Innovative heap leach pad draindown modelling using a spreadsheet model (FastDraindown)

Authors: Zhan, G; Halford, K; Jackson, T Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_78

Cite As:
Zhan, G, Halford, K & Jackson, T 2026, 'Innovative heap leach pad draindown modelling using a spreadsheet model (FastDraindown)', 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_78



Abstract:
Active management of residual leach solutions, which no longer have commercial value, represents both a significant financial liability and an opportunity to optimise heap leach closure. The duration and strategy of active management must be carefully planned from both technical and financial perspectives, using draindown models grounded in unsaturated matrix flow formulations. This paper presents an innovative Excel Visual Basic for Applications (VBA) modelling approach that incorporates the key variables describing a heap leach pile, including geometry, material type and dynamic solution recirculation with time. The heap can be discretised into 1D columns (leaching cells) with variable areas, heights, hydrologic properties (i.e. saturated hydraulic conductivity, water retention curves), unsaturated hydraulic functions (i.e. Brooks & Corey 1964; van Genuchten 1980; Fredlund & Xing 1994), draindown stages and time-dependent solution recirculation strategies. An Excel-based model provides a practical and transparent alternative to complex 2D or 3D numerical simulations. Because Excel is widely available and familiar to engineers, planners and decision-makers, models can be developed, adapted and applied without specialised software or extensive training. This approach enables rapid scenario testing, sensitivity analyses and ‘what-if’ evaluations at minimal cost. Its transparency also facilitates regulatory review, quality control and communication with stakeholders, reducing the risk of hidden errors and increasing confidence in the results. The method is demonstrated through an application at an exemplary, undisclosed mine in which laboratory-obtained leach ore hydrologic properties are refined by calibrating to a large column leaching test and the field condition. The application highlights the effectiveness of the proposed method for post-closure leach pad water-balance modelling and optimisation of solution management strategies. This Excel VBA approach offers a flexible, cost-effective and reliable tool to support informed planning and decision-making during heap leach closure.

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