What is mining/mineral resource development?
Mining or mineral resource development as it is sometimes called is the profitable extraction of mineral resources from the earth or oceans.
People have been mining and using mineral resources since before the beginning of recorded history. People who lived during the Old Stone Age dug flints out of chalk formations for making weapons and tools. Native gold and copper probably were used as early as 8,000 B.C., and bronze was being made by 4000 B.C.
Metallic ores are the sources of iron, copper, lead, zinc, aluminum, tin, nickel, and numerous other metals. The useful nonmetallic minerals include salt, sulfur, gypsum, borates, potash, phosphate, barite, fluorspar, asbestos, and many others. Sand, gravel, stone, and clays for the construction industry are useful nonmetallic materials. Coal and petroleum are used chiefly as fuel, but they are also important sources of chemicals.
The mining of these mineral resources is fundamental to the manufacture, transportation, and distribution of all goods and to the production of food, energy, and chemical products.
What determines the method of mining to be used?
The mining method depends greatly on the type of mineral resource deposit and the economics involved with its extraction. In some cases, where the ore occurs in veins or beds which extend deep into the earth or where the overburden is very thick, underground mining is required. Where the deposit is near the surface, open pit or strip mining is possible. In-situ mining is often used for soluble mineral resources. Some deposits may be worked by placering, the use of hydraulic jets or mechanical shovels or dredges to extract unconsolidated material for concentration of the desired mineral resource. Thus, the type of equipment required is determined by the character of the ore.
What are some of the most common mining techniques?
For deposits at or near the surface, one of several surface methods may be used, including open-pit, strip, alluvial, or in-situ mining and their variations. If all or a major part of the deposit is at an appreciable depth, one of the many underground mining methods is likely to be selected.
Open-Pit Mining is used to extract massive deposits that are at or near the surface and are large in all three dimensions. The methods may be used in almost any kind of surface terrain. An open-pit mine has the appearance of an oval or irregular bowl with sides that may be formed by a series of benches or terraces.
The mining process starts with heavy earth-moving equipment (dozers, scrapers, draglines, etc.) removing any overlying dirt or rock (overburden) that is present. Single or multiple rows of holes are drilled downward in a bench near its outer edge. The holes are loaded with explosive, and the ore is blasted or shaken to allow extraction. The fragmented ore then is loaded into haulage equipment for transport out of the pit.
Open-Pit Strip is a term used almost exclusively for the surface mining of coal, but it sometimes is applied to the mining of other mineral deposits of similar shape and low cohesive strength, such as some pebble phosphate and uranium deposits. The method is applicable to deposits that are at or near the surface and are large in horizontal dimensions, but are relatively thin (2-50 feet, or 0.6-15 meters) and lie flat or slightly inclined. The most suitable terrain is flat to moderately rolling. A strip mine has the appearance of a wide, shallow, flat-bottomed pit. Its most characteristic feature is the parallel rows of waste (spoil) banks that fill the mined-out portion of the pit with giant corrugations.
Initially, mining starts with excavation of the overburden from a strip along one side of the property. Removal of the coal from the strip follows closely behind excavation of the overburden. A parallel strip then is started in the opposite direction, and its overburden is placed into the adjacent strip previously mined. This sequence continues until the property limits are reached or the overburden becomes too thick for economic mining.
Alluvial Mining is used to develop alluvial (placer) deposits, in which valuable mineral particles are intermixed with silt, sand, and gravel that occur along banks and shores of streams, rivers, lakes, and oceans. |
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Panning is the simplest form of alluvial mining. The miner scoops sand, gravel, and water into a shallow pan and shakes it with a rotary motion to wash out the sand and gravel. Heavy minerals such as gold settle to the bottom of the pan. A larger device working on the same principle is the sluice box, a long shallow trough with wooden riffles across its bottom. Sand and gravel are washed through the box, and the heavier minerals are trapped behind the riffles.
In Hydraulic Mining, nozzles direct high-pressure water streams at a gravel bank to cave in and wash the material into sluice boxes or other concentrating devices.
Dredges are the modern way to mine large alluvial deposits. The dredge, often as large as a three-story house, floats in a natural or artificial pond. It uses buckets on a continuous chain or rotary cutting heads and a suction hose to remove material from depths to 200 feet (60 meters) below the water surface. Equipment on the dredge separates mineral particles from the sand and gravel. Boom conveyors on the dredge then deposit the waste (tailings) in the area already mined. A large dredge can handle 1,000 tons of gravel per hour.
Underground Mining is used when the deposit lies deep beneath the earth's surface, or when massive extraction efforts are not needed (vein deposit). First, the miners drive (dig) an opening into the earth's surface. A vertical opening is called a shaft. A passage that is nearly horizontal, dug into the side of a hill or mountain, is called an adit. In coal mining, it is called a stope. From these main passages, miners dig systems of horizontal passages called levels. Various mining methods are available for removing the ore. Types of underground mining include:
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room-and-pillar mining |
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longwall mining |
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sublevel stoping |
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cut-and-fill mining |
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block caving |
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sublevel caving |
What is aggregate and how is it mined?
Deposits of aggregate are formed as rocks are eroded by water, wind, and ice. The deposits consist of sand (particles of quartz and feldspar less than 2 mm across), silt, clay, and gravel (rock fragments). Aggregate is used primarily in construction (for making concrete) and road building. Stringent specifications apply to the composition of concrete in many applications and, therefore, the various components of the aggregate are sorted and segregated. Crushing reduces the size of cobbles and boulders. Screening separates the different sized particles, and washing removes the very fine grains, such as clay.
Because aggregate is expensive to transport, nearly all sand and gravel operations should be located as near as possible to cities where the materials will be used. Aggregate mining operations located near cities may become surrounded by the city as the population grows. In order to have continued access to aggregate, some municipalities have zoned special areas as natural resource districts reserved for the expansion of sand and gravel operations. Advanced landscape planning at most mining sites can result in valuable real estate when mining ceases. Former gravel excavations are now the sites of shopping centers, housing projects, and parks.
Sand and gravel outrank all other minerals in terms of value and the amount mined. In addition to inland deposits, considerable gravel is now mined from shallow seas bordering many countries.
Underwater deposits are very similar to inland deposits; but they are harder to find and evaluate, and they are more expensive to mine.
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