The present work considers the problems of mining lost ore reserves out of protection pillars, which were unprofitable to develop before. At present time due to the deterioration of mining and geological conditions, it is sometimes economically reasonable to return to the previously mined sections and develop the pillars at the upper horizons which were preserved under the exploitation. These pillars usually have over 25% of balance reserves of metallic ore, up to 60–70% of potassium salts and more than 30% of coal. The technology of mining these pillars plays important role under the assessment of the possibility of their excavation, because the protection pillar, as a rule, represents highly fissured and tectonically disturbed ore massif. When mining protection pillars two situations are possible: in the first one – strength characteristics of ore body are significantly higher than strength and stability of enclosing rock; in the second one – strength characteristics of enclosing rock are significantly higher than the characteristics of ore massif. Taking into account all stated by the authors, it is suggested to fulfill the excavation of reserves out of protective pillars with chamber systems of development with preliminary strengthening of enclosing rock in the first situation, and in the second situation – perform it under the protection of concrete support created in ore body in the shape of volumetric grating. The suggested technology has been tested at Berezovsky deposit and Zyryanovsky lead plant. The results of the investigations permit to recommend the technology developed by the authors to be used at other enterprises with similar mining and geological conditions.
The work considers the problems of recurring mining of lost ore reserves. Recurring development of deposits contributes to the improvement of the subsoil use completeness. Primary development is based on the method of maintaining overlying rock and stoping zone, whereas under the recurring excavation it is usually necessary to meet significant integrity damage of ore massif and enclosing rock. For this reason the production of the lost ore reserves with traditional methods is near-impossible. When selecting the method of underground recurring development it is necessary to take into account the factors which determine the practicability of these works: when excavating ore with low content of metal the factor of production cost acquires crucial importance; in case of works in the disturbed massif, the factor of safety is especially important; works in disturbed zones requires significant resources to develop and maintain the workings, thus, the method of development has to provide significant production output. By way of example of lost ore production, brand new technology is suggested, the essence of which consists in the additional output of caved rock mass out of the stopping zone in heavy suspensions.