Mineral Deposits of Southern Africa, 1, 1-23

The nature and distribution of mineral deposits in Southern Africa, in relation to the tectonic framework, is portrayed in geochronological sequence on a set of sketch maps. Although tectonostratigraphic domains may be sharply outlined, the boundaries of the encompassed mineral provinces are frequently vague, owing to facies transitions of the host rocks or poorly known subsurface geology. The advance of crustal evolution through geologic eras is reflected in distinctive types of ore deposits generated in different environments. Superposition of provinces has created regions of exceptional mineral wealth as exemplified by the Transvaal which undoubtedly represents the richest portion of the Earth's crust. Archaean mineral provinces are characterized by greenstone belts consisting mainly of ultramafic-mafic lavas and intrusive sheets enriched in Cr, Fe, Au, and Ni and in some cases Sb and W. The emplacement of diapiric masses of granite led to upgrading of Au in vein systems and formation of chrysotile asbestos. In the late Archaean the epicratonic basin of the Witwatersrand province received clastic Au and U under an oxygen-deficient atmosphere. Proterozoic I mineral provinces include the vast layered mafic complexes of the Great Dyke and the Bushveld containing the world's largest resources of Cr, Pt, and V. In addition, the Bushveld mafic phase contains Ni, Co, Fe, and Ti; Sn, W, and F arc associated with the later Lebowa Granite Suite. The Phalaborwa Complex yields Cu and P. Sedimentation during this era favoured volcano-sedimentary deposition of Fe, Mn, and diagenetic F in the Transvaal-Griqualand West basins, as well as strata-bound Cu in Magondi subprovince. Amphibole asbestos developed in the iron-formations. During Proterozoic II a vast branching geosyncline formed across the subcontinent. Sedimentary Cu of marginal grade is widely distributed in the Namaqua province, while metamorphosed and deformed strata-bound deposits of Pb, Zn, Ag, and Ba are clustered in its Bushmanland subprovince. Pegmatites in this area as well as in Lurio subprovince yield Sn, W, Be, Li, and REE. The Pilanesberg subprovince is characterized by generally alkali volcanic pipes containing F and P, and by kimberlitic diamonds. Proterozoic III mineral provinces yield a wide spectrum of ore types: sedimentary Cu, Pb, Zn, Ag, Fc, and Mn; volcanogenic Cu and Zn; pegmatitic and hydrothermal Sn, W, Be, Li, and U. The diversity may be ascribed to the different environments created by plate tectonic mobility of the crust. In the Phanerozoic the stable platform of Southern Africa provided shallow basins suitable for precipitation of sandstone-type U. Proliferation of the biomass accounts for large resources of coal and submarine petroleum gas. In the late Mesozoic the crust was perforated by volcanic pipes introducing diamonds, P, and F from the mantle. Fluvial processes produced alluvial diamond fields and, assisted by wave action, concentrated diamonds in terraces along the West Coast. Calcified river gravels were enriched in U. Ti-rich sands accumulated along the East Coast. Under favourable climates various kinds of industrial mineral deposits formed across Southern Africa.
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Mineral Deposits of Southern Africa, 1, 1005-1008


The Havercroft-Streatham andalusite deposit is situated in the upper pelitic unit of the Timeball Hill Formation of the Pretoria Group. Contact metamorphism. caused by the Bushveld Complex, has reached medium grade with the development of andalusite-bearing hornfels in the pelites. The andalusite crystals are large (60 mm long), known as macle, and used locally and in the export market as a raw material in the refractories industry. The material mined in this area is of a higher grade than the small crystal andalusite produced in the Groot-Marico District of the Western Transvaal.
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Mineral Deposits of Southern Africa, 1, 1009-1017


The Uitkomst nickel-copper deposit is hosted by layered ultramafic body which is intrusive into the basal sedimentary rocks of the Transvaal Sequence. As exposures are poor and contacts are often obscured by scree, the present study is based largely on the examination of borehole cores. This has revealed that the ultramafic body has a narrow sill-like form with maximum horizontal dimensions of 5,2 by 1,1 km. The intrusion averages approximately 150 m in thickness, with a maximum thickness close to 300 m. The basal contact, which dips 8 to 10x north-west, is generally conformable with the quartzites and minor dolomites of the Black Reef Quartzite Formation. As a result of the gently undulating nature of the basal contact in places, however, the intrusive also lies on either Archaean granite or Malmani Dolomite. The north-eastern and south-western contacts have not been accurately defined, but borehole evidence indicates that the intrusion lenses out with only thin apophyses of the various ultramafic units remaining in the sediments of the Transvaal Sequence. The Uitkomst Complex consists of an inverted stratified sequence of mafic to ultramafic units and becomes progressively more ultrabasic upwards. Four zones have been recognized and these include, from the base upwards, a Basal Gabbro Zone, a Pyroxenite Zone, a Chromititic Pyroxenite Zone and a Peridotite Zone. The interrelations between the various zones comprising the ultramafic intrusion are not well understood as contacts are generally gradational and the layered sequence is commonly affected by deuteric alteration, assimilation of country rock sediments, and the presence of extensive younger diabase sills. It has been suggested that the Basal Gabbro Zone is a younger intrusive phase, but it may also represent a contaminated portion of the overlying ultramafics. The main sulphide concentration occurs in the lower three units, i.e. the Basal Gabbro, Pyroxenite, and Chromititic Pyroxenite zones. The copper content of the intrusion decreases upwards in agreement with the apparent inverted differentiation trend. Sulphide mineralization takes the form of disseminated blebs, stringers, and irregular aggregates which are interstitial to gangue mineral grains. The major sulphide minerals are pyrrhotite, pentlandite, chalcopyrite, and lesser pyrite. The Uitkomst Complex is believed to be coeval with, or slightly younger than, the mafic phase of the Bushveld Igneous Complex on the basis of a single Rb-Sr determination on biotite which yielded an age of 2 025 Ma. Petrochemistry and microprobe analyses of chromite indicate affinities with the Lower Critical Zone of the Bushveld. A number of problems relating to the genesis of the Uitkomst ultramafic body, including the apparent inverted differentiation sequence, remain to be solved. Furthermore, if Uitkomst is indeed of Bushveld affinity its position at the edge of the Transvaal Basin, about 80 km from the exposed contact of the Bushveld Intrusion, requires explanation.
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Mineral Deposits of Southern Africa, 1, 1019-1020

The Geological Society of South Africa's 1964 publication The Geology of Some Ore Deposits in Southern Africa appeared in two volumes, the first of which included a collection of papers dealing with the gold deposits of the Witwatersrand Basin. A benchmark contribution was that by R. Borchers, entitled Exploration of the Witwatersrand Basin and in Extensions, which was first delivered to the Society on 7 April 1961, as a Presidential Address and represented the following week to the Seventh Commonwealth Mining and Metallurgical Congress. The review of exploration and discovery was illustrated by two maps, prepared in 1960, which, for more than 20 years, served as the standard references on Witwatersrand surface and subsurface geology. These maps were entitled: Diagram No. 1: Surface Geology, based on publications of the Geological Survey of the Union of South Africa; simplified by the author. Diagram No. 2: Distribution of the Witwatersrand System as indicated by available exploratory data, and as revealed by the removal, where necessary, of all the obscuring, overlying, younger formations. In the 25 years that have elapsed since the compilation of these benchmark maps, an impressive volume of new information has been obtained from advances in mining and exploration in the Witwatersrand Basin, and the preparation of successor volumes to the 1964 publication seemed, to the Geological Society of South Africa, an appropriate occasion to revise and update Borchers's maps. It was decided that only one new map should be published and that this should replace Diagram No. 2. The availability of surface geological maps, on a scale of 1:250 000, prepared by the Geological Survey of South Africa and covering all the outcrop areas of the Witwatersrand Supergroup, rendered it unnecessary to issue a new edition of Diagram No. 1. The Geological Society commissioned General Mining Union Corporation Limited to prepare a first-draft version of a new map showing the surface and subsurface distribution of the Witwatersrand Supergroup, based on as much up-to-date information as could be made available by all the mining groups active in the exploitation and exploration of the Witwatersrand Basin. It was agreed that the draft map would then be circulated to all the major mining groups for their comments, amendments, and additions and that such added information would be integrated into, and reconciled with, the draft map by the Economic Geology Research Unit. The scale of the new map was decided on as 1:500 000, in contrast to the scale of 1:600 000, which Borchers had employed.
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Mineral Deposits of Southern Africa, 1, 113-154

Gold has been mined in the Barberton Mountain Land for over a century. Recorded production figures for the period l884 to l983 indicate that 251 553 kg (8 087 429 oz) of gold and 8 875 kg (285 331 oz) of silver have been recovered from more than 350 gold occurrences in the Archaean volcano-sedimentary successions of the Barberton greenstone belt located in the Eastern Transvaal and North-western Swaziland. Regionally, more than 95 per cent of the gold has been recovered from the north-west flank of the Barberton greenstone belt, the remainder having been mined in Swaziland (2,7%) and from scattered occurrences elsewhere in the granite-greenstone terrane. Most of the gold deposits are clustered in a number of subregions that have been subjected to complex structural disturbances within the greenstone belt. Many of the more significant gold deposits are located within six kilometres of the granite contacts or are located adjacent to major regional faults, many of which have undergone several stages of reactivation involving sliding, thrusting, and transcurrent dislocation. Approximately 70 per cent of all the gold produced in the Barberton Mountain Land has been derived from four mines (Sheba, New Consort, Fairview, and Agnes) located in the Jamestown, Sheba, and Moodies hills in close proximity to the historic town of Barberton which was founded in 1884. The concentration of gold into only a few ore bodies is illustrated by the fact that only 44 deposits have produced more than 311 kg (l0 000 oz) of gold. Of these only 16 deposits have yielded 1 555 kg (50 000 oz) and only nine deposits have recorded production in excess of 3 110 kg (100 000 oz). This paper outlines the geology and structure of the Barberton greenstone belt as well as the surrounding granitic terrane and provides an overview of the nature and distribution of the gold occurrences within this volcano-sedimentary and granitic framework. The separate gold subregions within the Barberton greenstone belt are briefly described and aspects dealing with the mineralogy of the gold ores and their treatment are discussed. Criteria relating to the classification of Archaean gold occurrences in Southern Africa are considered and the genesis of the different types of gold deposits is discussed in relation to the geologic evolution of the Barberton granite-greenstone terrane. Finally, a list is provided of all the known gold occurrences in the Barberton Mountain Land together with their localities, stratigraphic position, host rock setting, ore mineralogy, and gold and silver production data.
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Mineral Deposits of Southern Africa, 1, 155-161

More than 25 fracture-hosted ore bodies, in a variety of structural and lithological settings, have been exploited at Sheba Gold Mine from the year 1886 to the present day. To date a minimum of 69 t of gold have been produced. The steeply-dipping, isoclinally-folded, metasediments and metavolcanics in which the ore bodies are located form part of the Barberton greenstone belt, which has undergone several phases of deformation and only low-grade metamorphism. The ore bodies are steeply-plunging, sulphide-impregnated, zones of limited width and strike, which are developed to considerable depth. The ore shoots are irregularly developed over a strike distance of approximately 6 km, in a 2 km-wide zone within which ore-bearing fractures are associated with anticlinal structures, contiguous with a regional strike fault. The cores of the anticlines generally comprise a sequence of fuchsitic quartz schists, carbonate rocks and cherts. The auriferous zones are characterized by the presence of sulphides, quartz veins and wall rock discolouration. Inflections of the fracture planes or intersections with other planes are often sites of improved mineralization.
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Mineral Deposits of Southern Africa, 1, 163-168

The New Consort Gold Mine exploits steeply plunging auriferous sulphide shoots associated with the intensely folded contact between fine-grained metasediments of the Fig Tree Group in the hanging wall, and fine-grained mafic and ultramafic schists, lavas and serpentinite of the Onverwacht Group in the footwall. This contact is locally known as the Consort Contact or, where comprising a silicified horizon the Consort Bar. Gold mineralization associated with sulphide occurs below this contact. In the No. 7 Shaft area, however, this strongly laminated, siliceous horizon (Consort Bar) hosts the auriferous, apparently interlayered, sulphide bands, but is barren of sulphide or gold where exposed elsewhere. The Consort Contact and associated ore shoots have been affected by later faulting and folding. Numerous granite pegmatite bodies, barren of sulphide or gold, have been intruded along fractures and faults, some of which have displaced the ore shoots.
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Mineral Deposits of Southern Africa, 1, 169-179

The Fairview Gold Mine is situated in the Sheba Hills of the Barberton Mountain Land. Mining commenced in 1886 on free milling quartz reefs and on oxidized sulphidic rocks. During the period 1885-1983, 43 774kg gold and 1 427kg silver were recovered from 4 173 703t of ore exploited on the Fairview claim area. The claim area covers a variety of rocks of the Barberton Sequence. The volcanic Onverwacht Group is overlain by the argillaceous Fig Tree Group which in turn is overlain by the predominantly arenaceous Moodies Group. The property is situated along the central and southern portions of the Eureka Syncline and Ulundi Synclinorium. These structures are separated by the Sheba Fault and bounded to the north by the Lily Fault and along the south by the Barbrook Fault. The synclinal structures were refolded about a north-west axis which resulted in the development of fractures which served as hosts for the main mineralizing phase. Two types of auriferous ore bodies are mined at Fairview. Sulphidic reefs include disseminated-to-massive pyrite and arsenopyrite in concordant and discordant fractures in greywackes and shales of the lower Fig Tree Group. The fractures resulted mainly from tangential shear movement during the major folding periods and vary from 20mm to 2m in width. They may persist for up to 500m along strike, but payable gold values are found in several discrete payshoots, seldom greater than 60m in strike length. Quartz reefs, consisting of discrete quartz-filled fractures in the brittle quartzite horizons of the Moodies Group, form the second main type of mineralization. The veins occur at right angles to the strike of the host rocks, and the Sheba Fault, and were formed during the refolding of the synclines around a north-west-trending fold axis. The pale-grey to blue-black vein quartz, which varies in thickness from 10mm to 1,5m, normally carries very little pyrite and arsenopyrite and often contains visible gold as disseminated specks and plates. The main ore minerals in the sulphidic ore are pyrite and arsenopyrite with small to trace amounts of chalcopyrite, sphalerite, pyrrhotite, stibnite, native antimony, ullmannite, galena, enargite, pentlandite, niccolite, safflorite, skutterudite and graphite. Calcite, quartz and sericite are the most important gangue minerals. It is estimated that 50 per cent of the gold is included in pyrite, 20 per cent in arsenopyrite and associated minerals and 30 per cent occurs as free gold. In the quartz reefs the gold generally occurs in free form as irregular grains with minor sulphide minerals. Two generations of quartz have been recognized, often with free gold along their contacts. The close relationship between the gold and the sulphides, their impregnation into the host rock, and the structural relationship of the ore bodies to the host rock, indicate a hydrothermal origin for the ore. The primary source of the gold is thought to be the thick assemblage of Onverwacht volcanic rocks and perhaps the Fig Tree sediments. The gold was probably mobilized by the intrusion of the Kaap Valley tonalite pluton and was precipitated in favourable fractures and structural sites formed during successive stages of deformation. A total of 41 gold-bearing fractures are known, of which 22 have payable ore and 10 are being actively exploited at present at Fairview.
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Mineral Deposits of Southern Africa, 1, 181-185

The Agnes Gold Mine currently exploits two of a number of near vertical easterly plunging, ore bodies which are located in a zone of shaly, shallow water clastic sediments within the Moodies Group of the Barberton Sequence. These sediments, which have been folded locally to assume near vertical dips, have been affected by low-grade metamorphism only and show good preservation of sedimentary textures. Two types of ore are known. The first consists of swarms of calcareous vein-quartz which are generally strata-conformable, but can also be cross-cutting. The second ore type is manifested by strata-conformable concentrations of pyrite and minor quartz veining.
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Mineral Deposits of Southern Africa, 1, 187-196

A brief account is given of the geology and mineralogy of the Lily Mine, a small gold deposit located north-east of Barberton. The mine, essentially an oxidized deposit, is regarded as typical of the many small-scale mining undertakings that ceased production once sulphide ore was encountered in the deeper levels of the ore bodies. The relationship between gold fineness and depth in the Lily Mine suggested a form of enrichment in the upper oxidized workings where some exceptionally rich pockets of gold were found concentrated in favourable structural traps. This gold is believed to be essentially of secondary origin, derived from the altered protore, and was probably concentrated by supergene and residual processes of enrichment in the oxidized and semi-oxidized sections of the mine. Many of the old gold workings in the Barberton area are thought to have been similar types of deposit and in this paper some thoughts are offered as to how this type of gold occurrence may have been formed.
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Mineral Deposits of Southern Africa, 1, 197-203

The Fumani Gold Mine and its immediate environs were studied in an attempt to determine the factors controlling gold mineralization in the area. The mine occurs at the eastern extremity of the Sutherland greenstone belt where gold mineralization occurs within intensely folded and sheared banded iron-formation which forms part of the Giyani Formation of the Sutherland Group. These rocks are considered to be similar to those found in the lower part of the Onverwacht Group in the Barberton Mountain Land. The occurrence of gold mineralization is controlled spatially by the presence of isoclinal folding, which caused the gold to concentrate in fold hinges. The gold is texturally associated with a sulphur-rich arsenopyrite indicating a temperature of formation of 503±50°C. Close similarities exist between the Fumani and Homestake-type of gold occurrences.
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Mineral Deposits of Southern Africa, 1, 205-211

The Eersteling Goldfield in the Northern Transvaal is the site of the first lode gold discovery in South Africa in 1871. Available records indicate that the area produced more than 35 000 ounces of gold during this century. In 1935 the Eersteling field ceased to be an important producer. The gold occurrences of the Eersteling field are situated in basaltic rocks of the Archaean Pietersburg greenstone belt. Four types of gold occurrences are distinguished: (i) gold-quartz veins, (ii) impregnated sheared schists, (iii) sulphidic banded iron-formations, and (iv) alluvial deposits. On the basis of field observations, and ore microscopic and geochemical investigations it is proposed that the vein and impregnated schist deposits were formed as a result of regional metamorphism and that the gold of these deposits had its source in the volcanic country rocks. The sulphidic banded iron-formations are metamorphically disturbed syngenetic stratiform deposits which show local gold enrichments due to supergene processes in the weathering zone.
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Mineral Deposits of Southern Africa, 1, 213-220

The Mount Robert gold placer near Potgietersrus occurs in coarse, matrix-supported conglomerates of the Uitkyk Formation within the Pietersburg greenstone belt. Sedimentological and mineralogical investigations indicate that the conglomerates and the ore minerals were derived from a greenstone provenance, and that they were deposited in a braided river environment within a rapidly subsiding trough. Lack of sedimentological concentration of the heavy minerals is considered to be the main reason for the low and erratic gold grades encountered (usually below 1 g/t) and, thus, the failure of all past mining ventures. The mineralogical composition of the Mount Robert ore closely resembles that of the Witwatersrand deposits. However, uraninite is absent, probably as a result of its complete removal by weathering processes. Remaining small uranium concentrations can still be detected within the conglomerates where they occur associated with grains of carbonaceous matter, leucoxene aggregates, and secondary iron-hydroxides.
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Mineral Deposits of Southern Africa, 1, 221-230

Reef zones bearing gold, together with bismuth and associated with copper and iron sulphides, occur in granulite facies rocks close to the northern edge of the Limpopo Belt. The reefs transgress, and are severely contorted by, the steep southerly dipping isoclinal folding and gneissosity of the Limpopo Belt. Post-granulite facies pegmatites have invaded the reef zones, resulting in "pegmatoid" alteration and sulphide mineralization. From the distribution of metals and the macro and microtexture of ore and host rocks, it is concluded that the reefs are exhalative deposits containing gold, bismuth and iron. They have survived the high grade metamorphism due to anhydrous conditions and have been overprinted by a later hydrothermal deposition of copper and iron sulphides, coincident with retrograde metamorphism. The opalescent and blue-grey quartz of the Renco reefs have similar characteristicts to the varieties constituting the pebbles of the Witwatersrand conglomerates. This aspect, together with the relatively high fineness of the gold, points to a wider distribution of this environment for the occurrence of gold within the provenance of the Witwatersrand Basin.
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Mineral Deposits of Southern Africa, 1, 231-236

The Empress nickel-copper deposit, located in the Gweru mining district of Central Zimbabwe, occurs in folded Archaean mafic and ultramafic rocks associated with andesitic and felsic volcanic and pyroclastic rocks of the Maliyami Formation. The succession is intruded by numerous dykes and sills of diorite, dolerite, gabbro and amphibolite as well as a granodiorite-tonalite stock that has produced contact metamorphism in the mine area and surroundings. Three ore bodies have been delineated, of which only one has proved economically viable. The main ore body is contained within an amphibolite-metagabbro unit which also includes crudely layered mafic and ultramafic lenses which are folded in the upper levels of the mine but which wedge out at depth. The principal ore types mined at Empress can be grouped into disseminated sulphide, blebby sulphide and vein sulphide. The main ore minerals consist of pyrrhotite with exsolved pentlandite and subordinate chalcopyrite. Pyrite, magnetite, ilmenite, sphalerite, violarite, vallerite, and chalcocite represent minor components of the ore and are only locally developed. The deposits have been folded and sheared and primary and secondary sulphide textures suggest that two phases of mineralization are present at the mine.
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Mineral Deposits of Southern Africa, 1, 237-241

The Madziwa nickel-copper deposits are hosted in altered pyroxenites, gabbros and norites of the Madziwa Complex 150km north-east of Harare, Zimbabwe. Both massive and disseminated sulphide mineralization are present. Petrography and field relations suggest that rocks of the Complex were formed from ultramafic magma intruded along fractures in Archaean granitic terrane and that the magma stoped and digested granitic xenoliths to form gabbroic hybrids. The intrusive relations of rocks of the Madziwa Complex with both the granites and the Mashonaland dolerites suggest that the age of the Complex is between 2 600 and 1 800 Ma. The occurrence of nickel and copper sulphides interstitial to silicate crystals suggests that the disseminated mineralization is magmatic and was possibly formed from immiscible sulphide droplets in the ultramafic melt. Mineralization in the gabbros and norites occurs close to, or along the margins of, pyroxenite bodies. This feature is suggestive of initiation of sulphide concentration and crystallization by the contamination of the ultramafic magma with granitic material. The role of gravity in the formation of the disseminated mineralization is unknown since data on way-up is lacking. The structural control of the massive ore in joints and along contacts of rocks of the Madziwa Complex, and younger quartz veins, suggests tectonic concentration of this ore possibly from originally disseminated sulphides.
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Mineral Deposits of Southern Africa, 1, 243-248

Two relatively small, but high-grade nickel-copper sulphide ore deposits, the Phoenix and the Selkirk, have been proved within the Tati greenstone belt in Eastern Botswana. Nickel-copper mineralization occurs in different host rocks; a fine- to medium-grained feldspathic amphibolite at the Phoenix deposit, and a granular metagabbro at the Selkirk deposit. Nickel and copper grades, as well as the ratio between these two metals and the mineralogy also differ in the two deposits. The relatively high copper content and low nickel/copper ratio distinguish the deposits from komatiite-hosted Archaean nickel deposits. They can, instead, be classed with Archaean mafic intrusive varieties of nickel-copper deposits. The mainly massive sulphide ore in the Phoenix deposit and the core of massive sulphide ore in the Selkirk deposit are thought to have concentrated from magmatic disseminated sulphides in the host rocks during a thermal event which accompanied the intrusion of granitic rocks into the Tati greenstone belt.
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Mineral Deposits of Southern Africa, 1, 249-253

Nickel sulphides at Trojan Mine are hosted in a sequence of komatiitic ultramafic lavas. The mineralization occurs as disseminated, massive or near-massive ore. The basal position of the near-massive ore and of layers of massive ore relative to the disseminated ore, and the decrease in the nickel content from the footwall of the ore bodies to the hanging wall, suggests that the ores are of magmatic origin and were formed by gravity settling of the sulphides during crystallization of the ultramafic lavas. The high Ni:Cu ratio of 20:1 is consistent with other data for nickel sulphide deposits in ultramafic lavas. The structural control of some of the massive ore in veins and in "breccias" suggests local secondary concentration of remobilized nickel sulphides. The main sulphide minerals, in order of abundance, are pyrrhotite, pentlandite and chalcopyrite. Minor amounts of millerite and pyrite, and the arsenides maucherite, niccolite, cobaltite and gersdorffite are present.
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Mineral Deposits of Southern Africa, 1, 25-31

It is generally acknowledged that Southern Africa has a mineral endowment that is equalled by few other regions in the world. This is true, not only with respect to the estimated value of minerals produced from the region, but also the spectrum of different minerals that are currently being exploited from the sub-continent. This paper will not attempt to provide any geological interpretation concerning the Southern African mineral endowment, a subject which is dealt with in some detail in many of the papers that follow. The objective of this contribution is rather to identify and to discuss briefly those factors which have contributed to the creation and maintenance of an environment that is conducive to mineral exploration and exploitation. It is believed that such an environment is as crucial as mineral endowment itself.
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Mineral Deposits of Southern Africa, 1, 255-262

The Epoch nickel deposit occurs in talc-carbonate rocks forming a steeply south-dipping apophysis projecting westwards from the top of a large differentiated ultramafic complex. The altered and recrystallized ore host has undergone the same low-to-medium grade metamorphism that affected the country rocks. The disseminated ore assemblage of millerite-pyrite-magnetite+ polydymite+pentlandite is sulphur-rich and is not considered to have crystallized directly from a sulphide melt. Ore genesis possibly involved a combination of (i) alteration of a pre-existing magmatic association, and (ii) formation of sulphur-rich magnetite-bearing aggregates during serpentinization and subsequent talc-carbonation at high sulphur-fugacities. Footwall sulphide-facies cherts could have been a source of additional sulphur.
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Mineral Deposits of Southern Africa, 1, 263-273

The five Damba nickel sulphide deposits lie in the same lithostratigraphic positions as the other nickel sulphide deposits around the Shangani batholith. The deposits are hosted by the most ultramafic members at the base of a komatiitic sequence, which has been altered to varying degrees. The combination of preserved primary textures with nickel and chromium geochemistry has enabled the peridotitic komatiite sequence to be subdivided into individual lava flows. The sulphide mineralization, which consists primarily of pentlandite and millerite, appears to be better developed in the thicker, lowermost flows of peridotitic komatiite. The mineralization is generally found in footwall depressions which may be fault controlled and each body comprises a number of stacked mineralized flows. The sulphide bodies probably formed by the gravitational settling of an immiscible sulphide liquid to the base of the flows and were trapped in depressions which were maintained during the eruption of successive flows.
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Mineral Deposits of Southern Africa, 1, 275-279

The Matopos Dam sulphide nickel-copper occurrence is located in Archaean Bulawayan Group rocks in southern Zimbabwe. Lenses of generally low-grade sulphide mineralization with a Ni:Cu ratio of about 4:1, and represented at surface by gossan occurrences, are located at places along the contacts of an apparently bilobate, pipe-like, body of talc-carbonate rock, which is about two hectares in surface extent. The talc-carbonate rock, which is presumably intrusive into the surrounding schistose metabasaltic rocks, is everywhere mantled by a selvedge of fibrous amphibolite and, in this and other ways, the occurrence is reminiscent of that at Shangani, to the north of Bulawayo.
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Mineral Deposits of Southern Africa, 1, 281-285

The Bon Accord nickel sulphide deposit was discovered by Eland Exploration (Pty) Limited in the course of investigation of the nickel potential of the Barberton Sequence. Mineralization occurs in rocks of the lower Tjakastad Subgroup within a cherty succession near the contact with altered ultramafics. Drilling has outlined a thin, tabular zone of mineralization with a potential reserve of 900 000t grading 1,23% nickel, occurring as bands and disseminations of sulphides in quartz-muscovite schist host rocks. Pyrite is the dominant sulphide species throughout, with pentlandite the major nickel-bearing sulphide as massive mineralization, and gersdorffite the dominant nickel-bearing phase in disseminated ores. Copper sulphides are rare and the deposit is characterized by a very high nickel-to-copper ratio. Geochemically the mineralization has strong ultramafic affinities and is considered to be related to nickel-sulphide-bearing komatiites which were emplaced penecontemporaneously with the formation of cherts. The deposit is broadly similar to other komatiite-related Archaean nickel deposits, but unusual features concern the occurrence of the nickel sulphides in siliceous rocks as well as the ore mineralogy. It is suggested that the host rocks are sulphide-bearing komatiites which have undergone intense silicification and shearing, or alternatively, the nickel sulphides from the komatiites may have preferentially accumulated in semi-consolidated, inter-flow cherty material. The nickel sulphide mineralization occupies a stratigraphic position similar to that of the nearby, well-documented, sulphur-poor Bon Accord West nickel deposit and the two types of mineralization may be related.
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Mineral Deposits of Southern Africa, 1, 287-291

The geology and petrology of the Bon Accord nickel deposit in the Tjakastad Subgroup is reviewed. The mineralogy of the deposit is complex, containing several new minerals previously described. Thermochemical calculation supports the evidence gained in the field, i.e., that the deposit was metamorphosed by granitic rocks associated with the Stentor pluton emplaced 2,75 Ga ago. The high NiO content, low sulphur content, and the presence of a reduced chromium spinel, all contribute to the unique character of the deposit. Evidence suggests that the deposit represents an oxidized and subsequently metamorphosed nickel-rich meteorite, or an oxidized and subsequently metamorphosed segregation of nickel-rich sulphide. The present state of knowledge does not permit a distinction to be drawn between these two alternatives. If the meteorite hypothesis is correct, any success as a result of exploration will be governed by chance. The alternative supports the notion that the Barberton greenstones were deficient in sulphur leaving only a remote possibility that large sulphide ore bodies can be found.
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Mineral Deposits of Southern Africa, 1, 293-320

