Optimization of Waste and Low-Grade Ore Management for Acid Rock Drainage Potential
Copper Mountain Mine is an operating open pit copper mine located near Princeton, British Columbia. Production resumed in 2011 after having been temporarily shut down from 1996. The current operation was re-started with the requirement in its mining permit to segregate and separately manage waste rock and low-grade ore with potential for acid rock drainage (ARD) despite the lack of observation of ARD at the site after a century of mining. Potentially acid generating (PAG) rock remaining at the end of mining is required to be rehandled and backfilled so that it is prevented from oxidizing by a water cover.
SRK assists with annual interpretation of monitoring data collected as part of the mine’s waste rock and tailings management plans. This includes post-depositional sampling of segregated PAG rock, tailings, waste rock seeps, and groundwater.
The post-depositional sampling of non-PAG rock confirmed its characteristics but PAG waste rock and low-grade ore showed it had low potential for ARD (i.e. non-PAG). SRK determined that blasting preferentially partitioned acid-consuming minerals into blast fines, which was linked to these minerals occurring as fracture fillings in the rock. Based on a statistically designed sampling program, SRK confirmed the observation systematically and showed that the bulk characteristics of the rock could be PAG, but blast fines were consistently non-PAG. It was recommended that segregation for ARD potential was not needed and on this basis Copper Mountain Mining requested a modification of its permit to remove the requirement. Following negotiation with the provincial Ministry of Energy, Mines and Petroleum Resources, the government agreed to lift the requirement allowing reclassification of existing PAG rock as non-PAG and allowance for mining of waste rock without segregation. As part of the acceptance of the change, an enhanced monitoring program was designed to evaluate the robustness of the findings on an ongoing basis. The program includes alert levels and triggers for reimplementation of segregation. The benefit to the operation has been to reduce the cost of mining because there are more options for waste placement and there is no requirement for rehandling waste rock at the completion of mining.
