Geochemistry of organic-rich black shales overlying the natural nuclear fission reactors of Oklo, Republic of Gabon

Journal Article · Wed Jul 01 04:00:00 EDT 1998 · Energy Sources

DOI:https://doi.org/10.1080/00908319808970077· OSTI ID:624378

Mossman, D J ^[1]; Gauthier-Lafaye, F ^[2]; Nagy, B; Rigali, M J ^[3]

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1. Mount Allison Univ., Sackville, New Brunswick (Canada). Dept. of Physics, Engineering and Geoscience
2. Centre National de la Recherche Scientifique, Strasbourg (France). Centre de Geochimie de la Surface
3. Univ. of Arizona, Tucson, AZ (United States)

The organic-rich black shales of the Franceville Series` FB Formation overlying the uranium ores, and natural nuclear fission reactors of Oklo, Gabon, are not notably metalliferous. Chromium, gold, silver, and barium are slightly enriched in average Oklo black shale (AOK) relative to black shale standard SDO-1. Geochemical variations among the black shale samples of the sedimentary sequence include enrichment in potassium, barium, chromium, and silver in the four lowermost samples, the presence of a bleached zone depleted in organic carbon lowermost in the sequence, and elevated rare earth element (REE) content in samples closest to the Oklo reactor zones. Hydrothermal activity has influenced the geochemistry of the black shale but is evidently not linked to reactor-driven processes. Chondrite-normalized REE patterns of Oklo black shale samples show slight enrichment in light REE and slight depletion in heavy REE, especially in the sample closest to the reactor zone. However, comparison of REE content with various petrographic facies in and near the Oklo reactors shows no apparent enrichment in fission product (intermediate) REE. With few exceptions, reactor facies all contain more REE than AOK. The chondrite-normalized REE pattern of AOK resembles that of greywacke-shale turbidites of Archean greenstone belts. The paucity of uranium and manganese in AOK is a curious anomaly in an area of world class uranium and manganese deposits.

• Sponsoring Organization: Natural Sciences and Engineering Research Council of Canada, Ottawa, ON (Canada)
• OSTI ID: 624378
• Journal Information: Energy Sources, Journal Name: Energy Sources Journal Issue: 6 Vol. 20; ISSN 0090-8312; ISSN EGYSAO
• Country of Publication: United States
• Language: English

Related Subjects

04 OIL SHALES AND TAR SANDS
BLACK SHALES
GEOCHEMISTRY
HYDROTHERMAL ALTERATION
MULTI-ELEMENT ANALYSIS
OIL SHALE DEPOSITS
OKLO PHENOMENON