(Fig 2, page 399), Distribution of Fe and Mn in ferromanganese nodules of the Eningi-Lampi Lake, Russia

The distribution of Mn and Fe in water, sediments, hydroxide nodules and crusts of Eningi-Lampi ore-bearing lake is regular, and concordant from the source to the areas of accumulation of these components. Mn-Fe hydroxide nodules and crusts occur at the water-sediment interface, and more rarely in the upper (0-5 cm) film of brown watery mud. The leading role in the formation of Mn-Fe nodules and crusts is played by the chemosorption and auto-catalytic oxidation in the course of interaction of component-bearing solutions with active surfaces. This is considered to be the basic process for the model of ferromanganese ore formation in recent basins. Despite the differences in the physico-geographical and geochemical characteristics of lakes, mediterranean seas and oceans, the formation of ferromanganese hydroxide nodules and crusts in these basins may be explained by this model.

Analysis of Mn-deposits from Lake Eningi-Lampi

The processes of formation of iron-manganese nodules and crusts have been studied on an example of the Eningi-Lampi lake, Central Karelia, where the relationships between the source of the ore, sedimentary materials and areas of their accumulation prove relatively simple and apparent. Nodules and crusts are composed mostly by birnessite, amorphous hydrous ferric oxides and hydro-goethite. They occur, as a rule, on the surface of relatively coarse-grained sediments, at the ground-water interface. Considerably in a lesser extent are found the nodules in the upper part (0ó5 cm) of the red-brown flooded watery mud covering dark-green, black muds. The nucleus of nodules, or the basis of crusts of iron-manganese hydroxides are various, frequently altered, fragments of rocks, sometimes pieces of wood. Distribution of Mn and Fe in sediments and waters of the lake is considered. It is shown that the Mn/Fe ratio decreases considerably in waters, sediments and nodules of the lake while moving off a distance from the source. The main role in the process of formation of iron-manganese nodules belongs to the selective chemosorption interaction (with auto-catalytic oxidation) of component-bearing solutions with active surfaces.