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Epithermal Gold Deposits: Characteristics, Processes, Products, and Interpretation Noel C. White Modified by Steve Garwin for Southern Arc Minerals Selodong Camp, SW Lombok, Indonesia 15 th April, 2011

Epithermal Gold Deposits A very y important p style y of g gold deposit p • Can be very big: • Lihir,, PNG G 170 0 Mtt @ 3.5 3 5 g/t Au u • Porgera, PNG 85 Mt @ 5.8 g/t Au, 33 g/t Ag

• Can be very y rich: • Cripple Creek, USA 630 t Au in veins grading 15 - 30 g/t • Hishikari, Japan 220 t Au, Honko veins 70 g/t Au, 49 g/t Ag

Epithermal E ith l gold ld deposits d it are very important economically

Relative Amounts of Gold (>5 Moz deposits, 1997)

50% Witwatersrand 12% Epithermal 10% Porphyry (+ intrusion hosted) 12% Sediment hosted (incl. 4% “Carlin”) 9%

Greenstone lode (“orogenic”)

7%

Other (Fe Fm, VHMS, etc.)

Arribas, 2000

Giant Gold Deposits (31 >20 Moz deposits)

1 (7) Witwatersrand 7

Porphyry (+ 1 intrusion hosted)

8

Epithermal (3 HS, 2 IS, 1 LS, 2 LSa)

6

Sediment hosted (incl. 2 “Carlin”)

5

Greenstone lode (“orogenic”) ( orogenic )

4

Other (Fe ox, Fe Fm, Archean diss.) Sillitoe, 2000

Epithermal Gold Deposits: Production + Reserves (~2000)

Inter sulfidation Inter. Alkalic a c LS S subtype

Vi?

Total Au and Ag in Low and Intermediate Sulfidation Epithermal Deposits (n=58)

LS LS (alkalic) IS

Au

Gemmell, 2004

Ag

0

Gemmell, 2004

Mare Baia M Creede Mt M Muro Aurrora Araccata Sacarrimb Victtoria Gunung Pongkkor Tonap pah Fresnillo Ke elian San Cristo obal Comstock Lo ode Zacatecas Rosia Monta ana Berego ovo Tayo otita Bag guio Guanaju uato Pacucha-R Real Sunnysside Miilos Golden Cro oss Profitis Illlias Mogollon Cracow El Bronce Ova acik Karangaha ake Takata ama Baia M Mare Gosowo ong Lebong Tand dai Pera ama Tham mes Bo odie Kushikkino Oatm man Montana Tunn nels Bullffrog Slee eper Konomai El Lim mon Misim ma Repu ublic Pajingo Miidas McLaughlin Esq quel El Pen non Cerro Vanguardia Wa aihi Hishikari Round Mtn aley Ba Empe eror Porg gera Cripple Crreek Ladolam

Billion n $ (US)

Value of Epithermal Deposits (Au and Ag) 16 Ag $ A $ Au

10

Intermediate sulfidation

8

Au $390 US/oz Ag $6 US/oz

6

Low and Intermediate Sulfidation Epithermal Deposits only

LS (alkalic) N=4

14

12

Low sulfidation

N=12 N=6

4 ~5 Moz Au eq. q

2

Location of Principal Epithermal Gold Deposits

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Different classes of epithermal deposits

What does “Epithermal” Epithermal mean? Refers to deposits formed at low temperature. “Epizonal” Epizonal refers to deposits formed at shallow depth depth.

The term Epithermal was coined by Lindgren in 1933 based on observations of – mineralogy of ores and alteration – textures of ores and alteration

and d inferences i f about b – temperature of deposition – depth of formation

We can recognise epithermal deposits by • Their characteristic minerals and textures • Their characteristic hydrothermal alteration mineralogy and zoning

From these we can infer that they • Formed at low temperatures (100o-320o, typically 170o-280o)

• Developed at shallow crustal levels ((typically yp y