ABSTRACT: The slope stability of rock masses which the engineering constructions build on is controlled by thestrength parameters of discontinuity surfaces rather than shear strength parameters of rock bodies. Inaddition, it is known that the aperture, persistence, roughness, and if it presents, thickness and type of infill materials are the major parameters which control the strength of discontinuities. In this study, theshear strength parameters of discontinuities in the hornfels lithology in the Doğu Ocak (eastern sector ofBalıkesir-Şamlı-Iron Open Pit Mine) were determined by using the Barton empirical failure criterion. Theprobable rock slope failure modes were established by means of kinematic analyses performed consideringthe orientations and shear strength parameters (cohesion and internal friction angle) of discontinuitysurfaces. It is proposed that the orientation of the slopes are 218° in northern side and 15° in southern sidewhereas bench slopes are 65° and 60° in W3 and W3-W4 weathering zones respectively, in accordancewith the stability analyses performed in the light of the information obtained from the models in the DoğuOcak.