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DISCUSSION FORUM FOR RESEARCHERS IN NUCLEAR GEOLOGY- PROGRAMME ABSTRACTS AND NEWSLETTER PELINDABA REPUBLIC OF SOUTH AFRICA
1 -2 NOVEMBER 1984
by
H J Brynard (Editor)
NUCLEAR DEVELOPMENT CORPORATION OF SOUTH AFRICA (PTY) LTD x N U C O R m PRIVATE BAG X266 PRETORIA 0001 a, oo
JANUARY 1985
Jill iltiitl PER-88
NUCLEAR DEVELOPMENT CORPORATION OF SOUTH AFRICA (PTY) LTD
DISCUSSION FORUM FOR RESEARCHERS IN NUCLEAR GEOLOGY- PROGRAMME ABSTRACTS AND NESLETTER PELINDABA REPUBLIC OF SOUTH AFRICA
1 -2 NOVEMBER 1984
by
H J Brynard* (Editor)
'Geology Department POSTAL ADDRESS: Private Bag X256 PELINDABA PRETORIA January 1985 0001
ISBN 0-86960-768-5 DISCUSSION FORUM FOR RESEARCHERS IN NUCLEAR GEOLOGY MAIN AUDITORIUM, PELINDABA 21 - 22 NOVEMBER 1984
PROGRAMME
WEDNESDAY 21 NOVEMBER
P D Toens -Welcome and introductor- remarks
(NUCOR)
SESSION 1: URANIUM IN GRANITES CONVENOR: A E SCHOCH (OOFS)
P R Simpson Plenary address: Uraniferous high (British Geological heat production granites and their Survey) mineralising systems
L J Robb The distribution of uranium in (E G R U) Archaean basement granites from the provenance region of the Witwatersrand Basin
R J Hart Petrological and geochemical MAG Andreoli studies of the Vredefort Structure: (NUCOR) new clues to the evolution of the pre-Witwatersrand basement
MAG Andreoli Radioelement fertilisation in R J Hart granulites of the Mozambique and (NUCOR) Kibaran belts
N Niemand Uranium and thorium distribution in (NUCOR) the Verena and Makhutso gran, tes of the Bushveld Complex
D Twist Distribution of U and Th in the (U P) Rooiberg silicic lavas of the Loskop Dam Area, southeastern Bushveld - 2 -
A E Schoch - The radioelement host mineral (U 0 F S) spectrum of the Contreberg granite, Darling
A 0 Fuller - Radiometric surveys of the south (U C T) western Cape Province
A E Schoch - Summary remarks: Uranium in granites
SESSION 2: URANIUM IN SEDIMENTARY DEPOSITS CONVENOR: W E L MINTER (U C T)
E S Cheney Plenary address: Pyrite as a geo- (University of chemlcal trap for uranium and other Washington) ores
M J Duane The genesis, mineralogy and (B P I) geochemistry of uranium in the Gortdrum mine, Tipperary, Ireland
S G Buck* Pal aeocur rent and lithologic fades university of Redding, control of uranium and gold UK mineralisation in the Carbon Leader W E L Minter* placer, Carletonville Goldfields (U C T)
DEL Minter* Mineraloglcal changes In the (U C T) Wit waters rand placer uranium during C E Feather* Proterozoic weathering, Welkom C W Glatthaar* Goldfield (A A C) - 3 -
THURSDAY 22 NOVEMBER
SESSION 2: URANIUM IN SEDIMENTARY DEPOSITS (Continued) CONVENOR: W E L MINTER (U C T)
V R W Harvey - Sedimentological and uranium (U C T) mineralisation characteristics of Karoo sandstone bodies at Drlefontein in the Fraserburg District
G I Schneider* - Stratigraphic distribution of (G S 0) uranium within the Karoo Sequence
P E Wipplinger* - The occurrence of uranium in baked (G S 0) mudstone of the Karoo Sequence
WEI Minter - Summary remarks: Uranium in sedimentary deposits
TEA
SESSION 3: URANIUM MINERALOGY AND GEOCHEMISTRY CONVENOR - D K HALLBAUER (C M)
I fl Evans - Recent advances in fission track (B P I) dating techniques
SESSION 4: RADIOACTIVE WASTE DISPOSAL
B B Hambleton-Jones - A review of recent research relating and N J B Andersen to the NUCOR Radioactive Waste (NUCOR) Disposal Project
ANNUAL MEETING OF THE COMMITTEE FOR THE COORDINATION OF NUCLEAR GEOLOGY (Attendance by invitation only)
* This meeting is primarily aimed at providing a forum for NUCOR-sponsored researchers to table the results of their researches and to exchange views. Contributions of persons not sponsored by NUCOR are indicated thus (*). - * -
1.1 INTRODUCTORY IDIAIKS - P D TOEBS MANAGER: GEOLOGY DEPARTMENT
It is indeed a pleasure to velcoae you all here today to our third annual discussion forua for researchers in nuclear geology. In doing so I aust stress that this aeeting Is arranged primarily for the purpose of providing a forua for researchers in uranlua geology sponsored by NUCOR to report on their progress. It also provides an ideal opportunity for industry to be kept abreast of developaents in this field of endeavour and to aake suggestions regarding future research projects.
As is usual, we have a number of guest lecturers whose researches are not sponsored by NUCOR and I would like to thank then for their presence here today. Our prograaae Is further enhanced by the presence of Dr P II Slaps on of the British Geological Survey and Professor E S Cheney of the University of Washington, who have been invited to South Africa by NUCOR to assist the University of Pretoria In assessing the uranium potential of the Bushveld Coaplex and related rocks.
It should be stressed that NUCOR does not undertake exploration as such but sees Itself aainly in a co-ordinating role in the closest possible co-operation with the universities, the mining industry and the Geological Survey with the ultimate ala of providing possible targets for prospecting operations. In particular, close co-operation is maintained with the Geological Survey and care Is taken that there is no duplication of effort.
The programme has to be carried out within definite budget constraints and preference has to be given to projects judged most likely to accomplish the objectives In mind. - 5 -
While in no way wishing to stifle fundamental research, NUCOR-sponsored researchers must appreciate that we have a definite mandate and objectives in mind, and we dare not bleed off more than a small percentage of our research budget for fundamental work, so those wishing to pursue research in the earth sciences of a more fundamental nature would be well advised to seek funding elsewhere. In accordance with this policy the reconstltution of working groups in uranium will be discussed at the meeting of the Coordinating Committee when it meets after the technical sessions.
It is becoming increasingly desirable that a viable uranium province should be located outside the Witwatersrand Basin and for this reason the major thrust of NUCOR-sponsored research has in recent years tended to shift towards the granitic areas. It is therefore our intention over the next five years to examine in as much detail as our resources will allow, the uranium potential of the Bushveld Complex and related rocks and the Natal/Namaqua province as these seem to represent the best potential target areas. Some attention will, however, continue to be devoted to the Archaean granites as potential source rocks, the Witwatersrand and the Karoo as well as geochemlcal, minerological, geochronologlcal and sedimentological studies of a more general nature.
The question is often asked - Why prospect for uranium when it is In such oversupply and the market so depressed?
Firstly, it is In times such as these that one should cake stock of the situation and plan for the future. Secondly, most market surveys indicate that uranium demand will exceed currently projected production by the late 1980s and that by 1992 significant inventory reductions will be achieved, resulting in market improvements In real terms. This is borne out by official forecasts of U.S. uranium spot and contract prices as of January 1984 and illustrated in the figure. It would therefore seem that a turnaround is not far off.
