-66-
Uranium Metallogenic Studies: Charleboi s Lake and Cup Lake
by D. Thomas*
New detailed geological maps have been produced fo r the two areas Charlebois
Lake and Cup Lake (see accompanying folder).
Both areas contain radioac t ive
"pegmat it es " and have been periodically investigat ed sin ce the early 19SO's.
The
present mapp i ng is part of a broader metallogenic investigation into uranium occurrences of Aphebian/Hudsonian age in the Sa skatchewan Shi eld.
Pinkish banded felsic gneisses, the main rock t ype at both localities, are
a ssociat ed with a varied supracrustal suite.
The radioa c tive "pegma tites " occur
in both localities close to the felsic gneis s- s upracru stal contact.
The pegmatites
at Cha rlebois Lake comprise a complex a ssemblage of aplitic to pegmatitic rocks of
granodiori tie composition, which appe ar to have formed by extens ive melting of a
largely non-graphitic pelite unit.
At Cup Lake, by contrast, r ad ioactivity occurs
in pegmatitic calc-silicate rocks and "granitoid segr egations" derived from grap hitic pelites.
1.
Charlebois Lake Area
Rock types
Felsic gneisses (1) of granodioritic to granitic composition, and of mediumto coarse-grain size (0. 5-2 .0 cm) , make up at least 60 percent of the area (Fig. 1).
Colors r ange from light grey, particularly for th e finer-grained varieties, to pink
for coarser varieties .
Up to 10 percent biotite is generally present, while amphi-
bole is rare ex cept near the con tact with ma fi c rich metasediments.
Compo s it ional
and grain size banding is characteristic of most of the felsic gneisses.
The pre-
sence of biotite gneiss bands up to several metres wide within the fel sic gneisses
suggests a possible supracrustal origin .
Migmatized pelites (2a) with subordinate quartzite, amphibolite and calcsilicate bands, were mapped around the Pegas us Lake f e lsic gneisses and in the area
of the Cathy, Fox Bay and U.R. s howings .
A large part of this unit has been remo-
bilized into a complex of concordant to subconcordant aplite-pegmatite sheets and
*
This DMR project was undertaken in part fulf i llment of a Master of Science
program at the University of Regina.
- -- ·--··----------··" ··--···---·
.. ...-....
.
- 67-
l-
104•50•
A
II
(7a) Granodiodte· tone l I te
I
(7b) Al as <i t e granite
( 6)
59• 25'
Sill i...,ni te- garn et pe ll t es
and f e l dspath i c ps armiites
{5)
SUPRACRUSTAI
ROCKS
(APHE!>IAN ?)
La1111inated amphi bol e gnei sses
(4a) Grey s i ll i mon ite -qa rne t
quartzi tes
(4)
Pe li t e s , sem ipe 1ites "nd
ps a11t11ite s . loca lly t ransfomrd
t o "gra nito1d" 9ne1ss~s
( J)
Calca reous schi s t s and gnei sses
(2b) A.mptii bo l e gflei ssl:!!', and schis ts
( 2a) Hi (Jlliti zed µelHe~ and assoc i·
FU SI(
GNEISSES
(AR CHEAN')
at ed radi oac t i ve roc ks of
apl i t'e--ra·· peg~ tl"te' ·cliar;,,ct~r
(1)
Granodior it tc to gn, niti c
fel si c gne i sses
104• 50'
~ - ~ - -,------ ,
0
CiJ GLACIAL
2
~ SUPRACRUSTAL RO CKS (APHEBIAN?)
~Q
3 '"'
e
DR IFT
FElSIC GNEISSES ( ARCHE AN ' )
RADIO AC TI VE O CC URRE N CE
. . - G EOLO GICAL CONTACT
.,,,., FAULT
. . · · ·. O UTLI NE OF MA P ARE A
Fi g. l - Genera l ized geol og ica l map (A) and s tra tigraphic successi on (B) ,
Char1ebois Lake area . Note: Patterns on the ma p are not meant to
relate t o those in the cciiurnn.
