Porphyry Deposits
The Importance of Porphyry Deposits as a Copper and Gold Resource
Gold Resources Copper Resources
A Geological Cross Section through the Batu Hijau Porphyry Deposit, Indonesia
(920 million tons of ore grading 0.55 wt.% Cu, 0.42 g/t Au)
Batu Hijau Porphyry Cu-Au Deposit, Indonesia
Batu Hijau Porphyry Cu-Au Ores
SupergeneHypogene
Chalcopyrite
Bornite
Malachite
Spatial Distribution of Porphyry Deposits
The Origin of Porphyry Cu-Au-Mo Magmas Hydration Melting
Porphyry-epithermal-skarn system - overview
Idealized Porphyry Alteration/Mineralization (Lowell and Gilbert, 1970)
Schematic Porphyry-Epithermal AlterationSillitoe (2010)
Potassic Alteration
High Grade Ore
BorniteChalcopyrite
Porphyry Ore and Alteration Textures
Phyllic Alteration
Potassic Alteration Revealed by Staining
3KAlSi3O8 + 2H+ = KAl3Si3O10(OH)2 + 6SiO2 + 2K+
K-feldspar Muscovite Quartz
Hydrothermal Alteration – Chemical Controls
2KAl3Si3O10(OH)2 + 2H+ + 3H2O = 3Al2Si2O5(OH)4 + 2K+
Muscovite Kaolinite
Metal Zonation in Porphyry SystemsBingham Mineral Park
Tectonic Setting of Porphyry Deposits
Porphyry metal associations as a function of intrusive composition
Fluid Overpressure and Porphyry Ore Formation
Porphyry-Epithermal System Evolution
LV inclusions VL inclusions
LVHS inclusions
Fluid Inclusions in Porphyry Ore Depositing Systems
Aqueous-carbonicFluid inclusion
100 m
Primary, Pseudosecondary and Secondary Fluid Inclusions
Primary and pseudosecondary fluid inclusions in dolomite
Fluid Inclusion Microthermometry
Salinity Determination from Ice Melting
Microthermometry of Aqueous Fluid Inclusions
Salinity Determination from Halite Dissolution
Isochores for Fluid Inclusions in the System H2O
Isochores for Halite-bearing inclusions
Isochores for the System NaCl-H2O
P-T-X Relationships in the System NaCl-H2O
Salinity-Temperature Relationships in Porphyry Systems
Note existence of high temperature VL and LVS inclusions. Evidence of boiling or condensation?Data from the Sungun Cu-Mo porphyry, Iran (Hezarkhani and Williams-Jones, 1997)
Laser Ablation ICP-MS and Fluid inclusions
Stable Isotope Data for Porphyry Deposits
Chemical Controls on Ore Formation
CuClo +FeCl2o + 2H2S + 0.5O2= CuFeS2 + 3H+ + 3Cl- + 0.5H2O
Deposition of Chalcopyrite (CuFeS2)
Deposition favoured by an increase in f O2, an increase in f H2S and an increase in pH
What about temperature?
Decreasing Temperature – the Main Control on Porphyry Copper Ore Formation
(Hezarkhani and Williams-Jones, 1998)
Cu-Mo Zoning in Porphyry SystemsPorphyry Cu-Mo deposits are commonly zoned with a deeper, higher temperature molybdenite-rich zone and a shallower, lower temperature chalcopyrite-rich zone.
Cooling of an aqueous fluid initially containing 2 m NaCl, 0.5 m KCl, 4000 ppm Cu and 1000 ppm Mo in equilibrium with K-feldspar, muscovite and quartz.
Fum arolesVolcanicaerosols
Vapour Liqu id
Halite
600 Co
800 Co
Partitioning Dep
th (
km)
M agm aticFluid
Porphyry fluid inclusionsH O - NaCl
2
0
1.5
3
4.5
0.01 0.1 1.0 10 100
0
500
1000
1500
Pre
ssu
re (
bar
)
NaCl (wt% )
l
l
v
v
s
s
xb
Magma Emplacement, and the Nature of the Exsolved Fluid
A Model for the Formation of Porphyry Deposits
Transport of Metals by Vapour?
Extinct fumarole
Summit of Merapi volcano, Indonesia
Fumarole emitting magmatic gases at 600 oC
Mo3O8.nH2O
Ilsemanite
Quartzmonzoniteporphyry
Equigranularmonzonite
>0.35%
Cu
<0.35% Cu
SedimentaryRocks
upper lim it ofc ritic al-typeinc lusions
<1 vol %quartz veins
5-10 vol. %quartz veins
b rin e in clu s io n s
c ri tic a l -ty p e in clu s io n s
v a p o r- ri ch in clu s io n s
2.5
3.0
3.5
2.0
Paleo-depth(km)
NNW
halite
opaq ue
va por
va por
va por
va por
sylvite
liq uid
liq uid
liq uid
chalc opyrite
10 m
10 m
10 m
hema titeSSE
The Bingham Porphyry Deposit - A Case for the Vapour Transport of Copper
(Williams-Jones and Heinrich, 2005)
The Solubility of Chalcopyrite in Water Vapour
Increasing PH2O promotes hydration (and solubility) and increasing temperature inhibits hydration.
Migdisov et al. (2014)
From Hypogene to Supergene
SupergeneHypogene
Chalcopyrite
Bornite
Malachite
Oxidised zone
Primary zone
Enriched zone
Leached zone
Mineralized gravel
Mineralized bedrock
Barren gravel
Supergene enrichment
FeS2 + H2O + 7/2O2= Fe2+ + 2SO42- + 2H+
2Fe2+ + 2H2O + 1/2O2 = Fe2O3 + 4H+; 2Cu+ + H2O = Cu2O + 2H+
2Cu+ + SO42- = Cu2S + 4O2
Leached zone – acidity creation
CuFeS2 + 4O2= Fe2+ + Cu2+ + 2SO42-
Oxidised zone – Fe and Cu oxides, acidity creation
Enriched zone – reduction and sulphide deposition
Cu2+
MalachiteCu2(OH)2CO3
Cuprite Cu2 O
Native Cu
Covellite
Chalcocite
H2 O
H2
O2 H
2 O
Eh
pH
Supergene enrichment
References
Seedorff, E., Dilles, J.H., Proffett Jr, J.M., Einaudi, M.T., Zurcher, L., Stavast, W.J.A, 2006, Porphyry Deposits: Characteristics and origin of hypogene features in Hedenquist et Al. (eds) Economic Geology One Hundreth Anniversary Volume, p.251-298.
Williams-Jones, A.E. and Heinrich, C.H., 2005, Vapor transport of metals and the formation of magmatic-hydrothermal ore deposits: Econ. Geol., 100, p.1287-1312.
Evans, A.M., 1993, Ore geology and industrial minerals, an introduction: Blackwell Science, Chapter 14.
Pirajno, F. 2009, Hydrothermal processes and mineral systems, Springer, Chapter 5.
Sillitoe, R.H., 2010, Porphyry copper systems: Econ. Geol., 195, 3-41.