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THE APPLICATION OF BLENDED WASTE ROCK AND TAILINGS FOR COVER SYSTEMS IN MINEWASTE MANAGEMENT 1

Waste rock, tailings, and slag from a mine in Sudbury, Ontario were blended to create a material with superior physical and hydraulic properties for the potential construction of a cover system on a large tailings impoundment. The new material, termed Co-Mix, has a low hydraulic conductivity, a high Air Entry Value, and low compressibility. These properties indicate that the Co-Mixed waste rock, tailings, and slag can be used to restrict oxygen entry and water seepage, thus minimizing acid generation and metal leaching within the sulfide bearing mine tailings. The results of laboratory testing for various blend ratios together with soil cover model simulations are used to design a field scale experiment. Field scale test trials using selected Co-Mix blends of waste rock, tailings, and slag were constructed in October, 2004 at the Copper Cliff mine in Sudbury, Canada. The field scale test trials consist of 5 lysimeters measuring 15x15 m, with a total depth of about 2500 mm. These test trials are currently being used to evaluate the performance of the new material for cover systems that may potentially be constructed on the tailings impoundment upon closure. The lysimeters were constructed with thicknesses of Co-Mix cover material ranging between 600 mm and 1000 mm along with various blend ratios of waste rock, tailings, and slag. The lysimeters will be used to measure seasonal net infiltration rates together with oxygen fluxes to the underlying tailings. The construction of the lysimeter was recently completed and early results with respect to field performance during the spring snow melt period and summer months are presented in this paper for comparison with model predictions.