Clusters of gold, Poison lagoons. Cyanide springs

Clusters of gold, Poison lagoons. Cyanide springs

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By Philip M. Hocker

The low cost and widespread application of heap leaching, the rush for new deposits, and the general flexibility of the Mining Law and government officials create a dangerous synergy. Hundreds of wilderness areas and passageways for wildlife are vulnerable to open pit gold mining, thanks to cyanide leaching.
The rise of gold mining:

While part of this boom is attributed to the enlargement or reopening of old mines, it is largely the result of an impressive technological revolution: the application to gold ore of an ancient mining technique called "heap leaching", in which it is sprayed a solution of cyanide on vast accumulations of ore exposed to the open air in order to extract the gold. But there is one side of the cumulus leaching that doesn't shine: its environmental impacts.

Gold and Cyanide

Gold mining always requires the extraction of the gold itself from a much larger mass of rocky ore. When gold appears in fairly coarse grains in a gravel bed, the "panning" process makes it possible to extract it by gravity. When gold comes from rockier sources (poorer ore), more sophisticated methods are required.

Most of the deeper mines exploited in the United States during the gold rushes of the 19th century used mercury amalgamation to concentrate the gold powder after crushing the quartz in a mill. Even today, the residues from mercury amalgamation are present in the environment, polluting many streams, both in the Appalachian Mountains and in the West.

In addition to environmental damage, the mercury process was inefficient. A typical recovery of gold from the mine was 60%. The inventors looked for another method, and in Scotland, in 1887, a process was developed that used cyanide for the first time; it was immediately employed in the new Witwatersrand gold fields in South Africa. With the increased efficiency of cyanide extraction, over 97% at the mills, it was profitable to mine much lower grade minerals.

Exquisitely toxic

But cyanide is better known for being an extremely toxic poison than for its impact on the economic history of gold mining in South Africa, and for good reason. Sodium cyanide is "one of the fastest-acting deadly poisons and is well known to the public for disasters such as the Jonestown mass suicide and deaths from cyanide-contaminated Tylenol." At a lethal dose, which for humans can be as little as a tablespoon of 2% cyanide solution, symptoms manifest in seconds. Death soon follows.

However, the miners claim that there is no record of any human death from a cyanide accident, that cyanide decomposes rapidly in the medium, and that cyanide is a natural component of many biological processes. Why get so agitated?
And they are right. However, the matter is more complicated. First, the general term, "cyanide," refers to various compounds. They all have the fundamental ion CN- in common, which is carbon combined with nitrogen, but apart from this similarity the different combinations have properties that vary widely. Most public and regulatory attention is directed to the extremely toxic hydrogen cyanide gas and the simple compound NaCN, sodium cyanide, the form used in mining as a solid or as a liquid solution.

Unlike many other chemicals that are harmful to the environment, cyanide is not known to bioaccumulate - that is, it does not accumulate in animal tissues. It is not generally considered to cause mutations or to be a carcinogen, although more research is needed on the subject. Most of the cyanide ingested - some common foods contain small amounts - breaks down naturally. It is only deadly when a lethal dose is consumed at once; it then blocks oxygen transport through cell walls. Indeed, the victim suffocates despite having fully oxygenated blood; the central nervous system is the first organ to succumb.

In the natural environment, most cyanide decomposition is harmless: it decomposes when exposed to sunlight or neutral pH conditions. However, there is substantial evidence that cyanide persists in groundwater, tailings, or abandoned leach heaps, particularly where alkaline conditions are maintained.

Given the chemical mechanism of its toxicity, it is not surprising that fish are particularly sensitive to cyanide in liquid solutions. Hydrogen cyanide concentrations in excess of 0.1 milligrams per liter can be lethal to sensitive fish species, and concentrations equivalent to one-twentieth of that level have been shown to inhibit fish reproduction. The criteria established in 1980 by the Environmental Protection Agency (EPA) for freshwater aquatic life with respect to free cyanide, allow a maximum of 3, 5 micrograms per liter for an average of 24 hours, with a limit of 52 micrograms per liter at all times.

