Computer-Aided Cut-off Grade Optimisation for Open Pit Mines using Lane's Approach*

Abstract

The value of a mining project is dependent on the applied cut-off grade. Kenneth Lane proposed a now widely accepted cut-off grade policy in the mining industry, which maximises the NPV of a mining project while constrained by the production capacities and the grade-tonnage distribution of an ore deposit. Lane's approach considers the time value of money and is incorporated in many mining commercial software. Many cut-off grade policies based on Lane's approach have been proposed and coded into computer applications. However, these applications are not available for general use or are expensive to obtain often requiring that the user be trained on how to use them. In this paper, a user friendly computer application dubbed Cut-off Optimiser 1.0 based on Lane's iterative algorithm for single mineral deposits is developed using C++/CLI in a Visual Studio 2008 Integrated Development Environment. Data from an operating gold mine is used to run Cut-off Optimiser 1.0. The results obtained are compared to those from Whittle’s 4X Cut-Off Grade Optimisation (Type 2), a benchmark for this study, for the same data. Cut-off grades obtained from Cut-off Optimiser 1.0 ranged from 0.85 g/t to 1.54 g/t while in Whittle’s 4X Cut-off Optimisation (Type 2) Node the grades ranged from 0.893g/t to 1.328 g/t. Although results of the two applications very comparable, Cut-off Optimiser 1.0 generally yields slightly higher NPVs and more optimistic values than those obtained in Whittle 4X.