INTRUSION-RELATED GOLD DEPOSITS

SE Europe Geoscience Foundation

Shortcourse

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
 OVERVIEW

• Part 1: Classification, nomenclature & deposit

comparison

• Part 2: Examples: Tintina Gold Province

• Part 3: Other examples & exploration

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 (Thompson et al., 1999)
• Granitoid Au (Goldfarb et al., 1999)
• Thermal aureole gold systems (Wall, 2005)
 CHARACTERISTICS

• Intrusion related Au deposits in Sn-W terranes

• Metals
– 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)

 CHARACTERISTICS
• 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
– Sheeted, breccia, stockwork, flat-vein, disseminated

(Thompson et al., 1999)

 LOCATION OF MAJOR
GRANITE RELATED GOLD DEPOSITS

(Lang & Baker, 2001)

 Shallow-level examples

Porphyry-style examples

Type-examples

Pogo

GEOLOGICAL EXPLORATION MODEL

INTRUSION RELATED GOLD SYSTEMS IN Sn-W PROVINCES

(Baker et al., 2005a)

 Metallogenic Region/ Granite SiO2 Granitoid Alumina saturation Accessory minerals
Association Deposit type wt % Series (in addition to zircon & apatite)

Sn-W-Bi Cornwall S 71-74 Ilmenite peraluminous ilmenite, monazite, andalusite,

topaz, fluorite

Sn-W-Bi Herberton I 73-77 Ilmenite peraluminous ilmenite, monazite, topaz, fluorite

Sn-W-Bi Fairbanks- I 71-77 Ilmenite peraluminous ilmenite, titanite, monazite,

Circle tourmaline, topaz

Sn-W Western I/S 70-74 Ilmenite peraluminous ilmenite, andalusite, pyrrhotite

Thailand
W-Sn-Mo Jiangxi S 66-76 Magnetite peraluminous magnetite, ilmenite, garnet,
monazite, tourmaline, fluorite

W-Cu-Mo E Yukon I 67-77 Ilmenite metaluminous to ilmenite, monazite, garnet,

peraluminous andalusite, allanite, tourmaline

W-Mo-Sn-Bi Altaid I 63-77 Magnetite metaluminous to magnetite, titanite, monazite,

orogenic belt peraluminous allanite, ilmenite

W-Mo-Bi-Sn Herberton I 56-72 Magnetite metaluminous to allanite, fluorite, ilmenite

peraluminous

W-Sn-Au Iberia I/S 62-76 Ilmenite metaluminous to cordierite, garnet, titanite,

peraluminous andalusite, sillimanite, tourmaline,
topaz

Au-Bi-W Tintina Gold I 50-74 Ilmenite metaluminous to ilmenite, titanite, allanite

Province peraluminous

Au-Bi-Mo Tasman Fold I 49-78 Both metaluminous to magnetite, ilmenite, titanite,

Belt peraluminous fluorite

Cu-Au-Mo SW Arizona I 48-79 Magnetite metaluminous to magnetite, titanite

peraluminous

(Baker et al., 2005a)

 MAGMAS & METALS

10

7
Na2O + K2O (wt %)

6
Sn
5

4
W
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)

Sn

(Baker et al., 2005a)

 MAGMAS & METALS

10
oxidised

Cu-Au W

1
Fe2O3/FeO

magnetite series
ilmenite series

0.1

Au-(Bi)
Sn
0.01 reduced
0.001 0.01 0.1 1 Rb/Sr 10 100 1000

(Baker et al., 2005a)

GRANITE Au-Bi & Sn-W COMPARISON
COMPARISON WITH OTHER ORE SYSTEMS

Epithermal/epizonal gold

Porphyry Cu-Au (PCD’s)

Skarn & sed-hosted Au

(Carlin-like)

Mesothermal/orogenic
gold
 COMPARISON WITH OROGENIC GOLD
• Differences
– Metals: Au-As-Sb-(W-Bi-Te)
– Magma: Lacks spatial/temporal relationship
– Structure: Regional scale faults
– Ore: Py abundant
– Alteration: Varies: host rock/metamorphic grade
• Similarities
– Metals: Intrusion-hosted may have W-Bi-Te
– Magma: Lacks spatial/temporal relationship
– Structure: Deeper IRG have regional stress influence
– Ore: Low-mod sulfide, reduced Po-Asp
– Alteration: Albite, carbonate, quartz
– Fluids: Low salinity, H2O-CO2-(CH4)
 EPITHERMAL/EPIZONAL GOLD
• Shallow-level IRG
• Donlin Creek, Brewery Creek, Korri Kollo

