PKL 212

ATOMIC ENERGY BOARD

SOME FAVOURABILITY CRITERIA IN THE SEARCH FOR URANIUM IN THE MAJOR SEDIMENTARY FORMATIONS OF

by

J.W. von Back&trom

•a m PELINDABA g PRETORIA

REPUBLIC OP SOUTH AFRICA March, 1972 I'll 212

ATOMIC ENERGY BOARD

SOME FAVOURABILITY CRITERIA IN THE SEARCH FOR URANIUM IN THE MAJOR SEDIMENTARY FORMATIONS OF SOUTH AFRICA

by

J.W. von Backstrom*

* Director: Geology

PELDMDABA POSTAL ADDRESS: Private Bag X256, March 1972 Pretoria. SAMEVATT1NG ABSTRACT Die voorkoms van uraan en gunstige kenmerkevirdie opsporing van nuwe afsettings in die belangrikste geologiese afsettings word bespreek. The occurrence of uranium and f avourability criteria for locating new deposits in Die belangrikste uraanh'udende sedimentêre formasies van die Republiek word the major geological formations of South Africa are discussed. bespreek en daar word met die basale sedimentêre lid van die Dominiumrifeisteem begin. The major uranium-bearing sedimentary formations of the Republic are described^- Die ekonomiesbelangrikekonglomeraatriwwe.diealgetneneverspreidingvan die minerale starring with the basal sedimentary member of the Dominion Reef System. An account of met inbegrip van ryk stroke in hierdie riwwe, die geskiedenis van die sedimentasie, die the economically important conglomerate reefs, the general distribution of the minerals, verwantskap tussen goud en uraan, die mineralogie en die ertsgraad word bespreek. including pay-streaks within these reefs, the history of the sedimentation, the relationship Oor die baie groot afsettingsgebied van die Witwatersrandsisteem in en between gold and uranium, the mineralogy and the ore-grade are described. die Oranje-Vrystaat wat oorspronklik oor tienduisende vierkante kilometer moes gestrek / Over the very wide area of deposition of the System in the Transvaal \ net, is uraan in die sedimente van die Dominiumrif- en die Witwatersrandsisteem in / and Orange Free State Basin,(^hich originally must have covered some tens of thousands ' etlike duidelike siklusse ingebring, terwyl die mineralisasiepieke by sekere gunstige of square kilometresy uranium was introduced into the sediments of the Dominion Reef stratigrafiers horisonne plaasgevind het, gewoonlik deur die banketriwwe aangedui. 'n and Witwatersrand Systems in several distinct cycles, the peaks of mineralisation occur­ Kort samevatting van die geologie en mineralisasie van die Witwatersrandsisteem uit ring at certain favourable stratigraphical horizons, usually marked by the banket reefs. verskillende plekke in die kom, soos die werklike Witwatersrand, die gebied tussen A short summary of the geology and mineralisation of the Witwatersrand System from en , die Klerksdorpgsbied en die Oranje-Vrystaat, word verskaf. different localities within the basin, such as the Witwa.ersrand proper, the country be­ Daar word verslag gedoen ~,n 'n bespreking gelewer oor die uitwerking van diskordansies tween Randfontein and Potchefstroom, the Area and the Orange Free State, is en diskonformiteite, - die aard van die mineralogie met betrekking tot ryk stroke, die given. The effects of unconformities and disconformities, the nature of the mineralogy 8troomkanale, die vloer van die afsetting, die mineralogie en die moontlike bron van die with regard to pay-streaks, the stream channels, the floor of deposition, the mineralogy uraan. Boorgatresultate word met betrekking tot uraanhoudende siklusse ontleed, en die and the possibh source of the uranium are reported on and discussed. Borehole results gemiddelde uraaninhoud vir sekere sones en vir die Witwatersrandsisteem as 'n geheel are analysed with regard to uraniferous cycles, and the average content: of uranium for word verstrek. certain zones and for the Witwatersrand System as a whole are given. Die Republiek van Suid-Afrika het, binne die Witwatersrandsisteem, omvattende The Republic of South Africa has, within the Witwatersrand System, extensive low- laegraadse afsettings van uraniniet wat met goud, piriet en klein hoeveelhede ander grade deposits of uraninite-associated with gold, pyrites and small quantities of other metaalagtige sulfiede en koolwaterstowwe verband hou. Hoewel die gouderts baie min metallic sulphides^atid hydrocarbons. Altnough the uranium content of the gold ores is uraan bevat, kan die uraan as 'n neweproduk van goud herwin word en geen mynbou- en very low.jheuranium can be recovered as a by-product of gold and thus does not have to vergruisingskoste is dus daaraan verbonde nie. Suid-Afrika het tot dusver geheel en al op bear mining and crushing costs. South Africa's uranium output has so far depended almost die huidige goudmynbedrywighede vir sy uraanopbrings staatgemaak, en die geweldige entirely on current gold mining operations, and the enormous rise in working costs during styging in bedryfskoste gedurende die afgelope twintig jaar het die beherende faktor in the past 20 years has become the governing factor in mining economics. mynbou-ekonomie geword. The geology of the Transvaal and Systems, including the Ventersdorp Die geologie van die Transvaal- en Ventersdorpsisteem, met inbegrip van die Contact Reef, are described and the uraniferous nature of the conglomerates and of the Ventersdorpkontakrif, word beskryf en die uraanhoudende aard van die konglomerate en Black Reef Series are indicated. Borehole results are illustrated by means of radio­ van die Swartrifserie word aangedui. Boorgatresultate word deur middel van radio- metric logs and the results obtained are analysed. met riese boorgatopnames toegelig en die resultate wat verkry word, word ontleed. The heavy-mineral fossil-beach deposits of the Area, developed in the Die fossielstr and afsettings van swaar minerale in die Bothavillegebied wat in die Middle-Ecca Stage of the Karroo System, are described and the general lack of uranifer­ fetage Middel-Ecca van die Karroosisteem ontwikkel het, word beskryf en die «lgemene ous material in rocks of the Karroo System, in spite of a relatively high carbon content, gebrek aan uraanhoudende materiaal in rotse van die Karroosisteem, ten spyte van 'n is discussed. betreklike hoë koolstofinhoud, word bespreek, Mention is made of the Kalahari Formation and of results obtained by radiometric Hierbenewens word die Kalahariformasie, resultate wat van radiometriese boorgat­ borehole logging as well as beach and river sands which contain radioactive minerals in opnames verkry is, asook strand- en riviersand bevattende radioaktiewe minerale in certain areas. sekere gebiede genoem.

ISBN 0 86960 316 7 PI I 212 1. INTRODUCTION become one of the world's major resources of fissionable

