Post on 01-Jun-2020
1935 /&.-o ¢ 4-
BUREAU OF MINERAL RESOURCES, GEOLOGY AND GEOPHYSICS
RECORD
RECORD 1985/20
MINERALOGY AND MAJOR ELEMENT ANALYSIS OF CAINOZOIC SEDIMENTS AT LAKE GEORGE, NEW SOUTH WALES.
by
R.S. ABELL, J.L. FITZSIMMONS AND T.I. SLEZAK
The information contained in this report has been obtained by the Bureau of Mineral Resources, Geology and Geophysics as part of the policy of the Australian Governmept to assist in the exploration and development of mineral resources. It may not be published in any form or used in a company prospectus or statement without the permission in writing of the Director.
(
\ \ \
RECORD 1985/20
MINERALOGY AND MAJOR ELEMENT ANALYSIS OF CAINOZOIC SEDIMENTS AT LAKE GEORGE, NEW SOUTH WALES.
by
R.S. ABELL, J.L. FITZSIMMONS AND T.I. SLEZAK
l
( i )
CON TEN T S
SUMMARY
INTRODUCTION
Geography and climate
Geology
Geomorphology
Modern hydrologic regime
Previous work
CLAY MINERALOGY
Analytical methods
Quantitative aspects
IDENTIFICATION AND DESCRIPTION
ILLITE
Distribution
Origin
KAOLINITE
Outcrop distribution
Distribution in drillcore
Stratigraphy
Origin
MONTMORILLONITE
Distribution
Origin
CHLORITE
Distribution
Origin
1
1
2
4
5
6
7
7
8
10
11
11
11
12
13
13
14
14
15
16
16
18
18
19 V
(i i)
Page
MIXED-LAYER CLAYS 20
Distribution 20
Origin 21
NON-CLAY MINERALS 21
DETRITAL MINERALS 22
QUARTZ 22
Distribution 23
Origin 23
FELDSPAR 23
Distribution 24
Origin 24
AMPHIBOLE 25
Distribution 25
Origin 25
GARNET 25
SECONDARY MINERALS 26
CALCITE AND DOLOMITE 26
SIDERITE 27
GYPSUM 27
BARYTES 28
HALITE 28
IRON OXIDES AND HYDROXIDES 29
Hematite 29
Lepidocrocite 30
(i i i)
RESULTS AND DISCUSSION
CLAY MINERALS
Assemblages and lithostratigraphy
Weathering
Palaeoclimate
Post-depositional alteration
SECONDARY MINERALS AND GEOCHEMISTRY
Carbonates
Evaporites
MAJOR ELEMENTS
Analytical techniques
RESULTS
Significance of the element analysis
CONCLUSIONS
ACKNOWLEDGEMENTS
REFERENCES
TABLES
1. Detection limits of clay and non-clay minerals (after
Carroll, 1970).
2. Distribution of illite
3. Distribution and origin of kaolinite
4. Distribution of montmorillonite
Page
30
30
30
31
31
32
33
33
34
35
35
36
39
41
42
42
(iv)
5. Distribution of chlorite
6. Distribution and origin of mixed-layer clays
7. Factors affecting the lithostratigraphic distribution
of feldspar
8. Clay mineral assemblages and depositional environment of
the Lake George Basin
9. Clay and non-clay mineral distribution in the Lake George
Basin
10. Semi-quantitative distribution of major elements in
drillhole C354
11. Mobility of major elements
12. Factors affecting the occurrence of metals in the Lake
George Basin
FIGURES
1. Lake George basin and drillhole locations
2. Geology of the Lake George Basin
3. Lithostratigraphic units
4. Hydrologic effects of the seiche
5. Composite log of the mineralogy in drillhole C353
6. Composite log of the mineralogy and major elements in
drillhole C354
( v )
7. Provenance of clay minerals
8. Vertical distribution and relationship of kaolinite and
feldspar in drillhole C353
9. Vertical distribution and relationship of kaolinite and
feldspar in drillhole C354
10. X-ray diffractograms for montmorillonite showing
variation in peak character and position
11 . X-ray diffractograms for chlorite
12. X-ray diffractograms for montmorillonite mixed-layer
clays
13. X-ray diffractograms for illite mixed-layer clays
14. X-ray diffractograms for illite-montmorillonite mixed-
layer clays
15. Typical X-ray diffractogram of quartz from clay in the
Bungendore Formation
16. Typical X-ray diffractogram of quartz from sand in the
Ondyong Point Formation
17. X-ray diffractogram of feldspar from sand in the
Ondyong Point Formation
18. Legend for drillholes C353 and C354
SUMMARY
Semi-quantitative clay and non-clay mineral data is reported for over
700 core samples from two drillholes in early Palaeozoic bedrock and
Cainozoic fluvio-lacustrine sequences in the Lake George Basin.
Illite, kaolinite, montmorillonite and mixed-layer clays represent the
main clay mineral groups. The clay minerals which may be detrital and/or
authigenic occur as simple illite-kaolinite and complex illite-kaolinite
montmorillonite-chlorite and mixed-layer clay assemblages. These
assemblages reflect source rock, lithostratigraphic and palaeoclimatic
signatures in the basin. Detrital non-clay minerals are quartz, feldspar
and traces of amphibole. Authigenic minerals are represented by halite,
gypsum, iron oxides and hydroxides, calcite, siderite and traces of dolomite.
The mineralogy results from a complex depositional environment and
post-depositional processes of diagenesis and weathering. Evaporitic
sequences are absent.
Twenty major elements from drillhole C354 were identified by semi
quantitative emission spectroscopy. Initially the elements have been
derived from bedrock in the catchment and then hydrogeochemically dispersed
and concentrated in the lakebed sediments.
INTRODUCTION
Coincident with a drought period, Lake George dried out briefly from
July 1982 until May 1983, providing an opportunity for drilling on the dry
lake bed. A drilling and downhole geophysical logging program obtained
data on a Cainozoic sequence of fluvio-lacustrine sediments overlying
Palaeozoic bedrock. Detail on the drillhole logs, lithostratigraphy and
history of the Lake Geoge Basin are given in Abell (1985).
The core from two adjacent drillholes (C353 and C354) was sampled.
The main objectives of the study were (a) to identify the clay and non-clay
mineralogy of the fluvio-lacustrine sediments and weathering profiles, (b)
determine the distribution of major elements, (c) interpret the clay
mineral assemblages and chemistry.
The analysis and identification of the clay minerals was undertaken by
J.L. Fitzsimmons. The analysis and identification of the major elements
was undertaken by T.l. Slezak. The computer program devised to handle the
chemical data for C354 was developed by R.S. Hill and D.G. Walton of the
computer assisted cartographic group of the BMR drawing office. For
reference purposes the X-ray diffractometer traces are held in the clay
mineralogy section of the BMR Division of Petrology and Geochemistry.
Geography and climate
The Lake George drainage basin is an elongate, meridionally oriented
basin of about 930 km2 within the Southern Tablelands of New South Wales
(Fig. 1). The lake lies at latitude 35°05 1 S and longtitude 149°25 I E, about
40 km northeast of the national capital, Canberra, and about 100 km inland
from the sea. The floor of the lake is about 674 m a.s.l. (above sea
level).
-2-
The present warm, temperate, continental climate over the Lake George
Basin is typified by hot summers and cold winters with altitude moderating
summer and lowering winter temperatures. The mean January and July
temperatures for the nearest meteorological stations - Canberra Forestry
(581 m a.s.l.) and Yass (505 m a.s.l. ) are 20.1°C/21.5°C and 4°C/4.9
respectively (Singh, Opdyke and Bowler, 1981). Prevailing winds are mostly
from west to northwest. The proximity of the basin to the coast mean that
onshore southeast humid sea breezes may reach inland to bring temporarily
cooler or more humid conditions from January to March (McAlpine and Yapp,
1969). Frosts are common in winter, particularly along the sheltered lee
side of the Lake George escarpment. The mean annual precipitation on Lake
George is estimated as 750 mm based on records from two rain gauges in the
catchment at Bungendore and Collector. Precipitation is distributed fairly
evenly throughout the year with a maximum in October (Jacobson and Schuett,
1979). However arid and more humid climates are known to have existed
during the history of Lake George (Coventry, 1976; Bowler, 1982).
Geology
A simplified geological map of the Lake George Basin is shown in
Figure 2. The pre-Cainozoic bedrock geology comprises a thick pile of
marine turbidite sediments of Middle to Upper Ordovician age overlain
unconformably by late Silurian acid and basic volcanics and quartz
turbidite units. The sediments have been invaded by different generations
of Siluro-Devonian acid and basic intrusions. The sequence has been folded,
faulted and weakly metamorphosed by a series of Palaeozoic earth movements
which give a strong meridional trend to the geological structure. Late
Palaeozoic and Mesozoic rocks have not yet been identified in the basin; it
seems unlikely that Permo-Triassic sedimentation extended southwestwards
beyond the confines of the Sydney Basin. Since the Permian the local q
-3-
region has remained sufficiently stable for an ancient landscape to have
developed by the late Cretaceous.
In the Tertiary, the Lake George Basin originated by faulting,
possibly rejuvenating late Palaeozoic faults (Abell, 1985). The Cainozoic
sediments in the basin were deposited in a normal fault-angle basin. The
extent and nature of Tertiary sedimentation is largely obscured by a cover
of Quaternary sediments. Beneath Lake George, drilling has revealed the
existence of more than 150 m of fluvio-lacustrine sediments which have so
far been dated to the late Miocene (Singh et al, 1981; Truswell, 1984;
Abell, 1985).
In an earlier investigation, the Cainozoic sequence in the lake area
was divided into two lithostratigraphic units: a lower Gearys Gap Fomation
and an upper Lake George Formation (Abell, 1985). The amended
lithostratigraphy now shows a threefold division (Fig. 3). The Gearys Gap
Formation is the oldest Cainozoic unit predating the Lake George basin.
The Ondyong Point Formation is a fluvio-lacustrine unit representing the
oldest sediments in the basin. The Lake George Formation has been renamed
the Bungendore Formation in accordance with the reservation procedures of
the Stratigraphic Nomenclature Committee. These units will be defined and
reported in the geology of the Canberra 1:100 000 sheet (Abell in
preparation). Pre-basin sediments in this report are defined as sediments
existing prior to the formation of the Lake George Basin. Basin sediments,
fill or sequence are sediments deposited during the formation of the basin.
The Gearys Gap Formation consists of deeply weathered fluvial sand and
gravel with minor silt and clay. These early Tertiary? deposits were laid
down unconformably on Palaezoic bedrock, burying a palaeotopography incised
into bedrock and the remains of a prior drainage system which originally
flowed northwest. The oldest unit of the basin sequence is the Ondyong l 0
-4-
Point Formation. This unit consists of fluvial sand and lacustrine clay
and silt deposited disconformably on deeply weathered pre-basin sediments.
The Bungendore Formation comprises lacustrine clay and silt. The two basin
units appear conformable and are separated by a laterally persistent layer
of sand and silt. They represent deposition in a closed drainage basin
where lithofacies is largely a function of climatic change. Preliminary
palynology by E.M. Truswell (in Abell, 1985) dates the lake sediments to
the late Miocene.
Quaternary sediments are recorded by colluvial deposits which have
accumulated on the flanks of hills and along the Lake George escarpment.
Lagoonal, lacustrine and aeolian deposits formed near the strandline.
Ancient beach lines up to 37 m a.l.b (above lake bed) testify to some very
large fluctuations of water level in prehistoric times. Above this height
the lake would overflow through Gearys Gap into the Yass drainage system
(Coventry, 1976). Since the Pleistocene, alluvial deposition has continued
along major streams draining towards Lake George. With the advent of
European settlement in the 19th century, land clearing, gully erosion and
sand mining have modified natural land forms in the basin.
Geomorphology
The Lake George Basin is a small tectonic depression representing a
base level of internal drainage. The basin margin is defined by the
topographically subdued watershed of the Great Divide in the east and the
Lake George range to the west. At its northern and southern limits, the
margin comprises a subdued topography with low saddles, a complex of
natural and artificial drainage lines and swampy lagoonal areas. Within
the basin topographic relief commonly ranges from 680-900 m a.s.l.
-5-
Streams in the basin occupy wide open valleys in their upper reaches.
They converge towards Lake George by meandering across flat alluvial plains
and embayments. Morphotectonic evidence of faultline rejuvenation is
demonstrated by the disrupted headwater system of the Yass river as
indicated by elevated river gravels, the remnant of a broad topographic
expression at Gearys Gap and the barbed drainage of creeks flowing into the
northern end of Lake George (Taylor, 1907; allier, 1978; Abell, 1985).
Modern hydrologic regime
Lake George is an outstanding example of a lake in a closed drainage
basin. It is estimated that the lake, when full, constitutes about 16% of
the total area of the drainage basin. Several creeks and watercourses
converge towards the lake; Collector from the north, Alliagonyiga, Taylor
and Butmaroo from the east and Turallo from the south (Fig. 1). There is
little direct runoff to the lake from the escarpment on the western side of
the basin. Jacobson and Schuett (1979) have estimated from a water balance
study that 50 m3 /year enters the lake from runoff.
Lake George is a shallow body of water which shows large fluctuations
in level and salinity which are mainly attributable to relative changes in
rainfall and evaporation. The hydrograph for Lake George is one of the
oldest and most continuous water level records in Australia (Russell 1886).
