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

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 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

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National Co-ordinator

Subject Co-ordinators Prof. M.S. Sethumadhav Centre for Advanced

Studies
(e-mail: Prof. D. Nagaraju
epggeology640@gmail.com) Dept of Earth Science
Prof. B. Suresh
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.

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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.

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 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

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 · Manganite: MnO3 .H2O
· Rhodochrosite: Mn CO3
· Hausmanite: Mn3O4
· Jacobsite: MnFe2O4
· Cryptomelane: K2 Mn8O18
· Hollandite: Ba2Mn3O16
· Nsutite (MN4+Mn2+) (O, OH) 2
· Braunite: 3Mn2O3. MnSiO3
· Todorkite 3MnO2 (Na,Mn)(OH)2.xH2O
· Lithiophorite (Al,Li)(OH)2. MnO
· Vrendenburgite 3Mn3O4.2Fe3O4
· Nsutite Mn4+0.85O1.7Mn2+0.15(OH)0.3
· Bixbyite (Mn,Fe)2O3.
· Rhodonite (Mn, Fe, Mg, Ca)SiO3
· Birnessite (Ca,Na)(Mn2+Mn4+)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).

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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.

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 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

8
 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

9
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.

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Fig 6. WORLD DISTRIBUTION OF IMPORTANT MANGANESE DEPOSITS

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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.)

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 Ø Penganga beds (846 – 945 Ma.)

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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

13
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.

14
 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.

15
 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.

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 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.

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 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

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 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.

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 (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.

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 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.

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· 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.

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