• Similarities: depth; As-Sb-Hg association

• Differences:
• General geological & tectonic environment
• LS – lack textures & wide structurally-controlled veins
• HS – lack acidic fluids & related-alteration features; low Cu
• Shallow IRG - High CO2 content to fluids

• Epizonal orogenic gold

• Less well defined
• Shallow IRG – spatial & temporal association with intrusions
 SKARN & SED-HOSTED GOLD
• Parallels with reduced Au skarns (Meinert,2000)
– Part of total hydrothermal system
– Calcareous host rocks
– Associated with ilmenite series diorite to
granodiorite
– Reduced sulfide mineralogy; Au-Bi common

• Non-carbonate sequences may have links to

Carlin systems (Poulson et al, 1997)
 COMPARISON WITH PCD’s

• Metals: Cu-Au-Fe-Pb-Zn-Ag-Mo
• Magmas: Oxidized I-type, higher Fe content
• Style: Multiple intrusions, stockwork & breccia
• Ore: High sulfide content, oxidized
• Alteration: Extensive, variety of types
• Fluids: High salinity, aqueous; carbonic rare
 REDUCED PCD’s (Rowins, 2000)

• Most examples NOT Cu deposits

• Some overlap with shallow porphyry-hosted

environment (e.g. Shotgun but again no Cu)

• Also distinct from alkalic Au & Cu-Au systems

• More parallels with W-Sn-Mo systems

THERMAL AUREOLE GOLD SYSTEMS

(Wall, 2005)
 OVERVIEW

• Part 1: Classification, nomenclature & deposit

comparison

• Part 2: Examples: Tintina Gold Province

• Part 3: Other examples & exploration

 TGB EXAMPLES
Deposit Size Grade Country rocks Intrusion Deposit type Age Metal
(Mt) (g/t ) composition (Ma) suite
Tintina Gold Belt

z.
.o0.8
Fort Knox, Alaska 158 5 M Mica-quartz Porphyritic Sheeted veins 92 Bi, Te, Mo,
> schist granite As, Sb, W
Pogo, Alaska 10
M oz.
.~15 Gneiss Granite, aplite Flat lenses 107-92? Bi, Te, As,
> 5 Ag, Cu, Pb
Ryan Lode, Alaska 4.1 3.1 Quartz-mica Granodiorite Veins, breccia 90 As, Sb
schist
True North, Alaska 16.5 2.5 Schist & Granite Disseminated, 90 As, Sb, (Hg)
eclogite breccia
Dublin Gulch, 50.3 0.9 Qtz-bt & Granodiorite Sheeted veins 92 Bi, Te, Mo,
Alaska
M.oz. calcareous As, Sb, W,
~ 2 schist Pb
Brewery Creek, 13.3 1.4 Calcareous Monzonite, Disseminated, 91.4 As, Sb, (Hg)
Yukon schist syenite veinlets
Shotgun, Alaska ~1M.oz. Quartz-biotite Granite Stockwork 70 Ag, Bi, Mo,
schist Te, Cu
Donlin Creek, 111
M oz.
.2.9 Greywacke & Rhyodacite Veins, veinlets 70 Ag, As, Sb,
Alaska > 25 shale Hg

(Thompson et al., 1999)

TINTINA GOLD BELT
0 500
Tintina Gold Belt
kilometres
Tombstone Plutonic Suite

Tungsten P lutonic Suite

Major gold deposits
Gold occurrences
Fort Knox, Ryan Lode
& True North Alaska Yukon

Dublin
Pogo Gulch
Donlin Brewery
Creek Creek
Shotgun

Kula Kula
(85Ma) (56Ma) Farallon
(100Ma)

(Flanigan et al., 2000)

 TECTONIC SETTING
• Central-eastern Alaska & Yukon
• Orthogonal subduction Farallon plate 115-100 Ma
• Continued subduction - dextral component 100-85 Ma
• Coincident magmatism – younging cratonwards
• Strong crustal component (NdT –7.6 to –15; 87Sr/86Sr 0.709-0.702)
• Kula plate oblique subduction,dextral strike-slip 85 Ma

