Dispersion of tailings from the Stirling Zn-Pb-Cu mine site, Cape Breton Island, Nova Scotia

The Stirling Zn-Pb-Cu mine, located at Stirling in Richmond County, Cape Br eton Island, was active between 1935 and 1938, and 1952 and 1956, when one million tons of ore were produced grading 6.21% Zn, 1.48% Pb, and 0.73% Cu. During the first period, 180 000 t of tailings were discharged directly in to Strachans Brook, whereas in the 1950s the tailings, totalling 800 000 t, were impounded. Since that time there has been ongoing erosion and downstr eam dispersion of tailings. The purpose of this study was to quantify this dispersion, to determine the effectiveness of neutralization of acid genera tion in the tailings, and to evaluate levels of downstream contamination. Downstream sediments in Strachans Brook have mean metal enrichments of 70x Zn, Ph and Cu, 35x Cd, As, and Ag, 20x Au, and 10x Mn, compared to upstream sediments. Close physical and geochemical similarities between tailings an d downstream sediments indicate a severe level of downstream contamination. Runoff from the tailings is pH-neutral, strongly enriched in sulphate, Ca, Mg, Fe, Mn, Zn and Cu, and slightly enriched in Cd, As, Sb, Se, Co, Ni, V, and Cr. However, downstream water is less acidic than upstream water and is slightly enriched only in Ca, Mg, Mn, and Zn. Dispersion of metals in solu tion is minimized due to effective neutralization by dolomite of acid gener ation within the tailings, and its impact on the downstream environment is reduced by upstream dilution of the effluent from the tailings.