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Nunavut diamond-gold deposit mirrors SA’s Witwatersrand Goldfields

A sample of pebbly rock from an outcrop in Nunavut. The rock was found to contain both gold and diamonds—a rare combination similar to that found in the world’s richest gold deposit in South Africa. (Image courtesy of the University of Alberta).

Researchers from the University of Alberta, Penn State University and the University of Padua have discovered diamonds in an outcrop atop an unrealized gold deposit in Canada’s Nunavut territory, an association that mirrors what can be found in South Africa’s Witwatersrand Goldfields.

The Witwatersrand Goldfields comprise the world’s biggest gold deposit, responsible for more than 40% of the gold ever mined on Earth.

Led by Graham Pearson, a research team travelled to the Kitikmeot Region and bashed off 15 kilograms of conglomerate from Silver Range Resources’ (TSX-V: SNG) Tree River property. Then, they used mass spectrometry equipment to date the rocks and established their deposition to be about three billion years ago.

The samples were then sent to the Saskatchewan Research Council, whose experts found three small diamonds, less than a millimetre in diameter.

“My jaw hit the floor,” Pearson said in a media statement. “Normally people would take hundreds of kilograms, if not tonnes of samples, to try and find that many diamonds. We managed to find diamonds in 15 kilos of rock that we sampled with a sledgehammer on a surface outcrop.”

“We managed to find diamonds in 15 kilos of rock that we sampled with a sledgehammer on a surface outcrop”

Graham Pearson, Researcher

According to the scientist, the geologic implications of this finding are immense.

After identifying an inclusion in one of the diamond samples, Pearson’s team proposed the idea of the diamonds being derived from a small, deep but cool lithospheric root, which is the thickest part of the continental plate.

“This is something completely unexpected from what we think conditions were like three billion years ago on Earth,” Pearson said.

He said that stable diamonds exist only in cool parts of the mantle, so their discovery suggests there must have been very deep, perhaps 200-kilometre-thick cold roots beneath parts of the continent very early in Earth’s history.

In the researcher’s view, although there is always an argument about the relationship between inclusions and diamond deposits, in this case, there is no argument because they now know that the rocks were eroded onto the Earth’s surface.

“It tells us there’s an older source, a primary source of diamonds that must have been eroded to form this diamond-plus-gold deposit,” he said. “This also means mining diamonds in the area would not necessarily require very deep mines if more economic outcrops of these rocks can be found.”