Purpose. Development of a methodology for determining the level of actual losses and dilution of ore based on the identified patterns of the influence of occurring ore body elements and the stope parameters when mining thin slope deposits using a system for delivering ore by the blasting force. Methods. The task set is solved using an integrated approach, including the analysis of literary sources and the existing practical experience on the issues of losses and dilution, conducting experimental-industrial experiments in the conditions of the Akbakai deposit to assess the recommended method effectiveness for determining the values of excess losses and dilution of ore, geomechanical assessment of the mass using the methods of limit equilibrium, numerical and probabilistic analyses. Findings. A methodology for determining losses and dilution when mining thin slope deposits using a system for delivering ore by the blasting force is proposed, which makes it possible to predict excess losses and dilution coefficients arising from stope roof caving and incomplete ore delivery. The actual losses and dilution of ores in the Akbakai deposit have been determined based on the proposed methodology and instrumental surveys. The developed methodology for determining the values of excess losses and dilution makes it possible to take preliminary measures to prevent the stope roof caving with the complete ore mass delivery using the blasting force. Originality. New dependences have been revealed for the conditions of the Akbakai deposit: logarithmic – the value of dilution depending on the angle of the ore body occurrence; polynomial – the stope maximum span depending on the ore body dip angle; exponential – ore losses depending on the angle of the ore body occurrence. Practical implications. The practical significance, confirmed in the course of pilot-experimental work, is in minimizing the percentage of loss and dilution of the useful component when mining thin slope ore deposits using a sublevel blast-hole stoping system with an open stope space, which makes it possible to reduce the cost of the produced mineral.