Exploration of radioactive minerals and recent developments

T U R K ISH ATOMIC

ENERGY AUTHORITY

ÇEKMECE

NUCLEAR RESEARCH AND TRAINING CENTER

İ S T A N B U L - TURKEY

Technical

Report

No: 168-A

EXPLORATION OF RADIOACTIVE MINERALS

AND

RECENT DEVELOPMENTS

B. İPEKOĞLU, H. ER Dİ NE, R. ÜZMEN

March 1978

TURKISH ATOMIC ENERGY AUTHORITY

ÇEKMECE NUCLEAR RESEARCH AND TRAINING CENTER

Technical Report No: 168-A

EXPLORATION OF RADIOACTIVE MINERALS

AND

RECENT DEVELOPMENTS

B. İPEKOĞLU, H. ERDİNE, R. ÜZMEN

March 1978

EXPLORATION OF RADIOACTIVE MINERALS AND RECENT DEVELOPMENTS B.İPEKOĞLU', H.ERDİNE", R.UZMEN'".

INTRODUCTION:

Uranium is an unique energy source to meet the energy demand of the world in near future and in long term if used efficiently. Although the uranium reserves known at the moment may seem sufficient to meet the demand until the end of this century, and some difficulties can occur in the supply of it. The application of Advanced Reactor Technology in long term will enable the more rational use of uranium. For example, if light water Reactor is used, uranium demand in the year 2050 will be about 38 million tons, however in the case of advanced reactors the demand is estimated to be 8-9 million tons for that year.(1) But until the advanced reactors are developed to meet the demand, it is necessary to explore unknown and important uranium reserves. By considering long term technological development, thorium reserves should also be explored.

The energy crises of the last decade has affected the economies of the developing countries more than the advanced ones. As a result of this most of the countries whether they have any oil reserves or not have given special atten­ tion to uranium oreexploration studies since nuclear energy is seen as the most important solution of the world energy problem in the future. For this reason prospection studies and investments has reached to a record level.

The first criteria for prospection investments is to obtain definite re­ sults in short time. However, from developing countries point of view there are certain problems, that is prospection methods which will give good results in short time will require advanced technology, technical specialists and of course great deal of an investment. There are two ways open for these countries:

( ' ) Mining Engineer (M.Sc.) Nucl.Fuel Techn.Dept. Ç.N.R.T.C. ( '' ) Mining Engineer (M.Sc.) " " " " "

a) To give permission to foreign firms for prospection in their countries.

b) To maintain the prospection work with her own staff but with some assistance from foreign technology.

Turkey has already decided on the latter and so far she has been quite succesful.

In this paper, all the techniques available for radioactive mineral explo­ ration are reviewed and emphasis is made on the choice of an optimum method and also on the co-operation among the RCD countries.

METHODS AVAILABLE FOR RADIOACTIVE MINERAL EXPLORATION

All the research work which has been carried out until now show that none of the methods used in the mineral exploration perfect and certain by itself. However use of the combination of these methods in certain order will be succes­ ful .

The choice of methods and the order of their application will depend closely on the field conditions, climate, geological structure and on the type of the deposited However, the squence of the application techniques is as follows

1- Careful appraisal of geological maps and reports to determine regions or rock formations in which a favourable enviranment exists for uranium depo­ sits. This is of course dependent upon the type of uranium deposits sought.

2 Airborne scintillometer or yray spectrometer survey. -3- Evaluation of detailed geological and radiogenic mapping.

4- Detailed scintillometer grid surveys on the ground to pinpoint the targets to be surface trenched or drilled.

5- A drilling program in which the pattern is governed by the type of deposit.

All the methods available for these standard procedure and their recent developments are reviewed below.

A - CONVENTIONAL METHODS

1 - RADIOMETRIC METHODS :

aircraft, an automobile or on foot, prospection to pinpoint the targets and radioactive mineral deposits.

Radiometric methods based on the detection of radioactive mineral decay products form the first step in the process of uranium ore exploration. Satis­ factory results are obtained when it is applied in combination with other methods.

1.1) y -ray Spectrometry Methods

For the application of this method from air, instrument systems are mounted in either fixed-wing aircraft or helicopters depending on the topography. An airc­ raft flies to about 200-400 feet distances along the survey line and counts are recorded with an interval of 1-4 seconds. The spectra obtained is then evaluated to obtain the approximate amounts of the radioactive elements in the area and to find their distribution.

In this method potassium is measured directly but uranium is obtained from

214 208

Bi and thorium from T1 . The ratios of these three elements are also obtained. Results are shown in graphs, diagrams and figures.

