C 3 MINERAL RESOURCES EVALUATION - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9493/11/11_chapter 3.pdf · Chapter - 3 MINERAL RESOURCES EVALUATION ... 1977), Namakkal District

Chapter - 3

MINERAL RESOURCES EVALUATION

3.1 GENERAL

The crust of the earth (lithosphere) is believed to be made up of a

dozen or more plates that are growing at ocean ridges by addition of new

material from the mantle, moving independently, colliding, and descending

into the mantle where they are remelted. The plates are as much as 150 km

thick. They comprise both continents and oceanic crust and they serve as

conveyor belts for both. (Dewey & Bird, 1970; Walker, 1971; Guild, 1971).

They are the surface expression of convection cells within the earth. Most of

the world’s mineral deposits are associated with plate boundaries and

development of faults and shear zones within the plates are also provided the

pathways for the mineralizing fluids.

Lineaments are generally regarded as morphotectonic features (Gold,

1980); and lineament analysis facilitates the recognition of different tectonic

settings for mineral deposits (Taylor, 1984; Bian, 1980). Therefore, lineament

studies applied to mineral exploration are crucial and some lineament

patterns have been defined to be the most favorable structural conditions in

control of various mineral deposits, such as: the traces of major regional

lineaments, the intersections of major lineaments or both major (regional) and

local lineaments, lineaments of tensional nature, local highest concentration

(or density) of lineament, between en echelon lineaments, and lineaments

associated with circular features. LANDSAT images of the known Cu, Pb, and

Zn deposits of the northwest China, which showed the presence of linear and

ring structures and noted that the mineral deposits in this area occur

primarily at the junctions of four concentrated linear-structures zones, and at

the margins of various ring structures (Kezheng, 1980). Analysis of the

Chapter 3 – Mineral Resources Evaluation

Geoinformatic Modelling for Certain Georesources and Geohazards of Attur Valley, Tamil Nadu, India.

204

circular features in LANDSAT images and field studies in the central Andes

and southwest United States have revealed a genetic relationship between

acid volcanic complexes and a variety of mineral deposits (Baker & Nash,

1984). Studies in the Los Andes region of Venezuela utilized X-band radar

mosaics and computer processed LANDSAT images for geologic studies later

on accompanied by field check (Vincent, 1980), resulted in establishing the

exploration targets for copper, petroleum, and uranium for further

geophysical work. Longman (1984) emphasizes the importance of lineament

interpretations and digital lineament analysis in localizing the major mineral

deposits and notes that there is a strong correlation between mineral deposits

and lineaments. He illustrated his statements with mineral deposits case

studies in Western Australia. Lineament analysis of enhanced LANDSAT

images in the Lachan Fold Belt has facilitated the recognition of distinctly

different tectonic settings for the porphyry copper/gold deposits and the

disseminated gold deposits (Taylor, 1984). Detailed interpretations of the

aerospace data of the mining region of the Eastern Trans-Baikal region is used

to recognize several different kinds of structures of central type which are

related to known mining areas and sites (Kolodh, Misnik & Shevchuk, 1990).

An analysis of mapped lineaments is important to the exploration geologist,

and fractures, especially intersecting ones, may have been avenues of

mineralization for mineral laden fluids in a portion of the South Mountain

Batholith, west of Halifax, Canada (Schupe & Akhavi, 1989).

Floyd F. Sabins (1999) has used Remote sensing images for mineral

exploration in two applications: (1) map geology and the faults and fractures

that localize ore deposits; (2) recognize hydrothermally altered rocks by their

spectral signatures. He reinstated that digitally processed TM ratio images

could identify two assemblages of hydrothermal alteration minerals; iron

minerals, and clays plus alunite and hyperspectral imaging systems could



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identify individual species of iron and clay minerals, which can provide

details of hydrothermal zoning.

Chan Chiang Liu et al. (2000) have used photogeological techniques to

analyze Landsat-TM images of the Paraiba State, which resulted in the

identification of the following structures: lineaments of regional extent, short

en echelon lineaments, intricate ramification of the wrench system, and

infrastructures among major lineaments and circular or ring structures. This

lineament map was correlated to existing geological maps, to areas of known

hydrothermal mineralization (Cu, Au, Mo, Ni, W and Ti), and the lineament

map was verified in the field reconnaissance.

A band ratio derived from the image spectra (4/8, 4/2, and 8/9 in

RGB) and a mineral extraction method based on n-dimensional spectral

feature space have been developed, and tested against other conventional

methods, and known auriferous alteration zones (Safwat Gabr et al., 2010).

Salem province known for its mineral wealth, has many mining

industries. Origin of mineral deposits has been attributed to different

episodes of earth history but their localization was primarily controlled by

rock types and structures. So the mineral map was prepared from District

Resource Map (DRM) and its localization was identified with the help of

lineaments. This may help us in two ways, 1) to date the lineaments and 2) to

detect the zones of alterations related to metallogeny.

Other important loci of mineral deposits are rocks. So important

mineral bearing rocks, such as ultramafic rocks, granites and pegmatites,

alkaline rocks. So, important mineral deposits like bauxite, gold, multi-metal

bearing ultramafics, rare earth elements (REE) bearing granites and

pegmatites and dykes. Salem province is known for iron ores, and they form

a marker bands within Attur valley. Because of its fragmented nature and its

occurrence as huge heaps, no distinct deformation and changes could be

recorded.