Both public attention and the response of the mining industry have focused on the spectrum of human deaths from cyanide. Its long-term health effects have been considered to be minor compared to the threat of immediate death, and are therefore ignored. However, there is good reason to suspect that a compound as aggressive as cyanide in lethal doses also has serious health effects under conditions of chronic low-level long-term exposure. Correlations have been observed between chronic low-level absorption and specific diseases in humans, and animal experiments have shown progressive damage to tissues, such as those of the nervous system.

And there is much that is simply still unknown about cyanide and its effects. We have already seen the high price of this ignorance: "There is very little information on the interactions between cyanide and birds," reported a comprehensive study in 1978.

Tragically, since then, a lot of empirical evidence has emerged. Thousands of birds have died as a result of ingesting the water from open cyanide ponds at mining sites, since as we learned later, birds are highly sensitive to cyanide.

Cumulus leaching

For centuries, miners have sought ways to extract metal from ores without having to dig the ore out of the ground, grind it into a fine powder, and treat it in expensive facilities inside a mill.

Taking this dream to its limits, this ambition gave rise to "in situ" mining, in which a chemical solution is injected into the mineral through wells drilled in the earth, to extract it by means of pumps from the extraction wells drilled. in the ore at a distance. This process depends on the mineral being naturally porous, or being fractured in place by explosions of dynamite.

Attempts have been made to apply such a process (recovery of gold by cyanide injection) in Colorado, but it is not in commercial use. The US Bureau of Mines suggests that it would be wise to try; they turn a blind eye to the possible threats of massive contamination of groundwater.

From the miners' point of view, the next best alternative to on-site mining is piling the ore into large clumps and spraying them with a metal-extracting solution. Moving a liquid containing the metal is cheaper than moving masses of ore, and the metal can be mined to produce a high-quality product. This technique, known as "tank leaching" has been used in copper mining since its inception in the Rio Tinto area of ​​Spain around 1750. In the case of copper, sulfuric acid is the common leaching chemical. This brings its own set of environmental hazards ... but that's another story.

In 1969, the US Bureau of Mines proposed the open air cyanide soak system as an inexpensive method of treating large volumes of low grade gold ores. The suggestion came at a good time. Rising labor costs made open-pit mines more competitive than underground mines that required large amounts of labor, and new discoveries were made of large volumes of low-grade gold ore. The low costs and the ability to process huge amounts of material that characterized the new technique, later known as "heap leaching," immediately attracted attention. Its use has accelerated as the ability to handle this new technology has developed.

Starting from scratch in the early 1970s, heap leaching became an industry that treated almost 4 million tons in 1980 - one third of all gold processed in the country. By 1987 the annual rate increased to 65 million tons. Bucket leaching (also using cyanide) had tripled in those 7 years, but cumulus leaching increased by 16. The growth rate continues to increase.

Still, for perspective, heap and ore deposit leaching in the copper industry uses many times more ore than the gold industry and is growing rapidly, though not as explosively as in the case of gold. (A "heap" is mineral piled up on an impermeable - or supposedly impermeable - lining (geomembrane); a deposit is simply mineral placed on the surface of the earth.)

The concentration levels of cyanide used in cyanide leaching are quite low: 0.015% to 0.25% of sodium cyanide relative to its weight in the solution. It is a common belief in the mining industry that solutions do not present a real danger. In fact, the managers of the mines that do the heap leaching like to tell visitors that they could drink the water from the solution ponds without suffering major effects. However, simple calculations show that, in fact, less than a quarter of the low concentration leach solution contains a lethal dose.

The rapidity of the expansion of gold mining in the 1980s, and the increasing exposure of the environment to unknown risks, can be seen in terms of increases in the use of sodium cyanide: North American consumption of cyanide - mainly in the mining industry - has increased from 142 million pounds (63.9 million kilograms) in 1988 to 215 million (96.75 million kilograms) in 1989, an increase of 51% in a single year. North American demand in 1990 is estimated to be 254 million pounds (114.3 million kilograms). Recently, DuPont recognized that global demand will exceed production capacity from time to time in the next 5 years, despite the fact that since 1986 manufacturing capacity has tripled.


