Assessment of cover systems for waste rock in the Antamina Mine, Peru

Cover systems have been included as a closure and long-term planning strategy for the estimated 1,539 Mt of waste rock at the Antamina Mine (Peru). A cover study was initiated to determine the most suitable type of cover system for the waste rock dumps at Antamina. The purpose of the four cover systems proposed in this study was to reduce net percolation to underlying waste rock via the combination of a low-permeability and a store-and-release cover, thereby limiting weathering and metal leaching from the waste rock. The low-permeability cover works as a barrier to percolation, whereas the store-and-release layer acts as a medium growth for vegetation, accumulates water during rain events and later releases most of it back to the environment through evapotranspiration. Four field-scale cover systems were constructed of native, low permeability materials and topsoil at Antamina. Climate data, runoff and infiltration through the covers were continuously monitored for one year in the field. A numerical model was created with the purpose of predicting the covers systems’ long term performance and the assessment of possible modification(s) to the design. Results after the first year indicate that the proposed cover systems reduced net percolation to the underlying waste rock from 70% (for the control lysimeter with no cover installed) to 53%-63%. No runoff was generated from any of the lysimeters and evapotranspiration is the only mechanism available to reduce net percolation through the cover systems. Materials characteristics and construction methodology were recognized as the potential reasons for the observed performance of the cover systems. Recommendations were given to improve the performance of the cover systems by further reducing the permeability of low-permeability layers and/or decreasing the thickness of the store-and-release layers of the cover systems. The feasibility of these recommendations depends on Antamina’s site specific conditions and remains to be evaluated. Finally, it was recognized that the data available to date is insufficient to draw major conclusions for the performance of each independent cover system. The Antamina cover study will continue over the following years and conclusions presented herein will be verified when new field data becomes available.Applied Science, Faculty ofMining Engineering, Keevil Institute ofGraduat