The history of the discovery and development of South material, the uranium present being from 5 to 50 times more African uranium is a unique example of international co­ plentiful than gold. In the succeeding investigation it was operation in mineral studies. As long ago as 1923 it was re­ shown that these two metals are strangely consistent in their ported by R.A. Cooper, a South African mineralogist, that co-existence in the rocks of the Witwatersrand System as minute amounts of uraninite were present in black sand con­ reported by D.J. Simpson (1952). He states that:- CONTENTS Page centrates from the Witwatersrand System. This work sugges­ Page "From the assay of some half a million samples ted, however, that the content of uraninite in run-of-mine 5.2 Black Reef Series 22 covering the whole Witwatersrand System, it has been 1. INTRODUCTION •• 5 ore was little more than a trace, only 720 grams of con­ 5.2.1 Conglomerate •• ~ •• 22 established that a relation exists between the occur­ 2. THE DOMINION REEF SYSTEM •• •• 6 centrate containing 44.0& U,Og being recoveredfrom 300 000 5.2.2 Mineralised conglomerate pebbles - •• 22 rence of gold and uranium in these sediments In 2.1 General Description •• 6 5.2.3 Mineralised quartzite ~ 23 tons of ore - a uraninite yield of about 1/50 000 that of gold. •• 6 all cases the more persistent element is the uranium, 2.2 Klerksdorp Area (C.F. Davidson, 1953). 5.2.4 Results of radiometric survey - 23 and this is subjected to fluctuations in content which 2.2.1 Conglomerates •• 6 5.2.5 Economic aspects 23 In May, 1945 Professor George W. Bain of Amherst tend to take place sympathetically with variations in 2.2.2 Pay-streaks •• 7 5.3 Pretoria Series ~ 23 College, United States of America, found that various samples the gold content The close affinity between the two 2.2.3 Mineralisation •• 7 6. THE KARROO SYSTEM 23 of gold reef (specimens collected by him on the Witwaters­ elements therefore allows the detection of the uranium 2.3 Area •• 8 6.1 Heavy Mineral Beach Deposits 24 rand during 1941) showed a radioactivity far in excess of to act as a guide to the possible presence of gold". 2.4 Mineralogy » 8 7. OTHER OCCURRENCES 25 expectations. These specimens came from an extensive area 2.5 Ore Reserves • • 9 The relationship is clearly illustrated by Fig. 1, showing 7.1 Mozaan Formation 25 on the Far East Rand and had been collected to study the 3. THE WITWATERSRAND SYSTEM • 9 typical gold/uranium values of four different reefs from the .. 9 7.1.1 Geology 25 origin of the gold ores. The general indications of radio­ 3.1 General Description Klerksdorp area. In general, this relationship is a loose one, 7.1.2 Basal conglomerate zone 25 activity over the wide area represented by the specimens 3.2 Disconformities •• 12 but in places such as the reworked channel deposits, Kimber­ 7.1.3 Uranium mineralisation 26 suggested that the quantity of uranium present might be 3.3 Effects of Disconformities .. i2 ley Reef on the East Rand, the relationship is a very close 7.2 Godwan Formation 26 economically and strategically significant. The British 3.4 Structure » 13 one with a gold/uranium ratio of 1:20. Figure 1 indicates a 7.3 The Upper Witwatersrand Rocks Surrounding Government was advised of the occurrence and forwarded 3.5 Relation of Ore Deposits to Structures 14 well pronounced relationship in the Basal, Vaal and May the Vredefort Dome 26 the information to the Government of the Union of South 3.6 Nature of the Mineralisation 14 Reefs, as well as the Carbon Leader. 7.3.1 Geology 27 Africa as it was then known. As a result of these communi­ 3.7 Mineralogy 15 7.3.2 Uranium mineralisation •• •• - 27 cations Professor Bain and Dr. C.F. Davidson of the United 3.8 Source of the Uranium » • 16 Kingdom Geological Survey were invited to come to South 3.9 Ore Reserves 18 8. RECENT DEPOSITS 27 Africa to confer with the geologists wor Icing on uranium in 3.10 Production 19 8.1 General Description 27 that country. OH. Vft - Vbol 4. THE VENTERSDORP SYSTEM • 20 CL-Corbon 8.2 Kalahari Formation •• ~ 28 Preliminary investigations of specimens from the col­ 4.1 General Description • 20 8.3 Beach and R;er Sands 28 lections of the Geological Survey in the Transvaal Museum, 4.2 Conglomerates • 20 ACKNOWLEDGEMENTS 29 Pretoria, were made by means of Geiger-Muller counters, 4.3 Ventersdorp Contact Reef • 21 TABLE 18 wich indicated that many of the gold-bearing reefs were 5. THE TRANSVAAL SYSTEM •• • 21 LIST OF FIGURES appreciably radioactive. This was further confirmed by a 5.1 General Description •• « • 21 study of specimens in the museum of Anglo American Cor­ poration. Specimens rich in carbon from the Kimberley Reefs of the Daggafontein and East Daggafontein Mines on the Far East Rand showed remarkably high radioactivity. The sites of the original specimens had been mined out long since and specimens then taken (1945)of the Main Leader in the East Daggafontein Mine averaged 0,28 per cent over »• it I» I' ft t* t» it »• IT ii it it »• 4«g Au MP fit M» At MM» 4» mm mm» AAww tflt mhl writ 19 cm width of reef. Fig. I . fVtotton bftwtcn gold and uranium value> These early studies indicated not only that there were encouraging possibilities of recovering uranium as a by­ product of gold mining, but also that the gold ores could well PEL 212 - 6 IMI 212 - " material derived from the erosion of earlier conglomeratic Extensive geological exploration and research work deposition, and these local variations seem to indicate areas were not seen and cross-cutting quartz, calcite or oth.'r and arenaceous rocks. In this reef there is also a relatively have subsequently proved that low-grade concentrations of suitable for the concentration of uraninite. veins that might have acted as feeders, are conspicuousl> The sediments arc composed largely of the disinte­ high concentration of detrital monazite and cassiterite. The uraninite occur in auriferous conglomerate and occasional absent. gration products of the Basement Granite. The sediments reef, varying in thickness from 5 to 120 cm, consists of grit layers of pyritic quartzite in four contiguous Precambrian It would appear that conditions during and after de­ consist of medium to coarse-grained feldspathic and some­ with scattered pebbles and is remarkably consistent over the position of the sediments were such that they permitted the sedimentary formations in the Southern Transvaal and ad­ what micaceous sandstone or quartzite in which there are whole area. Where it is thin, the concentration of uraninite forma~ion of a thin Upper Reef or, in places, an almost pure joining pans of the Orange Free State. From the oldest to lenticular bodies of grit and conglomerate. Evidently the may be very high with sections of 2 to 5 cm thick assaying as black sand well-endowed with a full range of heavy alluvial the youngest they are the Dominion Reef System, the Wit- micaceous or sericitic material in the rocks was derived high as one per cent uranium. This Reef is the main carrier material such as uraninite, monazite, cassiterite, zircon and watersrand System, the Ventersdorp System and the Trans­ from the breakdown of the original detrital grains of feld­ of uranium. The layer of grit is virtually a consolidated garnet. This reef is completely different in appearance from vaal System. Both uranium and thorium are present in certain spar. A conglomerate along or close to the base of the black sand and, apart from the abovementioned minerals, the main conglomerate body and is amazingly consistent horizons of the Mozaan Formation in the Eastern Transvaal arenaceous sediments and another higher up in the suc­ carries minor amounts of detrital chromite, garnet, zircon, with an average width of about 13cm. and Northern Natal. cession, which have been worked or prospected for gold, are ilmenite and columbo-tantalite. It is completely different Although this reef always carries uraninite a very wide 2. THE DOMINION REEF SYSTEM known as the Dominion Reefs. The thickest bodies of conglo­ in appearance from the main conglomerate and is very per­ range of values is encountered. The concentrations occur in 2.1 General Description merate, some of them up to three or more metres thick, sistent. At the Dominion Reefs Mine it was never absent well-defined bodies of considerable width with very little over some 900 metres of underground development on strike. The Dominion Reef, Witwatersrand, Ventersdorp and occupy depressions in the old granite floor, whereas the internal low-grade ore. These so-called pay-streaks vary In most respects the Dominion Reef conglomerate Transvaal Systems are unconformable to one another, and conglomerates are absent on humps. Usually the lowest bed in width from 130 to + 300 metres and no high values have closely resembles the Witwatersrand banket and is likewise each of them is found to rest at places with a sedimentary of conglomerate is separated from the underlying granite by been encountered outside these shoots. Recognition of the composed of pebbles of vein-quartz set in a dark grey, highly contact directly upon rocks of the Basement Complex of a band of sheared granite, or by a variable thicbiess of abovementioned feature is naturally of extreme importance silliceous, fine-grained matrix. The pebbles show variations Archaean age. Where they occur together, the Witwatersrand transition beds comprising one or more of the following rock as far as mining operations are concerned. As far as could in their packing index. They are usually not closely packed System rests on different horizons of the sequence of the types: arkose, grit and quartz-sericite schist. Where there is be established these streaks ali follow a north-east to south­ and sometimes only isolated pebbles are present in the tine- Dominion Reef System. In turn, the Ventersdorp System was no basal conglomerate,, feldspathic sandstone often grades west trend and represent ancient shore lines or a channel grained matrix. The pebbles are often severely sheared and laid down on flat-lying or inclined Witwatersrand and Do­ imperceptibly into the granite below. In many prospecting system under deltaic conditions. fissured and are also replaced along their edges and along minion Reef Beds eroded to varying ntratigraphic depths. boreholes the contact between them could only be established The width and consistency of the streaks seem to in­ fissures by the surrounding matrix materials. In some areas In some localities the Ventersdorp System overlaps on to the radiometrically. dicate continuity down to considerable depths and indeed the pebbles are well-sorted, with the larger ones at or near the Basement Granite. The Black Reef Series forming the base 2.2 Klerksdorp Area auriferous shoot in the Lower Reef, which has supplied base and are orientated with the largest axis parallel to the of the Transvaal System rests with a profound unconformity Dominion Reef Mines with ore for eighteen years, was mined 2.2.1 Conglomerates direction of strike. Some are split in half along their central on all older formations. The Precambrian formations and to a vertical depth of 800 metres. As mentioned above, the axis parallel to the dip and are slightly displaced. the Basement Complex pass underneath an extensive cover In the Klerksdcrp area two payable conglomerate bands, average width of the mineralised Upper Reef is approximately of horizontal beds of the Karroo System, which straddles the also known as reefs, separated by barren conglomerate, or The iiiiT'-ix is spo/adically mineralised by pyrite and 13 cm and it has well-defined partings above and below it. Palaeozoic and Mesozoic Eras. also by a layer of quartzite, are present in the basal sedi­ veins of pyrite have also been observed in fissures in the This allows the application of mining methods which, to­ The Dominion Reef System comprise* a basal group of ments. They are known as the Upper Reef and Lower Reef. pebbles. In weathered conglomerate the matrix becomes gether with ore-sorting, should permit a low tonnage and a conglomeratic, arkosic and quartzitic rocks up to 100 metres The Lower Reef, which occurs at the base of the con­ stained by yellow-brown oxidation products of hydrated iron high grade mill feed. thick, followed by about 900 metres of lava of andesitic or glomerate zone, occupies depressions in the erosion surface oxide and le-icoxene. 2.2.3 Mineralisation acidic composition. The zone or group of quartzose sediments of the Basement Granite. It is lenticular, and was the main 2.2.2 Pay-streaks is of economic importance since its conglomerate beds are gold carrier in the mined area. It shows marked variation The general distribution of the economically valuable Pay-streaks similar to those found in alluvial deposits auriferous and are exploited lor uranium. The sediments are in texture where it rests on irregular portions of the pre- minerals of the Dominion Reef conglomerates is as follows: are a feature of these reefs, but unfortunately there is not overlain by amygdaloidal lava (resembling that of the Venters- Dominion erosion surface and more uniformity where the i) The main auriferous areas are in the Lower Keef and a general uniformity in grade and the distribution of the dorp System), rhyolite,granophyre (derived from and grading basement is fairly even. On the whole, the conglomerate these have supplied the bulk of the ore mined by the uranium minerals is neither characteristic nor a significant into rhyolitic tuffaceous rocks), schist, and Wonderstone thickens and pinches in a manner reflecting the surface on Dominion Reef Mine for more than 80 years. feature everywhere. There appears to be a connection, how­ (occurring as intercalated lenses in rhyolite). A large num­ which it 'was deposited. ever, between the distribution of detrital minerals like ii) Northwards the Upper Reef assumes importance and in ber of deep boreholes prove that intercalated sediments, The Upper Reef occurs some 18 metres or more higher monazite and cassiterite and that of uraninite in the pay- this area it was mined for its gold content with excep­ from 60 cm to 40 metres thick, occur in the first 60 metres up in the succession of conglomeratic, arkosic and quartzitic streaks. The pay-streaks appear to haw been formed by tionally high uranium values present. The Lower Reef of the overlying andesitic lava. Superimposed on this regional rock. The reef is a small pebble conglomerate passing stream action and not by the introduction of later?! miner­ variation are local variations which are apparently connected laterally into a thin layer of grit with scattered pebbles, k in this area deteriorates in grade and in some arearf alising solutions. Features such as the alteration of wall with fluctuations in topographical elevation in the floor of probably consists of reworked and concentrated detrital disappears completely, rocks or uranium mineralisation crossing the stratification, iii) In some localities the lower Keef is absent, while the PEL 212 - 8

