geology of the etoqui zn au skarn district

Geology of the El Toqui Zn‐Au Skarn district Aysen Region Chiledistrict, Aysen Region, Chile

Steven Bussey – Western Mining Services

Alejandro Kakarieka – IAMGOLD Corporation

Larry Meinert – Smith College

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Geology of the El Toqui Zn‐Au Skarn district

• Introduction

• Regional Geologic Setting

•District Geology

• Porvenir and Aserradero Orebodies

• Zonation

•GeochronologyGeochronology

• Summary

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Introduction ‐ Location

1300 km south of Santiago in the AysenRegion of southern Chile, South America

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Introduction – Exploration History1970 Discovery1970 Discovery1974 Metallgesellschaft AG1983 El Toqui Start‐Up1987 Lac Minerals1991 Doña Rosa orebody discovery1994 B i k1994 Barrick1997 Breakwater Resources2001 Aserradero Gold Skarn discoveryy2006 Porvenir discovery2007 Mina Profunda Gold Skarn discovery

Regional Geologic Setting 

Somuncura (North Patagonia) massif

Carboniferous suture

Deseado massif

Carboniferous suture(Pankhurst et al. 2006)

Rio Mayo embayment

Patagonia BatholithChon Aike volcanic province

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District Geology ‐ Stratigraphy

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District Geology – Host Rock Sequence

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District Geology – Main Manto limestone

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District Geology – Geologic Map

1 Z ñi A t li

Orebody, projected to surface

1 Zuñiga-Antolin 2 Concordia 3 Mallines 4 Estatuas 5 San Antonio6 M lli M i 6 Mallin-Monica 7 Doña Rosa 8 Mina Profunda 9 Aserradero10 Porvenir

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District Geology – Main Manto Alteration

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Porvenir and Aserradero ‐ Geology

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Porvenir and Aserradero ‐ Geology

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Porvenir and Aserradero ‐ Alteration

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3 cm

14blue-green pyroxene red-brown garnet

153 cm

Sphalerite Arsenopyrite

PDT‐66‐334m

16Pyroxene

Porvenir and Aserradero ‐ Alteration

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Porvenir and Aserradero ‐ Zn

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3 cm

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307.10m

amphibole > pyroxeneamphibole > pyroxeneamphibole > pyroxeneamphibole > pyroxene

pyroxene > amphibole pyroxene > amphibole

Shells replacedShells replacedShells replacedShells replacedby sphaleriteby sphalerite

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Porvenir and Aserradero – Au

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Aserradero Ore

22amphibole arsenopyrite sphalerite

District Geology – Alteration at Depth

Porphyry‐style mineralization encountered at depthat depth

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District Geology – Alteration at Depth

ATZ 3 973ATZ‐3‐973

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District Geology – ZonationFe-poor sphaleritePyrite-onlyPb & Ag-richAs-poor

No skarn mineralsChlorite, sericite, rhodochrositeLocal silicification

Lower temperature f f i

Fe-rich sphalerite

of formation

pPyrrhotite + pyriteMagnetite locallyPb & Ag-poorAs-richLate gold event

Higher temperature

Garnet, pyroxene skarn with a zone of late amphibole

temperature of formation

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Au > 2g/t

District Geology ‐ Geochronology

1 – Palacios et al., 19962 Townley and Palacios 1999

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2 – Townley and Palacios, 1999

District Geology – Mineralization Timing

North Toqui North and South Toqui

Possibility 1 Possibility 2

porphyry style

North Toquicarbonate‐replacementand veins 117 Ma

North and South Toqui~117 Ma

San Antonio rhyolite sills120 Ma

porphyry‐stylestockworks118‐120 Ma

porphyry‐stylestockworks118‐120 MaSan Antonio 

rhyolite sills120 Ma

South ToquiZi k d

South ToquiAu‐Co actinolite

Au+Co+actinolite

Zinc skarn and Au‐Co actinolite111‐109 Ma

Au+Co+actinolite

Au Co actinolite111‐109 Ma

Porvenir dacite sill113 Ma

Porvenir dacite sill113 Ma

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Conclusions

•The district is zoned from higher temperatures in the south to cooler temperatures in the north

A hib l ld i hi i i h h• Amphibole‐gold overprints this zonation in the south

•Two mineralization events are recognized:  120‐117 Ma and 111‐109 Maand 111 109 Ma

•The 120‐117 Ma event is associated with compressive deformation and emplacement of rhyolite sills

•The 111‐109 Ma event is associated with dacite sill emplacement at 113 Ma

G ld i li ti d d i th 111 109 M•Gold mineralization occurred during the 111‐109 Ma event

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Thank You

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