Sandover River, Northern Territory (Second Edition). 1:250 000 Geological Map Series Explanatory Notes, SF 53-08

DEPARTMENT OF BUSINESS, INDUSTRY AND RESOURCE DEVELOPMENT NORTHERN TERRITORY GEOLOGICAL SURVEY

SANDOVER RIVER, SF 53-03 SF 53-04 SF 54-01 FREW RIVER AVON DOWNS MOUNT ISA Northern Territory

CARBEEN MILNE GEORGINA Second Edition SF 53-07 SANDOVER RIVER SF 54-05 ELKEDRA SF 53-08 URANDANGI ARGAD- BARRY Sheet SF 53-08 ARGADA GORDON PLAIN CREEK 1:250 000 GEOLOGICAL MAP SERIES EXPLANATORY NOTES SF 53-11 SF 53-12 SF 54-09 HUCKITTA TOBERMORY GLENORMISTON PD KRUSE, LC MOHAMMED, NT QLD JN DUNSTER and ML DUFFETT

Government Printer of the Northern Territory Darwin, December 2002 NORTHERN TERRITORY DEPARTMENT OF BUSINESS, INDUSTRY AND RESOURCE DEVELOPMENT MINISTER: Hon Paul Henderson, MLA CHIEF EXECUTIVE OFFICER: Peter Blake

NORTHERN TERRITORY GEOLOGICAL SURVEY ACTING DIRECTOR: Richard Brescianini

BIBLIOGRAPHIC REFERENCE: Kruse PD, Mohammed LC, Dunster JN and Duffett ML, 2002. Sandover River, Northern Territory (Second Edition). 1:250 000 geological map series explanatory notes, SF 53-08. Northern Territory Geological Survey, Darwin.

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

ISBN 0 7245 7050 0 (Hard copy), ISBN 978-0-7245-7137-6 (CD version) 559.429

EDITOR: TJ Munson

KEYWORDS: Geological mapping, Geophysical interpretation, Structural geology, Economic geology, Sedimentary geology, Stratigraphy, Northern Territory, Sandover River, Palaeoproterozoic, Cambrian, Ordovician, Cenozoic, Altjawarra Domain, Georgina Basin.

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

1 Formerly Australian Geological Survey Organisation (Geoscience Australia)

Printed for the Northern Territory Geological Survey by the Government Printer of the Northern Territory

Disclaimer This 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 le data, and their employees, agents and contractors, in respect of all liability for actions, claims costs or expenses, loss damage or injury, which may be suffered by them, or any other person, arising from the use of the data, or as a consequence of any unlawful or negligent act or omission of the user.(H

ii ABSTRACT

SANDOVER RIVER1 encompasses a portion of the southern Georgina Basin. Unmetamorphosed and essentially undeformed Late Cambrian to Early Ordovician and Cenozoic sedimentary rocks cover the sheet area. In the subsurface, basement metavolcanic schist and Middle to Upper Cambrian sedimentary units have been intersected in drillholes. The platformal marine Thorntonia Limestone was deposited in the early Middle Cambrian during a widespread marine transgression. This unit consists predominantly of dolostone, with local basal terrigenous sediments and a medial interval bearing pyritic-carbonaceous black shale interbeds. It largely coincides with the Middle Cambrian depositional sequence 1. Sequence 2, spanning the remainder of the Middle Cambrian, is primarily of Arthur Creek Formation and includes a basal interval of anoxic, basinal pyritic-carbonaceous black shale which constitutes a major potential petroleum source rock. The upper Arthur Creek Formation is of aerobic carbonate, deposited in normal marine waters. Quartzic dolostone and quartz sandstone of the overlying Steamboat Sandstone in the eastern sheet area complete sequence 2. The Late Cambrian Arrinthrunga Formation is primarily peritidal. It includes calcimudstone, microbial laminite, peloid/intraclast and ooid grainstone, stromatolite boundstone and quartzic limestone and their dolomitised equivalents, together with minor quartz sandstone. The evaporitic Chabalowe Formation (including the Hagen Member) occurs in the western sheet area subsurface and is equivalent to the basal Arrinthrunga Formation. Cambro-Ordovician deposition consisted of two principal depofacies: peritidally in uenced, platformal marine carbonate rocks of the Ninmaroo Formation in the east, which inter nger with terrigenous quartz-glauconite sandstone of the marine Tomahawk Formation in the west. The corridor of inter ngering falls within the southern sheet area. Continental Cenozoic deposits indicate pedogenic and lacustrine (Austral Downs Limestone), and other terrestrial environments. The southern Georgina Basin is strongly prospective for petroleum. Excellent potential source rocks and seal in the lower Arthur Creek Formation are juxtaposed against potential reservoir dolostone in the underlying Thorntonia Limestone. The Ha- gen Member is also prospective, offering vuggy dolostone reservoir rocks and an evaporite seal. Diamonds are being actively sought in the region, but no metalliferous occurrences are known.

1 Names of 1:250 000 and 1:100 000 mapsheets are shown in large and small capital letters, respectively, eg SANDOVER RIVER, ARGADARGADA. iii CONTENTS 3 Porosity, density and magnetic susceptibility data of drillhole Ross 1...... 22 Abstract ...... iii Introduction ...... 1 FIGURES Terminology and classification...... 1 Location and access...... 1 1 Location of SANDOVER RIVER...... 1 Climate...... 2 2 Regional geological setting...... 3 Physiography...... 2 3 Simplified solid geology...... 4 Vegetation...... 2 4 Metavolcanic rock...... 6 Previous investigations...... 2 5 Marly dolomudstone interbeds in Regional geological setting ...... 2 Arrinthrunga Formation...... 9 Stratigraphy ...... 4 6 Flat-pebble intraclast conglomerate in Palaeoproterozoic...... 4 Arrinthrunga Formation...... 9 Metavolcanic rock (LPlv)...... 4 7 Nodular evaporite in dolomudstone of Cambrian...... 4 Arrinthrunga Formation...... 9 Thorntonia Limestone (–Cmt)...... 4 8 Domical stromatolite in Arrinthrunga Arthur Creek Formation (–Cma)...... 6 Formation...... 10 Steamboat Sandstone (–Cms)...... 7 9 Siliceous nodules in Arrinthrunga Formation...... 11 Chabalowe Formation (–Cuc)...... 7 10 Ovoid concretions in Arrinthrunga Formation...... 11 – – Arrinthrunga Formation (Cua)...... 8 11 Asymmetric ripples in unit Cuas of Cambro-Ordovician...... 10 Arrinthrunga Formation...... 11 – – Tomahawk Formation (COt)...... 10 12 Tabular quartz sandstone in unit Cuas of Ninmaroo Formation (–COn)...... 14 Arrinthrunga Formation...... 12 Palaeogene-Neogene...... 16 13 Tomahawk Formation quartz sandstone Austral Downs Limestone (Cza)...... 16 ridge overlying dolostone interbed...... 13 Palaeogene-Neogene-Quaternary...... 17 14 Intraformational conglomerate in Quaternary...... 18 Tomahawk Formation...... 13 Structure and tectonics ...... 19 15 Intraformational conglomerate in Geophysics ...... 19 Tomahawk Formation...... 14 Gravity...... 20 16 Dolograinstone bed in basal dolostone unit – Magnetics...... 20 COtd of Tomahawk Formation...... 14 Radiometrics...... 20 17 Deformation in quartz sandstone of Downhole geophysics...... 21 Tomahawk Formation...... 15 Geological history ...... 21 18 Wavy to columnar stromatolites in Economic geology ...... 22 Ninmaroo Formation...... 15 Petroleum...... 22 19 Columnar stromatolites in Ninmaroo Formation...... 16 Diamonds...... 24 20 Ooid dolograinstone in Ninmaroo Formation...... 17 Copper-lead-zinc...... 24 21 Basal conglomerate of Ninmaroo Formation...... 17 Groundwater...... 25 22 Interbedded dolostone and dolomitic quartz Acknowledgments ...... 26 sandstone of Ninmaroo Formation...... 18 References ...... 26 23 Pedogenic alpha fabric of Austral Downs Limestone...... 18 TABLES 24 Pustular stromatolite boundstone in Austral Downs Limestone...... 19 1 Pre-Quaternary lithostratigraphy of Georgina 25 Schematic lithologs and downhole geophysical Basin...... 5 logs of SANDOVER RIVER drillholes...... 23 2 SANDOVER RIVER drillhole locations and 26 Microdiamond and diamond indicator available downhole geophysical data...... 22 mineral locations...... 25

iv INTRODUCTION datum, and are deemed accurate to ± 50 m. Within the text, the Universal Grid Reference style is used as explained The First Edition SANDOVER RIVER explanatory notes on the mapface (eg Yellow Hole Dam at MGA 727400mE and map (Nichols 1966) were based on eldwork in 1963 by 7604200mN is represented as QS274042). Full MGA grid of cers of the then Bureau of Mineral Resources (BMR)1, references are provided in tables. However, eld experience supplemented by stratigraphic drilling in 1962 (Milligan during mapping was that the last two digits in both eastings 1963). An associated BMR regional reconnaissance gravity and northings could be unstable, and so quoted values for survey was conducted in 1957-1961 (Barlow 1966), and a these digits in the present notes should not be relied upon. To preliminary aeromagnetic survey in 1963-1964 (Wells et al convert from the AGD66 AMGs used on older maps, block 1966). shift all data 126 m to the east and 169 m to the north. For the present Second Edition map, the entire sheet was remapped in 2001 by Northern Territory Geological Survey Terminology and classiﬁ cation (NTGS) geologist PD Kruse (eastern portion) and contract geologist LC Mohammed (western portion). Colour aerial Grainsize terminology follows Wentworth (1922). Sandstones photographs at 1:50 000 scale provided the eld base for are classi ed according to Folk (1974). Carbonate rock this remapping. classi cation follows the revision of Wright (1992). The PD Kruse wrote the bulk of these explanatory notes term quartzic, often used herein with regard to dolostones, and acted as compiler. LC Mohammed contributed to the indicates a signi cant but not dominant admixed detrital Cambrian and Cambro-Ordovician sections. JN Dunster quartz component. prepared Diamonds and Copper-lead-zinc, and ML Duffett wrote the Geophysics section, other than Downhole Location and access geophysics. Groundwater was prepared with reference to a report by Bob Read (Natural Resources Division, SANDOVER RIVER is bounded by latitudes 21°00’S and Department of Infrastructure, Planning and Environment, 22°00’S and longitudes 136°30’E and 138°00’E (Figure 1). Alice Springs). This is a remote and sparsely populated area, with station Cited locations in this publication are based on Map homesteads at Argadargada and Georgina Downs, the latter Grid of Australia zone 53 coordinates and the GDA94 map currently not permanently occupied. Beef cattle grazing is the principal land use. The unsealed Sandover Highway 1 Subsequently renamed Australian Geological Survey Organisation traverses the northwestern sheet and skirts the northern (AGSO), now Geoscience Australia (GA). sheet boundary. It links the region with Alice Springs, some

135˚00' 136˚30' 138˚00' 139˚30' 20˚00' BARKLY 20˚00' Avon Downs Soudan RANKEN HIGHWAY BUCKLEY RIVER

BUCKLEY RIVER

RIVER RIVER Barkly Austral Downs Epenarra Downs

Mount FREW Isa

Lake Nash 21˚00' Mount Guide 21˚00' Elkedra Mount Guide Annitowa Creek Georgina Downs GEORGINA HIGHWAY

Bybby ROAD

MOUNT ISA URANDANGI Ammaroo Argadargada Urandangi SANDOVER

RIVER Walgra SANDOVER Ooratippra Carandotta 22˚00' RIVER 22˚00' Derry Downs Manners Creek

BUNDEY Linda Downs Arapunya Lucy Creek Tobermory DONOHUE HIGHWAY Roxborough Downs

Tarlton HIGHWAY Baikal Downs PLENTY Huckitta Marqua Jervois Queensland Glenormiston 23˚00' Northern Territory 23˚00' 135˚00' 136˚30' 138˚00'm02-065.dgn 139˚30' 0 25 50 75 100 km

Major road Minor road Drainage Homestead Town, settlement

Figure 1 Location of SANDOVER RIVER

1 500 km to the southwest, and with Urandangi and other Shrubs over 2 m high constitute the tallest stratum. These centres in western Queensland to the east. Station tracks are dominantly of Acacia and Eucalyptus, with some Hakea provide access to most areas of the sheet, although access to and Grevillea. Spinifex (especially Triodia pungens) is a the northwestern quadrant and southern margin is limited. common cover, particularly on thicker sands in the northwest. Fuel may be obtained at Alpurrurulam (weekdays only) on E. microtheca is characteristic of denser vegetation on the Sandover Highway immediately north of the northern oodplains such as the Sandover River oodout. sheet boundary, and in Queensland at Urandangi, Boulia, Open Astrebla tussock grassland mantles grey-black, Mt Isa and Camooweal. self-mulching, cracking clay soils in the central and eastern area. The principal Astrebla (Mitchell grass) species is A. Climate pectinata; Dichanthium and other grasses also contribute. Total foliage cover is in the range 30-70%. The climate is arid with median annual rainfall of 200-250 mm. Most rain falls in the summer months of Previous investigations October to March, but totals may vary greatly from year to year. Summers are hot, with mean maximum and minimum The earliest geological observations in SANDOVER RIVER January temperatures of 36-39°C and 21-24°C, respectively. were by Winnecke (1882: 21), who in 1880 traversed Winters are mild with mean maximum and minimum July southwestward along Milne Creek (now the upper reaches temperatures of 21-24°C and 6-9°C, respectively (Bureau of of Bybby Creek) and recorded ‘granite and conglomerate’ Meteorology 1988). The winter months of April to September to the north of Mt Hogarth. In 1931, C Ogilvie named are the most congenial for eldwork. fossiliferous carbonate rocks in the vicinity of the Georgina River the Georgina Limestones. As mapped by Whitehouse Physiography (1936), this now defunct term embraced Middle Cambrian to Cambro-Ordovician rocks straddling the Northern Low uplands of Ninmaroo Formation and Tomahawk Territory-Queensland border. From the Ogilvie and other Formation extend across southern SANDOVER RIVER. The collections, Whitehouse (1931) proposed an initial trilobite Ninmaroo Formation tends to form broad, rounded rises in the biozonation for the Cambrian of the region. Whitehouse southwestern and south-central areas, capped by rugged hills (1936) summarised regional investigations to that date and and ridges of Tomahawk Formation. Uplands in the southeast commented on the lithostratigraphy. Noakes and Traves display well exposed bedding in the Ninmaroo Formation and (1954) reviewed the geology of the Barkly region, of so are slightly more terraced. The Arrinthrunga Formation which SANDOVER RIVER is a part. Fossiliferous pebbles typically outcrops as moderate hills and ridges in the north. collected by DM Traves (BMR) in 1947-1948 from the Open undulating plains of grey-black clay-rich soils cover oodplain of the Sandover River near Argadargada were central and eastern SANDOVER RIVER. In the west, these later traced by AA Öpik and JN Casey (BMR) to exposures are mantled by thick colluvial sand, which has been reworked of the Sandover beds (now Arthur Creek Formation) in along the Sandover River oodout. ELKEDRA to the west (Öpik 1956b). The Ninmaroo Formation-Tomahawk Formation uplands The Georgina Basin was specifically surveyed by represent a local watershed. To the north, drainage tracks the then BMR and GSQ during 1957-1965. Within this the general easterly fall into the Georgina River. In the programme, SANDOVER RIVER was systematically southeast, Imbordjudu, Manners, Chelcheta and Shank mapped in 1963, resulting in the First Edition geological map Creeks follow a more indirect course to enter the Georgina (Nichols 1964, 1966). A 1962 regional BMR core drilling River further downstream. The Georgina River system programme (Milligan 1963) included the drilling of Grg 14 ultimately debouches into channel country in southwestern in SANDOVER RIVER (see Downhole geophysics). Queensland. Petroleum company activity in the region commenced in the late 1950s (see Petroleum). In this early exploration Vegetation phase, photogeological evaluation by Amuedo (1963) and geological mapping by Wilson (1963) impinged on Three broad vegetation styles are recognised in SANDOVER SANDOVER RIVER. Metalliferous exploration in the area RIVER (AUSLIG 1990). In the rst two described, the tallest began in the early 1970s, and diamond exploration in the stratum represents less than 10% of the total vegetation. The 1980s (see Economic geology). third is open grassland. Smith (1972) summarised work in the Georgina Basin Low open Acacia woodland characterises the Tomahawk up to that date. The BMR conducted a fresh Georgina Formation-Ninmaroo Formation uplands across the south. Basin project (Druce 1974) during the later 1970s and early The thinner soils there support a tallest woodland stratum, 1980s, including additional drilling, selective remapping typically less than 10 m high, of mixed desert acacias, and focussed research programmes. eucalypts (such as Eucalyptus argillacea and E. terminalis) and, on more calcareous soils, gidgee (Acacia georginae). REGIONAL GEOLOGICAL SETTING The understorey is mainly of Acacia, Cassia and Carissa shrubs, or grasses such as Astrebla (Mitchell grass) and SANDOVER RIVER falls within the southern Georgina Dichanthium. Basin, here taken as that portion of the basin to the In the northwestern and extreme southern areas, tall south of 21°S (Figure 2). This latitudinal boundary open Acacia shrubland is developed on more sandy soils. approximately coincides with the transition from the

2 deeper, basinal Cambrian succession in the south into of the Davenport Province of the Tennant Inlier. However a thinner platform succession to the north. The basinal Elkedra (2001) considered these enveloping terranes succession is characterised by pyritic-carbonaceous black to be more akin to Proterozoic mobile belts. There are shale (a potential petroleum source rock) in the Thorntonia insuf cient geochronological data to distinguish between Limestone and lower Arthur Creek Formation (Middle these basement models. However, the northern margin of Cambrian). the Altjawarra Domain, which extends through northern The basin architecture and basement configuration SANDOVER RIVER and southern AVON DOWNS, can be inferred from NTGS high-resolution aeromagnetic does approximate to the position of the basin-to-platform data, basement drillhole intersections and seismic sections. transition within the Georgina Basin. Depth-to-basement modelling by Teasdale and Pryer (2002) The Georgina Basin succession in SANDOVER shows that the southern Georgina Basin is 1500-2000 m RIVER incorporates Middle Cambrian to Cambro- thick and has subdued basement topography overall. The Ordovician rock units. There is to date no record of the scant available geochronological data from granite and thick Neoproterozoic to Early Cambrian succession that gneiss basement in petroleum exploration wells indicate is exposed along the southern margin of the basin in metamorphic or magmatic ages in the range 1850-1600 Ma. HUCKITTA, TOBERMORY and HAY RIVER. Nor are Magnetic patterns in the basement led Teasdale and Pryer the younger Ordovician, Devonian or Jurassic-Cretaceous (2002) to invoke an Archaean-like ‘craton’ substantially rocks of that region preserved within the map area, under the southern portion of the Georgina Basin, which even though pervasive burial diagenesis is indicated Myers et al (1996) termed the Altjawarra craton (Altjawarra by coarsely recrystallised dolostone fabrics, implying a Domain herein). substantial overburden in the past. The repeated tectonism Teasdale and Pryer (2002) considered that the basement experienced by the southern basin margin has had minimal terrane enveloping the northern margin of the Altjawarra effect in SANDOVER RIVER, and its sedimentary rocks Domain could be likened to the buried southern extension remain essentially at-lying.

