BHP Billiton-owned Ekati Diamond Mine senior geologist Joe Heimbach shows off a piece of kimberlite from the wall of the Koala North. - Thorunn Howatt/NNSL photo

BHP Billiton's Koala North kimberlite, part of the Ekati mine, is an experiment in underground diamond mining. Other diamond excavation at Ekati is done through open pit methods.

The trial is important because nearly one-third of Ekati's remaining diamond value will have to be mined using underground techniques.

"The life expectancy of underground Koala North is about three years," said BHP Billiton's project director Scott Williams.

Workers are driven down into the mine -- kind of like an underground parking lot ramp -- via big, Humvee-like vehicles. The floor is both rocky and muddy and the tunnel's diameter is about 30 feet.

Koala North is a small kimberlite wedged between two large pipes -- Koala and Panda. It was discovered only four years ago. A kimberlite pipe is a carrot shaped, volcanically-formed rock formation leading toward the centre of the earth. Some kimberlites have diamonds in them.

Koala North couldn't be mined by open-pit methods because its mouth would have run into the neighbouring Koala and Panda pipes. That's when it was decided to experiment with underground mining techniques.

"Some kimberlite was processed from the Koala North pit but only to sample the ore," said Williams adding that the focus of the project was always to use it as an opportunity for underground operations.

Koala North diamonds will head to commercial production early in the new year. Small gems are coming out of the pipe now. About 1,200 tonnes of kimberlite ore are carried to the surface every day yielding only a half a carat gem per ton. The mining technique is based on a model supplied by the South African Finch Mine owned by De Beers.

A joint venture company has been contracted to mine the shaft. Procon Mining and Tunnelling Ltd. joined forces with Kete Whii Ltd., a 50-50 partnership between the Dogrib Treaty 11 communities of Rae-Edzo, Wha Ti, Gameti and Wekweti and the Akaitcho Treaty 8 communities of Dettah, Ndilo and Lutsel K'e for the project.

Procon specializes in underground mining and has a Northern history. It was the mining contractor used at Yellowknife's Giant Mine 10 years ago. So far the Koala mine's costs have totalled about $12 million. The project employs 11 BHP Billiton workers and 65 Procon people.

Most of the contractors are not Northerners but, "One of the commitments that Procon has is they will be training Northerners," said Williams.

Considering Yellowknife's underground gold mining history and the closing of Nanisivik and Polaris Mines in the high Arctic, Procon shouldn't have trouble finding them. The underground project will bring dangers to the diamond mine that haven't been there in the open-pit mines. Less than two weeks ago a miner's leg was broken when rock fell.

"There is a level of danger there that's not in a lot of surface operations," said Williams. The Koala North experiment is a warm-up for a proposed underground mine beneath the ultra-rich Panda pit.

"Koala North's diamonds are as good as Panda's but there aren't as many of them," said Williams.

Feasibility analysis of the Panda project is in its infancy, but if all goes well, it could be underground mined in three years.

Ekati is located about 300 kilometres northeast of Yellowknife.

It produces about $1.7 million worth of diamonds every day. BHP Billiton Diamonds Inc owns 80 per cent of it and geologists Charles E. Fipke and Dr. Stewart E Blusson own 10 per cent each.