1. SANDSTONE-HOSTED URANIUM
DEPOSITS, SOUTH AFRICA: A REVIEW
AO Kenan and M Tsanwani
Council for Geoscience, Pretoria, South Africa
International Atomic Energy Agency
Technical Meeting on Origin of sandstone uranium deposits: A global perspective
Vienna, Austria
29 May – 1 June, 2012

2. CONTENTS
• Introduction
• Historical background
• Geological setting
• Mineralization
• Metallogenesis
• Ore body characteristics
• Recent developments
• Conclusion

3. INTRODUCTION
• Sandstones of
the Adelaide
Subgroup
(Beaufort
Group).
• SW of the Karoo
basin
• Extends from NE
of Western
Cape, across SE
of Northern
Cape, and into
Free State.
• Stretches east to
CE
V IN Cradock in the
P RO Eastern Cape
M
N
IU includes smaller
RA satellite area
U
O located to the
RO
KA ENE of
Bloemfontein.

4. HISTORICAL BACKGROUND
 Radioactivity first reported in 1964.
 Presence of uranium first noted by Southern Oil Exploration Corporation
in1967.
 Union Carbide Exploration Corporation begun exploration in 1970.
 First resource estimates in 1972.
 Large-scale exploration initiated in 1973.

5. HISTORICAL BACKGROUND (Cont)
Discovery sequence:
 1972 – Rietkuil ~ 300 t U
 1974 – Vindragersfontein ~ 600 t U { 10 COMPANIES}
 1975 – Rystkuil ~ 900 t U {11 COMPANIES}
 1977 – Tierhok, Suurkop, Eselfontein, Sandgat, Quaggasfontein
~ 10 200 t U {13 COMPANIES}
 1978 – Banksgaten, Bok Se Plaas, Swartkop, Blaauwhoogte
~ 12 700 t U
 1979 – Kareepoort, De Pannen, Rondom, Plathoek, Dassieskloof, DR 3,
GT-7, Agtersteland ~ 22 900 t U
 1980 – Niewuwveldsfontein, Combrinckskraal
~ 23 200 t U
 1981 – Haanekuil, Davidskol
~ 27 400 t U {4 COMPANIES}
 By 1985, ~ resource 28 996 t U
 By 1986, prospecting ceased with a total of 31 211 t U estimated.

6. GEOLOGICAL SETTING
Lithostratigraphy:
 Beaufort Group: Tarkastad & Adelaide Subgroups.
 Karoo Uranium Province lies the Late Permian Adelaide Subgroup (except
satellite area, Late Triassic Elliot and Molteno Formations).
 Adelaide Subgroup: Teekloof & Abrahamskraal Formations.
 Poortjie Member (Teekloof Formation) holds more than 80% of the known
uranium in the basin.
 Mudstone, sandstone & mudstone-pebble conglomerate.
 Lithofacies in the sandstone packages:
 Horizontally-bedded & low-angle stratified sandstone (fine to very fine-
grained sandstone).
 Massive sandstone (fine to very fine-grained sandstone).
 Trough cross-bedded, planar cross-bedded and ripple cross-bedded
sandstones. Also mudstone-pebble conglomerate, siltstone &
mudstone.
 Sandstone packages were deposited by perennial rivers that were
episodically interrupted by ephemeral floods that followed tract of
straight and braided channels.

7. GEOLOGICAL SETTING (Cont)

8. GEOLOGICAL SETTING (Cont)
Tectonic setting:
 Accumulated in a retro-arc foreland basin to the north of the fold-thrust belt
(Cape Fold Belt) which was the major source area for the fluvial sediments.
 Beaufort Group sediments deposited on a vast alluvial plain;
 Abundant mudrock represents flood-plain & lacustrine deposits
 Sandstone represents fluvial channel deposits.
 Fluvial systems (palaeochannels) in the Beaufort Group (in the Karoo
Uranium Province):
 NE FLUVIAL SYSTEM: at least 7 sandstone packages were deposited
by the NE fluvial system, including the extensive Poortjie and Oukloof
Members.
 NNW FLUVIAL SYSTEM: only a small segment of the NNW fluvial
system is present in the Karoo Uranium Province. Five sandstone
packages including Katberg Formation.
 ESE FLUVIAL SYSTEM: only two sandstone packages.

