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An exhaustive description of open-air mining and cyanide heap leaching, translated from the original in Spanish found at the Costa Rican website semueve.netfirms.com . Text prepared by the Costa Rican Ecological Association - Friends of the Earth (AECO - AT) for the National Front Against Open-Air Mining, Costa Rica.

1.1. WHAT IS OPEN-AIR MINING?

1.1.1. Definition And Description Of Open-Air Mining And Its Impacts

(...) Open-air mining is one of those industrial activities that has important environmental, social and cultural impacts. It is also unsustainable by definition, as exploitation of a given resource must lead to its total depletion.

The technical innovations adopted by the mining industry in the last sixty years have radically changed it. Whereas mineral extraction from rich underground veins was the main activity before, now many companies specialize in open-air exploitation of low grade ores spread over large surface or near-surface deposits.

Open-air mining first removes the soil and rock layers above the mineral deposit; in order to expose these low grade ores, this is done over wide areas. Today's modern digging equipment, conveyor belts, massive machinery, improved consumables and fluid conveyance piping make it possible to lay low a whole mountain in a matter of hours. Thus, even if a ton of ore yields under a gram of gold, this kind of mining is still profitable.

The general consensus expressed by the literature on this field is that no industrial process is as environmentally, socially and culturally aggressive as open-air mining (OAM).

Open-air gold mining employs huge amounts of cyanide, a very toxic substance that separates gold from its surrounding material. Vast areas of land are involved and, as this low yield ore is excavated, gigantic craters are left behind, some as huge as 150 hectares (370 acres) wide and 500 meters (460 yards) deep.

Vaughan's opinion (1989) is that "on environmental and social terms, no enterprise is more devastating than surface [open-air] mining".

According to Kussmaul (1989), in order to fully comprehend the environmental impact of any mining enterprise, four factors must be taken into account:

1. Its size, meaning the operation's production volume and its consequences, such as the degree of disturbance and waste (both solid and liquid) left behind.

2. Its location, meaning not only the immediate placement of the mining operation, but also the situation of population centers in relation to it, as well as the characteristics of the local natural environment and topography.

3. The kind of exploitation method employed, which depends on the characteristics of the mineral deposit to be exploited. There are three main methods, each closely related to impacts of different extent in nature and society:

a. Open-air (or surface) mining,
b. Underground mining,
c. Dredging.

4. Characteristics of the minerals to be extracted and their intended use, as this determines the treatment they shall receive as they are mined. Minerals can be divided in to:

a. Non-metallic minerals (such as those used to make construction materials) which require little physical treatment, like crushing and grinding, and no chemical treatment at all.

b. Metallic minerals, which require a high level of processing as well as the application of many chemical reactants, all of which generates great amounts of waste.

1.1.2. Impacts Of Mining

There are different stages in any mining activity, each of which is related to a particular kind of environmental impact. In a wide sense, these stages are the following:

* prospecting for deposits and surveying the land,
* development and setup of mines,
* exploitation of mines,
* treating the extracted ores and minerals in order to obtain marketable products.

Salinas (1993) cites the following individual activities that can have an environmental impact during the PROSPECTION phase:

* setting up roads to approach the concerned area,
* topographical and geological mapping,
* setting up camps and auxiliary installations,
* geophysical works,
* hydrogeological research,
* digging of reconnaissance wells and ditches,
* sample collection

During the EXPLOITATION phase, the verified impacts will depend on the mining method employed in a given operation. According to different authors (Vaughan (op. cit.), Salinas (op. cit.) and Elizondo (1994)), the main environmental effects of open-air mining (OAM) in its exploitation phase are:

* Perturbation of the surface: OAM devastates the surface, severely modifying ground morphology and uncovering and piling up great amounts of barren material. It disrupts or outright destroys cultivated and wildlife areas, sometimes even altering the flow of watercourses and creating vast lakes or lagoons where waste material accumulates.

* Perturbation of the environment in general: OAM radically transforms the landscape, which loses any scenic appeal it might have had. Also very disruptive is the amount of noise produced by processes such as digging, crushing, grinding, energy generation, transport, loading and unloading of ores and tailings both from the mine and the mill.

* Air pollution: The air can be polluted by solid impurities that can reach the lungs, such as dust and toxic or inert fuels produced or employed at different times during the mining process. Possible additions to this are residual gases or vapors containing cyanide, mercury and sulphur dioxide, liberated by incomplete combustion processes, ponds or lagoons with stagnant, polluted water and/or decomposing organic material.

