1. ANATEXIS AND URANIUM PROTORE IN
THE WOLLASTON DOMAIN,
SASKATCHEWAN
McKechnie, Christine L. 1
Annesley, Irvine R. 1, 2, and Ansdell, Kevin M.1
1
Department of Geological Sciences, University of
Goldschmidt 2012 Saskatchewan
June 2012 2
JNR Resources Inc., Saskatoon, SK

2. Outline
• Geological Setting
• Pegmatite Mineralogy and Geochemistry
• Model for Granitic Pegmatite/Leucogranite
Generation
• U protore?
The aim of this project was to determine whether
these [granitic pegmatites and leucogranites]
represent a distinct target for uranium exploration
in Saskatchewan and/or if the mineralization is
somehow related to unconformity-type uranium
deposits

3. Regional Geology
• Hearne Province
• Deformed and metamorphosed
during the Paleoproterozoic
(ca. 1.9-1.8 Ga) Trans-Hudson
Orogeny (THO)
• ~ 25 km SE of the
Mesoproterozoic Athabasca
Basin
• In the Eastern Wollaston
Domain, which consists of:
• Archean orthogneisses
(mostly granitic)
• Paleoproterozoic Wollaston
Group metasedimentary
rocks
• Hudsonian granites,
amphibolites, migmatites,
leucogranites, and granitic
pegmatites
• Study area shown in red box

4. Fraser Lakes Geology
• NE-SW regional
fabric
• Zone A is in a NNE- es
up s s
ro nei
G g
plunging synformal on ary
st t
and Zone B is in an o lla en
W dim
NNE-plunging ta
se
e
antiformal fold nose m
se nta p
e is e o u
ry
• 5 km section of a r er
iv r
gn edim Gr
li e R ie
In on I nl
as o n
complexly folded
s
te ns te
ni
et st
a oh a ni
m olla
electromagnetic Gr J r
G
es
W
k
(EM) conductor (i.e. rL
a
as
e
o ne
graphitic pelitic Fr rZ
a
gneisses) is Fraser Lakes
She ai n
Zone B lls om
adjacent to Zones A Fa eD
ak
le rL
and B Fraser Lakes Zone A ed e
Ne
t
Pe
After Ray, 1979

5. Fraser Lakes Geology
After Ko, 1971

6. Granitic pegmatites and
leucogranites
• Granitic pegmatites and
leucogranites with
variable amounts of quartz,
feldspar, biotite, and other
minerals
• Overall coarse grained to
pegmatitic
• Variable width (cm to dm scale)
• Complexly zoned (igneous AFC
processes)
• Multiple generations of
granitic pegmatites
• 1850-1780 Ma U-Pb
chemical ages (CHIME)
for magmatic uraninite

7. Mineralogy
Highly Variable!
* Magmatic and/or peritectic minerals

8. Group A and Group B Granitic
Pegmatites/Leucogranites
Group A Intrusives Group B Intrusives
• Contain abundant uraninite, • Monazite-rich w/ zircon, thorite,
thorite, and zircon and minor allanite, and xenotime
allanite • Intrude the central part of the
• Intrude the western part of the antiformal fold nose
antiformal fold nose

9. Major element
geochemistry
• Group A intrusives tend to
be more Si-rich than
Group B intrusives, with
significant overlap
• Group B intrusives overlap
with pelitic gneisses
• Controlled by sample
mineralogy
• (i.e. high SiO2 = quartz-rich;
low SiO2= higher
mafics/oxide content)
• Controlled by host rock
composition
• Archean granitic
orthogneisses vs. Wollaston
Group metasedimentary
gneisses

10. Trace element geochemistry
• The two groups
also have
dissimilar trace
element
geochemistry
related to their
accessory
mineral contents
• U- plus Th-
rich (Group A)
• Th- and
LREE-rich
(Group B)

11. REE Geochemistry
Group A Intrusives Group B Intrusives
• Generally flat or slightly • Generally show LREE
HREE-enriched patterns, enriched patterns, higher
low total REE content, total REE content, and
variable Eu anomalies strong –Eu anomalies

12. Metamorphic Mineral Assemblages
in host migmatitic pelitic gneisses
• Garnet
• Biotite
• Cordierite
• Sillimanite
• Spinel
• Quartz
• Plagioclase
• K-feldspar
• Rutile
• Myrmekite
• NO prograde
muscovite
Upper amphibolite
to granulite facies
peak thermal
metamorphism
during THO

