Microstructural control on trace element distribution in komatiite hosted Ni sulphide deposits,Yilgarn Craton (Western Australia)

摘要

Komatiite hosted Ni sulphides deposits that are exposed to different degrees of deformation show significant microstructural differences.Highly deformed komatiite-hosted massive Ni sulphide from the Flying Fox deposit (Yilgarn Craton,Australia)consists mainly of pyrrhotite (Fe1-xS),pentlandite ((Fe,Ni)9S8) and pyrite (FeS2).Electron backscatter diffraction analysis (EBSD) shows that all the phases recorded a certain amount of crystal plasticity.Pyrite records the least amount of deformation (mild lattice distortion),followed by pentlandite (formation of subgrains).Pyrrhotite records the largest amount,expressed through crystallographic preferred orientation (CPO),deformation twins and subgrains.The microstructural work has been followed up with laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analysis.Elemental maps showed that Bi and Pb are showing higher concentrations along the subgrain boundaries in pyrrhotite and in the certain extent Ni and Co.Such behavior confirms well known observation that subgrain boundaries (and lattice defects) represent preferential diffusion paths.