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3.2 BAUXITE

3.2.1 Nature of Deposits

Irregular lenses and pockets of bauxite / bauxitic laterite occur in the

high level laterite cappings over charnockite in the Shevaroy Hills (1535–

1649m) (Krishnaswamy, 1958), Salem District and Kolli Hills (1148–1386m)

(Mani, 1977), Namakkal District. The thickness and areal extent of the

individual occurrences varies widely. In all the areas the laterite is

presumably derived by the sub aerial weathering of charnockite and is

exposed as patches on the hills. Within the laterite, bauxite occurs as streaks

and pockets extending to different depths. The areal extent of the individual

cappings also varies widely. In Salem District a total of six deposits of bauxite

occupying 6 hill tops (hill Nos. I to VI) are known in the Shevaroy Hills

(Plate-IXA). The areal extent of the individual deposits ranges from 22,000 sq

m (hill No.VI) to 1,55,000 sq m with an aggregate of 4,05,000sq m. The

thickness of the bauxite zone is inferred to be 5 to 15 m. The reserves were

originally estimated to be about 5.3 million tonnes but Madras Aluminium

Company have been exploiting the deposits for more than 25 years and the

net reserves now available are likely to be about 2 million tonnes only. The

grade is highly variable and the ore is reported to analyse only 40–43% Al2O3.

Nineteen bauxite cappings are known from the Kolli Hills - Five in

Velavanchinadu area; eight in Ariyurnadu area, two in Selurnadu area and

four in Tinnanurnadu area. Both primary cappings and detrital spreads

around them have been recorded. The thickness of the bauxite varies from 4

to 7m as seen from excavated pits and even more in certain places where the

pits have not reached the bottom of laterite cappings. The reserves are

estimated to be 3.04 million tonnes. (Al2O3 content 35 to 40% - 1.308 million

tonnes : 40 to 45% - 1.269 million tonnes : 45 to 50% - 0.456 million tonnes and

above 50% - 6000 tonnes.)



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3.2.2 Bauxite Deposits Vs Neotectonic Lineaments

The bauxite deposits were restricted to Shevaroys and Kolli hills. In

Shevaroys the lateritic bauxites were restricted to 1535m and above. These

high reliefs were observed only around Manjakuttai and Sholakardu area

where the hill top capping could be seen. The peaks were linearly stretched

along NE-SW direction parallelized by L89 and L70 and along eastern and

western side were bounded by N-S trending L71 and L39. The lineament L77

and L78 were bounding the northern and southern side of the centrally

elevated peaks.

The profile AB (Fig. 3.1A) was drawn along NE-SW direction and

shows major altitudinal variation from 1400m to 800m along L77 and from

1450m to 870m at the southern side lineament L78. The profile CD (Fig.3.1B)

was drawn along E-W which indicated the abrupt relief variations along L70

and L39 in the east and L71 and L 89 in the west. These topographic variations

clearly suggested the block faulting along these lineaments leaving the central

block relatively high among this plateau and thus preserved the bauxite

deposits. It was convenient to conclude that the formation and preservation of

bauxites in Shevaroys were completely neotectonically controlled.

In Kolli hills the bauxites were distributed in central and southern part

of hills with the NE-SW trend parallel to L43, L55 in the east and L61 in the

west. The E-W trending L76 and L81 were observed along southern and

northern side of the central bauxite deposits. The profile EF (Fig.3.1C) was

drawn along N-S direction the lower altitude was observed corresponding to

L3, L81 in the north and L76 in the south of bauxite deposits. The profile GH

(Fig.3.1D) was drawn in NW-SE direction and the sharp change in altitude

from 1300m to 1000m was observed along NE-SW trending L43 and L55 in

the east and L61 was forming the western boundary of the hill as well as for

the deposits. The Kolli hill is relatively flat and undissected than Shevaroys

but slope of the hills was very steep and suggesting recent modifications by



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Neotectonic lineaments. The lineaments L43, L55, L61, L3 and L81 keep the

hills elevated and preserving the bauxites. And similar control was observed

in southern part bauxite deposits.

Fig. 3.1 Bauxite Vs Neotectonic Lineaments



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3.3 OTHER METALLIC MINERALS

3.3.1 General

Apart from major deposits like iron ores and bauxite, many other

important mineral deposits like Chromite, Platinum, Nickel and Magnesite

are occurring in the study area. These minerals are found in association with

ultramafic rocks.

3.3.2 Chromite

Important chromite bearing amphibolite bands which form sill like

bodies along the foliation planes of anorthosite - gneiss, are traced over a

stretch of 12.8km between Sittampundi and Karungalpatti (between lat. 11º16’

and 11º18’N and long. 77º50’ and 78º01’E) in Namakkal District. The

chromiferous amphibolite (chromitites) varies in thickness from 8cm to 3.05 m

and contains on an average over 60 % chromite, chemical analysis shows

Cr203 21.72 -28.20%, Al203 24.04 - 41.31%, Fe203 10.20-25.59% and Fe0 10.18-

12.20%. The reserves are estimated at 0.221 million tonnes upto a depth of

6.1m (GSI, 2006).

Now, GSI has declared the occurrence of platinum group minerals

with chromite and made a memorandum of understanding (MOU) with the

Tamil Nadu government for winning the same (Annexure –IF).

3.3.3 Platinum

Within the anorthosite gneiss, distinct bands and lenses of chromitite /

chromiferous metapyroxenite of varying dimensions (a few mm to 3.00 m) are

noticed in the entire complex. These bands, forming the main target for PGE

mineralisation, show pinching and swelling in several places. Primary

igneous structures such as rhythmic layering and cumulus banding are

observed within the hornblende anorthosite gneiss (gabbroic anorthosite /

anorthositic gabbro) with fine streaks and stringers of chromitite /

chromiferous meta-pyroxenite. The Sittampundi Complex is divided into

three main blocks viz. Karungalpatti, Chettiyampalaiyam and



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Tasampalaiyam (from east to west) for the purpose of Platinoid Group of

Elements (PGE) exploration. In Karungalpatti Block nine parallel to sub-

parallel chromitite bands with intervening anorthosite gneiss in this block are

identified. The samples from Band III, IV & VIII have analysed significant

values of PGE from 0.06 to 2.2 ppm of Pt and 0.03 to 3.3 ppm of Pd. The PGE

mineralization in Sittampundi complex is confined to the chromitite and PGM

phases occur as inclusions within the chrome-spinel or at the contact between

chrome-spinel and amphibole

3.3.4 Nickel Ore

Peridotite / dunite from Chalk Hills, Salem District has yielded up to

0.40% Ni and occasional composite grains of Pentlandite + Pyrrhotite +

Chalcopyrite have been recorded from the Red Hills.

