The Geology of the Penokees:

What’s In Those Rocks Anyway?

This is the fourth in a series of eight posts which together comprise an in-depth article concerning a proposed iron ore mine in the Penokee Hills of Northern Wisconsin and the widespread resistance to the project. Two installments of the article are posted weekly.

Well, first of all there are rocks, and out of rocks come minerals. (I think.) I must confess I never took a geology class in school and never missed it. But in August, 2014 I took a weekend class on the geology of the Penokees with Tom Fitz, a geology professor at Northland College. Fitz loves rocks and figuring out what they’re made of, and he has become rather notorious in Wisconsin for what he’s found in those rocks in the Penokees. (More on that later.)

There were about two dozen of us in that class. We spent the first day in a room at the college and the second out in the field, scouring the Penokees with Fitz, looking at rocks. After the first half-day of class, I felt like my head was spinning, as if it had just been hit by a meteor. A meteor did in fact hit, near what is now Lake Superior, but that was about 1.85 billion years ago, according to Fitz.

The impact of the meteor was such a shock that it caused massive tsunamis, the oceans  swayed and shook, and the chemistry of seawater was altered irrevocably. One upshot of this geologic Judgement Day was that it marked the end of iron formation.

Ironwood Formation in Penokees-0875

Iron-rich rock in the Penokees

A long strip of iron-rich rock called the Ironwood Formation forms the backbone of the Penokee Range. It is sandwiched between the wider Tyler Formation on the north and the Palms Formation to the south. The main minerals in the Ironwood Formation are quartz and magnetite, an iron oxide. It is this second mineral that interests the mining companies.

When we went out in the Penokees, we found that a compass would sometimes go haywire because of the high level of ferrous iron in the magnetite. The needle of the compass would point toward the rock rather than true north. Geology professor J.A. Latham from the University of Wisconsin walked this same range in 1858 and reported the presence of iron ore. A trapper discovered the first commercial iron ore body in 1879. The first boom began in 1885 and went bust two years later. Between about 1885 and 1964, miners extracted over 325 million tons of ore from the eastern end of the range. This was a softer, high-grade ore, containing 60 percent or more magnetite. Miners used narrow shafts and tunnels to dig it out, and then it was shipped directly to the blast furnaces. Mining died out in the Penokees when this high-grade ore grew scarce.

What remains today is taconite, a low-grade rock that can still be mined profitably provided it is rich enough in magnetite. It needs to be at least 20 percent iron by weight, according to Fitz, and he says the taconite ore found in the Penokees is 25 to 30 percent iron. New technology and the magnetic property of the taconite make it relatively easy to crush and extract the ore using large magnets. The deposit in the Ironwood Formation is said to contain about 3.7 billion tons of ore that could be profitably extracted, making it one of the largest iron reserves remaining in North America.

But there are problems. Al Gedicks, a sociology professor at UW-La Crosse and an anti-mining activist who has been working with Wisconsin’s Indian tribes for several decades, argues that modern mining is inherently problematic due to the nature of the remaining resource.

“There’s no such thing as small projects anymore,” Gedicks contends, “because the reality is that all the rich deposits have already been exhausted.

“The remaining deposits are low-grade, which means, in order to make a profit, you have to increase the volume, which means, for the most part, open-pit mining, which means moving vast amounts of material, over 90 percent of which ends up as waste.”

A major obstacle would be the fact that the Ironwood Formation is tilted to the north at about a 65 degree angle, due to tectonic forces dating back over a billion years. This would make it more cumbersome to reach the ore.  Since the ore is sandwiched between two other formations, miners would need to dig through the slate and quartz of the aforementioned Tyler Formation to access it. This waste rock, called overburden, would have to be stored on site, along with the tailings, which is the quartz that remains when the taconite is crushed down into small particles.

A report prepared by GLIFWC in 2011 estimated that a mine producing 8 million tons of taconite pellets per year would also produce 24 million tons of ore, ten million tons of waste rock and 16 million tons of tailings.

“The deeper you go, and the steeper the slopes, the greater the possibility of the entire structure collapsing of its own weight,” Gedicks told me when I met with him in La Crosse in early 2014. “This is clearly a major challenge to what is proposed in the Penokee Hills.” The year before, he said, the slopes collapsed at the largest open-pit copper mine in the world, in Salt Lake City, causing major damage.

