EPITHERMAL GOLD DEPOSIT

 

Gold

Epithermal Gold Deposit

Characteristic, Processes, Products, and Interpretation

 

Noel C. White

noelcwhite@hotmail.com

SEG-MGEI Workshop, Mataram, Indonesia

November 2010

Epithermal gold deposits

A very important style of gold deposit

-can be very big:

1. lihir, PNG 170 Mt @3.5g/ton Au

2. porgera, PNG 85 Mt @5.8 g/ton Au, 33g/ton Ag

 

-can be very rich:

1. cripple creek, USA 630 ton Au in veins grading 15-30 g/ton

2. Hishikari, Japan 220 ton au, Honko veins 70 g/ton Au, 49 g/ton Au

 

Ephitermal gold deposits are very important economically.

Relative amount of gold

(> 5 Moz deposits, 1997)

50% Witwatersrand

12% Epithermal

10% Porphry (+ Intrusion Hosted)

12% Sediment Hosted (Incl. 4%”carlin”)

9% greenstone lode (orogenic)

7% Other ( Fe Fm, VHMS, etc)

Arribas, 2000

 

3 Categories Epitermal Deposit Gold

1.       Low Sulfidation’

2.       Intermediete Sulfidation’

3.       High Sulfidation

Ephithermal means :

Refers at deposit low temperature

Epizonal refers to deposit at shallow depth.

 

How to regocnize epitermal deposit with 2 points:

1.       Their characteristic mineral and textures

2.       Their characteristic hydrothermal alteration mineralogy and zoning

We can inferred that they

-          Formed at low temperature

(100-320, typically 170-280°C)

-          Developed at shallow crustal levels

( typically <1 km below the water table)

 

Origins of Deposits

1.       Magmatic

2.       Magmatic-Meteoric

3.       Meteoric

 

CHARACTERISTIC TEXTURES

Neutral-pH, meteoric Low Sulfidation	Acid-pH, magmatic High Sulfidation
-banded veins -brecia vein -drusy cavites -crustification -latice texture	-Vuggy quartz -Massive quartz -Massive sulfide veins -Crudely banded veins

 

White and Hedenquist, 1995