**2.3 X-ray investigation results**

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

#### **Figure 4.**

*Micrographs of the ferromanganese crust with different magnifications: (a) numerous columns of stromatolites are seen (top view); (b) microcrystals of apatite lying on bacterial mats.*

#### **Figure 5.**

*Micrographs of bacterial mats: (a) a mat completely covered with filamentous bacteria; (b) a mat with void zones formed by cyanobacteria.*

Mathematical processing of the obtained data allowed us to find out the elemental composition of each layer under study, the numerical data of which are presented in **Table 1**.

According to **Table 1**, up to 20 different elements – metals, as well as phosphorus and silicon-were found in each layer of the studied crust. The average mass ratio in the crust is dominated by Fe (%), Mn (%), and P (%). Si and Al are also present in significant amounts. All these data were used to conduct a layer-by-layer phase analysis of the studied crust.

**Figures 6**–**8** shows X-ray diffractograms of all layers of the studied crust. The diffractograms were decoded for all phases, but we reverse special attention (highlight in the diffractograms) on Fe and Mn oxides. The main mineral phase in the relict layer (**Figure 6a**) is Fluorapatite, as well as minerals (calcium silicate, corundum, pargasite and pyrosmalite). Fe and Mn oxides compounds are detected in **Figure 6b**.

It is extremely difficult to perform a quantitative phase X-ray analysis of the studied layers of the ferromanganese crust: they consist of associations of a large number of minerals and nanoscale, often amorphous, oxide compounds of iron and manganese.

**9**

goethite and hematite.

*from layer to layer.*

**Table 1.**

**2.4 Mossbauer spectroscopy**

*Study of Deep-Ocean Ferromanganese Crusts Ore Components*

**Sample R I-1 I-2 II III** Al 3.78 1.02 2.17 4.33 3.49 Bi 0.11 0.09 0.00 0.00 0.00 Co 0.28 0.00 0.00 0.00 0.00 Cr 0.00 0.07 0.04 0.13 0.00 Cu 1.64 0.86 0.81 0.75 0.76 Fe 13.06 40.17 37.33 25.74 45.11 Mg 2.15 0.66 1.12 1.00 1.58 Mn 44.81 46.53 33.47 20.64 30.63 Mo 0.11 0.26 0.10 0.03 0.12 Nb 0.03 0.04 0.03 0.07 0.02 Ni 5.16 2.27 1.38 2.06 1.42 P 36.44 0.00 25.82 26.69 9.70 Pb 0.27 1.21 0.62 0.28 0.44 S 0.00 0.00 0.00 1.66 0.00 Sb 0.00 0.12 0.05 0.08 0.00 Si 2.68 2.94 3.97 11.00 8.63 Sn 0.00 0.09 0.00 0.08 0.04 Ti 2.75 2.08 1.79 3.00 1.44 V 0.88 0.37 0.31 0.49 0.21 W 0.08 0.07 0.08 0.09 0.07 Zn 0.91 0.65 0.43 0.48 0.42 Zr 0.46 0.78 0.68 0.74 0.60 *The lines of the main elements of the ore component Fe and Mn are highlighted in color for clarity of their change* 

As a result, the X-ray reflexes of oxides are very weakened and broadened in comparison with the reflexes of minerals of microcrystals. Their intensity is often comparable to the error limit of the method (2%). Therefore, we performed only to qualitative analysis. The observed broad peaks of Mn- oxides were deciphered by introducing todoroctitis and unstable buserite, which explains significant increase in the intensity and area of the peaks in the previously identified diffractogram angles: 35°

*Elemental composition obtained by means of X-ray fluorescence analysis.*

and 63° - 67°. Iron oxides on diffraction patterns (**Figures 6**–**8**) are represented by

