A Cr isotopic study of the Bon Accord NiO body in the Barberton greenstone belt, South Africa

•The ε53Cr for the Bon Accord oxide body is 0.00 epsilon units.•The precursor of the Bon Accord oxide body was probably not a meteorite.•The Bon Accord body is surrounded by both komatiite and depleted peridotite.•A deep mantle source is compatible with the geochemistry of the Bon Accord body.

An unusual oxide body, enriched in Ni and the platinum-group elements, was found in the north-western part of the Barberton greenstone belt, South Africa, in the 1920s. With mineralogy and geochemistry which are extremely anomalous, and do not conform to that of any other Ni-rich crustal rocks, it has been interpreted as either an Archaean paleo-meteorite or of terrestrial deep-mantle origin. Cr isotopic ratios were used to evaluate the merits of these two possibilities. Isotopic analyses returned values for ε(53) of 0.00 epsilon units, within a 2 s error, relative to a terrestrial standard. We interpret this information, together with trace element data from the surrounding peridotites, as pointing to a terrestrial origin for the body, and conclude that the current dataset is not inconsistent with a deep-mantle origin, as a remnant of core formation, with subsequent transport to and emplacement in the lithosphere by a mantle plume.