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.
By mining underground and only bringing ore to the surface, Twin Metals will not have any waste rock piles stored on the surface the way a typical open-pit mine does. No strip ratio, no waste rock. The geology and location of our mineral deposit result in our ability to mine this ore surgically deep underground. This method removes one of the sources of potential acid rock drainage.
Tailings, on the other hand, will be stored on the surface, utilizing the best available technology: dry stack storage. Based on ongoing extensive testing, to be assessed by regulators and the public in the coming years, the sulfur content remaining in our project’s tailings will be too low to generate acid rock drainage. This removes the second source of potential acid rock drainage.
Twin Metals has invested more than $450 million to date to develop a mine proposal that will highlight new technologies and sustainable tailings management. All of this in a state that has the most rigorous environmental and labor standards in place to ensure it is done right. This point in particular is one the Editorial Board very poignantly brought to light in the opening paragraph of its Nov. 12 “Our View” editorial, “Twin Metals poised to prove it’s responsible.”
Northeastern Minnesota is home to 99% of this country’s known nickel resources, 88% of its cobalt, over half of its platinum and palladium, and a third of the country’s copper. We all have a responsibility to mine this critical mineral resource appropriately — while protecting Minnesota’s environment for future generations.
Twin Metals takes that responsibility seriously, and our team is proud of the work we have done.
We expect to submit our mine plan of operations to regulators soon, kicking off a multi-year environmental-review and permitting process. This will provide many opportunities for public input. I hope that as we move through this process, we can sit down at the table and have a good dialogue about the project and concerns regarding mining. My door is always open.
Julie Padilla is chief regulatory officer for Twin Metals Minnesota. She works out of St. Paul.