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Sishen |
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Northern Cape, South Africa |
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Fe
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Sishen iron ore deposit is situated in the Northern Cape Province of South Africa, 280 km north of Kimberley and 800 km north-east of its export port at Saldanha Bay north of Cape Town, to which it is connected by a 1 m gauge rail line. It is just to the SW of the township of Kathu (#Location: 27° 45' 32"S, 23° 0' 0"E).
The mine is owned and operated by Kumba Resources Limited and produces around 27 Mt pa of 65% Fe hard hematite ore with a high lump proportion, and impurity levels of generally less than 0.05% P, 2.5% SiO2 and 1.2% Al2O3.
Regional Setting
The major iron deposits of South Africa, which include Thabazimbi and Sishen that are 700 km apart, are developed on iron formations in the Palaeoproterozoic Transvaal Sequence, which was deposited between ~2.4 and 2.1 Ga within an intracratonic basin on the Kaapvaal Craton. The Kaapvaal Craton comprises a 3.4 to 2.8 Ga granite-greenstone basement, which is separated from the Zimbabwe Craton to the north by the 2.5 to 2.0 Ga Limpopo Mobile Belt. The granite-greenstone basement terrane is overlain by a series of intracratonic basins, the axes of which migrated northward with time from the early Neoarchaean to the late Palaeoproterozoic Waterberg System to the north.
The oldest of these, the Pongola System is a 10 000 m thick, ~3.0 Ga succession comprising a lower basaltic volcanic and lesser quartzite sequence overlain by alternating argillaceous and arenaceous sedimentary rocks with intercalations of BIF. The overlapping ~9000 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 volcanic rocks 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 1100 x 350 km, NE-SW elongated area of remaining exposure. This sequence originally covered an area of ~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 that 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 to 3000 m of rhyolitic lavas that make up the ~2100 Ma Rooiberg Group, marking the stage of emplacement of the Bushveld Complex.
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, banded iron formation and sedimentary manganese deposits of the Hotazel Formation, and finally the Mooidraai Dolomite.
The Transvaal Sequence is unconformably overlain by the shales and red-bed sandstones of the Gamagara Formation, the basal member of the post-2000 Ma Olifantshoek Supergroup. Tha latter sequence is interpreted to be an erosional remnant of the extensive red-bed successions that developed on the Kaapvaal
Craton and its margins during the Palaeoproterozoic, including the extensive thick arkosic arenites of the 2000 to 1700 Ma Waterberg Group further to the east.
The angular unconformity between the banded iron formations of the upper Transvaal Sequence and the overlying Gamagara Formation represents a considerable hiatus in deposition during which the iron formation underwent erosion, exposure, oxidation and supergene processes.
Deposit Geology
The Sishen deposits are hosted by the Palaeoproterozoic Transvaal Supergroup within the Griqualand West sub-basin. It is situated on the Maremane Dome which is defined by the carbonate sequence of the Transvaal Supergroup, the Campbellrand Subgroup and the overlying host iron formations of the Asbesheuwels Iron Formation. These units dip outwards at less than 10 degrees on the eastern margin of the dome. In the central and western sections of the dome, this part of the sequence is concealed by the unconformably overlying red-bed clastic Gamagara Formation of the Olifantshoek Group.
A unit of ferruginous chert breccia (the Wolhaarkop Breccia) that grades upwards into a disturbed banded iron formation of the Manganore Iron Formation) and is wedged between the underlying Campbellrand carbonates and the unconformity at the base of the Gamagara Formation. The Wolhaarkop Breccia is matrix supported and consists of unsorted angular chert fragments in a hematite to manganese bearing siliceous matrix.
Some 80 to 90% of the ore at the north-south elongated 12 x 1.5 km Sishen deposit is hosted by the Manganore Iron Formation, which is correlated with the Asbesheuwels Iron Formation, and is found immediately below the unconformity with the overlying clastic Gamagara Formation. Subsequent to deposition, Asbesheuwels Iron Formations are interpreted to have locally slumped onto a palaeo-sinkhole dominated surface developed in the underlying Cambellrand sub-group carbonates to produce the Wolhaarkop Breccia and Manganore Iron Formation during the period of erosion prior to the deposition of the Gamagara Formation.
