When asked to imagine what a mine looks like, many people think of a dark tunnel supported by wooden beams and cutting into the side of a mountain. Social media, including cartoons, have popularized this perception, and while this image is indeed what some mines look like, not all mines look like this.
There are vastly different types of mines, many of which appear to be unrelated to each other. Any basic discussion on mining technology is incomplete without first knowing about the various methods of mining.
At its core, mining is an activity that extracts valuable substances from the earth. In most cases, less valuable rock covers the target mineral deposit, and this overburden must first be removed to gain access to the precious ore. These deposits can be found in both land masses and underwater, and their physical properties can vary from site to site, which is why people also developed many diverse ways of proceeding with mining.
Also, the total project cost and the environmental impact are both influenced by the mining method used, so it is essential to carefully consider each option during the planning stage of the project.
Some deposits lie relatively near the surface and hence can be extracted directly by removing all of the overburden in the top layers. An applicable method here includes open-pit mining, where soil and rock are removed layer by layer until the mineral deposit is reached.
The massive amounts of earth transferred require the use of heavy machinery, which increases the capital cost of open pit mines. It is also harder to restore the local environment after mining due to the large area of land affected by this type of mining. However, the relatively easy access to the ore and the elimination of the need for tunnels means that the productivity and occupational safety of open pit mines is high.
Aside from the removal of the ore in solid form, aqueous extraction methods can be used if a suitable solvent is available to dissolve the ore. The chosen solvent is allowed to make contact with the deposit before being drawn back up into the surface, where they recover the dissolved minerals from the solvent. The use of a liquid carrier for the target mineral reduces the need for costly machinery, but this method can only be applied for certain minerals that can reversibly dissolve in the solvent.
Modern technology is sometimes used for mining resources found on the seabed, HYPERLINK “https://www.straterra.co.nz/mining-in-nz/mining-101/types-of-mining/” although the cost is more burdensome. Miners separate the underwater material from the sea floor before being sucked by pipes connected to a specialized vessel. HYPERLINK “https://www.straterra.co.nz/mining-in-nz/mining-101/types-of-mining/”
Once onboard, the material is processed to remove the valuable minerals, and they pump the remaining content back to the sea. Another set of pipes is used to inject the material back to the seabed to prevent excessive sediment dispersion.
For deposits that are deeper underground, merely removing the overburden might not be economically feasible. In these cases, tunnels are carved underground to gain access to the valuable ores. The pits may sometimes need support to prevent cave-ins, although in some cases they can be left unsupported if the surrounding rock is strong enough. The ecological impact of underground mining is less pronounced than surface mining, but safety risks are higher due to the risk of flooding, suffocation, or tunnel collapse.
One common small-scale mining method is placer mining, popularized once again by the media. This technique involves sifting through river sediments and other loose materials to recover valuable minerals. Professional miners usually use water as the separating medium, and the density difference between the heavier minerals and the lighter sediments is utilized to separate them.