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Platinum-group elements and minerals in the lower and middle group chromitites of the western Bushveld Complex, South Africa

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Abstract

The chromitites of the Bushveld Complex in South Africa contain vast resources of platinum-group elements (PGE). However, knowledge of the distribution and the mineralogical siting of the PGE in the lower group (LG) and middle group (MG) chromitite seams of the Bushveld Complex is limited. We studied concentrates from the LG-6 and MG-2 chromitites of the western Bushveld Complex by a variety of microanalytical techniques. The dominant PGM are sulfides, namely laurite, cooperite-braggite, and malanite-cuprorhodsite, followed by PGE-sulfarsenides, sperrylite, and Pt-Fe alloys. Laurite is the most abundant PGM (vol%). The matching sets of PGM present in the LG and MG chromitites of both the western and the eastern Bushveld Complex, and in the UG-2 chromitite, show strong similarities which support the assumption of a characteristic and general chromitite-related PGM assemblage. Palladium and Rh contents in pentlandite are low and erratic although maximum contents of 7730 ppm Pd and 6020 ppm Rh were detected. Rare thiospinels of the polydymite-linnaeite-greigite series have PGE contents of 1430 ppm Pt, 5370 ppm Rh, and 1460 ppm Pd. The various PGE occur in different deportment: Platinum is generally present in the form of discrete PGM (sulfides, arsenides, alloys). Palladium is present as a large variety of discrete PGM and also incorporated in pentlandite. Rhodium forms discrete PGM and is occasionally present in pentlandite. The IPGE (Os, Ir, and Ru) are dominantly incorporated in laurite (often as inclusions in chromite) and also occur as sulfarsenides.

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Acknowledgments

Thanks to SYLVANIA Platinum Ltd. for supplying the concentrates from their operations and for the contribution of additional analytical data as well as information on the metallurgical processes involved. Many thanks for the critical and helpful input of Sarah-Jane Barnes, which together with the thorough and constructive comments of Bernd Lehmann and Marco Fiorentini improved the quality and clarity of argumentation of our presentation. This work is a contribution of the German/South African R&D project “AMREP”—Applied Mineralogy for Resource Efficiency of Platinum-Group Metals—funded by the German Ministry of Education and Research (BMBF).

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Authors and Affiliations

  1. Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655, Hannover, Germany

    Malte Junge & Thomas Oberthür

  2. Helmholtz Institute Freiberg for Resource Technology, Halsbrücker Strasse 34, 09599, Freiberg, Germany

    Inga Osbahr

  3. SYLVANIA Platinum Ltd., P.O. Box 976, Florida Hills, 1716, South Africa

    Paul Gutter

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  1. Malte Junge
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Correspondence to Malte Junge.

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Editorial handling: M. Fiorentini

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Junge, M., Oberthür, T., Osbahr, I. et al. Platinum-group elements and minerals in the lower and middle group chromitites of the western Bushveld Complex, South Africa. Miner Deposita 51, 841–852 (2016). https://doi.org/10.1007/s00126-016-0676-6

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