The second largest man made hole in the world (Bingham Copper Mine in Utah being number one) is the Mirny Diamond Mine. It is located in eastern Siberia. Excavation began in 1955 to supply the Soviet Union's needs for industrial grade diamonds. It is 1,722 deep and 3,900 feet across.
Open pit mining has ceased, but during its peak years it was producing 10 million carats of diamonds annually- a good percentage of which were gem quality. Additional photos and information available at Atlas Obscura