A Sb-Au mineralizing peak at 360 Ma in the Variscan Belt, an insight into Central Brittany (France)

Abstract : Numerous Sb-Au deposits are known in the European Variscan belt and are often associated with the late Variscan hydrothermal events linked to postorogenic extension and strike-slip faults, through the whole belt. Central Brittany hosts several Sb-Au occurrences, such as the Le Semnon Sb-Au deposit or the Saint-Aubin-des-Châteaux base metal-Sb-Au occurrence. In order to provide new constraints on the Sb-Au mineralization framework of the Central Brittany, structural, geochronological and chemical analyses have been performed on the Le Semnon deposit and the Saint-Aubin-des-Châteaux occurrence. Main results show that Sb-Au trapping of these two occurrences occurred at ca. 360 Ma. This indicates an Early Carboniferous economic Sb-Au mineralizing peak in the eastern part of the Central Brittany. Moreover, a mafic magmatism is widespread in the region and can acted as the plumbing system for Sb-Au mineralizing fluids, such as the dolerite dyke of the Semnon Sb-Au deposit. Absolute dating of this mafic magmatism coupled with the early character of hydrothermal alteration associated with Sb-Au mineralizing fluids strongly suggest that the emplacement of Sb-Au mineralization and mafic magmatism was coeval. It appears that the emplacement of mafic magmatism represent a major trigger for this mineralizing system at shallow depths (less than 3 km). These new data and the ca. 360 Ma massive sulfides of south Iberia emphasize that the Early Carboniferous mafic magmatism has to be taken into account for the understanding of the genesis of mineralizing systems and the redistribution of metals in the crust, at the scale of the whole Variscan belt.