OVERVIEW OF EPITHERMAL GOLD DEPOSITS

Abstract

This review aims to evaluate the geological, geochemical, and hydrothermal properties of low- and high-sulfidation epithermal systems within a holistic framework. Fluid compositions, pH–fO₂ conditions, alteration mineral zonation, metal transport patterns, and ore precipitation mechanisms described in the literature are comparatively investigated. In high-sulfidation systems, a low pH (≤2), high oxygen fugacity, and low salinity (≤5 wt.% NaCl) fluid regime, resulting from the condensation of SO₂-dominated magmatic vapor, controls advanced argillic alteration (alunite–pyrophyllite) and porous silica development, while mineralization is linked to magmatic fluid–meteoritic water mixing or deep vapor absorption. In contrast, low-sulfidation systems develop in a hydrothermal environment dominated by meteoric, neutral-pH, and low-salinity fluids with reducing properties. Au transport is controlled by the stability of Au–bisulfide complexes. The loss of H₂S/CO₂ from boiling triggers gold precipitation by influencing both pH gradients and the illite–adularia–calcite stability fields. A comparison of the two systems demonstrates that fluid sources, volatile behavior, and hydrothermal instabilities play decisive roles in the formation of epithermal deposits. This review provides a useful conceptual basis for understanding epithermal mineralization and developing ore exploration models.

Keywords

• Epithermal deposits
• low sulphidation
• high sulphidation
• vuggy silica

EPİTERMAL ALTIN YATAKLARINA GENEL BAKIŞ

Abstract

Bu derleme çalışması, düşük ve yüksek sülfidasyon epitermal sistemlerin jeolojik, jeokimyasal ve hidrotermal özelliklerini bütüncül bir çerçevede değerlendirmeyi amaçlamaktadır. Literatürde tanımlanan akışkan bileşimleri, pH–fO₂ koşulları, alterasyon mineral zonlaşması, metal taşınım formları ve cevher çökelme mekanizmaları karşılaştırmalı olarak incelenmiştir. Yüksek sülfidasyon sistemlerinde SO₂-dominant magmatik buharın yoğunlaşması ile gelişen düşük pH (≤2), yüksek oksijen fugasitesi ve düşük tuzluluklu (≤5 wt.% NaCl) akışkan rejimi; ileri arjilik alterasyon (alünit–pirofillit) ile boşluklu silika gelişimini kontrol ederken, cevherleşmenin magmatik akışkan–meteorik su karışması veya derin buhar absorbsiyonuna bağlı olduğu görülmektedir. Buna karşın düşük sülfidasyon sistemleri, meteoritik kaynaklı, nötr pH’lı ve indirgen karakterli düşük tuzluluklu akışkanların egemen olduğu bir hidrotermal ortamda gelişmekte; Au taşınımı Au–bisülfür komplekslerinin kararlılığı ile denetlenmektedir. Kaynama kaynaklı H₂S/CO₂ kaybı hem pH değişimlerini hem de illit–adularya–kalsit stabilite alanlarını etkileyerek altının çökelmesini tetiklemektedir. Her iki sistemin karşılaştırılması, epitermal yatakların oluşumunda akışkan kaynakları, uçucu davranışı ve hidrotermal dengesizliklerin belirleyici rol oynadığını göstermektedir. Bu derleme, epitermal cevherleşmenin anlaşılmasında ve cevher arama modellerinin geliştirilmesinde kullanışlı kavramsal bir temel sunmaktadır.