3.3.5 Magnesite

In Tamil Nadu the most prominent deposit of magnesite is located on

Chalk Hills, Salem District spreads 17 sq. km. Other minor occurrences are

located in other areas in Salem District and parts of adjoining districts.

Magnesite on Chalk Hills occurs as criss-cross veins traversing dunite

/ peridotite (Aiyengar and Krishnan, 1943). The veins vary in length from a

fraction of a metre to 100's of metre and thickness from less than a centimetre

to as much as 1.5 m. The total reserves in the Chalk Hills are estimated at 44

million tonnes. Minor occurrences are reported from Chettipatti,

Jalakandapuram, Rajampalayam, Sirappalli, Siranganur and Vimanayakanur

in Salem District.

3.3.6 Host Rock – Ultramafic Rocks

A group of ultrabasic rocks ranging in composition from dunite,

peridotite, websterite, garnetiferous gabbro, gabbroic anorthosite and

anorthosite occur closely associated with the Sathyamangalam Group in the

central belt of Tamil Nadu, around Mettupalayam and Sittampundi areas.



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They occur as enclaves within the gneisses as a part of the dismembered

sequence. Large volume of garnetiferous gabbro and hornblendic anorthosite

with chromitite layers as well as small lenses of eclogitic rocks are the

characteristic features of this suite (Gopalakrishnan, 1994b). They are

considered to have been emplaced along reactivated lineaments, shear zones,

fracture zones or as tectonic slices.

Ultramafic rocks are the host for several metal ores and industrial

minerals. Magmatic minerals include chromite, and Fe, Ni, and Cu sulphides,

sometimes with Co. Ultramafic complexes are also the major economic source

of platinum group element (PGE) minerals. Olivine is an essential constituent

of many ultramafic rocks, and where serpentinisation is not pervasive and

olivine is the dominant mineral, as in dunites, a deposit of commercial value

may be present. Chrysotile asbestos is an important product of the

serpentinisation of ultramafic rocks. It occurs commonly as veins, but where it

is a rock-forming mineral with the fibres in an interlocking texture it can

constitute an exploitable resource.

Sulphide and PGE ore mineral assemblages are usually changed

significantly as a consequence of serpentinisation (Ramdohr, 1967; O’Hanley,

1996). The primary magmatic sulphides, dominated by pyrrhotite and

pentlandite, are replaced at lower temperature by Ni sulphides and native

metals. Post-serpentinisation processes, including metamorphism,

metasomatism, and alteration, referred to as epigenetic mineralisation by

O’Hanley (1996), can result in further hydration and carbonatisation of the

serpentine and other minerals. This can lead to the formation of other

industrial minerals, including talc, magnesite, sepiolite and sometimes very

uncommon minerals such as huntite and hydromagnesite (Scott, 1987;

Ebrahimi-Nasrabadi, 1990; Stamatakis, 1995). Deep tropical weathering of

ultramafic rocks creates an important source of lateritic Ni and Co. In

sulphide poor ultramafic rocks, the bulk of the Ni and Co is held within the



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olivine structure and the weathering process can concentrate these elements

in secondary hydrous silicates, such as garnierite and Ni-saponite.

3.3.7 Mapping of Ultramafic Rocks

Since ultramafic rocks host many valuable metal ores like chromite,

platinum ore, ore of nickel, gold and minerals like magnesite , asbestos and

semi precious silica and many more, an attempt was made to locate some

newer locations by field study and analyzing its relation with the Neotectonic

lineaments.

3.3.7.1 Field study

The study window displays many ultramafic bodies including Chalk

hills where active Magnesite mining is going on. Ultramafic suite with

alkaline rock – shonkinite was found to be aligning with NE-SW lineament.

The Chalk hills (Plate-IXB) shows E-W elongation near north of Nagaramalai

and show strike slip along NW –SE lineament near southern part where the

Salem- Dharmapuri national highways NH7 passes.

Bands and lenses of ultramafics with composition of metapyroxenite/

talc (Steatite) schists are exposed as bands and lenses within the banded

gneiss (Plate-IXC). Major mappable bands frequently occur in the area

around Dasanur, south and west of Karuvalli, NW and west of Omalur.

Metapyroxenite is dark grey, medium to coarse grained, massive and heavy.

It is coarse grained, granoblastic and consists mainly of orthopyroxene and

clinopyroxene. Magnetite occurs as an accessory mineral. A few bands of

talc/tremolite bearing schist, are also exposed which were quarried in a few

pockets for grinding stone. These lenses and bands show their long axes

oriented parallel to the regional foliation.

Siddhar koil near northern flank of Kanjamalai dunite and peridotite

with magnesite occurrences was reported. The original extensions of the rocks

were mapped during the field study by the author during the year 2008



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where peridotite extensions were observed parallel to the E-W lineament.

Near Ariyanur (Salem-Erode NH47) on the southern flank of Kanjamalai,

ultramafic rocks emplacement was observed during field study on the Shiva

temple Hillock (.306 m. 78.085º, 11.595º) and Makkalur hill (.296m. 78.057º,

11.583º). Syenite was also found on the way from Omalur to Mecheri road

near Silakardu hill (.426m) which crudely aligning with a NE-SW lineament

and an E-W lineament viz.L34 and L78.

3.3.8 Ultramafic Rocks Vs Neotectonic Lineaments

The ultramafic dykes were observed south of Toppal Ar i.e. south of

ENE-WSW lineaments L26 and L85. Another ENE-WSW trending L77

sinisterly shift the metapyroxenites dykes near west of Naduppatty on the

NH47 from Salem to Dharmapuri. The Lineament L78 separates the folded

Omalur ultramafics from nearly N-S trending metapyroxenites. The N-S

trending L2 lineament was aligning with the ultramafics near Reddiyur. The

E-W trending L40 passing through ultramafics in Kanjamalai and they have

opened up many springs along its path which were locally used by peoples

for their holy dip.

