Trevorite: Ni-rich spinel formed by metasomatism and desulphurisation processes at Bon Accord, South Africa

The 3.5 Ga Bon Accord Ni-deposit occurs within the lowermost serpentinised mafic-ultramafic lavas of the Barberton greenstone belt (South Africa). Though presently completely mined out, it comprised a suite of rare Ni-rich minerals that led to its interpretation as either an extraterrestrial body or as an oxidised fragment of Fe-Ni alloy originating from the terrestrial core. In this study, we draw on detailed petrographic observation and mineral chemical data to re-evaluate these ideas. Evidence is presented at both the thin-section (<1 mm) and regional scales (~10’s km) in favour of an alternative origin for Bon Accord, as an oxidized Ni-sulphide deposit, probably formed in association with ocean floor komatiite eruption.