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01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
01 wulser  iaea vienne 2012
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01 wulser iaea vienne 2012

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  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. 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. 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. 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. 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. 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. 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. “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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Thank you for your attention 31 Genesis & Preservation of U mineralisation in Australian sed

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