Great Dyke

  The Great Dyke is a linear feature that trends nearly north-south through the center of Zimbabwe passing just to the west of the capital, Harare. It consists of a band of short, narrow ridges and hills spanning for about 320 miles (515 km). The hills become taller as the range goes north, and reach up to 1,500 feet (460 meters) above the Mvurwi Range. The range is host to vast metal and mineral ore deposits, including gold, silver, chromium, platinum, nickel, tin, mica and asbestos.

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Geology

Geologically the intrusion is a dike and represents a rare near vertical layered ultramafic intrusion that extends across Zimbabwe for approximately 550 km with a strike of about N10°E. The width of the intrusion varies from 3 to 12 km. The dike is unusual in that most ultramafic layered intrusions are near horizontal sill or sheet form. The dike may have been originally a sill that has subsequently been tilted by tectonic forces. Four separate mineral rich complexes are recognized, Musengezi, Hartley, Selukwe, and Wedza. The Selukwe complex just to the southwest of Harare contains the richest platinum deposits.

The dike lies within an Archean craton and has been dated at 2.5 billion years old. The dike contains large amounts of platinum group metals and chromite as well as magnetite and other ore minerals. The huge Bushveld igneous complex of South Africa lies less than 500 km south of the southern end of the dike.

The Great Dyke was first reported in 1867 by the explorer Carl Mauch . However the existence of rich ore deposits was not realized until around 1918.

References

• Guilbert, John M., and Park, Charles F., Jr. (1986) The Geology of Ore Deposits, Freeman, ISBN 0-7167-1456-6
• Mining in Zimbabwe