CHEAT AND HACK 4 ANDROID

Factors controlling mineral availability
Mineral concentrations in the crust of the Earth are produced by the interplay of various
geological processes. However, even if such a concentration is located and explored, it can not
be exploited till several critical factors are satisfied. The main factors controlling the
availability of mineral deposits in this sense are: geological, engineering, environmental and
economic (cf. Kesler, 1994).
All the metals commonly exploited in ore deposits are found in all crustal rocks, but in very
minute quantities (such crustal abundance of metals being expressed in ‘Clarke’ values, which
represent a ratio of a particular element in a rock to the average amount of the element in the
Earth’s crust). Various crustal processes like magmatism, metamorphism, sedimentation etc. bring
about concentrations of such dispersed metals in crustal rocks in specific geological settings. For
example a copper skarn deposit is found only where a felsic pluton has intruded into an impure
limestone country or a concentration of refractory kyanite is found only where aluminous
sediments have undergone regional metamorphism. Thus geological factors play a paramount role
in the availability of mineral deposits.
However, even if a mineral deposit is identified, it may not be workable unless certain engineering
constraints are satisfied. For example, present level of mining engineering in advanced countries
does not allow deposits to be worked at depths greater than about 4 km, while the deepest oil wells
are about 8 km long. Any resource beyond these limits is unavailable for exploitation. Some of
these engineering constraints are also closely linked to the economics of exploitation. For example,
the Kolar gold mine (Champion Reef) closed down because, although possible, it was not
economically viable to mine at depths of 11,000 feet where a huge expense was borne for airconditioning
of the mines. At times, mineral technology also does not allow the exploitation of a
known resource. For example, the large Pb-Zn sulfide deposit at McArthur River in Australia
could not be mined for several years because the fine grained ore was not amenable to
beneficiation and hence an ore concentrate for smelting could not be produced.
Environmental factors play an equally vital role in the exploitation of a known resource. A large
deposit of uranium has been located and explored in recent years in the Lambhapur area of
Srisailam district of Andhra Pradesh. But will this deposit be given environmental clearance for
mining by the Ministry of Environment and Forests since it is located within the Rajiv Gandhi
Tiger Reserve? We will need to wait and see. If environmental degradation is assessed to be high a
good known resource may not be allowed to be exploited by mining.
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Factors of economics play the most crucial role in the exploitation of a resource. Profit remains the
major reason for mining a particular resource, except in the case of strategic minerals which can be
mined without considering economic factors at a time of emergency, such as, war. In a free
economy, the cost of mineral production will regulate the price of the commodity. Even for a good
deposit with high grade and reserve, if the cost of extraction, beneficiation and environmental
protection is too high, it may not be amenable to mining at a particular point in time, when it might
be cheaper for a country to import that metal from abroad. The other important factor controlling
the price is demand and supply. Demand for a metal may change over a short period of time
because of stock piling, recycling as well as substitution and availability of new technology.
Global mineral reserves and resources
The global demand for minerals has increased steadily since the industrial revolution and
exponentially in the latter half of the 20th century. In the last few decades the demand is not only
for higher tonnage but also for a range of mineral commodities, such as the high tech metals like
In, Ga, Ge etc. which are required for specific applications due to their physical and chemical
characters, and electrical conductivity. The increasing global population and affluence of societies
is bound to keep this demand rising.
The global economy, at least a significant part of it, is clearly dependant on mineral production
which is the backbone of modern industrialization. This is more than obvious from the large value
and amount of global mineral production (Fig. 1A & B).
Fig. 1: (A): The value of world’s mineral production in the 1990s (modified from Kesler, 1994).
(B): Quantity of world’s mineral production in 2004, based on British Geological Survey data.
However, several complex issues are involved in the understanding of mineral resources in the
context of global economy. Only some major issues are highlighted here. There is ample statistical
data available to show the remarkable correlation between economic activity of a country,
industrial production and consumption of basic mineral commodities. A good indication of this
correlation should be obtained by comparing the value of mineral production in a country with the
Gross Domestic Product (GDP) (Kesler, 1994). We however, find that mineral production in USA
and Japan makes up less than 2 % of the GDP while it is about 25% for Saudi Arabia and 35% for
Kuwait, the two major oil producing countries in the Middle East. This is in spite of the fact that
USA is the leading producer of 19 different mineral commodities in the world.
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Another aspect is that the pattern of consumption of mineral commodities in a country and their
availability in it shows no relationship in the modern world. Countries with large and important
mineral resources, such as South Africa and Australia are no doubt economically strong, but Japan
with very limited mineral resource is also equally strong, if not more. As it is mineral resources are
neither uniformly distributed in different parts of the world (see a later section for more details),
nor are they consumed equitably by the different countries. For example, 95% of world resources
of chromium are found in South Africa alone. This has led to conflicts and even war in different
periods of history. Even today the control of strategic world resources like petroleum continues to
play a major role in world politics. Besides, in recent years, stringent environmental laws have
made mining economically unviable in many developed countries though their requirements of
mineral raw material have not diminished at all. Many of the remaining high grade resources occur
in the developing world where the pressure and impact of mining is continuously increasing.
While many of the developed countries like USA, Canada, Australia, South Africa, Sweden,
Finland and a few developing countries like Chile and Botswana have achieved considerable
economic success through reliance on metals whereas many developing world nations with long
history of mining have failed to get the direct benefit from the exploitation of their resources. In
general, in the initial stages of development of a country the raw materials are exported to earn
much needed foreign exchange. With time and with the earnings from these exports the industrial
infrastructure of the country is put in place and manufactured goods and products are then
exported which fetch much more revenue. India is probably going through this phase now. But in
the context of the developed countries with limited mining activities and that of Japan in particular,
import reliance is the key factor. To safeguard continuous supply of raw materials most of these
developed countries, including Japan, are investing in the promotion of mining projects in foreign
countries. For example the railway infrastructure to transport the Bailadila iron ore from Bastar to
the port of Vishakhapatnam was fully aided by Japan in early 1970s. India earns substantial
foreign exchange by selling a part of its vast resource of iron ore. It is almost self sufficient in
aluminium, manganese (though chemical grade of Mn has to be imported) and lead-zinc but has to
import copper, nickel and tin. Thus the concept that the security of a country depends on its
mineral supply does not hold in the contemporary world in the era of free trade. A developed
country can buy whatever mineral it needs in the world mineral market which however, is
controlled by large multinational groups or companies. A better idea of the distribution of
important mineral commodities in the world will be obtained in a later section.
Geological setting, mineralogical characteristics and distribution of important mineral
deposits in India
Metals
Iron
Iron is one of the most abundant metals and has the third highest crustal abundance (5.6 %), next
to aluminium (8.2%) and silicon (28.2%). Iron accounts for more than 95% of all metals used by
the modern society. In fact, the industrial growth of a country is measured, amongst other criteria,
by the amount of iron consumption and steel production. The ore minerals from which iron is
extracted are hematite (Fe2O3), magnetite (Fe3O4) and goethite (FeOOH). Iron smelting is carried
out by reducing iron oxides to iron metal by reaction with carbon monoxide gas, usually derived
from coke (Craig et al., 1996).
Iron ores of magmatic, sedimentary and metamorphic origin are found in different geological
settings. Magnetite occurs associated with layered mafic-ultramafic intrusions as magmatic
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segregations. Volcanic exhalations are also thought to be responsible for magnetite mineralization,
as in Kiruna type deposits of Sweden. Magnetite and micaceous hematite (specularite) are
produced by contact metamorphism, as in Iron springs, Utah, USA. Iron ores, initially of
sedimentary origin, are the ones which account for the largest resource of the metal and are
exploited extensively the world over. They are discussed in detail in the next section. Lateritic iron
ores are prevalent in tropical humid regions over ferruginous bed rocks. Two major groups of ironrich
sedimentary rocks are commonly recognized (James, 1966):
Banded Iron Formations (BIF): These are represented by extensive thick sequences of
Precambrian (Proterozoic) age. Typically laminated with fine grained hematitic layers interbanded
with chert/jasper/quartzite. The hematite is generally non-oolitic.
Different terminologies are used for referring to BIFs in different countries: taconite in Lake
Superior region of U.S.A, Itabirite in Brazil; Calico rock in S. Africa; Jaspilite in Western
Australia and Banded Hematite Quartzite (BHQ)/Banded Magnetite Quartzite (BMQ) in India.
BIFs are often loosely termed as ‘iron ores’, although they are the protoliths of most large iron ore
deposits.
Iron stones: These are poorly banded, non-cherty and oolitic ores, represented by hematite and
goethite. They are Phanerozoic in age.
Gross (1966) distinguished two main types of BIFs from the Precambrian. These are the Archean
Algoma type and the Proterozoic Superior type of Iron Formations. The former is characterized by
thin banding and absence of oolitic and granular texture, limited lateral extent and close
association with volcanic rocks, greywackes and pyritic black shales. The latter is characterized by
thick bandings, large lateral extent and close association with sediments like quartzites, dolomites
and pelites with no direct affiliation with volcanic rocks. This two-fold classification of the BIFs is
however, problematic. For example, in India the BIFs possess the characteristics of both Algoma
and Superior types. The same is true for the West Australian deposits, particularly those in the
Hammersley basin. In terms of environment of deposition, most Proterozoic BIFs are typical of
platform association while their Archean counterparts show characteristics of deep water
environment.
The BIFs, particularly in the Archean, often show the development of four different facies (James,
1954). These are: oxide facies with magnetite and hematite subfacies; silicate facies; carbonate
facies and sulphide facies (Fig. 2). The relationship of these four facies, which rarely occur
together at the same place, has been described to be gradational, one type passing into the other
from oxide facies in the shallow waters to the sulfide facies in the deep waters.
Fig. 2. Cartoon depicting the four facies of iron formations developed in a shallow
sea.
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Indian distribution
The iron ore deposits of India can be divided into four groups according to their mode of
formation. The most important group includes the banded iron ores of Precambrian age. These
deposits are the back bone of iron and steel industry in India and their export to countries like
Japan fetch a huge amount of foreign exchange for the country. The total reserves are estimated at
over 17,000 million tons, of which 14,000 million tons represent hematitic ores and the rest are
magnetitic ores. These iron-ore deposits can be considered under two main groupings
(Radhakrishna et al., 1986): (a) those occurring within complexly folded BIFs in high grade terrain
in parts of Andhra Pradesh, southern Karnataka, Kerala and Tamil Nadu, and (b) those confined to
the Archean schist (greenstone) belts in Jharkhand, Orissa, Madhya Pradesh, Maharashtra, Goa,
and Karnataka, accounting for the predominant Iron resource of the country. The first group
deposits are considered to be > 3000 Ma old whereas the deposits of the second group formed
during the period 2900 to 2600 Ma.
Continuous bands of Iron Formations are exposed in three principal belts around the Singhbhum
granite massif in south Jharkhand - northern Orissa: 1. Gorumahisani and Badampahar hills of
Mayurbhanj district of Orissa in the east; 2. Jamda-Koira valley deposits (including the well
known Noamundi deposit of TISCO) to the west and 3. The E-W trending formations of the
Sukinda valley including the Tomaka-Daiteri and Malayagiri deposits in the south. The deposits in
the region provide the iron ore to the SAIL steel plants at Rourkella, Bokaro, Durgapur and Kulti,
besides TISCO.
Prominent iron ore deposits occur extensively in the Bailadila range and Rowghat hills of Bastar
district of Chhattisgarh The Dhalli-Rajhara deposits in Durg district of Chhattisgarh serve as the
captive mines to the Bhillai steel plant.
Extensive deposits of BMQ and BHQ occur in the hilly tracts of Goa and Karnataka. In the latter
state, prominent occurrences are found in the Bababudan hills, at Kudremukh, in Bellary and
Sandur. Proved magnetite deposits are confined to the Chikmagalur district of Karnataka
(Bababudan and Kudremukh) and also in the high grade terrains of Salem and North Arcot in
Tamil Nadu. The distribution of the important iron ore occurrences in India is shown in Figure 3.
The second group comprises the apatite-magnetite ores of the Singhbhum shear zone, in Jharkhand
and the titaniferous, vanadiferous magnetite deposits associated with intrusive mafic plutons in
Mayurbhanj district of Orissa. The former is concentrated as small lensoid bodies all along the 150
km long shear zone, to the foot wall side of the Cu and U orebodies.
The third group consists of sedimentary iron-ores of limonitic or sideritic composition. In Raniganj
and Jharia coalfields of lower Gondwana age, ironstone shale formations are encountered in the
Barren Measures overlying the lower coal-measures. It is middle Permian in age and its thickness
is about 650 metres in the Jharia coalfield. In Raniganj coalfields, the thickness of ironstone shale
is about 500 metres. These low grade iron concretions were used as raw material in the Iron works
at Kulti, West Bengal, before the advent of the first blast furnace at Tatanagar, now in Jharkhand.
Lastly, the lateritic iron-ores found extensively on the Eastern and Western Ghats, are derived
from the sub-aerial alterations of iron-bearing minerals in igneous, metamorphic and sedimentary
rocks. The basic lavas of the Deccan traps and Rajmahal traps are altered, under humid and
tropical climatic conditions, resulting in the formation of hydrated oxides of iron, along with
aluminium and manganese. These lateritic iron-ores are low-grade commodities, containing only
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25% to 35% of Fe, so they are not considered now as a source of iron, but in future when the highgrade
iron ore deposits will be fully exploited, they may provide the main resource of iron.
Manganese
In comparison to iron and aluminium, manganese is much less abundant (0.095%) in the earth’s
crust. Hence, manganese deposits are not as common or abundant as the iron ore deposits.
However, manganese a metal vital to steel production occurs in deposits of diverse genetic types in
many countries and in a large span of the terrestrial geological record. These were produced by
direct hydrothermal activity, sedimentary processes, continental weathering (Roy, 1981). They
also occur as ferromanganese nodules on many parts of the deep ocean floor. Most of the existing
demand for manganese is met from the sedimentary and residual deposits. The deep sea nodules
form future resource of manganese and some other important metals such as cobalt, nickel, copper
etc.
Indian distribution
Manganese deposits of Archean age are found to occur in parts of Orissa, Andhra Pradesh and
Karnataka (Fig. 3). Mn oxide ores interstratified with shale occur in the Iron Ore Group rocks at
Joda, Kalimati, Gurda, Phagua and Mahulsukha areas in Orissa. These deposits are considered to
have formed in cratonic shelf environment at ca. 3.0 Ga (Roy, 1981). The Eastern Ghat sequence
in Kodur, Garividi and Garbham in Andhra Pradesh, metamorphosed to granulite facies, host Mn
oxide ores in a conjectured shallow water shelf environment. The oxide ores are located in these
Archean (>2.6 Ga) high grade, pelitic and calc-silicate granulites while Mn silicate-carbonate
rocks occur in calc-silicate granulites and garnetiferous quartzites (Roy, 1981). These ores and
their host rocks were described as Kodurites by Fermor in 1909. The Kodurites of Andhra Pradesh
are considered to be hybrid in character, due to granitic assimilation of the manganese bearing
sediments. Similar deposits are described from the Khondalites of Kalahandi and Koraput districts
of Orissa. Similar koduritic manganese-ore occurrences have also been reported from Goldongri
Fig. 3. Distribution of iron, manganese and chromium deposits in India.
