Hostname: page-component-8448b6f56d-m8qmq Total loading time: 0 Render date: 2024-04-23T10:54:13.553Z Has data issue: false hasContentIssue false
  • English
  • Français

Petrographic relationships between mineral phases and bitumen in the Oklo Proterozoic natural fission reactors, Gabon

Published online by Cambridge University Press:  05 July 2018

John Parnell
John Parnell*
Affiliation:
School of Geosciences, Queen's University of Belfast, Belfast BT7 INN, UK
Get access Rights & Permissions [Opens in a new window]

Abstract

Several of the Proterozoic natural fission reactors at Oklo, Gabon contain abundant organic matter (bitumen), with which much of the reactor uranium is associated. An understanding of the petrography of the bitumen is important in assessing its role in element retention following fissiogenic reactions. The bitumen is replacive and includes vestiges of detrital grains and clays of the host sandstones. It also contains several generations of mineral phases related to the migration of uranium and daughter lead, and other elements mobilized by hydrothermal activity in the reactor zones. The minerals include (primary) uraninite precipitated after reduction of uranium by organic matter, silicates concentrated in radiation halos around the uraninite, and native lead, galena and further uraninite which migrated from the primary uraninite. The silicates are illitic clays in the immediate vicinity of the reactors, and chloritic more distant from the reactors. Authigenic clays in radiation halos are compositionally distinct from earlier host rock clays. Local migration of uranium and lead is evident as dispersion of the elements through the radiation halos; cross-cutting veinlets of uraninite, native lead and galena, including veinlets extending directly from the primary uraninite crystals; and concentrations of the elements at the margins of bitumen masses. The limit of observed uranium dispersion is within clay immediately beyond the bitumen margins.

Keywords

natural fission reactorsbitumenuraniumOkloGabon
Type
Petrology
Information
Mineralogical Magazine , Volume 60 , Issue 401 , August 1996 , pp. 581 - 593
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1996

