EXPLANATORY NOTES GEOLOGY OF THE YILGALONG 1:100 000 SHEET

by I. R. Williams

1:100 000 GEOLOGICAL SERIES MONTAGUE DRYSDALE- MEDUSA SD 52 SOUND LONDON- BAN DERRY KS 12 5,9 10 CAMDEN SOUND ASHTON CAMBRIDGE PRINCE REGENT- GULF 16 15, 13 14 PENDER YAMPI o CHARNLEY MT LISSA 16 ELIZABETH DELL 2 3 4 1 2 BROOME DERBY LENNARD LANSDOWNE DIXON RIVER RANGE 6 SE 51 7 8 5 6 LA GRANGE MT NOONKAN- MT RAMSAY GORDON SE 52 ANDERSON BAH DOWNS 10 11 12 9 10 MANDORA MUNRO McCLARTY CROSSLAND MT BANNER- BILLILUNA HILLS MAN PORT 13 14 15 16 13 HEDLAND- 14 YARRIE ANKETELL o DAMPIER ROEBOURNE BEDOUT JOANNA DUMMER CORNISH LUCAS 20 BARROW SPRING ISLAND ISLAND 2 3 1 2 3 4 1 4 1 2 RALOOLA PYRAMID MARBLE NULLAGINE PATERSON SAHARA PERCIVAL HELENA STANSMORE ONSLOW YA R BAR RANGE 8 5 6 7 5 6 7 SF 51 8 5 6 SF 50 BALFOUR ROY HILL RUDALL TABLETOP URAL WILSON WEBB SF 52 NINGALOO YANREY WYLOO MT BRUCE DOWNS 10 11 12 9 10 11 12 9 12 9 10 TUREE NEWMAN ROBERTSON GUNANYA RUNTON MORRIS RYAN MACDONALD SF 49 MINILYA WINNING EDMUND POOL CREEK 15 16 13 14 15 16 13 16 13 14 14 COLLIER BULLEN TRAINOR MADLEY o MT PHILLIPS MT WARRI COBB RAWLINSON 24 QUOBBA KENNEDY EGERTON RANGE 2 3 4 1 2 3 4 1 4 1 2 NABBERU STANLEY HERBERT GLENBURGH ROBINSON PEAK HILL BROWNE BENTLEY SCOTT SHARK WOORAMEL RANGE BAY- 8 5 6 7 5 6 7 SG 51 8 5 6 SG 50 GLENGARRY WILUNA YOWALGA SG 52 SG 49 YARINGA KINGSTON ROBERT TALBOT EDEL BYRO BELELE COOPER 10 11 12 9 10 11 12 9 8,12 9 10 CUE SANDSTONE SIR DUKETON THROSSELL WESTWOOD LENNIS AJANA MURGOO SAMUEL WAIGEN 15 16 13 14 15 13 14 16 13 14 o KIRKALOCKA YOUANMI LEONORA LAVERTON RASON NEALE VERNON 28 GERALDTON- YALGOO WANNA HOUTMAN ABROLHOS 2 3 4 1 2 3 4 1 1 2 MENZIES EDJUDINA PERENJORI NINGHAN BARLEE MINIGWAL PLUMRIDGE JUBILEE MASON

7 8 5 6 7 8 DONGARA- 6 SH 51 5 6 SH 50 JACKSON KAL- SEEMOR LOONGANA HILLRIVER URNALPI CUNDEELEE E SH 52 MOORA BENCUBBIN GOORLIE K FORREST 12 9 10 11 5, 9 10 11 12 9 10 BOOR- PERTH KELLER- SOUTHERN WIDGIE- ZANTHUS NARETHA MADURA EUCLA BERRIN CROSS ABBIN MOOLTHA 13 14 15 14 15 16 16 13 14 o CORRIGIN HYDEN LAKE NORSEMAN BALLA- CULVER BURN- 32 PINJARRA JOHNSTON DO NOONAERA NIA ABBIE 2 3 4 1 2 3 4 1 2 COLLIE DUMBLE- NEWDE- RAVENS- ESPERANCE- MALCOLM- YUNG GATE THORPE MONDRAIN CAPE ARID ISLAND 6 7 8 5 7, 11 BUSSELTON- SI 50 SI 51 BREMER 6, 10 AUGUSTA PEMBERTON- MT BAY 5, 9 IRWIN INLET BARKER- 10, 14 11, 15 12 ALBANY

120o o 114o 126

MOUNT EDGAR YILGALONG BRAESIDE 2955 3055 3155

NULLAGINE SF 51-5

EASTERN NULLAGINE CREEK PEARANA 2954 3054 3154

IRW195 07.05.07 GEOLOGICAL SURVEY OF WESTERN AUSTRALIA

GEOLOGY OF THE YILGALONG 1:100 000 SHEET

by I. R. Williams

Perth 2007 MINISTER FOR RESOURCES Hon. Francis Logan MLA

DIRECTOR GENERAL, DEPARTMENT OF INDUSTRY AND RESOURCES Jim Limerick

EXECUTIVE DIRECTOR, GEOLOGICAL SURVEY OF WESTERN AUSTRALIA Tim Griffi n

REFERENCE The recommended reference for this publication is: WILLIAMS, I. R., 2007, Geology of the Yilgalong 1:100 000 sheet: Western Australia Geological Survey, 1:100 000 Geological Series Explanatory Notes, 45p.

National Library of Australia Card Number and ISBN 978-1-74168-101-7

ISSN 1321–229X

Grid references in this publication refer to the Geocentric Datum of Australia 1994 (GDA94). Locations mentioned in the text are referenced using Map Grid Australia (MGA) coordinates, Zone 51. All locations are quoted to at least the nearest 100 m.

Copy editor: D. P. Reddy Cartography: A. Blake Desktop publishing: K. S. Noonan

Published 2007 by Geological Survey of Western Australia This Explanatory Note is published in digital format (PDF) and is available online at www.doir.wa.gov.au/GSWA/publications. Laser-printed copies can be ordered from the Information Centre for the cost of printing and binding.

Further details of geological publications and maps produced by the Geological Survey of Western Australia are available from: Information Centre Department of Industry and Resources 100 Plain Street EAST PERTH, WESTERN AUSTRALIA 6004 Telephone: +61 8 9222 3459 Facsimile: +61 8 9222 3444 www.doir.wa.gov.au/GSWA/publications

Cover photograph: Constructive travertine falls, 2.5 m high, composed of calcium carbonate fl owstone deposited in a small creek incised in Carawine Dolomite, southwest Ripon Hills (MGA 261106E 743607N) Contents

Abstract ...... 1 Introduction ...... 1 Previous investigations ...... 4 Climate, vegetation, and physiography ...... 5 Regional geological setting ...... 6 Pilbara Craton ...... 6 East Pilbara Terrane ...... 8 Unassigned Pilbara Supergroup rocks (API-xmbs-mus, API-mc) ...... 9 Kelly Group ...... 9 Euro Basalt (AKEe-xmbks-mbs, AKEe-bk, AKEe-mh, AKEe-bb, AKEe-ml, AKEe-cc) ...... 9 Emu Pool Supersuite (3325−3290 Ma) ...... 11 Elsie Creek Tonalite (AEMel-mgtn) ...... 12 Cleland Supersuite (3275–3225 Ma) ...... 12 Biotite monzogranite (ACE-gmm) ...... 12 Leucocratic trondhjemite and tonalite (ACE-gtl) ...... 13 Structure of the East Pilbara Terrane on YILGALONG ...... 13

D2 (3325–3290 Ma) ...... 13

D2B (3290–3274 Ma) ...... 13

D3 (3274–3240 Ma) ...... 14 Later Archean deformation events ...... 14 Hamersley Basin ...... 14 Fortescue Group ...... 14 Mount Roe Basalt (AFOr-scp, AFOr-bbg) ...... 15 Hardey Formation (AFOh-scp, AFOhb-fr, AFOhb-frp, AFOh-sg, AFOh-spa, AFOh-sfv) ...... 16 Bamboo Creek Member (AFOhb-fr, AFOhb-frp) ...... 16 Conglomerate and sandstone unconformably overlying the Bamboo Creek Member (AFOh-sg) ...... 17 Kylena Formation (AFOkm-kts, AFOk-xfa-spv, AFOk-xbb-bk, AFOk-bng) ...... 17 Succession beneath the Mopoke Member ...... 18 Mopoke Member (AFOkm-kts) ...... 18 Succession above the Mopoke Member ...... 19 Tumbiana Formation (AFOti-bntt, AFOtm-kts, AFOt-bbg) ...... 19 Mingah Member (AFOti-bntt) ...... 20 Meentheena Member (AFOtm-kts) ...... 20 Maddina Formation (AFOm-bb, AFOmk-bntt) ...... 20 Kuruna Member (AFOmk-bntt) ...... 21 Jeerinah Formation (AFOj-xcl-kd, AFOjb-bnth) ...... 21 Baramine Member (AFOjb-bnth) ...... 22 Mafi c intrusive rocks in the Fortescue Group (AFO-od) ...... 22 Hamersley Group ...... 23 Carawine Dolomite (AHAc-kds, AHAc-kdx) ...... 23 Pinjian Chert Breccia (!pj-ccx) ...... 25 Structure of the Fortescue and Hamersley Groups ...... 26

D6 deformation (2775−2750 Ma) ...... 26

D7 deformation (<2500 Ma, ?Opthalmian Orogeny) ...... 26 Unassigned quartz veins (!zq) and dolerite or gabbro dykes (!o) ...... 26 Collier Basin ...... 27 Manganese Group ...... 27 Unassigned sedimentary rocks(#MN-ss, #MN-sh, #MN-sgp, #MN-sl, #MN-st) ...... 27 Unassigned Proterozoic dolerite intrusions ...... 28 Proterozoic Round Hummock Dolerite Suite (#RH-od, #RH-og) ...... 28 Paleoproterozoic to Neoproterozoic deformation ...... 28

D8 deformation (<1830 Ma) ...... 28 Phanerozoic rocks ...... 29 Unassigned dolerite intrusions (_od) ...... 29 Canning Basin ...... 29 Paterson Formation (CPpa-sgpg) ...... 29 Regolith ...... 31 Cenozoic deposits ...... 31

Residual or relict units (R3cbvb, R3rf ) ...... 31 Colluvial unit (C3) ...... 31 Oakover Formation (NOA-ktzl, NOA-ktpl) ...... 31 Residual or relict unit (R2k) ...... 32 Alluvial units (A2t, A2k) ...... 32

iii Colluvial units (C2, C2f ) ...... 32

Residual or relict units (R1gpg, R1tpa) ...... 32

Alluvial units (A1c, A1b, A1f, A1fcb, A1i, A1v) ...... 32 Low-gradient slope units (W1, W1f ) ...... 33 Colluvial units (C1, C1q) ...... 33 Eolian unit (E) ...... 33

Lacustrine unit (Lpcb) ...... 33 Probable impact site ...... 33 Economic geology ...... 34 Vein and hydrothermal mineralization ...... 34 Precious metal — gold ...... 34 Base metal — copper ...... 35 Mineralization in regolith ...... 35 Precious mineral — diamond ...... 35 Steel industry metal — manganese ...... 35 References ...... 37

Appendices

1. Gazetteer of localities for YILGALONG ...... 42 2. Defi nition of new stratigraphic names on YILGALONG ...... 43 3. Company data on GSWA WAMEX open fi le for YILGALONG ...... 45

Figures

1. Regional geological setting of YILGALONG ...... 2 2. Physiography and drainage map of YILGALONG ...... 3 3. Simplifi ed bedrock geology and tectonic features of YILGALONG ...... 7 4. Total magnetic intensity image for YILGALONG ...... 8 5. Mopoke Member nonconformably overlying the Little River Trondhjemite ...... 19 6. Silicifi ed stromatolitic dolomite, Mopoke Member ...... 19 7. Thin section of zoned amgydale in the Maddina Formation ...... 21 8. Interbedded siltstone and accretionary lapilli beds showing graded bedding, Kuruna Member ...... 21 9. Remnant of the Carawine Dolomite enclosed within the Pinjian Chert Breccia ...... 23 10. Carawine Dolomite ...... 24 11. Eastern rim of ‘The Crater’ doline, Ripon Hills ...... 25 12. Ice-polished south-facing ramp on western margin of ice-scoured valley ...... 30 13. Ice-polished pavements on a ‘roche moutonnée’ ...... 30 14. Probable meteorite impact crater on YILGALONG ...... 33 15. Aerial photograph view of probable meteorite impact crater on YILGALONG ...... 34

Tables

1. Summary of geochronology samples collected from YILGALONG ...... 9 2. Summary of the geological history on YILGALONG ...... 10 3. Fortescue Group stratigraphic correlation chart — a historical comparison for YILGALONG ...... 15

iv Geology of the Yilgalong 1:100 000 sheet

by I. R. Williams

Abstract

The YILGALONG 1:100 000 sheet lies towards the eastern margin of the Archean Pilbara Craton. The East Pilbara Terrane is exposed only in the southwest corner of YILGALONG, and elsewhere is unconformably overlain by Neoarchean volcanic and sedimentary rocks of the Fortescue and Hamersley Group in the Northeast Pilbara Sub-basin of the Hamersley Basin. On YILGALONG the East Pilbara Terrane is represented by part of the Kelly Group of the Pilbara Supergroup, and by the northern half of the Yilgalong Granitic Complex. The c. 3.35 Ga Kelly Group is locally composed of metamorphosed mafi c rocks of the Euro Basalt. A small area of mafi c schist and metachert exposed on the eastern margin of the Yilgalong Granitic Complex may also belong to this formation. The Yilgalong Granitic Complex is predominantly composed of gneissic to strongly foliated tonalite and granodiorite belonging to the 3.32 – 3.29 Ga Emu Pool Supersuite. It is intruded by small, weakly foliated monzogranite and trondhjemite bodies of the 3.27 – 3.22 Ga Cleland Supersuite. The. 2.77 – 2.63 Ga Fortescue Group and the disconformably overlying c. 2.54 Ga Carawine Dolomite of the Hamersley

Group are distributed around a major D7 fold — the Oakover Syncline. The Carawine Dolomite includes a distinctive microtektite and microkrystite spherule-bearing megabreccia marker horizon interpreted to be an asteroid impact-triggered tsunami deposit. The Paleoproterozoic Pinjian Chert Breccia unconformably overlies and is restricted to the Carawine Dolomite. Small areas of epiclastic sedimentary rock, correlated with the Mesoproterozoic Manganese Group of the Bangemall Supergroup, unconformably overlie the Carawine Dolomite and Pinjian Chert Breccia. Both the Pinjian Chert Breccia and overlying sedimentary rock succession are intruded by c. 523 Ma (Lower Cambrian) dolerite sills.

Deformation events recognized on YILGALONG include the 3.32 – 3.29 Ga D2 deformation of the East Pilbara Terrane, and

the D6 (2.77 – 2.75 Ga) and D7 (<2.50 Ga) events of the Hamersley Basin. Large transpressional, steep reverse, and related

faults post-date the D7 structures and are assigned to D8 (1.83 – 1.76 Ga Yapungku Orogeny). Some of these structures may have been further reactivated during later Proterozoic events (>678 Ma Miles Orogeny and c. 550 Ma Paterson Orogeny). The Archean and Proterozoic rocks are unconformably overlain by the fl uvioglacial Carboniferous–Permian Paterson Formation. The formation is largely restricted to the north-northwesterly trending Wallal Embayment of the Canning Basin that transects the eastern half of YILGALONG. The current survey discovered a feature interpreted to be a recent impact structure 13.7 km west of Carawine Pool.

Recorded mineral production on YILGALONG is restricted to local manganese mining of residual and supergene deposits that overlie the Pinjian Chert Breccia and Carawine Dolomite in the Ripon Hills area. Alluvial gold workings are north and south of Elsie Creek in the southwest corner, and copper mineralization was explored 4 km west of Mopoke Well.

KEYWORDS: Archean, Proterozoic, Kelly Group, Yilgalong Granitic Complex, Fortescue Group, Hamersley Group, Paterson Formation, Pilbara Craton, regional geology, geochronology, structure, mineralization.

Introduction (Fig. 1). YILGALONG falls within the Marble Bar District of the Pilbara Mineral Field. It derives its name from The YILGALONG* 1:100 000 sheet (SF 51-5, 3055) occupies Yilgalong Creek, a north-northeasterly fl owing tributary the central-northern part of the NULLAGINE 1:250 000 of the Oakover River. sheet (SF 51-5). The area is bound by latitudes 21°00'S and 21°30'S and longitudes 120°30'E and 121°00'E, and There are no settlements, pastoral homesteads or lies close to the northeastern margin of the Pilbara Craton current mining activity on YILGALONG. The Warrawagine pastoral (cattle) lease extends southeastwards from Warrawagine to cover the broad Oakover and Nullagine * Capitalized names refer to standard 1:100 000 map sheets, unless river valleys north, east, and southeast of the Ripon otherwise indicated. Hills (Fig. 2). The adjoining and abandoned Meentheena

1 Williams

20° 117° 118° 119° 120° 121° ? INDIAN E ? OCEAN N RA MB

SUPERTER A R A

WEST PILB ZONE ANE 21° MB CENTRAL PILBARA TECTONIC YILGALONG BRAESIDE MOUNT Yilgalong Granitic PS EDGAR Complex W EAST PILBARA TERR MB NULLAGINE EP EASTERN PEARANA MCB CREEK 22° P I L B A R A C R A T O N Rat Hill Inlier

Wyloo Dome EP Turkey, Rooney, and MCB Springo Inliers Milli Milli Billinooka Rocklea Dome 23° Cooninia Inlier Dome Inlier KURRANA TERRANE

MAP PILBARA CRATON AREA

CAPRICORN OROGE N Sylvania Inlier 100 km YILGARN CRATON

IRW196 07.05.07 Mesoproterozoic–Phanerozoic rocks

Hamersley Basin

West Pilbara Central Pilbara East Pilbara Terrane Other terranes Superterrane Tectonic Zone (EP) (WPS)

roup Mosquito Creek Mallina Basin (MB) MCB Basin (MCB)

De Grey

Superg Whim Creek Group

Pilbara Craton Greenstone Greenstone Greenstone Kurrana Terrane

Northern Pilbara Craton GraniteGranite Granite Unassigned Greenstone Granite

Major fault Proposed, concealed basin boundary

Figure 1. Regional geological setting of YILGALONG

2 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet '

W Oakover

DE GREY 00 a GREGORY ° DRAINAGE r ra RANGE w 121 BASIN a iver gi Walgunya R ne Ck g Parsons

Coonanbunna Creek Yilgalon

River

Ro BASIN ad

BASIN FZ10 203 m FORTESCUE BOTANICAL DISRICT Creek Bookabunna M39 Cree 244 m

k Creek GE Creek

Bunmardie

Nullagine 1 Creek

425 m Yilgalong Ck Ripon DRAINA RIPON Hills gan HILLS muralba

AGE Murra Road YILGALONG Gingarri

DRAIN Pulgorah Cone 288 m NULLAGINE

DRAINAGE k Cree

FORTESCUE igan DISTRICT NMF 625 BOTANICAL Gingarr 467 m Creek

BASIN ge ad g n e g R id M

Elsie OAKOVE Ck Ck River LittleYilgalong 120°30' 21°30' 10 km

Dissected paleovalley Alluvial channels with mesas Alluvial floodplain Paleovalley

Alluvial floodplain with playa lakes or Dissected plateau claypans, expansive clay (gilgai) Alluvial–colluvial plain with isolated residual hills OLD LAND SURFACE (CENOZOIC–PERMIAN)

Depositional Major drainage divide Scree and outwash fans Drainage Eolian sandplain Sealed road Low hills, rock outcrops and pavements Formed road RECENT LAND SURFACE Horizontal control Range; strike-controlled ridges 467 Major Erosional Rugged hills with dendritic drainage 268 Minor

IRW197 27.06.07

Figure 2. Physiography and drainage map of YILGALONG

3 Williams pastoral lease that previously occupied the rough hilly a report on the probability of fi nding artesian water for country west and southwest of the Ripon Hills is now pastoral purposes along the upper reaches of the De Grey under the jurisdiction of the Department of Environment and adjoining Oakover river valleys (Smith, 1898). and Conservation. The Ripon Hills and elevated country to Maitland (1906) presented the fi rst regional geological the south-southeast, which separate the Warrawagine and coverage of the area in a map of the Pilbara Goldfi eld. Meentheena pastoral leases, are Crown Land. Over the next 50 years successive publications showed only minor changes to the regional geology, with the The Ripon Hills road, which services the Telfer stratigraphic age of the successions being the main gold, Woodie Woodie manganese, and Nifty copper concern. The fi rst specifi c regional mapping project to mines, transects YILGALONG from west to east, skirting cover YILGALONG took place in the late 1950’S and is the southern side of the Ripon Hills (Fig. 2). The old presented in Geological Survey of Western Australia Port Hedland – Woodie Woodie road, now designated (GSWA) Bulletin 115 (Noldart and Wyatt, 1962). Around the Warrawagine road, diagonally crosses the northeast the same time (1956) the Commonwealth Government quarter of the sheet. A new road, constructed along the introduced export permits for a percentage of new drainage divide between Yilgalong and Gingarrigan manganese ore reserves and, in consequence, the Ripon creeks, links the Warrawagine road with the Ripon Hills Hills manganese deposits were discovered in 1957 road. Pastoral tracks give reasonable access to the valleys (O’Driscoll, 1958; de la Hunty,1960, 1963). This was of the Oakover and Nullagine rivers. Old and more recent the fi rst offi cially recorded mineralization on YILGALONG. mining exploration tracks, many severely degraded, give A comprehensive report on the Ripon Hills manganese some access to the abandoned manganese mines in the deposits was published by Denholm (1977). rugged Ripon Hills area and to alluvial gold and base metal exploration areas along the southwest margin of Similar economic interest in the region followed the YILGALONG south of the Ripon Hills road. The remaining lifting of the iron ore export embargo in 1960 by the trackless, rugged hill country in the headwaters of the Commonwealth Government. The subsequent regional Midgengadge and Gingarrigan creeks, along tributaries mapping projects, undertaken by the GSWA throughout of the Yilgalong Creek south of the Ripon Hills road, and the Pilbara region, established the broad stratigraphic along the Bookabunna and Coonanbunna creeks west of framework for the newly recognized Hamersley Basin. Ripon Hills, is roughly accessible to four-wheel drive This stratigraphy included the Fortescue and Hamersley vehicles. Groups that make up the bulk of rocks exposed on YILGALONG (MacLeod et al., 1963). Previous investigations Further stratigraphic and structural data from the YILGALONG area were recorded in the NULLAGINE 1:250 000 The fi rst recorded description of the YILGALONG countryside sheet and Explanatory Notes (Hickman, 1978) and can be found in F. T. Gregory’s 1861 exploration journal GSWA Bulletin 127 (Hickman, 1983). Reconnaissance (Gregory and Gregory, 1884; Feeken et al., 1970). The geophysical work for NULLAGINE (1:250 000) that involved expedition travelled down the Nullagine River from total magnetic intensity (Bureau Mineral Resources, 1987) MOUNT EDGAR to a point about 2 km north of the junction and regional gravity survey mapping (preliminary Bouguer with Bookabunna Creek from where they resumed an east- anomalies; Bureau Mineral Resources, undated) also southeasterly course towards the Ripon Hills. They crossed covered the YILGALONG area. the northern part of the rugged Ripon Hills with diffi culty. Continuing eastwards, Gregory recorded a northeast- Renewed interest in the geology of YILGALONG arose trending sandy stream ‘50 yards wide’, now called in the early 1980s as part of broader regional studies of Yilgalong Creek, before reaching a broad sandy river lined Fortescue Group rocks. Such studies developed in two with Cadgeput (paperbark) trees. Gregory subsequently directions. Blake (1984), the fi rst to recognize the role named it the Oakover River. The expedition continued of intra-Fortescue Group unconformities and discrete south-southeast upstream passing onto the adjoining depositional basins within the Fortescue Group, proposed a sequence-based stratigraphic approach for the Fortescue BRAESIDE sheet. On the return journey, one and half months later, the expedition followed the Oakover River Group. This concept was later extended to cover all the Mount Bruce Supergroup (Blake, 1993). The alternative downstream across the northeast corner of YILGALONG and descriptive lithostratigraphic format, initiated in earlier on to WARRAWAGINE. They continued down the Oakover River to its junction with the De Grey River, which they GSWA publications, was used in a more recent overview then followed to the northwest Pilbara coast. of the Fortescue Group (Thorne and Trendall, 2001). As part of this program the Gregory Range component of As a direct consequence of Gregory’s positive report YILGALONG, lying east of the Oakover River, was mapped on the pastoral potential for the De Grey region, the fi rst at 1:100 000 scale (Trendall, 1991). settlement in the northwest, the De Grey Station, was taken up in 1863 near the mouth of the De Grey River. Over the The first detailed research studies pertaining to next 32 years, sheep and later cattle leases were taken up specifi c geology on YILGALONG commenced in the second along the De Grey and Oakover river valleys, including the half of the 1980s. This research was directed towards eastern parts of YILGALONG. sedimentological studies of the Carawine Dolomite in the Ripon Hills areas (Simonson and Jarvis, 1993; Simonson Although YILGALONG was included in the Pilbarra (sic) et al., 1993b). These studies led to the discovery of a Goldfi elds proclaimed in July 1889 (Woodward, 1894), spherule-bearing dolomixtite, interpreted to be a dolomitic the fi rst geological sketch map of the area accompanied debris-fl ow deposit. The origin of the glassy spherules

4 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet was attributed to a major bolide impact (Simonson, 1992). Province (Beard, 1980). Hummock grassland (spinifex) Further research (Simonson and Hassler, 1997) showed is a ubiquitous groundcover for the shrub and tree steppes that as well as microtektites, many of the spherules were that cover rugged hills, dissected plateau, and strike- microkrystites (spherulitic silicate-melt condensates controlled ranges in the western half of YILGALONG and and droplets) and that such debris-flow material may in the Gregory Range in the northeast. Kanji (Acacia be connected to an impact-generated tsunami in a deep inaequilatera), together with sparsely scattered Grevillea, oceanic environment (Simonson et al., 1998, 2004; Hassler Hakea, and various smaller Acacias are the main fl oral et al., 2000; Hassler and Simonson, 2001). The recognition varieties. Occasional snappy gum (Eucalyptus brevifolia) and timing of this impact event has led to further and and desert bloodwood (Corymbia dichromorphloia) have ongoing research, debate, and discussion (Simonson et al., also been noted in the hilly basalt country southwest and 2000, 2002; Glikson, 2004; Rasmussen and Koeberl, 2004; south of the Ripon Hills and in the Gregory Range. The Rasmussen et al., 2005; Glikson and Vickers, in prep.). groundcover consists primarily of soft spinifex (Triodia pungens), but is mixed with buck spinifex (Triodia There has also been some research on the sulfi de- wiseana) in the northern half of YILGALONG, including the bearing shales of the Fortescue Group in connection with Gregory Range. The tree steppe, confi ned to the rocky their importance in understanding the Archean sulfur Ripon Hills, consists of scattered snappy gum (Eucalyptus cycle and early life forms. Samples have been collected brevifolia) and a groundcover of soft and buck spinifex and worked on from drillcore intersecting the Carawine (Triodia pungens, Triodia brizoides). Dolomite and Jeerinah Formation in the Ripon Hills area (Ono et al., 2003; Eigenbrode and Freeman, 2003). The broad Oakover River valley, transecting the eastern half of YILGALONG, carries a sparse shrub steppe Overall, there have only been a limited number of of Acacia bivenosa and groundcover of buck spinifex research projects on YILGALONG in comparison with (Triodia brizoides). In addition, three fl orally limited units adjoining map sheet areas. This may partly be attributed are restricted to specifi c landforms within the Oakover to its remoteness and, prior to the construction of the valley. The fi rst unit covers small treeless grass alluvial Ripon Hills road, diffi culty in accessing the sheet area, and plains that are developed over swelling-clay (gilgai) partly to a perceived paucity of economically interesting and gravelly sandy fl ats. The former carries Roebourne granite–greenstone terranes in the region. Plains grass (Erogrostis setifolia) together with other annual and perennial grasses, and the latter soft spinifex Fieldwork for mapping YILGALONG was undertaken (Triodia pungens). The second unit consists of narrow between June 2002 and August 2003. The sheet was strips of riverain sclerophyll woodland. It is found along compiled from 1:25 000-scale colour aerial photographs the margins of the major alluvial channels and on adjacent fl own in April 1999. Samples for geochronology were overbank levees. The woodland comprises red river gum collected from the Yilgalong Granitic Complex and (Eucalyptus camaldulensis) and paperbarks (Melaleuca the Kylena Formation. All GSWA geochronological leucodendron). This unit is characteristic of the Oakover data referenced in this publication are available on CD and Nullagine rivers and the lower parts of Yilgalong (Geological Survey of Western Australia, 2006). Creek. The third unit corresponds to the tops of mesas and small tablelands that roughly parallel the western side of Oakover River. These mesa landforms are remnants of Climate, vegetation, and the Oakover Formation and are characterized by a sparse cover of buck spinifex (Triodia wiseana) and are almost physiography completely devoid of shrubs (Beard, 1975).

The climate on YILGALONG is classifi ed as arid (Beard, The physiographic schema adopted for YILGALONG is 1975), and more recently as hot desert – winter drought based on earlier proposals (Hickman, 1983; Williams, (Stern et al., 2004). Very hot summers with mean 1999, 2001) that have been subsequently modifi ed and maximum temperatures in the low forties (°C) are followed expanded to cover the whole Pilbara region (Hickman, by mild winters with mean minimum temperatures around 2004). It is formulated on the recognition of old (Cenozoic 11–12°C (Sturman and Tapper, 1996). The mean annual to Permian) and Holocene land surfaces. The Holocene rainfall is around 270 mm, and the region has an average land surfaces are, in turn, subdivided into erosional and annual evaporation rate of over 3700 mm. However, depositional units (Fig. 2). rainfall is erratic with most precipitation falling during the cyclone or monsoon period, commonly between YILGALONG is situated towards the eastern margin December and early April. The heaviest rain is associated of the Pilbara Natural Region (Beard, 1975). Twelve with decaying, south- to southeast-tracking cyclones physiographic units are recognized, comprising six recent and monsoonal thunderstorms. Sometimes more general depositional land surface units, three recent erosional land light to moderate rains fall in the late autumn and early surface units, and three eroded older (Cenozoic–Permian) winter months (May–June). This rain is the product of land surface units (Fig. 2). The six recent depositional and the northwest Australian cloud band weather systems two of the older land surface units are confi ned, for the interacting with the southern frontal systems (Tapp and most part, to a large paleovalley occupying about a third Barrell, 1984).The remainder of the season is dry and of the area, forming the most prominent physiographic drought conditions may exist at any time of the year. feature on YILGALONG. This broad, northwest-trending valley, between 20 and 25 km wide, is now occupied by the YILGALONG lies close to the northeastern margin of the present-day Oakover River. The paleovalley is bordered by Fortescue Botanical District of the Eremean Botanical the dissected plateau unit, represented by the Ripon Hills

5 Williams and Gregory Range Inlier (Williams, 2001) and by rugged NULLAGINE 1 Trig Point in the Ripon Hills. The drainage hills with dendritic drainage in the headwater region of divide between the Oakover River and Yilgalong Creek the Midgengadge Creek along the southwest margin of reaches 400 m AMSL at the southern border between the valley. These units rise abruptly 60–100 m above the YILGALONG and EASTERN CREEK. present valley fl oor, increasing to more than 200 m in the Ripon Hills. The paleovalley contains ferruginized The drainage on YILGALONG is dominated by the large Permian fl uvioglacial deposits overlain by remnants of north-northwesterly fl owing Oakover River and the north- Neogene lacustrine Oakover Formation now preserved as northeasterly flowing Nullagine River and associated scattered buttes, mesas, and dissected small tablelands. tributaries. However, for most of the sheet area the two These landforms may rise 70 m above the current thalweg. drainages are separated by the Yilgalong Drainage Basin, This paleovalley lies towards the southern end of the which is a large north-northeasterly fl owing tributary of Wallal Embayment, which is a tectonic unit of the Canning the Oakover River (Fig. 2). Although all drainages on Basin (Hocking et al., 1994; Williams, 2003). YILGALONG are ephemeral, the Oakover and Nullagine rivers and Yilgalong Creek may fl ow for some time after The present-day Oakover River occupies incised heavy or prolonged rains. Semipermanent rockholes are alluvial channels within the broad paleovalley and is scattered through the Ripon Hills and in rugged hilly bordered by alluvial fl oodplains, some carrying numerous country, as for example in the headwaters of Midgengadge claypans and broad tracts of expansive clays (gilgai or Creek. crabhole). Similar units are also present in the lower parts of the Nullagine River northwest of the Ripon Hills where an older alluvial–colluvial plain with isolated residual hills is incised by the river. The margins of the Oakover Regional geological setting paleovalley and smaller areas adjacent to the mesas and The regional geological setting for YILGALONG is shown tablelands in the central parts of the valley are covered in Figure 1, and the simplified bedrock geology and with the coarse scree and outwash fans unit. Small areas major structural elements in Figure 3. A total magnetic of the eolian sandplain lie towards the western edge of the intensity image (GSWA, 2005a)† is given in Figure 4. Oakover River valley. These deposits are probably derived Geochronological data are presented in Table 1 and from the sandy alluvial units adjacent to the major drain- the geological history for YILGALONG is summarized in ages and redistributed by the prevailing easterly winds. Table 2.

