- 117 -

leconnaissance revel and ll:!tailed Surveys in the Exploratioo for Uraniun by a Biogeochemical Metood

by Cblin E. D.mn

D.rring the past three surnrers, biogecx:han:i.cal s~ys were corrlucted by the author in the vicinity of the J\ti:lean lake uranium deposits (D.mn, 1979, 1980, 1981). Unusually high ooncentrations of uranium are present in many types of ~getation, in particular the twigs (less tre needles) of black spruce (Picea mariana) which l ocally coota.in in excess of 1000 ppn uranium. 'lwigs are fast and easy to collect. Hc,,..,e~r , care must re taken to sarrpl e a similar arrount of growth (e .g . the latest ten years) f ron each tree, recause of the coosiderable variat ion in the uranium cootent of each annual growth. Uranium migrates toward the out.er extremities of the trees (~, 1980); thus , by taking the lat.est ten years grcMth, variations in annual accumulations are S!OOtied out . A sample sufficiently large to obtain 1 g of twig ash can re collected in less than ooe minute .

Objectives

Bl ack spruce twigs and needles ....ere the only vegetat ion collected this year. Problems that had arisen or were outstanding £.ran the earl ier studies were as follo,;s:

1 . Background. What constitutes background, and a t what distance fran the M:::Clean Lakeareaare "nonna.l" level s (i.e. a few ppm U in twig ash} encountered?

2 . Seasonal varia tioo in U uptake . SCJ!E vegetation exhi bits ronsiderable seasonal variation in ccncentratioos of elerrents. The rehavior of urani un needed eY.aminatioo .

3. Annual vari ation in uraniun accumulation. wa.ild a tree , resarrpl ed aft.er a year, yield a ooncentratioo similar to the first tirre sanpled?

4 . Quantity of sarrpl e that needs to re collected . What is the minimun?

S. Track Etch and soils. How would data frO'll soils and Track Etch cups correlate with biogecx::rernical data in areas of no known mineraliza tioo?

6. Intense biogeochemical anonalies in urrlrilled areas . Th:!se warranted closer examination and detailed sarrpling in order to refine them mre precisely .

The firs t phase of investigations took place in J une ; the secooo early in August. Sampling was extended £ran the l>tClean Lake area to include a) a transect across the Athatasca Basin from Wollaston Lake to Black lake; b) ooth sides of the Black Lake fault; c) the general vicinity of Urani um City; am d) a transect across the carS\-.ell Structure (Fig . 1).

Iesults

1. Background

In 1979 the 1 km traverses across the !lti:lean Lake North zone showed a positive biogeoc!Eni­cal respcnse to uranium mineralization occur­ring reneath 150 m of Athabasca Sandstooe (Dunn, 1979, 1981). However, the traverses

d id not extend to areas \\here values were suff i ciently consistent to re considered "background" Even 15 km southeast fron MC:Clean Lake values exceeded 200 tirres those nonnally expected and 20 km to the west they were 100 tines higJ-er (cf . 0 . 6 Hl11 U estimate of back­ground in asJ-ed vegetatioo , Brooks, 1972).

In 1981 sarrpling carnrenced near the camumity of Southend, aoout 200 km south of Mct:lean Lake and cont inued at intervals of 10 km northward as far as the Geikie River , then at 5 km intervals to Minor Bay (south end of Wollaston Lake), and at 2 km intervals to Rabbit Lake (Fig . 1) . Concentratioos of uranium in the ashed twigs are generally 2 to 4 ppn in the southern part of the traver se . However, northward fran the Wathanan Bath:>l i th (i.e . Needle Fall s/Parker Lake Shear Zone area), and into the Wollastcn D:Jnai n , the va::ues are 4 to 6 ppn. Beyond the Geikie River cmcentra­tibns steadil y increase until just north of the llmpherville River (near Ahenakew lake) they abruptly rise to over 100 ppn U. This i s close to the southern limit of a uranillll biogeochernical ananaly which ext.ends at least a) sooth t o Waterbury Lake , b) north to HatcJ-et Lake , c) east to Wollaston Post, and d) v.est to the Wat.erfound River (coincident with the projected Cable Bay Shear z01e of .Famaekers am Hartling , 1979) . This ananal ous :regioo is greater than 3600 Jcm2, every sarrpl e fran it cootaining at least 10 tines rrore uraniun than nonral , with local ccncentrations 1000 tines normal . TJ-e region i s r eferred to as the Wollaston Biogeochemical Ananaly (Fig. 1) .

