The theory of declining optimimum cut-off grades is more than 25 years old, but for a number of reasons it is still not widely used in industry. A lack of faith in the veracity of estimated grades is not in itself a reason to abandon any attempt to optimise cut-off grades. The use of declining cut-off grades has been thought to cause high-grading, but in fact this is only true if an artificially high discount rate is used in the calculations._x000D_
Perfect application of an optimum cut-off grade should ensure that only ore generating more than a minimum net return is mined, and that as much as possible of the ore capable of generating that return is mined._x000D_
Therefore differing mining costs in different parts of some underground mines necessitate local modifications to cut-off grade. Optimisation of cut-off grade is of necessity an iterative process._x000D_
Integration of that process into a feasibility study need not be excessively time-consuming. A number of approximations can be made to speed the optimisation (any attempt to achieve a high level of accuracy is probably doomed to failure by a lack of precise cost and price projections). A procedure is outlined for optimising cut-off grade during planning of a typical underground mine.