Optimisation and sensitivity analysis of final pit limits is now an accepted
procedure for open pit planning studies. Tools to assist the design
engineer in an underground metalliferous mine to make optimal choices
for the selection of major development, stope geometry and cut-off grade
analysis have not been available. The engineer has had to rely on
experience and a limited analysis of design alternatives. A new tool called the `floating stope' has been developed to define the
optimal (boundary) limit for material that can be economically extracted
by underground stoping methods. The method is analogous to the
`floating cone' method of open pit optimisation. The geology and mineralisation are modelled as a regular or subcell
block model. Included in the model are structural and geotechnical
features, and any previously mined out areas. Inputs to the procedure include the minimum stope dimensions, cut-off
grade, stope head grade, and the way in which dilution is to be calculated.
The optimisation procedure can be directed to maximise ore tonnes,
grade, contained metal or the economic (dollar) value of material mined. The procedure can be applied at each stage of mine evaluation and
design to assist with preliminary resource appraisal, selection of stoping
methods, and detailed mine design. As with open pit optimisation procedures, manual intervention by an
experienced engineer is required to produce practical and detailed
designs. This practical design should follow the optimised design as
closely as possible. The paper outlines the algorithms used in the definition of the stope
envelope, and describes the analysis and results of several case studies
where the optimisation procedure has been applied.