1 1.0 Introduction 2.0 Mineralogy 3.0 Textures Exhibited by Manganese

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MANGANESE DEPOSITS OF INDIA 1. Details of Module Module details Subject Name Geology Paper Name ECONOMIC GEOLOGY & MINERAL RESOURCES OF INDIA Module Name/Title MANGANESE DEPOSITS OF INDIA Module Id GEL-05-158 Pre-requisites Before learning this module, the users should be aware of • Stratigraphy of India • Geological time scale. • Genesis of Manganese formations. Objectives • Importance and uses of Manganese ores • Mineralogy and textural features of manganese ores. • Genesis of manganese minralization and its relation to crustal evolution. • Manganese mineralization in space and time. • World’s distribution and Indian occurrences of manganese ores. • Manganese nodules – origin and future prospects. Keywords Manganese, Manganese ores of India, mineralogy of Manganese.

2. Structure of the Module-as Outline: Table of Contents only ( topics covered with their sub-topics) 1.0 Introduction 1.1 Importance of Manganese mineralization. 1.2 Uses 2.0 Mineralogy 3.0 Textures exhibited by manganese . ores 4.0 Genesis of manganese mineralization 4.1 Volcanogene-sedimentary deposit 4.2Non-volcanogene-sedimentary deposit 4.3 Manganese mineralization & crustal evolution 5.0 World distribution & Indian occurrences of manganese ores 5.1 World occurrence 5.2 Manganese deposits of India 5.2.1 Manganese deposits associated with Precambrian Iron Ore Group 5.2.2 Manganese deposits associated with Khondalite Group 5.2.3 Manganese deposits associated with Aravalli Supergroup 5.2.4 Manganese deposits associated with Champner Group

5.2.5 Manganese deposits associated with Sausar Group 5.2.6 Manganese deposits associated with Gangpur Group 5.2.7 Manganese deposits associated with Penganga beds 5.2.8 Manganese deposits associated with Dharwar Supergroup 6.0 Manganese nodules 7.0 Future outlook 8.0 Summary & conclusions

3.0 Development Team

Role Name Affiliation National Co-ordinator

Subject Co-ordinators Prof. M.S. Sethumadhav Centre for Advanced (e-mail: Prof. D. Nagaraju Studies [email protected]) Prof. B. Suresh Dept of Earth Science University of Mysore, Mysore-6 Paper Co-ordinator Prof. M.S. Sethumadhav Centre for Advanced Studies Dept of Earth Science University of Mysore, Mysore-6 Content Writer/Author(CW) Prof. M.S. Sethumadhav Centre for Advanced Studies Dept of Earth Science University of Mysore, Mysore-6 Content Reviewer (CR) Prof. A. Balasubramaian Centre for Advanced Studies Dept of Earth Science University of Mysore, Mysore-6 Language Editor(LE)

1.0 INTRODUCTION Manganese is the 12th. most abundant element and is represented in nature by only one stable isotope, 55Mn.. Manganese exists in +2, +3 and +4 valence states.

1.1 IMPORTANCE OF MANGANESE MINERALIZATION: Commercially exploitable deposits of manganese occur both on the continents and on the floors of the present day marine and lacustrine basins. During the last two decades, emphasis on the study of manganese deposits has shifted considerably from those located on the land to the large accumulation on the floors of the present day basins. The study of manganese nodules (and crust) on the floors of recent basins has not only shed new light on the resource potential but has also provided adequate opportunities to observe the process of formation of manganese deposits at any given time. The study of ocean floor deposits in conjunction with the concept of plate movements unravels the complete geochemical cycle of manganese: The metal is derived from the weathering of crustal rocks or volcanic exhalations and is deposited on the ocean floor, consumed in the subduction zones riding on the oceanic crust and is recycled to form new igneous rocks and associated ore bodies. Many manganese deposits now resting on the continents have been recognized as having originally formed the ocean floor and thus a connecting bridge between the deposits on the continents and those occurring on ocean floors has been established. 1.2 USES: Manganese is the most important ferro alloy metal, essentially employed in the manufacture of high –manganese steels and also carbon steels. 95% of Manganese is used for metallurgical purposes and minor amounts in the manufacture of alloy like bronze. Manganese is essential to iron and steel production by virtue of its sulfur- fixing, deoxidizing and alloying properties. Among a variety of other uses, manganese is a key component of low-cost stainless steel formulations. Small amounts of manganese improve the workability of steel at high temperatures. In the iron and steel industry, manganese ore containing 28 to 35% manganese is used. Ore size generally varies from 10 to 40 mm. For manganese ore used in ferro-manganese industry, besides manganese content, other important considerations are high manganese to iron ratio and a very low content of harmful phosphorus. Manganese alloy is the largest produced ferro-alloy in the world with a share of about 41% of the global production of ferro-alloys. Aluminium with a manganese content of roughly 1.5% has an increased resistance against corrosion. In the chemical industry, generally high-grade material is used for potassium permanganate. Ore containing MnO2 80% (min), SiO2 5% (max), Fe2O3 5% (max) and

