A PGE-mineralized ultramafic body in the Ubendian belt, Tanzania

What is it about?

Detailed exploration work on the Nkenja ultramafic body of southern Tanzania, including over 70 drillholes and thousands of samples analysed, have shown widespread mineralization of the platinum-group elements and gold. The mineralization ocurs at low grades throughout most of the ultramafic rocks, which are dominated by clinopyroxene-bearing dunite and olivine clinopyroxenite, but locally the grades are higher.

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Why is it important?

The textures and composition of olivine (Fo88-92), chromite and clinopyroxene of the ultramafic rock suggest it represents a slice of depleted lithospheric mantle that has been refertilised by PGE-bearing basaltic melts, or possibly the lower ultramafic cumulate portion of an ophiolite complex. Field relations show a probable Palaeoproterozoic age for these ultramafic and mafic rocks. Very few ophiolites of this age have been identified, and none with such extensive PGE mineralization.