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Evaluation of Techniques for Assessing the Uranium Potential of Lake Covered Areas

Introduction

During the second field season of the three-year project, further modifications

to the techniques developed in 1975 were evaluated . In addition, preliminary

evaluation of two experimental underwater scintillometers was undertaken. Earlier

work on this project is detailed in Beck, Parslow and Hoeve (1975, in press) and

Hoeve (1975).

Two areas were studied in detail. Eight week's work was carried out on

Seahorse Lake, a lake known to contain anomalous amounts of uranium in its

sediment and which actually overlies a portion of the Key Lake uranium deposit.

The remainder of the season was spent surveying Prince Lake, near Uranium City,

which lies on the projected trace of the St. Louis fault.

The field method employed was essentially the same as in 1975 .. Nylon guide

ropes strung across the lake 50 m apart and tagged every 20 m have proven to be an

efficient, accurate method of locating sample points with the added advantage that

drj_fting of the boat is kept to a minimum. Figures 1 and 2 illustrate the

sampling density and traverse lines for the two areas. Echo sounding and

scintillometer bottom profiles were run along each traverse and the recording tapes

marked at the 20 m tags. At the latter,water samples were collected for radon and

uranium analysis and bottom samples collected for uranium, LOI, and general multi­

element analysis.

Part I Geochemistry

by G.R. Parslow

Problems encountered in 1975 were: non-reproducibility of radon results,

'aging' of water samples in transit to the laboratory, the rather slow fluorometric

determination method for uranium, and the specific problem of massive fluorescence

quench effects caused by the lake sediment matrix. To a large extent these

problems have been eliminated following a winter research effort to streamline the

analytical techniques and by the introduction of certain modifications to the field

methods. Interpretation of the results has not been completed but the following

text outlines the advances made and the outsta11ding problems.

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Figure I: Seahorse Lake and Key Lake

0 2

Scale in miles

Figure 2 : Prince Lake

0 2

Sca le in miles

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Radon Determination

In 1975 water samples for radon analysis were collected 1 m above the lake

bottom using a standard tube style sampler. Samples were collected at that depth

following the suggestion of Dyck (pers. comm.) that temperature and ·turbulence

effects would be at a minimum. The results were however most disappointing. The

reason for this was considered to be that a sample collected at depths of 20 to 40 m

would contain dissolved gases in equilibrium with a confining pressure of 150 to

300 kPa (1 atm 100 kPa). However, because the water sampler is only water-tight,

significant degassing occurs as the sample was raised to the surface. Thus special

pressure vessels were constructed at the University of Regina and the degassing

unit of the radon analyser modified to accept samples in a pressurised state. In

this way it was hoped to avoid any radon loss between sample site and field

laboratory. Since automating the filling and sealing of these vessels at depth

requires a very sophisticated sampler, it was decided to use scuba divers to

operate the vessels manually. It was found that replicate precision was improved

and repeated sampling over a period of weeks at one site gave consistent results.

On the other hand, virtually no radon anomalies were found except a few values 3

to 4 times background in the immediate vicinity of drill holes close to the northern

end of Seahorse Lake. The holes had been drilled the previous winter to outline

the southwestern extent of the Key Lake ore body.

The tentative conclusion is that the lake sediment contains uranium which is

not in equilibrium and therefore radon is present in insignificant quantities. In

addition, it would seem that the radon diffusion rates from the equilibrated ore

beneath the lake are slow enough that decay losses preclude anomalies.

It is noted here that these results are quite different from those obtained

for waters from radioactive muskegs in the area. These muskeg waters give very

large radon anomalies. An examination of the muskegs indicated that gas bubbles,

generated by rotting vegetation, are rising continuously through the water and may

act as carriers diffusing radon at much faster rates than in normal lakes.

Further work will be carried out this winter and next summer on this problem.

After two years of work on radon in lake waters it appears that the radon

technique is not suitable for detecting uranium mineralisation covered by lake

waters.

Uranium determination

Over the winter of 1975-76 extensive research was carried out on the

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possibility of speeding up the basic fluorometric method and yet maintaining

acceptable levels of precis ion and accuracy . The method detailed in Parslow and

Dwairi (1976a, in press) and Parslow and Dwairi (1976b, in preparation) has a

precision of ±8% over the range 0.3 to 1,000+ ppm for a turn-around of 200 samples

per man day. The method can be used in the field and next year it will be possible

to obtain analyses for the survey party with at most a two-day lag. This rapid

method should prove useful for modifying surveying procedures while in the field

as anomalies become apparent . Accuracy has been checked by comparing the results

with neutron activation/delayed neutron counting analysis of selected samples . In

general the results agree to within ±10%, which is acceptable for exploration work.

