Abstract

The Archean Fiskenaesset complex contains low concentrations of Pt, Pd, and Rh in comparison with the Stillwater Complex, Montana, but variations in these concentrations with stratigraphic height show trends related to the results of igneous differentiation, even though most of the rocks have been metamorphosed and the complex has been fragmented by granitoid intrusions and repeatedly deformed. Pt, Pd, and Rh are concentrated in ultramafic rocks and chromitites, but relatively high concentrations also occur locally in anorthosite and leucogabbro which are rich in disseminated sulfides. The concentrations of Pt and Pd are inversely related: the Pt:Pd + Pt ratio tends to increase upward. The Rh: Pd + Pt + Rh shows less variation but tends to increase slightly in the upper part of the intrusion. A new fire-assay atomic absorption method was developed to analyze the low concentrations of these metals present in the Fiskenaesset complex, and this method is described.

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