Porphyry Gold Deposits - Cmi Capital Limited

“PORPHYRY” GOLD DEPOSITS
SE Europe Geoscience Foundation
Conference
Dr Tim Baker
Economic Geology Research Unit, School of Earth Sciences, James Cook University
Townsville, QLD 4811, Australia
Ph: 61-7-47814756, Email: Timothy.Baker@jcu.edu.au

INTRUSION RELATED GOLD DEPOSITS
CHARACTERISTICS
• Sillitoe (1991)
– Gold-rich porphyry deposits
– Epithermal & skarn in porphyry Cu environments
– Gold related to alkalic magmatism
– Mostly associated oxidized intrusions
– Intrusion related gold deposits in Sn-W terranes
(Thompson et al., 1999)

NOMENCLATURE
• Porphyry Au (Hollister, 1992)
• Fort Knox-style Au (Bakke, 1995)
• Intrinsic Au (Newberry et al., 1995)
• Plutonic Au (McCoy et al., 1997)
• Intrusion-related Au in Sn-W terranes (Thompson et al., 1999)
• Granitoid Au (Goldfarb et al., 1999)
• Reduced porphyry Cu-Au deposits (Rowins, 2000)
• Thermal aureole Au systems (Wall, 2005)
• Granite-related Au-(Bi) deposits (Baker et al. 2005)

• Metals
CHARACTERISTICS
– Au, Bi, Te, W, Mo, As (Sb, Sn, Pb, Cu)
• Magmas
– Intermediate to felsic (wide range SiO2)
– I-type (crustal input, transitional S-type)
– Ilm>Mag
– W-Sn-Mo association
(Thompson et al., 1999)

MAGMAS & METALS
10
9
8
7
Na2O + K2O (wt %)
6
5
4
W
Sn
3
2
Cu-Au, Au-(Bi)
1
0
50 55 60 65 70 75 80
SiO2 (wt %)
(Baker et al., 2005a)

MAGMAS & METALS
Cu-Au, Au-(Bi)
W
Sn
(Baker et al., 2005a)

MAGMAS & METALS
10
oxidised
Cu-Au
W
Fe2O3/FeO
1
0.1
magnetite series
ilmenite series
Au-(Bi)
Sn
0.01
reduced
0.001 0.01 0.1 1 10 100 1000
Rb/Sr
(Baker et al., 2005a)

• Tectonic environment
– Continental setting, inboard, commonly late
• Age
– Phanerozoic (Precambrian – Archean)
– Intrusions = mineralization
• Ore
– Au, Bi, Te, W, Mo, As (Sb, Sn, Pb, Cu)
– Reduced (no Mag-Hem), low sulfide (Po-Py-Apy)
• Style
CHARACTERISTICS
– Sheeted, breccia, stockwork, flat-vein, disseminated
(Thompson et al., 1999)

LOCATION OF MAJOR
GRANITE RELATED GOLD DEPOSITS
(Lang & Baker, 2001)

Shallow-level examples
Donlin Creek - >25 M.oz.
Porphyry-style examples
Kidston - ~4 M.oz.
Plutonic-style examples
Fort Knox - >5 M.oz.
Pogo
- >5 M.oz.
GEOLOGICAL EXPLORATION MODEL

TINTINA GOLD BELT
0 500
kilometres
Tintina Gold Belt
Tombstone Plutonic Suite
Tungsten Plutonic Suite
Major gold deposits
Gold occurrences
Fort Knox, Ryan Lode
&TrueNorth
Alaska
Yukon
Shotgun
Donlin
Creek
Pogo
Brewery
Creek
Dublin
Gulch
Kula
(85Ma)
Kula
(56Ma)
Farallon
(100Ma)
(Flanigan et al., 2000)

TPS WESTERN YUKON

FORT KNOX (> 5 M.oz.)

FORT KNOX

FORT KNOX (looking W)
N
S
50m
Schist
Med.Grani t e
Coarse Granite
(Bakke, 1994)
Vein
Shear Zone
Pegmat it e

• Vein Characteristics
FORT KNOX
Pegmatites & sheeted veins (min’l)
Overprinted quartz filled faults (min’l)
Au-Bi-Te-As-Sb-W-Mo (inc. deeper)
Sulfide 960 fineness
Au:Bi 0.86
(Bakke, 1994; McCoy et al., 1997)

FORT KNOX

DUBLIN GULCH (~2 M.oz.)
Biotite hornfels and calcsilicate
skarn aureole
Granite and aplite
Granodiorite
Eagle
Zone
Ray
Gulch
N
Peso-Ag
Ag-Pb
Rex-Ag
1.6 km
Au-Bi
W
Grit Unit
(Maloof et al, 2001)
Upper Schist
Central Quartzite
Lower Schist

DUBLIN GULCH
(Maloof et al, 2001)

DUBLIN GULCH
carb-ser
Bi/Pb
sulfosalt
Au
0.2mm
py
carb
qtz
1.8mm
(Maloof et al, 2001)

