Exploration Challenges of the 21st Century 12 October 2011

Big challenges

Discovery – especially better grade, world-class deposits • Copper/gold – average deposit/mining grade declining • Increasing capital, operating, energy, water intensity

Development – license to operate, power and water, people • Timelines extending – discovery to mine: 10+ years? • Complexity increasing – no short-cuts

Technology – Improvements but no game changers • Opportunities – drilling, technology, data and interpretation

Copper – porphyry deposits • Review – current understanding • Challenges

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Global distribution of major porphyry copper deposits

3

2 – 10 Mt Contained CuEq

10 – 31 Mt Contained CuEq

>31 Mt Contained CuEq

• Mature continental and island arcs

• Preserved arc terranes

• Deposits dominantly Mesozoic and Tertiary

65% of annual production 35% from Chile

Porphyry model

• Magmatic fluids from crystallization of arc magmas • Form at convergent plate margins because:

• Subduction generates volatile-rich magmas • Arcs provide structural settings for high-level magma

emplacement, fluid flow and deposition

• Variations include the metal suite, composition of intrusions, depth of formation (<1 to 8km), evolution of magmatic fluids/vapours, structural and lithological controls, and role of external fluids

From Tosdal and Richards, 2004

Regional controls – area selection

Regional framework • Tectonics • Magmatic events • Timing • Ocean plate and arc

structure • Overprints

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Regional controls – modern arcs

6

30o 40o

55o

65o >70o

EQ <300km EQ

>600km

From Garwin, 2003

Porphyry deposits in BC

Mapped Terranes Stikine Quesnel Porphyry Occurrences Alkalic Calc-alkalic Roads Towns/Cities Prince George

Dease Lake

Bella Coola

Kamloops

Galore Creek

Lorraine

Mt Milligan

Mount Polley

Iron Mask (Afton, Ajax)

Copper Mountain

Highland Valley

From Chamberlain, 2010

Wrangelia

− Arc terrane deposits − Post-accretion deposits

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El COLORADO

70

5100

00 E

5200

00 E

5300

00 E

5400

00 E

7680000 N

7690000 N

7700000 N

7710000 N

7720000 N

7670000 N

76 4 0000 N

76 6 0000 N

76 5 0000 N

70

5100

00 E

5200

00 E

5300

00 E

5400

00 E

7680000 N

7690000 N

7700000 N

7710000 N

7720000 N

7670000 N

76 4 0000 N

76 6 0000 N

76 5 0000 N

70

5100

00 E

5200

00 E

5300

00 E

5400

00 E

7680000 N

7690000 N

7700000 N

7710000 N

7720000 N

7670000 N

76 4 0000 N

76 6 0000 N

76 5 0000 N

UJINA

1

2

3

4 ROSARIO

QB

COPAQUIRI

• Structure • Intrusions – magma chemistry • Clusters • Remote sensing – colour anomalies • Geophysics – magnetics, gravity , EM • Geochemistry – streams, minerals

Regional exploration

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40 50 60 70

4

8

12

16

SiO2 (wt%)

Na 2

O +

K2O

(wt%

)

high-K calc-alkalic

silica-undersaturated alkalic

silica-saturated alkalic

0

low- to medium-K calc-alkalic

Cu-Mo

Cu-Au

Cu-Au (-Mo)

Cu-Au

Cu-Au

Modified from Lang et al. 1995

Magma series and deposits

Magmas and minerals

• Composition – magma suites • Mixing – role of mafic magmas • Fractionation – hornblende, rare earth elements • Oxidation state – Fe (III)/(II); Zircon Ce(IV)/Ce(III) • Mineralogy – heavy mineral concentrates:

• PIM: apatite, rutile, garnet and titanite

Contribution to exploration?