• Western Alaska
• Magmatic arc 77 to 58 Ma
• Local N-S compression – plate reorganization ~ 70 Ma
• Kuskokwim magmatism – shallow at continental margin

(Flanigan et al., 2000; Goldfarb et al., 2000)

TINTINA GOLD BELT

(Goldfarb et al., 2000)

 Shallow-level examples

Porphyry-style examples

Type-examples

Pogo

GEOLOGICAL EXPLORATION MODEL

TPS WESTERN YUKON
TINTINA GOLD BELT
0 500
Tintina Gold Belt
kilometres
Tombstone Plutonic Suite

Tungsten P lutonic Suite

Major gold deposits
Gold occurrences
Fort Knox, Ryan Lode
& True North Alaska Yukon

Dublin
Pogo Gulch
Donlin Brewery
Creek Creek
Shotgun

Kula Kula
(85Ma) (56Ma) Farallon
(100Ma)

(Flanigan et al., 2000)

FORT KNOX
FORT KNOX
 FORT KNOX (7.2 M.oz.)
• Exploration & mining
– Placer gold 1902 in creeks down stream
– Au-W veins & skarns 1913 peripheral to FK
– Bismuthinite with Au 1980 proximal creeks
– Visible Au in granite 1984
– Advanced exploration 1987 to 1994
– Construction 1995; bulk tonnage open pit
– Production 1996; 169 Mt @ 0.93 g/t
– 1 M.oz. 1999

(Bakke, 1994)
 FORT KNOX
• Intrusion Characteristics
Tombstone suite
Granodiorite to granite
Ilmenite series, I-type
Late aplites & pegmatites
Locally UST & brain rock textures
• Age
U-Pb 92 Ma - Intrusion
Ar-Ar ~88-86 Ma - Muscovite alt.
Re-Os 92.5 Ma -Molybdenite
(Bakke, 1994; Hart et al., 2001)
 FORT KNOX

150m

Med.Granit e Schist

Coarse Granit e Shear Zone

(Bakke, 1994)
 FORT KNOX (looking W)
N S

50 m

Schist Vein
Med.Granit e Shear Zone
Coarse Granit e
Pegmat it e

(Bakke, 1994)
FORT KNOX (looking W)

(Bakke, 2000)
 FORT KNOX
• Vein Characteristics
Pegmatites & sheeted veins (min’l)
Overprinted quartz filled faults (min’l)
Au-Bi-Te-As-Sb-W-Mo (inc. deeper)
Sulfide <1% - Py, Po, Apy, Mo, Sch
• Ore Characteristics
Bi, Bi2S3, Bi2Te3
Free Au, ~111microns, >960 fineness
Au:Bi 0.86
(Bakke, 1994; McCoy et al., 1997)
FORT KNOX
FORT KNOX
FORT KNOX
 FORT KNOX
• Alteration
Early Albite > K-feldspar
Quartz-Sericite-Carbonate
Regional propylitic & pyrite halo
• Fluids
Low salinity aqueous-carbonic
250-500°C @ >1.5kbar, >5km
Oxygen isotopes fluid 5 to 10 per mil
Sulphur isotopes 0±5 per mil

(Bakke, 1994; McCoy et al., 1997)

DUBLIN GULCH
 DUBLIN GULCH (~2 M.oz.)
• Exploration
– Placer Au mining established 1895 – 1898;scheelite reported
– Rex-Peso Pb-Zn-Ag veins explored 1910
– Cassiterite found – Tin Dome (<0.3 % Sn)
– Au-W-Bi reported (Boyle, 1965)
– W-skarn targeted;soil sampling& mapping – 1970-1980
– Ray Gulch 5.4 Mt.@ 0.82 % WO3
– Gold in peripheral veins explored – 1986-1988
– 1991 to 1996 gold soil anomaly around Eagle Zone drilled

(Maloof et al, 2001)

