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 along the image plane. 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 suitable for studies of ores that commonly contain minerals spanning the range of densities of natural earth 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 location, size, and shape of mineral grains or pores of interest within a sample, establishing the framework for conventional petrographic studies and the collection of other forms of data. Another area of application is for the study of porosity in natural materials, as well as the distribution of fluid inclusions. Synthetic products, e.g. concrete, asphalt, etc., can also be evaluated with CT.
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. CT procedures are reviewed on the UTCT website, and an overview on its application to mineralization studies was provided by Kyle and Ketcham (2015).
Research related to CT studies of mineral resources in Texas include:
- Mineralization controls of the Round Top REE deposit
- Molybdenite and critical mineral associations in the Cave Peak deposit
- Development of the Shafter secondary silver concentrations
- Porosity and cementation histories of carbonate strata
- Distribution and origin of gases within diapiric salt
Theoretical linear attenuation coefficients as a function of X-ray energy for REE-bearing and associated mineral phases compared with dominant rock-forming minerals at the Round Top deposit. Values shown are based on end-member compositions and densities and were calculated using the XCOM Photon Cross-Sections Database (Berger and others, 1998). Click chart to view larger.
References
Berger, M. J., Hubbell, J. H., Seltzer, S. M., Chang, J., Coursey, J. S., Sukumar, R., Zucker, D. S., and Olsen, K., 1998, XCOM: Photon cross sections database: NIST Standard Reference Database 8 (XGAM).
Kyle, J. R., and Ketcham, R. A., 2015, Application of high resolution X-ray computed tomography to mineral deposit origin, evaluation, and processing: Ore Geology Reviews, v. 65, p. 821-839. doi.org/10.1016/j.oregeorev.2014.09.034
Wright, K. A., 2017, Cu-Fe sulfides and Au mineralization in the Ertsberg-Grasberg District of Papua, Indonesia using volumetric analysis and trace element geochemistry: Master's thesis, The University of Texas at Austin.
