A MIXED CRUSTAL SOURCE MODEL FOR THE IGLE SIENTE PB-ZN ORE-DEPOSITS (SW SADINIA) - LEAD-ISOTOPE EVIDENCE

Lead isotope analyses applied to the major stratabound Pb-Zn ore depos its hosted in Lower Cambrian carbonates of SW Sardinia reveal, despite the apparent homogeneity of the data, the existence of significant va riations between the Cambrian host rocks and the associated sulfides. These results are interpreted by a mixed crustal source model involvin g the Paleozoic sedimentary pile of SW Sardinia and an old crustal com ponent, similar to the pre-Variscan basement of the Eastern Pyrenees. Furthermore, preliminary data would support the long-held assumption o f a Mississippi-Valley-type origin for these deposits, but involving a major remobilization of disseminated Cambrian metals during the Early Ordovician ''Sardic tectonic phase''.