From a New York Times Op Ed by Walter Mondale and Theodore Roosevelt IV. http://www.nytimes.com/2016/07/02/opinion/protect-minnesotas-boundary-waters.html?smid=fb-share
"But this kind of heavy-metal mining is in a destructive class all its own. Enormous amounts of unusable waste rock containing sulfides are left behind on the surface. A byproduct of this kind of mining is sulfuric acid, which often finds its way into nearby waterways. Similar mines around the country have already poisoned lakes and thousands of miles of streams."
"It is irresponsible to jeopardize an irreplaceable resource for something readily available elsewhere. President Theodore Roosevelt, who created Superior National Forest in 1909, implored Americans to “cherish” the nation’s “natural wonders” as a “sacred heritage for your children and your children’s children.”
'Do not, he continued, 'let selfish men or greedy interests skin your country of its beauty, its riches or its romance.'"