(GEA748| June 1987 THE URANIUM POTENTIAL OF THE BUSHVELD IGNEOUS COMPLEX A CRITICAL REAPPRAISAL Investigators: MAG Andreoli R J Hart H J Brynard F A G M Camisani-Calzolari ATOMIC ENERGY CORPORATION OF SOUTH AFRICA LIMITED PRETORIA THIS DOCUMENT MAY NOT BE COPIED IN ANY WAY WHATSOEVER PER 158 GEA 748 ATOMIC ENERGY CORPORATION/UNIVERSITY OF PRETORIA WORKING GROUP ON URANIUM IN THE BUSHVELD COMPLEX Progress Report No. 4 THE URANIUM POTENTIAL OF THE BUSHVELD IGNEOUS COMPLEX A CRITICAL REAPPRAISAL Investigators: MAG Andreoli R J Hart H J Beynard F A G M Camisani-Calzolari POSTAL ADDRESS: Department of Geotechnology P 0 Box 582 PELINDABA PRETORIA June 1987 0001 ISBN 0 86960 848 7 PER-158 GEA-748 ATOMIC ENERGY CORPORATION/UNIVERSITY OF PRETORIA WORKING GROUP ON URANIUM IN THE BUSHVELD COMPLEX Progress Report No. 4 THE URANIUM POTENTIAL OF THE BUSHVELD IGNEOUS COMPLEX A CRITICAL REAPPRAISAL Investigators: MAG Andreoli R J Hart H J Brynard F A G M Camisani-Calzolari DEPARTMENT OF GEOTECHNOLOGY ATOMIC ENERGY CORPORATION OF SOUTH AFRICA LIMITED P 0 BOX 582, PRETORIA (0001) June 1987 ISBN 086960 848 7 PER-158- i - CONTENTS Page Samevatting/Abstract vi LIST OF ABBREVIATIONS ii-iii LIST OF TABLES iv LIST OF FIGURES v 1 INTRODUCTION 1 2 ON THE POSSIBILITY OF A GIANT OLYMPIC DAM-TYPE DEPOSIT JN THE BUSHVELD COMPLEX 3 3 THE WATERBERG COVER: A TARGET FOR UNCOMFORMITY-TYPE DEPOSITS? 19 4 ADDITIONAL TARGETS FOR URANIUM EXPLORATION 25 5 DISCUSSION & RECOMMENDATIONS 27 6 ACKNOWLEDGEMENTS 30 7 REFERENCES 30 LIST OP IBBEKVIAÏIOIIS All allanite amp amphibole apa apatite bar barite bas bastnaesite bor bornite bra brannerite car carbonate cat carnotite cha chalcocite chl chlorite cof coffinite cpy chalcopyrite cov covellite dav davidite dig digenite ena enargite fer ferberite flo florencite flu fluorspar gal galena gum gummite hem hematite mi>: microcline mon monazite mt magnetite mol molybdenite mus muscovite Raf albite-oligoclase phi phlogopite pit pitchblende pyr py/ite pyt pyrrhotite pyx pyroxene PER-158- iii - LIST OF ABBREVIATIONS (continued) qtz quartz rut rutile sea scapolite sen scheelite ser sericite sid siderite sil silver smaltite sph sphene spl sphalerite tor torbenite tou tourmaline ura uraninite urf uranofane xen xenotime zir zircon F.apa fluoroapatite F.phl fluorite-bearing phlogopite Fe.rut ilmeno-rutile REE.F.car fluorocarbonate with Rare Earths Elements (REE) Nb.rut niobian rutile Th.bra thorian brannerite Ti.hem ilmeno-hematite Ti.mt titanomagnetite V.tuch uranium-rich hydrocarbons gel (tucholite) V.mt vanadian magnetite LILE Large Ion Lithophile Elements (e.g. U, Th, REE, K, Rb, etc.) REE Rare Earth Elements t tens (metric) 9 6a 10 years PER-158- iv - LIST OP TABLES Page TABLE 1 Uranium Deposits in the pre-mesozoic basement of South Australia TABLE 2 South Australia provisional copper inventory 10 TABLE 3 South Australia provisional uranium inventory 10 TABLE 4 Frovisional uranium inventory of the Bushveld Igneous Complex and Northern Transvaal, South Africa 11 TABLE 5 K-, Ha-rich granitoids of South Australia 12 TABLE 6 K-rich rhyolites (1-3) and granitoids (4-8) of the Bushveld Complex 14 TABLE 7 Calculation of U,0o reserves in the Vergenoeg Pipe 18 TABLE 8 Comparative geochronology of uncomformity related uranium deposits 21 TABLE 9 Comparati/e geology of uncomformity-type deposits and central N Transvaal 23 PER-15*- v - LIST OF FIGURES Page Figure 1 Distribution of principal uranium occurrences in S. Australia listed in Table 1 8 Figure 2 Distribution of uranium occurrences in the Bushveld Complex and adjacent areas in relation to regional geology and relevant metallogenic provinces 9 PER-158- vi - ABSTRACT A review of published literature supported by field observations on the uranium potential of the Bushveld Complex indicates that this geological region may host deposits with reserves in the range of a few.thousand tons U.O . The possibility that the Bushveld Complex or its cover rocks hosts, or has ever hosted in the past, giant uranium deposits such as those of Olympic Dam, Key Lake, Jabiluka or Rossing is considered to be unlikely. The potential for volcanogenic, caldera-type deposits in the Rooiberg Felsites remains at present untested. Recommendations for research currently sponsored by the AEC at the University of Pretoria are presented. PER-158- 1 - 1 IHTKODOCTIOH Since 1983 the Atomic Energy Corporation has actively supported scientific investigations on the uranium potential of the Bushveld Complex with the aim to locate target areas for a major uranium deposit outside the Witwatersrand Basin. These studies were conducted by the Institute for Geological Research on the Bushveld Complex at Pretoria University in conjunction with visiting experts from the USA (E S Cheney) and the UK (P R Simpson). These