Uranium mineral systems: How and where they...
Transcript of Uranium mineral systems: How and where they...
Uranium mineral systems: How and where they form
Roger Skirrow
Section Leader, Mineral Exploration PromotionMinerals and Natural Hazards DivisionGeoscience Australia
Exploration in the House, Sydney, 20 June 2012
Outline
1. A mineral systems framework for U deposit classification and description
2. Fluids
3. Basin-related U mineral systems
4. Example: ‘sandstone’ U in the Frome region, SA
Summary
Exploration in the House, Sydney, 20 June 2012
Uranium deposit classification IAEA ‘Red Book’
1. Breccia complex (IOCG) 71%2. Unconformity-related 19%3. Sandstone 4%4. Surficial (‘calcrete’) 3%5. Metasomatite 2%6. Metamorphic7. Volcanic 1%8. Intrusive9. Vein10. Quartz-pebble conglomerate11. Collapse breccia pipe12. Phosphorite13. Lignite14. Black shale
(From A. McKay, Y. Miezitis, S. Jaireth, I. Lambert)
• Types based on host-rock or deposit morphology• Relationships between deposit types not clear
x
Deposit type (% of Australian resources)
BeverleyHoneymoonOlympic Dam
RangerJabiluka
Kintyre
Yeelirrie
Crocker Well
x
Australia holds ~36% of world’sU resources(recoverable at low cost)
Exploration in the House, Sydney, 20 June 2012
Magmatic-hydrothermal
fluids
‘Metamorphic’fluids
(incl. metamorphicrock-buffered)
Meteoric, seawater
Groundwaters
Formation waters / connate waters
Diagenetic fluidsm
ixing
mixing
mixi
ng
Deep (mgt) IOCG
(1) Shallow U-bearing hematite
IOCG
(2) Unconformity U (PGE, Au)
(3) Sandstone U (V, Cu)
(4) Calcrete U
(7) Volcanic(8) Intrusive(9) Vein
BASIN- and SURFACE- RELATED
U SYSTEMS
‘METAMORPHIC’- RELATED
U SYSTEMS(6)
MAGMATIC- RELATED
U SYSTEMSHYBRID
U SYSTEMS(1,5,9,10,11)
(5) Metasomatic(9) Vein
(10,12,13,14)
(7) Volcanic
(#) represent deposit types from IAEA Red Book & Dahlkamp (1990)
A mineral systems framework for U deposit types
• Three end-member fluids• Continuum of deposit styles• Emphasis on commonalities• Hybrids are expected
[From Skirrow et al. 2009, GA Record 2009/20]
Exploration in the House, Sydney, 20 June 2012
Magmatic-related U (“intrusive”)
Surface-related U (“calcrete”)
Basin-related U (“sandstone” & “unconformity”)
Metamorphic- related U (“incl. metasomatic”)
oxidise
d
reduced
1ppm
0.01ppm
0.0001ppm
Dissolved U content(log U ppm)
pH buffered by K-feldspar and muscovite
From Bastrakov et al. (2010)GA Record 2010/29
Fluids in uranium mineral systems:a fundamental control on how and where they form
Orefluid carrying 0.1 ppm
dissolved Uat 25°C
Precipitationof uraniumminerals
‘spent’ore fluid
(1ppm)
Exploration in the House, Sydney, 20 June 2012
LakewaterBitternBasinal / connate brineMeteoric waterMetamorphic fluidOil / gas / H2 S (reductants)
‘sandstone U’ styles: paleochannel
rollfronttabular
‘Westmoreland’ style U deposit
Basin- & surface-related uranium systems
radiogenicheat
SCALE: 1 to 50 km
1 to 5 km
Different deposit styles: related processes
mafic
shale aquicludeshale aquicludesst aquifer
basement(meta-sedimentary, meta-igneous)
weathered U-rich granite
From Skirrow et al. (2009)
volcanic-bearing reductants
‘unconformity-related U’(basement hosted style)
U-rich granite
redu
ctan
ts
‘calcrete U’
Exploration in the House, Sydney, 20 June 2012
Basin-related U systems
Example of ‘sandstone-hosted’ uranium systems, Frome region, SA
Mapping of mineral system components: - U sources - ‘Driver’ of fluid flow (energy source) - Fluid pathways - Ore depositional gradients
Exploration in the House, Sydney, 20 June 2012
Uranium sources for basin-related U systems: Identify using radiometrics and whole-rock geochemistry of igneous rocks
(continental datasets from Geoscience Australia)
Schofield (2009)
U2/Th
Radiometics(ternary U Th K)
Exploration in the House, Sydney, 20 June 2012
U-channel on DEM backdropU-channel on DEM backdrop
RADIOMETRICS
High-uranium potential sources High-uranium potential sources
TOPOGRAPHY
Gravity: the driverof fluid flow intoCenozoic & Mesozoicbasins[± radiogenic heat?]
