The article aims to develop the resource-saving technology when mining steep ore bodies applying 250 mm-diameter boreholes to break ore into the compressed environment. This will reduce dilution of the mined ore mass in conditions of rock pressure around blocks. When mining iron ore deposits of Kryvyi Rih basin, applied mining systems allow for creation of the compensatory space as the first stage. However, these stopes fail under rock pressure, this influencing negatively ore breaking and extraction. The degree of extraction can be increased through breaking ore mass into the compressed environment. The width of the ore layer to be broken onto the compressed environment is determined through industrial investigations. To enhance breaking conditions, it is suggested to apply boreholes of a larger diameter. However, there is no technique developed for determining thickness of the ore layer to be broken depending on the borehole diameter and the fragmentation factor. When applying 250 mm boreholes, increase of thickness of the layer to be broken from 2 to 10 m is found to cause compaction of the previously broken layer up to 3 m with the optimal ore fragmentation factor of 1.3-1.5 and 3-fold decrease of lumps yield. This results from the fact that drilling a 250 mm borehole to secure even provision of the massif with explosives reduces the line of the least resistance.