Underground hard-rock mining refers to various underground mining techniques used to excavate "hard" minerals, usually those containing metals,[1] such as ore containing gold, silver, iron, copper, zinc, nickel, tin, and lead. It also involves the same techniques used to excavate ores of gems, such as diamonds and rubies. Soft-rock mining refers to the excavation of softer minerals, such as salt, coal, and oil sands.
- ^ de la Vergne, Jack (2003). Hard Rock Miner's Handbook. Tempe/North Bay: McIntosh Engineering. p. 2. ISBN 0-9687006-1-6.