Metallogenesis and Geodynamic Context in the Lower-Middle Cambrian of Montagne Noire (France) and Sardinia (Italy)

Abstract

A sedimentological comparison of Lower-Middle Cambrian sequences indicates that southwestern Sardinia was closer to the Precambrian African shield and more stable than Montagne Noire. In both regions the main tensional event straddles the Lower-Middle Cambrian boundary, when shallow water carbonates were gradually replaced by deeper-water deposits. Sedimentological evidence, coupled with metallogenic data, suggests that repeated phases of extensional tectonics in the Cambrian induced recurrent circulation of metal-rich hydrothermal brines. These produced early epigenetic or syngenetic-to-syndiagenetic mineralizations. Cambrian metallogeny in the Asturian-Sardinian province appears to reflect the geodynamic evolution of the eastern Gondwana passive margin in the Early Paleozoic, and to be controlled by the initial paleogeographic setting: polymetallic mineralizations (Pb, Zn, Ba-As, Cu, Au, Bi) are scattered at various stratigraphic levels in the external mobile areas (Montagne Noire), whereas in internal and more stable areas such as southwestern Sardinia, lead-zinc sulphides (with associated barite) occur essentially in connection with the main tectonic phase (Lower-Middle Cambrian transition).