The Murchison greenstone belt hosts one of the world's largest antimony producing areas currently responsible for approximately 20 per cent of the total world antimony production. A "line" of antimony deposits 50 km in length and containing some 18 mines and occurrences is described. The Antimony Line occupies higher ground in the centre of the greenstone belt and is situated immediately south of the resistant hills of the quartzitic Antimony Bar. A poorly exposed and weakly developed possible "southern Antimony Line" occurs about 1 km to the south of the main Antimony Line. Both "lines" occur within the Weigel Formation which is bounded to the south by the ultramafic to mafic volcanic-dominated Mulati Formation, and to the north by the mafic to felsic volcanics of the Rubbervale Formation which host volcanogenic copper-zinc mineralization. The structural interpretation of this lithologically asymmetrical greenstone belt is discussed. Quartz-chlorite and quartz-muscovite schists are the main lithological components of the Weigel Formation and hence are the country rocks to the Antimony Line. Petrographic and geochemical evidence indicates that the chloritic schists are magnesium-rich pelites (magnesiopelites) in which the quartz-muscovite schist represents felsic tuffaceous accumulations. The Antimony Line represents a linear shear or fault zone displaying intense deformation. It comprises a range of talcose and carbonate rocks in which stibnite mineralization is developed in anomalous thickenings of quartz-carbonate rocks. The main rock types recognized often show a broad zonation and include (from the periphery to the centre of the Antimony Line) talc-chlorite schist, talc-carbonate schist, quartz carbonate schist, green fuchsitic quartz-carbonate schist and chert-carbonate rocks. Mineralogical and geochemical evidence is presented which provides an explanation for the origin of these rocks. It is shown that talcose schists represent the alteration products of komatiites and that the quartz-carbonate rocks result from further alteration of the talc-carbonate schists. The geochemistry of the quartz-carbonate rocks is similar to that of komatiites and quite unlike that of carbonate sediments. The conspicuous green fuchsitic carbonate schists are shown to be the results of potassium-metasomatism which is linked to the mineralization. The origin and economic significance of the chert-carbonate rocks, which host the major ore bodies within the carbonate centres, is discussed. The main mineralized centres, which are also described elsewhere in this volume, are referred to and an account is given of each of the minor stibnite occurrences of the Murchison Range. The mineralization follows a consistent pattern of occurrence in nearly all workings. Stibnite-bearing quartz veins and stibnite impregnations occur in the competent, siliceous, cherty carbonate rocks and in associated green fuchsitic quartz-carbonate schist which generally occupies the centres of quartz-carbonate alteration zones within talcose schist. The antimonial ores are divided into three types, namely tetrahedrite ores, pure stibnite ores, and complex antimonial ores. Only the pure stibnite ores are mined. Sulphur isotope data is presented for sulphide minerals from the Monarch Mine. The origin of the antimony mineralization is discussed and an epigenetic model is proposed. The view is held that metamorphic fluids transported antimony from the enriched magnesiopelites and deposited it at a slightly younger stage in the more competent carbonate alteration zones marked by the anomalous carbonate centres.
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Mineral Deposits of Southern Africa, 1, 321-332

The adjoining Gravelotte and Alpha shafts exploit the same ore body which has been the mainstay of antimony production in the Archaean Murchison greenstone belt since the late 1940s. Country rocks include a range of quartzites, quartz-sericite schists, chloritic schists, metaquartzwackes and magnesium-rich metabasalts. Mineralization occurs within a carbonate lens situated on the stratigraphically continuous "Antimony Line". Talc-chlorite schists form a discontinuous peripheral assemblage to the carbonate lens. They generally increase in carbonate content towards the centre of the carbonate lens, becoming grey and green chloritic carbonate schists. Antimony mineralization is often localized on the south side of a thin cherty carbonate zone, probably representing a silicified fault or shear plane. The most important Gravelotte (near surface) and Alpha (at depth) ore bodies are associated with the tight to isoclinal, steeply plunging Alpha-Gravelotte fold, with the better mineralization concentrated in what are thought to be cymoidal structures related to a major shear zone along the Antimony Line. A number of mineralized veins and fractures branch from the main bodies, with the so-called "C Line" reefs occurring in the nose of the fold. A minor, but very continuous reef, the North Reef, is associated with an adjacent, steeply-plunging, isoclinal fold, the North Reef Fold. The folds are well defined by the folded, competent, quartzitic "Antimony Bar" and have formed as a result of a left-lateral shear couple with movement along the "Antimony Line" rocks immediately to the south of the former. These less competent rocks have been carbonatized, and the more competent carbonates still further deformed to provide the mineralized channels in tensionally created structural sites. The final location of the mineralization within the controlling structures can be ascribed to multiple remobilizations and concentrating episodes applied to structurally located antimonial sulphides, possibly derived from a primary volcanic source. The main ore mineral is stibnite. Lesser amounts of berthierite occur together with varying, but smaller, amounts of gersdorffite, ullmanite, corynite (a mixture of gersdorffite and ullmanite), gudmundite, pyrite, arsenopyrite and scheelite. Native gold and aurostibite are important constituents. Native antimony is developed within the Black Reef where mineralized chloritic talc-carbonate schists have been metamorphosed to a dark serpentinitic assemblage by the intrusion of a dolerite dyke.
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Mineral Deposits of Southern Africa, 1, 33-41

This contribution serves to introduce 35 papers in his volume dealing with aspects of Archaean mineralization of Southern Africa. It further provides an overview of the close genetic relationship existing between various lithological subdivisions of the Archaean greenstone belts and their surrounding granitic terranes and the diverse mineralization types found in these environments.
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Mineral Deposits of Southern Africa, 1, 333-338

The Athens ore zone is one of the larger antimony and gold deposits on the "Antimony Line" within the Murchison greenstone belt in the North-eastern Transvaal. The stibnite mineralization is confined to a narrow (10-25m) zone of massive quartz-carbonate rock within an envelope of schistose chloritic quartz-carbonate rock and talc-carbonate schist. Chloritic schist and phyllite, derived from magnesiopelites, form the immediate country rocks of the Antimony Line. The ore zone is steeply dipping and has a steep plunge to the east. The stibnite occurs as random veins and stringers which are erratically distributed within the quartz-carbonate rock. A hydrothermal origin, with the antimony and gold having been derived largely from the country rocks during a metamorphic episode, is favoured. The Antimony Line is considered to represent a major shear zone within mafic, or even ultramafic rocks and was the locus of major hydrothermal carbon dioxide metasomatism. The best antimony mineralization occurs in anomolous structural sites along the Antimony Line.
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Mineral Deposits of Southern Africa, 1, 339-348

The Monarch Cinnabar Mine is one of the few mercury mines located in Archaean rocks, a phenomenon restricted to Southern Africa. Discovered in 1936, the deposit was worked between 1939 and 1945 when it was closed due to poor market conditions. Approximately 4200 flasks of mercury were recovered and the ore reserves were considered to be nearly exhausted at the time of closure. The mercury occurrence is centrally situated in the Archaean Murchison greenstone belt and lies within Weigel Formation rocks. Cinnabar mineralization occurs in quartz-carbonate rocks similar to, but north of, those of the "Antimony Line". These carbonate rocks have geochemical characteristics indistinguishable from those of the talc-carbonate schists with which they are associated. The talcose rocks, in turn, have compositions very similar to komatiites and it is considered that the mineralized carbonate rocks were ultimately derived from komatiite parent rocks. Two near vertically disposed ore bodies are described, the larger Harington Kop body, which extends to a depth of 190 m, and the minor Monarch Kop body. The ores are shear and fracture controlled and exhibit replacement textures. Either coarse ankeritic carbonate or silicification accompanies the cinnabar. Associated ore minerals include tetrahedrite, stibnite, chalcopyrite, digenite, and covellite. The mineralization is considered to have been formed after the development of the carbonate rocks, probably during the waning phase of metamorphism. Unusual low-iron, high-magnesium metabasaltic rocks to the north of the mine are thought to have been the source of the mercury, while the localization of the ore was strongly controlled by a left-lateral shear (striking N083°E) at a low angle to the subvertical strata which strike N065°E.
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Mineral Deposits of Southern Africa, 1, 349-357

Antimony mineralization has been known on the farm Amo 259 JU in the Malelane area of the Barberton greenstone belt for many years. The original deposit together with three more recently located occurrences are all confined to a so-called antimony-bearing pelitic schist zone. This zone, of uncertain stratigraphic position, averages 200m in width and can be traced for at least 12km. It occurs largely conformably within a broadly synclinal sequence of Moodies Group quartzites and conglomerates. Main rock types of the schist zone include micaceous quartz schists, chert, cherty greenschists with fuchsite, carbonate-rich schist, and talc-carbonate rock. Volcanic rocks, including felsic varieties as well as serpentinite and probable tuffs, suggest a strong effusive component. Contacts between the pelitic schist zone and adjoining quartzites are generally gradational. Antimony mineralization, mainly in the form of stibnite, occurs in quartz veins hosted in a range of carbonate and siliceous carbonate rocks. The carbonate rocks can be green and fuchsitic and invariably have high Ni and Cr contents. They have a close resemblance to similar antimonial carbonates of the Antimony Line of the Murchison greenstone belt with which they have been compared. The results of soil and rock geochemical studies are presented, as are the results of diamond drilling. Good grade, but very erratic stibnite mineralization was intersected in some areas with the largest ore body consisting of approximately 10 000 t grading 5% antimony. The similarities of the occurrences with those of the major antimony ore bodies of the Murchison greenstone belt make the Amo mineralization of considerable interest from a genetic point of view.
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Mineral Deposits of Southern Africa, 1, 359-375

In this contribution the principal chrysotile asbestos occurrences in Zimbabwe, South Africa, and Swaziland are described, emphasis being place on the regional geological settings and host rock stratigraphy of the mineralized areas. The paper also serves to introduce the following five papers in this volume that describe a selection of chrysotile asbestos deposits in the regions mentioned. All the more important asbestos ore deposits in Southern Africa are Archaean in age (~2 500-3 500 Ma old), being associated with ultramafic complexes occurring either as sill-like bodies in greenstone belts or as later cross-cutting intrusions. The ultramafic bodies can be grouped into three varieties. These, in order of decreasing age, are:
1. the layered complexes associated with komatiites and komatiitic basalts, and forming part of the Lower Ultramafic Unit of Southern African greenstone belts;
2. layered ultramafic bodies associated with the intermediate to acid volcanic rocks that constitute part of the Mafic-to-Felsic Unit of greenstone belts; and
3. ultramafic intrusive bodies that postdate the greenstone belts, but which are still affected by Archaean tectonic disturbances that arise from the emplacement of granites.
All the principal asbestos-bearing complexes show magmatic segregation into layered, often cyclically repetitive, differentiation sequences. These single or multicyclic sequences may consist of two or more of the following rock types: dunite, peridotite, harzburgite, lherzolite, wehrlite, bronzitite-enstatolite, websterite, gabbro, norite, and gabbroic anorthosite. Where fractional crystallization of the ultramafic magma has been most efficient, many layers at, or near, the base of the complexes comprise monomineralic cumulate phases. These commonly consist of dunites and Mg-rich orthopyroxenites. With increasing distance from the base, progressive Mg depletion and Fe enrichment of the successive layers take place. Although chrysotile asbestos may commonly be encountered in all serpentinized ultramafic rock types, optimum development of economically exploitable fibre generally occurs in dunites, peridotites, or harzburgites. All the Southern African Archaean layered complexes appear to have been derived from magmas of ultramafic composition in contrast to magmas of tholeiitic parentage that gave rise to the great stratiform intrusions like the Bushveld, Stillwater, and many others. The Great Dyke in Zimbabwe, unlike the others, also acts as host to small chrysotile deposits developed in serpentinized dunite or harzburgite. In addition to the asbestos mineralization found in the layered complexes, subordinate deposits. occurring in serpentinized dolomitic rocks associated with the ~2 200 Ma old Transvaal Sequence, are briefly described. Whereas faulting and fracturing is generally acknowledged as being largely responsible for the local development of asbestos fibre, examples from the Southern African greenstone belts demonstrate that folding is often a dominant regional controlling factor in the localization of asbestos mineralization in ultramafic rocks.
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Mineral Deposits of Southern Africa, 1, 377-393

Chrysotile asbestos is a widespread mineral found in the majority of the Zimbabwian ultrabasic bodies. Economic deposits are found in those areas where all the controlling factors of suitable host rock, the presence of solutions, and structural control have been satisfied. The tendency has been to assume a universal growth mechanism, but field evidence indicates that fibre occurs as stress-controlled dilation seams, as a recrystallization product of serpentine minerals, and as a result of serpentinization of olivine. The Zvishavane (Shabani) ore bodies are located in partially serpentinized dunite, with localized structural control a noticeable feature. The Sheffield Claims deposit is an example of the recrystallization of picrolite to chrysotile fibre. The Gath's deposit differs from Zvishavane in that the structural control is more regional. King Mine is an example of fibre formation in a serpentinite with a typical structural pattern. The complexity of the geology has a direct bearing on the selection of mining methods and sequence.
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Mineral Deposits of Southern Africa, 1, 395-407

The Havelock asbestos deposit is one of the most important occurrences of cross-fibre chrysotile in southern Africa. The asbestos ore body occurs within a serpentinized dunite-harzburgite that contains the primary serpentinite assemblage lizardite-chrysotile brucite-magnetite. While the transition from dunite to harzburgite is a progressive change in composition, consistent with fractional crystallization in a layered intrusion, the ultramafic complex does not itself occupy a stratigraphic horizon. Structural relations and the absence of gabbroic or similar differentiates suggest, instead, that the serpentinite was emplaced along fractures as a solid body. Though the serpentinite is allochthonous, it may be derived from the crustal ultramafic successions of the Barberton greenstone belt. However, the rather depleted compositions of undeformed Havelock serpentinites are also comparable with metamorphic peridotites from younger orogenic belts and serpentinites dredged from the present sea floor. An alternative hypothesis, that the Havelock body is an Alpine-type serpentinite, cannot be excluded from the present evidence. Although the margins of the Havelock body are tectonic, large plastic strains are only recorded in the centre of the serpentinite. A deformed zone of ribbon-textured serpentinites parallels one margin of the asbestos deposit and indicates that internal deformation of the serpentinite and formation of the chrysotile ore body were synchronous. Fibrous chrysotile within the ore body probably formed by diffusion of fluids into dilating cracks at temperatures below dehydration of lizardite serpentinites. Massive circulation of fluids is suggested from the presence of talc zones with fault-like geometry, and the extent of ore body hydration and carbonation. A model is described in which processes of rock dilatancy, diffusion and fluid circulation operated in that part of the serpentinite where tectonic stress rose to relatively high levels.
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Mineral Deposits of Southern Africa, 1, 409-420

The Msauli asbestos deposit, one of the largest chrysotile fibre-producing mines in Southern Africa, is situated in the south-eastern portion of the Barberton greenstone belt and is associated with rocks forming part of the upper succession of the Onverwacht Group of the Barberton Sequence. Four chrysotile asbestos ore bodies, all structurally interrelated, occur in the same light-green serpentinite that forms part of an Archaean layered ultramafic intrusion striking in a north-easterly direction and extending over a distance of 3 km. Serpentinization of the host rock dunites and pyroxenites occurred during the cooling phase of the intrusion at relatively low temperatures and pressures. This is reflected by the presence of lizardite and chrysotile, the major serpentine minerals. Carbonitization occurred after the asbestos fibre was formed and most of the talc-carbonate rocks surrounding the ore deposits are thought to represent altered serpentinites. Minable asbestos fibre is confined to structurally and chemically favourable localities within the serpentinite. The fibre occurs mainly as cross fibre veins but areas containing ribbon fibre, slip fibre, and mass fibre have also been encountered. Acid solutions, containing either chlorine or sulphate anions, leached the serpentinite and subsequently entered pre-existing tension fractures as a gel. Dehydration of this gel resulted in the formation of fibre and released acid which was made available for further dissolution. This resulted in successive phases of asbestos formation.
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Mineral Deposits of Southern Africa, 1, 421-426

The New Amianthus Mine must rank as one of the most interesting chrysotile asbestos deposits in the world. Chrysotile asbestos occurs as cross-fibre in parallel to sub-parallel seams of the Ribbon Line and also as irregular seams in the Footwall Reef. Host rock control, source of serpentinous solutions, fibre growth mechanism, and structural control are clearly illustrated. Unique cone structures are developed in certain parts of the Ribbon Line.
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Mineral Deposits of Southern Africa, 1, 427-435

Chrysotile asbestos deposits in the Barberton Mountain Land are mainly confined to layered ultramafic complexes. Most, but not all, of these ultramafic complexes appear to be penecontemporaneously associated with basaltic and peridotitic komatiite successions found in the lower division (Tjakastad Subgroup) of the Onverwacht volcanic sequence. The Kalkkloof Complex is of this type and occurs in a greenstone remnant that is separated from the Barberton greenstone belt by a trondhjemitic gneiss pluton which was intruded into the region approximately 3 200 Ma ago. The Kalkkloof ultramafic body consists of a number of alternating serpentinized dunite and orthopyroxenite layers together with interlayers of talcose schists. The complex has undergone considerable faulting and shearing and the original cumulate assemblages have been extensively altered by CO2, Mg, and SiO2 metasomatism. The chrysotile asbestos occurs mainly as cross fibre and is preferentially developed near and parallel to contact between the soft, green, serpentinized dunite and the hard, massive, grey-green, serpentinized orthopyroxenite. The main controls for fibre formation are: (i) the presence of suitable high-Mg serpentinized dunite host rocks, (ii) the differential structural competence between the dunites and the orthopyroxenites, (iii) several episodes of faulting and fracturing of the Kalkkloof layered body and, (iv) the availability of suitable serpentinous solutions to assist in fibre development. These solutions were probably first generated at the time of emplacement of he trondhjemitic gneiss pluton and again, later, following Proterozoic dyke and sill intrusion.
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Mineral Deposits of Southern Africa, 1, 43-112

In 1981 Zimbabwe was the eleventh most important gold-producing country in the western world with a production of 11 691 kg (3758740z). The deposits in Zimbabwe are classified into stratabound and non-stratabound types. Stratabound deposits incorporate iron-formations, banded sulphides (in non- ferruginous host rocks), and volcaniclastic- and clastic-hosted deposits. Vein deposits and mineralized shear zones constitute the non-stratabound types. Nearly 62 per cent of Zimbabwe's gold production has come from vein deposits, 20 per cent from mineralized shear zones, 12,8 per cent from iron-formations, 4,7 per cent from volcaniclastic-hosted deposits, and the balance from clastic-hosted and banded sulphide mineralization. The nature, distribution and genesis of the deposits are discussed in relation to the Archaean stratigraphy of the Rhodesian Craton, namely the c. 3,5 Ga Sebakwian Group, c. 2,9 Ga Lower Greenstones, and c. 2,7 Ga Upper Greenstones and overlying Shamvaian Group. The total cumulative strike of Archaean iron-formations exceeds 5 900 km, nearly 70 per cent of which are intercalated with volcanic rocks, predominantly mafic. The greatest gold production has come from iron-formations interbedded with sedimentary rocks (32%) and mafic rocks (31%), with 26 per cent from ultramafic environments and 11 per cent from a felsic association. In relative terms, the most productive association has been the ultramafic with a production of 37kg Au per kilometre of strike of iron-formation, followed by the sedimentary (32 kg/km), mafic (22 kg/km), and felsic (21 kg/km) associations. Stratigraphically, most gold has been derived from iron-formations of the Bimodal Unit (Upper Greenstones) (42%), and the Sebakwian Group (30%). Iron-formation of the volcanic western succession of the Upper Greenstones have produced considerably more gold than those of the volcano-sedimentary eastern succession. The only gold-bearing banded sulphide deposit of note is the Roma Mine. Three significant deposits, the How, Nando, and Shamva, have produced gold felsic volcaniclastic rock and a small production has been derived from quartzites and conglomerates.
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Mineral Deposits of Southern Africa, 1, 437-449

The pegmatites described in this paper, which include those of the Selati Line and Olifants River mica field, lie within the confines of the Archaean Kaapvaal Craton between Mica in the south and the Sutherland greenstone belt in the north. These pegmatites are thought to be igneous in origin and may, in part, be related to the intrusion of the potash-rich Mashishimala Granite which occurs immediately south of the Murchison greenstone belt. Four principal types of pegmatite deposit are recognized in the region. One of each is described from a select locality in the area; namely the corundum-bearing Bird-Cage Camp prospect, a tantalite-columbite occurrence from the Palakop region, beryl and emerald deposits from the Gravelotte Emerald Mine and an economic deposit of quartz-feldspar-muscovite from the Union Mine at Mica. The granitic pegmatites of the North-eastern Transvaal are generally considered to be barren, and mineralization, in the case of corundum and emeralds, is the result of interaction between invading pegmatitic fluids and vapours and pre-existing greenstone remnants. In the case, however, of beryl and molybdenum at Gravelotte and beryl and tantalite-columbite at Palakop, the source of mineralization is an albitite pegmatoid, a rock type hitherto little recognized in the region.
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Mineral Deposits of Southern Africa, 1, 451-460

Two discrete V-bearing, Ti-magnetite-rich layers are present within the upper portion of the mafic Novengilla Gabbro Suite of the Rooiwater Complex in the eastern sector of the Murchison Range. These layers are continuous for at least 14 km along strike and represent potential ores for the production of one or more of ilmenite, high-titania slag, vanadium pentoxide and iron or steel. The ores consist largely of granoblastic polygonal Ti-magnetite crystals that are characterized by a wide variety of complex ilmenite and pleonaste micro-intergrowths. Variable, but significant, amounts (10-20%) of relatively coarse-grained ilmenite are present interstitially between the generally larger Ti-magnetite crystals. The ores have been metamorphosed and show varying degrees of recrystallization which is reflected by the highly modified nature of their micro-intergrowths and the development of abundant intergranular ilmenite. Increased temperatures during regional metamorphism resulted in partial breakdown and spheroidization of original lamellar ilmenite and pleonaste micro-intergrowths. This also contributed to continual external granule exsolution of ilmenite to form abundant intergranular ilmenite: The ores of the lower layer contain moderate amounts of TiO2(14,5-15,1%) and V205(1,3-1,1%) and are thus chemically similar to the economically important Main titaniferous magnetite layer of the Bushveld Complex. The Rooiwater ores, however, contain 10 to 15% coarse-granular ilmenite and are thus amenable to beneficiation. The upper layer contains a maximum of 24,5% TiO2 and correspondingly more coarse-granular ilmenite (15-20%). The V2O5 contents are lower (0,8%), but can be upgraded to approximately 0,9% by separation of the coarse ilmenite fraction.
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Mineral Deposits of Southern Africa, 1, 461-467

The economic potential of the banded magnetite quartzite layers that outcrop on Zandrivierspoort 851 LS and adjoining farms was first recognized in 1974. These metamorphosed ferruginous chemical sediments are equivalent to the Algoma-type iron-formations, and are thought to be part of the Archaean Pietersburg greenstone belt. The deposit is located just south of the orthoamphibole isograd forming the boundary between the Limpopo Metamorphic Complex and the Kaapvaal craton, and has been subjected to upper greenschist to lower amphibolite facies metamorphic conditions. The greenstone assemblages around Zandrivierspoort have been affected by four stages of polyphase deformation, the most intense being the initial isoclinal first stage that was responsible for convoluting the main ore zone into a unit which, in places, is four to five times the original thickness. This "soft sediment" style of deformation is characterized by ubiquitous, small-scale, sympathetic, isoclinal folds in the major fold hinge zones, as well as the squeezing out of interlayered amphibolite to leave a thick, homogeneous, magnetite quartzite unit. The major mineral components of the ore zone are magnetite (in varying stages of alteration to haematite), quartz, and actinolite or grunerite. Chert and calcite have been noted as minor components in places, while apatite occurs in trace amounts. The alteration of the amphibole has resulted in the goethite and calcite seen in weathered specimens. The ore is characterized by a rather uniform banded texture with 1 to 5 mm-thick, predominantly magnetite bands, alternating with bands consisting predominantly of quartz and amphibole. The segregation is not complete. Three to five per cent of the opaques consist of primary exsolution lamellae of haematite, while haematite forming spongy rims around magnetite grains, together with near-surface specularite, have resulted from the oxidation of magnetite. One hundred and thirty-five diamond drill boreholes and 37 air drill boreholes have outlined a open-cast minable deposit which is in excess of 500Mt of ore and containing approximately 40 per cent recoverable magnetite. Liberation tests have shown the ore to be amenable to upgrading by simple wet magnetic separation resulting in a "super-concentrate" (>70% Fe) product.
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Mineral Deposits of Southern Africa, 1, 469-472

Tungsten mineralization occurs on the north-eastern flank of the Archaean Sutherland greenstone belt in late-stage, cross-cutting, pegmatites, quartz veins and stringers. The mineralization, which consists of scheelite with minor amounts of emerald, is associated with zones of alteration represented by biotite schist within a sequence of tremolite and tremolite-actinolite schists, together with pelitic schists and banded iron formation. Serpentinites, metapyroxenites and metagabbros found in the area provide indications of an early, layered, sill-like differentiated body. The Shangoni tungsten occurrence, which is uneconomic at the present time, appears to represent a late-stage hydrothermal deposit associated with the intrusion of a volatile-rich granite along the south-eastern margin of the Sutherland greenstone belt.
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Mineral Deposits of Southern Africa, 1, 473-487

Pyritic placer mineralization in conglomerates of the 3 000 Ma-old Pongola Sequence of the south-eastern Transvaal, northern Zululand, and Swaziland, supported a number of small gold-mining operations, from 1890 to 1930. Recently, several attempts have been made to find uranium in the Pongola sediments, and some of the old gold workings are currently being reassessed. Mineralogical, geological, and geochemical findings, gathered from the following four occurrences, are discussed: (i) Redcliff-Kranskop area, near Amsterdam; (ii) Gunsteling area, south-east of Piet Retief; (iii) Denny Dalton area, near Ulundi; and (iv) Cooper's Store area, near Nkandla. The conglomerates, in which the largely pyritic mineralization occurs, represent lenticular, polymictic, usually poorly-sorted, clastic intercalations in quartzitic series. Deposition of the arenites is envisaged to have taken place on braided alluvial plains which were frequently submerged by shallow marine waters. Reworking of the conglomerates occurred only to a minor extent, as suggested by the predominance of matrix-supported conglomerates, by the poor concentration of heavy minerals, and by their often poor rounding. Well-developed mineralization, carrying gold contents in the range from 1 to 4 g/t are usually restricted to inconsistent clast-supported conglomerate layers. The mineralogical composition of the ores resembles broadly that of the Witwatersrand reefs, and detrital, as well as a number of authigenic ore minerals, which formed as a result of diagenesis and mild metamorphic overprint, were found. Gamma- and alpha-spectrometric data prove the presence of radioactive disequilibria in the weathered conglomerate outcrops. The absence of uraninite, thus, may be due to recent removal of uranium by supergenic processes.
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Mineral Deposits of Southern Africa, 1, 489-493

Twenty years have elapsed since the appearance of the most comprehensive collection of papers on the geology of the Witwatersrand Basin and its contained goldfields, that has yet been compiled. The late Sydney H. Haughton was asked by the Geological Society of South Africa to assemble and edit a series of accounts of various aspects of the basin, as a whole, and of the individual goldfields, and these were published by the Society, in 1964, as Volume 1 (Gold Deposits of the Witwatersrand Basin) of The Geology of Some Ore Deposits of Southern Africa. Contained in the volume were 18 papers which summarized what had been learned of Witwatersrand geology and mineralization during the course of almost 80 years of mining and prospecting. The publication came to be accepted as the handbook of the geology of the Witwatersrand Basin, a distinction which it still enjoys. The invited authors undertook their tasks during the years 1959-1961, just as a significant new phase of geological investigation was starting. Systematic, quantitative, sedimentological studies of the gold- and uranium-bearing reefs and associated stratigraphic units were about to be attempted for the first time, to help gain a better understanding of how the concentrations of heavy minerals had come about, of why and where optimum sites of accumulation of gold and uranium had developed, and of where there might be areas of undiscovered potential within the basin. New information, brought to light by sedimentological investigations, resolved many of the long-standing problems and differences of opinion, permitted the formulation of conceptual models of the nature, geometry, and evolution of a goldfield, and provided revolutionary bases for the design of exploration strategies and tactics. The lives of existing mines were extended, new mines discovered, and the boundaries of goldfields pushed well beyond their previously assumed limits. Within two decades, sedimentology had become an accepted, normal, routine adjunct of exploration and mining geology. Its impact on Witwatersrand geology has been as significant as that of geophysical exploration techniques, introduced in the early 1930s.
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Mineral Deposits of Southern Africa, 1, 495-496

The age of the Witwatersrand Supergroup has not yet been reliably determined, in spite of this being probably the most studied geological formation in Southern Africa. SACS (1980) placed the Witwatersrand Supergroup between the ages of ca. 2 800 and ca. 2 300 Ma, respectively the ages of the Dominion Group and the Ventersdorp Supergroup. While these age limits are probably correct, neither of the ages involved can be said to be well constrained by modern standards. Furthermore, a narrower age range, ca. 2 800 to ca. 2 600 Ma, is cited in the 1984 Edition of the Geological Map of South Africa and in SACS (1980). The purpose of this note is to summarize the available evidence! including unpublished data recently obtained at the Bernard Price Institute of Geophysical Research, with specific reference to the causes of uncertainty.
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Mineral Deposits of Southern Africa, 1, 497-539

Eleven mines in the golden triangle between Allanridge, Welkom, and Virginia, in the Orange Free State, have, between them, produced 8,7 million kilograms of gold from five, stratigraphically separate placers. These placers were probably derived from an Archaean source, dated at 2 660 Ma, and lying to the west and south-west of Welkom, and were deposited into the south-western corner of closure of the Central Rand Group basin. This area, located 270 km south-west of Johannesburg, is at an elevation of 1370 m above sea level, is buried beneath 500 m of Karoo strata, and represents the outcome of geophysical and diamond-drilling exploration. Prospecting in the area during the early 1930s, the discovery of buried Witwatersrand strata in Borehole WE 1, in 1931, and the extraordinary concentration of gold intersected in Bore hole GD 1, in 1916, are highlights in the events that eventually led to the pouring of the first bar of gold from the Orange Free State in 1951. The placers in the Welkom Goldfield are associated with eight fluvial-fan formations that were deposited as synthems, in response to local folding. Collectively, they record a classic history of Witwatersrand placer development preserved at a lower-greenschist stage of metamorphism and, for this reason, have provided the grounds for a number of fundamental studies that are reported in this paper. Extensive mining of the Basal, Steyn, Saaiplaas, and Leader placers, in particular, has provided the opportunity to study and document detailed sedimentological aspects concerning the size and shape of the fans, the pattern of channel distribution, the sedimentary facies preserved in the placers, and the spatial distribution of heavy minerals within them. The palaeodip continuation exposed has revealed mineralogicaI changes related to sorting, which variations distinguish between proximal and distal placer deposits. These records provide confirmatory evidence of the original placer nature of the deposits and provide a framework within which the tectonic controls can be reviewed. It has been established that the major faults which disrupt the goldfield are of early Ventersdorp age and did not control deposition of the placers, which are, apparently, a response to folding.
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Mineral Deposits of Southern Africa, 1, 541-547

