Geotectônica e Metalogenia Global: Ouro e

Metais Bases

Richard Goldfarb e David Leach (USGS)

SIMEXMIN 2012

SECULAR TRENDS FOR MINERAL DEPOSITS

SECULAR TRENDS RELATE TO SUPERCONTINENT HISTORY

after Rogers, 1996

GOLD & Active Margin Fluid Flow Environments

• Grasberg porphyry Cu-Au

deposit, Indonesia: 2560 t

Au (and lots of Cu)

Shallow Magmas Can Form Giant Deposits at

SHALLOW (<3 km) Crustal Depths

<1 g/t Au

~20 g/t Au

1000-4000 g/t Au

• Hishikari epithermal vein

deposit, Kyushu, Japan:

330 t Au (70 g/t average

grade)

Batu

Hijau

Oyu Tolgoi

Cerro

Colorado

Bajo de la

Alumbrera

Minas Conga Reko

Diq

Cadia

Almalyk

Panguna

Philippines PNG – Irian Jaya

Galore

Creek Dalneye

Cerro

Casale

Locations of giant Au-rich porphyry deposits

.

Location of Principal Epithermal Gold Deposits

EASTERN

PACIFIC BELT

WESTERN

PACIFIC

BELT

TETHYS BELT

Erosion Rates and Deposit Depth

Low Preservation Potential for Au Systems:

Porphyry and Epithermal Au Deposits

Tectonic Controls on Global Gold Resources

CHANGING GLOBAL

TECTONICS WITH TIME

Older mineral deposits with greater preservation potential!

JURASSIC-CZ OROGENIC GOLD—AMASIA?

Jurassic to

Cretaceous

Gold:

Deformed

Terranes

above Young

Cover

Changes in far-field stresses is ultimate control

— example: Juneau gold belt, Alaska

• A change from orthogonal to

oblique subduction at ca. 55

Ma in the N Pacific basin

caused a shift to strike-slip

motion on terrane-bounding

faults

• A series of seismic events

between ca. 57-54 Ma formed

the gold belt

• Changes from compression to

transpression or transtension

triggered orogenic gold

mineralization

• Ca. 124 Ma – emplacement of the Ontong-Java plume

Changes in far-field stresses — Mesozoic

orogenic Au in California and east Asia

135 Ma 122 Ma

change in plate motions

changing stresses along continent margins

formation of orogenic Au deposits in California and east Asia

LAURENTIA/GONDWANA TO PANGEA GOLD

Terra Australis Orogen: Paleozoic Au

Lode Gold

Deposits,

Tasman Fold

Belt

PALEOZOIC ANTARCTICA

Paleozoic Gold

7 Moz prod.

100 Moz 100 Moz

250 Moz

150 Moz

GIANT OROGENIC AU DEPOSITS OF

CAOB: 650-280 Ma

after Yakubchuk et al (2005)

Most outboard deposits: ca. 285 Ma for 5000 km

Phanerozoic Goldfields

Precambrian Orogenic Gold

Boring

Billion

• Granite (30%) - greenstone (10%); high-grade gneiss terrains (60%)

• Greenstone belts = broad greenschist facies

• Plate tectonics (plume-driven?) vs. anorogenic tectonics; lateral vs.

vertical growth

• Crustal heat production = 2x-4x present

• Tectonometamorphic ages decrease with structural level

• Late Archean = >50% cont. crust

Late

Archean

Gold

Preserved

in

Cratons:

Kenorland

Sutures?

• NA/Greenland +/- central Australia, Africa/SA. N. Asia

• 63% gneiss, 12% plutonic, 25% metasupracrustal (mostly gs)

• Supracrustal = turbidites and greestone belts (Churchill, Guyanas, Birimian)

• Stable shelf facies; uplift and erosion of shelves/Archean cratons

• Au in Paleoprot. (Ghana) and Archean ( Moro Velho; Gabon) rx

Paleoprot.