135°00' 136°30' 138°00' 139°30' 20°00' -- 20°00'

C2 -- PLl Mz C2

PLl PLl PLl -- C2

C-- 2

PLl PLg

PLg PLl

PLu -- C2 -- PLl C2 PLl PLg

Cz 21°00' 21°00'

Cz PLg PLl -- C3

PLu -- PLl

PLu -- PLg PLu -- C2 C2

Cz PLg PLg

C-- 3 PLg 22°00' 22°00' PLg

C-- O

-- Mz -

CO C- 3 D --

CO C-- 3

Cz -- PLu O -- CO C2 Cz PLg O PLg O

C-- 3

PLl PLg PLg O

-- -- Mz

-- C2

-- Mz

PLC D CO CO

PLg C3 -- -- PLl PLu -- C2 C2 Mz D Mz C3 Cz 23°00' 23°00' 135°00' 136°30' 138°00' m02-067.dgn 139°30' ARUNTA PROVINCE, DAVENPORT

PROVINCE, MOUNT ISA INLIER GEORGINA BASIN --

PLC-- Neoproterozoic-Cambrian C3 Late Cambrian Cz metamorphic rocks D Devonian Cenozoic

PLg Palaeoproterozoic granite C-- 2 Middle Cambrian O Ordovician Mz Mesozoic

Palaeoproterozoic metamorphic PLu C-- O PLl rocks Neoproterozoic Cambro-Ordovician

Figure 2 Regional geological setting of SANDOVER RIVER

3 STRATIGRAPHY (2002) included them in the ‘felsic-intermediate basement complex’ of the Altjawarra Domain. Only the Arrinthrunga Formation (Late Cambrian) and younger lithostratigraphic units are exposed in SANDOVER CAMBRIAN RIVER (Figure 3). Non-exposed Middle and Upper Cambrian units are intersected in drillholes Grg 14, Mulga 1 The Middle Cambrian succession in the Georgina Basin and Ross 1, and older basement rocks in Ross 1 (Table 1). has been treated in a sequence stratigraphic context by Southgate and Shergold (1991), who recognised two broad PALAEOPROTEROZOIC depositional sequences. Sequence 1, including an upper, tectonically enhanced sequence 1a, is of Ordian-early Metavolcanic rock (LPlv) Templetonian age and incorporates the Thorntonia Limestone. The more substantial sequence 2, of late Templetonian to Cored drillhole Ross 1 bottomed in 24.4 m of dark green-grey early Mindyallan age, includes the Arthur Creek Formation metavolcanic rock, consisting of altered plagioclase laths and and Steamboat Sandstone. This scheme was modi ed by phenocrysts in an intergranular texture with chlorite (after Gravestock and Shergold (2001), who transferred the former pyroxene) and disseminated pyrite (Figure 4). At intervals sequence 1a to sequence 2. Both sequences are represented the rock is cut obliquely by quartz veins or horizontally in the subsurface in SANDOVER RIVER. by quartz-lined carbonate veins. An oblique to subvertical schistosity is de ned by alignment of chlorite. Rare biotite Thorntonia Limestone (Cmt)_ and stilpnomelane suggest regional metamorphism to upper greenschist facies (Martin in Kress 1992). Plagioclase is of The Thorntonia Limestone (Öpik 1956a) is intersected in oligoclase to andesine composition. Martin (op cit) proposed the interval 934.3-978.1 m depth in cored drillhole Ross 1, an original andesitic, or less likely basic (basaltic, doleritic) giving a thickness of 44 m (see Figure 25). In this drillhole, precursor. These rocks are undated, but Teasdale and Pryer it rests with possible angular unconformity on basement

136°30' 138°00' 21°00' 21°00'

C-- ua

C-- uas Cza

C-- uas

C-- ua

C-- uas

-- -- COt

COt

-- COn COt --

d COn --

COt C-- Ot

C-- On

C-- Ot m02-076.dgn 22°00' 22°00'

136°30' 138°00' --

COt Tomahawk Formation ( C -- Ot d - basal dolostone) Cza Austral Downs Limestone

-- Cua -- Arrinthrunga Formation ( C ua s - medial sandstone) COn Ninmaroo Formation

Figure 3 Simpli ed solid geology of SANDOVER RIVER

4 Table 1 Pre-Quaternary lithostratigraphy of Georgina Basin in SANDOVER RIVER and environs

UNIT, MAP SYMBOL, LITHOLOGY DEPOSITIONAL BASAL CONTACT CHARACTERISTIC FEATURES MAX THICKNESS ENVIRONMENT CENOZOIC Austral Downs Limestone, silicified to Terrestrial brackish Unconformable on Rhizoliths, alveolar texture, soil Limestone (Cza) 8 m chert and chalcedony lacustrine, pedogenic _COn, Olk glaebules, circum- and intragranular cracks, brecciation; plateau forming CAMBRO- ORDOVICIAN Ninmaroo Formation Limestone, dolostone, Subtidal open marine, Disconformable on _Cua Synaeresis features, flat-pebble (_COn) 795 m minor quartz sandstone restricted marine, conglomerate, cross-beds including peritidal herringbone, stromatolites, invertebrate fossils, conodonts, joints; laterally interfingers with _COt Tomahawk Formation Quartzose and glauconitic Subtidal open marine, Disconformable on _Cua Cross-beds, ripples, current structures, (_COt) 190 m sandstone, minor restricted marine, flat-pebble conglomerate, dolostone, limestone, littoral to sublittoral ichnofossils, invertebrate fossils, dolomitic quartz sandstone, conodonts, mesoscale deformation of conglomerate sandstone beds; laterally interfingers with _COn CAMBRIAN Arrinthrunga Dolostone, limestone, Peritidal, restricted Conformable on _Cuc, Stromatolites, thrombolites, nodular Formation (_Cua) 975 m minor quartz sandstone, shallow subtidal _Cms, _Cma evaporites, gypsum crystals, fenestrae; siltstone, shale, marl, marine local karst at top conglomerate Chabalowe Formation Dolomitic quartz Peritidal Conformable on _Cma; Evaporite dissolution fabric, nodular (_Cuc) 342 m sandstone, dolomitic- disconformable on evaporites, cross-beds, siliciclastic siltstone; minor Palaeoproterozoic intraformational breccia, pyrite; lateral quartzic to silty dolostone, ?Hatches Creek Group to basal _Cua mudstone, granule in ELKEDRA; conglomerate; basal nonconformable on arkosic conglomerate Palaeoproterozoic granite in BARROW CREEK Hagen Member (_Cuh) Dolostone; minor quartzic Hypersaline intertidal Conformable on _Cma; Evaporite: bedded to massive gypsum, 160 m dolostone, quartz to supratidal (sabkha) disconformable on lesser anhydrite sandstone, siltstone Palaeoproterozoic ?Hatches Creek Group in ELKEDRA Steamboat Sandstone Quartzose and High-energy marine Conformable on _Cma; Some cross-beds (_Cms) 80 m calcareous/dolomitic barrier possibly quartz sandstone, quartzic disconformable on dolostone Quita Formation in URANDANGI- GLENORMISTON Arthur Creek Upper: dolostone, Upper: open to Disconformable on Nodular evaporite, shredded to Formation (_Cma) 457 m limestone restricted subtidal _Cmt brecciated texture, invertebrate fossils, Lower: foetid pyritic- marine disseminated pyrite carbonaceous black shale, Lower: deeper anoxic laminated dolostone marine Thorntonia Limestone Limestone, dolostone; Open to restricted Disconformable on Red Nodular chert, nodular evaporite, (_Cmt) 103 m medial pyritic- subtidal marine Heart Dolostone or older phosphate and glauconite lithoclasts, carbonaceous black shale units; nonconformable bitumen, disseminated pyrite, interbeds; basal terrigenous on Palaeoproterozoic invertebrate fossils sandstone, greywacke, granite mudstone rocks, and is disconformably overlain by the Arthur Creek in CAMOOWEAL is the implied type area. Southgate and Formation. Shergold (1991) assigned the formation to their sequence 1. The Thorntonia Limestone comprises grey limestone, The formation is richly fossiliferous, the biota comprising a partially dolomitised limestone and dolostone with nodular variety of fossil groups including an age-diagnostic Ordian- chert and minor phosphorite. It is extensive around the eastern early Templetonian (early Middle Cambrian) trilobite (Queensland) and southern (Northern Territory) margins of assemblage of Redlichia, Xystridura, Pagetia and Peronopsis the Georgina Basin (Shergold and Southgate 1986, Ambrose (Whitehouse 1939, 1941, Öpik 1968, 1970, 1975, Jell 1975, et al 2001, Kruse et al 2002). It attains a maximum known Shergold 1975b, 1981, Schmitt and Southgate 1982; Shergold thickness of 103 m in Morstone 1 petroleum exploration et al 1985). well in CAMOOWEAL (Stewart and Hoyling 1963). No A stratigraphically successive, threefold light-dark-light type section has been designated, but the Thorntonia area grey colour subdivision was recognised by Kruse et al (2002)

5 This bed was initially assigned to stratigraphic sequence 1a by Southgate and Shergold (1991), but has since been transferred to sequence 2 by Gravestock and Shergold (2001). The medial and upper intervals bear connected vugs, which tend to reduce the drillcore to rubble. Both intervals are therefore likely to be excellent petroleum reservoirs (see Petroleum).

Arthur Creek Formation (Cma)_

The Arthur Creek Formation (Freeman 1986 after Smith 1964) is intersected in the interval 669.9-934.3 m depth (thickness 264 m) in cored drillhole Ross 1, and in the interval below 799 m depth (thickness 117+ m) in Mulga 1 (Questa 1994, Ambrose et al 2001). It is assigned to sequence 2 of Southgate and Shergold (1991). The formation is widespread in the southern Georgina Basin and outcrops in HUCKITTA, TOBERMORY and HAY RIVER. Two informal subdivisions are recognised (Ambrose et al 2001, Kruse et al 2002): a lower interval of deeper water, foetid pyritic-carbonaceous black shale with planar to undulose dolostone laminations (anaerobic facies of Stidolph et al 1988), passing into an upper interval of paler carbonate exhibiting dolomudstone to dolograinstone textures (aerobic facies of Stidolph et al 1988). Morris (1986) interpreted laminites of the lower interval as anoxic rhythmites on the basis of grading within lamination couplets and the absence of bioturbation. Other features of Figure 4 Dark green-grey metavolcanic rock, probably an andesite this lower interval are early diagenetic dolomite nodules; or basalt/dolerite, which has been regionally metamorphosed to upper greenschist facies. Altered plagioclase laths and phenocrysts disseminated pyrite of microbial origin (Ferris 2000); thin occur in an intergranular texture with chlorite (after pyroxene) and (centimetre-scale) granule to pebble intraclast, intraclast- disseminated pyrite. Subvertical schistosity is de ned by alignment bioclast and quartz sandstone beds (interpreted as turbidity of chlorite and plagioclase. Horizontal quartz-lined carbonate vein at current deposits by Morris (1986)); and a fauna of agnostine bottom. Scale bar = 2 mm. Photomicrograph C72829, crossed nicols; trilobites, lingulate brachiopods and spiculate sponges. Basal 982.7 m depth in drillhole Ross 1; ARGADARGADA PR567857 black shale beds constitute a potential petroleum source rock and is evident in Ross 1. The lower light grey interval is 7 m (see Petroleum). thick (top at 971.0 m depth), and comprises dolomudstone Dolomicrosparstone and dolosparstone of the upper with local admixed or thinly interbedded siliciclastic mud interval show recurring ghost grainstone textures; these rocks and granule intraclasts; minor cryptomicrobial dolostone; alternate with centimetre-scale calcimudstone-siliciclastic and a basal pink dolostone with admixed quartz and other mudstone interbeds. Disseminated and fracture-lining pyrite, lithoclastic sand and pebbles in a variously clast- to matrix- nodular evaporite, and shredded to brecciated textures due supported, conglomerate to breccia texture. Pyrite is common to evaporite dissolution and collapse are present. The upper in the medial portion of the interval. interval bears a varied fauna of miomeran and polymeran The darker medial interval is 12 m in thickness (top at trilobites, lingulate and calciate brachiopods, hyoliths, 959.5 m depth) and consists of mid- to dark grey stylolitic molluscs, echinoderms and spiculate sponges. Hos (in dolostone with darker grey siliciclastic wisps and laminations, Kress 1992) additionally reported lamentous algae and the together with coarsely mottled stylonodular dolosparstone. acritarchs Leiosphaeridia and Micrhystidium. Altogether, the The 25 m-thick upper light grey interval is primarily of Arthur Creek Formation ranges in age from Templetonian stylobedded dolosparstone with local vague mottling and (pre-Triplagnostus gibbus Zone) to Boomerangian (Lejopyge scattered granule lithoclasts. It is capped by a thin (2 dm), laevigata Zone), ie spanning the medial and late Middle light brown, coated-grain dolowackestone with granule-size Cambrian (Laurie 2000b, former Marqua Formation of pisoids/onkoids. This interval in TOBERMORY-HAY RIVER Shergold 1985: 11, Shergold et al 1985, Shergold 1995, cf was attributed a Templetonian (early Middle Cambrian) Geyer and Shergold 2000). Jago (in Kress 1992) identi ed age by Shergold (1985), and more specifically an early an ostensibly Ordian trilobite fauna of Redlichia, Peronopsis Templetonian age by Donnelly et al (1988; their ‘Upper Hay and Pagetia in the lower Arthur Creek Formation at 908 m River Formation Member 1’). Part or all of the upper interval depth in cored drillhole Ross 1. However, Laurie (2000a) may therefore correlate with the Bronco Stromatolith Bed recognised a Floran trilobite fauna below this level, in (Southgate 1986), a distinctive thin (1-30 cm) marker bed the interval 917-928 m. Laurie (pers comm August 2002) of limonite-stained, stratiform to low-domical stromatolites subsequently resolved this apparent paradox when he directly overlying an irregular and indurated erosion surface identi ed these notionally Ordian age-diagnostic ‘Redlichia’ at the top of the Thorntonia Limestone in CAMOOWEAL. as the younger Chondranomocare sp.

