Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

Chapter 6 Provenance of Detrital Zircons from the Wolkberg Group and Transvaal Supergroup

6.1 Introduction The Wolkberg Group and Transvaal Supergroup (Fig 6.1) are sequences that preserve a ca. 600Ma long, almost continuous record of late Archean (ca. 2.7Ga) to Paleoproterozoic (ca. 2.1Ga) sedimentation (Fig 6.2) on the Kaapvaal Craton.

In an attempt to trace source populations of detrital zircons for the Wolkberg Group and Transvaal Supergroup, representative samples of zircons from several prominent quartzite successions were analysed by SHRIMP (sensitive high resolution ion microprobe) in order to obtain 207Pb/206Pb radiometric ages. Based on these results two

94 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

95 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup important geological issues in South African geology are to be addressed in this chapter namely: a) Whether the Wolkberg and correlative Buffelsfontein Group belong to the Transvaal Supergroup and if the sediments could have been sourced from the Limpopo Metamorphic Belt. b) What are the ages of source areas (provenance ages) of different unconformity- bounded sequences in the Pretoria Group of the Transvaal Supergroup?

Radiometric ages of between 2670 and 2600Ma (Gutzmer and Beukes, 1998; Barton et al., 1995) suggest that deposition of the Wolkberg Group and Schmidtsdrif Subgroup of the Transvaal Supergroup in Griqualand West (Fig 6.1) occurred concurrently with granulite facies metamorphism in the Limpopo metamorphic complex (Fig 6.2). It is widely accepted that granulite facies metamorphism in the Limpopo Mobile Belt occurred at ca. 2660Ma (Barton and Van Reenen, 1992). However, a period of ca. 2000Ma granulite facies metamorphism has also been identified in the Limpopo Belt (Holzer et al., 1998). It therefore remains uncertain when the Zimbabwe and Kaapvaal cratons became connected. Many studies of the Limpopo Belt have identified magmatic and metamorphic zircon with radiometric ages between 2.7-2.6Ga (i.e. McCourt and Armstrong, 1998; Kröner et al., 1999; Barton et al., 1992; Barton et al., 1994; Kreissig et al., 2001). If the collision between the Kaapvaal and Zimbabwe cratons occurred at ca. 2.7-2.6Ga, then one would expect to find a large population of 2.7-2.6Ga zircons in the Wolkberg Group. This is one of the hypotheses to be tested in this chapter of the thesis.

Furthermore, the recently proposed revised correlation for the Transvaal Supergroup in the Griqualand West and Transvaal areas (Beukes et al., 2002) can be tested. The correlation subdivides the Transvaal Supergroup into six sequence stratigraphic units (Fig 6.2), based on the presence of major unconformities in the succession (Coetzee, 2001, Beukes et al., 2002). Amongst other consequences, the Dwaal Heuvel Formation of the Pretoria Group is now regarded laterally equivalent to the beds of the Gamagara/Mapedi Formation in Griqualand West (Fig 6.2)(Beukes et al., 2002). Measuring the radiometric ages of detrital zircons within each of the unconformity-bounded sequences, may help

96 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup understand the ages of rocks that sourced the sequences and also perhaps place age constraints on the boundaries of sequences. In addition, the variation in detrital zircon populations may indirectly provide some information about the plate tectonic history of the Kaapvaal craton during the deposition of the Wolkberg and Transvaal successions. In other words, data may provide some insights into the tectono-sedimentary events that led to formation of the unconformity-bounded sequences.

6.2 Stratigraphic Setting 6.2.1 Wolkberg Group and Correlatives The Wolkberg Group is an up to 2000m thick sedimentary succession (Button, 1973, Bosch, 1992), that crops out in the Limpopo Province, South Africa (Figs 6.1 and 6.3). It consists of alternating feldspathic quartzites and argillaceous sedimentary rocks, coarse quartz arenites, some conglomerates, basaltic lava and minor stromatolitic carbonate beds (Fig 6.3)(Button, 1973, Bosch 1992). It is correlated with the Buffelsfontein Group of the Thabazimbi area (Fig 6.1)(Tyler, 1979). The Wolkberg Group comprises from the base upwards the Sekororo, Abel Erasmus, Schelem, Selati, Mabin and Sadowa Formations (Fig 6.3)(Button, 1973 and Bosch, 1992). The basal Sekororo Formation overlies Archean basement granite and greenstone of the Kaapvaal craton with an erosional unconformity (Button, 1973). Barton et al. (1995) obtained an age of 2664±0.7Ma for rhyolitic lava in the Witfonteinrand Formation of the Buffelsfontein Group that is thought to be correlative to the Abel Erasmus lavas (Fig 6.3)(Tyler, 1979). The basement granites and greenstone belts to the Wolkberg Group have radiometric ages that vary from 2.78 (Henderson et al., 2000) to greater than 3Ga (De Wit et al., 1992; De Wit et al., 1993; Brandl and De Wit, 1997; De Wit and Ashwal, 1997; Armstrong et al., 1990; Nelson et al., 1999).

It appears, as if the Kaapvaal craton was mildly flexed prior to the deposition of the Wolkberg Group (Button, 1973; Beukes, 1983). The formations of the Wolkberg Group thicken in pre-Transvaal trough structures, and thin and pinch out against pre-Wolkberg basement domes (Button, 1973). The Wolkberg Group thickens towards the northeastern margin of the present day Kaapvaal craton, suggesting that it covered a much larger area

97 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

98 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup during its deposition. Paleocurrent directions for the Wolkberg Group are predominantly from the northeast and north (Button, 1973; Bosch, 1992).

The Wolkberg and Buffelsfontein Groups could perhaps be correlated with the Schmidtsdrif Group in Griqualand West. This correlation is based on recent zircon ages of 2669±5Ma and 2650±8Ma from tuffaceous beds within the Schmidtsdrif Subgroup (Fig 6.3)(Gutzmer and Beukes, 1998). These ages are similar to the age of the Buffelsfontein Group rhyolite obtained by Barton et al. (1995). It therefore appears as if the Wolkberg Group and Schmidtsdrif Subgroup are time equivalent successions, deposited simultaneously on different parts of the Kaapvaal craton (Fig 6.3).

The Schmidtsdrif Subgroup consists predominantly of quartzite, shale, carbonate and some lava, in contrast to the predominantly coarse-grained siliciclastic rocks of the Wolkberg Group (Fig 6.3). The differences in lithologies could indicate that the Wolkberg Group and Schmidtsdrif Subgroup were deposited in two subbasins separated by the Ganyesa dome (Fig 6.3). Only after the deposition of the Motiton Member in Griqualand West did these two basins become connected. The Motiton Member is suggested here to be equivalent to the Black Reef Formation that marks the onset of Transvaal Supergroup deposition at approximately 2590Ma (Fig 6.3).

Previously, it was suggested that the Wolkberg Group is equivalent to the Ventersdorp Supergroup (Eriksson et al., 1993). However, the basal Vryburg Formation of the Schmidtsdrif Group overlies the upper Allanridge Formation of the Ventersdorp Supergroup with a marked erosional unconformity (Fig 6.3). It is therefore unlikely that the Wolkberg Group is equivalent to the Ventersdorp Supergroup. A SHRIMP 207Pb/206Pb zircon age of 2709±4Ma (Armstrong et al., 1991) has been obtained for quartz porphyry of the Makwassie Formation of the Ventersdorp Supergroup (Winter, 1976) and is thus markedly older than the Wolkberg Group.

99 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

6.2.2 Transvaal Supergroup 6.2.2.1 Chuniespoort and Ghaap Groups The Wolkberg Group is unconformably overlain by the Black Reef Formation, which marks the base of the Transvaal Supergroup in the Transvaal area and southeastern Botswana (Fig 6.3)(Button, 1973). Given new geochrological restrictions the most likely correlative to the Black Reef quartzite in the Northern Cape Province becomes the quartzite of the Motiton Member at the top of the Monteville Formation (Figs 6.2 and 6.3)(Beukes, 1978). This is a very different concept from the commonly accepted idea that the Black Reef quartzite in the Transvaal area corresponds to the base of the Vryburg Formation in Griqualand West (Beukes et al., 2002). Radiometric 207Pb/206Pb ages of 2602±14Ma (Gutzmer and Beukes, 1998) obtained for the Monteville Formation (top of the Schmidtsdrif Group) and 2550±3 (Walraven and Martini, 1995) and 2583±5 (Martin et al., 1998) for the Oak Tree Formation (base of the Malmani Subgroup) suggest that the deposition of the Black Reef Formation in the Transvaal area commenced at ca. 2590Ma (Figs 6.3 and 6.4A).

According to the new correlation, deposition of the Black Reef Formation of the Transvaal Supergroup in the Transvaal area commenced at the same time as the onset of the deposition of the Motiton Member on top of the Monteville Formation, in Griqualand West. This contact represents a 2nd order sequence boundary in the Transvaal Supergroup (Fig 6.2)(Coetzee, 2001). Present day outcrop of the Transvaal Supergroup suggests that the erosional surface along the sequence boundary covered the whole of the Kaapvaal Craton (Fig 6.4A).

Lithostratigraphic correlation is unequivocal between the Ghaap Group in Griqualand West (Beukes, 1978) and the Chuniespoort Group (Obbes, 1995) in the Transvaal area. Stromatolitic dolostone units and BIF can be correlated almost bed for bed (Fig 6.2), suggesting the presence of a very uniform, shallow marine shelf depositional environment at this time on the Kaapvaal craton. Present day outcrops (Fig 6.1) suggest that the carbonates and iron formation of the Transvaal Supergroup once covered the

100 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

101 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup entire Kaapvaal craton (Beukes, 1983). The chemical sedimentary sequences of the Chuniespoort Group of the Transvaal Supergroup thicken towards the present day northeastern margin of the Kaapvaal craton (Button, 1973). An up to 60m thick quartzite unit within the Malmani dolomite (Button, 1973) suggests that there was probably exposed continent towards the northeast of the present day Kaapvaal craton during the deposition of these chemical sedimentary sequences. A change in carbonate facies from shelve to basinal (Beukes, 1978) suggests that there may have been open ocean located towards the west of the present Kaapvaal Craton. Deposition of shelf carbonates commenced at ca. 2590Ma, marked by the Black Reef/Motiton quartzite (Figs 6.2 and 6.4B). Ages in the range of 2480-2432Ma have been obtained for several tuffaceous units in the Asbesheuwels Subgroup and Penge Iron Formation (Fig 6.2)(Compston in Trendall et al., 1990; Armstrong in Martin et al., 1998; Trendall (unpublished data) in Nelson et al., 1999; Gutzmer and Beukes, 1998). However, the Koegas Subgroup overlying the Asbesheuwels Subgroup that consists mosly of banded iron formation, shale and carbonate, with at least one prominent erosional unconformity in the west of the Kaapvaal craton may preserve iron formation that is as young as 2400Ma (Fig 6.2). The importance of these ages is that deposition of chemical sediments in the lower part of the Transvaal Supergroup corresponds to the time when granulite facies metamorphism occurred within the Limpopo belt (Barton and Van Reenen, 1992). Granulite facies metamorphism during this period is defined by the mineral assemblage garnet, sillimanite, cordierite and quartz (Stevens and Van Reenen, 1992). Granulites occurring in thrust sheets are complexly folded (Smit and Van Reenen, 1997). Deformation and metamorphism is thought to have occurred during continental collision between the Zimbabwe and Kaapvaal cratons (Van Reenen et al., 1987). This collision is thought to have caused crustal thickening similar to the currently occurring crustal thickening in the Himalayas (Van Reenen et al., 1987). It is thought that erosion and tectonic erosion contributed to rapid isothermal uplift (Van Reenen et al., 1987). This poses a problem, as the sediments eroded from the Limpopo Belt during that time would have caused pronounced siliciclastic and not chemical sedimentation.

102 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

Overlying the Asbesheuwels Subgroup, the lower part of the Koegas Subgroup may correlate with the Tongwane Formation that overlies the Penge Iron Formation in the northeastern part of the Kaapvaal Craton (Fig 6.2). The top of the Koegas Subgroup (Rooinekke Formation) preserves the youngest stratigraphy known from the lower part of the Transvaal Supergroup, i.e., the Ghaap and Chuniespoort Groups prior to deposition of the overlying Pretoria and Postmasburg Groups (Figs 6.2 and 6.4B).

6.2.2.2 Pretoria and Postmasburg Groups With regards to the Pretoria and Postmasburg Groups in the Transvaal area the erosional surface at the base of the Duitschland Formation and Pretoria Group is thought to represent a second order sequence boundary caused by a regression (Fig 6.2)(Coetzee, 2001). A whole rock Re-Os age of 2320Ma (Hannah et al., 2002) has been obtained for shale from the lower Timeball Hill Formation that directly overlies the Duitschland Formation in the Transvaal area. In Griqualand West, the unconformity below the Makganyene Formation eroded into ca. 2260-2400Ma stratigraphy (Fig 6.2). Combined, the erosional surfaces below the Duitschland and Makganyene Formations appears to be responsible for the loss of approximately 80Ma of depositional history, i.e. the period between 2400-2320Ma in the Transvaal succession (Fig 6.2).

The erosional surface at the base of the Duitschland Formation (Coetzee, 2001) does not erode through the carbonate rocks of the Ghaap and Chuniespoort Groups of the Transvaal Supergroup anywhere in the preserved basin that covered the entire Kaapvaal craton prior to the deposition of the Duitschland Formation. It is thus quite possible that none of the sediments in the Duitschland Formation was derived from a source area on the Kaapvaal craton. The lower part of the Duitschland Formation is characterized by the deposition of mostly fine-grained shales, carbonates and diamictite (Figs 6.2 and 6.4B).

The base of the upper part of the Duitschland Formation is marked by a 50m thick conglomerate in the Duitschland area that overlies a 3rd order sequence stratigraphic boundary (Figs 6.2 and 6.4C)(Coetzee, 2001). The greater thickness of Duitschland Formation sedimentary rocks in the northeastern part of the present day Kaapvaal Craton

103 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

104 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup and their thinning and fining towards the southwest (Fig 6.5B)(Coetzee, 2001) suggests that the source area for these rocks was located towards the northeast of the present day Kaapvaal craton. During the deposition of the upper part of the Duitschland Formation, the depositional environment changed from one of chemical sedimentary precipitation to one of siliciclastic deposition.

According to Coetzee (2001), a 3rd order sequence stratigraphic boundary forms the base of the Timeball Hill Formation (Fig 6.2). This sequence boundary is followed by a transgression and the deposition of the lower shales of the Timeball Hill Formation (Figs 6.2 and 6.4C). The quartzite of the Gatsrand Member marks a regression within the Timeball Hill sequence (Coetzee, 2001). The Timeball Hill Formation thickens towards the northeastern and northern margins of the present day Kaapvaal craton (Fig 6.5C). This suggests that source areas for the Timeball Hill sedimentary rocks were located also north and northeast of the present day Kaapvaal craton, similar to that of the Duitschland Formation (Fig 6.5B). During the deposition of the Timeball Hill Formation, the Kaapvaal craton was covered not only by the chemical sedimentary successions of the Ghaap and Chuniespoort Groups, but also the siliciclastic sequence of the Duitschland Formation. It may, therefore, be suggested that none of the sediment in the Timeball Hill Formation was derived from basement rocks that are presently exposed on the Kaapvaal craton.

The Timeball Hill Formation is separated from the overlying Boshoek conglomerate by a third order sequence boundary, which developed during a time of regression (Fig 6.2)(Coetzee, 2001). The most probable correlative for the erosional surface at the base of the Boshoek Formation in Griqualand West is the erosional unconformity below the Makganyene diamictite (Figs 6.2 and 6.4D). Makganyene/Boshoek erosion was succeeded by sea level rise reflected by the deposition of the Boshoek Formation and Makganyene Formations. Deposition of the Boshoek and Makganyene Formations ended with outflow of the Hekpoort/Ongeluk lava (Figs 6.2 and 6.4D).

105 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

Lavas of the Hekpoort cover an area of at least 500 000km2 in the Transvaal, whereas the Ongeluk lava covers an area of at least 300 000km2 in Griqualand West. These lavas mark a major volcanic event in the history of the Pretoria and Postmasburg Groups of the Transvaal Supergroup. The Hekpoort Formation is characterized by massive and amygdaloidal lava flows with, flow top breccias and some volcanoclastics, typical of a volcanic unit that was terrestrially extruded (Coetzee, 2001). In the Griqualand West area, the Ongeluk Formation contains massive lava flows but also pillow lavas, hyoloclastites and jasper and chert beds that suggests that this unit was extruded subaquaeously (Gutzmer et al., 2001A). During the outflow of these lavas, open ocean was therefore probably located towards the west of the Kaapvaal craton, similar to the underlying Timeball Hill and Duitschland Formations. The volcanism of the Hekpoort and Ongeluk Formations took place at around 2230Ma (Fig 6.2)(see Chapter 3 of this thesis). Above the Ongeluk Formation in Griqualand West, iron formation and carbonates of the Hotazel and Mooidraai Formations are preserved (Figs 6.2 and 6.4D). These beds record deposition of strata in the time period between outflow of the Hekpoort and Ongeluk lavas and the development of the erosional unconformities at the base of the Gamagara and Dwaal Heuwel Formations (Figs 6.2 and 6.4D).

The Gamagara-Dwaal Heuvel erosional surface (Beukes et al., 2002) overlies various older formations of the Transvaal Supergroup along the western side of the Kaapvaal craton in Griqualand West and only the Hekpoort lava in the central part of the Kaapvaal craton in the Transvaal area (Fig 6.6A)(Beukes et al., 2002). This configuration is explained by more intense folding of Transvaal strata along the western margin of the Kaapvaal craton than in the interior of the craton during development of the pre- Gamagara/Dwaal Heuvel erosion surface (Fig 6.6A). The Gamagara-Dwaal Heuwel erosional surface is thought to represent a 3rd order sequence stratigraphic boundary within the upper Pretoria and Postmasburg Groups (Fig 6.2)(Coetzee, 2001). Coarse- grained fluvial red bed sequences of the Gamagara Formation on the western part of the Kaapvaal Craton grade into well sorted marine quartzite of the Dwaal Heuvel Formation along the eastern part of the Kaapvaal Craton (Fig 6.6B)(Van Schalkwyk and Beukes, 1986; Dorland, 1999; Beukes et al., 2002).

