This paper presents a sensitivity analysis of the impact the ore grinding level (% +212 microns) has upon the rougher flotation performance, where the main copper losses are related refine particles (less than 12 microns) with high content of soluble copper and coarse particles (larger than 212 microns) that are less liberated. Firstly, a one year grinding data set, considering average daily shifts, was analysed and it was shown that the classical Bond correlation properly describes the average trend of the grinding circuit operation in terms of ore tonnage, operational work index, product particle size d(80) and power availability. On the other hand, the rougher flotation kinetic was characterized from plant testing. Thus, copper and moly recoveries were correlated by Klimpel＇s model to describe the rougher flotation performance, at different particle size classes, in terms of design and operating variables. The copper recovery was found to be critically dependent on the ore grinding level, % +212 microns, and the soluble copper content. Using the grinding and flotation correlations, a plant simulator, that integrates the grinding and flotation capacities, was built. The simulator was validated with plant data for a range of ore tonnage, for different grinding levels and at two power levels. The simulator is useful in selecting the grinding reference, to identify critical requirements of instrumentation, bottlenecks limiting plant capacity, and to complement the supervisory control strategy. Thus, a powerful tool to estimate the best compromise between ore tonnage and grinding level in order to maximize the values recovery, was established.