MURRAY BASIN: WESTERN MARGIN

EASTING (meùss)

LEGEND

Ulupa Sihstone Buna Group Umberatana GrouP Mstasediments Black Hill Norite Gabbro

Mylonite?

Ultramafic rocks Granite

Dark colours: based on outcroP and drillcore ^(Q) Light colours: inlerred

3870ü) 3t0m0

Figure 5.2: Regional interpretation of the Eastern Magnetic Zone: magnetic units outlined ^(see leg-end),

boundlry

^between

^EMZ

^and

cMZ

^indicated

by bold line. Drill

hole locations after Wegmarn (1980) and Lewis, P. (1985).

CHAPTER 5.

REGIO¡üAL GEOPHYSICAL OVERVIEW ⁵⁹

Eastern Magnetic ^Zone

The

western

margin of the Murray

Basin forms

the

present eastern

limit of the

Kanmantoo Group

outcrop. A

grey-scale image

of the BMR data

over

the EMZ is

shown

in

Figure 5.6.

Intensity and

^character

of

magnetic anomalies change

sharply

acloss

the

Palmer-Milendella

Fault.

Gradients of well over hundreds of nanoTeslas mark

the

contact between

the

CMZ and

the EMZ

establishing

the EMZ

as a signifrcantly different magnetic

"terrane". ^The

^{contact is}

essentially linear and trends NS.

Linear,

moderately strong magnetic ^anomalies against

a

low-relief magnetic ^background

typify the

response due

to

the weak

to

moderately magnetic Kanmantoo Group

in the

CMZ.

ih"

Morruy Magnetic High

(MMH)in

the EMZ is characterized by multiple, intense anomalies.

The MMH ^{may be}

^separated

into an

eastern

and

western

band. The

western

band

of

the MMH is

^dominated

by

a sequence of circular

to

oblate magnetic anomalies of the order of several thousands of nanoTeslas. The ^source of these magnetic anomalies are Cambro-Ordovician granitoids and gabbros (e.g. Black

Hill Norite)

which Foden et al.

(in

press) associate

with

^an

ãxtensionai post-Delamerian phase. The granitic and gabbroic rocks vary widely

in

composition (Wegmann,ISAO; Foden et

al.,in

press; Turner et

a\.,1989).

The eastern band of the

MMH

^is

ìor^"a ^by

wide, linear anomalies. Basalt and tholeiite have been discovered

in drill

holes into these anomalies (Wegmann, ^1980; Lewis, P., 1985)'

A

simplified interpretation ^based on

drill

hole data, outcrops and rnagnetic response is pre- sented

in

Figure

5.7.

The varying magnetic properties and petrology

of

these intrusions (and extrusions?) are discussed

in

Section

6.2.

Anomalies which could be caused

by

sediments are

only rarely

seen as

the high

^magnetic

relief

caused

by the

neat-sutface, igneous sources ^ob-

..or",

low-amplitude signais also coming from

the

same

depth.

Between the two bands, linear anomalies are occasionrlly foutrd which could be caused

by

the metasediments

of

the Adelaide Supergroup

or

Kanmantoo

Group. Drill

^holes

in

a number of these ^areas have intersected low- gru,d"-r.t",irts and greywackes which have been

tentatively

correlated

with

Kanmantoo Group (Preiss, pers. comm.).

The

Murray

Magnetic High ^was identified as

"strip ^7"

^by Wellman and Greenhalgh (1988).

The abundance of granitoids, gabbros and basalt dykes

in

the

MMH

lends credence to the post- Delamerian extensi,onal ^phase proposed by Foden et aL (in press). Further east, ^a quiet magnetic

pattern

marks

the

eastern edge

of the MMH. The MMH is

sigmoidal

in

shape.

It

^{follows an}

-arc,

trending SE near Coonalpyn, NS parallel

to

^the Palmer-Milendella

Fault,

and swings

to

^a

NE

trend following the trend of the ^Nackara

Arc. It

is a major magnetic feature and delineates the edge of exposed Precambrian rocks

in

Australia'

Within ^this

magnetic zone, \Megmann (1980) discovered mylonite

in the

Marne River, just east

of longitude tãg"30,.

Susceptibility measurements

on the

outcrop returned

high

values

-

¹⁵⁰⁰

^{x 1¡-5 SI)}

^and

^the

^mylonite zone has been correlated

with a

15 km long, NS trending narrow magnetic

high. It is

possible

that the

Morgan

Fault (Firman,

¹⁹⁷⁴⁾

is

related

to

the mylonite

zÃe.