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hill, north of Jothvad, Panch Mahal district, Gujarat. Mn oxide ores, interstratified with chert and
phyllite and closely associated with stromatolitic limestone, occur in Chitradurga-Tumkur, Kumsi-
Hornhalli areas of Karnataka. These Chitradurga Group strata are believed to have developed on
the shallow platform margins about 2.6 Ga ago (Roy, 1981). Similar association of Mn oxide ores
is also found extensively in the Sandur and Shimoga schist belts in Karnataka, spatially adjacent to
the Banded Iron Formations.
Large scale deposition of Mn ores started from the Early Proterozoic. The Proterozoic (ca. 2.0 Ga)
Saussar Group, spreading from Maharastra to Madhya Pradesh in central India (Figs. 3, 4) hosts
the largest concentration of Mn ores in India, mostly in gonditic rocks. These regionally
metamorphosed manganiferous sediments from central India were first described and named
Gondite by L. L. Fermor in 1909. The gondites are quartzose rocks containing spessertite and
rhodonite, usually associated with Mn minerals like braunite, along with bixbyite, hausmanite and
jacobsite. These Mn silicate-oxide rocks are complexly deformed and interstratified with
metapelites and orthoquartzites in the Mansar Formation and less commonly occur as conformable
lenses in carbonate rocks of the older Lohangi Formation. The litho-sequence is metamorphosed to
grades ranging from low greenschist facies in the east to upper amphibolite facies in the west. It
represents metamorphosed equivalents of a limestone-shale-orthoquartzite assemblage that formed
in a cratonic shelf environment without any volcanic rock association (Roy, 1966; 1981). The well
known deposits are in Ukwa and Bharweli in Balaghat district in the east, Chikla, Tirodi and
Mansar in the central part of the belt and Gowari Wadhona in Chindwara district in the west.
Manganese oxide ores interbedded with chert and enclosed in limestone also occur in the Late
Proterozoic (ca. 800 Ma) sedimentary sequence of the Penganga Group in Andhra Pradesh,
developed in the Godavari valley, a major continental rift in the Indian peninsula (Roy, 1981).
Lateritoid manganese ores include both in situ residual ores (lateritic) and the replacement deposits
formed by enrichment of manganese in meteoric water from other rocks and subsequent
precipitation from solution. Thus, these ores are clearly epigenetic with respect to their host rocks.
Such epigenetic ore deposits are found in fairly large quantities in Dharwar Supergroup rocks in
Belgaum, Karnataka, Maharashtra, Goa, parts of Madhya Pradesh and in Iron ore Group rocks of
Fig. 4. Location of Mn deposits in central Indian Sausar Belt in
Maharashtra and Madhya Pradesh (after, Roy, 1966).
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Singhbhum district, Jharkhand, and Keonjhar district, Orissa (Fig.3). In many such lateritic
deposits, Al and Fe are characteristically concentrated in the upper zone and Mn in the lower zone
of a weathering profile. In the Sausar Group a large supergene deposit with a strike length of 1.5
km and a thickness exceeding 130 m occurs at Dongri Buzurg, Nagpur district, Maharashtra. The
deposit was formed by oxidation of pre-existing metamorphosed Mn oxide and Mn silicate rocks
(Roy, 1981).
The total reserves of manganese in India is estimated to be 93,000,000 ( 93 Mt ) metric tons
(USGS, Mineral commodities summary, 2005).
Chromium
Chromium is extracted from the spinel group mineral chromite (FeCr2O4). The chromite ore is
used for three principal industrial purposes: (1) Metallurgical, (2) Chemical and (3) Refractory.
The metal is required for alloying with steel, for chrome plating and for production of chemicals
like potassium dichromate (K2Cr2O7). For metallurgical use the chromite ore must have a
minimum of 48% Cr2O3, with a Cr/Fe ratio of 3:1.
Chromium is concentrated in basic to ultrabasic magma and thus it commonly gets concentrated as
chromite ore in gabbros, peridotites, dunites and anorthositic plutonic rocks. The chromite deposits
display two distinct modes of occurrences: as stratiform, layered deposits in large igneous
complexes, known as the Bushveld type, or as podiform or sackform deposits in orogenic belts,
known as the Alpine type. Sometimes the characteristics of both types are found in some
occurrences.
Indian distribution
The major chromite occurrences in India are restricted to the states of Orissa, Jharkhand,
Karnataka, Goa and Tamil Nadu (Fig. 3). Minor chromite occurrences mainly of academic interest
are also found in Ladakh in the Indus suture zone.
The igneous complex around Boula-Nausahi, in the Keonjhar district of Orissa, is intruded into the
Precambrian metasedimentaries of the Iron Ore Group. The 2000 Ma-old ultramafic suite of rocks,
extending in a NW-SE direction as a lense with a length of 3 km and a width of 0.5 km, is
represented mostly by dunite-pyroxenite and subordinate amounts of pyroxenite. Four prominent
sub-parallel chromite lodes are present and are named as Durga lode, Laxmi lode, Sankar lode and
Ganga lode. The stratiform nature of the mineralization is obvious though later deformation has
affected the layerings. This igneous complex is also an important repository of Ti-V bearing
magnetite and Platinum Group Elements (PGE + Au) mineralization. The latter is associated with
base metal sulfides in a breccia zone located in the junction of ultramafic and mafic rocks (Baidya
et al., 1999).
Chromitites of the Sukinda valley (Chakraborty and Chakraborty, 1984) can be traced along the
strike for about 8 miles in the NE-SW direction, from Saruabil in the east to Katpal in the west in
the Cuttack and Dhenkanol districts of Orissa, respectively. The dunite-peridotite body hosting the
chromite ores is intrusive into the quartzites and Banded Iron Formation of Precambrian age. The
chromitite layers show evidence of gravitative settling during magmatic crystallization. Four
chromitite layers occur near Kalrangi, in the Cuttack district at the southwestern end of the
Sukinda ultrabasic belt. Sackform chromite deposits also occur at the intersection of olivine
gabbro dykes near Moulabhanja hills in the Dhenkanal district. These dykes intrude Precambrian
granite gneiss of the Eastern Ghat orogenic belt.
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Well known chromite deposits, now nearly exhausted, occur in ultrabasic rocks at Jojohatu in the
Singbhum district of South Jharkhand. The serpentinised ultrabasic rocks ranging from dunite to
enstatitite occur as laccolithic intrusions within slates and phyllites of the Iron Ore Group.
In Karnataka, chromite deposits and occurrences are located in the Archean Nuggahalli, Shimoga
and Sargur schist belts (Radhakrishna, 1996). The best known deposits occur at Byrapur and
Aladahalli in Nuggihalli belt within serpentinised peridotite. Other known chromite occurrences in
ultramafic rocks are at Anthargange in Shimoga belt and Sindhuvalli in Sargur schist belt.
Stratiform chromite ores are found associated with metamorphosed anorthositic rocks of the
Sittampundi complex in Tamil Nadu. These are of sub-economic grade.
The total reserves of chromium reserves in India is estimated to be about 25,000,000 (25 Mt)
metric tons (USGS Mineral commodities summary, 2004).
Copper
Copper is the most useful base metal. Due to its electrical conductivity and ductility, it is used
widely in the manufacture of wires, plates and rods for use in electrical industry and domestic
utility. Mineralogically, copper ores are divided into four groups: native metal, sulphides, oxides
and complexes. The native copper (occurring as an individual mineral with 100% Cu) is
commonly found in oxidised zones. The sulphide ores are the most valuable and are commonly
associated with intrusions of quartz monzonite and related calc-alkaline plutonic rocks, and also
with mafic volcanic rocks. They also occur in clastic sedimentary rocks. The complex ores
containing copper may also be associated with zinc, lead, gold and silver minerals.
Copper deposits have originated by diverse processes, but most of them are either the direct result
of hydrothermal activity, submarine exhalations, bacteriogenic precipitation and oxidation and
supergene enrichment. Porphyry copper deposits, the main present-day resource of copper, are
large, epigenetic, low grade (0.5 to 1 % Cu), disseminated, hypogene mineralisation that can be
exploited by bulk-mining techniques. Such ores are closely associated with intrusions of
monzonite, quartz monzonite, or quartz porphyry. Contact metasomatism also accounts for some
deposits of copper in carbonate rocks. Most copper deposits in unglaciated regions have
undergone oxidation and some supergene enrichment with rich grades at the upper levels just
below the water table.
Indian distribution
The major copper deposits in the country are located in the states of Jharkhand, Rajasthan,
Chhattisgarh and Karnataka. Minor occurrences of copper in polymetallic association are found in
Sikkim, Maharashtra and Andhra Pradesh. Their distribution is shown in Fig. 5.
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The Singhbhum Thrust Belt, a 160-km long arcuate structural zone in the southern part of
Jharkhand state is host to several mineral occurrences of economic importance. This belt hosts
several copper, uranium and apatite-magnetite deposits (Fig. 6). Besides nickel, gold,
molybdenum, silver, tellurium and selenium are being extracted as by-products from the copper
and uranium ores. The copper sulfide mineralization is found along the entire shear zone, right
from Baharagora in Mayurbhanj district of Orissa in the southeast to Galudih-Duarpuram in the
west in Jharkhand. However, only certain sections are mineralized richly to be of economic or subeconomic
importance. These sections are: Baharagora, Badia-Mosabani, Pathargarah-Surda,
Kendadih-Chapri, Roam-Rakha Mines-Tamapahar, Ramchandra Pahar-Nandup-Turamdih.
Fig. 5. Distribution of copper deposits in India.
Fig. 6. Distribution of mineral deposits along the Singhbhum shear zone
(after Sarkar, 1984).
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Out of these, the Badia-Mosabani sector is the richest. Here the mineralization is localized in the
soda granite close to the contact with the underlying Dhanjori metabasalts. The Mosabani mine
first went into production in 1928 and was continuously being mined up to depths of around 1100
m but was closed a few years ago by Hindusthan Copper Ltd. This mine had two sub-parallel lode
structures dipping generally at 20 degrees to the NE, one designated as the Main Lode and the
other more productive one as the West Lode. The host rock of mineralization for other deposits in
the belt is biotite-chlorite-quartz schist grading at places to chlorite schist. Though opinions vary
widely regarding ore genesis in the Singhbhum Copper Belt, considering all aspects a model
proposing volcanic hydrothermal activity along a syn-volcanic thrust zone seems to be most
satisfactory (Sarkar, 1984). Total estimated reserves for mines under HCL’s lease in the entire belt
were 173 Mt at 1.38 % Cu, out of which Mosabani contributed 19.77 Mt at 1.70 % Cu (Mining
Magazine, November, 1983).
Hindusthan Copper Ltd’s Malanjkhand mine is the biggest open pit base metal mine in India. It is
located in the Balaghat district of Chhattisgarh state, 90 km NE of the town of Balaghat. Lode-type
copper (-molybdenum) mineralization occurs within calc-alkaline tonalite-granodiorite plutonic
rocks of early Proterozoic age (Sarkar et al., 1996). The mineralized host rock is about 2 km in
strike, has a maximum thickness of 200m, dips 65 to 75 degrees along which low grade
mineralization is traced upto a depth of 1 km. A conservative estimate of the ore reserve is 92
million tonnes with an average Cu grade of 1.3 %. At 0.83 % Cu, the reserves escalate to 789
million tonnes (Sikka, 1989). Supergene oxidation with limited enrichment is recorded upto a
depth of 100m. The bulk of the mineralization occurs in sheeted quartz-sulfide veins and K-silicate
alteration zones. The main primary minerals are chalcopyrite and molybdenite. In terms of several
geological aspects this deposit is comparable to Phanerozoic (and reported Precambrian) porphyry
copper systems in other parts of the world (Sikka, 1989; Sarkar et al., 1996).
The 100 km long Khetri Copper Belt (KCB) in Jhunjhunu district of Rajasthan contains copper
mineralization (from north to south) at Banwas, Madan Kudan, Kolihan, Chandmari, Usri,
Akwali, Sathkui, Dhanaota and Charana. Of these, larger concentrations have been exploited by
HCL at Madan Kudan, Kolihan and Chandmari. A total reserve of 83 Mt of ores with 0.88 to 1.5
wt. % Cu was estimated at the KCB (Sarkar, 2000). The orebodies in KCB are in the form of
single or compound lenses hosted by garnetiferrous chlorite schist and banded amphibolitequartzite
in Madan Kudan and Kolihan, and only garnetiferous chlorite schist at Chandmari. In the
south, the mineralization is hosted by carbonaceous phyllite. The mineralization is concentrated at
the interface between the Alwar and Ajabgarh Groups of the Delhi Supergroup. Chalcopyrite,
pyrite and pyrrhotite are the principal sulfide phases. Opinions about ore genesis along the KCB
ranges from epigenetic hydrothermal to sedimentary diagenetic with later metamorphism.
In Karnataka, Chitradurga Copper Company mined a small pyritic copper deposit within
Chitradurga Group volcanic rocks at Ingaldhal, a few km away from the town of Chitradurga. This
deposit attracted special attention in recent years when gold was detected in the footwall pyritic
zone.
It is presently estimated that India holds about 5.3 million tonnes of copper reserves (HCL News,
2005).
Lead-Zinc
The metal zinc generally occurs in combination with other elements, most commonly with lead.
The important minerals of zinc include: sphalerite or zinc blende (ZnS), smithsonite (ZnCO3),
12
zincite (ZnO) and hemimorphite (2ZnO.SiO2.H2O). Similarly, the most common lead mineral is
galena (PbS). Other minerals containing lead are cerussite (PbCO3) and anglesite (PbSO4).
Zinc is used extensively for coating and galvanizing iron and steel products, in the manufacture of
pigments, as a component in alloys like brass, bronze and German silver. Zinc dust and plates are
used to precipitate gold from cyanide solutions in the treatment of gold ores. Lead is widely used
in the manufacture of electric storage batteries and in various electric appliances. It also finds use
in water pipes, chemical plants, ammunitions, solders, pewter, nuclear shield in atomic plants and
in certain lead chemicals.
Majority of the lead ore deposits of the world are also zinc producers and most zinc ore deposits
carry lead. Both lead and zinc bodies usually occur as veins and massive or tabular lodes, and as
disseminations and patches, commonly in limestone or dolomites, but also in shales. Majority of
lead-zinc ores occur as cavity-filling and replacement bodies formed by low-temperature
hydrothermal solutions of diverse origin.
Indian distribution
The lead-zinc ore deposits and prospects are distributed widely in India, with the predominant part
of the resources being confined to the state of Rajasthan. Other states with some lead-zinc resource
are Andhra Pradesh, Orissa, Gujarat, Sikkim, Uttaranchal, Maharashtra and Jammu & Kashmir
(Fig. 7).
