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"Giant Gold Mine, NWT: A Complex and Expensive Legacy of Arsenic Contamination"

By: Heather Jamieson, Geological Sciences and Geological Engineering, Queen’s University

Abstract

The case of the Giant mine illustrates how a large, long-lived gold (Au) mine has resulted in a complex regional legacy of arsenic (As) contamination and an estimated remediation cost of almost one billion Canadian dollars. The mine, located a few km north of the city of Yellowknife produced more than 7 million troy ounces of Au. Arsenopyrite-bearing Au ore was roasted from 1949 to 1999 as a pretreatment for cyanidation. Poor emission controls in the early years resulted in the release of an estimated 20,000 tonnes of roaster-generated As2O3 to the surrounding environment through stack emissions. Other roaster products include As-bearing iron oxides deposited with tailings and re-mobilized into creek and lake sediments.

Ore roasting increases the solubility, toxicity, and bioaccessibility of As by converting sulfide-hosted As to oxide-hosted As. At Giant, understanding the processing history is critical to characterizing mine waste, assessing the risk to human and ecosystem health, and predicting long-term stability and optimal management. Roasting is still used worldwide today for improving recovery of refractory Au ores and for removing As from copper ores, but in modern operations As-bearing roaster products are managed as hazardous waste or sold for use in various industrial applications.

The history of Giant mine is also a remarkable example of how relations between mining companies, local population, and government authorities have evolved over the last 75 years. Local Aboriginal communities were not consulted when mines were first established in the 1930’s and 1940’s yet were affected by removal of access to their traditional land and exposed to As contamination along with other local residents. In contrast, modern mining operations in the Northwest Territories require multi-stage permitting and extensive community consultation.

The objective of this paper is to report the lessons learned from research on the history and nature of As contamination at the Giant mine site. Factors that resulted in this widespread and complex contamination are discussed in the hope that modern mining will avoid such potentially damaging and costly problems and that risk assessment of other abandoned sites will benefit this example.

Bio

Heather E. Jamieson’s expertise is in the area of environmental geochemistry, particularly the mineralogical controls on the mobility and bioaccessibility of metals and metalloids such as arsenic, antimony, rare earth elements and lead in mine waste. She has pioneered the application of synchrotron-based X-ray experiments and other microanalytical methods to metal speciation in mine tailings, soils and sediments.

Much of her fieldwork is in the Canadian Arctic but she has also conducted research in Nova Scotia, California, Montana, Spain and Australia. She supervised more than 30 graduate students, most of whom are now working as environmental consultants or regulators. She has published more than 50 papers and has recently coedited and contributed a chapter to a new book Arsenic: Environmental Geochemistry, Mineralogy and Microbiology.


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