Mining Terms

Active workings – Any place in a mine where miners are normally required to work or travel, which are ventilated and inspected regularly.

Advance – Mining in the same direction, or order of sequence.

Airway – Any passage through which air is carried; also known as an air course.

Aquifer – A water-bearing bed of porous rock, often sandstone.

Auger – A rotary drill that uses a screw device to penetrate, break, and then transport the drilled material (coal).

Auger Mining – A form of underground mining that uses an auger, which looks like a large carpenter’s wood drill. The auger bores into a coal seam and discharges coal out of the spiral onto a waiting conveyor belt. When mining is finished, the openings are back-filled. This method is usually employed to recover any additional coal left in deep overburden areas that cannot be reached economically by further contour or area mining.

Back – The roof or upper part in any underground mining cavity.

Backfill – Rock and other material used for refilling after excavation.

Barricading – Enclosing part of a mine to prevent inflow of noxious gasses from a mine fire or an explosion.

Barrier – Barrier pillars are solid blocks of coal left between two mines or sections of a mine to prevent accidents due to inrushes of water, gas, or from explosions or a mine fire.

Beam – A bar or straight girder used to support a span of roof between two support props or walls.

Bed – A stratum of coal or other sedimentary deposit.

Belt conveyor – A looped belt on which coal or other materials can be carried and which is generally constructed of flame-resistant material or of reinforced rubber or rubber-like substance.

Belt idler – A roller, usually of cylindrical shape, which is supported on a frame and which, in turn, supports or guides a conveyor belt. Idlers are not powered but turn by contact with the moving belt.

Belt take–up – A belt pulley, generally under a conveyor belt and inby the drive pulley, kept under strong tension parallel to the belt line. Its purpose is to automatically compensate for any slack in the belting created by start-up, etc.

Bench – Layers of a coal seam separated by slate or formed by the process of cutting the coal.

Beneficiation – The treatment of mined material, making it more concentrated or richer.

Bit – The hardened and strengthened device at the end of a drill rod that transmits the energy of breakage to the rock. The size of the bit determines the size of the hole.

Bituminous coal – A middle rank coal (between subbituminous and anthracite) formed by additional pressure and heat on lignite. Usually has a high Btu value and may be referred to as “soft coal.”

Black damp – A term generally applied to carbon dioxide. It is a mixture of carbon dioxide and nitrogen. It is also applied to an atmosphere depleted of oxygen, rather than having an excess of carbon dioxide.

Blasting agent – Any material consisting of a mixture of a fuel and an oxidizer.

Blasting cap – A detonator containing a charge of detonating compound, which is ignited by electric current or the spark of a fuse. Used for detonating explosives.

Blasting circuit – Electric circuits used to fire electric detonators or to ignite an igniter cord by means of an electric starter.

Bleeder or bleeder entries – Special air courses developed and maintained as part of the mine ventilation system and designed to continuously move air-methane mixtures emitted by the gob or at the active face away from the active workings and into mine-return air courses.

Borehole – Any deep or long drill-hole, usually associated with a diamond drill.

Bottom – Floor or underlying surface of an underground excavation.

Break line – The line that roughly follows the rear edges of coal pillars that are being mined; the line in which the roof of a coal mine is expected to break.

Btu – British thermal unit. A measure of the energy required to raise the temperature of one pound of water one degree Fahrenheit.

Cage – In a mine shaft, the device, similar to an elevator car, that is used for hoisting personnel and materials.

Clean Coal Technologies – A number of innovative, new technologies designed to use coal in a more efficient and cost-effective manner while enhancing environmental protection. Several promising technologies include: fluidized-bed combustion, integrated gasification combined cycle, limestone injection multi-stage burner, enhanced flue gas desulfurization (or “scrubbing”), coal liquefaction and coal gasification.

Coal – A solid, brittle, more or less distinctly stratified combustible carbonaceous rock, formed by partial to complete decomposition of vegetation; varies in color from dark brown to black; not fusible without decomposition and very insoluble.

Coal dust – Particles of coal that can pass a No. 20 sieve.

Coal Gasification – The conversion of coal into a gaseous fuel.

Coal mine – An area of land and all structures, facilities, machinery, tools, equipment, shafts, slopes, tunnels, excavations, and other property, real or personal, placed upon, under, or above the surface of such land by any person, used in extracting coal from its natural deposits in the earth by any means or method, and the work of preparing the coal so extracted, including coal preparation facilities.

Coal miner – One who is engaged in the extraction of coal. In 2005, 81,000 coal miners in the United States produced about 6.3 tons of coal per hour each.

Coal reserves – Measured tonnages of coal that have been calculated to occur in a coal seam within a particular property.