* Perturbation of surface water: The silty quality of some of the waste produced at the exploitation area may cause the sedimentary layers of the region's rivers to grow. Dams and oxidation ponds, badly built, maintained or used, can lead to the contamination of surface waters by spillage of liquid waste. Equally damaging and likely are the inadequate usage, storage and/or transport of different consumables, such as fuels, lubricants and chemical reactants.

* Perturbation of phreatic or groundwater: Groundwater can be contaminated by used oils, reactants and mineral salts leached by rainwater from the waste piles of solid post-treatment residuals. Likewise, spillage or leakage from tailings dams, or polluted water that escapes during the extraction process, may reach the phreatic layers. Finally, if local groundwater is used to supply the significant needs of an open-air mining operation, the water table may drop significantly.

* Soil perturbation: OAM implies the total removal of soil from the exploitation zone and leads to the dessication of the surrounding area's soil. Agricultural and farming yields are also diminished, and sometimes the ground can subside or turn into a bog if the water table rises again after the mining operation is over. Besides that, waste piles undermine soil fitness.

* Impact on flora: OAM necessitates a removal of the mined area's flora, as well as a partial destruction or perturbation of the surrounding flora, mostly due to the alteration of the water table. Forests are particularly vulnerable, as they may be destroyed not only by the mining activity itself, but also by the mounting pressure to quickly exploit them before mining takes place.

* Impact on fauna: Fauna is disturbed and/or driven away by noise and air and water pollution, as well as sediment accumulation in rivers. Furthermore, the erosion of waste piles will leach contaminants into the water cycle, making aquatic life -and through it, other animals, even those living far away- particularly vulnerable to poisoning.

* Impact on human populations: OAM may provoke conflicts about land usage rights, stimulate an uncontrolled proliferation of settlements (with the social problems such lack of planning entails) and destroy areas with tourism potential. The return of activities such as fishing and farming diminishes due to poisoning of soil and water and changes in watercourses and sedimentation levels. OAM's local economic impact can be very negative, as an operation that is essentially temporary displaces or makes outright impracticable other present and/or future economic undertakings of a more sustainable nature.

* Microclimate changes: OAM may cause changes in the local microclimate, and through these a proliferation of pathogen vectors in the ponds and lagoons filled with stagnant water.

* Lasting scenic impact: OAM leaves deep craters in the landscape. Filling them would be extremely costly, enough to make a mining operation unprofitable.

1.2. OPEN-AIR MINING OF GOLD THROUGH CYANIDE HEAP LEACHING

The growing interest of very different companies in gold mining is due to the rising prices of this metal (nowadays, an ounce is quoted at around US$ 395), which means very juicy profit margins, as well as the recent development of profitable methods of mining gold out of very poor deposits. We are talking, of course, of cyanide heap leaching technology, which does indeed prove very profitable when only material investment costs are considered.

According to DuPont Corporation (cited by Alberswerth), it is economically viable to exploit ores that contain as few as 0.01 ounces of gold per ton. Cyanide heap leaching technology supplanted mercury amalgamation, now considered an inefficient mining method, as it managed to extract only 60% of the gold present in the ore, compared to the 97% allowed by cyanide heap leaching (amalgamation is the process by which two metals become bonded; in this case, gold bonds with mercury and is in this way separated from its ore).

The Gold Institute (Young, 1993) reports that gold production by cyanide leaching went from 468,284 ounces in 1979 to 9.4 million ounces in 1991. This latter number means that over 683 million tons of ore were leached with a cyanide solution in 1991 alone.

1.2.1. Cyanide Heap Leach Mining: Technology and Technique

Mining operations that employ cyanide heap leaching technology in open-air mines must have at their disposal these six main elements:

* An ore source
* An ore heap and a pad to build it on
* Cyanide solution
* Delivery and collection systems
* Solution storage ponds
* A plant for metal separation

Most cyanide heap leaching operations use open-air mining to get the ore; as we already know, OAM disturbs great extension of land. Sometimes waste material previously extracted constitutes the ore to be processed. This is crushed and heaped up over a leach pad.

Heap size varies. A small heap may be made up of 6,000 tons of ore, whereas a large one may contain up to 600,000 tons and be hundreds of feet tall and hundreds of yards wide. Thus, leach pad size varies, too: it may go from 1 to 50 acres (1 hectare = 2.47 acres). Pad size depends on the magnitude of the operation and leaching technique. Usually leaching pads are lined with synthetic and/or natural materials, the function of which is to TRY to prevent leakage. Sometimes, mines employ double or triple linings, the argument being that this is still economically viable and advantageous for the environment. Nevertheless, the time an operation lasts is infinitely shorter than the time that follows it, and given enough time, ALL materials wear down. Therefore, not only are leakages not avoidable with current practices: they are guaranteed to happen.

