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Abstract

Manganese mineralization is diverse in occurrence, origin, mineralogy and geochemistry. These variations reflect differences in the processes of formation and depositional environments, which in turn are a response to changes in the land — ocean — atmosphere system over geological time. As such, manganese deposits can act as markers of major events in the dynamic evolution of the Earths surface. Modern manganese accumulations provide insights into key factors controlling manganese deposition that cannot readily be determined from examination of ancient ores. A knowledge of oceanic currents, ocean chemistry or small-scale variation in physicochemical patterns of recent basins, for example, may extend our understanding of depositional processes in the past. Equally, the study of Precambrian deposits not only elucidates ancient mechanisms of manganese metallogenesis, but also helps to unravel the impact of comprehensive environmental changes on metal deposition on a scale not realised in younger geological times. The volume includes a review of the range of terrestrial Mn deposits and their relative abundance through geological time. This is followed by six papers on Precambrian deposits that cover the manner in which Mn mineralization reflects changes in planetary and environmental chemistry. Ten papers on Cenozoic deposits show the wide diversity of genetic types of the younger deposits, from nodules, crusts and stratabound layers, to deposits precipitated from hydrothermal fluids. Five papers in the last section consider the geochemistry and mineralogy of Mn deposits. Experimental and modelling approaches to Mn geochemistry and mineralogy can further aid our understanding of the formational and depositional processes involved and thereby our interpretation of deposit metallogenesis.