TRACING THE MOVEMENT OF METALS IN A COASTAL ENVIRONMENT DISTURBED BY MINING: THE CALLAHAN CU-ZN-PB MINE, MAINE

The Callahan Cu- Zn-Pb mine produced ~800,000 tons of ore (4.91% Zn, 1.30% Cu, 0.35% Pb) from lenses hosted by a thick sequence of Cambrian marine volcanic and volcaniclastic rocks. The mine, located in an estuary—Goose Pond—is now an EPA Superfund site; ~5 M tons of sulfide-bearing waste and unprocessed ore remain on-site. Mineralogy (XRD), trace element (EMPA, LA-HR-ICPMS), and Pb isotope geochemistry (TIMS, LA-HR-ICPMS) illustrate metal redistribution among host rocks, ore, tailings and waste piles, stream and estuary sediments, and the aquatic biota (e.g., bivalve shells). Pyrite from waste piles contains Cu (~2-4500 ppm), Pb (~2-2100 ppm), and As (0-2.0 wt %). Sphalerite contains Cu (~25-2800 ppm), Pb (~10-1800 ppm), and Cd (~1500-2700 ppm). Sediment cores (n=18) from Goose Pond contain minor sulfide (~<1-3%, mainly pyrite, rare sphalerite) and show wide variations in Zn (88-1590 ppm), Cu (14-268 ppm), Pb (4-1070 ppm), As (4-55 ppm), and Cd (up to 83 ppm). Microanalysis of bivalve shells collected from sediment cores (n=6) shows distinct metal-rich zones and variable metal contents for Cu (5-74 ppm), Zn (6-443 ppm), and Pb (1-76 ppm) that parallel variations in metal contents of enclosing sediments. Published analyses of clam tissue (n=13) from the site are in the range 0.71 to 43 ppm Pb (US-EPA, 2008) and the FDA safety tolerance level is 1.7 ppm Pb (ATSDR). Pb isotope compositions of acid-leach and residue aliquots of estuary sediments (208Pb/207Pb = 2.4223-2.4696; 206Pb/207Pb = 1.1544-1.1965) span a wide range relative to host rocks (208Pb/207Pb=2.4817 -2.5466; 206Pb/207Pb=1.2254-1.2537), massive sulfide layers, and tailings piles (208Pb/207Pb= 2.4224-2.4350; 206Pb/207Pb=1.1566-1.1646). These data plot in a broadly correlated field with a positive slope on a 208Pb/207Pb and 206Pb/207Pb diagram and the field encloses all bulk and growth-band spot analyses of bivalve shells (208Pb/207Pb ~2.43-2.45, 206Pb/207Pb ~1.16-1.18). The bivalves likely incorporated Pb by ingestion of fine sulfide particulates in addition to dissolved Pb. The chemical and isotopic variations in estuary sediments reflect core depth, bulk mineralogy, and proximity to waste piles. The Pb isotope and trace element data show a link between mining and ore processing activities and the metals that are distributed in host rocks, ore, tailings and waste piles, stream and estuary sediments, and aquatic biota.