An experimental study of silver partitioning in sulfide-oxide-melt systems at 800 degrees C

Abstract

Silver solubility, and partitioning of silver between pyrrhotite and magnetite at a(Ag) = 0.13 ± 0.04 (1σ) has been determined at 800°C, and a range of fS2 between -4.06 and -0.18 and fO2 between -14.90 and -11.62 . Solubility is reported at 2800 ± 700 (1σ) ppm for pyrrhotite and 200 ± 100 (1σ) ppm for magnetite, at an a(Ag) = 0.13 ± 0.04 (1σ). Data indicate that silver partitions to a larger extent into pyrrhotite as compared to magnetite, = 13 ± 14 (1σ). Silver solubility in a melt, and vapor and brine present at 800°C, 140 MPa and fO2 ranging between QFM and NNO in Ag-metal saturated hydrothermal experiments were quantified by using LA-ICP-MS. Approximately 1 ppm silver is soluble in peralkaline silicate melts at an a(Ag) = 0.10. is approximated at 7 at 800ºC, 140 MPa, fO2 ranging between QFM and NNO, and a(Ag) = 0.10.

Models presented in this study indicate that Au, Ag, and Cu concentrations in silicate melts are impacted by the fractionation of magnetite and pyrrhotite. Sulfide mineral fractionation has a larger effect on ore metal budgets in silicate melts than magnetite. Magnetite does not remove as significant quantities of ore metals as does pyrrhotite; in high fO2 melts the minimal effects of Au, Ag, and Cu sequestering by magnetite should yield a high removal of these metals by the MVP. Small variations in fO2 can affect metal budgets in magmatic-hydrothermal systems because of the partially overlapping stability fields of pyrrhotite and magnetite.