The remaining two-thirds of YILGALONG is subdivided between the three recent erosional land surfaces and the dissected plateau, which is an older land surface postulated Pilbara Craton to be a correlate of the Hamersley Surface (Campana et al., 1964). The recent erosional land surfaces exhibit a strong The YILGALONG 1:100 000 sheet was not included in the relationship to the underlying bedrock. The low hills, rock 1995–2000 joint National Geoscience Mapping Accord outcrop, and pavement unit is restricted to the Yilgalong (NGMA) project for the reassessment of the northern Granitic Complex. The range and strike-controlled ridge Pilbara Craton (Blewett et al., 2001). This joint project had unit is developed over moderately dipping, Fortescue involved the Australian Geological Survey Organisation Group rocks of mixed lithology southwest of the Ripon (AGSO, now renamed Geoscience Australia, GA) and Hills. The rugged hills with dendritic drainage unit is GSWA. formed over shallow-dipping, mainly basaltic rocks of the Fortescue Group, particularly along the northern margin YILGALONG is close to the northeastern margin of of the Yilgalong Granitic Complex. the Pilbara Craton (Fig. 1; Trendall, 1990). The oldest exposed units, components of the Paleoarchean Mount The dissected plateau unit is particularly well Elsie greenstone belt and Yilgalong Granitic Complex, developed in the Ripon Hills area where relief is over are confined to the southwest quarter of the sheet. 200 m, and along the western margin of the sheet area. These units belong to the 3530–3170 Ma East Pilbara In the Ripon Hills the dissected plateau corresponds to a Terrane — the oldest component of fi ve terranes and fi ve large exposure of erosion-resistant Pinjian Chert Breccia basins recognized in the northern Pilbara Craton (Van overlying the Carawine Dolomite of the Hamersley Group. Kranendonk et al., 2006). The dolomite contains some widely spaced, collapsed dolines and sinkholes, some already known (Webb, 1994), The granite–greenstone components of the East others located during the current project. Pilbara Terrane on YILGALONG are also basement for the unconformably overlying Neoarchean Fortescue The highest elevations attained on YILGALONG are within the dissected plateau unit. These elevations reach Group and Carawine Dolomite of the Hamersley Group 467 m above mean sea level (AMSL) at the NMF 625 Trig (Thorne and Trendall, 2001; Blake et al., 2004; Trendall Point* in the southwest corner and 425 m AMSL at the et al., 2004). This widespread succession is deposited in the Northeast Pilbara Sub-basin of the Hamersley Basin. In addition, over half of the area occupied by the Hamersley Basin succession on YILGALONG is * The MGA coordinates (GDA94) of all place names used in these Explanatory Notes are listed in Appendix 1. unconformably overlain by Proterozoic, Carboniferous– † From the north Paterson airborne geophysical survey, 2005. Available Permian, and Cenozoic rocks, including unconsolidated for download, free of charge, from . superfi cial deposits.

6 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

21°00'

120°30' 5

NORTHE

RN O

AKOVER

SYNC OAK

OVER SYNCLINE LINE

9

7

9 4

6 2 6 3 9

1 121°00' 6 21°30' IRW210 05.06.07

G Paterson Formation Cleland Supersuite

ool

BASIN

TON

rane Dolerite sill CANNIN Elsie Creek Tonalite

Ter

Emu P Emu

Supersuite Sedimentary rocks a Granite– Group Euro Basalt

a

BASIN

Manganese

Bangemall

Kelly

Supergroup

COLLIER Pinjian Chert Breccia Group

y

PILBARA CRA

East Pilbar Greenstone

Pilbar

Carawine Dolomite Supergroup Mafic and ultramafic schist

Group

Hamersle Dolerite dyke or sill

Unassigned Anticline

Jeerinah Formation TON Syncline

rgroup Maddina Formation

p Tumbiana Formation Syncline concealed Kylena Formation 10 km

PILBARA CRA

HAMERSLEY BASIN Hardey Formation

Mount Bruce Supe

Fortescue Grou Bamboo Creek Member

Mount Roe Basalt

Figure 3. Simplifi ed bedrock geology and tectonic features of YILGALONG. 1 = Midgengadgi Monzogranite, 2 = Little River Trondhjemite, 3 = Elsie Creek Tonalite, 4 = Mount Elsie greenstone belt, 5 = Gregory Range Inlier, 6 = Yilgalong Granitic Complex, 7 = Miningarra Anticline, 8 = Meentheena Centrocline, 9 = Pearana Southwest Fault

7 Williams

21°00'

121°00'

120°30' 21°30' IRW198 10 km 22.05.07

Figure 4. Total magnetic intensity (TMI) image for YILGALONG (GSWA, 2005a)

East Pilbara Terrane northern half of the Yilgalong Granitic Complex (cf. Yilgalong Granite; Hickman, 1983), which occupies the The lithotectonic characteristics of the East Pilbara Terrane, remainder. characterized by broad granitic domes separated by synformal greenstone belts of the Pilbara Supergroup, have The Mount Elsie greenstone belt is a narrow, north- been described in detail and comprehensively reviewed northeasterly trending belt in the southwest corner of in a number of recent publications (Van Kranendonk YILGALONG. The belt, extending 17 km northwards from et al., 2002, 2004b, 2006; Hickman, 2004; Hickman and the EASTERN CREEK boundary, is sandwiched between Van Kranendonk, 2004). On YILGALONG the exposed part the unconformable Mount Roe Basalt of the Fortescue of the East Pilbara Terrane is restricted to the southwest Group to the west and a sheared intrusive contact with corner where the terrane occupies about 9% of the the Elsie Creek Tonalite to the east. Only the Euro sheet area. The exposed East Pilbara Terrane in this area Basalt has been identifi ed in the Mount Elsie greenstone consists of the Mount Elsie greenstone belt (Hickman, belt on YILGALONG. A small area of schistose mafi c and 1983), which occupies about 4% of the area, and the ultramafi c rocks 35 km to the east is also intruded by the

8 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

Table 1. Summary of geochronology samples collected from YILGALONG

Sample MGA coordinate Rock description Age Method Reference number Easting Northing (Ma)

178090 274361 7624961 Tuffaceous volcaniclastic sandstone, 2735 ± 6 SHRIMP U−Pb zircon Bordokos et al., 2006b Kylena Formation; Dingo Well 178086 278939 7623973 Porphyritic dacite, Kylena Formation; 2749 ± 5 SHRIMP U−Pb zircon Nelson et al., 2006 Carawine Pool 178089 276390 7623252 Leucocratic monzogranite, Midgengadgi 3274 ± 5 SHRIMP U−Pb zircon Bordokos et al., 2006a Monzogranite; Dingo Well 169260 256340 7627380 Foliated biotite tonalite; Bullyarrie Well 3277 ± 6 SHRIMP U−Pb zircon Nelson, 2005s 3308 ± 5 169263 244390 7623250 Tonalite gneiss, Elsie Creek Tonalite; 3290 ± 4 SHRIMP U−Pb zircon Nelson, 2005d Bullyarrie Well 169261 252440 7627290 Gneissic tonalite, Elsie Creek Tonalite; 3291 ± 4 SHRIMP U−Pb zircon Nelson, 2005b Bullyarrie Well 169262 247570 7626520 Foliated biotite granodiorite, Elsie Creek 3291 ± 4 SHRIMP U−Pb zircon Nelson, 2005c Tonalite; Bullyarrie Well 144682 244910 7621670 Foliated biotite tonalite, Baroona Hill 3299 ± 10 SHRIMP U−Pb zircon Nelson, 2004a

Yilgalong Granitic Complex. This greenstone material is The mafi c–ultramafi c succession in this area is strongly the easternmost exposure of the East Pilbara Terrane on foliated and intruded lit-par-lit by numerous foliated YILGALONG. granitic and microgranitic dykes. Figure 4, a total magnetic intensity image, used in Unassigned Pilbara Supergroup rocks combination with Figure 3, shows that the buried northern edge of the domal Yilgalong Granitic Complex, which (API-xmbs-mus, API-mc) is nonconformably overlain by the Fortescue Group A small unnamed greenstone belt, 2 km long and 500 m succession, is traceable from the Mount Elsie greenstone wide comprising mafi c and ultramafi c schist (API-xmbs- belt contact in the west to the area of mafi c and ultramafi c mus) and metachert (API-mc), lies 19 km east-southeast of schists just described. This would support a proposal that Dingo Well on the eastern margin of the Yilgalong Granitic the Mount Elsie greenstone belt may wrap around the Complex (Fig. 3). It is intruded by the Elsie Creek Tonalite northern edge of the Yilgalong Granitic Complex and and unconformably overlain by felsic units (AFOk-xfa-spv) that the mafi c and ultramafi c schists in the area described of the Kylena Formation of the Fortescue Group. are probably a continuation of this belt. Such a proposal is supported by the similarity in the petrography and The mafic and ultramafic schists (API-xmbs-mus) structural fabrics of the two greenstone areas. consist of schistose fi ne-grained amphibolite interlayered with chlorite–tremolite schist and amphibolitic schist with deformed ocelli indicative of komatiitic basalt parentage. Kelly Group The schistose fi ne-grained amphibolite consists of darker layers of almost pure hornblende alternating with light- The newly defi ned Kelly Group (Van Kranendonk et al., coloured layers of plagioclase, hornblende, and quartz. 2004b) encompasses an age range from 3420 to 3315 Ma Much of the plagioclase is sericitized, with patches of (Van Kranendonk et al., 2006). Although the Kelly Group epidote and clinozoisite and very minor titanite. Poorly comprises the basal Strelley Pool Chert, Euro Basalt, defi ned, crosscutting veins contain quartz, albite, and Wyman Formation, and Charteris Basalt, on YILGALONG actinolite (Purvis, 2003c; GSWA 169291). only the Euro Basalt is exposed in the Mount Elsie greenstone belt. Thin, but persistent, metachert beds (API-mc) are interlayered with the mafic and ultramafic schists. Euro Basalt (AKEe-xmbks-mbs, AKEe-bk, Petrographically, the rock is predominately recrystallized AKEe-mh, AKEe-bb, AKEe-ml, AKEe-cc) quartz with minor muscovite and carbonaceous matter, traces of cloudy albite, and rare pyrite (Purvis, 2003c; The Euro Basalt (Hickman, 1977; Van Kranendonk et al., GSWA 169290). In outcrop the metachert is faintly banded 2004b) is the sole greenstone unit in the Mount Elsie and strongly lineated. The banding is compositional greenstone belt and the oldest exposed formation on with thin (<2 mm), coarse-grained, quartz-rich layers YILGALONG. The formation can be traced continuously alternating with thicker (<8 mm), fi ner grained layers southwards onto EASTERN CREEK (Farrell, 2006) and of quartz, microcrystalline schistose muscovite, and southwestwards onto NULLAGINE (Bagas, 2005) where it disseminated carbonaceous matter. Zircon is absent, which is overlain by the felsic c. 3315 Ma Wyman Formation suggests a chert rather than a quartzite progenitor. (GSWA, 2006; GSWA 144681).

9 Williams

Table 2. Summary of the geological history on YILGALONG

Age (Ma) Geological events

Pre-3500 No evidence for older crustal material within the Yilgalong Granitic Complex on YILGALONG

3500–3400 Granite–greenstone material for this period is not exposed on YILGALONG 3350–3325 Voluminous eruption of mafi c–ultramafi c lavas of the Euro Basalt in the Mount Elsie greenstone belt; attributed to mantle plume activity

3325–3290 D2: Beginning of major doming within the East Pilbara Terrane, such as expressed in the signature granitic domes surrounded by synclinal greenstone belts; on YILGALONG this is refl ected in the initial moderate dips away from the developing dome of the Yilgalong Granitic Complex and faulting (both normal and steep reverse) of the Euro Basalt 3299–3290 Intrusion of the Euro Basalt by the Elsie Creek Tonalite (Emu Pool Supersuite); contact metamorphic aureoles in greenstone belts adjacent to intrusive granitic bodies

3290–3274 D2B: After intrusion of the Elsie Creek Tonalite, late D2 involved renewed uplift (doming) of the granitic material that produced the strongly sheared margins both within the greenstones and adjacent granitic rocks

3274–3240 Renewed mantle plume activity and doming (D3); intrusion of monzogranite, granodiorite, trondhjemite (Cleland Supersuite) into the Yilgalong Granitic Complex; this event may be connected to the strong shearing at the margins both in the greenstones and adjacent granitic rocks (Elsie Creek Tonalite); uplift and erosion

3200–2775 Deformation (D4–5) structures not recognized on YILGALONG; uplift, erosion, and weathering of the Yilgalong Granitic Complex and Mount Elsie greenstone belt 2775–2766 Onset of an extensional regime related to marginal cratonic rifting; outpouring of the Mount Roe Basalt, basal unit of the Fortescue Group on the western side of the Yilgalong Granitic Complex; coeval growth faulting, mild folding and local erosion

2766–2752 Deposition of epiclastic–volcaniclastic Hardey Formation in the western parts of YILGALONG; effusive and explosive eruption (including synvolcanic intrusions) of the c. 2766–2760 Ma Bamboo Creek Member; continuation of local growth

faulting and mild folding; erosion; structures developed in the c. 2775−2752 Ma period assigned to D6 2749–2730 Renewed mostly subaerial and local subaqueous basaltic and komatiitic fi ssure eruptions of the Kylena Formation; a pause in volcanic activity marked by the thin lacustrine stromatolitic carbonate Mopoke Member in the lower third of the formation 2727–2719 Deposition of phreatomagmatic volcaniclastic and volcanogenic sedimentary rocks with minor basaltic lavas of the c. 2727–2721 Ma Mingah Member and c. 2719 Ma lacustrine stromatolitic carbonate Meentheena Member of the Tumbiana Formation 2718–2713 Subaerial fi ssure eruptions of basalt and andesite lavas of the Maddina Formation, including the deposition of the c. 2713 Ma volcaniclastic Kuruna Member 2690–2629 Deposition of the marine sedimentary and mafi c volcanic Jeerinah Formation 2741–2629 Intrusion of consanguineous mafi c sills throughout the Fortescue Group c. 2548 Deposition of the Carawine Dolomite, Hamersley Group; evidence for distal impact of an asteroid in an oceanic environment in a chaotic spherule-bearing megabreccia in the lower part of the formation c. 2500 Deposition of Pinjian Chert Breccia concordant with the weathering and karstifi cation of the Carawine Dolomite <2500 Fortescue and Hamersley Groups broadly folded and faulted by episodic mild readjustments between sinking older

greenstone belts and adjacent rising domal granitic complexes; this D7 deformation represented by the major Oakover and Meentheena Synclines; Fortescue and Hamersley Group rocks subjected to very low grade greenschist-facies burial metamorphism >1070 Deposition of fl uvial and marine sedimentary rocks of the Manganese Group over the eastern margin of the Pilbara Craton; preserved in the Ripon Hills 1830–550 Brittle normal faulting with downthrow to west and east (?reactivated basement faults), later dextral and sinistral transpressional and steep reverse faulting with small tight folds on eastern side of the compressional faults; postulated to be connected to the Paleoproterozoic to Neoproterozoic convergent tectonics initiated by the collision between the West Australian Craton and the North Australian Craton (Yapungku Orogeny), and reactivated during the Miles (>678 Ma) and

Paterson (550 Ma) Orogenies; assigned to D8 c. 755 Intrusion of Round Hummock Dolerite Suite c. 523 Intrusion of dolerite sills (Kalkarindji large igneous province) 304–284 Carboniferous–Permian ice cap and subsequent melting, erosion, and deposition of the fl uvioglacial Paterson Formation 95–20 Ferruginous duricrusts (laterites) developed c. 5–2 Deposition of the lacustrine Oakover Formation

10 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

The lower part of the formation is extensively intruded Metasedimentary rocks are a minor intercalated by granitic rocks of the 3292–3255 Ma Yilgalong Granitic component within the basaltic succession of the Euro Complex that borders the eastern side of the Mount Elsie Basalt on YILGALONG. Most outcrops are weathered greenstone belt. The upper parts of the formation to the and commonly ferruginized, making identification of west and north are unconformably overlain by units of the the parent material diffi cult. A thick northwest-dipping Fortescue Group. Overall, the Euro Basalt dips steeply to band of variably red-brown ferruginized and silicifi ed moderately west and northwest away from the Yilgalong psammopelitic schist (AKEe-mh) lies 3 km south- Granitic Complex. Thickness estimates are diffi cult to southwest of Mopoke Well. The band forms a prominent calculate due to strong shearing and faulting, but the topographic high with cliffs marked by rock overhangs succession would appear to be at least 2000 m thick. The and small caves eroded in the weathered metasedimentary succession, shown from fi eld relationships to be older rocks. A thinner horizon of the psammopelitic schist than the 3299–3255 Ma Yilgalong Granitic Complex, (AKEe-mh), 5 km south of Mopoke Well, appears to be a has not been directly dated on YILGALONG. However, faulted continuation of this unit. Similar rocks have been depositional ages between 3395 and 3332 Ma have been recorded from EASTERN CREEK (Farrell, 2006) where they proposed (Van Kranendonk et al., 2002) and more recently are described as interbedded metamorphosed siltstone and a volcaniclastic sandstone within the Euro Basalt yielded a fi ne- to medium-grained sandstone. date of 3350 ± 3 Ma (GSWA, 2006; GSWA 178042). Adjacent to the Yilgalong Granitic Complex a second The Euro Basalt, adjacent to the Yilgalong Granitic metasedimentary horizon is intercalated with the mafi c Complex, consists mainly of mafi c schists derived from schists derived from komatiitic and tholeiitic basalts komatiitic and tholeiitic basalts (AKEe-xmbks-mbs). The (AKEe-xmbks-mbs). This is a fine-grained, weathered schist component, marginal to the Yilgalong Granitic pale greenish-grey pelitic rock (AKEe-ml) consisting Complex contact, varies in width between 400 and 1000 m. mainly of quartz and chlorite, minor leucoxene, and The schists are mostly brown-weathering, grey-green, fi ne- limonite after pyrite. The fabric in thin section is schistose grained rocks containing variable proportions of chlorite, as outlined by the chlorite, but most of the quartz is actinolite, tremolite, epidote, microcrystalline quartz, recrystallized. The protolith of this horizon is unclear. altered plagioclase (albite), carbonate, leucoxene, and Local thin metachert and thick white, grey, and blue- accessory opaque minerals (Purvis, 2003a; GSWA 169250). black banded metachert beds (AKEe-cc) are part of this A pervasive planar foliation is present throughout together horizon. These are particularly prominent 5 km northeast with several generations of quartz and quartz–carbonate of Salvation Well. Such beds can be traced continuously veining. Zones of pervasive carbonate alteration are also over several kilometres. They commonly exhibit local associated with the komatiitic component of the schist. mesoscale contorted fold patterns. Massive grey and Ultramafi c talc–carbonate and tremolite–chlorite schist pale-green quartzites are also locally developed in the are a minor component in the schist unit. Overall, most metasedimentary horizon. Some quartzites carry green primary textures have been destroyed. Thin granitic and micaceous layers (fuchsite), leucoxene, and limonite clots microgranitic dykes lit-par-lit intrude the schists adjacent to probably after pyrite. the Yilgalong Granitic Complex. The regional confi guration Metamorphosed, mostly pillowed tholeiitic basalt, of the schists and their associated metamorphic grade (upper minor massive dolerite and gabbro, and komatiitic basalt greenschist facies) suggest that there was an initial contact (AKEe-bb) is the youngest unit in the Euro Basalt on metamorphism followed by strong shearing between the YILGALONG. Good but limited exposures are restricted to intrusive granitic rocks and the host Euro Basalt. areas 2.5 km southwest and 4.5 km south of Mopoke Well adjacent to the overlying Fortescue Group. The tholeiitic Metamorphosed, green-grey, fi ne-grained komatiitic basalt is a grey-green, fi ne-grained rock comprising altered basalt (AKEe-bk) is the thickest unit on YILGALONG. It feldspar, actinolite, epidote, quartz, and minor carbonate, overlies the mafic schist derived from komatiitic and leucoxene, and accessory opaque minerals. Partly tholeiitic basalts (AKEe-xmbks-mbs) and is overlain by deformed pillow structures with vesicles congregated the psammopelitic schist (AKEe-mh). The komatiitic towards the top of the pillows indicate way-up to the north basalt is more subdued in outcrop than the tholeiitic and northwest. Small lenses of medium-grained dolerite basalt (AKEe-bb), and is best exposed in the areas south of and coarse-grained gabbro intercalated within the basalt Elsie Creek and 8.5 km northeast of Salvation Well. The pile are probably subvolcanic sills consanguineous with komatiitic basalt consists of actinolite, epidote, altered the basalts. feldspar (albite), carbonate, quartz, accessory leucoxene, and opaque minerals. The komatiitic basalt is distinguished by common ocelli texture (Ashwal, 1991) towards the Emu Pool Supersuite (3325−3290 Ma) margins and larger varioles in the central cores of the deformed pillow structures. The regional deformation Almost the entire Yilgalong Granitic Complex on has commonly fl attened the ocelli to elliptical lenses up YILGALONG is made up of the 3299–3290 Ma Elsie Creek to 30 mm long, 8 mm wide, and 2–3 mm long (Purvis, Tonalite (Appendix 2; Table 2), a large intrusive body 2003c; GSWA 169254). The ocelli contain randomly belonging to the Emu Pool Supersuite (Van Kranendonk oriented albite, epidote, amphibole, carbonate, leucoxene, et al., 2006). The Yilgalong Granitic Complex has a and opaque minerals. The ocelli lack the radiating structure semiconcordant, variously deformed intrusive contact associated with the varioles. Feathery (amphibole after with the Euro Basalt on the western side and with the pyroxene) and rare platy spinifex texture (after olivine) unassigned mafi c–ultramafi c schist (API-xmbs-mus) on have been found in less deformed areas. the eastern side (Fig. 3). The complex is nonconformably

11 Williams overlain to the north and east by rocks of the Fortescue Various ages are evident, with the oldest dykes exhibiting Group. Two small, related granitic inliers, surrounded by similar foliations to the host gneisses, whereas other dykes Fortescue Group rocks, are exposed in the headwaters of post-date these foliations. Midgengadge Creek adjacent to the northeast margin of the Yilgalong Granitic Complex. Seven kilometres northwest of Bullyarrie Well and adjacent to the Fortescue Group nonconformity, a The Elsie Creek Tonalite is intruded by small granitic 1 km2 area of the Elsie Creek Tonalite is characterized bodies and dykes belonging to the 3275–3225 Ma Cleland by numerous mafi c and ultramafi c xenoliths and rafts Supersuite (Table 2). These include the newly named (AEMel-jmgtn-mw). This would suggest that the area Midgengadgi Monzogranite and Little River Trondhjemite is close to the northern edge of the Yilgalong Granitic (Appendix 2). Complex, which, in this area, must be buried beneath the Fortescue Group rocks.

Elsie Creek Tonalite (AEMel-mgtn) Four samples of the Elsie Creek Tonalite, collected The Elsie Creek Tonalite (AEMel-mgtn; Appendix 2; across a distance of 10 km in the western half of the Table 2) underlies 99% of the area occupied by the Yilgalong Granitic Complex, yielded sensitive high- Yilgalong Granitic Complex on YILGALONG, including resolution ion microprobe (SHRIMP) U–Pb dates the two small inliers along the northeastern margin of the ranging from 3299 ± 10 Ma (Nelson, 2005a; GSWA complex. A weathered Archean paleosurface is preserved 144682) to 3290 ± 4 Ma (Nelson, 2005e; GSWA 169263). on the Yilgalong Granitic Complex, particularly along The remaining two samples yielded identical dates of the northern margin adjacent to the Fortescue Group 3291 ± 4 Ma (Nelson, 2005c,d; GSWA 169261 and nonconformity, and on the higher parts of rugged hills 169262). All the dates are within error and indicate that the that lie towards the southern boundary of the sheet. This Elsie Creek Tonalite is c. 3291 Ma in age. A similar date of weathered paleosurface is broadly undulating with relief 3292 ± 4 Ma (Nelson, 2005f; GSWA 178008) was obtained in excess of 100 m. In consequence, fresh granitic rocks from foliated biotite−muscovite tonalite, 6 km north of are best preserved in the broad valleys as scattered tors and Mount Elsie in the southwestern corner of the Yilgalong sheets or along the sides of the more incised drainages in Granitic Complex on EASTERN CREEK (Farrell, 2006). the hilly country.

On YILGALONG the Elsie Creek Tonalite is strongly Cleland Supersuite (3275–3225 Ma) deformed throughout the Yilgalong Granitic Complex. The deformation intensity increases towards the moderately Intrusions assigned to the Cleland Supersuite are more steep intrusive contact with the adjacent greenstone common in the eastern half of the Yilgalong Granitic belts. Protomylonitic tonalite and granodiorite gneiss, Complex on YILGALONG. Although the composition exhibiting low amphibolite-facies metamorphism, are ranges from monzogranite to tonalite, monzogranite is more common. Intrusive bodies belonging to the Cleland exposed adjacent to the contact with the greenstone 2 belts along the western margin of the Yilgalong Granitic Supersuite consist of widely separated, small (<4 km ) Complex, particularly in the Elsie Creek area. Such stocks and microgranitic dykes, many of which are too rocks are grey to speckled white, fi nely laminated, and small to register on the map sheet. have complex foliation patterns suggestive of an S–C fabric. Some gneisses contain single or small clusters of Biotite monzogranite (ACE-gmm) plagioclase augen up to 6 mm in size. Away from the sheared contact the rocks are fi ne- to medium-grained, Biotite monzogranite (ACE-gmm) outcrops at the eastern and locally coarse-grained, foliated to gneissic grey-green margin of the Yilgalong Granitic Complex, 17 km metatonalite, with minor pinkish-grey metagranodiorite southeast of Dingo Well. On NULLAGINE (1:250 000) and local metamonzogranite (AEMel-mgtn). Close to Williams and Hickman (in prep.) named this unit the the margin such rocks have been described as tonalite Midgengadgi Monzogranite (ACEmi-gm), which is and granodiorite gneiss (Purvis, 2003a; GSWA 169247, also defined in Appendix 2. The monzogranite forms 169249, and 169252). an appendage to the main Yilgalong Granitic Complex and is almost completely surrounded by high ridges of The assemblages consist predominately of plagioclase nonconformably overlying Kylena Formation of the (andesine–oligoclase and myrmekite), quartz, microcline, Fortescue Group. Fresh exposures of the monzogranite are biotite, and muscovite. Opaque minerals, titanite, apatite, found in fl at sheets together with large tors and boulders. allanite, and zircon are accessory. The biotite–muscovite flakes in most areas define a variable S–C fabric. The monzogranite is unfoliated, seriate to porphyritic, Plagioclase can be saussuritized or irregularly replaced medium to coarse grained, and leucocratic. It consists of by sericite and carbonate. Biotite is partly replaced by plagioclase (andesine–oligoclase), quartz, microcline, chlorite. The mineral assemblages suggest that a low- biotite, minor muscovite, and accessory opaque-oxide temperature alteration has been superimposed on an earlier minerals and zircon. Myrmekite is abundant in places and amphibolite-facies metamorphism (Purvis, 2003b; GSWA commonly enclosed in microcline. Poikilitic microcline 169260 and 169261). can be up to 8 mm long. Plagioclase is widely altered to sericite, epidote, chlorite, and carbonate minerals and Pegmatite zones and dykes and microgranite (aplite) biotite is commonly replaced by chlorite, epidote, and dykes are common throughout the Elsie Creek Tonalite. minor leucoxene (Purvis, 2003b; GSWA 178089).

