Solubility of molybdenite (MoS2) in aqueous fluids at 600-800 °C, 200 MPa: A synthetic fluid inclusion study

If combined with Mo concentrations measured in natural fluid inclusions, our data provide important constraints on the fO2 and fS2 conditions of ore formation. While Mo contents of fluids trapped at magmatic conditions agree well with predicted MoS2 solubilities along the magnetite-pyrrhotite fO2-fS2 buffer, Mo concentrations in hydrothermal brines trapped at 400-500 °C require orders of magnitude higher fO2 or lower fS2 conditions relative to this buffer. The fact that fS2 in porphyry systems usually increases relative to the magnetite-pyrrhotite buffer during cooling from >700 °C to 400 °C suggests that the observed high Mo contents are due to high fO2, which is in agreement with the general trend of increasing fO2 during subsolidus cooling of granitic plutons.