le73/7/

ery\3DEPARTMENT OFMINERALS AND ENERGY

BUREAU OF MINERAL RESOURCES,GEOLOGY AND GEOPHYSICS

Record 1973/71

OFFICER BASIN DETAILED GRAVITYsuRvEys W.A., 1972

OPERATIONAL REPORT

by

I. Zadoroznyj

The information contained in this report has been obtained by the Department of Minerals and Energyas part of the policy of the Commonwealth Government to assist in the exploration and development ofmineral resources. It may not be published in any form or used in a company prospectus or statementwithout the permission in writing of the Director, Bureau of Mineral Resources, Geology and Geophysics.

BMRRecord1973/71

c.3

1

Record 1973/71

OFFICER BASIN DETAILED GRAVITYSURVEY, W.A., 1972

OPERATIONAL REPORT

by

I. Zadoroznyj

CONTENTS

SUMMARY

Page

1.^INTRODUCTION 1

2.^OBJECTIVES AND PROGRAM 2

3. FIELD OPERATIONS 3

4. RESULTS 5

5.^REFERENCES 5

APPENDIX 1. Survey details 6

APPENDIX 2. Staff and equipment 8

ILLUSTRATIONS

PLATE 1. Traverse location map - Warburton Range Road traverse

PLATE 2. Traverse location map - Emu Road traverse

PLATE 3. Preliminary gravity, magnetic, and radiometric profiles -Warburton Range Road traverse

PLATE 4. Preliminary gravity, magnetic, and radiometric profiles -Emu Road traverse

1

I I I I I I I I I I I I I I I I I I I I

SUMMARY

The Bureau of Minelfal Resources made a detailed gravity survey in the southwest Officer Basin in Western Australia between August and November 1972. The survey provided gravity coverage at one-kilometre spacing along the Warburton Range Road from the vicinity of Lake Throssell for 214 kilometres towards the Warburton Mission, and on short traverses across the Warburton Range Road traverse, providing data supplementary to a concurrent seismic survey. The survey also provided detailed gravity coverage for 136 kilometres along the Emu Road between Lake Yeo and Neale Junction, near the southern boundary of the Officer Basin in Western Australia. Magnetic and radiometric measurements were made in addition to gravity observations at most stations.

The traverses were surveyed in an area covered recently by a Bureau of Mineral Resources reconnaissance helicopter gravity survey. The Bouguer anomaly profiles along the main traverses show departures of up to five niilligals from profiles interpolated from the reconnaissance data. The most significant magnetic feature was a high-amplitude magnetic anomaly with a half-width of about 2 kilometres which was revealed in the northwest corner of the Westwood 1:250 000 Sheet area. This high coinCided with one of two significant Bouguer anomaly highs.

This report describes the survey operations and presents survey statistics. The results of the detailed work along the Warburton Range Road and the 20-kilometre cross-traverses across it will be used with the seismic information to interpret the structure of this part of the Officer Basin.

1. INTRODUCTION

The Bureau of Mineral Resources (BMR) conducted a detailedgravity, magnetic, and radiometric survey in the southwest of the OfficerBasin in Western Australia from August to November 1972. The OfficerBasin covers a large area of Western Australia and South Australia. Inthe basin the thickest sedimentary pile is more than 6000 m. In the WesternAustralian part of the basin the sediments are mainly of Proterozoic age,largely overlain by a thin layer of Palaeozoic sediments. Hunt Oil Companycarried out an active exploration program in the western part of the OfficerBasin. That company drilled four shallow exploration wells after extensivegeological and geophysical investigation before relinquishing its explorationpermit in 1966. In 1970, BMR and the Geological Survey of WesternAustralia (GSWA) commenced a joint mapping project of the W.A. part ofthe Officer Basin. In addition to the joint mapping project and the work byHunt Oil Company, other investigations completed have been a BMR seismicsurvey in the northern part of the basin and resistivity probing in the southfor the W.A. Department of Public Works. A BMR reconnaissance helicoptergravity survey at a grid spacing of 11 km was recently completed.