12 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

A sample of the monzogranite yielded a SHRIMP D2 (3325–3290 Ma) U–Pb zircon date of 3274 ± 5 Ma, which is interpreted to be the age of igneous crystallization (Bodorkos et al., The earliest structures on YILGALONG are preserved in 2006a; GSWA 178089). the Kelly Group of the Mount Elsie greenstone belt. On EASTERN CREEK Farrell (2006) assigned these old structures — a metamorphic foliation, mineral lineations, and

Leucocratic trondhjemite and tonalite (ACE-gtl) various minor folds — to ‘DEP1’. He reported that these structures must be older than the Elsie Creek Tonalite Leucocratic trondhjemite and tonalite (ACE-gtl) originally (3299–3290 Ma) because the oldest structures in that described as an albite granite (Hickman, 1978) lies 10 km unit (D ) are superimposed on the D structures. On southeast of Dingo Well on the eastern side of Yilgalong EP2 EP1 YILGALONG this conclusion is supported by the observation Creek. Williams and Hickman (in prep.) named this unit that early folding of the Euro Basalt was prior to intrusion the Little River Trondhjemite (ACElr-gtl), which is also of the formation by the Elsie Creek Tonalite. Within the defined in Appendix 2. The trondhjemite intrudes the Kelly Group the Euro Basalt is conformable with the Elsie Creek Tonalite and is nonconformably overlain to overlying 3325–3315 Ma Wyman Formation, requiring the south, west, and north by the Kylena Formation. The the age of the fi rst deformation to be less than 3325 Ma. intrusion is not well exposed and is restricted to scattered, Accordingly, the fi rst deformation event in the Mount weathered boulder-strewn outcrops and water-eroded Elsie greenstone belt correlates with the regional D2 sheets along the eastern edge of Yilgalong Creek. event (Hickman, 1983, 1984), which Van Kranendonk et al. (2002) related to intrusion of granitic rocks now The trondhjemite is a massive, fine- to medium- assigned to the 3325–3290 Ma Emu Pool Supersuite (Van grained, pale-pink (leucocratic) granite. It comprises about Kranendonk et al., 2006). 70% albite (albitized plagioclase), 30% quartz, minor sericite, accessory rutile, and rare zircon. K-feldspar is The fi rst observable structural event on YILGALONG was absent, although albite has also replaced large poikilitic folding of the Euro Basalt, with development of a regional, crystals that may have been K-feldspar. These poikilitic west-dipping, north-northwesterly to north-northeasterly crystals enclose albitized plagioclase. trending foliation and tight, small-scale recumbent, north- plunging folds in chert 6 km northeast of Salvation Well The petrography suggests that the granite is an (MGA 247400E 7631300N). Such structures are best albtized and weakly sericitized, undeformed leucocratic preserved away from the contact with the Elsie Creek trondhjemite with low-temperature alteration (Purvis Tonalite, which was sheared by later deformation. The 2003a; GSWA 169272 and 169277). primary layering in the Mount Elsie greenstone belt, A weakly foliated biotite tonalite, collected 3.3 km mainly in mafi c and ultramafi c volcanic rocks interbedded west-southwest of Bullyarrie Well, yielded a SHRIMP with chert and metasedimentary rocks, dips to the west U–Pb zircon date of 3277 ± 6 Ma for the time of igneous and north-northwest away from the Yilgalong Granitic crystallization and zircon xenocrysts dated at 3308 ± 5 Ma Complex. Pillow structures indicate way-up to the west (Nelson, 2005b; GSWA 169260). The tonalite is part of a and northwest. This part of the Mount Elsie greenstone small, irregular-shaped body intruding the strongly foliated belt is presumed to be the eastern limb of a regional D2 Elsie Creek Tonalite. Thick dykes of unfoliated porphyritic syncline, the western limb of which lies buried beneath microgranodiorite and micromonzogranite, 8 km south of the overlying Fortescue Group to the west. Mopoke Well (MGA 247872E 7631109N) and 13 km east- southeast of Dingo Well (MGA 273970E 7628375N), are D (3290–3274 Ma) assigned to the Cleland Supersuite. 2B The second deformation event on YILGALONG produced a strong tectonic foliation in the 3299–3290 Ma Elsie Structure of the East Pilbara Terrane on Creek Tonalite and a parallel, moderate to steeply dipping metamorphic foliation in the Euro Basalt. Both foliations YILGALONG are parallel to the western contact of the Yilgalong Granitic Regional structural relationships developed in the granite– Complex, as in most other granitic domes of the East greenstones of the East Pilbara Terrane have been widely Pilbara Terrane (Hickman, 1983, 1984). Within the Euro discussed in the literature (Hickman, 1983, 2004; Hickman Basalt the regional foliation exhibits local small tight and Van Kranendonk, 2004; Van Kranendonk et al., 2002; folds, crenulation kinks, and steep intersection and mineral Blewett, 2002). The structural data from YILGALONG can lineations that plunge to the south and north in the contact be linked to data from EASTERN CREEK (Farrell, 2006), and metamorphic zone adjacent to the Yilgalong Granitic to the regional structural development of the East Pilbara Complex. These foliations are best preserved in mafi c Terrane. and ultramafi c schists (AKEe-xmbks-mbs), which are also host to arcuate high-strain zones that parallel the granitic Because the oldest rocks exposed on YILGALONG are contact. The 3299–3290 Ma contact metamorphism in c. 3350 Ma in age, this area preserves no evidence for the Euro Basalt is interpreted to have reached at least older deformation events recorded elsewhere in the East amphibolite facies. The internal fabric of the Yilgalong Pilbara Terrane. However, to describe the structural history Granitic Complex adjacent to the contact with Mount Elsie of YILGALONG within a regional context, the deformation greenstone belt is a protomylonite in which the regional events are, where possible, correlated with regional events foliation in the granitic gneiss is parallel to that developed described by Van Kranendonk et al. (2002). in the mafi c and ultramafi c schists. This protomylonite is

13 Williams related to doming of the Yilgalong Granitic Complex, and Neoarchean Carawine Dolomite of the Hamersley Group, must be syn- or post-3290 Ma. which are components of the Mount Bruce Supergroup, and the Paleoproterozoic Pinjian Chert Breccia. The latter Farrell (2006) recorded that this event (DEP2 on EASTERN is controlled by the distribution of the Carawine Dolomite. CREEK) pre-dated 3274 Ma, the age of the Midgengadgi The Hamersley Basin succession is unconformably Monzogranite, which on YILGALONG intruded the overlain by scattered outliers of Mesoproterozoic tectonic deformation of the second deformation. In the sedimentary rocks, assigned to the Manganese Group of Yilgalong Granitic Complex the Emu Pool Supersuite is the Bangemall Supergroup (Martin et al., 2005), in the 5–10 m.y. younger than in granitic complexes of the Ripon Hills area and by Permian fl uvioglacial sedimentary central East Pilbara Terrane, suggesting that in the rocks (Williams, 2001) in the region now occupied by the southeast East Pilbara Terrane D2 doming, accompanying Oakover River valley. and following granitic intrusion, probably continued for some time after 3290 Ma. Van Kranendonk et al. (2006) concluded that D2 doming, metamorphism, and subsequent Fortescue Group erosion probably continued to c. 3270 Ma. Following the cratonization of the Pilbara Craton the onset of a regional extensional regime (rifting) triggered D3 (3274–3240 Ma) the deposition of the thick volcanic and sedimentary On EASTERN CREEK Farrell (2006) recorded a third succession of the Fortescue Group. This regime fi nally led to the breakup of the craton and its eventual evolution into deformation event (DEP3) that resulted in large-scale shear folds in the centre of the Mount Elsie greenstone a subsiding passive continental margin (Blake, 1984, 1993; belt and along the southwestern contact of the Yilgalong Tyler and Thorne, 1990; Blake and Barley, 1992; Thorne Granitic Complex. He noted that these structures truncated and Trendall, 2001). A historical comparative stratigraphic chart for the Fortescue Group is given in Table 3. DEP2 structures, which he interpreted to indicate a post- 3274 Ma age. Porphyritic monzogranite dykes of Cleland The complete Fortescue Group succession of the Supersuite age intrude the Mount Elsie greenstone belt on Mount Roe Basalt and the Hardey, Kylena, Tumbiana, EASTERN CREEK (Farrell, 2006), and small populations of Maddina, and Jeerinah Formations (Thorne and Trendall, c. 3250 Ma zircons are recorded in samples of the Elsie 2001) occupies parts of a 16 km-wide zone that extends Creek Tonalite. On the eastern margin of the Yilgalong from near the southeast corner of YILGALONG (Fig. 3) Granitic Complex the strongly foliated Elsie Creek diagonally across to the northwest corner. This zone Tonalite is intruded by two unfoliated granitic intrusions lies to the west and south of the Ripon Hills and is the of the Cleland Supersuite, Little River Trondhjemite, and southwestern limb of the regional southeast-plunging Midgengadgi Monzogranite. The lack of any deformation Oakover Syncline (Hickman, 1983). Basal formations fabrics in these intrusions indicates no signifi cant post- of the Fortescue Group extend south along the western 3274 Ma deformation on the eastern side of the complex. border of YILGALONG. The Jeerinah Formation at the top of the Fortescue Group is also exposed in the far Elsewhere in the Pilbara Craton, D3 was a tectono- thermal event during intrusion of the 3275–3225 Ma northeast corner, where it constitutes part of the Gregory Cleland Supersuite and deposition of the 3270–3235 Ma Range Inlier (Williams and Trendall, 1998a). Altogether the Fortescue Group accounts for more than 60% of the Sulphur Springs Group (D3 of Van Kranendonk et al., 2002). Hamersley Basin succession exposed on YILGALONG, and is about 5.6 km thick.

Later Archean deformation events The Fortescue Group unconformably overlies the Pilbara Supergroup and the Yilgalong Granitic Complex Later Archean deformations (D4, D5) are neither preserved of the East Pilbara Terrane. The group is disconformably nor expressed in the Mount Elsie greenstone belt and overlain by the Carawine Dolomite of the Hamersley Yilgalong Granitic Complex on YILGALONG (cf. Williams Group in the Ripon Hills, Midgengadge Creek area, and and Bagas, in prep.). northeast of the Oakover River in the northeast corner. Subsequent brittle faulting that disrupts the contact Permian fluvioglacial sedimentary rocks unconform- between the Mount Elsie greenstone belt and Yilgalong ably overlie the Fortescue Group southeast of the Ripon Granitic Complex is probably Neoarchean to Proterozoic Hills. because these faults also displace the Fortescue Group There is an approximately 500 m.y. gap between the rocks. This faulting is probably D8 (see Structure of the emplacement of 3277–3274 Ma intrusions of the Cleland Fortescue and Hamersley Groups). Supersuite in the Yilgalong Granitic Complex (Bodorkos et al., 2006a; GSWA 178089), which is the last recorded event in the East Pilbara Terrane on YILGALONG, and the Hamersley Basin initial deposition of fl uvial deposits at the base of the c. 2775 Ma Mount Roe Basalt, which is the lowermost Lithostratigraphic units of the Northeast Pilbara Sub- unit of the Fortescue Group (Hickman, 1983; Arndt basin of the Hamersley Basin occupy over 60% of the et al., 1991). This hiatus corresponds to a long period sheet area. Such units, in decreasing order of exposed of erosion and weathering, which is particularly evident abundance, are the weakly metamorphosed volcanic in the granitic rocks of the Yilgalong Granitic Complex. and sedimentary Neoarchean Fortescue Group and the The paleotopography is also considerable (>1000 m) in

14 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

Table 3. Fortescue Group stratigraphic correlation chart — a historical comparison for YILGALONG

NULLAGINE 1:250 000 YILGALONG 1:100 000 Sequence stratigraphy Hickman (1978) Williams (this report) Blake et al. (2004)

Lewin Shale (#fl ) Jeerinah Formation (AFOj-sk) Mount Jope Supersequence (2) Baramine Member (AFOjb-bnth) Maddina Basalt (#fm) Maddina Formation (AFOm-b) Kuruna Siltstone (#fs) Kuruna Member (AFOmk-bntt) Nymerina Basalt (#fn) Maddina Formation (AFOm-b) Tumbiana Formation (#ft) Tumbiana Formation (AFOt-xb-k) Mount Jope Supersequence (1) Meentheena Carbonate Member (#ftc) Meentheena Member (AFOtm-kts) Mingah Tuff Member (#ftt) Mingah Member (AFOti-bntt) Kylena Basalt (#fk) Kylena Formation (AFOk-bng) Nullagine Supersequence Mopoke Member (AFOkm-kts) Kylena Formation (AFOk-xbb-bk) Hardey Sandstone (#fh) Hardey Formation (AFOh-xs-f) Quartz–plagioclase porphyry (#p) Bamboo Creek Member (AFOhb-fr) Mount Roe Basalt (#fr) Mount Roe Basalt (AFOr-bbg)

that the basal Mount Roe Basalt, Hardey Formation, and and consist dominantly of plagioclase with fresh or altered lower units of the Kylena Formation are missing from the clinopyroxene, and skeletal or dendritic opaque oxides Fortescue Group where it nonconformably overlies the set in a quenched or fi ne-grained groundmass. Anatase Yilgalong Granitic Complex along its northern and eastern is accessory. Porphyritic basalt fl ows contain thin platy contacts. However, the Mount Roe Basalt and Hardey plagioclase phenocrysts that in some areas aggregate to Formation unconformably overlie with moderate dip the form glomeroporphyritic textures popularly known as Euro Basalt of the Mount Elsie greenstone belt, which lies Chinese writing stone (Bevan et al., 1999). These fl ows west of the Yilgalong Granitic Complex. This indicates tend to lie in the upper parts of the formation. that the Yilgalong Granitic Complex was a basement high during the early depositional stages of Fortescue Group. The amygdales and vesicles are fi lled or partly fi lled with microcrystalline quartz, carbonate (calcite), chlorite, and the occasional sulfi de bleb. Individual fl ows can be Mount Roe Basalt (AFOr-scp, AFOr-bbg) identifi ed by scoriaceous, amygdale-rich, and vesiculated flow tops. A small area of ocelli-bearing dark-grey The Mount Roe Basalt (Kriewaldt, 1964; Thorne and metabasalt, 3.5 km west of Mopoke Well, on the fl oor Trendall, 2001) is confi ned to the southwest margin of of a deep valley beneath a thick sequence of Mount Roe YILGALONG, where it unconformably overlies the Euro Basalt, may belong to the underlying older Euro Basalt. Basalt of the Kelly Group. Farther east the Mount Roe However, the rubbly nature of this exposure makes the Basalt is absent above the Fortescue Group unconformity spatial relationships between the basalts difficult to with the Yilgalong Granitic Complex. The formation ascertain. The metabasalt is a carbonate–chlorite–albite– is unconformably overlain by the Hardey Formation quartz assemblage. The ocelli are circular, elliptical or and faulted against the younger Kylena Formation. slightly amoeboid. The ocelli are now altered to carbonate The formation outcrops on the eastern rim of the and minor chlorite pseudomorphing stubby crystals that Meentheena Centrocline (Blake, 1993) and in the core of may have been clinopyroxene (Purvis, 2003c; GSWA the Miningarra Anticline (Fig. 3). 192002). A small area of moderately dipping polymictic In the core of the Miningarra Anticline, and particularly pebble conglomerate, sandstone, grey siltstone, and shale in the area around 8 km east of Meentheena Homestead (AFOr-scp), unconformably overlying the Euro Basalt, (MGA 237155E 7643350N on MOUNT EDGAR), the basalts underlies a thick (600 m) basalt succession 4.3 km south- are strongly altered and intersected by numerous quartz southwest of Salvation Well. This sedimentary succession and laminated or banded chalcedony veins and dykes. appears to be a representative of the fl uvial deposits locally Ferruginous gossans are associated with some of the known elsewhere to exist at the base of the Mount Roe quartz veins. The basalts are characterized by extensive Basalt (Thorne and Trendall, 2001; Williams and Bagas, carbonate (ferroan dolomite), silica (quartz), sericite, clay, in prep.). chlorite, and leucoxene alteration. The carbonate alteration may be pervasive or restricted to thin veins. The Mount Roe Basalt consists mainly of massive, porphyritic, vesicular, and amygdaloidal subaerial basaltic The Mount Roe Basalt has not been dated on YILGALONG, lavas with some local pillowed subaqueous basaltic fl ows but a SHRIMP U–Pb zircon date of 2775 ± 10 Ma has been (AFOr-bbg). The basalts are dark grey to greenish-grey obtained elsewhere (Arndt et al., 1991).

15 Williams

Hardey Formation (AFOh-scp, AFOhb-fr, lenticular bodies extending onto YILGALONG from adjoining AFOhb-frp, AFOh-sg, AFOh-spa, AFOh-sfv) MOUNT EDGAR (Williams and Bagas, in prep.). These include a small outcrop (<1 km2) on the west side of the The mixed epiclastic and felsic volcanic Hardey Formation Nullagine River, 1 km north of the Ripon Hills road, a (Thorne et al., 1991; previously called Hardey Sandstone, felsic succession more than 300 m thick and over 11 km MacLeod et al., 1963) is restricted to the southwestern long, which lies west and southwest of the Meentheena quarter of YILGALONG. Although the formation is up to copper prospect, and a third body (up to 300 m thick and 800 m thick along the southwestern margin, where it 7 km long) that extends from north of Salvation Well to unconformably overlies the Mount Roe Basalt and locally the southwest margin. A small area (around 1 km2) of the the Euro Basalt of the East Pilbara Terrane, it thins rapidly Bamboo Creek Member also lies 3 km west of Mopoke eastwards across the sheet area. Seven kilometres south of Well, where it is faulted against the Kylena Formation. Mopoke Well the Hardey Formation rests nonconformably on the Yilgalong Granitic Complex with a considerably The Bamboo Creek Member consists mainly of red- reduced thickness of about 300 m. The formation brown weathering, dark-grey to black, fi ne- to coarse- disappears altogether from the nonconformity about 6 km grained, porphyritic rhyolite, rhyodacite, and dacite south of Bullyarrie Well. From this locality eastwards the (AFOhb-fr). The phenocrysts are quartz, greenish sodic overlying Kylena Formation rests nonconformably on the plagioclase, pink alkali feldspar (orthoclase) and rare Yilgalong Granitic Complex. altered biotite, amphibole, and pyroxene. Such porphyritic rocks in the past have been called quartz–feldspar The Hardey Formation can be subdivided into fi ve porphyries or porphyry complexes (Hickman, 1983; distinct units or successions, similar to those described Blake, 1993). The medium- to coarse-grained porphyritic on MOUNT EDGAR (Williams and Bagas, in prep.). These rocks are commonly in the thicker successions, suggesting are a basal coarse- to fi ne-grained clastic sedimentary that they may be subvolcanic intrusions. Thin-section succession, the felsic volcanic Bamboo Creek Member, petrography shows that most felsic rocks of the Bamboo a thin-bedded, coarse- to fi ne-grained clastic sedimentary Creek Member have alteration assemblages of quartz, succession restricted to the Salvation Well area, a albite, carbonate, sericite, chlorite, and leucoxene. feldspathic coarse- to fi ne-grained clastic sedimentary succession, and an uppermost clastic sedimentary to A porphyritic dacite, 3.2 km west of Mopoke Well volcaniclastic succession. All units are discontinuous on (MGA 245380E 7638264N), contains unusual orbicular YILGALONG and vary considerably in thickness. or accretionary structures up to 25 mm in diameter. The shells of the orbicules are composed of massive fi ne- The basal polymictic, matrix-supported cobble to grained chlorite between 0.5 and 1.5 mm wide. The boulder conglomerate, sandstone, siltstone and local shale shells are interrupted by, and post-date, the plagioclase (AFOh-scp) is up to 300 m thick and has been deposited and quartz phenocrysts. The groundmass outside the on a pre-existing eroded surface developed on top of the orbicular chlorite shells is rich in quartz and sericite and Mount Roe Basalt or Yilgalong Granitic Complex. The has a fl ow texture defi ned by leucoxenized microlites. matrix-supported polymictic conglomerate, containing Internally, the chlorite shells contain abundant granular a high proportion of clasts derived from the underlying and microgranular quartz, minor to abundant chlorite, and Mount Roe Basalt, is found in outcrops on the western microcrystalline leucoxene that is not elongate or oriented. margin of YILGALONG 3 km south of the Ripon Hills Road, Lenses of chalcedony and sometimes sparry carbonate and 8 km west of Bookabunna Well. The proportion of are also present within the orbicules. The orbicular basalt clasts decreases in outcrops farther south around structures resemble expanded spherulites and seem to the eastern margin of the Meentheena Centrocline and have formed during the crystallization or devitrifi cation are absent from equivalent basal conglomerates overlying of the groundmass (Purvis, 2003a; GSWA 169232). the Yilgalong Granitic Complex farther east. The basal Welded ignimbrite, volcanic breccia, and accretionary Hardey Formation unit overlying the Yilgalong Granitic lapilli in resedimented pyroclastic deposits have been Complex disappears around 8 km south-southeast of locally recorded elsewhere in the Bamboo Creek Member Mopoke Well. Conglomerates unconformably overlying (Williams and Bagas, in prep.). the Yilgalong Granitic Complex 12 km further to the southeast and 6 km south of Bullyarrie Well are now Although the Bamboo Creek Member has not been correlated with the uppermost epiclastic–volcaniclastic dated on YILGALONG, the same horizon on adjacent unit of the Hardey Formation (cf. Williams, 2005). The MOUNT EDGAR has yielded a SHRIMP U–Pb zircon date basal unit near Salvation Well is mainly dark-grey to blue- of 2766 ± 7 Ma from a cutting on the Ripon Hills road grey siltstone and shale with interbedded thin sandstone 3.5 km west-northwest of King Rockhole (Nelson, 2004b; and pebble conglomerate. Locally, thick units of dark- GSWA 169037). grey (carbonaceous) shale and micaceous siltstone overlie A number of coarse- to fi ne-grained dacite, rhyodacite, the polymictic conglomerates, as in the area west of the and rhyolite dykes (AFOhb-frp) intrude the Mount Roe Meentheena copper prospect. Basalt in the core of the Miningarra Anticline 9 km west of Bookabunna Well. The dykes are generally less than a kilometre long and trend west-northwest. A similar Bamboo Creek Member (AFOhb-fr, AFOhb-frp) trending dyke on MOUNT EDGAR intruded in the Mount The Bamboo Creek Member (AFOhb-fr; Thorne and Roe Basalt and in close proximity to the YILGALONG dykes, Trendall, 2001; cf. Bamboo Creek Porphyry, Noldart yielded a conventional zircon U–Pb date of 2765 ± 2 Ma and Wyatt, 1962; Hickman, 1983) is exposed in three (Thorne and Trendall, 2001).

16 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

A prominent porphyritic quartz–K-feldspar–plagioclase probably due to erosion prior to deposition of the overlying rhyodacite dyke intrudes the Elsie Creek Tonalite, 11 km Kylena Formation. The succession consists of sandstone, southeast of Dingo Well. The quartz and feldspar siltstone, shale, local pebbly sandstone and conglomerate phenocrysts are set in an altered microspherulitic interbedded with volcaniclastic sandstone, accretionary groundmass. The K-feldspar may also rim some of the lapilli beds, and minor thin carbonate beds (AFOh-sfv). plagioclase phenocrysts. Petrographically, the dyke shows many features identical to the Bamboo Creek Member The youngest succession (AFOh-sfv) is continuously feeder dykes previously described from MOUNT EDGAR exposed around the eastern side of the Meentheena (Williams and Bagas, in prep.) to which this dyke has Centrocline (Fig. 3) northwest of Salvation Well in the been correlated. The dyke is unconformably overlain by southwest corner of the sheet area, where it is commonly the Kylena Formation. less than 200 m thick. Here, the youngest succession conformably overlies the feldspathic sandstone, pebbly sandstone, and conglomerate with minor fine-grained Conglomerate and sandstone unconformably sandstone and siltstone succession (AFOh-spa). On overlying the Bamboo Creek Member (AFOh-sg) the western boundary of YILGALONG, 10 km north of The Bamboo Creek Member is unconformably overlain Salvation Well, the succession unconformably overlies to the west and north of Salvation Well by a lenticular the older Bamboo Creek Member. This relationship is unit up to 120 m thick of thin-bedded conglomerate also recorded 3 km west of Mopoke Well. At this locality and sandstone, with local interbedded minor wacke and the youngest succession extends from the Bamboo Creek siltstone (AFOh-sg). The clasts in the conglomerate are Member disconformably onto the adjacent underlying mostly quartz pebbles and the associated medium- to basal polymictic, matrix-supported cobble to boulder coarse-grained sandstones are commonly feldspathic. conglomerate, sandstone, siltstone, and local shale Similar rocks have been described from MOUNT EDGAR, succession (AFOh-scp) The youngest succession also where it can be shown that much of the clastic material in disconformably overlies the basal succession of the Hardey this unit was probably eroded from the underlying Bamboo Formation (AFOh-scp) 6 km south of Mopoke Well. It also Creek Member (Williams and Bagas, in prep.). unconformably overlies the Elsie Creek Tonalite of the Yilgalong Granitic Complex 8 km southeast of Mopoke Several thick units of red- to purple-weathering, blue- Well. The youngest succession continues to thin eastwards grey laminated siltstone lie 1.5 km northwest of Salvation and is absent from the Fortescue Group unconformity Well. The siltstone is interbedded with thin quartz-pebble with the Yilgalong Granitic Complex about 6 km south- conglomerate and medium- to coarse-grained feldspathic southeast of Bullyarrie Well, where the overlying Kylena sandstone beds. A number of exploratory costeans, up Formation rests directly on the Yilgalong Granitic to 50 m long, have been excavated in the siltstone units. Complex. These relationships support the proposal that the Overall, this succession is upward fi ning. Yilgalong Granitic Complex was a basement high during the deposition of the Hardey Formation. An almost continuous succession of feldspathic sandstone, pebbly sandstone, and conglomerate with The epiclastic component of the uppermost succession minor fi ne-grained sandstone and siltstone (AFOh-spa), consists of red-brown- to brown-weathering, fi ne-grained up to 250 m thick, can be traced around the southeast to pebbly sandstone and pebbly conglomerate with portion of the Meentheena Centrocline. West of Salvation quartz and felsic volcanic clasts interbedded with fl aggy, Well this unit disconformably overlies the thin-bedded yellow-weathering grey siltstone and shale. Volcaniclastic conglomerate, sandstone, local wacke, and siltstone unit tuffaceous siltstone, shale, sandstone, and reworked lapilli- (AFOh-sg), whereas 5 km north of Salvation Well the unit bearing tuffaceous rocks are more common in the upper unconformably overlies the Bamboo Creek Member. This parts of the succession. Thin-section studies show that the latter relationship is also present on the western margin, tuffaceous lithic–crystal sandstone contains carbonate- 1.5 km north of the Ripon Hills road. The discontinuous and microcrystalline chlorite-altered mafi c shards that nature of the epiclastic units within the Hardey Formation may form up to 35% of the rock (Purvis, 2003a; GSWA is exemplifi ed in exposures 6 km west of Bookabunna 169240). Rare thin-bedded grey carbonate lenses are Well, where the feldspathic sandstone, pebbly sandstone, interspersed through the succession. and conglomerate with minor fi ne-grained sandstone and siltstone succession (AFOh-spa) lies disconformably on the A felsic tuffaceous horizon interbedded with basal conglomerate, sandstone, siltstone, and local shale terrigenous fl uvial deposits in the upper part of the Hardey succession (AFOh-scp). Formation on NULLAGINE has a SHRIMP U–Pb zircon date of 2752 ± 5 Ma (Blake et al., 2004). Conglomerate clasts in the feldspathic sandstone, pebbly sandstone, and conglomerate succession (AFOh- spa) are mostly quartz with minor coloured chert. The Kylena Formation (AFOkm-kts, AFOk-xfa-spv, sandstone beds become fi ner grained towards the top of AFOk-xbb-bk, AFOk-bng) the unit. Tabular and trough cross-beds have been observed in the sandstone. The Kylena Formation (Kojan and Hickman, 1998; Thorne and Trendall, 2001) occupies a broad zone that stretches The youngest succession of the Hardey Formation from the southern margin of YILGALONG, 14 km west of the is also the most laterally widespread unit. Although southeast corner, northwest to the Nullagine River area and discontinuous in outcrop (Williams and Bagas, in prep.) central parts of the western margin (Fig. 3). The formation the scattered nature of the outcrop on YILGALONG is is well exposed throughout and reaches a maximum

17 Williams thickness of about 1800 m between Mopoke and Mishap porphyritic, and amygdaloidal andesite, basaltic andesite, Wells. The Kylena Formation is predominantly composed and dacite interlayered with volcaniclastic conglomerate, of tholeiitic basalt with lesser komatiitic basalt, basaltic sandstone, siltstone, shale, accretionary lapilli, and felsic andesite, and dacite. However, the lower portion of the tuffaceous beds (AFOk-xfa-spv). This latter succession also formation contains a widespread and distinctive carbonate unconformably overlies granitic rocks of the Yilgalong marker horizon — the Mopoke Member (AFOkm-kts). Granitic Complex and directly underlies the Mopoke Locally, beneath the Mopoke Member, there is also Member where present. The andesitic and dacitic fl ows and an unnamed succession of andesite, basaltic andesite, volcaniclastic rocks are commonly pale to dark grey and and dacite fl ows and associated volcaniclastic material greenish-grey. Phenocrysts are commonly plagioclase, but (AFOk-xfa-spv). The Mopoke Member separates the some altered mafi c phenocrysts, probably clinopyroxene Kylena Formation into two chemically distinct basaltic or amphibole, are also locally present. Small elliptical successions. amygdales contain quartz, carbonate, chlorite, and sulfi des — generally pyrite, but also some sphalerite. The Succession beneath the Mopoke Member groundmass is commonly an altered assemblage of albite, K-feldspar, chlorite, sericite, leucoxene, carbonate, and The lower succession of the Kylena Formation (AFOk- quartz. xbb-bk) that lies beneath the Mopoke Member is unconformably transgressive on the underlying Hardey The volcaniclastic material includes mixtures of Formation in the southwest corner of the sheet area. lithic clasts, mainly granitic material, quartz, and From 5 km north-northwest of Bullyarrie Well to an area microcline, with reworked accretionary lapilli and glassy 16 km southeast of Dingo Well the lower succession shards, now mainly chlorite. Some of the material may noncomformably overlies the Elsie Creek Tonalite of be phreatomagmatic in origin. Layered, finer grained the Yilgalong Granitic Complex. This lower succession tuffaceous siltstone and sandstone contain mixed reaches a maximum thickness of around 500 m in the assemblages of chlorite, clay, albite, leucoxene, and altered Mopoke Well area. From here it progressively thins to lithic and glassy fragments together with grains of quartz, the east where it overlies a basement high composed of plagioclase, and microcline. the Yilgalong Granitic Complex. At the eastern end of the Yilgalong Granitic Complex exposure, between 10 Two samples were collected from the mixed mafi c– and 19 km southeast of Dingo Well, the lower basaltic felsic volcanic and volcaniclastic succession (AFOk-xfa- succession of the Kylena Formation disappears altogether spv) for SHRIMP U–Pb zircon dating. A fi ne-grained, and the unnamed felsic component of the lower succession dark-grey dacite, collected from the northeastern side of a low rocky hill 17 km west of Carawine Pool was (AFOk-xfa-spv), the Mopoke Member (AFOkm-kts), and dated at 2749 ± 5 Ma (Nelson et al., 2006; GSWA the upper succession of the Kylena Formation (AFOk- bng) all nonconformably overlie parts of the Yilgalong 178086). Fine-grained, dark greenish-grey tuffaceous Granitic Complex. At the base of all these units there volcaniclastic sandstone, collected from the top of a is a thin veneer of conglomerate, containing quartz and rocky hill 12.6 km east-southeast of Dingo Well, yielded granitic clasts, mixed with pebbly arkosic sandstone and a date of 2735 ± 6 Ma. This is interpreted as the age of feldspathic sandstone. This material may be grus eroded igneous crystallization of the tuffaceous component of the from the granitic rocks prior to deposition of the Kylena volcaniclstic sandstone (Bodorkos et al., 2006b; GSWA Formation. 178090). This sample also contained a high proportion of detrital zircons, incorporated into the volcaniclastic The lower succession consists of multiple thick fl ows sandstone via sedimentary processes, which yielded dates of massive, fi ne-grained to vesicular and amygdaloidal, ranging from c. 2781 to c. 3391 Ma. These dates agree grey-blue basalt and greenish-grey komatiitic basalt with an 2741 ± 3 Ma age obtained from mafi c tuffaceous (AFOk-xbb-bk). Locally, well-exposed pillow structures material and collected from the near the base of the Kylena indicate subaqueous conditions, probably lacustrine, Formation on NULLAGINE (Blake et al., 2004). because most fl ows appear to be subaerial as shown by columnar jointing and scoriaceous flow tops. In thin Mopoke Member (AFOkm-kts) section the primary plagioclase–clinopyroxene–feldspathic mesostasis of the basalt show albite–sericite–prehnite– The Mopoke Member (AFOkm-kts, Appendix 2) is a pumpellyite–leucoxene–chlorite alteration. Amygdales discontinuous, but distinctive, carbonate marker bed contain varying amounts of chlorite, pumpellyite, lying between two chemically distinguishable basaltic carbonate, and prehnite. Fine-grained pyroxene-spinifex successions of the Kylena Formation. This chemical textures have been noted in the komatiitic basalts. distinction, shown by the radiometric (K, Th) pseudocolour image, can be used to separate the lower basaltic The lower basalt succession has a distinctive succession with low K and Th from the upper succession radiometric (K, Th) pseudocolour signature that indicates with moderate to high K and Th when the Mopoke low potassium and thorium when compared to the Member is absent (Williams and Bagas, in prep.). upper basalt succession (high K and Th) of the Kylena Formation. These signatures were first identified on Within the Kylena Formation the Mopoke Member EASTERN CREEK (Farrell, 2006) and later confirmed on is particularly useful in identifying the stratigraphic MOUNT EDGAR (Williams and Bagas, in prep.). position of the component basaltic rocks where the formation is disrupted by later faults. The Mopoke The lower basalt succession is overlain in the area Member unconformably overlies the Little River 11 to 19 km southeast of Dingo Well by massive, Trondhjemite 9.5 km southeast of Dingo Well (Fig. 5) and

18 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

increasingly potassic upwards, although a geochemical traverse immediately south of YILGALONG indicated that the most felsic rocks are andesites (Glikson et al., 1986). Individual flows are up to 15 m thick and commonly exhibit scoriaceous flow-tops. Columnar jointing is locally developed. Some rare large pillow structures 4 km northwest of Bookabunna Well in a road cutting on the Ripon Hills Road (MGA 247408E 7646985N) are associated with stacked subaerial fl ows 2 to 3 m thick, suggesting that the pillow lavas are local and limited to shallow-water conditions. Both flow forms carry amygdales and vesicles. The basalts consist of partly altered plagioclase and clinopyroxene set in a mesostasis of chlorite, K-feldspar, IRW199 06.06.07 opaque minerals, and accessory apatite. Alteration products include albite, sericite, chlorite, patchy quartz, Figure 5. Mopoke Member (dark colour) nonconformably carbonate, pumpellyite, and smectite. Amygdales can overlying the Little River Trondhjemite (light colour; be ovoid or irregular in shape and fi lled with carbonate, MGA 269362E 7627124N) chlorite, and quartz, including chalcedony.

On YILGALONG the upper basalt succession in the Kylena Formation is alkali enriched (Blake et al., 2004), the Midgengadgi Monzogranite of the Yilgalong Granitic as fi rst described in the west Pilbara (Kojan and Hickman, Complex 17 km southeast of Dingo Well. In both areas the 1998). This observation is supported by the ternary carbonate is underlain by thin beds of calcareous pebble radiometric image for the NULLAGINE 1:250 000 sheet conglomerate and calcareous feldspathic sandstone. The (GSWA, 2005b). clasts in the conglomerate are quartz and locally derived granitic material. Tumbiana Formation (AFOti-bntt, AFOtm-kts, The Mopoke Member consists of cliff-forming, AFOt-bbg) silicified blue-grey carbonates, mostly limestone or dolomitic limestone, up to 5 m thick. The carbonates are The Tumbiana Formation (Lipple, 1975; Thorne and interbedded and overlain by thin-bedded, grey to cream Trendall, 2001) is continuously exposed over a distance of siltstone, shale, and fi ne-grained sandstone (AFOkm-kts). 46 km. The formation extends from the western margin, The siltstone and shale beds are sometimes calcareous 9.5 km north of the Ripon Hills road, southeastwards to and tuffaceous. Wave-based ripple marks of up to 1 cm amplitude are locally present. The carbonate is partly silicifi ed, particularly where stromatolites and microbial laminations are present (Fig. 6). Stromatolites are more plentiful in the upper parts of the member and range from centimetre-scale fl at-laminated, columnar and cumulate forms to large low-profi le domes 1–2 m across in the thicker beds. Thin blue chert beds are locally present.

The Mopoke Member appears to be a lacustrine deposit similar, but on a smaller scale, to the overlying Meentheena Member of the Tumbiana Formation. Although not directly dated, the Mopoke Member is younger than the underlying mafi c–felsic volcanic and volcaniclastic succession (AFOk-xfa-spv) dated around 2749–2735 Ma.