^There are several similar anomalies

in the MMH

^(Figure

5.7). Mylonite

^zones are indicative of high strain.

6.2.2 Gravity data

Regional

gravity

surveys, cond,ucted

by SADME

and

BMR,

cover

all of

South

Australia at

^a ,pu-riog

olx

Z

km

(Coppin

et

aL,1973).

A

detailed coverage of the Noarlunga, Willunga, Onka-

p"rt"go

and Echungo

.ir""tr

has recently been completed

by N.

Sjarif and

Prof.

Boyd (spacing

CHAPTER 5. ^REGIONAL

GEOPHYSICAL OVERVIEW ⁶⁰

r 1.2km).

The Mannum ^and. Cambrai sheets are being covered

by Prof.

Boyd and S. Turner.

Gravity ^data

over small areas have been collected

by

Honours students

at the

University of Adelaide: profile ^across the Mannum

to

Adelaide pipeline (Middleton, 1973), along the western margin of

lhe Murray

Basin

(Mclnerney,l974;

Hansen, 1975) and

in

the region of the Monarto Granite (Lewis,

4.M.,

^1985).

The main gravity features

in

the region include:

1.

Genera,lly low ^values over much of the

Mt.

Lofty Ranges and the Flinders Ranges probably reflect the sequence of thick metasediments

in

the Adelaide Geosyncline

but

are otherwise inconclusive.

2. A ^gravity

high runs parallel

to

and

partly

coincides

with the Murray

^Magnetic

High. It

extends

further

eastwards than the

MMH.

Mancktelow (1979) identifies the gravity high

in

the region ^as

the

Murray Ridge and ^suggests

that it

may represent a cratonic high.

Several local gravity highs

in

the broad gravity

higli

have been investigated

in

more detail (Mclnerney

,

t974; Hansen, ^1975; Boyd, pers. comm.). comparison of magnetic interpreta-

tion

of

the MMH

and locai gravity observations indicates

that

the local gravity highs are due to extensive basic

intrusion.

The Black

Hill

Norite is more ^dense than the surrounding granite an¿

this

together

with its

characteristic magnetic properties (Section 6.2.2) per-

mits

the identification

of

similar bodies (Figures 5.7 and Figure

6'1). This

interpretation has been confirmed by

drilling (drill

hole locations given

in

\Megmann, 1980).

3.

Middleton (1973) completed ^a gravity profile along the pipeline from Mannum to Adelaiâe' There is no signíficani density difference between the metasediments of

the

Adelaide Su-

pergrollp and the Kanmantoo Group ^so

that

no gravity anomaly would be expected ^across

ihe contact.

There

is a high

over

the

migmatites west

of the

Palmer

Granite,

^{and an} apparent

fault

east of the granite.

Granites may be associate,il

with

^gravity lows (Hansen, 1975)

or

highs (e.g. the Monarto Granite

in

Lewis,

A. M',

1985).

The

basement

inliers

(Barossa Complex) are associated

with local gravity highs.

The deep-seated magnetic ^sources

in

the

WMZ

which are interpreted

to

be Barossa Complex

,o.k,

ut depth ^(see above) are not obviously related to a gravity anomaly. The

fault

which was inferred between

the

southern and northern arcs of

the

Barossa Complex anomalies (Figure 5.3) is marked by a gravity gradient (Sjarif,

in

prep')'

4. A

steep gradient trends NS and parallel

to

the Nairne Fault

in

the Echungø region (Boyd,

p"rr. .oÃ-.). ^It

^follows

^the

^{contact between}

^the

Kanmantoo Group and

the

Adelaide Sop"rgrorrp

but

is caused

by

a contact

at

a depth of several kilometres. The source of the

gtrai*t

may be ^a

fault within

^deep Barossa Complex rocks

in

the core of the Strathalbyn Anticüne (Plate 5).

The basement

inlier

near Normanville is

in fault

contact

with

the metasediments of Ade- laide Supergroup. Preliminary interpretation ^suggests

that

the contact dips east

(Sjarif

in

prep.).

ÃoJur.or, (1gT5)

in

his cross section ^across the

inlier

shows

that

^{the western limb}

is overturned and

that

an easterly dipping late reverse

fault

displaces the folded ^beds.

Both the Morgan Fault

(EMZ)

and the Encounter Fault (CMZ

-

^this

^fault

^{trends NE and}

transects the main study area in the south) wete pïoposed on the basis of gravity gradients

(Firman,

Ig74)

.

