# Geochemical footprints of peraluminous rare-metal granites and pegmatites in the northern French Massif Central and implications for exploration targeting

Matthieu Harlaux, Olivier Blein, Christophe Ballouard, Daniel J Kontak, Denis Thiéblemont, Anne Dabosville, Blandine Gourcerol

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Matthieu Harlaux, Olivier Blein, Christophe Ballouard, Daniel J Kontak, Denis Thiéblemont, et al. Geochemical footprints of peraluminous rare-metal granites and pegmatites in the northern French Massif Central and implications for exploration targeting. Ore Geology Reviews, 2024, 176, pp.106409. 10.1016/j.oregeorev.2024.106409. hal-04866394

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# Geochemical footprints of peraluminous rare-metal granites and pegmatites in the northern French Massif Central and implications for exploration targeting☆

Matthieu Harlaux<sup>a,∗</sup> ID, Olivier Blein<sup>a</sup>, Christophe Ballouard<sup>b</sup>, Daniel J. Kontak<sup>c</sup>, Denis Thiéblemont<sup>a</sup>, Anne Dabosville<sup>a</sup>, Blandine Gourcerol<sup>a</sup>

## ARTICLE INFO

**Keywords:**

Geochemical footprints

Rare-metal granites and pegmatites

Metasomatic halos

French Massif Central

European Variscan belt

## ABSTRACT

Peraluminous rare-metal granites and pegmatites (RMGP) formed in late-orogenic settings represent an important source of elements essential to the energy transition and the electronics industry, such as Li, Ta, Nb and Sn. However, exploration for RMGP in crystalline basement is hampered by their typically small size, lack of distinctive petrophysical characteristics, and proximity with earlier, larger barren composite granitic plutons that may mask their presence. This paper reviews the main geochemical features of late-Variscan, 315-to-310 Ma RMGP in the northern French Massif Central (FMC) to better define useful geochemical proxies relevant to exploration targeting. The northern FMC defines a ca. 150 km-long metallogenic province that hosts three types of RMGP: (i) the Beauvoir and Montebras leucogranites, (ii) the Chédeville pegmatite field, and (iii) the Richemont rhyolite. Based on a compilation of whole-rock geochemical data for these RMGP (n = 151) and other late-Variscan peraluminous granites in the FMC (n = 1953), we examine the enrichment of rare elements (Li, F, Be, Nb, Ta, Sn, W) as well as indices of magmatic fractionation and hydrothermal alteration in these settings. The RMGP are variably enriched in Li (372–11,200 ppm; avg = 3500 ppm), F (1475–40,000 ppm; avg = 15,010 ppm), Be (3–506 ppm; avg = 107 ppm), Nb (25–200 ppm; avg = 79 ppm), Ta (23–447 ppm; avg = 116 ppm), Sn (19–13,311 ppm; avg = 1069 ppm) and W (3–312 ppm; avg = 38 ppm), of which the Beauvoir leucogranite is the most enriched. Compared to the peraluminous cordierite-biotite and two-mica granites in the FMC, the RMGP are strongly fractionated with very low Σ(Fe + Mg + Ti), low Nb/Ta (<2), Zr/Hf (<20) and Th/U (<1) ratios, and high Rb/Sr ratios (>10). In addition to these striking features, the RMGP show a systematic spatial association with evolved two-mica granites containing elevated contents of Li (avg = 627 ppm), F (avg = 4462 ppm), Be (avg = 28 ppm), Nb (avg = 32 ppm), Ta (avg = 14 ppm), Sn (avg = 122 ppm) and W (avg = 19 ppm), which are 2–4 times higher relative to other peraluminous two-mica granites in the FMC. The emplacement of these evolved granites was synchronous with magmatism at ca. 330–315 Ma, preceding and partly overlapping the formation of RMGP. Interpolated element distribution maps from the studied areas show large geochemical halos for Li, Be, F and Sn (±W) around the granites spatially associated to RMGP, with concentrations exceeding ten times upper continental crust values, and extending several km from the plutons. Due to their highly-evolved character and large geochemical footprints (>10 s km²), the granitic plutons associated with RMGP represent pre-enriched, specialized precursors for rare-metal mineralization. Given the regional extent of evolved peraluminous leucogranites in the northern FMC, we conclude that there is a significant mineral potential for rare metals (especially Li) and that future geochemical surveys should considerer areas near specialized leucogranites as high-priority targets to search for new concealed RMGP occurrences.

<footnote><sup>a</sup> BRGM, F-45060 Orléans, France</footnote>

<footnote><sup>b</sup> Université de Lorraine, CNRS, GeoRessources, 54000 Nancy, France</footnote>

<footnote><sup>c</sup> Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada</footnote>

<footnote>* This article is part of a special issue entitled: 'EIS and mineral systems' published in Ore Geology Reviews.</footnote>

<footnote>* Corresponding author.
E-mail address: m.harlaux@brgm.fr (M. Harlaux).</footnote>
# 1. Introduction

Exploring and discovering new mineral deposits is one of the major challenges facing the mining industry as the demand increases for mineral resources deemed necessary for the energy transition to a carbon-neutral economy. A common approach now used by exploration and mining companies is to identify and quantify alteration footprints that can be translated into vectors to deposits based on large litho-geochemical datasets, remote sensing technologies and mineral potential mapping (e.g., Large et al., 2001; Gonçalves et al., 2018; Ford et al., 2019; Skirrow et al., 2019; Halley, 2020; Stanley, 2020; Winterburn et al., 2020). In recent years, the number of studies aiming to improve the exploration of Li-Cs-Ta (LCT) pegmatites has increased significantly, notably for identifying alteration features and defining geochemical footprints (e.g., Galeschuk and Vanstone, 2005; Selway et al., 2005; Cardoso-Fernandes et al., 2019; Pfister et al., 2023; Sweetapple et al., 2024). Specifically, numerous studies have focused on identifying criteria to distinguish between barren versus mineralized granitic/pegmatitic systems enriched in rare elements (e.g., Li-Be-Ta-Sn) based on mineralogical, geochemical and metasomatic alteration features (Roza Llera et al., 2019; Ballouard et al., 2020; Barros et al., 2020; Kaeter et al., 2021; Errandonea-Martin et al., 2022; Pfister et al., 2023; Sweetapple et al., 2024). This approach is part of the Horizon Europe – Exploration Information System (EIS) project (https://eis-he.eu), which aims to develop new mineral system models and digital exploration tools for reevaluating the critical mineral potential of Europe.

In this paper, we focus on the French Massif Central (FMC), which is one of the case studies of the EIS project dedicated to Li-Sn-Ta-W-bearing granite/pegmatite-related systems. The FMC is located in the Western European Variscan belt that hosts numerous rare-metal (Li, Be, Sn, W, Ta, Nb) deposits related to late Carboniferous peraluminous granitic plutons (Raimbault et al., 1987; Stussi, 1989; Marignac and Cuney, 1999; Cuney et al., 2002; Bouchot et al., 2005; Harlaux et al., 2018a,b; Monnier et al., 2018). Similar types of deposits occur elsewhere in the European Variscan belt, including Cornwall, the Erzgebirge, the Iberian Massif and the Armorican Massif (Ballouard et al., 2024; Borrajo et al., 2024; Breiter et al., 2017; Chappell and Hine, 2006; Gourcerol et al., 2019; Michaud et al., 2020; Michaud and Pichavant, 2020; Roda-Robles et al., 2018; Romer and Kroner, 2016; Simons et al., 2016, 2017). In France, indicated and measured Li resources are estimated by the BRGM to approximate 458 kt Li₂O with significant further potential for Li mineralization associated with specialized granites and pegmatites, and the FMC is identified as representing the most prospective area (Gloaguen et al., 2018; Gourcerol et al., 2021).

In the northern FMC, peraluminous rare-metal granites and pegmatites (RMGP) define a ca. 315-to-310 Ma province that formed during the late-orogenic evolution of the Variscan belt (Cuney et al., 2002; Cuney and Barbey, 2014; Melleton et al., 2015). These deposits include the Beauvoir and Montebras leucogranites, the Chédeville pegmatite field, and the Richemont rhyolite (Aubert, 1969; Burnol, 1974; Cuney et al., 1992, 2002; Raimbault et al., 1995; Raimbault and Burnol, 1998; Deveaud et al., 2013, 2015; Cuney and Barbey, 2014; Villaros and Pichavant, 2019; Marcoux et al., 2021). These RMGP host disseminated-type mineralization of Li (e.g., lepidolite-zinnwaldite, petalite, amblygonite-group minerals), Be (e.g., beryl, herderite, bertrandite), Sn (e.g., cassiterite) and Ta-Nb (e.g., columbite- and pyrochlore-group minerals), which have generally been interpreted to reflect magmatic processes (Cuney et al., 1992; Raimbault et al., 1995; Linnen and Cuney, 2005; Pichavant, 2022). In addition, hydrothermal Sn-W and U mineralization occur in close spatial association with RMGP in the FMC, including veins, stockworks, breccias, greisens, and stockscheiders (Cuney et al., 1990, 1992; Vallance et al., 2001; Harlaux et al., 2018b, 2021, 2024; Monnier et al., 2018, 2020; Marcoux et al., 2021).

Recognizing the presence of unexposed RMGP in crystalline basement such as the FMC is difficult because: (i) they generally form small intrusive bodies of limited spatial extent (i.e., <10 km²); (ii) they do not

bear markedly distinctive petrophysical features, which hampers geophysical exploration; and (iii) they are frequently associated with/or part of earlier, larger barren composite granitic plutons that may mask their presence (Linnen and Cuney, 2005; Gloaguen et al., 2018; Gourcerol et al., 2019; Romer and Pichavant, 2021). In this context, the objective of this work is twofold. Firstly, to characterize the geochemical footprints of RMGP in the northern FMC based on their whole-rock chemistry and related metasomatic halos in the surrounding host rocks. Secondly, to define alteration patterns in metasomatized rocks that might vector towards concealed RMGP. Following a description of the main RMGP deposits in the northern FMC (Beauvoir, Montebras, Chédeville, and Richemont), we review the critical components and mappable criteria for exploration using the mineral system concept (McCuaig et al., 2010; McCuaig and Hronsky, 2014). To address the objectives listed above, this work utilizes a geochemical database consisting of individual whole-rock analyses of RMGP and associated barren host granitic rocks in the northern FMC as well as interpolated element distribution maps from georeferenced geochemical data. Based on this compilation, we examine the main geochemical characteristics of RMGP in comparison to peraluminous granites in the FMC and we discuss the implications for exploration targeting of future geochemical surveys.

# 2. Geologic background of the FMC

The FMC belongs to the Moldanubian zone of the European Variscan belt that formed during continental collision between Gondwana and Laurussia during the Upper Paleozoic. The geologic structure of the FMC is generally interpreted as a stack of three major metamorphic nappes that are from top to bottom (e.g., Ledru et al., 1989; Faure et al., 2009; Vanderhaeghe et al., 2020; and references therein; Fig. 1): (i) the Upper Gneiss Unit (UGU) of ortho- and para-gneisses derived from Cambrian to Lower Ordovician protoliths (530–470 Ma) that experienced amphibolite- to granulite-facies metamorphism at 360–330 Ma; (ii) the Lower Gneiss Unit (LGU) of high-grade ortho- and paragneisses similar to those of the UGU that were inherited from Ediacaran protoliths (620–540 Ma); and (iii) the Para-Autochthonous Unit (PAU) of low-grade metasedimentary rocks (micaschists, metagreywackes, and quartzites) that were derived from Neoproterozoic to Early Cambrian protoliths (650–530 Ma).

