Purpose. The present paper aims to enhance methodology for determining the safety and stability parameters of room mining systems with backfilling of the mined-out area when mining uranium ores in underground mines of the State Enterprise “Skhidnyi Mining and Beneficiation Plant” (SE “SkhidGZK”). Methods. The analytical research method used in the presented paper includes the analysis of previous relevant instructions and reports on the research performed at the SE “SkhidGZK”, as well as publications on the subject, operational geological survey documentation containing monitoring data on the stress-strain state of the rock mass surrounding the formed cavities and the actual state of the mined-out blocks in all underground mines of SE “SkhidGZK”. Findings. The research performed enables development of a new instruction for determining the safety and stability parameters of the room systems with backfilling when mining uranium ores in the SE “SkhidGZK” underground mines. Based on the developed new instruction, the stability of outcrops in mined-out rooms has been calculated, considering the actual time of their life. The obtained parameters fully correspond to actual stability of rooms in blocks of all underground mines. This indicates that the new instruction is more advanced as compared to the current Instruction and its implementation will contribute to mine safety enhancement. Originality. The increased depth of mining uranium ore in the SE “SkhidGZK” underground mines and the increase in lifetime of mined-out rooms require regular adjustment of the methodology for determining their safety and stability parameters. Based on the accumulated production experience, the observations conducted and a thorough analysis of the actual state of cavities, new and adjusted current dependences have been obtained that more accurately consider the impact of both determined factors and those unprovisioned in the current Instruction for determining the safety and stability parameters of rooms. Practical implications. The advanced methodology for determining the safety and stability parameters of room systems in comparison with the methodology described in the current Instruction at the “SkhidGZK” underground mines provides higher accuracy when determining the design parameters of rooms in the stoping blocks and greater reliability of predictive stability of both individual outcrops and rooms in general.

Decrease in grade and high losses of broken ore are stated to be important problems that accompany the process of marketable production in mining of iron ore deposits by underground methods. The article analyzes and generalizes causes of high losses and dilution of broken ore during its drawing underground. It is found that dilution of ore with waste rocks results in the decreased iron content in the extracted ore mass as compared to that in the ore massif. The research performed enables development and scientific substantiation of a rational technology of ore drawing and transportation that improves the mined ore grade by more complete extraction of broken reserves of clean iron ore from the ore body footwall.

The main indicators of the iron ore quality are the content of iron, silica, phosphorus and other components. It is ascertained that the quality of ore depends on its grain-size composition. The article proves that when crushing 16-0 mm fraction ore to 5-0 mm, Fe content is reclassified by sizes due to liberation of both martite and hematite at this grain size. To reduce energy consumption during grinding, it is recommended to install high pressure grinding rolls for crushing the 16-1 mm fraction and consider this operation as the first stage of grinding. Martite liberation in the -1.0+0.0 mm material shows that significant predominance (87.0 vs. 13.0%) of free grains over aggregates is observed in the -0.071+0.05 mm fraction material. Free martite aggregates make 57.12% in the -0.16+0.071 mm material. Complete (100%) liberation of martite is observed in the -0.05 mm material. Sieve analysis of the A56 sinter ore sample crushed to 5-0 mm in the industrial roll crusher enables ascertaining that the greatest increase in recovery (Fetot = 60.05%) of sinter ore occurs at the -0.16+0.071 mm grain size.

The work contains studies of the problem of stabilizing geodynamic processes in the rock massif, preservation of the daylight surface and ecological balance in the mined-out and operating mine fields of Ukraine. The main regularities of influence of sublevel-room mining systems with backfilling on changes of the stress-strain state of the rock massif and the main structural elements of the block are determined. Rich iron ore mining by underground methods and subsequent transition to the sublevel-room mining system with backfilling is modeled. New technologies for mining ore deposits are developed and current ones are enhanced to prevent the earth’s surface failures, stabilize landslide and displacement zones within the boundaries existing at the time of transition to systems with backfilling. The developed resource-saving technologies of mining can significantly enhance ore extraction indicators and the environmental condition of the basin by locating waste dumps and disposing wastes of mining enterprises in the mined-out area of underground mines.

The work analyzes current technologies of ore mining applying self-propelled equipment in underground conditions; studies practices of using the equipment in general and for broken ore transportation only; considers performance of mining enterprises in similar mining-geological and miningtechnical conditions; analyzes and generalizes causes of high ore loss and dilution rates in underground mining in Kryvyi Rih iron ore basin, thus revealing a problem of providing high efficiency and increased ore extraction with minimal quality deterioration. Marketable ore production is affected by decreased quality and high broken ore losses. Incomplete balance ore extraction when breaking and drawing ore from the stope results in deterioration of mining indices. Ore dilution with waste rocks leads to decreased ore content in the mined mass as compared with that in the ore massif. The research enables development and substantiation of the rational technology of ore drawing and transportation as well as designing a new structure of the loading face to ensure increase of the drawn ore quality indices.