Isotopic constraints on the genesis of base-metal ores in southern and central Sardinia
Ludwig, Kenneth R.; Vollmer, Roald; Turi, Bruno; Simmons, Kathleen R.; Perna, Giulianο
European Journal of Mineralogy Volume 1 Number 5 (1989), p. 657 - 666
published: Nov 16, 1989
manuscript accepted: Jun 5, 1989
manuscript received: Dec 22, 1988
ArtNo. ESP147050105006, Price: 29.00 €
Abstract The Pb-Zn-Ag deposits of southwestern and central Sardinia occur within a restricted region, but comprise a variety of mineralization ages and styles. New Pb-isotope data, together with published data provide a reasonably coherent picture of possible sources for the various types of deposits. Early stratabound deposits hosted by Cambrian carbonates obtained their metals from a very homogeneous source whose age cannot be greatly different from the age of their host rocks. Although the source is thought to have been crustal in nature for a very long time, its isotopic homogeneity does not suggest the involvement of a heterogeneous Precambrian terrane ; rather, a homogeneous, ultimately igneous source is suggested, though Cambrian sedimentary/diagenetic processes seem necessary to provide concentration to ore grade. Simple, two-stage Pb-evolution models are adequate to account for the observed Pb isotopic compositions, however, and no involvement of granulitic rocks is required. Vein and skarn deposits related to Hercynian plutons appear to be variable mixtures of Hercynian-magmatic Pb with older Cambrian-stratabound-Pb, although in some cases (e.g. Montevecchio) virtually all of the Pb is magmatic. The Pb in the Funtana Raminosa district (thought to be Ordovician/Silurian-volcanogenic in nature) is indistinguishable from Hercynian magmatic Pb, suggesting that these deposits are also Hercynian in age.