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TitleAn experimental investigation of the solubility and speciation of uranium in hydrothermal ore fluids
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LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorRempel, K U; Williams-Jones, A E; Fuller, K
SourceTargeted Geoscience Initiative 5: grant program final reports (2018-2020); by Targeted Geoscience Initiative Coordination Office; Geological Survey of Canada, Open File 8755, 2021 p. 281-288, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in Targeted Geoscience Initiative 5: grant program final reports (2018-2020)
RelatedThis publication is related to An experimental investigation of the solubility and speciation of uranium in hydrothermal ore fluids
File formatpdf
Subjectseconomic geology; geochemistry; Science and Technology; Nature and Environment; mineral deposits; uranium; hydrothermal deposits; ore mineral genesis; mineralization; ore controls; modelling; uranium geochemistry; solubilities; tectonic setting; hydrothermal systems; fluid dynamics; oxidation; precipitation; fluorides; chloride; alkalinity; acidity; oxides; hydroxides; Methodology
Illustrationsschematic diagrams; tables; plots
ProgramTargeted Geoscience Initiative (TGI-5) Knowledge Management Coordination
Released2021 10 27
AbstractExperimental data on the solubility and speciation of uranium in hydrothermal solution is required to improve genetic models for the formation of ore deposits, yet very few data of this type have been published. Of particular interest is the oxidation state of the uranium in solution, as conventional wisdom suggests that U is dissolved in the oxidized U(VI) state and precipitated as reduced U(IV) minerals, yet recent experiments have shown ppm-level solubility for U(IV).
This study investigated the mobility of reduced U(IV) and oxidized U(VI) in acidic (pH = 2), fluoride- bearing and alkaline (pH = 10), chloride-bearing solutions at 100-200°C and 1 to 15.8 bars (0.1-1.58 MPa). Preliminary data for the mobility of U(IV) in pH 2 fluids with 0.01 m F- show concentrations of 1.76 to 3.92 ppm U at 200°C, indicating that, contrary to common belief, the reduced U(IV) can be transported in solution. We have also conducted experiments on U(VI) solubility in pH 2 fluoride-bearing, and pH 10 chloride-bearing solutions. Uranium concentrations in the F- -bearing experiments ranged from 624 to 1570 ppm (avg. 825 ppm, n = 6) at 100°C, 670 to 1560 ppm (avg. 931 ppm, n = 4) at 150°C, and 3180 to 7550 ppm (avg. 5240, n = 9) at 200°C. In comparison, U concentrations in the Cl- -bearing runs range from 86.1 to 357 ppm (avg. 185 ppm, n = 15) at 200°C. Clearly, oxidized U(VI) is very readily mobilized in hydrothermal fluids. However, the measured concentrations of U(VI) are independent of those of F- or Cl-, suggesting the formation of U oxide or hydroxide species rather than U chlorides or fluorides.
These experimental data will be verified and supplemented in future experiments, which will be used to derive the stoichiometry and thermodynamic constants for the dominant uranium species in hydrothermal solutions. The data from this study will then be integrated into a comprehensive genetic model for uranium ore-forming systems.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques, which will result in more effective targeting of buried mineral deposits. This compendium is the result of the TGI Grant Recipients 2018-2020.

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