In historic times the lake has shown marked seasonal fluctuation in water
depth and area. Over longer but less frequent periods, changes in the
regional rainfall pattern has caused the lake to dry out (Jacobson &
Schuett, 1979). Over the last 167 years (1818 to present) the hydrographic
record shows that the water depth in Lake George has rarely passed 6 m and
as far as is known has not exceeded 7.5 m. Commonly its depth is between
1.5-4.5 m and its area 130-160 km 2•
-6-
When the lake is about 4 m deep, the water is considered fresh
(approx. 300 mg/l TDS) but as depth and volume decrease the water becomes
progressively more saline with sodium chloride (Nacl) the dominant dissolved
salt. A major problem associated with Lake George is the dispersion of
salt. A lake of this size which has existed since the Tertiary should have
accumulated large amounts of salt. Lack of surface salts suggests their
removal from the lake by deflation (Jacobson et al~ 1979) or an interchange
of salt between the lake and the groundwater system (Singh et al, 1981).
The lake has a seiche which is induced by northerly or southerly winds
spreading thin sheets of water across the lake bed (Burton 1972). This
type of water movement gives visible changes in water level and area
leading to water losses by increased evaporation or in filtration (Fig. 4).
Torgersen (1984) notes that seiche movements are a necessary consideration
in the estimation of water and salinity budgets. Other wind-induced
movements on the water surface cause turbulence and current systems.
Bottom sediments are disturbed and fine muddy sediment of often carried in
suspension.
Little is known about the groundwater regime in the basin. At this
stage it is assumed to be a closed system and mimic to some extent the
surface water hydrology (Abell, 1985).
Previous work
Data is sparse on the clay mineralogy and geochemistry of the
sediments in the Lake George Basin.
White clay deposits at Bungendore have been sampled to assess their
suitability in the manufacture of bricks (Gibbons & Bunny, 1963). X-ray
diffraction showed the clay contained quartz, kaolinite, sericite and I~
-7-
traces of feldspar and chlorite.
Coventry (1967) took 29 soil samples from a series of soil
stratigraphic units in the Shingle House catchment immediately west of the
Lake George escarpment. The assemblage of clay minerals was kaolinite,
illite and chlorite; montmorillonite was not identified.
At the northern end of Lake George, Singh et al (1981) report
geochemical data for the upper 11 m of the lacustrine sequence in ANU
drillhole LG4.
CLAY MINERALOGY
Analytical methods
Two drillholes (C353 and C354) in the central portion of Lake George
(Fig. 1), were sampled for mineral analysis. Two hundred and thirty -one
samples were taken from C353 and four hundred and eighty-three samples from
C354. The core from C354 was selected because it was the deepest hole and
had the best recovery. An adjacent drillhole (C353), one kilometre to the
east was sampled for comparison. Cylindrical samples of core weighing 3-4
gms were taken at 25 cm intervals where recovery, lithology and state of
core permitted. Prior to sampling and to avoid contamination, the core was
sliced thinly along its length to remove a surface coating of drilling mud.
In C353 samples covered a depth range of 1.3-149.0 m and in hole C354 0.25-
168.0 m.
Clay minerals were ientified by X-ray diffraction using a Philips PW
1010 generator with a PW 1050/25 goniometer. The analysis was undertaken
on a smear of a natural sample mixed with alcohol and mounted onto a
stainless steel slide; a size fraction was not selected. A 40kV/20mA
stabilised power source irradiated a Cu/Ni source to produce X-rays. The
operating details required a time constant of 4, collimator slits of widths I~
-8-
1°, 0.2°, 1°, a scanning speed of 1°/min, a chart speed of 10mm/min and a
vertical chart scale of 4 x 102 c.p.s. (counts per second). The clay
minerals were only X-rayed in detail from 4-15°2t; similar detail on
rational sequences of secondary diffractions beyond 15°2t is unavailable.
Thirteen samples were selected from hole C353 for tests to confirm
illite, kaolinite, montmorillonite and chlorite. In these tests another
portion of the core plug was sampled and a smear of the sample was mounted
on two stainless steel slides. One of the slides was heated with ethylene
glycol for two hours at 60°C (glycolation) and then X-rayed from 4-15°2~at
room temperature. The other sli~e was heated for a series of two hour
periods at temperatures of 110°C, 300°C, 600°C and 750°C. After each
temperature interval this slide was also X-rayed from 4-15°2tat room
temperature.
Quantitative aspects
The clay and non-clay mineralogy is depicted in a semi-quantitative
manner as shown in drillholes C353 and C354 (Figures 5 and 6). An estimate
of the relative abundance of some minerals was made by measuring and
comparing the intensities of basal diffraction peaks above background
levels. Following this approach, an arbitrary division of peak intensity
for illite and kaolinite is given below:
Trace - small poorly defined peak less than 20 mm height.
Minor - distinct but moderate peak 2-35 mm in height.
Major - strong peak greater than 35 mm in height.
In the case of montmorillonite measurement of peak intensity was not
attempted; an arbitrary division is taken to be:
-9-
Minor - some definite indication of presence i.e.:
broad shouldered hump.
Major - definite broad peak.
In other clay mineral groups such as chlorite and mixed-layer clays,
semi quantitative categories were not applied and the minerals are shown as
present or absent.
Quartz is always present. In clays,quartz in minor quantities is
usually marked by two major peaks at 26.65°2&and 20.8°2&-. In silty and
sandy layers it is depicted in larger quantities where XRD traces show
subsidiary peaks between 36.5-55°2&.
Feldspar is given an arbitrary division into three categories:
Trace - some definite indication of presence ie. poorly
defined peak.
Minor - a distinct peak not greater than 40 mm in
height.
Major - a strong peak greater than 40 mm in height.
Other non-clay minerals were not quantitatively categorised as peak
intensities were poorly developed. These minerals are shown as being
present or absent.
In drillhole LG4, gypsum, carbonates (calcite and magnesite carbonate)
and halite are known to occur in the upper 11 m of core (Singh et al,
1981). Their geochemical analysis shows gypsum averages 0.15%, carbonates
2% and halite not less than 0.5%. X-ray traces for the top 11 m of
drillholes C353 and C354 show these minerals are unevenly distributed.
Assuming they have similar percentage levels to those quoted for LG 4, then
quantities below 1% are probably beyond the detection limits of XRD., The
-10-
sporadic occurrence of gypsum suggests limits of 2-3%. Table 1 lists some
of the lowest identifiable percentage levels of clay and non-clay minerals
reported in the literature.
MINERAL LOWEST % I DENTI F IABLE
Kaolinite 5%
Illite 5%
Montmorillonite 10%
Mg Chlorite 1%
Fe Chlorite 10%
Feldspar 5%
Calcite 5%
Dolomite 1%
Hal ite 5%
Table 1. Detection limits of clay and non-clay
minerals (after Carroll, 1970).
IDENTIFICATION AND DESCRIPTION
The clay minerals were recognised by their characteristic basal
spacings corresponding to X-ray diffraction maxima as outlined in Carroll
(1970). The clay mineral assemblage identified consists of illite,
kaolinite, montmorillonite, chlorite and mixed-layer clays. A summary of
the distribution of clay minerals in drillholes C353 and C354 is given in
figures 5 and 6.
-11-
ILLITE
A 2:1 layered potassic-rich clay mineral that is closely related to
the micas (muscovite and sericite). Illite is easily identified on the
X-ray diffraction chart by a strong, sharp, first order basal peak (001) at
about 10Ao (8.8°2&). Illite was confirmed by maintenance of the (001) basal
peak after heating to a temperature of 750°C.
Distribution
The relative abundance of illite and its association with kaolinite
assists in defining lithostratigraphic units in the Lake George Basin
(Table 2). In the deep weathering profile, illite is preserved in
ferruginous bedrock but is subordinate to kaolinite in zones of leached
sand and gravel in the Gearys Gap Formation. Illite is abundant in clay
and silt of the basin sediments (Ondyong Point and Bungendore Formations).
Origin
Illite is a detrital clay mineral derived by weathering and erosion of
late Ordovician and Siluro-Devonian turbidite sequences outcropping in the
lake catchment. Lesser sources of illite come from the weathering of
potash feldspar in acid volcanic and granitic rocks (Fig. 7).
The retention of illite in the basin sediments is attributed to the
stability of muscovite and sericite in the weathering and erosion cycle.
Illite degrades to kaolinite by removal of K+ ions in leached zones of the
deep weathering profile. Illite tends to to be preserved in alkaline
environments. Water analyses from Lake George give average pH values of
8.6 (Jacobson and Schuett, 1979).
-12-
STRATI GRAP H I C ILLITE ILLITE/KAOLINITE COMMENTS
UNIT ASSOCIATION
BUNGENDORE Major I ) K FORMATION
V')
I-z LLJ ONDYONG Illite ::E: ...... POINT Major I > K locally C\ LLJ FORMATION subordinate V')
z to kaolinite ...... at 69.7-73.5m V')
c:t (C353) and lXl
75.8-81.5m Top deep weathering profile (C354).
---- --------------- ---------- ------------------- -------------GEARYS GAP Variable
V') FORMATION (trace I < K III ite l- to degraded to z LLJ minor) koalinite in ::E: ...... leached C\ LLJ zones; V')
z preserved in ...... ferruginous V') c:( bedrock. co
I LLJ 1..-..-._ .A._ 0::: ".. ~~ ~~- -0...
BEDROCK Major I > K
Table 2. Distribution of illite
KAOLINITE
A stable 1:1 layer type clay mineral. Kaolinite shows a strong first
order basal peak (001) at 7Ao (12.6°2t). The peak is somewhat broader than
for illite. Kaolinite was confirmed by a collapse of the (001) peak when
samples were heated to 600°C for two hours. Hallyosite (a member of the
kaolinite group) has a similar (001) basal spacing to illite at 10Ao
(8.8°2&). This mineral is normally distinguished from illite by a shift in
its peak from 10Ao to 7Ao on heating to 110°C. It was concluded that
hallyosite was absent since the peaks for kaolinite and illite were
unchanged when samples were X-rayed after heating at this temperature.
-13-
Outcrop distribution
White and pale grey kaolinitic clays occur in any rocks e.g. quartz
turbidite sediments, outcropping in low relief areas of the Lake George
basin (Figure 7). Leached slates of Ordovician age are exposed in railway
cuttings near Bungendore railway station (MR 225/958)*. Several shafts
sunk to investigate the economic potential of the clay show it extends more
than a kilometre south of Bungendore and to a depth of more than 20 metres
(Lloyd 1960, Loughnan 1960 and Gibbons and Bunny, 1963). Kaolinitic clays
are also exposed in a deep weathering profile on the watershed seperating
the Lake George and Molonglo drainage systems (Abell, 1985). Kaolin is
present in strongly leached Silurian shale and sandstone. The deposits are
currently worked in brick shale pits south of Woodlands HS, close to the
Bungendore - Hoskinstown road at MR 210/870. Similar outcrops occur in a
disused brick shale pit close to the Bungendore - Queanbeyan railway line
at MR 225/958.
Comparable kaolin deposits have been investigated in the Goulburn -
Bungonia area. The clays in this area are typical of well ordered residual
kaolin as they plot between 0.7-1.3 on Hinckleys crystalline index (Baker
and Uren, 1982).
Distribution in drillcore
Kaolinite is generally abundant in bedrock and overlying fluvio
lacustrine sediments. The vertical distribution of kaolinite for
drillholes C353 and C354 is shown by a plot of peak intensity heights on
the (001) basal spacing at 12.60 2& (Figures 8 and 9).
*Map references given in the text refer to the Canberra 1:100 000
topographic sheet No. 8727.
-14-
In the pallid zone of the deep weathering profile kaolinite is the
dominant clay mineral. The uniform distribution of kaolinite in this
profile is well displayed by C354. The distribution is unrelated to
lithological change and reflects a residual origin from the degradation of
feldspar and other clay minerals.
Kaolinite is unevenly concentrated in basin sediments above the deep
weathering profile. Local concentrations are denoted by a grouping of high
peak intensities in hole C353 at 40-45 m and 68-72 m and in hole C354 at
30-32 m and 47-53 m. Kaolinite tends to be less abundant in some of the
coarse sandy layers in the Ondyong Point Formation.
Stratigraphy
The relative abundance of kaolinite, cystallinity index (CI) and
association with illite assist in defining lithostratigraphic units (Table
3). The commonly used "half peak width/peak height" is appropriate enough
to define a crystallinity index for kaolinite as an aid to characterising
the stratigraphy. Other methods such as Hinckleys Index (Baker & Uren,
1982) were not used as the clay minerals were only analysed in detail over
the 4-15°2~range.
Origin
Prior to basin formation kaolin formed as a residual clay mineral by
alteration of feldspar in weathered shale, granitic rocks, acid volcanics,
acid porphyries and fluvial sands and gravel of the Gearys Gap Formation
(Fig. 7). In the basin sediments, kaolinite was deposited as a detrital
clay mineral (recycled or transported kaolin) by weathering and erosion of
pre-existing kaolinised bedrock in the catchment bordering Lake George.
The formation of kaolinite deposits by weathering is favoured by humid
climate, acidic weathering conditions and good drainage allowing leaching
-15-
of soluble products. Residual kaolin formed under these conditions is well
ordered and crystalline (Baker & Uren, 1982).
When the Lake George Basin was formed in the Miocene, kaolinitic
bedrock was uplifted in marginal areas of the catchment. Kaolin was
weathered out and transported downslope towards the depositional area of
Lake George. According to Baker and Uren (1982), detrital kaolin formed in
this manner will be disordered and poorly crystalline.
Drillholes on the lake bed and alluvial plains bordering the lake show
the subsurface preservation of the full thickness of the deep weathering
profile (Abell 1985). This profile has been protected from erosion by a
cover of late Tertiary-Quaternary fluvio-lacustrine sediments.
