Geology of the Merrie 1:100 000 sheet - Microsoft...3 GSWA Explanatory Notes Geology of the Merrie...

GEOLOGICAL SURVEY OF WESTERN AUSTRALIA

GEOLOGY OF THEMERRIE1:100 000 SHEET

byN. G. Adamides

Perth 2000

MINISTER FOR MINESThe Hon. Norman Moore, MLC

DIRECTOR GENERALL. C. Ranford

DIRECTOR, GEOLOGICAL SURVEY OF WESTERN AUSTRALIADavid Blight

Copy editor: C. D’Ercole

REFERENCEThe recommended reference for this publication is:ADAMIDES, N. G., 2000, Geology of the Merrie 1:100 000 sheet: Western Australia Geological Survey,

1:100 000 Geological Series Explanatory Notes, 37p.

National Library of Australia Card Number and ISBN 0 7309 6662 3

ISSN 1321–229X

Grid references in this publication refer to the Australian Geodetic Datum 1984 (AGD84)

Printed by Quality Press, Perth, Western Australia

Copies available from:Information CentreDepartment of Minerals and Energy100 Plain StreetEAST PERTH, WESTERN AUSTRALIA 6004Telephone: (08) 9222 3459 Facsimile: (08) 9222 3444

Cover photograph:General view of granite tors in the area 6 km east of the Canning Stock Route (AMG 427317).

iv

Contents

Abstract ................................................................................................................................................................. 1Introduction .......................................................................................................................................................... 1

Location and access ...................................................................................................................................... 1Climate and vegetation ................................................................................................................................. 2Physiography ................................................................................................................................................. 3Previous investigations ................................................................................................................................. 3Stratigraphic nomenclature ........................................................................................................................... 3

Regional geological setting ................................................................................................................................. 6Geochronology ..................................................................................................................................................... 6Archaean geology ................................................................................................................................................ 7

Merrie greenstone belt .................................................................................................................................. 7Ultramafic rocks (Au, Auf ) .................................................................................................................... 7Mafic rocks (Ab, Aba, Abae, Abaf, Abf, Abe, Aby) ............................................................................... 9Metasedimentary rocks (As) .................................................................................................................. 9

Granite (Ag, Agm) ......................................................................................................................................... 9Felsic porphyry and felsic volcaniclastic rocks (Afp, Afs) .................................................................. 13

Structure and metamorphism ...................................................................................................................... 14Proterozoic geology ........................................................................................................................................... 14

Dolerite dykes (#dy) ................................................................................................................................... 14Yerrida Group ............................................................................................................................................. 15

Windplain Subgroup ............................................................................................................................ 15Juderina Formation (#Yj, #Yjf, #Yjs) ............................................................................................ 15

Mooloogool Subgroup ......................................................................................................................... 18Killara Formation (#Yk, #Ykf, #Ykb, #Ykd) ................................................................................. 18Maraloou Formation ..................................................................................................................... 19

Earaheedy Group ......................................................................................................................................... 20Yelma Formation (#Ey, #Eyc, #Eya, #Eys, #Eyo, #Eyw) .................................................................. 20

Sweetwaters Well Member (#Eyw) .............................................................................................. 20Frere Formation (#Ef, #Efg, #Efgz, #Efs, #Efi) .................................................................................. 24Windidda Formation (#Ed) .................................................................................................................. 28

Karri Karri Member (#Edk) .......................................................................................................... 28Chiall Formation (#Ec) ........................................................................................................................ 28

Wandiwarra Member (#Ecw) ....................................................................................................... 28Structure and metamorphism ...................................................................................................................... 28

Cainozoic geology ............................................................................................................................................. 29Geochemistry ..................................................................................................................................................... 30Economic geology .............................................................................................................................................. 30

Gold ............................................................................................................................................................. 30Iron .............................................................................................................................................................. 30Uranium ....................................................................................................................................................... 31Base metals .................................................................................................................................................. 31Groundwater ................................................................................................................................................ 31

References .......................................................................................................................................................... 33

Appendices

1. Gazetteer of localities mentioned in text ................................................................................................. 362. Listing of open-file reports on MERRIE .................................................................................................... 37

Figures

1. Location map .............................................................................................................................................. 22. Physiographic map of MERRIE .................................................................................................................... 43. Saprolitic granite ........................................................................................................................................ 54. Magnetic map and model ........................................................................................................................... 85. High-grade amphibolite ........................................................................................................................... 106. Rock textures from the Merrie greenstone belt ....................................................................................... 117. Lithological features of granite ................................................................................................................ 128. Ternary diagram of granite composition ................................................................................................. 13

v

9. Geological sections through the Juderina Formation .............................................................................. 1610. Sedimentary structures in the Finlayson Member ................................................................................... 1711. Palaeocurrent indicators in the Juderina Formation ................................................................................ 1812. Association of quartz and epidote in dolerite .......................................................................................... 1913. Feldspathic sandstone at the base of the Yelma Formation .................................................................... 2114. Sweetwaters Well Member ...................................................................................................................... 2215. Siltstone and sandstone of the Sweetwaters Well Member ..................................................................... 2316. Geological sections through the Frere Formation ................................................................................... 2517. Textures of jaspery granular iron-formation ........................................................................................... 2618. Siliceous iron-formation .......................................................................................................................... 2719. Folding of siltstones of the Karri Karri Member ..................................................................................... 29

Tables

1. Proterozoic stratigraphy of MERRIE ............................................................................................................ 52. Geochronology data on rock types exposed on MERRIE ............................................................................ 63. Trace-element analyses of samples from MERRIE .................................................................................... 31

1

GSWA Explanatory Notes Geology of the Merrie 1:100 000 sheet

Geology of the Merrie 1:100 000 sheet

by

N. G. Adamides

AbstractMERRIE is located at the junction between the northern extension of the Archaean Eastern GoldfieldsProvince and the Palaeoproterozoic Yerrida and Earaheedy Basins. The Archaean rocks contain apoorly exposed greenstone belt (Merrie greenstone belt) composed of metabasalt, amphibolite, andmetamorphosed felsic volcaniclastic and sedimentary rocks. The greenstone belt is metamorphosed tolower greenschist facies with higher metamorphic grades adjacent to the granite. Three periods ofdeformation have affected the Archaean rocks and resulted in the present synclinal structure of theMerrie greenstone belt. A major linear structure, the Merrie Range Fault, is associated with the thirddeformation event (D3) and is the northerly continuation of the Celia Lineament. The Yerrida Group isunconformable on Archaean basement and represented by shallow-water sandstones and siltstones(Juderina Formation) intruded by sills of the Killara Formation. The Earaheedy Group is unconformableon both the Yerrida Group and Archaean basement, and is represented by clastic sedimentary andchemical rocks of the Yelma, Frere, Windidda, and Chiall Formations. Deformation during the CapricornOrogeny is indicated by the presence of easterly trending structures within the granite and folding ofthe Earaheedy Group rocks. Overprinting of these structures suggests a later (?Bangemall) deformationevent associated with northwest-directed compression. Displacement of rocks of the Earaheedy Groupalong the Merrie Range Fault also suggests late rejuvenation of this structure with a strong sinistraldisplacement. The Yelma Formation contains the Sweetwaters Well Member, which is a dolomitesequence with lead–zinc mineralization. The Frere Formation is predominantly a granular, Superior-type iron-formation, with potential for significant iron ore mineralization. The Windidda Formation(Karri Karri Member) shows, in places, black-shale affinities suggesting the possibility of base metalmineralization.

KEYWORDS: Archaean, Merrie greenstone belt, Palaeoproterozoic, Yerrida Group, Earaheedy Group,mineralization, base metals, iron, gold

Introduction

Location and accessThe MERRIE* 1:100 000 map sheet (SG 51-5, 2946)occupies the southwestern corner of the NABBERU

(1:250 000) map sheet and is bounded by latitudes 25°30'and 26°00'S and longitudes 120°00' and 120°30'E (Fig. 1).It is located in the northern extension of the EasternGoldfields Province of the Yilgarn Craton (Griffin, 1990)and includes part of the eastern extension of thePalaeoproterozoic Yerrida Basin (Pirajno et al., 1996), andthe western extension of the Earaheedy Basin (Bunting,1986). The area is located 90 km north of Wiluna†

(population 260; 1996 census) and 150 km northeast ofMeekatharra (population 1270). Access from these townsis via the unsealed Wiluna North Road, which leads toNeds Creek Homestead and then joins the Great NorthernHighway 83 km to the northwest of MERRIE. Access to thenortheastern parts of MERRIE is along the Canning StockRoute, and to the north via the Vermin-proof fence. Bothof these access routes are rendered impassable after heavyrain. A privately maintained track starts from the WilunaNorth Road about 9 km north of the southern edge ofMERRIE and reaches the northeastern part of the areathrough Doyle Well, Joe Bore, and Nabberu Tank. Anumber of other tracks, typically passable only by four-wheel drive vehicles, provide access to other parts of thearea.

Geological mapping was carried out using 1:50 000-scale monochrome photography (Project numberWA3594, 1995) available from the Department of Land

* Capitalized names refer to standard 1:100 000 map sheets. Where 1:100 000and 1:250 000 sheets have the same name, the 1:100 000 is implied unlessotherwise indicated.

† Coordinates of localities mentioned in text are shown in Appendix 1.

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N. G. Adamides

Administration (DOLA). Landsat Thematic Mapper(TM) images plotted at photo scale, and 400-m line-spaced aeromagnetic data (flown by Australian GeologicalSurvey Organisation (AGSO) in 1996) were used in thefield and to interpret geological features beyond localitiesvisited. A Trimble (Ensign XL) navigation aid was usedfor the determination of Australian Map Grid (AMG)coordinates of outcrops and localities mentioned in thetext.

Climate and vegetationThe climate of the area is semi-arid to arid with long,hot summers and mild winters. Mean daily maximumsummer temperatures are between 35 and 40°C andminimum temperatures between 20 and 23°C (Bunting,1986). In winter, average maximum temperatures arearound 20°C and minimum temperatures 6°C with frostscommon on clear nights. Mean annual rainfall is inthe range of 200 to 240 mm and is unreliable, related toboth summer cyclones and winter depressions. Potentialannual evaporation may average between 2400 and3000 mm.

MERRIE lies within the eastern extension of theGascoyne subprovince of the Eremaean Botanical District(Beard, 1990). The subprovince includes the CarnegieSalient — the system of lakes that includes Lake Nabberu,Lake Wells, and Lake Carnegie. The vegetation of the salt-lake regions is dominated by samphire communities at thelowest topographic levels, followed by Frankenia–Atriplexcommunities at higher levels. Acacia shrub dominates thesandhills that surround the lakes. Mulga (Acacia aneura)is the commonest shrub in all the other habitats,accompanied by other acacia species (A. quadrimanginea,A. grusbyi) on areas of iron formation. Low shrubs ofthe Eremophila and Cassia families are widespreadand, together with a variety of grasses, form theunderstorey to the taller shrubs. A characteristic slender-branched species of Eremophila is particularly prolific onoutcrops of granular iron-formation; sandstone outcropsof the Juderina Formation are vegetated with wattle andmulga. Vegetation on granite outcrops is typically sparse,and represented by mulga, isolated yellow cassia(C. luerssenii), and turpentine bush (E. fraseri). Riverchannels are commonly lined with tall river red gum(Eucalyptus camaldulensis) and sandplains are mostlycovered by spinifex (Triodia sp.).

Figure 1. Map showing the Earaheedy Basin and location of the MERRIE 1:100 000 sheet

Ban

gem

all

Bas

in

Sunbeam Group(Officer Basin)

Collier Group

Scorpion Group

Mulgarra Sandstone

Kulele Limestone

Wongawol Formation

Princess Ranges Member

Chiall Formation

Windidda Formation

Frere Formation

Yelma Formation

Bryah and Padbury Basins

Yerrida Basin

RMH39a

119°30' 121° 122° 123°

26°

Malmacinlier

Shoemakerimpact structure

MARYMIA

FAIRBAIRN

METHWIN

RHODES

MUDAN

GLEN AYLE

DOOLGUNNA THADUNA

MERRIE

NABBERU

GRANITEPEAK

EARAHEEDY LEE STEERE

COONABILDIE

LANCELOT

CARNEGIE

WINDIDDA

WONGAWOLBALLIMORE

MT BARTLEMOOLOOGOOL

COLLURABBIEYELMA

LINKE

BOUCAUTKAHRBAN

WILUNA SANDALWOODLAKE VIOLETMEREWETHERYANGANOO

CUNYU

MILLROSE

27°

VON TREUER

LAKE WELLS

STRAWBRIDGEDELAPOER

14.3.00

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loo

Sub

grou

pEar

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dy G

roup

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ian

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sin

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Sub

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Fault

Geological boundary

DeformedEaraheedy Group

50 km

THREERIVERS

Phanerozoicsedimentary rocks

Archaean granite–greenstone,Yilgarn Craton, and outliers

3


PhysiographyThe physiography of MERRIE is dominated by the NabberuLake system, which occupies much of the northernpart of the sheet (Fig. 2). This easterly trending system ofplaya lakes is part of a major palaeodrainage that joinswith the southward-draining Lake Carnegie system. Thispalaeodrainage dates back to the early Tertiary and iscommonly preserved on the relict duricrusted surface (the‘Old Plateau’ of Jutson, 1934). Palaeodrainage preserv-ation is related to a change, at that time, from a humid toa typically arid climate (van de Graaff et al., 1977). Theradial arrangement of drainage on MERRIE is governed bythe presence of this playa system, and its association withextensive calcrete suggests that recent drainage probablyfollows the old channels with little modification.

A second major physiographic feature is the extensivesandplain, which dominates the southeastern part ofMERRIE. The sand overlies duricrust over granite. Theduricrust, consisting of lateritized, kaolinitized, andsilcretized granite, fringes the areas of sandplain in theform of shallow breakaways, with fresher granite exposedas low whalebacks and tors (see cover photograph) wherepresent drainage cuts through the old surface. Thetransition from granite to the overlying sand is commonlymarked by a mottled facies in the form of ferruginous andbleached fragments locally exposed in creeks, as inthe area 5.6 km east-southeast of Bungarra Bore (AMG293226*; Fig. 3). Recent studies (Morris et al., 1997; Pellet al., 1999) on the genesis of desert sands confirm theirderivation from local sources with little eolian transport.

The topography of MERRIE is typically subdued, withhighest elevations (620 m) in the southeastern part of thearea, and lowest (540 m) around Lake Nabberu. Thetopographic expression of the various rock types varieswith their resistance to erosion. The granular iron-formations of the Frere Range in the northeastern partof MERRIE form resistant ridges rising several tens ofmetres above the surrounding plain. Associated siltstonesand shales form recessive units occupying the low ground.The Merrie Range area in the central part of the sheet ischaracterized by mesas where resistant sandstone capsgranite. Verscher Range to the west, consisting ofsandstones of the Juderina Formation intruded by sillsof the Killara Formation, is characterized by a hillytopography with elevations up to 60 m above thesurrounding plain.

