The Sioule region in the northern part of the French Massif Central of the Variscan belt hosts the Echassières complex, where a large W(-Sn) quartz vein system was intruded by the Beauvoir rare-metal granite (RMG) hosting disseminated Sn, Nb-Ta and Li mineralization. We combined whole-rock geochemical data, zircon U-Pb geochronology of migmatites and felsic igneous rocks of the Sioule area, along with U-Pb dating of cassiterite, wolframite, and apatite in the Echassières complex to reconstruct the regional magmatic and metallogenic evolution. Results reveal: (i) early W mineralization at 351 ± 9 Ma, coeval with peraluminous granite magmatism (Chantelle and St-Gervais massifs) and a N115-striking dextral shear zone; (ii) a second W mineralization phase at 329 ± 5 Ma, linked to rare-metal-rich rhyolitic dykes and the Colettes granite during NW-SE extension, synchronous with regional biotite microgranites (Pouzol-Servant Massif) and trachy-dacitic tuffs and lavas; and (iii) late-orogenic emplacement of the Beauvoir RMG with minor hydrothermal Sn and W at ca. 320-310 Ma, synchronous with biotite granites hosting quartz-tourmaline orbicules (Champs Massif) and pyroclastic flows. Our study reveals a 40 Myr-long metallogenic evolution with hydrothermal W mineralization preceding hydrothermal Sn and magmatic Li-Sn-Nb-Ta. Each mineralization period coincided with widespread crustal magmatism involving the anatexis of late-Ediacaran metasedimentary rocks and Cambrian-Ordovician metagranites, as shown by the dating of zircon in migmatites and inherited zircon in Variscan igneous rocks. However, rare-metal-enriched magmas remained spatially confined to the Echassières complex suggesting a structural corridor that repeatedly focused magmas and fluids from a localized fertile source.
Ballouard et al. (Mon,) studied this question.