AlkalicAlkalic porphyry Cuporphyry Cu--Au Au deposits: a BC deposits: a BC specialityspeciality

Thomas Bissig, MDRUThomas Bissig, MDRU

Acknowledgements: Acknowledgements: Dick Tosdal, Dave Cooke, Kirstie Simpson, Claire Chamberlain, CrDick Tosdal, Dave Cooke, Kirstie Simpson, Claire Chamberlain, Craig aig Hart, Janina Micko, Kevin Byrne, Heidi Pass, Meghan Jackson, PauHart, Janina Micko, Kevin Byrne, Heidi Pass, Meghan Jackson, Paul l Jago, Adam Bath.Jago, Adam Bath.Geoscience BC and sponsors of the MDRU Geoscience BC and sponsors of the MDRU alkalicalkalic projectproject

Outline

• What are alkalic porphyry deposits and how are they different from calc-alkalicones?

• BC examples: Galore Creek (silica undersaturated) and Mount Milligan (silica saturated)

• Regional volcanic setting and characteristics of host rocks

• Conclusions

alkalic

sub-alkalic

40 50 60 70

4

8

12

16

SiO2 (wt%)

Na 2

O +

K2O

(wt%

)

High-K calc-alkalic

Cu-Au(-Mo)

Silica-undersaturatedalkalic

Cu-Au

Silica-saturated alkalic

Cu-Au

Modified from Lang et al., 1995

• Porphyry Cu-Au-Mo deposit classification

Arizona calc-alkalic

Cu-MoCu-Au

SW Pacificcalc-alkalic

Free gold in quartz-bornitevein, Ridgeway, NSW

Igneous Associations

General alteration model(calc alkalic type)

BAJO DE LA ALUMBRERA (1975, pre-mining)

QzQz--mtmt +/+/-- KK--sfpsfp, barren, barren

BiBi--kspksp +/+/-- mtmt ((potassicpotassic))

QzQz--ser +/ser +/-- clay overprint (clay overprint (phyllicphyllic +/+/-- argillicargillic))

EpEp--chlchl ((propyliticpropylitic))

Se also Ulrich and Heinrich, 2002)

Not shown: Advanced argillic/silicic lithocap

Alkalic porphyry Cu-Au:N-Parkes, NSW, Australia

MZ

Biotite altered mineralized rock

Alteration footprint is narrow, less evident than calc-alkalic cousins

Alkalic porphyry Cu-Au deposits: alteration model

Jensen and Barton, 2000

Distal Propylitic (chlorite sub-zone: chl-carb hm )± ±epi

Skarn (py-hm-mt-chl-carb-gt)

Skarn propylitic (epi-py)

Alkalic lithocap (ab-kf-ser-carb--py-tm)

Sodic (ab-qz-hm)

Outer Propylitic (albite-actinolite subzone: ab-act-qz-carb-py)Inner Propylitic (actinolite-hematite-epidote subzone: ab-chl-act-epi -qz)-hm

Legend - Alteration

Outer calc-potassic(Kf-chl-bt-ab-act-qtz-cp)Inner calc-potassic(bt-act-mt-kf-ab-qtz-bn)

Reddened propylitic halo(hematite dusting of feldspars, negative S isotopes in sulfides, increasing magnetic susceptibilitytowards ore, Zn and Pb geochemical anomaly)

Skarn (mt skarn may form in limestone or reactive volcanic / volcaniclastic rocks,magnetic high)

Alkalic lithocap (albite - K-feldspar - sericite- quartz - carbonate tourmaline) - chargeability high, magnetic low±

Calc-potassic or potassic core(magnetic high, Cu-Au-Mo geochemical anomaly)

Wilson et al. 2003

• Cu-Au association• Includes some of the highest gold grades in

porphyry systems (Ridgeway, Cadia Far East)• PGE enrichment in some systems (Copper

Mountain, Afton, Lorraine) • Magnetite locally very abundant (sold as Fe ore)• Environmentally benign (low pyrite, high

neutralization capacity of some host rocks)• Untapped potential in BC and elsewhere

Why target alkalic porphyry Cu-Au systems?

