The objective of this study is to determine an optimal grinding circuit tuning for the maximisation of the economic value of the concentrate produced by the subsequent flotation process. The complexity of defining optimisation criteria and optimum operating conditions has been extensively discussed in Kelly 999 and Spottiswood (1982) and Kelly (1991). Bascur (1991) has proposed a profitability concept defined by relating profit, recovery, tonnage and grind in order to co-ordinate the overall grinding and flotation objectives. He showed that there is an optimal profit as a function of the milling rates and proposed control strategies for maximising the revenue. Morrison (1993) discussed also various optimisation strategies such as minimum energy and maximum recovery philosophies and studied the impact of the grinding circuit tuning on the metal recovery. In those studies the right questions about optimisation of mineral processing plants are raised, but there is no complete methodology offered to optimise plant performance.