Porphyry Introduction-1ACHF SEG10Lombok
113
Chuquicamata, Chile Porphyry Ore Deposits: Their geology and genesis Anthony Harris, CODES University of Tasmania
description
Materi Porphyry
Transcript of Porphyry Introduction-1ACHF SEG10Lombok
Chuquicamata, ChileChuquicamata, Chile
Porphyry Ore Deposits:Their geology and genesisPorphyry Ore Deposits:Their geology and genesis
Anthony Harris, CODES University of Tasmania
Porphyry Deposits - Characteristics
Large tonnage and low grade bulk mineable deposits
Large volumes of hydrothermal alteration
Stockwork and breccia-hosted ore
Related to porphyritic intrusions
Supergene enrichment
Cadia Hill Cu-Au porphyry, NSW
Fracture controlled sulfide mineralisation localized inand around porphyritic intrusions
Porphyry Deposits - Characteristics
Bingham, USA
Porphyry Deposits - Characteristics
Striking relationship between Cu-bearing hydrothermal veins and igneous rocks that display porphyritic texture
A variety of textures preserve aqueous phase separation (and bubble formation) and volatile streaming in the melt
Porphyritic rocksPorphyritic rocks
Decompression volatile exsolution + rapid crystallization of residual melt
Bingham, USA
from Shinohara and Hedenquist, 1997
Deposit Genesis
Cu Mo (*10)
Au (*10,000)
Calc-alkalic
Alkalic
High-K calc-alkalic
Increasing SiO2
content of magmas
• Increasing magnetite contents in early-formed veins and alteration assemblages
• Decreasing depth of emplacement
isla
nd a
rc s
ettin
gs
Continental arc settings
Craton
Classification by Metal Content
Modified from Kesler (1973) and Thompson (1994)
Giant porphyry copper deposits
El Teniente, Chile (82 Mt of contained Cu)
Giant porphyry copper deposits
0
10
20
30
40
50
60
70
80
90
Con
tain
ed
cop
per
meta
l (M
t)
Behemothian
Super-giant
Oyu
Tolg
oi
Akto
gay-A
iderly
El Te
nie
nte
Rio
Bla
nco
Gra
sb
erg
Los P
ela
mb
res
Cerro
Colo
rad
o
La G
ran
ja
Reko D
iq
Cu-Mo deposits
Ch
uq
uic
am
ata
Colla
hu
asi
Bin
gh
am
Escon
did
a
Rad
om
iro To
mic
El S
alv
ad
or
Cu-Au deposits
Bu
tte
Can
an
ea
Lon
e S
tar
More
nci - M
etc
alf
Peb
ble
East
Resolu
tion
Pim
a
Cu
ajo
ne
Peb
ble
West
Cu-Au-Mo deposits
Where in the world? The largest porphyry Cu-Mo deposits / districts
Porphyry Cu-Mo
Northern ChileNorthern Chile
Aktogay-AiderlyAktogay-Aiderly
Southern PeruSouthern PeruLa GranjaLa Granja
ButteButte
SW Arizona /Sonora
SW Arizona /Sonora
Central ChileCentral Chile
Map source: http://www.gebco.net
Giant gold-rich porphyry deposits
Bingham, USA (1800 t of contained Au)
0
400
800
1200
1600
2000
2400
2800
Gra
sb
erg
Bin
gh
am
Oyu
Tolg
oi
Peb
ble
East
Cad
ia d
istric
t
Peb
ble
West
Kal'm
akyr
Daln
eye
FS
E/L
ep
an
to
Cerro
Casale
Pan
gu
na
Ok Te
di
Reko D
iq
Batu
Hija
u
Min
as C
on
ga
Tam
pakan
Escon
did
a
El Te
nie
nte
Galo
re C
reek
Alu
mb
rera
Frie
da R
iver
Atla
s
Sar C
hesh
meh
Ch
uq
uic
am
ata
Sip
ilay
Gold
(to
nn
es)
Giant gold-rich porphyry deposits
Cu-Mo deposits
Cu-Au deposits
Cu-Au-Mo deposits
BatuHijauBatuHijau
Porphyry Cu-Au
Oyu TolgoiOyu Tolgoi
CerroColoradoCerroColorado
Bajo de laAlumbreraBajo de laAlumbrera
Minas CongaMinas Conga
Reko Diq
Reko Diq
CadiaCadia
AlmalykAlmalyk
PangunaPanguna
PhilippinesPhilippines
PNG – Irian JayaPNG – Irian Jaya
GaloreCreekGaloreCreek DalneyeDalneye
Cerro CasaleCerro Casale
Map source: http://www.gebco.net
Locations of giant Au-rich porphyry deposits
alkalic
sub-alkalic
40 50 60 70
4
8
12
16
SiO2 (wt%)
Na 2
O +
K2O
(w
t%)
High-K calc-alkalic
Cu-Au(-Mo)
Silica-undersaturated alkalic
Cu-Au
Silica-saturated alkalic
Cu-Au
Modified from Lang et al., 1995
• Porphyry Cu-Au-Mo deposit classification
Alkalic or Subalkalic?
