McCullough, CD, Schultze, M, Vandenberg, J & Castendyk, D 2024, 'Mine waste disposal in pit lakes: a good practice guide', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2024: Proceedings of the 17th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1063-1076, https://doi.org/10.36487/ACG_repo/2415_76
(https://papers.acg.uwa.edu.au/p/2415_76_McCullough/)
Abstract: Pit lakes are formed through the inundation of empty mine voids and can be a significant legacy landform for mine closure when complete backfill is not possible. Increasingly, mine wastes are disposed into pit lakes to reduce post-closure land disturbance and integrate two final landforms into one with consequent cost savings. Subaqueous storage of mine wastes that present potentially acidic and/or metalliferous drainage (AMD) hazards is considered best practice for geochemical stability and through hydrogeologic containment (where inward gradient is permanently maintained). Subaqueous storage also reduces wind and water erosion rates compared to subaerial deposition in waste rock dumps or tailings storage facilities.
However, subaqueous mine waste disposal can also introduce closure risks, such as contamination of pit lake, surface and groundwaters. Accordingly, planning for mine waste disposal requires a detailed characterisation of mine wastes and their behaviour in the particular pit lake environment, in addition to a cost-benefit analysis of other waste disposal options. This information allows for waste placement that can be implemented during operational phases and into closure. Knowledge of this information early in the mining process, or pre-mining, allows for a wider range of options that can improve the success of the pit lake.
We summarise the state of knowledge and practice for mine waste backfill into pit lakes and identify key benefits, issues and strategies that have led to successful mine closure outcomes globally. Based on these findings, we provide guidance for mine waste disposal into pit lakes.

Keywords: closure planning, pit lakes, tailings, mine waste, repurposing, waste rock dump, tailings dam