1:250 000 Geological Map Series Explanatory Notes...NORTHERN TERRITORY GEOLOGICAL SURVEY 1:250 000 Geological Map Series Explanatory Notes LIMBUNYA SE 52-07 Northern Territory Government

NORTHERN TERRITORY GEOLOGICAL SURVEY

1:250 000

Geological

Map Series

Explanatory Notes

LIMBUNYA SE 52-07

Northern Territory Government Department of Business, Industry & Resource Development

Northern

Territory

Geological

Survey

2nd Edition

i

NORTHERN TERRITORY DEPARTMENT OF BUSINESS, INDUSTRY AND RESOURCE DEVELOPMENT

NORTHERN TERRITORY GEOLOGICAL SURVEY

LIMBUNYANorthern Territory

Sheet SE 52-07

1:250 000 GEOLOGICAL MAP SERIESEXPLANATORY NOTES

A CUTOVINOS, PR BEIER,PD KRUSE, ST ABBOTT,JN DUNSTER and RF BRESCIANINI

Government Printer of the Northern TerritoryDarwin, September 2002

SE 52-2

LISSADELL

SE 52-6

DIXON

RANGE

SE 52-10

GORDON

DOWNS

SE 52-12

WINNECKE CREEK

SE 52-3

WATERLOO

SE 52-11

BIRRINDUDU

SE 52-7

LIMBUNYA

NEGRI

4763

GREGORY’S

DEPOT

4963

MOUNT

BARTON

4962

INVERWAY

4862

NAPIER

4762

LIMBUNYA

4863

133 30’o

133 30’o

127 30’o

127 30’o

19 00’o

17 00’o

19 00’o

17 00’o

SE 52-8

WAVE HILL

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VICTORIA

RIVER DOWNS

W.A

.

N.T

.

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NORTHERN TERRITORY DEPARTMENT OF BUSINESS, INDUSTRY AND RESOURCE DEVELOPMENTMINISTER: Hon Paul Henderson, MLACHIEF EXECUTIVE OFFICER: Peter Blake

NORTHERN TERRITORY GEOLOGICAL SURVEYDIRECTOR: Dr R Dennis Gee

BIBLIOGRAPHIC REFERENCE: Cutovinos A, Beier PR, Kruse PD, Abbott ST, Dunster JN and Brescianini RF, 2002. Limbunya,Northern Territory (Second Edition). 1:250 000 geological map series explanatory notes, SE 52-07. Northern Territory GeologicalSurvey, Darwin and Alice Springs.

(1:250 000 geological map series, ISSN 0814-7485)Bibliography

ISBN 0 7245 7044 6559.429

KEY WORDS: Geological mapping, Structural geology, Economic geology, Sedimentary geology, Northern Territory, Limbunya,Palaeoproterozoic, Mesoproterozoic, Neoproterozoic, Palaeozoic, Mesozoic, Cenozoic, Birrindudu Group, Limbunya Group,Wattie Group, Auvergne Group, Duerdin Group, Antrim Plateau Volcanics, Goose Hole Group, Birrindudu Basin, VictoriaBasin, Wolfe Creek Basin, Ord Basin, Diamonds, Base metals, Hydrocarbons, Industrial minerals, Gemstones, Groundwater.

For further information contact:Reference GeologistNorthern Territory Geological SurveyGPO Box 3000Darwin NT 0801Phone: +61 8 8999 5281Web site: http://www.minerals.nt.gov.au/ntgs

© Northern Territory Government 2002

Printed for the Northern Territory Geological Surveyby the Government Printer of the Northern Territory

DisclaimerThis information is provided on the understanding that the user agrees to release and indemnify the Northern Territory,the Commonwealth of Australia, companies who supplied and acquired open file data, and their employees, agents andcontractors, in respect of all liability for actions, claims costs or expenses, loss damage or injury, which may be sufferedby them, or any other person, arising from the use of the data, or as a consequence of any unlawful or negligent act oromission of the user.

iii

ABSTRACT

LIMBUNYA1 includes portions of the Proterozoic Victoria and Birrindudu Basins, the Phanerozoic Ord Basin, and an extensivethin veneer of Cambrian basalt and Cenozoic sediments. A basement rise in the central part of the mapsheet is represented bytwo small inliers of quartz-muscovite schist that probably correlate with rocks of the Halls Creek or Pine Creek Orogens.

In LIMBUNYA, exposed sedimentary rocks of the Birrindudu Basin are represented by eleven formations of the LimbunyaGroup. The Birrindudu Group, which unconformably underlies the Limbunya Group in BIRRINDUDU, does not outcrop inLIMBUNYA, but undifferentiated mudstone assigned to this group has been intersected in drillholes. The Limbunya Group isa 1300 m thick package of alternating siltstones, sandstone and dolostone which was deposited mainly in widespread shallowmarine and evaporitic conditions. However, the Kunja Siltstone and Blue Hole Formation contain regionally extensive deeperwater facies. The Birrindudu Basin is unconformably overlain by the two lithostratigraphic groups of the Victoria Basin. Theoldest is the Wattie Group, a thin succession of undifferentiated siltstone, sandstone and minor dolostone, which is unconformablyoverlain by the Auvergne Group. Only the two lowermost units of the Auvergne Group, the Angalarri Siltstone and JasperGorge Sandstone, are present in LIMBUNYA. Neoproterozoic glacial deposits of the Wolfe Creek Basin unconformably overliethe Victoria Basin succession.

Cambrian flood basalts of the Antrim Plateau Volcanics blanket much of LIMBUNYA and overlie the Proterozoic rockswith an angular unconformity. The Antrim Plateau Volcanics are succeeded by early Middle Cambrian peritidal to marinelimestones. This marine transgression can be viewed as a direct consequence of crustal sag following the cessation of AntrimPlateau volcanism. The Goose Hole Group embraces all Middle and Upper Cambrian sedimentary rocks of the Ord Basin. Thegroup is 700 m thick and is subdivided into the Negri Subgroup and overlying Elder Subgroup.

Cenozoic silcretes cap Proterozoic carbonates of the Limbunya Group and Cenozoic sediments cover approximately half ofthe mapsheet.

Exploration has focused on diamonds and base metals. The Victoria and Birrindudu Basins have potential for Century-styleepigenetic mineralisation and syngenetic, stratiform, sediment-hosted base metals similar to the McArthur River ore body.Extensive barite veins occur on Inverway Station.

1 Names of 1:250 000 and 100 000 map sheets are shown in large and small capital letters, respectively, eg LIMBUNYA, NAPIER

iv

CONTENTS

Abstract ............................................................................ iiiIntroduction ...................................................................... 1Regional geological setting ............................................... 1Orogenic basement rocks ................................................. 1

Inverway Metamorphics (LPi) ....................................... 1North Australian Platform Cover ................................... 3Birrindudu Basin .............................................................. 4

Birrindudu Group ............................................................ 5Undifferentiated Birrindudu Group ............................. 5

Limbunya Group ............................................................. 5Stirling Sandstone (LPhs) .............................................. 6Margery Formation (LPhr) ............................................ 7Pear Tree Dolostone (LPhp) .......................................... 7Amos Knob Formation (LPho) ...................................... 8Mallabah Dolostone (LPhm) ......................................... 8Kunja Siltstone (LPhj) ................................................... 8Farquharson Sandstone (LPha) ...................................... 9Blue Hole Formation (LPhl) .......................................... 9Campbell Springs Dolostone (LPhb) ........................... 10Fraynes Formation (LPhf) ........................................... 11Killaloc Formation (LPhk) ........................................... 13

Victoria Basin .................................................................. 13Wattie Group ................................................................. 14

Wickham Formation (LPiw) ........................................ 14Burtawurta Formation (LPib) ...................................... 15Hughie Sandstone (LPih) ............................................. 15Mount Sanford Formation (LPio) ................................ 15Neave Sandstone (LPin) .............................................. 15Gibbie Formation (LPig) ............................................. 16Seale Sandstone (LPim) ............................................... 16

Auvergne Group ............................................................ 16Jasper Gorge Sandstone (LPaj) .................................... 16Angalarri Siltstone (LPaa) ........................................... 16

Tectonics and structure ..................................................... 16Economic geology of the Birrindudu andVictoria Basins .................................................................. 18

Base metals .................................................................... 18Diamonds ...................................................................... 18Geochemical sampling .................................................. 18Hydrocarbons ................................................................ 18Groundwater .................................................................. 18

Wolfe Creek Basin .......................................................... 19Duerdin Group .............................................................. 19

Undifferentiated diamictite (LPou) .............................. 19Cambrian volcanic rocks ............................................... 19

Antrim Plateau Volcanics (C_ la) ................................. 19Economic geology of the Antrim Plateau Volcanics ....... 20

Stratabound copper occurrences ................................... 20Barite ............................................................................. 21Amethyst and other semi-precious stones ..................... 21

Ord Basin ........................................................................ 21Goose Hole Group ........................................................ 21Negri Subgroup ............................................................. 21

Headleys Limestone (C_ Gh) ....................................... 21Nelson Shale (C_ Gn) ................................................... 22Linnekar Limestone (C_ Gl) ......................................... 22Panton Formation (C_ Gp) ........................................... 23

Elder Subgroup ............................................................. 24Eagle Hawk Sandstone (C_ Ge) ................................... 24

Overland Sandstone (C_ Go) ........................................ 24Ord Basin structure ........................................................... 25Mesozoic and Cenozoic geology .................................... 26

Mesozoic rocks ............................................................. 26Cenozoic units ............................................................... 26

Silcrete/duricrust (Czo) .............................................. 26Laterite (Czl) .............................................................. 26Grey clay-rich soil (Czb) ........................................... 28Superficial soils and calcrete (Czs) ........................... 28Alluvium (Qa) ............................................................ 28Undifferentiated alluvium and colluvium (Cz) ......... 28

Geological history ........................................................... 28Acknowledgements ......................................................... 29References ........................................................................ 30Appendix 1 - Location of measured sections ................ 33Appendix 2 - Geochemical analyses ofLimbunya Group rocks .................................................. 34

FIGURES

1 Regional geological setting ........................................ 2 2 Structural and tectonic elements ................................. 3 3 Stratigraphy of Birrindudu and Victoria Basins ......... 4 4 “Coxco needles” in Campbell Springs Dolostone ...... 6 5 Typical outcrop of Fraynes Formation ....................... 7 6 Stromatolites in Amos Knob Formation ..................... 9 7 Dolostone and siltstone in Mallabah Dolostone ......... 9 8 Typical outcrop of Campbell Springs Dolostone ..... 11 9 Bioherm in Campbell Springs Dolostone ................. 1210 Stromatolites in Campbell Springs Dolostone ......... 1211 Concretions in Fraynes Formation ........................... 1312 Compaction feature or fold-like structure in

Fraynes Formation .................................................... 1313 Section through fold-like structure in

Fraynes Formation .................................................... 1414 Regional structural interpretation of

central LIMBUNYA ................................................. 1715 Diamictite of Duerdin Group.................................... 1916 Antrim Plateau Volcanics overlying

Campbell Springs Dolostone .................................... 2017 Typical outcrop of Headleys Limestone ................... 2218 Siliceous nodules in Headleys Limestone ................ 2219 Basal 2 m of Linnekar Limestone ............................ 2320 View northwest toward Mt Panton ........................... 2421 Halite hoppers in Panton Formation ......................... 2522 Nodular floatstone in

Shady Camp Limestone Member ............................. 2523 Floatstone in Corby Limestone Member .................. 2624 Sandstone and mudstone of

Eagle Hawk Sandstone ............................................. 2725 Desiccation-cracks in Eagle Hawk Sandstone ......... 2726 Plateau scarp of Overland Sandstone ....................... 2727 Cross-bed set in Overland Sandstone ....................... 2828 Fault-associated monocline in

Headleys Limestone ................................................. 29

TABLES

1 Lithostratigraphy of Limbunya Group ....................... 5 2 Summary of geochronological data .......................... 12

1

INTRODUCTION

LIMBUNYA is located between latitudes 17°00'S and18°00'N and longitudes 129°00'E and 130°30'E. The Bureauof Mineral Resources undertook First Edition mapping in1972 and a detailed report was written by Sweet et al (1974a).Second Edition geological mapping was undertaken as partof a larger study of the Victoria and Birrindudu Basins bythe Northern Territory Geological Survey. Consequently,field based studies have concentrated on section measuringand map amendments. Stratigraphic sections for this studywere measured with Jacobs staff and Abney level. Thesesections are located on the map and are referred to in the textwith the prefix MS to distinguish them from type sectionsdefined during First Edition mapping. Stratigraphic namesand mineral occurrences have been updated and theLimbunya and Goose Hole Groups have been remapped indetail.

Fieldwork was undertaken during the 1997, 1998 and1999 field seasons. A simultaneous mapping program wascarried out in AUVERGNE, DELAMERE, VICTORIARIVER DOWNS, WATERLOO and WAVE HILL.

Most access was gained using four-wheel drive vehicles.Inaccessible areas were visited by helicopter. Compilationwas undertaken using 1:50 000-scale colour aerialphotographs and digital base maps modified from AUSLIGdata. References to specific locations are given using theGeocentric Datum of Australia (GDA94) and the MGA94map grid coordinate. To convert from the AGD66 AMGsused on older maps, block shift all data 131 m east and 161 mnorth.

Airborne magnetic and radiometric data (north-southlines, 400 m line spacing, 60 m average terrain clearance)were flown by the Northern Territory Geological Surveyduring 1998.

Mendum (1972) and Sweet et al (1974a) described thephysiography, climate and logistics of LIMBUNYA.

In these notes, the Proterozoic is subdivided as follows,after Plumb (1991): Palaeoproterozoic (2500-1600 Ma),Mesoproterozoic (1600-1000 Ma) and Neoproterozoic(1000-545 Ma). The terms ‘stromatolite’ and ‘stromatolitic’,as used in this report, refer to planar, domed, columnar,cuspate and conical forms and their variants.

Cited locations are based on Map Grid of Australiazone 53 coordinates and the GDA94 map datum, and aredeemed accurate to ± 50 m. In some parts of the text, theUniversal Grid Reference style is used as explained on themapface (eg Mt Panton at MGA 523200mE, 8081200mN isrepresented as EF232812). Full MGA grid references areprovided elsewhere and in tables.

REGIONAL GEOLOGICAL SETTING

The regional geological setting of LIMBUNYA is depictedin Figure 1. Detailed structural and tectonic elements areshown in Figure 2. The region is divided into 6 principaltectonostratigraphic components. A basement rise in centralLIMBUNYA is manifested as two small inliers of theInverway Metamorphics. These are unconformably overlainby stacked Palaeoproterozoic to Mesoproterozoic basins(Birrindudu, Victoria and Wolfe Creek Basins). A thin cover

of Lower Cambrian flood basalts (Antrim Plateau Volcanics)blankets a large portion of the mapsheet and separates thePalaeozoic Ord Basin from the Victoria and BirrinduduBasins.

Sweet et al (1974a) defined the main tectonic elementsof the Birrindudu and Victoria Basins (Figure 2 ). Asoutheast-trending fault-monocline, which is recognisableas a major regional lineament, marks the southwestern marginof the Ord Basin. This structural feature can be tracedsouthward into a series of north-trending faults and folds inthe Limbunya Group of the Birrindudu Basin.

The surface expression of the Neave Fault is a prominent,east-trending fault ridge in the southeastern corner of themapsheet. The Antrim Plateau Volcanics occur to the southof the fault (the downthrown side) and abruptly terminateagainst the fault ridge. This major structural lineamentextends southward into BIRRINDUDU as a prominentmagnetic feature.

In the centre of the mapsheet, the east-trending LimbunyaFault dissects outcropping Limbunya Group rocks. On theupthrown southern side, basement is shallow and is overlainby the two basal formations of the Limbunya Group. On thenorthern side of the fault, the complete Limbunya Groupsuccession is well exposed.

OROGENIC BASEMENT ROCKS

Inverway Metamorphics (LPi)

Two small inliers of Inverway Metamorphics (Sweet et al1974a) are exposed as low, rounded symmetrical hills. Thelargest outcrop, which is about 2 km2, is located 12 km tothe southwest of No 19 Bore (at 603000mE, 8062000mN)and occupies the core of a northeast-trending anticline ofthe Limbunya Group. The other recessive and dissected inlieris about 0.5 km2 in area and is within a small isolated valley,25 km to the southwest of the bore (at 594500mE,8053500mN). Exposed rocks comprise steeply dipping,brown muscovite quartz schist, which has at least twocleavages, grey to reddish-grey acid volcanics and minorsiltstone. Concordant quartz veins are common and formmassive, 2-4 m thick reefs of white quartz that cut through boththe schist and volcanics. The thickness of the unit is unknown.Metamorphic grade is sub-greenschist to greenschist facies.

Shallow drillhole LMDH13, which was located 5 km tothe southwest of Swan Yard (Hurrell 1992, 1993), intersected5 m of quartz muscovite schist and 27 m of metasandstonesof the Inverway Metamorphics. These are overlain by up to25 m of apparently unmetamorphosed interbedded mudstoneand siltstone, interpreted to be part of the Birrindudu Group.

Thin sections of the volcanics were described by Sweetet al (1974a) as schistose. They consist of subhedral andanhedral grains of quartz and green feldspar up to 5 mmacross in a groundmass of quartz, sericite and iron oxidethat contains flakes of muscovite. Quartz grains are rounded,have embayed edges and in places retain a beta-quartz crystalshape. Feldspar is completely altered to sericite.

The absolute age of these rocks has not been determined,however the most likely correlation is with rocks of the HallsCreek or Pine Creek Orogens, which were cratonised between1880-1850 Ma, during the Barramundi Orogeny.

2

--

C1b

--

C2

N

--

C1b

N

V6

g5

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C1b

19°00'

129°00' 130°30'

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C1b

V6

13°00'

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15°00'

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NO

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TER

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OR

YW

ESTE

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AU

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A

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Bonaparte Basin

Quaternary sediments

Cenozoic sediments

Cretaceous sedimentary rocks

Cambrian Basins(Wiso, Daly, Hardman, Ord Basins)

m02-034.dgn

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Antrim Plateau Volcanics

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C1b

0 100 km

AUVERGNESD 52-15

WATERLOOSE 52-3

WAVE HILLSE 52-8

FERGUSSONRIVER

SD 52-12

PINE CREEKSD 52-8

CAPE SCOTTSD 52-7

PORT KEATSSD 52-11

BIRRINDUDUSE 52-11

WINNECKE CREEKSE 52-12

TANAMISE 52-15

DELAMERESD 52-16

VICTORIA RIVERDOWNSSE 52-4

LIMBUNYASE 52-7

V10

Wolfe Creek Basin

Duerdin Group

Auvergne Group

Wattie, Bullita, Tijunna Groups

V9

V8

Victoria Basin

Limbunya Group

Pine Creek Orogen

Inverway Metamorphics

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V6 Birrindudu and Tolmer Groups

N Tanami Region

Birrindudu Basin

Orogenic Basement

Major Fault

Halls Creek Orogen and Lamboo Complex

Fitzmaurice GroupV9a

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Figure 1 Regional geological setting of LIMBUNYA

3

NORTH AUSTRALIAN PLATFORM COVER

The Birrindudu and Victoria Basins are exposed over about120 000 km2, mainly within the northwestern part of theNorthern Territory (Figure 3 ). These stacked basins form amajor geological region of the Northern Territory and arepart of the extensive North Australian Platform Cover(Plumb 1979). They contain thick, Palaeoproterozoic toNeoproterozoic successions, which are unmetamorphosed,flat-lying to moderately folded and faulted, and 1800-750

million years old. The Birrindudu and Victoria Basinsunconformably overlie Palaeoproterozoic terrains of theTanami Region, Pine Creek Orogen and possibly the HallsCreek Orogen. Remnant glacial sediments of theNeoproterozoic Wolfe Creek Basin unconformably overliethe Victoria Basin, but are mainly confined to AUVERGNE,WATERLOO and LIMBUNYA.

