Mineralogical association and Ni-Co deportment in the Wingellina oxide-type laterite deposit (Western Australia)

The Wingellina deposit (currently owned by Metals X Limited) is an oxide-type Ni-Co laterite, with 168 Mt of ore grading 0.98% Ni and 0.08% Co. The laterite profile is derived from the weathering of the olivine-rich maficultramafic layered intrusion of the Giles Complex (Mesoproterozoic) and consists of a well-developed limonitic ore and a thin saprolite horizon. XRPD, SEM-EDS and EMPA analyses revealed that the ore zone is dominated by Fe- and Mn-(hydr)oxides, which are the main carriers of both Ni and Co. The mineralogy of the Mn-hydroxides is complex, and high concentrations of Co and Ni occur mainly in a lithiophorite-asbolane intermediate phase, which has been subdivided into types I, II, III and IV, with significant differences in their Co/Ni ratios and A1 content. The enrichment of metals in the lithiophorite-asbolane phases is mainly controlled by the Co and Ni replacement of A1 in gibbsite-like layers, and rarely by Ni incorporation in the vacancies of Mn-(hydr)oxides. Other, less important, metal-bearing Mn-(hydr)oxides at Wingellina include romanechite, ernienickelite-jian-shuiite, manganite, and birnessite. The texture and chemistry of the Mn-(hydr)oxides suggest that the lithiophorite-asbolane phases were formed at a later stage with respect to the other manganiferous phases, after repeated leaching and re-precipitation of the Mn-(hydr)oxides. This process could be one of the main factors controlling the enrichment of Co and Ni in the limonite zones during lateritization.