"Supercontinent cycles through time
and formation of large intracontinental
sedimentary basins, privileged host of
sandstone related U deposits"
Michel CUNEY
UNIVERSITE DE LORRAINE - GeoRessources - CREGU – CNRS
CREGU
- CNRS
F54 GéoRessources
506, Vandoeuvre- les
NANCY
- FRANCE
UNIVERSITE DE LORRAINE
54 506, Vandoeuvre les NANCY FRANCE [email protected]
Vienna 06-2015 – Karoo U Basins
Supercontinent cycles
The cycle of supercontinent assembly & breakup first proposed
by Worsley et al. (1982, 1984)
The Earth has experienced several supercontinent cycles since
2.7 Ga
Pangaea, the last one, breakup into the current plate
configuration is the best constrained, whereas for the older
assemblies, there are still many uncertainties and debates
The driving mechanism is mantle convection
Supercontinent cycles
The assembly and dispersal of supercontinents are closely related
with mantle dynamics:
 mantle super-downwelling along multiple subduction zones
aids their assembly,
 mantle upwelling generates plumes and superplumes
associated with :
 fragmentation of the supercontinent
 formation of large igneous provinces
 enhanced ocean anoxia
Supercontinent cycles
Paleomagnetism is the only quantitative method to reconstruct prePangean continents to an absolute paleogeographic reference
frame
Broad-scale concordance of paleomagnetic latitude estimates
with paleoclimatic indicators such as evaporite basins for the
past two billion years implies that a paleomagnetic reconstruction
can be tested
Example of
reconstruction of
the core of the
NUNA
supercontinent
1.9–1.3 Ga
paleomagnetic
poles from
Siberia,
Laurentia/Slave &
Baltica
Supercontinent cycles
Craton collision peaks at 1850 & 600 Ma with small ones at 1100 & 350 Ma
Minima at 1700-1200, 900-700, and 300-200 Ma.
No simple relationship in craton collision frequency or average plate velocity
between supercontinent assemblies and breakups.
Nuna assembly (1700-1500 Ma) correlates with very low collision rates
For Rodinia (1000-850) & Gondwana (650-350 Ma) moderate to high rates
Very low collision rates during supercontinent breakup:
2200-2100, 1300-1100, 800-650, and 150-0 Ma.
Peaks in plate velocity:  450-350 Ma early stages of growth of Pangea
1100 Ma initial stages of Rodinia assembly
Craton numbers ≥ 20 before 1900 Ma to 13–17 after with the collision and
suturing of numerous Archean blocks
Supercontinent cycles
The cause of supercontinent cycles is not understood.
LIP (large igneous province) age peaks at 2200, 2100, 1380 (and 1450?), 800,
300, 200 and 100 Ma correlate with supercontinent breakup
LIP minima: 2600, 1700-1500, 1100-900, 600-400 Ma supercontinent assembly
But other major LIP age peaks do not correlate with the supercontinent cycle
The period of the supercontinent cycle is highly variable, ranging from 500 to
1000 Myr if the late Archean supercratons are included.
Duration :
 Nuna ~ 300 Ma (1500-1200 Ma)
 Rodinia 100 Ma (850-750 Ma),
 Gondwana-Pangea 200 Ma (350-150 Ma)
Breakup durations are short, generally 100-200 Myr.
Supercontinent cycles (Condie 1976-1982)
Compilation of radiometric ages (> Rb/Sr) for periods of majorGaorogenesis in Earth history
Supercontinent cycles
Comparison of orogenic peaks (arrows) from radiometric data by Runcorn (1962) with U–
Pb detrital zircon ages Hawkesworth et al. (2010) & times of supercontinent assembly
Kenorland
Supercontinent cycles (zircon ages)
Condie and Aster, 2010
Rate of creation of juvenile continental crust
Dominion
+Witswat.
Huronien.
Kombolgie
Athabasca
Karoo
Jurassic
Ceanozoic
Condie, 1998
Condie & Aster 2010
Major U continental
sandstone basins
3.2 Ga
2.2 Ga
2.0
1.8
1.5
EVOLUTION Of U-GEOCHEMISTRY DURING EARTH HISTORY : 2
3.2-2.2 Ga : ARCHEAN & Upper PALEOPRO.
Kaapval
High-K granites
Singhbum
Closepet …
U rich
calc-alkaline
magmas
Tanco
U rich
calc-alkaline
pegm.
magmas
U-rich
peraluminous
syn-magmatic magmas
concentrations
in pegmatoids
Kola
concentrations
in metamorphic
rocks
Metamorphism
Crust partial
melting
magmatic differentiation
Subduction:
+
oceanic crust +
mantle
sediments
partial melting
metasomatized
Mantle
Start of subduction:
recycling of
U-Th-K-rich crust material
stronger magmatic enrichment :
first K-U-Th granites
PRE-3.1 Ga GRANITES - WITWATERSRAND BASIN (S.A.)