Upper Reef has in places a high uranium content, varied between 107 and 127 cm. Uranium values averaged iv) In other places the conglomerates thicken to 6 metres about 0,5 kg per tonne with only a trace of gold. Detailed PEL 212 - 9 of the order of 12. and more with the Lower Reef not particularly evident. borehole logs were published by Von Backstrom (1962). Note, System have a combined thickness of about 4 500 metres in The assays indicate a relationship between uranium and The Upper Reef is very consistent and is characterised however, that the basal conglomerate is erroneously shown which finer-grained and argillaceous rocks preponderate; gold and it is estimated that ore treated for uranium will by a number of pay-streaks of which two major bodies on the text figure to be Ventersdorp, instead of Dominion beds of auriferous conglomerate do occur, particularly in have a gold content of 2 grams per tonne, which, by normal with an aggregate length of 450 metres on strike and a Reef in age. the middle of the Government Reef Series of this division, width of at least 130 metres have been located and de­ extraction either before or after uranium treatment, should but they have not proved to be of economic importance in 2.4 Mineralogy veloped underground, yield 1,4 gm of gold per tonne as a by-product. this area. The Upper Division has a greater proportion of v) In other areas the conglomerates thicken to about 15 The following description of the mineralogy applies 2.5 Ore Reserves quartzitic and conglomeratic rocks. Mining of the auriferous metres with a corresponding increase in width and de­ mainly to the Upper and Lower Reefs of the Dominion Reefs conglomerates or "reefs" as they are termed in both the Exploration by means of core drilling of the urani­ crease in unit grade of the Upper Reef. System from the area of the Dominion Reefs Mine, which lower Main-Bird Series, and the Upper Kimberley-Elsburg ferous conglomerates present in the basal sedimentary The uranium mineralisation contained in these two reefs have been studied intensively. Series has produced almost the whole of the Transvaal's rocks of the Dominion Reef System west of Klerksdorp, appears to be related solely to sedimentary structures and Uraninite is the most important radioactive mineral. gold output to date. continued unabated and upwards of 200 boreholes with a com­ there are no exposures which illustrate that enrichment had Appreciable amounts of monazite, thorite, columbite-tanta- bined depth of almost 15 000 metres have been completed by Emphasis should be placed upon the following features taken place at the contacts of intrusive bodies. lite, betafite, euxenite, radioactive leucoxene and radio­ the mining industry to date. On an average, boreholes vary disclosed by mining in this type area. active zircon are also present. Only a trace of coffinite was 2.3 Ottosdal Area in depth from less than 300 metres to more than 1000 metres. observed. i) The variability in the relationship of the "reefs" within Although fairly extensive deposits of uranium of good grade Around the village of Ottosdal, situated 60 km west of Uraninite reaches a high concentration in the Upper Reef the Main-Bird Group of conglomerates when traced from have been proved, associated gold values are very low and no Klerksdorp, extensive areas are underlain by a succession and it forms nearly ten per cent by weight of the heaw con­ the Central Rand both eastwards and westwards, developed mines are in existence. Thus their economic mine- of quartzite, shale, gold and uranium-bearing conglomerate, centrate. In some samples from the Lower Reef it is present ii) The local unconformities that are apparent, ability would be heavily dependent on a satisfactory price for tuff and lava cX the Dominion Reef System which, lithologic- in smaller amounts; in others it could not even be detected. a) between the base of the Main-Bird Series and the uranium based on long term contract a. ally, closely resemble similar rocks of the Klerksdorp area. The uraninite grains are usually concentrated in fairly thin underlying Jeppestown Series. Two areas, one to the north and the other to the south layers parallel to the bedding, and locally even form clusters. 3. THE WITWATERSRAND SYSTEM b) within the Main-Bird Group of conglomerates, of the town, have uraniferous conglomerate zones developed Other heavy minerals, notably monazite and leucoxene, are c) within the Bird Reef conglomerates in the West 3.1 General Description at or near the base of the succession, which have been pros­ preferably accumulated in the same layers as the uraninite. Rand Mines, and pected by trenching and drilling. The uraninite of the Dominion Reef has a fairly high con­ Over the very wide area underlain by rocks of the Wit- d) within the Kimberley Group of conglomerates in the North of the town eleven boreholes were drilled along tent of thorium and rare earths, and in this respect it re­ watersrand System, which must originally have covered some Far East Rand Mines. a strike length of some 8 km and intersected uraniferous sembles the crystalline varieties of uraninite found in peg­ tens of thousands of square kilometers, uranium was intro­ ill) The irregularity of gold values within a single reef, fonglomerate at depths between 75 and 343 metres below matites. duced into the sediments in several distinct cycles, the peaks particularly in the May Reef of the Kimberley Group. surface. Values ranged from less than 0,055 to about 0,341 kg Uranothorite grains are present in small amounts in of mineralisation occurring at certain favourable strati- Iv) The low uranium content of the members of the Main per tonne, over reef widths which varied from 15 to 500 cm. most of the samples investigated. Two types of thorite could graphic horizons usually marked by the banket reefs. At these Reef Croup on the Central Rand compared with that of Gold is present in trace amounts only. One borehole on be distinguished. The first, formed at the expense of urani­ favourable horizons, however, uranium deposition is only the Carbon Leader of the West Wits area, Goedgedacht 323 10, intersected a conglomerate layer 15 cm nite, was described in detail byOrtlepp(1962,p. 197). It has slightly affected by fades changes. In between the urani­ v) The differences of the uranium/gold ratios of the Main ferous cycles the sediments are relatively non-radioactive thick at a depth of 132 metres, which assayed 2 kg per tonne, a low reflectivity and contains inclusions of galena similar Reef Group on the one hand and those of certain of the and do not greatly differ radiometrically from the Karroo but this bard could not be traced farther to the south. to those in uraninite. In polished thin sections the thorite is Bird and Kimberley Reefs on the other. sediments, Ventersdorp lavas and Kimberley shales. For In two boreholes drilled on Lucaskraal 154 HO south of translucent. The second type of thorite is present in the Between Randfontein and Potchefstroom the Witwaters­ descriptive purposes the Witwatersrand System has been Ottosdal, a number of thin pebble-washes and the main form of fairly large reddish-brown grains which contain subdivided on a geographical basis into the following four rand Beds are almost covered entirely by a varying thick­ conglomerate layer were penetrated between 120 and 127 inclusions of galena and, in some grains, also pyrite. regions: ness of younger rocks. However, the exposures of lower metres. Values were disappointing. Gold was present in Monazite is one of the most abundant heavy minerals Witwatersrand Beds to the west of the West Rand Fault show trace amounts only and uranium values ranged between present in the Upper Reef and is preferentially associated 1. Within the area of the Central Rand, East Rand and this lower group to have a thickness there of over 6 000 0,19 kg and 0,1 kg per tonne. with uraninite. In the Lower Reef the concentration is much West Rand proper, stretching from the East Rand to Rand- metres, the Increase in thickness compared with that of the Between Ottosdal and Klerksdorp, 13 boreholes were lower. In thin section the monazite is to be seen as small fonteln with as Its approximate centre, the Central Rand being due mainly to a thickening of the beds drilled on 315 IP and two holes on Rietfontein grains, many of them well-rounded, of the order of 0,1mm Witwatersrand System, from the base of the Orange Grove that lie above the Hospital Hill Series. The succession of 284 IP. Two boreholes intersected a conglomerate band at in diameter and always traversed by cracks. All samples Quartzite to the top of the Elsburg Beds, Includes nearly the upper group is not complete, since either the beds of depths of 70 and 116 metres. The thickness of the band tested contained some monazite', the percentage in the ore is 7 500 metres of sediments consisting of fine and coarse­ the Ventersdorp System or the later beds of the Transvaal grained quartzite, grit, conglomerate, and argillaceous rocks. System overlap it unconformably. The Main-Bird Series is The three series of the Lower Division of the Witwatersrand present and, as at Randfontein, the number of both conglo- PEL 212 - 10 Pl-l 212 - H merate beds and of productive reef horizons in it are greater dorp townlands and in boreholes to the south of the townlands. the Hospital Hill Series to the west of the faulted zone and than on the central and eastern parts of the Witwatersrand. Above it occur 300 metres or so of dense quartzites followed borings have disclosed the presence of magnetic shale as­ Roberts and Kransdorff (1938) have recorded that, at Rand- by darker coarser quartzites and grit which lie below the sociated with dark shale and white quartzite that could well fontein, as many as 300 separate conglomerate layers are locally developed Bastard Reef. The latter marks the lower be ascribed to this series. present in the upper Witwatersrand Beds, of which 20 have limit of quartzites that carry several groups of conglomerates, Exploration by drilling was devoted mainly to locating been mined for gold (Toens, et al 1964). known as the Elsburg Stage, some of which are worked in the what is known in the field as the Basal Reef, a generally Western Reefs Mine. The whole group is of variable thick­ 2. The area known as the Far West Rand is divided into thin body of well-mineralised small-pebble conglomerate ness; in addition to local thinning and thickening of individual an eastern section and a western section by the Bank Fault carrying "carbon", gold, and radioactive materials. The members, the group underwent uneven erosion in pre- which has a downthrow to the west. In the western section the Basal Reef lies either conformably or disconformably on Ventersdorp times, so that the Ventersdorp lavas rest on an important Carbon Leader is present, some 60 metres or so quartzite, usually designated as "Footwall Quartzite", which irregular surface. At the base of the I«vathere is in places, below the Main F. f and just below the Green Bar marker. contain layers of conglomerate - "Intermediate Reefs" - a reef similar to the Ventersdorp Contact Reef. It is mined Attention should be drawn to the presence in the eastern with low gold values and occasionally marked radioactivity on Western Areas. Of great interest from the point of view section of the Ventersdorp Contact Reef, which is both auri­ as evidenced by radiometric logging. These normally occur of the minimum age of mineralisation is the fact that large ferous and uraniferous. This reef rests on eroded beds of some hundreds of metres below the Basal Reef. The Basal blocks and boulders of auriferous Witwatersrand banket the Upper Witwatersrand System, and is overlain hy lava of Reef is followed upwards by sediments of varying thickness occur in the volcanic breccias that are part of the Venters­ the Ventersdorp System. It is considered to represent sorted which includes the Khaki Shale and has as its top the Leader dorp System. (Nel, 1935). or unsorted detritus which were deposited in depressions on Reefs, which is generally more robust than the Basal Reef tut whose importance as a gold carrier varies considerably an erosional surface that predates the lava. 4. In the Orange Free State Goldiields, the rocks of the from point to point (Figure 2). 3. In the Klerksdorp area the lower Witwatersrand Witwatersrand System are wholly concealed under a cover System is divisible into the same series as on the Rand of varying thickness of younger rocks of Ventersdorp and Between the Leader Reef and the lava of the Venters­ proper; indeed, some of the "markers" of the latter are pre- Karroo age. Their succession and structure can be revealed dorp System there is a variable thickness of quartzitic rocks ssnt there, as well as in the succession around the Vrede- only by drilling or mining. Correlation of the various gold- with conglomerates in which occurs generally one valuable fon Dome. Near Klerksdorp, on Buffelsdoom and elsewhere, bearing zones with those of the Klerksdorp, Far West Rand, marker of shaly or argillaceous quartzitic beds known as the auriferous conglomerates in the Government Reef and in the and Central Rand areas has been attempted on lithological Upper Shale Marker. Above this marker the succession known Jeppestown Series have been mined for gold and uranium. grounds and, by Simpson (1952) on the basis of radiometric as the Gold Estates Reef zone contains numerous layers of These conglomerates do not all lie on the same horizon. They logging. Uranimity has not yet been attained, although there conglomerate, some of which are of importance as carriers vary in thickness and sometimes pinch out completely. Gold is a large measure of agreement. There is little doubt that of gold. The chief of these, in ascending order, are the B is not always confined to a pebble layer but, as in the case the Gold Estates Stage of the Klerksdorp area is the equival­ Reef, the Big Pebble Conglomerate, and the A Reef, the of the Buffelsdoorn Reef, may be present in streaks in ent of the Kimberley Reef of the Orange Free State and position of each of which -whenpresent- can be recognised coarse quartzite. elsewhere. There is also a good correlation between the Vaal in radiometric logs. Northwest of Odendaalsrus there is a In the Klerksdorp area, the lower part of the Upper Reef of the Klerksdorp area and the Basal Reef of the Orange local development of numerous conglomerates "Which give Division follows apparently without change of dip on the Free State. rise to anomalous radiometric logs - the so-called Rainbow Jeppestown Series and contains the Ada May and Commonage Toens and Griffiths (1964) in comparing sections Reefs of the Lorraine Mine. These lie within the considerable Reefs. To the east and south the important Vaal Reef under through the Main-Bird Series of the West Rand and Klerks­ thickness of quartzite and conglomeratic rocks which occur a cover of rocks belonging to the Ventersdorp System and dorp areas, consider the White Reef to be the equivalent of between the Gold Estates Group and the Ventersdorp lava, the Black Reef Series lies some distance up in the succession the "Basal Grit" which lies 0-30 metres below the Vaal so-called VS sediments of the Elsburg Stage (Winter 1964). above these two reef horizons. The dip is south-easterly, Reef, the Monarch Reef to be the equivalent of the Vaal Reef These sediments consist in places almost wholly of dark and the beds have been cut by a series of faults. Above this and the Upper Monarch Reefs are correlated with the Vaal multi-coloured conglomerate of which the constituents range from angular fragments to rounded pebbles or cobbles of succession of conglomerate and quartzite there is in places Reef and Leader Reefs. (See also Whiteside, 1970). various rock types. When this rock was encountered in the a later group of quartzite and conglomerate resting uncon- The Witwatersrand rocks of the area are considerably Initial stages of drilling the succession was regarded as the formably upon the earlier beds. This group contains at its faulted. Differentially elevated or depressed blocks constitute basal beds of the Ventersdorp System and therefore called base the Gold Estates Reef and is known as the Gold Estates a block mosaic. The preservation of the Upper Division of the VS sediments. Later drilling indicates that these sedi­ Stage. It is correlated with the Kimberley Stage of the Central the System appears to be due to the presence of a graben- ments probably represent a facies change in the Elsburg Rand and the Orange Free State (Wilson, et al 1964). It is of structure of a complex nature. Magnetometric and other Series. variable thickness as disclosed in outcrops on the Klerks­ geophysical surveys have suggested the presence of beds of PEL 212- 12 PI i 212 - n

An interesting feature shown by the radiometric logs Elsburg Series on the Far East Rand; carrying away in suspension of the finer clay constituents of 3.4 Structure the earlier material, the pebbles, black sand, and silica of a number of boreholes in the Orange Free State is the vi) that which locally occurs below the Basal Reef of the Cognisance must be taken of the tectonic changes that remaining to form the Hybrid Reefs. These carry a relatively partial independence of the nature of the sediments and the Orange Free State and the Vaal Reef of the Klerksdorp must have affected the Witwatersrand System prior to the large amount of carbon specks and carbon seams which, with radioactive material. Although mineralisation tends to be area. This is especially well-developed in the President deposition of the Ventersdorp System, at least in the K'erks- pyritic bands, are diagnostic of high gold values. Some of the concentrated in certain conglomerate layers, and particularly Brand and President Steyn areas; dorp area. Here, folding, tilting and possibly even fauIt ing of vii) those below the base of and within the Main Reef Group. Footwall Reef sediments occur as isolated bodies completely in those named in the preceding paragraph, there are, in the succession up to and including part of the Main-Bird Series surrounded by impervious argillaceous material, but these certain holes, well-developed conglomerates in the section Widespread, usually thin, layers of conglomerate were with subsequent partial erosion preceded the formation of the isolated bodies contain both gold and uraniferous hydrocar­ above the Gold Estates Reef Zone that show no radioactivity, deposited upon the flat erosion surfaces marking such in- Go'd Estates and Elsburg groups of sediments and reers. bons. while thinner layers in this zone and in the beds below it traformational disconformities. They consist largely of re­ The Ventersdorp rocks on the other hand were laid down The "value zones" in the Vaal Reef at Mine are characterised by the presence of uranium. worked and reconcentrated waste material derived from the over the whole area between Kandfontein and the Orange appear to have the character of the Footwall as their con­ 3.2 Disconformities underlying beds. There is a close relationship between the Free State Gold Fields on a surface of strong relief. No trolling influence. Where the footwall is formed of grit and distribution of uranium and gold values in the reefs above evidence has been adduced to show that the folding of the Another interesting feature that has been disclosed conglomerate the Vaal Reef takes on the appearance of the and that of the rocks below them. The distribution pattern of Lower Witwatersrand System in the Rietkuil syncline, in from the study of borehole cores, of radiometric logs, and footwall and is poor in gold. Where quartzite forms the foot­ uranium and gold values in an overlaying reef is clearly which the uraniferous reef of the Afrikander and Babrasco of underground development is the presence of several wall, gold distribution is erratic but always payable. determined by the varying depths to which the beds below it Mines occur, or the pre-Ventersdorp faulting of the area disconformities or breaks within the succession, and a In at least some of the mines in the Orange Free State were eroded. around Klerksdorp, took place before consolidation of the tendency for gold and uranium contents to be higher immedi­ the Basal Reef lies immediately above a stratigraphic break; There are, on the other hand, also important gold and sediments affected by these movements. Nel (1935) considers ately above such a break in sedimentation. and evidence is accumulating in favour of the view that gold uranium carriers that have not been shown to lie immediately that, in this area, "dislocation of the Witwatersrand Systen> The best known of these breaks within the Upper Wit- values in this reef are closely bound up with the presence above stratigraphic breaks. Reference in this connection may started in pre-Ventersdorp times" and conclucus that the watersrand beds, from the top downwards, are: of such a disconformity. Radiometric logs disclose also high be made to the lenticular reefs of the Government Reef and loci of some of the Ventersdorp explosions which produced uranium values in the reef immediately above discon­ i) that below the Ventersdorp Contact Reef or below the Jeppestown Series at the Afrikander and Babrcsco mines volcanic agglomerate and breccia were disposed along pre- formities. The disconformity is especially well seen in the Ventersdorp System as a whole. The Ventersdorp Con­ near Klerksdorp, to the Ada May and Commonage Reefs of Ventersdorp faults. Among the material forming these rocks, President Brand and President Steyn Mines, both of which tact Reef in both the Far West Rand and Klerksdorp Klerksdorp, to the Carbon Leader of the Blyvooruitzicht Nel has recorded the presence of large blocks of auriferous are uranium producers. areas is auriferous only when it consists of material and neighbouring mines, and to the Monarch and White Reefs conglomerate derived from Witwatersrand rocks; while he These examples are cited as instances of close con­ shed in the vicinity of auriferous beds that were out­ of the West Rand, the last two not being important gold has also reported the p/esence of "large boulders of Wit­ nection between mineral concentrations and sedimentary cropping in the pre-Ventersdorp landscape; carriers. watersrand conglomerates", which are auriferous, in con­ breaks. On the other hand, there are important carriers ii) that at the base of what has been called the VS 5 con­ glomerates within the Ventersdorp succession. Gold, at 3.3 Effects of Disconformities within the system that have not been shown to lie immediately glomerate in the Orange Free State area. This con­ least, must have been present in those conglomerates of the above strarigrr.phic disconformities and examples are the glomerate normally lies above the Gold Estates Group A study of the geological relationships of the May Reef Witwatersrand System from which these blocks were derived lenticular uraniferous reefs of the Government Reef Series and may be found resting on beds lower in the succession of the Kimberley-Elsburg Series in the eastern East Rand, before they became incorporated in the volcanic breccias near Klerksdorp, the Ada May and Commonage Reefs of the because of erosion of some or all of the members of demonstrates its disconform ability to the beds on which it and sedimentary conglomerates. that group before its deposition; lies, and the fact that it is formed of a concentrate of the Klerksdorp area, the Carbon Leader of the far West Rand, Similarly, in the Far East Rand, the Jeppestown Series iii) that at the base of the Big Pebble Conglomerate immedi­ detritus produced on erosion of earlier-formed beds of the and the Monarch and White Reefs of the Bird Reef Group of were f lexured and partially eroded before the deposition of ately below the Basal conglomerate and the Gold Estates series. The gold among its mineral content has been directly the West Rand, mentioned earlier. Group in the Klerksdorp area. This conglomerate trans­ derived from these earlier beds which were mildly folded An example of an apparent correlation between uranium the Upper Witwatersrand System. Erosional debris from the gresses downwards as far as the Jeppestown amygdaloid and eroded before the deposition of the May Reef. content and sedimentation has been pointed out by Or. B.B. lower beds was incorporated in the upper beds. Prospecting on the Klerksdorp Commonage - and there is probably J.A. Papenfus (1956) has dealt in detail with the mode Brock. He states: "The 'middle reefs' at Western Holdings boreholes near Leslie indicate that this intraformational evidence in that area of minor faulting in pre-Gold of occurrence of a number of channel infillings containing and elsewhere between Leader and Basal Reefs and commonly unconformity transgresses east-south-east across the Jep­