The presence of rocks of the Witwatersrand Supergroup (2 300-2 800 Ma) under cover of Karoo sediments (Carboniferous-Permian) in the area south of the Orange Free State Goldfield was indicated by geophysics and proved by drilling prior to the Second World War. The search at that time was for gold deposits, the significance of the accompanying uranium mineralization not yet being recognized. Structural complications, rudimentary knowledge of stratigraphic correlations and the lack of encouraging gold values resulted in the termination of exploration in this southern area during 1940. Several unsuccessful exploration efforts were launched after the war and in 1969 Union Corporation Limited (now part of General Mining Union Corporation Limited) commenced a drilling programme which located the payable gold and uranium deposits described below. This success was due to the unravelling of complicated, overfolded, basin-edge structures, stratigraphic correlations, and an understanding of the sedimentary environment hosting the deposits. Stratimetric surveying and the directional wedging of boreholes for the solution of fault problems as well as radiometric logging for stratigraphic correlation and monitoring core recoveries are described.
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Mineral Deposits of Southern Africa, 1, 549-598

Gold was discovered in the Klerksdorp area in 1886, soon after the discovery of the Witwatersrand, and the area was the scene of small-scale mining until 1936, when the Western Reefs Mine was started, followed in the 1940s and 1950s by the development of several large mines based on the Vaal Reef. These are currently the Vaal Reefs (North and South Lease Area), Vaal Reefs (Afrikander Lease Area), Stilfontein, Buffelsfontein, and Hartebeestfontein mines which, in 1984, milled 18,229 Mt and recovered 154 411 kg of gold and 3 012 760 kg of U308. Conglomerates that have been mined, or are being mined, include the Elsburg and Gold Estates reefs of the Turffontein Subgroup, "C" Reef, Vaal Reef, and Ada May/Commonage Reefs of the Johannesburg Subgroup, the Inner and Outer Basin Reefs and the Buffelsdoorn Reef of the West Rand Group, the Ventersdorp Contact Reef, and the Black Reef. The full sequence of the Witwatersrand Supergroup is represented and is, overall, somewhat coarser than in other parts of the Witwatersrand Basin and contains a higher proportion of quartzites and conglomerates. The entry point for the sediments probably lay to the north-west. The sequence is described in relation to the new lithostratigraphic terminology. The Klipriviersberg Group of the Ventersdorp Supergroup is the main member of the supergroup represented in the area and consists of amygdaloidal and porphyritic lavas, agglomerates, and tuffs. The characteristics of marker horizons, such as the Altered Zones and Purple Zones, are outlined. The structure reflects, in part, tectonic movements during sedimentation, as well as major periods of faulting subsequent to the outpouring of the Klipriviersberg lavas. Most of the faults trend north-east~south-west, are normal, and have downthrows either to the north-west or south-east. There is some faulting which is post-Ventersdorp and also post-Transvaal. Post-Karoo faulting is minor. The main periods of dyke intrusion were post- Klipriviersberg, post-Transvaal, and post-Karoo when, firstly, quartz diabases and ilmenite diabases were intruded, followed by carbonatites, lamprophyres, and, finally, Pilanesberg and Karoo dolerites. The Vaal Reef is a quartz-pebble, oligomictic conglomerate, containing gold and uranium which was derived from a northerly to north-westerly source the reef is usually no more than 50 cm thick and is composed of pebbles up to 22 mm in diameter. The Ventersdorp Contact Reef is a coarse, quartz-pebble conglomerate, up to 2 m thick, with pebbles in places up to 60 mm in diameter, but, more normally, 20 to 30 mm in diameter; it contains gold, but little uranium; two facies are present, the Terrace-type, which is thin and confined to non-channel areas, and the Channel-type, which is present in channels as much as 7 m deep, trending north-west to south-east, the richest part of the reef usually being in the channels. The Black Reef, at the base of the Transvaal Supergroup, is not extensively developed or mineralized and has been mined only in two areas, one near Klerksdorp and the other at Machavie, reef thickness is very variable, as is pebble composition and pebble size; reef development is best in channels with a north-easterly trend, but, in all cases, reef development degenerates rapidly down dip from the present outcrops.
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Mineral Deposits of Southern Africa, 1, 599-648

The stratigraphic column of the Witwatersrand Supergroup of the West Wits Line has, with due consideration to the subdivisions proposed by the South African Committee for Stratigraphy for the Central Rand, been revised by the introduction of new group, subgroup, formation, member, and reef nomenclature. A closer correlation, both regionally and in more detailed aspects, has been effected with the adjoining areas of the West Rand and the Klerksdorp goldfields. The division between the Central and West Rand groups has been established at the base of the North Leader/Carbon Leader succession, in contrast with the previously accepted division at the top of the Jeppestown Shale. The Carbon Leader of the West Wits Line is correlated with the Main Reef of the West and Central Rand (West Reef of Randfontein Estates)and the Green Bar with the Cab or Black Bar of the West Rand. The identification of the Green Bar horizon in the Klerksdorp Goldfield has been confirmed, and a correlation of the Commonage and Ada May reefs of this area with the Carbon Leader and the North Leader of West Wits is proposed. The previously known Main Reef of the West Wits Line has been designated the Middelvlei Reef and is correlated with the South Reef of the West Rand (Leader Reef of Randfontein Estates). The Doornfontein Reef at the base of the Booysens Formation of the West Wits Line has been identified and is correlated with the Monarch Reef of the West Rand and the Vaal Reef of Klerksdorp. The uraniferous zones of the Upper Monarch Reefs of the West Rand are comparable with similar horizons within the Cobble Reefs of the West Wits Line. The Kleinfontein Reef, forming the base of the Robinson Formation of the West Wits Line is correlated with the Leopard Reef of the West Rand, the B Reef of the East Rand and Orange Free State, and, tentatively, with the C Reef of the Klerksdorp area. The Simmer Formation of the West Wits Line has been extended with the inclusion of the basal conglomerate, the Libanon Reef, which is correlated with the Battery or Horsham Reefs of the West Rand, the May Reef of the East Rand, and the A Reef of the Orange Free State. The Kloof Member of the Simmer Formation of the West Wits Line has its counterpart in the Panvlakte Member of the Cooke Section of Randfontein Estates, and a closer comparison of the individual beds and reefs is foreseen. The basal conglomeratic Elandsrand Member of the Elsburg Formation of the West Wits Line is correlatable with a similar conglomerate zone of the Waterpan Member of the West Rand and the Bastard Reef of Klerksdorp. Finally, the Deelkraal Reefs at the top of the Elsburg Formation of the West Wits Line are equated with the Massive Reefs of the Western Areas section of the West Rand and with the Orkney Reefs of Klerksdorp. The Carbon Leader is transgressive and dependent, in physical development and mineral content, on its footwall beds. In the areas to the east and west of the West Driefontein/Blyvooruitzicht sector, the Carbon Leader deteriorates to a scattered grit, completely devoid of gold. Here, specific footwall conglomerates of the Carbon Leader have been preserved and are being mined. Where the transgression is more pronounced, it is coupled to a corresponding increase in the gold content of the Carbon Leader, which implies that this reef derived its gold from footwall sources. The presence of well-rounded, as well as dreikanter-shaped pebbles, indicates a littoral environment where both sub-aqueous and sub-areal agencies were operative. The Middelvlei Reef comprises several well-developed conglomerate bands which rest on an erosional surface. It is postulated that a braided-stream depositional model best fits the features displayed within pay shoots. The VCR is regarded as a lag gravel composed exclusively of Witwatersrand detritus deposited by a shallow, transgressive sea and modified, on further uplift, by atmospheric and fluvial agencies. As a result of pre-VCR folding and tilting, there is invariably an unconformable relationship between the reef and the underlying Witwatersrand beds along the north-western rim of the Upper Witwatersrand basin, stretching from Luipaards Vlei in the east, to Western Reefs in the west. The nature of the footwall beds has a marked influence on the physical development and the mineral content of the VCR. The structure of the West Wits Line is dominated by the fold structures of the Rand and Bank anticlines which were contemporaneous and afterwards adjusted by major faults, such as the West Rand and Master Bedding faults. These faults were partly instrumental in lowering broad wedges of Klipriviersberg lava to levels which preserved them from Black Reef planation.
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Mineral Deposits of Southern Africa, 1, 649-688

The regional geological setting of the West Rand Goldfield is described, with particular reference to the geology of the Cooke Section of the Randfontein Estates Gold Mine and the Western Areas Gold Mine. The geology of the White Reef, in an older portion of the goldfield, in the vicinity of Krugersdorp, is also described. The Cooke Section of Randfontein Estates and the Western Areas Gold Mine are relatively new and lie on the southern limb of the West Rand Goldfield. They are of particular interest in that their ore bodies are palaeoplacers situated in the uppermost or Turffontein Subgroup of the Central Rand Group. One of the most notable features of the West Rand Goldfield is a system of faults which define the edges of an arcuate structural block, known as the Witpoortjie-Panvlakte Horst. The horst block is bounded in the east by the Panvlakte Fault, which is the locus of zero isopachs for the Westonaria and younger formations of the Cooke Section and Western Areas mines. Incipient movement on this fault gave rise to a pebbly, braided, alluvial plain which has been divided into an ephemeral-flood facies, which brought material into the depository, and a perennially reworked facies which concentrated placer minerals and pebbles, while winnowing out the lighter sand and clay fraction. Gold and uranium were concentrated by this placer-winnowing process. The distribution of economic mineralization is explained by the sedimentology of the reefs, a strong relationship between the palaeocurrent dispersal and the orientation of payshoots, having been established. The White Reef which lies to the north of the Witpoortjie-Panvlakte Horst Block is situated in the Johannesburg Subgroup and has similar mineralization controls to reefs belonging to the Turffontein Subgroup, south of the horst block. The main lithofacies and palaeocurrent directions in this reef are directly related to the distribution of gold and uranium mineralization. In most instances, the optimum concentration of gold is to be found higher up the palaeoslope than uranium, and this is quantitatively demonstrated by the uranium/gold ratio parameter.
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Mineral Deposits of Southern Africa, 1, 689-703

The South Rand Goldfield lies 80 km south-east of Johannesburg, in a distal part of the Witwatersrand Basin, where the Witwatersrand succession is somewhat thinner than farther north, partly because of intra-formational unconformities. Reef development, principally the Kimberley Reef, is sporadic and the content of gold and uranium variable and generally low-grade. Mining and exploration activity have always been at a low level and active only when high metal prices made the mining of low-grade ore feasible. In the period 1964~1979, information from 31 boreholes, as well as from fieldwork and geophysical investigations, has been obtained which is presented and discussed. The stratigraphy of the Witwatersrand and Ventersdorp supergroups is described. Sedimentological data and payshoot trends indicate sedimentation from the north-east, with a possible sediment entry point to the east. The main structure is a synform, plunging to the north-west, cut by post-Ventersdorp, east-west faults, with up-throws to the north.
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Mineral Deposits of Southern Africa, 1, 705-730

The Evander Goldfield is located approximately 120 km east-south-east of Johannesburg. The principal economic horizon is the Kimberley Reef placer which was deposited in a subsidiary, sedimentary basin during the early stages of the Turffontein Subgroup of the Central Rand Group of the 2 500 Ma-old Witwatersrand Supergroup. Exploration in the area was started in 1903, with the advent of diamond drilling and progressed, intermittently, through various major exploration phases, involving geophysics and diamond drilling, to the incorporation of the first mine in 1955. Exploration, both surface and underground, still continues. A geophysical case history of the discovery of the Evander Goldfield is given in the historical review. Sediment of the Witwatersrand Supergroup unconformably overlie the Archaean Basement, and these Witwatersrand sediments are, in turn, overlain by rocks of the Ventersdorp Supergroup and the Transvaal and Karoo sequences. The generalized lithology of each of the successions is examined and tabulated, with special emphasis being placed on the sediments of the Witwatersrand Supergroup. It is interesting to note that, of the three subgroups comprising the West Rand Group, only the Hospital Hill and Government subgroups are present in the Evander Goldfield. Three ages of intrusives are present in the Evander Basin, namely Bushveld, Ventersdorp, and Karoo. These intrusives are present as both dykes and sills. Contact metamorphism, both on a local and a regional scale, has affected the Witwatersrand sediments. The Booysens Shale Formation, the only argillite within the Central Rand Group, is an excellent metamorphic indicator, and five metamorphic zones within the aureole of the Kalabasfontein pluton, have been defined. The highest grade of metamorphism observed falls within the hornblende-hornfels facies. The Evander Basin has undergone extensive structural dislocation. Faulting is the most common form of deformation, and both primary and secondary fault-features are recognized and are briefly described. The Kimberley Reef represents the distal facies of a fluvial placer that was deposited by a system of braided-streams which flowed down a north-easterly-dipping palaeoslope. The reef is oligomictic and comprises a composite sequence of channel-sediments that define longitudinal gravel bars and sand bars with pebbly veneers. Multi-channelling is well developed in areas of thick reef, a maximum thickness of 3,2 m being measured in the south-east of the basin. The detailed lithology of the Kimberley Reef was examined with the aid of surface-borehole intersections, and the moving-average distribution of various reef parameters has been investigated. Limited palaeocurrent studies have been undertaken on various sedimentary units within the Witwatersrand Supergroup, and the implications relating to their various palaeotransport directions are discussed. Although no detailed basin analysis has yet been undertaken in the Evander Goldfield, a number of observations and conclusions have been drawn relating to the possible sequence of events that occurred during the evolution of the Evander Basin. After deposition of the Main Conglomerate Formation, basin subsidence and a diminished sediment-supply caused a major transgressive phase that was terminated during the deposition of the Booysens Shale Formation. Uplift to the north of the basin then caused the progradation of sediments of the Leandra Quartzite, Zandfontein Quartzite, and Winkelhaak Conglomerate formations into the basin in a south-westerly direction. Renewed uplift to the south-west then resulted in another progressive phase, finally terminated by the extrusion of the Ventersdorp lavas. The uplift resulted in the rapid progradation of sediments (Evander Quartzite, Leandra Quartzite, and Brendan Conglomerate formations) into the basin along a regular, even palaeoslope striking north- west-south-east, but dipping to the north-east. Initial erosion of the elevated basin-margin resulted in the deposition of the Kimberley Reef in a network of braided-channels. Major faulting and dislocation occurred in late-Ventersdorp times, and the final tectonic event, which involved a tilting of the whole basin to the north of 8 to 10°, occurred in post-Transvaal times.
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Mineral Deposits of Southern Africa, 1, 731-752

Since the publication of Feather's and Koen's (1975) review on the mineralogy of Witwatersrand reefs, a massive amount of new information has become available. This has been made possible, to a large extent, by the application of new techniques and methods. The more significant results which have crystallized from the new investigations of the principal materials are:
1. there were different provenance areas for the various fans in the Witwatersrand Basin, often characterized by local variations in mineral characterized by local variations in mineral chemistry;
2. the majority of the provenance areas appear to have been different geochemically from the Archaean Barberton Mountain Land. This is reflected in the geochemistry of detrital quartz, gold, and pyrite;
3. a large proportion of the gold in Witwatersrand deposits has retained its detrital features, including its original fineness; 4. several features of the detrital minerals, including fluid inclusions and the mercury content of gold, point to relatively low temperatures, during the metamorphic stage, in the vicinity of 120 to 250 °C; 5. the modified placer theory is, in principle, still valid, although less modifications to a straight placer origin are necessary than originally envisaged; 6. there is no convincing evidence that large amounts of gold or uranium were transported in solution; 7. it appears that the depositional environment developed in an oxygen-deficient atmosphere. No indications have been found, pointing to a general reducing environment, but such environments formed locally in stagnant pools; and 8. in distal facies and, locally, in low-energy environments of certain reefs, such as the Carbon Leader Reef and Vaal Reef, organic growth of algal and/or bacterial affinity played an important role in the concentration of gold and uranium. Although these results allow of a good qualitative description of the Witwatersrand gold-uranium deposits, a relatively small amount of quantitative data, describing the distribution of economically important minerals by regional geochemical variations, is at present available. Such information, however, when combined with sedimentological data, is of vital importance to practical mining, at a time where increasing production costs call, not only for selective mining, but for a high degree of probability in advanced planning. The question of the origin of the Witwatersrand mineral assemblage is still largely unanswered.
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Mineral Deposits of Southern Africa, 1, 753-772

Rock mechanics as practised on Witwatersrand gold mines is concerned with, among other topics, the design and layout of mines, strata control, and rockburst research. In all these fields, geological features have to be considered, especially in deep mines. Important factors include the pre-mining state of stress, the strength and elastic properties of the individual rock types, the relative differences in competence between the strata, the attitude of the strata, the degree of stratification, and the occurrence of faults, joints, dykes, and sills. Results of in situ stress measurements in Witwatersrand gold mines are summarized, as are the rock-mechanics properties of the various strata. This information is important for the siting of long-life excavations, such as shafts and service tunnels. Support methods depend on both the type of rock in which a tunnel is developed and the ambient field stresses. Structures which may weaken a rock, such as closely-spaced bedding planes or joints, also have to be considered. Larger structures, such as faults, dykes, and sills influence tunnel layout and mining practice. Often dykes or losses of ground due to faulting may be utilized as pillars, to improve the regional stability of the mine. However, they may also be hazardous, especially if they have markedly different elastic properties from those of the country rock. This situation permits the fault or dyke to store large amounts of elastic strain energy which can be released violently. Stored strain energy may also be relaxed in a stable manner, if the strength of the rocks around the excavation is such that fracturing can occur.
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Mineral Deposits of Southern Africa, 1, 773-777

The general geology of the Welkom (Orange Free State) Goldfield has been adequately described by Coetzee (1960), and it is sufficient to state that the near-surface formations consist of Middle Ecca shale, with sandstones of the Beaufort Subgroup in the east. Locally, dolerite outcrops are present, and, in the valley of the Sand River, alluvial deposits of Pleistocene and Recent age occur. It is probable that some near-surface sands are of aeolian origin. The sediments of the Karoo Sequence overlie lavas and sediments of the Ventersdorp Supergroup and arenaceous sediments of the Witwatersrand Supergroup, with an angular unconformity. The shales of the Middle Ecca Group weather to clays consisting essentially of illite and montmorillonite and exhibit highly expansive characteristics. Some transported alluvial clays in the valley of the Sand River and its tributaries also consist of expansive montmorillonite. These residual and alluvial clays have resulted in severe damage to houses and other surface structures. Prior to the completion of a pipeline from the Vaal River, the mines were dependent on local water supplies for domestic and industrial purposes. The only feasible supply was groundwater, and the search for suitable aquifers became part of the geologist's duties. Saline water under artesian pressure issued from a number of deep diamond-drill holes drilled during the exploration stage in the Orange Free State. This water was generally accompanied by methane gas. Water-bearing fractures intersected during the course of shaft-sinking and development delayed operations presented a severe hazard, and created a complicated hydrogeological problem. Also, the salinity of the underground water created a severe disposal problem. In the early 1950s, the disciplines of engineering geology and hydrogeology applied to mines were in their infancy, at least in South Africa, and the technical approach may well appear today to have been rather simplistic. However, necessity forced solutions, and it is felt that the manner in which the problems were solved may be of interest, despite the considerable advances in the sciences that have been made in the interim.
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Mineral Deposits of Southern Africa, 1, 779-781

The existence of rather exceptional groundwater conditions in the Harmony Mine area was already indicated by intersections of artesian water in a considerable number of the early exploratory boreholes. With the advent of mining operations, it was also found that the water-pressure at certain points exceeded the expected hydrostatic pressure for the depth at these points. The boreholes in question are generally situated on lower-lying ground within the Sand River valley, and the water issuing from the boreholes was found to be at an average temperature of 28,4°C, containing an average of 4 150ppm of dissolved solids. It is of interest to note that approximately 90 per cent of the total of dissolved solids is represented by sodium chloride. The artesian water was generally found to be accompanied by emissions of a gas mixture, containing approximately 0,1% carbon dioxide, 0,1% carbon monoxide, 0,1% hydrogen, 0,2% oxygen, 0,5% argon, 6% helium, 20% nitrogen, and 73% methane. The reader interested in more detailed statistics in respect of the dissolved salts and gas content of the water and in the possible economic importance of the helium is referred to Coetzee (1960), Hugo (1963), and Greig (1971). Coetzee (1960) pointed out that the artesian water came from the pre-Karoo rocks and that the water was not necessarily intersected at great depths. He also stated that the artesian flow decreased and eventually stopped, due to the draining of the pre-Karoo formations through pumping by the mines.
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Mineral Deposits of Southern Africa, 1, 783-789

Since the late 1940s, considerable engineering activity has occurred around the Welkom Goldfield. A new city has sprung up, with associated industrial areas. It is not surprising, therefore, that a great deal of information is now available on the engineering aspects of the geology of the area. With the establishment of three new mines, Unisel, Beisa and Beatrix, and extensions to the existing ones in recent years, e.g. President Brand No. 5 Shaft, Free State Geduld No. S Shaft, and the Erfdeel Project, housing extensions to the city and major developments to Riebeeckstad are currently under way. Figure 1 shows the area and some of the industrial-site investigations carried out over the past few years for the Anglo American Corporation. Site investigation has become an essential part of design and planning programmes since the expansive-clay problem and the alternating wet and dry seasons have been recognized as causing foundation problems throughout the area.
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Mineral Deposits of Southern Africa, 1, 791-796

Results of research in regard to fissuring and karstification of dolomite are utilized in determining precautions against uncontrollable water inflow into underground works. Metastability on dolomitic terrane is explained, and factors contributing towards instability are outlined, together with the time-dependency of surface settlement due to water-table drawdown. Precautionary measures and special techniques are enumerated to serve as guidelines in selecting suitable sites for township and industrial development. Transmissivities and storage capacities in dolomite, as deduced from Theis curves, are applied in predicting reservoir behaviour along the West Wits Line after cessation of mining activities.
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Mineral Deposits of Southern Africa, 1, 797-809

The groundwater in the sub-Karoo compartments of the Evander Goldfield is of sub-artesian nature, with a regional piezometric surface at 1 534 m above mean sea-level, prior to the commencement of mining operations. Progressive lowering of the water table and a study of the statistical trends of the hydrological data established the existence of a dolomite and a sub-dolomite water-compartment. These are separated by lavas of the Klipriviersberg Group which have a relatively low transmissibility and storage capacity. The degree of interconnection between water-bearing fissures in any one compartment and between compartments, is greatest immediately below the Karoo Sequence and diminishes rapidly with depth. The transmissibility and storage capacity of the sub-Karoo water compartments are influenced by a number of factors, of which the degree of fracturing, pre-Karoo exposure and weathering, depth of cover, and physical characteristics of lithological types are the more important. The high transmissibility zone immediately below the Karoo Sequence transgresses over both compartments and all lithological types and behaves in the manner of a semi-infinite, porous, water-bearing medium under conditions of laminar flow. All the Evander mines, except Kinross, commenced mining operations in the proximity of this zone. Dewatering of this zone is rapid, and the quantity of water made is proportional to the pressure-head, the area exposed underground, and a permeability factor which relates to the combined-flow characteristics of water in fissures. The inter-connection between fissures became progressively poorer with successive lowering of the water table in the sub-dolomite compartment. The ingress of water from the dolomite compartment, usually along well-defined fissures, is, at present, the major source of the water made underground. It is probable that conditions of turbulent flow occur in individual fissures, and the quantity of water made is proportional to {(2gh/k), where g is the gravity acceleration, h is the pressure head, and k is a factor related to friction and to the physical dimensions of the fissures. The cumulative total area exposed under ground has little effect at greater depths, where the interconnection between fissures tends towards zero. Inflammable gas has been intersected in varying quantities in surface boreholes drilled in an area of over 250 km², in shaft sinking, in underground development, and in underground boreholes. A concentration of strong gas flows in the underground workings is usually associated with elevated areas in the pre-Karoo floor topography, above the depleted sub-dolomite water table. The composition of gas from the Witwatersrand and from Karoo strata sources is significantly different. Interesting trends exist between the helium and nitrogen, the helium and carbon dioxide, and the argon and nitrogen percentages.
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Mineral Deposits of Southern Africa, 1, 811-817

The Transvaal (north-eastern) sub-basin of the Transvaal Sequence comprises up to 15 000 m of relatively undeformed sediments and volcanics. The basin is asymmetrical, thinning rapidly to the north and more gradually to the south of an east-north-east-trending depositional axis. The ca. 2 400 to 2 100 Ma-old basin commenced with deposition in a relatively small proto-basin. With time, the deposition spread to cover an area of up to 500 000 km². During the terminal stages of deposition, the basin size decreased. Clastic sediments were introduced into the basin from mountainous source areas lying north and north-east of the basin. In general, depositional facies graded from braided fluvial arkoses, through tidal flat sediments to mature sandy shelf deposits. Distal shelf deposits are mainly shales and carbonaceous shales. Macrotidal conditions probably prevailed, and tidal flats faced directly on to the shelf. At times the shelf and its surroundings must have been tectonically very stable, since up to 3 000 m of carbonates and iron formation were deposited. Sedimentation ceased some 2 100 Ma ago. with the intrusion of the Bushveld Complex and the rising of the Vredefort Dome. The present shape of the Transvaal sub-basin is largely controlled by these post-Transvaal events.
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Mineral Deposits of Southern Africa, 1, 819-828

In this contribution the lithostratigraphic subdivision of the Transvaal Sequence in the Griqualand West basin is based on the findings of Beukes (1979, 1980a, b, 1983a). It supplements the subdivisions, established by SACS (1980), by making provision for detailed studies, lateral facies changes, and duplication caused by thrust faulting. It also emphasizes the unity of the Transvaal Sequence as a very distinctive rock assemblage in Southern Africa because correlation of stratigraphic units between the Transvaal and Griqualand West areas are excellent from a broad to, in many cases, even a very detailed stratigraphic sense (Beukes, 1978).
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Mineral Deposits of Southern Africa, 1, 829-835

A 100 to 130 m-thick, chert-free dolomite unit, the Lyttelton Formation, occurs near the top of the Malmani Dolomite in the Southern Transvaal and constitutes the source of carbonate blast furnace flux for Iscor's steel works at Pretoria, Vanderbijlpark and Newcastle. Stratigraphically the unit is interbedded with chert-rich formations, but its general low dip and wide outcrop and suboutcrop zones are conducive to open-pit mining. The fairly consistent and chemically pure composition of the chert-free dolomite facilitates processing to a uniform high-grade product for furnace operations. Two mines, viz. Mooiplaas at Pretoria, and Glen Douglas near Vanderbijlpark, produce, respectively, about 500 000 and 1200 000 t per year of metallurgical grade dolomite heal product from relatively ample in situ reserves. The final product contains less than 3,5% SiO2, 0,5% Al2O3 and 0,2% alkalis.
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Mineral Deposits of Southern Africa, 1, 837-841

Fluorspar forms low-grade deposits at the top of a thick carbonate sequence, the Malmani Subgroup. The mineralization of a previously cavernous stromatolitic dolomite resulted in the "algal ore" (80 per cent of the resources), and the replacement of dark dolomite yielded "blockspar" (about 20 per cent of the resources). Fluorspar, accompanied by variable amounts of lead and zinc, is also found in collapse breccia formed by karst development prior to the deposition of the Pretoria Group. The deposits, which are developed within the metamorphic aureole of the Bushveld Complex, are of the Mississippi Valley type. Economically the fluorspar field appears to be one of the largest in the world as the resources at 20% CaF2 are estimated to comprise about 100 Mt.
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Mineral Deposits of Southern Africa, 1, 843-849

The Witkop Fluorspar Mine is situated some 18 km south of the town of Zeerust in the Western Transvaal. The fluorspar deposits occur as large stratabound bodies in a well-defined stratigraphic unit in the upper part of the Malmani dolomite sequence. They also appear to be closely related to a major south-south- westerly-trending fault or fracture zone. Mineralogical investigations have shown that fluorspar, late stage quartz, and base metal sulphides are clearly secondary replacements within the host dolomitic limestone, and no evidence of a syngenetic origin for the fluorspar could be found. The Witkop fluorspar deposits are thought to closely resemble the classical Mississippi Valley bedded replacement fluorspar-lead-zinc deposits of southern Illinois in the United States.
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Mineral Deposits of Southern Africa, 1, 851

Marico Fluorspar (Pty) Ltd operates the Bulhoek Mine, one of the largest fluorspar producers in the Republic. The mine is located in the Groot-Marico District of the Western Transvaal, 16km south of Zeerust in an area of gently rolling grassland. Exploration started in earl 1970 by means of diamond drilling on the former Mosega properties, and this was extended to neighbouring farms. By 1972 a sufficiently large ore reserve had been proved to justify on site pilot plant tests and a detailed feasibility study. These indicated the proposition to be viable, and production commenced in late 1975. The bulk of the fluorspar mineralization occurs as a number of discontinuous zones in the Frisco Formation of the Malmani Subgroup (dolomite) of the Transvaal Sequence. These rocks have been variably affected by thermal metamorphism related to the emplacement of the Bushveld Complex, resulting in the formation of such minerals as talc, chlorite, and tremolite (Martini, 1976).
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Mineral Deposits of Southern Africa, 1, 853-860

The geological setting of a borehole intersection of lead-zinc mineralization in the Malmani Dolomite Subgroup in the Carletonville area is discussed. It is suggested that the lead and zinc ions were derived from the overlying shales, transported as bisulphide complexes in silica-enriched, alkaline solutions, and deposited during silicification in the upper part of the dolomite succession which contains relic evaporites. Lead isotope data suggests that the known lead-zinc deposits in the Transvaal sequence are not of major importance. However, the dolomites are regarded as very probable hosts for Mississippi Valley type base metal deposits and offer important exploration targets.
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Mineral Deposits of Southern Africa, 1, 861-866

