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Chapter 5
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Chapter 5 Mineralogy of the Regolith
Mineralogy of regolith materials from the White Dam region was investigated
through the analysis of field samples using VNIR and SWIR spectroscopic and X-ray
diffraction (XRD) techniques. Surficial materials were collected within the HyMap
coverage area, with a detailed examination of the materials over the White Dam
Prospect. Figure 5.1 shows the distribution of sampled localities on a regional scale and
Figure 5.2 shows the surface samples collected at the White Dam Prospect. The
mineralogy was determined through the examination of spectral measurements, which
were validated using quantitative XRD analysis. A comparison was made between the
spectral mineralogical interpretations from the data collected in the field and airborne
hyperspectral data.
Part 1 Sampling of the White Dam Prospect
Surface Samples Prior to the excavation of the costeans, a 50 x 50 m spaced sampling grid of 70
points (10 samples per east-west traverse) were collected by Brown, A.D. 2003 (pers.
comm.) over the White Dam Prospect (Figure 5.2). Soil samples consisted of scrapings
of the top surface, collected without the larger surface lag material and vegetation
debris. The samples were collected from topographically elevated mounds, away from
the downslope paths of drill spoils. Larger fractions (>20 mm) of surface lags and other
obviously transported materials were not collected, as they were not representative of
the underlying soil and could contain contamination from another source. Stakes placed
by EXCO Resources N.L. and Polymetals Mining Services Pty Ltd, marked with AGD
66/AMG 54 coordinates and elevation information, were used to orientate the sampling
grid. Where present, the height component was recorded for the creation of a prospect
scale DEM (Figure 5.3). Spectral measurements were not collected in situ due to the
unavailability of a spectrometer at the time of field work.
White Dam Prospect Costeans Six costeans were excavated over the White Dam mineralisation in early July
2003 by EXCO Resources N.L. to evaluate cost-effective methods of extracting the
mineralisation from the saprolite (Cooke 2003). The costeans were dug in a north-south
orientation, traversing a series of different regolith-landform units (Brown & Hill,
2003). Two costeans were located near the northeasterly trending creek and the other
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four were closer to the bedrock exposures, in the southeastern area of Figure 5.2. Figure
5.4 is an oblique air photograph taken from the northwest, showing the spatial locations
of the costeans and surrounding regolith-landform features.
Figure 5.1 Sample localities across the White Dam area. The small transparent circles represent sites where a GPS measurement and site descriptions were recorded. The filled circles represent sites where photographs were taken and the large transparent circles represent sites where a sample was collected and spectral measurements were recorded. Sites were used to validate remotely sensed imagery and characterise the regolith-landforms.
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Figure 5.2 Sample points overlain on the White Dam Prospect 1:2 000 Regolith-Landform Map compiled by Brown & Hill (2003), displaying the costean locations (red font) with respect to the regolith-landform units. Arrow shows the orientation of Figure 5.4. Surface soil samples (black font) increase in numerical order from left to right and to the south.
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Figure 5.3 (a) Digital elevation model generated from points measured with a differential global positioning system (DGPS) over the White Dam Prospect. (b) A NW-SE topographic profile. (c) A three dimensional perspective image of the topography, looking towards the east.
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Figure 5.4 An oblique air photograph looking east-southeast over the White Dam Prospect area, taken of July 2003, after recent rainfall. The six north-south orientated costeans can be seen in the middle distance. The northeast flowing creek occupies the foreground. Bright patches in the distance and left portion of the photograph are ponded water on the depositional landforms.
Costean Descriptions Detailed logs of the regolith stratigraphy and properties were recorded for five of
the six costeans, where are presented in Figure 5.6. Regolith carbonate morphology,
ferruginisation and regolith materials were recorded for the whole section, as well as
sample locations and sample colour. Saprolite materials are for the individual sections
in latter diagrams.
WDTR05 (Figure 5.2 and Figure 5.4) was approximately twenty metres long
and was excavated to a depth of six metres, as shown in Figure 5.5. The upper most
layer consisted of PSA (0.2 m), which overlayed a Red-Brown (RB) Pedal Unit (0.5 m),
a massive Yellow-Brown (YB) Unit (0.5 m) and coarse gravel-lag layers within a YB
matrix (1 - 1.5 m). Below this, a sequence approximately 0.5 - 1.0 m thick of small
mottles of powdery RCAs overlayed moderately to heavily weathered bedrock. The
regolith carbonate mottles overlying the basement occurred at various depths along the
profile and ranged in size from 7 mm to 50 mm in diameter. Weathered basement
materials consisted of a pallid zone, with ferruginous-rimmed mottles and pale-yellow-
green cores. With increasing depth the profile graded into a pale grey saprolite, which
displayed an obvious fabric.
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Figure 5.5 North orientated view of costean WDTR05, excavated over the White Dam Prospect in June 2003. The east-northeast trending alluvial channel occurs in the background. The bench level is approximately 2.5 m and the base of the costean is 6 m from the surface. The scale bar in the middle distance is 2 m in length.
WDTR01 was approximately thirty metres long and excavated to a depth of six
metres through PSA (0.2 m), RB Pedal (0.5 m) and YB/lithic gravel deposits (1.5 m).
The costean showed a more developed regolith carbonate horizon in the southern end,
where the mottles were up to 100 mm in diameter. Gravel-lag layers occurred as
slightly concave-upwards lens of sub-rounded, poorly-sorted stained quartz, with clasts
5 - 15 mm in diameter. Bands of heavy mineral sands were found in the lower portion
of the channel sequence. The saprolite was generally very friable and broke up into a
sandy powder on impact with a hammer. Sub-vertically orientated carbonate veins were
found in the saprolite where infilling of fractures or replacement of readily weathered
materials had occurred. Weathering was more prominent around the margins of the
veins. Some of the sub-vertical structures in the saprolite contained red-brown material,
which appeared to be soil infilling fractures and joints after burial of the bedrock.
Preferential weathering of Fe-rich minerals (such as biotite) in the saprolite has caused
Fe-stained layers parallel to fabric.
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The resistive leucocratic layers of albititic material remained in the moderately-
weathered samples, accentuating the folding and fabric.
WDTR02 was excavated to a depth of 6 m through PSA (0.2 m), RB Pedal (0.5
m) and YB layers (2 m), with a well developed horizon of RCA mottles up to 150 mm
in diameter. Minor gravel-lag horizons were observed in isolated locations throughout
the section.
WDTR03 was the deepest of the costeans with a bench at 3 m below the surface.
The powdery RCAs occurred as a discontinuous, undulating horizon with a fragmented
hardpan of regolith carbonate directly overlying the saprolite. This costean was not
sampled.
WDTR04 was 30 m in length and excavated to a depth of 4 m. The powdery
RCA mottles, seen in the costeans to the northwest, were not observed in this section.
Small accumulations (~50 mm) of powdery regolith carbonate material occurred
approximately 0.8 m below the RB Pedal layer. The saprolite consisted of quartzo-
feldspathic gneiss, pegmatite and an amphibolite dyke in the southern end of the
costean.
WDTR06 was the shortest and shallowest costean at 15 m in length and 3 m
depth. It displayed a condensed regolith profile without a clearly definable layer of
powdery RCAs. Nodular carbonate, approximately 10 mm in diameter, occurred
between the RB Pedal Unit and the saprolite. The saprolite was capped with a 0.1 – 0.2
m thick hardpan of laminar regolith carbonate that had infiltrated the fractured and
jointed saprolite to a depth of ~1 m below the hardpan-saprolite interface. A prominent
amphibolite dyke, found in the southern-most portion of WDTR04, occurred in the
northerly end of this costean. As with WDTR04, there was an abundant amount of
pegmatitic saprolite material throughout the section.
Costean Sample Collection Samples were collected at 0.25 m intervals down the profile at spacings of 10 m
(Figure 5.7). Where an obvious physical change in the materials of the costean had
occurred within the 10 m lateral spacings, an extra profile was taken at a 5 m interval.
This was performed to prevent omission of key features. In WDTR02, sample spacings
were located at 5 m apart, with additional profiles at 2.5 m where sudden changes in the
regolith materials occurred. Approximately 550 samples were collected from five of the
six costeans (Figure 5.6).
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205
Figure 5.6 Sections of the five analysed costeans from the White Dam Prospect showing the regolith stratigraphy, regolith carbonate morphology, extent and style of the ferruginisation and the colour of the materials sampled. Vertical: Horizontal=1
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Figure 5.7 Example of sample spacing from the costeans excavated over the White Dam Prospect. Samples were collected laterally every 10 m in profiles with 0.25 m vertical spacing. Infill sampling was performed at a lateral distance of 5 m if there a significant change in the overlying transported materials or saprolith occurred.
Part 2 Sample Preparation and Measurement A 20 g subset of each of the main samples was collected from the bags after
drying at 60°C for 24 hours. The samples were placed in plastic chip trays and taken to
the CSIRO/CRC LEME ARRC laboratories in Bentley, Western Australia, for
measurement with an ASD FieldSpec Pro FR instrument (Lau et al. 2003). A small
petri dish with approximately 10 g of sample was placed on the vertically mounted
contact probe (see Chapter 4, Figure 4.27) and repeat measurements were recorded on
the sample after stirring. Raw spectrometer measurements were converted to ENVI
spectral libraries using Spectral International Inc SpecWinTM software. Correction (‘de-
stepping’) for minor detector offsets was performed on the spectral libraries using a
CSIRO Division of Exploration and Mining software add-on to ENVI (Figure 5.8). The
spectra for each sample were displayed and the measurements with the highest and
lowest albedo were discarded. Spectra with abundant noise or errors induced by the
sampling procedure were also not used in the subsequent processing steps.
The surface and costean samples were separated into separate datasets and
analysed independently. A spectral library of representative spectra of the soil
measurements was imported into the CSIRO developed The Spectral Geologist (TSG)
version 4b for analysis. A spectral library of the costean samples was imported as a
separate file, with an information log consisting of geographic coordinates, elevation,
depth, regolith-landform unit, Munsell colour, Munsell code, XRD results, quantitative
XRD results (where analysis was performed on the corresponding sample) and a
description of the sample from field and photographic interpretations.
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Figure 5.8 Spectral plots demonstrating the correction of the ASD FieldSpec measurements for variations between detector regions. The dashed spectra represent the corrected data using the ‘D-step’ ENVI plug-in developed by CSIRO MMTG.
Part 3 Results and Data Analysis of Surface Samples
ASD Spectral Analyses of Surface Samples Preliminary Mineralogical Interpretations
Examination of the summary screen of TSG was performed to evaluate for
materials known to be absent in the dataset or thought to be a misclassification. The
man-made materials were removed from the active The Spectral AssistantTM (TSA)
(Berman et al. 1999) algorithm and the mineral classes were reprocessed.
It must be noted that the results of TSG are software interpreted result of the
mineralogical constituents of materials that had been measured with the ASD
spectrometer. The algorithm involves the comparison of the measured spectrum with
training datasets (built in references or user defined libraries) to model the closest fit of
one or two minerals to the analysed sample. The resulting difference between the
spectra and the modelled interpretation are reported as residual means squares error.
Interpretations with significantly high residual means squares errors were defined as
having a poor correspondence to the mineralogy of sampled material and were not
included in the results. The collection of multiple spectral measurements for each
sample allowed the validation of the remaining measurements to ascertain if they also
contained high residual means squares errors in TSA, and if not then the measurement
representing the average of the spectra with low residual means squares errors was used
in the analysis. Although TSA provides a good estimate of the SWIR-spectrally active
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mineralogy of a spectrum, it should be noted that the results should be visually validated
to ensure consistent and meaningful results.
Visual examination of the stacked image of the depths of absorption features
showed that the spectral profile of the samples displayed little variation. Minor
differences in the 0.4 - 0.53 µm region, the depth and width of the 1.915 µm H20
feature, and the asymmetric width of the 1.415 µm OH feature were observed.
When the spectra were plotted as stacked plots (Figure 5.9), differences become
slightly more apparent, although discrimination of features remained difficult. From the
observations it became evident that calculations (user defined scalars) using absorption
features and spectral slopes would be required to differentiate the spectral classes, rather
than relying on TSA results alone.
The results of TSG discussed throughout the text refer to the results of the
estimated mineral abundances from interpretations made by TSA algorithms on the
measured spectra in comparison to inbuilt spectral libraries. These results are referred
to as TSA mineralogy abundances. Calculations made from spectral parameters by the
use of indices or band ratios are referred to as TSG results, as they are calculated using
the software. For example, kaoliniteTSA would refer to the abundance of kaolinite
calculated by TSA from the comparison of the spectrometer data with the spectral
absorptions in the TSA mineral library. SmectiteTSG refers to the calculation of the
abundance of smectite minerals from parameters based on clay absorption features.
KaoliniteTSA, montmorilloniteTSA, illiteTSA, Fe2+ goethiteTSA and hematiteTSA
were found to be the most abundant minerals. Minor minerals consisted of ankeriteTSA,
magnesiteTSA and topazTSA, all of which corresponded to lithic fragments from the
surface lag component of samples WD069 and WD070 (Figure 5.9 viii). All samples,
except for WD058, WD069 and WD070, were identified by TSA as having kaoliniteTSA
as the secondary mineral that contributed to the spectral features of the SWIR region.
The three samples that did not contain kaoliniteTSA were collected from the regolith-
landform unit (RLU) mapped as slightly weathered saprolite on an erosional rise
(SSer1), corresponding to the areas of more prominent surface lags of lithic material.
Analysis of gravel sized lithic fragments produced absorption features that contrasted
with the soil materials, reflecting the primary mineralogy of the spectrally active
materials in the local basement rocks.
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Figure 5.9 Collective ASD measurements of the soil-grid samples. Each group of ten spectra represent a west to east traverse. Samples were collected 50 m apart. WD01 represents the most northwestern sample and WD70 was collected in the southeastern corner of the grid. The lithic fragments found in the samples WD68 and WD70 are shown in (viii).
Mineral Abundance Calculations
Detailed examinations of the spectral regions were performed using a series of
algorithms, some of which were part of TSG (termed as ‘scalars’) and others written
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within TSG by the user. Wavelength positions and band ratios of targeted spectral
features were utilized by the scalars to calculate proportions and abundances of mineral
groups. These were used to interpret the mineralogy, regolith association and other
properties of the spectra. Details on the properties and wavelengths used in the scalars
are located in Appendix I. In the VNIR region the scalars focused on Fe-oxide spectral
features, including specific indices to examine the CFA and the presence of Fe2+ ions.
Analysis was performed on the SWIR region for Al-OH related features, kaolinite,
white micas, water inclusions in quartz, smectite, and features in the 2.3 µm region
relating to carbonates and Mg-OH minerals.
Mineral Distribution Map Creation
The spectral calculations and TSA mineral abundances were exported to a
spreadsheet and edited for import into ArcView (version 3.3). A point shapefile
containing the spatial information and mineral abundances was created in ArcView and
used in ArcGIS (version 8.3) to generate surface grids. An Inverse Weighted Distance
(IDW) technique was used on the approximately even-spaced grid points to produce a
surface distribution map of the spectral calculations and TSA mineral abundances of the
soil samples. Negative and null values in the distribution maps created by the gridding
technique were removed in ArcView. Selective results of the surface soil ASD
measurements are shown in Figure 5.10 and Figure 5.12.
Fe-Oxide Mineral Analysis
Mineral distribution maps created from the normalised ‘Fe-oxide Abundance’
TSG and ‘Fe-oxide Intensity’TSG Indices displayed similar spatial patterns (Figure 5.10 i).
The same overall trend was seen for the alluvial units, Aap (alluvial material on an
alluvial plain), Afa (alluvium in an alluvial fan) and Aed2 (alluvium in an erosional
depression), which all displayed highs, whereas the northeast trending Aed4, that ran
through the centre of the area, had a moderate Fe-oxide AbundanceTSG. A mixed
response of low and moderately-high values were obtained for the SSer (slightly
weathered saprolite on an erosional rise) unit. Variation in this region was inferred as a
reflection of the lithological variation of the basement exposures. The neighbouring
CHer (sheetflow on an erosional rise) unit replicated the variation, displaying values
similar to the adjacent saprolite localities. This was attributed to the dispersion of
weathered materials, by overland flow and other colluvial processes, from the saprolite
exposures upslope.
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Figure 5.10 Surface mineralogical distribution over the White Dam Prospect, interpolated from ASD measurements and analyses of soil samples. Saprolite is exposed in the SE corner of the area and displays high-interpreted abundances of hematiteTSA, as does the central portion of the area, which corresponds to the surface projected mineralisation outline (not shown). The area above mineralisation also displays a higher abundance (although, still small) of chlorite/epidoteTSG related spectral features. These highs are associated with the NE trending alluvial erosional depression and could be a collection of transported ferromagnesian minerals derived from the outcrop upslope to the south.
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Four samples out of seventy returned non-null values for the CFA IndexTSG,
indicating only a small proportion of the soils possessed absorption features with
sufficient intensities to produce results. Spectra of the four samples displayed
moderately well defined CFA, with a maximum absorption feature in the 0.85 µm
region. The hematite mineral abundance, calculated by TSA, was more successful at
identifying minerals with Fe-absorption features than the CFA IndexTSG (e.g. 41 of 70
samples). Alluvial materials, in the northwestern portion of the sampled area showed a
lower concentration of hematite (Figure 5.10 ii), whereas the sheetflow dominated and
saprolite regions displayed patchy-high abundances of hematiteTSA.
Four samples out of seventy returned non-null values for the CFA IndexTSG,
indicating only a small proportion of the soils possessed absorption features with
sufficient intensities to produce results. Spectra of the four samples displayed
moderately well defined CFA, with a maximum absorption feature in the 0.85 µm
region. The hematite mineral abundance, calculated by TSA, was more successful at
identifying minerals with Fe-absorption features than the CFA IndexTSG (e.g. 41 of 70
samples). Alluvial materials, in the northwestern portion of the sampled area showed a
lower concentration of hematite (Figure 5.10 ii), whereas the sheetflow dominated and
saprolite regions displayed patchy-high abundances of hematiteTSA.
