The concentration of the platinum-group elements in South African komatiites : implications for mantle sources, melting regime and PGE fractionation during crystallization

Maier, Wolfgang D.
Roelofse, Frederick
Barnes, Sarah-Jane

Publication date

January 2003

DOI

Abstract

We have analysed 18 samples of komatiite from five consecutive lava flows of the Komati Formation at Spinifex Creek, Barberton Mountain Land. Our samples include massive komatiite, various types of spinifex-textured komatiite, and flow-top breccias. The rocks have low platinum-group element (PGE) contents and Pd/Ir ratios relative to komatiites from elsewhere, at 0·45–2 ppb Os, 1–1·4 ppb Ir, <1–5 ppb Ru, 0·33–0·79 ppb Rh, 1·7–6 ppb Pt, 1·6–6·1 ppb Pd, and Pd/Ir 3·3. Pt/Pd ratios are c. 1·1. Platinum-group elements are depleted relative to Cu (Cu/Pd = 15 300). They display a tendency to increase in the less magnesian samples, suggesting that the magmas were S-undersaturated upon eruption and that all PGE were incompatible with respect to cry...