Arizona calc-alkalic
Cu-Mo
Cu-Au
SW Pacificcalc-alkalic
Free gold in quartz-bornite vein, Ridgeway, NSW
Classification can be difficult due to K- and Na-metasomatism
Modified from Blevin, 2003
Magma Chemistry
Cu - Au
Sn ± W
Mo
WW - Mo
Cu - Mo
Sn
Increasingfractionation
Increasingoxidation
Rb/Sr
Fe2O3 /FeO
101
100
10-1
10-110-210-3 102101100 103
Metal endowment ofintrusion-related deposits controlled by the magma’s:• oxidation state• compositional
evolution (e.g., SiO2)
Anhydrite phenocryst with apatite inclusions, North Parkes, NSW
Epochs of porphyry deposit formation
Calc-alkalic
High-K calc-alkalicAlkalic
Magmatic affinity Tectonic Setting
0 100 200 300 400 500Age (Ma)Age (Ma)
0 100 200 300 400 5000
10
20
Continental arcIsland arcCollision zoneArc of unknown type
Data source: Kirkham & Dunne, 1999
Coppins GapPorphyry Mo
~2800 Ma
CadiaPorphyry Cu-Au ( Mo)
~440 Ma
BinghamPorphyry Cu-Au-Mo
~37 Ma
GrasbergPorphyry Cu-Mo-Au
~2.5 Ma
Geodynamic Settings
Cadia (440 Ma)2,979 Mt @ 0.45 g/t Au, 0.26 % Cu
Cadia (440 Ma)2,979 Mt @ 0.45 g/t Au, 0.26 % Cu
Lihir (0.9 – 0.4 Ma)~44 Moz AuLihir (0.9 – 0.4 Ma)~44 Moz Au
Emperor (3.9 Ma)~12 Moz AuEmperor (3.9 Ma)~12 Moz Au
Panguna (3.5 Ma)~6.5 Mt Cu & 28 Moz AuPanguna (3.5 Ma)~6.5 Mt Cu & 28 Moz Au
Ok Tedi (1.2 – 1.1 Ma) ~5.5 Mt Cu & 23 Moz Au
Ok Tedi (1.2 – 1.1 Ma) ~5.5 Mt Cu & 23 Moz Au
Porgera (6.0 Ma)~23 Moz AuPorgera (6.0 Ma)~23 Moz Au
Grasberg (3 Ma)~28 Mt Cu & 90 Moz Au
Grasberg (3 Ma)~28 Mt Cu & 90 Moz Au
Wafi (10 Ma)501Mt @ 0.95% Cu, 0.64 g/tAu
Wafi (10 Ma)501Mt @ 0.95% Cu, 0.64 g/tAu
• Porphyry deposits emplaced in
narrow time interval
• Similar magma suites
• General relationship to subduction environment
Relationship to tectonic change
Porphyry Provinces
Island arc
Andean arc
Accreted arc Post orogenic belt
Behind-belt magmatic centres (shoshonitic)
Tectonic SettingTectonic Setting
Island Arc Subduction Continental Arc Collision
www.geol.lsu.edu
Porphyry copper deposits are the product of magma genesis at convergent plate margins
Melting of lower crust by upwelling lithospheric and asthenosphic mantle is the source of primitive and oxidized, metal- and volatile-rich magmas, but
Tectonic SettingTectonic Setting
Deposits also occur in post-collision settings
Lower crust melts as it is pushed into the lithospheric mantle forming primitive and oxidized, metal- and volatile-rich magmas
Porphyry ore deposits are generally emplaced at depths of 2-4 km below the Earth’s surface
Geologic SettingGeologic Setting
Kelvin porphyry Cu prospect, Arizona
Deposits emanate from wet, evolved magmas
Geologic SettingGeologic Setting
Porphyry ore deposits have long been recognized to form beneath or within
andesitic stratovolcanic successions
Geologic SettingGeologic Setting
Conceptual model developed in part from geologic observations of the Bajo de la Alumbrera host rocks
New assessment of these rocks reveals- the dominance of extensive basin-fill deposits - volumetrically minor lavas, and- peperites throughout
Nested dome complexes were the surficial expression of the silicic volcanism coeval with at least the earliest porphyritic intrusions
Alumbrera, Argentina
USGS/Cascades Volcano Observatory
Mount St. Helens, USA
Geologic SettingGeologic Setting
Volcano-sedimentary basins are increasingly being recognized as the geological setting for porphyry systems
Given the complex array of environments where porphyry deposits can form requires more diverse exploration models
Models will need to account for geologically-controlled variation in near-surface hydrothermal features
Hydrological models will be influenced by host rock architecture
Lowell and Guilbert, 1970
Veins
Veins? ? ?
?? ? ?
?
