ENVIRONMENTAL EFFECTS OF THE OLD DUNBRACK MINE DUMP, MUSQUODOBOIT HARBOUR, NOV A SCOTIA

Abstract

The Dunbrack Pb-Cu-Zn prospect, located 5 km north of Musquodoboit Harbour and 45 km east ofHalifax, Nova Scotia, ceased operations in 1920. The Devonian Musquodoboit Batholith hosts the minerals in a ca. 300 Ma quartz vein which occupies the contact between the batholith and a felsic dyke. The dump from the deposit is in the woods 50 m from Highway 327 and 200 m from the Musquodoboit river system. This thesis attempts to evaluate whether the dump poses an environmental risk in terms of releasing base metals. Samples of minerals, balsam fir, and lichens from the vicinity of the dump were studied. In addition an experiment was carried out to assess the solubility of base metals in rainwater. Analysis of heavy mineral concentrations from a grab sample from the Dunbrack mine dump by atomic adsorption spectrometry gave 45% Pb, 3.5% Cu, and 1 % Zn. Textural relationships between the main sulphides give the following order of estimated relative ages: chalcopyrite, galena, bornite, covellite, then sphalerite. Results from an experiment involving rainwater combined with crushed dump sulphides show a drop in pH of0.81 and 0.93 pH units and an increase in the rainwater of Pb, Cu, and Zn concentrations by factors of 100-1000. The balsam fir and lichens in the vicinity of the dump contain anomalous concentrations of lead, copper, zinc, and cadmium, although the only obvious stunting of the biota occurs directly on the dump. The balsam fir lead concentrations at a distance of 60 m to the north and east of the dump are 1.8-20 times greater than a control location. Concentrations on the dump are 1 7 5 times higher than the control location. Other heavy metal concentrations (Cu, Zn, and Cd) are 1.5 to 5 times greater than the control location at a distance of 60 m from the dump, and are up to 13.5 times greater on the dump. Lichens from the dump and surroundings are emiched 2-4.5 times in Cu, Zn, Pb, and Cd, particularly the more sensitive species Parmelia sulcata. It is concluded that the dump has anomalous amounts of base metals in the balsam fir and lichens surrounding the dump, but beyond a few hundred metres from the dump it poses little risk.

Keywords: Dunbrack, dump, Musquodoboit Batholith, heavy metals, textural relationship, biogeochemistry, pH, sulphides, balsam fir, lichens (Parmelia sulcata, Hypogymnia physodes).