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International audience; Driven by a global move towards renewable energy through the last decade, lithium has become a strategic metal due to its physical and chemical properties (e.g., lightest solid element and excellent conductor of heat and electricity) making it an excellent candidate for electrification of transport and green technologies such as Li-ion batteries and other energy storage devices. In this context, European interest in lithium mining and exploration has risen sharply and many countries are currently assessing their own mineral resources and reserves in order to secure their supplies. From this perspective, a geographically-based compilation of the European lithium hard-rock occurrences and ore deposits with their corresponding features (e.g., deposit types, Li-bearing minerals, Li concentrations) is presented. Accordingly, it appears that lithium is not particularly rare and is well represented and distributed through various deposit types related to several orogenic cycles from Precambrian to Miocene ages. Thus, about thirty hard-rock deposits have been identified mostly resulting from endogenous processes such as lithium-cesium-tantalum (LCT) pegmatites (e.g., Sepeda in Portugal; Aclare in Ireland; Läntta in Finland), rare-metal granites (RMG; Beauvoir in France; Cinovec in Czech Republic) and greisen mineralisation (Cligga Head, Tregonning-Godolphin, Meldon in UK; Montebras in France). Local exogenous processes such as hydrothermal and erosion transport may be also related to significant secondary Li-endowments including jadarite precipitation in the Jadar Basin (Serbia) but are rarely related to economic grade of lithium (e.g., Mn-(Fe) deposits, bauxite). Moreover, a systematic assessment of metallogenic processes in the Li endowment has been conducted and several relevant parameters have been identified and may offer exploration guidance for mining companies and governments. These parameters are: 1) a pre-existing Li-rich source related either to paleoenvironmental sedimentation conditions or a crustal anomaly; 2) presence of lithospheric thickening, which may reflect a favourable process to concentrate Li; 3) a regional or local extensional regime; and 4) existence of fracture sets acting as channel ways for exogenous processes.

International audience; The French Massif Central (FMC) forms the hinterland of the west-European Variscan belt and was subject to numerous tectonic and metamorphic events from Devonian to Permian times. The accreted tectonic units belonging to Gondwana and Laurussia were variably involved in subduction, nappe stacking and syn-to post-orogenic extension. Besides, plutons and migmatites showing syn-collision crust melting are very common in the Variscan belt. Such orogenic evolution implies that the resulting finite structure likely reflects the interference between fabrics formed at different stages of the orogenic cycle with different degrees of overprinting, depending on e.g. the spatial strain gradients, lithologies, structural level or partial melting grade. We present a model of finite strainfield of the western FMC based of the analysis/interpolation of ductile and brittle fabrics, at regional to local scale, using geostatistics. Ductile fabrics within autochthonous units and syn-collisional plutons are poorly disturbed and reflect the transition from syn-thickening to extensional lateral flow of the partially molten mid-lower crust. In contrast, allochtonous units are affected by numerous perturbations including polyphased ductile shearing, folding and faulting inducing local bloc tilting and rotations. Taking into account the overprint of late tectonic events, we show that early fabrics related to High Pressure metamorphism or nappes' stacking have suffered intense reorientations. The finite trend of the related lineations L1 must be treated with extreme caution and may not reflect the original direction of stretching and shearing that occurred during the initial compressional stages. Taking into account i) the spatial distribution and amount of reorientation of these D1 fabrics and ii) the deconvolution of these disturbances, we propose that:-The high dispersion of lineation trend can be simply explained by passive rotations, during late isoclinal folding, rather than two superposed tectonic phases, as previously inferred.-The allochtonous units formed one single tectonic unit.-This D1 event looks related to the exhumation of the subducted continental crust due to partial melting-The formation of Variscan orogenic prism in western FMC only results of continuous south-directed thrusting rather than a switch from NE-SW to NW-SE thrusting.

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.