The E-W trending L1 separates the Chalk hills into two mineralized

zones passes north of Nagaramalai hills where mylonites with good

porphyroclasts was observed and Pseudotachylyte near Gorimedu. L38

aligning with the ultramafics near IMPL magnesia mine which lies within an

isolated plug with E-W trend. Along the lineament L74 there was marginal

dislocation of the ultramafics with the sinistral sense was observed. The NW-

SE trending L75 was aligning with an isolated ultramafic body near

Panamarathupatti which also cut through the Chalk hills and passing SW of

Nagaramalai. The NE-SW trending L46 and NW-SE trending L10 were

aligning with ultramafics near Vembakavundampudur which displaced the

evidences of carbonate metasomatism and intense shearing (Fig.3.2).



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The E-W trending L23 and L83 and NE-SW trending L4 were aligning

with the ultramafics in the NE side of Kalrayan hills near Manimukta River.

Fig. 3.2 Ultramafics Vs Neotectonic Lineaments



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E-W trending L93 and NW-SE trending L30 and L31 form the lower

boundary of the ultramafics near Pakkinayakanpatti NE of Kalrayan hills. L31

shows sinistral dislocation of the ultramafics near NE part of Kalrayan hills.

A NE-SW trending L43 lineament was aligning with Kanankadu ultramafics

near SW of Mamandur. Along L4 the ultramafics of Sitampundi complex

bifurcate out with NW-SE trend. The N-S trending L86 was parallel to the F1

fold axis and L76 with E-W trend was lying along the F2 fold axis of the

Sitampundi folded ultramafics.

Alteration of dunite into magnesite by hot ascending hydrothermal

fluids and alteration of pyroxenites into steatites are very common in the

study window. Though these alterations could not be correlated with

neotectonism the reactivation of the lineaments was undoubtedly happened

during the last main igneous phase of emplacement of Sankagiri granite and

which are equivalent to Pan-African orogeny. But there were much younger

igneous plugs with less or no shearing effects could signify a later igneous

event (Fig.3.2).

3.4 GOLD

3.4.1 Image Processing

Attur valley area provided an ideal setting for emplacement of

ultramafic bodies, syenite and carbonatites since it lies in a region bounded by

Pakkanadu - Mulakkadu alkaline suite and Chalk hills ultramafics which are

aligning with NE-SW and E-W lineaments. Similar lineament could be traced

within Attur valley with NE-SW trend and also with E-W traversing

lineaments cutting across alkaline rocks could be expected. Moreover DRM

indicates occurrences of carbonatites in Attur valley. People like Aiyengar

(1948), Gopala Rao (1966) Venkatesan (1967) and Shrivastava and Saleem

Ahmed Khan (1982) have done some exploration in these places for gold

occurrences. In fact gold in these places was also known to the local people

for a very long time and panning for gold have been carried on for several

centuries (Aiyengar, 1964).



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Fig.3.3 Gold Mineralization - Prospective Area

Digital image processing generated several products ranging from false

color composite bands 7, 4 and 2, principle components and ratioing (bands

5/7, 5/1 and band 4, and bands 5/7, 4/5, 3/1 in RGB). False color composite

(FCC) bands 7, 4, and 2 images have been used in regional tectonic

analyses and provide excellent images as bases for geological maps

(Kusky And Ramadan, 2002,). In the Shalatein district, Eastern Desert of

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Egypt, Landsat Thematic Mapper (TM) data and fieldwork were combined

with mineralogical and geochemical investigations in order to detect and

characterize alteration zones within Pan-African rocks. The processing of

LANDSAT TM data using ratioing (bands 5/7, 4/5, 3/1 in red, green, and

blue) showed two different types of alteration zones Talaat M. Ramadan and

Agnes Kontny (2004).

Similar band ratioing technique was applied for LANDSAT ETM data

with the image processing software ENVI 4.4. The bands ratioed bands 5/7,

4/5, 3/1 in Red, Green, Blue and the image showing bright colour as shown

in Figure 3.3. The bright color corresponds to carbonate gneiss of the Attur

valley. This combination of band ratio brings out alteration by alkaline rich

fluids. Already GSI has reported (DRM) carbonatites near south of Sarkar

Valappadi and ultramafic rock dunite with Magnesite veins were exploited

for magnesite near Vembakavundanpudur by some local miners. So, field

work was intended in this alteration zone to study the evidences for

possibilities of Gold mineralization. With this idea an attempt was made to

demarcate prospective area for gold in Attur valley.

3.4.2 Field Observations

Field observations was planned so as to find possible occurrences of

alkaline igneous suite

3.4.2.1 Carbonatites

Carbonatites outcrops were observed near Umayalpurampudur (E78°

28' 8.39", N11° 37' 30") and Karippatti (E78° 17' 13.2", N11° 39' 28.79"). Near

the first location the NW-SE trending dykes were completely fractured by the

intrusion of the carbonatite and the mine was not operating due to the poor

quality of the produce. The carbonatite veins invading the joints present in the

charnockite were observed near Karippatti and metasomatic effects of the

intrusion could be seen on the vein –rock contact these carbonatites were

calcitic in hand specimen and may be classed as Sovite (Plate VII-E).



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North of Ishwaramurtipalaiyam linear band of carbonatite was

observed it was brown in color and probably belongs to ankeritic or para-

ankeritic type.

3.4.2.2 Corundum Syenites

New outcrops of syenites were located in Attur valley during field

study and were reported near Vembakavundanpudur (E78° 25' 12" , N11° 31'

12"). These syenites are found to be associated with ultramafic rocks and

aligning with NE-SW trending lineament.

