Synchrotron XRF and XANES investigation of uranium speciation and element distribution in fluid inclusions from unconformity‐related uranium deposits

Abstract

International audienceFluid inclusions from two quartz samples of the McArthur River and Rabbit Lake unconformity-related uranium deposits (Athabasca Basin, Canada) were analysed by synchrotron X-ray fluorescence (SXRF) and X-ray absorption near-edge spectroscopy (XANES) to shed light on (i) the detailed chemistry of the fluids having transported the uranium and (ii) the speciation of uranium in these fluids. The analysed samples contain variable proportions of NaCl-rich or CaCl2-rich (2535 wt% salts) fluid inclusions that homogenise into the liquid phase between 120 and 200 degrees C. For unknown reason, all of the CaCl2-rich fluid inclusions decrepitate under X-ray beam after a few seconds, precluding any SXRF or XANES measurement. SXRF on 12 homogenised NaCl-rich fluid inclusions from the Rabbit Lake sample shows that the fluid inclusions contain appreciable amounts of Br, Fe, Sr, transition metals (Mn, Ni, Cu, Zn), Pb, U and rare earth elements (REE) (La, Ce), with concentrations being relatively homogeneous among fluid inclusions. Within the complex McArthur River sample (numerous fluid inclusions+randomly distributed solids), statistical analyses of hyperspectral SXRF images were performed using the non-negative matrix approximation (NNMA) method. This strategy allows distinguishing the three domains contributing to the overall signal: (i) the quartz matrix, which notably contains significant amounts of Cr, Cu and Pb; (ii) the fluid inclusions characterised by high amounts of Br, Fe, Sr and transition metals; and (iii) La-Ce +/- Fe solids. Part of the U and REE are spatially associated with distinct optically invisible solids within the quartz matrix. XANES on four McArthur River sample fluid inclusions at room temperature and at 150 degrees C (fluid inclusion trapping temperature) as well as in solid and liquid U(IV) and U(VI) standards, respectively, shows that the uranium has remained in the form of U(VI) from trapping to present in the fluid inclusion

Exploring Actinide Materials Through Synchrotron Radiation Techniques

“…Philippot et al demonstrated that a high concentration of uranium was present in the Streltsov fluid inclusion and displayed a relatively homogeneous distribution throughout the inclusion through SR‐μ‐XRF. Richard et al also studied fluid inclusions from two quartz samples of uranium deposits by SR‐μ‐XRF and found considerable amounts of U and other elements (mainly transition metals and rare earth elements) in the fluid inclusions, which all distributed homogeneously among the samples. Jernström et al measured plutonium‐containing particles originating from Runit Island soil by SR‐μ‐XRF and found two types of Pu‐rich particles: the first type was with pure Pu matrix, and the other was particles with plutonium heterogenously included in Si/O‐rich matrix.…”

Role of fluid and melt inclusion studies in geologic research

“…More recently, infrared synchrotron X‐ray fluorescence, X‐ray absorption near edge structure (XANES) measurements have been used to determine element speciation in single inclusions (Richard et al . ).…”

“…Use of infrared light microscopic methods (Campbell et al 1984) also allowed analysis of single inclusions in opaque ore minerals (Kouzamanov et al 2010). More recently, infrared synchrotron X-ray fluorescence, X-ray absorption near edge structure (XANES) measurements have been used to determine element speciation in single inclusions (Richard et al 2012).…”

Insights into B-Mg-Metasomatism at the Ranger U Deposit (NT, Australia) and Comparison with Canadian Unconformity-Related U Deposits

“…Based on fluid inclusion and stable isotope studies, the mineralising fluids are widely accepted to be 100-200 • C basinal brines, which underwent significant modification by interaction with basement lithologies [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Halogen geochemistry of fluid inclusions indicates that the basinal brines were produced by evaporation of seawater [9,[21][22][23][24]. In addition to basinal brines, a low-salinity fluid of possible meteoric origin was also involved at the time of U deposition in the Australian deposits [9,10].…”