South Africa currently produces about 16,5 % of the Western World's uranium and holds 14,0 % of its resources. If we are to maintain this prestigious position in the years to come, a sustained research effort is required. - 6 -
For additional information, the reader is referred to the publications listed in the bibliography.
BIBLIOGRAPHY
CAMISAK1-CALZ0LAFÏ, F.A.C.M.; DE KLERK, W.J.; VAN DER MËRWE, P.J.; Assessment of South African uranium resources! methods and results. July 1984. (In print. To te published by the Geological Society of South Africa.)
Nuclear Development Corporation of South Africa. Geology Department. Resource Evaluation Group. Uranium in South Africa: 1963 Assessment of resources and production. Pelindaba: Kl'COR, June 1984.
Surflclal uranium deposits: a handbook prepared by the IAEA Working Group 6 on Uranium Geology. Vienna: IAEA, 1984. 247 p.
Survey of United States uranium marketing activity 1983. Department of Energy. Energy Information Administration, August 1984.
TOENS, P.D.; DE KLERK, W.J. South African uranium resources and production potential: paper presented at Atomic Industrial Forum Uranium Seminar 30 September - 3 October 1984, Keystone, Colorado. Pretoria: NUCOR, September 1984.
United States uranium mining and milling industry, a comprehensive review: a report to the Congress by the President of the United States. U.S. Department of Energy, May 1984,
Uranium resources, production and demand: a joint report by the OECD. Nuclear Energy Agency and the International Atomic Energy Agency. Parist OECD, 1983. 348 p. - 7 -
ABSTRACTS OF FORUM PROCEEDINGS
2.1 URANIUM IN GRANITES Convenor : A E Schoch (U 0 F S) - 8 -
URANIFZROUS HIGH HEAT PRODUCTION GRANITES AND THEIR MINERALISING SYSTEMS
P R Simpson
British Geological Survey, London
The geochemistry and geological setting of metalliferous and mineralised uraniferous granites is discussed with particular reference to the Caledonides and Hercynides of Britain. The geochemistry of Sn-U granites, which is described using trace element plots r.ortraHsee.1 to primordial mantle, is related to modes of crustal evolution at destructive plate margins. Sn-U granites, which generally have high heat production, are generated in tens tonal regimes following orogenesis or in cratonic rift zones over dry mantle previously metasomatised by F (CI). Transfer of high heat production granites to the upper crust has been an essential part of cratonisation probably since at least the early Proterozoic. The evolution of metalliferous granites from Cu and Mo porphyries to Sn-U granites can be modelled in terms of decreasing hornblende separation and Increasing plagioclase and potassium feldspar separation and does not require the involvement of upper crustal melt components as proposed in the "S-type" (sedimentary protolith) model for Sn-U granites.
The association between the magma genesis of metalliferous granites and block movement on deep faults, which is particularly important for Ho ana Sn-U granites, is emphasised. The emplacement of granites in seismically active zones also provides a mechanism for initiating and maintaining the conditions of high heat flow and permeability necessary to sustain hydrothermal circulation systems to form economic mineral deposits.
The redistribution of elements from primary minerals Into secondary si.tte as a result of Interaction of rock with aqueous solutions is considered. Elements such as Sn and W require the Involvement of a hot ( > 500 °C) acid reducing aqueous phase to form mineral deposits.
The geological modeTo developed and the primary trace element signatures of metalliferous and mineralised granite?, are evaluated for the British - 9 -
Caledonides and Hercynides for which comprehensive geochemical and isotopic data are available. Models of granite genesis require modification for the Caledonides since, in contrast to Andean-type continental margin or oceanic island-arc systems, metalliferous granites were emplaced almost contemporaneously (410-390 Ma), postdating the main tectonothermal events by as much as 90 ma in the orthotectonic Caledonides. Nevertheless the main types of metalliferous granite suites ranging from Cu and Mo porphyries to Sn-U granites can be identified, the most widespread metal association Indicated by regional geohemical maps being U-Mo.
The Kercynian granites of southwest England which form the high points of a bathollth at least 200 km in length seems to maintain a rather uniform composition down to depths of 10 km. The geochemical signature of this batholith closely resesible3 that of the Metalliferous Caledonian Cairngorm batholith in the Grampian Highlands of Scotland. The crustal settings of these two batholiths are shown to have little in common, but the tectonic regimes in operation at the time of emplacement were broadly similar; in both provinces compressive stresses ended and a phase of limited extension associated with block movements coincided with the onset of granite magmatism.' The geochemical similarities of the batholiths are thought to reflect similarities in the processes of magma genesis and emplacement; the ultimate source of the granites being metasomatised mantle rather th. n crustal material. The contrast between the Cairngorm batholith, which lacks significant mineralisation, and the extensively mineralised southwest England batholith (Cu, Sn, W, U, Co, Ni) is attributed to differences in the crustal setting of the batholiths.
The models for U-Sn mineralisation developed for the British Isles are used to aid the understanding of selected examples of U and/or Sn ore deposits in Canada, China, South Africa and the USA. ^M: ZAssooajs
- 10 -
THE DISTRIBUTION OF URANIUM IN ARCHAEAN BASEMENT GRANITES FROM THE PROVENANCE REGION OF THE WITWATERSRAND BASIN
L J Robb
Economic Geology Research Unit, University of the Witwatersrand
Uranium in the Dominion and Witwatersrand Basin occurs in essentially two modes; firstly in detrital minerals (e.g. uraninite, zircon, etc.) which have been flushed more or less intact into the depository, and secondly in minerals which formed authigenically either at some temporary locality intermediate between source and depository, or within the basin itself (e.g. uraniferous leucoxene, brannerite, pitchblende, etc.) Consequently, consideration of the source of the uranium must account not only for the detrital constituents but also for a component of labile uranium derived from an unstable or easily leachatle host.
Semi-quantitative fission track micro-mapping provides the means whereby the detailed distribution of uranium in Archaean basement granites from probable provenance areas of the Witwatersrand and Dominion Basins can be assessed. Examination of granites from the Johannesburg-Pretoria and Schweizer-Reneke domes indicates that uranium Is hosted in a wide variety of forms, including minerals that are likely to have withstood the rigours of erosion and fluviatile transport and others which, upon weathering and decomposition, are likely to have liberated uranium. Also examined are a series of regoliths or palaeosols developed on basement granites and preserved beneath overlying Proterozolc successions. These rocks illustrate the distribution of uranium in response to near-surface chemical processes active long after the source rocks actually formed but before the material was eventually transported into the basin.
