While Minnesota is no stranger to hard rock mining like taconite, the mining operation that Polymet proposes to establish is a sulfide mine.  Historically speaking sulfide mining has never operated in Minnesota.  However, it has operated in other states such as California, Montana, New Mexico, and Nevada.

A Sulfide mine is defined as hardrock mining for metals from sulfide-bearing rock by digging deep pits to excavate these precious metals.  This practice, in Minnesota, would extract precious metals such as copper and nickel with trace amounts of cobalt, platinum, palladium, and gold from iron(II) sulfide otherwise known as pyrite or “fool’s gold”. 

The Northmet mine would excavate pyrite from three large pits, each ~650ft deep, and the waste rock would be deposited next to the pits in 20 story piles.  The crude metals would then be transported to a refining plant, where the crude product would be refined further.  

However, when sulfide-bearing rock is exposed to air and moisture it reacts to create sulfuric acid (H2SO4).  This phenomenon is called acid mine drainage.  Acid mine drainage poses serious problems for Minnesota and its residents.