STRA TI GRAP H I C KAOLINITE CRYSTALLINITY COMMENT ORGIN UNIT INDEX (C I)
BUNGENDORE Major Uniform Some FORMATION (ave. 0.05) kaolinite
(/) residual in
I- weathering Detrital Z W profil es; (disordered) ::E ........ less abundant Cl W ONDYONG Variable Variable in coarse (/)
Z POINT (trace to clastic
........ FORMATION major) sediments (/) c::( co
Top deep weathering profile ---- ----------- ----------- ----------------- -------------- ------------
Z GEARYS GAP Major Uniform Residual ....... (/)
(/)1- FORMATION (ave 0.025) (ordered) c::(Z COW
iA.. ...... ,.._~ .::E ........ Wcl 0:: W BEDROCK Major o..(/)
--Table 3. Distribution and origin of kaolinite
MONTMORILLONITE
A 2:1 layered magnesian-rich clay mineral belonging to the smectite
group with well known cation exchange properties.
-16-
Montmorillonitic clays display a broad range of peaks from 11-17Ao
(8.5-5.2°2$-) corresponding to the (001) basal spacing. Sharper peaks in
this range at about 12.4Ao (7.1°2~) indicate sodium montmorillonite and at
15°A (5.7°2&) may indicate the presence of calcium montmorillinite or
sodium montmorillonite with 2 water layers (Deer, Howie & Zussman, 1966).
Montmorillonite was confirmed by an expansion of the crystal lattice to
17Ao (5.2°2.) after glycolation. When heated to 300°C to remove the
interlayer water, the 11 -17Ao peak disappeared. The peak shift to 9 - 10Ao
(9.8°-8.8°2&) sometimes enhanced the illite peak. Examples of X-ray
diffractograms for montmorillonite are shown in Figure 10.
Distribution
Montmorillonite is commonly distributed in lacustrine clays of the
basin sequence. In the top 74 m of hole C353 and top 71 m of hole C354,
montmorillonite may occur in major quantities. Minor amounts are found in
fine to coarse grained clastic sediments and in association with
intermittent ferruginous weathering profiles (Figures 5 and 6). The
relative abundance of montmorillonite assists in characteristising
stratigraphic units (Table 4). It is a common clay mineral in the Bungendore
Formation and in clays of the Ondyong Point Formation. Montmorillonite is
absent from deeply weathered pre-basin sediments and bedrock.
Orgin
Montmorillonite maybe derived by weathering of basic igneous rocks.
Intrusive rocks of the Lockhart basic complex, numerous dolerite intrusions
and the Currawang Basalt provide sources of plagioclase, pyroxene and
amphibole (Fig. 7). Montmorillonite can form by the weathering of these
minerals which are rich in Ca and Na ions but deficient in K ions.
Montmorillonite may be a primary detrital mineral in the lacustrine clays
-17-
of the basin sequence. However authigenic montmorillonite in the lake
sediments is favoured by high silica and cations, poor leaching and
drainage conditions, and neutral to alkaline pH.
Decrease or absence of montmorillonite in some ferruginous weathering
profiles has been recorded in hole C353 at 21.25-29.75 m; 62.5-66.0 m
and in hole C354 at 4-6.5 m; 16-18.75 m and 25-32.5 m. Weathering and
leaching (desilicification) converts montmorillonite to kaolinite (allier
1984). A similar conversion has been documented for the Morney deep
weathering profile in the Winton Formation of southwest Queensland (Senior
1979) .
STRA TI GRAPH I C MONTMORILLONITE COMMENT UNIT
BUNGENDORE Major (/')
I-FORMATION
z LlJ Degraded to 2: ......... kaolinite in 0 LlJ ONDYONG Variable weathering (/')
z POINT (Minor and major) profiles .........
FORMATION (/') <:::( 00
Top deep weathering profile ---- ------------- ---------------------- ----------------z (/') GEARYS GAP ......... I-
FORMATION Absent (/') z <:::(LlJ
(trace) 002: -_.-.- ........... I ......... 'V,... ___ _
LlJ 0 0:: LlJ
BEDROCK 0... (/')
--Table 4. Distribution of montmorillonite
A post-depositional origin for some of the montmorillonite is
suggested by its close association with mixed-layer clays. Sodic and
calcic montmorillonite may form by cationic exchange processes during
silification.
-18-
CHLORITE
A 2:1 layered clay mineral with a structure closely resembling the
micas. Its identification is often obscured by the presence of the broader
peaks of montmorillonite and montmorillonitic mixed-layer clays. Chlorite
was distinguished from montmorillonite by the detection of a sharp (001)
basal peak at 14Ao (6.3°2t). Examples of X-ray diffractograms for chlorite
are shown in Figure 11. Attempts to confirm chlorite by glycolation and
heating tests were unsuccessful. Difficulty reproducing the sharp basal
peak in these tests may have been influenced by mounting procedures or
absence in repeat samples. The position of the (001) basal peak is similar
to vermiculite. However indentification of chlorite is preferred as it is
an abundant constituent of Palaeozoic rocks outcropping in the catchment.
Distribution
Chlorite is most common in the lacustrine clays of the basin sequence.
Its distribution follows a similar pattern to montmorillonite and
associated mixed-layer clays, but it is less abundant and more random in
occurrence. Chlorite is confined to the upper 70.5 m of hole C353 and
upper 77.75 m of hole C354 (Figs. 5 and 6). The distribution of chlorite
helps to substantiate the lithostratigraphy of the basin. It is common in
the upper 16 m of the Bungendore Formation. Concentrations of chlorite
near the bottom of this formation (41.5-46.75 m in hole C353 and 46.75 -
53.00 m in hole C354) provide a possible means for stratigraphic
correlation. Sporadic chlorite occurs in clays of the Ondyong Point
Formation. Chlorite is absent from deeply weathered pre-basin sediments
(Table 5).
-19-
Origin
Chlorite is a common mineral constituent of basic and acid igneous
rocks. It is formed mainly by the alteration of ferromagnesian minerals
(biotite, amphibole and pyroxene). Chlorite is also derived from low grade
regionally metamorphosed (greenschist facies) argillaceous sediments in
turbidite sequences (Fig. 7).
Chlorite is primarily a detrital clay mineral in the fluvio-lacustrine
sediments of the basin. Diagenetic chlorite may form as an authigenic
mineral in close association with montmorillonite and mixed-layer clays if
there is sufficient availability of Fe and Mg ions in the sediments.
STRATIGRAPHIC CHLORITE COMMENT UNIT
BUNGENDORE Commonly Stratigraphic FORMATION present indicator at
V) base of I-z formation \.J.J :E: 1-1 CI \.J.J V)
ONDYONG z POINT Sporadic 1-1 V)
c:t: FORMATION o::l
Top deep weathering profile ---- ---------------- -------------- --------------------zv) GEARYS GAP 1-11- FORMATION Absent V) z c:t:\.J.J o::l:E: -. _.A. .... _ .....
I 1-1 ----,.. ... ~
\.J.J CI O::L1J BEDROCK c.. V)
--Table 5. Distribution of chlorite
-20-
MIXED-LAYER CLAYS
These are clays in which certain clay minerals are regularly or
randomly interstratified. In the Lake George Basin, mixed-layer clays are
divisible into (a) montmorillonite mixed-layer clays and (b) illite mixed
layer clays (degraded illite). Gradations between these two types are
illite - montmorillonite mixed- layer clays. X-ray traces of these clays
do not show well defined peak intensities but are recognized as areas of
higher intensity background over wide 2tranges. Examples of the three
types of mixed layering are given in Figures 12, 13 and 14.
Montmorillonite mixed-layer clays appear as a broad zone of peak
intensity between 17.6Ao (5°2.) and 11.1Ao (8°2&). Small subsidiary peaks
often occurring in this zone indicate a large proportion of the mixing is
due to various forms of montmorillonite and chlorite.
Illite mixed-layered clays are characterised by a narrow shoulder on
the low 2~ side of the illite peak between 10Ao (8.8°2~) and 11.1Ao (8°2&).
Distribution
Illite mixed-layer clays are common in the deeply weathered pre-basin
fluvial sediments and bedrock. In hole C354 these clays have a fairly even
distribution which appears to be more or less independent of lithology.
The restriction of these clays in hole C353 is probably due to poor sample
recovery.
Montmorillonite mixed-layer clays are unevenly distributed in fluvio
lacustrine sediments above the deep weathering profile. They are markedly
reduced in the Ondyong Point Formation which has a high proportion of
coarse grained clastic sediments, but most common in the lacustrine clays
and silts of the Bungendore Formation.
-21-
The lithostratigraphic distribution of mixed-layer clays is summarised
in Table 6.
Origin
Mixed layering reflects the adjustment of clay minerals to post-
depositional processes. The availability of Fe, Mg, Al, Ca, K and Na
cations in the lacustrine sediments ensures that clay minerals with cation
exchange properties will revert to mixed-layer complexes.
In the deep weathering profile clay mineral assemblages are more
stable and there is less tendency to form mixed-layer complexes. Illite
has low exchange capacity and kaolinite is a stable 1:1 layer clay mineral.
STRATIGRAPHIC MIXED-LAYER ORIGIN UNIT CLAYS
BUNGENDORE Montmorillonite FORMATION type
V') with Diagnetic I- subordinate z w illite-montmorillonite :a: ...... type Cl w V')
z ONDYONG ...... POINT V') c::( FORMATION co
Top deep weathering profile ---- ---------------- ------------------------ --------------
GEARYS GAP I11 ite ~~ FORMATION type Diagnetic ~~ .- .... ~ ... --~---'f~
~ ................ ~--v .... w Cl BEDROCK 0::: W Cl.. V')
--Table 6. Distribution and origin of mixed-layer clays.
NON-CLAY MINERALS
The non-clay mineralogy may be divided into two major groups:
Detrital minerals introduced during the deposition of the
fluvio-lacustrine sediments (allogenic minerals). These are
-22-
quartz, feldspar, amphibole and trace minerals such as garnet .
. Secondary minerals formed at the time or shortly after
deposition of the sediments (authigenic minerals). These are
carbonates (calcite, dolomite and siderite), evaporites (halite,
gypsum and traces of barytes) and iron oxides (hematite and
traces of lepidocrocite).
The sample preparation for the non-clay minerals followed that for
clay minerals, except the samples were mounted onto glass rather than
stainless steel slides. The samples were X-rayed for non-clay minerals
from 4°-60°2& at a scanning speed of 2°/minute using Cu radiation and a
graphite monochromator. The minerals were recognised by various X-ray
diffraction peaks corresponding to their characteristic crystal structure.
A summary of the distribution of non-clay minerals in drillholes C353 and
C354 is given in Figures 5 and 6. As far as possible the identification of
non-clay minerals followed the procedures in Brindley and Brown (1980).
DETRITAL MINERALS
QUARTZ
Quartz was identified by its major peak at 3.34Ao (26.65°2~) and its
secondary peak at 4.27Ao (20.8°2&). Samples with minor quartz (normally
clays) are denoted only by major peaks at 3.34 and 4.27Ao. Subsidiary
peaks in the 36.5° - 55.0 0 2&range indicate quartz in major quantities
(mainly silt, sand etc.). Hence the relative IIpeakiness" of X-ray
diffraction traces in the 4-60°2. range is an indication of the abundance
of quartz. This technique can provide a rough method for distinguishing
silts from clays in lacustrine sediments. X-ray diffractograms for quartz
are given in Figures 15 and 16.
-23-
Distribution
Quartz is present in all samples. Its distribution in the sedimentary
sequence is a function of lithology. Quartz varies sufficiently for its
use as a stratigraphic indicator. Generally it occurs in minor quantities
in clay and silt of the Bungendore Formation and is relatively more
abundant in sand and gravel of the underlying Ondyong Point and Gearys Gap
Formations (Figs. 5 and 6).
Origin
A detrital mineral transported into the depositional area by the
weathering and erosion of quartz turbidite sediments and acid igneous rocks
in the catchment. The abundance of quartz in the sediments reflects its
long term stability in the depositional system of the basin.
There is no clear evidence for authigenic quartz in the basin
sequence. However a silcrete exposed at the base of the Lake George
escarpment about 1 km south of Gearys Gap (Abell 1985) indicates silica
mobility has occured during the history of the Lake George basin.
FELDSPAR
Feldspars are framework silicates which can be divided into two main
groups, potash feldspars and the plagioclases. Feldspar was identified by
a consistent peak at about 3.19Ao (28.2~). In some samples feldspar shows
an extra peak at 3.24Ao (27.5° 2&). This double peaked X-ray signature
indicates the present of plagioclase and only occurs in samples from
(fluvial) sands {Fig. 17}. Confirmation of plagioclase was achieved by the
recognition of a strong secondary reflection near 4.03Ao (22.2°2~). Potash
feldspar was judged to be absent as the strong reflection in the spacing
range 3.1S-3.22Ao was not found (Brindley and Brown~ 19S0).
-24-
Distribution
The distribution of feldspar assists in characterising
lithostratigraphic units (Table 7). Feldspar may occur in trace amounts,
but is usually absent in deeply weathered sediments of the Gearys Gap
Formation and Palaeozoic bedrock. Feldspar is most abundant in basin
sediments above the deep weathering profile. The mineral is most prominent
in silt, sand and gravel of the Ondyong Point Formation, but reduced to
trace and minor quantities in clay and silt of the Bungendore Formation.
Origin
Detrital feldspar is derived mainly from igneous rocks east of the
depositional area of Lake George (Fig. 7).