Succession above the Mopoke Member The upper succession of the Kylena Formation makes up the bulk of the area occupied by the formation on YILGALONG, and is up to 1700 m thick in the Dingo Well area. Two small faulted inliers of the upper succession lie within the Maddina Formation 15 km east and 18 km east-southeast of Dingo Well. Field mapping indicates that IRW200 06.06.07 the succession consists mainly of massive, amygdaloidal, and vesicular fi ne- to coarse-grained, grey and bluish-grey Figure 6. Silicifi ed stromatolitic dolomite, basalt and basaltic andesite (AFOk-bng). Radiometric Mopoke Member (MGA 246377E data (GSWA, 2005b) show the succession to become 7641976N)

19 Williams where it is truncated by a regional strike-slip fault, 13.5 km The Meentheena Member is composed of lenticular east of Dingo Well. In addition, three small faulted inliers units of stromatolitic, dark-grey siliceous limestone containing the Mingah Member lie between 6 and 8 km and dolomite within laterally variable sequences south-southeast of this easternmost outcrop. There are no of volcaniclastic sandstone and siltstone, including further exposures on YILGALONG. The next outcrops are accretionary lapilli beds, together with calcareous recorded 25 km to the south on EASTERN CREEK (Farrell, sandstone, carbonaceous shale, local quartz sandstone, and 2006). The formation ranges in thickness from 500 m in conglomerate (AFOtm-kts). The characteristic low cliff- the northwest to about 300 m in the southeast exposures. lines in this member are exclusively carbonate, whereas On YILGALONG the Tumbiana Formation is composed the volcaniclastic and classic material underlie the scree of the lower Mingah Member (AFOti-bntt) and upper slopes. The limestone and dolomite units are up to 15 m Meentheena Member (AFOtm-kts). South of the Ripon thick and the fi rst thick carbonate unit (1−2 m) marks the Hills road these two members are separated by a thick base of the Meentheena Member. vesicular amygdaloidal and massive basaltic unit (AFOt- bbg). This unit consists of lenticular subaerial basaltic The carbonate units locally carry abundant flows up to 250 m thick. Amygdales contain quartz, stromatolites with a broad range of morphological types. banded chalcedony (agate), and epidote. North of the These include extensive tabular and domed biostromes, Ripon Hills road the Tumbiana Formation is intruded by domed bioherms, and individual turbinate and bulbous multiple dolerite sills and dykes (AFO-od). The Tumbiana columns and local oncolites. Good exposures of several Formation conformably or disconformably overlies the stromatolitic forms are on the western end of a prominent Kylena Formation. hill 2 km east of Bookabunna Well on the northern side of the Ripon Hills road. Nonstromatolitic carbonate beds may be micritic, oolitic, laminated, and fenestrated. Mingah Member (AFOti-bntt) A variety of sedimentary structures are found in the The Mingah Member (AFOti-bntt; Thorne and Trendall, carbonates and interbedded volcaniclastic and epiclastic 2001; cf. Mingah Tuff Member, Lipple, 1975) is the basal material. These include cross-bedding, wave and current member of the Tumbiana Formation on YILGALONG. It is ripple marks, including climbing ripple sets over less prominent than on adjoining MOUNT EDGAR (Williams stromatolitic bioherms, edgewise breccias, desiccation and Bagas, in prep.) and is between 350 m thick in the cracks, tepee structures, and pseudomorphs of evaporate northwest to 190 m thick in the southeast. The Mingah minerals (Packer, 1990; Awramik and Buchheim, 1997, Member is not well exposed and is characterized by low 2001; Thorne and Trendall, 2001). Although some workers strike ridges of the more resistant coarser volcaniclastic favour sublittoral to supralittoral coastal conditions and epiclastic beds. adjacent to shallow-marine shelf-facies deposits (Packer, 1990; Thorne and Trendall, 2001), other workers suggested The Mingah Member is composed of basaltic to that lacustrine deposition was more likely (Buick, 1992; andesitic volcaniclastic grey-green sandstone and siltstone, Awramik and Buchheim, 1997, 2001). commonly interbedded with accretionary lapilli beds, local quartz sandstone, shale and thin lenticular stromatolitic Samples collected elsewhere from volcaniclastic rocks carbonate units (AFOti-bntt). Accretionary lapilli beds in the upper part of the Tumbiana Formation (Meentheena are up to 1 m thick with individual lapilli ranging from Member) have yielded dates between c. 2719 and 2715 Ma 2 to 10 mm in size. Such beds are well exposed on the (Arndt et al., 1991; Nelson, 2001; GSWA 168935). northern side of the Ripon Hills road 2.5 km northwest of Bookabunna Well. The closely packed accretionary lapilli beds show normal, reverse, and nongraded layers Maddina Formation (AFOm-bb, AFOmk-bntt) indicating primary pyroclastic fall deposits (Boulter, 1987; The Maddina Formation (Kojan and Hickman, 1998; Thorne and Trendall, 2001). Such deposits may represent cf. Maddina Basalt, MacLeod and de la Hunty, 1966) is the products of phreatomagmatic eruptions (McPhie et al., continuously exposed from near Boodalyerri Creek in 1993). the southeast corner diagonally across YILGALONG to the northwest corner where it occupies the core of the large The Mingah Member has yielded SHRIMP U–Pb Oakover Syncline (Fig. 3). From here it can be traced a zircon dates ranging from 2727 ± 5 to 2721 ± 4 Ma from further 13 km eastwards along the northern boundary of WARRIE (Blake et al., 2004). YILGALONG where the formation is exposed in the northern limb of the Oakover Syncline. The Maddina Formation Meentheena Member (AFOtm-kts) is more than 1000 m thick where it is intersected by the Nullagine River. However, south of the Ripon Hills road The Meentheena Member (AFOtm-kts; Thorne and it is diffi cult to estimate thicknesses due to extensive later Trendall, 2001; cf. Meentheena Carbonate Member, faulting. The Maddina Formation conformably overlies the Lipple, 1975) is a distinctive, commonly cliff-forming Tumbiana Formation in the western half of the sheet area, upper unit of the Tumbiana Formation. The member but east of Yilgalong Creek a large transpressional fault thins gradually from 250 m in the northwest to around juxtaposes the Maddina Formation against the underlying 100 m in the southeast. The unit is absent from the faulted Kylena Formation. inliers farther south. The Meentheena Member appears to conformably overlie the tuffaceous Mingah Member The Maddina Formation (AFOm-bb) is made up of north of the Ripon Hills road and the unnamed basalt unit stacked, massive, amygdaloidal, and vesicular, fi ne- to (AFOt-bbg) south of the road. coarse-grained basalt fl ows. The thin to thick fl ows (2 to

20 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

quartz smectite

prehnite chlorite

IRW201 0.5 mm 22.05.07 IRW202 06.06.07

Figure 7. Thin section of zoned amgydale in the Maddina Figure 8. Interbedded siltstone and accretionary lapilli beds Formation (GSWA 169287; MGA 281671E 7623044N) showing graded bedding, Kuruna Member (MGA 245467E 7664613N)

50 m thick) are intercalated with comagmatic, medium- The Kuruna Member (AFOmk-bntt) consists of fi ne- to coarse-grained dolerite sills and local thin tuffaceous to medium-grained volcaniclastic rocks of basaltic and volcaniclastic horizons. Rough, silicified scoriaceous andesitic parentage, commonly including accretionary fl ow-tops, sometimes with quartz–epidote veining, mark lapilli, khaki-brown- to olive-brown-weathering siltstone, the individual fl ows. Vesicles and amygdales generally shale, and fi ne-grained sandstone, with local stomatolitic congregate towards the top of the fl ows. Large irregular- carbonate. The stromatolitic carbonate tends to lie towards shaped gas cavities up to 25 cm have been observed in the top of the member and resembles the dolomite and some fl ow-tops. Amygdales are generally spherical or limestone in the underlying Tumbiana Formation. Good elliptical in shape and contain quartz, banded chalcedony exposures lie 6.7 km south of Walgunya Well on the (agate including pink carnelian), carbonate, chlorite, western side of the Nullagine River where three carbonate prehnite, opaque minerals, and leucoxene (Fig. 7). Locally, horizons are separated by volcaniclastic siltstone, pipe amygdales are found towards the base of some fl ows. accretionary lapilli beds, fine-grained sandstone, and Thick basalt fl ows towards the top of the formation are shale. The carbonates are partly silicifi ed, particularly the locally columnar jointed. stromatolitic horizons that include fl at domal bioherms up to 2 m. The interbedded accretionary lapilli horizons are The primary mineralogy of calcic plagioclase and normally graded and the fi ne-grained sandstone is ripple clinopyroxene (pigeonite and augite) is variably altered to marked (Fig. 8). albite–chlorite–epidote–prehnite–pumpellyite–carbonate– sericite–quartz–leucoxene assemblages (Thorne and Trendall, 2001; Purvis, 2003a). Jeerinah Formation (AFOj-xcl-kd, AFOjb-bnth) The Maddina Formation has yielded dates elsewhere Shale, chert, and dolomite (AFOj-xcl-kd) of the Jeerinah ranging from 2718 to 2713 Ma (Nelson, 1998; GSWA Formation (MacLeod et al., 1963) was previously mapped 144993; Blake et al., 2004). as Lewin Shale in this area (Hickman, 1978) and later assigned to the Jeerinah Formation (Hickman, 1983). This subunit of the Jeerinah Formation is exposed in the central Kuruna Member (AFOmk-bntt) and northwestern parts of YILGALONG along the southern The Kuruna Member (Thorne and Trendall, 2001; cf. and western margins of the Ripon Hills. Further exposures Kuruna Siltstone, MacLeod and de la Hunty, 1966) forms are in the far northeast corner east of the Oakover River a prominent marker horizon in the upper part of the valley in the Gregory Range Inlier (Williams and Trendall, Maddina Formation throughout most of its distribution on 1998a). The exposures rimming the Ripon Hills area YILGALONG, apart from in the southeastern corner. The last are strongly disrupted by complex faulting and folding. signifi cant exposure of the Kuruna Formation lies 10.5 km Farther north along the Nullagine River valley the southwest of Pulgorah Cone. Possible scattered remnants formation is intruded by thick, coarse-grained dolerite sills of the Kuruna Member are within and overlying (as small (AFO-od). A similar situation exists in the Gregory Range mesa-like hills) faulted blocks of the Maddina Formation Inlier where the Jeerinah Formation is intruded by thick around 18 km southwest of Pulgorah Cone. The Kuruna dolerite sills and intersected by several steep reverse faults. Member is up to 150 m thick 6.5 km north of Mount Ian In addition, thick lenticular bodies of the mafi c volcanic Well in the central parts of YILGALONG. From here the Baramine Member (AFOjb-bnth) are found in both areas. member thins to the southeast to less than 100 m and to The complex faulting and later mafi c intrusions make it the northwest to less than 60 m. Thick, lenticular, coarse- diffi cult to calculate the thickness of the formation. East grained dolerite sills (AFO-od) locally intrude the Kuruna of Yilgalong Creek and around 17 km west-southwest of Member, particularly northwest of the Nullagine River. Pulgorah Cone, a north-dipping succession of the Jeerinah

21 Williams

Formation is at least 500 m thick. About 5 km farther north northeast of Bookabunna Well, 9 km east-southeast of of this locality and on the west bank of Yilgalong Creek an Walgunya Well, and in the northeast corner in the Gregory exploratory diamond drillhole (RHDH2A; MGA 274508E Range Inlier. 7644780N) in Carawine Dolomite terminated in Jeerinah Formation after intersecting 246 m of the unit (Richards, The Baramine Member consists of massive, 1985). The Jeerinah Formation disconformably overlies, or amygdaloidal, and vesicular dark-grey to grey-green basalt is faulted against, the underlying Maddina Basalt. and basaltic andesite, interlayered with basaltic volcanic sandstone and siltstone, and local accretionary lapilli beds Shale, chert, and dolomite of the Jeerinah Formation (AFOjb-bnth). Pillowed basalts are locally developed in (AFOj-xcl-kd) includes shale, siltstone, fi ne- to medium- Coonanbunna Creek 7.5 km northwest of Nullagine 1 grained sandstone, coloured and banded cherts, dolomite, Trig Point. Thin-bedded, grey-blue silicifi ed mudstone and local stromatolitic limestone. The basal disconformity is also locally interbedded with the basalts. The basaltic with the underlying Maddina Formation is well exposed rocks are composed of plagioclase, clinopyroxene, and to the south and west of the Ripon Hills. Some exposures opaque minerals, including titanomagnetite and ilmenite. of the uppermost Maddina Formation are ferruginized, Feathery quenched textures are sometimes preserved in suggesting possible weathering prior to deposition of the carbonate-altered mesostasis. Thin carbonate veins are Jeerinah Formation. locally common. Altered olivine has also been recorded. Vesicles contain carbonate, quartz, and local sulfide. North of the Nullagine River the basal unit is red- Albite–sericite–carbonate–leucoxene–clay alteration is brown-weathering, grey to grey-blue, blocky, fine- present throughout the succession. grained quartz sandstone. This sandstone is commonly ripple marked with both current and wave-based ripples. The volcaniclastic component of the Baramine Member Progressing to the southeast the basal sandstone unit appears to be a mixture of resedimented syneruptive changes to silicifi ed dark-grey siltstone and shale. South volcaniclastic deposits and volcanogenic sedimentary of the Ripon Hills the basal sandstone is overlapped by deposits (McPhie et al., 1993). Very fi ne to coarse-grained blue-grey limestone. This latter unit, which includes banded dark-grey and speckled white, volcanic labile brown, orange, and grey dolomite elsewhere, consistently sandstones are grain supported. These are dominated by overlies the basal sandstone and siltstone when these basalt clasts altered to albite, chlorite, clay, leucoxene, and lithologies are present, particularly in the northwest. The local carbonate. Minor quartz grains are also present. Most carbonates, both limestone and dolomite, locally carry bedding is planar, but some grading and cross-bedding microbial laminations and stromatolites that exhibit small have been noted (Purvis, 2003a; GSWA 169227). Other columnar and low domal forms. The carbonates are thin volcaniclastic rocks have a large component of reworked to medium bedded and commonly overlain by ripple- pyroclastic material, including accretionary lapilli, shards, marked fi ne-grained sandstone. This sandstone is overlain and tuffaceous vitric, lithic, and crystal grains. by interbedded multicoloured chert, banded black, blue, and white chert, siltstone, thin-bedded carbonate, and The components of the Baramine Member on shale. Scattered framboidal pyrite (marcasite) balls (now YILGALONG appear to be more distal from volcanic centres goethite) weather from the shale and chert units. The upper than those described on adjacent WARRAWAGINE, BRAESIDE, sections of the Jeerinah Formation consist mostly of white- and ISABELLA (Williams, 2001; Williams and Trendall, weathering, black and grey carbonaceous and pyritiferous 1998a, 1998c). In these areas many of the bedforms shale with thin interbeds of siltstone and coloured and resemble pyroclastic surge deposits associated with banded chert beds. More than 20 m of carbonaceous shale phreatomagmatic eruptions, and debris-flow deposits are exposed in Parsons Creek 6 km east of Little River generated from the collapse of volcanic edifi ces (McPhie Well in the Gregory Range Inlier. et al., 1993). Geochronological samples were not collected from the Jeerinah Formation during the present survey. Samples Mafi c intrusive rocks in the Fortescue collected from a tuffaceous band close to the top of the Group (AFO-od) Jeerinah Formation (from the Roy Hill Shale Member, just beneath the Marra Mamba Formation on the NEWMAN Thick dolerite sills and associated dykes (AFO-od) 1:250 000 sheet) yielded a SHRIMP U–Pb date of preferentially intrude the Mopoke, Mingah, Meentheena, 2629 ± 5 Ma (Trendall et al., 2004). and Kuruna Members, which are volcaniclastic and carbonate members intercalated within the largely basaltic Baramine Member (AFOjb-bnth) pile, and the uppermost sedimentary–volcanic Jeerinah Formation of the Fortescue Group on YILGALONG. Such The Baramine Member (AFOjb-bnth; previously defi ned sills are most numerous in the Jeerinah Formation around as the Baramine Volcanic Member, Hickman, 1983; the core of the Oakover Syncline in the Nullagine River redefi ned in Williams and Trendall, 1998c) is exposed in a valley area, and in the extreme northeast corner. In the number of localities. It is unclear whether this distribution lower members of the Fortescue Group such sills are up to is a structural artifice or reflects a primary lenticular 150 m thick, whereas in the Jeerinah Formation they may distribution within the Jeerinah Formation. A continuous exceed 300 m in thickness, although such estimates are outcrop over 12.5 km lies along the southern margin of made diffi cult by the poor outcrop. the Ripon Hills where it occupies the central part of the Jeerinah Formation. The thickness varies between 100 and The dolerite sills are dark-green to grey-green, fi ne- to 250 m in this area. Smaller faulted areas lie 9 km north- coarse-grained, altered granular to ophitic rocks. Rare

22 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet patches of granophyric texture have been noted in thicker infi lls a pre-existing karst topography dissolved and eroded dolerite sills intruded into the Jeerinah Formation. The within the dolomite (Fig. 9). An exploratory diamond primary assemblage includes plagioclase, clinopyroxene, drillhole RHDH2A on the west bank of Yilgalong Creek, and accessory skeletal titanomagnetite, titanite, and 17.5 km west of Pulgorah Cone, intersected about 185 m apatite. All dolerite sills exhibit varying degrees of of Carawine Dolomite before entering the underlying alteration similar to the Fortescue Group basaltic rocks. Jeerinah Formation (Richards, 1985). A second hole, Such alteration takes the form of clay-altered and RHDH1, 11.5 km west of Pulgorah Cone, spudded in prehnite-altered interstitial material and albite–prehnite– Permian Paterson Formation 1 km northeast of exposed pumpellyite–chlorite–clay–carbonate–epidote–leucoxene Carawine Dolomite failed to intersect the Carawine assemblages partly replacing the primary mineralogy. Dolomite. This hole intersected 158 m of Permian Paterson Formation, 85 m of dolerite (probably a sill), These thick dolerite sills are probably subvolcanic and 134 m of the Jeerinah Formation (Richards, 1985). On intrusions consanguineous with the Fortescue Group nearby PEARANA to the southeast an exploratory drillhole basalts. intersected 500 m of Carawine Dolomite (Williams and Trendall, 1998b). Hamersley Group The contact between the Carawine Dolomite and underlying Jeerinah Formation is either disconformable Exposed Hamersley Group rocks account for only 10% of or faulted. The disconformity is positioned by the fi rst the area occupied by the Hamersley Basin on YILGALONG appearance of dolomite above a thick succession of shale, and this succession is represented solely by the Carawine most of which is carbonaceous and tuffaceous. The Marra Dolomite. Mamba Iron Formation that separates the Carawine Dolomite from the underlying Jeerinah Formation on Carawine Dolomite (AHAc-kds, AHAc-kdx) BALFOUR DOWNS more than 100 km to the south is absent on YILGALONG (cf. Williams and Trendall, 1998b). The Carawine Dolomite (AHAc-kds; Noldart and Wyatt, 1962; Hickman, 1983) is almost continuously exposed The Carawine Dolomite on YILGALONG can be divided along the southern and western margins of the high into two facies: a lower deep-water basinal deposit and an dissected plateau of the Ripon Hills in the central-north upper, evaporite- and stromatolite-bearing shallow-water of YILGALONG. The formation is also widely exposed in platform deposit (cf. Simonson and Hassler, 1997). In the scattered outcrops along gorges in the northeastern half Ripon Hills region a distinctive marker horizon composed of the Ripon Hills, and also along the western side of the of a chaotic spherule-bearing megabreccia (AHAc-kdx) lies Gregory Range Inlier to the east of the Oakover River within the lower basinal facies. The western and southern valley in the northeast corner of YILGALONG. Two other very margins of the Ripon Hills are dominated by the cliff- small outcrops are found at Cave Bore and 17 km south- forming basinal facies of the Carawine Dolomite. This southwest of Pulgorah Cone. The restricted exposure of is mostly brown-weathering, grey to blue, recrystallized the formation in most areas is due to the overlying erosion- massive and laminated dolomite, intercalated with thin- resistant and spatially related Pinjian Chert Breccia. bedded blue chert and minor shale and siltstone. The dolomite averages about 20% MgO and is commonly low The thickness of the Carawine Dolomite is diffi cult in silica (Jahn and Simonson, 1995). to estimate due to the irregular contact with the overlying Pinjian Chert Breccia that unconformably overlies and The scattered exposures of the Carawine Dolomite in the central, eastern, and northeastern parts of the Ripon Hills, and particularly in the Gregory Range Inlier, mostly belong to the upper shallow-water platformal facies of the Carawine Dolomite. The dolomite in the upper facies is a brown-weathering, grey recrystallized dolomite with greater variations in bedding thickness. Thin blue chert, shale, and siltstone interbeds are locally present. The dolomite in the upper facies is characterized by a wide range of sedimentary features indicative of shallow-water deposition. These include oolites, wave ripples, reverse- graded pisolites, oncolitic flat-pebble conglomerate, dololaminites, stromatolites, oncolites, and evaporitic crystal pseudomorphs after aragonite, gypsum, and halite (Simonson et al., 1993b; Simonson and Jarvis, 1993). Stromatolite horizons are commonly silicifi ed. Small columnar forms, larger discrete hemispherical forms up to a metre in size, and laterally linked hemispherical

IRW203 06.06.07 stromatolites have been recorded. Well-exposed stromatolitic dolomite lies along the north bank of Parsons Figure 9. Remnant of the Carawine Dolomite enclosed within Creek, 6 km east of Little River Well in the Gregory the Pinjian Chert Breccia, western side of the Ripon Range Inlier. Stromatolitic dolomite is also common in Hills (MGA 261142E 7645673N) outcrops along the margins of a narrow, north-trending

23 Williams

a) by faulting (Glikson and Hickman, 2005). The SBM can be cliff-forming or occupy recessive scree slopes between cliffs of bedded dolomite. This distinctive marker horizon is in the lower basinal facies of the Carawine Dolomite. It is positioned from about 30 m above the base of the Carawine Dolomite along the southern margin to about 150 m above the base along Coonanbunna Creek on the western margin of the Ripon Hills. The SBM was not found in the Gregory Range Inlier succession even though dolomites corresponding to basinal facies are present beneath stromatolitic dolomite in Parsons Creek. This supports observations recorded in Glikson and Vickers (in prep.) that the SMB has not yet been identifi ed north of Mount Sydney in the Gregory Range Inlier. The chert and dolomite clasts and megaclasts are mostly autochthonous, although some banded chert clasts resemble lithologies in the underlying Jeerinah Formation. The megabreccia unit varies between 10 and 30 m in thickness. The base of the SBM is generally eroded into the underlying dolomitic strata. This is shown by local dislodgement of metre-scale blocks of dolomite and chert. b) The fractures between the blocks are, in turn, injected by fi ne- to medium-grained breccia, which is also found as sheets, veins, tongues, and wedges below the base of the main SBM unit (Glikson and Vickers, in prep.). The association of sand-sized spherules of K-feldspar within the distinctive megabreccia unit (SBM) in the Ripon Hills was fi rst identifi ed by Simonson (1992) who also recognized their connection to silicate melt generated by a bolide impact. These melt droplets, later referred to as microkrystites (Glass and Burns, 1988), and associated microtectites (Simonson and Glass, 2004), are common in the fi ne-grained to microbreccia components of the SBM, particularly in the uppermost parts of the megabreccia pile. They are also sparsely scattered in deeper levels of IRW204 22.05.07 the megabreccia pile, mainly in breccia veins injected into fractures between dolomite and chert blocks Figure 10. Carawine Dolomite: a) contact between the base (Glikson and Vickers, in prep.). Thin-bedded layered of the chaotic spherule-bearing megabreccia and carbonates conformably overlie the megabreccia. Detailed the lower basinal facies of the Carawine Dolomite petrographic descriptions and geochemical studies of the (hammer head resting on contact), southwest side of microkrystites and microtectites are given in Simonson the Ripon Hills (MGA 261330E 7643717N); b) close-up of the upper part of the chaotic spherule-bearing and Glass (2004) and Glikson and Vickers (in prep.). megabreccia showing scattered spherules, some There has been the gradual recognition that the spherules circled in red microkrystite- and microtectite-bearing megabreccia is the product of an asteroid impact in an oceanic environment. The resultant tsunami-wave effect produced erosion and Permian glacial valley 5.5 km southwest of Bunmardie resedimentation of the deep-water Carawine Dolomite. In Well on the eastern side of the Ripon Hills. On the western addition the fallout of ejecta material (silicate spherules) margin of the Ripon Hills stromatolitic dolomite is 3.7 km from the asteroid impact cloud became incorporated in southwest of Nullagine 1 Trig Point about 100 m above the the disrupted Carawine Dolomite (Hassler and Simonson, megabreccia marker horizon. 2001; Hassler et al., 2000; Glikson and Vickers, in prep.). A chaotic spherule-bearing megabreccia containing Detailed descriptions of the SMB, the nature and origin angular, coarse- to fi ne-grained dolomite and chert clasts of the microkrystites and microtectites, and the possible with a microkrystite- and microtectite-rich matrix (AHAc- correlation with similar horizons in the Wittenoom kdx; Simonson 1992; Glikson and Vickers, in prep.; also Dolomite and Jeerinah Formation elsewhere can be found referred to as the Spherule-bearing Tsunami Marker, SBM; in numerous publications over the last 14 years (Simonson, Fig. 10a,b) can be traced almost continuously for more 1992, 2003; Simonson and Harnik, 2000; Simonson and than 38 km along the southern and western margins of Hassler, 1997; Simonson and Glass, 2004; Simonson and the Ripon Hills. The SMB extends from a point 13.2 km Jarvis, 1993; Simonson et al., 1998, 2000, 2004; Glikson, west-southwest of Pulgorah Cone northwest to a point 2002, 2004; Glikson and Vickers, in prep.; Rasmussen 12.5 km southeast of Walgunya Well where it is truncated et al., 2005).

24 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

There has been considerable discussion as to the age time saw the development of secondary breccias and of the Carawine Dolomite and its stratigraphic relationship karstification. This process has continued up to the to the Wittenoom Formation in the Hamersley Ranges present time where the remaining Carawine Dolomite is (Simonson et al., 1993a). Jahn and Simonson (1995) continuing to dissolve, creating further collapse of the obtained a Pb–Pb isochron age of 2541 ± 32 Ma. Somewhat Pinjian Chert Breccia into the new cavities. Locally, the later a carbonate Pb–Pb date of 2548 +26/–29 Ma was breccia is enriched in iron and manganese oxides, derived obtained for the Carawine Dolomite and a 2541 +18/–15 Ma from the dissolution of the Carawine Dolomite. date for the SBM unit (Woodhead et al., 1998). The Bee Gorge Member of the Wittenoom Formation has yielded The Pinjian Chert Breccia in the Ripon Hills is host SHRIMP U–Pb zircon dates of 2561 ± 8 Ma for a crystal- to deep sinkholes and collapsed dolines, four of which rich tuffaceous shale (Trendall et al., 1998) and 256olomite are recorded on YILGALONG (Williams, 2005). The largest, there has to be some doubt as to whether the dated known locally as ‘The Crater’ (MGA 260695E 7651365N) tuffaceous dolomite came from the Carawine Dolomite, as lies on the western edge of the plateau, 2.8 km west of the claimed (Rasmussen et al., 2005), or from dolomitic beds Nullagine 1 Trig Point. This is a collapsed, oval-shaped in the underlying Jeerinah Formation, which would agree doline 132 m (north–south axis) by 100 m (east–west with the isotopic date. In this area the Jeerinah Formation axis) and is 55 m deep to a sandy fl oor in the middle of the consists of interbedded tuffaceous and calcareous shale, doline (Fig. 11). A cave beneath the overhanging western siltstone, and dolomite. side of the doline slopes steeply down to 70 m below the surface (Webb, 1994). The doline and caves at this locality are developed Pinjian Chert Breccia (!pj-ccx) entirely within the Pinjian Chert Breccia. It would appear The Pinjian Chert Breccia (!pj-ccx; Noldart and Wyatt, that a large cave in the Carawine Dolomite beneath the 1962) is widely distributed throughout the Ripon Hills doline had collapsed and subsequently stoped its way and northward to the east bank of the Nullagine River, through the overlying Pinjian Chert Breccia to the present- 7 km west of Outcamp Bore. Further outcrops lie east day surface. The doline post-dates a pre-existing incised of the Oakover River in the Gregory Range Inlier and valley in the Pinjian Chert Breccia thus emphasizing that along a high ridge 16.5 km south-southwest of Pulgorah the doline is not a sinkhole. The cave entrance lies about Cone on the western margin of the Oakover River valley. 380 m AMSL and 140 m above the large Coonanbunna In all localities the Pinjian Chert Breccia is closely Creek, 3.4 km to the west. A second deep sinkhole (MGA associated with Neoarchean Carawine Dolomite. It is 262107E 7656582N), 5.4 km north-northeast of ‘The a strongly outcropping unit characterized by spinifex- Crater’, is developed at the contact between the Carawine covered high rounded hills. The breccia has a highly Dolomite and Pinjian Chert Breccia. irregular unconformable contact with the underlying Carawine Dolomite. This contact surface is postulated to be a paleokarst topography (Hickman, 1978; Williams, 1989; Williams and Trendall, 1998b). The paleokarst surface can be observed at the contact with the dolomite where the breccia can be seen to fi ll fi ssures, caves, and dolines. The karst development appears to be ongoing or episodic throughout the Proterozoic and Phanerozoic. This is supported by the apparent underlying control in the sediment distribution shown by overlying Proterozoic and sometimes Permian sedimentary rocks in blind valleys (poljes) and the development of recent caves, collapsed dolines, and sinkholes, both in the Carawine Dolomite and Pinjian Chert Breccia.

The Pinjian Chert Breccia consists of randomly mixed angular fragments of chert and banded chert that are chaotically or crudely bedded. The initial deposition occurred in the early Paleoproterozoic soon after the deposition of the Carawine Dolomite and consisted of bedded, coloured, and banded cherts. An example of this chert bedding is preserved in a cliff-line 4 km southeast of the Nullagine 1 Trig Point. On commencement of the karstifi cation processes in the underlying Carawine Dolomite, the overlying Pinjian Chert began to collapse into the growing voids within the dolomite. In addition, thin chert beds and silicifi ed dolomite components were IRW205 06.06.07 released during dissolution of the dolomite and contributed further chert fragments to the growing breccia piles Figure 11. Eastern rim of ‘The Crater’ infi lling the cavities. The chert breccia was later resilicifi ed doline, Ripon Hills (MGA during Cenozoic times. Further weathering during this 260695E 7651365N)

25 Williams Structure of the Fortescue and this situation it would indicate coeval development. The west-northwest–east-southeast Oakover Synclinal axis Hamersley Groups that passes through the northwest corner of the sheet area was previously called the Northwest Oakover Syncline Fortescue and Hamersley Group rocks on YILGALONG lie (Blake, 1993). on the eastern side of the Northeast Pilbara Sub-basin of the Hamersley Basin and along the western edge of The southeast margin of the Meentheena Centrocline the Gregory Range Inlier (Thorne and Trendall, 2001). (Blake, 1993) unconformably abuts the Mount Elsie The current distribution of these rocks in both areas is greenstone belt in the southwest corner of YILGALONG. controlled by the large Oakover Syncline (Hickman, The Miningarra Anticline (Williams and Bagas, in prep.) 1978). Numerous northwest- to north-trending faults that separates the Oakover Syncline from the Meentheena transect YILGALONG, and include normal, steep reverse, and Centrocline is truncated by a north-trending fault (east-side transpressional faults. down), 4 km northwest of Mopoke Well. Small synclines and anticlines in the Mount Roe Basalt and Hardey Formation parallel the Miningarra Anticline in the area D6 deformation (2775−2750 Ma) around the Meentheena copper prospect, 4.5 km west of Mopoke Well. Unlike the Mount Edgar Granitic Complex to the northwest there are no exposed ring faults (Hickman, As recorded elsewhere (Williams and Bagas, in prep.), 1984; Collins 1989; Van Kranendonk et al., 2004a) or the Fortescue and Hamersley succession regionally dips evidence for reactivation of such faults intersecting away from the pre-existing granitic domes. This also Fortescue Group rocks on YILGALONG (cf. Williams applies to the Yilgalong Granitic Complex where the and Bagas, in prep.). However it is evident from the Kylena Formation offlaps the granitic complex with distribution of the Mount Roe Basalt, Hardey Formation, low to moderate dips to the north and east. Gravity and and the overlying Kylena Formation that the Yilgalong TMI data (Blewett et al., 2000; Wellman, 2000) show Granitic Complex was a basement high during their that synclines containing the Fortescue and Hamersley deposition. All Fortescue Group rocks dip away from the Group successions preferentially overlie Paleoarchean to Yilgalong Granitic Complex to the west and north. The Mesoarchean synformal greenstone belts. bedding is generally steeper in the Mount Roe Basalt than in the younger Kylena Formation. This common coincidence of Paleoarchean, Mesoarchean, and Neoarchean to Paleoproterozoic Although there is no direct evidence on YILGALONG for synclines was first pointed out by Kriewaldt (1964), folding and faulting (D6) of the basal Mount Roe Basalt and suggests that D7 folding in the northeast Hamersley prior to the deposition of the Hardey Formation, the high Basin included reactivation of underlying older structures percentage of locally derived basalt clasts in the overlying (Hickman, 1983; Van Kranendonk et al., 2004a). basal Hardey Formation points to uplift and erosion of the Mount Roe Basalt. This activity has been attributed to syndepositional growth faults on MARBLE BAR (Van Unassigned quartz veins (!zq) Kranendonk, 2003) and MOUNT EDGAR (Blake, 1993; Williams and Bagas, in prep.). and dolerite or gabbro dykes (!o) Prominent quartz veins (!zq) are scattered throughout the Yilgalong Granitic Complex, particularly towards the D7 deformation (<2500 Ma, ?Opthalmian sheared western margin. These range from short (<1 km) Orogeny) to long (~8 km) strike ridges up to 20 m high and 50 m wide. Many short veins trend between 290° and 310°, The regional confi guration of the Fortescue and Hamersley whereas larger veins trend between 030° and 350°. Group rocks on YILGALONG is dominated by the large Oakover Syncline, the southeast-plunging axis of which The larger veins link to large faults that cut the extends from MOUNT EDGAR in the northwest corner of Neoarchean Fortescue Group, which may indicate the sheet area east-southeasterly to the Oakover River reactivated basement faulting during the Proterozoic. valley (Fig. 3). This axis is postulated to curve south- Such faults within the Fortescue Group are also marked by southeastwards down the Oakover River valley between the single or en echelon quartz ridges up to 5 km long. Ripon Hills and Gregory Ranges (Gregory Range Inlier) beneath Permian Paterson Formation cover (Hickman, Most quartz veins are massive to faintly banded, 1983). However, it is also possible that the synclinal axis cryptocrystalline white quartz with local brecciation and postulated to occupy the Oakover River valley may instead later siliceous annealing. extend north-northwest onto WARRAWAGINE. If this were the case the north-northwest synclinal axis underlying The Yilgalong Granitic Complex is intruded by a the Oakover River valley (Northern Oakover Syncline, number of fi ne- to coarse-grained, massive, homogeneous Fig. 3) may either truncate the east-southeasterly dolerite and gabbro dykes (!o). Such dykes are short, plunging axis previously mentioned, which would make being less than 3 km long and trend between 040° and the Oakover River valley axis younger or, more likely, 310°, roughly parallel to nearby quartz veins. The dolerite the Oakover River valley axis may bifurcate into a west- and gabbro dykes are generally weathered and outcrops northwesterly and north-northwesterly trending axes. In are low and rubbly.