The most important zinc-lead deposits of economic value in India are the Rampura-Agucha,
Rajpura-Dariba and Zawar deposits in Bhilwara, Rajsamand and Udaipur districts of Rajasthan,
respectively. The Rampura-Agucha deposit is the most important Zn-Pb-(Ag) deposit in India
producing 9 x 105 tonnes per annum with a total reserve of 63.7 Mt with 13.6% Zn, 1.9% Pb and
45 ppm Ag (cf. Sarkar, 2000). The rock types around the single ore lens are: garnet-biotite-
Fig. 7. Distribution of Pb- Zn deposits in India.
13
sillimanite gneiss (GBSG) with bands of calc silicate rocks and amphibolites intruded by
pegmatite/aplite veins with graphite-mica-sillimanite schist hosting the ore. The major mineralogy
of the ore is simple: sphalerite, pyrrhotite, pyrite, galena and graphite are the main phases. The
available geological information indicates that the deposit is sediment-hosted and the
mineralization localized by the anoxic environment. The Dariba-Rajpura-Sindeswar Kalan-
Bethumni belt is a 17 km long mineralized zone with a 16.85 Mt of ore reserve in the richest
Dariba-Rajpura sector, with a grade of 8% Zn and 2.26% Pb (Sarkar, 2000). Cu and Ag are
obtained as by-products and Cd, Hg and Tl are important trace metals in the ore. Metamorphosed
siliceous dolostone and graphite-mica schists are the main host rocks of the mineralization which
at Dariba, show zoning from Cu in the footwall through Pb-Zn in the middle to Fe in the hanging
wall. The ores here have the characteristics of a sedimentary exhalative deposit. In Zawar area, the
Mochia Magra, Balaria, Zawar Mala and Baroi Magra Hills contain extensive deposits. The main
mine is located in the Mochia Magra hill (reserve 19.3 Mt of 3.8% Zn + 1.7% Pb), with smaller
mines in Balaria (reserve 16 Mt of 5.66% Zn + 1.44% Pb), Zawarmala (reserve 16 Mt of 3.72%
Zn + 2.16% Pb) and at Baroi Magra (reserve 11 Mt with 1.33% Zn + 4.29% Pb). The principal
rock type of Zawar area consists of phyllites, slates, mica schists, dolostones and quartzites of the
Aravalli Supergroup. But sulphide mineralization is solely confined to the dolomites, whereas
adjoining phyllites are almost barren. The localization of the ore is structurally controlled along
shears. The initial mineralization is believed to have taken place during sedimentation and early
diagenesis with the bulk of the mineralization being translocated along extensional fractures and
shears during later deformation (Sarkar, 2000).
Zinc and lead ores have been located in different parts of Andhra Pradesh. The most important
deposit is found in Agnigundala belt in Guntur district in the Nallamalai hill range. The most
important deposit, till recently mined by Hindusthan Zinc Ltd., is at Bandalamatto. The
mineralization is in the form of veins and stringers of galena associated with sphalerite,
chalcopyrite and pyrite. The host rock is brecciated dolomite, dolomitic limestone and coarse
grained calcareous quartzites belonging to the Cuddapah Supergroup.
A Pb-Zn deposit was being mined by Hindusthan Zinc Ltd. around Sargipalli in Sundergarh
district of Orissa till a few years ago. This early Proterozoic Pb-Zn deposit is hosted by graphitesillimanite
schist of the Gangpur Group (Sarkar, 1974).
Polymetallic Zn-Pb-Cu ore lenses are found around Ambaji in the Banaskantha district of Gujarat
and 8 km away at Deri in the Sirohi district of Rajasthan. These ores occur in metamorphosed
basalt-rhyolite bimodal volcanic suite, now represented by cordierite-anthophyllite-chlorite rocks
belonging to the South Delhi fold belt. The Ambaji ore zone contains 8.29 Mt of ores with 5.52%
Zn, 4.91% Pb and 1.75% Cu (Deb, 2000).
Polymetallic Cu-Pb-Zn mineralization is also found at Rangpo in Sikkim within phyllites,
quartzites and metabasic rocks of the Daling Group (GSI, 2001).
It is estimated that India has 176.8 million tonnes recoverable reserves of lead and zinc ore as on
April 2000.
Gold
Gold is a noble metal which has the yellow radiant colour and high reflectance. It is also highly
malleable and ductile and has high specific gravity. Its main use is for monetary purposes,
14
followed by use in jewelry. Gold is also used for therapeutic purposes, in dentistry and specialized
equipments.
Both primary and secondary processes produce gold concentrations in nature. Fluids play a key
role in concentrating gold in both these environments. In early Archean times, Mg-Fe-rich or
ultramafic lavas reacted with sea water creating primary greenstones and concentrating gold along
with nickel, copper and iron. With subsidence and tectonism, the primary greenstones underwent
partial melting and differentiation and gave rise to silica-rich plutonic rocks which had more gold
abundance than their precursors. Subsequent hydrothermal activity leached the metal and
concentrated it in lodes to produce the gold-quartz veins along structural locales. While primary
mineralization served as the principal source of gold for several centuries, of late, gold
concentrations associated with low temperature processes in supergene environment have been
located in laterites in South America, South Africa, Western Australia, Madagascar and southern
India. Gold eroded from primary ore deposits also commonly accumulates as detrital particles in
streams and are in many ways younger, smaller versions of the ancient gold-uranium-bearing
conglomerates of the Witwatersrand type. The origin of this large gold resource however, is
debated in recent years with two strong opposing views: sedimentary (diagenetic) and
hydrothermal.
Beginning of gold use has been traced back to more than six thousand years ago. During the ‘prehistoric
and ancient times’ a total of more than 10 thousand tones of gold is estimated to have been
produced (Bache, 1987). At best a small part of it could be primary. Same must be true for the
gold produced during the ‘middle ages’.
Indian distribution
Most known primary auriferous zones in India are the vein type deposits located in the eroded
remnants of ancient volcano-sedimentary rocks, known as schist belts or greenstone belts of late
Archaean age in the Dharwar geological province in South India (Fig. 8). Thus the largest cluster
of gold occurrences is located in the states of Karnataka and Kerala. Gold is also known to have
high potential in south Jharkhand, parts of Madhya Pradesh and in south Rajasthan.
Gold occurs in a variety of geological settings. The following modes of occurrences are recorded
in India (Radhakrishna and Curtis, 1999):
Lode Gold (quartz–carbonate vein type) deposits: Usually confined to metamorphosed volcanic
rocks forming linear schist belts of late Archaean age (Greenstone belt) and invariably occupying
fissure and shear zone and commonly persisting to great depths. This type of deposit still remains
as the chief source of gold in India. The best examples are Kolar gold field in Karnataka, passing
into the junction of Andhra Pradesh and Tamil Nadu; Hutti gold field in Karnataka. The most
typical of this type of occurrence is the Champion lode of the Kolar Gold Field which is the richest
gold-bearing quartz lode so far encountered in India.
Gold in banded iron formations: Generally occurs in association with schistose amphibolite and
banded iron formation of late Archaean age. Best examples are Ajjanahalli and Sandur deposits in
Karnataka and Sonadehi in Madhya Pradesh.
15
Gold in granulite terrain: This type is similar to the vein and stratiform types described above
under 1 & 2. Example is the Wynad gold field in Kerala.
Disseminated gold: Gold commonly occurring in disseminated form throughout an intrusive body
or volcanic rock. Such deposits are of low grade but often amenable to open cast mining. Example
is Malanjkhand copper deposit in Chhattisgarh where gold is detected in the ore and not in the host
rocks.
Gold associated with early Proterozoic volcanic or sediment-hosted polymetallic sulphide
deposits: In this category are included deposits of copper, lead and zinc containing values of gold,
silver and other metals which can be extracted as by-products. Examples are Rajpura-Dariba
deposit in Rajsamand district; Danva prospect in Sirohi district, and Khetri copper belt of
Jhunjhunu district, Rajasthan.
Gold in quartz pebble conglomerates and quartzites (ancient placers): Detrital gold commonly
occur in quartz-pebble conglomerates resting unconformably on older gneisses, schists at the
Archaean-Proterozoic boundary. Some of the world’s largest concentrations are found in this
deposit type known commonly as QPC or Witwatersrand type. Examples are found in Bababudan
hills in Karnataka and at the base of the Dhanjori basin in Jharkhand.
Greywacke or turbidite-hosted deposits: These deposits occur in late Archaean sedimentary
successions along with volcanic intercalations and may form part of greenstone belts. Examples
are Gadag in Karnataka.
Fig. 8. Distribution of primary gold deposits in India.
16
Carbonate-hosted deposits: Gold in this environment may be present as invisible type in carbonate
rocks in close spatial association with granitic rocks. Example is Bhukia gold in Banswara district
of Rajasthan.
Gold in coal: Possible in lamproite dyke rocks intruding Gondwana coal-bearing succession.
Epithermal bonanza type deposits of Tertiary age: The younger granites of fold mountain chains
and altered volcanic rocks are likely to show such concentration of gold. Yet to be identified in
Central Himalayan Range or in Andaman islands.
Placer and alluvial gold: Alluvium of rivers draining auriferous tracts and showing concentrations
of detrital gold. Nilambur valley, Kerala; Subarnarekha River, Jharkhand.
Gold in laterite, soil and weathering profiles: This is a newly recognized mode of occurrence of
economically exploitable gold. Example is in Nilambur valley in Kerala.
Aluminium
Aluminium is extracted from bauxite ore which may contain one or more of the aluminous
minerals, gibbsite (Al2O3.3H2O), boehmite (Al2O3.H2O) or diaspore (Beta Al2O3.H2O). It also
invariably contains various iron hydroxides and titanium oxides. Bauxite is used not only for the
extraction of Al metal but also in chemical industry, as refractory material and as an abrasive. It is
also used to produce ‘cement fondu’, aluminous cement characterized by rapid hardening
qualities. Metallic aluminium is light weight and has 60% of the electrical conductivity of copper.
Even then in countries not having enough copper it is used for making electrical wires, as in India.
The process of bauxitisation is primarily related to processes of mechanical disintegration,
chemical weathering, and leaching under favourable hot and humid climate where heavy rainfall
and good drainage pattern accelerates the process. The bauxite deposits may be produced by
chemical sedimentation, by solution and redeposition, chemical replacement of pre-existing rocks,
sub-aerial weathering in situ or detrital deposition, from high altitude to low lying areas. Usually
occurs as blanket deposits. Any igneous (excepting ultramafic), sedimentary and metamorphic
rock can act as the protolith of bauxite deposit provided it contains tangible amount of Al2O3.
Indian distribution
Large resources of low grade bauxite ores have been explored by Government agencies on known
aluminous laterite occurrences (Krishnan, 1935) capping flat-topped plateaux in a 300 km stretch
of the Eastern Ghat belt from East Godavari district of Andhra Pradesh to Sambalpur and Bolangir
districts of Orissa covering an area of almost 25,000 sq.km (Fig. 9). These are underlain by
Precambrian granulite facies metamorphites comprising an interlayered sequence of khondalites
and leptynites, the former being the bed rock of blanket-type deposits with large aerial extent (~
0.5 km), appreciable thickness (max. ~50 m) and usually good profile differentiation with little or
no overburden (Deb and Joshi, 1984). The well known aluminous laterite occurrences in this East
Coast Bauxite Province are at Anantagiri area in Vishakhapatnam district of Andhra Pradesh
where bauxite cappings at altitudes of 1090 to 1445 m are found at Galikonda, Raktakonda,
Katuki and Chittamgondi (Raman, 1976). In Orissa, aluminous laterite deposits occur at Pottangi,
Panchpatmalli and Baphlimalli hills in the Koraput district, around Kashipur in Kalahandi district
and on the Gandhamardan plateau of Bolangir district. A rough estimate of the bauxite resources
in the East Coast bauxite province is of the order of one billion tonnes of aluminous laterites with
about 40 % Al2O3.
17
Fig. 9: Distribution aluminium deposits in India.
The bauxite belt of Central India, some 400 km long and 50 km wide, trends in ENE-WSW
direction and comprises a string of mesas with group of bauxite deposits at Balaghat, Amarkantak,
Putkapahar and Mainpat, Jamirpat, Bagru-Manduapat-Neturhat. This belt is sub-parallel and south
of the Son-Narmada lineament, extending from from Madhya Pradesh through Chhattisgarh to
Jharkhand. All these deposits occur above the critical contour of 2,500 ft. at the contact of
contrasting litho-units.
A large area of about 4000 sq. km between latitudes 23o00’ and 23o30’ and longitudes 84o00’ and
84o45’ in Ranchi and Palamau districts of Jharkhand contain valuable deposits of bauxite
underlying lateritic capping. The bed rocks in the area include Chotanagpur granite gneiss, older
metamorphics of the Iron Ore Supergroup and some basaltic trap rocks in the western part of the
area in the plateaus of Netarhat, Jamira Pat and Luchutpat. Segregations of bauxite are present in
the laterites as small pockets, continuous bands or beds, 1 to 1.5 m in thickness, seen on the scarp
face. The bauxite deposits of Khamar Pat and Mandua Pat in Ranchi district are close to the town
of Lohardaga. They have high grade bauxites with Al2O3 content varying between 49.7 and 60 %.
Most important occurrence of bauxite in the Lohardaga region is Bagru hills where rich bauxite
with upto 51.6 % Al2O3 is exploited for production of alumina in the Muri plant of the Indian
Aluminium Company. Isolated pockets and bands of high grade bauxite also occur in Pokhra Pat
and Dudhia Pahar areas on the Ranchi plateau. Another promising area nearby is the Serangdag
plateau, skirted by Koel river, containg more than 3.5 Mt of bauxite. In Palamau district bauxite
occurs on the Netarhat plateau. The best deposits of high grade pisolitic bauxite, with upto 58 %
Al2O3, occur on the western edge of the Burha river valley. High level laterites with thickness
varying from 9 m to 61 m, containing irregular patches of bauxite, also occur in the Kharagpur
hills in the Monghyr district of Bihar at Khapra, Maira-Maruk and Maira areas.
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There are three main bauxite-producing areas in Madhya Pradesh and Chhattisgarh. These are in
the Sarguja-Raigarh-Bilaspur districts, continuing from the laterites of Ranchi and Palamau; in the
Maikala range in the districts of Durg, Mandla and Balaghat; and Katni-Newer-Jabalpur areas of
Jabalpur district. In the first area, lateritic cappings is found on Deccan traps which at places overly
the Lametas. In Bilaspur district the principal occurrences of bauxite with 50 to 55 % Al2O3 are in
Korba, Churi and Uprora areas. Although there is an alumina plant in Korba, much of these
bauxites are well suited for refractory use. The Amarkantak plateau bauxites are the principal
source of raw material used by HINDALCO at Renukoot, Mirzapur district of U.P, close to the
border with M.P. The Amarkantak plateau with an extensive blanket of laterite is situated at the
source of the river Narmada and has the best development of bauxite in the southern end of the
plateau. Massive bauxite deposits, about 3 m in thickness, are found at several places under the
pisolitic laterite. The Al2O3 content varies between 55 and 60 %. The total reserve of such high
grade bauxite in this plateau is at least 5-6 Mt. In Jabalpur district, the aluminous laterites and
bauxites are generally found associated with lower Vindhyan limestones. The bouldery bauxites
near Katni are very high grade with about 60 % Al2O3 and low silica and occur at times in the
alluvium in the valleys.
