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 It may not be published in any form or used in a company prospectus or statement without the permission in writing of the Director.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 .-

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C1) 0 o.~ .~ <{ 0:: ::E ~~ ~

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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.. - -

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Z 0 .- E 0 E 0 0 2 c:

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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

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Fig I Lake George Basin and drill hole locations

Goulburn

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BMR dnllhole with number

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11/155-16/60

•

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--==;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

•