Application of high resolution X-ray computed tomography to mineral deposit origin, evaluation, and processing

High resolution X-ray computed tomography (CT) is the industrial equivalent of medical CAT scanning and provides a mechanism for non-destructive studies of the three-dimensional nature of geological materials. HRXCT produces two-dimensional images (slices) that reveal the interior of an object as if it had been sliced open along the image plane for viewing. A CT image is generated by differences in X-ray attenuation that arise from differences in density and composition within the object. By acquiring a contiguous set of slices, volumetric data for all or part of a sample can be obtained, allowing three-dimensional inspection and measurement of features of interest.CT is particularly effective in the study of metallic ores that commonly contain minerals spanning the range of densities of natural materials. Available software can produce grain shape, size, and orientation data from the scanned volume, which can be particularly useful for oriented samples. CT is particularly useful for studies of gold and other precious metal-bearing minerals that typically have significant contrast even with common metallic mineral phases. CT precisely defines the in-situ location of mineral grains of interest within a sample, which then can be studied in conventional petrographic sections, and other forms of data collected, e.g. isotope or trace element geochemistry. Another area of application is fluid inclusions, which can be discerned even in opaque phases, and fluid and vapor volumes measured for sufficiently large occurrences.We summarize CT principles and review available instrumentation, as well as scanning and data reduction protocols that provide unique three-dimensional information for diverse ore types and applications in mineral deposits geology. CT applications for economic geology and other fields will continue to expand as instruments continue to evolve and as scanning protocols and applications are extended for more precise quantification of three-dimensional relationships, particularly for fine-grained particles and small fluid inclusions in larger volumes and for separation of minerals with limited contrast.