Previous investigationsThe earliest reports on the geology of the area were byexplorers, and their work is described in Feeken et al.(1970). In 1874, John Forrest traversed the area in ajourney that started south of the Kimberley Range, andpassed through the Frere Range to Weld Spring. However,the first detailed geological investigation of the area wasby Talbot (1920, 1928) who accompanied A. W. Canning

in a preliminary survey of the stock route between Wilunaand Halls Creek, and subsequently covered the area inmore detail. Talbot’s interpretations were accepted untilthe early 1960s when regional investigations by Sofoulisand Mabbutt (1963) resulted in the inclusion of allProterozoic rocks under one unit.

MERRIE includes part of the Nabberu Basin as initiallydefined by Hall and Goode (1975, 1978) and Buntinget al. (1977). These authors correctly identified theunconformity between the Archaean granite–greenstonebasement and younger rocks, and an unconformitybetween older Proterozoic rocks and the BangemallGroup. The older rocks were included in a NabberuSupergroup deposited in the Nabberu Basin. Rocks onMERRIE were included in a regional synthesis by Horwitzand Smith (1978) and Gee (1990). Sanders and Harley(1971) carried out a regional survey of the hydrogeologyof the area around MERRIE.

The Nabberu Basin was initially subdivided from eastto west into the Earaheedy, Glengarry, and Padbury Sub-basins; all these sub-basins were later elevated to basinstatus (Gee and Grey, 1993), with the Glengarry Basinlater partitioned into the Bryah and Yerrida Basins (Pirajnoet al., 1996). MERRIE straddles the boundary between theYerrida and Earaheedy Basins.

Systematic mapping of NABBERU (1:250 000) wascarried out in 1975–76 and the results presented inBunting et al. (1982). Bunting (1986) presented a detailedaccount of the geology of the Earaheedy Basin. Recently,Morris et al. (1997) presented an account of regolithgeochemistry on NABBERU (1:250 000).

Stratigraphic nomenclatureThe Proterozoic stratigraphic sequence on MERRIE isshown in Table 1. The stratigraphy of the Yerrida Groupfollows the terminology of Occhipinti et al. (1997).Exposed rocks belong to the Windplain Subgroup(Juderina Formation) and are locally intruded by sills ofthe Killara Formation (Mooloogool Subgroup).

The nomenclature of the Earaheedy Group wasinitially established by Hall et al. (1977) and the group wassubdivided into the basal Tooloo Subgroup and an upperMiningarra Subgroup based on deposition in two distinctcycles. The Tooloo Subgroup included the Yelma, Frere,and Windidda Formations. The Miningarra Subgroupincluded the Wandiwarra Formation, Princess RangesQuartzite, Wongawol Formation, Kulele Creek Limestone,and Mulgarra Sandstone. This nomenclature was adoptedby Bunting et al. (1982) for the description of NABBERU

(1:250 000).

As a result of recent mapping, there has been somemodification of the stratigraphy of the Earaheedy Group:the upper sandy part of the Wandiwarra Formation andPrincess Ranges Quartzite have been downgraded tomembers of the new Chiall Formation; the lower, shalypart of the Wandiwarra Formation is now the Karri KarriMember of the Windidda Formation. The dolomite andassociated chert breccia at the contact with the Frere

* Localities are specified by the Australian Map Grid (AMG) standard six-figure reference system whereby the first group of three figures (eastings)and the second group (northings) together uniquely define position, onthis sheet, to within 100 m.

4

N. G. Adamides

Figure 2. Physiographic map of MERRIE

Major drainage channels

Lake deposits

Colluvial and alluvial sheetwash plain

Sandplain

Calcrete

Outcrop and fringing scree slopes

Track

Bore or well

Lake

NGA109 24.11.99

25°30'12

0°00

'

120°

30'

26°00'

LakeNabberu

LakeNabberuLake

Nabberu

LakeKing

LakeGregory

Can

ning

Sto

ck R

oute

verm

in-p

roof

fenc

e

VERSCHER

RANGE

5 km

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Figure 3. Mottled saprolitic granite at the boundary between lateritic duricrust and underlying weathered granite.From an outcrop 5.3 km east-southeast of Bungarra Bore (AMG 293226). The diameter of the lens capis 5.5 cm

Table 1. Proterozoic stratigraphy of MERRIE

Group/Subgroup Formation Lithology Approximate Depositional environmentthickness

(m)

Earaheedy Group Chiall Fomation Thin-bedded quartz arenite and ?500 Shallow-marine, transgressiveWandiwarra Member interbedded shale

Windidda Formation Laminated siltstone and shale ?500 Deposition below wave-base,Karri Karri Member with sandstone lenses rare interbedded, storm-

derived sandstones

Frere Formation Granular and banded iron- 1 200 Shallow marine. Transgressiveformation, shale, chert, minorcarbonate

Yelma Formation Quartz arenite, shale, minor 1 500 Shallow marine, locallycarbonate, chert, and conglomerate fluvial near base.

Transgressive

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ unconformity ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Yerrida Group Maraloou Formation Thin-bedded siltstone, shale, ?100 Deposition below wave-baseMooloogool Subgroup minor marl

Killara Formation Fine- to medium-grained mafic 200 Preliminantly sills ofintrusive rocks; sills continental affinities intruding

Juderina Formation

Windplain Subgroup Juderina Formation Quartz sandstone, subordinate 500 Shallow marine to intertidalsiltstone, and chert breccia

6

N. G. Adamides

Formation form the new Sweetwaters Well Member of theYelma Formation. On MERRIE, only the basal members ofthe Earaheedy Group are present, and the WandiwarraMember of the Chiall Formation is the youngestoutcropping unit.

Regional geological settingMERRIE is located at the northwestern extension of theEastern Goldfields Province (Griffin, 1990) of the YilgarnCraton and contains, at its northern and western parts,rocks of the Yerrida and Earaheedy Groups. The groupsare part of the Capricorn Orogen (Gee, 1979; Myers,1990; Tyler et al., 1998), an assemblage of sedimentarybasins and associated metamorphic and igneous rocks,which resulted from the collision and fusion of theYilgarn and Pilbara Cratons between 2000 and 1800 Ma.The Capricorn Orogeny includes the Gascoyne Complexand the Ashburton Basin (Thorne and Seymour, 1991),in addition to the Earaheedy, Yerrida, and Bryah Basins.Collision between the two cratons is thought to havebeen oblique; it commenced at the southeastern parts ofthe Pilbara Craton and migrated northwestwards, whereasthe Ashburton Basin evolved as a foreland basin (Tylerand Thorne, 1990). The orogen is about 800 × 300 kmin exposed dimensions and is elongated east–west. Bothits eastern and western extensions are covered byPhanerozoic sedimentary rocks. The suture between theYilgarn and Pilbara Cratons is interpreted, on geophysicalevidence (Drummond et al., 1981), to be located 80 km

south of Newman. The basement to the Proterozoic rockson MERRIE is therefore, part of the Yilgarn Craton.

The Archaean rocks on MERRIE are part of the EasternGoldfields Province and in the western end of the sheetform a basement high called the Wiluna Arch (Gee, 1990).The north-northwesterly orientation of this featurematches that of major folds, faults, greenstone belts, andshear zones in the region (Griffin, 1990; Wyche et al.,1997). The Wiluna Arch was probably a positive featureduring sedimentation in the Proterozoic, and is coveredto the northwest by sandstone and dolerite of the Juderinaand Killara Formations of the Yerrida Group, and to thenorth by the chemical and clastic sedimentary rocks of theEaraheedy Group.

GeochronologyA summary of geochronology data relevant to rock unitsexposed on MERRIE is presented in Table 2. Data from thegranite basement, which underlies the Proterozoic units,suggest ages of crystallization around 2624–2648 Ma(Nelson, 1996, 1998). The age of the basal units of theYerrida Group (Juderina Formation) is probably around2200 Ma, as suggested from Pb–Pb isochron data fromstromatolitic carbonate of the Bubble Well Member(Woodhead and Hergt, 1997).

The geochronology of the Earaheedy Group isconstrained by the age of the Bangemall Group, whichunconformably overlies it. Historical data from the

Table 2. Geochronology data relevant to rock types on MERRIE

Age (Ma) Lithological unit Dating method Interpretation Source

1638 ± 14 Bangemall Group, SHRIMP U–Pb Age of emplacement of Nelson (1995)Coobarra Formation zircon porphyritic rhyolite, lower

Bangemall Group

1700 Earaheedy Group, K–Ar (glauconite) Minimum age of deposition Preiss et al. (1975)Yelma Formation

1590–1710 Earaheedy Group, Rb–Sr (glauconite) Minimum age of deposition Preiss et al. (1975)Yelma Formation

1688 ± 72 Earaheedy Group, Glauconite Minimum age of deposition Horwitz (1975)Wandiwarra Formation

1700 Earaheedy Group, Pb isotope (galena) Age of lead mineralization Johnston and Hall (1980),Yelma Formation Richards and Gee (1985)(Sweetwaters Well Member)

1785 ± 11 Earaheedy Group, SHRIMP U–Pb zircon Maximum depositional age Nelson (1996)Mount Leake Formation based on detrital zircons

2173 ± 80 Juderina Formation, Pb–Pb isochron Depositional age Woodhead and Hergt (1997)Bubble Well Member

2624 ± 8 Goodin Inlier SHRIMP U–Pb zircon Crystallization age of granite Nelson (1996)

2648 ± 19 Yilgarn Craton (CUNYU) SHRIMP U–Pb zircon Minimum crystallization age Nelson (1998)of granite

7


Bangemall Group (Compston and Arriens, 1968) suggesta minimum age of 1100 Ma. Recent dating of porphyriticrhyolite intercalated with rocks of the Coobarra Formation(basal Bangemall Group) suggests a maximum age of1638 ± 14 Ma for the emplacement of the rhyolite (Nelson,1995).

Samples of glauconite from the basal units of theEaraheedy Group on the DUKETON (1:250 000) sheetgave minimum K–Ar ages of around 1700 Ma andminimum Rb–Sr ages of between 1590 and 1710 Ma(Preiss et al., 1975). Horwitz (1975) reported an age of1688 ± 72 Ma from glauconite in sandstone of theWandiwarra Formation. Richards and Gee (1985) reportedlead isotope ages of 1700 Ma from galena withinstromatolitic dolomite of the Sweetwaters Well Member(Yelma Formation). Recently, Nelson (1997) obtained asensitive high-resolution ion microprobe (SHRIMP) ageof 1785 ± 11 Ma on detrital zircons from the Mount LeakeFormation on BRYAH, which is tentatively correlated withthe basal Earaheedy Group. The age of the EaraheedyGroup is, therefore, constrained by that of the BangemallGroup, probably around 1650 Ma, and that of the YerridaGroup (2100–2200 Ma), with an age around 1800 Mabeing the most likely.

Stromatolite biostratigraphy fails to provide a moreprecise determination of age: Grey (1995) commentedon the lack of correlation between the taxa of theEaraheedy Group and taxa of presumably similar age(1500–1800 Ma) from the McArthur Basin (NorthernTerritory), and highlighted the similarities between twoof the Earaheedy Group taxa (Asperia digitata andPilbaria deverella) to taxa in older (1840–1890 Ma)successions, such as the Duck Creek Dolomite. On thebasis of this evidence, Grey (1995) suggested that the ageof the Earaheedy Group may lie between 1800 and1900 Ma.

Archaean geologyThe Archaean rocks on MERRIE belong to the EasternGoldfields Province of the Yilgarn Craton (Griffin, 1990).The province is an assemblage of granitoid and greenstonerocks that probably formed between 2780 and 2630 Maas a result of intense volcanic, plutonic, and metamorphicactivity (Myers and Swager, 1997).

Merrie greenstone beltOutcrops of greenstones on MERRIE are sparse, invariablydeeply weathered, and confined to the central-western andsouthwestern part of the sheet. They form the northerlycontinuation of similar outcrops on CUNYU. The Cunyugreenstone belt (Adamides et al., 1999) is thus the southernextension of the Merrie greenstone belt. Due to lack ofsurface outcrop, most of the information is derived frompetrographic examination of drillhole samples.

The aeromagnetic image of the greenstone belt(Fig. 4a) outlines a major north-northwesterly trendingfold bounded to the east by the Merrie Range Fault. The

core of the structure is occupied by metamorphosed felsicvolcaniclastic and sedimentary rocks, weathered outcropsof which, with well-developed subvertical cleavage, arepresent 3.5 km west-southwest of the abandoned 6 MileWell (AMG 156497).

A synclinal structure has been considered likely for theMerrie greenstone belt on the basis of the local presenceof poorly preserved, vaguely defined, subvertical pillowforms, as in the area 600 m southeast of Doyle Well (AMG167410), with westerly facing consistent with theirlocation on the eastern limb of a syncline. Furthermore,neighbouring greenstone belts, such as the Yandal andLake Violet belts (Phillips et al., 1998; Stewart, 1997), arealso synclinal in form. However, the most conclusiveevidence for a synclinal structure is provided bygeophysical modelling of magnetic features (Fig. 4b). Thisinterpretation is at variance with that of Liu (1997) andMyers and Hocking (1998), who interpreted the structureof the belt as anticlinal.

Deformation of the rocks in the Merrie greenstone beltis strongly heterogeneous, with undeformed typesjuxtaposed against strongly schistose types. In the latter,the schistosity is defined by an alignment of phyllo-silicates, commonly chlorite. Cleavages are locallyaffected by crenulation, defined by the bending of chloriteflakes, indicating a later period of deformation.

Alteration has affected the rocks to varying degrees,with the main minerals being quartz, chlorite, epidote,biotite, and carbonate. Many of these alteration mineralsare also members of the metamorphic assemblage.Distinction between the two modes of genesis is made onthe basis of crosscutting vein assemblages and replace-ment of the matrix by alteration minerals. Biotite alterationis strongly evident in some samples and interpreted asevidence of potassium metasomatism. Similarly, epidotiz-ation is interpreted as evidence of CO2 metasomatism.Carbonate alteration, commonly indicating strong CO2metasomatism, has been identified only in one drillhole1 km north of Doyle Well (GSWA 152707, AMG 162423).The alteration assemblages observed in the Merriegreenstone belt have been interpreted by Farrell andAdamides (1999) as indicative of temperatures around410–430°C, under low fluid CO2 concentrations (XCO2<0.18), and net addition of potassium. Carbonate alterationis a common feature of assemblages proximal to gold-bearing veins in some deposits in the surrounding region,such as the Bulletin deposit at Wiluna (Chanter et al.,1998), and the Nimary deposits of the Yandal greenstonebelt (Byass and MacLean, 1998); its scarcity in thelocations studied to date in the Merrie greenstone belt isinterpreted as indicating that XCO2 in the fluids was toolow for the deposition of carbonate.

Ultramafic rocks (Au, Auf )

Outcrops of ultramafic rock are very sparse on MERRIE

and mainly represented by laterite. The interpretationof the presence of ultramafic units is based on sub-surface information associated with linear magneticanomalies.

