the geochemistry of uranium through geological … geochemistry of uranium through geological time...
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The Geochemistry of Uranium
Through Geological Time and the
Evolution of Uranium Deposits
By
Mostafa Fayek
Department of Geological Sciences
University of Manitoba
Workshop
Mendoza, Argentina
April 11-15, 2016
Genesis of Uranium Deposits
Factors influencing solubility of uranium:
1. Temperature
2. Redox (fO2)
3. pH
4. Activity of complexing anions
5. Partial pressure of volatiles (e.g. CO2)
6. Microbial activity
UO2
U4O9
U3O8
UO2F3-
UO2SO4o
UF22+
Fe2O3
FeCO3
Fe2+
FeS2
Bn
Cpy
Ksp
Serc/
Chl
KaolAlunUO6
Ka
ol
Modified from Romberger (1984)
Uraninite (UO2)
Uranophane Torbernite
Common oxidation states 4+ and 6+
15 main types of deposits and 38 subtypes
1. Intrusive
2. Granite-related
3. Polymetallic hematite breccia complex (IOCG)
4. Volcanic-related
5. Metasomatite
6. Metamorphite
7. Proterozoic unconformity
8. Collapse breccia pipe
9. Sandstone
10. Paleo-quartz pebble conglomerate
11. Surficial
12. Coal-lignite
13. Carbonate
14. Phosphate
15. Black shales
Approximately 75% of the world’s U
reserve comes from 5 principal types of U
deposits
IAEA 2013 Classification
(Fayek, 2013)
The type of uranium deposit-varied through time
CONTINENTAL
CRUST
1.7 ppm U
Alaskites
Vein
IOCG (U)
Volcanic
MANTLE
Upper continental
crust2.7 ppm U
Primitive mantle: 21 ppb
Carb. Chondrites: 7 ppb
Calcretes/Lignite/Coal
Conglomerates
Phosphates
Black shalesRollfront
Tabular
Tectonolitho
Breccia pipes
Unconformity
LT-Metamor
HT-Metamorphic
Na-Metasom
Magmatic
SEDIMENTARY
ROCKSIGNEOUS
ROCKS
METAMORPHIC
ROCKS
Basal channelA
BC
T(°C)
(A) alteration, erosion, transport, deposition, (B) diagenesis, metamorphism, and
(C) partial melting, crystal fractionation. Modified from Cuney (2009).
Geochronology of Uranium Deposits
Why is geochronology of uranium deposits important?
Source Transport Mechanism
Geological Environment
or
Depositional Mechanism
Timing
Cuney (2009, 2010)
4.55 to 3.1 Ga
3.1 to 2.2 Ga
2.2 to 0.45 Ga
0.45 to present
Hadean Archean Proterozoic Paleozoic
4.55 Ga 3.1 2.2 0.45
1 2 3 4
4 Major Periods of U Geochemistry Evolution:
Uranium Deposits Through Time
Uranium Deposits Through Time
1.Hadean-Paleoarchean (4.55 to 3.1 Ga)
• Thin mafic crust, U few ppm
• U4+ oxidation state in magmas and in aqueous fluids.
• U was in accessory minerals such as zircon
• No free oxygen (anoxic atmosphere)
Abbott et al. (2012)
No Uranium Deposits
Valley et al. (2014)
4.374 Ma
Uranium Deposits Through Time
2. Mesoarchean to Paleoproterozoic (3.1 to 2.2 Ga)
• Subduction and recycling of U-Th rocks
• First granites at ~3.1 to 2.8 Ga
• Peraluminous granites at 2.6 Ga (e.g., Tanco suite)
• Atmospheric rise of oxygen at ~2.5-2.2 Ga
• Uraninite in highly fractionated granites and pegmatites
Placer Uranium Deposits(Witwatersrand, Elliot Lake)
Cuney (2009, 2010)
27°E
27°S 27°S
27°E0 50 100km
N
Central Rand Group
West Rand Group
Dominion Group
Archean granitoid
Greenstone
Witw
ate
rsra
nd
Superg
roupMajor fault
U-Au deposit
Vredefor
t
Johannesburg
Modified from Frimmel (2005)
Witwatersrand Basin
Sediments 2740 Ma
Uraniferous minerals 3050±50 Ma
and 2050±100 Ma
Meteorite impact at 2050 Ma
Rundle & Snelling (1977)
Huron Claim, MB
Sharpe and Fayek (2011)
Huron
ON
Age of host pegmatite- 2640±7 Ma
Age of uraninite- 2575±38 Ma
Resetting event (Rb-Sr) muscovite-2580±8 Ma
