Minimizing dilution in open stope mining with a focus on stope design and narrow vein longhole blasting

Abstract

This thesis presents the results of three years of research which focused on minimizing dilution in open stope mining. The research encompassed both stope design and narrow vein longhole blasting. A new empirical design approach has been developed for estimating unplanned dilution from open stope hangingwalls and footwalls. The resulting design charts are based on quantifiable measurements of overbreak/slough made with the Cavity Monitoring System (CMS), and were developed from a comprehensive database o f stoping histories compiled from six (6) Canadian underground open stoping operations. A new parameter termed ELOS (equivalent linear overbreak/slough) has been introduced and incorporated into the design charts as a measure of unplanned dilution. Theoretical justification for the design methodology has been demonstrated through a numerical modelling study examining the zone of relaxation around open stopes. Statistical methods, neural networks, and additional case histories have been used to validate the proposed design zones. This new approach to stope design is an improvement over existing methods in that it allows stope sizes to be determined based on an "acceptable" level of dilution rather than qualitative descriptions of stability such as: "stable"; "transition zone"; or "potentially unstable". In narrow vein open stope mining, even i f stopes are sized to be inherently stable (i.e. good stope design), blast induced overbreak can result in high levels of unplanned dilution. This study assessed the performance of three narrow vein blast patterns: the 3:2 pattern; the 2:1 (dice-five) pattern; and the 1:1 (stagger) pattern. The study was carried out at the Lupin Mine (NWT). The patterns were evaluated on the basis of: cost; blast damage potential; charge interaction; fragmentation; and tolerance to lapses in quality of drilling and loading practice. Guidelines have been developed regarding the choice and implementation o f narrow vein patterns.