Estates times; the Footwall Reefs which are found below the Main Reef quite high in U3Og. As these are small lenticles undisturbed pestown Series onto the Government Reef Series and per­ iv) that at the base of theB Reef in the Orange Free State. Leader and are incised into the Jeppestown shales in Govern­ by faultt-.g and bearing no relation to observed structure, haps even the Hobpital Hill Series. This reef normally lies above the Upper Shale Marker ment areas and New State areas. According to him, the one concludes that they are purely sedimentational irregu­ Apart from the large-scale faulting which has affected but transgresses downwards on the E.L.1 quartzite at deposits within these channels are variable and carry con­ larities. This brings to mind the carbon-uranium rich auri­ the Witwatersrand System in all the areas that are being St. Helena where it was identified by Frost and Mclntyre glomerate, puddingstone, quartzite and grit, as well as ferous lenticular masses of the upper part of the Government mined, development 'ias disclosed much minor faulting and as the Leader Reef; banded pyritic quartzite. Hybrid Reefs were formed as the Reef Series at the Babrasco and Afrikander Mines of the the presence of intrusions of dyke rocks. These faults have v) that immediately below the May Reef of the Kimberley- result of erosion of earlier material in the channels and the Klerksdorp Area". caused vertical displacements of reefs and a certain amount PI I 212 - 15 PEL 212 - 14 Summarising, the uranium which is intimately related to separated by barren medium-grained and gritty quartzite thucholite in the Basal Reef. of attention has been paid to their effect on the gold and gold occurs in bedded conglomerate and quartzite near the containing occasional conglomerate lenses. The values in Features such as these seem to show clearly that uranium contents of a reef on both sides of a fault. In the margin of a continental structural basin which is situated these conglomerate bands are low, although the top band, uranium and gold were present in the matrix of the conglo­ developed areas faults and/or dykes have no effect whatever in most cases, contains relative?, greater concentrations of merate reefs at a very early stage. Collectively, the criteria on the location or amounts of either the gold or the uranium well within the boundaries of what is regarded as a uranium gold and uraninite than the bottom band. lend little support to the idea of these elements having been values in the Carbon Leader or the Basal Reef. A study of province. The presumption is that the uranium and the gold Uraninite and gold are often concentrated along or near introduced by hydrothermal solutions emanating from some values near faults and dykes in development headings of the were precipitated together as an integral part of the sedi­ the base of the conglomerate reefs, especially in reefs like unknown magmatic source in post-Witwatersrand times. The Vaal Reef at Stilfontein does not indicate any appreciable mentary series, but after the conglomerate was laid down the Leader and B Reefs, which have well-developed foot­ uraninite and gold could have been originally deposited as change in gold or uranium content. Similarly, a cursory having been transported by water no very great distance wall beds from which they are separated by a distinct parting detrital particles simultaneously with the pebbles and other study of the Free State mines reveals no obvious relationship from an original source, still unknown, to the north and that usually marks a break in sedimentation. Concentrations heavy detrital materials of the gravel sheets. Alternatively, between the distribution of uranium and taulting. west. also occur higher up in the middle and upper parts of a con­ uranium and possibly some of the gold may have been chemi­ These statements show that, even though reefs are 3.6 Nature of the Mineralisation glomerate reef. At some places in the southern area, for cally precipitated by carbonaceous matter derived from algae faulted, the presence of such faults does not affect the general Both uraninite and gold can in general be said to be example, the highest values are in the upper parts of the A or by some other precipitating agent in these gravels from distribution of uranium values, leading to the conclusion that more or less uniformly and regularly distributed in the and Basal Reefs. the water in which the sediments were being laid down. They the uranium mineral was present within the ore body prior conglomerate reefs when the whole extent of the gold-field Stream channels filled with eroded detritus occur in could also have been precipitated from ground water con­ to faulting. Moreover, the fauks appear to be later than the is considered. However, when comparison is drawn with some localities in the surface of erosion below certain reefs. tained in the gravels long before they became fully con­ consolidation of the beds affected. the much greater variation in the distribution of values A number of post-Basal and pre-Leader erosion channels, solidated and cemented into compact, impermeable conglo­ 3.5 Relation of Ore Deposits to Structures shown by nearly all lodedeposits, there are variations, often for instance, have been encountered in the Virginia and merate reefs by secondary silicificationandbymetasomatic marked, in uranium content within the limits of the ground The distribution of uraninite and gold in the conglo­ Harmony mines. In both mines quartzite and lenses of con­ changes integral with the regional metamorphism of the Wit­ of a single mine, and from mine to mine. The richer urani­ merate is intimately related to certain lithological and glomerate, some of them less than 0,3 cubic metre in vol­ watersrand System. Both these processes could possibly nite and gold concentrations tend to collect in pay-streaks, structural features of sedimentary origin as exhibited by ume, appear to have been originally sand and pebble detritus, have contributed to the existing distribution of these two usually characterised by a closer packing of well-rounded such ore bodies in the Witwatersrand, Dominion Reef, derived from eroded portions of the Basal Reef and adjacent elements in the Witwatersrand System. and sorted pebbles composed mainly of quartz and by a sandstone, that was deposited in hollows or channels. These Ventersdorp and Transvaal Systems. 3.7 Mineralogy greater concentration of other heavy mineral particles in­ Mineralisation is confined to the ore-bearing conglo­ conglomerate lenses, referred to as hanging wall or Upper cluding those which are of detrital origin. Except for local The major uranium-bearing mineral present is crystal­ merate and seldom ever crosses the stratification into the Basal Reefs, are completely surrounded by quartzite and deviations, the pay-streaks generally run roughly parallel line uraninite. In addition, there is sometimes present a less arenaceous wall-rock, except where it has obviously been contain up to 500 gram of gold per tonne and relatively high to the original shoreline. Enrichment in gold and iraninite crystalline pitchblende-likematerial. Uraninite occurs: derived from the conglomerate ore-body itself. There is a uranium values. is usually more pronounced where the conglomerate reefs close relationship between the distribution of values and Mining operations at the Virginia mine exposed, in a i) as free grains in the matrix of a conglomerate some­ rest on planes of intraformationaldisconformities and,from purely sedimentary features. Richer concentrations are raise, an erosion channel in the intraformational plane of times embedded in the soft sericitic part of the matrix, the information available, this would seem to be particularly commonest near the base of the conglomerate along well- disconformity at the base of the Leader Reef wnich had cut sometimes partly in sericite and partly in quartz, and ;he case where these conglomerates occupy depressions or defined shaly or schistose footwall partings, and in con­ down into the footwall beds of the Basal Reef. Systematic sometimes with quartz moulded around them. Frequently, hollows in the floor of deposition or where they He against glomerate less than 30 cm thick. sampling of a remnant or "island" of Basal Reef left in the such grains tend to be grouped in clusters which are slight barriers across the floor which acted as traps. The general distribution of payable concentrations of channel revealed that the values were typical of those in very irregularly distributed. In some reefs (such as the In the Virginia area high values are present in well- gold and uranium in the Upper Witwatersrand conglomerate the Basal Reef on either side of the channel, and relatively Ventersdorp Contact Reef at Western Reefs Mine, which developed conglomerate^ illing depressions that are relative­ is parallel to the original shoreline of the sedimentary high values along more or less the middle of the reef on the lies immediately above a disconformity) such individual ly shallow and which have gentle slopes. However, where the basin as inferred from the spread of the coarser sediments. "island" were also present in the same position in the reef grains frequently show alteration rims; depth of a depression becomes excessive and especially when Richer concentrations in the conglomerate tend to be disposed on the opposite banks of the channel. On the other hand, the ii) in association with nodules of "carbon" (thucholite or its marginal slope suddenly steepens, the conglomerate de­ in pay-streaks which have many of the characteristics of channel filling of poorly sorted quartzite, loosely packed hydrocarbon) which lie within the fine-grained matrix; velopment in the centre of the hollow is poor compared with those found in modern placers, and a similarity in mode of conglomerate and compact, massive conglomerate surround­ ill) in association with massive "carbon", which tends to that along the periphery. The peripheral portions of such deposition is strongly indicated. An ore-bearing conglo­ ing the "island" of Basal Reef was completely barren except occur as layers or bands within a conglomerate, but depressions are chaT acterised by well-developed and closely merate sheet may break up into isolated lenticular bodies, for some rare sporadic gold values on or near the bottom which occasionally fills cracks in the matrix or in the packed conglomerate generally containing high values of gold which diminish in size and number until ultimately they are of the channel. Another featur » of the channel filling is the pebbles of a banket. and uranium, whereas in the central portion of the depres­ paucity of pyrite mineralisation and the absence of thucholite spaced too far apart for profitable mining. There is a de­ The individual grains occurring in the matrix are, in sions there are usually two relatively thin conglomerate crease in pebble size and metal content outwards from the or uranium-bearing hydrocarbon as compared with about some reefs, rounded to various degrees, oval-shaped grains bands - one against the hanging and the other on the footwall - point of entry into the depository. 5 per cent of rounded grains of pyrite and minor amounts of being predominant. There can be little doubt that they a'e PEL 212- 16 PH. 212 - 17 primary constituents of the conglomerate, forming part of over uraninite, occurring as patches, veinlets and stringers posited close to the shores, the finer and lighter material Jeppestown amygdaloid. Values below 0,003 per cent the transported detritus which became the matrix. It is sig­ ir> the matrix or penetrating cracks in quartz pebbles and in deeper water. As the area covered by water shrank, the L^Og were not listed in the records save as 'trace' nificant that, in the Ventersdorp Contact Reef at Western being often intimately associated with sulphide minerals and coarser equivalents of the Dominion Reef, Hospital Hill, or 'nil'. For each hole, a value equal ro or greater Reefs mine, in the Kimberley Reef at East Daggafontein and particularly with pyrite. Government Reef, and Jeppestown Series would be exposed than this has been multiplied by the thickness of the in the at Stilfontein, these grains predominate in The relations which exist between the uranium content and, on denudation, could have contributed their quotato the section yielding this value to give a cm per cent value quantity over the uraninite associated with "carbon", where­ of the sediments and the various earth movements which material that now forms the upper two series of the system. for each such section-, the totals of such thicknesses as the reverse is true in the Carbon Leader of Blyvooruit- have affected them have an important bearing on the problem There is, moreover, abundant evidence that processes such and of such per cent values were then found for each zicht. Grains are often traversed by cracks. of the mode and time of origin of the uranium in these rocks. as fluctuations of water level within the basin and local hole, and the sum totals for the eight holes obtained. In some cases, sulphides or gold have penetrated these Attention h?"- already been drawn to a probable concen­ tectonic mcvements led to considerable reworking of already Excluding igneous intrusion, the eight holes penetrated cracks, while occasionally sulphides may wholly or partially tration of uranium content »t the base of a zone of deposits deposited material during the deposition of the beds of at a total of 7 035 metres of strata: of these, 200 metres - surround a grain of uraninite. Grains may also show altera­ which follow immediately upon a sedimentary hiatus within least the upper series, certainly in the areas that are being or 2,8 per cent - carried values of 0,003% el'300 or tion rims. the system, indicating derivation of uraninite from earlier mined. higher with an average value of 0,008 per cent. C.F. Davidson (1953) has dismissed the possibility of beds that were eroded and reworked during the period of the If the uranium now present in the Witwatersrand Beds In the same way, eight holes in the Ventersburg uraninite physically withstanding the "prolonged natural mil­ break. The fact of concentration of such horizons is in­ were syngenetic, it could have been carried into the basin district penetrated 4 068 metres of sediments between ling which, were it of placer origin, it would have received disputable. It would be more difficult to explain by a theory either in solid form or in solution or both. But having arrived the base of the Ventersdorp lavas and the Footwall at the time of deposition of these quartz-penble alluvials". of post-Wi'watersrand hydrothermal invasion than by one of there it had to remain, subject to the natural processes of quartzites just below the Basal Reef. Of this thickness, This, however, can scarcely be accepted as a serious physical redeposition. decay and, if in solution, of ground-water movement. 1,33 per cent yielded eL^Og values of 0,003 per cent argument. Assuming the presence of uraninite as an original The source rocks of the Witwatersrand sediments are or higher, with an average value of 0,0107 per cent. 3.8 Source of the Urariium heavy-mineral constituent of material transported into the known to be mineralised and their mineralisationwas almost Complete assays of 4 943 metres of core from bore­ There are two obvious possible primary sources of the basin, it is inconceivable that any amount of attrition would wholly pre-Wirwatersrand in age. Part of the mineralisation holes on the Klerksdorp Townlands sunk through various uranium present in the Witwatersrand sediments: result in the complete physical disappearance of the mineral. is a uranium mineralisation. The question naturally arises, thicknesses of Upper Witwatersrand sediments (inc lud- Liebenberg's studies (1955) have shown that the individual (i) older rocks from whose destruction were derived the therefore, whether the quantity of uranium present in the ing the Gold Estates group, the Vaal Reef, and the Ada grains of uraninite in the banket are of extremely small materials that form the shale, quartzite and conglome­ Witwatersrand beds, and particularly in the beds above the May and Commonage Reefs) showed that 5,29 per cent size. rate of the succession, and Jeppestown Series of which we have the more detailed of the sediments carried eUoOg values of 0,003 per cent Within the nodules of "carbon" that are to be found (ii) fluids containing uranium that penetrated the sediments knowledge, is greater than could be accounted for on the or higher with an average value of 0,011 per cent. The in the matrix of the conglomerate, uraninite is physically during or after their deposition and from which the oxide assumption of a syngenetic origin. shallowness of some of the holes in this area introduces included in the form of small to extremely small sub- was precipitated. Any attempt to answer such a question involves con­ the possibility that in certain of the core samples in­ rounded to sub-angular fragments, the degree of angularity sideration of a number of factors of which our knowledge cluded the radioactive material is in disequilibrium, The Witwatersrand rocks were deposited in a large increasing with decreasing grain size. The fragments are is only very s<:ant. Among these are the total original extent and that the equivalent U30g values obtained are not intracratonic basin whose boundaries have not yet been frequently cracked - as arethenodules of "carbon". Lieben- of the sediments of the succession, the degree to which true uranium values." precisely defined. If we consider the Dominion Reef System berg has described a rj>dule of "carbon" from the Western earlier beds in It were eroded and incorporated into later with its preponderance of lava over sediment as part of the The important but at present unknown factor concerning Reefs mine which carries, in addition to grains of uraninite, beds, the average uranium content of the source rocks, and Witwatersrand System and if we accept the correlation til the these cores is the actual average uranium content of the a fragment of quartz which uself encloses an oval grain of the average uranium content of the existing remnants of the partly exposed rocks of the God wan beds, of the Uitkyk sections which carry less than 0,003 per cent. Simpson's urarinite. system. Formation, and of the Derdepoort strip near the Transvaal- borehole logs of radioactivity show adequately that the radio­ The massive "carbon" such as occurs at Blyvooruit- Only in the case of the last of these factors have we Botswana border with the lower beds of the system, it is active content of quartzitic members of the succession is zicht frequently har a laminated appearance. It contains sufficient information available to enable a rough approxima­ clear that this basin of deposition diminished considerably variable from layer to layer and from hole ro hole. A few numerous .ncluded grains of uraninite as well as occasional tion to be made. This information is derivable from assays as time progressed. random specimens have yielded, on assay, values up to of core samples from comparatively few of the hundreds of inclusions of quartz andoyrite. Si ringers of sericite material 0,001 per cent eL^Og; but it would be hazardous to accept The material that was transported into this basin muse boreholes that have been drilled in the search for aurife­ are found in it. The material is cracked, the cracks often this, or any other figures, as an average of all material have been derived primarily from the exposed pans of the rous reefs in the Upper Witwatersrand beds. Nel (1958) being partly filled with gold. There appears to he evidence carrying less than 0,003 per cent in order to arrive at an Basement Complex - from the sediments and metamorphosed states: of local partial replacement of uraninite by "carbon". average for the whole succession in a given area. The other uraniferous constituent present in the banket sediments of the Kheis and Swaziland Systems (sensu lato) "Complete core assays have been made of 8 bore­ A significant fact revealed by these figures is that the is described by Liebenberg as "pitchblende-like material". and the magmatic rocks intruded into them-mainly granites holes sunk in the Potchefstroom area. These hole.3 important concentrations of uranium are to be found only in According to him, in some reefs (the Vaal Reef and the and pegmatites, the so-called "Old Granite". In such a basin, penetrated the preserved part of the Upper Witwaters­ certain narrow zones which form usually less than 5 per cent Monarch Reef are examples), this material predominates coarser and heavier sediments would tend to have been de­ rand succession, in five cases reaching the top of the of the whole upper Witwatersrand sequence - the average IM-l 212 - 1« PEL 212- 18 of uranium from the Witwatersrand basin is therefore the Annual production of uranium rose to a peak of some being usually about 2 per cent. The remainder is not barren Only a significant price increase of both gold and maximum speed of mining and selling the country's gold re­ 6 500 short tons in 1959/60, at which time there were 27 and generally shows a "normal" on the radiometric logs which uranium would materially affect the South African reserve serves. This limits the maximum possible uranium production mines producing uranium-bearing ore for treatment in 17 is higher than that of the igneous material intrusive into the figures. Should the price of gold, for instance, be doubled, to about 6 500 short tons of uranium per annum unless new extraction plants. Thereafter, as demand for uranium waned, sediments. But there is not, in this 95-98 per cent of the the uranium reserves within the different price categories mines are established. annual production decreased to some 2 900 tons in 19t>5, by sediments, anything like the concentration found in the other would only increase by between 15 and 20 per cent on the The abovementioned considerations have led to a criti­ which stage only 12 mines were producing ore for treatment 2-5 per cent. average,and not before the price of uranium increases to cal reassessment of the uranium available as a by-product in 7 extraction plants. In response to a quickening demand As has been shown, there is generally within these around ?15 per pound would significant additional deposits of gold mining. In the forecast the rising trend of working for nuclear power since the middle 1960"s, the South African zones of concentration a relationship between the uranium of uranium come within economic limits of exploitation. In cost was taken into account and a fixed gold price of ?35 per uranium production has increased steadily and some 4 119 a>*d gold contents - high uranium values in general accom­ this regard the data on further potential resources of uranium ounce was assured, but no account was taken of a possible tons of uranium were produced during 1970. At present 14 panying high gold values with the uranium-to-gold ratio given in Table 1 are important. combined pay limit for gold and uranium. mines are producing uranium for treatment in eleven ex­ tending to decrease as the gold value increases. However, South Africa's uranium output to date has depended traction plants. examination of the variability of uranium values within a almost entirely on current gold mining operations and pro­ 3.10 Production Calculations based on figure 3 show that the estimated particular band of conglomerate, as plotted on a mine plan, duction is dependent upon production of gold. The enormous The past and projected future gold and uranium produc­ shows that the uranium is by no means evenly distributed rise in total working costs over the past twenty years, from tion for existing market conditions, based on the latest avail­ production of uranium from the existing gold mines for the throughout the layer. R2-63 to R6-29 per ton milled, has become the governing able information.are shown on Figure 3. The graph represents period 1971-1990 (twenty years) should be about 1000O0

