##### C O N S U L T I N G L T D TECHNICAL MEMORANDUM

EF5BM=[ P80+10.3 1.145×P80] ( 3 ) The EF4 formula requires both the rod mill and ball mill work index (rod mill Wi is used to calculate the optimal feed size) and because this is a "single-stage ball mill" calculation, the F80 is actually the rod mill feed size (10,000 µm) from Table 1 and the P80 is the ball mill circuit product. The EF5 factor only applies below 75 µm to ball