"lit-par lit" .
The pelit es are medium-to coarse - grained (0. 25-1 . 0 cm) and c ontain
s illima nit e , garne t and t rac e s of graphite loc ally.
Four distinc t roc k t ypes we r e
id entified i n the apl it e-pegma tite c ompl ex :
1.
Ma s s ive me dium-t o coarse -grained, generally granod i oritic, r oc ks commonl y
con taining b io t ite books up t o 15 cm di amete r.
2.
Coar se t o pegmatitic roc ks oft en with euhedr al f eld s pars " f loating " in a
quartz matrix .
3.
Dark grey "waxy" qua rtzi tic rocks wi th biot ite books and a ccessory
molybdeni te .
4.
Fine-grained to ap l itic granodior i t e .
Fine-to medium-grained (0.05-0.25 cm) amphi bole-ri c h s c hists and gneis ses (2b )
out crop on the west side of Charle bois Lake , a ppearing in p lace of t he peli tes of
Unit (2a) .
Locally , a strong hornblende lineation i s noticeable i n contrast to
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t he preva l ent planar f abri c of t he se r ocks.
Calc areous s chis t s and impure marbles (3) ind iv idually up t o 5 m t hic k, but
i nter layered with pelites , occur i n a continuous unit 400 m thick throughout the
a rea.
The ma in rock t ype is a f ine - grained seri ci te-biot i te /phl ogop i te-diop s lde
schi st .
Fine- gra ine d grey i s h impure t a lc- diops i de ma rbl e and t remo l ite /ac tino l ite-
diopsid e g neis s wi th va r iable amounts of free cal ci t e a l so occur .
Pelites , semipelit es and psammites (4) f orm a he t e r ogeneous unit , which has
been locally transformed in t o fe l sic gne i sses.
Si llimanit e and garnet occur in
mino r amount s whi l e magne t it e appears as sma ll (1.0 nun ) euhed r a l g rain s.
The
t ransf orma t ion of these r ocks t o fe lsic gneis ses i s ma rked by a progres sive dec reas e
i n mafi c mine r a l s and a coars en i ng of t he fe l sic componen ts .
Poorl y l a yered , f i ne -
graine d (0.1 cm) grey quar tz it es (4a) containing sillirnan i t e and garne t outc r o p
along t he no rth s ho r e of Higgin s on La ke.
Hornblende gneis s es ( 5) with 25 t o 50 perc ent ho r nblende a nd up to 10 percent
bi o tit e , wh ich are c harac t eriz ed by del i cate (1 t o 5 cm t hic k) hornblend e- pl ag ioclase
or d iopside- ca l ci t e l a mi nae,form a d i st incti ve unit.
Magne t ite l oca ll y fo rms up to
4 percen t of t hese rocks .
Pe l i t e schist s (6 ) with s ubordina t e fel dspathic psanuni tes lie stra t igr aphically
above Un i t ( 5) approx i ma t ely 2 km wes t of the Pegasus Lake ant i fo rm.
These schist s
are medium-grained (0. 25-0. 5 cm) and are l ocally s t ained by hematite .
Si l l iman ite
and gar net are irr egular l y d i str i buted t hroughou t t he unit .
Irregula r dy ke a nd s ill-l ike masses , rarely more t han 10 m t hi ck , of gener a l ly
med ium- to coarse- gr aine d granodiorit e - tonalit e (7a) and a l askite gr an ite ( 7b) occur
in the area and are pr obably derived by melt ing of supr ac rustals and fel sic gneisses
r es pec tivel y.
Struc tu re
The fel s i c gne i sses lie in t he cor es of ma j or an tifo rms and have an apparently
comformab l e contact wit h th e supracrustal uni ts .
The s upr a cr u stal r ocks are intr i-
cately fol ded on steep sou ther l y to sou t heaster l y di pping axial plan es .
