Gold rush in Uruguay

Gold rush in Uruguay

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By Víctor L. Bacchetta

Shortly before the Aratirí project reached public status, gold mining took firm steps in Uruguay and was placed as an example, but not only is this assessment questionable from an environmental angle but, given the current escalation of projects, it is another key sector of the debate on the fate of the country's natural resources.

105 kilometers from the city of Rivera, Minas de Corrales was born in 1878 when the French Gold Mines Company of Uruguay settled in the place, attracted by the gold rush of that time. The first settlers came from Germany, France, Italy, the Basque Country, England, Argentina, Chile and Brazil. The rest of the population was native to the place.

Livestock was also one of the main activities. When it was declared a town, on November 9, 1906, Minas de Corrales was surrounded by excellent natural grasslands for raising and fattening cattle. The heyday of gold in the late 19th and early 20th centuries ended in 1916, when mining became unprofitable.

When the mines were closed, most of the foreigners left and the life of the town declined. In 1996, a Canadian, American and Australian multinational returned to explore the area. After several changes of firms, the Canadian Orosur Mining began extraction in San Gregorio in 2003 and in 2004 extended it to the Arenal deposit, 3 km southeast of that deposit.

According to figures published that year, Orosur exported doré gold bars (70% gold, plus silver and copper) for two million dollars per month, declaring an expense of one million dollars and a contribution to the state of 8,000 dollars. in the same period. Already then it was carrying out prospecting and exploration work in eight more departments.

Orosur is presented today as a regional company, with an annual production of 95,000 ounces of gold and "700,000 hectares of exploration permits", of which 600,000 ha would be in Uruguay and 100,000 ha in Chile. By Uruguayan law, a single firm could not retain that area in mining titles, but Orosur practices reproduction in joint-stock companies that, consented to by the state, allows it to multiply surfaces and terms.

Open sky

The rationale for open pit mining is that when ore is close to the surface, it costs less to extract from above than through underground galleries. To this fact, which also implies a less risky procedure, is added the development of technologies to process minerals with very low concentrations of metal.

Today, the minimum cut-off grade of a gold deposit (the minimum percentage of the metal that makes its exploitation profitable), if it is done underground, is 1.5 grams per ton (g / tn) and in the open air. it is 0.5 g / tn. These figures allow us to get a fairly accurate idea of ​​the only physical impact of an open pit gold mine.

This means that to obtain one gram of gold in an open pit mine, up to two tons of the mineral can be extracted and to this volume, the rock that surrounds the mineral vein must be added, which is also necessary to extract. Typically, the volume of rock discarded on the side of the crater is more than four times that of the ore mined.

An example, taking the data from Orosur in 2008. In San Gregorio, with a grade of 2.45 g / tn, they produced 2819.8 kg (90,668 ounces) of gold, extracting 1,796,608 tn of ore and 11,458,993 tn of rock. Rounding off the figures, the conclusion is that for every gram and a half of gold, one ton of ore and almost seven tons of rock were removed.

This fully explains the size of the craters, rock mountains, and tailings reservoirs (final disposal), as well as the amounts of explosives and energy required to fracture, transport, and grind the materials. Ignoring the physical and chemical impacts of the above, we go to the gold separation method.

Cyanide role

The growing interest in gold mining stems from both the rise in gold prices (see chart) and the recent creation of profitable methods for extracting gold from extremely poor deposits. Cyanidation is a technique for the extraction of gold from low quality ore, converting the gold into soluble complex metal ions.

This technology has come to replace the recovery of gold by amalgam with mercury, a process that saves only 60% of the mineral, compared to more than 97% obtained with cyanide. According to the Gold Institute, global production of gold by cyanide leaching increased from 468,284 ounces in 1979 to 9.4 million ounces in 1991.

Most of the operations that use cyanide are open pit mines. The ore rocks are crushed and piled up on a leach pad. The size of the piles and the platform depends on the magnitude of the operation and the technique used. Rigs often use a membrane to try to prevent leaks.

