Applying threshold analysis to the selection of tailings and waste rock closure covers

ABSTRACT: This paper describes a framework that was used to guide the selection of tailings and waste rock covers for a mine remediation project in Northern Canada. Previous analyses had shown that no remediation option would eliminate the need for long-term water treatment; however, cover construction could reduce the volume of water that required treatment. A trade-off study was completed comparing the higher cost of more complex (lower infiltration) covers to the associated savings in long-term water treatment costs to identify cases where the construction of lower infiltration covers could potentially “pay for themselves.” Threshold analyses were completed to test the robustness of the base case conclusions to changes in input assumptions and identify priority areas for further studies. The results for the waste rock dumps were robust and showed clear patterns for constructing very low infiltration (geosynthetic) covers on higher-strength waste rock dumps. The results for the tailings were less clear, and the optimal cover selection was dependent on many factors including reasonable changes in construction cost assumptions, cover performance (infiltration), tailings geochemistry, and timing of future water quality changes.