Minerals are found in the earth’s crust distributed in different types of rocks, landscapes and environments. On all continents, the oceans, and ultimately, from pole to pole, appear concentrations of minerals – metalliferous, nonmetallic, nuclear, industrial, and application rocks – which are likely to be economically exploited.
the rocks as a whole, this is the igneous formed by the outflow of the magmas, the metamorphic by the pressure of the minerals in the terrestrial interior or the sedimentary rocks by the wear, transport and accumulation in the surface, they all contain different types of minerals hosted.
The tectonic movements that break the crust into blocks, can drag these rocks and their minerals to different depths or at different heights. On the other hand, minerals can be concentrated in small spaces, in case of a vein or be scattered in large volumes of rock.
What is underground mining
When the minerals are found in rich veins but in large volumes of sterile rocks, the only way to mine them is the underground mining method. These consist of opening galleries, tunnels, and other forms of mining art that allow us to take advantage in an orderly manner of the veins in their three-dimensional development. Normally, a vertical master well, called a pique, is made, from which the vein is accessed through horizontal galleries.
The material obtained, usually precious minerals or non-ferrous metals, are moved to the surface where they are subjected to grinding and concentration processes to benefit them and enrich them, separating the useful metal from the ore, from the accompanying or sterile mineral, called gangue.
The Aguilar mine (Jujuy), which in 2013 completed 84 years of uninterrupted work, is a deposit of zinc silver that is mined underground. The Witwatersrand gold mine in South Africa is an excellent example of underground mining that exploits gold from ancient rocks at depths of up to 4 km underground.
What is open pit mining
On the other hand, open-pit mining is the most common mining and ranges from very low-priced minerals to finely disseminated gold deposits.
Among the low-priced ones we find clay quarries for the manufacture of bricks quarries for the exploitation of construction aggregates (gravel, sands), quarries for the extraction of rocks for lime (limestone), for cements (marl, gypsum, limestones), for ornamentation (marbles, granites, onyx), among others.
If the deposit has enough mineral, if the prices of the markets are favorable, and this is added another kind of dozens of positive variables then the deposit can be exploited in the open through the opening of an open pit called in the international jargon an “OPEN PIT”.
As can be seen, no one chooses to exploit an open or underground pit, but the conditions of nature that concentrate the metals in one way or another. A “Disseminated” deposit, such as a Copper porphyry, can not be exploited underground, just as a Lead vein (galena) can not be exploited in the open. To try to change this is to pretend to change nature.