<p>Knowledge of molybdenum (Mo) speciation under hydrothermal conditions is a key for understanding the formation of porphyry deposits which are the primary source of Mo. Existing experimental and theoretical studies have revealed a complex speciation, solubility and partitioning behavior of Mo in fluid-vapor-melt systems, depending on conditions, with the (hydrogen)molybdate (HMoO<sub>4</sub><sup>-</sup>, MoO<sub>4</sub><sup>2-</sup>) ions and their ion pairs with alkalis in S and Cl-poor fluids [1-3], mixed oxy-chloride species in strongly acidic saline fluids [4, 5], and (hydrogen)sulfide complexes (especially, MoS<sub>4</sub><sup>2-</sup>) in reduced H<sub>2</sub>S-bearing fluids and vapors [6-8]. However, these available data yet remain discrepant and 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., [9]). A potential missing ligand for Mo may be the recently discovered trisulfur radical ion (S<sub>3</sub><sup>&#8226;-</sup>), which is predicted to be abundant in sulfate-sulfide rich acidic-to-neutral porphyry-like fluids [10]. We performed exploratory experiments of MoS<sub>2</sub> solubility in model sulfate-sulfide-S<sub>3</sub><sup>&#8226;-</sup>-bearing aqueous solutions at 300&#176;C and 450 bar. We demonstrate that Mo can be efficiently transported by S<sub>3</sub><sup>&#8226;-</sup>-bearing fluids at concentrations ranging from several 10s ppm to 100s ppm, depending on the fluid pH and redox, whereas the available data on OH-Cl-S complexes cited above 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 S<sub>3</sub><sup>&#8226;-</sup> in Mo transport by geological fluids.</p><ul><li>1. Kudrin A.V. (1989) <em>Geochem. Int. </em><strong>26</strong>, 87&#8211;99.</li>
<li>2. Minubayeva Z. and Seward T.M. (2010) <em>Geochim. Cosmochim. Acta</em> <strong>74</strong>, 4365&#8211;4374.</li>
<li>3. Shang L.B. et al. (2020) <em>Econ. Geol. </em><strong>115</strong>, 661&#8211;669.</li>
<li>4. Ulrich T. and Mavrogenes J. (2008) <em>Geochim. Cosmochim. Acta </em><strong>72</strong>, 2316-2330.</li>
<li>5. Borg S. et al. (2012) <em>Geochim. Cosmochim. Acta</em> <strong>92</strong>, 292&#8211;307.</li>
<li>6. Zhang L. et al. (2012) <em>Geochim. Cosmochim. Acta</em> <strong>77</strong>, 175&#8211;185.</li>
<li>7. Kokh M.A. et al. (2016) <em>Geochim. Cosmochim. Acta </em><strong>187</strong>, 311&#8211;333.</li>
<li>8. Liu W. et al. (2020) <em>Geochim. Cosmochim. Acta</em> <strong>290</strong>, 162&#8211;179.</li>
<li>9. Kouzmanov K. and Pokrovski G.S. (2012) <em>Soc. Econ. Geol. Spec. Pub.</em> <strong>16</strong>, 573&#8211;618.</li>
<li>10. Pokrovski G.S. and Dubessy J. (2015) <em>Earth Planet. Sci. Lett. </em><strong>411</strong>, 298&#8211;309.</li>
</ul>
The Role of Fe2O3 and Light Induced on Dielectric Properties of Borosilicate Glass