Bariandite Oklo Natural Nuclear Reactor Zone Riker - Gabon

Bariandite, Francevillite Uranium Minerals from Oklo Gabon

The minerals, Bariandite with minor Francevillite were recovered from Gabon's Oklo natural nuclear reactor zone. The Bariandite at the Oklo natural nuclear reactor site (Mounana uranium mine) and was first discovered there in the early 1970s. This specimen includes minute fibrous aggregates of blackish-green Bariandite, with minor Francevillite, a vanadium-rich uranyl mineral often formed during the oxidative alteration of the original uranium orebody. The co-occurrence reflects the unique post-reactor geochemistry of the Oklo, Okelobondo, and Bangombé natural nuclear fission zones.

Bariandite at Oklo is relatively rare and typically found in association with other vanadium minerals. It occurs as minute blackish-green fibrous aggregates. The presence of Bariandite with Francevillite represents the unique oxidized mineral assemblage resulting from the post-depositional alteration of the original uranium orebody for about 2 million years. The Bariandite at Oklo was originally part of the primary uranium orebody before being remobilized and incorporated into secondary minerals during post-depositional alteration.

Geological Significance of Oklo and Okelobondo

The Oklo natural nuclear reactor zones, located in the Haut-Ogooué province, Gabon, are famous Paleoproterozoic uranium deposits where self-sustaining nuclear fission reactions occurred ~2 billion years ago. These natural atomic fission reactions ran for hundreds of thousands of years. The system reached criticality with the neutron moderator being principally natural water and the unique geological layering of the deposits in the region.

French geologists first discovered the uranium deposit in 1956. Post-1972, international scientific investigations discovered ~17 natural fission zones (including Okelobondo and Bangombé) in the Francevillian Basin uranium district.

The Unique Geology for a Natural Nuclear Reactor

The Oklo natural nuclear reactor began nearly 2 billion years ago when uranium-235 levels in natural ore were around 3.1%—sufficient for sustained fission. Permeable sandstone hosted the uranium, and groundwater acted as a neutron moderator, triggering self-sustaining chain reactions. Mined as both open-pit and underground operations, Oklo's reactor zones are mostly shallow, while Okelobondo lies about 300 meters deeper than the others.

The Francevillian Basin and Uranium Legacy

Seventeen reactor zones (RZ-1 to RZ-17) were originally identified at the Oklo site in Gabon's Haut-Ogooué province due to signs of uranium-235 depletion. Today, only 15 zones are recognized: 13 at Oklo, one at Okelobondo, and one at Bangombé reflecting more accurate geochemical assessments. Together, these 15 zones are referred to as the "Oklo Natural Nuclear Reactor Zone."

About the Oklo Reactors:

It's interesting to note that early speculations about the Oklo reactors included the idea that perhaps the reactors shut themselves off by burning out neutron-absorbing impurities like vanadium. The xenon isotope studies (Meshik et al. 2004) definitively showed a periodicity consistent with water moderation cycles and inconsistent with a "poison-burnout model" caused by the presence of vanadium.

Physicists and geochemists concur that vanadium-bearing minerals had an influence on the Oklo natural reactors chiefly by their neutron absorption characteristics. Vanadium likely prevented many potential natural reactors from igniting in parts of the Francevillian uranium field by absorbing neutrons in the critical early stages. At the Oklo site, where vanadium was comparatively scarce, a reactor was able to start and run; during operation, vanadium present in the rock simply absorbed some neutrons poisoning the reaction but not enough to stop it.

There is no evidence that vanadium provided any meaningful neutron moderation, nor that it acted as a dynamic “poisoner” that turned the reactor off during its cycling – those roles were filled by water and by short-lived fission product poisons. Geochemically, vanadium did play an indirect role by shaping the ore’s composition and post-reactor mineralogy.

Semantics and Key Points:

• Mounana served as the primary mining center for accessing the Oklo uranium deposits, which includes the natural nuclear reactor zones. Oklo refers to the uranium deposit and fission zones.
• The Mounana Mine refers to the mining infrastructure used to extract and study those deposits.

The Oklo and Okelobondo reactors are located within the same Paleoproterozoic sedimentary sequence—the Francevillian Basin—and share a common geological origin. Okelobondo, in particular, is now understood to be a deeper, southern extension of the Oklo ore system. While the terms “Oklo,” “Okelobondo,” and “Mounana” are sometimes used interchangeably in scientific and geological literature, it is more accurate to distinguish Mounana as the mining town, Oklo as the host of multiple reactor zones, and Okelobondo as one of those zones. Geologically, both Oklo and the often cited Okelobondo (only because it was the deepest), are both hosted within the uranium-rich FA Formation of the Francevillian Series and are considered components of the same mineralized system.

Specifications

• Riker case size: 8 1/4" X 6 1/4" X 7/8"
• Specimen size: 28mm H x 16mm W x 10mm D, Wt: 2.47 grams
• Disk size: 1 3/4" diameter X 1/2" D
• Note: Display stand and sizing cube not included.
• Chemistry: Bariandite: Mn²⁺(V⁵⁺O₄)(OH)·nH₂O, Francevillite: (Ba,Pb)(UO₂)₂(VO₄)₂·5H₂O
• Information for this product was gathered from 52 different scientific research sources.

What's Included:

• Certificate of Authenticity
• Tag and tag stand
• A Scientific Paper about the Oklo Natural Nuclear Reactors and some information about Bariandite/ Francevillite.
• A Copy of the Oklo natural nuclear reactor zone map sites. 
• NOTE: Specimens are priced by size. The artwork was printed in-color on professional quality Epson paper. 

Important Handling Note:

Due to the small size of the specimen, the radioactivity is medium. As with any mineral specimen, handle with care and wash your hands after handling. Do not inhale the dust.

A Truly Rare, Significant Geological Specimen

This specimen is exceedingly rare, and this attractive, top-tier Riker display makes Oklo's Bariandite with Francevillite an exceptional addition to any geological collection. This is definitely one of the rarest geological materials on our planet!

This Bariandite, Francevillite from the Oklo District, Gabon, is Guaranteed Authentic. It was professionally and legally collected and arrives with a Certificate of Authenticity, information, tag, tag stand, and scientific paper. The artwork was printed in-color with quality Epson paper. Specimens are priced by size.