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Geological Society, London, Special Publications; 2002; v. 204; p. 213-228;
DOI: 10.1144/GSL.SP.2002.204.01.13
© 2002 Geological Society of London

Older Orogenic Systems

The timing of W-Sn-rare metals mineral deposit formation in the Western Variscan chain in their orogenic setting: the case of the Limousin area (Massif Central, France)

M. Cuney1, P. Alexandrov2, C. Le Carlier de Veslud2, A. Cheilletz2, L Raimbault3, G. Ruffet4,5 & S. Scaillet6

1 UMR 7566 G2R-CREGU-Université Henri Poincaré, BP 239, 54506, Vandoeuvre-lès-Nancy, France michel.cuney{at}g2r.uhp-nancy.fr
2 CRPG-CNRS & ENSG, Rue du Doyen Marcel Roubault BP 40, 54500 Vandoeuvre-lès-Nancy, France
3 Centre d’Informatique Géologique, Ecole des Mines, 35, rue St Honoré, 77305 Fontainebleau Cedex, France
4 Géosciences Azur, UMR 6526 CNRS-UNSA-UPMC-IRD, Parc Valrose, 06108 Nice Cedex 2, France
5 Géosciences Rennes, Université de Rennes, 1, Av. Général Leclerc, 35042 Rennes Cedex, France
6 LSCE, CEA-CNRS, Avenue de la Terrasse, 91198, Gif sur Yvette, Cedex, France

New 40Ar/39Ar dating performed on Rare Metal Granites and W ± Sn deposits in the northern Limousin has provided evidence of two metallogenic episodes. An Early Namurian episode (c. 325 Ma) was contemporaneous with the emplacement of the large peraluminous leucogranite bodies, which are associated with small W ± Sn deposits, but also with some larger deposits, at Puy-les-Vignes (323.4 ± 0.9 Ma) and Moulin-Barret (323.7 ± 0.8 Ma) formed at a shallower level above cryptic granite plutons. These new data indicate that the metallogenic potential of the Namurian leucogranites might have been underestimated. Most other W ± Sn deposits in the northern Limousin area are attributed to a Mid-Westphalian episode (c. 310 Ma), and are contemporaneous with the emplacement of all the Rare Metal Granites. Both episodes were related to leucogranite emplacement and associated fluid circulations, but in two different geodynamic contexts. The Early Namurian episode may be related to syncollisional extension of the Variscan belt, whereas the Mid-Westphalian one occurs during generalized extension and rapid exhumation of the belt associated with the granulite-facies metamorphism of the lower lithosphere probably related to the delamination of the lower lithosphere. Thus, W ± Sn and rare metals (Ta, Nb, Be, Li) deposits are clearly temporally and probably genetically related to leucogranitic magmatism.