DISTRIBUTION AND REACTIVITY OF METAL-RICH MINE TAILINGS IN THE MARINE ENVIRONMENT NEAR TWO ABANDONED COPPER MINES IN NEWFOUNDLAND

Historical marine disposal of tailings from two abandoned copper mines has contaminated coastal areas of Notre Dame Bay, Newfoundland. At the Little Bay Mine, an impoundment containing 1.8 million tonnes of tailings failed in 1991. Since then, 30–50% of the tailings have flowed into a sheltered estuary. At the Tilt Cove Mine, 5–6 million tonnes of tailings were slurried directly into a high-energy marine environment from 1957 to 1967. The objectives of this study are to (1) determine the spatial extent and mobility of tailings on the seafloor; (2) characterize the processes that control the cycling and fate of metals in the tailings; and, (3) assess if there is a benthic meiofaunal response to contamination. In July 2001, multibeam bathymetry, side-scan sonar and sub-bottom profiler data were collected near the tailings deposits. Gravity cores and/or grab samples of sediments were collected at distances up to 5 km and 3 km away from the tailings sources at Little Bay and Tilt Cove, respectively. Pore waters were extracted from all cores by centrifugation, and from two cores using diffusion gradient thin film (DGT) samplers, for analyses of dissolved metals. A comparison of the multibeam data with previous surveys shows that erosion of tailings from the Little Bay impoundment has led to progradation of a tailings delta west of the breached dam, and infilling of some bedforms. Tailings deposits near Tilt Cove show evidence of re-working by waves, currents, and iceberg scour. The ranges of As, Cd, Cu, Pb and Zn concentrations in sediments from Little Bay are (mg/kg): 3–52, 0.04–0.92, 13–520, 1–10, and 19–136; and, from Tilt Cove are: 3–310, 0.02–4.5, 8–1600, 2–110, and 28–2900, respectively. Dissolved metal concentrations in sediment pore waters from both sites are relatively low. The DGT profiles suggest that the tailings serve as a sink, instead of a source, of metals to the overlying water. Foraminifera have responded to contamination, as evidenced by distorted chambers, abrupt changes in coiling direction / chamber arrangement, misplaced apertures, and twinning. C. arctica, S. biformis, and V. advena have the highest proportion of deformed specimens: at Little Bay, 1.5–8% show abnormalities, and 3–6% at Tilt Cove. In general, the percentage of deformed specimens is highest in the most contaminated sediments at both sites.