01 wulser iaea vienne 2012

Genesis and preservation of uranium
mineralisations in Phanerozoic
Australian sedimentary basins

Pierre-Alain Wülser

Origin of Sandstone Uranium Deposits: A Global Perspective
IAEA – Vienna 29th of May – 1st of June 2012

AUSTRALP SARL, P.O. Box 72, 1292 Chambésy, Switzerland
pierre-alain.wulser@australp.ch

Objectives & plan
 Most sandstone-hosted uranium occurrences in Australia share
common characteristics which may relate to similar genetic
histories in defined locations (X,Y,Z) and potentially to a same
metallogenic epoch (t)
 Using these observations, can we restrict Sst-hosted U targets to
smaller geological objects, restricted strata?
 To document this, we will review U occurrences in Phanerozoic
Australian basins and look at several aspects
 Selected mineralisation description, depositional environment
of host formations
 Sea level variations and paleoclimate
 Geochronology of uranium ore in sandstones
 We will then try to define the best periods of U mobility for
sandstone-hosted mineralisations
 Giving new tools for exploration

2
Genesis & Preservation of U mineralisation in Australian sed

Uranium in Phanerozoic Australian basins
 Australia is a relatively low
standing continent
 Sea level variations have
controlled the development of
sedimentary basins
 Sst-hosted Uranium occurrences
in Australia are dominantly
located in Cretaceous –
Cainozoic strata
 Less important resources occur
in Lower Carboniferous
sandstones units
 Dominantly two types settings:
 Intracontinental sandstone
plateau or molassic basins
 Estuarine (deltaic) setting in
Selected Phanerozoic basins of Australia either marine or lacustrine
& Sandstone hosted occurrences environments

3

Uranium primary sources
 Many U-rich Archean and
Proterozoic granites (>10
ppm)
 The U-rich sources are
drained into
 Closed intracontinental
sedimentary basins (Central
Australia, Eyre basin / fluvial
to lacustrine transition)
 Open basin (fluvial to
marine transition)
 Spatial link between
Sst-hosted U & sources
Source: Geoscience Australia
Radiometric map of Australia in ternary colors (U-Th-K)
& Sandstone hosted occurrences

4

Characteristics of Sst-hosted mineralisations

 66% of Sst-U is located in Cretaceous-Eocene strata, only 21% in
Early Carboniferous and 13% in Miocene-Pliocene strata
 54% of known Sst-U is located in South Australia
 67% of U stands below actual sea level

5

Sea level variations & impact on Sst-hosted
uranium mineralisations
Lake Eyre
Basin

 A sea level rise of 100 m provides a rough image of how
landscape must have looked like during Cainozoic sea
transgressions
 Most deposits sit under present sea level and marine, lacustrine
estuarine protective caps developed on the top of the
sandstones formations during transgressions

6

Altitude & localisation of mineralisations
 NT mineralisations
formed in
intracratonic
basin, were later
tectonically &
verticalized.
Mineralisations are
partly oxidised
and occur at
surface (carnotite,
U phosphates,
etc.)

 Deposits with high standing U show evidence of Miocene-
Pliocene uplifting (e.g. Mulga Rocks, Four Mile W, Warrior,
Angela Pamela, Bigrlyi, Walbiri)
 Miocene (and/or Pliocene) marine or lacustrine clayey formations
are overlying all mineralisations, except at Angela-Pamela, Walbiri
& Bigrlyi (NT)

7

“The coyote is always looking for what is odd;
like him, I am looking for what is not at its
normal location” Bernard Tagini, 1975
 Several “chosen” deposits will be discussed
here:
1. Oobagooma (WA)
2. Mulga Rock (WA)
3. Mullaquanna (SA)
4. Beverley (SA) & Four Mile East (SA)

 Initially low-standing (+50 to -50 m) sandstones seem to host
most of Sst-U in Australia
 The odd: Mulga Rock (WA)
 Early Cretaceous - Eocene strata seem to host most of Sst-U in
Australia.
 Discussed exception: Oobagooma (WA) & Beverley (SA)
 Can we use U-Pb geochronology of U ore to constrain our
understanding the age of uranium deposition?
 New U-Pb isotopic geochronology studies on Beverley & Four Mile East
mineralisations

8

1. Oobagooma deposit (NE Canning Basin)
 Oobagooma is
West Kimberley
crystalline basement hosted by Early
Oobagooma Carboniferous
U Yampi Sst
-ri
c hs  The sandstone is
Ki oun

ou exposed at the
S
ng d

rce surface in the
Robinson River
catchment
 Yampi Sst were
deposited in a
fluvio-deltaic
environment
during warm,
humid tropical to
sub-tropical
Radiometric map of the West Kimberley region climate
Map based on Geoscience Australia data

Oobagooma: 9950 t @ 1200 ppm U3O8

9

1. Detailed setting of Oobagooma deposit

r
Rive
son
Robin

 Yampi Sst : Deltaic / fluvial sequence (strong tidal influence)
 Currently connected with the Robinson River drainage
 Fault-bounded basin
 Mineralisation occur at a salinity transition (300 to 700 µΩ.cm-1)
between saline marine / fresh water from the Robinson drainage
 Did uranium deposited during Palaeozoic?