- 118 -

; uc•

i - ,>

L .. ~ ,..'{"

J I -1- f I .. c-.,

I <ll)- .-, I J ,j' ···I ··-vr·-· ..

-r ·

'·-· J + i

)

4 , ... H~J .-5, , l ·: ( ...,, .,/ . ··""r\

"J J.,~

<} ·, AT IH ABASC A

I - ------"'!··

+-

.,. . .rl.~::., .f

I ~ .; ·'._'.Pi;-,,,.. ;.,· .. ··~//':)~

; ,:1 -lf,

I , ( of, 1:)~·

T -I

- ~ ... ~ .. I I

~ :.r 0~ .J I

~ ", .J I

~''I

n I ,.

- .+ - 1,r'

>l l ,, .. ,: ' l'· .. . ~~ . ·" ! ~) ,! / ~

I I

p . .,, ,

fz ~ ··~ .> ~6urnEND'

/ >

:: 4~ ,c: ~·

Fig . 1 - Uranium in t he as h o f black s pruce twi gs

2 . Seasooal Variation in u Uptake

seasonal vari ations in plant chemist.Iy take place (Guha , 1961) recause of fluctuatioos in rainfall , tenperature and hunidi ty, and there­fore also in the transpiration rates and the

trans l ocati on of elerrents within the plants . No data are know, to tre author on variaticns in urani\.Dl\ uptake in black spruce, so trees at 20 sites ~re sarrpl ed in both J une and August , 1981. Results of twig ash analyses (Table 1) shC1.ll appreci able differences in

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Table 1 : Seasrnal Differences in the Concentrations of u in Asred Black Spruce (Picea mariana) Twigs and Needles.

Site U (ppm) in Spruce U(pµn) in Sprure No . Twig Ash - 1981 Needle Ash - 1981

June August June August

l 253 264 13 8 2 179 238 19 15 3 202 157 15 8 4 153 198 27 23 5 169 140 16 10 6 1090 615 71 43 7 303 333 17 14 8 256 244 18 11 9 413 354 28 19

10 411 335 34 16 11 556 460 35 22 12 315 323 9 8 13 229 356 15 15 14 886 653 57 42 15 169 153 15 10 16 145 149 10 7 17 239 304 15 15 18 334 288 20 15 19 315 418 18 17 20 291 175 1 9 12

coocentrations, but at nine sites values \>.ere higher (rrean increase 21.2 percent) and at 11 sites they ~ los.-.er (rrean decrease 20 . 8 percent) , giving an overall rrean difference of 0 .2 percent. It was shcJl..n (Dunn , 1980) that l ocal variatioo and variation around a tree of ±15 percent is to be expected , and that "a map depicting centaur intervals of less than 20 percent of tre rredian value is utlikely t o reflect significant variatioo in tre data" . In the light of this variaticn , it is ccnclooed that no discernible syste­matic change in the uranium ccntent of tre black spru:::e twigs took place fran June to August .

'lhe needles , h<M:ver, present a different picture (Table 1) . 'Ihere was a rrean decrease fran June to August of 27. 3 percent, and no sanple gave a higher value in August.

3. Annual Variation in U J'>ccunulation

Twig ash from trees in the vicinity of tie »::Clean Lake North Zone yielded consi stently higrer ccncentrations in 1980 than fran the sane trees sanpled in 1979. In 1981 twenty­seven sites \>.ere sanpled for a secood tirre, and seven for a third tirre . Ccncentraticns

are of tre same order as those for 1980, (Table 2). A.t 17 sites there was a decrease in uran­i um cootent (n:ean loss of 17 .4 percent) , where­as at eight sites there was an increase (rrean gain of 16 percent) . 'lhus the annual varia­tion is similar to the seasaial, and, within the limits of al:x:>ut ±15 percent of natural l ocal variaticn , no discernible systematic loss or gain of uraniun to the vegetaticn took place fran 1980 to 1981. Hc,.,.ever, this is not tre case for the needles. At the sane 27 sites, all but one tree s~ a substantial drcp (rrean loss of 40 perc:ent) in tre uraniun content of the needles fran 1980 to 1981 .