The Morgan Fault has also been related

to

the

right

angle change

in

the course of the Murray

River.

Several NE trending faults have been mapped using magnetic data (Plate

5)

and these are subparallel

to

the Encounter Fault.

CHAPTER 5.

NEGIONAL GEOPHYSICAL OVERVIEW ⁶¹

6.2.3 Seismic data

No deep crustal seismic reflection experiments have been carried

out in

South

Australia.

How- ever,

siLple

models of the structure of the crust may be deduced from earthcluake and explosion seismic d,ata. Greenhalgh ^eú a/. (1989;

in

press) have compiled and reinterpreted a'll available earthquake and explosion seismic (quarry blasts)

data.

Using a simple average model, they in- ferred

that

the thickness of the crust is ³⁸ km

with

a P wave velocity equal to 6.32

km/s.

Results of

interpreting

^{quarry blasts}

within

^the Adelaide Geosyncline indicate

that

the crust is layered

with

an upper layer raogiog

in

thickness

from

10

to

¹⁸ km, and an aveïage P wave velocity (P1)

of

5.g4kms-1 overlying-a ^second layer

with

velocity

6.42kms-l. Both ^crustal

discontinuities shallow towards

the Murray Basin.

The underlying mantle velocity has been calculated

to

be 8.05 kms-1.

The

average

P

wave velocity

in the uppeÌ 20km of the crust

varies

laterally

and ranges between 5.g4 and ^6.42

kms-1.

Greenhalgh

et

al. (1989) found ^a high velocity ridge which trends

NE

through the Flinders Ranges. This is coincident

with

positive Bouguer

gravity

values' The axis

of

an elongate conductor mapped using geomagnetic deep sounding arrays (Chamalaun, 1gg6) runs through the centre of the high velocity ridge. The depth ^{and cause} of this conductor are

not

clear. Parallel to the Torrens Hinge Zone, the ^P1 velocity high coincides

with

^{a Bouguer} gravity low.

From the limited seismic and gravity data available, the Flinders and

Mt.

Lofty Ranges ^do not appear to have a significant crustal

root.

During the Delamerian Orogeny when the Kanmantoo

C-op

^formed an orog"nic upland, the mountain ranges may have had a corresponding crustal

root.

However, following subsequent erosion, isostatic compensation would have resulted

in

the disappearance of the mountain root.

Note

that

^the epicentres of earthquakes ate concentrated

in

the Flinders Ranges,

Mt.

Lofty Ranges and

in the

Broken

Hill area.

Wellman and Greenhalgh (1988) computed

the

^average focaf depths and found

that

seismicity

in

South Australia is shallow

in origin.

They determined

the

predominant

principal

stress

to

be NE-SW compression and suggest

that this

caused the

faulting

and

uplift

of the

Mt' Lofty

Ranges.

CHAPTER 6. GEOPHYSICAL

RESPONSES OF KNOW¡ü

NOCK

^{TYPES 62}

Chapter ^ö

Geophysical ^responses of kno\ ^¡n

rock ^types

Magnetic, radiometric and geological data have been compared

to

determine

the

geophysical

,".p1o." of

different stratigraphic and lithological

units.

The

majority of

magnetic anomalies

.r" do" to

susceptibility differences

within

metasediments and between igneous rocks and the country

rocks.

^Faults, shear zones and lineaments have distinctive radiometric and ^magnetic signatures. Basement rocks, i.e. basement

to

the Adelaide Supergroup, and some mineralized zones have also been correlated

with

characteristic signatures.

Some magnetic anomalies have ^been named to make

it

easier to refer to them.

In

sorne cases' an individ.ual magnetic

unit

has been named (".g. the curviiinear magnetic anomaly ^associated

with the

Talisker Ca,lc-siltstone which

is

folded

by the

Macclesfield Syncline has been named

TC-MS). In

^others

^a

^group

^of

anomalies has been classified (e.g. magnetic anomalies ^caused by Tapanappa Formation magnetic horizons

in

the Dawesley region are referred

to

as

TP-DM).

Thesenames have been indicated on Plate

2

^{ar.d are used}

ⁱⁿ

^the description of structures

in

the

next

chapter.

