Unless you spend your summers canoeing the Boundary Waters or live on the shores of Lake Superior, the term "sulfide-ore copper mining" may be a bit of a mystery to you. We have a quick primer on the mining process – and possible environmental impacts.
"Sulfide-ore copper mining" describes a process for removing copper, nickel, and other metals from sulfide ore. You may hear the short-hand phrase "sulfide mining," but that’s not really accurate because mining companies are digging for precious metals, not the sulfide rock itself.
Sulfide-ore copper mining begins with finding "commercially exploitable" concentrations of minerals – enough metals and other minerals in the rock for it to be profitable to dig up. The type of mine used depends on the size and depth of the rock to be extracted: An open-pit mine removes the top layers of rock, soil, and plants to expose ore close to the surface. Underground mines are used to reach bodies of ore farther below. Constructing either type of mine also involves adding buildings, power lines, access roads, and other infrastructure.
"Waste" rock – ore that does not contain enough metal to be worth processing – is dumped at the mine site. Mineral-rich ore is taken to a nearby processing facility, where the ore is crushed and doused with chemicals to "concentrate" the minerals. A report from the Great Lakes Indian Fish & Wildlife Commission provides the example of a proposed mine in Wisconsin where the natural ore contains 8.4 percent zinc and 0.7 percent lead. After processing, the "concentrate" could contain up to 60 percent zinc and lead, which the mining company would ship to a smelting facility to remove the rest of the impurities. The process of concentrating mineral-rich ore creates a waste product called "tailings" – small particles combined with wastewater that may contain chemicals, other metals, and explosives residue. Tailings are stored in open-air ponds called "tailing ponds." The Great Lakes Indian Fish & Wildlife Commission published a thorough explanation of this mining process.
Two companies have proposed sulfide-ore copper mining operations in northeastern Minnesota. The Twin Metals Minnesota mine would be located just a few miles from the Boundary Waters Canoe Area Wilderness and would be the largest underground mine in Minnesota history (up to 25,000 acres). PolyMet Mining’s open-pit mine would be located within Superior National Forest close to two tributaries of the St. Louis River, which flows into Lake Superior. PolyMet plans to use a former taconite processing facility about eight miles away from the proposed mine site to process the sulfide ore.
Results May Be Hard to Swallow
The concern with these mines is water – specifically, how the mines would affect the surrounding waterways.
Save the Boundary Waters estimates that less than one percent of the sulfide ore mined at these sites would contain enough minerals to be worth processing. That would leave millions of tons of sulfide ore sitting in rock piles or dumped back into the mines. When exposed to air and water, the sulfides in the ore create sulfuric acid – a highly corrosive liquid that can leach into streams, wetlands, and lakes in a process known as "acid mine drainage." Sulfuric acid contributes to the leaching of toxic heavy metals from waste rock, including lead, mercury, arsenic, and cadmium, which are then released into the environment.
Open-air tailings ponds can also cause environmental issues. These "ponds" can be the size of lakes and are filled with fine particles of ground-up sulfide. Toxins from these ponds can seep through man-made retention dams into groundwater or overflow with heavy storm water runoff. Contaminants can also become airborne during blasting operations, handling of broken rock, and when tailings dry out.
After a mine closes, contaminated water and toxic tailings must be contained and/or treated forever – and even then they pose health risks. In December 2016, as many as 10,000 migrating snow geese took refuge in a retired open-pit copper mine in Montana that had been closed since 1979. News sources report that thousands of snow geese died from drinking the highly acidic water laced with heavy metallic compounds that now fills the pit.
Digging For Profit
Minnesota has been home to mining for centuries, but it wasn’t until deposits of copper and nickel were discovered near Duluth in 1948 that companies became serious about mining these resources, according to a report from the Minnesota Legislative Reference Library. In 1972, Minnesota’s governor created a task force to examine the possible effects of mining these deposits. In 1974, two mining companies started preparing environmental assessments for copper-nickel projects and the state initiated a five-year regional study on the environmental impact. However, a drop in copper prices and problems with refining methods led the companies to abandon mining plans. About 10 years ago, new interest emerged.
The so-called "Duluth Complex," an area from Minnesota’s Canadian border south to the city of Duluth, may contain the world’s largest untapped copper deposit – an estimated 4 billion tons of copper-nickel ore worth more than $1 trillion, according to the Center for Biological Diversity. Mining companies have applied for more than 100 exploratory drilling permits in this area – most of which lies inside the boundaries of Superior National Forest.
PolyMet and Twin Metals are not the only companies exploring this area – they are the two closest to moving forward with mining operations.
Where Things Stand Today
PolyMet Mine Nears the Finish Line: PolyMet Mining released a draft environmental impact statement for a proposed sulfide mine in 2009 that was deemed "Unsatisfactory/Inadequate" by the Environmental Protection Agency (EPA) in 2010. The company released a supplemental draft environmental impact statement in December 2013. In March 2014, EPA issued a comment letter citing "Environmental Concerns/Insufficient Information" in PolyMet’s supplemental draft. In November 2015, PolyMet published a final environmental impact statement, which the Minnesota Department of Natural Resources (DNR) determined was "adequate" in early 2016. In November 2016, PolyMet submitted an application for a permit to mine, which is subject to further environmental analysis and review by the Minnesota DNR.
Twin Metals Mine Hits a Roadblock: In December 2016, the Bureau of Land Management (BLM) announced that it would not renew mineral leases held by Twin Metals Minnesota. The expired leases, which Twin Metals acquired from other mining companies, had previously been renewed without any environmental analysis. At the same time, the U.S. Forest Service submitted an application to the Secretary of the Interior to withdraw more than 200,000 additional acres surrounding the Boundary Waters from new mineral permits and leases.
Earlier in the year, the Forest Service had issued a statement that the agency was "deeply concerned" about the proposed mine due to its location near the Boundary Waters. The governor of Minnesota denied Twin Metals access to state lands for advance work on the project, citing similar environmental concerns.
This is not the end of the road for the Twin Metals mine. The company had already filed a lawsuit in September seeking to overturn the Department of the Interior opinion that BLM had the right not to renew Twin Metals’ mineral leases. A court hearing is scheduled for April 2017.
Proposed sulfide-ore copper mines in Superior National Forest are part of a much larger push for mining exploration across Minnesota, Wisconsin, and Michigan. As we wait to see how the PolyMet and Twin Metals projects will (or will not) proceed, we need to keep an eye on similar projects.
Izaak Walton League national Conservation Policies state:
"All relevant agencies in states where sulfide mining is proposed should withhold permits from any sulfide mining operations until appropriate criteria are developed and enforced to ensure that the operations and closing down of those operations are protective of natural resources. In addition, mining companies need to be held accountable for any reclamation or other clean-up costs associated with sulfide mining operations."
Whether any of the proposed projects meets these criteria remains to be seen. Stay up-to-date through Izaak Walton League Action Alerts and e-newsletters. Sign up today at http://members.iwla.org/news.