There are two ways to mine a deposit. Some mines are open pit and others are underground. Choosing the mine type depends on a variety of factors such as deposit depth, deposit footprint, and extraction costs.
- Deposit depth: If the deposit is closer to the surface, an open pit mine is the preferred option.
- Deposit footprint (the visible trace left by the mine): The idea is to minimize the environmental impact. For example, if the mine is in a wildlife sanctuary then an underground mine is preferable.
- Extraction costs: An underground mine is the best choice if there is an excessive amount of overburden (or topsoil and waste rock) to remove.
Open pit mines
For an open pit, a spiral hole is dug and 2- to 15-meter benches are formed. These will be dynamited to extract the ore. Then ore is loaded using diggers and transported to a concentrator by huge trucks that can carry hundreds of tons of ore at a time.
Open pit mines are often described as “gigantic” or “massive” due to the impressively large holes and oversized machinery. This is the case with the Mont-Wright open pit mine near Fermont, with an area of 24 km², equivalent to 2,222 soccer fields.
At first glance, underground mines resemble anthills. In reality they are huge networks of vertical and horizontal tunnels that provide access to ore deposits. Once extracted, the ore is brought to the surface via shafts and sent to the concentrator.
What’s inside an underground mine?
- An access ramp: A large spiral tunnel communicating with all levels of the mine. It allows vehicles to rapidly access the different galleries at each level.
- The galleries: Long tunnels leading to the deposit to be mined.
- Access shaft: A vertical passage used to take equipment and machinery underground, to transport personnel, and to bring ore up to the surface. It is essentially the backbone of the mine.
- Air shafts: These shafts ensure the ventilation, air filtration, temperature, and air quality of the galleries.
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