GEOE GEOL 362 2011 EpithermalAuAg

7/27/2019 GEOE GEOL 362 2011 EpithermalAuAg

1/48


2/48

Gold De osits1. Shallow environments

Epithermal (HS, LS, ILS) Submarine exhalative

wa ersran

.

Porphyry

Carlin

Skarn

Manto

3. Deep environments


3/48

Geological setting of gold deposits

EPITHERMAL:

at shallow depth: fromthe surface to as deep

over the temperaturerange of >150 to 300

.

Poulsen, 1996


4/48

Hagemann and Brown (2000), p. 2


5/48

Richards 2009- Geology v. 37 p. 247-250


6/48

Epithermal Gold Deposits

in subduction-

related,

continental-

(Kirkham andSinclair, 1995;

In Sinclair,2007

arc, and islandarc settings, or

back arcs.

hosted byvolcanic,

volcanoclastic

rocks,

and sometimes

n e asemen

units.


7/48

Sillitoe, 2010


8/48

Host rocks and a es1. subaerial volcanic rocks of magnetite series calc-alkaline

suites most of the deposits

2. shoshonitic or alkalic igneous rocks in: mature crustal thickness > 20 km intraoceanic arcs e. .

Landolam and Emperor mines)

continental regions (Cripple creek mine)

Ages:

western Pacific: late Miocene, Pliocene and Quaternary (10 Ma-R).

Western America and Caribbean: early Cretaceous to late Miocene(110- 9 Ma)

Precambrian (metamorphosed) epithermal deposits


9/48

or str ut on

Taylor, 2007


10/48

Gold and Tonnage of Low and High Sulfidation deposits

Hedenquist, 2000


11/48

Tonnageand

Median tonnage/grade:

C: Creede-type LS

P: Porphyry-type

H: Hishikari LS

I: E In o HS

Taylor, 2007


12/48


13/48

Nomeclature

Hedenquist etal., 2000


14/48

3 4

Tennantite: (Cu,Fe)12As4S13Chalcopyrite: CuFeS2

Corbett and Leach, 1998


15/48

adularia



16/48

Alteration

Cobertt and

Leach, 1999


17/48


18/48

Low SulfidationLow SulfidationAuAu--Ag depositsAg deposits


19/48

3 4

Tennantite: (Cu,Fe)12As4S13Chalcopyrite: CuFeS2



20/48

Low sulfidation Au-Cu: t es and model


21/48

Low sulfidation: temporal and spatial zonations


22/48

Alteration in Low Sulfidation Deposits

Hedenquist et al., 2000


23/48

LS de osit : alteration mineralo


24/48

alteration

with low

deposits


25/48

veins withquartz

w e an

adularia

(pink) cutby

hematite

,

from NF,

Canada


26/48

LS Au-Ag deposit

ou wes eva a


27/48

or str ut on

Taylor, 2007


28/48

Round Mountain

Large

disseminated

orebody with277 Mt at 1.2

g/t Au reserves


29/48

Round Mountain:geology andmineralization

Most of the oreoccurs in the

poorly welded

tuffs (26.7 Ma)

Veins or fissure

fil ling in welded

Stratabound

(low grade) in

poorly welded tuffHedenquist, 1996


30/48

Round Mountain: alteration and grade

Hedenquist, 1996


31/48

Hi h SulfidationHi h SulfidationAuAu--Ag DepositsAg Deposits


32/48

High sulfidation: controls


33/48

Hedenquist et

al., 2000


34/48

Highsulfidationalteration

Core:

Intermediate: quartz +

alunite +

pyrophyllite

(kaolinite)

Outer zone:

- clay minerals

At las of al teration: Thompson and Thompson, 1996


35/48


36/48

High

alteration

Core:

Intermediate: quartz +

alunite +

pyrophyllite

(kaolinite)

Outer zone:

- clay minerals

At las of al teration: Thompson and Thompson, 1996


37/48

High sulfidation: alteration


38/48


39/48

High sulfidation: genetic model


40/48

M h i f t l i i LS d


41/48

Mechanisms of metal zoning in LS and

-



42/48

Solubility of gold



43/48

Solubilit of Au, Cu and Zn


44/48

Sillitoe, 2010


45/48

SILLITOE, 2010


46/48

enet c uest ons:

WHAT ARE THEIR CHARACTERISTICS? Where did the solution s in a h drothermal

system originate?

What was the force that made the solutionflow?

What were the sources of the metals?

What caused the solution to depositminerals?


47/48

Discussions

Exploration guidelines Environmental issues: HS vs LS de osits

Mining: relationship alteration and rock

property Processing: mode of occurrence of Au

and Ag and relationship with other

alteration minerals Economic and socials issues


48/48

Corbett and Leach (1998) Southwest Pacific Rim Gold-Copper Systems: Structure, Alteration

and Mineralization. Societ of Economic Geolo ists S ecial Publication Number 6 237 .

Hagemann, S.G., Brown, P. E. (2000). Gold in 2000. Reviews in Economic Geology, v.13, 559

p.Hedequist, J.W., Arribas, A.R. and Gonzales-Urien, (2000). Exploration for Epithermal Gold Deposits. In

Gold in 2000. Reviews in Economic Geology, v. 13, p 245-314

Hedequist, J.W., Izawa, E., Arribas, A., White, N.C. (1996). Epithermal gold deposits: Style,

characteristics, and exploration. The Society of Resource Geology, Special Publication n.1.

Jannas, R. Bowers, T. S. and Petersen, U. and Beane, R. (1999). Geology and Ore Deposits of

the Central Andes. Society of Economic Geologists, special publication n. 7Poulsen, K.H., Robert, F., and Dube, B (2000). Geological Classification of Canadian Gold Deposits;

Geological Survey of Canada, bulletin 540, 106 p.

There are a great variety of good papers published in Economic Geology and Mineralium Deposita

in Epithermal Gold Deposits.

GEOE GEOL 362 2011 EpithermalAuAg

Documents

Transcript of GEOE GEOL 362 2011 EpithermalAuAg