Underground Stope Optimization

3 May, 2018 | White paper

Daniel Roy

Daniel Roy, P.Eng.

Senior Consulting Expert, Drill and Blast Applications

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In May 2017, a Canadian underground gold mine operation mandated BBA to carry out the design of a complex secondary stope where we had to install the necessary instrumentations to perform a detailed analysis of the vibration impacts on its walls. The break modelling was done jointly using thermodynamic coded software followed by a 3D isometric representation of the break envelopes. Given that the mine does not have a primary crusher underground, the fragmentation of the site had to be less than 400mm, the opening dimensions of their Grizzly. Knowing the desired particle size, a break envelope was set and calculated from the thermodynamic equations, maximizing overlap and minimizing out-of-profile breakage and dilution, could be generated by the Break module, considering the following parameters : powder factor, energy values of explosives, tonnage, detonation velocity of the explosive and distribution along the stope walls, orientation of the mineralized block, waste / ore properties and rock compressive and shear velocities (P and S waves). The optimized burden and spacing that came out of the analysis were 2.5 mx 2.8 m, respectively, noticeably larger than what the mine planners had been applying recently. Some special instrumentations were placed in drill holes and used during the various stages of the monitoring program. A trajectory probe was used to measure the deviation of the 100mm holes to control their distance from the hanging wall. A high speed data collector unit was used to measure the detonation velocity (V.O.D.) and the effect of electronic delays selection between two (2) closely spaced holes on a same ring, or between two successive rings. Seismographs equipped with high frequency geophones have been installed at known distances to record the vibrations produced by the only 2 blasts required for the entire stope extraction. In addition, 10K g accelerometers were installed in diamond drill holes to measure the acceleration forces produced by the nearest explosive charges at 5 m and 8 m in the hanging wall. As a result of these steps, the blasts fragmentation was impeccable throughout the mucking process. (Source : www.convention.cim.org)

This paper was the subject of a presentation at the IMPC: XXVIII International Mineral Processing Congress Proceedings.