INCIDENTS

Omai Mine - Tailings Dam Failure, Guyana, August 1995

BACKGROUND:

The tailings dam at Omai Gold Mines Ltd. failed during the night of August 19-20, 1995, resulting in the release of an estimated 4.5 million m³ of cyanide-bearing mill process solution into the Omai River, which feeds into the Essequibo. Three days after the accident, Guyanese President Cheddi Jagan declared 80 km of the Essequibo an environmental disaster zone.

Omai Gold Mines Ltd. is a joint venture of Montreal-based Cambior Inc. (65 percent share) and Denver, Colorado-based Golden Star Resources (30 percent) with Guyana's government, holding a 5 percent stake. In August, 1991, the company entered into a Mining Agreement with the Guyana Government to mine for gold, other precious metals as well as diamonds in an area comprising 11,232 acres in the Omai River basin and catchment. The mill was built, the pond constructed, and the company commenced full gold production in January, 1993. Since then, workers have mined the site for ore, pulverising and drenching it in a cyanide solution to leach out the gold. The failed dam contained cyanide-treated wastes that had been accumulating for two years.

TYPE OF INCIDENT:

• Tailings dam failure from internal dam erosion

• Release of 4.5 million m³ of cyanide-bearing mill process solution

IMPACTS:

• 80 km of Essequibo River was declared an environmental disaster zone

• Loss of animals and aquatic life in the river system

• Children suffered nausea, lesions and skin rashes

• Over 50% of the local residents reported some type of health effect

• Severe effect on potable water supply

• Affected food supplies of 33% of households

• Three cases of suspected cyanide poisoning reported

• Possibly affected the life of nearly 50,000 Amerindians

• Cleanup costs = G$426 million (government share = G$314 million)

LINKS:

• Dam Review Team. Preliminary Report on Technical Causation Omai Tailings Dam Failure. Submitted to Guyana Geology and Mines Commission. 16 November 1995 

• Report of Commission of Inquiry into Discharge of Cyanide and Other Noxious Substances into the Omai and Essequibo Rivers. 5 January 1996.

• The Ugly Canadian: The Philippines, Guyana, Omai

• Technical Issues - Tailings

• Technical Issues - Cyanide Management

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