Uranium Deposits Through Time
3. Proterozoic to early Paleozoic (2.2 to 0.45 Ga)
• High pO2 atmosphere and pH hydrosphere
• Oxidation of detrital uraninite
• Uranyl species in solution (e.g., [UO2]2+)
• Increase in organic-rich sediments, phosphorite
• First redox controlled U deposits
• Genesis of large uranium provinces
Many Different Types of Uranium Deposits(Unconformity, Skarns, Metasomatite, IOCG)
Cuney (2009, 2010)
Oklo Uranium Deposits
Main ore- uraninite (UO2)
Tabular-sandstone deposits
Age- 2 billion years old
Uraninite achieved criticality 1.95 billion years
ago
Chemistry of uranium ore resembles the
chemistry of spent nuclear fuel
Ore temperatures over 1000oC for over
100,000 years
3
6
9
3.0 2.25 1.5 0.75 0
0
3.68 % Oklo
Unconformity
0.7254 %
23
5U
/23
8U
x 1
00
Time (Ga)
0 100 m
W E
Black Shale (FB)
Sandstone (FA)
OKLO open pit151-2
3-67-9
13
10-16
Okelobondo
Archean Basement
FB Sandstones
U-rich Layer
Reactor Zones
Faults
Black Shale (FB)
Okelobondo
Sandstone (FA)
10-16
13
100 m0
Archean Basement
Faults
(modified from Gauthier-Lafaye et al., 1996)
Oklo Natural
Fission Reactors
•First redox controlled deposit
•Age: 2050 Ma
•Criticality: 1950 Ma
Athabasca Basin Uranium Deposits
Rabbit Lake, Athabasca Basin, CA
Uranium ore- uraninite (UO2)
Age = ~1.6 billion years old
Unconformity-related hydrothermal deposits
Over a billion pounds of uranium
World’s richest uranium deposits
Provides 18% of worlds uranium
Uranium Deposits Through Time
4. Paleozoic (0.45 Ga to present day)
• Land plants
• Organic-rich sediments (reduced clastic sediments)
• Organic matter uranium traps
• Microbial activity
Most Hydrothermal-Volcanic Uranium Deposits
Sandstone hosted Deposits (roll-front)
Near Surface Deposits (calcrete, bogs)
(Some of these deposits may not have been preserved in older rocks)
Cuney (2009, 2010)
Tabular deposits
Colorado, USA
Sandstone Uranium Deposits
Roll-front deposits
Colorado, USA
oxidized
Reduced
0
0.05
0.10
0.15
0.20
0.25
0 21 3
207Pb/235U
206P
b/2
38U
A- 1362±11 Ma
293±16 Ma
(MSWD: 6.4)
B- 1287±16 Ma
136±116 Ma
C- 959±31 Ma
AB
C
1200 Ma
800 Ma
400 Ma
(2s errors)
(Cumming and Krstic, 1992)
Cigar Lake
100 mm
uraninite
coffinite
Ca-U-Oxy
•Simple matrix: UO2
•Complex mineralogy
Geochronology of Uranium Minerals
uraninite
coffinite
Ca-U-Oxy
75 mm
In Situ Isotopic Analytical
Technique Required
Uraninite
500 mm
Athabasca Basin
Sue Zone
Secondary Ion Mass Spectrometry (SIMS)
Sample block
1 cm
100 mm
The Athabasca Basin
Uranium Deposits
• The geology/structures-
sandstone and basement
hosted-Proterozoic basins
• Large alteration haloes
• Mineralogy: UO2 and coffinite,
low Th/U-hydrothermal
• Redox system: oxidizing and
reducing fluids, pH ~6
• Temperature: 250 oC, Depth: 5
km
• Timing/Geochronology: 1600
Ma-300 Ma
• Knowledge Gap:
• Age of mineralization
• Source of U
•Two Fluids
•Polymetallic (Ni, Co,
As. Cu)
•High total REEs
•HREEs/LREEs ~1
•Single fluid
•Mono metallic
•Low total REEs
•HREEs/LREEs >1
(Jefferson et al., 2007)
Genesis of the Athabasca Uranium Deposits
0 100 m
Clay
alteration
Surface
Athabasca
Group
Aphebian
Metasediments
Fault
Unconformity
(modified from Marlatt et al., 1992)
Uraninite
Basment fluids
200 oC
Basin fluids
200 oC
1500, 1400, 1300, 900 MaBrine 200 oC
1477 Ma900 Ma250 oC
1590 Ma,1380Ma,
1280 Ma, 900 Ma,
500 Ma, 300 Ma
Illite
Quartz cements
Illite
Chlorite
Uraninite
500 mm (Alexander et al. 2009; Cloutier et al. 2010)
