X-ray imaging of uranium in individual fluid inclusions

The spatial distribution of major (K, Ca, Mn, Fe) and trace elements (Ti, Cr, Cu, As, Br, Rb, Sr, Zr, Pb, Th, U) were determined in individual fluid inclusions from quartz veins of the Streltsov uranium deposit, Russia, using synchrotron radiation X-ray fluorescence (SXRF). The analyses were performed on the beamline ID-ZZ Micro-FID (Fluorescence, Imaging, Diffraction) of the European Synchrotron Research Facility (ESRF, Grenoble, France). Fluorescence X-ray maps of single fluid inclusions show a relatively homogeneous distribution of most elements throughout the inclusion, whereas Fe and, to a lesser extent, Sr display highly localized count rates. This observation argues for the presence of minute, optically invisible, compounds that are precipitated inside the inclusion. Simple model calculations indicate that relatively diluted solutions (10-100 ppm U) trapped at geologically relevant temperatures (e.g. 250 C) would precipitate submicron sized particles. These particles would be highly reactive to the photon flux but not necessarily visible under the microscope, These results indicate that third-generation synchrotron light source can be a powerful technique to study the physical processes undergone by the fluid. When combined with chemical data, this technique can help to clarify fluid transport properties in natural systems.