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Investigation of the Long -Term Performance of Betafite and Zirconolite in Hydrothermal Veins From Adamello, Italy

Published online by Cambridge University Press:  10 February 2011

G. R. Lumpkin ,
R. A. Day ,
P. J. McGlinn ,
T. E. Payne ,
R. GierÉ  and
C. T. Williams
G. R. Lumpkin
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
R. A. Day
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
P. J. McGlinn
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
T. E. Payne
Affiliation:
Australian Nuclear Science and Technology Organisation, PMB 1, Menai, NSW 2234, Australia
R. GierÉ
Affiliation:
Dept. of Earth and Atmospheric Sciences, Purdue Univ., West Lafayette, IN 47907 -1397, USA
C. T. Williams
Affiliation:
Dept. of Mineralogy, The Natural History Museum, Cromwell Rd., London SW7 5BD, UK
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Abstract

Betafite and zirconolite occur in Ti-rich hydrothermal veins emplaced within dolomite marble in the contact aureole of the Adamello batholith, northern Italy. Zirconolite contains up to 18 wt% ThO2 and 24 wt% UO2, and exhibits strong compositional zoning. Some zirconolite grains were corroded by the hydrothermal fluid. Betafite, the Ti-rich member of the pyrochlore group, often occurs as overgrowths on zirconolite. The betafite is weakly zoned and contains 29-34 wt% UO2. In terms of end -members, betafite contains approximately 50 mole percent CaUTi2O7 and is the closest known natural composition to the pyrochlore phase proposed for use in titanate waste forms. Amorphization and volume expansion of the betafite caused cracks to form in the enclosing silicate mineral grains. Backscattered electron images reveal that betafite was subsequently altered along crystal rims, particularly near the cracks. EPMA data reveal little difference in composition between altered and unaltered areas, except for lower totals, suggesting that alteration is primarily due to hydration. The available evidence demonstrates that both betafite and zirconolite retained actinides for approximately 40 million years after the final stage of vein formation. During this time, betafite and zirconolite accumulated a total alpha -decay dose of 3-4 x 1016 and 0.2-2 x 1016 α/mg, respectively.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 793
Copyright
Copyright © Materials Research Society 1999

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