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OROGENIC GOLD TARGETING What is important and why? Using the five questions approach This approach identifies the processes that form the gold deposit (it does not describe the deposit) across the full range of scales

OROGENIC GOLD TARGETING Criteria 1 Fractionated basalt sequence often hosting nickel sulphide deposits in a back arc basin setting Basalts are derived from magma crystallising magnetite in the source region Fractionation of magnetite adds oxygen (O) to the SubContinental Lithospheric Mantle (SCLM)

This event can pre-date the gold event by tens to hundreds of millions of years

Kalgoorlie Geochronology 2720

2700

2680

2660

2640

Thol. Basalt +/- UM volcanism Komatiite

TTG volcaniclastic (Black Flag) Bimodal (Teutonic) dolerite

Coarse clastic

High-Ca Granite

Low-Ca Granite

Mafic Granite

De

De Ni

D2 VMS

Au

Laverton Geochronology 2820

2800

2780

2760

2740

2720

2700

2680

2660

2640

Thol. Basalt +/- UM volcanism Calc-alk andesite Komatiite/Thol. Basalt Volcaniclastic Coarse clastic High-Ca Granite

Low-Ca Granite

Mafic Granite

Ni

Au

WINDARRA

ADMIRAL HILL

Syenite

Ni AGNEW

Au GRANNY SMITH, SUNRISE, WALLABY

OROGENIC GOLD TARGETING Criteria 2 Boundaries of cratonic blocks are faults that extend to crust mantle boundary Large scale continental collision Subduction adds water (H2O) back into the SCLM that was lost during mafic magma extraction

S-O-H2O are necessary pre-cursors to create thiosulphate complexes that will carry gold from the mantle

Backarc/Peri-cratonic: VMS & CD base metal, Ni sulphide

VMS Base Metal: Melting of metasomatised CLM (metal source) Most favored if spreading ridge migrates into CLM Moderate preservation potential if peri-cratonic basin narrow

Graham Begg, 2011

Back-arc/Peri-cratonic : Orogenic Au

Orogenic Au: Flanked by metasomatised CLM (metal source) Closure and suturing leads to selective melting of source Reduced sediments are a good host rock High deposit preservation potential

Graham Begg, 2011

OROGENIC GOLD TARGETING Criteria 3 Late basin develops after first collisional event Basin inversion during second compressive deformation creates large scale anticline in the hanging wall of mantle tapping fault Source of reductant CH4 (methane) is black shale within the late basins and methane drives gold deposition by destabilising the thiosulphate complex

REGIONAL

SEISMIC CROSS SECTION KALGOORLIE 100moz GINDALBIE TERRANE

KALGOORLIE TERRANE Kunanalling Shear

Bullabulling Dunnsville Shear Anticline

Avoca Fault Scotia-Kanowna Anticline

Mt Monger Fault

Emu Fault

{does not outcrop in this section because it is intruded by the Arcoona Granites}

Arcoona Granite

5 Basal detachment ?

10 V =1 H

10km

Upper basalt

Undivided basalt

Early granite

Felsic gneiss

Felsic volcanic rocks

Lower basalt

Komatiite

Late granite

Basal felsic schist

Felsic volcanic unit

CDP

7200 0

9200

11200

13200

Greenstone sequence (in Bardoc Shear Zone)

GINDALBIE TERRANE

KALGOORLIE TERRANE

15200

KURNALPI TERRANE

17200

5

Two-way time (s)

Depth (km)

IDA FAULT

Kurrawang Syncline Mt Pleasant BARDOC Zuleika Anticline Deformation Zone Shear

KURNALPI TERRANE

10

15 0 20

10 km

MID CRUST ANOMALY V/H = 1 (approx) for a Velocity of 6.0km/s

OROGENIC GOLD TARGETING Criteria 4 Mafic granites are High Calcium suite granites that have a mantle component added to the magma chamber at the base of the crust

Granites are emplaced along mantle tapping faults to high crustal levels (basement cover sequence boundaries) and are emplaced into large anticlines These granites carry gold rich fluids from base of the crust to upper crustal levels then exsolve fluids at fluid saturation at lower pressure

Non-reflective zone; intrusive complex that produces the gravity-low.

Seismic section courtesy of Ned Stolz, Gold Fields, St Ives

Interpretation of Seismic Section

Paringa Basalt

Paringa Basalt

Porphyry Complex

Tripod Hill Komatiite

Lunnon Basalt

Lower Felsic Complex

KD3011 607m, 1.23g/t

Anhydrite vein

Disseminated pyrite

Significant Au and pyrite content in porphyries that are not notably altered; => Fluid is in equilibrium with the porphyry. Some of the St Ives porphyries are inherently enriched in Au and S

3D Model of the Beta Porphyry 1billion tonnes mean gold grade = 0.37g/t ~ 12 million ounces

Footwall porphyries commonly have 100mt to 1,000mt of porphyry @ 0.05 to 0.5 g/t Au, e.g. Victory, Revenge, New Celebration, Binduli, Mt Pleasant, Kundana, Granny Smith, Lancefield, Mt Morgans, Agnew, etc

All gold-rich porphyries have the same enriched trace element signature!!!

FI 7, Beta Porphyry

Interplay of fluids-architecture Revenge through Victory-Defiance After Ned Stolz & Janet Tunjicja

OROGENIC GOLD TARGETING Next Steps Testing of regional targets with multi-element geochemistry at low density (1 sample per 16 km2) will identify mineralised systems

Darlot, 4m oz Agnew, 5m oz

Thunderbox, 2m oz

Sons of Gwalia, 10m oz Tarmoola, 2m oz

Scale 330km by 150km 3000 samples

OROGENIC GOLD TARGETING Mineral systems have characteristic spacing of gold deposits within the system Archaean gold systems in the Yilgarn are defined by 60km by 60km boxes within which deposits are spaced at 30km The crust is 30km thick at Kalgoorlie and Laverton

The gold systems are spaced at 130km

OROGENIC GOLD TARGETING What is important and why? Using the five questions approach

OROGENIC GOLD TARGETING