 However, the purchase turned out to be a regrettable decision for ARCO.Lack of experience with hard-rock mining, and a sudden drop in the price of copper to sixty-odd cents a pound, the lowest in years, caused ARCO to suspend all underground mining operations in Butte in 1980.ARCO closed the Berkeley Pit and shut off the deep pumps in 1982, allowing the pit and mines to fill with water.