International audience

International audience; Numerous Sb-Au deposits are known in the European Variscan belt and are often associated with the late Variscan hydrothermal events linked to postorogenic extension and strike-slip faults, through the whole belt. Central Brittany hosts several Sb-Au occurrences, such as the Le Semnon Sb-Au deposit or the Saint-Aubin-des-Châteaux base metal-Sb-Au occurrence. In order to provide new constraints on the Sb-Au mineralization framework of the Central Brittany, structural, geochronological and chemical analyses have been performed on the Le Semnon deposit and the Saint-Aubin-des-Châteaux occurrence. Main results show that Sb-Au trapping of these two occurrences occurred at ca. 360 Ma. This indicates an Early Carboniferous economic Sb-Au mineralizing peak in the eastern part of the Central Brittany. Moreover, a mafic magmatism is widespread in the region and can acted as the plumbing system for Sb-Au mineralizing fluids, such as the dolerite dyke of the Semnon Sb-Au deposit. Absolute dating of this mafic magmatism coupled with the early character of hydrothermal alteration associated with Sb-Au mineralizing fluids strongly suggest that the emplacement of Sb-Au mineralization and mafic magmatism was coeval. It appears that the emplacement of mafic magmatism represent a major trigger for this mineralizing system at shallow depths (less than 3 km). These new data and the ca. 360 Ma massive sulfides of south Iberia emphasize that the Early Carboniferous mafic magmatism has to be taken into account for the understanding of the genesis of mineralizing systems and the redistribution of metals in the crust, at the scale of the whole Variscan belt.

International audience; Numerous methods of mineral prospectivity mapping have been developed during the last decades and it is often difficult to evaluate their reliability and adequacy. Some objective a posteriori approaches allow calculating their performance such as, for instance, AUC values on ROC curves. However, we believe that field control is a necessary step, especially in the context of mineral targeting in greenfield exploration. Mineral prospectivity mapping generally relies on unequivocal associations between discrete data (e.g., known deposits) and polygons (e.g., lithology, geophysics, geochemistry, etc.). Consequently, the quality of results obtained from 'classical' methods (e.g., Weight of Evidence, Fuzzy Logic, Logistic Regression, Neural Network, etc.) strongly depends on the accuracy of input data (location of points and contours of polygons) which, in many cases, may be questionable. To address this issue of geographic inaccuracy of map elements, BRGM has developed the CBA (Cell Based Association) method. Its base principle is not to rank polygons in which known deposits are located, but to identify favorable association neighboring these deposits (i.e. in cells of a regular grid containing them). In order to assess the adequacy of CBA for mineral targeting in early exploration phases, we have done a first field validation campaign for Sb in the Vendée region (western France). 107 soil samples have been collected (auger drill) in both favorable and unfavorable cells (according to CBA results) and across know Sb-bearing veins. They have been analyzed at ultra-trace level using ICP-MS/ICP-AES (detection range of 0.05 to 10 000 ppm for Sb). In this contribution, we present an overview of the CBA method, its resulting prospectivity map for Sb in Vendée, the sampling and analyzing procedure, the preliminary results we have obtained and the first conclusion they allow.

International audience; The W-Sn veins of Panasqueira are connected with a massive quartz-muscovite greisen cupola. This greisen results from interactions between granitic rock and acid Sn-W hydrothermal fluid, which causes the destruction of feldspars of the Panasqueira granite. Greisenisation can constitute an important factor of control on fluid flow, and its role on metal transport remains to be established. Mineral reactions of greisenisation involve a decrease of the rock volume and thus an increase porosity (~6%). Consequently permeability increases significantly (10-20 to 10-17 m²) enhancing fluid flow in the greisen cupola and promoting further hydrothermal alteration and transport of metals. Finally a part of the mineralization is trapped in this porosity, with precipitation of cassiterite and sulfides. Therefore, Sn-W fluids are able to generate their own pathways in initial impermeable granite via greisenisation reactions.

National audience; Palaeozoic oolitic ironstones layers are widespread in Europeand North Africa, mainly in external parts of the Variscanorogeny where they have been preserved from intense deformationand metamorphism. These ironstones are mainly of two types,either composed of carbonates and silicates (siderite-chlorite), ormade of oxides and silicates (magnetite-chlorite). In the first case,ironstones are chemically very reactive to crustal fluid circulations.In the central domain of the Armorican Massif (Western France),it has been demonstrated (Gloaguen et al., 2007) that the ooliticiron ore from the Saint-Aubin-des-Châteaux quarry suffered anepigenetic transformation by hydrothermal fluids that led to thedissolution of the iron ore and its replacement by massive sulphidelenses. Such hydrothermal alteration is still localized atthe intersection between the ironstone layer and Variscan rightlateralstrike slip faults. Both, structural constraints, parageneticsequence and geochronological results (Gloaguen et al., 2007;Tartèse et al., 2015) underline 100 Ma of successive fluid flowsand polyphazed hydrothermal alteration of the ironstone. A verysimilar type of oolitic-hosted epigenetic gold deposit has beendescribed by Couto and Moëlo (2011) in the Banjas gold mine(Dúrico-Beirã district, Valongo, Portugal; Couto et al., 1990;Combes et al., 1992). This argues for a widespread distributionof such epigenetic mineralization through these two orogenic segmentsof the Ibero-Armorican arc at least. Since these Palaeozoicironstone layers are frequently hosted within, or close to, thicksandstone formations, outcrops are generally scarce. Moreover,because of the lack of magnetite and a thickness in a range 2to 6 m, these layers are not well targeted by geophysical approaches.Then, development of a specific targeting focused onintersections between faults and palaeozoic siderite-bearing ironstonelayers may lead to several significant new discoveries ofAu-Ag-Sb, Cu-Pb-Zn ore deposits.