The mode of occurrence and possible origin of lead mineralization in the Malmani dolomite on the farm Leeuwbosch, 14 km north of Thabazimbi, is discussed. Lead has been mined sporadically over the years and the estimated production has been 1500 t of galena. Three distinct, but interrelated types of mineralization occur. Vertical, west-north-west-trending fissures, limonitic and hematitic on surface, pass at depth into brecciated fissure material with siderite hosting galena. Pyrite and sphalerite are rare constituents. A second variety consists of pod-like bodies of siderite with galena in pre-existing karstic cavities. A stratabound horizon of poor grade mineralization is present in the lower part of the Lyttelton Formation of the Malmani Subgroup. It is localized within an algal laminated stromatolitic horizon. Mineralization consists of weakly disseminated, fine-grained galena associated with minor brecciation. Siderite is an ubiquitous gangue mineral and minor amounts of sphalerite and chalcopyrite are found. High grade hematitic iron ore derived from a ferruginous fissure has been concentrated in adjacent karren (karstic) terrane. These areally extensive, but relatively thin iron ore deposits were mined by ISCOR. An early (pre-Pretoria Group) open-space filling and replacement origin is invoked for the lead mineralization. Fractures in the dolomites became enlarged by dolomite dissolution with the formation of karst cavities in favourable, chert-free horizons. Fluids, possibly derived from the underlying Tygerkloof and Black Reef formations, moved along the fissure conduits, which also provided access to the karstic cavities and to permeable stratigraphic horizons in the dolomite. The iron, associated with the lead mineralization, was probably derived from the overlying Penge Formation. The mixing of these different upward and downward moving fluids could have been a viable precipitation mechanism for the metals. Tilting and erosion resulted in the present-day exposure of the different styles of palaeo-lead mineralization.
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Mineral Deposits of Southern Africa, 1, 867-874

Exploration has proved a resource of about 18 Mt grading 3,6% zinc and 0,6% lead in flat-lying Lower Proterozoic algal dolomites with intercalated carbonaceous shale beds. Sphalerite and galena are the ore minerals, usually disseminated but sometimes colloform or crustiform, occurring in subhorizontal stratabound lenses and subvertical breccia zones. There is minor pyrite and trace chalcopyrite and the gangue is calcite or dolomite. The sphalerite is a low-iron variety and the galena has no significant silver content. The only syngenetic mineralization is marcasite/pyrite in the Lokammona shales lower in the sequence. The zinc-lead mineralization is envisaged as being due to metal-rich fluids derived from dewatering of the underlying Lokammona sediments. These became hypersaline brines and formed a corrosive solution capable of causing chemical dissolution and hydraulic fracturing in breccia zones near surface. As the blocks in the breccias became cemented the ore fluids spread outwards along readily leached stromatolite layers where there was sufficient carbon to cause sulphate reduction and sulphide precipitation.
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Mineral Deposits of Southern Africa, 1, 875-889

Diagenetic, disseminated zinc-lead mineralization occurs in stromatolitic dolomite at Pering, approximately 160km north-north-west of Kimberley in the Northern Cape Province. Semi-massive to massive sulphide accumulations, with a higher ratio of lead to zinc than that of the disseminated ore are probably the result of partial, differential remobilization. The ore has a low precious- and trace-metal content and is compositionally simple. Weathering of the upper part of the ore body has resulted in sulphide dissolution, dedolomitization of the host rock, and the formation of supergene minerals which include smithsonite, hydrozincite, cerussite, anglesite, secondary galena, descloizite, and calcite. The distribution of these minerals is explained in terms of changing pH/Eh environments.
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Mineral Deposits of Southern Africa, 1, 891-900

Transvaal Supergroup carbonates cover a large area of Griqualand West in South Africa. Marginal shelf facies shallow water carbonates in the north pass through a stromatolite-rich barrier into a southerly basinal facies. Bushy Park is 35 km north-east of Griekwastad, near the southern boundary of the shelf facies. Mineralization is disseminated sphalerite and galena in sub-vertical zones of brecciated dolomite, forming an oval structure. Local bedrocks include partially silicified, dolomitized stromatolitic micrite with fenestral fabric layers, oolite interbeds, thin chert zones, and carbonaceous shale units. Esso Minerals optioned the property in 1975, recognizing a similarity to deposits in East Tennessee, Mapping, soil sampling and percussion drilling by them proved a resource of 3,25 Mt, grading 7,19 percent zinc and 0,43 percent lead. Shell metals took over exploration in 1981 to search for associated strata-bound ore. Infill diamond drilling showed mineralization only occurred as blebs scattered through three steeply dipping zones of mosaic/rubble brecciated dolomite, with an almost complete lack of interhole correlation, leaving only small disconnected pods of ore-grade material. The resource at 95 percent confidence is 0,59 Mt grading 3,5 percent zinc and 0,04 Mt grading 2,8 percent lead. Ore genesis envisages hydraulic fracturing of the rocks by siliceous solutions along pre-existing joint/fracture systems, with the zinc and lead derived from connate water expelled from dewatering of basinal sediments in the sequence.
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Mineral Deposits of Southern Africa, 1, 901-910

Eight amosite asbestos deposits are known to exist in the Penge Iron-formation in the Penge area of the North-eastern Transvaal. The deposits have been mined extensively since 1914 and a resource of 2,3 Mt of asbestos has been indicated. Nine potential amosite reefs are known, four of which have been mined extensively. The reefs are confined to specific lithological units of the iron-formation sequence, but along strike such units may be barren of amosite, contain small amounts of fibre, or could constitute an economic amosite deposit. The deposits are confined to minimum stress areas in domal structures formed by the interference of gentle, open, east-north easterly and northerly-trending anticlinal fold axes.
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Mineral Deposits of Southern Africa, 1, 911-921

The crocidolite deposits of the Pomfret area are situated in eight different mesobanded, magnetitic, ferhythmite reef zones in the Kuruman Iron-formation. Major deposits are, however, confined to the Red Reef situated in a magnetite-hematite pod- and waverhythmite unit of the iron-formation sequence with subordinate deposits in the Lower Main and Upper Green reefs, i.e. greenalitic siderite-magnetite ferhythmite units. Economically mineable deposits within reef zones are related to the hinge zones of gentle dome and basin structures followed by cross-folding, suggesting that crocidolite fibre grew parallel to tensional stress areas in folds. Stipnomelane lutite units, representing ash-fall tuff deposits, are closely related with the reef zones indicating that the sodium present in the crocidolite and associated riebeckite could have been derived from fumarolic activity and/or devitrification of volcanic ash. Fibrous growth of crocidolite took place in pressure shadows (saddle reefs) along competent magnetite microbands which were folded on a microscopic scale during deformation. Other micro- and mesoband types adjusted to deformation through material flowage and non-fibrous riebeckite crystals formed. The Pomfret Mine has a potential to produce 70 000 t of crocidolite per year and estimated resources are in the order of 2,3 Mt.
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Mineral Deposits of Southern Africa, 1, 923-929

The iron ore deposits at Thabazimbi occur in the basal iron-formations of the Penge Formation, immediately above a lowermost shale unit. The shale is in turn underlain by dolomites of the Malmani Subgroup. These units are part of the Transvaal Sequence. Both wall rocks and ore deposits dip to the south at about 50x; in depth the ore bodies pass into talc-hematite and carbonate-hematite rocks which comprise low-grade ore deposits. Waterberg tectonism has led to the duplication of the Penge Formation in the Thabazimbi area. Most of the iron ore is brecciated, consisting of primary hematite fragments set within a secondary hematite matrix. The genesis of the iron ore deposits at Thabazimbi reflects primary chemical sedimentation and subsequent metamorphism and supergene processes. Intrusion of the Bushveld Complex led to contact metamorphism and the southward tilting of the dolomites and iron-formations. Waterberg tectonism gave rise to thermodynamic metamorphism of the iron-formations, producing the talc-hematite and carbonate-hematite rocks. A long period of weathering followed and solution of the dolomites led to brecciation of the overlying iron-formations, talc-hematite and carbonate-hematite rocks. Karst activity took place just above the groundwater table and the porous brecciated zone was subjected to epigenetic ferruginization, whereby slow supergene replacement of chert, calcite and talc by goethite and hematite occurred. The basal shales of the Penge Formation acted as a barrier to percolating iron-rich groundwaters. Post-Karoo fault zones filled with iron ore indicate a second period of supergene ferruginization.
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Mineral Deposits of Southern Africa, 1, 931-956

The Sishen iron ore deposit, situated in the Northern Cape Province of South Africa, is a high-grade (65% iron) hematite deposit with a potential opencast ore reserve of about 1000 Mt. Annual production is in the order of 18 Mt beneficiated ore and 75 Mt total rock mined. Between 80 and 90% of the potential ore reserve is situated in the Manganore Iron-formation immediately below an unconformity that separates it from the overlying Gamagara Formation of the Olifantshoek Group. The Manganore Iron-formation is a correlative of the Asbesheuwels iron-formation succession of the Transvaal Sequence and slumped into palaeosinkhole structures in the underlying Campbellrand carbonate sequence during the period of erosion that preceded the deposition of the Gamagara Formation. During slumping, silica was leached from the iron-formation by alkaline ground water solutions and ferrous minerals were oxidized to hematite. At the same time some iron was added to the sequence as hematite to form high- grade laminated and breccia supergene ore bodies. Subsequently, these ore bodies were eroded and hematite pebble conglomerates accumulated in alluvial fan environments at the base of the overlying Gamagara Formation to form conglomeratic ore representing approximately 10 to 20% of the potential ore reserve. The Gamagara Formation is a red bed sequence and is a correlative of the Mapedi Formation of the Olifantshoek Group. The Makganyene diamictite and Ongeluk lava of the Transvaal Sequence are thrust over the Gamagara Formation to the west of the mine. The Sishen iron ore body is elongated in a northerly to north-north-westerly direction and has a highly undulating floor with thickest ore developed in basinal, i.e. palaeosinkhole, structures in the underlying Campbellrand dolomite. The ore contains, on average, less than 2,5 per cent silica and it is very low in phosphorus, sulphur, potassium and sodium. Detrital ore of the Gamagara Formation has a higher titanium, aluminium, and strontium content than the supergene-enriched, laminated ores of the Manganore Iron-formation.
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Mineral Deposits of Southern Africa, 1, 957-961

The manganese deposits at Glosam and Bishop and the haematite deposit at Beeshoek are related to the unconformity between the Gamagara Formation and the underlying Campbellrand dolomite sequence in the Maremane dome of the Sishen and Postmasburg areas. Where this unconformity cuts across manganiferous dolomite units, manganese deposits are developed in the Sishen shale member of the Gamagara Formation. In contrast, supergene haematite ore is developed in the Manganore Iron Formation (a possible correlative of the Kuruman Iron Formation) which occurs in palaeosinkhole structures in the Campbellrand dolomite below the Gamagara Formation. The manganese ore mined contains between 20 and 50 percent manganese. The haematite ore is of high grade aver aging more than 60 percent iron.
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Mineral Deposits of Southern Africa, 1, 963-978

At Mamatwan Manganese Mine, the lowermost of three manganese layers interbedded with iron- formation of the Hotazel Formation of the Transvaal Sequence, is exploited. The manganese layer is 45 m thick. It is subdivided into a 19,5 m thick upper uneconomic zone containing 30 per cent manganese with a Mn/Fe ratio of 3, a central economic zone which is 19,7 m thick and contains 38% manganese with a Mn/Fe ratio above 8, and a lower uneconomic zone which is 6 m thick and contains 30% manganese with a Mn/Fe ratio of 5. The ore consists of banded, very fine-grained braunite-kutnahorite lutite containing concretionary ovoids, laminae and lenticles of Mn-calcite with which hausmannite is commonly associated. Subordinate amounts of hematite, jacobsite, and rhodochrosite are also present. The relatively high Mn/Fe ratio of the economic zone makes the ore very suitable for the production of high-manganese (>78% Mn) alloys. The relatively large carbonate content of the ore, reflected in the Co content of 12 to 16%, makes it virtually self-fluxing. Proven reserves of economic grade ore are in the order of 300 to 400 Mt mined presently at a maximum production capacity of 1,8 Mt per annum. Total reserves in the Kalahari manganese field are estimated at 13 613 Mt. Three symmetrical sedimentary lithofacies cycles are present in the Mamatwan manganese ore bed. Each consists of a braunite-rich central subzone with large white Mn-calcite ovoids grading both upwards and downwards into braunite-kutnahorite lutite. The latter contains a higher carbonate content and smaller carbonate ovoids than the central braunite-rich subzone. The small carbonate ovoids are typically brown in colour because of inclusions of hausmannite crystallites. The sedimentary cyclicity is also reflected in the mineralogical and chemical composition of the ore bed. The Mn/Fe ratio and the contents of braunite, manganese, and silica increase towards the central braunite-rich subzones and the contents of manganese carbonates and iron decrease. The central braunite-rich subzones contain on average more than 50% braunite which grades to values of between 38 and 46% in the adjacent braunite-kutnahorite lutites. Corresponding manganese contents are 38 to 40% in central subzones with values down to 27 to 30% outside them. The ore bed grades at its base and at its top into hematite lutites which, in turn, grade into banded iron-formations of the Hotazel Formation. Jacobsite is preferentially developed in the transition zones between manganolutite and hematite lutite. Variations in the composition of manganolutite in the lithofacies cycles of the ore bed reflect changes in primary chemical sedimentary conditions in the depository. In contrast, variations in the composition of concretionary carbonate laminae and ovoids are related to the diagenetic history of the manganese ore which is thought to be of a volcanogenic-sedimentary origin.
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Mineral Deposits of Southern Africa, 1, 979-983

The Middelplaats manganese deposit, located in Griqualand West, was discovered in 1965 following a regional ground geophysical survey and exploration drilling programme. The manganese ore body occurs within iron-formation of the Hotazel Formation of the Postmasburg Group at a vertical depth of between 300 and 400 m and dips gently to the north-east. It is considered that the manganese was chemically or biochemically precipitated, probably within a closed, fresh-water basin. At full production the mine will produce a total of 1,1 Mt of metallurgical grade manganese ore per year.
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Mineral Deposits of Southern Africa, 1, 985-989

The Gopane manganese deposits, located 56 km north-west of Zeerust were discovered in 1958 and have produced continuously from 1961 to 1980. More recently production has been suspended. The manganiferous zone extends both north-westwards and south-eastwards, for a total strike distance of 15 km from Schilpadhek to beyond Livingstone's Poort and for some 25 km in Botswana. Economic manganese mineralization has, however, only been proved along a strike of 12 km in Bophuthatswana and 10 km in Botswana. The orebody occurs in the Polo Ground Member of the Rooihoogte Formation, Pretoria Group. Mineralization is confined to a 1 to 7 m zone in a stromatolitic, dolomitic limestone bed and consists of pyrolusite, cryptomelane and nsutite. The orebody averages 0,8 m in thickness and extends down dip for an average of 124 m. The manganese-content of the body ranges from 15 to 85 percent manganese dioxide. It has been affected to a limited extent by transverse faulting with vertical displacements varying from 8 to 15 m. Ore formation is thought to have involved a process of solution, distribution and reprecipitation of manganese dioxide, the source of which could have been the dolomitic limestone host rock. Since the commencement of full scale production up to the end of 1980, a total of 0,79 Mt of saleable material has been produced.
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Mineral Deposits of Southern Africa, 1, 991-992

Rocks of the Pretoria Group of the Transvaal Sequence outcrop to the west and north-west of the town of Vereeniging where they form a crescent of low bushy hills known as the Houtkop ridge. Considerable tonnages of weathered and fresh shales are mined by Verref Mining (Pty) Ltd at Houtkop and further south at Leeuwkuil (Fig. 1). These shales are used in the manufacture of building bricks, burnt clay sewer pipes and some acid-ware ceramic products. At Houtkop, the Transvaal rocks have been folded into an open anticline with the axis plunging to the north-west. The dips of the sediments on the limbs of the anticline vary locally between 9 and 38x. Prominent outcrops of the Klapperkop Quartzite Member of the Timeball Hill Formation form the higher ground in the Houtkop ridge, while lower shales of the Timeball Hill Formation, occurring between klapperkop quartzite and Eccles dolomite, form the south-east facing scarp slopes. Verref Mining (Pty) Ltd operates quarries on the lower and upper Timeball Hill shale zones. The shale varies in colour from yellow, where fairly fresh, to reddish at outcrop. The southern limb of the anticline strikes southward into the farm Vanderbijlpark, where it is apparently faulted to the east. South of this fault, Pretoria rocks are largely covered by Karoo sediments and are obscured by urban and industrial development. They are only rarely exposed where the younger formations have been eroded. On the farm Leeuwkuil 596, a dark blue-grey shale is being quarried by Verref Mining (Pty) Ltd. This shale has been mapped as Daspoort shale (Silverton Shale of new subdivision) on the 1 : 125 000 scale Geological Survey Sheet 62, Vereeniging, but could be Timeball Hill shale as it is overlain, in the quarry, by a basic intrusive rock which could be correlated with the diabase sill intruding the Timeball Hill Formation at Houtkop. The appearance of the blue-grey Leeuwkuil shale (referred to as "Panclay"), is, however, different to the to yellow Timeball Hill shales being mined at Houtkop. Panclay also has a lower iron content than the Houtkop shales. A road cutting into the Leeuwkuil quarry has exposed a strong angular unconformity between the north-west dipping Pretoria Group sediments and the basal contact of the Dwyka tillite of the Karoo Sequence. Raw material selection and quality control are based on the firing and physical properties requited by the manufacturing processes used to produce the various ceramic products. The Houtkop and Panclay quarries are thus regularly sampled and selectively mined to produce raw materials acceptable to the manufacturing plants concerned. As all the products manufactured from these shales require a certain degree of vitrification, high melting point materials are not required. A low alumina content and relatively high iron and silica content are thus acceptable. Physical characteristics controlling behaviour of the clay bodies during extrusion, drying, and firing are important quality control factors. This is particularly true in the case of burnt clay sewer pipes where shape, dimensions, and quality of the fired product must conform to close tolerances.
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Mineral Deposits of Southern Africa, 1, 993-1004

As a result of the emplacement of the Bushveld Complex, pelitic rocks of the Pretoria Group were subjected to varying degrees of metamorphism. Contact-metamorphism, without a stress component, prevailed in most areas, except along the north-eastern margin of the complex, where dynamic- metamorphism also occurred. The metamorphic effects resulted in the widespread, roughly zonal development of cordierite-sillimanite, andalusite (chiastolite), and biotite-chloritoid hornfelses and slates. Extensive deposits of andalusite are found in areas of optimum metamorphic grade and chemistry of the host rocks. Exploitation of these deposits takes place where the concentration of andalusite is of economic grade, the country rock is suitably weathered for easy extraction and the quality of the material has not deteriorated due to retrograde metamorphism or secondary alteration. Such conditions exist at a number of places in the south-western, the eastern, and the north-western Bushveld margin. Total identified resources of andalusite are estimated at 67 Mt and the resources of recoverable high-grade andalusite are of the order of 35 Mt.
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Mineral Deposits of Southern Africa, 2, 1021-1029

Since the appearance of the last volumes on Some Ore Deposits in Southern Africa in 1964, revolutionary changes have occurred in the thinking on the genesis of layered complexes generally, and the Bushveld Complex and its associated ore deposits in particular. When the volumes mentioned above were issued, there was little consensus concerning the origin of the Bushveld Complex, its magnificent layering and especially of its stratiform ore deposits. However, by the time the 1969 biennial congress of the Geological Society of South Africa, which dealt with the Bushveld and other layered complexes, was held, the cumulus theory had become more or less firmly entrenched as the mode of origin of layered complexes and their cogenetic mineralization (Symposium on the Bushveld Igneous Complex and Other Layered Intrusions, Pretoria, 1970). This thinking persisted at least up to the time of the second International Platinum Symposium held in Denver, Colorado, in 1975 although, even at that stage, doubts were being expressed regarding the universal applicability of the cumulus theory to the observed mineralization and other features of layered complexes. The settling of cumulus crystals through, and the application of convective overturn involving thick magma piles on the macroscale, as well as the anomalous behaviour of thin magma layers in the formation of cyclic units, apparently in isolation from the rest of the huge magma volume on a microscale, caused serious doubts about the postulated mechanisms of cumulate formation in layered complexes. Consequently, many extra ordinary and involved mechanisms had to be formulated to explain the field phenomena and mineralization observed using the cumulus theory. Moreover, as modelling of magmatic systems became increasingly sophisticated, using progressively more rigid mathematical constraints, it became obvious that the cumulus theory alone was no longer tenable to explain the Bushveld rocks or their geochemistry.
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Mineral Deposits of Southern Africa, 2, 1031-1038

An outline of the geology of the Bushveld Complex, parts of the Transvaal Sequence and the Kaapvaal Craton is explained with the aid of LANDSAT imagery. This imagery provides a synoptic a synoptic view of the Bushveld Complex and its surroundings and, as an interpretive aid, permits the assessment of many regional, interacting. Analysis of the lineament patterns visible on the regional mosaic has resulted in the subdivision of the terrane into six lineament domains, each with a characteristic lineament pattern. A synthesis of the LANDSAT data leads to the conclusion that there is no evidence for the concept that deep-seated crustal fractures influenced the location and from of the Bushveld Complex.
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Mineral Deposits of Southern Africa, 2, 1039-1040

On the occasion of the publication of the ore deposits volume by the Geological Society of South Africa, it is considered appropriate to include a brief note on the stratigraphic nomenclature of the Bushveld Complex. Considerable changes have been made to the formal lithostratigraphic nomenclature of South African rocks in general and to the rocks of the Bushveld Complex in particular. Therefore, an explanation of the philosophy of lithostratigraphy and the relation of the present subdivision to those formerly accepted should, to some extent, assuage the seeming confusion which exists at the present time.
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Mineral Deposits of Southern Africa, 2, 1061-1090

Regional and detailed geological features of Union Section, Rustenburg Platinum Mines Limited, are described. The strike length of the Merensky Reef is 9 km, truncated to the north and south by magnetite gabbros of the Upper Zone which transgress the underlying zones to form the so-called "gap" areas. The stratigraphy of the Critical Zone from the MG4 chromitite to the Bastard Reef unit is described in detail. Four types of Merensky Reef development are recognized at Union Section: normal, pothole, contact, and lens types. A 5 — wide harzburgite layer, known as the "pseudo-reef", is of particular interest; it occurs 15 m below the normal-type Merensky Reef and is the horizon immediately above which pothole-type reef forms. Potholes are generally ovoid areas in which the Merensky Reef has truncated its footwall stratigraphy and has developed as pothole-type reef resting on the "pseudo-reef". Potholes are small (˜50 m diameter) in the north-eastern part of the mine but increase in diameter and abundance to the south-west and down-dip. The Spud Shaft pothole is a regional feature, at least 4 km in extent. Normal-type reef, up to 7 m thick, occurs in the north-eastern part of the mine but narrows progressively towards the areas of abundant potholing in the south-west and down-dip parts of the mine, where it is only 1 to 2 m thick. A correlation therefore exists between reef thickness and pothole size and abundance. Thinning of normal-type reef takes place as individual potholes are approached. Contact-type reef is developed on the sides of potholes between normal-type and pothole-type reef elevations. Lens-type reef is developed where remnants of the normal-type reef footwall norite succession occurs above the "pseudo-reef" within larger potholes. The Merensky Reef is a pegmatoidal feldspathic pyroxenite, olivine- bearing and harzburgitic towards the base, and bounded by top and bottom chromitite layers a few centimetres thick. Another platiniferous layer, known as the UG2, occurs 36 m below the Merensky Reef. The main layer takes the form of a 60 cm-wide chromitite layer, with two to three hanging wall leader layers.
The UG2 has not yet been mined at Union Section. The mineralogy of the Merensky Reef and UG2 is described in detail. Pyrrhotite, pentlandite and chalcopyrite are the main base-metal sulphides in normal-type Merensky Reef. In addition, cubanite and nickel-mackinawite occur in pothole-type reef. The Merensky Reef at Union Section is characterized by an abundance of intricate platinum-iron alloy, base- metal sulphide intergrowths over laurite, and sperrylite as well as by platinum- palladium tellurides. Some 38 percent of the PGMs are associated with base-metal sulphides and 62 percent are entirely surrounded by silicate gangue. In the UG2 chromitite layer, laurite, platinum-iron alloy, cooperite, and platinum-iron alloy/cooperite intergrowths are the most common platinum minerals. Under narrow, normal-type reef conditions, platinum group element (PGE) grades are high, but, as the reef widens, the grade decreases. In wider reef, a very marked concentration of PGE values at the top of the reef is evident, with high PGE values closely associated with the top chromitite layer and upper 20 cm of the reef. Below this, PGE values decrease rapidly, becoming sporadic and relatively quite low. In general, a noticeable, but less significant, PGE concentration exists in the vicinity of the bottom chromitite layer. A broad sympathy between copper and nickel values and PGMs is evident. It is suggested that, with the narrowing of the reef, a natural concentration of the PGM and base-metal sulphides takes place. Dolerite dykes of two different ages are found on the mine and follow several well-defined directions. The most prominent dyke and fault direction is normal to the strike of the layered sequence. Dyke and fault directions correlate well with regional linear features observed on LANDSAT imagery.
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Mineral Deposits of Southern Africa, 2, 1091-1106

The Impala Platinum Mines are situated north of the town of Rustenburg in the south-western portion of the western lobe of the Bushveld Complex. The upward succession from the UG1 chromitite layer to the top of the Bastard unit is described. In contrast to the generally accepted use, the term "Merensky Reef" is used to describe that portion of the Merensky unit which is mined and, as such, is a "sack" name which does not refer to a particular layer. The terms Merensky pyroxenite, Merensky chromitite layer and Merensky pegmatoid describe the various layers constituting the "Merensky Reef". Consistency dictates that the term "Reef" should not be used to describe the pyroxenite layer at the base of the Bastard unit - instead, in this report, the term Bastard pyroxenite is used. The top of the Bastard unit is taken as the top of the Critical Zone. The Merensky Reef is variously described as an "B" or "C" reef depending upon which footwall layer it rests. The Reef may be either of the "pyroxenite" or the "pegmatoid" type. The origin of potholes is thought to be due to the slumping of a heavy layer into a partly consolidated footwall layer with subsequent shaping of the pothole by vortex currents generated as a result of this slumping. Unlike potholes, where the surrounding footwall layers are not disrupted, certain infill structures are described in which a fine-grained, light-brown norite occupies downwarped hollows in the footwall layers. This norite is thought to represent pre-Merensky sedimentation, remnants of which are locally present in hollows or redistributed as thin norite lenses in the Merensky Reef.
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Mineral Deposits of Southern Africa, 2, 1107-1134

Rustenburg Section of Rustenburg Platinum Mines Limited is the oldest of the presently-producing platinum mines in the Bushveld Complex, having commenced operation in 1929. The stratigraphy of the Critical Zone of the Bushveld Complex in the Rustenburg area is described. Seven major rhythmic units, grading from pyroxenite (with chromitite) through norite to anorthosite, are recognized in the Upper Critical Zone. The Merensky Reef forms the base of the sixth unit and the uppermost seventh unit commences with the Bastard Reef. Particular attention is focused on the platinum-bearing UG2 chromitite layer as well as a number of distinctive anorthositic marker horizons in the foothill of the Merensky Reef. Variations in thickness of the generally narrow (25 cm wide) Merensky Reef are described. The reef, defined by a pegmatoidal feldspathic pyroxenite bounded by a thin top and bottom chromitite layer, varies from 200 cm in thickness to a mere chromitite contact. Pothole structures are widespread at Rustenburg Section and form the most important aberration of the Merensky Reef. The anatomy of large, deep potholes, as well as shallow potholes which give rise to so-called "rolling reef", are described. Volatile activity appears to have played a part in the development of many of the large potholes. The mineralogy of the Merensky Reef is described and it is evident that the most abundant platinum-group minerals (PGM) are the platinum/palladium sulphides braggite and cooperite. These, and the other PGM are closely associated with base-metal sulphides. Lateral platinum-group element (PGE) value distribution is remarkably constant and the Reef lacks any form of pay shoots. The vertical value distribution pattern shows 70 percent of the PGE concentrated in the Merensky Reef with the remainder occurring in both the hanging wall and footwall. Footwall values, not abundant in the eastern sector of the spinel, are well developed in the west where they are associated with mafic clusters in the leuconorite. The Merensky Reef is unique, when compared to other similar deposits, in that it has an exceptionally high Pt/Pd ratios of 2,4.
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Mineral Deposits of Southern Africa, 2, 1135-1142

At the Western Platinum Mine, copper, nickel and platinum metals occur in the form of sulphides, arsenides, bismuthides, and tellurides within the Merensky Reef pyroxenite layer. These minerals are concentrated close to a 1 mm-thick chromitite layer near the top of the 2 to 5 m-thick Reef which dips 10x to the north. Economic mineralization also occurs in the UG2 chromitite layer, 130 m below the Merensky Reef. The intervening anorthosites have been divided into 12 units. Potholes and replacement bodies, exhibiting a north-westerly trend, are responsible for structural disturbances in the mine area.
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Mineral Deposits of Southern Africa, 2, 1143-1154

Atok Platinum Mine is situated on the northern extremity of the eastern lobe of the Bushveld Complex. Platinum-group elements, copper, nickel and cobalt are produced from the Merensky Reef which lies close to the top of the Critical Zone, an assemblage of rocks consisting of conformably layered pyroxenites, norites, and anorthosites. The mineable Merensky Reef consists of a poikilitic feldspathic pyroxenite delineated by two thin chromitite seams, about 50 cm apart, contained in a thicker layer of pyroxenite forming the base of the Merensky unit. Slump structures, or potholes, disturb the otherwise regular and tabular Reef layer. The UG2, a platiniferous chromitite layer located in pyroxenite, forming the base of the UG2 unit, is a second economic horizon some 350 m below the Merensky Reef. Platinum-group element mineralization of the Merensky Reef is associated with base-metal sulphides and largely coincident with, but not limited to, the layer including the two chromitite seams. Higher concentrations of platinum-group minerals can occur in the silicate rocks immediately above and below the upper chromitite layer than in that layer itself. Platinum-group minerals include braggite, cooperite, laurite, moncheite, platinum-iron alloy, sperrylite, paolovite, atokite and several unnamed minerals. The nature, relative abundance, mineral association, and grain size of the platinum-group minerals varies along strike and between Reef and footwall mineralization. The major associated base-metal sulphides are pentlandite and chalcopyrite with minor pyrrhotite, pyrite, millerite, mackinawite, galena, bornite, and sphalerite. Platinum-group element mineralization of the UG2 layer is again associated with base-metal sulphides and chromite and consists of braggite, cooperite, laurite, platinum-iron alloy, vysotskite and an unnamed (Pt, Rh, Cu, Ir, S) phase. Vertical and horizontal variations in mineralogy and grain size occur.
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Mineral Deposits of Southern Africa, 2, 1155-1181

