Characterization of micropyrite populations in low-grade metamorphic slate: A study using high-resolution X-ray tomography

Traditionally, SEM has been used to characterize micropyrite populations. However, for this study, a new technique in this field was applied, namely, high-resolution X-ray tomography (micro-CT), which allows for 3D visualization and analysis of the stone's structure, based on the differences in the X-ray attenuation coefficient of the component minerals. As complementary technique, transmitted and reflected optical microscopy was used. Size and population distributions of the micropyrites were measured using SEM and micro-CT and then statistically analyzed. SEM was able to determine the morphology and size of micropyrites in 2D, while micro-CT provided statistically relevant information about the size histogram of the micropyrites. The data obtained indicate the existence of three overlapping populations of micropyrites. Two of them have small sizes and a narrow range of distribution, which can be attributed to sedimentary processes, and the other have larger sizes and a broader range of distribution, attributed to the effect of metamorphic processes. In summary, micro-CT coupled with SEM and accurate statistical analysis proved capable of differentiating between overlapping micropyrite populations in a sample of low-grade metamorphic slate.