VeinsPeripheralcp-gal-siAu-Ag
Peripheralcp-gal-siAu-Ag
Low pyriteshell
py 2%
Low gradecore
low total sulfide
cp-py-mb
Oreshell
py 1%cp 1-3%
mb 0.03%
Mag >py Mag >
py, cp
Mag + py
Pyriteshell
py 10%cp 0.1 -3 %
mb tr
Veinlets Veinlets
Veinlets >disseminated
Veinlets >disseminated
Veinlets >disseminated
Disseminated
Disseminated+
Microveinlets
Deposit FormDeposit Form
Propylitic Zone
Phyllic ZonePotassic Zone
FOV 3.5 km
EAST WEST
Bajo de la Alumbrera, Argentina
Deposit Form
Antapaccay, PeruFar South East, Philippines North Parkes, NSW
Intrusive Geology
-66°
36’1
5
P2
EP3
LP3
LA
-27°20’
LP3
100 m
N
Post-Mineralization
Porphyry
Northwest Porphyry
LEGEND
P2 Porphyry
Northeast Porphyry
Andesite volcanic and
volcaniclastic rocks
Early P3 Porphyry
Late P3 Porphyry
Quartz Eye Porphyry
Alluvium
Los Amarillos Porphyry
and igneous breccia
P2
EP3
LP3
LA
from Proffett, 2003
Intrusion Geometries
3-D geology block model Dinkidi Stock (Wolfe, 2001)
Blind intrusions
Blind intrusions
QMPQMP
Biotite-altered trachyandesiteBiotite-altered trachyandesite
E27 open pit, North Parkes, NSW
Granodiorite PQM PQM
Rio Blanco, Chile
Multi-phase intrusions
Multi-phase intrusions
Biotite quartz monzonite intruded by quartz monzonite porphyry, NorthParkes, NSW
Multi-phase intrusions • Multiple pipes, dykes or sills
typically comprise mineralised intrusive complexes
• Only one or two intrusive phases create significant mineralisation
• A number of factors may affect an intrusion’s capacity to exsolve abundant volatiles and metals, including:
• depth of emplacement • volatile content • crystallisation history• seismic activity
Early, high grade quartz monzonite porphyry cut by later, lower grade crystal-richQuartz monzonite porphyry, North Parkes porphyry Cu-Au deposit, NSWEarly, high grade quartz monzonite porphyry cut by later, lower grade crystal-richQuartz monzonite porphyry, North Parkes porphyry Cu-Au deposit, NSW
Intrusion Geometries
Laramide volcanic edifice
Laramide Intrusive complex
PC intrusions
Arizona Cu-Mo PCDs
Ordovician Volcanics
Ordovician Intrusive complex
North Parkes Cu-Au PCDs
• Plutons (deep)
PCD PCD
• Pipes
• Dykes (shallow)
Early
Late
• Stocks
Subeconomic PCDSubeconomic
PCD
Sections from Lang and Titley (1998) and Lickfold et al. (2003)
E26E26
E37E37 E31E31
E27E27
E48E48
E22E22
E28E28
Endeavour porphyry Cu-Au deposits, North Parkes, NSW
Endeavour porphyry Cu-Au deposits, North Parkes, NSW
Deposit Clusters
Quartz-sulfide veins in hematite-altered quartz monzonite porphyry, Hopetoun Au, NSW
Alteration and Mineralisation
• Porphyry deposits are characterized by several alteration assemblages:
Potassic Propylitic Phyllic (QSP) Intermediate argillic Advanced argillic
• Understanding their spatial distributions is vital for exploration
From Holiday and Cooke (2007), with inspiration from Sillitoe and Thompson (2006)
qz-cp veins in orthoclase-altered dacite porphyry, Ampucao, Philippines
Epidote veins and alteration, Mankayan,
PhilippinesVuggy quartz, Lepanto,
Philippines
Bladed calcite-cemented breccia, Kelian, Indonesia
Biotite-magnetite and orthoclase-altered
trachyandesite, E27, NSW
Biotite-magnetite-altered hb-qz diorite porphyry, Philex, Philippines
Actinolite-cemented hydrothermal breccia, El Teniente, Chile
Prehnite-calcite-pyrite vein in chlorite-altered basalt, Ridgeway, NSW
Lepanto mineLepanto mine
Mankayan lithocap, Philippines
Alteration assemblages:
Qz-mt-cp veins in potassic-altered monzodiorite, Grasberg
Hydrothermal Alteration
Biotite-K-feldspar magnetite-quartz-albite
(Potassic)Garnet-epidote-actinolite chlorite-magnetite-hematite
(Calc-silicate)
Chlorite-epidote-albite
(Propylitic)
Earl
y
Chlorite-sercite (Intermediate
Argillic)
Pyrophyllite-kaolinite
(Advanced Argillic)
Sercite-quartz-pyrite
(Phyllic)
Late
Hydrothermal Alteration Assemblages
Mineralogy, nature and style
Observations need to include:• alteration type (dominant mineral/mineral assemblage)
• dominant• subordinate
• mineral assemblage• texture • intensity• distribution
Dominant ‘mineral’ Mineral Assemblage Composition Generic Term
Kaolinitic Kaolinite-montmorillonite ( sericite- chlorite)
K, Ca, Mg-metasomatism Argillic
Pyrophyllitic Pyrophyllite-kaolinite ( quartz-sericite) K, Ca, Mg-metasomatism Advanced argillic
