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.
- Vat leaching is where extracted ore is mixed with a cyanide solution in vats. The resulting waste, known as tailings, is stored behind large dams (tailings impoundments).
- The more common process is heap leaching, where a cyanide solution is sprayed over huge heaps of crushed ore. The solution slowly trickles through the heap, dissolving the precious metals into the solution as it drains.
Heap leach piles are built atop leach pads that collect the gold-bearing cyanide solution and channel it into a holding pond where the gold can be removed and the cyanide solution recycled through the heap.
Unfortunately the leach pads often leak. And holding ponds too often overflow during storm events.
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:
- Kumtor Gold Mine, Kyrgyzstan, central Asia, 1998: A truck carrying 2 tons of sodium cyanide crashed into the Barskoon river. 2,600 poison cases and 4 deaths were reported in the aftermath.
- Zortman-Landusky Mine, Montana, 1982: 52,000 gallons of cyanide solution poisoned the aquifer that supplies fresh drinking water for the town of Zortman. The accident was discovered when an employee of the mine noticed the smell of cyanide in his tap water at home. Thanks to a 1998 citizen-passed law, cyanide leaching is now banned in Montana.
In recent years, a string of cyanide-related mine accidents has added to environmental concerns:
- Mexico, 2014: 500,000 gallons of cyanide solution spilled from a retaining pond at the Proyecto Magistral mine, after heavy rains.
- Aural Gold Plant Romania, eastern Europe, 2000: A tailings dam ruptured, spilling 3.5 million cubic feet of cyanide-contaminated waste into the Tizsa river and into the Danube, killing aquatic wildlife and poisoning water supplies as far as 250 miles downriver in Hungary and Yugoslavia
- Summitville Mine, Colorado, 1992: Summitville gold mine was responsible for contaminating 17 miles of the Alamosa river with cyanide and other contaminants.
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:
- The Code is voluntary, meaning the most irresponsible operators -- arguably those in most need of oversight -- don’t follow it.
- The Code doesn’t discourage or minimize cyanide use, or encourage the use of alternatives.
- The Code doesn’t prevent spills. Even after signing and implementing the Cyanide Code, Golden Star Resources’ Bogoso/Prestea gold mine in Ghana suffered from cyanide spills.
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:
- Earthworks Cyanide Leach Packet
- Earthworks Cyanide Fact Sheet
- Earthworks Cyanide Uncertainties
- Earthworks More Cyanide Uncertainties
- UNEP The Cyanide Spill at Baia Mare, Romania: Before, During and After
- Status of cyanide use
- USGS Cyanide toxicity in birds
- IRMA Standards for Responsiblle Mining Draft 1.0 on the management of Cyanide
- Cyanide Code