Role of the Sardic tectonic phase in the metallogenesis of SW Sardinia (Iglesiente): lead isotope evidence

Lead isotope analyses were applied to the major Pb-Zn ore-deposits hosted in Lower Cambrian carbonates of SW Sardinia. The isotopic composition of lead in barren Cambrian carbonates is shown to be less radiogenic than in ores and in adjacent wall-rocks. A minimum 60 Ma time gap between sediment deposition and ore emplacement can be deduced. Moreover, Pb isotope ratios in Cambrian-hosted deposits are identical with those in Ordovician-hosted ores and in Ordovician conglomerates. These results are interpreted to indicate an epigenetic origin for these deposits during a Middle-Upper Ordovician event probably connected to the ''Sardic distensive phase s.l.''.