Gold

Cratonization = Buoyant SCML

• SCLM depleted in Fe & Al, so lighter than surrounding mantle

• SCLM has melt-depleted peridotite buoyancy so balances isostatic

equilibrium (i.e., still dense enough to prevent significant uplift)

Precambrian Orogenic Gold

Boring

Billion

TECTONIC RECONSTRUCTION OF RODINIA: EVIDENCE OF

PHANEROZOIC-STYLE PLATE TECTONICS

BUT NO GOLD

TEMPORAL DISTRIBUTION OF OROGENIC GOLD DEPOSITS: A STRONG

REFLECTION OF TECTONIC AND LITHOSPHERIC EVOLUTION

斑岩型

Carlin

Gold

Ores:

Inland of

Accreted

Terranes

CTGD – Models Crystallizing magma produced

heat + hydrothermal fluids + metals (Sillitoe & Bonham, 1990; Henry & Ressel, 2000;

Johnston & Ressel, 2004)

Deeply circulating meteoric fluids leached and

remobilized metals (Ilchik & Barton, 1997;

Emsbo et al., 2003)

“Wispy” unit

0.006 oz/t 1.42 oz/t

Metamorphism produced ore fluids that transported

metals (Seedorff, 1991; Hofstra & Cline, 2000)

From Cline, SEG Nevada

Frimmel, SEG 2005

Supercratons & Supercontinents & Wits Au

SUMMARY--Part 1

• Most mineral deposits show distinctive temporal patterns

• These patterns partly relate to factors such as: • position within supercontinent cycle • secular evolution of Earth processes

• Gold deposits show mixed formational-preservational patterns due to: • progressive cooling of the Earth • change from plume-influenced/dominated tectonics to plate tectonics • decreasing buoyancy of subcontinental lithospheric mantle • depth of formation

• Orogenic gold deposits formed in convergent margins throughout Earth history, but show preservational influenced patterns; shallower epithermal and porphyry deposits also define times & sutures of supercontinent formation, but are lost from the geologic record

N. America

Craton

Red Dog

Alaska

Sediment-hosted Zn-Pb deposits

in the rock record:

tectonics-environmental-preservation

Not an academic issue: fundamental

insights for exploration

David L Leach

Global Geoscience Consulting

Red Dog sub-seafloor replacement

MVT and Clastic Dominated * Pb-Zn (SEDEX) Ores

Transport and Deposition

• Extraction and transport: At temperatures < 250 C, Mobile in presence of Oxidized sulfur and immobile in presence of Reduced sulfur (the sulfur god!). Requires minimum salinity of ~ 10 wt%

• Deposition: Mainly increase in reduced sulfur (i.e., local sulfate reduction or fluid mixing with reduced sulfur).

More than Tectonics! * Clastic Dominated

includes true SEDEX

0

5

10

15

20

25

30

35

40

194519501955196019651970197519801985199019952000

Discovery Year

Pb +

Zn (

Mt)

Discovery Year of CD Deposits vs. Pb+Zn (Mt)

Hilton-George Fisher

Red Dog

HYC

Century

Howards Pass

Rampura-Agucha

Changba-

Lijagou

Anarraaq

Kholodninskoye

Approaching Zn Deficit

Exploration for undiscovered

sediment-hosted Zn-Pb deposits

Potentially fertile tectonic

environments (distributed

unequally in rock record)

Focus on passive margins and

few select rift-sag basins (marine

connected)

Environmental factors:

evaporative, reduced siliciclastic

sections, carbonate platforms and

carbonate-bearing siliciclastic

sequences, hydrocarbon-rich

regions

Preservation issues (Archean

roots, accreted island arcs)

60

50

40

30

20

10

0

Pb

+Z

n (

Mt)

Broke

n Hill

Hilton

-Geo

rge

Fishe

rRed

Dog

HYC

How

ards

Pas

s

Kholodn

insk

oye

Mou

nt Is

aSul

livan

Ram

pura

-Agu

cha

Cen

tury

Cha

ngba

-Lijiag

ouGam

sber

g

Don

gshe

ngm

iao

Dug

ald

River

Can

ning

ton

Filizc

hai

Ram

melsb

erg

Faro

Broke

n Hill

Meg

gen

Anarraa

q

Rajpu

ra-D

ariba

Sinde

sar K

hurd

Dairi

(Sop

okom

il)

Big S

yncline

Lady

Lor

etta

Balm

at Lik

Cirq

ue

Black

Mou

ntain

CS

PM

BA

BHT

RF

Leach et al., 2010

Taylor et al., 2009

Tectonic Settings of Clastic

Dominated ZN-Pb (SEDEX): Top

30 deposits

Rifts of the World: Sengor and Natalin, 2001

Where are Continental Rifts with Sediment-hosted Zn-Pb Deposits?

