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The alteration of pyrochlore to columbite in carbonatites in Tanganyika1 (With Plates XX and XXI.)

Published online by Cambridge University Press:  14 March 2018

T. C. James  and
Duncan McKie
T. C. James
Affiliation:
Geological Survey, Dodoma, Tanganyika
Duncan McKie
Affiliation:
Geological Survey, Dodoma, Tanganyika
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Summary

The formation of columbite has been observed in two carbonatites in south-west Tanganyika where it is due to autometasomatism following the emplacement of the bodies. Disoriented aggregates of columbite crystallites are formed as pseudomorphs after eubo-octahedra of pyrochlore in sövite. This alteration is accompanied by the addition of Fe, conversion of amphibole and biotite in the sövite to a ferruginous tale. the formation of an iron-bearing carbonate, and the introduction of colloform silica: Ca and Na are lost in part. The general alteration of the sövite can be ascribed to the influx of iron-bearing solutions at relatively low temperature and high pressure.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 31 , Issue 242 , September 1958 , pp. 889 - 900
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1958

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