 DUBLIN GULCH
Biotite hornfels and calc-
silicate skarn aureole N

Granite and aplite

Granodiorite Ray
Gulch
Eagle
Zone

Peso-Ag

Rex-Ag Upper Schist

Central Quartzite
1.6 km Grit Unit Lower Schist
(Maloof et al, 2001)
 DUBLIN GULCH
• Intrusion Characteristics
Granodiorite to granite
Ilmenite series, I-type
Late aplites & pegmatites
• Vein & Ore Characteristics
Predominantly sheeted veins (2 main stages)
Au-Bi-Te-As-Sb-Pb-W-Mo (inc. deeper)
Sulphide <3% - Py, Po, Apy, Sch, Gal, Au-Pb-Bi-Te-Sb
Free Au & Au-Bi, ~155microns, ~1000 fineness
Au:Bi – 0.89

(Maloof et al, 2001)

 EAGLE ZONE
granodiorite
200 m
Ore zone

43
69
65

53
63

(Maloof et al, 2001)

EAGLE ZONE PARAGENESIS
Stage I StageII
Qtz
Ksp
Ab
Sch
Po
Apy
Py
Chl
Mus
Carb ?

Gal
Pb/Bi/Sb
sulfosalts
Moly
Bism
Bi
Gold

(Maloof et al, 2001)

EAGLE ZONE VEIN
EAGLE ZONE PARAGENESIS

carb

quartz carb/ser
frac
K-spar
scheelite
1.8mm

(Maloof et al, 2001)

 EAGLE ZONE PARAGENESIS

Bi/Pb
sulfosalt
carb-ser
Au

0.2mm

py

qtz
carb
1.8mm

(Maloof et al, 2001)

 EAGLE ZONE GEOCHEMISTRY

Au Bi As Sb Ag Mo W Zn Pb
Cu 0.14 0.15 0.59 0.56 0.63 0.23 0.00 0.59 0.64
Pb 0.08 0.07 0.68 0.89 0.89 0.08 0.00 0.93
Zn 0.03 0.02 0.58 0.74 0.77 0.10 0.00
W 0.03 0.00 0.00 0.00 0.00 0.55
Mo 0.15 0.17 0.07 0.04 0.07
Ag 0.24 0.21 0.79 0.85
Sb 0.07 0.05 0.61
As 0.28 0.24
Bi 0.90

(Maloof et al, 2001)

 RAY GULCH
W LOOKING NORTH E

CALC-SILICATE SKARN
(scheelite bearing)
APLITE DYKES 60m
GRANODIORITE
BIOTITE-QUARTZ HORNFELS AND PHYLLITES

(Brown et al, 2001)

 RAY GULCH PARAGENESIS
Stage I Stage II Stage III Stage IV Stage V
(Alt'n) (Alt'n) (Vein) (Vein) (Vein)
Qtz
Wol
Pyx
Gnt
Sch
granodiorite

aplite
Fsp
Amp
Cal
Chl
Mol
Py
Po
Apy

(Brown et al, 2001)

EAGLE ZONE GEOCHEMISTRY
Ave.
Au up to 40 g/t 0.83
Bi up to 500 ppm 19
W up to 2000 ppm 11
Mo up to 700 ppm 6
As up to & >10,000 ppm 195
Pb up to & >10,000 ppm 59
Zn up to & >10,000 ppm 108
Sb up to 5,000 ppm 11
Cu up to 355 ppm 34

(Maloof et al, 2001)

 RAY GULCH GEOCHEMISTRY

W Mo Sn Au Bi Sb As Zn Ag
(ppb)

Wol-Qtz <334 <6 bd bd <1 <0.5 1-5 bd bd

Skarn
(n=2)
Pyx Skarn 200 to <180 bd bd <1 <5 <5 <300 bd
50000 (10, 38,
(n=9) 13)
Vein 0 to <90 bd bd <1 <5 <14 <150 bd
>100000 (148)
(n=14)

(Brown et al, 2001)

 RAY GULCH VS EAGLE ZONE

• RG skarn replacement > vein (~10 vol. %)

• EZ sheeted veins
• EZ Stage II key – Au-Bi event
• Stage missing in RG skarn
• Stage III-V RG = Stage I EZ – Qtz-Fsp-Sch

(Brown et al, 2001)

 3. Shallow-level examples

2. Porphyry-style examples

1. Type-examples

4. Pogo

OUTLINE OF EXAMPLES IN SHORTCOURSE

SHOTGUN (~1 M.oz.)

