Since the 1970s the mining industry has used cyanide solution to extract gold from ore on an industrial scale. 

The average large gold mine uses over 1,900 tons of cyanide per year. A rice grain-sized dose of cyanide can be fatal to humans and even smaller amounts can be fatal to fish.

However, cyanide is highly toxic. When it mixes with water or becomes a gas it becomes a threat to aquatic and terrestrial – including human -- life even in small doses.

How is cyanide used in mining?

Mining companies use cyanide because it is extremely efficient at recovering gold from ore.

Because cyanide is efficient, it makes mining profitable at lower ore grades. Consequently modern mines are much larger, and create vast open pits and produce huge quantities of waste. A single gold ring creates more than 20 tons of mining waste -- thanks to cyanide.

There are two types of cyanide leaching processes used in mining.

Cyanide in the environment

Cyanide use is inherently dangerous to the environment. Cyanide spills have resulted in major fish kills, contaminated drinking water supplies and harmed agricultural lands.Fish and other aquatic life are particularly sensitive to cyanide exposure at small concentrations.

The mining industry and regulators claim that cyanide isn’t a long term problem because it rapidly breaks down in surface water (streams and rivers) into relatively harmless compounds (nitrates, ammonia), but this is only part of the cyanide story. Cyanide also breaks down and reacts with other chemicals to form compounds that are toxic to fish and other aquatic organisms.

Cyanide can be a very significant problem when it seeps into groundwater as a result of spills or leaks from the leach pad, holding pond or tailings impoundment. In the absence of sunlight, cyanide can persist for a long period of time and be a source of contamination to drinking water aquifers.  Contaminated groundwater can also be a persistent source of cyanide pollution to neighboring streams that are hydrologically connected.

For example, at the Beal Mountain Mine in Montana, which closed in 1998, cyanide has seeped into groundwater that feeds neighboring trout streams, resulting in cyanide violations in those streams long-after the mine closed (see diagram of violations from 2003-2005).

Source: Tetra Tech, 2006 Surface Water Quality Monitoring Summary, Beal Mountain mine.

Cyanide and public health risks

As cyanide use continues, so do serious accidents and spills. Water supplies that have been contaminated with cyanide have threatened lives and resulted in deaths:

Cyanide spills

In recent years, a string of cyanide-related mine accidents has added to environmental concerns:

The international response to cyanide threats & spills

After the Aural Mine spill in Romania, an international group of stakeholders created the International Cyanide Management Code for the Manufacture, Transport and Use of Cyanide in the Production of Gold (Cyanide Code).

The Cyanide Code is a voluntary compliance process for companies that want to more responsibly manufacture, transport and manage cyanide use in gold mining. An independent third party assesses a company’s compliance with the Cyanide Code in a publicly-available audit. Though the Code is widely adopted within the mining industry, it has significant shortcomings. Among them:

Community response to cyanide spills

In the wake of spills at Zortman-Landusky, and state taxpayers financial responsibility for cleanup after the mining company went bankrupt, the citizens of Montana (state motto, “The Treasure State”) shocked the industry and the world when they voted by direct ballot initiative to ban cyanide heap leach mining - the most spill prone type of cyanide mining.

The Montana ban has served as a model for other jurisdictions, and served as a cautionary tale to the mining industry as to the strength of potential reaction to irresponsible mining. Montana is a politically conservative, historically pro-mining state.

The bottom line

The record demonstrates that cyanide-leach mining is not being practiced safely. The hardrock mining industry has a history of cyanide spills, with billions of gallons of cyanide contamination released into the environment since the 1970s. Spills and leaks – which continue to this day – are probable and very dangerous to the environment, wildlife and humans.

For more information:

Tagged with: mining, heap leach, cyanide

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