Uranium Redistribution Under Oxidizing Conditions in Oklo Natural Reactor Zone 2, Gabon

Abstract

AbstractThis mineralogical study was completed to elucidate the relationships between uranium distribution and alteration products of the host rock of natural reactor zone 2 at Oklo. The samples used were from the reactor core and reactor zone clays just below the reactor core. Uraninite is preserved without any alteration in the reactor core. Uranium minerals found to be present in the fractures in the reactor zone clays associated with iron-mineral veins, galena and Ti-bearing minerals. Uranium, for which the phases could not be identified, occurs in iron-mineral veins and the iron-mineral rim of pyrite grains in the reactor zone clays. Uranium is not associated with granular iron minerals occurring in the illite matrix of the reactor zone clays. The degree of crystallinity and uranium content of the three iron-bearing alteration products suggest that they formed under different conditions; the granular iron minerals, under alteration conditions where uranium was not mobilized while the iron-mineral veins and the iron-mineral rim of pyrite, under conditions in which uranium is mobilized after the formation of the granular iron minerals.