Abstract:

Seasonal precipitation patterns can significantly impact drainage water quality at mine sites, and it is important that this influence is not overlooked by using larger time steps in predictive modelling. To capture this seasonality for a semi-arid area, statistical distributions of the annual maximum time between rainfall-runoff events and the magnitude (volume) of the dry-spell-ending runoff event were calculated. Quantiles from each distribution were combined to represent a range of potential solute-loading scenarios. Solute inputs included primary soluble salts in the ore and non-ore lithologies plus secondary soluble salts produced by the oxidation of sulfide minerals in the pit and ore stockpiles. Concentrations were calculated from the solute mass reporting to the calculated volume of a given rainfall-runoff event. This work integrates the results of geochemical and mineralogical characterization and up-scaling of laboratory-derived solute release rates with climate modelling and conceptual models of flow and transport in the pit and ore stockpiles. Geochemical modelling was used to equilibrate the predicted solutions and implement solubility controls. The equilibrated solutions were then mixed in accordance with the site-wide water balance and re-equilibrated at key mixing points in the process water circuit. This work provides a method to predict process circuit water qualities linked statistically to quantiles of rainfall frequency and intensity that can be integrated into risk-based operational decision making.

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Kate Duke