8

N. G. Adamides

Figure 4. Modelling of magnetic features in the Merrie greenstone belt:(a) Total Magnetic Intensity image of MERRIE showing location of modelling traverse (data used with permission from

AGSO), with 400 m spacing between flight lines. Outcropping part of the Merrie greenstone belt is shown;(b) Profile of geophysical traverse and associated interpretation of features, which suggest a synclinal form for the

Merrie greenstone belt. Modelling performed by D. Bui

TabularS=0.5626

TabularS=0.5874

TabularS=0.4384 Tabular

S=0.4946

5000 10000 15000 20000 25000 30000 35000

5000 10000 15000 20000 25000 30000 35000

5000 10000 15000 20000 25000 30000 35000

0

100

5500

5000

4500

0

1000

2000

3000

4000

TabularS=0.4845Tabular

S=0.5303

NGA114

Line: TRAV9

A B

Modelled

Residual

1.3.00

TabularS=0.5021

Magnetic response

Observed

b)

a)

Merrie

Merrie

Range

Range

FaultFaultM

errieM

errie

Syncline

Syncline

BB

AA

MERRIE GREENSTONE BELT

MERRIE GREENSTONE BELT

120°

30'

120°

30'

26°00'26°00'

25°30'25°30'

120°

00'

120°

00'

9


Interpreted ultramafic rocks (Au) and their foliatedequivalents (Auf ) are typically represented by anassociation of chlorite and lath-like crystals of talc ininterlocking aggregates. The opaque minerals are alteredto leucoxene. Cleavage in the foliated types is defined bythe alignment of chlorite crystals. In other cases,ultramafic rocks are composed of an intimate associationof chlorite and abundant tremolitic amphibole, withscattered, microcrystalline titanite.

Mafic rocks (Ab, Aba, Abae, Abaf, Abf,Abe, Aby)

Only undifferentiated mafic rock (Ab) has been mappedat the surface from the Merrie greenstone belt and includesfine- and medium-grained mafic rocks, as well asintermediate types. The other units are identified only inthe subsurface from drillhole information.

Amphibolite (Aba) has been intersected in drillholesin the southern parts of the Merrie greenstone belt. On thebasis of the interpretation of this belt as a northerlyplunging syncline, the presence of this rock type isconsistent with deeper levels of the greenstone belt.Samples of amphibolite contain an assemblage ofhornblende crystals up to 4 mm in length, and plagioclase(?oligoclase), which commonly preserves its igneouszoning. The opaque minerals are mostly altered aroundmargins to microcrystalline titanite.

A small outcrop of high-grade amphibolite, a fewsquare metres in size, is located 6 km south-southeastof No 3 Govt Well (AMG 417409) and probablyrepresents a raft within the granite. The rock has a foliatedstructure (Fig. 5a) and mafic appearance, with a grain sizeof 0.1 – 0.3 mm. The amphibolite rock consists of stronglypleochroic hornblende, subordinate clear clinopyroxene,and minor quartz and plagioclase (Fig. 5b). Foliation isdefined by alignment of the hornblende crystals. Euhedralmagnetite, marginally altered to hematite, is the opaquemineral enclosed in the hornblende. The amphibole isretrogressively replaced locally along cleavages by amicrocrystalline mixture of epidote and quartz.

In schistose mafic types (Abf, Abaf ), the schistosity isdefined by the alignment of chlorite flakes. Epidotizedrocks (Abe, Abae) are characterized by abundant epidote,which occurs both in veins and the groundmass. In thelatter paragenesis, the epidote occurs in granularaggregates of crystals, which overprint the earlierassemblages and do not bear any relationship to thecleavage.

Strongly fractionated types (?meta-andesites) arepresent, with abundant plagioclase as a phenocryst phase.Such plagioclase-phyric varieties (Fig. 6a) typicallyconsist of plagioclase laths up to 0.5 mm in length,enclosed in a fine-grained matrix of abundant albitizedplagioclase, with secondary minerals including quartz,chlorite, and actinolite after ferromagnesian components.

Hornblende diorite was intersected in one drillhole,close to the core of the Merrie syncline, 3.7 km southeastof 21 Well (GSWA 152709, AMG 147476). The rock is

coarse grained (grain size >4 mm) and composed ofeuhedral to subhedral plagioclase and anhedral, uralitizedclinopyroxene. K-feldspar is totally absent. Incipientbrittle deformation is indicated by kink-banded plagio-clase lamellae. The opaque minerals are represented byskeletal crystals totally replaced by well-crystallizedtitanite. This diorite is considered to be an integral partof the greenstone sequence compared to adjacentgreenstone belts, such as Millrose (Farrell, T. R., 1999,pers. comm.).

Mafic rocks on MERRIE typically consist of anassemblage of albite, chlorite, actinolite, epidote, andquartz. The original mafic minerals are replaced byactinolite; plagioclase is commonly albitized. The fine-grained mafic rocks consist of interlocking plagioclaselaths in a matrix composed of chlorite and actinolite. Invesicular types (Aby), vesicles are commonly filled withquartz, chlorite, and clinozoisite, with the last two mineralsreplacing plagioclase.

Metasedimentary rocks (As)

Deeply lateritized outcrops of folded and schistosemetasedimentary rocks (As) are present in the core ofthe syncline 3.5 km west-southwest of 6 Mile Well(AMG 156497), and spatially associated with felsicvolcaniclastic units (Af ). The metasedimentary rocks showa laminated texture that is preserved through thelateritization, and contain quartz, actinolite, and epidote.Strongly pleochroic alkali amphibole (?arfvedsonite)forms acicular crystals partially oriented along thecleavage. A zonation between quartz-rich and quartz-poorassemblages, abundance of epidote, and complete absenceof feldspar are used as evidence in the interpretation ofthese rocks as metasedimentary.

Granite (Ag, Agm)Granite outcrops are located mainly in the eastern partsof MERRIE, with greenstones confined to the southwest. Amajor north-northwesterly trending structure, the MerrieRange Fault (Myers and Hocking, 1988, 1998), forms theboundary with the greenstones of the Merrie greenstonebelt. The Merrie Range Fault is a D3 structure (seeStructure and metamorphism) that has been reactivatedin Proterozoic times.

Most of the granite (Ag) is lateritized and silcretized.Outcrops of fresh monzogranite (Agm) are commonlylimited to ‘windows’ in the lateritic duricrust. The granitevaries from fine to coarse grained, with medium-grainedgranite being the most common; the granite is commonlybiotite rich and porphyritic, with subordinate aphyrictypes. Porphyritic granite contains phenocrysts ofK-feldspar up to several centimetres long, and is locallypresent in well-defined nests within fine-grained granite;in other cases, it veins fine-grained granite (Fig. 7a) andis in turn veined by later, fine-grained granite. Theserelationships suggest penecontemporaneous emplacementof the fine- and coarse-grained types. Thin (30 cm) veinsof pegmatite cut the granite and are composed of quartzand feldspar crystals up to 5 cm long (Fig. 7b).

10

N. G. Adamides

Figure 5. High-grade amphibolite:(a) Foliated amphibolite, interpreted as a raft in granite. Outcrop 5.9 km south-southeast of No 3 Govt

Well (AMG 417409). The lens cap is 5.5 cm;(b) High-grade amphibolite composed of hornblende, clinopyroxene, and quartz with minor plagioclase.

Foliation is defined by alignment of hornblende crystals. GSWA 152852, plane-polarized light

11


Figure 6. Rock textures from the Merrie greenstone belt:(a) Plagioclase-phyric mafic rock, with abundant plagioclase in groundmass composed mainly of

epidote and biotite. Merrie greenstone belt. GSWA 152875, plane-polarized light;(b) Felsic volcaniclastic rock with recrystallization of kaolinite to illite around quartz phenocrysts.

GSWA 152892, transmitted light, crossed polars

12

N. G. Adamides

Figure 7. Lithological features of granite.The diameter of the lens cap is5.5 cm:(a) Crosscutting relationships

in granite, with fine-grainedgranite veined by coarsergrained granite. Outcrop7 km east-southeast ofBungarra Bore (AMG307223);

(b) Pegmatite in a vein thatintruded granite. Outcrop5.6 km southeast of No 3Govt Well (AMG 437423);

(c) Primary igneous layeringin granite. Outcrop 15 kmsouth-southeast of No 3Govt Well (AMG 427317)

13


A primary igneous layering is evident on much of thegranite outcrop, defined by a general alignment offeldspars (Fig. 7c). In some cases, the layering takes theform of alternating coarse- and fine-grained facies and isassociated with minor shearing, probably indicatingtectonism during emplacement. Commonly, the igneouslayering is enhanced by parallel development of joints.

Grain counting of a number of samples from MERRIE

(Fig. 8) confirms that the granite is dominated by amonzogranite composition. Grain size varies from 1 to2 mm in the fine-grained types, to 4–5 mm in the coarse-grained varieties. The mineralogy of all granitic types isbroadly similar. Fine-grained granite shows equigranulartexture with quartz, K-feldspar with abundant microcline,saussuritized plagioclase, biotite, and trace amounts ofwhite mica. The plagioclase in places contains bleb-likeor amoeboid inclusions of quartz, and is euhedral againstthe microcline, which is in turn euhedral against thequartz. The microcline encloses rounded quartz andaltered plagioclase. Biotite is chloritized with anomalous

purple birefringence and commonly associated with fine-grained, euhedral epidote; muscovite is a late-stage,fracture-filling mineral. In medium-grained varieties, someof the plagioclase has a well-defined calcic interior thatis completely saussuritized, with a shell of sodic, mostlyunaltered plagioclase. Accessory minerals in the graniteinclude titanite, commonly as microgranular inclusions inbiotite, opaque oxides, apatite, zircon, and carbonate. Thequartz is commonly strained and encloses sparse rutileneedles. The mineralogy of the granite, with the presenceof biotite and titanite and the complete absence of mineralssuch as cordierite, garnet, sillimanite, and andalusite, istypical of I-type granitoids (Shelley, 1983).

Felsic porphyry and felsic volcaniclasticrocks (Afp, Afs)

In the area 2.7 km northwest of Curvaceous Carly Bore(AMG 135251), a northerly trending, dyke-like body ofquartz porphyry (Afp) cuts the granite. The body is poorly

Figure 8. Plot of mineral proportions for granite from MERRIE (crosses) and from theGoodin Inlier (filled circles)

60 60

2020

Quartz

Alkali feldspar Plagioclase

QS QM QMDQAFS QGQD

QA

M MDSAFS G,A

Q

QRG

MGSG GD TAFG

35 65

NGA113 18.1.00

Alkali feldspar syeniteAFSAFG Alkali feldspar graniteG, A Gabbro, AnorthositeGD GranodioriteM MonzoniteMD MonzodioriteMG MonzograniteQ QuartzoliteQA Quartz anorthositeQAFS Quartz alkali feldspar syenite

QDQGQMQMDQRGQSSSGT

Quartz dioriteQuartz gabbroQuartz monzoniteQuartz monzodioriteQuartz-rich granitoidsQuartz syeniteSyeniteSyenograniteTonalite

14

N. G. Adamides

exposed in the form of low, rubble-strewn outcrop. Thereis no perceptible fabric in the rock, which has amicroporphyritic texture, with phenocryst phases ofquartz, K-feldspar (including microcline), plagioclase, andminor brown biotite. Lithic fragments of graniticderivation are present in a fine granular matrix composedof a mixture of plagioclase, microcline, quartz, andabundant white mica. The rock is interpreted to be felsicvolcanic or volcaniclastic that probably crystallized atshallow levels in the crust and did not reach the surface.A weakly schistose equivalent of this rock (Afs) from thecore of the Merrie syncline 3.5 km west-southwest of6 Mile Well (GSWA 152892, AMG 156493), containsboth a laminated, fine-grained, kaolinitic facies withsparse, angular quartz clasts and a clast-rich facies inwhich both euhedral, as well as embayed and fragmentaryquartz and minor feldspar, are enclosed in a fine-grained,kaolinitic matrix. This matrix is recrystallized around theclastic fragments into radial aggregates of illite (Fig. 6b).Similar illite forms along poorly developed cleavages asa result of recrystallization of the kaolinite by deformation.

Structure and metamorphismThe Merrie greenstone belt is inferred to have had thesame deformation history as adjacent greenstone belts(Liu et al., in prep.; Farrell and Wyche, in prep.); bycomparison, therefore, with the geology of those belts, itsdeformation history is described below.

The first deformation event (D1) is considered to beone of recumbent folding and thrusting, and is reflectedin the greenstones by a subhorizontal foliation.

The second period of deformation (D2) is in the formof open, upright folds that were initially aligned east-northeast. Planar fabrics associated with these structuresare rarely seen (Griffin, 1990).

The event responsible for the present north-north-westerly linearity of the Merrie and adjacent Wiluna andYandal greenstone belts is attributed to a third period ofdeformation (D3). This event is considered to be a complexcombination of folding and strike-slip faulting. The MerrieRange Fault is a structure probably associated with D3, andthe north-northwesterly orientation of the Merriegreenstone belt is also the result of this deformation event.In the greenstones, D3 is reflected by the presence of asubvertical, northerly trending cleavage (S3). The graniteis typically undeformed, with the exception of local brittledeformation and cleavage development commonlyassociated with faulting and quartz veining. The quartzveins are predominantly oriented east-southeast, parallelto similarly oriented faults that terminate against theMerrie Range Fault. These faults are probably Proterozoicin age, were affected by later rejuvenation of the MerrieRange Fault, and are described later (see Structure andmetamorphism, p. 28). All faults are represented by zonesof decreased magnetic intensity, attributed to destructionof magnetite by hydrothermal alteration along these faults(Phillips et al., 1998).

The Merrie Range Fault is a major north-northwesterlytrending structure that juxtaposes Proterozoic sedimentary

rocks against Archaean rocks, and has a distinct responseon Landsat TM, gravity, and aeromagnetic images. It is,together with a second structure called the LockeridgeFault (on NABBERU), considered to be a continuation ofthe Celia Lineament (Hall, 1979). The surface outcrop ofthe Merrie Range Fault is very poor and mostly markedby zones of shearing, brecciation, and quartz veining.In the area of the Merrie greenstone belt, movementsalong the fault resulted in the development of a broadzone of isoclinal folding, interpreted from recent drilling,and named the Cunyu Tectonic Corridor (MarymiaExploration NL, 1998).

The greenstones contain metamorphic assemblagesthat suggest peak metamorphism of lower amphibolitefacies. Amphibolites are mainly confined to the southern,deeper parts of the belt and characterized, in the coarsergrained types, by prismatic hornblende in association withplagioclase (?oligoclase) and titanite. Most of the othermafic assemblages in other parts of the belt containminerals characteristic of lower greenschist faciesmetamorphism (albite, epidote, chlorite, actinolite). Inthe metamorphic assemblages, chlorite and actinolitereplace the ferromagnesian minerals, and chlorite,clinozoisite, and quartz locally pseudomorph plagioclase.The association of tremolite and chlorite replacingferromagnesian minerals in ultramafic units is alsoconsistent with lower greenschist facies. Biotiteand epidote, in addition to being common associates ofthe metamorphic assemblage, locally overprint themetamorphic minerals, suggesting potassium and CO2metasomatism respectively. The potassium metasomatismmay be related to later granitoid intrusions, as suggestedby the incursion of granitoid into the greenstones at thesouthwestern side of the Merrie greenstone belt (seesimplified geology on map).