The factors which are important for this method are: a) The height of an aircraft

b) The crystal volume of the detector used c) The speed of an aircraft

d) The topography

e) An atmospheric conditions. (3)

A preliminary knowledge of an very large sedimented area is obtained inex­ pensively, in short time by this method. (4) For example, an area of at least

2

20 k m can be traced in 1 hour. (2)

Advancedcountries such as, U.S.A., Canada have adopted this method for their long term programmes. In some other countries like Algeria, Argantine,Egypt, Finland, Greece with the application of the same method from air most of their areas have been surveyed succesfully. (5)

The determination of the concentration of K, U, Th in born hole by this method will be possible in near future. The trial of the method for low grade areas have already been succesful. If thorium and potassium is also present in the area with uranium, an increase in the k - count is observed. The main reason for this is due to presence of thorium while the contribution of potassium is negli­ gible .

Towards the end of 1975, the development of a calibration system has been completed to determine the amounts of three natural radioactive source, uranium, thorium and potassium. The method used in Czechoslovakia for geological mapping and prospection has been quite succesful.

In the mean time with recent researches carried out in U.S.A., low energy photo­ peaks which occur as a result of uranium and thorium decay are resolved by using germanium dedector. The studies on the subject are still going on.

1.2) The Gross Natural Gamma-ray Method

Instruments employed in the application of this method are geiger counters and scintillometers. The method can be applied with an aircraft, an automobile,on foot and in drilling holes.

This method is used to place the deposits which are about 15-20 m.below the surface of the ground. This method are being replaced by V — ray spectrometry for airborne application.

The application of this method for detailed survey of the surface is quite convenient and it has easy ^-radiation detection as well. Geiger counters and scintillometers used will make the surveys on foot easy since they are portable and not heavy. The survey therefore designates the definite radioactivity of the environment.

In areas with road nets suitable for transportation Radiometric carbone survey is applied. With the use of geiger counters and scintillometers placed in vehicles, measurements are recorded simultaneously from both sides of the road.(6)

This method is also applicable to drilling holes by using water-proof geiger counters and scintillometer probes ( Y - ray logging), commonly used all over the world for testing friable rocks that do not yield good cores and for coreless drilling of overburden. Log measurements are carried out immediatly after the drilling by considering the drilling hole contamination. Logging sys­ tem should be calibrated for each one of those three elements (U, Th, K,) in JJ.S.A. in drilling holes of 6 million feet in depth at 1967. (7)

The method which is in current use in many countries all over the world, such as U.S.A., Canada, South Africa, Finland, U.K. India, Yugoslavia, Australia,., etc.has been quite succesful and it is still improving with new developments.

1.3) Neutron logging Methods:

There are two available ways of application of the method:

a) By using a neutron source to interrogate the formation and detection of neutrons returning.

b) By direct uranium assaying in the bore hole based on the measurement 235

of fission neutrons induced in U (fission neutron logging).

Logging systems that measure uranium directly by detecting induced fis­ sion neutrons offer the most promise for the industry. Neutrons induced by the

235 source rapidly thermalized by the hydrogen in the formation and causes U to fission thus producing a neutron population which is proportional to the uranium

252

content. Generally Cf is utilized as a neutron source. '

In U.S.A., typical natural gamma-log and direct uranium log corresponds 214

to the uranium in formation while the gamma-log corresponds Bi which is not in equilebrium with uranium.

Direct uranium logging method is potentially valuable to uranium explora­ tion. The relative overall operational merits of each system must await extended field testing. Future improvements in all systems can be anticipated. (3)

1.4) Emanometry Methods:

Emanometry is a special category of nuclear geophysics based on the measu­ rement of the noble gas products of the radioelement decay series, specifically

222 238 220 232

the alpha-emitting Rn in the U chain, Rn from the Th chain, and

4

stable radiogenic He. Simple portable field instruments for measuring radon in soil gas have been used throughout the world since the early 1950's. Most of these depend on detecting alpha particles from the decay of radon using either a)small ionization chamber or b) a zinc sulphide and phototube detector.The track etch technique developed recently in U.S.A. uses a dielectric film that is sensitive to o^-radiation from decay of Radon. In a similar method which is introduced in Canada and U.S.A. in 1976 for measuring =*-radiation in the ground solid state

oc-detectors are being used. (3)

In India, Radon measurement technique which is considered as one of the most promising uranium exploration method available has given good results at the same time it has proved to be better than the natural y - ray logging.These

-research results proves the correlation between the radon amount and the uranium content of the soil. (8)

This method when combined with geochemical methods gives very good results. Radon measurements depend on the a) Porosity, b) Temperature, c) Pressure, d) Half-life of Rn. Apart from these the effect of meteorological factors on Radon measurements are quite important. Radon measurement technique has been applied succesfully in regions such as the shields of Canada or Scandinavia, red-sand stones of Scotland, aluvioner layers of Eastern Europe and Asia. (8)

The dominant helium in the atmosphere and geological environment is radige- 4

nic He having an average concentration in dry air of 5.2 ppm. The use of helium in prospection for uranium has been investigated since 1950's. Recent studies on the subject has been carried out in U.S.A. and the projects have been sponsored by ERDA financially. In this technique which is generally applicable in drilling

A 3 3 6 A holes uranium content is evaluated from the ratios of He /He and Ar /He .

