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.本研究以卡累利阿中部埃宁吉-兰皮湖（Eningi-Lampi）为研究实例，对铁锰结核与铁锰结壳的形成过程展开了系统探究。该湖区的矿质来源、沉积物质及其堆积区域之间的相互关系相对简洁直观。铁锰结核与结壳主要由水钠锰矿（birnessite）、无定形含水氧化铁以及水纤铁矿（hydro-goethite）构成。通常情况下，这类结核与结壳赋存于相对粗粒沉积物的表面，即地下水界面处。而在覆盖深绿、黑色泥层的红棕色淹水淤泥的上部（0~5 cm），结核的分布则相对稀少。铁锰氢氧化物结核的核芯或结壳的基底多为经频繁蚀变的各类岩石碎屑，偶尔也可见木质残片。本研究还分析了湖体沉积物与水体中锰、铁的分布特征，结果表明，随着与矿质来源距离的增加，湖区水体、沉积物以及结核中的锰铁比（Mn/Fe）均显著降低。铁锰结核的形成过程中，核心驱动机制为含组分溶液与活性表面之间的选择性化学吸附作用（伴随自催化氧化过程）。