Polyphase W-Sn mineralization and rare metal magmatism in relation to the late-Variscan tectono-metamorphic evolution of the southeastern French Massif Central

The southeastern French Massif Central represents an ideal area to study the linkage between regional metamorphism, crustal partial melting, emplacement of granitic magmas, and hydrothermal Sn-W mineralization in a polyphase tectono-metamorphic setting related to the late-Variscan orogeny. Here, we describe the mineralogical, structural, geochemical, and geochronological characteristics of cassiterite–wolframite-bearing quartz veins at St-Mélany, a small uneconomic Sn-W occurrence located in the North Cévennes area. The veins show evidence of ductile deformation (boudinage, asymmetric folding, dynamic recrystallization) consistent with a synkinematic emplacement during the regional low-pressure–medium-temperature metamorphism at ca. 320–315 Ma. This dominantly water-fluxed melting event reaching muscovite breakdown conditions ( T Nb-Sn-Be enrichments. Emplacement of the granitic dikes was coeval with the regional low-pressure–high-temperature metamorphism at ca. 305–300 Ma, reaching biotite dehydration melting conditions ( T > 800 °C, P ≈ 0.4 GPa), which led to the formation of the Velay anatectic dome possibly linked to lower crust granulitization. We conclude that polyphase emplacement of W-Sn-mineralized veins at ca. 320–310 Ma and rare metal granitic dikes at ca. 305 Ma results from contrasting crustal melting conditions, in relation to the late-Carboniferous orogenic evolution of the southeastern French Massif Cent