Environmental Problems, Their Causes, and Sustainability 1

How Are Buried Mineral DepositsRemoved? Heavy Digging and LiftingShallow deposits of mineral deposits are removedby surface mining, and deep deposits are removedby subsurface mining.After suitable mineral deposits are located, several differenttypes of mining techniques are used to removethem, depending on their location and type. Shallowdeposits are removed by surface mining, and deep depositsare removed by subsurface mining.In surface mining, mechanized equipment stripsaway the overburden of soil and rock and usually discardsit as waste material called spoils. Surface miningextracts about 90% of the nonfuel mineral and rock resourcesand 60% of the coal (by weight) that are usedin the United States.The type of surface mining used depends on theresource being sought and on local topography. Thereare several types of surface mining. One is open-pitmining (Figure 16-11a), in which machines dig holesand remove ores (such as iron and copper), sand,gravel, and stone (such as limestone and marble). Asecond method is dredging (Figure 16-11b), in whichchain buckets and draglines scrape up underwatermineral deposits.A third method used where the terrain is fairly flatis area strip mining (Figure 16-11c). A gigantic earthmoverstrips away the overburden, and a huge powershovel digs a cut to remove the mineral deposit. Thenthe trench is filled with overburden and a new cut ismade parallel to the previous one. The process is repeatedover the entire site. If filling it does not restorethe land, area strip mining leaves a wavy series ofhighly erodible hills of rubble called spoil banks.Contour strip mining (Figure 16-11d) is used onhilly or mountainous terrain. A power shovel cuts a seriesof terraces into the side of a hill. An earthmover removesthe overburden, a power shovel extracts thecoal, and the overburden from each new terrace is(a) Open Pit Mine(b) Dredging(c) Area Strip Mining(d) Contour Strip MiningFigure 16-11 Major mining methods used to extract surface deposits of solid mineraland energy resources.http://biology.brookscole.com/miller14341