Fig. 22


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Conceptual model of the Puy-les-Vignes ore-forming hydrothermal system. (A) Crustal-scale model showing the stack of metamorphic nappes (UGU = Upper Gneiss Unit, LGU = Lower Gneiss Unit, PAU = Para-Autochtonous Unit) in the Limousin area. The formation of the W breccia pipe results from a W-rich magmatic fluid that exsolved from an evolved leucogranite and interacted with volatile-rich metasedimentary country rocks and/or possibly mixed with low-salinity metamorphic fluids issued from devolatilization of deep-seated metasediments. The estimated temperatures correspond to a regional geothermal gradient of 40 °C km−1. (B) Schematic cross-section of the Puy-les-Vignes breccia pipe showing the superimposition of three concealed granitic intrusions: (i) a peraluminous granite emplaced at ca. 324 Ma generating microgranite dykes exposed at the present-day surface, (ii) an evolved leucogranite emplaced at ca. 318 Ma yielding the formation of the quartz-supported breccia pipe and wolframite-bearing quartz veins, and (iii) a rare-metal granite emplaced at ca. 311 Ma that produced a disseminated magmatic-hydrothermal Nb–Ta mineralization overprinting the W-mineralized system.

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