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Multiple Merensky Reef of the Bushveld Complex, South Africa

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Abstract

The Merensky Reef (MR) of the Bushveld Complex is known for containing the lion’s share of the world’s reserves of platinum group elements (PGE). It is commonly described as a single, relatively thin layer (or package) of chromite- and sulphide-bearing orthopyroxenite hosted by almost barren norite and/or anorthosite. Here, we present a drill-core section that contains; however, four separate MR orthopyroxenite layers hosted by mottled anorthosites. Each of these orthopyroxenites is distinguished through occurrence/absence of marginal chromitite seams, grain size, petrographic composition, and PGE abundance. We interpret them as multiple undercutting MR that occurs as sill-like apophyses extending laterally from a pothole margin into the footwall. The undercutting MR is attributed to in situ crystallization within sheet-like melt-filled cavities at potholes margins, which are produced through thermal and/or chemical erosion of the footwall rocks by replenishing magmas. This finding indicates that the MR-forming event involved several distinct pulses of replenishing magmas whose crystallization products were mostly eroded away in the stratiform portions, but remained locally preserved in apophyses within footwall rocks. The mineralized MR formed a few meters below a temporary chamber floor is indicative of strong thermal/compositional convection in the basal layer of the Bushveld’s chamber. The convection was able to deliver large volumes of fresh magma for the scavenging of PGE by sulphide and chromite growing within the sheet-like cavities of the MR potholes.

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Map is slightly modified from Latypov et al. (2017a)

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Acknowledgements

The research was supported by DST-NRF CIMERA grants to Rais Latypov and Sofya Chistyakova, and by National Research Foundation (NRF) grants to Rais Latypov. Any opinion, finding and conclusion or recommendation expressed in this contribution is that of the authors and the DST-NRF CIMERA and NRF do not accept any liability in this regard. The authors also gratefully acknowledge support from Pilanesberg Platinum Mine for fieldwork undertaken at their open pit and access to drill cores. We would like to specifically thank Jan Van der Merwe, Jan Aucamp and Janus Westraat for allowing us to visit open pits, and much assistance and advice during the field work and sampling of drill cores. We are grateful to Emma Hunt for comments and editing that have significantly improved the manuscript. Official reviews of the paper by F. Roelofse and I. J. Basson and editorial handling by Chris Ballhaus are gratefully acknowledged.

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  1. School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa

    Sofya Chistyakova, Rais Latypov & Kirsten Youlton

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  1. Sofya Chistyakova
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Correspondence to Rais Latypov.

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Chistyakova, S., Latypov, R. & Youlton, K. Multiple Merensky Reef of the Bushveld Complex, South Africa. Contrib Mineral Petrol 174, 26 (2019). https://doi.org/10.1007/s00410-019-1562-x

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