The George Fisher Underground Mine at Mount Isa applies the long hole open stoping methodology. During the reconciliation process of transverse stopes in the George Fisher North mine it was identified that excessive underbreak was regularly experienced, with the major contribution coming from the toe area inside the stope.
While over break and the resultant dilution was well investigated and well understood, limited work was done on underbreak improvement. It was decided that a re-engineering process would be followed in an attempt to improve results. The prevailing stoping practices were scrutinised and the possible causes were listed.
Some of the identified causes were design, drilling accuracy, equipment condition, mucking practices and direction of firing. It was identified that in most instances the underbreak was initiated in the slot area of the stope during the first firings. Once this happened, it was impossible to get good recoveries on the rest of the stope. The slot area was carefully scrutinised and the blasting practices were changed individually.
following two years several different strategies were trialled to increase the
toe recoveries. The results indicated an overall improvement of six per cent
reduction in underbreak on average, by ensuring drilling accuracy and changing
the direction of firing. The economic significance of these results outweighed
the time and additional work load expended to establish the cause of the
problem. This paper outlines the continuous improvement process undertaken to
identify and rectify the major contributing factors to the problem. It also
presents a set of recommendations to be followed in order to achieve positive
Grobler, J J,
2011. Mining reconciliation in long hole open stopes at George Fisher mine, in
Proceedings 11th AusIMM Underground Operators’
, pp 63-72 (The Australasian Institute of Mining
and Metallurgy: Melbourne).