Before revision: In mining, they were used to drill into the soft carbonate rocks of lead and zinc hosted regions to extract bulk samples of the ore. Churn drills are also called percussion drills as they function by lifting and dropping a heavy chisel-like bit which breaks the rock as it falls.
After revision: ,In mining, they were used to drill into the soft carbonate rocks of lead and zinc hosted regions to extract bulk samples of the ore. Churn drills are also called percussion drills as they function by lifting and dropping a heavy chisel-like bit which breaks the rock as it falls.