Open pit mining can be defined as the process of excavating any metallic or non-metallic mineral deposit near the surface by digging or cutting at the surface, using one or more horizontal benches to extract the mineral.
While the ore is being extracted, overburden and tailings are dumped at a special disposal site outside the excavation boundary.
Open pit mining is used for the extraction of metallic and non-metallic minerals, however, the application of this mining method in coal is less common.
Production tonnages for open pit mines range from less than 15,000 t (metric tons)/year at small iron ore operations to over 360 Mt/year at large porphyry copper operations such as Escondida in Chile.
As of 2008, there are approximately 2,500 industrial scale open pit metal mines in the world, accounting for approximately 52% of all industrial scale mining operations.
Iron ore (44%), copper (38%) and gold (15%) together account for 97% of the total volume of open pit excavation.
What deposits are extracted with open pit mining?
By definition, mineral bodies extracted through opencast mining They are on or near the surface.
Although the geometry of ore bodies varies, as a general rule it can be said that the opencast mining favors mineral deposits that can be mined on a large scale (for example, extensive mineral deposits with low grade ratios).
The porphyry copper deposits such as Chuquicamata (from the company Codelco) and Escondida in Chile, and Bingham Canyon in the United States, are excellent examples of such large low-grade ore deposits.
Other common forms of ore bodies include stratiform deposits, such as the Western Australian iron ore deposits and Zambian copper belt mineralization,
Also diatremes of kimberlites (Jwaneng in Botswana) and carbonatites (Palabora in South Africa).
However, there are cases in which a vein system (hydrothermal veins) can be exploited with opencast mining, is the case of the Core Gold mine in Ecuador, where the 10 m wide veins are very close to the surface and can be mined in the open pit.
It is also common for this extraction method to be applied to industrial materials, that is, construction materials and non-metallic minerals such as kaolinite and various clays of interest.
Characteristics of open pit mining
- Open pit mining is mainly done for the exploitation of minerals in shallow deposits, that is, they are less than 300 meters deep underground.
- The type of exploitation is carried out by building banks, berms and ramps distributed in such a way that they allow the extraction of the mineral of interest with the help of mining machinery and sometimes explosives.
- Generally, its most important environmental impact is visual (obvious landscaping change), the generation of noise, the generation of dust and the accumulation of tailings.
- It is used for the exploitation of low-grade and high-volume deposits, such as copper porphyries, non-metallic minerals (clays) and aggregates for construction.
Parts of an open pit mine
The parts of an open pit mine are written in English because this part of engineering is very important for mining engineering students to know the terms in English.
What are the impacts of open pit mining?
In this aspect the opencast mining is always frowned upon by the majority of people, especially when they are not part of the fields related to mining engineering and geology, and it is because it is thought that the opencast mining represents a high impact on the environment.
It is worth mentioning that, if it is true that this type of mining does cause a considerable environmental impact, however, the mining legislation in the world that regulates the mining companies that apply this method of exploitation, directs that what is known as mine closure, which will be mentioned later.
Negative impacts (disadvantages) of open pit mining
So what are the impacts of this method at first glance?
- The main impact is visual, because the excavation, the hole, the hole that is observed to be made in the earth or soil, if it is large-scale mining, it is usually quite large, that is, a change in topography is clearly observed.
- The second impact is that the local flora and fauna are affected, however, the effect is reduced to the area of influence of the mine.
- An indirect impact is usually that to get to the mine it is necessary to build alternative roads, which will also affect the environment.
- If the deposit was in a quiet and remote place, now with the mine there will also be noise pollution.
- Finally, I can mention that due to the increase in industrial machines and the influx of people, air pollution from cars and industrial machines can increase, as well as an increase in garbage due to the increase in people.
Positive impacts (advantages) of open pit mining
Perhaps you think that an open pit mine and that the opencast mining They are only bad things, however, the positive effects are much more.
- The first positive impact that I mention is that a mine near a town represents economic development for the residents, since the increase in people makes people set up businesses to supply the mine workers.
- The increase in work or employment is another positive impact, because mining companies need many people to build the mine and to work directly with the company in various areas, and most of them hire people from the community and close to the mine. community or sector where the mine is located.
- The taxes that entail the extraction of the mineral, will be reflected in infrastructure improvement works in the towns near the mine or mining project, these works include: road improvement, construction of new roads, construction of schools and colleges, construction of businesses (bakeries, butchers, shops, etc.), improvement of squares, churches and construction of recreational centers such as parks and courts.
What about the environmental impact?
As mentioned in the negative impacts, the opencast mining if it generates environmental impacts, such as changes in topography, increased noise, effects on fauna and flora, and a little pollution.
However, mining processes and mining projects are currently regulated by the government in each country and now it is necessary for mining companies to take environmental aspects into account.
And it is there that an environmental management plan and a mine closure are always presented.
This means that the mining company has the obligation to close the mine, and deliver the area with the least possible environmental impact and even much better than it was at the beginning of the project, that is, environmental remediation of the area.
Therefore, it is concluded that now the mining companies and the opencast mining does not generate a considerable environmental impact and that the positive impacts of this practice are much more than the negative ones.