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The dependence of alumina and silica contents on the extent of alteration of weathered ilmenites from Western Australia

Published online by Cambridge University Press:  05 July 2018

M. T. Frost ,
I. E. Grey ,
I. R. Harrowfield  and
K. Mason
M. T. Frost
Affiliation:
CSIRO Division of Mineral Chemistry, P.O. Box 124, Port Melbourne, Victoria 3207, Australia
I. E. Grey
Affiliation:
CSIRO Division of Mineral Chemistry, P.O. Box 124, Port Melbourne, Victoria 3207, Australia
I. R. Harrowfield
Affiliation:
CSIRO Division of Mineral Chemistry, P.O. Box 124, Port Melbourne, Victoria 3207, Australia
K. Mason
Affiliation:
CSIRO Division of Mineral Chemistry, P.O. Box 124, Port Melbourne, Victoria 3207, Australia
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Abstract

The distribution of the minor impurities, aluminium and silicon, between co-existing phases in altered ilmenite grains from three Western Australian localities has been investigated using SEM and electronmicroprobe analyses. A striking dependence of the impurity levels on the Ti/(Ti + Fe) fraction is observed. For compositions with Ti/(Ti + Fe) between 0.45 and 0.60, i.e. between ferrian-ilmenite and pseudorutile, the impurity content is virtually independent of Ti/(Ti + Fe), and is very low (0.2 wt. % Al2O3. 0.05 wt. % SiO2). For compositions between those of rutile and pseudorutile, there is a direct correlation between the impurity contents and the Ti content of the alteration phase. The impurity levels increase with increasing Ti/(Ti+Fe) to about 3 wt. % Al2O3 and 1 wt. % SiO2 for compositions close to TiO2. Thus during the latter stages of ilmenite alteration, alumina and silica are extracted from the ambient environment and are coprecipitated with, or adsorbed on to, the alteration products. The observed dependence of the alumina and silica contents on extent of alteration is consistent with a two-stage alteration mechanism earlier proposed (Grey and Reid, 1975).

Type
Research Article
Information
Mineralogical Magazine , Volume 47 , Issue 343 , June 1983 , pp. 201 - 208
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1983

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