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Detrital chrome-spinel grains in heavy-mineral sand deposits from southeast Africa

Published online by Cambridge University Press:  05 July 2018

M. Pownceby  and
P. Bourne
M. Pownceby*
Affiliation:
CSIRO Minerals, Box 312, Clayton South, VIC 3169, Australia
P. Bourne
Affiliation:
CSIRO Minerals, Box 312, Clayton South, VIC 3169, Australia
*
*E-mail: Mark.Pownceby@csiro.au
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Abstract

Detrital chrome-spinels are contaminant grains within ilmenite concentrates produced from heavy-mineral deposits along the coast of southeast Africa. The presence of even minor levels of chromia in the predominantly ilmenite-rich concentrates, downgrades their market value as potential feedstocks for the production of titania pigment. An understanding of their composition can assist in their removal from the ilmenite concentrates.

Compositions from a database of close to 900 chrome-spinel analyses shows the major element components and their ranges (in wt.%) are: Cr: 0.4-45.3, Al: 0.0-31.0, Fe: 8.5-69.6 and Mg: 0.0-12.2. Minor components include Ti: 0.1-11.4 and Zn: 0.0-13.7.

The chrome-spinel data fall into two compositionally distinct groups. The first group of spinels is dominated by a strong trend reflecting the mutual substitution between Al3+ and Cr3+ in the spinel structure. The second group of spinels is characterized by compositions containing abundant Fe3O4magnetite component. The clear division between chrome-spinel compositional types indicates the grains are derived from at least two chemically dissimilar provenances.

The compositional differences between the chrome-spinel groups has a positive impact on subsequent ilmenite upgrading treatments as the spinels which contain the highest magnetite component are easily removed via low-intensity magnetic separation procedures.

Keywords

chrome-spinelsoutheast Africailmenite concentrates
Type
Research Article
Information
Mineralogical Magazine , Volume 70 , Issue 1 , February 2006 , pp. 51 - 64
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2006

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