Exploration and mining of lateritic gold (Part II): Resource estimation, geometallurgy and environmental considerations

Abstract

This study examines the resource evaluation and processing of gold in the ferruginous gravels and duricrust (FGD) deposits, encompassing lateritic residuum or similar ferricrete. Evaluating lateritic gold deposits presents significant challenges, leading to variability and bias in results, particularly in the low-grade ranges that often characterize these deposits. The surveyed technical reports reveal that FGD deposits generally contribute less than 10% to total deposit resources, comprising only about 5 wt% of their total gold content. Limited exploration in lateritic domains may underestimate the size and grade of gold deposits in the lateritic environment. Expanding the number of drill holes over larger areas can yield significantly higher resource estimates than those derived from restricting exploration to zones directly above the primary mineralization. Of the 63 projects surveyed for this study, 45% defined a lateritic domain, yet only 30% progressed to the resource evaluation phase. Discrimination of domains improves resource estimates and significantly impacts mining operations, notably enhancing metallurgical recovery. Bulk cyanidation tests indicate that rapid leaching kinetics contribute to high gold extractions (95–97%) in lateritic samples. While gravimetric gold recoveries are lower for FGD deposits and oxidized materials than transition and sulphide domains, the opposite is observed in leaching. This behavior is likely due to greater cyanide accessibility and the morphology of secondary gold grains. Operating costs for lateritic deposits are lower than those for primary mineralization, despite variability in mining costs. Processing costs for lateritic gold projects are generally similar, regardless of the apparent compositional differences. From an environmental perspective, lateritic projects with low stripping ratios and increased rock friability may have smaller carbon footprints. However, uncertainties arise in the water footprint due to clay-rich tailings’ potential for non-recoverable water consumption. The analysis of public reporting of lateritic deposits shows a need for more rigor in characterizing and evaluating these deposits. Most mining operations on weathered ores require more detailed studies to ensure good practices and international quality standards. Therefore, a revised model for lateritic gold deposits with a new perspective, including in their technological, economic, and environmental settings, based on operational sustainability thinking, is required for the global gold mining industry.