The abundances of the mineral Fe2+ goethiteTSA (Figure 5.10 iii) were the direct
opposite of the results for the hematiteTSA, with the saprolite regions generally displayed
lower proportions of goethiteTSA. Mineral distributions of hematiteTSA and Fe2+
goethiteTSA were compared to the Hematite:Goethite IndexTSG (Figure 5.10 iv) to
evaluate the ability of TSA and indices to discriminate the different Fe-oxides. Similar
trends were obtained, with a slight displacement of the hematiteTSA and goethiteTSAG
highs. The Hematite:Goethite IndexTSG showed a transition from hematite high regions
to an intermediate distribution of both Fe-oxides and to areas of high goethite. It was
concluded that the Hematite:Goethite IndexTSG provided a more informative output over
the mineral abundance calculations for the Fe-oxide minerals, as it was able to better
account for the mixing of the two Fe-oxides.
The Fe2+ IndicesTSG were found to be limited in their usefulness, as all of the
samples soil samples lacked the strong spectral features of minerals relating to the
presence of Fe2+ and Fe3+ ions. No samples were found to contain fluid inclusions using
the Quartz H2O IndexTSG, although interpretation of the spectra showed there was a
significant 1.9 µm absorption feature due to the presence of water in clay minerals.
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The Munsell colour measurements were found to have a slight correlation with
the presence of the ferruginous minerals. Red and dark-red Munsell colours were
expected to correspond to the occurrence of hematite, whereas Fe2+ goethite was
predicted for the yellowish red soils. Munsell measurements of alluvial regions in the
northern portion of the area displayed darker soil colours than the area of exposed
saprolite (Figure 5.11). Comparisons to the hematiteTSA and goethiteTSA abundance
maps showed the dusky red and weak red/dark red areas in the northern portion of the
sampled area to correspond to high hematiteTSA abundances. Fe2+ goethiteTSA appeared
to be more associated with the samples with a yellowish red Munsell colour.
Figure 5.11 Comparison of Fe-oxide IntensityTSG and Munsell colour measurements of the surface soil samples from the White Dam Prospect. The saprolite displayed Yellowish red/reddish brown colouration, which corresponded to low Fe-oxide IntensitiesTSG, whereas the alluvial regions displayed higher intensities and were associates with dark red coloured samples. Yellowish red coloured samples roughly correlated with moderate value areas for the Fe-oxide Intensity IndexTSG.
Ferromagnesian and Carbonate Mineral Analysis
The ‘Dolomite Intensity’ IndexTSG (Figure 5.10 v) was used in an attempt to
estimate the presence of regolith carbonate, as the index used parameters that focused
on the depth of spectral features in the 2.3 µm region. High values were obtained for
the lithic material found in the southeastern region of the grid, but otherwise the
outcome of this index consisted of null values for all the soil samples. The use of this
index was found to be unsatisfactory for identifying areas containing regolith carbonate
accumulations at the surface in regolith-dominated terrains, due to the low overall
percentage of the mineral calcite and the masking of the absorption features by clays
and other surface coatings on the carbonate nodules.
The Chlorite/Epidote IndexTSG was successful at highlighting several regions of
interest on the colluvial RLUs in the central portions of the sampled area (Figure 5.10
vi). Medium-low abundances were found for the saprolite, reflecting the strong Al-OH
mineralogy of the exposed rocks. A low abundance of Chlorite/EpidoteTSG was
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obtained for the alluvial channel, as well as the northeastern portion of the sampled area,
where the regolith materials consisted of colluvial sheetwash sediments on a
depositional plain (CHpd). High abundances for the colluvial sheetwash erosional
plains (CHep) may relate to carbonate material in these areas of thin transported regolith
cover, although carbonates were not detected by the Dolomite IndexTSG in these regions.
An analysis to determine the presence of the mineral amphibole was performed
using the Talc IndexTSG. The ratio attempts to identify talc (and other Mg-OH minerals
with similar absorption features) by examining the spectral features that occur in
shorter wavelength portion of the 2.31 µm absorption feature. Although no talc was
seen while logging the sections, this scalar was predicted to identify minerals with
similar absorption features as talc, such as hornblende, tremolite and actinolite. The
distribution of amphiboles mapped using the Talc IndexTSG displayed a high spatial
correlation with amphibole identified in the XRD analyses, which are discussed latter in
the chapter. There also appeared to be a close match between the distribution of calcite
from the XRD analyses and the spectrally mapped amphibole.
Spectral Analysis of Aluminous Layer Silicates
The Al-OH Intensity IndexTSG showed a trend of increasing values from the
southeastern portion of the sample area to the northwest (Figure 5.12 i). This reflected
changes in the regolith-landform toposequence that occurred across the area. The
southeastern area consisted of saprolite on an erosional rise, which sloped down to the
northwest, onto an erosional plain of colluvial material. A small, northeast trending
erosional depression marked a break in slope. This feature is shown in the three-
dimensional display of the surface derived DEM (Figure 5.3). To the northwest of the
erosional depression there was a slight topographic rise, up towards the alluvial channel.
Areas of exposed saprolite (SSer) in the southeastern region displayed low values for
this index, which was attributed to the abundance of aspectral feldspar and quartz
minerals, such as albite, in the mineralogy of the saprolite.
The Al-OH Wavelength IndexTSG displayed the position of the deepest feature in
the 2.2 µm region (Figure 5.12 ii). The lithic fragment (WD070rf) and sample WD050
were found to have a 2.2080 µm wavelength for their Al-OH absorption feature,
whereas the majority of soil samples had absorptions in the 2.2067 - 2.2078 µm region.
This trend reflected the relatively consistent Al content of soils and the higher
abundance of Mg and Fe minerals in the saprolite and associated in situ pedogenic
materials.
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Figure 5.12 Surface mineralogical distribution over the White Dam Prospect, interpolated from ASD measurements and analysis of soil samples. Comparisons of Al-OH related wavelength features and minerals. Overall, the abundance maps display minor to high correlations.
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Kaolinite Crystallinity
The Kaolinite Crystallinity IndexTSG (Figure 5.12 iii) utilised the outcomes of
two slope indices, which calculated the slope changes in absorption features in the 2.184
- 2.190 µm region, to estimate the crystallinity of kaolinite minerals (Figure 4.19). A
second index, ‘KXTSG’ (Figure 5.12 iv), was found to produce similar kaolinite
crystallinity scores. Comparisons of the two indices are shown in Figure 5.12 (iii & iv),
although the colour scale was reversed in the KX IndexTSG, with areas of high
crystallinity having low values.
The Crystallinity Indices produced trends similar to the Al-OH intensity (with a
high positive correlation). The alluvial sediments in the northwestern region of the
sampled area had the highest kaolinite crystallinityTSG. Lower crystallinity for the other
areas may have been influenced by the presence of transported kaolinite within the PSA
layer that mantled the surface of the sheetflow dominated RLUs.
The kaolinite from the PSA materials had a low crystallinity due to the
destruction of the crystal lattice during transportation by overland flow. The PSA
material was derived from the weathering of soil mantles, which would have already
had low crystallinity for kaolinite. The crystallinity of the soil mantles would have been
further reduced by the transport processes prior to their deposition as the PSA layer.
Materials in the channel had a greater abundance of kaoliniteTSA derived from the
weathering of feldspar minerals and had a higher crystallinity. The channel material
consisted of sub-angular lithic clasts of feldspars, with a small abundance of muscovite
and clay material. The high kaoliniteTSA abundance (Figure 5.12 v) for the alluvial
channel samples was supported by the XRD analyses, which had high percentages of
kaolinite and low albite abundances.
White Mica Intensity
The White Mica Intensity IndexTSG involved the use of a mask that filtered out
samples without a muscovite, illite, phengite or paragonite TSA classification. The
distribution of the mineral illiteTSA was limited to the central and southwestern portion
of the sample area, which corresponded to CHep (sheetflow on an erosional plain),
CHpd (sheetflow on a depositional plain) and Aed RLUs (Figure 5.12 vi). Outputs of
the White Mica Wavelength IndexTSG displayed the approximate wavelength of the Al-
OH absorption feature for white mica minerals. The results were inconclusive, although
there was a slight increase in wavelength of the Al-OH feature in the northern portion of
the sample area.
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Smectite Index and Montmorillonite Abundance
Areas associated with alluvial RLUs displayed the highest values for the
Smectite IndexTSG (Figure 5.12 vii). The elevated smectiteTSG abundances were
attributed to the occurrence of clay minerals and the presence of water in the alluvial
regions. A medium-low smectiteTSG abundance was recorded for the alluvial channel
(ACa-WD001), which was attributed to a different mineralogy than that of the alluvial
fan regions (Afa-WD031 and WD041). A greater abundance of coarse fraction
materials, such as quartz and lithic fragments, were found in the alluvial channel,
whereas the fan and depositional plains displayed a finer particle size. The channel was
associated with higher energy transport mechanisms that would keep the clay minerals
in suspension during ephemeral-flow events.
Overland sheetflow was the dominant transport mechanism of materials on the
depositional plain. This process would be more conducive to the deposition of finer
particle fractions and therefore contain a higher abundance of clay-sized minerals. The
saprolite and flanking RLUs displayed high abundances of smectiteTSG, which could be
due to the weathering of the primary minerals and transport by overland flow away from
the outcrop exposure. A lower abundance of smectiteTSG was observed for the
depositional plains than the erosional rises.
The results for the mineral montmorilloniteTSA (Figure 5.12 viii) were found to
be slightly correlated to the Smectite IndexTSG. The Spectral Assistant results showed
that a majority of the samples collected to have a montmorilloniteTSA mineralogy,
whereas the regions that displayed a low Smectite IndexTSG correlated with the presence
of illiteTSA. The distribution of illiteTSA minerals in the central and southwestern portion
of the area may be related to material originating from granitic exposures to the
southwest of the sampled area.
Conclusions of the ASD Measurement of Soil
Samples over the White Dam Prospect
The soil samples displayed subtle spectral features with small variations in the
depths and inflection features of absorptions. These were attributed to minor changes in
the mineral abundances of the samples, related to the location of the sample in the
landscape. Soil samples collected from alluvial regions displayed high Fe-oxide
IntensitiesTSG, reflected by higher goethiteTSA abundances.
The alluvial channel and surrounding region displayed a high Al-OH
IntensityTSG, which was accompanied by high kaoliniteTSA abundance and
crystallinityTSG. The outcome of the Crystallinity IndexTSG was surprising, as the
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materials of the channel are of a transported origin. The transport of high crystalline
kaolinite would lead to the destruction of the crystal lattice and hence, a low
crystallinity. Therefore, the kaolinite in the alluvial region may be derived from the in
situ weathering of feldspars and other lithic materials after transport and deposition.
An alternative explanation of the higher crystallinityTSG of the materials in the
alluvial channel involves the presence of drill spoil materials at the surface and their
transport to the areas lower in topography. The presence of drill spoils can be seen on
the 1997 air-photographs (Figure 5.30) and the 1998 HyMap imagery (Figure 5.35 viii).
Observations of the site over the duration of the project (2001 to 2004) noted a decrease
in the abundance of spoil material (from the pre-1997 drilling) at the surface. It is
proposed that the spoils have been denuded by erosive processes since their formation,
which has led to the dispersion of the materials to the lower-lying regions in the area,
however, this is unlikely to be the cause of the higher kaolinite abundances in the
channel. Spectral measurements of samples collected in 2001, found the mineralogy of
the spoils to vary from muscovite-rich to highly crystalline kaolinite with low
abundances of Fe-oxides. Further SEM analysis on the soil samples in the alluvial
channel would be required to determine their origin and if the kaolinite has been formed
in situ.
The bedrock exposure displayed a hematiteTSA and montmorilloniteTSA
spectrally interpreted mineralogy. The saprolite was also found to have high
abundances for the Chlorite/Epidote IndexTSG and longer Al-OH WavelengthTSG
features. The sheetwash slopes adjacent to the saprolite exposures displayed similar
mineralogical characteristics, which were attributed to the presence of lithic material
derived from the neighbouring basement. An anomalous area existed around 460120
mE 6449080 mN, displayed Talc IndexTSG values that were higher than the surrounding
region. This area coincided with the projected amphibolite dyke that was logged in the
saprolite of the costeans. The dyke was seen in the northern end of WDTR06 and the
southern end of WDTR04.
Sheetflow dominated regions to the north of the Aed (in the centre of the area)
were influenced by the transport of material from upslope. Minor alluvial additions
from flood events were seen in the sheetflow RLUs close to the drainage features. This
resulted in smectiteTSG dominated mineralogy and a low crystallinityTSG for kaolinite.
Chapter 5
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XRD Analysis of Surficial Materials Introduction
X-ray diffraction (XRD) is an analytical tool involving the measurement of the
characteristic angle of scattered X-ray radiation from the interaction with electrons in
atoms of crystalline minerals (Jenkins 1974). The arrangement of the atoms and the
spacing between the crystalline planes yields different angles of scattering. The Bragg
equation is used to calculate the distance between the planes, and is expressed as;
?=2d sin?
where ? is the wavelength of the incident X-ray and d is the atomic spacing.
The angle (?) of the scattered X-ray is measured by a diffractometer. Most plots are
labelled ‘2-theta’ (or 2?), defining the angle between the incident x-ray beam and the
recorded diffracted beam.
The material that is being irradiated by a parallel beam of monochromatic X-
rays acts as a three-dimensional diffraction-grating. The X-rays are diffracted at
specific angles related to the spacings in the atomic lattice. The measured angle of
diffraction can be used to identify the crystallographic structures of materials. XRD
allows the differentiation of minerals with similar compositions but with distinctly
different crystallographic properties (Klug & Alexander 1974; Cullity 1978).
Sample Preparation
A suite of samples were selected for XRD analysis from the surface and the
surficial portions of the profiles collected from the costeans (Figure 5.2). Additional
samples selected from the costeans were chosen to verify the mineralogy identified from
spectral measurements with the ASD FieldSpec spectrometer, and are discussed in part
4 of this Chapter. The samples selected for XRD consisted of a northwest trending
traverse of the 50 m spaced grid, which was surveyed to coincide with the projected
mineralisation at the White Dam Prospect.
Clay separation analysis was performed on two samples to validate the nature of
the smectite mineralogy of the soil samples. Results of such analyses suggested that the
analysis of bulk fractions was sufficient.
Surface Data XRD Analyses Summary
A total of 35 surface soil samples were analysed and found to contain quartz
kaolinite, albite, orthoclase, mica/illite and hematite. The samples did not contain the
minerals jarosite, aragonite or gypsum, as found in the saprolite and transported
materials of the costeans. Only seven samples were found to have calcite, and ten
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samples contained the mineral amphibolite, with both of these minerals occurring in
small abundances (0 - 3%).
On average, the samples were found to have quartz (44%), albite (25%),
smectite (15%), orthoclase (6%), mica/illite (5%), kaolin (3.75%) and hematite (2%).
Variation for orthoclase was minimal throughout the samples.
Comparison of XRD Analyses Results for Adjacent Samples
Results of the quantitative XRD were tabulated with their corresponding GPS
coordinates and saved as a (.dbf) file and imported into ArcView. Samples WD040 and
WDTR06D0 were located within five metres of each other, as shown in Figure 5.13.
Other samples from the surficial layer of the costean samples (WDTR06B0 and
WDTR06C0) (16;5, 13;14 mica/illite; smectite respectively) contained similar
mica/illite concentrations as WDTR06D0. Surface soil sample WD030 possessed
similar values to WD040 (5;13 mica/illite; smectite), as shown in Table 5.1. Other
samples in the region did not possess detectable amphibole concentrations.
Figure 5.13 Distribution of surface samples used in the quantitative XRD analysis.
Circles represent surface-grid soil samples and boxes represent costean samples
collected within 100 mm of the surface.
Chapter 5
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Samples WD039 and WDTR04BC0 were taken within five metres of each other
(Figure 5.13) and possessed similar concentrations of the minerals kaolinite (WD039
3%; WDTR04BC0 3%), albite (23;28), orthoclase (8;5), mica/illite (5;4), hematite (2;1)
and amphibole (2;1). However, there were differences in the abundances of calcite
(0;1), quartz (44;36) and smectite (13;21). The results for the XRD analysis around
460230 mE 6449100 mN are displayed in Table 5.1 for comparison.
Sample Name
Qua
rtz
Kao
lin
Alb
ite
Ort
hocl
ase
Mic
a/ill
ite
Smec
tite
Hem
atit
e
Am
phib
ole
Cal
cite
WD040 38 4 23 6 6 20 1 1 0 WDTR06D0 43 1 27 5 19 3 1 0 0 WDTR06B0 40 3 25 10 16 5 1 0 0 WDTR06A0 41 6 21 4 13 14 1 0 0 WD030 44 4 25 7 5 13 2 0 0
Table 5.1 Quantitative XRD results for samples collected from the surface around the
location of 460230 mE 6449100 mN.
Sample Name
Qua
rtz
Kao
lin
Alb
ite
Ort
hocl
ase
Mic
a/ill
ite
Smec
tite
Hem
atit
e
Am
phib
ole
Cal
cite
WDTR04A0 24 9 13 4 4 45 1 0 0 WDTR04BC0 36 3 28 5 4 21 1 1 1 WD039 44 3 23 8 5 13 2 2 0 WDTR04C0 32 4 28 7 2 24 1 2 0 WDTR04D0 29 5 30 5 3 23 2 2 1 WD014 53 3 22 6 4 10 2 0 0
Table 5.2 Quantitative XRD results for samples collected from the surface around the
location of 460180 mE 6449080 mN. Spectral plots of some of the samples
corresponding to the XRD samples of Table 5.1 and Table 5.2 are shown in Figure 5.14.
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Figure 5.14 Spectra corresponding to XRD samples in Table 5.1 and Table 5.2. Spectra in plot (a) are surface samples collected from the 50 x 50 m grid. Plots (b) and (c) are from surface samples from costeans WDTR04 and WDTR06 respectively. The continuum removed plots all have very similar VNIR and SWIR features, with only small variations observable in the 1.9 µm spectral region due to differences in water abundances.
