X-Ray Data and Chemical Analyses of Some Titanomagnetite and Ilmenite Samples from the Bushveld Complex, South Africa

T. C. Molyneux1
Department of Geology, University of Pretoria
1Present address: c/o Anglo American Corporation of South Africa, Limited, P.O. Box 61587, Marshalltown, Transvaal.

Summary: The cell dimensions of powder samples of some Bushveld titanomagnetites and ilmenites were determined using a 114·6 mm AEG Guinier camera. The average cell dimension of the titanomagnetite is 8·400±0·005 Å and there is no definite relationship between the cell edge of the samples and their position in the layered sequence. The average cell parameters of coarse-grained ilmenite are a 5·085±0·005 Å and c 14·09±0·02 Å. Ilmenite that has replaced ulvöspinel has on average a value of some 0·003 Å greater than that of associated coarse ilmenite grains.

Chemical analyses indicate that titanomagnetite from pegmatoidal plugs and from the top of layered sequence was generally subject to late-stage magmatic alteration and hence lies in the Titanomagnetite II field. In the Bushveld Complex there is an increase in the TiO2 content of titanomagnetite from some 12 % at the base to 18 % at the top of the Upper Zone. However, Bushveld titanomagnetite tends to be poorer in TiO2 than similar samples from the Skaergaard intrusion.

A discrepancy between modal and normative hercynite in the Bushveld samples indicates that a considerable amount of hercynite is probably still in solid solution in the titanomagnetite.

Chemical analyses of Bushveld ilmenites reveal that they lie in the same tholeiitic field as those of the Skaergaard intrusion.

Mineralogical Magazine; September 1972 v. 38; no. 299; p. 863-871; DOI: 10.1180/minmag.1972.038.299.09
© 1972, The Mineralogical Society
Mineralogical Society (www.minersoc.org)