Morphology, Geochemical Association and Genesis of Fe-Mn Nodules from the Central Indian Ocean Basin
Authors’ name
Present Address:
A
Dr.
SaurabhKumarBarman1✉Phone+91 9795680102Emailbarmansaurabh51@gmail.comProf.
SanjayKumarTiwari1Emailsktiwari.bhu@gmail.comDr.
ManvendraSinghChauhan2Phone+91 9415410123Emailmanvendra.ceng@bbau.ac.inShahIzharAhmed3Phone+917007702375Emailnayab.ansari78@gmail.com
Dr.
AshwaniKumarSonkar4Phone+91 7080907063Emailaksonkariitbhu@gmail.comTel.1
Tel.1
1Department of Geology, Institute of ScienceBanaras Hindu University221005VaranasiU.PIndia
2Department of Civil EngineeringUIET, Babasaheb Bhimrao Ambedkar University226025LucknowIndia
3Shah Izhar Ahmed, Assistant Hydrogeologist, CGWB380061AhmedabadGovt. of India
4Department of Civil Engineering, Department of Mining EngineeringAshoka Institute of Technology and Management, Indian Institute of Technology (Banaras Hindu University)221005Varanasi, VaranasiIndia
Saurabh Kumar Barman 1*, Sanjay Kumar Tiwari1, Manvendra Singh Chauhan2, Shah Izhar Ahmed3 and Ashwani Kumar Sonkar4
*Corresponding Author
Addresses
1Department of Geology, Institute of Science, Banaras Hindu University, Varanasi-221005, India
2Department of Civil Engineering, UIET, Babasaheb Bhimrao Ambedkar University, Lucknow-226025, India
3Shah Izhar Ahmed, Assistant Hydrogeologist, CGWB, Ahmedabad-380061, Govt. of India
4Department of Civil Engineering, Ashoka Institute of Technology and Management, Varanasi & Department of Mining Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi-221005, India
Contact information of authors
*Corresponding Author: Saurabh Kumar Barman1, Tel. +91 9795680102, E-mail: barmansaurabh51@gmail.com
Prof. Sanjay Kumar Tiwari1, Tel. +91 9453038452, E-mail: sktiwari.bhu@gmail.com
Dr. Manvendra Singh Chauhan2, Tel. +91 9415410123, E-mail: manvendra.ceng@bbau.ac.in
Shah Izhar Ahmed3, Tel. +917007702375, E-mail: nayab.ansari78@gmail.com
Dr. Ashwani Kumar Sonkar4, Tel. +91 7080907063, E-mail: aksonkariitbhu@gmail.com
Complete address of the corresponding author:
Dr. Saurabh Kumar Barman
Department of Geology,
Institute of Science,
Banaras Hindu University,
Varanasi 221005, U.P., India
Tel: +91 9795680102
E-mail: barmansaurabh51@gmail.com
Abstract
Larger nodules are poor in grade and better in Fe, Co and wet contents and suggest their genesis at deeper depth by a hydrogenous method. N/n (size of nodule/nucleus) ratios and nucleus size increase with increasing nodule size, supporting view that smaller and large nodules have been formed otherwise at completely different places. Among nodules of different sizes, only medium sized of 3–6 cm are higher in grade and their exploitation looks to be economical. The smaller nodules are better in grade (Cu + Ni + Co %), Mn and Zn contents.
Elemental association and their correlation indicate that Mn is negatively correlated with Fe, Co, Pb, Sr while Fe show negative correlation with Cu, Ni, Zn. Similarly, Cu show negative correlation with Co, Pb, Sr, CaO, Na2O, TiO2 while Ni show negative correlation with Co, Pb, Na2O, TiO2 while Zn show negative correlation with Co, Pb, Sr, CaO, Na2O. Similarly, Mn show Positive correlation with Cu, Ni, Zn; Fe show Positive correlation with Co, Pb, Sr, CaO, Na2O, K2O, TiO2 Which can be possibly sourced from hydrolytic release of terrigenous materials; Cu show Positive correlation with Ni, Zn; Ni show Positive correlation with Zn; Co show Positive correlation with Pb, Sr, CaO, TiO2; Pb show Positive correlation with Sr, CaO; Sr show Positive correlation with CaO, Na2O, P2O5; Al2O3 show Positive correlation with CaO; CaO show Positive correlation with P2O5; Na2O show Positive correlation with K2O, TiO2 Which might be possibly sourced from remobilization of metals in marine sediments and pore water.
