The Mineralogy of Xenoliths from Orapa, Botswana

  1. F.R. Boyd and
  2. Henry O.A. Meyer
  1. Simon R. Shee1 and
  2. John J. Gurney2

Published Online: 19 MAR 2013

DOI: 10.1029/SP016p0037

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

How to Cite

Shee, S. R. and Gurney, J. J. (1979) The Mineralogy of Xenoliths from Orapa, Botswana, in The Mantle Sample: Inclusion in Kimberlites and Other Volcanics (eds F.R. Boyd and H. O.A. Meyer), American Geophysical Union, Washington, D.C.. doi: 10.1029/SP016p0037

Author Information

  1. 1

    De Beers Consolidated Mines Limited, Box 616, 8300 Kimberly, S. Africa

  2. 2

    Department of Geochemistry, University of Cape Town, 7700 Rondebosch, S. Africa

Publication History

  1. Published Online: 19 MAR 2013
  2. Published Print: 1 JAN 1979

ISBN Information

Print ISBN: 9780875902135

Online ISBN: 9781118664858

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Keywords:

  • Biminerallic assemblage;
  • Chromite;
  • Clinopyroxenes;
  • Diamond and graphite genesis;
  • Garnet;
  • Orthopyroxene;
  • Xenoliths mineralogy

Summary

Xenoliths of eclogite and megacrysts from the upper mantle have been found at Orapa, Botswana. Peridotire has been found in kimberlites in the same cluster, but not at Orapa.

Minor phases in the ec!ogitic rocks include orthopyroxene, chromite, amphibole, phlogopite, rutile, kyanite, corundum, graphite and diamond.

The eclogites are divided into two main groups on textural and chemical grounds. A wide range in mineral chemistry which is very similar to that reported for Roberts Victor has been observed. The coefficient for Fe/Mg distribution between co-existing garnet-cpx pairs shows a wide range which has been interpreted as being partly due to differences in equilibration temperature and partly due to the effect of increased calcium in garnet. Garnet megacrysts are high titanium, low chrome pyropes similar to those from Monastery Mine. Cpx megacrysts fall into two groups: high chrome, calcic and low chrome, sub-calcic as in the Colorado/Wyoming kimberlites. Ilmenites are chrome rich picroilmenites.

Garnet xenocrysts appear to be derived from disaggregated eclogite and peridotitc xeno!iths, and from megacrysts.

The inclusions in the Orapa diamonds are predominantly eclogitic, with important sulphide and minor peridotitic components.