9. GEOLOGICAL SETTING (Cont)

10. MINERALIZATION
The primary uranium-bearing minerals: coffinite and uraninite.
The uranium-bearing sandstones are fine-grained and consists fragments of
quartz & feldspar.
Quartz averages between 35 and 40% in the Adelaide Subgroup while feldspar
(albite and orthoclase) comprise up to 50% of the sandstone.
Two types of uranium mineralisation have been proposed:
Laminated-sandstone-hosted mineralization, also known as carbon ore
Carbonate-cemented sandstone-hosted mineralization
Laminated-sandstone-hosted mineralization:
Clast-supported fabric & occurs in the basal part of the sandstone body.
Contains high values of both U & Mo.
Sandstone that is devoid of mineralization is normally free of organic material.
 Ore predominates in the fine-grained, horizontally bedded and low angle
stratified sandstones (effective permeability).

11. MINERALIZATION (Cont)
Carbonate-cemented sandstone-hosted mineralization:
 Matric-supported fabric & occurs at both the basal part and elevated part of
the sandstone body.
 Hosted by pods and lenses of fine-grained sandstone cemented by
carbonate.
 Outcrops are characterized by a weathered, greyish brown to dark greyish
brown crust known as “koffieklip” which is caused by encrustation of iron
and manganese oxides on the outer surface of the sandstone.
 Fresh rock is grey to dark grey in colour and comprises both massive and
horizontally bedded or low-angle stratified, fine-grained sandstone.
 Mo values significantly lower than those found in the laminated-sandstone
ore.
 Carbonaceous plant debris is common.

13. METALLOGENESIS
• Metallogenesis of uranium: source, transport & precipitation.
 Source of uranium
 Most common proposed sources of U by various workers include;
 granites of the Cape Granite Suite,
 pegmatites and granites of the Namaqua-Natal Metamorphic Belt,
&
 volcanic detritus/ashes (e.g., magmatic arc).
 Moon (1974): U-Pb age of 1050 Ma on detrital zircon from Beaufort
Group (corresponds to Namaqua-Natal Metamorphic Belt).
 Duane et al. (1989): 1063 Ma; and between 466 to 556 Ma (correspond
to Namaqua-Natal Metamorphic Belt & Cape Granite Suite).

14. METALLOGENESIS
 Transport of U from source
 Inflowing rivers transported uranium from source either in solution
and/or adsorbed by clay minerals & organic matter.
 Volcanic detritus were:
 wind-blown into basin or
 wind-blown to Cape Fold Belt & fluvial-transported into basin, or
 fluvial-transported into basin straight from source (magmatic arc).
 Mineralizing fluids
 Most workers agree that mineralizing fluid was low temperature & non-
brinal. Permeability of the host rock was important.
 Pretorius (1985): obtained δ18O value of -19.4‰ (fresh water component) &
salinity of 0.28 wt%NaCl (non-brinal).

15. METALLOGENESIS (Cont)
According to Cole & Wipplinger (2001):
 Mineralizing fluids for carbonate-cemented sandstone U mineralization
 Local derivations from both sandstone & mudstone, slightly oxidizing,
uranyl carbonate complexes, low temp & alkaline.
 Mineralizing fluids for laminated-sandstone-hosted U mineralization
 Local derivations from both sandstone & mudstone, oxidizing or slightly
oxidizing, low temp, acidic, with complexes of sulphate, chloride,
hydroxide, or UO2(HPO4)2-

16. METALLOGENESIS (Cont)
Precipitation of uranium
Uranium precipitated upon encountering a reductant, i.e., carbonaceous
matter and/or H2S.
Presence of carbonaceous materials, as well as H2S, were crucial for
precipitation of uranium:
 Pretorius (1985); Cole & Wipplinger (2001); etc., indicated the
association of uranium with carbonaceous material. E.g., uranium
mineral replacing phytoclast.
 Presence of framboidal pyrites, and other sulphides, indicate the
importance of H2S in the precipitation of uranium.