It is suggested that the uranium required to form the significant authlgenlc component in the Witwatersrand Basin need not have been derived In situ by the breakdown of detrital uraninite. Indeed, this is unlikely if one considers the extent and degree of preservation of these grains, a feature enhanced by the common presence of a protective coating of authigenically derived minerals around them. Many of the components (including uranium) of authigenic minerals in the Witwatersrand sediments may have been externally derived from mobile constituents in solution. Hto'- Z^GO^C
- 11 -
PETROLOGICAL AND GEOCHEMICAL STUDIES OF THE VREDEFORT STRUCTURE: NEW CLUES TO THE EVOLUTION OF THE PRE-WITWATERSRAND BASEMENT
P J Hart and M A Andreoli
Geology Department, Nuclear Development Corporation of South Africa (Pty) Ltd
This paper is focussed on an enigmatic ring-belt of charnockoid rocks from the core of the Vredefort structure. The charnockoid rocks correlate spatially with the transition zone between the Outer Granite Gneisses and the underlying Inlandsee Leocogranofels. The rocks of this belt are strongly anomalous and are characterised by a powerful (2 000 Ma old) magnetic field, by high light-REE/heavy-REE ratios, and \y a sudden decrease in dynamic metamorphisTi. Major pseudotachylite zones separate this belt froir outer granitoid gneisses. A comparison of the REE trends of the Outer Granite Gneisses with those of the Inlandsee Leucogranofels shows that these two segments of crust must have evolved separately and independently frcr each other and confirms the concept of a two-layered crust beneath the Witwatersrand Basin. Tty- iA*soofc3">
- 12 -
RADIOELEMENT FERTILISATION IN GRANULITES OF THE MOZAMBIQUE AND KIBARAN BELTS
M A Andreoli and R J Hart
Geology Department, Nuclear Development Corporation of South Africa (Pty) Ltd
Deep crust mafic and ultramafic granulites are exposed at the northern and southern frontal ramps of the 1 000 Ma old Lurio orogenfc belt in Central and Southern Malawi respectively. Petrological and geochemical data indicate the presence of abnormal enrichment processes which introduced volatiles, U and other LIL suite elements (defined as the KREEPUTH component) in more ancient granulites and eclogltes. In the Nsanje area of Southern Malawi the fertilisation event was probably contemporaneous with the extrusion or Rift-type volcanics in the overlying ca. 1 000 Ma old cover sequence of the Lurian cycle (equivalent of the Rio Molocue Group in adjacent Mozambique). Literature data indicate that comparable fertilised granulites characterised by mica-amphibole-scapolite-apatite-díopside (MASAD) assemblages have wide distribution in the Kibaran and Pan-African terranes of Southern Africa. The authors favour a proto-Rift model interlinking mantle metasomatic processes (Havkesworth, Erlank, Haggerty and others) lower crust fertilisation and high-level mineralisations (Rositter and Ferguson, Sawkins and others). - 13 -
DISTRIBUTION OF Th AND U IN THE VERENA AND MAKHUTSO GRANITES OF THE BUSHVELD COMPLEX
N Niemand
Geology Department, Nuclear Development Corpcration of South Africa (Pty) Ltd
Major and trace element analyses were performed on surface rock samples of the Verena (81 samples) and Makhutso granites (36 samples) in an effort to determine Th and U distribution in these rocks.
The Verena granite is typically a fine to medium grained porphyritlc granite with local coarse grained varieties, but in the south it grades into a medium grained equigranular variety. Although very similar in major element composition, differences in trace element contents between porphyritic and equigranular Verena granite can he demonstrated. Textual, mineralogical and chemical evidence suggests that porphyritic Verena granite was subjected to hydrothermal alteration in an open system, while some evidence of contamination by Fe-rich roof rocks exists. Equigranular Verena granite could have been the source of a part of the volatile phase which affected the porphyritic variety, and which could have led to mineralisation at the Albert silver mine.
The Makhutso granite seems to be more evolved than the Verena granite. Again, major element composition of the two rocks are similar, and differences can only be found in trace element contents. In general the incompatible elements are enriched in the Makhutso granite relative to Verena granite. Less evidence of alteration is obvious, although the occurrence of a mineralised greisen body in the Makhutso granite suggests hydrothermal/deuteric alteration.
In a hydrothermal model for mineralisation the formation of an ore body is not only dependent on the chemistry of the granite; the presence of a structural/geochemical trap would seem to be essential. Both Verena and Makhutso granites have high Th and U contents, but no U mineralisation i
- 14 -
has been reported from these rocks as to date. It would therefore seem that although Th and U have been mobilised to some extent, the absence of a suitable structural and/or geochemical trap has prevented mineralisation in these rocks. TRu'. ZASSoofc^
- 15 -
DISTRIBUTION OP U AND Th IN THE ROOIBERG SILICIC LAVAS OF THE LOSKOP DAM AREA, SOUTHEASTERN BUSHVELD
by
D Twist
Institute for Geological Research on the Bushveld Complex, University of Pretoria
Mapping of the Rooiberg Felsite in the Loskop Dam area has led to the recognition of nine major stratigraphic units of lava. Although the primary chemistry of these lavas has been severely modified by alteration, certain elements (e.g. Ti, P, Nb, Zr, Y) have not been redistributed by secondary processes and form a useful tool with which to study the behaviour of U and Th.
Thorium exhibits a systematic increase with stratigraphic height through the succession, is relatively enriched in the more evolved compositions, and generally defines linear mágmatic trends against the immobile elements on binary data plots. These observations suggest that Th was relatively immobile during the alteration process. On the other hand, U shows no systematic relationships with stratigraphic height, with Th contents, or with any of the immobile indices of magmatic differentiation. Th/U ratios show a gradual increase from about 3,5 at the base of the succession to almost 7 at the top. The lower ratios are believed to represent primary magmátic Th/U concentrations, but, taken together with the other evidence, the higher ratios point to substantial U loss from the upper parts of the succession.
Conservative estimates imply that at least several thousand tons of U have been leached from and not re-deposited in the Rooiberg lavas. It Is suggested that this V was transported into the overlying sedimentary sequence (Loskop Formation/Waterberg Group) but the trap rocks have not yet been identified. If suitable trapping conditions existed, the overlying sedimentary units would represent credible exploration targets for U. 2A?SoobOo
- 16 -
THE RADIOELEMENT HOST MINERAL SPECTRUM OF THE CONTREBERG GRANITE, DARLING
J C Theron and A E Schoch
Geology Department University of the Orange Free State, Bloemfonteln
The investigation of one of the two large plutons of young Cape granite near Darling (Schoch 1975) revealed complex distribution patterns of U, Th and Mo (Schoch and Scheepers 1982), as well as the presence of eplsyenite bodies resulting from successive K, Na, F and Ca metasomatism in limited areas (Scheepers 1982). The final results of the Investigation of the other large granite pluton (the Contreberg pluton) is presented in this report. It has previously been demonstrated in an Interim report that this granite differs much as regards petrographic properties, and that it has an unexpected relatively low content of radloelements (Schoch and Theron 1983), though still exhibiting a similar complex distribution pattern.
Detailed mapping revealed that the pluton consists of iwo granites with a gradational relationship and with a marked difference in radiometric properties, namely, the dominant small-phenocryst bearing Contreberg granite (CB) and minor bodies of the more leucocratic and fine even-grained Wolfkloof granite (WK). The average modes (volume %) Illustrate the differences, which are also reelected in the chemical compositions (mass %):
Qz. Ksp. Plag. Blot. Chi. Muse. S10
CB 37 42 7 8 2 3 71,69 WK 38 46 8 5 1 1 72,86
The country rocks into which the young granite Intruded are the coarsely - 17 - porphyritic Darling granite and its highly contaminated phase, the Darling hybrid granodiorite (HD), which has a lower radioelement content than any of the young granites. A comparative study of the three spatially associated rc*k types in the Contreberg region (CB, WK and HD) reveals that the uranium and thorium are present in primary trace minerals only.