Studies on radon measurement method which is adopted by many countries is still going on and new techniques are developed in order to reduce it's disadvan­ tages .

2- GEOCHEMICAL METHODS:

This method which has found more application in recent years is proved to be succesful in the radioactive mineral exploration.

The purpose of the studies on this method is to determine whether geoche­ mical and radiochemical data obtained from radioactive mineral springs can be used in the exploration of deeply hurried uranium deposits. Geochemical methods provide more research facilities compared to radiometric ones. These surveys are applied proceeding the radiometric surveys from air. (10)

In U.S.A. an elemental composition of the water samples from springs,wells and their precipitates have been examined and uranium and radium measurements are taken.

Some factors such as temperature of water and air, pressure, movement of water and its P... etc. must be recorded when samples are taken from springs, lakes and wells. An evaluation of water and sediment samples taken will play an important part in the uranium exploration. The method has been applied succes­ fully in wells, springs, lakes and soils with small uranium content. (11)Geochemi­ cal methods are currently used in U.S.A., Canada, Yugoslavia, Czechoslovakia.

B- UNCONVENTIONAL METHODS:

1- INDICATOR ELEMENTS

Indicator elements are those which exist with natural Uranium such as Cu, Pb, Mo, Se, Vanadium and As. These elements have not as yet been found to be of much use as indicators. Lead has been used in tracing the extension of a known ore body and Mo values have been correlated with Uranium-bearing structures in Scotland.

2- RADIOGENIC LEAD IN NONRADIOACTIVE MINERALS:

Tests carried out in the U.S.A. and U.S.S.R. have shown that nonradioactive

205

minerals such as galena and pyrite carry abnormal amounts of radiogenic lead Pb 207

and Pb when they occur in proximity to Uranium occurrences. (6) More analyses are required on a world-wide basis before this method can be established but it is one that shows considerable promise.

3- NON-NUCLEAR GEOPHYSICAL METHODS:

The non-nucler methods are indirect. Geological units which depend on uranium or related clay sulphates and structures can be discovered by this method. These methods are applicable on both surface and borehole measurements and include a)elect­ rical resistivity b) induced polarization c) magnetic susceptibilty d) electro­ magnetic and e) seismic surveys. As an example, magnetic susceptibilty provides information on alteration of the magnetic mineral suite, principally magnetite. Magnetic susceptibility can commonly be related to the alteration associated with uranium deposits in sandstone.

The U.S.A. geological survey investigation the application of non-nuclear methods in 1968 has shown that the correlation of uranium with magnetic minerals

(Fe, Mn, etc.) is an current prospection method in areas that might contain uranium. These non-nuclear techniques because of their high cost are not practical to exp­ lore relatively shallow and sand stone type deposits. However as exploration expands into deeper parts of basins and into new geological environments where drilling costs escalate, then conventional geophysics may well offer alternatives for subsurface investigations. (3)

C- NEW METHODS:

1- RADIOGENIC_HEAT MEASUREMENT METHOD

A new method which is based on the heat anomalities of the geological structure due? to its uranium content has been developed in recent years. (12) Considerable radiogenic heat is produced during the decay of uranium and its daughter products. A ton of uranium in equilebrium produces 730.000 Cal of heat per year so that heat flow to the surface over the uranium deposite should be considerably greater than normal. Two techniques are appropriate to use.

1) Use of thermal sensor to measure heat at the surface

2) Application of high-resolution thermal infra-red scanning from an aircraft.

In the latter approach an equipment capable of detecting thermal changes of + 0.25°C at altitudes of up to 3000 m.is employed. (6)

2- AIRBORNE GEOCHEMISTRY:

Two methods of approach are also possible in the case of airborne geoche­ mistry .

222

a) Measurement of Rn below an inversion layer using^an ionization chamber or other detector system in an aircraft.