More accurate studies of nanoscale iron oxide compounds in different layers of CMC can be carried out by the method of Mössbauer spectroscopy on the Co57 isotope. Due to its selectivity (only the Fe57 nuclei reflexes are recorded in the spectra), the method makes it possible to separate iron-containing minerals from the total mineral mass. According to the parameters of the Mössbauer spectrum. It is possible to determine the valence state of iron, the symmetry of its local neighborhood from the Mössbauer spectra parameters and therefore to determine the iron-containing


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


*Study of Deep-Ocean Ferromanganese Crusts Ore Components DOI: http://dx.doi.org/10.5772/intechopen.98200*

*The lines of the main elements of the ore component Fe and Mn are highlighted in color for clarity of their change from layer to layer.*

#### **Table 1.**

*Iron Ores*

**Figure 4.**

**Figure 5.**

**8**

presented in **Table 1**.

*zones formed by cyanobacteria.*

analysis of the studied crust.

Mathematical processing of the obtained data allowed us to find out the elemental composition of each layer under study, the numerical data of which are

*Micrographs of bacterial mats: (a) a mat completely covered with filamentous bacteria; (b) a mat with void* 

*Micrographs of the ferromanganese crust with different magnifications: (a) numerous columns of stromatolites* 

*are seen (top view); (b) microcrystals of apatite lying on bacterial mats.*

According to **Table 1**, up to 20 different elements – metals, as well as phosphorus and silicon-were found in each layer of the studied crust. The average mass ratio in the crust is dominated by Fe (%), Mn (%), and P (%). Si and Al are also present in significant amounts. All these data were used to conduct a layer-by-layer phase

**Figures 6**–**8** shows X-ray diffractograms of all layers of the studied crust. The diffractograms were decoded for all phases, but we reverse special attention (highlight in the diffractograms) on Fe and Mn oxides. The main mineral phase in the relict layer (**Figure 6a**) is Fluorapatite, as well as minerals (calcium silicate, corundum, pargasite and pyrosmalite). Fe and Mn oxides compounds are detected in **Figure 6b**. It is extremely difficult to perform a quantitative phase X-ray analysis of the studied layers of the ferromanganese crust: they consist of associations of a large number of minerals and nanoscale, often amorphous, oxide compounds of iron and manganese.

*Elemental composition obtained by means of X-ray fluorescence analysis.*

As a result, the X-ray reflexes of oxides are very weakened and broadened in comparison with the reflexes of minerals of microcrystals. Their intensity is often comparable to the error limit of the method (2%). Therefore, we performed only to qualitative analysis.

The observed broad peaks of Mn- oxides were deciphered by introducing todoroctitis and unstable buserite, which explains significant increase in the intensity and area of the peaks in the previously identified diffractogram angles: 35° - 37° and 63° - 67°. Iron oxides on diffraction patterns (**Figures 6**–**8**) are represented by goethite and hematite.

#### **2.4 Mossbauer spectroscopy**

More accurate studies of nanoscale iron oxide compounds in different layers of CMC can be carried out by the method of Mössbauer spectroscopy on the Co57 isotope. Due to its selectivity (only the Fe57 nuclei reflexes are recorded in the spectra), the method makes it possible to separate iron-containing minerals from the total mineral mass. According to the parameters of the Mössbauer spectrum. It is possible to determine the valence state of iron, the symmetry of its local neighborhood from the Mössbauer spectra parameters and therefore to determine the iron-containing

#### **Figure 6.**

*X-ray diffractogram of the relic layer of the ferromanganese crust: (a) analysis of minerals components; (b) analysis of Fe- and Mn- oxides.*

mineral [8], as well as to estimate the particle sizes of iron compounds from the temperature dependence of Mössbauer spectra [9, 10].

We performed the Mossbauer investigation of all the Iron-manganese crust layers (**Figure 1**) at room temperature. Five spectra of the different layers are presented in **Figure 4**.

