Anne‑Marie Whittaker

B. Sc. Honours Thesis

Experimental Evaluation of Subaqueous Disposal of Acid Generating Sulphide Minerals in the Meguma Supergroup, Southern Nova Scotia.

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Development and construction projects that require the disturbance and excavation of sulphide rich bedrock in Halifax and southern Nova Scotia produces large quantities of waste rock material. This material poses a high risk potential for acid rock drainage (ARD), a commonly known geoenvironmental issue in Nova Scotia. Acid drainage is associated primarily with the iron sulphides, pyrrhotite and pyrite, in addition to marcasite, sphalerite, galena, arsenopyrite, and chalcopyrite found in the Cambro/Ordivician Meguma Supergroup, which underlies 200000km2 of Nova Scotia's most populated and developed region. Variations of sulphide mineral type, mineral texture, the presence or absence of acidophillic bacteria (Thiobacillusferroxidans and Thio bacillus thiooxidans) and the availability of oxygen and water determine the reactivity and consequently the rate of generation of acidic solutions. The technique of subaqueous disposal is currently a potential method for waste management of excavated sulphidic waste rock of the Meguma Supergroup in Nova Scotia. This concept is based on the premise that acid generation is chemically suppressed in low oxygen conditions at depth in submerged sites. This method has yet been evaluated with regards to the sulphide bearing waste materials of the Meguma Supergroup and in particular, to disposal in marine environments.

This project investigates in a laboratory experiment, subaqueous disposal of sulphide bearing rock from the Meguma Supergroup in seawater compared to fresh water. Polished thin sections were prepared from a drill core sample near the Halifax International Airport. The main sulphide minerals of focus were pyrrhotite,marcasite, pyrite, and chalcopyrite. The experiment was conducted using distilled water, seawater and lakewater from local, natural environments. One thin section was submerged in SOOmL of each of the three water samples at a depth of 32 cm in graduated cylinders unexposed to atmospheric conditions at room temperature (~21 ^oC). One thin section was maintained in air as a control. Dissolved oxygen and pH measurements were obtained for the water samples at initial and final stages. Observations of surface features under reflected light were recorded and digitally imaged at 6, 15, and 40 days. Surface coatings, color, and topography of sulphide minerals were used as an indication of sulphide mineral reaction. Results indicate that in general, the rate of sulphide reactivity is higher in seawater compared to freshwater.

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Pages: 97
Supervisor: Marcos Zentilli