Relationships between granitoids and mineral deposits: three-dimensional modelling of the Variscan Limousin Province (NW French Massif Central)

Multidisciplinary three-dimensional modelling, involving geophysical, struc tural and geochemical data, has been used to study the relationships betwee n magmatism, tectonics, fluid circulation and mineralisation in the norther n Limousin, and to provide P-T-Z-t paths constrained by the available datin g. The ore deposit occurrence displays little spatial relationship with gra nites emplaced in the 360-320 Ma period, probably because the low global pe rmeability and tectonic regime did not allowed vertical fluid exchanges to be established. In contrast, the change in the tectonic regime induced by t he delamination of the lower lithosphere (320-300 Ma), and characterised by the passage to general extension, has played a major metallogenic role. Ho wever, the ore deposit processes appear to be specific to each metal. Most of the W-Sn deposits appear to be synchronous with rare metal granites empl acement, at c. 310 Ma, that allowed the focus of fluids of different origin s towards the apex of plutons. In contrast, for Au and U, the whale mineral isation process covers several tens of millions of years. It is controlled by the regional tectonic evolution of the Limousin area during the same per iod, and especially by a rapid exhumation of the ductile crust which occurr ed in the 310-300 Ma period.