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Target definition

• Geophysics – IP +/- Magnetics, EM • Geochemistry – soils, talus • Geology – characteristics and zoning

• Veins (rare in alkalic systems) • Metals • Alteration

• Mineralogy • Mineral chemistry

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EDM Vein B Vein

A Vein D Veins

Vein types

Unidirectional solidification textures (UST)

Vein controls: - temperature

- Ductile to brittle fracturing

- equilibrium

600-700OC

400-500OC

450-600OC

350-450OC

300-400OC

Cu-Mo (Au)

Cu-Au

Py (+/- Pb-Zn-Ag-Au) Au (As-Sb-Hg-Tl)

8 Km

Au-As

Pb-Zn Cu-Mo-Au

(Babcock et al., 1995; Cunningham et al., 2004)

Metal zoning Bingham Canyon, Utah

www.newmont.com

914 Mt @ 0.53 % Cu & 0.40 g/t Au

Batu Hijau: “Designer porphyry”

Vain and alteration zoning: propylitic to intermediate argillic to advanced argillic

Batu Hijau

Alteration depth-time relationships

Sericitic

Late Early 0.5-3 Ma Deep

Shallow

1-4

km

Advanced argillic

Inte

rmed

iate

a

rgilli

c

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El Salvador – lithocap zoning

Watanabe and Hedenquist, 2001

Watanabe and Hedenquist, 2001

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21

From Sillitoe and Hedenquist, 2004

• Empirical and genetic models – understood

• Dramatic features • Scale – large systems • Strong zoning

Porphyry model

• Disseminated Cu+/-Mo, Au, Ag mineralization spatially associated with porphyritic intrusions – defines regional metallogeny

• Size: 100 to >5000 million tonnes; 0.5 to 1.5% Cu; vertical cylinder ~500 x 500 x 1000m

• Cluster of intrusions and deposits – 10 x 20 km areas

• Concentric alteration zones – 2->5 times the size of the deposit; vertical zoning ~500-3000m

Should be easy!

Porphyry copper deposits

Exploration challenges

• Complexity and variability • Depth of emplacement and erosion • Geometry

– Intrusive system – Structure – Host rock form/composition

• Big targets with internal complexity – Post-mineral intrusions and breccias – Non/less-reactive wallrocks – Lithocaps

• Structural modification and disruption

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Arc - fold and thrust belt porphyry Cu-Mo/Au - Granodiorite - Alteration/mineralization controlled by reactive rocks

K silicate/phyllic

Pure limestone

Clastic sediments

Marble front

Exoskarn

Endoskarn

Skarn/manto

Shallow (<2km), volcanic-hosted porphyry deposit – Marte, Chile

Deep (>2km), carbonate-hosted porphyry-skarn deposit – Antamina, Peru

Moderate depth, mixed clastic-limestone-hosted porphyry deposit – Bingham Canyon, USA

Alkaline porphyry system – Cadia, Australia

BC deposits – variability

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Scale – target testing

Understanding the system • Think big • Escondida

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2 km

Escondida, Chile ~10% of gobal produciton

Escondida discovery

Big system • Leached cap interpretation • Discovery: Hole 6

28 Behn et al, 2001 Sillitoe, 1995

5 km

Deformation and disruption

Faulting and rotation – Arizona/Sonora

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Hagstrum et al 1987

Lowell and Guilbert, 1970

Ajo, Arizona

San Manuel - Kalamazoo, Arizona

Deformed porphyrys

• Deformation style • Heterogeneous deformation

• Large intrusions – buttress • Alteration influence

• Resulting geometry

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Aitik, Sweden

Treaty Glacier, Iskut

Cover challenge

Central BC – Quesnelia • Complex cover

– Pre-/syn-mineral units/intrusions – Younger volcanics – Glacial till and sediments

The Gap!

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Development challenge

Porphyry deposits - large mines • Scale – 30,000 to >200,000 tpd – throughput is critical • Blasting, crushing and grinding – fractures and hardness

• Recovery and saleable concentrate • Copper mineralogy • As, F

Geometallurgy 32

Conclusions

Porphyry systems • Scale, clusters, variability, complexity • Understanding the geology is critical

Cover • Geophysical tools and inversion modeling • Geochemistry – selective/partial leach/interpretation

Developments • Drilling • Downhole and core measurements • Geometallurgy

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