Notable case, Yellowknife, Northwest Territories, Canada
Giant Mine
A gold mine that produced more than 7 million ounces between 1948 and 2004. Roasting the ore generated arsenic trioxide: 237,000 tonnes of dust are stored in underground chambers, which the remediation plan will keep permanently frozen.
At a glance
- Status
- Remediation under way
- Activity
- 1948–2004
- Media
- soil, groundwater, surface water, air
- Kind of site
- mining
- National list
- ListedFederal Contaminated Sites Inventory – Class 1, High Priority for Action / Inventaire des sites contaminés fédéraux – Classe 1, priorité d’intervention élevée
Contaminants
Metalloids
National list
Active (confirmed contamination, action under way or still required)Canada
Federal contaminated sites, High Priority for Action (Class 1) (Federal Contaminated Sites Inventory – Class 1, High Priority for Action / Inventaire des sites contaminés fédéraux – Classe 1, priorité d’intervention élevée)
- Official id
- C1048001 ↗
About this list
Federal sites (land of federal departments, agencies and consolidated Crown corporations, plus non-federal sites for which Ottawa accepted financial responsibility) classified Class 1 under the CCME National Classification System for Contaminated Sites: the available information indicates that action (further characterization, risk management, remediation) is required to address existing concerns.
The class is the current one recorded in the inventory; for closed sites it is the last one assigned before closure. The FCSI does not publish when a site was classified or closed, so listed and delisted are empty. Contaminants are FCSI categories: 'metals', 'halogenated hydrocarbons' and other mixed categories stay in contaminants_raw only. custodian is the reporting federal organization. Eight sites have no name in the inventory: name is '[unnamed]' followed by custodian and place.
Status
Remediation under way
Remediation is under way under the approved closure plan; in 2022 the estimated cost was revised to C$4.38 billion.
Story
The mine was run by Falconbridge until 1986, then by Pamour, Royal Oak Mines (1990–1999) and finally Miramar until 2004. Before 1951 the arsenic produced by roasting the ore went straight into the air; from 1951 to 1999 the arsenic trioxide dust was collected and stored in 15 sealed underground chambers about 75 metres down.
The remediation is run by the federal government. The chosen remedy is the frozen block: keeping the chambers permanently frozen to prevent groundwater seepage. The cost, first estimated at about C$1 billion, rose to C$4.38 billion in 2022.
Timeline
- 1948Production begins.
- 1951Collection of arsenic trioxide dust begins.
- 1999Roasting ends; Royal Oak Mines leaves the site.
- 2004The mine closes.
- 2014Remediation plan approved.
- 2022Estimated cost revised to C$4.38 billion.
Remediation
- 2014ground freezingFrozen block: permanent freezing of the underground chambers holding the arsenic trioxide.
From the literature
Species that acted on one of this site's contaminants in at least one study. The list is automatic and takes no account of this site's soil, concentrations or climate.
Plants
- Pteris vittataChinese brake fernEvidence: field
- Arundo donaxGiant reedEvidence: greenhouse
- Azolla carolinianaCarolina mosquito fernEvidence: laboratory
- Lemna minorCommon duckweedEvidence: laboratory
Fungi
- Funneliformis mosseaeEvidence: greenhouse
- Aspergillus nigerBlack mouldEvidence: laboratory
- Fomitopsis pinicolaRed-belted conkEvidence: laboratory
- Mucor circinelloidesEvidence: laboratory
Sources
- Giant Mine Remediation Project, Crown-Indigenous Relations and Northern Affairs Canada, 2026
- Giant Mine, Wikipedia, 2026
Draft compiled from public sources, not yet reviewed.