In Karnataka, high alumina, high silica and ferruginous bauxites occur in different regions. Rich
bauxite deposits occur on bed rocks of Deccan traps in Belgaum district of northwestern part of the
state. The estimated reserves in the district are about 7 Mt with good deposits, with more than 50
% Al2O3, found at Kasarpada and in the Mogalgad areas.
The total reserve of aluminium ore in India is estimated to be 2650 Mt, located mainly in the states
of Andhra Pradesh, Orissa, Madya Pradesh, Maharashtra and Jharkhand.
NON-METALS
Non-metallic minerals, including industrial rocks and building stones, form the major part of
natural resources used by modern societies in terms of their total output and value. These minerals
form the back bone of several industries such as chemical, ceramic, fertilizer, refractories etc. and
India is endowed with some of the largest deposits of these industrial minerals (cf. Deb, 1980).
Unfortunately, much less R & D is carried out on these important economic minerals compared to
their metallic counterparts. As a result there is a dearth of scientific literature on them as also of
reference text books in the field. The brief account of the important industrial minerals in India
(see Fig. 10) that follows is based primarily on the above reference.
Refractory minerals
Refractory minerals are those which can withstand high temperatures as well as sudden
temperature changes, abrasion and shock, and have good resistance to different chemicals and
changing pressures under extreme conditions. They are used for various purposes, the most
important use being in the linings of furnaces for smelting and refining metals. They are also used
for lining incinerators, kilns in ceramic industry and in glass and cement manufacture, for coke
ovens/boilers used in gas or electric plants. They also find use in spark plugs for automobiles. With
the tremendous growth in metallurgical plants in India in recent years the use and geology of
refractories has acquired special significance.
19
The refractory minerals are divided into three categories, based on their reaction with various
kinds of slags:
Acidic Neutral Basic
Silica: Quartzite
etc
Fire clay, Ball
clay
Chromite Magnesite
Kyanite Graphite Dolomite
Sillimanite Asbestos Bauxite
Acid refractories:
Silica
Silica for refractory purposes is derived from quartzites, sandstones, vein quartz and sands. Such
quartzites are of metamorphic origin, sandstones and sand of sedimentary derivation and vein
Fig.10. Distribution of selected non-metallic mineral deposits in India.
20
quartz from igneous (hydrothermal) source. These above mentioned rock types occur in almost all
the geological formations, from the Precambrian to Recent.
Because of their heat resistant property, these refractories are widely used in the arches and crowns
of furnaces. Silica bricks are used in open hearth furnaces, in acid Bessemer converter and in
electric furnaces.
Indian distribution
Quartzites
Quartzites occur commonly in the geological formations belonging to the Dharwar, Aravalli,
Kurnool, Cuddapah and Vindhyan Supergroups. State-wise, the major exploitable occurrences are
as follows:
Bihar: In the Kharagpur hills, fine grained, massive quartzite occurs, composed predominantly of
quartz, with garnet, magnetite, biotite, and muscovite as accessories. Silica content varies between
97.5% and 98%.
Jharkhand: Quartzites occur in Singhbhum district, near Chandil and Chaibasa. Large quantites are
also available in Gangpur Group of rocks.
Karnataka: Quartzites consisting almost entirely of pure quartz occur in the Dharwar schist belts of
Karnataka. Near Bhadravati alone, in the Shimonga schist belt, about 2 Mt of quartzites are found.
Quartzites also occur near Bangalore, Krishnarajasagar, Holalkere, Holenarsipur and in the
neighbouring areas of Mysore city.
Andhra Pradesh: In Cuddapah and Kurnool formations there are ferruginous silica beds in the
Chaiyar Group of rocks found on the Oopalpad plateau and in the vicinity of Yadakee.
Fire clay
Fire clays are refractory sedimentary clays characterized by very low alkali content. They are
commonly found in the coal measures of the Gondwana coal fields. They may be plastic or nonplastic
in character. When very finely ground the plasticity increases. In most of the fire clays,
kaolinitic and bauxitic materials occur together in different proportions along with free quartz and
other impurities. Mineralogically the fire clays comprise the aluminium hydroxides, diaspore or
gibbsite. The SiO2 content varies between 45-55% and Al2O3 content between 30-40%. The
plastic fire clays are similar to ball clays, and used as bond clays for the manufacture of saggers,
glass pots, crucibles, mortars, and refractory cement. Non-plastic fire clays usually contain a high
proportion of silica and are low in clays and aluminous minerals. The fire clays generally have
fusion point usually above 1600oC.
Indian distribution
Jharkhand produces the highest quantity of fire clays from the coal fields of Karanpura and Jharia.
West Bengal comes next in order of importance, producing fire clays from the Raniganj coal
fileds. Chhattisgarh also contributes to fire clay production much of which comes from Korba
coal field. Orissa also produces good quality fire clay from Sambalpur and Denekanal districts. In
some other states such as Karnataka and Tamil Nadu refractory kaolin occurring in Precambrian
strata are regarded as substitutes for fire clays or refractory clays.
Ball clays
These are greyish-white to light cream in colour, fine-grained, sometimes carbonaceous and are
highly plastic in nature. They have high bonding capacity and tensile strength. They are extracted
21
from sedimentary formations in lumps or in ball-shaped forms and are marketed in the raw stage,
without any beneficiation. The chemical composition of ball clay is almost similar to kaolin or
china clay, except that it is high in silica and poor in alumina. Ball clays cannot be easily shaped or
used in casting or dewatered easily by filter pressing. High shrinkage causes fine cracks or hairlike
lines on the body of the fired wares. On firing, the ball clays produce a vitreous substance at a
much lower temperature than Kaolin. These clays are extensively used in bonding furnace sands
and refractory materials.
Indian distribution
Ball clays are distributed mainly in states of Maharastra, Rajasthan, Gujarat, Kerala and Tripura.
Several localities of ball clays are found near Bombay and surrounding areas in Maharashtra and
near Barmer in Rajasthan.
Kyanite (Al2SiO5)
The mineral is characterised by its bluish colour, bladed form, good cleavage and varying hardness
in different cleavage directions. It usually occurs in crystalline schistose rocks formed under high
pressures at great depths and associated with minerals, such as, corundum, staurolite and
andalusite. The transparent crystals are used as semiprecious gemstones.
Indian distribution
India has the largest resource of kyanite in the world. The state-wise distribution of this important
refractory mineral is as follows:
Jharkhand: Kyanite deposits at Lapsa Buru in Singhbhum district contain massive development of
high grade kyanite of great economic importance. The Lapsa hill forms the central high portion of
a long ridge about 3 km in length and rises about 300 m above the plains, where there are kyaniteproducing
quarries of TISCO. The kyanite-bearing rocks form segregations in the mica schists.
Along the extension of the Lapsa Buru hills, towards east and south-east in Seraikela near
Kharswan, massive kyanite rocks occur in association with aluminous mica schists and kyanitequartz
rocks. In and around Sini, in Singhbhum district, there are also several exposures of coarse
bladed kyanite within mica schists, appearing as seggregated veins.
Andhra Pradesh: Kyanite-quartz rocks have been reported from Nellore district. The deposits
occur in mica schists of Nellore mica-belt, northwest of Saidapuram. Kyanite forms in pockets and
lenticular bands having lengths upto 150 m. Kyanite also occurs intercalated with quartz schists
and quartzites. In Khamman district, there are several exploitable deposits of kyanite and garnet.
The productive area is about 15 sq. km containing garnetiferous kyanite mica rocks.
Rajasthan: Pockets and lenticles of quartz and kyanite, as big as 0.3 to 1m in size, occur randomly
along the contact of pegmatites and quartz veins intruded into biotite-garnet-kyanite schists in
Dungarpur district. All these highly metamorphosed rock formations are overlying the Banded
Gneissic Complex basement.
Sillimanite (Al2SiO5)
The mineral occurs in compact radiating masses and fibrous aggregates in high-grade
metamorphic rocks. Colour varies from grey to light brown or pale green; the lusture is often
vitreous. It is distinguished easily by its acicular needle shaped crystal habit. Sillimanite is a
product of high-grade metamorphism of aluminous rocks often occurring directly at the contact
with igneous rocks. Sillimanite also occurs in crystalline schists in association with metamorphic
minerals such as cordierite, corundum, andalusite and spinel.
22
Indian distribution
Sillimanite deposits are widely distributed in India, particularly in the Precambrian crystalline
complexes in Meghalaya, Rajasthan, Madhya Pradesh, Bihar, Orissa, Kerala, Andhra Pradesh and
Tamil Nadu.
Meghalaya: This state alone possesses nearly 70% of the total reserves in India. India’s richest and
unique deposit of sillimanite is situated at Sonapahar in Khasi hills. The deposit has been traced in
an area of 78 sq. km. It is associated with highly aluminous rocks, such as cordierite-biotite-quartzmicrocline
gneiss and sillimanite-quartz schist enveloped in granite. The main exposures are at
twelve different places. The sillimanite is of massive variety and occurs in huge boulder form.
Madhya Pradesh: Sillimanite occurs in Pipra in Waidhan tehsil of Sidhi district. Both boulder and
vein deposits are reported.
Maharashtra: Corundum, kyanite and sillimanite bearing rocks are found for a length of 5 km
between Dahegaon and Pipalgaon in Bhandara district.
A small quantity of sillimanite is reported from Tannilai mine in Tiruchirapalli district, Tamil
Nadu and Madar mine, Udaipur district, Rajasthan. India also possesses extensive deposits of
sillimanite associated with the beach sands of Kerala, Tamil Nadu and Orissa.
Neutral refractories
Chromite (FeCr2O4)
High grade chromite ore, which is hard and lumpy, is used in the manufacture of chrome bricks,
chrome-magnesite bricks and allied refractory products. The refractory grade chromite ore should
have moderate to high (30-48%) Cr2O3 and Al2O3 content between 12-30%. They should have
low Fe2O3 (<15%) and SiO2 (<5%) as well. In industrial practice, an excess of MgO is added to
the chrome ore in order to combine all the excess silica.
The mode of occurrence and Indian distribution of chromite deposits (cf. Fig.3) has been covered
in the foregoing section on metallic deposits.
Graphite (C)
Graphite occurs in two forms: Natural graphite which includes (a) crystalline and (b) amorphous
varieties, and artificial/manufactured graphite. The inherent qualities of graphite, for which it is so
much in demand in the manufacturing industries, are its high lubricity, refractoriness or ability to
withstand high temperature, good electrical and heat conductivity, and resistance to reaction with
ordinary chemical reagents. Thus, flaky graphite is used in the manufacture of crucibles for
melting metals. It is also used in the manufacture of lead pencil, batteries, lubricants and brushes.
It is also used in atomic reactors. The commercial graphite is graded mainly on its carbon content.
Graphite can develop by four different geological processes: regional metamorphism and contact
metamorphism; crystallisation in igneous rocks, such as in basalts and nepheline syenites, and
through hydrothermal solutions from deep-seated magma, such as vein graphite in pegmatites.
Majority of graphite deposits form by the metamorphism (both contact and regional) of
sedimentary carbonaceous matter, such as, those present in black shales. Graphite is also found in
iron meteorites. The best known graphite deposits in the world are found in Sri Lanka and
Madagascar.
23
Indian distribution
The major share of graphite production in India comes from the states of Orissa, Jharkhand,
Karnataka and Andhra Pradesh.
Orissa: Graphite in Orissa is reported from khondalitic rocks of the Eastern Ghats. The deposits
occur in form of veins, lenses and pockets. Two varieties are reported, namely, flaky and
amorphous. The graphite from Orissa has fixed carbon content between 55% and 60%. The rich
deposits of graphite are found in Patna, Sonpur, Atmallik, Koraput, and Kalahandi districts of
Orissa.
Jharkhand: Graphite occurs in khondalites, schists and gneisses, pegmatites, limestones, calcgranulites
and quartzites in Daltonganj and Palamau districts. Rich graphite concentrations are
known in the Sokra, Khamdih and Rajhara areas. The carbon content of graphite ore in these
occurrences is around 50%.
Andhra Pradesh: Graphite occurs in khondalites of East Godavari district of the Eastern Ghat belt.
Graphite is reported in the form of irregular lenses and pockets and rarely as veins of varying
thickness. In Vishakhapatnam district graphite occurs in the form of irregular veins and as highly
disseminated material in an area called Marupalli. Krishna and west Godavari districts also have
graphite occurrences.
Karnataka: Fine grained, amorphous variety of graphite is reported from Kolar schist belt in
Bangarpet taluk and flaky variety is found in crystalline schists near Mavinhalli and Tonavalli
areas of Mysore district. Graphite is also found in areas of Chitradurga schist belt and in the
Bababudan hills.
Asbestos
Asbestos is a commercial name for a group of minerals characterized by fibrous habit and wide
variety of compositions. Depending on the strength and flexibility of fibres they are used for
various purposes. The fibrous nature and its high resistance to fire makes it commercially so
important. Asbestos has two distinct groups, namely, the serpentine group and the amphibole
group. The former includes the elastic and the silky chrysotile variety and the latter comprises
short and brittle-fibred anthophyllite, tremolite, actinolite etc. Asbestos is mixed with magnesite in
the proportion of 85% MgCO3 and 15% asbestos powder to produce a quality refractory material.
Three main factors control the formation of asbestos in different kinds of rocks, particularly the
ultramafic rocks. The process of serpentinisation plays an important role in the development of
chrysotile asbestos. Another important consideration is the transformation of non-fibrous
serpentine into the fibrous mineral, and lastly the gradual change of chrysotile into tremolite
asbestos. Generally accepted view about the genesis of asbestos is that the hydrothermal residual
solution left after the consolidation of ultrabasic magmas was responsible for the transformation of
peridotite and dunite into serpentine and later to asbestos.
Indian distribution
The best quality chrysotile asbestos is found in the state of Andhra Pradesh while the amphibole
asbestos is widely distributed in Jharkhand, Rajasthan, Tamil Nadu and Karnataka.
Andhra Pradesh: The most important occurrences are in the districts of Kurnool and Cuddapah
and the less important ones in Anantpur district. In the Pulivendla taluk of Cuddapah district,
between Brahmanapalle and Lopalanutola, asbestos was formed over a distance of 15 km by
24
contact metasomatism of the Vempalli limestones and shales by a dolerite body. The asbestos is
cross fibred chrysotile variety with an average thickness of 0.9m. Numerous veins of chrysotile
asbestos also occur in Rajupalam area of Cuddapah district. In Kurnool district asbestos occurs in
Dhone taluk in Vempalli limestones associated with trap rocks.
