VHMS mineralization in the Yilgarn Craton: greenstone prospectivity & new results from the Eastern Goldfields

DISCOVERY THEME, MINERALS DOWN UNDER FLAGSHIP

S.P. Hollis, C.J. Yeats, S. Wyche, S.J. Barnes, T.J. Ivanic, P. Gillespie, D. Mole, A. Pumphrey, A. Verbeeten, S. Tessalina, S.M. Belford & D. Podmore

27th Feb. 2015 l GSWA Open Day, Esplanade Hotel, Fremantle

Nimbus Ag-Zn deposit: stringer pyrite and sphalerite in coherent dacite Jaguar Cu-Zn deposit: main lode (image from Jabiru/IGO)

Talk Outline • VHMS mineralization in the Yilgarn Craton • Timing and common associations in the Youanmi Terrane & Eastern Goldfields • Unconventional VHMS e.g. Nimbus

Hollandaire: Supergene chalcocite

Nimbus: high-grade massive sulfides

MACPHERSONS RESOURCES 2012

SILVER LAKE RESOURCES 2012

DISCOVERY THEME, MINERALS DOWN UNDER FLAGSHIP

Archaean Yilgarn Craton, WA Major metallogenic province: world class Au, Fe and Ni mineralization Big drive to look for VHMS mineralization in 1970s due to the discovery of world class Kidd Creek deposit in Canada One substantial find made at Gossan Hill in 1971 (15.9 Mt @ 2.6% Cu, 1.5% Zn, 21g/t Ag, 0.6g/t Au) Smaller, higher grade Teutonic Bore discovered in 1976 (produced: 1.68 Mt @ 10.7% Zn, 3.5% Cu, 140g/t Ag)

By 1980s a lack of success and increasing Au prices led to VHMS mineralization falling off the WA exploration agenda for ~25 years

Mineralization in Yilgarn Craton

Recent interest due to new discoveries and an increased understanding of: • Appropriate geophysical techniques • Regolith processes • Yilgarn groundwaters • Lithogeochemical alteration vectors (+hyperspectral) • Favourable host sequences

Timing: Youanmi

2725 Ma Gum Creek GB (The Cup, Bevan, Blind Bat) 2760-2745 Ma Greensleeves Fm (Hollandaire, Mt. Mulcahy, Chesterfield, Dalgaranga) 2818-2813 Ma Yaloginda Fm & Kantie Murdana (Windimurra, Quinns, Just Desserts) 2.93-2.97 Ga Golden Grove, Ravensthorpe, Weld Range, Tallering, Twin Peaks

Hollis et al. (2015) stratigraphy from Van Kranendonk et al. (2013)

Episodic extension in the Cue Zone • 3.0 Ga: early extension and

extraction of Cue zone crust from mantle (Mole et al. 2015).

• Linear belts of ca. 2.97-2.93 Ga bimodal volcanics (e.g. Golden Grove, Weld Range, Mt. Gibson)

• 2815 Ma: Large mafic-ultramafic intrusions emplaced into pre-existing rift zone (e.g. Ivanic et al. 2010) - Plume?

• Localized areas of extension during ca. 2750 Ma Greensleeves Formation (e.g. Chesterfield, Hollandaire, Dalgaranga)

• ca. 2.72 Ga Yalgowra Suite during Glen Group - coeval with EGS plume event

(stars=base metal occurrences) COLD colours = juvenille crust HOT colours = evolved crust

Modified after: Champion & Cassidy (2002))

Huston et al. (2014))

Hollis et al. (2015) VHMS review – Precamb Res.

Felsic rocks: after Campbell, Lesher, Piercey & Hart VHMS related •FW Gossan Hill/Scuddles •Jaguar •Teutonic Bore •Hollandaire •Quinns/Austin •‘ca.2815 Kantie Murdana suite’ (e.g. Youanmi) •SE Gum Creek GB •Glenview (Weld Range) •Dalgaranga GB

Other (prospective?) •Abbotts •Jillewarra/Chesterfield •Emily Well •Bore Well •Melita •Mount Gill (Yamarna)

Discriminating ‘fertile’ signatures

Hollis et al. (2015)

Ratios: Zr/Y, La/Yb, Th/Yb, Sc/V etc. Precious metal rich VHMS (e.g. Eskay Creek, Canada) form in distinct tectonic setting Cu-Zn deposits -Shallower waters, thicker crust -Significantly higher Zr/Y, La/Yb & Th/Yb and lower Sc/V

Th/Yb Hot colours – extensive crustal recycling

Cold colours – tholeiitic & VHMS

Zr/Y (left) & Sc/V (right) Hot colours – deep melting, calc-alkaline & barren Cold colours – shallow melting, tholeiitic & VHMS

Geochemical maps for felsic rocks and granites - simple kriging method, arcGIS Data sources in Hollis et al. (2015), plus GSWA granite database (inc. AMIRA, UWA).

