Oaks Estate River Gravel Seismic Refraction Survey ... · The nature ot the surface material along each traverse i8 tabled below and senee aa an aid in the interpretation of the seilJlic

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BMR Record 1972151

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01 572G

COMMONIIIIEALTH OF AUSTRALIA

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Record 1972/51

OAKS ESTATE RIVER GRAVEL SEISMIC REFRACTION SURVEY, ACT,d.9?2

by

P.J. Hill

The infonnation contained in this repon has been Obtained by the Oepertment o f National Development as part 01 the policv of the Commonwealth Government to a~ist in the e>cplorllion end dewlopment of mineral f&$Oun::es. It may not be published in any form or used In 8 company prospectus or statement without the permi~on in writing of the Director, Bureau of Minerai Resources. GeotogV.& Geophysics.

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Rooord Bo. 1972/51

OAKS ESTATE RIVER GRAVEL SEISMIC REFRACTION SORVEr,

ACT, 1972

P.J. Hill

The iDtormatloD conta1Ded 1n this report haa been obtained by the Department of National Development aa part of the polioy ot the Commonwealth Government to "Blat in the exploration and dev.lo~nt ot mineral resource.. It ~ not be published in aQ7 form or used in a company prospectus or .tate .. nt vltnout the per.18alon in writing ot the Direotor, Bureau ot Mineral B.loureee, 0.01017 and Geophysics.

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1.

2.

,. 4.

5.

6.

CONTENTS

. Page

S1JMMAllY

INTRODUCTION 1

DESCRIPTION OF DEPOSIT 1

METHOD AND ElQUIP!!EIiT 2

SEISMIC RESULTS 2

CONCLUSION 3

REFERENCES 4

ILLUSTliATIONS

Plate 1 I Locali V II&p and. plan of aune,. area snowing s.ismic traveree locatioDs.

Plate 2 I Seismio croas- sectioDS ot Traverses 1 and 2.

Plate 3 Seismic oross-sections ol Traverses , &Dd 4.

Plate 4 5elBB1c croBs-sections of Traverse. 5, 6, and 7.

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SUMllARY

A seismic retraotion aurveT vas .ad. by the Bureau or Mineral Resources, Geology &: GeOpqsic8 to detemine the Q.U&Dti V and distribution or sand and gravel on a sit. b.1 the Molonglo River Dear Quean'be;yau. The depoe! ta On the area oODsiat or ancient alluvial rll1e and t08B11 aeolian Band dunes together vlth recent alluvium depoaltion aloD6' the river. Reaerve. or commercial material .. ountiDg to about 400,000 cubio metres and extending to depths ot up to 16 _tree are indicated b,y the survey results.

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1 • INTRODU<:rION

. The granting of a leaae to a private company tor the extraotion of Band and gravel from a river deposit on tbe Molonglo River near Queanbeyan is being oonsidered by the Department of the Interior. The area on Block 105, Gungahlln is shown In Plate 1. It 1s proposed atter completion of gravel extraction that the site be developed into a recreational area. In order to plan the working of the deposit and for assessing the operator's rental, the depths over the site and the total amount of commercial material on the a1 te are required. A request vas made by the Commonweal tb Department of Works for the Bureau of Mineral Resources, Geology & Geophysics (BMR) to conduct a survey on the aite and map the deposit.

The work vas done in January 1972, uaing the sels.1c refraction method, by a party from the Engineering Geophysics Group of the Bureau conSisting of P.J. Hill (CeopQysicist), S. Hall (Field Assistant), and P. FUrlonger (Student).

2. DESCRIPTION OF DEPOSIT

The area investigated lIes at the end of a low spur Ins1de a sharp band of the Moloaglo River about 700 metres dOVDstream from the Queanbeyan River junction. FrOIl the river, which f Orall!l much of the 8ite's boundar,r, & low lying river flat extends about 50 metres, there is then a steep rise in elevation to the remaining part of the site about 15 metree above river level.

Moat of tbe site except for the east section has been worked to some degree, and in the elevated central area removal of surface material has exposed fresh sand and gravel. This alluvium Is fairly clean and 811ght~ cemented and 1s thought to originate from ancient fluviatile deposits (van Dljk, 1959). As one proceeds northwards the ma terlal becomes Iss8 coarse and the percentage of cl~ appears to increase. From mapping done in 1964 (Gardner, 1966) it is believed that here transition into fossil aeolian sand dune deposits occurs. Deposits of this kind are common on the Queanbeyan-Canberra plaiD and are thought to have been laid down in cycles during the late Pleistocene and early Recent times trom sand blown from river flats by strong vest or north­vest winds during periods of frigid climatic conditions.