13. Granitic Pegmatites /
Leucogranites –
Partial melting at depth vs. in-
situ?
• Migmatites in close association with
the radioactive intrusives
• Leucosomes tend to be boudinaged,
but also form small pegmatitic veins
• Crystallized melt occasionally
forms thin rims around minerals,
and locally larger blobs
• Biotite frequently shows
degradation due to partial melting

14. Model for Fraser Lakes Zone B granitic
pegmatites/leucogranite-hosted mineralization
schematic mid-crustal cross-sections
• Primary magmatic U (+/-Th, REE) mineralization within late-tectonic granitic
pegmatites and leucogranites; 1850-1780 Ma (related to THO)
• Partial melting of metasedimentary gneisses (i.e. Wollaston Group equivalent)
at depth during peak thermal metamorphism (THO)
• Melt migrated upwards along the structural discontinuity/contact between
Archean and Wollaston Group, undergoing igneous assimilation-fractional
crystallization (cross-section A)
• Melts concentrated preferentially in antiformal fold noses
• Similarities to Rössing and Husab (formerly Rössing South) uranium deposits in
Namibia (cross-section B)
A) Modified from Ray, 1979 B) Extract Resources, 2009

15. Granitoid-hosted U mineralization
After Parslow and Thomas, 1982 after Cuney, 2005

16. Alteration of granitic
pegmatites/leucogranites and
remobilization of U, Th, Pb
Post-Crystallization
Alteration (during cooling)
•Chlorite (Chl)
•Epidote (Ep)
•Sericite (Ser)
•Quartz (Qtz)
Hydrothermal Alteration
•Fluorite (Fl)
•Chlorite (Chl)
•Hematite (Hem)
•Clay minerals
•Sausserite
•Carbonate (Cal)
•Quartz (Qtz)
•With secondary hydrothermal
U-Th-REE minerals

17. U protore?
• Chlorite, clay (including illite), and
hematite alteration found drill core;
similar to that of basement-hosted
unconformity-type U deposits
• Erosion to an estimated depth of
150-200 m below the Athabasca/
basement unconformity
• Brittle faulting cross-cuts the
mineralized zone
• Conduit for fluid and heat flow?
• Uranium (and other metals)
remobilized along fractures away
from primary magmatic uraninite
• Alteration of monazite may have
also led to uranium remobilization
• Drilling has yet to intersect a
basement-hosted unconformity-
type U deposit in the area – does
not mean it does not exist
Modified from Ray, 1979

18. Unconformity-type uranium deposits: possible
model
Evaporated Sea Water: high salinity fluids [Cl]
Richard et al. (2011)
Geochim. Comsochim. Acta 75, 2792-2810
Mercadier et al., (2012) Geology Sea
Basin 1.75-1.5 Ga ty
percolation into the mi
1.4–1.1 Ga UO2 n for
basement with leaching co
Mercadier et al. (2010) +/- REEs, Au, Cu, Un
Lithos 115, 121-136 Co, Ni, As… Basement 2.8 - 1.7 Ga
ore
[U]crust ~ 1.7 ppm
× 105 !!!
[U]ore ~ 20%
UO2 > 20%
Abundant U source
(e.g. monazites, uraninites) Up to 200.000 t U at
Hecht & Cuney (2000) Fraser Lakes approx. 20%: Giant
Mineral. Deposita 35, 791-795 Zone B uranium deposits of
Salinity [U]: 10-6 to 10-2 mol/L, pH:3-4.5 high grade
Richard et al. (2012), Nature Geoscience
cf. presentations of Michel Cathelineau, 2011 and Mercadier et al., 2012

19. Conclusions
• Structurally controlled, basement-hosted magmatic U and Th mineralization (+/-
REE mineralization)
• Hosted by Hudsonian granitic pegmatites and leucogranites intruding at/near
the highly deformed contact between Wollaston Group metasediments and
Archean orthogneisses
• Formed by partial melting of metasedimentary rocks in the middle to lower crust
followed by transport and assimilation-fractional crystallization
• Similarities to Rössing and Husab (Rössing South) granitoid-hosted U deposits
• Granitic pegmatites experienced post-crystallization alteration and
remobilization of U and Th and other metals
• The magmatic U mineralization is potential protore for basement-hosted
unconformity-type uranium deposits in the Fraser Lakes area (yet-to-be
discovered) and elsewhere in the Wollaston Domain and Athabasca Basin
• Magmatic U mineralization may represent a new type of economic uranium
deposit in northern Saskatchewan

20. Questions?