18th century lead smelting in central north America: Evidence from lead isotope and INAA measurements

Abstract

Archaeological and historical studies suggest that metallic lead artefacts from early 18th century historic sites in the central United States were smelted from local ores. Direct confirmation of this can be obtained from lead isotope ratio measurements. The isotopic composition of leads from galena (PbS) deposits in south-east and central Missouri (SEM-CM) are different from those of ores from the upper Mississippi valley (UMV) in Iowa-Illinois-Wisconsin, and also from leads originating in north-western Europe. There is no evidence that smelting alters the isotopic ratios, so that the sources of metallic artefacts can also be determined. Samples of galena and lead recovered from four sites in Illinois (Kolmer, 11R50; Guebert, 11R1; Fox Encampment, MI-6; Newell Fort, near Starved Rock) were analysed. The isotopic data show that smelting of galena from the Missouri deposits began prior to 1730; UMV ores were being smelted prior to 1722. At least two sources of galena in SEM-CM were exploited, as distinguished by a combination of lead isotope and neutron activation analysis. Only one source in UMV appears to have been utilized. Metallic lead-rich artefacts of European origin, such as bale seals, musket balls, and pewter form a small fraction (~15%) of the artefact set. This is consistent with historic records which suggest that smelting of local galena began soon after the arrival of European colonists.