Vol 49 Iss. 1

At the Zapolyarny mine of the Norilsk Combine, the complex conditions of the disseminated ore deposit make it difficult to develop mining systems and select their individual design elements. The lack of similar examples in the global mining practice forced to search for new ways of solving mining engineering issues, to check and correct the decisions made. Rapid growth rates of ore production led to the fact that the experimental application of new variants of systems and methods of mining pressure control went simultaneously with operational works. Sometimes this helped to solve problems as quickly as possible, and at other times, on the contrary, it made it difficult to reach the right conclusions.

The disseminated copper-nickel ore deposit developed by the Zapolyarny Mine is represented by a gabbro-diabase deposit up to 30 meters thick, dipping at an angle of 12-20°. Above the ore-bearing intrusion lie effusive rocks (porphyrites, gabbro-diabases) with a total thickness of 180-250 m.

It is known that mass explosion of ore by boreholes or mine charges under the system of forced storey collapse can be carried out on preformed compensation chambers or without them. The latter method - one-stage ore stripping in a clamped environment - is currently used at the apatite mine named after S. M. Kirov. S.M. Kirov apatite mine, Zapolyarny mine of Norilsk Combine, Salair mine, mine named after XXII Congress of the CPSU of Zyryanovsky Combine and others. The method of stripping affects the physical and mechanical properties of the stripped ore: if in variants with compensation chambers the coefficient of initial loosening of the ore immediately after blasting the block varies from 1.3 to 1.6, then at one-stage stripping this coefficient varies from 1.1 to 1.3.

The correct choice of the underground development system and its main structural elements is especially important for enterprises developing complex vein forms. At such enterprises, the production process usually ends with the production of concentrates, so an efficient development system should ensure the minimum cost of the final product. In this regard, the choice of development system includes the following stages: selection of effective development systems on mining and technical and technical-economic factors; comparative economic evaluation of selected development systems; industrial research selected development systems and clarification of their basic design elements; technical and economic analysis of systems and recommendation of the most effective options.

The Rasvumchorr-Circus and Tsentralny apatite open pits are located in the central part of the Khibiny massif and develop part of the arc-shaped apatite deposit.The deposit area is characterized by harsh climatic conditions: low negative temperatures in winter (up to -36° C), snow blizzards and storms. The number of days per year with negative temperatures on the high-mountainous plateau of Rasvumchorr reaches 300, on the Rasvumchorr-Cirk open pit - 270. The duration of the winter period is 9 months; the thickness of snow cover on the plateau exceeds 3 meters. Frequent fogs and avalanche-prone slopes significantly complicate the work of open pits in winter. According to the project of the institute “Giproruda” the productivity of open pits: Rasvumchorr-Cirk 1.8 million tons, Central 12 million tons of ore per year. However, the actual productivity of the Rasvumchorr-Tsirk open pit significantly exceeded the design.

One of the polymetallic deposits of the Union, where vein thickness varies from a few centimeters to 2-3 m and dip angles from 25 to 90°, is represented by a variety of vein forms, among which branching ore bodies are widespread. The development of veins branching along the uprise is particularly difficult, as the acceptability of a productive system with ore storages on thin veins is determined by the possibility of partial release of ore from the branched storages to the common floor drift. This determines the choice of the development system option,* the volume of preparation and cutting works, labor productivity and ore cost. The possibility of partial release at simultaneous stripping in all branching veins (main vein and apophysis) is determined by the rate of ore flow from the stores along the vein and apophyses.

In the underground development of non-ferrous metal deposits quite often ore inter-chamber pillars are replaced by artificial usually concrete “pillars” - supports to achieve the most complete extraction of rich ores, to get the opportunity to use high-productive methods of ore stripping both in the chambers and in the mining of pillars. From the point of view of reducing the cost of ore, the thickness of supports and the strength of concrete should be as small as possible. At the same time, the concrete supports should be strong and stable enough until the end of ore extraction operations, and sometimes for a longer period of time. Therefore, choosing the optimum dimensions of concrete supports is very important and responsible. However, there is still no definite methodology for calculating the parameters of concrete piers. Their sizes and concrete strength grades are usually determined on the basis of practice data.

