Controls on the genesis and emplacement of komatiite-hosted Ni-Cu-PGE-sulphides at Albion Downs (Agnew-Wiluna Belt, Western Australia): a case study on the development of PGE lithogeochemical vectors to Ni-Cu-PGE-sulphide deposits

Albion Downs is a structural domain within the Agnew-Wiluna Greenstone Belt of Western Australia, which contains one of the most highly Ni-endowed komatiite sequences in the world. Albion Downs comprises adcumulate-textured pods and lenses, which are flanked by thinner meso- and orthocumulate-textured units. Basal massive nickel-sulphide mineralisation (e.g. Jericho) generally occurs in the thinner meso- and orthocumulate-textured units, whereas stratabound disseminated nickel-sulphide mineralisation (e.g. Jordan) is hosted in the largest adcumulate-textured pod. After reaching sulphide-saturation, basal massive sulphides formed in settings where magma flow was less fast and turbulent than in channels. Conversely, in channel-like settings sulphide blebs were entrained in the flow, thus forming disseminated sulphides. Platinum-group element lithogeochemistry indicates that the signature associated with the ore-forming process is only recorded <100 m-away from nickel-sulphide mineralisation, where samples display a positive relationship between Pd + Pt and MgO and Pd + Pt and S. Conversely, the PGE signature of samples collected farther away is not directly controlled by sulphide segregation. Understanding the scale at which ore-formation processes operate is crucial to the development of any lithogeochemical exploration vector that is dependent on PGE variation.