These stacked tectono-metamorphic units were intruded by various granitoids during the Late Devonian through the Carboniferous (ca. 360–300 Ma), which include four main petrological types (Stussi, 1989; Cuney, 2014; Moyen et al., 2017; Laurent et al., 2017; Villaros et al., 2018; Vanderhaeghe et al., 2020; Fig. 1): (i) amphibole-bearing metaluminous calc-alkaline granitoids (ACG in the classification of Barbarin, 1999) which consist of tonalites, granodiorites and granites that frequently contain mafic enclaves and associated small gabbroic and dioritic stocks. The ACG are interpreted as arc magmas originating from partial melting of metasomatized upper mantle during early Variscan subduction, with variable degrees of mixing with crust-derived granitic melts; (ii) high-K metaluminous to peraluminous sub-alkaline granitoids (KCG), which include amphibole-bearing porphyritic granites and granodiorites to quartz-diorites typically hosting abundant microgranular mafic enclaves. The KCG are attributed to mixing between crust-derived felsic magmas and mantle-derived Mg-K-rich magmas, or to the differentiation of Mg-K-rich mafic magmas (e.g., vaugnerites) derived from metasomatized mantle during continental crust subduction; (iii) two-mica (biotite-muscovite)-bearing peraluminous granitoids (MPG); and (iv) biotite ± cordierite-bearing peraluminous granitoids (CPG). The MPG and CPG mostly represent crust-derived magmas originating from partial melting of Al-rich protoliths such as metapelites and orthogneisses that was initiated by crustal thickening.

The distinctive petrological features of MPG and CPG may reflect different temperatures of partial melting (Moyen et al., 2017; Laurent et al., 2017; Villaros et al., 2018) with MPG originating from low degrees, possibly fluid-assisted, of partial melting close to muscovite-
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Simplified geological map of the northern French Massif Central (FMC) distinguishing the various petrological types of granitoids (modified from Vanderhaeghe et al., 2020) and showing the location of major rare-metal granites and pegmatites (Beauvoir, Montebras, Chédeville, Richemont). The names of the main granitic plutons are reported on the map for reference.</figcaption></figure>

breakdown conditions at < 750 °C, whereas CPG relate to higher degrees of partial melting at > 750 °C due to biotite-breakdown reactions with the possibility of mixing with mantle-derived magmas. The chemical characteristics of these different granitoids were extensively studied between the 1970 s and 1990 s which showed that the late-Carboniferous (ca. 325–300 Ma) MPG suites are the most prospective from a metallogenic perspective, particularly for Sn, W, Li, Be, Ta, Nb and U mineralization (e.g., Barbier, 1970; Burnol, 1974; Cuney et al., 1990, 1992, Gauthier, 1973, 1974, Raimbault et al., 1987, 1995; Stussi, 1989).

The RMGP define an approximately 150 km long province through
the northern FMC that trends E-W and extends west to east through the
Limousin and Sioule regions (Fig. 1). This suite is dated at ca. 315-310
Ma and represents one of the latest magmatic stages during the late-
orogenic evolution of the FMC (Marignac and Cuney, 1999; Cuney
et al., 2002; Cuney and Barbey, 2014; Melleton et al., 2015; Gourcerol
et al., 2019). Emplacement of RMGP followed the development of
ductile shear zones synchronous to peraluminous granitic magmatism at
c.a. 335-320 Ma (Cartannaz et al., 2007; Rolin et al., 2009, 2014;
Gébelin et al., 2007, 2009; Vanderhaeghe et al., 2020). This province
contains three main types of RMGP that share similar geochemical
characteristics which includes, from the east to the west: (i) the Beauvoir
and Montebras leucogranites; (ii) the Chédeville pegmatite field; and
(iii) the Richemont rhyolite (Aubert, 1969; Burnol, 1974; Cuney et al.,
1992, 2002; Raimbault et al., 1995; Raimbault, 1998; Raimbault and
Burnol, 1998; Deveaud et al., 2013, 2015; Gloaguen et al., 2018; Villaros
and Pichavant, 2019; Marcoux et al., 2021). Despite being emplaced in

different settings ranging from plutonic to subvolcanic, the RMGP of the
northern FMC show similar geochemical affinities and fractionation
trends (Raimbault et al., 1995; Cuney and Barbey, 2014) characteristic
of peraluminous high-phosphorus rare-metal granites (PHP-RMG), as
defined by Linnen and Cuney (2005). Smaller occurrences of RMGP have
been documented in other parts of the FMC, including Chavence
(Mourey, 1985), Fabras (Ballouard et al., 2023) and Saint-Mélany
(Harlaux et al., 2024).

**3. Rare-Metal granites and pegmatites in the northern FMC**

3.1. *Beauvoir*

The Beauvoir leucogranite (latitude 46°10′42″ N, longitude 2°57′12″ E), located in the Echassières district within the Sioule region (Fig. 1), has been extensively studied during and since the 1980 s due to the 900 m scientific borehole of the “Deep Geology of France” program (Cuney and Autran, 1987). These studies provided detailed petrological, geochemical, geophysical, structural, and geochronological descriptions of the Beauvoir granite and its host-environment, thus making of it one of the best studied rare-metal granitic systems globally (Linnen and Cuney, 2005). This leucogranite is hosted by the Sioule micaschists of the PAU (Do Couto et al., 2016) and the Colettes porphyritic two-mica and cordierite-bearing granite dated at 317 ± 8 Ma (Rb/Sr isochron age from Pin, 1991, recalculated by Carr et al., 2021). The Colettes granite is interpreted as a syntectonic pluton emplaced during the late-orogenic extension of the northern FMC (Gagny and Jacquot, 1987;
Faure et al., 1993). The contact between the Colettes granite and the Beauvoir leucogranite is marked by a transitional zone interpreted as a metasomatic replacement front (Aubert, 1969; Cuney et al., 1992; Raimbault et al., 1995).

The Beauvoir granite was emplaced at ca. 315–310 Ma based on $^{40}$Ar/$^{39}$Ar lepidolite dating (308 ± 2 Ma; Cheilletz et al., 1992), U/Pb columbite-tantalite dating (317 ± 6 Ma; Melleton et al., 2015), and U/Pb apatite dating (314.6 ± 4.7 Ma; Rocher et al., 2024). It has a strongly peraluminous composition with disseminated Sn-Li-Ta-Nb-Be mineralization (Aubert, 1969; Cuney et al., 1992; Raimbault et al., 1995). Both the Colettes and Beauvoir granites crosscut the La Bosse W deposit, which consists of a micaschist-hosted quartz-wolframite stockwork with polyphase development (Aubert, 1969; Aïssa et al., 1987; Cuney et al., 1992; Monnier et al., 2019). The emplacement of the La Bosse W deposit is constrained to between 335.5 ± 3.0 Ma (U/Pb monazite; Monnier et al., 2021), 333.4 ± 2.4 Ma (U/Pb wolframite; Harlaux et al., 2018a) and 316.5 ± 5.3 Ma (U/Pb wolframite; Carr et al., 2021), although an older age of 355 ± 6 Ma has been reported from a vein alteration halo (U/Pb monazite; Monnier et al., 2021). On the northern margin of the Colettes granite, other W ± Sn vein deposits occur at the localities Suchot and Mazet, which have been dated between 331 ± 5 Ma (U/Pb monazite; Monnier et al., 2021) and 328 ± 5 Ma (U/Pb rutile; Monnier et al., 2021), and 279.1 ± 7.1 Ma (U/Pb wolframite; Carr et al., 2021), respectively.

The Beauvoir pluton consists of three main units, all topaz- and amblygonite-bearing, which from top to base are referred to as: (i) the B1 unit (–100 to –450 m) of fine- to medium-grained, albite-lepidolite-rich seriate-textured leucogranite containing idiomorphic quartz and rare anhedral perthitic K-feldspar; (ii) the B2 unit (–450 to –750 m) of medium-grained lepidolite-rich seriate-textured granite also with idiomorphic quartz and low amount of perthitic K-feldspar; and (iii) the B3 unit (–750 to –880 m) which also contains idiomorphic quartz in a medium- to locally coarse-grained and hypidiomorphic granite with abundant pink-colored perthitic K-feldspar and zinnwaldite. The abundance of rare-metal-bearing accessory minerals (cassiterite, columbite-group mineral, microlite, and Li-Be phosphates) increases upward from the B3 to the B1 units, the latter being the most evolved (Cuney et al., 1992; Raimbault et al., 1995). Recent core drilling exploration of the upper 300 m of the Beauvoir granite led to inferred resources of 117 Mt with average grades of 0.9 % Li₂O, 0.13 % Sn and 0.02 % Ta, which correspond to metal contents of 489,153 t Li, 152,100 t Sn and 23,400 t Ta, respectively (Imerys, 2022).

The uppermost B1 unit is exposed in an open pit kaolinite quarry. It exhibits greisen zones consisting of a quartz-muscovite (± topaz) assemblage localized to fractured zones without significant rare-metal mineralization (Fig. 2a-b; Monnier et al., 2020, 2022; Harlaux et al., 2023). Greisen formation is constrained to between 314.3 ± 5.5 Ma and 311.7 ± 8.1 Ma based on U/Pb apatite dating (Rocher et al., 2024). Late hydrothermal alteration of the granite resulted in the formation of secondary Li-bearing donbassite and tosudite along veins prior to the deposition of kaolinite and randomly interstratified illite/smectite (Merceron et al., 1988, 1992). These lower temperature alterations are dated between Permian (273 ± 6 Ma to 268.3 ± 20.4 Ma) and Upper Jurassic (151 ± 4 Ma to 148.5 ± 26.6 Ma) based on K/Ar muscovite and illite ages and U/Pb apatite ages (Merceron et al., 1992; Rocher et al., 2024).

## 3.2. Montebras

The Montebras leucogranite (latitude 46°19′18″ N, longitude 2°17′54″ E) is located in the Eastern Marche district, at the limit between the Aigurande region to the north and the Limousin region to the south (Fig. 1), in a tectonically-complex area affected by major E-W-trending shear zones (La Marche, Boussac) that were active during the Upper Carboniferous (ca. 335–320 Ma; Gébelin et al., 2007; Cartannaz et al., 2007; Rolin et al., 2009). It is hosted by the Chanon biotite-cordierite

granite (357.2 ± 2.1 Ma, U/Pb zircon; Marcoux et al., 2021), corresponding to the northeastern termination of the Guéret batholith (356 ± 10 Ma, Rb/Sr isochron age; Duthou et al., 1984), and by a small K-feldspar porphyritic muscovite ± topaz microgranite (316.1 ± 4.3 Ma, U/Pb apatite; Marcoux et al., 2021). Although only locally exposed in the lower part of the Montebras open pit quarry and an old pit nearby, the porphyritic microgranite likely constitutes the apex of a largely unexposed, high-level granitic intrusion emplaced into the Chanon granite (Aubert, 1969; Marcoux et al., 2021).

The Montebras leucogranite frequently includes pluri-metric angular enclaves of the Chanon granite and rounded enclaves of porphyritic microgranite, the latter exhibiting a mineral reaction rim with newly crystallized albite (Marcoux et al., 2021; Fig. 2c), thus supporting their early emplacement relative to the leucogranite. The Montebras leucogranite was injected as an intrusive sheet at the interface between the overlying Chanon granite and the underlying porphyritic microgranite and shows an ovoid shape of variable thickness (5–50 m), which becomes thicker in its western part (Gloaguen et al., 2018; Marcoux et al., 2021). Its emplacement is constrained to ca. 310 Ma from concordant radiometric ages: $^{40}$Ar/$^{39}$Ar lepidolite (309.9 ± 1.4 Ma; Cuney et al., 2002), U/Pb columbite (309.3 ± 4.3 Ma, 310.9 ± 2.3 Ma, and 314 ± 4 Ma; Melleton et al., 2015; Marcoux et al., 2021), U/Pb cassiterite (304.9 ± 4.9 Ma; Marcoux et al., 2021), and U/Pb apatite (310.5 ± 8.7 Ma; Marcoux et al., 2021).