As mentioned above, the highest metamorphic grades(upper amphibolite facies) on MERRIE are associated withan outcrop of hornblende–clinopyroxene amphibolite,probably representing a raft within granite. Retrogressionof the high-grade metamorphic assemblage to greenschistfacies is indicated by replacement of the amphibole byepidote and prehnite along cleavages.

Proterozoic geologyDolerite dykes (#dy)The area has been intruded by a series of mafic dykes ofpresumed Proterozoic age. These have been interpretedmostly from aeromagnetic data and have a predominantlynortheasterly orientation. They probably belong to thepost-cratonization dyke suite of Hallberg (1987),which is developed throughout the Yilgarn Craton.On MERRIE, the dykes are indicated by linear zones ofmostly normal polarity. On the northern part of MERRIE

in the area around Frank Well (AMG 246600 and235567), poorly exposed dolerite dykes intrude graniteand partly follow east-southeasterly trending interpretedfaults. The rocks are fine grained, unaltered, undeformed,and have a holocrystalline texture. Locally, a ribbedstructure is present, resembling flow layering, and

15


probably resulted from differential weathering of rockof variable composition. The dykes contain equalproportions of plagioclase and clinopyroxene, and havean alteration assemblage of quartz, epidote, chlorite, andtitanite. Pyrite is locally present in the form of subhedralconcentrations commonly associated with chlorite, whichis strongly pleochroic and shows anomalous purple andbrown birefringence. The opaque minerals also includemagnetite and ilmenite altered to leucoxene. Thereplacement of the original igneous assemblage bysecondary minerals characteristic of the lower greenschistfacies is compatible with metamorphism of the dykesunder hydrous conditions.

Yerrida GroupThe Yerrida Group (Table 1; Occhipinti et al., 1997)includes clastic sedimentary, chemical sedimentary,and volcanic rocks that were deposited in the YerridaBasin. The age of the group is poorly constrained between2200 and 1900 Ma, based on a Pb–Pb isochron fromstromatolitic carbonate of the basal Juderina Formation(Woodhead and Hergt, 1997), and the age of theEaraheedy Group, which is currently estimated at1800–1900 Ma (Grey, 1995). The group is subdivided intoa basal Windplain Subgroup, interpreted as a sag-basinsuccession, and the Mooloogool Subgroup, which overliesit and is interpreted as a rift succession. On MERRIE, theWindplain Subgroup is represented by the JuderinaFormation, which is intruded by sills of the KillaraFormation (Mooloogool Subgroup). The MaraloouFormation is interpreted from adjacent THADUNA (Pirajnoand Adamides, 1998) to underlie parts of the western edgeof MERRIE.

Windplain Subgroup

The Windplain Subgroup consists of two formations, theJuderina Formation and the overlying Johnson CairnFormation. The Juderina Formation, in areas where fullydeveloped, consists of quartz arenite overlain by, or locallyinterbedded with, chert breccia after stromatoliticcarbonate (Bubble Well Member, Occhipinti et al., 1997).Quartz siltstone is interbedded with sandstone, andconglomerates form an important component in places.The Juderina Formation is interpreted as a predominantlyshallow water sequence, with local development of sabkhaconditions (Gee and Grey, 1993).

The Johnson Cairn Formation conformably overliesthe Juderina Formation and consists of argillaceoussiltstone and minor turbidite units. The formation isinterpreted as signalling deepening of the Yerrida Basinand the transition from a sag-basin to a rift facies in itsdevelopment. The Johnson Cairn Formation is not presenton MERRIE, but is exposed on adjacent THADUNA (Pirajnoand Adamides, 1998).

Juderina Formation (#Yj, #Yjf, #Yjs)

The type locality for the Juderina Formation is aroundJuderina Bore on DOOLGUNNA, where it is represented by

a thin (50 m) sequence of ripple-marked quartz arenite andinterbedded siltstone and chert breccia (Gee, 1987).Elsewhere, the formation is much thicker and shows morecomplex lithological relationships.

On MERRIE, outcrops of the Juderina Formation aremainly distributed in the central-western parts of the sheet,around Verscher Range, with limited outliers at MerrieRange and in the central parts where they unconformablyoverlie granite. The outcrops are commonly coveredunconformably by chert breccia of the basal EaraheedyGroup (Yelma Formation).

The thickness of the Juderina Formation is difficult toestimate due to shallow dips, possible fault repetition, andintercalated dolerite intrusives; however, on the basis ofgeological sections in the Verscher Range area (Fig. 9), itis estimated to exceed 2 km. This thickness includes thedolerite intrusives.

The basal unconformity is exposed at several placesin the Merrie Range area. At an outcrop 1.4 km northwestof Dingy Well (AMG 249501), for example, the uncon-formity surface is marked by a 1 m-thick band ofgranulestone consisting of subrounded quartz in a fine-grained, quartzose sandy matrix. Above the granulestone,the arenite is predominantly thinly bedded with localflaggy interbeds, parallel and planar cross-laminations,and mudflakes on bedding planes.

The lithology of the Juderina Formation on MERRIE

mainly comprises well-bedded quartz arenite (#Yjf )interbedded with quartz siltstone (#Yjs). The assignmentof the whole of the outcrop of Juderina Formation to theFinlayson Member (#Yjf ) is due to the abundant presenceof ripple marks, which are the characteristic feature of thismember. The Juderina Formation (#Yj) is not subdividedon the simplified geology map (see map).

The quartz arenite is typically well bedded, fine tomedium grained, and well sorted, with beds 20–40 cmthick. Thin-bedded and flaggy sandstone units are alsopresent. Quartz grains vary from well rounded to angular.A purplish, hematitic surface colouration is locally present,and the arenite is commonly affected by secondarysilicification. There are local interbeds of conglomeraticsandstone, with the moulds of original rounded clasts ina silica-cemented sandstone matrix.

Although in most outcrops the arenite occurs in beds20–50 cm thick, thicker bedded arenite is also present;for example, 2.3 km west-northwest of Wynn Well(AMG 060516), with individual beds 70–100 cm thick.This arenite is silica cemented, medium grained, andwell sorted with mainly angular grains; it is associatedwith matrix-supported breccias in beds over 1 m thickconsisting of quartzite clasts in a sandy matrix.

The arenite units are characterized by an abundanceof sedimentary structures. The most common structureson bedding planes include symmetrical and asymmetricalripple marks, and shallow troughs; rare current lineationsare present on thin-bedded sandstone units. Interferencebetween ripple marks, probably the result of side currentsor wind effects, is locally present (Fig. 10a). Structures

16

N. G. Adamides

within the beds include parallel, planar, herringbone, andtrough stratification. Delicate cross-laminations are presentin some beds (Fig. 10b), probably indicating ripplemigration under varying current and bed-load conditions

Figure 9. Geological sections through the Juderina Formation:(a) Geological section through the Juderina and Killara Formations on MERRIE;(b) Detailed section through the Juderina Formation showing the main lithological features

(Coleman and Gagliano, 1965) in a shallow-waterenvironment. Soft-sediment deformation features, in theform of distortion of laminations (Fig. 10c), suggest localsediment movement prior to diagenesis. Beds of coarse,

20 m

Present land surface

Ripple-marked quartz arenite

Carbonate-spotted quartz areniteThick-bedded, silica-cemented quartz arenite

Quartz siltstone

Dolerite sill

Thick-bedded, mostly structureless quartz arenitebeds 50–70 cm, local planar, cross-stratification

Ripple-marked quartz arenite, dense carbonate spotting

2 km

AMG 016515 AMG 048503MER3310 AMG 077482

a)

b)

NGA111 13.3.00

chert breccia

17


clast-supported intraformational breccia on the other hand,composed of angular sandstone fragments identical to theenclosing rocks, suggest post-diagenetic brecciation,probably by synsedimentary tectonism, and incorporationof the breccias in the form of scree deposits within therock sequence.

Brown spotting, probably after carbonate, is commonand locally intense, resulting in a dense, fine-honeycombtexture and a spongy appearance of the arenite. Thespotting appears to be limited to specific beds with othersbeing comparatively clean. At an outcrop 1.5 kmsouthwest of Mount Paterson (AMG 032506), concentricstructures varying from a few millimetres up to 10 cm indiameter are present in the arenite (Fig. 10d). These arecomposed of annular arrangements of brown (?carbonate-rich) and light-coloured layers, which overprint theenclosing arenite and suggest an early diagenetic origin,probably by a liesegang process.

The orientation of palaeocurrent indicators (Fig. 11a)suggests a northwesterly palaeoshoreline, with pre-dominant transport direction towards the northeast(Fig. 11b). Opposing current directions are consistentwith a shallow-water environment. A statistical examin-

ation of ripple marks around Mount Paterson (AMG046512) indicates wavelengths of 3–9 cm and amplitudesof 0.2 – 1.5 cm, with a linear relationship between the twoparameters.

The quartz arenite typically varies in grain size from0.1 to 0.2 mm and is commonly very well sorted. Quartzgrains are commonly defined by dust rings and surroundedby crystallographically continuous overgrowths that infillintergranular spaces. Locally, a bimodal distribution ofgrains is present, with larger grains up to 0.3 mm indiameter scattered in a matrix of well-sorted, fine-grainedquartz. The grains are well packed and show mildcompaction, but no obvious deformation. Pellets ofkaolinitic clays are locally present within the arenite andin the same size range as the quartz grains. Zircon andtourmaline are the dominant heavy minerals.

Quartz siltstones (#Yjs) are interbedded with the quartzarenite at several levels (Figs 9a, b). They are commonlythinly bedded and finely laminated, and when weathered,give rise to a scree of slab-like blocks. The siltstones arebest exposed on cliff faces, elsewhere forming recessiveunits. Beds are 2–10 cm thick and show delicatemillimetre-scale laminae. They are dark grey on the

Figure 10. Sedimentary structures in the Finlayson Member, Juderina Formation. The lens cap is 5.5 cm in diameter:(a) Interference between ripples of two orthogonal orientations, 1.4 km south-southwest of Mount Paterson (AMG

039501);(b) Delicate cross-laminations in quartz arenite, 3 km northwest of Mount Paterson (AMG 024532);(c) Soft-sediment deformation structures in quartz arenite, 4 km northwest of Mount Paterson (AMG 012533);(d) Diagenetic (?liesegang) structures in quartz arenite, 1.5 km west-southwest of Mount Paterson (AMG 032506)

18

N. G. Adamides

weathered surface, locally with a pitted texture infilledwith ferruginous material.

The quartz siltstones typically have a hematiticcolouration and are strictly parallel laminated, with thelaminae defined by alternations of clay-rich and quartz-rich material. There is abundant clastic quartz and detritalwhite mica. Laminae are 0.2 – 2 mm thick and composedof thinner laminae of around 30 µm.

In the area 1.2 km south-southwest of QuartzWell (AMG 989558), thicker bedded (20 cm) dolomiticsiltstones underlie the quartz siltstones. Dolomitic siltstoneis laminated on a millimetre scale, with alternatinglayers of clastic carbonate rock and thin, argillaceous,ferruginous laminae. The carbonate is composed ofclasts up to 30 µm in diameter set in a ferruginousmatrix. The laminae have an irregular wavy appearanceand are probably of microbial origin. Disseminatedcarbonate, in the form of rhombic crystals, is present inthe matrix.

Mooloogool Subgroup

The Mooloogool Subgroup (Occhipinti et al., 1997) iscomposed of the Thaduna, Doolgunna, Killara, andMaraloou Formations. The Doolgunna and ThadunaFormations are predominantly turbidite sequences thatwere deposited in a northeasterly trending rift. TheDoolgunna Formation is mainly a kaolinitic quartz wackeof granitic derivation with interbedded siltstone; theThaduna Formation is a mafic litharenite partly sourcedfrom a volcanic terrain. Interfingering relationshipsbetween these two formations are demonstrated onTHADUNA (Pirajno and Adamides, 1998). The KillaraFormation consists of tholeiitic basalt, dolerite, and gabbroand intrudes rocks of the Yerrida Group at all levels. Theformation is interpreted to be related to rifting, withlava extrusion controlled by northeasterly or northerlystructures. Locally, as on THADUNA, MOUNT BARTLE,and CUNYU (Pirajno and Adamides, 1998; Dawes andPirajno, 1998; Adamides et al., 1999), the end of thevulcanicity of the Killara Formation is marked by achemical-evaporitic unit, the Bartle Member (Occhipintiet al., 1997). The Maraloou Formation is composed ofcarbonate, siltstone, and black shale that, in places, isunconformable on the older rocks of the Yerrida Group.The relationship between the Killara and MaraloouFormations is transitional to discordant, with up to 100 mof intercalated mafic and sedimentary rocks defining theboundary on MOOLOOGOOL and MOUNT BARTLE (Pirajnoet al., 1998; Dawes and Pirajno, 1998).

On MERRIE, the Killara Formation is the onlyrepresentative of the Mooloogool Subgroup, with theMaraloou Formation inferred to underlie parts of thewestern edge of the sheet by extrapolation from THADUNA.

Killara Formation (#Yk, #Ykf, #Ykb, #Ykd)

The Killara Formation (Occhipinti et al., 1997) is namedafter Killara Homestead on GLENGARRY (1:250 000) andis an association of mafic intrusive and extrusive rocks andsubordinate chemical precipitates (Bartle Member), whichis well developed particularly in the south and southeastparts of the Yerrida Basin.

On MERRIE, rocks assigned to the Killara Formation(#Yk) are confined to the western part of the sheet in theVerscher Range area, where they intrude rocks of theJuderina Formation. They are subdivided, on the basis ofgrain size, into fine-grained basaltic rocks (#Ykf ) andmedium-grained dolerite (#Ykd). Both rock types aretexturally and mineralogically similar. An outcrop ofbasalt (#Ykb), probably extrusive, is present in the areaof Quartz Well, on the western edge of the map. Extensiveoutcrops of basalt, with unequivocal extrusive character-istics, are present on adjacent THADUNA (Pirajno andAdamides, 1998).

Outcrops of the Killara Formation commonly formpositive features. The rocks are brownish-black on theweathered surface, with the coarser grained varietiesweathering into large blocks of rounded outline, and thefiner types into smaller round blocks, which is the resultof exfoliation weathering. A rough surface texture is

Figure 11. Palaeocurrent data from the Finlayson Member,Juderina Formation:(a) Rose diagram showing crest orientation of

symmetrical and asymmetrical ripple marks inthe Finlayson Member. The figure suggests anorthwesterly oriented palaeoshore;

(b) Rose diagram of directional palaeocurrentdata in the Finlayson Member, highlightingthe bidirectional nature of the palaeo-currents consistent with a shallow-waterenvironment. Predominant current directionswere to the northeast and southwest

0

90

180

270

0

90

180

270

a)

b)

NGA110 12.10.99

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characteristic, and microphenocrysts commonly stand outas positive relief by differential weathering. A faint flowlayering is present in places, and the rocks are stained bywidespread green alteration (nontronite), with localveining by quartz, epidote, and sulfides. A crude columnarjointing is present in some outcrops with the cooling jointsgiving the attitude of the intrusions. Traces of sulfides aredisseminated in the rocks. The dolerite typically has lowmagnetic susceptibility (50–60 × 10-5 SI), suggesting thatno widespread crystallization of magnetite has taken place.Thick (30 cm) quartz–epidote–carbonate veins are presentin places, with the epidote forming nests severalcentimetres long composed of acicular crystals (Fig. 12),commonly occupying the walls of the veins. This veinassociation suggests limited, fracture-controlled movementof hydrothermal fluids in the rocks of the KillaraFormation.

