1. Epithermal Deposits

2. Epithermal Systems
Low and high sulphidation deposits

3. Submarine Epithermal Systems

4. The significance of Epithermal Deposits as a Gold Resource

5. Distribution of Epithermal Deposits
High Sulphidation
Low Sulphidation

6. Surface expression of a low sulphidation epithermal deposit

7. Low Sulphidation Deposits Ore Styles and Alteration Assemblages

8. Low Sulphidation Deposits Fluid Inclusion Temperatures and Salinities

9. Low Sulphidation Deposits Oxygen and Hydrogen Isotopic Data

10. Low Sulphidation Deposits Temperature-pH Conditions
3 KAlSi3O8 + 2 H+ = KAl3Si3O10(OH)2 + 6 SiO2 + 2 K+ oC
500
400
Andalusite
Muscovite
K-feldspar
Kaolinite
300
200 1 2 3 4 5 6
Log mK+/mH+

11. The Low Sulphidation Epithermal – Geothermal Link
Old Faithful, Yellowstone
Champagne Pool, New Zealand
Wairakei Geothermal Power Plant, New Zealand
Up to 90 g/t Au

12. The Low Sulphidation Epithermal – Geothermal Link

13. Geothermal Well Scalings from Cerro Prieto, Mexico
Electrum
Sphalerite
Chalcopyrite
Clark, J.R. & Williams-Jones, A.E., (1990) Analogues of epithermal gold-silver deposition in geothermal well scales: Nature, v. 346, no. 6285, pp

14. Controls on the Solubility of Gold
Au(HS)2- +H H2O
= Au + 2H2S +0.25O2
Au(HS)o H2O
= Au + H2S +0.25O2
AuCl H2O
= Au + 2Cl- + H O2
Williams-Jones et al. 2009

15. A model for the formation of low sulphidation epithermal deposits
Au(HS)2- + H H2O =
Au O2 + 2H2S
Removed by boiling
Magmatic vapour condenses in meteoric water
Gold transported as Au (HS)2-
Water rises and boils, releasing H2S and destabilizing Au(HS)2-
Gold deposits as the native metal

16. Epithermal Systems
High sulphidation deposits

17. High Sulphidation Deposits Ore Style and Alteration Assemblages

18. Acid-Sulphate Alteration
Vuggy silica
Advanced argillic alteration
Pyrite
All components of the rock leached leaving behind vuggy silica (pH < 1)
Alunite (KAl3(SO4)2(OH)6
Kaolinite (Al2Si2O5(OH)4
Quartz and Pyrite

19. Conditions of Acid-Sulphate Alteration
King et al., 2014

20. The high sulphidation Pascua epithermal deposit, Chile
Chouinard et al., 2005

21. Mineralization at Pascua

22. High Sulphidation Deposits Oxygen and Hydrogen Isotopic Data

23. High Sulphidation Deposits Fluid Inclusion Temperatures and Salinities

24. A Model for the Formation of High Sulphidation Deposits
Cooke and Simmons, 2000

25. Controls on the Solubility of Gold
Au(HS)2- +H H2O
= Au + 2H2S +0.25O2
Au(HS)o H2O
= Au + H2S +0.25O2
AuCl H2O
= Au + 2Cl- + H O2
Williams-Jones et al. 2009

26. Lessons from Indonesia
Sangihe

27. The Sangihe Au-Ag Deposits
Py I Au 1.1 ppm
Ag 33 ppm
Py II Au 1 ppm
Ag 81 ppm

28. Metal zoning in pyrite Copper map for Py II at Sangihe Gold map for
pyrite at Pascua
Cu (green) As (blue) maps for
pyrite at Pascua

29. The Lycurgus Cup – dichroic glass and nanogold
A possible explanation for “invisible gold” in pyrite – electrostatic attraction
of negatively charged nanogold particles to the surfaces of positively charged
pyrite
Williams-Jones et al. 2009

30. The Sangihe Model
King et al.(2014)

31. Kawah Ijen - High Sulphidation Epithermal Deposit in the Making?
Mining sulphur
Dacite Dome
Alunite/pyrite
Acid lake pH 0.5

32. Sulphur condensation and acidity creation 600 oC pH -O.6
4H2O (gas) + 4SO2(gas) = 2S (solid) + 2H2SO4 (gas)
H2SO4(aq) = 2H+ + SO42-

33. Sampling the gases Giggenbach bottle New dome Alunite/pyrtite Au?
Gas condenser

34. Residual silica in andesite pillow
Acid Sulphate Alteration at Kawah Ijen
Residual silica in andesite pillow
Cristobalite-alunite spine
Alunite-pyrite alteration
Alunite-pyrite vein

35. Distribution of Alteration at Kawah Ijen
Scher et al. (2013)

36. Gold Silver mineralisation at Kawah Ijen
Sangihe
Kawah Ijen

37. Solubility of Silver in HCl-H2O Vapour
Silver solubility increases with hydration
Migdisov and Williams-Jones (2013)

38. Epithermal Au Ore Formation
Vapour-dominated hydrothermal plume rises from magma transporting Au and depositing it as temperature drops below 400C
Hurtig and Williams-Jones (2014)

39. References
Chouinard, A., Williams-Jones, A.E., Leonardson, R.W., Hodgson, C.J., Silva,P., Téllez, C, Vega, J., and Rojas, F., 2005a, Geology and genesis of the multistage high-sulfidation epithermal Pascua Au-Ag-Cu deposit, Chile and Argentina: Econ. Geol., v. 100, p. 463–490.
Clark, J.R. and Williams-Jones, A.E., (1990) Analogues of epithermal gold-silver deposition in geothermal well scales: Nature, v. 346, no. 6285, pp
Cooke, D.R, Simmons, S.F., Characteristics and genesis of epithermal gold deposits. In: Hagemann, S.G., Brown, P.E. (Eds.), Gold in 2000, Reviews in Econ. Geol. vol. 13. Society of Economic Geology, Boulder, CO, pp. 221–244.
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
King, J., Williams-Jones, A.E., van Hinsberg, V., and Williams-Jones, G. High sulfidation epithermal pyriote-hosted Au (Ag-Cu) ore formation by condensed magmatic vapors on Sangihe Island, Indonesia: Economic Geology, v. 109, p