Once the crushed ore is heaped onto the pad, the heap is uniformly sprayed with a cyanide solution. A sprinkler system typically distributes this solution at a rate of 0.005 gallons per minute per square foot; for a small heap (say, 200 x 200 feet), this rate is equivalent to 200 gallons per minute. Cyanide solutions contain between 0.3 and 5 pounds (0.14 and 2.35 kg) of cyanide per ton of water, which means an average cyanide concentration of 0.05% (250 milligrams per liter). As the cyanide solution percolates through the heap, it washes the microscopic gold particles off the ore and bonds them to the cyanide. Leaching cycles may last from a few days to several months, depending on heap size and ore quality. Thanks to the action of gravity, the gold bearing "pregnant" solution flows towards a storage pond; from here, pumps or lined ditches drive the solution to the metal separation plant.

The most common methods employed to separate gold from cyanide are zinc precipitation (Merril-Crowe method) and carbon absorption. In the first case, powdered zinc and lead salts are added to the pregnant solution. Gold precipitates (separates) as zinc bonds with cyanide; this precipitate is later melted and the final products of this process are gold ore bullion and a "barren" cyanide solution, which is transferred to a tailings dam. Slag material, made up of impurities including heavy metals, is also generated and usually unloaded onto a waste heap.

The alternative preferred in most mining operations is, however, carbon absorption, particularly in smaller mines and in those cases in which there is a smaller amount of silver associated with the gold in the pregnant solution. In this process, the solution is pumped through columns of activated carbon. The gold and silver in the liquid stick to the carbon, whereas the barren solution, which still contains cyanide, is taken to a tailings pond. Gold and silver are separated by means of hot caustic soda; later, this new solution passes through a cell containing a stainless steel anode and a cathode to plate the metal. Spent carbon is reactivated in an oven and reused.

In mining operations where leaching is used, storage dams are employed for keeping the cyanide solution before spraying it over the ore piles, once it is "pregnant" with the leached gold, and also when the gold has been separated and the solution has become "barren". Due to environmental and economic reasons, all storage ponds include linings that attempt to prevent cyanide leakage.

When managing cyanide solutions, this kind of operation may use either a "closed" or an "open" system. In an "open" system, the "barren" solution remaining once the gold has been taken out is treated or diluted until cyanide concentrations comply with what is mandated by water quality laws; it is then released into the environment. In a "closed" system, the "barren" cyanide solution is recycled or reused, so that the need for more cyanide is minimized and the demands made by the environmental laws applicable at the particular mining site may be met. Several mining operations being carried out in federal land (USA) are making use of "closed" systems.

1.3. ENVIRONMENTAL IMPACTS OF MINING GOLD BY THE CYANIDE LEACHING METHOD

Mining operations that use cyanide leaching technology have, by definition, a strong environmental impact that may, in many cases, reach the proportion of true environmental disasters.

1.3.1. About The Bibliography On This Topic

The sizable and many times dramatic environmental and social impact of this kind of mining is amply documented. We recommend the following authors, among others: Alberswerth et al. (op.cit.); AMIGRANSA (op.cit.); Bliss & Olson (op.cit.); Bravo (1994); Danuron Dickson (op.cit.); Emberson-Bain (op.cit.); Hartley (1995); Hocker (1989); Knudson (1990); Mineral Policy Center (1988); Mineral Policy Institute (op.cit.); Moody (op.cit.); Panos Institute (1996), Reece (1995); Sartorio de Ponte (op.cit.); U.S. Department of Labor (1981,), Young (1993).

In the case of Costa Rica, the only mine that has functioned with open-air techniques is Macacona, which constitutes the only case [in that country ] for which both environmental and social impacts can be documented. In this respect, ICEA (1989) and Umaña (1990) are recommended.

1.3.2. About The Use Of Cyanide In Leach Mining

Given the high toxicity and natural reactivity of cyanide, use of this substance is one of the main worries in mines that use leaching technology. The deleterious effects of cyanide have been documented in fish, wild life and humans.

a. Toxicity of Cyanide

Cyanide is extremely toxic for both plants and animals. Cyanide spills can kill vegetation and have an impact on photosynthesis and plants' reproductive capabilities. As for animals, cyanide can be either be absorbed through the skin, ingested or inhaled. When in the air, concentrations of hydrogen cyanide equal to 200 parts per million (ppm) are already lethal for animals, whereas in water, concentrations as low as 0.1 miligrams per litre (mg/l) are also lethal for sensitive aquatic species. Besides, sub-lethal concentrations have an effect on reproductive organs, both in animal and plant life.

