Slope stability of leached copper stockpiles

This paper considers the effects of copper leaching and long-term weathering on the stability of mine stockpiles that are constructed with inter-bench slopes at the angle of repose. It is not generally known whether acid leaching and weathering generate sufficient clay minerals to decrease slope stability, or if chemical cementation and consolidation also occur such that slopes eventually become more stable. Geotechnical and geochemical field sampling and testing of stockpile materials were conducted at a porphyry copper mine to evaluate the physical and chemical processes that may be affecting slope stability. A geochemical model was developed to simulate continued pyrite oxidation and acid weathering of stockpile material as meteoric water infiltrates through the stockpile after mine closure. The study concludes that the stability assessments of existing stockpile slopes associated with altered, porphyry-hosted copper deposits is a reasonable prediction of future stockpile stability.