Thin section of a corundum syenite specimen from the magnesite mine

near Vembakavundanpudur exhibits porphyritic texture consisting of large

corundum crystals within feldspar matrix. The colourless subhedral

corundum hexagons showing two sets of perfect cleavages (partings) and pale

greenish chlorite set in a fine grained sericitized feldspar matrix. Opaque

minerals probably magnetite and ilmenite and rhombic carbonates forms the

accessories (Plate VIII-E).

3.4.2.3 Lamprophyre

Lamprophyre was observed in a well cutting near Koraiyar (E78° 19'

12" N11° 29' 24") which would be significant in claiming the rift related

alkaline suite was emplaced in Attur valley as they are always associating

with alkaline rocks and direct bearer of mantle signatures. The lamprophyres

are the last manifestation of igneous activity in a given alkaline region.

Liquid immiscibility plays a dominant role in the origin of carbonatites

and lamprophyres, all of them may be considered to have derived from the

same parent \ magma and emplaced along reactivated fractures

(Plate VIII-D).

Thin section of lamprophyres exhibits a coarse grained panidiomorphic

texture consisting of euhedral pyroxene {both ortho and clino} set in a



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clouded plagioclase matrix. There are a few irregular shaped grains of olivine

much highly pleochroic deep brownish biotite,/phlogopite and a few

pyroxene crystals show marginal alteration in to green chlorite.

Fig.3.4 Quartz Pods and Alkaline Rocks



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3.4.2.4 Ultramafic rocks

Four discrete bodies of Dunite/ peridotite were located in Attur valley

area near Timmanayakkanpatti. These rocks were altered to magnesite and

they were relatively less deformed and they lie parallel to NE-SW lineaments.

These rocks must be younger in age as they have not possessed chromites or

associated with anorthosite whereas in Sitampundi and chalk hills they

contain chromites (Janardhan, et al., 1975).

Pyroxenite in Timmanayakkanpatti was represented by a thick

elongated lens of outcrop southeast of Pusariyur and they contain carbonates

as depicted by etching and solution pits on the surface of the outcrops.

3.4.2.5 Quartz Veins

Numerous swarms of quartz veins were noticed in the hills southeast

of Ishwaramurtipalaiyam. Swarms of quartz veins are also found south of

magnesite quarry, around hill .391 and mound .334.

Quartz veins were found along the stony waste ridge NNW of

Vellalakundum and plains NE of mound .438. Almost all the quartz veins are

pure milky white and massive with iron coatings on parting surfaces. Rarely,

they do show sulphide specks and malachite stains. A great majority of

carbonatite are intruded by cross cutting quartz veins and others have quartz

veins in their close proximity. The length of quartz veins vary from less than

5 m to over 700m with a thickness range of 2 to l0m (Fig.3.4).

3.4.3 Mechanism of Gold Mineralization

A process of carbonatisation, similar to fenitisation, has affected the

country rocks around carbonatites and adjoining area, leading to the

formation of pinkish siderite-ankerite bearing quartzofeldspathic gneisses

(termed as carbonated gneisses). Some mafic rocks are also affected by

carbonatisation giving rise to carbonated mafic rocks and they are of small

dimensions and patchy in occurrence. This type of carbonate metasomatism

has been reported from carbonatite complexes as well as from certain major



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shears zones. Similar process of carbonatisation has affected a sizable area

around Kangankunde Carbonatite Complex, west of Lake Chilwa, Nyasaland

(Garson, 1958), where the surrounding rocks were first permeated by

strontianite rich ankerite and siderite material and later remobilized to K-

feldspar-ankerite-siderite rock. Regional carbonatisation connected with Epi-

Hercynian tectogenesis was also reported from southern Tien Shan (Baratov

et al., 1984).

Since siderite- ankerite carbonates which are involved in carbonate

metasomatism in the area are also the primary carbonates of all the

carbonatite bodies in the Attur Valley, the process of carbonatisation seems

related to the emplacement of carbonatites, not only spatially but also

genetically, at least in this area. However, carbon isotope study of carbonates

from these litho units is necessary for confirming their consanguinity.

The timing of gold-bearing mineralization in quartz pods must be

related to alkaline metasomatism unleashed out by the carbonatite intrusion

in these zone must be the plausible mechanism involved. There must be much

more carbonatite outcrops, the presence of such irregular dykes in a restricted

area has been attributed to a deep seated "Parent Complex" source

(Eckermann, 1948). The detail study using high resolution hyper spectral data

and detailed field study would be handy since this region seems to be much

prospective for gold mineralization.

This study demonstrates the utility of orbital remote sensing for

finding unknown alteration zones within crystalline rocks and carbonate

gneiss in the Attur valley.

3.4.4 Gold Mineralized Zone Vs Neotectonic lineaments

EPMA dating of monazite from a post-kinematic pegmatite which

intrudes the crystalline basement hosting the alkaline rocks yields an age of

478±29 (2σ) Ma and provides a lower bracket for the main phase of tectonism

in this part of the Southern Granulite Terrain (Upadhyay, et al., 2006) and

hence the correlation to neotectonism seems futile except shearing and lesser



222

degree of alteration. But the Neotectonic lineaments L6, L7, L8, L9, L10, L11,

L32, L36, L40, L41, L42, L46, L53, L56, L61, L63, L65, L66, L75, L79, L82 and

L97 passing through this zone have correlation with the general trend of the

alkaline rocks. So, they may be presumed as proterozoic lineaments and

reactivated at least in Pleistocene (Fig.3.5).

Fig.3.5 Gold Mineralization Zone Vs Neotectonic Lineaments



223

3.5 BASE METAL MINERALIZATION

Prominent base metal sulphides occur in the Mamandur of Cuddalore

District which was explored by geological, geochemical and geophysical

methods and exploratory drilling and mining. There are two generations of

mineralisation, the first is a multimetal lode comprising zinc, lead, copper,

silver and cadmium and the other is a disseminated copper sulphide.

