Abstract
A sedimentological study of the early Proterozoic Black Reef Quartzite Formation in the south-western parts of the Transvaal province of South Africa was undertaken with the primary aim of examining the sedimentological controls of gold mineralization in the Black Reef placer, which occurs at the base of this Formation. A second aim of the study was to investigate the early history of the basin in which the Transvaal Sequence of South Africa was deposited. The thin, siliciclastic Black Reef Quartzite Formation, which is informally subdivided into a lower Conglomerate Unit and an upper Quartzite Unit, is underlain by Archaean rocks belonging to the basement complex and the Witwatersrand and Ventersdorp Supergroups, and is overlain by a thick succession of carbonate rocks of the Malmani Subgroup. The pre-Transvaal palaeosurface is characterised by elongated northeast to southwest trending grabens and partly-eroded horst blocks. The Black Reef Quartzite Formation, which has a maximum thickness of about 30 m in the study area, typically comprises a succession of interbedded arenites and mudstones, with a sporadically-developed basal Conglomerate Unit. Thickness trends are similar to the dominant structural trend of the pre-Transvaal palaeosurface. At localities where the Conglomerate Unit is absent, the Formation invariably overlies quartzites of the Witwatersrand Supergroup directly. The palaeocurrent distribution of the Conglomerate Unit is unimodal, with modes towards the southwest in the southern parts of the study area and towards the north in the northern regions. Most of the palaeocurrent distributions of the Quartzite Unit are unimodal, too, but bimodal distributions were found at three localities. Pebble size of the Black Reef placer is largest in the northeastern parts of the study area, but no orderly lateral size variation was found. Pebble roundness, too, varies greatly and apparently randomly. The composition of the pebble assemblage is not constant, but no systematic lateral change could be detected. A petrographic study of the arenites of the Formation reveals a remarkable textural and mineralogical maturity, especially for the upper beds. It is concluded that the pre-Transvaal palaeosurface had a palaeorelief of up to 30 m and that the topography of the palaeo-landscape was the dominant factor controlling early sedimentation in the basin. The palaeo-grabens probably constituted the valleys of shallow braided stream systems that drained south-westwards and northwards from a palaeo-drainage divide in the northern parts of the study area. Sediment, including detrital gold, was derived from erosion of Witwatersrand rocks and fed to the graben valleys via several alluvial fans. During a subsequent transgression, the fluvial systems became drowned and transgressive estuarine conditions ensued. During the final stages of siliciclastic sedimentation, the upper quartzite beds of the Formation were probably reworked by shallow marine processes before carbonate precipitation commenced. The cause of the marine transgression is not known beyond doubt. It is suggested, however, that lithospheric rifting, which initiated the extrusion of the underlying Ventersdorp lavas, resumed during early Transvaal times, resulting in complete severing of the continental crust and the creation of a linear sea.
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References
Allen, P.A., Allen, J.R. (1990) Basin analysis: principles and applications. Blackwell, Oxford
Antrobus, E.S.A., Brink, W.C.J., Brink, M.C., Caulkin, J., Hutchison, R.I., Thomas, D.E., Van Graan, J.A., Viljoen, J.J. (1986) The Klerksdorp Goldfields. In: Anhaeusser, C.R., Maske, S. (eds.) Mineral deposits of Southern Africa. Geol. Soc. S. Afr. Publ. I:549–598
Boothroyd, J.C., Ashley, G.M. (1975) Processes, bar morphology, and sedimentary structures on braided outwash fans, north-eastern gulf of Alaska. In: Jopling A.V., McDonald, B.C. (eds.) Glaciofluvial and Glaciolacustrine Sedimentation. Soc. Econ. Paleont. Miner. Spec. Publ. 23:193–223
Cooper, J.A.G. (1993) Sedimentation in a river-dominated estuary. Sedimentology 40:979–1017
Cotter, E. (1978) The evolution of fluvial style, with special reference to the Central Appalachian Paleozoic. In: Miall, A.D. (ed.) Fluvial sedimentology. Mem. Can. Soc. Petrol. Geol. 5:361–384
Davis, J.C. (1973) Statistics and data analysis in geology. Wiley, New York
Elliott, T. (1981) Clastic shorelines. In: Reading, H.G. (ed.). Sedimentary environments and facies. Blackwell, Oxford, pp. 143–177
Els, B.G. (1993) Anomalous pebble size variation in an erosive, late Archaean braided stream: the Middelvlei gold placer, Witwatersrand, South Africa. Sedimentology 40:41–52
Engelbrecht, C.J., Baumbach, G.W.S., Matthysen, J.L., Fletcher, P. (1986) The West Wits Line. In: Anhaeusser, C.R., Maske, S. (eds.). Mineral deposits of southern Africa. Geol. Soc. S. Afr. Publ. I:599–648
Friedman, G.M. (1961) Distinction between dunes, beach and river sands from their textural characteristics. J. Sediment. Petrol. 31:514–529
Fuller, A.O. (1985) A contribution to the conceptual modelling of pre-Devonian fluvial systems. Trans. Geol. Soc. S. Afr. 88:189–194
Galehouse, J.S. (1971) Point counting. In: Carver, R.E. (ed.). Procedures in sedimentary Petrology. Wiley, New York, pp. 385–407
Harrel, J.A., Eriksson, K.A. (1979) Empirical conversions for thin-section and sieve derived size distribution parameters. J. Sediment. Petrol., 49:273–280
Karpeta, W.P. (1993) Volcanism and sedimentation in part of the late Archaean rift: the Hartbeesfontein basin, Transvaal, South Africa. Basin Res. 5:1–19
Krumbein, W.C. (1941) Measurements and geological significance of shape and roundness of sedimentary particles. J. Sediment. Petrol., 11:64–72
McManus, J. (1988) Grain size determination and interpretation. In: Tucker, M. (ed.) Techniques in sedimentology. Blackwell, Oxford, pp. 63–85
Miall, A.D. (1990) Principles of sedimentary basin analysis, 2nd edn. Springer, Berlin Heidelberg New York
Middleton, G.V. (1976) Hydraulic interpretation of sand size distribution. J. Geol. 84:405–426
Minter, W.E.L. (1972) Sedimentology of the Vaal reef in the Klerksdorp area. Unpublished Ph.D thesis, Univ. Witwatersrand, Johannesburg, 170 pp
Nichols M.M., Biggs, R.B. (1985) Estuaries. In: Davis R.A. (ed.) Coastal sedimentary environments, 2nd edn., Springer, Berlin Heidelberg New York, pp. 77–186
Nel, L.T. (1935) The Geology of the Klerksdorp — Ventersdorp Area. Expl. Geol. Map., Geol. Soc. S. Afr.
