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GeoSoilEnviroCARS The University of Chicago X-ray Microprobe for Fluorescence and Absorption Spectroscopy Matt Newville, Steve Sutton, and Mark Rivers X-ray microbeam s Chemical composition, speciation, and local atomic structure for elements in heterogeneous materials at a micron scale. X-ray Microprobe Station at GSECARS Cu Speciation in Hydrothermal Fluid Inclusions Sample Stage: x-y-z(-q) stage, 1mm resolution Data Collection: Flexible software for x-y mapping, XAFS, tomography scans. Hydrothermal ore deposits are the main source of Cu, Au, Ag, Pb, Zn, and U. Metal complexes in high-temperature, highpressure solutions are transported until cooling, decompression, or chemical reaction cause precipitation and concentration in deposits. Fluorescence detector: 16-element Ge detector [shown], Wavelength Dispersive Spectrometer, or Ion Chamber To further understand the formation of these deposits, the nature of the starting metal complexes need to be determined. XRF and XAFS are important spectroscopic tools for studying the chemical speciation and form of these metal complexes in solution. Optical Microscope: (5x to 50x) with external video-capture system X-ray MicroFocusing: Horizontal and Vertical Kirkpatrick-Baez mirrors, typically focusing to 3mm x 3mm Natural Cu and Fe-rich brine fluid inclusions in quartz from Cu ore deposits from New South Wales, Australia were examined at room temperature and elevated temperatures by XRF mapping and XAFS. XAFS measurements at low and high temperature we also very different, with a very noticeable differences the XANES indicating a change in speciation This is challenging to do at and above the critical point of water (22MPa, 375oC). Fluid inclusions from hydrothermal deposits can be re-heated and used as sample cells for high temperature spectroscopies. Low temp: Cu2+ Incident Beam: Monochromatic x-rays from LN2-cooled Si (111), ~1012 photons/sec X-ray Microprobe Station at GSECARS Natural Cu and Fe-rich brine fluid inclusions in quartz from Cu ore deposits were examined at room temperature and elevated temperatures by XRF mapping: Cu and Fe Ka fluorescence intensities were recorded as a function of x-y position across a fluid inclusion by moving the sample in 5mm steps with an x-ray beam of 5mm x 5mm. Initial Expectation: chalcopyrite (CuFeS2) would be precipitated out of solution at low temperature, and would dissolve into solution at high temperature. We would study the dissolved solution at temperature XRF mapping showed that a uniform solution at room temperature was becoming less uniform at temperature. This was reversible. Cu 25oC Fe 25oC Cu 495oC Fe 495oC High temp: Cu1+ These results are consistent with Fulton et al [Chem Phy Lett. 330, p300 (2000)] study of Cu solutions near critic conditions: Cu2+ solution at low temperature, and Cu associated with Cl at high temperatures. O 2.35Å Cu2+ O 1.96Å Cl 2.09Å Cu1+