10

2. Mulga Rock (& Warrior), Eucla basin
Hou et al. (2008)  Mulga Rock (& Warrior)
deposits are located in Eocene
paleovalleys on the internal
margins of the Cainozoic Eucla
Basin
 The incised valleys were filled
Mulga Rock with fluvial Mid-Eocene
sandstones, lignitic sandstones
and locally lignite
Warrior

Mulga Rock

Warrior

Hou et al. (2008)

11

2. Mulga Rock deposits (Eucla basin)

Energy Minerals Australia Pty Ltd

 U is contained in (1) sandstone and (2) lignitic sandstones
(coffinite) and in (3) overlying lignite (organometallic binding
with UO2+ complexes)
 The drainage is close to crystalline basement containing U-rich
Archean granites (& TTG)
Mulga Rock: 27100 t @ 560 ppm U3O8

12

2. Mulga Rock cross-section & mineralogy
 Organometallic complexes with lignite host most of U and Ti, V,
Co. Polymetallic concentrations are present in the lignite: Co-
Ni-Fe-Cu (as sulfides) and REE, Sc, Ti in complex speciation.
Uranium is hosted by coffinite in sandstones
 A) Fe,Co sulfides in lignite
 B & D) Chalcosite & covellite in clayey lignite
 Ti-Si (Sc)-rich layers in lignite layers (Fig. C)

Fe,Co Cu

Cu
Ti-Si

13

2. Eucla Basin general & unequal uplifting
 Uranium mineralisations from
Eucla basin have been subject to
differential uplifting from their
original elevation (+100-200 m for
the western Eucla Basin)
C’
 Uplift occurred from 10 Ma (Late
C Miocene – Pliocene)

Hou et al. (2008)

Hou et al. (2008)

14

2. Mulga Rock summary (Eucla Basin)
 The Middle Eocene fluviatile paleovalley fill at Mulga Rock is
built on the Gunbarrel basin (Early Permian-Late Carboniferous
glaciogenic sedimentary basin) and on the Proterozoic / Archean
crystalline basement
 The fluviatile Middle Eocene sequence is covered by oxidised Late
Eocene, Miocene to Pleistocene strata. Two major Miocene
transgressions (lacustrine turbidites and diamictites & estuarine
sandy, clayey successions) are recorded. The depositional
environment was mostly fluviatile /fluvio-lacustrine /marginal
marine.
 The entire Eucla basin & Southern Yilgarn Craton was uplifted
during the Late Miocene-Pliocene (10 – 0 Ma)
 The Miocene overlying basin consists of clay and sandy clay
formed in a estuarine, marginal marine environment (typical
Miocene transgression present all around Australia)

15

3. Mullaquanna / Blackbush deposit (SA)
 Mineralisation occurs in
coarse, reduced, lignite-
bearing, pyritic Eocene
sands and lignite beds
 Fluvial incised paleo-valley
(marginal marine,
estuarine setting)
 The deposit is located at
the margin of a U-rich
catchment from the Gawler
Craton (Archaean –
Proterozoic granites)

Mullaquanna: 19000 t @ 280 ppm U3O8

16

4. Mineralisations from the Lake Eyre Basin
(Callabonna sub-basin)
 The Callabonna sub-basin
contains most of Sst-hosted
Australian uranium resources
Mount Painter
 Miocene tectonic uplift subdivided Domain
the Lake Eyre basin into sub-
basins at ~10 Ma
 Past connection between the Tirari
sub-basin and Pirie-Torrens basins
existed until then
 Major Recent-Pliocene uplift
increased and U-rich sources
exposure (Mt Painter Domain) and
triggered uranium mobility
 Sea-level variations and climatic
conditions (humid or dry) have
impacted on Lake Eyre Basin, with
several sea transgressions

17

4. Mineralisations from the Lake Eyre Basin
 Extraordinary primary U sources from the Mt Painter Domain
with granites up to 150 ppm U (in white on radiometric map)
 Dispersion of U-rich sediments into the Lake Eyre Basin ~150-200
meters over the sandstone-hosted mineralisations