All the spectra are broadened paramagnetic doublets, which indicates the superparamagnetic state of the iron oxide particles [11]. Mathematical processing of the spectra made it possible to decompose them into components corresponding to various iron oxides. Thus, a layer-by-layer quantitative phase analysis of the iron compounds of the studied crust was carried out. The figure shows that the smallest effect value (4.6%) is observed in the relic layer. There are significantly fewer ironcontaining minerals in R-layer than in layers I. 1 and I. 2 (7.4% and 6.8%), in which

**11**

**Figure 8.**

*X-ray diffractograms of layer II, III.*

**Figure 7.**

*X-ray diffractograms of layer I-1, I-2.*

*Study of Deep-Ocean Ferromanganese Crusts Ore Components*

bacterial activity is already observed. The R-layer phase compositions differs from the subsequent layers: in addition to trivalent oxides, it contains amorphous ferrihydrite (5Fe2O3. 9H2O) and divalent (FeO) wustite. In the subsequent layers I. 1 and I. 2, only trivalent iron oxides are present, which is explained by the active activity of iron-oxidizing bacteria. A comparative analysis of the Mossbauer spectra taken at room and nitrogen temperatures allowed us to estimate the size of these superparamagnetic particles. They are lesser than 7 nm for goethite, and lesser than 5 nm for hematite. The obtained estimate of the particle sizes of goethite and hematite corresponds to the sizes of biogenic nanoparticles [12]. Results are shown in **Figure 8**.

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

*Study of Deep-Ocean Ferromanganese Crusts Ore Components DOI: http://dx.doi.org/10.5772/intechopen.98200*

*Iron Ores*

**10**

presented in **Figure 4**.

*(b) analysis of Fe- and Mn- oxides.*

**Figure 6.**

mineral [8], as well as to estimate the particle sizes of iron compounds from the

*X-ray diffractogram of the relic layer of the ferromanganese crust: (a) analysis of minerals components;* 

All the spectra are broadened paramagnetic doublets, which indicates the superparamagnetic state of the iron oxide particles [11]. Mathematical processing of the spectra made it possible to decompose them into components corresponding to various iron oxides. Thus, a layer-by-layer quantitative phase analysis of the iron compounds of the studied crust was carried out. The figure shows that the smallest effect value (4.6%) is observed in the relic layer. There are significantly fewer ironcontaining minerals in R-layer than in layers I. 1 and I. 2 (7.4% and 6.8%), in which

We performed the Mossbauer investigation of all the Iron-manganese crust layers (**Figure 1**) at room temperature. Five spectra of the different layers are

temperature dependence of Mössbauer spectra [9, 10].

**Figure 7.** *X-ray diffractograms of layer I-1, I-2.*

**Figure 8.** *X-ray diffractograms of layer II, III.*

bacterial activity is already observed. The R-layer phase compositions differs from the subsequent layers: in addition to trivalent oxides, it contains amorphous ferrihydrite (5Fe2O3. 9H2O) and divalent (FeO) wustite. In the subsequent layers I. 1 and I. 2, only trivalent iron oxides are present, which is explained by the active activity of iron-oxidizing bacteria. A comparative analysis of the Mossbauer spectra taken at room and nitrogen temperatures allowed us to estimate the size of these superparamagnetic particles. They are lesser than 7 nm for goethite, and lesser than 5 nm for hematite. The obtained estimate of the particle sizes of goethite and hematite corresponds to the sizes of biogenic nanoparticles [12]. Results are shown in **Figure 8**.

Based on the results obtained, it is possible to trace the changes that occurred in the crusts over millions of years and make assumptions about the changes in the external conditions of their formation (**Figures 9** and **10**).

Since the main source of iron in the crusts was the products of volcanic eruption and collapsing basalts, the iron presented in the base of the crust in a metallic or divalent state. After that, under the influence of oxidizing bacteria, iron ions are oxidized to a trivalent state. This explains the presence of low concentrations of divalent wustite in the relict layer and the high content of trivalent iron in the composition of nanosized oxides: amorphous ferrihydrite, goethite, and hematite. In the subsequent layers I-1 and I-2, in which iron-oxidizing bacteria are active and ore-bearing stromatolites appear, an increase in the magnitude of the effect of the goethite and hematite phases is observed, with goethite as the most intensive phase.

