**2.1 Object of study**

*Iron Ores*

identified.

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

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

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

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.

brilliantly confirmed by scanning electron microscopy [4].

ferromanganese crusts with the ore-compound metals [6].

This work is devoted to such research.

**4**

**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 the crust.

#### **Figure 1.**

*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.*

The method of layer-by-layer studies of the crust was as follows:


#### **2.2 Experimental microscopy results**

The surface layers of the ferromanganese crust analysis performed by digital optical microscopy (**Figure 1**) showed that they consist of associations of a large number of minerals with different degrees of crystallization and dispersion. There is also an increase in yellowish-red inclusions from the lower layer I to the upper layer III. These inclusions correspond to iron oxide compounds (goethite, hematite, etc.), i.e., there is an increase in the iron-ore component from the lower layer of the crust to the upper one, and the proportion of accessory minerals decreases. It is difficult to analyze the content of the manganese-ore component in the crust layers by this method, since manganese oxides are very dark, and it is hard to distinguish them from other dark-colored phases. However, we were able to identify an interesting region that has a colomorphic structure, which is most likely formed by manganese oxides (**Figure 2a**) by examining the sample from the R-layer in detail [7].

We examined this region of the R-layer using a scanning electron microscope (**Figure 2b**) to clarify the assumption about the manganese nature of the colomorphic structure. The Energy Dispersive analysis performed on the electron microscope allowed us to obtain a picture of the distribution of chemical elements in this region of the R-layer (**Figure 3**). The analysis shows that manganese and oxygen occupy the same positions in the colomorphic structure, which indicates that they are combined in the form of manganese oxide. At the same time, calcium and phosphorus also occupy identical positions, which indicates that they are connected in a common structure, most likely apatite. No iron compounds were found in this area.

**7**

**Figure 3.**

*Study of Deep-Ocean Ferromanganese Crusts Ore Components*

By increasing the magnification of the scanning microscope (x10, 000), we were able to see columns of stromatolites, layers of bacterial mats with fossilized

*Distribution of chemical elements in a colomorphic structure on the surface of the P-layer and their percentage.*

*Optical (a) image of a colomorphic structure on the surface of the R-layer and electron microscopic image* 

Elemental analysis of each layer of the studied crust was carried out at 8 separate points of its surface area (a surface area was selected, which will later be analyzed using an X-ray diffractometer) using the SciAps X-200 analyzer. The built-in camera made it possible to obtain an image of the analyzed area of the sample and

bacteria, and microcrystals of accessory minerals (**Figures 4** and **5**).

accurately determine the measurement point of the X-ray spectrum.

**2.3 X-ray investigation results**

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

**Figure 2.**

*(b) of the same structure.*

**Figure 2.**

*Iron Ores*

another.

**2.2 Experimental microscopy results**

The method of layer-by-layer studies of the crust was as follows:

changes in the phase composition of the crust from layer to layer.

traces of bacterial activity that leads to the growth of ore formations

composition for each layer of the crust.

1.Color optical images were obtained from all layers of the crust section using the Keyence VHX – 5000 digital optical microscope which allows us to record

2.A TESCAN VEGA scanning electron microscope was used to study the morphology and relative position of various crystal phases, as well as to search for

3.The elemental composition of each layer at individual points along its surface was determined using a portable X-ray fluorescence analyzer SciAps X-200, which has a collimated X-ray beam with a diameter of less than 3 mm. These results were then mathematically processed to obtain the average elemental

4.The results of the elemental composition were entered into the High Score Plus program of the PANalytical Empyrean X-ray diffractometer, which was used for X-ray diffraction analysis to determine the nature of ore and accessory

5.The Mössbauer spectra were taken and analyzed for each layer to clarify the phase composition of the ultrafine iron-containing compounds that make up the thoracic component. Mathematical processing of the obtained Mossbauer spectra made it possible not only to determine which iron oxide compounds are contained in each layer of the crust, but also to trace quantitative and qualitative changes in their composition during the transition from one layer to

The surface layers of the ferromanganese crust analysis performed by digital optical microscopy (**Figure 1**) showed that they consist of associations of a large number of minerals with different degrees of crystallization and dispersion. There is also an increase in yellowish-red inclusions from the lower layer I to the upper layer III. These inclusions correspond to iron oxide compounds (goethite, hematite, etc.), i.e., there is an increase in the iron-ore component from the lower layer of the crust to the upper one, and the proportion of accessory minerals decreases. It is difficult to analyze the content of the manganese-ore component in the crust layers by this method, since manganese oxides are very dark, and it is hard to distinguish them from other dark-colored phases. However, we were able to identify an interesting region that has a colomorphic structure, which is most likely formed by manganese oxides (**Figure 2a**) by examining the sample from the R-layer in detail [7]. We examined this region of the R-layer using a scanning electron microscope (**Figure 2b**) to clarify the assumption about the manganese nature of the colomorphic structure. The Energy Dispersive analysis performed on the electron microscope allowed us to obtain a picture of the distribution of chemical elements in this region of the R-layer (**Figure 3**). The analysis shows that manganese and oxygen occupy the same positions in the colomorphic structure, which indicates that they are combined in the form of manganese oxide. At the same time, calcium and phosphorus also occupy identical positions, which indicates that they are connected in a common structure, most likely apatite. No iron compounds were found

minerals, and assess accompanying growth of ore formations.

**6**

in this area.

*Optical (a) image of a colomorphic structure on the surface of the R-layer and electron microscopic image (b) of the same structure.*

**Figure 3.** *Distribution of chemical elements in a colomorphic structure on the surface of the P-layer and their percentage.*

By increasing the magnification of the scanning microscope (x10, 000), we were able to see columns of stromatolites, layers of bacterial mats with fossilized bacteria, and microcrystals of accessory minerals (**Figures 4** and **5**).