Keywords

• Epitermal Yataklar
• Düşük Sülfürlü
• Yüksek Sülfürlü
• Boşluklu silika

References

1. Arribas, A., Jr., 1995, Characteristics of high-sulphidation epithermal deposits, and their relation to magmatic fluid: Mineralogical Association of Canada, Short Course Handbook, v.23, p. 419-454.
2. Cooke, D.R., ve Simmons, S.F., 2000, Characteristics and genesis of epithermal gold deposits: Society of Economic Geologist Reviews, v.13, p. 221-244.
3. Corbett, G.J., 2009, Anatomy of porphyry-related Au-Cu-Ag-Mo mineralised systems: Some exploration implications: Northern Queensland Exploration and Mining 2009, Extended Abstracts, p. 33-46.
4. Deb, M., 2008, Epithermal Gold Deposits: Their Characteristics and Modeling, (online), Available psdg.bgl.esdm.go.id/makalah/Bandung-Gold-Mihir.pdf, August 23, 2010
5. Einaudi, M.T., Hedenquist, J.W., ve Inan, E.E., 2003, Sulfidation state of fluids in active and extinct hydrothermal sysytems: Transitions form porphyry to epithermal environments in Society of Economic Geologists Special Publication 10, p. 285-312.
6. Giggenbach, W.F., 1997, The origin and evolution of fluids in magmatichydrothermal systems, in Barnes, H., ed., Geochemistry of hydrothermal ore deposits, 3rd ed.: New York, John Wiley and Sons, p. 737-796
7. Groves, D.I., Goldfarb, R.J., Gebre-Mariam, M., Hagemann, S.G., Robert, F., 1998, Orogenic gold deposits- a proposed classification in the context of their crustal distribution and relationship to other gold deposit types. Ore Geology Reviews 13, 7-27.
8. Hayba, D.O., Bethke, P.M., Heald, P.M., ve Foley, N.K., 1985, Geologic, mineralogic, and geochemical characteristics of volcanic-hosted epithermal precious-metal deposits: Reviews in Economic Geology, v.2, p.129-167.

9. Hedenquist, J.W., ve Lowenstern, J.B., 1994, The role of magmas in the formation of hydrothermal ore deposits: Nature, v.370, 519-527.
10. Hedenquist, J.W., Matsuhisa, Y., Izawa, E., White, N.C., Giggenbach, W.F., ve Aoki, M., 1994, Geology, geochemistry, and origin of high sulfidation Cu-Au mineralization in the Nansatsu district, Japan: Economic Geology, v.89, p.1-30.
11. Hedenquist, J.W., Izawa, E., Arribas, A.R., ve White, N.C., 1996, Epitheramal Gold Deposits: Styles, Characteristics and Exploration: The Society of Resource Geology: Resource Geology Special Publication number 1, 70p.
12. Hedenquist, J.W., Arribas R.A., ve Gonzalez-Urien, E., 2000, Exploration for Epitermal Gold Deposits: Society of Economic Geology Reviews, v. 13, p. 245-277.
13. Lindgren, W., 1933, Mineral deposits, 4th ed.: New York, McGraw-Hill, 930p.
14. Pirajno, F., 2009, Hydrothermal processes and mineral systems, Dordrecht; London, Springer, Geological Survey of Western Australia, 1250 p.
15. Rye, R.O., 1993, The evolution of magmatic fluids in the epithermal environment: The sstable isotobe perspective: Economik Geology, v.88, p.733-752.
16. Sillitoe, R.H. (2003) Iron Oxide-Copper-Gold Deposits: An Andean View. Mineralium Deposita, 38, 787-812.
17. Sillitoe, R.H., ve Hedenguist, J.W., 2003, Linkages between volcanotectonic settings, ore-fluid compositions, and epithermal precious metal deposits in volcanic, geothermal, and ore forming fluids: rulers and witnesses of processes within the earth, Special Publication No 10, Society of Economic Geologists, pp.315-345.
18. Simmons S.F., White N.C., ve John, D.A., 2005, Geological Characteristics of Epithermal Precious and Base Metal Deposits, Society of Economic Geologists, Inc., p. 485-522.
19. Taylor, B.E., 2007, Epithermal gold deposits, in Goodfellow, W.D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-Types District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods: Geological Association of Canada, Mineral Deposits Division, Special Publication No.5, p.113-139.
20. White, N.C., 1991, High sulphidation epithermal gold deposits: characteristics and a model for their origin, in Matsuhisa, Y., Aoki, M., and Hedenquist, J.W., eds., High temperature acid fluids and associated alteration and mineralisation: Geological Survey of Japan Report v. 277, p. 9-20.
21. White, N.C., ve Hedenquist, J.W., 1995, Epithermal gold deposits: Styles, characteristics and exploration: SEG Newsletter, v.23, p.1, 9-13.