Chapter 5
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The similar abundance of amphiboles was encouraging, as amphibole was found
in the spectra of samples at depth in the costean, and suggests that variations of smectite
may be able to be seen in the ASD FieldSpec spectra. Examination of the
corresponding spectra found the recognition of the XRD abundances of the spectrally
active minerals to be difficult. This may be due to the difference in material that is
being analysed by the two techniques. Samples WDTR04C0, WDTR04D0 had similar
mineral abundances to WDTR04BC0. WDTR04A0 possessed different concentrations
of the minerals (smectite:45 %, quartz:24 %, albite:13 %) and the absence of amphibole.
WD014 and WDTR04D0 had very similar values for all minerals (quartz
(53;53), kaolin (3;4), albite (22;18), orthoclase (6;6), mica/illite (4;6), smectite (10;11)
and hematite (2;1)), except amphibole (0;1) and calcite (0;1).
Surface Distribution Maps using ArcView Spatial AnalystTM
Grids were plotted of the surficial XRD results using spline and tension type
methods using ArcView and ArcGIS Spatial AnalysisTM. Minerals that lacked
detectable concentrations in all of the samples (for example, calcite and amphibolite)
displayed distribution maps that strongly reflected the sample points where such
minerals were present. Only one sample (WDTR1D0) in the northwestern portion of
the sampling transects displayed calcite. This was seen in costean WDTR01, where
calcite was found at greater depths throughout the profile than the southern costeans,
reflecting the greater thickness of the transported cover sequences. Samples in the
southeastern portion of the sampled area were located closer to bedrock exposures and
proximal to numerous amphibolite dykes trending in a northeasterly direction.
Field mapping of the WDTR06, WDTR04 and WDTR02 costeans demonstrated
a large abundance of regolith carbonate at shallower depths in comparison to WDTR01
and WDTR05, where the transported cover sequences were much thicker.
A large population of rabbit warrens were found in the southeastern portion of
the sampled area. Excavation of the burrows by the rabbits had brought powdery
carbonate material to the surface. The soil in this region was a pale-yellow-brown
colour, which contrasted the surrounding RB soil in the region.
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Figure 5.15 Surface distribution of minerals over the White Dam Prospect interpolated from quantitative XRD analysis for (i) mica/illite, (ii) orthoclase, (iii) kaolinite, (iv) smectite and (v) albite of soil samples. Abundances are in percent, with dark areas having a low abundance and light areas a high abundance. The blue dots indicate where samples were used in the gridding process.
Chapter 5
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Figure 5.16 Surface distribution of minerals over the White Dam Prospect interpolated from quantitative XRD analysis for (i) amphibole, (ii) calcite, (iii) quartz, and (iv) hematite soil samples. Abundances are in percent, with dark areas having a low abundance and light areas a high abundance. The blue dots indicate where samples were used in the gridding process.
I C Lau Regolith Mineralogy
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Mica/illite Distribution
The mica/illite results had a slightly higher abundance at the eastern edge of the
sample grid, with a low directly to the north and west of WDTR06. Low abundances
were recorded for the alluvial plain and the absence of mica/illite at the surface was
seen in the northeastern corner of the grid (Figure 5.15 i). The lack of analysed samples
makes the distribution maps less reliable in this area. The high abundance in the central
portion of the area occurred near the northern end of WDTR03, although no data were
recorded for this costean. The lack of mica/illite in the alluvial regions was attributed to
the high attrition rate of muscovite by alluvial transport (Ollier 1984). The lack of large
outcrops associated with retrograde shear zones, as found in the Kalibity Shearzone
Ranges to the south, could also be related to the lack of mica/illite. The presence of
mica/illite in the central regions may be related to transported material from the
southwest. The analysis of more samples in this region is required to confirm if this
distribution correlates with the ASD results, which indicated a higher abundance for
illite in the southwestern region of the sampled area.
Smectite Distribution
Smectite had a poorly correlated and almost inverse relationship with mica/illite,
as shown in Figure 5.15 iv and i. The high abundance of smectite-clays between the
northern ends of WDTR06 and WDTR04, was associated with an area depleted in
feldspars and mica/illite and enriched in kaolinite. This region coincided with the
projected location of the amphibolite dyke.
Albite and Orthoclase Distribution
The distribution of albite displayed an almost perfect inverse relationship with
kaolin with high abundances recorded for the saprolite exposure and a low percentage
around the northern end of WDTR04, as shown in Figure 5.15v. The albite low at
WD001 correlates with the highest abundance of kaolinite in the channel, which was
attributed to the weathering of the feldspar materials. An elevated abundance of albite,
was found in the soil sample WD002, which was collected close to the alluvial channel
(ACa). This may be due to the abundance of lithic fragments in the channel and
surrounding alluvial area. Orthoclase displayed a similar inverse relationship with
kaolin (Figure 5.15 ii) and a complementary relationship with albite. The distribution of
orthoclase was marginally more abundant in the saprolite region, with a maximum of
8% at WD039 (Figure 5.15 ii). The percentage of orthoclase was stable over the rest of
Chapter 5
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the area, with an average abundance of 6%. The orthoclase high coincided with a
maximum concentration of amphibole (2%).
Kaolin Distribution
Kaolin displayed a high concentration to the northeast of WDTR04 and to the
west of WDTR06, with decreasing values in the areas of deeper transported cover
(Figure 5.15 iii). An anomalous high abundance occurred in the northwestern corner of
the sampling area, which may be related to the weathering of transported materials
deposited by the northeast trending ephemeral creek.
Quartz Distribution
Quartz displayed a low concentration in the eastern portion of the sample area,
increasing to the west and northwest. The region between WDTR04 and WDTR06
displayed a low abundance of quartz, as shown in Figure 5.16 iii, which were influenced
by the small concentrations of quartz in samples collected from WDTR04. Quartz
displayed lower abundances for the saprolite areas, contrasted by a gradational increase
from the southeastern corner to similar moderate to high abundances for the rest of the
area. This dispersion pattern closely matched the thickness of transported material seen
in WDTR04 and WDTR06, which displayed an increase to the north, as shown in the
section logs (Figure 5.6).
Hematite Distribution
The dispersion of the mineral hematite was uncorrelated with any other mineral,
with the greatest hematite occurrence (4%) situated in the southeastern region of the
sampled area, corresponding to the saprolite exposure (Figure 5.16 iv). The abundance
decreased to the north to 1 - 2%, with an incidence of 3% in the alluvial RLUs WD002
(Aap) and WD044 (Aed). Significant low abundances occurred in the zone above the
amphibolite (WDTR04D0 and WDTR06A), to the east of WD003 and in the central
portion of the area.
It was unclear if the XRD results were identifying hematite or goethite. The
appearance of the XRD results display similarities to the Fe-oxide Intensity map,
generated by the ASD measurements. Considering that hematite was the only mineral
identifiable in the soil samples that had a diagnostic signature in the VNIR, the presence
of Fe-oxide spectral features was expected in the ASD FieldSpec measurements.
Amphibole Distribution
Amphibole displayed a restricted distribution to near WDTR04 and WDTR06
and regions to the south of these costeans (Figure 5.16 i). The lack of significant
numbers of samples containing amphibole, low abundance and the limited suite of
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samples make the results for this distribution map inconclusive. However, results show
there was a slightly elevated abundance in the alluvial depression (Aed).
Calcite Distribution
Calcite was identified in two of the five soil samples. The samples with the
above zero abundances of calcite occurred in the southeastern corner of the grid area
(sample WD069 Figure 5.16 ii). Comparisons of the distributions of calcite,
amphibolite and quartz show similar patterns, with quartz displaying an inverse
relationship to the other two minerals. This distribution is related to the distance from
the bedrock exposures, which also corresponds to increasing thicknesses of transported
cover and depths to the saprolite.
Calcite (Figure 5.16 ii) was found to coincide with amphibole (Figure 5.16 i) in
four of the five occurrences of the carbonate mineral. The remaining four amphibole
occurrences were not associated with calcite. Calcite and amphibolite distribution was
highest in the southeastern region of the sample area and decreased to the north, away
from the saprolite exposure.
The lower abundance of calcite was attributed to the increasing thickness of the
transported profile with greater distance from the basement outcrop. The increased
profile thickness corresponded to a greater depth to the fragmented RCA hardpan,
which predominantly occurred at the interface between the saprolite and transported
material.
In areas of thicker transported cover the profile containing an abundance of
powdery carbonate mottles at approximately 2 m depth, whereas in regions of shallow
transported cover, the depth to the fragmented hardpan was within 1 m. The fragmented
regolith carbonate hardpan consisted of a greater volume of material than the mottles or
nodules and therefore could possibly have contributed more material to the upper soil
horizons. The carbonate material may have been translocated to the surface by the
processes of eluviation or bioturbation, where the RCAs occurred at shallow enough
depths to be incorporated in these processes.
The weight of influence that the distribution of minerals related to surface sheet-
flow process or subsurface pedogenic associated processes is unclear from the surface
XRD results. An investigation into the abundances and distribution of minerals in the
regolith profile was conducted using spectral and XRD analyses. This is discussed in
Part 4 of this Chapter.
Chapter 5
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Part 4 Results and Data Analysis of Subsurface Samples
Spectral Analysis of the Costean Samples The de-stepped ASD FieldSpec data (Figure 5.8) were checked for errors, which
consisted of examining for spectra with low albedo or measurements that mis-
represented the bulk sample. The corrected ENVI spectral library of the entire 3400
measurements were imported into TSG with the data logs and analysed for dominant
mineralogy. Minerals used in the TSA algorithm for the VNIR were restricted to
hematiteTSA, Fe2+ goethiteTSA, Fe3+ goethiteTSA and jarositeTSA. Sulphide minerals were
omitted from the TSA algorithm as they were not visually observed during sample
collection.
A similar analytical technique to the one described in Part 3 of the Chapter for
the surface soil ASD measurements was performed on each of the sampled costeans’
spectral measurements. Mineralogical results from TSA were treated as abundance
percentage and scaled between 0 - 100 %. The Spectral Geologist’s calculations were
scaled as high or low values, as they were dependant on the wavelength features that
were under scrutiny. Spectral measurements were subdivided and gridded to represent
the individual vertical faces of the northerly trending costeans (Figure 5.17, Figure 5.21,
Figure 5.22, Figure 5.24, Figure 5.26). The figures include additional information to
Figure 5.6 on the in situ regolith materials of the costeans, along with regolith carbonate
morphology, type of ferruginisation, colour of the in situ materials and the regolith
stratigraphy.
WDTR01 - Thick Transported Cover In WDTR01, the in situ materials were dominated by highly weathered
saprolite-pedolith materials that displayed little to no remaining fabric. The saprolite
was pallid to light grey in colour except where pegmatitic layers occur, which appear
less weathered than the quartzo-feldspathic gneiss derived saprolite.
Fe-Oxide Spectral Analyses
The Spectral Analysis identified the presence of Fe2+ goethiteTSA (Figure 5.17
xiii) and a low hematiteTSA abundance from the Hematite:Goethite RatioTSG (Figure
5.17 viii) in the lower regions of the section. The areas of the profile that showed a high
abundance for Fe2+ goethiteTSA coincided with higher CFATSG wavelengths, which is
typical for this mineral (Figure 5.17 ix). This feature can be used to discriminate
materials that are hematite-rich, which would have a shorter CFATSG wavelength. The
I C Lau Regolith Mineralogy
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distribution of the mineral hematiteTSA was found to be limited to a small area in the
upper northern portion of the costean (Figure 5.17 xvii). The identification of the
presence of hematiteTSA was impeded by the dominance of Fe2+ goethiteTSA in most of
the spectral measurements.
Carbonate Spectral Analyses
The Dolomite IndexTSG (Figure 5.17 iii) displayed a high value in the northern
region, where the pegmatite material was mapped, although it did not show a strong
relationship to the presence of regolith carbonate mottles.
The presence of the mineral SideriteTSA (Figure 5.17 xi) in the ASD
measurements was perplexing, as no Fe-carbonate material was observed in the field.
The spectra were most likely classified by TSA as sideriteTSA based on the presence of
2.305 µm absorption features. SideriteTSA identified by TSA coincided with regions
recorded as having high abundances for the Chlorite/EpidoteTSG Index (Figure 5.17 i).
This Index examines the spectra in the 2.25 µm wavelength region for features related to
Fe-OH. Kaolinite has been found to possess absorption features in this region related to
the substitution of Fe2+ for Al in the octahedral sites. The lower northern portion of the
costean contained an abundance of pegmatite, which may have contributed to the higher
values Chlorite/EpidoteTSG and high abundances for the material classified as
sideriteTSA. The presence of the mineral sideriteTSA was inferred to be related the
regolith carbonate accumulations and was most likely the mineral calcite, which was
identified in the XRD analysis of the costean profiles.
Spectral Analyses of Aluminous Layer Silicates
The KaoliniteTSG Index and Al-OH-related calculations displayed a consistent
distribution, with the exception of Al-OH WavelengthTSG (Figure 5.17 vi). The mineral
kaoliniteTSA, identified by TSA, coincided with the calculations for Al-OH IntensityTSG
(Figure 5.17 v), Kaolinite CrystallinityTSG (Figure 5.17 vii) and Al-OH WavelengthTSG.
The presence of the mineral kaolinite corresponded with the distribution of Fe2+
goethiteTSA (Figure 5.17 xiii). Areas coinciding with smectiteTSG and
montmorilloniteTSA (Figure 5.17 iv and Figure 5.17 xv) were found to have longer Al-
OH WavelengthsTSG (Figure 5.17 vi). Pegmatitic material in the lower northern end of
the costean displayed a lower Al-OH WavelengthTSG and kaoliniteTSA abundance but a
higher Kaolinite CrystallinityTSG. The shorter wavelength was attributed to the higher
abundance of feldspar and white mica. Materials mapped in this portion of the costean
appearing less weathered than the grey saprolite material in the southern end.
Chapter 5
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Mica and Smectite Spectral Analyses
IlliteTSA (Figure 5.17 xvi) and muscoviteTSA (Figure 5.17 xviii) were found
throughout the transported materials of the profile, although they rarely occurred
spatially together. Surface materials (PSA) became more illite-rich to the north, which
was attributed to the proximity to the alluvial channel and the decrease of lithic material
transported by overland flow from upslope.
MontmorilloniteTSA (Figure 5.17 xv) and smectiteTSG (Figure 5.17 iv) displayed
a similar distribution, with high concentrations corresponding to the YB-Unit, in the
northern end of the costean. This region was proximal to the alluvial channel and may
have been a depositional area for clays from overflow events or overbank deposits. An
alternative explanation is the greater abundance of parna in the YB-Unit from aeolian
additions.
Clay pellets in aeolian materials have been observed in the Fowlers Gap region,
in Western New South Wales by Chartes (1981). The BII horizon was found to consist
of large proportions of aeolian materials. The YB Unit seen at the White Dam Prospect
are thought to be of similar origin. MontmorilloniteTSA was not found in the uppermost
regolith unit. This was thought to be due to the quartz-rich nature of the PSA material.
The presence of gypsumTSA (Figure 5.17 x) was identified in the upper southern
and lower northern ends of the costean, hosted in different materials (Figure 5.18). The
small gypsumTSA anomaly in the lower northern end of the costean coincided with the
pegmatitic saprolite. Opal was found by TSG to be a minor constituent of the
mineralogy of the ASD measurements in the lower portions of the YB Unit and the
pegmatite. The mineral was most likely amorphous silica materials from veins and
gravels.
The southern anomaly occurred in the YB Unit and may have been due to the
presence of regolith carbonate in the measured sample. Field logging found the YB
Unit to contain numerous horizons of gravel material and quartz lag, associated with
horizontal RCAs (Figure 5.19).
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Figure 5.17 WDTR01 gridded mineralogical abundances sections, calculated from spectral measurements collected from costean samples. The Fe-oxide mineralogy and related indices correlate with the transported and in situ materials. Similarly, the kaolin mineralogy and the features related to Al-OH are associated with different regolith materials. Sections denoted ‘ASD” are mineral abundances, whereas ‘TSG” denotes an index calculation based on absorption feature depths. Due to the griding technique used, anomalous regions in the interpolated regions between the sampled profiles are more uncertain and should be treated classified accordingly.
I C Lau Regolith Mineralogy
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Figure 5.18 Profile WDTR01 E (6449192 mN) showing the gypsiferous minerals occurring 1 m below the surface.
The formation of such gravel horizons is thought to occur through a wide range
of geological processes. The gravel lag may represent an old palaeosurface that
possessed abundant amounts of quartz lag, which has subsequently been buried by a
depositional event. Soil eluviation and bioturbation can yield gravel materials at the
surface (Hill, S.M. 2004, pers. comm.). These movement processes result in a mixing
of the soil materials by biota, as well as the swelling and settling of clay minerals in
soils. It is unknown if these processes can form horizontal layers of gravels in soil
horizons. A third explanation for the presence of the linear gravel horizons is the
previous occurrence of a channel at this location. The proximity of the alluvial channel
to the north could be related to the gravel horizons.
Chapter 5
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Figure 5.19 Photograph of profile WDTR01C (6449212 mN), showing the lithic gravels ~1.5 m below the surface. WDTR01 occurred in the northern region, away from the exposed bedrock and has a thicker succession of transported materials overlying saprolite and in situ pedolith materials, which occur ~4m below the surface (not shown). The YB unit displays the greatest variation of thickness when compared in all the costeans.
I C Lau Regolith Mineralogy
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WDTR02 The in situ materials of WDTR02 were generally less weathered than the two
northern costeans (WDTR01 and WDTR05). The material in the northern end was
more highly weathered and had a greenish colouration. Towards the middle of the
costean (grid reference 6449045 mN) there was a small region of amphibolite, which
was overlayed and adjacent to a sizable pegmatite body. The material between the
pegmatite and the amphibolite was highly weathered and displayed a goethitic orange-
yellow-brown colouration, which extended to the bottom of the costean at 6449047 mN.
Directly above this region the in situ and transported materials were in direct contact
and were not separated by a regolith hardpan. The lack of a hydromorphic barrier could
be related to the increased weathering in the lower portions of the profile.
Ferromagnesian Silicate Spectral Analyses
The presence of amphibolite was shown in the spectra by the identification of
the minerals hornblendeTSA and nontroniteTSA (Figure 5.21 i and Figure 5.21 ii).
Nontronite represents the clay-weathering product of amphibole minerals (Raven, M.