Mt MilliganMt Milligan

1 10 100 1000 10000.01

.1

1

10

Au

ppm

Mt

SulphuretsMt Milligan

Total CadiaDistrict

Red Chris

Mount Polley

Kerr

Copper Mountain

Total Galore Creek

AftonAjax

Lorraine

Ladolam

Epithermal

Porphyry

0.1 t Au

1 t Au

10 t Au

100 t Au

Grade and Tonnage-Alkalic systems

BC porphyriesOther locations

Au in alk. Epith. Deposit, LkCowal

Alkalic vs Calc-Alkalic

Alkalic districts typically have…

Several small deposits

N-Parkes

Complicated and apparently small alteration footprint.

Potassic, calcic, sodic altn, abundant mt, hem dusting typical. Phyllic and argillic altn scarce and qz veins only in deposits related to silica saturated rocks. Generally low py

Breccias important in some deposits particularly in silica undersaturated types. May host high grade

Myarolitic cavity filled with Bn-cpy, N-parkes

Ab-ep-act-chl +/- carb alteration, Mt Milligan

Mt Polley NE zone

MagnetiteMagnetite--Apatite veins, Afton, BCApatite veins, Afton, BC

Pegmatite style KPegmatite style K--fspfsp, coarse bi veins , coarse bi veins with late with late cpycpy, Copper Mountain, BC, Copper Mountain, BC

Gnt-diop-biot-cemented breccia, Galore Creek Megacrystic Or-plag-phyric monzonite, Galore Creek

Garnet

Features reminding of IOCG’s, Skarns

StuhiniGroup

Takla &Nicola Groups

StikiniaTerrane

QuesnelliaTerrane

Cache CreekOcean

Slide Mountain Ocean

HazeltonGroup

StikiniaTerrane

TaklaGroup

QuesnelliaTerrane

800 kmCache Creek

Ocean

208-193 Ma: Mihalynuk et al., (1994)

Structural and Tectonic Environment of BC AlkalicCu-Au Porphyry Deposits

Highland Valley

Red ChrisGalore Creek

Lorraine

Mt. Milligan

Mount Polley

Afton

Gibraltar

KemessSulphurets

Kerr

Copper MountainVancouver

Dease Lake

Prince Rupert

Prince George

Stewart

Pacific Ocean

USA

Yukon

Alberta

Alkalic Cu-Au porphyries

Calc-alkalic Cu-Au porphyries

-Si+Si

The Galore Creek ProjectJ. Micko, PhD candidate, K. Byrne MSc

The Galore Creek district contains 5 deposits and 7 prospects.

Silica undersaturated class, age roughly between 210-203 Ma

The overall measured and indicated resource is estimated at 785.2 million tonnes grading at 0.52% Cu, 0.29g/t Au and 4.87 g/t Ag(NovaGold Resources Inc; press release June, 2008).

Currently owned by “Galore Creek Mining Company” (GCMC), a 50:50 joint venture between NovaGold Resources Inc. and Teck Cominco Ltd. The Galore Creek district -

(after NovaGold Resources Inc., 2007)

Galore Creek- Geology

Micko, in prep.

Geology of the NGL

EW

Hydrothermal alteration and mineralization (NGL)

W E W E

From Micko, in Prep

Potassic (orthoclase, biotite, magnetite ± hem)

Calcic (Garnet, diopside ± anhydrite )

Propylitic (chlorite, epidote, carb. ± muscovite)

Sulfur isotopes distribution (NGL)

W E W E

Sulfide sample locations δ34S isotopic zonation

From Micko, in Prep

Mt Milligan

• Resource figures, pictures590 Mt at 0.193 % Cu and 0.35 g/t Au

Silica saturated Alkalic porphyry, Age: ~185 Ma

Panoramic view over pre-mining deposit

Mount MilliganMount MilliganP. Jago, P. Jago, MScMSc

Plan provided by Placer Dome Inc.

DWBX zoneDWBX zone = Cu= Cu--rich, Aurich, Au--moderatemoderate

WBX zoneWBX zone = Cu= Cu--rich, Aurich, Au--poorpoor

MBX zoneMBX zone = Cu= Cu-- and Auand Au-- rich rich

““6666”” zonezone = Cu= Cu--poor, Aupoor, Au--richrich

Mount Milligan rocks

Volcanic host rocks, strong bi +/-mt altn, augite phenos replaced by sulfides

Flow-banded rainbow dyke. Sulfides in flow bands. K-spar +/- bi alteration

Ab-ep-act-chl +/- carb alteration (inner propylitic)

