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Magnetic hausmannite from hydrothermally altered manganese ore in the Palaeoproterozoic Kalahari manganese deposit, Transvaal Supergroup, South Africa

Published online by Cambridge University Press:  05 July 2018

J. Gutzmmer ,
N. J. Beukes ,
A. S. E. Kleyenstuber  and
A. M. Burger
J. Gutzmmer
Affiliation:
Department of Geology, Rand Afrikaans University, P.O.Box 524, Auckland Park 2006, South Africa
N. J. Beukes
Affiliation:
Department of Geology, Rand Afrikaans University, P.O.Box 524, Auckland Park 2006, South Africa
A. S. E. Kleyenstuber
Affiliation:
MINTEK, Private Bag X3015, Randburg 2125, South Africa
A. M. Burger
Affiliation:
MINTEK, Private Bag X3015, Randburg 2125, South Africa
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Abstract

Hausmannite (Mn3O4), a manganese oxide with a tetragonally distorted spinel structure, is considered to be ferrimagnetic with a very low Curie temperature of 42.5 K. However, strongly magnetic hausmannite has been discovered in some of the hydrothermally altered high-grade manganese ores of the giant Kalahari manganese deposit in South Africa. EDS-electron microprobe analyses indicate magnetic hausmannite to contain on average between 3 and 11.3 wt.% Fe2O3. In contrast non-magnetic hausmannite contains on average about 1–3 wt.% Fe2O3. X-ray powder diffraction analyses reveal small changes in cell dimensions of the magnetic hausmannite related to the high iron content. Mössbauer spectroscopy suggests that all iron is in the trivalent state. Optical microscopy and scanning electron microscopy (electron back-scatter imaging) proved the magnetic hausmannite to be homogeneous in composition, containing only a few minute inclusions of hematite. Magnetic blocking temperatures of the iron-rich hausmannite, approximating the Curie temperature, are of the order of 750 K. It is suggested that the ferrimagnetic state of hausmannite is stabilized and enhanced by replacement of Mn3+ by Fe3+.

Keywords

hausmanniteKalahari manganese fieldWessels mineferrimagnetismiron content
Type
Mineralogy
Information
Mineralogical Magazine , Volume 59 , Issue 397 , December 1995 , pp. 703 - 716
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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