CHAPTER-IV

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CHAPTER-IV

GEOLOGICAL SETUP

4.1. REGIONAL GEOLOGY The study area is a part of Singhbhum-Orissa Craton (SOC) of eastern India. The

general geological framework of Singhbhum-Orissa Precambrian belt was established

through the works of Dunn (1937) and Dunn and Dey (1942). Later on, work by

Sarkar and Saha (1962, 1977,1983), Saha (1988, 1992, 1994) and Mahadevan (2002)

tried to established the stratigraphy of the area based on geological, structural and

geochronological studies.

The Singhbhum-Orissa Craton is one of the oldest Archean nucleus of eastern India.

Major part of SOC is occupied by Singhbhum Granite Batholith (SBG) (after Saha,

1994; Sengupta et al., 1997 in Mondal et al., 2006) (Figs.4.1a & b). The SOC covers

about 40,000 sq.km. in the eastern Indian shield forming a triangular crustal block

(Saha,1994).

The Singhbhum crustal province can be divided into two distinct provinces: the, (i)

Singhbhum Group (Sarkar and Saha, 1962) which is youger and occupy the northern

part of the Craton. This northern part of the Craton is also known as North

Singhbhum Mobile Belt (NSMB) (Bhattacharya and Mahapatra, 2008) or Singhbhum

Mobile belt (SMB) (Misra, 2006)., (ii) the southern portion which is older than

NSMB is known as, Iron Ore Series (Jones, 1934), or Iron Ore Group (IOG) province

(Sarkar and Saha,1962), also known as Archean granite-greenstone terrain or

Singhbhum Granite Craton (Acharya, 2008; Sengupta et al.,1997 in Mondal et al.,

2006 and Mukhopadhyay, 2001) (Fig. 4.1a).

The boundary between the North Singhbhum Mobile Belt (NSMB) supracrustals and

Singhbhum-Orissa Craton is demarked by the prominent shear zone known as the

Singhbhum Shear Zone (SSZ) (Fig. 4.1a), which shows multiple reactivations, the

oldest being at ~3.09 Ga, followed by subsequent reactivation during Paleo and

Mesoproterozoic periods (Misra and Johnson, 2005). The shear zone trend eastward

from Parahat in western Singhbhum to the Chakradharpur and then it takes a

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southward swing in the close to Jamshedpur. This shear zone marks the northern

boundary of this nucleus while the Sukinda thrust and the Gondwana boundary fault

of the Talcher coal field form the southern boundary.

4.2 GENERALIZED STRATIGRAPHY OF SINGHBHUM ORISSA REGION

The Three important group of rocks make up the Archean nucleus of Singhbhum –

Orissa Craton of eastern India. They area are the (i) Older Metamorphic Group

(OMG), (ii) Older Metamorphic Tonalite Gneiss (OMTG), (iii) different phases of

Singhbhum Granite Batholith and (iv) younger supracrustal rocks including those of

the Iron Ore basins. Generalized chrono-stratigraphic succession according to their

ages and position is given in Table 4.1.

Older Metamorphic Group

Older metamorphic Group (OMG) rocks are the oldest rocks that occur south of

Singhbhum Shear zone which have been named by Dunn (1929) as the “Older

metamorphics”. The rocks consist predominantly of amphibolitic facies, pelitic-

schists, quartz-magnetite-cummingtonite schists, quartzite, banded calc-gneiss and

para- and ortho-amphibolites. The siliceous bearing pelitic schists contain elliptical

zircon grains. The siliceous aluminous sediments containing detrital zircon were

derived from a granitic province suggesting that the existence of older sialic micro

continents (Mukhopadhyay, 2001). The 207Pb-206Pb ages of zircon cluster around 3.5,

3.4 and 3.2 Ga (Mishra et al., 1998).

The ortho-amphibolite show slight Light Rare Earth Element (LREE) enrichment and

nearly flat Heavy Rare Earth Element (HREE) pattern (Sharma et al., 1994; Ray et

al., 1991). An eleven point whole-rock Sm–Nd isochron for the OMG ortho-

amphibolites yield an age of 3305±60 Ma which is interpreted to represent the

crystallization age (Sharma et al., 1994).

Older Metamorphic Tonalite Gneiss (OMTG)

The OMG rocks are intruded by the Older Metamorphic Tonalitic Gneiss (OMTG).

