Geochemical Assessment and Modelling of Open Cut Pit, Mount Morgan, Queensland, Australia

C. Gimber, M. Preda, P. Scott, and C. McCombe (Australia)


AMD, acidic mine pit lake, PHREEQC modelling, geochemical prediction, model calibration.


This paper demonstrates the practical application of geochemical modelling to the prediction of water quality in a pit lake at the Mount Morgan mine site in Queensland, Australia. A laboratory simulation of the pit lake was undertaken using samples collected from site. The experiment simulated inflows from major sources including ARD impacted surface and groundwater and sludge return from the onsite treatment plant. Major outflows that were also simulated include withdrawal, seepage and evaporation. The laboratory simulation over 80 days represented 23 years at field scale. The laboratory simulation results were used to calibrate a geochemical model (PHREEQC); the procedure adopted for calibration is discussed. The calibrated model was then modified to include additional inflows to the pit that were not included in the laboratory simulation. Predictions of changes to pit lake water quality are made over 100 years. The paper demonstrates: 1. the importance of collecting physical data in order to calibrate geochemical models; 2. a procedure that can be used for model calibration; 3. how geochemical modelling can be used for prediction to inform decision making.

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