Witwatersrand Basin
South Africa
Intracratonic basin
Large fluvio-deltaic
systems
3.09 < dep. < 2.7 Ga
Metamorphic peak :
2-3 kbar - 350 °C
Frimmel, Earth-Sci Rev 70 (2005) 1–46
3.2 Ga
2.2 Ga
2.0
1.8
1.5
EVOLUTION Of U-GEOCHEMISTRY DURING EARTH HISTORY : 2
Erosion-alteration in anoxic conditions
3.2-2.2 Ga : ARCHEAN
Kaapval
Singhbum
Uraninite Witwatersrand
High-K granites
Closepet
deposits in – Elliot Lake
U rich
quartz-pebble
calc-alkaline
conglomerate
magmas
U rich
calc-alkaline
Tanco
pegm.
U-rich
peraluminous
syn-magmatic magmas
concentrations
in pegmatoids
& Upper PALEOPRO.
Large intracratonic basins
anoxic atmosphere => U(IV) only
magmas
Kola
concentrations
in metamorphic
rocks
PLACER TYPE U DEPOSITS
1rst type of U deposit on the Earth
Metamorphism
Crust partial
melting
magmatic differentiation
Subduction:
+
oceanic crust +
mantle
sediments
partial melting
metasomatized
Mantle
conglomerates with detrital uraninite:
Witwatersrand, Eliott Lake …
3.2 Ga
2.2 Ga
Erosion-alteration
in anoxic conditions
Kaapval
High-K granites
Witwatersrand
– Elliot Lake
Singhbum
Closepet
U rich
calc-alkaline
magmas
Tanco
U rich
calc-alkaline
pegm.
magmas
U-rich
Kola
peraluminous
syn-magmatic magmas
concentrations
in pegmatoids
GOE
Uraninite
deposits in
quartz-pebble
conglomerate
Mantle
1.8
1.5
FIRST RED BEDS WITH U
DEPOSITS BEFORE THE
NUNA
Oklo
3A1
Paleoproterozoic
2.2-2.0 Ga
passive margin
sediments
high pO2
uranyl ion [UO2]2+ in solution
concentrations
in metamorphic
rocks
Metamorphism
Crust partial
melting
magmatic differentiation
Subduction:
+
oceanic crust +
mantle
sediments
partial melting
metasomatized
2.0
U rich precursors :
Organic-rich shelf sediments,
phosphorites
First chemical deposit
(redox controlled) :
Oklo (Gabon) at 2.0 Ga
Oklo - Okélobondo the first redox controlled U-deposits
Mineralized + Reaction
C1 layer
zones
15
1-2
3-6
7-9
W
E
FB black shales
13
Archean
Basement
10-16
OK84bis
Okélobondo mine
100 m
FA sandstone
Redox
boundary
Nuna – Columbia Supercontinent
The Palaeo-Mesoproterozoic supercontinent Columbia is the first
coherent supercontinent in Earth history (Rogers & Santosh, 2002)
Maximum packing between 1.90 &1.85 Ga (Thélon+Trans-Hudson)
Attempted breakup phases at ~1.72–1.70 Ga &1.6 Ga but probable
brake-up at 1.3–1.2 Ga
Others consider that Columbia remained intact until at least 1.0Ga
Soon after reformed as Rodinia with minimal palaeogeographic
changes during the transition from Columbia to Rodinia
Tectonic
assemblage map
of Nuna
(Columbia)
Nuna’s formation (2.0-1.8 Ga)
followed by breakup
Siberia separation at
1.27 Ga, concomitant
with Mackenzie radiating
LIP & opening of the
Poseidon Ocean
Reconstructed to time of
initial mid-Mesoproterozoic
breakup
Siberia
Baltica
Laurentia
Pre-2.3 Ga
craton
ca. 1270 Ma
dikes & sills
ca. 1380-1350 Ma
dikes & sills
2.3-1.8 Ga
orogens
1.8 -1.1 Ga
orogens
Simplified
from Evans &
B : Baltica
CA : C. Australia
EA : E. Antarctica
G : Greenland
Ind : India
M : Madagascar
NA : N. America
NC : N. China
S : Siberia
SA : S. America
SAf
SAf : S. Africa
SC : S. China
T : Tarim
WA : W. Australia
WAf : W. Africa
YM: Yavapai-Mazatzal
NC
I
&
«Hudsonian
orogens»
S
SC
G
T
Europe
CA
North
America
EA
Ind
NUNA
B
SA
YM
M
WA
Post-Archean
2.1-1.8 Ga orogens
Archeaen Craton
Zhao, 2002 modified
2000 km
3.2 Ga
2.2 Ga
Erosion-alteration
in anoxic conditions
Kaapval
High-K granites
Tanco
U rich
calc-alkaline
pegm.
