Abstract
The isotopic composition of galena lead from a recently discovered weak sulphide mineralization within the Norra Kärr nepheline syenite complex has been analyzed. The data suggest a lead source with 238U/204Pb- and 232Th/204Pb-ratios comparable to a primitive or slightly depleted Earth's mantle. Since the calculated lead model ages of 1525 Ma are similar to the Rb-Sr whole-rock isochron age of the alkaline complex the U/Pb and Th/Pb data are taken as further evidence for an upper mantle origin of the Norra Kärr alkaline rocks.