Keyword:
AAS
Central Indian Ocean Basin
Correlation matrix
Ferromanganese Nodules
HR-SEM
Nodule Morphology
XRD
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1. Introduction: Morphological, mineralogical and geochemical research on nodules of various sizes gathered from parts of Central Indian Ocean Basin (CIOB) display two suits of nodule genesis by oxic diagenetic and hydrogenous method ensuing into distinct properties. They normally vary in length from 0.5 to 25 cm in diameter (small: 0–3 cm, medium: 3–6 cm and large: >6 cm) but average diameter being 2 to 4 cm. Marine Fe-Mn polymetallic nodules (Mn-nodules) are composed of Mn oxides and Fe oxides/hydroxides, which might be sourced and prompted from the seawater or floor-sediment pore water. They incorporate a huge variety of metallic sources with excessive potential economic values, in particular Mn, Ni, Cu, Fe, Mo, Li, Co and REEs (Glasby et al., 1978; Halbach et al. 1981; Cronan et al. 1991; Hein and Koschinsky 2013, 2014; Bau et al. 2014a; Hein et al. 2015).
These nodules usually have a complex texture especially characterized by way of irregular, concentric micro-layers around a nucleus (Wegorzewski et al., 2014). Although, previous studies have centered on the majority-nodule mineralogical and geochemical compositions (Halbach et al., 1982; Nath et al. 1992; Hlawatsch et al., 2002; Pattan et al., 1993; Verlaan et al., 2004; Cronan 2006; Takahashi et al. 2007) yet a specific have a look at of the nodules of CIOB are needed, which may additionally replicate the growth processes leading to different genetic kinds of nodules: Hydrogenetic and Diagenetic precipitation (Reyss et al. 1985; Wegorzewski et al., 2014; Guan et al. 2019a).
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These nodules are marine authigenic sedimentary rocks that occur at the bottom of ocean basins in different types of terrain. In this study polymetallic (Mn-nodules) samples are primarily acquired from the latitude 9.5ºS to 12ºS and longitude 74ºE to 78.5ºE and water depth ranges from 4,900-5,900m in the Central Indian Ocean Basin which is represented in the above bathymetric map (Fig. 1) prepared in ArcGIS 10.4. Nodules programme of India aims at exploration and development of technologies for extraction of nodules from the Central Indian Ocean Basin (CIOB), having an area of 75,000 km2, located about 1600 km away from the southern tip of the Indian Peninsula. Nodules are concretions on the ocean bottom formed of concentric layers of Fe and Mn hydroxides around a core. These are most valuable mineral deposits in the ocean containing many metals above crustal abundances and hence aptly called Fe-Mn nodules. Mn concentration is greater within the nucleus of nodule and its concentration decreases closer to periphery. Fe-components suggests a reverse trend and is greater concentrated closer to the peripheral a part of nodule.Hydrogenetic Fe-Mn nodules are primarily composed of vernadite (δ-MnO2), which is intergrown with X-ray amorphous Fe-oxyhydroxide nanoparticles (Hein et al., 2000; Koschinsky et al. 2010). At some stage in the diagenetic precipitation, the nodules consist of various manganese minerals, 7Å and 10Å manganates, along with todorokite (Burns et al. 1978a, 1978b).
The nodule reserves of world oceans are abundant and contain more than 3×1012 ton, rich in Fe, Mn, Cu, Co, and Ni. The nodules occur in different regions and have various main components such as CIOB nodules are rich in Mn where Mn/Fe ratio is high. The REE content in the nodules are well above marine sediments and seawater. Usually, the REE content is 10 to 100 times higher than in deep-sea sediments or seawater (Zhang et al. 2012).
2. Material and Method: Samples of Mn-nodules, have been obtained from CIOB. Sampling was done by boomerang grabs during cruise attachment GA-REAY-1-1985. Different size nodules were selected for the study depending on availability. The samples had been selected on the premise in their colour, outside morphology and size. The selected samples had been reduce vertically in two halves with reference to their position at the seafloor earlier than macroscopic inner descriptions and physical, XRD and qualitative analysis.
As a result of the availability of current best-scale analytical instruments (viz. XRD, AAS, HR-SEM, SEM-EDS, and ICP-MS) morphological, geochemical and mineral compositions were studied. The mineral compositions were determined by X-ray Powder Diffraction (XRD) using fine powder of Fe-Mn nodule to collect diffraction patterns. Morphological, internal structure, microtextural and 3D textural mineral study was performed using SEM and HR-SEM.
The methodology includes the experimental design and methods adopted during the study. Thirty dried nodules samples have been considered here. The shape, size and surface texture of each nodule was described before it was crushed for bulk analyses. These samples were cut into two halves and were polished and used for mineralogical studies. The samples then were powdered in agate mortar which is the non-abrasive disaggregation process. The samples were then sieved. For this purpose sieves of 63µ was used. The sieved samples thus obtained were washed thoroughly by distilled water. Later these were dried in an oven at 110º C for 3 hours. The powdered samples were used for mineralogical studies by XRD. Some parts of the samples was used for chemical analysis and leaching analysis.
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The dry nodule samples were carefully overwhelmed and ground in an agate mortar. Major and trace (which includes REE) elements concentrations were analyzed by way of Atomic Absorption Spectrophotometer (AAS) (Table. 1). In chemical analysis 0.5g of samples was used with NaOH pellates in Ni crucible and the material was transferred into 250 ml flask.