Sericitic-Chloritic Chlorite-sercite ( montmorillonite-illite-smectite-calcite-epidote)
K, Ca, Mg-metasomatism Intermediate argillic
Sericitic Sercite-quartz-pyrite (chlorite) K, Na, Ca, Mg-metasomatism
Phyllic
Albitic Albite epidote-chlorite-hematite Na, Ca, Mg-metasomatism Sodic
Feldspathic K-feldspar biotite-quartz-sericite-albite-anhydrite-epidote
K-metasomatism Potassic
Biotitic Biotite K-feldspar-magnetite-quartz-albite-anhydrite
K-metasomatism Potassic
Chloritic? Garnet-epidote-actinolite-chlorite-carbonate magnetite-hematite
Ca-, Na-metasomatism Calc-silicate
Chloritic Chlorite-epidote-albite carbonate-sericite-montmorillonite-pyrite-hematite
Ca-Mg-metasomatism Propylitic
Chloritic Actinolite-chlorite-albite epidote Ca, Na-metasomatism Calc-sodic
Defining alteration assemblages
Original component Typical alteration replacement product
Magnetite, ilmentite and titano-magnetite Pyrite, leucoxene, titanite, pyrrhotite, hematite
Pyroxene, amphibole, olivine, and biotite Chlorite, illite, quartz, calcite, pyrite, anhydrite
Plagioclase Calcite, albite, K-feldspar, quartz, anhydrite, chlorite, illite, kaolinite, montmorillonite, epidote, sericite
Anorthoclase, sanidine and orthoclase K-feldspar, albite, sericite
Quartz Microcrystalline quartz
Hydrothermal Alteration Assemblages
K-bearing minerals alter to similarly K-bearing minerals…
Keep in mind what the ‘original’ mineral could have been, as typically
Mineral assemblage
Hydrothermal Alteration of Mafic Volcanics
bt-mt-Kspar-py mt-bt-act-Kspar-py alb-ep-act-chl-py chl-ep-act-py
Infill textures (veins)
Breccias
Replacement textures
Alteration Textures
Pervasive(Strong Kflds)
Selective(chl alt mafics and
ser-chl alt feldspars)
Vein Halo(K-feldspar selvage to tourmaline vein)
Vein(qtz stockwork)
Alteration Textures
Alteration Intensity
IntensePervasive Kspar
StrongPervasive Kspar
ModeratePervasive Kspar (chl)
Weak-ModeratePervasive Chl
Increasing alteration intensitydecreasing textural preservation
Rio Blanco
Alteration Intensity
IntensePervasive Kspar
StrongPervasive Kspar
ModeratePervasive Kspar (chl)
Weak-ModeratePervasive Chl
Most crystal edges visibleCrystal core common replaced
Most crystal edges visible, some ghostingCrystal core common replaced/recrystallized
Most crystal edges ghosted (rimmed by alt. minerals)Crystal cores are near all replaced
Rock texture is totally obscured
inner potassic(Kspar-bt-mt-qtz)
potassic(bt±Kspar-mt-qtz)phyllic
(illite±qtz-py)
cross sectional view
surface view
Source: Proffett, 2003
Alteration Zonation
Kflds(pervasive)
bt-Kflds(pervasive)
tm-bt-Kflds-mt(pervasive)
bt-tm-Kfldschl overprint
Rio Blanco
Potassic Alteration Assemblages
Calc-Silicate Alteration (Skarn)
Mt-hm-epi-chl-cp skarn,
Little Cadia, NSW
Gt-px-epi-qz-py-cp skarn, Bingham Canyon, Utah
Alkalic PCDHigh-K calc-alkalic PCD Calc-alkalic PCD
Mt-anh-cp skarn, Atlas, Philippines
Propylitic Alteration
Alkalic PCDCalc-alkalic PCD Alkalic PCD
Epi-cp-py veins with hematitic alteration selvage, Ridgeway, NSW
Propylitic alteration, Mankayan, Philippines
Epi-ab alteration, North Parkes, NSW
Sodic Alteration
Albite-sericite alteration Cadia East, NSW
Alkalic PCD
Intermediate Argillic Alteration
Int arg alt cut by qz-il alteration, FSE, Philippines
Pervasive int. arg. alteration, Philex, Philippines
Chl-altered rock flour matrix breccia + hem alteration halo, Cadia Hill, NSW
Alkalic PCDCalc-alkalic PCD Calc-Alkalic PCD
Phyllic Alteration
Alkalic PCD
Calc-Alkalic PCD
Int arg alt cut by qz-illite alteration, FSE, Philippines
Pervasive phyllic alteration of QMP, E48, NSW
Vein Arrays
Ridgeway Cadia Hill
E26NE26N
“A” veins “B” veins “D” veins
Multi-phase vein stages
A veins:• Granular quartz-K-feldspar-anhydrite-sulfide veins
• generally lack internal symmetry• irregular and discontinuous
“A” veins“A” veins
“B” veins“B” veins
“D” veins“D” veins
Vein Types (Gustafson and Hunt, 1975)
B veins: • continuous planar quartz veins• contain molybdenite• lack K-feldspar and any obvious alteration halos
D veins: • Late sulfide veins contain pyrite and lesser bornite, chalcopyrite, enargite, tennantite, sphalerite and galena
• Quartz-anhydrite gangue • Phyllic alteration halos
Qtz-alb-K-spar (py-cpy-moly) vein
Bt-mt-alb
Ser-py-qtz vein
Careful observation of cross cutting relationships
Temporal Distribution of Alteration Textures
2.
2.
1.
1a.