3.9 Ore Reserves factor in mining economics. Several of the larger mines estimates of production at a sale price of not less than ?7 per short tons. Surface material which can be treated economi­ have held or even cut their unit costs by extensions of milling lb U3O8 in 1971, escalated at 3 per cent per annum. cally by conventional processes is included, but material A comprehensive estimate of the uranium content of capacity, but it is a combination of the fixed price of gold, the South African ores mined for gold, including slimes the threat of creeping inflation and the rise in working costs dams, sand dumps, indicated ore reserves in the mining which determine the lives of mines. Examination of the costs areas of existing mines as well as future gold-mining areas, of a number of companies of exceptional steadiness of oper­ with no account being taken of price per pound as made by Figure 3 ation appears to confirm that an upward cost trend is about wrnwrERsaAM) GOLOFKLOS the Government Mining Engineer during 1965, is given in •OLD MO MMMUM HMWIMI *n> BTMOTfS OF fUTIMf WtlO Table 1. 4,0% per annum. The optimum condition for the exploitation 12 ^ 31 30 » 2» U 20 "\ 27 2« 25 - \ TABLE 1 24 GOLD MOOUCTKM 0 00UCT, 23 (OZ.MUJtMS) t^tsr-ns ^'ZZ^ " °" ESTIMATE OF URANIUM CONTENT OF SOI TH AFRICAN OHES 21 21 20 \ (No account being taken of price per lb) \ 1* \ 10 - MEASURED TONNAGES INDICATED TONNAGES 17 (FULL* DEVELOPED * .SLIMES DAMS A SAND DC'MPS (BASED ON BOREHOLE TOTAL If Ave­ \ READY FOR STUPING) RESULTS) . 1» \ Grade L.o Con- U 0„ Con- I;' bQ ton­ rage \ V 0 Con­ Ore Tons 's 0 Ore Tons % > 8 Ore Tons 3 8 lb/ S Ore Tons lent Ton* So tent Tons tent Tons tent Tons ton -J 11 l.O lb/ton 10 14 133 OOO 9 OOO 205 7'46 000 131 100 879 OC 0 I'lO 10O 1,27 - and over - - ?19 * * h H U, SX • UHAMUM POOOUCTKM \ {LBS. MK.H0M) 0,5 - l.o 1 - V rJ '42 313 OOC 1) 800 10 ibU 000 ) OOO ; 120 800 376 lb/ton 323 55 « 000 131 000 137 600 0,73 t J \r-^ s S 0,2 - 0,5 * - 29 3^5 OOO k OOO '»2 137 ooo 6 -'lOO 276 8f>7 OOO >*6 200 3'»8 V»9 000 r.7 000 0,33 lb/ton 3 - > r 1 - J TOTAL 85 791 OOO 27 200 52 ilOl 000 9 -'ioo 806 167 000 .'»98 10O oy, 359 OOO n'» 700 0,71 D , s — _i^ — — 1 . . • mi me IMS IMO ItID I*TJ IMO IMS mo *M