At two-stage development of powerful steeply falling deposits with replacement of inter-chamber ore pillars with concrete wall supports it is very important to choose the right wall thickness and concrete grade. The methodology of such calculations is insufficiently covered in mining engineering literature. Laboratory studies on models at the Leningrad Mining Institute have shown that inter-chamber concrete supports in mining systems with ore storage or under-storey stripping (with subsequent filling of chambers with stockpiles) resist lateral loads like thin slabs with different fixing along the contour. The final destruction of the wall under the action of lateral loading occurs from the loss of stability by overturning or shear (wall subsidence).

In the mines of the Baltic oil shale basin, extensive industrial tests of different variants of the chamber mining system have been carried out for several years. In order to correctly determine the parameters of the system, the manifestation of mining pressure was studied at the mine No. 3 of the Slantsy Combine, in particular, the stability of the pillars was investigated. The industrial oil shale bed with a total thickness of 2 -3 m is almost horizontal at a depth of 30-100 m in the conditions of the basin and consists of four layers of oil shale and three rock layers. In the roof and soil of the formation, limestones are interbedded with clay and oil shale.

Usually rocks are fractured, so to judge the deformation of the rock during impact or explosion, it is necessary to be able to determine the wave resistance of fractured rocks.As a first approximation, let us assume that parallel cracks in the rock are combined into systems, in each of which the crack opening d and the distance between them a are constant. Let us assume that the rock is penetrated by three mutually perpendicular systems of cracks and that the cracks are filled with a substance with wave resistance. Let us denote the ratio of crack openness in each system (è = 1. 2, 3).

At development of any deposit numerous variants of development systems are possible according to the order of development of the front of works in the open pit. The final evaluation of variants with the choice of the most economical of them is carried out according to the usual methodology.

The development of calculation methods for rock transfer beyond the contour of the open pit is associated with the design of the development of a group of bauxite deposits and further work on the definition and implementation of rational parameters of mining operations for rock transfer by walking draglines. Usual design calculations are carried out on many cross-sections with drawing of each drift. The labor intensity of this method is high, and the accuracy, depending on the distance between adjacent cross sections, is low, because the number of sections to speed up calculations is limited to.

Tikhvin bauxite deposits, on the example of which are considered dependencies in the development of the front of work at open pits, dangerous for landslides, are characterized by an irregular shape, a small width (an average of 200-300 m) and a significant length (0.5-3 km). Due to the small thickness of deposits, mining works are carried out by one ledge, sometimes with division into sublevels, using upper and lower loading by excavators with buckets of 1-4 m3. The thickness of covering rocks is characterized by layered structure, change of lithological composition in transverse and longitudinal directions, fall of clay layers in some areas towards the mined-out space of the quarries, as well as watering of gravelly pebble deposits, sands, fractured limestone and bauxite rocks.

At quarries of the Leningrad region granite stripping is conducted, placing charges of explosives in vertical wells in diameter of 105 mm. Usually after explosions the bottom of a ledge turns out extremely uneven, ledges (sills) sometimes reach one third of height of a ledge. Due to the uneven bottom of the ledge productivity of excavators EKG-4 does not exceed 250 thousand m^3/ year, ie about half as much as at the advanced mining enterprises.

As is known, the hydraulic method of development provides a comprehensive mechanization of labor and high technical and economic performance. As applied to the development of alluvial deposits, one of the urgent tasks is the determination of design parameters and improvement of hydraulic mining systems.Specific water consumption in short-season hydraulics with natural head depends both on the natural conditions of each particular placer (physical and mechanical properties of the soil, the thickness and width of the placer, the slope and nature of the dam, etc.) and on factors related to the organization of placer mining (head and water quantity, mining system, adopted equipment, the length of the excavation area, etc.).