Because cyanide is so notoriously toxic, the mining industry is used to taking preventive measures. Any discussion of cyanide has to lead to the fact that there are no reported cases of human death caused by accidental cyanide poisoning in the mining industry. This is an impressive record, and credits the care and training of many users and manufacturers, particularly DuPont.

However, limiting our concern about cyanide to human fatalities is falling victim to what one biochemist calls the "corpses in the street" theory of toxicology: the attitude that as long as no corpses are seen, all is well. Despite the absence of human corpses, there are indications that all is not well.

The most dramatic evidence has been bird deaths from cyanide poisoning at mining sites. Thousands of waterfowl deaths have been reported from cyanide poisoning; More deaths are supposed to have been hidden, but we may never know. Even more concerning is the unknown number of sick birds that have managed to fly out of the poisoned ponds, only to die elsewhere.
The mining industry has tried to reduce the number of casualties, mainly by trying to chase birds away from the lagoons using flags and noisemakers, and angrily responding that waterfowl deaths have been reduced to negligible numbers. However, discussions with officials from the Department of Wildlife (US) indicate that cooperation is still limited and reluctant. The State of Nevada has adopted a Memorandum that only requires that the lagoons of toxic solutions "be covered in such a way as to avoid, or at least inhibit, access by birds," and that the lagoons "be made in a manner not attractive to wildlife. "

The flexibility of this Nevada State Wildlife Agency policy may be due to the fact that it was actually developed by the Nevada Mining Association. Federal land prosecutors, with similar flexibility, consistently fail to notify wildlife agencies of proposals to open new mines, preventing planning of preventative measures.

There are other more subtle threats from the widespread use of cyanide, in addition to the deaths of birds and other forms of wildlife. Numerous leaks in the linings placed underneath the cumulus clouds have been reported. In several cases, leaks have caused the contamination of drinking water sources. But there are probably many more leaks that continually inject a cyanide solution into, and into, groundwater and go unnoticed.

A layer of impermeable material is placed underneath each accumulation of gold ore, to ensure that the cyanide solution containing the gold ends up in the treatment equipment, and not on the ground. After all, the recovery of gold is the goal of the operation. However, while there is an incentive to recover the solution, there is another incentive to minimize the cost of the liner. "Shortcuts" in liner construction save money in the short term. "Many deck liners are punctured during the construction of the cluster," an industry article suggests. Early heap leaching operations used to use clay liners, which, in practice, are extremely difficult to maintain without leakage.

Today, synthetic membranes are commonly used as liners, usually made of high-density polyethylene. However, as mineral clumps to be leached progressively accumulate to reach up to 150 feet (45.45 meters) in height, many liners can fail due to progressive settlement and breakdown caused by the massive weight of the material on the thin geomembrane.

Very few practical studies have been carried out on the behavior of geomembranes under these circumstances. In leaching copper, they sometimes make use of "deposits", accumulations that are simply placed on the ground without lining. Where lining has been recommended underneath copper ore deposits to protect groundwater, the industry response has been that: "... (lining) has not been shown to be viable for operations covering hundreds hectares and containing millions of tons of ore. The massive size of such operations can result in shear forces that would destroy the integrity of the liner. " If linings below copper ore deposits cannot be trusted, why then should we rely on liners placed below gold ore heaps that are of comparable size?

Cyanide can be spilled in other easier ways. In a small-scale mining operation, a barrel of chemicals can be dumped into a stream. A careless operator may miss a misadjusted valve in the complex piping loop of a large leach site and not realize it until tens of liters of cyanide have seeped into the ground. Heavy rains can overflow the lagoon and pipe system and wash toxic solutions downstream. Examples of all these types of incidents have been recorded.

To safely prevent environmental damage, a mine and a heap leach plant would have to at least be concerned with the following:

-The management of precipitations (rains), to prevent the flow of rainwater in the cyanide leaching system from causing the leaching solution to overflow into the rivers and groundwater.

-A control of surface waters to permanently divert water currents and effluents around the mining area, and prevent sediments from reaching rivers.