The apparent dominance of plagioclase in the basin sediments is
unusual as the mineral has low durability in the erosion cycle. The
abundance of plagioclase in bedrock and closeness of the depositional site
of Lake George to source areas, might explain its retention in the basin
sediments. The mineral is available in outcropping basic intrusive and
volcanic rocks and may have been derived from a more extensive Tertiary
basaltic cover to the east now removed by erosion. However the apparent
lack of potash feldspar in the basin sediments is even more problematic
since the mineral is known to be durable and occur in acid intrusive and
volcanic rocks outcropping extensively in the catchment.
In the deeply weathered, leached profile uniformly high kaolinitic
peaks support a proposition of in situ weathering and almost total
degradation of feldspar. The increased amount of feldspar retained in the
fluvial sand and silt of the Ondyong Point Formation suggest a rejuvenated
topography and drainage shedding increased amount of sediment into the
basin.
•
Stratigraphic Unit Feldspar Faulting Origin Tectonic
Climate Sedimentary
--. Environment Envi ronment
V> BUNGENDORE Variable Tectonic Lacustrine r-z FORMATION (trace to minor) Quiescence w ::2: Detrital Fluctuating -0 feldspar (humid with arid W U) (plagioclase) Tectonic periods becoming
Z ONDYONG Activity seasonal)
-V> Variable <t POINT (rejuvenotion and FI uvio-ID (minor to major) increased erosion lacustrine
FORMATION ond deposition)
TOP DEEP WEATHERING PROFILE --1-------1------- - -- ------ ------ ------ ------V> r-z Feldspar w GEARYS GAP Z originally Fluvial - detrital 0 FORMATION w Mostly absent Tectonic V> (now degraded to Humid z (traces) kaolin by in situ Qu iescence - f.rvvv'- ~~~ ~~~
• U) weathering) <t ID I BEDROCK
w a:: a..
11/155-16/73
Table 7. Factors affecting the lithostratigraphic distribution of feldspar.
- - - .. - - - - - - - - - - - - - - - -
-25-
Local increases of feldspar in silty lake sediments may relate to
higher run off conditions in wetter climatic periods. The non-correlation
of feldspar and kaolinite in the basin sequence suggests a detrital origin
for kaolinite (Table 7, Figs. 8 and 9).
AMPHIBOLE
Amphiboles are chain silicates identified by a sharp (110) peak at
8.3Ao (10.6°2~) situated between first order basal peaks of illite and
kaolinite. The amphibole peak is found most commonly on the clay mineral
diffractogram. Sufficient amphibole was sometimes present for the peak to
show at 3.08Ao (28.95°2~).
Distribution
Amphibole has only local occurrence in the sediments. Trace and minor
quantities are found to depths of 51 m in C353 and 68.5 m in C354. The
mineral is confined stratigraphically to the Bungendore Formation and
uppermost portions of the Ondyong Point Formation.
Origin
The small quantities of detrital amphibole in the cores suggests local
derivation from basic igneous rocks in the catchment. The instability and
low durability of amphibole in the erosional cycle suggests it is unlikely
to be retained in large quantities in the basin sediments.
GARNET
In drillhole C354 a single grain of spessartite garnet was found in
lacustrine clay at a depth of 49.75m. X-ray traces of spessartite showed
clear reflections at 2.61Ao (34.3°2&), 2.34Ao (38.4°2~), 1.6Ao (57.5°2&)
and two other major peaks. The garnet is assumed to be detrital and to
have been derived from igneous or sedimentary rocks in the catchment.
-26-
SECONDARY MINERALS
CALCITE AND DOLOMITE
Calcite (CaC0 3 ) is the commonest carbonate mineral and is identified
by a small broad peak at 3.03Ao (29.4°2&). Small shifts in the peak
position to 2.98Ao (30.0 0 2t) are due to small differences in spacings
probably arising from the limited replacement of Ca by other divalent
cations such as Mg. Dolomite [CaMg(C03)2] which is much less common
than calcite is recognised by its major peak at 2.90Ao (30.85°2t). X-ray
diffraction results indicate magnesian calcite exceeds dolomite. Aragonite
was not detected.
Carbonates are ubiquitous in the pre-basin and basin sediments. The
size of the X-ray reflections suggests calcite and magnesian calcite only
occur in trace quantities in the Lake George Basin. However strong peaks
for dolomite show it is a common mineral in the upper 5 m of the Bungendore
Formation, notably at 1.3 m (C353) and 1.5 m (C354).
Some primary calcium carbonate maybe derived from the breakdown of
shell debris. Coxiella gastropod and ostracod tests are known to occur in
the upper 11 m of drill core in LG4 (Singh et al, 1981 and De Dekker, 1982)
and also in C354, C355, C358, C360 and C355 (Abell, 1985). However most
calcite is authigenic in origin. Secondary calcite may form in pedogenic
processes by leaching and reconstitution as calcareous segregations (Singh
et al, 1981). Under low water or even dry lake conditions calcite might be
precipitated by evaporation from carbonate-rich surface and subsurface
waters. Chemical analyses for Lake George waters in low lake level stands
in 1969 and 1973 showed a marked increase in HC03 and C03 ions (Jacobson
and Schuett, 1979).
Dolomite is known to form under varied depositional settings (Folk,
1974; Leeder, 1982). Singh et al, (1981) note the absence of dolomite in
-27-
the top 11 m of core in LG4. They note that Ca exceeds Mg by a ratio of
about 10:1 and imply that dolomite will only form if lakewater salinities
are greater than 100g/litre (100,000 mg/litre). In chemical analyses of
lakewaters, Mg exceeds Ca with the ratio increasing markedly in times of
low lake levels (Jacobson and Schuett, 1979). Major element analyses in
drillhole C354 also confirm that Mg occurs in excess of Ca.
SIDERITE
Siderite (FeC03) was identified by its major peak at 2.79Ao (32.002~).
The position of the siderite peak is similar to the major halite peak at
2.82Ao (31.8°2&). It was not possible to seperate both minerals if they
were present because the scanning speed of the X-ray machine was 2°/min.
In such cases confirmation of either or both minerals was achieved by
finding their subsidiary peaks. In drillhole C354, siderite was confirmed
by the analysis of a composite nodule, approximately 1 cm in diameter, from
a sample of black clay at a depth of 48 m. Subsidiary reflections for
siderite occurred at 3.59Ao (24.8°2~), 2.34AO(38.4°2t), 2.13Ao (42.4°2&),
1.96Ao (46.2°2t) and 1.80Ao (50.8°2~).
Traces of secondary siderite detected in weathered bedrock and in
parts of the Gearys Gap Formation probably formed after these sediments
were inundated. Siderite is common in the Ondyong Point Formation where it
appears to show some association with weathering profiles. The mineral
only occurs in trace amounts in the Bungendore Formation. The formation of
siderite is typical of the non-marine diagenetic conditions and sub
tropical weathering patterns in the Lake George basin.
GYPSUM
Gypsum (CaS04. 2H20) is readily identified on the clay mineral scans
by a sharp peak at 7.63Ao (11.6°2&? situated close to kaolinite.
-28-
In C354, gypsum is concentrated locally at a depth of 48.0-55.5 m,
straddling the boundary between the Ondyong Point Formation and the
Bungendore Formation. Gypsum is most common in the upper 16 m of the
Bungendore Formation.
In the upper 11 m of the lakebed sediments, Singh et al. (1981) report
that sulphates average 0.15%. In low lake conditions sulphate values in
lakewaters increase well beyond 2,000 mg/litre (Jacobson and Schuett,
1979). Gypsum maybe precipitated from evaporating saline lakewater or
shallow saline groundwater in local drought or prolonged arid conditions.
The lack of gypsum in the lacustrine sediments suggests it is carried down
and dispersed into the underlying groundwater system during and after
periods of dessication (Singh et al, 1981).
BARYTES
In drillhole C354, barytes (BaS04) was found as a white inclusion
within the clay matrix at 54.25m. X-ray traces for barytes showed strong
reflections at 3.43Ao (26.0 0 2&), 3.31Ao (26.95°2~), 3.09Ao (28.85°2~),
2.12Ao (42.65°29), 2.10Ao (43.1°2~) and other smaller peaks. Barytes is an
authigenic mineral and appears to be associated with a local concentration
of gypsum already reported at a depth of 48.0-55.5 m.
HALITE
Halite (NaCl) is more common in the basin and pre-basin sediments than
gypsum. It is identified by its major peak at 2.82Ao (31.8°2&), but not
confirmed by its subsidiary peak at 1.99Ao (45.7°2&). The subsidiary peak
at this position is masked by clay minerals. Seperation was not clear
because the scanning speed of the x-ray machine was 2°/min.
Occasional traces of halite occur in the pre-basin sediments and the
Ondyong Point Formation. Halite is fairly well distributed through the
-29-
Bungendore Formation in trace quantities. Local concentrations of halite
in C353 occur at 6.25-7.25 m and 31.00-31.5 m; in C354 they are at
2.00-3.75 m, 6.00-10.25 m, 11.5-14.75 m and 23.0-24.25 m.
Drill holes on the lake bed show little evidence for large scale
precipitation of evaporitic salts in the sediments. Jacobson et al. (1979)
note that the salinity of Lake George increases as the lake dries out. In
a low level stand in February 1973, salinity reached 44,800 mg/l TDS
(seawater is approx. 36,500 mg/l TDS). The presence of halite in the
Bungendore Formation suggests that in dry periods it is precipitated by
evaporation of lakewater or perhaps by evaporative pumping of shallow
saline groundwater.
IRON OXIDES AND HYDROXIDES
In drill core iron is evident in weathering profiles where it is
recognised by red and yellowish brown colour mottling, banding and small
concretionary growths. The iron minerals occur in forms ranging from
poorly structured (amorphous) oxides to the more crystalline hydroxides.
Hematite
Hematite (Fe203) proved difficult to identify by X-rays. The
mineral sometimes shows a small peak in the vicinity of 2.70Ao (33.2°2&).
Subsidiary peaks for hematite were not identified.
In drill hole C354, hematite is concentrated near the base of the
Gearys Gap Formation and top of weathered bedrock at a depth of 159.5-
165.25 m. X-ray data from drill hole C353 suggests hematite may occur in
trace quantities in the Bungendore Formation, but in C354 it was not
identified in the basin sediments.
-30-
The drill core logs indicate that hematite is probably more common in
the Lake George Basin than is suggested by the X-ray analysis. It is taken
to form as an authigenic mineral in the deep weathering profile and in
pedogenic zones of intermittent weathering profiles in the basin sediments.
Lepidocrocite
In drillhole C354 lepidcrocite [FeO(OH)], was identified in a nodule
at 48 m by peaks at 6.15 AO (14.4°~), 2.46Ao (36.5°2t), 1.90Ao (47.0°2&)
and 1.73Ao (52.8°2&). Iron in this form may occur where sediments are
elevated enough to allow weathering processes to oxidise siderite.
RESULTS AND DISCUSSION
CLAY MINERALS
Assemblages and lithostratigraphy
The clay mineral assemblages outlined in Table 8, equate with (a)
deeply weathered bedrock and fluvial sediments formed prior to the basin
and (b) fluvio-lacustrine sediments deposited within the basin.
In the pre-basin sediments, a simple clay mineral assemblage of
illite, kaolinite and illite mixed-layer clays probably reflects
inheritance from sedimentary rocks and weathering processes. As Table 9
shows, illite is more evident than kaolinite (I> K) in ferruginous bedrock.
However in leached sand and gravel of the Gearys Gap Formation, kaolinite
exceeds illite (K> I).
The basin sediments are characterised by a complex assemblage of
illite, kaolinite, montmorillonite, chlorite and montmorillonite mixed
layer clays. The kaolinite and illite are largely detrital; the
montmorillonite and mixed-layer clays are authigenic.
- - - -- - - - - - - - - - - - - - - -•
>-en U) Clay 0 CI)
Source Weathering Age Formation 0 'u Mineral Hydrology Climate pH Eh .c: c Area Conditi ons - LL Assemblage
-I
>- COMPLEX 0::: Closed <t tV Illite Intermittent drainage z = c: Negat ive 0::: (/) BUNGENDORE .- .-
en ~ Acid and basic weathering system FLUCTUATING redox W I- ...... ..-
Kaol in ite z FORMATION >- III
~ e ::I igneous rocks profi les Neutral potential w u Lacustrine <t :E u e Montmorillonite a qtz turbid ite Humid/temperate (locally => - --l conditions , a 0 sed iments interspersed positive w Chlorite
t (/) exposed in basin Palaeosols form Internal with arid Alkol ine in z tV Mixed layer
(\. c: catchment in dry lake circulat ion of periods weathering - >- .-clays w (f) ~
e ..- conditions major elements. profi les) wz <3: ONDYONG U CI)
CD ::I (Montmort /Ion/te ~w ~ u Groundwater
<tu POINT ..- e type) - --10
.- ...... system may be CJ)
FORMATION ...... 0 - .-~ " > open at depth. c: ::I'
e U. TOP DEEP WEATHERING PROFILE
r-- f- - ------ r-UL -- ------ ------ 10------ ------ ------ ---- f- - --
-(\. - :>-.
>- (f) tV e > -
~~ I- e~ -
GEARYS GAP e z ~ ..- .- SIMPLE Bedrock in Deep Open drainage w ~::: > 0:::-~ FORMATION '0 en ::I
<t~ - enlarged weathering system - c: L. U. I II ite wO::: 0 e 0
W w (/) .: catchment areas profile UNIFORM ~ (f) E Kaolinite extending east. Fluvial Positive ---z Mixed layer Clay minerals processes Worm/humid Acid redox -vvvv
(/) vv v vvvvv v
~ U <l c-I ays mainly reflect Full thickness domi nant. High rainfall potentia I CD tV
0 -
~ weathering retained below Loss of maj or
~N I .- (Illile type) '0 w conditions. basin sediments. elements 0::0 0:: BEDROCK ..c
<t w n. ... ::I
w<t --I N ~ <t ..-
a.. 0 11/155-16/74
Table 8. Clay mineral assemblages and depositional environment of Lake George Basin.
