293 THE FIRST AUSIMM INTERNATIONAL GEOMETALLURGY CONFERENCE / BRISBANE, QLD, 5 - 7 SEPTEMBER 2011 INTRODUCTION Most gold deposits and particularly those that show a high- nugget effect, display a variable grade distribution. On the micro-scale this represents variability in the in situ abundance and distribution of gold particles. Grade is usually correlated to gold particle size, where higher grades relate to more abundant coarse gold and/or clustered ine gold particles (Dominy and Platten, 2007; Dominy, Xie and Platten, 2008b). The size/shape, deportment, distribution and abundance of gold particles affect both the sampling/evaluation and metallurgical characteristics of a gold deposit. Gold particles can range from colloidal or solid solution to ine (<100 µm) and greater than 2000 µm in size and be spatially disseminated and/or clustered (Figure 1). In some gold deposits, there is evidence to show that the ine- and coarse-gold particles are part of separate paragenetic stages (Dominy, Xie and Platten, 2008b). In general, the ine gold particles are likely to be relatively disseminated through the orebody and responsible for a ‘background’ grade of between 0.5 g/t Au and 5 g/t Au. The coarse particles may be more clustered and related to higher grade zones. Gold particle 1. FAusIMM(CP), Executive Consultant, Snowden Mining Industry Consultants Pty Ltd, 300 Adelaide Street, Brisbane Qld 4000. Email: sdominy@snowdengroup.com 2. Adjunct Professor, Western Australian School of Mines, Curtin University, Bentley Campus, Perth WA 6102. 3. Senior Principal Consultant, Snowden Mining Industry Consultants Ltd, The Magdalen Centre, Robert Robinson Avenue, Oxford Science Park, Oxford OX4 4GA, England. 4. Researcher and CT Specialist, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, England. 5. Post-Doctoral Fellow, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, England. 6. Leader – Mining Consultancy, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, England. 7. FAusIMM, JCI Professor of Mineral Resources and Reserves, School of Mining Engineering, University of Witwatersrand, Private Bag 3, WITS 2050, South Africa. 8. Research Associate, Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, England. Characterisation of Gold Ores by X-Ray Computed Tomography – Part 2: Applications to the Determination of Gold Particle Size and Distribution S C Dominy 1,2 , I M Platten 3 , L E Howard 4 , P Elangovan 5 , R Armstrong 6 , R C A Minnitt 7 and R L Abel 8 ABSTRACT For any gold deposit-based geometallurgical study, the collection and processing of representative samples for gold grade and recovery tests is critical. Sampling protocols should be designed to suit the style of orebody in question. The proportion and size of gold particles has a direct impact on the effectiveness of sampling protocols and metallurgical recovery processes employed. Studies focussing on ore mineralogy and gold particle deportment, size and distribution are required. Key issues are the presence of gold particle clustering (important for sampling optimisation) and proportion of coarse versus ine to refractory gold. X-ray computed tomography (CT) is a radiographic technique that produces high-resolution 3D computerised models of objects based on density distribution. The ‘virtual’ specimens are made up of voxels, the 3D equivalent of pixels each assigned a grey value based on X-ray absorption. This paper presents the results of recent research on the imaging of in situ gold particles in a coarse gold-bearing ore. The technique shows promise as a rapid non-destructive method for preliminary characterisation to facilitate more detailed studies. Early and rapid gold particle determination enables sampling protocol optimisation and metallurgical recovery parameters to be deined prior to detailed feasibility studies. FIG 1 - Range of gold particle sizes from ine (<300 µm) to extreme coarse (>10 000 µm) from the Ballarat project (Victoria, Australia). Dominy_40.indd 293 2/08/2011 10:24:13 AM