Development of a methodology for the characterisation of native graphite in a gold ore by an automated mineralogy system

Abstract

When a gold deposit contains carbonaceous material such as graphite, the processing plant may face a loss in the gold recovery because of the preg-robbing generated. The preg-robbing capacity of the carbonaceous material, and therefore the associated gold loss, depends on several parameters such as the surface and the crystallinity/maturity of the carbonaceous material, but also on the organic matter content, as well as the presence of different functional groups on the surface of the carbon material. Thus, it is necessary to be able to characterise it. This thesis focuses on a technique of characterisation of graphite (carbonaceous material) by an automated mineralogy system based on a scanning electron microscope that allows to evaluate the liberation and associations of minerals and to quantify them. To do this, samples must be mounted in polished blocks, however, the usual preparation, which consists of a homogeneous mixture of epoxy resin, hardener and an aliquot of material, poses several problems such as differential sedimentation of the particles, touching particles and systematic orientation of the particles. In addition, the backscattered electron image of the scanning electron microscope shows a low contrast between graphite and epoxy resin due to their similar average atomic number. Tests had been done in the past at the University of Liège to solve this issue but were inconclusive. The main objective of this thesis was to develop a polished block preparation that allowed the native graphite of a gold deposit to be analysed via a scanning electron microscope. A series of tests based on the preparation usually used at the University of Liège and on the information found in the literature review was conducted. The results of the various tests carried out made it possible to establish a polished block preparation allowing the characterisation of the native graphite by an automated mineralogy system based on a scanning electron microscope although additional work on the method of polishing is necessary.