Mining Institute of Kola Science Center of Russian Academy of Sciences (Apatity, Russia):

Fokin V. A., Leading Researcher, Doctor of Engineering Sciences, e-mail: fva666@goi.kolasc.net.ru

„Kovdor Ore Dressing and Processing Enterprise“ JSC (Kovdor, Russia):

Togunov M. B., Chief Drilling and Blasting Specialist of Quality Control Department
Semkin S. V., Chief Engineer of Mine
Shitov Yu. A., Deputy Chief Drilling and Blasting Engineer of Mine

Development of main open pit of Zheleznyy mine („Kovdor Ore Dressing and Processing Enterprise“ JSC) is realized by its reconstruction project. This reconstruction foresees the increasing of depth of open pit to -650 m and is based on increasing of slope angle of its edges due to setting of high benches (24-30 m) with vertical or steeply inclined slopes into final position. Formation of such benches is realized by the following methods:
-preliminary formation of cracks (formation of end stope on the whole height of future bench);
-following blast preparation of blocks of upper (over-berm) and lower (berm) horizons with observation of principle of stage decreasing of intensity of dynamic influence of huge blasts by bringing of blasted blocks to limiting contour of open pit („soft blasting“ technology).
Certain experimental and industrial works were carried out for definition of actual grade of safety of rock massif behind the end stope. These works included estimation of actual grade of rock massif safety by indirect visual indicator — size and quantity of lumps from the first range in the time of blasting of benches with steeply inclined slopes (formed in 2010-2011 by controlled blasting on temporary non-operating area of open pit). At the same time, parameters of blasting of blocks of over-berm (upper 15 m) and berm (lower 15 m) horizons corresponded to the set technology, without any changes in the first range (without strengthening of the first range of deep-hole charges). As a result of experimental and industrial works, there was defined a large yield of lump from the first range of deep-hole charges, which was carried out on over-slope surface of bench. This fact confirms the following conclusions:
-end stope, formed by method of preliminary formation of cracks, has high protection properties during blasting preparation of near-edge blocks, according to the soft blasting technology;
-rock massif behind the end stope is saved practically in initial state and has rather high lifting properties, which makes possible to provide long-term stability of high benches with vertical and steeply inclined slopes.

1. Fokin V. A., Tarasov G. E., Togunov M. B., Danilkin A. A., Shitov Yu. A. Sovershenstvovanie tekhnologii burovzryvnykh rabot na predelnom konture karerov (Improvement of technology of drilling and blasting operations on limiting contour of open pits). Apatity : Kola Science Center of Russian Academy of Sciences, 2008, 224 p.
2. Togunov M. B., Shitov Yu. A., Danilkin A. A., Melik-Gaykazov G. V., Fokin V. A. Gornyi Zhurnal — Mining Journal, 2012, No. 10, pp. 45–49.
3. Fokin V. A., Togunov M. B., Semkin S. V., Shitov Yu. A. Vzryvnoe delo — Blasting work, 2011, No. 106/63, pp. 100–111.