210 210 b) Measurement of one or more decay products of radon namely Pb ,Bi and Po210

Solid decay products become attached to aeresols and could well be col­ lected on a network of fine nylon threads wound on box frames and towed behind an aircraft or helicopter. (6,13)

3- X-RAY FLUORESCENCE METHOD:

Geological researches, although they have an great importance in uranium prospection studies take rather a long time since geological mapping and also an analysis of samples in labs far from the field are required. In order to at­ tain results in comparatively short time, it will be practical to analyse the geochemical samples in the field. By considering all these points an X-ray met­ hod has been developed within the last 10 years.

The principle of the method is based on the characteristic rays of an element due to excitation of electrons of the sample by particles emitted from radioactive source of long-lived isotope, with detection of characteristic rays and their energies by different systems, the elements and their relative amounts will be found using a standard.

Portable XRF instruments that are developed for prospection studies are already in current use in U.S.A.

The employment of these (portable XRF)instruments to detect the elements necessary for uranium exploration such as Cu, Pb, Cn, Mo and Se by using a dif­ ferent radioactive sources in the field in relatively short time will be very practical in geological mapping.

-RESULT AND CONCLUSIONS

Increasing energy crisis in recent years has been affecting the economies of the developing countries deeply. The only significant solution to the energy problem of the world seems to be the use of nuclear energy in the future. There­ fore the weight of an importance given to uranium prospection studies by most countries of the world has increased in great deal. The speed of studies and investments has reached an extra ordinary level as well. The interest given to this subject by developing countries should be more than the other countries. Following conclusions can be drawn from the facts presented in this paper.

— Gamma ray spectrometry from air seems to be the fastest productive method for developing countries.

— Application of combined geochemical studies following the airborne gamma ray spectrometry will be the best way to find areas which contain radiac- tive minerals.

— New methods, such as, XRF and geobotanic which will prevent some disadvantages and will open new prospection possibilities should be applied without delay.

— When other mineral explorations rather than uranium are being done, examination of core samples for radioactive minerals will save time and money.

By carrying out this co-operation in the way described below, the studies done by each country in the field will accelerate.

1) The exchange of technical know-how and knowledge.

2) For the application and development of new techniques, mentioned above, preparation of joint projects between the RCD countries will sav#time and money.

3) Gamma ray airborne prospection along the borders of the RCD countries has to be considered as a joint project.

4) Application of XRF method for the fast analysis of geochemical samples and preparation of joint projects to fabricate portable XRF instruments are suggested.

ACKNOWLEDGEMENTS

REFERENCES :

(1) IAEA - Bulletin Vol. 9, No. 4, August 1977 pp. 52.

(2) LITTLE, H.W., SMITH, A.Y.

"Techniques currently used in uranium prospecting in Canada". (Nuclear Techniques and Mineral Resources - IAEA Vienna 1969)

(3) EUGENE W. Grutt, Jr. "Uranium Exploration Methods Development" Speech Pre­ sented To American Mining Congress September 28, 1976

(4) KING, J.W. "Türkiye’de uygulanmakta olan Modern Uranyum'arama yöntemleri" (T.M.M.O.B. Maden Müh.Odası - Türkiye Madencilik Bilimsel ve Teknik 5. Kongresi, Ankara 1977.)

(5) URANIUM, "Resources, Production and Demand," OECD Nuclear Energy Agency and IAEA December 1977.

(6) BOWIE, S.H.U. "Methods, Trends and Requirements in Uranium Exploration" (Uranium Exporation Methods, IAEA, Vienna, 1973)

(7) DODD, P.H., DROULLARD, R.F. and LATHAN, C.P. "Borehole Logging Methods for Exploration and Evaluation of Uranium Deposits." (Mining and Groundwater Geophysics/1967)

(8) BHATHAGER, A.S. "Radon Measurement in Soil in the Exploration for Uranium in India" (Nuclear Techniques for Mineral Exploration and Explotation, IAEA, Vienna 1971)

(9) MILLER, J.M. OSTLE, D. "Radon Measurement in Uranium Prospecting" (Uranium Exploration Methods, IAEA, Vienna, 1973)

(10) SIMIC.V, PANTIC. R, KONJEVIC. S, "Methodology of Uranium Exploration in Yugoslavia" (Uranium Exploration Methods, IAEA, Vienna, 1973)

(11) CADIGAN, R.A. and FELMLEE, J.K."Radioactive Springs Geochemical Explora­ tion, 8, 1977,(381-395)

(12) HARDISON, J .E."Geothermal Exploration" U.S.Patent 3,874,232 1 Apr.1975. Filed Date 15 Jan 1972. 6 p.

(13) DALL'AGLID, M. "Geochemical Exploration for Uranium" (Uranium Exploration Methods, IAEA, 1973)

(14) Nuclear Techniques in Geochemistry and Geophysics, Proceedings of a Panel, Vienna, 25-29 November 1976, IAEA STI/PUB/425