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)