APPLICATION OF HIGH RESOLUTION X-RAY COMPUTED TOMOGRAPHY IN ECONOMIC GEOLOGY

High resolution X-ray computed tomography (CT), the industrial equivalent of medical CAT scanning, provides a means for non-destructive studies of the three-dimensional nature of geological materials. CT produces two-dimensional images of an object’s interior as if it had been sliced along the image plane. A grayscale 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 a sample can be produced, allowing three-dimensional inspection and measurement of features of interest. Although CT has application to diverse natural and synthetic materials, it 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 size, shape, and orientation data from the scanned volume, which can be particularly useful for oriented samples. Volumetric data can be converted to mass concentrations of the scanned volume, providing information of possible use in ore processing. 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 objects of interest within a sample, which then can be studied in conventional petrographic sections, and other forms of data collected. Selected CT studies of ores will be reviewed, including work on the Cripple Creek gold district. CT applications for economic geology and other geologic studies 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 in larger volumes and for separation of contiguous grains with limited contrast.