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  • Glossary
| Last Updated:11/08/2023



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Active Workings

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

Acid Mine Water

Mine water that contains free sulfuric acid, mainly due to the weathering of iron pyrites

Acid Deposition or Acid Rain

Refers loosely to a mixture of wet and dry "deposition" (deposited material) from the atmosphere containing higher than "normal" amount of nitric and sulfuric acids. The precursors or chemical forerunners of acid rain formation result from both natural sources, such as volcanoes and decaying vegetation, and man-made sources, primarily emissions of sulfur and nitrogen oxides resulting from fossil fuel combustion.


In coal mining, (1) the weight of the rocks above a narrow roadway is transferred to the solid coal along the sides, which act as abutments of the arch of strata spanning the roadway; and (2) the weight of the rocks over a longwall face is transferred to the front abutment, that is, the solid coal ahead of the face and the back abutment, that is, the settled packs behind the face.

Air Split

The division of a current of air into two or more parts.

After Damp

Gasses resulting from underground combustion, normally carbon monoxide. This is a loose term implying any fatal gas in a mine after an explosion or fire.


Mining in the same direction.


A nearly horizontal passage from the surface by which a mine is entered and dewatered.

Angle of Repose

A hard natural coal of high luster.

Angle of Draw

In coal mine subsidence, this angle is assumed to bisect the angle between the vertical and the angle of repose of the material and is 20° for flat seams. For dipping seams, the angle of break increases, being 35.8° from the vertical for a 40° dip. The main break occurs over the seam at an angle from the vertical equal to half the dip.

Angle of Dip

The angle that a magnetic needle makes with the plane of the horizon.


Instrument for measuring air velocity


Any passage through which air is carried


A surveying term that references the angle measured clockwise from any meridian (the established line of reference). The bearing is used to designate direction. The bearing of a line is the acute horizontal angle between the meridian and the line.

Auxiliary Ventilation

Portion of main ventilating current directed to face of dead end entry by means of an auxiliary fan and tubing.

Auxiliary Operations

All activities supportive of but not contributing directly to mining.

Augur (or Punch) Mining

A form of unmanned underground mining offering minimal capital cost and relatively short start up periods. Large augers or remote-controlled mine equipment bore into coal seams from roadways established on the floor of surface exposures.


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

Area (of an airway)

Average width multiplied by average height of airway, expressed in square feet.


Fracture processes around a mine opening, leading to stabilization by an arching effect.


A water-bearing bed of porous rock.


An upward fold or arch of rock strata.

Anthracite Coal

A hard natural coal of high luster.

Ash Content

Laboratory measurements of the amount of sediment deposited with vegetation (carbonaceous material) while a coal seam was formed. Ash content within a coal seam may consist of thin bands of visible sediments such as mud-stones or be non visible sediments distributed within the seam.


In metallurgy, the act or state of being stirred or shaken mechanically, sometimes accomplished by the introduction of compressed air.

Autogenous Grinding

The process of grinding ore with ore in a rotating cylindrical mill using large pieces of ore instead of steel rods or balls.


A chemical test by wet or fire methods performed on a rock sample to determine the amount of valuable metal contained.

Adiabatic Efficiency

  1. A compression term obtained by dividing the power theoretically necessary to compress the gas and deliver it without loss of heat, by the power supplied to the fan or compressor driveshaft.

Abyssal Theory

  1. A theory of mineral-deposit formation involving the separation and sinking of ore minerals below a silicate shell during the cooling of the Earth from a liquid stage, followed by their transport to and deposition in the crust as it was fractured (Shand, 1947). Modern thought ascribes more complex origins to mineral deposits.

Abbe Jar

  1. In mineral processing, a porcelain jar used for laboratory batch grinding tests in ceramic ware.

Accumulator Conveyor

  1. Any conveyor designed to permit accumulation of packages or objects. Usually roller, live roller conveyor, roller slat conveyor, or belt conveyor.

Accordion Roller Conveyor

  1. A roller conveyor with a flexible latticed frame that permits variation in length.


  1. Grapelike; applied to the structure of clustered mineral aggregates.
  2. Granulated; like grape seeds; applied to the texture of some mineral aggregates.

Air Power Operated Mine Door

  1. Mine doors help to keep the air flow in shafts and mine working areas constant. In cases of explosions, doors "give" to relieve the pressure, then close automatically. The doors are mobile and can be set up in any location. They are opened and closed by a compressed-air cylinder and are designed to be used where haulage equipment operates on a trolley wire.

Air Operated Winch

  1. A small, compressed-air drum haulage or hoist used for lifting, dragging, or skidding work in mines. With capacities ranging from 660 to 4,400 lb (300 to 2,000 kg), these winches have powerful piston motors and are capable of continuous operation. They are easy to move from job to job and are used for shaft sinking and moving wagon drills at quarry and opencast operations.

Allen O'Hara Furnace

  1. A horizontal, double-hearth furnace for calcining sulfide ores.


  1. In mine subsidence, an inward movement from the side, resulting in a pull or draw beyond the edges of the workings.

Air Barrage

  1. The division of an opening in a mine by an airtight wall into two sides; one side is used as an air intake, the other side as a return.


  1. In coal mining, bodies of combustible gases that tend to collect in higher parts of mine workings and at the edge of goaves and wastes. They are found in cavities, at ripping lips, at other sheltered places protected from the ventilating current, and at the higher sides of rise faces.
  2. The concentration or gathering of oil or gas in some form of trap. Commercial accumulation is a volume or quantity sufficient for profitable exploitation.