Silica is believed to have been leached from the slumped and brecciated iron formation by alkaline supergene fluids at the time of slumping, while ferrous ions were oxidised to hematite, and additional transported supergene iron was added. Erosion of the hematite mineralisation and resultant accumulations of hematite pebble conglomerates in alluvial fan environments are preserved as the Doornfontein Conglomerate at the base of the Gamagara formation and account for around 10-20% of the orebody. The Doornfontein Conglomerate is best developed immediately adjacent to pockets of Manganore Iron Formation.
The Manganore Iron Formation is more restricted in areal extent than the Wolhaarkop Breccia. It is composed of 7 zones/bands from the base, namely: Zone 1 - a spotted carbonaceous and dark brown shale with chert pillows and hematite nodules; Zone 2 - hematite micro-banded white chert with interbeds of intercalated cherts and black-brown shale; Zone 3 - chert banded hematite ferhythmites with cycles of hematite-lutite to hematite-microbanded chert, to hematite ribbon, wave and pillow-rhythmite; Zone 4 - hematite rhythmites that represent the bulk of the banded ore; Zones 5 and 6 of hematite-greenalite banded lutites. The first 6 zones were derived from the Kuruman Iron Formation, the lower of the 2 Asbesheuwels units, while a zone 7 composed of hematite lutite with meso-bands of peloidlutite is correlated with the overlying Griquatown Iron Formation. Chert bands within the Manganore Iron Formation are porous, with partially infilling platy hematite. Boundaries of high grade ore cut across primary sedimentary boundaries.
Three types of ore are present in the Manganore Iron Formation, namely:
i). Laminated ore - composed of both thickly laminated alternating massive, porous hematite meso-bands with dull and bright micro-banded 2 to 15 mm thick meso-bands, and of thinly laminated micro-banded hematite comprising very thin microbanded high lustre hematite with equally thin earthy hematite meso-bands;
ii). Massive ore - massive to very poorly bedded, fine grained, porous aggregates of platy hematite;
iii). Breccia ore - of two types which may be developed anywhere in the iron formation, comprising oligomictic hematite rhythmite breccia derived from laminated ores, and oligomictic hematite-lutite breccia.
The Makganyene diamictite and Ongeluk Lava of the Postmasburg Group which unconformably overlies the Ghaap Group and unconformably underlies the Gamagara Formation of the Olifantshoek Group, were subsequently thrust over the deposit and host sequence from the west. Much of the sequence in the region is concealed by around 50 m of Tertiary Kalahari Formation cover.
The 2001 mineral reserve estimate for the Sishen deposit was 877 Mt, and the mineral resource estimate was 1724 Mt. Some 70 km to the south at the Sishen South (or Welgevonden) deposit there is a high quality resource of 259 Mt of high lump ore to be developed by 2006.
In 2005, the proved + probable reserve at Sishen totalled 1021 Mt @ 59.0% Fe, plus a quoted resource of 1957 Mt @ 57.2% Fe.
The proved + probable reserve at Sishen South in the same year was 167 Mt @ 64.2% Fe, plus a resource of 248 Mt @ 65% Fe.
In 2008, the proved + probable reserve at Sishen totalled 956.9 Mt @ 59.6% Fe, plus a quoted resource of 1628 Mt @ 56.4% Fe.
The proved + probable reserve at Sishen South in the same year was 214.1 Mt @ 64.1% Fe, plus a resource of 153.2 Mt @ 64.3% Fe.
Reserves and resources from Kumba Iron Ore website and annual report.
The most recent source geological information used to prepare this decription was dated: 2010.
Record last updated: 23/1/2015
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.