With the help of 1:1 HCl the volume was made 250 ml. This acts as solution A and was used for SiO2 and Al2O3 analysis through U-V spectrophotometer.
Then, 0.1g of samples was taken for the preparation of solution B through acid digestion. This samples was kept in the tephelon bomb followed by adding few drops of HF, HCl and HNO3. The samples was digested for about 2 hours and was then transferred into 100 ml flask with the help of 1:1 HCl and made the volume 100 ml.
This solution was used for various trace and major elements analysis through AAS by using Perkin Almer model 2380. Some of this solution was also used for the determination of TiO2 and P2O5 through U-V spectrophotometer. Elemental composition of Fe, Mn, Cu, Ni, Co and Zn was determined using AAS of the samples.
In this study, we've received excessive-resolution chemical data of the Fe-Mn polymetallic nodules from the CIOB. The morphology and mineralogy of the distinct size class of nodules followed with the aid of their analysis and revealing the incidence and enrichment techniques of the economic metals of the nodules had been accomplished.
3. Nodule Morphology: Morphological study shows large variations in size, shape and surface characteristics in the CIOB nodules. Nodules are characterized with the aid of using distinct morphological sorts viz. tabular, discoidal, ellipsoidal, irregular, cylindrical and subspherical but the major morphological types are spheroidal, ellipsoidal and irregular with rough surface texture are dominant. The Tabular, Faceted, and Biological nodule types are scanty in existence and the disparity is high. The nodule form might be associated with the form of the core. The nodules display a huge variety of densities, weights, sizes, and morphologies. Although 06 different nodule types have been recognized in this study, there may be many more in other parts of the CIOB. The floor texture is easy to hard and botryoidal. Edges of nodules are typically rounded. Surface coloration varies among deep brown and black, is unconventional of the shape or size of the nodule, and displays the essential chemical composition of the outer part of the samples viz. Fe oxyhydroxides (darkish brown to black coloration) and Mn oxides (black coloration). Fractures with special directions, much less than 1cm in width and variable length, are seen at the surface, in particular in relatively huge nodules. These fractures may be open or full of bottom sediment and mineral precipitates (González et al. 2010).
Higher occurrence of small to medium size nodules of spheroidal and ellipsoidal shape in both the Indian and Pacific Oceans, therefore, suggest their formation more or less under similar conditions with faster growth rates in comparison with the other nodule types (Valsangkar et al., 1992). The decrease within the relative variety of nodules with large diameter can be because of separation mechanisms or selective burial of the bigger nodules, conjugation of smaller nodules into large ones, or may be higher conditions for nodule nucleation and accretion. They are set up by numerous millimeter-thick layers of Fe and Mn oxyhydroxides nearby the nucleus.
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Nodule distribution with respect to size further show that in small, medium and intermediate size nodules, occurrence of spheroidal and ellipsoidal types are maximum. It is also noticed that, from small to large size nodules the percentage of occurrence for rough surface nodules decreases whereas that of smooth surface nodules increases. Here are some hand specimen photograph (Fig. 2) of small size (0–3 cm), medium size (3–6 cm) and large size (> 6 cm) nodules sample which was collected during cruise attachment from CIOB.The shape of the nodules is mostly spherical and cauliflower-like. We have studied total 30 samples which are classified into two size class viz. < = 4 cm and size class > 4 cm. The primary morphology are [S] = Spheroidal, [E] = Ellipsoidal, [D] = Discoidal, [P] = “Poly' or Coalespheroidal, [B] = Biological (containing tooth, bone, or vertebra), [T] = Faceted (due to angular nucleus or fracturing). The surface textures are: s = smooth (or microgranular), r = rough (or microbotryoidal) b = botryoidal. The examples are: 1[D]b = large discoidal nodule with uniform botryoidal surface; m[D-E]bS= medium nodule transitional between Ellipsoidal and Discoidal in shape with a smooth upper surface and botryoidal lower surface and m-1[F]r = medium to large nodule fragment with a rough surface (Roonwal 1986). The nodular physical properties equivalent to most density, diameter, porosity, and weight are just like those nodules reportable from the Pacific and East Indian Ocean basins (Raab et al., 1977; Stackelberg 1977; Palma et al. 2000).
4. Mineralogy:
4.1 SEM and HR-SEM Analysis: For detailed observation of the increase textures of individual microlayers within the Fe-Mn nodules, SEM analyses were performed at the (CIF) IIT-BHU, Varanasi. The nodule samples had been Cut into thin slabs throughout the profile and had been analyzed using a Scanning electron microscopy: SEMEDS Model: EVO-Scanning Electron Microscope MA15/18, CARL ZEISS MICROSCOPY LTD. EDS: 51N1000-EDS System, Oxford Instruments Nanoanalysis with an engaged electron beam delivered by a field emission gun (W-crystal) utilizing a 20 kV acceleration under high vacuum conditions (10 − 9 mbar). The scanning electron microscope lens has a beam size of 2 to 20 µm measurement with a greatest 10 KX magnification.