200 to 250 mesh ore size is used. Manganese sulphide is used in the manufacture of salts and in calico printing. Manganese chloride is used in cotton textile as a bronze dye. Manganese salts are used in photography and in leather and matchbox industries.

Manganese dioxide is used for manufacturing dry cell batteries in which it functions as a depolariser of hydrogen.

Manganese dioxide has been used since antiquity to neutralize the greenish tinge in glass caused by trace amounts of iron contamination. Manganese is also used as a brown pigment that can be used to make paint and is a constituent of natural umber.

Manganese compounds have been used as pigments and for the coloring of ceramics and glass. In the glass industry, ore analyzing MnO2 80% (preferably 86% min),

Fe2O3 5% (preferably 0.75%max), SiO2 2.8% (max), Al2O31.1% (max), BaO 1.3% (max), CaO 0.4% (max) and MgO 0.4% (max) is preferred.

Manganese also finds use as driers for oils, varnishes and paints. Manganese is an essential trace nutrient in all known forms of life. Manganese has no satisfactory substitute in its major applications.

2.0 MINERALOGY Manganese-bearing minerals occur as oxides, hydroxides, carbonates, silicates, and rarely as sulfides, arsenates, and phosphates. However, manganese deposits composed of oxide-, hydroxide- and carbonate- minerals of manganese constitute economic grade ore deposits. The various ore minerals of manganese are:-

• Pyrolusite: MnO2

• Psilomelane: MnO. MnO2.H2O

• Manganite: MnO3 .H2O

• Rhodochrosite: Mn CO3

• Hausmanite: Mn3O4

• Jacobsite: MnFe2O4

• Cryptomelane: K2 Mn8O18

• Hollandite: Ba2Mn3O16

4+ 2+ • Nsutite (MN Mn ) (O, OH) 2

• Braunite: 3Mn2O3. MnSiO3

• Todorkite 3MnO2 (Na,Mn)(OH)2.xH2O

• Lithiophorite (Al,Li)(OH)2. MnO

• Vrendenburgite 3Mn3O4.2Fe3O4

4+ 2+ • Nsutite Mn 0.85O1.7Mn 0.15(OH)0.3

• Bixbyite (Mn,Fe)2O3.

• Rhodonite (Mn, Fe, Mg, Ca)SiO3

2+ 4+ • Birnessite (Ca,Na)(Mn Mn )7O14.3H2O 3.0 TEXTURES EXHIBITED BY MANGANESE ORES Manganese ores commonly exhibit the following textural features: STALACTITIC: Elongated forms of manganese minerals deposited from solution by slowly dripping water (Fig.1). BANDED: Containing alternate bands of silicate mineral and manganese ore (Fig.2). BEDDED ORE: Consisting of alternate layers of host rock and manganese ore (Fig.3). OOLITIC/PISOLITIC: Spherical grains of manganese minerals composed of concentric layers of diameter 0.25–2 mm are oolites; rocks composed of concentric layers larger than 2 mm are called pisolites (Fig.4). CAVITY FILLING: Growth of crystals on the walls of planar fractures in rocks, with the crystal growth generally occurring normal to the walls of the cavities (Fig.5).

