Bushveld Complex

Bushveld Complex [¦bu̇sh‚veld ′käm‚pleks]

(geology)

In South Africa, an enormous layered intrusion, containing over half the world's platinum, chromium, vanadium, and refractory minerals.

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Bushveld Complex 

deposits of platinum and chromites, situated in Transvaal Province of the Republic of South Africa, on the territory of the districts of Rustenburg, Potgietersrus, Waterberg, and Lydenburg. Processing of the deposits began in 1924.

The Bushveld deposits coincide with the Precambrian Bushveld lopolith, an intruded massif with a flexure-like base, about 39, 000 sq km in area. The upper granitic zone of the lopolith is mixed with a zone of gabbro and norites, with pseudostrata of vanadistic titanomagnetitic ores. Lower, there is a sharply differentiated pseudostratified “critical” zone of pyroxenites, of anorthosites, and partly of dunites and transitional rocks carrying platinum, chrome, and nickel ores. In the lowest zone gabbro, norite, and a few pyroxenites are found. The platinum deposits of the Bushveld complex contain huge reserves of platinoides, estimated at several hundred tons. The ores in the feldspar pyroxenites of the critical zone have the greatest significance, particularly in the so-called Merenskii reef (horizon). Platinum minerals are associated with interspersions of sulfides of iron, copper, and nickel. The platinoid content of worked ores is usually 7-9 mg per kg (7-9 g per ton), although it can on rare occasions be greater than 15 mg per kg (15 g per ton).

There are deposits of another type where tube-shaped and other body forms of hortonolitic dunites cut the pyroxenites and dunites of the critical zone. Uneven, frequently high platinoid contents (3 to 19 mg per kg, or 3 to 19 g per ton), as well as the absence of chromites, are characteristic of these deposits. Two large platinum mines, the Rustenburg and the Union, are in operation. In 1966 about 25.5 tons of platinoids were obtained.

The chromium deposits of the Bushveld complex, the potential resources of which are estimated at 2 billion tons, are found in pseudostrata, persistent for considerable distances, of ingrained and massif ores, 2 cm to 2 m thick in the pyroxenites and anorthosites. They are characterized by a raised ferriferousness of the chrome spinels. The chrome-bearing belts of Rustenburg and Lydenburg are distinguished by expanses of tens of kms, with two to three ore strata in each. Figured to a depth of 150 m, the reserves are 150 million tons. The mined ore contains an average of 44 to 48 percent Cr₂O₃. The yearly yield is 800, 000 to 900, 000 tons. About 90 percent of the mined ore is exported, designated for chromium industries. In the Republic of South Africa the processing of ores into carbon ferrochromium has begun, basically for export.

REFERENCE

Du Toit, A. Geologiia Iuzhnoi Afriki. Moscow, 1957. (Translated from English.)

G. A. SOKOLOV