Vein stage 1 cut by stage 2
Spatial Distribution of Alteration Textures
Increasing gradeswitch from replacement to vein style alteration
Copper Moutain
Mapping out similar alteration assemblages in contrasting alteration texturescan be useful in determining proximity to ore
Spatial Distribution of Alteration Textures
Mapping out disseminated versus vein/fracture controlled magnetite
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QMP
Latite
Volcaniclasticsandstone
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Irregular magnetite veinlets Quartz-calcite-sulphide stockwork (sericite-hematite alteration halos)
Calcite-orthoclase-bn-(cp)veins (orthoclase halos)
Quartz-bornite stockwork(orthoclase halos)
Fault zone with quartz-pyritecarbonate base metals infill (sericite alteration halo)
Calcite-anhydrite-(gypsum)-fluorite veins
Pyrite veins
Pervasive sericite alteration
Vein-halo sericite alteration
Mottled hematite-sericite alteration
Monzonite dykes
Biotite-magnetite alteration
Propylitic-altered trachyandesite
Quartz-bornite veins (sericite halos)
F
E48 - Wolfe, 1994
Alteration Paragenesis
Sodic (alb-chl-py-cpy) overprint early formed Potassic (bt-mt-act) alteration assemblagesCu and Fe sulfides replace bt-mt altered ferromagnesian minerals
Copper Mountain, BC
· Main ore minerals: chalcopyrite, bornite, gold, molybdenite
Hypogene mineralisation
11,000E
9,600RL
9,450RL
9,800RL
10,000RL
10,200RL
E26, NSW - Cu & Au Grades
10,800E10,600E 11,200E
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>2 g/t Au
1 - 2 g/t Au
0.5 - 1 g/t Au
>2 % Cu
1- 2 % Cu
0.5 – 1 % Cu
• Gangue: qz, or, anh, mt, bt ± ser ± py
• Sulfide zonation:
• bornite-rich core (+ Au)
• chalcopyrite
• outer pyrite halo
• Late-stage veins with abundant pyrite and base metal sulfides can complicate zonation patterns
House, 1994Bornite – chalcopyrite - orthoclase intergrowths, Dinkidi, Philippines
VeinMinor disseminate
Disseminated2-5 vol.%
DisseminatedTrace (<1 vol. %)
Sulfide Abundance and Texture
Deposit Form
Alkalic deposits
Afton, BC Magnetite-apatite veins
Alkalic porphyry Au-Cu deposits
Distance
Cal
c-p
ota
ssic
Po
tass
ic
Propylitic
SodicT
ime
act-gnt-bt-mt-or-alb qtz-ep-ap-ttn-cal
or-alb-act-ap-mt-chl-cal qtz-ttn-rt
chl-hem-or-alb-ep-ap-mt-cal qtz-ttn-rt-act
alb-qtz-chl-calill mt-ttn-rt-scap
Au-Cu Ag-(Pd-Te)
0 km 0.8 km0.3 km
Copper Mountain, British Columbia
Ore is localized in chemically reactive rocks…….
Smoke around the Fire
High K calc-alkalic deposits
High-K Calc-Alkalic porphyry Au-Cu deposits
Distance
Po
tass
icPropylitic
Tim
e
bt-Kspar-mt
chl-ep-mt-cal qtz-ttn-rt
Au-Cu
chl-serIntermediate Argillic Argillic
0 km 0.8 km 1.0 km
bt
2.0 km
actepi veins
3.0 km
epi-chl
Ag-Zn-Pb
Nfract = 30-15/m
Ksap >> Alb
inner potassic(Kspar-bt-mt-qtz)
potassic(bt±Kspar-mt-qtz)phyllic
(illite±qtz-py)
cross sectional view
surface view
Source: Proffett, 2003
Bajo de la Alumbrera, Argentina
MnCO3 veins
D vein, Bajo de la Alumbrera
1.1 Mt @ 6.36 g/t Au and 126 g/t Ag
3.5 km (x 150m x 25m)
Smoke around the Fire
Volatile-saturated intrusion undergoes catastrophic brittle
failure due to hydrostatic pressure exceeding lithostatic load and the tensile strength
of the wallrocks
1 - Magmatic-hydrothermal breccias
• Containment and focussing of volatiles
birth of a magmatic-hydrothermal ore
deposit
Breccias in Hydrothermal Systems
• Permeability enhancement through the formation of a subsurface breccia body allows for focussed fluid flow
• Can precipitate abundant, well-mineralised cement which contains hypersaline & vapour-rich fluid inclusions
• Clastic matrix and clasts may be altered to high temperature mineral assemblages (e.g. biotite)
from D. Cooke, 2010
Sulfide Mineralisation StylesSulfide Mineralisation Styles
Clast alteration
VeinCement
Tourmaline breccia, Río Blanco, Chile
• Hydrothermal cement• Alteration of rock flour
• Alteration of clasts• Cross-cutting veins
Maar-diatreme breccia complex
Late intrusion into active
hydrothermal system
2 - 5
km
p
ale
od
ep
th
2 – Phreatomagmatic breccias
• Clastic matrix & milled clasts abundant
• Surficial and subsurface breccia deposits
• Bedded and massive breccia facies
• Venting of volatiles to the surface
Þ death of a porphyry deposit
Þ shortcut to the epithermal environment
Breccias in Hydrothermal Systems
from D. Cooke, 2010
Late-stage diatreme breccia, Dizon porphyry Cu-Au, Philippines
Supergene enrichment
Oxidation can upgrade low grade resources
From Titley, 1982
EnrichmentBlanket
Idealised supergene enrichment blanket
Deposit Genesis
Batholithic Roots - Yerington, Nevada
Ann-Mason PCD McArthur PCD
Dilles et al., 2000
Dismembered PCD and source Batholith
Porphyry Cu Deposit
Phyllic alteration
Advanced argillic alteration
Tosdal 2008
Comb quartz layers (USTs) in intra-mineral monzonite, Ridgeway porphyry Cu-Au deposit,
NSW
Magmatic-hydrothermal transitionMagmatic-hydrothermal transition
15 cm15 cm
• ‘Slushy’ textures are features of the transition from magmatic to hydrothermal conditions:
unidirectional solidification textures (USTs)
miarolitic cavities vein dykes pegmatite pods and pegmatite veins
• These textural features provide evidence for volatile exsolution and concentration in the top of mineralizing intrusions
fertile magmas crystallise in batches They may release volatiles episodically
through a significant part of their crystallisation history
Comb-layered quartz, KoreaComb-layered quartz, Korea
Volatile Exsolution
Felsicmagma
Volatilemigration
• Tectonic trigger (e.g., ridge subduction)
• Multiple phases of intrusive activity – one or more of which efficiently concentrates and releases metals
• Incompatible behaviour of metals and volatiles allows magmatic transport of metals and sulfur
• Cycles of volatile accumulation and release at the apex of the mineralizing intrusion (multiple seismic events)
• Fluid exsolution may be triggered by mafic magma underplating of felsic magma chamber
Mafic magma (?)Mafic magma (?)