2004 pers. comm.). The distribution of these two minerals was closely related to the
presence of green coloured material, identified during the mapping of the costean. A
Talc IndexTSG calculation was performed to investigate if the spectral features of
hornblende and nontronite could be identified. The results show the spatial patterns to
be slightly similar (Figure 5.21 iii), with a distinct low value for the transported
materials. The mineral jarositeTSA (Figure 5.21 iv) was found to occur in similar regions
as hornblendeTSA and nontroniteTSA and was closely associated with regions of higher
weathering and ferruginous mottles. The occurrence of jarositeTSA was thought to be an
indicator of the previous presence of sulphides.
Mica and Smectite Spectral Analyses
IlliteTSA and muscoviteTSA were predominantly found to be mutually exclusive.
IlliteTSA was found in the RB Pedal layer and was absent in the PSA layer. SmectiteTSG
had a similar distribution as muscoviteTSA and illiteTSA, occurring within the transported
materials above the saprolite. A low abundance for illiteTSA, muscoviteTSA and
smectiteTSG were seen in the central and northern surface regions of the costean. The in
situ pedolith material in the northern lower portion of the costean had a moderately high
smectiteTSG value, which corresponded to the clayey materials mapped in this region
while collecting the samples (Figure 5.20).
Chapter 5
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Figure 5.20 Weathering of the in situ materials to pedolith in the lower-northern end of WDTR02 (profile A). The shelf (at the top of the photograph) occurred 2.75 m below the surface and the floor of the costean (shown at the bottom of the photograph) occurred at 3.75 m below the surface. The green-yellow material in the lower portion of the costean contained high abundances of Fe2+ goethite and nontronite and jarosite, interpreted from the spectral measurements.
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Figure 5.21 WDTR02 gridded mineralogical abundances sections, calculated from spectral measurements collected from costean samples. Sections denoted ‘ASD” are mineral abundances, whereas ‘TSG” denotes an index calculation based on absorption feature depths.
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Spectral Analysis of Aluminous Layer Silicates
The saprolite regions high in magnesium minerals were found to have low
values for kaoliniteTSA and Al-OH minerals, as seen in Figure 5.21 v-viii. KaoliniteTSA
was found to prominently occur in the red-ferruginous layered saprolite at 6449028 mN.
The transported materials displayed a low abundance of kaoliniteTSA, although still
possessed a similar wavelength to the kaolinite-saprolite. The presence of a consistent
wavelength for the Al-OH absorption feature indicates the samples are constituted by
similar proportions of minerals and that there is not a significant change in composition.
Changes in the crystallinity are not directly accompanied by compositional changes in
the mineralogy, although increased weathering may alter the proportions of minerals.
The Al-OH WavelengthTSG was influenced by the presence of the magnesium-rich
materials and the pegmatite (Figure 5.21 vii). Distribution of the Al-OH IntensityTSG
(Figure 5.21 v) produced highly correlated results to the presence of the mineral
kaoliniteTSA.
PalygorskiteTSA (Figure 5.21 ix) was classified by TSA as occurring in a similar
region as the carbonate mottles in the central portion of the costean. The significance of
the presence of palygorskiteTSA, a magnesium bearing chain-lattice clay, with regolith
carbonates has yet to be identified. It is most likely as mis-interpretation by TSA and
the mineralogy is actually calcite with some kaolinite or halloysite and montmorillonite.
Fe-Oxide Spectral Analyses
Fe2+ goethiteTSA had an increasing abundance with depth, starting from the lower
portion of the YB Unit, where the regolith carbonate mottles occurred. Above this
horizon the abundance of goethiteTSA was low (shown as a heterogeneous area of green
in Figure 5.21 xviii). The highest abundances of goethiteTSA were seen in grey and
pallid saprolite. The pegmatite (6449045 mN) and amphibolite areas (6449063 mN)
had a lower abundance of Fe2+ goethiteTSA than the adjacent grey saprolite. These
results are clearly shown when the regolith stratigraphic interpretation and the mineral
abundance section of goethiteTSA (Figure 5.21 xviii) are compared.
Conversely, hematiteTSA was not found in the saprolite materials and displayed
medium values for the transported materials (Figure 5.21 xix).
Carbonate and Other Spectral Analyses
OpalTSA (Figure 5.21 xi) was identified by TSA in WDTR02, near a region
logged as containing gravel material (WDTR02H, 6449022 mN). The abundance map
of the mineral opalTSA suggests the distribution of the gravels occur over a wider area
than mapped while in the field. Examination of the digital-photographs of the profile
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showed a lens of gravels, with large cobbles, at 1 m below the surface ,in profile
WDTR02I (6449017 mN).
A TSG calculation used to identify hydrothermal quartz (Quartz-H20 IndexTSG)
was found to have a dissimilar distribution to the lithic gravels (Figure 5.21 xii). The
calculation corresponded more to the distribution of montmorilloniteTSA (Figure 5.21
xvi), suggesting that the index was mapping the 1.9 µm absorption feature due to H20 in
the clays. It was concluded that the Quartz-H20 IndexTSG, constructed for the
examination of fresh rock from drill core, was not suited for analysing regolith
materials.
SideriteTSA (Figure 5.21 x) was found to occur in association with pegmatite and
saprolite in the 6449050 mN region. Examination of the spectra for this region showed
an absorption feature in the 2.345 µm region.
The identification of small abundances of the mineral calciteTSA (Figure 5.21 xx)
by TSA was a significant result. Mixtures of minerals containing calcite often do not
display distinctive carbonate absorption features. Calcite absorption features are
normally masked when mixed with common soil minerals, such as kaolinite or smectite.
Spectral experiments on soils by Cudahy et al. (1999), found that an abundance of >40
% by weight of calcite was required before a measurable spectral feature, related to
carbonate, was observed.
From laboratory measurements it was found that even a whole nodule of
carbonate, measured without cleaning, would often not produce carbonate absorption
features. This was due to the rind of soil materials coating the nodule, producing Al-
OH and Fe-oxide features. A 2.3 µm carbonate absorption was obtained once the
nodule was cut in half or crushed. The materials spectrally analysed from the White
Dam Prospect costeans that were identified as containing calcite would have required a
high abundance of CaCO3 to produce the observed absorption features. However, if a
broken surface of a nodule of regolith carbonate was measured, the spectra may have
reflected this ‘nugget’ of calcite.
From the observations of experiments on carbonate nodules, it was concluded
that homogenising the bulk sample may have resulted in the mixing of sufficient
amounts of calcite to produce observable carbonate absorption features. During
sampling it was noted that the pale colour of the saprolite was similar to the carbonate
material, making it difficult to determine the abundance without closer examination of
each sample. The carbonate materials often occurred in vertical veins of the fractured
and jointed weathered saprolite. A sample that included such materials would result in
I C Lau Regolith Mineralogy
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a local calcite high if the quantity of calcite was sufficient to produce an observable
absorption feature.
WDTR04 –Amphibolite Dominated Section WDTR04 was excavated closest to the exposed saprolite (Figure 5.4) and
displayed the thinnest transported cover sequence, shown in Figure 5.6. A large section
of the in situ material was mapped as amphibolite during field logging. A thick regolith
carbonate hardpan was observed throughout the costean, which occurred at increasingly
deeper levels to the north. The transported sequences were discontinuous and generally
thin, although increased in thickness to the north towards the depositional plain.
Fe-Oxide Spectral Analyses
A low Fe2+ AbundanceTSG (Figure 5.22 i), contrasted by a high hematiteTSA
abundance (Figure 5.22 ii) was found for the transported cover in WDTR04. The Fe-
oxide IntensityTSG calculation showed a high correlation with the presence of the YB
Unit and RB Pedal Unit, with values for this index decreasing in the lower portions of
the costean, corresponding to the regolith carbonate hardpan and weathered saprolite.
Figure 5.22 i, ii & iii show the relationship between the Fe-oxide Indices and mapped
abundances with the thickness of the transported cover. The amphibolite region
(centred around 6449062 mN) displayed a low abundance of both Fe-oxide minerals,
hematiteTSA and goethiteTSA (Figure 5.22 i and Figure 5.22 ii).
Ferromagnesian Silicate Spectral Analyses
The amphibolite indicator minerals, hornblendeTSA (Figure 5.22 ix) and the
weathering product, nontroniteTSA (an Fe-smectite), displayed a high abundance in the
region depicted as having low values for the Fe-parameters (centred around 6449062
mN). HornblendeTSA displayed a high spatial correlation to the areas mapped as
amphibolite, whereas the nontroniteTSA abundance section, generated from the spectral
measurements, was slightly juxtaposed to the south (to the left on Figure 5.22 x) of
hornblendeTSA.
The Talc IndexTSG was successful at identifying the amphibolite bedrock
material, with a high abundance recorded at the bottom of profile 6449065 mN (Figure
5.22 viii). Very low abundances were recorded for the Talc IndexTSG in the transported
material, due to the absence of 2.3 µm absorption features.
The presence of the mineral jarositeTSA (Figure 5.22 xi) was observed to have a
similar distribution as the mapped amphibolite and the associated ferromagnesian
minerals. Sulphide mineralisation (specifically pyrite and chalcopyrite) may have
occurred in the amphibolite, which created acid leaching conditions during weathering.
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Anomalous Cu values associated with amphibolite were found near the surface (<15 m)
in diamond drill holes WD15 and WD17 (Busutill & Bargmann 2003), suggesting
mineralisation may have occurred in these samples that were collected within 3 m of the
surface. A region of intense weathering of the in situ materials to yellow-green clays
(WDTR02A Figure 5.20) corresponded to where the mineral jarositeTSA was found.
GypsumTSA produced a similar abundance distribution as jarositeTSA with a high
occurring in the southern portion of WDTR04 (Figure 5.22 xii). A small, truncated
bullseye was located in the upper northern section of the costean and corresponded to an
area in the transported material mapped as containing gravely material. Re-evaluation
by photographic interpretation, visually confirmed the presence of gypsum, with the
profile displaying characteristics similar to the ones seen in Figure 5.18.
Mica and Smectite Spectral Analyses
The mineral montmorilloniteTSA (Figure 5.22 v) displayed a high abundance in
the upper regions of the costean, with a bullseye high at 6449058 mN. The results
showed a greater abundance of smectiteTSG above the amphibolite material than found
in the northern regions of the costean, where grey-pallid saprolite was mapped.
The illiteTSA abundance map featured a distinct high bullseye that corresponded
to an occurrence of lithic gravels at 6449088 mN (Figure 5.22 xv). MuscoviteTSA
displayed an isolated high, slightly below the anomalous montmorilloniteTSA result at
6449058 mN (Figure 5.22 xvi and Figure 5.22 vi). The boundary between these two
materials marks the unconformity surface between the in situ saprolite and the overlying
transported YB Unit. The smectiteTSG calculation (Figure 5.22 v) displayed a marginally
similar distribution to the minerals montmorilloniteTSA and hornblendeTSA, although the
Smectite IndexTSG recorded a high value at 6449078 mN, where a hornblendeTSA low
occurred.
Carbonate Spectral Analyses
The presence of spectral absorption features related to calciteTSA was expected in
the ASD measurements of WDTR04, due to the thick hardpan of regolith carbonate.
This was not the case, with only an isolated calciteTSA occurrence in the lower-northern
saprolite portion of the costean (Figure 5.22 vii). However, the Dolomite IndexTSG
(Figure 5.22 iv) was found to display an similar distribution to the areas containing
regolith carbonate, indicating the spectral features of carbonate could be used to identify
RCAs where abundances were high enough.
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Figure 5.22 WDTR04 gridded mineralogical abundances sections, calculated from spectral measurements collected from costean samples. Sections denoted ‘ASD” are mineral abundances, whereas ‘TSG” denotes an index calculation based on
absorption feature depths.
I C Lau Regolith Mineralogy
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Examination of the individual spectra from these regions found that the
magnitude of the carbonate features were distorted by kaolinite absorptions, and were
too small to be identified by TSA. The samples collected from areas mapped as having
RCA hardpans displayed broad symmetric absorption feature around 2.2899 µm - 2.299
µm (shown in Figure 5.1 as E9.
Figure 5.23 Carbonate absorption features of observed in samples collected from indurated horizons in WDTR04. Sample E1 collected from the Red-Brown Pedal Layer and contains no traces of regolith carbonate, whereas E2 has a low reflectance in the 2.4 µm region related to the 2.5 µm calcite feature. E1 and E2 contain montmorillonite and display a large, broad absorption at 1.9 µm, due to water. E3 and E4 were collected from the indurated regolith carbonate hardpan and show slight absorption peaks at 2.28 µm, which could be related to carbonate. CD4 and A9 possessed very strong calcite absorptions, as well as a kaolinite doublet at 2.16 - 2.2 µm, with A9 featuring the 2.5 µm calcite feature. A sample of goethititic saprolite collected below the hardpan (A10) did not display calcite absorptions like A9, although the low reflectance in the NIR related to Fe2+ is observed.
Chapter 5
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Spectral Analysis of Aluminous Layer Silicates
The mineral kaolinite was found to have a high abundance in the lower portion
of the northern end of the costean (Figure 5.22 xvii). A low abundance occurs in the
southern end of the costean where the saprolite has been mapped as grey weathered
gneiss. There was a distinct lack of the mineral kaoliniteTSA in regions mapped as
amphibolite derived saprolite. The soil materials displayed a low abundance of
kaolinite in the regions overlying amphibolite (6449085 mN), whereas the abundance
was higher in the soil material overlying the grey weathered saprolite (6449085 mN),
suggesting that there had been some soil-saprolite mixing of this showllow material.
The Al-OH intensityTSG (Figure 5.22 xvii) displayed a similar distribution as the results
for the mineral kaoliniteTSA, highlighting the low intensity for the 2.2 µm absorption
feature in the amphibolite region.
The Kaolinite Crystallinity IndexTSG (Figure 5.22 xx) closely resembled the
distribution of kaolinite and the Al-OH IntensityTSG. This was an encouraging result as
this parameter is often used to discriminate transported and in situ materials (e.g.
Pontual et al. 1997; Tan et al. 1998; Lau et al. 2003).
The Al-OH WavelengthTSG (Figure 5.22 xix) possessed a low value for the
amphibolite regions, whereas the saprolite and overlying cover had a higher value
(longer wavelength of the absorption feature in the 2.2 µm region). The low in the
upper northern portion of the costean was an artefact from the gridding method, as this
region was above the surface and should be zero.
WDTR05 –Thick Profiles of Transported Cover WDTR05 was situated adjacent to WDTR01, in the northern portion of the study
area and possessed the thickest succession of soil and transported materials. The YB
Unit contained two indistinct sequences, consisting of an upper gravely section and a
lower section dominated by mottles of powdery regolith carbonate. Only three profiles
were sampled in this costean, due to its short length. Difficulties were encountered
when attempting to grid the results, due to the large interpolated area between the
profiles. Many of the distribution maps possessed large bullseye highs or lows in the
zones adjacent to the middle profile.
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Figure 5.24 WDTR05 gridded mineralogical abundances sections, calculated from spectral measurements collected from costean samples. Sections denoted ‘ASD” are mineral abundances, whereas ‘TSG” denotes an index calculation based on
absorption feature depths.
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Ferromagnesian Silicate Spectral Analyses
Although there was no evidence seen in the field for amphibolite in this costean,
nontroniteTSA (Figure 5.24 i) and magnesium claysTSA (Figure 5.24 ii) were identified by
TSA. The occurrence was isolated to one sample (6449247 mN, 203 m elevation),
collected in the lower portion of the gravely section of the YB Unit. A positive
identification for the mineral jarositeTSA was also obtained from this sample (Figure
5.24 iv). The Talc IndexTSG (Figure 5.24 iii) highlighted areas above and below the
sample at 6449247 mN, 203 m elevation, which possessed higher than average values
for spectral features in the 2.3 µm region. The upper transported sequences for the Talc
Index all had value of zero and were not gridded by ArcGIS.
Carbonate Spectral Analyses
The Dolomite IndexTSG was found to define the in situ regolith materials
corresponding to the lower profile and expressed a high abundance in the northern
portion of the costean (Figure 5.24 v). The SWIR/VNIR Reflectance Slope IndexTSG
(Figure 5.24 vi) displayed a similar pattern as the abundance of dolomiteTSG, as well as
produced a distribution that correlated with the discontinuous, undulating horizon of
regolith carbonate mottles and the underlying pedolith materials.
Fe-Oxide Spectral Analyses
The ferruginous indices displayed a gradation in horizontal magnitude, closely
reflecting the regolith stratigraphy. HematiteTSA (Figure 5.24 ix) displayed moderate
abundances in the transported and soil layers, but was absent in the lower regions of the
profile. Fe2+ goethiteTSA (Figure 5.24 viii), which displayed an inverse distribution to
hematiteTSA, with high values for the in situ saprolite-pedolith materials. Low CFATSG
wavelengths were recorded for the PSA Unit (Figure 5.24 vii), which increased in the
RB Pedal Unit to a high wavelength for the materials at the boundary with the
underlying YB Unit. The shelf of the costean exhibited a slightly lower CFATSG
wavelength than the underlying and overlying units, which was attributed to the mixing
of materials by collapse of the costean walls and down-washing of PSA material.
Mica and Smectite Spectral Analyses
The values for the Fe-oxide Intensity IndexTSG were highest in the upper portion
of the YB Unit, corresponding to the gravely material (Figure 5.24 x).
MontmorilloniteTSA (Figure 5.24 xii) was found to have a similar distribution of to the
Fe-oxide Intensity IndexTSG, and to a minor degree, smectite (Figure 5.24 xi). The
Smectite Index was partially successful at reproducing the distribution of the mineral
montmorilloniteTSA. Gravel horizons occurred throughout the length of WDTR05 at
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approximately 1 m depth, and appeared to have a high abundance of montmorilloniteTSA
associated with them.
IlliteTSA (Figure 5.24 xiii) and muscovite (Figure 5.24 xiv) mineral abundances
were shown to predominately occur in the upper region of the profile, although not
spatially adjacent, as seen in the other costeans. MuscoviteTSA was found in the
northern portion of the surface and near the bottom of the profile at 6449247 mN. In the
middle-horizons of the costean, muscoviteTSA and illiteTSA were found to coexist at the
top and base of the regolith carbonate mottles. IlliteTSA was also found within the
carbonate hardpan region in the northern portion of the costean. The presence of
muscoviteTSA was interpolated throughout the regolith carbonate mottles.
