Porphyry Gold Deposits - Cmi Capital Limited
Porphyry Gold Deposits - Cmi Capital Limited
Porphyry Gold Deposits - Cmi Capital Limited
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“PORPHYRY” GOLD DEPOSITS<br />
SE Europe Geoscience Foundation<br />
Conference<br />
Dr Tim Baker<br />
Economic Geology Research Unit, School of Earth Sciences, James Cook University<br />
Townsville, QLD 4811, Australia<br />
Ph: 61-7-47814756, Email: Timothy.Baker@jcu.edu.au
INTRUSION RELATED GOLD DEPOSITS<br />
CHARACTERISTICS<br />
• Sillitoe (1991)<br />
– <strong>Gold</strong>-rich porphyry deposits<br />
– Epithermal & skarn in porphyry Cu environments<br />
– <strong>Gold</strong> related to alkalic magmatism<br />
– Mostly associated oxidized intrusions<br />
– Intrusion related gold deposits in Sn-W terranes<br />
(Thompson et al., 1999)
NOMENCLATURE<br />
• <strong>Porphyry</strong> Au (Hollister, 1992)<br />
• Fort Knox-style Au (Bakke, 1995)<br />
• Intrinsic Au (Newberry et al., 1995)<br />
• Plutonic Au (McCoy et al., 1997)<br />
• Intrusion-related Au in Sn-W terranes (Thompson et al., 1999)<br />
• Granitoid Au (<strong>Gold</strong>farb et al., 1999)<br />
• Reduced porphyry Cu-Au deposits (Rowins, 2000)<br />
• Thermal aureole Au systems (Wall, 2005)<br />
• Granite-related Au-(Bi) deposits (Baker et al. 2005)
• Metals<br />
CHARACTERISTICS<br />
– Au, Bi, Te, W, Mo, As (Sb, Sn, Pb, Cu)<br />
• Magmas<br />
– Intermediate to felsic (wide range SiO2)<br />
– I-type (crustal input, transitional S-type)<br />
– Ilm>Mag<br />
– W-Sn-Mo association<br />
(Thompson et al., 1999)
MAGMAS & METALS<br />
10<br />
9<br />
8<br />
7<br />
Na2O + K2O (wt %)<br />
6<br />
5<br />
4<br />
W<br />
Sn<br />
3<br />
2<br />
Cu-Au, Au-(Bi)<br />
1<br />
0<br />
50 55 60 65 70 75 80<br />
SiO2 (wt %)<br />
(Baker et al., 2005a)
MAGMAS & METALS<br />
Cu-Au, Au-(Bi)<br />
W<br />
Sn<br />
(Baker et al., 2005a)
MAGMAS & METALS<br />
10<br />
oxidised<br />
Cu-Au<br />
W<br />
Fe2O3/FeO<br />
1<br />
0.1<br />
magnetite series<br />
ilmenite series<br />
Au-(Bi)<br />
Sn<br />
0.01<br />
reduced<br />
0.001 0.01 0.1 1 10 100 1000<br />
Rb/Sr<br />
(Baker et al., 2005a)
• Tectonic environment<br />
– Continental setting, inboard, commonly late<br />
• Age<br />
– Phanerozoic (Precambrian – Archean)<br />
– Intrusions = mineralization<br />
• Ore<br />
– Au, Bi, Te, W, Mo, As (Sb, Sn, Pb, Cu)<br />
– Reduced (no Mag-Hem), low sulfide (Po-Py-Apy)<br />
• Style<br />
CHARACTERISTICS<br />
– Sheeted, breccia, stockwork, flat-vein, disseminated<br />
(Thompson et al., 1999)
LOCATION OF MAJOR<br />
GRANITE RELATED GOLD DEPOSITS<br />
(Lang & Baker, 2001)
Shallow-level examples<br />
Donlin Creek - >25 M.oz.<br />
<strong>Porphyry</strong>-style examples<br />
Kidston - ~4 M.oz.<br />
Plutonic-style examples<br />
Fort Knox - >5 M.oz.<br />
Pogo<br />
- >5 M.oz.<br />
GEOLOGICAL EXPLORATION MODEL
TINTINA GOLD BELT<br />
0 500<br />
kilometres<br />
Tintina <strong>Gold</strong> Belt<br />
Tombstone Plutonic Suite<br />
Tungsten Plutonic Suite<br />
Major gold deposits<br />
<strong>Gold</strong> occurrences<br />
Fort Knox, Ryan Lode<br />
&TrueNorth<br />
Alaska<br />
Yukon<br />
Shotgun<br />
Donlin<br />
Creek<br />
Pogo<br />
Brewery<br />
Creek<br />
Dublin<br />
Gulch<br />
Kula<br />
(85Ma)<br />
Kula<br />
(56Ma)<br />
Farallon<br />
(100Ma)<br />
(Flanigan et al., 2000)
TPS WESTERN YUKON
FORT KNOX (> 5 M.oz.)
