Linear trend in the 207 Pb/ 204 Pb vs. 206 Pb/ 204 Pb diagram, extending from a normal Caledonian lead composition ( 206 Pb/ 204 Pb nearly equal 17.9) to highly radiogenic values ( 206 Pb/ 204 Pb nearly equal 26.0). Early Proterozoic Svecokarelian basement as source of the radiogenic component. Selective leaching of different minerals in the Svecokarelian rocks and mixing with various proportions of nonradiogenic, Caledonian magmatic lead.--Modified journal abstract.

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