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?