- - - - - - - - - - - - - - - -•
CLAY MINERALS NON-CLAY MI NERALS
Q) Q) ~ m
Kaolinite - >. + a. =0 0 Q) Q) Q) ,-... .- c: c:- -...... .c. .52 Q) o 0 0 .... - E Q) -- (K) Q) .... 0 0 0 - .-...... m - - .... N Q) -- a. c: :::J .-
FORMATION Q) ,c: .- .- . .:: ~ -Q) - .0 - 0 - .... .... =>. .... m .- 0 .- rn .... .- ~.~ 0 0 o 0 -0 0 -0 .c. ..c - c.. Q) E - - 0 - - E .c. E- ...... - :::J - a. '- >. -0 Q)
...... CI 0 - U _-0 -0 0 If E 0 :::r: (!) en 0 - c: c: Q) Q) u :::r: Index
C1) 0 o.~ .~ <{ 0:: ::E ~~ ~
/ ... .. • 0 0
E • c. Q) '0 Q) c: c: (/) BUNGENDORE L.. L.. ... 0 ::c E E 0 -
0 0 0 E , .0 t:I ..... . ~ .... .~ t:I 0 0 .£ E c..>
0 .- t:I E .- - .- E z FORMATION ~ c: ~
L.. t.... 0 0 t:I 0 0 '" 0 ...J
W ::> 0
~ u • > .:: > ~ u -c: E c: t:I - .::;.
0 L.. ~ 0 ~ - 0 - c..> 0 E 0 E 0 0
w " u c..> -(/) t:I -.. E .3 E 0
2 0 -.:: 0 ...J >-... ... L-0 Q) .~ u 0 U z ONDYONG Q) '-
Q) Q)
- _ 0 - - 0 Q) 0 c: >
(/) .0 E .0 .0 E - '- - E - 0 0 0 0 0 .0 0 E « POINT 0 2 .- .£ u .~ 0 2
m .- L.. .- 0 .- c..> E L..
t:I ... 0 ... 0
t:I '" 0 '" ...J ~ ... ...J 0 FORMATION > 0 > > 0 0 0
~ ~ > c U .-~ ~
E TOP OEE':
~
WEATHERING PROFILES ~ - -------- - - - - -- - - -- -- -- - - -- - - -- -- - - -"'- - -
(J"I 0
1\/ 1\/ 1\/ 1\/ 1\/ Q) c: .....
GEARYS GAP - E Z .0 ...... -t:I
0 W .- .£ " c..>
2 FORMATION ... ~
0 0 '" u --J - > E • 0 -
w - • E c: c: 0 ~ ... L- 0 0 c..>
(/) L.. - -
0 0 E 0 E 0 0 0 '+- ...... c..> c..> -
Z 0 .- E 0 E 0 0 2 c:
1/\ 1/\ 1/\ - ::> 0 ~ 0 ...J ...J >-In U U
L..
« Q) ... > m 0 ~
I BEDROCK ...... " w 0 .... 0:: :?:: Q.
111155-16/75
+ MaInly calcite and ma9nes1an calcile wtfh traces of dolomite
• Unils containing authigenic cloy minerals.
Trace minerals found include spessartlfe, lepidocrocite and baryles
Table 9. Summary of clay and non-clay mineral distribution for Lake George Basin.
- - -Detrital Minerals
I II i te
Kaolinite
Montmorillonite
Chlorite
Quartz
Feldspar
Amphibole
Authigenic Minerals Kaolinite
Montmorillonite
Chlorite
Mixed-layer cloys
Carbonates
Hali te
Gypsum
Siderite
Hemalite
-
Cl Index=Wldih at 1/2 peak height
Peak height
-31-
The lithostratigraphy is confirmed by the distribution levels of clay
and non-clay minerals (Table 9). The Bungendore and Ondyong Point
Formations maybe seperated on the distribution of montmorillonite,
chlorite, quartz, feldspar, halite, siderite and the crystallinity index of
kaolinite.
Weathering
A deep weathering profile predates the late Miocene formation of the
Lake George Basin (Abell 1985). The top of this profile can be defined by
a change in the mixed-layer clays, lack of feldspar and montmorillonite and
presence of residual kaolinite with a uniform crystallinity index (Figs. 5,
6, 8 and 9). Although core recovery in sand and gravel was poor and
samples were widely spaced, the top of the profile has been placed at 82 m
in C353 and 106 m in C354.
Intermittent ferruginous weathering events in the basin sediments may
relate to a depletion or absence of montmorillonite (Figs. 5 and 6) and
marked accumulations of kaolinite (Figs. 8 and 9).
Palaeoclimate
Clay minerals in sediments are commonly used as indicators of
palaeoclimatic change (Singer 1984). In the continental sediments of the
Tarkarooloo basin, Callen (1977) used smectite rich sediments as an
indicator of aridity to demonstrate a subtropical to semi-arid climatic
trend from the medial Miocene to the Pleistocene. Similar changes within
the same timescale have been documented by Thompson et al (1982) for
intermontane basins in the northern Rockies.
Following the weathering model of Ollier (1984, pp 73-76), a warm
humid climate will promote strong leaching and desilicification of clay
minerals. In the deeply weathered pre-basin sediments where the
-32-
hydrological system was open, kaolinite and iron oxides will form with
removal of silica and cations in solution. Conversely for basin sediments
deposited in a closed hydrologic system, silica and cations cannot easily
move from the depositional site. The reverse process of silicification
will lead to an accumulation of more complex clay minerals such as
montmorillonite which are independent of climatic parameters.
In summary, kaolinite attests to a high leaching, humid climate.
Montmorillonite (in soils) on the other hand maybe an indication of aridity
in that leaching is reduced. However the montmorillonite in the Lake
George sediments is mainly authigenic, deposited in a swampy environment
and therefore reflecting humid conditions.
Post-depositional alteration
A literature survey of non-marine clay mineral data in Grim (1968),
indicates that only slight diagenetic changes can be expected in freshwater
lake sediments. However the listing of authigenic clay and non-clay
minerals in Table 9, suggests that post-depositional alteration may
influence the distribution pattern of clay and non-clay minerals in the
basin sediments.
It has been noted that the mobility of silica and adequate amounts of
K, Ca, Na and Mg ions will ensure alteration of clay minerals by depletion
or accumulation of silica and cation exchange processes. Other factors
such as pH conditions, salinity levels and release of porewaters during
sediment compaction may have roles in post-depositional alteration that
await investigation.
-33-
SECONDARY MINERALS AND GEOCHEMISTRY
Carbonates
Calcite, dolomite and siderite occur in small quantities in the Lake
George sediments. Models for the genesis of these minerals maybe
speculative but their presence is possibly evidence for climatic change and
post-depositional alteration in the basin.
Dolomite can form from any natural solution providing the Mg/Ca ratio
is over 1:1. It can also be precipitated by ionic dilution when Mg-rich
saline water is diluted with freshwater (see figs 1 and 2 in Folk and Land,
1975). In the Lake George Basin dolomite may crystallise where there is an
interaction of fresh (meteoric) lake water with saline groundwater (a
process aided by seiche activity). The mixing zone is likely to be within
the top few metres of the lake bed sediments where dolomite has already
been identified in the cores. In another model phreatic groundwater
recharging sandy sediments marginal to the lake and moving towards the
centre of the basin may take up available Mg ions and precipitate dolomite.
Such a model might explain the occasional dolomite lower in the basin
sequence.
At Lake George, an environment may periodically exist for the
formation of dolomite by evaporation of saline groundwater. Dolomite
in the upper few metres of the lake bed sediments may form by evaporative
pumping during relatively dry periods of climate. Dolomite has also been
reported from the upper 2 m of lacustrine muds at Lake Keilambete in
Victoria (Bowler, 1981).
According to Leeder (1982). siderite will form in diagenesis where low
dissolved sulphide concentrations are coupled with high dissolved
carbonate, high Fe/Ca ratios, low Eh and near neutral pH. Such geochemical
conditions tend to restrict siderite to non-marine diagenetic environments
-34-
low in S04 ions and where abundant Fe2+ is present as in subtropical
weathering conditions. The mineral therefore is expected to form in
deltaic swamp facies where there is restricted water circulation; similar
conditions have existed locally in the f1uvio-1acustrine environment in the
Lake George Basin.
Evaporites
The poor development of evaporite salts is an u&Usua1 feature of the
lake sediments. Since Lake George lies in a closed drainage basin
evaporites might be expected in greater quantity in upper portions of the
lake sediments. The lack of evaporites may be identified with observations
that (a) the basin is not a groundwater discharge area, (b) the regional
climatic system is such that the lake does not dry out seasonally; in fact
as the modern hydrographic record shows, water remains in the lake over
long time periods, (c) replenishment of the lake is by low salinity
meteoric water (rainfall and run off) rather than high salinity brines, (d)
the basin sediments do not show characteristics of a playa-like complex.
Playa conditions only form temporarily during terminal phases of the lake.
A model is needed to explain the dispersal and long term accumulation
of salt (halite and gypsum) in the basin sediments. Rain-bearing westerly
winds from the interior of the continent and easterly winds from the coast
deposit salt over the basin. Weathering and erosion of rocks in the
catchment also releases salt which is carried towards Lake George by
surface runoff. Presumably the result of these processes is a long term
increase in the amount of salt trapped in the depositional system of the
basin.
-35-
An interchange of salt between lake and groundwater bodies is
postulated by Singh et al (1981). In dry phases, vertical diffusion
carries halite and gypsum down to the groundwater body. The salt storage
capacity of groundwater in the Lake George Basin will depend on the
hydrogeologic regime, the permeability distribution of the basin sediments
and the palaeohydrolgic behaviour of Lake George. A study of seiche
activity on Lake George by Torgerson (1984) suggests that low salinity lake
water may infiltrate the lake bed to moderate salinity levels in the
groundwater system (see Fig. 4).
At present it is unclear whether the groundwater body in the Lake
George Basin functions as an open or closed system (Abell 1985). The
mineralogical evidence from drill hole logs C353 and C354 (Figs. 5 and 6)
indicate that halite and gypsum decrease in the Ondyong Point Formation and
pre-basin sediments. This maybe evidence for an open hydrologic system at
depth. If there is slow groundwater leakage from the basin it can be
expected that evaporite minerals will not be precipitated since groundwater
salinities have not evolved enough for salts to remain in solution.
MAJOR ELEMENTS
Analytical techniques
The specimens from C354 were analysed for major elements by optical
emission spectroscopy using a Hilger spectrograph. The analytical method
employed was an adaptation of one used by Waring and Annell (1953).
A small portion of sample was oven dried at 120°C for 24 hours. The
dry sample was ground to a powder in an agate pestle and mortar. The
sample was loaded into a preformed graphite electrode (National Carbon
Company Type L4206). The anode was arced for 60 secs using a 6 amp DC
current, which drove off the more volatile elements such as Na, K, Li, Sn,
Cu and Pb. Another arcing for 60 secs using a 12 amp DC current drove off
-36-
the remainder of the elements. Two types of spectrum analysis plates were
used for identification of the elements. The Kodak No.1 plate had a range
up to 4,300Ao and the Kodak No.3 plate, a range up to 5,500Ao. The plates
were developed over a 5 minute period at 20°C using Kodak D-19 developer.
The spectrogram of the elements was identified using a Jarrel ash double
beam comparator.
The total number of elements analysed ws 20. The relative abundance
of the elements was estimated in a semi-quantitative manner by division
into three groups as shown by a range of approximate percentages (Table
10). The semi- quantitative estimation of the percentage ranges for the
elements was by visual comparison of the intensity and thickness of
spectral lines. A computer program was devised to handled the
spectrographic data. The distribution of major elements in drillhole C354
is shown by simplified histograms (Fig. 6).
Zinc is not listed among the major elements analysed as the optical
emission method used in this investigation was unsuitable for the detection
of zinc especially when sodium is present. It is assumed that zinc is
present in the local geochemical environment. West of Woodlawn mine, Ryall
& Nicholas (1973) describe zinc anomalies which show hydromorphic
dispersion downslope of the ore zone.
RESULTS
The assemblage of major elements identified in C354. largely reflect
their dispersion and retention characteristics in the natural geochemical
environment of the Lake George Basin. Table 11 is an attempt to classify
the elements in terms of their expected mobility in the secondary
environment of weathering, erosion and sedimentation (data adapted from
Levinson 1974 and Butt and Smith, 1980). The more important factors
I I I I I I I I I I I I I I I I I I I I
Major 0/0 ppm Distribution elements
Major >0-5 >5000 Si, Ti, AI, Fe , Mg , (Na), (K), (Ca) .
Minor 0-05-0·5 500-5000 Mn, Ca, No I K, Ba , (Cr) I (Sr)
(Ba)
Trace <0-05 <500 Sr, Li, V, Co, Ni, Cn, Sn, Pb, Cr, Mo
11/155-16/16
Minerals in brackets may also occur frequently in another category_
Record 1985/20
Table 10. Semi-quantitive distribution of major elements in C354_ •
I I I I I I I I I I I I I I I I I I I I
Mobile Immobile
elements elements
Mg Si
Ca AI - -Na Fe Ti
K Mn Cr
Co Ni Sa
Sr Li Sn
V Pb
Mo
Cu
11/155-16/77
MOBILE ELEMENTS are dispersed easily in a geochemical
environment.