The Montebras leucogranite consists of fine-grained equigranular albite-muscovite-rich granite hosting disseminated-type Li-Sn-Be-Nb-Ta mineralization (cassiterite, columbite-tantalite, Li-phosphates, Li-muscovite, lepidolite) and is similar geochemically to the Beauvoir leucogranite (Aubert, 1969; Raimbault et al., 1995; Belkasmi and Cuney, 1998; Marcoux et al., 2021). Inferred resources are estimated at 3.5 kt Li₂O for the Montebras leucogranite with an average grade of 0.1 % Li₂O and 30 kt Li₂O for the Montebras microgranite with an average grade of 0.5 % Li₂O (Gloaguen et al., 2018). The contact between the Montebras leucogranite and the Chanon granite is marked by various metasomatized lithologies, including a K-feldspar-rich pegmatite-like body up to 15 m thick ("stockscheider" sensu Breiter et al., 2005; Fig. 2d), a massive quartz cap ("quartzglocke"), quartz-mica greisens and cassiterite-bearing quartz veins with inferred resources of 3.5 kt Sn (Aubert, 1969; Gloaguen et al., 2018; Marcoux et al., 2021). Inferred resources are estimated at 8.7 kt Li₂O with an average grade of 1.5 % Li₂O for lepidolite greisen (Gloaguen et al., 2018).

The formation ages of the stockscheider pegmatite (313.4 ± 5.3 Ma to 309.7 ± 4.5 Ma; Marcoux et al., 2021) and the cassiterite-bearing veins (303.8 ± 4.8 Ma; Marcoux et al., 2021) overlap with the Montebras leucogranite, thus indicating a temporal continuum in the magmatic-hydrothermal system. The Montebras leucogranite and overlying Chanon granite record several episodes of pervasive alterations, with quartz-lepidolite greisens followed by the formation of tosudite and interstratified illite/smectite during kaolinization (both hydrothermal and supergene) of the granitic stocks (Creach et al., 1986; Dudoignon et al., 1988).

## 3.3. Chédeville

The Chédeville rare-metal pegmatite field (latitude 45°58′44″ N, longitude 1°23′8″ E), located in the Monts d'Ambazac district within the Limousin region, is situated in the southern part of the ca. 324 Ma Saint-Sylvestre leucogranitic complex that intruded as a thin laccolith (ca. 2–3 km in thickness) in the LGU and PAU (Fig. 1; Audrain et al., 1989; Cuney et al., 1990; Holliger et al., 1986; Le Carlier de Veslud et al., 2013; Scaillet et al., 1996a). The Saint-Sylvestre intrusive complex consists of four major biotite ± muscovite granitic units (Brâme, Châteauponsac, Saint-Sylvestre and Saint-Goussaud) emplaced sequentially between 328 ± 3 Ma and 320 ± 3 Ma (U/Pb zircon; Holliger et al., 1986; Villaros et al., 2014). The Chédeville pegmatite swarm was emplaced during a regional late-orogenic NW–SE extensional stage at ca. 310–305 Ma and
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Photographs illustrating various mineralogical and textural features of rare-metal granites and pegmatites in the northern French Massif Central. (A) Upper part of the kaolinized Beauvoir leucogranite intrusive into the Sioule micaschists showing large zones of greisenization and veining. (B) Close-up view of greisenized zones and greisen bordered veins into the Beauvoir leucogranite. (C) Montebras leucogranite intruded into the host muscovite ± topaz microgranite. The contact between the two granitic units is marked by a mineral reaction rim with newly crystallized albite (photo courtesy of Eric Marcoux). (D) Stockscheider pegmatite at the interface between the Montebras leucogranite and the overlying Chanon biotite-cordierite monzogranite (photo courtesy of Eric Marcoux). (E) Alternating lepidolite-rich and K-feldspar-rich aplitic layers showing unidirectional solidification textures (UST) in the lower part of the Chédeville pegmatite. (F) Large phenocrysts of variably altered petalite rimmed by lepidolite in the upper part of the Chédeville pegmatite. (G) Outcrop of the Richemont rhyolite observed near the border of the dike exhibiting disseminated albite phenocrysts in a glassy groundmass (photo courtesy of Eric Gloaguen). (H) Albite phenocrysts disseminated in flow-banded aphanitic groundmass from the Richemont rhyolite. Abbreviations: Ab = albite, Fsp = feldspar, Lpd = lepidolite, Ptl = petalite, Qtz = quartz.</figcaption></figure>
synchronous with exhumation and uplift of the Saint-Sylvestre complex and the overlying metamorphic formations (Faure and Pons, 1991; Le Carlier de Veslud et al., 2013). In this area, more than 100 pegmatite bodies, most belonging to the beryl-columbite subtype of the LCT class of Černý and Ercit (2005), have been identified (Barbier, 1970; Burnol, 1974; Raimbault, 1998; Deveaud et al., 2013; Gloaguen et al., 2018).

The Chédeville pegmatite swarm, which belongs to the lepidolite-
subtype, is one of the largest in the area and extends over ca. 1.2 km
along a SW-NE direction. Its emplacement is constrained to ca. 310 Ma
from dating of lepidolite (309 ± 1 Ma $^{40}$Ar/$^{39}$Ar; Cheilletz et al., 1992)
and columbite-tantalite (309 ± 5 Ma U/Pb; Melleton et al., 2015). The
distribution of the pegmatite clusters in the Monts d'Ambazac is related
to a N-trending fault system, but there is no spatial relationship between
each of the pegmatite subtypes and the different leucogranitic units of
the Saint-Sylvestre complex (Deveaud et al., 2013). Previous studies
concluded that the Monts d'Ambazac pegmatites originate from discrete
episodes of partial melting of a heterogeneous crustal source rather than
being derived from leucogranite via extreme differentiation (Deveaud
et al., 2015; Villaros and Pichavant, 2019).

The Chédeville pegmatites have a complex mineralogical assemblage of quartz, K-feldspar, albite, muscovite, zircon, lepidolite, petalite and Li-Al-phosphates with accessory Sn-Nb-Ta oxide minerals (Raimbault, 1998; Deveaud et al., 2015; Gloaguen et al., 2018). Inferred resources for the Chédeville pegmatites are estimated at 6 kt Li₂O with an average grade of 1.04 % Li₂O (Gloaguen et al., 2018). However, these values should be treated with caution due to the heterogeneity of Li grades that range from 1 to 5 % Li₂O in the Chédeville pegmatites (Gloaguen et al., 2018). The dikes are 0.5 to 3 m thick and exhibit a vertically-zoned internal structure of layered aplitic facies with alternating lepidolite-rich and feldspar-rich units with unidirectional solidification textures (UST) in the lower part (Fig. 2e) that progress to a pegmatitic facies in the upper part containing pluri-centimetric phenocrysts of lepidolite-rimmed petalite (partially replaced by K-feldspar) in a quartz-albite matrix (Fig. 2f; Raimbault, 1998; Gloaguen et al., 2018). Metasomatism of the pegmatites resulted in secondary K-feldspar replacing topaz and micas along veinlets and the local development of greisen-like muscovite- and lepidolite-rich units (Raimbault, 1998). In other pegmatites from the Monts d'Ambazac mostly belonging to the beryl-columbite subtype, pervasive sodic metasomatism is common and well expressed, as for example in the Chabannes pegmatite (located about 4 km to the northwest of Chédeville) where secondary albite replaced K-feldspar in the aplitic and pegmatitic units (Deveaud et al., 2015).

In addition to pegmatites, there are several Sn-W-bearing quartz
veins within and peripheral to the Saint-Goussaud two-mica granite,
which belongs to the most differentiated unit of the eastern part of the
Saint-Sylvestre leucogranitic complex (Cuney et al., 1990; Leger et al.,
1990). This W ± Sn mineralization is dated at 328 ± 6 Ma (U/Pb
wolframite age; Harlaux et al., 2018a), i.e., synchronous with crystal-
lization of the leucogranitic complex and predates the emplacement of
the Chédeville pegmatite swarm. Younger $^{40}$Ar/$^{39}$Ar ages of ca. 305 Ma
were obtained on muscovite from the granite, close to the W(−Sn)
mineralization, and are thought to reflect closure of the Ar isotope
system during the cooling and exhumation of the Saint-Sylvestre com-
plex (Le Carlier de Veslud et al., 2013; Scaillet et al., 1996a,b).

3.4. Richemont

The Richemont rhyolite (latitude 46°3'40" N, longitude 1°2'45" E), located in the Monts de Blond district within the Limousin region (Fig. 1), occurs north of the Blond leucogranitic complex intruding at the contact between the UGU and the LGU. This peraluminous two-mica- or muscovite-bearing leucogranitic complex, with an exposed area of ca. 60 km², shows concentrically zoned textural variations marked by variable proportions of K-feldspar, quartz and Li-mica phenocrysts (Soufi, 1988; Ebougué, 1995; Soufi et al., 2015). To the southwest, the complex is separated from the Glane biotite-bearing granite by the NW-SE-

trending Oradour shear zone (Soufi et al., 2015), and to the southeast,
it intrudes into the Cieux-Vaulry biotite-cordierite granite (352 ± 17
Ma, Rb/Sr isochron age; Duthou et al., 1984). Small fine-grained topaz
± cassiterite-bearing leucogranitic dikes and stocks (e.g., La Puelle)
locally intrude the Blond leucogranite in its western part (Soufi, 1988;
Soufi et al., 2015; Soufi et al., 2018). A series of mostly N-S to NE-SW
oriented microgranitic to rhyolitic dikes (e.g., Gacherie, Brillac) sur-
round the Blond leucogranite and intrude the metamorphic host rocks;
they occur in the southern and northern parts of the granitic complex.
The Blond granitic complex was syntectonically emplaced along the
Oradour dextral shear zone at 319 ± 7 Ma (U/Pb zircon; Alexandrov
et al., 2000) and was affected by successive hydrothermal events at ca.
310–305 Ma (Alexandrov et al., 2002).

The Richemont rhyolite, one of the many dikes in the area, occurs as a 5 km-long, up to 6 m wide, N-S trending dike that cuts older biotite granites and metamorphic rocks of the UGU. Its emplacement is constrained to 313.4 ± 2.8 Ma ($^{40}$Ar/$^{39}$Ar muscovite age; Cuney et al., 2002), thus overlapping the emplacement of the Blond leucogranite. Numerous occurrences of Sn-W-bearing quartz veins crosscutting both the greisenized Blond leucogranite and the metamorphic host rocks are documented, notably at its eastern contact (Vallance et al., 2001); these formed at ca. 310 Ma based on $^{40}$Ar/$^{39}$Ar muscovite (309.0 ± 1.4 to 311.1 ± 0.7 Ma; Cuney et al., 2002) and U/Pb wolframite (310.6 ± 4.0 Ma; Carr et al., 2021) dating.

Typical facies of the Richemont rhyolite consist of small phenocrysts of albite, K-feldspar and muscovite, with rare micro-phenocrysts of pyrochlore-group minerals (U-eurenite) disseminated in an aphanitic groundmass (Raimbault and Burnol, 1998; Fig. 2g-h). Other textural variants include a microcrystalline facies in the center of the dike, and a banded facies with chilled margins near the contacts with the surrounding rocks (Raimbault and Burnol, 1998). Geochemically, the rhyolite dike is strongly peraluminous with high contents of Li, F, Sn, Ta and W (Ebougué, 1995; Raimbault and Burnol, 1998). Inferred resources for the Richemont rhyolite are estimated at 3 Mt with average grades of 0.78 % Li₂O and 0.05 % Sn, which correspond to metal contents of 10.9 kt Li and 1.5 kt Sn over the entire extent of the dike (Gloaguen et al., 2018). Although high-temperature alteration (e.g., greisenization) and quartz veining are overall absent, sparse rounded aggregates of phosphates (mainly Mn-rich apatite and amblygonite-group minerals) hosting micro-inclusions of ore minerals (löllingite, arsenopyrite, W-ixiolite, scheelite, cassiterite, wolframite, tennantite-tetrahedrite) have been found in association with muscovite phenocrysts (Raimbault and Burnol, 1998). Devitrification of a former glassy rhyolitic matrix is frequent and resulted in formation of a fine-grained mixture of quartz, lepidolite, feldspar and rare cassiterite aggregates dispersed throughout the groundmass.