The ininera logical trace mineral spectra of the rock types under discussion were established by means of quantitative separation of heavy minerals, autoradiographic investigation of thin sections and mineral concentrates, and electron microprofce analysis of selected grains. The main results are illustrated in the figures, and are suprisingly different from the results obtained for granites from the Klipberg region (Scheepers 1982) :
URANIUM CB WK HD
Uraninite 94 % Monazite 82 % Coffinite 58 % Xenotitne 5 % Xenotime 11 % Xenotime 35 % Monazite 1 % Zircon 7 % Monazite 7 %
THORIUM Monazite 92 % Monazite 100 % Monazitc 56 7 Xenotime 4 % Zircon 0 % Zircon 2 X Urantnite 3 % Xenotime 0 % Xen ot i me 2 % Zircon 1 % Coffinite 0 7,
The very low radioelement content of the abundant zircon and apatite, especially with respect to uranium, is remarkable. The quarry company, Cape Portland Cement, was kind enough to supply diamond drill core, and the absence of uraninlte from the WK spectrum may reflect the fact that only surface samples were used for this granite since the core samples in this case were too small to be representative. However, even if uraninlte should be present in WK below the zone of weathering, the relative ratios of the other primary minerals would not be affected, and would remain \.'.y dissimilar to those of CB and HD. The determined relative amounts of the trace minerals account within experimental error for all of the uranium present, as known from chemical analysis of - 18 -
representative whole rock samples and from gamria-s pec trome trie field data.
For two of the rock types (CB and HD) the determined relative amounts of the trace minerals account for only about half of the thorium present, as known from gan-ma-s pec trome trie determinations, and it may well be that small amounts of black thorium-ricb minerals such as thorite and thorianite went undetected. However, the dominant role played by monazite is firmly established.
No evidence was found of localised metasoratic processes which could have affected redistribtuion and concentration of the radioelements, with the exception of minor calcitisation, serici tisation and sanssuritisation. The anomaly pattern exhibited by the high resolution radiometric maps (1:1000) must be the result of subtle variations in the relative amounts of the trace minerals identified above. The essential differences between the radioelement distribution of the Contreterg pluton and the Klipterg pluton are now regarded as explained.
REFERENCES
Scboch, A.E. (1975): The Darling granite batholith. Ann. Univ. Stellenbosch, Al(l), 1 - 104.
Schoch, A.E. and Scheepers, P. (1982): Uranium and carbon dioxide in the Klipberg granite, Darling, Cape Province. Abstract, Symposium: Uranium distribution in geological materials, NUCOR, Pelindaba.
Scheepers, R. (1982): Die uraan-, thorium- en molibdeen-verspreiding in geselekteerde leukograniete van die Kaapgraniet-suite. I'npubl. M.Sc. thesis, Univ. Stellenbosch, 256 p.
Schoch, A.E. and Theron, J.C. (1983): Uranium and thorium distribution in young granites of the Cape Granite Suite near Darling. Abstract, Symposium for researchers in Nuclear Geology, NUCOR, Pelindaba, 12-14. QUANTITATIVE U308 AND TH02 DISTRIBUTION CONTREBERG GRANITE U303 TH02
100
90
80
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30
20
10
MONAZITE ZIRCON XENOTIME RADIOACTIVE TRACE MINERALS
Fraa aicraprtbt 4it* : U0F5 : Novtabar 1914 QUANTITATIVE U308 AND TH02 DISTRIBUTION WOLFKLOOF GRANITE
u3o8 TH02
% 100 7"H*ff^ 90
80 . % % *4 % % % % %' \ *« *« *« ** *« ** %' 70
60
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20
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0 MONAZITE ZIRCON XENOTIME URANINITE RADIOACTIVE TRACE MINERALS Frw •lenprabe 4iU : UOFS : Npvwttr ISM -21-
o
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- 22 -
RADIOMETRIC SURVEYS OF THE SOUTHWESTERN CAPE PROVINCE
A 0 Fuller
Geology Department University of Cape Town
Five projects were undertaken during the year.
J " í>r-tí>rr." •"•'-•jnt > Hornetcr survey «ras carried cut ti» define more prfc»s(-:.v arin?rsiies revealed during a preliminary survey run in 1SO3. The 1984 survey generated data which recorded average readings on individual traverses as veil as anomalously high readings. All data were plotted on ortbophoto naps. Coordinates were calculated to 0,0001 of a degree. The X,Y,Z set v&z submitted fcr computer contouring. Several anomalies were defined. One oi fit.-, • i.\ý, within the area covered by orthophoto map 3318 BC 24 Abbotsdaie, w.?s intensively examined. Scintillometer readings ranged from about 1C to 230 cps, the highest readings being associated with iateritic soils. Spectrometer readings were obtained for all major rock and soil fades in the area. The Instrument has not yet been calibrated. Preliminary Inspection of the data shows that both uranium and thorium are enriched in the laterite, with thorium more than uranium.
2 The project concerned with the application of radiometric data to geological mapping, started in 1983, was continued. An extensive data set was ohtained for all maior snV?virions of the Malmesbury Group. A particular objective <">* '•.; a.^ whether or not the Franschoek Formation resembled any of the other subdivisions of the Malmesbury Group. Statistical analysis «hows conclusively that ft does not. Each of the formations appears to have a distinctive radiometric signature, although some overlap does occur. An interesting result Is that the Malmesbury rocks in the Strand-Gordons Bay area, which are correlated wifh the Tygerberg Formation, are radiotnetrically indistinguishable from the Portervllle Formation, and - 23 -
hence their stratigraphic position and structural relationships may have to be re-examined.
3 A start was made with a study of the Piekenierskloof Formation in the Elandsbaai district. This unit is at the base of the Cape Supergroup and contains alluvial fan facies. Scintillometer readings in excess of 100 times background were obtained locally in association with ferruginous gossans. All major facies and mineralised zones were sampled with the spectrometer. Preliminary examination of the data reveals that only uranium shows marked enrichment.
A The late-Proterozoic, early-Phanerozoic (?) unconformity at the base of the Cape Supergroup in tne Vanrhynsdorp district was examined. The possibility exists that at least part of this unconformity represents a pr«?-Cape land surface unmodified by erosion preceding Cape Supergroup deposition. The area tested is of very rugged relief and much of the unconformity is concealed by the scree. Readings obtained show a consistent slight increase in radioactivity at or immediately below the unconformity.
5 Airborne radiometric survey maps available on open file at the Belvilie offices of the Geological Survey were studied aid an inventory of all anomalies prepared. There are many anomalies over the Cape Supergroup that should be followed up, but this has not been possible in the present programme. - 24 -
2.2 URANIUM IN SEDIMENTARY DEPOSITS Convenor : W E L MJnter (U C T) - 25 -
PYRITE AS A GEOCHEMICAL TRAP FOR URANIUM AND OTHER ORES
Dr E S Cheney
University of Washington (Visiting Professor, University of Pretoria)
Roll-type uranium deposits in sandstones in Wyoming, USA, have three zones: the roll-ore body, exterior barren ground (EBG) outside of the orebody, and interior barren ground (IBG) inside the orebody. The presence of pyrite, coalified wood, and calcite cement In EBG records reducing and alkaline conditions. The same assemblage plus uraninite (and other minor sulphides and selenides) occur in the roll; however, adjacent to IBG, rolls commonly contain a disequilibrium zone characterised by euhedral pyrite, hematite, and corroded pyrite. In IBG the absence of sulphides, coalified wood, and calcite, together with the argllllc alteration of feldspars indicate that conditions were oxidising and acidic. The Isotopic composition of pyrite and calcite in EBG are bacterial; however, much of the roll is isotopically lighter than that in EBG. These mineralogical and isotopic characters tics suggest that roll-orebodies formed inorganically where groundwaters characterisitic of IBG reacted with pyritic EBG. Sulphides and uraninite were precipitated along the solution front by the oxidation, pyrite does oxidise to sulphite, which disproportionates to sulphate and bisulphide ions. The latter does precipitate uraninite and sulphides.
