¹Lake Superior Ecosystem Research Center, Department of Biological Sciences and
²Department of Civil and Environmental Engineering, Michigan Technological University, Houghton, Michigan 49931
³NOAA Great Lakes Environmental Research Laboratory, 2205 Commonwealth Blvd., Ann Arbor, MI 48105

Summary

         Metal mining around Lake Superior has been extensive, concentrating on greenstone belts and a continental rift system. The amounts of ore processed (iron, copper, zinc, gold, and silver; more recently palladium, platinum, and nickel) are large, and yet long-term environmental impacts are poorly researched, especially regarding establishment of a Zero-discharge Region for mercury. Mining signatures are found in many places, ranging from Silver Bay (taconite tailings) to Sault Ste. Marie (copper, iron, zinc). We include a brief historical review of mining and then examine a particular example, copper mining on the Keweenaw Peninsula, where the EPA has adopted remediation strategies and yet faces long-term problems with shoreline tailing migration. Around the turn-of-the 20th-century (1855-1968), copper stamp mills sluiced 360 million metric tonnes (Mt) of copper-rich tailings into rivers and waterways, including 64 Mt directly into Lake Superior. The amount of copper released was massive, 4-10X greater than the existing copper inventory found down to 20 cm depth in Lake Superior sediments. Whereas Superfund activities have concentrated on remediation of stamp sands in low-energy interior sites, coastal piles have spread kilometers along high-energy shorelines. The coastal discharges have created a major copper “halo” around the Peninsula, producing a copper maximum, now buried, in sediments. Copper from the pulse appears to have spread out into Lake Superior via sediment focusing and sediment-water interactions. During investigations, we uncovered a high correlation between copper and mercury, related to parent ore composition. Mercury occurs in many regional metal (copper, silver, gold) ores and in accessory minerals (e.g. zinc mineral sphalerite). Anthropogenic mining inputs and erosion of natural ore deposits contribute to the 5-8 fold greater copper and mercury inventories in Lake Superior sediments beyond regional atmospheric deposition. The association of mercury with mining also poses a dilemma, as voluntary reporting is simply not working.