Gawler Craton: potential for unconformity-related uranium

Gawler Craton: potential for unconformity-related uranium - spectral insights

John Keeling Geological Survey of South Australia

15 April 2015, SAREIC

www.statedevelopment.sa.gov.au

Which are the giant uranium deposits?

Unconformity-related uranium accounts for ~20% of world uranium production Include the highest-grade deposits

2 Department of State Development

(from Kurt Kyser – IAGOD 2010)

Proterozoic intracontinental basins

1.6 – 1.3 billion years


Unconformity-related uranium deposits

(after Karlstrom et al. 2001)

Unconformity-related uranium - Athabasca Basin model


Chlorite Zone

Outer Illite-Chlorite Alteration Zone± Late Carbonate-Quartz Chlorite Veinlets

Inner Chlorite Zone

Chlorite

Clay & Hematite

PyriticAlteration

Clay

Intense Fracturing

Illitic (Cigar Lake) orKaolinitic (Key Lake)

Alteration

PaleoregolithInner Illite ± ChloriteDravite, Hematite Zone

Silification in Sandstoneover Quartzite Basement Ridges

Dickite +/- Illite

0m

-200m

-400m

-600m

-800m

Unconformity

(from Kyser, 2010)

Fluid models for uranium deposition 1. Fluids originate within the sandstone, then

penetrate the basement where they react with reductants and U is deposited.

2. Basin fluids mix with basement-derived fluids at the unconformity and U deposited.

3. Fluids originate from the sandstone, then penetrate the basement where the U is leached before deposition in the fault.

sandstone

basement 1

Department of State Development

3 2

Cariewerloo Basin Approx. 430km NW-SE up to 170km wide

At least 1500m thick

Age poorly constrained

<1575 Ma Gawler Range Volcanics

1450 - 1420 Ma Rb/Sr whole rock and 40Ar/39Ar illite/mica alteration


Oak Dam East

Carrapateena

Olympic Dam

Prominent Hill

Samphire

line of section

100 km

136°

31°

Cariewerloo Basin showing “HyLogged” holes and basement uranium

Cariewerloo Basin section


Cover sediments Gawler Range Volcanics Proterozoic (undiff.)

AFZ – Andamooka Fault Zone

Oak Dam East

0

200

400

600

800

1000

1200

Uranium occurrence 1

4 3 2

Pandurra Members

W E

Pernatty Upwarp

Vanguard 01: Wavelength vs depth (Al-OH absorption at ~2200 nm)


Member 4 3 2 1

474 ±10 Ma 1200 ±24 Ma

AD10: Oak Dam East – Pandurra Fm

9

468 – 474m U3O8 334 ppm

403 – 408m U3O8 220 ppm

412 – 415m U3O8 380 ppm

(Chemical data courtesy BHP Billiton)


Base

Vanguard 01: 403m ‘hairy illite’ alteration of dickite Depth

(m)

4

3

1 2

450

600

750

900

1050 20 μm dickite

illite

Sandstone diagenesis: Burial depth and dickite crystal thicknesss


600 m

3000 m

3500 m

4000 m

5000 m

• Kaolinite / dickite crystallisation in sandstones is related to depth of burial (and temperature gradient?)

• Dickite to Illite transformation requires influx of K+ ions and possibly warmer fluids (>150°C)

(from Lanson et al. 2002)

Hole LY2: 629 m - blocky dickite (3000 – 4000 m burial depth?) Depth

(m)

4

3

1 2

450

600

750

900

1050 10 µm

(approx. equivalent depth Vanguard 01)

12

dickite

Vanguard 01: Pandurra - Member 4 (714m) Depth

(m)

4

3

1 2

450

600

750

900

1050 30 µm

zircon dickite

illite

APS

13


(m)

4

3

1 2

450

600

750

900

1050 14

2μm

Halite

Illite quartz


(m)

4

3

1 2

450

600

750

900

1050 15

20 μm

quartz

mica


(m)

4

3

1 2

450

600

750

900

1050 16

K-Feldspar

10 µm

Platy illite/muscovite

Cariewerloo Basin: fluid flow illite/mica zone


Cover sediments Remnant dickite alteration Gawler Range Volcanics

AFZ – Andamooka Fault Zone

Oak Dam East

Proterozoic undiff.