IMMOBILE ELEMENTS are generally stable and retained In
weathering oroflles
Fe, Mn, Nt and Lt may be mobile or Immobile depending on the
nature of the geochemical environment.
Record 1985/20
Table II. Mobility of major elements •
-37-
affecting the mobility of these elements in the natural geochemical
environment will be pH, Eh, fluid media (surface and groundwater
distribution), solubility of salts and the adsorption properties of various
clay minerals and oxides. At this stage it has not been possible to
evaluate the relative importance of these parameters with regard to the
element data in C354. Further, since samples from only one drillhole were
analysed only a very preliminary interpretation can be placed on the
analysis.
In this investigation the distribution of major elements is
interpreted as a function of the capacity of clay minerals and
iron/manganese oxides to adsorb the more mobile elements dispersed in the
geochemical environment. Distinct correlations are not possible with clay
and non-clay mineralogy, weathering profiles and units of the
lithostratigraphic sequence. Unfortunately there are no other element
analyses of subsurface sediments in the basin available for comparison.
The quantitative distribution of the elements seems to be
representative of normal geochemical background levels. For example values
of Mn, Ba, Sr, Cr, Cu, Ni, Li Pb, Sn, Mo, V and Co compare favourably with
the range of abundance of these elements in soils (Levinson 1957, table 2-1
and figure 3-13). There is no indication that these elements occur in
anomalous quantities in the sediments of the Lake George Basin. It is
expected that elements such as Si, Al, Fe, Mg, Ca, Na, K and Ti will occur
in major quantities since they are common components of rock-forming
minerals.
Elements showing the greatest degree of change in the sequence are Na,
K, Mn and Cr. Sodium and potassium vary independantly of one another.
Potassium is known to be a major element in illite, but the change in the
intensity levels of illite as measured by peak height did not find any
-38-
obvious consistency with variation in potassium shown by emission
spectroscopy. Manganese and chromium have similar chemical properties and
tend to be immobile in the geochemical environment. It is assumed that
their variability relates to differing capacities for cation adsorption by
clay minerals.
Titanium is found regularly in major amounts. It is derived from
basic rocks containing oxides e.g. ilmenite, which are resistant to
weathering. Titanium tends to be insoluble and poorly mobile and is
enriched in the deep weathering profile. In the basin sediments titanium
is depleted locally to minor levels.
Tin is strongly resistant to weathering and occurs as a detrital
element in trace proportions in the Gearys Gap Formation (119.75-139.75m).
Tin appears to have been remobilised and re-deposited in the younger
formations of the basin sequence.
Iron is common as a major element, particularly in weathering
profiles. However it is moderated locally in the leached kaolinitic
portions of the deep weathering profile (130.25 - 134.75 m).
Molybdenum occurs in trace quantities in the Bungendore Formation.
Its origin is not clear but according to Wedepohl (1978), molybdenum is a
mobile element and can be enriched by adsorption in organic rich clays.
Some of the black clays in the Bungendore Formation appear to be rich in
organic matter, but there is a lack of supporting quantitative data.
A background level for copper is indicated by its consistent trace
quantities throughout the sequence. These levels are exceeded where copper
occurs locally in minor quantities near the top and bottom of the Bungendore
Formation. Its concentration may be due to cation adsorption by
montmorillonite after carriage as a chloride complex in subsurface saline
-39-
groundwater.
Significance of the element analysis
The Lake George Basin maybe a useful study area to determine and
perhaps monitor geochemical processes operating in fault-bounded drainage
basin. Assuming for the most part that normal background levels of metals
exist in surrounding bedrock, there must be potential for the
redistribution and concentration of these metals into the closed
depositional system of the Lake George Basin. Some of the factors expected
to influence such a distribution of metal ions are summarised in Table 12.
At this stage there is no evidence of anomalous mineralisation in the
basin sediments. A study involving subsurface sediment analysis and
hydrogeochemical sampling could provide a conceptual model that outlines
the geochemical parameters affecting metal deposition in the Lake George
Basin. If the study was positive enough to show the basin was a
potentially suitable environment for the entrapment of metals, if might
find application as an exploration aid to other similar depositional
environments in humid areas of Australia.
When the lakebed is again accessible for drilling, it is recommended
that water samples are obtained to study the hydrogeochemical dispersion of
elements in the ground water system. In the meantime a substantial amount
of drillcore is stored in refrigerated premises at Fyshwick. The core has
been packed in an attempt to retain as far as possible the original
moisture content and condition of the sediments.
LAKE GEORGE BASIN
PRE-BASIN TERRAIN
-40-
Rejuvenated terrain; partly fault bounded basin; truncation of surface drainage; reduced catchment area; deep weathering profile attenuated in catchment but full thickness preserved beaneath fluviolacustrine deposits. Distribution of elements in basin sediments will reflect nature of catchment bedrock, weathering and mineralisation (Woodlawn Mine).
Complex hydrological and hydrogeochemical conditions; subsurface saline environment; ground water main transporting agent for accumulation of metals in sediments.
Clay dominated lacustrine sediments and intermittant weathering profiles suggest accumulation of metals and major elements by cation adsorption (Cu, Mo etc.); rapid changes in pH and redox conditions; permeable paleodrainage lines in pre-basin terrain cut off from recharge maybe in a reducing environment favourable for uranium.
Top deep weathering profile
Moderately dissected palaeorelief.
Open hydrological conditions; surface runoff in drainage lines directed NW, catchment areas large and extending E: heavy minerals (zircon, tourmaline, ilmenite, magnetite etc.) and metals (Sn, Au etc.) expected to occur as placer deposits in sands and gravels associated with drainage lines.
In situ chemical weathering; oxdising environment with acid pH values; gossan formation; concentration of immobile elements (Al, Fe, Mn, Ti, etc.) in the weathering profile.
Table 12. Factors affecting the occurence of metals in in the Lake George Basin.
-41-
CONCLUSIONS
(1) A clay mineral assemblage of illite, kaolinite and illite mixed-layer
clays equate with early Palaeozoic bedrock and early Tertiary? fluvial
sediments formed prior to the Lake George Basin.
A younger and more complex clay mineral assemblage of illite,
kaolinite, montmorillonite, chlorite and montmorillonitic mixed-layer clays
is associated with late Tertiary and Quaternary fluvio-lacustrine sediments
deposited within the basin.
(2) Clay and non-clay minerals (a) largely reflect a provenance of acid
and basic igneous rocks and quartz turbidite sediments outcropping in the
catchment to the east of the lake area and (b) confirms in a general way
the late Miocene to Recent lithostratigraphic divisions proposed for the
sediments in Lake George.
(3) Weathering processes and post-depositional diagenesis in the Lake
George Basin accounts for the presence of authigenic mixed-layer clays,
carbonate minerals, halite and gypsum. Evaporite sequences are absent.
(4) The clay mineralogy is not quantitative enough to be used as an index
of palaeoclimatic change. Kaolinite in deeply weathered pre-basin
sediments indicates warm, humid, leaching conditions prior to the late
Tertiary. The presence of montmorillonite in the basin sediments also
indicates humid conditions as it forms when the lake is full. Depletion of
montmorillonite in weathering profiles suggests drier phases and a
fluctuating climate in the late Tertiary and Quaternary.
-42-
(5) In the pre-basin sediments, uniformly high levels of residual
kaolinite supports a proposition of in situ weathering and almost total
degradation of feldspar. In the basin sediments a detrital origin for
kaolinite is supported by its uneven distribution and non-correlation with
feldspar.
(6) The distribution of major elements in drillhole C354 is a function of
the capacity of clay minerals and Fe/Mn oxides to adsorb the more mobile
elements. The semi-quantitative distribution of the elements seems to
indicate normal geochemical background levels. There is no evidence of
anomalous mineralisation in the basin sediments.
ACKNOWLEDGEMENTS
The authors are grateful to colleagues at B.M.R. for their helpful
suggestions and advice. The senior author (R.S.A.) wishes to thank
Dr P.J. Cook (Continental Geology Division) for originally suggesting the
sampling program and analysis of drill hole samples for clay mineralogy.
The manuscript was edited by Dr C.D. Ollier, M. Gibson and Dr. G. Wilford.
The figures and tables were drawn under the supervision of Mr M. Moffat of
the B.M.R. drawing office (Continental Geology Division).
REFERENCES
ABELL, R.S., 1985 - Geology of the Lake George Basin, N.S.W. Bureau Mineral
Resources, Australia, Record 1985/4.
BAKER, C.J., & UREN, R.E., 1982 - Kaolin in New South Wales. Geological
Survey New South Wales, Mineral Resources Series, 44.
BOWLER, J.M., 1981 - Australian salt lakes - a palaeohydrological approach.
Hydrobiologia, 82, p 431-444.
-43-
BOWLER, J.M., 1982 - Aridity in the late Tertiary and Quaternary of
Australia in EVOLUTION OF THE FLORA AND FAUNA OF ARID AUSTRALIA.
Edited by W.R. Barker and P.J.M. Greenslade. Peacock Publications
Adelaide
BRINDLEY, G.W. & BROWN, G., 1980 - Crystal structures of clay minerals and
their X-ray identification. Mineralogical Society Monograph No.5
(3rd edition).
BURTON, G.M. 1972 - Lake George, N.S.W. - Notes for sedimentologists
excursion, November 1970. Bureau Mineral Resources, Australia, Record
1972/79.
BUTT, C.R.M., & SMITH, R.E., 1980 - Conceptual models in exploration
geochemistry. Journal geochemical exploration, 12 (2/3),
p 89-138.
CALLEN, R.A., 1977 - Late Cainozoic environments of part of northeastern
South Australia. Journal Geological-Society, Australia, 24(3),
p 151-169
CARROLL, D., 1970 - Clay minerals: a guide to their X-ray identification.
Geological Society America, Special Paper, 126.
COVENTRY, R.J., 1967 - The geology of the Shingle House Creek Valley, New
South Wales, with particular reference to its Cainozoic history.
B.Sc. (Hans) thesis, A.N.U.
COVENTRY, R.J. 1976 - Abandoned shorelines and the late Quaternary history
of Lake George, New South Wales. Journal Geological Society,
Australia, 23(3), p 249-273.
-44-
DEER, W.A, HOWIE, R.A., & ZUSSMAN, J., 1966 - An introduction to the rock
forming minerals. Longmans.
FOLK, R.L., 1974 - Petrology of sedimentary rocks. Hemphill Publishing
Co., Austin Texas.
FOLK, R.L., & LAND L.S., 1975 - Mg/Ca ratio and salinity: Two controls
over crystallisation of dolomite. American Association Petroleum
Geologists Bulletin, 59(1), p 60-68.
GIBBONS, G.S., & BUNNY, M.R. 1963 - Notes on clay. Bungendore. New South
Wales Geological Survey Report GS 1963/040 (unpubl.).
GRIM, R.E., 1968 - Clay mineralogy. McGraw Hill International Series
(2nd edition).
JACOBSON, G., & SCHUETT, A.W. 1979 - Water levels, balance and chemistry of
Lake George, New South Wales. Bureau Mineral Resources Journal
Geology Geophysics, 4(1), p 25-32.
LEEDER, M.R., 1982 - Sedimentology - process and product. George, Allen
and Unwin ••
LEVINSON, A.A., 1974 - Introduction to exploration geochemistry.
Applied Publishing Ltd., Calgary.
LLOYD, J.C., 1960 - Ceramic resources of New South Wales. New South Wales
Department of Mines, Technical Report, 5, for 1957, p 214-220.
LOUGHNAN, F.C., 1960 - The origin, mineralogy and some physical properties
of the commercial clays of New South Wales. University of New South
Wales, Geological series. 2.
-45-
area in lANDS OF THE QUEANBEYAN-SHOAlHAVEN AREA, A.C.T. AND N.S.W.
land Research Series, CSIRO, Australia, 24, p 57-75.
OllIER, C.D., 1978 - Tectonics and geomorphology of the Eastern Highlands
in lANDFORM EVOLUTION IN AUSTRALASIA. Edited by J.l. Davies and
M.A.J. Williams, A.N.U. Press, p 5-47.
OllIER, C.D., 1984 - Weathering (2nd edition) - lONGMANS.
RUSSEll, H.C., 1886 - Notes upon floods in lake George. Journal and
proceedings of the Royal Society of New South Wales, 20, p 241-260.
RYAll, W.R., & NICHOLAS, T., 1979 - Surface geochemical and biogeochemical
expression of base-metal mineralisation at Woodlawn, N.S.W.,
Australia. Journal Geological Society, Australia, 26(4), p 187-195.
SENIOR, B.R.,1979 - Mineralogy and chemistry of weathered and parent
sedimentary rocks in southwest Queensland. Bureau Mineral Resources
Journal Geology and Geophysics, 4, p 111-124.
SINGER, A., 1984 - The palaeoclimatic interpretation of clay minerals in
sediments. Earth Science Review, 21, p 251-293.
SINGH, G., OPDYKE, N.D., & BOWLER, J.M 1981 - late Cainozoic stratigraphy,
palaeomagnetic chronology and vegetational history from lake George,
N.S.W. Journal Geological Society Australia, 28(4), p 435-452.
TAYLOR, T.G., 1907 - The lake George Senkungsfeld, a study of the evolution
of lakes George and Bathurst. Proceedings of the linnaean Society,
N.S.W. 32, P 325-345.
