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Mineralium Deposita

, Volume 45, Issue 1, pp 93–109 | Cite as

Platinum-group element distribution in the oxidized Main Sulfide Zone, Great Dyke, Zimbabwe

  • Marek Locmelis
  • Frak Melcher
  • Thomas Oberthür
Article

Abstract

In the Great Dyke mafic/ultramafic layered intrusion of Zimbabwe, economic concentrations of platinum-group elements (PGE) are restricted to sulfide disseminations in pyroxenites of the Main Sulfide Zone (MSZ). Oxidized ores near the surface constitute a resource of ca. 400 Mt. Mining of this ore type has so far been hampered due to insufficient recovery rates. During the oxidation/weathering of the pristine ores, most notably, S and Pd are depleted, whereas Cu and Au are enriched. The concentrations of most other elements (including the other PGE) remain quite constant. In the oxidized MSZ, PGE occur in different modes: (1) as relict primary PGM (mainly sperrylite, cooperite, and braggite), (2) in solid solution in relict sulfides (dominantly Pd in pentlandite, up to 6,500 ppm Pd and 450 ppm Pt), (3) as secondary PGM neoformations (i.e., Pt–Fe alloy and zvyagintsevite), (4) as PGE oxides/hydroxides that replace primary PGM as the result of oxidation, (5) hosted in weathering products, i.e., iron oxides/hydroxides (up to 3,600 ppm Pt and 3,100 ppm Pd), manganese oxides/hydroxides (up to 1.6 wt.% Pt and 1,150 ppm Pd), and in secondary phyllosilicates (up to a few hundred ppm Pt and Pd). In the oxidized MSZ, most of the Pt and Pd are hosted by relict primary and secondary PGM; subordinate amounts are found in iron and manganese oxides/hydroxides. The amount of PGE hosted in solid solution in sulfides is negligible. Considerable local variations in the distribution of PGE in the oxidized ores complicate a mineralogical balance. Experiments to evaluate the PGE recovery from oxidized MSZ ore show that using physical concentration techniques (i.e., electric pulse disaggregation, hydroseparation, and magnetic separation), the PGE are preferentially concentrated into smaller grain size fractions by a factor of 2. Highest PGE concentrations occur in the volumetrically insignificant magnetic fraction. This indicates that a physical preconcentration of PGE is not feasible and that chemical, bulk-leaching methods need to be developed in order to successfully recover PGE from oxidized MSZ ore.

Keywords

Great Dyke Main Sulfide Zone Platinum-group minerals Beneficiation PGE oxides 

Notes

Acknowledgements

We acknowledge the support by K.-P. Burgath, Gina Ehlers, Simone Sturm, Andreas Scheibner, Jerzy Lodziak (BGR), V.V. Knauf (NATI Research), and O.A.R. Thalhammer (Leoben) with mineral separation. Some PGE analyses were carried out by Thomas Meisel (Leoben). Maria Sitnikova (BGR) is thanked for MLA analyses. Part of the field work and sample preparation was carried out by Dipl. Ing. Lothar Gast (BGR). We thank Greg Holland, Ray Brown, Andrew Du Toit, Humphrey O´Keefe, and the managements of BHP, Delta Gold, Anglo American Zimbabwe, and Zimplats for their continuous assistance during field work and provision of samples. We appreciate the constructive input of the reviewers, Chusi Li and Bernd Lehmann. This is contribution 607 from the Australian Research Council National Key Centre for the Geochemical Evolution and Metallogeny of Continents (www.es.mq.edu.au/GEMOC).

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Marek Locmelis
    • 1
    • 2
  • Frak Melcher
    • 1
  • Thomas Oberthür
    • 1
  1. 1.Federal Institute for Geosciences and Natural Resources (BGR)HannoverGermany
  2. 2.ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC), Department of Earth and Planetary SciencesMacquarie UniversitySydneyAustralia

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