The nodules samples were analyzed using High Resolution Scanning electron microscopy at (CIF) IIT-BHU, Varanasi; HR-SEMEDS: Nova Nano SEM 450: FEI Company of USA (S.E.A) PTE, LTD EDS: Team Pegasus Integrated EDS-EBSD with Octane Plus and Hikari Pro: EDAX Inc. with an engaged electron beam delivered by a field emission gun utilizing a 15 kV acceleration. The scanning electron microscope lens has a beam size of 1 to 100 µm and 500 nm breadth with a maximum 20 KX magnification and resolution (eV) 125.3.
The main components of nodules are: goethite, lepidocrocite, 7Å manganates, 10Å manganates, pyrolusite, quartz and phyllosilicates. Accessory minerals related to these major phases dolomite, calcite, siderite, pyrite, rhodochrosite, marcasite, potassium feldspar, chalcopyrite, zircon, rutile, ilmenite, apatite and chlorite. Gypsum is gift as a trace secondary mineral. Fe-Mn oxides and oxyhydroxides constitute an average of > 70 wt% of the nodular mass and that they form a vital part of the layers. Nuclei are composed of carbonates (essentially siderite to rhodochrosite), silicates in minor percentage and disseminated fool's gold (pyrite) as an accent mineral. Silicates (particular in detritus layers) and carbonates distributed within the oxide layers and focused inside the nuclei represent constitute approximately 30 wt% of the nodular mass.
The SEM pictures show micro-crystalline mosaic of parallelogram crystal sections closely inter-grown during a cryptocrystalline matrix wherever detritus fragments and framboids are spread during a varying quantity of abundance.
These rhombus formed crystals vary between 2 and 20 µm, upto a 100 µm in size and ordinarily gift with iron ore goethite, and the nucleus of those crystals is developed by a combination of goethite and Mn oxides. Matrix additives are developed by a combination of phylosilicates, Mn oxides, and carbonates (crammed in micro-fractures).
Silicates and alternative detritus fragments are spread in the matrix, or form layers wealthy in detritus (detritus structure) and poor in Fe-Mn oxides. Goethite forming framboidal and sub-idiomorphic cubic/octahedral aggregates derived from partial or total replacement of fool's gold (pyrite) and substituting carbonates of the shells of marine organisms also are observed.
The center presentations the similar micro-crystalline mosaic of parallelogram crystals because the ferromanganese layers, however the symmetric crystals are fashioned by a zoned carbonate between siderite and rhodochrosite in a very matrix of phyllosilicates with dispersal detritus fragments primarily quartz and feldspar and fool's gold (pyrite).
SEM observations conjointly revealed presence of shape like microbes and filament like morphology. Fibrous texture like microbes coated by Mn oxides and wealthy in organic carbon have been known within the pores of a few samples.
Fig. 3
Scanning Electron Microscope (SEM) Photograph of different Size of Mn-Nodules
SEM analysis were used to study morphology & biomineralisation of nodules.
Microorganisms are present in nodules; analysis indicates that within nodules, both round-shaped cocci and elongated rods on surface of nodules (Fig. 3).
The areas rich in microorganisms are also rich in Mn, while in regions where no microorganisms are found, Si is dominant. We suggest that growth of Mn-nodules starts with formation of micronodules. After accretion of biogenic and additional nonbiogenic minerals, the micronodules assemble to large nodules on sea floor through additional inclusion of nonbiogenic material.
Fig. 4
a: HR-SEM Plot of Small Nodules (0–3 cm)
Fig. 4
b: HR-SEM Plot of Medium Nodules (3–6 cm)
Fig. 4
c: HR-SEM Plot of Large Nodules (> 6 cm)
The HR-SEM spectrum of small nodule shows high values of V, Ti, Mn and Fe and low value of Mo, Th, Ti, V, Co, Ni, Cu and Zn (Fig. 4a). The O, Cr, Mn and Ti content shows high values in the medium nodules while low value of Ni, Co, Ti, Zn, Cu and Fe (Fig. 4b). Similarly the value of Fe, Cu, Co and Cr is high in large nodules while there is low values of Ti, Ni and Mn (Fig. 4c). In general the value of Mn is higher in small and medium nodule in comparison to larger ones.
4.2 XRD analysis: The Mn-nodules mineral compositions mainly manganese oxide and other accessory mineral phases were determined by X-ray Powder Diffraction (XRD) pattern using fine powder of Fe-Mn nodule to collect diffraction patterns. Mineralogical XRD profiles from 2θ = 3–60° (40kV and 15 mA) in 0.0200 steps were obtained for 08 samples using Model: Rigaku Smart Lab 9kW Powder type (without χcradle), RIGAKU Corporation at (CIF) IIT-BHU, Varanasi, India. The concentration of Mn is high in Mn-nodules.