The Pegasus
Lake a nt iform plunges t o t he sou t hwest , as possibly do the o t her ma j or a ntifo rms in
t he a r ea .
Two major fa ult s sys t ems wer e i den tified.
Two east-wes t f aults appear to pass
t hrough Char lebo i s Lake and anot he r fau lt t hrough Hi gginson Lake .
trending faul t s were i den t ified ar o und t he Pegasus Lake mass .
- - --·---·-------- -- ..
·-· -
No r t h-no r t heas t erl y
The ap pa r ent la t eral
- 69-
d is pla cements are gene rall y of less than a few hund r ed metres .
Metamorphism
The mineral paragenesis of sil limani t e-almandine garnet-or t hoclase in Unit s
(2) , (4 ), (6) a nd the coexistence of hornblende-diopside - plagioclase i n Unit (5)
ind i cat es me tamorphic condi t ions withi n the amphibol ite facies .
Chlorite af t e r
biotit e a nd tr emolite after possible diops ide s uggest l ocalized l a t e me t amorphic
r e trogr essi on.
Economic Geology
The most recent e xploratory work in this l ocali ty , was conducted by Urange sellscha ft (Canada) Ltd., i n jo int venture with the SMDC during 1 976 mainly on properties
opti oned from Fosago Explo rat i on Ltd.
The uranium mineraliza t ion des cr jbed by Mawds l ey (1957) i s due t o
" cubic
grai ns of uraninit e ... averaging 0.2 0 mm i n d i amet er, a l most always i n or i n cont act
with biotit e" ... oc curs mainl y in the med ium-grain ed gr2nodiorit e- tonalite r ocks of
the aplite - pegma tite complex of Un i t (2a) .
Radioac t iv ity was also noted i n a
possibly la te waxy s iliceous phase of th i s complex.
The radioactive zones are quite
i r r egular in width and r es tric t ed in strike l ength.
The amount of yellow ura nium
bloom, l a r ge biot ite "books" (up to 15 cm acr oss), and molybdenite gene rally increase in proportion with the r adioac tivi t y .
Pale green apati t e and black tour-
mali ne were found in some a r eas of uranium mineralizat ion (Row a nd U. R. s howings) .
2.
Cup Lake Area
Rock types
Felsic gneisses (1 ) i n the Cup Lake area (f ig . 2) are medium-to coar se- grained
(0. 25-1. 0 cm) pink to brown grani to i d rocks .
Fr om 5 to 10 percent biot ite is com-
monly pres ent, and ho rnbl ende and hyper sthene occur in some wa xy charnockitic varie t ies.
Compositional and gr ain siz e banding is st rongl y developed in most areas ,
and granobl as tic f abrics predominate.
Local flattening of quar tz and feldspar
grains is in places a ccompanied by segregation of biotite into schlierern.
The
presence of garnetiferous bi otit e gneiss band s wi thin the f elsic gneisses and t he
abs ence of identifiable intrus ive i gneous feat ures s ugges t a supracru stal origin
for these roc ks.
-70-
106°47'
A
B
.. .
'; , ·
. DRlff .. .
,,
I
I
<l '
(Sa) Megacrys ti c feld spar bi otite
quartz gneiss
"
I
(5)
Sil l iman ite- garnet-cord i er ite
pelites , fe l dspa thic semipel i t es and rsammi tes
(4)
Ca lcareous s ch i sts and gneisses
I
I
/
\
(3c ) Diops i de-hyperst hene me ta-arkose
( 3b) Graphite-garne t-hypers theneafll)hi bo1e gneiss
( 3a) Calcareous rocks, ~.!1)9.!'lY
radioact i ve
(3) Graphitic pelites and semi pel i tes wi th "granito id " s egre gations , £_onmonl y radioactive
56°09'
(2b) Amph1 boli t e and amphi bo l e
schists and gneisses
( 2a) Hornb 1 ende -harzberg i t e
106°47'
km O
1.,_:·.:;;j GLACIAL
2
DRl fl
~,.;.:;! ~PRACRUSTAL ROCKS (APHEB IAN ?)