-A leak monitoring system below the leach pad and throughout the entire pipeline system. A double synthetic liner should be required on a specially designed clay substrate, with leakage monitoring between each of the three liners. The system should be shut down once a leak is detected in the first liner, until it is repaired.

-A safe design against failures in the entire process system, so that any spillage caused by operator errors can be contained.

-The establishment of monitoring wells in groundwater, with frequent tests. Several wells should be established at lower elevations with at least one well serving as a pattern at higher elevations.

-The protection of wildlife, including absolute measures of physical prevention of any access of wildlife to cyanide solution lagoons or tailings (waste), where concentrations exceed the state standard for water quality.

-Sanitation and ecological reconstruction of the site, with measures to prevent acid drainage and the leaching of toxic metals from abandoned mining waste heaps and leached heaps. This may require runoff controls, waste leachate treatment, or encapsulation of waste heaps with impermeable layers of clay.

A long-term monitoring program should be a requirement for all mining sites upon completion of operations and mine closure. This should include testing of surface and groundwater, and a plan for corrective action if acidic or toxic drainage occurs.

Guarantee funds for these measures to be implemented should be required before the start of a mining operation is allowed, so that taxpayers do not have to bear the burden of cleanup costs after the brightness of the operation dims. .

Beyond Cyanide

The impacts mentioned in this article are only the immediate impacts of cyanide leaching gold mining.

The long-term problems arising from the leaching of heavy metals from waste heaps from operations using cyanide leaching probably outweigh the direct impact of cyanide itself.

The low cost and widespread application of heap leaching, the rush for new deposits, and the general flexibility of the Mining Law and government officials create a dangerous synergy. Hundreds of wilderness areas and passageways for wildlife are vulnerable to open pit gold mining, thanks to cyanide leaching.

But it is not directly the failures of cyanide mining technology or the cyanide itself that are to be blamed. It is preferable to blame a series of laws and a series of mentalities that allow the coincidences of geology to decide whether an area will be exploited or not, instead of using an intelligent process of planning of multiple activities that allow its value to be weighed in relation to the of the minerals to be exploited.

The verdict

Is fear of cyanide use in mining partly unjustified? Yes, technically, it is.

Do we have the necessary knowledge to accept the risks that we are currently running with the use of this aggressive poison? No, definitely not.

Are the government bodies we depend on to control risks acting responsibly and firmly?No, sadly they are not. The design requirements are inadequate, the inspection of the corresponding direction is minimal, the application of the law and the fines are nothing but words. Since the spills have basically occurred in remote places, since the victims have not been human, we have not become fully aware of this problem. We are spraying tens of thousands of tons of one of the most dangerous poisons known to mankind throughout the environment. There will be more deaths if tight control is not put in place over this program, and the deaths will not just be in birds and animals. Cyanide manufacturers, users, and regulators need to adopt an attitude of: "Yes, we have a problem. We are going to solve it; come and see. " But in many cases, the answer is, "There is no problem. Go away." Obscenity suppressed. That attitude is not going to reassure public opinion, and when spills do occur, the reaction will be bitter. The matter should not get to that point. It is not necessary. But I'm afraid it will end that way.


Taken from: Mineral Policy Center Educational Materials, Fall 1989, pp.6-11. Free translation made by the Costa Rican Ecologist Association-Friends of the Earth Costa Rica. Bold paragraphs have been highlighted by the article editor
This article is the result of investigations by the Mineral Policy Center in Washington and at various mining sites, conducted over the past 18 months. We thank Frederick W. de Vries of E.I. duPont de Nemours & Company, Susan van Kirk, Jim Jensen of MEIC, Dr. Glenn Miller, Steve Botts of Newmont, various anonymous agency officials, and Congressional staff for assistance and data sources. In particular we want to thank Representative George Miller for his efforts in an attempt to reduce the number of migratory bird deaths. The opinions expressed in this article are those of the author, and in expressing my thanks to these friends it is not my intention to imply that they agree with them.

Video: Robert Glenn Ketchum: Using Pictures to Save The World (July 2022).


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