The multimetal lode follows the lithological contact (garnetiferous -

biotite - sillimanite gneiss) and copper mineralisation is observed in the shear

planes on the footwall side. Two ore bodies, sphalerite rich multimetal ore

and a chalcopyrite rich one on the footwall side have been delineated. The

sphalerite rich ore body extends over a strike length of about 300m with an

average width of 3.15m and persists to a depth of 280m along the dip. The

reserves in this ore body are estimated to be 0.66 million tonnes with a metal

content of 5.53% Zn, 1.15% Pb and 0.45% Cu. The chalcopyrite ore body

which extends over a strike length of 180 m with a width of about 7 m and a

depth persistence of 34 m, is estimated to contain 0.13 million tonnes of ore

with a metal content of 0.62% Cu, 0.69% Zn, 0.12%Pb and 37 g/t Ag (GSI

2006)

3.5.1 Basemetal Mineralisation Vs Neotectonic Lineaments

The mineralized zone was untraceble from satellite data and the

control of neotectonic lineaments over basemetal mineralisation could not be

estabilished. The proximity of L43 was observed but neotectonic control was

unclear (Fig. 3.6).



224

Fig.3.6 Basemetal Mineralisation Vs Neotectonic Lineaments



225

3.6 AMPHIBOLE ASBESTOS

A mound of amphibolite (E78° 3' 36", N11° 34' 12") with intervening

Fig.3.7 Amphibole Asbestos Mineralization

mylonites was observed during the field study near Chinnasirangapadi

village. The amphibolite show higher degree of alteration in to asbestos where



226

the hornblende biotite gneiss contains sericite in patches near the asbestos

pockets (Fig. 3.7).

The amphibolite asbestos was formed in pockets and the

mineralization was restricted to the contact zone Moyar- Bhavani- Salem-

Attur shear zone and the N-S to NNE-SSW trending Tiruchengode shear

zone. The termination of the Tiruchengode shear zone against the MBSASZ

indicates reactivation of the E-W shear after the formation of Tiruchengode

shear zone syntectonic to Sankagiri granite emplacement (Plate IX-D).

3.6.1 Amphibole Asbestos Mineralization Vs Neotectonic Lineaments

The Amphibole Asbestos was formed at the intersection of E-W

trending MBSASZ zone and N-S to NE-SW trending Tiruchengode shear

zone. The L89 which was aligning with Tiruchengode shear and L8 which

was parallel to MBSASZ were intersecting at the amphibolite body. Another

lineament L86 with NNE-SSW trend was passing through the amphibolite

asbestos (Fig.3.8).

3.7 DOLERITE DYKES

3.7.1 Occurrences of dykes

The northern part of Tamil Nadu, north of Noyil-Cauvery Rivers

(north of 11°latitude) is characterised by dyke swarms, in contrast to the areas

south of Noyil-Cauvery Rivers where they are absent. In general, the mafic

dykes trend WNW-ESE and NNE-SSW and rarely N-S and NNW-SSE. In the

central part of Tamil Nadu, ENE-WNW to NE-SW trending mafic dykes are

seen transecting the charnockite and migmatites in Nilgiri and Kolli Hills.

Although most of these mafic dykes show textural characteristics of dolerite,

gabbroic / basaltic variants are not uncommon. The mineral assemblages of

these dykes indicate quartz-gabbro / quartz–dolerite composition with minor

variations to olivine-gabbro/dolerite. Petrochemical studies indicate that the

majority of these dykes are quartz normative tholeiites, while olivine-dolerite



227

dykes show basaltic komatiite chemistry (Krishna Rao and Nathan, 1999).

The chemical attributes of these dykes suggest that they were emplaced in a

continental tectonic setting. The available K-Ar ages for the mafic dykes of

Tamil Nadu are clustering around 1700Ma (Radhakrishna and Mathew

Joseph, 1993; Sarkar and Mallick, 1995) indicating that they were emplaced

during a major extensional tectonic regime in the Southern Peninsular Shield.

Fig. 3.8 Amphibole Asbestos Mineralization Vs Neotectonic Lineaments



228

A large number of mafic intrusives comprising medium to coarse

grained dolerites to fine grained basalts are encountered in the study area.

These dyke bodies traverse across almost all the rock types mainly along NE-

SW, E-W and NNW-SSE trends. Local variation of a few degrees in trends of

these dykes was common since most of them are of swerving nature and a

few were branching. The general trend of above sets of dykes roughly follow

the regional fold axes and shear zones; and timing of their emplacement could

also be related to the regional episodes of folding and dislocations. Among

the vast number of dykes encountered in the area, the following were the

major ones:

(a) NNW-SSE trending 7.5 km. long discontinuous dolerite dyke

extending from southeast of hill .711 to the south of Karippatti.

(b) NNW-SSE trending 2.5 km. long coarse grained dolerite dyke with

highly varying thickness, passing between hill .601 and hill .413.

(c) NE-SW trending 2.5 km. long dolerite dyke and swerving at two places

extends from NE of Mudiyanur to south of .413.

(d) two NE-SW trending dolerite dykes, about 2 km. long, one to the NE of

Palaniyapuram and the other to the NW of Singipuram.

(e) NE-SW trending highly mylonitlzed 2 km. long dolerite between hill

.698 and hill .711 showing branching long doleritc

(f) NE-SW trending discontinuous dolerite dyke extending from SW of

Vembakavundanpudur to east of Tirnmanayakkaapatti (combined

length - 5 km. ).

(g) A NE-SW trending faulted dolerite dyke south of Pusariyur.

In addition to the above listed dykes, there are several dolerite dykes

relatively smaller dimensions, extending in both NNW-SSE and NE-SW

directions.



229

They are generally dark greenish to black (melanocratic), hard and

compact massive and less jointed, but quite a few show shearing and

mylonitisation, which was obivious by the presence of pseudotachylyte veins.

Most of the dykes either stand out prominently as low ridges or

exposed as exfoliated boulders in plains. Extremely well developed

exfoliation in coarse grained dolerite dykes could be seen along the road

cutting between hills .601 and .413 and east of hill.413.

