In Response Column / It's true: No waste-rock piles, no acid mine drainage at Twin Metals
21 Nov 2019
We at Twin Metals always appreciate an opportunity to educate the public on mining and our project, a 21st-century underground mine that will utilize dry stack storage technology to manage its tailings. A Nov. 16 commentary in the News Tribune (In Response: “Twin Metals is selling Minnesota a fantasy”) suggested that I lied to the News Editorial Board regarding waste rock. It seems appropriate to respond.
The comments brought into question are related to the fact that there are two primary potential sources of acid rock drainage at a mining operation. The first is waste rock piles, which are generally defined as bedrock mined and transported out of a pit, which has no mineral concentrations of economic interest. The second potential source are tailings, the finely ground residuals that remain after the mill process has removed the valuable minerals from the ore. When exposed to air and water, waste rock and tailings that contain high sulfur can potentially produce acid rock drainage if not managed properly.