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Tin (Sn) and tungsten (W) have been established as strategic metals, whose resources are mainly related to highly evolved, volatile-rich granitic systems and related hydrothermal fluids. Their transport and enrichment results from a combination of melt- and fluid-driven processes. To evaluate the relative importance of these processes, we propose to combine the study of natural and synthetic fluid inclusions (FIs). Natural FIs occurring in early (associated with cassiterite) to late hydrothermal (associated with wolframite) quartz of the Argemela magmatic-hydrothermal system (Central Portugal) are mainly of aqueous (average XH2O = 0.94±0.04) L+V±S type. Raman spectrometry revealed an evolution from V-rich CO2-CH4-N2 to L-rich CO2±N2-CH4 inclusions through the transition and graphite is present in several early inclusions, suggesting relatively reduced conditions and a potential inheritance from the source. In addition, and because further work is needed to understand the fluid/melt partitioning of Sn and W, several experiments were conducted at 700 and 800°C, 200MPa and variable fO2 and salinities to synthetize FIs. A synthetic glass was produced to mimic the major element composition of the Argemela highly peraluminous intrusion and concentrations of W, Sn, P and Li were varied. Inclusion-free quartz were used to trap the fluids. First results prove the feasibility of the study. Microthermometry and LA-ICP-MS analyses are in progress for both natural and synthetic FIs.

International audience; Geological processes leading to lithium-rich rare metal (RM) pegmatites and granites remain poorly constrained. To acknowledge geological processes related to Li-rich melt generation, we applied complementary approaches in the Montagne Noire (MN) and in the Monts d’Ambazac (MA). In the MN, the mineralogy of pegmatite clusters depends of the nature of the migmatitic host rock. Geostatistical studies demonstrate that pegmatite clusters are scattered and do not appear randomly. Lithium isotopes tracing (7Li, ‰) show that the mineralized pegmatites are not fractionated and display likely a crustal signature. Rb/Sr dating on lepidolites shows that their emplacements are synchronous with regional partial melting. In MA, structural studies and 3D modelling suggest the presence of an anatectic dome masked by a granite. Geostatistic studies demonstrate that emplacement of pegmatite clusters are controlled by normal faulting. Lithium isotopes show that the mineralized pegmatites are not fractionated and have a crustal signature. Rb/Sr dating on lepidolites show that pegmatite emplacement postdates the granite emplacement.A compilation of RM intrusions in France has been conducted in the present work and shows that: i) they are usually located in or along antiformal structures; ii) the core of antiformal structures consists of migmatites, amphibolite-grade metasediments or anatectic granites; iii) RM granites are spatially associated with major faults; iv) Li-rich RM pegmatites are absent in the case of LP-HT partial melting. These results point to an anatectic origin of RM pegmatite fields with a strong tectonic control of the intrusions near migmatitic domes. Then, the presence of RM pegmatite indicates presence of an underlying partial melting zone which should be more distal in the case of a granite. Moreover, the absence of Li-rich intrusions in the case of LP melting conditions suggests that pressure has a key role in magma enrichment processes during partial melting.

