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Growth and Alteration of Uranium-Rich Microlite

Published online by Cambridge University Press:  10 February 2011

R. Gierí ,
R. J. Swope ,
E. C. Buck ,
R. Guggenheim ,
D. Mathys  and
E. Reusser
R. Gierí
Affiliation:
Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA; giere@purdue.edu
R. J. Swope
Affiliation:
Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA
E. C. Buck
Affiliation:
Chemical Technology Division, Argonne National Laboratory, Argonne, IL 60439, USA
R. Guggenheim
Affiliation:
SEM Laboratory, University of Basel, CH-4056 Basel, Switzerland
D. Mathys
Affiliation:
SEM Laboratory, University of Basel, CH-4056 Basel, Switzerland
E. Reusser
Affiliation:
Institute of Mineralogy and Petrography, ETH Zentrum, CH-8092 Zürich, Switzerland
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Abstract

Uranium-rich microlite, a pyrochlore-group mineral, occurs in 440 Ma old lithium pegmatites of the Mozambique Belt in East Africa. Microlite exhibits a pronounced growth zoning, with a U-free core surrounded by a U-rich rim (UO2 up to 17 wt.%). The core exhibits conjugate sets of straight cracks (cleavage planes) which provided pathways for a late-stage U-enriched pegmatitic fluid which interacted with the U-free microlite to produce a distinct U enrichment along the cracks and led to the formation of the U-rich rim. Following the stage of U incorporation into microlite, a second generation of hydrothermal fluids deposited mica along the cleavage planes. Subsequent to these two hydrothermal stages, the host rock was uplifted and subjected to intense low-temperature alteration during which Na, Ca and F were leached from the microlite crystals. This alteration also led to a hydration of microlite, but there is no evidence of U loss. These low-temperature alteration effects were only observed in the U-rich rim which is characterized by a large number of irregular cracks which are most probably the result of metamictization, as indicated by electron diffraction images and powder X-ray patterns.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 608: Symposium QQ – Scientific Basis for Nuclear Waste Management XXIII , 1999 , 519
Copyright
Copyright © Materials Research Society 2000

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References

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