106 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

107 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

A similar pattern is also discernable in the Magaliesberg-Lucknow Formations, where the Lucknow Formation in the west is characterised by coarser sediments (Van Niekerk, 2004) than the Magaliesberg Formation in the east. The entire Magaliesberg/Lucknow successions does, however, appear to be of shallow marine and marine deltaic origin, suggesting that the whole of the Kaapvaal Craton was drowned once again during deposition of the Lucknow and Magaliesberg quartzite. This is unlike the time of deposition of the Dwaal Heuvel/Gamagara successions when it would appear as if the fluvial strata of the Gamagara Formation were deposited in the west at the same time as marine strata of the Dwaal Heuwel Formation were deposited in the east (Fig 6.4E). This implies that during the deposition of the upper part of the Pretoria and Postmasburg Groups, the source area for sediments was situated towards the west of the present day preserved Kaapvaal Craton and that there was open ocean towards the east of the Kaapvaal Craton. This suggests that the symmetry of the Transvaal basin changed dramatically from a basin that deepened in a westerly direction prior to the onset of deposition of the Dwaal Heuwel and Gamagara Formations to a basin that deepened in an easterly direction.

In summary, the deposition of the Wolkberg Group and Transvaal Supergroup can be described as follows:

· Ca. 2690-2590Ma Deposition of siliciclastic sediments in the Wolkberg basin and carbonates in the Schmidtsdrif basin that were apparently separated by the Ganyesa dome (Figs 6.3 and 6.4A). Possible 1st order sequence stratigraphic boundary at the base, and several internal erosional surfaces of unknown sequence stratigraphic significance present within the Wolkberg Group and Schmidtsdrif Subgroup. Influx of sediments mostly from the northeast and north (Fig 6.5A).

· Ca. 2590-2400Ma An erosional unconformity of 2nd order sequence stratigraphic significance at the base of the Black Reef Formation and Motiton Member, followed by the deposition of the

108 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup chemical sedimentary sequences of the Ghaap and Chuniespoort Groups (Figs 6.2, 6.3 and 6.4B). Several internal erosional surfaces are present within these sequences. Deposition of chemical sedimentary units may have lasted until 2340Ma, but are not preserved due to erosion at the base of the Pretoria and Postmasburg Groups.

· Ca. 2330-2260Ma The 2nd order sequence stratigraphic boundary at the base of the Duitschland Formation developed at approximately 2330Ma, which possibly removed more than 60Ma of older sedimentary deposits. This marks the base of Pretoria Group deposition (Figs 6.2, 6.4B and 6.4C). Deposition of the lower Duitschland Formation was followed by a third order erosional surface and deposition of the upper Duitschland Formation. The Duitschland Formation is overlain by a 3rd order sequence stratigraphic boundary at the base of the Timeball Hill Formation. Influx of sediment was mostly from the northeast and north (Fig 6.5C).

· Ca. 2260-2200Ma. A 3rd order sequence stratigraphic boundary is present at the base of the Boshoek and Makganyene Formations (Fig 6.2). The Makganyene Formation may have removed up to 140Ma of depositional history, similar to the Duitschland and Timeball Hill Formations on the western side of the Kaapvaal craton. Deposition of the Hekpoort/Ongeluk, Hotazel and Mooidraai Formations followed the deposition of the Makganyene and Boshoek Formations (Figs 6.2 and 6.4D).

· Ca. 2200-2070Ma A 3rd order sequence stratigraphic boundary at the base of the Gamagara/Dwaal Heuvel Formation marks the deposition of the upper Pretoria and Postmasburg Groups (Figs 6.2 and 6.4E). Presence of red beds, lava and carbonates with enriched d13C signatures in similar stratigraphic positions ensure well defined stratigraphic correlation for the upper Pretoria and Postmasburg Groups in the west and east of the Kaapvaal craton. Basin swing from northeast-southwest configuration to configuration with uplift in the west and deepening towards the east (Fig 6.6).

109 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

6.3 Detrital Zircon Studies 6.3.1 Sampling The Schelem Formation of the Wolkberg Group and the Duitschland, Timeball Hill, Hekpoort, Daspoort and Magaliesberg Formations of the Transvaal Supergroup were selected for sampling detrital zircons (Figs 6.1 and 6.2). The stratigraphic settings of these samples are described in the following paragraphs.

6.3.1.1 Schelem Formation The Schelem Formation of the Wolkberg Group overlies basaltic lava of the Abel Erasmus Formation with an erosive contact (Fig 6.3). It is composed of conglomerate, quartzite, siltstone, mudstone and minor basaltic lava (Fig 6.3)(Button, 1973, Bosch, 1992). The formation attains a thickness of more than 150m in the Selati through, but pinches out against paleohighs constituted of basement granite (Fig 6.5A)(Button, 1973). Sedimentary successions are predominantly upwards fining within the Schelem Formation (Button, 1973; Bosch, 1992). Paleocurrent directions are mainly from the north and north east (Fig 6.5A). Shales of the Selati Formation overlie the Schelem Formation with gradational contact (Fig 6.3).

Zircons for detrital zircon analyses were separated from the basal feldspathic quartzite of the Schelem Formation on the farm Rietfontein 34KS (S24°09’19.8” E29°14’32.9”) in the Button Kop area (Fig 6.7). This is the northernmost outcrop of the Schelem Formation on the Kaapvaal craton, where it is nearest to the source area as suggested by its thickness and grain size. The basal feldspathic quartzite is approximately 20-30m thick in this area. Small hand-sized samples were collected approximately every 1.5m over a stratigraphic interval of 30m in order to ensure a representative composite sample of the quartzite.

6.3.1.2 Duitschland Formation The Duitschland Formation of the Transvaal Supergroup has a thickness of about 1000m in the type area on the farm Duitschland 95KS (Figs 6.5B and 6.8)(Swart, 1999; Coetzee, 2001). It overlies the Penge Iron Formation of the Chuniespoort Group of the Transvaal

110 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

Supergroup with an erosive contact. An edgewise chert-clast conglomerate is developed at the base of the succession (Fig 6.8). The basal conglomerate is overlain by a lower diamictite that is between 30 and 200 meters thick. The diamictite is overlain by finely laminated black and green shale coarsening upward into fine-grained quartzite (Fig 6.8). Stromatolitic dolostone that grades upwards into green laminated shale and siltstone occurs above the lower quartzite. This lower unit of the Duitschland Formation is

111 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup overlain with sharp erosive contact by two successive conglomeratic quartzite beds (Fig 6.8). The quartzite unit is, in turn, overlain by finely laminated shale and quartzite.

112 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

The latter contains abundant wave-ripple marks and wave cross lamination (Coetzee 2001). The cross-laminated quartzite bed is overlain by a coarsening upward lithofacies unit commencing with black shale and ending in fine-grained quartzite, again with ripple marks (Fig 6.8). A fourth depositional unit follows, commencing with dark to grey to green, poorly bedded shale/silstone with interbeds of stromatolitic limestone (Fig 6.8). This unit coarsens upwards into wackestone that is overlain with sharp contact by a ~1m thick diamictite bed (known as the upper diamictite). This diamictite was sampled for zircon provenance studies (Fig 6.8). The diamictite, in turn, is succeeded by a bed of stromatolitic dolomite and limestone followed by a lithofacies unit of siltstone and shale, with interbeds of dolostone. Near the top of the succession, a thick brown dolomite is developed which is overlain by a 25m thick chert breccia that defines the top of the Duitschland Formation and the base of the Timeball Hill Formation (Fig 6.8)(Coetzee, 2001).

The Duitschland Formation thins from the north towards the south (Fig 6.5B)(Coetzee, 2001). This may indicate that the source area of the Duitschland Formation was situated towards the north of the Kaapvaal craton.

The upper diamictite was sampled on the farm De Hoop 53KS (S24°10’30.5”E28°10’10.7”)(Figs 6.1 and 6.8) for detrital zircon analyses. The diamictite was selected for provenance studies because it should yield a representative, well mixed and random sample of detrital zircons from the source areas that supplied detritus to the Duitschland Formation. The fine-grained matrix of the upper diamictite is light yellow to pinkish in colour. Angular to subangular chert clasts are floating in this fine-grained matrix. A sample of approximately 7kg was taken from this metre thick diamictite, from which zircons were separated.

6.3.1.3 Timeball Hill Formation The Timeball Hill Formation of the Transvaal Supergroup is subdivided into a lower and upper shale unit, separated from each other by a quartzitic unit known as the Gatsrand Quartzite Member in the western Transvaal and the Klapperkop Quartzite Member in the

113 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup central and eastern Transvaal (Fig 6.2)(Schreiber, 1990). Paleocurrent measurements indicate source areas towards the north, north-east and west (Fig 6.5C)(Visser, 1969; Button, 1973). The quartzite unit is known to host one or more oolitic ironstone units (Fig 6.5C)(Wagner, 1928; Button, 1973; Dorland, 1999, Schweigart, 1965). Cross- bedded quartzite of the Gatsrand Member overlies this basal shale unit with a gradational contact.

The thickness of the central quartzite unit of the Timeball Hill Formation varies between 0 and 275 meters (Fig 6.5C). It was sampled for zircon provenance studies in drill core EBA1 near Potchefstroom in the western Transvaal (Fig 6.1). The quartzite is approximately 60m thick in the drill core (Fig 6.9) and comprises three stacked coarsening upward successions in drill core EBA1 (Fig 6.9)(Coetzee, 2001), with iron oolites sparsely distributed in parts of the quartzite. The drill core was sampled by splitting the core and then taking small samples approximately every meter. The samples were then combined before crushing in order to obtain a representative composite sample of the entire quartzite unit.

6.3.1.4 Hekpoort Formation The Hekpoort Formation was sampled at a depth of 230m in drill core EBA1, which was drilled near Potchefstroom, in the Northwest Province (Fig 6.1, Coetzee, 2001). In a typical profile of the Potchefstroom area, the Hekpoort Formation (which is in the order of 750m thick) overlies a unit of reworked volcaniclastic and siliciclastic strata, which constitute a transition zone between the Boshoek and Hekpoort Formations (Fig 6.10). The lower part of the Hekpoort Formation is comprised of a basal lava flow overlain by volcaniclastics sandstones interbedded with thin lava flows (zone 1). This is followed by a zone (zone 2) consisting of thin lava flows (individual flows less than 30m thick), a zone (zone 3) of thick lava flows (40-60m thick) with flow top breccias, and a top zone (zone 4) consisting of two thick lava flows with a chert and tuff bed at its base.

A thin quartzitic unit within the succession of thick lava flows, defined as zone 3 of the Hekpoort Formation by Coetzee (2001) was sampled for zircon-based provenance

114 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup studies. This quartzitic unit is 40cm thick and crossbedded. It consists almost entirely of fine to medium grained angular quartz grains. The entire quartzite bed was sampled by splitting the core and crushing it for heavy mineral separation.

6.3.1.5 Daspoort Formation The Daspoort Formation is a 25-150m thick (Visser, 1969, Button, 1973, Schreiber, 1990) ortho-quartzite unit with high mineralogical and textural maturity (Button, 1973).

115 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

It rests with a gradational contact on the shales of the underlying Strubenskop Formation (Figs 6.2 and 6.11) in the Pretoria Group.

Paleocurrent measurements and isopach contours indicate that most of the sediment for the Daspoort Formation was derived from source areas towards the northwest and north of the present day outcrop area (Fig 6.5C)(Button, 1973, Visser, 1969, Schreiber, 1990).

The Daspoort quartzite was sampled at Strubenskop (S25°45’, E28°15’) in Pretoria (Figs 6.1 and 6.12). At this locality the Daspoort quartzite is approximately 40m thick; it is massive, although some crossbedding, as well as wave and current ripple marks were noted. Small hand samples were collected at intervals of about 1.5m throughout the

116 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup succession. The samples were combined before crushing and zircon separation to obtain a representative composite sample of the entire quartzite unit.

6.3.1.6 Magaliesberg Formation The Magaliesberg Formation consists mainly of fine to medium grained quartzite, with abundant crossbedding and current as well as wave ripple marks (Button, 1973; Visser, 1969). Paleocurrent directions indicate that sediment for the Magaliesberg Formation was again derived from source areas towards the north and north-east (Fig 6.5E)(Button, 1973; Visser, 1969, Schreiber, 1990). The Magaliesberg Formation was sampled in the Magalies Mountains at S25°51.674’ E27°29.99’ (Figs 6.1 and 6.12). In this area, the Magaliesberg Formation is approximately 200m thick, forming a prominent escarpment.

117 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

Small chip samples were collected every two metres through the succession. The samples were combined before crushing and zircon separation to ensure a representative composite sample of the unit.

6.3.2 Analyses and Results Analyses of zircons for the Schelem, Timeball Hill and Daspoort Formations were performed by SHRIMP at the Australian National University, while zircons of the Duitschland, Hekpoort and Daspoort Formations were analysed by SHRIMP at Curtin University. Zircons were mounted, photographed and studied microscopically by cathodoluminescence prior to analyses to ensure that all morphological and textural populations were analysed (Appendix I).

118 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

6.3.2.1 Schelem Formation The zircons of the Schelem Formation are between 68 and 410micron in length, angular to rounded and mostly elongated rather than equant in shape (Fig 6.13). Many of the grains display oscillatory zoning. A total of 55 zircon grains were analysed for the Schelem Formation (Table 1, Fig 6.14). Of these 22 grains were concordant within 10% (Table 6.1). The youngest concordant zircon in the populations yielded an age of 2635±18Ma (Analyses 44.1, Table 6.1 and Fig 6.13). This specific zircon is angular in shape and approximately 200 micron in length (Fig 6.13) and has an anhedral core surrounded by a thick rim.

The detrital zircons in the Schelem Formation display prominent 207Pb/206Pb age populations at 2840-3010Ma and 3170-3340Ma (Fig 6.11). These two peaks may be split up into four subpopulations, between 2850-2880Ma, 2900-2950Ma, 2970-3010Ma and 3170-3230Ma (Figs 6.15 and 6.16). The zircons of the 2840-2880Ma population vary in length between 102-395mm. They are rounded to subrounded and zoned or unzoned in appearance (detailed descriptions for the zircons are provided in Appendix II). The 2900- 2950Ma zircon population is on average 189mm in length, very angular to well rounded, zoned and unzoned (Fig 6.16). The 2970-3010Ma population is on average 127mm in length, very angular to rounded, zoned and unzoned. Zircons of the 3170-3340Ma population are euhedral to well rounded, zoned and unzoned and grains are as large as 232mm. The oldest analyzed grain (36.1) is subrounded, equant, and approximately 190micron in length. It displays distinct igneous oscillatory zoning (Fig 6.13). Analyses was conducted close to the margin of this zircon and yielded an age of 3336±8Ma (Table 6.1).

119

Table 6.1: Summary of SHRIMP U-Pb data for zircons from the Schelem Formation.

(1) (1) (1) (1) % Ppm ppm ppm 206Pb/238U 207Pb/206Pb 208Pb/232Th % (1) (1) (1) Err 206 232 238 206 207 * 206 * 207 * 235 206 238 Grain Spot Pbc U Th Th/ U Pb* Age Age Age Discordant Pb / Pb ±% Pb / U ±% Pb/ U ±% corr 11.1 -- 38 13 0.35 18.9 2,964 ± 89 2,923 ±18 3,030 ±140 -1 0.2123 1.1 17.08 3.9 0.584 3.8 .960 12.1 0.10 146 56 0.40 65.3 2,697 ± 76 3,097.4 ± 9.8 939 ± 59 13 0.2366 0.62 16.95 3.5 0.519 3.5 .985 13.1 0.09 130 82 0.65 74.4 3,279 ± 87 3,241.0 ± 8.1 3,239 ±110 -1 0.2591 0.52 23.68 3.4 0.663 3.4 .988 14.1 -- 32 16 0.51 15.0 2,830 ± 89 3,000 ±19 2,742 ±120 6 0.2226 1.2 16.91 4.0 0.551 3.9 .956 15.1 0.37 333 256 0.79 99.8 1,923 ± 55 3,020.6 ± 8.4 1,105 ± 42 36 0.2255 0.52 10.81 3.3 0.348 3.3 .988 16.1 0.37 273 232 0.88 72.8 1,735 ± 51 3,072.0 ± 8.8 2,549 ± 87 44 0.2329 0.55 9.92 3.4 0.309 3.3 .987 17.1 0.21 792 734 0.96 152 1,297 ± 38 2,684.9 ± 6.9 383 ± 14 52 0.18351 0.42 5.64 3.3 0.2228 3.2 .992 18.1 0.30 423 112 0.27 58.2 953 ± 30 2,735 ±17 857 ± 44 65 0.1892 1.0 4.16 3.5 0.1594 3.4 .957 19.1 0.05 54 37 0.70 12.6 1,544 ± 57 2,882 ±17 1,426 ± 65 46 0.2069 1.0 7.72 4.3 0.271 4.1 .971 11.1 0.41 187 261 1.45 58.3 1,991 ± 57 2,874 ±11 469 ± 21 31 0.2060 0.70 10.28 3.4 0.362 3.3 .979 12.1 0.17 384 863 2.32 107 1,809 ± 52 2,913.5 ± 7.0 657 ± 22 38 0.21103 0.43 9.42 3.3 0.324 3.3 .991 13.1 0.36 364 166 0.47 116 2,021 ± 57 3,058.9 ± 6.9 1,780 ± 96 34 0.23099 0.43 11.73 3.3 0.368 3.3 .992 15.1 0.28 256 217 0.88 84.1 2,083 ± 59 2,837.7 ± 9.3 2,332 ± 80 27 0.2014 0.57 10.59 3.3 0.381 3.3 .985 16.1 0.98 506 549 1.12 130 1,670 ± 48 2,883 ±11 987 ± 37 42 0.2071 0.69 8.45 3.4 0.2958 3.3 .979 17.1 0.04 231 18 0.08 114 2,932 ± 78 2,990.7 ± 6.9 659 ±150 2 0.22137 0.43 17.57 3.3 0.576 3.3 .992 18.1 0.58 239 325 1.40 85.8 2,240 ± 63 2,940 ±12 955 ± 36 24 0.2146 0.75 12.29 3.4 0.415 3.3 .976 19.1 0.13 156 56 0.37 39.8 1,670 ± 51 2,866 ±21 1,523 ± 69 42 0.2049 1.3 8.36 3.7 0.296 3.5 .935 20.1 0.06 108 55 0.53 47.3 2,663 ± 73 2,873 ±11 2,812 ±100 7 0.2058 0.65 14.51 3.4 0.511 3.4 .982 21.1 0.80 492 170 0.36 71.6 1,002 ± 30 2,867 ±14 1,473 ± 59 65 0.2050 0.83 4.75 3.4 0.1681 3.3 .969 22.1 0.26 236 102 0.45 85.9 2,271 ± 63 2,958 ±14 2,350 ± 92 23 0.2170 0.86 12.63 3.4 0.422 3.3 .968 23.1 0.17 281 265 0.98 123 2,655 ± 71 2,869.0 ± 7.4 2,618 ± 87 7 0.20533 0.45 14.43 3.3 0.510 3.3 .991 24.1 0.37 343 197 0.59 112 2,075 ± 59 2,715 ±16 2,565 ± 98 24 0.1869 0.99 9.79 3.5 0.380 3.3 .958 25.1 0.19 157 103 0.68 61.7 2,419 ± 67 3,194.4 ± 9.2 1,967 ± 74 24 0.2515 0.58 15.79 3.4 0.455 3.3 .985 26.1 0.26 2817 238 0.09 116 299.9 ± 9.4 2,512.7 ± 6.5 669 ± 25 88 0.16550 0.39 1.087 3.2 0.0476 3.2 .993 27.1 0.52 624 98 0.16 133 1,421 ± 41 2,685 ±21 2,341 ± 92 47 0.1835 1.3 6.24 3.5 0.2467 3.3 .929 28.1 -- 143 89 0.65 33.3 1,548 ± 46 2,890 ±19 1,448 ± 53 46 0.2081 1.1 7.79 3.6 0.2714 3.4 .946 29.1 0.04 68 42 0.64 34.2 2,971 ± 82 2,989 ±11 3,059 ±110 1 0.2211 0.70 17.86 3.5 0.586 3.5 .980 30.1 0.09 158 178 1.17 55.6 2,214 ± 62 2,744 ±10 2,609 ±120 19 0.1902 0.64 10.75 3.4 0.410 3.3 .982 31.1 0.86 491 404 0.85 81.5 1,129 ± 34 2,689 ±15 540 ± 28 58 0.1839 0.88 4.86 3.4 0.1915 3.3 .966 32.1 0.50 373 205 0.57 105 1,813 ± 51 2,925.4 ± 7.6 548 ± 30 38 0.2126 0.47 9.52 3.3 0.325 3.3 .990 33.1 2.20 280 122 0.45 51.4 1,225 ± 37 2,699 ±36 282 ± 94 55 0.1851 2.2 5.34 4.0 0.2094 3.3 .838 34.1 -- 122 63 0.53 62.9 3,040 ± 81 2,972 ±10 3,043 ±120 -2 0.2189 0.64 18.18 3.4 0.603 3.3 .982 35.1 0.39 499 338 0.70 123 1,616 ± 47 3,114 ±12 1,864 ± 84 48 0.2391 0.74 9.39 3.4 0.2849 3.3 .976 36.1 0.22 85 32 0.39 49.4 3,313 ± 88 3,336.3 ± 8.4 3,124 ±120 1 0.2753 0.54 25.50 3.4 0.672 3.4 .988