6 The transition between the two intervals is abrupt in the mudstone, which is commonly shredded due to evaporite type section in cored drillhole NTGS99/1 (TOBERMORY), dissolution. The dominant sandstone is locally cross-bedded in which the lower and upper intervals are respectively and occasionally bears pyrite and nodular evaporites. In 272.1 m and 179.4 m thick (Kruse et al 2002); elsewhere the type section, the formation is conformably overlain the transition may be gradational or interdigitating. The by Arrinthrunga Formation and rests nonconformably on formation attains a maximum thickness of 457 m in cored Palaeoproterozoic granite; the basal beds are punctuated by drillhole Hacking 1 in TOBERMORY (Weste 1989). arkosic conglomerate of granite-derived granules to cobbles In Ross 1, the Arthur Creek Formation is disconformable in a quartz sandstone matrix. on the Thorntonia Limestone; elsewhere it may rest on Eastward in ELKEDRA, the proportion of quartz older units. It is overlain with apparent conformity by the sandstone diminishes and the unit comprises ning-upward Chabalowe Formation in Ross 1, and by the Steamboat cycles of cross-bedded, dolomitic to gypsiferous quartz Sandstone in Mulga 1. sandstone and succeeding siltstone, shale and dolostone Overall, the formation denotes an initial rapid transgression (Stidolph et al 1988). Intraformational breccias are common. and the onset of anoxic conditions, succeeded by gradual The ner siliciclastic beds may be grey-green, but are regression into more aerobic, restricted marine conditions more commonly oxidised to a reddish tone distinctive of above wave base. the formation. A basal Hagen Member (see below) was recognised in this region. Steamboat Sandstone (Cms)_ The entire Chabalowe Formation was deposited under restricted peritidal conditions. Morris (1986) portrayed the In its type area in URANDANGI-GLENORMISTON, formation as laterally interdigitating with the Arthur Creek the Steamboat Sandstone (Noakes et al 1959) comprises Formation and as gradational into the overlying Arrinthrunga 60-80 m thickness of calcareous sandstone and quartz Formation, but following reinterpretation of geophysical data sandstone, and minor quartzic grainstone and dolostone. by Ambrose et al (2001), the formation is now viewed as Smith (1972) and Shergold et al (1985) provided summaries being entirely lateral to the basal Arrinthrunga Formation. It of the formation. Agnostine and polymeran trilobites indicate is therefore deemed to be of early Late Cambrian age. an age within the terminal Middle Cambrian Lejopyge The record of the Chabalowe Formation in Ross 1 laevigata Zone, extending to the Middle-Late Cambrian marks the most easterly confirmed occurrence of the passage Zone of Damesella torosa-Ascionepea janitrix formation in the Georgina Basin. It is 257 m thick in this (Shergold et al 1985). drillhole and is intersected in the interval 412.5-669.9 m In URANDANGI-GLENORMISTON, the Steamboat depth. The undifferentiated upper portion of the formation Sandstone is possibly disconformable on the Quita there comprises interbeds of reddish dolomitic-siliciclastic Formation and is undoubtedly conformable beneath the siltstone, grey stylobedded calci/dolomudstone and Mungerebar Limestone. In SANDOVER RIVER, the occasionally mottled or quartzic, grey peloid/intraclast formation is here recognised in the interval 602-799 m depth dolopackstone, as well as thin intraclast granule conglomerate in drillhole Mulga 1, where it is conformable between the beds and evaporite dissolution fabrics. Arthur Creek Formation below and Chabalowe Formation above. At 197 m, this is by far the thickest known occurrence Hagen Member (_Cuh) of Steamboat Sandstone, and compares with a con rmed thickness range of 17-49 m in adjacent TOBERMORY to At the base of the Chabalowe Formation, the lenticular the south (Kruse et al 2002). Where uncemented, such a Hagen Member (Morris in Stidolph et al 1988) is body of quartz sand would represent a signi cant potential distinguished by a relative abundance of evaporite and a petroleum reservoir (see Petroleum). However, Laing much lesser proportion of terrigenous detritus. This member (1965) described the sandstone as indurated and pyritic, was recognised in ELKEDRA (type section in cored drillhole with the constituent well rounded, medium to coarse quartz NTGS ELK7-7A) and subsequently in HUCKITTA (see grains cemented by syntaxial quartz and lesser ‘chloritic’ Questa 1994) and SANDOVER RIVER. Its maximum (glauconitic?), kaolinitic and argillaceous cement; the known thickness is 160 m, in cored drillhole Randall 1 sandstone is therefore stated to be generally tight, with poor (HUCKITTA; Wakelin-King 1992). Characteristic bedded intergranular porosity. to massive gypsum and lesser anhydrite are notable within predominantly light grey dolostone including microbial Chabalowe Formation (Cuc)_ (both stromatolitic and thrombolitic) and intraclast types, together with dolomudstone. Grey-green to red siltstone, The Chabalowe Formation (Morris et al in Stidolph et al quartz sandstone and quartzic dolostone are minor. Other 1988) extends across the southwestern Georgina Basin. features include intraformational intraclast conglomerate and It outcrops in BARROW CREEK and ELKEDRA, replacement by chert. Common vugs bear calcite, uorite, and is intersected in the subsurface in HUCKITTA and hydrocarbon stains and minor galena or pyrite. Deposition SANDOVER RIVER. Its greatest known thickness is 342 m, took place in hypersaline intertidal to supratidal (sabkha) in cored drillhole Randall 1 (HUCKITTA; Wakelin-King environments (Stidolph et al 1988). 1992). Morris (op cit) nominated a 161 m-thick type section The Chabalowe Formation interval 544.3-669.9 m in cored drillhole NTGS BC5 in BARROW CREEK, where it depth in Ross 1 is assigned to the Hagen Member. Bedded is primarily of light grey-brown, medium to coarse dolomitic evaporites are absent in this drillhole, but calcite nodules quartz sandstone, with minor quartzic to silty dolostone and after precursor evaporites recur.

7 Arrinthrunga Formation (Cua)_ known as BMR Sandover River No. 14; Kennard 1981: 3). The Arrinthrunga Formation wedges out to the north above Late Cambrian sedimentary rocks in SANDOVER RIVER underlying Middle Cambrian units. were formerly assigned to the Meeta beds (Nichols and Fehr Recrystallisation to dolomicrosparstone or dolosparstone 1964, Nichols 1966; see Smith 1972), but are now recognised has commonly imposed a sucrosic fabric on the component as Arrinthrunga Formation (Smith 1964), following Kennard dolostones, particularly the dolograinstones, but primary (1980, 1981). The Arrinthrunga Formation is widespread depositional textures are locally discernible. Rock types across the southern Georgina Basin. It outcrops from eastern exposed in SANDOVER RIVER include light yellow-grey BARROW CREEK eastward as far as westernmost MOUNT to yellow-brown, parallel-laminated calci/dolomudstone WHELAN and northward to southern AVON DOWNS. It is with nodular dolomite or cauli ower chert after evaporites; the oldest lithostratigraphic unit exposed in SANDOVER peloid or intraclast (dolo)grainstone; ooid (dolo)grainstone; RIVER. planar to wavy microbial (dolo)laminite; stromatolite The Arrinthrunga Formation comprises peritidal doloboundstone; quartzic dolostone; and minor quartz limestone and dolostone and minor interbedded quartz sandstone. Exceptionally, normally recessive, thin to sandstone, siltstone and shale. It attains a maximum 975 m medium, light grey marly dolomudstone interbeds are thickness in HUCKITTA (Smith 1972: 104). Due to the exposed in a hilltop quarry at QS758460 near No 3 Bore structural complexity and incompleteness of the type section Georgina Downs (Figure 5). (Smith 1964) in the Elua Range, Kennard (1980) nominated Sedimentary and diagenetic structures in these carbonate a complementary reference section GEO 802 in the nearby rocks include synaeresis features, ripples, millimetre- to southern Dulcie Range area (HUCKITTA). centimetre-scale cross-beds, at pebbles at various angles to The peritidal nature of the formation has severely limited bedding (locally forming intraclast conglomerate) (Figure 6), its invertebrate fossil content, so that its Late Cambrian fenestrae, nodular evaporites (Figure 7), stylobeds, planar age is deduced from its stratigraphic position relative and columnar stromatolites (Figure 8) and horizontal to biostratigraphically dated units above and below; it ichnofossils. Some ooid dolograinstones incorporate lies conformably on the Middle Cambrian Arthur Creek reworked ooid grainstone intraclasts, indicative of episodic Formation (or Steamboat Sandstone where present) and sea oor cementation. Accessory minerals include quartz, disconformably beneath the latest Cambrian Tomahawk muscovite, plagioclase, microcline, iron oxides, zircon and Formation or Ninmaroo Formation. Westward, it is opaques. Noteworthy outcrops of stromatolite boundstone conformable on the Chabalowe Formation. The Arrinthrunga are at PS901120; as 0.5 m-diameter domes of radiating Formation thus appears to span the early to medial Late columns atop a ledge of sucrosic cross-bedded dolostone Cambrian (Shergold 1985, Shergold et al 1985). Beneath on the east bank of a broad channel at QS095064; and as the Tomahawk Formation, the top of the Arrinthrunga domes up to 30 cm diameter within very coarse sand to Formation is a locally karstic erosion surface, as is shown by granule intraclast grainstone in a gutter atop a north-facing irregular topography with associated pisoids and cavity- ll slope at QS420313. breccia. However, the disconformity is dif cult to identify Altogether, these rocks are indicative of at least the where overlain by the Ninmaroo Formation, as the mixed peloidal lime mud, ooid dolostone, laminated microbial carbonate rock types above and below are similar (Kennard (‘algal’) boundstone, microbial (‘algal’) mound and possibly 1981). In SANDOVER RIVER, mapping of this contact is the very ne grainstone-lime mudstone lithofacies of Kennard constrained by occurrences of ostensibly basal Ninmaroo (1981). Outcrop of these diverse, at-lying and well bedded Formation conglomerate at QS505226 and QS660184 (see carbonate rocks ranges from low, rubbly exposures to Ninmaroo Formation). substantial ridges. In the east, outcrop is in grey clay-rich Kennard (1981) documented a variety of component soils (Czb); in the west, outcrop tends to be obscured by _ carbonate rock types in the Arrinthrunga Formation blanketing aeolian quartz sand (Czs) derived from Cuas (see including microbial (‘algal’), peloid, ooid and minor below) and the Tomahawk Formation. mudstone textures, together with quartzic carbonate, marl All of these component rock types may be cherti ed, and minor quartz sandstone. Sedimentary structures include either as rough-surfaced bedding-parallel sheets and nodules stromatolites, thrombolites, ripple cross-lamination, at- (Figure 9), or as smooth-surfaced ovoid concretions pebble conglomerate, gypsum pseudomorphs and nodular (Figure 10). This silici cation appears to be late diagenetic. anhydrite. Altogether, these rock types constitute elements Intraclast and ooid grainstones in particular are commonly of eight discrete lithofacies (Kennard 1981). In HUCKITTA red-brown silici ed, often with better preservation of primary (Freeman 1986) and southeastern ELKEDRA (Stidolph et al depositional textures than in precursor dolostone. Examples 1988), a unit of peritidal quartz sandstone, which contains of such silici cation are on a southeast-facing slope above distinctive halite hopper casts, is distinguished as the Eurowie Bybby Creek at QS423348, where concretions occur in Sandstone Member (Smith 1964). grey wavy microbial laminite; on an east-facing slope at The Arrinthrunga Formation outcrops extensively across QS555341, where sheets, nodules and spheroids are present the northern half of SANDOVER RIVER. It is intersected in light grey, thinly bedded dolo/calcimudstone; and on the completely in uncored drillhole Mulga 1 (58-602 m depth; northern slope of an extensive rise at QS895204, where thickness 544 m) and in drillhole Ross 1 (12.5-412.5 m; low outcrops of a single thick bed of locally cross-bedded thickness 400 m), although only the lowermost 17 m of dolostone bear nodular concretions. the formation was cored in the latter. The lower 184 m of Selective conservation of these resistant silici ed rocks the formation is intersected in cored drillhole Grg 14 (also and quartz sandstone during weathering has generated

8 Figure 5 Arrinthrunga Formation. Light grey marly dolomudstone interbeds in hilltop quarry. GEORGINA QS758460, near No 3 Bore Georgina Downs

Figure 6 Arrinthrunga Formation. Flat- pebble intraclast conglomerate. Scale bar = 2 mm. Photomicrograph C75160, plane polarised light; GEORGINA QS797406, Abadabada Creek

Figure 7 Arrinthrunga Formation. Dolomudstone with nodular ferroan dolomite after evaporites. Scale bar=2 mm. Photomicrograph C75158, plane polarised light; MILNE QS423348, near No 34 Bore Georgina Downs

9 iron-rich (haematite, limonite) matrix. Thin (0.25-3 cm) interbeds of red/brown siltstone are minor. The Arrinthrunga Formation was deposited on an extensive, restricted to locally emergent carbonate platform, bordered in the west and north by an evaporitic, mixed carbonate-siliciclastic shoreline (Kennard 1981: 26). The formation thus records general shoaling from a more open subtidal setting (upper Arthur Creek Formation) through a seaward high-energy quartz sand barrier (Steamboat Sandstone) into characteristically restricted, shallow subtidal to peritidal conditions. Hypersalinity on the platform limited grazing skeletal invertebrates and so permitted microbial mats to ourish, forming planar, wavy, domical and columnar stromatolites according to depth and hydrodynamic conditions. Gypsum and nodular evaporites (anhydrite) precipitated in intertidal to supratidal ats. Siliciclastic mud and ne sand was shed onto the platform from the hinterland. Kennard (1981: 30) postulated a rapid sea-level rise in mid- Arrinthrunga time, leading to the wide establishment of microbial mound lithofacies on the platform. Quartz sandstone and mixed ooid-quartz sandstone lithofacies are surmised to have migrated across the platform as shoaling resumed, culminating in intermittent emergence and the reestablishment of hypersalinity (Eurowie Sandstone _ Member and Cuas. Stromatolites continued to propagate in areas bypassed by terrigenous sediments. This cycle of sea-level rise and shoaling was repeated before regression Figure 8 Arrinthrunga Formation. Domical stromatolite comprising exposed the platform and subjected its carbonate blanket gently radiating columns of diameter 1-3 cm. GORDON CREEK QS095064, near Bilbilba Waterhole to karsti cation. a distinctive grey and red, pebble to cobble lag, which CAMBRO-ORDOVICIAN mantles most Arrinthrunga Formation outcrops and is shed as broad talus aprons (Czc) into adjacent Cenozoic soils. Tomahawk Formation (COt)_ This characteristic lag further assists in distinguishing the Arrinthrunga Formation from the otherwise similar The Tomahawk Formation (former Tomahawk beds of Smith Ninmaroo Formation. 1964) was formalised by Kruse et al (2002), with a type As in adjacent ELKEDRA (Stidolph et al 1988), section and lower boundary stratotype in cored drillhole sandstone in the medial Arrinthrunga Formation is NTGS ELK6 (ELKEDRA) and a reference section and upper treated here as correlative with the Eurowie Sandstone boundary stratotype in the Tarlton Range (TOBERMORY). _ Member, but is mapped as a distinct unit, Cuas. This It is dominantly a sandstone unit with minor siltstone, unit is characterised by cross-beds, current scour features conglomerate and carbonate interbeds. A maximum recorded and common ripples (Figure 11), but lacks halite hopper thickness of 225 m was measured in section X54 (Smith 1972) casts. Bevelled ripples in ELKEDRA indicate intermittent in the western Dulcie Range (northwestern HUCKITTA), emergence of these sands. Together with other, minor but the upper portion of this interval may represent the Kelly _ sandstones not separately mapped, unit Cuas constitutes a Creek Formation. The true thickness is probably in the order medial siliciclastic-carbonate unit, which separates lower of 150-190 m; 149 m was intersected in NTGS ELK6. and upper carbonate units of the formation (Stidolph In SANDOVER RIVER, drillhole Ross 1 intersected the et al 1988). These informal intervals are not individually Tomahawk Formation down to 12.5 m depth, but this interval delineated on the Second Edition mapface but their was not cored (Kress 1992). distribution is inferred from the mapped occurrences The Tomahawk Formation is widespread in the _ _ of Cuas in the northwest. Unit Cuas forms prominent southwestern Georgina Basin and inter ngers laterally with hills of grey to brown, more or less ferruginous quartz the carbonate-rich Ninmaroo Formation in the southeast. sandstone in 3-20 cm-thick tabular beds (Figure 12). This corridor of inter ngering traverses southwestern and Fresh sandstone surfaces are white to beige and weather south-central SANDOVER RIVER and can be traced to pink-brown. Grainsize ranges from ne to coarse, southward into TOBERMORY. The Tomahawk Formation with occasional granules, but the sandstone is generally rests disconformably on the Arrinthrunga Formation and medium grained and well sorted. Primary quartz grains is overlain with apparent conformity by the Kelly Creek are rounded to subrounded; syntaxial quartz cement Formation. Trilobites and rostroconch molluscs indicate an locally imposes an interlocking fabric. Chert, chalcedony Iverian to Payntonian (medial Late Cambrian) age for the and zircon occur as traces. Ferruginous examples bear an basal beds (Casey and Gilbert-Tomlinson 1956: 65, Jones

10 Figure 9 Arrinthrunga Formation. Rough- surfaced siliceous nodules in dolostone. CARBEEN PS842364, near Carbeen Bore

Figure 10 Arrinthrunga Formation. Smooth- surfaced ovoid concretions in dolostone. Concretions are 5-7 cm thick. MILNE QS162371, near G2 Bore

Figure 11 Arrinthrunga Formation. _ Asymmetric ripples in unit Cuas. CARBEEN PS590343, near access track to Annitowa homestead