Outflow and mineralisationOutflow and mineralisation
Episodic fluid accumulation and release
Episodic fluid accumulation and release
Severa
l km
sS
evera
l km
s
Porphyry ore genesis
Magma flow in dykes
Scale
Chang
e
~5 k
m
Upper cru
stPCD?PCD?
PCD?PCD?
Upper crustal magma chamber
Arc-transverse lin
eaments
Magma flow in dykes
Diatexite
Sh
ear Z
on
e
~20
km
Low
er c
rust
Magma flow by percolation
Magma flow by percolation
Magma flow in plugs and diapirs
Hypogene Ore Genesis
A
A: Fertile Magma Production• Partial melting in migmatitic zone
at base of crust• Melts transferred to upper crust
along dykes in shear zones
B B: Volatile Exsolution• Magma ascends to neutral
buoyancy level• Shutdown of volcanism?
• Volatiles exsolved during fractional crystallisation (mafic magma involvement?)
Modified from Richards (2003)
• Interaction of mafic and felsic magmas may be an effective method of enhancing the volatile and metal budget of felsic magmas
1991 eruption of Mt Pinatubo, Philippines (image from http://www.unep-wcmc.org/resources)
• Thermal and chemical instabilities can be caused by mafic underplating of felsic magma bodies • metal, volatile and
fluid exsolution • magmatic-
hydrothermal mineralisation
Mafic magmas as fertilizersMafic magmas as fertilizers
Fluid SourcesFluid Sources
Primitive hydrous K-rich mafic magmas have been shown to be important in the formation of porphyry ore deposits
e.g., Northparkes (Lickfold et al. 2007)
Mantle-derived CO2-rich fluids
Source of the sulfur…
E22, Australia
Ajax, Canada
Mingling of primitive alkalic magmas
Bingham, USA
Pd- and Pt-bearing (Au-rich) ore
Magmatic sulfides (rich in Ni-Cu Zn-As-Ag-Pb, Se-Mo-Pd)
Cu-Ni-rich melt inclusions
LMP, Bingham
Contributions of Cu, Au, PGEs and S
Deposit Ag (g/t) Au (g/t) Pd (g/t) Pt (g/t)
Copper Mnt 92 5.0 1.37 0.06
Afton 16.4 4.7 3.5 0.07
Skouries 57 35.8 2.67 0.20
Bingham na 0.02 0.10 0.93
Elatsite 33 13.6 0.72 0.15
Santo Tomas II 45 40 2.67 1.85
Ok Tedi na 17 0.62 0.02
Representative PGE analysesCadia Hill
Fluid SourcesFluid Sources
Fluid PathwaysFluid Pathways
e.g., E26 (Lickfold et al. 2003)
Extreme magmas oxidized meltsCu Au-Mo bearing volatilesCl-, F, SO4
2-, CO32-. PO4
3-, OH-
Quartz-magnetite UST Ridgeway, NSW
Anhydrite-apatite E26, NSW
Fluid PathwaysFluid Pathways
Fe-Zn-Cu : RGB composite
Red – Fe; Green – Zn; Blue – Copper
Fe
Ridgeway, Australia
Just as volatile-rich granite preserves evidence of volatile accumulation…
1.0 mm
‘Quartz Eyes’
Magma EmplacementMagma Emplacement
Bajo de la Alumbrera
Magma EmplacementMagma Emplacement
Ridgeway, Australia
Cathodoluminescence image
CL imaging of comb-quartz layered textures reveals well-defined luminescent bands disrupted by irregular embayments and tubules
Th (V L): ~ 365CX: 45- 47 wt.% NaCl equiv.
Boiling TrailsTh (V L): up to 550CX: 45 wt.% NaCl equiv.
Near-Critical BehaviourTh (V L): ~ 310CX: 3 wt.% NaCl equiv.