120

Table 6.1 continued (1) (1) (1) (1) % Ppm ppm ppm 206Pb/238U 207Pb/206Pb 208Pb/232Th % (1) (1) (1) Err 206 232 238 206 207 * 206 * 207 * 235 206 238 Grain Spot Pbc U Th Th/ U Pb* Age Age Age Discordant Pb / Pb ±% Pb / U ±% Pb/ U ±% corr 37.1 0.22 88 43 0.50 43.4 2,931 ± 80 2,905 ±14 2,854 ±120 -1 0.2099 0.88 16.66 3.5 0.576 3.4 .968 38.1 0.27 106 76 0.74 44.1 2,540 ± 71 2,894 ±11 2,420 ± 90 12 0.2085 0.71 13.88 3.4 0.483 3.4 .979 39.1 0.12 46 26 0.58 22.3 2,882 ± 81 2,941 ±18 2,876 ±120 2 0.2146 1.1 16.68 3.7 0.564 3.5 .951 40.1 -- 226 15 0.07 123 3,154 ± 82 3,201.7 ± 5.1 2,890 ±110 1 0.25269 0.32 21.99 3.3 0.631 3.3 .995 41.1 1.07 460 363 0.82 68.3 1,018 ± 31 2,675 ±12 713 ± 26 62 0.1825 0.71 4.30 3.3 0.1710 3.2 .977 42.1 -- 64 17 0.28 35.5 3,220 ± 87 3,189 ±10 3,596 ±140 -1 0.2506 0.66 22.39 3.5 0.648 3.4 .982 43.1 0.03 171 54 0.33 84.7 2,934 ± 78 2,937.9 ± 7.3 2,888 ±110 0 0.21423 0.45 17.03 3.3 0.576 3.3 .991 44.1 0.04 34 14 0.41 14.6 2,602 ± 78 2,635 ±18 2,548 ±110 1 0.1780 1.1 12.20 3.8 0.497 3.6 .959 45.1 -- 67 26 0.41 36.4 3,159 ± 86 3,291 ±12 3,239 ±130 4 0.2675 0.76 23.32 3.5 0.632 3.4 .977 46.1 0.27 202 303 1.55 53.2 1,721 ± 50 2,833.9 ± 9.3 224 ± 10 39 0.2009 0.57 8.48 3.4 0.306 3.3 .985 47.1 0.01 115 137 1.22 57.1 2,930 ± 78 2,860.4 ± 7.7 2,893 ± 98 -2 0.20425 0.47 16.21 3.4 0.575 3.3 .990 48.1 -- 59 30 0.53 31.8 3,163 ± 86 3,210.8 ± 9.5 3,080 ±110 1 0.2542 0.60 22.20 3.5 0.633 3.4 .985 49.1 0.36 82 42 0.53 30.9 2,336 ± 67 2,869 ±15 932 ± 57 19 0.2054 0.89 12.36 3.5 0.437 3.4 .967 50.1 -- 96 95 1.02 47.6 2,940 ± 79 2,954.4 ± 8.6 2,929 ±100 0 0.2164 0.53 17.24 3.4 0.578 3.4 .988 51.1 0.01 303 18 0.06 145 2,863 ± 75 2,926.8 ± 5.0 2,730 ±130 2 0.21277 0.31 16.40 3.3 0.559 3.3 .996 52.1 0.01 199 29 0.15 95.1 2,855 ± 76 2,921.9 ± 5.9 2,809 ±110 2 0.21213 0.37 16.29 3.3 0.557 3.3 .994 53.1 0.02 592 46 0.08 159 1,752 ± 50 2,561.9 ± 5.1 1,726 ± 70 32 0.17043 0.31 7.34 3.2 0.312 3.2 .996 54.1 1.42 1170 361 0.32 174 1,016 ± 30 2,321.8 ± 9.9 609 ± 28 56 0.14790 0.58 3.48 3.3 0.1707 3.2 .984 55.1 0.15 38 19 0.51 17.3 2,743 ± 81 2,941 ±15 2,493 ±110 7 0.2147 0.93 15.70 3.7 0.530 3.6 .969 Errors are 1-sigma; Pb* indicate the common and radiogenic portions, respectively. Error in Standard calibration was 1.37% (not included in above errors but required when comparing data from different mounts). 204 (1) Common Pb corrected using measured Pb

121 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

122 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

6.3.2.2 Duitschland Formation A total of 72 zircon grains were analysed for the upper diamictite (Fig 6.8) of the Duitschland Formation (Table 6.2, Fig 6.17). Of these grains 55 were concordant within 10%. The zircons separated from the diamictite vary from 60 and 129 micron in length, and are mostly angular to subrounded (Fig 6.18). The youngest concordant zircon analysed (analyses 21) has a 207Pb/206Pb age of 2424±12Ma (Table 6.2). The oldest population of detrital zircons (3380-3410Ma) is represented by two zircon grains only. The oldest zircon (analyses 65.1, Table 6.2) has an age of 3416±10Ma, it is 108mm in length, well rounded and zoned (Fig 6.18).

There are four other significant populations of detrital zircons in the Duitschland Formation, namely between 2420-2570Ma, 2650-2810Ma, 3020-3100Ma and 3170- 3200Ma (Figs 6.16 and 6.19). The most significant population is the one between 2420-

123 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

2570Ma, were 37 zircons within 10% discordancy are present (Fig 6.16). This population is a dense cluster, but there is a small gap of approximately 10Ma present between the youngest four zircons and the rest of the population (Fig 6.16). This population is especially well defined between 2450 and 2540Ma (Fig 6.16). The zircons of this population vary in length from 64-132micron with an average length of 87mm. The zircon grains vary from angular to well rounded with zoned to unzoned appearance (Figs 6.16 and 6.18)(Detailed descriptions of zircons in Appendix II).

The detrital zircon population between 2650-2810Ma has the highest concentration of ages between between 2770 and 2810Ma (Fig 6.16). In this sub population zircon grains are up to 150mm in length, euhedral to very angular and zoned (Fig 6.16). The zircons in the

124 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

125

Table 6.2 Summary of SHRIMP U-Pb data for detrital zircons from the Duitschland Formation.

(1) (1) (1) % ppm ppm 232Th ppm 206Pb/238U 207Pb/206Pb % (1) (1) (1) 206 238 206 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th / U Pb* Age Age Discordant Pb / Pb ±% Pb / U ±% Pb / U ±% Err.corr 1.1 0.03 55 35 0.66 28.7 3,077 ±33 3,176 ±12 3 0.2486 0.75 20.96 1.6 0.6117 1.4 .878 2.1 0.75 329 200 0.63 120 2,265 ±16 2,450 ±10 8 0.15942 0.62 9.256 1.1 0.4211 0.86 .813 3.1 0.58 105 134 1.32 37.0 2,202 ±21 2,443 ±18 10 0.1588 1.1 8.91 1.6 0.4071 1.1 .724 4.1 0.01 113 96 0.87 58.5 3,040 ±28 3,089.4 ± 8.4 2 0.2354 0.53 19.56 1.3 0.6025 1.2 .912 5.1 0.23 142 84 0.61 56.4 2,438 ±21 2,479 ±12 2 0.1622 0.69 10.28 1.2 0.4597 1.0 .830 6.1 0.41 316 286 0.93 111 2,208 ±16 2,465.4 ± 9.2 10 0.16093 0.55 9.064 1.0 0.4085 0.86 .845 7.1 2.36 363 186 0.53 71.9 1,310 ±11 2,404 ±21 45 0.1552 1.2 4.821 1.5 0.2253 0.90 .598 8.1 0.08 203 124 0.63 81.6 2,471 ±20 2,503.4 ± 8.6 1 0.16459 0.51 10.60 1.1 0.4672 0.95 .880 9.1 0.05 170 89 0.54 68.7 2,486 ±20 2,466 ±11 -1 0.1610 0.66 10.44 1.2 0.4705 0.98 .831 10.1 1.00 259 379 1.51 82.1 2,007 ±16 2,459 ±13 18 0.1603 0.78 8.072 1.2 0.3653 0.91 .756 11.1 0.07 120 76 0.66 47.9 2,464 ±29 2,502 ±11 1 0.1644 0.68 10.55 1.6 0.4656 1.4 .900 12.1 0.11 115 84 0.76 45.0 2,420 ±22 2,484 ±13 3 0.1627 0.77 10.22 1.3 0.4555 1.1 .821 13.1 0.09 164 100 0.63 73.0 2,696 ±22 2,790.2 ± 8.9 3 0.1956 0.55 14.01 1.1 0.5193 0.98 .873 14.1 0.07 131 58 0.46 57.8 2,671 ±23 2,752 ±10 3 0.1911 0.62 13.52 1.2 0.5133 1.0 .858 15.1 0.74 158 165 1.08 50.6 2,023 ±20 2,403 ±18 16 0.1551 1.1 7.88 1.6 0.3687 1.1 .732 16.1 6.57 1721 2464 1.48 187 721.2 ± 6.8 1,900 ±28 62 0.1163 1.5 1.898 1.8 0.1184 10 .542 17.1 0.13 252 199 0.82 109 2,632 ±19 2,702.9 ± 7.4 3 0.18552 0.45 12.90 1.0 0.5042 0.90 .894 18.1 -- 145 80 0.57 64.8 2,696 ±24 2,651.4 ± 9.1 -2 0.17984 0.55 12.88 1.2 0.5194 1.1 .892 19.1 0.57 374 224 0.62 160 2,598 ±18 3,025.7 ± 6.2 14 0.22625 0.39 15.48 0.92 0.4963 0.84 .908 20.1 0.57 374 224 0.62 160 2,598 ±18 3,025.7 ± 6.2 14 0.22625 0.39 15.48 0.92 0.4963 0.84 .908 21.1 0.15 167 138 0.86 65.4 2,423 ±20 2,424 ±12 0 0.1570 0.69 9.88 1.2 0.4562 0.98 .818 22.1 0.68 496 344 0.72 157 2,013 ±15 2,333.9 ± 9.7 14 0.14895 0.57 7.526 1.0 0.3665 0.84 .829 23.1 1.73 257 295 1.18 70.5 1,760 ±14 2,636 ±15 33 0.1782 0.90 7.712 1.3 0.3139 0.91 .711 24.1 0.18 190 159 0.87 65.5 2,175 ±18 2,481 ±11 12 0.1624 0.63 8.98 1.1 0.4013 0.96 .834 25.1 0.05 189 145 0.79 85.8 2,729 ±21 2,798.4 ± 7.8 2 0.19663 0.48 14.29 1.1 0.5270 0.96 .895 26.1 1.79 281 144 0.53 88.6 1,986 ±15 2,403 ±16 17 0.1551 0.94 7.72 1.3 0.3608 0.90 .690 27.1 0.10 58 35 0.62 33.7 3,331 ±34 3,383 ±10 2 0.2836 0.66 26.45 1.5 0.6765 1.3 .894

126

Table 6.2 continued (1) (1) (1) % ppm ppm 232Th ppm 206Pb/238U 207Pb/206Pb % (1) (1) (1) 206 238 206 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th / U Pb* Age Age Discordant Pb / Pb ±% Pb / U ±% Pb / U ±% Err.corr 28.1 0.53 250 324 1.34 113 2,718 ±20 3,028.6 ± 7.3 10 0.2267 0.46 16.39 1.0 0.5244 0.89 .891 29.1 0.13 166 91 0.56 65.1 2,418 ±21 2,496 ±18 3 0.1639 1.1 10.29 1.5 0.4552 1.0 .689 30.1 0.17 187 110 0.61 74.2 2,446 ±21 2,507 ±10 2 0.16491 0.60 10.49 1.2 0.4615 1.0 .862 31.1 0.05 80 73 0.94 31.5 2,423 ±25 2,516 ±16 4 0.1659 0.97 10.44 1.6 0.4563 1.2 .784 32.1 1.22 261 118 0.47 103 2,418 ±18 2,477 ±13 2 0.1621 0.74 10.17 1.2 0.4552 0.91 .772 33.1 0.68 393 139 0.37 104 1,725 ±20 2,332 ±11 26 0.14877 0.65 6.292 1.5 0.3068 1.4 .901 34.1 0.21 96 56 0.61 38.3 2,464 ±35 2,473 ±13 0 0.1616 0.80 10.38 1.9 0.4656 1.7 .904 35.1 0.05 156 98 0.65 71.1 2,739 ±32 2,791.4 ± 8.4 2 0.1958 0.51 14.29 1.5 0.5295 1.4 .941 36.1 0.22 198 222 1.16 103 3,046 ±23 3,197.4 ± 6.9 5 0.2520 0.44 20.99 1.0 0.6040 0.94 .905 37.1 0.20 177 115 0.68 65.3 2,302 ±19 2,495 ±11 8 0.1638 0.63 9.69 1.2 0.4292 0.96 .837 38.1 0.06 170 118 0.72 68.0 2,460 ±20 2,517.0 ± 9.7 2 0.16593 0.58 10.63 1.1 0.4646 0.97 .858 39.1 0.37 246 133 0.56 85.4 2,180 ±18 2,476 ±10 12 0.1620 0.62 8.99 1.1 0.4023 0.95 .838 40.1 0.77 219 181 0.85 77.8 2,213 ±18 2,442 ±14 9 0.1587 0.80 8.96 1.3 0.4096 0.98 .776 41.1 0.02 273 219 0.83 107 2,430 ±19 2,468.7 ± 7.5 2 0.16124 0.44 10.18 1.0 0.4579 0.92 .902 42.1 1.26 219 203 0.96 55.2 1,644 ±14 2,481 ±19 34 0.1624 1.1 6.504 1.5 0.2904 10 .672 43.1 0.04 121 128 1.09 48.6 2,476 ±22 2,521 ±11 2 0.1663 0.68 10.74 1.3 0.4683 1.1 .841 44.1 0.08 170 154 0.94 66.9 2,433 ±21 2,499 ±10 3 0.16413 0.61 10.38 1.2 0.4586 1.0 .861 45.1 0.10 101 90 0.92 42.5 2,564 ±24 2,552 ±13 -1 0.1694 0.78 11.41 1.4 0.4886 1.1 .821 46.1 1.04 276 341 1.28 97.6 2,204 ±17 2,476 ±12 11 0.1619 0.73 9.10 1.2 0.4076 0.93 .786 47.1 0.97 485 398 0.85 119 1,610 ±14 2,360 ±12 32 0.1513 0.68 5.916 1.2 0.2836 0.99 .825 48.1 0.07 166 107 0.67 73.5 2,675 ±23 2,730 ±11 2 0.1886 0.67 13.37 1.2 0.5142 1.0 .838 49.1 -- 83 92 1.14 35.0 2,561 ±25 2,565 ±13 0 0.1708 0.78 11.49 1.4 0.4878 1.2 .837 50.1 0.20 101 93 0.95 39.6 2,410 ±23 2,493 ±14 3 0.1636 0.85 10.23 1.4 0.4533 1.1 .799 51.1 0.08 169 96 0.59 67.9 2,472 ±20 2,508.0 ± 9.7 1 0.16505 0.58 10.64 1.1 0.4674 0.98 .860 52.1 0.87 305 249 0.84 140 2,738 ±20 3,266.1 ± 9.4 16 0.2632 0.60 19.21 1.1 0.5293 0.88 .825 53.1 0.10 200 101 0.52 91.6 2,755 ±30 2,802.2 ± 8.1 2 0.19709 0.50 14.49 1.4 0.5332 1.3 .937 54.1 0.04 160 98 0.63 65.0 2,493 ±21 2,493 ±14 0 0.1636 0.82 10.65 1.3 0.4721 10 .771 55.1 0.25 181 140 0.80 72.6 2,466 ±31 2,484 ±10 1 0.1627 0.62 10.45 1.7 0.4659 1.5 .928