2 episodes of VHMS: • 2690-2680 Ma - Teutonic Bore-Jaguar-Bentley - Erayinia (2680 Ma?) - Jungle Pool (2680 Ma?) - Melita/Bore Well? • 2705-2700 Ma - Anaconda (2698 ± 5 Ma) assoc. between felsic rocks &

komatiitic flows - Ni sulfides (=S isotopes)

Timing in the (western) Eastern Goldfields

Modified after Czarnota et al. (2010)

Kurnalpi zone • VHMS potential revealed through Nd &

Pb isotopes (Huston et al. 2014) & geochemistry

– Juvenile lead (low μ) and younger ɛNdt (Huston et al. 2014)

– HFSE & FIII affinity felsic rocks (i.e. shallow melting and elevated crustal heat flux)

• Nimbus – Margin of Kurnalpi rift zone – Unknown age (Black Flag or 2.71 Ga plume?)

COLD colours = juvenille crust HOT colours = evolved crust

Modified after: Huston et al. (2014)

Nimbus Ag-Zn-(Au) deposit: unconventional VHMS

• 17km ESE of Kalgoorlie • RAB 1995 • Oxide and supergene zones:

– 0.319 Mt mined at 352g/t Ag between 2004-2006 by Polymetals

• 3.6 Moz Ag and 6.5t Hg

• Primary sulfide zone: – Reserve 1.1Mt @ 297g/t Ag-eq – Resource 4.88 Mt @149 g/t Ag-eq

• 79 g/t Ag • 1.3% Zn • 0.29 g/t Au

DISCOVERY PIT EAST PIT

DISCOVERY PIT

EAST PIT

Ag Zn

Local geology HW: • Lithic tuff & volcanic breccia • Polymict conglomerate (dacite

+ mudstone fragments in similar matrix)

• Carbonaceous mudstones Host/FW: • Coherent quartz-feldspar

phyric dacite dominates stratigraphy with assoc. autoclastic facies

Basalt (at least three units) –

invasive flows/shallow sills

Primary sulfides • Lenses of well developed

massive pyrite (replacing glassy dacitic rocks)

• Underlying high grade Ag-Pb-Zn-(Cu-Au) assoc. with autoclastic facies

• Stringer sulfides in coherent dacite at depth

• Unique mineral assemblage: – Pyrite, high & low Fe sphalerite,

galena, arsenopyrite, chalcopyrite – Pyrargyrite [Ag3SbS3] – Marrite [AgPbAsS3] – Boulangerite [Pb5Sb4S11] – Ag-tetrahedrite – Bournonite [PbCuSbS3] – Cinnabar [HgS] – Electrum – Native silver – Amalgam [Ag,Hg] – Jalpaite [(Ag,Cu)2S]

Hydrothermal alteration

Mafic hyaloclastite

Coherent mafic

Nimbus geochemistry on Box Plot of Large et al. (2001)

Intense silicification

Silica-sericite-carbonate

Quartz-chlorite veining

Cr-V mica (fuchsite?) psudobreccia

Felsic rocks: • Indicative of deep melting &

reduced crustal heat flux • Distinct to all other VHMS Mafic rocks: • Distinct to younger VHMS:

• calc-alkaline FW • BABB HW

• Low Th tholeiite suite of Barnes et al. (2012)

• Geochemically resemble Lunnon basalt

Petrochemistry

Jaguar data from Belford et al. (2015, in prep)

• Subseafloor, replacive – Fluids focussed along lithological boundaries e.g.

mafic/dacite contacts, autoclastic facies – Abundant thin stacked lenses – System sealed by thick sequences of carbonaceous

sediments & early massive pyrite

• Low temperature – Hg-Ag rich fluids – Lack of significant Cu-Au – Little chlorite (late veins) & low Mg gains

• Shallow water depth (500m-1000m?) – No pillows/vesicles & autoclastic facies – Boiling fluids/ lower temperature mineralization – Significant Zn (i.e. >500m) – Pulsing debris flows from subaerial or shoreline

(emergent dacite dome) into anoxic basin

• Intermediate sulfidation – Pyrite, tetrahedrite (some chalcopyrite)

• Age? – SHRIMP & Re-Os geochronology

Nimbus model

Trofimovs et al. (2006)

Conclusions • Recent work on the timing, setting and style of VHMS mineralization in the Yilgarn Craton has emphasized the importance of reactivated linear zones, which provide strong controls on the focus of mineralization.

• There is significant room for new discoveries across the craton

• A broad exploration perspective is required for the discovery of different styles of VHMS particularly regarding alteration & fertility (Au and Ag rich VHMS)

Hollandaire: Supergene chalcocite

Nimbus: high-grade massive sulfides

MACPHERSONS RESOURCES 2012

SILVER LAKE RESOURCES 2012

DISCOVERY THEME, MINERALS DOWN UNDER FLAGSHIP

Steve Hollis Postdoctoral Fellow t +61 8 6436 8668 e steven.hollis@csiro.au

DISCOVERY THEME, MINERALS DOWN UNDER FLAGSHIP / CESRE

Thank you

Jaguar stringer stockwork (image from Jabiru/IGO)