FORT KNOX
FORT KNOX (looking W)<br />
N<br />
S<br />
50m<br />
Schist<br />
Med.Grani t e<br />
Coarse Granite<br />
(Bakke, 1994)<br />
Vein<br />
Shear Zone<br />
Pegmat it e
• Vein Characteristics<br />
FORT KNOX<br />
Pegmatites & sheeted veins (min’l)<br />
Overprinted quartz filled faults (min’l)<br />
Au-Bi-Te-As-Sb-W-Mo (inc. deeper)<br />
Sulfide 960 fineness<br />
Au:Bi 0.86<br />
(Bakke, 1994; McCoy et al., 1997)
FORT KNOX
DUBLIN GULCH (~2 M.oz.)<br />
Biotite hornfels and calcsilicate<br />
skarn aureole<br />
Granite and aplite<br />
Granodiorite<br />
Eagle<br />
Zone<br />
Ray<br />
Gulch<br />
N<br />
Peso-Ag<br />
Ag-Pb<br />
Rex-Ag<br />
1.6 km<br />
Au-Bi<br />
W<br />
Grit Unit<br />
(Maloof et al, 2001)<br />
Upper Schist<br />
Central Quartzite<br />
Lower Schist
DUBLIN GULCH<br />
(Maloof et al, 2001)
DUBLIN GULCH<br />
carb-ser<br />
Bi/Pb<br />
sulfosalt<br />
Au<br />
0.2mm<br />
py<br />
carb<br />
qtz<br />
1.8mm<br />
(Maloof et al, 2001)
Shallow-level examples<br />
Donlin Creek - >25 M.oz.<br />
<strong>Porphyry</strong>-style examples<br />
Kidston - ~4 M.oz.<br />
Plutonic-style examples<br />
Fort Knox - >5 M.oz.<br />
Pogo<br />
- >5 M.oz.<br />
GEOLOGICAL EXPLORATION MODEL
TIMBARRA CROSS SECTION<br />
(Mustard, 2001)
TIMBARRA GRANITE FACIES & Au<br />
(Mustard, 2001)
Shallow-level examples<br />
Donlin Creek - >25 M.oz.<br />
<strong>Porphyry</strong>-style examples<br />
Kidston - ~4 M.oz.<br />
Plutonic-style examples<br />
Fort Knox - >5 M.oz.<br />
Pogo<br />
- >5 M.oz.<br />
GEOLOGICAL EXPLORATION MODEL
SHOTGUN (~1 M.oz.)<br />
(Rombach & Newberry, 2001)
SHOTGUN TEXTURES<br />
A - Stockwork<br />
C - Breccia<br />
D - UST/brain rock<br />
Au-Bi – 0.73<br />
(Rombach & Newberry, 2001)
KIDSTON<br />
AUSTRALIA<br />
~4 M.oz.<br />
(Baker & Andrew, 1991)
KIDSTON TEXTURES
DONLIN CREEK (>25 M.oz.)<br />
(Ebert et al., 2000)<br />
• Geology & mineralization<br />
– Rhyolite dykes hosted in<br />
reduced flysch sediments<br />
– Magmatism & mineralization<br />
71 to 66 Ma<br />
– Fault controlled NE & NW<br />
strike-slip<br />
– Narrow Au-As-Sb-Hg veins in<br />
dykes>sediments<br />
– Ore within NNE extensional<br />
fracture zone<br />
– Epithermal/epizonal<br />
characteristics
DONLIN CREEK VEINS
Shallow-level examples<br />
Donlin Creek - >25 M.oz.<br />
<strong>Porphyry</strong>-style examples<br />
Kidston - ~4 M.oz.<br />
Plutonic-style examples<br />
Fort Knox - >5 M.oz.<br />
Pogo<br />
- >5 M.oz.<br />
GEOLOGICAL EXPLORATION MODEL
POGO REGIONAL SETTING<br />
65 o<br />
147 o 146 o 145 o 144 o 64 o<br />
N<br />
Sillimanite isograd<br />
Pogo<br />
Surficial deposits<br />
Shaw Creek Fault<br />