In case of ingestion, a lethal dose for a human being is as little as 1-3 mg/kg of body weight; if assimilation occurs through the skin, the number goes up to 300 mg/kg, and to 100-300 ppm if inhalation occurs. This means that a portion of cyanide smaller than a rice grain is enough to kill an adult. Long term exposure to a sub-lethal dose might cause headaches, appetite loss, weakness, nausea, dizziness and irritation of the eyes and respiratory organs. In order for workers to prevent harmful contact with cyanide, special care must be taken when handling it. Nevertheless, according to the mining industry, there are no cases of human fatalities in mines that use cyanide leaching techniques.

In the face of this fact, many times used by mining companies as an argument in their favour, Philip Hocker (op.cit.) says that "to limit our concern over cyanide to human fatalities is to fall prey to what one biochemist calls 'the dead body in the street theory of toxicology:' the attitude that if you don't see corpses, everything is okay. Despite the absence of human corpses, there is evidence that everything is not okay."

Mining workers may come in contact with cyanide, particularly during the mixing of the cyanide solution and when gold is recovered from it. For mining workers, the main risks are cyanide dust, cyanide vapors (HCN) from the solution and contact of cyanide with the naked skin.

1.3.3. On The Impact Of Cyanide On Wildlife and Bodies Of Water

Although profitable for mining companies, cyanide heap leach mines are environmental time bombs, as demonstrated by the ample study carried out by the National Wildlife Federation of America (Alberswerth et al., 1992). The following concerns are cited from that document:

* In the process of extracting millions of tons of ore from open-air mines, cyanide leaching operations disrupt wild life habitats and water basins, which in turn may pose various dangers for both health and environment. Several phases of the mining process may have negative impacts of this kind.

* Cyanide ponds seduce wildlife. The death of wild animals, particularly birds attracted by the lure of open water, has frequently been recorded around these ponds. Even though there are methods to prevent these deaths, such as fences and nets to cover leaching platforms and storage ponds, the general extension of the wild animal mortality rate in the installations that utilize the said process has raised worries in the U.S. Fish and Wildlife Service.

* After leaching, the processed ore heaps still hold vestiges of the highly toxic cyanide solution, as well as concentrated heavy metals that have precipitated from the ore. Many mining operations opt for treating these waste heaps by rinsing them with fresh water until the cyanide concentration drops below the maximum amount allowed (a number that varies in the different states/countries). Once this is accomplished, the ore heaps are usually left where they are. Compaction and the effort to ecologically reconstruct the site may or may not be attempted.

* If rinsing of the spent ore and waste rocks is not carried out, or if they are left untreated, cyanide may continue to seep into the environment. Both cyanide and the heavy metals it liberates (such as arsenic, antimony, cadmium, chrome, led, nickel, selenium and thallium), as well as other toxic substances found in the heap (such as sulphides), are a threat to gullies, rivers and lakes, for underground water, for fish, wildlife and plants (cited also by Hartley, 1995).

Other authors call attention to the following:

* Cyanide solutions used in mining may seep into the underground (phreatic) water table (Engelhardt, 1989, cited by Hocker, 1989; Hilliard, 1994).

* The long term problems resulting from the leaching of heavy metals from waste heaps probably exceed the direct impact of cyanide itself. (Hocker, 1989).

Even in the U.S.A., current federal and state regulations do not properly address the impacts of cyanide leach mining. In spite of the great increase of this kind of gold mining and its known impact, the responsible federal and state bodies have been less than expedient in dealing with the problem.

1.3.4. On Typical Accidents That May Occur In Open-Air Gold Mines That Employ Cyanide Leaching

1.3.4.1. About Cyanide Leaks Into The Environment

The cyanide used in the cyanide leaching process may -and does- cause environmental damage. The two most common kinds of leak result from:

a. Faulty lining (geomembranes placed under ore heaps and ponds), which allows seeping due to inadequate design, manufacture defects, poor installation and/or damage (holes) inflicted during the mining process.

In his excellent review of geomembrane liners used in mining, Reece (op.cit.) states: "All liners leak. That is the most important thing to understand about the geomembranes used in cyanide leach mining. The only difference among them is that some have had leaks, whereas others will" (italics from author's text).

b. Cyanide solution spilling over from storage ponds, which causes damage to plants and animals that come in contact with it in lethal concentrations. These spillages also threaten underground (phreatic) waters.

Generally, storage ponds are designed to resist great storms and floods. Nevertheless, they do not always manage to prevent overflows. The heavy metals and cyanide-contaminated water that escape from such a pond are most damaging when they flow directly into a natural water course. Concentrations may be enough to kill fish and other types of aquatic life, as well as tainting drinking water resources.