This study investigates the environmental impact of pyritic waste dumps and associated catchment ponds at the southern portion of the Steep Rock mine site, an abandoned iron mine north of Atikokan, Ontario. The primary concern of these piles is the oxidation of pyrite and the production of acid rock drainage (ARD). In this study, only the top one meter of waste rock piles was sampled; thus the redox front was not transected and only materials within the oxidizing zone were studied.
The dominant mineral phases present in the waste rock piles are quartz, goethite and hematite. The presence of goethite and hematite stems partially from oxidation of pyrite to these iron oxides, although the majority of these minerals were present in the original mine wastes. The flow of contaminated groundwater produces precipitates in the waste rock materials and lake sediments. The primary product is gypsum; however, jarosite is also produced, although in lower abundances. Acid rock drainage contaminated water ultimately flows from the waste rock piles into adjacent catchment ponds via groundwater flow or surface runoff. These ponds consequently have serious water quality concerns, characterized by pH as low as 2.5, sulphate concentrations as high as 2000 mg/L and high concentrations of metals such as iron, calcium, magnesium, manganese, aluminum, nickel and zinc. In some areas, carbonate minerals are able to partially buffer the low pH.
The former mine pits at the Steep Rock site have flooded since mining operations ceased, and the lake levels continue to rise. The rising water level will ultimately flood the study area and result in the pit lakes merging, and this combined lake will eventually reach the former lake level. The presents a unique situation of a pit lake with a littoral zone, and in this case the littoral zone will consist of pyritic waste rock materials. This interaction of shallow, oxygenated water with the waste rock materials presents long term concerns about the potential for continued production of acid rock drainage, and the resultant water quality of the combined lake.
For more details about this thesis contact Dr. Andrew Conly