Summary
Proterozoic sulfide deposits within the basement of northern Sweden have lead isotopic compositions that fall on a mixing line in the206Pb/204Pb-207Pb/204Pb diagram. These deposits contain a highly radiogenic Phanerozoic lead component that was leached from the Proterozoic basement at around 0.4 Ga during the Caledonian orogeny. Within the Proterozoic deposits, the less radiogenic lead isotopic compositions occur in undeformed and little deformed sections, while the more radiogenic lead isotopic compositions are observed along fault, fracture, and shear zones. These zones with radiogenic Phanerozoic lead also have higher contents of lead, zinc, and gold, respectively, than the other parts of the deposits, which suggests that these metals were introduced together with the radiogenic lead at a much later event than the metals in the unaltered Proterozoic deposit. The Proterozoic deposits acted as traps for metal additions along Caledonian reactivated fault and shear zones in the Proterozoic basement.
Zusammenfassung
Proterozoische Sulfidvererzungen im proterozoischen Grundgebirge weisen Bleiisotopenzusammensetzungen auf, die auf eine Mischungslinie im206Pb/204Pb-207Pb/204Pb Diagramm fallen. Die proterozoischen Vererzungen enthalten eine Komponente radiogenen Bleis, welches im Verlaufe der kaledonischen Orogenese aus dem proterozoischen Grundgebirge ausgelaugt wurde. Wenig oder nicht deformierte Abschnitte in den proterozoischen Sulfidvererzungen weisen weniger radiogene Bleiisotopenzusammensetzungen auf, als Bruch- und Scherzonen in denselben Vererzungen. Diese Zonen mit radiogenem, kaledonischem Blei weisen auch höhere Blei-, Zink- und Gold-Gehalte auf als die übrigen Teile der Vererzung, was andeutet, daß diese Metalle zusammen mit dem radiogenen Blei zu einem viel späteren Zeitpunkt in die Vererzung eingebracht worden sind. Die proterozoischen Vererzungen bewirkten die Metallausfällung aus Fluiden, die entlang von kaledonisch mobilisierten Verwerfungen und Scherzonen flossen.
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Romer, R.L. Caledonian upgrading of Proterozoic low-grade base-metal deposits in Northern Sweden. Mineralogy and Petrology 50, 271–285 (1994). https://doi.org/10.1007/BF01164610
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DOI: https://doi.org/10.1007/BF01164610