Spectral Analysis of Aluminous Layer Silicates
The Kaolinite CrystallinityTSG (Figure 5.24 xv) and the distribution of the
mineral kaoliniteTSA (Figure 5.24 xvi) were found to be isolated to the northern and
lower portions of the costean, respectively. Difficulty was found producing acceptable
grids for the distribution of mineral abundance of kaoliniteTSA, due to the lack of
vertical profiles, making the results less reliable than the other costeans. Al-OH
IntensityTSG produced a similar distribution to the region mapped as in situ saprolite-
pedolith materials with red-brown ferruginous mottling (Figure 5.24 xvii).
WDTR06 – Regolith Carbonate Dominated Shallow Section The eastern-most costean consisted of a shallow sequence of soil and transported
material over slightly weathered saprolite. A regolith carbonate hardpan was situated
overlying the saprolite, with various minor RCAs occurring in the lower portion of the
transported materials. The quantity and thickness of regolith carbonate was extensive,
with material infilling fractures and joints in the underlying saprolite. In portions of the
costean, deeply weathered grey-green corestones of saprolith-pedolith were surrounded
by regolith carbonate hardpan material.
Fe-Oxide Spectral Analyses
HematiteTSA was found in the upper transported sequences, corresponding to the
RB Pedal unit and, to a lesser extent, the PSA horizon. High abundances were also
discovered for a zone in the underlying saprolite at 6449088 mN (Figure 5.26 i), where
there was an abundance of ferruginised material. Fe2+ goethiteTSA had a low value for
the materials in the upper portion of the profile, whereas the upper saprolite regions
displayed very high abundances. Saprolite materials at depths greater than 3.5 m below
the surface were considerably lower in goethite abundance than the materials near the
regolith carbonate hardpan (Figure 5.26 ii). A close inverse relationship was observed
I C Lau Regolith Mineralogy
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with the Talc IndexTSG (Figure 5.26 xv), which indicated the presence of magnesium
silicates, such as hornblende. This would explain the low Fe2+ goethiteTSA abundance in
the lower-central portion of the costean (6449098 mN). This relationship is discussed
further in the ferromagnesian analyses of WDTR06.
The Hematite:Goethite RatioTSG (Figure 5.26 iii) reflected the higher
hematiteTSA abundance in the upper profile, but did not entirely correspond to the
distribution of Fe2+ goethiteTSA in Figure 5.26 ii. However, CFA Wavelength (Figure
5.26 v), showed an increase in the wavelength of materials with depth, corresponding to
an increase in the abundance of goethiteTSA.
The unusual presence of the mineral Fe-tourmalineTSA (Figure 5.26 vi) was
found in the lower profile of the southern end of the costean (6449082 mN). An
interesting observation was made when the distribution of the mineral Fe-tourmalineTSA
and Fe-oxide IntensityTSG (Figure 5.26 iv) were compared. The area mapped as having
a high abundance of Fe-tourmalineTSA corresponded to low Fe-oxide IntensitiesTSG,
whereas areas with high intensities had no tourmaline. This distribution may be
coincidence, as there were only a small number of tourmalineTSA occurrences. Another
explanation for the presence of tourmaline maybe related to the presence of pegmatite
materials in the saprolite. The presence of Fe-tourmaline is discussed further in the
alumino-silicate spectral analyses section of WDTR06.
The calculation of the Red Reflectance PeakTSG divided by the CFATSG
wavelength was performed and returned noteworthy results. Theoretically, a sample
containing hematiteTSA would have a high reflectance for red wavelengths and a low
wavelength for the CFATSG. GoethiteTSA would have a lesser reflectance for the red
peak and a longer CFATSG. This would ideally produce an image with a distribution
that was similar to the Hematite:Goethite RatioTSG. The results were partially as
expected (Figure 5.26 vii), although the upper section of the profiles, which were
recorded as having a high hematiteTSA abundance in Figure 5.26 i, did not show a high
value as expected.
Spectral Analysis of Aluminous Layer Silicates
The abundance of kaoliniteTSA (Figure 5.26 xi), Kaolinite Crystallinity (Figure
5.26 xii) and Al-OH IntensityTSG (Figure 5.26 xiii) were found to have near-identical
distributions. A similar pattern was found for the Dolomite IndexTSG (Figure 5.26 xx),
which had almost no correspondence to the presence of mapped regolith carbonate. The
mineral calciteTSA was not seen in the spectral samples analysed from this costean, even
though the regolith carbonate hardpan was locally over 1 m thick. This was attributed
Chapter 5
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to the selective sampling of the profile, and as a result, the absence of diagnostic
absorptions. As a consequence the only feature that related to the presence of the
regolith carbonate was the lack of Fe2+ goethiteTSA in the northern section of the costean
where the prominent RCA hardpan occurred.
The high abundance of kaoliniteTSA, Kaolinite CrystallinityTSG and Al-OH
IntensityTSG in the lower southern portion of WDTR06 was correlated to the presence of
Fe-tourmalineTSA at 6449082 mN. Figure 5.25 is a photograph of the eastern costean
face, showing the albitic intrusion that contained Fe-tourmaline veins. Goethite
occurred at the margins of the contact with the grey saprolite, as well as regolith
carbonate, which had penetrated fractures in the in situ materials.
Figure 5.25 Albitic intrusion hosting Fe-tourmaline veins, in WDTR06, profile “E” (grid reference 6449082 mN). Photograph was taken of the costean eastern face.
Ferromagnesian Silicate Spectral Analyses
Although not obvious in the costeans during field mapping, the presence of
amphibolite was inferred to be present in the 6449102 mN profile, by the occurrence of
the mineral hornblendeTSA (Figure 5.26 xiv). This was accompanied by the proximal
identification of nontroniteTSA (Figure 5.26 xvi) and ‘magnesium clayTSA’ (Figure 5.26
xvii), both associated with the weathering of ferromagnesian silicate minerals. The
magnesium claysTSA were found below the region mapped as an expanse of regolith
carbonate hardpan, whereas the nontroniteTSA was found below hornblendeTSA in the
same profile.
I C Lau Regolith Mineralogy
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Figure 5.28 WDTR06 gridded mineralogical abundances sections, calculated from spectral measurements collected from costean samples. Sections denoted ‘ASD” are mineral abundances, whereas ‘TSG” denotes an index calculation based on
absorption feature depths.
I C Lau Regolith Mineralogy
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Mica and Smectite Spectral Analyses
SmectiteTSG abundance (Figure 5.26 ix) appeared to have a dissimilar
distribution to the mineral montmorilloniteTSA (Figure 5.26 x). The surface sample
collected at 6449102 mN did not have high smectiteTSG abundance (Figure 5.26 ix), but
corresponded to the mineral illiteTSA. The highs in the lower-northern portion of the
costean, shown in both the smectiteTSG and montmorilloniteTSA images, are artefacts
from the gridding process.
IlliteTSA and muscoviteTSA (Figure 5.26 xviii and Figure 5.26 xix, respectively)
were found to have a mutually exclusive relationship, with illiteTSA occurring in the
upper-northern portions of the costean and muscoviteTSA in the southern surficial
regions. MuscoviteTSA was also found in association with the gravel material at
6449102 mN and the deeply weathered saprolite/pedolith at 6449082 mN. The mineral
muscoviteTSA was not found in the sample collected in the region of the profile mapped
as having gravel material, at 6449082 mN.
The surficial relationship of muscioviteTSA and illiteTSA was attributed to the
dispersion of micas from the weathering og the saprolite exposures. The process of
overland flow would decrease the crystallinity of micas and increase the rate of
weathering. This would allow the loss of interlayer K and the formation of illite. The
higher abundance of illiteTSA further away from the saprolite exposures supports these
observations.
Conclusions of the ASD Measurement of White Dam Prospect Costeans Spectral analyses of regolith materials collected from the costeans at the White
Dam Prospect were able to identify:
• Regolith materials and stratigraphy on their spectral properties and mineralogy.
• Correlate the mapped regolith profiles with spectral abundance maps.
• A PSA Unit, which was characterised by low: montmorilloniteTSA, carbonates,
kaoliniteTSA, Al-OH IntensityTSG, Kaolinite CrystallinityTSG, Al-OH WavelengthTSG,
goethiteTSA, low Mg- and Fe-OH absorptions features and CFATSA, and medium to
high hematiteTSA.
• A RB Pedal Unit, high: hematiteTSA and illiteTSA, low: kaoliniteTSA, low Mg- and
Fe-OH absorptions features, carbonates, CFATSA.
• A YB Unit, minor: opalTSA, high: smectiteTSG, hematiteTSA, low: TalcTSG,
goethiteTSA.
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• Gravel horizons, High: opalTSA, gypsumTSA, muscoviteTSA, montmorilloniteTSA.
• RCAs, High: dolomiteTSG, Mg- and Fe-OH absorptions features, palygorskiteTSA,
muscoviteTSA and illiteTSA, SWIR/VNIR ReflectanceTSA.
• Grey and pallid saprolite, High kaoliniteTSA, Al-OH IntensityTSG, CFATSG, Kaolinite
CrystallinityTSG, Al-OH WavelengthTSG and goethiteTSA, low: hematiteTSA and low
Mg- and Fe-OH absorptions features.
• Amphibolite derived saprolite, high: nontroniteTSA, jarositeTSA, magnesium claysTSA,
hornblendeTSA, montmorilloniteTSA and can have high Al-OH WavelengthTSG and
goethiteTSA, low hematiteTSA, goethiteTSA, kaolinite, Al-OH intensity, CFA,
Kaolinite Crystallinity, Al-OH WavelengthTSA.
• Pegmatitic saprolite: gypsumTSA and sideriteTSA.
• Albitic saprolite: Fe-tourmalineTSA.
XRD Analyses of the Costean Profiles Samples from selected horizons of costean profiles were chosen for quantitative
XRD analysis to interpret the variation in mineralogy of the different regolith sequences
with depth. A total of eleven profiles were analysed, with between five and eight
samples for each profile. The profile of WDTR02K was selected as an example of the
average mineralogical distribution of the typical materials of the regolith over the White
Dam Prospect. This section of the costean was also sampled by Brown A.D. (2003
pers. comm.) for geochemical analysis.
The profiles from the costeans WDTR01 and WDTR05 represent the regolith
profiles with a greater thickness of transported material and were characterised by the
presence of regolith carbonate mottles. Samples from the profile of WDTR05C
contained regolith carbonate, and were analysed to determine the amount of variation in
mineralogy in these materials. A homogenised sample was collected from the wall of
the costean, rather than the individual accumulations of regolith carbonate in an attempt
to get an average abundance for he horizon. Another prominent feature of WDTR05C
was the presence of lithic gravels between the intervals 0.75 and 2.75 m below the
surface.
XRD Profile of WDTR06
WDTR06D
The costean WDTR06 was situated furthest to the east and possessed a thin
transported cover over a substantial regolith carbonate hardpan, which overlaid variably
weathered saprolite and pedolith. WDTR06D was found to have a very low abundance
I C Lau Regolith Mineralogy
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of kaolin in the PSA Unit (D0), as shown in Figure 5.27. This was reflected by a high
albite and mica/illite content, which was attributed to a greater input of lithic materials
derived from the saprolite exposures on the erosional rise to the south. The surface
horizon also contained an evidently elevated proportion of quartz and orthoclase, as
well as a low amount of smectite. The lack of smectite and kaolin reflects the lack of
alteration of the lithic materials to clays.
Sample D1 (RB Unit) contrasted the overlying PSA Unit (D0) by possessing a
very high abundance of smectite. The proportions of quartz, albite and mica/illite were
much lower than the unit above. The mineralogy was similar to the expected
proportions of the RB Unit, as seen in other profiles throughout the area. The YB Unit
(D4) contained minor amounts of gravely material. This unit possessed a notably lower
abundance of smectite than the RB Unit, as well as higher abundances of quartz,
mica/illite and calcite. The significant presence of the mineral gypsum was also noted
and was thought to be correlated with the occurrence of the gravel layers. The gypsum
minerals occurred as the dehydrated form, bassanite.
Figure 5.27 Quantitative XRD results from selected profiles of costean WDTR06. The intervals of depth are not to scale.
The thick regolith carbonate hardpan at this location was sampled at 1.5 m (D10)
and found to have a similar mineralogy as D4, with a higher abundance of calcite,
mica/illite and kaolin, with lesser amounts of quartz.
Below the regolith carbonate hardpan, the slightly weathered saprolite displayed
a mineralogy of kaolin, albite, quartz and mica/illite, with a small abundance of calcite
Chapter 5
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and the absence of smectite and orthoclase. The saprolite varied from grey-pallid
material to leucocratic-layered pegmatite in Figure 5.27.
WDTR06B
Figure 5.27 shows the PSA material from the top of profile WDTR06B (B0) and
contained a high abundance of orthoclase and a higher amount of kaolin than
WDTR06D (D0). The underlying RB Unit (B1) contains a higher abundance of kaolin
and smectite with lesser amounts of orthoclase, albite and quartz than the overlying PSA
Unit.
The sample collected from 0.75 m below the surface (B3) was immediately
above a thick regolith hardpan. The yellow-brown coloured, blocky textured material
contained abundant regolith carbonate nodules. The mineralogy showed a high
abundance of calcite for this material. Smectite displayed a very low abundance, while
mica/illite was almost the same percentage as the overlying RB Unit. The other
minerals all showed a lower percentage of similar proportions.
Samples B5 and B12 were collected from the grey saprolite. The upper sample
possessed minor carbonate infilling the fractures and displayed as a low abundance of
calcite. The mineralogy consisted of albite, mica/illite, quartz, orthoclase and kaolinite
with minor smectite. The mineral jarosite was also recorded to be present at this
location.
WDTR06A
The upper material of WDTR06A (A0 - PSA) contained a higher abundance of
kaolin and smectite, as well as less orthoclase and albite than the other two samples for
this costean. This trend reflects the increasing distance from the saprolite exposures to
the south and the lesser amounts of lithic material transported by colluvial processes.
The higher kaolin and smectite are indicative of a greater magnitude of weathering of
the minerals. Figure 5.27 shows the RB Unit has a similar mineralogy and proportions
as seen in the other profiles for WDTR06, showing a higher abundance of smectite than
the PSA Unit and a lower proportion of albite and quartz. No calcite was found in the
samples from the upper two horizons.
Sample A3 was collected from similar materials as B3 and displayed a
comparable mineralogy, although with a lower calcite abundance and higher smectite
percentage. Below the regolith carbonate nodules a hardpan overlayed the saprolite.
Samples were collected from the saprolite material (A5) that possessed no calcite
minerals. The saprolite contained a low abundance of kaolin and quartz, with high
I C Lau Regolith Mineralogy
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amounts of orthoclase, albite and mica/illite. A similar mineralogy was found for A8,
with more albite and less kaolin.
A result of interest was the lack of calcite in the XRD results for the PSA and
RB Units in costean WDTR06. Although the thickness of cover was shallow and there
was a large abundance of regolith carbonate at greater depths, no calcite occurred in the
upper profile. A possible explanation involves the presence of the thick regolith
carbonate hardpan that indurated the uppermost portion of the saprolite.
The formation of the hardpan may have occurred through the process of
dissolution of the carbonate from the upper soil horizons by meteoric water, followed by
its reprecipitation at the hydromorphic barrier created by the saprolite. The lateral
transport of ground water carrying materials in solution would also contribute carbonate
minerals.
In the areas where the transported regolith profile is thicker (e.g. the YB horizon
is >1.5 m thick) there is a lesser degree of regolith carbonate induration of the upper
portion of saprolite. Mottles of powdery regolith carbonate occur in the overlying
horizons and in the upper portion of the YB Unit. Regolith carbonate forms sand-sized
accumulations within RB and upper YB horizons. The term ‘pedogenic’ carbonate is
often used by soil scientists to describe these occurrences. The abundance and volume
of this material is minor in comparison to the massive hardpans, as a consequence there
is a lack of spectral signatures of carbonate in the upper portion of the profile.
XRD Profiles of WDTR04
WDTR04D
The costean WDTR04 possessed a shallow transported cover overlying an
indurated hardpan of regolith carbonate. The in situ saprolite and pedolith materials,
occurring below the RCAs, were of variable origin, with pegmatite, amphibolite and
banded-feldspathic gneiss lithologies seen throughout the section.
Comparison of the XRD quantities for the PSA Unit in WDTR04D (Figure 5.28)
found the profile to be unlike the other costeans due to the high abundance of smectite,
albite and the presence of amphibole and calcite. At the surface of WDTR04D (D0) the
mineral amphibole and calcite were found and the abundance of mica/illite was very
low. Below the PSA Unit a thin RB Unit was present (~0.25 m), which overlaid a thick
sequence of indurated regolith carbonate. The hardpan (D3) displayed both calcite and
aragonite carbonate mineralogy, a large percentage of amphibole, smectite and albite, as
well as low abundances of kaolin and quartz. Mica/illite was not present.
Chapter 5
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The hardpan extended to approximately 1 m below the surface, below this depth
carbonate was restricted to infilling of fractures in the pedolith-saprolite material. In
this region (D5) the abundances of materials were much the same as the overlying D3,
although not as weathered. This was reflected in the mineralogy as having a greater
abundance of albite and less clay minerals (smectite and kaolin).
The sample collected at 2 m depth (D8) was found to have no amphibole,
although the XRD results showed a small abundance of gypsum. The mineralogy
lacked orthoclase and quartz, but had more kaolin than the above regions and an
abundance of smectite. The Fe-oxides from this region displayed a goethite-like XRD
pattern. Below this atypical region (sample D11) the abundances of the minerals albite
and amphibole were similar to D5, with a lack of quartz, orthoclase and calcite. The
difference between the horizons was supplemented by mica/illite.
WDTR04CD
The XRD results for the profile of WDTR04CD started at 0.25 m depth with
CD1 (Figure 5.28). The samples mineralogy consisted of predominantly smectite, with
lesser abundance of albite, and quartz. The sample was also composed of minor
amounts of kaolinite, orthoclase, amphibolite and a very small abundance of mica/illite.