26 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet Collier Basin The basal units of the sedimentary succession are variable. Successions include interbedded fine- to The Mesoproterozoic Collier Basin (Martin and Thorne, coarse-grained red and brown sandstone, red, brown, and 2001; Martin et al., 2005) is the younger of two basins grey siltstone, and local micaceous siltstone (#MN-ss); replacing the extensive Bangemall Basin (Muhling purple-, red-, grey- to white-weathering shale, including and Brakel, 1985). Small areas of unmetamorphosed ferruginous and manganiferous shale, and local, thinly sedimentary rocks in the Ripon Hills and the Gregory interbedded, brown to grey siltstone and sandstone Range Inlier on YILGALONG are postulated to be possible (#MN-sh); and interbedded poorly sorted, granule correlates of the Manganese Group. and pebble polymictic conglomerate, with coarse- to medium-grained, grey-white to brown lithic and quartz sandstone (#MN-sgp). The last described conglomerate Manganese Group and sandstone succession is the most widespread basal unit. It is found in many of the smaller, more peripheral The Mesoproterozoic Manganese Group occupies a outcrops in the Ripon Hills and in the Gregory Ranges northeasterly trending sub-basin of the older-than-1070 Ma north of Gingarrigan Well. The conglomerates are matrix Collier Basin (Tyler and Hocking, 2002). The Manganese supported and contain poorly sorted, subangular clasts of Group unconformably borders the southeastern part of coloured and banded chert, jasper, and vein quartz. The the Pilbara Craton and the Northeast Pilbara Sub-basin sandstone and conglomerate are locally ferruginous. Cross- of the Hamersley Basin. Units of the Manganese Group bedding and ripple marks are present in some sandstone (Muhling and Brakel, 1985; Williams, 1989) can be traced units. The basal assemblages appear to be fluvial to within 4 km south of the Pearana Rockhole on PEARANA deposits. (Williams and Trendall, 1998b). This siliciclastic and carbonate succession of the Manganese Group, part of the The basal units in the largest exposure, 4 km south- Woblegun Formation (Williams, 1989), lies about 95 km southeast of the Nullagine 1 Trig Point, are overlain and southeast of the Ripon Hills. overlapped in places by green to grey-green mudstone and siltstone, both locally micaceous (#MN-sl). The green mudstone is massive, with a conchoidal fracture. The Unassigned sedimentary rocks rock is largely composed of clay, quartz, minor detrital (#MN-ss, #MN-sh, #MN-sgp, #MN-sl, #MN-st) muscovite, and rare brown and green biotite. Patchy carbonate cement is also present and a single patch of Scattered paleo-interior valleys or poljes in the central barite was observed in thin section (Purvis, 2003a; GSWA parts of the Ripon Hills surrounding the Nullagine 1 169228). Trig Point contain mixed siliciclastic sedimentary successions very similar to those described from the In the same area the green mudstone and siltstone unit ( MN-sl) is overlain by fi ne- to coarse-grained, red- Mesoproterozoic Manganese Group on PEARANA to the # southeast (Williams and Trendall, 1998b). Similar small brown-weathering, blue-grey lithic and quartz sandstone outcrops of mixed siliciclastic sedimentary material are (#MN-st). The mixed sandstones form low rubbly cliffs. also found between 4 and 6 km north of Gingarrigan Well Medium- to coarse-grained sandstones locally carry in the Gregory Ranges east of the Oakover River. The base abundant greenish clay pellets, probably smectite, that of the interior valleys in the Ripon Hills can be more than are similar to glauconite pellets found in greensands. It is 140 m below the surrounding hilltops of Pinjian Chert postulated that the pellets are possibly derived from the Breccia. alteration of glauconite. Shale intraclasts are also common within the sandstone succession. The sedimentary successions all dip moderately off Glauconite is recorded from a number of localities the Pinjian Chert Breccia and towards the centre of the on BALFOUR DOWNS (Williams, 1989) to the south. Both depositional basins, that is, the interior valleys. Modern- the basal Coondoon and Woblegun Formations of the day drainage has subsequently broached the interior Manganese Group that onlaps the Pinjian Chert Breccia valleys. Intact remnants of the sedimentary succession in this area contain glauconitic sandstone. In both cases suggest that it was more than 200 m thick. In all areas the the glauconitic sandstone lies towards the top of the sedimentary succession unconformably overlies eroded exposed succession. The glauconitic sandstone and and previously weathered Paleoproterozoic Pinjian Chert associated siltstone and shale were interpreted to Breccia. indicate shallow-marine conditions (Williams, 1989). The glauconite-bearing succession in the Ripon Hills is Previous work assigned these sedimentary rocks to down-faulted on the eastern side against the Pinjian Chert the Waltha Woora Formation, which was at that time part Breccia, which may help to explain its preservation in this of the Bangemall Group (Hickman, 1978). Subsequent area. remapping of PEARANA and BRAESIDE showed that the Waltha Woora Formation was a westward extension of These observations indicate that the Mesoproterozoic the younger Tarcunyah Group (Williams and Trendall, Collier Basin was much more extensive than previously 1998a). Nevertheless, the current study tentatively supports interpreted. The disappearance of the thick succession correlation of the sedimentary succession in the Ripon that appears to have blanketed the eastern Pilbara may Hills with the Woblegun Formation (Williams, 1989), be due to later Permian glaciation, evidence for which which was originally part of the superseded Bangemall is still preserved on the surface of the Pinjian Chert Group and now part of the Collier Group. Breccia.

27 Williams Unassigned Proterozoic dolerite Because of mutual interference, Hickman (1983) proposed that the Round Hummock Dolerite Suite might intrusions be a conjugate set with the north-northeasterly trending The contact between the Jeerinah Formation and the 755 ± 3 Ma Mundine Well Dolerite Suite (Wingate and Carawine Dolomite is intruded by a fresh, fi ne-grained Giddings, 2000). dolerite (#od) along the eastern side of Coonanbunna Creek and west of Ripon Hills. The mineralogy consists of plagioclase, clinopyroxene, altered olivine, and Paleoproterozoic to orthopyroxene with very minor quartz and carbonate. Neoproterozoic deformation Skeletal opaque minerals are accessory. The olive phenocrysts are altered to carbonate and a pale-green D deformation (<1830 Ma) phyllosilicate, possibly phlogopite. The orthopyroxene is 8 fresh (Purvis, 2003a; GSWA 169216). This sill is displaced The large D7 folds in the Fortescue and Hamersley Groups by later faulting. are intersected by numerous west-northwesterly to north- northeasterly trending faults. The oldest are north-trending, A number of fresh to very weakly altered dolerite vertical-dipping, brittle normal faults with downthrow to dykes (#od) up to 30 km long intersect the Yilgalong the east or west. Such faults correspond in places to large Granitic Complex, Fortescue Group, Carawine Dolomite, recrystallized quartz ridges in the Yilgalong Granitic and Pinjian Chert Breccia. The dykes trend roughly north, Complex, suggesting that they may, in some cases, be west, and northwest and exhibit strong negative magnetic reactivated basement faults. They appear to be related anomalies. The surface expression ranges from fresh to west-northwest trending faults that displace them or bouldery outcrops in the Yilgalong Granitic Complex to are displaced by them. All of these faults intersect the weathered dolerite occupying joints, fractures, and valley Fortescue and Hamersley Group successions as well as the fl oors in the Fortescue Group, Carawine Dolomite, and Oakover Synclinal axis. Such faults are easily recognized Pinjian Chert Breccia. The dykes post-date most fault lines where they displace the Tumbiana Formation. They are on YILGALONG. also present, but less obvious in the overlying Carawine The fresh dolerite is massive and dark grey with ophitic Dolomite and Pinjian Chert Breccia. and subophitic textures. Fresh or partly sericitized zoned A second series of faults are arcuate transpressional plagioclase (labradorite to andesine) and clinopyroxene with both dextral and sinistral strike-slip movements. (both augite and pigeonite) are the primary minerals. Rare These faults trend from west-northwest around to north brown hornblende and biotite partly rim the pyroxenes. and are concentrated along the southwestern and western Small and scattered interstitial patches of clay, including margins of the Ripon Hills. On a regional setting these chlorite–smectite and ferrostilpnomelane are present. transpressional fault extend southeastwards across EASTERN Needles of apatite and opaque minerals are accessory. CREEK to link up with a major sinistral transpressional fault Some dykes carry interstitial granophyre. that diagonally transects PEARANA, where it also displaces Hamersley and Fortescue Group rocks (Williams and Trendall, 1998b, Williams, in prep.). Proterozoic Round Hummock RH RH The arcuate fault on southwestern margins of the Dolerite Suite (# -od, # -og) Ripon Hills has juxtaposed the Carawine Dolomite against Several medium- to coarse-grained unmetamorphosed the Kuruna Member of the Maddina Formation 6 km east dolerite dykes (#RH-od) and an unusual totally altered of Mount Ian Well. Although initially this juxtaposition gabbro dyke (#RH-og) belonging to the Round Hummock appears to be a normal fault with a northeast-block-down Dolerite Suite (Hickman, 1983) intrude the Fortescue movement, the presence of numerous small folds axes, up Group and Yilgalong Granitic Complex in the southwest to 5 km long, parallel or slightly oblique to these faults corner of YILGALONG. The linear dykes are up to 15 m on the northeast and east side of the faults lines and their wide, trend northwest to west-northwest, and extend absence from the southwest side points to southwesterly onto adjacent MOUNT EDGAR (Williams and Bagas, in directed compression. This in turn suggests that faults have prep.). They post-date the folding and most faulting in the a thrust movement to the southwest. This is further borne Fortescue Group. out by small strike-slip displacements along the faults, which tend to be sinistral in the southeast and dextral on The gabbro dyke is a coarse-grained, pale-grey the northern extensions of the faults. Many of the older granular rock with an altered assemblage, but with good north-trending faults in this region terminate against the textural preservation. The plagioclase, up to 2 mm in grain transpressional faults, although some also displace them, size, is mostly replaced by carbonate. Very coarse grained, suggesting later reactivation. large prismatic and ophitic pyroxene grains are largely altered and replaced by irregular aggregates of highly Faults truncating the Jeerinah Formation, Carawine clouded, orange-brown quartz. Interstitial areas are fi lled Dolomite, and Pinjian Chert Breccia in the Gregory with chlorite and rare carbonate. Euhedral titanomagnetite Range Inlier are transpressional, steep reverse faults is leucoxenized (Purvis, 2003a; GSWA 169243). Copper with movements similar to those described from the mineralization in the Meentheena copper prospect is in southwestern and western sides of the Ripon Hills. These quartz veins within the sheared margins of this gabbro have been described in detail by Trendall (1991) and dyke (Purvis, 2003a; GSWA 169243). Williams and Trendall (1998a–c).

28 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

All the faults described above are Proterozoic. The Paterson Formation (CPpa-sgpg) allocation of these faults to specifi c events related either to Scattered exposures of the Carboniferous–Permian the initial 1830–1765 Ma Paleoproterozoic collision of the Paterson Formation (CPpa-sgpg; Traves et al., 1956; West Australian Craton with the North Australian Craton Hickman, 1983; Stevens and Apak, 1999; Haines et al., (the Yapungku Orogeny; Myers et al., 1996; Bagas, 2004), 2004) in the Oakover River valley are limited to low or to the later older-than-678 Ma Neoproterozoic Miles mesas and breakaways, rubble-covered low hills, and Orogeny (Bagas, 2004) and c. 550 Ma Paterson Orogeny locally eroded stream banks along the Oakover River, (Bagas, 2004) — events in the adjacent Paterson Orogen and Gingarrigan and Murramuralba creeks. Locally, — remains a matter of conjecture. the Paterson Formation is disconformably overlain by mesas of the Neogene Oakover Formation. Most of these exposures lie in the southeast quarter of YILGALONG. Phanerozoic rocks Noldart and Wyatt (1962) had divided the Permian succession in the Oakover River valley into a basal Unassigned dolerite intrusions tillite, called the ‘Braeside Tillite’ (Clapp, 1925), and the (_od) overlying fl uvioglacial sandstone, grit, conglomerate, and shale, called the ‘Bunmardie Beds’. The type area for the A cluster of fi ne- to medium-grained dolerite sills and ‘Braeside Tillite’ (the diamictite component of the Paterson dykes (_od) intrude the Pinjian Chert Breccia and Formation) was about 7.5 km south of Gingarrigan Well sedimentary rocks correlated with the Manganese Group. on the west side of the Oakover River. The ‘Bunmardie They occupy an area of about 15 km2 in the central parts Beds’ were named after good exposures along Bunmardie of the Ripon Hills centred 3.5 km southeast of Nullagine 1 Creek. Both of these terms are no longer in use (Hickman, Trig Point. 1983).

The primary minerals in the dolerite consist of Remnants of the fluvioglacial Paterson Formation plagioclase and partly ophitic augite and pigeonite. are also preserved in ice-scoured basins, channels, and Disseminated K-feldspar was identifi ed in the fi ne-grained U-shaped valleys in the central and eastern parts of the groundmass together with patchy, but locally common, Ripon Hills where the formation unconformably overlies granophyre. There is minor magmatic quartz, minor to the Carawine Dolomite and Pinjian Chert Breccia. An rare green and brown hornblende and biotite, and rare ice-scoured valley in Pinjian Chert Breccia containing olivine. Opaque minerals and apatite are accessory and Paterson Formation is also 16 km south-southwest of zircon, zirconolite, and baddeleyite have been recorded Pulgorah Cone, south of Midgengadge Creek. At this (Purvis, 2003a; GSWA 169230 and 169231; Rasmussen locality the Pinjian Chert Breccia is faulted against the and Fletcher, 2004). Contact metamorphic hornfels have Maddina Formation. In general, the ice-scoured basins been formed in green-grey mudstones intruded by a thin and valleys, containing Paterson Formation or the residual dolerite sill 4 km south of the Nullagine 1 Trig Point. ‘boulder beds’ (R1tpa) derived from weathered Paterson Formation, are elongated in a north-northwest direction. A Rasmussen and Fletcher (2004) reported mean zircon, particularly good example of this style of linear valley lies zirconolite, and baddeleyite 207Pb/206Pb and 238U/206Pb ages 6.5 km southwest of Bunmardie Well. of about 524 and 510 Ma respectively for the large dolerite sill intruded into Manganese Group sedimentary rocks, Polished striated pavements have been recorded from 2.9 km southeast of Nullagine 1 Trig Point (T. S. Blake several localities on YILGALONG. All indicate a north- in conjunction with Consolidated Minerals Ltd, 2004, northwesterly to north-northeasterly directed movement of written comm.). the overlying ice cover. Striated pavements on YILGALONG were fi rst recorded by Forman (1960) in the Ripon Hills, These results are consistent with the sills belonging to 2.5 km east-southeast of Nullagine 1 Trig Point. During the Kalkarindji large igneous province (Glass, 2002; Glass the present survey striated pavements were recorded on and Phillips, 2006). These are the fi rst recorded Cambrian unassigned Proterozoic sandstone overlying Pinjian Chert ages from the Pilbara Craton. Breccia 5 km north of Gingarrigan Well and on Pinjian Chert Breccia in the fl oor of a north-northeasterly trending valley 16.2 km south-southwest of Pulgorah Cone in the Canning Basin Midgengadge Creek area (Figs 12 and 13). The pavements are highly polished and exhibit ice striae, grooves, pitting, The eastern half of YILGALONG is crossed by the southern and chatter marks. The Pulgorah Cone and Ripon Hills extension of the Wallal Embayment of the Canning localities contain rock drumlins. Basin (Hocking et al., 1994). The embayment, covering about 30% of the sheet area, contains fluvioglacial The total thickness of the Paterson Formation on Carboniferous–Permian rocks of the Paterson Formation, YILGALONG is unknown. An exploratory drillhole, mesoform remnants of the overlying lacustrine Neogene RHDH1, just east of the Ripon Hills, intersected 158 m Oakover Formation, and superfi cial Cenozoic deposits. of interbedded clayey shale, siltstone, poorly sorted dirty The embayment on YILGALONG is fl oored by Fortescue and sandstone, and local pebble beds. This succession was Hamersley Group rocks of the Northeast Pilbara Sub-basin assigned to the Paterson Formation (Richards, 1985). A of the Hamersley Basin, which, in turn, overlies the eastern shallow rotary chip and corehole intersected 91.4 m of margin of the Pilbara Craton. claystone and mudstone interpreted to be ‘Braeside Tillite’

29 Williams

IRW206 06.06.07 IRW207 06.06.07

Figure 12. Ice-polished south-facing ramp on western margin Figure 13. Ice-polished pavements on a ‘roche moutonnée’. of ice-scoured valley. Residual boulders weathered Ice movement was to the north away from the from diamictites of the Carboniferous–Permian viewer; Midgengadge Creek area (MGA 284448E Paterson Formation in foreground, Midgengadge 7629206N) Creek area (MGA 283813E 7628878N)

(diamictite) 4.5 km east of Outcamp Bore (Kempton, 1976). the Neogene Oakover Formation. Exposures of the basal On WARRAWAGINE to the north exploratory stratigraphic diamictite, locally weathered to boulders, cobbles, and holes intersected up to 259 m of Paterson Formation. pebbles in clay, silt, and sand (R1tpa), are found 13 km west-southwest of Pulgorah Cone and 6 km south- Associated seismic refraction lines suggest depth to southwest of 20 Mile Well along the eastern margin of the Archean basement to be around 661 m in the centre of the Ripon Hills, and on the western bank of the Oakover River, Oakover River valley west of Chukuwalyee Well (MGA 7 km south of Gingarrigan Well. The basal diamictite 277136E 7693462N; Sentinel Mining Company, 1967; is overlain by interbedded matrix-supported pebble and Williams, 2001). cobble conglomerate, pebbly sandstone, grey to brown coarse- to fi ne-grained sandstone, siltstone, shale, and The Paterson Formation consists of diamictite, claystone. The fi ner grained units carry the occasional mudstone, siltstone, sandstone, and conglomerate (CPpa- cobble and small boulder dropstones. Sandstones sgpg). Exposures within the Ripon Hills are confi ned are commonly planar and trough cross-bedded. Such to small elongate depressions or linear valleys mainly successions are probable fl uvioglacial deposits. surrounded by Pinjian Chert Breccia and locally by Carawine Dolomite. The configuration of the clastic The Paterson Formation has been assigned to material, which includes moderate dips away from the depositional Sequence Pz5 (Middleton, 1990) covering valley sides and towards the depression or valley centre, the Early Permian (Sakmarian–Asselian age) and Late shows that the preserved successions are not always Carboniferous period (Mory and Backhouse, 1997; continuous between outcrops in adjoining valleys. Stevens and Apak, 1999; Haines et al., 2004). Palynology studies of material obtained from shallow drillholes The succession in the Ripon Hills is commonly coarser (Kempton, 1976) between Warrawagine Homestead grained towards the base with polymictic conglomerate and Mount Sydney Creek (on BRAESIDE) along the and pebbly sandstone passing up to interbedded sandstone, Oakover River valley suggested a Late Sakmarian age siltstone, and white claystone. Cross-bedding is common for the Paterson Formation on YILGALONG (Backhouse, in the sandstones. The clasts in the conglomerate are 1976). commonly allochthonous quartzite, sandstone, and chert, but with little local input from the surrounding Pinjian Recent reviews of the Permo-Carboniferous glaciation Chert Breccia. The latter, after erosion, was probably in Western Australia (Playford, 2001, 2002) have transported northward by the ice movement. Diamictites concluded that new evidence from the preserved glacial are found in some of the more extensive outcrops such landforms, particularly those from the Oakover River as those along the track to the abandoned Ripon Hills valley region, indicate major wet-based ice sheets, several manganese mines 4 km northeast of the Nullagine 1 Trig kilometres thick. These probably extended across all or Point. Here, the diamictite contains polished and faceted most of Australia. The ice cap, moving away from the boulders of assorted granitic rocks, basalt, quartzite, polar regions, moved north-northwest across Western sandstone, and chert. Australia. This differs from earlier suggestions and interpretations of the more restricted glaciated valley The Paterson Formation in the Oakover River valley environments (Traves et al., 1956; Noldart and Wyatt, is more weathered, locally lateritized, and overlain by 1962).

30 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet Regolith land surface that can be seen to pre-date the lacustrine Oakover Formation. The fl at-lying, residual clay and silt

unit with gilgai surface (R3cbvb) is contained within or Cenozoic deposits overlies the colluvial unit (C3). Cenozoic deposits cover around 40% of YILGALONG and of these deposits more than 90% are in the Oakover River valley. The remaining Cenozoic deposits in the Ripon Hills Oakover Formation (NOA-ktzl, NOA-ktpl) and adjacent areas to the southwest, and in the Gregory The Oakover Formation (Noldart and Wyatt, 1962) is Range Inlier, are mostly Quaternary or older alluvium and scattered throughout the Oakover River valley and in colluvium associated with drainage systems. widely spaced outliers in the Nullagine River valley north The Cenozoic deposits can be allocated to five and northeast of Rocky Pool. The widespread distribution main categories on YILGALONG: eroded residual deposits of the remnant outcrops shows that at one time it covered including laterite that pre-date the Oakover Formation; the entire Oakover River valley between the Ripon Hills the lacustrine Oakover Formation and associated and Gregory Ranges. The formation is now preserved in colluvium; pre-Quarternary consolidated and eroded a series of distinctive cliffed tablelands, mesas, buttes, colluvial, alluvial, and residual deposits; Quaternary and scarps roughly parallel to, and mostly on the western semiconsolidated and unconsolidated, recent or currently side of, the present-day Oakover River. These landforms active colluvial, low-slope, alluvial, and residual deposits; rise to 70 m above the present-day Oakover River bed. and recent lacustrine and eolian deposits. Similar, but less dramatic, exposures line the eastern side of Yilgalong Creek northeast of the Ripon Hills and the upper reaches of the Tanguin Creek (Williams, 2001) Residual or relict units (R3cbvb, R3rf ) between Outcamp Bore and 20 Mile Well. The Tanguin Creek drainage lies between the Nullagine River and Residual and sheetwash clay and silt with a gilgai Yilgalong Creek. (expansive clay) surface (R3cbvb) is exposed along elevated divides between north-fl owing streams southeast of Rocky Regional mapping in the early 1990s distinguished Pool in the Nullagine River valley. This unit overlies an upper unit of vuggy, white to grey opaline silica, dolerite (AFO-od), fragments of which are mixed with the silicifi ed carbonate rock, and minor calcareous sandstone clay and silt. A similar elevated area of gilgai-surfaced (NOA-ktzl). This distinctive siliceous unit overlies a more- clay and silt deposit surrounds Cave Bore on the northeast widespread lower unit of blue, grey, and fawn limestone, side of the Ripon Hills. In this area the unit is adjacent to calcareous sandstone, and packstone (NOA-ktpl; Williams exposed Carawine Dolomite and underlies the Oakover and Trendall, 1998a,b). Although some silica replacement Formation. Dolerite fragments were not found in this of pre-existing carbonate is evident in the upper unit, much locality. of the silica (opaline) appears to be directly precipitated from solution. Small patches of massive, pisolitic, and nodular ferricrete or laterite (R3r f ) overlie remnants of the The lower unit intertongues with colluvium (C2) Paterson Formation in the Ripon Hills area. These are eroded from the adjacent bedrock on the valley margins. remnants of a previously extensive, but now dissected, The unit also overlies lateritized Paterson Formation and laterite that overlies a pallid weathered horizon mainly abuts or overlies the Pinjian Chert Breccia, Carawine developed on the underlying Paterson Formation. This Dolomite, and Jeerinah Formation. The upper siliceous ferruginous duricrusted surface is more widespread in the unit is only ever observed overlying the lower carbonate Oakover River valley, particularly along the high ground unit. The upper siliceous cliff-forming unit (NOA-ktzl) marking the drainage divide between Yilgalong and varies from 3 to 10 m thick, whereas the lower carbonate Murramuralba creeks. Similar deposits lie in the upper unit (NOA-ktpl) is up to 45 m thick on YILGALONG. reaches of the Gingarrigan Creek, and around Pulgorah Cone. Laterite remnants in the form of low breakaways Although the Oakover Formation is mentioned in also overlie the Paterson Formation. The ferruginized many earlier publications (see table 3 in Williams and duricrusted surface pre-dates the Oakover Formation. Trendall, 1998a) its genesis remains unclear. The general consensus supports a lacustrine environment (Towner and Gibson, 1983; Middleton, 1990; Williams and Trendall, Colluvial unit (C3) 1998a,b) developed during a stillstand event that included stagnant drainage with little or no detrital input into the Widespread aprons of consolidated colluvial sands, silt, valley. The Oakover Formation has much in common and gravel (C3) rim major bedrock exposures along the with the carbonates of the Lawford Formation (Kimberly margins of the Oakover River valley and, to a lesser extent, area) and Nadarra Formation (Carnarvon Basin; Hocking the Nullagine River valley and larger subsequent streams et al., 2005). such as Coonanbunna Creek. The colluvium slopes gently upward to bedrock where there is an abrupt change of Undiagnostic ostracods have been recorded from the slope. These colluvial pediments are well developed along Oakover Formation (Veevers and Wells, 1961, p. 197) and the northeast margin of the Ripon Hills. They are dissected fossiliferous oolitic limestone has been described from by numerous shallow streams and are commonly covered the base of the Oakover Formation near the abandoned with a scattered veneer of small pebbles. The uniform and Braeside Homestead on the western margin of BRAESIDE. widespread dissection of this surface indicates an older The latter gave a Miocene–Holocene age range (Cockbain,

31 Williams

1978). A precise age of deposition for the formation is pisolites, laterite and ferruginous duricrust, is confi ned still under review due to paucity of diagnostic palynology to the Oakover River valley. In most areas the unit and paleontology. However, more recently, a growing lies adjacent to or is near ferruginous duricrust (R3r f ) understanding of regolith stratigraphy and climatic outcrops. The ferruginous colluvium is well exposed along changes from the Mesozoic to the present-day period Gingarrigan Creek 2 km west of Barbilgunyah Hill. places the Oakover Formation in the Pliocene (Hocking et al., 2005). Residual or relict units (R1gpg, R1tpa) Residual or relict unit (R2k) A small area of residual quartzofeldspathic sand, with a thin veneer of quartz and granitic rock fragments (R1gpg), Partly silicifi ed sheets of dissected, secondary carbonate overlies the contact between the Elsie Creek Tonalite and or residual calcrete, comprising massive, nodular, and Midgengadgi Monzogranite 16 km southeast of Dingo cavernous, white to grey limestone (R2k), is locally Well. exposed along Coonanbunna Creek adjacent to or overlying the Carawine Dolomite and Jeerinah Formation. Residual boulders, cobbles, and pebbles in clay, Similar dissected calcrete overlies weathered komatiitic silt, and sand, including locally transported material and carbonate-rich basalts of the Euro Basalt 5 km south (R1tpa) form a distinctive eluvial deposit that invariably of Mopoke Well. In both areas adjacent or underlying overlies weathered Permian fluvioglacial Paterson carbonate-rich rocks are the source of the calcrete Formation. The unit includes allochthonous, sometimes deposits. The development of pedogenic calcretes appears faceted and striated, boulders and cobbles of mixed to be related to increasing desiccation during a prevailing granitic rocks, basalt, quartzite, and chert enclosed in continental climate in Pliocene times and is possibly unconsolidated clay, silt, and sand. Jumbled, disoriented, coeval with the lacustrine Oakover Formation (Hocking and very large broken boulders of the chaotic spherule- et al., 2005). bearing megabreccia (AHAc-kdx), covering an area of about 10 m2, overlie north-dipping Jeerinah Formation rocks, 13.6 km west-southwest of Pulgorah Cone on the Alluvial units (A2t, A2k) southern side of the Ripon Hills road. The megabreccia is postulated to be a glacial erratic. The boulders lie at the Dissected consolidated alluvial gravel, sand, and silt, western edge of the residual ‘boulder bed’ unit (R1tpa) locally with carbonate cement (A2t) is widespread and are more than 500 m south of the nearest in situ along the margin of the Oakover and Nullagine rivers occurrence of the megabreccia. This position, south of and Yilgalong Creek. The cemented alluvium is locally known outcrops, and the orientation of the boulders in cliff forming where undergoing current erosion. The relation to the underlying Jeerinah Formation suggest local unit is crudely bedded and gravel beds exhibit current ice-transport. imbrication, supporting an alluvial genesis.