International audience; Geological processes that lead to lithium-caesium-tantalum-rich pegmatites remains poorly constrained and understood. This type of rare-metal pegmatites, which sometimes constitutes economic Li±Sn±Ta±Be deposits, are generally encountered in the vicinity of large pegmatite fields frequently focused on migmatitic areas. Two distinct models for pegmatitic melt generation are proposed:1-products of the end-of-crystallization melts of fractionated granites; or2-products of low-rate partial melting of metasedimentary rocks.In order to constrain geological processes related to pegmatitic melt generation, we applied several approaches (field work, statistical spatial analyses, mineralogical, geochemical and isotopic studies) on two well-known areas hosting rare-metal and barren pegmatite fields: 1) the Montagne Noire migmatitic dome; and 2) the Ambazac Mounts.In the Montagne Noire migmatitic area, the mineralogy of pegmatite clusters mimics the host-rocks with biotite-bearing pegmatites mainly hosted by migmatitic paragneisses and muscovite-bearing pegmatites mainly hosted by migmatitic orthogneisses. statistical spatial analyses studies demonstrate that pegmatite clusters are scattered in the center of the dome and do not appear randomly. Lithium isotopes show that the mineralized pegmatites are not fractionated and have likely a crustal signature. Rb/Sr dating on lepidolites shows that pegmatite emplacements are synchronous with the regional partial melting. Secondly, in the Ambazac mounts area, structural studies and 3D modelling suggest that this area may correspond to an anatectic dome masked by a granite, where pegmatite clusters are hosted by the Saint-Sylvestre granite. This granite crops on the border of the dome. Statistical spatial analyses studies demonstrate that emplacement of pegmatite clusters are controlled by normal faulting. Lithium isotopes show that the mineralized pegmatites are not fractionated and have also a crustal signature. Rb/Sr dating on lepidolites shows that pegmatite emplacement postdates the granite emplacement and is coeval with a late regional partial melting event. Following this, a compilation of the geology of rare-metal pegmatites fields of France has been conducted. This compilation underlines several common features between the distinct pegmatites fields: i) they are usually located in or along antiformal structures; ii) the core of antiformal structures consists of migmatites if erosion level is sufficient, otherwise the core consists of metasedimentary rocks or is occupied by anatectic granites; iii) the highest density of pegmatites occurs mainly in migmatites; iv) rare-metal pegmatites seem to be absent in the case of LP-HT partial melting. Thus, these results point to an anatectic origin of pegmatite fields with a strong tectonic control of pegmatite cluster emplacements above migmatitic domes. Then, the presence of pegmatite indicates presence of an underlying partial melting zone. Moreover, the absence of mineralized pegmatites in the case of low-pressure melting conditions suggests that pressure has a key role in magma enrichment processes during partial melting.

Rare metal granites result from the crystallization of highly evolved magmas enriched in volatiles and fluxing elements (F, Li, P, B) and in metals such as Sn, Nb, Ta and W. In the Western Europe Variscan belt, these granites are attributed to a late orogenic episode of rare metal magmatism. Since the 60’s, numerous studies have focused on the specific geochemical signature of rare metal granites and several models have been proposed for their genesis. However, several questions remain and, in particular, the context and mechanisms of magma emplacement have been only rarely addressed. In order to build a comprehensive understanding of magmatic, hydrothermal and tectonic processes and mechanisms responsible for (i) rare metal magma generation, (ii) magma emplacement and geometry, (iii) specific geochemical signature and metal enrichment, a multi-approach and multi-scale study has been performed on the example of the rare metal granite of Argemela (Central Iberian Zone, Portugal). It has been complemented by an experimental study on the genesis of rare metal magmas. Results of the structural analysis highlighted the special structural context of emplacement of the Argemela intrusion. Several criteria suggest a fast vertical and channelled magma ascent up to shallow subvolcanic levels. The petrological and geochemical study of the granite and related mineralization allow the identification of key events and processes involved during the magmatic-hydrothermal transition. Mechanisms of concentration/transportation and deposition of metals have been also specified. The experimental study indicates that a single step low degree partial melting is not efficient enough to produce rare metal magmas, since most are sequestered into the restite. However, remelting of enriched restitic assemblages, a mechanism which remains to be tested, could well produce the required rare metal concentrations. Finally, this study demonstrates the necessity to combine several approaches, since processes and mechanisms are interrelated in these mineralized systems.; Les granites à métaux rares sont issus de la cristallisation de magmas très évolués enrichis en volatiles et fondants (F, Li, P, B) et en métaux tels que Sn, Nb, Ta et W. Dans la chaîne Varisque d’Europe de l’Ouest, ils résultent d’un magmatisme tardi-orogénique spécifique. Depuis les années 60, de nombreuses études se sont intéressées à la signature géochimique de ces granites et différents modèles de genèse ont pu être proposés. Malgré cela, plusieurs questions subsistent; le contexte et les mécanismes de mise en place de ces granites particuliers ne sont que rarement abordés. Afin d’avoir une vision complète des processus et mécanismes responsables de (i) la genèse des magmas à métaux rares, (ii) la géométrie et la mise en place de ces granites, (iii) leur signature géochimique et leur enrichissement en métaux, une étude multi-approches et multi-échelles a été menée sur l’exemple du granite à métaux rares d’Argemela (Zone Centro-Ibérique, Portugal). Elle a été complétée par une étude expérimentale portant sur la genèse des magmas. Les résultats de l’étude structurale montrent que l’intrusion d’Argemela se met en place dans un contexte particulier. Plusieurs critères suggèrent une remontée verticale rapide et chenalisée du magma jusqu’à un niveau très superficiel, subvolcanique. L’étude pétrologique et géochimique du granite et des minéralisations associées a permis de mettre en évidence les évènements clés et les processus mis en jeu durant la transition magmatique-hydrothermale. Ceci a également permis d’appréhender les processus de concentration/transport des métaux et les mécanismes de dépôt des minéralisations. L’étude expérimentale indique qu’un seul stade de fusion partielle à faible taux ne permet pas de générer des magmas suffisamment enrichis en métaux. Cependant, un mécanisme de refusion de restites enrichies, qui reste encore à tester, pourrait produire les concentrations en métaux requises. Enfin, cette étude démontre la nécessité de combiner les approches car l’ensemble des processus sont interdépendants dans ce type de systèmes minéralisés.