XRD analysis yielded similar X-ray powder diffraction styles for the polymetallic nodules (small, medium, large) analyzed. The diffraction peaks of nodules primarily correspond to todorokite, vernadite (δ-MnO2), quartz, zeolite and feldspar (Fig. 5). Infact crystallinity is not excellent therefore the peaks are not terribly high, clear and nicely defined. The nodules comprise moderate concentrations of iron and no reflections of Fe-phase minerals were recorded within the nodules. This can be because of bad crystallinity (X-ray amorphous) of iron oxides/hydroxides. It is tough to estimate the percentage of every phase because of the presence of amorphous phase. However, the important Mn mineral is vernadite, that is common in most marine hydrogenetic Mn oxides (Hein et al. 2013c, 2016), and minor quantities of todorokite in nodules. The todorokite incorporates a comparatively high crystallinity and suggests apparent sharp X-ray reflection, different vernadite that suggests a large and susceptible X-ray reflection, suggesting that vernadite has bad crystallinity. The high peak corresponds to quartz although lesser in amounts and also other detrital minerals viz. feldspar, Phillipsite etc. indicates that possible terrigenous detrital source is far away (Guan et al. 2017). However, todorokite in association with quartz, Feldspar and phillipsite is observed in the nodules. The Preliminary result suggests that Mn released from smectite clay mineral and early diagenesis are responsible for their formation.
Fig. 5
a: XRD pattern of small size nodules (0–3 cm)
Fig. 5
b: XRD pattern of medium size nodules (3–6 cm)
Fig. 5
c: XRD pattern of large size nodules (> 6 cm)
Todorokite and delta MnO2 are the two predominant minerals present within the nodules. Generally, nodules wealthy in Mn have todorokite and those wealthy in Fe have δ-MnO2. The X-ray diffraction pattern of 08 nodule samples indicates small and broad peaks of todorokite in small size nodules. The major Mn minerals viz. todorokite, δ-MnO2 (vernadite) and Quartz occur as an important minerals (Fig. 5a). In smaller nodules occurrence of phillipsite and feldspars is less and that of birnessite is rare. The important mineral occurring in the medium size nodules are todorokite, δ-MnO2 (vernadite), Feldspar, phillipsite and Quartz (Fig. 5b). It has been noticed that the profile peaks of todorokite decreases from small to larger size nodules with few exceptions as visible in XRD profile of large nodules (Fig. 5c). These mineral stages are intergrown with the X-ray indistinct Fe oxides/hydroxides, which may have been solidified to goethite (Hein and Koschinsky 2014). Also, detrital aluminosilicate minerals, for example, quartz and minor feldspars are available in the nodules. The feldspars are present within the nodules. Fe-Mn oxides and oxyhydroxides are usually > 70 wt% of the nodular mass (Barman. S.K and Tiwari. S.K 2021).
The relationship between Mn and Ni content in Fe-Mn nodules illustrate the mineralogical control on minor metal concentration. Infact, the higher Mn and Ni content illustrate the concentration of todorokite as the main Mn mineral and lower % of Mn, Fe represent the δ-MnO2. Besides this todorokite is also found at greater depth whereas δ-MnO2 is found at lesser depth.
Hydrogenetic polymetallic nodules are basically made out of vernadite (δ-MnO2), which is intergrown with X-ray indistinct Fe-oxyhydroxide (Hein et al., 2000; Koschinsky et al. 2010). During the diagenetic development, the nodules comprise of various manganese minerals, 7Å and 10Å manganates, for example, todorokite, phyllomanganates; (Burns et al. 1978a, 1978b), buserite (Usui, A & Someya 1997), and birnessite (Usui, A & Someya 1997; Hein et al. 2013a). X-ray indistinct Fe oxyhydroxides were additionally answered to contain feroxyhyte, ferrihydrite and goethite (Baturin 1988).
Mn show strong negative correlation with Fe, Co, Pb, Sr; Fe show strong negative correlation with Cu, Ni, Zn; Cu show strong negative correlation with Co, Pb, Sr, CaO, Na2O, TiO2; Ni show strong negative correlation with Co, Pb, Na2O, TiO2 while Zn show strong negative correlation with Co, Pb, Sr, CaO, Na2O. Similarly, Mn show strong Positive correlation with Cu, Ni, Zn; Fe show strong Positive correlation with Co, Pb, Sr, CaO, Na2O, K2O, TiO2; Cu show strong Positive correlation with Ni, Zn; Ni show strong Positive correlation with Zn; Co show strong Positive correlation with Pb, Sr, CaO, TiO2; Pb show strong Positive correlation with Sr, CaO; Sr show strong Positive correlation with CaO, Na2O, P2O5; Al2O3 show strong Positive correlation with CaO; CaO show strong Positive correlation with P2O5; Na2O show strong Positive correlation with K2O, TiO2. (Table: 2).
