Use of QEMSCAN® for the characterization of Ni-rich and Ni-poor goethite in laterite ores

Nickel laterites are mineralogically complex, yet increasingly important sources of nickel and cobalt. To be successfully exploited they require accurate characterization of the mineralogy, texture and grade. As spatially resolved mineralogical techniques, automated scanning electron microscopy-based analysis systems (such as QEMSCAN®) offer significant advantages over traditional bulk compositional and mineralogical methods. This project tests how QEMSCAN® can be employed to characterize goethite and potentially interfering mineral compounds in nickel laterites. This involves the development and testing of a Species Identification Protocol (SIP) that discriminates goethite on the basis of nickel, chromium, and manganese content. The SIP is calibrated to quantitative compositional data obtained by electron-probe microanalysis (EPMA). The SIP is tested on ore specimens from Çaldağ (Turkey), Acoje (the Philippines) and Devolli (Albania). The project demonstrates the advantages of increased X-ray acquisition rate for the characterization of low-Ni concentrations and the significance of EPMA analysis for the quantitative validation of mineral identifications in the SIP.