Once the crushed ore is stacked on the platform, it is sprayed with a cyanide solution that leaches (lava and amalgamates) the microscopic gold particles as it passes through the pile. The combination of cyanide and gold - called the impregnated solution - flows by gravity into a reservoir from where it is sent to the metal recovery plant.

The cyanide solution without the gold ("sterile") is diverted to a reservoir as a final destination. Other materials containing heavy metals that are sent to another waste material deposit are also discarded. All storage reservoirs use membranes made of synthetic and / or natural material to prevent cyanide spillage.


Reservoirs are designed to prevent seepage and withstand storms and floods, but they do not always prevent overflows. The two most common classes of cyanide releases to the environment from leach operations are the result of:

a) The membranes below the piers and reservoirs that allow leaks due to improper design, manufacturing and installation defects, and damage during the process.

b) Overflows from tailings reservoirs that damage plants and animals, come into contact with lethal concentrations of cyanide solution, and pose a long-term threat to groundwater.

The San Gregorio tailings reservoir was 75 ha (hectares) in size and now a second one of 47 ha has been added. The waterproofing consists of a clay base and a polyethylene membrane. According to a spokesperson for the company, it is "conditioned for a period of time exceeding hundreds of years." And then what?

"All membranes have leaks. That is the most important thing to understand about the geomembranes used in mining that uses cyanide leaching. The only difference between them is that some have leaks and others will," says researcher B Reece in his review of membranes in gold mining.

The argument often used by mining companies is that there are no human fatalities in mines that use cyanide leaching. This is what biochemists in toxicological theory call "dead in the streets." In other words, as long as there are no sudden deaths of human beings, everything is in order.

The impacts

Open pit mining removes the fertile soil layer to exploit low-quality deposits from the subsoil. Powerful machines, explosives, new chemical inputs and pipelines allow the removal of mountains and the transfer of mineral to great distances and in a short time, exposing huge craters and deposits of polluting waste.

For the process to be profitable, the ore must cover large areas and be close to the surface. Craters are dug that can reach hundreds of hectares in surface and up to 400 meters deep. The debris occupies surfaces several times larger than that of craters and can reach a height of one hundred meters.

Mining operations that use cyanide carry high environmental impacts. Cyanide spills can kill vegetation and affect photosynthesis. In animals, cyanide can be absorbed through the skin, ingested, or breathed in. Even very low concentrations affect the reproductive systems of animals and plants.

A portion of cyanide less than a grain of rice can kill an adult human. A sublethal dose can cause headaches, loss of appetite, weakness, nausea, vertigo, and irritation of the eyes and respiratory system. Workers often come into contact with cyanide when preparing the solution and later recovering the gold.

Cyanide is not the only poison associated with gold mining; When rock is exposed to rain and air for the first time, sulfides react with oxygen to produce sulfuric acid. This acid releases heavy metals such as cadmium, lead, and mercury, which are harmful to people and fish, even at low concentrations.


In Rivera, Orosur production continues in San Gregorio and Zapucay, but gold exploration reaches the Isla Cristalina Belt, with drilling in Veta Rodrigo and Castrillón, to the west, and Vichadero, Cerro Chato, Vaca Muerta and Cortume to the east. And in the rest of the country, they extend to Soriano, Colonia, Florida, Treinta y Tres; San José, and Lavalleja.

The usual argument to legitimize these projects is the contribution of employment, but outside of Minas de Corrales, which was born and survived with these mines, in the rest of Rivera and the other departments, mining faces owners and tenants of agricultural-livestock operations that are affected as soon as the mining company enters their fields.

On the other hand, the labor history of Orosur is not an exception within the sector, where the workers are hostages of the conditions of the company. Orosur lost some lawsuits for claiming unpaid rights to former workers and the subsequent reaction was to force the staff to sign a document renouncing those same rights.

In order to know if things are done well, a fundamental aspect is state controls, because they are complex operations that cannot be assessed at first glance.

Orosur announced drilling in Sierra de Mahoma, San José department, in March and released results in April. By Decree 349/505 that regulated Environmental Impact Assessments, drilling requires authorization from the Dinama (National Directorate of the Environment). However, when requesting access to the corresponding file, the agency responded that it has no information.


