Determination of the local structure and speciation of zinc in individual hypersaline fluid inclusions by micro-XAFS


X-ray absorption fine structure (XAFS) spectra were obtained for the first time from metal complexes in individual fluid inclusions in quartz using the synchrotron X-ray microprobe (X26A) at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory. Analysis of Zn K-edge absorption spectra obtained from hypersaline fluid inclusions in quartz indicate that the dominant complex of zinc in these inclusions at room temperature is ZnCl42-, having a Zn-Cl bond length of 2.33 Å, coordination number of 4.2 atoms and a mean-square relative displacement of the atoms of 0.004 Å2. The presence of ZnCl42- is consistent with results of previous spectroscopic studies of zinc chloride solutions having high Cl/Zn ratios and with solubility studies of zinc compounds in chloride solutions. The results demonstrate the potential of micro-XAFS as a tool for direct measurement of the structure of aqueous metallic species in fluid inclusions.

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Canadian Mineralogist