Drilling and blasting parameters for Gavrilovo granite deposit

It is well known that the cost of blasting can be 25 % of a mineral production cost, while poor fragmentation of rocks by blasting results in the increased cost of excavation and haulage and in the scaled up wear of equipment. This article describes the method to determine parameters of drilling and blasting based on the overlapping of cracking zones generated by camoufl age explosion of single cylindrical charges with regard to the charge design. It is proposed to determine the amount of stemming with allowance for the size of the cracking zones at the ends of the hole charges, namely, the size of predestruction zones in the overlaps in the upper block should be taken into account and the charge in the current block should be arranged with regard to the predestruction zones. Accounting for predestruction zones in the face area of a block and for oversize will make it possible to reduce the yield of oversize in the upper part of the block. The recommendations on the standard production blast design in an open pit mine take into account physical and mechanical properties of rock samples and rock mass, knock values of explosives, dynamic loading of rock mass at a wave stage of explosion as well as the fracture zones generated at the bottom of blasthole charges of the previous explosion. The data and analysis of pilot explosion in Gavrilovo open pit granite mine in the Leningrad Region are given. The particle size distribution in shattered rock mass is analyzed using photo planimetry, and the cost of secondary fragmentation of oversize (change in explosive consumption to crush oversize) is evaluated. The cumulative frequency curves of fragmentation in diff erent parts of a rock block are plotted, and feasible variants of reduction in the yield of oversize by varying blasting patterns and explosion directions are analyzed. The current and newly proposed drilling-and-blasting parameters and the resultant economic performances are compared.The authors express their gratitude to S. V. Repetukh, Chief Engineer, Garvilovo Open Pit Mine Management, for the assistance in the commercial-level experimentation.