The detailed gravity survey was carried out concurrently with aBIVIR seismic survey (Harrison, 1973) which shot several refraction andreflection probes along the Warburton Range Road. Gravity, magnetic, andradiometric observations were made at 188 shot-points. A total of 351gravity observations were made at one-kilometre intervals along parts ofthe Warburton Range and Emu Roads. To obtain broader gravity coveragealong the Warburton Range Road, 203 stations were established along cross-traverses which were generally 20 km long and 10 km apart. The locationsof all stations are shown in Plates 1 and 2. The survey was integrated withprevious gravity surveys, conducted by Hunt Oil Company from 1963 to1965 and BMR in 1971-72, by tying to permanently marked gravity stations.All stations were optically levelled by surveyors from the Department ofthe Interior. Magnetic and radiometric observations were made at mostgravity stations.

Sand plains with longitudinal dunes, commonly 10 to 15 m high,cover much of the area. Elsewhere the country is flat with occasionalsmall hills and outcrop escarpments. The soft surface of Lake Throssellpresented a severe obstacle to access. Vegetation is sparse and consistsmainly of spinifex bushes, mallee, and mulga trees. The mulga often occursin very thick patches.

This report describes the work done during the field survey andincludes preliminary Bouguer anomaly, vertical magnetic intensity, andradiometric profiles along the main traverses. Detailed analysis of the dataobtained, in relation to the reconnaissance gravity information and the

-2-

results of the seismic survey, will be required for an integrated interpretation. A discussion of the geology of the area and previous geophysical investigations may be found in the pre survey reports for the seismic and gravity surveys in the Officer Basin (Pinchin & Mathur, 1972; Zadoroznyj & Brown, 1972).

2. OBJECTIVES AND PROGRAM

Objectives

The primary objective of the survey was to obtain detailed gravity information, along parts of the Warburton Range and Emu Roads, which will help to define the structure of the southwest margin of the Officer Basin. The gravity work along the Warburton Range Road provided information complementary to a concurrent seismic survey, and the work along the Emu Road was to investigate two gravity minima west of Neale Junction. The magnetic and radiometric measurements were proposed to provide additional information.

Program

Two long gravity traverses were proposed: (a) one along the Warburton Range Road extending from as~rofix T092 towards Laverton for 190 km, and (b) the other along the Emu .Road for 136 km between bench marks XOl18 and X08'1.

The station spacing along the roads was to be one kilometre. Cross-traverses 20 km long and 10 km apart along each road were also planned . .In addition observations were to be made at seismic shot-points.

Apart from the cross-traverses, the program as proposed was carried out. Access problems on the cross-traverses Slowed the rate of progress considerably. Many of the cross-traverses were relocated to make best use of open country, and a series of stations was also established on the north side of Lake Throssell because several of the cross .. traverses were cut short on the southern edge of the lake. Time did not permit the establishment of cross-traverses along the Emu Road.

The locations of the gravity stations established are shown in Plates 1 and 2.

-3-

3. FIELD OPERATIONS

Surveying

Stations along the Warburton Range Road and the Emu Road were located by vehicle odometer and compass traversing, and were optically levelled. Elevation control was maintained by ties to benchmarks every 4km along the road.

The six cross-traverses farthest from Laverton were pegged and levelled using a theodolite. Thereafter, chain and compass traversing was employed for pegging, and a spirit level f0l1 levelling, as this method was considered faster and without significant loss in accuracy.

Photo-identification of ma;ny Stations ,was attempted, particularly those on the road traverses and at the ends of cross-traverses. Owing to the sparseness of easily identifiable features, however, only 14 stations could be pinpricked on the airphotos.

