Acid mine drainage (AMD) and the management of acid-generating tailings and waste rock represent the largest environmental liability faced by the mining industry in Canada today. Researchers with the SDKI Sustainable Management and Rehabilitation of Mine Sites for Decision Support project are working collaboratively with industry to improve information gathering and analysis techniques to bring a geographic approach to mine site reclamation and acid mine drainage monitoring.

Figure 1. Area of active tailings disposal at the Copper Cliff tailings impoundment near Sudbury, Ontario

The Copper Cliff tailings impoundment near Sudbury, Ontario covers a 3000 hectare area and contains a large volume of contaminated media resulting from mining operations, such as waste materials from mine excavation, and tailings from mineral separation activities (Fig. 1). The ability to characterize and monitor these sites is vital to understanding the risks, and developing appropriate remedial approaches for progressive reclamation and long-term closure.

When in contact with oxygen and water, the reactive sulphides in tailings and waste rock oxidize and generate an acidic leachate that can carry heavy metals and dissolved salt. Using remote sensing technology, SDKI researchers produced a series of maps to study the distribution of AMD minerals at Copper Cliff (Figure 2). Hyperspectral earth-observation imagery can be used to uniquely identify minerals at the surface, based on absorption features in the visible and short-wave infrared wavelengths. Selected maps show jarosite and hematite, common products of the oxidation of iron-sulfide tailings. Jarosite is associated with the initial stage of the oxidation, during which a strong-acid environment is present. These acid environments often coexist with more leachable heavy metals. Hematite, a more stable iron-oxide, is the final product of iron sulfide oxidation. Pyrrhotite is subject to oxidation easily; therefore, it only appears in fresh/unoxidized tailings.

Figure 2. Maps of Copper Cliff tailings show distribution of minerals associated with acid mine drainage. Clockwise, from top left: false colour image of the scene; coloured areas indicate distribution of pyrrhotite; distribution of jarosite; distribution of hematite. Red boundaries indicate location of dams. Labels indicate different tailings disposal areas at the site.

The integration of mineral maps derived from remote sensing into a geographic information system will facilitate modelling and improve the understanding of geochemical changes at mine waste sites. In addition, the collection of geographic data on tailings chemistry can supplement regular water sampling strategies to assess the risks

Acknowledgements

Inco: Inco is a research and development leader in the global mining industry.

Falconbridge: Falconbridge is a leading low-cost producer of nickel, copper, cobalt and platinum group metals. They are also one of the world's largest recyclers and processors of metal-bearing materials.

McMaster University: McMaster Website

University of Waterloo: Waterloo Website

Mine Environment Neutral Drainage (MEND): Website