Several low calcrete mesas, consisting of silicifi ed Alluvial units (A1c, A1b, A1f, A1fcb, A1i, massive, nodular, and cavernous limestone (A2k) trace A1 ) out a probable earlier course of Midgengadge Creek v 14 km southwest of Pulgorah Cone. The calcrete overlies YILGALONG has a well-developed drainage system (Fig. 2). the Maddina Formation and is up to 15 m above the bed Sand, silt, and gravel in active drainage channels within of the present-day Midgengadge Creek with which it bedrock areas and clay, silt, and sand in poorly defi ned intertwines. drainage courses on fl oodplains (A1c) are widespread. Such units tend to be narrow and linear in the bedrock Low dissected mesas of alluvial calcrete also lie areas of the hilly southwest portion and broader and parallel to and west of the Nullagine River 6.5 km south- more meandering in the fl atter areas of the Oakover River southwest of Rocky Pool. This calcrete has a white valley. The large Oakover, Nullagine, and Little rivers, crumbly upper surface. However, it is possible that these Yilgalong Creek, and the lower reaches of Boondalyerri, exposures are outliers of the Oakover Formation, which Walgunya, and Coonanbunna creeks are occupied lies 10.5 km to the north. with broad, active, anastomosing channels fi lled with

unconsolidated sand, silt, and gravel (A1b). Such channels can carry point bars up to 2 m high. The unconsolidated Colluvial units (C2, C2f ) material is confi ned within well-defi ned channels with banks incised into fi ner grained overbank and fl oodplain Remnants of partly consolidated colluvial sand, silt, deposits of silt, sand, and gravel (A1f ) or older alluvium and gravel (C2) are dissected older proximal outwash (A2t). fans, scree, and talus. The unit is mostly confi ned to the Oakover River valley where it overlies or is eroded from Some parts of the Oakover River valley fl oodplain, the Oakover Formation. It is common along Gingarrigan including broad valleys between outcrops of the Oakover Creek, but most exposures are limited in area by overlying Formation, carry a distinctive unit of sand, silt, and clay recent colluvial deposits. with gilgai (crabhole) surface in areas of expansive clay (A1f cb). This unit is well developed 4 km east of Outcamp Dissected consolidated ferruginous colluvium of sand, Bore, 3 km east of Cave Bore, 2 km south and west of silt, clay, and rock fragments (C2f ), mostly reworked New 20 Mile Well, north and south of Gap Well, and 8 km

32 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet west-southwest of Barbilgunyah Hill. A second distinctive eolian sand along the edge of the Ripon Hills is derived floodplain unit is characterized by numerous small from Yilgalong Creek and adjacent fl oodplains and is claypans. This is a mixed fl oodplain deposit of sand, silt, indicative of the prevailing easterly winds. The sand in the and clay (A1i). It is generally close to major drainage lines southeast corner is derived from the Oakover River that and locally fringes or is close to the gilgai unit (A1f cb). An lies 2.5 km to the east on BRAESIDE. example of the latter lies 4.7 km east of Outcamp Bore. Other exposures are scattered along the lower reaches of Yilgalong Creek, and 1.5 km west of Yilgalong Pool, Lacustrine unit (Lpcb) 2 km south of Little River Well, and 6.7 km southwest of Barbilgunyah Hill. A small claypan of lacustrine clay and silt with gilgai surface and sparse samphire vegetation (Lpcb) lies 6.6 km Recent well-developed alluvial fans consisting of west-northwest of the New 20 Mile Well. Unlike the pebbly silt and sand (A1v) lie along the base of the west- numerous claypans that occupy fl oodplains adjacent to facing scarp of an eroded low (20 m) tableland of Oakover the major drainages (A1i), this discrete claypan occupies a Formation, 5.5 km east of Outcamp Bore. The pebbly slight depression in a plateau of Oakover Formation that material is mostly opaline silica from the upper siliceous forms the major divide between the Nullagine and Oakover unit of the Oakover Formation. River drainage basins (Fig. 2).

Low-gradient slope units (W1, W1f ) Probable impact site A few widely scattered areas of silt, sand, and pebbles on An investigation of a probable meteorite impact crater was distal sheetwash fans (W1) are found in the Oakover River carried out during fi eldwork in July 2003. The crater was valley and on the margins of the Nullagine River valley initially recognized during preliminary aerial photograph 4.5 km north and 3 km northeast of Rocky Pool. Larger interpretation carried out prior to fi eldwork. areas lie 3 km west of Outcamp Bore on the northern boundary of the sheet area, and 7 km south-southwest The impact crater is on the northeast-facing slope of of Pulgorah Cone where the unit is surrounded by low an east-draining tributary of the Oakover River (MGA cliffs of the Oakover Formation. The sheetwash has a 281672E 7623041N; Figs 14 and 15). The site is 23 km distinctive striping of alternating bare and vegetation-rich south-southwest of Pulgorah Cone in fresh amygdaloidal (generally Acacia sp.) bands. The banding, called ‘tiger and vesicular medium-grained basalt of the Maddina bush’ (Wakelin-King, 1999), is developed at right angles to Formation. Large amygdales are filled with quartz, the general sheetwash fl ow. The bare silty and sandy areas chalcedonic quartz (agate), smectite, prehnite, chlorite, and have a thin veneer of opaline silica and quartz pebbles. traces of copper mineralization (malachite). In general, the basalt resembles the fl owtop component of a basalt fl ow. Ferruginous sheetwash deposits of silt, sand, and No impact structures such as shatter cones were identifi ed ferruginous nodules (pisolites) in distal outwash fans on the exposed host rock. The rim is rubbly and broken on (W1f ) are marginal to ferruginous duricrust and low the surface, but appears to be intact beneath this surface. laterite ridges in the Murramuralba Creek area southwest The actual crater is fi lled with sand and rock rubble, of Gap Well. The unit is similar to the previously some of which appears to have fallen in from the sides. described sheetwash unit except that the thin veneer is A shallow pit (~0.5 m) dug in the lowest part of the crater almost exclusively of pisolitic nodules with minor quartz met with compacted, but broken or shattered, basalt. pebbles.

Colluvial units (C1, C1q) Small areas of unconsolidated colluvial sand, silt, and gravel (C1) in scree and talus in proximal mass-wasting deposits are scattered throughout the southwestern half of YILGALONG and in the Gregory Range. More extensive scree areas and outwash fans surround and abut many of the Oakover Formation mesas and tablelands in the Oakover River valley. A colluvial apron of quartz debris in sand, silt, and clay (C1q) surrounds a large quartz ridge occupying a major fault line 13 km south of Walgunya Well on the southeastern side of the Nullagine River.

Eolian unit (E) IRW208 06.06.07 Several small areas of light to dark-red eolian sand (E) lie Figure 14. Probable meteorite impact crater on YILGALONG, close to the northeast margin of the Ripon Hills. Similar viewed from 800 m to the north. Low hills in the eolian sand is found in the southeast corner where it is background are Maddina Formation (MGA 281672E banked up against scarps of the Oakover Formation. The 7623041N)

33 Williams

1938; Williams and Trendall, 1998a). However, it was not until the 1950s, during the so-called ‘manganese rush’ triggered by a sudden increase in price for manganese on the U.S. markets, that serious exploration was undertaken in the region. The fi rst recorded mineralization on YILGALONG — the Ripon Hills manganese deposits — was discovered in 1957 (O’Driscoll, 1958). Over the next 50 years there was ongoing, but mostly low key, mineral exploration and prospecting by large international companies, mining syndicates, and individual prospectors with little positive results. This work has been directed towards manganese, iron, base metals, nickel, gold, diamond, and coal exploration.

An overview of the economic mineral potential, IRW209 200 m 06.06.07 production, and mineral occurrences for the east Pilbara, which covers YILGALONG, is presented in Ferguson Figure 15. Aerial photograph view of probable meteorite impact and Ruddock (2001). Additional information covering crater on YILGALONG (MGA 281672E 7623041N) company exploration data for YILGALONG is available from the Western Australian mineral exploration (WAMEX) open-file system held in the Department of Industry and Resources’ (DoIR) library (Appendix 3). Current The crater is slightly elliptical in shape with outer information for all mines, deposits, and process plants, north–south dimensions totalling 27 m and east–west with the exception of petroleum and gas, for Western dimensions of 36.3 m. The internal crater-fl oor dimensions Australia is recorded in the Western Australian mines and are 18.2 m north–south and 17.5 m east–west. A crater rim mineral deposition information (MINEDEX) database, higher than the crater fl oor is developed on the northern, available on CD (Cooper et al., 2002). western, and southern sides, but is absent from the eastern side. Here, because of the primary northeast hill slope the The description of mineral deposits and occurrences rim spills down the slope. The western rim is the highest in these notes follows the format outlined in Ferguson and widest, rising 1.75 m above the crater floor and and Ruddock (2001) and is adopted on the accompanying extending 12.1 m in width. The general orientation of the YILGALONG map sheet (Williams, 2005). Western Australian crater suggests a steep descent from the northeast for the mineral occurrence (WAMIN) database reference impact body. numbers* (Ferguson and Ruddock, 2001) are shown in brackets next to the deposit or prospect. The dimensions of the Yilgalong crater, apart from the shallow depth, are similar to those of the well-known Dalgaranga crater (25 m) in the Murchison region of Western Australia (Bevan and McNamara, 1993). Vein and hydrothermal A thorough search of the crater and surrounding mineralization areas did not reveal any recognizable meteoritic material or metal artefacts suggestive of a bomb crater, which is Precious metal — gold another possible explanation for the crater. The exposed The Euro Basalt in the Elsie Creek greenstone belt, in Neoarchean Maddina Formation basalt at the impact site the southwest corner of YILGALONG, has been explored is weathered to the same extent as all the surrounding for gold. During the current survey several old shallow basalts in the area, suggesting that it pre-dates the current shafts sunk on quartz-reef-bearing shear zones and weathering cycle. The possible age of the impact is associated alluvial patches were located north and south unknown. Kanji (Acacia inaequilatera) growing on the of Elsie Creek between 3.3 and 7.7 km south-southwest of crater rim is up to 4 m high. Salvation Well. Old alluvial workings surround a shallow shaft at Elsie Creek 3 (17671). Recent bulldozing at the Elsie Creek diggings (17673) and Elsie Creek 2 (17672) Economic geology indicate ongoing metal-detecting activity of alluvial ground alongside drainage lines on what appears to be Mineral exploration and prospecting on YILGALONG has, older workings. up to the present time, only yielded minor manganese-ore production, mainly for metallurgical and benefi ciation A deep shaft, located during recent exploratory work testing, from the Ripon Hills area and scattered alluvial and pinpointed on airphotos in the current survey, is gold workings with unrecorded production from the presumed to be following up gold indicators. This shaft is Elsie Creek area in the southwest corner. The previously 6.4 km south-southwest of Mopoke Well in sheared Euro unrecorded Meentheena copper prospect is reputed to Basalt (Yilgalong IRW 6; 17676) have been found in the early part of last century and the YILGALONG area in general would have been explored for base metals around the same time because of its proximity * Operating status of sites are denoted as follows: 5224 = mineral to the Braeside lead fi eld in the Gregory Ranges (Finucane, deposit; 5224 = mineral occurrence or prospect.

34 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

Five bulldozed costeans spread over a strike distance Steel industry metal — manganese of 675 m (Salvation Well NW, 17674) intersect the interbedded quartz-pebble conglomerate, sandstone, The geological aspects and metallurgical properties wacke, and grey-blue to purple siltstone unit (AFOhb-frp) of manganese mineralization, centred in the Ripon of the Hardey Formation 1.5 km northwest of Salvation Hills on YILGALONG, have been previously documented Well. The costeans lie towards the base of this unit where (O’Driscoll, 1958; Muskett, 1960; de la Hunty, 1960, it unconformably overlies the Bamboo Creek Member. 1963, 1965; Noldart and Wyatt, 1962; Longreach Metals Some thin quartz veinlets were noted in the costeans, but NL, 1974; Denholm, 1977; Hickman, 1983; Ferguson there was no obvious gossanous material. and Ruddock, 2001). The main mineralized area in the Ripon Hills is about 14 km2, lying between 2 km east A sixth large costean cuts the basal polymictic, matrix- and 4 km northeast of Nullagine 1 Trig Point. This area supported cobble to boulder conglomerate, sandstone, encompasses 10 manganese prospects designated A to siltstone, and local shale (AFOh-scp) unit of the Hardey J (Denholm, 1977), which are given WAMIN database Formation 4.7 km north-northeast of Salvation Well. The numbers of 5219, 5220, 5221, 5222, 5223, 5224, 5225, lithology exposed in this costean is mostly thin-bedded, 3503, 5226, 5227 respectively (Williams, 2005). A further grey micaceous siltstone. Local, thin crosscutting veins fi ve prospects are scattered throughout the remaining parts of a sky-blue mineral were identifi ed as turquoise with of the Ripon Hills: prospect K (5228), 2.5 km northwest of a small amount of an admixed impurity, suspected to be the Nullagine 1 Trig Point; Ripon Hills southeast prospect berlinite (AlPO4; R. M. Clarke, W.A. Chemistry Centre, (5231), 8.3 km south-southwest of Little River Spring 2002, written comm.). Bore; Ripon Hills south prospect (5232), 5.7 km south of Mount Ian; Little River Spring prospect (17678), 1.8 km The nature and type of mineralization explored for at west-northwest of Little River Spring Bore; and Cave these localities is unclear and no supporting documents Bore SW prospect (17680), 10.5 km southwest of Cave have been identifi ed. However, the basal Hardey Formation Bore. A manganese occurrence, Midgengadge Creek S is known to carry gold mineralization (Hickman, 1983; (17679) was also noted overlying Pinjian Chert breccia, Bagas, 2005). 15 km south-southwest of Pulgorah Cone. Overall production fi gures are diffi cult to extract. Apart Base metal — copper from large bulk samples collected for benefi ciation and metallurgical tests (Williams, 1958, 1960), production The previously unrecorded and recently rediscovered appears to have been bulked with ore mined from other Meentheena copper prospect (17677) lies 4 km west of areas (Hickman, 1983). A combined drill-proven, indicated Mopoke Well. The prospect consists of a series of shallow and inferred resource is estimated at 56 000 000 tonnes pits (<1.5 m deep) sunk on a series of small en echelon with average grade of 19.4% Mn and 25.9% Fe, using a gossanous quartz veins, striking about 290° and dipping 15% Mn cutoff (Denholm, 1977). These resource fi gures steeply (70° to 80°) to the south-southwest. The quartz are reduced to 12 000 000 tonnes if a cutoff grade of veins occupy sheared contacts between the Mount Roe 20% is used to produce an average grade 24.6% Mn and Basalt and a dolerite – altered gabbro dyke belonging 23% Fe. The average depth of the orebody in this case to the Proterozoic Round Hummock Dolerite Suite. would be 8 m (Denholm, 1977). Mineralization has been found in the sheared contact on both sides of the dyke, which is up to 6 m wide. Unlike the high-grade deposits (>45%) in the Woodie Woodie area (Williams and Trendall, 1998b), the main The main copper mineralization can be traced Ripon Hills deposits are of much lower grade with an intermittently over a distance of 250 m, mostly on the iron content up to 25% and manganese less than 40% northern side of the dyke. It is represented by patchy (Denholm, 1977). malachite and probable chrysocolla in vuggy gossanous quartz and thin patinas of green copper minerals along The area where the main ferruginous manganese joint and fracture planes in the sheared basalt and dolerite mineralization is developed is underlain by Pinjian adjacent to the quartz veins. It is doubtful if any copper ore Chert Breccia. The mineralization is confined to a was removed from the prospect. broad shallow north–south-trending depression, partly faulted on the eastern side and along the southwestern margin. Such depressions may have a karst genesis as Mineralization in regolith observed elsewhere in the Ripon Hills. The manganese mineralization overlies or replaces remnants of shale Precious mineral — diamond (#MN-ss) belonging to the Proterozoic Manganese Group. In some areas the ferruginous manganese ore overlaps Loam sampling along the southern side of Yilgalong Creek the shale to lie directly on or replace the Pinjian Chert where it fl ows out of the Ripon Hills, an area singled out Breccia (Denholm, 1977). All the rocks in this region by airborne and ground magnetic anomalies, returned a show remnant effects of ferruginization (lateritization) single macrodiamond and a few chromites (Knight, 1994). and supergene enrichment in post-Permian times (Late Follow-up sampling failed to fi nd further diamonds or Cretaceous − Early Miocene; Hocking et al., 2005). indicator minerals. It was concluded that the previous samples may have been derived from remnant Permian The higher grade manganese ores have a dark fluvioglacial rocks that outcrop in the area (Home, bluish colour with a botryoidal appearance, whereas the 1995). ferruginous manganese is coated with brownish-orange

35 Williams limonite–goethite. The main manganese mineral is very Trig Point in that it is associated with Manganese Group fi ne grained pyrolusite (manganese oxide) intergrown with sedimentary rocks. All the other localities in the Ripon hematite, with local bixbyite (iron–manganese oxide) and Hills and at Midgengadge Creek are small and associated braunite (manganese silicate). The main gangue minerals with the Pinjian Chert Breccia. are kaolin and diaspore (Denholm, 1977). The manganese prospect K (5228) is similar to that found in the main mineralized areas east of Nullagine 1

36 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

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38 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

HOME, D. P., 1995, Final report on exploration completed within School of Mines of Western Australia, Kalgoorlie, Ore-dressing exploration licence E45/1439 (Carawine 1) Nullagine 1:250 000 Investigations Report No. 710, 11p. mapsheet, Western Australia, CRA Exploration Pty Limited: Western MYERS, J. S., SHAW, R. D., and TYLER, I. M., 1996, Tectonic Australia Geological Survey, Statutory mineral exploration report, evolution of Proterozoic Australia: Tectonics, v. 15, no. 6, A43403 (unpublished). p. 1431–1446. JAHN, B. M., and SIMONSON, B. M., 1995, Carbonate Pb–Pb ages of NELSON, D. R., 1998, 144993: dacite, Booloomba Pool, in Compilation the Wittenoom Formation and Carawine Dolomite, Hamersley Basin, of geochronology data, 1997: Western Australia Geological Survey, Western Australia (with implications for their correlation with the Record 1998/2, p. 133–135. Transvaal Dolomite of South Africa): Precambrian Research, v. 72, p. 247–261. NELSON, D. R., 2001, 168935: volcaniclastic sandstone, Sophie Tank, in Compilation of geochronology data, 2000: Western Australia KEMPTON, N. H., 1976, Relinquishment Report, Temporary Geological Survey, Record 2001/2, p. 175–177. reserves 5984H–5988H Western Australia: Western Australia Geological Survey, Statutory mineral exploration report, A35830 NELSON, D. R., 2004a, 144682: foliated biotite tonalite, Baroona Hill; (unpublished). Geochronology dataset 274, in Compilation of geochronology data, June 2006 update: Western Australia Geological Survey. KNIGHT, B. K., 1994, Annual report on exploration completed within exploration licence E45/1439 (Carawine 1) for the period ending NELSON, D. R., 2004b, 169037: porphyritic rhyolite, King Rockhole; October 1994, Nullagine 1:250 000 mapsheet, Western Australia, Geochronology dataset 152, in Compilation of geochronology data, CRA Exploration Pty Limited: Western Australia Geological Survey, June 2006 update: Western Australia Geological Survey. Statutory mineral exploration report, A43323 (unpublished). NELSON, D. R., 2005a, 169260: foliated biotite tonalite, Bullyarrie Well; KOJAN, C. J., and HICKMAN, A. H., 1998, Late Archaean volcanism in Geochronology dataset 569, in Compilation of geochronology data, the Kylena and Maddina Formations, Fortescue Group, west Pilbara: June 2006 update: Western Australia Geological Survey. Western Australia Geological Survey, Annual Review 1997–98, NELSON, D. R., 2005b, 169261: gneissic tonalite, Bullyarrie Well; p. 43–53. Geochronology dataset 570, in Compilation of geochronology data, KRIEWALDT, M., 1964, The Fortescue Group of the Roebourne region, June 2006 update: Western Australia Geological Survey. North-West Division: Western Australia Geological Survey, Annual NELSON, D. R., 2005c, 169262: foliated biotite granodiorite, Bullyarrie Report 1963, p. 30–34. Well; Geochronology dataset 571, in Compilation of geochronology LIPPLE, S. L., 1975, Defi nitions of new and revised stratigraphic units data, June 2006 update: Western Australia Geological Survey. of the eastern Pilbara Region: Western Australia Geological Survey, NELSON, D. R., 2005d, 169263: tonalite gneiss, Bullyarrie Well; Annual Report 1974, p. 58–63. Geochronology dataset 572, in Compilation of geochronology data, LONGREACH METALS NL., 1974, Ripon Hills manganese/iron June 2006 update: Western Australia Geological Survey. exploration, 1971–1974: Western Australia Geological Survey, NELSON, D. R., 2005e, 178008: biotite–muscovite tonalite gneiss, Statutory mineral exploration report, A3973, A5053 (unpublished). Mount Elsie; Geochronology dataset 548, in Compilation of MacLEOD, W. N., and de la HUNTY, L. E., 1966, Roy Hill, W.A. (1st geochronology data, June 2006 update: Western Australia Geological edition): Western Australia Geological Survey, 1:250 000 Geological Survey. Series Explanatory Notes, 27p. NELSON, D. R., LOVE, G. J., BODORKOS, S., and WINGATE, MacLEOD, W. N., de la HUNTY, L. E., JONES, L. E., and HALLIGAN, M. T. D., 2006, 178086: porphyritic dacite, Carawine Pool; in R., 1963, A preliminary report on the Hamersley Iron province, Geochronology dataset 631, Compilation of geochronology data, North-West Division: Western Australia Geological Survey, Annual June 2006 update: Western Australia Geological Survey. Report 1962, p. 44–54. NOLDART, A. J., and WYATT, J. D., 1962, The geology of portion of the Pilbara Goldfi eld: Western Australia Geological Survey, Bulletin 115, MAITLAND, A. G., 1906, Third report on the geological features 199p. and mineral resources of the Pilbara Goldfi eld: Western Australia Geological Survey, Bulletin 23, 92p. O’DRISCOLL, D., 1958, Report on the inspection of manganese deposits in Western Australia. September, 1957: Australia Bureau of Mineral MARTIN, D. McB., SHEPPARD, S., and THORNE, A. M., 2005, Geology Resources, Record 1958/7a, 19p. of the Maroonah, Ullawarra, Capricorn, Mangaroon, Edmund, and Elliot Creek 1:100 000 sheets: Western Australia Geological Survey, ONO, S., EIGENBRODE, J. L., PAVLOV, A. A., KHARECHA, P., 1:100 000 Geological Series Explanatory Notes, 65p. RUMBLE III, D., KASTING, J. F., and FREEMAN, K. H., 2003, New insights into Archean sulfur cycle from mass-independent sulfur MARTIN, D. McB., and THORNE, A. M., 2001, New insights into the isotope records from the Hamersley Basin, Australia: Earth and Bangemall Supergroup: Western Australia Geological Survey, Record Planetary Science Letters, v. 213, p. 15–30. 2000/5, p. 1–2. PACKER, B. M., 1990, Palaeontology, sedimentology, and stable isotope McPHIE, J., DOYLE, M., and ALLEN, R., 1993, Volcanic textures — a geochemistry of selected formations in the 2.8 Ga old Fortescue guide to the interpretation of textures in volcanic rocks: University of Group: Los Angeles, U.S.A., University of California, PhD thesis Tasmania, Centre for Ore Deposit and Exploration Studies, 189p. (unpublished). MIDDLETON, M. F., 1990, Canning Basin, in Geology and mineral PLAYFORD, P. E., 2001, The Permo-Carboniferous glaciation of resources of Western Australia: Western Australia Geological Survey, Gondwana: its legacy in Western Australia: Western Australia Memoir 3, p. 425–457. Geological Survey, Record 2001/5, p. 15–16. MORY, A. J., and BACKHOUSE, J., 1997, Permian stratigraphy and PLAYFORD, P. E., 2002, Palaeokarst, pseudokarst, and sequence palynology of the Carnarvon Basin, Western Australia: Western stratigraphy in Devonian reef complexes of the Canning Basin, Australia Geological Survey, Report 51, 41p. Western Australia, in The sedimentary basins of Western Australia 3 MUHLING, P. C., and BRAKEL, A. T., 1985, Geology of the Bangemall edited by M. KEEP and S. J. MOSS: Petroleum Exploration Group — the evolution of an intracratonic Proterozoic basin: Western Society of Australia, Symposium, Perth, W.A., 2002, Proceedings, Australia Geological Survey, Bulletin 128, 266p. p. 763–793. MUSKETT, G. H., 1960, Benefi ciation of manganese ores from Balfour PURVIS, A. C., 2003a, Mineralogical Report No. 8318: Kent Town, Downs and Ripon Hills, Pilbara, W. A.: Australia CSIRO and the South Australia, Pontifex & Associates Pty. Ltd., 93p.

39 Williams

PURVIS, A. C., 2003b, Mineralogical Report No. 8331: Kent Town, Scientifi c Program on the response of the earth system to impact South Australia, Pontifex & Associates Pty. Ltd., 81p. processes edited by I. GILMOUR and C. KOEBERL: Heidelberg, Springer-Verlag, p. 81–213. PURVIS, A. C., 2003c, Mineralogical Report No. 8414: Kent Town, South Australia, Pontifex & Associates Pty. Ltd., 26p. SIMONSON, B. M., and JARVIS, D. G., 1993, Microfabrics of oolites RASMUSSEN, B., BLAKE, T. S., and FLETCHER, I. R., 2005, U–Pb and pisolites in the early Precambrian Carawine Dolomite of Western in edited by zircon age constraints on the Hamersley spherule beds: Evidence for Australia, Carbonate microfabrics R. REZAK and a single 2.63 Ga Jeerinah-Carawine impact ejecta layer: Geology, D. LAVAI: New York, Springer–Verlag, p. 227–237. v. 33(9), p. 725–728. SIMONSON, B. M., SCHUBEL, K. A., and HASSLER, S. W., 1993b, RASMUSSEN, B., and FLETCHER, I. R., 2004, Zirconolite: A new Carbonate sedimentology of the early Precambrian Hamersley Group U–Pb chronometer for mafic igneous rocks: Geology, v. 32(9), of Western Australia: Precambrian Research, v. 60, p. 287–335. p. 785–788; Correction to text, Geology, v. 32, p. 892. SMITH, R. N., 1898, The probability of obtaining artesian water between RASMUSSEN, B., and KOEBERL, C., 2004, Iridium anomalies and the Pilbara Goldfi elds and the Great Sandy Desert: Western Australia shocked quartz in a Late Archean spherule layer from the Pilbara Geological Survey, Bulletin 1, part 2, p. 24–27. craton: New evidence for a major asteroid impact at 2.63 Ga: STERN, H., de HOEDT, G., and ERNST, J., 2004, Objective Geology, v. 32(12), p. 1029–1032. classifi cation of Australian climates: Commonwealth of Australia RICHARDS, M. N., 1985, Final report on exploration completed within 2004, Bureau of Meteorology, viewed 22 April 2005, Gingarrigan Creek 45/05, Nullagine SF 51-5, Western Australia: STEVENS, M. K., and APAK, S. N., (compilers), 1999, GSWA Western Australia Geological Survey, Statutory mineral exploration Empress 1 and 1A well completion report, Yowalga Sub-basin, report, A15932 (unpublished). Officer Basin, Western Australia: Western Australia Geological SENTINEL MINING COMPANY, 1967, 1967 Report, TRs, 4102– Survey, Record 1999/4, 110p. 4107H Warrawagine Basin, TR 4090H Mt Cecelia: Western Australia STURMAN, A. P., and TAPPER, N. J., 1996, The weather and climate Geological Survey, Statutory mineral exploration report, A1153 of Australia and New Zealand: United Kingdom, Oxford University (unpublished). Press, 476p. SIMONSON, B. M., 1992, Geological evidence for a strewn fi eld of TAPP, R. G., and BARRELL, S. L., 1984, The northwest Australian impact spherules in the early Precambrian Hamersley Basin of cloud band: climatology, characteristics and factors associated with Western Australia: Geological Society of America, Bulletin, v. 104, development: Journal of Climatology, v. 4, p. 411–424. p. 829–839. THORNE, A. M., and TRENDALL, A. F., 2001, Geology of the SIMONSON, B. M., 2003, Petrographic criteria for recognizing certain Fortescue Group, Pilbara Craton, Western Australia: Western Australia types of impact spherules in well-preserved Precambrian successions: Geological Survey, Bulletin 144, 249p. Astrobiology v. 3, no. 1, p. 49–65. THORNE, A.M., TYLER, I. M., and HUNTER, W. M., 1991, Turee SIMONSON, B. M., BYERLY, G. R., and LOWE, D. R., 2004, The early Creek, W.A. (2nd edition); Western Australia Geological Survey, Precambrian stratigraphic record of large extraterrestrial impacts: in 1:250 000 Geological Series Explanatory Notes, 29p. The Precambrian Earth: Tempos and Events in Precambrian Time TOWNER, R. R., and GIBSON., D. L., 1983, Geology of the onshore edited by P. G. ERIKSSON, W. ALTERMANN, D. R. NELSON, Canning Basin, Western Australia: Australia Bureau of Mineral W. U. MUELLER, and O. CATUNEANU: Elsevier, Developments Resources, Bulletin 215, 51p. in Precambrian Geology, 12, p. 27–45. TRAVES, D. M., CASEY, J. N., and WELLS, A. T., 1956, The geology SIMONSON, B. M., DAVIES, D., WALLACE, M., REEVES, S., and of the southwestern Canning basin, Western Australia: Australia HASSLER, S. W., 1998, Iridium anomaly but no shocked quartz from Bureau of Mineral Resources, Report 29, 74p. Late Archean microkrystite layer: Oceanic impact ejecta?: Geology, v. 26, p. 195–198. TRENDALL, A. F., 1990, Pilbara Craton — introduction, in Geology and mineral resources of Western Australia: Western Australia Geological SIMONSON, B. M., and GLASS, B. P., 2004, Spherule layers Survey, Memoir 3, p. 128. — Records of ancient impacts: Annual Review Earth and Planetary Sciences, v. 32, p. 329–361. TRENDALL, A. F., 1991, Progress report on the stratigraphy and structure of the Fortescue Group in the Gregory Range area of the SIMONSON, B. M., and HARNIK, P., 2000, Have distal impact ejecta eastern Pilbara Craton: Western Australia Geological Survey, Record changed through geologic time?: Geology, v. 28, p. 975–978. 1990/10, 38p. SIMONSON, B. M., and HASSLER, S. W., 1997, Revised correlations TRENDALL, A. F., COMPSTON, W., NELSON, D. R., de LAETER, in the Early Precambrian Hamersley Basin based on a horizon of J. R., and BENNETT, V. C., 2004, SHRIMP zircon ages constraining resedimented impact spherules: Australian Journal of Earth Sciences, the depositional chronology of the Hamersley Group, Western v. 44, p. 37–48. Australia: Australian Journal of Earth Sciences, v. 51, p. 621–644. SIMONSON, B. M., HASSLER, S. W., and SCHUBEL, K. A., 1993a, TRENDALL, A. F., NELSON, D. R., de LAETER, J. R., and HASSLER, Lithology and proposed revisions in stratigraphic nomenclature of S. W., 1998, Precise zircon U–Pb ages from the Marra Mamba Iron the Wittenoom Formation (Dolomite) and overlying formations, Formation and Wittenoom Formation, Hamersley Group, Western Hamersley Group, Western Australia: Western Australia Geological Australia: Journal of Earth Sciences, v. 45, p. 137–142. Survey, Report 34, Professional Papers, p. 65–79. TYLER, I. M., and HOCKING, R. M., 2002, A revision of the tectonic SIMONSON, B. M., HASSLER, S. W., SMIT, J., and SUMNER, units of Western Australia: Western Australia Geological Survey, D., 2002, How many Late Archaean impacts are recorded in the Annual Review 2000–01, p. 33–44. Hamersley Basin of Western Australia?, Abstracts, 33rd Lunar and Planetary Science Conference, Houston, Texas, 2002: Oberlin College TYLER, I. M., and THORNE, A. M., 1990, The northern margin of Geology, Ohio, Abstract no. 1772. the Capricorn Orogen, Western Australia — an example of an early Proterozoic collision zone: Journal of Structural Geology, v. 12, SIMONSON, B. M., HORNSTEIN, M., and HASSLER, S. W., 2000, p. 685–701. Particles in Late Archean Carawine Dolomite (Western Australia) resemble Muong Nong-type tektites, in Impacts and the early Earth; VAN KRANENDONK, M. J., 2003, Stratigraphic and tectonic proceedings of the fi rst workshop of the European Science Foundation signifi cance of eight local unconformities in the Fortescue Group,

40 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

Pear Creek Centrocline, Pilbara Craton, Western Australia: Western WILLIAMS, I. R., 2003, Yarrie, W.A.: Western Australia Geological Australia Geological Survey, Annual Review 2001–02, p. 70–79. Survey, 1:250 000 Geological Series Explanatory Notes, 84p. VAN KRANENDONK, M. J., COLLINS, W. J., HICKMAN, A. H., WILLIAMS, I. R., 2005, Yilgalong, W.A. Sheet 3055 (Version 1, June and PAWLEY, M. J., 2004a, Critical tests of vertical vs. horizontal 2005): Western Australia Geological Survey, 1:100 000 Geological tectonic models for the Archaean East Pilbara Granite–Greenstone Series. Terrane, Pilbara Craton, Western Australia: Precambrian Research, WILLIAMS, I. R., in prep., Nullagine, W.A. Sheet SF 51-5 (Version 1): v. 131, p. 173–211. Western Australia Geological Survey, 1:250 000 Geological Series. VAN KRANENDONK, M. J., HICKMAN, A. H., SMITHIES, R. H., WILLIAMS, I. R., and BAGAS, L., in prep., Geology of the Mount NELSON, D., and PIKE, G., 2002, Geology and tectonic evolution of Edgar 1:100 000 sheet: Western Australia Geological Survey, the Archean North Pilbara Terrain, Pilbara Craton, Western Australia: 1:100 000 Geological Series Explanatory Notes. Economic Geology, v. 97, p. 695–732. WILLIAMS, I. R., and TRENDALL, A. F., 1998a, Geology of the VAN KRANENDONK, M. J., SMITHIES, R. H., HICKMAN, A. H., Braeside 1:100 000 sheet: Western Australia Geological Survey, BAGAS, L., WILLIAMS. I. R., and FARRELL, T. R., 2004b, Event 1:100 000 Geological Series Explanatory Notes, 39p. stratigraphy applied to 700 million years of Archean crustal evolution, Pilbara Craton, Western Australia: Western Australia Geological WILLIAMS, I. R., and TRENDALL, A. F., 1998b, Geology of the Survey, Annual Review 2003–04, p. 49–61. Pearana 1:100 000 sheet: Western Australia Geological Survey, 1:100 000 Geological Series Explanatory Notes, 33p. VAN KRANENDONK, M. J., SMITHIES, R. H., HICKMAN, A. H., BAGAS, L., WILLIAMS, I. R., and FARRELL, T. R., 2006, Revised WILLIAMS, I. R., and TRENDALL, A. F., 1998c, Geology of the lithostratigraphy of Archean supracrustal and intrusive rocks in Isabella 1:100 000 sheet: Western Australia Geological Survey, the northern Pilbara Craton, Western Australia: Western Australia 1:100 000 Geological Series Explanatory Notes, 24p. Geological Survey, Record 2006/15, 63p. WILLIAMS, K. L., 1958, Manganese ore from Rippon (sic) Hills, VEEVERS, J. J., and WELLS, A. T., 1961, The geology of the Canning Western Australia: Australia CSIRO, Mineragraphic Investigations, Basin, Western Australia: Australia Bureau of Mineral Resources, Report No. 747, 4p. Bulletin 60, p. 197. WILLIAMS, K. L., 1960, Manganese ore from Ripon Hills, Western WAKELIN-KING, G. A., 1999, Banded mosaic (‘tiger bush’) and Australia: Australia CSIRO, Mineragraphic Investigations, Report sheetfl ow plains: a regional mapping approach: Australian Journal of No. 825, 11p. Earth Sciences, v. 46, p. 53–60. WINGATE, M. T. D., and GIDDINGS, J. W., 2000, Age and WEBB, R., 1994, A new caving area — East Pilbara (EP): W.A. paleomagnetism of the Mundine Well dyke swarm, Western Australia: Speleological Group, The Western Caver, v. 34, p. 51–53. implications for an Australia–Laurentia connection at 755 Ma: Precambrian Research, v. 100, p. 335–357. WELLMAN, P., 2000, Upper crust of the Pilbara Craton, Australia; 3D geometry of a granite/greenstone terrain: Precambrian Research, WOODHEAD, J. D., HERGT, J. M., and SIMONSON, B. M., 1998, v. 104, p. 175–186. Isotopic dating of an Archean bolide impact horizon, Hamersley Basin, Western Australia: Geology, v. 26, p. 47–50. WILLIAMS, I. R., 1989, Balfour Downs, W.A.: Western Australia Geological Survey, 1:250 000 Geological Series Explanatory Notes, WOODWARD, H. P., 1894, Mining Handbook to the Colony 38p. of Western Australia, Written especially for Prospectors and Strangers to the colony who are interested in mining, by authority WILLIAMS, I. R., 1999, Geology of the Muccan 1:100 000 sheet: of The Commissioner of Crown Lands: Perth, Western Australia, Western Australia Geological Survey, 1:100 000 Geological Series Government Printer, 68p. Explanatory Notes, 39p. WILLIAMS, I. R., 2001, Geology of the Warrawagine 1:100 000 sheet: Western Australia Geological Survey, 1:100 000 Geological Series Explanatory Notes, 33p.

