, Volume 30, Issue 2, pp 146-151

A volcanic-exhalative origin for the world's largest (Kalahari) Manganese field

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Abstract

The ∼ 2220 Ma Kalahari Manganese field of South Africa is the world's largest Mn resource and a major producer. Current models for its origin rely on those developed for Phanerozoic deposits, invoking a submarine redox boundary and water movements across a continental shelf, precipitating Mn oxides from the sea. Here we report the discovery of major hydrothermal alteration in the thick andesitic volcanic pile beneath the Mn ore. This and other evidence shows that the Kalahari manganese is actually a volcanic exhalative deposit, analogous in some respects to those forming at present day mid-ocean ridges. Important differences in depth and oxygen supply account for the smaller area and high grade of the Kalahari Manganese Field, compared with the widespread but thinly developed modern ocean floor Mn deposits.