Abstract:

Two technological advances are changing the way we characterize and predict the greatest environmental liability that mining operations face: acid rock drainage and metal leaching (ARD/ML). Reactive transport modelling and modern mineralogical techniques are becoming mainstream methods for environmental predictions for mine waste facilities due to their ability to reduce uncertainty. Each of these tools are moving from development and applications in other sectors (academia and metallurgy) to more routine applications for environmental studies for operating mine sites. Together, they form a step forward in ARD/ML prediction that is bringing clarity to mine planning.

We present real-world applications of using the reactive transport modelling code MIN3P to quantify oxidation of sulphide minerals and various associated geochemical processes and physical transport in waste rock and tailings at two mine sites. These mechanistic models can help bridge the gap between small-scale laboratory tests and full-scale waste facilities in a more comprehensive and defensible way than is possible with traditional development of water quality source terms. Traditional static and kinetic testing remains important in this approach. But modern mineralogy techniques such as the automated scanning-electron microscopy (SEM) method TESCAN integrated mineral analysis (TIMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are uniquely capable of quantifying mineralogical compositions, metals contents in minerals, and mineral liberation in much greater resolution than is possible with traditional methods. Particularly due to the improved resolution, these modern mineralogy techniques can quantify sulphide, carbonate, and secondary/amorphous minerals critical to ARD/ML prediction, and metals contents in each, despite these commonly being difficult or impossible to detect with traditional methods. In each of the applications, results from traditional and modern mineralogy methods were incorporated in MIN3P to simulate release of selenium, cobalt, copper, cadmium, and other metals from sulphide minerals in the mine waste facilities. Simulations were calibrated to release rates in laboratory tests and seepage from the full-scale facilities, and the models were then used to forecast likely geochemical evolution and seepage water quality. The combination of these tools allowed for mine operators to better understand potential water treatment requirements, and the calibrated reactive transport models provided a platform to efficiently evaluate closure alternatives such as different cover systems.

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Mackenzie Bromstad