Surveying progress was severely hampered by difficult access to the cross-traverses, and much of the program would not have been completed with one surveying crew. Consequently a second surveying team was employed for the last eight weeks of the survey, and a bulldozer was used. In addition two field hands were employed to assist in line clearing. The

, surveyors were in the field for a total of twenty weeks. In the first twelve weeks 195 km of road traverse and 102 km of cross-traverse were surveyed.

" , In the last eight weeks 155 km of road traverse and 410 km of cross traverse .',r', ,were surveyed. Use of the bulldozer increased theaverage surveying rate

iCo. on cross-traverses by a factor of about three; in very thick mulga, the ..... , . factor was as high as 10.

Stations were marked with wooden stakes except at the ends of each traverse and every 10 km along the traverses, where they were marked

,;s,'. by a steel picket. Plastic flagging was used to help locate stations.

The overall rate of observing was tied to the rate of surveying. The gravity crew could easily observe along a traverse twice as fast as it could be surveyed, a,ven with the magnetometer and scintillometer. There is thus a need for at least two surveying crews per gravity crew.

-4-

Gravity

Survey details and information on staff and equipment are given in Appendices 1. and 2. The gravity survey was tied to a previous Hunt Oil Company survey, to the BMR-1971-72 reconnaissance helicopter gravity survey, and to 'lsogal' stations at Warburton Range Mission and Lake Yeo.

Drift control was maintained by repeat readings at selected stations every one or two hours. Reading time was about two minutes. Transport-time between stations varied considerably depending on accessibility.

The meter behaved erratically at the start of the survey. Checks were conducted to determine the reason for a large drop in scale value but no major fault was apparent. The meter became stabilized and no further trouble was experienced. A report on the meter performance was submitted when the meter waS returned to the BMR Regional Gravity Group.

Magnetic

Vertical magnetic intensity measurements were made at all but 15 gravity stations. Three readings about 10 metres apart were made at each station to eliminate bias due to the effect of any small surface concentrations of magnetic materials. The readings were made on range 3 of the magnetometer with a sensitivity specified to be about 30 gammas per division and a full-scale deflection of about 7500 gammas. The dial of the meter was such that it could be read to one division. Readings were made in the courSe of a gravity loop at gravity stations and usually took about two minutes. In areas of anomalous magnetic field readings, additional readings were made at closer spacing.

The meter was not sufficiently damped, for the dial needle oscUlated considerably with minor variations from the vertical. Readings were particular difficult on windy days. Consequently the accuracy of any particular reading is estimated, on field experience, to be about ~ 15 gammas at best. The BMR Geophysical Services Section is currently investigating this problem.

Radiometric

Radiometric observations were made at all but 46 gravity stations with the detecting head of the scintillometer about three centimetres above the ground.

-5-

4. RESULTS

The preliminary Bouguer anomaly, vertical magnetic intensity,and radiometric profiles along the two main traverses are shown inPlates 3 and 4. The Bouguer anomaly profiles follow the general trend ofthe profile interpolated from the reconnaissance data but show departuresof up to five milligals in places. These departures indicate local andpossibly near-surface geological variations. A high-amplitude magneticanomaly with a half-width of about 2 km was measured in the northwestcorner of WESTWOOD 1:250 000 Sheet area. The character of theanomaly suggests that it arises from a vertical dyke of magneticmaterial. The anomaly coincides with the western side of a gravityridge, which is about 8 km wide.

The results of this survey will be integrated with those fromprevious geological and geophysical results and the results of the seismicsurvey to give an integrated interpretation of the area.

5. REFERENCES

PINCHIN, J. & MATHUR, S.P., 1972 - Presurvey report on Officer Basinseismic survey, W.A. 1972. Bur. Miner. Resour. Aust. Rec. 1972/95(unpubl.).

BARLOW, B.C., 1970 - National report on gravity in Australia, July 1965to June 1970. Bur. Miner. Resour. Aust. Rec. 1970/62 (unpubl.).

HARRISON, P.L., 1973 - Officer Basin seismic survey, W.A. 1972 -Operational report. Bur. Miner. Resour. Aust. Rec. 1973/62 (unpubl.).