Fig 1. STALACTITIC Fig 2. BANDED Fig 3. OOLITIC/PISOLITIC

Fig 4. CAVITY FILLING Fig 5. BEDDED ORE

4.0 GENESIS OF MANGANESE MINERALIZATION Genesis of manganese ore is believed to have occurred due to precipitation from hydrothermal solutions (volcanogene-sedimentary deposit) or by sedimentary processes (non-volcanogene-sedimentary deposit). 4.1 Volcanogene-sedimentary deposit: Formation of manganese deposits of different geological ages from hydrothermal fluid has been suggested. This is supported by occurrence of many deposits at or near active seafloor spreading centers, such as mid- Atlantic, mid- Indian, pacific-Antarctic ridges and sea floor bottom fractures zones. The seawater may act as a metasomatic fluid and substantial leaching of heavy metals by seawater, followed by their precipitation on re-emergence on the ocean floor has been visualized. Deposition of hydrothermal manganese- and iron - manganese oxides may either take place by direct precipitation from hypogene fluid forming hydrothermal deposits, or through interaction of the hypogene fluid and the basinal waters, leading ultimately to hydrogenous precipitation. 4.2 Non-volcanogene-sedimentary deposit: The process of chemically controlled sedimentation is responsible for the formation of the vast majority of the manganese deposits in recent and ancient geological sequences. The major sources of metals are identified as fluids derived from endogenous system (mainly submarine volcanism and circulation of water at considerable depth) and exogenous processes of weathering of pre-existing rocks. Where endogenous systems provide the source and manganese deposits are ultimately formed by the process of sedimentation in a hydrodynamic regime, the term volcanogenic-sedimentary is used. Such deposits exhibit characteristic sedimentary features and conformable interstratification. For sedimentary deposits formed in a regime devoid of effects of volcanism and through derivation of metals from weathering zones situated either on the continents or on the seafloor, the term non-volcanogene sedimentary is applied. Studies in the present-day marine and lacustrine basins have clearly demonstrated that in most cases no single source or mechanics, by itself, could give rise to manganese deposits. Many sedimentary manganese deposits were subsequently modified through metamorphism of different intensities.

Frequently, metasedimentary manganese oxide ore bodies and manganese silicate rocks show an intimate and conformable relationship in a syngenetic sequence, although one may also occur in the absence of the other. Supergene concentration process at or near the surface in the weathering zones of mainly tropical countries was responsible for the formation of many large manganese deposits. Supergene concentration process involves leaching by surface and sub surface water, leading either to dissolution of elements other than manganese in the country rock or dissolution and re-precipitation of manganese in the near- surface environment within the weathering crust. The solubility of manganese is far greater than that for iron or aluminum and solubility of manganese is very effectively accelerated by simple organic decay and possible by bacterial reduction. Among the various genetic types of manganese ores, the largest accumulations of rich varieties occur in supergene settings associated with lateritic crusts. 4.3 MANGANESE MINERALIZATION & CRUSTAL EVOLUTION The various genetic types of manganese deposits now resting on the continents can be broadly correlated with the general pattern of the crustal evolution. In the early stage of basin volcanism, manganese ore bodies associated with greenstone and jasper predominated. With the development of the eugeosynclines, manganese ore concentrations were formed in association with pyroclastics, volcanic rocks (basalt, andesite, dacite) and stratiform iron and basemetal sulfide deposits on the seafloor. In more advanced stages of geosynclinal development, manganese deposits also formed substantially in the miogeosynclinal domain. The most conspicuous development of manganese deposits in geological history, however, is found on platforms which are mostly devoid of volcanic rock association. The remarkable metallogenic province of Morocco contains within a relatively small area, manganese deposits ranging in age from Precambrian to Mio-Pliocene. 4.4 MANGANESE MINERALIZATION0 IN SPACE & TIME Manganese deposits show a very wide range of distribution both in space and time. Manganese formation extends through the greater part of the geological history of earth and they are extensively distributed both on the continents and on the bottoms on the present-day ocean, shallow sea, and lakes.