11 Figure 12 Arrinthrunga Formation. Thick _ tabular beds of quartz sandstone in unit Cuas CARBEEN PS803339, Sandover Highway near Carbeen Bore

et al 1971: 21, Pojeta et al 1977). Conodonts provide an formations are mapped separately within this corridor upper age range, given by Shergold and Druce (1980: 161) of inter ngering. Minor, thin occurrences of Tomahawk- as late Datsonian (Cordylodus oklahomensis-C. lindstromi type quartz sandstone to the east of this corridor are Zone). This stage was then regarded as Early Ordovician, but mapped as Ninmaroo Formation on the present Second is now assigned to the latest Cambrian (Shergold and Nicoll Edition SANDOVER RIVER map, but are depicted in 1992), and the recently rati ed global Cambrian-Ordovician Tomahawk Formation colour. The converse applies for boundary in Newfoundland is correlated by Cooper et al dolostone interbeds within the Tomahawk Formation in (2001) with the base of the succeeding Warendian stage in the southwestern corner of the mapsheet. Australia. Brachiopods, hyoliths, pelecypods, gastropods, The dominant sandstone is commonly leached to pale echinoderms and possible sponge spicules are also recorded grey or white, but with a red-brown to orange-brown patina. from the formation (Freeman 1986, Stidolph et al 1988), Most sandstone is a well sorted ne to medium (to coarse) though none has been described. quartz arenite of rounded to subrounded quartz with trace Late Warendian conodonts reported by Nicoll (1991b) to accessory tourmaline, iron oxides and opaques. In thin from the Dulcie Range (HUCKITTA), in an interval section, most quartz grains show straight extinction and attributed to the uppermost Tomahawk beds, may well be exhibit syntaxial quartz overgrowths. A minority is of from Kelly Creek Formation (Kruse et al 2002). This is composite grains with sutured boundaries, implying some supported by the report of Jones et al (1971: 21) of late metamorphic provenance. Datsonian conodonts in the uppermost Tomahawk beds In southwestern SANDOVER RIVER and elsewhere, and Kelly Creek Formation in the Tarlton Range area. sandstone bears horizontal planar lamination, ubiquitous The Tomahawk Formation has thus yielded no fauna cross-beds (including solitary and festoon sets and rare of con rmed Ordovician age, although a putative Early herringbone cross-beds), ripples, synaeresis features, Ordovician fauna of the trilobite Lycophron sp, pelecypod mud pebble moulds, current markings (including current Sthenodonta sp, indeterminate costate orthide brachiopods lineations, ute moulds and current bounce or skip marks), and indeterminate pseudoplanispiral gastropods has been wrinkle marks and tabular sandstone-intraclast beds identi ed by Laurie (2000b). (Freeman 1986, Stidolph et al 1988, Kruse et al 2002). Sandstone dominates the Tomahawk Formation. In the Ichnofossils are common on planar and rippled bedding subsurface, in cored drillhole NTGS ELK6, this is a dolomitic surfaces. Horizontal traces of Planolites type, Palaeophycus, glauconite-quartz sedarenite. At surface, the glauconite is Teichichnus, bilobed trails, Corophioides, Skolithos, readily leached to produce the weathered outcrops of friable Arenicolites or Diplocraterion, and arthropod traces such as brown quartz sandstone characteristic of the formation. These Monomorphichnus, Diplichnites, Rusophycus and Cruziana appear as well sorted, locally dolomitic, ne to medium (to have been recorded from the Tomahawk Formation (Stidolph coarse) quartz arenite and minor quartzwacke, subarkose et al 1988, Kruse et al 2002). Of these, Planolites-type and sublitharenite, with thin interbeds of micaceous siltstone trails and Cruziana are here con rmed from SANDOVER and shale. Subarkose contains plagioclase, microcline and RIVER. The total assemblage indicates littoral to open perthitic feldspars (Freeman 1986). marine conditions [Skolithos and Cruziana ichnofacies of In southwestern SANDOVER RIVER, the Tomahawk Seilacher (1964)]. Formation outcrops as prominent ridges (Figure 13). There, Quartz sandstone and conglomerate depicted as Mesozoic only the lower portion of the formation is present. Eastward, on the First Edition map of SANDOVER RIVER is where it inter ngers with the Ninmaroo Formation, it indistinguishable from typical Tomahawk Formation. Indeed, typically surmounts the broader, more gentle rises of that some such outcrops (eg around QR258945, 2 km northwest unit as low rubbly outcrops, hills and ridges. The two of Top Waterhole) preserve synaeresis features and horizontal

12 muscovite, clays and iron oxides (Figures 14, 15). Chloritic pebbles represent either original glauconite or ma c metamorphic rocks. Composite quartz clasts with sutured grain boundaries are more certainly of metamorphic provenance. Outcrop summits tend to be ferruginised or silici ed and reflect proximity to an overlying (or formerly overlying) geomorphic surface. Ferricrete and lesser manganocrete (Czf) thus cap many hills (see Cenozoic). Remnant quartz grains and bedding are vaguely discernible in some of these ferricretes. Replacement minerals include haematite, goethite and manganese oxides. Dolostone beds are locally developed within the dominant sandstone. These are westerly continuations of Ninmaroo Formation carbonate facies (see Ninmaroo Formation), but are included in the Tomahawk Formation as dolostones are present in reference sections in HUCKITTA (Smith 1964, 1972) and TOBERMORY (Kruse et al 2002). In southwestern SANDOVER RIVER, they tend to be exposed on low rises beneath and between sandstone hills (Figure 13). They are thickly bedded, generally at-lying and cream to light grey to yellow- brown in colour. Primary depositional textures are rarely preserved; most are dolomicrosparstone to dolosparstone and have a corresponding sucrosic fabric. Nevertheless, relict ooid grainstone texture is discernible in some dolostones; nely laminated dolomudstone also occurs. Figure 13 Tomahawk Formation. Typical orange-brown quartz sandstone exposed as prominent ridge above at-lying yellow-grey These dolostones are occasionally interbedded with dolostone interbed. Dolostone ledge is about 1 m high. ARGADARGADA more quartzic rocks, showing laminations highlighted by PR792741, near No 14 Bore Argadargada admixed quartz and small-scale cross-beds. Rip-up clasts from these more quartzic intervals are locally incorporated ichnofossils characteristic of the Tomahawk Formation. into overlying beds. _ Mesozoic rocks are therefore not recognised in the Second A distinctive basal quartzic dolostone unit, COtd, was Edition map. mapped by Stidolph et al (1988) in adjacent ELKEDRA. _ Purple-brown siltstone and greywacke are locally COtd outcrops as medium to thick beds said to gradationally interbedded with the sandstone (eg at PR866952 and overlie Arrinthrunga Formation. The unit displays centimetre- QR156856). to decimetre-scale bidirectional cross-beds (Figure 16), Minor conglomerate and breccia contain rounded to bioclast-rich beds, relict ooids (up to 25%) and 5-25% ne subangular granule to pebble clasts of medium quartz quartz. As with other dolostone beds, this unit is an example arenite (some laminated), greywacke, quartz, and possible of Ninmaroo Formation facies. In SANDOVER RIVER, it is metamorphic rock in a matrix of medium to coarse quartz, arbitrarily mapped as far east as Argadargada homestead.

Figure 14 Tomahawk Formation. Intraformational conglomerate with granule to pebble quartz and quartzite clasts. GORDON CREEK QR491799, near Imbordjudu Creek

13 ichnofacies may denote occupation by opportunistic species after high-energy events, with more diverse Cruziana ichnofacies taxa populating the sediments in less stressful low-energy interludes (Ekdale et al 1984). The common cross-bedded units represent migrating straight and lunate megaripples, and together with other current indicators, record episodes of current activity occasionally strong enough to cause scouring. Rare herringbone cross-beds indicate that reversing tidal currents played a role in megaripple migration. Minor conglomerate and breccia imply shallowing into turbulent conditions of the foreshore, as a result of progradation in response to uplift and erosion of the hinterland.

Ninmaroo Formation (COn)_

The present conception of the Ninmaroo Formation is due to Casey (1959), who emended the former Ninmaroo Limestones and Ninmaroo Series of Whitehouse (1936). The type section is at Black Mountain (BOULIA; Jones et al 1971) in the Burke River Structural Belt of the eastern Georgina Basin, where the formation is 795 m thick. Five formal members are recognised in the type section (Shergold and Druce 1980), but these are not identi ed in SANDOVER RIVER. Much work on conodont (Jones et al 1971, Druce and Jones 1971, Druce 1978, Druce et al 1982, Nicoll 1990, 1991a, 1992, Nicoll and Shergold 1991, Nicoll et al 1992) and trilobite biostratigraphy (Shergold 1975a) Figure 15 Tomahawk Formation. Intraformational conglomerate has been conducted in the Burke River region, together with granules to pebbles of quartz, quartzite and chloritic rock (centre and centre right). Compare with Figure 14. Scale bar = 2 mm. Photomicrograph C75138, crossed nicols; GORDON CREEK QR491799, near Imbordjudu Creek

Whereas all these dolostone interbeds are typically at-lying, associated sandstone tends to be structurally deformed at mesoscale (including kink folds; Freeman 1986). This deformation is widespread in HUCKITTA, ELKEDRA, SANDOVER RIVER and TOBERMORY. Sandstone outcrop usually displays greatly varying dips that can change signi cantly in magnitude and direction within metres (Figure 17). This renders it dif cult to obtain reliable regional dips. Folding can be broad enough to occupy a moderate-sized hill, but commonly occurs on metre and decimetre scales. Beds tend to dip into a hill on all sides. Freeman (1986) invoked subsurface cavernous solution _ of underlying carbonate rock ( COtd and Arrinthrunga Formation) by groundwater, with consequent progressive subsidence of the lithified sandstone, to explain this lithology-selective deformation. This would account for many instances of sandstone and dolostone in close lateral juxtaposition. The Tomahawk Formation represents the episodic shedding of terrigenous sand, possibly from exposed Arunta Province or Davenport Province basement to the present west, onto a broad marine platform otherwise dominated by the correlative Ninmaroo Formation in the east. Deposition took place in dynamic littoral to sublittoral environments extending a considerable distance offshore, within restricted Figure 16 Tomahawk Formation. Bidirectional cross-beds in _ to open marine waters that were moderately deep, yet still thick dolograinstone bed of basal dolostone unit COtd. OORATIPPRA above storm wave base. Ichnofossil elements of the Skolithos PR515727, southeastern corner of ELKEDRA

14 Figure 17 Tomahawk Formation. Deformation in fine quartz sandstone. GORDON CREEK near QR195705, south of Towners Best

Figure 18 Ninmaroo Formation. Wavy to columnar stromatolites. Handlens (left) is 4.5 cm long. BARRY PLAIN near QS649166, 4.6 km east of Waggon Hole Bore

with documentation of rostroconch and polyplacophoran been recognised in SANDOVER RIVER. These deposits molluscs (Pojeta et al 1977, Runnegar et al 1979). The age were subject to burial and uplift diagenesis, including of the Ninmaroo Formation at Black Mountain is thus well widespread dolomitisation (Radke 1982). constrained, ranging from the mid-Payntonian (medial Late The formation is extensive across southern SANDOVER Cambrian) Hispidodontus appressus Assemblage Zone to RIVER and interfingers with the laterally equivalent the Warendian (earliest Early Ordovician) Chosonodina Tomahawk Formation in the south-central and southwestern herfurthi/Cordylodus angulatus Assemblage Zone (Shergold portions. Minor thin Tomahawk-type quartz sandstones to and Nicoll 1992). The conformably underlying Chatsworth the east of this corridor of inter ngering are here mapped Limestone is absent in SANDOVER RIVER, where the as Ninmaroo Formation, but depicted in Tomahawk Ninmaroo Formation is considered to be disconformable on Formation colour. The best outcrop is in the broad massif the Arrinthrunga Formation, although the contact is dif cult of smoothly rounded hills in the southeast, where bedding to identify in the eld (Kennard 1981: 5). The interval above traces are clearly identi able on aerial photographs. Much 58 m depth in uncored drillhole Mulga 1 is attributed to the more Ninmaroo Formation is identi ed on the Second Ninmaroo Formation (Laing 1965). Edition map than in the First Edition, which portrayed The Ninmaroo Formation includes ooid, peloid, bioclast, the southwest of the sheet as being entirely Tomahawk intraclast (including at-pebble conglomerate), microbial Formation. and mixed-lithology limestone and dolostone, as well as Constituent rock types in SANDOVER RIVER are minor quartz sandstone. These were deposited on a broad predominantly light grey to yellow-grey or yellow- epeiric platform under normal open marine to restricted and brown sucrosic dolomicrosparstone and dolosparstone. emergent evaporitic conditions (Radke 1980, 1981, in Druce Locally, these have relict textures indicative of laminated et al 1982). The shoaling cycles of Radke (1980) have not dolomudstone, intraclast dolopack/grainstone and ooid

15 This suite of rock types and sedimentary structures indicates carbonate platform deposition under variable energy conditions, punctuated by recurring high-energy episodes, consistent with the depositional models of Radke (1980). Silici cation is largely con ned to the basal beds of the formation, where occasional red-brown nodules and bedding- subparallel sheets are present (eg at RS020002 east of No. 36 Bore Lake Nash and QS444084 opposite Peter Waterhole). These occurrences are not accompanied by the silici ed lag characteristic of the underlying Arrinthrunga Formation. Exceptionally, nodular chalcedony in laminated dolostone higher in the formation at QR253748 may denote precursor evaporites, silici ed due to their proximity to Tomahawk Formation quartz sandstone 2-3 m stratigraphically above. Minor red-brown to yellow-brown, medium quartz sandstone assigned to the Ninmaroo Formation is indistinguishable from that of the Tomahawk Formation. Horizontal trails or burrows are preserved in low hills of Ninmaroo Formation quartz sandstone at QR575866 and QR580863 south of G46 Bore Lake Nash. At the latter locality, at least four size classes, of width 1-2 mm, 5 mm, 2 cm and 3 cm, are preserved. Exposed Tomahawk-Ninmaroo contacts are rare. One exception is at QR299707, where a well exposed small promontory of Ninmaroo Formation projects from the base of a massif of Tomahawk Formation red-brown quartz sandstone. There, the two formations are laterally Figure 19 Ninmaroo Formation. Columnar stromatolites. Scale adjacent, with local drape of Tomahawk Formation around bar = 2 mm. Photomicrograph C75137, plane polarised light; the margins of the Ninmaroo Formation promontory. GORDON CREEK QR384994, near Kings Waterhole The latter consists of medium to thick beds and lenses of light yellow-brown sucrosic dolostone, interbedded with dolograinstone and their quartzic equivalents; planar to normally recessive, thin to nodular beds of ne to coarse crinkled microbial dololaminite; stromatolite doloboundstone dolomitic quartz sandstone (Figure 22). (Figures 18, 19); and minor, more or less dolomitic quartz The dominant trend of joints throughout the Ninmaroo sandstone. Relatively well preserved ooid dolograinstone Formation in SANDOVER RIVER is southwesterly. is exposed in a track along an east-west boundary fence at This joint trend set continues into adjacent northeastern QR066921, 1 km east of the fence corner; and at QR131793 TOBERMORY. (Figure 20). An accessible and well exposed stromatolite biostrome in the basal Ninmaroo Formation at QS476239 is PALAEOGENE-NEOGENE crossed by a station track 1.2 km north-northwest of No. 9 Bore Lake Nash. This biostrome is up to 1 m thick and at least Austral Downs Limestone (Cza) 50 m across, of parallel columns 1-2 cm in diameter, which extend through the entire thickness of any one exposure. Noakes and Traves (1954) erected the Austral Downs No biostromal margin is preserved, but scattered probable Limestone for terrestrial lacustrine limestone within dolomudstone clasts suggest stratigraphically adjacent low- the Georgina River catchment, including HAY RIVER, energy conditions. TOBERMORY, SANDOVER RIVER, AVON DOWNS Dolomudstone is generally thinly to medium and parallel and adjacent areas of Queensland. This is a pale grey bedded, though locally millimetre-scale cross-bedded, with limestone, partially silici ed to resistant red-brown and synaeresis features and rare horizontal ichnofossil trails or white chert and chalcedony. burrows up to 1 cm wide (eg at QS505226). Grainy rock Western Queensland outcrops were described by types are medium to thickly bedded, but may have local, Paten (1964), who noted a similarity with modern millimetre- to decimetre-scale cross-beds, bidirectional calcareous spring travertine deposits in that area. He ripples (eg at QR195705), dolomudstone flat pebbles, further recognised brecciation within the limestone, and including imbricated examples (eg at QR434839), or a basal reworked ferruginous interval which he took to stylobeds. indicate that the Austral Downs Limestone postdated a Distinctive conglomerate of very coarse, quartzic widespread Cenozoic ferruginisation episode (part of dolostone-bearing, matrix-supported, subangular-subrounded Czf herein) in the region. Whitehouse (1940) recognised dolostone granules to small pebbles at QS505226 and pedogenic limestone within the unit. Rare charophyte QS660184 is regarded as basal Ninmaroo Formation and other algal remains, plant tissue, ostracodes and (Figure 21). foraminifers additionally indicate brackish lacustrine

16 Figure 20 Ninmaroo Formation. Ooid dolograinstone with reworked ooid dolograinstone pebbles. Scale bar = 2 mm. Photomicrograph C75139, plane polarised light; GORDON CREEK QR131793, south of Towners Best

Figure 21 Ninmaroo Formation. Basal conglomerate of very coarse quartzic dolostone with matrix-supported dolostone granules to small pebbles. Scale bar=2 mm. Photomicrograph C75157, crossed nicols; MILNE QS505226, near No 9 Bore, Lake Nash

conditions (Paten 1964). Lloyd (1968a) reported the where the formation outcrops as prominent plateaux (Kruse foraminifer Ammonia beccarii from the Austral Downs et al 2002). Limestone, for which Lloyd (1968b) deduced a Miocene age. Grimes (1980) invoked damming of an ancestral PALAEOGENE-NEOGENE-QUATERNARY Georgina River, generating up to 35 m thickness of sediment. Nichols (1966) reported a minimum thickness Ferricrete and manganocrete (Czf) of 13 m in SANDOVER RIVER, in No 37 Bore Lake Nash (QS948726). Super cial dark, iron-rich (haematitic or goethitic) crusts up The Austral Downs Limestone is exposed in northeastern to several metres thick locally cap dolostone of the Ninmaroo SANDOVER RIVER, as cobble lags to low rises that Formation and especially, highly weathered sandstone of the unconformably overlie the Arrinthrunga Formation. Tomahawk Formation. Nodular and massive types are the Constituent pale grey limestone is commonly fractured to most common, and encrustations and botryoidal textures brecciated, with circum- and intergranular cracks indicative much less so. Where developed on Tomahawk Formation of pedogenic glaebules (Figure 23; see Esteban and Klappa sandstone, relict textures and quartz sand grains may be 1983). Rare microbial boundstone with poorly developed preserved. Locally, the crusts are partially silici ed, or wavy to pseudocolumnar laminations at RS027642 manganiferous up to the point of being more properly called (Figure 24) and QS944722 is interpreted as lacustrine or manganocrete. They have a distinctive dark photopattern, but marginal lacustrine. not all such dark areas are ferricrete; some are ferruginous A greater diversity of pedogenic indicators is exhibited sandstone, and probably represent areas from which a former by the Austral Downs Limestone in adjacent TOBERMORY, ferricrete cover has been stripped.

