Transport and fate of mine tailings in a coastal fjord of British Columbia as inferred from the sediment record

Eight gravity cores collected from Alice Arm and Upper Observatory Inlet in British Columbia were analyzed for Pb-210 to determine the sediment accumulation rates. Sediment samples were also analyzed for Al, Ba, Cd, Cu, Fe, Mn, Pb, and Zn to establish the transport and fate of mine tailings in Alice Arm. Sediment accumulation rates ranged from 0.17 to 0.76 g cm(-2) per year in Upper Observatory Inlet; in Alice Arm the accumulation rates ranged from 1.39 g cm(-2) per year near the sill to above 2 g cm(-2) per year in the upper sections of the arm. The significantly lower sedimentation rates in Observatory Inlet suggest that much of the sediment and mine tailings entering Alice Arm are trapped within the arm. Elevated Cd, Pb and Zn concentrations in the cores taken from Alice Arm indicate the presence of tailings from an open-pit molybdenum mine at the head of the Arm (Kitsault). Ba, Fe and Mn increase deep in cores from the head of Alice Arm, and a maximum in the Ba concentration around 1956 in a core from near the sill are probably associated with tailings disposed earlier into the Kitsault River at the head of the inlet (Dolly Varden mines). Post-1900 increases, particularly in Cu and Zn, for sediments from upper Observatory Inlet coincide with mining and smelting operations by Anyox at Granby Bay. Both the sediment accumulation rates and the sediment metal concentrations suggest that Alice Arm is an effective trap for most of the tailings supplied to it. The application of Principal Component Analysis on the metals data set shows a remarkably clear separation between Alice Arm (Cd, Pb, Zn) and Observatory Inlet (Cu, Zn) sediments; it appears that the submarine tailings discharge used by the most recent mine at Kitsault (Amax) deposited most tailings near the outfall and down the centre of the fjord.