Characterization of Clay Minerals in the Athabasca Basin Using Shortwave Infrared (SWIR) Reflective Spectroscopy
Date
2000
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Masters
Abstract
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.
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Degree
Master of Science (M.Sc.)
Department
Geological Sciences
Program
Geological Sciences