17 Figure 22 Ninmaroo Formation. Outcrop of interbedded dolostone and dolomitic quartz sandstone. GORDON CREEK QR299707, south of Towners Best

Figure 23 Austral Downs Limestone. Pedogenic alpha fabric of soil glaebules with intra- and circumgranular cracks. Scale bar = 2 mm. Photomicrograph C75162, plane polarised light; GEORGINA RS027642, east of Beantree Bore

Clay-rich soil (Czb) deep drifts over the Arrinthrunga Formation. It is derived from _ the Tomahawk Formation and unit Cuas of the Arrinthrunga Grey-black clay-rich soil plains occupy most of central and Formation. eastern SANDOVER RIVER. Seasonal wetting and drying of these soils produces characteristic gilgai with associated QUATERNARY deep cracks. Regolith (Cz) Siliciﬁ ed talus (Czc) This term embraces in situ weathering products and shallow Outcrop of Arrinthrunga Formation in central and eastern skeletal soils, not otherwise categorised herein, which are SANDOVER RIVER is mantled by a characteristic grey and directly derived from underlying shallow subcrop with little red, pebble- to cobble-weathering lag of resistant silici ed active transport. It is depicted on the mapface in the colour of dolostone and quartz sandstone. This material is shed as broad the parent unit, but with a superimposed grey stipple. talus aprons into adjacent clay-rich soil (Czb). Where present, this talus distinguishes the Arrinthrunga Formation from the Alluvium (Qa) otherwise similar Ninmaroo Formation. Alluvium of sand and minor gravel, silt and clay is deposited in the Unconsolidated sand (Czs) beds and banks of watercourses. Flat Qa oodplains are generally demarked from adjacent colluvial sand (Czs) by a break in slope. Unconsolidated colluvial sand and minor silt blankets much of In oodout areas where oodwaters dissipate into a sheet, the western SANDOVER RIVER. In the northwest, it develops as boundary between Qa and Czs may become arbitrary.

18 Figure 24 Austral Downs Limestone. Pustular stromatolite boundstone. Scale bar = 2 mm. Photomicrograph C75125, plane polarised light; GEORGINA RS027642, east of Beantree Bore

Claypans (Qp) and a nominal terrain clearance ranging from 60 m (1999 Elkedra survey) to 80 m (2001 Eromanga survey). In Clay accumulates in poorly drained depressions on these surveys, gamma radiometric data were sampled at a oodplains and along relict drainage. Many are poorly nominal interval of 70 m using 33 L Tl-doped NaI crystals. vegetated, but a waterlogged minority supports denser Full technical speci cations and views of the datasets vegetation. are accessible on the website http://www.dbird.nt.gov. au/ntgs/geophysics/airborne.html. The remaining portion STRUCTURE AND TECTONICS of SANDOVER RIVER, a narrow strip on its southeastern edge, was own in 2002 to similar spec cations (Georgina The SANDOVER RIVER region largely escaped the repeated survey). Commercial airborne geophysical (magnetic and tectonism that moulded the present southern margin of the radiometric) data are limited to northwestern GEORGINA, Georgina Basin in HUCKITTA, TOBERMORY and HAY where approximately 800 km2 were own at 300 m line RIVER and its adjacent Arunta Province basement (Mawby spacing as part of CRAE’s Lake Nash survey, which et al 1999, Hand et al 1999). extended through AVON DOWNS to the north (Allnutt Basement metavolcanic schist penetrated in Ross 1 has and Bubner 1985). a near-vertical schistosity and is of unknown age. The rock Geoscience Australia gravity data are available and fabric could relate to a number of orogenic events that throughout SANDOVER RIVER at 11 km nominal spacing. affected the Arunta Province, or simply be a remnant of an The GA data were acquired by road and helicopter traverses older basement cratonic segment that escaped the repeated in 1959 and 1961, respectively (Barlow 1966). The GA orogenic events of the Arunta Province to the south. gravity database also contains data from two commercial The unmetamorphosed Georgina Basin succession, surveys. Alliance Petroleum observed a long traverse spanning the Middle Cambrian to Early Ordovician in through southern SANDOVER RIVER as part of their SANDOVER RIVER, remains at-lying to only gently Tarlton Downs gravity survey (Lonsdale and Ingall 1964). folded. The underlying Altjawarra Domain (sensu Myers The stations on this traverse are approximately 1.6 km et al 1996), a region of thickened, stable crust with low apart, except in the vicinity of Mulga 1, where a series of crustal temperatures and low heat ow, evidently preserved short lines was observed at half this station spacing. As part the succession in relatively pristine condition. APC (1993) of a basin-wide survey, several northeast-trending gravity recognised gentle folds with west-southwesterly axes within traverses were also acquired across SANDOVER RIVER the Cambro-Ordovician succession in the south-central (Paci c Oil and Gas 1991). These lines are 25 km apart, and southwestern sheet area. The trends of these fold axes with 1 km station spacing. A third commercial survey of do not coincide with the dominant southwesterly joint set over 400 stations was conducted around Blenheim Hill in affecting these rocks. What little folding is present is likely northern SANDOVER RIVER by CRAE (Bubner 1987). to relate to the Alice Springs Orogeny, the last major tectonic Unfortunately, these data were collected without reference to episode in the region. absolute elevation and gravity ties and thus cannot be used to augment existing gravity databases without eldwork to GEOPHYSICS recover their base station. Experimental seismic work by BMR, totalling SANDOVER RIVER is entirely covered by recent NTGS approximately 28 line km near Gordon Creek and the airborne magnetic and radiometric surveys. The majority Mulga 1 drillhole, failed to obtain signi cant re ections of the mapsheet has been traversed by two surveys on (Montecchi and Robertson 1966). This constitutes the only north-south-oriented ight lines at a line spacing of 400 m seismic data recorded to date from SANDOVER RIVER.

19 Gravity be tentative. Some inferences on basement composition may nevertheless be made, supplemented by the few basement SANDOVER RIVER contains regionally low Bouguer intersections made in drillholes. These data generally accord gravity values, with none exceeding 0 μm.s-2 (Bouguer with previous interpretations (Wells et al 1966, Teasdale and reduction density 2.67 t.m-3). Much of the sheet area apart Pryer 2002), which postulate magnetic basement depth to from the western and southern margins was designated increase gently, with little undulation, from around 800 m in the Sandover Gravity Low by Barlow (1966). The the northwest to at least 1500 m in the southeast. highest anomaly amplitudes and gradients are observed in Northwestern SANDOVER RIVER is dominated by southwestern SANDOVER RIVER, with Bouguer gravity curvilinear magnetic anomalies that are northeasterly differences up to 300 μm.s-2 over a distance of 12 km strike continuations of features interpreted as subcropping observed to the southeast of Mt Hogarth. These and other Wauchope Subgroup on ELKEDRA by Donnellan and anomalies of substantially lesser gradient and amplitude in Johnstone (in prep). Similar anomalies are also observed southwestern SANDOVER RIVER are consistent with a in central-western SANDOVER RIVER near Argadargada basement of discrete felsic and ma c components. At least homestead, albeit with a change in strike to southeasterly some of the former is apparently in the form of a granitoid across a discontinuity which presumably indicates a major that intruded late in the geological history of the basement, basement fault roughly coincident with the Sandover as the associated gravity low centred to the south of Mt Highway. There are similarities between these areas and the Hogarth evidently truncates magnetic trends, particularly anomalies in northern SANDOVER RIVER, but the latter to the northwest. are more discontinuous and of more variable amplitude. This Subcropping granites have been interpreted within a may indicate an area of complexly faulted and deformed small proportion of northern SANDOVER RIVER, based Wauchope Subgroup, but the possibility that this region may mainly on the magnetic signature (see Magnetics). However, have more direct af nities with other metamorphic terranes the long-wavelength gravity low in this region indicates to the north (Murphy Inlier), east (Mount Isa Inlier) or south that these bodies may be connected at depth, with granite (Arunta Province) cannot be discounted. Irregular magnetic intruded beneath much of a Wauchope Subgroup succession, at spots within northern SANDOVER RIVER indicate which is inferred to extend eastward in the subsurface from granitoid plutons, which evidently interrupt overall east-west the exposed Davenport Province in ELKEDRA (Donnellan magnetic anomaly trends of possible Wauchope Subgroup and Johnstone in prep). The overall gravity low in northern af nity (Teasdale and Pryer 2002). SANDOVER RIVER is interrupted by two discrete gravity In contrast, substantial magnetic anomalies (up to 500 nT highs, but since each is known only from one or two stations, amplitude, superimposed on a regional magnetic high) in little can be inferred from them. It may be that these stations southwestern SANDOVER RIVER present no dominant are sampling a particularly ma c portion of the Wauchope structural grain. They indicate a complexly deformed terrane Subgroup succession, which is interpreted to be around with a large proportion of ma c igneous rocks (represented 900 m deep in this area (Teasdale and Pryer 2002), or by the metavolcanic rock intersected at a depth of 978 m in alternatively that these anomalies have intrabasinal sources Ross 1, on the ank of a magnetic high). These were possibly due to a concentration of low-porosity carbonates. Based on emplaced in multiple episodes, interspersed with felsic unconstrained additional gravity acquisition, Bubner (1987) material. There is some indication of west- to southwest- concluded that the more westerly of these anomalies, to the trending faults transecting this basement region. north of Scarr Hill, had an intrabasement source. Central and southeastern SANDOVER RIVER contain The remainder of SANDOVER RIVER generally has magnetic lows of little internal character. These areas have little gravity character, with amplitudes rarely exceeding been interpreted as basement granites (Teasdale and Pryer 100 μm.s-2 over wavelengths of 10 km or more. As 2002), but subtle curvilinear magnetic ridges within the discussed below (Magnetics), a metamorphosed basement central region, coupled with the lack of a pronounced gravity of felsic to intermediate composition may underlie much low (see Gravity) indicate that at least part of the basement of central SANDOVER RIVER. There is some indication in this area may be a metamorphosed succession of felsic to that basement in southeastern SANDOVER RIVER may intermediate composition. be somewhat denser (ie less felsic) than that in the central Most high-frequency magnetic anomalies in eastern and region, but it is dif cult to distinguish this possibility from southern SANDOVER RIVER are associated with incised that of increasing basin depth, with concomitant increase in watercourses, presumably due to maghaemite concentrations the proportion of carbonate. within them. A sinuous high-frequency magnetic feature, several kilometres wide, curves northeastward through Magnetics northwestern SANDOVER RIVER. This feature and associated ‘tributaries’ are interpreted as lled palaeochannels, Magnetic anomaly amplitudes range up to 1600 nT (reduced from their topographic context in a broad, at valley and from to pole), with TMI ranging between –330 nT and 1160 nT. the association elsewhere of high-frequency anomalies with However, none of the sources of these anomalies outcrops currently active drainage. (magnetic susceptibility of Georgina Basin sediments being essentially nil in this context), and indeed the nearest Radiometrics outcrop of basement is over 65 km from SANDOVER RIVER. Consequently, any correlation of basement-sourced Some of the lowest radiometric responses in SANDOVER geophysical features with geology exposed elsewhere must RIVER are observed over outcropping Arrinthrunga

20 Formation rocks, albeit with several exceptions in the form of a record from the lower Arrinthrunga Formation to the isolated patches of high Th and U, in particular on ridgetops Thorntonia Limestone and penetrating basement. such as around PS640460 and QS850381. This signature The downhole record of Ross 1 best illustrates changes into one of bland low-level Th and U where the the geophysical responses of the succession (Table 3, Arrinthrunga Formation is mantled by talus aprons (Czc) Figure 25). Basement metavolcanic rock shows a moderate shedding into and merging with Cenozoic material. gamma response. High downhole magnetic susceptibility The Tomahawk Formation is characterised by a distinctly (5210 x 10-5 SI) was also recorded from this rock (Kress bimodal radiometric signature, with apparent topographic/ 1992). Signi cant, stepped adjustments of the gamma trace weathering control. Crests of Tomahawk Formation to a low base level clearly delimit the Thorntonia Limestone outcrops are characterised by high Th and U, whereas K at base and top. Within the formation, a local gamma peak is dominant within a generally lower radiometric response coincides with mottled and therefore more siliciclastic on actively eroding slopes, which are denoted by steeper dolostone of the medial interval. In the Arthur Creek terrain. The former is probably sourced from ferricrete Formation, gamma values increase down-section toward and manganocrete cappings and opaque minerals within the base; this distinctive log signature enables recognition Tomahawk Formation sandstone, whereas the latter signature of pyritic-carbonaceous black shale in the basal Arthur arises from glauconitic, micaceous or shaly components of Creek Formation. This is a potential petroleum source the succession. rock (see Petroleum). In Ross 1, the resistivity log mimics In southeastern and southern SANDOVER RIVER, this downward gamma increase. A dramatic decline in the the Ninmaroo Formation has a high Th and U component, gamma log to a very low baseline marks the Arthur Creek generally similar to that of the adjacent Tomahawk Formation-Hagen Member boundary. A moderate decrease Formation. However, in the southeastern sheet area, the in baseline of the resistivity log approximately coincides Ninmaroo Formation signature changes to one where Th with the relatively more siliciclastic undifferentiated and U are almost absent, although these radioelements portion of the Chabalowe Formation. This feature facilitates have accumulated in topographic depressions in this recognition of that unit in drillholes throughout the southern area. Within a few kilometres of the northeastern limit of Georgina Basin. Ninmaroo Formation outcrop, at the edge of Barry Plain, the K component diminishes as well, leaving little or no GEOLOGICAL HISTORY radiometric response and the signature of the formation thus appears to be similar to that of much of the Arrinthrunga Metavolcanic rock at the bottom of cored drillhole Ross 1 is Formation. This absence of radioelement response is the only record of basement in SANDOVER RIVER. The consistent with silici cation, which has been noted in the precise age of its parent andesite or basalt remains uncertain, basal Ninmaroo Formation in this area. but it was regionally metamorphosed to upper greenschist Patches of high U distinguish portions of the Austral facies (Martin in Kress 1992) and a schistosity imparted Downs Limestone. However, radioelement concentrations prior to the Middle Cambrian. Most of the Georgina Basin in the Austral Downs Limestone generally appear to be basement is interpreted as felsic and ma c rocks in stable low, except where the unit has been covered by transported cratonic areas. These were voluminously intruded by granites material. Cenozoic sediments tend to contain relatively that relate to those in the Davenport and Arunta Provinces. moderate levels of radioelements; higher concentrations Little is known of the orogenic events that affected these of K are due to clays in soil plains (Czb) and in particular, basement terranes. alluvial oodplains (Qa). Radiometric response, particularly Neoproterozoic and Early Cambrian sedimentation in the K channel, is exceptionally prominent over apparently recorded along the southern margin of the Georgina Basin particularly clay-rich portions of Quaternary alluvium (Qa; (Walter 1980, Walter et al 1979) apparently did not extend eg PS790100) and claypans (Qp; eg north and south of northward into the present area of SANDOVER RIVER. Georgina Downs homestead). Widespread transgression in the early Middle Cambrian (Ordian-early Templetonian) led to deposition of initial Downhole geophysics local terrigenous sands and subsequent restricted to open marine carbonate sediments of the Thorntonia Limestone. Downhole geophysical data are available for SANDOVER This constitutes depositional sequence 1 of Southgate and RIVER drillholes BMR Grg 14 (Milligan 1963, Nichols and Shergold (1991), on a broad carbonate platform facing open Fehr 1964), Mulga 1 (Laing 1965) and Ross 1 (Kress 1992), ocean to the present east, beyond the Tasman Line. Brief as shown in Table 2. episodes of anoxia generated thin black shales among the Grg 142 was drilled to elucidate the age and succession dominant carbonate sediments on the platform. The platform of notionally ?Lower Cambrian to Lower Ordovician was at least locally exposed at the conclusion of Thorntonia dolostone units (Figure 25). The hole was continuously Limestone deposition and local karsti cation of the sediment cored throughout and intersected only the lower Arrinthrunga pile ensued. Formation. Only six short cores were taken at intervals Renewed transgression in the late Templetonian from percussion hole Mulga 1, which intersected the basal marked the commencement of sequence 2 (Southgate and Ninmaroo Formation to lower Arthur Creek Formation. Shergold 1991). Deeper marine, basinal anoxic conditions Ross 1 was continuously cored from 396 m depth, providing initially prevailed throughout much of the southern Georgina Basin, generating pyritic-carbonaceous black 2 Also known as BMR Sandover River No 14; Kennard 1981: 3. shale of the lower Arthur Creek Formation. Agnostine

