The composition of ferromanganese nodules of the Chukchi and East Siberian seas

Ferromanganese nodules from the floors of the Chukchi and East Siberian seas were examined by means of analytical electron microscopy and plasmic and chemical analysis. It was found that the nodules consisted of aggregates of colloform and poorly crystallized matter of globular and irregular shapes, in which the minerals of iron and manganese were mainly presented by hematite, vernadite, and asbolane. The samples from the Chukchi Sea contained single micrograins of native gold. The tested nodules were comparable to oceanic ones in iron content. The contents of manganese, ore elements, and most of microelements are well below those of the ocean. The comparison of the composition of bottom sediments and considered nodules showed that the latter were enriched during their formation by factors of 100–200 in manganese, of 10–18 in cobalt, and of 4–8 in iron, nickel, and zinc. However, the process of diagenetic accumulation of metals by nodules in the marine environment is less effective than in the open ocean with the sediments of higher con-tent of mobile element forms and of higher exposure time compared to marine sediments.