Only a small

part

of the main study area is occupied by the

WMZ

and

EMZ,

and therefore

in

^detailed discussions (Chapters

6

and

7) the CMZ

^and

main study

area are deemed

to

be

equivalent. On

this

basìs,

the KNSZ

and KRSZ include ^adjacent

WMZ

area, and

part

of the

trMZ

is included

in

the

ISZ

(compare Figures 5.3 and 5'5)'

This chapter begins

with

a discussion of magnetic anomaües

in

the Kanmantoo Group. This is followed

by

sectiãns on

the

other metasedimentary units

in the

study area:

the

Normanville Group and the Adelaide Supergroup. The response of the Barossa Complex rocks, granites and

granitic

^{gneisses, gabbros,} amphibolites and dolerites follows. The radiometric ^response of the rocks is also discussed. Structures referred

to

are found on Figure 1'2 and on Plate

5.

Measured magnetic susceptibilities are tabulated

in

Tables

2.4

and 2.5 and iisted

fully in

Appendices B and

C.

parameters determined from mod.elling magnetic anomalies aïe listed in Appendix

I,

and

the

modelled cross-sections are presented

in

Appendix

J.

The depths

to the

tops of magnetic sources are given

with

^reference

to

the ground surface'

CHAPTER 6.

GEOPHYSICAL RESPO/VSES OF KNOW]V

ROCI{

TYPES ⁶³

6.1 Metasediments 6.1.1 ^{Kanmantoo GrouP}

Middleton Sandstone

The Middleton Sandstone represents the youngest exposed Kanmantoo Group

unit,

^as its upper boundary is unknown.

It

^{must have been overlain by} a considerable thickness of sediments, ^as

it

is intruded by the coarse-grained Encounter Bay Granites (Daily and Milnes, 1973). On Fleurieu peninsula the formation has been mapped only near Middleton,

its

^type

^locality.

^{Better expo-}

sures have been identified on the ^coast of Kangaroo

Island.

The formation

is

composed mainly

of

well laminated arkosic san,ilstones (see

Boord,

1985

for

facies descriptions)' The lithologies are

in

sharp contrast

to the

greywacke facies

of the

underlying Petrel Cove, Balquhidder and

Tunkalilla

^Formation

but

are similar

to

the sandstone facies

of the

Backstairs ^Passage Forma-

tion.

The Middleton Sandstone probably accumulated

in

a shallow marine environment (Boord, 1e85).

Bands

rich in the

heavy minerals, zircon,

ilmenite,

magnetite,

rutile,

sphene, epidote and

actinolite

have been

found in

Kanmantoo Group metasediments

on

Kangaroo

Island (Flint,

19Z6). They occur as lenticular bodies, varying

in

length

from

5-50 metres and

in

thickness up

to

0.25 metres. Of the five localities mentioned by

Flint

(op.

cit.),

a map of the island produced

by

Mancktelow (1g79) shows

that four

are located

within Middleton

Sandstone

outcrop.

(The

hluuy

minerals

at

the

fifth locality

are associated

with

Recent beach and dune sand deposits).

Daily and Milnes (1g73) ^record. conspicuous segregations ^of epidote developed consistently rvithin the

Middleton

Sandstone

at

Middleton beach.

Magnetic susceptibility measurements near Middleton (Table 2.4) were of the ^order. of 1000

x

10-5

SI. ^{From the}

aeÌomagnetic contour

map of Fleurieu

Peninsula and

part of

l(angaroo Island.

(SADME,

1983),

Middleton

Sandstone outcrop was found

to

be associated

with

strong anomalies.

Detrital

magnetite is probably the cause for most anomalies ^as heavy mineral bands are common

within

the sandstone. One sample measured for ferrous and

total

iron shorved very small

total iron

content (2.76%)

but

high oxidation rario (65.7%). This result is similar

to

those obtained

for the

Backstairs ^Passage Formation (Section 2'3)'

Anomalies MS1

to

MS4 (Plate

2)

are

part

of a large complex of magnetic anomalies which extends to Middleton beach and

into

Encounter Bay. Magnetic sources are

within

^a few hundred metres of

the

surface

but

are concealed

by Tertiary

rocks and Recent sediments of the

Mulray Basin. The

anomalies

MS|-MS4

are similar

in

style and very

likely

share

a

common ^source' MS1 appears to be continuous

with

^a magnetic anomaly over exposed Middleton Sandstone llear

Middleton.

The most likely cause of the anomalies MS1-MS4 is the strongly magnetic Middleton Sandstone which forms the core of the south-plunging synclines of the Kanmantoo Synclinorium (see Section

7.2). Without drill hole data, this

inference

is speculative. Alternatively,

^the Èncounter Bay suite of granites (Mancktelow, ¹⁹⁷⁹⁾

might

extend

into

the region of the

MSl-

MS4 anomalies, though

iheit

low measured susceptibilities makes

it

unlikely

that

they could be

the cause of the magnetic anomalies.