In layer II, one can notice significant changes that have occurred with the iron oxides in the crust. Probably, during the global glaciation corresponding to the age of this layer (3.8–2.4 million years), other types of bacteria appeared with changes

**13**

*Study of Deep-Ocean Ferromanganese Crusts Ore Components*

in external conditions (changes in pH, temperature, environmental composition, including a large content of decaying endangered organisms). It leads to the trivalent iron contained in nanoscale goethite and hematite transformation to divalent in

In layer III, the phases of goethite and hematite are again observed. Probably, by the time of the formation of this layer, the reduction processes in the environment stopped and the colonies of oxidizing bacteria began to work actively again.

A comprehensive layer-by-layer analysis of the ferromanganese crust showed that the crust is practically a composite consisting of clastic and volcanogenic micron-sized minerals and stromatolites, consisting of fossilized biofilms filled with nanoparticles of iron and manganese oxide compounds, which are bacteria waste products. The lower layers of the crust are very dense: they contain many clastic minerals, and ore-bearing stromatolites grow between them. During the growth of the crust, bacteria constantly carry out their vital activity, therefore stromatolites grow continuously, occasionally changing their direction and shape under the influence of external conditions. And minerals: apatite, quartz and others come to the place of crust growth only occasionally - after a volcanic eruption. Therefore, the proportion of the iron-ore and manganese-ore components increases from the lower crust layer to the upper layer, which is almost entirely composed of these components. This leads to the fragility of the upper layers of the crust.

Experimental methods have provided objective evidence of the biogenic nature of the ore components of ferromanganese crusts. And the method of Mössbauer spectroscopy, first applied to these objects, made it possible to obtain a quantitative phase analysis of iron ore components in different layers of the crust. Based on this analysis, it was possible to trace how the composition of iron oxides changes in

different layers of the crust, depending on changes in external conditions.

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

wustite and partially divalent in magnetite.

*Quantitative phase composition diagrams of all layers of the studied crust.*

**3. Conclusion**

**Figure 10.**

**Figure 9.** *Mössbauer spectra of various layers of the crust.*

*Study of Deep-Ocean Ferromanganese Crusts Ore Components DOI: http://dx.doi.org/10.5772/intechopen.98200*

**Figure 10.**

*Iron Ores*

Based on the results obtained, it is possible to trace the changes that occurred in the crusts over millions of years and make assumptions about the changes in the

Since the main source of iron in the crusts was the products of volcanic eruption and collapsing basalts, the iron presented in the base of the crust in a metallic or divalent state. After that, under the influence of oxidizing bacteria, iron ions are oxidized to a trivalent state. This explains the presence of low concentrations of divalent wustite in the relict layer and the high content of trivalent iron in the composition of nanosized oxides: amorphous ferrihydrite, goethite, and hematite. In the subsequent layers I-1 and I-2, in which iron-oxidizing bacteria are active and ore-bearing stromatolites appear, an increase in the magnitude of the effect of the goethite and hematite phases is observed, with goethite as the most intensive phase. In layer II, one can notice significant changes that have occurred with the iron oxides in the crust. Probably, during the global glaciation corresponding to the age of this layer (3.8–2.4 million years), other types of bacteria appeared with changes

external conditions of their formation (**Figures 9** and **10**).

**12**

**Figure 9.**

*Mössbauer spectra of various layers of the crust.*

in external conditions (changes in pH, temperature, environmental composition, including a large content of decaying endangered organisms). It leads to the trivalent iron contained in nanoscale goethite and hematite transformation to divalent in wustite and partially divalent in magnetite.

In layer III, the phases of goethite and hematite are again observed. Probably, by the time of the formation of this layer, the reduction processes in the environment stopped and the colonies of oxidizing bacteria began to work actively again.
