Abstract:The evolution of mineral-bearing layer permeability during the acid in-situ leaching (ISL) process was clarified through a field tracer test conducted in the "one injection and four pumping" unit of the C12 mining area in the Bayan Ula uranium deposit. The test quantitatively assessed the flow rate characteristics of the leaching solution within the mineral-bearing layer, with variations in flow rate reflecting the evolution of the layer""s permeability. The experimental results show that after one year of ISL, both the number of migration pathways and the flow rate of the leaching solution generally decrease. After two years of ISL, blockage in the mineral-bearing layer is intensified, with the flow rate of leaching solution cumulatively decreass by 6.25% to 45.00%. In some migration pathways, the leaching solution can no longer permeate. The reduction in permeability is more pronounced in the more permeable pathways, with feldspar clay alteration and gypsum precipitation identified as key mechanisms contributing to the blockage in the mineral-bearing layer.