Assessing the risk of leakage from heap leach pads used in mining operations

Risk assessment is increasingly used in the context of mining activities, at various stages of mining projects. This applies also to mineral heap leach pads that are used for the recovery of gold, copper, silver and several other metals and non-metals. A heap leach pad consists of a lined facility (typically a composite liner) onto which ore is placed and then leached using, for example a strong acid or alkaline solution. This paper proposes an assessment of the risk of leakage through the composite liner of a heap leach pad, with the objective of illustrating how different types of uncertainty can be jointly propagated through the risk model. The proposed approach aims at avoiding the biases introduced by the common confusion between aleatory uncertainties (reflecting random variability) and epistemic uncertainties (reflecting the incomplete nature of available information). The joint propagation method provides estimates of the (imprecise) probability that leakage through the base of a heap leach pad should be lower than a certain value. It is shown how the proposed method aims to promote a more consistent approach to uncertainty representation and propagation in risk assessment, in order to contribute to the decision-making process in a more robust and transparent fashion.