Rare metal granites result from the crystallization of highly evolved magmas enriched in volatiles and fluxing elements (F, Li, P, B) and in metals such as Sn, Nb, Ta and W. In the Western Europe Variscan belt, these granites are attributed to a late orogenic episode of rare metal magmatism. Since the 60’s, numerous studies have focused on the specific geochemical signature of rare metal granites and several models have been proposed for their genesis. However, several questions remain and, in particular, the context and mechanisms of magma emplacement have been only rarely addressed. In order to build a comprehensive understanding of magmatic, hydrothermal and tectonic processes and mechanisms responsible for (i) rare metal magma generation, (ii) magma emplacement and geometry, (iii) specific geochemical signature and metal enrichment, a multi-approach and multi-scale study has been performed on the example of the rare metal granite of Argemela (Central Iberian Zone, Portugal). It has been complemented by an experimental study on the genesis of rare metal magmas. Results of the structural analysis highlighted the special structural context of emplacement of the Argemela intrusion. Several criteria suggest a fast vertical and channelled magma ascent up to shallow subvolcanic levels. The petrological and geochemical study of the granite and related mineralization allow the identification of key events and processes involved during the magmatic-hydrothermal transition. Mechanisms of concentration/transportation and deposition of metals have been also specified. The experimental study indicates that a single step low degree partial melting is not efficient enough to produce rare metal magmas, since most are sequestered into the restite. However, remelting of enriched restitic assemblages, a mechanism which remains to be tested, could well produce the required rare metal concentrations. Finally, this study demonstrates the necessity to combine several approaches, since processes and mechanisms are interrelated in these mineralized systems.; Les granites à métaux rares sont issus de la cristallisation de magmas très évolués enrichis en volatiles et fondants (F, Li, P, B) et en métaux tels que Sn, Nb, Ta et W. Dans la chaîne Varisque d’Europe de l’Ouest, ils résultent d’un magmatisme tardi-orogénique spécifique. Depuis les années 60, de nombreuses études se sont intéressées à la signature géochimique de ces granites et différents modèles de genèse ont pu être proposés. Malgré cela, plusieurs questions subsistent; le contexte et les mécanismes de mise en place de ces granites particuliers ne sont que rarement abordés. Afin d’avoir une vision complète des processus et mécanismes responsables de (i) la genèse des magmas à métaux rares, (ii) la géométrie et la mise en place de ces granites, (iii) leur signature géochimique et leur enrichissement en métaux, une étude multi-approches et multi-échelles a été menée sur l’exemple du granite à métaux rares d’Argemela (Zone Centro-Ibérique, Portugal). Elle a été complétée par une étude expérimentale portant sur la genèse des magmas. Les résultats de l’étude structurale montrent que l’intrusion d’Argemela se met en place dans un contexte particulier. Plusieurs critères suggèrent une remontée verticale rapide et chenalisée du magma jusqu’à un niveau très superficiel, subvolcanique. L’étude pétrologique et géochimique du granite et des minéralisations associées a permis de mettre en évidence les évènements clés et les processus mis en jeu durant la transition magmatique-hydrothermale. Ceci a également permis d’appréhender les processus de concentration/transport des métaux et les mécanismes de dépôt des minéralisations. L’étude expérimentale indique qu’un seul stade de fusion partielle à faible taux ne permet pas de générer des magmas suffisamment enrichis en métaux. Cependant, un mécanisme de refusion de restites enrichies, qui reste encore à tester, pourrait produire les concentrations en métaux requises. Enfin, cette étude démontre la nécessité de combiner les approches car l’ensemble des processus sont interdépendants dans ce type de systèmes minéralisés.