U1
U11495 ± 26 Ma
U3
U3
1088 ± 22 Ma
U4 855 ± 27 Ma
The Athabasca Uranium Deposits
(Sheahan et al. 2016)
Kianna Deposit, W Athabasca
1227 Ma
856 Ma
1002 Ma
Coffinite
Uraninite
75 mm 100 mm
Uraninite
The Athabasca Uranium Deposits
Errors ± 15 MaCigar Lake, E Athabasca
(Fayek et al. 2002)
The Athabasca Uranium Deposits U-Pb Ages
Fluid events: 1550 Ma, 900 Ma
0
0.1
0.2
0.3
0.4
0 2 4 6
400
800
1200
1600
2000
960+66 Ma70+23 Ma
(MSWD 2.9)
(e)
20
6P
b/2
38U
207Pb/235U
313+11 Ma
0 2 3 4
207Pb/235U
2000
1600
1200
800
400
207Pb/235U
0
0.1
0.2
0.3
0.4
0 2 4 6
400
800
1200
1600
2000
1543+8 Ma508+13 Ma
(MSWD 1.4)
(a)
20
6P
b/2
38U
0.1
0.2
0.3
0.4
0 2 3 4
0
206P
b/2
38U
2000
1600
1200
800
400
Oklo Uranium Deposits
Main ore- uraninite (UO2)
Tabular-sandstone deposits
Age- 2 billion years old
Uraninite achieved criticality 1.95 billion years
ago
Chemistry of uranium ore resembles the
chemistry of spent nuclear fuel
Ore temperatures over 1000oC for over
100,000 years
0 100 m
W E
Sandstone (FA)
Oklo open pit151-2
3-67-9
13
10-16
Okelobondo
FB Sandstones
U-rich Layer
Reactor Zones
Okelobondo
Sandstone (FA)
13
100 m0
(modified from Gauthier-Lafaye et al., 1996)
Archean Basement
Black Shale (FB)
Fault
The Oklo-Okélobondo Fission Reactors
Genesis of the Oklo-Okélobondo
Natural Fission Reactors
0 100 m
Sandstone (FA)
Archean
Basement
Uraniferous Fluid
~140 oC
Fault
Uranium Deposits
Clay Alteration
(modified from Gauthier-Lafaye and Weber, 1989)
Hydrocarbon Migration 140 oC
Black Shales (FB)
•Clays: 2036 Ma
•Fission: 1968 Ma
•Diagenesis:
1450 Ma, 860 Ma
•Dike: 850 Ma
•Uraninite: 2050 Ma, 2018 Ma,1780 Ma, 1500 Ma, 850 Ma, 755 Ma, 265 Ma, 68 Ma
The Oklo-Okélobondo Fission Reactors
U-Pb Ages
dike emplacement
898±46 Ma
(RZ 10, OKE)
1945±50 Ma
570±48 Ma
criticality event
(RZ 2, 9, 13)
206P
b/2
38U
0.1
0.2
0.3
0.4
0
207Pb/235U
0 2 3 4
2000
1600
1200
800
400
2000
1600
1200
800
400
207Pb/235U
0 2 3 4
Athabasca Deposits
0
1
2
3
4
5
6
7
8
9
0 500 1000 1500 2000 2500
Age (Ma)
No. of
Anal
yse
s
Pinwarian
(~1.5 Ga)
Ryholites & granites
(1.45 Ga)
Age of
U deposits
(~1.55 Ga)
Post-Pin:
dike swarm
(~1.4-1.2 Ga)
Grenvillian
dike swarm (1.0 Ga)
(~1.3-1.0 Ga)
Rhodinia
Rifting:
(~0.9-0.7 Ga)
Pangea
(~300 Ma)
Oklo-Okélobondo
Fission Reactors
0
1
2
3
4
5
6
0 500 1000 1500 2000 2500
Age (Ma)
No. of
Anal
yse
s
Accretion:
Atlantica
(~2 Ga)Pan-African
(~0.5 Ga)Pangea
(~300 Ma)
Benue Rift
(~100-40 Ma)
Criticality
(~1.95 Ga)Age of
U Deposits
(~2.0 Ga)
Diagenesis
and Tanzinian
(~1.45-1.35 Ga)
Rhodinia
Rifting
(~0.9 Ga)
Rifting
(1.54Ga)
Tectonic Evolution of W. Africa
Rogers, 1996
Atlantica and deposition of seds ~2 Ga
Accretion of Tanzanian craton ~1.35 Ga
Rodinia 980-730 Ma
Pan African ~500 Ma
Lower Benue Rift ~100 Ma
Uranium Deposits
Oklo, Gabon
Lower Benue
Rift 100 Ma
Diffusion Model
For uranium minerals consisting of
multiple size domains, Pb will diffuse
faster from smaller domains relative to
larger domains.
D=m2/sec
Mark Escher
phase A
10 nm
phase B
10 nm
Si
U
5 nm
phase B
•Evolution of uranium deposits related to major
global events
•Ages correlate with tectonic and other geologic
events
•Large-scale events cause element migration-
geochronology of fluids
Conclusions
Acknowledgments
Prof. Kurt Kyser- Queen’s University
Prof. Alfredo Camacho- University of Manitoba
Prof. Rodney C. Ewing- Stanford University
Prof. Michel Cuney- Université de Lorraine
Canada Research Chairs
www.chairs-chaires.gc.ca