Methods for determination of the source of iron in precontact Inuit and Dorset culture artifacts from the Canadian Arctic

Abstract

The period during which Dorset Culture peoples and precontact Inuit used iron was widespread and overlapped the appearance of the Norse in Greenland. In Greenland and Arctic Canada, three sources of iron in artifacts have been reported: terrestrial native iron, Norse wrought iron and meteoritic iron from the Cape York iron meteorite. We investigated the source of iron from fourteen samples of iron artifacts recovered from one precontact Inuit and three Dorset culture sites. Polished mm-scale samples mounted in polyester resin blocks yielding a roughly rectangular 1 × 2 mm cross section to preserve as much of each sample as possible were examined. Petrographic examinations by reflected light microscopy and SEM observation coupled with energy-dispersive analysis revealed the presence of Widmanstätten structure (an intergrowth of kamacite and taenite), a suite of minerals comprising kamacite, taenite, daubreelite and schreibersite and nickel-content at iron meteorite levels indicating all fourteen samples were unambiguously of meteoritic origin. With the meteoritic origin confirmed, Goldstein’s (1965) model relating half-width of the kamacite lamellae in the Widmanstätten patterns to the Ni-content of the lamellae was used to determine whether the meteoritic iron originated from the Cape York meteorite. A test of the method used the mean kamacite bandwidth and the bulk Ni-content of the Cape York mass Savik I, which demonstrated the validity of the basis of the method. Using the experimentally-derived relation between kamacite half-width of the bands and composition of the kamacite, the nickel-content of the kamacite lamellae ranged from 6.13 to 6.61 wt% Ni. These compositions are consistent with bandwidths that are narrower than the mean for Cape York, the anticipated source. The discrepancy may be attributed to flattening of the kamacite lamellae by cold working in the manufacture of the artifacts. As well, it has been shown that a range of bandwidths is typical in large iron meteorites such as Cape York. Thus, this method cannot definitively identify Cape York as the source of the meteoritic iron in the fourteen samples; however, the results can serve to identify meteoritic artifacts if the material that has not been intensively cold worked and if sufficient bandwidths can be measured in order to establish a mean thickness.