127

Table 6.2 continued (1) (1) (1) % ppm ppm 232Th ppm 206Pb/238U 207Pb/206Pb % (1) (1) (1) 206 238 206 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th / U Pb* Age Age Discordant Pb / Pb ±% Pb / U ±% Pb / U ±% Err.corr 56.1 0.03 199 94 0.49 90.3 2,729 ±21 2,743.7 ± 7.8 1 0.19018 0.47 13.82 1.1 0.5271 0.95 .895 57.1 0.11 209 154 0.76 84.3 2,484 ±19 2,501.0 ± 8.7 1 0.16436 0.51 10.65 1.1 0.4701 0.94 .877 58.1 0.13 83 38 0.48 43.6 3,074 ±29 3,055 ±10 -1 0.2304 0.63 19.41 1.3 0.6110 1.2 .883 59.1 0.08 71 53 0.76 28.8 2,480 ±26 2,515 ±15 1 0.1657 0.92 10.72 1.5 0.4692 1.2 .804 60.1 0.56 88 56 0.66 34.0 2,391 ±25 2,497 ±18 4 0.1640 1.0 10.15 1.6 0.4491 1.3 .771 61.1 2.00 340 475 1.44 85.6 1,628 ±13 2,345 ±17 31 0.1500 1.0 5.942 1.3 0.2874 0.87 .654 62.1 0.04 163 72 0.46 65.2 2,469 ±20 2,501 ±13 1 0.1644 0.74 10.58 1.2 0.4667 0.98 .798 63.1 0.04 143 63 0.46 58.5 2,512 ±21 2,530 ±10 1 0.1672 0.62 10.98 1.2 0.4765 1.0 .853 64.1 0.09 52 20 0.39 20.5 2,445 ±29 2,492 ±19 2 0.1635 1.1 10.40 1.8 0.4613 1.4 .783 65.1 0.09 62 54 0.91 36.5 3,376 ±34 3,416 ±10 1 0.2896 0.64 27.48 1.5 0.6882 1.3 .897 66.1 0.18 132 89 0.70 59.1 2,706 ±23 2,782 ±10 3 0.1947 0.63 14.00 1.2 0.5216 1.1 .858 67.1 -- 59 60 1.04 24.2 2,514 ±28 2,519 ±15 0 0.1661 0.90 10.93 1.6 0.4770 1.3 .827 68.1 0.14 117 46 0.41 53.2 2,738 ±24 2,777 ±10 1 0.1941 0.63 14.16 1.2 0.5291 1.1 .862 69.1 0.69 140 168 1.23 53.0 2,336 ±20 2,470 ±15 5 0.1614 0.90 9.72 1.4 0.4367 1.0 .751 70.1 0.08 193 170 0.91 79.0 2,512 ±20 2,508.6 ± 9.2 0 0.16510 0.55 10.85 1.1 0.4764 0.95 .865 71.1 0.02 130 134 1.06 53.1 2,504 ±22 2,468 ±13 -1 0.1611 0.75 10.55 1.3 0.4747 1.0 .812 72.1 0.22 196 141 0.74 72.8 2,313 ±19 2,488 ±11 7 0.1631 0.67 9.71 1.2 0.4317 0.96 .818 Table 6.2 continued Errors are in 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectively. Error in Standard calibration was 0.27% (not included in above errors but required when comparing data from different mounts).

(1) Common Pb corrected using measured 204Pb.

128 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

populations between 3020-3100, 3120-3200 and 3380-3440Ma are angular to well rounded, zoned and massive, and on average around 100mm in length (Fig 6.16).

6.3.2.3 Timeball Hill Formation The detrital zircons that were analysed for the Timeball Hill Formation varied in length between 61 and 146mm (Fig 6.20). Their shape is typically subangular to rounded (Fig 6.20)(see Appendix II for detailed zircon descriptions). A total of 43 zircon grains was analysed for the Timeball Hill quartzite (Table 6.3, Fig 6.21). Of these, 25 grains yielded results that are concordant within 10%. 207Pb/206Pb ages define four populations for these 25 detrital zircons in the Timeball Hill Formation, namely between 2320-2430Ma,

129 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

130 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

131 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

132 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

2450-2560Ma, 2570-2640Ma and 2740-2930Ma (Figs 6.16 and 6.22). The youngest zircon (Analyses 7.1, 2324±17Ma, Table 6.3) is 122 µm in diameter, rounded and display zoning. The oldest concordant zircon is grain 21.1 (3614±5, Table 6.3). It is 104 µm in length, rounded and appears unzoned (Fig 6.20).

6.3.2.4 Hekpoort Formation A total of 49 zircon grains were analysed from a volcaniclastic quartzite bed in the upper part of the Hekpoort Formation from drill core EBA1 near Potchefstroom (Table 6.4, Fig 6.23). Of these 25 grains were concordant within 10%. The average size of the zircons ranges between 100mm and 150mm (Fig 6.24). The shape of the zircons varies between elongated and prismatic (zircons Hek 1.1 and Hek 4.1) to well rounded (zircon Hek 6.1)(Fig 6.24). Zoning is present in most of the zircons (i.e. zircon Hek 1.1)(Fig 6.24)(see Appendix II for detailed zircon descriptions). Five significant populations of detrital zircons are defined by their 207Pb/206Pb ages, between 2230-2250Ma,

133 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

134

Table 6.3 Summary of SHRIMP U-Pb data for detrital zircons from the quartzite unit of the Timeball Hill Formation.

(1) (1) (2) (3) (1) Total Total (1) (1) (1) (1) Grain. % ppm ppm 232Th/ ppm 206Pb/238U 206Pb/238U 206Pb/238U 207Pb/206Pb % 238U/ 207Pb/ 238U/ 207Pb*/ 207Pb*/ 206Pb*/ Err 206 238 206 206 206 206 * 206 * 235 238 Spot Pbc U Th U Pb* Age Age Age Age Disc Pb ±% Pb ±% Pb ±% Pb ±% U ±% U ±% corr 1.1 0.01 139 118 0.88 53.8 2,391 ±33 2,308 ±39 2,401 ±36 2,697 ± 11 11 2.227 1.6 0.1849 0.68 2.227 1.6 0.1848 0.68 11.44 1.8 0.4490 1.6 .924 2.1 0.11 134 104 0.80 53.1 2,439 ±33 2,426 ±41 2,451 ±36 2,489 ± 12 2 2.171 1.6 0.1642 0.68 2.174 1.6 0.1632 0.73 10.35 1.8 0.4599 1.6 .912 3.1 0.05 283 233 0.85 106 2,332 ±29 2,285 ±34 2,332 ±32 2,524.4± 9.48 2.293 1.5 0.16710 0.50 2.295 1.5 0.16667 0.56 10.01 1.6 0.4358 1.5 .935 4.1 0.02 690 415 0.62 198 1,853 ±22 1,779 ±24 1,837 ±24 2,360.0± 6.321 3.002 1.4 0.15142 0.36 3.003 1.4 0.15125 0.37 6.945 1.4 0.3330 1.4 .967 5.1 0.09 79 63 0.83 32.7 2,541 ±38 2,550 ±51 2,547 ±42 2,513 ± 15 -1 2.068 1.8 0.1663 0.85 2.069 1.8 0.1655 0.92 11.03 2.0 0.4832 1.8 .894 6.1 0.89 ### 484 0.43 339 1,863 ±22 1,795 ±24 1,878 ±23 2,344 ± 24 20 2.954 1.3 0.1578 1.3 2.980 1.3 0.1499 1.4 6.92 1.9 0.3352 1.3 .692 7.1 0.13 91 61 0.69 35.2 2,399 ±36 2,418 ±46 2,405 ±39 2,324 ± 17 -3 2.215 1.8 0.1492 0.89 2.218 1.8 0.1481 1.0 9.20 2.0 0.4508 1.8 .868 8.1 0.49 932 553 0.61 285 1,954 ±22 1,886 ±25 1,963 ±24 2,383.9± 6.918 2.808 1.3 0.15777 0.29 2.822 1.3 0.15343 0.40 7.49 1.4 0.3541 1.3 .956 9.1 -- 234 168 0.74 96.4 2,527 ±31 2,521 ±40 2,526 ±34 2,547.0± 8.51 2.084 1.5 0.16876 0.50 2.084 1.5 0.16892 0.51 11.18 1.6 0.4800 1.5 .946 10.1 0.02 419 314 0.77 198 2,825 ±32 2,824 ±47 2,831 ±35 2,826.9± 5.40 1.818 1.4 0.20025 0.33 1.818 1.4 0.20008 0.33 15.17 1.4 0.5499 1.4 .973 11.1 0.11 130 79 0.63 64.0 2,911 ±39 2,910 ±59 2,917 ±41 2,914.8± 9.90 1.750 1.6 0.2122 0.58 1.752 1.6 0.2112 0.61 16.62 1.8 0.5707 1.6 .937 12.1 0.12 440 544 1.28 133 1,943 ±23 1,896 ±26 1,940 ±27 2,249 ± 12 14 2.839 1.4 0.14279 0.61 2.843 1.4 0.14176 0.68 6.87 1.5 0.3517 1.4 .898 13.1 -- 392 224 0.59 149 2,360 ±28 2,328 ±34 2,391 ±29 2,489.7± 6.85 2.262 1.4 0.16301 0.40 2.262 1.4 0.16325 0.41 9.95 1.5 0.4421 1.4 .960 14.1 0.02 635 172 0.28 255 2,470 ±28 2,470 ±35 2,472 ±28 2,473.1± 5.40 2.141 1.3 0.16183 0.31 2.141 1.3 0.16166 0.32 10.41 1.4 0.4670 1.3 .973 15.1 0.02 141 115 0.85 56.6 2,475 ±33 2,472 ±43 2,478 ±37 2,486 ± 13 0 2.136 1.6 0.1630 0.68 2.136 1.6 0.1629 0.79 10.51 1.8 0.4681 1.6 .898

16.1 1.90 ### 1180 0.28 193 314.5 ± 4.4 298.1± 4.2 318.0± 5.31,652 ±120 81 19.61 1.3 0.1180 4.0 19.99 1.4 0.1015 6.6 0.700 6.8 0.04999 1.4 .211 17.1 0.08 748 596 0.82 166 1,479 ±18 1,403 ±18 1,486 ±20 2,259.4± 7.735 3.874 1.3 0.14337 0.40 3.877 1.3 0.14264 0.45 5.072 1.4 0.2579 1.3 .949 18.1 0.01 328 200 0.63 113 2,172 ±26 2,106 ±30 2,176 ±28 2,490.3± 8.013 2.496 1.4 0.16340 0.47 2.496 1.4 0.16332 0.48 9.02 1.5 0.4006 1.4 .948 19.1 ### ### 1285 1.15 492 2,072 ±31 2,064 ±72 2,059 ±92 2,525 ±320 18 2.023 1.3 0.348 6.7 2.528 1.7 0.170 18 8.7 19 0.3790 1.9 .096 20.1 0.08 150 82 0.57 64.5 2,621 ±35 2,583 ±45 2,621 ±37 2,733 ± 11 4 1.991 1.6 0.1897 0.64 1.993 1.6 0.1889 0.65 13.07 1.7 0.5018 1.6 .927 21.1 0.02 309 210 0.70 193 3,528 ±39 3,386 ±83 3,531 ±41 3,614.8± 4.52 1.372 1.4 0.32963 0.29 1.373 1.4 0.32950 0.29 33.09 1.5 0.728 1.4 .979 22.1 -- 177 251 1.46 71.3 2,478 ±32 2,468 ±40 2,481 ±38 2,512.4± 9.61 2.134 1.5 0.16524 0.57 2.134 1.5 0.16547 0.57 10.69 1.6 0.4687 1.5 .937 23.1 0.02 240 181 0.78 97.6 2,501 ±31 2,500 ±40 2,503 ±34 2,504.0± 8.70 2.109 1.5 0.16483 0.51 2.110 1.5 0.16465 0.52 10.76 1.6 0.4740 1.5 .944 24.1 0.01 652 437 0.69 223 2,162 ±25 2,119 ±29 2,158 ±27 2,375.3± 5.89 2.510 1.4 0.15273 0.33 2.510 1.4 0.15261 0.34 8.38 1.4 0.3984 1.4 .970 25.1 0.10 ### 444 0.43 202 1,290 ±15 1,180 ±15 1,291 ±16 2,568.8± 6.350 4.508 1.3 0.17207 0.33 4.513 1.3 0.17115 0.37 5.228 1.4 0.2216 1.3 .962

135

Table 6.3 continued (1) (1) (2) (3) (1) Total Total (1) (1) (1) (1) Grain. % ppm ppm 232Th/ ppm 206Pb/238U 206Pb/238U 206Pb/238U 207Pb/206Pb % 238U/ 207Pb/ 238U/ 207Pb*/ 207Pb*/ 206Pb*/ Err 206 238 206 206 206 206 * 206 * 235 238 Spot Pbc U Th U Pb* Age Age Age Age Disc Pb ±% Pb ±% Pb ±% Pb ±% U ±% U ±% corr 26.1 -- 354 231 0.67 163 2,772 ±34 2,769 ±48 2,773 ±36 2,778.5± 6.40 1.861 1.5 0.19424 0.39 1.861 1.5 0.19425 0.39 14.39 1.5 0.5373 1.5 .968 27.1 0.01 380 228 0.62 152 2,460 ±29 2,471 ±37 2,465 ±31 2,423.1± 7.2-2 2.151 1.4 0.15705 0.40 2.152 1.4 0.15695 0.42 10.06 1.5 0.4647 1.4 .958 28.1 0.33 522 407 0.80 179 2,161 ±25 2,116 ±29 2,175 ±28 2,389.9± 8.310 2.501 1.4 0.15689 0.36 2.510 1.4 0.15395 0.48 8.45 1.4 0.3983 1.4 .942 29.1 0.03 498 235 0.49 195 2,421 ±28 2,409 ±35 2,423 ±29 2,465.5± 6.42 2.193 1.4 0.16118 0.36 2.194 1.4 0.16093 0.38 10.11 1.4 0.4558 1.4 .964 30.1 0.09 ### 327 0.30 322 1,846 ±21 1,796 ±23 1,847 ±22 2,203.6± 5.416 3.013 1.3 0.13887 0.29 3.015 1.3 0.13811 0.31 6.314 1.4 0.3316 1.3 .973 31.1 -- 739 570 0.80 256 2,187 ±25 2,130 ±29 2,178 ±27 2,463.4± 5.311 2.476 1.3 0.16059 0.30 2.475 1.3 0.16073 0.31 8.95 1.4 0.4040 1.3 .974 32.1 0.13 229 130 0.59 79.9 2,194 ±28 2,122 ±32 2,190 ±30 2,530.3± 9.413 2.463 1.5 0.16841 0.55 2.467 1.5 0.16726 0.56 9.35 1.6 0.4053 1.5 .936 33.1 0.06 342 288 0.87 129 2,351 ±28 2,302 ±33 2,377 ±31 2,549.4± 7.78 2.270 1.4 0.16971 0.42 2.272 1.4 0.16917 0.46 10.27 1.5 0.4401 1.4 .951 34.1 0.21 661 591 0.92 225 2,145 ±25 2,095 ±28 2,150 ±28 2,400.7± 6.611 2.527 1.3 0.15683 0.32 2.532 1.3 0.15492 0.39 8.43 1.4 0.3948 1.3 .961 35.1 0.05 120 72 0.62 48.5 2,485 ±34 2,486 ±44 2,489 ±36 2,481 ± 14 0 2.125 1.6 0.1628 0.70 2.126 1.7 0.1624 0.85 10.53 1.9 0.4703 1.7 .887 36.1 -- 309 241 0.81 126 2,503 ±30 2,478 ±38 2,503 ±32 2,587.7± 8.43 2.108 1.4 0.17305 0.50 2.108 1.4 0.17308 0.50 11.32 1.5 0.4745 1.4 .943 37.1 0.04 379 441 1.20 125 2,091 ± 25 1,987 ±27 2,214 ±28 2,625.9± 7.820 2.608 1.4 0.17750 0.44 2.610 1.4 0.17710 0.47 9.36 1.5 0.3832 1.4 .948 38.1 0.06 398 545 1.42 137 2,172 ±26 2,099 ±29 2,353 ±29 2,524.8± 7.614 2.494 1.4 0.16721 0.40 2.496 1.4 0.16671 0.45 9.21 1.5 0.4007 1.4 .951 39.1 0.03 320 164 0.53 136 2,585 ±30 2,488 ±37 2,615 ±32 2,868.9± 6.710 2.027 1.4 0.20555 0.41 2.027 1.4 0.20532 0.41 13.96 1.5 0.4933 1.4 .960 40.1 0.06 339 256 0.78 111 2,086 ±25 2,011 ±28 2,104 ±27 2,484.9± 8.316 2.616 1.4 0.16333 0.44 2.617 1.4 0.16280 0.49 8.58 1.5 0.3821 1.4 .944 41.1 0.07 825 575 0.72 243 1,899 ±22 1,843 ±24 1,911 ±24 2,272.7± 5.916 2.917 1.3 0.14432 0.31 2.919 1.3 0.14374 0.34 6.788 1.4 0.3425 1.3 .969 42.1 -- 122 42 0.35 52.7 2,627 ±35 2,625 ±47 2,627 ±36 2,633 ± 11 0 1.989 1.6 0.1772 0.63 1.988 1.6 0.1779 0.66 12.34 1.8 0.5031 1.6 .925 43.1 0.00 401 147 0.38 162 2,487 ±29 2,491 ±37 2,488 ±30 2,473.9± 6.3-1 2.124 1.4 0.16174 0.37 2.124 1.4 0.16173 0.37 10.50 1.4 0.4708 1.4 .966 Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectively. Error in standard calibration was 0.60% (not included in above errors but required when comparing data from different mounts. 204 (1) Common Pb corrected using measured Pb.

136 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

137 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

2270-2450Ma, 2500-2520Ma, 2560-2650Ma and 2860-2890Ma (Figs 6.16 and 6.25).

