The geological setting, composition, and origin of the Fraser Lakes Zone B granitic
pegmatite-hosted U-Th-REE mineralization, Wollaston Domain, northern Saskatchewan, Canada
Austman, Christine L. 1, 3
Annesley, Irvine R. 1, 2, and Ansdell, Kevin M.1
1 Department of Geological Sciences, University of Saskatchewan2 JNR Resources Inc., Saskatoon, SK3 CanAlaska Uranium Ltd., Saskatoon, SK
GAC-MAC 2011May 2011
Outline
• Purpose• Regional Geological Setting• Fraser Lakes Geology• Granitic Pegmatite Mineralogy and
Geochemistry• Metamorphism and Migmatization• Model for Pegmatite Generation
Purpose of this study
Describe the granitic pegmatite-hosted U-Th-REE mineralization at Fraser Lakes Zone B
Develop a metallogenetic model for pegmatite-hosted U-Th-REE mineralization in the Fraser Lakes area
Build upon previous work done on pegmatite-hosted uranium mineralization in northern Saskatchewan
Regional Geology The Wollaston
Domain consists of: Archean
orthogneisses (predominantly granitic gneisses)
Paleoproterozoic Wollaston Supergroup metasedimentary and metavolcanic rocks
Hudsonian granites, amphibolites, leucogranites, migmatites, and granitic pegmatites
Complexly deformed during the 1.8 Ga Trans-Hudson Orogen
Fraser Lakes Geology
• NE-SW regional fabric• Two mineralized
zones: A and B• Zone A is in a NNE-
plunging synformal and Zone B is in an NNE-plunging antiformal fold nose
• 5 km section of a complexly folded electromagnetic (EM) conductor (i.e. graphitic pelitic gneisses) is adjacent to Zones A and B
After Ray, 1979
Fraser L
akes Gra
nite In
lier
(Arc
hean)
Johnson River G
ranite
Inlier (
Archean)
Wolla
ston G
roup m
etas
edim
enta
ry
gneiss
esWollaston G
roup metasedim
entary
gneisses
Fraser Lakes Zone B
Fraser Lakes Zone ANeedle Falls
Shear Z
one
Peter Lake D
omain and
Wath
aman Bath
olith
Fraser Lakes Zone B
• The surface expression of the EM conductor adjacent to Fraser Lakes Zone B is a swampy, low-lying area
• Zone B mineralization outcrops at surface on the eastern edge of the swamp
• Fold nose is visible from the air
Fraser Lakes Zone B geology
Modified from Ko, 1971
WYL-08-526
WYL-08-524WYL-08-525
Granitic pegmatites
• Granitic pegmatites with variable amounts of quartz, feldspar, biotite, and other minerals
• Overall coarse grained to pegmatitic
• Variable size (cm to several m scale)
• Complexly zoned (igneous AFC processes)
• Multiple generations of granitic pegmatites (late-tectonicto post-tectonic)
• 1810-1790 Ma uraninite U-Pb chemical ages in mineralized pegmatites
Mineralogy
• Quartz (Qtz)• Feldspar (Fsp)• Biotite (Bt)• Magnetite (Mgt)• Ilmenite (Ilm)• Pyrite (Py)• Fluorite (Fl)• Sphalerite
Highly Variable!
• Uraninite (Urn)• Uranothorite
(Uth)• Monazite (Mz)
• Zircon (Zrn)• Allanite (Aln)• Xenotime
(Xen)
U-Th-REE Minerals
• Molybdenite• Apatite (Ap)• Titanite • Garnet• Rutile• Chalcopyrite• Pyrrhotite• Nb oxide• Graphite
Primary Minerals
Uraniferous pegmatites
Uraninite- and uranothorite-bearingAlso contain
zircon and minor allanite
Monazite is very rare
Typically intrude the western part of the fold nose
Th- and LREE Pegmatites
• Monazite-rich• Also contain
zircon, uranothorite-thorite, altered allanite, and xenotime as the main U-Th-REE hosts
• Rare Nb oxide
• Generally confined to eastern portions of the fold nose
Major element geochemistry
Legend
Alumina saturation index
Samples range from strongly peraluminous (off the chart) to slightly metaluminous
No distinct difference between U and Th mineralized pegmatites
S-type granitoids
Trace element geochemistry
Two major compositional subdivisions of pegmatites; correspond to mineralogical subdivisionsU- plus Th-richTh- and LREE-rich
Metamorphic Mineral Assemblages in host pelitic gneiss
Garnet Biotite Cordierite Sillimanite Spinel K-feldspar Quartz Plagioclase Rutile Myrmekite NO prograde
muscovite
Upper amphibolite to granulite facies metamorphism
Pegmatites – Partial melting at depth
vs. in-situ?
Migmatites associated with the granitic pegmatites
Leucosomes tend to be boudinaged, but also form small pegmatitic veins
Melt occasionally forms thin rims around minerals, and locally larger blobs
Biotite frequently shows degradation due to partial melting in thin section
Model for Fraser Lakes Zone B pegmatitesschematic mid-crustal cross-section
• Melts generated at depth (a)
• Transported upwards along the structural discontinuity/contact between Archean and Wollaston Group (b)
• Underwent igneous assimilation-fractional crystallization during transport and crystallization
• Melts were concentrated in antiformal fold noses (c)
• Peraluminous chemistry agrees with the pegmatites forming due to partial melting of pelitic gneisses
a
b
c
Similarities to Rössing/Rössing South
• Uranium mineralization is in late-tectonic to post-tectonic granitoids
• Structurally controlled mineralization -concentrated in antiformal fold noses
• Concentrated in areas of highest metamorphic grade
• Melt generated by partial melting of metasedimentary gneisses
Extract Resources, 2009
Modified from Ray, 1979
Conclusions
• Structurally controlled, granitic pegmatite-hosted U and Th mineralization (+/- REE mineralization)
• Hosted by Hudsonian granitic pegmatites intruding at/near the contact between Wollaston Group metasediments and Archean orthogneisses
• Regional metamorphism up to granulite facies
• Granitic pegmatites formed by partial melting of metasedimentary rocks in the middle to lower crust followed by transport and assimilation-fractional crystallization
• Similarities to Rössing and Rössing South granitoid-hosted U deposits
Acknowledgements JNR Resources Inc. – access to drill core,
outcrops, geological and geophysical datasets, logistical support, and financial assistance
NSERC - Discovery Grant (Ansdell)
University of Saskatchewan Graduate Scholarship (Austman)
Saskatchewan Research Council – geochemical analysis
Blaine Novakovski – thin section preparation
Kimberly Bradley – assistance with petrography
Steven Creighton and Tom Bonli – assistance with electron microprobe analyses