November 2008

The iciest ice

By M. Kerawala

Diavik Diamond Mine is currently in the midst of a $700 million expansion and transition works program that will see the augmentation of infrastructure to support the gradual switchover from open pit to underground mining.

To say that the Diavik Diamond Mine on East Island in Lac de Gras, Northwest Territories is an isolated operation is an understatement. The Arctic Circle lies just 220 kilometres north and Yellowknife, 300 kilometres to the southwest. Early explorers nicknamed the desolate surrounding tundra “the barren lands” because of its lack of trees due to permafrost. Such is the climatic setting of Diavik.

But this frozen lunarscape is home to some of the world’s richest diamondiferous kimberlite. One of Diavik’s three ore bodies, the A154 South pipe (the others being A154 North and A418) yields upwards of five carats per tonne of ore, many times more than the world average of less than one carat.

Established in 1996, Diavik Diamond Mines Inc., a Rio Tinto subsidiary, operates the mine as a joint venture with Harry Winston Diamond Corporation. The ground was originally staked in 1991 and exploration commenced in 1992. The next few years were dedicated to exploration, surveys, reviews, permitting and licensing. Construction started in 2001 and after an outlay of $1.3 billion, production began two years later, crossing the first million-carat milestone within months. The projection for 2008 is 10 million carats.

While the story sounds simple, it has been much more complex. Long-term employee and spokesperson for Diavik, Tom Hoefer, remembers every step of the journey.

The “where” determines the “how”

Diavik’s remote, Subarctic location governs all aspects of its operations. “The construction of Diavik offered many challenges because of its remoteness,” recalled Hoefer. Among the first tasks was building a 1,600-metre airstrip to accommodate everything from small personnel-carrying aircraft to Boeing 737 and Hercules transports.

“With no power lines in the region, we also had to generate our own electricity,” said Hoefer. Five diesel-fed Caterpillar engines generate 4.4 megawatts of power each. Housed in a 2,160 square-metre plant, three operate at any given time. One is held in reserve while another undergoes maintenance. To maximize their efficiency, Diavik collects waste heat from the power plants and uses it to heat the shop, process plant and accommodation buildings. Three 700-horsepower boilers provide additional heat to keep workers toasty warm in the frigid depths of winter. An aboriginal joint venture firm prefabricated the well-appointed residential camp units in Alberta before they were trucked to Diavik. Four three-storey wings house around 400 workers. Other facilities include a cafeteria and a recreation centre with a gymnasium, a running track and a squash court.

This was not all that the frosty location necessitated. Everything had to be built on hard permafrost, a very difficult task given the short construction season, said Hoefer. The extreme cold impacts production too. “We operate 24 hours a day, seven days a week, year-round,” he said. “But when it’s minus 50 degrees, even steel breaks. That’s when you begin feeling the effects of real cold.”

In addition to being remote, Diavik faced another location-related challenge, as it is built on an island. The ore bodies were discovered just offshore of the island, under the 60 kilometre-long lake, Lac de Gras, compelling Diavik to develop innovative approaches to facilitate mining. “We had to build a very sophisticated system to collect water from the island and treat it before releasing it back to Lac de Gras,” Hoefer explained. “In addition, to be able to access the underwater ore bodies, we had to develop a unique dyke design to hold back the water temporarily for mining.”

The first of these dykes is the 3.9-kilometre long A154,  completed in July 2002. Made of six million tonnes of rock, it averages 10 metres in height, with maximum depths of 28 metres. A piping system collects seepage on the inside base, and the structure’s thermosyphons (refrigeration systems) maintain the permafrost where the dyke crosses islands. Over 1,000 sensors monitor dyke integrity, temperature, pressure and movement. “Needless to say, such a sophisticated dyke technology required a $400 million capital cost,” Hoefer said, adding that land-based mines face no such expenses. A second dyke, the A418, was completed in 2007.

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