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Alpern, B. (1978) Etude petrographique de la matiere organique d'Oklo. In Les Reacteurs de Fission Naturels. IAEA-TC-119, Vienna, 333—51.Google Scholar
Brookins, D.G. (1983) Migration and retention of elements at the Oklo natural reactor. Environment. Geol., 4, 201-8.CrossRefGoogle Scholar
Brookins, D.G. (1984) Geochemical Aspects of Radioactive Waste Disposal. Springer-Verlag, Berlin.CrossRefGoogle Scholar
Brookins, D.G. (1990) Radionuclide behaviour at the Oklo nuclear reactor, Gabon. Waste Management, 1, 285-9 .CrossRefGoogle Scholar
Cassou, A.-M., Connan, J., Correia, M. and Orgeval, J.-J. (1975) Etudes chimiques et observations micro- scopiques de la matiere organique de quelques mineralisations uraniferes. In Le Phenomene d'Oklo. IAEA- SM-2 4, Vienna, 195-2 .Google Scholar
Cortial, F., Gauthier-Lafaye, F., Oberlin, A., G., Lacrampe-Couloume and Weber, F. (1990) Characterization of organic matter associated with uranium deposits in the Francevillian Formation of Gabon (Lower Proterozoic). Org. Geochem., 15, 73–85.CrossRefGoogle Scholar
Curtis, D., Benjamin, T., Gancarz, A., Loss, R., Rosman, K. , De Laeter, J., Delmore, J.H. and Maeck, W.J. (1989) Fission product retention in the Oklo natural fission reactors. Appl. Geochem., 4, 49— 2.CrossRefGoogle Scholar
De Laeter, J.R. (1985) The Oklo reactors; natural analogues to nuclear waste repositories. Search, 1, 193-6.Google Scholar
De Laeter, J.R., Rosman, K.J.R. and Smith, C.L. (1980) The Oklo natural reactor: cumulative fission yields and retentivity of the symmetric mass region fission products. Earth Planet. Sci. Letters, 5, 238–4.CrossRefGoogle Scholar
Durrance, E.M. (1986) Radioactivity in Geology, Principles and Applications. Wiley, London.Google Scholar
Eakin, P.A. (1989) Isotopic and petrographic studies of uraniferous hydrocarbons from around the Irish Sea Basin. J. Geol. Soc., Lond., 14, 3–73.Google Scholar
Eberly, P., Janeczek, J. and Ewing, R.C. (1994) Petrographic analysis of samples from the uranium deposit at Oklo, Republic of Gabon. Radiochim. Acta, 455—1.Google Scholar
Fischer, R.P., Hall, J.C. and Rominger, J.F. (1947) Vanadium deposits near Placerville, San Miguel County, Colorado. Colorado Sci. Soc. Proc., 15, 115–34.Google Scholar
Friedlander, G. and Kennedy, J.W. (1902) Nuclear and Radiochemistry. Wiley, New York.Google Scholar
Gauthier-Lafaye, F. and Weber, F. (1981) Les concentrations uraniferes du Francevillien du Gabon: leur association avec des gites a hydrocarbures fossiles du Proterozoique inferieur. Comptes Rendus Acad. Sci., 292, 9–74.Google Scholar
Gauthier-Lafaye, F. and Weber, F. (1989) The Francevillian (Lower Proterozoic) uranium ore deposits of Gabon. Econ. GeoL, 84, 2267—85.CrossRefGoogle Scholar
Gauthier-Lafaye, F. and Weber, F. (1993) Uranium- hydrocarbon association in Francevillian uranium ore deposits, Lower Proterozoic of Gabon. In Bitumens in Ore Deposits Parnell, J., Kucha, H. and Landais, P., eds. Springer-Verlag, Berlin, 27—8 .Google Scholar
Gauthier-Lafaye, F., Weber, F. and Ohmoto, H. (1989) Natural fission reactors of Oklo. Econ. Geol., 84, 228-95.Google Scholar
Geffroy, J. (1975) Etude microscopique des minerals uraniferes d'Oklo. In Le Phénomène d'Oklo. IAEA- SM-2 4, Vienna, 133-51.Google Scholar
Hemond, C., Menet, C. and Menager, M.T. (1992) U and Nd isotopes from the new Oklo reactor 1 (Gabon): evidence for radioelements migration. Materials Research Society Symposium Proceedings, 257, 489–9.CrossRefGoogle Scholar
Hidaka, H., Holliger, P. and Masuda, A. (1993) Evidence of fissiogenic Cs estimated from Ba isotopic deviations in an Oklo natural reactor zone. Earth Planet. Sci. Letters, 114, 391—6.CrossRefGoogle Scholar
Lancelot, J.R., Vitrac, A. and Allegre, CJ. (1975) The Oklo natural reactor: age and evolution studies by U- Pb and Rb-Sr systematics. Earth Planet. Sci. Letters, 25, 189–9..CrossRefGoogle Scholar
Leventhal, J.S., Daws, T.A. and Frye, J.S. (198 ) Organic geochemical analysis of sedimentary organic matter associated with uranium. Appl. Geochem.y, 1, 241–7.CrossRefGoogle Scholar