Several other types of ore deposits seem to form by the same mechanism. Good examples are the roll-like copper-silver deposits at White Pine, Michigan, and Spar Lake, Montana, (which are similar in age and geological setting to the Zambian Copperbelt). The unconformity-type uranium deposits in and below the Middle Proterozoic Athabasca Group of Saskatchewan may have formed when groundwater flowed through the basal conglomerate and encountered sulphide-bearing shear zones in the basement rocks. Supergene enrichment of sulphide deposits and of tetravalent uranium deposits occurs by the same mechanism if climatic and mineralogical conditions are favourable. - 26 -
In short, pre-existing sulphides can be the geochemical trap for a variety of ore deposits, including uranium. As in the early history of exploration for petroleum, we now are trying to locate traps. The next step will be to determine whether the proper source rocks and aquifers existed to deliver metals to the geochemlcal traps. - 27 -
THE GENESIS, MINERALOGY AND GEOCHEMISTRY OF URANIUM IN THE GORTDRUM MINE, TIPPERARY, IRELAND
M J Duane
Old address: Department of Geology, Trinity College, Dublin, Ireland New address: Bernard Price Institute for Geophysical Research, university of the Witwatersrand
The Gortdrum Cu-Hg-Ag-Sb-U orebody occurs in Lower Carboniferous, Devonian and Silurian strata on the downthrown side of a major east-northeast transcurrent fault system in Southern County Tipperary, Republic of Ireland. The deposit comprises a linear discordant zone deposited epigenetlcally along fractures and chemical fronts resulting from tectonism and alteration of the host rocks.
Field and laboratory based geophysics in this study indicated anomalous radioactivity associated with the main copper orebody and in particular with the altered breccias within this zone.
The metal association Cu-Hg-Ag-Sb-U is considered unique for Irish Carboniferous carbonate-hosted copper deposits. However, the low temperature mineral assemblage of early uranium-bearing minerals with later sulphide stages is reminiscent of many vein-type hydrothermal ore deposits.
The geochemistry of uranium-enriched rocks indicates that the alteration of the basic dykes was a most significant event in the trapping of uranium within the limestones. Propylitisation of the early basic dykes by COj-bearing fluids produced the alteration which led to the development of hematite, leucoxene and clay minerals. The reducing environments attendant with such mineralogy created a favourable environment for uranium precipitation. The reduction of the U to - 28 -
U by oxidation of reduced iron in dolomitised brecciated limestone occurred prior to the main sulphide mineral sequences. The genesis of uranium in Gortdrum Mine Is considered to be radioelement remobillsatlon from uranium-bearing heavy minerals In sediments of Upper Devonian-Lower Carboniferous age. The uranium became available to low temperature hydrothermal fluids which carried and then deposited the uranium along a synmlneralisation transcurrent fault system. The source of the heavy minerals Is considered to be the Leinster Granite to the east, at which time the unroofing of the main pluton had commenced. TVJ • eA^oo444
- 29 -
PALEOCURRENT AND LITROLOGICAL FACIES CONTROL OF URANIUM AMD GOLD MINERALISATION IN THE WITWATERSRAND CARBON LEADER PLACER, CARLETONVILLE GOLDFIELD, SOUTH AFRICA
* + S G Buck and W E L Mlnter
* Redding University + Geology Department, University of Cape Town
The Carbon Leader placer in the Carletonville goldfield is a pebbly quartz-arenite that occupies numerous low sinuosity channelways which trend down a southerly paleoslope. The placer sediment is distinctively grey and siliceous in comparison with the hounding lithologles both above and below the orebody. The most common facies sequence established by Markov analysis consists of an irregular scoured base overlain by oligomictic lag conglomerates, which grade upward into quartz-arenitea, quartz-wackes, and finally into shales. The sequences are repeated several times in thicker placer accumulations and are interpreted as fluvial. The channels are up to 2 m deep, 500 m wide, and can be traced over distances of more than 2 km. They represent the erosional etches caused by a fluvial degradation that truncated the underlying sediments and produced an angular unconformity that has an erosional gradient of approximately 1:100. This represents an almost planar regional 2 paleosurface that covers 400 km .
The uniform distribution of the Carbon Leader placer across such an extensive surface indicates that it was deposited upon a very wide fluvial plain by either a large network v' streams or by a small network of streams that migrated widely. The incidence of large deep channels is distinctly concentrated at two positions, located 12 km apart on the eastern and western preserved parts of the paleosurface. These two positions are considered to represent major Influx positions and the drainage patterns outlined diverge radially from both of them.
The sites of uranium and gold concentration correlate well with each other and are associated with linear zones of thick placer accumulations in channelways, particularly where the cumulative thickness of conglomerate is greater. Mineral concentrations associated with thin - 30 - placer accumulations Indicate areas where higher stream-power prevailed. The mineralisation decreases westwards, across the goldfield, and is related to the nature of the host sediment, which contains less gravel and more immature sediment westwards. These sedimentary changes are related to differences in fluvial conditions that are thought to have been prevalent in the various channelways that traversed the palaeoslope. Besides being geographically separate, these channels may have been active at different times when conditions affecting mineral supply and concentration were not the same. The differences noted indicate that deeper, more active channels, probably occupied by perennial streams, deposited more, coarser, and better mineralised placer sediment down the eastern part of the detailed study area. In contrast to this, channelways down the western part of the detailed study area were probably occupied ly more ephemeral streams that deposited less gravel, more sand, and more immature, poorly mineralised, sediment. The same conclusion Is reached by analysing the uranium/gold ratio pattern across the detailed study area. In this Instance, ratios exceeding 12 demarcate the immature western part of this area. High ratios also define distal facies and these clearly indicate that the data in the southwestern part of the detailed study area are on the margin of a distal environment In which the uranium content will be higher than that encountered further upslope. Such positive correlation between sedimentary and mineralisation trends clearly Illustrates the detrital nature of the deposit. - 31 -
MINERALOGICAL CHANGES IN VITVATERSRAND PLACER URANIUM DURING PROTEROZOIC WEATHERING, WELKOM GOLDFIELD, SOUTH AFRICA
* + + W E L Minter, C E Feather and C W Glatthaar
* Geology Department, University of Cape Town + Anglo American Corporation
The Eldorado paleosurface marks the last major period of erosion in the Witwatersrand succession in the We Ikon go Id* it-Id. Fluvial and debris-flow pediments on this surface contain placer concentrates that were ultimately derived by the repeated erosion of suivronpiïig placer?, which occur within a sequence of onlapping formations, separated - 32 - SEDIMENTOLOGICAL AMD URANIUM MINERALISATION CHARACTERISTICS Or KAROO SANDSTONE BODIES AT DRIEFONTEIN IN THE FRASERBURG DISTRICT V R W Harvey Geology Department, University of Cape Town A sequence of five interbedded, laterally extensive sandstone and siltstone units in the Poortjie Sandstone of the Karoo Supergroup on the farm Driefontein 464 near Fraserburg are associated with peneconcordant uranium mineralisation. Although the lithology and fades arrangement of the sandstones are similar, only the 3rd and 5th sandstone bodies are mineralised. The sandstones are composed of arkoses and lithic arkoses and were derived from a mixed source composed of acid igneous and basic igneous rocks. They vary laterally in thickness, and stratigraphically they thin upwards. The sequence is sandwiched between thick siltstone units and the sandstones are thought to have been deposited in shallow braided channels during waning flow. From the presence of calcrete nodules In the sequence it is thought that the paleoclimate was probably semi-arid. The uranium mineralisation Is displayed by bleached sandstones with hematitle brown patches. The pods and lenses which contain uranium mineralisation are