Mechanisms of lead release from uraninite in the natural fission reactors in Gabon

Journal Article · Mon May 01 04:00:00 EDT 1995 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/0016-7037(95)00117-4· OSTI ID:79272

Janeczek, J ^[1]; Ewing, R C ^[2]

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1. Silesian Univ., Sosnowiec (Poland)
2. Univ. of New Mexico, Albuquerque, NM (United States)

Twenty-four samples of uranium ore from the natural fission reactors in Gabon were studied by detailed electron microprobe analysis and backscattered electron imaging in order to determine the behavior of radiogenic Pb and fissiongenic nuclides. Lead content in uraninite varies from 19 wt% PbO in relicts of pristine uraninite, which were found only in reactor zone 10, to less than 5 wt% in altered uraninites. Different mechanisms of Pb loss from uraninite prevailed in different reactor zones and included leaching, grain boundary diffusion, exsolution via continuous precipitation, and volume diffusion. As a result of these processes, Pb content in uraninites from all the reactor zones, except for reactor zone 10, are similar and vary around a mean value of 5.2 wt% PbO. All of these processes were thermally activated and episodic. The predominance of any single mechanism in a particular reactor zone was controlled by the accessibility of solutions to the uranium ore. The thermal event which caused Pb mobilization in the deposits resulted from regional igneous activity in the Franceville Basin more than 1100 Ma after the reactors sustained spontaneous fission reactions. Reducing conditions prevented the long distance migration of Pb, as well as of fissiongenic Mo and Ru.

• OSTI ID: 79272
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 10 Vol. 59; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
54 ENVIRONMENTAL SCIENCES
ECOLOGICAL CONCENTRATION
ELECTRON MICROPROBE ANALYSIS
GABON
LEAD
MIGRATION
MOLYBDENUM
NATURAL ANALOGUE
OKLO PHENOMENON
RUBIDIUM
SPONTANEOUS FISSION
URANINITES
URANIUM DEPOSITS
URANIUM ORES
Yucca Mountain Project