Types of surface mining

Borehole Mining

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Borehole mining is done to mine many industrial materials like uranium, iron ore, quartz sand, gravel, gold, diamonds and amber. It is a remote controlled method of underground mining. It is also used in exploration, oil, gas, and water stimulation. Borehole mining consists of two pipes one for pumping down high pressure water and another that delivers slurry back to the surface.

A BHM tool consists of water jet pump, hydro monitor section, an extension section and a hub. The tool is lowered into a well until the hydro monitor reaches the depth of the hole where the borehole mining is started. Then the high pressure water is pumped down and receives back productive slurry. In the tank, slurry is collected. The water is drained and ore is taken out of it.

The Bore hole Mining belongs to the underground mining category. But personnel don't go underground but work from the surface. The advantage of Borehole mining is there is high level of safety and has the ability to work in a collapsing environment. Other advantages include it requires less laborious, does not pass through dangerous and expensive mining process like overburden, shaft building, ventilation, de-watering, underground personnel transportation, life support and more. This method can lead to reduction of overall cost of the final product from 15% to 75%.

Underground Mining

Underground mining is carried out when the rocks, minerals, or precious stones are located at a distance far beneath the ground to be extracted with surface mining. To facilitate the minerals to be taken out of the mine, the miners construct underground rooms to work in. The mining company selects the best feasible way to get the minerals extracted out. Most mining is carried out using; Continuous mining that employs a continuous mining mechanism to cut the coal deposits from the walls. This means there is less of blasting and drilling and utilizes fewer miners down in the mines. It is safer than the yester year techniques of mining that is being described on our coal mine tour page.

This kind of mining is done when the rock or mineral is on the side of a mountain. This makes it an easy, cheaper way to mine. Minerals that are mined with draft mining are gold, coal etc. with slope mining, the coal or mineral bed is located very deep and parallel to the ground. It is called a slope mine because the shafts are slanted. Shaft mining has a vertical man shaft, a tunnel where men travel up and down in an elevator. Shrinkage stoping is a flexible mining method for narrow ore bodies that need no backfill during stoping. Long wall mining consists of multiple coal shearers mounted on a series of self-advancing hydraulic ceiling supports. Retreat mining is the last phase of a common type of coal mining technique referred to as room and pillar mining. Retreat mining is a process that recovers the supporting coal pillars, working from the back of the mine towards the entrance, hence the word retreat. Room and pillar mining advances inward, away from the entrance of the mine. Other underground mining methods include Hard rock mining, bore hole mining, drift and fill mining, long hole slope mining, sub level caving and block caving.

Two prominent ways through which underground mining is done are:

Underground mining (hard rock) and Underground mining (soft rock)

Underground mining (hard rock)

Underground hard rock mining refers to various underground mining techniques used to excavate hard minerals such as those containing metals like gold, copper, zinc, nickel and lead or gems such as diamonds. In contrast soft rock mining refers to excavation of softer minerals such as coal, or oil sands.

Mine Access

Underground Access

Accessing underground ore can be achieved via a decline (ramp), vertical shaft or adit. Declines can be a spiral tunnel which circles either the flank of the deposit or circles around the deposit. The decline begins with a box cut, which is the portal to the surface. Depending on the amount of overburden and quality of bedrock, a galvanized steel culvert may be required for safety purposes.

Shafts are vertical excavations sunk adjacent to an ore body. Shafts are sunk for ore bodies where haulage to surface via truck is not economical. Shaft haulage is more economical than truck haulage at depth, and a mine may have both a decline and a ramp. Adits are horizontal excavations into the side of a hill or mountain. They are used for horizontal or near-horizontal ore bodies where there is no need for a ramp or shaft. Declines are often started from the side of the high wall of an open cut mine when the ore body is of a payable grade sufficient to support an underground mining operation but the strip ratio has become too great to support open cast extraction methods.

Ore Access

Levels are excavated horizontally off the decline or shaft to access the ore body. Stopes are then excavated perpendicular (or near perpendicular) to the level into the ore.

