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Oklo Mine, Franceville, Haut-Ogooué Province, Gabon

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Latitude & Longitude (WGS84): 1° 30' South , 13° 16' East
Latitude & Longitude (decimal): -1.50000,13.26667
Köppen climate type:Aw : Tropical savanna, wet

This mine near the Mouana Mine is the site of over a dozen precambrian natural nuclear reactors. It is particularly known as the "Oklo phenomenon". Secondary enrichment of uranium oxides in cm to meter sized veins moderated by ground water consumed six tons of U-235 and elevated temperatures to a few hundred Celsius. This uranium isotope, normally standing for less than 1% of the uranium ore, is predicted to be at 3% level in Oklo in the beginning (now relatively strongly depleted). Remarkably the non-volatile fission products moved only a few cm in the veins during the last 1.5 billion years!

Gillberg-Wickmann (1983) points at Oklo as the only natural example of a significant isotope fractionaction between U-235 and U-238.

Meshik (2005) states, that (1) U-free Al phosphate minerals from the deposit concentrate the highest amount of xenon found in natural material; (2) once upon a time over 2 tons of plutonium 239 were generated within the deposit.

See also Bangombé, another natural nuclear reactor in the same area.

Mineral List

43 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

1600 - 2500 Ma

ID: 1378137
Paleoproterozoic intrusive and metamorphic terranes

Age: Proterozoic (1600 - 2500 Ma)

Comments: Mixtures of metamorphic and intrusive or plutonic rocks, tracts known as crystalline, migmatitic terranes, moderately to highly metamorphosed rocks of unknown origin with or without intrusions. This classification is inherently prone to variable interpretation, as other compilers might distinguish some packages by their metamorphic or gneissic protoliths, and the associated age ranges may be more variable.

Lithology: Intrusive and metamorphic terranes

Reference: Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d. [18]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


- Econ Geol 84 (1989) 2286-2295.
- Radiochimica Acta 66/67 (1994) 455-461.
- Dymkov, Y., Holliger, P., Pagel, M., Gorshkov, A., and Artyukhina, A. (1997): Characterization of a La-Ce-Sr-Ca aluminous hydroxy phosphate in nuclear zone 13 in the Oklo uranium deposit (Gabon). Mineralium Deposita 32, 617-620.
- Janeczek, J. (1999): Mineralogy and geochemistry of natural fission reactors in Gabon. Reviews in Mineralogy and Geochemistry, 38, 321-392.
- Meshik, A. P. (November 2005): "The Workings of an Ancient Nuclear Reactor". Scientific American
- Hidaka, H. (2007): Geochemical characteristics of an ancient nuclear reactor "Oklo". Journal of Nuclear and Radiochemical Sciences 8, 99-103.

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