Geologist Phil Larson of Duluth Metals talked about the unique geology of northeastern Minnesota at a talk he gave at Sugarloaf Cove Nature Center in Schroeder on August 17. The processes that went into creating this mountainous terrain left the area with a wealth of minerals. He is a self-described “rock licker” who lived in Hovland as a kid.
A long, long time ago, a rift in the North American continent created a valley, leaving a depression in the region of what is now Lake Superior. Into the rift erupted molten rock—a “mantle plume”—possibly from as deep as the boundary between Earth’s crust and its core. Over time, sediment settled in and became rock.
“…Geophysical studies have indicated that this is the deepest failed or healed rift on the planet,” according to a document entitled Geologic Analysis of Priority Basins for Exploration and Drilling prepared in April 1999 for the U.S. Department of Energy.
“…Many other rifts have formed, then continued to open, and eventually formed seas or open ocean basins, but no other rift appears to have proceeded to open so deeply, then stopped, without becoming an ocean. This has left an extraordinary accumulation of plutonic, volcanic and sedimentary rocks in the system.”
The geologic activity in this area has given northeastern Minnesota unique characteristics. One of them is that two points on the North Shore—the Eagle Mountain/ Brule Lake area in Cook County and the Cloquet Lake area in Silver Bay—create the highest gravity anomaly in the United States—and people weigh more there than anywhere else. People going just about anywhere from there will lose weight!
These were some of the geologic facts shared by Hovland native Phil C. Larson, Ph.D., senior geologist with Duluth Metals, at Sugarloaf Cove Nature Center in Schroeder on August 17, 2013. He described himself as “a rock licker,” and knowing that his audience might include opponents of mining in this region, he stated that his credentialing requires him to follow a set of professional ethics.
Minerals in this region
“All the earth is made up of little pancakes of rock,” Larson said. Some rocks contain uranium, which decays, allowing scientists to estimate their age. Relatively new compared to other rocks in this area are the vast deposits of copper and nickel in the Iron Range and the Duluth Complex spanning Cook, Lake, and St. Louis counties.
On an ongoing basis, magma sits underneath the surface of the earth and “cooks,” Larson explained. Other rocks fall into it and melt, including sedimentary rocks containing sulfur, which separates out at those temperatures like oil in water. When the magma cools, copper and nickel in it attach to the sulfur droplets near them.
This is how nonferrous minerals are bound to sulfur, which is released as an acid when it hits both air and water. Skeptics of nonferrous mining are concerned that even modern mining practices will not be able to keep that acid out of the area’s watersheds.
“We’ve had some unique geological processes that account for the mineral deposits we see here,” Larson said. “This is one of the most significant mineral deposits in the world that we’ve found.” Unlike two other locations where significant quantities of these minerals are found— Michigan’s Upper Peninsula and South Africa—northeastern Minnesota has a huge deposit in a small area.
Of the mineral resources in the U.S., Minnesota contains 99 percent of the nickel, 90 percent of the iron, 88 percent of the cobalt, 51 percent of the platinum, 48 percent of the palladium, 40 percent of the magnesium, 34 percent of the copper, 30 percent of the titanium, 11 percent of the silver, and 3 percent of the gold. The state of Minnesota owns about 13 million acres of mineral rights—the third largest owner of mineral rights in the U.S. behind the federal government and the state of Alaska.
“These mineral resources aren’t small,” Larson said. “These are big deposits. … They’re significant.” He said, people around the world “in smoke-filled rooms in Hong Kong, London, [and] New York” are talking about how significant the Duluth Complex is.
Practices have changed
“Sixty years ago, there were no environmental laws to speak of regarding the mining industry,” Larson said. “You weren’t accountable to anyone or anything.”
Years ago in Coeur d’Alene, Idaho, miners went on wildcat strikes demanding that the company repaint their cars because the smog was ruining them, Larson said. They weren’t protesting about the effect of that smog on their children. The company put in a tall smokestack to get the smoke out of the valley, and it ended up as acid rain somewhere else.
Larson said mining companies used to deliberately put mining tailings into creeks because that was the easiest way to get rid of it.
A century ago, sulfide rock was burned in smelters and used for heating, creating smoke that caused acid rain, Larson said. In modern mines, processed rocks are put into a slurry. The water is recycled and the sulfur is sold as a byproduct.
Today, mining companies have a very strong economic incentive to use as much of the materials they mine as possible. “If you don’t recover the sulfur,” Larson said, “you don’t recover the copper or the nickel.”
“Ideas have changed, and techniques have changed,” Larson said.
“Sustainability” is a term now being used in the mining industry. Mining companies are thinking about how the land will be turned to productive use when the mining is done, Larson said. New rock dumps on the Iron Range are being engineered more carefully than in the past, with more gradual slopes that are easier for trees to grow on, and land that has been disturbed is being reclaimed as it is used.
Economic viability
Some may wonder why areas that have already been mined are being considered for more mining now. The process of analyzing rock formations for the presence of minerals has improved over time, Larson said, and companies are finding high-grade minerals that they did not know about previously.
“You can’t sell a copper mine on the moon,” Larson said in regard to the willingness of investors to spend money on a potential mining project. Companies such as Duluth Metals whose stocks are traded on the Toronto stock exchange have been highly scrutinized in order to ensure as much safety as possible for investors. Projects are more likely to be economical in the Duluth Complex than anywhere else, Larson said.
The value the world places on the minerals in this region will affect how much companies are willing to pay to extract them. Some question whether the government will set the environmental bar high enough. If the minerals are really valuable, extracting them might still be economically viable even if the environmental controls are costly.
This is the first in a series on mining in the Northland. The next article will focus on environmental concerns that have been raised in regard to nonferrous mining in the Duluth Complex.
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