South Africa - Inkaba.org
South Africa - Inkaba.org
South Africa - Inkaba.org
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
A PGE-rich rock type from the Barberton greenstone belt,<br />
<strong>South</strong> <strong>Africa</strong><br />
Tredoux, M. 1 , Chabangu, N. 1 , Wildau, A. 1 , Miller, D.E. 2 and Madala. F. 1<br />
1. Geology Dept, Univ. of the Free State, PO Box 339, Bloemfontein, 9300 <strong>South</strong> <strong>Africa</strong>; mtredoux@ufs.ac.za<br />
2. C.M.E., Univ. of Cape Town, Rondebosch, 7701 <strong>South</strong> <strong>Africa</strong>; embo@telkomsa.net<br />
ABSTRACT<br />
The mafic and ultramafic rocks of the Barberton greenstone belt can be interpreted as the remnant of an Archean<br />
ophiolite, named the Jamestown complex. Ultramafic rocks of the lowermost stratigraphic unit of this ophiolite is<br />
exposed in the northwestern flank of the belt. All the contacts are sheared; its geochemistry shows a severe<br />
depletion in the LILEs, and Sm-Nd and Pb-Pb systematics point to ~3.5 Ga as the most likely time for the<br />
depletion. This rock is therefore interpreted as the depleted upper mantle restite from which the overlying<br />
komatiites were extracted at an Archean ridge system. In 1920, a very Ni-rich body (>30% NiO, whole rock),<br />
containing unusual Ni minerals such as trevorite and nepourite, was discovered embedded in the ultramafite. It has<br />
been described as an oxidized meteorite or of a deep mantle origin, potentially from the D” layer. Investigation of<br />
sub-mm sized phases in the trevorite has indicated the presence of Fe-Ni alloy, and metallic Si. The body is highly<br />
enriched in the PGE (PGEtot > 5000 ppb).<br />
KEYWORDS: Archean, ophiolite, PGE.<br />
81