Application of HPGR and X-Ray CT to investigate the potential of Witwatersrand gold ore for heap leaching : a process mineralogy approach

Abstract

Auriferous conglomerates of the Archaean Witwatersrand Basin in South Africa host one of the largest known gold resources and rate as the world’s most outstanding example of a fossil megaplacer deposit. For the past 40 years, Witwatersrand gold production in South Africa has been progressively declining due to problems related to high energy costs, decreasing grade, accessibility to greater depths, health and safety issues, labour union unrest and economic uncertainties: thus the overall viability of current gold production is questionable. Ultimately, the future of Witwatersrand gold mining relies on devising smarter strategies across the entire industry, but in particular critical areas such as comminution and extraction. With the continuous increase in mining depth, dominance of low-grade gold ores and strict safety regulations, metallurgical processing options have become limited. Heap leaching is a well-established technology which continues to grow in use and provides several benefits to solve some of these problems. High pressure grinding rolls (HPGR) is another technology with significant potential, especially for its application in coarse particle heap leaching due to its ability to induce micro-cracks as well as its high grinding efficiency and low energy requirements. This study explores the use of these two technologies in a process mineralogical framework using novel 3D X-ray computed tomography mineralogical analysis in order to assess a potential of the Witwatersrand gold ore for heap leaching.