International audience; Les appareils de fluorescence X portables (FPXRF) sont couramment utilisés lors des campagnes d'exploration.Le faible coût de ces analyses, leur rapidité d'acquisitionsur échantillons bruts, sur le terrain ou en laboratoire, ainsi que des gammes de teneurs analysables variant de quelques dizaines de ppm à plusieurs pourcents, sont des arguments forts pour une généralisation de cette technique en exploration.Cependant, de nombreux paramètres relatifs à la qualité des échantillons et conditions analytiques influent sur la pertinence et l'exploitabilité des résultats.De ce fait, la validité des analyses FPXRF par rapport aux analyses géochimiques classiques est encore largement débattue. Afin de comparer les analyses géochimiques ICP-AESet FPXRF, et les réponses des différents éléments métalliques, deux lots d'échantillons de type streamsédiments prélevés lors de l'inventaire minier français (années 1970-80s) ont été ré-analysés par FPXRF au moyen d'unNiton XL3t 600S GOLDD. Les échantillons testés correspondent à la fraction inférieure à 125 µm et présentent un taux d'humidité inférieur à 3%. Après plusieurs tests, le temps d'analyse a été fixé à 60s en mode sol et en mode mine. La Zone 1 est centrée sur l'amas sulfuré à Cu-Pb-Zn de Chizeuil. La Zone 2 comprend les indices à U de Sandelesse, les indices à Sb de la Marnière et de la Ramade, les indices à BaSO 4 de Saint-Merd-la-Breuille, les indices à As d'Allevergue et Foliat, et les indices à F de Veaumas, ainsi qu'une forte anomalie géochimique à W.

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.

International audience; The Armorican belt is part of the westernEuropean Variscan belt. Although the region was oneof the world leader producers of antimony at thebeginning of the 20th century, the geological controlsbehind these deposits remain badly constrained. Herewe present a spatial statistical analysis of the Sbmineralisation,together with geophysical andgeological data [1]. Results show that the Sbmineralisationis spatially associated with strongpositive gravity and magnetic anomalies which mustbe linked to the presence of mafic/ultramafic bodiesat depth. This spatial link is further supported by thenumerous outcropping occurrences of dolerite dykesand sills close to the Sb-deposits and sometimeshosting the mineralisation. This mafic magmatism,dated by in-situ U-Pb analyses on apatite at ca. 360Ma, appears as a regional-scale event at theDevonian-Carboniferous boundary. In addition, newdata suggests that mafic magmatism may haveprobably played a role in the early distribution orredistribution processes of metal stock in thesubsequent history of the antimony in the VariscanArmorican belt.[1] Pochon et al. (2016). Terra Nova, doi:10.1111/ter.12201

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International audience; This work describes the use of conformer-selective laser spectroscopy following supersonic expansion to probe the local folding proclivities of four-membered ring cyclic β-amino acid building blocks. Emphasis is placed on stereochemical effects as well as on the structural changes induced by the replacement of a carbon atom of the cycle by a nitrogen atom. The amide A IR spectra are obtained and interpreted with the help of quantum chemistry structure calculations. Results provide evidence that the building block with a trans-substituted cyclobutane ring has a predilection to form strong C8 hydrogen bonds. Nitrogen-atom substitution in the ring induces the formation of the hydrazino turn, with a related but distinct hydrogen-bonding network: the structure is best viewed as a bifurcated C8/C5 bond with the N heteroatom lone electron pair playing a significant acceptor role, which supports recent observations on the hydrazino turn structure in solution. Surprisingly, this study shows that the cis-substituted cyclobutane ring derivative also gives rise predominantly to a C8 hydrogen bond, although weaker than in the two former cases, a feature that is not often encountered for this building block.

