On 17 November 2016, an unexpected slope failure occurred in an open pit copper mine which causes loss of lives and machinery. The geological and hydrogeological properties of the mining area were investigated with a concentration on the failure area. In the northern part, where the failure happened, the limestone and dolomitic alluvium has formed a highly permeable weak but cohesive formation lying on more competitive splits which are quite impermeable. The study is performed to find the main reasons for catastrophic failure. The geological sections containing hydrogeological and geotechnical data were applied to perform two-dimensional limit equilibrium method (LEM) analyses for undrained and drained conditions. As it is expected, in a permeable formation, excess pore water pressure can be tolerated until the saturation level has not broken a certain threshold level; on the other hand, it would be a trigger factor leading to a slope failure. The initial results proposed that the sliding initiated in the permeable zone which was overlying on impermeable strata and saturated after a 3-day downpour. The stable geometries for benches and overall slopes were then determined. The stable bench parameters have been defined for each geological unit so the mine planning can be performed based on a block model. These models divide the mining area into geological units which each of which contains specific geotechnical data. The output of the research can be applied to mine sites facing a similar geohazard.