magmas
U-rich
Kola
peraluminous
syn-magmatic magmas
concentrations
in pegmatoids
Uraninite
deposits in
quartz-pebble
conglomerate
Mantle
1.5
Unconformity
related
Oklo
Paleoproterozoic
passive margins
Athabasca
Kombolgie
sediments
U rich
calc-alkaline
concentrations
in metamorphic
rocks
Metamorphism
Crust partial
melting
magmatic differentiation
Subduction:
+
oceanic crust +
mantle
sediments
partial melting
metasomatized
1.8
Oxyatmoversion EVOLUTION Of U-GEOCHEMISTRY
Witwatersrand
DURING EARTH HISTORY : 3C
– Elliot Lake
Singhbum
Closepet
U rich
calc-alkaline
magmas
2.0
Vein deposits
Beaverlodge
magmas
Albitite deposits
Partial
melting
synmagmatic
deposits in
pegmat-
Ukraine
Lagoa Real
oids
Charlebois
Trans-Hudson type orogen
B : Baltica
CA : C. Australia
Uchur-Maya
EA : E. Antarctica
G : Greenland
Yangtze/Cathaysia
Ind : India
Hornby
Thelon
M : Madagascar
NA : N. America
NC : N. China
Athabasca SC
S : Siberia
SA : S. America
Kombolgie
SAf : S. Africa
SC : S. China Kimberley
T
T : Tarim
SAf
WA : W. Australia
WAf : W. Africa
YM: Yavapai-Mazatzal
Vindhyan
NC
NUNA
Sayans
Aldan
Anabar
&
«Hudsonian» orogens
& Proterozoic
Independence
Fjord
Basins
Thule
S
Otish
G
E
?
CA
Waterberg
Cariweerloo
NA ?
B
SA
Pasha-Ladoga
Karku
EA
I
Ind
YM
Satakunta/Muhos
M
Proposed extension
Méso-Protérozoïques bassins
Post-Archean
2.1-1.8 Ga orogens
Archeaen Craton
Bothnian Sea
WA
Belt-Purcell
East Continent Rift
Roraima
Franceville
Central Metasediment. Basin
Espinhaço
Zhao, 2002 modified
2000 km
ATHABASCA BASIN AREA GEOLOGY & U DEPOSITS
BL = Beaverlodge
CB = Collins Bay
112°
102°
110°
104°
60°
106°
108°
60°
CF = Cluff Lake
CL = Cigar Lake
DL = Dawn Lake
Charlebois
BL
GU
EP = Eagle Point
MB
FL = Fond du Lac
NI
FL
SI
WP
Jackfish
GU = Gunnar
59° Basin
59°
JB = Jeb
MFc
KL = Key Lake
LR
OF
MFd
JB
LR = La Roque
FP
EP
CL
CF
LzL WP
WP
MA = McArthur R. Basementcore
Cree MW DL SU CB
core
structure
LL
MB = Maurice BayCarswellstructure
MR
CL
MFc
RL RH
SC
MFb
LL
MI = Millenium
58°
58°
WP
WB
ML = MacLean
MA
LzL
MO = Moore Lake
MI
MFc
Beatty Trough
MR = Maybelle R.
Basin
MO
MFa
MW = Midwest
KL
Patterson
BMT
NI = Nicholson
MFb
High
Moore
PP
Reilly Basin
57°
Lake
57°
PP = P Patch
112°
102°
110°
104°
106°
108°
RH = Raven
Horseshoe
Very large unconf . related U deposit
Hudsonian U mineralization
Not mined U deposit
deposit
RL = Rabbit Lake
or U showings
Late -Hudsonian U deposit
Large unconf . related U deposit
SC = Shea Creak
Carswell Formation
Douglas Formation
SU = Sue
Paleozoic sediments
FP= Fair Point, MFa-MFd= Manitou Falls, LZ= Lazenby Lake,
SI = Stewart Island
WP= Wolverine Point, LL= Locker Lake, OF= Otherside
WB = West Bear
modified from Ramaekers and Catuneanu, 2004
Airborne γ-spectrometry Athabasca area
Darnley et al., 2004
ATHABASCA
U
Th
ATHABASCA
Total
“Concensus”
Rodinia
Li et al. (2008)
RODINIA
India
Kalahari
Laurentia
Siberia
Baltica
Mid-life Rodinia stretching to the high latitude at above a mantle superplume,
widespread erosion, and continental rifting
A: Amazonia; A: E-Avalonia; AN: Arabia-Nubia; wA: W-Avalonia; B: Baltica; C: Congo; CAFB: C. Asian Fold B.;
EA: E.Antarctica; ES: E.Svalbard; G: Greenland; I: India; K: Kalahari; L: Laurentia; NA: N.Australia; NC: N.China;
R: Rio Plata; S: Sahara; SA: S. Australia; SC: S. China; Sf: Sao Francisco; Si: Siberia; T: Tarim; WA: W. Africa
The Rodinia Supercontinent
Scarcity of sedimentary record over the Rodinia
 Remnants of high topography (i.e., mountain ranges) that formed during
the assembly of Rodinia between ca. 1100 Ma and 900 Ma may still have
existed at ca. 825 Ma.
 Doming above the Rodinian superplume and individual plumes, similar
to the high elevation of present-day Africa above the African superplume,
could have occurred for at least the high-latitude end of Rodinia.