The texture of the dolerite is commonly equi-granular, with clinopyroxene and plagioclase (andesine–labradorite) in subequant crystals averaging 0.5 – 1 mmin size. The plagioclase is commonly weakly alteredalong veinlets and fractures to finely granular clinozoisiteand carbonate, with the clinopyroxene remaining generallyfresh. In typical examples, first-generation plagioclaseabout 0.1 mm in size is enclosed in larger plagioclaseand clinopyroxene, which are in interlocking aggregatesof grain size 0.8 – 1 mm. In other cases, the plagioclaseis altered to sericite. Hypersthene, in the form ofeuhedral crystals partly pseudomorphed by serpentine, ispresent in a corona-type texture, poikilitically enclosing

euhedral altered plagioclase and partly surrounded byfresh clinopyroxene, probably augite. Thin veinlets ofmagnetite are associated with the alteration productsof orthopyroxene. These mineral associations suggestearly crystallization of calcic plagioclase, followed byorthopyroxene and then, in turn, by simultaneouscrystallization of more sodic plagioclase and clino-pyroxene.

The opaque minerals in the dolerite are titanomagnetiteand ilmenite, commonly altered to fine-grained alterationproducts (leucoxene).

Traces of chalcopyrite are locally present within thealtered matrix of magnetite. Weak pyritization affects therocks in the form of veinlets and concentrations ofeuhedral pyrite following intergranular boundariesbetween plagioclase and clinopyroxene. These features, inassociation with quartz–epidote–carbonate veining,suggest the presence of weak mineralization. In situationsof more intense alteration, the plagioclase is totally alteredto chlorite, epidote, and quartz, with the clinopyroxeneremaining mostly unaffected. Two types of chlorite withcontrasting optical properties are present and associatedwith quartz and sulfides.

Maraloou Formation

The Maraloou Formation (Bunting et al., 1977) is asequence of argillaceous sedimentary rocks, black shale,marl, dolostone, and minor chert, and forms the uppermost

Figure 12 Association of quartz and epidote in dolerite of the Killara Formation. The diameter of the lens capis 5.5 cm

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N. G. Adamides

unit of the Yerrida Group (Occhipinti et al., 1997).The formation interfingers with the Killara Formationon MOUNT BARTLE (Dawes and Pirajno, 1998), butunconformable contacts with the Doolgunna Formationhave been established during recent mapping on THADUNA

(Pirajno and Adamides, 1998).

On MERRIE, the Maraloou Formation is not exposed;however, it is interpreted from the adjacent THADUNA sheetto underlie part of the western end of MERRIE. Thelithology of the formation on THADUNA (Pirajno andAdamides, 1998) consists of thin-bedded, laminatedsiltstone and interbedded ferruginous shale with inter-calated marly bands.

Earaheedy GroupDetails of the lithology of the Earaheedy Group(Hall et al., 1977) are contained in Bunting (1986).Modifications of the stratigraphy of the group havebeen described previously (see Stratigraphic nomen-clature). The group contains clastic and chemicalsedimentary rocks that were deposited in the EaraheedyBasin c. 1800–1900 Ma during the Capricorn Orogeny.The Earaheedy Basin is exposed in an east-southeasterlytrending synclinorium, with minor outcrops of presumedbasal Earaheedy Group rocks also present in severallocalities west of the main basin, unconformably over-lying the rocks of the Yerrida and Bryah Groups.On MERRIE, only the Yelma and Frere Formations areexposed with isolated outcrops of the Karri Karri andWandiwarra Members in the northeastern corner of thesheet.

Yelma Formation (#Ey, #Eyc, #Eya, #Eys,#Eyo, #Eyw)

The Yelma Formation (Table 1) is a complex associationof sandstone, shale, arkosic conglomerate, and stromato-litic dolomite. The formation is overlain conformably bythe Frere Formation, and the contact is locally defined bylenses of stromatolitic dolomite, the Sweetwaters WellMember. In the absence of the dolomite, the contact isplaced at the first appearance of iron formation. The YelmaFormation forms the basal unit of the Earaheedy Groupand is distributed throughout the basin. The formationshows wide variations in thickness, from a few metres inthe southeastern parts of the basin, to about 1500 m in thenorthwest (Bunting, 1986).

On MERRIE, the Yelma Formation (#Ey) is representedmainly by chert breccia after stromatolitic dolomite(#Eyc), local feldspathic sandstone (#Eya), and siltstone(#Eys). The type locality for the Sweetwaters WellMember (#Eyw) is located within the sheet area. Thethickness of the formation, based on drillhole evidence andsurface geology, is estimated to be around 700 m.

Outcrops of chert breccia (#Eyc) are widely scatteredthroughout the central and western parts of MERRIE, wherethey commonly overlie quartz arenite of the JuderinaFormation (Finlayson Member). Although they arecommonly spatially related, they were found nowhere to

be interbedded with the quartz arenite. Bunting et al.(1982) assigned these breccias to the Glengarry (Yerrida)Group, thus considering them equivalent to similarbreccias in the Bubble Well Member. However, theidentification of numerous species of Asperia digitataduring the current mapping, a stromatolite that ischaracteristic of the Yelma Formation (Grey, 1995),suggests that the breccias unconformably overlie theJuderina Formation and belong to the basal EaraheedyGroup.

The best outcrops of these breccias are present 3 kmsouth-southwest of Wynn Well (AMG 076486) and in asecond outcrop 1500 m further north. In these areas, anassociation of thin-bedded, cross-laminated, impure,brown feldspathic quartz sandstone, siltstone, chert, andchert breccia is exposed. The chert is laminated in shadesof grey, with local hematitic jasper bands. A thinconglomerate is present close to the contact with thequartz arenite of the Juderina Formation. Abundantcolumnar stromatolites are present in these outcrops, andBunting et al. (1982) reported a rich microfauna mainlyof algal filaments from chert in this area.

Arkosic sandstone (#Eya) is present in a series ofoutcrops close to the basal unconformity with theArchaean granite in the area 2.4 km southeast of BoodyHole Well (AMG 226615). The outcrops are in the formof brown-weathering, medium- to coarse-grained, poorlysorted, feldspathic sandstone in beds around 40 cm thick,locally associated with cross-laminated sandstone.Bedding is commonly planar but locally hummocky, andthere are local interbedded pebbly bands. The sandstonevaries in grain size from 0.2 to 0.7 mm and is composedof quartz and abundant K-feldspar. The outlines of grainsare well defined by dust rings. There is cementation ofthe quartz grains by crystallographically continuousovergrowths, but no observable deformation. The feldspargrains are rounded to subrounded (Fig. 13), commonlyunaltered, and include abundant microcline. There iswidespread white mica; however, no plagioclase ispreserved. The amount of matrix is highly variable, locallyforming a considerable part of the rock. The arkosicsandstone is probably derived from a proximal graniticsource with minimal reworking of material.

A small outcrop at the western edge of MERRIE, 900 msouth of Quartz Well (AMG 991563), consists of thin-bedded, coarse-grained, poorly sorted, pebbly quartzsandstone. This outcrop is the easterly continuation ofan outcrop of conglomerate (#Eyo) on THADUNA (Pirajnoand Adamides, 1998), which is located close to theunconformity with the Yerrida Group. The sandstone ishighly immature with abundant chlorite probably afterbiotite, and minor white mica. Lithic fragments includefine-grained quartzite and chert. Detrital quartz, locallywith overgrowths from a previous silicification event,suggests partial derivation from a recycled sedimentaryenvironment.

Sweetwaters Well Member (#Eyw)

The type locality for the Sweetwaters Well Member(#Eyw) is about 3.5 km southeast of the abandoned

21


Sweetwaters Well on MERRIE. The member is representedby a low-dipping sequence of laminated stromatoliticdolomite. It defines the upper contact of the YelmaFormation at this locality, and is separated from theoverlying Frere Formation by a thin (5 m) sequence ofhematitic siltstone. Smaller outcrops of this member, inthe same stratigraphic position, are present furthernorthwest of the type locality, and an extensive area ofcalcrete surrounding Sweetwaters Well is probablyunderlain by this unit.

The carbonate is in the form of grey, well-beddedstromatolitic dolomite (Fig. 14a). A section about 10 mthick is exposed at the type locality, but in excess of 300 mof interbedded siltstone and dolomite were intersected ina diamond drillhole northwest of Mount Deverell(Johnston and Hall, 1980). The stromatolites Asperiadigitata (Fig. 14b) and Pilbaria deverella are thepredominant species associated with domical stromatolites(Fig. 14c). Murgurra nabberuensis is present in isolatedoutcrops. The association of Asperia and Pilbaria isinterpreted, in light of similar associations in thelithologically equivalent Duck Creek Dolomite (Grey andThorne, 1985), as indicative of upward-shallowingsequences in a lagoonal to intertidal setting. At least threesuch cycles have been identified in the exposed section(Grey, K., 1999, pers. comm.), representing successivetransgressions and regressions.

The dolomite is composed of clear microcrystallinecarbonate in irregular, probably microbial laminae, withvariations in grain size from fine-grained carbonate withcrystals 50 µm in diameter to coarse-grained carbonateover 1 mm in length occupying areas of dissolution.Empty spaces are filled with an assemblage of detritalquartz and clays. Stylolitic fractures are abundant in thecarbonate and commonly filled by chlorite in associationwith sulfides.

At the type locality, the contact between the stromato-litic dolomite and the Frere Formation is marked by a 5 m-thick band of thinly bedded and laminated hematiticsiltstone. Similar siltstone, locally associated with thin-bedded, glauconitic quartz sandstone, is exposed 1 kmwest of Mount Deverell (AMG 330676) at the samestratigraphic level below the basal iron-formation. At thislast locality, the siltstone shows abundant lenticularlaminations on a microscopic scale (Fig. 15a) with thetexture defined by dark-coloured, ferruginous, micaceousand quartz-rich material, alternating with clay-richlaminae. The clays show moderate, bedding-parallel,preferred orientation due to diagenetic compaction andbelong to the illite group, as judged from their opticalproperties. The laminations are 0.1 – 0.3 mm thick andare composed of thinner laminae around 20 µm thick. Thefine-grained quartz arenite, which is interbedded withthe siltstone, is thin bedded with obstacle scours on

Figure 13. Feldspathic sandstone showing subrounded quartz, K-feldspar, and subordinate lithic fragments at thebase of the Yelma Formation. GSWA 152883, transmitted light, crossed polars

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N. G. Adamides

Figure 14. Sweetwaters Well Member:(a) Well-bedded stromatolitic

dolomite, exposed at thetype locality 3.5 km south-east of Sweetwaters Well(AMG 389649);

(b) Digitate stromatoliteAsperia digitata, typelocality of Sweetwaters WellMember. The diameter ofthe lens cap is 5.5 cm;

(c) Domical stromatolite, typelocality, Sweetwaters WellMember. The diameter ofthe lens cap is 5.5 cm

23


Figure 15. Siltstone and sandstone associ-ated with the Sweetwaters WellMember:(a) Small-scale, lenticular

laminations in siltstone.GSWA 152822, plane-polarized light;

(b) Obstacle scours inglauconitic sandstoneassociated with siltstone.Outcrop 1 km west of MountDeverell (AMG 330676).Length of field of view is20 cm;

(c) Texture of glauconiticsandstone of (b) showingflattened glauconite pelletsassociated with quartz andpyrite in a fine-grained,quartz-rich matrix. GSWA152823, plane-polarizedlight, length of field of viewis 3.5 mm

24

N. G. Adamides

bedding planes (Fig. 15b). The unit is silica cemented,moderately sorted, and composed of subangular quartzwith the grains defined by dust rings, together withwidespread elliptical glauconite pellets (Fig. 15c).Tourmaline is the predominant heavy mineral. There is noobservable deformation and the glauconite has retained itsoriginal shape. Considerable empty space suggests thepresence of weathered-out labile grains. Some of thesegrains may have been feldspars and there are alsowidespread, large (0.4 mm across) concentrations of micasmostly weathered to kaolinite. Diagenetic pyrite occurs ascubes 0.3 mm in diameter, replaced by iron hydroxides.The glauconite pellets and some intermixed quartz grainsare larger in size than the matrix quartz, probablysuggesting an intraclastic origin of the glauconite andderivation from adjacent parts of the basin.

The lenticular laminations in the siltstone and thepresence of glauconite, typically considered to be anindicator of low sedimentation rates (Amorosi, 1995),suggest quiet conditions of sedimentation in a restrictedbasin where the bottom currents were commonly weak(Reineck and Wunderlich, 1968). The lithologicalassociations are consistent with a subtidal to intertidalsetting.

Frere Formation (#Ef, #Efg, #Efgz, #Efs,#Efi)

The Frere Formation (Hall et al., 1977) is composed ofgranular iron-formation and interbedded shale, and namedafter the Frere Range on NABBERU (1:250 000). Theformation conformably overlies the Yelma Formationthroughout the Earaheedy Basin, with the contact placedat the first occurrence of granular iron-formation. Theupper contact with the Karri Karri Member of theWindidda Formation is placed at the last occurrence ofiron formation.

Detailed studies of the granular iron-formations of theEaraheedy Group (Hall and Goode, 1978; Goode et al.,1983; Bunting, 1986) highlighted their textural similaritiesto similar rocks in the Lake Superior region of NorthAmerica (Gross, 1972; French, 1973; Klein, 1974; Floranand Papike, 1975). Peloidal, pelletal, and oolitic texturesare common in both and have been interpreted as the resultof the formation of these rocks as chemical sedimentsfollowed by disruption of sedimentary layers prior todiagenetic consolidation.

The Frere Formation occupies the northern part ofMERRIE, and represents parts of the southern limb of aregional syncline structure, which affected the rocks of theEaraheedy Group. The formation is subdivided, on thegeological map, into several lithotypes: iron-rich,commonly jaspery iron-formation (#Efg); grey, siliceousiron-formation (#Efgz); laminated siltstone and shale(#Efs); and laminar iron-formation (#Efi).

At the type locality of the Sweetwaters Well Member,the basal unit of the Frere Formation is a grey, siliceousiron-formation. A similar association is present 3.8 kmnorthwest of Mount Deverell (AMG 312702). At thislocality, greenish-grey, massive to peloidal iron-formation,

in beds around 30 cm thick, is overlain by siltstone withthin interbeds of peloidal chert. Shallow, slightlyasymmetrical ripple marks are present in peloidal chertinterbedded with the siltstone. The upper part of thesection is taken up by well-bedded, peloidal, grey,siliceous granular iron-formation in beds averaging 30 cm,with sparse intraclastic facies and disrupted cherty layers.

