November 16, 2022
Canada’s first rare earth mine is the result of a geological rift and the keen eye of a young geologist.
Nearly 30 years ago Chris Pedersen went out prospecting about 110 kilometres southeast of Yellowknife, between the Dene communities of Dettah and Lutselk'e.
While others had noted promising rocks there in the 1970s, Pederson is the one credited with the 1983 discovery of deposits now at the heart of the Nechalacho rare earth mine, operated by the Yellowknife-based Cheetah Resources Corp.
Today, Pedersen is Cheetah's chief geologist.
This article is included in the latest edition of the Unlocking Our Potential Magazine. Look for it at this year’s Yellowknife Geoscience Forum or you can read it (on line) here.
The project comprises two principal deposits located at Thor Lake, eight kilometres north of the Hearne Channel on Great Slave Lake.
Back when Pedersen first saw potential in the rocks around Thor Lake, there was little interest in the REEs.
Photo credit: Chris Pedersen, Chief Geologist, Cheetah Resources/billbradenphoto
"They used to call them the underappreciated elements," said Pedersen, adding that wasn't until the demand for colour televisions increased that interest in REEs began to take off.
To its credit, Nechalacho is really a "giant" deposit, Pedersen says. "It's got all the right chemistry. This particular one happened to be very rich in rare earth elements."
That's due to geologic processes that concentrated much of the rare earths at depth, and then, through tectonic plate movements combined with the movement of molten rock or magma through the Earth’s crust, brought them to near the surface during the Proterozoic era, some 2.2 billion years ago.
“The target zone for mining at Nechalacho — which now features an open-pit operation at the North T Zone — is basically "super-concentrated" in REEs near the upper part
"Other zones are deeper down which can be extracted in the future," Pederson says.
A plus for the Nechalacho deposits is that they are clean, he notes, with virtually no radioactive heavy element, like uranium and thorium, which are found only in low concentrations.
"There is a bit of thorium, but even when it's concentrated in the ore, even as a concentrate, the little thorium that is there is below actionable levels, below any concern for public health," Petersen says. "It's a very clean deposit by any mine standards."
Most of the rock containing the REEs is quartz, which is basically pure silica, "so there are really not any deleterious elements that need to be handled," he adds.
Other areas of the Northwest Territories are also thought to have undergone rifting, although evidence of that history is often obscured by younger plate tectonic events. Geologists can be challenged to identify these areas and their rift-related rocks with good potential for critical mineral deposits, like at Nechalacho.
These days the NWT Geological Survey is working to build its knowledge about the presence of REEs and other critical minerals and metals— 31 in all, increasingly sought for their role in clean energy technology.
These critical minerals and metals also include tin, copper, lithium, nickel and zinc.
John Ketchum, Director of the N.W.T. Geological Survey, says his department is building on historic knowledge and previous mapping projects to respond to an escalation of interest in the NWT’s potential for rare earths and critical minerals.
"People 20 years ago were looking for diamonds," Ketchum said. "Today it's more focused on the critical minerals. Fortunately, the location of previously-noted critical mineral occurrences or ‘showings’ hasn’t changed and that helps us to understand where to go back to and take a closer look".
Praising the detailed map work done by geological surveys, Pederson believes there's "absolutely potential in an area as vast as the NWT for more REE deposits.
"You're looking for these unusual geological areas, this rifting," he says. "If they said here's another rifting area, people like me would be out there in a heartbeat."