ZADOROZNYJ, I., & BROWN, F.W., 1972 - Presurvey report on detailedgravity survey, Officer Basin, W.A., 1972. Bur. Miner. Resour. Aust.Rec. 1972/107 (unpubl.).

-6-

APPENDIX 1

SURV:£Y DETAILS

1. The survey commenced on 21 August 1972 and was completed on 24 November 1972.

2. Observations

I I I I I I

Gravity Magnetic Radiometric

Number of stations occupied

Number of new stations

3. Ties to previous gravity surveys

Previous survey

Hunt Oil 1963-65 6361-0045

" " " 6361-6001

BMR 1971-72 7102-3939

reconnaissance 7102-3942

helicopter 7102-3945

gravity 7102-3953

survey 7102-3961

7102-3963

7102-3970

7102-3979

7102-4188

7102-4190

7102-4195

7102-4199

7102-4202

7102-4216

7102-4218

830

811

Observed grav­ity (previous survey) (mGal)

979040.16

979037.94

979032.83

979021.17

979002.28

978993.90

978986.27

978966.49

979057.64

979065.72

979071.59

979065.87

979061.72

979051.45

979055.29

889

889

Observed ~ray­ity (present survey) (mGal)

979040.06

979037.89

979032.92

979031.08

979002.21

978993.74

978986.11

978966.30

979057.73

979065.69

979071.52

979065.73

979061.65

979051.38

979055.25

830 I 830

I

I I

-0.10

-0.05 I +0.09

-0.09 I -0.07

-0.16 I -0.16 I -0.19

+0.09 I -0.03

-0.07 I -0.14

-0.07 I -0.07

-0.04 I I

-7-

4. The survey was tied to 'Isogal' stations (Barlow, 1970) at Warburton Range Mission (6491-9969) and at Lake Yeo (6792-9204).

5. The gravity meter used was Worden 169.

A calibration factor of 0.1011(6) mGal/div was obtained at the Canberra range on 11 August 1972 and a value of 0.1010(3) mGal/div was obtained there on 7 December 1972. The former value was adopted for the preliminary calculations.

6. The stations were optically levelled. The levels were adjusted to a series of Department of the Interior benchmarks: numbers XN39 to XN87 on the Warburton Range Road, and X0118 to X087 on the Emu Road.

7. Stations were pOSitioned by one of the following methods: .

(1) Compass and vehicle speedometer (road traverses)

(2) Compass and chain (cross-traverses)

(3) Theodolite and stadia (cross-traverses) To improve horizontal control, stations were pinpricked on

airphotos where possible.

8. A denSity of 2.2 g/ em 3

was adopted to make Bouguer corrections. This is the value adopted for the Gravity Map of Australia.

9. The 'survey number' for the survey in BMR's Regional Gravity filing syst~m is 7201.

-8-

APPENDIX 2

STAFF AND EQUIPMENT

A party of six began the survey - 1 geophysicist, 1 technical assistant, 1 f'ield hand, 1 surveyor, and 2 surveying f'ield assistants.

• ~ The addition of a second surveying crew and 2 field assistants increased the number to 11 for the last eight weeks of the survey. I Staff -

Geophysicist

Technical Assistant

Surveyors

Surveying Field hands

Field Hands

Bulldozer operator

Equipment

Gravity meter

Magnetometer

10 Zadoroznyj

J .C. Allen

P. Douglas 10/7/72 - 27/8/72 A. Lyons 27/8/72 - 6/10/72 P. Johnson 1/10/72 - 24/11/72 W. Martyr 6/10/72 - 24/11/72

10 Hunt 10/7/72 - 27/8/72 H. Powell " " D. Buck~e 27/8/72 - 6/10/72

• I

Dept of tJ Interior I

I E. Cameron " "Dept of the I P. Jones 1/10/72 - 24/11/72 Interior J. Oliver 27/10/72 - 24/11/72 ,-J. Wheeler 1/10/72 - 24/11/72 I D. Louis 6/10/72 - 24/11/72