Jaspery granular iron-formation (#Efg) is present attwo stratigraphic levels separated by ferruginous shale(Fig. 16a). At outcrop scale, the unit is interbedded withsiliceous iron-formation and shale, with a commonlylensoidal arrangement of layers (Fig. 16b). Beds rangefrom 10 to 40 cm in thickness, commonly have a flintytexture, and are interbedded with siltstones. The jasperlayers locally display a texture of jigsaw fit of fragmentswith interstitial silica, suggesting that the fragments haveundergone only minimal displacement from the site offormation. Such jasper grades laterally into peloidal jasper,which incorporates intraclasts of siliceous iron-formationderived from adjacent parts of the basin. Elsewhere, thin,continuous jasper layers are enclosed within thicker semi-continuous layers, which display pelletal or peloidaltextures.

Jaspery iron-formation is typically composed offerruginous peloids, mainly of jasper in the form ofmicrocrystalline aggregates of finely divided iron oxidesand silica, or in other cases of platy hematite 20–80 µmin size. Other peloids consist totally of euhedral magnetiteor hematite. The peloids are in the form of elliptical bodiesaveraging 0.5 – 1 mm in size (Fig. 17a) and commonlydisplay syneresis cracks. Open-weave peloids are alsopresent, composed of a jasper shell within which iscoarsely crystalline hematite growing on the walls, withthe interior of the peloid occupied by a quartz mosaic.The silica interstitial to the ferruginous peloids is in theform of grains 10–15 µm in diameter, reaching up to30 µm in the recrystallized types. The relationship of thesiliceous matrix with the peloids indicate epitaxial growthof the quartz and suggest that the silica is a later cement,and not the original matrix of the peloids. Peloidscomposed of coarse, euhedral magnetite are also present,and in the weathered samples the mineral is martitizedalong crystallographic directions. In some cases, roundedjasper peloids enclosed within later peloids provideindications of a complex history of gel deposition,synsedimentary disruption, and diagenesis (Fig. 17b). Anumber of peloids consist of magnetite–hematite, with themagnetite in the form of large octahedra and the hematitein smaller platy crystals. This may suggest that bothminerals were stable in the environment of deposition ofthese rocks.

The siliceous iron-formation (#Efgz) is commonlyexposed in the form of beds, around 30 cm thick,composed of grey quartzite and interbedded cream-coloured chert, and gives rise to scree of irregular-shapedboulders. The unit is composed of elliptical peloids ofpartly recrystallized chert (Fig. 18), intermixed withferruginous peloids. Many of the chert peloids displayfeatures of partial replacement by euhedral magnetite(altered to hematite). This suggests that most of theferruginization in this unit may be secondary. The material

25


interstitial to the peloids is made up of quartz, with grainsize 30–50 µm, which displays an epitaxial relationshipwith the peloids, suggesting that it is a later cement. Inother cases, the interstitial material is made up of radiatingsheaves of chalcedony. In some facies of the siliceousiron-formation, the peloids are composed of brownish,interlocking polygonal aggregates of quartz where thereare disseminated needles of possible stilpnomelane. Theassociation suggests that the peloids may have had agreenalite precursor, altered to stilpnomelane during low-grade metamorphism, as documented in iron formationsfrom North America (French, 1973).

Sedimentary structures are abundant in both types ofgranular iron-formations. These include synsedimentarydisruption of chert bands, which occur in the form ofsemi-continuous, locally boudinaged layers. Thisdisruption was produced when the chert was still in asemiplastic state, as suggested from the fact that associatedjasper beds are free of similar features. Coarse, angularintraclasts, predominantly of chert, suggest post-diageneticbrecciation and deposition as intraformational breccia. Insome cases, disrupted siliceous layers show imbricationdue to lateral movement. Bedding in the jaspery iron-

Figure 16. Geological sections through the Frere Formation:(a) Composite section showing the distribution of ferruginous and siliceous facies of iron formation and relationships

with shale and laminar iron-formation;(b) Detailed section showing relationships between rock types of the Frere Formation

formation is mostly planar; however, many of the tops ofsiliceous beds show irregular load casts, suggesting a moreplastic behaviour probably due to the higher water content.Poorly preserved ripple marks are present in both typesof iron formation and current lineations have beenobserved on some bedding planes. Minor structures withinthe beds include gentle, wavy laminations and local,shallow cross-laminations. All these features arecompatible with a shallow-water environment.

Siltstones (#Efs) interbedded with the iron formationsare hematitic, commonly laminated, and variablyferruginous. Locally, for example, 3.1 km northeast ofMount Deverell (AMG 354703), the siltstones are buff-coloured and dolomitic. Beds average 10–30 cm inthickness, and the bedding is planar with small-scalelenticular lamination. Thick-bedded, massive, grey quartzsiltstones with beds up to 40 cm thick are also present2 km northeast of Lake Nabberu at the eastern edge ofMERRIE (AMG 487679), and are typically composed ofclastic quartz and white mica in a fine-grained matrix. Thissuggests that periods of predominantly chemicaldeposition were periodically interrupted by clasticsedimentation.

Ferruginous shale. Gradation into Karri Karri Member

Laminar iron-formation

Laminar iron-formation

Siliceous GIFFerruginous shale

Ferruginous shale

Ferruginous jaspery GIF

Ferruginous shale

Ferruginous jaspery GIF

Siliceous GIFStromatolite dolomite, Sweewaters Well Member, Yelma Formation

150 m

150 m

25 m

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30 m

20 m15 m

40 m

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a) b)

Ferruginous shale

Peloidal textures

Massive jaspery iron-formation

Siliceous iron-formation

Intraclasts

NGA112 18.1.00

Siliceous granular iron-formation (GIF)

26

N. G. Adamides

Figure 17. Textures of jaspery iron-formation:(a) Jaspery, peloidal iron-formation composed predominantly of jasper and subordinate ferruginous

chert peloids in a siliceous matrix. Note syneresis cracks in the ferruginous chert peloid at left.GSWA 149377, plane-polarized light;

(b) Rounded ferruginous peloid enclosed within larger peloid. The texture suggests a protractedhistory of deposition, disruption, and redeposition of ferruginous material. GSWA 152832,plane-polarized light

27


Figure 18. Granular siliceous iron-formation showing typical peloidal texture and partial ferruginization of chertpeloids. GSWA 152841, plane-polarized light

Typical mesobanded iron-formation consisting ofdecimetre-scale alternations of microbanded silica-richand iron-rich layers is absent on MERRIE. Laminar iron-formation (#Efi) consists of finely laminated ironstonewith very sparse siliceous bands, forming topographicallypositive features within shales. The thickness of these unitsvaries from a few tens of centimetres upwards to 2 m. Atleast two bands of laminar iron-formation are exposedwithin the uppermost shales, which define the contact ofthe Frere Formation with the overlying Karri KarriMember (Fig. 16a).

The ferruginous layers in the laminar iron-formationare made up of minute crystals of hematite (2–5 µm) in amatrix that is dominated by iron hydroxides. Martitizedporphyroblastic magnetite, in crystals up to 50 µm in size,is dispersed throughout and probably secondary afterhematite. The siliceous layers consist of mostly aphaniticmaterial, which consists of disseminated euhedralmagnetite crystals and subordinate acicular hematite. Rare,altered carbonate rhombs are present in the groundmass.Intraclastic fragments are commonly enclosed within thesiltstone layers.

Lateritic weathering resulted in the almost totalobliteration of primary mineralogy of iron formations onMERRIE, with the exception of silica and iron oxides.However, examination of unweathered samples fromdrillcore (Adamides, in prep.a) from adjacent NABBERU

indicated the presence of abundant stilpnomelane, bothprimary and early diagenetic, widespread minnesotaite,minor greenalite, and various types of carbonate (dolomite,ankerite, siderite). Interbedded siltstones are locallycomposed of a microcrystalline assemblage of quartz andchlorite. All these assemblages are directly comparable toexamples from North America (Gross, 1972; Floran andPapike, 1975) and suggest a similar genesis. The quartz–chlorite association has been described from Algoma-typeiron-formations of the Weld Range (Gole, 1981), whereit was interpreted as a primary sedimentary assemblage.

Secondary processes affecting the iron formations arerepresented by carbonate alteration in the form of trailsof euhedral carbonate rhombs (probably ankeriteand siderite) following fractures. Ferruginization takesthe form of fracture-controlled replacement by euhedralmagnetite, or the partial replacement of siliceouspeloids. Distinction between primary and secondarymagnetite is made on the basis of crosscutting relationshipswith the primary assemblages. Almost complete replace-ment of siltstone by a carbonate–stilpnomelane assemblagewas noted in drillhole samples from the area 3.5 kmnortheast of Mount Deverell (AMG 366698). Thestilpnomelane replaces the matrix and forms veinscomposed of acicular birefringent crystals. Abundantporphyroblastic carbonate is present and associatedwith disseminated magnetite; chlorite is an additionalcomponent of the vein assemblage.

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N. G. Adamides

Windidda Formation (#Ed)

The Windidda Formation (after Windidda Homestead onthe KINGSTON 1:250 000 sheet) consists of siltstone, quartzsandstone, and carbonate, and conformably overlies theFrere Formation. The lower contact is placed at the lastoccurrence of iron formation. The upper contact withthe Chiall Formation is defined by the occurrence of thin-bedded quartz sandstone and siltstone. The WindiddaFormation is represented by outcrops of the Karri KarriMember in the northeastern part of MERRIE.

Karri Karri Member (#Edk)

The Karri Karri Member (new name, after Lake KarriKarri on the NABBERU 1:250 000 sheet) is typicallycomposed of parallel-laminated siltstone and shale, withlocal quartz sandstone lenses.

The siltstones are typically argillaceous and parallel-laminated, and were deposited at water depthsbelow storm wave-base. The laminae are defined byalternations of clay-rich and quartz-rich material andtrails of weathered ferruginous material, probablyrepresenting sedimentary diagenetic sulfides. The presenceof diagenetic pyrite, in association with anomalousmanganese and base metal values in similar rocks fromEARAHEEDY (Adamides, in prep.b), suggests that the shaleswere partly deposited in anoxic conditions. Thisconclusion may have an important bearing on themineralization potential of the Earaheedy Basin (seeEconomic geology).

Chiall Formation (#Ec)

The Chiall Formation (new name, after Chiall Spring onthe KINGSTON 1:250 000 sheet) is a sequence of thinlybedded quartz sandstone and siltstone (WandiwarraMember) with local orthoquartzite lenses (PrincessRanges Member), which conformably overlies theWindidda Formation. On MERRIE, only the WandiwarraMember is present, confined to the northeast corner of thesheet.

Wandiwarra Member (#Ecw)

On MERRIE, the Wandiwarra Member (after the abandonedWandiwarra Well on the KINGSTON 1:250 000 sheet) isvery limited in extent and represented by a sequence ofgrey quartz arenite and interbedded siltstone. The areniteis mostly structureless with the exception of widespreadmud clasts in the body of the rock and parallel laminationsin the higher parts. Mud-clast moulds are rounded andrange up to several centimetres in size. There are local,poorly preserved ripple marks and current lineations.The arenite is well sorted and composed of subroundedto subangular grains around 0.2 mm in diameter, withgrain boundaries defined by fine dust rings; the arenite issilica cemented and contains kaolinitic pellets in the samesize range as the quartz grains.

A sample of siltstone spatially associated with thequartz arenite was found to be laminated on a millimetre

scale and strongly chloritic, with dense disseminations ofiron hydroxides. Chlorite is abundant in the matrix of therock, either in small flakes or larger grains, and is stronglypleochroic from yellow to deep green with anomalousbirefringence. It is similar in nature to chlorite associatedwith the iron formations and may be derived from them.

Structure and metamorphismThe earliest Proterozoic structures are probably repre-sented by a series of east-southeasterly trending faultsthat are exposed within granitoid rocks on centraland eastern MERRIE. Both the faults and associated quartzveins are steeply dipping. They are reflected on aero-magnetic images by linear negative anomalies, and havelaterally displaced the Yandal greenstone belt on CUNYU

(Adamides et al., 1999). The structures terminate againstthe Merrie Range Fault, suggesting that this structurehas been rejuvenated during the Capricorn Orogeny. Thefaults have an associated conjugate set of faults andfractures oriented northeast and are also defined by quartzveins.

MERRIE is located at the junction between the Yerridaand Earaheedy Basins and the deformational regimevaries accordingly. The Juderina and Killara Formationsare typically undeformed, resting unconformably onArchaean basement. The outcrop forms part of the stableParoo Platform (Gee and Grey, 1993), which passesnorthwestwards into a belt of strong deformation andisoclinal folding between the Goodin and Marymia Inliers.This belt has been termed the Glengarry Fold Belt by Gee(1987). Deformation along this belt, related to northwest-directed compression, has not affected the Yerrida Groupon MERRIE.

Deformation of the Yerrida Group was followed bydeposition of the Earaheedy Group and its subsequentdeformation. The Earaheedy Group is folded into an east-southeasterly plunging synclinorium (Bunting, 1986),with part of the southwestern limb exposed on thenorthern part of MERRIE. On FAIRBAIRN (Adamides andPirajno, in prep.), abundant evidence of small-scalethrusting and associated bedding-parallel quartz veining,particularly evident in the granular iron-formations, isprobably related to compression associated with thisfolding.

Mesoscale folding, with well-developed axial-planecleavage (Fig. 19) within Windidda siltstones at thenortheast end of MERRIE, indicates orientations of fold axesoblique to the synclinorial axis and suggests the presenceof cross folds, which are oriented north-northeast. Thecross folds are related to a later period of deformation,which on FAIRBAIRN (Adamides and Pirajno, in prep.) isindicated by the presence of crenulation cleavage in thesiltstones of the Yelma Formation. This later deformationimplies northwest-directed compression and may berelated to a Bangemall event. Similar northeasterlytrending folds have been identified on NABBERU, whereinteraction with structures associated with the LockeridgeFault resulted in small-scale dome and basin interferencefolds (Hall, 1979).

29


After the deposition and deformation of the EaraheedyGroup, movements along the Merrie Range Fault resultedin the disruption of the outcropping Yelma and FrereFormations and the earliest easterly structures evident inthe granite. Observations of the outcrop pattern (seesimplified geology on map) suggests a possible left-lateraldisplacement of several kilometres along this structure.

The most sensitive indicators of metamorphism arethe mafic rocks of the Killara Formation. These rocksusually preserve most of their primary mineralogy.Plagioclase is commonly weakly altered along veinlets andfractures to granular clinozoisite and carbonate, or,elsewhere, to sericite commonly associated with chlorite.The titanomagnetite is altered to leucoxene and ilmenite.Hypersthene is serpentinized. The alteration is non-pervasive and may be interpreted as mostly the result ofautometasomatism, probably coupled with the effects ofmild, hydrothermal metamorphism indicated by quartz–epidote–carbonate veining.

The sedimentary rocks of the Yerrida Group (JuderinaFormation) preserve their primary sedimentary features,which also suggests that they have not undergonesignificant metamorphism. Quartz grains in the areniteunits are defined by dust rings and are commonlyundeformed. Associated siltstones commonly preservetheir original clay mineralogy, with minor formation ofillite. This suggests very mild metamorphism, probablyequivalent to the archimetamorphism grade of Kisch(1987).