Gravity: the driverof fluid flow intoCenozoic & Mesozoicbasins[± radiogenic heat?]
x
Four Mile
x
x
GEOLOGY(From 1:1m Surface Geology of Australia)
Mt Painter Inlier
Curnamona Province
Mesozoic
Proterozoic
Paleozoic
Cenozoic
Exploration in the House, Sydney, 20 June 2012
Paterson: 2007-2008Area: 47,600 km2
Line km: 28,200Line spacing: 200 m to 6 kmGA Record 2010/12
Paterson: 2007-2008Area: 47,600 km2
Line km: 28,200Line spacing: 200 m to 6 kmGA Record 2010/12
Pine Creek: 2008-2009Area: 73,700 km2
Line km: 29,900Line spacing: 200 m to 5 kmGA Record 2011/18
Pine Creek: 2008-2009Area: 73,700 km2
Line km: 29,900Line spacing: 200 m to 5 kmGA Record 2011/18
Frome: 2010Area: 95,450 km2
Line km: 32,317Line spacing: 2.5 km & 5 kmGA Record 2012/40
Frome: 2010Area: 95,450 km2
Line km: 32,317Line spacing: 2.5 km & 5 kmGA Record 2012/40
AEM conductance images3% of Australia!
Mapping fluid flow pathways and U depositional settings using airborne electromagnetic (AEM) data
Exploration in the House, Sydney, 20 June 2012
Mapping fluid pathways (paleovalleys) using regional AEM
Conductivity depth slice (80-100m)
From Roach (2012),GA Record 2012/40
Exploration in the House, Sydney, 20 June 2012
Four Mile East uranium mineralisation: biogenic
pyrite as a reductant for U
[Field emission SEM micrographs,Schofield et al., 2009, GA Record 2009/40]
Py Py
U depositional gradients: oxidation-reduction fronts(organic- and/or sulfide-rich sediments)
[Fluorescence micrograph from Michaelsen & Fabris, 2012, Organic facies of the Frome Embayment and Callabonna Sub-basin: What are the U reductants? Geological Survey ofSouth Australia]
Organic matter as U reductant:Namba facies 1
Exploration in the House, Sydney, 20 June 2012
FROME URANIUM PROVINCE EVOLUTION
Paleogeographic reconstruction from Langford et al. (1995)
[From Skirrow (ed.) 2009, GA Record 2009/40]
Exploration in the House, Sydney, 20 June 2012
FROME URANIUM PROVINCE EVOLUTION
[From Skirrow (ed.) 2009, GA Record 2009/40]
Exploration in the House, Sydney, 20 June 2012
EromangaBasin
NorthernQueensland
Pine CreekOrogen (AEM)
PatersonProvince
(AEM)
South Australia & Frome (AEM)
Onshore Energy Security Program (2006-11) study areas and uranium mineral potential assessments
Geoscience Australia studies of uranium mineral systems
Known U resources,by tonnesin region
SouthernNT
U deposits,by size
Exploration in the House, Sydney, 20 June 2012
Schofield (2010),GA Record 2010/20
Exploration in the House, Sydney, 20 June 2012
OlympicIOCGProvince
Olympic DamOlympic Dam
Prominent HillResulProminent HillResul
CarrapateenaCarrapateena N. Portia Cu-Au(-U)N. Portia Cu-Au(-U)
KalkarooCu-AuKalkarooCu-Au
U-bearingIOCG province?
U-bearingIOCG province?
U-bearing IOCG prospectivity map of Gawler-Curnamona region
From:An assessment of the uranium prospectivity of east central South Australia(Huston (ed.) 2011, GA Record 2011/34)
Exploration in the House, Sydney, 20 June 2012
SUMMARY• New mineral system scheme places known deposit types
into a framework based on three end-member fluids
• Shows (genetic) relationships between deposit types, and allows for ‘hybrid’ types involving more than one fluid
• Fundamental control is fluid chemistry: U is mobilised in oxidised fluids and deposited via reduction and/or pH incr.
• Australia has world’s largest resources of U, yet still has potential for discovery of giant ‘sandstone-U’, magmatic- related U, IOCG-U, and unconformity-related U
Exploration in the House, Sydney, 20 June 2012
Uranium deposits through timeFrom Cuney (2009)
OlympicDam
Kazakhstan‘sandstone-U’
Rössing & Streltsovkamagmatic- related-U
Does Australia host giant ‘sandstone-U’ and magmatic- related U deposits?