?

0

200

400

600

800

1000

1200

W

1

4 3 2

Pandurra Members

E

Pernatty Upwarp

Pandurra Formation Base of Member 4 Diagenetic alteration: –

Dickite vs White mica


Dickite White mica

High

Low

Mixed

100 km

Line of section

Source of reductant: Fe2+ from silicates


Fe2+ from chloritisation of biotite or illitisation of hornblende in basement rocks is a potential reductant (Alexandre, et al., 2005) :

biotite + H+ + H2O + Mg2+ => chlorite + K+ + SiO2 + Fe2+

or hornblende + K+ + H+ => illite + Na+ + Ca2+ + Fe2+ + Mg2+ + SiO2 + H2O

and then

U6+ + 5H2O + 2Fe2+ = UO2 + Fe2O3 + 10H+

(after Yeo and Potter, 2010)

20

Basement Geology below

Cariewerloo Basin (yellow outline)

N

100 km

Upper Gawler Range Volcanics Lower Gawler Range Volcanics Hiltaba Suite granite

Wallaroo Group – high-grade metamorphic Wallaroo Group – low-grade metamorphic

Donnington Suite / Lincoln Complex Archean volcanics

fault trace

Legend

Summary • Evidence for circulation of oxidising fluids capable of leaching uranium from

monazite and zircon within Pandurra sandstone.

• Fluid circulation in basal sandstone (Member 1) was restricted by authigenic mica and overlying aquitard (Member 2).

• Active fluid circulation occurred in Members 3 and 4, at ~1200 Ma, but interaction with crystalline basement was limited to basin margins, active fault zones, and region of the “Pernatty Upwarp”.

• Basement rocks at “Pernatty Upwarp” and along the eastern basin margin were a potential source of reductant (Fe2+).

• Spectral data facilitate mapping of diagenetic mineral alteration that can assist in interpreting fluid circulation and thereby help to focus future exploration for unconformity-related uranium.


References • Alexandre P, Kyser K, Polito P, Thomas D, 2005. Alteration mineralogy and stable isotope geochemistry of

Paleoproterozoic basement-hosted unconformity-type uranium deposits in the Athabasca basin, Canada. Economic Geology 100: 1547-1563.

• Karlstrom KE, Ahall K-I, Harlan SS, Williams ML, McLelland J, Geissman JW, 2001. Long-lived (1.8-1.0 Ga) convergent orogen in southern Laurentia, its extensions to Australia and Baltica, and implications for refining Rodinia. Precambrian Research 111: 5-30.

• Kyser K, 2010. Why don’t large uranium deposits always form? Giant Ore Deposits Down-Under, Proceedings 13th Quadrennial IAGOD Symposium 2010, Adelaide South Australia 6-9 April: 395-396.

• Lanson B, Beaufort D, Berger G, Bauer A, Cassagnabere A, Meunier A, 2002. Authigenic kaolin and illitic minerals during burial diagenesis of sandstones: a review. Clay Minerals 37, 1-22.

• Yeo GM, Potter EG, 2010. Review of reducing mechanisms potentially involved in the formation of unconformity-type uranium deposits and their relevance to exploration. (in) Summary of Investigations 2010, Vol. 2, Saskatchewan Geological Survey, Sask. Ministry of Energy and Resources, Misc. Rep. 2010-4.2, Paper A-12, 13p.


Contact

www.statedevelopment.sa.gov.au

Department of State Development Level 4, 11 Waymouth Street Adelaide, South Australia 5000 GPO Box 320 Adelaide, South Australia 5001

T: +61 8 8463 3135 E: [email protected]

John Keeling Senior Principal Geologist Geological Survey of South Australia

Documents

Gawler Craton: potential for unconformity-related uranium