Mining Terminology - J

Jackleg - A percussion drill used for drifting or stoping that is mounted on a telescopic leg which has an extension of about 2.5 m. The leg and machine are hinged so that the drill need not be in the same direction as the leg.

Jackrock – A caltrop or other object manufactured with one or more rounded or sharpened points, which when placed or thrown present at least one point at such an angle that it is peculiar to and designed for use in puncturing or damaging vehicle tires. Jackrocks are commonly used during labor disputes.

Jaw crusher - A machine in which rock is broken by the action of steel plates.

Jig - A piece of milling equipment used to concentrate ore on a screen submerged in water, either by the reciprocating motion of the screen or by the pulsation of water through it.

Job Safety Analysis (J.S.A.) - A job breakdown that gives a safe, efficient job procedure.