Sishen
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Selected References:
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Alchin D J and Botha W J, 2006 - The structural/stratigraphic development of the Sishen South (Welgevonden) iron ore deposit, South Africa, as deduced from ground gravity data modelling: in Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc. v115 pp 174-186
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Bekker, A., Slack, J.F., Planavsky, N., Krapez, B., Hofmann, A., Konhauser, K.O. and Rouxel, O.J., 2010 - Iron formation: the sedimentary product of a complex interplay among mantle, tectonic, oceanic, and biospheric processes: in Econ. Geol. v.105 pp. 467-508
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Bekker, A., Slack, J.F., Planavsky, N., Krapez, B., Hofmann, A., Konhauser, K.O. and Rouxel, O.J., 2010 - Iron formation: the sedimentary product of a complex interplay among mantle, tectonic, oceanic, and biospheric processes: in Econ. Geol. v.105 pp. 467-508
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Beukes N J and Gutzmer J, 2008 - Origin and Paleoenvironmental Significance of Major Iron Formations at the Archean-Paleoproterozoic Boundary: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore Reviews in Economic Geology v15 pp 5-47
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Carney MD, Mienie PJ 2002 - A Geological Comparison of the Sishen and Sishen South (Welgevonden) Iron Ore Deposits, Northern Cape Province, South Africa: in Proceedings, Iron Ore 2002 Conference, 9-11 September 2002, Perth, Western Australia, The AusIMM, Melbourne, pp 145-151
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Clout, J.M.F. and Simonson, B.M., 2005 - Precambrian iron formation and iron formation-hosted iron ore deposits: in Hedenquist, J.W., Thompson, J.F.H., Goldfarb, R.J. and Richards, J.P. (eds.), Economic Geology, 100th Anniversary Volume Society of Economic Geologists pp. 643-679
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Dalstra, H. and Rosiere, C.A., 2008 - Structural controls on high-grade iron ores hosted by banded iron formation: A global perspective: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology, v.15 pp. 73-106
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Gutzmer, J., Chisonga, B.C., Beukes, N.J. and Mukhopadhyay, J., C.A., 2008 - The geochemistry of banded iron formation-hosted high-grade hematite-martite iron ores: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore, Reviews in Economic Geology v.15 pp. 157-183
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Halbich I W, Scheepers R, Lamprecht D, van Deventer J L and De Kock N J, 1993 - The Transvaal-Griqualand West banded iron formation: geology, genesis, iron exploitation: in J. of African Earth Sciences v.16 pp 63-120
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Horstmann U E and Halbich I W 1995 - Chemical composition of banded iron-formations of the Griqualand West Sequence, Northern Cape Province, South Africa, in comparison with other Precambrian iron formations: in Precambrian Research v.72 pp 109-145
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Klemm D D, 2000 - The formation of Palaeoproterozoic banded iron formations and their associated Fe and Mn deposits, with reference to the Griqualand West deposits, South Africa: in J. of African Earth Sciences v.30 pp 1-24
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Lobato L M, Figueiredo e Silva R C, Hagemann S and Thorne W, 2008 - Hypogene Alteration Associated with High-Grade Banded Iron Formation-Related Iron Ore: in Hagemann S, Rosiere C, Gutzmer J and Beukes N J, (eds.), 2008 Banded Iron Formation-Related High-Grade Iron Ore Reviews in Economic Geology v15 pp 107-128
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Stoch, B., Anthonissen, C.J., McCall, M-J., Basson, I.J., Deacon, J., Cloete, E., Botha, J., Britz, J., Strydom, M., Nel, D. and Bester, M., 2018 - 3D implicit modeling of the Sishen Mine: new resolution of the geometry and origin of Fe mineralization: in Mineralium Deposita v.53, pp. 835-853.
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Van Schalkwyk J F, Beukes N J 1986 - The Sishen Iron Ore Deposit, Griqualand West: in Anhaeusser CR, Maske S (Eds), 1986 Mineral Deposits of Southern Africa Geol. Soc. of South Africa, Johannesburg v1 pp 931-956
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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, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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