Kiritchenko I. Elabaration of technological methods of breaking of at the utmost depth of iron ore surface mines

The conditions of breaking off of the rocks at the utmost depth of superdeep pits have been inves-tigated. The influence of water availability, solidity and crack-formation of the mountain-mass as well as parameters of the working site on the very proctss of rocr's destruction. Due to that some technological methods of breaking off the rocks were elaborated, which were based on application of special disposition of in two or three rows in the angles of equilateral triangles. Thus one can increase the efficiency of ex-plosion up to 30 per cents and cut down the quantity of demolition explosives to 23 per cents. To make it possible to break-down the rocks compactly during the two rows'explosion in is recommended to explode the second row first, and then with an interval of 2 - 3 m/sc the explosive loads of the first row. Such a short time retardation gives optimal conditions for preliminary destruction of the mountain-mass, in order to receive in this way the most qualitative fractions and compact break-down of the rocks exploded. These methods were tested at the surface mine 1 of the Central Mining Concentratton Group. 850.000 squ. Metres of rock were broken off and economic efficiency amounting to 429.800 Hrn.