The Fitzmaurice Group, a succession of unmetamorphosed,but strongly folded and faulted clastic sediments, is exposed tothe northeast of the Birrindudu and Victoria Basins and is

ANTRIM PLATEAU VOLCANICS - Basalt, sandstone, limestone

DUERDIN GROUP - Sandstone, conglomerate, siltstone, diamictite

ORD BASIN

WOLFE CREEK BASIN

BIRRINDUDU BASIN

AUVERGNE GROUP - Sandstone, siltstone, dolostone, conglomerate, dolarenite

CAMBRIAN

610 Ma

1.61 - 1.57 Ga

1.66 - 1.62 GaLIMBUNYA GROUP - Dolostone, siltstone, sandstone, tuffite

VICTORIA BASIN

Kirkimbie

Inverway

Limbunya

17° 00'

18° 00'

129° 00' 130° 30'17° 00'

18° 00'129° 00' 130° 30'

010 10 20 30 40 50 km

Ba

b

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q

GOOSE HOLE GROUP - Limestone, sandstone

INVERWAY METAMORPHICS - Schist, acid volcanics

WATTIE GROUP - Siltstone, sandstone, dolostone

Fault

m02-080.dgn

Anticline, Syncline, Monocline, Plunge direction Strike and dip of strata, dip 5° to 15°

Figure 2 Structural and tectonic elements of LIMBUNYA

4

separated from them by the northeast-trending Victoria RiverFault Zone. This group was considered to be part of theplatform cover succession by Sweet et al (1974a), but wasprobably deposited in an active rift or foreland and cannot beeasily correlated with units of the adjacent basins.

BIRRINDUDU BASIN

The Birrindudu Basin (Figure 3 ) contains Palaeoproterozoicsandstone, mudstone and shallow water evaporitic carbonaterocks, which are referred to the Birrindudu and LimbunyaGroups and their correlatives (Table 1 ). The majority of thebasin is exposed to the south of the Victoria Basin, apartfrom the Tolmer Group, which is located on the northernmargin in FERGUSSON RIVER and PINE CREEK.

The Birrindudu Group comprises the basal GardinerSandstone, Talbot Well Formation and Coomarie Sandstone.It is essentially a sandstone-dominated succession, althoughthere are carbonate rocks and mudstone in the upper part.The succession is conformable and reaches a maximumknown thickness of 6000 m (Blake et al 1975), where it isbest exposed in TANAMI and BIRRINDUDU. The GardinerSandstone is younger than 1790 Ma (Smith 2001), which isthe age of the youngest granites in the underlying TanamiRegion basement. An age for the sandstone of about 1560 Mawas determined by K-Ar and Rb-Sr methods on glauconite(Blake et al 1979), but the unit is now believed to be olderthan the Limbunya Group which has yielded SHRIMP U-Pbages of about 1640 Ma (Smith 2001; Table 2 ). The DepotCreek Sandstone at the base of the Tolmer Groupunconformably overlies granites as young as 1825 ± 7 Ma(Umbrawarra Leucogranite, see Wyborn et al 1996) andmetamorphic rocks of the Pine Creek Orogen.

In LIMBUNYA, the majority of the Birrindudu Basinsuccession is referred to the Limbunya Group. This unit is1250 m thick and consists of cyclic, hypersaline carbonateand siliciclastic rocks. It unconformably overlies the poorlyexposed Inverway Metamorphics and a unit of undivided,steeply dipping, commonly dolomitic and carbonaceousmudstone, which has been intersected in shallow drillholesin the central part of the mapsheet (Hurrell 1992, 1993). Thismudstone has not been metamorphosed, and on this basis,cannot be equated with the Inverway Metamorphics. Hence,it has been placed within the Birrindudu Group.

The age of the Limbunya Group is constrained bySHRIMP U-Pb zircon ages of about 1640 Ma (Table 2 ) forthe Kunja Siltstone, Blue Hole Formation and CampbellSprings Dolomite, as reported by Smith (2001). These arecomparable with a U-Pb zircon age of 1639 ± 3 Ma(Southgate et al 2000) from the Barney Creek Formation(McArthur Group, McArthur Basin) and 1639 ± 28 Ma(Hussey et al 2001) for the Shillinglaw Formation(Namerinni Group, Ashburton Province, Tennant Inlier). TheLimbunya Group also contains aragonite pseudomorphs,formerly known informally as “Coxco needles” (Figure 4) ,which are virtually identical to those found in rocks of similarage in the McArthur Basin (Jackson et al 1987, Pietsch et al1991) and the Ashburton Province (Hussey et al 2001).

Shoal Reach Formation

Spencer Sandstone

Lioyd Creek Formation

Saddle Creek Formation

Pinkerton Sandstone

Angalarri Siltstone

Stubb Formation

Jasper Gorge Sandstone

Banyan Formation

Battle Creek Formation

Nero Siltstone Bynoe Formation

Skull Creek Formation

Timber Creek Formation

Seale Sandstone

Gibbie Formation

Neave Sandstone

Mount Sanford Formation

Hughie Sandstone

Burtawurta Formation

Wickham Formation

Killaloc Formation

Fraynes Formation

Campbell Springs Dolostone

Blue Hole Formation

Farquharson Sandstone

Kunja Siltstone

Mallabah Dolostone

Amos Knob Formation

Pear Tree Dolostone

Margery Formation

Stirling Sandstone

AUVERGNEGROUP

TIJUNNAGROUP

BULLITAGROUP

WATTIEGROUP

LIMBUNYAGROUP

VIC

TO

RIA

BA

SIN

m02-029.dgn

TOLMERGROUP

BIRRINDUDUGROUP

Mt. Gordon Sandstone

Weaner Sandstone

Coomarie SandstoneTalbot Well FormationGardiner

Sandstone

Stray Creek Sandstone

Depot Creek Sandstone

Inverway Metamorphics

Pine CreekGeosyncline

Wondoan Hill Formation

BIR

RIN

DU

DU

BA

SIN

Hinde Dolostone

Figure 3 Stratigraphy of Birrindudu and Victoria Basins

5

UNIT, (MAP SYMBOL),TYPICAL THICKNESS

LITHOLOGY DEPOSITIONALENVIRONMENT

STRATIGRAPHICRELATIONS

Killaloc Formation (LPhk)104 m

Dolostone, dolarenite stromatoliticdolostone, dololutite, dolomiticsiltstone; minor sandstone

Marine/lagoonal Unconformable with overlyingWickham Formation;conformable on FraynesFormation

Fraynes Formation (LPhf)165 m

Laminated dolomitic siltstone andmudstone; minor silty dolostone,dolostone, tuffite, siltstone and veryfine sandstone

Low-energy, nearshore shallowmarine

Conformable on CampbellSprings Dolostone

Campbell Springs Dolostone (LPhb)160 m

Stromatolitic dolostone; minordolarenite, dolorudite anddolosiltite; rare tuffite

shallow to very shallow marine,reworked by waves and currents;some storm deposits

Conformable on Blue HoleFormation

Blue Hole Formation (LPhl)maximum 330 m

Dolomitic mudstone, stromatoliticmudstone, dolostone, mudstone,siltstone; minor tuffite, dolarenite,sandstone and shale

Shallow marine with periods oflow-energy deeper marine

Conformable on FarquharsonSandstone

Farquharson Sandstone (LPha)40-110 m

Fine sublitharenite and quartzarenite, dolomitic siltstone; minordolostone and mudstone

Shallow marine/fluvial with periodsof subaerial exposure

Conformable on Kunja Siltstone

Kunja Siltstone (LPhj)60-65 m

Green and grey mudstone andsiltstone (some dolomitic),carbonaceous in lower intervals;rare dolostone and tuffite

Low-energy shallow marine, belowwave base

Conformable on MallabahDolostone

Mallabah Dolostone (LPhm)10-100 m

Laminated to thinly beddeddololutite, dolarenite and shale,stromatolitic dolostone; minorcarbonaceous mudstone; rare siltydolostone

Storm-influenced, shallow marinewith periods of low-energy deepermarine, below wave base

Conformable on Amos KnobFormation

Amos Knob Formation (LPho)40-50 m

Stromatolitic dolostone, dolarenite,mudstone, siltstone and shale

Low-energy shallow marine; upperlevels higher energy, shallowmarine

Conformable on Pear TreeDolostone

Pear Tree Dolostone (LPhp)75-92 m

Dolarenite, dolorudite, dololutite,stromatolitic dolostone, dolomiticmudstone and oolitic dolostone;minor carbonaceous mudstone

Storm-influenced shallow to veryshallow marine

Conformable on MargeryFormation

Margery Formation (LPhr)116-125 m

Stromatolitic dolostone (silicified),dolarenite, dololutite, siltstone,sandstone and claystone

Shallow marine to intertidal, basalpart terrestrial

Conformable on StirlingSandstone

Stirling Sandstone (LPhs)120 m

Quartzarenite, dolomitic sandstone,conglomerate, minor claylaminations

Shallow marine with periods ofsubaerial exposure, syntectonic

Unconformably overliesbasement of InverwayMetamorphics

Table 1 Lithostratigraphy of Limbunya Group in LIMBUNYA

Birrindudu Group

Undifferentiated Birrindudu Group

A succession of steeply dipping mudstone, which is commonlydolomitic and carbonaceous, siltstone and minor thin intervalsof quartz arenite and felsic volcanics have been intersected inshallow drillholes in central LIMBUNYA (Hurrell 1992, 1993).These rocks are not obviously metamorphosed and areunconformably overlain by the Limbunya Group. Blackcarbonaceous mudstone, up to 55 m thick, has been intersectedin drillholes LMDH8, LMDH10 and LMDH12, and appears tobe confined within fault blocks as localised thick wedges. Insome intervals, carbonaceous shale with reactive pyrite hasundergone oxidisation and hydration, so as to form iron sulfate.Contorted laminae of green shale, disseminated pyrite, and veinsof pyrite, siderite, quartz and talc are visible within the fracturedcarbonaceous mudstone. Chalcopyrite, pyrite, pink/brownmagnesite and coarse white quartz are associated with talc veins.Felsic rocks, identified as rhyolites, from LMDH10 have amicrocrystalline groundmass with fresh alkali feldspar andquartz, and sericitised plagioclase, but contain no sulfides(Hurrell 1992, 1993).

An angular unconformity between red haematitic quartzarenite of the Stirling Sandstone (basal Limbunya Group)and the underlying mudstone unit was intersected indrillholes LMDH8, LMDH10 and LMDH11 (Hurrell 1992,1993). The contact is fractured, and clay and talc alterationis common in thin quartzite pebbles and lenses within theStirling Sandstone.

Limbunya Group

The Proterozoic Limbunya Group (Sweet et al 1974a) isdivided into eleven formations and has a composite thicknessof 1300 m (Table 1 ). The group is essentially a successionof cyclic carbonate and siliciclastic packages. A unit at thebase of the succession, the Bunda Grit (Mendum 1972),which was previously an unassigned formation, is nowrecognised as a facies variation of the Stirling Sandstoneand the name Bunda Grit is therefore abandoned.

The best outcrops occur along Stirling Creek near BlackSprings (Figure 5 ), Moonbool Creek to the east of KirkimbieStation in LIMBUNYA and Farquharson Gap in WAVEHILL. The group also outcrops in structural windows inAUVERGNE, WATERLOO and BIRRINDUDU.

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An anticline to the north of Kirkimbie Homestead, whichwas portrayed as undivided Limbunya Group in the FirstEdition LIMBUNYA mapsheet has been subsequentlyremapped as Kunja Siltstone, Farquharson Sandstone, BlueHole Formation, Campbell Springs Dolostone, FraynesFormation and Killaloc Formation.

Stirling Sandstone (LPhs)

The Stirling Sandstone forms rocky pavements and smallridges in central LIMBUNYA and is best exposed in ananticline 15 km to the southwest of No 19 Bore2 (at603100mE, 8061000mN), where the type section wasnominated by Sweet et al (1974a). Elsewhere, the formationforms rubbly outcrop, which thins to the south, so as toproduce a thin veneer over the Inverway Metamorphics.Cored drillholes LMDH 8-13 (Hurrell 1993) intersected80-90 m of basal to upper Stirling Sandstone in centralLIMBUNYA and drillhole DD90VRB2 near FarquharsonGap on WAVE HILL intersected 57 m of upper StirlingSandstone (Roiko 1992). In the type section, the formationreaches a maximum thickness of 120 m.

The basal Stirling Sandstone consists of massive, purple,thickly bedded coarse quartz sandstone. A localised pebbleconglomerate, which contains clasts of rounded quartzite(some up to 20 cm in diameter) and angular silicified phyllite,is present in the first three metres of the formation in thetype section. The remainder of the formation consists ofthinly to medium bedded, moderately sorted, medium tocoarse quartz arenite and minor, thin conglomerate interbeds.Distinctive dark yellow-green clay minerals occur as 1 cmdiameter spheroidal patches in the red matrix in all drillcoreand outcrops. These could have been derived from evaporites.Abundant low-amplitude stylolites, which contain dark greenclay, and subvertical fractures lined with pyrite are presentin the upper Stirling Sandstone, in core from drillholeDD90VRB2.

Interference ripple marks, low-angle trough cross-beds,rip-up clasts and current lineations are common within theformation, as are spindle-shaped synaeresis cracks in swales

between ripples, and desiccation pavements. Features similarto lenticular millet seed gypsum are present near the contactwith the Margery Formation. Despite their appearance, thesehave been interpreted as early diagenetic ferroan carbonatelozenges (John Warren, Petroleum Geoscience, Universityof Brunei Darussalam, pers comm 1999).

The western limb of an anticline, 22 km to the south ofKirkimbie Station, contains a coarse unit previously mappedas Bunda Grit and originally thought to be up to 1200 mthick (Sweet et al 1974a). This is now interpreted to be abasal conglomeratic facies of the Stirling Sandstone. It occursonly in association with the north-trending Negri Fault. Theformation thickens into the fault but is significantly thinnerthan documented by Sweet et al (1974a). Clasts are mainlyof quartzite and white vein quartz up to 20 cm in diameterand have been derived from the fault wall. Quartz veins,which crosscut the conglomerate and individual clasts,indicate that fault activity was probably contemporaneouswith deposition of the Stirling Sandstone.

The Stirling Sandstone overlies the InverwayMetamorphics with a high-angle unconformity. A basalconglomerate up to 30 cm thick was intersected by drillholeLMDH11 (Hurrell 1993). In drillcore LMDH10, the basalcontact consists of 20 cm of haematitic quartz arenite thatrests unconformably on haematitic sericitic mudstone of theInverway Metamorphics. The transition to thedisconformably overlying Margery Formation is gradationalthrough thinly interbedded sandstone (up to 10 cm) intooxidised claystone, and brown silicified dolomitic shales andcarbonates of the Margery Formation. The Stirling Sandstoneis correlated with the Masterton Sandstone of the McArthurGroup (McArthur Basin). Both contain evaporites and areoverlain by an evaporitic carbonate unit.

The Stirling Sandstone was deposited during awidespread marine transgression, which led to theaccumulation of quartz sand in south-central LIMBUNYA.

2 On previously published mapsheets, No 19 bore was incorrectlypositioned further to the south at 602100mE, 8058300mN.Consequently, this section was described as being 3 km to the northof the bore in Sweet et al (1974a).

Figure 4 “Coxco needles” in CampbellSprings Dolostone in Stirling Creek. Theseare interpreted as neomorphic aragoniteseafloor cements (575000mE, 8085500mN)

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The upper Stirling Sandstone was deposited in a shallowwater to intertidal marine environment, as is indicated bythe thin to medium bedding, synaeresis cracks, asymmetricalripples and rip-up clasts.

Margery Formation (LPhr)

The Margery Formation disconformably overlies the StirlingSandstone (Sweet et al 1974a) and is a 125 m thicksuccession of dolomitic rocks, which is poorly exposed invalley floors and along creeks. Outcrop is mostly of subduedrelief, but subcrop is extensive. In drillhole DD90VRB2 theformation is 106 m thick (Simeone 1991). Cherty rubblysubcrop interpreted as Margery Formation occurs in the southof LIMBUNYA near Inverway and Kirkimbie Stations. Thebest exposures are in an anticline 15 km to the southwest ofNo 19 Bore and 3 km to the south of Swan Yard.

The type section is located in the axis of an anticline(section MS36 at 601170mE, 8061575mN). It contains a 7 mthick basal interval of oxidised claystone, which may havebeen deposited subaerially. Overlying the claystone are thininterbeds of fine to medium sandstone. These are in turnoverlain by a stromatolitic chert horizon, dolarenite,dololutite, minor claystone, and an upper heavily silicifiedstromatolitic dolostone that contains interbeds of silicifiedintraclastic dolarenite. Large unsilicified domed stromatolitesup to 0.5 m across are common in the upper MargeryFormation.

In drillhole DD90VRB2, the basal 7 m of the MargeryFormation consists predominantly of red oxidised claystoneand minor thin interbeds of fine to medium sandstone. Thisclaystone contains abundant scour and fill features, sporadicgypsum-filled vugs, evaporite collapse breccias andmudcracks. A 27 m thick stromatolitic chert horizon anddolostone overlies the claystone, and is in turn overlain bythinly interbedded dolarenite, dololutite, dolomitic siltstoneand minor claystone. Cauliflower cherts, scour and fillfeatures, mudcracks and dewatering structures are commonin these intervals. The upper Margery Formation consists ofheavily silicified stromatolitic dolostone that containsinterbeds of medium to coarse, silicified intraclasticdolarenite. Flake breccia interbeds and cauliflower chertnodules with cores of calcite and purple fluorite are common,as are evaporite collapse features and later diageneticbreccias. Minor bitumen occurs in stylolites.

