Abstract
Water quality modeling of mine sites generally apply a conservative approach to the development and application of geochemical source terms. Despite the evolving geochemical state that many exposed geological materials (in particular, those that are potentially acid generating) experience, such approaches often use a single condition (for example, the steady-state conditions of a kinetic test that has begun producing acidity) to represent geochemical characteristics in perpetuity.
In this case study, we present an approach that was applied in a mine site water quality model which allowed for the representation of a waste rock storage facility becoming gradually acid generating over time. A module was developed in GoldSim to track the tonnage of all recently exposed waste rock as it was deposited in a storage facility. It incorporated a discretization within the tonnages by geochemical domains, as well as sub-domains based on acid generation potential, namely short-term, long-term, and non-potentially acid generating. A defined lag-time for each sub-domain was then applied, which allowed for the tracking of the tonnage of aged material. Combined with loading rates developed specifically for recently exposed and aged material, the result was a gradual shift of loading rates reflective of recently exposed conditions, to those of aged material conditions over time. Further, this approach was successfully modified for the ore stockpile to account for both the addition and removal of ore, often simultaneously, while still tracking this gradual shift between recently exposed and aged material. Other potential applications of this straightforward module will also be discussed.