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Area strip mining
Type of strip mining used where the terrain is flat. An earthmover strips away the overburden and a power shovel digs a cut to remove the mineral deposit. The trench is then filled with the spoils, and a new cut is made parallel to the previous one.
Astenosphere
Zone within the earth’s mantle made up of hot, partly melted rock that flows and can be deformed like soft plastic.
Continental drift
The slow movement of continents across the earth’s surface
Countour strip mining
Form of surface mining used on hilly or mountainous terrain. A power shovel cuts a series of terraces into the side of a hill. An earthmover removes the overburden, and a power shovel extracts the coal. The spoils from each new terrace are dumped onto the one below.
Convergent boundary
Area where the earth’s lithospheric plates are pushed together. See subduction zone. Compare divergent plate boundary, transform fault.
Core
Inner zone of the earth. It consists of a solid inner core and a liquid outer core. Compare crust, mantle.
Crust
Solid outer zone of the earth. It consists of oceanic crust and continental crust. Compare core, mantle.
Depletion time
The time it takes to use a certain fraction (usually 80%) of the known or estimated supply of a nonrenewable resource at an assumed rate of use. Finding and extracting the remaining 20% usually costs more than it is worth
Divergent boundary
Area where the earth’s lithospheric plates move apart in opposite directions.
earthquake
Shaking of the ground resulting from the fracturing and displacement of subsurface rock, which produces a fault, or from subsequent movement along the fault.
gangue
The waste material that is discarded when ore is extracted during mining.
high-grade ore
Ore containing a large amount of a desired mineral. Compare low-grade ore.
igneous rock
Rock formed when molten rock material (magma) wells up from the earth’s interior, cools, and solidifies into rock masses. See rock cycle. Compare metamorphic rock, sedimentary rock
lithosphere
Outer shell of the earth, composed of the crust and the rigid, outermost part of the mantle outside the asthenosphere. See crust, geosphere, mantle.
low-grade ore
Ore containing a small amount of a desired mineral. Compare high-grade ore.
mantle
Zone of the earth’s interior between the core and the crust.
metamorphic rock
Rock produced when a preexisting rock is subjected to high temperatures (which may cause it to melt partially), high pressures, chemically active fluids, or a combination of these agents. See rock cycle. Compare igneous rock, sedimentary rock.
mineral
Any naturally occurring inorganic substance found in the earth’s crust as a crystalline solid. See mineral resource.
mineral resource
Any naturally occurring solid, liquid, or gaseous material in or on the earth’s crust in a form and amount such that extracting and converting it into useful materials or items is currently or potentially profitable. Mineral resources are classified as metallic or nonmetallic.
mountain-top removal
Type of surface mining that uses explosives, massive power shovels, and large machines called draglines to remove the top of a mountain and expose the seams of coal beneath. Compare area strip mining, contour strip mining.
open-pit mining
Removing minerals such as gravel, sand, and metal ores by digging them out of the earth’s surface and leaving an open pit behind. Compare area strip mining, contour strip mining, mountaintop removal, subsurface mining.
ore
Part of a metal-yielding material that can be economically extracted from a mineral; typically containing two parts; the ore mineral, which contains the desired metal, and waste minerals (gangue). See high-grade ore, low-grade ore.
overburden
Layer of soil and rock overlying a mineral deposit.
reserves
Resources that have been identified and from which a usable mineral can be extracted profitably at present prices with current mining or extraction technology.
rock
Any solid material that makes up a large, natural continuous part of the earth’s crust. See igneous rock, metamorphic rock, mineral, sedimentary rock.
rock cycle
Largest and slowest of the earth’s cycles, consisting of geologic, physical, and chemical processes that form and modify rocks and soil in the earth’s crust over millions of years. See igneous rock, metamorphic rock, sedimentary rock.
sedimentary rock
Rock that forms from the accumulated products of erosion, and in some cases, from the compacted shells, skeletons, and other remains of organisms. See rock cycle. Compare igneous rock, metamorphic rock.
smelting
Process in which a desired metal is separated from the other elements in an ore mineral.
spoils profile
A vertical section of soil that shows the layers of material and their properties resulting from excavation or mining activities. It reflects the different types of soil and rock that have been disturbed.
spoils
Unwanted rock and other waste materials produced when a material is removed from the earth’s surface or subsurface by mining, dredging, quarrying, or excavation.
strip mining
Form of surface mining in which bulldozers, power shovels, or stripping wheels remove large chunks of the earth’s surface in strips. See area strip mining, contour strip mining, surface mining. Compare subsurface mining.
subsurface mining
Extraction of a metal ore or fuel resource such as coal from a deep underground deposit. Compare surface mining.
surface mining
Removing soil, subsoil, and other strata and then extracting a mineral deposit found fairly close to the earth’s surface. See area strip mining, contour strip mining, mountaintop removal, open-pit mining. Compare subsurface mining.
tailings
The materials left behind when ore is separated from rock waste. Tailings can be left in piles, or flushed into ponds where fine particles then settle out.
tectonic plates
Various-sized areas of the earth’s lithosphere that move slowly around with the mantle’s flowing asthenosphere. Most earthquakes and volcanoes occur around the boundaries of these plates. See lithosphere, plate tectonics
transform plate boundary
Area where the earth’s lithospheric plates move parallel to each other in opposite directions. Compare convergent plate boundary, divergent plate boundary.
tsunami
Series of large waves generated when part of the ocean floor suddenly rises or drops.
volcano
Vent or fissure in the earth’s surface through which magma, liquid lava, and gases are released into the environment.
weathering
Physical and chemical processes in which solid rock exposed at the earth’s surface is changed to separate physical particles and dissolved minerals, which can be moved to another place as sediment.