4. Mineral system for Rare-Metal granites and pegmatites in the northern FMC

To summarize the key critical processes involved in RMGP formation
in the northern FMC and translate them into effective exploration tar-
geting criteria, we applied the mineral system concept that has been
developed over the past decades (e.g., McCuaig et al., 2010; McCuaig
and Hronsky, 2014). Such an approach has been effectively applied to a
variety of deposit types, including for example, sediment-hosted Cu, Zn-
Pb, U systems (McCuaig et al., 2018) and IOCG settings (Skirrow et al.,
2019), but has not yet been applied to Li mineral systems in the Variscan
orogen. Based on previous work on Archean LCT pegmatite systems
(Duuring, 2020), we review the mineral system for RMGP in the
northern FMC with reference to the essential geological processes,
'theoretical criteria' and 'mappable criteria' for each of the four mineral
system components (i.e., source, pathway, trap, and preservation/
modification) as listed in Table 1.
<caption>**Table 1**</caption>

Components of the mineral system for peraluminous rare-metal granites and pegmatites in the northern French Massif Central, modified from Duuring (2020).

<table><thead><tr><th>Mineral system component</th><th>Theoretical criteria</th><th>Mappable criteria</th><th>Scale</th><th>Dataset</th></tr></thead><tbody><tr><td rowspan="2">Source</td><td rowspan="2">Extreme fractionation of evolved peraluminous granitic plutons ("residual model")</td><td>Late-orogenic granitoid suites (ca. 320–300 Ma) emplaced in metamorphic terranes dominated by orthogneisses, paragneisses and micaschists</td><td>Regional to district</td><td>Geological maps, geochronology</td></tr><tr><td>Evolved peraluminous S-type granitoid with high contents of lithophile elements (e.g., Li, Cs, Rb, Sn, Be, Ta) and crustal εSr(i)-εNd (i) whole-rock values</td><td>Regional to district</td><td>Litho geochemistry, geochemical maps</td></tr><tr><td rowspan="2">Partial melting of fertile crustal protoliths ("anatectic model")</td><td>Low magnetic anomalies, low gravimetric anomalies, and high K-U radiometric anomalies</td><td>Regional to district</td><td>Geophysical maps, petrophysical data</td></tr><tr><td>Migmatite suites spatially associated to late-orogenic two-mica leucogranites (ca. 320–300 Ma) and major shear zones</td><td>Regional to district</td><td>Geological maps, geochronology</td></tr><tr><td rowspan="2">Pathway</td><td>Evolved peraluminous S-type granitoid with high contents of lithophile elements (e.g., Li, Cs, Rb, Sn, Be, Ta) and crustal εSr(i)-εNd (i) whole-rock values</td><td>Regional to district</td><td>Litho geochemistry, geochemical maps</td></tr><tr><td>Low magnetic anomalies, low gravimetric anomalies, and high K-U radiometric anomalies</td><td>Regional to district</td><td>Geophysical maps, petrophysical data</td></tr><tr><td rowspan="5">Trap</td><td>Lithospheric faulting or shearing</td><td>Shear zones and ductile/brittle fault zones (1st order) in proximity to suitable parental granites and/or pegmatites</td><td>Regional to district</td><td>Geological maps, geophysical maps, structural data</td></tr><tr><td rowspan="2">Pegmatite distributions, geometries</td><td>Fault intersections (2nd to 3rd order) in spatial relation with granites/pegmatites distribution</td><td>Regional to district</td><td>Geological maps, geophysical maps, structural data</td></tr><tr><td>Spatial and geometric relationships between pegmatites, potential parental granites and/or migmatitic rocks</td><td>Regional to district</td><td>Geological maps, structural data</td></tr><tr><td>Alteration pathways in country rocks</td><td>Geometric relations between structural fabrics in metamorphic host rocks and pegmatites</td><td>Regional to district</td><td>Geological maps, geophysical maps</td></tr><tr><td>Potential trap rocks and structures</td><td>Mineralogical and geochemical zonation related to alteration halos (e.g., Li, Rb, Cs, F, Sn)</td><td>Regional to district</td><td>Litho geochemistry, drill hole data</td></tr><tr><td rowspan="2">Degree of fractional crystallization</td><td>Proximity to evolved peraluminous S-type granitic rocks (ca. 320–300 Ma) and shear zones</td><td>Regional to district</td><td>Geological maps, geophysical maps, geochronology</td></tr><tr><td>Compositionally and texturally zoned pegmatites/granites marked by specific mineral associations (e.g., lepidolite, cassiterite, montebasite, fluorite, topaz) and geochemical proxies (e.g., elevated Li, Rb, Sn, Cs, Ga, Rb/Sr, Nb/Ta values)</td><td>Regional to district</td><td>Litho geochemistry, mineral chemistry</td></tr><tr><td rowspan="5">Preservation / modification</td><td rowspan="5">Preservation of hard, resistant pegmatites/granites in outcrop Exposure of rocks that have been buried to mid- to shallow-crustal levels</td><td>Pervasive hydrothermal alterations affecting the host rocks (e.g., albitization, greisenization, silicification)</td><td>District to deposit</td><td>Geological maps, litho geochemistry</td></tr><tr><td>Metasomatic halos with high concentrations of lithophile elements (e.g., Li, Rb, Cs, Be, Sn, F) in host granitic and metamorphic rocks</td><td>District to deposit</td><td>Litho geochemistry</td></tr><tr><td>Stream-sediment and/or soil geochemical anomalies with key element indicators (e.g., Li, Rb, Cs, Ta, Be)</td><td>District to deposit</td><td>Geochemical maps</td></tr><tr><td>Presence of alluvial indicator minerals (e.g., cassiterite, beryl, apatite, columbite-tantalite)</td><td>District to deposit</td><td>Mineralogy</td></tr><tr><td>Outcrops of granites/pegmatites along topographic highs and ridges with possible extension under local country rocks</td><td>Regional to deposit</td><td>Geological maps, geophysical maps</td></tr><tr><td rowspan="2">Near surface anomalies</td><td>Country rocks recording retrogressed regional metamorphic facies or contact metamorphic aureole related to a concealed intrusion</td><td>District to deposit</td><td>Geological maps, geophysical maps</td></tr><tr><td>Stream-sediment and soil anomalies (e.g., Li, Sn, Ta, Cs, Rb, Be), heavy minerals in alluvial sediments (e.g., cassiterite, columbite-tantalite, topaz), chemistry of indicator minerals (e.g., cassiterite, apatite, mica)</td><td>District to deposit</td><td>Litho geochemistry, geochemical maps</td></tr></tbody></table>

## 4.1. Source and fertility

An essential process in the formation of RMGP is the generation of highly-fractionated granitic magmas with elevated contents of lithophile fluxing elements (Li, F, P). The RMGP suites are generally thought to originate from extreme differentiation via crystal fractionation (typically > 99 wt%) of less evolved peraluminous granitic plutons ("residual model"; e.g., Hulsbosch et al., 2014; London, 2018; Wu et al., 2020), or directly produced via low-degree partial melting of fertile crustal protoliths ("anatectic model"; e.g., Romer and Kroner, 2016; Müller et al., 2017; Bonzi et al., 2021; Koopmans et al., 2024). However, alternative models have been proposed for the origin of RMGP, notably in the European Variscan belt, which involve specific protoliths and partial melting conditions, but nonetheless implying a modest amount of magmatic differentiation. Those models include: (i) granulite-facies metamorphism of the lower crust generating Li-F-rich metamorphic fluids that in turn enhanced fluxed melting of the overlying upper crust and the formation of RMGP melts (Cuney and Barbey, 2014; Simons et al., 2016); (ii) high-temperature (>800 °C) biotite-dehydration melting of restitic metasedimentary protoliths (Wolf et al., 2018;

Michaud et al., 2021; Simons et al., 2016); (iii) staurolite-breakdown melting reactions of Li-rich metapelites (Konzett et al., 2018; Knoll et al., 2023); and (iv) mica-dehydration melting of peraluminous orthogneisses in fluid-absent conditions (Ballouard et al., 2023).

Considering for simplicity the residual and anatectic models only, we can identify mappable criteria that apply to each. In the first case ("residual model"), one of the key mappable criteria from the regional to district scales in the northern FMC is the distribution of MPG suites (ca. 320–300 Ma) emplaced in metamorphic terranes dominated by variably migmatitic orthogneisses, paragneisses, and micaschists (i.e., UGU, LGU and PAU). In the second case ("anatectic model"), the key mappable criterion is the occurrence of migmatite suites spatially associated to MPG (ca. 320–300 Ma) and major shear zones. In both cases, RMGP are expected to be found structurally above late-Variscan anatectic complexes, as documented in the Velay anatectic dome area in the south-eastern FMC (Harlaux et al., 2024) and in the Fregeneda-Almendra pegmatite field in the Iberian Massif (Ballouard et al., 2024). Additional mappable proxies include evolved peraluminous S-type geochemistry of the granites with high contents of lithophile elements (e.g., Li, Cs, Rb, Sn, Be, Ta), crustal Sr-Nd isotopic values, and
prospective geophysical signatures corresponding to low magnetics, low gravimetric, and high K-U radiometric anomalies.

## 4.2. Architecture and pathways

Previous studies have shown that the emplacement of syn-to-late- orogenic peraluminous granites (ca. 335–315 Ma) in the northern FMC overlaps with development of major ductile shear zones (Cartannaz et al., 2007; Gébelin et al., 2009; Rolin et al., 2009, 2014; Gébelin et al., 2007). This has been demonstrated for example in the Millevaches granitic complex (Fig. 1) where the emplacement of mylonitic leucogranites (313 ± 4 Ma) was coeval with development of cordierite-bearing migmatitic gneisses (315 ± 4 Ma) and vertical lenses of leucosomes (316 ± 2 Ma) in strike-slip shear zones (Gébelin et al., 2009). Lithospheric-scale ductile structures have thus played a major role in controlling the spatial distribution of peraluminous granitic rocks and driving hydrothermal fluid circulation during the Variscan late-orogenic evolution of the FMC (Marignac and Cuney, 1999; Bouchot et al., 2005). Mapping the distribution of first-order shear zones in proximity to syn-to-late orogenic leucogranites and/or migmatites is considered as a favorable criterion for exploration of RMGP at the regional scale using available geological and geophysical maps.

Moreover, structural studies in the Echassières district (Gagny and Jacquot, 1987; Jacquot and Gagny, 1987) and the Monts de Blond district (Soufi et al., 2015) have highlighted the relationship between transcurrent deformation and the emplacement of rare-metal enriched granitic magmas. Such relationship was also documented in other areas of the Variscan belt, such as in Iberia (Michaud et al., 2020; Ballouard et al., 2024), or in Precambrian orogenic systems (Ballouard et al., 2020; Silva et al., 2023). Therefore, late-Variscan strike-slip tectonic setting generating vertical dilational structures (e.g., shear zones and faults, pull apart, Riedels and tension gashes) optimizing the ascent of flux-rich magmas toward upper structural levels could be considered as a favorable proxy for RMGP exploration. For example, the distribution and geometric relationship of pegmatites with fault zones was highlighted as an important criterion for mapping areas of potential in the Monts d'Ambazac district (Deveaud et al., 2013; Gloaguen et al., 2018). Finally, the pathways of RMGP magmas are also characterized by alteration halos in the surrounding rocks as reflected by enrichment in key element indicators (e.g., Li, Be, Sn, F), as documented in the Echassières district where large geochemical anomalies have been defined around the Beauvoir leucogranite (Aubert, 1969).

