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slippery rock gAzette
Superior Northern Continued from page 24
Duluth Complex
Around 1.1 billion years ago, the North American continent literally began to tear itself in half. Driven by a plume of heat rising up through Earth’s mantle, the landscape that straddles today’s Minnesota- Wisconsin state line cracked open, with Minnesota heading northwest- ward, and Wisconsin pulling away to the south. This feature is called the Midcontinent Rift, and it was potentially the birth of a new ocean.
As the tectonic plate started to rupture into two pieces, basal- tic lava oozed up and filled in the cracks. The plate stretched further apart, more lava seeped in, and the sequence repeated. The stretched and broken crust created a low area in the landscape; a basin, if you will. This process went on for mil- lions of years, and the basin wid- ened and eventually filled with water. The Atlantic Ocean was formed the same way, and is still continuing to widen today, pulling Europe and North America ever
farther apart by about an inch each year.
But the Midcontinent Rift stopped rifting, and geologists still aren’t exactly sure why. After around 20 million years the action stopped. An ocean wasn’t destined to sep- arate Wisconsin and Minnesota after all, and North America re- mained united as a single continent. Geologists call this a ‘failed rift,’ which seems a bit judgmental.
The Midcontinent Rift left behind a layer 10 miles thick of various ig- neous and volcanic rocks. Today, old lava flows form beautiful cliffs along the north shore of Lake Superior. An expanse of dark col- ored, dense igneous rock now sits north of Lake Superior, called the Duluth Complex. Most of the rocks in the Duluth Complex didn’t erupt like lava. They were formed in vast, underground pools of magma that cooled slowly over millennia. As the magma cooled, the semi-mol- ten rock separated out into layers of different chemistries and densities. Pockets of metallic elements settled to the bottom of the magma cham- ber. Today, ores of nickel, cop- per, and platinum are found in the Duluth Complex, setting the stage for mining.
Amid Mining Controversy, Quarry is ‘A Win’
Public opinion in the rural Ely area is sharply divided over pros- pects for a new copper mine. Mining for metallic ores has a tragic legacy of land and water that remains con- taminated for generations to come, forcing residents to choose between economic gain and environmental loss. But that dilemma is thankfully
moot when it comes to a granite quarry – natural stone is inert and nonpolluting.
“We can do what we do with- out releasing any sulfur and with- out discharging water that has contaminants in it,” says Barkley. Quarrying stone “is something you can do here that benefits eco- nomics and the community and the state, but we’re not doing all these
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Sawing an exposed granite cliff face before dropping and processing the raw blocks.
harmful things along the way” Barkley says that people in the region are “hypersensitive to heavy metal mining,” and the topic is fraught with conflict. Amidst that controversy, the quarry offers a
more agreeable option.
“We’re viewed as kind of a big
win for this type of work in this in- dustry,” he says.
From Stones to School Funding
Mining royalties are an important economic contribution to the state of Minnesota. Companies that ex- tract minerals and rock from pub- licly-owned land pay a royalty to the public coffers. The Superior Northern quarry sits on School Trust land, which means that the royalties help fund the state’s school system. In 2020, Minnesota’s School Trust lands generated $28 million in roy- alties for public education.
“It’s a pretty good deal,” says Barkley.
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