 Elimination of oceanic ridges between the continental blocks after the
final assembly of Rodinia at ca. 900 Ma means a global reduction in the total
volume of mid-ocean ridges, and therefore a net increase of total ocean
volumes and thus a lower sea level
The Rodinia Supercontinent
~ 680 Ma: continental breakup spread over much of Rodinia
Two hypothesised antipodal superplumes were likely active
With large igneous provinces (LIPs) developing:
 within the new oceans basins that opened between postRodinian continents,
 above the superplume antipodal to the Rodinian superplume
Resulted in an increase in the proportion of young oceanic
lithosphere and likely emplacement of LIP-related oceanic plateaus
635 Ma: apart from Siberia and Baltica, all other continents had
separated from Laurentia
RODINIA
Rodinia breakup
India
and sea-level rises
Laurentia
Siberia
Baltica
Kalahari
A: Amazonia; A: E-Avalonia; AN: Arabia-Nubia; wA: W-Avalonia; B: Baltica; C: Congo; CAFB: C. Asian Fold B.;
EA: E.Antarctica; ES: E.Svalbard; G: Greenland; I: India; K: Kalahari; L: Laurentia; NA: N.Australia; NC: N.China;
R: Rio Plata; S: Sahara; SA: S. Australia; SC: S. China; Sf: Sao Francisco; Si: Siberia; T: Tarim; WA: W. Africa
Supercontinent cycles
Rodinia: first geological evidence of assembly and break-up
(Moores, 1991; Dalziel, 1991; Hoffman, 1991)
Birth of Gondwanaland (600–530 Ma) Hoffman (1991) first
suggested that the break-up of the Rodinia supercontinent involved;
- fragmentation around Laurentia
- with continental pieces moving away from Laurentia and
- colliding on the other side of the Earth to form Gondwanaland.
Formation of Gondwanaland
High continental
and the
level
Rodinia breakup
completion:topography,
complete isolation
of lowering
Laurentia,ofS.sea
China
colliding with
India W. Gondwanaland was largely formed & E. Gondwanaland nearly assembled
Siberia
N. Australia
S. China
India
E. Africa
Laurentia
Baltica
Sahara Congo
W. Africa
W-Avalonia
Kalahari
Amazonia
A: Amazonia; A: E-Avalonia; AN: Arabia-Nubia; wA: W-Avalonia; B: Baltica; C: Congo; CAFB: C. Asian Fold B.;
EA: E.Antarctica; ES: E.Svalbard; G: Greenland; I: India; K: Kalahari; L: Laurentia; NA: N.Australia; NC: N.China;
R: Rio Plata; S: Sahara; SA: S. Australia; SC: S. China; Sf: Sao Francisco; Si: Siberia; T: Tarim; WA: W. Africa
The Gondwana supercontinent
Definition of Gondwanaland: Eduard Suess, Austrian geologist in
reference to Upper Paleozoic & Mesozoic formations in the
Gondwana region, Central India
 ca. 600 Ma West Gondwana was largely together with the
exception of Kalahari and some minor terranes
 Late Precambrian (540-530 Ma) full assembly by the closure of
Mozambique Ocean & amalgamation of E & W Gondwana
 Final assembly of Gondwanaland by the formation of a
network of orogens around the cratons the “Pan-African orogens”
Gondwana = southern half of the Pangea
The Gondwana supercontinent
550 Ma: counterclockwise rotation between N & S Australia completed
S. China still rotating against the NW margin of Gondwanaland
Andean-type active margin along the paleo-Pacific margin of
Gondwana
Laurentia, Baltica, Siberia & N. China isolated within palaeo-oceans
Mid-Late Cambrian: N. China drift toward Australia joins E. Gondwana
final docking of India to Australia–E. Antarctica along Pinjarra Orogen
Much of Gondwanaland was elevated due to the extensive
continental collision
 erosion and terrestrial deposition were widespread
The Gondwana supercontinent
Gondwana supercontinent incorporated: S. America, Africa, Arabia,
Madagascar, India, Sri Lanka, Australia, New Zeland, Antarctica
South & North China blocks were close to Australia, as indicated
by bioprovince connections with east Gondwana during the Early to
mid-Palaeozoic
Cambrian–Ordovician: deposition of a thick pile of Qz-rich
sandstones on the Gondwana over > 6000 km from the Atlantic
coast of N. Africa to Arabian Peninsula
In Europe  Armorican Quartzite Formation
 Its breakup started in the Early Jurassic (180 Ma)
Formation of Gondwanaland
High continental topography, and the lowering of sea level
Siberia
N. Australia
S. China
India
E. Africa
Laurentia
Baltica
Sahara Congo
W. Africa
W-Avalonia
Kalahari
Amazonia
A: Amazonia; A: E-Avalonia; AN: Arabia-Nubia; wA: W-Avalonia; B: Baltica; C: Congo; CAFB: C. Asian Fold B.;
EA: E.Antarctica; ES: E.Svalbard; G: Greenland; I: India; K: Kalahari; L: Laurentia; NA: N.Australia; NC: N.China;
R: Rio Plata; S: Sahara; SA: S. Australia; SC: S. China; Sf: Sao Francisco; Si: Siberia; T: Tarim; WA: W. Africa
Map of Gondwana showing position of the cratonic nuclei (after Gray et al., 2008).
THE KAROO FORMATION
Series of basins developed on the Gondwana continent.