On the river flat the material consists of 100s8 gravel, Band, and silt - recently brought down from upstream or derived from eroeion of the old in situ fluviatile deposits. Where the spur drops down sbarply to the narrow river flat on the f ar east side of the site rock outcrop can be asen on the steep slope and a180 at ita bass. The rock is a bedded fine-grained argillaceous sandstone striking approximately north and with a dip of about 700 to the east, and would belong to the Pit~ FOrmation - sediments of Ordovician age which run through the Que.anbeyan area (Henderson & Strusz, 1971).

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3. IIE'I'lIOD AND E9,UlPMENT

The seismic refraction method (Dobrin, 1952) vas used to obtain depth information on the survey &real the equipment employed was standard equipment used by BMR tor surveys of this type, and consisted of a 24-channel SIE Bsisaograph and 20-Hz TIC geophones.

Seismic recording vas done on Traver_sa 1 to 7 (shown in Plate 1). Traversee were located on representative parte of the Bite, in addition the sitee selected tor the geophones vere as flat &8 possible to allow easier and more accurate interpretation of result_.

Spreads were la1d w1 th 81 ther a 2 or 3--metre geophone spacing, thus giving spread (or traverse, in this case) leDBtha of 46 and 69 metree respeot! vely. For the energy source, small ChargeB of gel1gni te were exploded with instantaneous electric detonators on the surface or buried within about 60 em of the surface. Pbr Bach spread shots vere fired at the centre and at, 1 metre and about 50 metree beyond Bach end.

Depths of the refracting layers were oaloulated using interoept times troll the Ume-ci1stance plots and a modified 'reciprooal method' (HavkiDs. 1961).

4. SEISMIC RESULTS

The 8ei .. io oroal-sections ot Traver.e. 1 and 2, Traverses , and 4, and Travereas 5, 6, and 7 are shown in Plate 1, Plate 2, and Plate 3 respectively.

The nature ot the surface material along each traverse i8 tabled below and senee aa an aid in the interpretation of the seilJlic lqera.

Traverae No.

1 elight17 oemented river aand and gravel (coarae), silty at vest end

2 weakly cemented ail t, aand, and granl

3 sllghtl1 cemented river sand and gravel (coar •• )

4 weakly cemented silt, sand, and graTel

5

6

7

oUt

loose river gravel (up to cobble size) at east and, to medium-grained d:r7 aand at vest end

SOlI, fine sand, alIt.

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From. the surface geology in the area and the result. ot a sand inT8.tlgatlon (Gardner, 1966) the 881 .. 1e interpretation 1s •• Collovat

deposit

Seismic velcciEr (m/a)

310

440

760 - 1210

1500

1750 - 2100

3000 - 3600

3600 - 4300

Material

50111

10088 land, (drT

or gravel

Weakly bonded silty gravel

cemented sand and gravel, ancient dune sand (tine)

Vater saturated Band or gravel

Modera te 1;r to highly weathered. sandstone

Slightly weathered sandstone.

Fresh 8andBtone ~

The results indicate a large thickness (up to 16 metres) of OD the elevated central and central north area ot the site.

Tbe seismic velocity of the weathered bedrock layer OD Traverses 1, 3, 5, and 6 could not be accurately determined from the t1me-dlstance plots owing to the presence of the 1500-m/s vater-saturated alluvium, which haa a velooity lover than but close to that of the weathered bed­rock. A value of 2000 m/s vas adopted, Which 18 also the velocity expected from consideration of velocities recorded on Traverse 7, the vest end of Traverse 2, and the southwest end of Traverse 4. Tbe small uncertain.ty' in the veloei t7 haa the effect of introducing BODIe error into determination of the bottom ot the vater-saturated alluvium.

For sand and gravel saterial a.bove the water-table the quantity estimated to be present 00. the aite i. 260,000 CUbic metres, coneidering material below the vater-table aa vell. the estimate becomes le88 preci8e and a value of 400,000 oubic _tres is obtained.

5. CONCLUSION

On the basis of the seiaa1c refraction results the quantity ot commercial sand and gravel on the SurTe;r area is estimated to be 400,000 cubic metres, moat of the material being concentrated in the central and central north part of the area.

