Principles of a Sediment Sorting Model and its Application for Predicting Economic Values in Placer Deposits
- M. Marzo and
- C. Puigdefábregas
Published Online: 14 APR 2009
Copyright © 1993 The International Association of Sedimentologists
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
- Published Online: 14 APR 2009
- Published Print: 16 SEP 1993
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.