Underlying this horizon was the regolith carbonate hardpan (CD2), which displayed a
high percentage of calcite and amphibole. The proportions of kaolin, orthoclase, quartz
and smectite were lower, whereas mica/illite and albite were similar to the overlying
layer.
Amphibolite-derived pedolith/saprolite (CD3) occurred immediately below the
hardpan. The mineralogy was dominated by amphibole, albite and smectite, with minor
calcite, orthoclase and quartz. Kaolinite and mica/illite were absent in this portion of
the profile. Sample CD7 was collected from intensely weathered material at the shelf
section of the costean. This material consisted of pale-yellow-brown clayey pedolith
with a goethititic overprint. The material was found to contain albite, quartz, mica/illite
and smectite, with a very small abundance of amphibole, orthoclase and calcite.
The Fe-oxides were more likely goethite than hematite. Spectral measurements
of the samples showed a strong absorption at 0.9 µm related to the CFA feature of
goethite. The lowest sample analysed (CD12) in the profile displayed a higher
abundance of hematite than CD7. The mineralogy was dominantly albite with lesser
abundances of quartz, mica/illite, smectite, amphibole and orthoclase. Very small
abundances of kaolin were found, and no calcite. The samples CD7 and CD12
contained a high abundance of mica/illite in comparison to the samples higher in the
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profile. A leucocratic layer of pale material was recorded in this region of the costean
while field mapping. These samples may represent a more felsic intrusive, which
consisted of lesser amounts of amphibole and more quartz and mica/illite. The
abundances of orthoclase and albite remain relatively similar throughout the pedolith-
saprolith region and do not vary with the differing materials.
WDTR04BC
An obvious change in the in situ materials was observed in the costean,
prompting a profile to be collected at 6449073 mN (WDTR04BC). The top sample
(BC0 - PSA) contained a very small abundance of amphibole and calcite, with the
mineralogy predominantly quartz, albite and smectite (Figure 5.28). Kaolin, orthoclase
and mica/illite occurred in small proportions. The underlying RB Unit (BC1) displayed
a high abundance of smectite as well as significant amounts of quartz and albite. There
was a higher abundance of kaolin than the PSA material with no amphibole or calcite
present at 0.25 m below the surface.
Sample BC3 sampled the RCA hardpan and displayed a very high calcite
percentage with similar proportions, but lower abundances of the other minerals. The
samples collected below the hardpan displayed a high abundance of albite and
orthoclase, with a lesser abundance of quartz and kaolin. Calcite was found in small but
significant amounts, representing the material found in fractures and joints in the
saprolite. Mica/illite and smectite were found in very small percentages. The profile
WDTR04BC represents a slightly weathered albitic-pegmatite intrusion and contrasts
the lithologies found in the other costeans.
WDTR04A
The thickness of the transported material increased in the northern end of
WDTR04, which contained an abundant amount of lithic gravel. The saprolite and
pedolith in the profile of WDTR04A displayed a high degree of weathering, with little
or no fabric remaining. Layers were defined by bands of pale feldspars, which
remained in the highly weathered examples. The surface sample (A0) displayed a high
abundance of smectite and kaolin (relative to the percentages of kaolin in the other
surface samples), with lesser amounts of quartz, albite, orthoclase and mica/illite
(Figure 5.28). No calcite or amphibole were found in A0.
The YB Unit (A2) displayed a large amount of gravel material and was found to
have a higher quartz and albite abundance than the PSA Unit. The presence of the
mineral gypsum was noteworthy as it also occurred in other costeans where gravels
Chapter 5
- 176 -
were found, and was also identified in the spectral measurements. The percentage of
kaolin and smectite were lower in A2 than the top layer, typical of the YB Unit.
In the lower portion of the YB Unit (A5) there was a higher abundance of
orthoclase, albite quartz and gypsum (7%), with lesser smectite and kaolin. Below this
horizon a thick layer of intensely weathered material occurred, which had been
indurated by regolith carbonate. The mineralogy of the saprolite displayed a high
abundance of kaolin and albite, quartz and mica/illite also occurring in significant
amounts. Orthoclase was found to occur in an unusually small amount, which may be
related to the high abundance of kaolin. Calcite occurred in a small abundance in A8
but was found as a major constituent of the underlying A9 sample.
The lowest sample in the XRD profile for WDTR04A (A9) displayed the highest
abundance of kaolin and lowest percentage of albite. The sample contained lower
abundances of quartz and mica/illite and higher smectite than A8.
XRD Profiles of WDTR01
WDTR01D
Two profiles were analysed from WDTR01 (Figure 5.29). The southern profile
(WDTR01D) contained a typical mineralogy for the PSA Unit (D0) as seen in the other
analysed samples, with the exception of containing a small abundance of calcite. The
RB Unit (D1) contained a high abundance of smectite, with lower quartz and albite.
The horizon contained a slightly higher abundance of calcite and mica/illite. The
sample analysed from 2 m depth, associated with the YB Unit (D8) was collected from
a region containing large carbonate mottles. This was reflected in the XRD results with
an increased abundance of calcite. The sample contained a lesser amount of smectite
and mica/illite than the RB Unit (D2), with higher proportions of albite, orthoclase,
kaolin and a small abundance of the mineral gypsum.
Two samples (D15 and D18) were collected from a grey-pallid saprolite, in the
lower portion of the profile. The mineralogy was dominated by the primary minerals
orthoclase, albite and mica/illite. Kaolin has an increasing abundance in the two
samples and was found in the highest abundance in the lowest sample. The abundance
of smectite was low and calcite is not found. Gypsum was found in the upper saprolite
sample, but not in D18.
Figure 5.28 Quantitative XRD results from selected profiles of costean WDTR04. The intervals of depth are not to scale.
I C Lau Regolith Mineralogy
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Figu
re 5
.28
Qua
ntita
tive
XR
D re
sults
from
sel
ecte
d pr
ofile
s of
cos
tean
WD
TR
04.
The
inte
rval
s of
dep
th a
re n
ot to
sca
le.
Chapter 5
- 178 -
WDTR01A
The PSA Unit (A0) of WDTR01A displayed a similar mineralogy as D0, but
without the presence of calcite, shown in Figure 5.31. The underlying RB Unit
displayed a higher or similar abundance of all minerals except for quartz. The most
noteworthy trend was the increase in kaolin and the lack of increase in smectite, which
was seen in most comparisons of the two horizons. The sample collected immediately
below this at 0.5 m (A2) contained a very high abundance of kaolin, mica/illite and
calcite. This was mirrored with a low abundance of orthoclase, albite, quartz and
smectite.
The sample A9 was collected from a depth of 2.25 m, within the lower portion
of the YB Unit that contained small RCA mottles. There was a lower abundance of
kaolin, mica/illite and calcite, whereas the concentration of orthoclase, albite, quartz and
smectite were higher. The abundance of quartz was significantly higher in WDTR01D,
corresponding to the identification of opalTSA in the spectral measurements. The lowest
sample analysed (A17) contained a moderately high abundance of kaolin, mica/illite,
orthoclase and quartz, although did not contain a significant abundance of albite.
Individual XRD Profiles
WDTR05C
The surface sample (PSA Unit) of WDTR05C (C1) displayed a similar
mineralogy as the average of the samples of the surface grid, with a slightly higher
proportion of mica/illite Mica/illite was absent in the RB Unit, which contained less
quartz and an increase in smectite. Unlike most other RB horizons sampled, there was
an abundance of calcite. The reason for the high percentage of calcite at shallow depths
in this profile was unknown. The layer below the RB Unit contained an abundance of
gravel clasts and displayed a higher percentage of mica/illite, kaolinite, smectite and
quartz, with less albite than the RB Unit and no calcite.
At 2 m below the surface (C8) the profile contained a low abundance of
carbonate material and lithic gravels. The mineralogy was similar to the surface
material with a higher abundance of smectite and hematite. The horizon directly below
(C9) contained small carbonate mottles and had a low abundance of calcite, with less
smectite than C8. The abundance of calcite increased down the profile for the next two
samples (0.5 m), which occurred within the mottled RCA zone. The RCAs contained
an increase in the abundance of kaolinite and mica/illite, with less albite, orthoclase and
quartz. Figure 5.29 Profiles of the quantitative XRD results from the costeans WDTR01, WDTR05 and WDTR02. The intervals of depth are not to scale.
I C Lau Regolith Mineralogy
- 179 -
Figu
re 5
.29
Pro
file
s of
the
quan
titat
ive
XR
D re
sults
from
the
cost
eans
WD
TR
01, W
DT
R05
and
WD
TR
02.
The
inte
rval
s of
dep
th a
re n
ot to
sc
ale.
Chapter 5
- 180 -
The sample C13 was collected 3 m below the surface in the pedolith/saprolite
material that contained carbonate veins penetrating the fractures of the in situ materials.
The mineralogy was similar to the overlying horizons. The materials in this portion of
the profile represent pedolith derived from in situ materials that weathered to clays
(smectite and kaolinite/halloysite). The calcite abundance reflects the regolith
carbonate veins throughout the material.
The abundance of lithic gravels in the middle section of the overlying
transported sediments was shown by the consistent abundances of albite, orthoclase and
quartz, as well as the lack of calcite. The materials in the upper section of the sequence
between the carbonate mottles and the RB Unit were different from the materials of the
YB Unit, found in the costeans to the southeast.
WDTR02K
The PSA Unit displayed high amounts of quartz and albite with low abundances
of smectite, kaolin and mica. No calcite was found in this unit, as demonstrated in
Figure 5.29. In the RB Unit the proportion of kaolin, mica and smectite increased,
whereas albite, orthoclase and quartz decreased. The upper layers of the YB Unit
displayed similar proportions as the RB Unit, with a slightly lower abundance of kaolin
and higher hematite and calcite. At 1.5 m below the surface (K6), a large abundance of
gypsum was found, relating to a region of large carbonate mottles and highly weathered
pedolith. The gypsum-rich sample also contained calcite with a lower abundance of
quartz, smectite and albite than the samples closer to the surface.
The in situ materials displayed a much higher abundance of kaolin and smectite
in the upper regions (sample K10). This was accompanied by a percentage of albite.
The saprolite in this profile displayed an abundance of carbonate veins infilling
fractures. The sample at K14 displayed a high abundance of calcite, with a lower
abundance of quartz, orthoclase and smectite than the samples above.
Discussion of Hematite XRD Results
Throughout the XRD samples there was very little variation in the abundance of
hematite (1 - 3%), with only one location found to have a high abundance (9%). The
lack of variation in the abundance of iron-oxides in the profiles contrasted the results
obtained from spectral methods, which showed a large variation in the absorption
features related hematite and goethite. The cause for the variation is attributed to the
selection of material analysed by each technique. Spectral measurements
interact with the surficial materials in a sample, whereas XRD analysis examines the
I C Lau Regolith Mineralogy
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crystallographic structure of a bulk sample. Surface rinds may exist on grains, which
may be opaque or transparent. Fe-oxides often occur as thin surface coatings on
regolith materials causing a red-brown or yellow-orange-brown colouration where
ferruginisation has occurred. The ferruginous coatings may constitute only a small
abundance of bulk mineralogy and therefore have only small percentages in the
quantitative XRD analysis.
Part 5 Analysis of the Drill Core with the HyLogger
Introduction Sixteen diamond drill core holes drilled over the White Dam mineralisation by
MIM Exploration prior to 1998 were selected for spectral analysis using the CSIRO-
developed Automated Core Logger instrument, subsequently named the HyLogger
(Huntington et al. 2004; Keeling et al. 2004). The location of the drill holes are shown
in Figure 5.30. The HyLogger is a spectral measuring instrument adapted from the
airborne OARS line scanner that has been mounted above a motorised moving table
(Figure 4.28). A line-scanning Charge Couple Device (CCD) camera has been mounted
on the frame to simultaneously record a colour image of the core. Prior to
measurements, the core was cleaned and the depths of each segment were logged. The
depth information was entered into a database that allowed each spectral measurement
to be recorded with a reference of its spatial position, along with the position of the core
in the tray and the tray number. Measurements were taken every one centimetre along
the core over the wavelengths 0.416 - 2.5 µm with a total number of 189 bands.
The spectral measurements and the corresponding depth information were
imported from ENVI into TSG version 4b and analysed with TSA algorithms (Berman
et al. 1999), which estimated the mineral composition. The VNIR and SWIR were
analysed independently, with the output consisting of an estimate of the dominant
mineral and secondary mineral for the two regions.
Presentation of the line-scanned image with accompanying spectral information
allowed the rapid visual evaluation of the entire length of the drill hole. The summary
screen and scatterplots were utilized for the on-screen display and analysis of the results
of the whole drill hole (Figure 5.31). The software facilitates the importation of
accompanying geochemical and geophysical information, which allowed the rapid
assessment of similar mineralogical zones, which may host mineralisation. The digital
Chapter 5
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format also allows the calculation of user specified information extraction formulas
(scalars).
The diamond drill core were selected to gain a perspective of spectral properties
and mineralogy of the regolith, and fresh materials of the White Dam Prospect. A
number of holes had previously been extensively geochemically and geophysically
analysed (Busutill & Bargmann 2003), although only a limited dataset was available for
comparison to the spectral interpretations. The core was transported from Challenger
Geological Services in Edwardstown, South Australia to the PIRSA Core Library at
Glenside, South Australia in September 2003, where it was cleaned, ready for depth
logging. The depth measurements were inputted into the database and each core tray
scanned. The raw data were processed by Mauger, A.J. 2004 (pers. comm.) and the line
scanner images colour balanced. The final exported TSG datasets, tray photos and
ENVI spectral libraries were supplied for analysis and interpretation.
Interpretation Of the sixteen drill cores that were analysed only five consisted of material
extending from shallow depths (Table 5.3). The remaining eleven cores consisted of
previously drilled RC holes which were collared at depth and diamond drilled.
Hole Name Start Depth Finish Depth WD15 2.8 96 WD16 2.7 87 WD17 2.8 94 WD18 2.3 71
Shallow Holes
WD19 2 137 WD29 60 201 WD31 61 185 WD61 104 177 WD69 73 146 WD71 85 157 WD111 150 465 WD176 115 248 WD191 144 198 WD193 136 146.5 WD194 149 198
Deep Holes
WD195 137 196
Table 5.3 Diamond drill holes over the White Dam Prospect selected for HyLogger analysis. Location of the drill holes is shown in Figure 5.30.
I C Lau Regolith Mineralogy
- 183 -
Figure 5.30 Location of the diamond drill holes analysed by the HyLogger core scanner (a). Perspective view (b) and 3D drill hole projections (c) of the White Dam Prospect.
Chapter 5
- 184 -
Shallow Holes WD15 (2.8 - 96 m)
The material at the top of the drill hole consisted of a red-brown pedolith at 2.8
m. The material appears to contain white, rounded nodules of RCA. The minerals
identified by TSA consisted of dickiteTSA, gypsumTSA and pyriteTSA. The presence of
dickite is usually associated with hydrothermal alteration, although it has been alleged
to occur as a weathering product of feldspars (Pontual et al. 1997). The identification of
dickite by TSA, is more likely to be kaolinite or halloysite. The spectral resolution of
the HyLogger instrument is not sufficient to identify the characteristic dickite
absorption features at 1.398 and 2.19 µm (Mauger, A.J. 2004, pers. comm.). The region
from the top of the hole to the depth of 2.882 m, represented a mottled zone, which
consisted of cores of kaolinitic material rimmed by a ferruginous matrix.
Pyrite most likely represents a weak hematiteTSA spectral response that has been
poorly identified by TSA. The VNIR region showed a clear CFA due to the presence of
Fe at 0.952 - 0.963 µm. A similar response was found for the ASD measurements of the
subsurface in situ pedolith material, above the saprolite in the costeans. The costean
samples displayed similar features to the HyLogger data in the VNIR and the SWIR at
0.68 µm, 0.94 µm and 2.206 µm.
Below the mottled zone was a deeply weathered saprolite with little to no fabric
remaining. The region between 2.9 and 3.2 m consisted of friable, crushed core with
sideriteTSA, halloysiteTSA, gypsumTSA and hornblendeTSA mineralogy interpreted by
TSA. The spectra possessed a high SWIR reflectance with a peak occurring at 2.136
µm. Amphibolite occurred at depths of 5.8 – 15.3 in the hole, indicated by the presence
of hornblendeTSA, montmorilloniteTSA, kaoliniteTSA, sideriteTSA, Fe2+ goethiteTSA,
opalTSA and magnesium claysTSA, nontroniteTSA and gypsumTSA minerals.
WD16 (2.7 - 87 m)
WD16 intersected highly weathered amphibolite at shallow depths. The upper
sections of the hole had a similar appearance to the materials of the costeans. Figure
5.31 demonstrates a scatterplot of depth verses identified minerals, showing a spatial
relationship of mineral species and weathering. The colour of the upper saprolite grades
from a brown to red-brown material with very faint fabric to a grey material with red-
brown streaks where the ferruginous layers had weathered. At 3.75 m the weathered
saprolite had little to almost no fabric remaining, and the material was greenish in
colour. The mineralogy suggested that the material was mafic in origin, possibly a
I C Lau Regolith Mineralogy
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weathered amphibolite dyke with a hornblendeTSA, magnesium clayTSA, palygorskiteTSA,
nontroniteTSA and montmorilloniteTSA mineralogy.
Throughout the intervals of hornblende-rich mineralogy, there was a large
abundance of jarositeTSA minerals in the VNIR. The ferruginous red-brown weathering
of the grey layers can be seen to a depth of 18.5 m. From 4 m TSA mineralogy was
mostly ‘aspectral’ with some hornblendeTSA and magnesium clayTSA classes. The
aspectral results represent the inability of TSA to resolve the spectral features of the
HyLogger data due to mixed spectra, low signal to noise or the presence of materials
without diagnostic SWIR absorptions.
The mineral identified as dickite, representing the kaolin group in the upper
profile, occurred until the depth of 3.39 m. At this depth a small zone of carbonate
minerals (dolomiteTSA and ankeriteTSA) occurred and below this layer the mineralogy
was dominated by Mg-OH clays and hornblende. The HyLogger spectra of the mineral
displayed the characteristic deep 2.18 µm absorption of dickite, but was most likely
halloysite, due to its position in the regolith profile. At 9 m the lithology returned to a
banded gneiss, characterised by an increase in the dickiteTSA and kaoliniteTSA content.