Big<br />
Delta<br />
Delta Junction Surficial deposits<br />
Post Metamorphic<br />
Igneous Rocks<br />
Volcanic & sedimetary<br />
rocks<br />
Tertiary granite<br />
0 25 50<br />
Km<br />
Metamorphic rocks<br />
Ultramafic rocks.<br />
High and Intermediate-pressure amphibolitefacies<br />
gneiss, schist, amphibolite, and marble.<br />
Greenschist-facies schist, semischist, quartzite,<br />
marble, greenstone and phyllite.<br />
Amphibolite-facies schist, gneiss, augen gneiss,<br />
amphibolite, quartzite, and minor marble.<br />
Strongly metamorphosed<br />
pluton. Amphibolite facies.<br />
Cretacous granite<br />
Prehnite-pumpellyite and greenschist-facies quartzite,<br />
argillite, phyllite, and minor metalimestone.<br />
(Smith et al., 1999)
Pogo Surface Plan<br />
Goodpaster<br />
River<br />
L1 Zone<br />
UPPER<br />
CAMP<br />
L2 Zone<br />
UPPER ORE<br />
ACCESS<br />
LOWER<br />
.<br />
CAMP<br />
PORTAL<br />
LOWER<br />
ORE<br />
ACCESS<br />
Liese Creek<br />
0 1,500 ft<br />
Pogo Creek<br />
Pogo Ridge
POGO (>5 M.oz.)<br />
View to North<br />
L1<br />
L2<br />
L3<br />
• Topo relief - 830m (1225m -<br />
400m ASL)<br />
• Deepest Drilling is 230m ASL<br />
returned 2.5m @ 7.16 g/t Au at<br />
L3 level.<br />
• 1500m relief from deep bottom<br />
drilling to Top Hill 4021<br />
(Roberts, 2005)
POGO
• Host rocks<br />
POGO<br />
– L. Proterozoic - M. Paleozoic gneiss<br />
• Amphibolite facies<br />
– M. Cretaceous granite dykes, aplites & pegmatites<br />
• Reduced I-type, 15% vol.<br />
– Post-mineralization dolerites<br />
• Age<br />
– U-Pb 107 to 93 Ma – Intrusions<br />
– Ar-Ar ~91-92 Ma - Mica alt<br />
– Re-Os ~104Ma - Molybdenite<br />
(Smith et al., 1999; Selby et al., 2002)
POGO (> 5 M.oz.)<br />
(Smith et al., 1999; Selby et al., 2002)
• Ore<br />
Sulphide ~3%<br />
POGO<br />
Reduced assemblage: Po-Lo-Apy-Py-Ccp<br />
Au-Bi-Pb-Te-Ag-S phases; Au:Bi 0.89<br />
0.89<br />
(Smith et al., 1999)
LOCATION OF MAJOR<br />
INTRUSION RELATED GOLD DEPOSITS<br />
(Lang & Baker, 2001)
<strong>Gold</strong> deposit model<br />
Tien Shan<br />
Taror 3 M.oz.<br />
Amantaitau 4 M.oz.<br />
Muruntau 175 M.oz.<br />
Jilau 3 M.oz.<br />
Zarmitan 11.3 M.oz.<br />
(Yakubchuk et al., 2002)
CONCLUSIONS: GRANITE RELATED GOLD SYSTEMS<br />
• Coherent, useable set of empirical exploration<br />
characteristics<br />
• Critical features include<br />
– Vertical & lateral zonation about mod-reduced granitic<br />
intrusions<br />
– Set of pathfinder elements including Au, Bi, Te, As, W, (Mo,<br />
Sn, Sb)<br />
– Variety of target types<br />
• Distinct from porphyry copper-gold systems
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