21 Table 2 SANDOVER RIVER drillholes in chronological order with locations and available downhole geophysical data. Resist = resistivity/ conductivity; SP = self potential; Veloc = acoustic velocity

Hole name Easting (mE) Northing (mN) Gamma Resist SP Sonic Density Neutron Veloc Grg 14 742200 7652400 +++ Mulga 1 773115 7598206 +++ ++ Ross 1 656709 7585692 ++ +++

Table 3 Porosity, density and magnetic susceptibility data recorded in downhole logging of Ross 1 (Kress 1992), summarised by formation. Note that absolute calibration of the density logging tool seems to be erroneously high, especially in view of 2620 kg m-3 density measured on two Arrinthrunga Formation samples from 194.5 m and 194.8 m in BMR Grg 14 (cf Arrinthrunga Formation this Table). However, relative density contrasts observed between various intersected units appear valid. Fm = Formation; Mbr = Member

Unit Number of Porosity (%) SG bulk wet SG standard Magnetic Depth from Depth to (m) readings (kg m-3) deviation susceptibility (m) (x 10-3 SI ) Arrinthrunga Fm 2857 15.2 2730 0.15 0.02 12.5 538.0 Hagen Mbr 865 10.4 2840 0.08 0.01 538.0 669.9 Arthur Creek Fm upper 847 9.4 2780 0.09 0.03 669.9 798.8 Arthur Creek Fm lower 776 8.5 2840 0.03 0.05 798.8 917.2 Arthur Creek Fm basal shale 112 8.8 2870 0.03 0.05 917.2 934.3 Thorntonia Limestone 287 8.8 2870 0.06 0.01 934.3 978.1 metavolcanic rock 154 12.7 3010 0.06 52.10 978.1 1002.5 trilobites and other organisms ourished in these open associated semi-emergent shoals and cyclic sedimentation. ocean waters. Aggradation during the remainder of the Terrigenous quartz sand (Tomahawk Formation) was shed from Middle Cambrian led to shallowing above wave base into a western landmass (Arunta Province or Davenport Province) normal open marine platformal conditions. Agnostines into littoral and sublittoral settings above wave base on this declined in importance as other groups ourished. This platform. Abundant benthic soft-bodied organisms produced platform was eventually subjected to more restricted open marine Cruziana and littoral Skolithos ichnofacies traces. waters, with limited development of nodular anhydrite Intraclast-bearing layers and hummocky cross-strati cation within carbonate sediments destined to become the upper were deposited by storms. Arthur Creek Formation. Although adjacent areas to the south and west were Deposition on the platform during the early to medial inundated through the Early and Middle Ordovician and in the Late Cambrian (Arrinthrunga Formation) reflected mid-Devonian and Jurassic-Cretaceous, SANDOVER RIVER widespread, restricted marine to peritidal conditions. An has seemingly remained exposed since mid-Early Ordovician evaporitic, mixed carbonate-siliciclastic shoreline rimmed the time. Continental conditions in the Cenozoic led to ferricrete platform on the present west and north. Quartzic sediments and silcrete development in the Palaeocene, Oligocene and (Steamboat Sandstone) and local ooid-peloid grainstone Mio-Pliocene (Grimes 1980). Lacustrine conditions in the (basal Arrinthrunga Formation) formed a seaward high- Georgina River catchment generated the pedogenic Austral energy barrier. Hypersalinity on the platform precipitated Downs Limestone. During the Quaternary, widespread evaporites and permitted the expansion of microbial colluvial quartz sand has been reworked in alluvial oodplains stromatolites and thrombolites during a postulated sea level and claypans. rise. Renewed shoaling culminated in intermittent emergence and the reestablishment of hypersalinity to the west and south ECONOMIC GEOLOGY (Eurowie Sandstone Member), but in SANDOVER RIVER _ less restricted quartz sands (Cuas) were deposited. A further Petroleum transgressive cycle ensued before nal regression, exposure and karsti cation of the platform in the mid-Late Cambrian Petroleum exploration and prospectivity in the Georgina Basin (Iverian). The Arrinthrunga Formation may thus represent two was summarised by Questa (1994) and the petroleum system distinct depositional sequences. thoroughly revised by Ambrose et al (2001). As the system Marine platformal conditions were widely reestablished by is of Cambrian-Ordovician age, it belongs to the Larapintine the Payntonian (late Late Cambrian) and continued through supersystem of Draper (2000). the Early and Middle Ordovician to the south and west. In The Bureau of Mineral Resources (BMR) undertook initial SANDOVER RIVER, there is evidence of continued deposition reconnaissance of Georgina Basin petroleum prospectivity into the Early Ordovician. A broad carbonate platform in the in the 1950s. Through the late 1950s and early 1960s, east (Ninmaroo Formation) extended into Queensland. Ooid, petroleum companies, including Frome-Broken Hill, peloid and skeletal sands again formed a seaward barrier Geosurveys of Australia, Alliance Petroleum (Wilson 1963), system, with consequent salinity increase on the platform, French Petroleum, Australian Aquitaine Petroleum and Shell

22 ROSS 1 MULGA 1

RESISTIVITY SONIC GAMMA SELF ohm m s/ftu API units POTENTIAL SONIC GAMMA DEPTH (m) mV s/ftu API units 0 05000 140 40 0 200 DEPTH (m) 0 160 140 40 0200 TOMAHAWK FM 0

50 NINMAROO 50 FORMATION

100 100

150

200

250

250 ARRINTHRUNGA FM

300

350

400

450

500

500 CHABALOWE FM

550

600

650 HAGEN MBR

650

700

750

800 STEAMBOAT SANDSTONE ARRINTHRUNGA FORMATION

800

850

ARTHUR CREEK FM 850

900 FORMATION 900 ARTHUR CREEK

950 THORNTONIA LST

META- BMR GRG 14 1000 VOLCANIC SELF RESISTIVITY POTENTIAL GAMMA ohm m mV API units DOMINANT LITHOLOGY DEPTH (m) 0 dolomudstone, dolowackestone ZOIC mottled dolostone CENO- intraclast-bioclast dolograinstone 50 microbial dololaminite quartzic dolostone, quartz sandstone 100 mixed and silty limestone and dolostone

coarsely recrystallised dolostone 150 pyritic-carbonaceous shale, shale-dolostone laminite ARRINTHRUNGA FM siltstone, mudstone 200 metavolcanic rock m02-058.dgn Figure 25 Schematic lithologs and downhole geophysical logs of SANDOVER RIVER drillholes

23 Development, reviewed aspects of the region. In 1962, Phillips- reservoir and overlying anhydrite seal in the Hagen Member Sunray drilled the rst petroleum well in the Georgina Basin: of the Chabalowe Formation, as intersected in Ross 1 and Black Mountain 1 in BOULIA, Queensland. Investigations drillholes to the west (Ambrose et al 2001). continued throughout the eastern, southern and central portions of the basin during the early to mid-1960s. In SANDOVER Diamonds RIVER, BMR drilled Grg 14 in 1962; Milligan (1963) and Nichols and Fehr (1964) reported asphaltic material at 171- From 1984 to 1987, CRAE conducted a sustained diamond 220 m depth in this drillhole (lower Arrinthrunga Formation). search over the Georgina Basin. The original area included the Alliance Petroleum drilled Mulga 1 in 1965, on the crest of a whole of SANDOVER RIVER (Allnutt and Bubner 1985). closed gentle anticline (Laing 1965). The survey included airborne geophysics, stream sediment The impact of this early exploration phase was to sampling of trap sites at a nominal density of one per 20 km2 downgrade the perceived prospectivity of the entire Georgina and loam sampling of circular features identi ed on aerial Basin, and exploration virtually ceased until the early 1980s. photographs and from airborne magnetic data. Numerous However, the BMR and latterly the NTGS continued to chromite grains were found in southern SANDOVER RIVER drill stratigraphic holes and acquire geophysical data. One and single microdiamonds were collected from No 2 Creek just notable exception during this interregnum was the drilling of above Rocky Creek junction, the headwaters of Shank Creek, Ethabuka 1 in the Toko Syncline on MOUNT WHELAN by and a oodout southeast of Towners Best (Allnutt 1986). Alliance Oil in 1974. This well yielded the only sizeable ow Subsequent work focussed on the Scarr Hill to Blenheim of hydrocarbons to date from the Georgina Basin: 7080 m3/day Hill area, where abundant chromite grains were reported. of dry gas from the Early Ordovician Kelly Creek Formation A single microdiamond with no accompanying kimberlite (Radke and Duff 1980). indicator minerals was recovered from an aeromagnetic Pacific Oil and Gas (a subsidiary of CRA) renewed anomaly, 8 km to the east of the Sandover Highway. In the exploration activity in the southern Georgina Basin nal interpretation of CRA, the microdiamonds were not during 1988-1991 and took up permits over the Dulcie considered signi cant and the chromites were regarded as and Toko Synclines. During this period, the company exotic (Bubner 1987, 1988). acquired 675 line km of seismic data, although none was Cratonised rocks, similar to those in the eastern Siberian in SANDOVER RIVER, and drilled eight exploration/ Platform, might underlie part of the Georgina Basin and this stratigraphic wells. One of these wells, Ross 1 (Kress 1992), has led to a resurgence in diamond exploration. The model is was located in southwestern SANDOVER RIVER. Ross 1 based on the inferred Altjawarra Domain (sensu Myers et al was drilled to test a photogeologically de ned four-way dip 1996), a region of thickened, stable crust with relatively low closure and yielded some hydrocarbon shows (bitumen or heat ow and low crustal temperatures believed to underlie asphalt, live oil, oil stains and bleeds, methane and ethane much of TOBERMORY, SANDOVER RIVER and eastern gas) below 250 m depth, in the lower Arrinthrunga Formation HUCKITTA (Elkedra 2001, Teasdale and Pryer 2002). Any and older units. The Thorntonia Limestone was identi ed diamondiferous kimberlite pipes younger than 500 Ma would as a prospective reservoir in this drillhole. Overall, pyritic- be preserved in the overlying Georgina Basin sedimentary carbonaceous black shale in the basal Arthur Creek Formation cover. As of March 2002, over 90% of SANDOVER RIVER was identified as a world class source rock during this was under Exploration Licence application by De Beers and exploration phase. Total organic carbon (TOC) contents were Elkedra Diamonds. found to be in the range 0.5-16%, but were more commonly Figure 26 shows the distribution of diamond indicator up to 10%. For Ross 1, the maximum determined TOC of minerals and microdiamonds in SANDOVER RIVER. 5.15% was from this black shale interval. Altogether, Middle Cambrian sediments in the southern Copper-lead-zinc Georgina Basin are marginally mature to overmature for oil generation, with maturity increasing southward. Western Systematic base metal exploration in SANDOVER RIVER SANDOVER RIVER is thus in the oil generation window, began in the early 1970s after minor occurrences were but the eastern portion is only marginally mature to immature detected during water bore drilling. ‘Detrital Cu’ and ‘other (Questa 1994: 74, Ambrose et al 2001). Forty billion tonnes metallic minerals’ were noted within limestone at 24 m, 40 m of oil were estimated to have been generated from Cambrian and 120 m depth in Tolly Bore to the east of Argadargada sedimentary rocks in the southern Georgina Basin (SIBGEO homestead (Aberlour 1971). Alliance Petroleum Mulga 1 1992). Potential reservoirs are in the Coolibah Formation, drillhole intersected several intervals of anomalous Pb Kelly Creek Formation, Arrinthrunga Formation, Chabalowe including 0.26% Pb at 104 m (Uttley 1973, Nenke 1977a). Formation (including Hagen Member), Steamboat Sandstone, These anomalies, in what was then known as the Meeta upper Arthur Creek Formation, Thorntonia Limestone and beds (now Arrinthrunga Formation), were followed up by Mount Baldwin Formation (Questa 1994). Most porosity Aquitaine Australia Petroleum. Several limonite samples in the carbonate rocks is due to secondary dissolution and that were thought to be pseudomorphs of galena were dolomitisation. Of greatest relevance to SANDOVER collected from outcrop 8 km to the east-southeast of Mulga 1. RIVER is the stratigraphic juxtaposition of reservoir and Ten traverses, containing 400 augered soil samples from source-seal in the succession from black shale-bearing structural targets, were analysed for Pb and Zn only. Pb medial Thorntonia Limestone, to porous and vuggy upper values were typically 10-25 ppm but ranged up to 300 ppm. Thorntonia Limestone, to basal Arthur Creek Formation The highest Zn, up to 400 ppm, was coincident with elevated black shale. Also relevant is a potential vuggy dolostone Pb. These anomalous samples, from a small area 2.5 km to

24 136°30' 21°00'

HIGHWAY Milne

Cr SANDOVER

Figure 26 Locations of microdiamonds and diamond indicator minerals in SANDOVER RIVER, overlaid on aeromagnetic image the southwest of Mulga 1, were not considered worthy of and soil sampling programs from the lease failed to locate further work (Uttley 1973). any signs of economic mineralisation (Nenke 1977a). Work CRAE targeted several areas in the Georgina Basin for in east-central SANDOVER RIVER consisted of a rock Mississippi Valley-type (MVT) mineralisation based on chip traverse over the Ninmaroo Formation from Bulgera geological similarities with the Turkey Creek/Box Hole Waterhole to Bathurst No 1 Bore. Maximum values obtained prospect in HUCKITTA. The area from Mt Hogarth to the were 8 ppm Cu, 36 ppm Pb and 13 ppm Zn (Nenke 1977b). southwestern corner of the sheet was considered to be the most prospective in SANDOVER RIVER. Analyses of Groundwater BMR aeromagnetic, reconnaissance soil, stream, rock and bore water sampling data over the Tomahawk and Ninmaroo Groundwater constitutes the primary water source for Formations in this area failed to detect any significant pastoral properties in SANDOVER RIVER. Within the anomalies (Tham 1971). mapsheet, 178 bores (including stratigraphic and exploration During the mid-1970s, Carpentaria Exploration undertook drillholes) have been drilled, predominantly on clay-rich soil a regional search for MVT mineralisation in the southeastern plains in the central and eastern sheet area. Standing water Georgina Basin. This included a follow-up of the Aquitaine levels are in the range 29-122 m depth, total dissolved solids work and reconnaissance sampling in southeastern and 460-7100 mgL-1 and yields up to 18 Ls-1 (Read 2002). Bore east-central SANDOVER RIVER. Anomalous soil samples yields are low overall, with median yield 2.2 Ls-1; 21 bores that were identi ed by Aquitaine were found to correspond have yields exceeding 4 Ls-1. Variation in bore yields re ects to ferruginous quartz grits and limonite-rich material, permeability variation as determined by the development of and are almost certainly related to a weathering surface. solution joints in these carbonate aquifers. Only 21 bores yield -1 Stream sediment and soil sampling traverses con rmed over potable water, ie with total dissolved solids <1 000 mgL , NO3 300 ppm Pb but this was accompanied by 17.9% Fe and <45 mgL-1 and F <1.5 mgL-1. Nevertheless, supplies suitable 4500 ppm Mn. Corresponding chips of fresh rock yielded only for stock (ie with total dissolved solids <5 000 mgL-1) are 91 ppm Pb and 82 ppm Zn, leading Carpentaria Exploration widely available. to conclude that the anomaly was due to scavenging. The The most extensively used aquifer is within the possible pseudomorphs of galena could not be relocated. Arrinthrunga Formation. A minority of bores in the southeast Highly ferruginous rock chips from the area contained appear to draw stock supplies from the Ninmaroo Formation. 121 ppm Pb and 712 ppm Zn and this was also attributed In both units, dolostone aquifers yield water relatively to lateritic concentration. Other reconnaissance rock chip high in magnesium. Bores in the southwest, collared in

25 the Tomahawk Formation, appear to be completed in the Bubner GJ, 1988. EL4608 Blenheim Hill, NT. Final report, underlying Arrinthrunga Formation. period ending 12th October 1987. CRA Exploration Pty Ltd. Northern Territory Geological Survey, Open ACKNOWLEDGMENTS File Company Report CR1987-0300.