17. METALLOGENESIS (Cont)
Cole & Wipplinger (2001)
Carbonate-cemented sandstone-hosted U mineralization predominant in basal
parts of sandstone body and, in some cases, above base (up to 18m):
– Solutions probably flowed laterally along palaeochannel, as well as
vertically due to capillary rise or downward movement in vadose zone.
– Precipitation then occurred just below the palaeowater-table, where
carbonaceous matter would have been preserved.
– Paucity of Mo in the basal carbonate ore may be due to alkaline solution
responsible for carbonate-rich ore would not have been favourable for
– adsorption of Mo by organic matter.
 Mineralization occurred shortly after deposition (early diagenesis):
(Turner, 1985; Le Roux, 1993; Cole and Wipplinger, 2001)
 Presence of crumpled flakes of molybdenite (pressure-deformed) in
the sandstone; and
 Uranium minerals filling undeformed cell structures in fossilised
wood fragments.

18. METALLOGENESIS (Cont)
m7
Up7
p0
0

19. METALLOGENESIS (Cont)
• REMOBILIZATION OF URANIUM
 There is no or limited post-diagenetic remobilization of uranium
mineralization in the Karoo Uranium Province
 The fine-grained to very fine-grained sandstone of the Adelaide
Subgroup in the south-western Karoo basin would become almost
impermeable for any remobilization to take place, more so with
carbonate ore.
 However, post-diagenetic uranium mobilization have been reported in
the satellite body (Molteno & Elliot Formations) contributed by their
relatively coarser-grained sandstones than the sandstone in the south-
western Karoo basin (principal mineral is beta-uranophane).

20. METALLOGENESIS (Cont)
 Extensive oxidation of the mineralized sandstone especially along fracture
zones, as a result of Recent exposure and weathering is evident in the
south-western Karoo basin.
 The presence of numerous secondary hexavalent uranium minerals
(uranophane, beta-uranophane, carnotite, etc) suggests they were
formed by oxidation of the primary tetravalent minerals (coffinite &
uraninite) in highly oxygenated ground waters.
 In areas of this extensive Recent oxidation, sandstones are bleached
due to the action of sulphuric acid. Limonite is also abundant.
 There is a limited redistribution, in terms of distance, of the secondary U
minerals away from the primary ore.

21. ORE BODY CHARACTERISTICS
• Ore bodies are tabular, peneconcordant, and lenticular.
• The U deposits in the Karoo are small and relatively low in grade averaging
1280 ppm U3O8 vertically along a width of one metre. The average thickness
is generally about 0.9 m.
• Only the six large deposits about (or above) 3 million tons of ore (including
Ryst Kuil, Riet Kuil, DR-3 & Mooifontein).
• Most deposits contain between 0.5 and 1 million tons of ore.

22. RECENT DEVELOPMENTS
Following the increase of uranium price, uranium interest was renewed in the
Karoo basin in the year 2004. By the end of the year 2005, several exploration
were active in the area.
From 2005 to 2010, more than 35 prospecting licences were issued to more
than 25 exploration companies (including junior companies).
Exploration included:
Re-evaluating the historical drill holes,
High-resolution radiometric survey,
Infill and additional drilling,
Pre-feasibility and feasibility studies.

23. RECENT DEVELOPMENTS

24. RECENT DEVELOPMENTS
There are small number of exploration companies currently conducting
exploration in the Karoo Uranium Province.
Since 2011, Peninsula Energy has drilled about 210 holes including both RC
and diamond drilling. The drilling, coupled with interpretations of about 167
historical drill holes, has resulted in good uranium intersections. Further drilling
is on-going.
Paddy’s Pad 1183 (Pty) Ltd and Batla Minerals SA hold several prospecting
rights for the Mooifontein Uranium Deposit, 80 km south of Bloemfontein.

25. CONCLUSION
• Largest & richest ores occur in thickest sandstones (e.g., Poortjie Member).
• Thin sheets of ore may mean open-cast would have high stripping ratios
and underground mining would have limited stope width.
• Sandstone-hosted uranium deposits in SA, once they become operational,
will represent the first primary uranium extraction in the country.
• With Eskom announcing plan to increase its nuclear generation capacity,
the Karoo Uranium Province is envisaged to be one of major contributors of
uranium towards the planned expansion.

26. THANK YOU