Chromites are unique spinels that form stratified deposits in layered igneous intrusions. Their mineralogy, chemical composition and classification, as well as their stratigraphic geochemical behaviour in terms of their contained elements, have been investigated. The stratiform chromitite deposits, along with their host complexes, occur in stable cratonic areas and are characterized by their extreme lateral persistence and depth extent, along with their consistent sequential stratigraphic positioning as a predictable geochemical progression. These features have genetic connotations, although the origin of chromitites and the method of their deposition, are still open to debate. The in situ chromite resources of the Bushveld Complex, the Great Dyke and the Archaean Selukwe deposits have been reassessed in terms of practical mining considerations and are examined in terms of their global importance. Historical data on the production of chromite ores and ferrochrome are adjudged in a world context, along with the capacity of the existing facilities in South Africa and Zimbabwe and their historical contribution to production and their growth patterns in supply. To the basic framework noted above, as much of the intervening picture as possible has been filled in, by providing those elements of supply and demand which are of importance to the chromium industry and its future. Finally, an attempt is made to forecast the supply/demand equation to the end of this century, with a clear warning that this is a difficult and risky prognosis during a period of world recession, into which this subcontinent is presently being dragged. The conclusion is that, given their indigenous resources, South Africa especially, but also Zimbabwe, have a compelling role to play in future chromite, ferrochrome, and possibly even stainless steel supplies, almost regardless of what the demand may be - a demand which may escalate if the world awakens to the energy predicament looming ahead and is forced into the logical oil-from-coal option to solve it.
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Mineral Deposits of Southern Africa, 2, 1183-1188

The Winterveld chrome mine, located approximately 10 km from Steelpoort in the Eastern Bushveld Complex, exploits the Steelpoort chromitite layer developed in the Mooihoek Pyroxenite which together with the overlying Winterveld Norite- Anorthosite, forms the Critical Zone of the Rustenburg Layered Suite. Aspects of the geology and mineralogy of the deposit are described.
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Mineral Deposits of Southern Africa, 2, 1189-1195

Both the Groothoek and Montrose chrome mines are located in the Lebowa Homeland and exploit the so-called Steelpoort Chromitite Layer and are, for this reason, described together. There is no difference in the geology of the two mines. Although the Leader Chromitite Layer is within a metre of the Steelpoort Layer, it is not being mined at present. Magnetometer surveying has indicated large north-south-trending faults which have, in places, been intruded by dolerite. The Steelpoort Layer is an average one metre thick and the ore produced ranges from 38 to 47 percent Cr2O3, with a silica content from 0,5 to 8 percent. The Cr/Fe ratios are up to 1,65:1. Most of the ore produced is of a friable nature, from which very consistent concentrate products are derived.
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Mineral Deposits of Southern Africa, 2, 1197-1208

The UG2 chromitite layer occurs at the base of a cyclic unit within the upper chromitite group of the Critical Zone of the Bushveld Complex. Exploration on the farm Maandagshoek 254 KT was confined to the location of the UG2 chromitite layer and the distribution of the associated platinoid mineralization. A detailed petrological study of borehole MDH7 shows that the upper chromitite group consists of four cyclic units. Chromitite and, in places, olivine are found at the base of each cyclic unit which grades upwards through orthopyroxenite, norite, and leuconorite to an overlying anorthosite layer. Three specific structural features interfere with the regularity of the layering. Ultrabasic pipe-like bodies cause marginal downwarping of the layering. A pothole is recognized at surface and a major fault has been interpreted from borehole information. Sampling of the UG2 chromitite layer on the surface and in the boreholes shows that the platinum to palladium ratio decreases from 1,78 to 0,99 and the average content of platinum plus palladium increases from 4,06 to 6,45 g/t. Whole-rock analyses show a good correlation between the platinum and palladium content and the chromitite layers, except in the UG3 layer where palladium is depleted. Copper and nickel distribution follow that of the platinoids, except in the UG3 layer where copper and palladium are depleted.
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Mineral Deposits of Southern Africa, 2, 1209-1215

The chromitite layers mined at Kroondal Chrome Mine occur in the pyroxenites of the lower Critical Zone. The succession of chromitite and silicate layers here differs from the succession in other parts of the Bushveld Complex. Both the leader and main chromitite layers, less than one metre apart, are mined. About 67 percent of the chromite grains vary between -20 and +100 mesh in size, and approximately 50 percent of the ore produced is of the "hard-lumpy" variety. Thus Cr2O3 content of the concentrates produced range between 43 and 46 percent and the silica content ranges from less than 1 to 2,5 percent. The ore reserve at the mine is in excess of 35 Mt. Exploration has indicated the presence of a dyke-like intrusion of pegmatoid which disrupts the chromitite layers.
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Mineral Deposits of Southern Africa, 2, 1217-1227

The chromitite layers at the Zwartkop Chrome Mine are present in the pyroxenitic lower half of the Critical Zone. Chromitite layers in the lower half of this subzone display a reversal in the normal fractionation trend up to the level of the New seam (LG4), which is associated with the most magnesian, olivine-bearing cumulates in the layered sequence. According to the latest hypothesis, such reversals and the repetitive appearance of chromitite layers must be ascribed to addition of undifferentiated magma into the magma chamber. Nine chromitite layers are present at the mine, of which several have been exploited in the past. The Cr2O3 content of the ore produced from these layers varies between 44 to 53 mass percent and the Cr/Fe ratio from 1,5 to 2,4. The bulk of the ore has been produced from the Magazine seam (LG6) and chromite resources are estimated to be in excess of 30 Mt.
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Mineral Deposits of Southern Africa, 2, 1229-1235

The Groot-Marico outlier of the Bushveld Complex in the Western Transvaal, contains four, or possibly five, chromitite layers, varying in thickness from 13 to 40 cm. The layers are numbered from 1 to 4 from the base upwards. The outcrop traces of the chromitite layers are roughly kidney-shaped, with inward dips varying from 4 for the No. 1 layer, to 14x for the No. 4 layer. The geological setting of the Groot-Marico body is somewhat similar to that of the Bushveld Complex to the west of the Pilanesberg and the chromitite layers can be compared with the lower group seams in the western part of the Complex. The chromite produced from the Groot-Marico deposit generally has a higher chrome/iron ratio than that of the chromite of the main Bushveld Complex and has been found to be a superior ore for the manufacture of chromite refractories.
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Mineral Deposits of Southern Africa, 2, 1237-1249

Chromitite layers presently being mined on the farms Grasvally 293 KR and Zoetveld 294 KR are confined to a horst-like block of Lower Zone harzburgites. The chromitite is restricted to olivine-rich rocks and is superior in grade to any other chromitite presently being mined in the Bushveld Complex. The chromitite layers formed after about 66 percent of the known Lower Zone had crystallized and are situated in the succession some 620 to 690 m below a zero datum in the middle of the Critical Zone. The petrology of the chromitite- bearing sequence of the Lower Zone closely resembles that of the Great Dyke in Zimbabwe. Chromite-rich rocks have Mg/(Mg + Fe2+) ratios for olivine and orthopyroxene as high as 0,946 and 0,910, respectively. Values greater than 0,900 for olivine have been found in chromite-poor layers in the lowest stratigraphic horizons in the Lower Zone. Chromitite layers occur in beheaded and incomplete cyclic units on Grasvally. From locality to locality, the chomitite layers are highly variable in thickness, grade, and texture. Increases in the grade of the chromitite layers are always accompanied by a degree in thickness of the layer and by the development of coarse-grained, massive chromitite. Chromite chemistry within the layers is highly variable and is not correlatable along strike. Textures indicate that the original chromite-rich cumulates have been extensively modified and upgraded by post-cumulus sintering processes.
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Mineral Deposits of Southern Africa, 2, 1251-1266

The upper 1750 m of layered basic rocks of the Bushveld Complex contain approximately 8% magnetite disseminated in gabbroic rocks, plus a further 20 m of pure magnetite distributed through in excess of 20 discrete magnetite layers. Other occurrences of magnetite in the Bushveld Complex are: disseminated in a gabbroic stratiform layer in the Main Zone, in discordant pegmatoidal sheets which are most abundant in the Main Zone, and as plugs of almost pure magnetite in the Main and Upper zones. These last occurrences are volumetrically insignificant. The magnetite shows microscopic evidence of extensive recrystallization and exsolution. Chemically, it contains V2O5 and TiO2; the former decreasing in amount upwards from approximately 2 to 0 per cent, while the latter increases from about 12 to 20%. No discrete vanadium minerals are present, but vanadium occurs in solid solution in the magnetite. A magnetic concentrate is processed to recover the vanadium. Field relations and chemical data are reviewed and previously-unpublished information is presented. Chemical data include whole-rock analyses of magnetite layers and detailed analyses of magnetic concentrates. An assessment of total proven ore reserves is presented based on mining-company surveys, although much greater tonnages of lower-grade ore also exist. The various hypotheses for the origin of magnetite layers are reviewed, with specific reference to their relevance to the Upper Zone of the Bushveld Complex.
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Mineral Deposits of Southern Africa, 2, 1267-1286

The Bushveld Complex contains the world's largest resources of vanadium-bearing titaniferous iron ores in the form of discrete titaniferous magnetite-rich layers of considerable lateral extent. Between 10 and 30 of these layers are usually developed in the Upper Zone of the Rustenburg Layered Suite and are present in all areas where the Upper Zone is present. They represent products of the normal fractional crystallization processes that are operative within large basic intrusions of this nature. The economically important main titaniferous magnetite layer, or its equivalents, are developed along a strike length of approximately 420 km in the eastern, western and Potgietersrus lobes of the Complex. The ore layers consist essentially of closely packed, polygonal, multiphase, titaniferous magnetite crystals that meet in distinct triple junctions with interfacial angles that approximate 1200. Minor, but variable, amounts of coarse-grained ilmenite and silicates are also normally present in the ores. The grain-boundary relationships within the ores are indicative of considerable postcumulus growth and readjustment that is ascribed to the combined effects of sintering and adcumulus growth. The constituent titaniferous magnetite crystals are characterized by the widespread development of exsolved ulvospinel, which is indicative of the existence of low oxygen fugacities during this stage of subsolidus cooling. Externally exsolved ilmenite granules and variously sized ilmenite lamellae are also sparingly present as oxidation/exsolution products, particularly at certain levels in the intrusion. These developed under slightly higher oxygen fugacities. A variety of transparent spinel exsolution bodies, showing both granular and lamellar morphologies, are also present. The development of the various microstructures is explained in terms of current exsolution theory. The ores show the effects of late-magmatic and deuteric alteration. Transgressive magnetite veinlets are developed and localized oxidation has occurred. Minor, but variable degrees of alteration and replacement of Ti-magnetite by ilvaite, sphene, biotite, amphibole, chlorite, and sulphides have also occurred. At surface the ores are extremely oxidized and hydrated, showing the development of maghemite, martite (haematite), geothite, lepidocrocite, and leucoxene at the expense of the original ore minerals.
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Mineral Deposits of Southern Africa, 2, 1287-1299

In the Potgietersrus limb, the acid rocks of the Bushveld Complex and associated formations exhibit complex intrusive relationships. The older Rooiberg Group felsites and pyroclastics are intruded by Stavoren Granophyre, which in turn is intruded by granophyric granulite. This succession, i.e. the Rooiberg Group and the Rashoop Granophyre Suite, acted as a roof for the emplacement of the Lebowa Granite Suite, which comprises various textural and petrological variations of the Nebo Granite, particularly the late-stage Bobbejaankop and Lease Granites. Tin mineralization is a result of fractional crystallization of these late melts. The replacement of the younger granites resulted in updoming, fracturing and brecciation of the less-competent roof zones. Widespread hydrothermal cassiterite (with some associated tungsten), sulphide, and tourmaline mineralization is present in sheet-like disseminated form in the Bobbejaankop Granite, as well as in metasomatic lenticular bodies, pipes, lodes, pockets, and fissures in the Lease and Bobbejaankop Granites. In the Rooiberg Group, tin mineralization is found in contact breccia deposits, in bedded breccias, and in fracture-stockworks. As a result of different levels of intrusion, three distinct styles of mineralization can be observed, i.e. endogranitic ore at Zaaiplaats, telescoped mineralization in the Groenvley-Appingendam area, and exogranitic ore at Welgevonden and Welgelegen. Mineralization at Zaaiplaats represents a closed pressure-temperature system, whereas the roof zones of the granite domes in the Groenvley-Appingendam and Welgevonden-Welgelegen environments had been increasingly penetrated and fractured during the formation of the ore deposits.
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Mineral Deposits of Southern Africa, 2, 1301-1305

Cassiterite was discovered on the farm Doornhoek 342 KR in 1908 and tin concentrates were produced intermittently until 1953; since then 10 000 t of tin metal have been recovered. The cassiterite occurs as very fine-grained crystals associated with fractures in a tuffaceous sedimentary rock, locally known as the Union Tin shale, intercalated in barren felsites of the Rooiberg Group. The cassiterite mineralization is considered to have originated from the Bushveld Granite, which outcrops south of the property.
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Mineral Deposits of Southern Africa, 2, 1307-1327

The history of tin mining in the Rooiberg area covers a period of some 500 years. However, intensive mining only began early this century. Annual production from the four operating mines totals 500 000 t at 0,50 percent tin, accounting for approximately one percent of the world supply of tin. To date ore produced totals 11,2 Mt at 0,62 percent tin. Cassiterite is extracted by heavy media separation and flotation. High-grade concentrates are smelted on site. There are no viable byproducts. The Rooiberg Fragment lies within the western lobe of the Bushveld Complex. The continental shallow marine sedimentary and volcanic rocks of the Transvaal Sequence, which constitute the Fragment, were deposited on the Archaean Kaapvaal Craton in an intra-cratonic, graben- controlled basin. The combined thickness of the Pretoria and Rooiberg groups within the Fragment varies between 2 000 and 3 500 m. The Pretoria Group consists of the basal clastic Leeuwpoort Formation conformably overlain by volcanosedimentary rocks of the Smelterskop Quartzite Formation. These, in turn, are conformably overlain by the Rooiberg Group felsites and volcanoclastic rocks which are regarded as the terminal phase of the Transvaal Sequence. The roughly triangular-shaped fragment is surrounded by granophyres of the Rashoop Granophyre Suite and by granites of the Lebowa Granite Suite, the latter being clearly intrusive. In addition, felsitic, andesitic, gabbroic, syenitic, and doleritic dykes and sills intruded at various stages. The rocks of the Rooiberg Fragment have been subjected to two phases of concentric open folding. Vertical to subvertical tectonics, caused by the intrusion of the Bushveld Complex, accounts for the presence of both a steeply dipping and horizontal system of fractures. Widespread recrystallization and the presence of low-grade metamorphic mineral assemblages in attributed to contact metamorphism. Geochemical data indicate that the uppermost portion of the Boschoffsberg Quartzite Member consists of aluminium-rich sodic arkoses and thus a tonalitic- granodioritic Archaean basement provenance is proposed. The Rooiberg tin deposits are stratabound and classified as conformable or unconformable according to their geometric relationship with the bedding. Conformable mineralization includes pockets, bedding-plane mineralization, bedded lodes, and bedding-plane related stringers. Pocket-type mineralization refers to bedding- plane and fracture controlled, cassiterite-bearing, irregularly shaped nodules. Bedding-plane mineralization is defined as disseminated cassiterite dispersed within sheet-like bodies that tend to lie parallel to the major fracture directions. The prevailing ore assemblage is: cassiterite, pyrite, chlorite, tourmaline, and carbonates associated with varying amounts of magnetite, haematite, chalcopyrite, quartz, and potassic feldspar. The close spatial association between bedded lodes and steep fractures is obvious in all the mines. The hydrothermal system that operated within the Rooiberg Fragment was extremely complex. It caused a pervasive, intricate alteration pattern, the significance of which has yet to be understood. Very low niobium concentrations in cassiterite and experimental data from quartz fluid inclusions indicate a low temperature of formation. The genesis of these deposits is a controversial subject as several observations are inconsistent with the classic exogranitic model. Further research is required on this aspect.
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Mineral Deposits of Southern Africa, 2, 1329-1335

The Rooibokkop-Boschhoek prospect, with a surface manifestation of prominent ridges of ferruginous rocks, is located 12 km N40°E of Marble Hall, Transvaal, in the Eastern Bushveld Complex. Reconnaissance drilling revealed that sulphide-bearing siderite veins of hydrothermal origin, which were emplaced along a fracture zone within the Nebo Granite, constitute the deposit. This major event was succeeded by the introduction of several sulphide assemblages which precipitated chiefly in a quartz host at the hangingwall or footwall of the siderite veins. The main copper sulphide is chalcopyrite containing trace amounts of silver. Sphalerite is of minor importance. At the surface, the mineralization displays zonal distribution of the sulphides, with copper occurring in a central elongated belt, bordered on both sides by zones in which galena and sphalerite progressively increase in importance, relative to chalcopyrite, in an outward direction. Recurrent fracturing greatly increased the permeability of the rocks and permitted the circulation and mixing of meteoric and later hydrothermal fluids, resulting in the pervasive sericitization of the granite in the fracture one. Oxygenated waters of atmospheric origin gained access to deeper levels in more recent times and caused the hematitization of siderite and the replacement of chalcopyrite by bornite. Although the assay data, for copper, lead, zinc, and silver, on chip samples collected at the surface from trenches dug across the gossanous outcrops are promising, the mineralization is considered to be sub-economic since core samples show the distribution of the copper to be patchy and erratic.
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Mineral Deposits of Southern Africa, 2, 1337-1341

The general geology of the Buffalo Fluorspar Mine is described. The country rocks of the fluorite deposits comprise leptite and Bushveld Granite. North-west of the mine property, felsite is encountered, while sediments and lavas of the Karoo Sequence cover the older rocks west and east of the mine. The leptite is considered to represent granitized sediments of Transvaal age, the rocks occurring as metasedimentary xenoliths surrounded by the Bushveld Granite. Mineable fluorite is confined to veins in the leptite and occurs predominantly as parallel to sub-parallel bands located along horizons interpreted as palaeo-bedding planes. Higher -grade areas of mineralization have been delineated as ore bodies and the five major deposits are described. The origin of the fluorite mineralization is discussed and interpreted as being of pneumatolytic origin, related to the emplacement of the Bushveld Granite. Mineralization took place predominantly by replacement crystallization from a gaseous phase along the palaeo-bedding planes within the leptite.
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Mineral Deposits of Southern Africa, 2, 1343-1349

The fluorite deposits on Zwartkloof 470 KR are structurally controlled and occur as erratically developed fracture fillings in the felsites of the Rooiberg Group. The felsites represent a succession of rocks occurring from the intrusive contact of the Bushveld Granite to the overlying sedimentary rocks of the Swaershoek Formation and include a marker horizon of pyroclastic sediments which is correlated with the Union Tin pyroclastic beds. Siderite, quartz, chlorite, sphalerite (protore), fayalite (Fa97), pyrite, chalcopyrite, galena, magnetite, and ilmenite occur with the fluorite.
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Mineral Deposits of Southern Africa, 2, 1351-1393

The Lomagundi Metallogenic Province is in the Lomagundi Basin, part of the Zambezi Basin on the north-western margin of the Rhodesian Craton. The form and shape of the Lomagundi Basin is controlled by the nature of the underlying Archaean floor, and especially the resistant granite masses that have created a string of alternating basins and intervening highs in the east. The Lomagundi Supergroup succession is, from the base up: Deweras clastic group, mainly arkose, with some volcanics; the Mcheka Group, quartzite, shale, and dolomite; the Nyagari striped slate and quartzite; the Piriwiri Group, phyllites and greywackes; and the Chiwuyu-Godzi sediments and volcanics. Fractures and zones of weakness in the underlying crust facilitated local tectonic activity and the restricted emplacement of igneous material into this sequence of basin sediments that were derived from an eastern source. The mineral deposits show a strong structural control, in which the mineralized bodies, commonly associated with igneous rocks, occur along north to north-east-trending belts that coincide with major crustal facture systems or tectonically active zones of weakness. The copper (silver) deposits of the Deweras mineral belt, the main mineral deposits of the Lomagundi Province, are in the main stratabound bodies containing copper sulphides in the Deweras and Mcheka groups. The dominant host rock is feldspathic quartzite or arkose, but in places coarser and finer clastics and carbonate formations are also mineralized. One small deposit is in a volcanoclastic host and some are close to intrusive rocks. The ore minerals are generally disseminated, but occur as aggregates and seams where the host rocks are sheared. The formations are variably folded, and ore bodies occur in gentle anticlines and synclines, and in places are tightly folded. Most deposits are accompanied by secondary ferruginization. The ore deposits were formed from solutions that penetrated fracture systems to favourable hosts and structures. A number of minor mineral belts in the Lomagundi province contain small deposits of diverse types, ranging from skarn to volcanic and pegmatitic. The Sabi Metallogenic Province occupies the western part of the supracratonic Sabi Basin, which constitutes a south-western extension of the large Proterozoic Mozambique Basin of the Rhodesian Craton. The small Umkondo deposits are associated with quartzites within a thick sequence of argillites. Shales in or adjacent to the quartzites are preferentially mineralized to form ore bodies that occur in shallow-plunging anticlinal structures. The small Mary Ann deposit constitutes hydrothermal, fumarolic mineralization along fissure feeder systems that culminate upwards in unusual ore pods within fragmental tuffs of a volcanic pile. The formation of these ore deposits is equated with the thermo-tectonic activity associated with the formation of the basin by a sub-crustal convection cycle.
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Mineral Deposits of Southern Africa, 2, 1395-1420

The Namaqualand Metamorphic Complex is a polyphase deformed and metamorphosed gneissic terrane consisting of paragneisses derived from various sedimentary and volcanic rocks, intruded by a great variety of igneous rocks. The Complex can be divided into a number of regions distinguished by structural, lithological, and geochronological differences, and by locality. The Kheis Subprovince of the Kgalagadi Province, east of the Complex, skirts the Kaapvaal Province and is separated from the main part of the Namaqua Province by the Gordonia Subprovince, a north-west-trending, dextral, strike-slip orogen. The Richtersveld Subprovince is a wedge-shaped complex bounded by the Gordonia Subprovince in the north-east, by the Bushmanland Subprovince in the south and by the Late-Precambrian Gariep Subprovince in the west. The igneous rocks of the Richtersveld Subprovince become increasingly deformed as the outer limits are approached and merge with those of the Bushmanland Subprovince. The West Coast Belt is marked by the presence of many sinistral north-north-east, north, and north-north-west-trending sinistral shear zones associated with Pan-African deformation. The Complex extends into South West Africa/Namibia where the rocks of the Rehoboth Subprovince crop out only west and north-west of a large area of Nama and Karoo sediments. The rocks of the Natal Subprovince have been thrust onto the Kaapvaal Province in the east. All parts of the Namaqualand Metamorphic Complex have undergone polyphase deformation, but with varying degrees of intensity. Major north-west-trending right-lateral shear zones or wrench faults transect the Complex and a less well developed set of fractures strikes east-north-east. The rocks of the Kheis and Richtersveld subprovinces have undergone greenschist facies metamorphism. Most of the Namaqualand gneisses have been metamorphosed to amphibolite facies, but granulite facies metamorphism is found along the central spine of the Gordonia Subprovince and in an extensive area in western Namaqualand. Pan-African metamorphism was superimposed on the rocks of the West Coast Belt. The oldest rocks (˜ 3000Ma) are found near the contact with the Kaapvaal Province and the rocks of the Richtersveld Subprovince have been dated at between ˜2000 and ˜1730 Ma. The main event of deformation and metamorphism of the rocks in the Namaqua Province has been dated at ˜1200 Ma and numerous age determinations of ˜1000 Ma are thought to indicate the time of rapid uplift and isotopic resetting. Those mineral deposits which are obvious on surface have probably all been found, but the Namaqualand Metamorphic Complex still holds promise for the discovery of other large base metal sulphide deposits.
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Mineral Deposits of Southern Africa, 2, 1421-1445

Although already discovered in 1685, mining of the copper deposits of the Okiep District in the North-western Cape Province only started in 1852 and continued on a relatively small scale until 1931. Ore produced and ore still in reserve for the years 1940 to end 1979, a period of continuous operation by the O'okiep Copper Company Limited, total 93,8 Mt at 1,75 percent copper. Copper metal produced since 1852 and copper contained in reserve is 2 Mt. Most of this copper is located in deposits at 27 separate localities. The greatest depth reached by mining and exploration is 1 600 m below outcrop. The Okiep District, covering 3 000 km², is situated in the Namaqualand Metamorphic Complex. The rocks are of Proterozoic age and have undergone high-grade metamorphism and polyphase deformation. Previously regarded as representing mainly a pile of ultrametamorphosed and granitized sedimentary rocks, the lithostratigraphic column is now subdivided into a metavolcano-sedimentary succession, the Okiep Group (quartz-feldspar-biotite granulite and gneiss, metapelite and quartzite, amphibolite and calc-silicate rock), which has been intruded by the Gladkop Suite (two phases of fine- to medium-grained quartz-microcline granite gneiss), the Klein Namaqualand Suite (two phases of quartz-microcline-biotite granite gneiss) and the Spektakel Suite (three phases of quartz-microcline granite). Emplacement of the intrusive rocks was mainly sheet-like and took place at different stages relative to the main structural and metamorphic events. The copper deposits are confined to the Koperberg Suite, the youngest major group of intrusives in the district, which occurs as a swarm of generally irregular, easterly trending, steep north-dipping, dyke-like bodies, usually 60 to 100 m wide, and seldom exceeding 1 km in continuous strike length. Emplacement of the Koperberg Suite appears to have been predisposed to a large extent by enigmatic structural features, referred "steep structures", that are typically narrow antiformal linear features along which continuity of the adjoining rocks has been interrupted by piercement folding and shearing. In places, pipe-like bodies of megabreccia that generally lie along steep structures, are host structures to the Koperberg Suite. Steep structures, megabreccias, and intrusion of the Koperberg Suite postdate the major fold events. The Koperberg Suite consists mainly of diorite, anorthosite, and norite, in order of decreasing abundance. The dominant silicate constituents are andesine/labradorite, hypersthene, biotite, and phlogopite. Evidence exists of sequential emplacement at some localities of anorthosite, succeeded progressively by more basic types. Copper sulphides are preferentially associated with the more basic varieties. The copper content of the Koperberg Suite is erratic, varying from a mere trace to several percent in different parts of the same body and even over very small distances. The distribution, shape, and dimensions of copper orebodies within the Koperberg Suite are extremely variable. Mines consist of isolated orebodies of as little as 200 000 t, to several orebodies lying within the same intrusive aggregating up to 37 Mt. The copper sulphides are mainly chalcopyrite, bornite, and subsidiary chalcocite. Distribution of the sulphides generally ranges from disseminations to vein-like aggregates. Substantial massive concentrations have formed in a few places. The Koperberg Suite was formed from magma in which copper and sulphur were primary constituents, but the source of the magma remains a matter of conjecture.
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Mineral Deposits of Southern Africa, 2, 1447-1473

During 1972 Phelps Dodge's exploration staff discovered three large base-metal deposits at Aggeneys in the Namaqualand District of the north-western Cape Province. These deposits are known as Black Mountain, Broken Hill, and Big Syncline. In January 1980, the Broken Hill deposit was brought into production at an initial milling rate of 1,125 Mt per annum. The Aggeneys copper-lead-zinc- silver deposits occur in the Precambrian metavolcanic metasedimentary Bushmanland Group which forms part of the Namaqua land Metamorphic Complex. The generalized stratigraphic succession encountered at Aggeneys consists of basal augen gneiss, overlain by pink gneiss, aluminous schist, white quartzite, and the Aggeneys Ore Formation which consists of a 200 m-thick succession of pelitic schist in which occurs the three stratiform orebodies. Overlying the Aggeneys Ore Formation and constituting what is thought to be the top of the stratigraphic succession in the area, is a variable sequence of conglomerate, amphibolite, and leucocratic grey gneiss. Four phases of deformation have been recognized which have resulted in the formation of highly complex structures. The various rocks, including the stratabound ore deposits, have been subjected to dynamothermal metamorphism bordering on granulite facies. The economic base- metal sulphides are intimately associated with banded iron-formations and consist of varying proportions of chalcopyrite, galena, and sphalerite, which, together with pyrite and pyrrhotite, often constitute massive sulphide concentrations. The orebodies display systematic variations in base-metal content and mineralogy in both a vertical and a lateral sense. The Aggeneys orebodies are considered to be stratabound exhalative sedimentary deposits with close genetic affinities with the Broken Hill deposits in Australia and the New Brunswick deposits of Canada.
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Mineral Deposits of Southern Africa, 2, 1475

During the period between the compilation of the paper by Ryan et al. (1985) and the final acceptance of material for this volume, a large amount of information has accumulated during the course of routine mining operations, from detailed underground mapping and from diamond drilling. This data have thrown new light on some of the theories and interpretations presented in the earlier work. In particular, the structure of the western extremity of the orebodies has been re- evaluated. The detailed underground drilling, which preceded the development and mining of the western portion of the orebody, provided information which led to a distinction being made between the upper and lower orebody massive sulphide units on the basis of metal ratios. Using this method, the surface drill information was re-interpreted, and it was found that the lower orebody massive sulphide formed a continuous thin unit which could be used to elucidate the structure. This was subsequently borne out by underground development mapping. The upper orebody massive sulphide, in contrast, is confined to a thin lens, the lower orebody thus giving rise to the continuous massive sulphide in the fold closure. Figure 1 shows the structure of this critical area determined from the more recently acquired data. This should be compared with Figure 3 from Ryan et al. (1985). Unlike the earlier interpretation it has now been shown that the orebody is gently folded with no evidence of isoclinal duplication by F1 or F2. Pegmatite is locally well represented and corresponds to the position of an F3 shear zone on surface (Ryan et al. , 1985, Fig. 3) . It is suggested that the observed folding of the orebody is of F3 age and is related to this shearing. Closely similar structural situations have also been drilled and partially mapped at higher and lower elevations within the mine, and it is reasonable to assume that this is a consistent feature throughout the orebody. The other evidence of F1 folding invoked by Ryan et al. (1985), viz. the duplication of the ferruginous garnet quartzite, is not seen in the underground exposures of the areas that have been mapped and drilled. This unit occupies a consistent stratigraphic position in the hanging wall throughout most of the orebody, but appears to be absent, and is certainly not duplicated, at the western closure. This may be explained by the simple F3 folding as now postulated. The base-metal distribution on the massive sulphides unit of the lower orebody provides quantitative evidence which further emphasizes that no duplication in a tight F1 fold has occurred. Copper values decrease systematically from greater than 1 percent in the west, to less than 0,2 percent in the east. The lead/zinc ratio increases correspondingly from less than 1 to greater than 2. This laterally asymmetric zonation is similar to that found in many relatively undeformed exhalative orebodies, and is thought to represent a primary depositional feature. This simple trend would be unlikely in an orebody duplicated by a tight F1 fold. A detailed analysis of the metal zonation throughout the ore body is in progress, and it is hoped to publish this in due course (P. Smith, in prep.). This work, in general, provides no indication of F1 duplications, and a great deal of evidence for the simpler interpretation.
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Mineral Deposits of Southern Africa, 2, 1477-1488