less than 1,5 m thick, 10 m long, and collectively form linear belts that vary in size from 150 m to 600 m in length and are less than 25 m wide. Most of the mineralisation occurs in low angle trough cross-bedded sandstone, near to the scour contact, at the base of the sandstone, and also in channel-lag deposits. Where channel-lag and low angle trough cross-bedded sandstone is adjacent, the mineralisation is often transgresslve between them but it is always associated with a high carbonaceous content. - 33 - Stratigraphically the mineralisation occurs in only two of the sandstone bodies and is located in the most sinuous channel sections. It was probably emplaced during or soon after the deposition of the sandstones, but before diagenesis. The mineralised sandstones also possess more channel-lag per unit outcrop than the unmlneralised sandstones. There appears to be a linear relationship between the amount of mineralisation and the sinuosity and the amount of channel-lag per unit outcrop. The distinction between mineralised and unmineralised sandstones in this study area is that the mineralised sand bodies appear to have been deposited by more sinous paleocurrents, contain more channel-lag per unit outcrop, and is directly associated with a greater abundance of kerogen. - 34 - ST1AT1GRAPHIC DISTtlBOTIOB OF URANIUM WITHIN THE KAROO SEQUENCE G I C Schneider Geological Survey, Pretoria During the Karoo airborne radiometric survey and research work carried out by the Geological Survey and various mining companies several uranium occurrences were detected within the sediments of the Karoo Sequence. An accumulation of these occurrences was found in the Beaufort West area in the southwestern Cape Province. The geological environment of Beaufort West is characterised by sandstone and mudstone of the Teekloof and Abrahaaskraal Formation of the Adelaide Subgroup of the Beaufort Group, Most of the uranium occurrences are located in the so-called Poortjie Sandstone - a member of the Teekloof Formation; although some could be found below the Teekloof/Abrahamskraal contact in the lower Abrahamskraal Formation. The aim of the current research work is to obtain Information about the exact stratigraphlc position of the uranium occurrences in relation to the Teekloof/Abrahamskraal contact. The investigated uranium anomalies in the Beaufort West area show a maximum of incidences at the base of the Poortjie Sandstone with an upwards decreasing tendency. The overlying Hoedemaker Shale contains orly little uranium, while the Oukloof Sandstone, which follows the Hoedemaker in the succession, exhibits another, smaller maximum. The uranium occurrences below the Teekloof/Abrahamskraal contact belong to the Hoordenaars Sandstone, which is the uppermost member of the Abrahamskraal Formation. The distribution of the investigated uranium occurrences in the stratlgraphic column Is believed to be closely related to the llthology of the rocks of the Beaufort Group, - 35 - THE OCCURRENCE OF URANIUM IN BAKED MUDSTONE OF THE KAROO SEQUENCE P E Wipplinger Geological Survey, Pretoria The ground follow-up of the Karoo airborne radiometric survey revealed uraniferous muds tone beside sandstone-hosted uranium occurrences, usually with dolerite intrusions in the vicinity. As a number of these occurrences have uranium values between 300 and 835 ppm eU.O., i.e. above the cut-off grade used by exploration companies for uraniferous sandstones, twenty anomalies were selected for a more detailed investigation. These anomalies outline two uranium provinces - the one centred on Hanover over Beaufort Group sediments and the other on Brandvlei over the Whitehill Shale Formation. Closer examination of mudstones within the sphere of influence of dolerite intrusions revealed no mobilisation and secondary concentration of uranium as the result of magmatic intrusion. Areas with higher uranium values were found to be small and associated with subsurface secondary uranium oxide minerals as a result of weathering. The economic potential of the anomalies visited appears to be small. 2.3 URANIUM MINERALOGY AND GEOCHEMISTRY Convenor : D K Hallbauer (C M) 2±K V-^n^ - 37 - RECENT ADVANCES IN FISSION TRACK DATING TECHNIQUES I B Evans Bernard Price Institute for Geophysical Research University of the Witwatersrand Recent advances in the understanding of the theoretical and practical aspects of the fission track dating technique have led to a proliferation of the potential users of the technique. These advances have been achieved through the application cf the external detector method. The application of this technique and the types of information that it can yield will be discussed. The limits of the technique will also re discussed. One of the important applications of the fission track method is that it car often he applied to dating of rocks that are difficult or impossible to date by other techniques; in particular the method has been applied to the dating of young volcanic rocks. The partial annealing of fission tracks in apatite takes place in the temperature range 80 - 125 °C. This temperature bracket coincides with the thermal window for maximum generation of liquid hydrocarbons from organic matter in sedimentary rocks. This fission track dating of apatite can yield important information regarding the thermal history of the host rock from which it is derived. In addition the dating of detrital zircon and sphene grains from the same sedimentary formations can yield important provenance data concerning the host sediments. The other important application of the fisssion track method is in uplift studies. The technique has been applied to study the uplift of orogenic belts and young continental margins. - 38 - 3 NEWSLETTER NUMBER TWO NOVEMBER 1984 3.1 SUMMARY OF NUCOR-SPCNSORED AND IN-HOUSE RESEARCH Co-ordination of nuclear geology research forms an important part of the activities of the Geology Department of NUCOR. Research agreements have been concluded with all the universities which previously received grants from NUCOR. The functioning of the subcommittees of the Committee for the Coordination of Nuclear Geology has been somewhat disappointing and to rectify this a number of working groups are in the process of being established to supplement the very important aspect of co-ordination of nuclear geology research. A working group in earth sciences, to co-ordinate the activities of the NUC0R-8ponsored researchers at the University of the Witwatersrand, and another working group to co-ordinate research on uranium in the Bushveld Complex and related rocks have been established recently. Two distinguished scientists in the field of uranium geology, Dr P R Simpson of the British Geological Survey and prof E S Cheney of the University of Washington, have been invited to South Africa by NUCOR and the University of Pretoria to undertake studies on the uranium potential of the Bushveld Complex. One member of the Geology Department of NUCOR Is currently studying fluid dynamics and practical aspects of flume experiments at the University of Chicago, Illinois, with a view to undertaking flume experiments at the National Research Institute for Oceanology at Stellenbosch next rear. Two researchers formerly on the staff of the Cbeiristry Department joined the ranks of the Geology Department and are conducting their research at the NPRU but spend between 10 to 20 X of their time at Pelindala. - 39 - 3.2 UranluB in Granites - A E Schoch (U 0 F S) Progress continued to be made during 1984 concerning our knowledge of uranium in South African granites. Most of the recent research results are of a preliminary nature because they reflect progress of projects with time-budgets exceeding one year. Investigations on radioelement distribution in granites continued at several universities: (i) University of the Witwatersrand (MAG Andreoli and R J Hart of NUCOR are finalising their study of Vredefort and the Natal belt granitoids, and are starting work in tbe Vaalputs-Steenkampskraal area; L J Pobb of E G R U is progressing with his study of the relationship between uranium in the Witwatersrand Supergroup and the older granites.) (ii) University of the Orange Free State (A E Schoch and J C Theron are finalising their study of the Contreberg granite, and are starting a complementary study of some Cape granites in the northwestern Cape Province.) (ill) University of Pretoria (F Fiemand and D Twist are respectively reporting considerable progress concerning granites and felsites of the Pushveld Complex.) (iv) University of Cape Town (A 0 Fuller and co-workers are still conducting regional radiometric investigations in the southwestern Cape Province.) (v) University of Stellenbosch (P Scheepers is continuing with his study of granites in the Darling-Paarl region.) - 40 - Progress has been steady, but much remains to be done before the knowledge of radloelement distribution in South African granites becomes comparable to that of our European and North American counterparts. The financial support for these projects should therefore be maintained or expanded. 