Ventilation

Door for directing ventilation in an old lead mine. The ore hopper at the front is not part of the ventilation. One of the most important aspects of underground hard rock mining is ventilation. Ventilation is required to clear toxic fumes from blasting and removing exhaust fumes from diesel equipment. In deep hot mines ventilation is also required for cooling the workplace for miners. Ventilation raises are excavated to provide ventilation for the workplaces, and can be modified to be used as escape routes in case of emergency.The main sources of heat in underground hard rock mines are virgin rock temperature, machinery, auto compression, and fissure water although other small factors contribute like people breathing, inefficiency of machinery, and blasting operations.

Mining Methods

Cut and Fill mining is a method of short hole mining used in narrow ore zones. An access ramp is driven off the main level to the bottom of the ore zone to be accessed. Using development mining techniques a drift is driven through the ore to the defined limit of mining. Upon completion the drift (or "cut") is filled back to the access ramp with the defined type of backfill, which may be either consolidated or unconsolidated. Another drift is driven on top of filled cut. This process continues until the top of the stope is reached.

Drift and Fill is similar to cut and fill, except it is used in ore zones which are wider than the method of drifting will allow to be mined. In this case the first drift is developed in the ore, is backfilled using consolidated fill. The second drift is driven adjacent to the first drift. This carries on until the ore zone is mined out to its full width, at which time the second cut is started atop of the first cut.

Room and Pillar mining : Room and pillar mining is commonly done in flat or gently dipping bedded ore bodies. 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 stope access, allowing the roof to collapse and fill in the stope. This allows a greater recovery as less ore is left behind in pillars.

Block Caving such as is used at the Northparkes Mine in NSW, Australia, is used to effect with large sized orebodies which are typically composed of low-grade, friable ore. The method works best with cylindrical, vertical orebodies. Pre-production mining development work consists of driving accesses underneath the orebody. This includes the formation of "drawbells" by undercutting and blasting. Initially, blasted ore is removed via the extraction level underneath the drawbells until a sufficient area of unsupported ore is formed that the orebody begins to fracture and cave on its own. The eventual aim of the block caving method is that the friable ore needs no blasting and continues to fracture and break up on its own, flowing down the drawbells to the extraction level, where it is removed from the ore chute mouths with loaders and sent off for processing. Eventually the fracturing will propagate to the surface, resulting in subsidence. One of the main hazards associated with block-caving is that fracturing can potentially stop before it reaches the surface unbeknownst to the people in control of the mine. If fracturing stops propagating upwards and extraction continues, a large void can be formed, resulting in the potential for a sudden and massive collapse and catastrophic windblast throughout the mine.

Underground mining (soft rock)

Underground mining (soft rock) refer to a group of underground mining techniques used to extract coal, oil shale and other minerals or geological materials from sedimentary ("soft") rocks. Because deposits in sedimentary rocks are commonly layered and relatively less hard, the mining methods used differ from those used to mine deposits in igneous or metamorphic rocks (see Underground mining (hard rock)). Underground mining techniques also differ greatly from those of surface mining.

In underground coal mines, an environmental risk is fire. Hundreds of coal mines smolder in the United States, China, Russia, India, South Africa, and Europe.[citation needed] The inaccessibility and size of these fires make many impossible to extinguish or control.

Mining Methods

Longwall mining: Longwall mining machines consist of multiple coal shearers mounted on a series of self-advancing hydraulic ceiling supports. Almost the entire process can be automated. 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 or continuous 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.

Blast mining - An older practice of coal mining that uses explosives such as dynamite to break up the coal seam, after which the coal is gathered and loaded onto shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with "cutting" the coalbed so it will break easily when blasted with explosives. This type of mining accounts for less than 5% of total underground production in the U.S. today.

Shortwall mining- A coal mining method that accounts for less than 1% of deep coal production, shortwall involves the use of a continuous mining machine with moveable roof supports, similar to longwall. The continuous miner shears coal panels 150-200 feet wide and more than a half-mile long, depending on other things like the strata of the Earth and the transverse waves.

Surface Mining

Surface mining is a form of mining in which the soil and the rock covering the mineral deposits are removed. It is the other way of underground mining, in which the overlying rock is left behind, and the required mineral deposits are removed through shafts or tunnels.

Surface mining is basically employed when deposits of commercially viable minerals or rock are found closer to the surface; that is, where overstrain (surface material covering the valuable deposit) is relatively very less or the material of interest is structurally unsuitable for heavy handling or tunneling (as would usually be the case for sand, cinder, and gravel).