The deposits occurring on the land belong to geological formations of various ages ranging from early Precambrian to Recent. However, concentration of manganese ores was not uniform at all ages and major epochs of manganese deposition can be broadly identified. Manganese ore concentration was most extensive during the Cenozoic, followed by the Precambrian, the Paleozoic and Mesozoic in that order. In the present day basins, evidence of deposition of manganese oxides has been found in sedimentary record since the Eocene and the process continues even today. A variety of factors controlling the evolution of earth, viz. tectonic activity, volcanism and climatic variations, have been invoked individually or jointly, to explain the distribution of manganese ore deposits in space and time, but no unique model has been unambiguously recognized. 5.0 WORLD DISTRIBUTION & INDIAN OCCURRENCES OF MANGANESE ORES Only a small fraction of global manganese reserves is clearly economic. This fact continues to support interest in deep-sea manganese nodules, which constitute an enormous untapped resource. Most nodules are found in areas of deep-sea floor at water depths of 5 to 7 km. The Pacific Ocean alone is estimated to contain about 2.5 billion tonnes nodules containing about 25% Manganese, making them similar in abundance to low-grade land-based deposits. 5.1 WORLD OCCURRENCE: More than 95% of global production of manganese today is from barely 7 countries viz. CIS, RSA, Brazil, Gabon, Australia, China and India. . South Africa accounts for about 75% of the world’s identified manganese resources. Most major steel-making nations lack manganese resources.

Fig 6. WORLD DISTRIBUTION OF IMPORTANT MANGANESE DEPOSITS 5.2 MANGANESE DEPOSITS OF INDIA: India is one of the largest producers of manganese ore in the world. The distribution of manganese ore resources production of Manganese ores in India is given in Figs. 7.

Fig 7. DISTRIBUTION OF INDIA’S MANGANESE ORE RESOURCES Manganese ore mining in the country is carried out by opencast as well as by underground methods. Manganese ore deposits of India can be classified into two major genetic types viz; (a) Volcanogene-sedimentary and (b) Non-volcanogene sedimentary. Several of these deposits were also subjected to various degrees of supergene alteration/enrichment/partial dissolution and redeposition. Manganese deposits of hydrothermal origin have not been reported from the Indian subcontinent. Manganese deposits of India range in age from late Archaean (~ 3000Ma.) to middle Proterozoic (~900 Ma.) and are distributed in the states of Jharkhand, Orissa, Andhra Pradesh, Karnataka, Rajasthan, Madhya Pradesh, Maharashtra, Goa and Gujarat (Fig. 8). The manganese deposits of India are found in association with the following groups of Precambrian supracrustal rocks: - Ø Iron ore group (2950 – 3200 Ma.) Ø Dharwar supergroup (2900 – 2600 Ma.) Ø Khondalite group (2650 – 1600 Ma.) Ø Aravalli supergroup (950 – 1500 Ma.) Ø Champner supergroup (950 – 1500 Ma.) Ø Sausar group (846 – 986 Ma.) Ø Gangpur group (846 – 945 Ma.) Ø Penganga beds (846 – 945 Ma.)

72 84 96 36

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KERALA KHONDALITE GROUP TAMILTAMILTAMIL NADU NADUNADU TAMILTAMILTAMIL NADU NADUNADU DHARWAR SUPER GROUP ARAVALLI SUPER GROUP CHAMPNER GROUP SAUSAR GROUP GANGAPUR GROUP 4 PENGANGA GROUP

Fig.8 DISTRIBUTION OF MANGANESE ORES OF INDIA

5.2.1 Manganese deposits associated with Precambrian Iron Ore Group: Manganese deposits confined to the supracrustal rocks of iron ore group are encountered in the states of Jharkdhand and Orissa. The manganese oxide ores are intimately associated with tuffaceous shales and cherts of the Iron ore group and both stratiform and lateritoid type manganese ores are reported. Mineralogically, the stratiform manganese ores are composed of pyrolusite, cryptomelane, todorokite and minor manganite and braunite. Lateritic manganese ores consist of pyrolusite, cryptomelane with minor lithiophorite. Fermor (1909) and Engineer (1956) proposed a lateritic origin for the manganese ores of the region. Spencer (1948) suggested a hydrothermal origin, while Sen (1951) proposed a submarine volcanic origin. Prasad Rao and Murthy (1956) opined that the manganese solutions derived from weathering of syn-sedimentary manganiferous formations at depth gave rise to manganese deposits. Subramanyam and Murthy (1975) and Banerjee (1977) favoured a volcanic source for the manganese deposits. Roy (1981, 1986) preferred a volcanogenic or terrigenous source for the stratiform manganese deposits of the region. 5.2.2 Manganese deposits associated with Khondalite Group: Stratiform manganese ores of the metasedimentary type hosted in the Precambrian Khondalite group occur extensively in the Srikakulam district of Andhra Pradesh and Koraput and Kalahandi districts of Orissa. The Khondalite group is composed of calc-granulite, garnet- sillimanite-graphite granulite, garnetiferous quartzite and quartzite. The manganese ore

