Surface Mining Methods
When resources are available close to the surface, a strip mine is the most efficient method of extraction. The layers of regolith covering the resource are taken away, and the exposed ore is mined. This method is also called open-pit mining.
Subsurface Mining Methods
When the natural resource lies far underground, it is far more efficient to dig tunnels to access the ore than to remove the overlaying rock and regolith. Since Mars has only about 38% as much gravity as Earth people should be able to extend mines to a depth about 2.6 times as deep as on Earth without the tunnel collapsing from hydrostatic pressure. This should allow the search for valuable minerals to a depth of more than 5 miles. There are many subsurface mining methods, and they are often used in conjunction with each other.
Drift mining consists of primarily horizontal tunnels. These are most often dug into a hillside.
Slope mining uses diagonal tunnels to access ore.
Vertical shafts are used in shaft mining.
Room and Pillar Mining
In this method, large galleries are dug into the ore. Pillars of ore are left at regular intervals to support the ceiling. After all the ore has been removed, these pillars may be removed through retreat mining, leading to the collapse of the chamber. This collapse may lead to surface subsidence.
Longwall mining begins with a long horizontal shaft. The roof is held up mechanically by moveable supports. One side of the shaft is mined along its entire length. As this mine progresses, the mechanical supports move forward with the face. The old area of the mine is left unsupported, and allowed to collapse under its own weight, often leading to surface subsidence.
The artificial caves are a nice side effect. They can be used to expand the settlement with storage rooms, living rooms, underground greenhouses, gas container for energy storage or storage of chemicals.
- McGRAW-HILL ENCYCLOPEDIA OF Science & Technology, 8 th edition, vol. 10 (c) 1997 page 527