Brief Review of the Giant Mine Arsenic Mess

Posted by Stop Ajax Mine on June 18th, 2012 5:16pm


Giant Mine operated as an underground gold mine, and later also as an open pit mine from 1948 until 2004 very close to Yellowknife, NWT. The arsenopyrite ore which was mined contained both gold and arsenic. The gold was separated from the arsenopyrite ore using a roasting process, and this process produced highly toxic arsenic trioxide (As2O3) in the form of a dust. The dust was stored in sealed, underground chambers and it was thought at the time that permafrost would ensure the safe storage of the arsenic trioxide indefinitely.  


Over a period of 50 years of operation about 237,000 tonnes of arsenic trioxide dust were stored in this manner, although from the 1960s through to the mid 1970s "stopes"  (working chambers from which the ore had been extracted) were used, rather than chambers specifically built for the purpose. In recent years it became apparent that something must be done to prevent leakage of the arsenic trioxide dust from the storage chambers. In May 2011 there was leakage from the tailings pond. This facility contains thousands of tonnes of sludge contaminated with arsenic trioxide. The natural draining for such leakage is into nearby Great Slave Lake. Dettah is a Great Slave lakeshore First Nation community a few miles south (and downstream) of Giant Mine. Yellowknife itself takes its water supply from a source close to the mouth of the Yellowkife River, upstream from the Giant Mine site. The discovery that some of the underground mine workings were flooding caused the federal government to decide to take action. The cost of dealing with the mess left by the mine's operators will be borne by the taxpayers of Canada. (See, "MANAGEMENT OF ARSENIC TRIOXIDE BEARING DUST AT GIANT MINE, YELLOWKNIFE, NORTHWEST TERRITORIES.")

The owners of Giant Mine were for many years allowed to pass along an arsenic storage problem to subsequent owners without financial cost regarding remediation. In 1999 the owner of the mine went into receivership, and the final owner of the mine only bought the property on condition that the federal government would assume responsibility for the pre-existing environmental conditions of the mine site. The estimated total cost of the Giant Mine remediation is about $500, 000, 000.  There will also be a continuing cost of two million dollars per year in perpetuity or until a permanent solution is found.    Most of these costs are related to the underground storage of about 237,000 tonnes of arsenic trioxide.  These costs may not reflect the total cost of cleaning up the entire mine site, including a tailings pond highly contaminated with arsenic, which has already leaked into Back Bay, Great Slave Lake. And the Canadian taxpayer is stuck with the bill. 

In 1968 the City of Yellowknife was forced to relocate its source of water using a subterranean pipe to a point 8 kilometres away, upstream of the location of Giant Mine, simply because of arsenic leakage into the nearby local bay (Back Bay) of Great Slave Lake. That pipe now has to be replaced at an estimated cost of $2 million (+100% or -25%). And it won't be the former mine owners paying for that pipeline, it will be Yellowknife's taxpayers. This kind of situation should never be allowed to develop with regard to any proposed mine and its impacts within or beyond the perimeter of the mine.

For more more information on the Giant Mine Mess click on any of the following links:

Giant Remediation Project, Aboriginal Affairs  and Northern Development Canada

MANAGEMENT OF ARSENIC TRIOXIDE BEARING DUST AT GIANT MINE, YELLOWKNIFE, NORTHWEST TERRITORIES. Authors: N. Thompson, P. Spencer, P. Green Department of Indian Affairs and Northern Development. P.O. Box 1500, Yellowknife, NT, X1A 2R3

Alleged Arsenic Leaks.

Fixing up a Giant mess

For information on the Sudbury mess go to:


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