Integrating targeted geochemical experiments and process-based modelling to support defensible mine closure water quality predictions at Iron Crown mine

Authors: Volden, L; Kirste, D; Sexsmith, K Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_87

Cite As:
Volden, L, Kirste, D & Sexsmith, K 2026, 'Integrating targeted geochemical experiments and process-based modelling to support defensible mine closure water quality predictions at Iron Crown 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. 1-14, https://doi.org/10.36487/ACG_repo/2615_87



Abstract:
Mine closure planning for mine-impacted water bodies requires predictive tools capable of defensibly forecasting long-term water quality under evolving hydrologic and geochemical conditions. At the Iron Crown mine (British Columbia, Canada), Canyon Lake provides a case study demonstrating an iterative, closurefocused approach to developing a process-based water quality model to support closure design and risk management. An initial PHREEQC-based model developed in 2019 identified key uncertainties in source loading, sediment reactivity and seasonal stratification that limited confidence in long-term closure predictions. A subsequent gap assessment informed a targeted characterisation program in 2023, including expanded lake profiling, detailed sediment geochemistry and laboratory batch experiments designed to constrain sediment–water interactions. Batch experiments on representative shallow and deep sediments, reacted with synthetic low- and circumneutral-pH waters, were coupled with kinetic reaction path modelling to quantify mineral dissolution and precipitation, sulphide oxidation, and adsorption processes. History-matched simulations were used to derive defensible, process-based source terms, replacing empirical assumptions and reducing uncertainty in model inputs critical for closure planning. The updated, seasonally resolved PHREEQC model incorporates a refined water balance, improved source loading estimates for tailings run-off, seepage, groundwater and natural inflows, and geochemical controls constrained by experimental results. Model validation demonstrates that the revised configuration reproduces observed stratification and worst-case deep-water conditions. Results confirm that tailings beach run-off is the dominant closure-relevant loading pathway, with secondary contributions from oxidised shallow sediments, while deep sediments remain effectively non-reactive. Application of the calibrated model to evaluate tailings cover performance indicates that a reduction in tailings run-off of approximately 75% is required to achieve near-neutral pH and concentrations below screening criteria for most constituents of interest, with residual cobalt loading attributed to shallow sediments. The close agreement between measured and predicted concentrations in Canyon Lake supports the use of the model as an appropriate tool for evaluating the effectiveness and limitations of potential remediation measures.

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