20 km
Lac Frome
Beverley

Four Mile E
Pic
tu Four Mile W
re
vie
w


Geoscience Australia (2009) Beverley- 4 Mile district = 57000 t @ >2000 ppm U 3O8

18

The fate of 222Rn & its impact on U-Pb
geochronology : zoom in
Direct 238U measurement by prompt fission neutrons  The duration of the
(PFN.) radon stage during
Bourdon et al. (2003)
radioactive decay is
highly changing fro the
three series
 For 238U series, 222Rn
stage is 50000 x
longer than 219Rn stage
(235U decay series)
T1/2222Rn
T1/2219Rn
= 50000 ( = 1) T1/2220Rn
= 300  and for 232Th series,
T1/2219Rn 220
Rn stage is 300 x
longer than 219Rn stage
 Radon loss is more
effective for 222Rn

Indirect U measurement U-Pb isotopic
on 214Bi γ emission measurement

19

Insights from Gamma (γ) vs. PFN log data –
Direct evidence for 222Rn leakage in ore
 Comparison between calibrated
Gamma spectrometric log (214Bi)
& Prompt fission neutrons logs
(238U) assays
 Average disequilibrium at 0.70
for 214Bi/238U
  30% of the expected 206Pb
must have be lost (in average)
 Measured 206Pb/238U isotopic ratio
(Gamma)

in whole-ore can be readjusted
Wülser et al. (2012) for 214Bi/238U disequilibrium

(PFN)
 It is expected that 235U/207Pb ratios
are valid after common lead
deduction (204Pb-based or 208Pb
Equivalent U3O8 grades from correction if no 232Th is present)
gamma log versus grades from
PFN - Four Mile East deposit (SA)

20

Example 1: Shirley Basin, Wyoming, USA -
further evidence for 222Rn migration
 Common Pb correction applied based
on 204Pb
 Mineralisation hosted by Early Eocene
Wind River Formation
charcoal  Evidence for 222Rn migration and
pyrite accumulation of 206Pb in “charcoal”
Overall identical 207Pb/235U ratio in whole
n


tio
Rn migration

ore, charcoal and pitchblende
ra
ig
m
Pb

 Minor remobilisation of radiogenic Pb
ic

from pitchblende into pyrite
g en
io
222

d
Ra

 Interpreted age of 24 ±3 Ma
Whole-ore
(Oligocene) for ore genesis (207Pb-235U-
Pitchblende based)

Ludwig 1978, Economic Geology, 73, 29-49

21

Example 2: U-Pb geochronology by ICPMS
at Beverley & Four Mile East
Pitchblende FME
Dense
 Porous coffinite nodules
Qz
pitchblende in mudstone at Beverley
U
 Pitchblende cement in
high-grade FME sands
 Very reducing
microenvironments
Coffinite Beverley present in lacustrine silts
of Beverley, with
bacterial activity
 Pitchblende yielded
concordant age of 6.7
Ma at Beverley
Coffinite Beverley
Whole-ore
Four Mile East
 Pitchblende gives
207
Pb/235U ages of 12.8 to
2.8 Ma at FME
 Coffinite gives 0.4 to
2.6 Ma 207Pb/235U ages at
Beverley

22

La-ICPMS U-Pb Geochronology at Four Mile
& Beverley. Miocene-Pliocene U migration
Carnotite  Concordant carnotite at Beverley: 5.5 – 3.4 Ma
 In summary, 207Pb-235U, common Pb corrected
ages on pitchblende & coffinite at Beverley & FME
give:
 Beverley: 6.7 - 0.4 Ma
 FME: 12.8 - 2.8 Ma
 Denser pitchblende retain 222
Rn better and give
higher 206Pb/238U ratio
 Late Miocene to Pliocene mineralising events
in the Lake Eyre Basin

Wülser et al. 2011, Economic Geology, 106, 835-867.

23

U-Pb geochronology of sandstone-hosted
uranium mineralisations: summary
 Because of the longer half-life of 222Rn, radon leakage mostly, or
only affect the 238U-206Pb decay series
 Porous U ores (coffinite coatings) allow important loss of 222Rn
(~30% at Four Mile East), possibly trapped by charcoal in the ore
(e.g. Shirley Basin, Wyoming)
 U-206Pb system is partly open in most sandstone-hosted
238

uranium mineralisations, but radon loss (219Rn) has only limited
effect on 235U-207Pb decay series.
 Dense pitchblende cement retain radon better and can provide
good 207Pb-235U ages after common lead correction Crystalline
minerals (e.g. carnotite) retain 100% of radon and can provide
concordant ages
 U-Pb isotopic data need completely different interpretation from
classic U-Pb mineral dating (e.g. zircon) and the notion of
“concordance”, “207Pb/206Pb ages and “lead loss” is erroneous when
effective 222Rn loss is present.

