Platinum Exploration on the Great Dyke of Zimbabwe

Abstract The Great Dyke extends for 540 km along strike, to unknown depth, and varies in width from 3 km to 11 km. Rb/Sr age determinations gives values of approximately 2470 Ma.
The Dyke consists of a variety of mafic and ultramafic rocks, many altered to serpentinites. These include, from top to bottom, successions of gabbro/norites, pyroxenites, peridotites/harzburgites, and dunites/picrites.
The layers dip in from either margin, steepest at the edges (20°) and flattening toward the central sections. Four separate complexes are present. From north to south these are termed the Musengezi, Hartley, Selukwe and Wedza Complexes, and are described as 'boat-shaped' or 'pig-troughed'. All are similar in petrologjcal sequences. Physiographically, the Dyke is spectacular in the north, where as a mountain range it meets the Zambezi Escarpment. Elsewhere in the central parts there is little surface expression and wide open treeless vleis. Dyke rocks cut through granite and schist belt terrain and are termed 'The Magnesia Belt'.
Vast mineral resources exist. These include chrome, asbestos, platinoids, nickel, copper and gold. Up to eleven chrome seams numbered from top to bottom occur in the lower ultramafic sequences. Seams are narrow at 10 cm to 30 cm but of high grade. The platinum occurs 10 m to 40 m below the norite/pyroxenite contact.
A 60 m wide zone of Light Sulfide Mineralization (LSM) of less than 1% sulfides extends from the lower gabbronorites into the upper pyroxenites. In this LSM, four enriched zones carry up to 5% sulfides. The most widespread is termed the Main Sulfide Zone (MSZ), below which is No. 2, No. 3 and No. 4 Sulfide Zones. The MSZ carrying pyrite, pyrrhotite and chalcopyrite is a multielement ore with components of PGE (Pt-Pd-Rh), nickel, copper and cobalt, and gold and silver.
Extensive exploration programs have been carried out and the intention is to begin large-scale mining. However, with Russia supplying metals to the western markets, South Africa's cutback on production, and an end to the Cold War, delays have arisen.
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Summary: The basis of the tomographic velocity imaging technique is briefly described and an application of the method to detect and image a cross-section through a chromite pod is presented. Using the chromite application as an example, the relative costs of tomographic data acquisition and processing are compared with those of diamond drilling to obtain similar resolution. A number of different tomographic survey configurations and the potential role of the method in surface and underground...
Publication: Exploration & Mining Geology
Author(s): B.C. DYER
Issue: 4
Volume: 3
Year: 1994
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Summary: In recent years the Environmental Research Group of the KVI has been developing a number of radiometric techniques that may be employed in mineral sand exploration. These techniques involve: radiometric fingerprinting for assessing sand provenances and mineralogical composition; thermoluminescence for dating and provenance determination of sediments; a towed seabed detector to map seafloors for radiogenic heavy minerals and assessing heavy mineral volumes; and simplified transport mechanism...
Publication: Exploration & Mining Geology
Author(s): R.J. de MEIJER, I.C. TANCZOS, C. STAPEL
Issue: 4
Volume: 3
Year: 1994
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Summary: The Riviera tungsten occurrence in the Cape Province of South Africa was discovered in October 1979 as a result of stream-sediment panned concentrate sampling. The Cape age granite and late Precambrian Malmesbury Group carbonates and chlorite schists which it intrudes and which host the mineralization are covered by between 10 m and 30 m of Tertiary/Recent alluvium and clay. The scheelite/powellite and molybdenite mineralization occurs in a greisenized granite cupola with an overprint of...
Publication: Exploration & Mining Geology
Author(s): P.W.A. WALKER
Issue: 4
Volume: 3
Year: 1994
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Summary: The Merelani graphite-tanzanite deposit is located in northeast Tanzania, 14 kilometers south of Kilimajaro International Airport and in close proximity to the towns of Moshi and Arusha. The graphite mineralization is hosted by relatively undeformed linear Proterozoic metasedimentary gneisses, several of which have been subjected to hydrothermal alteration resulting in tanzanite mineralization. Exploration work comprised detailed geological mapping coupled with pit and trench channel sampling...