-
AMPHIBOLITES, ETC. (INTRUSIVES ?)
( l)
J km
e
Pink ' granitic' fels i c gne i ss
in part charnokitic
RADIOACTIVE O CCURRENCE
,.--/ GEOLOGI CAL CON TAC T
*-
MUSKEG
~ fElSIC GNEISSES (ARCHEAN?)
Fig. 2 - Generalized geol ogi ca l map (A) and Strati graphic Succession (B) in the
Cup Lake area . Note: Patterns on the map are not meant t o rel at e
t o those in the column .
Ma fic gneisses and ultramafi c rocks (2) occur at t wo l ocalities .
Hornblende-
harzbergite s (2a) a r e charac t eri zed by hypersthene mega crysts up to 8 cm long and
by surfac e pitt i ng (Munday , 1977) .
posure.
Possible igneous layering was not ed i n one ex-
Amphibolites and amphibol e gne i sse s/ schists (2b) are c losel y assoc iated
with Un i t ( 2a ), and r ange from fine-to medi um-grained l aminated hor nblend e- plagioclase gneisses to me d i um-to coar s e-grained (0.25 - 1 cm) amphi bolit es .
Graphitic pelites (3) are found int erlayer ed wi t h subord ina t e feldspa thic
ps ammites in which s illimanite , garne t, and cordierite are irregularl y dis tr i buted .
Radioac tive " granitoid segr egations " occur in these rocks within a few hundred
me t res of the con t ac t with the f e l sic gneisses , but a re o the rwise not widespread .
Fine-grained calcite- biotite / phlogopite-scapolite -diops ide rocks and pegma ti tic
diop side ro cks (3a) form dis continuous lenses or boudins al so c lo se t o the c ont ac t
of th e suprac rus tal s and f e l sic gneisses .
- - -- - --······-····--·---··-···---··-····-·-··.-·· .
The uranium mineralization
i s hos t ed
-71-
in coar se-. to pegrnatitic white tonalite s egregations, as wel l as i n the pegmatitic
di opside rocks themsel ves .
Dark gr ey f ine-grained graphi ti c- garnet- hypersthene-
amphibole gneisses (3b ) and a continuous ba nd of vaguely banded medium- g r a ined
(0 . 1-0 . 50 cm) pink diopside/hypersthene meta- arko se (3c) out crop on the west side
of Cup Lake.
Calc areous rocks (4) con sis t o f tremolite-diopsid e- ca l cite-biot i te / phlogopitequa r tz schist s int erlayer ed with diopsidic ma rbl es and s ome pelitic o r psammitic
r ocks .
Pelites , fel dspa th ic semipe lite s and psanunites (5) , whi ch con stitute the
highest s trat i graphic unit i n the a rea, ar e medium-gra ined (0 . 1-0 . 5 cm) rocks
commonl y containing s illimanite, toge ther wi th either g r aph i te or magnetite.
Granobl as tic garnet and cordierite occur i n overgrowths .
A t hin lense consis ting
of a bio tit e-pla gioclase-qua rtz gneis s (Sa ) with fe l dspar megacrysts i s postulated
to have a py roclastic origin .
Struc ture
The Cup Lake area is part o f t he Mudj a t ik l ithostru ctur al domain, i n which
t hree majo r episodes of deformation D t hrough o have be en r ecognized (Pea r son ,
3
1
1972; Sibbald, 1973; Pearson and Lewry, 1974; Lewry 197 4) . The Cup Lake str ucture
is marked by a sou th plunging
Dz
synform which i s r efold ed on a
No c learly defined lineament s wer e ob served in the area .
o3
synformal axis .
On e poss i ble area of
fa ulting occur s along the con tac t between t he f el sic g neisses and the metas ed i men t s ,
in a narrow zone (5 m) of sheared quar t zofeldspathic rock .