41 Williams

Appendix 1

Gazetteer of localities for YILGALONG

Locality _MGA coordinates __ Easting Northing

Barbilgunyah Hill 288891 7648165 Bookabunna Well 250773 7644502 Bullyarrie Well 259368 7628908 Carawine Pool (BRAESIDE 1:100 000) 303080 7615893 Cave Bore 264918 7670602 Dingo Well 262196 7633614 Gap Well 283597 7655635 GingarriganWell 290248 7673531 Little River Spring Bore 277894 7651067 Little River Well 283482 7671072 Meentheena copper prospect 244790 7638975 Mishap Well 253810 7636096 Mopoke Well 248661 7638951 Mount Ian 266422 7646424 Mount Ian Well 258398 7640701 New 20 Mile Well 279115 7669495 NMF 625 Trig Point 245210 7632292 Nullagine 1 Trig Point 263456 7651701 Outcamp Bore 264580 7674802 Pearana Rockhole (PEARANA 1:100 000) 317186 7576390 Pulgorah Cone 291892 7643893 RHDH1 (borehole) 280266 7642601 RHDH2A (borehole) 274508 7644780 Rocky Pool 248883 7669618 Salvation Well 243171 7627058 20 Mile Well 269086 7665917 Walgunya Well 245866 7670850 Yilgalong Pool 283611 7674744

42 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

Appendix 2

Defi nition of new stratigraphic names on YILGALONG

Midgengadgi Monzogranite (ACEmi-gm) Elsie Creek Tonalite (AEMel-mgtn) Derivation of name: Midgengadge Creek, a northeasterly Derivation of name: Elsie Creek, a west fl owing tributary fl owing tributary of the Oakover River (MGA 286100E of the Nullagine River (MGA 244000E 7622000N). 7632000N). Distribution: Apart from the Midgengadgi Monzogranite Distribution: A small intrusion of unknown shape and Little River Trondhjemite, it occupies the remainder of unconformably overlain by Fortescue Group rocks, the Yigalong Granitic Complex that lies along the southern exposed dimensions are roughly 2 km northeast by margin of YILGALONG in the southwest corner. 2 km northwest, lies on the southeastern margin of the exposed part of the Yigalong Granitic Complex. Possibly Type areas: In gorges along the western margin of the further small unfoliated tonalite, microgranodiorite and Yilgalong Granitic Complex 150 to 200 m east of the micromonzogranite intrusions and dykes scattered through contact with the Mount Elsie greenstone belt: a) in the Yigalong Granitic Complex belong to the Cleland unnamed creek (MGA 244390E 7623250N); b) on south Supersuite bank of Elsie Creek (MGA 244910E 7621670N).

Type areas: Well exposed tor-covered sheets (around Lithology: Gneissic to foliated, fi ne- to medium-grained MGA 276390E 7623252N), 17.5 km southeast of Dingo biotite tonalite and granodiorite, minor monzogranite, Well. tonalite gneiss; protomylonitic at the margin with Mount Elsie greenstone belt. Lithology: Nonfoliated, seriate to porphyritic, medium- to coarse-grained leucocratic biotite monzogranite. Relationships: Belongs to the Emu Pool Supersuite, has a sheared intrusive contact with the Euro Basalt of the Mount Relationships: Belongs to the Cleland Supersuite, intruded Elsie greenstone belt on the western side and unassigned into Elsie Creek Tonalite, unconformably overlain by the amphibolites on the eastern edge on the Yigalong Granitic lower and upper successions of the Kylena Formation Complex, and is unconformably overlain by the Hardey including the Mopoke Member. and Kylena Formations of the Fortescue Group along the northern margin. Age: Main body has a sensitive high-resolution ion microprobe (SHRIMP) zircon U–Pb date of 3274 ± 5 Ma Age: Five SHRIMP zircon U–Pb dates have been obtained (GSWA 178089; Bordokos et al., 2006). A weakly from the Elsie Creek Tonalite: a) 3299 ± 5 Ma (GSWA foliated biotite tonalite gave a SHRIMP zircon U–Pb date 144682; Nelson, 2004); b) 3291 ± 4 Ma (GSWA 169262; of 3277 ± 6 Ma (GSWA 169260; Nelson, 2005a). This Nelson, 2005c); c) 3291 ± 4 Ma (GSWA 169261; Nelson, sample also contained fi ve zircon xenocrysts that have a 2005b); d) 3290 ± 4 Ma (GSWA 169263; Nelson, SHRIMP zircon U–Pb date of 3308 ± 5 Ma. 2005d).

Little River Trondhjemite (ACElr-gtl) Mopoke Member Derivation of name: Little River, a northeasterly fl owing Derivation of name: Mopoke Well (MGA 248661E tributary of Yilgalong Creek (MGA 262300E 7622000N). 7638951N). Distribution: A faulted (western edge) semicircular Distribution: Exposed discontinuously across the intrusion, unconformably overlain by Fortescue Group southwest quarter of YILGALONG; lies in the lower third of rocks, lies on the northern margin towards the eastern end the Kylena Formation between 5 km north of the Ripon of the exposed Yigalong Granitic Complex. Hills road on the western edge and the southern edge of the sheet area, 17 km southeast of Dingo Well. Type areas: In water-worn sheets along the eastern side of Yilgalong Creek, 9.9 km southeast of Dingo Well (MGA Type areas: Prominent low cliff-lines (2–3 m high) of 268987E 7626599N). Mopoke Formation on southern side of Ripon Hills road (MGA Zone 51 244521E 7648675N), 7.5 km Lithology: Massive, fi ne- to medium-grained leucocratic northwest of Bookabunna Well; small cliffed cuesta quartz trondhjemite. (3 m high) of stromatolitic dolomite, interbedded chert and ripple-marked, fi ne-grained sandstone and siltstone Relationships : Probably belongs to the Cleland Supersuite; (MGA Zone 51 246377E 7641976N), 3.8 km northwest intruded into Elsie Creek Tonalite; unconformably of Mopoke Well; a rubbly cliffed exposure (3 m high) overlain by the lower and upper successions of the Kylena of dolomite and calcareous, pebbly sandstone resting Formation including the Mopoke Member. nonconformably on Little River Trondhjemite (Yilgalong Age: Post-Elsie Creek Tonalite, therefore younger than Granitic Complex; MGA 269362E 7627124N), 9.6 km c. 3290 Ma. southeast of Dingo Well.

43 Williams Lithology: Cliff-forming, silicifi ed blue-grey carbonates, References mostly limestone or dolomitic limestone, up to 5 m thick, interbedded and overlain by thin-bedded, grey to cream, BODORKOS, S., LOVE, G. J., and NELSON, D. R., and WINGATE, calcareous and tuffaceous siltstone and shale, ripple- M. T. D., 2006, 178089: leucocratic monzogranite, Dingo Well; marked fi ne-grained sandstone and thin blue chert beds; Geochronology dataset 632, in Compilation of geochronology data, partly silicifi ed carbonates locally carry stromatolites and March 2006 update: Western Australia Geological Survey. microbial laminations. NELSON, D. R., 2004, 144682: foliated biotite tonalite, Baroona Hill; Geochronology dataset 274 in Compilation of geochronology data, Relationships: A discontinuous marker bed in the lower June 2006 update: Western Australia Geological Survey. third of the Kylena Formation. It separates the lower NELSON, D. R., 2005a, 169260: foliated biotite tonalite, Bullyarrie Well; succession of grey-blue tholeiitic basalt and greenish-grey Geochronology dataset 569 in Compilation of geochronology data, komatiitic basalt from the upper succession of grey and June 2006 update: Western Australia Geological Survey. bluish-grey basalt and basaltic andesite, both successions NELSON, D. R., 2005b, 169261: gneissic tonalite, Bullyarrie Well; have distinctive radiometric signatures; it locally overlies a Geochronology dataset 570 in Compilation of geochronology data, mixed mafi c–felsic volcanic and volcaniclastic succession June 2006 update: Western Australia Geological Survey. 16.5 km southeast of Dingo Well; has been recognized on NELSON, D. R., 2005c, 169262: foliated biotite granodiorite, Bullyarrie the adjoining EASTERN CREEK and MOUNT EDGAR sheets. Well; Geochronology dataset 571 in Compilation of geochronology data, June 2006 update: Western Australia Geological Survey. Age: The Mopoke Member has not been dated directly; however, it is younger than the mafi c to felsic volcanic and NELSON, D. R., 2005d, 169263: tonalite gneiss, Bullyarrie Well; volcaniclastic succession dated at c. 2749–2735 Ma of the Geochronology dataset 572 in Compilation of geochronology data, Kylena Formation and older than the overlying c. 2727 Ma June 2006 update: Western Australia Geological Survey. Mingah Member of the Tumbiana Formation.

44 GSWA Explanatory Notes Geology of the Yilgalong 1:100 000 sheet

Appendix 3

Company data on GSWA WAMEX open fi le for YILGALONG

WAMEX Duration Exploration title Company Item no.*

965 1965–1966 Spinaway copper–zinc exploration CRA Exploration 2275 1965–1970 Reedy Creek copper exploration Conwest Australia 1957 1966–1968 Cookes Creek copper–molybdenum–tungsten D.F.D. Rhodes 1840 1966–1973 Nullagine and Balfour Downs iron–manganese Goldsworthy Mining, Sentinel Mining 966 1969–1972 Ragged Hills copper/lead Western Mining Corporation 3279 1970–1973 Yarrie nickel–copper/copper–molybdenum Woodreef Mines, Australian Anglo American, Kitchener Mining 3018 1970–1976 East Pilbara nickel–copper Mogul Mining 4146 1971–1974 Ripon Hills manganese/iron Longreach Metals 6348 1974–1979 Woodie Woodie manganese Broken Hill Pty, Dampier Mining 3224 1974–1982 Ragged Hills lead Hancock & Wright Prospecting 11530 1975–1975 Shaw River/Oakover River coal Shell Australia 3194 1982–1983 Rocky pool/Coonanbunna Creek lead–zinc CRA Exploration 2345 1982–1984 Bamboo Creek gold Carpentaria Exploration 4148 1982–1985 Woodie Woodie manganese Preussag Australia 2655 1983–1984 Ripon Hills lead–zinc CRA Exploration 6734 1986–1987 Baroona Hill gold exploration Intercontinental Gold and Minerals 12777 1989–2000 Ripon Hills/Woodie Woodie manganese Valient Consolidated, Valient Manganese 5851 1990–1991 Carawine gold/base metals MIM Exploration 6948 1993–1993 Outcamp Bore West manganese Valient Consolidated 8015 1993–1994 Carawine diamond CRA Exploration 7504 1993–1994 Ripon Hills manganese Valient Consolidated 8855 1993–1996 Gingarrigan Well manganese Valient Consolidated 8875 1993–1996 Nullagine River base metals Normandy Exploration, Ocean Resources 9193 1993–1997 Gingarrigan Well manganese Valient Consolidated 12043 1993–1998 Baroona Hill/Meentheena gold Mr M. G. Creasey 10015 1993–1998 Meentheena gold Normandy Exploration 10470 1993–1999 Gingarrigan Well manganese Consolidated Minerals, Valient Consolidated 13250 1993–2000 Baroona Hill/Meentheena gold Mr M. G. Creasey 8321 1994–1995 Yilgalong gold Mr R. J. Watson 9525 1994–1997 Yilgalong gold Mr R. J. Watson 11770 1994–2002 Yilgalong gold/nickel Mr B. J. O’Brien, Plenty River Corporation, Plenty River Gold Mines, Plenty River Mining 11427 1994–2002 Yilgalong gold/base metals Plenty River Mining 10191 1997–1999 Mount Elsie gold Darkdale Pty, Minair Exploration 10990 1999–2000 Warrawagine diamond Stockdale Prospecting 11225 1999–2001 Warrawagine diamond De Beers Australia Exploration 11923 2000–2002 Haoma Nullagine diamond Haoma Mining 11841 2000–2003 Yilgalong diamond Douglass Mitchell

NOTES: WAMEX: Western Australian mineral exploration database containing statutory mineral exploration reports as submitted to the GSWA * Information available from Department of Industry and Resources Library, Mineral House, 100 Plain Street, East Perth, W.A. 6004

45 WILLIAMS

The geology of the YILGALONG 1:100 000 sheet is dominated by exposures of the Neoarchean Fortescue Group (mainly basaltic rocks) and Hamersley Group (sedimentary rocks), which unconformably overlie Paleoarchean– Mesoarchean granites, greenstones, and sedimentary basins of the Pilbara Craton. Deep erosion of the Fortescue Group on southern YILGALONG has exposed a small part of the East Pilbara Terrane of the Pilbara Craton. This terrane is locally composed of the c. 3350 Ma Kelly Group (dominantly greenschist-facies metabasalt) and 3320– 3220 Ma metamorphosed granitic rocks of the Emu Pool and Cleland Supersuites. Overlying the Fortescue Group the Hamersley Group is represented by the c. 2540 Ma Carawine Dolomite, which includes remarkably well preserved asteroid impact deposits. Younger Proterozoic units are the Pinjian Chert Breccia, which is a residual deposit on the Carawine Dolmoite, and the Manganese Group. All the Precambrian rocks are unconformably overlain by the fluvioglacial Carboniferous– Permian Paterson Formation.YILGALONG records a long tectonic history, in which deformation after c. 1830 Ma was related to collision between the Pilbara Craton and the Paterson Orogen. Mineral production onYILGALONG has been restricted to manganese deposits along the Carawine Dolomite – Pinjian Chert Breccia unconformity, and small-scale gold workings Geology of the Yilgalong 1:100 000 sheet along shear zones in the Euro Basalt.

These Explanatory Notes are published in digital format (PDF) and are available online at: www.doir.wa.gov.au/GSWA/publications. Laser-printed copies can be ordered from the Information Centre for the cost of printing and binding.

Further details of geological publications and maps produced by the Geological Survey of Western Australia are available from: EXPLANATORY NOTES Information Centre Department of Industry and Resources 100 Plain Street East Perth, WA 6004 Phone: (08) 9222 3459 Fax: (08) 9222 3444 Www.doir.wa.gov.au/GSWA/publications AUSTRALIA 1 : 100000 GEOLOGICAL SERIES GEOLOGICAL SURVEY OF WESTERN AUSTRALIA SHEET 3055

120^30' 40' 50' 121^00' Warrawagine Homestead 19 km

42 44 46 48 ä50 52 54 56 58 ä60 62 64 66 68 ä70 72 74 76 78 ä80 82 84 86 88 ä90 92

21^00' C1 ñFOmk-bntt ñFO-od Springs A1¤ C1 C1 A1ª 21^00' ñFOmk-bntt 180 A1¤ A2t ñFOj-xcl-kd Geological boundary Fracture, joint, or extension vein, showing strike and dip 240 ñFO-od C3 ñFOjb-bnth C3 ìod ìod C1 L²c£ E ñFO-od 10 ñHAc-kds ðpj-ccx C1 A1ª Yard ñHAc-kds 85 20 ñFOj-xcl-kd 16 Noa-ktpl æåpa-sgpg Noa-ktpl A1ª 76 exposed...... inclined...... ñFOm-bb 200 240 ñFO-od

ñFOj-xcl-kd 18 10 14 220 C2f 180 180 Noa-ktpl 16 A1¤ A1§c£ A1¹ C1 ñFOj-xcl-kd concealed...... Meteorite impact structure...... 12 W1 ðpj-ccx Lacustrine unit 20 18 C1 ìod 220

10 A2t 180 Outcamp Bore (abd) (PD) 200 15 Fault Stromatolite fossil locality...... 220 Noa-ktpl Well W1 C3 L²c£ Lacustrine clay and silt with gilgai (crabhole) surface in claypans; generally vegetated Noa-ktzl Unassigned 15 280 C1 Noa-ktzl A1£ Yilgalong Pool 178086 ñFO-od æåpa-sgpg 180 Eolian unit exposed, with relative displacement...... Isotopic age determination site with identification number...... 74 ñFOmk-bntt W1 10 Noa-ktpl 16

ñFOm-bb W1 A1¤ ñFOm-bb E Eolian sand, typically adjacent to hilly areas of bedrock; no dunes

A1§ 180 240 A1£ C2 ñFOjb-bnth concealed...... 200 10 C1 C2f 240 12 A1§c£ ñFOj-xcl-kd ðo C3 40 10 220 74 reverse, triangle on upthrown side...... Road; sealed...... ñFOj-xcl-kd Noa-ktpl WARRAWAGINE Noa-ktpl OAKOVER 22 ðpj-ccx ðzq 11 C1q

5 ñFOjb-bnth 15 Noa-ktpl A1ª C2f A1¤ A1§ C1 C1 W1 W1f reverse, concealed, triangle on upthrown side...... Road; unsealed......

20 240 Creek 200

C1 R3´f 200 RIVER W1 C3 Fold, showing axial trace and generalized plunge direction Major track...... ðo 14 ðpj-ccx A2t 240 A1¤ ñHAc-kds C1 Noa-ktpl C3 ìod ñFO-od 72 220 A1¤ anticline, exposed...... Track...... 8 C3 11 ROAD C1 A1¤ A1£ A1§ A1§c£ A1ª A1¹ A1§ A1ª ñFOj-xcl-kd ðzq A1¹ 200 20 syncline, exposed, concealed...... Fence, generally with track...... Creek C3 Noa-ktpl 5 A1¤ A1ª 3 14 Noa-ktpl 72 Small-scale fold axis, showing trend and plunge Building...... 5 Noa-ktpl W1 A1¤ L²c£ Noa-ktzl 12 20 Walgunya C3 Bore ñHAc-kds 220 26 anticline...... 20 Yard...... Yard A1¤ A1ª Walgunya Well (PD) 14 R3c£v£ A1¤ R1gp¨ R1tpa 16 S A1¤ ñFO-od W1 0 Noa-ktpl Little River Well (abd) S-vergence...... 40 Horizontal control; major, minor......

26 Cave Bore C3 85 Creek 6 180 10 10 Parsons C1 8 M A2t ìod 30 30 A1§c£ Noa-ktpl RIVER 10 Spring 12 280 îì70 NULLAGINE A1¤ 9 Springs Colluvial units M-vergence...... Contour line, 20 metre interval...... 260 C3 A2t Coonanbunna C3 ñHAc-kds A1§c£ ñFO-od Z Rocky Pool A1§ C1 Colluvium sand, silt, and gravel in outwash fans; scree and talus; proximal mass-wasting deposits; unconsolidated Z-vergence...... 20 C3 A1ª 10 10 Noa-ktpl C1 200 Colluvial quartz debris in sand, silt, and clay; derived from proximal mass-wasting of quartz veins Watercourse with ephemeral pool or waterhole...... ñFOm-bb A2t ñFOj-xcl-kd C1q Bedding, showing strike and dip C2 îì70 A1¤ New 20 Mile Well (abd) ñFOjb-bnth Low-gradient slope units 10 Pool...... Pool

C1 Noa-ktzl A2t A1ª 180 inclined...... 220 30 Silt, sand, and pebbles in distal sheetwash fans; no defined drainage Pump W QUATERNARY W1 Rockhole...... Rockhole

ell (abd) 240 200 18 Glacial striae, showing trend and direction of ice movement 200 C1 ìMN-sgp W1f Ferruginous sheetwash deposits; silt, sand, and ferruginous nodules in distal outwash fans ñFOjb-bnth 18 Waterhole...... Waterhole A1¤ 8 220 ñFOj-xcl-kd 240 240 Noa-ktzl Noa-ktpl sense of direction known...... 68 C1 C3 ðpj-ccx 38 Alluvial units 200 Noa-ktpl Noa-ktzl Sinkhole...... Sinkhole 280 5 ðpj-ccx Noa-ktpl 17 22 A1¤ Sand, silt, and gravel in active drainage channels; includes clay, silt, and sand in poorly defined drainage courses on floodplains Way-up indicator Noa-ktpl A1§c£ C3 26 A1¤ 260 20 A1£ Sand, silt, and gravel in the beds of major active drainage channels Spring...... Spring ñFO-od 10 ñFOj-xcl-kd C3 A2t pillow structure...... 16 ñHAc-kds A1ª ìMN-sgp 68 15 A1§ Floodplain deposits; sand, silt, and gravel adjacent to main drainage channels

260 23 Noa-ktpl 15 Bore, well...... Bore Well 280 A1§c£ Sand, silt, and clay on floodplains, with gilgai surface in areas of expansive clay Metamorphic foliation, showing strike and dip ñFOmk-bntt R3c£v£ A1§c£ Noa-ktpl Windpump...... A1¤ R3c£v£ C1 7 M 40 12 Creek C1 A1ª Mixed floodplain deposits; sand, silt, and clay adjacent to main drainage channels; numerous small claypans inclined...... C3 A1¤ A1ª A1§ ñFOj-xcl-kd A1¤ A1¹ Pebbly silt and sand on alluvial fans Dam...... Dam vertical...... 66 260 A1¤ ñFOm-bb Residual or relict units Abandoned...... (abd)

ìod Bore CAINOZOIC Lineation, unspecified, showing trend and plunge 6 280 landing ground 20 Mile Well C3 C2 15 260 ìod Noa-ktpl ñHAc-kds Residual quartzofeldspathic sand, with quartz and rock fragments; overlying and derived from granitic rock (PD) 15 landing ground C1 R1gp¨ Position doubtful...... 220 ñFOmk-bntt C2 ñHAc-kds Old 20 Mile Well (PD) C2 66 inclined...... 5 200 5 C3 200 R1tpa Residual boulders, cobbles, and pebbles in clay, silt, and sand; includes locally transported material; derived from fluvioglacial PATERSON FORMATION A1£ R1tpa 14 ñFO-od ñFOj-xcl-kd 10 ñHAc-kds C3 Blood W A2t 200 Mineral lineation, showing trend and plunge Mining locality...... RIPON HILLS ñFOm-bb 10 A1£ 10 10 ood Well (PD)

10 A1¤ M 220 inclined...... 18 Deposit, prospect, or occurrence...... Ripon Hills C Yard 12 ñFOj-xcl-kd 18 Bore Noa-ktzl ng A1ª C2 C2f A2t A2k R2k 300 A2t ñFOj-xcl-kd ñFOjb-bnth C1 ðpj-ccx 64 C3 ðpj-ccx Yilgalo BeddingÊcleavage intersection lineation, showing trend and plunge Battery or treatment plant, abandoned...... Bore R3´f PHANEROZOIC 260 æåpa-sgpg 260 200 Noa-ktzl æåpa-sgpg 40 260 A1¤ C2 Colluvial units inclined...... 22 Mineral exploration drillhole, showing subsurface data ...... RHDH1

C1 A1§ 10 C3 A1ª ñFO-od 22 19 C2 Partly consolidated colluvial sand, silt, and gravel in proximal outwash fans; scree and talus; dissected by present-day drainage A1§ C3 220 Noa-ktpl C3 ñHAc-kds 64 Drillhole name; RHDH Ripon Hills Drillhole ñFOj-xcl-kd A2k A1¤ 0 W1 Noa-ktpl 17680 A1§c£ C2f Ferruginous colluvium; consolidated sand, silt, clay, and rock fragments in proximal outwash fans and scree; dissected by present-day drainage ñFOmk-bntt C3 ñFOj-xcl-kd Cave Bore SW C2f Gingarrigan Well (PD) 260 260 ñFOjb-bnth Mn C1 C3 Alluvial units C3 ñFO-od 26 ñHAc-kds Stock Well (PD) A2t Consolidated alluvial gravel, sand, and silt, local carbonate cement; dissected by present-day drainage ñFO-od ðzq ñFOm-bb ñHAc-kdx ñHAc-kds Noa-ktpl 12 200 A2t A2k Alluvial or lacustrine calcrete; massive, nodular, and cavernous limestone, variably silicified; probably includes units of similar ages to OAKOVER and MILLSTREAM FORMATIONS 62 4 C3 A2k ñFOj-xcl-kd 280 A1¤ 220 260 ìod ñHAc-kds Residual or relict unit ñFOm-bb 12 200 A1¤ ðzq ñFOm-bb 10 A1¤ 280 Noa-ktpl OAKOVER ñFOtm-kts C1 Creek 62 R2k Residual calcrete; massive, nodular, and cavernous limestone; variably silicified; may be of similar age to OAKOVER FORMATION 320 C1 260 C1 æåpa-sgpg C3 FZ 10 14 14 E 203 m

C1 220 Baxter Well (abd) 8 ñHAc-kdx C3 A1§

ñFOti-bntt220 260 280 A1ª C3

ñFO-od 240 Øoa-ktzl Øoa-ktpl 20 A2t 260 Noa-ktzl ðzq ñFOtm-kts ñFOj-xcl-kd 300 C3 Vanadium A1§ 17 ðpj-ccx 220 C îì60 240 C1 A2t A1ª 260 280 13 A1ª (abd) Bunmardie Well (PD) OAKOVER FORMATION

9 ðzq ñFOmk-bntt C3 ñHAc-kdx C2 Gingarrigan 200 A1£ A1¤ 15 Creek Creek Øoa-ktzl Upper unit; vuggy, white to grey opaline silica, silicified carbonate rock, and minor calcareous sandstone; lacustrine deposit 12 ñHAc-kds 6 Noa-ktzl 27 280 Bore (abd) A1£ îì60 280 A1¤ Bunmardie RIVER 12 ñHAc-kdx R3´f Øoa-ktpl Lower unit; blue, grey, and fawn limestone and calcareous sandstone; packstone; lacustrine deposit INTERPRETED BEDROCK GEOLOGY Intrusive rocks C3 12 30 Noa-ktpl A1¤ A2t 24 12 R2k ñHAc-kds 4 C1 ñFOti-bntt 220 Noa-ktpl Mejajagee Pool Colluvial unit ñHAc-kds 320 ñHAc-kds A1£ C1 A1¤ æåpa-sgpg Noa-ktpl æåpa-sgpg Consolidated colluvial sand, silt, and gravel related to old land surface; dissected by present-day drainage æåpa-sgpg Paterson Formation ðzq ðpj-ccx C3 ñFOj-xsk-b BASIN ðzq ñFO-od 12 ðpj-ccx 260 8 A2t ñFOj-xsk-b ðpj-ccx ìod CANNING C3 A1§ 10 40 ñHAc-kdx ñFO-od 58 Dam Bookabunna C3 ñHAc-kdx C1 C1 C3 ìod A1§c£ 200 ìod ñHAc-kds 40 P I L B A R A A1¤ RIVER ðpj-ccx êod Dolerite sill ðzq ñFOtm-kts 19 ñFOjb-bnth M I N E R A L F I E L D R3c£v£ R3´f ñFO-od 280 ìod 4 12 200 10 2 ìMN-ss PALEOGENE to NEOGENE 10' ðzq 12 ñFOmk-bntt C1 260 M 39 10' ìRH-od ìRH-og ñFOti-bntt ðzq 5 C3 C1 244 m 58 C1 ñFOj-xcl-kd 26 æåpa-sgpg 3 A1¤ ñFOj-xsk-b A1¤ A1¤ 12 4 R3´f Residual or relict units C3 ñHAc-kdx 280 44 ðpj-ccx ñFOm-bb ñFOj-xcl-kd 16 60 A2t ìRH-od Dolerite dyke Coonanbunna ñHAc-kds 240 C3 R3c£v£ Residual and sheetwash clay and silt overlying basalt or dolerite; expansive clay with gilgai surface; locally underlies OAKOVER FORMATION

NULLAGINE 260 260

260 Dolerite Suite 260 300 10 æåpa-sgpg A1ª ìRH-og Gabbro dyke ìMN-sgp Round Hummock 14 Sinkhole 8 A1ª Noa-ktpl R3´f Ferruginous duricrust; includes massive, pisolitic, and nodular ferricrete; locally underlies OAKOVER FORMATION ñFO-od ñFOk-bng C1q 20 360 34 ñHAc-kds A1§ 6 56 A2t Creek 10 ñHAc-kds 220 ñHAc-kdx M A R B L E ñFOm-b ìod Dolerite dyke 280 ñFO-od B A R D I S T R I C T æåpa-sgpg 16 ðpj-ccx ñHAc-kds 58 C3 ñHAc-kds W1f R3´f ìod ðpj-ccx 320 R1tpa

C3 ìod 260 8 ñFOt-xb-k Sedimentary rocks

ìMN-s BASIN S 56 æåpa-sgpg PATERSON FORMATION: diamictite, mudstone, siltstone, sandstone, and conglomerate; fluvioglacial deposits Group ðzq ðzq 40 R3´f Gap Well (PD) C2 æåpa-sgpg COLLIER A1§ Bangemall

15 Supergroup

260 Manganese

ìMN-sh C1 C2f 240

ñFO-od 240 20 R1tpa

ÊPERMIAN ñFOkm-kts ñFOj-xcl-kd 280

æåpa-sgpg CANNING BASIN

36 æåpa-sgpg 5219 R3´f W1f Noa-ktzl ðo Dolerite dyke 220 280 C1 ñFOjb-bnth Ripon Hills A ðpj-ccx ñHAc-kds CARBONIFEROUS ñFO-od 260 ñHAc-kdx ñHAc-kds 16 20 9 Noa-ktpl 16 340 5220 5 ñFOj-xsk-b A1¤ 280 Mn 24 ìod Pinjian Chert Breccia 54 ñFOm-bb 5222 8 A1¤ 200 Noa-ktpl Noa-ktpl ðpj-ccx ðpj-ccx

