**1. Introduction**

Ferromanganese crusts were first discovered at the bottom of the Pacific Ocean. The crusts samples were taken on board by the English ship "Challenger" and described in 1873 during the first complex oceanological expedition in the history of world science. However, until the middle of the XX century, only the chemical composition of crusts was analyzed. It was found out that ferromanganese crusts consist of up to 20% Mn, 15% Fe and 0.3–2.5% Co. In addition, they can contain complexes of noble, non-ferrous, rare and rare earth metals (up to 70 elements). All this data obtained stimulated further complex investigations on the topic. Many expeditions, mainly in the Pacific Ocean, were conducted to find and obtain ferromanganese crusts by USSR, USA, Germany, China, Japan and other countries in 1970–1980. Currently, crusts are found in all oceans, including the Arctic Ocean. They are often spread on basalts and clastic volcanic rocks in the depth range of 400–7000 m. The crusts are relatively thin continuous covers lying on the slopes of seamounts of volcanic origin. The thickness of the crusts can reach 26–40 cm. The crusts age is usually determined by Be, U, and Os – isotope dating methods [1]. The average age reaches several tens of millions of years. The most common crustal growth rates found in all oceans vary between 2 and 4 mm/mln.yr.

Researchers of ferromanganese crusts have always had 2 questions: 1) where do the colossal masses of manganese and iron come from to the places where the crusts form? and 2) what is the mechanism of the crusts formation and why does it differ a lot from the usual bottom depositions? Until the middle of the XX century, the idea of hydrogenic mineralization (the deposition of metals from the oceanic water) prevailed. It is known that the flow of substances from various sources into the ocean water is dynamically balanced by their removal to the bottom depositions. Thus, the salt composition of ocean water remains stable. However, model experiments and real observations did not reveal the deposition of large amounts of iron and manganese to the ocean floor. In the second half of the XX century, more attention was paid to the underwater volcanic eruptions, mantle fluid flows and post-volcanic hydrothermal activity i.e. processes that are actually recorded, which may be the main suppliers of metals for the oxide ferromanganese ores formation. Accordingly, the volcanogenic-sedimentary type of mineralization was identified.

By the end of the 1990s, marine geologists, microbiologists, and micropaleontologists had developed and validated the biological concept of ferromanganese oxide ore formation. According to this concept, crusts are considered as products of the vital activity of bacterial communities that can oxidize divalent iron and manganese compounds and precipitate metal oxides in a crystalline or amorphous form on the cell surface or even within the cell, as well as in the matrix of biological films [2, 3]. The biological concept of oxide ferromanganese ore genesis has been brilliantly confirmed by scanning electron microscopy [4].

Developing and fossilizing biofilms (0.5 to 2 microns thick or more) form bacterial mats with a multilayer structure: stand-alone bundles of biofilms separated by cavities, clusters of filamentous bacteria, and layers of glycocalyx. Therefore, in bacterial mats, dense, massive micro-layers and porous, loose ones are distinguished. It is bacterial mats that form columnar stromatolites of ferromanganese crusts, which are the ore components. During the entire time of stromatolite growth (millions of years), extreme events periodically occurred (underwater volcanic eruptions, tectonic phenomena, global glaciation, etc.) that affected the vital activity of microorganisms and were imprinted in the crustal sections by the formation of interlayers with different types of columns (the thickness and density of columns as well as their growth direction changed, and bushy branches were formed) [5]. At the same time, the growing crusts, having a high porosity and a fine structure, demonstrate a large sorption capacity. As a result, they are saturated with complexes of non-ferrous, rare and rare earth metals. The biofilm matrix contains a significant concentration of polysaccharides with a negative charge. Due to this, metal cations are able to accumulate on the surface of the extracellular polymer matrix, forming strong complexes. These processes can explain the mechanism of enrichment of ferromanganese crusts with the ore-compound metals [6].

The structure, composition and genesis of ferromanganese crusts have been studied by scientific laboratories in many countries for more than 50 years (since their industrial significance was discovered). However, the nature of the oxide ferromanganese ore formation has not been fully revealed yet. This is due to the fact that the crusts are very complex in composition and structure layered formations. The nanoscale oxide ore components of biogenic origin are also the significant part of the crusts composition in addition to numerous clastic and dispersed minerals formed as a result of volcanic activity. Therefore, it is obvious that the study of such objects requires subtle chemical and physical methods of studying their composition, structure and morphology, which appeared only at the end of the XX century. This work is devoted to such research.

**5**

**Figure 1.**

*Study of Deep-Ocean Ferromanganese Crusts Ore Components*

**2. Analysis of ferromanganese crusts phase composition and** 

crusts by studying the composition and structure of these layers.

A characteristic feature of ferromanganese crusts is their layered structure, which shows a history of their origin and growth. If the crust is sliced, one can usually observe from 3 to 5 layers with an average thickness of 2–3 cm, differing in structure, physical properties and composition of components. Usually, the lower layers of the crust are dense and strong, while the upper layers are more porous and brittle. It is possible to consistently trace the processes of ore accumulation and global changes in the external conditions for the formation of ferromanganese

**Figure 1** shows a section of the crust studied in our work, isolated at a depth of 1200 m from the surface of the guyot of the Magellan Mountains of the Pacific Ocean. This crust has a special feature: it has a "relic" layer (R) of pre-existed crusts that underlies the main section and situated on the weathered basalt. The thickness of the R – layer reaches 8 cm. The stratification of the crust section was carried out by marine geologists M. Melnikov and S. Pletnev (from the Institute of Oceanology, Gelendzhik). The layers are named (below): I-1, I-2, II and III, which were formed in the time intervals indicated on the geochronological scale placed to the left of

*Section of the studied sample of the ferromanganese crust, compared with the geochronological scale (in the* 

*interval of 70 million years). Optical images of the various layers are on the right.*

*DOI: http://dx.doi.org/10.5772/intechopen.98200*

**morphology**

**2.1 Object of study**

the crust.