Stratigraphic limits:
• between Carboniferous and Jurassic (360-180 Ma), end with the regional
basalt flooding event
• theoretically ended with the initiation of the Gondwana break up during
Lower Jurassic
Paleogeographic extension of the Karoo sedimentation:
• S & E of Africa from South Africa to Somalia-Ethiopia (largest development),
• West Africa: Angola, Namibia, Democratic Republic of the Congo,
• North of Africa: Niger, …
• South America (Paraguay, Argentina, Brazil, …)
• Asia (Saudi Arabia, ….)
Basin and genetic association with uranium mineralization.
Calculated effect of supercontinent cycle on sea level during Phanerozoic
Comparison with first-order eustasy, degree of platform flooding & number of continents
K A R O O
Permo-Triassic, Jurassic, Cretaceous fluvio-deltaic Gondwana sediments
potential for U mineralisation in:
 Beaufort Group, Karroo basin of South Africa (Le Roux, 1985),
 Parana basin, S. America (Barretto, 1985),
 France (Comte et al., 1985),
 Niger (Cazoulat, 1985),
 Ngalia, Amadeus & Cooper basins, Australia
 Gondwana basins, India.
 Callingastaupstata Basin, Sierra Pintada, Argentina
Proliferation of land plants & their incorporation in fluvial to marginal marine,
poorly sorted sediments derived from fertile granitic & metamorphic rocks with
high U contents in interbedded tuffaceous rocks (as an additional source of U)
make Gondwana sediments a favorable host for sandslone type U deposit.
(Finch & Davis, 1985; Le Roux & Toens, 1987)
THE KAROO
Basins
In the
southern half
of Africa
THE KAROO FORMATION
A variety of deposit types:
• deposits in the basement (potential sources): Precambrian granites,
metamorphic formations, peralcaline complexes and carbonatites, …
• sandstone hosted deposits: tabular versus roll front, basal channel,
• coal-lignite deposits
• surficial uranium deposits
Role of sedimentology:
• fluvial, lacustrine, near shore ….
• for the location of reductants
• for syngenetic enrichmnent
• characteristics of the trap (channel, permeability, …)
• the sealing of the productive layer for ISL
U source: external/internal (U-rich basement, volcanic ash and/or syngenetic)
THE KAROO FORMATION
Reductants (synsedimentary carb. matter / migration from oil-gas reservoirs)
Associated metallic elements: V, Cu …
Thermal –tectonic fluid circulation drivers:
• Extensive magmatic activity during Jurassic during one of the phases in the
break-up of Gondwana
-dolerite dykes and sills intruded the Karoo Basin
-roots and the feeders of the thick Drakensberg basalt (183-182 Ma)
• magmatically-driven Jurassic-aged hydrothermal systems within the Karoo
Basin and genetic association with U mineralization.
KAROO BASINS IN SOUTH AFRICA
The Karoo Basin
The Karoo Basin
The Karoo U Province
Two types of U deposits are present in strata of the Karoo Supergroup in
South Africa:
(1) fluvially-deposited sandstone-hosted, peneconcordant, tabular deposits
in the Late Permian lower Beaufort Group (Adelaide Subgroup) and Late
Triassic Molteno and Elliot Formations within the main Karoo Basin,
(2) coal-hosted deposits in the Late Permian uppermost part of the
Hammanskraal Formation within the Springbok Flats Basin
The Karoo U Province sediments
Includes parts of Adelaide Subgroup, & a smaller, crescent-shaped satellite
region in the Molteno and Elliot formations.
Thickest sandstones host the largest ore bodies & these sandstones are
up to 70 m thick in Adelaide Subgroup & up to 40 m thick in Molteno & Elliot
Formations.
Sandstone bodies = meandering river & sheet flood deposits in Adelaide
Subgroup,
= braided & meandering deposits in Molteno Formation
= meandering & sheet flood deposits in Elliot Formation
Sandstone bodies interbedded with dark green, greyish red & maroon
mudstone + subordinate siltstone, more abundant in Adelaide Subgroup &
Elliot Form. and = to sandstone in the Molteno Formation.
Ore bodies
Normally 1 m thick, but may attain 7 m, vertically stacked, combined thickness
of 20 m x100 m long, up to 200 m wide, elongated along the palaeochannel
thalweg in the lower portion of enclosing fluvial sandstone body
Ore-bearing sandstone bodies generally form multi-storey broad sheets with
width to height ratios exceeding 100:1. In the Adelaide Subgroup and Molteno
Formation, the sandstone bodies cluster into packages up to 350 m thick
In Adelaide Subgroup, Poortjie Member, hosts 80 %t of the identified U
resources & all resources of the Molteno Formation are contained within the
Indwe Member.
MINERALOGY
Uranium minerals = coffinite and less abundant uraninite
Sulphides = molybdenite, pyrite, arsenopyrite, chalcopyrite
Mo possible by-product of uranium
Gangue minerals = quartz + feldspar + calcite (common in Adelaide Subgroup)
Fossilised carbonaceous plant fragments are ubiquitous.
Metallogenesis :
1) uranium source;
2) palaeoclimate;
3) availability of a reductant.