Mn | Fe | Cu | Ni | Zn | Co | Pb | Sr | SiO2 | Al2O3 | CaO | MgO | Na2O | K2O | TiO2 | P2O5 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Mn | 1 | |||||||||||||||
Fe | -0.817 | 1 | ||||||||||||||
Cu | 0.94 | -0.847 | 1 | |||||||||||||
Ni | 0.873 | -0.803 | 0.944 | 1 | ||||||||||||
Zn | 0.722 | -0.815 | 0.791 | 0.746 | 1 | |||||||||||
Co | -0.857 | 0.942 | -0.868 | -0.829 | -0.792 | 1 | ||||||||||
Pb | -0.783 | 0.837 | -0.797 | -0.724 | -0.791 | 0.878 | 1 | |||||||||
Sr | -0.631 | 0.705 | -0.581 | -0.441 | -0.502 | 0.629 | 0.582 | 1 | ||||||||
SiO2 | -0.0829 | 0.24 | -0.136 | -0.196 | -0.241 | 0.217 | 0.21 | 0.122 | 1 | |||||||
Al2O3 | -0.318 | 0.456 | -0.298 | -0.242 | -0.379 | 0.302 | 0.343 | 0.451 | 0.325 | 1 | ||||||
CaO | -0.491 | 0.629 | -0.505 | -0.383 | -0.573 | 0.523 | 0.591 | 0.786 | 0.0288 | 0.551 | 1 | |||||
MgO | 0.0251 | 0.013 | 0.0052 | 0.0138 | -0.142 | -0.0425 | 0.0246 | 0.0689 | -0.155 | 0.208 | 0.345 | 1 | ||||
Na2O | -0.449 | 0.695 | -0.517 | -0.525 | -0.518 | 0.499 | 0.37 | 0.503 | 0.235 | 0.478 | 0.435 | 0.118 | 1 | |||
K2O | -0.333 | 0.62 | -0.419 | -0.373 | -0.431 | 0.49 | 0.469 | 0.456 | 0.0941 | 0.256 | 0.393 | -0.106 | 0.655 | 1 | ||
TiO2 | -0.418 | 0.613 | -0.528 | -0.598 | -0.431 | 0.621 | 0.459 | 0.289 | 0.313 | 0.106 | 0.248 | -0.195 | 0.515 | 0.297 | 1 | |
P2O5 | -0.214 | 0.397 | -0.24 | -0.176 | -0.369 | 0.281 | 0.283 | 0.549 | -0.0803 | 0.429 | 0.866 | 0.248 | 0.321 | 0.287 | 0.15 | 1 |
Table No: 3 Correlation Matrix for Small Size Nodules (0–3 cm) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Mn % | Fe % | SiO2% | Al2O3% | CaO % | MgO % | Na2O % | K2O % | Cu % | Ni % | |
Mn % | 1 | |||||||||
Fe % | -0.54662 | 1 | ||||||||
SiO2% | -0.10004 | 0.53981 | 1 | |||||||
Al2O3% | -0.1294 | 0.184287 | 0.596182 | 1 | ||||||
CaO % | -0.37623 | 0.385081 | 0.614206 | 0.682819 | 1 | |||||
MgO % | -0.74466 | 0.332906 | 0.193492 | 0.210202 | 0.119187 | 1 | ||||
Na2O % | -0.10006 | 0.715754 | 0.684682 | 0.052079 | 0.039101 | 0.199159 | 1 | |||
K2O % | 0.377441 | 0.105667 | 0.309029 | -0.20665 | -0.041 | -0.16947 | 0.300491 | 1 | ||
Cu % | 0.426287 | -0.8826 | -0.51567 | 0.031642 | -0.17367 | -0.30414 | -0.87984 | -0.22737 | 1 | |
Ni % | 0.530208 | -0.70709 | -0.35596 | 0.239747 | -0.02512 | -0.31144 | -0.75951 | 0.077816 | 0.846115 | 1 |
Table No: 4 Correlation Matrix for Medium Size Nodules (3–6 cm) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Mn % | Fe % | SiO2% | Al2O3% | CaO % | MgO % | Na2O % | K2O % | Cu % | Ni % | |
Mn % | 1 | |||||||||
Fe % | -0.23705 | 1 | ||||||||
SiO2% | -0.26781 | 0.354908 | 1 | |||||||
Al2O3% | -0.19039 | 0.248567 | 0.877773 | 1 | ||||||
CaO % | -0.23965 | 0.205366 | 0.801257 | 0.826642 | 1 | |||||
MgO % | -0.24227 | 0.012579 | 0.572109 | 0.655629 | 0.68966 | 1 | ||||
Na2O % | -0.2903 | 0.407391 | 0.7808 | 0.576751 | 0.553093 | 0.667748 | 1 | |||
K2O% | -0.26744 | 0.698664 | 0.772449 | 0.608611 | 0.74823 | 0.456045 | 0.790102 | 1 | ||
Cu % | 0.918867 | -0.08717 | -0.33846 | -0.29005 | -0.48159 | -0.43149 | -0.36864 | -0.3784 | 1 | |
Ni % | 0.884975 | -0.10454 | -0.32856 | -0.31887 | -0.39829 | -0.46929 | -0.33464 | -0.27522 | 0.906469 | 1 |
Table No: 5 Correlation Matrix for Large Size Nodules (> 6 cm) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
Mn % | Fe % | SiO2% | Al2O3% | CaO% | MgO % | Na2O % | K2O % | Cu % | Ni % | |
Mn % | 1 | |||||||||
Fe % | -0.4981 | 1 | ||||||||
SiO2% | -0.46791 | 0.62568 | 1 | |||||||
Al2O3% | -0.45447 | 0.616773 | 0.917833 | 1 | ||||||
CaO % | -0.42246 | 0.523558 | 0.27441 | 0.221941 | 1 | |||||
