Radiolysis evidenced by H 2-O 2 and H 2-bearing fluid inclusions in three uranium deposits

Abstract

H 2 with or without O 2 has been identified by Raman spectroscopy in fluid inclusions in quartz from three Precambrian uranium deposits: Oklo (Gabon), Rabbit Lake and Cluff Lake D (Saskatchewan, Canada). In the Oklo uranium deposit, heterogeneous trapping of fluids in the system H 2O-H 2-CH 4-salts is spatially associated with the natural nuclear reaction zones. At Rabbit Lake and Cluff Lake D, fluid inclusions show heterogeneous trapping of an aqueous liquid phase and a vapour phase with variable X(O 2) X(H 2) ratios always greater than one. H 2 and O 2 formation is discussed in terms of chemical reactions, chemical reactions indirectly induced by nuclear reactions and radiolytic processes. Numerical calculations of water radiolysis were carried out for two models: 1) water at the contact with an uranium oxide and 2) water inside a fluid inclusion containing either dissolved uranium or a small UO 2 crystal. The concentrations of O 2 and H 2 inside fluid inclusions from Rabbit Lake and Cluff Lake D deposits are consistent with the first model. In the Oklo deposit, the H 2-bearing fluid inclusions found in the quartz and the anomalous high O C atomic ratio of organic matter from nuclear reactor zones could result from radiolysis of water and organic matter due to the fission products of the chain nuclear reactions, but α radiolysis is not definitely ruled out.