P. West 6/10/72 - 24/11/72 A. Robinson 13/10/72 - 24/11/72 M. Leahy 1/9/72 - 20/9/72 P. Theilade 23/9/72 - 2/11/72

G. Baker 23/10/72 - 2/11/72

I I I

Worden 169 (C.F. 0.10116 mGal/division) I Jalander 7303 I

I I

Scintillometer

Barometers

Surveying equipment

Camping equipment

Transceivers

Vehicles

-9-

SCintillation counter (crystals 5 cm diametel x 30 8 cm long) with portable rate meter A.A.E.Co type 239

3 Mechanisms barometers

2 Tl'aegers (1 BMR, 1 D. of I.)

3 LWB Landrovers (2 BMR, 1 Do of I.) 3 Toyota Landcruisers (D. of I.) 2 Caravans (accommodation, D. of I.) 2 x 150-gallon water trailers (D. of I.) 1 International TD8 bulldozer (equivalent to Caterpillar D4)

I I I I

I I I I I ------

I I I I o

o p.09'5 S

o P.IIOI

I o p.09'.)9

I I I I I ---,

" '---- ---"-

To accomp any Record No 1973/71

,

o o

o

" o

o A0905

PERTH

o

o

WA I I

) I

o

o o o

o

o

/ REFERENC

STANDARD 1:2~O~O AUSTRALIA 00 MAP SERIES

YOWALGA

RASON NEALE

'" ,,0 o

0"

o

"f,.

o

o

o o o

o

5 ~"'~~F3~~FAJO~====~I"""""""""~I~O======~"""",,,,~ I 15

KEY TO GRAVITY I 210 KILOMETRES STATION NUMBERING

8'7102 A,7201

o A-0409

o o

o o

o o

/

,-- R oad or trllck

_ Drainage

o G ' ravrfy station

@ Permanentl gra vit 'I marked

y station

.,0 o

~ ,

o

o

o

o

o

r)A036D

o

o

o

o

o

o

40

o ~O'2.~\

o

o

~S 6,

o

o

o

o

o ADZ-55

o

o

OFFICER BASIN GRAVITY SURVEY

OPERATIONAL REPORT

TRAVERSE

o

o

o

1972

-()- Magnetic b not made 0 servotions

____________ -=::::~~~~~W;A~R~BURTON LOCATION MAP

RANGE ROAD TRAVERSE

o

o

o

o

o

o

o

o

o

y,

PLATE I

"-

G51/B2-25

\ \

PLATE 228°oo'

Lank" inEw,■ii,POINT^HILL ;.lyNc7:-

H■*" SUNDA Y

on,

u^C;'270 0

-0ron

YEO LAKE cj 6 c-)^.-C.00^uv_\:„._\: Li) rj

-----9 -----15a/ c_., 'i- ' - - v - )

'--"‘ -c7".--i^1^ '.^YE0 LAKE

,^.r :t2,,,-:' ,„--,\,-^I; ' ■,CV

•. ,c* 7--- ,,'^iv' *„...5^

V ( n)JV̀ -,./j^r ,

,^-...N.

N.N^ 1,'

\ .1

0 CVCt. 0^ N...

A ,I.)cr coo^ I

00) o oi^,..3140^ )

I 0", 1 7 c'') o^4) G'-' 40„,o

0 0 0

P:

0

4.ro04,

pAo'91T040

0

o00 °

0

0 CO0: 0 _0 ,.,

Iv0------^_ ..----.^ -- ^o•-...,^__ ___ ___ — ___ ___^_^--^ o

C's^- N'o

0^•

\o,

a)

^

CP f°- 0-- '0^ 0 co 0A^0^o ....a)1°--Co -o -0- 0- . cr. 42

e CO-.