The basal claystone was probably deposited in terrestrialor subaerial conditions. Dolomitic sediments of the formationwere deposited in a shallow marine to intertidal environmentwith localised evaporitic conditions.

Pear Tree Dolostone (LPhp)

The poorly exposed Pear Tree Dolostone (formerly Pear TreeDolomite) is conformable on the Margery Formation.Outcrop is confined to Swan Yard in central Limbunya andto the western margin of WAVE HILL near Farquharson Gap.The lower contact is marked by nodular silicification,displacive botryoidal quartz nodules (cauliflower cherts) andhorizons of fenestrae that have been infilled by secondarygypsum. Subcrop of a banded, pale brown dolostone unitand an overlying cherty, ridge-forming unit can be traced onaerial photographs.

The type section, as originally defined by Sweet et al(1974a), is 2 km to the south-southeast of Swan Yard andcontains fault repetition. At this locality, only 46 m of theupper Pear Tree Dolostone is exposed (section MS4;589450mE, 8060040mN). Granular dolorudite, dolarenite,silty dolostone, oolitic dolarenite and intraclastic breccia forma succession that generally coarsens up-section. This iscapped by a stromatolitic chert bed that marks the top of theformation.

The lowest exposed rocks of the Pear Tree Dolostone aredolarenite and coarse to granular dolorudite. These areoverlain by an interval of stromatolitic dolostone and siltydolostone, which contains large hemispherical bioherms (2 mdiameter and 0.5 m synoptic relief). Abundant, laterallylinked, branching digitate columnar stromatolites occurwithin, and on the outer surface of the bioherms. Accordingto Dunster (1988), interlinked, branched conical stromatolitesup to 0.5 m high and 0.3 m across similar to Jacutophytonor Balbirina prima in the McArthur Basin also occur(compare Plate 8 of Sweet 1977 with Figure 158 of Jacksonet al 1987). These stromatolites are overlain by increasinglysandy and intraclastic phases up-section. Oolitic dolareniteand intraclast breccias are present in the upper part of theformation.

Associated with the stromatolitic facies are imbricatedplate breccias, oolitic cross-beds, botryoidal quartz nodules(cauliflower cherts), pseudomorphs after anhydrite and minorFigure 5 Typical outcrop of Fraynes Formation along Sterling

Creek

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malachite. Numerous barrel-shaped crystals of silicified,ferroan carbonate up to 3 mm long occur immediately belowthe chert horizon at the top of the formation. These crystalswere described by Jackson et al (1987) as pseudomorphsafter anhydrite or gypsum, but are now interpreted as earlydiagenetic textures, related to through-flushing of Fe-Cl-richbasinal brines (John Warren, Petroleum Geoscience,University of Brunei Darussalam, pers comm 1999).

Drillhole DD90VRB2 (Simeone 1991) intersected a 92 mthick section of Pear Tree Dolostone that consists ofstromatolitic dolostone, dolarenite, dolorudite anddololutite (stromatolitic laminite). Recessive outcrops ofdolomitic mudstone and carbonaceous mudstone alsooccur. Sedimentary and diagenetic structures includecommon scour and fill features and stylolites lined withbitumen or carbonaceous material. Pyrite occurs in veins andfractures.

The oolitic dolostone was probably deposited in a shallowhigh-energy, agitated environment. Stromatolitic dolostonealso indicates shallow to very shallow marine conditions.Burne and Moore (1987) described modern examples ofunlinked conical stromatolites up to 85 cm high, in water1.5 m deep in Lake Clifton in Western Australia. Imbricatedintraclast plate breccias are interpreted as storm deposits.

Amos Knob Formation (LPho)

The Amos Knob Formation is a recessive, mudstone-dominated unit that is exposed in two main areas in centralLIMBUNYA (east and west of Swan Yard), and along thewestern margin of WAVE HILL. It is conformable on thePear Tree Dolostone. On aerial photographs, it displaysdistinctive pale pink tones, which are coincident withsubdued topography, and multiple bedding traces formed byalternating beds of carbonate and siltstone. The formation isabout 50 m thick in the type section (Sweet et al 1974a) andin drillhole DD90VRB2 (Simeone 1991). Due to therecessive nature of outcrop, descriptions of this unit aremostly based on drillcore from DD90VRB2.

In outcrop, the Amos Knob Formation is dominated byred and green mudstone beds that are interbedded with 1-3 mthick stromatolitic dolostone intervals and thin dolarenite.The fine to medium dolarenite is cross-bedded andinterspersed with planar and low-relief stromatoliticlaminations. Domed stromatolites up to 3 m in diameter arewell exposed in a small north-trending creek near Swan Yard(Figure 6 ).

In drillcore DD90VRB2, the lower 30 m of the Amos KnobFormation consists of maroon-green mudstone with sporadic1-3 m thick stromatolitic dolostone interbeds. The upper sectionconsists of thinly interbedded dolarenite and dolomiticmudstone, which becomes progressively more dolomitictowards the top. The dolarenite is fine to medium and cross-laminated. Plate breccias, compaction structures, cross-beds andgutter casts are common in this carbonate interval.

The transition from dolostone to mudstone indicates amarked increase in water depth following deposition of thePear Tree Dolostone. Abundant plate breccia, cross-beds,gutter casts and large stromatolites within the upper carbonatefacies of the Amos Knob Formation indicate a return to ahigh-energy, shallow marine environment.

Mallabah Dolostone (LPhm)

The Mallabah Dolostone (formerly Mallabah Dolomite) ispoorly exposed, and is conformable and in part gradationalon the Amos Knob Formation. Its distribution is confined tocentral LIMBUNYA and the northwestern corner of WAVEHILL. Scattered pavements of low outcrop are located nearSwan Yard and No 19 Bore in LIMBUNYA, and nearFarquharson Gap on WAVE HILL. The formation is 100 mthick in the type section (Sweet et al 1974a), 50 m thick indrillholes LMD 1-15 (Hurrell 1992, 1993) and 13.5 m thicknear Farquharson Gap.

Exposures of the Mallabah Dolostone are mostly oftabular, thinly laminated and thinly bedded, ferruginous,stromatolitic dolostone grading to dolomitic mudstone(Figure 7 ). Silicified conical stromatolites with up to 15 cmof synoptic relief are abundant and are assigned toConophyton sp. Intraformational plate breccias occur locally.

Drillholes LMDH 3, 4, 5 and 7 intersected a 50 m thicksuccession of dololutite, interlaminated black carbonaceousshale and minor pale grey dolarenite. The carbonaceous shaleis consistently 18 m thick and contains fine disseminatedpyrite throughout. Minor veinlets of galena and sphaleriteoccur in diagenetic dolomite concretions and on beddingplanes within the black shale interval. Calcite-infilled fracturesand stylolites are common.

Stromatolites and intraformational plate breccias indicatedeposition under storm-influenced, shallow marineconditions. The laminated dolostone and black shale faciesare indicative of a lower energy, slightly deeper marineenvironment, probably below wave base.

Up to 750 ppm Zn was obtained from a sample ofMallabah Dolostone in section MS22 (Appendix 2, seeEconomic geology of the Birrindudu and Victoria Basins,Geochemical sampling).

Kunja Siltstone (LPhj)

Poorly exposed, homogenous, recessive flaggy mudstone andsiltstone beds of the Kunja Siltstone outcrop near No 19 Bore,Swan Yard, Mt Rose and Kirkimbie in LIMBUNYA, atFarquharson Gap on WAVE HILL and in the southeasterncorner of WATERLOO. Sweet et al (1974a) estimated athickness of 61 m at the type section, which is 2 km to the east-northeast of Swan Yard, and a complete section of 50 m wasintersected in drillhole LMDH4 (Hurrell 1992, 1993).

Fresh outcrops of the Kunja Siltstone consist of ahomogenous succession of laminated mudstone and siltstonebounded by silty dolostone. Drillcore from LMDH4 containslaminated green and maroon mudstone, and subordinateinterbedded siltstone. Minor scour and fill features and cross-beds are visible.

Drillhole DD90VRB2 (Simeone 1991) intersected anincomplete basal succession of interbedded grey dolomiticmudstone, olive-green siliciclastic mudstone that containsintervals of carbonaceous mudstone, and minor tuffitebeds that mark the upper horizon. Tuffaceous intervalsalso occur in dril lcore from LMDH4. Pyrite isdisseminated through all lithologies. Thin beds of orangewaterlain tuffite, present in drillcore from DD90VRB2,contain zircons that have yielded a SHRIMP U-Pb age of

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1635 ± 19 Ma (Fanning 1991). This is considered to bethe depositional age of the formation.

The predominance of mudstone and absence ofshallow-water sedimentary features indicates that the KunjaSiltstone was deposited in quiet conditions in water deeperthan the carbonate units above and below it. The formationmay therefore correspond to a maximum flooding surface.

The basal Kunja Siltstone contains carbonaceous materialwith up to 2.2 % total organic carbon (TOC) and is weaklyanomalous in Au, Pb and Zn (Simeone 1991).

Farquharson Sandstone (LPha)

The Farquharson Sandstone forms hogbacks and cuestas alongthe major northwest-trending fault zone that runs through thecentre of LIMBUNYA. Exposure is confined to centralLIMBUNYA and Farquharson Gap in WAVE HILL. Thesandstone is blocky and massive, finely micaceous anddominantly sublitharenite. Recessive interbeds of siltstone andmudstone occur near the top of the succession. Sweet et al(1974a) described thin dolostone beds that outcrop near Mount

Rose and a 1 m thick stromatolitic dolostone bed occurs nearthe top of the formation to the east of Kirkimbie Station.

The sandstone facies commonly contains ripple marks,gutter casts, low-angle small-scale trough and planar cross-beds, planed ripples, tool marks, current lineations, halitepseudomorphs, and desiccation and synaeresis cracks inripple troughs. These indicate a moderate- to low-energy,mostly shallow marine and evaporitic depositionalenvironment that was possibly fluvial in part. Desiccationfeatures indicate periods of emergence. The FarquharsonSandstone is probably part of a clastic-dominated low standsystems tract (Dunster 1998).

Blue Hole Formation (LPhl)

Dolomitic mudstone, dololutite, minor stromatoliticdolostone and dolarenite are the dominant lithologies of theBlue Hole Formation (section MS1). This unit conformablyoverlies the Farquharson Sandstone and is characteristicallypurple-pink in weathered exposures, owing to its high Feand Mn content. The lower contact is characterised by orange

Figure 6 Stromatolites in Amos KnobFormation (589650mE, 8060460mN)

Figure 7 Laminated dolostone anddolomitic siltstone in Mallabah Dolostone;coin at upper left for scale (597866mE,8063823mN)

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lithic sandstone of the Farquharson Sandstone, which isoverlain by dolostone, dolarenite and interbedded buff chertcontaining common intraformational breccia. The uppercontact is conformable and grades from red-brownstromatolitic dololutite to grey crystalline dolostone of theCampbell Springs Dolostone.

In LIMBUNYA and AUVERGNE, the Blue HoleFormation is separated from the overlying Campbell SpringsDolostone by distinctive maroon-purple bioherms of digitatestromatolites. This is recognised as a regional upper boundingmarker bed in LIMBUNYA (sections MS1, 5) and inAUVERGNE. The Blue Hole Formation has a bandedappearance on aerial photographs; darker bands representdolomitic facies and lighter bands represent clastic facies.The best exposures occur on the flanks of mesas in StirlingCreek and in an anticline near Moonbool Creek, 7 km to theeast of Kirkimbie Station. A nearly complete section of 330 mwas intersected in drillhole LMDH4 (Hurrell 1992, 1993)and a 160 m thick section occurs along Stirling Creek (sectionMS1). Sweet et al (1974a) estimated the maximum thicknessto be 320 m at Farquharson Gap in WAVE HILL.

In sections MS1, 5 and drillhole LMDH4, purple to red,laminated to thinly bedded dololutite and dolarenite aretypical lithologies. The proportion of mudstone increases up-section. Subordinate lithologies include laminated dolomiticsiltstone, 2-3 cm thick waterlain tuffite intervals, which areconfined to the upper intervals, and imbricated plate breccia.The basal section is dominated by irregularly laminated,flaggy dolosiltite and muddy dololutite. Small domedstromatolites mark the contact.

Pseudomorphs of aragonite near the base of section MS5occur as radiating clusters of acicular crystal casts up to 1 cmlong. The crystal casts are typically orientated perpendicularto bedding. These radiating crystals are after a CaCO3

precursor (aragonite) and probably formed as submarinecements (Winefield 2000). Similar features in rocks fromthe McArthur Basin have been interpreted as pseudomorphsafter evaporites such as gypsum (Walker et al 1977).

Sedimentary structures within the Blue Hole Formationinclude syn-sedimentary slumps and possible soft-sedimentdeformation injection features, which are aligned alongfractures near Moonbool Creek. Golfball-sized concretionsare locally abundant near the upper boundary. Minor scours,very rare intraclast breccia, rare gutter casts and tool marksup to 2 cm wide are present near the base of the type section(MS1).

In drillcore from LMDH4, the basal to middle parts ofthe formation consist of alternating thinly bedded andlaminated carbonate and clastic intervals. The dominantlithologies include dolarenite, dololutite and mudstone.Small domed stromatolites at the lower contact with theFarquharson Sandstone have synoptic relief of up to 5 cmand form aggregations. The middle to upper parts of theformation consist of laminated green to maroon mudstone,purple siltstone, dolarenite and maroon dolostone. Themudstone content increases up-section, indicating increasingwater depth. Diagenetic brecciation, stylolites, small-scaletrough cross-beds and intraformational pebble conglomerateare present.

The Blue Hole Formation was deposited mostly inquiescent shallow marine conditions, as is indicated by

stromatolitic carbonate cycles, but there were some periodsof deeper water deposition, as is indicated by laminatedsiltstone and black shale.

Campbell Springs Dolostone (LPhb)

The Campbell Springs Dolostone (formerly CampbellSprings Dolomite, Sweet et al 1974a) is spectacularlyexposed in gorges along Stirling Creek (Figure 8 ) andMoonbool Creek in LIMBUNYA. It also outcrops instructural windows in WAVE HILL, WATERLOO andAUVERGNE. It typically consists of alternating cyclicstromatolitic dolostone, dolarenite, dolorudite anddolosiltite, and minor interbeds of dolomudstone andwaterlain tuffite. The extensive grey-blue, blocky outcropis easily distinguishable on aerial photographs and satelliteimages.

A composite type section (MS6-11), which is 160 m thick,is located along Stirling Creek in central LIMBUNYA. Theunit is also 160 m thick in drillhole CRA99VR901 (Simeone1991). The basal part of the type section is marked by a seriesof large distinctive hemispheroidal stromatolites, boundedby intraclastic breccias. This stromatolitic horizon is overlainby dolosiltite and fine dolarenite. Immediately above thisinterval is a 4.5 m thick bioherm, which contains smallconical stromatolites at the base grading upward to alternatingdigitate non-branching, small convex domed and conicalforms.

Laterally continuous black chert beds and locallyabundant pinolitic prisms of ferroan carbonate occur nearthe lower contact in section MS6. The ferroan carbonateprisms are interpreted as evidence of sub-surface diageneticreplacement of platform carbonates, related to through-flushing of Fe-Cl-rich brines (J Warren, PetroleumGeoscience, University of Brunei Darussalam, pers comm1999). Similar examples from the McArthur Basin wereinterpreted as pseudomorphs of evaporites by Pietsch et al(1991). Another interpretation of the pinolitic prisms is thatthey may have originally been pyrite cubes that subsequentlyunderwent brine-flushing, resulting in ferroan carbonateminerals (such as brunerite) nucleating on pyrite cubes, soas to create hollow, pinolitic-shaped crystal casts.

The middle to upper Campbell Springs Dolostone istypically dominated by peloidal dolarenite and dolorudite,which are interbedded with intraclast breccia, andstromatolitic dolosiltite that contains small digitatestromatolites, waterlain tuffite and radiating aragonite(‘Coxco needle’) splays. The ‘Coxco splays’ are radiatingclusters of acicular crystal casts which are common in adistinctive, laterally-extensive marker horizon in the upperCampbell Springs Dolostone. Walker et al (1977) interpretedthem as pseudohexagonal pseudomorphs of gypsum. Thisinterpretation was subsequently used by Jackson et al(1987) and Pietsch et al (1991). These coxco splays havebeen subsequently reinterpreted (Winefield 2000) to bepseudomorphs after a CaCO3 precursor such as aragoniteand are described as typical tropical marine seafloortextures from the Mesoproterozoic. The uppermost horizonis marked by a distinctive series of stromatolitic bioherms,up to 4.5 m thick. These consist of turbinate columns or largeconvex domes (35-40 cm relief), which grade up-section

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through pseudocolumnar (tuberous shaped) to columnar anddigitate non-branching forms (Figures 9, 10 ). The bases andthe tops of the bioherms are clearly sharp and erosional.

Sedimentary structures in the Campbell SpringsDolostone include abundant massive and thinly beddedintraformational flat pebble breccias that overlie stromatolitehorizons. These lenses of imbricated breccia, up to 40 cmthick, persist along strike for tens of metres and are commonlyswirled in plan view. Ooids, peloids and cross-beds arecommon in dolarenite horizons. High-amplitude stylolitesare also common throughout the formation along beddingplanes.

A SHRIMP U-Pb zircon age of 1638 ± 9 Ma (Table 2 )was obtained from waterlain tuffite beds of the CampbellSprings Dolostone in LIMBUNYA (at 573500mE,8086800mN). This date, taken as the depositional age, isequivalent to that of the Teena Dolomite (including theCoxco Member) of the McArthur Group of the McArthurBasin (Southgate et al 2000).

The predominance of stromatolites, dolarenite,dolorudite, and presence of ooids and peloids indicatedeposition in a shallow to very shallow marine setting, inwhich currents and waves reworked the sediments. Swirledimbricated plate breccia represent storm deposits.

Fraynes Formation (LPhf)

Fine-grained dolomitic rocks and siltstone dominate theFraynes Formation (Sweet et al 1974a), which outcrops inwestern and central LIMBUNYA. The best exposures arealong Stirling Creek (Figure 5 ) in central LIMBUNYA andto the east of Moonbool Creek near Kirkimbie Station. TheFraynes Formation also outcrops in WAVE HILL andAUVERGNE. The alternating bands of recessive siltstoneand more resistant dolostone of this formation formprominent terraced hills and a ribbed pattern on aerialphotographs. In general the carbonate content of theformation increases up-section. Dolostone is often weathered,silicified, or obscured by calcrete.

