The article is devoted to the issues of OAO «Gaisky GOK» Concentrating Plant expansion project realization. Design stages related to the facilities, subjected to expansion and upgrade from 2004 to the present day, as well as implementation of design works at different engineering stages, including the Feasibility Study and Detailed Design, are described. The adopted concepts related to processing technology and metallurgical results, design-layout and arrangement concepts, equipment implementation of the adopted technology, are described in detail. Construction stages of the Concentrating Plant facilities, subjected to expansion, as well as progress of erection works are reflected. The results, achieved in ore processing and saleable output during start-up stage, are presented, and the main trends for improvement of achieved performance indices are indicated.