MSJ

is

a groltp

of

anomalies, "closed"

to the north

and widening southwards and deflned

by

a steep gradient

in

the west. The diffuse nature of the eastern boundary indicates probable

faulting by

the Bremer

Fault

(Plate 5).

CHAPTER 6.

GEOPHYSICAL RBSPONSES OF

I(NOWN ROCI(

^{TYPES 64}

Petrel Cove, Balquhidder and Tunkalilla Formation

Along the south

coast

of

Fleurieu Peninsula, where ^exposures are good,

the

rocks between the Tapanappa Formation and the Middleton Sandstone have been divided

into

the Tunkalilla, Balquhiddet

""d ^petrel

^{Cove Formation}

^(Daily

and Milnes, 1973). ^Elsewhere

it is

diffi.cult to distinguish between these

units

and the underlying Tapanappa Formation (Mancktelow, ¹⁹⁷⁹⁾ owing

to

^the

similarity

of

their

lithologies.

Whole rock analyses (Mancktelow, 1979) gave average values of

total

iron

in

these sediments

as follows: 2.16%in petrel Cove, 5.J4Toin Balquhidder and ^5.02% in Tunkalilla Forrnation. Mag- netic susceptibility measurements on samples (Figure 2.5) were

uniformly low'

Higher cluality aeromagneii.

drtr

over the south coast of Fleurieu Peninsula would ^be invaluable

in

demarcating formatiãns, as the example used

in

Section 5.1 (Figures 5.1 and 5.2) indicates.

Two curvilinear anomalies

YKG-M

have been marked on Plate

2.

The one

in

the southwest corner

of Plate

²

is a

negative anomaly and

is

terminated against

the

Encounter

Fault'

The second.

yKG-M

anomaly is easily identified ^{as a} weak,linear anomaly which is ^caused by younger Kanmantoo Group ^sediments folded

into the

Strathalbyn

Anticline.

Neither anomaly can be delineated

in the

older survey

(SADME,

1983).

'Ihe

cause

of

magnetic anomalies

is likely

to be

pyrrhotite

and magnetite bearing

pyrite

schists, as bands rich

in iron

sulphi<les are common

within

these formations (Mancktelow,

1979).

Several anomalies

which

have been placed in

the

Tapanappa

Formation

^(e.g.

TP-SM, TP-HH -

^see below) could instead

be in

^younger

Kanmantoo Group formations. However, lack of continuity has prevented correlation'

Tapanappa Formation

The Tapanappa Formation has been mapped ^as outcropping extensively

within

the study area' Mancktelow-(1g79) identified

two

facies

variants:

greywacke and sandstone.

The

^proportion

of

siltstone

to

sand.stone

in this

facies

is

variable,

but

over most of

the

outcrop area medium- graine¿ greywacke

is the

dominant

lithology. With

increasing metamorphic grades,

the

rocks have been metamorphosed into micaceous quartzites, meta-arkoses, quartz-feldspar-mica ^schists and andalusite-staurolite ^schists.

Along the

south coast

of

Fleurieu Peninsula,

the dark

coloured greywacke facies

is

more common.

In the

more northern areas, east and northeast of

Truro,

grey massive or larninated siltstones crop

out. The

siltstone

units

occasionally contain bands which are

rich in iron

sul-

phides. On the

south coast

of

Fleurieu Peninsula these bands are

rich in

pyrrl-Lotite. When

.trongly

metamorphosed the bands are rich

in

muscovite and

pyrite'

Even when the more ^dis-

tinctive

greywacke facies dominates,

the first

few metres above

the

Talisker Calc-siltstone ^are often sandstones.

Away from the south ^coast of Fleurieu Peninsula, the lithologies of the Tapanappa Formation are moïe akin

to the

sandstone facies of the Backstairs Passage

Formation'

^The rocks are well laminated,

light

coloured (less

biotite)

arkosic and quartz-rich sandstones. Mancktelow (1979) has observed

thin,

heavy mineral beds and laminae containing 80-90 % magnetite

*

haematite

in

arkosic facies

of the

Tapanappa

Formation. The

^thickness

of

these layers ranges

up to

30 centimetres.

Continuous

linear

anomalies, consistent

in

anomaly characteristics over

long

distances, is

typical of

^magnetic

units within this formation.