The Gamsberg zinc deposit, discovered in the Namaqualand District of the Cape Province in 1972, has published ore reserves of 150 Mt averaging 7,1 percent zinc and 0,5 percent lead. The orebody forms part of a Precambrian volcano- sedimentary succession, the Bushmanland Group, which lies in the Namaqualand Metamorphic Complex and has been subjected to polyphase deformation and medium- to high-grade metamorphism. The succession at Gamsberg consists of a basal quartzo-feldspathic gneiss overlain by a thickness of up to 450 m of sillimanite-bearing pelitic schist and metaquartzite on which follows an iron formation (0-80 m), succeeded by psammitic schist, lenses of conglomerate, quartzite, and amphibolite (400-500 m). The iron formation, comprising mainly fine-grained pelitic and calcareous metasediments, is characterized by prominent banding, a high concentration of iron in the oxide and sulphide state, and the presence of base-metal sulphides and barite. The distribution of the oxide, silicate, sulphide, sulphate, and carbonate facies displays vertical and lateral zoning. The sulphides include pyrite, pyrrhotite, marcasite, marmatitic sphalerite, galena, and alabandite. Ore fabrics such as the general coarse nature of the sulphides, exsolution of pyrrhotite from sphalerite and twinning in sphalerite, reflect the relations of a metamorphosed deposit. The depositional environment of the succession is considered to have been a relatively large shallow basin, Iron formation, which has limited extent, was deposited in a restricted basin, an environment ideal for accumulation of fine- grained siliceous and aluminous clastic sediments, chemical precipitates, as well as of iron and base-metal sulphides. Termination of the chemogenic cycle was succeeded by erosion and sedimentation in a high-energy environment. Two alternative models of ore deposition are tentatively proposed: (i) a sedimentary environment related to a distant island arc, and (ii) a Red Sea intercontinental environment.
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Mineral Deposits of Southern Africa, 2, 1489-1502

The existence of a sulphide ore deposit on the farm Putsberg 203 to the south- east of Pofadder was proved by the Johannesburg Consolidated Investment Company Limited during 1974. Mineralization was located beneath sand and calcrete cover, employing a multi-disciplinary exploration approach with geophysics as the principal technique, supported by geochemistry, remote sensing, geological mapping, and drilling. The mineralization occurs in a supracrustal sequence of metasedimentary and minor metavolcanic rocks of the Bushmanland Sequence. The area is structurally complex, showing evidence of at least three phases of deformation. The mineralization comprises disseminated sulphides in a sequence of quartzo-feldspathic gneiss, quartzite, aluminous schist and minor carbonate rocks and amphibolite. The main sulphide minerals, in order of decreasing abundance are pyrite, pyrrhotite, chalcopyrite, sphalerite, and galena. The deposit bears a number of similarities to the Aggeneys and Gamsberg deposits of central Bushmanland, but the main metal present at Putsberg is copper, with minor lead and zinc.
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Mineral Deposits of Southern Africa, 2, 1503-1527

Minimum original reserves calculated for the Prieska massive sulphide deposit amounted to 47 Mt grading 1,7 percent copper and 3,8 percent zinc with an average specific gravity of 3,8. The massive sulphide ore zone forms part of a 10 to 100 m-wide stratabound layered sequence of pyritic metasediments within a succession of sulphide-poor, fine-grained, laminated gneisses. These gneisses, some of which can be recognized as metasediments, form part of the strongly deformed high metamorphic grade Namaqualand Metamorphic Complex. The sulphide- bearing sequence is made up of an outer, quartz-rich zone, containing trace amounts of copper, zinc, and lead in sharp contact with an inner, silica-poor zone hosting the economic sulphides (sphalerite, chalcopyrite, and galena) in a matrix of pyrite, carbonates, sulphates, and calc-silicate minerals. Structure near the orebody conforms to the regional style of deformation. Tight, but not isoclinal folds form an interference pattern. The tabular orebody extends along strike for just over 2 000 m and persists to a depth of at least 1 000 m. True width varies from less than a metre to 30 m (average 7 m) and the orebody has a plunge of 45x with its dip generally exceeding 60x. On dip sections, pyrrhotite and carbonate contents increase towards the structural hanging wall. On a strike section, average copper and zinc values show distinct trends parallel to the plunge of the body. High zinc values coincide with low copper values. Sedimentary textures in the ore and hanging wall gneiss have survived granulite grade metamorphism and indicate that the ore was precipitated as a chemical sediment. Textures previously considered to be of volcanic origin are reinterpreted as metamorphic textures. No explosive volcanic activity is evident and, in terms of the volcanogenic concept, the deposit is classified as "distal". A progressive variation in depositional environment, commencing with clastic sedimentation and culminating with the precipitation of the sulphides, is postulated. The variety and contrast of mineral associations in the chemical sediments of the ore zone are interpreted as having formed in a sea-floor environment associated with an interface between anoxic brine and normal water in a stratified basin.
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Mineral Deposits of Southern Africa, 2, 1529-1537

The Areachap copper-zinc massive sulphide deposit near Upington, Gordonia District, Northern Cape Province, is situated in Precambrian gneisses and schists of the Copperton-Areachap Formation, which is believed to represent a metamorphosed volcano-sedimentary sequence. The sulphide body is confined to a biotite-garnet schist host which is enclosed mainly by amphibole gneiss and amphibolite. The biotite-garnet schist is probably of sedimentary origin. The amphiboles gneiss and amphibolite are believed to represent metamorphosed, intermediate lavas. The massive sulphide is coarse grained and probably completely recrystallized. The sulphides are chiefly pyrite and pyrrhotite, with chalcopyrite and sphalerite as important constituents. Galena and altaite occur in minor amounts. Minor amounts of silver tellurides have been identified. Reserve calculations indicated 8,9 Mt of massive and discriminated ore, grading 0,4 percent copper and 2,24 percent zinc, or 6,7 Mt of massive ore grading 0,95 percent copper and 2,88 percent zinc. Silver and gold values are low. A prominent gossan is developed on surface. It consists mainly of silicified, massive haematite with nests of goethite and veins and films of copper carbonates and oxides. Oxidation and leaching has been recognized to a depth of 70 m. Supergene-enriched sulphide with covellite and chalcocite is present between 70 and 90 m. Below 90 m fresh hypogene sulphide has generally been intersected. The Areachap massive sulphide deposit is probably of syngenetic origin and formed subaqueously from hydrothermal or gaseous solutions. It seems unlikely that near-surface extensions or additional bodies will be located in the Copperton- Areachap Formation north of the Orange River. However, there is a possibility of finding extensions to the present body by deep drilling.
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Mineral Deposits of Southern Africa, 2, 1539-1545

A basic to ultrabasic, intrusive, copper-nickel sulphide-bearng was discovered during an airborne electromagnetic survey, on the farms Jacomynspan and Hartebeestpan, located in the Kenhardt District of the Northern Cape Province. The body, primarily a steeply dipping, differentiated, tremolite schist dyke together with some serpenti nite, has a strike length of approximately 5 000 m. The dyke intrudes quartz- feldspar-biotite gneiss of the Namaqualand Metamorphic Complex. Sulphide mineralization occurs predominantly in the upper por tion of the dyke-like body and consists mainly of disseminated pyr rhotite, pentlandit, and chalcopyrite, averaging between 1 and 3% total sulphides. Higher-grade sulphide diseminations (up to 20% total sulphides) occur in units of nono-schist-tose hypersthenite within the tremolite schist. The in sityu tonnage and grade poten tial of the portion ofd the body occuring on the farmn Jacomynspan has been estimated at 114 Mt to a vertical depth of 900 m, at a grade of 0,25% nickel and 0,17% copper. Preliminary appraisal studies indicate that the body is not economically viable at present due to its low grade and near vertical attitude which would necessitate underground mining.
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Mineral Deposits of Southern Africa, 2, 1547-1552

The iron-copper-silver bodies of the Lutzputs area in the Gordonia District of the northern Cape Province occur as impersistent, narrow, shear-controlled veins in the amphibolite facies rocks of the Namaqualand Metamorphic Complex. Locally they grade into quartz veins which show pervasive green staining and secondary, hydrated, copper arsenides and chlorides. The steeply dipping, north-north-east-striking, magnetite-hematite bodies, which at surface have maximum dimensions of 400 x 6 m, extend to a minimum depth of 150 m, but probably do not persist below 300 m. The sulphide mineralization is generally confined to the sheared portions of the magnetite-hematite veins which are associated with propylitic alteration of the wall rocks. Veinlets and disseminations of sulphides also occur in parts of the shear zone where no iron oxides are present. The sulphide minerals are fine-grained and are not usually visible macroscopically. Microscopic examination suggests the following paragenetic sequence: magnetite, manganese oxide, arsenopyrite, pyrite, pyrrhotite, freiburgite, chalcopyrite, sphalerite, bismuthinite, pyrargyrite, and gold. Hematite formed penecontemporaneously with magnetite. Chalcocite, bornite, and digenite are present and represent products of secondary enrichment. Bench scale flotation tests showed that both the copper and silver contents of the ores are amenable to concentration with approximately 95 to 97 per cent of the copper and 84 to 86% of the silver reporting in the rougher concentrates which represent between 14,2 and 17,2 mass per cent of the feed. These concentrates analysed between 11 and 13% copper and 556 and 623 g/t silver. The veins, which are considered to be hydrothermal in origin, are too small and irregular to be commercially exploited under current economic conditions.
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Mineral Deposits of Southern Africa, 2, 1553-1558

Six quartz-tourmaline vein zones cut Proterozoic medium- to high-grade metamorphosed sedimentary and volcanic rocks preserved in a tight synform and intruded by anatectic granites. Exploration has proved a resource of 2,5 Mt in the major vein zone. Wolframite, scheelite and cassiterite are the ore minerals with quartz, fluorite and tourmaline gangue. Minor molybdenite, magnetite, haematite, ilmenite, and chalcopyrite are also present. Wolframite is intergrown with, and commonly replaced by, scheelite, while cassiterite often has magnetite inclusions. Mineralization is zoned. Cassiterite and pervasive tourmaline-rich wall rock alterations predominate in the east. Tourmaline and fluorite are closely related with the ore minerals. If the boron and fluorine are from a volcanic source then a remobilized exhalative genesis is possible. However, dewatering of "specialized" tin-tungsten-bearing granites may be a better explanation for the geochemical association.
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Mineral Deposits of Southern Africa, 2, 1559-1565

Calc-alkaline volcanic and plutonic rocks with distinctive geochemical, metamorphic, and geochronological characteristics, constitute the Richtersveld Province. In the vicinity of the Lorelei copper prospect, the calc-alkaline volcanic assemblages of the Orange River Group include basic lavas (basaltic-andesite and andesite), intermediate lavas (dacite), acid lavas, pyroclasts, and minor sedimentary rocks. These volcanic rocks are intruded by granodiorite, leucocratic granite, and aplite which are components of the Vioolsdrif Suite of calc-alkaline plutonic, granitoid rocks. Leucogranite constitutes a minor phase of the Vioolsdrif Suite and is the main carrier of disseminated and vein-type chalcopyrite and molybdenite mineralization at the Lorelei copper prospect. The mineralization is associated with sericite-pyrite and K-feldspar-biotite alteration assemblages. Weathering and supergene alteration of chalcopyrite has given rise to malachite staining which is to be seen in shears, quartz veins, and on joint planes. It is concluded that the Lorelei copper deposit is similar to, although considerably older than, the plutonic-type of porphyry copper deposits which are developed in the Canadian Cordillera.
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Mineral Deposits of Southern Africa, 2, 1567-1585

The Haib porphyry copper-molybdenum prospect is developed in the undeformed, low-grade metamorphic calc-alkaline volcanic and plutonic assemblages constituting the Richtersveld Province. The oldest rocks in the vicinity of the Haib prospect comprise dacitic, andesitic, rhyolitic, and acid tuffaceous volcanics. These extrusive volcanic rocks are intruded by a cogenetic suite of plutonic rocks, including granodiorite, adamellite, leucogranite, and the metal-bearing quartz-feldspar porphyry, forming the Haib porphyry stock. The distribution of silicate alteration assemblages on a regional and local scale have been examined. Alteration patterns on a regional scale are similar to the classic porphyry model in which a central potassic core (Haib porphyry stock) is surrounded by phyllic and prophylitic alteration haloes. The main zone of mineralization occurs within the Haib porphyry stock where a zone of moderate to intense phyllic alteration overprints and is superimposed on the earlier potassic alteration which affected the entire Haib porphyry stock. Two phases of alteration and mineralization have been identified. The early phase is characterized by potassic alteration together with chalcopyrite-molybdenite-pyrite mineralization, while the late phase is represented by phyllic alteration and chalcopyrite-pyrite mineralization. Clay mineral assemblages and low-sulphur sulphide assemblages such as bornite, covellite, and digenite developed under low temperature, late stage hydrothermal activity. It is concluded that multiple events of tectonism, intrusion, alteration, and mineralization were more or less superimposed on one another to produce the Haib copper prospect which represents the integrated effect of these processes.
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Mineral Deposits of Southern Africa, 2, 1587-1591

The Marinkas Kwela porphyry molybdenum prospect occurs within the Tatasberg Complex: one of the Kuboos-Bremen line of intrusions composed mainly of alkali-rich rocks and subordinate carbonatites of Cambrian age. Available information suggests that the mineralization is hosted entirely by alkali granite which is partially surrounded by syenite. The prospect is characterized by pronounced hydrothermal alteration consisting predominantly of quartz, sericite, carbonate, and pyrite. A poorly developed chlorite-epidote-carbonate outer zone is also present within the prospect area. Anomalous values of molybdenum, copper, lead, and zinc define a partly annular mineralization distribution pattern over the prospect.
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Mineral Deposits of Southern Africa, 2, 1593-1607

The Rosh Pinah zinc-lead sulphide deposit occurs in the south-western part of South West Africa/Namibia close to the Orange River. Production started in 1969 and approximately 420 000 t are now treated annually. The deposit is stratabound in arkosic and quartzitic rocks of the late Precambrian Rosh Pinah Formation which forms part of the lower sequence of the Gariep Complex. Acid volcanic components are important in the Rosh Pinah Formation. The rocks of the Gariep Complex, which locally overlie the Rosh Pinah Formation, belong to the Hilda and Numees formations. The basement to the Gariep Complex comprises rocks belonging to the Orange River Group, Vioolsdrif Suite and Namaqualand Metamorphic Complex. Probable stratigraphic equivalents of the Rosh Pinah Formation away from the type area are indicated and a subdivision and re-naming of parts of the Hilda Formation to conform with these concepts are suggested. The rocks of the Gariep Complex have been affected by several phases of deformation with the main structural trend varying from due north to north-north-west. The ore bed consists of a well-bedded to massive carbonaceous cherty zone, in places grading into argillite, various carbonate-bearing rocks, lenses and bands of massive sulphide (mixed pyrite, sphalerite, galena), argillite, and intercalations of generally poorly mineralized quartzite. Barium-rich carbonate is an important constituent of parts of the ore bed. In contrast to the hanging wall quartzite, which is generally unfractured, the quartzite underlying the ore bed is fractured, silicified, and. in parts, traversed by sulphide veins. A broad spatial relationship exists between the extent of footwall brecciation and the intensity of mineralization. A distinct structural control of the well-mineralized parts of the ore zone is evident. The deposits are about 800 to 1100 Ma old and are regarded as syngenetic with the associated sediments, with an underwater fumarolic source for the major constituents of the ore zone.
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Mineral Deposits of Southern Africa, 2, 1609-1627

A number of small leucogranite or alaskite bodies intrude the Modderfontein augen gneiss on the farm Nooitgedacht, south-west of Springbok. These intrusions, correlated with the Kweekfontein Granite of the Spektakel Suite, are anomalously enriched in uranium and thorium, and certain of them have been assessed as potential low-grade deposits. The leucogranites are highly differentiated and are characterized by a pervasive alteration which has sericitized the feldspars and propylitized the biotite. Alteration was probably of a deuteric nature, associated with the late magmatic-early subsolidus stages, and was neither a low-temperature, open system event, nor was it related to regional retrogressive metamorphism. The leucogranite bodies have I-type characteristics and appear to have been derived by partial melting of lower crustal material. Typical depleted lower crust is ruled out as a source, however, because of the necessity to markedly enrich the leucogranite magma in elements such as K, Rb, U and Th. Scatter in Rb-Sr isotope ratios for the Nooitgedacht alaskites indicates that the source may have been heterogeneous and/or anomalously fertile in certain selected elements. In addition, a component of scatter was probably introduced during the extensive alteration of the rocks.
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Mineral Deposits of Southern Africa, 2, 1629-1649

A number of small leucogranite or alaskite intrusions in the Namaqualand Metamorphic Complex south-west of Springbok contain anomalously high concentrations of uranium and thorium. Detailed, quantitative fission track micro-mapping has indicated a three-fold uranium distribution pattern:
1. uranium in primary sites represented by biotite and magnetite as well as a suite of accessory minerals including allanite, zircon, apatite, and other complex, monazite-like, silico-phosphates of calcium and the light rare earth elements;
2. uranium in sites created during deuteric alteration and represented by phases such as chlorite, epidote, ilmenite, manetite, and other titanium-rich alteration products; and
3. in secondary sites, particularly in weathered surface samples, where beta-uranophane is developed or uranium is associated with ferruginous oxide/hydroxides in micro-cracks and intergranular pore spaces.
Uranium mineralization in the leucogranites is related to processes which involved the generation of a magma at lower crustal levels, the upward movement of the magma to fairly shallow levels such that significant differentiation occurred, and prolonged interaction between an attendant igneous vapour phase and the rock-forming minerals. The leucogranites are enriched in uranium because this element was retained within the system, rather than being removed and concentrated into extraneous hydrothermal veins, breccias, or pegmatites.
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Mineral Deposits of Southern Africa, 2, 1651-1662

Confined to a belt approximately 450 km long and between 15 and 30 km wide, and extending from near Vioolsdrif in the west via Kakamas to Putsonderwater in the east, the pegmatites of the North-western Cape Province are part of the Namaqualand Metamorphic Complex. These pegmatites form bodies that range in shape from thin veins, a few centimetres wide, to dykes and irregular masses more than 3 km in length and over 100 m wide. Two general types of pegmatite are present, namely homogeneous and inhomogeneous. The homogeneous type cannot be divided into units of contrasting mineralogy and texture and commonly do not yield any minerals of economic importance. Inhomogeneous pegmatites show some degree of systematic arrangement of their constituents and are classified into simple and complex pegmatites, according to their economic mineral content and degree of complexity of internal structure. The cores of the larger simple pegmatites, generally comprised of three, but never more than four zones, usually consist of quartz and microcline-perthite and are generally suitable for the production of feldspar. Complex pegmatites have three or more zones, commonly associated with replacement bodies and fracture fillings, and are generally producers of beryl, muscovite, lithium ores, tantalite-columbite, and bismuth minerals. Descriptions are given of eight major pegmatites containing substantial reserves of feldspar (Noumas I, Swartkop, Marchand, Sidi Barrani and Angelierspan II), mica (Noumas I and Straussheim I), and beryl (Angelierspan I). According to production statistics for the period 1975-1979, the pegmatite field produced approximately 30 percent of the total quantity of potassium feldspar used in the ceramics industry in South Africa, about 10 percent of the mica consumed by the paint and insulation industry, all of the beryl exported as well as minor quantities of spodumene, tantalite-columbite, bismuth minerals, and rose quartz. It is concluded that with only a few of the
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Mineral Deposits of Southern Africa, 2, 1663-1669

The deposits were discovered by a regional geochemical survey and subsequently defined by diamond drilling and underground exploration. Extensive ferruginous and siliceous gossans overlie the three primary deposits. The economic sulphides are confined within a stratiform mafic sill enclosed in highly folded and metamorphosed Precambrian metasediments. The dominant sulphide is pyrrhotite, with pentlandite and chalcopyrite the main sources of nickel and copper respectively. Although the mineralization appears to be isochronic the subsequent remobilization due to folding and metamorphism has resulted in a structurally controlled ore body. Early interpretations of the structure show a major overturned anticline, with basement rocks exposed in the core. The Selebi, Selebi North, and Phikwe deposits were originally described as isolated ore bodies 7 Km apart, however, back analysis of exploration data and the subsequent drilling programme have provided a detailed stratigraphy resulting in a re-interpretation of the regional structure. The re-definition inverts the succession and postulates that the structure is dominated by a major refolded synform. In 1983 diamond drilling confirmed the re-interpreted structure, outlining large areas of potential ore available to the mining complex.
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Mineral Deposits of Southern Africa, 2, 1671-1688

The Messina copper deposits in the Central Zone of the Limpopo Belt are of hydrothermal origin and originated at shallow depth. The ore bodies are of varying shape and consist of hydrothermal replacement bodies generally conformable to the layering of the gneiss, pipe-like breccia bodies exhibing collapse features and associated mineralized fractures and fissures. The structural relations point to an overall control by wrench fault tectonics at the site of ore deposition. The individual mining areas are situated on fault splays along a branch of a large fault, preferentially in areas where the fractures cut the contact between granitoid gneiss and thick beds of metaquartzite. The shape of individual bodies is influenced by an interplay of fold structure, fracturing, and lithology. The only metal of economic value is copper. It is found as chalcopyrite, bornite, and chalcocite. Chalcopyrite tends to be found along the periphery of ore bodies and is replaced gradually by bornite, chalcocite, and native copper towards the centre and downwards. The alteration sequence of the host rock follows the zonation of the sulphides by a general increase in hydration of silicate minerals, leaching of quartz, and the development of albite, zoisite, and epidote, leading to complete destruction of the host rock. The wrench fault and associated fractures developed in stages over a prolonged period. Ore deposition and host rock alteration likewise must have taken a long time. The time and the source of the mineralization are controversial. It has been postulated that the deposits are genetically linked with hidden alkaline intrusive rocks of late Karoo age. Recently published fluid inclusion studies and oxygen isotope data point to convective cells of meteoric water as the mineralizing agent for the closing stage of the mineralization. The cells are thought to have been active during the late Karoo or early Waterberg volcanic period.
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Mineral Deposits of Southern Africa, 2, 1689-1694

Chromite mineralization at Sithilo occurs in an obducted body of serpentinite within the northern portion of the Natal sector of the Namaqua-Natal mobile belt. The low alumina, locally metallurgical grade chromite is typically podiform in character and is considered to represent a Precambrian equivalent of an alpine-type, ophiolitic chromite deposit.
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Mineral Deposits of Southern Africa, 2, 1695-1708

At least six substantial Ti-magnetite-rich layers are present in the gabbroic rocks of the Mambula Complex. The individual layers vary between 1 and 5 m in thickness, but are rarely pure and contain between 10 and 30 volume percent of silicate phases. The ores are medium grained and consist largely of polygonal crystals of Ti magnetite together with lesser amounts of granular ilmenite and pleonaste. The silicates consist largely of plagioclase and clinopyroxene with lesser amounts of hypersthene. Well-defined complex corona structures are developed around the margins of the silicates at places where they are in contact with opaque oxides. The Ti magnetite is characterized by a wide variety of ilmenite and pleonaste micro-intergrowths, the development of which is described in terms of modern exsolution theory. The textures of the ores are consistent with their having undergone extensive modification as a result of heating at elevated temperatures of the amphibolite facies during the 900 to 1 200 Ma Namaqua-Natal regional metamorphic event. The Ti-magnetite ores are characterized by both moderate TiO2 (9,4-16,3%) and V2O5 (0,5-0,8%) contents while their Fe content is variable (38-55%). The low values reflect the presence of significant amounts of silicate impurities. The ores are amenable to beneficiation by virtue of their grain size, simple grain boundary relationships and the presence of abundant granular ilmenite. Beneficiation will yield an ilmenite concentrate (50,4-52,9% TiO2) and a Ti-poor (3,0-8,0%) magnetic concentrate containing approximately 1,1 percent V2O5. The economic potential of the deposit is constrained by the small size of the igneous intrusion and moderate TiO2 and V2O5 contents. The nature and occurrence of the ores is consistent with their having formed by fractional crystallization processes during the later stages of crystallization of a mafic magma from which the Mambula Complex crystallized.
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Mineral Deposits of Southern Africa, 2, 1709-1717

Northern South West Africa Namibia contains a great variety of mineral deposits, ranging from volcanogenic-exhalative deposits about 2 000 Ma in age, to Cainozoic uranium and diamond occurrences. However, chromium, nickel, and platinoid mineralization is virtually absent. The distribution of copper, tin, tungsten, and uranium deposits of different ages define metallogenic provinces. The strong east-north-east-west-south-west tectonic grain, and to a lesser extent a north-north-west-south-south-east direction, has influenced the geology and distribution of mineral deposits throughout most of the geological history of the country, but reached its maximum expression during the Pan-African event.
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Mineral Deposits of Southern Africa, 2, 1719-1723

The Kopermyn copper deposit is situated in north-western South West Africa\Namibia near the town of Outjo. It was mined intermittently between 1953 and 1975 and production during this period is estimated to have been approximately 100 000t of ore with an average grade exceeding 2 per cent copper and 10g\t silver. Copper sulphide mineralization is hosted in hydrothermally altered, rhyolitic volcanic breccia of the Khoabendus Group (Lower Proterozoic). It is surmised that much of the original deposit was removed by erosion in pre-Damara times and that the present deposit is the remains of stringer ore in an alteration pipe adjacent to a volcanic vent. An analogy is drawn between the morphology of the Kopermyn deposit and that of Archaean volcanogenic base metal sulphide deposits of Canada.
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Mineral Deposits of Southern Africa, 2, 1725-1738

The Klein Aub Copper Mine contains approximately 6 Mt of ore at between 1 and 2% copper and 50 to 100 g/t silver. The copper mineralization is stratabound, confined to a clastic sedimentary succession with no associated volcanic rocks. These sediments belong to the Klein Aub and Doornpoort formations, are Late Proterozoic in age and form part of a north-east-trending zone of molassic, red bed deposits on the southern foreland of the Damaran Orogenic Belt. Copper sulphide mineralization is common in the Klein Aub and Doornpoort formations, but the Klein Aub Mine is the only economic deposit in this zone at the present time. Sediment facies analysis in the Klein Aub area indicates deposition on a broad alluvial fan surface and in marginal lacustrine environments in response to regional basement uplift. Two transgressive and one regressive lacustrine episodes are identified, intercalated with alluvial fan conglomerates and sandstones. The association of red beds and possible evaporitic minerals and the correlation of sedimentary class types with exposed basement rocks at Klein Aub, indicate a predominance of mechanical over chemical weathering, suggesting that deposition took place in semi-arid to arid climatic conditions. The Klein Aub deposit consists of six to ten disseminated, zoned, sulphide bodies in reduced clastic sediments of lacustrine origin. More specifically the copper is confined to the first reduced sediments of the initial lacustrine transgression and is specially related to finely bedded laminites. The mineralized horizons rest adjacent to a thick conglomeratic unit which represents a zone of major sediment and water discharge on the alluvial fan. This association, which is recognized elsewhere in the Klein Aub and Doornpoort formations, suggests a relationship between copper and alluvial fan sediment plus surface and groundwater discharge. Further evidence of a syngenetic origin is implied by the coincidence of lacustrine palaeocurrent directions and the orientation of copper ore shoots. Lead isotopic studies of trace lead in sulphides and whole rock lead from mineralized horizons and basement rocks suggest that the sedimentary lead, and by inference the copper, is basement-derived. Sulphur isotopic data point to sulphide formation during diagenesis in response to bacterial action and organic decay. The sulphur source could be from either basement or magmatic-derived sulphate. The evidence for fractionation of sulphur isotopes and the interstitial nature of the copper sulphides rules out a detrital particulate sulphide origin. A model for ore genesis of the Klein Aub copper deposits is proposed. A period of copper release and concentration of a basement copper source during semi-arid to arid weathering is envisaged. Subsequent uplift and erosion led to the transport of copper initially as copper sulphate and later as fine malachite particles in the suspended sediment load of alluvial fan distributaries. The deposition of detrital malachite at lake margins adjacent to zones of major sediment and water discharge is envisaged, with further concentration by lacustrine currents. Bacterial action and the breakdown or organic matter during diagenesis led to the formation of sulphides and copper fixation. The zonation of copper and iron sulphides is considered to reflect the original malachite distribution within the ore horizons.
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Mineral Deposits of Southern Africa, 2, 1739-1754