(Rombach & Newberry, 2001)

 SHOTGUN

• Geology & Mineralization

– Granite porphyry (70 Ma)

– Stockwork & breccia; local UST/brain rock

– Early albite, later sericite-carbonate

– Apy-Py-Po-Loel-Cpy-Mo-Bn-Sch

– Au-Bi-Te (Au:Bi 0.76)

(Rombach & Newberry, 2001)

 SHOTGUN
• Fluids

– Reduced ore assemblages (δS –5.5 to –5.0)

– Fluid inclusions: vapour & brine; 300-600C

– Vapour: H2O>CO2>CH4, low salinity

– Brine: 40-60 wt.% NaCl equiv.

– Pressure/depth: ~0.5 kbar/ ~2 km

– O, H, S isotopes & fluids = magmatic

(Rombach & Newberry, 2001)

SHOTGUN PARAGENESIS

(Rombach & Newberry, 2001)

SHOTGUN TEXTURES

A - Stockwork
C - Breccia
D - UST/brain rock
Au-Bi – 0.73
(Rombach & Newberry, 2001)
 3. Shallow-level examples

2. Porphyry-style examples

1. Type-examples

4. Pogo

OUTLINE OF EXAMPLES IN SHORTCOURSE

TINTINA GOLD BELT
0 500
Tintina Gold Belt
kilometres
Tombstone Plutonic Suite

Tungsten P lutonic Suite

Major gold deposits
Gold occurrences
Fort Knox, Ryan Lode
& True North Alaska Yukon

Dublin
Pogo Gulch
Donlin Brewery
Creek Creek
Shotgun

Kula Kula
(85Ma) (56Ma) Farallon
(100Ma)

(Flanigan et al., 2000)

 DONLIN CREEK (28 M.oz.)
• Exploration

– Placer gold 1909

– Lode ore found 1940 above placer fields

– Ongoing exploration 1970-1990’s

– Rock chip & soil sampling (>250ppb over ore)

– RC & diamond drilling

(Ebert et al., 2000)

DONLIN CREEK
• 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
(Ebert et al., 2000)
DONLIN CREEK VEINS
TINTINA GOLD BELT
0 500
Tintina Gold Belt
kilometres
Tombstone Plutonic Suite

Tungsten P lutonic Suite

Major gold deposits
Gold occurrences
Fort Knox, Ryan Lode
& True North Alaska Yukon

Dublin
Pogo Gulch
Donlin Brewery
Creek Creek
Shotgun

Kula Kula
(85Ma) (56Ma) Farallon
(100Ma)

(Flanigan et al., 2000)

 BREWERY CREEK (1.4 M.oz.)
• Exploration
– Discovered in 1987
– Soil geochemistry
– >25ppb over 12km strike
– Reserve trend ~12 major gold zones
– Open pit mining between 1997 & 2001

(Diment, 1996)
 BREWERY CREEK
• Geology
– 80 % ore hosted in Tombstone suite intrusions
– 20 % hosted in Cambrian-Carboniferous sediments
– Reserve trend comprises
• Lies outside magnetic high (aureole/intrusion)
• E-W monzonite
• Normal, dip-slip E-W, NW & NNE brittle faults
• Veins & ore trend E-W with NNE component
(Lindsay, 2002)
BREWERY CREEK MAP

(Lindsay, 2002)
BREWERY CREEK MAGNETICS

(Hart et al., 2000)

BREWERY CREEK CROSS SECTION

(Diment, 1995; Lindsay, 2002)

BREWERY CREEK GRADE TRENDS

Golden Kokanee

(Lindsay, 2002)
 BREWERY CREEK
• Ore
– Mineralization in monzonite, 3 vein stages
1) pyrite-quartz-carbonate-roscoelite
2) arsenopyrite-carbonate-quartz-gold
3) stibnite-quartz-carbonate-adularia
– Only oxide ore processed (weathering ~10-30m)
– Hypogene gold in arsenopyrite & arsenian pyrite

(Mark, 2002)
BREWERY CREEK PARAGENESIS
BREWERY CREEK
 POGO (> 5 M.oz.)
• Exploration
– Geochemical sampling Goodpaster River 1981
– Au, As, W anomalies in Pogo & Liese Creeks
– Soil sampling & surface-exploration 1993