MgO % | -0.45049 | 0.389991 | 0.461285 | 0.284566 | 0.750002 | 1 | ||||
Na2O % | 0.13546 | 0.271251 | 0.476093 | 0.580399 | 0.151141 | 0.189548 | 1 | |||
K2O % | 0.09964 | -0.00651 | -0.01272 | 0.069759 | -0.03105 | -0.31048 | 0.540408 | 1 | ||
Cu % | 0.89307 | -0.51979 | -0.40311 | -0.39534 | -0.39537 | -0.23543 | 0.237644 | -0.0123 | 1 | |
Ni % | 0.709259 | -0.55335 | -0.35512 | -0.45997 | -0.12576 | 0.067526 | 0.154056 | -0.05434 | 0.872659 | 1 |
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Mn shows strong positive correlation with Cu and Ni in medium and large nodules while it also shows strong negative correlation with Fe in small nodules. Fe shows strong negative correlation with Cu and Ni in small and large nodules. Cu shows strong positive correlation with Ni in all size nodules (Table: 3, 4 & 5).A
5. Genesis: Regarding the various phases and types of the nodules, the ternary diagrams are very useful tools for study. In this ternary diagram (Ni + Cu + Co) x 10-Fe-Mn (Fig. 6), the two genetic types of nodules have been demarcated viz. hydrogenetic which is primarily derived from oceanic precipitation and diagenetic in which the underlying and the pore water also play a major role in the addition, growth and remobilization of metals. The portion between the two occurs at value 5. Towards left of it, it is entirely hydrogenetic types of nodules and towards right it is entirely diagenetic nodules. The samples under study belongs mainly to hydrogenetic type. This ternary diagram was given by (Bonatti 1983).A
The Cu-Ni-Zn ternary diagram (Fig. 7) indicates that there are various types of nodules found from different locations reported by different authors. The samples tally more with the nodules as reported by (Mero 1965) from the Pacific Ocean.From the Al-Mn-Fe ternary diagram (Fig. 8) it is important to note that all the nodules have poor Al content. This is because of the fact that Al is basically terrigenous in nature and as the nodules do not contain terrigenous elements, they are comparatively poorer in Al. In this case also the samples fall within the composition range as reported by (Mero 1965).
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The Fig. 9 indicates the various phases on the basis of Si, Mn and Fe composition such as oxide, hydroxide, sulphide and silicate phases. The samples belong to oxide and hydroxide phases. The following ternary diagrams act as important gear to examine the nodule compositions with the opposite metalliferous deposits:i. (Cu + Ni + Co) x 10 - Mn - Fe (Fig. 6) ii. Cu - Zn - Ni (Fig. 7)
iii.
Al - Mn - Fe (Fig. 8) iv. Si - Mn - Fe (Fig. 9)
Figure 6: (Ni + Cu + Co) x10-Fe-Mn ternary diagram showing field of hydrogenetic nodules
● Represent nodules of the present study
Figure 7: Cu-Ni-Zn diagram showing composition of oceanic Fe-Mn deposit on the basis of Cu-Ni-Zn contents.
Fig. 8
Composition of oceanic ferromanganese deposits based on Al-Mn-Fe contents.
Sources: 
Nodules, (Mero 1965), O-E. P. R. sediments, Δ Baur deep sediments, (Heath and Dymond 1977), ▲ pelagic clays, (Calvert and Price 1977), ● Nodules of the present study.
Figure 9: Si-Mn-Fe diagram to show various sediments phase. ● Nodules of present study
These figures demarcate the fields of hydrothermal/metalliferous sediments, oceanic ferromanganese nodules (as quoted by various authors), pelagic clays etc. The nodules under study belong to the idealized nodule fields of the other oceans and fall within the range of oxides/hydroxide fields (hydrogenetic & diagenetic).
