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Demonstrated reserves�C A collective term for the sum of coal in both measured and indicated resources and reserves.

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.

Detectors- Specialized chemical or electronic instruments used to detect mine gases.

Detonator- A device containing a small detonating charge that is used for detonating an explosive, including, but not limited to, blasting caps, exploders, electric detonators, and delay electric blasting caps.

Development mining- Work undertaken to open up coal reserves as distinguished from the work of actual coal extraction.

Diffusion- Blending of a gas and air, resulting in a homogeneous mixture. Blending of two or more gases.

Diffuser fan- A fan mounted on a continuous miner to assist and direct air delivery from the machine to the face.

Dilute- To lower the concentration of a mixture; in this case the concentration of any hazardous gas in mine air by addition of fresh intake air.

Dilution- The contamination of ore with barren wall rock in stopping.

Dip- The inclination of a geologic structure (bed, vein, fault, etc.) from the horizontal; dip is always measured downwards at right angles to the strike.

Dragline�C 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 dumps the material on a spoil bank, in a hopper, or on a pile.

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

Draw slate- A soft slate, shale, or rock from approximately 1 cm to 10 cm thick and located immediately above certain coal seams, which falls quite easily when the coal support is withdrawn.

Drift- A horizontal passage underground. A drift follows the vein, as distinguished from a crosscut that intersects it, or a level or

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