Below 0,2 9b 69« oou 81 200 665 838 000 ko 5002 2k5 OOO 0,10 lb/ton 6 30oljL698 7°9 000 1*61 128 000 PEL 212 - 20 PEL 212 - LM in low grade dumps, which might be treated by processes and thus it is possible to have all gradations between a centimetre to more than 20 metres in thickness. Many of mines along the West Wits Line. Potentially exploitable still to be developed, are excluded. greywacke conglomerate and a granite pebble or arkosic them are mineralised and contain small amounts of uranium Ventersdorp Contact Reef is confined to those areas where 4. THE VENTERSDORP SYSTEM conglomerate where the source area is granite. Intercalated which varies from trace amounts to 0,025 per cent. No de­ the Ventersdorp System overlies tilted and eroded gold and sand-grade and mud-grade tuff aceous sediments with recog­ posit of economic value has been encountered despite a large uranium-bearing horizons in the Upper Witwatersrand Sys­ 4.1 General Description nisable sedimentary structure help to distinguish volcanic number of deep exploration boreholes drilled through these tem. The Ventersdorp System comprises a predominantly conglomerates from agglomerates. conglomerate bands in the area between Klerksdorp and the 5. THE TRANSVAAL SYSTEM volcanic sequence unconformably overlying the Witwaters- Close to major faults, massive boulder conglomerate Orange Free State goldfields. rand System. As a result of extensive diamond drilling is encountered which is restricted to the immediate vicinity 5.1 General Description 4.3 The Ventersdorp Contact Reef activities in the area between Klerksdorp and the Orange of the faults. Sediments consolidated from sands, muds and The beds of the Transvaal System unconformably Free State gold fields Winter (1965) was able to construct a carbonates interfinger with the conglomerate. There is a The Ventersdorp Contact Reef occupies a stratigraphi- overlie those of the Ventersdorp System. The Transvaal standard scale of reference for the Ventersdorp System. rapid gradation to an end-product of dark carbonate rocks cal position at the contact between the older Witwatersrand System has been sub-divided on lithological grounds into a In the type area the geological column is separated by un­ in areas where less liian 10 per cent conglomerate is de­ System and the younger Ventersdorp System of which it forms bottom or Black Reef Series consisting of quartzite, conglo­ conformities into three primary sub-divisions. These again veloped. the basal member in certain areas. It is composed largely of merate, and minor shale, a middle or Dolomite Series of are sub-divided on lit ho logical grounds into formations. Talus breccia and conglomerate reflect the nature of resistant materials such as pebbles, quartz grains and dolomitic limestone, shale, chert, and accessory quartzite, Local names are attached to the formations, pending cor­ the source rocks. In the New Kameeldoorns Formation heavy concentrates derived from the denudation of under­ and a top or Pretoria Series comprising shale, quartzite, relation with well-established formations or groups of form a- volcanic conglomerate consists predominantly of fragments lying Witwatersrand conglomerate and qu-.rtzite. The Ven­ subordinate limestone and an impersistent tillite. The Black tions outside the type area. of older rocks such as the Langgeleven Formation, admixed tersdorp Contact Reef was laid down on the old land surface Reef Series at the base of the Transvaal System is entirely The Ventersdorp System can clearly not be considered pebbles of shale, quartzite, grit and older conglomerate in the form of a thin layer of eluvial scree which accumulated unconformable to the Ventersdorp and Witwatersrand System as one System in the classical definition of the term, being containing pyrite stringers. They can be matched with strata in thicker alluvial sheets in depressions, valleys and stream and other older formations. It is largely formed of quart­ unified only by the abundance of andesitic lava in all three of the Upper and Lower Divisions of the Witwatersrand beds. There is evidence of successive layers of conglo­ zite which frequently carries thin pebble washes or in per­ sub-divisions. The Lower Ventersdorp shows greater struc­ System. Sedimentary structures indicate that these rocks are merate being washed into deeper hollows in the basement. sistent conglomerate especially along or close to the bottom. tural affinities with the Upper Witwatersrand System, and of clastic derivation and not pyroclastics. These are frequently separated by layers of sand, and The bottom beds of the Series tend to assume some of the the Upper Ventersdorp with the Transvaal System. The Rietgat Formation consists predominantly of lava argillaceous or volcanic tuff. This auriferous conglomerate characteristics of the underlying formations. When they lie The Lower Ventersdorp System was warped, tilted and but contains subordinate sedimentary and pyroclastic rocks. is distinguished from those in the Witwatersrand System by directly on granite they become arkosic. On Ventersdorp block-faulted but contains no radioactive rocks of potential The sediments contain a high percentage of coarse conglo­ the dark colour of its matrix due presumably to volcanic ash. lava, amygdales, hardly smoothed by attrition, are common economic interest. The sedimentary rocks of the New merates which are indistinguishable from those of the New Over extensive stretches the Reef is represented by a in the conglomerate. Evidently an appreciable number of the Kameeldoorns Formations of the Middle Ventersdorp are Kameeldoorns Formation. single line of cobbles or pebbles which are not contiguous. components of the Black Reef conglomerate were not carried considered to represent a greywacke facies filling fault The sediments in the Bothaville Formation display a Lava and/or tuff in places occupy the interstitial spaces far from their sources. troughs and are subject to rapid changes in facies. The con­ cycle of sedimentation commencing with conglomerate, gra­ and may lie directly on the Witwatersrand sediments. The occurrence of three very prominent and persistent glomerates contain radioactive minerals in limited amount ding into quartzite and shale, and then again increasing in Nodules of black hydrocarbon material aref airly proli­ quartzite zones has made possible a further sub-division of but such zones are ncc expected to be continuous over long grain size to conglomerate. In the basal conglomerate there fic in places in the Ventersdorp Contact Reef and closely the Pretoria Series into a bottom or Timeball Hill Stage, a distances. Similar types of sediments including conglo­ are abundant pebbles of quartz porphyry, basic lava and resemble those found in the Carbon Leader and the Bird middle or Daspoort Stage and a top or Magaliesberg Stage. merates are developed in the Rietgat and BothavilleForma­ sedimentary rocks derived from rock-types known to exist and Kimberley Reefs. Chemically they are closely similar The Timeball Hill Stage comprises, from the base upwards, tions which are sepa . .ed by a distinct unconformity. No below the unconformity in the vicinity whilst in the upper to low-volatile bituminous coal. Uraninite occurs as rounded a variable basal succession of shales, calcareous or dolo­ gold or uranium values have been found in lava that forms conglomerate considerable quantities of rounded pebbles of and angular inclusions in the hydrocarbons. Many of the mitic in places; a lenticular development of Bevet's Conglo­ part of the stratified formations, nor do they occur in the quartz and quartzite occur together with fewer red jasper grains show fine stringers of galena and partial replacement merate; a thin but persistent chert-quartz grit, known as the igneous rocks intrusive into them. and banded chert pebbles. of the hydrocarbon by phyllosilicates and gold. Pologround quartzite; a great thickness of well-laminated 4.2 Conglomerates Clay pellet conglomerates denote exposures of the The Ventersdorp Contact Reef, from a metasomatic grey to black shale (often altered to slate); followed by the depositional surface to the atmosphere. The presence of and mineral association point of view, is very similar to Most conglomerates of the Ventersdorp System are Timeball Hill quartzite which often contains a number of red jasper pebbles at all elevations also suggests terrestrial the Witwatersrand bankets and represents a valuable gold greywacke conglomerates, containing a poorly sorted assem­ deposition. The uppermost conglomerate is considered to be horizon, additional to the Main Reef Group. Unfortunately intercalated shale hands. The Daspoort Stage is represented blage of cobbles, pebbles and fragments of volcanic, igneous, an eluvial type, closing the sedimentary cycle and presenting its uranium content is too low to justify economical exploita­ by massive shale followed by quartzite with which there is metamorphic and sedimentary rocks in a very dark-grey, tion. frequently associated a well-developed glacial phase of typi­ sandy to clayey matrix. Depending on the source area, a relatively flat upper surface. The economic significance of the Ventersdorp Contact cal tillite and laminated shale. These are followed by the pebbles of any one lithological type may locally predominate, Individual conglomerate bands vary from less than a Reef may be judged from the fact that highly payable ore Ongeluk lava -which attains a thickness of nearly 610 metres is now being mined from this horizon in several major gold - the upper Daspoort shale and the Daspoort quartzite which PEL 212 - 22 PI 1 2\2 - i:\ form the prominent range with similar name. TheMagalies- Results of a detailed underground radiometric survey 5.2.3 Mineralised quartzite Hill shales within the Pretoria District consist of from berg Stage comprises mostly massive grey and black shale 180 to 240 metres of soft and well-bedded shale and flagstone illustrate a pronounced irregular mineralisation pattern. Somewhat unusual at Kaapse Hoop is the presence of a followed by quartzite. In the Western Transvaal the lower weathering cream, yellow or red. They arc gre> or dark- Values of between 0,002% and 0,09% U3O8 and of 0,187% highly mineralised quartzite about 2 metres thick which part of the shale becomes definitely graphitic to form two blue when fresh and metamorphosed in many places to slate. ThC>2 have been noted over a distance of 75 metres in a underlies the conglomerate and forms the basal portions of well-marked carbonaceous horizons in the Zeerust district. They may swell out to more than 900 metres in the North- zone 2,5 cm thick in the footwall of the Black Reef conglo­ the Black Reef Series. The highest values obtained in the By reason of its massive character the quartzite builds the Eastern Transvaal. merate. Average values obtained were 0,018% U3Og and quartzite were 440 grams per tonne of gold, 0,096% L'3Og very prominent Magaliesberg range. 0,032% ThOj over a thickness of 220 cm of conglomerate. The Daspoort shales, when unaltered, resemble those and 0,187% Th02. Average values were 4,5%, 0,017% and of the Timeball Hill Stage and are always identified by their 5.2 Black Reef Series Gold values of 9 grams per tonne in the conglomerate in­ 0,03% respectively. dicate that in places the basal rocks of the Black Reef Series association, two-thirds up in the sequence, with a thick body 5.2.1 Conglomerate 5.2.4 Results of radiometric survey carry gold and uranium in payable quantities and that further of contemporaneous lava - the Ongeluk Volvanics. The pebbly seams at or near the base of the Black prospecting of these beds appears to be justified. A radiometric survey of the Black Reef Series indicated The Magaliesberg shales, the uppermost of the three Reef Series are often very like those of the Witwatersrand The richest mineralisation occurs near the footwall that, almost everywhere along the footwall contact, radiation argillaceous members, are a full 600 metres thick but, by System in carrying pyrite, gold, carbon, chromite, zircon, contact and is independent of the nature of the underlying is at a peak. It may be 50 times background, equivalent to reason of their proximity to the Bushveld Complex, have rutile, ilmenite and traces of other sulphide minerals. These rocks. Mineralisation decreases gradually upward until only 0,07% U3Og but is more often less than 10 times background, experienced considerable metam irphism. In the Zeerust reefs have been worked for gold at a number of places near traces are discernible. equivalent to 0,01% U3O8. District the lower part of the shale becomes definitely the Rand, between Klerksdorp and Potchefstroom and also In some sections the main mineralisation is confined There is no relationship between the radioactivity of graphitic and forms two well-marked carbonaceous horizons. far to the east in the Haenertsberg overlooking the Letaba to the uppermost parts of bands of conglomerate developed the Black Reef footwall contact and the underlying rocks, viz. Shales of the Pretoria Series have a very characteristic Valley. Uranium values are found in associated pyritic above the footwall contact. Quartzite intercalated in the con­ the Kaap Valley granite and the Godwan Formation. The background of radioactivity varying from above-average to quartzite as well as in the conglomerate but no production glomerate show- a much lower degree of mineralisation question has to be considered, whether the Black Reef high. The highest activity is associated with the lower two- has been possible owing to low grades. than the conglomerate itself. contact can be investigated radiometrically by airborne thirds of the succession, i.e. shales of the Timeball Hill and Mining operations on the East Rand have revealed that methods. First of all the Black Reef crops out along the Daspoort Stages. Samples show zircon and monazite to be 5.2.2 Mineralised conglomerate pebbles auriferous conglomerate in the Black Reef fills stream steep slopes of valleys so that rim-flying with a helicopter mainly responsible for the radioactivity but no deposits of channels and was also deposited in depressions that were Because of its high radioactivity (20 times background) along the escarpment would be required. Even if the pilot economic value have been located. The shape of the radio­ scoured out in older rocks. Such occurrences of the Black a pyritic pebble 20 x 8 cm in diameter, present in the con­ were prepared to fly to within 100 metres of such outcrops metric borehole log is specific to the formation and is Reef contain gold and uraninite, along with pyrite, where glomerate, merits special attention. It consists of sericitic and mineralisation were to continue over a distance of a easily distinguishable and recognised. In contrast to the they lie on or close to underlying gold and uraninite-bearing quartzite and is well-rounded. An outside yellow-grey zone kilometre, the chance of picking up the attendant anomaly shale, the Ongeluk substage and the Bevet's Conglomerate Witwatersrand beds. surrounds a dark grey core, in which a uranium content of under such circumstances appears to be small. have a low radioactivity background, Fig. 4. about 1,0% U O was radiometrically determined. Uraninite In the Eastern Transvaal the basal conglomerate of the 3 g 5.2.5 Economic aspects 6. KARROO SYSTEM was identified by X-ray diffraction analysis. Several of the Black Reef Series south of Kaapse Hoop, near Nelspruit, is uraninite grains are surrounded by sericite which is radially The strata of the Karroo System forms ahuge and very uranium-bearing; grab samples gave values up to 0,34% So far the investigation has shown that there seems disposed around them. This shows that the age of the urani­ gently dipping structural basin, which measures over 1 300 L^Og. Good exposures of Black Reef quartzite, forming little possibility of the Black Reef conglomerate being de­ nite is premetamorphic and that these grains could even have high cliffs, demarcate the edge of the Drakensberg escarp­ veloped as an exploitable uranium deposit. The highest kilometres east-west and 650 kilometres north-south. It a detrital origin. The matrix in which the pebble is embedded ment. At the base of the quartzite a conglomerate is de­ average uranium content over amineable thickness of 110 cm covers about 570000 square kilometres of which roughly contains 0,043% U Og. veloped sporadically. It contains more or less well-rounded 3 is only 0,002% ^Og. The richest uranium-bearing sample 26000 square kilometres consist of Stormberg lavas. Al­ contains 0,096% U30g which is less than the average value though the maximum thickness is generally in the south, pebbles which measure up to 5 cm across. They consist of The outermost zone of the pebble shows a much lower of 0,2% at present required when deposits are mined for it is developed in different localities for each sub-division, black chert, blue quartzite, slate and quartz. The matrix is uranium content (0,15% U3Og) than the core. If there were mostly siliceous and contains abundant pyrite at some lo­ uranium only. The average content over the Black Reef so that the total thickness of the system at any one point secondary mineralisation from the outside, one would expect calities. The basal conglomerate reaches 6 metres in thick­ conglomerate exposed by adits in this area is less than probably does not exceed 6 000 metres. that the enrichment would get less from the outside to the 0,005% U3O8 and uranium could not therefore be profitably ness. The conglomerate and its footwall are auriferous in The occurrence of radioactive minerals in the Karroo inside, therefore it seems more likely that the pebble was extracted, even as a by-product. If the mining for gold can places and have supported considerable mining activity in the rocks is well-known and has been described by Koen (1955). mineralised before its deposition in the Black Reef conglo­ past, as is evidenced by stopes, adits, trenches and pits carry the mining costs it might be pousible to extract the Radioactivity logging of boreholes has registered many which are situated along the escarpment and in the valley of merate. This information suggests prospecting for uranium uranium in selected parts of the Black Reef conglomerate. occurrences of monazite in different members of the system. Button's Creek. in the rock formation from which the pebble originated. This 5.3 Pretoria Series Herzberg (1968) described thedeposit and the following formation could be the Moodies quartzite in the Barberton Samples taken from cores have invariably proved monazite Shales form a prominent pan of all four stages of the information is culled from his report: mountain land. Pretoria Series. In their typical development the Timeball to be responsible for the radioactivity. PI i 21: L'n

