In order to provide an uniform feed to the processing plant, the mined from a porphyry copper deposit ore is blended in the following proportions: Propylites 31-35%; Argilizites 30-33%; Secondary quartzites 30-36 % (roughly 1:1:1). Those three types of ore differ in particle size, as well as in mineral composition. The variations in the mineral composition of the treated ore are due to the varying content of primary and secondary copper sulphides as well as of oxide minerals. There are also significant amounts of clay minerals in the ore. A recent research program shows that the propylite compound in the feed ore will increase significantly. Approximately 68 -70 % of the ore blend, entering the processing plant will be composed of propylites, 28% - argilizites and 4% secondary quartzites. Therefore, for the purpose of analyze and evaluate the performance of comminution equipment in the processing plant, an industrial experiment for several work shifts with the above mentioned percentage content of the run of mine have been conducted. Furthermore, one of the autogenous mill (AG) was converted in semi-autogenous mill (SAG) with adding 8% grinding media, appropriate lifters and liners profile, and discharge grates with 15 and 30 mm openings. The aim of the industrial experiment was to assess the benefits of SAG mill grinding, and to evaluate the grinding and classification efficiency of the associated ball mills closed with hydrocyclones. The particle size distribution curves showed that there is no significant difference between the current ore blend (1:1:1) and the experimental mixture (68-70% Propylites). Sampling was carried out in order to determine the distribution of the material flows (quantitative assessment) to the subsequent comminution sections, such as secondary and tertiary crushing, ball mill grinding and classification. The results showed that a combination of semi-autogenous and ball mill grinding is an appropriate way of comminution circuit optimization.