The Ernest Henry mine (EHM) is a copper-gold mine located 38km north-east of Cloncurry in north-west Queensland, Australia. The mine produces 6.8Mtpa of ore from a chalcopyrite-rich breccia pipe plunging at approximately 45 degrees using the sublevel cave (SLC) mining methodology.
A novel design was proposed that combined the rise and slot widening blasts into a single design using current design principles. WebGen™ was used to pre-charge the widening shot. This enabled the rise to be fired conventionally and mucked first with the widening shot fired secondary leveraging the height and void of the rise to obtain the required width. This proposed design allowed for the removal of the slot drives. Initial trials were similar to previous rise firings achieving 80% height but with unfavourable width profiles. A substantial design review was conducted, and a secondary trial undertaken.
The rise design review used the Lovitt Success Factor for initial design changes followed by a technical review using 1st principles. These reviews resulted in the following changes – from a 4.0 x 4.0m blind uphole rise to a 4.0 x 2.8m rise, rotated 180 degrees, reduced true burden in the centre stripping holes, removing angled holes, changing toe primer locations, slower timing for stripping holes, and adding an extra three hole stripping ring.
The successful application of a single rise / slot widening blasting regime to create independent drives has enabled EHM to eliminate slot drives. This has reduced lateral development by an average of 150m or 4.5% per level. Other direct outcomes of removing slot drives are discussed in the paper.
Author: M Hawtin, J Say, P Cann, and L Carlon
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