# Rare-metal mineralization and crustal magmatism in a collisional orogen: protracted evolution of the Sioule metallogenic zone (Variscan French Massif Central)

Christophe Ballouard, Patrick Carr, Loïs Monnier, Jean-Charles Fidalgo, Océane Rocher, Nicolas Esteves, Oscar Laurent, Marie Daoulas-Gerardin, Alexis Plunder, J. Mercadier, et al.

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## To cite this version:

Christophe Ballouard, Patrick Carr, Loïs Monnier, Jean-Charles Fidalgo, Océane Rocher, et al. Rare-metal mineralization and crustal magmatism in a collisional orogen: protracted evolution of the Sioule metallogenic zone (Variscan French Massif Central). GeoTolosa 2025, Jun 2025, Toulouse, France. hal-05288856

HAL Id: hal-05288856

https://cnrs.hal.science/hal-05288856v1

Submitted on 30 Sep 2025

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# Rare-metal mineralization and crustal magmatism in a collisional orogen: protracted evolution of the Sioule metallogenic zone (Variscan French Massif Central)

Christophe Ballouard *<fnref n="1" />, Patrick Carr <fnref n="1" />, Loïs Monnier <fnref n="2" />, Jean-Charles Fidalgo <fnref n="1" />, Océane Rocher <fnref n="1" />, Nicolas Esteves <fnref n="3" />, Oscar Laurent <fnref n="2" />, Marie Gérardin <fnref n="1" />, Alexis Plunder <fnref n="4" />, Julien Mercadier <fnref n="1" />, Jérémie Melleton <fnref n="4" />

The West European Variscan Belt (360-300 Ma) is a major metallogenic province for rare metals, hosting both magmatic and hydrothermal deposits. Magmatic mineralization occurs in granitic or pegmatitic intrusions enriched in Li-Sn-Nb-Ta, while hydrothermal deposits are found in quartz veins and metasomatic rocks containing Sn±W. Although these two mineralization types are often spatially associated within the same deposit particularly at the margins of granitic batholiths, they typically exhibit complex, multiphase evolutionary histories that are difficult to reconcile with a single metallogenic event. This issue is well exemplified in the Sioule region, an archetypal metallogenic zone within the Variscan Belt. There, a large quartz vein system mineralized in wolframite (W) and minor cassiterite (Sn) was later intruded by the Beauvoir rare-metal granite, which notably hosts disseminated Li-micas along with magmatic cassiterite. While the late-orogenic nature of rare-metal magmatism (315-310 Ma) is well constrained, the timing of the hydrothermal W-Sn mineralizing events and their relationship to regional tectonic and magmatic processes remains controversial, with previously proposed ages ranging from 330 to 310 Ma, and even older than 360 Ma.

To address this, a petro-geochemical study combined with U-Pb zircon-apatite geochronology was conducted on metasediments and felsic igneous rocks from the Sioule Metallogenic Zone (SMZ), along with direct U-Pb dating of ore minerals including cassiterite and wolframite. Our data indicate that the protoliths of Sioule series migmatites include Late-Ediacarian (< 540 Ma) detrital sediments as well as peraluminous orthogneisses dated at 510-490 Ma. Partial melting likely occurred during or before Early Variscan peraluminous magmatism at 354±6 Ma, marked by the emplacement of now variably deformed biotite±garnet±cordierite granitoids (Chantelle and St-Gervais massifs). This magmatic event was subsynchronous with N110-trending dextral shearing, and early W hydrothermalism as confirmed by a wolframite U-Pb age at 351±9 Ma. By 333±6 Ma, the southern part of SMZ was exhumed, and metaluminous to peraluminous felsic magmas were either erupted as tracy-dacite tuffs or crystallized at depth as biotite microgranite (Pouzol-Servant massif). Further north, highly peraluminous and Li-rich granitic magmatism, a precursor of rare-metal granite magmatism, formed rhyolitic dykes and granitic pluton (Colettes massif), possibly linked to N60 senestral shearing. Such event was likely accompanied by a second W mineralizing phase, constrained by apatite U-Pb dating at 329±5 Ma. Between 320 and 310 Ma, the southeastern part of the SMZ experienced a new plutonic-volcanic episode marked by the emplacement of biotite granite (Champs massif) and trachy-dacite tuff. Such volcanism appears geochemically similar to the regionally recognized Visean volcanic event at ca. 330 Ma. At this time, magmatic

<footnote n="1">¹ GeoResources, University of Lorraine, France</footnote>

<footnote n="2">² Géosciences Environnement Toulouse, University of Toulouse, France</footnote>

<footnote n="3">³ Centre de Recherches Pétrographiques et Géochimiques, University of Lorraine, France</footnote>

<footnote n="4">⁴ Bureau de Recherches Géologiques et Minières (BRGM), France</footnote>
fluids exsolved from the crystallizing Beauvoir rare-metal granite precipitated hydrothermal cassiterite (319±7 Ma) and a third generation of wolframite.

This study highlights the protracted magmatic and hydrothermal history of a metallogenic zone of the Varican belt in relation to episodic peraluminous magmatism. It also supports the common temporal decoupling of Sn and W deposition events, even within the same deposit.