## 4.3. Depositional trap

In the northern FMC, the RMGP are systematically associated with late Carboniferous (ca. 320–310 Ma) peraluminous granitic complexes, however, their emplacement level, shape, nature of the host rock, and spatial relationship with granites and shear zones are highly variable (Marignac and Cuney, 1999). As was noted previously, the Beauvoir leucogranite comprises three successive intrusive units interpreted as stacked granitic sheets injected into the Sioule micaschists at the southern margin of the Colettes granitic complex (Cuney et al., 1992). In contrast, the Montebras leucogranite is interpreted as an intrusive sheet emplaced within the Chanon biotite granite in proximity to the La Marche dextral shear zone (Marcoux et al., 2021); the contact is marked by brecciated textures (i.e., metric-size enclaves) and metasomatized units (i.e., stockscheider, quartzglocke, greisens). The Chédeville pegmatite swarm was emplaced at the southern margin but within the Saint-Sylvestre leucogranitic complex during synkinematic extension (Gloaguen et al., 2018; Le Carlier de Veslud et al., 2013). The Richemont rhyolite dike is hosted in amphibolites and gneisses a few km to the north of the Blond leucogranitic complex, which was syntectonically emplaced along the Oradour dextral shear zone (Raimbault and Burnol, 1998; Soufi et al., 2015). Late-orogenic MPG in proximity to major fault zones and their immediate surrounding rocks represent therefore

favorable hosts for RMGP at the regional scale. Conversely, RMGP are unlikely to occur in contemporaneous migmatites formed in deep structural levels.

Furthermore, the degree of fractional crystallization and water content of the RMGP magmas are variable depending on the emplacement level (i.e., depth/pressure) and geometry of the granitic bodies (i. e., sill, dike, cupola), thus resulting in different styles of hydrothermal alteration and mineralized footprints affecting the host rocks. For example, the micaschists at the roof of the Beauvoir granite contain high concentrations of Sn, F, Li and Rb, decreasing upward over a hundred meters, but the upward-continuous Ta and Nb enrichment observed within the granite stops abruptly at the top of the cupola, which reflects the variable geochemical mobility of these elements during hydrothermal alteration (Cuney et al., 1992). Targeting stream-sediment and soil geochemical anomalies (e.g., Li, Rb, Cs, Be, Sn, F) and/or alluvial indicator minerals (e.g., cassiterite, beryl, apatite, columbite-tantalite, wolframite) are therefore favorable proxies for the occurrence of near-surface RMGP deposits at the district scale. It is noteworthy that RMGP deposits are often spatially associated with hydrothermal Sn ± W deposits, as documented in the Echassières, Eastern Marche, Monts d'Ambazac and Monts de Blond districts; these regions are fertile areas from a metallogenic perspective and should be considered favorable targets for RMGP exploration.

## 4.4. Preservation and modification

The preservation and/or modification of RMGP deposits is a function of several factors, including the emplacement depth of magmas, the rates of uplift and exhumation, and surficial weathering and erosion processes. In the northern FMC, the RMGP were emplaced at shallow levels in the upper Variscan continental crust, estimated at 3 km for the Beauvoir granite (Cuney et al., 1992), and likely even shallower for the Richemont rhyolite (Raimbault and Burnol, 1998). The uplift rate of the northern FMC during the late-orogenic Variscan stage is not well known, but previous studies based on Ar dating and thermal modeling in the Limousin region indicate an exhumation rate of 0.4–0.6 km Myr⁻¹ during the 345–335 Ma period that progressively increased to 1.0–1.5 km Myr⁻¹ during the 305–300 Ma period (Le Carlier de Veslud et al., 2013; Scaillet et al., 1996a,b). Other constraints from stable isotope paleoaltimetry estimate a paleo-elevation of 3.4 ± 0.7 km for the Limousin region during the 315–310 Ma period (Dusséaux et al., 2021).

Together, these data suggest that the RMGP emplaced at shallow level (2–3 km) during the late-orogenic extensional stage (ca. 315–310 Ma) may have been partly exposed to surface and eroded since the end of the Paleozoic. However, additional data is needed to estimate the paleoaltimetry and exhumation rate in other parts of the FMC, particularly to the east of the Sillon Houiller shear zone, where the Beauvoir granite is located (Fig. 1). Preservation of concealed RMGP deposits in the northern FMC may be indirectly indicated from the mapping of metamorphic rocks that have been buried to mid- to shallow-crustal levels (e.g., retrogressed regional metamorphic facies, contact metamorphic aureoles), or from near-surface mineralogical and/or geochemical anomalies (e.g., alluvial heavy minerals, soil and stream-sediment geochemistry).

# 5. Data compilation and Processing

We have compiled the whole-rock major and trace element compositions of the four main RMGP deposits in the northern FMC described above (Beauvoir, Montebras, Chédeville, and Richemont), as well as those of their immediate granitic host rocks, to characterize the regional geochemical footprints. Data for the main RMGP settings were compiled from available literature, including journal articles, technical reports, and Ph.D. theses, and correspond to rock samples collected at surface and from drill cores. This dataset includes 569 individual whole-rock analyses of granitic rocks from RMGP settings, including 179 from the
Echassières district, 87 from the Eastern Marche district, 196 from the Monts d'Ambazac district, and 107 from the Monts de Blond district (see Supplementary Material 1 for the complete list of data and references). Of these 569 analyses, 196 represent data for RMGP (151 least altered and 45 altered), including 131 from the Beauvoir granite, 31 from the Montebras granite, 19 from the Chédeville pegmatite, and 15 from the Richemont rhyolite.

In addition, we also compiled georeferenced trace element data (Li, Be, F, Sn, ± W) for rock samples that were collected in and around the studied granitic massifs (Colettes, Montebras, Saint-Sylvestre, Blond). The georeferenced data were then processed using ArcGIS software to create element distribution maps based on an inverse distance weighted (IDW) interpolation. This technique is commonly used in exploration geochemistry to interpret stream-sediment geochemical data at regional scale (e.g., Lancianese and Dinelli, 2015; Kirkwood et al., 2016; Parsa et al., 2017). The efficiency of the IDW interpolation depends on certain factors, such as the sampling grid, sampling density, and homogeneity of the dataset, but importantly produces reliable maps when compared to other interpolation methods (Lancianese and Dinelli, 2015). Due to the regular sampling grids and the density of geochemical datasets covering the different study areas, IDW interpolation was used in this work. For each element, six classes of concentrations were generated using quantile classification from the distribution histograms. Samples with element values below the limits of detection limits were set to half the lower detection limit prior to IDW interpolation (Kirkwood et al., 2016). Finally, geochronological data for peraluminous granitoids (MPG, CPG and RMGP) from the northern FMC were also compiled from published ages (see Supplementary Material 2 for the complete list of data and references).

Following the data compilation, we characterized the geochemical footprints of RMGP occurrences by calculating the molar proportions of major cations (Na, Ca, K, Fe, Mg) which are readily affected by metasomatic processes (Blein et al., 2022). The rationale for this approach is that least-altered igneous rock samples have relatively balanced proportions of these cations, whereas metasomatized rocks show distinct compositions with one or two dominant elements (e.g., Na, K) that reflect the type of hydrothermal alteration (e.g., albitization, K-feldspathization, muscovitization, greisenization). Using these values to plot the molar proportions for the samples in a barcode format in discriminant geochemical diagrams provides a visual representation to characterize the evolution of metasomatic ore systems through space and time and to identify the distinctive associations of alteration facies. This approach has been shown to be particularly useful for unraveling complex metasomatic systems where multiple overprinting hydrothermal alterations occurs, as is typically exemplified by IOCG and IOA deposits (e.g., Klein et al., 2022; Corriveau et al., 2022).

The defined barcodes were plotted in the K/Al versus Na/Al molar ratio diagram, which is convenient to characterize the alteration trends typically seen in granitic rocks (i.e., sodic and potassic along with silicification and greisenization) and associated mineralogical changes (Davies and Whitehead, 2010; Stanley, 2020). The reference field for the least-altered granitic rocks was designed from the whole-rock compositions of peraluminous granites (both MPG and CPG) from the FMC (n = 1953) based on existing data compilations (e.g., Moyen et al., 2017; Bonin et al., 2020; Harlaux et al., 2021). In addition to the major elements (Na, Ca, K, Fe, Mg), we also plotted the variation of absolute concentrations for relevant trace elements (Li, Be, Nb, Ta, Sn, W) in the K/Al versus Na/Al molar ratio diagram, where element concentrations are proportional to bubble size according to a quantile classification (5%, 25%, 50%, 75%, 95%, 100%). Frequency histograms of log-transformed element concentrations were generated with a summary of descriptive statistics.

# 6. Results

## 6.1. Trace element enrichments of RMGP compared to peraluminous granites in the FMC

Compared to the dominant peraluminous granites in the FMC, including both MPG and CPG, the least altered RMGP (i.e., Beauvoir, Montebras, Chédeville and Richemont) appear as the most fractionated endmembers of those granite suites as shown by their very low contents of Fe + Mg + Ti (Fig. 3). The rare-element contents of RMGP generally correlate positively with the degree of magmatic fractionation, as expressed by a decrease of $\Sigma(Fe + Mg + Ti)$, but vary as follows (Table 2): 372–11,200 ppm for Li (avg = 3500 ppm, med = 3136 ppm), 1475–40,000 ppm for F (avg = 15,010 ppm, med = 14,500 ppm), 3–506 ppm for Be (avg = 107 ppm, med = 77 ppm), 25–200 ppm for Nb (avg = 79 ppm, med = 75 ppm), 23–447 ppm for Ta (avg = 116 ppm, med = 84 ppm), 19–13,311 ppm for Sn (avg = 1069 ppm, med = 708 ppm), and 3–312 ppm for W (avg = 38 ppm, med = 31 ppm). These values correspond (on average) to enrichments, relative to upper continental crust (UCC values from Rudnick and Gao, 2014), of approximately 145 times for Li, 27 times for F, 50 times for Be, 6.5 times for Nb, 128 times for Ta, 510 times for Sn, and 20 times for W.

Also, compared to RMGP the concentration values for the CPG and MPG in the FMC (Table 2) are lower by one to two orders of magnitude and partly overlap in their abundances (respectively) of Li (avg = 85 ppm and 180 ppm; med = 80 ppm and 150 ppm), F (avg = 802 ppm and 1604 ppm; med = 792 ppm and 1480 ppm), Be (avg = 5 ppm and 17 ppm; med = 4.9 ppm and 16 ppm), Nb (avg = 12 ppm and 15 ppm; med = 12 ppm and 14 ppm), Ta (avg = 1.7 ppm and 4.7 ppm; med = 1.5 ppm and 3.2 ppm), Sn (avg = 14 ppm and 61 ppm; med = 9 ppm and 24 ppm), and W (avg = 2.6 ppm and 11 ppm; med = 1.4 ppm and 6.3 ppm). These latter values correspond to enrichments between 1 and 8 times that of the UCC on average for CPG and MPG, except for Sn in the MPG that is enriched up to 30 times the UCC.

The MPG spatially associated with the RMGP (i.e., Colettes, Montebras, Saint-Sylvestre and Blond) have intermediate compositions between those of RMGP and MPG with relatively elevated contents of Li (avg = 627 ppm, med = 492 ppm), F (avg = 4462 ppm, med = 3900 ppm), Be (avg = 28 ppm, med = 19 ppm), Nb (avg = 32 ppm, med = 28 ppm), Ta (avg = 14 ppm, med = 9.7 ppm), Sn (avg = 122 ppm, med = 80 ppm) and W (avg = 19 ppm, med = 16 ppm; Table 2). These values correspond to enrichments relative to the UCC of 26 times for Li, 8 times for F, 13 times for Be, 2.6 times for Nb, 15 times for Ta, 58 times for Sn, and 10 times for W on average. The latter values therefore make the regional MPG units as specialized precursors compared to RMGP. This conclusion is even more striking when looking at relevant discriminant element ratios such as Nb/Ta, Zr/Hf, Rb/Sr, and Th/U, which clearly show how the RMGP and specialized MPG precursors can be distinguished from the other MPG and CPG in the FMC (Fig. 4).