The four youngest concordant zircons (2.1, 11.1, 24.1 and 41.1) are between 2230- 2250Ma old (Table 6.4). The length of these zircons varies from 80-140mm with an average length of 110 µm. The zircons are euhedral to very angular and display zoning (Fig 6.24).

6.3.2.5 Daspoort Formation The zircons that were analysed for the Daspoort Formation ranged in size from 40 – 170mm, and they were euhedral to well rounded (Fig 26)(see Appendix II for detailed zircon descriptions). A total of 50 detrital zircon grains were analysed from the Daspoort Formation. Of these 15 were concordant within 10% (Table 6.5, Fig 6.27). Based on 207Pb/206Pb radiometric ages five detrital zircon populations are defined for the Daspoort

138

Table 6.4 Summary of SHRIMP U-Pb data for zircons from a volcaniclastic quartzite of the Hekpoort Formation.

(1) (1) (1) % ppm ppm ppm 206Pb/238U 207Pb/206Pb % (1) (1) (1) 206 232 238 206 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th Th/ U Pb* Age Age Discordant Pb / Pb ±% Pb / U ±% Pb / U ±% Err.corr 1.1 0.14 427 604 1.46 161 2,346 ±19 2,389.5 ± 5.4 2 0.15388 0.32 9.314 1.0 0.4390 0.96 .950 2.1 0.09 112 56 0.52 40.2 2,251 ±21 2,243 ± 11 0 0.14130 0.65 8.14 1.3 0.4178 1.1 .863 3.1 0.05 362 219 0.62 148 2,501 ±20 2,515.5 ± 4.9 1 0.16579 0.29 10.83 1.0 0.4739 0.97 .958 4.1 10.72 1437 1090 0.78 332 1,365 ±41 1,571 ±330 13 0.097 17 3.16 18 0.2358 3.4 .187 5.1 0.16 363 133 0.38 135 2,321 ±25 2,311.0 ± 6.0 0 0.14698 0.35 8.78 1.3 0.4333 1.3 .964 6.1 0.04 162 183 1.17 78.3 2,882 ±34 2,886.1 ± 5.9 0 0.20750 0.36 16.13 1.5 0.5636 1.4 .969 7.1 -- 123 80 0.67 59.1 2,870 ±25 2,877.8 ± 7.3 0 0.20643 0.45 15.96 1.2 0.5607 1.1 .923 8.1 1.17 806 769 0.99 181 1,475 ±13 1,940 ± 68 24 0.1189 3.8 4.21 3.9 0.2570 1.1 .267 9.1 0.06 703 32 0.05 213 1,947 ±16 2,198.4 ± 8.4 11 0.13769 0.48 6.695 1.1 0.3527 0.98 .896 11.1 0.64 236 314 1.37 84.2 2,225 ± 33 2,250 ± 32 1 0.1419 1.9 8.06 2.6 0.4123 1.8 .688 12.1 0.25 719 515 0.74 143 1,339 ± 20 1,956 ± 31 32 0.1200 1.8 3.821 2.4 0.2309 1.7 .694 13.1 0.02 288 212 0.76 118 2,514 ± 36 2,507.3 ± 5.0 0 0.16497 0.30 10.85 1.7 0.4771 1.7 .985 14.1 -- 122 143 1.21 44.0 2,260 ± 36 2,357.2 ± 8.4 4 0.15100 0.49 8.74 2.0 0.4200 1.9 .968 15.1 0.36 1001 368 0.38 233 1,538 ± 23 2,213 ± 44 31 0.1389 2.6 5.16 3.1 0.2694 1.7 .551 16.1 0.15 233 37 0.17 88.1 2,347 ± 34 2,352.1 ± 6.5 0 0.15055 0.38 9.12 1.8 0.4392 1.7 .976 16.1 0.43 458 112 0.25 119 1,690 ± 36 2,172 ± 16 22 0.1356 0.93 5.60 2.6 0.2996 2.4 .932 18.1 16.07 1070 203 0.20 293 1,457 ± 82 2,288 ± 260 36 0.145 14 5.07 16 0.254 6.2 .375 20.1 2.46 664 193 0.30 180 1,720 ± 30 2,028 ± 26 15 0.1249 1.5 5.27 2.5 0.3057 2.0 .803 21.1 0.12 147 134 0.94 73.0 2,940 ± 96 2,884 ± 16 -2 0.2072 1.0 16.52 4.2 0.578 4.1 .971 22.1 18.87 1001 369 0.38 339 1,721 ± 72 1,769 ± 440 3 0.108 23 4.6 25 0.306 4.8 .193 23.1 0.44 174 71 0.42 70.2 2,467 ± 35 2,579.0 ± 7.2 4 0.17219 0.43 11.07 1.8 0.4662 1.7 .970 24.1 0.02 293 120 0.42 99.5 2,145 ± 31 2,248.9 ± 5.9 5 0.14176 0.34 7.72 1.7 0.3948 1.7 .980 25.1 27.80 1279 86 0.07 333 1,225 ±100 1,210 ±1700 -1 0.081 83 2.3 87 0.209 9.4 .108 26.1 0.00 449 207 0.48 174 2,403 ± 34 2,434.2 ± 4.3 1 0.15798 0.25 9.84 1.7 0.4518 1.7 .989 27.1 0.04 271 111 0.42 97.6 2,254 ± 33 2,301.8 ± 6.0 2 0.14618 0.35 8.44 1.7 0.4186 1.7 .980 28.1 2.94 214 128 0.62 78.2 2,211 ± 33 2,314 ± 17 4 0.1472 1.0 8.30 2.0 0.4091 1.8 .865 29.1 0.22 2457 583 0.25 344 972 ± 27 1,466 ± 32 34 0.0919 1.7 2.063 3.4 0.1627 3.0 .872

139

Table 6.4 continued (1) (1) (1) % ppm ppm ppm 206Pb/238U 207Pb/206Pb % (1) (1) (1) 206 232 238 206 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th Th/ U Pb* Age Age Discordant Pb / Pb ±% Pb / U ±% Pb / U ±% Err.corr 30.1 0.18 734 163 0.23 212 1,868 ± 27 2,269.9 ± 8.6 18 0.14351 0.50 6.65 1.8 0.3362 1.7 .959 31.1 0.03 503 177 0.36 178 2,222 ± 32 2,609 ± 15 15 0.1753 0.89 9.95 1.9 0.4115 1.7 .886 32.1 0.85 599 312 0.54 233 2,385 ± 34 2,644.1 ± 4.4 10 0.17906 0.26 11.05 1.7 0.4476 1.7 .988 33.1 0.15 918 351 0.39 170 1,258 ± 19 1,777.1 ± 7.5 29 0.10866 0.41 3.229 1.7 0.2155 1.7 .972 34.1 2.12 93 188 2.09 35.6 2,321 ± 35 2,415 ± 48 4 0.1562 2.8 9.33 3.4 0.4334 1.8 .543 36.1 1.34 370 168 0.47 132 2,205 ± 33 2,468 ± 30 11 0.1611 1.8 9.06 2.5 0.4078 1.8 .707 37.1 0.05 465 408 0.91 171 2,295 ± 33 2,332.1 ± 4.5 2 0.14879 0.26 8.77 1.7 0.4277 1.7 .988 38.1 0.06 43 22 0.53 20.8 2,891 ± 44 2,873 ± 11 -1 0.2058 0.66 16.06 2.0 0.566 1.9 .943 41.1 3.69 126 69 0.57 42.6 2,060 ± 31 2,230 ± 35 8 0.1403 2.0 7.28 2.7 0.3765 1.8 .661 42.1 1.00 296 201 0.70 112 2,330 ± 34 2,502.7 ± 6.8 7 0.16454 0.40 9.88 1.8 0.4353 1.7 .974 43.1 0.42 665 125 0.19 181 1,767 ± 26 2,153.4 ± 7.2 18 0.13419 0.41 5.83 1.8 0.3153 1.7 .972 44.1 4.76 2341 884 0.39 494 1,345 ± 26 1,584 ± 260 15 0.098 14 3.13 14 0.2320 2.3 .163 45.1 0.11 941 637 0.70 219 1,547 ± 24 1,960.7 ± 4.9 21 0.12030 0.27 4.500 1.8 0.2713 1.8 .988 46.1 0.31 342 152 0.46 129 2,340 ± 36 2,440 ± 22 4 0.1586 1.3 9.57 2.2 0.4375 1.8 .810 47.1 0.09 491 148 0.31 167 2,150 ± 31 2,286.5 ± 5.5 6 0.14489 0.32 7.91 1.7 0.3959 1.7 .983 48.1 1.54 846 286 0.35 179 1,398 ± 24 2,039 ± 88 31 0.1257 5.0 4.20 5.3 0.2422 1.9 .358 49.1 1.82 265 97 0.38 88.2 2,067 ± 30 2,299 ± 11 10 0.14594 0.64 7.61 1.8 0.3781 1.7 .937 Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions, respectively. Error in standard calibration was 1.07% (not included in above errors but required when comparing data from different mounts).

(1) Common Pb corrected using measured 204Pb.

140 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

141 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

Formation (Figs 6.16 and 6.28). The age ranges of these populations are between 2225- 2250Ma, 2260-2280Ma, 2360-2420Ma, 2770-2800Ma and 2860-2910Ma (Fig 6.16).

6.3.2.6 Magaliesberg Formation The zircons analysed from the Magaliesberg Formation ranged in size from 60-215mm and were mostly subrounded to well rounded (Fig 6.29)(see Appendix II for detailed zircon descriptions). A total of 29 zircon grains were analysed, of which 19 grains were nearly concordant (concordant within 10%)(Table 6.6, Fig 6.30). Only two significant detrital zircon populations are defined by 207Pb/206Pb ages, namely between 2200- 2220Ma and 2230-2270Ma (Figs 6.16 and 6.31). The 2200-2220Ma population is represented by only two concordant grains (15.1, 27.1). The two grains are both well rounded, but one (15.1) is oscillatory zoned and the other (27.1) massive in appearance

142

Table 6.5 Summary of SHRIMP U-Pb data for detrital zircons from the Daspoort Formation.

(1) (1) (1) % ppm ppm ppm 206Pb/238U 207Pb/206Pb % Total Total (1) (1) (1) (1) err 206 232 238 206 238 206 207 206 238 206 * 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th Th/ U Pb* Age Age Discordant U/ Pb ±% Pb/ Pb ±% U/ Pb ±% Pb / Pb ±% Pb / U±% Pb / U±% corr 1.1 0.15 109 65 0.61 52.8 2,874 ±67 2,900 ±13 1 1.777 2.9 0.2106 0.69 1.780 2.9 0.2092 0.79 16.21 3.0 0.562 2.9 .965 2.1 0.07 35 32 0.94 13.9 2,476 ±71 2,397 ±26 -3 2.134 3.4 0.1552 1.4 2.136 3.4 0.1546 1.5 9.98 3.8 0.468 3.4 .914 3.1 3.34 1115 236 0.22 143 867 ±22 2,302 ±25 62 6.71 2.7 0.1758 0.82 6.95 2.7 0.1462 1.5 2.902 3.1 0.1440 2.7 .878 4.1 0.14 170 119 0.72 77.8 2,746 ±63 2,879 ±11 5 1.881 2.8 0.2078 0.63 1.883 2.8 0.2066 0.69 15.13 2.9 0.531 2.8 .971 5.1 -- 161 75 0.48 57.2 2,226 ±53 2,281 ±13 2 2.426 2.8 0.1438 0.72 2.424 2.8 0.1444 0.75 8.21 2.9 0.413 2.8 .966 6.1 0.18 201 87 0.45 61.3 1,953 ±47 2,261 ±14 14 2.820 2.8 0.14440 0.68 2.825 2.8 0.1428 0.80 6.97 2.9 0.3539 2.8 .961 7.1 0.09 128 128 1.03 49.4 2,392 ±57 2,400 ±14 0 2.224 2.9 0.1557 0.75 2.226 2.9 0.1548 0.82 9.59 3.0 0.449 2.9 .962 8.1 0.09 214 173 0.83 74.1 2,178 ±51 2,271 ±13 4 2.486 2.8 0.1444 0.77 2.488 2.8 0.1436 0.78 7.96 2.9 0.402 2.8 .963 9.1 2.19 2157 432 0.21 78.5 261.8± 6.9 2,161 ±22 88 23.60 2.7 0.15408 0.53 24.13 2.7 0.1347 1.3 0.770 3.0 0.0414 2.7 .902 10.1 3.04 1180 807 0.71 145 839 ±21 2,017 ±24 58 6.98 2.7 0.15084 0.60 7.19 2.7 0.1241 1.3 2.379 3.0 0.1390 2.7 .894 11.1 0.80 355 444 1.29 81.4 1,513 ±37 2,390 ±20 37 3.75 2.7 0.1611 0.69 3.78 2.7 0.1540 1.2 5.62 3.0 0.2646 2.7 .922 12.1 1.04 756 283 0.39 78.6 729 ±19 2,424 ±17 70 8.26 2.7 0.1662 0.61 8.35 2.7 0.1570 1.0 2.592 2.9 0.1198 2.7 .939 13.1 12.77 1538 834 0.56 83.6 346.4± 9.2 2,477 ±47 86 15.80 2.7 0.2756 0.46 18.11 2.7 0.1621 2.8 1.234 3.9 0.0552 2.7 .696 14.1 1.00 501 245 0.50 113 1,491 ±36 2,614 ±11 43 3.80 2.7 0.18476 0.42 3.84 2.7 0.1759 0.66 6.31 2.8 0.2602 2.7 .971 15.1 1.44 555 179 0.33 82.2 1,012 ±26 2,209 ±21 54 5.80 2.7 0.15132 0.62 5.89 2.7 0.1386 1.2 3.246 3.0 0.1699 2.7 .917 16.1 0.06 42 34 0.84 16.3 2,409 ±65 2,407 ±24 0 2.205 3.2 0.1561 1.4 2.207 3.2 0.1555 1.4 9.71 3.5 0.453 3.2 .915 17.1 0.12 195 94 0.50 61.4 2,012 ±48 2,245 ±18 10 2.727 2.8 0.1426 0.78 2.730 2.8 0.1415 1.1 7.14 3.0 0.366 2.8 .936 18.1 1.00 698 258 0.38 70.1 706 ±18 2,329 ±17 70 8.55 2.7 0.15742 0.59 8.64 2.7 0.1485 0.99 2.370 2.9 0.1157 2.7 .939 19.1 1.64 599 237 0.41 88.6 1,009 ±25 2,277 ±20 56 5.81 2.7 0.15862 0.56 5.90 2.7 0.1441 1.2 3.365 3.0 0.1694 2.7 .917 20.1 0.68 539 185 0.35 73.7 946 ±24 2,244 ±16 58 6.28 2.7 0.14736 0.57 6.32 2.7 0.1413 0.93 3.082 2.9 0.1581 2.7 .946 21.1 1.06 468 128 0.28 112 1,574 ±38 2,990 ±14 47 3.578 2.7 0.2306 0.69 3.616 2.7 0.2212 0.84 8.43 2.8 0.2765 2.7 .955 22.1 2.25 726 789 1.12 152 1,377 ±35 2,174 ±43 37 4.10 2.8 0.1557 0.87 4.20 2.8 0.1358 2.4 4.46 3.7 0.2382 2.8 .754 23.1 1.50 410 325 0.82 77.9 1,272 ±31 2,182 ±22 42 4.52 2.7 0.14967 0.60 4.59 2.7 0.1364 1.3 4.10 3.0 0.2180 2.7 .909 24.1 2.59 1501 845 0.58 209 946 ±24 1,784 ±27 47 6.16 2.7 0.13157 0.49 6.33 2.7 0.1090 1.5 2.377 3.1 0.1581 2.7 .878 25.1 3.91 1096 462 0.44 84.8 535 ±14 2,276 ±30 76 11.10 2.7 0.17876 0.52 11.55 2.7 0.1440 1.8 1.719 3.2 0.0866 2.7 .836 26.1 1.73 667 414 0.64 85.5 883 ±22 2,206 ±23 60 6.70 2.7 0.15361 0.58 6.82 2.7 0.1383 1.3 2.797 3.0 0.1467 2.7 .897

