Chemical composition of Fe-Mn manifestations from the Laptev Sea

In sediments of the Laptev Sea unknown earlier ferromanganese manifestations have been found. On the basis of structural-textural external signs they have been divided to five groups: 1) tube- and spindle-shaped pseudomorphs after and within invertebrates; 2) nuclear and non-nuclear nodules; 3) flagellum- and tube-like skeletons of polychaetes; 4) flat and flattened crustate nodules and crusts; 5) micronodules. All types of ferromanganese manifestations have been sorted in three main genetic series: eigenferrous formations of autochthonous (polychaetes, goethite micronodules) and allochthonous (nuclear nodules) nature; ferromanganese nodules formed under mild hydro-geodynamic conditions at the sediment-seawater geochemical barrier; and ferromanganese manifestations formed under conditions of the variable physico-chemical environment. Ferromanganese manifestations of allochthonous type have signs of littoral zones. They contain both ferrous and ferric iron and have low oxidation degree of manganese in comparison with the autochthonous type manifestations. Manganese minerals with moderate oxidation degree are represented by vernadite and buserite. Such features of iron and manganese indicate different conditions of their formation and occurrence. The main distinctive feature of ferromanganese mineralisation in the Laptev Sea is the redox barrier: the oxidized water layer enriched in oxygen and reduced sediments. This barrier provides favorable conditions for bacterial formation of ferromanganese ores. Understanding of the genesis of ferromanganese manifestations should be found in a study of organic matter reworking by bacteria.

Chemical composition of ocean Fe-Mn ores

The monograph includes the study of chemical and mineral compositions of terrestrial and marine manganese ores, methods of their analysis, dependence of manganese crust geochemistry on tectonic position of their formation, problems of manganese genesis and sources of manganese in ocean ores in connection with geohistorical aspects of ocean formation and development. A hypothesis is offered that formation of giant manganese mineral basins on continental margins resulted from a large asteroid fall to the ocean.

Rare earth elements in standard samples of ocean Fe-Mn nodules and crusts

Contents of rare earth elements (REE) in standard samples of Fe-Mn nodules (SDO-5, 6), Fe-Mn crust (SDO-7), and red clay (SDO-9) have been determined by ICP-MS and instrumental neutron activation analysis. Reproducibility of ICP-MS was 5-6%. These results are discussed and compared with other data. It has been found that distribution of REE in the standard samples of ocean Fe-Mn ores and red clay is highly homogenous.

Speciations of Mn and Fe in Fe-Mn nodules from the western part of the Clarion-Clipperton ore province

Hydrogenic forms of iron and manganese occurrence were studied in samples of ferromanganese nodules sampled within two polygons during Cruise 28 of R/V Dmitry Mendeleeev (1982) in the western part of the Clarion-Clipperton ore province. Contents of labile exchangeable Fe and Mn, amorphous hydroxides and poorly soluble compounds of Fe and Mn were analyzed. In nodules from DM28-2474 Polygon labile exchangeable Fe and Mn and amorphous hydroxides dominated; in nodules from DM28-2483 Polygon poorly soluble compounds dominated. Analysis of contents of labile forms of Fe and Mn occurrence in different morphological types of nodules distinguished predominantly hydrogenous botryoidal nodules, spheroidal and ellipsoidal intergrowth nodules, and hydrogenic-diagenetic discoid nodules.

Uranium and radioactive isotopes in bottom sediments and Fe-Mn nodules and crusts of seas and oceans

The main stages of the sedimentary cycle of uranium in modern marine basins are under consideration in the book. Annually about 18 thousand tons of dissolved and suspended uranium enters the ocean with river runoff. Depending on a type of a marine basin uranium accumulated either in sediments of deep-sea basins, or in sediments of continental shelves and slopes. In the surface layer of marine sediments hydrogenic uranium is predominantly bound with organic matter, and in ocean sediments also with iron, manganese and phosphorus. In diagenetic processes there occurs partial redistribution of uranium in sediments, as well as its concentration in iron-manganese, phosphate and carbonate nodules and biogenic phosphate detritus. Concentration of uranium in marine sediments of various types depending on their composition, as well as on forms of its entering, degree of differentiation and of sedimentation rates, on hydrochemical regime and water circulation, and on intensity of diagenetic processes.