Role of serpentinization in platinum group element (PGE) mobilization—Evidence from experiments

Reducing conditions are typical of incipient serpentinization in which sulfides and alloys break down to form secondary phases. Sulfides and alloys are the main hosts of platinum group elements (PGEs) in serpentinites, and the role of serpentinization in the remobilization of these elements is controversial. Here, we replicated early serpentinization using cold-seal pressure vessels, reacting a mixture of olivine, synthetic laurite, and water at 50 MPa and temperatures of 250−350 °C for durations of 1−4 d. Olivine reacts partially to form serpentine and brucite. Laurite breaks down to form RuSx with variable Ru:S ratios plus euhedral FeS grains. There are no systematic relationships among temperature, time, water content, and the composition of the Ru phase. No neoformed Ru phases were identified, consistent with limited Ru mobility during serpentinization. Silicate mineral assemblages and breakdown of primary laurite are consistent with observations in natural and experimental systems where incipient serpentinization occurred at highly reducing conditions. The results are consistent with decoupling of Ir group PGEs and Pd group PGEs during serpentinization and suggest that serpentinization may affect PGEs differently in different geodynamic settings, with consequences for global PGE cycling.