Coal resources – Total coal deposits, regardless of whether they can be mined or recovered. The United States is estimated to have 4 trillion tons of coal resources by the U.S. Geological Survey.

Coal washing – The process of separating undesirable materials from coal based on differences in densities.

Coke – A hard, dry carbon substance produced by heating coal to a very high temperature in the absence of air.

Continuous miner – A machine that constantly extracts coal while it loads. This is to be distinguished from a conventional or cyclic unit, which must stop the extraction process in order for loading to commence.

Contour – An imaginary line that connects all points on a surface having the same elevation.

Conventional mining – The first fully–mechanized underground mining method involving the insertion of explosives in a coal seam, blasting the seam, and removing the coal onto a conveyor or shuttle car by a loading machine.

Conveyor – An apparatus for moving material from one point to another in a continuous fashion. This is accomplished with an endless (that is, looped) procession of hooks, buckets, wide rubber belt, etc.

Core sample – A cylinder sample generally 1-5” in diameter drilled out of an area to determine the geologic and chemical analysis of the overburden and coal.

Crusher – A machine for crushing rock or other materials. Among the various types of crushers are the ball mill, gyratory crusher, Handsel mill, hammer mill, jaw crusher, rod mill, rolls, stamp mill, and tube mill.

Deposit – Mineral deposit or ore deposit is used to designate a natural occurrence of a useful mineral, or an ore, in sufficient extent and degree of concentration to invite exploitation.

Depth – The word alone generally denotes vertical depth below the surface. In the case of incline shafts and boreholes it may mean the distance reached from the beginning of the shaft or hole, the borehole depth, or the inclined depth.

Dragline – A large excavation machine used in surface mining to remove overburden (layers of rock and soil) covering a coal seam. The dragline casts a wire rope-hung bucket a considerable distance, collects the dug material by pulling the bucket toward itself on the ground with a second wire rope (or chain), elevates the bucket, and moves the material to another location.

Drainage – The process of removing surplus ground or surface water either by artificial means or by gravity flow.

Drift mine – A coal mine entered directly through a horizontal opening drilled into the side of a hill or mountain.

Drill – A machine utilizing rotation, percussion (hammering), or a combination of both to make holes. If the hole is much over 0.4m in diameter, the machine is called a borer.

Dump – To unload; a load of coal or waste; the mechanism for unloading, e.g. a car dump (sometimes called tipple); or, the pile created by such unloading, e.g. a waste dump (also called heap, pile, tip, spoil pike, etc.).

Entry – An underground horizontal or near-horizontal passage used for haulage, ventilation, or as a mainway; a coal heading; a working place where the coal is extracted from the seam in initial mining.

Extraction – The process of mining coal.

Face – The exposed area of a coal bed from which coal is being extracted.

Face cleat – The principal cleavage plane or joint at right angles to the stratification of the coal seam.

Fan, auxiliary – A small, portable fan used to supplement the ventilation of an individual working place.

Feeder – A machine that feeds coal onto a conveyor belt evenly.

Fill – Any material that is put back in place of the extracted coal to provide ground support.

Fire damp – The combustible gas, methane, CH4. Also, the explosive methane-air mixtures with between 5% and 15% methane. A combustible gas formed in mines by decomposition of coal or other carbonaceous matter, and that consists chiefly of methane.

Floor – That part of any underground working upon which a person walks or upon which haulage equipment travels; simply the bottom or underlying surface of an underground excavation.

Fluidized-bed combustion – A clean coal technology process with a high ability to remove sulfur from coal combustion. The process involves suspending crushed coal and limestone in the bottom of a boiler by an upward stream of hot air. While the coal is burned in this liquid-like mixture, sulfur combines with the limestone to form a solid compound that is recovered with ash.

Fly ash – The finely divided particles of ash suspended in gases resulting from the combustion of fuel.

Fossil fuel – A naturally occurring fuel of an organic nature, such as coal, crude oil and natural gas.

Gasification – Various processes by which coal is turned into low, medium, or high Btu gases.

Gob or goaf – The term applied to that part of the mine from which the coal has been removed and the space more or less fills up with waste. Also, the loose waste in a mine.

Haulage – The horizontal transport of ore, coal, supplies, and waste. The vertical transport of the same is called hoisting.

Haulageway – Any underground entry or passageway that is designed for transport of mined material, personnel, or equipment, usually by the installation of track or belt conveyor.

Highwall – The unexcavated face of exposed overburden and coal in a surface mine or in a face or bank on the uphill side of a contour mine excavation.

