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.