Local, Regional, and Global Implications of Elemental Mercury in Metal (Copper, Silver, Gold, and Zinc) Ores: Insights from Lake Superior Sediments W. Charles Kerfoot 1,* , S. L. Harting 1 , J. Jeong 1 , John A. Robbins 2 , and Ronald Rossmann 3 1 Lake Superior Ecosystem Research Center and Department of Biological Sciences Michigan Technological University Houghton, Michigan 49931 2 NOAA Great Lakes Environmental Research Laboratory 2205 Commonwealth Blvd. Ann Arbor, Michigan 48105 3 United States Environmental Protection Agency Mid-Continent Ecology Division Large Lakes Research Station 9311 Groh Road Grosse Ile, Michigan 48138 ABSTRACT. Anthropogenic inventories for copper (229 ± 89 ug/cm 2 , N = 30), and mercury (470 ± 307 ng/cm 2 , N = 25) in Lake Superior sediments are much greater than inventories in remote lakes (Cu 50 ± 31 ug/cm 2 , Hg 64 ± 34 ng/cm 2 , N = 16) that receive inputs largely from long-distance atmospheric sources. Whereas the absolute concentration of mercury in Lake Superior sediments is not high (80–110 ng/g), enrichment ratios along coastal margins indicate industrial sources. An example of previously unre- ported mining-related inputs comes from native copper mining on the Keweenaw Peninsula. Around the peninsula, sediment inventories for mercury, silver, and copper are highly correlated and can be traced back to shoreline tailing piles, smelters, and parent ores. Elemental mercury occurs as a natural amalgam or solid solution substitution in native metal (copper, silver, gold) deposits and associated gangue minerals (e.g., sphalerite, ZnS) at μg/g or higher concentrations. Native copper stamp mills discharged more than 364 million metric tons of “stamp sand” tailings, whereas copper smelters refined five million metric tons of copper, liberating together at least 42 metric tons of mercury. Release of trace mercury from Lake Supe- rior mining deserves regional attention as preliminary estimates resemble EPA Region #9 patterns and could help explain the 4–7 fold sediment inventory discrepancies. We show that the Keweenaw situation is not unique geographically, as mineral-bound trace mercury is commonplace in U.S. and Canadian Green- stone Belts and of worldwide occurrence in precious (gold, silver) and massive base metal (copper, zinc) ore deposits. INDEX WORDS: Sediments, Lake Superior, mining, trace mercury, base metal ores, copper smelting, gold, silver, copper, mercurian sphalerite, mercury release, mercury inventories. J. Great Lakes Res. 30 (Supplement 1):162–184 Internat. Assoc. Great Lakes Res., 2004 INTRODUCTION The Lake Superior watershed is under considera- tion as a Zero-discharge Region for mercury by the Lake Superior Binational Program (LSBP 2002). Because progress toward such a designation requires information about past and present mercury sources * Corresponding author. E-mail: wkerfoot@mtu.edu 162 and cycling, here we emphasize that 1) anthro- pogenic inputs from mining and industrial centers are superimposed upon long-distance deposition pat- terns, often locally overriding these signals, and 2) regional rock sources of mercury have contributed to mercury sediment fluxes (erosional and anthro- pogenic inputs). These ancillary sources help to explain why Lake Superior anthropogenic metal