Characterization of Clay Minerals in the Athabasca Basin Using Shortwave Infrared (SWIR) Reflective Spectroscopy
This thesis presents results of a short-wave infrared (SWIR) reflectance spectroscopic study of clay minerals from the Athabasca Basin. Clay minerals (dickite, kaolinite, illite, and chlorite) are widespread in the Athabasca Basin and are particularly abundant in the alteration haloes associated with the unconformitytype uranium deposits. Many previous studies have emphasized a complex paragenesis of the Athabasca kaolinite-group minerals from detrital or early diagenetic origin in unaltered sandstones to occurrences in the alteration haloes associated with uranium mineralization and in the bleached zones and late fractures. SWIR reflectance spectroscopic analysis revealed that dickite is a characteristic phase in the unaltered sandstones, whereas kaolinite is a common clay mineral in the alteration haloes and also occurs in the bleached zones and late fractures. The presence of dickite has been confirmed by combined methods of XRD, EMPA, SEM, TEM and SWIR. Although the kaolinite-group minerals of the Athabasca sedimentary rocks do not exhibit any significant variation in composition, a wide range in crystallinity (Hinckley index of 0.12 to 1.61) has been revealed by XRD analysis. This variation in crystallinity of kaolinite is related to paragenesis. A linear relationship was established between the Hinckley index and the S WIR absorption feature at 1400 nm. Therefore, SWIR reflectance spectroscopy is a useful paragenetic indicator. All samples of illite examined in this study were collected from alteration haloes associated with uranium mineralization and belong to the 3T polytvpe or mixtures of 3T and 2M. XRD analysis revealed that these samples of illite vary in crystallinity from 1.39 to 4.0. Unfortunately, Pima II is incapable of distinguishing 3T and 2M polytypes of illite. Also no correlation was found between crystallinity and the SWIR spectra of illite. Two types of chlorite (clinochlore and sudoite) are present in the Athabasca Basin, although the latter is particularly common in the alteration haloes and has been studied in some details. Sudoite is almost invariably interlayered with illite and exhibits a wide range of compositional variation. Spectral study lias revealed that the intensities of the absorption near the 2200 nm region increase with the increase of relevant chemical compositions (AI and Fe). Artificial mixture experiments using well-characterized mineral Standards have revealed that the spectral features vary systematically with the change of the mineral abundances. Results of these artificial mixtures were used to modify an existing method for the quantitative analysis of clay minerals in the Athabasca Basin.