3.3 Sponsored Research at Universities Sponsored research at universities continued apace and agreements were concluded with universities as outlined in the summary of progress below. 3.3.1 University of the Witwatersrand Researcher Prof H L All8opp Institute Bernard Price Institute for Geophysical Research Project Isotopic investigations relating to uranium mineralisation in the Wltwatersrand Supergroup and Karoo Sequence Progress Research on the Witwatersrand Supergroup received little attention during the past year as the emphasis was placed on the Karoo uranium occurrences, where two suites of samples have been investigated to date, the first from the Beaufort West area and the second from the Ficksburg area. Daughter- and Intermediate- daughter product loss rendered the Interpretation of the data difficult, with the Pb-Pb age far in excess of the age of sedimentation in the former area and far less In the latter. This inconsistency is ascribed to preferential loss of Pb-206. Mineralisation ages range from 162 to 212 Ma in the Ficksburg occurrences and from 146 to 815 Ma In the Beaufort West occurrences. More detailed work in the Beaufort West area is desirable and will be undertaken during 1985. - 41 - Researcher : Prof C R Anhaeusser Institute : University of the Witwatersrand Project : A reconnaissance radiometric study of the Archaean granitic verrane in the Eastern Transvaal south of the Barberton Greenstone Belt Progress : Due to other commitments by the researcher this project has been terminated Researcher : Dr L J Robb Project : Fissicn-track micro-mapping of uraniferous granites and Witwatersrand Conglomerates Progress : This is a new project and forms part of the programme on uranium mineralisation in granites. The present project will attempt to characterise the nature and distribution of uranium in the Archaean granitic floor and provenance area of the Vitwatersrand Basin and their relationships to the sedimentary depository itself. Major and trace element geochemistry of over 50 surface samples has been carried out and a number of discrete granitic phases identified. Detailed fission-track studies of uranium distribution in the rocks have shown that certain granites in the provenance area of the Witwatersrand Basin appear to represent more fertile sources of uranium than others. These granites are characterised by hydrothermal alteration and represent high-level intrusions. Paleosols ''eveloped over granites and currently covered by younger sediments represent sites of pre-concentration of uranium. 3.3.2 University of Cape Town Researcher : Prof 0 A Fuller Project : A ground radiometric survey of parts of the south western Cape Province - 42 - Progress : The project has been subdivided into five subprojects entailing the following: (i) Car-borne follow-up survey of radiometric anomalies detected during 1983 The work to date entailed a follow-up of radiometric anomalies detected over sediments of the Malmesbury Formation near Abbotsdale. The survey has shown a clear relationship to exist between radiometric anomalies and lateritic soils, with an enrichment of both uranium and thorium in the latter. (II) The application of radiometric data to geological mapping The major formations of the Malroeshiry Croup were spectrometrically surveyed and the Malmesbury Formation in the Strand and Bloubergstrand areas, which are correlated with the Tygerberg Formation, were found to be radlometrically different. The Strand Formation is radlometrically not significantly different from the Main Portervllle Clay Slate and the possible equivalence of these formations will require a revision of the geological map of the area. In addition, the enigmatic Franschoek Formation has been shown to resemble no other formation of the Malmesbury Croup radiometrically. (III) A study of available radiometric anomalies on published maps of the Geological Survey A register of radiometric anomalies in the southwestern Cape for further study has been compiled from data availatle at the Geological Survey Office in Pelville. (iv) A study of the Piekenier Formation In the Elandsbaai area Of the seven subareas In the Formation only two were found to show a significant content of radioactive minerals: the first in a fracture in the Elandsbaai area and the second In an lmpersistent - 43 - gossanous outcrop shoving uranium mineralisation associated with a fault zone on the farm Grootdrif southeast of Elandsbaai. (v) A study of the Cape Supergroup basal unconformity A study of this unconformity in the Vanrhynsdorp district revealed a slight increase in radioactivity below or at the unconformity between the Nardouw Formation and the underlying Kama Croup, the cause of which has yet to be established. 3.3.3 University of the Orange Free State Researcher : Prof í E Schoch Project : A comparative study of the uranium and thorium contents of selected granites in the western and northwestern Cape Province Progress : The U-CL levels of the currently studied Contreberg granite near Darling have been found to be very 1 /, namely 2 + 0,1 ppm on average, compared with the average content of 30 + 2,0 ppm of the previously studied Klipberg granite. The values for Th are lower, varying between 19 and 34 ppm, as compared with the average content of 54 + 3,8 ppm for the Klipberg granite. The comparative enrichment of the Klipberg granite is ascribed to the possible introduction of carbon dioxide-rich fluids along a fault zone traversing the southern part of the latter body, causing the mineralisation. Quantitative trace mineral separations are in progress and although the characteristic radioelenient trace mineral spectrum cannot yet be given for the Contreberg granite, it can already be stated that it is different from those determined for members "f the Hildebrand Complex and all other Cape granites which have been studied so far. - 44 The suspected role of carbon dioxide-rich fluids in the mobilisation of uranium has been confirmed by detailed petrographic work. The importance of hydrothermal alteration in the mobilisation of uranium to secondary environments where deposits may form is also borne out by the present study. 3.3.4 University of Pretoria Researcher Prof G von Gruenewaldt Project Investigations relating to uranium mineralisation in the granites of the Bushveld Complex Progress Prof E Cheney, vho is to resume this project after the resignation of the previous researcher, arrived in South Africa during September. Following an initial reconnaissance trip of the Bushveld Complex by Prof Cheney, work on this project is now progressing well. Researcher Prof G von Gruenewaldt Institute University of Pretoria Project A stratigraphic-geochemical investigation of the Rooiberg Felsite Progress Napping of an area around Loskop Dam has revealed a sequence which is divisible into eight stratlgraphic units of lava which exhibit complex geochemical variation, but a general upward enrichment in SiO- and K20 and the incompatible elements Nb, Zr and Y. Uranium and thorium analyses of the felsites show an anticipated upward enrichment in thorium content. However, uranium does not show the same trend and a substantial loss of uranium from the system to the overlying sediments is suggested. The finding of suitable trap rocks for this lost uranium could represent a viable exploration target. - 45 - 4 HUCOR IN-HOUSE RESEARCH 4.1 Research on Pre-Karoo Occurrences Subprojects reported here are investigations which have been initiated by Drs Hart and Andreoli at NEPU, Witwatersrand University, and their research in these fields is continuing. 4.1.1 Petrography and Geochemistry of Vredefort Granites An overturned section of the Archaean crust at Vredefort has been studied with respect to petrology and trace-element geochemistry. The results of these studies have provided overwhelming evide-c? for a two-layered earth crust. Two traverses were sampled across the structure and the available data are consistent with a tectonic transition between a high-level outer-granite gneiss and a deeper situated leuco-granofels, the position of contact between the two reck types sir.g marked by a pseudotachylite zone and a geochemical anomaly particularly with respect «... :h«° rare-earth elements and high uranium and thorium values. 