Apatit JSC, Apatity, Russia:

A. S. Sakerin, Head of Drilling and Blasting Department, ASakerin@phosagro.ru
D. O. Konstantinov, Chief Specialist of the Drilling and Blasting Department

Mining Institute, Kola Science Center, Russian Academy of Sciences, Apatity, Russia:
S. A. Kozyrev, Head of a laboratory, Doctor of Engineering Sciences

Orica CIS, Moscow, Russia:
M. N. Overchenko, Chief Executive Officer

Apatit company mines apatite–nepheline ore using mainly the underground method which produces more than 70 % of the overall minerals extracted. In accord with the accepted mining technology, the operating horizons are developed from the center to the sides, with one or two cuts to get to another level. When two cuts are made on a horizon, in order to reach the required production output, two mining fronts are advanced toward each other, which results in formation of a block–pillar, and this intersection is cut at the end of the horizon development. After the analysis of the actual geotechnical, geological and geomechanical conditions, a production blast to break the intersection in Kirov Mine has been evaluated and prepared. Total volume broken by the blast is 726 thou t. Overall weight of explosive to break this intersection is 320 thou kg. Based on the geometry of the intersection and the number of blast hole rings, it has been decided to blast the holes from the sides toward the center of the intersection. As per the seismic safety standards, maximum weight of explosive per delay stage is evaluated, and blasting patterns and sequence are described. Considering particulars of the production blast in the intersection, the classical scheme of nonelectric blasting was used in combination with the electronic blast initiation system EBIS i-kon II manufactured by Orica CIS, which allowed blasting with seismically safe weight of explosive per delay stage. The production blast at the intersection used 1500 electronic detonators (total number of borehole charges was 2050). EBIS were installed in the blasthole rings, but their simultaneous blasting endangered the seismic safety. In blasting per rows with seismically unsafe weight of explosive per delay stage, the rings of holes were blasted uniformly, with a delay of 3–5 ms between the holes. The control and execution blocks had modem communication. Blasting was executed from the surface by means of telephone circuit. Orica CIS personnel controlled actuation of each delay stage using a special program. Seismic eff ect of the blast on buildings and structures was estimated using Instantel equipment (Canada) including 8-channel seismic measuring devices Minimate Plus. Actual PPV at all measurement points were below the maximum allowable values. The production blasting with the electronic initiation systems has yielded higher quality fragmentation of ore with the ensured seismic safety of the surface buildings and structures.

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