33 G L O SSA R Y aggregate Uncrushed or crushed gravel crushed stone or rock sand or artifcially produced inorgan ic materials that form the major part of concrete alloy A substance with metallic qualities that is composed of two or more chemical elements of which at least one is an elemental metal anthracite See ranks of coal assayer One who analyzes ores and alloys espe cially bullion to determine the value and proper ties of precious metals auger mining A form of underground coal mining that uses an auger which looks like a large car penters wood drill The auger bores into a coal seam and discharges coal out of the spiral onto a waiting conveyor belt When mining is fnished the openings are backflled This method is usu ally employed to recover any additional coal left in deep overburden areas that cannot be reached economically by contour or area mining backfll Reflling an area where overburden has been removed May also refer to the material used to refll an excavation base metals An y of the nonpr ecious metals c opper lead and zinc ar e usually c onsider ed the primary base metals but tin aluminum and mag nesium ar e also among those impor tant t o modern societ y bedrock Any solid rock exposed at the surface of the earth or overlain by unconsolidated material bioleaching Addition of naturally occurring bacte ria to extract or remove a soluble substance from or e bituminous coal See ranks of coal blasting The operation of breaking coal ore or rock by boring a hole in it inserting an explosive charge and detonating or fring it Also called shot fring bond As a pr er equisit e f or obtaining a mining per mit c ompanies must post a r eclamation bond t o ensur e that the r egulat ory authorit y will ha v e suf fcient funds t o r eclaim the sit e in the e v ent the c ompan y f ails t o c omplet e the r eclamation plan appr o v ed in the permit Btu British thermal unit This is a measure of the energy required to raise the temperature of one pound of water one degree Fahrenheit On aver age coal contains about 22 million Btu per ton bullion Mixture of gold and silver in cast bars Also called dore cage An elevator used to carry people and ma terials up and down a mine shaft Cages may be single or multidecked Of t en there are two cages in simultaneous operation in separate ar eas of the shaft traveling in opposite directions captive mine A mine whose coal is used largely or totally by its owners or a subsidiary operation clean coal technologies A number of innovative technologies designed to use coal in a more ef cient and costefective manner while enhancing environmental protection These include process es applied before during and after combustion and also involve those that change coal into a gas or liquid coal resources Total coal deposits both identifed and undiscovered The World Energy Conference estimated there may be as much as 14 trillion short tons of coal worldwide the United States is esti mated to have 4 trillion tons of coal resources by the USGS coal seam A bed or stratum of coal Usually ap plies to a large deposit coke A hard dry carbon substance produced by heating coal to a very high temperature in the ab sence of air Coke is used in the manufacture of iron and steel concentrate The result of separating ore or metal from its containing rock or earth continuous mining Underground mining in which the continuous mining machine cuts coal from the face see face and loads it onto conveyors or