Reconstructing the pyrite deformation mechanism map

Deformation mechanism maps are important tools to understand how minerals deform across a range of pressure, temperature and strain rate conditions. Recent studies have suggested that the current deformation mechanism map for pyrite is in need of revision, with plastic deformation evident over a much wider range of conditions than it proposes. This study uses stress–strain data from experimentally deformed pyrite, combined with electron backscatter diffraction (EBSD) results from a range of experimental and natural samples to construct a revised pyrite deformation mechanism map. This map corresponds to polycrystalline pyrite with a grain size of ~ 35 μm and suggests the onset of crystal plasticity at geological strain rates (~ 10− 12–10− 16 s− 1) occurs at temperatures as low as ~ 260 °C. The revised mechanism map is based upon all available data, experimental data for pyrite are limited and acquired at geologically unreasonable, fast strain rates (10− 4–10− 5 s− 1), and strain rates for the naturally deformed samples can only be estimated. Therefore, considerable extrapolation is required and whilst this revised map is an improvement upon the existing map, it should still only be considered a ‘guide’ to the potential deformation mechanisms, which may operate across a range of P–T conditions in polycrystalline pyrite-rich ores.

Research Highlights
► Orientation contrast images allow identification of plastic distortion in pyrite.
► This study suggests plastic distortion is widespread in deformed pyrite ores.
► Recrystallisation processes are rare in naturally deformed pyrtic ores.
► This study has reconstructed the pyrite deformation mechanism map.