Australian Rift-Sag basin

From Betts et al., 2003

Marine Connected

Archean Rooted

Special time in Earth History

World map showing modern passive margins (Bradley, 2008).

CD Zn-Pb ores forming today in passive margins

Why and where sediment- hosted Pb-Zn occur? - a

tectonic and metallogenic framework for exploration.

Passive margins from Bradley, 2008; Deposits from Leach et al., 2005

NU

MB

ER

OF

PA

SS

IVE

MA

RG

INS

AGE (Ma)

100

24

22

2018

161412

108642

90

80

70

60

50

40

30

20

10

00 500 1,000 1,500 2,000 2,500 3,000

Pb

+Z

n (

Mt)

PHANEROZOIC PROTEROZOIC ARCHEAN

Neo- Meso- Paleo-

2nd O 2 GOE

*

* *

GOE Great Oxidization Event

2nd O2 Second Great Oxidization Event

UN

PM

BAC

CS

RF Passive Margins through time

Indicates poorly constrained age

Evolution of seawater sulfate

concentrations (from

Lowenstein et al., 2003)BHT

MIS

SO

4 m

mo

l/(k

g H

2O

)

1,000

100

10

1

0.1

0.01

0.001

0.0001

Atm

ospheric O

2 (

perc

enta

ge o

fPA

L)

10 2 3 4

Age (billions of years ago)

Prevailing view of atmospheric oxygen evolution over time (modified from Kump, 2008)

Compatible with proxies

Compatible with some proxies

Incompatible with proxies

G - GondwanaR - Rodinia

N - ‘Neo’P - Pangea

Supercontinents

P

G

R

RN P

Supercontinent

Juvenile Crust Creation

Supercontinent

Superplume Events

Breakup

Formation

?

MIS Mass Independent Sulfur Isotopes

Leach et al., 2010

580-740Ma

Snowball Earth cycle MVT ores with dates

The Perfect Storm

Modern Ocean and atm. O2

Vast Carbonate Platforms

Pangea in Low Latitudes

Leach et al., 2010

Permo-Carboniferous 300-250 Ma

Leach et al. (2001) Reconstruction from Scotese, 1999

Irish Midlands

Gays River

E. Tennessee SE Missouri

N. Arkansas

Tri-State

C. Tennessee

C. Missouri UMV

>The Carboniferous of the Irish Midlands was in far field extensional domain of Hercynian orogenic belt.

>Irish Midlands was located in an analogous position with the US mid-continent MVT ores and the Gays

River deposit- in a foreland bounded by a foredeep and inboard of a Pangean tectonic belt.

> Late stage (post-suturing) convergence across the Pangean could account for the “post-Variscan”

deformation of some ore deposits.

Variscan shortening ended in Ireland ~300 Ma, in the Ouachita ~ 305 Ma, and in Gays River ~300

Ma

Bradley and Leach, 2003

The most important point for MVT deposits!

Genesis, Attrition and Preservation

Life Cycle of Passive Margins

Evaporative Factories:

Passive margins and

ocean closure basins

(foreland basins)

Wilson Cycle of Ocean Basins

Exploration for undiscovered

sediment-hosted Zn-Pb deposits

Potentially fertile passive margins for

CD Pb-Zn deposits are <~1.85 Ga

with evaporite and/or carbonate

environment in the platform sections

and organic-rich sections in

siliciclastic section.

MVT ores are most abundant in Late

Neoproterozoic or younger

platform carbonate sections with

organic-rich units AND have

experienced orogenic deformation.

Preservation issues (Archean roots,

accreted island arcs)