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October 30, 2003
Research

 


Discovering Labrador’s mantle
Kimberlites – Nature’s high speed elevator

The MUN crew on Gossan Ridge at Voisey's Bay
Photo by Dawn Evans-Lamswood
The MUN crew on Gossan Ridge at Voisey's Bay, known affectionately as Disco Hill. (L-R) Dr. Derek Wilton, Michelle Huminicki (PhD student working on study of Voisey's Bay), Jason Letto (B.Sc.'03), exploration geologist with Voisey's Bay Nickel Co. and Dr. Paul Sylvester. Inset: Rock fragments in the pipe.

By Deborah Inkpen
Bringing diamonds to the earth’s surface is the job of kimberlites. Kimberlites are a peculiar kind of volcanic rock that originate deep within the earth’s mantle and are brought to the surface at really high speeds. Unlike a typical volcano, kimberlites emerge violently at the surface, producing a pipe-like structure, and don’t leave a volcanic edifice.

“Kimberlites are full of volatiles, and are very explosive,” explained Dr. Derek Wilton. Dr. Wilton and Dr. Paul Sylvester, geology professors in the Department of Earth Sciences, have been doing research in northern Labrador on kimberlites. Dr. Wilton likens the eruption of kimberlites to a high-speed elevator.

“Kimberlites punch their way up through the earth’s crust and as they come up to the surface they pick up all sorts of fragments, including diamonds,” said Dr. Wilton. “Diamonds only form very deep at the base of the crust and we never see them on the surface in the rocks in which they formed. Kimberlites are the movers of the diamonds from the lower crust to the surface. Not all kimberlites contain diamonds, however, and you have to examine them closely to determine if they are diamondiferous.”

The rocks that Wilton/Sylvester team are looking at are from the Torngat Mountains, Saglek and the Makkovik areas of Labrador. The Torngat ones are similar to those found on the nearby Ungava Peninsula of Quebec which have been confirmed to contain diamonds. For diamonds to form in the mantle, Dr. Wilton explained that the land like that of Labrador has to have mantle-friendly roots, meaning that the land has to have been there for a long time without a lot of movement.

“You look for diamonds on really ancient continents and northern Labrador has got some of the oldest rocks in the world,” he said. “We have been able to date some rocks from Labrador at 3.9 billion years old which is phenomenal when you realize that the earth is only four-and-a-half billion years old.”

Part of their study is evaluating the diamond potential of the Labrador examples. Master’s student Glen Penny from Holyrood has been investigating whether the kimberlites are diamond-bearing. “The other exciting thing about kimberlites is that not only do they bring up diamonds but they bring up other things from down in the mantle, so by examining them, we can actually can tell something about what the mantle is like underneath Labrador,” said Dr. Wilton.

Based on earlier work by former postdoctoral fellow Dr. Richard Cox, Mr. Penney is also developing a technique to date a mineral which appears in kimberlites called perovskite.

“It’s an unusual mineral because you only find in kimberlites or meteorites,” explained Dr. Wilton. “We have been working on a means of dating it in our department by using the LAM-ICP-MS (or laser ablation microprobe-inductively coupled plasma- mass spectrometer) instrument.

“Because diamonds seem only to have formed before two-and-a-half billion years ago while kimberlites can be as young as 50-million years,” said Wilton. If we can date individual kimberlites then we can say whether they are related to ones that we know are diamond bearing. The technique has a potential application for diamond exploration and some are suggesting that Canada may become the largest diamond producer in the world in the next 10 to 15 years.”


 


 
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