-46-
THOMPSON, G.R., FIELDS, R.W., & ALT, D., 1982 - Land based evidence for
Tertiary climatic variations: Northern Rockies. Geology, 10,
p 413-417.
TORGERSEN, T., 1984 - Wind effects on water and salt loss in playa lakes.
Journal of Hydrology, 74, p 137-149.
TRUSWELL, E.M., 1984 - Lake George: preliminary palynology of deep
sediments. BMR Research Newsletter, 1, p 12-13.
WARING, C.L., & ANNELL, C.S., 1953 - Semi-quantitative spectrographic
method for analysis of minerals, rocks and ores. Analytical
Chemistry, 25(8), p 1174-1179.
WEDEPOHL, K.H., 1978 - Handbook of geochemistry (5 volumes. Springer
Verlag, Berlin-Heidelberg.
I I I I I I I I I I I I I I I I I I I I
'" o C!> ~
Queonbeyan
Record 1985/20
I I I
(
I I
I
!
Fig I Lake George Basin and drill hole locations
Goulburn
""C1"'"
~ /i"",,,,,,,!"
\ ,""''''''', .
• • """>'In ... • _.~. ,. "",",. I- ,
~''':':::;:'r'-'-'
• C353
.LG4
o I
. "'~ "'" l. ... " o L~,~~~
1 I
BMR dnllhole with number
ANU drillho/e with number
IOkm
11/155-16/60
•
I I I I I I I I I I I I I I I I I I I I
... ::: .. ==;:==1 +
... ... ...
...... ~ ... ~ ~ +, ... ... ...
+ + + +'
+ + i', + " ... + ....
\ --=--t--l!I'?-il\
--==;l~~\
\
====s; '" -----,'." . , ____ -"r
------". -----,j .•
Record 1985/cJ
LAKE GEORGE
,~,,~ .! ,
," v --j -\---' '\
\ V V \
'J.< v V\ ' 1 V V
,¥ v V:" , \ V V " "
, V \I , V:, ,I
, ,
t N
I
u
~ D" A/iuvlOl and lacustnne Z ' depOSits (undlfferentloted) <l u AJ\.I'J\.AI"VV"V\..fVVV"V\. Z ~ Z o > lJ.J o
:J a:: <t: w , Z <t
Ofz turbidite
Acid volcanocla5tlcs and sedifnents
BaSIC volcamcs
ACid volcanics
D + ... +
+ +
BaSIC intrusions
Grande and porphyry
~ BaSIC intrusions
~o' ~ Of? turbidite and t=.=j block slate
o
Unconcealed fault
Concealed fault
Basin limit
GeologIcal boundary (accurate)
GeologIcal boundary (inferred)
IOkm
II!I55-16!b'
Fig 2 Geology of the Lake George Basin
•
I I I I I I I I I I I I I I I I I I I I
Oepth Lithology and Age Weathering (m) Formation environment
04------r--~--------------------~------_,r_----~----~--------------~ >-0:: « z 0:: w BUNGENDORE r- (J) « I-::J z
FORMATION
0 w
t ~ -0
50 - w w Z
(J)
l.LI z U -
(J)
0 <t - CD ~
ONDYONG POINT
(\' FORMATION W r-< -I
----~---
~---
---I-- - -----I--- --- --f-- -- -----I-- ----f-- ----f-- -----................ f--- -----f..-- -----
LACUSTRINE
(silt and clay)
.:,' :.'. ,', • , FLUVIO-I' '" •• "I ~ -=-=- LACUSTRINE
",: '::: : :,: (sand, sill and clay) : I" .'.: •••
----I-..........
THIN INTERMITTENT
WEATHERING
PROFILES
(ferruginous)
:':';': .~::: ~ ':.: Disconformily TOP DEEP 100~-___ +-~~ __________________ ~='~'~'~·~~'~~~~n~n,~~n~~.n~~.LJ~,~~~ ___ ~~~~ ___ ~
I- - - WEATHERING PROFILE
>-0:: < -r-0:: W
150 - .-(\.
>-...J 0:: < W
200 -+-------l
u
>-0 -IN 0::0 <tLtJ W<t
...J < a.
Recorr1 ;385/20
(J)
~ Z W ~
o w (J)
z
GEARYS GAP
FORMATION
----4' .0' • D • d , 0 ,'0' .0.
• • ," o· '0' (I · ~ .' ....... ~ q, <:>. d • ••• ' •• • C;;
• O. Q. • 00.
.c::. •• tIr. ••• e:,:Q1. II. t. '" ~ • O· • o • <I •••
~F===-===-.::::::;_ Fluvial sand, <& I, •• a. • '0 d ,', ,~", ,c.,' gravel an minor ,<l "~ oc .. silt ond clay in 6"' 4' ::, •••
• ,', ,: c' ,6, pre-basin 0': ~: 0. :,: <). drainage lines
p.;-
.<Q •• ~ •• 0 •• od 4'
• <Q ,I •.. , ., '0 • t:a
, , c' , ' , (/) ,~'()"Q,'t\, « , ' ... , CD .~, '0' , Q I:l I "'4' ••••
'0·' I'.' ~', c, . W • , Q, <) '(I, , Unconformity ~ ~------------------------~AAAA~~V¥'Vv,vvvv,vv,vv,vv'~v'~v'v~'v~.vA'v~,v a..
BEDROCK
(slrongly folded
flysch and foliated
baSIC and acid
~ /l ~ igneous rocks)
DEEP WEATHERING
PROFILE (kaolinilic and •
ferruginOlls)
11/1'>5-16/62
G j Clay and Sill CJ Sand ~ ~ Sand and gravel
Fig.3. Lithostratigraphic units
I I I I I I I I I I I I I I I I I I I I
1 N
DRY BED
~ Relief
Fig.4 Hydrologic effects of the seiche
D" Infiltration where . '. :: dry lake bed is covered
~ Evoporation where ~ wet lake bed is exposed
- - - Initial lake area
- New lake area
~ Direction of initial water movement
... -. Return water movement 11/155- 16/63
•
.." <D
(J1
n 0 iD 3 ())
-0 '" 0 "-'" (j) 0 -(l)
0" <D
0 -.. --::r (l)
3 :::> (l) .., £. 0
<D '<
:::>
a. .., = -::r 0 (l)
(")
UJ (J1 UJ
cr; ocr; Ui :J::; (;j N -- 0 <.0 NO
II 0 0 0 0 0 0 0
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I 00 ~ ~ ~ 6 ~ 6 0 0
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~o~~~~~~:_O_, ~~I~I~~'~I~:_O~~~i~! ~1~i~I~I~I~I~I~I~I~I~1 ~I~I~I~I~~I~I~I~I~~I~I~I~I ~1~1~1~I~i~I~I~I~I~~1 ~I~I~I~I_I~I~I ~I~I~I~I ~I~I~I~~I DEPTH (m)
~ 0 ~ D~ -
1Jf Tr-LJTI ill T I -
lr D 0 "J' - --- --, I7 0 " - M
~ 00 0 on
---------------------- -- .----_ ___ _________ -'-1 --'L~L__'_I ___'T'___'=_E __ =M--'I___'X_'___'=E'_"'_O _ - LAY E R CLAY$
ACID
PITTMAN FORMATION GE A RY S GAP FORMATIO N - --
LATE ORDOV I CIAN
r T T T'l T l -r"l -
'----' tJ LJ L.J
T T PlTT J"1 'T I Lr I Ii I I l/
Q. o.o.n
ONDYONG P OI NT R TI AR Y
h:VJLJr ill FI/----7L\r -"T
.,, :'! .... nro,..,An'n 0..0.
-------
M 0 N T ~ 0 R _I L LON I T E
NEUTRAL
M I X E O- LAYER CL AYS
T 0 ALKALINE
_I_' FO R MATION BUNGENDORE FORMAT ION I
----___ -,;)'--' -----------------QUATERNARY
01111 11' V I' 111'l ...... ~ . I
QUARTZ
FELDS PAR
CARBONATE
HALITE
GYPSU M
AMPHIBOLE
SIDER ITE
HAEMAT ITE
LITHOLOGY
WEATHERING
ENVIRONMENT
I LLiTE (I)
KAOLINITE (K) I > K K>I MONTMORILLONITE
CHLORITE
M I XED- LAYER CLAYS
pH
FORMATION AGE
(") o 3 u o Ul -'" o
'" o ~
:::r (1)
3 :::J (1)
o o
'" '<
o :::J 0-
3 E.
~ <t> 3 <t> :::J -Ul
. OJ o (1)
i:i o o Q.
-, H
'" '" J
'"
I I I [I I 'I <D <D (IJ o
1 1 1 (IJ
o
I I
SILICA
TITANIUM
ALUMINIUM
IRON
MANGANESE
MAGNESIUM
CALCIUM
SODIUM
POTASSIUM
BARIUM
LITHIUM
Sr 0 0 U U c:=::::J U U LJ c=J I DID c::::J I c::J LJ I I a 0 Y'?" 0 90 P P '1]1 U 1 LJ=1l[JY P' '? Y' '9 Fv---P?'"T1'l1 0 HIP 9 0=,00 IlIJP"", , 19 °IP 0' 1 ' 1' 1°<+=HC:;::::=::? LJ=1=Tl=rm::? STRONTIUM
Pb U I I I I U I 0 o I
V Uo,-~o-curc'==~LOrLDTUcr~~~~======nj~==~1:~==::::TC~~O-C~~1:'======::::T'LDIT'nIOnC::::::::::::==::::T~OC~~Ucr--~pr<',Or--UO--'--rrU"1:=~9~U-'~ODO-''-_'On=::::n'_'O~O~o-r--,~==n~~-'OTnI ~~DOT"'VO--,~==::::noryP1:~~FI~,==~'LDn~~~~L~~,~,~,==~========~'C' ~~IL' ==~I 1~,==~~::::n~~~~~::::T
Cr 1J'1]-lfO LLJ:;TIrO r,:;lf"LJ1J~TlOITOl'g:::;r-TDITrlf1i::;==:=n;' tt::rrl-;::::;=TILiLJ1]-'=;-n7cyn9 ''fLrl;:;-rP'LfLJ"lfLJ1jmm::'-nflDDTj' hl:;n:::hrn:::J::;n::;-TlJGr::l'U=---'1]IJ'-I?~-'RHT~y;rr;:Lri::;:rrro lfP TTnO orr'-iPPlDITIIlOiOrrTOrT-iLJirrTOi---r;'1]rTl TL??TrI?TflillfO -L~:::;-;:;::;:;-;::::::;-;:::;-;:::;;::;:;::;::::;::ll[J7T~;:::;;::::;-;::::;::::;:::::::;-;::;::::;::;:;-;:::::;:::::::;:;-,::;-;::;:;;:::::;;:;::;::n,::;:;, ,::;:, ::;::::rj:' hTlJ"="TTUT=rl::;:;::;;=~::;::::::;:n-c:r=n=u=tJTD=UJ;::::;:;::::;-;:::::::;-;::;:::;--;:;-;:T COuO,----",'~OT'-r--~I~rUr-T','-rrO----T'LDrcD~O~"",r", r'T'~OT'--'-~O-UOT','~V1:D~--DOLOTtVIT','~Ur,------~u-',Or--'-----UOL~~-9~-"~ODo-----,Vn91'i-,O~VVU-r--,iLV~9punD~,iTinll,OTnJ!T"iri--,orcUImUI'TIU~iTi--C=~Ur<iniUrrIT)p~~I)TiT)'~S?JiILO~'::;:i======~iLVnD~inil-',i-VVVVn)ln'T"nD~V1:Un~::::TVO~ULOnOniLUnri
Niuo,-"cunJ====~iLVrLDTCUr-~~--C======nl~==~1:~==::::TC~~U-C~~1:,======::::riCDITILDn'====T' C~~----~pr<,Or--UO-----UoL~~-,q~-.~VDO-,,--.Vn=::::nI-.~U~U-'--LUn=::::nC?=?~pTnI~::::TDOT"iVU--,U~~=nUryp1:~::::TFF===~=rr'CDn~~~~1:I::;:' ==~i~i~11CI ~~~ ______ ~~~=nOnl~'~i==~iLI========~
CU ~o'-~U~Unl====~~DTCUr-~~--C======nl~=¥~1:~==::::TC~~U-C~~1:,==~~::::r'CDITiLDn'====T'C~~Ucr--~or<,Or--UO--'--UOL~~~V~-'~UDO-''-_'Un=::::nI _'~U~u-'--L~==n~~-'OTn~~DOT" 'VU--L::::==;::::;::::==TTI==~iCDn~rT~~~~;::::~~==~==::::T' C' ==~'L'==~::;:J J~~~::::n~~~~~~ I... r I U I I r- - j II I lL...J!U U[ I I I11U .. U I U I IU J
01 , II U I ill LJI I I I IDLJ 0110 I I 1 U I I U I i I I I I ,t I I I , II o I II Ii' II iIi 0 U I DO
LEAD
VANADIUM
CHROMIUM
COBALT
NICKEL
COPPER
TIN Sn U
MOD I I I I I 0 I ' U 0' I I I 'U I I 0 I ,III I I I , , IOu II I DO I 110 I I MOL YBENUM
1 Iii ---J o
Iii 1 I 1 (J) o
1 1 1 ()J
o
1 1 1 .j> o
1 1 I 1 Iii I ii I I 1 1 1 0J I\l o 0
1 1 1 I 1 -o
1 1 1 1 o o
I 1 1 1 I <0 o
\J LXJ i j
i I I I I Q)
o I i I
--J o
I I I i I
U' V-j'O
(J) o
I I ill I 01 o
1 ill 1 ill 1 I 1 1 Iii 1 ill 1 1 1 I 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 .j> 0J I\l 0 0 DEPTH lm) o 0 0
QUARTZ
FELDSPAR
CARBONATE HALITE
GYPSUM
AMPHIBOLE
SIDERITE
HAEMATITE
LITHOLOGY
WEATHERING
ENVIRONMENT ILLITE (I)
KAOLINITE lK)
I>K K>I
VuJJU UVJO [ _AJJ Vl~ VV W [ J LJV 'J W MONTMORILLONITE
............. - ........... _-_ ...... _...... CHLORITE
MIXED-LAYER CLAYS
pH
FORMATION AGE
~ .1 --------,-----------,------------,----------,-----------.1-----------,-----------,-----------,----------,-----------TI-----------.-----------,-----------.----------.-----------~I----------~----------~----------~----------~--------~I 1.0 l11 0 Ul 0 (IJ 0 0 0
LAKE GEORGE
f N
I
F/uviO lacustrine deposits (undifferentiated)
LITHOLOGY
Acid VOlcanicsjdacite and rhyodacite Acid intrusion (Qtz porphyry and adamelli/e)
Basic volcanics (basalt) Basic intrusions (dolerite, qabbro etc)
Qlz turbidite sediments (sandstoJe, siltstone and shale
Unconcealed fault
Concealed fault
Basin limit
o
CLAY MINERALS
Kaolinite Illite (Chlorite)
Montmorillonite (Chlorite) .