Papenfus, J.A. (1964) The Black Reef Series within the Witwatersrand basin with special reference to its occurrence at Government Gold Mining Areas. In: Haughton, S.H. (ed.) The geology of some ore deposits in southern Africa (1). Geol. Soc. S. Afr. Publ., pp. 192–218
Pettijohn, F.J. (1975) Sedimentary Rocks, 3rd edn. Harper & Row, New York
Pettijohn, F.J., Potter, P.E., Siever, R. (1972) Sand and sandstone. Springer, Berlin Heidelberg New York
Pouroulis, S., Austin, M.A. (1989) The Geology of the Black Reef at North East Prospect Shaft Consolidated Modderfontein Mines Limited (abstract). In: Other Reefs Symposium, Geol. Soc. S. Afr. Publ, pp. 99–104
Press, F., Siever, R. (1986) Earth, 4th edn. Freeman, New York
Pretorius, D.A. (1986). The Goldfields of the Witwatersrand basin. In: Anhaeusser, C.R., Maske, S. (eds.) Mineral deposits of southern Africa. Geol. Soc. S. Afr. Publ. I:489–494
Ridgway, K.D., DeCelles, P.G. (1993) Stream-dominated alluvial fan and lacustrine depositional systems in Cenozoic strike-slip basins, Delani fault system, Yukon Territory, Canada. Sedimentology 40:645–666
Rust, B.R., Koster, E.H. (1984) Coarse alluvial deposits. In: Walker, R.G. (ed.) Facies models, 2nd edn. Geol. Ass. Can. Publ., pp. 53–70
South African Committee for Stratigraphy (SACS) (1980) Stratigraphy of South Africa, part 1. In: Kent, L.E. (ed.) Lithostratigraphy of the Republic of South Africa, South West Africa/Namibia and the Republics of Bophuthatswana, Transkei and Venda. Handbook Geol. Surv. S. Afr. 8
Schumm, S.A. (1968) Speculations concerning paleohydrologic controls of terrestrial sedimentation. Geol. Soc. Am. Bull. 79:1573–1588
Sellwood, B.W. (1978) Shallow-water carbonate environments. In: Reading, H.G. (ed.) Sedimentary environments and facies. Blackwell, Oxford, pp. 259–313
Selley, R.C. (1982) An introduction to Sedimentology, 2nd edn. Academic Press, London
Sims, J.F.M. (1969) The stratigraphy and palaeocurrent history of the upper division of the Witwatersrand System on President Steyn Mine and adjacent areas in the Orange Free State goldfields with specific reference to the origin of auriferous reefs. Unpublished Ph.D thesis, Univ. Witwatersrand, Johannesburg, 181 pp
Smith, N.D. (1980) A short course on braided river systems. Section 1, course notes. Department of Geology, Rhodes University, Grahamstown, 55 pp
Steyn, L.S. (1975) Sedimentological control on gold and uraninite mineralisation in the White Reef of the West Rand. Unfinished thesis, Univ. Witwatersrand, Johannesburg, 199 pp
Tankard, A.J., Jackson, M.P.A., Eriksson, K.A., Hobday, D.K., Hunter, D.R., Minter, W.E.L. (1982) Crustal evolution of southern Africa — 3.8 Billion years of earth history. Springer, Berlin Heidelberg New York, 523 pp
Van den Berg, W.A. (1994) The stratigraphy and sedimentology of the Black Reef Quartzite Formation, Transvaal Sequence, in the Klerksdorp, Potchefstroom and Ventersdorp districts. Unpubl. M.Sc. dissertation, Potchefstroom Univ. for C.H.E., Potchefstroom, 131 pp
Visher, G.S. (1972) Physical characteristics of fluvial deposits. Soc. Econ. Paleont. Miner. Spec. Publ. 16:84–97
Winter, H. de la R. (1976) A lithostratigraphic classification of the Ventersdorp succession. Trans. geol. Soc. S. Afr. 79:31–48
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Els, B.G., van den Berg, W.A. & Mayer, J.J. The Black Reef Quartzite Formation in the western Transvaal: sedimentological and economic aspects, and significance for basin evolution. Mineral. Deposita 30, 112–123 (1995). https://doi.org/10.1007/BF00189340
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DOI: https://doi.org/10.1007/BF00189340