Authors: Herrell, MK; Prestia, AL; Bowell, R; Bosley, G

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Herrell, MK, Prestia, AL, Bowell, R & Bosley, G 2022, 'Pit lake geochemical modelling methods for closure', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 429-438,

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Open pit mining can result in the formation of pit lakes at closure for projects that extend below the water table and have a positive water balance. The water quality of the pit lake has important implications for closure, rehabilitation and long-term management of mining projects, both financial and environmental. A prediction of future pit lake water quality is therefore necessary so appropriate mitigation strategies can be developed and implemented if required. In addition, in many environments the lake can represent a potential long-term benefit dependent on water quality. An understanding of pit lake water quality is evaluated through the application of predictive geochemical and hydrogeological models that rely on real world inputs to define the overall system. The water quality of the pit lake is dependent on several factors, including: the quality of the groundwater and surface water entering the pit; the contribution of chemical load from the exposed talus on benches and surfaces in the highwall above the pit lake; the prevailing climate conditions and hydrodynamics of the pit lake; and pit lake water management activities. In the absence of a present day analogue, accurate prediction of future pit lake water quality can be challenging, even when industry best practices are followed. This paper presents a case study of a pit lake geochemical model focusing on the approach and lessons learned. Generalised guidance for updating pit lake modelling best practices is also provided.

Keywords: pit lakes, geochemical modelling

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