The Saaiplaas Quartzite Member: A Braided System of Gold- and Uranium-Bearing Channel Placers within the Proterozoic Witwatersrand Supergroup of South Africa

  1. J. D. Collinson and
  2. J. Lewin
  1. S. G. Buck

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch43

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Buck, S. G. (1983) The Saaiplaas Quartzite Member: A Braided System of Gold- and Uranium-Bearing Channel Placers within the Proterozoic Witwatersrand Supergroup of South Africa, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch43

Author Information

  1. Geology Department, Anglo American Corporation of South Africa, P.O. Box 20, Welkom 9460, South Africa

  1. Sedimentology Research Laboratory, Department of Geology, University of Reading, Reading RG6 2AB, UK

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 7 FEB 1983

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

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Keywords:

  • Saaiplaas quartzite member - braided system of gold- and uranium-bearing channel placers within Proterozoic Witwatersrand supergroup – South Africa;
  • quartz arenite;
  • clastic sediments;
  • Steyn Placer;
  • sedimentary deposits

Summary

Channel-like bodies of quartz arenite occur at a number of stratigraphic levels within a sequence of diamictic quartz wackes in the Harmony Formation (Witwatersrand Supergroup) of the Welkom Goldfield, South Africa. The lowermost level of channel bodies, referred to as the Saaiplaas Quartzite Member, contain economic concentrations of gold and uranium. The quartz arenites and quartz wackes are the deposits of an extensive alluvial fan system which prograded northwards across the Welkom Goldfield. Quartz arenite channel bodies accumulated from networks of semi-perennial sandy braided streams during periods of frequent rainfall, while the quartz wackes were deposited by ephemeral mud flows during periods of less frequent rainfall.

The precious minerals of the Saaiplaas Quartzite Member were derived locally from the reworking of the underlying Steyn Placer. Gold, uranium and pyrite were segregated from lighter sand grains during bedload transportation and accumulated as discrete deposits upon scour surfaces and within the matrices of conglomerates, the lowermost laminae of horizontally laminated quartz arenites, the upper foreset laminae of trough cross-bedded quartz arenites and the stoss surfaces of rippled quartz arenites. Reworking of the upper parts of the bedforms during the accumulation of the quartz arenites resulted in the preferential preservation of precious minerals as segregations upon scour surfaces and within horizontally laminated quartz arenites and conglomerates.