Preferred orientation of experimentally deformed pyrite measured by means of rieutron diffraction

Abstract

Neutron diffraction texture goniometry indicates that naturally deformed polycrystalline pyrite ores from Mt. Lyell (Tasmania) and Degtiarka (Ural Mountains) have weak lattice preferred orientations. During experimental deformation involving dislocation flow at elevated temperatures and pressures, these initial fabrics have been modified to produce new lattice preferred orientations.Polycrystalline pyrite form Mt. Lyelt (B-l) has an initial <lll>-fibre texture perpendicular to a grain-size layering. After 24% shortening perpendicular to the <lll>-fibre axis at 700 ~ a new, but weak <100> texture has developed parallel to the shortening axis. The Degtiarka pyrite (PN-6) initially has two weak fibre components. The somewhat stronger component is a < 100>-fibre texture, similar to that in the experimentally deformed B-1 pyrite. The other one is a <lll>-fibre texture similar to the intital B-1 preferred orientation. After 30% shortening oblique to both initial fibre axes at 600 ~ weak < 110>-and < 111 >-fibre textures have developed. The experimentally produced fabrics have developed during deformation involving dislocation flow, dynamic recrystallisation and some microcracking. Intergranular sliding may also have been involved. Differences between lattice preferred orientations developed in the 600 ~ and 700 ~ experiments are interpreted to indicate a change in the dominant flow mechanism with changing temperature.tn comparison with other cubic minerals that have been deformed experimentally by dislocation flow mechanisms, the pyrite shows an unusually weak preferred orientation which can be detected only by means of neutron diffraction texture goniometry.

Slip systems and critical resolved shear stress in pyrite: an electron backscatter diffraction (EBSD) investigation

“…Where grains are constrained by adjacent grains, during deformation, internal deformation via glide or creep mechanisms will result in rotation of the crystal lattice relative to the strain axis (Hobbs et al, 1976). A number of studies of dislocation glide mechanisms and crystallographic fabrics has been carried out on sulphides (Hennig-Michaeli, 1985;Jansen et al, 1998;McClay and Ellis, 1983;Siemes et al, 1993) and these suggest a CPO can develop, while some neutron diffraction studies of pyritic ores have also identified weak CPOs (Gehlen, 1971;Siemes et al, 1993). However, the most recent studies of experimentally deformed pyrite using EBSD indicate that even with strains up to 40% samples do not develop a CPO (Barrie et al, 2007).…”

Microstructural evolution and trace element mobility in Witwatersrand pyrite

“…This slip system has not previously been recorded in pyrite. However, this may reflect the fact that most studies of pyrite deformation have used either a multigrain fabric approach to infer slip systems (Cox et al 1981;Siemes et al 1993) or have analysed the geometry of individual dislocations using the transmission electron microscope (Cox et al 1981;Graf et al 1981;Levade et al 1982). In both cases, the approach tends to recognize the dominant slip system and is unlikely to lead to the recognition of less common ones.…”