a zircon rich in hafnium. In the hidrotermal phase, the enrichment proccesses are developed in Hf of this mineral. Cassiterite, the REE minerals and a large number of radiactive mineral have their formation restricted to the hidrotermal phase. Amongst the proposed classification for the mineralized granites, the Granite Desemborque has an peralkalkine mineralized approach to rare metals with a wide tendency to create deposits or Nb and REE occurences. The opposition could be the fact that this body is not peralkaline (it is peraluminous) and the Y and REE mineral potentials only have been recorded in the hosted mineral inclusions in the cassiterite grains (yttrocolumbite) and of zircon (xenotímio). The lack of profitable Nb-Hf-Sn mineral concentrations associated to the Granite Desemborque can be magma anhydrous character (type-A) and the lack or limitation of the hydraulic fracturing. The absence of profitable mineral concentrations because of the erosive removal of the apical zone is not in agreement with the prospective results found, once the presence of chromite in the samples of the active stream bed collected at the draining which is established exactly in the basis of the granite body indicates the preservation of remaints roof pendant the wall rocks (ortognaisses with boudins of ultrabasic rocks).

Un nombre croissant d’études académiques et de rapports d’organismes internationaux relèvent une dépendance accrue des nouvelles technologies de l’énergie vis-à-vis d’une catégorie de ressources souvent prénommés métaux rares. Parallèlement, il se forme depuis plusieurs années des inquiétudes sur la disponibilité économique de ces métaux pour opérer la transition énergétique nécessaire à la lutte contre le réchauffement climatique. Cette thèse a donc pour objectif de souligner l’ensemble des contraintes et des risques qu’implique l’usage fréquent et généralisé de ces métaux dans les nouvelles technologies de l’énergie. Une première partie de la thèse est consacrée aux indicateurs et aux théories reliées à la disponibilité économique de long terme d’une ressource non renouvelable tout en faisant apparaitre un ensemble de traits communs partagés par les métaux rares. La seconde partie de cette thèse démontre les risques attachés à une absence d’élasticité prix de l’offre de métaux rares du fait d’une contrainte de sous-produit. Elle offre également une analyse approfondie des causes et des conséquences relatives à l’absence de marché à terme pour la quasi-totalité de ces métaux rares. Enfin, son dernier chapitre propose d’explorer la liaison très forte existant entre le secteur de l’énergie et le secteur des métaux. Il y est démontré que cette connexion s’accentue et qu’elle implique la possibilité d’un cercle vicieux entre des énergies toujours moins concentrées (avec un contenu en métaux grandissant) et des métaux qui consomment toujours plus d’énergie sous l’effet de leur épuisement. / A growing number of academic studies and international organizations reports have noticed an increasing dependency of new energy technologies on a specific class of natural resources often called minor metals. For several years, worries about economic availability of these metals in order to realize the energy transition have appeared. This thesis aims at underline the broader risks and constraints involved by general use of these metals in new energy technologies. A first part of this thesis is devoted to theories and indicators related to the depletion of non renewable resources. This part also shows that minor metals share many characteristics and that they can form a group of metal consistent. In a second part, this thesis addresses the issues linked to the absence of price elasticity for the supply of minor metals due to the byproduct constraint. Another chapter offers an analysis of causes and consequences connected to the absence of futures markets for almost all minor metals. Finally, a last chapter highlights the strong link existing between the energy sector and the metals sectors. This connection is increasing and can create a vicious circle between energies which are less and less concentrated and metals which consume more and more energy due to their depletion.