Highwall miner – A highwall mining system consists of a remotely controlled continuous miner which extracts coal and conveys it via augers, belt or chain conveyors to the outside. The cut is typically a rectangular, horizontal cut from a highwall bench, reaching depths of several hundred feet or deeper.

Hoist – A drum on which hoisting rope is wound in the engine house, as the cage or skip is raised in the hoisting shaft.

Hoisting – The vertical transport coal or material.

Hopper Car – Open freight cars with a floor sloping to one or more hinged doors for discharging bulk materials such as coal. A car for coal, gravel, etc., shaped like a hopper with an opening to discharge contents.

Inby – Toward or in the direction of the working face and away from the mine entrance. Opposite of outby.

Intake – The passage through which fresh air is drawn or forced into a mine or to a section of a mine.

Intermediate section – A term used in belt and chain conveyor network to designate a section of the conveyor frame occupying a position between the head and foot sections.

Immediate roof – The roof strata immediately above the coal bed, requiring support during the excavation of coal.

Lamp – The electric cap lamp worn for visibility. Also, the flame safety lamp used in coal mines to detect methane gas concentrations and oxygen deficiency.

Layout – The design or pattern of the main roadways and workings.

Lift – The amount of coal obtained from a continuous miner in one mining cycle.

Liquefaction – The process of converting coal into a synthetic fuel, similar in nature to crude oil and/or refined products, such as gasoline.

Longwall Miner – A deep mining machine that uses a steel plow or rotating drum, which is pulled mechanically back-and-forth across a long face of coal.

Longwall Mining – One of three major underground coal mining methods currently in use. Employs a steal plow, or rotation drum, which is pulled mechanically back and forth across a face of coal. The working area is protected by a movable, powered roof support system. The loosened coal falls onto a conveyor for removal from the mine.

Main fan – A mechanical ventilator installed at the surface; operates by either exhausting or blowing to induce airflow through the mine roadways and workings.

Manhole – A safety hole constructed in the side of a gangway, tunnel, or slope in which a miner can be safe from passing locomotives and cars. Also called a refuge hole.

Man trip – A carrier of mine personnel, by rail or rubber tire, to and from the work area. Also called personnel carrier.

Manway – An entry used exclusively for personnel to travel from the shaft bottom or drift mouth to the working section.

Metallurgical coal – Various grades of coal suitable to make coke for steel manufacture.

Methane – A potentially explosive gas formed naturally from the decay of vegetative matter, similar to that which formed coal. Methane, which is the principal component of natural gas, is frequently encountered in underground coal mining operations and is kept within safe limits through the use of extensive mine ventilation systems. In recent years, coalbed methane has been recognized as an important energy resource and its production for that purpose has increased.

Methane monitor – An electronic instrument often mounted on a piece of mining equipment that detects and measures the methane content of mine air.

Mine development – The term employed to designate the operations involved in preparing a mine for coal extraction. These operations include tunneling, sinking, cross-cutting, drifting, and raising.

Mountaintop mining – See surface mine.

MSHA – Mine Safety and Health Administration; the federal agency which regulates coal mine health and safety.

Natural ventilation – Ventilation of a mine without the aid of fans or furnaces.

Outby – Toward the mine entrance and farther from the working face. The opposite of inby.

Permissible – That which is allowable or permitted. It is most widely applied to mine equipment and explosives of all kinds which are similar in all respects to samples that have passed certain tests of MSHA and can be used with safety in accordance with specified conditions where hazards from explosive gas or coal dust exist.

Permit – As it pertains to mining, a document issued by a regulatory agency that gives approval for mining operations to take place.

Pillar – An area of coal left to support the overlying strata in a mine; sometimes left permanently to support surface structures, sometimes systematically removed to regulate subsidence..

Plan – A map showing features such as mine workings or geological structures on a horizontal plane.

Portal – The structure surrounding the immediate entrance to a mine; the mouth of an adit or tunnel.

Preparation plant – A facility where coal is crushed, sized, and mechanically cleaned prior to shipment.

Ranks of coal – The classification of coal by degree of hardness, moisture and heat content. The major ranks are lignite, subbituminous, bituminous and anthracite.

Reclamation – The restoration of land and environmental values to a surface mine site after the coal is extracted. Reclamation operations are usually underway as soon as the coal is removed from a mine site. The process includes restoring the land to its approximate original appearance by restoring topsoil and planting native grasses and ground covers.

Recovery – The proportion or percentage of coal mined from the original seam or deposit.

Reserves – Known identified resources from which usable coal can be extracted at the time of determination.

Return – The air or ventilation that has passed through all the working faces of a split.

Rib – The side of a pillar or the wall of an entry. The solid coal on the side of any underground passage.

Roof – The rock or other material above a coal seam; the overhead surface of a coal working place. Same as “back” or “top.”

