The electrochemical behaviour of a massive chalcopyrite after chemical leaching, or microbial leaching using a mixed culture of mesophilic microorganisms (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirilum ferroxidans), were compared. Linear voltammetry was used as the analytical technique to follow the compositional changes on the electrodes. Preliminary tests on particulate electrodes (graphite, elemental sulphur and Ag2S) were also included to determine the electrochemical reaction in these silver-catalysed systems. In both leaching and bioleaching, a silver sulphide coating appeared on the surface. However, its thickness was higher and elemental sulphur was produced on the chalcopyrite surface by the microbial leaching. These results confirmed the catalytic mechanism of the Ag+ cations on the chalcopyrite leaching, which was proposed by Miller and later reported by many researchers.