and invariably frosted over. A 90 per cent concentrate of Scries or /one monazite contains 7,3 (1 0,2) per cent Th0 and 0,4 (1 0,1) 6.1 Heavy-Mineral Beach Deposits 2 Approximate per cent UO2 (Mukerjee, 1960). Large consolidated deposits of heavy minerals occur Formation l.ithology thickness in the Bothaville District of the Orange Free State and in the 7. OTHER OCCURRENCES (metres) , Delmas and Carolina Districts of the Trans- Outside the Witwatersrand Triad, which has been very Karroo Ecca shale - vaaL The Bothaville and Wolmaransstad deposits, which thoroughly investigated by the mining industry, the following Dwyka tillite ~ have been studied in greater detail by Behr (1966), occur geological formations are considered to warrant further -0-0-0-0-0- Unconformity in sandstone commonly known as the Middle Ecca Stage of investigation and to offer the best chances of locating urani- Mozaan Shp.le-quartzite + 300 the Karroo System. The remaining deposits probably occupy ferous deposits: Quartzite-ironstone 180 a similar stratigraphic position. Basal conglomerate 0 - 210 Mozaan Formation In the Bothaville area deposits are sub-parallel to -0-0-0-0-0- Unconformity Godwan Formation each other, and are present over a maximum discontinuous Insuzi Upper volcanic 690 The Upper-Witwatersrand rocks surrounding the strike length of 16 kilometres in a zone approximately Quartzite-dolomite 750 Vredefort Dome 13 kilometres wide. The longest continuous outcrop extends Banded shale 60 - 240 for almost 5 kilometres. The width of individual deposits 7.1 Mozaan Formation Lower volcanic 0-120 ranges from one to just over 900 metres, the average The rocks of the Mozaan Formation extend from Basal quartzite 0-60 being close to 130 metres. The thickest beach deposit rich in Amsterdam in the Eastern Transvaal in a south-easterly -0-0-0-0-0- Unconformity heavy minerals known to date is 6,3 metres; the average is direction past Piet Retief into Swaziland and to beyond Basement Granite gneiss close to 2,7 metres. Louwsburg in Natal. In the east and south-east they rest on 7.1.2 Basal Conglomerate Zone Archaean granite, whilst in the west and north-west they lie Delpierre (1969) further sub-divided the Basal Con­ unconformablyonthe Insuzi Formation. The Mozaan Forma­ glomerate Zone as follows, in the course of an investigation tion consists of shale and phyllite that alternate repeatedly by a mining company into the uranium and gold content of with rather subordinate bands of quartzite containing beds of this zone: Figure 4 conglomerate in places. RADIOMETRIC GRAPH SHOWING TYPICAL ANOMALIES OF DIFFERENT Because of the lithological and mir.eralogical resem­ Metres FORMATIONS ENCOUNTERED IN BORE-HOLES IN THE EASTERN TRANS­ blance of the conglomerate to those of the auriferous banket VAAL Upper leaders 6 reefs of the Witwatersrand System a number of them have Intermediate quartzite 6-15 SENSITIVITY: FULL SCALE 10 COUNTS PER SECOND been prospected for gold in the past. Lower leaders 0-6 SPEED: FAST: 17 FEET PER MINUTE Gold discoveries drew attention to the Denny Dalton SLOW: 5 FEET PER MINUTE Denny Dalton Conglomerate 0-4 region during the last decade of the 19th century. The Denny This graph is repeated in larger format facing page 30. Basal quartzite 0-30 Dalton Mine was started in 1894. Mining operations con­ tinued intermittently until 1908, the last record being of The Denny Dalton Conglomerate outcrops at a number The most striking features of the beach deposit are retreating of the dump in 1926. Numerous references to of places over a strike length of 10 000 metres and attains a zones about one metre thick, which are rich in heavy min­ gold discoveries appear in the Annual Reports of the Com­ maximum thickness of 4 metres on the farm Mount Sophia. erals, and the presence in these zones of thin but regularly missioner of Mines for Natal and Zululand for the years The conglomerate consists of poorly sorted white and dark alternating dark and light beds which differ not only in 1888 to 1910. quartz and chert cobbles up to 30 cm in diameter. The colour but also in thickness, average grain size, mineral All the basal conglomerates of the Mozaan Formation average diameters are between 10 and 13 cm. Occasional composition and degree of sorting. The minerals of the dark on which the Denny Dalton Mine was founded were sampled shale fragments are present in aquartziticmatrix containing beds in approximate descending order of abundance are for gold. Nine boreholes were drilled (945 metres of core) fair amounts of pyrite. ilmenite and its alteration products (goethite, leucoxene, and 127 trenches made by a Mining Company in 1945. The anatase and authigenic rutile) zircon, garnet, monazite, The Denny Dalton Gold Mine was founded on the con­ area was mapped and described by Matthews (1967). quartz, chromite, staurolite, tourmaline, spinel, pyroboles glomerate reef on the Farm Tusschenby 411. The reef is 7.1.1 Geology and xenotime. from 0,3 to 3 metres thick but only the basal 0,5 to one In the Bothaville deposits the recoverable percentage of The stratlgraphical succession, based on the work of metre carry any values. monazite amounts to 0,4 per cent. Individual grains are well Matthews, is as follows: The principal workings consist of 10 adit levels, seven rounded to sub-spherical, lemon-yellow to pale greenish, PFI 212 - 26 PI-1 212 - 27 of which are on the south side of the Nxobongo creek and the borehole cores which had considerably lower average values the presence of these and numerous other anomalies on the individuals (5 to 12,5 cm being the longest diameter) scat­ rest on the north and west side. They are driven in on reef of the order of 0,005 per cent. Kimberley and Bird Reef zones within the area of the Dome. tered among a group of smaller pebbles arc common. The at varying angles with each other and about 30 metres sep­ The Kimberley Reef zone was formerly known as the average width of the pebbles is probably a little more than 7.2 Godwan Formation arates the entrance portals. Three blocks have been partly Amazon, Yellow or Rous Reefs, and the Bird Reef zone as 1,5 cm. The matrix of the conglomerate may be either fine Along the escarpment between Kaapse Hoop and Kowyn's stoped out. In addition a considerable amount of ore was ob­ the Meister, Red or Odin Reefs. Numerous trenches, pits or coarse quartzite or grit which, when fresh, is seen to Pass, and in the lower parts of the valleys intersecting it, tained from open-cast workings on either side of the above- and small inclined shafts are situated on both these zones. contain a fair amount of pyrite, often idiomorphic. At, or mentioned creek Very little was mined from the adits on are intermittent occurrences of rocks bearing a striking close to the surface, pyrite is either leached out or decom­ 7.3.1 Geology the north side of the creek. resemblance to, and almost certainly to be correlated with, posed to brown iron oxides. the Dominion Reef System. The name Godwan Beds has been The principal features of the auriferous portion of the A considerable series of arenaceous rocks, including Narrow bands of red slatey-looking rocks may be applied to those rocks. Preserved only in the troughs of conglomerate are the presence of large rounded quartz- one or two slate bands, is grouped under the term Kimberley- associated with the conglomerate here and there. They are synclines, they intervene unconformably between Archaean pebbles, globular iron pyrites up to 1,25 cm in diameter or, Elsburg Series. The quartzite is dull-weathering, generally of two types, viz. reddish fine-grained igneous dykes, so rocks below and rocks of the Transvaal System above and where this has been weathered away, a honeycombed ap­ with a brownish tint on the surface, relieved now and then often observed in the Kimberley-Elsburg quartzite, and consist of a lower and an upper stage of sedimentary rocks pearance. The mineralised zone is overlain by a blue pyrite by & band of light-coloured rocks. The quartzite is coarse­ which sooner or later cross the strike of the beds, or slate and an intermediate stage of predominantly volcanic rocks. layer in which the pebbles are smaller, the pyrites cubical grained and includes many bands of grit and conglomerate. of a rather sandy nature. These small slate lenses do not The lower stage is composed of shales below which may be and present in smaller ratio. This is followed by layers and Ripplemarks and current-bedding were noticed. Deposition necessarily occupy a definite horizon with regard to the quartzites, arkoses or conglomerates. The middle stage lenses consisting of pebble washes, coarse grit and quart- in very shallow water, possibly under littoral conditions, conglomerates. consists of basic to somewhat acid amygdaloidal and non- prevailed for a considerable period prior to the outflow of zite. Although faulting of the Kimberley Reef zone is ex­ amygdaloidal lavas, which alternate with thin bands of the Ventersdorp amygdaloidal lava. The upper, in contrast 7.1.3 Uranium mineralisation tremely frequent, both on small and large scale (vertical agglomerate, quartzite, tuff and conglomerate. The upper to the lower group, is characterised by a stronger develop­ Information regarding the possibility of the presence stage comprises feL'spathic and somewhat gritty sandstones ment of conglomerate. In the lower group the pebble-bed displacements reach 900 metres), it does not in all cases of source material in the rocks of the Mozaan came to light and quartzites and shale or tuff. does not appear to be present along the immediate contact carry through to the Main-Bird Series. when a borehole was sunk at a strategic position to obtain At the contact between the Nelspruit Granite and the of the quartzite. Bands of small inconstant conglomerate, 7.3.2 Uranium mineralisation unweathered rock specimens, 20 kilometres north-east of Godwan Formation, a well-developed casal conglomerate seldom more than 15 cm thick, may occur. The pebbles of Boreholes drilled in the Kimberley Reef zone indicated Piet Retief. The borehole penetrated 216 metres of Mozaan is exposed along Kowyn's Pass which traverses the escarp­ the reefs in the lower groups are small, averaging about a marked reef deterioration in that no thick conglomerate Formation before passing into the underlying lava of the ment near Graskop. Unfortunately this conglomerate appears 1 cm in diameter; they are formed largely of quartz and bands were intersected at depth. Uranium and gold values Insuzi Formation, and was stopped at 218 metres. not to be mineralised as it gives a similar radiometric quartzite and are set in a coarse quartzite or grit matrix obtained were too low to be of significance. The best value A radiometric survey of the borehole showed that reading to that of the Nelspruit Granite and the rocks com­ which is generally pyritic. obtained gave 0,13 kg per tonne U3Og; 1,1 gram per tonne certain zones in the conglomerate, quartzite and the schist prising the Godwan Formation. A fairly persistent zone of conglomerate beds, locally Au and 0,3 gram per metric tonne Ag over a corrected width of were radioactive. Their width varied from 5 to 7,5 cm in 7.3 The Upper