'lhe reason for the increase in uranium e<ntent of the twigs fran 1979 to 1980 is th:)ught to re related to tre high l evel of dri lling activ­ity during that period, resulting in uraniferous

Table 2: Annual Variation in u content of Ashed Black Spruce (Picea mariana) 'Iw.i.gs .

Site No. U(Wffi) in Spruce 'Iwig Ash

June 1979 June 1980 Jtne 1981

l 77* 181* 143* 2 88* 237* 264* 3 113* 229* 253* 4 94* 288* 179* 5 89 492 389 6 52 188* 183* 7 84 145 164 8 63 255 247 9 103* 249* 215*

10 103 228* 283* 11 88* 190* 124* 12 60 147* 136* 13 78 172 133 14 55 179 206 15 60* 132* 16** 80 81 17** 281* 230* 18** 264* 256* 19 289 291 20 149* 118* 21 198 275 22 161 195 23 182* 166* 24 531* 520* 25 294 173 26** 511 397 27** 564* 486*

* Sane tree sanpled. Where no asterisk , another tree was sanpl ed at ~ sarre site within a radius of 5 m.

** Remote fran kna-m. mineral.izat.ion .

- 120 -

fonnation waters reaching the roots . In 1979 the surface WlS rel atively undisturbed by drilling because mineralizat i01 had only recently tee n discovered . By 1980 a large area of peat bog had been cleared, rrany more hol es drilled, and considerable leakage of fonraticn waters to tie surface had taken place. Spruce are sensitive to s ubtle changes in water chemistry , and because the twigs are such s t rong concentrators of urani wn, they s:)()n reflected such changes . For example , in the Carswell Structure of northwestern SaskatcheWln , pl.lllping of uraniferous water into a tail ings pend began in No\elTiber , 1980. '!wig ash fran u.o spruce in a nearby s tand scnpled in August, 1981 yielded 1480 pµn u and 1120 pµn U, ~reas background values for this area are about 6 pµn U. Similarly, twig ash fran a spruce grwing close to the nortrem edge of the Rabbit Lake cpe.n pit, yielded 2270 ppm U. Finally, at McClean Lake in 1979, a few samples collected fran two sites about 5 km a:way, wrere no drilling was taking place, yielded valoos similar to those taken in 1980 and 1981.

I t is concl uded that only minimal annual variatioo of U in twigs takes place , and that uraniun ions progressively migrate a l 01g the twigs as new growth fonns. Thus , i f ten years of growth of twigs i s regularly collecta:1, analytical data fran sauples collected in ooe year may .l::e integrated with trose from another, provided no envircnrnental disrupti01 has taken place. Thz needles, hov.ever, slnw appreciable annual variation .

4. ~at ~ve r,Stu:i~ of U in Bulk Sarrple _ and u _ m a sm9. e 'lwl.9:

In view of the inhatogeneity of uraniun distri­bution within a given tree, it is desirable to collect 300 to 500 g of rraterial at each s i te in order to snooth the intra- site variations , and obtain the 1 g of twig ash desirable for neutra'l activation and possible subsequent multi-elerrent analysis . H~ver, thi s sanplirg prooodure gerx:rrates a large volurre of material in a short ,Eeriod of tine, and u.o workers usually end the day with vecy l arge packs. If electric ~r is availabl e at the base carop, the samples can be dried in a micro,.rave oven and separated into reedles and twigs an site , thereby reducing ten-fold the bulk of material that needs to be shipped out.

In order to retennine ~ther or not similar biogeocl"EITI.i.cal profiles for uraniun could be obtained by taking nuch srraller sanples, one traverse was selected at random for study. Bulk samples of tre usual size ~re collected, and one twig with its needles was taken fran each bag for separate prca:!ssing. Thz five sample splits fron each s i te that ~re prepared

for analysis \\ere:

a) ash fran bulk s aiple of twigs; b) ash fran bulk sanpl e of needles; c) ash fran singl e twig; d) ash fran needles on singl e twig; e ) dry , ground needle s fran singl e twig .

results (Fig . 2) shJw similar profiles for the five splits , except for a greater degree of "noise" in tre profile for tre dcy needles doo t o the law levels of U rreasured (1 to 5 ppn U) .

