Author Topic: Mining techniques  (Read 4984 times)

crazy

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Mining techniques
« on: April 24, 2007, 09:37:09 AM »
Surface mining

Strip mining is a type of mining in which soil and rock overlying the mineral deposit is removed. It is the opposite of underground mining, in which the overlying rock is left in place, and the mineral removed through shafts or tunnels.

Surface mining is used when deposits of commercially useful minerals or rock are found near the surface; that is, where the overburden (surface material covering the valuable deposit) is relatively thin or the material of interest is structurally unsuitable for tunneling (as would usually be the case for sand, cinder, and gravel). Where minerals occur deep below the surface—where the overburden is thick or the mineral occurs as veins in hard rock— underground mining methods are used to extract the valued material. Surface mines are typically enlarged until either the mineral deposit is exhausted, or the the cost of removing larger volumes of overburden makes further mining uneconomic.

In most forms of surface mining, heavy equipment, such as earthmovers, first remove the overburden - the soil and rock above the deposit. Next, huge machines, such as dragline excavators, extract the mineral.


Types of surface mining

There are four main forms of surface mining, detailed below.

Strip Mining

Strip mining is the practice of mining a seam of mineral by first removing a long strip of overlying soil and rock (the overburden). It is most commonly used to mine coal or tar sand. Strip mining is only practical when the ore body to be excavated is relatively near the surface. This type of mining uses some of the largest machines on earth, including bucket-wheel excavators which can move as much as 12,000 cubic feet of earth per hour.

There are two forms of strip mining. The first, and more common one is area stripping, which is used on fairly flat terrain, to extract deposits over a large area. As each long strip is excavated, the overburden is placed in the excavation produced by the previous strip.

Contour stripping involves removing the overburden above the mineral seam near the outcrop in hilly terrain, where the mineral outcrop usually follows the contour of the land. Contour stripping is often followed by auger mining into the hillside, to remove more of the mineral. This method commonly leaves behind terraces in mountainsides.

Among others, strip mining is used to extract the oil-impregnated sand in the Athabasca Tar Sands in Alberta. It is also common in coal mining. Bucket excavators are widely used for this purpose, however, they are prone to damages and require many millions of dollars to repair.

Open-pit mining

Open-pit mining refers to a method of extracting rock or minerals from the earth by their removal from an open pit or borrow. Although open-pit mining is sometimes mistakenly referred to as "strip mining", the two methods are different

Mountaintop removal

Mountaintop removal (MTR) is a relatively new form of coal mining that involves the mass restructuring of earth in order to reach the coal seam as deep as 1,000 feet below the surface. It is used where a coal seam outcrops all the way around a mountain top. All the rock and soil above the coal seam are removed and the spoil placed in adjacent lows such as hollows or ravines. Mountaintop removal replaces previously steep topography with a relatively level surface.

The technique has been used increasingly in recent years in the Appalachian coal fields of West Virginia, Kentucky, and Tennessee in the United States. The profound changes in topography and disturbance of pre-existing ecosystems have made mountaintop removal highly controversial.

Advocates of mountaintop removal point out that once the areas are reclaimed as mandated by law, the technique provides premium flat land suitable for many uses in a region where flat land is at a premium. They also maintain that the new growth on reclaimed mountaintop mined areas is better able to support populations of game animals.[1]

Dredging

Dredging is a method often used to bring up underwater mineral deposits. Although dredging is usually employed to clear or enlarge waterways for boats, it can also recover significant amounts of underwater minerals relatively efficiently and cheaply.


Sub-surface mining

Sub-surface mining or underground mining refers to a group of techniques used for the extraction of valuable minerals or other geological materials from the earth. In contrast to the other main type of excavation, surface mining, sub-surface mining requires equipment and/or manpower to operate under the surface of the earth.

In underground coal mines, another major environmental risk is fires. Hundreds of coal mines smolder in the United States, China, Russia, India, South Africa, and Europe. The inaccessibility and size of these fires many impossible to extinguish or control.

Methods

Longwall mining : Longwall mining machines consist of multiple coal shearers mounted on a series of self-advancing hydraulic ceiling supports. The entire process is mechanized. Longwall mining machines are about 800 feet (240 meters) in width and 5 to 10 feet (1.5 to 3 meters) tall. Longwall miners extract "panels" - rectangular blocks of coal as wide as the mining machinery and as long as 12,000 feet (3,650 meters). Massive shearers cut coal from a wall face, which falls onto a conveyor belt for removal. As a longwall miner advances along a panel, the roof behind the miner's path is allowed to collapse.
Room-and-pillar mining : Room and pillar mining is commonly done in flat or gently dipping bedded ores. Pillars are left in place in a regular pattern while the rooms are mined out. In many room and pillar mines, the pillars are taken out, starting at the farthest point from the mine haulage exit, retreating, and letting the roof come down upon the floor. Room and pillar methods are well adapted to mechanization, and are used in deposits such as coal, potash, phosphate, salt, oil shale, and bedded uranium ores.

Engineer Forum

Mining techniques
« on: April 24, 2007, 09:37:09 AM »

carlprince2009

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Re: Mining techniques
« Reply #1 on: May 04, 2009, 10:11:53 AM »
            What type of mining device would you used in Mining strip.


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