Comminution Circuits Predictions of mill throughput from a porphyry copper open pit based on comminution test results of 22 composites and the available motor power of a Standard SAG Mill Ball Mill circuit consisting of one 40 ft dia x 22 ft EGL SAG Mill rated at 24 MW GMD and two Ball Mills each 26 ft dia x 40 ft EGL and rated at 16 4 MW GMD