URANIUM SOURCE
In Adelaide Subgroup, U was probably sourced from granites located W,
SW, & S of the main Karoo Basin + minor intrabasinal provenance,
Volcanic ash derived from a magmatic arc situated in southern S. America,
along a subduction zone descending beneath SW Gondwanaland.
Restriction of Mo to the SW of the main Karoo Basin  source confined to
granitic terranes W , SW & S of the basin
In the Molteno and Elliot formations in the N-central part of the main Karoo
Basin U is derived from granitic terranes SE of the basin. Clastic material
containing U was transported into the basin by entrainment within fluvial
sediments + some volcanic ash
Metals transported either in solution and/or adsorbed by clay minerals &
organic detritus, dispersed in basin mud and fluvial sands before being
mobilised & transported in slightly oxidised and alkaline solutions
URANIUM TRANSPORT AND DEPOSITION
Early diagenetic processes are inferred from U minerals filling undeformed cell structures
in fossilised wood fragments and a matrix-supported fabric of calcite-cemented ore.
U was transported in solution in the flood basin mud and the sandstone bodies.
Precipitation of metals occurred in relatively sparse, reduced zones with carbonaceous
debris in the basal part of the sandstone below a low palaeo-water table.
Oxidising conditions were prevalent given the warm, semi-arid palaeoclimate in the main
Karoo Basin during Late Permian to Late Triassic times (Smith, 1990).
U was initially adsorbed by organic matter and then reduced by H2S or the sorbent itself.
The scarcity of calcite in the Molteno and Elliot formation ores suggests that the
mineralising solutions were acidic to neutral and slightly oxidised and were probably
generated within the sandstone bodies.
Presence of the largest ore bodies within thick composite sandstones due to differential
compaction of the lower portion of the sand body relative to the flood basin muds
 This resulted in a relatively high water table within the sands and consequently a larger
reducing zone for precipitation and preservation of U.
RESOURCES
Total identified resources in the Karoo U Province = 32,832 t U
with 95 % in the Adelaide Subgroup (OECD/IAEA, 2008).
Ore bodies generally contain less than 1000 t U, but in the Adelaide
Subgroup in the SW of the main Karoo Basin, 8 deposits contain
between 1659 and 6791 t U. Average recoverable grades are 0.76
kg U/t + 28,000 t Mo at 0.8 kg Mo/t (Cole and Wipplinger, 2001).
Ryst Kuil, some 45 km southeast of Beaufort West where
reasonably assured resources of 6791 t U and 7420 t Mo have
been calculated.
Riet Kuil
Rietkuil-Dominion
Ryst Kuil
3 265
54 956
19 290
560 ppm
880 ppm
U is present in most Permo-Triassic basins of Gondwanaland.
In South Africa it occurs in the Beaufort & Stormberg groups in most parts of the
Karoo Basin, but predominantly in the south-west.
Adelaide Subgroup of the Beaufort Group = 4 upward-fining megacycles
reflecting tectonic pulses in the source areas to the S. U is preferentially in the basal
sandy members of each cycle, which are more reduced because of rapid burial.
'Tabular' & 'ribbon' channel sandstones both contain U, but mineralized lenses are
commonly thicker, narrower, more continuous in the ribbon channels. Braided
stream sediments with low overall U grades are present in the NW of the basin.
Mineralogy : U occurs in U(IV) in the reduced zone : uraninite, coffinite and as
U(VI) minerals in weathered zones + Mo, Cu & As, calcite as gangue mineral.
Reduction : Organic carbon to precipitate the U. About 1 kg/t
U Source: volcanic ash in the sandstones + Namaqua-Natal type granites to the S.
Remobilization of U into permeable zones during diagenesis led to the formation of
ore grade deposits, during Cape Orogeny, which elevated groundwater temperature
Ryst Kuil
In a thick sandstone 2000 metres above the basal contact of the Beaufort
Group and the underlying Ecca Group in an area of gentle folding.
Northern margin mineralisation is terminated by a normal fault with a
displacement of 30 m preserving a large part of the original deposit on its
downthrow side over 10 km to the SW
The host sandstone reaches a max thickness of 60 m and is approximately 3
km wide deposited by a low-sinuosity river which flowed in a NE direction.
Fluvial-sand system, with point-bars, abandoned channels, channel lag
conglomerates, trough & ripple cross-bedding, horizontal lamination,
massively bedded sedimentary structures. The sedimentary units are
arranged in upward-fining cycles.
Sandstone comprises at least 2 major sedimentary cycles, with the U.
The Rietkuil deposit
Host sandstone = arkosic-wacke, 10 to 20 m thick, lenticular, and elongated in the
mean direction of palaeocurrent. Moderately sorted, green to grey in colour,
composed of Qz, K-feldspar + volcanic rock fragments
Disseminated carbonaceous material is fairly abundant.
U mineralisation at the base in cross-bedded or horizontally laminated sandstone, &
mud-pebble conglomerate with abundant carbonaceous material.
High grade in thicker more continuous sandstones with higher sandstone/mudstone.
Ore body is tabular, slightly dished at its margins, where U grade increases
Association between U-Mo(jordisite)-Cu, high values of Cu & Mo offset from high U
Minor As, Pb, Zn, & Fe-sulphides also.
