Highland Presents Evidence That Copperwood Ore is Acid-Neutral

• The Copperwood ore is chalcocite, with an average copper content of 1.5 percent

• It contains sulfides, so it’s correct to call it “a metallic sulfide ore”

• However, there’s reason to believe that, unlike other ore deposits, it’s incapable of producing acidic runoff

Opponents of the proposed Copperwood project call it a “sulfide mine.” Technically, that’s true – the Copperwood ore is chalcocite, a sulfide mineral.

But that doesn’t necessarily mean it’s a threat for acid mine drainage -- unlike other metallic sulfide mines in the United States and around the world. (Miners prefer the term “acid rock drainage” because acid runoff can occur naturally or from any large-scale disturbance of sulfide-rich rock, not just from mining. The mining-specific term is used here).

Under the right conditions, sulfide-rich mine waste can generate sulfuric acid, which is comparable to battery acid and is capable of dissolving toxic metals such as iron, arsenic, and lead. If it escapes into the environment as acid mine drainage, it can have catastrophic effects on plant, animal and even human life.

But the Copperwood ore in “non-acid generating,” according to Copperwood project director Dr. Wynand van Dyk.

Mine developer has evidence that the Copperwood ore deposit is pH-neutral

“If you look at, chemically, what happens with this rock, you cannot form sulfuric acid just from a chemical reaction perspective,” van Dyk said during an Oct. 24 media tour of the mine site. 

The tour was staged for Ironwood Daily Globe photographer Brenda Moseley and Mark Doremus of The906Report. It included a stop at a pile of Copperwood ore that was excavated almost 70 years ago by a subsidiary of AMAX, once a leading copper producer, which owned the project at the time.

The ore has been piled on the ground, exposed to air and water, ever since and has not produced acid mine drainage, according to van Dyk and Highland Copper Co., Inc., the owner of the Copperwood project. 

“You'll hear the opposition saying, ‘It's a sulfide ore body, and all sulfur ore bodies generate acid mine drainage,’” van Dyk said. “Sulfuric acid is not one of the byproducts” of mining the Copperwood ore deposit, “and that's why something like this is lying here for years and years, and you don't have the typical acid mine drainage.”

State regulators have agreed that the Copperwood ore is non-aciding generating, according to Highland Copper.

“The Michigan Dept. of Environment, Great Lakes, and Energy (EGLE) accepted the mining company’s geochemical testing, which showed that the Copperwood orebody is a metal sulfide that does not oxidize into acidic byproducts, in 2018, when the agency issued an amended mining permit for the project,” according to a Dec., 2024, email to The906Report from Highland Copper.

And scientific testing of rock samples has confirmed that the Copperwood ore is non-acid generating, according to the company. 

Those test results were published in 2016 by Prof. Theodore J. Bornhorst of Michigan Technological University and a colleague. 

In addition to rock samples, drainage water from underneath the rock pile was also collected and lab-tested. Both were found to be acid-neutral, as indicated by their pH values.

The range of the pH scale is from 0 to 14, with 7 being neutral. The rock samples and the drainage water were found to have a pH of 7.4 and 7.2, respectively. Sulfuric acid has a pH of 1 or less.

“So then, somebody can say, ‘we don’t necessarily believe the test results,’ van Dyk said, gesturing to the 70-year-old rock pile and the surrounding woodlands. “Well, come and have a look here. At the end of the day, the proof is what you can see now.”

The Bornhorst study was published in a peer-reviewed scientific journal. The authors acknowledged that analytical work and the initial interpretation of the drainage waters was completed by them as consultants for Orvana Minerals Corp., a prior owner of what is now the Copperwood project.

“However,” they added, “Orvana did not financially support producing this manuscript, although they did encourage us to publish this paper. Orvana did not influence our interpretations or conclusions. The opinions and interpretations herein are the sole responsibility of the authors.”

Finely ground tailings can produce acid mine drainage 

At the Copperwood, tailings will be stored in a 320-acre basin called a “tailings disposal facility” (TDF), held in place by a dam that will be 151 feet above ground level at its highest point.

“The good news is we cannot create acid rock drainage,” van Dyk said. “But even with that, our tailings dam is still lined [with high-density polyethylene]. It's a double-lined system with leak detection so that you can make sure that even if, at the absolute low chance, there is some form of a leachate happening from that material, we recirculate all of that water back into the process plant” where water is used to separate minerals from the ore.“ And when we get to year five, and the project becomes water positive [produces more water than it can use for ore processing], that's where we have the water treatment plant” to remove contaminants before the water is returned to the environment.

You can access Highland’s detailed project plan here.

Responding to a request for comment, Tom Grotewohl of Protect the Porkies said:

“Regardless of whether or not Copperwood's ore is acid-generating, the disruptions from air, light, noise, and water contamination; subterranean blasting; heavy industrial roads, power-grid rollout and cell towers — as well as a 350-acre waste facility containing 30+ million tons less than 200 feet from the State Park, visible from the region's most famous overlooks — are absolutely incompatible with the iconic character of this area at the juncture of Porcupine Mountains Wilderness State Park, the North Country Trail, and Lake Superior.”

Grotewhohl added the following after this report was published as a subscriber email:

“For the record, when van Dyck (sic) states, ‘You'll hear the opposition saying, ‘It's a sulfide ore body, and all sulfur ore bodies generate acid mine drainage,’ this is not correct. You'll find no mention of acid mine drainage either on the website or the petition, and it has not been a talking point of our campaign in years.”