3.7.2 Dykes Vs Neotectonic Lineaments

The Neotectonic lineaments brought out marked changes in the

disposition of dykes. Dislocation were prominent with sinistral sense along

NE-SW trending lineaments L6, L8, L9, L27, L40, L44, L48, L52, L55, L65, L66,

L69 and L75 (Fig.3.9).

The lineaments L2, L3,L12, L15, L24, L43, L45, L50, L73 and L88 were

aligning parallel to the dykes and possibly indicating NE-SW and NW-SE

trending fractures which were proterozoic dykes, still remains as the place of

stress release in the form of wrench faults.

The lineaments L7, L 23, L26, L41, L78, L85 and L43 were showing

conspicuous termination of dolerite dykes.

Carbonatites outcrops were observed near Umayalpurampudur (E78°

28' 8.39", N11° 37' 30") and Karippatti (E78° 17' 13.2", N11° 39' 28.79"). Near

the first location the NW-SE trending dykes were completely fractured by the

intrusion of the carbonatite and the mine was not operating due to the poor

quality of the produce. These clearly indicate another late tectonic event was

completely obliterating the older dykes. The lineaments with E-W trend viz.

L8 and L40 were completely aligning with MBSASZ shows carbonatite

emplacement near south of Sarkar Valappadi (Plate-IX E&F).



230

Fig.3.9 Dykes Vs Neotectonic Lineaments

3.8 GRANITES AND PEGMATITES

The granites of Southern Granulite Terrain (SGT) can be grouped

under two broad categories, viz., the Late Archaean / Early-proterozoic

granites and the Late-Proterozoic / Early-Palaeozoic (Pan-African) granites.

The older granites are restricted to the northern part of SGT, while the

younger Pan-African granites are mostly found in central and southern parts

of SGT. Geochronological studies have yielded isochron age of 534 ±15 Ma for



231

the Sankari- Tiruchengodu, 619±35 Ma for the Maruda Malai and 471-475Ma

for the Punjai Puliyampatti granites. The field setting, mineralogical and

geochemical characters of most of the Pan-African granitoids of SGT

characterize them as Anorogenic A-type granites (Nathan et al., 2009).

The Granulite-Gneiss terrain of Central Tamil Nadu, representing the

marginal zones of Dharwar craton, witnessed wide spread Neoproterozoic

acid magmatism. This event is marked by the emplacement of several

granitoids (viz. Sankari-Tiruchengode, Punjai Puliyampatti, Karamadai and

Madura Malai granites) in a linear array within the E-W trending Cauvery

Shear Zone / Cauvery Suture Zone (CSZ) which is bound by Moyar-Bhavani

Attur Lineament (MBAL) in the north and Palghat-Cauvery Lineament (PCL)

in the south. The Sankari-Tiruchengode (ST) granite, occurring at the

intersection of the MBAL with the NNE-SSW trending Mettur lineament, is

emplaced within the Bhavani Gneissic Complex and the associated

supracrustal rocks of Sathyamangalam Group. The ST granite comprises two

distinct phases, viz. a leucocratic phase and a pink phase. The leucogranites,

showing grain size variation from medium grained to pegmatoidal, occur in

the peripheral parts of the ST pluton while the pink granites (coarse to

pegmatoidal) occupy the core.

Late archaean-early protenbrozoic periods in Tamil Nadu and

Pondicherry are characterised by granulitic facies metamorphism with

charnockite formation and concomitant anatexis of earlier rocks. A number of

small granite plutons were emplaced as culmination of migmatisation during

this period. The migmatite complex shown in the map at places includes

gneisses and granitoids generated during this period. The late archaean

granite is developed along the northern periphery of the state (to the north of

Palar River) around Tiruttani, Sholingar, Bisanattam, Ebbari and Krishnagiri

(Ca 2500 Ma) (Krogstad et.al. 1988; GSI 1991), while early proterozoic granite



232

is recognised around Gingee, Tiruvannamalai and Tirukovilur (2254Ma;

Balasubrahmanyan et.al. 1979).

Linear NE-SW trending granite outcrops were marking lineaments

with the similar trend were found in Thoppar ar valley near Mallapuram and

four exposures were found near Northern part of Chitteri hills. Similar NE-

SW trend of the granitic bodies were observed near Belukurichi, and

Thumbaipatti in the southwestern part of study area and also near Mukkanur

in the northeastern part of the study area. E-W trending granites could be

observed near central eastern part of the study area (Fig.3.10).

There are a large number of sheets, bands and lenses of pegmatoidal

granites confined to southern parts of Attur valley in general and to the south

eastern portions in particular. Maximun concentration of these bodies were

recorded around hill .419 and .513, north of .582, northeast of .600, south of

.601 and west of .626. In most of the cases they intruded into charnockites,

except at hill .419 and southeast of .654, where they are emplaced into a

pyroxene granulite.

The granite bodies vary in size from less than 5 meters to over a km.

long with a thickness range of 1-25 meters, but on an average, they are a

couple of meters thick. Longest of all pegmatoidal granites are found at hill

.419 (west of Singipuram), ridge west of .626 and northeast of .593, which are

around a km. long.

The exposures of grey granite near Pokkamalai (Δ539m) and pink

granites near Kudamalai (E78.59º, N11.46º) were found and the pink granite

found to be emplaced at the intersection of Gangavalli shear zone and Swetha

nadi fault. West of Chalk hills, pegmatite veins and rock exposures were

observed near Chettipatti and Reddiyur near Omalur and also near

Kachchirapalayam on the east of Kalrayan hills.



233

Many exposures of pegmatites were found near Taramangalam, and

adjoining area where feldspar and quartz are being mined. Good quality beryl

crystals are commonly found in these rocks.

Fig.3.10 Granites Vs Neotectonic Lineaments

Migmatites were found near Sitampundi south west corner of the

study area and also north of Bodamalai. The first one was found to be

trending NE-SW and the other one was trending WSW-ENE direction.