One sample of a blotchy-textured, poorly sorted quartzarenite from the area 1.6 km west-northwest of HadenWell close to the Merrie Range Fault (AMG 248458)contained widespread, newly formed tourmaline as areplacement of the matrix interstitial to the quartz grains.This tourmaline is interpreted as evidence of mild boronmetasomatism, probably from fluids originating from thisfault.

The metamorphism of the Earaheedy Group is similarto that of the Yerrida Group. The formation of illite islocally associated with axial-plane cleavage. Chertcrystallinity is commonly considered to be a sensitiveindicator of metamorphic grade, increasing in grain sizeparallel with increasing grade (Klein, 1983; Goode et al.,1983). Peloidal chert from the Frere Formation is typicallycomposed of grains around 5 µm in size, suggestingminimal recrystallization. This feature, together with thepreservation of primary to early diagenetic assemblagesin the iron formations (Adamides, in prep.a), suggests verylow grades of metamorphism.

Cainozoic geologyRecent deposits have been subdivided into Quaternary(prefixed Q) or Cainozoic (prefixed Cz) on the basis oftheir relative age of deposition and evidence of dissection.Older deposits are typically dissected and may representremnants of the old lateritic duricrust. This duricrust is

Figure 19. Mesoscale folding of laminated siltstones of the Karri Karri Member, showing axial-plane cleavage.Seven kilometres east of Eladgee Bore (AMG 440743). The diameter of the lens cap is 5.5 cm

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N. G. Adamides

mostly preserved in areas of outcrop of the Merriegreenstone belt, and is composed of indurated ferruginousand fragmentary laterite and associated coarse rubble(Czrf ). In granite terrain, silcrete (Czrz) is commonlydeveloped and gives rise to coarse, angular, boulderyscree. Silcrete is composed of angular quartz grains setin a siliceous aphanitic matrix. Laterite passes on flatground into finer grained rubble, commonly pisolitic(Czcf ), or on floodplains, where it is reworked by present-day alluvial processes, into ferruginous gravel (Qwf )mixed with soil. Lateritic ironstone (Czri), resulting frompercolation of iron-rich waters in fault zones, is commonlymassive to rubbly in outcrop and commonly associatedwith quartz veins.

Areas of outcrop are fringed by a mixture of loose orconsolidated gravel and silt, mixed with abundant angularrock fragments (Czc). This material grades at lower levelsinto sheetwash deposits (Qw). This last unit is commonlyindicated on aerial photographs by a characteristicarrangement of vegetation patterns, and is distinguishedfrom the smoother appearance of colluvial deposits. Thesheetwash deposits (Qw) and alluvium (Cza) areequivalent terms on the map, with the latter transferredfrom CUNYU (Adamides et al., 1999). A specific type ofcolluvium (Czcq) limited to areas around quartz veins, iscomposed predominantly of quartz rubble and debrisalmost to the exclusion of rock fragments. This passes atlower levels into sheetwash areas.

Active alluvial channels (Qa) are defined by zones ofsand, silt, and coarse gravel and boulders. These arecommonly lined with calcrete (Qak), a mixture ofcarbonate and opaline silica a few metres thick thatcommonly lines the main drainage channels. Theformation of calcrete is linked to precipitation below thewater table under conditions of low rainfall and highevaporation (Hocking and Cockbain, 1990). Claypans(Qac), composed mostly of silt and clay, form in low-lyingareas of sheetwash plains by the settling of material fromsuspension following flooding.

Quartz sand (Qs) forms extensive plains in thesoutheastern and southwestern parts of MERRIE andcommonly overlies granite. The sand, which is red–brownand composed of iron-stained, subangular quartz grainsaveraging 0.5 mm in diameter, is probably only a fewmetres thick. The sandplain is featureless except in thesouthern parts where northerly to northeasterly trendingdunes are present.

The playa lake-system of Lake Gregory – LakeNabberu is characterized by a complex system ofsediments. The lakes are floored by deposits of sand andsilt with subordinate evaporites (Ql), with the surroundinglow-lying areas composed of gypsiferous and salinedeposits (Qlg). Fringing the lakes are sand dunes (Qld)composed of fine-grained, red–brown sand and silt madeup of angular quartz grains mixed with lateritic ironstonegrains, which are polished by wind action. The depositsbuild gentle mounds a few metres high that are vegetatedmainly by mulga.

Lake calcrete (Qlk), distinctly different in genesis toalluvial calcrete, is particularly developed in the

inner parts of the lake system. Formation of this calcreteis linked to evaporitic processes and the deposit iscommonly gradational lakewards into the gypsite facies(Arakel and McConchie, 1982). Lake areas are commonlycharacterized by a distinct vegetation, with samphirecommunities being prominent.

GeochemistryTwo rock-chip samples were collected during mappingand analysed for a number of elements. Analyticalmethods and results are shown in Table 3. One sample ofironstone (GSWA 149379), spatially associated withchert breccia after dolomite (Sweetwaters Well Member),was found to be strongly anomalous in lead (4700 ppm),zinc (6200 ppm), and silver (0.4 ppm). The anomalism isrelated to mineralization within carbonates in this member(see Economic geology). The second sample (GSWA152849), collected from a fault zone in granite, isassociated with silicification, quartz veining, and localboxworks after pyrite. The sample is anomalous in gold(14 ppb), silver (1.6 ppm), and barium (3665.2 ppm). Theanomalous values are interpreted as due to the action ofhydrothermal fluids enriched in these elements, whichused the fault zone as a passageway to higher levels inthe crust.

Economic geologyA listing of exploration reports on open file in the WesternAustralian mineral exploration database (WAMEX) of theDepartment of Minerals and Energy is presented inAppendix 2 (April, 1999). The reports contain full detailsof exploration on MERRIE.

GoldPotential for gold mineralization exists within favourablelithologies and structures of the Merrie greenstone belt,and the area is currently subject to active exploration. Alimited study of the alteration mineralogy of thegreenstone belt (Farrell and Adamides, 1999) indicatedtypical weak alteration, dominated by epidote, biotite, andchlorite, with general scarcity of carbonates; however, thepossibility exists for stronger mineralization hosted insuitable structures.

IronThe iron-rich granular iron-formations and associatedferruginous shales of the Frere Formation are potentialhosts of economic mineralization, particularly inareas of supergene enrichment. Such areas of enrichmentare widespread in the Miss Fairbairn Hills area onFAIRBAIRN (Adamides and Pirajno, in prep.) and in thearea of Frere Range on MERRIE and FAIRBAIRN. Examin-ation of these occurrences (Item 590, Appendix 2) bygrab sampling detected assays up to 66% Fe withcorresponding low phosphorus (0.08%). Subsequent

31


drilling was aimed at locating synclinal structures withinshales, amenable to secondary enrichment.

UraniumThe playa system of Lake Gregory – Lake Nabberu, withits prolonged history of precipitation and evaporation,draining extensive areas of granite to the south, is afavourable site for carnotite deposition. Exploration, basedon this model, was performed on adjacent NABBERU

(Taylor, 1980).

Base metalsThe Sweetwaters Well Member of the Yelma Formationlocally contains traces of galena. Grab samples ofdolomite from the type locality assayed 6% Pb,53 ppm Ag, 31.4 ppm As, 80 ppm Co, 70 ppm Cu,1900 ppm Mn, 105 ppm Ni, and 230 ppm Zn (Hall andHaslett, 1978). Shallow drilling intersected highest Pb of1.6% over 1 m, with other intersections being 6 m of0.49 – 0.81% Pb. The mineralization either followsstylolitic fractures or forms in the cores of domalstromatolitic forms (Bunting et al., 1982). Diamonddrilling northwest of Mount Deverell (Johnston and Hall,1980) penetrated a thickness of interbedded dolomite andshale in excess of 300 m. This dolomite horizon has beenrecently explored by Renison Goldfields Consolidated

Table 3. Trace-element analyses of samples from MERRIE

GSWA sample 149379 152849AMG coordinates 329682 448440 Detection AnalyticalLithology ironstone silicified zone limit method

Parts per millionAg 0.4 1.6 0.1 A/MSAs 245 25 0.1 A/MSAu (ppb) 1 14 1 FA*/MSAu-Repeat (ppb) – 13 1 FA*/MSBa 230 3 665.2 0.1 A/MSBi 0.16 6.15 0.01 A/MSCo 78 22.6 0.1 A/MSCr <2 3 2 A/OESCu 102 115 1 A/OESMo 0.5 25.1 0.1 A/MSNi 220 4 1 A/OESPb 4 700 104 2 A/MSPd <1 <1 1 FA*/MSPt <1 <1 1 FA*/MSSe – 15 2 A/MSSn 0.6 0.7 0.1 A/MSTh 3.6 18.52 0.01 A/MSU 3.6 1.55 0.1 A/MSV <2 8 2 A/OESW 0.2 0.5 0.1 A/MSZn 6 200 16 1 A/OESMn 800 0.006 1 A/OESFe (%) 50 9.34 0.01 A/OES

NOTES: A/MS: Multi-acid digest including hydrofluoric, nitric, perchloric, and hydrochloric acids. Analyzed by inductivelycoupled plasma mass spectrometry

FA*/MS: Lead collection fire assay using new pots. Analyzed by inductively coupled plasma mass spectrometryA/OES: Multi-acid digest including hydrofluoric, nitric, perchloric, and hydrochloric acids. Analyzed by inductively

coupled plasma optical (atomic) emission spectrometry

(Item 9569, Appendix 2). The drilling intersectedwidespread, subeconomic lead mineralization both onMERRIE and NABBERU, with the best intersections around1% combined Zn+Pb over 2 m (Dörling, 1997).

The identification of lithologies with black-shale affinities in rocks of the Karri Karri Membersuggests the possibility that these rocks may have actedas repositories of a number of elements includingmanganese, barium, copper, zinc, uranium, and vanadium,as is the case in black-shale basins (Coveney and Martin,1983). Subsequent mobilization of these elements bytectonism may lead to concentration in suitable rock types(such as carbonates), resulting in the formation ofsediment-hosted, epigenetic base metal deposits. Thepresence of volcanic activity in close association withblack shales is commonly considered to be a favourablefactor, both in the mobilization of fluids and contributionof metals to the system (Delian et al., 1992). Mafic dykesare interpreted, from aeromagnetic data, to underlie theEaraheedy Basin rocks at shallow depths.

GroundwaterMost of the groundwater suitable for livestock is derivedfrom wells in calcrete and thick alluvial accumulations indrainage channels. Smaller quantities of water may beobtained from fractured, jointed, or weathered bedrock.The salinity of the water increases towards the Nabberu

32

N. G. Adamides

Lake system, reaching values up to 7300 ppm TDS (totaldissolved solids) in the areas around the salt lakes (Sandersand Harley, 1971) and values around 1000–3000 ppmTDS in areas away from the lakes.

The best potential for groundwater on MERRIE isoffered by the thick calcrete concentrations in the area

around Eladgee Bore in the northeast corner of the sheet,and the thick alluvial accumulations and calcrete depositsin the north-flowing Mibbeyean Creek on the westernedge of the sheet.

33


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van de GRAAFF, W. J. E., CROWE, R. W. A., BUNTING, J. A., andJACKSON, M. J., 1977, Relict early Cainozoic drainages in aridWestern Australia: Zeitschrift fur Geomorphologie, v. 21, p. 379–400.

WOODHEAD, J. D., and HERGT, J. M., 1997, Application of the‘double spike’ technique to Pb-isotope geochronology: ChemicalGeology, v. 138, p. 311–321.

WYCHE, S., FARRELL, T. R., LIU, S. F., LANDMARK, J.,FLETCHER, M., and HOPF, S., 1997, Archaean geology andmineralization of the northern part of the Eastern GoldfieldsProvince, Yilgarn Craton, Western Australia — a field guide:Western Australia Geological Survey, Record 1997/7, 54p.

36

N. G. Adamides

Appendix 1

Gazetteer of localities mentioned in text

Locality(a) Latitude Longitude AMG coordinates(S) (E) Easting Northing

6 Mile Well (abd) 25°44'21" 120°11'57" 219000 715020021 Well 25°45'30" 120°07'08" 211000 7147900Boody Hole Well 25°37'49" 120°12'56" 220400 7162300Bulletin gold mine 26°37'00" 120°14'00" 224500 7053000Bungarra Bore 25°58'41" 120°14'29" 223800 7123800Canning Stock Route 25°54'24" 120°21'53" 236000 7132000Chiall Spring 26°06'23" 121°51'07" 385200 7112000Curvaceous Carly Bore 25°59'11" 120°09'08" 214900 7122700Dingy Well (abd) 25°44'52" 120°16'07" 226000 7149400Doyle Well 25°49'10" 120°09'58" 215900 7141250Eladgee Bore 25°31'27" 120°22'55" 236900 7174400Frank Well (abd) 25°39'50" 120°16'46" 226900 7158700Frere Range 25°35'00" 120°27'41" 245000 7168000Haden Well (abd) 25°46'59" 120°16'15" 226300 7145500Halls Creek(b) 18°14'00" 127°40'00" 359000 7983500Joe Bore 25°42'41" 120°21'07" 234300 7153600Juderina Bore(c) 25°52'53" 119°12'03" 720500 7135600Killara Homestead(c) 26°20'55" 118°57'25" 695300 7084200Kimberley Range(c) 26°19'00" 119°48'00" 779500 7086200Lake Carnegie 26°10'00" 122°25'00" 441700 7105700Lake Karri Karri 25°36'21" 120°44'22" 273000 7166000Lake Nabberu 25°36'00" 120°07'00" 210400 7165400Lake Wells 26°40'00" 122°59'00" 498300 7050500Meekatharra(c) 26°36'00" 118°30'00" 649400 7057000Merrie Range 25°43'26" 120°14'57" 224000 7152000Miss Fairbairn Hills 25°14'00" 120°21'00" 233000 7206600Mount Deverell 25°35'13" 120°21'14" 234200 7167400Mount Paterson 25°43'35" 120°03'25" 204700 7151300Nabberu Tank 25°38'19" 120°25'13" 241000 7161800Neds Creek Homestead(c) 25°28'52" 119°38'52" 766200 7179100Newman(c) 23°16'00" 119°38'52" 762600 7424600No 3 Govt Well 25°46'32" 120°24'30" 240100 7146600Quartz Well 25°40'23" 120°00'09" 199100 7157100Sweetwaters Well (abd) 25°35'33" 120°22'18" 236000 7166800Vermin-proof fence 25°56'11" 120°02'41" 204000 7128000Verscher Range 25°44'00" 120°05'00" 207400 7150600Wandiwarra Well (abd) 26°22'30" 122°19'30" 432660 7082600Weld Spring 25°01'00" 121°35'00" 357000 7232400Wiluna 26°35'39" 120°13'25" 223500 7055500Windidda homestead 26°23'00" 122°13'00" 421900 7081600Wynn Well 25°43'35" 120°05'37" 208400 7151400

NOTES: (a) Localities are within Australian Map Grid (AMG) Zone 51 unless specified otherwise(b) Locality within AMG Zone 52(c) Locality within AMG Zone 50abd: abandoned

37


Appendix 2

Reports currently (April, 1999) on open file in theWestern Australian mineral exploration (WAMEX) database

