Evaluating saturated water covers for limiting oxidation of tailings: a 25-year case study from Mount Lyell mine

Authors: Jackson, L; Johnson, F; Koppelmann, R; Cordery, G; Young, K; Spong, A Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_133

Cite As:
Jackson, L, Johnson, F, Koppelmann, R, Cordery, G, Young, K & Spong, A 2026, 'Evaluating saturated water covers for limiting oxidation of tailings: a 25-year case study from Mount Lyell mine', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-9, https://doi.org/10.36487/ACG_repo/2615_133



Abstract:
The Mount Lyell copper mine in Queenstown, Tasmania, is one of Australia’s oldest mining operations and has a long legacy of mine waste discharge to the Queen River. For more than 75 years, multiple waste streams were released, including an estimated 97.4 Mt of tailings and large volumes of acid and metalliferous drainage pumped from underground workings (mainly from run-off from legacy waste dumps). Riverine tailings disposal ceased in 1994, after which Copper Mines of Tasmania constructed the Princess Creek tailings storage facility (PCTSF). The PCTSF contains approximately 42.2 Mt of potentially acid-forming tailings and mine mud, and has been raised through 6 consecutive lifts to a height of 52 m. Mining and processing operations at Mount Lyell mine ceased in 2014, when the mine was placed in care and maintenance, significantly reducing the availability of neutralisation inputs previously provided by the processing plant. In the subsequent care and maintenance period, substantial efforts were directed towards limiting oxidation of tailings by increasing tailings saturation. This involved dredging exposed tailings beaches and depositing the tailings below the decant pond level, ultimately achieving a water cover depth of greater than 10 m at the dam wall. A unique 25‑year water‑quality dataset was reviewed to assess the effectiveness of saturated water covers in limiting oxidation of tailings. The dataset spans both operational conditions, which include beached tailings and ongoing neutralisation inputs, and care and maintenance conditions, during which no active tailings deposition occurred. The results demonstrate that, in the absence of additional neutralisation, saturation of previously beached tailings is associated with measurable improvements in downstream water quality (i.e. total suspended solids, sulphate, copper, lead and zinc). These findings highlight the importance of water cover management as a mine closure strategy for active and legacy TSFs in wet climates. In addition, these data provide insight into the performance of the PCTSF for mine closure planning.

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