Lead isotope ratios in 16th century copperware traded to North America: the Swedish connection

Abstract

Isotope analyses have been made on the trace amounts of lead in a small set of late 16th century pure copper trade kettles and kettle debris from Indigenous sites in eastern Canada. The isotope ratios are highly correlated. We interpret these correlations as the mixing of copper from Precambrian Swedish ores with metal from one or more of the Palaeozoic deposits occurring in central Europe and the British Isles. The data enable us to identify samples of pure Swedish copper, metal consisting of mixtures of Swedish and central European – British copper, and with less certainty, samples derived entirely from the latter deposits. Although most of the trace element concentrations in the coppers are quite variable, it appears that nickel values may be less so (∼100 ppm in pure Swedish samples, and ∼1100 ppm in the central European – British sources). Based on these values, two-component mixing relations provide estimates of the fractions of Swedish end members in mixed samples. These results suggest that more than half of the copper used in forming the kettles originated in Sweden.