The Ilmenite Association at the Frank Smith Mine, R.S.A.

  1. F.R. Boyd and
  2. Henry O.A. Meyer
  1. Jill Dill Pasteris1,
  2. F.R. Boyd2 and
  3. P.H. Nixon3

Published Online: 19 MAR 2013

DOI: 10.1029/SP016p0265

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

The Mantle Sample: Inclusion in Kimberlites and Other Volcanics

How to Cite

Pasteris, J. D., Boyd, F.R. and Nixon, P.H. (1979) The Ilmenite Association at the Frank Smith Mine, R.S.A., 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/SP016p0265

Author Information

  1. 1

    Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520

  2. 2

    Geophysical Laboratory, 2801 Upton Street, N.W., Washington, D.C. 20008

  3. 3

    Department of Geology, The University, P.O. Box 4820, Port Moresby, Papua, New Guinea

Publication History

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

ISBN Information

Print ISBN: 9780875902135

Online ISBN: 9781118664858



  • Electron microprobe analysis;
  • Frank Smith mine;
  • Ilmenite nodules;
  • Lamellar intergrowths;
  • Petrography


Discrete nodules of ilmenite from the Frank Smith kimberlite pipe, South Africa, are polygranular with a range in grain size of 0.2–25 mm. They are characterized in polished section by surface pitting that delineates grain boundaries and that is variably developed within grains, depending on crystallographic orientation. The ilmenites usually contain spinel lamellae (∼1μ wide) of two types: short, black rods of pleonaste and longer, tan lamellae of titanomagnetite. Pyroxene-ilmenite lameilar intergrowths differ from those found at other pipes in that they are commonly sheared and in that enstatite-ilmenite intergrowths are as abundant as diopsidic varieties.

Compositions of ilmenites and intergrown silicates are similar to those from other South African kimberlites except that the Frank Smith ilmenites are distinctively rich in Mg. Discrete ilmenites have a range in Mg/(Mg + Fe 2+) of 0.376–0.525. Ilmenites from lameliar intergrowths are more restricted in Mg/(Mg + Fe2+) with a range of 0.463–0.499.

The fact that both the ilmenite discrete nodules and lamellar intergrowths at Frank Smith are distinctively rich in Mg is strong evidence that they are consanguineous in origin. It is suggested that at the time of eruption the discrete and lameliar ilmenites were equilibrated with diopside, enstatite, garnet, possibly olivine and small amounts of liquid with variable Mg/(Mg + Fe2+) over a depth range of the order of several tens of kilometers. The interstitial liquids may have had an aggregate composition like kimberlite and they and the nodules are believed to have been mixed together during eruption.