The influence of orientation, temperature and frequency on fatigue crack growth: Henderson, M. B. and Martin, J. W. Proc. Conf. Superalloys 1992, Champion, Pennsylvannia,USA, 20–24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 Commonwealth Dr, Warrendale, PA 15086, USA) 1992 pp 707–716

Abstract

Volcanic-associated nickel deposits in the Archaean greenstone belts of Western Australia show a variety of features related to post-depositional deformation and medium- to high-grade regional metamorphism. Deformation and accompanying remobilization have resulted in changes to the gross structure, shape and orientation of ore shoots, and have led to the development of separate offset ores, tectonic breccia ores, and irregular sulphide stringers. Physical remobilization of ore has been mainly on a mesoscopic scale (up to 150 m) and largely by mechanical processes, but with some fluid-assisted and stress-induced chemical remobilization of sulphur and possibly copper. Most of the present ore fabrics and textures are the result of combined deformation, metamorphically induced phase changes and recrystallization. Massive and matrix ores show well-developed tectonite fabrics defined by mineralogical layering, preferred orientation of pyrrhotite and alignment of silicate and spinel inclusions. Layering in the ores is probably the result of both strain-controlled exsolution from high-temperature phases and mechanical segregation of different minerals within polyminerallic aggregates during deformation. Observational and experimental data suggest that sulphide deformation was dominantly by dislocation-type mechanisms (kinking and twinning) at medium temperatures (300–550°C), with diffusional mechanisms becoming important at high temperature (500°C). Dynamic recrystallization during deformation probably accounts for the annealed state of individual mineral grains within most ores, except those deformed at a late stage.