Rhenium complexes in supercritical fluids: implications for Re fractionation in porphyry Cu-Au-Mo-W deposits

Most of the world’s rhenium (~90%) is obtained from molybdenite (MoS₂) of porphyry copper deposits. The highest Re contents in MoS₂ were observed in the Cu-type deposits with smaller values in Cu-Au, Cu-Mo and Mo-W types deposits (Barton et al., 2020). The goal of this study is to determine the mechanisms leading to such fractionations.

To assess the role of salt and sulfur in the behavior of Re and the accompanying metals in supercritical fluids, we combined thermodynamic modeling with solubility experiments in aqueous salt-sulfur solutions at 400°C and 550 bar in the presence of pH, fS₂ and fO₂ mineral buffers. We measured the solubility of major ore minerals (CuFeS₂, MoS₂, ReS₂ and Au) in such fluids and critically revised the speciation models for those metals.

Our data show that Au and Cu form complexes with (HS)^– and Cl^– whereas Mo forms oxyanions and their ion pairs with K⁺ that is typical for other similar chemically “hard” metals like W (Borchert et al., 2025). Re in its common oxidation state +4 is expected to be a chemically “soft” metal and is likely transported by Cl- and S-type complexes.

Finally, we will present first results of complementary ab initio molecular dynamics simulations of Re speciation in aqueous fluids with different ligands, (OH)^–, (HS)^– and Cl^–, and discuss structural parameters and the geometry of the hydrated complexes in solution.

[1] Barton et al. (2020) Min. Metall. Explor. 37, 21-37

[2] Borchert et al. (2025) Eur. J. Mineral. 37, 111–130