In the type section near Stirling Creek, the formation is103.5 m thick (MS13; 573440mE, 8086895mN). It is

115.5-124.5 m thick near a tributary of Moonbool Creek, tothe east of Kirkimbie Station (MS2). In this section, a basal,purple-green, fissile micaceous siltstone (black shalehorizon), up to 5 m thick, is overlain by up to 100 m oflaminated to thinly bedded yellow-brown dolomitic siltstone(dolosiltite), silty dolostone, dolostone and minor 15-30 cmthick tuffite beds. The basal clastic-dominated facies is welllaminated, and contains rare ripple cross-laminations andsmall-scale trough cross-beds. Displacive concretions up to20 cm across are locally abundant in the dolomitic siltstone(section MS2; Figure 11 ). Many concretions havenucleated on radiating clusters of “Coxco needles” andare commonly subspherical in shape, but a few are linkedto form ellipsoidal bodies. Tuffite beds are concentratedin the lower half of the formation and are up to 30 cmthick. Cored drillhole DD90VRB13 (Simeone 1991) nearDepot Pile in northeastern LIMBUNYA intersected acomplete 164.15 m thick section through the FraynesFormation. The upper 27 m of this section is a poorlyconsolidated chert breccia that was interpreted by Roiko(1992) as a possible palaeoregolith.

The middle to upper carbonate facies is well laminatedto thinly bedded and contains minor intraformational flatpebble breccia, nodules of diagenetic chert and incipient,bedding-parallel, low-amplitude stylolites, which are rarelyrelated to jointing. Minor gently convex stromatolites occurlocally. The dominant lithologies are dolosiltite, siltydolostone and dolostone. Subordinate dolomitic siltstone andsporadic thin tuffite beds also occur. Outcrop of thecarbonate-dominated facies is commonly altered to calcrete.

Locally abundant siderite and iron oxides occur alongjoints and are rarely parallel to bedding. Sub-millimetre pyritepseudomorphs, which form haloes around concretions, anddendritic manganese are common throughout the formation(sections MS13, 24). Barite and calcrete are commonlyexposed on bedding planes and joint surfaces. Sideriticcarbonate lozenges are confined to similar stratigraphichorizons in sections MS24 and MS13, suggesting a possiblestratigraphic control.

Figure 8 Typical cliff outcrop ofCampbell Springs Dolostone (575810mE,8085175mN)

3 647250mE, 8109700mN

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Possible preferential compaction features, some of whichresemble folds, (Figures 12, 13 ) are concentrated inparticular horizons near the base of the formation (sectionMS24; 572730mE, 8087960mN). These compaction featuresare bounded by flat-lying beds immediately above and belowthem and are uniform in length and distance from one other.Concretions are evident in the flanks of the folds. It ispostulated that silicification preferentially hardened jointsduring early diagenesis and subsequent uneven compactionproduced fold-like structures.

Bedding-parallel silicification increases up-section in thesilty dolostone- and dolostone-dominated succession. TheFraynes Formation is capped by duricrust, which is highlyvariable in thickness and which preserves the originalbedding and textures (sections MS24, MS31, MS29). Thisduricrust was originally mapped as a chert horizon withinthe Fraynes Formation but is now remapped as a Cenozoicunit.

In drillhole DD90VRB1, the formation is 86 m thick.It consists of a basal interval of thinly interbedded olive-green shale and tuffite, which is overlain by laminatedand thinly bedded green-purple dolomitic siltstone andminor dolostone. This is capped by a silicified brecciaor duricrust. Sedimentary boudinage, which wasprobably caused by d i ffe ren t ia l compact ion ofuncemented sediment, is evident in the upper part ofthe formation.

The upper Fraynes Formation in Moonbool Creek (near531950mE, 8041100mN) contains an unusual lithic quartzarenite ‘lens’, which lacks obvious bedding. The quartzarenite is medium-grained, massive and poorly sorted, andthins to the north, where it is capped by localised silcrete.Lithic components are of dololutite and were derived fromthe underlying Fraynes Formation. Due to its highlyirregular contact with the host carbonate, lack of bedding,irregular thickness, poor sorting and large angular clasts

Figure 9 Bioherm in cliff outcrop of Campbell Springs Dolostone(575810mE, 8085175mN)

Figure 10 Typical bioherm of interlinked and branchingstromatolites in Campbell Springs Dolostone

Formation Sample Grid reference Age (Ma) Source

Kunja Siltstone Tuff horizon, sample 2872501, CRAdrillhole DD90VRB2

631610mE 80922870mN 1635 ± 19 Fanning (1991)

Campbell Springs Dolostone Tuffite horizon, PRISE sample 4017iii 573500mE 8086800mN 1638 ± 9 Armstrong (1998)Campbell Springs Dolostone Tuffite horizon, GA sample 98776703 563000mE 8070700mN 1639 ± 7 Smith (2001)Blue Hole Formation Tuffite horizon, GA sample 98776702 532983mE 8041552mN 1636 ± 5 Smith (2001)

Table 2 Summary of geochronological data relevant to the Victoria and Birrindudu Basins. All samples from LIMBUNYA

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of laminated chert, this ‘lens’ is interpreted as a solutioninjection feature rather than an upper sandstone unit withinthe formation.

The depositional environment for the Fraynes Formationwas probably nearshore shallow marine, in which quietconditions prevailed.

Killaloc Formation (LPhk)

The Killaloc Formation (Sweet et al 1974a) is the youngestcomponent of the Limbunya Group and is conformable onthe Fraynes Formation. It is an evaporitic carbonate unit,and is readily distinguished from other formations of thegroup by the presence of abundant chert nodules and lenses,and surface silicification.

Outcrop is poor and forms low blocky strike ridges nearMoonbool Creek and along Stirling Creek in centralLIMBUNYA. Lower, carbonate-rich parts of the formationhave distinctive light grey hues on aerial photographs,whereas the more clastic-rich upper parts have light browntones.

At the type section (MS3) near Moonbool Creek, theKillaloc Formation is 104 m thick and consists of dolostone,dolarenite and stromatolitic dolosiltite, which fine upwardinto dololutite and dolomitic siltstone. The basal part of theformation is dominated by partly silicified and laminatedgrey dolosiltite and small, poorly formed, silicified domedand digitate stromatolites. The middle part consists oflaminated to ripple cross-laminated fine dolarenite, massivedolosiltite and dololutite, plus some intraclast breccia andsmall domed stromatolites. Possible pseudomorphs of millet-seed gypsum or rosette chert are abundant locally. Thesiliciclastic content increases up-section and upper parts ofthe Killaloc Formation are dominated by recessive yellowdolomitic siltstone.

Chevron halite hoppers, halite casts and possiblepseudomorphs of millet seed gypsum occur throughout theformation. Local displacive botryoidal quartz nodules(“cauliflower chert”), probably after anhydrite, are up to30 cm across. The presence of halite, cauliflower chert andmillet seed gypsum is consistent with a hypersaline shallowlagoon or evaporative shallow marine environment ofdeposition.

VICTORIA BASIN

The Victoria Basin unconformably overlies the BirrinduduBasin and contains several thousand metres of sedimentary

Figure 11 Unusual concretions in astylolaminated “Coxco needle” horizonof Fraynes Formation. Concretions to10 cm diameter (top right) sometimescontain radiating needles of neomorphicaragonite and weather out as discretepods (573560mE086750mN

Figure 12 Preferential compaction feature or fold-like structure inFraynes Formation; hammer (centre) for scale (572730mE,8087960mN)

14

rocks divided into four groups, of which only the Wattie andAuvergne Groups occur in LIMBUNYA. In general, theVictoria Basin succession consists of basal arenites that gradeupward into finer grained rocks and carbonates. Severalunconformities occur within this succession.

The depositional age of sedimentary units within VictoriaBasin is poorly constrained by geochronological data. Apossible correlation with strata of the Nathan Group(McArthur Basin) suggests that the Wattie and overlyingBullita Groups were deposited at 1.61-1.57 Ga (Lindsay1998). Berryman et al (1999) reported a SHRIMP U-Pbzircon age of 1.46 Ga for a kimberlite that intrudes the lowerBullita Group, and inferred this to be a minimum depositionalage. However, Belousova et al (2001) reported a muchyounger emplacement age of 179 ± 2 Ma for the TimberCreek kimberlites, from laser-ablation ICP-MS U-Pb datingof zircons. They indicated that the older date did not constrainthe age of sedimentation and instead interpreted it as beingindicative of a magmatic event in the deep lithosphere.

The deposition of the Auvergne Group may have occurredat 810-750 Ma (inferred from Walter et al 1995, Thorneet al 1999). Shale from the Angalarri Siltstone has beengiven a loosely constrained Rb-Sr whole-rock age of838 ± 80 Ma (Webb and Page 1977), but Sweet (1977)cautioned against using this age for regional correlation.However, a possible correlation between the Jasper GorgeSandstone-Angalarri Siltstone and Ahern Formation-Helicopter Siltstone of the east Kimberly region ofWestern Australia (Thorne et al 1999) suggests that theAuvergne Group may correlate with the approximately800 Ma Supersequence 1 of the Centralian Superbasin(Walter et al 1995).

Wattie Group

The Wattie Group is a dominantly siliciclastic successionwith subordinate carbonates. It contains seven formationsthat have a minimum total thickness of about 390 m inLIMBUNYA (Mendum 1972).

The best exposures of the Wattie Group are in westernWAVE HILL, where the group is approximately 300 m

thick, and southeastern WATERLOO, where at least 450 mis present. Regional thickness variations characteriseWattie Group strata, which generally thicken to the eastand north of type and reference localities nominated bySweet et al (1974a) in WAVE HILL. The group isirregularly distributed in local structural windows insouthwestern, central and eastern LIMBUNYA. Minorexposures occur in the north. In LIMBUNYA, the WattieGroup overlies the Limbunya Group with a markedangular unconformity and in turn is unconformablyoverlain by the Auvergne Group. Of the seven formationsin the Wattie Group, only the basal Wickham Formationis well exposed; the remainder are mainly recessive orform low ridges, plateaux and scarps.

Wickham Formation (LPiw)

The Wickham Formation (Sweet et al 1974a) generally formslow- to moderate-relief ridges and dissected plateaux, with thelower part of the formation forming minor small rounded knolls.It overlies the Killaloc Formation with a marked angularunconformity in section MS14.

According to Mendum (1972) the formation infills sinkholes and karren that developed on the underlying CampbellSprings Dolostone in the vicinity of Wattie Creek. Significantexposures occur around No 8 Rockhole, which is 5 km tothe north of Kirkimbie Homestead, and along Stirling Creek,where the unconformity with the underlying LimbunyaGroup is exposed. Small, poor quality outcrops are locatednear Depot Pile and in scarps adjacent to Soda Springs Creekin northern LIMBUNYA. Regionally, the WickhamFormation progressively overlies younger formations of theLimbunya Group from east to west (Mendum 1972).Although no complete section is exposed, Sweet et al (1974a)recorded a minimum thickness of 315 m in southwesternLIMBUNYA. In WAVE HILL, at the type section nominatedby Sweet et al (1974a), the formation is 176 m thick. Inadjacent WATERLOO, its thickness is unknown. Coreddrillhole DD90VRB1 was collared in the WickhamFormation and intersected 29 m of weathered, ferruginousfine sandstone (Simeone 1991).

Figure 13 Section through fold-likestructure (Figure 12) in Fraynes Formation

15

The Wickham Formation is characterised by fine tomedium, moderately well sorted sandstone (sublitharenite),minor interbedded pebbly sandstone, conglomerate and chert,and rare siltstone. The dominant sandstone is locallyferruginous and rarely micaceous. It contains white grainsof claystone, feldspar and chert, plus a small percentage ofclay matrix (Sweet et al 1974a). Horizontal laminations andstacked trough cross-strata are common in thickly to verythickly bedded sandstone throughout the formation, as aremud clasts, which are rarely imbricated. Symmetric orasymmetric ripples, megaripples and mudcracks are preservedon some bedding surfaces. Subordinate lithologies are morecommon in the lower part of the formation, although some coarsepebbly facies occur in the upper portion of section MS1.

Near the junction of Horse and Stirling Creeks, theunderlying Killaloc Formation has been silicified and jigsawchert breccia is present at the contact with the WickhamFormation. At this locality, medium to thickly beddedsandstones of the Wickham Formation are strongly cross-bedded and contain some discontinuous granular and pebblychert lags, derived from the underlying unit. Transported andin situ displacive botryoidal quartz nodules (cauliflowercherts, probably after anhydrite) are also present, as are scourand fill structures and ripple marks associated with rare tri-star casts after halite.

The jigsaw chert breccia might be the product of an earlyduricrust or regolith, formed before deposition of theWickham Formation, or it may be a surface feature reflectingcarbonate in the subsurface.. Previously, Sweet et al (1974a)included similar chert breccia as a sedimentary facies withinthe basal part of the formation.

The Wickham Formation was probably deposited duringa shallow marine transgression. There was also somesubaerial exposure, predominantly during the deposition ofthe lower levels of the formation.

Burtawurta Formation (LPib)

The Burtawurta Formation (Sweet et al 1974a) is typicallyvery poorly exposed in low scree-covered rises adjacent tomore arenaceous units in the eastern part of the mapsheet. Itconformably overlies the Wickham Sandstone. Mendum(1972) estimated a thickness of 18 m in LIMBUNYA, but itis probably up to 30 m thick. Siltstone, which is micaceousin part, dominates the formation and is interbedded withminor fine sandstone, mudstone and rare dolostone near thetop. Some siltstone is coloured with secondary reductionspots. Ripple marks, mudcracks, and casts after halite indicatea relatively low-energy, shallow marine environment ofdeposition, with some brine-logging of the sediments andoccasional subaerial exposure.

Hughie Sandstone (LPih)

This sandstone unit outcrops in the vicinity of Toms Rockand forms low, crudely terraced hills adjacent to Wattie Creekin central-eastern LIMBUNYA. Elsewhere the formation isrepresented by boulder rubble. It ranges in thickness from51 m at Neave Creek, which is 27 km to the east of TomsRock in WAVE HILL (Bultitude 1973), to about 90 m insoutheastern WATERLOO. In LIMBUNYA, the Hughie

Sandstone is conformable on the Burtawurta Formation, butin northern WATERLOO, the Burtawurta Formation islocally absent and the Hughie Sandstone overlies theWickham Formation, probably conformably (Sweet 1973).

The fine to medium quartz sandstone contains up to 15%chert, feldspar, clay and igneous rock fragments and ismedium to thickly bedded. It displays liesegang banding, iscross-stratified and rippled on some partings and containsshale clasts throughout. In the type section nominated bySweet et al (1974a) in WATERLOO, the lower half of theHughie Sandstone contains some scattered angular tosubangular chert pebbles and rare mudcracks. A transgressive,shallow marine depositional environment that included minorsubaerial exposure is probable.

Mount Sanford Formation (LPio)

The Mount Sanford Formation conformably overlies theHughie Sandstone and forms terraced ridges and minor recessiveoutcrops below tabular and blocky remnants of the overlyingNeave Sandstone in LIMBUNYA. It is characterised by bothlocal and regional variations in composition and thickness.Mendum (1972) estimated the thickness of the formation tobe 25-50 m in LIMBUNYA. In WAVE HILL, it is 23.5 mthick and this increases to the north to 52.5 m in the typesection in WATERLOO, and to at least 200 m further to thenorth (Sweet et al 1974a).

In order of decreasing abundance, the Mount SanfordFormation contains interbedded siltstone, dolostone (someof possible stromatolitic origin), fine sandstone, dolomiticmudstone, chert, and rare claystone and tuffite. Coarsesandstone is rare. The formation is gradationally morecarbonate-rich up-section and the presence of brecciated,silicified dolostones and green chert near the topdistinguishes it from the otherwise similar Gibbie andBurtawurta Formations (Sweet et al 1974a). Recessiveferruginous phases produce locally abundant lag. A widevariety of sedimentary structures includes ripple marks andripple cross-laminations. Diagenetic features include greenreduction spots, chert nodules and casts after halite.

The Mount Sanford Formation was probably depositedunder similar low-energy, shallow marine depositionalconditions to the Burtawurta Formation.

Neave Sandstone (LPin)

The Neave Sandstone is very poorly exposed to the east ofToms Rock in southeastern LIMBUNYA, where it isestimated to be only 12 m thick (Mendum 1972). It overliesthe Mount Sanford Formation, possibly disconformably. Thegrey-purple, fine to medium quartz sandstone contains up to15% feldspar, chert, clay and rock fragments of probableigneous origin (Sweet et al 1974a). Locally, chert derivedfrom the Mount Sanford Formation (Mendum 1972) formspebbly beds within the sandstone. Trough cross-stratificationis common and asymmetric ripple marks and mud flakes arepresent on some bedding surfaces.

The Neave Sandstone is more widely distributed inWATERLOO and WAVE HILL and probably represents ashallow marine littoral unit that formed during a transgressiveor regressive phase of deposition (Sweet et al 1974a).

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Gibbie Formation (LPig)

The Gibbie Formation is recessive and, like the conformablyunderlying Neave Sandstone, is only exposed 5 km to theeast of Toms Rock in southeastern LIMBUNYA. It is about25 m thick in this area (Mendum 1972) and is 31 m thick inadjoining WAVE HILL. It is composed of thinly bedded,variably micaceous, ferruginous and calcareous siltstone, finesandstone and rare stromatolitic dolostone. Sandstone istypically reddish-brown and is interbedded with green-purplesiltstone. Ferruginous phases, that are presumably pyritic atdepth, have minimal lag developed on them. A variety ofsedimentary structures includes mudcracks, ripple marks andripple cross-laminations, soft-sediment deformation features,halite casts, load casts and green mud flakes.

The Gibbie Formation was deposited under mostly low-energy shallow marine conditions, with periods of subaerialexposure, possibly in a lagoon or embayment.

Seale Sandstone (LPim)

The Seale Sandstone conformably but sharply overlies theGibbie Formation in LIMBUNYA. It forms low plateauxof off-white, massive and blocky rubble, and consistspredominantly of medium quartz sandstone. Contiguousoutcrop of Seale Sandstone is 111 m thick along NeaveCreek in WAVE HILL, but thins to about 5 m insoutheastern AUVERGNE (Dunster et al 2000). Likeother Wattie Group sandstones, the Seale Sandstonecontains up to 10-15 % lithic grains (Sweet et al 1974a).It is strongly cross-stratified and contains clay galls andrare chert pebbles.

The Seale Sandstone was probably deposited under high-energy, shallow marine transgressive conditions.

Auvergne Group

The Auvergne Group (Sweet et al 1974a) contains sevenformations, of which only two outcrop or are preservedin LIMBUNYA. It is unconformable on the LimbunyaGroup.

Jasper Gorge Sandstone (LPaj)

The Jasper Gorge Sandstone is confined to a few squarekilometres in the northeast of LIMBUNYA and outcrop ispatchy and rubbly. It presumably overlies the LimbunyaGroup with a low-angle unconformity, but the relationshipin LIMBUNYA is obscured by faults. The basal sectionconsists of red-brown medium to course sandstone, parts ofwhich are friable. Chert pebbles and sand-sized grains,derived locally from the underlying units, occur in the basal10 m. Cross-beds are common. In thin section, the rock isan orthoquartzite. Up to 10% of the quartz grains werederived from volcanic or metamorphic sources (Sweet et al1974b).