bodies are conformably interstratified with the various members of Khondalite group at different stratigraphic levels. The manganese ores and the associated rocks have been subjected to granulite facies metamorphism. Mineralogically, the metasedimentary manganese ore bodies are composed of braunite, hollandite, jacobsite, hausmannite, vredenburgite and the supergene minerals are represented by pyrolusite, cryptomelane and minor nsutite (Roy, 1960). Fermor (1909) proposed that the manganese ores in the area are formed from the supergene alteration of Kodurites (a hybrid rock consisting of spessartine garnet, K- felspar and apatite). Sriramadas (1963) Rao, (1963, 1964) and Roy (1960, 1966) opined that the manganese ores are of metasedimentary origin, which were later subjected to supergene alteration. 5.2.3 Manganese deposits associated with Aravalli Supergroup: Stratiform Manganese ore deposits confined to the Precambrian Aravalli group occur in the Jhabua district of Madhya pradesh and Udaipur district of Rajasthan. In Madhya Pradesh, manganese oxide ores are interstratified with gondite, quartzite and phyllite. Mineralogically, the manganese ores are composed of braunite, bixbyite, hollandite and jacobsite. In Rajasthan, manganese oxide ores occur as conformable beds within carbonaceous phyllites and are associated with phosphorite and copper mineralization in the Maton formation. Manganese minerals are represented mainly by pyrolusite and cryptomelane. Nayak (1966) opined that regional metamorphism of the manganiferous pelitic, psammitic and calcareous sediments resulted in the development of oxide- and silicate- ores of manganese. The metasedimentary manganese ores were later subjected to supergene alteration giving rise to supergene manganese ores. 5.2.4 Manganese deposits associated with Champner Group: Metasedimentary manganese oxide ores associated with the Champner group are reported from the Shivrajpur-Bamankua area of Panch Mahal district in Gujarat. Manganese ores in the area occur as bands interbedded and co-folded with cherty quartzite and phyllite. The ore-bearing sequences in the area have been metamorphosed to greenschist facies, as evidenced by the presence of braunite and recrystallized pyrolusite. Gondite is totally absent. The manganese-oxides are made of braunite, hollandite, bixbyite and hausmmanite and supergene alteration resulted in the formation of pyrolusite and cryptomelane. Manganese-silicates include garnet, rhodonite, and manganese-bearing

pyroxene. Supergene alteration of the metasedimentary manganese ores has yielded pyrolusite, cryptomelane and manganite. To the east of the Shivrajpur-Bamankua area in the Goldongri hill, manganese oxide ores are interbanded with manganese silicate rocks enclosed in calc- silicates. The metasedimentary manganese ores consist of braunite and hollandite with minor bixbyite and hausmannite. Supergene alteration of the metasedimentary ores resulted in the development of pyrolusite and cryptomelane. Sen (1964) and Roy (1967) proposed a contact metamorphic origin for the manganiferous rocks. 5.2.5 Manganese deposits associated with Sausar Group: Manganese ores associated with the Sausar group of rocks occur in Madhya Pradesh and Maharastra, extending as an arcuate belt for a length of over 200 km with an average width of about 30 km. Metasedimentary oxide manganese ore bodies interbedded with metasediments of the Sausar group (comprising of pelitic, psammitic and carbonate rocks) are encountered in Balaghat and Chindwara districts of Madhya Pradesh state and Nagpur and Bhandara districts of Maharashtra state. Manganese ore bodies occur at the bottom, middle and top of the argillaceous Mansar formation of the Sausar group and also within the underlying calc-silicate and marble-bearing Lohangi formation of the Sausar group. In the Mansar formation, interbedded Mn-oxide ores and manganese-oxide-silicate rocks (gondites) exhibiting primary sedimentary structures forming Syn-sedimentary sequences occur. The metasedimentary formations have been subjected to greenschist to amphibolite facies metamorphism. Manganese minerals reported are: braunite, hollandite, jacobsite, manganite and bixbyite, spessertine and rhodonite. 5.2.6 Manganese deposits associated with Gangpur Group: Manganiferous formations associated with Gangpur group are encountered in the Sundargarh district of Orissa. The manganese oxide ore bodies and gondite are interbanded and co-folded with the pelitic schists of Ghoriajor formation which constitutes the upper formation of the Gangpur group. The pelitic schists and the manganese ores have been subjected to amphibolite facies metamorphism. The manganese ore bodies are composed of braunite, bixbyite, hollandite, jacobsite, hausmannite, vredenburgite. 5.2.7 Manganese deposits associated with Penganga beds: In the Proterozoic Penganga beds that occur in the Godavari rift valley in parts of Andhra Pradesh and

