an update on the genesis of the unconformity uranium ... · - same as u deposits strong ne fabric -...

An Update on the Genesis of the Unconformity

Uranium Deposits in the Athabasca Basin, Canada

Ken Wheatley

Forum Uranium

Roll front in sandstones

and vein type in basement in early ‘70s

Forum Uranium 2

Unconformity deposits: Key Lake (1975)

Wyoming Mining Association website

Evolution of U/C Deposit Models

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Cigar (1980) and McArthur (1988)

sandstone

basement


Stolen from somewhere ?

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(from Cameco)

P-Patch (1997), Millennium (2000),

Roughrider (2008), Arrow (2015)

Vein-hosted basement

mineralization has been

known in the basement

since the discovery of

Rabbit Lake in the ’70’s,

and basement- hosted

deposits include Eagle

Point, Arrow and most

of the Cluff Lake

deposits.


Signatures of U/C Deposit Models

Archean granites and granite gneisses

Graphitic pelitic metasediments

Pelitic metasediments

Sandstone S-Type granite

ore

EM low Mag high

EM high, Mag low

EM low, Mag low

EM high Mag low Gravity low Resistivity low

Geophysical signatures of U/C uranium deposits

competency

Contrast – Archean

granite or meta-quartzite

Forum Uranium 5

S. Harvey M.Sc. thesis

Graphite and EM Strength EM strength is related to:

1) amount of graphite

2) alignment of graphite

3) connectivity of graphite

Tend to increase in fault zones

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Structure: the one thing in common with all the U/C deposits

EM response: EM high due to concentration, alignment and connectivity of graphite

EM low due to destruction of graphite by hydrothermal alteration

Gravity response: gravity low due to hydrothermal alteration, but this works for near

surface deposits only – the deeper the deposit, the fuzzier the gravity

Magnetic response: magnetic low, but these areas are widespread (PalaeoProterozoic

is typically mag low, Archean granites mag high)

Resistivity response: resistive low due to hydrothermal alteration, but like the mag

response, these areas can be large and usually don’t pinpoint U

Surface geochemical response: variable – Cigar Lake has anomalous geochem to surface

from 400m deep, McArthur has a silicified cap that

stopped the geochem from getting through

Structure: Every deposit is associated with a major structure (on it or next to it) and

usually one or more cross-structures

Signatures of U/C Deposit Models

Cigar Lake McArthur River

Total Field Mag Forum Uranium 8

Strong NNW fabric

- same as U deposits Strong NE fabric

- same as U deposits

Structural Control of U Deposits

East side deposits (all in NE quadrant) West side deposits (all in NW quadrant)

Maybelle

West Side East Side Shea Creek

Maurice Bay

Arrow Triple R

Forum Uranium 9 Structural Control of U Deposits


Smoke along the strike of

the structure, but dead

within 100m to the sides

Forum Uranium 10

Total Field Mag Forum Uranium 11


Athabasca Basin

Forum Uranium 12 A Rough Synopsis

1) U leached from sst and basement rocks all across basin

2) U deposited along pre-existing major structures in basement

3) Ni, Cu, Co, As (mainly east side), gold (mainly west side) from later

events, different fluids

3) U redistributed numerous times due to reactivation of structures

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Age of mineralization of uranium deposits in the Athabasca

Premineralization

1750Ma

(basement only

ie: Millennium)

Main Mineralization

1550Ma

(basement, U/C)

Post Mineralization

1350Ma, 1100, 900, 300

(basement, U/C)

(from Cameco)

A Rough Synopsis

Pre-Ore Alteration

Chlorite and illite are seen as the main pre-ore minerals Desilicification starts at this time

Alexandre et al, 2009

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Pre-Ore Alteration

Archean

sandstone

meta-pelite graphite

pre-ore

illite

pre-ore

chlorite

Can create up to

25% void space in

basement rocks

Quirt, Alexandre , Kotzer & Kyser, Derome, Cuney

desilicification

silicification

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Forum Uranium 16

Silica matrix breccias,

druzy quartz along fracture surfaces

Pre-Ore Alteration

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desilicification

and

chloritization

Pre-Ore Alteration

bleaching, illite

clays developed

Ore Forming Event

Uraninite, illite and chlorite are seen as the three main minerals formed during the main ore forming event


Forum Uranium 18

Oxidized sandstone basinal fluids at 200 C with NaCl were flowing through the basin, scavenging U from the rocks, then flowing along structures and out of the basin.