The Jasper Gorge Sandstone was deposited as maturesand on a stable, broad continental platform. Sedimentarystructures indicate a nearshore marine environment (Sweetet al 1974b).

Angalarri Siltstone (LPaa)

The Angalarri Siltstone is almost entirely recessive and isdominated by micaceous fissile siltstone and shale. It is exposedin an eastern arm of Uindiat Creek, 5 km to the southeast ofUindiat Springs. The contact with the underlying Jasper GorgeSandstone was not observed. Unconformably overlying theformation is the Fargoo Tillite of the Duerdin Group.

The Angalarri Siltstone is interpreted to be a moderatelydeep water, sub-wavebase shelf deposit, from the presenceof micro-hummocky cross-stratification, abundant flute casts,and well defined lamination and ripple morphologies.

TECTONICS AND STRUCTURE

There were several phases of deposition in the Birrinduduand Victoria Basins, which were related to periods ofintracratonic sag. These phases of deposition correspond tothe component lithostratigraphic groups. In its presentstructural configuration, the Birrindudu Basin is essentiallyan inverted basin with all stratigraphy younging towards thebasin margins. Uplift is attributed to a compressional eventthat was in part time-transgressive and initially focused inLIMBUNYA. There are no obvious structural controls onbasin formation apart from major basement uplift beforedeposition of the Stirling Sandstone. The basement rise incentral LIMBUNYA is manifested as two small inliers ofquartz-muscovite schist.

The north- to northwest-trending Negri Fault has adisplacement of 25 km in NAPIER and forms the southwesternmargin of the Ord Basin. To the west of Inverway Station, itshows evidence of being a growth fault within the lower tomiddle facies of the Stirling Sandstone. The formation isthicker on the downthrown eastern side; a basal conglomeraticfacies or fan dominates the western side. Quartzite clasts upto 20 cm in diameter, which were derived from the fault wall,and angular clasts of silicified phyllite, which were derivedfrom the underlying Inverway Metamorphics, make up theconglomeratic facies. Quartz veins crosscut individual veinquartzite clasts. The Stirling Sandstone is moderately tostrongly folded along north-trending fold axes and this foldtrend continues north through the upper Limbunya Group tothe east of Kirkimbie Station and into the Ord Basin. Inwestern and southwestern LIMBUNYA, the trends of anumber of north-northwest-trending faults and basalt dykesparallel the Negri Fault.

The predominant structural feature in central LIMBUNYAis the west-northwest-trending Limbunya Fault. Thisstructure was active during Proterozoic sedimentation, as isindicated by thickness changes across the fault consistentwith syndepositional activity. The fault was subsequentlyreactivated after extrusion of the Antrim Plateau Volcanicsand deposition of Cambrian sediments.

In central LIMBUNYA, three major structural zones,designated the Southern, Central and Northern Zones(Figure 14 ) were identified by Australian PhotogeologicalConsultants (Appendix 1 in Hurrell 1992). Each of thesezones is defined by quite different lithostratigraphicsuccessions.

The Southern Zone (SZ) is essentially undeformed anddips are generally less than 5°. A broad north-trending

17

antiform in the southeast exposes the Inverway Metamorphicsin its core. This antiform may have resulted from warpingover a basement high. The dominant fault/fracture trendwithin the Southern Zone is strongly aligned in a west-northwesterly orientation with a less dominant set of fracturestrending northeast.

By contrast, the Central Zone contains a thicker, moreheterogeneous, mildly deformed sedimentary assemblage ofthe Limbunya Group. This region experienced a degree oftectonic mobility during and after deposition of the LimbunyaGroup. Australian Photogeological Consultants divided itinto two ‘domains’ (Central Zone East and Central ZoneWest), which are separated by the west-northwest-trendingLimbunya Fault. Central Zone East (CZE) is characterisedby dome and basin structures which may be indicative ofbasement diapirism. Central Zone West (CZW) contains

essentially a gently north-dipping succession that is affectedby minor block faulting and tilting in the extreme west. Thedifferences between CZE and CZW may be related to majorstrike-slip movement on the Limbunya Fault. TheLimbunya Fault also displaces the Antrim PlateauVolcanics and Goose Hole Group, 7 km to the north ofBigley Springs. There is evidence for minor compressionin both Central Zone domains after sedimentation. Minortight folds occur adjacent to bounding faults. Minor foldsalso characterise the Pear Tree Dolostone in the CentralZone East domain.

The Northern Zone (NZ) forms part of a large north-plunging anticlinal or half-dome structure (Figure 14 ) witha wavelength of about 35 km. This is a post-sedimentarystructural feature and could represent movement in thebasement. Beds generally dip gently to the north or are

17°30'

129°45'0 5

CZW

NZ

NZ

CZE

SZ

m02-073.dgn

10 km

NZ .......

CZW.....

CZE .....

SZ ........

Northern Zone

Southern Zone

Central Zone (West)

Central Zone (East)

Major Faults

Anticline

Syncline

Bedding trends and dips

Palaeozoic/Cenozoic cover

Figure 14 Regional structural interpretation of central LIMBUNYA (after Australian Photogeological Consultants Pty Ltd in Hurrell 1992).NZ = Northern Zone; CZW = Central Zone (West); CZE = Central Zone (East); SZ = Southern Zone

18

horizontal and the predominantly carbonate succession ofthe middle to upper Limbunya Group is largely undisturbed.Four major north-northeast-trending fault systems have beendelineated within the Northern Zone. These are normal faultsand are probably post-sedimentary. They are most probablyrelated to basement warping which resulted in the formationof the large north-plunging anticline. The structures appearto terminate in the south against the Limbunya Fault.Pervasive jointing in the Campbell Springs Dolomite andFraynes Formation trends 010º and 330º. These trends areconsistent with conjugate joint sets associated with theanticlinal structure.

Along the northeastern margin of LIMBUNYA andextending along the western margin of WAVE HILL is aseries of closed anticlinal structures containing LimbunyaGroup rocks. In places, the eastern sides of these aretruncated by a major north-northeast-trending fault. Thefault face forms a prominent vertical cliff and the faultzone consists of breccia 10 m thick, composedpredominantly of angular fragments of chert and minorsandstone fragments in a silicified matrix (Wygralak andAhmad 1998).

ECONOMIC GEOLOGY OF THE BIRRINDUDU AND VICTORIA

BASINS

Base metals

The Victoria and Birrindudu Basins have potential forCentury-style epigenetic mineralisation and syngenetic,stratiform, sediment-hosted base metals similar to theMcArthur River ore body. Exploration conducted in the early1990s targeted stratiform Pb, Zn and Cu in the LimbunyaGroup, the carbonate and shale units of which are prospectivefor base metals. Target formations included the MallabahDolostone, Kunja Siltstone, Blue Hole Formation, CampbellSprings Dolostone and Fraynes Formation.

The Kunja Siltstone is known to contain pyritic shale unitsbut has not been explored extensively. Reconnaissance samplingand drilling produced weak anomalous Pb and Zn values in thebasal Kunja Siltstone (DD90VRB2; Simeone 1991). The upperPear Tree Dolostone (MS4) has anomalous Cu.

Geopeko drilled a total of 2830 m of RC percussionand 808.2 m of diamond core through the MallabahDolostone, Blue Hole Formation, Margery Formation,Stirl ing Sandstone, an undifferentiated andunmetamorphosed succession of carbonaceous shale andsiltstone (now interpreted to be part of the BirrinduduGroup) and the Inverway Metamorphics (Hurrell 1992,1993). Sampling of a conductive 20 m thick black shaleunit in the Mallabah Dolostone returned values of115 ppm Pb and 370 ppm Zn. A Pb isotope studyundertaken by CSIRO for Geopeko on mineralisedsamples of Mallabah shale and dolomite was interpretedto indicate a Mesoproterozoic age and more than onehydrothermal source (Hurrell 1992, 1993).

Minor anomalous Pb and Zn values were associatedwith rare thin dark shale interbeds in the Blue HoleFormation. The steeply dipping shale and siltstone of theprobable Birrindudu Group hosts a shear zone with quartz-pyrite vein stockworks in outcrop. Black graphitic shale

was intersected within this succession in drillholeLMDH8. Chalcopyrite occurs in the graphitic shale andwithin late-stage carbonate breccia veins. Reactive pyriteis also common.

Diamonds

Early diamond exploration in the 1980s focused onundifferentiated Limbunya Group rocks near Moonbool Creekand to the northwest of Limbunya. More regional programswere undertaken by Ashton Mining Ltd between 1981 and1983 (Ashton Mining 1983a-f). Minor chromite,kimberlitic zircons and three diamonds were found, butthe results of follow-up sampling were disappointing.Stockdale Prospecting undertook a stream sediment surveyin 1997 (Milikan 1998a-c, Winzar 1998). An abundanceof chromites were recovered, but their source may be theAntrim Plateau Volcanics.

Geochemical sampling

NTGS geochemical sampling of rock samples frommeasured sections in LIMBUNYA returned anomalousvalues of 750 ppm Zn in the Mallabah Dolostone,140 ppm Zn in the Campbell Springs Dolostone,190 ppm Pb in the Fraynes Formation, and 125 ppm Pband 125 ppm Zn in the Blue Hole Formation. AnomalousPb values are found in similar stratigraphic horizons inthe basal Fraynes Formation in measured sections MS13and MS24. No metal mineralisation was visible, but thegeochemistry might indicate enrichment in specificstratigraphic intervals (Appendix 1 ).

Hydrocarbons

Stratigraphic drilling by CRA intersected carbonaceousmaterial in the Kunja Siltstone. Petroleum geochemistryindicated poor to excellent source potential. Samplesappeared to be on the threshold of hydrocarbon generationor within the top of the oil window (CRA DD90VRB2;Simeone 1991).

Groundwater

The water resources of the Victoria River district werediscussed in detail by Tickell and Rajaratnam (1998).Numerous natural water sources, such as springs andcreeks, occur in LIMBUNYA. Stirling Creek flows formore than six months of the year, but for most of the time,creeks break up into chains of waterholes. These persistfor varying periods depending on depth and on whetheror not they are supplemented by spring flows. Significantsprings include Campbell Spring, Swan Creek Waterhole,Blacksprings, Unidait Spring, Fraynes Camp Spring,Buchanan Spring and Moonbool Creek. Campbell Springis a dolostone aquifer, which is faulted against FraynesFormation siltstone.

The Antrim Plateau Volcanics, Wickham Formation,Margery Formation, and Campbell Springs Dolostone areall reported to be good aquifers (Mendum 1972).

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WOLFE CREEK BASIN

The Wolfe Creek Basin records the deposition of severalthousand metres of Neoproterozoic glacial and fluvio-glacialsediments. An undifferentiated diamictite has been mappedfor the first time in LIMBUNYA and WAVE HILL and thisdiscovery extends known glacial deposits further to the eastand south in the Victoria River region.

Duerdin Group

The Duerdin Group was originally defined and described byDow and Gemuts (1969) and was subsequently mapped anddescribed by Sweet et al (1974a). The group has beensubdivided into five formations, but only undifferentiateddiamictite outcrops in LIMBUNYA. The diamictite was firstdiscovered by Stockdale Prospecting during a streamsediment survey in 1998.

Undifferentiated diamictite (LPou)

Undifferentiated diamictite is preserved as a small bench,which is approximately 0.5 km in area and 20 m thick. Itunconformably overlies the Angalarri Siltstone along theeastern arm of Uindiat Creek, and is overlain by the AntrimPlateau Volcanics. The massive diamictite contains scatteredclasts in an olive-purple clay matrix (Figure 15 ). Abundanterratics, which are flattened, subrounded, striated and up to40 cm in diameter, are scattered on the residual weatheringsurface and in the adjacent creek bed. Sandstone,dolostone, siltstone, meta-siltstone, schist, possiblevolcanics and granite are the most common types oferratics. Up to 90% of clasts are of sandstone, siltstone ordolostone; igneous and metamorphic rocks make up theremainder. Sedimentary dropstones were probably derivedfrom the Victoria Basin succession, whereas igneous andmetamorphic dropstones are probably from the HallsCreek Group to the west or Lamboo Complex (Bow RiverGranite) to the north.

The undifferentiated diamictite is considered to beequivalent to either the Moonlight Valley Tillite (Sweet

et al 1974b) or Fargoo Tillite (Dow and Gemuts 1969).The closest exposures of these units are in AUVERGNEand nor thwes tern WATERLOO, to the nor th ofLIMBUNYA, and in OSMOND RANGE and DIXONRANGE, in Western Australia.

Bofinger and Compston (1967) obtained a Rb-Sr ageof 739 ± 30 Ma for the Moonlight Valley Tillite. In a studyof similar rocks in the Kimberley area, Grey and Corkeran(1998) correlated the Fargoo and Moonlight Valley Tilliteswith the Olympic and Elatina Formations of the AmadeusBasin and Adelaide Geosyncline, respectively, and inferredan age of 610 Ma for the Moonlight Valley Tillite.

CAMBRIAN VOLCANIC ROCKS

Antrim Plateau Volcanics (C_ la)

The Antrim Plateau Volcanics (Mory and Beere 1985)outcrop extensively in LIMBUNYA (Figure 16 ) and formthe largest Phanerozoic flood basalt province in Australia,covering an area of at least 35 000 km2 (Bultitude 1976).The Victoria River region has the largest area of outcrop ofAntrim Plateau Volcanics in Australia, but they attain theirgreatest overall thickness (700-1000 m) in the east Kimberleyregion of Western Australia (Mory and Beere 1988). Thevolcanics consist of a series of 20-60 m thick lava flows,mostly of massive fine basalt with conspicuous vesicular flowtops, and less commonly of plagioclase-phyric basalt (Hanleyand Wingate 2000). The locations of major eruptive centresare difficult to determine, because of probable burial by laterlava flows (Bultitude 1976).

The Antrim Plateau Volcanics are considered to bestratigraphic equivalents of, and are geochemically identicalto the Peaker Piker Volcanics and Helen Springs Volcanicsin the Northern Territory, and the Colless Volcanics inQueensland (Bultitude 1976, LM Hanley unpublished data).Bultitude (1976) proposed that the regional extent of theAntrim Plateau Volcanics and stratigraphic equivalents couldbe up to 200 000-300 000 km2, which is comparable in sizeto some of the world’s major flood basalt provinces (Veeversand Powell 1984).

Figure 15 Typica l und i f fe ren t i a tedd iamic t i t e of Duerdin Group inLIMBUNYA, showing dropstones

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The Antrim Plateau Volcanics have not been datedaccurately, but have traditionally been considered to beEarly Cambrian (Bultitude 1976).

Beneath neighbouring basins, the Antrim PlateauVolcanics immediately underlie fossiliferous rock units(Tindall Limestone, Montejinni Limestone) of undoubtedearly Middle Cambrian (Ordian-early Templetonian) age(Shergold et al 1985, Kruse 1990, 1998). Their lower agelimit, however, is much less well constrained, and theymay conceivably be partly or wholly late Neoproterozoic.Walter (1972) described the conical stromatolitesConophyton basalticum and C. gaubitza, from theconstituent Mount Close Chert Member (Mory and Beere1985), and these would favour a Neoproterozoic age.However, this member may well represent the deposits ofhot springs, a distinctive environment, in which conicalstromatolites are known to develop even up to the present(Walter et al 1976). Conversely, arguments for a Cambrianage on the basis of purported Skolithos trace fossilsbeneath a laterally equivalent volcanic unit on HODGSONDOWNS (Dunn 1963, Plumb et al 1976) are underminedby their reinterpretation as abiogenic dewatering structures(Haines in Rawlings et al 1997). Nevertheless, fromtectonic considerations, an Early Cambrian age seemsmost probable.

The Antrim Plateau Volcanics are everywheresucceeded by early Middle Cambrian peritidal to marinelimestones. This marine transgression can be viewed as adirect consequence of crustal sag following the cessationof Antrim Plateau volcanism. In this scenario, the timegap separating deposition of the two rock bodies wouldbe brief. Support for this model can be found among theCambrian volcanic terranes of southeastern Australia,where biostratigraphically dated possible correlatives ofthe Antrim Plateau Volcanics include the Truro Volcanicsof the Stansbury Basin, South Australia (Jago et al 1984,Jenkins and Hasenohr 1989, Gravestock 1995), and theMount Wright Volcanics and Cymbric Vale Formation ofthe Gnalta Shelf, western New South Wales (Kruse 1982,Kruse and Shi 2000). Appropriately, all three units are ofBotomian (late Early Cambrian) age, that is, almostimmediately pre-Ordian.

Hanley and Wingate (2000) determined a SHRIMP U-Pbzircon age of 513 ± 12 Ma for the 250 km long Milliwindidolerite dyke from the western Kimberley region, which isconsidered to be equivalent to the Antrim Plateau Volcanics.

ECONOMIC GEOLOGY OF THE ANTRIM PLATEAU VOLCANICS

Stratabound copper occurrences

The top of the Antrim Plateau Volcanics succession, near andalong the contact with the overlying Headleys Limestone, carrieswidespread, but thus far economically insignificant coppermineralisation. Some copper is also hosted by the HeadleysLimestone close to the contact zone. In LIMBUNYA, anextensive exploration program for copper was conducted during1968-1970 by a joint venture headed by Metals ExplorationNL. The exploration was targeted to locate large, low-gradeLake Michigan-type copper deposits in the Antrim PlateauVolcanics (Erskine et al 1970). In the early 1970s, AmocoMinerals Australia Co carried out an exploration program totest for copper mineralisation in the Antrim Plateau Volcanics/Headleys Limestone contact (Miguel 1974). From these earlysurveys, four types of copper mineralisation were distinguished(Eskine et al 1970, Burt et al 1970, Miguel 1974):

(1) structurally controlled mineralisation in fault and shearzones in the Antrim Plateau Volcanics;

(2) mineralisation in the basal three metres of the HeadleysLimestone;

(3) mineralisation associated with agglomerate, vesicleinfills in flow tops, or disseminated in massive basalt inthe upper part of the Antrim Plateau Volcanics; and

(4) mineralisati o n l i n k e d w i t h black manganiferouslimestone blows of possible fumarolic origin.

The biggest copper prospect located during theseexploration activities, Caves prospect (526700mE,8062400mN), contains about 2000 t of ore grading2-20% Cu (Erskine et al 1970). Visible mineralisation is

Figure 16 Antrim Plateau Volcanics (left)overlying Campbell Springs Dolostone(627000mE, 8044800mN)

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fault-related and concentrated near the contact betweenthe Antrim Plateau Volcanics and Headleys Limestone.The main ore minerals are malachite and chalcocite. Acircular body of fumarolic deposits occurs adjacent to thevisible mineralisation.

