Principles of a Sediment Sorting Model and its Application for Predicting Economic Values in Placer Deposits

  1. M. Marzo and
  2. C. Puigdefábregas
  1. M. Nami and
  2. S. G. E. Ashworth

Published Online: 14 APR 2009

DOI: 10.1002/9781444303995.ch34

Alluvial Sedimentation

Alluvial Sedimentation

How to Cite

Nami, M. and Ashworth, S. G. E. (1993) Principles of a Sediment Sorting Model and its Application for Predicting Economic Values in Placer Deposits, in Alluvial Sedimentation (eds M. Marzo and C. Puigdefábregas), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303995.ch34

Editor Information

  1. Barcelona, Spain

Author Information

  1. Exploitation Technology, COMRO, PO Box 91230, Auckland Park, Johannesburg, Republic of South Africa

Publication History

  1. Published Online: 14 APR 2009
  2. Published Print: 16 SEP 1993

ISBN Information

Print ISBN: 9780632035458

Online ISBN: 9781444303995



  • sediment sorting model;
  • Sorting modelled by MIDAS;
  • Little & Mayer flume experiments;
  • reproducing trends in the sedimentology of an ancient rock record;
  • predicting the location of economic values in un-mined areas of a placer deposit


Mining geologists currently have to base their deductions regarding the distribution of economic minerals in sedimentary deposits on descriptive science, experience and empirical rules. A need for improved quantitative prediction of gold grade distribution in Witwatersrand gold-bearing deposits based on geological information has led to the development of a numerical simulation model of sediment transport and sorting in natural systems.

In this paper the fundamental principles of this model are described. The main processes considered are entrainment and deposition of sediment, and its transport rate as bedload and suspended load. The sorting of the sediment, both in size and density, can be predicted as a function of selective entrainment, differential transport and differential settling with the results being dependent on the flow conditions imposed. The model has been verified by comparison with published data and by conducting experiments in a large-scale flume.

This paper also considers the application of the model for predicting the location of economic values in the gold-bearing placer deposits of the Witwatersrand Basin. Geological observations of a placer, coupled with palaeohydraulic reconstruction techniques or back calculation from model runs allowed deduction of the hydraulic conditions and geomorphology that prevailed during deposition of the placer. The sediment transport model was then used to predict quantitatively the mineral composition of a placer deposit to assist in mine planning functions on various scales. Gold grade distribution and sedimentological variations have been modelled at selected sites on the gold mines of the Witwatersrand Basin and the results of these studies are presented.