geology of the etoqui zn au skarn district
TRANSCRIPT
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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
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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
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153 cm
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Sphalerite Arsenopyrite
PDT‐66‐334m
16Pyroxene
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Porvenir and Aserradero ‐ Alteration
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Porvenir and Aserradero ‐ Zn
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3 cm
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307.10m
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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
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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
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District Geology ‐ Geochronology
1 – Palacios et al., 19962 Townley and Palacios 1999
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2 – Townley and Palacios, 1999
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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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