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A PGE-rich rock type from the Barberton greenstone belt,
South Africa
Tredoux, M. 1 , Chabangu, N. 1 , Wildau, A. 1 , Miller, D.E. 2 and Madala. F. 1
1. Geology Dept, Univ. of the Free State, PO Box 339, Bloemfontein, 9300 South Africa; mtredoux@ufs.ac.za
2. C.M.E., Univ. of Cape Town, Rondebosch, 7701 South Africa; embo@telkomsa.net
ABSTRACT
The mafic and ultramafic rocks of the Barberton greenstone belt can be interpreted as the remnant of an Archean
ophiolite, named the Jamestown complex. Ultramafic rocks of the lowermost stratigraphic unit of this ophiolite is
exposed in the northwestern flank of the belt. All the contacts are sheared; its geochemistry shows a severe
depletion in the LILEs, and Sm-Nd and Pb-Pb systematics point to ~3.5 Ga as the most likely time for the
depletion. This rock is therefore interpreted as the depleted upper mantle restite from which the overlying
komatiites were extracted at an Archean ridge system. In 1920, a very Ni-rich body (>30% NiO, whole rock),
containing unusual Ni minerals such as trevorite and nepourite, was discovered embedded in the ultramafite. It has
been described as an oxidized meteorite or of a deep mantle origin, potentially from the D” layer. Investigation of
sub-mm sized phases in the trevorite has indicated the presence of Fe-Ni alloy, and metallic Si. The body is highly
enriched in the PGE (PGE tot > 5000 ppb).
KEYWORDS: Archean, ophiolite, PGE.
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