– >100ppb Au in soils anomaly 2km2

– Drilling soil anomaly 1994 – Liese zone
– Drive developed 1999-2000
– Pour first gold end 2005
(Smith et al., 1999)
 POGO
View to North

L1 L2

• Topo relief - 830m (1225m -

400m ASL)
• Deepest Drilling is 230m ASL
returned 2.5m @ 7.16 g/t Au at
L3 L3 level.
• 1500m relief from deep bottom
drilling to Top Hill 4021

(Roberts, 2005)
POGO
 POGO
• Host rocks
– 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)

 POGO
• Ore
Sulphide ~3%
Reduced assemblage: Po-Lo-Apy-Py-Ccp
Au-Bi-Pb-Te-Ag-S phases; Au:Bi 0.89

0.89

(Smith et al., 1999)

 OVERVIEW

• Part 1: Classification, nomenclature & deposit

comparison

• Part 2: Examples: Tintina Gold Province

• Part 3: Other examples & exploration

Late Paleozoic gold deposits, Tien Shan

(Yakubchuk et al., 2002)

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)

 LOCATION OF MAJOR
INTRUSION RELATED GOLD DEPOSITS

(Lang & Baker, 2001)

 KIDSTON (4 M.oz.)

• Regional Geology

• Kennedy Igneous Province

• Mid-Carboniferous-Permian intrusions

• I-type granites, crustally derived

• Similar tectonic setting to TGB?

• Regional Au-Sn-W-Bi-Mo-As-Sb

(Baker & Andrew, 1991)

 KIDSTON
• Deposit Geology
• Magmatic-hydrothermal breccia pipe
• Intrudes Proterozoic granitoid & gneiss
• Gold in breccia & sheeted veins
• Rhyolite sills & dykes
• Py-Po-Sph-Ccp-Mo-Gal-Apy-Bi; zoned
• Deeper Mo-W mineralization
• Ser-Carb-Qtz alteration
(Baker & Andrew, 1991)
KIDSTON MAP

(Baker & Andrew, 1991)

KIDSTON TEXTURES
 TIMBARRA (0.4 M.oz.)
• Geology & Mineralization

– Zoned granite pluton (250-245 Ma)

– Age ore & alteration = intrusion

– Disseminated Au-Bi-Ag-Te-(Mo-As-Sb)

– Sulfide < 1%; Apy-Py-Moly-Au-Bi-Te-Ag

– Magmatic-hydrothermal transition

(Mustard, 2001)
TIMBARRA MAP

(Mustard, 2001)
TIMBARRA CROSS SECTION

(Mustard, 2001)
TIMBARRA GRANITE FACIES & Au

(Mustard, 2001)
 TIMBARRA PARAGENESIS & FLUIDS
Late Transitional
Process Magmatic- Hydrothermal
Magmatic Hydrothermal
Mineralization
Stage 1 Stage 2a Stage 2b Stage 3 Stage 4
Style
Miarolitic cavities
Aplite dykes
Pegmatite veins
Vein-dikes
Quartz-moly veins
Fractures (Au)
Comb veins
Chalcedonic veins
Hematite staining
Melt Inclusions
High XCO2
Mod-Low XCO2
Mod-Low Salinity H2O

(Mustard, 2001; Mustard, 2000)

 SUMMARY CHARACTERISTICS
Style Alteration Metals Fluids
Shallow • veinlets, stockwork, • clays, • As,Sb,Hg • brine, CO2-
(<3km, breccia carb, fsp • Bi, Te vapour
<1 kbar) • dikes, stocks, sills • late H2O

Strong evidence for major magmatic input,

epithermal/porphyry style characteristics
Style Alteration Metals Fluids
Deep • sheeted, disseminated • fsp, carb • W, Mo • CO2-H2O
(>3km, • stocks, plutons • Bi, Te • some late brine
>1 kbar)

(Baker, 2002)
 Magmatic Meteoric
DEPTH-FLUIDS MODEL FOR IRGS CO2-H2O Brine H2O
km
Style Example
vv v v v
vv 0
Epithermal
Dyke, sill, dome Brewery Creek +
+
Veins Donlin Creek
Dis’minated

