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Surface Mining

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(Redirected from Surface mining)
Mining Processes

Surface mining is the process of extracting minerals and ores located in close proximity to the surface of the earth. A layer of soil, subsoil, and strata are removed to gain access to the minerals and ore. Subsurface mining is a variation of surface mining in which the ore or minerals are extracted from a deeper, underground deposit. Today, surface mining is the largest sector of mining in existence, accounting for over 60 percent of all materials mined.[1] Most mines start off as surface mines because it is more cost-effective and poses less danger. When the cost of excavating and removing the waste that must be mined for each ton of ore extracted becomes too great, then underground mining methods are deployed.[2]

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[edit] Process

Though surface mining encompasses a broad range of mining methods, one common denominator is the removal of overburden using heavy earthmoving machinery. Once the overburden has been removed, large dragline excavators are used to extract the minerals or ore from the earth.[3] Other common types of equipment used in surface mining include wheel loaders, wheel dozers, crawler tractors, motor graders, and heavy-duty dump trucks such as rock trucks and articulated dump trucks.[4]

After a surface mine is depleted, an area called a spoil bank is often left behind. This is the downside of surface mining—it has a devastating effect on the natural topography of the land and, as a practice, is often criticized for the havoc it causes on local ecosystems and the environment. A large part of good surface mining practices today involves implementing a land rehabilitation or land reclamation program in conjunction with mining operations. This is currently carried out with the systematic application of reclamation technology. Reclaimed spoil banks pose little distress and can be easily developed. Other reclamation programs associated with surface mining include restoring ground for agricultural and livestock farming, reforestation, recreation, housing, and industrial site development. The balance between good mining practices and the implementation of a beneficial land reclamation program has also become evident within the mining industry with the passage of regulations and ongoing research and development.[5]

[edit] Types

Open-pit mining involves a surface mine formed of large, terraced pits or burrows that penetrate into the earth the deeper they are driven and becoming enlarged as they do. Open-pit mining in usually executed by drilling and blasting rock and overburden and then removing it with different types of heavy earthmoving machinery.[6]

Quarries are mined similarly to an open-pit mine and with the same types of equipment. The primary difference is that materials or minerals mined from a quarry are used largely in industrial and construction applications.[7]

Strip mining is very similar to open-pit mining. In strip mining, access to a mineral seam is undertaken with the removal of the overburden in strips. Given the bulk of material needing to be removed, some of the machinery used in strip mining is some of the largest machinery ever constructed. Two examples are bucket wheel excavators and dragline excavators.

Area strip mining is a variation of strip mining, carried out over a large flat area or terrain. Cut strips are usually dug parallel to one another, forming adjacent trenches. As a new strip or trench is dug out of the earth, the overburden is used to fill the trench situated beside it.[8]

Contour strip mining is also a variation of strip mining executed on hilly or mountainous terrain. The mining operation follows the natural topography of the terrain being mined.[9] A power shovel is commonly used to cut benches or terraces into the hill or mountain.

Mountaintop removal mining, in which coal is extracted from seams located on mountaintops, is the newest method of surface mining. The top of the mountain is usually removed or leveled by blasting rock and overburden with explosives in order to reach sediment 1,000 feet (305 m) below the earth.[10]

Placer mining is a form of mining executed in a placer deposit consisting of mineral particles mixed with sand or gravel usually in a riverbed. Placer deposits also include beach deposits, offshore seabed sediments and glacial outflow deposits.[11]

Dredging is the process of mining placer deposits and the extraction of minerals underwater using dredging machinery. Chain bucks and draglines are used to scrape up the sand, gravel and other material in placer and surface deposits and covered by water.

Auger mining is a form of surface mining for recovering coal by boring into a horizontal or slightly pitched seam at the base of strata exposed after excavation. The coal is extracted with the use of auger drills that cut up at a horizontal axis up to 1,000 feet (305 m) into a mountainside.[12]

Highwall mining is a method of extracting coal from an exposed highwall seam in an open-pit mine using a continuous miner type machine driven from the surface by remote control.[13]

[edit] Equipment Used

[edit] References

  1. Mining. Encarta, 2008-09-29.
  2. Mining. Encarta, 2008-09-29.
  3. Surface Mining. Absolute Astronomy, 2008-09-29.
  4. Mining Machinery. Library.Thinkquest.org, 2008-09-29.
  5. Kennedy, A. Bruce. Surface Mining. SME, 1990, 752.
  6. Mining. Encarta, 2008-09-29.
  7. Surface Mining. Absolute Astronomy, 2008-09-29.
  8. Area Strip Mining. Britannica, 2008-09-29.
  9. Contour Strip Mining, 2008-09-29.
  10. Surface Mining. Absolute Astronomy, 2008-09-29.
  11. Mining. Encarta, 2008-09-29.
  12. vhttp://www.mininglife.com/Miner/surface/auger_mining.htm
  13. Highwall Mining. CSIRO Mining Automation, 2008-09-29.