Uraninite-water interactions in an oxidizing environment
- Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Earth and Planetary Sciences
- Queen`s Univ., Kingston, Ontario (Canada). Dept. of Geological Sciences
Exceptionally low {delta} {sup 18}O values of primary uraninite and pitchblende (i.e., {minus}32 per mil to {minus}19.5 per mil) from Proterozoic unconformity-type uranium deposits in Saskatchewan, Canada, in conjunction with theoretical uraninite-water oxygen isotope fractionation factors suggest that primary uranium mineralization is not in oxygen isotopic equilibrium with clays and silicates. The low {delta} {sup 18}O values have been interpreted to have resulted from the recrystallization of primary uranium mineralization in the presence of modern meteoric fluids having low {delta} {sup 18}O values of ca. {minus}18 per mil. The absence of apparent alteration in many of the uraninite and pitchblende samples requires that the uranium minerals exchange oxygen isotopes with fluids, with only minor disturbances to their original chemical compositions and textures. However, experiments on the interaction between water and natural uraninites, from these deposits, and detailed electron micro-probe analyses of natural uraninite and pitchblende indicate that, in the presence of water, old uraninite rapidly alters to curite. The hydration of uraninite to curite releases uranium and calcium into solution and becquerelite is precipitated. In the presence of Si-saturated waters, uranium silicate minerals, soddyite and kasolite are precipitated in addition to curite and schoepite. The mineral paragenesis observed in these experiments is similar to sequences observed in oxidized zones in uranium deposits and UO{sub 2}-water experiments. Therefore, it is unlikely that natural uraninite and pitchblende can simply exchange oxygen with an oxidizing fluid without a concomitant change in phase chemistry or structure, nor will oxidation of uraninite lead to the formation of U{sub 3}O{sub 7} as predicted by theoretical calculations used in natural analogue studies for the disposal of high level nuclear waste.
- Sponsoring Organization:
- Natural Sciences and Engineering Research Council of Canada, Ottawa, ON (Canada); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG03-95ER14540
- OSTI ID:
- 572275
- Report Number(s):
- CONF-961202--
- Country of Publication:
- United States
- Language:
- English
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