Metamorphism
The f ollowing fea tu res ind i c ate that upper amphibo l ite-lower granul ite me t a morphic conditions preva iled during and possibly out lasted the thre e deformat i on
ep i sodes:
1.
Cordi er i t e , sillimanite and orthoc lase in the pe lites , and hyperst hene in
the ultramafi c s , me ta-a rkose s a nd fe lsi c gneiss es.
2.
Qua rtz-cordieri te-s illi rnanit e kn ots and garne t elongat e i n the n
3.
Folded silli rnan it e , cordierite and garnet in the cores of
o
s truc tures .
4.
o
3
f abrics overgrown by gr a noblast ic garnet a nd cord i erite.
2
and
1
fol iat i on .
o
3
- 72-
Economic Geology
Radioactivi t y in the vicinity of the O.K. claims is found primarily in coarseto pegmatitic tonalite and i n l ate coarse - grained 'granitoid ' segregations from the
pelites of Unit (3), as well as in the pegma t itic diopsidic rocks of Unit (3a) .
Accessory molybdenite and apatite are observed i n some areas of radioactivity.
Uraninite i s reported t o be the main source of radioactivity , although the occurrence of allan ite i s mentioned in a Re port on CBS 1022.
In the Key Lake locality* (Fig. 2), approximately 4 km north of Cup Lake,
radioactivity occurs in white t o pinkish " lit-par-lit " pegmatites .
pegmatites and molybdenite in the Bear
in zones rare l y exceeding 2 m long.
Pyritic gossony
and Knob c laims display spotty radioactivity
Radioactive pegmatites in this a r ea are re-
ported to be generally associated with graphitic gneisses.
Published assays give values between 0.55 and 1.34 percen t
for the O.K. claims .
u3o8
Munday (1977) reports an assay of 0 . 28 percent
anomalously radioactive rocks in the Key Lake metasedimentary belt.
equivalent
u3 o8
f r om
Two r a r e
earth showings in pegmaties south of Cup Lake were reported by Sunlite Oil, giving
values of 0.095 and 0.12 percent Nb
o
2 5
, and 0.06 and 0 . 07 percent Tao 5 .
Refer ences
Beck, L. S . (1969): Uranium Deposits of the Atha basca Region Saskatchewan; Sask .
Dept. Min. Resources Rept. 126 .
Lewr y , J. F. and Sibbald , T. I. I. (1977) 1 Variation in lithology and tectonometamorphic relat i ons in the Precambrian of northern Saskathcewan; Can.
Jour., Earth Sci . , Vol. 14, No. 6, pp 1453- 1467 .
Mawdsley, J. B. (1950): The geology of the Charl ebois Lake area ; Sask. Dept. Min.
Re sources Rept. 5.
(1 957) : The geology of t he Charlebois Lake area; Sask . Dept. Min .
Resources Rept . 24 .
Morra, F. (1976): Geology and Uranium Depo si t s of t he Charl ebois-Higginson Lake
area, north Saskatchewan; unpublished M. Sc . thesis, Uni ve rsity of
Alberta, Edmonton.
Munday, R. J . C. (1977): The geology of the Mudjatik (east ) area; Sask. Dept. Min .
Resourc es Rept. 168.
Pearson, D. E. (1977): The geology of the Mudjatik (S . W. quarter) area: Sask . Dept .
Min . Resources Rept. 166.
*
·· ·-.. ····-·
No t t he Key Lake of t he Uranium-Inexco-SMDC joint venture
--- -. . .........
____
-73-
and J. F. Lewry (1974): Large-Scale Fold Interference Structures in the
Mudjatik River Area of northern Saskatchewan; Can. Jour., Earth Sci.,
Vol. 11, No. 5, pp. 619-634.
Ramsay, J. G. (1967): Folding and Fracturing of Rocks; McGraw-Hill Co., New York.
Sibbald, T. I. I. (1973): Mudjatik (N.W. \) area; Geological Investigations in
Precambrian of Saskatchewan, 1973 (L. S. Beck, Ed.) pp 35-42.