234

These rocks were very significant in the exploration of Thorium (Th)

sources and other Rare earth elements (REE) and hence a study on the

deposits is warranted.

3.8.1 Acid Intrusives Vs Neotectonic Lineaments

The places of emplacement of acid intrusives in Neoproterozoic period,

certainly proves the reactivation of the shears in this part of the area. Though

no direct evidences of link between granite emplacement and the neotectonic

lineaments, a positive correlation was done for the alignment of Neotectonic

lineaments and the exposures of acid intrusives.

NW-SE trending L30, L31, L49, L50, L53, L75 lineaments, E-W trending

L66 and L83 and NE-SW trending L9, L35, L37, L44, L46, L87 and L98 were

showing a parallelism or a crude cut across relationship with intrusive bodies.

3.9 SYNTHESIS

Though no new mineral deposits were formed after at least late

proterozoic in the study area except younger alluvial deposits, the impact of

recent tectonism or reactivated tectonism played a vital role in bringing

alteration in the parent rocks and produced mineral like steatite, asbestos and

magnesite and also dispersing the rock types hosting the mineral deposits.

Moreover, the alkaline magmatism in the study area has brought out the

probable gold mineralization in Attur valley. Still further study has to be done

to assess the viability of the deposits for mining. Bauxitization is the process

completely restricted high altitudes in tropical and subtropical countries

satisfying appropriate favorable condition. These bauxite cappings were

restricted to high peaks which were in turn formed due to tectono-

geomorphic events probably a block faulting. The Neotectonic lineaments

which are dispersing the rocks and bringing mineralization were listed in the

following Table 3.1.



235



236

Table 3.1 Mineral Resources Vs Neotectonic Lineaments

S.No

Sig

nif

ica

nt

Lin

ea

me

nt

Ne

ote

c.

Lin

ea

me

nt

Litho. Hosting Minerals

Dyke Type of minerals associated

with Neotectonic Lineaments

1 L1 NL1

Dunite

2 L2 NL2

Parallel

3 L3 NL3

Charnockite Parallel Bauxite

4 L4

5 L5

6 L6 NL4 Quartz, Carbonate

gneiss, Granite Dislocation Gold Granite


gneiss, Carbonatite Termination Gold

8 L8 NL6

Quartz, Carbonate gneiss, Mylonite,

Amphibolite

Dislocation, Carbonatite

Gold Asbestos

9 L9 NL7

Quartz, Carbonate gneiss, Migmatites,

Ca. Gneiss, Mylonite Dislocation Gold Migmatite


gneiss Gold


gneiss Gold

12 L12 NL10

Parallel

13 L13 NL11

14 L14

15 L15 NL12

Parallel

16 L16 NL13

17 L17 NL14

18 L18

19 L19

20 L20

21 L21

22 L22



237

23 L23 NL15

Termination

24 L24

Parallel

25 L25

26 L26 NL16

Termination

27 L27 NL17

Dislocation

28 L28 NL18

Pseudotachylyte

29 L29

30 L30

Granite

31 L31

Granite

32 L32 NL19

Quartz, Carbonate gneiss, Epidote

gneiss, Mylonite Gold

33 L33 NL20

34 L34

35 L35

36 L36 NL21 Quartz, Syenite,

Carbonate gneiss, Gold

37 L37 NL22

Garnet gabbro Granite

38 L38 NL23 Pseudotachylyte,

Dunite

39 L39 NL24

Bauxite

40 L40 NL25

Quartz, Dunite, Carbonate gneiss,

Carbonatite Dislocation Gold


gneiss, termination Gold


gneiss, Syenite, Dunite Carbonatites Gold

43 L43 NL28 Charnockite, Dunite,

Garnetiferous Gabbro Parallel, Breaking

Bauxite

44 L44 NL29

Dunite Dislocation Granite

45 L45 NL30

Mylonite Parallel

46 L46 NL31

Quartz, Syenite, Carbonate gneiss,

Granite, Gold Granite

47 L47

48 L48

Dislocation



238

49 L49

50 L50 NL32

Parallel

51 L51

52 L52

Dislocation


gneiss, Charnockite Gold

54 L54

Pseudotachylyte

55 L55

Dislocation Bauxite

56 L56 Quartz, Carbonate

gneiss, Gold

57 L57 Pseudotachylyte,

58 L58 Pseudotachylyte

59 L59

60 L60


gneiss, Charnockite Gold Bauxite

62 L62


gneiss, Gold

64 L64


gneiss, Dislocation Gold


gneiss, Dislocation Gold

67 L67 NL35

Mylonite

68 L68

69 L69 NL36

Dislocation

70 L70 NL37

Charnockite Bauxite

71 L71 NL38

Charnockite Bauxite

72 L72

73 L73 NL39

Parallel

74 L74 NL40

75 L75 NL41 Quartz , Dunite,

Carbonate gneiss, Dislocation Gold Granite



239

76 L76 NL42

Charnockite Bauxite

77 L77 NL43

Charnockite Bauxite

78 L78 NL44

Charnockite Termination Bauxite

79 L79 NL45 Quartz, Carbonatite,

Carbonate gneiss Dislocation, Carbonatites

Gold

80 L80 NL46

81 L81

Charnockite Bauxite


gneiss Gold

83 L83

Granite

84 L84 NL48

Epidote gneiss

85 L85 NL49

Termination

86 L86 NL50

Mylonite, Amphibolite Asbestos

87 L87 NL51

Granite

88 L88

Parallel

89 L89 Amphibolite,

Charnockite

Asbestos, Bauxite

90 L90

91 L91

92 L92

93 L93

94 L94

95 L95

96 L96


gneiss Carbonatites Gold

98 L98 NL52

Granite

99 L99 NL53

Epidote gneiss

Read as

L-Significant Lineaments; NL –Neotectonic Lineaments:

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