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Protecting Fish Habitat at the Diavik Diamond Mine

To say that Diavik Diamond Mines Inc. (DDMI) takes its environmental stewardship responsibilities seriously is as much of an understatement as saying Yellowknife gets a little chilly in January. After three years of environmental and socio-economic baseline studies, community and government consultation, and one of the Canadian mining industry's longest and perhaps most technical Federal environmental assessments, Diavik finally began producing diamonds in January of this year.

The Diavik Diamond Mine is located in the Northwest Territories of Canada, approximately 300 kilometers northeast of the capital city of Yellowknife, on a large 20 square kilometer island in Lac de Gras. Canada's only other operational diamond mine, the Ekati Mine is located 30 km to the northwest. When fully operational, Diavik will produce over 1.5 million tonnes per year of kimberlite ore over its estimated 16 to 22-year mine life, using a combination of open pit and underground mining methods. With an average value of US$62 per carat, Diavik's orebodies are expected to produce diamonds at a peak of about 8 million carats per year.

Diavik's four known diamond-bearing kimberlite pipes are located under the shallow water of Lac de Gras adjacent to the island. Because of this, dikes were constructed to isolate the lake bottom for pit construction.The first dike was completed in 2002 and dewatered that fall. Its alignment incorporates small islands in order to help minimize rock fill requirements.

Lac de Gras is typical of arctic lakes. It has low aquatic productivity resulting from relatively low concentrations of nutrients, low light levels during winter months, extended periods of ice cover and low water temperatures. Because of this, the protection of fish and the enhancement of fish habitat is a major priority for DDMI. Coarse rock fill on the outside of the dike forms new fish habitat, and granular fill is being placed behind the dike to create new fish habitat upon mine closure. Prior to dewatering, Diavik made efforts to transfer as many fish as possible from the pool on the inside of the dike to Lac de Gras. With production now in full swing, a significant monitoring project is being undertaken to understand the potential impact of explosive -induced vibration and water overpressure on northern lake trout spawning habitat.

The study is a joint collaboration between DDMI and the University of Alberta Biological Sciences and Geophysics Departments.

"During the first year of the project, four sites have been chosen as potential fish habitat, three of them within the blast area and one outside, which will serve as a reference site," says Marek Welz , a researcher at the University of Alberta.

The instrumentation will include advanced 4-component sensors with fully gimbaled geophones. Three of the components refer to the triaxial , self-orienting geophones, and the fourth component is a hydrophone. The sensors are each connected to an Instantel® Minimate Plus™ vibration and overpressure monitor. The sensors are designed for deep-ocean reservoir monitoring, but have been adapted by Instantel to work with the Minimate Plus monitors. The monitors will be deployed prior to a blast and set to trigger automatically by the geophone channels, when a set particle velocity is exceeded. Data will then be downloaded by DDMI and sent to the University of Alberta Geophysics Department for processing and analysis.

 "In all four sites, incubators have been placed beside the sensors. While the sensors measure the blast effects in the area, the incubators will study the survival rate of the fish eggs,"  says Welz. In the second year of the project, four more sites will be added within the blast area.

"Several things will come out of this study,  It will be the first in depth study of Northern Lake Trout, and a much greater understanding of blasting effects on fish habitat will be gained that will help the Department of Fisheries and Oceans establish guidelines for blasting in or near bodies of water." says Welz.

For DDMI, it's all part of doing business in the sensitive environment of the Canadian Arctic.