International audience; In order to define new metallogenic guides for Li, Nb and Ta supply, three Variscan LCT pegmatite fields are investigated. A multidisciplinary approach is favoured to discuss both the genetic and emplacement models for LCT-type deposits. The spatial statistical analyses demonstrate the high clustering rate of Li-rich pegmatites and the spatial relationships between Li-pegmatites location and surrounding damage fractured zone. The Li-isotopes analyses on micas suggest the absence of genetic continuum between surrounding granites and pegmatites since δ 7 Li values (‰) are similar through pegmatite field and inside granite samples. To refine these previous results, preliminary numerical models are developed to constrain the ascent of these low viscosity pegmatite-forming melts and determine key criterion of their uncoupling from parental magma source. According to these results, the high permeability seems to play a crucial role in the pegmatite melts collection and during their ascent. The combination of geostatistical, geochemical and numerical tools allows suggesting an alternative model of direct crustal anatexis to the common parental granite model. These high permeability damage shear zones are considered to favour the low volume of pegmatite-forming melt pumping and their escape from their deeper crustal magma source.

International audience; The European Variscan belt, which is characterized by a huge amount of granitic intrusions, displays several significant rare-elements pegmatites and/or granites fields which could represent an important source of raw materials. An overview of these occurrences gave the possibility to discuss the processes at their origin and their common classification. Indeed, the spatial and temporal distributions of rare-element pegmatites in the European Variscan belt suggest that rare-elements magmatism would rather be related to local specific conditions (in particular sources, tectonic and thermal regime) than lower crustal processes like rare-elements enrichment subsequent to their release during granulite metamorphism. Actual classification of rare-elements pegmatites, based on their geochemistry and mineral composition, does notallow to discern pegmatites formed in different tectonic regimes and which exhibit various internal structures (e.g. the pegmatites of the lepidolite-subclass from Western Iberia and from the Moldanubian domain of the Bohemian Massif for example).

International audience; A new type of large ultramafic intrusion-hosted Fe-Ti-V deposit has been discovered by BRGM in the West-African Archean craton. The N’Guérédonké intrusive complex (7 x 0.9 km) is composed of a dunite core surrounded by rims of wehrlites and pyroxenites. This syntectonic complex is emplaced within a crustalscale shear zone. The disseminated mineralisation made of ilmenite and magnetite is mainly hosted by pyroxenite units along the northern and southern contacts. Surface and drilling exploration work (47 drill holes totalling 10124 m) demonstrate polyphased injection of successive ultramafic melts from core to rims and also crosscutting of dunite core by a network of successive pyroxenite generations. A 3D modeling constrained by drilling and joined inversion of magnetic and gravity data ascribe the thickness of the intrusion up to 1000 m. A first very conservative titanium resource assessment on a small part of the intrusion (1000 x 100 x 250 m) lead to definition of 141.38 Mt ore @ 10.52 % TiO2. The lack of typical features of Ural-Alaskan type intrusions and strong differences with classical Gabbro-Anorthositehosted Fe-Ti-V deposits demonstrate a new type of large low grade high tonnage Fe-Ti-V deposit occurring in Archean craton

International audience; High-phosphorus peraluminous rare-elements granites and rare-elements LCT (Lithium, Caesium, Tantalum) pegmatites are the most important sources of raw materials for some critical metals like tantalum (1,2)represent important economic storehouses for industrial minerals like feldspar, quartz, mica or kaolin. They principally emplace in orogenic settings (3). Afast overview of three mainEuropean Variscan districts, i.e. the Moldanubian domain of the Bohemian massif, the French Massif Central (FMC) and the NW Iberia provides a basis for questioning the origin of rare-elements magmatism and the actual classification of rare-elements pegmatites, in particular the LCT pegmatites. Granitic pegmatites are widespread in most of the Bohemian Massifbut LCT pegmatites are most common in the Moldanubian domain. In this area, their emplacements seem mainly controlled by migmatitic domes and shear zones and correspond to two events(4). The older at ~ 333 ± 3 Ma just follow HT-MP event of the end of the Moravo-Moldanubian phase and the younger at ~ 325 ± 4 Ma is contemporaneous with beginning of the Bavarian phase (U-Pb ages on colombite and tantalite). In the FMC, most of the actually known rare-elements magmatic bodies form a province in the North Limousin area, which represents the northwestern part of the FMC.U-Pb dating of columbite-group minerals from Beauvoir, Montebras and Chèdeville rare-elements magmatic bodies leads to emplacement ages at 317 ± 6 Ma, 314 ± 4 Ma and 309 ± 5 Ma respectively. The contemporaneous Marche fault system (5), which crosscuts in a general E-W trend all the northern part of the Limousin, seems to be a key-structure for the rare-elements magmatism of the area.

