The central shaft reached a depth of 2980 feet and a southern shaft was sunk in 1928 to reach a depth of 3,600 feet . The central shaft reached a depth of 2980 feet and a south shaft was sunk in 1928 to reach a depth of 3600 feet . The south shaft reached a depth of 2980 feet and a central shaft was sunk in 1928 to reach a depth of 3600 feet .