authors - in view of the time constraints on thtir stay in SAuth Africa - concentrated on a preliminary assessment of the available published and unpublished material which was available at the end of 1985. Simpson & Hurley's (1986) study is largely of a geochemical nature and predicts that yet undisclosed uranium mineralizations probably occur (besides the Karoo sequence) at the base of the Waterberg Group or as hydro thermal vein deposits in areas with the following favourable features: (a) Fertile granite source (uranium-bearing proto-ore) (b) High he&c flow to drive the hydrothermal circulation (c) Availability of fluids in the thermal aureole (transport of U) (d) Tectonically produced channelways (faults/fractures) (e) Suitable geological traps to precipitate uranium Simpson & Hurley (1986) further identified four potential lineaments which transect the Bushveld and host the largest proportions of uranium (and tin-fluorspar) mineralizations. These lineaments would appear to provide a preliminary exploration target for uranium. The analysis by Cheney (1986) supports Simpson's conclusions, but limits the size of the potential hydrothermal mineralizations, which he considers to be very small (e.g. Albert Silver Mine) in size. While emph-sizing the need for accurate radiometric mapping and PER-158- 2 - regional hydrogeochemical grids oyer the Bushveld, Cheney (op., cit.) formulates five additional potential exploration targets (listed here in approximate order of decreasing priority): (i) Giant Olympic Dan U deposits in the coarse, oxidized sedimentary interbeds within the Rooiberg Formation (e.g. Cheney & Twist, 1986), or - more likely - in the sediments of the Vaterberg group/Loskop Formation (ii) Giant unconformity/vein-type deposits (e.g. Canada, Australia) at the base of the Waterberg sedimentary sequences (iii) Volcanogenic (e.g. caldera-related) uranium ores in the Rooiberg felsite (iv) Chemical precipitation of uranium that has been leachea froc acid igneous rocks such as felsite and granite (v) Nigmatitic-pegmatitic (Rossing-type) zones of uranium enrichment caused by the Rustenburg Layered Suite in the roof/floor rocks (e.g. Transvaal sediments, Rooiberg felsite) A different approach to the problem of the uranium in the Bushveld was proposed by Twist (1986) on his return from a visit to the world-famous Olympic Dam deposit. From the available data Twist modifies Cheney's (fip.. £i£.) interpretation and suggests that an equivalent of the Olympic Dam mineralization should not be searched for in coarse-grained (oxidized) volcaniclastic sequences in areas of graben, but rather in the more evolved granitic terranes. In accordance with this interpretation, the fluorspar mine of Vergenoeg (Crocker, 1985) is cited as a possible Olympic Dam equivalent. To date no written technical discussion or comment has yet been produced by the AEC geolqgical staff on these reports. The authors PER-158- 3 - intend therefore to analyse critically the above-mentioned prospecting targets to assist the planning of current, short-term research activities at the University of Pretoria. In this investigation the authors studied in detail the available scientific literature on the Australia and Canadian U mineralizations. In addition, field visits to uranium occurrences in the Rooiberg, Pietersburg and Bronkhorstspruit areas, led by Dr F Walraven, Messrs I Crocker and C Callahan (GSO), provided ample opportunity for discussion and brain-storming for all involved. Some limited petrographical work on selected samples has also been conducted. 2 OH THE POSSIBILITY OF A GIANT OLYMPIC DAM-TYPE DEPOSIT IH THE BUSHVELD COMPLEX Using data by Roberts & Hudson (1983), Cheney (1986) suggested that the sedimentary intervals within the Rooiberg group felsites could host an Olympic Dam deposit, for the following reasons: (a) The Rooiberg Group was deposited immediately before the atmosphere became oxidizing or shortly after (b) Fe, Pb, Zn sulphides have been prospected for in Rooiberg volcanics and agglomerates (c) The Selousrivier Volcanics have a sulphidic/hematitic character resembling that of the host rocks of the Olympic Dam deposit In Cheney's model U leached from the Bushveld granites could have been fixed within those sulphide-bearing sedimentary horizons because of (a) above. A new interpretation of the Olympic Dam deposit was subsequently proposed by Twist (1986). This was based on direct underground observations, and on broad similarities in setting, geochemistry, age and lithology between the Olympic Dam deposit and the Bushveld Igneous Complex. PER-158- 4 - Tables 1-4 and Figs. 1 and 2 indicate that there are appreciable and critical differences between this giant Australian deposit and the proposed South African equivalent. The Olympic