It appears, trerefore, that given a uranifer­ous environrrent, the s arre infamation on U

·~1 '°° ] \

u ••• 1......... I \ {ppm) • 1 . . ·,. .

/'\.,...-, . \ .,~ 1 -· / . '·-· / . . -· '--·-· '-....

...,)

uJ (ppm )

I ,:II) •

I O·-•-·

o•~ .-~----

Sompte S1t n

Somj'.J le S,tes

" ] U-••Hflot ~ ·ctnHolu ( ,.11qlt '• •Ill

•--·• . --,--, ' -._- I -, Sw1P

u 10 I

{ppm! 1 or

/\ !'· / ·-. \ . /-·-........ ___ / "· .

.--·- ./' .......... _.,,.,...

oL....... - ~ · ·~· · - ·- ~ · -·. ·~ ·- - -· -~ • Scmpl• Si tu

u : l lppml 21

,, l ~ ·· . ~· ·-· ~ · -~· Sompl• Silo

Fi g. 2 • Comparison of uranium biogeochemical profiles from

bulk sampl es and single twi gs of black spruce collec ted along a traverse near Mot fa tt Lake

- 121 -

distributicn can be obt.a.ined fran a single twig or the needles fran tre twig, as frc:m the oolk sanple, with the following provisos :

a) greater care must re taken to collect exactly the sane amount of growth (e .g .10 years) at each site, whereas variation of plus or minus a year or two can re toler­ated in collecting a bulk sanple;

bl greater care must re taken in v.eighing the ash fran a single twig. In this sttrly the ash weight varied from 0.04 to 0.22 g ; analytical precisicn can re irrproved by v.eighing to one-hundredth of a gram;

c) there is seascnal and annual variation in the uranium content of needles , hence any sttrly that is to rely upcn data from the needles must re undertaken within a short tirre-frane.

It is advisable to collect a bulk sample l::Jec:au9= it will provioo an average concentration for a given site. Furthernore, a larger sample will provide suff icient ash for additional trace elarent analysis, should other elarents prove of interest.

5. Q:rnparison of Track Etch, Scintillareter, Uraniun In Soils and Uran~un m 'lwI9s _

D.J.ring the stmrer of 1979, a team fran the C£ological Survey of canada placed Track Etch cups in the ground near the !IK::Clean Lake North Zone at the sites where vegetaticn and soil samples ~re collected by the author. In genera l there was a gocx:l correspcndence ootv.een contoured Track Etch data (using ooth unfiltered and thorcn-filtered cups) and uranil.lll in the vegetation (Omo, 1981) , but the soi ls yielded virtually no geochemical relief . In view of the high concentrations of uranium found in veget.ation growing a few kil anet.res to the east, where there is no kn0wn mineralizaticn, an area there, which was found the previous year to exhibit a U biogeochemical prof ile of high relief , was selected for investigation.

Fitcy "new inproved ·1rack Etch cups" were placed alcng several undisturbed traverses in this region, and ten cups ....ere placed at sites alcng the Wollaston lake road. 'Ihe - 80 rresh fracticn of Bp horizon soils at these sites was analyzed, and scinti llareter r eadings taken. Table 3 stmroarizes the data, and shCMS the following inportant points:

a) within the Canadian Co::idental prcperty , uraniun in soil shoos remarkably little geocremical relief whereas that in ashed spnx:e twigs ranges f ran 153 to 886 ppn. A few kilaretres to the south similar

Table 3: COrrparison Betv.een u in Soils, Ashed 'lwigs , Track Etch, Scintillareter and Type of Terrain

Site NO.

llrMi.Lll1 01,· Soils Twig /\sh

(1~:rn) (pt:rn)

Truck e t c h

(Tr/sq .nm)

Scint i llo ­metet· (q:,s )

