A complex copper/lead-zinc ore from the Raura plant (Peru) that contains secondary copper minerals was studied with respect to improving copper/lead separation from the copper/lead bulk concentrate. As with most Peruvian plants that treat copper/lead-zinc ores, the Raura plant uses a dichromate separation method, which is ineffective due to the presence of secondary copper minerals. The use of alternative copper/lead separation techniques, such as SO2-starch or heat methods, are restricted due to the high altitude of the plant, which is at over 4300 rn elevation. During this study, a new copper/lead separation method was developed and introduced into the plant with significant improvement to the metallurgical results, The new depressant is based on dichromate complexed with carboxy methylcellulose (CMC) and sodium phosphate (Na2HPO4). Apart from an improvement in the plant metallurgy, the level of chromium-6 (Cr+6) in the effluent was reduced ten-fold. This paper summarizes the development testwork in the laboratory and presents the results obtained in the plant using the new depressant.