Answer: A. digging a tunnel into the side of a mountain, often involving explosives.
Drift mining is a process of subsurface or underground mining. That involves horizontal digging a tunnel into the side of the mountain or hillside in order to extract mineral deposits. This results in a creation of a drift, a long dug with tunnel, a horizontal path towards mineral resources. Explosives are used to create tunnel in the subsurface layers of the mountain. Creation of tunnel can drift a person towards mineral deposits due to the action of gravity. This mining method can be used to extract minerals of economic importance like gold, coal, zinc and quartz.