Rare-metal contents for RMGP units from the northern FMC also vary depending on locality with enrichments in the range of 10–10² ppm for Be, Nb, Ta and W, and 10²–10⁴ ppm for Li and Sn (Fig. 5). Due to the significant number of data available (n = 106), the Beauvoir granite data show a larger range for metal abundances which reflects its internal zoning and contrasting enrichment for the B1, B2 and B3 units. In particular, the B1 unit is characterized by the highest contents of Li (598–9643 ppm; avg = 4609 ppm, med = 4970 ppm), F (3400–37,400 ppm; avg = 16,784 ppm, med = 17,700 ppm), Be (9–506 ppm; avg = 157 ppm, med = 114 ppm), Nb (29–200 ppm; avg = 105 ppm, med = 102 ppm), Ta (32–447 ppm; avg = 178 ppm, med = 161 ppm), Sn (170–13,311 ppm; avg = 1809 ppm, med = 1072 ppm) and W (11–312 ppm; avg = 50 ppm, med = 43 ppm) in comparison to the B2 and B3 units.

The Li contents of Beauvoir (442–9643 ppm; avg = 3581 ppm, med = 3266 ppm) are similar to those of Chédeville (571–11,200 ppm; avg = 5238 ppm, med = 5723 ppm) and Richemont (1379–3730 ppm; avg =
<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Rare element contents of various peraluminous granites in the French Massif Central as a function of the differentiation index $B = Fe + Mg + Ti$ (Debon and Le Fort, 1983). The composition of rare-metal granites and pegmatites (RMGP) from the northern French Massif Central (i.e., Beauvoir, Montebras, Chédeville and Richemont) is compared to that of muscovite-bearing peraluminous granites (MPG) and cordierite-bearing peraluminous granites (CPG). The specialized MPG correspond to the regional granites spatially associated to RMGP deposits (i.e., Colettes, Montebras, Saint-Sylvestre and Blond). Clarke values for the upper continental crust are shown as thick black lines (values from Rudnick and Gao, 2014). Data and references are available in Supplementary Material 1.</figcaption></figure>

2758 ppm, med = 2940 ppm), whereas those of Montebras (372–1388 ppm; avg = 883 ppm, med = 1024 ppm) are significantly lower by a factor 3 to 6 on average. Similarly, the F contents of Beauvoir (3400–37,400 ppm; avg = 17,686 ppm, med = 17,200 ppm) and Chédeville (30,000–40,000 ppm; avg = med = 35,000 ppm) overlap, while those of Richemont (5600–16,300 ppm; avg = 10,227 ppm, med = 10,300 ppm) and Montebras (1475–5700 ppm; avg = 2639 ppm, med = 2060 ppm) are lower. The Be contents of RMGP also contrast among the RMGP suites with Chédeville (83–401 ppm; avg = 227 ppm, med =

221 ppm) showing the highest values compared to Beauvoir (6.7–506 ppm; avg = 93 ppm, med = 46 ppm), Richemont (59–213 ppm; avg = 90 ppm, med = 86 ppm) and Montebras (3–10 ppm; avg = 6.6 ppm, med = 6.6 ppm).

In contrast, the Nb and Ta contents are overall similar among Beauvoir (Nb: 26–200 ppm, avg = 80 ppm, med = 64 ppm; Ta: 29–447 ppm, avg = 118 ppm, med = 90 ppm), Montebras (Nb: 25–95 ppm, avg = 60 ppm, med = 60 ppm; Ta: 23–221 ppm, avg = 166 ppm, med = 211 ppm), Chédeville (Nb: 42–130 ppm, avg = 75 ppm, med = 73 ppm; Ta:
<table><caption>**Table 2**
Rare-element contents of peraluminous granites in the northern French Massif Central.</caption><thead><tr><th></th><th>Li (ppm)</th><th>F (ppm)</th><th>Be (ppm)</th><th>Nb (ppm)</th><th>Ta (ppm)</th><th>Sn (ppm)</th><th>W (ppm)</th></tr></thead><tbody><tr><td colspan="8"><strong>Rare-Metal Granites and Pegmatites (RMGP, n = 146)</strong></td></tr><tr><td>Min</td><td>372</td><td>1475</td><td>3.0</td><td>25</td><td>23</td><td>19</td><td>3.0</td></tr><tr><td>Max</td><td>11,200</td><td>40,000</td><td>506</td><td>200</td><td>447</td><td>13,311</td><td>312</td></tr><tr><td>Mean</td><td>3500</td><td>15,010</td><td>107</td><td>79</td><td>116</td><td>1069</td><td>38</td></tr><tr><td>Median</td><td>3136</td><td>14,500</td><td>77</td><td>75</td><td>84</td><td>708</td><td>31</td></tr><tr><td>Std Dev</td><td>2072</td><td>8307</td><td>106</td><td>36</td><td>85</td><td>1805</td><td>33</td></tr><tr><td colspan="8"><strong>Specialized Muscovite-bearing Peraluminous Granites (Specialized MPG, n = 71)</strong></td></tr><tr><td>Min</td><td>28</td><td>600</td><td>2.0</td><td>8.2</td><td>0.5</td><td>3.0</td><td>0.4</td></tr><tr><td>Max</td><td>3570</td><td>12,600</td><td>167</td><td>72</td><td>47</td><td>515</td><td>178</td></tr><tr><td>Mean</td><td>627</td><td>4462</td><td>28</td><td>32</td><td>14</td><td>122</td><td>19</td></tr><tr><td>Median</td><td>492</td><td>3900</td><td>19</td><td>28</td><td>9.7</td><td>80</td><td>16</td></tr><tr><td>Std Dev</td><td>583</td><td>2837</td><td>31</td><td>14</td><td>11</td><td>119</td><td>21</td></tr><tr><td colspan="8"><strong>Muscovite-bearing Peraluminous Granites (MPG, n = 191)</strong></td></tr><tr><td>Min</td><td>20</td><td>130</td><td>4.1</td><td>1.0</td><td>0.6</td><td>2.6</td><td>0.3</td></tr><tr><td>Max</td><td>800</td><td>5200</td><td>61</td><td>171</td><td>37</td><td>414</td><td>233</td></tr><tr><td>Mean</td><td>179</td><td>1604</td><td>17</td><td>16</td><td>4.7</td><td>61</td><td>11</td></tr><tr><td>Median</td><td>150</td><td>1480</td><td>16</td><td>14</td><td>3.2</td><td>24</td><td>6.3</td></tr><tr><td>Std Dev</td><td>138</td><td>988</td><td>10</td><td>15</td><td>5.4</td><td>73</td><td>25</td></tr><tr><td colspan="8"><strong>Cordierite-bearing Peraluminous Granites (CPG, n = 219)</strong></td></tr><tr><td>Min</td><td>8.7</td><td>336</td><td>1.5</td><td>1.1</td><td>0.6</td><td>2.4</td><td>0.5</td></tr><tr><td>Max</td><td>274</td><td>1186</td><td>12</td><td>33</td><td>7.0</td><td>113</td><td>50</td></tr><tr><td>Mean</td><td>85</td><td>802</td><td>5.0</td><td>12</td><td>1.7</td><td>14</td><td>2.6</td></tr><tr><td>Median</td><td>80</td><td>792</td><td>4.9</td><td>12</td><td>1.5</td><td>8.8</td><td>1.4</td></tr><tr><td>Std Dev</td><td>47</td><td>186</td><td>1.9</td><td>4.5</td><td>0.7</td><td>17</td><td>5.4</td></tr></tbody></table>

26–234 ppm, avg = 116 ppm, med = 99 ppm) and Richemont (Nb: 65–87 ppm, avg = 79 ppm, med = 80 ppm; Ta: 72–84 ppm, avg = 78 ppm, med = 77 ppm). The Sn contents of Beauvoir (19–13,311 ppm; avg = 1240 ppm, med = 832 ppm) and Montebras (245–1700 ppm; avg = 1145 ppm, med = 1286 ppm) overlap, whereas those of Chédeville (117–1077 ppm; avg = 542 ppm, med = 555 ppm) and Richemont (396–518 ppm; avg = 467 ppm, med = 483 ppm) are lower on average. Finally, W contents show moderate variation with Beauvoir (11–312 ppm; avg = 42 ppm, med = 34 ppm) and Richemont (13–114 ppm; avg = 45 ppm, med = 41 ppm) having the highest values, whereas Chédeville (7.5–52 ppm; avg = 20 ppm, med = 18 ppm) and Montebras (3–21 ppm; avg = 10 ppm, med = 7.5 ppm) are comparatively less enriched.

## 6.2. Diagnostic barcodes and alteration trends of RMGP and regional MPG

The major element compositional data for RMGP (i.e., Beauvoir, Montebras, Chédeville and Richemont), including data for least-altered and strongly-altered samples (e.g., greisenized, albitized), were transposed into diagnostic barcodes in the K/Al versus Na/Al molar ratio diagram (Fig. 6). This graphical presentation was used to characterize at first-order the geochemical footprints and alteration trends of RMGP and their granitic hosts, but cannot however distinguish between Na enrichment due to magmatic crystallization (e.g., albite accumulation) versus metasomatic replacement based on lithogeochemical data only. For reference, the fields for the least-altered peraluminous granitoids (MPG and CPG) from the FMC are shown as a dashed-contoured domain in these diagrams.

The RMGP data plot approximately at mid-distance along the albite-muscovite segment with intermediate Na/Al molar ratios (~0.4–0.5) and are characterized by Na > K-dominated molar compositions (Fig. 6a). In comparison, the specialized MPG spatially associated with the RMGP-hosted deposits (i.e., Colettes, Montebras, Saint-Sylvestre and Blond) have geochemical footprints which are identical, in terms of major element molar proportions, to those of other MPG and CPG in the FMC (Fig. 6b). Two main metasomatic alteration trends influencing RMGP are evidenced from the major element data: (i) albitization resulting in a progressive increase of the Na/Al molar ratio (>0.5) concomitant with a decrease in the K/Al molar ratio (<0.2) towards the albite node; and (ii) greisenization characterized by extremely low (<0.1) Na/Al molar ratio values for variable K/Al molar ratios (0.1–0.4)

which plot along the muscovite-quartz join. Specialized MPG spatially associated with the RMGP suites also exhibit a greisenization trend, but are much less affected by albitization.

To investigate the effect of metasomatic alteration on rare-metal enrichment and redistribution in RMGP, the concentrations of Li, Be, Nb, Ta, Sn, and W have been computed as bubble plots in the K/Al versus Na/Al molar ratio diagram (Fig. 7). These diagrams show that the concentrations of the rare elements within RMGP vary between least-altered and altered samples, in addition to the natural variations between RMGP localities as described previously. We note, however, that large bubbles also occur at low Na/Al values, which can possibly be interpreted in two ways: 1) alteration resulting in secondary metal enrichment; 2) alteration superimposed on initially metal-rich samples. No clear correlation of metal enrichment/depletion is found in relation with metasomatic alteration from the present dataset. Nevertheless, the observed variations between samples suggest some redistribution of rare elements, in particular for Li and Sn, during hydrothermal alteration (Fig. 7). This is partly reflected by the left-skewed distribution of these elements in frequency histograms.

## 6.3. Spatial element distribution around RMGP deposits

Based on the georeferenced trace element data available for rock samples from the Echassières (Beauvoir), Eastern Marche (Montebras), Monts d'Ambazac (Chédeville) and Monts de Blond (Richemont) districts, we produced element distribution maps for Li, Be, F and Sn (and W for Montebras instead of Be, which is not available) using an IDW interpolation method (Figs. 8-11). The results are discussed below for each district.