Inclusion assemblages record volatile accumulation + release…
[inside an apparently ‘barren’ porphyritic intrusion]
Cathodoluminescence image
~70 MPa
~30 MPa
Average 0.3 wt.% Cu
What are A veins?
Extreme T fluids carried significant Fe and Si…
Vein EmplacementVein Emplacement
A veins diffuse sugary textured vein
Alumbrera, Argentina
Silicate melt inclusions in hydrothermal quartz veinsAlumbrera, Argentina
Cl
Cu
K
A veins preserve the magmatic-hydrothermal transition
Primitive and Cu-rich (up to wt.%) ore fluids
Rio Blanco, Chile
Vein EmplacementVein Emplacement
Recognition of these textures, including the quartz segregations, may provide immediate evidence for a potentially fertile magma
CO2-rich saline fluidsNaCl – H2O CO2 – KClrich in Fe-Cu-Zn-Mn-Ca-Ba-As (?REE)
Dinkidi porphyry Au deposit, Philippines
Wolfe, 2000
Ore-forming fluidsOre-forming fluids
30mm
~1500 ppm Cu (up to 2wt%)3-5 wt% NaCl equiv., 3-8 mol% CO2
Trapped at ~650°C, 2.5kb
Ore-forming fluidsOre-forming fluids
Butte (from J. Wilkinson)
Potassic alterationT = 350°C to 550°C, up to 845°C18O and D compositions Magmatic fluid
Phyllic alterationT = up to 400°C18O and D compositions Magmatic fluid (> 200°C)
Magmatic + Meteoric water (< 200°C)
Fluid SourceFluid Source
Meteoric water has long been thought to play a major role in hydrothermal alteration and ore deposition
continuum between high-T magmatic lower T meteoric water-dominated hydrothermal systems
Recognition of contrasting phyllic alteration is important because it means that the distribution of
alteration zones and mineralization may not fit the expected alteration pattern
so often used to focus drilling programs
Phyllic alteration assemblages need not be post-ore…
Fluid SourceFluid Source
Hypogene Ore Genesis
Hydrothermal Alteration
• Early K-metasomatism (brines): lithostatic load
• Late H-ion metasomatism (gases): hydrostatic load
Ore Formation
Cooling is a symptom, not a cause• The sulfur conundrum: H2S-
predominant fluids, but sulfur transported in the melt as SO2
• Sulfate reduction mechanism? (water-rock interaction, fluid mixing)
Bn-cp mineralisation, E27
Alteration mineralogy:Temperature and acidity controls
• Phase relationships for K-aluminosilicate phases have traditionally been plotted on activity ratio diagrams
• HCl(aq) and KCl(aq) are strongly associated species at high temperatures
• They dissociate strongly when T < 300°C
• Fluid evolution from feldspar- to mica- to clay-stable conditions equates to increasing acidity (i.e. decreasing pH)
P = 500 bars, qz saturated, log a (Al3+) = -5, log a (K+) = -1.3
250
275
300
325
350
375
400
425
450
475
T (
°C)
–3 –2 –1 0 1 2 3 4 5 6
log a (KCl(aq)/HCl(aq))
Al3+(aq)
Andalusite(advanced
argillicalteration) M
usco
vite
(phyllic a
ltera
tion)
Musco
vite
(phyllic a
ltera
tion)
Pyro
phyllite
(advance
d
arg
illic
alte
ratio
n)
Kaolinite(argillic)
K-feldspar(potassic
alteration)
K-feldspar(potassic
alteration)
AlO
H2+
Al(O
H)
2 +
from D. Cooke, 2010
0 1 2 3 4 5 6 7 8
pH
Alteration mineralogy:Temperature and acidity controls
• Clays and aluminosilicates are stable under acidic conditions Less hydrous clays
are stable at higher T
• Micas and feldspars are stable under weakly acidic to alkaline conditions
• Andalusite is predicted to be stable at high temperatures but is rarely observed in advanced argillic assemblages
P = 500 bars, qz saturated, log a (Al3+) = -5, log a (K+) = -1.3
250
275
300
325
350
375
400
425
450
475
T (
°C)
Al3+(aq)
Andalusite(advanced
argillicalteration)
Mu
scovit
e(p
hyllic
alt
era
tion
)M
uscovit
e(p
hyllic
alt
era
tion
)
Pyro
ph
yllit
e(a
dvan
ced
arg
illic
alt
era
tion
)Kaolinite(argillic)
K-feldspar(potassic
alteration)
K-feldspar(potassic
alteration)
AlO
H2+
Al(O
H)
2+
Al3+
Alkaline Strongly acidic from D. Cooke, 2010
Kal’makyr (Almalyk) Cu-Au, Uzbekistan 2.5 Gt @ 0.38% Cu and 0.5 g/t Au
Fluid evolution from feldspar- to mica-stable conditions equates to decreasing pH
Alteration mineralogy:Temperature and acidity controls
