Bushveld Igneous Complex
|THE BUSHVELD COMPLEX|
|the consultant is L. V. Razin;|
|the post-Bushveld alkaline and related rocks;|
|the Rooiberg felsite;|
|the tuff-schist stratum of the Praetorian series;|
|the Magaliesburg quartzite;|
|the leptite and granophyres;|
|the Bushveld granite;|
|the top zone;|
|the main magnetite layer;|
|the main zone;|
|the Merensky Reef;|
|the critical zone;|
|the main chromitite layer;|
|the basal zone;|
|the Transvaal system with the series of the "black reefs";|
|the rocks of the Archean;|
BUSHVELD IGNEOUS COMPLEX (EN: Bushveld; RU: Бушвелдский комплекс) is the largest layered pluton on the Earth, the Complex has been formed with the ore-bearing rocks, and is covering the area of 67 thousand square kilometres. The Complex is situated within the Republic of South Africa (the Transvaal province). See the Map.
The Bushveld Complex is the saucer-shaped body (lopolith), with the dip of the "layers" (horizons), which are forming the Complex, at the angle of 15-30 degrees to the centre of the massif (see the Map). The half of the area of the Bushveld Complex is overlain by the younger formations, namely, by the continental depositions (sandstones, schists with the subordinate strata of the volcanic rocks) of the Karoo system, namely, since the Upper Carboniferous till the Upper Triassic. The rocks and ores of the Bushveld Complex have formed themselves during the Proterozoic under the conditions, which were intermediate between geosynclinal and cratonic. There form the Bushveld Complex the strata, which have formed themselves sequentially: the rocks of the Transvaal system, including the andesitic volcanics with the same age; the lavas with the felsic composition (the Rooiberg felsite), in association with leptites and granophyres; the derivatives of the early intrusive phase (the Bushveld layered intrusives); the rocks of the late intrusive phase (the Bushveld granite); the post-Bushveld dikes of the alkaline rocks.
With the Bushveld Complex, there are genetically associated the diverse deposits with the useful minerals. The most rich magmatic ore deposits are confined to the layered series (to the intrusive). With this series, there are associated the largest deposits with the ores of the metals of the platinum group within the world (the identified reserves to the depth of 600 metres are 62.5 thousand tonnes), with the chromium ores (the reserves are more than 3 billion tonnes to the depth of 300 metres), and with the iron-titanium-vanadium ores (the reserves are from 4 to 6 billion tonnes, including 7.8 million tonnes of the V2O5 vanadium (V) oxide to the depth of 300 metres); there are accompanying the platinoid metals the deposits, which are unique according to the reserves, with gold (1100 tonnes), and with the sulfidic copper-nickel ores (the reserves according to the metal are 23 million tonnes, and 10 million tonnes, respectively), with magnesite (10 million tonnes), and the small deposits with the sulfidic copper-nickel ores. The stratum of the rocks of the layered series has the total thickness of approximately 8 kilometres, and has been formed at the bottom with the dunites, peridotites, and pyroxenites, while at the top with the norites, gabbros, anorthosites, and ferrodiorites. The structure of this magmatic series is zonal, with the marking of the zones with the ore-bearing layers. The main chromitite layer is situated within the sole of the 1000-metres critical zone. There fixes its upper boundary the extended platinum-bearing Merensky Reef (horizon), which has been traced to the distance of more than 250 kilometres, of which the territory with the length of 80 kilometres undergoes the process of the operation: at the west, there is the Rustenburg city platinum-bearing region, while at the east, there is the Lydenburg city region. The Reef has been traced to the depth of 1900 metres. The main magnetite layer (the iron-titanium-vanadium ores) is embedded within the sole of the 2000-metres top zone.
There are associated with the Bushveld granite, and with the acid rocks of the roof of the Bushveld Complex, the pegmatite and greisen deposits with cassiterite (approximately 40 thousand tonnes of tin), and of fluorite (31.4 million tonnes), and the hydrothermal deposits with the polymetallic ores. There are the product of the metamorphosing impact from the granitic intrusive the deposits with andalusite (the reserves are 11 million tonnes).
