The Geology of the southern portion of Otjimbingwe 104 South West Africa

Abstract

Abstract by author:

The Southern Zone of the Intracontinental Branch of the Damara Mobile Belt contains the economically important Matchless Member. The Matchless Member is a long narrow belt of amphibolitic schists, intercalated with mica schists of the Kuiseb formation. These amphibolitic schists represent original basaltic extrusions and gabbroic intrusions, and are believed to be the source of the metals which form the many cupreous pyrite massive sulphide deposits along the extent of the belt. The tectonic environment of formation of the Matchless Member amphibolites is an ensialic rift, which is immature in places, but has widened to the extent that oceanic crust has formed in other areas. Mineralisation is hosted in magnetite quartzites, quartz-muscovite schists and pelitic schists, forming conformable massive sulphide lenses. There are many similarities between the Matchless deposits and volcanic exhalative deposits and many features similar to hydrothermal replacement deposits. Features of the Kupferburg deposit favour an exhalative mode of formation, in which metals are precipitated from hot metal-bearing solutions or "gels" in brine pools on the ocean floor, during the waning phases of vulcanism or shortly thereafter. A modern analogy of the Matchless deposits is the Red Sea, in which metals are presently being precipitated on the ocean floor