Abstract:

Rehabilitation options are currently being evaluated for the abandoned Steep Rock Iron Mine, located near Atikokan Ontario. Several large open pits were developed as part of mine operations, and these pits began to fill with water following the cessation of mining in the 1970s. A significant amount of acid generating mine waste is present at the site and as a result, sulphate concentrations in the pit lakes are elevated. However, the pit lake waters have a neutral pH and low metal concentrations owing to the presence of carbonate bedrock. Eventually, the filling open pits will merge into one large pit lake before discharging to the environment. While discharge is not estimated to occur for a number of years, the final pit lake will have a volume of 770 Mm³, and the scale of the site presents a significant challenge for rehabilitation.

The overall objective of site rehabilitation is to ensure that the pit lake water quality is acceptable for discharge to the environment. To address this, modelling was conducted to estimate pit lake flooding time and water quality. Evaluation of historical data showed progressive improvement in pit lake water quality over time, including the development of meromictic conditions. Further, the overall evolution of pit lake water quality is occurring differently in each pit lake at the site, due to their unique configurations and limnologic conditions. A case history of water quality evolution in each pit lake will be presented along with projections of future water quality based on model results.

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Kristen Gault