Genesis and alteration of manganese ores in the giant Kalahari manganese field, South Africa

摘要

After sixty years of mining the giant Kalahari manganese field in the Northern Cape Province of South Africa continues to be the most important source of manganese ore to the world market. Despite its economic importance it has remained a largely enigmatic deposit. Several models have been proposed to explain the origin of this giant accumulation of manganese ore by syngenetic or epigenetic processes. But not only the primary origin of the manganese ores, but also the recognition of epigenetic alteration events - su-pergene and hypogene - and their relative importance for the formation of exceptionally high grade manganese ores in the northwestern part of the Kalahari deposit have been subject of controversial discussion. In this contribution results of recent and ongoing mineralogical and geochemical studies in the Kalahari manganese field are presented. The data support a (bio)-chemosedimentary mode of origin for the manganese ores and illustrate that fluid flow during the 1.3-1.0 Ga Namaqua-Natal Orogeny led to hydrothermal upgrading of the sedimentary manganese ores in the northwestern part of the Kalahari deposit of the Kalahari manganese field.