Optimizing the fuel consumption of truck fleets in open-pit mines is of great importance, as a major part of operating costs and environmental impacts are related to this sector. In this study, an integer mathematical programming model is developed for the optimal allocation of truck fleets, the main objective of which is to minimize the fuel consumption of the truck fleet during a work shift. The model is formulated considering real operational constraints. In this model, the availability of the fleet and the uncertainty due to truck breakdowns are considered. The proposed model was implemented using real data from the Sungun Copper Mine. The model outputs were compared with the actual mining operations for the same shift. The results of this comparison indicated that, under optimal truck allocation, the total mine production increased by approximately 37.5% compared to the actual operation, while the fleet fuel consumption decreased by about 78% relative to the real operational conditions. This significant reduction in fuel consumption, while reducing operating costs, has a positive impact on reducing environmental pollution and shows that optimizing the fleet management system can significantly improve the productivity and sustainable development of mining operations.