Classification of Gold-Bearing Particles Using Visual Cues and Cost-Sensitive Machine Learning

Ore sorting increases the grade of an ore feed stream by separating very low-grade particles (‘waste’) from those containing higher concentrations of the desired mineral (‘ore’), thus economically reducing the amount of material processed in further mineral concentration steps. This paper reports a preliminary study that aims to develop an automated method for discriminating waste and gold-bearing particles. The study used both hyperspectral measurements and RGB images of waste and gold-bearing particles from the Sunrise Dam Gold Mine as input to the discriminating method. Advanced feature extraction methods were employed to capture visual cues such as texture and colour from the RGB images, which were combined with hyperspectral features to give nine types of representative features. Feature selection was applied to groups of the representative features and resulting feature subsets were evaluated using three machine learning algorithms, namely a support vector machine, a naïve Bayes classifier, and a majority decision table, to identify a highly informative subset of features. Cost-sensitive training was used to minimise the nominal profit lost due to sorting error based on real cost values from the milling process, with the aim of economically balancing the ore acceptance rate with the waste rejection rate. A cost-blind support vector machine achieved an ore acceptance rate of 84 % and a waste rejection rate of 87 %, which resulted in $0.98 nominal profit lost per tonne of crushed rock particles. Cost-sensitive training reduced the nominal profit lost to $0.34 per tonne, undercutting the costs associated with refining all particles by $0.24 per tonne.