The drill core was mostly un-split in the central and extreme lower sections. The
sections that were not split possessed poorly classified mineralogical interpretations due
to poor spectra measurements.
WD17 (Depth 2.8 - 94 m)
Saprolite at the top of the hole was grey with prominent white layers. Minor
ferruginous staining occurred within the bands with some layers appearing to have
weathered to pedolith, where there was almost no remaining fabric. At 4.65 m, the
lighter layers of the saprolite appeared to have a light brown staining with the fabric of
some regions almost completely destroyed. Immediately below the ferruginous stained
interval, at 5 m, the saprolite was mostly grey with light bands overprinted by red-
brown ferruginous staining. At 5.41 m, the staining disappeared and the saprolite
appeared pallid and bleached.
The material graded back into the grey-layered gneiss until 8.17 m, where there
was an interval of pegmatite/granite intrusive of non-foliated rock, which finished as
8.77 m. There were patches of highly weathered ferruginous saprolite within the grey-
layered material until 11.84 m, where the mineralogy became hornblendeTSA dominated.
This marked the start of a thick layer of amphibolite, with minor pale veining. The
amphibolite was variably weathered, with some fresh regions displaying a dark to black
Chapter 5
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colour. The weathered regions appeared a light green or red-brown. Layers of
weathered ferruginous minerals occurred throughout the section.
Figure 5.31 TSG scatter plot of depth versus SWIR mineralogy for the upper 10 m of WD16.
I C Lau Regolith Mineralogy
- 187 -
Below the amphibolite was a pegmatite/granite layer at 19.5 m. The felsic
intrusive layer was pale to pink in colour with dark mineral flecks. The mineralogy
consisted predominantly of illiteTSA, dickiteTSA and kaoliniteTSA. The amphibolite
occurred again at 20.3 m and at approximately 22.5 m, where it was intensely
weathered. The interval displayed almost no fabric and consisted of mostly
montmorilloniteTSA mineralogy. The intensely weathered interval continued to 24.3 m,
where it returned to a grey-layered gneiss. The mineralogy in TSG was classed as
phlogopiteTSA, although on closer examination of the spectra, it was concluded that the
mineral was more likely to be biotite. Biotite displayed weak absorption features and
was difficult to identify.
The light coloured layers were classed by TSA as kaoliniteTSA or dickiteTSA.
This was attributed to the weathering of the feldspars-rich layers to Al-OH minerals.
The fabric was interlayered with red-brown ferruginous bands, which were classifies as
Fe2+ goethiteTSA.
Weathering effects can be seen down to depths of 78 m, where ferruginous and
clayey layers cease to occur. The mineralogy alternates between layered biotite gneiss
and a pale-pink granititic material, with dark mineral flecks. The granitic layers are
predominately illiteTSA or dickiteTSA/kaoliniteTSA. Where the weathering was
sufficiently intense, montmorillonite becomes the dominant mineralogy. Some of the
pale layers were classified as sideriteTSA, although they appear to be feldspar.
WD18 (2.3 - 71 m)
Mineralogy of this drill hole consisted of kaoliniteTSA, illiteTSA, with lesser
abundances of gypsumTSA and sideriteTSA minerals. However, the later two minerals
may be mis-identified by TSA. Significant abundances of muscoviteTSA and
hornblendeTSA were found with nacrite, nontronite and montmorillonite also occurring.
NontroniteTSA and montmorilloniteTSA occurred over similar intervals, especially
between 11 and 15 m. HornblendeTSA occurred between 10 and 31 m. A muscoviteTSA-
rich section occurred between the interval of 26 and 30 m. A small layer also occurred
at 20.5 m. These were related to pegmatite/granite lithologies, whereas the
hornblendeTSA corresponded to the layered gneiss and amphibolite. Difficulties were
found distinguishing between the dark minerals, hornblendeTSA and biotiteTSA.
WD19 (From 2 m to 137 m)
Hole WD19 consisted of an almost complete profile of pedolith-clayey saprolite,
highly weathered saprolite to slightly weathered material, and fresh material at the
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bottom of the hole. The upper portion of the hole had a similar appearance to the
profiles seen in the costeans. The upper section consisted of regolith carbonate material
mixed with saprolite and red-brown pedolith materials. The material below this was a
grey to pale-brown, sandy-clayey pedolith, which used to be intensely weathered
saprolite that had lost its fabric. The degree of weathering decreased down the hole and
at 8.6 m there was the first evidence of fabric. At approximately 18 m the core has a
coherent structure and was not crushed and broken. At 43 m the core was broken up
and powdered, possibly related to shearing.
Deep Holes The mineralogy and properties of the diamond drill holes collared at depths
greater than 60 m below the surface are summarised below. Individual spectral
descriptions of the holes are located in Appendix III. There were at least two distinct
groups of materials observed in the TSA results. The Al-OH minerals consist of
illiteTSA, muscoviteTSA, montmorilloniteTSA, phengiteTSA, and kaoliniteTSA with minor
paragoniteTSA. The other group were Mg- and Fe-OH minerals, hornblendeTSA,
biotiteTSA, serpentineTSA, chloriteTSA, phlogopiteTSA and epidoteTSA. Different species of
chloritesTSA were also seen (Fe, intermediate and Mg-rich), which may relate to
alteration zoning.
Weathering
The minerals were predominantly fresh and unweathered, except in areas where
fracturing was evident. In these regions the core displayed weathered materials such as
kaoliniteTSA, montmorilloniteTSA, magnesium claysTSA and jarositeTSA. These fractured
zones are thought to be related to faulting and shearing that occurs in the region and
have acted as conduits for penetrating fluids. The fluids have resulted in the weathering
of the fresh materials along the broken surfaces.
Intervals of the core appeared a reddish-brown colour on the broken surfaces.
These regions had a kaoliniteTSA SWIR mineralogy and a jarositeTSA/Fe3+ goethiteTSA
mineralogy in the VNIR, which may represent the weathering of sulphides.
Kaolin group minerals occurred throughout the cores to depths of approximately
110 m. Below this boundary ferromagnesian minerals dominated the mineralogy. This
level was estimated as the deepest extent of weathering of the rocks and marks the
saprock-fresh rock boundary. Isolated occurrences of weathered materials occur at
depths greater than 110 m where fracturing occurs, as mentioned above.
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Ferromagnesian Mineralogy
Biotite was found to be difficult to spectrally identify by TSA due to its subdued
reflectance and similar absorption features to amphibole minerals. The abundance of
biotiteTSA and phlogopiteTSA became greater with depth, corresponding to the presence
of the layered biotite-gneiss, which hosted mineralisation. PhlogopiteTSA was found in
greater abundances that biotite.
Dark layers in the line scan image were interpreted as phlogopite and biotite.
Epidote minerals displayed a greenish colouration in the line scan image. The epidote
minerals occurred adjacent to dark, folded layers. The grey and green folded layers had
an epidote-chloriteTSA mineralogy. These contrasted the muscovite-illiteTSA massive to
unfoliated intervals. Layers of pale pink pegmatite occurred throughout the holes.
These intervals contrasted the ferromagnesian minerals, displaying a muscovite-
phengiteTSA mineralogy.
The TSA algorithm had more trouble identifying the mineralogy where the core
was unsplit. Some of the pink leucocratic layers are not recognised in the unsplit core
and had an aspectral classification.
Mineralogical Analyses of the Near-Surface Regolith and the Fresh Basement using the HyLogger and ASD Instruments A comparison of the mineralogy of the fresh and weathered core was performed
to determine the relationship between the deep and subsurface minerals. A comparison
was also made between the material in the costeans, analysed with the ASD, and the
corresponding material from the top of hole material from the diamond drill cores,
measured with the HyLogger instrument.
The mineralogy of the White Dam drill core, at depths greater than 250 m,
consisted of muscovite, illite as well as minor phengite, magnesium chlorite,
intermediate chlorite and epidote. The mineralogy of the intervals above 250 m
consisted of a greater abundances of kaolinite/halloysite, with minor intervals of
montmorillonite. The mineralogy from the surface to approximately 90 m depth
predominately consisted of kaolinite/halloysite with lesser abundances of illite,
montmorillonite and muscovite. Above 90 m there was almost no chlorite, epidote,
biotite, white micas or hornblende, marking the extent of the oxidised zone.
The mineralogy of the material at the start of drill hole WD19 (between 2-5 m
depth) consisted of kaolinite and Fe2+ goethite with minor illite and montmorillonite
(Table 5.4). The surface regolith materials have a red-brown (2 m) colour, which
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grades into a yellow-brown-green (2.5 m), then into a yellow-grey (3 m) and finally into
a grey (6 m) colour, representing the gradation from the transition zone of transported
and in situ clayey pedolith, mottled pedolith, goethitic pedolith and into highly
weathered pallid saprolite. The saprolite becomes progressively less weathered with
depth, although intervals of highly weathered material exist throughout the hole until
approximately 90 m. The mineralogy of WD19 was representative of a majority of the
diamond drill holes from the White Dam Prospect. Where the lithologies were mafic a
different profile was observed. Drill hole WD15 (Table 5.5) represents the mineralogy
of a profile with an amphibolite near-surface lithology.
The mineralogy of the material in the near surface zone measured with the
HyLogger was consistent with the mineralogical interpretations from the regolith
materials in the costeans that were analysed with the ASD (Table 5.6 & Table 5.7).
Although the spectral resolution of the HyLogger was considerably lower than the ASD
and the profiles are not from the exact same locations, there is a good resemblance of
absorption features for similar regolith materials. The kaolinite dominated saprolite
profiles of the HyLogger and ASD were dominated by the minerals kaolinite and Fe2+
goethite, with minor abundances of clays and in the upper region. These clays represent
the pedolith and transported regolith materials.
Depth TSA_A_Min.1 TSA_A_Min.2 TSA_B_Min.1 TSA_B_Min.2 D=2.06058 Gypsum Fe2+Goethite Hematite D=2.28184 Kaolinite Illite Fe2+Goethite D=2.52418 Kaolinite Fe2+Goethite D=2.74544 Kaolinite Fe2+Goethite Hematite D=3.00127 Kaolinite Fe2+Goethite D=3.22780 Kaolinite Fe2+Goethite D=3.24887 Kaolinite Fe2+Goethite D=3.51754 Kaolinite Fe2+Goethite Hematite D=3.74704 Kaolinite Fe2+Goethite Hematite D=4.20536 Kaolinite Fe2+Goethite Hematite D=4.75094 Kaolinite Fe2+Goethite D=5.00381 Kaolinite Fe2+Goethite D=5.24911 Kaolinite Fe2+Goethite D=5.50192 Kaolinite Fe2+Goethite D=5.50704 Kaolinite Fe2+Goethite D=5.75280 Kaolinite Fe2+Goethite D=6.01291 Kaolinite Fe2+Goethite Hematite
Table 5.4 HyLogger Interpretation of Kaolinitic Saprolite Profile from WD19.
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Depth TSA_A_Min.1 TSA_A_Min.2 TSA_B_Min.1 TSA_B_Min.2 D=2.80358 Illite Gypsum Fe2+Goethite Hematite D=2.93970 Illite Gypsum Fe2+Goethite D=3.00418 Hornblende Dolomite Fe2+Goethite Hematite D=3.25493 Hornblende Gypsum e Fe2+Goethite D=3.45552 Hornblende Fe2+Goethite D=3.75642 Hornblende Gypsum Fe2+Goethite Hematite D=4.00761 Hornblende Gypsum No TSA result D=4.25119 No TSA result Fe2+Goethite Hematite D=4.50910 Montmorillonite Dolomite Fe2+Goethite Hematite D=4.75448 No TSA result Fe2+Goethite D=5.00522 Hornblende Gypsum Fe2+Goethite D=5.25597 Dolomite Gypsum Fe2+Goethite Copper Clay D=5.50672 Kaolinite Dolomite Fe2+Goethite
Table 5.5 HyLogger Interpretation of Mafic Saprolite Profile from WD15.
Depth TSA_A_Min.1 TSA_A_Min.2 TSA_B_Min.1 TSA_B_Min.2 D=0.00 Illite Kaolinite Fe2+Goethite Hematite D=0.25 Illite Kaolinite Fe2+Goethite Hematite D=0.50 Montmorillonite Kaolinite Fe2+Goethite Hematite D=0.75 Muscovite Kaolinite Fe2+Goethite Hematite D=1.00 Muscovite Kaolinite Fe2+Goethite Hematite D=1.25 Kaolinite Palygorskite Fe2+Goethite Hematite D=1.50 Kaolinite Muscovite Fe2+Goethite Hematite D=1.75 Kaolinite Fe2+Goethite D=2.00 Kaolinite Fe2+Goethite D=2.25 Kaolinite Fe2+Goethite D=2.50 Kaolinite Fe2+Goethite D=2.75 Kaolinite Fe2+Goethite D=3.00 Kaolinite Fe2+Goethite D=3.25 Kaolinite Fe2+Goethite D=3.50 Kaolinite Montmorillonite Fe2+Goethite D=3.75 Kaolinite Fe2+Goethite Jarosite D=4.00 Kaolinite No TSA result D=4.25 Kaolinite Fe2+Goethite
Table 5.6 ASD Interpretation of a Kaolinitic Saprolite Profile.
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Depth TSA_A_Min.1 TSA_A_Min.2 TSA_B_Min.1 TSA_B_Min.2 D=0.00 Montmorillonite Kaolinite Fe2+Goethite Hematite D=0.25 Illite Kaolinite Hematite Fe2+Goethite D=0.50 Muscovite Kaolinite Fe2+Goethite Hematite D=0.75 Montmorillonite Siderite Fe2+Goethite D=1.00 Nontronite Kaolinite Fe2+Goethite D=1.25 Hornblende Kaolinite Fe2+Goethite Galvanised Fe D=1.50 Hornblende Fe2+Goethite D=1.75 Kaolinite Hornblende Fe2+Goethite D=2.00 Kaolinite Fe2+Goethite D=2.25 Hornblende Fe2+Goethite D=2.50 Hornblende Nontronite No TSA result D=2.75 Nontronite Jarosite D=3.00 Nontronite Palygorskite Jarosite Fe2+Goethite
Table 5.7 ASD Interpretation of a Mafic Saprolite Profile.
The spectral plots corresponding to the mineralogical interpretations in Table
5.4, Table 5.5, Table 5.6 & Table 5.7 clearly show a change in the spectral
characteristics of different regolith materials, representing variation in the regolith
morphology (Figure 5.32 &Figure 5.33).
Figure 5.32 and Figure 5.33 compares near-surface profiles of regolith materials
measured with the ASD and HyLogger instruments. The upper of the two plots is of a
typical profile consisting of surface soil underlain by transported materials, which has
RCA materials in the lower portion of the transported layer. This grades into the highly
weathered in situ material of clay-rich pedolith, which overlies kaolinite-rich pallid
saprolite. The lower plot is from a profile through mafic saprolite. The mafic materials
consist of hornblende, nontronite and kaolinite. Although TSA interpretations of the
mineralogy are slightly different (especially for the mafic minerals) the overall mineral
groups and spectral features are similar for the HyLogger and ASD near-surface
profiles.
The cores analysed by the HyLogger do not contain material from the upper 2 m
of the profile and therefore have less information on transported and pedolith materials
(Figure 5.32). The spectra of the first two samples of the kaolinitic and mafic derived
cores is most probably back fill or RAB material that has fallen down the hole during
the preparation for diamond drilling. This material coincides with transported regolith
and soil and corresponds to the surface material analysed with the ASD (red spectra in
Figure 5.33). The brown spectra represent transported materials which grades into the
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pedolith, shown by the pink spectra. The pedolith from the kaolinite saprolite profile
contains a higher abundance of kaolinite and a lesser amount of montmorillonite. The
pedolith from the mafic profile contains both kaolinite and mafic minerals, shown by
the presence of 2.3 µm absorption features.
Figure 5.32 HyLogger profile of (a) WD DD 19 and (b) WD DD 15.
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Figure 5.33 ASD profiles from (a) quartzo-felspathic derived saprolite and (b) mafic derived saprolite. Samples were collected in 0.25 m intervals down the profile, through the topsoil, transported material and pedolith, into the saprolite. The thickness of the transported cover over the quartzo-felspathic derived saprolite is thicker than the mafic saprolite. An increase in kaolinite crystallinity can be seen down the profile (a) as the samples become less weathered. In the mafic profile (b) the abundance of kaolinite decreases with depth in the saprolite (green spectra) corresponding to the top of the saprolite/pedolith material being more weathered than the saprock.
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The mafic profiles display a decreasing abundance of kaolinite with depth,
representing a decreasing level of weathering. This is shown more so in the ASD
profile than the HyLogger spectra.
Regolith carbonate occurred in the kaolinite derived saprolite profile at the depth
of 1.25 m corresponding to a broad, shallow absorption feature in the 2.3 µm region
(Figure 5.33). This feature was identified as palygorskite by TSA (Table 5.6).
The results of the comparison of the near-surface profiles validate the spectral
characteristics of the HyLogger instrument for identifying common regolith materials
and minerals. The mineralogy is well interpreted by TSG in kaolinised-pallid saprolite
areas, however is less able to differentiate mafic materials. This may be due to the
darkness of the mafic minerals or the lack spectral resolution required to identify the
characteristic absorptions of different mafic minerals.
Conclusions of the HyLogger Spectral Interpretations
The HyLogger demonstrated the mineralogical variability of the materials in the
White Dam Prospect regions. The deep core samples showed that the fresh bedrock
materials predominantly contained ferromagnesian minerals, such as biotiteTSA,
phlogopiteTSA, hornblendeTSA and epidoteTSA, as well as muscoviteTSA. Weathered
minerals were also found at depth including kaoliniteTSA, illiteTSA, montmorilloniteTSA,
Fe2+ goethiteTSA, jarositeTSA and magnesium claysTSA. The weathering of at depths
greater than 100 m was related to shearing and faults, where fractured rock had been
weathered by penetrating water. Mineralisation and sulphides promoted higher rates of
weathering. Ferruginous and sodic alteration was also seen at isolated intervals
throughout the drill core.
