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The role of S3•- in molybdenum transport by hydrothermal fluids revealed by in situ X-ray absorption spectroscopy

The knowledge of molybdenum speciation under hydrothermal conditions is a key for understanding the formation of porphyry deposits which are the primary source of Mo. Previous studies have revealed a complex speciation of Mo including (hydrogen)molybdate ions, their ion pairs with alkalis, oxy-chloride species, and thiomolybdate complexes. However, these available data are unable to account for the observed massive transport of Mo in porphyry-related fluids revealed by fluid inclusion analyses demonstrating 100s ppm of Mo (e.g., Kouzmanov and Pokrovski, 2012). A potential missing ligand for Mo may be the trisulfur radical ion, which is predicted to be abundant in sulfate-sulfide rich acidic-to-neutral porphyry-like fluids.

We performed X-ray absorption spectroscopy (XAS) measurements at the Mo K-edge (20.0 keV) in a hydrothermal autoclave available at BM30 of ESRF synchrotron (Testemale et al., 2005) to study the molybdenite solubility in model S3•- rich aqueous solutions at 300°C and 500 bar. We found that Mo can be efficiently transported by S3•--bearing fluids at concentrations of several ppm, whereas the available data on OH-Cl-S complexes predict negligibly small (<100 ppb) Mo concentrations at our conditions. Work is in progress to extend the experiments to wider T-P-composition range of porphyry fluids and to quantitatively assess the role of S3•- in Mo transport by geological fluids.

K. Kouzmanov and G.S. Pokrovski, Soc. Econ. Geol. Spec. Pub. 16 (573–618), 2012; D. Testemale et al., Rev. Sci. Instr. 76 (043905), 2005.

Funding: Deutsche Forschungsgemeinschaft WI 2000/25-1, KL 1368/13-1, SCHM 2415/6-1, ESRF ES-1050.


Maria A. Kokh1, Manuela Borchert2, Stephan Klemme3, Christian Schmidt4, Jean-Louis Hazemann5, Denis Testemale5, Antonio Aguilar6, Elena F. Bazarkina7, Christoph Moeller8, Clément Laskar9, Gleb S. Pokrovski9, Max Wilke8
1Universität Potsdam, Institut für Geowissenschaften, Potsdam, Germany;Westfälische Wilhelms-Universtät, Institut für Mineralogie, Münster, Germany; 2Westfälische Wilhelms-Universtät, Institut für Mineralogie, Münster, Germany;Deutsches Elektronen-Synchrotron Hamburg, Germany; 3Westfälische Wilhelms-Universtät, Institut für Mineralogie, Münster, Germany; 4GeoForschungsZentrum Potsdam, Germany; 5Institut Néel, Grenoble, France;European Synchrotron Radiation Facility (ESRF), Grenoble, France; 6European Synchrotron Radiation Facility (ESRF), Grenoble, France;Institut de Chimie Moléculaire de Grenoble (ICMG), Université Grenoble Alpes, CNRS, Grenoble, France; 7European Synchrotron Radiation Facility (ESRF), Grenoble, France;Helmholtz Zentrum Dresden Rossendorf, Dresden, Germany; 8Universität Potsdam, Institut für Geowissenschaften, Potsdam, Germany; 9Géosciences Environnement Toulouse (GET), Université de Toulouse, CNRS, IRD, Toulouse, France
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