0

-f-

0 o^ I-----03^CV 0,

^

CO^A cr^ 0

--)-rf-'^.zt co^in^V Z. ^ 0- -0-0- 0- 03-0_0_ 0 _^ 1'7-^...cb

0 CD^ -4 ,--0^_0 - 0.-*--^-0 ^ \^(0 A0 Cr)^ --^A.^,... 4,- .^ <^t•^... COA V'^ 0 co 0- ."---^ --.11°'-'0- a- -0- o C.) +0 ...,- _

<2 CO^...„,_co .0 _0_0-0-^ 00_,__,^.7 ,00 ---0-- 0

0„. 0‘

—0-4P-0-0— -0

vv 0(1 050

/

^

/ cjun,Z^i.),___22_20_4________,_.

--...../— -- — -^0

'PO^...--^- ----^1 '-4 A.^ 0 0^e-,. .0'

^

, /I _ 0-,) C.^0 *600 /0 0 '^i

^

.7^© 0

/^ 00 27

Cb) 0 0

_

0 0 0

-^

00 ACR 16

00°CARR BOYD

ROCKS /rt

o^0o

%."R4,16(^, ,0

Osk

rf)0 0

1.0

28 ° 30'

28°30'

REFERENCE TO AUSTRALIASTANDARD 1:250000 MAP SERIES^5^0

^5^

10^15^20 KILOMETRES

WA

PERTH

THROSSELL WEST WOOD

RASON^

NEALE

Road or track

Drainage

o^Gravity station

Permanently markedgravity station

Secondary base station

Station positions between B4202

and B4218 are doubtful

TRAVERSE LOCATION MAP

EMU ROAD TRAVERSE

KEY TO GRAVITY STATION NUMBERING

A=7201^B=7102

H5I/B2-26

To accompany Record No /973/7/

(f)

...J <l <.9

...J

...J

~

(f)

<[

-30

-40

-50

-60

-2100

-1800

1971-72 RECONNAISSANCE SURVEY

ANOMALY

.., co 01 .., CD

,,;'::RlICAL MAGNETIC INTENSITY

0> r--0> .., CD

J !

-1

-'

~ -1200

! -sJ \;JIV "'_ ~//\./'

1(-2770)

(-2160) n (-2190)

fl

(f)

......... (/)

~ Z :J o o

G) (jI

........ OJ I\)

1 I\)

~ l>

at vvJ~~~ 200 ..

100

RADtOM ETRI C {'\ ! A. I \ I

'Vv~f'~1 , o

~ ;·1 .-

,., __ L ____ ----.l _______ :I L---_----L _ ___''___-L-_--'-__ _L__~_L_ __ ___''__ _ __'___.___J __ _L__ _ ___'_ ___ _+_---L----L-----L----L---

5150 50Cl~ . i 5200 5050 5100

STATIONS (~I kmspacing)

WARBURTON RANGE ROAD TRAVERSE

PRELIMINARY GRAVITY, MAGNETIC, AND RADIOMETRiC PROFILES

I -'; I '-

~~i II

in

VII ,

r---------------------.... -------------.... ----... -------------________ -_______ --------_-__ n_.--__ ·_· __ .~ _ -50

:3 -60 « <9

-l -l

~ -70

-80

-900 r-

(/)

« -600

~ -30) <9

0

? IOO[ z· ::)

0 () 0

BOUGUER ANOMALY

(\I

g

1971-72 RECONNAISSANCE SURVEY 'It til

VERTICAL MAGNETIC INTENSITY

Y'. /\ ---.~\.~

RADIOMETRIC

----- ,../ -~',

I J. I I

I

l

j 7000 7050 7100 7136

I 0'1

"­CD ('I)

I ('I)

0'1 ~

STAnoNSf:=="UcrJ'l~g) .

'THE ·EMU ROAD TRAVERSE

PRELIMINARY GRAVITY, MAGNETIC, AND RADiOMETRIC PROFILES

L-_____ --------------------------_____ ~_,_ ... __ , __

"U r )::: --, Fi

. ..f"