Operational Slope Stability Risk Management for Large Open Pits at the Mount Milligan Mine – A Case Study

Operational Slope Stability Risk Management for Large Open Pits at the Mount Milligan Mine – A Case Study

Authors: Greg Magoon1, Daniel Yang1, Teri Herbert2, Masimba Sowa2, Hubert Schimann2
Conference: Slope Stability 2024
Date: April 14-19, 2024

1 Knight Piésold Ltd., Vancouver, Canada
2 Centerra Gold Inc., Toronto, Canada

ABSTRACT

Mount Milligan Mine is located in Central British Columbia, Canada. Mining of the copper-gold porphyry deposit commenced in 2013 with a projected 16-year mine life. The geotechnical model and pit slope design criteria were developed based on limited geomechanical data collected from the 2007 feasibility study, resulting in some uncertainties relating to large-scale structural features, rock mass structure, and porewater pressure distribution. Risk management became a challenging task for the mine’s pit operations team.

3D laser scanning technology was applied to capture the orientations and frequencies of rock mass discontinuity planes after initial pit development. Geological structural mapping was also implemented to document the relationship between major structures and rock mass jointing patterns. The acquired data calibrated the structural model confirming the predominate kinematic failure mode was bench-scale wedge failures. Design adjustments were subsequently made for interim pit walls along with other remedial measures to reduce instability risks.

A real-time radar monitoring system was implemented once risk management became increasingly dependent upon slope monitoring and the implementation of appropriate operational protocols. Customized detection protocols and warning/alert thresholds were updated as the pit excavation advanced. The real-time slope monitoring identified risks of potential wall instabilities in advance and boosted the confidence of mining operations.

As mining progressed, increased knowledge of rock mass characteristics and slope performance factors led to an optimized slope design for the LOM pits. Mount Milligan Mine presents a good example of risk management for large open pits with limited geomechanical data at the onset of pit operations, where confidence in mine safety was gained over time through ongoing data gathering and interpretation, slope monitoring, targeted slope remediation, and slope optimization to achieve economic success throughout operations.

 

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