Sulfur-Ore Mining in Minnesota: Are Near-Term Economic Gains Worth Long-Term Losses?

Sam Duggan, MJLST Staffer 

Mining copper and nickel from sulfur-ore in Northern Minnesota is different than mining iron from taconite, and the environmental consequences are orders of magnitude greater. Unfortunately, the public discourse around developing copper and nickel reserves largely fails to consider this. As a result, the public is not armed with information needed to rationally debate whether sulfur-ore mining is a good choice for Minnesota.   

Taconite is a relatively unreactive iron-containing mineral. Although miners exposed to asbestos-like compounds from taconite dust are likely at increased risk of mesothelioma, proper dust mitigation practices and sound environmental planning/reclamation can limit long-term consequences to a scarred landscape. However, as with other types of mining, there are consequences associated with boom-or-bust economics.   

In stark contrast to taconite, sulfur-ore is highly reactive and has a particularly insidious property. A decommissioned mine slowly fills with rain, snowmelt and ground water. Sulfur reacts with water and oxygen to produce sulfuric acid, which dissolves metals contained in the sulfur-ore. Like a liquid miner, this acid liberates geologically sequestered metals into a dissolved, bioavailable and toxic form. As metals dissolve from the mine walls, more sulfur is exposed to oxygen and water. This produces more sulfuric acid which dissolves more metals. Through this chain reaction, the mine “mines” itself for centuries or more after its decommission. Importantly, mining target metals (i.e., copper, nickel) never occur alone. They co-occur with non-targets (i.e., lead, cadmium, manganese, arsenic, sulfate) that also dissolve from mine walls. Over time, concentrations of toxic compounds grow higher. Once the mine fills, acidic and metal-rich water (acid mine drainage) leach down-gradient and poison the watershed. Similar processes also occur in tailings piles stored outside the mine.

Sulfur-ore mines are responsible for numerous Superfund sites, including the infamous Berkley Pit copper mine. In 2016, thousands of snow geese landed in Berkley Pit’s toxic water and died en masse. Consider also the 2015 Gold King mine spill. At Gold King, a mine entrance cap was accidentally ruptured during routine monitoring and 3 million gallons of acidic, metal-rich water poured into the Animas River in Southwest Colorado. Related lawsuits seek many millions in damages. The history of mining in the Western U.S. is replete with other examples of sulfur-ore mines contaminating watersheds.

Methods exist for mitigating sulfur-ore mine pollution including capping, chemical neutralization, and constructing water treatment facilities specifically dedicated to the mine. However, these options cost millions and must be perpetually maintained, as it is nearly impossible to prevent water and oxygen from entering a mine. The chain reaction can linger for millennia, continually dissolving metals from rock and leaching toxins into the watershed.

Notably, the mining corporations who reap the lion’s share of a mine’s economic benefit escape long-term environmental liability because bankruptcy law and parent-subsidiary corporate structure often shield parent corporations from their mining subsidiaries’ environmental liabilities. For precisely this reason, the mine permitting process often requires corporations to offer financial assurances for potential environmental damages. However, financial assurances underestimate damages, and taxpayers are left with the bulk of sulfur-ore mine cleanup costs for generations.

The long-term consequences of sulfur-ore mines were recognized by the Obama Administration, particularly regarding mining in Minnesota’s Boundary Waters watershed. In 2016, the Obama Administration instituted a 2-year moratorium on mining permits near the Boundary Waters to study effects of sulfur-ore mining. That study could have led to a 20-year permitting moratorium. However, in 2018, after only 15 months, the Trump Administration decided that the study did not reveal new information and lifted the moratorium. Now, parent companies such as Chile’s Antofagasta can apply for mining permits within the Boundary Waters watershed via their subsidiary company Twin Metals. The permitting process is already underway for Polymet — an open pit, sulfur-ore copper mine just outside the Boundary Waters watershed. Importantly, Minnesota’s sulfur-ore resources could support dozens of mines.  

Given that sulfur-ore mines are economically viable for a few decades and an environmental scourge for centuries or more, decision makers should consider whether near-term economic gains are worth long-term losses.