Shallow-level examples
Donlin Creek - >25 M.oz.
Porphyry-style examples
Kidston - ~4 M.oz.
Plutonic-style examples
Fort Knox - >5 M.oz.
Pogo
- >5 M.oz.
GEOLOGICAL EXPLORATION MODEL

TIMBARRA CROSS SECTION
(Mustard, 2001)

TIMBARRA GRANITE FACIES & Au
(Mustard, 2001)

Shallow-level examples
Donlin Creek - >25 M.oz.
Porphyry-style examples
Kidston - ~4 M.oz.
Plutonic-style examples
Fort Knox - >5 M.oz.
Pogo
- >5 M.oz.
GEOLOGICAL EXPLORATION MODEL

SHOTGUN (~1 M.oz.)
(Rombach & Newberry, 2001)

SHOTGUN TEXTURES
A - Stockwork
C - Breccia
D - UST/brain rock
Au-Bi – 0.73
(Rombach & Newberry, 2001)

KIDSTON
AUSTRALIA
~4 M.oz.
(Baker & Andrew, 1991)

KIDSTON TEXTURES

DONLIN CREEK (>25 M.oz.)
(Ebert et al., 2000)
• Geology & mineralization
– Rhyolite dykes hosted in
reduced flysch sediments
– Magmatism & mineralization
71 to 66 Ma
– Fault controlled NE & NW
strike-slip
– Narrow Au-As-Sb-Hg veins in
dykes>sediments
– Ore within NNE extensional
fracture zone
– Epithermal/epizonal
characteristics

DONLIN CREEK VEINS

Shallow-level examples
Donlin Creek - >25 M.oz.
Porphyry-style examples
Kidston - ~4 M.oz.
Plutonic-style examples
Fort Knox - >5 M.oz.
Pogo
- >5 M.oz.
GEOLOGICAL EXPLORATION MODEL

POGO REGIONAL SETTING
65 o
147 o 146 o 145 o 144 o 64 o
N
Sillimanite isograd
Pogo
Surficial deposits
Shaw Creek Fault
Big
Delta
Delta Junction Surficial deposits
Post Metamorphic
Igneous Rocks
Volcanic & sedimetary
rocks
Tertiary granite
0 25 50
Km
Metamorphic rocks
Ultramafic rocks.
High and Intermediate-pressure amphibolitefacies
gneiss, schist, amphibolite, and marble.
Greenschist-facies schist, semischist, quartzite,
marble, greenstone and phyllite.
Amphibolite-facies schist, gneiss, augen gneiss,
amphibolite, quartzite, and minor marble.
Strongly metamorphosed
pluton. Amphibolite facies.
Cretacous granite
Prehnite-pumpellyite and greenschist-facies quartzite,
argillite, phyllite, and minor metalimestone.
(Smith et al., 1999)

Pogo Surface Plan
Goodpaster
River
L1 Zone
UPPER
CAMP
L2 Zone
UPPER ORE
ACCESS
LOWER
.
CAMP
PORTAL
LOWER
ORE
ACCESS
Liese Creek
0 1,500 ft
Pogo Creek
Pogo Ridge

POGO (>5 M.oz.)
View to North
L1
L2
L3
• Topo relief - 830m (1225m -
400m ASL)
• Deepest Drilling is 230m ASL
returned 2.5m @ 7.16 g/t Au at
L3 level.
• 1500m relief from deep bottom
drilling to Top Hill 4021
(Roberts, 2005)

POGO

• Host rocks
POGO
– L. Proterozoic - M. Paleozoic gneiss
• Amphibolite facies
– M. Cretaceous granite dykes, aplites & pegmatites
• Reduced I-type, 15% vol.
– Post-mineralization dolerites
• Age
– U-Pb 107 to 93 Ma – Intrusions
– Ar-Ar ~91-92 Ma - Mica alt
– Re-Os ~104Ma - Molybdenite
(Smith et al., 1999; Selby et al., 2002)

POGO (> 5 M.oz.)
(Smith et al., 1999; Selby et al., 2002)

• Ore
Sulphide ~3%
POGO
Reduced assemblage: Po-Lo-Apy-Py-Ccp
Au-Bi-Pb-Te-Ag-S phases; Au:Bi 0.89
0.89
(Smith et al., 1999)

LOCATION OF MAJOR
INTRUSION RELATED GOLD DEPOSITS
(Lang & Baker, 2001)

Gold deposit model
Tien Shan
Taror 3 M.oz.
Amantaitau 4 M.oz.
Muruntau 175 M.oz.
Jilau 3 M.oz.
Zarmitan 11.3 M.oz.
(Yakubchuk et al., 2002)

CONCLUSIONS: GRANITE RELATED GOLD SYSTEMS
• Coherent, useable set of empirical exploration
characteristics
• Critical features include
– Vertical & lateral zonation about mod-reduced granitic
intrusions
– Set of pathfinder elements including Au, Bi, Te, As, W, (Mo,
Sn, Sb)
– Variety of target types
• Distinct from porphyry copper-gold systems