Greg Ambrose (NTGS, Darwin) advised on aspects of Bureau of Meteorology, 1988. Climatic atlas of Australia. petroleum geology and downhole geophysical logging. The Reprint edition. Commonwealth Government Printer, authors thank local landholders for support and access to Canberra. their properties. Chris Field, Jim Allan and Steen Rosenberg- Nielsen assisted in the eld, with the able base support of Casey JN, 1959. New names in Queensland stratigraphy Martin Cardona. Figures were prepared by Richard Jong (part 5). Australian Oil and Gas Journal 5 (12), and Gary Andrews. The manuscript was formatted by Kirsi 31-36. Rahikainen. Casey JN and Gilbert-Tomlinson J, 1956. Cambrian REFERENCES geology of the Huckitta-Marqua region, Northern Territory. XX International Geological Congress, Aberlour, 1971. Progress exploration report–Georgina Basin Mexico 2, 55-74. [Reprinted 1957 Bureau of Mineral PA3085 Mt Hogarth South NT. Northern Territory Resources, Australia, Bulletin 49, 55-74]. Geological Survey, Open File Company Report CR1971-0080. Cooper RA, Nowlan GS and Williams SH, 2001. Global Stratotype Section and Point for base of the Allnutt S, 1986. Final report for the period to 30th July, ELs Ordovician System. Episodes 24, 19-28. 4612-4617, 4625-4627. CRA Exploration Pty Ltd. Northern Territory Geological Survey, Open File Donnellan N and Johnstone AL, in prep. Interpreted geology Company Report CR1986-0288. of the Tennant Inlier (1:500 000-scale geological special map). Northern Territory Geological Survey, Allnutt SL and Bubner GJ, 1985. Annual report for year Darwin. ending 2nd September 1985. CRA Exploration Pty Ltd. Northern Territory Geological Survey, Open Donnelly TH, Shergold JH and Southgate PN, 1988. File Company Report CR1985-0285. Anomalous geochemical signals from phosphatic Middle Cambrian rocks in the southern Georgina Ambrose GJ, Kruse PD and Putnam PE, 2001. Geology Basin, Australia. Sedimentology 35, 549-570. and hydrocarbon potential of the southern Georgina Basin, Australia. APPEA Journal 41, 139-163. Draper JJ, 2000. Petroleum supersystems in Queensland: a key to undiscovered petroleum resources. Queensland Amuedo CL, 1963. Photogeologic evaluation report of Oil and Gas July 2000, 42-47. Permit to Prospect for Petroleum 53, Northern Territory. Doeringsfeld, Amuedo and Ivey, Consulting Druce EC, 1974. Georgina Basin project 1974-1980: a Geologists for Australian Oil Corporation proposal. Bureau of Mineral Resources, Australia, (unpublished). Record 1974/44.

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28 Radke BM, 1981. Lithostratigraphy of the Ninmaroo Shergold JH, 1995. Timescales 1. Cambrian. Australian Formation (Upper Cambrian-Lower Ordovician), Phanerozoic timescales, biostratigraphic charts Georgina Basin, Queensland and Northern Territory. and explanatory notes. Second series. Australian Bureau of Mineral Resources, Australia, Report 181; Geological Survey Organisation, Record 1995/30. BMR Microform MF153. Shergold JH and Druce EC, 1980. Upper Proterozoic and Radke BM, 1982. Late diagenetic history of the Ninmaroo Lower Palaeozoic rocks of the Georgina Basin: in Formation (Cambro-Ordovician), Georgina Basin, Henderson RA and Stephenson PJ (editors) The Queensland and Northern Territory. BMR Journal of geology and geophysics of northeastern Australia. Australian Geology and Geophysics 7, 231-254. Geological Society of Australia, Queensland Division, Brisbane, 149-174. Radke BM and Duff P, 1980. A potential dolostone reservoir in the Georgina Basin: the Lower Ordovician Kelly Shergold JH, Jago JB, Cooper RA and Laurie JR, 1985. The Creek Formation. BMR Journal of Australian Cambrian system in Australia, Antarctica and New Geology and Geophysics 5, 160-163. Zealand. International Union of Geological Sciences, Publication 19. Read RE, 2002. Sandover River sheet, groundwater occurrence. Natural Systems Division, Northern Shergold JH and Nicoll RS, 1992. Revised Cambrian- Territory Department of Infrastructure, Planning and Ordovician boundary biostratigraphy, Black Environment, unpublished report 16/2002. Mountain, western Queensland: in Webby BD and Laurie JR (editors) Global perspectives on Ordovician Runnegar B, Pojeta J Jr, Taylor ME and Collins D, 1979. geology. Balkema, Rotterdam, 81-92. New species of the Cambrian and Ordovician chitons Matthevia and Chelodes from Wisconsin Shergold JH and Southgate PN, 1986. Middle Cambrian and Queensland: evidence for the early history of phosphatic and calcareous lithofacies along the polyplacophoran mollusks. Journal of Paleontology eastern margin of the Georgina Basin, western 53, 1374-1394. Queensland. Australasian Sedimentologists Group Field Guide Series 2. Geological Society of Australia, Schmitt M and Southgate PN, 1982. A phosphatic Sydney. stromatolite (Ilicta cf. composita Sidorov) from the Middle Cambrian, northern Australia. Alcheringa 6, SIBGEO, 1992. Provision of engineering type work for the 175-183. determination of the quality and maturity of source rocks in the Georgina Basin (4 volumes). Siberian Scrimgeour I and Raith JG, 2001. Tectonic and thermal Branch, USSR Academy of Sciences for Paci c events in the northeastern Arunta Province. Northern Oil and Gas Pty Ltd. Northern Territory Geological Territory Geological Survey, Report 12. Survey, Open File Petroleum Report PR1993-0002.

Seilacher A, 1964. Biogenic sedimentary structures: in Smith KG, 1964. Progress report on the geology of the Imbrie J and Newell ND (editors) Approaches to Huckitta 1:250,000 sheet, Northern Territory. Bureau palaeoecology. John Wiley, New York, 296-316. of Mineral Resources, Australia, Report 67.

Shergold JH, 1975a. Late Cambrian and Early Ordovician Smith KG, 1972. Stratigraphy of the Georgina Basin. Bureau trilobites from the Burke River Structural Belt, of Mineral Resources, Australia, Bulletin 111. western Queensland, Australia. Bureau of Mineral Resources, Australia, Bulletin 153. Southgate PN, 1986. The Gowers Formation and Bronco Stromatolith Bed, two new stratigraphic units in the Shergold JH, 1975b. Biostratigraphical synopsis: eastern Undilla portion of the Georgina Basin. Queensland Georgina Basin. Bureau of Mineral Resources, Government Mining Journal, October, 407-411. Australia, Record 1975/69. Southgate PN and Shergold JH, 1991. Application of Shergold JH, 1981. Palaeontological determinations of sequence stratigraphic concepts to Middle Cambrian phosphatic samples from the Undilla and Riversleigh phosphogenesis, Georgina Basin, Australia. BMR 1:100 000 sheet areas, Georgina Basin. Bureau of Journal of Australian Geology and Geophysics 12, Mineral Resources, Australia, Professional Opinion 119-144. 1981/21. Stewart HWJ and Hoyling N, 1963. Morstone No 1. Authority Shergold JH, 1985. Notes to accompany the Hay River- to Prospect 79 P – Queensland well completion Mount Whelan Special 1:250 000 geological report. Amalgamated Petroleum Exploration Pty Ltd. sheet, southern Georgina Basin. Bureau of Mineral Queensland Department of Natural Resources and Resources, Australia, Report 251. Mines, Open File Company Report 1173.

29 Stidolph PA, Bagas L, Donnellan N, Walley AM, Morris Wentworth CK, 1922. A scale of grade and class terms for DG and Simons B, 1988. Elkedra, Northern clastic sediments. Journal of Geology 30, 377-392. Territory. 1:250 000 geological map series explanatory notes, SF53-7. Northern Territory Weste G, 1989. Hacking No 1 well completion report, EP 12, Geological Survey, Darwin. Georgina Basin, NT. Paci c Oil and Gas Pty Ltd. Northern Territory Geological Survey, Open File Teasdale J and Pryer LL, 2002. Georgina SEEBASE and Petroleum Report PR1988-0079. GIS. SRK Consulting Services report to Northern Territory Geological Survey. Northern Territory Whitehouse FW, 1931. Palaeontologist: in Annual report Geological Survey Record 2002-0004. of the Under Secretary for Mines to the Honourable EA Atherton, MLA, Secretary for Mines, including Tham GHP, 1971. Lead/zinc search – Mt Hogarth the reports of the Wardens, Inspectors of Mines, Authority to Prospect 3183, NT. CRA Exploration. Government Geologists, and other ofﬁ cers, for the year Northern Territory Geological Survey, Open File 1930. Government Printer, Brisbane, 141-142. Company Report 1971-0021. Whitehouse FW, 1936. The Cambrian faunas of north- Uttley P, 1973. Exploration licence 758 Sandover eastern Australia. Part 1: Stratigraphical outline. Part River. Annual report (for the year ending 20th 2: Trilobita (Miomera). Memoirs of the Queensland November, 1973) and nal report. Aquitaine Museum 11, 59-112. Australia Minerals Pty Ltd. Northern Territory Geological Survey, Open File Company Report Whitehouse FW, 1939. The Cambrian faunas of northeastern CR1974-0008. Australia. Part 3: the polymerid trilobites (with supplement No 1). Memoirs of the Queensland Wakelin-King GA, 1992. Randall No 1 EP10, Museum 11, 179-282. Northern Territory well completion report. Paci c Oil and Gas Pty Ltd. Northern Territory Whitehouse FW, 1940. Studies in the late geological history Geological Survey, Open File Petroleum Report of Queensland. University of Queensland, Department PR1992-0025. of Geology, Paper 2 (1).

Walter MR, 1980. Adelaidean and Early Cambrian Whitehouse FW, 1941. The Cambrian faunas of northeastern stratigraphy of the southwestern Georgina Basin: Australia. Part 4 – Early Cambrian echinoderms correlation chart and explanatory notes. Bureau similar to the larval forms of Recent forms. Memoirs of Mineral Resources, Australia, Report 214; of the Queensland Museum 12, 1-28. BMR Microform MF92. Wilson RB, 1963. The geology and oil prospects of OP63, Walter MR, Shergold JH, Muir MD and Kruse PD, Northern Territory. Alliance Petroleum Australia. 1979. Early Cambrian and latest Proterozoic Northern Territory Geological Survey, Open File stratigraphy, Desert Syncline, southern Georgina Petroleum Report 1963-0015. Basin. Journal of the Geological Society of Australia 26, 305-312. Winnecke C, 1882. Herbert River and north-eastern exploring expedition. South Australian Parliamentary Wells R, Milsom JS and Tipper DB, 1966. Georgina Paper 121. Basin aeromagnetic survey, Queensland and Northern Territory 1963-1964. Bureau of Mineral Wright VP, 1992. A revised classi cation of limestones. Resources, Australia, Record 1966/142. Sedimentary Geology 76, 177-185.

rwin.

ness, 6° 30'E 6° urable 139° 30' cember r the loss

21° 00' 22° 00' 6° 15'E 6° 138° 00' 138° 00' Sandover River, Czb SF 54-09 SF 54-05 SF 54-01 MOUNT ISA URANDANGI GLENORMISTON Sandover River, Northern Sandover River,

B 21° 00' 22° 00' 138° 00' 138° 00' 00'E 6° 138° 00' 6454 6455 Plain Barry Georgina d Ot -- C 6355 6354 Milne Creek Gordon Highway Secondary road Vehicular track Landing ground Homestead Building Yard Fence Mountain / hill Bore Water tank / earth dam Waterhole Territory and state border SF 53-12

SF 53-04

s s 45'E 5° Northern Territory Geological Survey, Darwin. AVON DOWNS TOBERMOREY On ua -- -- C C A Development WARNING: Colours will fade with prolonged exposure to light. Territory 6254 6255 Argad- Northern argada A Detailed mapping B Airphoto interpretation SANDOVER RIVER SF 53-08 Carbeen Northern Territory Geological Survey, Darwin. MAGNETIC DECLINATION Industry and Resource Department of Business, Government RELIABILITY DIAGRAM 136° 30' SCARR HILL map. Information is current for 1997.

INDEX TO ADJOINING MAPS 5° 30'E 5° TOPOGRAPHICAL SYMBOLS B SF 53-07 SF 53-03 SF 53-11 ELKEDRA HUCKITTA FREW RIVER 136° 30' 136° 30' Blue lines show magnetic declination for epoch 1995 derived from

AGRF model. Annual change is 10.8" per year easterly at the centre of 22° 00' 21° 00' 5° 15'E 5° SHEET SF 53-08 SECOND EDITION 2003 Northern Territory Geological Survey 135° 00' 23° 00' 22° 00' 20° 00' 21° 00' ua SANDOVER RIVER -- C PD Kruse, LC Mohammed, NTGS PD Kruse, LC Mohammed, NTGS ML Duffett, NTGS J Christie, GK Andrews, IM Burgan, NTGS J Christie, IM Burgan, NTGS KG Smith, EN Milligan, RAH Nichols, WH Morton, BMR (now GA) C NORTHERN TERRITORY GOVERNMENT 2003 O Alluvium: sand, minor gravel, silt and clay Claypans, sheetwash: silt, clay Unconsolidated colluvial sand, minor silt Grey-black clay-rich soil Talus of silicified dolostone and quartz sandstone pebbles cobbles in Ferricrete, manganocrete Regolith, skeletal shallow soils on bedrock Limestone: cherty and chalcedonic Quartzose and glauconitic sandstone, minor dolostone ( ), limestone, dolomitic quartz sandstone and conglomerate Dolostone, limestone, minor quartz sandstone ( ) Dolostone, limestone, minor quartz sandstone ( ), siltstone, shale, marl and conglomerate Quartz sandstone, dolomitic, with siltstone and dolostone interbeds (schematic section only) Dolostone with gypsum beds, chert; minor claystone and fine sandstone interbeds (schematic section only) Quartzose and calcareous/dolomitic quartz sandstone, quartzic dolostone (subsurface in Mulga1) Upper: dolostone, limestone. Lower: foetid pyritic-carbonaceous black shale, laminated dolostone (schematic section only) Dolostone, limestone; medial pyritic-carbonaceous black shale interbeds; basal terrigenous sandstone (schematic section only) Dark green-grey metaandesite or metabasic rock (subsurface in Ross1) Richard Brescianini, Director, Northern Territory Geological Survey Ot On ua mc mh ms ma mt lv ------Qa Qp Czb Czc Cz Czs Czf Cza C C C C C C C C L P 2001 2001 2003 2003 2003 1963 lv ua mt SCALE 1:1 000 On ms L P ma ------Cza C C C C C 1 ELEVATION IMAGE 5 6 Czf 4 Grid of Elevation with illumination from north. QS4651 QS 0 53KQS4651 Qp Ninmaroo Formation Sandstone Steamboat ALICE SPRINGS NORTHERN 10 10 20 30 40 50 km TERRITORY DARWIN MAP LOCALITY Czc SCARR HILL s Geology: Compiled: Geophysical Interpretation: Design: Digital Cartography: First Edition Mapping: On caused by, or arising from reliance upon information provided herein. The information presented on this map is current to 19 De 19 current to information arising from reliance upon is information map provided herein. The or this presented caused by, on 2003. Future modifications may be made as new information becomes available. Produced demand and plot on by, created the Northern by, Territory Geological Survey, Cartographic Services, Department of Busi Hono Energy, the Mines and Minister for Resource the Development, Industry and authority of Darwin, Australia. the Issued under KONSTANTINE (KON) VATSKALIS, MLA. topographic LANDSAT NTGS Base map compiled National satellite 000 and from imagery data Mapping the 1:250 by supplied 7 by Division, Geoscience Australia, Department of Industry, Tourism and Resources. accompanied This map is text publication: a by Kruse PD, Mohammed Dunster and Duffett LC, JN ML, 2002. It is recommended that this map be referred to as: Kruse PD, Mohammed LC, Dunster JN and Duffett ML, 2003. MicroStation MapInfo and formats. in files digital and plots hardcopy as NTGS obtained from be can data Map DIGITAL DATA: Da Building, Centrepoint floor 3rd Counter, Sales NTGS from available are costs and conditions, release formats, Information on Phone (08) 8999 6443, or visit the NTGS web site at www.dbird.nt.gov.au/ntgs. The Northern Territory Government definitive, warrant map as does not free from accept this nor liability fo does not error and Territory (Second Edition). 1:250 000 geological map series explanatory notes, SF 53-08. Northern Territory (Second Edition). 1:250 000 geological map series, SF 53-08. -- C Cz d mc Ot -- -- C C Limestone TO GIVE A STANDARD REFERENCE ON THIS SHEET TO NEAREST 1000 METRES Austral Downs Czb Metavolcanic rock mh -- Thorntonia Limestone C Read letters identifying 100 000 metre square in which the point lies: Locate first VERTICAL grid line to LEFT of point and read LARGE figures labelling the line either in top or bottom margin, or on the line itself: Estimate tenths from grid line to point: Locate first HORIZONTAL grid line BELOW point and read LARGE figures labelling the line in either left or right margin, or on the line itself: Estimate tenths from grid line to point: If reporting beyond 9° N-S or 18° E-W prefix Grid Zone Designation, as: SAMPLE POINT: SAMPLE REFERENCE: Arrinthrunga Formation Arthur Creek Formation 1 2 3 4 5 Geological boundary Strike and dip of strata Trend line Lineament Joint Macrofossil locality Stromatolite locality Ichnofossil locality Drillhole with reference number (pa-position approximate) Qa s RR LITHOSTRATIGRAPHIC LEGEND LITHOLOGY 0 ua 8 -- Formation C Tomahawk Ross 1 20 Czs d UNIVERSAL GRID REFERENCE 0 000 mE Chabalowe Formation Ot 6 Ot -- 53K -- C 6 Hagen Member C Zone 53. Grid values are Zone 53. shown full at in southwest only the GEOLOGICAL SYMBOLS 0 7 100 000 METRE 136° 30' 136° 30' PS QS RS PR QR 21° 00' 22° 00' 0

SQUARE IDENTIFICATION 76

IGNORE the SMALLER figures of any grid number; these are for finding the full co-ordinates. Use ONLY the LARGER figures of the grid number; example: GRID ZONE DESIGNATION: Blue numbered lines 000 10 are metre intervals of the Map Australia, corner of the map. IDEUPPER MIDDLE