Barite

Pods and veins of barite occur in the Antrim Plateau Volcanicsand are commonly associated with quartz and calcite. Thebiggest deposit (occurrence LIMBUNYA No 006) includessix steeply dipping barite veins in the Kirkimbie Yard area,32 km to the north-northwest of Inverway homestead. Theveins occupy a fracture in the volcanics and are parallel tothe major regional lineament that forms the southwesternmargin of the Hardman Syncline in western LIMBUNYA(Sweet 1974a). Two were mined during 1970-1972 by SouthAustralian Barites Ltd. The main lode is about 3.3 km long,up to 2 m wide and has a strike of 330º. A bulk sample fromthis lode had a specific gravity of 4.28 g/cm3 and contained97.3% BaSO4, 2.05% SrSO4 and 0.33% SiO2 (Willis andNewton 1975). The second, western lode is 60 m long, up to2 m wide and has a strike of 355º. A bulk sample taken fromthis lode had a specific gravity of 4.54 g/cm3 and contained96.9% BaSO4, 2.4%SrSO4 and 0.33% SiO2. Total productionform both lodes was 35 000 t, but only the top 4-5 m of lodematerial was mined. The resource is estimated at 32 800 tper vertical metre (Mendum 1972). Total barite resourcesare estimated to be 475 000 tonnes to 20 m in depth (NibarMining 1986).

Amethyst and other semi-precious stones

Occurrences of amethyst, smoky quartz, prehnite, agate andcalcite are abundant in vesicular basalt of the Antrim PlateauVolcanics (Bultitude 1973). Amethyst vugs occur in basalts,25 km to the west of Limbunya Station. Some of the largeramethyst-lined amygdales have been sold as mineralogicalspecimens.

ORD BASIN

The Ord Basin is a tectonic unit straddling the WesternAustralia-Northern Territory border, which contains, fromsouth to north, the Hardman, Rosewood and Argyle Synclines(Matheson and Teichert 1948). Only the Hardman Synclinehas appreciable outcrop within the Northern Territory, innorthwestern LIMBUNYA. This syncline preserves the mostcomplete stratigraphic succession, and includes, in itsWestern Australian portion, Late Devonian sandstone andminor conglomerate of the Mahony Group.

Goose Hole Group

The Goose Hole Group (Mory and Beere 1985) embraces allMiddle and Late Cambrian sedimentary rocks of the Ord Basin(Wade 1924, McWhae et al 1958). Present lithostratigraphicnomenclature of the group follows Traves (1955) and mostrecent modifications were in Mory and Beere (1985). Thegroup attains some 700 m in thickness and is subdivided intothe Negri Subgroup and overlying Elder Subgroup.

Negri Subgroup

The Negri Subgroup attains a maximum thickness of530 m. It includes, in ascending order, the HeadleysLimestone, Nelson Shale, Linnekar Limestone and PantonFormation, which contains the Shady Camp and CorbyLimestone Members. On biostratigraphic and sequencestratigraphic grounds, the succession can be assigned tosequence 1 of Shergold et al (1988) and Southgate andShergold (1991), of early Middle Cambrian (Ordian-earlyTempletonian) age.

Headleys Limestone (C_ Gh)

The Headleys Limestone (Traves 1955) rests with apparentconformity on the Antrim Plateau Volcanics and isconformably overlain by the Nelson Shale. Its peritidalcarbonate sediments herald a widespread marine transgressiononto the North Australian Craton, which elsewhere is knownto have begun in the earliest Middle Cambrian. The formationlacks age-diagnostic fossils, but by analogy and from itsstratigraphic continuity with the securely dated LinnekarLimestone, which occurs higher in the succession, theformation is considered to be Ordian in age. Ferruginisationand silicification of the underlying basalts may be the resulteither of weathering prior to deposition of the HeadleysLimestone (Sweet et al 1974a), or of recent processes (Moryand Beere 1985).

The type section (Traves 1955) is in the vicinity ofHeadleys Knob in LIMBUNYA. More accessible sectionsare astride the Negri River at DG887130 (DIXON RANGE)and along the faulted southern margin of the HardmanSyncline in LIMBUNYA. The maximum thickness of theformation is 50 m (Mory and Beere 1988).

The formation is predominantly of grey stromatoliticlimestone and is expressed as bold ridge-like outcrops(Figure 17 ). Its lower portion comprises medium to thicklybedded stromatolitic laminite with common planar and minordomed stromatolites. Ovoid and flat siliceous nodulescharacterise the basal beds (Figure 18 ) and some of theseare of early diagenetic origin, as is indicated by compressionof adjacent stromatolitic laminae. Some beds show dark-lightgrey pseudobedding. Millimetre-size sulfide (pyrite?)pseudomorphs are here reported from the Negri River section,about 8 m above the formation base. Distinctive structuresthat are manifested as nested concentric rings on beddingplanes, and as smoothly upturned and breached beds invertical sections, are interpreted as cold seeps (J Reitner,Universität Göttingen, pers comm 1998).

The upper portion of the formation is of flat to slightlywavy, thinly bedded limestone that commonly has wrinkledsurfaces due to original microbial biofilms. Locally, commonmillimetre-scale siliceous nodules may represent formerevaporites.

The presence of planar stromatolites, fenestral fabrics andflat pebble conglomerates indicates an intertidal to possiblysupratidal depositional environment for the HeadleysLimestone. Numerous small copper occurrences have beenreported from basal beds (see Economic geology of the AntrimPlateau Volcanics).

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Nelson Shale (C_ Gn)

The essentially unfossiliferous Nelson Shale (Traves 1955)is conformably sandwiched between the Headleys Limestone(below) and the securely dated Linnekar Limestone (above),and is therefore regarded as Ordian in age. Girvanella is theonly fossil recorded from this poorly outcropping formation(Dow 1980). It comprises up to 183 m (Mory and Beere1985) of maroon to grey gypsiferous shale and mudstone,minor fine sandstone and rare laminated limestone. Thesewere deposited under peritidal conditions. Mory and Beere(1985) designated an approximately east-west type sectionthrough the Nelson Springs area to the east of Mount Panton.The upper boundary is well exposed at Bronte Bore(EF238887), where a 22 m-thick interval of uppermostNelson Shale is overlain with a sharp contact by the LinnekarLimestone.

Linnekar Limestone (C_ Gl)

The Linnekar Limestone (Traves 1955) lies conformablybetween the Nelson Shale (below) and Panton Formation

(above). Playford et al (1975) reported a maximum thicknessof 40 m for the formation. It is 31 m thick at White MountainBore (LIMBUNYA EF007859), 21 m near Junction Yard(DIXON RANGE DG887130), 19 m in the type section atthe junction of Linnekar and Brook Creeks (DIXON RANGEDF695591 to DF693600; Playford et al 1975) and 10 m tothe east of Mt Panton (LIMBUNYA EF239816). An informaltripartite subdivision comprises lower and upper stromatoliticunits that straddle a richly fossiliferous interval of thinlybedded limestone, marl and shale.

The lower unit, exposed in the Linnekar-Brook Creek andMt Panton sections, contains up to 3 m of basal, grey, thicklybedded to massive, planar to gently waved stromatolitic laminitewith abundant bedding-parallel siliceous nodules. Flat pebblebreccias, cold-seep structures (J Reitner, Universität Göttingen,pers comm 1998), medium-bedded fenestral limestone (locallyincorporating hyolith and brachiopod bioclasts), local impurequartzic calcimudstone and, in the Mt Panton section, distinctivedecimetre-scale LLH stromatolites and metre-size domedthrombolites occur up-section (Figure 19 ). This peritidal unitconstitutes the scarps of persistent cuesta outcrops that aretypical of the Linnekar Limestone.

Figure 17 Typical outcrop of HeadleysLimestone, near Blackfellow Rockhole(NEGRI EF095785)

Figure 18 Ovoid and flat siliceous nodulesin basal beds of Headleys Limestone, nearBlackfellow Rockhole. (NEGRI EF107777)

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The richly fossiliferous middle unit (Figure 20 ) is of greyto olive, thinly bedded, tabular to nodular marine shelflimestone (calcimudstone and bioclast wackestone topackstone), marl and shale. It contains the trilobite Redlichiaforresti (Etheridge in Foord 1890; see Öpik 1958), thebrachiopods Kyrshabaktella mudedirri Kruse 1990 and rareWimanella sp., and the hyolith Guduguwan hardmani(Etheridge in Foord 1890). Traves’ (1955) record ofGirvanella (presumably referring to onkoids) appears to befrom this interval. Together, these are taken to indicate anOrdian-early Templetonian (early Middle Cambrian) agefor the Linnekar Limestone. Hyoliths locally formgrainstones, some of which represent storm beds. This unitis best exposed along the margins of watercourses and atother sites of local relief; outcrop is poor on flat terrain.

The thin upper unit is of poorly outcropping, grey,peritidal stromatolitic laminite that contains planar, wavyand domed stromatolites.

Panton Formation (C_ Gp)

The Panton Formation of Mory and Beere (1985) embracesfive superseded formation-rank units of Traves (1955) andattains a maximum thickness of 308 m. It is conformable onthe Linnekar Limestone, and includes the Shady CampLimestone Member and the stratigraphically higher CorbyLimestone Member.

Playford et al (1975) nominated a type section at MtPanton (LIMBUNYA EF232812), where the interval up toand including the Corby Limestone Member is exposed(Figure 20 ), but this does not include the entire formationsensu Mory and Beere (1985), as is followed here. The MtPanton type section is here retained with a lower boundarystratotype at EF236815; the top of Mory and Beere’s (1985)Hudson Creek ‘reference section’ (DIXON RANGE DF952922)is here designated as the upper boundary stratotype.

The Panton Formation is richly fossiliferous in its medialportion, in and between the two named members, and thisconfirms an Ordian-early Templetonian (early MiddleCambrian) age. The medial, restricted marine shelf depositsare of recessively weathering grey, fissile shale and wavy-to nodular-bedded marl and marly limestone, which are

punctuated by several packages of resistant limestone up to3 m in thickness. Onkoids, stromatolitic laminite, flat pebblebreccias, thin sandstone beds and rare pseudomorphs ofhalite hoppers are locally present. Fine-grained malachiteand azurite have been recovered from acid residues of thislimestone at DIXON RANGE DG941132. The knownbiota includes the trilobites Redlichia amadeana (Öpik1970), Xystridura negrina (Öpik 1975) and a rareptychopariid; the brachiopods Kyrshabaktella mudedirriKruse 1990 and rarer Lingulella sp., Westonia sp. andWimanella sp.; Guduguwan hardmani (Etheridge in Foord1890) and four other hyolith species; the molluscLatouchella accordionata (Runnegar and Jell 1976);locally abundant indeterminate edrioasteroid plates;sponge spicules, chancelloriids, the calcimicrobeGirvanella; and stromatolites (Traves 1955). G. hardmanicommonly occurs in bioclast grainstone coquinas.

Above and below this interval, the Panton Formationis predominantly of maroon-purple gypsiferous shale andmudstone, and is otherwise unfossiliferous, apart from athin, partially dolomitised hyolith-bearing limestone bedin its upper part. This bed contains G. hardmani accordingto Playford et al (1975) and is of probable Ordian-earlyTempletonian age.

The lower gypsiferous shale is well exposed at MountPanton. In the upper Panton Formation of the HudsonCreek area, individual thin micaceous sandstone bedsbecome increasingly common within the prevailingmaroon shale over a 35 m stratigraphic interval below thehyolith limestone bed. At this locality, the hyolith bed is0.2 m thick, grey, quartzic and contains occasionalonkoids. Above the limestone, the uppermost beds of theformation are represented by about 15 m of grey to purpleand maroon, thinly bedded, marly fine sandstone. Thisuppermost interval is transitional into medium-beddedbrown sandstone of the conformably overlying EagleHawk Sandstone.

Elsewhere, the upper Panton Formation beside theNegri River at LIMBUNYA EF114961 shows ripples,pseudomorphs of halite hoppers (Figure 21 ), microbialwrinkled surfaces and possible desiccation cracks, consistentwith a peritidal depositional environment.

Figure 19 Basal 2 m of Linnekar Limestone,from Nelson Springs-Mt Panton track, nearMt Panton (NEGRI EF239816). Sectioncommences with planar microbial laminite(hammer), succeeded in turn by domedstromatolites (midway through section) anddomed thrombolites (top)

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Shady Camp Limestone Member (C_ Gps)

In its type section at Mt Panton (Mory and Beere 1985), theShady Camp Limestone Member is 3 m thick and commences48 m above the base of the Panton Formation (Figure 20 ).Elsewhere, it ranges up to 4 m in thickness and commencesbetween 30 m and 92 m above the base of the formation(Mory and Beere 1985). In the type section, the basal bedscontain grey, flat- to wavy-laminated stromatolites withgypsum lozenge moulds; these beds may locally contain flatto ovoid siliceous nodules. Succeeding medium to thick bedsof distinctive grey, onkoid-rich nodular hyolith floatstone(predominantly of G. hardmani) dominate the unit(Figure 22 ). Thin sections confirm the presence of thecalcimicrobial genus Girvanella in onkoid cortices. Peritidalto shallow subtidal depositional environments are indicated.

Corby Limestone Member (C_ Gpc)

The type section of the Corby Limestone Member in HudsonCreek (DIXON RANGE DF953916, Mory and Beere 1985)contains 4.6 m of grey, medium bedded, flat-laminatedstromatolitic limestone. The basal metre includes bedding-parallel flat siliceous nodules.

This member caps the summit of Mount Panton(Figure 19 ), where it is 2.4 m thick and fossiliferous. Itcontains a grey-brown-purple lower unit of medium-bedded

hyolith floatstone containing abundant G. hardmani, and adominant, cliff-forming upper unit of grey, thick-beddedonkoid bioclast floatstone containing G. hardmani andsilicified L. accordionata (Figure 23 ). Girvanella highlightsindividual laminations in thin sections of stromatoliticlaminite from LIMBUNYA EF117977. South of MountPanton at EF212726, the member is of medium to thicklybedded maroon bioclastic limestone, which in part, is low-angle cross-bedded.

The Corby Limestone Member was deposited in intertidalto shoreface and shallow subtidal environments.

Elder Subgroup

The Elder Subgroup reaches a maximum thickness of 370 m.It includes the Eagle Hawk Sandstone and the overlyingOverland Sandstone.

Eagle Hawk Sandstone (C_ Ge)

The Eagle Hawk Sandstone (Mory and Beere 1985)comprises tabular to blocky, feldspathic to micaceous, fineto medium sandstone, and minor siltstone and mudstone.Component feldspar may be sericitised; varying proportionsof interstitial iron oxides±clays impart a characteristic red-brown to maroon colour. Outcrop of the formation is generallypoor to moderate. Nevertheless, it is easily recognisable onaerial photographs by its prominent bedding trends.

Mory and Beere (1985) designated a type section atHudson Creek on the southwestern flank of WhiteMountain (northeastern DIXON RANGE), where theformation attains a maximum thickness of 210 m. Thecontact with the underlying Panton Formation isconformable and gradational, as is (according to Moryand Beere 1985, 1988), the contact with the overlyingOverland Sandstone, although this is not exposed inLIMBUNYA. The only known fossils are non-age-diagnostic trilobite tracks, figured by Mory and Beere(1988 Figure 21). These authors proposed a MiddleCambrian (Templetonian-Boomerangian) age for theEagle Hawk Sandstone, based on its conformity with theunderlying biostratigraphically dated Panton Formationand on lithological correlation with the Hart SpringSandstone of the Bonaparte Basin.

A 5 m thick section of the formation is well exposedat the Duncan Highway crossing of the Negri River(Figure 24 , LIMBUNYA EG000117). Sedimentarystructures in the maroon and grey sandstone at this localityinclude horizons of mud pebble and cobble moulds,decimetre-scale channels and cross-bed sets, desiccationcracks (Figure 25 ) and a variety of ripples. Mory and Beere(1988) recognised trough cross-bedded sandstone, parallel-laminated sandstone, and laminated siltstone and mudstonefacies in the Eagle Hawk Sandstone, which they interpretedas having been deposited in intertidal sand and mudflatenvironments.

Overland Sandstone (C_ Go)

Outcrop of the Overland Sandstone (Mory and Beere 1985)is limited to a steep-sided plateau in the northwest of

Figure 20 View northwest toward Mt Panton. Linnekar Limestoneplateau in foreground and middle ground. Panton Formation formsMt Panton. Shady Camp Limestone Member is midway up MtPanton. Corby Limetone Member caps summit

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Figure 21 Halite hoppers in upper part ofPanton Formation, on west bank of NegriRiver (NEGRI EF114961)

LIMBUNYA (Figure 26 ), about 9 km due west of the NegriRiver-Stirling Creek junction. This area includes the 230 mthick type section, which straddles the Northern Territory-Western Australia border. Outcrop is more extensive in theWestern Australian portion of the Hardman Syncline, fromwhere Mory and Beere (1985, 1988) reported a conformablecontact with the underlying Eagle Hawk Sandstone andunconformity with the overlying Mahony Group of Devonianage. A Late Cambrian age for the Overland Sandstone is implied.

The Overland Sandstone comprises white to pale greyor fawn, fine to medium lithic arkose and sandstone. Moryand Beere (1988) noted that lithic grains include quartz-mica schist, fine metasediment and quartzite. Theyrecognised trough cross-bedded, planar cross-bedded andparallel-laminated sandstone facies (Figure 27 ). In aplateau-margin cliff section at EG018002 in LIMBUNYA,sandstone is dominated by centimetre- to decimetre-scalecross-bed sets. Iron oxide stains highlight laminations insubordinate parallel-laminated sandstone, which also bearsstraight to sinuous current ripple marks.

From its composition and sedimentary structures, theOverland Sandstone is interpreted as being indicative of a

braided fluvial depositional system draining a hinterland oflow relief (Mory and Beere 1988).

ORD BASIN STRUCTURE

Among the three recognised constituent synclines of theOrd Basin, only the Hardman Syncline is represented innorthwestern LIMBUNYA. The greater part of theHardman Syncline lies in adjacent DIXON RANGE(Western Australia). In the LIMBUNYA portion, dips arelow except in strata adjacent to some faults. Three majorfaults, two of them named, cut the syncline in the sheet area.

