This paper studies an actual case of an 170–180-meter deep lignite mine in Northern Greece, where the combination of thin clay layers, overlaying deep sandy layers with an unfavorable inclination and complex tectonic formation have generated a slow moving landslide inside the mine pit. The landslide area which has an axial extend of around 1700 m and a lateral extend of around 600 m has been formed due to unfavorable geological—geotechnical conditions and anthropogenic operations. These operations, include the placement of spoil at the crest of the area and removing of material from the toe. Since this is an active mine, with large earthwork moving operations, it was important to accurately evaluate the mechanisms that led to the formation of the landslide, and the effects of the moving landslide body to the operations of the mine. During the investigation of this large landslide area, different data were utilized, starting from borehole data of more than 50 borings ranging from 150–300 m deep, 6 borehole in which High Resolution Acoustic Televiewer loggings where performed, and three deep inclinometers. All data were combined and critically evaluated to generate the possible landslide mechanisms and to evaluate different analysis methodologies.