Main Mineralizing Event

Archean

sandstone

meta-pelite

graphite

pre-ore

illite

The U is carried by the oxidized

basinal brines, and more illite,

chlorite and iron oxides are

deposited.

Deposition of U is due to mixing

with a reduced fluid or interaction

with reduced basement rocks,

oxygen fugacity change, drop in

pressure due to pore space or some

combination of them all.

pre-ore

chlorite

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silicification

Computer modelling by Australians showed fluids being pulled down into an active reverse fault Modelling by Japanese showed fluids forced out of an active reverse fault . . Deposits like Eagle Point and Arrow, up to 900m below the U/C, suggest U fluids are drawn into the basement

(from NexGen website)

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Arrow deposit

800m of vertical

surface

sandstone

basement


Sue Deposits Sue C open pit

15 metres

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1

2

Uraninite at 20 to 88%

Forum Uranium 22


Forum Uranium 23

54.5% uranium 110 ppm uranium

Maybelle River

J. Reyx (Areva)


Post-ore events include:

- dravite

- base metals

- silicification and

- late kaolinite clays from

surface waters

- remobilization of U


Forum Uranium 24

Post-Ore Events

Post-Ore Events

Archean

sandstone

meta-pelite

graphite

pre-ore

illite

Dravite is introduced with

a tectonic event, as are

arsenides and sulphides.

This later event

redistributes and

contaminates the uranium

pre-ore

chlorite

Forum Uranium 25

silicification

Cu

Co

Ni

As

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Post-Ore Events

Ni, As, Cu, Co . . .

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J. Reyx

Post-Ore Events

Ni, As, Cu, Co . . .

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Oxidized drill core at Key Lake

Post-Ore Events

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Post-Ore Events dravite

Triple R

Arrow

Midwest A

Athabasca Basin

Saskatchewan

Forum Uranium 30

Discovered by Areva

Midwest A

Northwest

Athabasca

MIDWEST A

- a classic unconformity-style U deposit

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Roughrider

Midwest A

Midwest

Midwest A

major N030

(fertile structure)

cross-cut by

minor N070’s

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Midwest Zone (1978)

Mae Zone (2005)

Roughrider

(2008)

Resistivity Survey – highlighted

areas of alteration along the

graphitic EM conductor

Midwest A

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bleached zone

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Midwest A

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quartz dissolution

and chlorite zone

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Midwest A

Forum Uranium

perched mineralization

7.7m @ 10% U

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Midwest A

Forum Uranium

High-grade near

unconformity

59% U

9,000 tonnes at 21.2% ave grade* *Denison Mines website

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Midwest A

Northwest

Athabasca

Midwest A

Athabasca Basin

Saskatchewan

Forum Uranium 37

Triple R

Arrow

Athabasca

sandstone

cover

The project was successfully

worked by Uranerz in the

70’s and early 80’s.

Showings were found by

surface prospecting and

following boulder fans to the

apex and drilling.

Palaeoproterozoic

basement

F Subcropping

Maurice Creek

Zone 2A

Maurice Bay

The area was explored again

by Cameco from 2004 to

2008: mag and EM surveys,

10 drill holes but no success

Forum Uranium 38

N

Lake Athabasca

5 km

Forum Uranium started

exploring in 2012, looking

for basement-hosted that

may have been missed,

based on a mag low,

gravity low, boron halo,

EM conductor

Ground Gravity of the NWA Project - filtered

2 km

19 gravity lows

Forum Uranium 39

Griffith

MWH Geo-Surveys Ltd.

