The Chelopech epithermal arsenic bearing high-sulphidation, copper-gold deposit located in Bulgaria is often considered as the richest European gold deposit. Selected physicochemical parameters have been measured at key flotation streams inside the processing plant. Sampling campaign has followed with samples being submitted to chemical and mineral liberation analyses. A quantitative analysis has enabled to link copper flotation response to the type of copper bearing minerals and physiochemical parameters such as redox potential (Eh), dissolved oxygen (DO), EDTA extractable Cu and Fe. Data from the mineral liberation analysis (MLA) have highlighted an important process- relevant information explaining the variable floatability in different particle size ranges. A low chalcopyrite recovery can be linked to the non-sufficient amount of dissolved oxygen inside the copper selective flotation. Given the finely-disseminated copper bearing minerals, copper losses due to particle locking could be suggested as well.