Soon after the discovery of a gold nugget at Sutter’s Mill in 1848 triggered the California Gold Rush, a diamond turned up among glacial debris in Ontario, Canada, followed by more isolated discoveries south of the Great Lakes. Unlike the rush to find gold, however, the search for Canadian diamonds progressed at a crawl. More than a century after the initial discoveries, that pace has picked up speed.
Located only 220 kilometers south of the Arctic Circle, Diavik Diamond Mine is one of three operating diamond mines in Canada’s Northwest Territories. Since beginning production in January 2003, the mine has produced an annual peak of about 8 million carats. Photo courtesy of Diavik Diamond Mines Inc.
Canada’s lag in diamond exploration contrasts with exploration in Africa, where mining companies started fighting for claims in the diamond fields about 14 years after the first confirmed diamond discovery along Africa’s Orange River in about 1867. The reason for the lag, geologists say, is that Canada’s geology and harsh climate make locating diamond deposits a notoriously slow and difficult process. The scene is changing, however, as explorers and miners now forge northward with refined exploration tools and models suited for the landscape.
Diamonds form deep below Earth’s surface at the roots of continental plates. At depths of about 150 kilometers, pressures and temperatures are high enough to convert carbon into diamond. Getting those diamonds to the surface, however, requires the presence of carrot-shaped pathways, tapered at the bottom, called kimberlite pipes, which are carved by magma making its way to the surface. Occasionally, the rising magma boosts the deep diamond-bearing, or “diamondiferous,” rock through the pipe and closer to Earth’s surface. Locating such pipes so that they can be mined is a goal of exploration groups worldwide.
Diamond-bearing kimberlite pipes tend to form where the cores of continents are thick, stable and about 2.5 billion years old. Those conditions are present below diamond-producing countries, of which the largest producer by mass in 2004 was Russia (see sidebar). South Africa, commonly thought of as a superpower in the diamond industry, ranked fifth, followed by Canada at sixth, according to a 2004 Natural Resources Canada report. Canada’s rank could change, however, as explorers continue to discover more kimberlite pipes.
Still, only about 23 of the world’s total 5,000 pipes actually contain enough diamonds to make their mining worthwhile, according to Diavik Diamond Mines Inc. Searching within diamond-producing countries, explorers rarely find a diamond resting on Earth’s surface. They look instead for traces on the surface of more common “indicator” minerals, such as garnet and olivine, which form alongside the diamonds deep inside Earth.
Tracing diamond indicator minerals back to their source is more straightforward in Africa than in Canada. In Africa, Tania Marshall, a private consultant and the technical director of Monroe Minerals, headquartered in Alberta, Canada, follows indicator minerals through old river systems back to the pipes of origin, which are then usually mined (if drill samples turn up enough diamonds to make the endeavor economically viable). In Canada, however, additional challenges posed by glaciers add complexity to the process, Marshall says.
In 1899, William Hobbs, a geologist at the University of Wisconsin in Madison, hypothesized that advancing and retreating glaciers would shave away the tops of kimberlite pipes and carry indicator minerals, along with any diamonds, far from their source. Indeed, Marshall says, “the whole landscape has evolved differently” compared with southern Africa, where glacial activity has been absent for 250 million years.
Recent glaciations have been “the difficulty in the north,” says Ralf Tappert, a diamond geologist at the University of Alberta in Edmonton, and were part of the reason why Canadian diamond sources have evaded discovery for so many years. Now, a significant amount of work for Canadian exploration geologists goes into reconstructing the movement of the ice so that they can try to follow the indicator minerals back to their source. But the problem remains that glacial activity spread the minerals far and wide. “We have to pretty much test the whole region,” Tappert says, to find high abundances of minerals.
Ten kilograms of glacial debris often turns up only a few grains of indicator minerals, Tappert says. But if explorers are lucky, they find regions with a high abundance of the minerals, and they can tighten the sampling grid, he says, and “nail it down to the source.”
Further complicating exploration, kimberlite pipes in Canada “are a little more difficult to find,” Marshall says, because some are buried under lakes or ice in “a bit more extreme conditions.” The Diavik Diamond Mine, for example, is located only 220 kilometers south of the Arctic Circle in Lac de Gras. The pipes of interest are just offshore an island, under a lake that is frozen for seven months each year.
To access the pipes, which formed about 55 million years ago within approximately 2.6-billion-year-old rock, engineers need to build a watertight dike around the pipes and pump out lake water. So far, the dike is “performing better than expected,” says Tom Hoefer, a spokesperson for Diavik, with minimum leakage that is then filtered and pumped back into the lake.
Engineers also considered environmental concerns unique to the northern latitudes, such as preserving permafrost in a region where the 3.9-kilometer-long dike meets small islands. Closed tubes installed within the dike hold liquid carbon dioxide, which has a cooling effect that is made active during summer months to prevent melting. The success of the dike, first drained in 2002, led to the construction of a second dike expected to be completed this year.
Getting materials to the site is also a chore. A year’s worth of supplies need to travel over a 350-kilometer-long ice road (75 percent of which is over frozen lakes) reconstructed annually each winter. For Diavik alone, about 2,000 truckloads of supplies make the journey across the ice road each winter, which typically opens in early February and can support trucks through April. The ice road opened to light loads in early February as usual, despite warmer than average temperatures this year.
Explorers and mining companies do not appear deterred by challenges posed by northern Canada’s geology and location. Diavik Diamond Mine is one of a growing number of mines in the region; DeBeers — the giant diamond mining and trading company that once had a near-monopoly on the industry in Africa — even has a presence, with two Canadian mines under development and a third in the permitting process. “I think it’s definitely a growing field,” says Thomas Stachel, head of the diamond research lab at the University of Alberta in Edmonton.
Explorers have already found about 600 kimberlite pipes in Canada, Tappert says, and “it is quite likely that there is still a lot undiscovered.” About 10 to 20 percent of those pipes are diamondiferous — a percentage similar to that of diamond fields in other countries. The difference, Tappert says, is that Canadian kimberlite pipes that contain diamonds tend to have them in very high concentrations and quality, which make them “worthwhile to mine, even under the difficult Arctic conditions.”