The rocks are mostly tonalitic-trondhjemitic; some are granodioritic. Sm-Nd isochron

diagram of OMTG are collinear with the OMG ortho-amphibolite plots and together

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they define a twenty two point whole rock isochron with an age of 3288±35 Ma

(Sharma et al., 1994). The Pb-Pb date is 3378±98Ma and the Rb-Sr whole-rock

isochron date is 3280±130Ma (Moorbath et al., 1986). An ancient core to the

Singhbhum rocks is built by the relatively small remnant of the Older Metamorphic

Group (OMG) and Older Metamorphic Tonalite Gneiss (OMTG) rocks, dated

between 3.4 and 3.5 Ga and metamorphosed to amphibolite facies (Sharma et al.,

1994; Saha, 1994). Recently they have been dated 3448 ± 19 Ma and 3527 ± 17 Ma

(Acharyya et al., 2010).

Singhbhum Granite (SBG)

Most part of SOC is covered by Singhbhum Granite (SBG) which ocuurs in a N-S

elongated trend in the centre of the craton and occupies about 8,000 sq.km. area

(Saha,1994). The north-south elongated outcrop of the Singhbhum Granite (SBG) is

made up of 12 separate magmatic bodies. Xenoliths of older tonalite gneisses,

migmatites and mafic-ultramific rocks are common within the Singhbhum Granite.

Petrographically the rocks are biotite-granodiorite grading to adamellitic-granite,

biotite-trondjhemite and leuco-granite. At the margin of the batholiths, chlorite and

epidotic granodiorite and pyroxene-diorite have been developed.

The rocks belonging to phase-I intrusions are relatively K-poor granodiorite-

tronjodiorites, while the phase-II and phase-III rocks are granodiorites grading to

adamellitic-granites. Three phases of SBG granites are of different ages are known as

SBG phase I, II and III which has been grouped under two group namely SBG-

A(Phase-I and II) and SBG—B(Phase-III) based on their Chondrite normalized REE

pattern (Saha,1994). Type A patterns are similar to those of the OMTG having

gently sloping REE pattern with moderately enriched LREE, flat HREE with no Eu

anomaly. Type B patterns have moderately enriched LREE, flat HREE and negative

Eu anomaly. Pb-Pb whole rock isochron dates from SBG phase-I and phase-II are

3442 ± 26 Ma and 3298 ± 63 Ma (Ghosh et al., 1996). Moorbath et al., (1986) have

also obtained a Pb-Pb isochron date of 3292±51 Ma for SBG phase-I and phase-II.

Hence the oldest phase of Singhbhum granite is almost as old as the OMTG, and the

REE pattern of the two is almost similar (Mukhopadhyay, 2001).

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Iron Ore Group (IOG)

The Iron Ore Group constitutes the major supracrustal unit in the SOIOC and referred

to as “Archean Supracrustals (Mahadevan, 2002)” and consists of low grade

metamorphic sediments including phyllites, tuffaceous shales, Banded Hematite

Jasper with Iron Ores, ferruginous quartzite, local dolomite and volcanics (Saha,

1994). The Meso to Neo Archean Iron Ore Group rocks occurring along the western

margin (the western iron ore basin) of the Singhbhum Granite massif in the

Singhbhum Craton could have been deformed during Iron Ore orogeny and are

deposited in a horseshoe-shaped synclinal structure in the eastern Indian shield

(Ghosh and Mukhopadhyay, 2007) . These IOG rocks are exposed in three major

basins, around the Singhbhum Granite Batholith Complex (SGBC) (Figs. 4.1a and

4.2). The major, “West Singhbhum-Keonjhar” basin is exposed on the western flank

of SGBC, extending from Chakradharpur to Malangtoli. The study area,

Kundarkocha gold deposit lies within the “Gorumahisani-Badampahar” schist belt

along the easternmost border of SGBC, extending from Jamshedpur in the north to

Naushahi in the south. The “Daitari-Pala-Lahara” basin occurring in the southern

fringes of the Craton is also known as “Sukinda Valley”.

