Open Pit Slope Stability Evaluation for Mine Closure: A Canadian Case Study Perspective

2021

Operating open pits are exposed to geotechnical stability risk throughout the life of mine. These risks are considered part of normal operating conditions and are managed by mining teams. Following the completion of mining, stability risks can continue to exist as pit slopes can deteriorate and exhibit progressive failure mechanisms. In some case these failure mechanisms can impact existing or planned mine infrastructure that is needed to achieve mine closure objectives (i.e., water treatment infrastructure, diversion channels, waste rock dumps, tailings facilities).

This paper presents a Canadian perspective for open pit closure as it applies to a case study at the Faro Mine, a former lead-zinc operation in The Yukon Territory, Canada. Provincial and territory guidelines for evaluating post-operational open pit slope stability conditions are summarized and compared against those used to evaluate the East Wall of the Faro Pit. The case study demonstrates some key components for the geotechnical stability evaluation of a weak rock slope that has exhibited obvious deterioration during and following operation. The slope is located directly below a diversion channel that is required to convey water around the mine complex and be positioned outside of the long-term slope break-back. The case study summarizes the field investigation, monitoring, geological/structural geology model, stability evaluation and acceptance criteria/considerations.