Jharkhand: Amphibole asbestos is found extensively in Singhbhum district of southern Jharkhand.
Crysotile asbestos is however rare. The former occurs in actinolite-tremolite talc chlorite rock
north east of Chaibasa and also around Manpur. Some amphibole asbestos is also found in the
chromite quarries west of Chaibasa where the country rock is dunite and peridotite. Asbestos also
exists in the Saraikela area.
Rajasthan: Chrysotile variety of asbestos is found in six localities of Udaipur district and two in
Ajmer district. All other remaining occurrences in Udaipur, Dungarpur, Bhilwara, Ajmer, Jodhpur
and Pali districts are of amphibole variety.
Basic refractories
Magnesite (MgCO3)
This carbonate of magnesium is found to occur in ultrabasic igneous rocks, formed by alteration of
Mg-rich silicates, and in dolomitic limestones. Its main use is in refractories. Dead burnt
magnesite, MgO, which is calcined at high temperature between 1400 oC and 1500 oC and
converts to crystalline periclase, is used in the manufacture of bricks for furnace linings. Magnesite
is also used as an ore of metallic Mg, but at present the entire production of Mg comes from brines
and seawater. Magnesite also finds use in chemicals and fertilizer industries.
Magnesite commonly occurs in veins and irregular masses derived from the alteration of Mg-rich
metamorphic and igneous rocks (serpentinites and peridotites) through the action of waters
containing carbonic acid. Such magnesites are compact, cryptocrystalline and often contain
opaline silica. Beds of cleavable magnesite are (i) of metamorphic origin associated with talc
schists, chlorite schists, and mica schists or (ii) of sedimentary origin, formed as a primary
precipitate or as a replacement of limestones by Mg-bearing solutions, dolomite forming as an
intermediate product. Mainly three varieties of magnesite are recognized: i) cryptocrystalline, ii)
crystalline, iii) amorphous.
Indian distribution
The major producers of magnesite in the country are the states of Tamil Nadu, Karnataka and
Uttaranchal.
Tamil Nadu: Magnesite occurs in biotite gneisses and charnockites which are intruded by dunites
of Chalk Hills in Salem district. The magnesite is found as irregular veins in ultrabasic intrusive
masses over an area of 11 sq. km. It has an average magnesium carbonate content of 95-97%. The
magnesite is of very good quality, white to grayish in colour, compact and massive. Estimated
reserves are more than 100,000 tonnes upto a depth of 15 m.
Karnataka: Magnesite in this state occurs as a decomposition product of ultrabasic rocks. It forms
as a network of veins, of various shapes and sizes, in the serpentinised rocks. Magnesite of
massive amorphous type occurs, particularly in Hassan, Mysore, and Coorg districts.
Uttaranchal: Magnesite deposits are associated mainly with dolomite and also at places with talc in
Almora and Someshwar districts. It occurs in the form of veins, stringers and as massive
25
crystalline deposits. Valdiya (1968) reported stromatolite-bearing dolomitic rocks with lentiform
deposits of coarsely crystalline magnesite in the Gangolighat formations of the calc-zone of
Pithoragarh district. The Magnesite deposits are very extensive, originating from the Kali river
valley towards east and continuing to the Alaknanda valley towards west.
Dolomite [Ca Mg (CO3)2]
Dolomite and calcite are common rock forming minerals. The dolostone, loosely called dolomite
in most literature, is considered as a principal raw material in the iron and steel industries. It is also
used as a refractory material, for which calcined products are preferred. Dolomite is used as a basic
lining in open hearth furnaces and in Bessemer converters, for which dead-burnt material is
required. Dolomite is also used in the manufacture of high magnesia lime, basic magnesium
carbonate, Epsom salts, and for the manufacture of metallic magnesium. Dolomite also finds use
in chemical industry, in manufacture of paper, leather, glass etc. and as building material, as
terrazzo stucco and also as crushed stones.
Dolomite is associated with sedimentary carbonate facies and occurs in all geological ages but the
economically important deposits are mostly confined to the Precambrian and Palaeozoic eras.
Usually the dolomites are associated with limestones and sometimes they occur as irregular beds,
lenticles, and pockets and rarely do they occur as hydrothermal vein deposits. Dolomite is
commonly found associated with gypsum, anhydrite and alkali salts in saline evaporative basins.
Dolomite also results from partial or complete dolomitization of the marine calcium carbonate
including marine shells and organic remains.
Indian distribution
Dolomite (Dolostone) and dolomitic marble occur extensively in several states in different
stratigraphic horizons.
West Bengal: Large deposits of dolomite which extend over an area of about 13 sq. km occur in
Buxa Duars area in the north-west of Jalpaiguri district. There are several varieties of dolomite in
this region out of which two are important: one is massive, compact, and light grey in colour, and
the other is dark brecciated type, possessing distinct bedding planes. Chemically both are pure
dolomites. A part of this dolomite band enters into Bhutan.
Rajasthan: This state has a large resource of dolomite, mostly occurring in the Delhi Supergroup of
rocks. The high grade dolomite deposits occur in Ajmer district in the areas known as Kesarpura,
Hatondi and Akhri. They are usually high magnesium crystalline dolomites, low in silica, alumina
and iron-oxides.
Karnataka: The dolomite deposits constitute part of the Dharwar Supergroup, occurring chiefly, in
Dharwar-Shimoga and Gadag-Chitradurga schist belts. Dolomite deposits are also found in the
lower Kaladgi Group of Cuddapah age. In Belgaum district large reserves of dolomite also occur.
Jharkhand: The dolomite occurs in Palamau district with most of the occurrences located near the
town of Daltonganj. The dolomite occurs as bands or as thin lenticular patches. The bands are
mostly associated with calc-silicate rocks, containing serpentine and diopside, but some of the
bands are also associated with magnetite-tremolite schist. Some outcrops of crystalline magnesium
limestones are also found in the iron ore group of rocks in Singhbhum district.
26
Orissa: Enormous deposits of dolomitic marble belonging to the Gangpur Group of rocks occur in
the Birmitrapur and Sundergarh areas of the state.
Minerals of Fertilizer industry
Three principal elements are necessary for plant growth and high crop yield. These are nitrogen,
phosphorous and potassium. Natural nitrates are hardly used now as they have been widely
replaced by nitrogenous fertilizers made from atmospheric nitrogen. Phosphatic fertilizers, earlier
produced from bones of dead animals, are now processed from phosphate rocks using sulfuric acid
to produce soluble super-phosphate. Potassium fertilizers are at places extracted from evaporate
deposits. Other minerals used as fertilizers, include gypsum, sulphur and borax.
Rock phosphates (Phosphorites)
Phosphorous is present in most rocks in minor to trace amounts. However, only in the phosphate
rocks or phosphorites the values can be as high as 40% P2O5. More than 180 mineral species are
known to contain 1% or more of P2O5. However, most of the phosphorous in the earth’s crust
occurs in the mineral apatite, which is a phosphate of calcium, with fluorine and chlorine. More
than 90% of rock phosphates are consumed in the manufacture of super-phosphates of different
strengths for increasing the soil fertility. A small part of the phosphate rock is used for the recovery
of elemental phosphorous, for the manufacture of phosphate chemicals such as disodiumphosphate,
monocalcium phosphate, used in different industries. Elemental phosphorous is used in
match industry as well as for the manufacture of incendiary bombs and fireworks.
Fig. 11. Cartoon depicting various modes of formation of different kinds of phosphate
concentrations (after, Craig et al., 1996)
Sedimentary phosphate deposits are known as phosphorites, which form beds, a few cm to tens of
meters thick, composed of cryptocrystalline fluorapatite, referred to loosely as collophane. Marine
phosphorites, which constitute the principal reserves of this material, account for roughly 80% of
world’s phosphate rock production. Major accumulations of this
27
resource appear to have developed only where upwelling cool phosphate-saturated sea waters
moved across near-shore continental margins. Here the phosphate precipitated by complex
microbiological processes, into phosphatic mud, nodules and crust (Fig. 11).
Indian distribution
Rajasthan: Large phosphorite deposits occur in the rocks of the Aravalli Supergroup in the vicinity
of Udaipur (Banerjee, 1971) and in Banswara districts. Phosphorite in the vicinity of Udaipur city
occurs in two zones. Jhamarkotra, Matoon, Kanpur, and Kharbaria-ka-Gurha deposits occur close
to the base of the Aravalli stratigraphy to the southeast of Udaipur. Bargaon, Nimachmata,
Sisarma and Dakankotra, occur to the west of Udaipur. The Jhamarkotra phosphorite deposit,
located about 24 km from Udaipur, represents the largest rock-phosphate deposit in India. The
Jhamarkotra deposit, like other deposits in the Aravalli Supergroup of the Udaipur area, is
associated with dolomitic limestone beds which have been metamorphosed to low grade and are
silicified and brecciated at places. They are also stromatolitic at many places. In Jhamarkotra, the
phosphorite-bearing horizon extends for more than 16 km in length with thickness varying from 1
to 25 m. The phosphorite horizon forms a broad arcuate belt, which overlies a very thick
orthoquartzite and cherty sequence. The phosphorite occurrences at Jhamarkotra comprise three
different types: i) columnar stromatolitic (algal) phosphorite; ii) laminar algal phosphorite; iii)
reworked, silicified and brecciated phosphorite showing fragments of stromatolites set in a cherty
and quartzose matrix. The P2O5 content of different varieties of phosphorites varies between 12
and 38 % at Jhamarkotra.
The Siriska and Kushalgarh formations of the Delhi Supergroup have minor occurrences of
phosphorites. A more or less regular bed of phosphorite, 2.5 to 3.9 m thick, occurs at Achraul, near
Siriska. The phosphorite contains 12.5 to 31.3% P2O5. Sedimentary phosphate deposits, both
stromatolitic and bedded varieties, of considerable economic importance have been found in
Birmania area of Jaisalmer district. The deposits are intimately associated with dolomite, chert,
carbonaceous shale, and sandstone. The rock sequence is correlated with the Marwar Supergroup,
considered equivalent to the Vindhyans. The phosphorite deposit here, 1 to 9 m thick, and having
8 to 13% P2O5, extends as a single horizon for 6.8 km.
Uttaranchal: Low-grade phosphorites occur in the basal chert member of the lower Tal Formation
in the Mussoorie hills of the Lower Himalayas. The phosphorites usually occur in granular, fine
grained, nodular and stromatolitic forms closely associated with black shale and chert, overlying
the Krol dolomitic limestone of the Mussoorie syncline.
Himachal Pradesh: Phosphorite occurrences have been reported from Sirmaur district, where
phosphate rocks are found along the Krol-Tal contact rocks and are confined mostly to the lower
Tal formation in close association with the chert. In an area known as Nigali-Dhar, the synclinal
structure contains fairly large amounts of phosphorites for a distance of 56 km.
Minerals of Cement industry
Limestone
The most important use of limestone is in the manufacture of cements. Cement grade limestone
contains four essential chemical elements: calcium, silicon, iron, and aluminium. It is also used
extensively as flux for smelting of various metallic ores. It is an important raw material for
chemical industry and also used in lithography. Finely crushed limestone is used as a soil
conditioner, for whitening and whitewashing. It is used as an aggregate in concrete, and as road
28
material. As a dimension stone for both construction purposes and for decorative exterior facings
limestone finds extensive use.
Limestones are sedimentary rocks, deposited in shallow or deep water marine environment. They
are often associated with silica, clay, pyrite and organic matters. Enormous accumulations of
calcareous materials are at first formed as calcareous silts containing dead marine plants and
invertebrate animal shells. In course of time, all these materials are progressively converted into
limestones which are composed of calcite crystals, with varying percentage of magnesium
carbonate and mechanically admixed impurities. Sometimes limestones are formed at the sea
bottom by the accumulation and lithification of particles of calcareous materials, originally
secreted in the sea water by living marine organisms. Usually oolitic limestones are formed in
littoral zones due to the coagulation of colloidal solutions of calcium carbonate around minute
sand grains. At first the oolites are composed of aragonite which is later converted into calcite.
However, calcite is relatively unstable in the weathering atmosphere due to its high solubility in
acidic waters.
Indian distribution
Calcareous rocks occur in all the principal geological formations of India, right from the
Precambrian to Recent. The most important economic concentrations are found in the Vindhyan
sequences of Bihar, Madhya Pradesh, Rajasthan, and Uttar Pradesh. The deposits in Bihar are
mostly in the Rohtas Formation of the Vindhyan Supergroup in Sahabad district. In Madhya
Pradesh, large deposits occur in the Semri Group rocks of the Jabalpur district. In Rajasthan,
dolomitic limestone in the Raialo Group occurs around Alwar, Nagaur, Kishengarh and Udaipur.
Tertiary limestones are distributed near Jaisalmer. In Uttar Pradesh, extensive deposits are found in
Mirzapur and Dehra Dun districts. The former are in Vindhyan sequence while the latter are in
Krol rocks. In Orissa, limestone is found in the Birmitrapur Formation of Gangpur Group in the
vicinity of Sundergarh. Reserves estimated are in the range of 250 Mt. Important occurrences are
also known from Sambalpur and Koraput districts. Andhra Pradesh also contains workable
limestone deposits in the Cuddapah basin. Narji limestone in the Kurnool Group and Vempalle
limestone in Anantapur district are exploited extensively. Extensive deposits of limestone are also
found in the Saurashtra region of Gujarat.
Gypsum (CaSO4.2H2O):
Pure gypsum is colourless to white. Satin spar is a fibrous variety of gypsum with silky lusture;
alabaster is the fine-grained massive variety and selenite is a variety that yields broad colorless and
transparent cleavage folia. Gypsum is mainly used for production of Plaster of Paris. Satin spar
and alabaster are cut and polished for various ornamental purposes but are restricted in their use
because of their softness. Gypsum also serves as a soil conditioner.
Gypsum is a common mineral widely distributed in sedimentary rocks, often as thick beds. It
frequently occurs interstratified with limestones and shales and is usually found as a layer
underlying beds of rock salt, having been deposited there as one of the first minerals to have
crystallized on the evaporation of salt waters. More rarely it may crystallize in veins, forming satin
spar. It is also found as lenticular bodies or scattered crystals in clays and shales. Found in volcanic
regions, especially where limestones have been acted upon by sulfur vapors. Also found
commonly as a gangue mineral in metallic veins. Usually the deposits have very little or no
overburden and the material being very soft and friable are very easy to mine.
Indian distribution
29
Rajasthan: This state is the biggest producer of gypsum in the country. The deposits are confined
to the Tertiary rock formations of Jodhpur region at Bhadwasi and Nagaur and in Bikaner region
at Jamser, Lunkaranswar etc. Barmer district also has potential deposits of dessert gypsum.
