mXRF and mXAFS with the GSECARS X-ray Microprobe

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mXRF and mXAFS with the GSECARS X-ray Microprobe
Matthew Newville, Steve Sutton, Mark Rivers,
Peter Eng, Tom Trainor Consortium for
Advanced Radiation Sources (CARS) University
of Chicago, Chicago, IL
Cu in Quartz Fluid Inclusions at Hydrothermal
Conditions
John Mavrogenes, Andrew Berry Australian National
University, Canberra, ACT
High-Pressure C K-Edge X-ray Raman Spectroscopy
H. K. (Dave) Mao, Carnegie Institute of
Washington, HP-CAT Yue Meng, Carnegie Institute
of Washington, HP-CAT Chi-Chang Kao, Brookhaven
National Lab Wendy Mao, University of Chicago
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Advanced Photon Source Undulator A
Period length 3.30 cm Number of
periods 72 Length 2.47 m
Minimum gap 10.5 mm Power (closed gap)
6 kW Kmax (closed gap) 2.78 Energy
Tuning Range 2.9 - 13.0 keV (1st
harmonic) 2.9 - 45.0 keV (3rd and 5th
harmonic) On-axis peak brilliance (at 6.5 keV)
9.6x1018 ph/s/mrad2 /mm2 /0.1bw On-axis
power density (closed gap) 167 kW/mrad2

Source Size and Divergence Vert s 16mm,
s 4mrad Horiz s 240mm, s 14mrad
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GSECARS Beamline Layout and Optics
GeoSoilEnviroCARS Sector 13, APS, Argonne
National Lab
Undulator Beamline High collimation allows
efficient focusing, for x-ray microprobe,
and x -ray
diffraction (small crystals, high pressure).
High Pressure Station Diamond-Anvil-Cell
Large Volume Press
Monochromator LN2-cooled Si (111)
Energy range 4.5 40keV
X-ray Microprobe XAFS, XRF,
fluorescence tomography
Diffractometer surface diffraction
inelastic scattering
Large Focusing Mirrors 1m KB pair
Storage Ring, undulator
BM Station tomography, diffraction, DAC, Large
Volume Press, bulk XAFS
Bending Magnet Beamline 2nd-generation source,
with high energy x-rays (up to 100KeV)
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GSECARS XRF/XAFS Microprobe Station
Focusing Kirkpatrick-Baez mirrors Rh-coated Si,
typically using 3x3mm spot sizes, at 50mm from
end of mirrors.
Incident Beam LN2 cooled Si (111)
Sample Stage x-y-z stage, 1mm resolution
Slits typically 200 to 300 mm, accepting 20
of undulator beam at 50m from source.
Data Collection Flexible, custom software for
X-Y XRF mapping, and XAFS, based on EPICS.
Optical Microscope 5x to 50x objective to
external video system / webcam.
Fluorescence detector 16-element Ge detector /
DXP electronics, Lytle Detector, or Wavelength
Dispersive Spectrometer
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Kirkpatrick-Baez Focusing Mirrors
The table-top Kirkpatrick-Baez mirrors use
four-point benders and flat, trapezoidal mirrors
to dynamically form an ellipsis. They can focus
a 300x300mm beam to 1x1mm - a flux density gain
of 105. With a typical working distance of
100mm, and an energy-independent focal distance
and spot size, they are ideal for micro-XRF and
micro-EXAFS. We use Rh-coated silicon for
horizontal and vertical mirrors to routinely
produce 2x3mm beams for XRF, XANES, and EXAFS.
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X-ray Fluorescence Detectors
16 element Ge Detector energy resolution 250
eV, which separates most fluorescence lines, and
allow a full XRF spectrum (or the windowed signal
from several lines) to be collected in
seconds. Limited in total count rate (to
250KHz), so multiple elements (10 to 30) are
used in parallel. Detection limits are at the ppm
level for XRF. XANES and EXAFS measurements of
dilute species (10ppm) in heterogeneous
environments can be measured.
Wavelength Dispersive Spectrometer has much
better resolution (20eV), and much smaller solid
angle, but can be used for XAS,
is able to separate fluorescence lines that
overlap with a Ge detector.
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Metal Speciation in Hydrothermal Fluid Inclusions
John Mavrogenes, Andrew Berry (Australian
National University)
Hydrothermal ore deposits are important sources
of Cu, Au, Ag, Pb, Zn, and U. Metal complexes
in high-temperature, high-pressure solutions are
transported until cooling, decompression, or
chemical reaction cause precipitation and
concentration in deposits. 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. 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.
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.
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Hydrothermal Fluid Inclusion Measurements
Linkham TS1500 Heating Stage. Normally, this can
easily heat to 1200C for optical microscopy. We
had to take off most of the protective front
plates to cut down on background Cu and Fe
fluorescence. In the end, we ran the quartz
inclusion samples in air, with water flowing, but
no heat shielding.
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Cu speciation in Hydrothermal Fluid Inclusions
XRF Mapping
Understanding the metal complexes trapped in
hydrothermal solutions in minerals is key to
understanding the formation of ore deposits.
Natural Cu and Fe-rich brine and vapor-phase
fluid inclusions in quartz from Cu ore deposits
were examined at room temperature and elevated
temperatures by XRF mapping and EXAFS. 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 (2mm pixel size) showed that for
large vapor-phase inclusions, a uniform
distribution of Cu in solution at room
temperature was becoming less uniform at
temperature. This was reversible, and seen for
multiple inclusions.
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Cu XANES Speciation in Fluid Inclusions
XAFS measurements at low and high temperature for
the vapor-phase inclusiong were also very
different, with a very noticeable differences in
the XANES Low temp Cu2 , aqueous
solution High temp Cu1 , Cl or S ligand.
These results are consistent with Fulton et al
Chem Phys Lett. 330, p300 (2000) study of Cu
solutions near critical conditions Cu2 solution
at low temperature, and Cu1 associated with Cl
at high temperatures.
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Cu XAFS in Fluid Inclusions
EXAFS from the high temperature phase.
Fit to high-temperature (450C) Cu solution in
fluid (vapor phase) inclusion can get good fits
with 1 Cl at 2.09Å and 1 O at 2.00Å, or 2 Cl
at 2.08Å. This is also consistent with the
model of for aqueous Cu1 of Fulton et al,
J. A. Mavrogenes, A. J. Berry, M. Newville, S. R.
Sutton, Am. Mineralogist 87, p1360 (2002)
Low temp High temp
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Inelastic X-ray Scattering X-ray Raman

• - 6-element Si (440) Crystal Analyzer
• - Kappa Diffractometer
• Large Beamline KB mirrors, giving 1013ph/s at
  10keV in a 20x80mm spot.
• Ideal for inelastic x-ray scattering in a Diamond
  Anvil Cell, including XANES-like information from
  X-ray Raman measurements.

DAC sample, lead-covered detector
Analyzer Crystals Si (440) 870mm Rowland circle
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X-ray Raman high pressure carbon
There is very little spectroscopic study of the
phase transitions from graphite -gt
hcp C -gt fcc C (diamond). Here is preliminary
X-ray Raman measurements on graphite in a
Diamond Anvil Cell (yes, background diamond is a
possibility!)