^Anomalies

^TP-SA

^and

^TP-MNS

^{have been} correlated

with pyrrhotite

bearing

pyrite

schists, which were

originally

siltstones

rich in

iron

CHAPTER 6,

GEOPHYSICAL RESPONS¿S OF

I(NOWN ROCI(

^{TYPES 65}

sulphides

and TP-EB

(Figure 7.5)

is likely to be

caused

by a similar rock type.

Magnetite u,r,ã

pyr.hotite

bearing phyllites folded

into

the Monarto Syncline (Lawrence, 1980) give rise to continuous,

narrow,linear

anomalies, collectively called

TP-MNS.

Kleeman and Skinner (1959) suggest

that the pyrite, like that of the

Nairne

pyrite

facies

of the

Talisker Calc-siltstone, ^is synlenetic

in origin.

^{TP-EB outlines what} is possibly ^a large fold

in

the formation (Figure 7.5)' Permian glacials obscure outcrop

but

the

fold is

significant

in

helping

to

explain

the

apparent great thickness of the Tapanappa Formation.

Sulphide mineralization

within

the Tapanappa Formation is often associated

with

^rnagnetic anomalies.

The

opaque

oúde

assemblages

of the

mineralized zones usually include pyrrhotite

I

^magnetite

^{(Both, in}

press). Invariably,

pyrite

schists

in the

Tapanappa Formation contain

pyrrhotite t magnetite.

Near Wheal

Ellen

and

the

Strathalbyn

Mine, pyrite

schists produce magnetic anomalies,

TP-WE

and

TP-SM

respectively.

The

anomaly

TP-WE is

negative and

-uy

^hurr" been caused

by the

presence

of

monoclinic

pyrrhotite.

Monoclinic

pyrrhotite

has occasionally been found (Askins, 1968; Spry, 1976) and self-reversal

in the pyrrhotite

may be responsible

for the

intense negative

anomalies. At

Kanmantoo

Mine (Lindqvist,

^{1969) and}

in ihe

Dawesley region (Benlow and

Taylor,

1963), sulphide mineralization

is

associa,ted

with

andalusite schists. Magnetite

is

an

important

component

of the

opaque oxide assemblages

of

these schists and

this

results

in

strong anomalies

(TP-KM

and

TP-DM

respectively).

Magnetite ore from the Kanmantoo Mine had the highest susceptibilities recorded

for

l(an- mantooGroup rocks: over

lSIunit. Theresult

of mining

activity

in the region makesit difñcult

to

isolate

the

magnetic effect of the

mineralization. TP-KM

consists

of

a number of bull's-eye anomalies,

at

least some of which are caused

by

cultural features.

The

maximum amplitude

of

anomalies

in the

Dawesley region (Figure 7.10)

is -

^L200nT.

The anomalies are caused by magnetite and

pyrrhotite within pelitic

schists of

the

Tapana'ppa Formation and are collectively ^defined

to be the

Dawesley Magnetic

Anomaly (DMA).

The Dawesley Magnetic Anomaly ^{has been} investigated by Mirams (1962), Benlow and Taylor (1963) and

Staltari

(1974).

Drill

hole

DDHl

(Benlow and Taylor, op.

cit.)

intersected magnetite bearing sulphide ^bands.

I

detected magnetite

in

staurolite schists (Appendix

D).

^{The rocks}

^{in the}

Dawesley area may represent relatively more oxidised rocks compared

to

the rocks along strike

further

south. This would then favour production of metamorphic magnetite. The anomaly is

riglit-laterally

faulted by the Dawesley Lineament

to

the

north

(Plate

5).

The axis of the Kanmantoo Syncline ^passes through

this

anomaly.

At

least two generations of folding have combined

to

produce a cornplex magnetic anomaly.

There

is a major

^problem

in

resolving

the

stratigraphy

in the

Tepko and Angasúon ^sheet areas

mainly in the

area covered

by the

Intermediate Subzone

(ISZ). The

lithologies

in

this area are

mainly

meta-arenites and migmatites. Mancktelow (1979) has

attributed

much of the outcrop in this area to the Backstairs Passage Formation but

it

should be noted here

that

similar lithotogies (meta-arenites) are common

in

the Tapanappa Formation (see Section 7.4)'

In the Karinya

Syncline, lower metamorphic ^grades and pre-metamorphic variations ^have combined

to

produce magnetic

units

which, though

linear,

are discontinuous,

vary rapidly

in anomaly characteristics along strike and extend

for

only few kilometres. TP-KRS

is

typical of such anomalies.