The process objective of the ball mill circuit control scheme is to maximise the grinding effort applied to solids delivered by the SAG mill. To prevent spillage and overload, the control scheme must allow the ball mill circuit to accept almost any amount of feed rate without overload. At high feed rates, this will compromise the grind size, so the SAG mill feed rate limits must be managed to ensure the right grind size versus throughput tradeoff is achieved. This can be done automatically if a cyclone OF particle size analyser is available. At very low feed rates the ball mill circuit should not overgrind the ore, despite the grinding capacity being available to do so.