Tamil Nadu: This state accounts for the largest resource of gypsum in south India. Usually the
deposits are found in highly fossiliferrous rocks of Uttatur and Trichinopoly Formations of
Cretaceous age. They are intimately mixed up with the black cotton soil and estuarine clays of
Pleistocene period or even the recent sediments. The three main gypsum-producing areas are in
Coimbatore district, Ramanathapuram district and Tiruchirapalli district.
Karnataka: Some amount of gypsum has been reported from alkaline earth regions in
Chamarajnagar taluk of Gulbarga district. Small occurrences are also known in Bellary district.
Himachal Pradesh: Gypsum has been reported from Chamba, Mahasu and Sirmaur districts,
mostly as lumps, veins and bands, associated with Krol limestones and dolomites and also with
Subathu Formation.
Jammu & Kashmir: In the districts of Baramula and Doda, rich gypsum occurs as lenticular bands
or as regular bedded deposits in the Precambrian Salkhala schists or associated with nummulitic
limestones of Eocene age.
Gujarat: In districts of Bhavnagar, Jamnagar, Junagarh and Kutch rich deposits of Gypsum have
been reported from several areas. The richest deposits are found to occur in Rann associated with
Gaj Formation.
Minerals of Chemical industry:
Sulphur (S)
Sulphur is a non-metallic mineral, occurring as native sulphur, sulphides of base metals, and
sulphates of calcium, magnesium and rarely potassium. The native sulphur and sulphides are the
principal sources of sulphur. A good amount of sulphur is recovered from gases from smelters
treating sulphide minerals. Sulphur is sometimes found as stalactites in caves and caverns and also
as earthy masses.
Native sulphur in India is reported as sulphur emanations in the bore-holes sunk by GSI, in Puga
valley of Jammu and Kashmir which is associated with borax and a small amount of arsenic.
Sulphur was/is recovered as by product from sulphurous fumes of copper smelters of HCL at
Moubhandar in Jharkhand and Khetri in Rajasthan.
Pyrite (FeS2), Pyrrhotite (Fe1-xS) and Marcasite
All these three iron sulphides are used for manufacture of sulphuric acid for various industrial
purposes.
Indian distribution
Bihar: Sedimentary pyrite deposits are reported from Amjhor, near Dehri-on-Son in Shahabad
district. The pyritic lenses and beds are hosted by carbonaceous Bijaigarh shales (Guha, 1971)
overlying the Kaimur Group rocks of the Vindhyan sequence.
30
Rajasthan: Pyrite-pyrrhotite deposits occur as concordant, stratiform bodies co-folded with the
host amphibolites (Sarkar et al., 1980) belonging to the Delhi Supergroup rocks at Saladipura,
south of Khetri Copper Belt.
Himachal Pradesh: Pyrite deposit occurs at Taradevi, near Chotashimla within Simla slates.
Karnataka: The copper sulphide deposit in mafic volcanic rocks at Ingaldhal, in the Chitradurga
schist belt, show good pyrite concentration in the footwall.
Barite
Pure barite is white, opaque to transparent and referred to as heavy spar. It is very heavy and its
specific gravity varies from 4.3 to 4.6., which helps to distinguish it from most other non-metallic
minerals. This non-metallic mineral is used in paint and varnish industry, as an extender and filler
in paper, linoleum and rubber. It is also used extensively as an ingredient in the heavy drilling
muds of oil drilling operations.
Workable barite deposits are chiefly of three different types: a) veins replacing limestones and
dolomites; b) residual deposits in argillaceous formations derived from the weathering of bariumbearing
rocks; c) bedded deposits of barite in volcano-sedimentary successions. Barites occur also
as common gangue mineral of many non-ferrous ore deposits.
Indian distribution
The most important barite occurrences are in Kurnool, Cuddapah, and Anantpur districts of
Andhra Pradesh. Smaller deposits are also found in Rajasthan, Jharkhand, Orissa, Madhya Pradesh
and Karnataka. Most of these deposits are of the vein type. Rare bedded deposits have been
recorded from the Archean Sargur succession at Ghattihosahalli in Karnataka and Proterozoic
volcano-sedimentary successions in Cuddapah district of Andhra Pradesh and Udaipur district of
Rajasthan.
Andhra Pradesh: In Cuddapah district, barite veins are reported from the neighbourhood of
Mittamidapalle, Uppalapalle and Rajupalem. Most of the veins appear to be related to the
Cuddapah traps and are found as replacement in the Vempalle limestone. One of the largest barite
deposits in the world occurs at Mangampet with a resource of 37 Mt. (Neelakantam, 1989). The
two lensoid bodies of barite occur interlayered with tuffs, carbonaceous shales and dolomites. The
barium in this bedded barite deposit is considered to have been contributed by volcanic sources
and the sulfate from the sea water. The northern lense is presently being mined by the Andhra
Pradesh State Mining Corporation.
In the Kurnool district, high grade deposits of barite occur at Ippatla, Midipenta, Nadipalle,
Kottapalle and Balapalapalle. In Kottapalle area the barite veins are about a metre wide and extend
for 2.5 km. They are fissure-filling type veins in dolomitic country rocks. In Anantapur district,
principal deposits of barite occur at Nerijumapalle, Mutsokota, and Chandana areas. Barite
occurrences are also known near Khammam.
Rajasthan: Barite lenses occur in a linear zone within mafic metavolcanics of the Delwara Group
underlying the Aravalli Supergroup sediments near Udaipur. A large lensoid deposit occurs at
Jagat near Udaipur in a mafic volcanic inlier within the Banded Gneissic Complex (Deb et al.,
1991). Veins of barite are also widespread within Alwar quartzites in Alwar district.
31
Building stones
Stones have always been used in a variety of ways in the building industry. In recent years, spurt in
building construction, structural works and road and pavement making have created a huge
demand for the minerals and rock-based materials of inorganic origin. Usually all types of stones
which are hard, tough, and can withstand weathering and abrasion, that is, high durability, are
preferred. The workability of building materials depend on their hardness. Colours of building
stones and their directional properties are considered to be other essential criteria. All types of
rocks, particularly granite-gneisses, crystalline schists, massive and compact sandstones and
limestones, dolomites, marble, slates, khondalites, and compact laterites, are used extensively as
building and roofing material and also as substitutes for bricks. These rocks are used directly with
some amount of trimming of the surface and sometimes by processing them in measured
dimensions after polishing of uneven surfaces. Such building stones which are cut and dressed
after quarrying are called dimension stones. The dimension stones are also used for other structural
purposes such as construction of bridge pillars, abutments, fences, retaining walls, monuments,
paving stones, switch-boards, etc. When the materials are broken into pieces, they are called
crushed stones. These are used in concrete materials with cement and lime.
Indian building stones
The gneisses, granites, charnockites, slates, crystalline limestones, marbles and quartzites of
Precambrian age are considered as excellent building materials in India.
Granite gneisses and granitic rocks are abundant in Peninsular India. They also occur in different
localities of extra-Peninsular India. The banded gneissose rocks, the Bundelkhand gneisses of
Rajasthan and Madhya Pradesh, Erinpura granites of Rajasthan and similar granite-gneissic
materials of Bihar, Madhya Pradesh, Andhra Pradesh, Karnataka and Tamil Nadu have provided
superb building materials for the construction of temples, palaces, monuments and tomb stones,
etc. in almost all the states in India. In Rajasthan, pink, white and grayish white granites of
Precambrian age are used in building royal palaces in Bikaner, Jodhpur, Mewar, and other areas.
Granite-gneisses of Archaean complex are used as size stones, slabs, pillars, pedestals and for
similar other constructional purposes. Some of these are exported to the foreign countries to serve
as kerb-stones and tomb stones. These stones are found in Chitradurga district and other districts of
Karnataka. In Bihar, Orissa, Madhya Pradesh and U. P. granitic rocks are extensively used as
building stones. In Koderma mica-belt of Jharkhand, most of the buildings of the mica-mines are
built of hard and compact mica-schists and granite-gneiss.
The charnockites of Tamil Nadu, Karnataka and Andhra Pradesh are considered as the most
durable stones in the world. The tomb of Job Charnock, earlier thought to be the founder of the
city of Calcutta, is made of charnockite from the St. Mary’s hill in the vicinity of Chennai. The
temples and monuments of Mahabalipuram, south of Chennai, have been carved out of solid and
compact charnockitic rocks.
Khondalites of Orissa and Andhra Pradesh are not as durable as the granites but still they are
extensively used as building stones in these two states. In Andhra Pradesh, most of the buildings
are made of khondalites and compact laterites. In Konarak and Puri temples of Orissa, most of the
stones are either khondalites or hard and compact laterites. The statues and figures are invariably
carved out of khondalites, particularly the gigantic wheels of the chariot in the Sun temple of
Konarak. Laterites of Western Ghats are used as building stones in different parts of Maharashtra,
Karnataka and Madhya Pradesh. Laterite can be cut and shaped very easily into required sizes and
it hardens considerably on exposure.
32
Crystalline limestones and marbles of Rajasthan, particularly the Makrana marbles, are being used
for many centuries as building and ornamental stones. Taj Mahal of Agra and Victorial memorial
of Calcutta are built from Makrana marble. Marbles of Raialo Group of Rajasthan are extensively
quarried in Raialo, Alwar, and Jaipur. In Mewar, marbles are exploited in Rajnagar, Kankroli and
Nathdwara. The white marble of Betul and multicolored marbles of Chindwara, Nagpur and
Narsinghpur are also used as building stones. Motipura marbles from Baroda district, Gujarat are
serpentinous marbles, mottled with pink and rose striations, which are used extensively in the
construction of temples. In Koraput district and Gangpur region of Orissa, there are several
varieties of crystalline limestones which are used as building materials. Vindhyan limestones of
lower Bhander Formation contain spherulitic structures, in which the semi-circular shells display
different colours. The deposits occur near Gwalior, in Sabalgarh area.
The limestone and sandstone deposits of Vindhyan Supergroup are quarried in Son valley in Bihar
and Uttar Pradesh, in Rewa and Jabalpur in Madhya Pradesh, in Guntur and Bhima area, Andhra
Pradesh. Vindhyan sandstones of Khatu area of Jodhpur district, Rajasthan, yield very good
flagstones particularly suitable for fine carvings and are considered good for fabricating perforated
and ventilating windows and screens, usually found in big palaces. Vindhyan sandstones of
Bhander Group of uppermost Vindhyan age are known as excellent building stones, due to their
regular bedded formation, uniform grain-size, soothing colours, high durability and easy
workability. The stones are cream and light grey in colour with crimson and pinky tints. The
famous Sanchi Stupa and stupas of Sarnath and Barhut are built of Vindhyan sandstones. The
famous Fatehpur Sikri, built by Emperor Akbar, is entirely of pink Vindhyan sandstones. The
Delhi secretariat and Rashtrapati Bhawan of New Delhi are made of red sandstones of Bhander
Group. A major part of the sandstones are quarried in Rajasthan, particularly in Bundi, Kota,
Dholpur, Jaipur, Bharatpur and Bikaner and also in Mirzapur district of U. P.
The Aravalli slates of Rajasthan, which can be cleaved, are used as roofing materials. The slates
occur in the vicinity of Ajmer and Jharol. The Alwar quartzites of Moundla and the micaceous
gritty rocks of Ajmer and Nasirabad produce thick and durable building slabs and blocks.
The Cretaceous Deccan Traps contain compact, hard, and durable building materials. In
Maharashtra, in the vicinity of Bombay, however, the light buff and cream coloured trachytes are
very much in use locally and they are preferred more than the dark coloured basalts. The ‘Gateway
of India’ in Bombay is entirely made of trachyte. The trachytes occur extensively in Salsette Island
near Bombay. The trachytic rocks are also quarried in Malad and Kharodi in the neighbourhood of
Bombay.
Gemstones
Diamond (C)
Diamond is the hardest substance known. When properly faceted, light falling on the stone
undergoes total internal reflection giving it the dazzling brilliance. Major part of diamond
recovered from the rocks is of the industrial variety, known as bort, carbonado etc. based on their
physical attributes. Only a minor part of diamond produced is of the gemstone variety. Primary
sources of diamonds are kimberlite pipes and vents, and lamproite, or peridotite dykes. Secondary
source is in conglomerate beds, alluvial gravels and sand. The kimberlites are dense, and darkcoloured
ultrabasic rocks, rich in magnesium, containing olivine, enstatite-bronzite, chromediopside,
phlogopite, and pyrope garnet with minor amount of ilmenite and perovskite. Diamonds
require very high pressures for generation and growth which is not realized in the normal crust of
33
the earth. It is therefore believed that diamonds originate in the upper mantle or in the root zone of
thickened continental crust and are brought to the crust as inclusions in kimberlite pipes.
Indian distribution
Madhya Pradesh: A belt of upper Vindhyan sandstones extend in ENE to WSW direction through
Panna in central India, on the south eastern side of Bundelkhand granite massif. This
diamondiferous belt covers an area of 1,000 sq. km stretching between Jhanda in the east and
Majhgawan in the west. The workings for diamonds are mostly confined to the alluvium and
gravel but there are also workings in conglomerates at the base of Rewa and Bhander sandstones
of upper Vindhyan age. Shahidan is the best known centre for diamond mining in Panna district.
The kimberlite pipes have been discovered in Majhgawan and some other localities, near Panna.
The pipes are represented by a circular depression containing calcareous tuffs mixed up with
serpentinous materials. The highly brecciated rock consists of highly altered pseudomorphs of
olivine along with phlogopite and leucoxene. Xenoliths of country rocks are also found in the pipe
rocks. In the Majhgawan and other pipes of Panna diamond field, diamond crystals occur as coarse
to fine, mostly imperfect to perfect crystals, sometimes even as fragments of crystals. Some of the
primary inclusions in diamonds are euhedral, green olivine, diopside, garnet, and spinel.
Andhra Pradesh: The districts of Cuddapah, Anantapur, Kurnool, Krishna and Godavari famous
for diamond production in south India. In all these areas, loose diamond crystals occasionally
picked up from the alluvium. Sometimes diamonds are recovered not only from the alluvium but
also from the conglomerates and sandstones of Banganapalli stage of the Kurnool Group
underlying the Palnad limestones. The region from where many valuable diamond crystals have
been recovered is Wajrakarur in Anantpur district.
Other common gemstones
Gemstones usually occur in gravels and in mineral veins of igneous origin. Sapphire and pyrope
occur in some of the diamondiferous kimberlites. Usually potash-rich or soda-lithium-rich
pegmatites are the host rocks of many beautiful gemstones, such as, topaz, sapphire, ruby and
zircon. Gems are also found in basic and andesitic lava flows, and granite intrusives. Although
metamorphic rocks are generally barren of gem stones, some contact-metamorphic limestones
may contain lapis lazuli and ruby. Opals are deposited from volcanic waters while amethyst
develops in vein deposits. Turquoise is a gem stone of supergene origin. Almost all gem stones are
found in stream gravels, due to their highly resistant and chemically inert character. Distribution of
these gemstones in the Indian sub-continent is shown in Fig. 12.
34
Fig. 12: Distribution of gemstones (other than diamond) in India and in some
adjoining countries.
