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Metal speciation in fluid inclusions using microbeam X-ray absorption spectroscopy
Journal of Geochemical Exploration 101 (2009) 51
Contents lists available at ScienceDirect
Journal of Geochemical Exploration j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j g e o ex p
Metal speciation in fluid inclusions using microbeam X-ray absorption spectroscopy Julianne James-Smith a,b, Joël Brugger a,c,⁎, Jean Cauzid d,e, Denis Testemale b, Jean-Louis Hazemann b, Weihua Liu f, Olivier Proux b a
Department of Geology and Geophysics, University of Adelaide, 5000, Australia Institut Néel MCMF, CNRS, 38042, Grenoble, France Division of Minerals, South Australian Museum, 5000, Adelaide, Australia d European Synchrotron Research Facility, 38043, Grenoble, France e Université de Nancy, Géologie et Gestion des Ressources Minérales et Energétiques, BP239, 54506 Vandoeuvre les Nancy, France f Division of Exploration and Mining, CSIRO, Clayton, Australia b c
Quantifying the nature, stability and structure of aqueous metal complexes at elevated pressure and temperature is a requisite for understanding the transport and deposition of metals in hydrothermal systems. The fluids trapped within fluid inclusions provide a unique window in which the chemical composition, temperature and pressure of the mineralizing environment are preserved. Laser Ablation Inductively Coupled Plasma Mass Spectroscopy, Particle Induced X-ray Emission (PIXE) and Synchrotron Radiation X-ray Fluorescence (SR-XRF) are currently used to obtain chemical analysis of single fluid inclusions. When used in conjunction with numerical modelling of ore transport and depositions, the chemical composition of fluids trapped in inclusions associated with hydrothermal minerals can be related to the mineral assemblages (i.e., mineral solubility) or used to infer the mineralizing processes (e.g., phase separation, fluid mixing, fluid–rock interaction). The accuracy of the predictions of these thermodynamic models relies on the availability of thermodynamic properties for all the important aqueous and vapour complexes as well as minerals under the conditions of interest. Using X-ray absorption spectroscopy (XAS), it is possible to probe the speciation (i.e., oxidation state, nature of aqueous complex) of metals in
natural fluid inclusions, from room-T to beyond the homogenisation temperature. These results can be compared with predictions from thermodynamic modelling and from experimental studies in simple model systems, and hence used to test the validity of our thermodynamic models. We measured the speciation of arsenic and copper in fluid inclusions from a variety of ore deposits. In the case of arsenic, beam-induced photo oxidation was a serious problem, preventing collection of good quality EXAFS data on all but the largest and Asrichest inclusions. XANES data reveal that at room temperature, aqueous and brine inclusions containing 100–500 ppm As contain reduced As minerals (e.g., arsenopyrite; orpiment or realgar). This corresponds to predictions from thermodynamic models. In some CO2rich inclusions containing high As contents (N 2000 ppm), As is present as As(OH)03 over the temperature range of 25–250 °C; this confirms predictions from experimental studies, and demonstrates that waterpoor, CO2-rich fluids can indeed carry large amounts of metals.
⁎ Corresponding author. Department of Geology and Geophysics, University of Adelaide, 5000, Australia. E-mail address: [email protected] (J. Brugger). 0375-6742/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2008.11.044
Contents lists available at ScienceDirect
Journal of Geochemical Exploration j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j g e o ex p
Metal speciation in fluid inclusions using microbeam X-ray absorption spectroscopy Julianne James-Smith a,b, Joël Brugger a,c,⁎, Jean Cauzid d,e, Denis Testemale b, Jean-Louis Hazemann b, Weihua Liu f, Olivier Proux b a
Department of Geology and Geophysics, University of Adelaide, 5000, Australia Institut Néel MCMF, CNRS, 38042, Grenoble, France Division of Minerals, South Australian Museum, 5000, Adelaide, Australia d European Synchrotron Research Facility, 38043, Grenoble, France e Université de Nancy, Géologie et Gestion des Ressources Minérales et Energétiques, BP239, 54506 Vandoeuvre les Nancy, France f Division of Exploration and Mining, CSIRO, Clayton, Australia b c
Quantifying the nature, stability and structure of aqueous metal complexes at elevated pressure and temperature is a requisite for understanding the transport and deposition of metals in hydrothermal systems. The fluids trapped within fluid inclusions provide a unique window in which the chemical composition, temperature and pressure of the mineralizing environment are preserved. Laser Ablation Inductively Coupled Plasma Mass Spectroscopy, Particle Induced X-ray Emission (PIXE) and Synchrotron Radiation X-ray Fluorescence (SR-XRF) are currently used to obtain chemical analysis of single fluid inclusions. When used in conjunction with numerical modelling of ore transport and depositions, the chemical composition of fluids trapped in inclusions associated with hydrothermal minerals can be related to the mineral assemblages (i.e., mineral solubility) or used to infer the mineralizing processes (e.g., phase separation, fluid mixing, fluid–rock interaction). The accuracy of the predictions of these thermodynamic models relies on the availability of thermodynamic properties for all the important aqueous and vapour complexes as well as minerals under the conditions of interest. Using X-ray absorption spectroscopy (XAS), it is possible to probe the speciation (i.e., oxidation state, nature of aqueous complex) of metals in
natural fluid inclusions, from room-T to beyond the homogenisation temperature. These results can be compared with predictions from thermodynamic modelling and from experimental studies in simple model systems, and hence used to test the validity of our thermodynamic models. We measured the speciation of arsenic and copper in fluid inclusions from a variety of ore deposits. In the case of arsenic, beam-induced photo oxidation was a serious problem, preventing collection of good quality EXAFS data on all but the largest and Asrichest inclusions. XANES data reveal that at room temperature, aqueous and brine inclusions containing 100–500 ppm As contain reduced As minerals (e.g., arsenopyrite; orpiment or realgar). This corresponds to predictions from thermodynamic models. In some CO2rich inclusions containing high As contents (N 2000 ppm), As is present as As(OH)03 over the temperature range of 25–250 °C; this confirms predictions from experimental studies, and demonstrates that waterpoor, CO2-rich fluids can indeed carry large amounts of metals.
⁎ Corresponding author. Department of Geology and Geophysics, University of Adelaide, 5000, Australia. E-mail address: [email protected] (J. Brugger). 0375-6742/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.gexplo.2008.11.044