Primary U minerals : uraninite & coffinite, replace carbonaceous material, calcite &
matrix Oxidation of primary U minerals: metatorbernite, uranospinite + uranophane
Volcanic source of U favoured on account of the high % feldspar and rock fragments
Mineralisation preceded folding, deep burial, and dolerite intrusion.
Matfieskloof
On the slopes of Groottafelberg within, or immediately adjacent to, the Poortjie Member of
the Teekloof Formation, Beaufort Group. Deposit is associated with a succession of fluvial
tabular sandstones interbedded with red, purple, and green mudstones and siltstones.
Uraninite + coffinite minor Mo as pods within abandoned loops of a meandering channels.
The geometry of the orebody suggests coalescence between sandstones played a major
role in the location of ore pods. The ore resource amounts to about 1 Mt.
DR-3 Anomaly
The DR-3 anomaly near Laingsburg (and W of Beaufort West), 500 m lower in the
stratigraphy than other large sandstone U deposits in the lower Beaufort Group.
Deposit occurs in a discrete, linear, east-trending palaeochannel, within an upwardcoarsening sequence part of a short-lived, rapidly prograding, delta lobe. The channel,
represent an abandoned distributary channel, with 2 zones of mineralisation
Reserves of 2 zones >1 Mt averaging >0.5 kg/t U3O8
U mineralisation = uraninite + 0.05% Mo, usually in its hanging wall.
Mineralization controlled primarily by channel geometry, and abundance of organic
detritus, and by the coalescence of two major sandstone sub-units within the channel.
Coal-hosted Uranium
U was probably derived from granite of Bushveld Complex (20 – 40 ppm U),
underlies most of Springbok Flats Basin, locally in contact with Coal Zones along the
palaeovalleys.
Degree of metamorphism of the coal, which results from increases in T & P after
burial of the original peat, was probably still in the lignitic stage given the limited
thickness of the Late Permian Beaufort Group overburden.
Oxidising groundwaters have transported U to the Coal Zone where it was
adsorbed by lignite under reducing & slightly acidic conditions & formation of organometallic compounds
Presently higher rank of the coal, which is in the bituminous stage was attained later
by at least 300 m of Late Triassic to Early Jurassic sediments and lavas (Roberts,
1992).
Total identified resources of Coal Zone, Springbok Flats Basin: 77,072 t U
(OECD/IAEA, 2008)
Karoo basin system in the NWtrending Ubende Belt
Tanzania & E. Congo reflects an early
stage of Gondwana break-up
Karoo basins, much larger than the
remaining ones, formed initially as a
result of tectonically controlled
subsidence during the Late
Carboniferous - Permian & were filled by
fluvial-deltaic to lacustrine sediments
Along the Ubende belt, they probably
formed 2 major basin systems:
 Kalemie-Lukuga -S.Tanganyika (KLT)
 the Rukwa - Songwe – N. Malawi
(RSM) troughs.
Damien DELVAUX 2001
Ruhuhu basin in South Tanzania
Samples of lower Karoo coal-bearing beds from the Ruhuhu basin in South
Tanzania (KREUSER et al. 1988) have determined that the maturity of
organic matter is into the "oil window" & implies a significant overburden.
Assuming a paleogeothermal gradient of 25-30°Cj/km, an estimated
2-3000m of sediments must have overlain the coalbearing Karoo beds in
the Ruhuhu basin (DYPVIK et al. 1990) indicates a maturity in the lower part
of the oil window for the Songwe-Kiwira basin
The Kayelekera uranium deposit is a Karoo
age, sandstone hosted U deposit located 35
km W of Karonga in the far north of Malawi
Stratigraphy
of
Kayelekera
Geologic map of Kayelekera
Conservative global resource of approximately 9000 t U3O8
Resource calculations at Kayelekera are complicated by the presence of
significant, variable secular disequilibrium between U and its daughters.
The complication arise because geophysical gamma-logging methods of
U grade estimation calculate an equivalent U grade based on a measure
of the gamma emissions from a U daughter product on the assumption
that the U is in secular equilibrium with the daughter products of its
decay chain.
At Kayelekera disequilibrium is closely associated with the redox state
of the mineralisation; in particular the oxide facies mineralisation is
highly depleted
Niger (Hoggar Massif)
Geological map of the
eastern part of the
Tim Mersoï basin
(after Julia 1960) & 2003
airborne perimeter
from M. Souley, IAEA, 2005
U mineralization in NIGER
Hosts of the U mineralization: arenitic formations of the:
 Guezouman (Visean)
COMINAK
 Tarat (Namurian)
SOMAIR
 Tchirozerine (Jurassic) (mainly Tchirozerine II) IMOURAREN
 Irhazer (Cretaceous)
Depositional environments = fluvial to deltaic within the Tim Mersoï
basin north part of the large Lullemmeden basin.