Ruby, Sapphire and Emerald
Both ruby and sapphire are the gem varieties of crystallized alumina called corundum. Sapphire of
different colours occurs in nature except red and pink, which are usually called ruby. In Kashmir
Himalayas, in and around Nanga Parbat, sapphire deposits are known to occur. The outcrops of the
sapphire-bearing formations lie hidden in the remote areas of the lofty mountain range. The
formations comprise granites and other igneous intrusions particularly pegmatites penetrating the
crystalline metamorphic schists. Intimately intermixed with the sapphire deposits are aquamarine,
rubicelle green tourmaline.
Al2O3, which is the main constituent of ruby and sapphire, forms spinel instead of corundum in the
presence of magnesia. Spinel and corundum of gem quality are found in several places in
Karnataka, particularly in Kadmane and Kelkoppa. They have deep colors and are harder than the
Burma rubies. Translucent dark coloured rubies are found at Adihali near Bageshpura and Hardur
district. Karnataka also produces rock crystals, opal, garnets, aquamarine and some emeralds.
The coloured and transparent varieties of beryl are sold in the market as emerald and aquamarine.
The deep green coloured mineral is known as emerald and the light green coloured stones are
known as aquamarine. Because of its deep green colour and rarity of occurrence, emerald is the
most expensive gem stone, other than diamond. The green colour is due to the presence of
35
chromium in the mineral. In India, the famous emerald deposits are found in Mewar region of
Rajasthan. The area is Kaliguman where emerald mines are present near the village of Amet in the
neighbourhood of the old fortress of Kumbhalgarh. The precious mineral occurs within bands of
biotite schists, very much like garnets and andalusite. Emeralds are also found at Banas in Ajmer
district, Rajasthan. The best quality of emerald is found in Burma and Sri Lanka.
Zircon (ZrSiO4)
Zircons are the common accessory minerals, occurring in granites and gneisses. The Indian name
of zircon is Gomed. Zircon is classified in four categories and it comes next to diamond in
brilliance and internal glow. Zircon crystallises in tetragonal system and is prismatic in habit with
pyramidal terminations. Hardness is high around 7.5, the colour being yellowish brown. Zircon is
transparent to translucent and usually contains monazite as small inclusions which render it
radioactive. Much of the colourless or transparent zircons are used as gemstones. When the
crystals are heated, they become colourless.
Zircon occurs in the beach sands of south-west India as placer deposits. In India, gem variety of
zircon is found in small quantities in nepheline syenite rock, in the neighbourhood of Kangayam,
in Coimbatore district of Tamil Nadu. Gem variety is also found in Kerala, near Travancore, in
pegmatite veins, associated with charnockite complexes and also in the pegmatite veins of
Kadavur, Tiruchirapalli district of Tamil Nadu. The Seitur graphite mines of Ramnad taluk of
Tamil Nadu produce considerable quantity of gem variety of zircon. The pegmatite veins in
Hazaribagh and Gaya districts, produce some zircon in Jharkhand.
Jade and Nephrite
The mineral includes two varieties: jadeite and nephrite. The latter is the more common form of
jade. This mineral is a monoclinic amphibole, very hard (between 6 and 6.5) and compact, with a
splintery fracture. The colour is usually leaf green to grass green, due to the presence of ferrous
iron. The pyroxene group jadeite is rarer than nephrite, and is very tough, compact and splintery in
character. The hardness varies from 6.5 to 7, with greenish white to emerald green colour. It is
available in ample quantity in the Darjeeling Himalayas and various types of jade-bearing articles
are sold in the markets of Darjeeling.
DISTRIBUTION OF MINERAL DEPOSITS IN SPACE AND TIME
The quest for minerals through the ages led to the observation that mineral deposits are distributed
non-uniformly on the crust of the Earth. For example, the largest concentrations of gold, chromite
and platinum are found in South Africa, nickel in Ontario province of Canada, tin in the Malaya
peninsula in Southeast Asia. In India, we have very large reserves of iron ores in Jharkhand and
Orissa, manganese ores in the contiguous parts of Maharashtra and Madhya Pradesh in central
India, and of mica in Bihar and Jharkhand.
Such uneven distribution, globally as well as regionally, has given rise to the concept of
Metallogenic provinces. These are regions of the crust generally more enriched with a single
metal, several metals or metal associations than are the adjacent regions (Wright, 1992).
Obviously, these provinces are characterized by some specific attributes of geology and tectonics,
such as, having the right kind of sedimentary basin or the right type of lineaments at different
periods of time to have been able to produce the exceptional concentration of one or more metals
or minerals. Several important metallogenic provinces for certain metals are depicted in Fig.13 and
some of the most prominent ones are identified in its caption. The Lake
36
Fig.13. World map showing metallogenic provinces of selected metals. Important concentrations
mentioned in text are: Iron: 1 = Lake Superior region, Canada-USA; 2 = Quadrilatero
Ferrifero, Brazil; 3 = Krivoi Rog, Ukraine; 4 = Kiruna, Sweden; 5 = Jharkhand-Orissa, India; 6 =
Hamersley Basin, Western Australia. Manganese: 1 = Minas Gerais, Brazil; 2 = Damara sequence,
Namibia; 3 = Nsuta, Ghana; 4 = Nikopol, Ukraine; 5 = Sausar belt, India. Chromium: 1 =
Bushveld Complex, South Africa. Gold: 1 = Superior province, Canada; 2 = Mother Lode,
California, USA; 3 = Carlin deposits, Nevada, USA; 4 = Witwatersrand, South Africa; 5 =
Murantao, Uzbekistan; 6 = Eastern Dharwar goldfields, India; 7 = Yilgarn craton, Western
Australia. Copper: 1 = Zambian copper belt, Africa. Lead-Zinc: 1 = Broken Hill; 2 = Mt. Isa belt,
Australia; 3 = Mississippi valley type deposits, Missouri, USA; 4 = Sullivan, British Columbia; 5
= Red Dog, Alaska. Aluminium = 1 = Jamaica, West Indies.
Superior region of Canada and USA, Quadrilatero Ferrifero in Brazil, Krivoi Rog in Ukraine,
Kiruna in Sweden and the Hammersley basin in Western Australia have some of the world’s
largest concentration of iron. Similarly, some of the best resources of manganese are found in
Minais Gerais, Brazil, Damara sequence in Namibia, Nsuta, Ghana, Nikopol in Ukraine and
Sausar sequence in central India. A major part of world’s total resource of chromium is found in
the Bushveld Complex in South Africa. Some of the largest concentration of gold is found in the
Superior province in Canada, Mother Lode, California, Carlin deposits, Nevada in western USA,
Witwatersrand in South Africa, Murantao in Uzbekistan, and Yilgarn craton in Western Australia.
For more than last three decades the porphyry deposits are the most important resource of copper
in the world. The largest concentration of porphyry deposits are found along the South and North
American Cordillera, from Chile in the south to British Columbia, Canada in the north. The copper
37
deposits in islands rimming the circum-Pacific region to the west are also of this type. Prior to the
advent of technology to mine the low grade-large tonnage porphyry deposits in the early 70s,
much of the world’s copper came from the Zambian copper belt in Africa. Rich Pb-Zn deposits are
located in the Broken Hill area and Mt. Isa belt of Australia, the type area for Mississippi valley
type deposits in Southern Appalachians in Missouri, USA, Sullivan deposits in British Columbia
and Red Dog deposit in Alaska. All the aluminium deposits in the world are found along the
equatorial belt, with some of the best deposits found in Jamaica, West Indies.
Equally interesting is the concept of Metallogenic epochs, periods in Earth’s history marked by the
development of exceptional concentration of a particular metal or metal association in a particular
metallogenic province. The concept of metallogenic province and epoch are well illustrated by the
somewhat rare metal tin (cf. Evans, 1997). Tin is found in a large metallogenic province, which
got separated into several parts, in the different continents around the Atlantic Ocean when it
opened up (Fig. 14, depicts the separation of S. American and African tin deposits with the
opening of Atlantic ocean). It is also conspicuous in the tin belts of south-east Asia and of eastern
Australia. All these concentrations took place in post-Precambrian metallogenic epochs in posttectonic
granites.
Fig. 14. Matching of tin belts across the Atlantic
Ocean (Modified from Evans, 1997)
The temporal distribution of various deposits, such as those of iron, nickel, gold and base metals,
record distinct patterns of deposition/concentration for a particular genetic type of metal deposit at
a particular period of Earth history (cf. Hutchinson, 1993). Thus, most hematitic Banded Iron
Formations in the world formed in the time window of 2.4 to 2.0 Ga while the Algoma-type
magnetite-rich iron formations formed in the middle to late Archean; Greenstone-hosted gold
deposits formed in the late Archean time between 2.8 and 2.6 Ga; nickel deposits in maficultramafic
flows were generated in the late Archean around 2.8 Ga while those in layered mafic
intrusions formed in the early Proterozoic around 1.8 Ga; volcanogenic polymetallic massive
sulfides (Pb-poor, Zn-Cu deposits) formed in the Archean (> 2.5 Ga) whereas similar Pb-rich, Zn-
Pb-Cu deposits formed in the early Proterozoic as well
38
Fig. 15. Schematic representation of secular variation of selected metal deposits. The vertical bar
signifies periods of high concentration.
as in the time span between late Proterozoic (1.0 Ga) to recent. The spatial and temporal
distribution of mineral deposits have far-reaching implications in exploration programmes in
different parts of the world and can be linked to crustal, mainly tectonic, and atmospheric
evolution of the Earth. Low partial pressure of oxygen in the reducing paleo-atmosphere before 2.4
Ga ago was responsible for detrital concentration of uraninite and pyrite around 2.6 Ga in Aubearing
paleoplacer deposits like the Witwatersrand, whereas enhanced oxygen levels after 2.4 Ga
was almost certainly a factor in the formation of super-large and extensive Banded Iron
Formations, sedimentary manganese deposits, red bed-hosted stratiform copper deposits and
unconformity-type uranium deposits. On the other hand, the porphyry copper deposits which
proliferated in the last one third period of the Phanerozoic, are the result of subduction of oceanic
plates and calc-alkaline magmatism along convergent plate margins. The porphyry copper deposits
being generally emplaced near the earth’s surface (< 4 km depth), it is possible that many of these
39
deposits were weathered and eroded away leaving only some here and there in the convergent
margin setting. Examples of some of the metal types and their secular distribution are shown
schematically in Fig. 15.
GLOBAL TECTONICS AND METALLOGENY THROUGH GEOLOGICAL TIMES
Tectonics involves the study of earth structures on a macroscopic scale. This branch of Geology
considers megastructures vis-à-vis the dynamics of their generation. Such mega-structures in the
continental or oceanic crusts are commonly produced during attainment of thermo-mechanical
equilibrium in the crust-mantle system.
The relationship between tectonics and ore genesis has been recognized since long when the
‘Geosynclinal concept’ was introduced in the later half of 19th century to explain mountainbuilding
or orogenesis. Ore geologists have tried to identify specific types of mineralization in
particular tectonic domains, such as, `shields’, ‘orogenic belts’, ‘stable platforms’ etc. Ore
mineralization was also linked to different units of the geosynclinal model, such as, with the
‘miogeosyncline’ or the ‘eugeosyncline’. With the advent of the ‘plate tectonics theory’ in the
1970s, which superceded the ‘continental drift theory’, a more direct correlation of specific types
of mineralization with tectonic setting was available (Mitchell and Garson, 1981; Condie, 1982,
1997; Sawkins, 1984; Sarkar, 1985).
Some basic ideas of plate tectonics need to be highlighted to comprehend the relationship of ore
mineralization with tectonic setting of a particular type. According to plate tectonics, the earth’s
outer shell, the lithosphere, is divided into eight large and some smaller segments called ‘plates’.
They are mechanically rigid and are in continuous motion relative to each other and with the axis
of earth’s rotation. Such plate movements are primarily the result of the basic requirement of the
mantle to dissipate heat. The convective transfer of this heat to the crust through various kinds of
magmatism not only makes the plates move and interact with each other, but also sets in motion
different potential ore-generating processes. This forms the basis of the relationship between plate
tectonics and ore genesis.
Three distinct types of plate margins are distinguished: the constructive boundary occurring at
ocean ridges where new oceanic crust is generated; the destructive boundary at oceanic trenches
where the oceanic crust sinks and is consumed; the transform faults along which the lithosphere
moves but is conserved. The plates may comprise only oceanic crust or more commonly, both
oceanic and continental crust. But plate generation (accretion) or destruction (subduction) takes
place only in the oceanic crust. The orogens produced by plate interactions are of three types also:
The Andean-type, where the oceanic crust subducts directly underneath the continent; the
(Japanese) island arc type, where the subduction takes place away from the continent and there is a
marginal sea between the continent and the arc; and lastly the Himalayan-type, characterized by
continent-continent collision when the intervening oceanic crust is totally consumed, or virtually
so.
40
Fig. 16: Mineralisation in terms of certain plate tectonic scenarios, discussed in the text (after,
Mitchell and Garson, 1981).
Two types of arcs are also recognized: the compressional and the extensional. The first,
represented by the Andean type, develops thickened crust, more differentiated volcanism
(andesite-dacite-rhyolite) and more acidic plutonic rocks. The second, represented by the
Japanese-arc type, is characterized by basalt-andesite volcanism and equivalent plutonism, limited
topography and consequently, restricted volcaniclastic sedimentary fans. Such plate tectonic
scenarios can easily be identified all through the Phanerozoic geological record and can also be
41
extended into the Proterozoic, but the application of plate tectonic model to the Archean remains a
controversial issue.
Ore mineralization at divergent or constructive boundary setting: Zones of initial divergence are
restricted to inter-continental rift zones, intra-continental hot spots, (Fig. 16 A, B) or oceanic
spreading centers (Fig. 16 C). The intrusive rocks in the continental situations, such as, along the
East African rift are peralkaline granites, alkaline rocks and carbonatites. Instances of
mineralization, such as those of tin, niobium, fluorite, are found in such continental environments,
e.g., in Nigeria, western Africa. Numerous metals, non-metals and elements are commonly
concentrated in carbonatites. These include Nb, Fe, Ti, Cu, REE, apatite, fluorite and vermiculite.
Aborted continental rift zones have a larger array of ore deposits. Besides the deposits found
around hot spots, apatite-magnetite mineralization, as well as hydrothermal copper, exhalative Pb-
Zn-Ag mineralization (Sullivan type), or carbonate-hosted Pb-Zn sulfide deposits (Mississippi
valley type) characterize such rifts. Where continental separation has taken place with the
accretion of an incipient oceanic crust, such as along the Red sea, base metal mineralized
sediments form around vents on the sea floor (Fig. 16 A). Deposition of massive Cu, Zn sulfides is
known from several oceanic spreading centres in the Pacific ocean, such as, the East Pacific Rise,
Galapagos rift (Cu), Juan de Fuca rift (Zn) etc. Cuprous pyrite deposits also form in the oceanic
crust at spreading centers (Fig. 16 C), to be eventually obducted on the land surface upon collision
(see section on collisional settings below). In the Atlantic Ocean however, the slow spreading
Atlantic ridge is characterized by the precipitation of Fe and Mn-oxides.
