UBC Reports | Vol. 49 | No. 12 | Dec.
Breaking new ground
By Michelle Cook
Thanks to an invitation to study an unusual deposit of kimberlite
in Canada’s Northwest Territories, UBC researchers have
discovered a new, cost-effective way to help diamond mining
companies search for the valuable minerals and develop mine
Kimberlite is a rare type of rock that sometimes, but not
always, contains diamonds.
While their findings may be new, researchers Ron Clowes and
Phil Hammer used an existing method of underground exploration
— seismic reflection — that is commonly used by the petroleum
industry to produce subsurface images but until now, has not
been considered effective for finding diamonds.
“There were a lot of unknowns from a research point
of view and we wanted to answer two questions,” says
Hammer, a research associate in the Dept. of Earth and Ocean
Sciences. “Is seismic reflection a cost-effective way
to explore for shallow kimberlite dykes and sills in a hard
rock environment like the Northwest Territories, and can seismic
reflection produce images of the kimberlite that would be
useful for mine planning?”
In a business where it can cost up to $300,000 to drill
one sample hole to reach certain types of kimberlite deposits,
mining companies want to know as much as possible about a
mineral deposit before breaking the earth’s surface.
Hammer says the work done at UBC proved seismic reflection
could be a very good exploration tool for some kimberlite
“The results suggest that we can use it to find the
thin, kimberlite sheets at depths of more than 1,000 metres.
In addition, the technique can show where kimberlite sheets
are really complex. That is of interest to mining companies
because it’s the complex areas that are going to cost
them extra money to mine.”
Hammer and Clowes became involved in Canada’s diamond
hunting race in 1999 when Clowes was approached by Vancouver-based
company, Diamondex Resources Ltd. A professor of earth and
ocean sciences and director of Lithoprobe, a 20-year national
earth sciences research project, Clowes has been working with
hundreds of geosciences researchers to explore Canada’s
geological history, including the development of seismic reflection
technologies needed to see what lies beneath the country’s
Diamondex Resources was interested in whether seismic reflection
could be used to explore a field of kimberlite at Snap Lake.
Seismic reflection, like sonar, uses sound waves to “map”
subsurface terrain. From previous geology work, the company
already knew that the Snap Lake kimberlite, located 100 km
south of the rich kimberlite deposits of Lac de Gras where
the Ekati and Diavik diamond mines now operate, contained
high-quality diamonds. The problem was that the kimberlite
at Snap Lake is unlike most of the world’s other kimberlite
Kimberlite formations are created when kimberlite magma
travels rapidly to the earth’s surface in massive explosive
eruptions. The eruptions typically form carrot-shaped pipes
with surface diameters hundreds of metres wide that taper
down into the earth for thousands of metres. Diamonds lie
buried in these long, vertical pipes.
Unlike the more common vertical pipes, the Snap Lake kimberlite
deposit is a thin, flat-lying sheet, two to three metres thick,
spread out over 25 square kilometres. It gently dips from
the surface to depths of 1,300 metres or more. It also feathers,
in places, into multiple strands.
The kimberlite’s unusual structure made it difficult
to detect with traditional exploration methods such as magnetic
and electromagnetic surveys done from the air. Without more
specific information about the type of deposit, drilling over
such a vast area would be prohibitively expensive, and mapping
the sheet for mine development purposes would be difficult.
Diamondex Resources, along with international diamond giant
DeBeers, which owns 70 per cent of the Snap Lake property
through its Canadian subsidiary, needed to find a different
way to gather detailed data. The companies asked Clowes for
“Knowing what we’ve been able to achieve with
helping base metal companies in applying seismic reflection
technologies to exploration, they wondered whether this method
would be feasible at Snap Lake,” Clowes says, adding
that, at first, even he was sceptical.
“Seismic reflection techniques are well suited for
mapping sub-horizontal structures so kimberlite dykes and
sills have the potential to be good seismic targets,”
Clowes explains. “But I didn’t know whether the
technique would work at Snap Lake. If you took a straight
rule-of-thumb analysis, it shouldn’t work because the
kimberlite is so thin relative to the depths we wanted to
look at — depths ranging from near the surface down to 1,500
metres, and you would not normally be able to see it without
extremely high frequencies which are quickly absorbed with
With funding from the two companies and a collaborative research
grant from the Natural Sciences and Engineering Research Council
of Canada, Clowes and Hammer first ran a computer-based feasibility
study using data taken from drill hole samples from the site.
Based on these results, they headed into the field in April
2001 to see if they could use seismic reflection to map the
underground kimberlite field beneath the tundra and the icy
surface of Snap Lake.
With more than 800 tiny geophones planted along a straight
line in the frozen ground to pick up subsurface sound waves,
the researchers ran seismic surveys using two methods to produce
vibrations — explosive charges and vibroseis, a way of pounding
the earth with a device mounted on a pickup-truck-sized vehicle.
The results surprised them. Emerging from the data was a striking
image of the kimberlite curving deep down into the earth.
“We thought we’d probably have success at shallower
depths, but we imaged the kimberlite to well over 1,500 metres
and that was very exciting and rewarding,” Hammer says.
The companies that sponsored the research are also pleased
with the results. Diamondex has since carried out a second
successful survey using vibroseis. DeBeers has plans to begin
mining the property, and has consulted with Clowes and Hammer
about running marine seismic surveys on Snap Lake with the
goal of further identifying the kimberlite’s characteristics.
The company has indicated that it wants to continue seismic
“If a 2D marine survey is successful, they can also
apply this technique in 3D fashion, and that’s what
they’re really interested in — mapping in 3D,”