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ID 21460
file
creator
Kikuchi, M.
Horie, K.
Gauthier-Lafaye, F.
NDC
Earth sciences. Geology
abstract
The isotopic analyses of rare earth elements (REE), Pb and U in several kinds of minerals from the clay and black shale layers above the Bangombe natural reactor, Gabon, were performed using a sensitive high-resolution microprobe (SHRIMP) to investigate the migration and retardation processes of fission products released from the reactor. REE isotopic data of the secondary minerals found in clays and black shales show that most of fission products were effectively trapped in the clays and not distributed into the black shales over the clays, which reveals that the clays play an important role in preventing fission products from spreading. Zircon crystals in the clays heterogeneously contain high-U regions (up to 28.3 wt%) with normal U-235/U-238 ratios (=0.00725) and significant amounts of fissiogenic REE, which suggest the occurrence of significant chemical fractionation between REE and U during the dissolution of reactor uraninite and the recrystallization of secondary U minerals. The Pb data suggest that galena grains in the clays were also formed by the mixing of the two components during a recent alteration event, and that a significant amount of Pb was derived from 2.05-Ga-old original uraninite rather than reactor uraninite. The U-Pb systematics of zircon provide chronological information on the old igneous activity associated with the basement rock formation at 2.8 Ga and geochemical evidence of the incomplete mixing of independent Pb and U sources. This result is consistent with previous chronological results in this area.
journal title
Geochimica et Cosmochimica Acta
volume
Volume 71
issue
Issue 19
start page
4716
end page
4726
date of issued
2007-10
publisher
Pergamon-Elsevier Science Ltd
issn
0016-7037
ncid
publisher doi
language
eng
nii type
Journal Article
HU type
Journal Articles
DCMI type
text
format
application/pdf
text version
author
rights
Copyright(c) 2007 Pergamon-Elsevier Science Ltd
relation is version of URL
http://dx.doi.org/10.1016/j.gca.2007.07.016
department
Graduate School of Science