In the Echassières district (Fig. 8), a large surface geochemical halo of 15 to > 20 km², already identified by Aubert (1969), is found around the Beauvoir granite for Li, Be, F and Sn contents, in which element concentrations exceed the UCC values by minimum factors of 7 for Li (>170 ppm), 2.8 for Be (>6 ppm), 1.5 for F (>796 ppm) and 27 for Sn (>57 ppm). Of note is that elemental dispersal (i.e., reflection of geochemical mobility) increases in the order Be, Li, F and Sn. Geochemical anomalies with extremely high values (>100 s-1000 ppm) of Li, F, Be and Sn are localized in the immediate vicinity (<0.5 km) of the Beauvoir granite, but can extend up to > 2 km away, overlapping with other known Sn-W occurrences.

In the Eastern Marche district (Fig. 9), a small surface geochemical
<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Geochemical characteristics of rare-metal granites and pegmatites (RMGP) from the northern French Massif Central (i.e., Beauvoir, Montebras, Chédeville and Richemont) compared to regional muscovite-bearing peraluminous granites (MPG) and cordierite-bearing peraluminous granites (CPG). The specialized MPG correspond to the regional granites spatially associated to RMGP deposits (i.e., Colettes, Montebras, Saint-Sylvestre and Blond). (A) Nb/Ta versus Zr/Hf plot discriminating the fields for rare-metal-related, Sn-W ± U-related, and barren peraluminous granites (Ballouard et al., 2016). (B) Nb/Ta versus Rb/Sr plot. (C) Nb/Ta versus Th/U plot. (D) Th versus U plot. Red arrow represents the magmatic fractionation trend of peraluminous granites (Chappell and Hine, 2006; Cuney, 2014; Ballouard et al., 2016). Data and references are available in Supplementary Material 1. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

anomaly of approximately 0.5 to 2 km² is spatially associated with the Montebras leucogranite, where high element concentrations are found for Li (>262 ppm), F (>1874 ppm) and Sn (>125 ppm) up to 1 km away from the intrusion, reflecting the possible extent of the mineralized envelope. These values translate into minimum enrichment factors relative to UCC of 11 for Li, 3.4 for F and 60 for Sn, respectively. Unexpectedly, W contents are lower at the locality of Montebras, but they still show elevated values (110–150 ppm), which progressively increase towards the west and southwest of the deposit (>175 ppm W). Another geochemical anomaly for Li-F-Sn of around > 1–2 km² in extent is marked to the east of the study area, correlating with the Grand-Roche two-mica granite (Fig. 9).

In the Monts d'Ambazac district (Fig. 10), the spatially associated Saint-Sylvestre and Saint-Goussaud leucogranites are already characterized by marked elevated contents of Li, Be, F and Sn with

concentrations more than ten times higher those of the UCC. Despite such anomalous geochemical background, a large geochemical anomaly of ca. 10–40 km² in area centered around the Chédeville pegmatite field, and particularly marked in granitic country rocks, is defined from the element distribution maps of Li (>308 ppm), Be (>21 ppm), F (>2650 ppm) and Sn (>39 ppm). The element dispersion is in the order of Be, F, Li to Sn, and extends up to 16 km to the north, 10 km to the northeast, and 8 km to the northwest of the Chédeville occurrence. Moreover, a significant Sn anomaly occurs at the northern and southern extremities of the Saint-Goussaud granite near to known W ± Sn occurrences.

In the Monts de Blond district (Fig. 11), the Blond leucogranite, located less than 4 km to the south of the Richemont occurrence, defines a large geochemical halo of ca. 30–40 km² with high contents of Li (>383 ppm), Be (>18 ppm), F (>2999 ppm) and Sn (>109 ppm), which correspond to minimum enrichment factors relative to UCC of 16 for Li,
<figure><img src="image_7.png" /><figcaption>Fig. 5. Box plots showing the range of concentrations in rare elements (Li, Be, Nb, Ta, Sn, W) for rare-metal granites and pegmatites (RMGP: Beauvoir, Montebras, Chédeville, and Richemont) from the northern French Massif Central.</figcaption></figure>

8.5 for Be, 5 for F and 52 for Sn, respectively. Although there is a large elemental anomaly found in the central and eastern parts of the granitic complex, of note is that the presence of a smaller one with the most elevated F values (ca. 5 km² with > 3851 ppm) in the western part of the leucogranite, where topaz-bearing leucogranites have been mapped (Soufi et al., 2015; Soufi et al., 2018). Additionally, a smaller F anomaly occurs to the east close to the Vaulry W ± Sn deposit.

# 7. Discussion

## 7.1. Specialized MPG suites as precursors to RMGP in the northern FMC

The geochemical data compilation presented in this study highlights the specificity of RMGP in comparison to other types of peraluminous granites in the FMC. Relative to CPG and MPG, the RMGP have average enrichments that are 20 to 41 times higher for Li (avg = 3500 ppm), 9 to 19 times higher for F (avg = 15,010 ppm), 6 to 21 times higher for Be (avg = 107 ppm), 5 to 7 times higher for Nb (avg = 79 ppm), 25 to 69 times higher for Ta (avg = 116 ppm), 18 to 74 higher for Sn (avg = 1069 ppm), and 3 to 15 times higher for W (avg = 38 ppm), respectively (Fig. 3, Table 2). High concentrations of fluxing elements (i.e., Li, F, P) in RMGP melts result in lowered liquidus and solidus temperatures (Pichavant, 2022) and reduced viscosity (Bartels et al., 2011), which together further extend crystal fractionation and magma differentiation and result in high rare-metal contents (Michaud et al., 2021; Michaud and Pichavant, 2020; Pichavant, 2022). Therefore, high Li-F enrichments of RMGP in the northern FMC were of pivotal importance in the formation of Li-micas, notably lepidolite (i.e., a mixture of trilithionite and polylithionite), as recently confirmed by experimental work on the Beauvoir granite (Pichavant, 2022). In addition to their high degree of magmatic fractionation and elevated rare-metal contents, the RMGP show low values of Nb/Ta (<2), Zr/Hf (<20), and Th/U (<1) ratios which depart markedly from those in the CPG and MPG and granites in general (e.g., Rollinson, 1993). Additionally, when combined with high Rb/Sr ratios (>10), these data readily discriminate the RMGP from other types of peraluminous granites in the FMC (Fig. 4). Specifically, the low Nb/Ta and Zr/Hf ratios are considered to be a general feature of RMGP, as demonstrated in other granitic complexes (e.g., Dostal and Chatterjee, 2000; Ballouard et al., 2016).

Another salient characteristic of the RMGP from the northern FMC is their systematic spatial and temporal association with early, large MPG

plutons having little to no mineralization. Thus, the leucogranites of Beauvoir and Montebras (ca. 310–315 Ma) are closely associated with the Colettes two-mica granite (317 ± 8 Ma; Pin, 1991) and the Montebras muscovite ± topaz microgranite (316 ± 4 Ma; Marcoux et al., 2021), respectively. Similarly, the Chédeville pegmatite (ca. 310 Ma) was emplaced into the Saint-Sylvestre two-mica leucogranitic complex (324 ± 4 Ma to 328 ± 3 Ma; Holliger et al., 1986; Villaros et al., 2014) whereas the Richemont rhyolite (ca. 313 Ma) is close to the Blond two-mica leucogranitic complex (319 ± 7 Ma; Alexandrov et al., 2000). These MPG plutons are related to a major magmatic episode in the FMC during the ca. 335–315 Ma period, preceding and partly overlapping the formation of RMGP at ca. 315–310 Ma (Cheillet et al., 1992; Cuney et al., 2002; Melleton et al., 2015; Marcoux et al., 2021; Harlaux et al., 2021) during the late-Variscan orogenic event (Fig. 12). Although the emplacement of the RMGP coincides spatially and in part temporally with that of the MPG in the northern FMC, it is noteworthy that these two types of magmas are not genetically related (Marignac and Cuney, 1999). For example, at Echassières the granites of Beauvoir and Colettes have distinct feeder zones according to gravimetric data which suggest separate ascent paths, and additionally different geochemical characteristics not simply related to crystal fractionation and magmatic differentiation (Cuney et al., 1992; Raimbault et al., 1995). Lastly their age differences (ca. 310 Ma versus 317 Ma) and depth of emplacement (ca. 3 km versus 4–5 km), respectively, further indicate that the Beauvoir and Colettes magmas evolved independently (Cuney et al., 1992).

The specialized MPG plutons spatially associated with the RMGP suites are of larger spatial extent (>5–10 km²) and represent highly fractionated granitic series (Figs. 3-4), of which almost all host hydrothermal vein-type Sn-W mineralization in addition to that in adjacent metamorphic wall rocks (Bouchot et al., 2005; Cuney et al., 2002; Harlaux et al., 2018a,b; Marignac and Cuney, 1999; Monnier et al., 2018, 2019, 2020). This includes in the geochronological order: (i) the La Bosse W deposit, dated between 335.5 ± 3.0 Ma (U/Pb monazite; Monnier et al., 2021), 333.4 ± 2.4 Ma (U/Pb wolframite; Harlaux et al., 2018a) and 316.5 ± 5.3 Ma (U/Pb wolframite; Carr et al., 2021), located on the southern side of the Echassières granitic complex and emplaced prior to the Colettes and Beauvoir granites (Aissa et al., 1987; Cuney et al., 1992; Monnier et al., 2018, 2019, 2020); (ii) the Saint-Goussaud granite-related W ± Sn mineralization dated at 328 ± 6 Ma (U/Pb wolframite age; Harlaux et al., 2018a), located in the eastern part of the Saint-Sylvestre leucogranitic complex; (iii) the Vaulry Sn ± W deposit,
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Major element signatures and diagnostic alteration trends of (A) rare-metal granites and pegmatites (RMGP: Beauvoir, Montebras, Chédeville, and Riche-mont) from the northern French Massif Central compared to (B) specialized muscovite-bearing peraluminous granites (MPG: Colettes, Montebras, Saint-Sylvestre, Blond) spatially associated to RMGP deposits. The proportions of major elements (Na, Mg, K, Ca and Fe) are plotted in the K/Al versus Na/Al molar ratio diagram (Stanley, 2020) as molar barcodes (Blein et al., 2022). The node locations of common silicate minerals are also plotted (Ab = albite, Bt = biotite, Kfs = K-feldspar, Ms = muscovite, Qtz = quartz). The compositional field for muscovite-bearing peraluminous granites (MPG) and cordierite-bearing peraluminous granites (CPG) from the French Massif Central is shown for reference (dashed line).</figcaption></figure>

dated at 310.6 ± 4.0 Ma (U/Pb wolframite; Carr et al., 2021), located on the eastern margin of the Blond two-mica granite (Vallance et al., 2001); (iv) the Montebras Sn (±W) deposit, dated at 303.8 ± 4.8 Ma (U/Pb cassiterite; Marcoux et al., 2021), directly related to the greisenized leucogranite cupola (Gloaguen et al., 2018; Marcoux et al., 2021); and (v) the Mazet W deposit, dated at 279.1 ± 7.1 Ma (U/Pb wolframite; Carr et al., 2021), located on the northern side of the Echassières granitic complex (Cuney et al., 1992; Monnier et al., 2018, 2020). Although these W-Sn mineralizations are polyphase and are not directly cogenetic with the RMGP, they highlight the metallogenic potential of the specialized MPG as key exploration targets on a regional scale.

