Genesis and preservation of uranium     mineralisations in Phanerozoic     Australian sedimentary basins                  ...
Objectives & plan   Most sandstone-hosted uranium occurrences in Australia share    common characteristics which may rela...
Uranium in Phanerozoic Australian basins                                              Australia is a relatively low      ...
Uranium primary sources                                                Many U-rich Archean and                           ...
Characteristics of Sst-hosted mineralisations   66% of Sst-U is located in Cretaceous-Eocene strata, only 21% in    Early...
Sea level variations & impact on Sst-hosted          uranium mineralisations                                           Lak...
Altitude & localisation of mineralisations                                                       NT mineralisations      ...
“The coyote is always looking for what is odd;                        like him, I am looking for what is not at its       ...
1. Oobagooma deposit (NE Canning Basin)                                                               Oobagooma is       ...
1. Detailed setting of Oobagooma deposit                                                     r                            ...
2. Mulga Rock (& Warrior), Eucla basin              Hou et al. (2008)             Mulga Rock (& Warrior)                 ...
2. Mulga Rock deposits (Eucla basin)Energy Minerals Australia Pty Ltd        U is contained in (1) sandstone and (2) lign...
2. Mulga Rock cross-section & mineralogy   Organometallic complexes with lignite host most of U and Ti, V,    Co. Polymet...
2. Eucla Basin general & unequal uplifting                                    Uranium mineralisations from               ...
2. Mulga Rock summary (Eucla Basin)   The Middle Eocene fluviatile paleovalley fill at Mulga Rock is    built on the Gunb...
3. Mullaquanna / Blackbush deposit (SA)                               Mineralisation occurs in                           ...
4. Mineralisations from the Lake Eyre Basin          (Callabonna sub-basin)   The Callabonna sub-basin    contains most o...
4. Mineralisations from the Lake Eyre Basin             Extraordinary primary U sources from the Mt Painter Domain       ...
The fate of 222Rn & its impact on U-Pb              geochronology : zoom inDirect 238U measurement by prompt fission neutr...
Insights from Gamma (γ) vs. PFN log data –      Direct evidence for 222Rn leakage in ore                                  ...
Example 1: Shirley Basin, Wyoming, USA -   further evidence for 222Rn migration                                           ...
Example 2: U-Pb geochronology by ICPMS        at Beverley & Four Mile EastPitchblende FME                                 ...
La-ICPMS U-Pb Geochronology at Four Mile & Beverley. Miocene-Pliocene U migration     Carnotite                        Co...
U-Pb geochronology of sandstone-hosted       uranium mineralisations: summary   Because of the longer half-life of 222Rn,...
Intermediate summary   A generally low standing altitude (-50 to + 50m)   Sea level variations / marine (lacustrine) tra...
Influence of paleoclimate on uranium mobility                                                                    1. Middle...
Cainozoic paleoclimate summary   Pliocene /Pleistocene  increasing aridity, drying    up of the lake systems, cyclic ari...
Uranium mobility – eustatic variations &          paleoclimate during Cainozoic                                           ...
REE distribution in uranium ores                                 High REE : REE are more soluble in the                  ...
Summary and conclusion   Sea level variations seem to have played a key role in forming    the right sedimentological set...
Thank you for your attention                                            31      Genesis & Preservation of U mineralisation...
Upcoming SlideShare
Loading in …5
×

01 wulser iaea vienne 2012

436 views
318 views

Published on

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
436
On SlideShare
0
From Embeds
0
Number of Embeds
70
Actions
Shares
0
Downloads
0
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

01 wulser iaea vienne 2012

  1. 1. Genesis and preservation of uranium mineralisations in Phanerozoic Australian sedimentary basins Pierre-Alain WülserOrigin of Sandstone Uranium Deposits: A Global PerspectiveIAEA – Vienna 29th of May – 1st of June 2012AUSTRALP SARL, P.O. Box 72, 1292 Chambésy, Switzerlandpierre-alain.wulser@australp.ch
  2. 2. 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
  3. 3. 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 inSelected Phanerozoic basins of Australia either marine or lacustrine& Sandstone hosted occurrences environments 3 Genesis & Preservation of U mineralisation in Australian sed
  4. 4. 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 & sourcesSource: Geoscience AustraliaRadiometric map of Australia in ternary colors (U-Th-K)& Sandstone hosted occurrences 4 Genesis & Preservation of U mineralisation in Australian sed
  5. 5. 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 Genesis & Preservation of U mineralisation in Australian sed
  6. 6. 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 Genesis & Preservation of U mineralisation in Australian sed
  7. 7. 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 Genesis & Preservation of U mineralisation in Australian sed
  8. 8. “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 Genesis & Preservation of U mineralisation in Australian sed
  9. 9. 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-tropicalRadiometric map of the West Kimberley region climateMap based on Geoscience Australia data Oobagooma: 9950 t @ 1200 ppm U3O8 9 Genesis & Preservation of U mineralisation in Australian sed
  10. 10. 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 Genesis & Preservation of U mineralisation in Australian sed
  11. 11. 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 Genesis & Preservation of U mineralisation in Australian sed
  12. 12. 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 Genesis & Preservation of U mineralisation in Australian sed
  13. 13. 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 Genesis & Preservation of U mineralisation in Australian sed
  14. 14. 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 (LateC Miocene – Pliocene) Hou et al. (2008) Hou et al. (2008) 14 Genesis & Preservation of U mineralisation in Australian sed
  15. 15. 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 Genesis & Preservation of U mineralisation in Australian sed
  16. 16. 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 Genesis & Preservation of U mineralisation in Australian sed
  17. 17. 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 Genesis & Preservation of U mineralisation in Australian sed
  18. 18. 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 EPic tu Four Mile W re vie w  Geoscience Australia (2009) Beverley- 4 Mile district = 57000 t @ >2000 ppm U 3O8 18 Genesis & Preservation of U mineralisation in Australian sed
  19. 19. The fate of 222Rn & its impact on U-Pb geochronology : zoom inDirect 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 222RnIndirect U measurement U-Pb isotopicon 214Bi γ emission measurement 19 Genesis & Preservation of U mineralisation in Australian sed
  20. 20. 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 Genesis & Preservation of U mineralisation in Australian sed
  21. 21. 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 Genesis & Preservation of U mineralisation in Australian sed
  22. 22. Example 2: U-Pb geochronology by ICPMS at Beverley & Four Mile EastPitchblende FME Dense  Porous coffinite nodules Qz pitchblende in mudstone at Beverley U  Pitchblende cement in high-grade FME sands  Very reducing microenvironmentsCoffinite Beverley present in lacustrine silts of Beverley, with bacterial activity  Pitchblende yielded concordant age of 6.7 Ma at BeverleyCoffinite 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 Genesis & Preservation of U mineralisation in Australian sed
  23. 23. 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 BasinWülser et al. 2011, Economic Geology, 106, 835-867. 23 Genesis & Preservation of U mineralisation in Australian sed
  24. 24. 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 Genesis & Preservation of U mineralisation in Australian sed
  25. 25. 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 Genesis & Preservation of U mineralisation in Australian sed
  26. 26. 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 Genesis & Preservation of U mineralisation in Australian sed
  27. 27. 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 Genesis & Preservation of U mineralisation in Australian sed
  28. 28. 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 Genesis & Preservation of U mineralisation in Australian sed
  29. 29. 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 leachingREE 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: milderweathering 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 Genesis & Preservation of U mineralisation in Australian sed
  30. 30. 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 Genesis & Preservation of U mineralisation in Australian sed
  31. 31. Thank you for your attention 31 Genesis & Preservation of U mineralisation in Australian sed

×