143

Table 6.5 continued (1) (1) (1) % ppm ppm ppm 206Pb/238U 207Pb/206Pb % Total Total (1) (1) (1) (1) err 206 232 238 206 238 206 207 206 238 206 * 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th Th/ U Pb* Age Age Discordant U/ Pb ±% Pb/ Pb ±% U/ Pb ±% Pb / Pb ±% Pb / U±% Pb / U±% corr 27.1 2.03 973 589 0.63 103 737 ±19 2,190 ±26 66 8.09 2.7 0.1550 0.66 8.26 2.7 0.1370 1.5 2.287 3.1 0.1211 2.7 .874 28.1 5.42 349 254 0.75 40.7 778 ±21 3,056 ±44 75 7.38 2.7 0.2784 0.62 7.80 2.8 0.2306 2.8 4.08 3.9 0.1282 2.8 .714 29.1 7.69 732 280 0.40 149 1,275 ±31 2,163 ±34 41 4.22 2.7 0.20291 0.39 4.57 2.7 0.1350 1.9 4.07 3.3 0.2187 2.7 .812 30.1 1.36 637 283 0.46 81.6 885 ±22 2,192 ±19 60 6.70 2.7 0.14919 0.52 6.79 2.7 0.1372 1.1 2.784 2.9 0.1472 2.7 .929 31.1 0.25 212 269 1.31 61.4 1,871 ±45 2,251 ±16 17 2.963 2.8 0.14416 0.68 2.970 2.8 0.1419 0.95 6.59 2.9 0.3367 2.8 .945 32.1 6.60 722 269 0.38 80.2 735 ±19 2,198 ±39 67 7.73 2.7 0.1960 0.67 8.28 2.7 0.1376 2.2 2.293 3.5 0.1208 2.7 .769 33.1 2.45 1238 1190 0.99 113 635 ±16 2,020 ±23 69 9.43 2.7 0.14587 0.46 9.66 2.7 0.1244 1.3 1.775 3.0 0.1035 2.7 .903 34.1 4.52 423 127 0.31 98.3 1,479 ±36 2,284 ±35 35 3.70 2.7 0.1848 1.1 3.88 2.7 0.1447 2.0 5.15 3.4 0.2579 2.7 .802 35.1 3.48 875 259 0.31 84.4 663 ±17 2,339 ±27 72 8.91 2.7 0.18036 0.54 9.23 2.7 0.1494 1.6 2.232 3.1 0.1084 2.7 .866 36.1 4.52 1900 1266 0.69 173 620 ±16 1,943 ±27 68 9.45 2.7 0.15873 0.37 9.90 2.7 0.1191 1.5 1.659 3.1 0.1010 2.7 .868 37.1 0.02 113 77 0.70 51.0 2,727 ±63 2,901 ±11 6 1.898 2.9 0.2096 0.65 1.899 2.9 0.2094 0.66 15.21 2.9 0.527 2.9 .974 38.1 0.05 131 54 0.42 48.9 2,323 ±55 2,281 ±14 -2 2.304 2.8 0.1449 0.74 2.305 2.8 0.1444 0.82 8.64 2.9 0.434 2.8 .961 39.1 0.13 120 42 0.36 44.2 2,290 ±55 2,233 ±15 -3 2.342 2.8 0.1416 0.75 2.345 2.8 0.1404 0.87 8.26 3.0 0.426 2.8 .956 40.1 0.15 311 128 0.42 82.3 1,730 ±41 2,267 ±11 24 3.243 2.7 0.14460 0.56 3.248 2.7 0.14323 0.66 6.08 2.8 0.3079 2.7 .972 41.1 0.76 234 262 1.16 45.9 1,317 ±33 2,213 ±22 41 4.38 2.8 0.1456 0.75 4.41 2.8 0.1389 1.3 4.34 3.1 0.2266 2.8 .906 42.1 0.69 119 118 1.02 41.3 2,175 ±55 2,861 ±17 24 2.475 3.0 0.2105 0.73 2.492 3.0 0.2043 1.1 11.30 3.2 0.401 3.0 .942 43.1 0.26 228 165 0.75 59.5 1,707 ±42 2,241 ±18 24 3.289 2.8 0.1434 0.75 3.298 2.8 0.1411 1.0 5.90 3.0 0.3032 2.8 .939 44.1 0.26 154 89 0.60 73.2 2,829 ±64 2,786 ±10 -2 1.811 2.8 0.1975 0.54 1.815 2.8 0.1952 0.62 14.83 2.9 0.551 2.8 .976 45.1 1.92 646 175 0.28 82.1 873 ±22 2,298 ±20 62 6.76 2.7 0.16289 0.50 6.89 2.7 0.1458 1.1 2.917 2.9 0.1451 2.7 .921 46.1 -- 58 20 0.36 21.8 2,362 ±61 2,382 ±22 1 2.263 3.1 0.1521 1.1 2.260 3.1 0.1532 1.3 9.35 3.3 0.443 3.1 .925 47.1 1.65 389 288 0.76 42.6 761 ±20 2,290 ±27 67 7.85 2.7 0.1597 0.72 7.99 2.7 0.1451 1.6 2.506 3.2 0.1252 2.7 .865 48.1 0.06 40 11 0.29 15.1 2,342 ±64 2,401 ±33 2 2.281 3.2 0.1555 1.3 2.283 3.3 0.1550 2.0 9.36 3.8 0.438 3.3 .857 49.1 2.15 15 18 1.25 6.59 2,605 ±88 2,797 ±68 7 1.966 4.0 0.2155 1.9 2.009 4.1 0.1964 4.1 13.48 5.8 0.498 4.1 .704 50.1 0.21 390 133 0.35 53.8 958 ±24 2,271 ±15 58 6.23 2.7 0.14545 0.64 6.24 2.7 0.1436 0.85 3.173 2.9 0.1602 2.7 .955 Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions respectively. Error in standard calibration was 0.79% (not included in above errors but required when comparing data from different mounts). (1) Common Pb corrected using measured 204Pb

144 Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

145

Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

146

Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

(Fig 6.29). The oldest concordant zircon grain (25.1, Table 6.6) is 190mm in length, subrounded to rounded, of low sphericity and oscillatory zoned (Fig 6.29). It yielded an age of 2874±6Ma (zircon 25.1, Table 6.6).

One of the most important aspects of the physical characteristics and 207Pb/206Pb ages obtained for detrital zircons from various formations of the Wolkberg Group and Transvaal Supergroup is that although although zircons may have 207Pb/206Pb ages that are very similar, these zircons may display highly variable physical characteristics. Zircons within the same age populations may, therefore, well have been derived from different source areas. It is also important to note that some small zircons still display

147

Provenance of detrital zircons from the Wolkberg Group and Transvaal Supergroup

148

Table 6.6 Summary of SHRIMP U-Pb data for detrital zircons from the Magaliesberg Formation.

(1) (1) (1) % ppm ppm ppm 206Pb/238 U 207Pb/206Pb % (1) (1) (1) 206 232 238 206 207 * 206 * 207 * 235 206 * 238 Grain.Spot Pbc U Th Th/ U Pb* Age Age Discordant Pb / Pb ±% Pb / U ±% Pb / U ±% Err.corr 1.1 0.88 164 189 1.19 52.8 2,036 ±27 2,258 ± 13 10 0.1425 0.76 7.30 1.7 0.3714 1.6 .900 2.1 0.10 153 78 0.52 55.0 2,249 ±18 2,250.2 ± 10.0 0 0.14188 0.58 8.165 1.1 0.4174 0.93 .849 3.1 0.08 75 33 0.45 36.3 2,880 ±24 2,789.7 ± 9.6 -3 0.1956 0.59 15.19 1.2 0.5633 1.1 .874 4.1 0.04 627 221 0.36 264 2,570 ±44 2,311 ± 14 -11 0.1470 0.83 9.93 2.2 0.490 2.1 .928 5.1 0.06 203 100 0.51 75.1 2,306 ±17 2,262.8 ± 7.8 -2 0.14291 0.45 8.475 10 0.4301 0.89 .891 6.1 0.07 792 334 0.44 208 1,718 ±13 1,809.2 ± 8.8 5 0.11059 0.49 4.657 0.98 0.3054 0.85 .868 7.1 0.11 141 60 0.44 52.4 2,315 ±18 2,249 ± 10 -3 0.14175 0.60 8.442 1.1 0.4320 0.94 .844 8.1 3.47 465 376 0.83 98.5 1,375 ±16 2,249 ± 40 39 0.1417 2.3 4.65 2.7 0.2377 1.3 .490 9.1 0.02 395 41 0.11 147 2,320 ±16 2,304.9 ± 5.5 -1 0.14645 0.32 8.746 0.89 0.4331 0.83 .934 10.1 0.03 146 45 0.32 55.3 2,358 ±18 2,254.2 ± 9.1 -5 0.14220 0.53 8.659 1.1 0.4416 0.93 .871 11.1 1.51 1166 292 0.26 102 618.5 ± 6.7 2,095 ± 12 70 0.12975 0.66 1.801 1.3 0.1007 1.1 .864 12.1 0.07 176 91 0.53 63.8 2,266 ±17 2,251.2 ± 8.6 -1 0.14196 0.50 8.243 1.0 0.4211 0.91 .878 13.1 0.05 152 58 0.40 56.6 2,316 ±18 2,258.3 ± 9.6 -3 0.14254 0.56 8.494 1.1 0.4322 0.93 .859 14.1 12.50 782 535 0.71 75.9 607.3 ± 6.8 1,928 ±150 69 0.1181 8.3 1.61 8.4 0.0988 1.2 .141 15.1 0.02 389 164 0.44 133 2,166 ±16 2,215.7 ± 6.5 2 0.13907 0.38 7.658 0.92 0.3994 0.84 .914 16.1 1.67 359 534 1.54 87.2 1,581 ±12 2,424 ± 11 35 0.1570 0.65 6.016 1.1 0.2779 0.87 .799 17.1 0.01 222 109 0.51 81.7 2,298 ±17 2,260.0 ± 7.3 -2 0.14268 0.42 8.427 0.98 0.4284 0.88 .903 18.1 0.17 259 132 0.53 93.6 2,263 ±16 2,258.7 ± 7.7 0 0.14258 0.45 8.268 0.97 0.4206 0.86 .888 19.1 0.07 177 82 0.48 67.0 2,354 ±18 2,412.5 ± 8.1 2 0.15598 0.47 9.481 1.0 0.4408 0.90 .884 20.1 1.53 452 310 0.71 75.1 1,123.6 ± 9.0 2,239 ± 24 50 0.1409 1.4 3.700 1.6 0.1904 0.87 .533 21.1 0.06 699 558 0.83 246 2,213 ±15 2,237.9 ± 4.5 1 0.14087 0.26 7.955 0.85 0.4096 0.81 .953 22.1 -- 153 26 0.18 56.2 2,300 ±18 2,260.8 ± 9.1 -2 0.14275 0.53 8.440 1.1 0.4288 0.93 .870 23.1 1.99 449 205 0.47 111 1,608 ±34 2,245 ± 58 28 0.1414 3.4 5.53 4.1 0.2833 2.4 .579 24.1 0.08 392 133 0.35 144 2,293 ±16 2,261.6 ± 7.5 -1 0.14282 0.43 8.412 0.94 0.4272 0.83 .887 25.1 0.01 169 81 0.50 80.8 2,855 ±21 2,873.9 ± 6.0 1 0.20594 0.37 15.82 0.97 0.5571 0.90 .925 26.1 0.82 539 176 0.34 85.4 1,082 ±10 2,214 ± 11 51 0.13893 0.63 3.500 1.2 0.1827 1.0 .852 27.1 0.28 269 103 0.39 84.8 2,012 ±17 2,205 ± 13 9 0.1382 0.76 6.980 1.3 0.3662 10 .795 28.1 1.35 1768 1439 0.84 146 584.6 ± 4.8 1,300 ± 17 55 0.08431 0.87 1.103 1.2 0.09492 0.87 .707 29.1 0.03 321 127 0.41 117 2,271 ±29 2,268.5 ± 6.3 0 0.14339 0.37 8.35 1.6 0.4223 1.5 .972 Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions respectively. Error in standard calibration was 0.18% (not included in above errors but required when comparing data from different different mounts. (1) Common Pb corrected using measured 204Pb.

149 Provenance of the Wolkberg Group and Transvaal Supergroup

150 Provenance of the Wolkberg Group and Transvaal Supergroup their primary euhedral shape and may therefore be first order zircons. Some of the larger zircons may be of second order, i.e. zircons that were previously deposited as part of older sedimentary successions that were uplifted and eroded to be deposited in the formations from which they were separated and analysed.

6.4 Discussion The interpretation of detrital zircon populations will first focus on the overall stratigraphic pattern displayed 207Pb/206Pb age distributions. The results will be used to identify possible source areas and a broad tectonic model for the deposition of the Wolkberg Group and Transvaal Supergroup will be proposed.

6.4.1 Stratigraphic Variation in Detrital Zircon Ages The ages of detrital zircons in the sedimentary rocks of the Wolkberg and Transvaal successions display a systematic younging of the youngest detrital zircons upwards in the succession from one unconformity-bounded sequence to the next (Fig 6.32). In addition, abrupt changes in prominent detrital zircon populations take place across major sequence boundaries in the succession, as outlined in figure 6.32.

6.4.1.1 Variation in Youngest Detrital Zircon Ages The youngest detrital zircons of the Wolkberg Group and Transvaal Supergroup display a systematic younging upwards in the succession from one unconformity-bounded sequence to the next (Fig 6.32). The youngest concordant grain in the Schelem Formation is 2635±18Ma in age (Table 6.1)(Fig 6.32). It appears very likely that this zircon was derived from the immediately underlying lavas in the Wolkberg Group such as the Abel Erasmus volcanics which is unconformably overlain by the Schelem Formation (Button, 1973; Bosch, 1992).

A 207Pb/206Pb age of 2424±12Ma was obtained for the youngest zircon in the Duitschland Formation (Table 6.2, Fig 6.32) at the base of the Pretoria Group. This 207Pb/206Pb detrital zircon age may be a good approximation for the age of the glaciation that occurred during the deposition of the Duitschland Formation (Coetzee, 2001; Bekker,

151 Provenance of the Wolkberg Group and Transvaal Supergroup

152 Provenance of the Wolkberg Group and Transvaal Supergroup

2001). It is in good agreement with the age of the oldest glacial deposits in the Huronian Supergroup (Young, 1995) at ca. 2450Ma (Krogh, 1984; Young, 1991). The youngest zircon in the Timeball Hill Formation has a 207Pb/206Pb age of 2324±17Ma (Table 6.3, Fig 6.32). This may indicate that the Timeball Hill Formation is significantly younger than the Duitschland Formation, or that new source areas were created immediately prior to deposition of the Timeball Hill Formation that was not present in Duitschland times.

The youngest zircon in the Hekpoort Formation has a 207Pb/206Pb age of 2230±35Ma (Table 6.4, Fig 6.32). This age may approximate the timing of volcanism in the Hekpoort Formation (see Chapter 4, this thesis). The youngest zircons in the Daspoort and Magaliesberg Formations have 207Pb/206Pb ages of 2233±26Ma and 2205±13Ma respectively (Tables 6.5 and 6.6; Fig 6.32). This may again indicate that new and younger source areas became exposed during the deposition of the Daspoort and Magaliesberg Formations.

6.4.1.2 Variation in Zircon Populations Significant 207Pb/206Pb age populations of detrital zircons in the Schelem Formation are between 2840-3010Ma and 3170-3340Ma in age (Fig 6.32). Approximately 50 persent of the zircons analysed for the Schelem Formation are rather large (200-400micron), and probably represent first cycle detrital grains derived from older basement granites that sourced siliciclastic material into the Wolkberg basin. Some of the smaller rounded grains may have been reworked from older sedimentary successions on the Kaapvaal craton. The radiometric 207Pb/206Pb zircon ages of older detrital zircon populations of the Wolkberg Group is somewhat similar to that of the Witwatersrand and Pongola Supergroups. Barton et al. (1989) determined detrital zircon populations of between 2900 and 3020Ma for the Orange Grove Formation and peaks between 2900 and 3000Ma and 3170 and 3230 Ma for the Ventersdorp Contact Reef. The oldest grain analysed in the Orange Grove Formation is 3330Ma old and for the Ventersdorp Contact Reef 3250 Ma. Robb et al. (1989) analysed detrital zircon grains for several formations throughout the Witwatersrand Group. Their 207Pb/206Pb zircon ages are all within a 2900-3200Ma range. The Pongola Supergroup displays a similar pattern for the 207Pb/206Pb zircon ages

153 Provenance of the Wolkberg Group and Transvaal Supergroup ranging between 2900 and 3200Ma (Nhleko, 2003). Therefore, detrital zircon populations in the Wolkberg Group may suggest that the sources similar in age to those that shed sediments during the deposition of the Witwatersrand Supergroup, supplied sediment into the Wolkberg basin. These sources may be identified as granite-greenstone terranes and volcanic rocks of the Nsuzi/Dominion successions (ca. 2.95Ga). However, these old sources are complemented by sources <2.9Ga. These sources may be the Ventersdorp Supergroup or the Kanye volcanic suite or age-equivalents.

Apart from the Duitschland Formation, all the formations of the Pretoria Group that where analysed, contain some zircons that have 207Pb/206Pb ages in the 2850-3010Ma range (Fig 6.32). These zircons are all distinctly smaller in size than those of the Wolkberg Group (Fig 6.16). There are no similarities between 207Pb/206Pb detrital zircon age populations in the Duitschland Formation at the base of the Pretoria Group and the Schelem Formation of the Wolkberg Group (Fig 6.32). However, it is important to note that the Duitschland Formation contains detrital zircon populations between 3020 and 3420Ma that are similar in age to some granites of the Kaapvaal craton (De Wit and Ashwal, 1997). Another important observation is the fact that apart from one well- rounded detrital zircon grain in the Timeball Hill Formation (Grain 21.1, Table 6.3), probably reworked from an earlier sedimentary sequence, the upper Pretoria Group does not contain any detrital zircons that are similar in age to granites common of the Kaapvaal craton granite-greenstone basement (i.e. Poujol et al., 1997).

The most prominent population of detrital zircon 207Pb/206Pb ages in both the Duitschland and Timeball Hill Formations occur between 2460-2550Ma (Fig 6.32). However, it is interesting to note that the zircons from this population are texturally very different between the two formations (See summary of physical characteristics, Fig 6.16). Zircons belonging to the upper Duitschland diamictite from this population are mostly angular to subrounded and on average 87µm in length. In contrast, those from the Timeball Hill zircons are rounded to well rounded, and on average 113µm in length (Fig 6.16). The fact that the zircons of the younger Timeball Hill Formation are better rounded than those of the Duitschland Formation may reflect the fact that they were fluvially transported and

154 Provenance of the Wolkberg Group and Transvaal Supergroup then reworked in a deltaic depositional environment in contrast to possible mass flow or even glacial transport (Bekker et al., 2001) of zircons in diamictites of the Duitschland Formation. However, the transport mechanism does not explain the larger size of zircons in the Timeball Hill Formation relative to those in the Duitschland diamictite. Perhaps the zircons were derived from different parent rock types (such as lava versus plutonic granite), but of similar age.

The quartzite bed of the Hekpoort Formation is characterised by a well defined detrital zircon 207Pb/206Pb age population between 2500 and 2520Ma. Apart from one zircon in the Lucknow formation of the Postmasburg Group (Van Niekerk, 2004), there are no zircons present in the 2460-2550Ma age population in formations above the Hekpoort Formation (Fig 6.32).

The second most important detrital zircon 207Pb/206Pb age population for the Duitschland diamictite falls into the period 2700-2820Ma. Within this population, six nearly concordant grains define a sub population between 2770-2810Ma. These six grains are on average 97micron in length, euhedral to very angular and zoned, suggesting that they may not have been transported for a significant distance before deposition. A few detrital zircons of similar age in the Timeball Hill, Daspoort and Magaliesberg Formations, suggest that there was a continuous supply of sediment shed from source areas of this age range, during the deposition of the upper Pretoria Group.

A small population of zircons with ages between 2370 and 2390Ma comes to the fore the first time in the Timeball Hill Formation. Detrital zircons of this age are also present higher up in the in the Hekpoort and Daspoort successions (Fig 6.32).