Maharastra states, the manganese oxide ores are interstratified with stromatolitic limestone and intermixed with chert, jasper and shales. The manganese ore beds exhibit penecontemporaneous deformation, pinch and swell and slump structures along with diagenetic features. Manganese is essentially composed of todorokite, pyrolusite, ramsdellite, nsutite, birnessite and minor braunite. Roy (1981) visualized a terrigenous source for manganese in the Penganga beds that was followed by diagenetic remobilization of manganese and reconstitution, leading to the formation of economic grade manganese deposits. 5.2.8 Manganese deposits associated with Dharwar Supergroup : Manganese ores confined to the Precambrian Dharwar supergroup of rocks occur in the NNW-SSE trending supracurstal belts and encountered in parts of Karnataka and Goa. In Karnataka, the manganese ores are encountered in North Kanara, Shimoga, Chitradurga and Sandur schist belts. Manganese deposits in the Karnataka craton are restricted to the Chitradurga group of rocks. Prominent deposits are encountered are in the Sandur schist belt of the eastern block of the Karnataka craton and Chitradurga, Shimoga and North Kanara belts of the western block of the Karnataka craton. The NNW-SSE trending Sandur schist belt is well known for its economic concentrations of iron and manganese and is one of the best examples of the Precambrian greenstone belts of the world containing iron and manganese mineralization. Manganese and iron ore deposits are confined respectively to Deogiri and Raman Mala formations. Iron- and manganese- bearing arenites consist of quartz, hematite, magnetite, pyrolusite, cryptomelane, lithiophorite and minor braunite. Manikyamba et al., (1995) reported derivation of iron and manganese of the Deogiri formation from volcanogene hydrothermal solutions. The manganese- and iron- bearing formations were deposited in the shallow shelf region within the photic zone and above the wave base. The manganese- and iron- oxides present in arenites, argillites, cherts and carbonates were subjected to supergene enrichment leading to mineable economic concentrations of manganese ore. North Kanara schist belt consists of > 2.6 Ga. supracrustal consisting of metabasalts overlain by continuous beds of metasedimentary rocks. The metasedimentary succession is represented by conglomerate, orthoquartzite-arenite, stromatolitic limestone/dolomite, phllyite/argillite, manganiferous formation and banded iron

formation, succeeded by a thick sequence of greywackes. The metasediments belong to the Chitraduraga group. The late Archaean manganiferous- and iron- formations occur along N- to NW- trending discontinuous ridges. Manganese exhibit massive, finely laminated and banded textures and are composed essentially of pyrolusite, cryptomelane. The host rocks exhibit isoclinal folding and greenschist facies. Mangenese and iron formations were intensely lateritized during the Neogene period. The manganiferous formation varies from massive layers and/or lenticular bodies, several metres thick sandwiched between phyllitic layers, to very thin banded layers interbeded with similar layers of either quartzite (metachert) or siliceous phyllite. Krishna Rao et al., (1989) invoke a volcanic source for the late Archaean manganiferous formation of the North Kanara region. Subsequent lateritic alteration caused extensive remobilization of Mn from the metasedimentary ores. Chitradurga Schist Belt is a linear belt of supracrustal rocks extending for about 350 km. Manganese mineralization is encountered mainly in the Chitradurga and Chikkanayakanahalli areas in the Chitradurga schist belt. Manganese mineralization is confined to manganiferous chert and phyllite. The uniformity in the composition of the manganese-rich bands and the co-folded nature of the manganese-bands indicate they are metasedimentary in origin. 6.0 MANGANESE NODULES Increasing global population, demand for metals and dwindling land resources, has led to the search of an alternative source for the metals could be in the world oceans. Oceans are considered as a 'warehouse' for minerals, amongst others, polymetallic ferromanganese nodules (Fig. 9), phosphorites, hydrothermal sulphides, placer deposits and sand. Polymetallic nodules deposits exhibit a variety of shapes (Fig. 10) black earthy colour with size ranging from 2 to 10 cm in diameter. Nodules occur at depths of about 4 to 5 km in the deep oceans and grow at a rate of about one millimeter in one million years. In the Indian Ocean, nodules occur in different basins such as the Central Indian Ocean Wharton Basin, Crozet Basin, Madgascar Basin, Somali Basin, South Australian Basin and Arabian sea.