• Calc-silicate and calc-potassic alteration assemblages are stable at high T and high pH
• Chlorite is stable under weakly acidic conditions when temperatures are less than ~350°C
P = 500 bars, qz saturated, log a (Al3+) = -5, log a (K+) = -1.3log a (Ca2+) = -5, log a (Fe2+) = -6.5, log a (Cl-) = 1, log a (SO4
2-) = -2
pH
250
275
300
325
350
375
400
425
450
475
T (
°C)
Alkaline Strongly acidic
Alu
nit
e(a
dvan
ced
arg
illic a
ltera
tion
)
Fe-biotite(potassic
alteration)
Fe-biotite(potassic
alteration)
Fe-chloriteFe-chlorite
Ca-g
arn
et
(calc
-silic
ate
alt
era
tion
)C
a-g
arn
et
(calc
-silic
ate
alt
era
tion
)
0 1 2 3 4 5 6 7 8
Andalu
site
Al3+
Al3+
AlO
H2+
Pyro
ph
yllit
eKaol
Mu
scovit
e(p
hyllic
alt
era
tion
)M
uscovit
e(p
hyllic
alt
era
tion
)
Kf
Kf
from D. Cooke, 2010
Alteration mineralogy:Redox and acidity controls
• Epidote and garnet contain Fe3+
they typically form under oxidizing conditions
• Chlorite and biotite contain Fe2+
they typically form under reducing conditions
• Propylitic and calc-potassic alteration assemblages are produced by alkaline fluids
T = 325°C, P = 500 bars, qz saturated, log a (Ca2+) = -5, log a (Fe2+) = -6.5,
log a (Al3+) = -5, log a (K+) = -1.3, log a (SO42-) = -2
pHAlkaline Strongly acidic
0 1 2 3 4 5 6 7 8–36
–34
–32
–30
–28
–26
–24
–22
–20
log
f O
2 (
g)
325°C325°C
Alu
nit
e(A
A a
ltera
tion
)
Ep
idote
Ep
idote
Mu
scovit
e(p
hyllic
alt
era
tion
)M
uscovit
e(p
hyllic
alt
era
tion
)
Pyro
ph
yllit
e(a
dvan
ced
arg
illic
alt
era
tion
)
Pyro
ph
yllit
e(a
dvan
ced
arg
illic
alt
era
tion
)
Fe-chloriteFe-chlorite
K-f
eld
sp
ar
(pota
ssic
alt
era
tion
)K-f
eld
sp
ar
(pota
ssic
alt
era
tion
)
Al3+(aq)
AlO
H2+
Al(
OH
) 2+
(aq
)
H2S
(aq
)
HS
O4-
(aq
)
Ca-g
arn
et
(calc
-silic
ate
alt
era
tion
)C
a-g
arn
et
(calc
-silic
ate
alt
era
tion
)
Fe-biotite(potassic
alteration)
Fe-biotite(potassic
alteration)
SO
42-
(aq
)
HS
- (aq
)H
S- (a
q)
MagnetiteMagnetite
HematiteHematite
from D. Cooke, 2010
• Phyllic alteration can be produced by magmatic-hydrothermal fluids
• The phyllic alteration zone can cut through potassic alteration zones, and be independently mineralised
Alteration Zoning Alteration Zoning
Lowell and Guilbert (1970) model
South American porphyry model
potassic
potassicpotassic
phyllicpropylitic propylitic
wallrocks
wallrocks
Alteration mineralogy:Reaction paths
• If K-feldspar stable fluids become more alkaline, epidote may be stabilized
T = 325°C, P = 500 bars, qz saturated, log a (Ca2+) = -5, log a (Fe2+) = -6.5,
log a (Al3+) = -5, log a (K+) = -1.3, log a (SO42-) = -2
pHAlkaline Strongly acidic
0 1 2 3 4 5 6 7 8–36
–34
–32
–30
–28
–26
–24
–22
–20
log
f O
2 (
g)
325°C325°C
Alu
nit
e(A
A a
ltera
tion
)
Ep
idote
Ep
idote
Mu
scovit
e(p
hyllic
alt
era
tion
)M
uscovit
e(p
hyllic
alt
era
tion
)
Pyro
ph
yllit
e(a
dvan
ced
arg
illic
alt
era
tion
)
Pyro
ph
yllit
e(a
dvan
ced
arg
illic
alt
era
tion
)
Fe-chloriteFe-chlorite
K-f
eld
sp
ar
K-f
eld
sp
ar
AlO
H2+
Al(
OH
) 2+
(aq
)
H2S
(aq
)
HS
O4-
(aq
)
Ca-g
arn
et
(calc
-silic
ate
alt
era
tion
)C
a-g
arn
et
(calc
-silic
ate
alt
era
tion
)
Fe-biotite(potassic
alteration)
Fe-biotite(potassic
alteration)
SO
42-
(aq
)
HS
- (aq
)H
S- (a
q)
• Acidification can cause transformations from K-feldspar to sericite• It is not possible for a fluid to evolve from K-feldspar-stable first to muscovite-stable and then to epidote-stable conditions
• Carefully observe textural relationships! from D. Cooke, 2010
Conclusions
• Porphyry Cu-Au-(Mo) deposits form in arc-related settings• Most abundant in Tertiary and Quaternary settings
(preservation)• Quartz stockwork veins and/or hydrothermal breccias
associated with potassic alteration typically host Cu-Au mineralization
• Replacement-style mineralization predominates in some deposits
Diopside – orthoclase – magnetite vein in diorite, Dinkidi alkalic porphyry Cu-Au deposit, PhilippinesDiopside – orthoclase – magnetite vein in diorite,
Dinkidi alkalic porphyry Cu-Au deposit, Philippines