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6. REFERElfCES

DOBRIN, M.B., 1952 - IlITRODUCTION TO GIXlPHYSICAL PROSPECTING. Bev York, McGraw-Bill Inc.

GARDNER, D.E., 1966 - Dune Band in the Molonglo River Yalley, Australian . Capital Territory. Bur. II1Der. ae8our. hat. Rae. 1966/156 (unpubl.)

RAWIDJS, L. V., 1961 - '!he reciprocal method of routine ahallow seismic refraction investigations. GeopSr8io8, 26(6), 806-819.

HENDERSON. G.A.M., & STRUSZ, D.L., 1911 - 1150,000 Geological Map, Canberra CIty', A.C.T. Bur. lUnar. Reaour. Auat. Ez::plaD. Notea.

VAN DIJX, D.C., 1959 - SolI features in relation to the erosional history In the ..,icinity of Canberra. ScI. ind. Rea. Org. Kelb.', SOU Publ. 13.

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CONTOUR I N f(RVAl !Ion

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LOCALITY MAP

SURVE Y AREA

OAKS ESTATE SEISMIC REFRACTION

RI VER GRAVEL SURVEY

(COtllo", rs in teel above seo le .. "O

TRAVERSE PLAN

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TRAVERSE 1

WEST

o SURFACE 10 20

o --------------------(4 40)

'·8

(830) (840)

~---------------­ ----------

:I:

t;: w o

10

20

'0

(1500)

i21---------__ _

(2000)

. --

To accompany Ii.cord No. 1972/ 51

---------------

(3940)

'0

(850)

---------- ------. ;:e

11500}

-------------------1~·6

(2000)

EAST WEST

40 o SURFACE

10

o

(770)

----------------"

/1980) 10

20

TRAVERSE 2

20

(830)

_______ 4.6-----

(1890)

(3580)

------

LEGEN D

- '0 1 --- o!fi(310)

(790)

----------;.;

(lBIOj

---- In lerpololed bounda ry

i'O-i Depth to refrac tor (me lrn)

(3000) Seismic veloc.il )' in formol ion (metres/second)

TRAVERSE AND 2

SEISMIC PROFILES

PLATE 2

EAST

40

155/85-150

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o

10

20

TRAVERSE 3

WEST

o SURFACE

10 20

(9601 (960) (960)

________ __________ __________ G.9 H------

MOO)

n--------------------- __ ---------

(2ooo)

(1500)

11·9

(2000)

------------------M-JOO--I---------------~

LEGENO

10 ·6 Depth 10 refractor (metres)

Inter pola ted boundary

(3000) Se;smic velocity in formotion {metres/second)

To accompany R~cord No. 1972/51

EAST

30

SOUTH - WEST

o SURFACE

o

(890)

61'--------'" " (1790) ~ -" :;; I

10

f-0.. W 0

20

TRAVERSE 4

10 20

(800) ( 760)

___________ --'r4

---_--- 40

(17501 (1720)

(3280)

TRAVERSE 3 AND ' 4

SEISMIC PROFILES

PLATE 3

NORTH-EAST

30

155/ 85-151

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o

10

o

20

TRAVERSE 5

WEST o 10 20

SURFACE

(3/0) (310; (JIO) 'j.'j-------

(1500) -------- 76--------------- "'i-1 2i' --____ (1500)

. ---_____ (1500) _-----"Ta(cOOOJ

(2000) -. N ---------

(2000)

{3000j

TRAVERSE 7

SOUTH o 10

((310) 20

SURFACE

• (310) _____________ 0:6 ----__________ (310)

N- - ~

(1140) (1170)

s:7-------------_ ----

(2100/

(4000)

(1210j

-------------_. -.. (2100)

ro accompany R.cord No . 1972/5f

EAST 30

o

10

NORTH

30

PLATE 4

TRAVERSE 6

WEST EAST

o 10 20 30 40 SURFACE

(310) (310) (310) ____ -------------H -----------------------i7 (/500)

- ----- (j500j __________ 2.2' 2-" ":-" __ _

--- - ----------_------ 3·3 ------(/500) (2000)

(2000) --.;......------"

(2000)

---------~-~ --------------------------

(3600)

LEGEND

Depth to refroctOf (metres)

In terpoloted boundary

(30oo) Seismic veloci ty in formation (metres/second)

TRAVERSE 5, 6, AND 7

SEISMIC PROFILES

155 / 65-152