Gold ore at Giant Mine was rich in arsenopyrite. To extract gold from the ore, a roasting process was used. This process created arsenic trioxide dust (As203), a highly toxic substance. Most of the dust was collected and pumped underground into 10 chambers and five mined-out stopes at the site.

Currently, there are 237,000 tonnes of arsenic trioxide dust stored underground at Giant Mine. This is equivalent to seven 11-storey office buildings.

Other sources of arsenic in the Giant Mine area include tailings, waste rock, underground mine workings and contaminated soils.

All ore processing at Giant Mine ceased in 1999.

Giant Mine is located within the municipal boundaries of the City of Yellowknife, on the shores of Great Slave Lake, about five kilometers from the downtown area. Ndilo and Dettah, two First Nations communities, are located approximately 2.5 kms and 9.8 kms from the site.

The Giant Mine site covers 2,345 acres (949 hectares), with mine workings reaching a depth of 2,000 feet.

Water entering the mine is pumped out to the tailings ponds on the surface. During the summer, this water is pumped to the on-site water treatment plant to remove arsenic and other contaminants. The treated water is transferred to the settling pond where the remaining contaminants settle to the bottom of the pond. The last step is the polishing pond. When water quality in the polishing pond meets the regulatory requirements set out in the mine's water licence, it is released into Baker Creek.

All water released into the natural environment from Giant Mine meets or exceeds water quality standards set out in its water licence.

Giant Mine Remediation Joint Project Office

2^nd Floor, Waldron Building, 5103 - 48th St.,
Yellowknife, NT X1A 1N5
Tel.: (867) 669-2426
Fax: (867) 669-2439
Email: giantmine@ainc-inac.gc.ca
www.giant.gc.ca
QS-Y289-001-EE-A1
Cette publication est aussi disponible en français sous le titre:
Gestion du trioxyde de diarsenic