Copper mineralization in the Witvlei area, South West Africa/Namibia occurs in disseminated, zoned sulphide bodies with grades of 0 to 2% copper and a maximum of 30 ppm silver. The copper mineralization is confined to the clastic sedimentary Late Proterozoic Doornpoort Formation, with no associated volcanic rocks. These deposits form part of a north-east-trending zone of molassic red bed sediments on the southern foreland of the Damara Orogenic Belt. Copper is common within this zone and is related to lacustrine sediments at Klein Aub, Kagas Noord, and Lake Ngami (Botswana) and to playa deposits at Witvlei, Okasewa, and Kojeka. Doornpoort Formation sediments in the Witvlei area are dominated by red bed alluvial fan conglomerates and sandstones with rapid lateral facies changes to playa, aeolian, and lacustrine deposits. The sequence has an apparent thickness of 11 Km and rests unconformably on mineralized basement. The thick, laterally impersistent nature of the Witvlei Fan suggests deposition from a narrow fan feeder zone in response to localized uplift. The association of red alluvial fan and aeolian sandstone suggests deposition in a semi-arid to arid climate. Copper mineralization is confined to marginal and distal playa deposits which form the first reduced sediments of the sequence. The regional association of alluvial fan conglomerates and copper mineralization suggests a similar source. Preferential concentration of copper on the western margin of the Witvlei Fan, adjacent to lacustrine sediments, implies a palaeo-drainage control. The diagenetic association of albite and calcite in alluvial fan sandstones is reflected by the occurrence of albite, calcite, and chalcopyrite intergrowths in adjacent reduced playa deposits. The interstitial nature of sulphides, the replacement of diagenetic pyrite framboids by copper sulphides, the presence of sulphide overgrowths, and the association of copper minerals and authigenic diagenetic silicate and carbonate phases point to a diagenetic copper origin. Sulphur isotopic evidence suggests that copper and iron sulphides were produced by bacteriogenic reduction of groundwater sulphate in a closed fractionation system during diagenesis. A model for ore genesis is proposed involving a period of copper release and concentration in provenance rocks during low latitude semi-arid to arid weathering. The subsequent uplift and erosion resulted in copper transportation dominantly in aqueous solution (as copper sulphate) with the concentration of copper-bearing solutions and detrital particles in topographic lows. Copper was fixed as sulphide in reducing playa sediments during diagenesis.
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Mineral Deposits of Southern Africa, 2, 1755-1760

The Matchless cupreous pyrite deposit, which is located in central South West Africa/Namibia, is a producer of copper and pyrite concentrates. Stratigraphically, it is closely associated with the amphibolitic Matchless Member (765 Ma old) which lies in the upper part of the Kuiseb Formation of the Damara Sequence. The Matchless Mine Sequence includes sericitic quartzite, biotite-sericite schist, amphibole schist, and amphibolite with lenses of magnetite-bearing quartzite. Amphibolites of the Matchless Member and the Matchless Mine Sequence are an ortho-amphibolite suite derived from oceanic tholeiitic lavas. Regional metamorphism to amphibolite facies was accompanied by three phases of deformation. The deposit consists of a footwall zone of stratabound pyrite mineralization and of three chalcopyrite-bearing copper ore shoots which transgress the upper units of the Matchless Mine Sequence. Pyrite mineralization is coarsely disseminated to massive within a sericite quartzite unit. Pyrite-chalcopyrite mineralization ranges from banded to massive in habit and is principally localized in structures generated by the second fold phase. Important pyrite-chalcopyrite mineralization also occurs within magnetite-bearing quartzite lenses in the upper amphibolite unit. The Matchless deposit is an example of the cupreous pyrite type of volcanogenic base metal sulphide deposits. Iron and copper (and minor zinc) sulphides are considered to be primary components of siliceous exhalites deposited on a sea floor. Regional metamorphism and tectonism has recrystallized much of the pyrite while chalcopyrite has, in general, migrated into favourable structural loci.
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Mineral Deposits of Southern Africa, 2, 1761-1787

The Tsumeb ore body is a polymetallic, pipe-like deposit located within the moderately folded, predominantly dolomitic succession of the Otavi Group of the late Precambrian Damara Sequence. Past ore production and present reserves total 22 Mt at an average grade of 11,9 per cent lead, 4,8% copper, and 4,3% zinc. The deposit also contains economically important silver, cadmium, germanium, and arsenic. The pipe is presently known to a depth of 1716 m and is vertically zoned in respect of total and relative metal abundance, ore mineralogy, and rock alteration. The pipe structure, which is sited on a narrow zone of folding, is defined by the distribution of mineralization, dolomite breccia, feldspathic sandstone (formerly termed pseudo-aplite), rock alteration, and by arcuate fracturing. The sandstone, distributed in variable amounts through the entire known vertical extent of the pipe, is correlated with the arenaceous facies of the Tschudi Formation, which disconformably overlies the Otavi Group. Two main breccia types, both formed by solution collapse, are present in the pipe locus. The origin of one type is attributed to solution by circulating meteoric water of folded, cleaved, and fractured dolomite above and below the North Break, a prominent conformable aquifer in the dolomite sequence. The subterranean solution channel eventually breached the floor of a basin in which deposition of the Tschudi Formation was in progress, thus allowing influx of mainly arenaceous sediment into cavities and parts of the breccia. Solution by ascending hydrothermal fluids, which also effected intensive rock alteration, was mainly responsible for the other type of collapse breccia. This event also induced arcuate collapse fractures in breccia and adjoining bedded dolomite into which unconsolidated arkosic sand was injected. Calcitization within the pipe extended upward to 570 m below present outcrop, reaching maximum intensity at about 1120 m depth. Farther down, silicification was the predominant alteration type. Regional deformation was active during evolution of the pipe and mineralization was synchronous with waning tectonism. The hypogene ores are of the epigenetic, hydrothermal, replacement, and fracture-filling type. The main ore minerals are galena, tennantite, sphalerite, chalcocite, bornite, and enargite, together with widely distributed, but erratic sulphides and sulphosalts of Ge, Ga, V, Sn, and W. Massive ores are concentrated mainly at the periphery of the deposit and in places as mantos in adjoining bedded dolomite, while in the deeper part disseminated and stringer ores contribute appreciably to the metal content. Secondary ores are of economic importance down to about 300 m depth and also from 750 to 1 160 m. The deep oxidation zone is related to the North Break aquifer. The indicated age of the deposit is 550 to 580 Ma and preliminary data show that primary mineralization occurred at a maximum temperature of 230 to 250°C under 700 bar pressure. The common ore sulphides have a relatively homogeneous spread of δ34S values with a mean δ34S of +20‰.
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Mineral Deposits of Southern Africa, 2, 1789-1805

The Kombat copper-lead-silver ore bodies comprise epigenetic, hydrothermal and metasomatic replacement and fracture-fill deposits hosted within relatively unmetamorphosed dolostone of the H ttenberg Formation, the youngest formation of the Upper Proterozoic Otavi Group of the Damara Sequence in South West Africa/Namibia. Mineralization is spatially associated with a regional disconformity between dolostone and younger slate, with discrete zones of penetrative deformation and with intruded bodies of feldspathic sandstone on the northern flank of the regionally extensive Otavi Valley synclinorium. Galena, chalcopyrite, bornite, and supergene chalcocite occupy a variety of loci including the matrices of tectonic and sedimentary breccias, calcitized dolostone, lenses of sandstone, shears, dilation fractures, and net-vein fractures derived through hydraulic fracturing.
Compositionally layered assemblages of magnetite, hausmannite, hematite, barite, calcite, tephroite, alleghanyite, and pyrochroite, surrounded by metasomatic aureoles, occur within steep zones of tectonic transposition at many of the centres of mineralization. These layered iron-manganese bodies are analogous to metamorphosed, volcanic exhalative deposits in respect to mineral layering, mineralogy and chemistry. The hypogene sulphides are, with the exception of minor epithermal veins, syntectonic, but the layered iron-manganese mineral assemblages may have had a precursor in the form of bedded iron and manganese carbonates and hydrous oxides. Rock alteration is ubiquitous. Broad zones of pervasive calcitization and manganese alteration flank the ore lenses and their root zones. Sandstone lenses display extreme kaolinization and sericitization. Preliminary studies indicate a homogenization temperature for fluid inclusions in gangue associated with early sphalerite at 300°C and a temperature range of 200 to 280°C for the main period of chalcopyrite-bornite mineralization. A magmatic affinity for the mineralization is supported by the sulphur isotope data (mean δ34S = -0,8‰) and by the association of the lithophile elements, Li, Be, and B, with some of the Kombat ores. Limited Pb-isotope data, radiometric dating of the Damaran orogeny, and several physical constraints indicate that the mineralizing episode at Kombat was related to the second Damaran tectono-thermal event, placed at between 550 and 570 Ma.
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Mineral Deposits of Southern Africa, 2, 1807-1818

Uranium-bearing granites, comprising both potentially economic deposits and source rocks for uranium deposits in duricrustal and sedimentary sequences, are confined chiefly to the mobile belts of Southern Africa and to the Cape granites emplaced during Late Precambrian times. The direct uranium potential of the mobile belts, i.e. the Damara, Namaqua-Natal and Limpopo Belts, decreases with an increase in the age of associated ensialic diastrophism. This review paper is thus mainly confined to the Damara Belt, although a brief discussion of the potential of the Namaqua Belt is presented. Aspects of the Damara Belt that are discussed in detail, with particular reference to the occurrence of uraniferous granite, include regional tectonic setting, stratigraphy, structure, metamorphism and the patterns and origin of the uranium mineralization. Initial concentrations of uranium in basement and Nosib rocks have led, through ultrametamorphism and fractionation, to uraniferous granites of both economic and sub-economic grade. These granites, in turn, have acted as sources of secondary mineralization in overlying superficial calcareous and gypsiferous deposits. The Damara Belt thus provides a good example of multicyclic processes of ore formation. With regard to the uraniferous granites of Namaqualand it is concluded that the porphyroblastic gneisses and late-intrusive Concordia granites, although not of direct economic interest, represent major sources of uranium for secondary superficial deposits. Smaller bodies of late-phase differentiates associated with the Concordia granitic gneiss may themselves, however, represent potentially economically viable deposits.
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Mineral Deposits of Southern Africa, 2, 1819-1832

The Rössing uranium deposit is located in the Namib Desert approximately 70 Km north-east of Swakopmund, in South West Africa/Namibia. Although the presence of radioactive minerals has been known in the general area since 1910, it was only in 1956 that serious, but limited, prospecting was done by the Anglo American Prospecting Company on a radioactive anomaly known as SJ. In 1966 Rio Tinto South Africa commenced an intensive programme of prospecting on the same radioactive anomaly, followed by a programme of underground bulk-sampling and pilot plant test work which was only completed in March 1973. This investigation indicated the existence of a very large, low-grade deposit of uranium that could be mined by open pit methods, and also showed that the uranium could be recovered by means of conventional metallurgical processes. The uranium mineralization is associated with a syntectic alaskite that shows wide textural variations ranging from aplitic, granitic to pegmatitic, and that displays concordant, discordant, and replacement relationships to the heavily folded gneisses, schists, marbles, and limestones of the Khan and Rössing formations. The uranium-bearing minerals are mainly uraninite and its alteration products, and minor betafite. The Rössing ore-zone is extremely complex and requires considerable detailed mine planning to ensure effective grade control. The recovery of uranium is effected in a metallurgical plant using gyratory crushing, cone crushing, and rod-milling, followed by a sulphuric acid leach, ion exchange, solvent extraction, ammonia precipitation, and calcination.
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Mineral Deposits of Southern Africa, 2, 1833-1843

The Goanikontes uranium occurrence is one of the mineralized alaskite bodies which have been prospected in recent years in South West Africa/Namibia, in search of other "Rossing-type'' deposits. The uranium is associated with alaskite granite of Lower Palaeozoic age emplaced in metasediments along the western flank of a granite-gneiss dome structure, located in the axial zone of the Damara Mobile Belt. The geology and the mineralization show certain strong similarities with other alaskite deposits of the area, but some specific and local differences, such as the deep level of erosion, could account for the present sub-economic potential of this deposit.
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Mineral Deposits of Southern Africa, 2, 1845-1862

Pegmatites of the Uis type containing rare metals (Sn, Ta, Nb, Be, Li, Ti, Th, U and W) within the Central Damara Orogen of South West Africa/Namibia, are invariably preserved in narrow regional belts interpreted as graben features, probably active since Proterozoic times. The pegmatites are usually associated with leucogranitic plutons, or diapiric intrusions of the "S" type which have been emplaced into a particular stratigraphic zone characterized by diablastic schistose or quartzose metasediments containing tourmaline and cassiterite. Detailed mapping at Uis, and at other localities within the Damara Orogen, has demonstrated the regional importance of the nodular and spotted schists (knotenschiefer) as a guide to the location of areas favourable for mineralization. The results from such projects further indicate a need to consider a revision of the nomenclature and lithostratigraphy as applied to the rocks of the area. At least four distinct phases of leucogranite and pegmatite formation have been recognized, including: 1. Early-syntectonic; 2. Syntectonic; 3. Late-syntectonic; and 4. Post-tectonic. Although rare metals occur in each of the four phases, only the third, or late-syntectonic phase is important with regard to the development of large tonnage Uis-type deposits. These pegmatites represent open-space fillings of en echelon tension gashes, resulting from a shearing couple of regional nature, which evolved slowly over a considerable timespan. It is believed that the development of an area of high-tensile stress, necessary to produce tension fractures of the size of the Uis pegmatites, can be explained by triple-junction fracture geometry.
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Mineral Deposits of Southern Africa, 2, 1863-1873

The sedimentary deposits of the Karoo Sequence are of Gondwana age ranging from early Carboniferous to late Jurassic. The depositional environments range from oceanic through alluvial to aeolian and reach a maximum thickness of 10 000 m in the southern Cape. The alternating basic and acid lavas reach a maximum thickness of 12 000 m. The sediments display an evolving, gradational continuum in which stratigraphic boundaries are frequently vague or ill-defined. The tectonic framework of sedimentation and climatic variations has produced a unique association of sedimentary facies. The validity of well-established stratigraphic units is unquestioned, but a genetic approach to these depositional systems is utilized in order to emphasize the dynamic nature of the sequence. Although there are a number of mineral deposits in the Karoo the most valuable by far are the large reserves of coal.
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Mineral Deposits of Southern Africa, 2, 1875-1878

Most of the important coalfields of Southern Africa are dealt with in this set of papers and are presented by authors who are familiar with the coal geology of the areas they have described. Coal resources contained in the 28 coalfields of Southern Africa amount to some 159 000 million minable tons in situ and 80 800 million run-of-mine tons. These resources are, in many cases, in the indicated as opposed to the proven category and will change with time as further exploration is done and as mining techniques are improved to achieve higher opencast and underground extraction rates. Another important factor influencing the resource estimates is the improved design of large power stations which enables them to burn a lower grade of coal than in the past. Resource figures generally apply to coal with less than 50 percent ash. If lower grade coals can be utilized, the estimates will need revision. The above figures include 115 530 million minable tons in situ and 58 919 million run-of-mine tons for the Republic of South Africa. These are the latest estimates published by the Geological Survey (De Jager, 1983) and compare with the estimate of Petrick et al. (1975) of 81 000 million minable tons in situ to a depth of 300 m and 25 000 million extractable tons. Estimates for individual coalfields described in these papers may vary considerably from those in Table I due to differences in coalfields boundaries, exclusion of anthracite from individual Natal coalfields and, in some cases, more up to date and reliable information that has become available to the Geological Survey. Comprehensive estimates for Southern Africa are presented in Table I, which has been modified from De Jager's (1983) estimates for the Republic of Southern Africa and from the contributor's estimates for Botswana. The authors have included their own estimates for Swaziland, South-West Africa/Namibia and Zimbabwe.
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Mineral Deposits of Southern Africa, 2, 1879-1898

This paper discusses the origin, formation, and distribution of coals in Southern Africa and reviews the conditions prevailing in Southern Africa during Karoo times. A brief comparison is made between the coal-forming conditions during Permian times with those in Europe during Carboniferous times. This is followed by a synthesis of the major structural and tectonic features controlling the accumulation of Karoo Sequence strata on the ancient continental crust of Africa. A detailed account of the macro- and microfloral evidence is described in relation to the climatic developments in Africa during this period of time. Extrapolation of this evidence to present-day climatic belts suggests that during Karoo times Africa was vegetated by a series of major floral belts, akin to latitudinal vegetal zones, due to the drift of the continent through or across major latitudinal changes. Evolution is a secondary factor mainly affecting the plant groups during their major periods of expansion. Set within the framework of these climatic and vegetational developments, the age and correlation of the coal seams appear to range from Upper Dwyka/Lower Ecca through to Upper Ecca and Lower Beaufort in the lower Karoo sequences. The correlation of seams is initially based upon the major floral belts (zones), and subsequently upon a more detailed subdivision (subzones) based upon the association and evolutionary development of the primary or selected major elements representative of the stable upland parent flora. The latter forms are the indicators of major latitudinal climatic changes. This technique precludes masking of the major stable climax vegetation by numerically abundant, spore- producing, non-stratigraphically controlled, lower-order plants. A brief review of the sedimentological environments of the coal-bearing sequences in the Main Karoo Basin of Southern Africa follows. The developments of cyclothems during Mid-Ecca times (Vryheid Formation in the north-eastern sector of the Main Karoo Basin) suggest that the coals formed at the close of periods of sedimentation, when the prevailing sea-shore levels were at their lowest ebb. Linked to the prevailing vegetational and climatic developments of this period, the proposal is made that these cyclothems are predominantly the manifestation of a series of minor waning ice ages with their centres on high craton ground probably on the continent of Antarctica. A secondary effect of sedimentation on a continental shelf associated with local transgressions and regressions is recognized. However, the extent of the cyclicity in many Southern African Karoo basins suggests that a wider regional factor must have controlled this pattern of sedimentation. An example of the effect of ice ages on cyclothem development is drawn from cyclothems with similar features encountered in North America and Europe during Late Palaeozoic times. Crowell (1983) expressed the view that these occurred probably in response to the contemporaneous waxing and waning of ice sheets in Gondwanaland. The significance in recognizing widespread cyclothems lies in the fact that they could represent widespread chronostratigraphic events, thereby permitting correlation of strata on a reliable chronological framework over vast continental distances. The paper concludes with a brief review of the variations in the type of coal encountered in South Africa and the significance of establishing the quantities and qualities of coal reserves in terms of this continent's future energy requirements.
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Mineral Deposits of Southern Africa, 2, 1899-1921

As the countries of Southern Africa depend almost entirely on coal for their energy requirements, the remaining reserves need to be evaluated in greater detail in order to ensure optimum utilization. Furthermore, with imminent expansion into the international markets, the rapid evolution of new technological uses of coal, and the potential of obtaining multi-products from improved washing plants, it is also becoming important for Southern Africa to characterize and classify both raw coals and beneficiated products as efficiently as possible. In order to achieve this, it is necessary to choose parameters and classification systems suitable for coals of all types. Unlike the Carboniferous coals of Europe and the United States of America, those of Permian age in Africa (and other southern hemisphere or Gondwana countries) are highly variable in composition, rank, and mineral inclusions. In these circumstances, the conventional parameters originally devised for European and American coals are not always suitable. In order to present the current status quo, this paper reviews the conventional major classification systems presently in use internationally. Finally, a proposed adaptation of one of the most recent systems to fit Southern African coal types is presented.
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Mineral Deposits of Southern Africa, 2, 1923-1927

The coal deposits between Greylingstad and Sasolburg, including those immediately north of Vereeniging, fall within one coal province. This coal province is divided into the South Rand Coalfield and the Vereeniging-Sasolburg Coalfield. The latter coalfield consists of three basins, namely the Comelia, Coalbrook, and Sigma basins. The coal deposits are found in the Vryheid Formation of the Ecca Group. The latter is separated from the pre-Karoo rocks by the Dwyka Formation. The coal zone is up to 30 m thick and three coal units or coal zones are present. Generally, the coal deposits in the three basins are very similar in character and rank. The coal seams are thick and lie close to the Dwyka diamictite in deep glacially scoured valleys.
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Mineral Deposits of Southern Africa, 2, 1929-1937

The OFS-Vierfontein Coalfield, although a coal-producer since the early years of this century, and examined by several hundred boreholes, is apart from the immediate area of the only producing colliery (Vierfontein, 1978 production - 1,466 million sales tons), relatively unknown due to unsatisfactory core recoveries. Coal resources are estimated to be as much as 3 750 Mt in situ of which only about 65 Mt can be regarded as proven. The present upsurge of prospecting activity will undoubtedly increase this latter figure. The two coal seams present are relatively thin (average mineable thickness 1,8 m), are of uncertain areal distribution and are of poor quality (air-dried calorific value 14-22 MJ/kg). The variable, rugged, pre-Karoo hill and valley topography is responsible for coal-seam deposition generally being limited to valleys and plains, pinching out over hills.
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Mineral Deposits of Southern Africa, 2, 1939-1952

The coal-measures of the Orange Free State (OFS) Coalfield occur in postglacial Permo-Carboniferous sedimentary environments of the Karoo Basin. Pre-Karoo geology and palaeotopography are the overriding controls on sedimentation and coal distribution. The tectonic framework of the OFS Coalfield may be considered in terms of two structural blocks; a northern block comprising a series of ridges and valleys, curvilinear with respect to the Vredefort Dome, and a southern block dominated by the pre-Karoo horst-graben topography of the underlying early-Proterozoic successions. The more important coal-bearing sediments occur within the Vryheid Formation of the Karoo Sequence in paralic depositional environments which appear to have accumulated on a 70 km-wide, north-south-trending archipelago coinciding with intermediate palaeorelief formed by underlying Proterozoic rocks. The Vryheid Formation is, on average, 70 m thick in the major valleys of the OFS Coalfield. Sedimentation is cyclothemic in character and four regressive cycles are recognized. Each basinward progradation is separated from the following one by a major coal seam. The coal seams are named Dwyka, Bottom, Middle, and Top (Nos. 1, 2, 3 and 4), respectively, from the base upwards. Microlithotype analyses from the four main coal seams indicate a high percentage of inertodetrinite and semifusinite, indicating that much of the coal was oxidized at the peat stage and remained so during coal metamorphism. This feature could account for the poor quality and washability of OFS coal. The Dwyka and Bottom coal seams frequently coalesce to form very thick seams (> 20 m). These thick coals are restricted to paraglacial benches flanking elevated pre-Karoo topography, and to distal lagoonal settings barred from active marine sedimentation by longshore-drift sand-shoals. The Middle and Top coal seams, by comparison, are much thinner (1-4 m) and less widely distributed. They occur at medial and distal locations in deltaic and strandplain sediments of the Vryheid Formation. The vitrinite/inertodetrinite ratio is higher for Top Seam coals and consequently Top Seam quality is generally higher than for the other seams. The OFS Coalfield contains in situ resources of some 16 000 Mt of coal occurring within numerous discrete basins. Sixty percent of these resources are located below a depth of 200 m and some 20 percent below 400 m. It is estimated that approximately 40 percent of these resources have been adversely affected by post-Karoo dolerite intrusions. The high fusinite-inertinite content of OFS coal precludes successful beneficiation. Coal of this type might be used for the production of synfuels and for the generation of electricity by ESCOM.
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Mineral Deposits of Southern Africa, 2, 1953-1961

The South Rand Coalfield lies within a southerly trending basin situated between Heidelberg and Villiers in the Southern Transvaal, and contains a potential of 2700 million in situ tons of low-grade bituminous coal. The coal measures, where mined, are complex in structure, deep, faulted and pervasively intruded by dolerite, resulting in severe mining problems. The coal seams present vary from a composite seam, locally up to 25 m thick in the central part of the field, to several thinner individual seams which may be sub-economic by virtue of their thickness and quality. Amcoal's new Springfield Colliery is mining in the deeper part of the coalfield and supplies coal to the 1 200 megawatt Escom Grootvlei Power Station at a rate of about 3,5 Mt per annum. Of particular interest are the unconventional mining methods on trial at the colliery to optimize extraction rates from the highly variable coal measures.
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Mineral Deposits of Southern Africa, 2, 1963-1968

The Syferfontein Colliery, situated on the farm Syferfontein 293 IQ, Westonaria District, produced approximately 1 300 t of low-grade coal at the beginning of this century. The coal overlies a Dwyka fill within a doline - a collapsed underground river, in the floor of a Dwyka palaeovalley scoured into dolomites of the Malmani Subgroup. A succession of Ecca shales, which form apart of the West Rand outliers, caps the sequence. The doline has a minimum length of 1,5 km, a width of about 130 m, and a minimum depth of 135 m. Underground development revealed that at least in parts, the doline walls were vertical. The coal and shale succession within the doline is about 64 m thick and contains several thin coal seams. These seams dip steeply towards the doline centre and have faulted contacts with the adjacent dolomite.
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Mineral Deposits of Southern Africa, 2, 1969-1984

The Springs-Witbank Coalfield extends over a distance of approximately 180 km from the Brakpan/Springs area in the west to Belfast in the east and about 40 km in a north-south direction. The coalfield currently accounts for 53 percent of the country's coal production, including supplies used in generating 41 percent of the Republic of South Africa's electricity. Five major coal seams are present, which were deposited in glaciofluvial, deltaic, and coastal plain settings. Dolerite sills and dykes are abundant and have locally displaced the generally horizontal strata and burnt or devolatilized large volumes of coal. The author's estimates of coal resources in the five seams, on the basis of current mining practices, are 17 700 million mineable tons in situ and approximately 13 200 million run-of-mine tons of which some 8 500 Mt are mineable by opencast methods to a 50 to 60 m depth and some 4 700 Mt are mineable by underground methods. The quality of the coal in the central part of this coalfield is considered to rank among the best in the Republic in terms of high yield export quality steam coal. For this reason these coals constitute South Africa's most important coal resource.
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Mineral Deposits of Southern Africa, 2, 1985-1994

The Highveld Coalfield lies in the South-eastern Transvaal south of the Witbank Coalfield and extends from Nigel and Greylingstad in the west to Davel in the east, covering an area of approximately 7 000 km². Large-scale mining operations commenced in 1975 and three large collieries, with a fourth in the planning stage have been established. The production in 1979 was 12 Mt and it is expected to grow to 57 Mt by the end of the present decade. Following the retreat of the Dwyka glaciers which deposited diamictite the Karoo Basin was filled with sediments ascribed to deposition in shallow marine and fluviodeltaic environmental settings. These sediments, which constitute the Vryheid Formation of the Ecca Group, contain several economically exploitable coal seams. An estimate of the extractable raw coal resources in the Highveld Coalfield is 9900 Mt which is 19,4 percent of the Republic of South Africa's total mineable coal reserves of 5 100 Mt as determined by the Geological Survey Division of the Department of Mineral and Energy Affairs during 1980/81. The No. 4 Coal Seam contains approximately 80 percent of the extractable reserves in the Highveld Coalfield. Over most of the coalfield the No. 2 and 4 Coal Seams contain low- grade bituminous coal with ash contents varying between 20 and 35 percent and calorific values varying between 18 and 25 MJ/kg. Most of this coal is best suited to power generation and synthetic fuel production. In some local areas the No. 2 Coal Seam has good washability characteristics and a high-grade product with a calorific value of 27 MJ/kg is producible at yields in excess of 70 percent. In certain areas a high-grade product is obtainable from the No. 4 Coal Seam at relatively low yields. The No. 5 Coal Seam contains high-grade coal, but has very poor coking characteristics.
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Mineral Deposits of Southern Africa, 2, 1995-2010

The Eastern Transvaal Coalfield is situated between Carolina and Dirkiesdorp and includes the districts of Hendrina, Breyten, Davel, Ermelo, and Morgenzon. It is flanked by the Witbank, Highveld, Klip River, and Utrecht coalfields. The Eastern Transvaal Coalfield has not been as fully explored or exploited at the Witbank and other better known coalfields. The limited amount of data available has biased this account in favour of the northern and central parts of the coalfield. It is in these areas that eight of the ten active collieries and the majority of the now defunct mining operations are situated. The stratigraphy is typical of the coal-bearing margins of the Karoo Basin. The succession consists of pre-Karoo basement rocks overlain by Dwyka Formation diamictites followed by Ecca Group sediments (Pietermaritzburg, Vryheid, and Volksrust Formations) with limited occurrences of Beaufort Group sediments in the southern highland areas. The Dwyka diamictites and Pietermaritzburg shales are best developed further into the basin where they line the deeper pre-Karoo valley floors. The Vryheid Formation is present over the whole area and contains five major coal seams. These seams are named from E at the base, to A at the top of the formation. Ten lithofacies, including the coal, have been identified in the north and central areas of the coalfield. Vertical and lateral arrangements as well as petrophysical log patterns indicate that at least four major cyclothems occur within the Ecca Group, each of which has one or more coal seams associated with it. All four cyclothems exhibit a regressive phase where sedimentation occurred in fluviodeltaic environments, followed by a transgressive phase where sedimentation was typical of both marine and non-marine transgressive shorelines. The mining potential of the seams varies throughout the area but in general the C seam is the most prospective, although the B, E and occasionally the D seams attain a mineable thickness over limited areas. The general distribution of the upper seams is often restricted by present-day topography, while the development of the lower seams is controlled by the pre-Karoo topography. Structurally, the seams are flat-lying with a gentle south-westerly dip. Major faulting occurs with increasing frequency to the south of the coalfield. The displacement along these faults may be as great as 250 m. Faults are, almost without exception, invaded by dolerite intrusions. Dykes are common over the whole coalfield while sills appear to be more numerous towards the south. Eight major sills have been identified in the coalfield. The dolerite sills can have two significant effects on the mineability of the coal: they displace the seams and cause structural complications, and more seriously, devolatilization of the coal. The coals are usually bituminous and have the following average air-dried raw quality parameters: calorific value 24 MJ/kg; ash 23 percent; volatiles 26 percent; inherent moisture 3 percent; fixed carbon 48 percent and sulphur 1,2 percent. However, particularly in the south, large volumes of coal may be converted to low volatile "lean" bituminous or semi-anthracitic coals by their proximity of major intrusions. Other coals may be totally destroyed by burning due to pervasive dolerite intrusion. There were ten collieries in production and one power station (Camden) operating in this coal field in 1980. A lack of comprehensive data for much of the Eastern Transvaal Coalfield has made the calculation of coal resources difficult. It is, therefore, considered more realistic to quote the resources given by the 1975 "Commission of Inquiry into the Coal Resources of the Republic of South Africa", namely 5 468 Mt of in situ mineable coal.
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Mineral Deposits of Southern Africa, 2, 2011-2022

The Utrecht Coalfield of Northern Natal covers an area of 5 000 km² within the magisterial districts of Utrecht and Paulpietersburg. Coal was first produced in 1889 but although production has continued almost without interruption since then, the field has never ranked as a major producer in national terms. At the present time production amounts to some 3,5 million sales tons per annum, about 3 percent of South African total production. Four economic coal seams occur within the Vryheid Formation of the Ecca Group. These seams, the Coking, Dundas, Gus and Alfred, produce a range of coals from high rank low volatile anthracite to coking coal, the rank being dependent upon the absence or presence of dolerite sills in close proximity to the coal. Not only do these control the rank of the coal, but they are also the major structural element within the field. Faults with throws of up to 150 m have been measured where the intrusions transgress the coal zone. Dykes are common throughout the area but generally are not associated with major displacements of the coal seams. The coal resources tabulated in this paper amount to 664,2 million run-of-mine tons. These resources do not, however, include coal with a thickness of less than 0,60 m or coal at depths greater than 400 m. The only potential for significant additions to the tonnages quoted herein would be with the exploitation of such resources if ever it became economical to do so.
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Mineral Deposits of Southern Africa, 2, 2023-2032

