Unlocking the formation and deformation of minerals: image processing approaches to leverage X-ray nano- and μCT
J.-P. Suuronen and M. Sayab
X-ray micro- and nanotomography are multi-scale and multi-dimensional tools to analyze rock microstructures and primary textures in 3D from hand-size samples down to individual mineral grains. Both techniques illuminate internal textures preserved in the sample, which can be precisely quantified based on the chemical inhomogeneities of different mineral phases. An advantage of synchrotron X-ray sources is high coherence and intensity of the X-ray beam, which allows integrated phase-diffraction, and fluorescence contrast imaging of, for example, trace element concentrations and strain within a crystal.
A 3D image of >2000 3 voxels is typically acquired within minutes at a synchrotron μCT beamline, followed by a standard workflow including visualization, segmentation, and quantification of different textures within a mineral or rock sample. In this presentation, the importance of the image analysis step is highlighted using two examples of phase contrast X-ray nanotomography data. In particular, the use of the IPSDK library to speed up the complex segmentation algorithm is demonstrated.
In the first example, the spatial distribution of refractory gold grains inside arsenopyrite crystals from Europe’s largest gold mine in Kittilä, Finland, was examined. Combined with μCT textural analysis of the sulfide distribution in drill cores, different generations of gold mineralization within arsenopyrite grains were identified and linked to the kn own deformation events of the deposit.
As a second example, 3D images the analysis of shocked zircon grains from the Sudbury impact structure in Ontario, Canada, were probed as useful tracers of small or large-scale impact structures on Earth. Characteristic impact-related textures like melt inclusions and conjugate fractures are easily distinguishable in 3D nanotomography images, but require a tailored image processing approach for quantitative characterization. The case of zircon also highlights the advantages of nanotomography as a
non-destructive analysis method, where distinct datable domains can be mapped and later compared with SEM imaging for U-Pb dating.
