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WT: Thanks for doing this Dr. Lindsay.  Zhang et al*, 2023 relate acid mine drainage as "a major source of pollution of world concern". Can you tell us about the Sherridon, Manitoba abandoned copper-zinc mine, why has this site been called one of the worst cases of acid mine drainage in the world?

Prof Matt Lindsay: Let me just clarify one thing, I am a Professional Geoscientist registered in SK and BC, I am not registered in Manitoba.  I have collaborated with researchers in the past on the Sherridon mine site, so I have some familiarity with Sherridon tailings.  As I mentioned previously, the (Sherridon) tailings contain various sulfide minerals, but in particular they contain an elevated content of the mineral pyrrhotite , particularly reactive and known to generate acid mine drainage at faster rates than some of the other sulfide minerals.

 WT: Can you give us an idea how much acid mine drainage could be generated at this site, and for how long potentially?

Lindsay: That's a complex question.  I don't have exact numbers on hand, but I do know there was a large volume of tailings transitioned into Camp Lake.  The idea is, if you put these high sulfide content minerals like pyrrhotite underwater, they will weather or oxidize very, very slow compared to tailings sitting on the surface.

One of the biggest challenges that played out during the (Sherridon) reclamation to this point is this: the approach of storing tailings underwater to prevent or mitigate acid mine drainage, assumes the material has not already undergone extensive oxidation or weathering.

This is important. As the tailings are sitting on the surface reacting with oxygen in the atmosphere, and water from rain and snow melt, they are weathering, generating acid mine drainage. Acidic water with high concentrations of metals forms additional minerals through the weathering process. Many of these soluble minerals generate acid and store acidity. In the Sherridon case, tailings that had been highly weathered for many decades were moved from the land surface into the lake. I would presume these minerals dissolved as those tailings were put in the lake, and that has caused the lake to become acidic.  I believe the remediation plan involved pH adjustment of the lake through the addition of lime. When you do that, you bring the pH up and you form iron floc. The iron floc settles to the bottom, but with windy conditions the particles can come up to the surface.



If we are seeing these iron particles coming up to the surface, there is mixing, it also means more oxygen coming in contact with the tailings. There is merit in subaqueous storage of sulfide tailings to mitigate acid mine drainage, but when a great deal of AMD has already happened, there are many other challenges to address.  It seems in this case, it has not played out the way the remediation plan had projected.

WT: What specific concerns do you have, and should Canadians have concerns about this acidic discharge contaminating the downstream environment? Can Camp Lake be contained or cut off from the circulation of the watershed?

Lindsay:   There are a few things to consider.  It sounds like at one time the lake had been isolated from the local flow through the area. One concern about blocking off inflows or outflows is that you could end up in a situation where water levels really rise and you have to deal with the excess to prevent flooding.  You don't want a situation where you are trying to isolate this really poor quality water, and then every now and then just dumping it into the environment anyway.  I don't know the hydrology of that specific area.  From my perspective, it makes sense to NOT allow that lake to discharge dissolved metals, particulates and lower pH water into the downstream environment.    

WT: Is there anything else we should be thinking about, talking about or asking about around this subject of acid mine drainage?

Lindsay: These sites are very complicated, and I really do feel for the community.  They are paying for decisions that were made many decades ago, and some decisions made more recently that did not go as planned.  Unfortunately I see these sorts of situations in other places. Governments, industry and the consultants that work for both need to ensure ongoing discussion.

Save Kississing Lake, Stop Acid Mine Drainage

*Zhang et al, article "A Review: The formation, prevention and remediation of acid mine drainage"  published in Springer Nature, Oct 17, 2023.