Where ever minerals occur deep below the earths crest or the overburden is too thick or the mineral occurs as strands in hard rock, Underground mining methods are employed to extract the valuable mineral deposits. Surface mines are naturally extended until either the valuable deposit is exhausted, or the cost of de-cresting larger volumes of overburden makes further mining an uneconomic option to shoulder.

In most types of surface mining, heavy paraphernalia's such as earthmovers are utilized. They 1st remove the overburden the soil and rock above the deposit. Then followed by the huge machines, such as dragline excavators, extract the mineral.

Types of surface mining

Strip mining is a kind of surface mining. The ore is very near to the surface of the land but has one or more layers of rock and filth on top of it. To mine the ore, these layers have to be removed.

The steps in strip mining are similar to open-pit mining. The steps are:

• The trees and bushes are pushed down through bulldozers.

• This waste, along with the filth or sand under it, is taken to a close area and dumped.

• Lots of minute holes are drilled from the rock that is above the coal or mineral bed [vein]

• Explosives are put in the holes and blazed. This breaks up the rock which is taken to the dumping area.

• When the coal or mineral is found, it may be broken up by the blazing. The size of the chunks is important because the miners don’t normally want it in minute pieces. They usually want it in pieces that are capable to be moved with big machinery.

• This mining is done in elongated, narrow strips. When the ore is done in one strip, the miners start to create another strip next to it. The waste, filth, and rock that they take off of the top of the next strip is put on top of the last one. This is recurring until the last strip is done and the waste from the primary strip is brought back to fill it.

Strip mining, like other types of surface mining, finishes in hurting the area around the mine. The rock, gravel, trees, plants, and filth are dumped in regions round the mine. When it rains, this runs over the land and into watercourse and rivers. The rain pushes the mine filth on top of the region topsoil and buries it. The streams lands up being blocked and rivers flood. Water is impure by the flooding.

The mined land was normally ruined, too. There were no vegetation left. The topper most layer of the soil was bulldozed under the rock. It became the cheap and swift way to mine awaiting the U.S. Government made mining firms fix [regain] the land when the mining was done.

To regain land, mining firms have to fix the land and make it like it was prior to. With strip mining, waste was pushed onto the final strip mined. This lands up making a whole bunch of rows that require to be leveled when mining is done. The mining firm has bulldozers flatten the elevated strips until they are all even. Topsoil is bulldozed over the top of the whole thing and trees and grasses are planted.

Open-pit mining, also known as opencast mining, open-cut mining, and strip mining, means a process of digging out rock or minerals from the earth by their elimination from an open pit or borrow.

The word is used to distinguish this type of mining from extractive methods that need tunneling into the earth. Open-pit mines are used when deposits of commercially helpful minerals or rock are found close to the surface; that is, where the overburden (layer material covering the valuable deposit) is comparatively thin or the material of interest is structurally inappropriate for tunneling. For minerals that happen deep underneath the surface-where the overstrain is solid or the mineral happens as veins in hard rock- underground mining methods take out the precious material.

Open-pit mines that manufacture building materials and dimension stone are usually referred to as quarries. People in few of the English-speaking countries are not likely to make a difference among an open-pit mine and other kinds of open-cast mines, like quarries, borrows, placers, and strip mines.

Open-pit mines are characteristically engorged until either the mineral resource is exhausted, or a mounting ratio of overburden to ore makes more mining uneconomic. When this occurs, the exhausted mines are at times converted to landfills for disposal of solid wastes. Nevertheless, some form of water control is normally required to keep the mine pit from becoming a lake.

Open Cut mines are dug on benches, which portray vertical levels of the hole. These benches are normally on four meter to sixty meter intervals, relying on the size of the machinery that is being utilized. A lot of quarries do not use benches, as they are normally shallow.

Most walls of the pit are normally dug on an angle less than vertical, to avert and lessen damage and hazard from rock falls. This relies on how weathered the rocks are, and the kind of rock, and also how a lot of structural weaknesses happen within the rocks, like a fault, shears, joints or foliations.

The walls are stepped. The inclined part of the wall is called the batter, and the flat part of the step is called as the bench or perm. The steps in the walls help avert rock falls continuing down the entire face of the wall. In some instances additional ground support is needed and rock bolts, cable bolts and shotcrete are utilized. De-watering bores might be used to ease water pressure by drilling horizontally into the wall, which is frequently sufficient to cause failures in the wall by itself.