The ores are being extracted mostly with the usage of the underground method. The deposits with the group of the platinoid metals within the Bushveld Complex are being developed since the 1919; there is the most large according to the reserves (32.5 thousand tonnes of the platinoid metals) the late magmatic chromitite layer (UG-2), which is situated within the Critical zone, for 15-370 metres below the level of the Merensky Reef. The extraction of the platinoid metals is performed by the "Western Platinum" company, at the "Marikana" mine (1.3-1.4 million tonnes of the ore, 4-4.35 thousand kilograms of the metal); by the "Impala Platinum" company, at the "Bafokeng" mine (northern and southern), and at the "Wild Beast Fountain" mine (the total extraction in terms of the metal is from 20.2 to 29.5 thousand kilograms); by the "Rustenburg Platinum" company, at the "Rustenburg" mine, and at the "Union Section" mine (the extraction at each of them is more than 3 million tonnes of the ore, and more than 40 thousand kilograms of the metal); and also by the "Amandelbult" company (1.8 thousand kilograms of the metal), and by the "Atok" company (1.4 thousand kilograms of the metal). Each company has its own beneficiation plants, and refining plants ("Brakepan", "Springs", "Rustenburg").
The deposits with the copper-nickel sulfide ores are confined to the zone of the Rustenburg city dip-slip fault with the north-western strike. The ore bodies have the columnar shape, with the diameter of up to 17 metres, and consist of the norite-pegmatite, with the inclusions of pyrrhotite, pentlandite, and chalcopyrite. The amount of the sulfides within these bodies decreases itself from the centre to the periphery. The extraction of nickel is 1.6-1.8 thousand tonnes, of copper is 1.0-1.2 thousand tonnes. The deposits with the ores of chromium form two belts with the lengths of 112 kilometres, and of 160 kilometres. The industrial extraction has started itself during the 1924. There are productive 5 ore-bearing horizons, within the limits of which, the depositions with the interspersed and continuous ores form the parallel, orderly along the strike, interlayers, with the thickness from 2 centimetres to 2 metres, which are subordinated to the pseudo-stratification of the enclosed pyroxenites and anorthosites. At the 15 mines ("Hendriksplaats", "Winterveld", "Henry Gould", "Zwartkop", and others), there is extracted more than 50% of the total amount of the chromium ores within the industrially developed capitalistic and developing countries. The productivity of the individual mine is approximately 300 thousand tonnes of the ore per year on average, while at the large mines, the productivity is up to 500 thousand tonnes per year. More than 70% of the ores, which are being extracted, are processed into ferrochrome (up to 800 thousand tonnes per year). The belt with the deposits with the iron-titanium-vanadium ores extends itself for more than 330 kilometres. The ore is being extracted at the "Mapahs" mine (the opencast method, approximately 1 million tonnes per year), at the "Kennedy's Vale" mine, and at the other mines, while the metallurgical conversion, and the production of the vanadium slags, are performed at the industrial plant within the Witbank city, and within the Bon Accord city, to the north of the Pretoria city. The deposits with the ores of tin belong to the formation of the intrusive zone, and are confined to the pegmatites, greisens, and quartzous veins. The ores of tin are extracted at the "Rooiberg" ("Ruiberh") mine (135-150 thousand tonnes of the ore, 2.3-2.5 thousand tonnes of tin), at the "Saiplats" mine (70-80 thousand tonnes of the ore, 300 tonnes in terms of the concentrates with 60% of Sn), and at the other mines. The total extraction of tin is approximately 3 thousand tonnes. The deposits with fluorite are being developed to the south of the Rooiberg city, and to the north of the Pretoria city, and of the Nylstroom city.
The content of the CaF2 calcium fluoride within the ores, which are being extracted, is from 20% to 40%. The beneficiation is performed according to the gravity-flotation schemes. The deposits with andalusite are situated within the narrow strip with the length of 80 kilometres to the north, while the deposits with magnesite are situated at the distance of 80 kilometres to the north-east, of the Steelpoort city. Their development is conducted with the usage of the opencast method.
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