The northwest-trending Negri Fault transects the entireHardman Syncline. It extends northwestward into DIXONRANGE and continues southward to link with a north-south fault system affecting the Limbunya and WattieGroups in southwestern LIMBUNYA. The Negri Faultaffects the Antrim Plateau Volcanics, the entire Goose HoleGroup, and in DIXON RANGE, the Upper DevonianMahony Group. Responses of Goose Hole Group units tofaulting vary. Near the upper reaches of the Negri River,the Headleys Limestone adjacent to the Negri Fault is

Figure 22 Prominent beds of onkoid-richnodular hyolith floatstone in Shady CampLimestone Member at Mt Panton (NEGRI

EF232812)

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fractured into numerous small fault blocks; some areinternally folded into broad synclines or anticlines withfold axes parallel to the fault trend. Faults in this area arerelated to copper mineralisation in the Antrim PlateauVolcanics and Headleys Limestone (eg Caves prospect).A narrow sliver of Headleys Limestone continuesnorthwestward along the fault almost to View Hill, and islocally associated with en echelon faulting. The HeadleysLimestone along this tract forms a spectacular monocline,whereby the flat-lying southwestern limb progressivelysteepens to about 80º in the uppermost beds of theformation on the northeastern limb (Figure 28 ).Associated parasitic folds, with axes subparallel to thefault trend, affect overlying Goose Hole Group units.Folding is best expressed in the limestone units (LinnekarLimestone, Shady Camp Limestone Member, CorbyLimestone Member), which clearly trace out the foldlimbs. Relatively ductile shale and mudstone of the NelsonShale and undifferentiated Panton Formation might beexpected to more readily accommodate movement, but thefolding is nevertheless discernible in bedding tracesdepicted on aerial photographs. Outcrop at View Hillappears to represent the nose of an equivalent fold in theEagle Hawk Sandstone.

The Limbunya Fault transects LIMBUNYA in a west-northwesterly trend. It intersects the Ord Basin at its

Figure 23 Cliff-forming thickly bedded onkoid bioclast floatstonein Corby Limestone Member at Mt Panton. Hammer (centre) forscale (NEGRI EF232812)

western extremity, where movement appears to be largelyaccommodated within the Nelson Shale and PantonFormation. However, a northwesterly extension of thefault, interpreted from aeromagnetic data, highlights someassociated folding in the Linnekar Limestone and CorbyLimestone Member, and possibly also in the Eagle HawkSandstone. The greatest impact of the Limbunya Fault onOrd Basin strata is upon the Headleys Limestone; adjacentto the Nelson Springs-Inverway track, the upthrown northernside is a monocline which steepens adjacent to the fault.Contorted thin shale and limestone beds on the flats belowindicate the fault trace.

A third, unnamed major fault to the north, trendinggenerally east near the lower reaches of Stirling Creek,likewise affects the Headleys Limestone. Fault splaysbound upthrown blocks of Headleys Limestone within theadjacent Nelson Shale. Tilting and folding of these blocksis minimal to moderate. Consequent slight uplift of rockunits as young as the Eagle Hawk Sandstone is shown byembayments in mapped formation boundaries to the west.The fault trace is marked by local fault breccia ofsubangular-subrounded pebbles to boulders of HeadleysLimestone in a darker lime matrix.

MESOZOIC AND CENOZOIC GEOLOGY

Mesozoic rocks

Small areas of undifferentiated Cretaceous sandstone andminor conglomerate outcrop in central LIMBUNYA.These are onshore remnants of a large marine basin thatoriginally covered much of the northeastern NorthernTerritory and northern Queensland. The thin successionis deeply eroded and lateritised.

Cenozoic units

About one third of the land area of LIMBUNYA is coveredby four Cenozoic units. These include a newly recognisedunit of duricrust.

Silcrete/duricrust (Czo)

Internally brecciated chert, up to tens of metres thick, islocally abundant on carbonates of the Limbunya Group.It was originally mapped as an upper chert horizon of theFraynes Formation (Sweet et al 1974a). Recent mappinghas shown that it is not restricted to the same stratigraphichorizon of the Fraynes Formation and that it also rests onthe Campbell Springs Dolostone. Identical chert brecciaalso occurs on the Skull Creek Formation including theSupplejack Dolostone Member, on the Timber CreekFormation and several other formations in AUVERGNEand on the Bynoe Formation in VICTORIA RIVERDOWNS. In all of these examples, textures are typical ofa siliceous duricrust.

Laterite (Czl)

Ferruginous laterite occurs in southern and northeastern partsof LIMBUNYA, where it is mostly associated with basalt of

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Figure 26 Prominent east-facing plateauscarp of Overland Sandstone, 9 km south-southwest of Mistake Creek community(NEGRI EG018002)

Figure 24 Interbedded sandstone andmudstone of Eagle Hawk Sandstone. Northbank of Negri River at Duncan Highwaycrossing (NEGRI EG000117)

Figure 25 Eagle Hawk Sandstone, showingdesiccation-cracked wrinkled surface,probably of microbial biofilm. North bankof Negri River at Duncan Highway crossing(NEGRI EG000117)

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the Antrim Plateau Volcanics. Complete laterite profiles aredeveloped in many places, particularly where the laterite hasformed on basalt (Sweet et al 1974a). A thin covering oflaterite has also formed on Limbunya Group rocks.

Grey clay-rich soil (Czb)

Areas of residual, dark grey clay-rich soil in LIMBUNYAwere derived from the Antrim Plateau Volcanics or underlyingcarbonates. The clay-rich soil borders major tributaries of SturtCreek and overlies low-relief basalt areas.

Superficial soils and calcrete (Czs)

Superficial sand, residual soil, eluvium and minor calcreteoccur throughout LIMBUNYA. Examples includeconglomeratic calcrete on Headleys Limestone atEF037769 and in situ white-brown laminated and pisoliticcalcrete at EF024735.

Alluvium (Qa)

River sediment up to 10 m thick occurs along the banksof all major rivers in LIMBUNYA. Most rivers andstreams are entrenched in their own alluvium. In theenvirons of the Negri River in Shady Camp paddock(NEGRI), consolidated river gravels are exposed. Clastsof cm-sized ironstone pebbles, rounded to tabular siliceouspebbles and cobbles, grey limestone and basalt occur inan ironstone matrix.

Undifferentiated alluvium and colluvium (Cz)

Cz consists of:

· unconsolidated gravel, drainage channel sand, andmud-rich sediments of adjacent black soilfloodplains; and

· unconsolidated colluvium, alluvium, skeletal soilsand residual soils that typically occur on the slopesand flanks of upland areas.

In the Cambrian Ord Basin, for example, residualquartzite, ironstone and quartz gravel occur on a hilltopoverlying the Nelson Shale (EF146981).

GEOLOGICAL HISTORY

Exposed rocks in LIMBUNYA range from Palaeoproterozoicto Cenozoic in age. The oldest are quartz muscovite schistsof the Inverway Metamorphics, which show evidence of atleast two periods of deformation. The age of the InverwayMetamorphics is not constrained, but is probablyPalaeoproterozoic. It is estimated that several hundredmillion years elapsed before overlying rocks from theBirrindudu and Limbunya Groups were deposited.

The Birrindudu Group is represented in LIMBUNYA byundifferentiated, steeply dipping mudstone, which was probablydeposited under low-energy marine conditions. An angularunconformity separates these rocks from the overlyingLimbunya Group and indicates a period of uplift and erosion.

Figure 27 High-angle cross-bed set in parallel-laminated sandstonefacies in Overland Sandstone, 9 km south-southwest of MistakeCreek community (NEGRI EG018002)

The age of Birrindudu Group rocks in LIMBUNYA is poorlyconstrained, but must be between 1640 Ma (age determinationfrom Limbunya Group) and 1790 Ma (age of youngest granitesin underlying Tanami Region basement).

The Limbunya Group comprises mixed siliciclastics andcarbonates. In the late Palaeoproterozoic, a major marinetransgression across the whole area resulted in a blanket ofsand (Stirling Sandstone) being deposited on the InverwayMetamorphics. A long period of sedimentation at or nearsea level is represented by the Margery Formation, Pear TreeDolostone, Amos Knob Formation and Mallabah Dolostone.Siltstone in the Amos Knob Formation and laminateddolostone and black shale in the Mallabah Dolostone indicaterelatively low-energy marine environments, possibly belowwave base. Other sediments were mostly deposited in moreenergetic shallow marine or intertidal settings.

The Kunja Siltstone overlies a sequence boundary andcorresponds to a marked increase in water depth, as isindicated by siltstone and shale. Little or no carbonate wasdeposited. The overlying Farquharson Sandstone was laiddown in very shallow marine, evaporitic and possibly fluvialconditions, during a period of tectonic uplift or infilling ofthe basin. A subsequent short-lived transgressive eventproduced shallow water marine conditions, and dolareniteand stromatolitic dolostone of the upper Blue Hole Formationwere deposited. Episodes of deeper water deposition arerepresented by basal laminated dolosiltites. A return to

29

shallow marine intertidal conditions resulted in the depositionof stromatolitic carbonate of the Campbell SpringsDolostone. Dolarenite and dolorudite indicate relatively high-energy conditions. SHRIMP U-Pb zircon ages of about1640 Ma have been obtained for several samples from theKunja Siltstone, Blue Hole Formation and Campbell SpringsDolomite. The zircons are from tuffite horizons and areevidence for distant volcanism.

The basal Fraynes Formation was deposited during aperiod of increased water depth. Fine dolomitic rocks,siltstone and the precipitation of aragonite seafloor cementssuggest a relatively quiet sub-wave base depositionalenvironment. A general shallowing led to the deposition ofcarbonate and silt of the Killaloc Formation under shallowmarine and evaporitic conditions.

Minor tectonic activity ensued, resulting in milddeformation and buckling of the Limbunya Group.

A second major regional transgressive event resulted indeposition of the Wattie Group. This succession wasdeposited under dominantly shallow marine conditions, withoccasional subaerial exposure. Overlying Bullita Group rockswere either not deposited in LIMBUNYA, or have since beenremoved by erosion. A possible correlation with strata of theNathan Group (McArthur Basin) suggests that the Wattieand Bullita Groups were deposited at 1.61-1.57 Ga.

A subsequent period of regional uplift and erosionresulted in the stripping of most of the Wattie Group fromthe region and this was followed by yet another regionaltransgression (Auvergne Group). The widespread JasperGorge Sandstone was laid down as mature sand in a stable,nearshore marine environment. Carbonaceous facies in theoverlying Angalarri Siltstone were deposited in deeper water.The age of the Auvergne Group is in the range 810-750 Ma andthe group possibly correlates with the 800 Ma Supersequence 1of the Centralian Superbasin of Walter et al (1995).

Erosion removed all but the lower Auvergne Group beforethe advent of a much colder climate caused rapid advance ofan ice sheet over at least the northern part of LIMBUNYA inthe Late Neoproterozoic. This episode is represented byundifferentiated diamictite of the Duerdin Group (WolfeCreek Basin).

Figure 28 Section through fault-associatedmonocline in Headleys Limestone, nearBlackfellow Rockhole (view to southeast atNEGRI EF095785). Nelson Shale underliesflat terrain at left

The cessation of Neoproterozoic sedimentation wasprobably related to reactivation of strike-slip faults andsubsequent regional uplift during the King Leopold Orogeny(560 Ma), prior to the widespread extrusion of flood basaltsof the Antrim Plateau Volcanics.

The Antrim Plateau Volcanics underwent a short periodof minor erosion prior to an extensive marine transgression,which resulted in the deposition of Middle and Late Cambriansedimentary rocks of the Goose Hole Group (Ord Basin).Peritidal to shallow marine conditions prevailed duringdeposition of the basal part of the succession (NegriSubgroup). Overlying sediments of the Elder Subgroupaccumulated under intertidal to fluvial conditions. Asubstantial hiatus followed the deposition of these sediments.

Mesozoic deposition is represented by remnant thinpatches of basin-margin sandstone and minor conglomerate.This was followed by a period of erosion, deep weatheringand lateritisation. Cenozoic deposits, derived fromcontinental processes of erosion and redistribution, form athin cover over much of the present land surface.

ACKNOWLEDGEMENTS

Field operations in the Limbunya region in 1997-1999 werea team effort and we would like to thank others members ofthe team for their enthusiasm for completing the work. Theyincluded geologists Ian Sweet and Steve Abbott and technicalstaff Jason Brown, Cameron McLean, Jeff Marsh and GaryTaylor. The advice of Arthur Mory (Geological Survey ofWestern Australia, Perth) was invaluable in initial fieldorientation in the Ord Basin. Local Aboriginal land custodianJack Cook provided able field guidance to PD Kruse onMistake Creek property by arrangement with Del Boyd(Central Land Council, Kalkaringi) and property managerSteven Craig. We also thank station leaseholders in theLimbunya area for facilitating access to their land. BarryPietsch coordinated the mapping team and provided guidancethroughout the project, including edits and rewrites of thetext. NTGS Director Dennis Gee and senior geologistsMasood Ahmad and Andrew Wygralak also providedassistance to this project. Russell Poole and Gary Andrews

30

prepared the accompanying map and figures. The text wasedited by Tim Munson with assistance from David Young,and formatted by Kirsi Rahikainen. Gary Andrews, RussellPoole and Stephen Cox drafted the figures.

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APPENDIX 1Location of measured sections. Fm = Formation; Dol = Dolostone; Sst = Sandstone.

Section Field code AMG co-ordinates Stratigraphic unit, thickness (m)

MS1 97LIMAC4001 533140mE, 8041825mN Blue Hole Fm (0-138); Campbell Springs Dst (138-150+)

MS2 97LIMAC4002 533140mE, 8040660mN Blue Hole Fm (0-15); Campbell Springs Dst (15-225); Fraynes Fm (225-336+)

MS3 97LIMAC4003 532590mE, 8040405mN Killaloc Fm (0-103.5)

MS4 97LIMAC4005 589450mE, 8060040mN Pear Tree Dst (0-46.5+)

MS5 97LIMAC4009 579545mE, 8084355mN Blue Hole Fm (0-67.5?)

MS6 97LIMAC4010 577530mE, 8084450mN Blue Hole Fm? (0-1.5); Campbell Springs Dst (1.5-58.5+)

MS7 97LIMAC4011 575875mE, 8084950mN Campbell Springs Dst (0-30+)

MS8 97LIMAC4012 576210mE, 8084620mN Campbell Springs Dst (0-28.5+)

MS9 97LIMAC4013 575725mE, 8085310mN Campbell Springs Dst (0-54+)

MS10 97LIMAC4014 574515mE, 8085450mN Campbell Springs Dst (0-40.5+)

MS11 97LIMAC4016 574095mE, 8086085mN Campbell Springs Dst (0-21+)

MS12 97LIMAC4017 573820mE, 8086970mN Campbell Springs Dst (0-15); Fraynes Fm? (15-25.5+)

MS13 97LIMAC4018 573440mE, 8086895mN Fraynes Fm (0-112.5)

MS14 98PRB1 530670mE, 8045910mN Wickham Fm (0-211.5)

MS15 98PRB2 532355mE, 8041835mN Wickham Fm (0-30)

MS16 98PRB3 570790mE, 8089470mN Killaloc Fm (0-1.5); no outcrop (1.5-4.5); Wickham Fm (4.5-21)

MS17 98PRB4 570015mE, 8089230mN Killaloc Fm (0-0.9); Wickham Fm (0.9-54+)

MS18 98AC3 571360mE, 8087880mN Fraynes Fm (0-46.5+)

MS19 98AC12 590935mE, 8062905mN Farquharson Sst (0-15); Blue Hole Fm (15-54+)

MS20 98LIMAC11 532685mE, 8041465mN Killaloc Fm (0-22.5+)

MS21 98LIMAC20 601365mE, 8061475mN Stirling Sst (0-10.5); Margery Fm (10.5-25.5+)

MS22 98LIMAC13 598280mE, 8063805mN Pear Tree Dst (0-21); Amos Knob Fm? (21-51);

Amos Knob Fm or Mallabah Dst (51-80)

MS23 98LIMAC2 581435mE, 8083670mN Campbell Springs Dst (0-49.5+)

MS24 98LIMAC4 572735mE, 8087965mN Fraynes Fm (0-82.5); karstic duricrust (82.5-87)

MS25 98LIMAC5 573950mE, 8086355mN Campbell Springs Dst (0-16)

MS26 98LIMAC6 576450mE, 8084675mN Campbell Springs Dst (0-54)

MS27 98LIMAC7 570670mE, 8088265mN Fraynes Fm (0-27)

MS28 98LIMAC9 563935mE, 8070420mN Blue Hole Fm (0-9); Campbell Springs Dst (9-25.5+)MS29 99LIJND01 572110mE, 8089155mN Fraynes Fm (0-34); duricrust (34-57.7)

MS30 99LIJND02 572290mE, 8089105mN Fraynes Fm (0-11.8)

MS31 99LIJND03 571930mE, 8088750mN Fraynes Fm (0-29.5); duricrust (29.5-61.5)MS32 99LIMAC10 576300mE, 8075200mN Blue Hole Fm (0-45); Campbell Springs Dst (45-79.5+)

MS33 99LIMAC14 577760mE, 8086110mN Campbell Springs Dst (0-73.5+)

MS34 99LIMAC15 577460mE, 8086185mN Campbell Springs Dst (0-70.5+)MS35 99LIMAC51 650685mE, 8114665mN Campbell Springs Dst (0-21); Fraynes Fm (21-115.5);

Wickham Fm (115.5-355.5); Jasper Gorge Sst (335.5-328.5)

MS36 01LIMPRB7 601170mE, 8061575mN Stirling Sst (0-36.5); Margery Fm (36.5-105+)

34

APPENDIX 2

Geochemical analyses of Limbunya Group rocks. Units are in ppm. Lower detection limits not shown in the table are given in theheader. Potassium values less than 10 000 ppm may be low due to the insolubility of potassium perchlorate. Samples are from measuredsections, as recorded in intervals of 1.5 m (eg MS2-224 refers to a sample taken from the 224th measured interval of 1.5 m in section MS2,or 336 m up-section). Locations are listed in Appendix 1and on the mapface. Dst = Dolostone; Fm = Formation; * upper part of thissection (MS12-11) may be Fraynes Formation; † upper part of this section (MS5-11.2) may be Campbell Springs Dolostone.