Three distinct volcano-sedimentary iron ore basins called as Noamundi-Jamda-Koira

in the west, Tomka-Daitari in the south and Gorumahisani basin in the eastern part

surround the Singhbhum granitoid platformal nucleus (Fig. 4.1a). In the Iron Ore

Group, the supracrustal sequence include the conglomerate, ferruginous shales,

tuffs, lavas and Banded Iron Formation (BIF) and the iron ores (Murthy and Acharya,

1975; Chakraborty and Majumder, 1986, Roy and Venkatesh, 2009 a,b, and

Upadhyay et al., 2010). Controversies still persists whether the BIFs in the different

basins are of the same age or not. According to Dunn (1940), Dunn and Dey (1942)

and Sarkar and Saha (1977) all the iron formations of Jharkahand and Orissa belong

to one group. The BIFs belong to different age groups, a view supported by Iyenger

and Murthy (1982), Banerji (1977), Banerjee (1982) and Acharya (1984). Acharya

(1984) is of the view that the BIFs belong to three different sequences. The BIF of

the first sequence extends from Gorumahisani-Badampahar southwards to Nausahi

and Sukinda and then continues eastward to Malayagiri. BIF of the second sequence

is exposed in the Tomka Daitari region, while the BIF of the Noamundi-Jamda-Koira

valley belongs to the youngest as the third sequence. The BIF of second sequence is

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in its turn unconformably overlain by gritty quartzite in the Tomka-Daitari belt; the

latter underlies the BIF of third sequence. There are some differences in the

mineralogy, geochemistry and lithlogical association of the BIFs in the three different

belts (Acharya 1984).

Singhbhum Group

Rock succession lying to the north of the Singhbhum Shear Zone extends in a series

of E-W folds for over 200 km. Sarkar and Saha (1963, 1977) have named the

succession lying to the north of the shear zone as Singhbhum Group. This further

divided in to a lower Chaibasa Formation and upper Dhalbhum Formation. The

Chaibasa Formation consists of mica schist and quartzite affected by lower grade

metamorphism.

Dhanjori Group

The Palaeoproterozoic Dhanjori Formation overlies the Singhbhum Granite and is in

turn overlain by the Chaibasa and Dhalbhum Formations constituting the Singhbhum

Group (Mazumder, 2005). The few km thick, Dhanjori Formation includes lavas in

its upper part, which were dated at 2100 Ma (Roy et al., 2002a). The entire meta-

sedimentary succession thus span than 500 million years of supracrustal

sedimentation history and is described to have suffered from severe thrusting and

multiphase folding and metamorphism. The rocks were thrusted towards the Cratonic

core, along the prominent and laterally extensive semi-circular Singhbhum Shear

Zone (SSZ) which encompasses mainly Dhanjori quartzites and schists and can be

followed for some 200 km along strike and for few km in width. This group consists

of basalt, conglomerate, arkose, quartzite and extensive lava flows. The succession is

unconformably deposited over the Singhbhum Granites and Iron Ore Group

(Mahadevan, 2002). Equivalent volcanic rocks are exposed in the Dalma hills in the

North of Singhbhum Shear Zone known as Dalma lava.

Kolhan Group

The main Kolhan basin intervenes between the IOG of the Noamundi basin and the

Singhbhum Granite (Dunn, 1940). The Proterozoic Kolhan sequence unconformably

overlies the Singhbhum Granite and the Iron Ore Group. The Proterozoic Kolhan

sequence unconformably overlies the Singhbhum Granite and the Iron Ore Group.

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The principal rock types are quartz arenite, local arkose and shale (Mukhopadhyay,

2001).

Newer Dolerites and other intrusives

These are the youngest intrusive bodies within the Singhbhum stratigraphy. These are

in the form of dykes, which are mafic-ultramafic in nature and represent the last

phase of orogenic movement in the region. However, these dykes are mostly found in

the southern Singhbhum and Keonjhar regions. The mafic dykes are most probably of

Neoarchaean age (2.8 Ga; cf. Roy et al., 2004) and strike NE-SW and NW-SE

Geochronological data reveals (Misra, 2006) that the equivalent granite bodies of the

Singhbhum Granite are the Bonai Granite, Nilgiri Granite and Chakradharpur Granite

Gneiss, occurring respectively at the western, southeastern and northern margins of

the Singhbhum Granite (Fig. 4.1b).

Bonai Granite (BG): The porphyritic variety of Bonai granite (Phase-II) intrudes the

IOG and contains large xenolithic blocks of these quartzites and metalavas.

