Geochemical behavior of gold and critical metals in the Goongarrie Ni-laterites, Western Australia

The Goongarrie South, situated northwest of Kalgoorlie in Western Australia, hosts a global resource (60Mt) of lateritic Ni-Co deposits at 1% Ni and 0.07% Co. The Goongarrie lateritic Ni-Co deposit extends over a strike length of 7.5 km and averages approximately 800m in width and 40m in thickness. These deposits originated from the weathering of serpentinized dunite. The lateritic profile is subdivided into lower saprolite, dominated by carbonate, talc, serpentine, chlorite, and mica, and upper ferruginous saprolite, representing the economic Ni-Co laterite, and dominated by goethite and hematite. The ultramafic index of alteration (100 x [(Al₂O₃+Fe₂O₃(_T)/(SiO₂+MgO+Al₂O₃+Fe₂O₃(_T)]) for the Ni-Co laterite is >60, contrasting with <60 in the lower saprolite and saprock. The laterite profile thickens up to 120 m over shear zones. In this study, we investigated the geochemical behavior of gold and some critical metals (REE, PGE, Sc, Ni, Cr, Mn, Co) in the Goongarrie South lateritic nickel deposits, using bulk and in-situ mineralogical, and geochemical methods. Our results show that gold and critical metals are concentrated in different horizons of the lateritic profile. Gold underwent leaching by acidic, halogen-rich, hypersaline groundwater, and has been enriched near the contact between the Ni-Co laterite and lower saprolite and saprock over shear zones, where the pH gradient increased. Additionally, gold is concentrated in paleoredox fronts within the Ni-Co laterite. The Au mineralization is Ag-poor, and occurs as cavity-filling, microcrystalline grains, and aggregates, indicating its supergene origin. Laser ablation ICP-MS mapping indicates that Ni was released from olivine in the lower saprolite and reprecipitated in nimite (Ni chlorite), while Sc is concentrated in serpentine and mica in the lower saprolite. In the Ni-Co laterite, Cr, Ti, V, Sc, Sb, and Y remained immobile; these elements are bound to Fe oxides and clays. Mobile elements such as Ni, Co, Li, Mo, W, Zn, Ce, Ru, and Pb are associated with Mn oxides at the base of the lateritic profile. The ΣREEs content in the laterite profile reaches up to 375 ppm. Cerium shows a weak positive correlation with the rest of REE, while positive Ce anomalies are associated with zones of Mn and Ce oxide enrichment. While there is no known magmatic sulfide mineralization associated with the host rock, chromite with Ru <0.15 ppm and inclusions of gold, Ni-Co-Cu-PGE-bearing sulfides, and sulfarsenides emerge as potential indicators for sulfide saturation.