The Ilmenite Association at the Frank Smith Mine, R.S.A.
- F.R. Boyd and
- Henry O.A. Meyer
Published Online: 19 MAR 2013
Copyright © 1979 by the American Geophysical Union.
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
- Published Online: 19 MAR 2013
- Published Print: 1 JAN 1979
Print ISBN: 9780875902135
Online ISBN: 9781118664858
- Electron microprobe analysis;
- Frank Smith mine;
- Ilmenite nodules;
- Lamellar intergrowths;
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.