--- ---· ------ --·--------22' 24* 26 * 28 * 30* 31 • 32* 33' 35 37 56 57 58 59 60 63 62

264 265 266 267 268 269

40 41 42 43

282 46 47

283 170 169 168 167 166 H,5 164 163 162

84 85 86 87 88 89 90 91 92 93 94 97 99

112 J 13 114

2 . 0 3. 2 2 . S 2 . 8 2 . 8 2 .4 3 . 1 1.9 L& 1.4

1.9

1. 7

1. 9 1.9 1. 9 2 . 0 L.6

1.6

2. 0 1. 8

1. 8 2. l 2. I 1. 8 1.8

1.8 L6 1.8

I . 3 1 . • 9 ]. 7

1.6

1.4 l. 4

- no soil hori zm

26 19 20 14 11

8 7 5

236 25S 315 113 334 156 239 145 152 145 \ 69 886 229 315 279 551\ 365 411 lj5J 413 230 25 6 486 408 252 226 198 374 303 171 227 120 H,9 Ed 201)

172 202 J 91 377 L4 3 264 2S3 179 334 264 214 228

95

31 195

25 12 25 38 25

101 94 63

7 119

9 56

101 23 54 23

122 93 84

173 126 200 129

72 22

1(,2 68 93 56 22

167 65 92

10 4 108

34 31 27 79

137 1.87 16

170 243 JlO 13 20 25 13 6 7

7 81 40 20

22 36 22 26 28 28 20 26 20 20 5

30 20 22 26 32 28 38 34 40 :15 40 J 4 28 26 ·12 40 25 20 30 34 26 26 26 28 36 38 10 JO 20 36 38 30 20 JO 28 22

6 7

12 7

20 10 30 20

5

2 2 3 3 2 3 2 3 3 5 2 3 2 2 2 2 1 2 2 3 l 2 2 2 2 2 2 2 2 3 2 2 2 2

6 6

2 3 3

2 ]

6

s 2 ',

3 3

• ~ sarples c lose t o the northern end o f the wollast.rn Lake road. R?Jll1lin<e r of ,;arrples fron Canadian (ttia,n t.al prt.ipcrty , near ~b ffatt l..ilk.e .

* 1t 'furrajn ccrl?s 1 = Boul dE:rs 2 ~ Ory ..oodl and 3 = Danp wnodl.and 4 = \•let \o,Q()(jl and 5 = Dal1p nuskeq 6 - W<>t muskeq

ccncentratims of urani um in soils occur where the twigs yield only 5 ppn U;

b) Track Etch data shav awreciable relief, but correlate rrore closely with scintillo­rreter readings than with the biogeochemical data.

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'Ire spatial relaticnship J::etween the Track Etch and the biogeocremical data sh<:Ms s:Jre coincidence of high valres, rut the pattern is not coosistent. 'll1is is due partly to the typically lCM scinti llcrreter and Traclc Etch recrlings obtained fran boggy areas, whereas the vegetaticn ananalies transgress terrains fran \\et muskeg to dry q:;,en \-,O()(Jland. It is notev.orthy, l'x:1..ever, that on dry ground many of the higher Track Etch results coincide with high uraniun values in vegetation. It should be arphasized that a high biexJeocremical ananaly wi ll coinc ide with a high Track Etch ananaly only v.hare the grotmd is dry and uraniun mineralization is close by, recause radon (detennined by Tracie Etch ~s fran its alpha radiatioo) will travel roly a short distance before decaying. In cx:mtrast, uraniun tbat accunulates in the trees may travel a considerable distance dissolved in grourrl and foIJT1atioo waters before teing extra=ted by the tree roots. No physical or chemical canpcnen t can yet be identified which has a significant bearing q:><n the wide range of urani un coocentrati.oos in the twigs .

