RECONSTRUCTION OF ARCHAIC COPPER MINING AND HOLOCENE ENVIRONMENTAL CONDITIONS ON ISLE ROYALE, MICHIGAN USING LAKE SEDIMENT BIOGEOCHEMISTRY

The Keweenaw Peninsula and Isle Royale (Michigan, USA) is host to North America’s largest native copper deposit. During the 19^th and 20^th centuries, thousands of copper mines were discovered throughout the region, and are now thought to be among the earliest examples of metallurgy in the world. However, the temporal and spatial patterns of prehistoric copper mining are still poorly understood. In 2016 CE, sediment cores were recovered from a small pond near prehistoric copper mines on the southwest side of Isle Royale and analyzed to investigate the timing of ancient mining emissions and to reconstruct past environmental conditions. Proxies analyzed include sorbed metal concentrations (Pb, Ti, Fe, etc.), C:N ratios, and δ¹³C of organic matter. Anomalously high Pb concentrations indicate that both historical and prehistoric mining emissions are detectable and were likely delivered to the pond via atmospheric fallout. Initial radiocarbon data suggest that the largest prehistoric increase in Pb concentrations occurs in sediment deposited ~6000 calendar years before present, contemporaneous with the timing of Pb increases in sediment cores previously analyzed on the Keweenaw Peninsula and Isle Royale. These results suggest that widespread mining occurred across the Keweenaw Peninsula and Isle Royale over the course of a few centuries in the Middle Archaic and that emissions from metalworking activities were distributed regionally via atmospheric transport.