Transvaal Basin Iron

Northern Cape, South Africa

Main commodities: Fe
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South Africa is Africa's leading iron ore producer, with an annual output of around 33 Mt, and 'reserves' of approximately 9 billion tonnes, 45% of which are located in the Northern Cape Province.   Production comes from two main areas, the Sishen mine in the Northern Cape Province, accounting for over 24 Mt of high grade 65% Fe ore per annum, and the Thabazimbi Mine in the Northern Province.   Thabazimbi generally provides iron to South African domestic smelters at Vanderbijlpark and Newcastle, at a rate of around 2 Mtpa, while almost all production from Sishen is exported through the port of Saldanha north of Cape Town.

Although 700 km apart, Thabazimbi and Sishen are both developed on iron formations in the Palaeoproterozoic Transvaal Sequence, which was deposited between sometime after 2400 Ma and 2100 Ma within an intracratonic basin on the Kaapvaal Craton.   The Kaapvaal Craton comprises a 3.4 to 2.8 Ga granite-greenstone basement, similar to the Zimbabwe Craton to the north which is separated by the 2.5 to 2.0 Ga Limpopo Mobile Belt.   The granite-greenstone basement terrane is over lain by a series of intracratonic basins, the axes of which migrated north with time from the early "upper" Archaean to the late Palaeoproterozoic Waterberg System to the north.

The oldest of these, the Pongola System is a 10 000 m thick, approx. 3.0 Ga succession comprising a lower basaltic volcanic and lesser quartzite sequence overlain by alternating argillaceous and arenaceous sediments with intercalations of BIF.   The overlapping ~9 000 m thick Witwatersrand Supergroup was deposited at between 3075 and 2715 Ma, commencing with early Dominion basaltic lavas, followed by a succession of mainly sandstones and shales with lesser locally gold bearing conglomerates.   These were in turn followed by the up to 5000 m thick Ventersdorp Supergroup composed dominantly of basaltic volcanics dated at 2714 Ma.

The up to 12 000 m thick Transvaal Sequence was deposited unconformably on the Ventersdorp Sequence, and occurs in two connected depo-centres, the Transvaal and Griqualand West sub-basins, which define a 1100x350 km, NE-SW elongated area of remaining exposure.   This sequence originally covered an area of approx. 500 000 sq. km.

In the Transvaal sub-basin, the Transvaal sequence commences with the up to 2000 m thick Wolkberg (or Buffalo Springs) Group of valley fill basalts and coarse clastics and lesser argillites.   These are followed by the few tens to 500 m thick Black Reef Quartzite, which grades up into the around 3000 m thick Chuniespoort Group which comprises the lower up to 2000 m thick Malmani Dolomite, variably composed of dolomite and chert, and the overlying up to 600 m thick Penge Iron Formation.

The Penge Iron Formation is the host to the Thabazimbi iron deposit and is composed of alternating carbonaceous shale and macro-, meso- and micro-banded BIF (quartz- magnetite- hematite- stilpnomelane- riebeckite- minnesotaite- grunerite and ferriferous carbonates).   The uppermost member of the Chuniespoort Group is represented by the dolomites, quartzites and shale of the locally preserved Duitschland Formation.   The Chuniespoort Group is unconformably overlain by the 7000 m thickness of quartzites, shales and minor basalts of the Pretoria Group and the 2-3000 m of rhyolitic lavas that make up the ~2100 Ma Rooiberg Group.

In the Griqualand West sub-basin, the Transvaal Sequence is represented by the Ghaap Group, which is unconformably overlain by the Postmasburg Group.   The Ghaap Group is sub-divided into the lower interbedded silici-clastics and carbonates of the Schmidtsdrif Subgroup followed by the limestones and dolomites of the Campbellrand Subgroup.   These are overlain by the Asbesheuwels Subgroup which is sub-divided into the lower Kuruman Iron Formation, composed of interlayered carbonaceous shale and a chert- carbonate- stilpnomelane- magnetite- hematite- greenalite- siderite iron formation, and the upper Griquatown Iron Formation, comprising siderite-hematite and siderite-greenalite lutites.   The Asbesheuwels Subgroup is host to the giant Sishen iron deposit.   The Ghaap Group is unconformably overlain by the Postmasburg Group, commencing with the thin Makganyene Diamictite, the thick Ongeluk basaltic pillow lavas, followed in turn by the jasper, BIF and sedimentary manganese deposits of the Hotazel Formation, and finally the Mooidraai Dolomite.   These are in turn unconfoirmably overlain by the shales and red-bed sanstones of the Olifantshoek Group.

The Transvaal Sequence is unconformably overlain to the north by the extensive thick arkosic arenites of the 2000 to 1700 Ma Waterberg Group.

The most recent source geological information used to prepare this summary was dated: 2002.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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