Northwest Athabasca

Density measurements: sandstone

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fresh sandstone: 2.42 gm/cc altered sandstone: 2.06 gm/cc

Northwest Athabasca

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Density measurements: basement

fresh basement: 2.71 gm/cc altered basement: 2.29 gm/cc

Northwest Athabasca

Ground Gravity of the NWA Project - filtered

2 km

Forum Uranium 42

Four targets tested, 3 of

them returned U in the

basement

Northwest Athabasca

Otis

Otis West: Plan View

Maurice Bay

showing

Otis West

Otis East

U/C elevation contours

Forum Uranium 43 Northwest Athabasca

Otis West: Cross Section

SW NE

10

0m

Forum Uranium 44

alteration halo

39.5m @ 0.15% U3O8

sandstone

basement Old model – U was at unconformity,

so holes were stopped 5 – 10m into

the basement to save money.

Sandstone Geochemistry

SW NE

10

0m

As Mo Ni Pb Th V B U

Barren 1 1 3 6 12 13 52 1

Near 1 2 46 34 20 29 259 5

Zone 2 2 123 24 46 71 1773 36

Forum Uranium 45

Basement Geochem

SW NE

10

0m

As Mo Ni Pb Th V B U

Near 1 1 71 14 21 110 164 13

Zone 40 58 164 86 14 157 465 2192

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Phoenix

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Soil Sampling for boron

down-ice from gravity lows

Northwest Athabasca

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Areas with up to 3,000ppm B

down-ice from 3 gravity lows

Gravity map background on

Fir Island Project

- dots are soil sample locations

Soil Sampling - Boron

Unconformity U is located

at the border of gravity

high to gravity low

Basement U is located at

the centre of a gravity low

Conclusions of gravity targets 1

1 km


Conclusions of gravity targets 2

Gravity lows that have a

shallow or one-sided

gradient are not fertile as

circular or elongated gravity

lows with a well defined

gradients

1 km


3 Types of U Mineralization

Unconformity

Maurice Bay Maurice Creek F-Subcropping

Basement (Vein Type)

Zone 1A Zone 2A

Basement (Millennium Type) Opie Barney Otis West

0.1 to 0.6% U 1 to 9% U 0.1 to 2.8% U


Triple R,

Arrow

Midwest A

Athabasca Basin

Saskatchewan

Forum Uranium 52

Discovered by Fission and NexGen

Northwest

Athabasca

Triple R, Arrow

Phoenix Saskatchewan

Forum Uranium 53

NexGen website

Triple R, Arrow Patterson Lake Trend

Forum Clearwater Project

Forum Uranium 54

Cluff Lake

Shea Creek

Boulder field (1970’s)

Boulder field has been

known for at almost 40 years

Detailed low-level airborne

radiometric survey relocated

the field, ground follow-up

work identified high-grade

pitchblende boulders

Quaternary studies led them

up-ice to an area with EM

conductors, and drilling

starts (similar to Key Lake

discovery)

High sensitivity airborne radiometric survey, followed by prospecting

NexGen website

Triple R, Arrow


Forum Uranium 55

- broken EM conductor

- circular gravity low

- on trend with Triple R

NexGen website

Arrow

Triple R, Arrow

Geologist from Forum


Forum Uranium 56

Arrow

NexGen website

Triple R, Arrow

Now almost

300 million lbs

Geophysical (gravity, EM, mag and resistivity),

geochemical (improvements in detection limits, isotope

ratios) techniques have improved considerably since the

70’s and can be used in previously explored areas to

develop new targets

Updated exploration models (variations of the

unconformity model) in the Athabasca Basin can be

successfully applied to old projects to find new deposits

Exploration geologists continually have to be kept up to

date with the latest discoveries so updated techniques

and models can be applied to their projects.

Forum Uranium 57 Conclusions

Uranium supply for the US – we are your friends

and neighbours; and we have lots of uranium.

Forum Uranium 58

NWA: Forum (Wheatley, Mazur, Tan, Williamson, Robertshaw, Harmeson)

Midwest A: Areva (Wheatley)

Arrow Zone: NexGen (G. Ainsworth) Triple R: Fission website

The End

Acknowledgements

an update on the genesis of the unconformity uranium ... · - same as u deposits strong ne fabric -...

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