Authors: Rohde, TK; Vogler, HG; Crosbie, J; Rieck, C; Green, G

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Rohde, TK, Vogler, HG, Crosbie, J, Rieck, C & Green, G 2022, 'Store-and-release cover column trials at Dugald River mine', 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. 1077-1090,

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The MMG Dugald River mine (the Mine) is located approximately (~) 85 km northeast of Mt Isa and 65 km northwest of Cloncurry in northwestern Queensland. The Mine includes an underground operation, a processing area, a 62.5 ha valley fill tailings storage facility (TSF) and two waste rock dumps (WRDs). Mining is done as conventional underground, longhole, open stoping and downhole benching of a massive zinc (Zn) and lead (Pb) deposit hosted within a black slate environment and copper (Cu) mineralisation in the adjacent hanging wall (the deposit). The deposit is estimated to contain ~53 Mt of Zn and Pb and 3.4 Mt of Cu which will be mined over a 28-year mine life, until about 2046. Waste rock is segregated based on sulphide concentration and temporarily stored in either a potentially acid forming (PAF) or non-acid forming (NAF) WRD. The PAF waste rock is temporarily stored above-ground and will be returned underground as stope fill in the future. NAF waste rock is an asset and will be used for rehabilitation work and other construction projects during operation. PAF tailings are thickened to a target solids content of 55% before discharge to the TSF or underground mine as stope fill. The PAF tailings require careful rehabilitation to minimise the risk of environmental harm to the receiving environment from acid rock drainage (ARD). The environmental licence currently prescribes a 2.1 m thick cover on the TSF surface. However, given the early phase of mining and the limited physical and chemical characterisation work completed on potential cover borrow material, MMG developed an innovative and cost-effective way to test several potential cover options that may provide a better environmental outcome then the cover currently prescribed in the environmental licence. The purpose of this paper is three-fold. Firstly, it describes the desktop cover design process that the Mine used to develop alternative cover options for the TSF that created an opportunity to improve environmental outcomes. Secondly, the paper describes the method and results of large (2.4 m tall) column trials that were used as a cost-effective way to trial four cover options, the result of the desktop cover design. Finally, the paper describes the cover design model that was built from the column trial results and how the model was used to scale up and assess the potential future performance of the alternative covers if they were built on the TSF.

Keywords: cover design, geochemistry, acid rock drainage

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