Underground Mining

Underground mining is the process of extracting minerals and ores that are buried too far underground to be mined using surface mining methods. The primary objective of underground mining is to extract ore from underground as safely and economically as possible while producing as little waste or tailings as possible.

Many forms of underground mining exist. However, every underground mine is similar in that it requires a point of entrance from the surface. This entry may be through an adit, mine shaft, or vertical or horizontal tunnel. The average underground mine will include a number of roughly horizontal levels that branch off at various depths from the main point of entry into the mine. A vertical, internal connection between two levels of an underground mine is called a winze when driven downward, and a raise when driven upward.^[1]

[edit] Process

In an underground mine, ore and minerals are extracted in stopes or rooms. Sometimes material, known as a pillar, is left behind to support the mine ceiling and then later recovered when mining is completed. Providing support to the roof is key in the prevention of falling rock—one the potential dangers of any underground mining operation. In the past, roof support consisted of bracing the roof of the mine with timber and eventually concrete. Ore was also mined mostly by hand with picks and shovels and then hauled back up to the surface by cart using a rudimentary hoisting system or small horses known as pit ponies.

Today, underground mining exists as a highly mechanized operation. Supporting the mine roof is accomplished using both temporary and permanent steel supports or, most commonly, by bolting the roof of the mine using roof bolting equipment. Ore is mined using a wide selection of specialized cutting and drilling equipment such as continuous miner and rock drills. Once extracted, the ore is hauled from the slope or room back up to the surface by rubber-tired vehicles known as shuttle car or load haul dump trucks (LHD), or by a conveyor belt system.

[edit] Types

• Room and pillar mining is the most common method of underground mining. The roof of the mine is supported by areas or columns of coal (pillars) spaced out at regular intervals in rooms from which the coal is mined. The two types of room and pillar mining are conventional and continuous mining.^[2]
• Longwall mining is a more modern method of underground to extract coal from a coal bed. The technique was developed to replace room and pillar mining and includes the mechanized removal of long panels of coal from a rock face using longwall mining equipment—coal shearers mounted on series of self-advancing hydraulic supports. As the longwall miner advances along the panel, the roof behind the miner’s path collapses.^[3]
• Cut-and-fill stoping is a method of underground mining used in vertical stopes and in mining high-grade irregular ore bodies. The rock mass surrounding the ore deposit is also usually weak—unable to support loads over an extended stoping height. As the name of the method implies, successive cutting of the ore into horizontal slices is carried out starting from the bottom of the stope and progressing upward, towards the surface. This horizontal slicing leaves a void that is backfilled with material to provide support until all the ore is extracted from the mine.^[4]
• Sublevel stoping is an underground mining method that involves vertical mining in a large, open stope that has been created inside an ore vein. Usually the stope operates as the center for production. In sublevel stoping, this is not the case. The stope is not meant to be occupied. Drilling, blasting, and mining are carried out at different elevations in the ore block.^[5]
• Block caving is an underground mining method that permits the bulk mining of large, relatively low-grade bodies of ore. As a sublevel mining process, block caving involves the controlled collapse of ore from under its own weight into chutes or draw points using gravity. In order for a block caving operations to be successful, the rock mass must be able to fracture naturally once an undercut has been applied.^[6]
• Borehole mining is a remote-controlled method of underground mining used to mine a broad range of natural resources and industrial materials. A borehole tool comprised of two pipes—one that delivers a stream of high pressure water, and another that delivers slurry back up to the surface—is used.^[7]
• Shaft mining is a form of underground mining using shafts driven vertically from the top down into the earth to access ore or minerals. Shaft mining, also termed shaft sinking, is particularly ideal for concentrated mineral deposits, such as iron or coal, that are deeply imbedded underground.^[8]
• Auger mining is a surface mining technique used to recover additional coal from a seam located behind a highwall produced either by stripping or open-pit mining. Auger mining is especially employed when contour strip mining has been exhausted and the removal of overburden to access additional coal no longer becomes economically feasible. Auger mining can also be utilized in underground mining when faulty or poor roof conditions are present or other problems preclude the use of other underground mining techniques.^[9]
• Vertical crater retreat, also referred to as vertical retreat mining, involves drilling large-diameter holes into the orebody vertically from the top of the mine, as opposed to the conventional blasthole stope method of drilling them in fans from bottom to top.
• Slope mining  is a type of underground mining where the coal bed is located very deep and parallel to the ground and the shafts are slanted. This type of mining is normally carried out when drilling shafts vertically downward becomes problematic.^[10]
  

[edit] References

1. ↑ Underground Mining Methods. Fact Monster. 23-06-2009.
2. ↑ Room-and-pillar Mining. TeachmMeFinance.com. 23-06-2009.
3. ↑ What is Longwall Mining? Wise Geek. 23-06-2009.
4. ↑ Cut and Fill Stoping. Mining Basics. 2008-10-07.
5. ↑ Hartman, L. Howard and Mutmansky, M. Jan. Introductory Mining Engineering. John Wiley and Sons, 2002. 344
6. ↑ Block Caving. Mining Lift.2008-10-07.
7. ↑ Borehole Mining. Answers.com, 2008-09-29.
8. ↑ Shaft Mining. Library.Thinkquest.org, 2008-09-29.
9. ↑ Argonne National Laboratory. Environmental Consequences of, and Control Processes For, Energy Technologies. William Andrew Inc., 1990.
10. ↑ Slope Mining. Library Thinkquest. 23-06-2009.