There is a recent NYT piece on the proposed iron mine project up on the Bad River in northern Wisconsin, and it is a big mine indeed:
The $1.5 billion mine would initially be close to four miles long, up to a half-mile wide and nearly 1,000 feet deep, but it could be extended as long as 21 miles. In its footprint lie the headwaters of the Bad River, which flows into Lake Superior, the largest freshwater lake in the world and by far the cleanest of the Great Lakes. Six miles downstream from the site is the reservation of the Bad River Band of Lake Superior Chippewa, whose livelihood is threatened by the mine.
The piece cites our own geologist, Marcia Bjorenrud, who evidently investigated the possibility of acid drainage from the project:
Before the passage of the bill, Marcia Bjornerud, a geology professor at Lawrence University in Appleton, Wis., testified before the legislature that samples she had taken from the mine site revealed the presence of sulfides both in the target iron formation and in the overlying rock that would have to be removed to get to the iron-bearing rocks. (When exposed to air and water, sulfides oxidize and turn water acidic, which can be devastating to rivers and streams, along with their fish populations.) Sulfide minerals, Professor Bjornerud said, would be an unavoidable byproduct of the iron mining. But the bill does not mandate a process for preventing the harm from the sulfide minerals that mining would unleash.
Acid drainage is a particularly nasty problem associated with many mining projects, so these issues tend to be at the fore of any mine permitting process. When sulfides are exposed to water and air, they oxidize and become acidic. The overhead shots from problem mines often look like someone dumped battery acid into a sink (see here from this photo essay of a particularly egregious case).
Thnx to “Mr. E” for the pointer.