Illite (Chlorite)
IOkm
•
~-----------------------~
Pecord !985/20 11/155-16/64
Fig.7 Provenance of clay minerals
PEAK INTENSITY OF KAOLIN ITE ON 001 BASAL SPACI N G AT 126°26 ( peak height in mm)
o 50 100
~
~
~
i=
r--
~
i--
150 Tr
§Clay k==~ Silt D Sand and grovel
Record 1985/20
u: <l: Q (j)
0 ...J w LL
Mi
~ ...J 0 <l: ::.::
(/)
Z <l: 0::: r-?
z ...J 0 <l: ::.:: ...J <l: :::J 0 (/)
W 0:::
~ Bedrock
DRILL HOLE LOG >-I Q
<l: >-E u: (9
0 (9 CRYSTAL LlNITY IN DEX KA OLI N ITE
I - ...J f- 0
f- <l: I WIDTH AT 112 PEAK HEIGHT Q u: W f-
f- PEAK HEIGHT 0 (j) ...J 0 02 04 0
10
z 0 f-<l:
20 ~ u: 0 LL
W u: 0 0
30 z w (9
Z ::)
en
50
z 0 f-<r ~ u: 0 LL
f-Z 0 Q
(9
Z 0 >-0 z . 0
8
90
• Kaolmi tic weolliering r :::::::::::j Deep weolliering prof ile :::::::::::::: prof/Ie
II / I 55- 16/ 5 2
Fig.8 Vertical distributi on and relationship of kaolinite and feldspar in drillhole C353
06
DRI LLHOL E
PEAK INTENSITY OF KAOLINITE ON 001 BASAL SPAC ING AT 126 0 2& (peak height in mm)
o 50 100 .50
0:: <r Q Ul 0 -1 w LL
MI Moj
t= bE ~
~
I
~ I
6:
~Clay [:::::j Sill D Sand and 9ravel
Record 1985120
lLJ l-n::: 0 Q (f)
z « n::: I-
?
.J « :::l o (f)
lLJ n:::
y: U o 0:: o w en
E2a Bedrock
E I f-Q W Cl 0
5
7
100
Fig . 9 Vertical distribution and re lationship of kaolinite and feldspar in drillhole C354
>-I Q <r 0:: (9
f-<r 0:: f-Ul
z 0
f-<t: ~ 0:: 0 LL
W 0:: o o z w (9
Z ::l en
z 0 f-<r ~ 0:: 0 LL
f-Z -0 Q
(9
z 0 >-0 z 0
>-(9
0 -1 0 I f--.J
CRYSTALLINITY INDEX KAOLIN ITE = WIDTH AT 112 PEAK HEIGHT
PEAK HE IGHT 0 02 04 06
• Kaol/n/t/c weather/fig I"":::;:':':'j Oeepweathenng profile :;:::;:;::::::: profile
11/155-16/53
J
J J ~J
J ]
]
]
]
J ]
J J J J J
Drillhole C354 Bungendore Formotion Depth 23·25m
w ~ Z ..J o « '"
w .... ...J ...J
" " "
I 400 , I I- 380
360
340 -;;;
;"320 ? c:
1 " ~300 3
,... ~ .2BO ~ . c:
2' - 260 .~
'" > 240 .2
Q)
'-'BO a::
-160
,-140
~-----r---___ -T; 120
16 14
Drillhole C354 Ondyong Point ForTT1otion Depth 90·75m
W I-
Z :::; o « '"
'6 14
~er.orr1 19A5 /20
'2 10 B
Degrees 2&
W I-
...J
...J
12 10 B
Degrees 2(s)
6
6
4
- 360
- 340
r 320 ,
~ 300 !
,...280 ~
i ~ ~ 260 § , 0
~240 ~ i '" 1- 220 .§ , c I
~ 200 ~ I=!
'80 ~ i ~ '60 (-
... ,40
! - 120
, ··80 4
Fig 10 X-ray diffractograms for montmorillonite showing variation in peak character and position 11/155-16/65
•
F-
--J ~
~
~
~
J ]
] ,
J :]
]
]
]
]
]
]
1 1 1
Drillhole C353 Bungendore Formation Depth 6 50 m
"', f-
2,
~I '" '"
I~
I' ,I ~, ..J ..J
J
'" f-
a: 0 ..J .I: u
r 400
~ 380
~ 360
~ 340
r 320
I ~ 300 Vi
~ 280
..........
~ co ~ 0 u
- 260 ~ >-
'iii - 240 co
Q)
c r 220 Q)
>
~200 ~ Q)
0:::
-180
- 160
- 140 I
L 120
----r-----r---l----r-~~-r----· 1 ! 00 -,--- -- 10 8 6 4
16 14 12
Drlll'10le C353 Bungendore Formation Depth 4225m
_. "---r---16
T~-
14
f-.'p~.')r~1 .985/20
T
12
Degrees 20
- T'
10
" " I,
"
Degrees 20
. T
8
w '= a: 0 -' I U
MI XED
LAYERING
6
- 400 ,
r 380
r 360 1 , ~ 340 I i I- 320
i Vl
f-300 ~ C ::>
280 0 u
>-260 ·iii
240
- 220
.. ~ 180
! ~ 160
~ 140
~ 120 4
c: Q)
C Q) >
.2
'" 0:::
Fig.11 X - ray dlffractograms for chlori;,71~5_'6/66
•
J J J J ]
]
J
J J J J J J ]
]
1 ]
]
]
Dr:llhole C354 Bungendo F D
. re ormotlon epth 39 25 m
16. 1
14
Drillhole C354 Bungendore Formotion Depth 505m
16 14
"
1-- .- -_. r
12 10
Degrees 20
·r~-- ~r-·
12 10
MONTMORILLON I T E MIXED-LAYER
CLAY
8
---~
6
UJ >--0: o ..J I U
~ 400
~ 380
- 360
- 340
IJ)
- 320 "? c ::J
- 300 0 u
- 280 :; If)
c ().)
- 260 C ().)
> - 240';:
~ ().)
-2200::
~ 200
- 180
T'160 4
r 400
~ 380 I
~ 360
. If)
:- 340 ::-C ::J
- 320 8
A~ -:::1 '~~260 0
. ().)
MONTMORILLONI~E - 2400::
-,-8
MIXED-LAYER CLAY ,·220
- 200
Degrees 20 Rl'!corr1 198~·/20
X~ray diffractogroms mixed-layer clays for mcntmorillonite 11/155-16/67
•
J J J
J
]
J J .J
J
J
J
Dnllhole C354 Gear ys Gap Formation (Jeep weotherln g prcf,'e) Dep!h i44 75rr
--.------. 16 14
Drillhole C354 Gearys Gap Formotlon (Deep weathering profile) Depth 147 Om
..., I-
z ...J 0 ~
"
.~
16 r 14
12
; \ .
ILLITE MIXED\ LAYE R CLAYS
\
\
--,--10 8 6
Degrees 219
..., ... :::; ~
12 10 8 6
De·Jrees 21S1
- 360
··340
- 320
- 300
-280 -III
'-'" -·260 C 6 u
- 240 -;:.
III
- 220 c Q)
c
- 200 Q)
.~
i .2 Q)
~ 180 0:
- 160
.. ,40
80 4
~ 300
L 280
r 260
~ 240 ~ I
~ 220
I f 200
I ... 180
~ 160 I
I ~ 140
120
. -.:.. 80 4
c :;J 0 ~
::: IJ)
c Q)
c Q)
>
a a:; cr
Fig.13 X-ray diffractograms for illite mixed-layer clays 111155-16(68
•
, ~.
J
J
J J
J
~J' \.
J
Drlilhole C354 Bungendore Format:on Depth 1600m
W I-
Z
-' o <l
"
II 'I II II
r 400
I l... 380 , I I r- 360 i
- 340 \ ~ \ ~ ~ 320
~, i
\ ,~ 1 W\J ~ ~Jj~ 300 ~ 1y'( W rrr"{, 1'":- 280 !
:- 260 .i;i c:
~41--------__ ~~~ ~
ILLITE - :- ~40 C MONTMORILLO'JITE .-MIXED-LAYER ~ CLf,y '- 22a .~
o a;
... 200 0: 1
~180
-160
r 14
-, - ~--... r r _·_·---1-140 16 12 10 8 6 4
Degrees 2&
Drlilhole C354 Bungendore Formation Depth 28·25 m
---OT'
16 14 12 10
Degrees 2& 8 6
Fig.14 X-roy diffractogroms for illitemontmorillonite mixed-layer clays
~ 260
! ~ 240
i ---+ 80
4
"1155-'6/69
•
:1 ) ) )
:1 ]
:1 ]
)
J )
J ]
] ~]
1 )
~ 200
Drillhole C354 Vl >-
Depth 19 Oem <t N -" t- u -180
'" <I :J v' 0 >-
<t -" ~160 u
'" ....... ~140 ~
c: ~ 0
I ~ -120 >-
'" c: N W <II
Vl .... ~ -100 C a: >- <t ~ <t 'l: ~ -"
U 0 0 <t - BO ~ '" '"
<II
>- a:: <1 ..J U
N I-
- 60 a: <l ::J 0
,~~>f ··40
, , 20
59 55 51 47 43 39 35 31 27 23 19 15 II 7
Jegrees 2~
Fig. 15 Typical X- roy diffractogram of quartz from cloy in the 8ungendore FormoJtion
DrillhOle C354 0epth 8725 IT'
N l-a: <t :J 0
N I-0: <1 ::J 0
59 55 51
N I-0: <l :J 0
47
N N
l- I-a: a: <t <t ::J ::J
0 0
N l-a: <t :J 0
43
N I-a: <t ::J 0
It 35 31 27 23 Degrees 21Sl
19 15 39
II
r 200 I
i -IBO
-160
, III
'" 140-;;;
c: ::J o
-120 ~
! ~ c:
-100 ~ c:
<II
~ 80
.~
~ <II
I a::
~ 60
- 40
- 20
Fig.16 Typical X-roy diffractogram of quartz from sand in the Ond yong Point Forma t ion il/155-16/ 7 0
•
r
J
J
J
]
J
J
J
Drillhole C3'5"3 Depth 51 25 m
N .... Il: <t :::J o
~--r--'--'--I'
60 56 52
Record '985/20
N .... a: <t :::J o
N .... Il: <t :::J o
N .... Il: <t :::J o N ....
a: <t :::J o
N fa: <t :::J o
N .... Il: <t :::J 0
UJ f<t Z o III a: <t u
II " ,I:::
a: <t :::J 0
" <to w 11.
W ...J III :::J 0 9 Il: <t 11. If)
0 ...J W u.
r---,-··· -'--T·" -r-···" "r-T- - r --'-"- r--- ,---"r--1- - '-----r--48 44 40 36 32 28 24
Degrees 2&
• "N ..... a: <t :::J 0
rl80
I ,
160
~ 140
I
r '" ~ 100 C
:J o U
>-'iii c
'" C
'" > , C i 60 '"
r ~ ! r40
I , ~ 20
1
r .. T -"--'-"-T-.-r-l 0 20 16 12 8
Fig 17 X-ray diffractogram of feldspar from sand in the Ondyong Point Formation 11/155 -16171
•
J J
Io--.• J .. ,.
J .. '" ,.
UNCONSOL I DATED SEQUENCE (CAINOZOIC) .. III ~ ~ III·· . .... . _, ., ... . · .... .
· . .. ..
· ." .
'Im
Clay
Black clay
Silt
Sandy clay
Sandy SI!t
E2J ....... . . •.... ~::.'~' .::.':.:~: Fine to medium -grained sand
Coarse-grained sand
Gravel
BEDROCK SEQUENCE (PALAEOZOIC)
~ Phyllite
E Siltstone
WEATHERING
D Unweathered
D Ferruginous
Kaolinitic
OTHER SYMBOLS
fIJVV\.!\.- Unconformity
ColC/le
• d Dolomite
Carbonate
Fig 18 Legend for drillholes C353 and C354
Oats are dota paints
~ major ~~?nCoer Continuous ~ecord
--absent over 25 em Inlervols
trace minor major
r=- trace minor major
Continuous record over 25 em inlervols
Continuous record over 25 em intervalS
Discontinuous record
Occurrence of major elements
11/155 -16/56
•