Solubility of Platinum in Pyrite and Pyrrhotite

Abstract

Abstract A temperature range of processes leading to the concentration of Pt in the crust widely varies from high-temperature orthomagmatic to low-temperature hydrothermal and biogenic. Pyrite FeS2 and pyrrhotite Fe1–xS are important components of sulfide ores, which contain platinum-group elements. Fe sulfides typically host from a few hundreds to a few tens ppm of dispersed (invisible) Pt. In this work, we summarized the available data on the solubility of Pt in pyrite and pyrrhotite, supplement them with the results of synthesis of these minerals in the presence of Pt phases, and present a model that can describe the solubility of Pt in a broad range of temperature and S2 fugacity. The resulting equations allow the calculation of the solubility of Pt (ppm) in a temperature range of 300 < t < 1100°C and S2 fugacity up to the equilibrium with Sl. Tables with the solubility of Pt in pyrite and pyrrhotite depending on temperature and S2 fugacity are presented. Isopleths of the solubility of Pt in Fe sulfides are plotted on a log f(S2)–1000/T diagram. The analysis of the position of the main field of ore formation on this diagram showed that pyrite and pyrrhotite dissolve up to a few and a few hundreds of ppm Pt, respectively, upon conditions typical of ore formation: t < 700°C and log f(S2) < –4. These estimations coincide with maximum Pt contents determined in minerals of natural sulfide ores.