GSWA WAMEX Reports Duration Title CompanyItem number(a)

1155 7 1972–76 Baumgarten nickel–copper exploration Dampier Mining Company Ltd180 1 1975–76 Corners Well manganese iron exploration Dampier Mining Company Ltd590 1 1977–78 Nabberu Basin iron exploration Dampier Mining Company Ltd2181 3 1977–80 Sweetwaters Well lead–zinc exploration Dampier Mining Company Ltd1138 2 1979–80 Bridleface Outcamp uranium exploration Uranerz Australia Pty Ltd2020 9 1981–82 Lake Gregory copper–lead–zinc exploration Esso Exploration Australia Inc.2684 1 1982–84 Quartermaine Well copper–uranium exploration Amoco Minerals Australia Company3223 1 1986–87 Cunyu Woolshed–Davis Well gold exploration BHP Minerals Pty Ltd4595 1 1987–90 Gray Well gold exploration Eon Metals5547 2 1987–90 Baumgarten gold exploration Eon Metals9247 8 1989–97 Nabberu diamond–gold exploration Resolute Resources Ltd4373 2 1989–90 Horseshoe gold exploration ACM Gold Ltd6077 1 1990–91 Terabubba gold exploration Western Mining Corporation7836 1 1991–94 Seven Mile base metals–gold exploration Plutonic Operations Ltd9016 5 1991–96 Simpson Well gold–diamond–base metals exploration Galtrad Pty Ltd9705 5 1991–97 Cunyu gold–base metals exploration Cyprus Gold Australia Corporation7939 3 1992–94 Lake Nabberu diamond exploration Stockdale Prospecting8511 1 1991–95 Merrie Range gold–diamond exploration Marymia Exploration NL9165 1 1991–96 Cunyu gold–diamond exploration Cyprus Gold Australia Corporation7858 3 1991–94 Bundel Well gold exploration Eagle Mining Exploration9613 1 1993–96 Teague base metals exploration Renison Goldfields Consolidated9569 5 1993–98 Canning Gap base metals–diamond exploration Renison Goldfields Consolidated8071 1 1993–93 Nabberu diamond exploration Cladium Mining Pty Ltd8979 1 1993–96 Canning Gap diamond exploration Renison Goldfields Consolidated9769 1 1993–97 Canning Gap lead–zinc exploration Renison Goldfields Consolidated8146 1 1994–95 Deary Bore gold–base metals exploration Plutonic Corporation Ltd9389 2 1994–97 Freshwater base metals exploration Renison Goldfields Consolidated9489 2 1996–97 Hawkins Knob lead–zinc exploration RGC Exploration Pty Ltd

NOTE: (a) Information is available from the Department of Minerals and Energy Library, Mineral House, 100 Plain Street, East Perth, WA, 6004

BARROWISLAND

DAMPIER ROEBOURNE BEDOUTISLAND

1 2 3 4

5 6 7 8SF 50

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NINGALOO YANREYWYLOO MT BRUCE

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Óc

Óc

Óc

Óc

Óc

Óa

6070

75

80

16

16

16

56

30

32

26

12

10

16

ÓcìEfs

Ócñg

Ócñg

Ócñg

Ócñg

ìEfgfìEfs

ìEyw

ìEcw

ìEyw

ìEdk

ñbeñbe

ñbe

ñbe ñbe

ñbañb

ñbañu

ñba

ñbf

ñbfñbf

ñfs

ñfs

ñbf

ñbe

ñfp

ñfp

ñfp

ñbe

ñbe

ñbe

ñbe

ñb

ñb

ñb

ñufñufñbae

ñbae

ñby ñbaf

ñbf

Pb

PEAK HILL MINERAL FIELD

MURCHISON MINERAL FIELD

MEEKATHARRA DISTRICT

W A R B U R T O N M I N E R A L F I E L D

ñbañbaeñbafñbfñbeñby

ñuf

Merrie Range Fault

?

30

Z

40

Merrie Synform

QUAT

ERNA

RY

CAIN

OZOI

C

PHAN

EROZ

OIC

PROT

EROZ

OIC

ARCH

AEAN

70

20

60

80

Clay and silt in non-saline claypans

Ferruginous gravel in low-gradient sheetwash areas

Calcrete associated with palaeodrainage and active drainage systems; locally silicified

Ferruginous duricrust; nodular, pisolitic, and massive ferricrete (laterite) and associated debris

Ironstone; ferruginized rock, massive to rubbly; includes degraded ferruginous duricrust

EARA

HEE

DY

BASI

N

Yerri

da G

roup

YERR

IDA

BASI

N

Granular iron-formation and granular siliceous iron-formation, in places peloidal; minor siltstone and shale

Siltstone and shale; subordinate granular iron-formation

Quartz sandstone and pebble conglomerate

Stromatolitic dolomite and dolomitic sandstone; includes chert breccia derived from dolomite

Fine-grained mafic intrusive rocks; sills

Siltstone and shale

Biotite monzogranite, commonly porphyritic

Metamorphosed mafic rock, undivided

Metamorphosed mafic rock, schistose (subsurface only)

Amphibolite (subsurface only)

Amphibolite, epidotized (subsurface only)

Amphibolite, foliated (subsurface only)

Metamorphosed mafic rock with epidote alteration (subsurface only)

Ultramafic rock, foliated (subsurface only)

Metamorphosed vesicular mafic rock (subsurface only)

Win

dpla

in S

ubgr

oup

Moo

loog

ool S

ubgr

oup

GN

MN

True north, grid north and magnetic north

are shown diagrammatically for the centre

of the map. Magnetic north is correct for

2 years.

TN

GRIDCONVERGENCE

1.2¾

GRID / MAGNETIC

1998 and moves easterly by about 0.1^ in

ANGLE 0.1°

2644

2645

2646

2647

2744

2745

2746

2747

2844

2845

2846

2847

2944

2946

2947

3044

3045

3046

3047

3144

3145

3146

3147

GABANINTHA

GLENGARRY

BRYAH

JAMINDI

YAGANOO

MOOLOOGOOL

DOOLGUNNA

MEREWETHER

THADUNA

MARYMIA

WILUNA

CUNYU

MERRIE

FAIRBAIRN

MILLROSE

NABBERU

METHWIN

SANDALWOOD

BALLIMORE

RHODES

GLENGARRY

NABBERU

WILUNA

PEAK HILL

SG 50-8

SG 50-12

SG 51-5

SG 51-9

MOUNT BARTLE

THREE RIVERS

GRANITE PEAK

LAKE VIOLET

Sand in dunes on and around playa lakes, in places gypsiferous

Metamorphosed sedimentary rock, undivided

Quartz rubble and debris adjacent to quartz veins

Eara

heed

y Gro

upYe

rrid

a Gro

up

YERR

IDA

BASI

NYI

LGAR

N C

RATO

N

Mafic dyke

Metamorphosed ultramafic rock

Frere Formation

Yelma Formation

Maraloou Formation

Killara Formation

Juderina Formation

SEA LEVELSEA LEVEL

4 km

2 km2 km

4 km

BADIAGRAMMATIC SECTION

Granular siliceous iron-formation and chert; subordinate siltstone and shale

75

22

Conglomerate and quartz lithic sandstone

Mafic rock, undivided

Windidda Formation

Wandiwarra Member: siltstone and shale with sandstone lenses

WINDIDDA FORMATIONKarri Karri Member: siltstone and shale; minor sandstone lenses

inclined.............................................................................

Gypsiferous and saline bedded deposits adjacent to playa lakes

Eara

heed

y Gro

up

Banded iron-formation; supergene enriched iron-formation

Chiall Formation

CHIALL FORMATION

EARA

HEE

DY

BASI

N

YILG

ARN C

RATO

N

FRERE FORMATION: granular iron-formation, siltstone, and shale; subordinate banded iron-formation

YELMA FORMATION:

mafic volcanic and intrusive rocksKILLARA FORMATION:

Sweetwaters Well Member:

JUDERINA FORMATION: quartz sandstone; subordinate siltstone and chert breccia

Finlayson Member: quartz sandstone, commonly ripple marked; subordinate siltstone

Aphyric tholeiitic basalt

2945

1:100Ý000 maps shown in black

1:250Ý000 maps shown in brown

Mafic dyke intruded into Archaean rock; dashed where interpreted from aeromagnetic data

TRANSVERSE MERCATOR PROJECTION

Grid lines indicate 1000 metre interval of the Australian Map Grid Zone 51

HORIZONTAL DATUM: AUSTRALIAN GEODETIC DATUM 1984

VERTICAL DATUM: AUSTRALIAN HEIGHT DATUM

0 1 2 3 4 5 6 7 8 9 10

KilometresMetres

1000

SCALE 1:100Ý000

Lacustrine deposits _ saline silt, mud, and minor sand in playa lakes, primarily associated with palaeodrainage

Sandplain _ unconsolidated sand and minor silt and clay; with scattered low, vegetated dunes

Colluvium _ loose to consolidated gravel, sand, and silt in moderate- to high-gradient slope deposits; locally dissected

Sheetwash deposits _ sand, silt, and gravel in low-gradient sheetwash areas that lack clearly defined drainage channels

Ferruginized rubble and colluvium _ dominantly ferruginized pisolites and nodules, ferruginized rock, and ironstone rubble; degraded lateritic duricrust

Sweetwaters Well Member

Alluvium _ sand, silt, and gravel in channels and channel systems

Windp

lain

Subg

roup

Subg

roup

Moo

lool

gool

Asperia digitata, Ephyaltes edingunnensis,

Geology by N. G. Adamides 1997

Granitoid rock, undivided; generally monzogranite

Felsic schist, commonly quartz-phyric

Monzogranite

Metamorphosed sedimentary and felsic rocks

Siliceous duricrust; nodular, pisolitic, and laminar silcrete, and intensely silicified bedrock

Ultramafic rock, undivided (section only)

Siltstone and shale (section only)

Pilbaria deverellastromatolitic dolomite and microbial limestone; minor siltstone and shale ( and )

Calcrete and gypcrete deposits in and around playa lakes

PALA

EOPR

OTER

OZOI

C

Metamorphosed felsic porphyry

Quartz in pods and veins

Alluvium _ semi-consolidated sand, silt, and gravel associated with palaeodrainage

undivided (simplified geology only)

Medium- to coarse-grained mafic intrusive rocks; sills

Metamorphosed felsic porphyry

ÔlÔld Ôlg Ôlk

ÔaÔac Ôak

ÔwÔwf

Ôs

Ócq Ócf

Órf Óri Órz

q

ìEcw

ìEdk

ìEfìEfg ìEfgz ìEfs ìEfi

ìEy

ìEyw

ìEys

ìEyc

ìEya

ìEyo

ìYkìYkf ìYkb ìYkd

ìYjìYjs ìYjf

ìdy

ñg ñgm

ñfp ñs ñfs

ñb

ñu

ñb

ñfsñsñfp

ñgmñg

ìYjfìYjsìYj

ìYkdìYkbìYkfìYk

ìEfiìEfsìEfgzìEfgìEf

CzrzCzriCzrf

ÓcfÓcq

ÔsÔwfÔwÔakÔacÔaÔlkÔlgÔldÔl

Óa Óc

ÓaÓc

Geological boundary

Fault

Small-scale fold axis, showing trend and plunge

Bedding, showing strike and dip

Igneous layering

Cleavage, showing strike and dip

inferred or concealed.............................................................

exposed...................................................................................

exposed, showing dip of fault plane....................................

concealed................................................................................

concealed, interpreted from aeromagnetic data................

strike-slip, showing relative displacement...........................

synform; exposed...................................................................

Z-vergence..............................................................................

inclined....................................................................................

trend........................................................................................

inclined....................................................................................

inclined...................................................................................

anticline...................................................................................

vertical....................................................................................

Fracture or joint, showing strike and dip

inclined....................................................................................

Stromatolite locality.......................................................................

Airphoto lineament........................................................................

Aeromagnetic lineament...............................................................

Formed road..................................................................................

Track...............................................................................................

Fence, generally with track..........................................................

Underground gas pipeline............................................................

Homestead.....................................................................................

Building..........................................................................................

Yard................................................................................................

Horizontal control, major..............................................................

Breakaway......................................................................................

Metamorphic foliation, showing strike and dip

Sand dune.....................................................................................

Contour line, 20 metre interval....................................................

Watercourse with ephemeral pools or waterholes.....................

Spring.............................................................................................

Bore................................................................................................

Well.................................................................................................

Windpump......................................................................................

Abandoned.....................................................................................

Mineral field boundary..................................................................

Mineral occurrence........................................................................

Lead........................................................................................

Mineral exploration drillhole, showing subsurface data............

ìdy

ìEc

ìEd

ìEf

ìEyw

ìEy

ìYm

ìYk

ìYj

ñgm

ñs+ñf

ñb

ñfp

ñu

120°00À 120°30À

120°00À 120°30À

GEOLOGICAL SURVEY OF WESTERN AUSTRALIA SHEET 2946

with modifications from geological field survey

This map is also available in digital form

Published by the Geological Survey of Western Australia. Copies available from the

Printed by the Sands Print Group, Western Australia

East Perth, WA, 6004. Phone (08) 9222 3459, Fax (08) 9222 3444

Topography from the Department of Land Administration Sheet SG 51-5, 2946,

ìYjsìYj

ìYk

ñg

ìYjf

ñu ñu ñu

ìdy

ñu

ñu ñu ñs+ñf

ñfpñb

ñu

ñfp

ñu

ñfp

ñfp

ñu

ñu

ñgm

ìYjf ìEya ìEyc

ñgm

ìEyaìEyc

ìEyw

ìEys ìEyc

ñgm

ìEys

ìyw

ìEfsìEfg

ìEfg

Edited by D. Ferdinando and G. Loan

Cartography by G. Fletcher and B. Williams

Information Centre, Department of Minerals and Energy, 100 Plain Street,

The recommended reference for this map is:

Western Australia Geological Survey, 1:100Ý000 Geological Series

ADAMIDES, N. G., 1999, Merrie, W.A. Sheet 2946:

25°30À

26°00À

25°30À

26°00À

10À 20À

40À

50À

20À10À

40À

50À

AUSTRALIA 1:100Ý000 GEOLOGICAL SERIES

0 5 10 15 20

Kilometres

SCALE 1:Ý500Ý000

¦ Western Australia 1999

DEPARTMENT OF MINERALS

AND ENERGY

L.C. RANFORD, DIRECTOR GENERAL

GOVERNMENT OF WESTERN AUSTRALIA

HON. NORMAN MOORE, M.L.C.

MINISTER FOR MINES

GEOLO

G IC A L SURVE

Y

WE

ST

E R N A U S T RA

LIA

GEOLOGICAL SURVEY OF

WESTERN AUSTRALIA

DAVID BLIGHT, DIRECTOR

PRODUCT OF THE NATIONAL

GEOSCIENCE MAPPING ACCORD

SIMPLIFIED GEOLOGY

SHEET INDEX

W.A.

N.T.

S.A.

N.S.W.

Vic.

Qld

Tas.

A.C.T.

SHEET 2946 FIRST EDITION 1999

ñu

A

B

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