Locally, the MPG are strongly metasomatized (Fig. 6), as in the Echassières district where the Colettes granite shows albitite and greisen zones close to the contact with the Beauvoir leucogranite (Cuney et al.,

1992; Raimbault et al., 1995). In terms of rare-element enrichment, the specialized MPG spatially associated with the RMGP record an intermediate degree of magmatic fractionation between the latter and other occurrences of MPG widespread in the FMC; they are characterized by enrichment factors that are approximatively 6 times lower for Li, 3 times lower for F, 4 times lower for Be, 2 times lower for Nb, 8 times lower for Ta, 9 times lower for Sn and 2 times lower for W compared to RMGP. Therefore, such pre-enriched MPG may be considered as specialized granitic precursors of RMGP in relation with the late-Variscan evolution of the FMC.
<figure><img src="image_9.png" /><figcaption>**Fig. 7.** Trace element signatures and diagnostic alteration trends of rare-metal granites and pegmatites (RMGP: Beauvoir, Montebras, Chédeville, and Richemont) from the northern French Massif Central plotted in the K/Al versus Na/Al molar ratio diagram (Stanley, 2020). The concentrations of trace elements (Li, Be, Nb, Ta, Sn and W) are proportional to bubble size according to a quantile classification (5 %, 25 %, 50 %, 75 %, 95 %, 100 %). Frequency histograms of log-transformed element concentrations are shown with a summary of descriptive statistics (avg = average, med = median, std = standard deviation, min = minimum, max = maximum, IQR = interquartile range). The node locations of common silicate minerals are also plotted (Ab = albite, Bt = biotite, Kfs = K-feldspar, Ms = muscovite, Qtz = quartz).</figcaption></figure>

## 7.2. Implications for exploration targeting of Li-Sn-Ta-mineralized granitic cupolas

The characteristic well-defined geochemical signatures of the RMGP settings is offset by their small surface expression (typically < 1 km²), which challenges exploration for future targets where the mineralized bodies are not exposed at surface. We note that for both the Beauvoir and Montebras settings the cupolas are only just exposed near surface. It is therefore emphasized in this context that previous studies of similar-type settings have shown that metasomatic aureoles enriched in Li, Be, F, Rb, Cs, Nb, Ta, Sn and W are excellent indicators for lithogeochemical exploration of buried peraluminous RMGP (e.g., Galeschuk and Vantstone, 2005; Selway et al., 2005; London, 2008; Gonçalves et al., 2018; Errandonea-Martin et al., 2022; Sweetapple et al., 2024). At the deposit

scale, enrichments of Li, Cs, Rb and to a lesser extent Sn, F, B, Be and Tl were recorded at distances of 0.5 to 2 times and up to 4–5 times the thickness of the pegmatite dike, with rapidly increasing concentrations proximal to the pegmatite margin (Errandonea-Martin et al., 2022; Keyser et al., 2024). At the regional scale, other studies showed that the lithogeochemical halos of large RMGP can extend laterally at least 200 m and up to several km along strike (Sweetapple et al., 2024). Additionally, Li usually displays the largest halos, followed by Rb and Cs typically being less extensive, and show indications of km-scale anomalies relating to structurally controlled fluid flow (Sweetapple et al., 2024).

The metasomatic halos defined using Li, Be, F and Sn in the Echassières (Beauvoir), Eastern Marche (Montebras), Monts d'Ambazac (Chédeville) and Monts de Blond (Richemont) districts demonstrate one
<figure><img src="image_10.png" /><figcaption>**Fig. 8.** Geological map and element distribution maps for Li, Be, F and Sn around the Beauvoir granite in the Echassières district. Inverse distance weighted (IDW) interpolation based on georeferenced lithogeochemical data from Aubert (1969) and Raimbault et al. (1995).</figcaption></figure>

more time the critical role of lithogeochemical data for delimiting surface geochemical anomalies. At Echassières, a concentric dispersion halo for F, Sn, W, Li, As, and Be in the micaschists surrounding the Beauvoir leucogranitic stock, with a spatial extent of several km², was first identified by the pioneering work of Aubert (1969). The micaschists within the first hundred meters from the granite contain > 100 ppm Sn, an anomaly interpreted by Cuney et al. (1992) to result from leaching of Sn from the Beauvoir leucogranite by hydrothermal fluid circulations and dispersion in the surrounding host rocks. High concentrations of Li and Sn (>10²-10³ ppm) have also been measured in micas (Monnier et al., 2022) and in quartz- and topaz-hosted fluid inclusions (Harlaux et al., 2017) from the W stockwork hosted in the micaschists, which was

strongly metasomatized by magmatic-hydrothermal fluids released from the Beauvoir intrusion (Cuney et al., 1992).

The IDW maps for Li, Be, F and Sn at Echassières (Fig. 8) show variable spatial extent of geochemical halos, possibly reflecting variable mobility of these elements during hydrothermal processes (i.e., highly-mobile Li versus less mobile Sn). In particular, elevated anomalies of Li, F and Sn extending up to 1 km south of the Beauvoir leucogranite suggest a southward extension of the granitic body, or the presence of another buried Beauvoir-like intrusion. The distribution of elevated Be contents has a much larger spatial extent compared to other elements, possibly reflecting a geochemical decoupling or remobilization effect. However, the delineation of metasomatic aureoles is not always
<figure><img src="image_11.png" /><figcaption>**Fig. 9.** Geological map and element distribution maps for Li, W, F and Sn around the Montebras granite in the Eastern Marche district. Inverse distance weighted (IDW) interpolation based on georeferenced lithogeochemical data from Aubert (1969) and Boissavy-Vinau (1979).</figcaption></figure>

successful, as for the Montebras leucogranite where no major geochemical dispersion halo is evident (Fig. 9) compared to Echassières. This difference may be explained by the smaller size of the Montebras granite compared to Beauvoir and therefore presumably reflecting the release of less fluid, as originally proposed by Aubert (1969). Alternatively, the smaller metasomatic footprint may be explained by the lower permeability of the Chanon granite hosting the Montebras leucogranite compared to the Sioule micaschists hosting the Beauvoir leucogranite at Echassières, which are fractured and folded in a NNW-SSE-trending km-scale antiform structure (Faure et al., 1993; Do Couto et al., 2016). However, we note that a moderate geochemical halo of 1–2 km² is associated with the Grand-Roche two-mica leucogranite located 2 km

east of Montebras (Fig. 9).

In the case of pegmatitic dikes associated with large granitic plutons, such as exemplified by the Chédeville swarm (Fig. 10), geochemical anomalies delineate large areas (>10 s km²) in the granitic stocks. Despite their smaller size, making them more difficult to detect, the rare-element pegmatite field can thus be targeted using the lithogeochemical data of specialized granitic plutons displaying larger metasomatic aureoles of Li, Be, F and Sn. The same is true regarding the few meters thick Richemont rhyolitic dike, which is spatially associated to the Blond leucogranite showing a large metasomatic footprint with high contents of Li, Be, F and Sn (Fig. 11). Although the Richemont rhyolite is a unique occurrence of subvolcanic equivalent of RMGP in the FMC, additional
<figure><img src="image_12.png" /><figcaption>**Fig. 10.** Geological map and element distribution maps for Li, Be, F and Sn around the Chédeville pegmatite in the Monts d'Ambazac district. Inverse distance weighted (IDW) interpolation based on georeferenced lithogeochemical data from Burnol (1974), Leger et al. (1990) and Villaros and Pichavant (2019).</figcaption></figure>

work is required to evaluate the exploration potential of rhyolite-hosted Li deposits on a regional scale. In summary, we show that specialized MPG associated to Li-Be-F-Sn metasomatic halos represent excellent proxies for targeting regional RMGP occurrences, which may be otherwise challenging to explore due to their small size. Given the large extent of the MPG plutons in the northern FMC, we conclude that there is a significant potential for the discovery of new concealed RMGP in the vicinity of known occurrences, which should be considered as high-priority target areas for future geochemical surveys.

## 8. Conclusions

This study presents a review of the main geochemical characteristics

of peraluminous RMGP in the northern FMC, including the Beauvoir and Montebras leucogranites, the Chédeville pegmatite field, and the Richemont rhyolite. Key conclusions derived from this work follow:

(i) Compared to peraluminous cordierite-biotite and two-mica granites in the FMC, the RMGP are strongly fractionated with very low $\Sigma(Fe + Mg + Ti)$, low Nb/Ta (<2), Zr/Hf (<20) and Th/U (<1) ratios, and high Rb/Sr ratios (>10). They show variable enrichments in Li (372–11,200 ppm; avg = 3500 ppm), F (1475–40,000 ppm; avg = 15,010 ppm), Be (3–506 ppm; avg = 107 ppm), Nb (25–200 ppm; avg = 79 ppm), Ta (23–447 ppm; avg = 116 ppm), Sn (19–13,311 ppm; avg = 1069 ppm) and W (3–312 ppm; avg = 38 ppm). These conform to well-known
<figure><img src="image_13.png" /><figcaption>**Fig. 11.** Geological map and element distribution maps for Li, Be, F and Sn around the Richemont rhyolite in the Monts de Blond district. Inverse distance weighted (IDW) interpolation based on georeferenced lithogeochemical data from Burnol (1974), Soufi (1988) and Ebougué (1995).</figcaption></figure>

classical signatures defined for rare-metal granitic suites and LCT pegmatites globally.

(ii) The RMGP show a systematic spatial and temporal relation with earlier (ca. 324–316 Ma) and strongly peraluminous two-mica granites (Colettes, Montebras, Saint-Sylvestre and Blond), which predate and partly overlap the emplacement of RMGP at ca. 315–310 Ma. These highly-evolved (or specialized) MPG are characterized by enrichments in Li (avg = 627 ppm), F (avg = 4462 ppm), Be (avg = 28 ppm), Nb (avg = 32 ppm), Ta (avg = 14 ppm), Sn (avg = 122 ppm) and W (avg = 19 ppm), two to nine times lower on average compared to those of RMGP. These findings concur with other studies showing similar such

associations of progenitor granites to rare-metal mineralized centres in other districts.

(iii) The granitic plutons associated to RMGP display large geochemical halos for Li, Be, F and Sn with spatial extents > 10 s km², and extending up to several km away from the pluton. Due to their highly-evolved character and their close spatial-temporal relations with the RMGP, these granites likely represent pre-enriched precursors for rare-metal mineralization. Future geochemical surveys should considerer areas in proximity to specialized MPG as high-priority targets to search for new buried RMGP occurrences.
<figure><img src="image_14.png" /><figcaption>**Fig. 12.** Summary of published ages for rare-metal granites and pegmatites (RMGP), muscovite-bearing peraluminous granites (MPG) and cordierite-bearing peraluminous granites (CPG) in the northern French Massif Central. Errors are reported at 2σ level of uncertainty. Black curves represent the probability density distribution of integrated ages. A weighted mean age is calculated for each group of granites for comparison. Data and references are available in Supplementary Material 2.</figcaption></figure>

**Declaration of competing interest**

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

**Acknowledgements**

This article is dedicated to the memory and scientific legacy of our colleague Dr. Eric Gloaguen (1977-2024), who very sadly passed away prematurely but only after having made great contributions to metallogeny of rare-metal granitic systems in the Variscan belt. This project was supported by funds from the Horizon Europe research and innovation programme under Grant Agreement number 101057357, EIS – Exploration Information System (https://eis-he.eu), and from the French National Research Agency through the ANR - Carnot Grant number 19-CARN-003-01. We are grateful to Michel Cuney, Eric Gloaguen, Eric Marcoux, Jérémie Melleton and Michel Pichavant for inspiring discussions and suggestions on an early version of the article. We also thank Maxime Picault, Guillaume Vic, Matthieu Chevillard and Alex Vella for providing useful references and suggestions on

geochemical data processing. This article benefited from the constructive comments of two anonymous reviewers, as well as editorial work by Vesa Nykänen and Huayong Chen, which helped to improve the quality of the manuscript.

**Appendix A. Supplementary data**

Supplementary data to this article can be found online at https://doi.org/10.1016/j.oregeorev.2024.106409.

**Data availability**

Data will be made available on request.

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