Publication: Exploration & Mining Geology
Author(s): C. DAVIES, R.J. CHASE SAMAX LTD.
Issue: 4
Volume: 3
Year: 1994
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Summary: In 1986, anomalous sampling results for heavy minerals were obtained at various sites in Namaqualand on the west coast of the Cape Province. Drilling in 1987 at Graauwduinen penetrated up to 35 meters of heavy mineral-bearing Tertiary sands which extend several kilometers inland from the coast. The heavy mineral suite includes ilmenite, rutile, leucoxene, zircon and monazite, along with garnet, pyroxene and amphibole. Three deposits are recognized, two of which comprise the resource to be...
Publication: Exploration & Mining Geology
Author(s): G.L. PALMER
Issue: 4
Volume: 3
Year: 1994
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Summary: Most of the gold in the Late Archean Witwatersrand Basin is of detrital origin but, in its present form, it is metamorphosed. The only relict detrital features preserved are the morphological characteristics of some placer gold particles. Regional burial metamorphism in the shallower and deeper levels of the Witwatersrand Supergroup reached temperatures around 300°C and 350°C at pressures between 2 kbar and 3 kbar, respectively, estimated from phase relations, chlorite-chloritoid exchange...
Publication: Exploration & Mining Geology
Author(s): H.E. FRIMMEL
Issue: 4
Volume: 3
Year: 1994
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Summary: Mineral exploration and research has led to the identification of four types of tungsten mineralization in the NE-trending, largely ensialic, inland branch of the late Proterozoic/early Paleozoic Pan-African Damara Orogen. The mineralization (mainly scheelite) occurs in a terrane (the Central Zone) that is characterized by multiple deformation, greenschist/amphibolite-facies metamorphism and numerous peraluminous S-type granitic and pegmatitic intrusions. The four major types of scheelite...
Publication: Exploration & Mining Geology
Author(s): N.M. STEVEN, J.L. KUYPER, J.M. MOORE
Issue: 4
Volume: 3
Year: 1994
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Summary: Banded iron formation rocks associated with massive sulfide lenses in the Broken Hill Pb-Zn-Cu-Ag deposit in the Namaqualand Metamorpnic Complex, South Africa, were investigated with respect to the geochemistry of manganiferous silicate-rich bands. Two common varieties of these are: amphibole- and garnet-rich iron formation bands. The results reveal that the former are enriched in Fe, Mg, Cu, Co and S. The garnet-rich bands are enriched in Mn, Ca, P, Pb and Ba with significant detrital...
Publication: Exploration & Mining Geology
Author(s): DENNIS HOFFMANN
Issue: 4
Volume: 3
Year: 1994
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Summary: The distribution of mineralized provinces is analyzed on the basis of their genetic link with specific blocks of the earth's crust including ancient platforms, mobile belts and zones of tectonic-magmatic activation. Mobile and fold belts surround the Siberian platform in Russia and the Kaap-vaal craton in South Africa, with decreasing age zoning away from ancient platform margins. The main differences in the geological development of the two cratonic areas are: (1) the long period before the...
Publication: Exploration & Mining Geology
Author(s): A.L. SOKOLOV, R.P. VILJOEN
Issue: 4
Volume: 3
Year: 1994
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Summary: Mineral deposits and prospects of the Pan African Saldanian erogenic belt in the southwestern Cape Province South Africa, are reviewed. Despite the entire absence of operating base or precious metal mines in the area, this study has established at least four metal associations that offer enticing exploration potential.
The poly-phase deformed, low-grade metamorphosed volcano-sedimentary Malmesbury Group constitutes a complex, poorly understood supracrustal sequence that has been loosely...
Publication: Exploration & Mining Geology
Author(s): A. ROZENDAAL, R. SCHEEPERS
Issue: 4
Volume: 3
Year: 1994
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