A VOLCANIC-EXHALATIVE ORIGIN FOR THE WORLDS LARGEST (KALAHARI) MANGANESE FIELD

The similar to 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 sh elf, precipitating Mn oxides from the sea. Here we report the discover y of major hydrothermal alteration in the thick andesitic volcanic pil e 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 an d high grade of the Kalahari Manganese Field, compared with the widesp read but thinly developed modern ocean floor Mn deposits.