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Richards Bay |
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KwaZulu-Natal, South Africa |
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Ti Zr
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Richards Bay heavy mineral sand (HMS) ilmenite zircon deposit is located along a 17 km strip of the KwaZulu-Natal coastline immediately to the north of Richards Bay and some 190 km north of Durban in South Africa. It covers the area between Lakes Mzingazi and Nhlabane.
The topography of the district is characterised by a straight coastline, a narrow beach, separated from a flat 40 m above sea level (asl) inland coastal plain, by high dunes of between 45 and 100 m asl.
The hinterland is occupied by Permo-Carboniferous to Cretaceous sediments of the Karoo intracratonic basin, the thick Jurassic Drakensberg (or Karoo) dolerites and lower Palaeozoic sediments, resting on the Mesoarchaean granite-gneiss-migmatite-greenstone basement of the eastern Kaapvaal craton.
The HMS deposits occur within aeolian dunes which are confined to a 1 to 1.5 km wide strip, immediately inland of, and parallel to the beach. The relief of the dunes, in contrast to the inland plain is very irregular. Two main dune types are recognised, namely: i). a low lying zone with small, irregular seif dunes, which may locally exceed 60 m asl, 15 m above their troughs; and ii). large dunes that are <1 km in width and up to 10 km in length, trending parallel to the coast, and are generally >70 m asl in height, and exceeding 100 m asl in the south.
The stratigraphy of the deposit area between Lakes Mzingazi and Nhlabane may be summarised as follows, from the base:
Cretaceous basement - of dark grey siltstone and mudstone, with a gentle rolling unconformable upper surface on which the overlying Pliocene was deposited;
Pliocene - which totals 9 to 24 m in thickness and comprises interbedded, hard, compacted medium- to coarse-grained, and poorly cemented, friable, sandstones, with intercalated bands of free-running, unconsolidated coarse-grained sands. Abundant shells are distributed throughout. Thin gravels from palaeo-streams are abundant. Inland the shelly sandstones pinch out against the basement and grade upwards into fluvio-lacustrine silty sands and clays that are 15 to 18 m thick. Close to the coast, the top of the Pliocene is marked by a 3 m thick clay, some 30 m asl. Following the deposition of the Pliocene, a drop in sea level caused the upper 20 to 25 m of the sequence to be eroded along the coast;
Pleistocene Port Durnford Formation - representing a barrier-lagoon-swamp complex formed by oscillating sea levels and alternating periods of deposition and erosion. The sequence commences with the:
- Lower Argillaceous Member, a marine sediment unconformably overlying the eroded Pliocene, composed of 4 to 6 m of dark-grey clay, silts and beach sands. This unit was subsequently unconformably overlain by
- the Lignite Beds, composed of lignites and carbonaceous clays deposited in swamps. Continued uplift resulted in erosion and the incision of channels and the lakes. Subsequent inundation deposited the
- Upper Arenaceous Member (or the Kwambonambo Formation) which is composed of 15 to 30 m of light grey, cross-bedded sands, containing appreciable clays. These sands are white and form prominent 8 to 12 m high cliffs along the beaches. Their upper surface forms a gently sloping unconformable floor to the orebodies some 20 to 40 m asl.;
Holocene to Recent - commenced with continued coastal uplift and erosion of deep channels along the coast. Loosely heaped sand was deposited along the coast, and subsequently blown up from the beach to form the dunes over the Upper Arenaceous Member. These dunes exclusively host the heavy mineral sand accumulations. Later Quaternary sea level fluctuations of up to 10 m provided the conditions for the development of these high dunes, particularly during regressive phases. These sands comprise an older reddish-brown variant that has been stained and locally slightly cemented by iron oxides, over lain by the upper pale-brown sands. There is no difference in heavy mineral content between the two. The dunes parallel the present coast and all show abundant aeolian cross-bedding, and have average heights of 19 m, and peaks of up to 60 m. Inland, the dunes are fine-grained, reddish to grey sands and silts, lacking the abundant heavy minerals of the coastal dunes.
Heavy minerals (SG >2.9) occur within the SSW trending main dunes. The average heavy mineral content is greatest in the low coastal dunes and is less in the higher dunes further inland. The heavy mineral suite in the deposits comprises well-rounded grains of ilmenite, hornblende, garnet (mainly pyrope with some almandine), pyroxene (mainly augite), magnetite, epidote, zircon, hematite, rutile, leucoxene, goethite, tourmaline, staurolite, kyanite, titanite, monozite, pyrite and feldspar. Quartz grains average 300 µm in diameter, while the heavy minerals are 100 to 150 µm. The ilmenite has a composition of 46 to 50% TiO2.
Mineralogical studies indicate that the provenance of the ilmenite is from the Jurassic Drakensberg Volcanics and from post-Karoo dolerites further inland, while the rutle and zircon was derived from the older basment granites and gneisses of the eastern Kaapvaal craton.
In 1974 the pre-mining resource was estimated at 770 Mt of sand with 13.8% HMS and a total of 5.86% ilmenite + rutile + zircon. The total HM content is very variable although the ilmenite:zircon ratio is very consistent, varying from 7 to 9, irrespective of the HM content. Similarly the ilmenite:rutile ratio is consistently between 16 and 18.
Reserves and resources at the end of 2007 are quoted at (Rio Tinto, 2008):
Proven + Probable reserves - 24.2 Mt of contained TiO2
Measured +Indicated + Inferred resources - 3.0 Mt of contained TiO2
The most recent source geological information used to prepare this decription was dated: 2008.
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.
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Fockema P D, 1986 - The heavy mineral deposits north of Richards Bay: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v2 pp 2301-2307
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