National audience; Les pegmatites sont des objets crustaux d’origine magmatiqueaux caractéristiques exceptionnelles : il s’agit toujours d’amasd’injections de très petits volumes enrichis à extrêmement enrichisen fluides et éléments incompatibles par rapport aux granitescrustaux. Leur variabilité géochimique et les différents contextesdans lesquels on peut les observer font des pegmatites des objetsd’intérêt tout particulier du point de vue du traçage de l’histoiredes circulations magmatiques et des fluides au travers de la croûte.Cependant, les processus de genèse, migration et mise en place deschamps de pegmatites restent mal connus, ceci étant illustré pardeux modèles diamétralement opposés : (i) les pegmatites dérivantd’un processus de fractionnement long à partir d’une chambremagmatique moins fractionnée et considérée être la source de cesliquides granitiques, (ii) les magmas formant les pegmatites directementextraits de sources de fusion partielle de bas taux dansla croûte continentale ; les mécanismes d’extraction, de remontéeet de mise en place des pegmatites devant alors fortement êtrecontrôlés par la localisation de la déformation dans la croûte continentale.Nous développons ici une approche d’analyse spatiale statistiquesur la répartition de pegmatites dans plusieurs champs de la ChaîneVarisque. En effet, alors que l’analyse des distributions spatialesd’objets en carte est souvent restreinte à une analyse purementvisuelle, des outils et méthodes de cartographie numérique permettentde quantifier les tendances de répartition ou d’associationspatiale entre objets. Dans le détail, les objets cartographiquesd’intérêt sont considérés comme jeu de données d’apprentissage.Différents calculs de paramètres sont alors possibles pour quantifierleur répartition cartographique et en particulier leur degré deregroupement/dispersion sur une gamme d’échelles continue.Un second objectif consiste à quantifier le degré de recouvrementou de proximité des pegmatites avec les granites et/ou les structures.Même si ces relations spatiales peuvent parfois paraîtreévidentes à la simple lecture d’une carte, les configurations cartographiquesne permettent pas toujours de bien appréhender lesassociations spatiales. Différents outils d’analyse spatiale peuventêtre appliqués afin de pouvoir formaliser la quantification du degréd’association entre les objets cartographiques.Les résultats montrent une caractéristique des pegmatites enrichiesen Li à former des regroupements à plusieurs échellescomme dans le champ de Barroso-Alvão (Portugal). En outre,la dispersion cartographique et l’alignement des corps pegmatitiquesminéralisés des Monts d’Ambazac (France) montrent uncontrôle clair de structures régionales.

The rotational spectra of seven isotopomers of XeCuF and eight isotopomers of XeCuCl have been measured in the range of 7-22 GHz using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by laser ablation of a Cu metal rod with a pulsed Nd:YAG laser at 1064 nm and allowing the plasma to react with appropriate precursors (Xe and SF6 or CI2) entrained in a carrier gas of Ar. Rotational constants, centrifugal distortion constants, internuclear distances, vibration frequencies, and Xe, Cu and CI hyperfme coupling constants have been evaluated. The Xe-Cu bonds are short and the molecules are rigid. The 1 3 1Xe nuclear quadrupole coupling constants in both XeCuF and XeCuCl are large (-87.8 and -81.4 MHz, respectively). The Cu nuclear quadrupole coupling constants differ radically from those of uncomplexed CuF and CuCl molecules. Ab initio calculations have supported the experimental results with short NgM bonds and rigid molecules. Mulliken populations and MOLDEN plots have also been calculated and both are consistent with strong interactions between the noble gas and the noble metal. The local energy densities were calculated to be negative and indicate the presence of a covalent XeCu bond. Both experimental and theoretical results are consistent with those reported earlier for other noble gas - noble metal halide molecules. The evidence is convincing for chemical bonding present between the noble gas and the noble metal in all NgMX molecules.