The preliminary results for uranium in lake sediment exhibit close posi tive

correlation with sediment particle size, lake depth, loss on ignition, and most

other metals determined, particularly Fe and Mn. The limiting fac tor on precision

has proven to be the rather erratic adsorption of uranium by the lake sediment.

All the evidence indicates that the uranium in lake sedimen t is chemically (either

organically or inorganically) precipitated and not present as elastic particles.

This precipitation is not consistent over even small areas of the lake bottom and

therefore problems of sample homogeneity become important. Proof of this is found

when replicate samples from ostensibly the same sample site are analysed, a

variation in uranium of up to ±15% is found. If the samples are then combined and

homogenized in a mill the subsequent analyses agree to ±1%. Variations of this type

are found even within the same sample bag prior to homogenization. It is suggested

that in all lake sediment surveys, tests of sample inhomogeneity be carried out as

standard procedure.

The uranium values for the lake sediment in the two areas show a background of

2-3 ppm but range in Seahorse Lake to as high as 1800 ppm and in Prince Lake up to

100 ppm.

The sampling and analysis of uranium in lake sediment is rapid and consis tent

results are obtained. Obvious anomalies do appear in areas of uranium

mineralisation and therefore the method is considered to be an excellent

exploration tool.

One outstanding problem is the understanding of the relationships of lakes to

groundwater flow. Basically, the field work revealed that lake sediment ,:lose to

uranium mineralisation is not necessarily enriched in uranium. As an example, the

northern section of Key Lake can be cited . This area is very similar to the

northern portion of Seahorse Lake in its geographic relationship to the Key Lake

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ore body. A few traverses were run over Key Lake but, with the exception of one

or two very slightly enhanced values, no uranium anomalies were observed.

Obviously, uranium-bearing ground water flow into Key Lake must be limited. More

work on groundwater systems will be critical in evaluating the potential of

uraniferous regions such as the Athabasca Formation.

In order to obviate the 'aging' problem of water samples and the costs of bulk

shipping of the water to Regina,A resin extraction technique was developed (Parslow

and Dwairi; 1976 c, in preparation). In the past,ion-exchange resins have had

limited field application because of the rather cumbersome resin column systems

required . Experiments this field season with pre-packaged resin in convenient

containers have proven to be a very successful field approach to ion-exchange

extraction. Although the method was designed specifically for uranium extraction

it can be adapted easily to other elements. With this procedure detection limits

of 0.02 ppb uranium were obtained and the precision was ±0.02 ppb uranium over the

range 0.02 to 30.00 ppb.

Although uranium anomalies in water are small, the work to date suggests that

this method has high potential, particularly in the study of uranium migration in

surface and ground waters.

Correlation of scintillometer count and uranium in sediment values

Details of the scintillometers used and their operation are given under

radiometric techniques. Although interpretation of the results has yet to be

comp l eted, it is pertinent at this point to illustrate the excellent correlation

between the geophysical and geochemical results. Figure 3 illustrates a traverse

of Seahorse Lake (plotted as raw data only). Given that the scintillometer defines

a total count continuous profile, and that lake sediment results for uranium are

from spot sampling, the correlation is impressive . Some aberrant values are to be

expected since from day to day it proved impossible to guide the probe exactly over

the sediment sampl e sites. Even a deviation of one or two metres can be expected

to cause a decrease in correlation. Detailed interpretation of the data over the

next few months will allow the precise calibration of the scintillometer in terms

of uranium content of the lake sediment.

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DEPTH

20 % LOI

20 RESISTIVITY

10 10-3 V

900 ppm URANIUM

300

TOTAL COUNT 1000 cps

200

100 m

References

Beck, L.S., Parslow, G.R. and Howeve , J. (1975, L, press) Evaluation of the uranium potential of areas covered by lake waters using geophysical, geochemical and radiometric techniques. Paper no. TC/25-14, IAEA, Vienna.

Hoeve, J. (1975) The St. Louis Fault Project. In Summary of Investigations by the Saskatchewan Geological Survey, edited by Christopher, J.E. and Macdonald, R. p 120-12L.

Parslow, G.R. and Dwairi, I. (1976 a, in press) Precision and accuracy of the fluorometric determination of uranium in lake sediment . In Sask. Geol . Soc. Spec. Pub. No: 3. Edited by Dunn, C. E. (see also extended abstract, IUPAC Symposium, Johannesburg, 1976).

(1976 b, in preparation) A consistent me thod for correcting optical density effects in pellets used for the fluorometric determination of uranium.

(1976 c, in preparation) The extraction of uranium ions from water: a rapid and convenient method sampling using prepackaged ion-exchange resins.