Controls on the U mineralization: tectonic, lithological, hydrogeological
and geochemical:
 either reduced (pitchblende, coffinite): Akouta, Arlit, Afasto, Madaouela
 or oxidized minerals (Imouraren)
STRATIGRAPHIC
CONTROLS
OF THE
LOCATION
OF THE
U – DEPOSITS
IN THE
TIM MERSOI
BASIN
West Air (Niger)
Genetic model of the U mineralization
d’après Forbes, 1989, modifié
Gondwana
sedimentary basins
in South America
and Africa
Paraná Basin sedimentation
area covers > 1,700,000 km2
(Paraguay, Uruguay, Argentina,
Brazil)
It may have been interconnected
with the Karroo (in Africa),
Paganzo (Argentina), & Tarija
Basins (Argentina and Bolivia)
Tarija
Parana
Precordilliera
Paganzo
Karoo
Parana basin
Sedimentary package deposited between
the Late Ordovician and the Late Cretaceous
Paganzo basin
(Argentina)
Paganzo basin (Argentina)
Located west of Argentina (30,000 km2) up to 2500 m thick
(Carboniferous to Permian).
Ramos (1988) retroarc foreland basin,
Fernandez Seveso & Tankard (1995) strike-slip basin
Milana et al. (2010) and Astini et al. (1995) parts are rift basins
The Paganzo basin may represent a series of interconnected
basins with different tectonic regimes.
The Paganzo basin is mainly continental
Received glacial sediments during and immediately after the late
to medium Carboniferous Gondwanan glaciation
Tajira basin
(Argentina,
Bolivia)
Tajira basin stratigraphy
Gondwana basins in India
EW Koel-Damodar & NS Rajmahal
basins composed of separate outliers
arranged linearly
NW-SE Son-Mahanadi & PranhitaGodavari basins (PG) continuous of
outcrops
 Son-Mahanadi (MR): funnel
shaped, narrow in SE & broad in NW
Pranhita-Godavari constant width
Satpura Gondwana basin to the NW
of Pranhita-Godavari basin is E-W
2008
Satpura basin, covers 14700 km'
in Central lndia be most potential
for U mineralisation
Anomalous U concentrations in 3
parallel zones extending 2-4 km x
50 -100 m.
Mineralised arenites: low Qz (av. 9
vol%), K-feld. (av. 3.6 vol%). Biot.
(av. 1.2 vol%), plag. (av. 0.7 vol%)
+ apatite/fluorapatite (av. 6.7 vol%).
+ traces of brannerite
2008
2008
Gondwana basins in Australia – Perth Basin
China
India
Gondwana basins in Australia – Perth Basin
PANGEA at 260 Ma
Modified from Meert (2012)
NCB=North China Block, SCB=South China Block, AI=Armorica, Avalonia & Iberia..
The Cretaceous-Eocene Phosphate Sea
U mineralization associated with phosphates are known since the Paleoproterozoic
But largest U resources with phosphates : late Cretaceous to Eocene (90-45 Ma)
All deposited on carbonate platforms under the same paleolatitude (8-15º N) :
S margin of Tethys Ocean: Turkey to Morocco, beyond Atlantic to Colombia & Venezuela
Exceptional conditions of deposition, combining :
(i) during Late Cretaceous creation of the Paleotethys Ocean : a continuous EW
seaway which merge with the Central Atlantic gulf already open during late Jurassic,
by rifting of the Pangea between Laurasia and Gondwana
(ii) development of broad carbonate plateforms along S margin of the Tethys Ocean
(iii) huge Late Cretaceous rise of the sea-level resulting from a global warming episode,
both (i) and (ii) made possible a circum-equatorial westward oceanic current in the Tethys,
(iii) location of the Tethys at low latitudes, with the warmest climatic conditions
(iv) dominant easterly winds producing a northward Eckman offshore transport of surface
waters inducing t upwelling of cold nutrient-rich waters all along the S Tethys shelves
 huge biogenic productivity.
Morocco, with geological U resources of about 6.9 million tons U @ 50 - 150 ppm :
¾ of the world U resources associated with phosphates.
Duane M J, Welke H J, Allsopp H L and Wilsher W A, 1989 - U-Pb isotope systematics,
ages and genesis of Karoo uranium deposits, South Africa : in S. Afr. J. Geol. v92 pp
49-64
le Roux J P and Toens P D, 1986 - A review of the uranium occurrences in the Karroo
sequence, South Africa: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of
South Africa Geol. Soc. South Africa, Johannesburg v2 pp 2119-2134
le Roux J P, 1991 - Flume experiments on permeability and organic matter as related to
the genesis of uranium deposits in the Beaufort Group: in S. Afr. J. Geol. v94 pp 212219
le Roux J P, 1990 - Flume study on the concentration of ilmenite in fine-grained sand and
implications concerning uranium mineralization in the Beaufort Group: in S. Afr. J. Geol.
v93 pp 785-794
Stuart-Williams V and Taylor C M, 1986 - The Matjieskloof uranium anomaly, Fraserberg
District: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol.
Soc. South Africa, Johannesburg v2 pp 2135-2139
Wadley R G and Hoffmann J, 1986 - A case history of the DR-3 uranium anomaly,
Laingsburg District: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South
Africa Geol. Soc. South Africa, Johannesburg v2 2141-2147