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Platinum-group element distribution in base-metal sulfides of the UG2 chromitite, Bushveld Complex, South Africa—a reconnaissance study

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Abstract

Two drill cores of the UG2 chromitite from the eastern and western Bushveld Complex were studied by whole-rock analysis, ore microscopy, SEM/Mineral Liberation Analysis (MLA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis. The top and base of the UG2 main seam have the highest bulk-rock Pd and Pt concentrations. Sulfides mostly occur as aggregates of pentlandite, chalcopyrite, and rare pyrrhotite and pyrite or as individual grains associated mostly with chromite grains. In situ LA-ICP-MS analyses reveal that pentlandite carries distinctly elevated platinum-group element (PGE) contents. In contrast, pyrrhotite and chalcopyrite contain very low PGE concentrations. Pentlandite shows average maximum values of 350–1,000 ppm Pd, 200 ppm Rh, 130–175 ppm Ru, 20 ppm Os, and 150 ppm Ir, and is the principal host of Pd and Rh in the studied ores of the UG2. Mass balance calculations were conducted for samples representing the UG2 main seam of the drill core DT46, eastern Bushveld. Pentlandite consistently hosts elevated contents of the whole-rock Pd (up to 55 %) and Rh (up to 46 %), and erratic contents of Os (up to 50 %), Ir (2 to 17 %), and Ru (1–39 %). Platinum-group mineral (PGM) investigations support these mass balance results; most of the PGM are Pt-dominant such as braggite/cooperite and Pt-Fe alloys or laurite (carrying elevated concentrations of Os and Ir). Palladium and Rh-bearing PGM are rare. Both PGE concentrations and their distribution in base-metal sulfides (BMS) in the UG2 largely resemble that of the Merensky Reef, as most of the Pd and Rh are incorporated in pentlandite, whereas pyrrhotite, chalcopyrite, and pyrite are almost devoid of PGE.

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Acknowledgments

Anglo American Platinum JV is thanked for the analytical data and logistic support. Their partners Royal Bafokeng Platinum and Atlatsa Resources (Bokoni Mine) are thanked for providing the borehole intersections for the study. Many thanks to Dirk Sandmann and Prof. Bernhard Schulz from the TU Bergakademie Freiberg for conducting the MLA and Helene Brätz from the GeoZentrum Nordbayern for her excellent LA-ICP-MS results. The reviewers provided constructive and helpful reviews and are acknowledged with thanks. Bernd Lehmann is thanked for his editorial support.

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Author notes

  1. Inga Osbahr

    Present address: Helmholtz-Institute Freiberg for Resource Technology, 09599, Freiberg, Germany

Authors and Affiliations

  1. GeoZentrum Nordbayern, University of Erlangen-Nürnberg, Schlossgarten 5a, 91054, Erlangen, Germany

    Inga Osbahr, Reiner Klemd & Anja Josties

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

    Thomas Oberthür

Authors
  1. Inga Osbahr
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  2. Thomas Oberthür
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  3. Reiner Klemd
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  4. Anja Josties
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Corresponding author

Correspondence to Inga Osbahr.

Additional information

Editorial handling: C. Li

Electronic supplementary material

Below is the link to the electronic supplementary material.

ESM 1

Whole-rock data of Pt, Pd, Rh (in ppm), Cu and Ni (in ppm). (XLSX 13 kb)

ESM 2

Correlation coefficients for binary plots of whole-rock PPGE, Ni and Cr. (XLSX 10 kb)

ESM 3

Depth, lithotype, modal content of sulfides and calculated weight fractions of pentlandite, chalcopyrite and pyrrhotite. (XLSX 10 kb)

ESM 4

Calculated proportions of PGE in BMS calculated for four samples of drill core DT46. (XLSX 11 kb)

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Osbahr, I., Oberthür, T., Klemd, R. et al. Platinum-group element distribution in base-metal sulfides of the UG2 chromitite, Bushveld Complex, South Africa—a reconnaissance study. Miner Deposita 49, 655–665 (2014). https://doi.org/10.1007/s00126-014-0538-z

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  • DOI: https://doi.org/10.1007/s00126-014-0538-z

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