Leventhal, J.S., Grauch, R.I., Threlkeld, C.N., Lichte, F.E. and Harper, C.T. (1987) Unusual organic matter associated with uranium from the Claude deposit, Cluff Lake, Canada. Econ. Geol., 82, 1169—7 .CrossRefGoogle Scholar
Loss, R.D., Rosman, K.J.R. and De Laeter, .R. (1984) Transport of symmetric mass region fission products at the Oklo natural reactors. Earth Planet. Sci. Letters, 8, 246—8.Google Scholar
Loss, R.D., Rosman, K.J.R., De Laeter, J.R., Curtis, D.B., Benjamin, T.M., Gancarz, A.J., Maeck, W.J. and Delmore, J.E. (1989) Fission-product retentivity in peripheral rocks at the Oklo natural fission reactors, Gabon. Chem. Geol., 7, 71–84.CrossRefGoogle Scholar
Loubet, M. and Allegre, C.J. (1977) Behaviour of the rare earth elements in the Oklo natural reactor. Geochim. Cosmochim. Acta, 41, 1539–48.CrossRefGoogle Scholar
Maurette, M. (1970) Fossil nuclear reactors. Annual Review of Nuclear Science, 2, 319–5.Google Scholar
Menet, C., Menager, M.T. and Petit, J.C. (1992) Migration of radioelements around the new nuclear reactors at Oklo: analogies with a high-level waste repository. Radiochimica Acta, 59, 395–4.Google Scholar
Mossman, D.J., Nagy, B., Rigali, M.J., Gauthier-Lafaye, F. and Holliger, P. (1993) Petrography and paragenesis of organic matter associated with the natural fission reactors at Oklo, Republic of Gabon: a preliminary report. Coal Geol., 24, 179—94.CrossRefGoogle Scholar
Nagy, B., Gauthier-Lafaye, F., Holliger, P., Davis, D.W., Mossman, D.J., Leventhal, J.S., Rigali, M.J. and Parnell, J. (1991a) Organic matter and containment of uranium and fissiogenic isotopes at the Oklo natural reactors. Nature, 354, 472–5.CrossRefGoogle Scholar
Nagy, B., Leventhal, J.S. and Gauthier-Lafaye, F. (1991b) Organic geochemical and petrological investigations of a natural reactor and its environs at Oklo, Gabon: a preliminary report. U. S. Geol. Surv. Circular, 1058, 65—7.Google Scholar
Nagy, B., Gauthier-Lafaye, F., Holliger, P., Mossman, D.J., Leventhal, J.S. and Rigali, M.J. (1993) Role of organic matter in the Proterozoic Oklo natural Fission reactors, Gabon, Africa. Geology, 21, 55–8.2.3.CO;2>CrossRefGoogle Scholar
Nagy, B., and Kigali, M.J. (1993) Newly discovered, organic matter-rich natural fission reactors at Oklo and Bangombe: Are they useful analogs for longterm anthropogenic nuclear waste containment? WM r93 Conference Proceedings Tucson, 897—9 .Google Scholar
Naudet, R., (1978) Conclusion sur le deroulement du phenomene. In The Natural Fission Reactors. Int. Atomic Energy Agency, Vienna, 715—34.Google Scholar
Parnell, J. (1984) The distribution of uranium in kolm: evidence from backscattered electron imagery. Geol Forenin. i Stockholm Forhandl., 106, 231—4.CrossRefGoogle Scholar
Parnell, J., and Eakin, P., (1987) The replacement of sandstones by uraniferous hydrocarbons: Significance for petroleum migration. Mineral Mag., 51, 505-15.CrossRefGoogle Scholar
Parnell, J., Monson, B. and Tosswill, R.J. (1990) Petrography of thoriferous hydrocarbon nodules in sandstones, and their significance for petroleum exploration. J. Geol Soc., Lond., 147, 837–42.CrossRefGoogle Scholar
Rimsaite, J. (1978) Layer silicates and clays in the Rabbit Lake uranium deposit, Saskatchewan. Geol. Surv. Canada Current Research. Part A, Paper 78–1A, 303–15.Google Scholar
Rimsaite, J. (1982) Mode of occurrence of secondary radionuclide-bearing minerals in natural argillized rocks: A preliminary report related to a barrier clay in nuclear waste disposal. Geol Surv. Canada Current ResearchPart A, Paper 82-1A, 247—59.Google Scholar
Rouzard, J.N., Oberlin, A. and Trichet, J. (1980) Interaction of uranium and organic matter in uraniferous sediments. In Advances in Organic Geochemistry 1979 A.G. Douglas, A.G. and J.R. Maxwell, eds. Pergamon Press, Oxford, 505—1.Google Scholar
Ruffenach, I.C., Hagemann, R. and Roth, E. (1980) Isotopic abundances measurements a key to understanding the Oklo phenomenon. Zeits. Naturforsch., 35a, 171-9.CrossRefGoogle Scholar
Smits, G. (1992) Mineralogical evidence for geochemical environment at the earth's surface during deposition of Witwatersrand reefs. Trans. Inst. Mining Metall. (Section B: Appl. Earth ScL), 101, 99–107.Google Scholar