24

Intermediate summary
 A generally low standing altitude (-50 to + 50m)
 Sea level variations / marine (lacustrine) transgressions have
generally capped the U-hosting formations
 Problems met in geochronology can be solved
 New U-Pb ages of mineralisations in SA indicate Late Miocene to
Pliocene ore deposition
 Uranium in Australian Phanerozoic formations is dominantly
located in organic-rich Middle Eocene sandstones. This also
indicates most of uranium mineralisation formed from Late
Eocene to Pliocene)
 Uplifting impacted on preservation and post-ore mobility
(oxidation & multiple remobilisations in deposits from central
Australia)

25

Influence of paleoclimate on uranium mobility
1. Middle
Eocene:
warmer &
wetter than
present
2. Early
Miocene:
warmer than
present
3. Middle
Miocene:
warmer than
present
Hou et al. (2008)
 Wetter and warmer climate (Middle Eocene) was certainly not adequate for uranium
release without dispersion (excess of flowing, with deeper chemical alteration of rocks).
 This period is responsible for large sandstone units generation, containing abundant
organic matter (presence of widespread rainforests) and that were later mineralised in
uranium

26

Cainozoic paleoclimate summary
 Pliocene /Pleistocene  increasing aridity, drying
up of the lake systems, cyclic arid / episodic wet
(following cycles of the Pleistocene glaciation)
 Late Miocene  progressive temperature decline
 Miocene  strong climatic warming, several sea
water influx into the Lake Eyre basins (dolphins fossils
& oolithic dolomite)
 Oligocene to Early Miocene  dominantly warm
and dry climate

 Middle Eocene-Early Miocene  drainage of the
Lake Eyre basin toward SW, into Pirie & Eucla basins
(zircon populations based). Early Eocene warming
 Palaeocene-Middle Eocene  much warmer than
present, warm sea influence with south-westerly
winds, development of temperate rainforest in South
Central Australia (Alley, 1998). Strongest warming in
the Middle Eocene

27

Uranium mobility – eustatic variations &
paleoclimate during Cainozoic
 U was not deposited
during marine
transgression periods
 Most of U is located
between -80 and 0
meters elevation
 Three periods of low
sea level correspond to
max emerged / marginal
setting
 U1 (0 – 5.3 Ma,
Pliocene-Pleistocene), U2
(5.5 – 12.6 Ma, Late
Miocene, U3 (23.4 – 28.6
Ma, Late Oligocene)
Modified from Hou et al. (2008)
 First U-Pb ages on U ores confirm U1 & U2 (Bev. & FME)
suggesting low sea level periods & cooler climate were more
favourable to uranium mobility & combined trapping

28

REE distribution in uranium ores
 High REE : REE are more soluble in the
source (apatite, bastnäsite, altered allanite)
(Mulga Rock)
 Strong negative Eu/*Eu anomaly:
Proterozoic-Phanerozoic granitic sources
(Beverley, Four Mile, South Callabonna,
Mullaquanna)
 Weak Eu/*Eu anomaly: typical Archean
granodioritic/greenstone cratons (Mulga
Rock, Yilgarn Craton)
 Absence of Eu/*Eu anomaly: mantle
source (no examples)
 Negative Ce anomaly: intensity of
oxidation process during primary U leaching
REE patterns document on under warm/humid (tropical) climate:
the source of uranium (Mullaquanna, Four Mile, South Callabonna)
and the processes of  Absence of negative Ce anomaly: milder
weathering of uranium uranium release from source under cooler,
temperate cilmate, mild weathering
conditions (Beverley, Mulga Rock)
Absence of neg. Ce* at Beverley agrees with mild Pliocene weathering release

29

Summary and conclusion
 Sea level variations seem to have played a key role in forming
the right sedimentological setting for U trapping
 Adequate trapping Sst strata formed during warm and wet
paleoclimate (Middle Eocene) and located at the right
elevation are strongly prospective areas in Australia
 U-Pb Geochronology works. 206Pb/238U system is fundamentally
different from 207Pb/235U system for Sst-U mineralisations because
of differential radon leakage
 Integration of new geochronology to paleoclimate /sea level
reconstitutions define the best periods of U mineralising
events: (U1) Pliocene-Pleistocene, (U2) Late Miocene, (U3) Late
Oligocene)
 Without surprise, the presence of U-rich exposed granitic sources
plays a fundamental role for uranium mineralisation genesis
 REE patterns are useful indicators of the source rock of the ore
(intensity & curve)
 Negative cerium anomalies can be used as a potential
paleoclimatic proxy for the conditions of U release

30

Thank you for your attention

31

01 wulser iaea vienne 2012

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01 wulser iaea vienne 2012