Twin Cities diamond mine? Yes! Well. Maybe.

Minnesota state geologist Harvey Thorleifson’s theory goes like this: Diamonds are being mined in Canada. The geologic structure holding the precious stones is similar to Minnesota’s.

He posits the odds are fifty-fifty of finding the formations in Minnesota where diamonds reside. One of the possible locations is right here in the Twin Cities.

Before you start digging in your backyard, Thorleifson, a University of Minnesota geology professor, points out there are plenty of diamond miners around the world who’ve dug all their lives and never seen the precious rocks.

Thorleifson is the opposite of a stuffy academic. Strap a microphone on him and he takes over with his game show style presentation and informative power point of the history of diamonds.

He spoke recently to a few dozen folks at the recent, A Sip of Science happy hour event at the Aster Cafe in Minneapolis. I bet he’d be willing to share it with other groups.

Here, for more, is an excellent piece of reporting on Minnesota diamonds by my now colleague Paul Tosto back when he worked for the Pioneer Press. Take it away, Paul!

Minnesota’s geology reveals road signs to diamond riches

Don’t start digging yet, but a study suggests a treasure trove lies beneath the state

BY PAUL TOSTO

Pioneer Press

They rarely yell “Eureka!” in the diamond exploration game. But surprising details from a just-released survey of Minnesota has the state’s top geologist saying: “Maybe.”

An exhaustive study by University of Minnesota researchers and an Australian mining company discovered geological markers across Minnesota similar to those in Canada that have led to huge diamond strikes over the past 10 years.

Held in secret for two years as part of a rare deal the U signed in 2004, the newly published findings reveal patterns researchers didn’t expect — mineral arrows that may point to pipes of kimberlite, the underground rock formations where diamonds are most commonly found.

“We did find something and it’s like the first hints” that led to diamond-field discoveries in Canada, said Harvey Thorleifson, head of the Minnesota Geological Survey and a world-renowned diamond geologist.

It’s no “X marks the spot” discovery. It will take several years to trace back the mineral markers to see if they lead to kimberlite and, perhaps, diamonds.

Thorleifson called the findings significant but compared them to a hunting dog picking up the scent of a fox: Sometimes the fox is never found.

He plans to unveil the findings next week at an international prospector’s convention in Toronto.

A diamond strike might seem unlikely in Minnesota. Scattered exploration in the central part of the state 20 years ago failed to find a mother lode. But geologists have long seen Minnesota’s glaciated terrain as potentially fertile diamond territory, and chemical and computer testing of soils to find diamond markers has improved dramatically.

Hired in 2003 to lead the Minnesota Geological Survey, Thorleifson helped develop many of the indicator-minerals tests as a scientist in the Geological Survey of Canada. That work helped establish Canada’s booming diamond industry, which didn’t exist 10 years ago.

Thorleifson’s reputation and the potential to discover a billion-dollar industry were compelling enough that the U in 2004 agreed to let the mining company, WMC Corp., withhold publication of the study’s most sensitive findings for two years.

Diamonds form in rock that is about 2.5 billion to 3 billion years old. They rise to the surface in explosive eruptions and can be found in the carrot-shaped formations of kimberlite, named for Kimberly, South Africa, where it was first discovered in the late 1800s.

Diamonds have been found around North America, including Wisconsin, but mining was nearly nonexistent. That’s changed over the past 20 years as geologists began examining the sandy sediments of land scraped by glaciers.

Because kimberlite is soft, some of it can catch in the glacier and leave a trail traceable to its source.

Geologists sample soils, looking for kimberlite indicator minerals, such as garnets. After a few hits, they follow the trail in the direction the glacial ice came from; if the number of markers increases, they may lead to kimberlite — and, maybe, to diamonds.

That’s how it has played out in Canada, now one of the world’s fastest-growing diamond producers.

Garnets with just the right chemical makeup were the survey’s “complete surprise” in Minnesota, Thorleifson said. Found in a couple of spots, including near the Twin Cities, the garnets held levels of magnesium and chromium that flag them as particularly good markers to lead the way to kimberlite.

It’s possible they may point the way to a kimberlite plume between the Twin Cities and Duluth or western Wisconsin, he added.

Canada began producing diamonds in 1998 when the EKATI diamond mine opened in the Northwest Territories. Two other mines have opened nearby since 2003.

With this multibillion-dollar business, officials say, Canada is now the third largest producer of rough diamonds by value after Botswana and Russia. At least two more Canadian mines plan to open in coming years.

Initial results here are exciting because they mirror those found in the early days of diamond exploration in northwestern Canada. Thorleifson and others, though, say there’s a long road ahead.

“The report looks thorough and is a good first step in assessing the potential for diamond deposits and other mineral deposits in Minnesota,” said Brooke Clements, vice president for exploration at Ashton Mining of Canada in Vancouver.

Clements, who explored central Minnesota in the mid-1980s with another firm, cautioned that the samples in this newest report had no more than one grain of each of the mineral species that might lead to kimberlite.

“While there are examples of instances where kimberlite pipes were discovered after an initial sample had only one indicator grain, more work is required to assess the significance of these results,” he said.

The next steps involve follow-up soil surveys that likely will include northwestern Wisconsin to see if the markers will lead to kimberlite formations, Thorleifson said. That process will take several years of work and consultation with other geologists.

“There is a source out there somewhere,” said Thorleifson. “Sometimes it’s kimberlite but there are no diamonds … or you might have a kimberlite with beautiful diamonds that might be too deeply buried. Sometimes you can’t find it.”

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