Three detrital zircon populations characterize the Hekpoort Formation (Fig 6.32). These populations range in age between 2350-2360Ma, 2280-2340Ma and 2230-2250Ma. The 2350-2360Ma population does not continue into any of the formations of the Pretoria Group above the Hekpoort lava (Fig 6.32). However, there are detrital zircons of this age range present within the Lucknow Formation of the Postmasburg Group (Van Niekerk,

155 Provenance of the Wolkberg Group and Transvaal Supergroup

2004). Both, the 2280-2340Ma and 2230-2250Ma populations of the Hekpoort Formation continue into the Daspoort, Magaliesberg and Lucknow Formations.

Two new detrital zircon populations become apparent in the Daspoort Formation, one in the age interval 2400-2410Ma and the other in the interval between 2270 and 2300Ma (Fig 6.32). Both populations extend into the Magaliesberg Formation but are not present in the Lucknow Formation, which is considered correlative to the Magaliesberg quartzite (Fig 6.28) in Griqualand West. One zircon grain in the Magaliesberg Formation has an age between 2400Ma and 2410Ma. This population of zircons is also not present in the Lucknow Formation. Zircons in the age range 2270-2300Ma are abundantly present in the Magaliesberg Formation, but not in the Lucknow Formation (Fig 6.32).

Two younger detrital zircon populations are present in the Magaliesberg Formation. The one defines a very narrow age interval between 2250Ma and 2260Ma that represents most of the concordant detrital zircon 207Pb/206Pb ages for the Magaliesberg Formation (Fig 6.32). Another population, subordinate to the 2250-2260Ma population, is present between 2200Ma and 2235Ma. This is the youngest group of detrital zircons analysed for the Pretoria Group. A similar age population of zircons are also present in the Hekpoort Formation, as dicussed above. It is important to note that some of these young zircon grains are rounded to well rounded, and approximately 110µm in length. Their roundness may be an indication of the high enegy, beach environment in which they were deposited. However, there are also euhedral grains in the 2250-2260 range that are similar in character to zircon grains from the Hekpoort Formation lower down in the succession (Fig 6.16). This may indicate that these grains were directly sourced from the Hekpoort lava itself and may not have been transported a significant distance, and/or been reworked in a beach environment.

6.4.2 Provenance and Tectonic Model Several tectonic scenarios may explain the appearance and disappearance of specific provenance areas as source of siliciclastic detritus to sedimentary basins. These tectonic scenarios may include:

156 Provenance of the Wolkberg Group and Transvaal Supergroup a) Compressional events attaching new source areas to existing continental blocks. b) Rifting that removes source areas. c) Burial of previously exposed source areas by younger sediments. d) Uplift and exposure of new source areas. e) Magmatic events associated with rifting and/or volcanic arc development that creates new source areas.

Based on these possibilities, some of the stratigraphic variations in detrital zircon populations in the Wolkberg and Transvaal successions may be explained.

6.4.2.1 Wolkberg Group Provenance- Implications for the Origin of the Limpopo Belt During the deposition of the Wolkberg Group, the Kaapvaal craton was probably in a passive margin setting (Fig 6.33A.1), as suggested by the deposition of the carbonate platform sequence of the Boomplaas Formation between 2670 and 2650Ma, followed by further carbonate deposition in the Lokammona and Monteville Formations, to about 2600Ma (Fig 6.33A.2).

The erosional surface at the base of the Wolkberg Group rests directly on basement granite and greenstone belts in the north of the present day Kaapvaal craton, suggesting that at least some of the Wolkberg Group sediments were derived from the underlying rocks of the Kaapvaal Craton. The Kaapvaal Craton contains mainly early to mid Archean basement granite, as well as greenstone belts (De Wit et al., 1992). The 2900- 3010Ma zircon populations of the Schelem Formation (Fig 6.32) may have been derived from granites of this age in the northern part of the Kaapvaal craton. Ages in the range of ca 2.8 Ga have been obtained for granites on the fringes of the Pietersburg Greenstone belt (De Wit et al., 1993, Brandl and De Wit, 1997) to the north of the area where the sample of the Schelem Formation was collected. Euhedral zircons from a conglomerate of the Uitkyk Formation of the Pietersburg Greenstone belt yield zircon 207Pb/206Pb ages in the order of 2960Ma (De Wit et al., 1993). The Murchison Greenstone belt to the west

157 Provenance of the Wolkberg Group and Transvaal Supergroup

158 Provenance of the Wolkberg Group and Transvaal Supergroup of the area where the Schelem Formation sample was collected formed between 3090 and 2970Ma ago (Poujol et al., 1997).

The 2850-2880Ma detrital zircon population in the Schelem Formation (Fig 6.32) is similar in age to the Schweizer-Reineke granite (2882±2Ma, Robb et al., 1992) or Kraaipan granodiorite (2846±22, Anhaeusser and Walraven, 1997). However, basin configuration and paleo current directions in the Schelem Formation suggest that source areas were located to the north and northeast of the present outcrop area, indicating that these two granites that are located to the west and northwest of the sample locality most probably did not source the succession.

The older 3170-3340Ma zircon population in the Schelem Formation (Fig 6.32) may have been derived from an older greenstone belt, such as the Barberton greenstone belt that is known to have been formed between 3450-3250Ma (Kamo and Davis, 1994; Armstrong et al., 1990, Kroner et al., 1996; Byerly et al., 1996). However, the Barberton greenstone belt itself is, located too far south to have sourced the Wolkberg Group at the locality where the sample was collected. This suggests that Barberton-aged greenstone belt rocks must have been located to the north of the locality where the sample for the Schelem Formation was collected at time of deposition of the succession.

There is one zircon present in the Schelem Formation with an age of about 2650Ma. This zircon could have been derived from contemporaneous volcanism in the Wolkberg and Buffelsfontein Groups (Barton et al., 1995; Gutzmer and Beukes, 1998). Most importantly, however, is the absence of zircons between 2650-2700Ma in age, the time when granulite facies metamorphism and the intrusion of post tectonic granite are inferred to have taken place in the Limpopo belt (Barton et al., 1992; Barton and Van Reenen, 1992; Barton et al., 1994; Mkweli et al., 1995; McCourt and Armstrong, 1998) makes it highly unlikely that a Himalaya-type collision suggested by Barton and Van Reenen (1992) took place between the Kaapvaal and Zimbabwe cratons at this time. Furthermore, during the period 2670-2600Ma a sequence of carbonate platform rocks was deposited along the western margin of the Kaapvaal craton in the form of the

159 Provenance of the Wolkberg Group and Transvaal Supergroup

Boomplaas Formation (Fig 6.3). Himalaya-scale mountain building as suggested for the Limpopo belt, would most probably have buried the Kaapvaal craton with a thick succession of siliciclastic sediments. A carbonate platform, which normally develops under clear water conditions, would almost certainly not have been able to develop under such conditions. It is therefore suggested that the Kaapvaal craton was not involved in the collisional event responsible for ca. 2.65Ga granulite facies metamorphism in the Limpopo Belt.

6.4.2.2 Chuniespoort/Campbellrand to Timeball Hill Times In the period between 2600 and 2430Ma, the Kaapvaal craton was probably in a passive margin setting, as suggested by the deposition of kilometre thick successions of carbonate and banded iron-formations of the Transvaal Supergroup (Figs 6.2 and 6.33A.2). Present day outcrop of the Transvaal Supergroup suggests that carbonate and banded iron formation covered the entire present day Kaapvaal craton prior to the deposition of siliciclastic sediments that contribute to the Pretoria Group (Beukes, 1983). Some influx of sediment occurred from the northeast, as suggested by thin quartzite units in the Malmani carbonates, suggesting the presence of continental terrain to the northeast of the Kaapvaal craton (Button, 1973; Beukes, 1983).

Only a thin sliver of the Penge Iron Formation is preserved on the eastern and central part of the present day Kaapvaal craton, suggesting that uplift occurred prior to deposition of the Duitschland Formation (Coetzee, 2001). Thickening of strata towards the northeast suggests that basin deepening took place in that direction during deposition of the lower Duitschland Formation (Fig 6.5B) (Coetzee, 2001)(Fig 6.33A.3). During the deposition of the upper Duitschland Formation, the tectonic setting of the Kaapvaal craton changed from a passive margin to a foreland basin-type setting (Fig 6.33B.4) with mountain building towards the northeast of the Kaapvaal craton (Coetzee, 2001)(Fig 6.33B.4).

The prominent population of detrital zircon 207Pb/206Pb ages between 2450-2550Ma in the Duitschland Formation corresponds to the period of craton-wide carbonate and banded iron-formation deposition on the Kaapvaal craton. The erosional surface at the

160 Provenance of the Wolkberg Group and Transvaal Supergroup base of the upper Duitschland Formation does not erode through the carbonates of the Transvaal Supergroup (Fig 6.2). This implies that the 2450-2550Ma, and for that matter all the other detrital zircon populations present in the upper Duitschland diamictite, must have been derived from a source other than what is presently preserved on the Kaapvaal craton, i.e. a source outside of the present day margins of the Kaapvaal craton. The thickness distribution of the conglomerate overlying the erosional unconformity at the base of the upper part of the Duitschland Formation (Fig 6.4C)(Coetzee, 2001) suggests that a continent collided to the northeastern side of the Kaapvaal craton (in its present day configuration; Fig 6.33B.4). The age of 2320 Ma in the lower shales of the Timeball Hill (Hannah et al., 2002) suggest that this collision may have occurred between 2320 and 2350Ma (Fig 6.2). It is speculated that the 2450-2550Ma detrital zircon population originated as part of magmatic activity in an Andean type setting, as the continent that collided with the Kaapvaal approached and oceanic crust was subducted under the Kaapvaal craton (Fig 6.33A.1).

The Duitschland Formation also contains some zircons that are of Ventersdorp/Fortescue sequence age (2700-2780Ma; The Ventersdorp volcanics range in age from 2709±4Ma (Armstrong et al., 1991)-2785Ma (Moore et al., 1993) and the Fortescue volcanics range from 2765-2687Ma (Arndt et al., 1991). It is, however, highly unlikely that the Pilbara craton could have sourced the 2460-2550Ma zircon population. Similar to the Kaapvaal craton, the Pilbara craton was covered by carbonate and banded iron formation sequences during the period 2597±5Ma, deposition of the Marra Mamba Formation (Trendall et al., 1998) and the period 2449±3 i.e. deposition of the Weeli Wolli Iron Formation (Barley et al., 1998; Pickard, 2002). It is suggested that the 2700-2780 extrusion of large volumes of lavas may not have been limited to the Kaapvaal and Pilbara cratons (Nelson et al., 1999). A cratonic fragment other than the Pilbara craton, on which Ventersdorp/Fortescue age lavas was extruded, may have been the source to the 2700- 2800Ma detrital zircon population in the Duitschland Formation. This fragment must have been situated to the north of the present day northern margin of the Kaapvaal craton, as sediment dispersal in the Duitschland Formation was from the north. The 3030- 3430Ma age zircons in the Duitschland Formation could also have been derived from

161 Provenance of the Wolkberg Group and Transvaal Supergroup

162 Provenance of the Wolkberg Group and Transvaal Supergroup such a cratonic block, with characteristics similar to that of the present day Barberton terrain of the Kaapvaal craton.

The thickness distribution of quartzite in the Timeball Hill Formation suggests that the sediments were not only sourced from a source areas towards the northeast, but also source areas towards the north-northwest of the present day limits of the Transvaal basin (Fig 6.5C). The most prominent population of detrital zircon 207Pb/206Pb ages for the Timeball Hill Formation is between 2450-2550Ma, similar to that of the Duitschland Formation (Fig 6.32). It is suggested that the 2450-2550Ma population of detrital zircons in the Timeball Hill Formation was derived from the same source area as that of Duitschland Formation.

Source areas for the 2320-2390Ma detrital zircon population of the Timeball Hill Formation are not present on the Kaapvaal craton. These zircons may also have been sourced from the craton that served as a source area for the 2450-2550Ma detrital zircon population. A single 3614±5Ma zircon suggests that a source area of middle Archean age was exposed during the deposition of the Timeball Hill Formation (Fig 6.32)(Table 6.3).

6.4.2.3 Hekpoort to Magaliesberg Times The youngest zircons of the Hekpoort Formation could be taken as indication of the timing of volcanism at approximately 2240Ma (see Chapter 3). Volcanism was followed by a period of erosion marked by the Gamagara-Dwaal Heuwel erosional surface. The Gamagara-Dwaal Heuvel Formations mark the first time in the history of the Transvaal Supergroup that input of sediment was predominantly from the west (Fig 6.33B.6), as opposed to sediment input mostly from the north and east in older siliciclastic units. This may be used to infer a mountain building event on the western side of the present western margin of the Kaapvaal craton. That such a collisional event took place is further supported by the fact that the Hotazel Formation overlying the Ongeluk lava in Griqualand West may have been deposited in a back-arc type basin (Beukes, 1983), with the actual volcanic arc situated further to the west of the present-day outcrop limit of the

163 Provenance of the Wolkberg Group and Transvaal Supergroup

Transvaal Supergroup in Griqualand West. This volcanic arc could have developed prior to the proposed collisional event that followed. The Daspoort, Magaliesberg and Lucknow (Van Niekerk, 2004) Formations do not contain any zircon populations older than 2920Ma, which suggests that the Kaapvaal craton collided with a continental block that contained abundant rocks that are some 600Ma younger than those common on the Kaapvaal craton. The collision folded strata of the lower Transvaal Supergroup along the western margin of the Kaapvaal craton (Fig 6.33B.6). During the collision, fluvial red bed successions were deposited on the western side of the Kaapvaal craton, with marine orthoquartzites deposited more distally in the east (Fig 6.33B.6)(Dorland, 1999; Beukes et al., 2002). The distribution of depositional environments suggests that during the outpour of the Hekpoort lavas, a cratonic fragment located to the east of the Kaapvaal craton rifted away. This created a passive margin setting on the eastern side of the craton, in which shallow marine quartzite of the Dwaal Heuvel Formation were deposited (Fig 6.33B.6)(Button, 1973). Following this breakup, collision of the Kaapvaal craton took place with another craton to the west, sourcing siliciclastics for the Gamagara/Dwaal Heuwel, Daspoort, Magaliesberg and Lucknow Formations.

6.4.2.4 Summary of Tectonic Model The tectonic model for the Kaapvaal craton as derived from the study of detrital zircon populations outlined above, can be summarized as follows:

· Ca 2690-2590Ma Deposition of Wolkberg Group and Schmidtsdrif Subgroup on the Kaapvaal craton, possibly in two separate basins (Figs 6.4A and 6.33A.1). The deposition of a carbonate platform on the western margin of the Kaapvaal craton suggests that the Kaapvaal craton was in a passive margin setting during this period. The absence of 2600-2700 Ma old detrital zircons suggest that the Limpopo metamorphic belt did not developed as the result of a Himalayan-type collision between the Kaapvaal and Zimbabwe cratons at ca 2650Ma, but probably due to a collision between the Zimbawe craton and an unknown cratonic fragment.

164 Provenance of the Wolkberg Group and Transvaal Supergroup

· Ca 2600-2350Ma Deposition of a kilometre thick succession of carbonates and iron-formation on the Kaapvaal craton (Figs 6.4B, 6.4C and 6.33A.2). The Kaapvaal craton was in a passive margin setting throughout this period.

· Ca. 2350-2330Ma Deposition of the upper Duitschland Formation (Figs 6.4B, 6.4C and 6.33B.1). A prominent 2450-2550Ma detrital zircon population and development of a significant erosional unconformity between the lower and upper parts of the Duitschland Formation possibly mark a collisional event between the Kaapvaal craton and an unknown craton of middle Archean age to the north of the present day Kaapvaal craton.

· Ca. 2330-2260Ma Deposition of the Timeball Hill, Boshoek and Makganyene Formations (Figs 6.4C and 6.33B.1). Erosion at base of the Makganyene Formation may have removed up to 140Ma of depositional history on the western side of the Kaapvaal craton. Persistence of the prominent 2450-2550Ma detrital zircon population suggests that the source area remained similar to that recorded by the Duitschland Formation.

· Ca. 2260-2200Ma Extrusion of Hekpoort/Ongeluk lavas and carbonate and deposition of banded iron and manganese formation of the Hotazel and Mooidraai Formations (Figs 6.4D and 6.33B.2). The Hotazel Formation was possibly deposited in a back arc basin setting. The most prominent detrital zircon population present in the Hekpoort Formation is 2230 and 2360Ma in age. The presence of a smaller detrital zircon population between 2450 and 2530Ma suggest that there was still an influx of detritus from the source that supplied the Duitschland and Timeball Hill Formations with sediment.

· Ca. 2200-2070Ma The ~2200Ma Gamagara-Dwaalheuwel Formation mark the first time in the history of the Transvaal Supergroup that the input of sediment was predominantly from the west. It

165 Provenance of the Wolkberg Group and Transvaal Supergroup is suggested that a collisional event that folded strata along the western margin of the Kaapvaal craton in Griqualand West was responsible for the change from a previous north-south basin configuration to a east-west basin configuration (Fig 6.33B.2). A marked population of 2200-2300Ma old detrital zircons occurs in the upper Pretoria and Postmasburg Groups. These were probably derived from the cratonic block that collided with the Kaapvaal craton.

6.5 Conclusions The most important conclusion about the zircon provenance of the ca 2670Ma Wolkberg Group is the absence of 2650-2700Ma detrital zircons in it. 2650-2700Ma is the time period during which the Limpopo mobile belt underwent peak metamorphism, and was intruded by large granitic plutons (Fig 6.2)(Barton and Van Reenen, 1992). The deposition of a carbonate platform sequence on the Kaapvaal craton during this period suggests that the Kaapvaal craton was in a passive margin setting during this period. It may therefore be assumed that the ca. 2.65Ga Limpopo Belt peak metamorphism was not associated with collision between the Zimbabwe and the Kaapvaal cratons.

Two significant age distribution patterns are recognized within the detrital zircon populations of the Pretoria Group of the Transvaal Supergroup. First, there is the continuous younging of the youngest detrital zircon that may indicate the continuous exposure of new source areas during the deposition of the Pretoria Group. Second, there are abrupt changes in prominent detrital zircon populations across major sequence boundaries. The occurrence of large peaks of detrital zircons of similar age to carbonates and banded iron formations of the Transvaal Supergroup suggests that cratons other than the Kaapvaal craton were sourced during the deposition of the Pretoria Group. The detrital zircon populations of the Wolkberg Group and Transvaal Supergroup suggests that the Kaapvaal craton may have a much more complex tectonic history than previously thought and that its history can not be understood as an isolated block, but that it has to be understood as a craton interacting with several other cratonic blocks.

