This exhaustion is evident in the following example: at the beginning of the last century, copper was extracted in the United States from minerals with ore of 5%, in other words, a percentage of metal of 5% in the rock. Currently, only an ore of 0.4% is being obtained from rocks. In terms of quantities, this means that from extracting 50 kg of copper per tonne of processed rocks, it has now moved to 4 kg of copper from the same quantity of rocks. This percentage continues to decrease.

Having exhausted the rocks which contain a high percentage of mineral ore, they began to process larger quantities of rocks which contained smaller amounts of metal. This greater distribution of metal in the rocks led them to abandon the former practice of digging tunnels which followed the mineral vein concentrated under the surface.

Now explosions are used to demolish entire mountains or to dig immense pits in the earth. Then with crane shovels, trucks and conveyor belts- all very large in size- the debris is transported to a location where it is grinded and converted into a powder or into small stones measuring two or three centimetres, depending on the method adopted for subsequent processing.

This crushed rock is piled up into gigantic heaps where they are sprayed with a chemical solution -a process called leaching- by using huge grinders with irrigators. These tools are a bigger version of the sprinklers used to water the garden. This process of spraying the piles of grinded rock with a chemical solution is carried out 24 hours a day, 7 days a week. The chemical solution with cyanide what is used to extract gold contains between 0.14 and 2.35 kg of cyanide per tonne of water, that is, a concentrate of anywhere between 0.1 and 2.35 milligrams of cyanide per litre. The process of heap leaching can last from several days to a few months, depending on the size of the heap and the mineral ore. On average, a typical leaching uses 3 millilitres of water per square metre per second. So for example, a large heap of 20 hectares will require 681 litres per second or almost 59 million litres of fresh water on a daily basis.

The composition of the chemical solution depends on which metals are desired for extraction and it usually contains other substances, such as sodium cyanide (a deadly poison ) when searching for gold, or sulphuric acid when extracting copper or uranium. In addition, it contains heavy metals such as litharge- lead oxide- or mercury, etc . The chemical solution draws the metals out of the rock, and then this is treated, using lime or carbon to recover the desired metals.

Firstly, the treated rock, known as sterile rock, which unavoidably contains some cyanide residue and many heavy metals, is piled up and abandoned at another location: the dump. Then, the chemical solution which remains after having extracted the metal concentrate is also abandoned in dykes after it has undergone some process to reduce the level of cyanide and other toxic chemicals to "acceptable levels" (legally) of toxicity. At least this is what is claimed in some cases.

There are a variety of ways to reduce the cyanide level in the residual chemical solution but each one is insufficient to a larger or lesser degree that in some cases they eventually dump it in a dam or waterway.

This general process varies in some ways. For example, one of these options entails that the crushed mineral, or a concentrate obtained from the leaching process, is converted into a mineral solution with the addition of a lot of water and it is then transported by pipeline to a remote location to be processed.

Whichever method applied, all display a common set of basic characteristics, among which the immense consumption of water stands out:

Open pit mines consume up to 70 million litres of water daily to keep production going. This volume is equivalent to the amount used in a large city. For each tonne of mineral, up to eight tonnes of water must be used.

Energy is also consumed in incredible quantities since it is essential for extraction and processing. Everything is ‘mega' in the projects. For example, regarding extraction carried out by Bajo de la Alumbrera in Catamarca, they became the ninth leading copper producer and fourteenth leading producer of gold in the world. They consume singly the most energy in the country , they use 80 tonnes of explosives every day and they grind 80,000 tonnes of rock to powder, as fine as flour, every day for 365 days. They say that they consume between 200,000 and 250,000 litres of diesel daily and the pit in the mountain will be 2.8 km deep by 2 km wide by 1.8 km long, etc.

Then in 2003, another line for crushing rocks was added. Currently, there are more employees and more processed rock, so that in 2007, more that 300,000 tonnes of rock was processed daily. Consequently, there will be a proportional increase in the amount of explosives, electrical and fuel energy used. Recent data shows that annual electrical energy consumption is 1500 GW/hour.

When carrying out an open air operation, in order to arrive at the mineral which contains the desired metals, the surface rock which does not contain said metals must be removed. This rock, otherwise known as ‘ballast' or ‘sterile rock' represents for example a ratio of 23:1 in the Cerro Vanguardia mine in Santa Cruz. In other words, 23 tonnes of sterile rock must be removed there in order to obtain 1 tonnes of rock from which a few grams of gold and silver can be obtained.

The only thing small is the number of labourers employed in this highly automated extraction process: 600 people, of whom a majority are foreigners. And the smallest of all, if in fact there is, is the money that is left in the country in exchange for taking away the gold, copper, land rarely used in microelectronics and superconductors, or rhenuim, for the aeronautical industry.

Another unavoidable characteristic of these mega-exploitations is the resulting pollution. Some of the known cases, such as the disaster in the Bajo de La Alumbrera zone in Catamarca and those in Romania and Spain , are painful testimonies of the reality of these mining exploitations and chemical processes. Each of these disasters can be put on the same scale as the Chernobyl nuclear reactor accident.

The enormous consumption of water , energy and the widespread pollution and destruction of the environment are all characteristics which lead to open-pit metal mining by employing chemical processes being called mega-mining.

Source: Notes on the socio-environmental effects of mega-mining, by Marcel Acuña, 11th April 2008