Fig. 9 FERROMANGANESE NODULES

Fig. 10 SHAPES OF POLYMETALLIC NODULES

Fig. 11 CROSS SECTION OF A NODULE Under the microscope, the cross section of a nodule (Fig. 11) shows alternative layers of iron (dark colour) and manganese (light grey colour) The prerequisite conditions to form the nodules are: • Low sedimentation rate • Availability of nucleus around which accretion of oxides takes place • Oxidising environment • Bottom currents of low velocity The average composition of nodules is given in Table 1.

(ppm)

Pb 712 Element (wt%) Mo 570 Si 9.20 Li 97 Al 2.80 Ba 1570 Fe 7.10 Y 102 Mn 24.4 Sr 679 Ti 0.43 La 132 Ca 1.63 Ce 528 Mg 1.90 Pr 33 Na 1.80 Nd 147 K 1.10 Sm 33 P 0.17 Eu 8 Cu 1.04 Gd 34 Ni 1.10 Tb 5 Zn 0.12 Dy 27 Co 0.11 Ho 5

Er 13 Tm 2

Yb 12

Lu 2

Table 1: AVERAGE CHEMICAL COMPOSITION OF POLYMETALLIC NODULES

There are three processes for the formation of nodules: Hydrogenous process whereby metals are supplied from the water column and these accrete on a suitable nuceli. Hydrogenous nodules have smooth surface texture and are rich in Fe, Co, Ti, P and Pb content. The Mn/Fe ratio of these nodules is ~1.

Diagenetic process supplies metals from the underlying sediment through the pore water by remobilisation. Diagenetic nodules have rough surface texture and are rich in Mn, Cu, Ni and Zn content. The Mn/Fe ratio is more than 2.5. Mixed type which is a combination of hydrogenous and diagenetic types. 7.0 FUTURE OUTLOOK Production of crude steel is the single most important factor in the demand for manganese ore. Steel industry accounts for approximately 90%world demand for manganese. Carbon steel is the principal market accounting for 65 to 70%manganese consumption. 8.0 SUMMARY & CONCLUSIONS • Commercially exploitable deposits of manganese occur both on the continents and on the floors of the present day marine and lacustrine basins. • The study of manganese nodules (and crust) on the floors of recent basins has not only shed new light on the resource potential but has also provided adequate opportunities to observe the process of formation of manganese deposits at any given time. • Manganese has no satisfactory substitute in its major applications. • Manganese deposits composed of oxide-, hydroxide- and carbonate- minerals of manganese constitute economic grade ore deposits. • Genesis of manganese ore is believed to have occurred due to precipitation from hydrothermal solutions (volcanogene-sedimentary deposit) or by sedimentary processes (non-volcanogene sedimentary deposit). • Supergene concentration process at or near the surface in the weathering zones of mainly tropical countries was responsible for the formation of many large manganese deposits. • The largest accumulations of rich varieties occur in supergene settings associated with lateritic crusts. • The various genetic types of manganese deposits now resting on the continents can be broadly correlated with the general pattern of the crustal evolution. • Manganese deposits show a very wide range of distribution both in space and time. • Manganese nodules constitute an enormous untapped resource in future. • Manganese deposits of India range in age from late Archaean (~ 3000Ma.) to middle Proterozoic (~900 Ma.)

• The manganese deposits of India are found in association with groups of Precambrian supracrustal rocks. • Increasing global population, demand for metals and dwindling land resources, has led to the search of an alternative source for the metals could be in the world oceans – Manganese nodules.