In the shallow intervals the spectra of materials, and subsequent mineralogy,
closely resembled those of the costean samples, with dominant mineralogy consisting of
weathered assemblages. Where amphibolite was present the mineralogy consisted of
hornblendeTSA, nontroniteTSA, montmorilloniteTSA, magnesium claysTSA, palygorskiteTSA
and opalTSA. Grey saprolith and pedolith materials were dominated by kaoliniteTSA, Fe2+
goethiteTSA, illiteTSA and gypsumTSA.
In the upper portion of the core (>3.5 m) the presence of regolith carbonate
material was noted with a relative increase in the abundance of carbonate minerals.
Carbonates were also seen in the deeper intervals (>20 m). However, these minerals are
more likely to be related to the bedrock processes and alteration than the formation of
the regolith. The HyLogger results were found to correlate with the costean samples.
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Part 6 Results and Data Analysis of HyMap Imagery
HyMap Mineralogical Maps Processing and Information Extraction
Surface mineralogical maps were constructed from the reflectance-corrected
airborne hyperspectral imagery for a region of similar extent to the soil sampling grid.
The spectral response for each pixel on a 10 m spaced grid was extracted as an ENVI
Spectral Library and recalculated to reflectance in nanometres. An accompanying
spreadsheet was generated with the pixel geocoordinates and the files imported into
TSG version 4b. The same spectral algorithms, as used on the surface and costean ASD
measurements, were applied to the HyMap data and exported for use in ArcView. The
files were gridded using the method described earlier in this chapter for the surface ASD
data and a standard violet to red (low to high) colour table was applied. The pre-
processing and correction of the HyMap data, as well as validation of the spectral
signatures of materials with comparison to ASD measurements is explained in Chapter
6.
Visual Interpretation of the HyMap Imagery
The five metre resolution of the HyMap imagery (Figure 5.34 i) produced a
highly comparable image to the 1.25 m ortho-image (Figure 5.34 v). However, the
HyMap imagery showed a larger contrast between features, which allowed greater
differentiation between the regolith-landform units. Although the three bands displayed
similar wavelength ranges in the RGB images, the HyMap data possessed many more
bands, with smaller bandwidths, which allowed for the better discrimination of spectral
features in the visible region. The HyMap data were georectified to the orthoimagery
using a triangulation method, which displayed only minor distortions of approximately
1 - 2 pixels (5 - 10 m). The drill spoils on the surface appeared prominently in both
images. In the HyMap image, the alluvial plain and saprolite regions had a high
contrast in comparison to the colluvial-dominated regolith units.
Gridded HyMap Mineral Distribution Maps
The gridded results, displayed in Figure 5.34 vi and Figure 5.35 , were found to
primarily identify ferruginous and aluminium hydroxide minerals. A very limited
distribution of green vegetation and carbonate minerals was also identified.
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Figure 5.34 HyMap surface mineralogical maps of Fe-minerals (iii, iv, vii), carbonate and green vegetation (viii). (i) Shows the distribution of pixels used in the analysis and gridding process over a HyMap TCC and (v) displays the ortho-imagery with the surface sample collection points that were measured with the ASD FieldSpec, and the 1:2000 Regolith-Landform boundaries (courtesy of Brown & Hill 2003). The location of the north-south orientated costeans are shown in red. Ratios of spectral parameters (ii &vi) display a slight correlation to the colour of the surficial materials. ‘HyMap’ refers to the abundance of the mineral, whereas ‘TSG’ are calculated from TSA algorithms.
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The SWIR/VNIR Reflectance calculationTSG (Figure 5.34 ii) was found to
highlight pixels that contained drill spoil materials The saprolite in the southeastern
corner and the alluvial units in the northwestern area were found to have low values for
SWIR/VNIR ReflectanceTSG, whereas the colluvial units displayed moderate values.
This pattern may be due to the greater abundance of quartz within these units and the
deeper absorption features for the kaolinite-rich saprolite and alluvial channel. Drill
spoils occurred as bullseye highs throughout the region for different minerals and
indices.
Vegetation and Carbonates
The identification of carbonate at 640150 mE 6449050 mN was a significant
result, as a thick hardpan of regolith carbonate occurred at shallow depths in this region.
The carbonate was associated with a northeast trending amphibolite dyke, which was
found in the costean WDTR04 and WDTR06. The region was covered by less than 1 m
of transported material, which may have allowed some carbonate to be present at the
surface. This region coincided with rabbit warrens discovered during ground truthing.
The warrens were constructed in the soft, friable substrate and overlying RCA hardpan.
The indurated material had been brought to the surface as a result of the excavation.
Figure 5.34 viii shows the areas that were found to have green vegetation and
carbonate spectral features. The presence of vegetation was shown by the green circles
whereas the predicted carbonate occurrences had a purple halo. The pixel that produced
the green vegetation anomaly occurred at the fringe of the depositional and erosional
plains on the western margin of the area. The pixel spectrum possessed a moderately
weak green vegetation feature in the VNIR region. A weaker feature of similar
appearance could be seen for many of the other pixels located in the vicinity of dark
pixels, but were not classed as vegetation by TSA. The dark pixels that occurred in the
alluvial channel at 459800 mE 64492025 mN, were unexpectedly not identified as
vegetation by TSA. Re-examination of the pixels used in the gridding for the process
found the spectra relating to the northwestern corner to contain abundant noise, most
likely representing the shadow component of trees, rather than the green foliage of the
top of the canopy.
Ferruginous Materials
Distribution of the Fe-oxide Abundance IndexTS (Figure 5.34 iii) showed a close
correlation between the bare soil areas (orange-red and yellow regions of (Figure 5.34
i), displaying high values in these regions. The drill spoils demonstrated a low value,
reflecting their grey-blue appearance on the RGB TCC image and lack of
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ferruginisation. The bare soil areas in the colluvial units were related to regions where
surface erosion had occurred and where the vegetation density was low. A clearing in
the central portion of the image at 460000 mE 6449050 mN, is thought to be where a
drill pad and temporary infrastructure was located during drilling. This area has
significantly less vegetation cover than the surrounding regions and therefore a higher
Fe response. Although the alluvial channel has a greater abundance of larger trees, it
generally has less chenopods (Atriplex sp. and Maireana sp.) and cryptogram cover
(lichen, moss, copper burrs and other low vegetation) due to the instability of the
substrate. This results in more areas of bare soil, and therefore, a higher abundance of
Fe-oxide related responses.
The Fe2+ Intensity calculation (Figure 5.34 iv) used similar parameters to the
CFA IndexTSG (not shown) and displayed a relatively different distribution than the Fe-
oxide Intensity IndexTSG (Figure 5.34 iii). The Red Reflectance Peak/CFA Index
(Figure 5.34 vi) produced a distribution that mapped out the darker areas of the imagery,
associated with vegetation. The CHpd5 RLU and the southern portions of CHpd4,
CHep1, Aed4 and CHer2 all displayed low values for this calculation. This was due to
the absorption at red wavelengths by vegetation obscuring the soil materials. The dry
and arid vegetation spectra would also cause a slight increase in the reflectance in the
NIR wavelength region. The presence of vegetation would influence the CFA
wavelength and the intensity of the feature.
The distribution of the mineral hematiteTSA was found to be associated with
portions of the previously mentioned HyMap grids. The central region of the grid
(Figure 5.34 vii) displayed a high abundance, similar to the Fe-oxide IntensityTSG
(Figure 5.34 iii) and a high for the area mapped as a sheetflow dominated depositional
plain (CHpd4). The areas that were suggested to be highly affected by vegetation in the
Red Reflectance Peak/CFA IndexTSG (Figure 5.34 vi) had moderate to low abundances
of hematite. This was attributed to the vegetation denuding the hematiteTSA features.
White Micas and Chlorite/Epidote Distribution
The distribution of smectite (Figure 5.35 i) was found to be similar to the inverse
of Fe-oxide IntensityTSG and phengiteTSA (Figure 5.35 ii). PhengiteTSA was found to be
closely associated with selective drill spoils. The drill spoils highlighted by phengite
are attributed to white mica minerals of the basement and slightly weathered saprolite.
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Figure 5.35 HyMap surface mineralogical maps of aluminium hydroxide minerals and associated parameters. The waste spoils from the diamond drill holes can be seen to display variations in mineralogy, from phengitic (ii) to having more chlorite/epidote (iii). ‘HyMap’ refers to the abundance of the mineral, whereas ‘TSG’ are calculated from TSA algorithms.
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The Chlorite/Epidote IndexTSG (Figure 5.35 iii) was also associated with a
number of the same drill spoils. However, the index also identified numerous locations
separate to the previously highlighted drill spoils (e.g. white mica). The spectra for
these pixels displayed a more pronounced absorption feature in the 2.25 µm region.
Due to the lower spectral resolution of the HyMap imagery compared to the ASD, the
exact cause of this feature cannot be directly identified. The mineralogy was either due
to the presence of Fe-rich mineral, such as chlorite, biotite, phlogopite, or Fe-
substitution in kaolinite. The most likely explanation would be due to the presence of
biotite or phlogopite, as it was one of the primary minerals in the fresh basement and
found extensively in the deep sections of the drill holes examined by the HyLogger.
Kaolinite and Al-OH Indices Distributions
The Kaolinite CrystallinityTSG calculation (Figure 5.35 v) identified many of the
point localities as either bullseye highs or lows. Some of these bullseyes correspond to
the points highlighted in the phengiteTSA and Chlorite/EpidoteTSG images, though there
are a number of new points. The three images suggest that there was a great deal of
variation in the mineralogy of the drill spoils, which may be sampling alternative
lithologies and regolith materials at different depths. The collective results give an
indication that the basement rocks consist of white mica, highly crystalline kaolinite and
biotite (or chlorite/phlogopite).
The occurrence of amphibole minerals in outcrop and the costeans suggests the
possibility of the presence of Mg-OH minerals. This was not seen directly seen in the
HyMap imagery, although the presence of ‘carbonate’ features could be attributed to
hornblende or magnesium clays.
The second Kaolinite CrystallinityTSG calculation (Figure 5.35 vi) did not
identify any high point localities, although there were several distinctive low regions.
The CHep2 and CHpd4 units displayed the greatest area of low crystallinity, whereas
CHpd5 and SSer1 displayed moderate values. The low at 460120 mE 6449000 mN
corresponded to a group of dark pixels in the HyMap data and ortho-image. Ground-
truthing of this locality identified a cluster of western rosewoods along the margins of
the saprolite exposure.
The Al-OH IntensityTSG was found to be similar to the Fe-oxide AbundanceTSG
distribution with the saprolite regions having a low value (Figure 5.35 iv). The alluvial
regions displayed moderately high values, reflecting the lesser amount of vegetation in
these regions.
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The Al-OH WavelengthTSG (Figure 5.35 vii) showed highs for the saprolite
(SSer) and the area adjacent to the alluvial plain (Aap and CHpd3). A number of point
localities with high wavelengths existed in the southwestern portion of the image. From
the SSer there was a gradual decrease in the Al-OH wavelength to the north. This trend
represented a colluvial dispersion pattern of decreasing kaolinite abundance and the
dispersion of material from the drill spoils. The CHfs RLU displayed a slightly longer
Al-OH WavelengthTSG, which may be attributed to the collection of dispersed materials
down slope and into Aed4. The materials in the depression were then transported by
alluvial processes during rainfall events to CHfa and re-deposited. This trend is seen in
the halloysite/kaoliniteTSA abundance map of the region, which has a high abundance in
the RLU corresponding to CHfs (Figure 5.35 viii).
Part 6 Integration of Mineralogical Results and Interpretations of the Regolith Mineralogy of the White Dam Prospect
Figure 5.36 shows a summary of the spectral interpretations of an average
profile from the costeans. The PSA Unit was found to occur throughout most of the
area and displayed similar features to the red-brown materials, but with broader and
shallower absorptions. This was attributed to the higher abundance of quartz and
feldspars, which do not have strong spectral features. The XRD results showed the PSA
unit on average to have high abundances of orthoclase, albite and quartz, with varying
concentrations of smectite and mica/illite.
HyMap spectra were found to have a very close resemblance of the PSA
material, as shown by the blue spectra in Figure 5.36 (a) and (c). The HyMap data were
unable to produce coherent data in the 1.4 µm and 1.9 µm regions due to atmospheric
water (Figure 5.36 b). The presence of Fe-oxides was mapped, although the
discrimination between hematite and goethite could not be determined due to noise in
the HyMap data at diagnostic wavelengths (Figure 5.36 a). The CFA and CTS were
clearly defined in the HyMap imagery with comparable spectral responses to the
laboratory measurements.
Regolith carbonate accumulations were difficult to distinguish using spectral
techniques in both the field spectrometer and the HyMap imagery. The carbonate
nodules from the profiles exhibited kaolinitic absorption features on the outer rind, but
once crushed or dissected displayed carbonate absorptions. When bulk samples were
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measured there was an absence or a minor Mg-OH absorption at 2300 nm, which
coincides with secondary Al-OH absorption features. In general, mixed soil samples
with a higher abundance of RCAs produced spectra of a higher albedo (larger
reflectance %), unless the outer surface of the nodules were completely coated with fine
soil material.
Surface soil samples measured with the ASD FieldSpec showed little variation
in their spectra. Persistent spectral signatures derived from the presence of poorly
ordered kaolinite, muscovite/illite, smectites and hematite. The presence of quartz,
identified by XRD analysis of the soil samples, weakened and diluted the absorption
features. The surface samples displayed a near symmetrical absorption feature at 2.207
µm, related to Al-OH (Figure 5.36 f). An inflection in the reflectance spectra, when
displayed with the hull-quotient removed (continuum removed -see Appendix VII),
occurred on the absorption at 2.156-2.177 µm and 2.227-2.245 µm as a result of the
mixture of clay minerals (kaolinite-illite-smectite) in the soils. The presence of these
minerals was confirmed by XRD analysis of the PSA materials. Water absorptions
occurred at 1.912 µm and 1.415 µm, the latter feature was also related to hydroxyl
features in minerals. The depths of these features can be related to the abundance of
free water interlayered with clay minerals and the distinction of pedolith and saprolith.
In the VNIR regions, the CFA of hematite was clearly definable by a broad
0.896 µm absorption and the CTS varied from 0.584 to 0.600 µm. Shifts in the
wavelengths of these features are related to the size fraction of the Fe-oxides, the ratio
of hematite to goethite, the abundance of opaque minerals and the substitution of Fe2+
and Al3+ (Cudahy & Ramanaidou 1997).
The ASD FieldSpec measurements of the costean profiles exhibited a variation
in spectral properties with depth. The upper samples displayed similar features to the
surface traverse samples, which were termed the PSA Unit. In the areas close to
exposures of saprolite, the PSA unit was only a few centimetres thick. These areas were
mapped as erosional rises (Brown & Hill 2003), demonstrating that slope-angle closely
corresponds with the thickness of material of the upper-most layers for these regolith-
landform units.
Below the PSA Unit a discontinuous transitional layer appears to be a mixture of
the upper-soil and the underlying RB Pedal Unit. The RB Pedal Unit could be
differentiated from the PSA Unit by the deeper 1.415 and 1.912 µm water features as
well as the stronger 2.207 µm absorption, related to the greater abundance of smectite.
This was identified by the XRD analysis, which also noted a lesser abundance of quartz
Chapter 5
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in the RB Unit. The CTS occurred at shorter wavelengths and the CFA was marginally
deeper. A shift in the CTS was observed between crushed peds and unconsolidated
sample material, to longer wavelengths and a more rounded shoulder feature in the hull-
quotient displayed reflectance spectra. This was attributed to the differing grain sizes of
the Fe-oxides (Crowley 1986; Hunt et al. 1971).
In the Al-OH region the 2.229 µm shoulder for pure kaolinite is represented as
an inflection in the right hand side of the peak. In the RB and following units there is an
increase in the depth of the 2.162 µm absorption feature and the presence of a 2.229 µm
shoulder, creating an inflection. An Increase in the depth of 2.169 µm and a decrease in
the 2.229 µm Al-OH absorptions occurs with increasing depth in the profile. The slope
of the shoulders become less smooth with increasingly prominent inflections on both
sides.
The unconformity between the top of weathered saprolite and the lower pedolith
can be determined by the change in crystallinity of the mineral kaolinite. The
crystallinity of kaolinite can be determined by the depth of the 2.162 µm absorption
with well ordered kaolinite possessing a deeper absorption. Poorly-ordered kaolinite is
indicative of pedogenic in situ soils and transported materials. The weathered basement
in the lower portion of the profiles displayed well-crystalline kaolinite spectral
signatures with deep 2.206 µm, 2.162 µm Al-OH absorptions and a 2.229 µm shoulder.
The spectra demonstrated a weak 1.912 µm feature representing a lack of water, and a
1.414/1.399 µm doublet with a lack of Fe-oxide absorptions. The presence of goethite
in the weathered saprolite was distinguishable from hematite by the deep broad 0.990
µm CFA and the presence of a 0.671 µm absorption related to the crystal field splitting
energy.
A change in the absorption features in the 0.400-1.500 µm region due to Fe-
oxides can be used the mark the boundary between the upper soil layer (Post European
unit) and the underlying pedal RB soil unit. The boundary between the basement and
the overlying soil layers can be identified by a change to well-ordered kaolinite
crystallinity as well as a shift in the charge transfer shoulder of Fe-oxides at
approximately 0.600 µm to shorter wavelengths in the saprolite. The presence of the
mineral goethite in the weathered saprolite occurred at various depths, shown by a shift
in the 0.896 µm CFA to longer wavelengths.
I C Lau Regolith Mineralogy
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Figure 5.36 Profile summarising the spectral properties of the regolith materials collected from the costeans at the White Dam Prospect. (a, b, c) A HyMap spectra from a pixel in a PSA dominated region of the White Dam Prospect is shown at the top of the profile as a comparison. Characteristic features were identified for each of the different regolith horizons, allowing the mapping of saprolite, in situ pedolith and three types of transported materials. Differentiation of the in situ materials (g - p) was able to be performed. See text for a detailed explanation of the figure.
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