porphyry deposits. the importance of porphyry deposits as a copper and gold resource gold resources...
TRANSCRIPT
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Porphyry Deposits
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The Importance of Porphyry Deposits as a Copper and Gold Resource
Gold Resources Copper Resources
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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)
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Batu Hijau Porphyry Cu-Au Deposit, Indonesia
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Batu Hijau Porphyry Cu-Au Ores
SupergeneHypogene
Chalcopyrite
Bornite
Malachite
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Spatial Distribution of Porphyry Deposits
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The Origin of Porphyry Cu-Au-Mo Magmas Hydration Melting
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Porphyry-epithermal-skarn system - overview
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Idealized Porphyry Alteration/Mineralization (Lowell and Gilbert, 1970)
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Schematic Porphyry-Epithermal AlterationSillitoe (2010)
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Potassic Alteration
High Grade Ore
BorniteChalcopyrite
Porphyry Ore and Alteration Textures
Phyllic Alteration
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Potassic Alteration Revealed by Staining
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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
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Metal Zonation in Porphyry SystemsBingham Mineral Park
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Tectonic Setting of Porphyry Deposits
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Porphyry metal associations as a function of intrusive composition
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Fluid Overpressure and Porphyry Ore Formation
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Porphyry-Epithermal System Evolution
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LV inclusions VL inclusions
LVHS inclusions
Fluid Inclusions in Porphyry Ore Depositing Systems
Aqueous-carbonicFluid inclusion
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100 m
Primary, Pseudosecondary and Secondary Fluid Inclusions
Primary and pseudosecondary fluid inclusions in dolomite
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Fluid Inclusion Microthermometry
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Salinity Determination from Ice Melting
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Microthermometry of Aqueous Fluid Inclusions
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Salinity Determination from Halite Dissolution
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Isochores for Fluid Inclusions in the System H2O
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Isochores for Halite-bearing inclusions
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Isochores for the System NaCl-H2O
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P-T-X Relationships in the System NaCl-H2O
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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)
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Laser Ablation ICP-MS and Fluid inclusions
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Stable Isotope Data for Porphyry Deposits
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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?
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Decreasing Temperature – the Main Control on Porphyry Copper Ore Formation
(Hezarkhani and Williams-Jones, 1998)
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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.
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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
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A Model for the Formation of Porphyry Deposits
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Transport of Metals by Vapour?
Extinct fumarole
Summit of Merapi volcano, Indonesia
Fumarole emitting magmatic gases at 600 oC
Mo3O8.nH2O
Ilsemanite
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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)
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The Solubility of Chalcopyrite in Water Vapour
Increasing PH2O promotes hydration (and solubility) and increasing temperature inhibits hydration.
Migdisov et al. (2014)
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From Hypogene to Supergene
SupergeneHypogene
Chalcopyrite
Bornite
Malachite
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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
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Cu2+
MalachiteCu2(OH)2CO3
Cuprite Cu2 O
Native Cu
Covellite
Chalcocite
H2 O
H2
O2 H
2 O
Eh
pH
Supergene enrichment
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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.