Unloading scheme to control sliding mass at Angouran open pit mine, Iran

Angouran zinc-lead open pit mine, located in the northwest of Iran, has experienced a large-scale slope failure in the order of 12Mm(3) volume. The main challenges due to this giant failure are subsequent responses of the sliding mass, geometry of the slip surface, and where unloading procedures should be performed to stabilize the slope and restart mining operation. To find solutions for the challenges, a comprehensive site investigation and monitoring was conducted to compare the primary and secondary discontinuity patterns, besides a three-dimensional discrete element modeling to identify the failure scenario and determine the governing mechanism. According to the results, the failure region was divided into three main parts: sheared, sliding, and crushed zones. Based on the slip surface geometry and the relative position of the main parts in the failure region, an unloading scheme was presented. It is estimated that over 4mm(3) should be unloaded to restart mining operation.