Thin fracture controlling sericitizationof feldspars, upper trachyte

Mount Milligan

Jago, 2008

Alteration geometry with Alteration geometry with ore gradeore grade

Jago, 2008

~500 m

Silica saturated monzonite

Fine grained basinal facies

Carbonate rocks

2

3

1

Magnetite richProximal Basalts

Silica undersaturated monzonite

4

5

6

Nicola, Takla, Stuhini groups Intrusive rocks

General volcanic setting for BC porphyry Cu-Au deposits

1: Mt. Polley2: Galore Creek3. Cu Mountain4: Mount Milligan5: Red Chris6: Lorraine

Subaqueous pyroxene phyric basalts

Nicola Group, Tackla Group, Stuhini Group

Medial facies basalts

0 2 4 6 80

50

100

150

200

Mag

netic

sus

cept

ibilit

y *1

0 S

I uni

ts-3

Fe O/Fe3+2+

Increasing oxidation state

group 2 group 1

Highly oxidized parts of the arc are more likely to host a Mt. PolleyOxidized rocks tend to be more alkalic

Mt P

olle

y, L

ac L

a H

ache

Titanaugite with magnetite inclusions

Augite without magnetite inclusions

Mt. Milligan and NE of Bridge Lake

Magnetic Susceptibility as Proxy for Oxidation State

Ongoing MDRU research; Bissig et al. 2010

0 50 100 150 2000

1

2

3

4

5

6

7

8

Magnetic susceptibility * 10 SI units-3

LT NavLT Npt

LT NpvLT Nvl

0 50 100 150 2000

1

2

3

4

5

6

7

8

Magnetic susceptibility * 10 SI units-3

Magnetic Susceptibility, Host rocks

Mt. Polley

Lac La Hache

Magnetic susceptibility generally high (>20*10-3 SI)

Mt. Milligan

Magnetic susceptibility * 10 SI units-30 50 100 150 2000123456789

10111213141516

Potassic alteration

Least altered basalts

0 50 100 150 2000

1

2

3

4

5

6

7

8

Magnetic susceptibility * 10 SI units-3

Magnetic susceptibility generally low (>10*10-3 SI)

Bridge Lk

COEVAL Cu-A

u

COEVAL Cu-A

u

20 M

a you

nger

Cu-Au

No Cu-A

u

Ongoing MDRU research; Bissig et al. 2010

QUEST Aeromagnetic Signatures

!

570000.000000

570000.000000

580000.000000

580000.000000

590000.000000

590000.000000

600000.000000

600000.000000

610000.000000

610000.000000

5810

000.0

0000

0

5810

000.0

0000

0

5820

000.0

0000

0

5820

000.0

0000

0

5830

000.0

0000

0

5830

000.0

0000

0

5840

000.0

0000

0

5840

000.0

0000

0

5850

000.0

0000

0

5850

000.0

0000

0

5860

000.0

0000

0

5860

000.0

0000

0

LegendMag2_Main.grdValue

High : 62759.687500

Low : 55648.089844

Mount Polley: Relatively high magnetic intensity in Nicola Gr. volcanic rocks

MP

Logan et al., 2010

Ongoing MDRU research; Bissig et al. 2010

QUEST Aeromagnetic Signatures

!

420000.000000

420000.000000

430000.000000

430000.000000

440000.000000

440000.000000

450000.000000

450000.000000

460000.000000

460000.000000

470000.000000

470000.000000

6080

000.0

0000

0

6080

000.0

0000

0

6090

000.0

0000

0

6090

000.0

0000

0

6100

000.0

0000

0

6100

000.0

0000

0

6110

000.0

0000

0

6110

000.0

0000

0

6120

000.0

0000

0

6120

000.0

0000

0

6130

000.0

0000

0

LegendMag2_Main.grdValue

High : 62759.687500

Low : 55648.089844

Mount Milligan: Generally subdued magnetic intensity in volcanic units. Mag high corresponds to mid Jurassic (169 Ma) intrusion

MM

Ongoing MDRU research; Bissig et al. 2010

Logan et al., 2010

Summary

- Most BC porphyry deposits have been tilted - Negative sulfur isotopes in sulfides vector to

mineralization- Magmatic-hydrothermal breccias are important

hosts- Porphyries represent a variety of volcanic and

igneous settings but host rocks to all are subaqueous basaltic rocks and K-spar megacrystic monzonite porphyries are commonly found in proximity to mineralization

- In most districts several discrete mineralized centers with varied Cu:Au ratios are present

Additional information

Geoscience BC Geoscience BC -- www.geosciencebc.comMDRUMDRU -- www.mdru.ubc.ca