km l 0

6. Intense Bi~ocremical U J\nanalies _ in Uldrilled Areas

In the course of attenpting to e stablish the regiooal bockgra.md for uraniun in spruce twigs within the McClean L~e area, sever al areas were di scovered wrere uraniun cx:ncentrations proved even higoor than in the vicinity of the ore zones . 1'bst notable of these i s about 5 km to the northeast, in the vicinity of a small lake knGl!l locally as "Tut" lake • In this regim (Figs. 3 and 4) , max.imun vali.Es of 1260 and 1080 ppn u are present in asood twigs collected fran trees along the north shore of Tut lake; several crlditional sites yielded in excess of 500 ppn U. ~ area is poorly drained, densely woc:rled, and divided by a nortm.est-treooing ITU1skeg. Draina(J:!, hcM:!ver , does not aEl)ear to bear a relationship to the uraniun uptake of the plants: sore trees in the poorly drained area ccntain less than 300 pµn U, whereas others en sparsely wooded, oouldecy, ~ll~aired hills (to the south and \\est of Tut lake), e<ntain in excess of 700 pµn U. 'Ire regi oo of the intense anaraly at

3 km

Fig. 3 - UranilJll in the ash of black s pr uce twigs , detail of Fi g. 1

- 123 -

SCAL E

O ~ OO m c== - -==:m- c==:::i

UNS!JRVE~E O

"rur"

LAKE

I LEGEND!

u ( ppm) - > 000 ( WI TH CON C~NTRAT ION ) - 401- 500

11EST0

11 w ~O J- 40 0

D 201-- 300

LAKE D 101- 200

1] < 10 0

( ~ ) MUSP<. EG

TRAC I<

-.IE AN VALUE F ROM T WO SAMF>LE S

r 0 3° ~o· 10 3 "' .. ~· 103° 401

I LOCATION MAP I

SCALE

I O I 2 3 4 5 ~'"

+

Fig . 4 - Ur ani um i n t he a s h of blac k s pruce twi gs, "Tut" La ke area

- 124 -

the north end of the l ake has not been drilled . 'Ite closest drill hole (Olli 20-77, Fig. 4), situated 300 m to the west,~ no signs of mineralization in e ither the Athabasca Sand­s t01.e or the basenent: a ll analyses of drill core material reported O. 5 ppm U or less (Canadian Cccidental Petrole un Ltd ., pers . cami.) . 'Ite mderlying basarent is meta-arkose , i nterpreted as Archean (Sibbald , 1980). Surveys of Tut Lake by Canadian Cx:cidental (pers. ccmn.) revealed the folloong :

a) I:Epth less than 2 m throll]hoot;

bl Sedirrent carpositirn: boulder s with silt in the west to clay- rich oozes in the east;

c) Alphaneter data: 1- 849 cph, with the highest value occurring in the northwest;

d) All oottan waters have less than 0. 001 ppm U;

e ) lake sedirrents: 1 - 3 ppm U;

of the Wollaston Bi ogeochemical Anaraly , and to <rteillline the general levels present in spruce gro,.,ing over the fonnations of the Athabasca Group as defined by Ranaekers (1979) .

West of lJnkno,mLake (Fig . 1) all twigs sampled yielded between 3 and 7 ppn U in their ash. 'Illus, at this l evel of r econnaissance sanpling, it was not possible to detect any difference in ''backgrC1JI'ld' 0n the M:mi.tou Falls Fbnnaticn, Wol verine Point Fm:mation, or the relatively phosphatic Locker Lake Fomation. It is considered , ho.,iever , that the shallo,., depth uraniun potential of the~ tire Athabasca Basin could be assessed by taking one sample per 100 km2 (i .e. just 700 sanples) .

b) Black Lake R:gion. No systanatic diff­erence was a pparent fran sanples collected to the west of the Black Lake Fault (i.e. on Athabasca Sarrlstone , range 3-18 ppn U) , and those east of the fault (i.e. greissose base­rrent, range 5 - 14 ppm U) . Tre 18 ppm u from ore tree near the ccrmu.mity of Black Lake is rrore than five times background for trees gra.,ing on the Athabasca Sandstone in this

f) Radon in the lake sediments : 0 - 6 cpm, area. and highest in the southeast;

g) Helium in the l ake sed.inents : 1.2 to 8 . 7 [ (cc He at NTP/cc sediment) x 10-B] , with the highest value occurring in the north­west .

