The paper describes a retrofit application of our computer-based mineral processing flowsheet design system. This system uses industry-accepted models together with economic objectives, to generate designs which can be realistically rated according to their financial returns. The system generates sets of economically 'good' flowsheets for a given task (production of a marketable concentrate from a specified ore) by an evolutionary, heuristic process. In its current form it is suitable for flotation-based processing, which may include comminution and size classification. Retrofit and process modification, as well as grass-roots designs, is possible and is specifically illustrated by a case study here. The results are shown to be competitive with those produced conventionally, and may increase the profits of large-scale operations by many millions of dollars annually.