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Preliminary investigations of Nb in melt-fluid systems using in situ X-ray spectroscopy

Preliminary investigations of Nb in melt-fluid systems using in situ X-ray spectroscopy. Adam J. Layman 1 and Alan J. Anderson 2 1 Dalhousie University, Halifax, Nova Scotia, Canada 2 St. Francis Xavier University, Antigonish, Nova Scotia, Canada. Introduction.

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Preliminary investigations of Nb in melt-fluid systems using in situ X-ray spectroscopy

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  1. Preliminary investigations of Nb in melt-fluid systems using in situ X-ray spectroscopy Adam J. Layman1 and Alan J. Anderson2 1 Dalhousie University, Halifax, Nova Scotia, Canada 2 St. Francis Xavier University, Antigonish, Nova Scotia, Canada

  2. Introduction The partitioning of Nb in hydrothermal fluid-melt systems is important to our understanding of the transport and deposition of Nb in crustal rocks. Recent experimental work (e.g., Linnen 2004 Lithos v.80) has advanced our knowledge of Nb solubility in granitic melts. However, there is still very little known about Nb transport in hydrothermal fluids.

  3. Evidence for fluid transport Nb - fenites - hydrothermal veins - albitized felsic rocks

  4. The behavior of Nb in melt-fluid systems is investigated using Synchrotron radiation micro-X-ray fluorescence (SR-μXRF) SR-μXRF allows for in situ, quantitative, measurements of experiments in the Hydrothermal Diamond Anvil Cell (HDAC), at geologically relevant pressures and temperatures

  5. Methodology Nb-bearing synthetic glasses - characterized by EMP analysis Glass WNb - peraluminous, CNb ~ 445 ppm Glass ASI06 - peralkaline, CNb ~ 5000 ppm

  6. Four experimental fluids - aqueous ± sodium carbonate - varying densities - CO32- concentrations (0, 0.5, 1 M) - Trace Br; 500 ppm, 1000ppm

  7. SampleChamber Thermocouples Gasket Heater Wires Tungsten Carbide Seat Hydrothermal Diamond Anvil Cell

  8. Synchrotron X-ray Microprobe

  9. Experimental Setup Microscope HDAC Detector

  10. Phase transitions T = 190°C T = 22°C T = 475°C T = 635°C

  11. Spatial resolution of microbeam T = 22 °C After experiment

  12. Distribution of elements in HDAC Nb X-ray map T = 22°C Br X-ray map T = 22°C

  13. X-ray Fluorescence Spectra Re L’s Br Ka Br Kb Compton Scattering Nb Ka Counts X-ray Energy (eV)

  14. Composition of Fluid Coexisting with Melt Br Ka Mo Ka Br Kb Counts Nb Ka X-ray Energy (eV)

  15. Br Ka Compton scattering Mo Ka Re L’s Br Kb Nb Ka Background fitting routine Fitting XRF Spectrum Counts X-ray Energy (eV)

  16. Peak Areas from Fitting Routine PeakEnergyArea Fe Ka 6.400 989.6 Ni Ka 7.472 2150.1 Re La 9.637 45766.8 Re Lb 10.179 0.0 Br Ka 11.907 4313.8 Br Kb 13.296 780.1 Nb Ka 16.584 7065.5 Mo Ka 17.443 3114.6

  17. Peak Areas from Fitting Routine PeakEnergyArea Fe Ka 6.400 989.6 Ni Ka 7.472 2150.1 Re La 9.637 45766.8 Re Lb 10.179 0.0 Br Ka 11.907 4313.8 Br Kb 13.296 780.1 Nb Ka 16.584 7065.5 Mo Ka 17.443 3114.6

  18. CNb PANb CBr PABr Quantification • Fundamental Parameters • incorporates absorption and matrix effects, pre-sample and pre-detector absorbing layers (diamond) • uses known Br concentration as an internal standard, to calculate Nb concentration

  19. Experimental Summary • - Initial experiments using glass WNb, CNb ~ 445 ppm, and 1 M sodium carbonate and pure water fluids • Experiments using ASI06, CNb = 5000 ppm, and 0.5 M sodium carbonate and pure water fluids • Evaluation of precision and accuracy using standard solutions in the HDAC and capillary tubes

  20. Results • Nb in pure aqueous fluid coexisting with a silicate melt is not detected at all P-T conditions • at relatively high densities, silico-aqueous single phase fluid • ≥ 0.95 g/cm3 for carbonate-bearing fluid • ≥ 0.965 g/cm3 for pure water • Nb does partition into carbonate-bearing fluid at high to submagmatic T

  21. Nb concentration in fluid D = 0.95 g/cm3

  22. With 1 M sodium carbonate fluid, Nb partitions strongly into the fluid phase. At high temperatures, in a single phase fluid, CNb= 25 ppm During cooling, two phases are apparent, a melt and a aqueous fluid. Nb is partitioned into the fluid, with CNb= 19 ppm at 600°C, 7 kbars, and CNb≤ 3ppm at 400°C, 3.5 kbars

  23. Conclusions Nb is not detected in pure aqueous fluid coexisting with a silicate melt. In contrast, significant amounts of Nb were measured in carbonate-bearing fluids at magmatic temperatures. Carbonate-bearing fluids may provide an alternate/parallel host and transport mechanism for Nb.

  24. Acknowledgements NSERC Advanced Photon Source, Argonne National Laboratory, and the United States Department of Energy Bill Bassett, Bob Mayanovic and I-Ming Chou GSECARS Beamline 13-ID, Steve Sutton and Matt Newville PNC-XOR Beamline 20, Robert Gordon, Steve Heald, Dale Brewe and Julie Cross Barrie Clarke Dalhousie University St. Francis Xavier University

  25. Methodology

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