Karen M. Kedgwick
B. Sc. Honours Thesis
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The Dunbrack Pb-Cu-Zn prospect, located 5 km north of Musquodoboit Harbour and 45 km east of Halifax, Nova Scotia, ceased major operations in 1920. The tailings from the deposit are in the woods 20 m from Highway 327 and 200 m from the Musquodoboit river system. The Musquodoboit batholith (dated 372 (2 Ma), hosts the minerals in a quartz vein (304 Ma) which occupies the contact between the Musquodoboit Batholith and a felsic dyke. Chemical analysis of a heavy mineral concentrate of Dunbrack rock tailings show 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 of 0.81 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 from the dump are 1.8-20 times greater than a control location, and suggest a preferred dispersal direction. Concentrations on the dump are 175 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. Lichen from the dump and surroundings are enriched 2-4.5 times in Cu, Zn, Pb, and Cd, particularly the more sensitive species Parmelia sulcata. Although the heavy metal content in the balsam fir and lichens 60 m from the dump is anomalous, based on the assumption that the concentrations of heavy metals in balsam fir and lichens decrease linearly away from the Dunbrack dump, the background concentrations may equal the control concentrations at a distance of 144 m from the dump.
Keywords: Dunbrack, tailings, Musquodoboit batholith, heavy metals, textural relationship, biogeochemistry, pH, sulphides, balsam fir, lichens (Parmelia sulcata, Hypogymnia physodes).
Supervisors: D. barrie Clarke and Marcos Zentilli