In open-pit coal mining, the collapse of in-pit overburden (OB) dumps can initiate hazardous granular mass flows, threatening safety of personnel and equipment near the active working face. Establishing a buffer zone around in-pit dumps is essential to enhance safety by limiting or prohibiting the movement of workers and machinery. The extent of this buffer zone depends on the runout characteristics of the failing mass. Previous studies using the discrete element method (DEM) to understand granular flow dynamics and runout behavior have primarily focused on homogeneous systems with spherical particles, lacking comprehensive analysis of shape variation and size distribution inherent in overburden dumps. This study investigates the influence of particle shape on runout behavior using DEM simulations, focusing on spherical, blocky, platy, and needle-shaped particles. Results reveal that granular mass movement, driven by gravity under unobstructed conditions, consistently forms three distinct zones: the highest velocity at the flow front and the lowest at the tail. Mixtures with diverse particle shapes in equal proportions exhibit enhanced interlocking and demonstrate the shortest runout distance. Spherical particles, while exhibiting efficient momentum transfer and the highest velocities in the flow flume, experience quicker kinetic energy dissipation upon contact with the horizontal deposit plane. Despite this rapid dissipation, spherical particles achieve the longest runout distance. These findings provide crucial insights for developing predictive models and effective mitigation strategies for overburden dump management in mining operations.