'!hese data , with a few exceptions such as the highest a).phameter readinq, do not render the area "highly prosi;ective" . Ore line of geo­cremi.cal evidence which is nore indicative is the analyses of lake sed:i.nents fran ~ffatt Lake (1 km dam drainge fran Tut Lake) which indicate slightly anorralou.s ccncentraticns of U, Ni, Co and Zn (Coker and Dunn, 1981, Fi g . 29) - an assanblage typical of 'sub­Athabasca tyi;:e ' urani un mineralization.

The biogeochemi.cal data derronstrate that "leakage" of waniun to the surface is taking p l ace , and the concentrations are of s uffic­ient magnitude to warrant c l oser investigation . At the present time i t is unkno,.,n wrether or not the anaralies are related to a) urani­ferous waters which have migrated several kilaretres :Eran the uraniun source , or b) uraniun mineralizaticn in the imrediate vicinity . It is the writer's suilllise that the l atter is the case .

7. ~~~l Studies

a) Athabasca Basin Interior. A few sanpl es were collected at 10 to 30 Ian intervals west­ward for 150 km fran WOllaston Lake, then northward for 70 km to Black Lake. The cbject ive was to define the western limit

c ) Uranium City legion. Val~s rar)Je f rort\ l ppn u (Johnston I s land) to 120 wn u near the St. Louis Fault at Eldorado. In general the spruce are l arger than in the other regions s tulied, and exhibit longer annual twig grc:Mth. Too geology i n this area i s a:xrplex, and this help:; to explain the wide range of uraniun concentrations in the trees. 'Ihe f ~ sanpl es collected across the Athabasca/ Tazin quartzite unconformity on Stewart Island gave no indication of mineralization , altrough, in the south~st comer of the island, uraniun shews ha....e been reported (Anon., 1981) . No sarrples were collected c l ose to the surface sho,.,ings because it was the intent of the survey to deteillline whe ther or not the mineralization could be detected in the trees grc:Ming in the genera l vicinity.

It is not&lorthy that the highest val~s in the Uranium City area occur in trees groong i_µ)n granitic or granodioritic greiss. The irrplication is that the latter lithology is rel a tively uraniferous, and the trees are reflecting the leadl.able urani\Jll content of the rock (i.e. that uraniun which is not strongly incorporated in the stru:::ture of resistate minerals) . The tree roots may spread o~r an area in excess of 10 rn2, and the.'."efore ccnstitute an averagi ng rrediun for that area , and provide a ''windcw" to the U potential of the urrlerlying rocks .

d) Carswell St.nx:ture. Spzuce twigs collected fron the central baseroont caiplex of the Cars­well Structure yield 4 to 8 ppn u. '!he excei:r

- 125 -

tion is in the vicinity of mineralizatico near Cluff Lake: 8 4 ppn U is recorded fran near the OP zcne, and 24 6 ppn U fran east of the D zone. By anal<XJY with the McClean Lake area (see Annual Variation, above), these e levated values could be the result of contamination frcm the rrobilizatian of relati vely urani­ferous grouna,,aters during drilling and mining operations. Clearly , the 148 0 ppn U recorded f rom one site at the edge of the tailings pond is a res ult of contamination fran uraniferous waters .

S\illtfily

1 . The work dare during 1981 has defined a a massive uraniun biogeochemical ancrnaly in black s pruce near Wollaston Lake, that covers at l eas t 3600 km2. Within this region local intense anaralies, notably near "Tut" Lake, may r eflec t undiscovered uranium mineralization, a lthough there are f ew other positive geochemical o r geolog­ical indications.

2. A subtle biogeocremi.cal change is indica ted across the Needle Falls Shear Zore .

3. As~d spruce twigs shaved no systematic seasonal variaticns in U uptake. Needles s haved a narked decrease from June to August, 1981.

4 . '!wigs collected near the M::Clean Lake zones o f mineralization in 1979 had lCMer U ccncentrations than those coll ected from the sane trees in 1980 . This is attributed to the increased drilling during that period, by rreans of which relat ively urani.ferous fonratian waters migrated up­ward and were absorbed by the trees . Fran 1980 to 1981 no systematic changes t ook p l ace at these sites , nor in other test areas . It is concluded tha t little annual variation takes p l ace in the twigs, provired there i s no disruptioo o f the environrrent. Needles , hcwever , shewed an appreciable decrease in U content from 1980 to 1981; therefore , the data f ran the two years cannot readily be integrated.