Porphyry Kidston +
+
Stocks, plugs Shotgun + 5
+
Breccias
Stockwork

Mesothermal Fort Knox + +

+
Plutons Dublin Gulch
+ + +
Sheeted Timbarra + + + + +
+ + + +
Dis’minated Pogo +
+
10
(Baker, 2002)
 IMPLICATIONS
• IRG possess range in characteristics

• Variation in part reflects depth of emplacement

• Magmatic carbon dioxide critical role

• High pressure devolatilzation

• Effect on other volatiles

• Volatile composition varies with depth

• Continuum of deposit types reflect depth & fluid composition

• Exploration criteria will vary between deep, shallow, proximal, distal

 ROLE OF BISMUTH
• Au-Bi-W-Mo-As geochemistry
• Spatial & temporal link to intrusions
• In detail spatial & temporal differences
• W early
• Au-Bi late
• Main ore zones spatially separate
• Re-emphasizes Bi association
 ROLE OF BISMUTH
• Bi significant in ppt. Au
• Bi low melting point (274C), dec. with inc.
pressure
• Bi will ppt. as a liquid rather than solid
• Experiments @ 300C show strong
partitioning Au in Bi liquid
• Bi may concentrate Au in fluids with very low
Au contents
• Low melting point Bi, Au-Bi will be late

(Douglas et al, 2000)

 APPLICATION OF
KEY EXPLORATION CHARACTERISTICS
– 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 within IRGS

 EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD
• Reviewed mineral occurrence data sheets &
1:500,00 scale maps (Hogdkinson Province)

• Regional Scale: Tectono-Magmatic Setting

– Continental arc environment

– Numerous W-Sn-Mo-Bi-As & Au occurrences

– Permo-Carb Kennedy Igneous Provence (KIP)

 EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD
• Regional Scale: Intrusive types
– Wide range of granite suites
– Including mod reduced I-types & transitional I-S to S
types
– Highly fractionated components
– Magmatic-hydrothermal transition textures
 EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD
• Regional Scale: Variety of crustal levels exposed
– Contact aureole development (& P-T information)
– Presence/absence syn-intrusive volcanic rocks
– Mineral occurrence styles

• Local Scale: Mineral Occurrence Data & Past Exploration

– Past Au exploration focussed on Kidston-breccia styles &/or porphyry
Cu-Au systems

– Wider range of IRGS styles not widely tested

– W-Bi-As-(Mo,Sn) prospects poorly tested for Au

 EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD
• Local Scale: Target Criteria
– Spatial associated with mod-red I-type KIP intrusives
– Geochemistry of mineral occurrences (including placer)
• Au-Bi ±(W-Sn-Mo-Cu-Pb-As) – highest potential
• Au-W (Bi commonly n/a)
• Bi±(W-Sn-Mo±Cu - no recorded Au – commonly n/a)
• Au-As-Sb – distal from intrusives, mesothermal-epithermal

– Target type
• Shallow (Donlin Creek-style); Mod-Deep proximal (Fort Knox-style);
Mod-Deep distal (Pogo-style)
N QLD HODGKINSON PROVINCE

(modified from Garrad & Bultitude, 1999)

EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD
 EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD

M2: 0.5ppm Au,

140ppm Bi

M5: 8.6ppm Au, 657ppm Bi

EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD
1000
Tinaroo regional
Mount Mascotte

100
Bi (ppm)

10

1
1 10 100 1000 10000
Au (ppb)
 EXAMPLE OF IRGS EXPLORATION
CHARACTERISTICS: NORTH QLD

T14 (1.26 ppm Au; 20.71 Bi) T18 (2.42 ppm Au; 58 ppm Bi)
Quartz-muscovite vein with narrow Quartz-muscovite pegmatite
muscovite (greisen-like) alteration halo -like vein
Tinaroo Creek
 CONCLUSIONS I
• IRGS have a 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 within IRGS
 CONCLUSIONS II
• Belts known for magmatic related W-Mo-Sn
systems are high priority target areas
– Au-(Bi-W) placer occurrences provide good
indicator
– Such regions commonly lack thorough testing of
IRGS model
– Commonly not sampled for Au & Bi
• Many regions can be regionally evaluated
quickly through database searches & GIS
approaches