AND LOWER CAMBRIAN NEOGENE 21° 00' 22° 00' ORDOVICIAN

PALAEOGENE QUATERNARY

138° 00' 138° 00' AAOOCCENOZOIC PALAEOZOIC PALAEOPROTEROZOIC 7 6 21°00' 5 7 6 30' 4 GEOLOGICAL LEGEND 10' 7 6 3 (schematic section only) 7 6 2 20' South Nicholson Group Hatches Creek Group and correlatives Warramunga Formation correlatives Granite Granite I-type (magnetic) granite Intrusion of intermediate composition Undifferentiated Proterozoic 7 6 1 7 6 0 7 6 9 138°00' 7 6 40' 8 7 6 7 7 5

RIVER 50' Cza 7 5 3 2 1 Qp 22°00' 7 5

Czb Creek 1 g g g lm , 8 L L L L Ll L9 T5-D6 T4 P P P P P NOTE All basement bodies on the section with exception of T, D, L prefixed units are interpreted only. Apart from these specified units, no timing relationships should be inferred from their order in the legend, which is entirely arbitrary. T, D, L prefixed units refer to Ahmad M, 2002, Geological Map of the Northern Territory, 1:2 500 000, Northern Territory Geological Survey. Cza ua Cza,Czb -- C ua 138°00' -- Qp Qa

C ua Cr GEORGINA -- C , No. 7 Bore Cza ,

RIVER Cza,Czb Czb Czs B Cza,Czb On ua Gordons Dam -- -- 3 Qp C C No. 10 Bore Lg P On

-- Moonta Speechley Bore C ua Czb On G 16 Bore BARKLY TABLELAND -- Speechley Dam Cz -- C C Qp No. 5 Dam Cz Cza Cza,Czb Creek ua G49 Bore --

Bull C Cz Coolibah Waterhole Cza G 17 Bore

No. 16 Dam Shank INCREASE Eastings by 126 metres. Patricks Dam

Creek INCREASE Northings by 169 metres. Czb Czs No. 4 Dam DECREASE Latitude by 5.29 seconds. G15 Bore INCREASE Longitude by 4.32 seconds. Cza Scotty Bore On -- ,Czs SHEET SF 53-08 Czs C Czs On --

WOODROFFE Creek C Cza,Czb Czc, G 24 Bore Lignum Hole Dam SCALE 1:1 000 0 0 HIGHWAY 8 8 LANDSAT IMAGE SANDOVER To convert from AGD66 to this map's coordinate system, GDA: On Qa -- G 19 Bore

ua C Cza -- Creek Czs C Cza,Czb ua Dam 15 Cza,Czb -- Cz Cza C Mac Dam G 36 Bore Cza 0

G 29 Bore G 21 Bore Creek Cza No. 29 Bore No. 37 Bore Czc Elditta Waterhole Cza,Czb Bull Creek Dam 10 10 20 30 40 50 km Abadabada 50'

ua OR Red Dam -- ,Czs Stoney Dam Cz

C Cza Cza,Czb Beantree Bore Wanda On Cinder Dam -- C Tyre Dam No. 4 Bore Qa 50' Waterhole ua G 18 Bore

-- G 28 Bore Mudgeegoolla C Cza,Czb No. 11 Bore

No. 31 Bore On No. 36 No. No. 19 Dam (Abd.) -- Cza,Czb C Cza,Czb Stan Bore No. 18 Dam (Abd.) 9 9 7 7 On --

C No. 26 Bore CREEK Czc ,Czs On On -- --

Creek C C ua Qa -- Qa C

Creek No. 30 Bore G 27 Bore No. 7 Dam G 23 Bore ,Czs Czs G 11 Bore Landsat (R,G,B = bands 7,4,2) image excerpt from Australian mosaic produced by ER Mapper and obtainable www.earthetc.com Charcoal Bore Czb On -- BARRY PLAIN

G33 Bore Chelcheta C Qa , Czs Creek Bybby On ua -- Qa Cz -- Cza Czs ,Czs C C Bloodwood Dam On 136° 30' 136° 30'

GORDON -- C Czc Piker Dam Mountain Dam 21° 00' 22° 00' Mudgeegoola Waterhole Winnecke Bore

B , Creek No. 28 Dam ua , ua -- -- Coolibah Dam Qp C C L9 Cza Czs 8 8 Cza Czs 7 7 s Qa Qp On

21° 00' 22° 00' On Creek C G43 Bore Czs -- C Qp 138° 00' 138° 00' Dam

T5-D6

Winnecke Waterhole

Creek Czs 40' Rocky

Qa Qa

Abadabada Bore -280 Abadabada -160 No. 18 Bore ,Czs Waterhole Creek -160 G 20 Bore On Mickey Mouse -- On ,Czs

C -- -200 40' Georgina Downs

C No. 2 Bathurst Bore -240 On On -- -- C Dam C Czs Czs HIGHWAY Quarry Dam

Mulga 1 Czb -280

No6 W.H. ua On

Gordon Yard

-- -- Dam -240 On Qa Ode Bore (Abandoned) Bloodwood G 4 Bore (Government) C C -- Manners C No. 32 Bore Qa s

No. 3 Bore Creek ua Qa On -- Cz -- ,Czs C C

ua Bybby --

No. 2 On C -- Czb On C , -- C Czc Creek Qp Dam C ua 7 7 -- G34 Bore 7 7 C

Dam F Czc Creek s Mountain Waterhole

No. 1 On No. 15 Bore -- C Dam D ,Czs Qp ua -- No. 8 Dam C On Dam U/S --

C Bull On

-3 -2 On

-- -160 -80

-240 -200 -360 C

SANDOVER On -280 -- -240 C -120 Qp

ua Czs -360 -- -320 Dinner Camp Dam Czc Czs C No. 9 Dam Whinjin Bore Czs Winkerty Dam Bubbleaner Waterhole No. 4 Dam No. 1 Bore Boulder Dam Qa -80

No. 4 Bore -240 -280 Waggon Hole Bore On

C Creek -240 Smoko Dam Qa On No. 1 Bathurst Bore -- Mussel Waterhole C No. 8 Bore 6 6 On Czc 7 7 -- Qa 30' C ua --

C Czs Southern 30' Dam G Dam F Kamikaze Dam No. 10 Bore s -120 SCALE 1:1 000 s Czs On Cz No. 19 Bore -- GRAVITY IMAGE Qp Pelican C Qp On On On -- -- ua -- ,Czs Qp

C -360 -- C C Waterhole C On ua ,Czs ua -- No. 27 Bore -- -- C C C s On On On -- Cz -- Stokes Dam -- C C No. 13 Bore C

Cz -280

-- No 20 Dam (abd) CREEK C Czb

-- -320 Czc River On C -- Creek C ua No. 4 Bathurst Tank -- On C -- Ot Czs --

Creek C Cz No. 9 Bore C , 10 10 20 30 40 50 km Lily Dam Ot -- Qp

Czs Czb Duck 5 5 7 -320 7 On -- Ot Qp C -- -240 Ot C -- s Ot

No. 2 Bore C

-- -160 BYBBY (Abandoned) C On On -- Bulgera Waterhole ua -- C

-- Qp

C -280

On C -- Woodroffe

C -160 Qa Ot On Stockman Waterhole On -- -- Qp On -- C C -- SCARR HILL ,Czs C C Qp Ot

-- -200 On No. 26 Bore C , --

,Czs

C -160

No. 9 Bore or No. 19 Bore or No. 5 Bore Peter Waterhole

Rabbit Waterhole Imbordjudu

Czs Czb On

Pseudocolour image of Bouguer gravity calculated with reference density 2.67 tm , contour interval 40µm.s . -- Sandy Dam -200

Czc Creek C On -280 ,Czs Qp -- Czs C Ot ,Czs On -- -- C C

On T4 --

-- -320

Qa Gordon C

C No. 5 Dam Creek BMR GRG 14 pa G39 Bore ,Czs 20' ua -240 G 3 Bore (Government) -- (Abandoned)

C -280

Czs Ot

-- Creek Bybby

Czc -- C -360 C -160 -120 On -- , C Kings Waterhole Ot On Ot On -- 20' No. 34 Bore -- -- No. 13 Bore -- C G 5 Bore (Government) C C C Never Fail Dam Czs Czb 4 4 7 Czc 7 On -- C s ua -- On Rankin Waterhole C -- 136° 30' 136° 30' Cz On C -- C Ot , -- 21° 00' 22° 00' Czb C Milne Dam On -- Czs Czb C , , On -- Heifer Dam Qa C Czs Czb ,Czs Czs Czb Ot -- G40 Bore C

21° 00' 22° 00'

,Czs , No. 22 Bore Stokes No. 25 Bore On Czs Ot Czs Czb -- -- C 138° 00' 138° 00' C ua -- No. 27 Dam (Abandoned) C Qp Ot Ot On ------Meeta Bore C C Czs C Ot Ot Ot -- -- No. 1 Bore -- ,Czs C C ,Czs C 2 On G 1 Bore (Government) Ot -- G 26 Bore Ot -- C No. 6 Bore Ot -- Scale : V/H = 5 C -- Lg P C C On -- On Czc Ocean Dam C -- C No. 11 Bore , 3 3 7 7 SCALE 1:250 000 Czs Czb ua No. 21 Dam Ot -- Ot -- -- C U C C Ot SCHEMATIC SECTION AB Czs

, Creek C Qa Czs ua ua Czs Qa -- -- ua C G 25 Bore C -- Cz Czf C ,Czs Mulga Dam ua K -- No. 24 Bore Ot ua MAP GRID OF AUSTRALIA 1994 (MGA94) C -- On Qp ua 50 -- C -- -- C C C ,Czs Ot Czb -- NORTHERN TERRITORY C Ot On -- -- , Qp C C 10' GEOCENTRIC DATUM OF AUSTRALIA 1994 (GDA94) Czs Czb Th Top Waterhole (No. 1 Dam) Ot Czc -- Junction Dam C SANDOVER RIVER Yellow Hole Dam 10' No. 3 Dam On Sandover Dam -- Czf Hidden Dam C CULLEN LOOKOUT UNIVERSAL TRANSVERSE MERCATOR PROJECTION, ZONE 53 On On G 9 Bore -- --

C C Ot Bybby -- No. 20 Bore Cz Czb Ot C -- Qp C Czs Czb Sandy Dam On Ot Ot ------C Y. Waterhole C C (Abandoned) Qa Ot Czf -- FLOODOUT Czf C 2 2 7 7 ua -- Ot C -- Cz ,Czs On C -- Qa C Qp No. 16 Bore On No. 21 Bore Qp -- On -- C 5 0 5 10 15 20 25 Kilometres C Ot Ot -- -- C Ot , ua C -- ,Czs -- Cz Sahara Dam C C ua Ot Czs Czb Qa -- -- ,Czs Ot C , C BLENHEIM HILL Towners Best -- RIVER Ot C Ot -- On ,Czs -- Ot -- C On -- C Czs Czb C ua -- Ot No. 2 Dam ,Czs C -- -- , C On Cz Cz Czf, C C -- ,Czf Ot C -- No. 23 Bore C Czs Czb G38 Bore Ot --

C G 2 Bore (Government) (Abandoned) area No. 10 Bore ua SCALE 1:1 000 -- Cz ? C Qp ua Cz -- (Abandoned) No. 11 Bore C Czs On , RADIOMETRIC IMAGE Czs -- On Ot , ,Czs -- -- C ua , ua ua C Qp C -- ua -- -- ua Ot No. 18 Bore Abd. -- Czs C C C -- Ot spinifex No. 17 Bore -- SANDOVER ua C No. 12 A Bore -- C -- C Qa C Czs Czb ,Czs C 1 1 7 7 0 Ot Ot -- -- C Qp ,Czs Qa C Qp

-- of HIGHWAY C Ot -- Ll P C Ot Czb Qa -- Cz C 10 10 20 30 40 50 km Czb 137°00' Linear histogram stretch with 99% limits applied to all channels. Qp ,Czs

Czs

, Edge On On Qp -- -- C C 137°00' Czs Czb Czs Qp mt -- ua -- C Qa Cz C ma Czs -- , Qp C Czs , ua -- ua ua C -- -- No. 7 Dam Bilbilba Waterhole (No. 6 Dam) C C Czs ,Czs , ua No. 16 Bore No. 7 Bore Ot ua -- No. 12 Bore -- Cz -- ua C C Ot On Czs C -- -- Ot -- Czs C ua -- C C -- C No. 9 Bore Czs ua C Argadargada Waterhole Czs Czs Qa -- , No. 8 Bore Czs C ua ua -- Cz -- lm C C ua Czs L P -- Czs C 0 0 7 7 Czs , ua On -- ua On Ot -- -- C -- -- Cz Czs Czs C , C C C Czs ua Ot Ot ua -- On -- -- ua -- -- Cz Cz C C C -- C ua

C Ot C On

------SANDOVER Ot MOUNT HOGARTH C C C -- Cz ua ua C -- -- No. 2 Bore C C ua -- ua Cz Czs C (Abandoned) , -- Cz C Webb Dam ua -- ua C -- Cz On C Qa -- C 136° 30' 136° 30' Ot ua -- Czf ua -- ua C -- Cz Czs C ua -- C -- Czs C Cz Ot 21° 00' 22° 00' C -- Ot Czs C -- Metards Bore C Ot -- Czf C ua Ot -- -- Czs C Czs C Qp Czs Cats Eye Dam , , Ot -- ua ua ua C ------C Czs C 21° 00' 22° 00' C , ,Czs Ot Ot Czs -- Ot Ot ua -- ua Ot -- -- ua -- C No. 15 Bore C Ot ------C C C -- C 50' C C C 9 9 138° 00' 138° 00' 6 6 Czb ua 50' Czs -- , C Czs ,Czs ua On ua -- On -- -- Czs -- C C C C On s -- C Toms Bank Bore ua -- C ua -- Tolly Bore ,Czs C ,Czs Czs , On Ot -- -- ua Czs C -- C , Argadargada C No. 11 Bore ua -- ua Czs C No. 13 Bore -- ,Czs Czs , C Ot Czs Ot -- , Ot ua -- Czs C Czs -- -- , On Czs Qa C On , C C Ot -- Cz -- Cz ua -- Czs C C -- , ua C Czs -- ua C -- C ua On C -- -- Cz Ot C C -- Czs Ot , C Desert Plain Bore ua -- -- 16 C Cz C ua 1 -- Czs ua , C g -- On Cz ua Czs C -- Cz L P , s On -- ua C -- Czs C -- Czf s On C 4 C ua -- ua -- Czs A -- C , ua C C -- Czb C 36 ua Ot 8 8 -- -- On 6 6 -- C C Cz C On On ua ------Cz C Czs C C Czs , Czs , 48 On -- ua ua Czf C -- -- C Ot C Czs , -- On Qa Czf -- Cz C Czs C , ua -- Czs Czb C ua -- Czs Czs , , C Carbeen Bore s

-- ua HIGHWAY Ot -- ua C Ot No. 14 Bore Ot ------C -- C C C C ua ua -- -- Ot Czs Cz C Czs -- ,Czs C , Cz Ot Czs C , -- C ua On ua ------C C C Czs ,Czs On Czs Ot -- Cz -- C C Ot On Czs , -- -- ua 40' Czf -- C C Czs C ua Argadargada SANDOVER RIVER -- Czs Ot , C ua -- Czs -- , Cz C C 40' ua s -- C FLOODOUT ua Czs -- , C ua Qa ua ua -- Ot -- -- Ot Czs -- C Cz C C -- 7 C 7 C 6 6 On -- Cz s ua d C -- Czs C SCALE 1:1 000 Ot ua -- Ot -- Cz -- C C ua C MAGNETIC IMAGE -- Qp C Czs On l Czs , -- Cz C L P ,Czs ua Qp ua d -- Czs -- , C 0 Czs C On Ot Ot No. 17 Bore -- ua -- mh -- Czf ua d C Czf -- --

C -- C ua

Czs C C -- C Czs SANDOVER C Ot s s 26 -- Czs C s ua ua Ot Ot -- -- Czs -- -- Czs mc C ua C Czf s -- C C -- Mulga Bore C C Qp Czs , ua 10 10 20 30 40 50 km -- Czs Ot C 8 Qp ua -- ua -- -- C C Czs C No. 17 Bore ua Ot -- -- Cz C C ua Czs ,Czs -- 42 Czs C Total magnetic intensity, reduced to pole, with illumination from 45° azimuth. Ot ua Ot ------ua 38 C C C -- Cz C d Ot No. 10 Bore -- 17 Czf Ot C 6 Ot -- 6 -- C s Czf C 6 ua -- 6 0 000 mE s Czs C A ua ua -- -- Czs Czs C Old Dam C ,Czs Qp ua 0m -- Ot d Ot 22 Czs C -- 32 -- Czf C C Ot Czs , -- Ot Ross 1 1000m 2000m Potato Bore Cz s -- C Ot C d -- d 6 C ua Qp,Qa ua -- ua -- Ot -- Ot C C ua Landerandera Waterhole -- AUSTRALIA 1:250 000 GEOLOGICAL SERIES -- Hughes Bore C -- C East Dam C Czs C 26 16 Qa 7 6 14 5 4 136°30' 3 2 7 6 1 7 6 10' 0 7 6 9 7 6 8 7 6 7 6 30' 7 6 7 6 40' 7 5 21°00' 50' 7 5 136°30' 20' 22°00' 7 7 5 0 000 mN 136° 30' 136° 30' 21° 00' 22° 00'