A top-down control structure is presented for the optimal steady-state operation of a base metal refinery. The economic cost function for the plant is derived in terms of the production rate of primary and secondary products, the losses of primary product to the secondary product streams, and the fixed and variable costs of the plant. The economic performance of the plant is largely defined by the operation of an exothermic pressure leach circuit. The leach efficiency of this circuit determines the potential production rate for the plant, its operation affects costs, and it is the source of all primary product losses. Given market prices for the primary and secondary products, and reagent and utility costs, the proposed control structure can be used to define the optimal operating region for the pressure leach circuit so as to maximize the profitability of the plant.