Roof bolt – A long steel bolt driven into the roof of underground excavations to support the roof, preventing and limiting the extent of roof falls. The unit consists of the bolt, steel plate, expansion shell, and pal nut. The use of roof bolts eliminates the need for timbering by fastening together, or “laminating,” several weaker layers of roof strata to build a “beam.”

Roof bolting – A method of supporting the ceilings of underground mines by inserting long steel bolts into holes bored into the strata forming the roof.

Roof fall – A roof collapse, especially in permanent areas such as entries.

Roof jack – A screw- or pump-type hydraulic extension post made of steel and used as temporary roof support.

Roof sag – The sinking, bending, or curving of the roof, especially in the middle, from weight or pressure.

Roof stress – Unbalanced internal forces in the roof or sides, created when material is extracted.

Roof support – Posts, jacks, roof bolts and beams used to support the rock overlying a coal seam in an underground mine.

Roof trusses – A combination of steel rods anchored into the roof to create zones of compression and tension forces and provide better support for weak roof and roof over wide areas.

Room and pillar mining – A method of underground mining in coal is left in place to support the roof of the active mining area. Large “pillars” are left while “rooms” of coal are extracted.

Seam – A stratum or bed of coal.

Self-contained breathing apparatus – A self-contained supply of oxygen used during rescue work from coal mine fires and explosions; same as SCSR (self-contained self-rescuer).

Self-rescuer or SCSR – A small filtering device carried by a coal miner underground, either on his belt or in his pocket, to provide him with immediate protection against carbon monoxide and smoke in case of a mine fire or explosion. It is a small canister with a mouthpiece directly attached. The wearer breathes through the mouth, the nose being closed by a clip. The canister contains a layer of fused calcium chloride that absorbs water vapor from the mine air. The device is used for escape purposes only because it does not sustain life in atmospheres containing deficient oxygen.

Shaft – A primary vertical or non-vertical opening through mine strata used for ventilation or drainage and/or for hoisting of personnel or materials; connects the surface with underground workings.

Shaft mine – An underground mine in which the main entry or access is by means of a vertical shaft.

Shortwall – A deep mining method in which small areas are worked by a continuous miner in conjunction with longwall-like hydraulic roof supports.

Shuttle car – A self-discharging truck, generally with rubber tires or caterpillar-type treads, used for receiving coal from the loading or mining machine and transferring it to an underground loading point, mine railway or belt conveyor system.

Slope – Primary inclined opening, connecting the surface with the underground workings.

Slope mine – An underground mine with an opening that slopes upward or downward to the coal seam.

Slurry – A mixture of water and any of several finely crushed solids, especially clay, or coal

Subbituminous – Rank of coal between lignite and bituminous.

Subsidence – The gradual sinking, or sometimes abrupt collapse, of the rock and soil layers into an underground mine. Structures and surface features above the subsidence area can be affected.

Surface mine – A mine in which the coal lies near the surface and can be extracted by removing the covering layers of rock and soil. Surface mines include: area, contour, open-pit, strip or auger.

Tipple – Originally the place where the mine cars were tipped and emptied of their coal, and still used in that same sense, although now more generally applied to the surface structures of a mine, including the preparation plant and loading tracks.

Ton – A short or net ton is equal to 2,000 pounds; a long or British ton is 2,240 pounds; a metric ton is approximately 2,205 pounds.

Tram – Used in connection with moving self-propelled mining equipment. A tramming motor may refer to an electric locomotive used for hauling loaded trips or it may refer to the motor in a cutting machine that supplies the power for moving or tramming the machine.

Transfer point – Location in the materials handling system, either haulage or hoisting, where bulk material is transferred between conveyances.

Underground mine – Also known as a “deep” mine. Usually located several hundred feet below the earth's surface, an underground mine's coal is removed mechanically and transferred by shuttle car or conveyor to the surface. Underground mines are classified according to the type of opening used to reach the coal, i.e., drift (level tunnel), slope (inclined tunnel) or shaft (vertical tunnel).

Unit train – A long train carrying roughly cars full of coal.

Ventilation – The provision of a directed flow of fresh and return air along all underground roadways, traveling roads, workings, and service parts.

Violation – The breaking of any state or federal mining law. The Federal Mine Safety and Health Act imposes “strict liability” on mine operators for violations of safety or health standards at the mine regardless of fault.

Void – A general term for pore space or other reopening in the rock. In addition to pore space, the term includes vesicles, solution cavities, or any openings either primary or secondary.

Waste – Material other than coal. Also called spoil.

Working section – From the faces to the point where coal is loaded onto belts or rail cars to begin its trip to the outside.