Witwatersrand Rocks Surrounding the Vrede- known as the Amazon Reefs, is present from about 90 to 80,6 cm at a depth of 147 metres. schist, to 2,5 to 10 cm in quartzite and conglomerate. A fort Dome 180 metres up from the base of the upper group, and marks The Bird Reef zone is represented by a number of later mineralogical examination revealed the source of the It has long been known that the gold-bearing conglo­ the strongest development of conglomerate in the Kimberley- thin (2 to 15 cm) small pebble conglomerate bands with radioactivity to be fine-grained (0,01 to 0,075 mm diameter) Elsburg Series. These conglomerates have attracted con­ merate of the Witwatersrand System outcrops on the sedi­ intercalated quartzite, the complete zone ranging from 0,3 concentrations of monazite, xenotime and zircon. siderable attention in the past on account of their economic to 3 metres. Sorting and packing of pebbles is of a high mentary collar around the Vredefort Granite Dome. Explo­ Despite the absence of any record of uranium minerals possibilities. order and radiometric counts up to 10 times background were ration and production of gold on a very small scale started it was decided to undertake a reconnaissance radiometric The bands of conglomerate are lenticular bodies, each registered in the field. The reef zone lithology is very con­ soon after 1886 when the Witwatersrand goldfields were survey of the conglomerates with a sensitive scintillation of which may dwindle away for another lens to reappear sistent and the stratigraphic top conglomerate was best counter, especially to establish the possibility of uranium discovered. farther along the strike at, or close to the same horizon. developed and also the richest in uranium. The average minerals being found in association with the gold. The area bounded by longitude 27° 10' and 27° 20' Several conglomerate bands may coalesce to form a pebble- values of five boreholes drilled were 0,326 kg/tonne U3o8, A radioactive survey of the old workings registered east and 26° 49' and 27<> 00' south, lies approximately 110 bed fully 3 or more metres wide. Contacts between the con­ l,3gm/tonne Au and 0,7gm/tonne Ag. The lowest and highest high readings in the old adits and stopes. Conglomerate kilometres south-west of Johannesburg. glomerate and quartzite are generally not sharply defined, uranium values obtained were 0,20 and 0,406 kilogram per outcrops likewise showed high readings at or near their Radioactivity ground surveys for uranium were first as the tendency of the pebbles is to become widely scattered, tonne L^Og. base. A number of samples taken of the old workings never­ carried out with a Geiger Muller counter during 1948 and or for the former to grade into the latter, which may contain 8. RECENT DEPOSITS theless showed very disappointing results and varied from two anomalies, approximately twice background, were a single pebble here and there. Mostly well-rounded and 8.1 General Description 0,004 to 0,052 per cent l^Og and an average of 0,015 per registered on Buffelskloof 511, Koedoesfontein 12, Roode- smooth, the pebbles are usually formed practically of quartz cent. The high readings were due to mass effect and high rand 510 and Nooitgedacht 508 in the Pot chef stroom District. and quartzite only, with occasional schistose, striped or The underlying rocks are concealed by soil, sand, radon concentrations. This was confirmed by analyses of the During 1969 an aerial scintillometer survey again confirmed platy types. They exhibit a great diversity in size. Large gravel, limestone and other superficial deposits of com- PEL 212- 28 PF.I. 212 - 29 REFERENCES paratively recent age, over large parts of South Africa. In should increase, radioactive minerals could conceivably be many areas the process of accumulation is still active, recovered as by-products during the extraction of the form er. Behr, S.H. (1965) Heavy-mineral Beach Deposits in Surv. Dep. Min. S. Afr., 9. whilst in others their degree of induration and erosion in­ Along the south-east coast, ilmenite sands occur at Morgan the Karroo System. Mem.56. Geol. Nel, L.T. (1958) The Occurrence of Uranium in the dicates a considerable antiquity. No clear dating can, how­ Bay, Umtata River Mouth, Port St. Johns, Hibberdene, Surv. Dep. Min. S. Afr. Union of South Africa. Proc. 2nd Un- ever, be assigned, since they have yielded few fossils. Umkomaas, Umgababa, lllovo Beach, Isipingo, Brighton Cooper, R.A. (1923) Mineral Constituents of Rand Con­ Geneva Conf. Paper P/U09. Beach, Umhlali and Lake St. Lucia, and they contain up to centrates. J. Chem. Met. Mining Ortlepp, RJ. (1962) On the Occurrence of L'ranothorite 8.2 Kalahari Formation 0,10 per cent zircon and up to 0,30 per cent monazite. Soc. S. Afr., 24. in the Dominion Reef. Trans. Geol. A continuous sheet of light calcareous sandstones or Eluvial and alluvial deposits of ilmenite, monazite and zircon Davidson, C.F. (1953) The Gold-Uranium Ores of theWi;- Soc. S. Afr., 65, 1. grits, becoming richer in lime towards the top and en­ occur in sand and gravel on the valley floors and slopes of watersrand. Min. Mag. Lond., Papenfus, J.A. (1956) The Geology of Government Gold closing small pebbles - in places passing into coarse cal­ the Umhlatuzi River and its tributaries on Bulls Run Estate, LXXXVIH. Mining Areas and the New State careous grits and conglomerates - underlies the vivid red 25 kilometres north-north-west of Eshowe. De.'ager, F.S.J. (1954) The Sympathetic Association of Gold Areas with particular reference to sand dunes of the Kalahari south of the Molopo River in the In the South-Western Cape, radioactive minerals have and Uranium in the May Reef (Un­ Channel Sediments and the Origin of districts of Gordonia, Kuruman and Vryburg. There can be been found in concentrates of river sands along the Kuils published). Minerals of Economic Importance. no doubt that this widespread deposit, with its occasional and Breede Rivers which contain zircon, monazite and Faulkner, R.L. (1967) Nuclear Power and Uranium Re­ Unpublished Doctor's Thesis, Univ. conglomerate, resting on the most diverse of rock groups, xenotime. Zircon is present in the concentrate of sand at serves. S.Afr. Min. Eng. J., July 12, of S. Afr. is largely of fluviatile origin. the mouth of the Olifants River. Along the West Coast, 1968. Roberts, E.R. and The Upper Witwatersrand System at In the continuous search for potable underground water samples of ilmenite-garnet-rich sands between Strandfon- Hatch, F.H. (1903) The Boulder Beds of Ventersdorp, Kransdorff, D. (1938) Randfontein Estates. Trans Geol. in this arid region a large number of deep boreholes were tein and the mouth of the Zand River contain an average of Transvaal. Trans. Geol. Soc. S.Afr., Soc. S. Afr., 41. drilled. For various reasons, but mainly because the relative­ 6 per cent zircon, which bears a ratio of 1 : 3 to the ilmenite Simpson, D.J. (1952) Correlation of the Sediments of the ly soft Kalahari beds tend to collapse on withdrawal of the content. At Cape Voltas, monazite forms 0,25 per cent of Herzberg, W. (1968) First Report on the Radiometric Witwatersrand System in the West casing, only 20 have been logged radiometrically. ilmenite-rich beach sand, and up to 2 per cent of ilmenite- Investigation of the Kaapse Hoop Witwatersrand, Klerksdorp and The boreholes penetrated bright yellow to brick-red bearing diamondiferous gravels which occur both at the Gold Mines. UnpubL Rep. G.lll Orange Free State Areas by Radio­ sandy material, grit, gravel and even loose stones embedded coast and farther inland. On the farm Meulin the Van Rhyns- GeoL Surv. Dep. Min. S.Afr. activity Borehole Logging. Trans. in the abovementioned sediments. Some stratified and oc­ dorp division an ilmenite sand concentrated from the dia­ Herzberg,W.(1968) Radiometric Investigation on the GeoL Soc. S. Afr., 55. casionally ochreous and calcareous sandstone and marl, mond-bearing gravels carries a small percentage of strongly Black Reef Conglomerate in the Simpson, D.J. (1952) Correlation by Means of Radioactiv­ soft in places but cemented in others, along with bands of radioactive monazite. Kaapse Hoop Area, Nelspruit Dis­ ity Logging in the Witwatersrand clay, limestone and conglomerate, were also present. As is well-known monazite contains other rare-earth trict. Unpubl. Rep. G.117. Geol. System in the Klerksdorp Area. All the sediments examined had a uniformly low radio­ metals apart from thorium, including uranium. Should these Surv. Dep. Min. S.Afr. Trans. Geol. Soc. S. Afr., 55. activity with no anomalies whatsoever, resulting in afeature- beach deposits be exploited economically for their titanium Heavy Minerals as an Aid to the The Geology of the West Rand. Ge- content, both thorium and uranium could be recovered as Koen, G.M. (1955) Toens, P.D. and less radiometric graph. logy of some Ore Deposits. S. Afr., by-products. Correlation of Sediments of the Kar­ Griffiths, G.H. (1964) 8.3 Beach and River Sands roo System in the Northern Part of 1, Geol. Soc. S.Afr. Spec. Publ. ACKNOWLEDGEMENTS the Union of South Africa. Trans. A Review of Volcanism in the Geo­ Small quantities of zircon or monazite, or of both to­ It is a pleasure to acknowledge the work of my two Truter, F.C. (1949) Geol. Soc. S. Afr., 58. logical History of South Africa. gether, are frequently associated with ilmenite or garnet- predecessors at the Atomic Energy Board Dr. S.H. Haughton The Occurrence and Origin of Gold Proc. Geol. Soc. S. Afr., 52. rich sands on beaches or river valley slopes. The known and Dr. L.T. Nel. Extensive use has been made of their Liebenberg, W.R. and Radioactive Minerals in the , Die Geologie van die Gebied om deposits of this type do not represent payable sources of published and unpublished work. Also that of various former (1955) Von Backstrom, J.W Witwatersrand System, the Dominion Ottosdal, Transvaal. Toeligting these radioactive minerals, but are mentioned as a guide colleagues and other authors. Wherever possible this has (1962) Reef, the Ventersdorp Contact Reef 2625D (Barberspan) en 2626C to further prospecting. If the demand for ilmenite and rutile been acknowledged by citing references. and the Black Reef. Trans. Geol. (Ottosdal). Geol. Surv. Dep. Min. S. Soc. S. Afr., 8. Afr.

Mukerjee,N.K.U960) A Study of the Monazite-bearing Whiteside, H.C.M. Uraniferous Precambrian Conglo­ Ilmenite Deposit from Bothaville, (1970) merates of South Africa. "Uranium Orange Free State, Union of South Exploration Geology". IAEA Publ. Africa. Bonn Univ. (Unpubl.) Vienna. Nel, L.T. (1935) The Geology of the Klerksdorp- Wilson, N.L. The Geology of the Vaal Reef Basin Ventersdorp Area. Spec. Publ. GeoL Oosthuizen, D.H. in the Klerksdorp Area. Geology of PEL 212 - 30

Brink, W.C.J, and some Ore Deposits in South Africa. GeoL Soc. S. Afr., 67.

Toens, P.D. (1964) 1. Geol. Soc.S.Afr. Spec. Publ. Winter, H. de la R. The Stratigraphy of the Venter sdorp Winter, H. de la R. A Revised Composite Radioactivity (1965) System in the Bothaville District (1964) Log of the Upper Division of the Witwatei srand System, Sand River and Adjoining Areas (Unpubl. Ph.D. Area, Orange Free State. Trans. Thesis). JÍ.".

J. ISBN O 86960 316 7

I