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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+