5. BF horizon soils shCJNed no geochemical relief for U, yet the spruce fran the sane sites r anged fran 5 - 886 ppn U in their twig ash .

6. Track Etch data shewed a rroderately good spatial correl ation with the biogeochemical data in dry te=ains , but the Track Etch and scintillCITEter readings sha..,ed a better overall correl a tion.

7. In a uraniferous environment the ash of a single twig may provide the s aire biogeo­chemical info:rrration as a bulk sanple.

8. On the Athabas ca Sandstone , background values of uranium in spruce twig ash are in the range 4 to 6 ppn. In the Black Lake r egi cn, valt.es range fran 3 to 18 pµn U, whereas near Uraniun City the range is 1 to 120 ppn U. Trees graving upon granitic gneiss in the latter region have the high­est concentrations. Within the Carswell Structure , background values are 4 to 8 ppm u, with conc enc.rations of 246 ppm U recor ded f rom near the 'D' zaie of min­eralization, and 1480 pµn U adjacent to the tailings pond.

9. It appears that this biogeochani.c al method i s capabl e of providing a ''wind::M" through the surface sedinents to assess the uran­iun potential o f tre underlying rocks.

Ackrnwledgerents

I am grateful to Canadian Occi dental Petrole um Ltd. and Inco ~tals Co. for their co-operation and hospitality whilst working on their prop­erty, and to Dr . R. Wa llis and N. Saracoglu for many relpful discussions a m for providing sorre of the data in this report. 'Ihe biogeo­chemical data , results and interpretation are entirely the responsibility of the a uthor. I thank, a l so , H. J ohnston and L. Smith for the high standard of their fie ld and labor a ­tory assi stance , and the Terradex Corporation for s upplying and prcx::essing the Tr ack Etch cups .

References

Anonyrrous (1981): The Stewart I s l and uraniun shcMing; CIM Geol ogy Divisi m Uraniun Field Excursion Guidebook , Sept. 8-13, p . 81-86.

Brooks, R.R. (1972): Goobotany and Biogeo­chemistry in Mineral Exploration; Harper and Rew, New- York, 290 p .

Coker, W.B. and Dunn, C. E. (1981): Lake water and sedinent geochemistry , NEA-IAEA Athabasca Basin - Wollaston Lake test area (64L, 74I}, Saskatchewan; Geol. Survey Can. , Open File 779 , 100 p .

Dunn, C.E. (1979 ): Biogecchemi.cal survey of two deeply buried uraniun deposits , NEA/ IAEA test area; in Summary of I nvesti­gations 1979, Sask. Geol. Surv. , Iept. 79-10, p. 166-167 .

- 126 -

Dunn, C .E. ( 1980) : Uraniun biogeochemisty: NEA/ IAEA test area; in Suranary o f Invest­i gations 19 8 0, Sask. Geol. Surv. , Misc . Rept. 80- 4, p . 60- 63 .

Dunn, C .E. (1981) ! The biogeochemical e}!J?res­sion of deepl y buried uraniun mineraliza­tion in Saskatchewan, Canada; J. Geochem. Expl or., v. 15, p . 437-452.

Gtha, M. (1961): A study of the trace elenent uptake of deciduous trees; unpub. Ph.D. Thesis, Univ. of Aberdeen (quoted in Brooks , 1972, p . 104).

Ramaekers , P. (1979): Stratigraphy of the Athabasca Basin; in Surrna.ry of Invest­igations 19 79, Sask . Geol. Surv. , Misc. Rept. 79-10, p. 154-160.

Farraekers, P. and Hartling, A.A. (1979): Structural geology and intrusive events of the Athabasca Basins and their bearing on uranium mineralization; in Uraniun E:xpl or ati on Techniques ed. G.R. ParslCM, Sask. Geol. Soc. , Spec . Publ . 4 . , p . 221-234 .

Sibbald, T.I.I. (1980): NEA/IAEA test area: Sub-Athabasca Group, baserrent geol ogy; in Suma.ry of Investigations 1980, Sask. Geol . Surv., Misc. Rept. 80-4, p . 57-58.