Creek ñHAc-kds Rockhole Ripon Hills B PALAEOZOIC

300 Ripon Hills D ñFOtm-kts 21 260 c. 523 Ma â Dolerite or granophyric dolerite sill or dyke, fine to medium grained Mn 260 A1§c£ C3 êod ñFOk-b R2k R3´f 5221 Mn Carawine Dolomite 15 260 E êod ñHAc-kds ñFOjb-bnth 22 30 Ripon Hills C Group ñFOk-xbb-bk 20 32 20 23 Rockholes ìod A2t 54 CAMBRIAN ñFO-od ñHAc-kdx Hamersley

Mn 5223 æåpa-sgpg 260 ìod 15 15 ñFO-od ìMN-s ñFO-od Dolerite dyke or sill

C1 5228 ìMN-sgp A1ª Ripon Hills Road 18 km ñFOh-spa 8 Ripon Hills E ñHAc-kds C1 A1ª æåpa-sgpg 200

260 ñHAc-kdx ìMN-sgp Ripon Hills K ìMN-sh A1ª ìod 280 38 22 Mn ñFOh-xs-f 10 Mn 5225 8 ñFOj-xsk-b Jeerinah Formation

C3 16 Spring Bore A1¤ ìRH-od ìRH-og ñFOr-b ðo ìod æåpa-sgpg 260 A1¤ R1tpa 52 22 Ripon Hills G 40 C3 æåpa-sgpg ìRH-od 300 260 A1ª ñFOt-xb-k ñHAc-kds ñFOm-b Maddina Formation 280 Mn 5224 ñFOj-xsk-b ñFOhb-fr C1 25 6 39 C1 Ripon Hills F320 ìMN-ss ðpj-ccx C1 ìRH-og Tumbiana Formation 280 260 E W1f A1§c£ ìRH-od Dolerite dyke, fine to medium grained ñFOt-xb-k NULLAGINE 1 æåpa-sgpg Dolerite Suite

ñFOk-bng 400 Mn C1 R1tpa ìRH-od

C1 52 Round Hummock ñFOmk-bntt R2k 425 m 220 ìRH-od æåpa-sgpg 17678 R3´f Creek Gabbro dyke

85 Sinkhole 5227 ìRH-og HAMERSLEY BASIN 340 22 ðzq RIPON HILLS ñHAc-kds 280 æåpa-sgpg ñFOk-b Kylena Formation 9 ìod Little River Spring NEOPROTEROZOIC A2t ñFOti-bntt 28 Ripon Hills J Bookabunna ìMN-ss Sinkhole 220 Creek ñFOt-xb-k 11 ñFOm-bb 300 20 Mn 50 3503 Mn Mount Bruce Supergroup 16 280 Little River Spring Bore (PD) (abd) 240 Noa-ktpl ñKEe-b ñFOh-xs-f Hardey Formation 220 arble Bar 82 km ðzq ñHAc-kdx Ripon Hills H C2f 400 ìMN-sl A1¤ Dolerite dyke, sill, or plug Fortescue Group Noa-ktpl ìod ìod PILBARA CRATON M ñFOkm-kts ðzq ñFOj-xcl-kd 10 Bore Bamboo Creek ñFO-od Mn ìMN-sh 5226 ñFOhb-fr ñFOhb-fr îì50 12 RIPON R3´f 280 20 C2f ìRH-od Member

12 ìMN-st 300 Ripon Hills I æåpa-sgpg C2 ñFOh-xs-f ñFOk-b ìod ñFOm-b ðpj-ccx 10 220 ìRH-od C1 ñFO-od 14 340 Mn A1ª ñFOtm-kts 320 280 C1 10 240 C1 A1§c£ ñFOk-b ñFOr-b Mount Roe Basalt

260 8 ñHAc-kds A1§ C3 260 15 A1¤ ìMN-sgp HILLS ìMN-ss Noa-ktpl îì50 ðo ñFOr-bbg ñFOm-bb 380 W1f Fine- to coarse-grained lithic and quartz sandstone; locally glauconitic ñFOhb-fr ñFOt-xb-k 360 ñHAc-kdx 18 C1 WD401/1 5 ìMN-st A1¤ 36 Noa-ktzl ñEMel-mgtn ñCE-g ñFOkm-kts RIPON HILLS ROAD Rockhole uralba ñFOr-b ðo ñCE-g Cleland Supersuite 36 10 280 6110 A1ª

300 êod 0 PROTEROZOIC 14 ñFOj-xcl-kd 16 38 æåpa-sgpg C1 240 ìod C3 38 êod 24 Carawine R3´f C1 ðo Murram ðo ñFOh-scp C1 ñHAc-kds 340 Dmd ìMN-sl Mudstone and siltstone; typically green to grey-green; locally micaceous ðo ìRH-od Elsie Creek Tonalite

280 C2f ñPI-xmbs-mus ñEMel-mgtn ñFOkm-kts Creek C1 48 300 ñFOti-bntt 10 Gingarrigan ðo

280 10 ìRH-od Emu Pool ðo ñCE-g Supersuite ðzq êod 5 16 ñKEe-b 16 ñFOk-xbb-bk 10 E Noa-ktpl

75 8 32 æåpa-sgpg C3 A1§c£ BARBILGUNYAH HILL ñKEe-b Euro Basalt 300 Kelly 12 14 10 ìMN-ss SCALE 1:Ý500Ý000 Group 220

Unassigned ìMN-ss 220 ìMN-sgp ìMN-sh 20 Greenstone Terrane ñHAc-kdx 24 æåpa-sgpg 48 COLLIER BASIN 300 ìod C1 0 5 10 15 20 East Pilbara GraniteÊ ñFOk-bng 5 20 ñFOmk-bntt 260 A1ª C2 Pilbara Mafic and ultramafic 380 18 22 280 Manganese Group C1 320 27 R3´f æåpa-sgpg Supergroup ñPI-xmbs-mus schist ñFOkm-kts360 ðpj-ccx Bangemall Supergroup ìMN-sl 18 240 MESOPROTEROZOIC Kilometres 16 8 A1¤ 16 22 14 Rockhole Spring ñFOtm-kts ìMN-st ìod A1§c£ ìMN-sgp Interbedded poorly sorted granule and pebble polymictic conglomerate and coarse- to medium-grained lithic and quartz sandstone C1 A1¤ ñHAc-kds Unassigned 360 18 ñFOj-xcl-kd êod ìMN-sgp Noa-ktpl 5 ñFO-od 320 Shale, ferruginous shale, and manganiferous shale; local thinly interbedded siltstone and sandstone 10 ñFOm-bb 240 R3´f ìMN-sh Fault Fold axes 300 260 8 46 260 ñFO-od 280 Sinkhole C1 Rockhole ðpj-ccx Interbedded fine- to coarse-grained sandstone and siltstone; local micaceous siltstone ñHAc-kdx MOUNT C2f Noa-ktzl ìMN-ss For further details, refer to main reference

ñFOkm-kts 14 ñFOmk-bntt Bore ñFO-od IAN 240 17 10 A1¤ 300 15 æåpa-sgpg ìMN-ss 240 ñFOh-spa æåpa-sgpg Noa-ktzl 46

28 12 C3 A1¤ æåpa-sgpg 30 400 A1£ ðzq ðo 14 12 16 A1¤ 0 C1 65 280 ñFOtm-kts 240 24 R3´f 12 ñFOk-bng 27 R2k ñHAc-kdx ðpj-ccx ìMN-sl C1 C2f Noa-ktpl ñFOkm-kts ñFOti-bntt 5 ñFOm-bb 4 400 ðpj-ccx A1¤ 320 Bookabunna Well (abd) ìMN-sgp R3´f A2t A1§c£

12 ñFOt-bbg 26 ñHAc-kds Creek ðzq Quartz vein; various generations of uncertain age ñFOhb-frp ñHAc-kds C1 10 C1 260 RHDH2A C1 44 27 18 ñFOj-xcl-kd Noa-ktpl ðo Dolerite or gabbro dyke; various generations of uncertain age

14 Bores 40 ñHAc-kdx ðpj-ccx A1¤

300 ñFOh-scp C3 15 20 ìod 340 8

16 8 ìod A1¤ ñHAc-kds 280 E ñFOhb-frp 20 ñHAc-kdx Dam

320 R3´f PULGORAH CONE 44 PINJIAN CHERT BRECCIA: chert breccia and poorly bedded chert; overlies CARAWINE DOLOMITE 300 Bore ðpj-ccx ðo 320 10 300 ìod C1 ìMN-ss A1ª

400 æåpa-sgpg A2t æåpa-sgpg 268 m 260 ðpj-ccx 240

ðo 360 ñHAc-kds 5231 280 Noa-ktzl TN 14 ñFOj-xcl-kd Rockhole R3´f Ripon Hills Southeast ñHAc-kds C2f ñFOr-bbg 340 21 R3´f

ðo ñFOm-bb Yilgalong 17 Mn æåpa-sgpg 340 GN

ñHAc-kdx Rockholes 340 ñHAc-kdx 42 8 ñHAc-kdx R3´f ñFO-od C1 c. 2548 Ma ä CARAWINE DOLOMITE: massive- to well-bedded, recrystallized dolomite, and stromatolitic dolomite; minor chert ñFOkm-kts A1¤ R2k 25 ñHAc-kdx 300 ñHAc-kds 360 ñFOtm-kts 260 14 ñHAc-kds ñHAc-kdx C1 RHDH1 Noa-ktpl MN ñFO-od 14 20 ñHAc-kdx ñFOj-xcl-kd 52 ñHAc-kdx ìod ñHAc-kds 240

44 18

300 ñHAc-kdx20 C2 C3 15 C3 R3´f Noa-ktzl MINERAL OCCURRENCES 12 360 26 12 ñHAc-kdx A1ª C2f Rockhole 20 ñFOj-xcl-kd Noa-ktzl 42 8 8 15 ñFOj-xcl-kd 260 12 ñHAc-kdx Chaotic spherule-bearing megabreccia; angular, coarse- to fine-grained dolomite and chert clasts with a microkrystite- and microtectite-rich matrix ìRH-od 380 ñFOtm-kts 22 A1¤ R2k 18 40 C2f ñFOt-bbg ðpj-ccx 8 GRID / MAGNETIC A1¤ ñFOti-bntt ñFOj-xcl-kd ìMN-ss æåpa-sgpg Hamersley Group ñFOmk-bntt 60 5 MINERAL AND ROCK COMMODITY GROUPS ANGLE 1.4¾ ìRH-od 320 Bore 20 ñFOjb-bnth ñFOjb-bnth 5 C1 MINERALIZATION STYLESÝ* 260 12 4 340 ñHAc-kds Mount Ian Well (abd) 5232 360

8 18 A1§ W1 10

ñFOkm-kts 30 30 M C1 Bore (abd) 340 Ripon Hills South îì40 C3 29 16 A2t ñHAc-kdx Vein and hydrothermal Precious mineral ñFOkm-kts ñFOm-bb C1 Mn R1tpa C2f C1 GRID 6 25 20 Bore

ìRH-og ñFOm-bb W1 7 æåpa-sgpg oodie Woodie Road 12 km ñFO-od Dolerite dyke or sill CONVERGENCE 320 300 24 Stratabound sedimentary and/or A1¤ 30 ñFOj-xcl-kd 24 25 RIPON HILLS ROAD W Precious metal ñFOh-sfv 28 ñFOjb-bnth ñFOj-xcl-kd sedimentary banded iron-formation 0.8¾

ñFOh-scp C1 50 10 9 îì40 17677 280 13 7 10 ñFOk-xbb-bk ðzq ñFOmk-bntt ñFOjb-bnth Dam Noa-ktpl260 Steel industry metal 20' Meentheena copper 20 Mopoke Well (abd) 30 C3 ñFOm-bb R3´f C2f 20' åè Regolith hosted 18 12 8 ðzq ðzq 27 15 2690Ê2629 Ma JEERINAH FORMATION 8 10 ñFOj-xcl-kd Creek Cu C1 4 40 C3 Base metal 6 6 48 18 15 ñFOm-bb 14 ñFOtm-kts S 240 ñFOmk-bntt Well Baramine Member RIPON HILLS ROAD 10 18 æåpa-sgpg C2f ñFOjb-bnth ìRH-og ñFOt-bbg 35 48 68 26 280 A1¤ Basalt and basaltic andesite, and basaltic volcanic sandstone and siltstone; with local accretionary lapilli 38 30 ñFOh-sfv ñFOk-bng 320 R2k 48 38 ñFOhb-fr ñKEe-cc 300 MINERAL AND ROCK COMMODITIES 15 ñFOh-scp 300 ñFOti-bntt ìod ìod æåpa-sgpg Noa-ktpl 26 340 45 340 ñHAc-kds Noa-ktpl Spring ñFOhb-fr 8 ñFOkm-kts ðzq ðzq ñFOj-xcl-kd Shale, chert, and dolomite; decimetre- to metre-scale bedding; includes uncommon, small domical stromatolites in dolomite Copper...... 8 30 ñFOkm-kts 240 38 Cu 300 8 7 ìRH-od A1¤ ñFOm-bb True north, grid north and magnetic north 42 25 14 ñFOkm-kts 14 10 Diamond...... Dmd 30 ìRH-og 280 2718Ê2713 Ma ê ì MADDINA FORMATION are shown diagrammatically for the centre 5 10 C1 ñKEe-bb ñFOkm-kts 300 16 Gold...... Au of the map. Magnetic north is correct for A1¤ 320 Gingarrigan W1 C3 Noa-ktzl ñFOk-xbb-bk ìRH-od 26 C1 5 c. 2713 Ma ê ñFOmk-bntt Kuruna Member: basaltic to andesitic volcaniclastic rocks (common accretionary lapilli), sandstone, siltstone, shale, and local stromatolitic limestone ñFOmk-bntt Manganese...... 2004 and moves easterly by about 0.1^ in 400 Mishap Well (PD) 8 Mn 36 ñFOr-bbg 2 years. ñKEe-mh 50 ñFOk-xbb-bk ñFOtm-kts 10 C3 20 ñFOtm-kts 260 C1 40 ìRH-od ñFOkm-kts ñFOkm-kts A1¤ OPERATING STATUS AND SITE IDENTIFICATION NUMBER 260 8 320 ñFOti-bntt 13 ñFOm-bb Basalt; massive, fine grained, vesicular and doleritic; thick flows and/or sills, to thin flows; local very coarse gas cavities filled with quartz ñKEe-bk ìRH-od ìod 12 17 ñFOmk-bntt 36 4 12 300 C3 260 ñFOmk-bntt Mineral deposit Ý e.g. 5224 48 40 ñFOtm-kts Noa-ktpl 20 9 ñFOt-bbg ñFOm-bb 2719Ê2715 Ma å ê î 10 360 ñFOk-bng 20 TUMBIANA FORMATION A1¤ ñFOk-bng 300 Mineral occurrence or prospect e.g. 5231 340 Meentheena Member: lenticular units of stromatolitic, dark-grey siliceous limestone or dolomite within laterally variable sequences of volcaniclastic SHEET INDEX 0 ñFOr-bbg ñFOt-bbg 34 25 280 8 ñFOt-bbg ñFOtm-kts

30 M Spring sandstone and siltstone (accretionary lapilli), calcareous sandstone, shale, and basalt; local quartz sandstone and conglomerate Rockhole 54 Mineral occurrences and numbers are from the GSWA WAMIN database. R2k ñFOti-bntt 280 ñFOti-bntt COORAGOORA CARDOMA BULGAMULGARDY ABSOLON QUIN ANKETELL 34 Spring ñFOh-sfv ñFOh-spa 44 30 C1 *ÝLarger symbols represent mines or deposits also in the DoIR MINEDEX database. 2957 3057 3157 3257 3357 3457 ñFOh-scp 360ñKEe-bb ñFOti-bntt 8 C1 A1¤ Rockholes 8 ñFOm-bb YARRIE ANKETELL ñFOk-xbb-bk 16 24 ñFOt-bbg Vesicular, amygdaloidal, and massive basalt 14 10

ñKEe-mh C1 Dingo Well (PD) A1§ SF 51-1 SF 51-2 280 34 13 ñFOkm-kts ìod 280 MUCCAN WARRAWAGINE ISABELLA WEENOO CHAUNCY ANGOVE 17676 A1¤

ñFOkm-kts 5 ñFOk-bng basaltic to andesitic volcaniclastic sandstone and siltstone (common accretionary lapilli), and local quartz sandstone, shale, and 2956 3056 3156 3256 3356 3456 260 Mingah Member: ìRH-od 280 A1ª Creek 2727Ê2721 Ma ê ñFOti-bntt

Yilgalong IRW 6 18 ñFOh-sfv 10 A1£ A2k 260 thin lenticular stromatolitic carbonate units; locally thick basalt flows 14 ñFOk-xbb-bk ìod 380 NMF 625 Au ñFOh-scp 9 C1 Noa-ktpl ñKEe-bk 28 ìod ìod 280 467 m 22 A1¤ 2749Ê2735 Ma ê ð ò KYLENA FORMATION MOUNT EDGAR YILGALONG BRAESIDE WAUKARLYCARLY COOLYU CUTTACUTTA 32 28 20 340 C1 ðzq 50 40 ñFOkm-kts 280 Noa-ktzl 20 22 ñFOk-bng Massive, vesicular, and amygdaloidal basalt and basaltic andesite 2955 3055 3155 3255 3355 3455 20 11 300 Midgengadge Noa-ktpl NULLAGINE PATERSON RANGE A1¤ 17675 40 30 48 C1 ðzq 20 40 Z ìRH-od ñFOh-scp A2k ñFOkm-kts C3 HAMERSLEY BASIN SF 51-5 SF 51-6 ñFOh-sfv Yilgalong IRW 5 12 32 ìRH-od ìod 32 ðzq 30 ñEMel-mgtn 80 ñFOkm-kts ðo ñFOk-bng NULLAGINE EASTERN CREEK PEARANA LAMIL PATERSON TERRINGA ñKEe-cc 300 Au ñFOti-bntt ðpj-ccx C1 grey carbonate rock; discontinuous, silicified microbial laminations and stromatolites; minor shale, siltstone, and sandstone C1 38 Z 15 ñCE-gmm ñFOkm-kts Mopoke Member: 2954 3054 3154 3254 3354 3454 46 ñKEe-xmbks-mbs A1¤ ñEMel-jmgtn-mw A1¤ ñFOk-bng 20 320 C1 ñFOk-xbb-bk 18 C1 12 440 280 R3´f ñKEe-cc 10 Mount Bruce Supergroup 1:100Ý000 maps shown in black A 16 ñFOkm-kts A1¤ Massive, porphyritic, and amygdaloidal andesite, basaltic andesite, volcaniclastic conglomerate, sandstone, siltstone, and shale; îì30 ðzq ðzq 30 A1¤ ñFOmk-bntt 15 2749Ê2735 Ma ð ò ñFOk-xfa-spv 400 Spring accretionary lapilli and felsic tuff 1:250Ý000 maps shown in brown 22 ðzq ìRH-od Yilgalong 20 ñFOj-xcl-kd 10 40 6

40 Fortescue Group 14 Well (abd) ìod ðzq 42

ñFOh-scp 49 ðzq 30 ìod 14 17679

ðzq ðzq 340 16 îì30 ðo 20 240 ðzq ðo C1 C1 280 Midgengadge Creek S ñFOk-xbb-bk Massive and amygdaloidal tholeiitic basalt and komatiitic basalt; local pillow basalt

300 14 A2k DATA DIRECTORY

11 20 340 Mn 10 10 ñKEe-cc Bullyarrie Well (abd) 320 340 5 ñFOr-bbg ñFOh-sfv ñFOm-bb 28

ñFOh-spa 28 ñFOh-sfv 300 ñFOmk-bntt æåpa-sgpg Theme Data Source Data Currency Agency 340 300 400 280 Noa-ktpl 17674 ðzq ñFOk-xbb-bk ðzq 4 32 20 ñFO-od 15 HARDEY FORMATION ðzq ñEMel-mgtn 22 20 R1tpa 28 ñFOh-sg 70 360 20 360 Geology GSWA 2002_2003 Dept of Industry and Resources

Salvation ðzq ñFOk-bng 10 c. 2752 Ma ê ñFOh-sfv Sandstone, siltstone, and shale; felsic volcanic clasts; local pebbly sandstone, conglomerate, and thin carbonate units

360 360 48 10 ðpj-ccx PILBARA CRATON Well NW ñKEe-cc ðzq 15 14 30 260 ñFOhb-fr 32 169262 ðzq 25 20 Structural data WAROX AUG 2004 Dept of Industry and Resources Au 62 ðzq 169260

20 8 ðo Creek æåpa-sgpg 28 320 C1 10 Salvation Well (abd) ðzq 169261 10 ñHAc-kds

42 20 ñEMel-mgtn 280 Feldspathic sandstone, pebbly sandstone, and conglomerate; minor fine-grained sandstone and siltstone ñFOkm-kts 13 34 340 E ñFOh-spa Mineral occurrences MINDEX* JUN 2005 Dept of Industry and Resources 70 34 14 300 ðo ðo ñFOk-bng 20 34 ìod ñFOti-bntt 300 R3´f (non-confidential) ðzq ðzq ñFOhb-frp 8 340 C3 A1ª WAMIN* JUN 2005 Dept of Industry and Resources 24 50 ðzq 30 A1¤ ñFOk-xbb-bk 22 ñFOk-bng 35 ñFOk-xbb-bk ðzq ðzq 40 240 N.T.

320 ðo ARCHAEAN C1 20 ñFOkm-kts ñFOh-sg Conglomerate and sandstone; local minor wacke and siltstone

26 28 Cadastre TENGRAPH APR 2004 Dept of Industry and Resources 340 340 ìRH-od 320 ñCE-gtl Qld A1¤ 320 B ðzq ñFOhb-frp ðzq ñFOk-xfa-spv Horizontal control GESMAR AUG 2004 Dept of Land Information 70 ðzq A1¤ W.A.

ðzq 340 ñEMel-mgtn 26 280

300 æåpa-sgpg

A1¤ ìod 15 280 Topographic nomenclature GEONOMA 2004 Dept of Land Information ðo 22 ìod 320 20 ñFOkm-kts ìRH-od 62 ñFOhb-fr S.A. ðzq ðzq ðo ñFOk-xbb-bk ñFOk-xfa-spv ñFOhb-frp

ñKEe-ml ðzq 178090 Rockhole C1 A1¤ Topography DLI and GSWA field survey 2004 Dept of Land Information ðzq 10 320 320 ðzq 44 17673 ðzq ñFOkm-kts ñFOk-bng 5 A1ª 20 ñFOk-xfa-spv N.S.W. Elsie Creek diggings ðzq C1 Noa-ktpl c. 2766 Ma âô ñFOhb-fr Bamboo Creek Member: rhyolite, rhyodacite, and dacite in flows and subvolcanic intrusions; alkali-feldspar and quartz phenocrysts; volcanic breccia, C1 320 48 C1 65 ðzq * GSWA and DOIR databases can be viewed online (www.doir.wa.gov.au/aboutus/geoview launch.asp) or can be downloaded from 24 Au ðzq ðzq ñFOh-scp ðo 5 ñPI-mc 60 Rockhole A.C.T. ñFOh-scp 60 ðzq 60 welded ignimbrite, and accretionary lapilli; resedimented pyroclastic deposits GSWA Data and Software Centre (www.doir.wa.gov.au/GSWA/downloadcentre) 65 ðzq ðo ñFOkm-kts R1gp¨ ðo 55 2766Ê2760 Ma âô ñFOhb-frp Porphyritic dacite, rhyodacite, and rhyolite; coarse- to fine-grained alkali-feldspar and quartz phenocrysts; locally as dykes Vic. 22 ðzq ðzq C3 340 50 ðzq 178086 17672 169263 ðo 15 ñEMel-mgtn ñFOk-xbb-bk C1 300 C3 0 ñPI-xmbs-mus 240 24

300 60 32 ñFOkm-kts 60 ðzq ñFOr-bbg Elsie Creek 2 ñFOh-scp ñFOkm-kts ðzq ñEMel-mgtn HARDEY FORMATION

30 320 A1¤ ñFOkm-kts 6 Creek 340 ñFOkm-kts ðzq Au 300 10 178089 A1§c£ Tas. ñFOr-scp ñKEe-cc 60 320 ðzq ñFOkm-kts C1 ñFOk-xbb-bk ñFOh-scp Polymictic, matrix-supported cobble to boulder conglomerate, sandstone, siltstone, and local wacke ðzq ñCE-gmm C1 320 ñFOm-bb 15 A1¤ A1¤ ñFOk-bng ðzq ñFOk-xbb-bk 320 30 80 Creek ðo ðzq ìRH-od 12 ñFOkm-kts Elsie Well (PD) ñFOkm-kts 20 River ðo Rockhole Elsie C1 ðzq Creek 16 340 ðzq Creek ñFOkm-kts îì22ôôôÜN ñFOk-bng ñEMel-mgtn ìod ìRH-od Boodalyerri

80 A1£ Creek A1¤ Well (abd) ðzq 340 ñFOk-xfa-spv

15 ðzq ñFOk-xbb-bk Little 28 ñFOk-xfa-spv 340 A1£ 360 ðo A1§ ñFOr-bbg ñFOr-scp ñFOk-bng 75 320 ñKEe-bk C1 20 ñFOkm-kts 10 340 45 280 22

17671 40 144682 ðzq ñEMel-mgtn ìRH-od Little ñFOkm-kts ñFOk-bng 380 24 300 C2 40 48 Yilgalong ðo ñFOkm-kts Elsie Creek 3 45 20 ñKEe-ml C2 Noa-ktpl MOUNT ROE BASALT Au ñFOk-xbb-bk ñFOk-bng 21^30' 21^30' c. 2772 Ma ââ ñFOr-bbg Massive, porphyritic, vesicular, and amygdaloidal basalt; some pillow basalt G IC A L S ä42ôôôÜE 44 46 48 ä50 52 54 56 58 ä60 62 64 66 68 ä70 72 74 76 78 ä80 82 84 86 88 ä90 92 O U R L V ñFOr-scp Polymictic pebble conglomerate; includes sandstone, siltstone, and shale O E

E Y

Department of Geological Survey of G

W A E I Industry and Resources Western Australia S L T A R 120^30' 40' 50' 121^00' E R T ñCE-gmm ñCE-gtl N A U S

ALAN CARPENTER, M.L.A. JIM LIMERICK TIM GRIFFIN c. 3275 Ma ò ñCE-gmm Biotite monzogranite; seriate to porphyritic; medium to coarse grained MINISTER FOR STATE DEVELOPMENT DIRECTOR GENERAL DIRECTOR

Cleland Supersuite ñCE-gtl Quartz_biotite trondjhemite and tonalite; leucocratic, massive, fine to medium grained Compiled by I. R. Williams 2003Ê2004 Geology by I. R. Williams 2002Ê2003 ñEMel-mgtn ñEMel-jmgtn-mw Geochronology by: SCALE 1:100Ý000 (1) B. Rasmussen and I. R. Fletcher, 2004, Geology, v. 32, p. 785Ê788. 3299Ê3290 Ma âä âô ñEMel-mgtn ELSIE CREEK TONALITE: foliated to gneissic biotite tonalite and granodiorite; minor monzogranite (2) J. D. Woodhead et al., 1998, Geology, v. 26, p. 47Ê50. 1000 0 1 2 34 5678910 ñEMel-jmgtn-mw Gneissic tonalite with numerous mafic and ultramafic xenoliths; metamorphosed (3) N. T. Arndt et al., 1991, Australian Journal of Earth Sciences, v. 38, p. 261Ê281. Emu Pool Supersuite Metres DIAGRAMMATIC SECTION (4) D. R. Nelson et al., 1999, Precambrian Research, v. 97, p. 165Ê189. UNIVERSAL TRANSVERSE MERCATOR PROJECTION Kilometres A ñFOk-xbb-bk B Mishap Well (PD) RIPON HILLS ROAD Bunmardie Creek C (5) T. S. Blake et al., 2004, Precambrian Research, v. 133, p. 143Ê173. HORIZONTAL DATUM: GEOCENTRIC DATUM OF AUSTRALIA 1994 ñFOh-sfv ñFOk-xbb-bk ñFOkm-kts ñHAc-kds ðpj-ccx ñHAc-kdx ðpj-ccx êod ìMN-sl êod ðpj-ccx æåpa-sgpg ðpj-ccx ñKEe-xmbks-mbs ñKEe-mh ñKEe-ml ñKEe-bb ñKEe-bk ñKEe-cc (6) D. R. Nelson, 1998, GSWA geochronology dataset, GSWA 144993. VERTICAL DATUM: AUSTRALIAN HEIGHT DATUM ñFOh-sg ñFOtm-kts ñFO-od ñFOm-bb ìMN-ss ðpj-ccx æåpa-sgpg ðpj-ccx SEA LEVEL ðzq æåpa-sgpg SEA LEVEL (7) D. R. Nelson, 2001, GSWA geochronology dataset, GSWA 168935. Grid lines indicate 1000 metre interval of the Map Grid Australia Zone 51 ðzq ñFOk-bng ñFOmk-bntt ñHAc-kds ñFOhb-fr ðzq ñFOh-scp ñFOkm-kts ñFOj-xcl-kd ñHAc-kds ñHAc-kdx ñHAc-kds ñHAc-kdx ñHAc-kds c. 3350 Ma âô EURO BASALT (8) D. R. Nelson, et al., in prep., GSWA geochronology dataset, GSWA 178086. ðzq ñFOh-sfv ñFOt-bbg ñFOj-xcl-kd ñFO-od ñFOh-spa ðzq ñKEe-xmbks-mbs Mafic schist after komatiitic basalt and tholeiitic basalt (9) S. Bodorkos et al., in prep., GSWA geochronology dataset, GSWA 178090, 178089. The Map Grid Australia (MGA) is based on the Geocentric Datum of Australia 1994 (GDA94) ñFOkm-kts (10) D. R. Nelson, in prep., GSWA geochronology dataset, GSWA 169037, 169033, ñFOh-scp ñFOr-bbg ñFOk-xbb-bk ñFOti-bntt ñFOj-xcl-kd ñFO-od ñFOm-bb ñKEe-mh Psammopelitic schist; variably ferruginized GDA94 positions are compatible within one metre of the datum WGS84 positions ñFOm-bb Kelly Group 169043, 169260, 169261, 169262, 169263, 178042. ñFOkm-kts East Pilbara GraniteÊGreenstone Terrane GEOCENTRIC DATUM OF AUSTRALIA ñFO-od ñFO-od ñKEe-ml Pelite, locally with metachert ñFOh-scp ìod ñFOmk-bntt ñFOmk-bntt ñFOm-bb (11) M. T. D. Wingate, 1999, Australian Journal of Earth Sciences, v. 46, p. 493Ê500. ìRH-od ñFOtm-kts ñKEe-bb Basalt, generally pillowed; minor massive dolerite, gabbro, and komatiitic basalt; metamorphosed Reference points to align maps based on the previous datum, AGD84, have been placed near the map corners ñFOk-xbb-bk ñFOtm-kts (12) D. R. Nelson, 2004., GSWA geochronology dataset, GSWA 144682. ñKEe-bk Komatiitic basalt; generally pillowed; metamorphosed 2 km ìRH-od ìRH-od ñFOkm-kts 2 km ñFOt-bbg ñFOti-bntt ñKEe-cc Chert; generally white, grey, and blue-black layered; locally massive blue-grey; weakly metamorphosed ñEMel-mgtn Edited by C. Strong and G. Loan ñKEe-bk ñEMel-mgtn ñFOti-bntt Pilbara Supergroup ñFOk-bng ñFO-od Cartography by D. Ladbrook and K. Greenberg ñKEe-cc ñFOh-scp ñFOk-bng êod ñFOkm-kts ñPI-mc ñPI-xmbs-mus Published by the Geological Survey of Western Australia. Digital and hard copies of this ñCE-gmm ñFOkm-kts ñFOkm-kts ñEMel-mgtn ñFOkm-kts map are available from the Information Centre, Department of Industry and Resources, ñFOkm-kts ñFOk-xbb-bk 100 Plain Street, East Perth, WA, 6004. Phone (08) 9222 3459, Fax (08) 9222 3444

ñFOk-xbb-bk Unassigned ñPI-mc Metachert, coarsely recrystallized ñKEe-xmbks-mbs ñPI-xb-s ñPI-xb-s ñgPEP WebÝ www.doir.wa.gov.au EmailÝ [email protected] SHEET 3055 FIRST EDITION 2005 4 km 4 km ñPI-xmbs-mus Mafic and ultramafic schist; amphibolite-facies metamorphism The recommended reference for this map is: Version 1.0 _ June 2005 ñgPEP Granitic rock, East Pilbara GraniteÊGreenstone Terrane ñPI-xb-s Unassigned Pilbara Supergroup greenstones Relative movement on fault; movement towards viewer movement away from viewer WILLIAMS, I. R., 2005, Yilgalong, W.A. Sheet 3055: Western Australia Geological Survey, 1:100Ý000 Geological Series. ¦ Western Australia 2005