Chemical provenance of pre- to post-contact period copper and copper-rich alloy artifacts from archaeological sites in Nova Scotia, Canada : a laser ablation ICP-MS study

Abstract

Copper had cultural significance to the Mi’kmaq peoples of the Maritimes, and was used in the fabrication of tools and personal, ceremonial, gift, and trade wares. In this study, LA-ICP-MS was used to characterize the trace elemental composition of artifacts from archaeological sites in Nova Scotia ranging from Early Woodland (2500-2400BP) to Protohistoric (450-350 BP) to European contact (1500+BP) periods in age, and samples of natural copper from potential sources with goals of: (i) differentiating artifacts derived from natural copper from those made from synthetic (refined) European (trade) copper and its alloys, and (ii) identifying the specific natural sources of copper that were exploited. The methodology used in this study improves on previous bulk analytical methods (e.g.,INAA,XRF) that suffer from the presence of contaminating mineral phases within the copper volume analyzed and are more destructive. LA-ICP-MS analysis of 57 artifacts identified 10 compositional groupings with specific elemental enrichment/depletions/ratios, notably involving Ag, Pb, Hg, Bi, Zn and As. Most single artifacts are compositionally homogeneous with respect to the majority of elements with <20% relative variation in concentration over 8-10 ablation spots. Patinas show preferential enrichment (e.g., Fe, Sn, Zn, Au) and depletion (e.g., Ni, Co, Ge, Ag) relative to the fresh metal. However, differences in source composition are significant enough that the patina can be diagnostic of provenance. Three groups have definitive provenance determined: six artifacts from Cap d’Or, Nova Scotia (natural Cu), six from Margaretsville, Nova Scotia (natural Cu), and nine artifacts of European origin (refined Cu or Cu-Zn-Sn alloys). Seven remaining artifact groups have unknown provenance and, importantly, sources analyzed from Michigan, USA (Keweenaw Peninsula) are ruled out. Contrary to the Lake Superior model, copper deposits from the Bay of Fundy were important but many other sources of the metal are likely and require further investigation.