International audience; Rare-elements (Li, Cs, Ta, Be, Sn...) magmatism is well expressed in the European Variscan belt with mainly pegmatites and granites. These bodies are known in most of the different realms of the belt, but they are particularly abundants in localized parts of the Iberian massif, the French Massif Central and the Bohemian Massif. U-Pb dating of columbite-tantalite from selected Variscan rare-elements granites and pegmatites of these three massifs has been performed using laser ablation system connected to a single collector magnetic SectorField - Inductively Coupled Plasma - Mass Spectrometer (LA-SF-ICP-MS). The main aims of this study are to investigate the timing of this magmatism in the Variscan belt and the chronological relationship with the surrounding granitoid suites. Our results highlighted the existence of several emplacement episods : - in the Moldanubian domain of the Bohemian Massif, rare-elements pegmatites emplaced at around 340-330 Ma. - in the North of French Massif Central, the Montebras and Beauvoir granites and the Chèdeville pegmatite lead to emplacement age at 315-310 Ma. - in the North of Iberian massif, three different events have been recognized, with the emplacement of the Argemela granite at 326 ± 3 Ma, a first group of pegmatites emplaced at 310 ± 5 Ma, a second at 301 ± 3 Ma. In this context, rare-elements magmatism do not look to be related to lower crust processes (i.e. granulitic metamorphism) and rare metal magmatism event appears diachroneous and polyphased.

International audience; U-Pb geochronological data were collected on columbite-tantalite from rare-elementpegmatites and granites (Li, Ta, Nb, Be, Sn) from the Iberian Variscan Massif in orderto investigate timing of rare-element events during the late evolution of the Variscanbelt and the connection with granitoid suites. Our data set emphasises three events: (i)The Argemela rare-element granite, from the Central Iberian Zone (CIZ), emplaced at326±3 Ma and predates the three main late orogenic granitoid suites, (ii) most of thestudied rare-element pegmatites of the LCT family from the Galicia-Trás-Os-MontesZone (GTOMZ) gave an average age of 310±5 Ma, contemporaneous with an earlysyn-D3 granodiorite-monzogranite suite and the syn-D3 two-micas granites suite; and(iii) The youngest event is dated at around 301±3 Ma and is marked by emplacements ofrare-element pegmatites of the LCT family in both the CIZ and in the South of theGTOMZ. This event postdates the late to post-D3 bt±crd-granodiorite-monzogranitesuite emplacements, which are probably not genetically related to rare-elementpegmatites. Several pegmatites dated during this study do not display contemporaneousages with neighbouring supposed "parent" granites.Contemporaneous rare-element pegmatites fields seem to be located along belts as it isobserved for granitoids suites. Considering both GTOMZ and CIZ fields, emplacementages look to decrease toward the South. This is in good agreement with the knownpropagation of deformation, metamorphism and magmatism between the differentgeotectonic zones of the Iberian Massif.Lower crustal processes are not at the origin of rare-element granite genesis since in theIberian Massif, RM magmatism is polyphased with at least three distinct events.Hypothetical sources of RM melts are supposed to be set in a middle to upper crustposition, as it has been shown for granitoid magmatism.

International audience

International audience; For a big part of the planet, the majority of economic deposits located near the surface have been targeted. Then, new exploration projects must aim to discover "hidden" deposits for which "traditional" methods of exploration like stream sediments or soil geochemical prospecting are unfortunately less efficient. However, groundwater interacts extensively with these deposits in subsurface. For a limited number of mineralization types, several studies have demonstrated the existence of geochemical and isotopic tracers in groundwaters. Metals related to peraluminous granites-related deposits like W, Sn, Ta or Cs are crucial for the developments of some "green" and "high" technologies. The Beauvoir-La Bosse deposits of Echassières, located in the North of the Variscan French Massif Central belongs to at least two distinct metallogenic systems, a stockwork constituted by quartz-wolframite veins, crosscut by the Beauvoir rare-elements granite. Moreover, in the southern watershed, Sb and Cu occurrences have been documented by former prospections. It is located on the top of a hill, and past and actual operations on the deposits provided good conditions for water-mineralization interactions. Waters from surrounding streams and springs located on and around the different deposits were collected. In order to investigate the hydrogeochemical signatures related to these deposits, we performed major, trace elements and rare-earth elements analyses as weel as isotopic measurement (O, D, C, Li, S, Zn, Cu and Sr isotopes). According to these preliminary results, we are able to decipher the geochemical signature of shallow and surface groundwater to understand water migration through the deposits and water-rock-interactions. Moreover, it is possible to distinguish several geochemical types that could be relied on the composition of the deposits. These results give thus good indications on the applicability of hydrogeochemical prospecting for these kinds of deposits, with valuable results in complex systems such as overlapping of several metallogenic systems

International audience