166 Provenance of the Wolkberg Group and Transvaal Supergroup

6.6 Further work This study certainly has only a reconnaissance character, determining the most important detrital zircon populations through the period 2.68-2.1Ga on the Kaapvaal craton. Single zircons were analysed from different formations using composite samples. Further analyses of zircons from different sections may yield different populations of zircons not recognized during this study. Further detrital zircon studies on specifically the Buffelsfontein Group which, may help further resolve the hypothesis developed in this thesis that the ca 2.65Ga metamorphism in the Limpopo belt is not related to a collision between the Kaapvaal and Zimbabwe cratons. Detrital zircon work on the Vryburg Formation, Wolkberg Group, Black Reef Formation, quartzite units within the Malmani dolomite and the Makganyene diamictite may greatly increase our knowledge about the tectonic history of the Kaapvaal craton during the early Paleoproterozoic.

6.7 References Anhaeusser, C.R., Walraven, F. (1997). Polyphase crustal evolution of the Archean Kraaipan granite-greenstone terrane, Kaapvaal Craton, South Africa. University of the Witwatersrand, Economic Geology Research Unit Information Circular (313), 1-27.

Armstrong, R.A., Compston, W., de Wit, M.J., Williams, I.S. (1990). The stratigraphy of the 3.5-3.2Ga Barberton Greenstone Belt revisited: a single zircon ion microprobe study. Earth and Planetary Science Letters, 101, 90-106.

Armstrong, R.A., Compston, W., Retief, E., Williams, I.S., Welke, H.J. (1991). Zircon ion microprobe studies bearing on the age and evolution of the Witwatersrand Triad. Precambrian Research, 53, 243-266.

Arndt, N.T., Nelson, D.R., Compston, W., Trendall, A.F., Thorne, A.M. (1991). The age of the Fortescue Group, Hamersley Basin, Western Australia, from ion microprobe U-Pb zircon results. Australian Journal of Earth Sciences, 38, 261-281.

167 Provenance of the Wolkberg Group and Transvaal Supergroup

Barley, M.E., Pickard, A.L., Sylvester, P.J. (1998). Emplacement of a large igneous province as a possible cause of banded iron formation 2.45 billion years ago. Nature, 385, 55-58.

Barton, E.S., Compston, W., Williams, I.S., Bristow, J.W., Hallbauer, D.K., Smith, C.B. (1989). Provenance ages for the gold-bearing Witwatersrand Supergroup: constraints from ion microprobe U-Pb ages of detrital grains. Economic Geology, 84, 2012-2019.

Barton, J.M., and Van Reenen, D.D. (1992). When was the Limpopo orogeny? Precambrian Research, 55, 7-16.

Barton, J.M., Blignaut, E., Salnikova, E.B., Kotov, A.B. (1995). The stratigraphical position of the Buffelsfontein Group based on field relationships and chemical and geochronological data. South African Journal of Geology, 98(4), 386-392.

Barton, J.M., Doig, R., Smith, C.B., Bohlender, F. and Van Reenen, D.D. (1992). Isotopic and REE characteristics of the intrusive charnoenderbite and enderbite geographically associated with the Matok Pluton, Limpopo Belt, southern Africa. Precambrian Research, 55, 451-467.

Barton, J.M., Holzer, L., Kamber, B., Doig, R., Kramers, J.D. and Nyfeler, D. (1994) Discrete metamorphic events in the Limpopo belt, southern Africa: Implications for the application of P-T paths in complex metamorphic terrains. Geology, 22, 1035-1038.

Bekker, A., Kaufman, A.J., Karhu, J.A., Beukes, N.J., Swart, Q.D., Coetzee, L.L. and Eriksson, K.A. (2001). Chemostratigraphy of the Paleoproterozoic Duitschland Formation, South Africa: Implications for coupled climate change and carbon cycling. American Journal of Science, 301, 261-285.

168 Provenance of the Wolkberg Group and Transvaal Supergroup

Beukes, N.J., (1978). Die karbonaatgesteentes en ysterformasies van die Ghaap Groep van die Transvaal-Supergroep in Noord Kaapland. Ph. D. thesis (unpublished) Rand Afrikaans University, Johannesburg, 580pp.

Beukes, N.J. (1983). Paleoenvironmental setting of iron-formations in the depositional basin of the Transvaal Supergroup, South Africa, 131-209. In: Trendall, A.C. and Morris, R.C., (Editors). Iron-Formation: facts and problems. Developments in Precambrian Geology, 6, Elsevier, Amsterdam, 558pp.

Beukes, N.J., Dorland, H.C., Gutzmer, J., Nedachi, M., and Ohmoto, H. (2002). Tropical laterites, life on land, and the history of atmospheric oxygen in the Paleoproterozoic. Geology, 30, 6, 491-494.

Bosch, P.J.A. (1992). Die Geologie van die Wolkberg Groep tussen die Abel Erasmuspas en Graskop, oos Transvaal. M.Sc. thesis (unpublished), University of Pretoria, South Africa, 290pp.

Brandl, G., and De Wit, M.J. (1997). The Kaapvaal Craton. In: Greenstone belts, editors De Wit, M.J. and Ashwal, L.D. Clarendon Press: Oxford. 581-607.

Buick, I.S., Maas, R. and Gibson, R. (2001). Precise U-Pb titanite age constraints on the emplacement of the Bushveld Complex, South Africa. Journal of the Geological Society, London, 158, 3-6.

Button, A. (1973). A study of the stratigraphy and development of the Transvaal basin in the eastern and northeastern Transvaal. Ph. D. thesis (unpublished), University of the Witwatersrand, Johannesburg, 133pp.

Byerly, G.R., Kroner, A., Lowe, D.R., Todt, W., Walsh, M.M. (1996). Prolonged magmatism and time constraints for sediment deposition in the early Archean Barberton

169 Provenance of the Wolkberg Group and Transvaal Supergroup greenstone belt: evidence from the Upper Onverwacht and Fig Tree Groups. Precambrian Research, 78, 125-138.

Coetzee, L.L. (2001). Genetic Stratigraphy of the paleoproterozoic Pretoria Group in the Western Transvaal. M.Sc thesis, unpublished, Rand Afrikaans University, 212pp.

Cornell, D.H., Schutte, S.S. and Eglington, B.L. (1996). The Ongeluk basaltic andesite formation in Griqualand West, South Africa: submarine alteration in a 2222Ma Proterozoic sea. Precambrian Research 79, 101-123.

De Beers (1998). Aeromagnetic map. Update on the distribution in time and space of southern African Kimberlites. Produced by Ayres, N.P., Hatton, C.J., Quadling, K.E., Smith, C.B.

De Villiers, S.B. (1975). Die Groep Wolkberg in die gebied Button’s Kop-Chuniespoort, Noord Transvaal. Annals of the Geological Survey of South Africa, II, 1-6.

De Wit, J. M., Roering, C., Hart, R. J., Armstrong, R.A., De Ronde, C.E.J., Green, R.W.E., Tredoux, M., Peberdy, E., Hart, R.A. (1992). Formation of an Archean continent. Nature, 357, 553-562.

De Wit, M.J., Armstrong, R.A., Kamo, S.L., and Erlank, A.J. (1993). Gold-bearing sediments in the Pietersburg greenstone belt: age equivalents to the Witwatersrand Supergroup sediments, South Africa. Economic Geology, 88, 1242-1252.

De Wit, M.J., Ashwal, L.D. (1997). Greenstone Belts.Clarendon Press:Oxford 809pp.

Dorland, H.C., (1999). Paleoproterozoic laterites, red beds and ironstones of the Pretoria Group with reference to the history of atmospheric oxygen. M.Sc thesis (unpublished) 147pp.

170 Provenance of the Wolkberg Group and Transvaal Supergroup

Eriksson, P.G., Schweitzer, J.K., Bosch, P.J.A., Schreiber, U.M., Van Deventer, J.L., Hatton, C.J. (1993). The Transvaal Sequence: an overview. Journal of African Earth Science, 16, 2, 25-51.

Froude, D.O., Ireland, T.R., Kinny, P.D., Williams, I.S., Compston, W., Williams, I.R. and Meyers, J.S. (1983). Ion microprobe identification of 4100-4200 Myr-old terrestrial zircons. Nature, 303, 616-618.

Gutzmer, J. and Beukes, N.J. (1998). High grade manganese ores in the Kalahari manganese field: Characterisation and dating of ore forming events. Unpublished Report, Rand Afrikaans University, Johannesburg, 221pp.

Gutzmer, J., Pack, A, Luders, V., Wilkinson, J.J., Beukes, N.J., Van Niekerk, H.S. (2001A). Formation of jasper and andradite during low-temperature hydrothermal seafloor metamorphism, Ongeluk Formation, South Africa. Contributions to Mineralogy and Petrology, 142, 27-42.

Gutzmer, J., Dorland, H.C., Beukes, N.J. (2001B). Iron ores of the Transvaal Supergroup- Products of Paleoproterozoic lateritic weathering processes. Gordon Research Conference ‘Inorganic Geochemistry’, Andover Academy.

Hannah, J.L., Stein, H.J., Bekker, A., Markey, R.J., Holland, H.D. (2002). Chondritic initial 187Os/188Os in Paleoproterozoic shale (seawater) and the onset of oxidative weathering. Geochim. Cosmochim. Acta, 67, A-34.

Henderson, D.R., Long, L.E., Barton, J.M. (2000). Isotopic ages and chemical and isotopic composition of the Archean Turfloop Batholith, Pietersburg granite-greenstone terrane, Kaapvaal craton, South Africa. South African Journal of Geology, 103(1), 38- 46.

171 Provenance of the Wolkberg Group and Transvaal Supergroup

Holzer, L., Frei, R., Barton, J.M., Kramers, J.D. (1998). Unravelling the record of successive high grade events in the Central zone of the Limpopo Belt using single phase dating of metamorphic minerals. Precambrian Research, 87, 87-115.

Kamo, S.L., Davis, D.W. (1994). Reassesment of Arhean crustal development in the Barberton Mountain Land, South Africa, based on U-Pb dating. Tectonics, 13, 167-192.

Kreissig, K., Holzer, L., Frei, I.M., Kramers, J.D., Kröner, A., Smit, C.A., Van Reenen, D.D. (2001). Geochronology of the Hout River Shear Zone and the metamorphism in the Southern Marginal Zone of the Limpopo Belt, Southern Africa. Precambrian Research, 109, 145-173.

Krogh, T.E., Davis, D.W., and Corfu, F. (1984). Precise U-Pb zircon and baddeleyite ages for the Sudbury area: Ontario Geological Survey Special Volume 1, 431-446.

Kröner, A., Hegner, E., Wendt, J.I., Byerly, G.R. (1996). The oldest part of the Barberton granitoid-greenstone terrain, South Africa: evidence for crust formation between 3.5 and 3.7 Ga. Precambrian Research, 78, 105-124.

Kröner, A., Jaeckel, P., Brandl, G., Nemchin, A.A., Pidgeon, R.T. (1999). Single zircon ages for granitoid gneisses in the Central Zone of the Limpopo belt, southern Africa, and geodynamic significance. Precambrian Research, 93, 299-337.

Martin, D.McB., Clendenin, C.W., Krapez, B., McNaughton, N.J. (1998). Tectonic and geochronological constraints on late Archean and Palaeoproterozoic stratigraphic correlations within and between the Kaapvaal and Pilbara Cratons. Journal of the Geological Society, London, 155, 311-322.

Martin, D.McB., Li, Z.X., Nemchin, A.A., Powell, C.McA. (1999). A pre-2.2Ga age for giant hematite ores of the Hamersley Province Australia? Economic Geology, 93, 1084- 1090.

172 Provenance of the Wolkberg Group and Transvaal Supergroup

McCourt, S., and Armstrong, R.A. (1998). SHRIMP U-Pb zircon geochronology of granites from the Central Zone, Limpopo Belt, southern Africa: Implication for the age of the Limpopo Orogeny. South African Journal of Geology, 101(4)329-338.

Mkweli, S., Kamber, B.S. and Berger, M. (1995). Westward continuation of the craton- Limpopo belt tectonic break in Zimbabwe and new age constraints on the timing of the thrusting. Journal of the Geological Society, London, 152, 77-83.

Moore, M., Robb, L.J., Davis, D.W., Grobler, D.F., Jackson, M.C. (1993). Archean rapakivi granite-anorthosite-rhyolite complex in the Witwatersrand hinterland, southern Africa. Geology, 21, 1031-1034.

Nelson, D.R., Trendall, A.F., Altermann, W. (1999). Chronological correlations between the Pilbara and Kaapvaal cratons. Precambrian Research, 97, 165-189.

Nhleko, N. (2003). The Pongola Supergroup in Swaziland. Unpublished PhD thesis, Rand Afrikaans University, Johannesburg, 303pp.

Obbes, A.M., (1995). The structure, stratigraphy and sedimentology of the Black Reef- Malmani-Rooihoogte succession of the Transvaal Supergroup southwest of Pretoria. M.Sc. thesis (unpublished), Rand Afrikaans University, Johannesburg, 137pp.

Pickard, A.L. (2002). SHRIMP U-Pb zircon ages of tuffaceous mudrocks in the Brockman Iron Formation of the Hamersley Range, Western Australia. Australian Journal of Earth Sciences, 49(3), 491-508.

Poujol, M., Respaut, J.P., Robb, L.R., Anhaeusser, C.R. (1997). New U-Pb and Pb-Pb data on the Murchison Greenstone Belt, South Africa and their implications for the origin of the Witwatersrand basin. University of the Witwatersrand, Economic Geology Research Unit Information Circular 319, 21pp.

173 Provenance of the Wolkberg Group and Transvaal Supergroup

Robb, L.J., Davis, D.W. and Kamo, S. (1989). U-Pb ages on single detrital zircon grains from the Witwatersrand basin: Constraints on the age of sedimentation and on the evolution of granites adjacent to the depository. Economic Geology Research Unit Information Circular 208.

Robb, L.J., Davis, D.W., Kamo, S.L., Meyer, F.M. (1992). Ages of altered granites adjoining the Witwatersrand Basin, with implications for the origin of gold and uranium. Nature, 357, 672-680.

Schreiber, U.M., (1990). A paleoenvironmental study of the Pretoria Group in the eastern Transvaal. Ph.D thesis (unpublished), University of Pretoria, Pretoria. 308pp.

Schweigart, H. (1965). Iron ores of South Africa. Economic Geology, 60, 269pp.

Smit, C.A. and Van Reenen, D.D. (1997). Deep crustal sheer zones, high grade tectonites, and associated metasomatic alteration in the Limpopo Belt, South Africa: Implications for deep crustal processes. Journal of Geology, 105, 37-57.

Stevens, G. and Van Reenen, D.D. (1992). Constraints on the form of the P-T loop in the Southern Marginal Zone of the Limpopo Belt, South Africa. Precambrian Research, 55, 279-296.

Swart, Q.D., (1999). Carbonate rocks of the Paleoproterozoic Pretoria and Postmasburg Groups, Transvaal Supergroup. M.Sc. thesis (unpublished), Rand Afrikaans University, Johannesburg. 126pp.

Trendall, A.F., Compston, W., Williams, I.S., Armstrong, R.A., Arndt, N.T., McNaughton, N.J., Nelson, D.R., Barley, M.E., Beukes, N.J., de Laeter, J.R., Retief, E.A., Thorne, A.M. (1990). Precise zircon U-Pb geochronological comparison of the volcano-sedimentary sequences of the Kaapvaal and Pilbara cratons between about 3.1 and 2.4Ga. Third International Archean Symposium, Perth, Extended Abstracts, 81-83.

174 Provenance of the Wolkberg Group and Transvaal Supergroup

Trendall, A.F., Nelson, D.R., de Laeter, J.R., Hassler, S. (1998). Precise zircon U-Pb ages from the Marra Mamba Iron Formation and the Wittenoom Formation Hamersley Group Western Australia. Australian Journal of Earth Sciences, 45, 137-142.

Tyler, N. (1979). The stratigraphy of the early-Proterozoic Buffalo Springs Group in the Thabazimbi Area, west-central Transvaal. Transactions of the Geological Society of South Africa, 8, 215-226.

Van Niekerk, H.S.V.N. (2004). PhD thesis (unpublished), Rand Afrikaans University, Johannesburg.

Van Reenen, D.D., Barton, J.M., Roering, C., Smit, C.A., Van Schalkwyk, J.F. (1987). Deep crustal response to continental collision: The Limpopo belt of southern Africa. Geology, 15, 11-14.

Van Schalkwyk, J., and Beukes, N.J. (1986). The Sishen iron ore deposit, Griqualand West. In: Annhaeusser, C.R. and Maske, S.S. (editors). Mineral deposits of Southern Africa. Geological Society of South Africa, Johannesburg, 931-956.

Visser, J.N.J. (1969). ‘n Sedimentologiese studie van die Serie Pretoria in Transvaal. Ph.D. thesis (unpublished), University of the Orange Freestate, Bloemfontein, 263pp.

Wagner, P.A. (1928). The iron deposits of the Union of South Africa. Geological Survey of South Africa, Pretoria, 120pp.

Walraven, F. (1997). Geochronology of the Rooiberg Group, Transvaal Supergroup, South Africa. University of the Witwatersrand, Johannesburg, Economic Geology Research Unit Information Circular, 316, 21pp.

Walraven, F. and E. Hattingh (1993). Geochronology of the Nebo Granite, Bushveld Complex. South African Journal of Geology, 96(1/2), 31-41.

175 Provenance of the Wolkberg Group and Transvaal Supergroup

Walraven, F., Martini, J., (1995). Zircon Pb-evaporation age determinations of the Oak Tree Formation, Chuniespoort Group, Transvaal sequence: implications for Transvaal- Griqualand West basin correlations. South African Journal of Geology, 98, 58-67.

Winter, H. De La R (1976). A lithostratigraphic classification of the Ventersdorp succession. Transactions of the Geological Society of South Africa, 79, 1, 31-48.

Young, G.M. (1991). Stratigraphy, sedimentology and tectonic setting of the Huronian Supergroup. Geological Association of Canada, Mineralogical Association of Canada, Society of Economic Geologists Joint Meeting, Toronto, 34.

Young, G.M. (1995). The Huronian Supergroup in the context of a Paleoproterozoic Wilson cycle in the Great Lakes region. Canadian Mineralogist, 33, 921-922.

176