This paper is to investigate alterations of wall rocks in Kankoy deposit. Kankoy deposit which is a Cu-Zn-Pb type volcanogenic massive sulfide (VMS) deposit, situated in the western central part of the eastern Pontide tectonic belt. The deposit is hosted predominantly by tuff, tuff-breccia, and flow-banded breccia of dacite which are all late cretaceous in age. Samples were systematically collected from surface outcrops, drill cores and the mineralized zones (accessed through underground workings) and were studied through petrographical and geochemical analyses. The results showed that the footwall rocks were variably altered. Alteration mineralogy is usually consisted of three distinctive zones. The inner zone was characterized by presence of quartz and sericite, extensively overprinted by kaolinite in places. This zone was graded outward into a sericite-chlorite and further into chlorite-montmorillonite zones. Mass-change calculations revealed that Al, Zr, Ti, and Y behaved as the immobile elements during the alteration and in that felsic footwall rocks gained Fe, Si, Mg, K and ore forming constituents, respectively. The most characteristic chemical changes near the ore bodies occurred in Na and Ca contents. They both showed strong depletion, mainly due to plagioclase destruction by the hydrothermal fluids. Chlorite alteration was manifested by the replacement of feldspars and a decrease in sericite abundance related to a net addition of Fe and Mg to the system. The REE contents also varied considerably depending on mass-change effects related to alteration. On the contrary to the footwall rocks, mass-changes associated with the hanging wall rocks of the region were generally much smaller.