Hydrogenetic nodules developed directly from seawater, while diagenetic nodules usually developed from sediments pore liquids that include seawater altered by chemical reactions inside the sediment section. Diagenesis may happen under oxic or suboxic conditions, and the mixed genetic Fe-Mn nodules are more typical than both of the two end-part types. In view of the contribution of diagenetic component in the diagenetic and mixed genetic nodules, their development rates are a lot higher than those of the hydrogenetic Fe-Mn nodules, and the more prominent diagenetic contribution to the nodules, the faster their development rates can be (Hein et al. 2013b).
7. Discussion & Conclusion: The average chemical composition of a nodule is inversely related to its size. In comparison to their larger nodules the smaller nodules have a higher grade. Thus, we may infer that besides morphological characters, the small and large nodules are distinct in their compositions. The two different types of nodules, therefore, indicate two different modes of formation viz. by diagenetic and hydrogenetic processes (Valsangkar et al., 1992; Valsangkar et al., 1994).
The geochemical analysis and variations in Mn/Fe and Cu + Ni ratios between smaller nodules (< 4 cm) to larger nodules (> 4 cm) is 3.06 to 2.50 and 2.05 to 2.22 respectively indicate some variation in source and an early diagenesis (Halbach et al. 1981; Valsangkar et al., 1988) suggest more or less the uniformity of regional geochemical conditions. This ratio of Mn/Fe indicates that the nodules are of mixed origin i.e. authigenitic as well as diagenetic. This is further evident from the variation in Mn/Fe ratios in the study area where nodules have grown to different sizes with varying compositions. Therefore, variation in Mn/Fe ratio also supports the view that different sized nodules have formed differently at different places in various sedimentary environments. Formation of nodules by different accretionary processes is obvious from Figs. 6 & 7 where the plots spread from diagenetic to hydrogenetic field. It is, therefore, clear that these processes were responsible for the formation of nodules, leading to distinguishable morphological, mineralogical and chemical properties. Owing to the fact that the different sized nodules occur close to one another on the seafloor, it is not reasonable to consider that the above processes were active either all at a time, alternatively or simultaneously in the area. This supports the view that formation of different sized nodules took place separately in different regions (Valsangkar et al., 1989; Valsangkar et al., 1992). Thus, larger nodules which are deficient in grade and Mn and Zn content suggest their formation mainly from seawater and so, are rich in Fe and Co contents. Formation of smaller nodules by diagenetic process with an additional supply source (such as CCD) explains why they are rich in grade and Mn and Zn contents. It is possible that initially the nucleus of the nodule was formed at a shallower depth and then it was transported to deeper depth due to the currents along the downslope, where it grew slowly from the seawater (hydrogenous).
It can be inferred that larger nodules were formed on a larger nucleus and vice versa. This further suggests that smaller nodules did not grow to the larger sizes, which, in turn, means that the processes of formation of smaller and larger nodules were operated separately and that the larger nodules did not grow from smaller ones.
Different sized nodules from the CIOB have distinct geochemical, mineralogical and morphological characteristics by which they can be distinguished as being of poor or high grades.
Poor grade nodules are hydrogenous and large in size and formed in deeper water.
Smaller nodules were formed at shallower depths and then may move towards deeper areas.
Average N/n ratio and nucleus size increase with increase in nodule size suggesting that smaller and large nodules were shaped at totally different places by different increasing processes.
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Acknowledgement
We are thankful to the Council of Scientific and Industrial Research (CSIR) for providing CSIR-JRF & CSIR-SRF fellowship and Head of the Department of Geology, Institute of Science, Banaras Hindu University, Varanasi, India for providing necessary facilities for conducting the research. We thank Central Instrumental Facilities (CIF) IIT (BHU) Varanasi for supporting in analyzing the samples using XRD, HR-SEM and SEM.
Declarations
1. The discrepancy identified between the submission system and the manuscript for Primary Abstract (~ 27.14%) is correct and the primary Abstract and Manuscript both are Identical.
2. Consent to publish
declaration: not applicable.
3. Ethics and Consent to Participate declarations: not applicable.
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Author Contribution
Saurabh Kumar Barman & Sanjay Kumar Tiwari: wrote and reviewed the manuscript.Manvendra Singh Chauhan and Shah Izhar Ahmed: They are helped during the sample preparation and analysis.Ashwani Kumar Sonkar: Helped in preparation of Maps
Manvendra Singh Chauhan2 and Shah Izhar Ahmed3: They are helped during the sample preparation and analysis.
Ashwani Kumar Sonkar4: Helped in preparation of Maps.
5. Competing Interest
declaration: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the research work reported in this study.
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Data Availability
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
7. Financial support
This work was financially supported by CSIR, New Delhi, India in the form of research support grant and teaching assistantship.
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