The Vryheid Coalfield situated in north-eastern Natal began producing coal in 1898. Since that time this coalfield has occupied an important position in the South African coal-mining industry, as it has been a consistent producer of high-quality metallurgical coal and anthracite. The present production level of approx imately 6 million run-of-mine tons per year is likely to be maintained for some time in the future. The economic coal seams of the area, four in number, are contained within the Vryheid Formation (Middle Ecca) of the Ecca Group. These sediments are characterized by a series of coal-capped upward- fining cycles. The coatlield has been disturbed by the intrusion of a number of major dolerite sills which have transgressed the coal zone. These intrusions, besides affecting the structure of the field, have also had a marked effect on the quality and rank of coal present. The resources tabulated in this paper total some 221,6 million mineable in situ tons which may yield 170,3 million run-of-mine tons. At present production levels, the resources of the Vryheid Coal field are sufficient for another 25 years. It should, however, be noted that there is likely to be a reduction in quality over the remaining life of the field, as the best quality coals have largely been extracted. The best potential for additional resources lies in the exploitation of very thin but high-quality coal seams.
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Mineral Deposits of Southern Africa, 2, 2033-2045

The Klip River Coalfield of Northern Natal has been a major coal producer since the latter part of the nineteenth century. Although its relative importance in terms of total South African coal reduction has waned, the present production level of approx imately 5 million sales tons per annum is likely to be main tained for some time to come. Ecca Group sediments, within which the only two commercially exploitable coal seams of the area occur, outcrop over the entire area of the coalfield. Apart from some minor faulting, all tectonic disturbances can be ascribed to post-Ecca dolerite intrusions. These intrusions have not only affected the structure of the area, but have also had a marked effect on the quality and type of coal present in the field. The resources of the Klip River Coalfield amount to 1 600 Mt in situ or 1 200 Mt run-of-mine coal, enough to sustain present production levels for some 200 years. Exploration is still active in the coal field and while it is unlikely that any major new resources will be located, it is possible that extensions to existing reserve areas may be found.
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Mineral Deposits of Southern Africa, 2, 2047-2055

It is demonstrated that the coal seams and coal zones in the Springbok Flats, Waterberg, Soutpansberg, and Limpopo coalfields, with the exception of the stratigraphically lower mat coals in the Waterberg Coalfield, are lithologically consistently of a certain type, namely assemblages of interbedded and interlaminated bituminous bright coal and carbonaceous mudstone. However, sandstone appears interbedded with the bright coal and carbonaceous mudstone units in the eastern sector of the Soutpansberg field. In the Komatipoort Coalfield, as in the Waterberg Coalfield, the coal succession can also be divided into a lower and an upper zone, tentatively correlated time- stratigraphically with the two zones in the latter field. However, in the Komatipoort Coalfield the coal has consistently reached the anthracite stage of metamorphism and sandstone is there prominently associated, in the upper zone, with the anthracite and carbonaceous mudstone. The paper further suggests that the bright coal/carbonaceous mudstone assemblages of the region under review, together with the overlying massive grey mudstone, constitute a remaining portion of a "Beaufort Group" of sediments below a surface of erosion (a disconformity) of palaeohighs and palaeolows. Above the disconformity there is a group of sediments with subdivisions, in upward succession, in turn conforming remarkably well lithologically with the Molteno, Elliot and Clarens Sandstone Formations as known elsewhere. This suite of formations, with the overlying lava, was historically grouped, as stages, under the designation of Stormberg Series. The lower coal zones in the Waterberg and Komatipoort coalfields, in sandstones as host rock, are assigned by the author to the Vryheid Formation of the Karoo Sequence. In view of the intimate association between bright coal and carbonaceous mudstone in the region, a run-of-mine (raw) product from these coals will have to pass through industrial beneficiation plants for acceptable end product
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Mineral Deposits of Southern Africa, 2, 2057-2061

The Limpopo Coalfield, about 70 km west of Messina, is contained in a basin of Karoo rocks which straddle the boundaries of the Transvaal, Botswana and Zimbabwe in an arid and sparsely inhabited territory remote from any industrial activity. The first intensive prospecting was undertaken by the Anglo American Corporation in 1967 with the programme culminating in the sinking of a prospect shaft. Two exploitable coal seams, 1,6 and 1,2 m thick, are contained in a 10 m coal zone in the Vryheid Formation. The flat-lying seams occur at depths of 20 to 200 m and are conducive to exploitation by opencast and underground mining methods. Industries are confined to several large east-west dykes. The coal is interbedded with thin shale bands which can be separated by washing at a high relative density. The coal has to be crushed to a small size to liberate the high percentage of vitrinite from the finely disseminated mineral matter. Beneficiation and coking tests have confirmed that the clean coal is of high quality and has potential for being a good quality coke. The proven resources are 102 Mt of run-of-mine raw coal or 48 Mt of saleable washed metallurgical coal while the estimated potential of the field is 267 million run-of-mine tons or 125 Mt of saleable washed coal.
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Mineral Deposits of Southern Africa, 2, 2063-2069

The Molteno Formation of the Karoo Sequence comprises a northward-thinning wedge of dominantly clastic sediments which were deposited during Upper Triassic times. The coalfield extends from Aliwal North to Maclear in the Northeastern Cape Province. Two of the major coal seams are present in the Bamboesberg Member which is at the base of the Molteno Formation, the Indwe Seam occurs between 18 and 24 m below the Guba Seam which is developed at the top of the member. The Indwe Sandstone Member contains no coal and it is overlain by the Mayaputi Member which has, at its top, the only other important coal, the Cala Pass Seam. The overlying Quiba, Tsomo, and Loskop members contain no coals of economic significance. Mining commenced in 1877 and reached a peak between 1900 and 1904 with an average annual output of about 2 Mt. Production subsequently declined and operations ceased in 1948. The Tank of the coal varies from low volatile bituminous to anthracite. For coals washed at an S.G. of 1,75 the ash content averages about 26,8 percent, the calorific value ranges from 16,2 to 27,3 Mj/kg and the sulphur content is generally about 0,5 percent. The amount of mineable coal remaining, assuming a minimum seam thickness of 1 m and allowing for 2,7 Mt already extracted, stands at approximately 36,9 Mt.
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Mineral Deposits of Southern Africa, 2, 2071-2085

Very large resources of high ash medium calorific value coal have been indicated at several localities in Botswana. Exploration has been confined mainly to the eastern and southern flanks of the Kalahari-Karoo Basin that underlies over 60 per cent of the country and which is continuous with the Karoo Sequence of the Northern Cape Province, South West Africa/Namibia, and Zimbabwe. The best coal so far found occurs within the Morupule area where approximately 7 910 Mt of in situ coal have been identified. Limited prospecting indicates that coal of similar quality is present at Mmamabula, where drilling has provided estimates of resources of about 5 175 Mt. Areas north of Morupule have been examined on a reconnaissance scale, but the presence of numerous late- or post-Karoo intrusions and faulting make the areas less attractive for coal exploration. Along the southern flank of the Kalahari-Karoo Basin, in the Dutlwe and Letlhakeng areas, very large resources of high-ash bituminous coal have been found. Large-scale development of the located deposits will depend upon rapid improvement in the country's infrastructure.
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Mineral Deposits of Southern Africa, 2, 2087-2089

The Karoo basins of Zimbabwe contain numerous coalfields. However, only a few are presently viable. Seven depositional models are described for the purpose of providing ideas for future exploration. The models and their palaeogeomorphologic settings are as follows: (I) Basin-end shoreline plain; (ii) Basin-side shoreline plain or strip; (iii) Basin-confluence inner-side shoreline plain; (iv) Basin-embayment shoreline plain; (v) Palaeoisland-side shoreline plain; (vi) Palaeoisland-protrusion shoreline plain; (vii) Palaeoisland-embayment shoreline plain.
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Mineral Deposits of Southern Africa, 2, 2091-2098

Coal-bearing strata in Zimbabwe occur within the lower part of the Karoo Sequence (Ecca Group) in graben basins trending north-east-south-west and flanking the similarly orientated central portion of the Archaean Rhodesian Craton along its north-western and south-eastern edges. The majority of the coal resources are located within the 12 m-thick Wankie Main Seam, the basal 4 m of which is of coking coal quality. Five coal areas have been described in varying detail and inferred tonnages are stated for each area and for the country as a whole. In 1980 Zimbabwe's total inferred in situ coal resources were estimated at 26 650 Mt.
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Mineral Deposits of Southern Africa, 2, 2099-2104

There are five coalfields in the Wankie area of Zimbabwe where the Main Seam coal is exploited. Proximal to distal relationships are discussed in the light of sedimentary facies changes and of variations in the coal quality. The best quality coal is located at the base of the Main Seam, where approximately 3 m of "straight coking coal" occurs within a section 9,55 m thick. The seam wedges out against high ground in the south and south-west while its quality deteriorates rapidly, in a basinward sense, to the east, where offshore conditions existed. It is envisaged that the basal part of the Main Seam would have an in situ origin while the upper part comprises mainly drift coal. The ratio of vitrinite to reactive semi-fusinite sympathetically decreases from the base up.
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Mineral Deposits of Southern Africa, 2, 2105-2118

Extensive heavy-mineral deposits are described in which the concen tration of ilmenite, zircon, and to a lesser extent garnet, rutile, and monazite has taken place. A discussion of their geological set ting in the Vryheid Formation of the Northern Facies of the Per mian Ecca Group attempts to establish the apparent relationship of these littoral deposits to the nearby, well- documented, coeval outbuilding deltas. These deposits were laid down during the regressive stages of cyclic sedimentation by high-energy (storm) swash action on the foreshores of a large, shallow, microtidal inland sea. The resources of heavy minerals run into tens of millions of tons, but to date, they have defied commercial recovery. Chromite contamination in the Bothaville deposits, the state of alteration of the ilmenite, and the pervasion of the cementing alteration prod ucts, goethite and post-depositionally mobilized silica, have caused serious recovery problems. 'ne alteration also has the effect of causing excessive sliming losses during ore dressing. Chemical ana lyses emphasize the high degree of concentration in the deposits and the geochemical differ-ences between the various districts.
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Mineral Deposits of Southern Africa, 2, 2119-2134

Uranium is present in most Permo-Triassic basins of Gondwanaland. In South Africa it occurs in the Beaufort and Stormberg Groups in most parts of the Karoo Basin, but predominantly in the south-west. The Adelaide Subgroup of the Beaufort Group consists of at least four upward-fining megacycles reflecting tectonic pulses in the source areas to the south. Uranium occurs preferentially in the basal sandy members of each cycle, which were deposited under more reducing conditions because of rapid burial. "Tabular" and "ribbon" channel sandstones both contain uranium, but the mineralized lenses are commonly thicker, narrower and more continuous in the case of the latter. Braided-stream sediments with low overall uranium grades are present in the north-western part of the basin. The uranium occur in tetravalent form in the reduced zone and as hexavelant uranium minerals in the weathered zone. Molybdenum, copper, and arsenic are the main associated elements, with calcite as a common gangue mineral. Organic carbon acted as a reducing agent to precipitate the uranium. The latter was probably derived from volcanic material in the sandstones and also from the equivalents of the Namaqua-Natal basement granites of the southern source areas. Remobilization of the uranium into permeable zones during diagenesis led to the formation of ore-grade deposits, a process possibly hastened by the Cape Orogeny, which elevated the temperature of groundwaters in the area.
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Mineral Deposits of Southern Africa, 2, 2135-2139

The Matjieskloof uranium anomaly (GT-7) is situated on the slopes of Groottafelberg at the base of the Nuweveld Escarpment in the Fraserburg District of the Cape Province. It lies within, or immediately adjacent to, the Poortjie Member of the Teekloof Formation, Beaufort Group. The deposit is associated with a succession of fluvial tabular sandstones interbedded with red, purple, and green mudstones and siltstones. Mineralization (uraninite, coffinite with minor molybdenum) is of a URAVAN type and occurs as pods within abandoned loops of a meandering channel system. The geometry of the orebody suggests that coalescence between sandstones played a major role in the location of ore pods. It is proposed that a weak REDOX front developed in the sandstone body during the mixing of discrete oxidizing and reducing fluids at the time of coalescence. Free carbon within this weak REDOX zone controlled the fixing and preservation of the uranium.
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Mineral Deposits of Southern Africa, 2, 2141-2147

The DR-3 anomaly near Laingsburg, Cape Province, is unusual in that it occurs some 500 m lower in the stratigraphy than other known large sandstone uranium deposits in the lower Beaufort Group of the Karoo Sequence. Its discovery was the result of a regional exploration programme covering over 4 000 km² and involving airborne radiometric surveying, mapping, extensive drilling, and the excavation of a short adit. The deposit occurs in a discrete, linear, east- trending palaeochannel, within an upward-coarsening sequence interpreted as being part of a short-lived, rapidly prograding, delta lobe. The channel, which is considered to represent an abandoned distributary channel, supports two zones of mineralization, up to 12 m apart, each having similar geometry to that of the channel itself. Overall reserves of the two zones are estimated to exceed 11 Mt at an average grade of over 0,5 kg/t eU3O8, including a small reserve with a grade in excess of 3,0 kg/t eU3O8. Molybdenum values of up to 0,5 kg/t may occur, usually in the hanging wall of the uranium mineralization, the latter being comprised predominantly of uraninite. Mineralization is controlled primarily by channel geometry, but also by the presence of abundant organic detritus, and the coalescence of two major sandstone sub-units within the channel. The existence of several blind bodies of mineralization within the deposit emphasizes the importance of geological modelling and the limitations of surface or airborne radiometric techniques in the exploration for deposits of this nature.
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Mineral Deposits of Southern Africa, 2, 2149-2158

The Insizwa Complex, near Kokstad on the Natal-Transkei border, is the only Karoo-aged intrusion ever mined for base-metal sulphides. It occurs at the centre of the intrusive activity within the Karoo Basin. Intermittent prospecting and exploration activity have continued since the end of the last century without proving a viable ore deposit. Nickel-copper sulphide mineralization occurs at the base of a thick differentiated sequence of olivine- gabbroic composition in the Waterfall Gorge area of the Insizwa Complex. The texture, composition, and spatial relationship to the gabbro have led to it being referred to as a classic example of an immiscible magmatic sulphide deposit. Widely disseminated and minor, localized, massive ores are present, which consist mainly of pyrrhotite, pentlandite, and chalcopyrite. The disseminated ore, which occurs in the basal olivine-hypersthene gabbro, averages 0,3 percent of both copper and nickel and less than 1 ppm of total platinum- group elements. The massive ore may contain up to 25 percent copper and 15 percent nickel. Geochemical calculations suggest that the original sulphide liquid contained 6 percent nickel, 6 percent copper and 10 ppm of platinum and palladium. The olivine compositions at the base of the intrusion are depleted in nickel suggesting segregation of a sulphide liquid prior to emplacement of the magma into its present position. Geochemical calculations indicate that a hidden resource of 26 Mt of nickel may exist at depth below the Insizwa Complex.
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Mineral Deposits of Southern Africa, 2, 2159-2166

Copper was known and has been exploited in the Mutandawhe area prior to the settlement of colonists in Zimbabwe. During the last 75 years several individuals and companies have carried out small-scale mining operations in the area. Copper has, however, been superseded by tungsten as the most important economic metal in the area. The copper-tungsten mineralization is hydrothermal in origin and is located in narrow quartz-carbonate veins which surround the Mutandawhe Complex. The mineralization is found along predominantly north-easterly-striking fissures and appears to be similar in all the veins examined, suggesting that it has been derived from the same source. Typical examples of the mineralized veins occur in the Cobra and Mutandawhe mines which are two of the larger producers in the area. An increase in arsenopyrite and pyrrhotite in the lower levels at Mutandawhe suggests mineral zoning, perhaps due to an increase of temperature with depth during mineralization.
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Mineral Deposits of Southern Africa, 2, 2167-2172

Phanerozoic barite deposits in Southern Africa can be subdivided into two major groups: - concretions and layers of detrital barite in shales and arenites of various formations of the Karoo Sequence in the central and northern parts of South Africa and adjoining parts of Zimbabwe; - partly mineralized veins along faults of post-Karoo age, mostly in the Northern Transvaal and North-western Zimbabwe. Minor barite occurrences are associated with post-Karoo carbonatites and volcanics and are also found in younger clays and salt pans. The major sedimentary deposit from Mabiligwe (North-eastern Transvaal) originated through the erosion and reworking of barite concretions in older clays and the selective enrichment of the resulting clastic grains in a placer deposit. A Waterberg age has recently been suggested for this deposit.
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Mineral Deposits of Southern Africa, 2, 2173-2191

In a world context apatite is the single most important commodity produced from copper from the Phalaborwa Complex, which also produces apatite, vermiculite, magnetite, sulphuric acid, zirconia, uranium, nickel, silver, gold, and plantinum group elements. No other mine in Southern Africa and perhaps in the world can match Phalaborwa for the variety of its products and potentially extractable metals (thorium, aluminium, potassium, and rare earth elements). Other localities where economic recovery of ore associated with carbonites and\or alkaline rocks has taken place are Glenover (Phoophate), Dorowa (Phosphate), Okorusu (fluorite), Pilanesberg (fluorite), Soutpan (soda), Tweerivier (magnetite), Spitskop (limestone) and Swartbooisdrif (semiprecious stone). These operations were all on a comparartively small scale. Prospecting has also taken place at numerous other occurrences. Interesting results have been obtained at Pilanesberg (uranium, niobium, and rare earths), Kruidfontein (fluorite), Schiel, Otjisazu, and Chishanya (Phosphate), whereas other locialities have not yet been adequately prospected (Goudini, Nooitgedacht, Keikamspoort). It is concluded that carbonitites could still be attractive exploration targets, especially for rare metals.
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Mineral Deposits of Southern Africa, 2, 2193-2214

The De Beers kimberlite pipe was discovered in 1871 and since then has produced approximately 25 million carats (5 metric tons) of diamond. The pipe is a complex geological body which measures 5,1 ha in area at the present land surface. Two distinctive morphological depth zones can be recognized, a regularly shaped upper (diatreme) zone and a much more irregular lower (root) zone. By analogy with other ICSS eroded pipes, an outward-flaring, near-surface, crater zone is assumed to have been present prior to erosion. Six discrete intrusions of hypabyssal-facies kimberlite and kimberlite breccia, which exhibit considerable textural and mineralogical variation, occur within the explored part of the pipe. These intrusions contain varying quantities of crustal and upper mantle-derived xenolithic material. They also contain cognate inclusions of earlier generations of kimberlite. The root zone of the pipe is characterized by the occurrence of broad zones of contact breccia, up to 50 m wide. The contact breccias may be entirely devoid of kimberlitic material and consist solely of locally derived, fragmented, country rock. In other instances the breccias contain interstitial kimberlite which represents an additional stage (or stages) of intrusion within the pipe. There are marked contrasts in diamond content between some of the intrusions. The grade of one of the intrusions decreases consistently with increasing depth, but in other instances there is little or no evidence of depth-related grade variations. Detailed studies of diamond populations from different intrusions within the pipe have revealed no significant differences in primary features such as the proportions of different crystal forms or the proportions of different colours. Furthermore, no significant differences in secondary features such as the degree of resorption or the nature of surface etch features are apparent. Comparison of De Beers Mine diamonds with those from three other Kimberley mines reveals close sim
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Mineral Deposits of Southern Africa, 2, 2215-2228

The Pilanesberg Complex, which is one of the world's largest known alkaline complexes, contains large resources of rare elements, some of which may be exploitable. The Complex has a well-defined ring structure which is clearly expressed topographically. It constitutes the main central body of an alkaline province and was emplaced as a cyclic sequence of volcanic activity and ring fracturing with the formation of lavas and pyroclastics and the intrusion of foyaitic cone sheets and ring dykes. A geochemical survey has indicated a general enrichment of rare elements typical of alkaline rocks - especially fluorine, light rare earths, strontium, thorium, and uranium. Besides the generally high background radioactivity due mainly to thorium, anomalous areas with particularly high responses are encountered that have, in addition, concentrations of other elements. Notable among these are a contact zone between foyaite and tinguaite on the hill Thabayadiotsa, located in the eastern sector of the Complex, where rich deposits of rare earths occur; a zone of tuff bands on the farm Rhenosterspruit with concentrations of uranium, contained in betafite and other minerals, and niobium contained in columbite and pyrophanite; a foyaite near the southern margin enriched in uranium and niobium and other elements and constituting a lowgrade orebody. The foregoing and other geochemically anomalous areas of interest are described. A brief account of fluorite occurrences is also given. The considerable potential of large-scale exploitation depends on the solution of metallurgical problems, and marketing the products.
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Mineral Deposits of Southern Africa, 2, 2239-2253

The Phalaborwa Complex consists predominantly of pyroxenitic rocks from which apatite is recovered on a large scale. In 1980 3,5 Mt of concentrate were produced from ores containing from 10 to 25 percent apatite. The Complex measures 6,5 km from north to south and consists of three coalescing, pipe-like features, each with a concentric zonal structure, named the Northern Pyroxenite, the Southern Pyroxenite, and the Loolekop Pyroxenite. Exploration has proven that the phosphate mineralization is vertically continuous to a depth of at least 1 000 m. Detailed mapping and sampling of FOSKOR's opencast mine on a portion of the Northern Pyroxenite has led to the recognition of nine different pyroxenitic rock types (as well as three different varieties with pegmatoidal texture), depending on relative proportions of diopside, phlogopite, apatite, and microcline. The field relations between these units involve both multiple intrusion and replacement. There is a general positive correlation between apatite and phlogopite content. The apatite occurs as microscopic single crystals, sugary aggregates, monomineralic concentrations, and crystals of pegmatitic dimensions, composed mainly of fluorapatite, with subordinate hydroxy apatite, and containing approximately 1 percent of rare-earth elements. A striking feature of the phosphate distribution is its absence in the central part of the Northern Pyroxenite. Apatite-rich pyroxenite, averaging 6,7 percent P2O5, forms an outer zone, about 500 m wide, and intrudes apatite-poor pyroxenite (0,1 % P2O5) with a sharp boundary. Seen in detail, however, apatite is irregularly distributed and sharp changes in P2O5 concentration take place over short distances. In the Loolekop Pyroxenite the foskorite zone, averaging 10 percent P2O5, constitutes an important source of phosphate, whereas the pyroxenitic zones carry 5 to 6 percent P2O5. As a result of exploration by drilling, a very large (about 6 km²), lower-grade phosphate deposit has also been established in the Southern Pyroxenite. The same lithologic units as in the Northern Pyroxenite have been recognized here except that the apatite-poor varieties are not represented. It is concluded that the Phalaborwa Complex was emplaced in a repetitive cyclical manner. This model takes account of the fact that two or more ages of most lithological types can be distinguished. During the first cycle, pre-existing dunite plugs were broken up and (?)phlogotized by the emplacement of apatite-poor pyroxenite magma, followed, in turn, by extensive pipe-like bodies of apatite-rich pyroxenite, separate plugs of syenite and foskorite, and carbonatite. Each pyroxenite stage consisted of consecutive substages characterized by increasing volatile and, therefore, phlogopite content, probably overlapping with each other and accompanied by metasomatic replacement, which resulted in much heterogeneity. During the second cycle, the four main stages of the first cycle were repeated, but in a more transgressive, dyke-like manner and of restricted extent.
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Mineral Deposits of Southern Africa, 2, 2255-2260

The Otjisazu Igneous Complex is a recently identified carbonatitic intrusive in which anomalous copper values are closely associated with apatite-enriched alkali pyroxenite, svite, and mafic pegmatoid. The areas of apatite and copper enrichment were readily outlined using conventional soil geochemistry techniques, and follow-up initial bulk sampling to a depth of 30 m has indicated a very large tonnage with average grade in the range 3 to 5% P2O5 together with traces of copper-bearing sulphides. The available geological evidence suggests a lower Palaeozoic age of emplacement.
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Mineral Deposits of Southern Africa, 2, 2261-2268

Sodalite of semi-precious grade is found in ankeritic carbonatite intrusive into sheared syenite dykes which occur surrounded by anorthosite near Swartbooisdrif (13x50'E,17 20'S) on the border between South West Africa/Namibia and Angola. It forms small plugs and irregular bodies of nepheline syenite, syenite, lamprophyre and carbonatite dykes) are intruded along faults and fractures, often in composite fashion. Within these dykes there is evidence of metasomatic replacement as well as magmatic flow of ankerite. The sodalite-rich carbonatite dykes are streaked, brecciated, and banded with ankerite, sodalite, analcite, cancrinite, albite and magnetite as principal constituents, often in the form of lenticular, nearly monomineralic layers. Solid blocks of sodalite reach dimensions of up to 8 m. It is suggested that the dykes owe their unusual composition to prolonged reaction of fenitizing fluids with pre-existing sheared syenite and locally with sheared anorthosite, followed by intermingling of the fenitized products with carbonatite magma during intrusion. 750 t of sodalite have been produced. There are good prospects for further production, especially if the lower grade material can be utilized as ornamental stone.
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Mineral Deposits of Southern Africa, 2, 2269-2287

Surficial uranium deposits are located in the north-western Cape Province of South Africa, in the Namib Desert east of Walvis Bay in South-West Africa/Namibia and in the Serule Block of Botswana. They have been classified into the valley-fill, lacustrine, and pedogenic types. Camotite is the main uranium-bearing mineral in the larger surficial deposits, with other minerals such as soddyite and phosphuranylite occurring locally. Uraninite or urano- organic complexes occur in the reducing environments of the diatomaceous earth, peat-rich deposits. Economically, the valley-fill type is the most important, with the largest deposits occurring in South-West Africa/Namibia. In South-West Africa/Namibia the valley-fill surficial uranium deposits occur in the Tumas and Langer Heinrich formations of the Tertiary to Recent Namib Group. The Tubas, Langer Heinrich, and Welwitchia deposits are discussed; in them, camotite occurs in calcareous and gypsiferous fluvial gravels. The pedogenic deposit at Mile 72 occurs in weathered granite, overlying gypcrete and has little economic potential. The economic potential of the surficial deposits in the north-western Cape Province is very limited in comparison with their South-West African/Namibian counterparts, but the most important deposits are the lacustrine type, in particular those containing peat and diatomaceous earth. The mechanisms for the precipitation and preservation of the uranium are discussed.
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Mineral Deposits of Southern Africa, 2, 2289-2299

The potential of the brines of Sowa Pan in the Makgadikgadi Depression of north-east Botswana for the production of common salt, soda ash, salt cake and potash has been under intermittent investigation since 1960. The above salts occur in solution in a brine occupying the pores of the clays and sands which underlie the northern third of Sowa Pan and adjacent areas, and can be extracted from the sands by pumping from boreholes. An area of 915 Km² is underlain by extractable brines, and reserves are at least 8 013 million m³ of brine containing 1026 Mt of NaCl, 233 Mt of Na2CO3 (including bicarbonate equivalent), 110 Mt of Na2SO4, and 34 Mt of KCl. The brine deposit underlies part of the bed of a lake which existed in this basin of internal drainage as recently as 16 000 years BP.
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Mineral Deposits of Southern Africa, 2, 2300-2321

Diamonds of the Lower Orange River are associated with the terrace gravels of the Miocene Arriesdrift Gravel Formation. These gravels were deposited by the hybrid fluvial system with a superimposed, meandering style. Concentration of diamonds mainly took place because of this mineral's extreme hardness (10 on Mohs' scale and 8 000 on Brook's scale), and its high relative density (3,52 as opposed to 2,67 of quartz). Diamonds, therefore, tended to concentrate in traps in the irregularly eroded bedrock surface as well as in hydrodynamically suitable sub-environments of the palaeo-river system. It can no longer be disputed that the diamonds concentrated on the West Coast of South Africa originated on land and were transported to the coast by rivers draining the plateau. These diamonds were, however, not necessarily freed directly from their original kimberlite source, and this fact presents a major point of controversy amongst geologists familiar with these deposits.
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Mineral Deposits of Southern Africa, 2, 2301-2307

Richards Bay Minerals produces ilmenite, rutile, and zircon from one of the most extensive deposits of beach-sand origin known today. These minerals are present in aeolian dunes of Recent age, which occur parallel to the beach along the north coast of Natal. Drilling was carried out over a distance of 17 km. Based on the results obtained from some 1 400 boreholes, the heavy mineral distribution, mineralogy, and ore reserves of the orebody in the dune area are described. In addition, 25 boreholes provided details of the stratigraphy of the underlying Tertiary and Quaternary sediments.
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Mineral Deposits of Southern Africa, 2, 2309-2321

Diamonds of the Lower Orange River are associated with the terrace gravels of the Miocene Arriesdrift Gravel Formation. These gravels were deposited by a hybrid fluvial system with a superimposed, meandering style. Concentration of diamonds mainly took place because of this mineral's extreme hardness (10 on Mohs' scale and 8000 on Brook's scale), and its high relative density (3,52 as opposed to 2,67 of quartz). Diamonds, therefore, tended to concentrate in traps in the irregularly eroded bedrock surface as well as in hydrodynamically suitable sub-environments of the palaeo-river system. It can no longer be disputed that the diamonds concentrated on the West Coast of South Africa originated on land and were transported to the coast by rivers draining the plateau. These diamonds were, however, not necessarily freed directly from their original kimberlite source, and this fact presents a major point of controversy amongst geologists familiar with these deposits.
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Mineral Deposits of Southern Africa, 2, 2323-2324

The existing 1:5 000 000 geological map of Southern Africa, last revised by the late Dr Sidney Haughton in 1968, has served its purpose exceedingly well over the years. Maps need to be revised from time to time, however, and for Southern Africa this had become particularly necessary. Not only have great advances been made in geology and geochronology since the 1960s, but major changes in stratigraphic nomenclature have also been introduced, coupled with modifications to certain long-range correlations in the area. In addition, the need for a small-scale map showing the most important mineral deposits and mineral fields of the subcontinent was also an underlying consideration for the revision of this map. The end product is a map to the scale of 1:4 000 000 covering the area south of the Kunene, Okavango, and Zambezi rivers.
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