MANGANESE METALLOGENESIS: A REVIEW

Abstract

Metallogenesis of manganese in space and time is reviewed here in the light of the progressive development of the atmosphere, the hydrosphere and the lithosphere attendant with the varied styles of tectonism. Economic deposits of manganese first appeared c.3000 Ma ago, postdating by at least 800 million years the oldest known geological sequence containing iron-formation and base-metal sulfide ores. The development of manganese deposits in the Archean as a whole, vis-à-vis that of iron-formation and stratiform massive sulfides, was minor. This is possibly a reflection of the composition of the then endogenic exhalations and/or the character of the atmosphere and the hydrosphere. The geologic setting of the manganese deposits of this age was always atypical of the Archean period.Deposition of manganese was intensified with the advent of the Proterozoic with the changing tectonic style leading to stabilization of the cratons and oxygenation of the hydrosphere and the atmosphere. Large to superlarge deposits were formed mainly through terrigenous input during this period. The Mesozoic era ushered in the supremacy of manganese deposition and the peak was reached in Cenozoic time. This was largely due to the formation of giant shallow-water deposits in areas of marine transgression as well as deposition of manganese-rich nodules and crusts in deep-sea environments.Three major aspects of manganese metallogenesis stand out as most important but enigmatic. These are: (a) the extreme fractionation of iron and manganese in nature and their reverse trend of metallogenic development; (b) the universal record of shallow-water deposition of manganese in land-based deposits in contrast with the deep-sea milieu observed in modern basins; and (c) the common evidence of biological activity in close association with manganese deposition which could be either causal or casual. All these aspects merit further in-depth study and metallogenic analysis in a broad spectrum.