A haul road is located at the side of the pit, forming a ramp up which trucks may drive, taking ore and waste rock.

Waste rock is piled up at the surface, near the edge of the open cut. This is known as the waste dump. The waste dump is also tiered and stepped, to lessen degradation.

Ore which has been processed is called as tailings, and is normally slurry. This is pumped to a tailings dam or settling pond, where the water fades away. Tailings dams may frequently be toxic due to the presence of unextracted sulfide minerals, few types of toxic minerals in the gangue, and frequently cyanide which is utilized to treat gold ore via the cyanide leach method.

Mountaintop removal mining also called as mountaintop mining is a form of surface mining that includes the topographical change and/or removal of a summit, summit ridge, or important portion of a mountain, hill, or ridge in order to get a desired geologic material.

This process involves the removal of coal seams by first completely removing the overload laying atop them, exposing the seams from above. This method differs from more conventional underground mining, where normally a narrow shaft is dug which allows miners to collect seams using various underground methods, while leaving the vast most common of the overburden undisturbed. The overburden waste resulting from MTR is either placed back on the ridge, attempting to reflect the estimated original contour of the mountain.

On the heels of the U.S. Environmental Protection Agency publication that it would allow a proposed coal mine involving mountaintop removal to go forward, 12 environmental scientists have published a review of the perform that attack it in no doubtful terms. "Mining permits are being issued despite the preponderance of scientific evidence that impacts are pervasive and irreversible and that improvement cannot compensate for losses," the scientists wrote. "Regulators should no longer ignore rigorous science.”

Dredging. Underwater excavation is called dredging. Dredging is the process by which a water body is deepened. In simple terms, dredging means removal of material from the bottom of a water body. Removal of sediment or other material from an aquatic area for the purpose of deepening the area, obtaining fill material, or maintaining existing structure is known as dredging. Dredging takes place to maintain the depth in existing ports, harbors and channels to provide ready and safe passage for commercial and recreational vessels. Dredging is done to create new or deeper access or berths for vessels. This means deepening and widening of channels and anchorages as well as the excavation of basins and marinas from areas of previously dry land.

Types of dredging vessel:

Suction: Suction dredges are essentially underwater vacuum cleaners. They are commonly used to pull material up from a stream bottom, run through a separation system to recover valuable minerals, and then redeposit the stream material back onto the bottom of the stream. Suction dredging is mostly done in a very dynamic environment, a natural stream or river.

Trailer suction:

A trailing suction hopper dredger is a large ocean going vessel. When the vessel starts dredging, the ship reduces its speed to some 1 to 2 knots and then lowers the suction pipes on both sides of the ship all the way to the seabed. Sand pumps transfer the sand dredged up by the suction head into the hold or hopper. The excess water is drained of via the overflow pipes. When the hopper is full, the ship sails to its destination, the reclamation area.

Cutter suction:

Cutter suction has to be towed to their work site by tugboats. Cutter suction dredgers are suitable to dredge hard soil or to pump o\up large amounts of sand in shallow water.

Auger suction:

Augur suction operates in the same manner as the cutter suction, except that the mechanical cutting tool is a rotating Archimedean screw placed at right angles to the suction pipe.

Pneumatic dredge: Pneumatic dredgers work on the evacutor principle. A chamber with inlets for bed material is pumped out with the inlets closed. The inlets are then opened and water and material drawn in. The mixture is then pumped out and the cycle repeated. The unit is generally suspended from a crane on land or from a small pontoon or barge. The dredging action is intermittent and suitable only for easily flowing material.

Air lift dredger: Air lift dredgers are very similar to the jet-lift dredgers but the medium for inducing water and material flow is high pressure air injected at the month of the suction pipe. As with jet-lift dredgers there are no moving parts in the flow system. Hard or other difficult to loosen materials cannot be dredged.

Amphibious dredgers: Amphibious dredgers have the unusual feature of being able to work afloat or elevated clear of the water surface on legs. They can be equipped with grabs, buckets or a shovel installation.

Some of the major dredging companies are Royal Boskalis Westminister, Jan De Nul, DEME and Van Oord Dredging and Marine Contractors.

Date: 2015-12-24; view: 1665