At a minesite, acid drainage can develop in several mine components, including waste
rock, tailings, and mine walls. Due to the more prevalent lack of information on mine
walls, this study was conducted with four specific tasks in mind. The completion of these
tasks has lead to a more detailed understanding of acid drainage from mine walls.
Firstly, a detailed literature review identifïed relevant information on the generation of
acid and its migration in various modes of water movement. The information on water
movement showed that mines can have hydrogeologic impacts to distances of tens of
kilometers. The reviewed information on acid generation indicated that accumulation of
acidity in unsaturated fractures could cause acidic conditions to develop within a pit during
flooding.
The second task was a detailed evaluation of information related to acid generation,
acid neutralization, metal leaching, and water movement at Equity Silver Mines, focussing
on the Main Zone Pit. This evaluation highlighted the locations in the pit which are
generating or will eventually generate net acidity as well as the locations which are not
expected to generate acidity at any time. The short-term monitoring of limited portions
of the pit walls indicated the average rate of acid generation was 11 mg SOjdaylm’, in
general agreement with rates measured at other minesites.
The third task involved the creation and application of a predictive. mode& named
MINEWALL, to the Main Zone Pit to determine if acidic conditions might develop during
decommissioning. For reliable predictions, MINEWALL requires detailed input on water I
movement,p. it design, fracture characteristics,a cid generation/neutralization, and metal
leaching. The best-fit simulation of the Main Zone Pit to current data indicated the water
in the pit Will always remain near neutral values, except during an initial flush of acidity as
flooding begins.
The developmento f recommendationsfo r further studiesa nd for draft criteria of pit ’
decommissioningc ompletedt his study. Theser ecommendationsh ighlighted the amount of
detailed data required for reliable predictions and emphasized the primat-y role that premining
studiesp lay in designinge ffective plans for decommissioninga nd closure. These
recommendations were developed by Morwijk Enter-prises Ltd. and do not necessarily
reflect the views of Equity Silver Mines Ltd., the mining industry, or the provincial and
federal regulatory agencies.
