The Svecokarelian anomalous ore lead line

Abstract

Ore lead isotope ratios from 37 deposits in the Svecokarelian of Fennoscandia are linearly related. Although the anomalous Svecokarelian ore lead line is generally compatible with the Stacey—Kramer two-stage model for the growth of primary lead, closer inspection reveals that the ore lead isotope variations are more consistent with a continuous mixing process. The anomalous lead line is consistent with Hietanen's plate tectonic model for the Fennoscandian Svecokarelinides. The ore lead isotope ratios are spatially related to a trench related to a sub-duction zone in the south-west of the region. This relationship is comparable to that observed in the 1.8-Ga younger Japanese island arc. The Svecokarelian leads are not true primary leads, and the mineralization age given by the Stacey—Kramer model is a minimum age. The apparent source age probably has no simple geological meaning.