Ore mineralization at convergent or destructive boundary setting: Three main types of such
boundaries are recognized: island arc type, continental margin type and collisional type. In the
first, the most important process operative in the convergent plate margins is the subduction of the
oceanic lithosphere. Mineralization takes place in the principal arcs, as well as in the inner side of
principal arcs. The arcs are linear belts of volcano-plutonic igneous rocks that are found above a
subducting lithosphere slab. Mineralisation of Zn, Pb, Cu, Fe, Mo, Au and Ag are closely
associated with calc-alkaline magmatism in principal arcs. The major part of the world’s
production of copper comes from the ‘porphyry copper deposits’ in such tectonic settings. These
deposits are more common in the compressional type arcs where the subduction takes place below
the thickened crust of the continent (Fig. 16 C), such as, along the American cordillera. In the
tensional arcs, such as the Japanese islands, the Kuroko type Zn-Pb-Cu sulfide deposits (Fig. 16 C)
are more common than the porphyry deposits. On the inner side of the principal arc, common
types of mineralization include contact metasomatic (skarn) deposits of Zn, Pb, Ag as well as WSn
vein, greisen and replacement type deposits. While the former group is conspicuous in Mexico
to Peru, the latter is found in Bolivia and Korea.
Ore mineralization at passive continental margin setting: This kind of setting does not show any
relative movement between the continental and oceanic lithospheres and occurs at the margin of
opening ocean basins commonly related to continental rifting. Such margins are characterized by
minimal tectonic and magmatic activity and are constituted by mature clastic sediments and
shallow water carbonates. Mineralization in the present day environment, such as the Atlantic
margin, is represented by evaporites and phosphorite deposits mainly. Pb-Zn mineralization in
both clastics and carbonates are common in older sequences (cf. Fig.16 C, left end).
Ore mineralization at collisional setting: This type of boundary is formed during and following
the final stage of subduction of the ocean floor between two continents, between two island arcs or
between a continent and an island arc. The important tectonic zones in this kind of setting are the
hinterland margins, the suture zone, foreland thrust belts and the foreland basins. The last three
42
zones are important from the point of mineralization. The suture zone often contains stratiform
exhalative cuprous pyrite mineralization of the Cyprus type (Fig. 16E), such as in the type locality
at Cyprus, and in New Foundland. Podiform chromite deposits are also found in the suture zone,
such as at Oman and along the Indus Suture zone in the Himalayas (Fig. 16 E). In the foreland
thrust belt, Sn-W mineralization occurs in S-type granites, best example being the deposits in
Cornwall-Devonshire in the SW of England. In the foreland mollase basin uranium mineralization
is found in the Siwalik Hills of Himachal Pradesh and Uttaranchal (Fig. 16D).
Ore mineralization at transform faults: Transform faults are plate boundaries along which plates
slide past each other. Normally the transform faults are not expected to be mineralized. Some
possible exceptions are the stibnite mineralization along the Cenozoic Chaman fault in Pakistan
and some late Cenozoic gold deposits in California. The Salton Sea geothermal system is a good
example of mineralization in short segments of actively rifting crust in a leaky transform fault.
The foregoing discussion on the distribution of metal deposits in space and time and their close
linkage with tectonic evolution of the crust allows us to relate metallogenesis with crustal
evolution through geological times. Five different stages of crustal evolution of the Earth can be
identified with their characteristic mineralization (cf. Radhakrishna, 1984):
The greenstone belt style of mineralization is characteristic of the Archean and early Proterozoic.
Typical mineral deposits formed during this period include Algoma type iron formations in
volcano-sedimentary successions; hydrothermal lode gold deposits and the massive Cu-Zn sulfide
mineralization in volcanogenic host rocks.
The cratonisation stage begins in late Archean and persists mainly in the early Proterozoic and thus
co-exists with and finally superseeds the earlier tectonic regime. This period is characterized by the
detrital-sedimentary gold-uranium paleoplacers (Witwatersrand type), the chemical sedimentary
banded iron formations (Superior type) and sedimentary manganese (Kalahari and gondite type).
The rifting stage around 1.8 Ga in the middle Proterozoic, which affected the previously stabilized
continental crust and produced extensive mafic-ultramafic magmatism. The typical deposits are of
the sedimentary exhalative types of base metal sulfides, intrusive-related nickel deposits and
hydrothermal unconformity-type uranium deposits.
The stable craton phase in the middle to late Proterozoic with alkalic volcanism and plutonism.
The significant deposits during this period are of exogenic type confined to the cratonic
sedimentary cover. Examples are of unconformity-related uranium, manganese and copper
deposits.
The Phanerozoic stage, characterized by abundant and varied mineralisations, particularly of the
hydrothermal type, often related to granitic plutonism in the Paleozoic orogenic belts. The gamut
of deposits range from vein deposits of gold, silver, tin, tungsten etc, porphyry Cu-Mo-Au deposits
, epithermal deposits of noble metals, Mississippi valley-type Pb-Zn deposits, the Kuroko and
Cyprus-type base metal sulfide deposits and ophiolitic chromite deposits.
It is obvious from the above outline that from early stages of crustal evolution to the more recent
ones, there is a proliferation of metallogenic processes. While the early part of earth history in the
Precambrian saw only a few distinct types of mineralization, the Phanerozoic was marked by
diverse types of mineralization.
43
METHODS OF MINERAL EXPLORATION, EXPLOITATION AND PROCESSING
The metals that we use in our everyday life, in some form or the other, go through several stages of
handling before they are available to us. The mineral deposit must first be located by geological,
geochemical and geophysical techniques and then explored by drilling and exploratory mining to
estimate its reserve and grade and workability in general. Only then the mineral is extracted from
the deposit either by underground mining or by surface or open-cast mining. The ore (a
combination of ore mineral/s of interest and useless gangue minerals) so extracted is then
processed to produce an ore concentrate by removing the gangue minerals which go into the
tailing. This process of producing the concentrate is called ore beneficiation. The ore concentrate is
next sent to the smelting plant where different metallurgical processes are used to extract the
metal/s. The metal/s so produced commonly undergoes further refining before it/they can be
marketed.
Exploration is the first and most important phase of the mineral supply. Several different methods
are available for exploration at different stages and in different environments. A potential area can
be targeted by a survey of existing literature, maps and documents. Most commonly, areas are
targeted in the vicinity of known deposits. Also possible is a systematic approach using all
applicable techniques, starting from remote sensing, stream and soil geochemistry, geobotany,
airborne and ground geophysics. A modern approach in regional exploration is a concept-oriented
or model oriented programme of intensive investigation of mineral occurrences in specific
geological environments. In India, till recently, exploration was limited to areas with old workings
or to test the strike and depth continuity of known deposits. Also, unlike in developed countries, in
India adequate consideration was seldom given to the cost and economics of exploration, as most
of the agencies involved belonged to the Government. With the liberalization of mineral policies in
the country, we now find comprehensive multi-technique exploration being carried out mostly by
multinational companies in different potential regions.
In all these approaches the basic requirement is of geological maps at various scales, starting from
a small scale for a large coverage, e.g 1:50,000 topo-sheet scale, to successively larger scales, such
as 1:25,000, 1:10,000, 1:5000 or even 1:1000 in which every outcrop in the ore zone can be
shown. Features, other than lithology, shown on the maps could be structural data, trace of
gossans, limits of old workings etc. Geochemical techniques include measurement of
concentration and dispersion of trace elements either in secondary stream sediments, in soil
samples or in bed rock chips which can then be linked with possible hidden mineral deposits. The
concentration in the bed rocks is called primary dispersion while that in stream sediments and soil
(Fig. 17) is referred to as secondary dispersion. The stream samples are commonly chosen from
different orders of streams while soil samples are commonly collected in a grid pattern and
contours of anomalies are drawn to locate the target area. Geobotanical techniques are based on
the possible relationship of vegetation and mineral deposits. Specific plants thrive when the
concentration of a particular metal in the soil is anomalous.
44
Only when a proper target is obtained using these techniques, drilling is resorted to. It is always at
a later stage because it is far more expensive. Initially the drilling is done in such a way that it
intersects the orebody at a shallow level and its strike continuity is established. These are called
first-order drill holes. In successive stages, second and third order drilling is done mainly to
establish the morphology and depth continuity of the orebody. In India, almost all drilling carried
out is of diamond drilling - coring type where bore hole cores are continuously recovered, laid out
sequentially and logged megascopically for rock characteristics and ore zone identification. While
this process is very good for reserve estimation and for easy future reference to any section of the
hole, it is a very slow, laborious and expensive process. Also maintenance of the cores is another
costly proposition. Only when possible reserve estimation has been carried out based on drilling, a
small scale exploratory mine is opened up either by open pitting or by underground methods. This
provides direct access to the ore body for various investigations and sampling. This stage also
helps in correlating what has been envisaged about the reserves by drilling with what is actually in
the ground. A successful positive correlation at this stage paves the way for actual mining and
exploitation of the mineral deposit.
There are two primary methods of extracting solid mineral resources from the crust of the Earth.
These are underground mining and surface or open cast mining (Fig. 18). The former is more
dangerous, expensive and slower process than surface mining because of the possibility of rock
fall, water inflow and gas build up in the workings. Depending on the deposit size, shape, depth
below the surface and grade (percentage of valuable mineral/metal) any of the two mining
methods is chosen. In fact, many mines which start as open cast end up as underground mines
when it is no more possible to make the pit deeper. Open pit or open cast mining is an economical
method of extraction which involves large reserves and high rates of production. The waste
material overlying the ore body must be thin enough to be removed easily. An open pit mine from
Fig. 17. Concentrations of copper determined in a regional geochemical survey in
southern Rajasthan from (A) stream sediments and (B) soils (after Joshi and Singh, 2000)
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which building stones or gravel is extracted is called a quarry. The largest open pit mine in the
world is at Bingham, Utah in SW USA. Another type of open pit mining is called strip mining
which is used for flat sub horizontal beds, like that of coal. Underground mining is carried out for
resources found at considerable depth from the surface. Such mines have one or more means of
access to the ore body through a vertical shaft, or a horizontal adit or slanting roadway called
incline. The mining in this case is done along horizontal tunnels parallel to the trend of the ore
body called drives and also cross cutting tunnels exposing the width of the ore body at a particular
depth (level), called cross cuts. Between successive levels of drives the block of ore is removed by
mining methods called stoping. Ventillation, roof support and dewatering are important aspects of
underground mining.
Ore beneficiation involves crushing and grinding of the ore as a first step, which is generally
carried out at the mine site. Magnetic minerals like magnetite or pyrrhotite are removed with the
aid of electromagnets. Density differences are also used for separation of the ore minerals from the
gangue since the former is always heavier than the latter. Most commonly the ground ore is
immersed in a heavy medium of organic liquid like xanthate or pine oil which attach to specific
minerals which float with the froth or bubble and is thus separated from minerals which do not
attach and sink. This process of beneficiation is called froth floatation and is widely used for base
metals.
Separation of the metals from the concentrate produced by beneficiation takes place in smelters
through pyrometallurgy. Here the concentrate melts into two immiscible liquids; metal-bearing
liquid being heavier sinks to the bottom of the furnace and is removed from the slag above.
Fig. 18. Cartoon depicting the basic elements of open-pit and
underground mining (modified after Kesler, 1994)
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ENVIRONMENTAL IMPLICATIONS
During the utilization of non-renewable natural resources, environmental impacts are created in
different stages: (i) during extraction (mining) of resources, (ii) during processing of resources, and
(iii) during use and disposal of various resource products.
Underground mines commonly have less impact on the surface unless there is a collapse in the
mined out area or unless mining requires lowering of the ground water table to prevent mine
flooding. Surface mining generally creates more obvious environmental damage than underground
mining because there is a larger volume of rocks excavated and moved and a large open pit with a
large pile of waste rock is created. The overburden removed during surface mining produces large,
ever-increasing dumps which can cover and damage a lot of useful land around the mine. Acid
mine drainage affecting the ground water quality in the neighborhood of the mine is a common
problem in base metal sulfide mining. Oxidation of sulfides, particularly of the common pyrite
(FeS2) produces sulfuric acid which enhances the capacity of the mine water to leach metals.
Particular concern here is the leaching of toxic metals. Other problems associated with mining
include the generation of dust, enhancement of noise level due to blasting and deployment of
heavy machinery (Sarkar, 2002).
Processing of resources or beneficiation consumes a large quantity of water and unless carefully
monitored and checked, affects the water quality around the mining and plant area. The water
consumption problem is addressed by recycling the water as much as possible. The escape of mine
and beneficiation plant water into the ground water aquifer in the area enhances its toxic metal
content due to the leaching of metals from the ore and host rocks in the mine, overburden dumps,
tailing dumps and leaching pads. The metals which are highly toxic even in small quantities
include Cd, Hg, Sb, As, and Pb. This problem is generally controlled by continuous monitoring of
the ground water chemistry and by creating and putting impermeable barriers against downward
movement of the waters. Special efforts and techniques are used where cynide solutions are used
for heap leaching of gold from mined ore material kept in heaps on the surface. Where careless
mining and processing are carried out, not only are the ground and surface waters polluted, but the
soil and sediments are affected as well. Smelting of metals in metallurgical plants also brings about
pollution in a different way. Harmful gases and dust are produced in many places. SO2 is the main
gas of concern because in humid regions in particular, it can produce acid rain in the region around
the smelter causing devastation of vegetation and agriculture. Some toxic metals present in the ore
concentrate, which can vaporize during smelting operations can get dispersed over wide areas by
emission from the plant chimneys. The processing of fossil fuels produces different kinds of
environmental pollution, related to the escape of various hydrocarbons. Atmospheric pollution
data in an highly developed country like USA (Kesler, 1994) shows that although there is an
overall trend in the decrease of air pollution due to mineral production, it still accounts for about
30 % of man-made Pb emission, 25% of particulate emission, 18% of SOx emission, 13% of
volatile organic compound (VOCs) emission, 3 % of CO emission and 2% of NOx emissions.
Once the metal is turned into a product of any sort, the product itself will have a finite life. After
some years of use it will have to be scraped or thrown into the garbage dump. In countries where
collection and recycling are well controlled, much less quantity of metals end up in the land fills
outside urban centres. But in many less developed countries where adequate legislations and
collection mechanisms are lacking, the unusable product (for example, batteries), ends up in a land
fill where it is further degraded with time and with water percolation, particularly in humid
climates, will eventually pollute the ground water system.
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All these environmental impacts caused by mining, utilization of raw materials and finally the
mine closure are now controlled in most countries through legislations and use of appropriate
technologies. But all these efforts to curb the environmental impacts carry substantial costs,
thereby raising the price of the final commodity. Therefore, in recent years, the start of a mining
project is always preceded by a cost-benefit analysis.