Abstract
Mine Rock Stockpiles (MRSs) typically represent the majority of acidity generation potential at a mine site; often greater that 75%, and sometimes up to 95% or more. Hence, MRSs represent multi-generational water quality risk in respect of metal leaching and acid rock drainage (ML-ARD) at a mine site. Often, the extent of this risk manifests from being unrecognized, and underfunded, to having substantive risk requiring management as a mine site moves into more detailed closure planning. In most of these situations, risk is managed by limiting adverse consequence effect to water resources (i.e., a receptor) through implementation of MRS effluent collection and treatment systems, combined with a cover system placed on the MRS.
This paper will continue 'telling a story', first presented to CIM in 2019, on the value of managing acidity generation and therefore ML-ARD risk from MRSs through source term control; the highest level of hierarchical risk control in respect of source-pathway-receptor risk management. In this context, 'value' is reflective of quantitative assessments of mining costs and water treatment costs, but as importantly, Indigenous people's connection to land and water, establishing and maintaining social license to operate, and enhancing capacity to permit an expansion or new mine.
Conceptualization of how MRS ML-ARD risk can be reduced through alternate mine rock placement methodologies will be presented. Case studies will be presented that compare mining costs using conventional mine rock placement methods that focus on optimizing haulage and geotechnical stability, with alternate mine rock placement methods where in addition to optimizing haulage and geotechnical stability, optimization of geochemical stability is assessed. The case studies will feature an integrated mine planning and closure planning modelling approach, while also presenting field-scale monitoring data to demonstrate risk reduction in respect of effluent water quality and treatment costs.