chapter 5 mineralogy of the regolith - university of...

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

- 132 -

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


- 133 -

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

- 134 -

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

- 136 -

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.


- 137 -

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

- 138 -

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.


- 139 -

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

- 140 -

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


- 141 -

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

- 142 -

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


- 143 -

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

- 144 -

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).


- 145 -

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.


- 147 -

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

- 148 -

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.


- 149 -

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.


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

- 150 -

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.


- 151 -

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.


- 153 -


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.


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

Chapter 5

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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


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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.


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).


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.

Chapter 5

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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.


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.


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.


- 159 -

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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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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- 163 -


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.


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.


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.


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

Chapter 5

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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.


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.


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


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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.


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.


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.


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- 169 -


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.

Chapter 5

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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


- 171 -

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


- 173 -

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


- 175 -

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.


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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

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re n

ot to

sca

le.

Chapter 5

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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.


- 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

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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


- 181 -

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.


- 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


- 185 -

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.


- 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

Chapter 5

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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

Chapter 5

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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.

Chapter 5

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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.

Chapter 5

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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.

Chapter 5

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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.


- 205 -

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.

chapter 5 mineralogy of the regolith - university of...

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