GTac was first planning a 4.5-mile-long mine, to eventually be stretched to 22 miles in length. They later proposed reducing the width of the mine from a mile and a half down to a half-mile wide. The narrow base could be a problem, Gedicks suggested. “The steeper the slopes and deeper you go, the larger the base you need to create stability.”

If the GTac mine was a half-mile wide, it would be slightly smaller than the largest open-pit iron mine in the world, which is at Hibbing, MN on the Mesabi Iron Range. If the proposed mine in the Penokees was a mile and a half wide, it would exceed the largest open-pit taconite mine.

Early mines in the Penokees “were principally local, underground mines that targeted high-grade ores in the upper Ironwood Formation, yet the Tyler Formation was consistently avoided in excavating mine shafts, presumably because of its low strength,” wrote Marcia Bjornerud in a study for GLIFWC. Bjornerud is a geology professor at Lawrence University in Appleton, Wisconsin. “This suggests that the walls of a deep open-pit mine in the Tyler Formation may be difficult to stabilize without extensive engineering,” she continued, seeming to concur with Gedick’s assessment.

Another major concern that her research revealed was the potential for acid mine drainage. Bjornerud found pyrite (iron sulfide) and other sulfide minerals prevalent throughout the Tyler Formation and in one section of the Ironwood. When pyrite and other sulfides are pulverized and come in contact with oxygen and water at the earth’s surface, they can undergo chemical reactions that create sulfuric acid. The acid can leach harmful metals and compounds that end up in ground and surface water.

“The presence of disseminated sulfide minerals at all levels within the overlying Tyler Formation makes the potential for acid drainage from an open-pit mine a serious concern,” Bjornerud concluded. “The very fine grain size and disseminated nature of the sulfides in the Tyler Formation could act to exacerbate the production of acidic solutions,” she continued. “Moreover, because rock from the Ironwood Formation would be crushed onsite as part of the magnetic separation process, this material would be left as especially fine-grained waste rock with very high acid generation potential unless it was carefully identified and isolated on a continuous basis as the mine excavation progressed.”

Tom Fitz - Northland College-0869

Tom Fitz of Northland College lecturing about the Ironwood Formation in the Penokees.

Perhaps the concern about the Penokee rocks that has attracted the most attention is the presence of asbestos. Actually, what Fitz and other geologists have found in the Penokees is not asbestos, which is a commercial term, but grunerite, one of a group of minerals called amphiboles. The amphiboles are composed of elements like silica, iron, magnesium and calcium. They are dangerous when they break down into long, skinny fibers that look like worms when viewed under a microscope.

Mining opponents like Dave Blouin of the Sierra Club’s Madison chapter point to a University of Minnesota study that linked exposure to grunerite among taconite miners in Minnesota to mesothelioma, a rare but lethal form of lung cancer.

Fitz says the grunerite was initially discovered by DNR scientists, who then invited him to go out in the field and look at it. Fitz went out several more times with a woman from the Bad River tribe in the fall of 2013. “We found it in a lot more places in Ashland County, and it started to get a lot more press. It wasn’t long after that that the legislature passed that bill that says you can’t go on the land anymore.”

Fitz was attacked by GTac on various blogs; the company claimed he didn’t know what he was talking about. “None of this really affected me that much because I’m just doing the science,” Fitz told me. “I honestly don’t care that they’re attacking me.”

Ironically, since GTac has left the state, the president of the La Pointe Iron Company has invited United States Geological Survey (USGS) scientists in to study the extent of amphibole minerals in the Penokee Range. USGS will also be researching the regional impact of that meteor, supposedly the second largest ever recorded.

When I met Fitz for dinner in Ashland after our day of prowling around in the Penokee Hills, I asked him what was really important, in the big scheme of things, when you are working in a science that uses millions of years as the base unit. I was a little surprised by his answer.

“In terms of the earth, I don’t care,” he said, “but I care a lot about people and that people have good lives, and that means that we have a clean environment to live in. It also means protecting culture, like the Native American culture and their heritage here.”

▪ ▪ ▪

All photos by Tom Boswell©2015. All rights reserved.

Next: Changing the Rules of the Game: Money Doesn’t Talk, It Swears


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