Two plant surveys were conducted at Lahanos Cu--Zn Concentrator under different operating conditions to assess the performance of the plant. In particular, an alternative process flowsheet, which was based on metal balance and quantitative mineralogy, was evaluated. First, a block survey was performed in the existing circuit. Next, cell-by-cell sampling was performed in the Cu rougher bank after the circulation of the scavenger concentrate to the feed was stopped. This allowed for the determination of the flotation kinetics of the minerals in the fresh feed and the effect of the circulation on the stream. Mass balancing results revealed that 14.3% and 12% of the copper was lost by the rougher and scavenger tails, respectively. Mineralogical analysis of the first survey showed that the scavenger concentrate primarily consisted of coarse/locked particles. According to the results, even the amounts of minerals in the rougher concentrates were similar in both surveys; liberation has improved by approximately 35-69% in the second survey particularly for copper minerals. It is concluded that recirculating the stream to the feed would negatively affect plant performance. Therefore, finer grinding was tested in the plant to assess the effect of decreasing feed tonnage on the liberation. It was found that copper loss in the tails was significantly decreased. Finally, possible flowsheet modifications based on these results are discussed.