UBC researchers are about to make diamond exploration history with the
publication of evidence supporting claims that the Slave region in Canada’s
Northwest Territories may hold the biggest diamond find of the century.
What is most intriguing, however, is that the research results — critical to
the diamond exploration industry — are being published, said Prof. Kelly
Russell, head of UBC’s Igneous Petrology Lab.
“Our discoveries and results on the Slave mantle are new to science. The irony
is, however, that many industry labs have similar scientific results which will
never be published,” he said. “Our corporate sponsor, Canamara Geological, is
remarkable in that they have provided us with valuable samples and are allowing
us to publish the results more or less immediately.
“The major corporations won’t give you the rocks. They’re afraid of giving up a
competitive edge. We’re getting rocks that most petrologists would die for.”
By analysing rock samples forced to the surface of the 2.6-billion-year-old
Slave craton — a very stable portion of the earth’s crust and upper mantle —
in explosive torrents of molten rock called kimberlite, petrologist Maya
Kopylova and Russell have constructed detailed geotherms–geological profiles
of the earth’s temperature with increasing depth and pressure. They are also
gaining insight into the composition of the earth’s mantle in the region
beneath the Slave craton.
“We’re changing the view of the Slave mantle. Rather than a homogenous region
of the deep earth, we are showing it to be diverse in composition and highly
disorganized,” said Kopylova, who studied in Russia and Australia and did post
doctoral work in South Africa before coming to UBC.
Information obtained by studying kimberlite samples and their xenoliths (chips
of mantle material) suggests the kimberlite pipes in the region are
characteristic of those in which diamonds can be found.
A kimberlite pipe is formed as kimberlite magma travels rapidly, from depths as
great as 400 km, toward the earth’s surface. From a depth of one or two
kilometres, the molten material explodes violently through the earth’s crust,
carrying fragments of mantle rock that it has collected along the way and, in
the right conditions, possibly diamonds to the surface. The magma falls back to
earth forming a mound of rock on the surface at the top of the conical
kimberlite pipe.
The geotherms show that at least some of the kimberlite pipes in the region,
which originated between 52 and 400 million years ago, passed through depths
and conditions in which diamond deposits are formed.
In South Africa, the world leader in diamond production, kimberlite pipes can
be as large as 800 metres in diameter at the surface. In contrast, the
kimberlite pipes in the Slave craton tend to be no larger than 100 metres in
diameter.
Millenniums of glaciation and erosion have worn away the upper portion of the
cone, leaving a progressively narrower portion exposed. Glaciers often carried
material from the kimberlite pipes thousands of kilometres, leaving kimberlite
debris along the way, before dumping their burdens of rock into the ocean.
The kimberlite samples Kopylova and Russell have examined came from a
kimberlite pipe known as Jericho and held by Canamara Geological, a Canadian
company that is one of several companies who have acquired land in the
region.
Foreign rocks, pieces of the earth’s mantle and crust carried to the surface
with the molten kimberlite, have provided the researchers with valuable
information. The rocks include primarily peridotite, which comprises the bulk
of the earth’s mantle, eclogite, which makes up the rest of the mantle, and
limestone which provides clues as to age.
Kopylova uses the Dept. of Earth and Ocean Sciences’ electron microprobe to
perform chemical analysis of the minerals from mantle xenoliths. Using her
findings, she has succeeded in mapping a “diamond window,” where mantle
pressures and temperatures are right for diamond formation.
And, by comparing geotherms derived from analysis of the Jericho pipe to
geotherms from other kimberlite pipes in North America and South Africa,
Kopylova and Russell can determine whether other Canadian pipes are likely to
have visited diamond deposits, generally at about 120 km beneath the surface,
on the voyage upwards.
This information might have made the search for diamonds undertaken by Charles
Fipke somewhat easier.
Fipke, who graduated from UBC with a BSc in 1973, is credited with the initial
discovery of the diamond-rich area. Fipke spent 20 years exploring the
Northwest Territories, said Russell, before finding glacial mineral deposits
that hinted at the presence of kimberlites and possibly diamonds at their point
of origin. Using the direction of glacial flow as a guide, he then travelled
1,200 km up-ice to find the kimberlite pipes in the Slave craton region.
