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 TARGETINGCriteria 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 Sub-Continental 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

Komatiite

TTG volcaniclastic (Black Flag)

Bimodal (Teutonic)

Coarse clastic

High-Ca Granite

Thol. Basalt +/- UM volcanism

dolerite

2640

Ni VMS Au

Low-Ca Granite

Mafic Granite

D2De De

Laverton Geochronology

2720 2700 2680 2660 26402820 2800 2780 2760 2740

Thol. Basalt +/- UM volcanismThol. Basalt +/- UM volcanism

Calc-alk andesiteCalc-alk andesite

Komatiite/Thol. BasaltKomatiite/Thol. Basalt

VolcaniclasticVolcaniclastic

Low-Ca GraniteLow-Ca Granite

SyeniteSyenite

Au

ADMIRALHILL

ADMIRALHILL

Mafic GraniteMafic Granite

Ni

WINDARRAWINDARRA

Ni

AGNEWAGNEW

Coarse clasticCoarse clastic

High-Ca GraniteHigh-Ca Granite

AuGRANNY SMITH, SUNRISE, WALLABY

OROGENIC GOLD TARGETINGCriteria 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 CLMModerate 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 sourceReduced sediments are a good host rockHigh deposit preservation potential

Graham Begg, 2011

OROGENIC GOLD TARGETINGCriteria 3

Late basin develops after first collisional event

Basin inversion during second compressive deformationcreates 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

SEISMIC CROSS SECTION KALGOORLIE 100moz REGIONAL

0

5

10

7200 9200 11200 13200 15200 17200CDP

Two-

way

tim

e (s

)

KALGOORLIE TERRANEGINDALBIETERRANE

KURNALPITERRANE

0 10 km

15

20V/H = 1 (approx) for a Velocity of 6.0km/s

MID CRUSTANOMALY

10km

10

5

Dep

th (k

m)

VH

=1

IDAFAULT

BullabullingShear

KunanallingShear

DunnsvilleAnticline

ZuleikaShear

KurrawangSyncline Mt Pleasant

Anticline

BARDOCDeformation

Zone

Scotia-KanownaAnticline Mt Monger

FaultEmuFault Arcoona Granite

Avoca Fault{does not outcrop in this

section because it is intrudedby the Arcoona Granites}

KURNALPITERRANE

GINDALBIETERRANEKALGOORLIE TERRANE

Basal detachment ?

Upper basalt

Lower basalt

Undivided basalt

Komatiite

Early granite

Late granite

Felsic gneiss

Basal felsic schist

Felsic volcanic rocks

Felsic volcanic unit

Greenstone sequence(in Bardoc Shear Zone)

OROGENIC GOLD TARGETINGCriteria 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

Lunnon Basalt

Tripod Hill Komatiite

Devon Consols BasaltDefiance Dolerite

Paringa Basalt

Paringa Basalt

Lower Felsic Complex

Porphyry Complex

Kapai Slate

Interpretation of Seismic Section

KD3011 607m, 1.23g/t

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

Anhydrite vein

Disseminatedpyrite

3D Model of the Beta Porphyry1billion tonnesmean 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, etcAll gold-rich porphyries have the same enriched trace element signature!!!

FI 7, Beta Porphyry

Interplay of fluids-architectureRevenge through

Victory-Defiance

AfterNed Stolz &

Janet Tunjicja

Conqueror Fault

Delta Fault

Playa Fault

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

Sons of Gwalia, 10m oz

Tarmoola, 2m oz

Thunderbox, 2m ozAgnew, 5m oz

Darlot, 4m 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