Fm Measured section -sample interval

Ag As Cd Co(0.5)

Cr Cu Fe(50)

Mn(5)

Mo K Th Pb Zn

Killaloc Fm MS3- 0 0.3 4 <0.2 2.5 5 27 5300 260 0.8 10 800 0.5 7 22

MS3- 6 <0.2 <3 <0.2 2 12 8 4050 330 0.3 8500 0.3 <2 5

MS3- 8 <0.2 <3 <0.2 1.5 11 4 3600 310 <0.2 1450 <0.1 <2 3

MS3-12 <0.2 <3 <0.2 2 12 6 3400 460 <0.2 3650 0.1 <2 3

MS3-16 <0.2 <3 <0.2 1.5 14 <2 2450 260 <0.2 750 <0.1 <2 5

MS3-20 <0.2 <3 <0.2 1.5 15 <2 1950 210 <0.2 700 <0.1 <2 7

MS3-24 <0.2 <3 <0.2 2 18 4 4200 290 0.2 11 800 0.2 2 5MS3-28 <0.2 <3 <0.2 2 19 3 3350 250 <0.2 10 100 0.2 3 3

MS3-32 <0.2 <3 <0.2 1.5 15 5 2250 270 <0.2 1100 <0.1 <2 <2

MS3-36 <0.2 <3 <0.2 2 14 18 2250 240 <0.2 950 <0.1 5 <2

MS3-40 <0.2 <3 <0.2 2 15 13 2350 280 0.2 1900 <0.1 4 3

MS3-44 <0.2 <3 <0.2 2.5 10 5 2000 310 <0.2 1000 <0.1 <2 <2

MS3-48 <0.2 <3 <0.2 2 12 3 1650 270 <0.2 550 <0.1 <2 2

MS3-69 <0.2 <3 <0.2 10.5 14 <2 4450 700 <0.2 7400 0.2 <2 6

Pear Tree Dst MS4-0.1 <0.2 <3 <0.2 1.5 11 <2 8400 500 <0.2 850 <0.1 <2 5

MS4-4 <0.2 4 <0.2 1.5 14 3 13 700 650 <0.2 6200 <0.1 3 5

MS4-8.2 <0.2 <3 <0.2 2.5 14 24 6400 550 <0.2 3900 <0.1 8 6MS4-12 <0.2 <3 <0.2 2.5 12 7 8550 700 0.3 1400 <0.1 3 7

MS4-16 <0.2 4 <0.2 4 11 12 9000 800 0.4 3150 <0.1 10 21

MS4-21 <0.2 8 <0.2 2.5 10 10 15 800 800 0.7 700 0.1 4 4

MS4-24 <0.2 4 <0.2 3.5 14 40 13 000 650 0.8 8350 0.2 25 11

MS4-25 0.2 8 <0.2 5.5 10 26 14 500 850 0.4 3850 <0.1 7 6

MS4-27 <0.2 6 <0.2 3.5 8 10 18 500 1050 0.4 1150 <0.1 <2 10

MS4-28 <0.2 8 <0.2 7.5 12 44 15 300 950 0.5 6750 0.2 7 5

MS4-31 <0.2 30 <0.2 4 10 210 20 700 900 0.6 1550 <0.1 2 <2

Fraynes Fm MS24-0 <0.2 <3 <0.2 2 13 13 9700 1150 <0.2 12 700 <0.1 4 4

MS24-4 <0.2 4 <0.2 4 37 <2 12 500 300 1.1 50 400 0.5 66 25

MS24-4.2 0.2 18 <0.2 7.5 16 9 13 000 850 1.9 13 600 0.4 32 7

MS24-8 <0.2 20 <0.2 6 40 28 20 400 250 5 42 300 1.1 26 25

MS24-12 <0.2 14 <0.2 4.5 31 14 17 700 290 2.9 38 700 0.9 15 24

MS24-16 <0.2 18 <0.2 6 29 28 18 300 320 4 38 000 0.8 23 26

MS24-20 <0.2 <3 <0.2 2.5 15 8 10 900 1050 0.8 14 400 0.1 8 18

MS24-24 <0.2 <3 <0.2 2 9 21 2600 40 0.3 3750 <0.1 8 15

MS24-24.2 <0.2 6 <0.2 4 17 16 10 800 500 0.8 29 300 0.3 13 12

MS24-27.2 <0.2 8 <0.2 3 10 9 9700 490 1.7 9300 0.1 6 3

MS24-31 <0.2 4 <0.2 2.5 12 4 7750 900 0.9 7900 <0.1 6 12

MS24-37 <0.2 6 <0.2 2.5 11 6 8900 650 1.3 7450 <0.1 8 19

MS24-41 <0.2 6 0.2 2.5 15 26 9500 320 1.4 16 800 0.2 22 46

MS24-42 <0.2 <3 <0.2 1.5 7 <2 550 20 <0.2 550 <0.1 <2 <2

MS24-45 <0.2 8 0.2 4.5 15 24 12 700 1900 0.6 11 700 0.1 19 59MS24-49 <0.2 <3 0.3 4.5 21 7 8950 1950 0.4 16 600 0.1 7 26

MS24-52 <0.2 <3 <0.2 2 10 14 23 300 1350 1.1 4450 <0.1 11 9

Blue Hole Fm MS1-0 <0.2 <3 <0.2 4.5 15 2 11 100 550 <0.2 14 800 0.2 4 12

MS1-4 <0.2 <3 <0.2 3 13 <2 7600 480 <0.2 11 400 0.2 4 12MS1-8 <0.2 <3 <0.2 2.5 14 3 10 500 1200 <0.2 9700 0.1 3 17

MS1-12 0.2 <3 <0.2 2.5 13 3 14 000 1950 0.3 8250 0.1 3 17

MS1-16 <0.2 <3 <0.2 2 15 2 5250 155 <0.2 13 300 0.2 3 12

MS1-20 <0.2 <3 <0.2 2.5 15 4 8100 150 <0.2 12 700 0.2 3 10

MS1-24 <0.2 <3 <0.2 1.5 12 <2 4450 240 <0.2 12 000 0.1 4 12

MS1-28 <0.2 <3 <0.2 2.5 10 3 4450 165 <0.2 8800 <0.1 3 7

MS1-32 <0.2 <3 <0.2 2.5 14 6 5850 260 <0.2 10 000 0.1 5 14

MS1-36 <0.2 <3 <0.2 2.5 13 3 7200 210 <0.2 12 300 0.2 4 11

MS1-40 <0.2 <3 <0.2 3 12 7 16 100 1000 0.3 11 500 0.2 7 38MS1-48 <0.2 <3 <0.2 2.5 14 5 15 900 1100 <0.2 11 900 0.2 5 24

35

APPENDIX 2 (cont.)

Fm Measured section -sample interval

Ag As Cd Co(0.5)

Cr Cu Fe(50)

Mn(5)

Mo K Th Pb Zn

Blue Hole Fm MS1-56 <0.2 6 0.6 6.5 13 23 21 400 750 2.4 23 600 0.2 125 125

MS1-85 <0.2 <3 <0.2 3.5 10 4 19 900 480 0.4 15 300 0.1 3 11MS1-89 <0.2 12 <0.2 2.5 5 7 13 300 45 0.5 104 000 0.2 8 4

MS1-96 <0.2 <3 <0.2 1.5 9 4 9100 280 <0.2 8350 <0.1 <2 3

Fraynes Fm MS13-1 0.6 18 <0.2 7.5 39 9 19 700 200 5 46 800 0.9 19 29

MS13-5 0.6 10 0.4 5.5 23 9 16 200 330 2.4 38 100 0.6 190 27

MS13-13 0.4 10 <0.2 4 15 11 13 000 330 0.8 29 100 0.3 9 10

MS13-16 <0.2 10 <0.2 4 15 3 7400 310 <0.2 22 200 0.3 5 15MS13-21 <0.2 <3 <0.2 2.5 12 6 9050 550 <0.2 13 700 0.1 <2 8

MS13 31.0 <0.2 <3 <0.2 3.5 18 10 11 900 600 <0.2 19 600 0.2 8 11MS13-35 <0.2 <3 <0.2 2.5 14 9 11 200 600 <0.2 19 000 0.2 3 7

MS13-40 <0.2 8 <0.2 5.5 8 12 10 100 750 0.7 11 900 <0.1 21 12

Blue Hole Fm MS2-0 <0.2 <3 0.3 4.5 9 3 25 800 550 0.4 17 600 0.3 40 42

MS2-4 <0.2 <3 <0.2 3.5 6 4 22 200 550 <0.2 12 700 0.1 14 20MS2-8 <0.2 <3 <0.2 3.5 7 2 15 800 450 <0.2 10 300 <0.1 6 9

Campbell Springs Dst MS2-12 <0.2 <3 <0.2 3 8 5 7450 240 <0.2 11 200 0.1 3 9

MS2-16 <0.2 <3 <0.2 2 6 2 2800 135 <0.2 1650 <0.1 <2 3MS2-20 <0.2 <3 <0.2 1.5 6 <2 2850 200 <0.2 400 <0.1 <2 21

MS2-24 <0.2 <3 0.3 2 6 <2 1900 230 <0.2 550 <0.1 <2 135

MS2-28 <0.2 <3 <0.2 2 7 2 1900 195 <0.2 2100 <0.1 <2 20MS2-32 <0.2 <3 <0.2 1.5 5 5 1800 175 <0.2 2650 <0.1 <2 <2

MS2-36 <0.2 <3 <0.2 1.5 6 9 2500 145 <0.2 2250 <0.1 3 11

MS2-44 <0.2 <3 <0.2 1.5 8 4 1800 180 <0.2 100 <0.1 <2 5MS2-48.2 <0.2 <3 <0.2 2 5 <2 1850 280 <0.2 200 <0.1 <2 6

MS2-52 <0.2 <3 <0.2 3.5 6 5 2050 350 <0.2 400 <0.1 3 8

MS2-56 <0.2 <3 <0.2 3 7 5 1900 220 <0.2 350 <0.1 <2 3MS2-60 <0.2 <3 <0.2 2 6 2 1100 270 <0.2 250 <0.1 <2 16

MS2-64 <0.2 <3 <0.2 2.5 5 3 2300 280 <0.2 850 <0.1 <2 11

MS2-68 <0.2 <3 <0.2 1.5 4 2 2300 190 <0.2 200 <0.1 <2 23MS2-72 <0.2 <3 <0.2 2 4 <2 2850 290 <0.2 50 <0.1 <2 15

MS2-79 <0.2 4 1.2 1.5 4 9 4750 650 0.6 19 100 0.2 8 100

MS2-80 <0.2 <3 <0.2 1.5 3 <2 1750 270 <0.2 200 <0.1 <2 19MS2-84 <0.2 <3 <0.2 1.5 4 4 1850 220 <0.2 250 <0.1 2 43

MS2-88 <0.2 <3 <0.2 1.5 3 <2 1850 165 <0.2 100 <0.1 <2 28

MS2-92 <0.2 <3 <0.2 1.5 4 2 2600 370 <0.2 100 <0.1 <2 37MS2-96 <0.2 <3 <0.2 1 4 <2 1550 230 <0.2 250 <0.1 <2 12

MS2-100 <0.2 <3 <0.2 1.5 3 <2 1600 230 <0.2 <50 <0.1 <2 15

MS2-104 <0.2 <3 <0.2 1.5 3 2 2450 270 <0.2 <50 <0.1 <2 23MS2-112 <0.2 4 <0.2 2 3 2 2400 260 <0.2 100 <0.1 <2 40

MS2-116 <0.2 <3 0.4 1.5 4 2 2200 250 <0.2 100 <0.1 4 140

MS2-124 <0.2 <3 <0.2 1.5 3 <2 2250 270 <0.2 500 <0.1 <2 41MS2-128 <0.2 <3 <0.2 2 4 <2 1750 240 <0.2 250 <0.1 2 72

MS2-132 <0.2 <3 <0.2 2 17 <2 4000 240 <0.2 4050 <0.1 <2 5

MS2-138 <0.2 4 <0.2 2.5 5 4 7350 200 <0.2 6050 <0.1 2 7MS2-142 <0.2 <3 <0.2 4.5 7 6 7000 250 3.9 11 300 <0.1 5 7

MS2-146 <0.2 4 0.3 2 6 12 6350 230 <0.2 5200 <0.1 7 9

Fraynes Fm MS2-150 0.2 <3 <0.2 2.5 3 6 8500 30 0.5 87 100 0.5 4 8

MS2-158 0.3 20 <0.2 7 22 30 19 000 340 4.7 35 200 0.5 20 27MS2-162 0.2 6 <0.2 7.5 20 14 17 400 550 3.2 48 500 0.6 17 20

MS2-166 <0.2 6 0.3 5 18 20 13 000 440 1.8 32 200 0.4 15 20

MS2-169 <0.2 4 <0.2 5 14 6 10 400 550 1.1 24 100 0.4 12 26MS2-173 <0.2 6 0.3 3.5 15 8 14 500 340 1.3 19 800 0.4 15 19

MS2-177 <0.2 6 0.2 5 16 10 13 300 460 2.4 23 400 0.4 15 23

MS2-182 <0.2 12 <0.2 3.5 20 16 12 800 220 1.6 29 000 0.5 20 14MS2-186 <0.2 4 <0.2 5.5 14 6 11 300 450 1.2 17 100 0.3 19 15

MS2-191B <0.2 4 0.4 2 12 4 5950 490 0.4 10 100 0.2 10 22

MS2-194 <0.2 6 0.6 3.5 12 8 9900 470 0.7 20 000 0.4 14 49MS2-196 <0.2 6 0.6 3 12 8 7350 370 0.6 19 700 0.4 26 49

MS2-204 <0.2 4 0.4 2.5 9 6 6050 650 0.7 7100 0.2 44 15

36

APPENDIX 2 (cont.)

Fm Measured section -sample interval

Ag As Cd Co(0.5)

Cr Cu Fe(50)

Mn(5)

Mo K Th Pb Zn

MS2-208 <0.2 <3 0.4 2 7 4 4150 420 0.3 2900 <0.1 14 12

MS2-216 <0.2 8 0.2 2 10 10 5500 600 3 6900 0.3 21 34MS2-220 <0.2 4 <0.2 3.5 11 10 6250 1550 0.8 6450 0.6 24 21

Campbell Springs Dst MS9-1.0 <0.2 <3 <0.2 1.5 3 <2 1600 240 <0.2 300 <0.1 <2 6

MS9-6.2 <0.2 <3 <0.2 1.5 4 <2 2050 140 <0.2 750 <0.1 <2 9MS9-8.2 <0.2 <3 <0.2 1.5 4 <2 1650 155 <0.2 1300 <0.1 3 37

MS9-13.0 <0.2 <3 0.7 1.5 4 <2 1700 210 <0.2 100 <0.1 5 105

MS9-19.2 <0.2 <3 <0.2 1.5 4 5 1350 300 <0.2 50 <0.1 4 74MS9-24 0.3 <3 <0.2 1.5 4 3 1800 240 <0.2 300 <0.1 5 54

MS9-35.2 <0.2 <3 <0.2 1.5 3 <2 1400 190 <0.2 50 <0.1 <2 12

Campbell Springs Dst* MS12-0 <0.2 <3 <0.2 4 12 <2 4650 440 <0.2 13 200 <0.1 <2 3

MS12-3 <0.2 <3 <0.2 2 8 <2 2850 290 <0.2 29 100 <0.1 <2 19

MS12-4 <0.2 <3 <0.2 3 5 <2 2950 490 <0.2 7000 <0.1 <2 <2MS12-5.2 <0.2 <3 <0.2 3 6 <2 3300 650 <0.2 5500 <0.1 <2 4

MS12-10 <0.2 <3 <0.2 2.5 5 <2 4600 480 0.6 1600 <0.1 <2 <2

MS12-11 <0.2 <3 <0.2 2.5 11 3 6400 450 <0.2 9800 <0.1 <2 3

Campbell Springs Dst MS6-0 <0.2 <3 <0.2 3.5 6 4 9800 650 <0.2 7100 <0.1 2 3

MS6-3.2 <0.2 <3 <0.2 2 7 <2 6400 310 <0.2 6650 <0.1 <2 7MS6-7.2 <0.2 <3 <0.2 2.5 69 <2 5150 290 <0.2 3200 <0.1 <2 5

MS6-12.2 <0.2 <3 <0.2 2 17 11 3200 190 <0.2 2600 <0.1 13 105

MS6-15.2 <0.2 <3 <0.2 2 10 3 4700 220 <0.2 6100 <0.1 3 5MS6-17.2 <0.2 <3 <0.2 2 7 <2 2450 260 <0.2 1300 <0.1 7 135

MS6-26 0.4 <3 <0.2 3 8 <2 2300 300 <0.2 150 <0.1 2 13

MS6-32 <0.2 <3 <0.2 2 7 <2 2300 310 <0.2 1300 <0.1 7 93MS6-34.2 <0.2 <3 <0.2 1.5 4 <2 1550 185 <0.2 100 <0.1 <2 22

MS6-37 <0.2 <3 <0.2 1.5 4 <2 1500 400 <0.2 <50 <0.1 11 78

Campbell Springs Dst MS11-0 <0.2 <3 <0.2 1.5 6 <2 1450 230 <0.2 <50 <0.1 3 9

MS11-2 <0.2 <3 <0.2 1.5 5 <2 1500 230 <0.2 50 <0.1 3 9

MS11-3 <0.2 <3 <0.2 2.5 9 <2 3100 185 <0.2 4900 <0.1 9 10MS11-5.1 <0.2 <3 <0.2 5.5 9 5 2950 180 0.2 5200 0.2 8 9

MS11-7 <0.2 <3 <0.2 2.5 6 <2 2400 200 <0.2 1300 <0.1 3 4

MS11-12 <0.2 <3 <0.2 2.5 9 11 4000 270 <0.2 5850 <0.1 6 8

Blue Hole Fm† MS5-0 <0.2 <3 <0.2 2.5 6 3 2050 240 <0.2 7700 <0.1 4 7

MS5-4 <0.2 <3 <0.2 4 9 <2 7750 360 <0.2 16 100 0.2 4 11MS5-6 <0.2 <3 <0.2 3.5 9 <2 6550 350 <0.2 15 100 0.2 4 11

MS5-8 <0.2 <3 <0.2 4.5 8 <2 7150 1400 <0.2 12 800 0.2 <2 9

MS5-11.2 <0.2 <3 <0.2 3.5 12 <2 10 400 800 <0.2 13 400 <0.1 <2 2

Pear Tree Dst MS22-5 <0.2 6 <0.2 8 11 7 10 200 750 0.6 2850 0.2 13 19

MS22-7 0.9 16 <0.2 10.5 16 44 18 800 950 1.1 3550 0.2 23 25MS22-8 0.3 16 <0.2 7.5 15 12 16 700 1100 1.3 2050 0.6 8 22

MS22-11.2 0.4 6 <0.2 2.5 7 18 18 400 850 0.9 5400 0.3 6 7

Mallabah Dst MS22-33 <0.2 <3 <0.2 5 8 2 15 600 850 <0.2 9350 0.1 3 25

MS22-38 <0.2 <3 <0.2 3 8 8 8400 400 <0.2 11 000 0.1 4 10

MS22-42 <0.2 <3 <0.2 3.5 10 2 10 000 550 <0.2 9750 <0.1 3 36

MS22-46 <0.2 <3 <0.2 3 11 5 7700 260 <0.2 11 200 0.1 5 65MS22-50 <0.2 <3 0.4 4.5 11 13 9150 460 <0.2 10 200 0.1 17 750

MS22-52 <0.2 4 <0.2 3 11 16 8900 550 0.2 10 400 0.1 13 67

MS22-53 <0.2 <3 0.3 4 11 27 4600 350 0.2 13 400 0.2 17 135

Campbell Springs Dst MS2-40 <0.2 <3 <0.2 2.5 5 4 3250 370 <0.2 300 <0.1 <2 8

Fraynes Fm MS2-212 <0.2 <3 0.4 2 6 5 3900 600 0.5 1450 0.2 8 33MS2-224 <0.2 <3 <0.2 2 6 5 4150 800 0.6 1200 0.2 6 9