4.1.2 Geochemistry of Wi twat'ersrand ores The discovery that primary gold in the Witwatersrand Supergroup contains significant fmouiitr? of Hg hold", thr po,:': iiry to better define the •.errce and conditions of formation ct Hold in thr Basin. A programme has ••••'••,." ' ' v> :•• 5! ,.~c.r*>* <•< ' • • j'oid i^riicles from pioducing r^eie \y neutron activation analysis, zwi to rodpl the results ?22Jnst known gold occurrences elsewhere in South Africa. Studies to date suggest that the Witwatersrand rests on an allochtonous basement affected by major tectonothermai events at 2 800 - 2 700 Ma. The new scenario for the Witwatersrana suggests that the uranium and the gold placer mineralisations were derived from the dismantling of early Proterozoic vein-type proto-ores and post-tectonic alaskites. - 46 - 4.1.3 Geochemistry and Petrology of the Vaalputs Granitic rocks in the Northwestern Cape Province This project, aimed at elucidating the petrogenesls of the Nora bees granitic rocks, has been initiated and chemical analyses of the rocks are currently being undertaken. Petrological investigations are also undertaken on behalf of the Bernard Price Institute to i'-ovide the necessary petrological data for geochronological interpretation. The first phase of this project, which Involves neutron-activation analysis of 33 samples of basement rocks from the Vaalputs area, has been completed. Recent studies indicate that typical mafic rocks of noritoid affinity are in principle capable of capturing radioeleirents more efficiently than granitic rocks, which may have Implications for radioactive waste disposal in the area. 4.1.4 Geochemistry of the Granite Basement West of Scott burgh, Natal The Umzinto-Scottburgh area is characterised by scattered uranium mineralisations within a general granitic terrain. Research to date has shown that the uranium has been introduced in its present position during a widespread U - REE element fluxing event at about 1 070 Ma. A multi- disciplinary approach has been employed to define the origin, pathways and final depositories of the uranium mineralising fluids. Available data suggest the probable occurrence in the area of an interesting belt of calc-sillcate and siliceous rocks affected by wlde8pead hydrothermal vein-type polymetalllc mineralisation. Uranium mineralisations in the region are possibly correlable to the abovementloned metallogenlc processes. Deposits of corresponding element associations are known elsewhere in the world. Two models are now envisaged for the uranium mineralisation in the aea west of Scottburgh: uranium related to pegmatites and to polymetalllc vein systems in shear zones. - 47 - 4.1.5 Uranium/Thorium Mineralisation in Southwestern Namaqualand The region extending from Plattakkies to Garies, Bitterfontein and Steenkampskraal contains a number of radioactive mineral occurrences poorly investigated to date. A combination of neutron activation and other geochemical and mineralogical techniques has been employed to date, with the ultimate aim of developing a satisfactory ore-genesis model. Petrographic descriptions have been completed on an initial set of 20 rock samples and indicate that the rocks have suffered at least two events of metamorphlsm, with the concurrent mobilisation of uranium particularly during the second event. Models developed to date envisage the development of uranium mineralisation to have occurred during hot spot activity which reintroduced volatiles and incompatible elements, producing anatexis near the base of the crust and causing the rising of melts to higher levels where swarms of pegmatites, alaskites and thorium/uranium bearing veins such as those occurring at Steenkampskraal were produced. 4.1.6 Mozambique Belt Uranium Mineralisation Current studies of kimberlite nodules in South Africa indicate significant K-Ba-REE-Ti-Zr metasomatism within the earth's mantle at about 1 000 Ma. Neutron activation and other techniques have to date been employed to investigate U/Th mineralised areas in Malawi and Mozambique to establish the possibility of addition of U and Th to the earth's crust during this event. This project, which forms part of the broad-based study of uranium mineralisation in the Namaqua-Natal-Mozambique belts, enjoys low priority at present. 4.2 Research on Karoo Occurrences 4.2.1 General Research on the main Karoo uranium occurrences has reached a stage of - 48 - consolidation where the existing knowledge Is being conpiled into a series of voluaes treating different aspects such as the sedlmentology, mineralogy and geochemistry of the occurrences. 4.2.2 Trace Element Distribution, with Emphasis on Uranium and Thorium, in the Wit bank Coal Field To date 300 coal samples from the Wit bank coal field have been analysed for U and Th. Contrary to popular belief, the results have Indicated that the distribution of U and Th is syngenetic and has largely been controlled by the distribution of the inorganic matter in coal. The proximal portions of the coal basins have been shown to be enriched in U relative to the central regions. The fundamental research on this project has been completed and several important conclusions drawn with regard to uranium and thorium distribution in the Wit bank coal basin, the most important being that the geochemistry of the coal can be used to Identify the depositlonal environment of the coal and the source rocks. The study also succeeded in answering the question as to what extent the geochemical composition varies vertically and laterally, and which trace-elements are organically bound In coal, which are related to sulphides and which to silicates. The continuation of this project Is aimed at meeting the objective of establishing the variation in concentration of uranium and thorium between different coal seams in South Africa and establishing the most likely target areas to find these. - 49 - 5 LIST OF DELEGATES N4ME ORGANISATION Prof H L Allsopp University of the Witvatersrand DrMAC Andre oil Nuclear Physics Pesearch Unit Prof C R Anhaeusser Economic Geology Research Unit F A Armstrong University of the Uitwatersrand Dr J K Bass on Nuclear Development Corporation Dr F A G M Catnisani-Calzolari Nuclear Development Corporation H J Brynard Nuclear Development Corporation Prof E S Cheney University of Pretoria D R Cloete Anglovaal Limited Dr B Corner University of the Witvatersrand Dr A S M de Jesus Nuclear Development Corporation W J de Klerk Nuclear Development Corporation Prof S A de Waal Potchefstroom University T W Downard Geneor Dr M Duane University of the Witvatersrand Dr I B Evans University of the Wltwatersrand J N Faurle Nuclear Development Corporation Dr C E Feather Anglo American Corporation Dr A Faanhof Nuclear Development Corporation Dr Frankenhauser Chamber of Mines Dr C Frick Geological Survey of SA Prof A 0 Fuller University of Cape Town Dr R Gatzweller Uran Bergbou Ctnbh. Dr D K Hallbauer Chamber of Mines Dr B B Harableton-Jones Nuclear Development Corporation Dr E C Hammterbeck Geological Survey of SA Nuclear Development Corporation Dr R J Hart University of Cape Town V R W Harvey Nuclear Development Corporation Dr A J Hayzen - 50 - R G Heard Nuclear Development Corporation R G Ingram Anglovaal Limited Dr U Kafri Israel R Klemm Rand Afrikaans University E Kostlln Gold Fields of SA M Levin Nuclear Development Corporation R G S M.icLennan Anglo American Corporation Dr J Harkgraaff Rand Afrikaans University Prof T S McCarthy University of the Witwatersrand Prof W E L Minter University of Cape Town Dr W M Stear Rand Mines N Niemand Nuclear Development Corporation E Raubenhelmer Nuclear Development Corporation Dr L J Robb Economic Geology Research Unit R Scheepers Stellenbosch University Prof A E Schoch University of the Orange Free State Prof J P F Sellschop Nuclear Physics Research Unit Dr M R Sharpe University of Pretoria Dr D J Simpson Retired Dr P R Simpson British Geology Survey Dr P D Smit Geological Survey of SA Dr P A Snowden Anglo American Corporation J M Strathern Anglo American Corporation V Stuart-Wllliams Johannesburg Consolidated Investment Co Ltd. J C Theron University of the Orange Free State Dr P D Toens Nuclear Development Corporation F Trumpelman Industrial Development Corporation Dr D Twist Institute for Geological Research on the Bushveld Complex P J van der Merwe Nuclear Development Corporation T A Venter Nuclear Development Corporation Dr M J Viljoen Johannesburg Consolidated Investment Co Ltd Prof G von Gruenewaldt University of Pretoria R Wadley Johannesburg Consolidated Investoent Co Ltd. - 51 - M B Watchorn Anglo American Corporation Dr J I W Watterson Nuclear Physics Research Unit E E W Weder Rand Mines Dr H J Welke BPI-Geophysics - Ifoiversity of the Witwatersrand Dr L Wolhuter Council for Scientific and Industrial Research