Open pit mining technology and cyanide leaching technology have caused serious environmental catastrophes in recent years, mainly due to the rupture of tailings reservoirs and toxic spills on soils and waterways, in the following countries:

  • United States - Summitville Mine, Colorado, and Brewer Mine, South Carolina, in 1992; Gold Querry Mine, Nevada, in 1997; and Homestake Mine, South Dakota, in 1998;
  • South Africa - Harmony Mine, in 1994;
  • Guyana - Omai Gold Mine, in 1995;
  • Bolivia - Comsur Mine, in 1996;
  • Spain - Los Frailes zinc mine, in 1998;
  • Panama - Minera Santa Rosa, El Corozal, in 1998;
  • Papua New Guinea - Tulukuma Mine, in 2000;
  • Romania - Aurul Bahía Mare Mine, in 2000; Y
  • Argentina - Mina Angela, Chubut, in 2001.


The cyanidation of gold is the most used process, but accidents and social questions have led to its prohibition in several countries and territories:

  • Germany - throughout the territory, since 2002.
  • Argentina - in the provinces of Chubut, in 2003; Río Negro, in 2005; Tucumán, La Rioja and Mendoza, in 2007.
  • Australia - in New South Wales, since 2000.
  • Costa Rica, throughout the territory, since 2010.
  • Ecuador, Cotacachi City, since 2000.
  • United States - in the state of Montana, by plebiscite in 1998, ratified in 2004, and in the state of Colorado, in Gunnison counties, in 2001, Costilla, in 2002, and Summit, in 2004.
  • Philippines - in the province of Mindoro, 25-year moratorium, in 2002.
  • Czech Republic - throughout the territory, since 2000.
  • Turkey - throughout the territory, since 1997.

The European Parliament proposed in 2010 to ban “cyanide-based mining technologies and eliminate any support (…) for mining projects that involve the use of this element”, but the executive body, the European Commission, did not accept it. There are numerous enterprises paralyzed by the opposition of the populations. The best known are in Peru, Argentina, Chile, Mexico, Ecuador, Honduras and Romania.

Berlin Declaration

In 2000, a Congress on Cyanide-Based Gold Mining was held in Berlin, attended by experts from around the world. In their conclusions, known as the Berlin Declaration, they reject the use of cyanide for gold extraction due to its irreversible damage to the ecosystem. We present excerpts from this statement:

1. Critical scientific analysis (…) shows without a doubt that the extraction of gold using cyanide cannot be accepted given its irreversible damage to the ecosystem. The safe technologies that would be necessary (such as detoxification, neutralization, reduced availability to ecosystems among other heavy metals) are accessible only to a limited extent. They cannot guarantee safe gold mining.

2. The analysis of the ecosystems at the operation sites indicates that periodic crises occur in tropical and subtropical zones. Technologies to reduce risk are not manageable and cannot be controlled. Dam failures, losses, transport accidents (…) and other minor accidents show around the world that the companies involved are not acting carefully.

3. The economic analysis indicates that the activities of the main gold producers (…) are concentrated in poor countries and regions with low production costs and insufficient legal and control standards.

4. Analysis of the social effects on people and the humanitarian situation shows that there are no positive effects in gold mining using the cyanide process. Short-term gains (more jobs) are always followed by a permanent drop from previous standards.

5. This negative balance shows that gold mining with cyanide permanently contradicts the Rio declaration of 1992. In the long term, it destroys the basic necessities of life and endangers an adequate diet. State monies earmarked by governments for the promotion of gold mining projects should be stopped and, where necessary, affected people should be compensated.

Victor L. Bacchetta. Uruguay

Photo Captions:

Vertical: Orosur extractive operation in Minas de Corrales

Apaisada: New 47 ha cyanide tailings reservoir under construction in Minas de Corrales.

Video: TEST OFICIAL - Marihuana Legal en Uruguay - Cámara Oculta PRANK (May 2022).


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