Therefore, the Bonai Granite is younger than the IOG supracrustals and

stratigraphically equivalent to SBG-III. The Bonai granite is separated from the main

Singhbhum Granite batholith by a belt of IOG supracrustals (Jamda-Koira horse-shoe

synclinorium) (Sengupta et al., 1991; Saha, 1994). Bonai granite is of two phases:

phase-I is migmatitic in nature (3369±57 Ma, Pb-Pb WR (Whole -Rock) and occurs

as small enclaves within the more porphyritic and equigranular biotite rich variety of

second phase of Bonai granite (3163±126 Ma,Pb-Pb WR) (Sengupta et

al.,1991,1996). Second phase of Bonai granite is intrusive within IOG quartzite

which is developed along its western margin. Enclaves of IOG quartzites are seen

within Bonai granite south of Darjing area. Bonai granite is intruded by pegmatite,

quartz veins and other basic and ultrabasic rocks. The IOG rocks along the western

margin of Bonai granite are exposed in a series of hills near Gurundia and south of it

and also near Baratangra in BurhaPahar, nearby Bagiyabahal village in Kukia reserve

forest and also north of Darjing near Birtola and in Phuljhari Pahar (Sarkar and Saha,

1992 and Saha, 1994).

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Nilgiri Granite: The Nilgiri Granite (Saha, 1994) forms the southeastern part of the

Singhbhum -Orissa craton, and is separated from the main Singhbhum Granite by a

narrow strip, 3–8 km wide of IOG phyllite and quartzites (Fig.4.1a). The Nilgiri

Granite varies in composition from TTG to granite. The Nilgiri pluton is seen

intruded by the Mayurbhanj Granite (anatectic product of SBG-III) along its margin.

The in-situ Pb-Pb zircon ages for second and third phases of Mayurbhanj granite are

3080±8 Ma and 3092±5 Ma respectively (Misra et al., 1999 in Mishra and Johnson,

2005).

Chakradharpur Granite Gneiss (CGG): The Chakradharpur Granite gneiss is an

isolated body of the Singhbhum Granite and occurs amidst the supracrustal rocks of

the Singhbhum Group (Bandyopadhyay and Sengupta, 1984; Sengupta et al., 1983,

1991) (Fig.4.1b). This granite gneiss forms the basement to the overlying Singhbhum

Group, while its pegmatoid phase intrude both the older gneiss and the enveloping

supracrustals. Geochemically, the older tonalite gneiss of the Chakradharpur Granite

Gneiss is considered equivalent to the SBG-I or SBG-II, whereas the pegmatoid

phase is considered equivalent to younger granite bodies (e.g. Arkasani Granite,

Mayurbhanj) that intrude the Singhbhum Group (Saha, 1994).

Soda Granite: Soda granite is one of the important granitic elements noted along

SSZ. The precise Pb-Pb whole rock four point isochron age of Soda granite pluton is

2220±54 Ma (Sarkar et al., 1985). The 2.22 Ga age has been interpreted as the age of

emplacement/crystallisation of soda granite whereas 1.68-1.63 Ga age is considered

as the reset age of soda granite due to shearing along Singhbhum shear zone and

associated metamorphism (Sarkar et al., 1985).

Dhanjori basin: Another basin unconformably deposited over the Singhbhum

Granites and Iron Ore Group are developed in the NE part of SBG is popularly

known as Dhanjori Group which consists of basal Au-U bearing quartz–pebble

conglomerate (QPC)–quartzites known as Phuljari Formation and the upper Dhanjori

is mafic volcanic dominated represented by quartzite-polymictic conglomerate

interlayered with phyllites and tuffs and extensive lava flows. Equivalent volcanic

rocks are exposed in the Dalma hills in the North of Singhbhum Shear Zone known

as Dalma lava. The Phuljhari Formation is intruded by Mayurbhanj granite

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(Acharyya et al., 2010). Sedimentological and stratigraphic evolution of the Dhanjori

basin was studied by Bhattacharya and Mahapatra (2008). Sunil Kumar et al., (1996)

has recorded chemical ages of detrital zircon grains from QPC between 3.044 to

3.090Ga and suggested that the sedimentary members of Dhanjori Group are likely to

be older than the presently assigned age of 2300Ma.

Volcanic Rocks in SOC: The three major mafic volcanic in SOC are known as

Dalma volcanics, Dhanjori volcanics and Simlipal volcanics. Dalma volcanic occurs

north of SSZ within Singhbhum mobile belt having a length of about 200km and

width of 3-7km with an east-west arcuate trend convex towards north. It represents a

bimodal mafic- felsic volcanic association (Mishra and Johnson, 2005) mainly

rhyolitic tuff (Singh et al., 2010) and highly magnesian ultrabasic lava followed by

another mafic lava separated by pyroclastic rocks (Saha, 1994). Dhanjori volcanic are

mainly mafic and ultramafic tuffs in lower part and tholeiitic basalt in upper part and

minor rhyolitic rocks (Gupta et al., 1985 and Basu, 2001 in Mishra and Johnson,

2005). The simlipal complex is situated at the eastern margin of SOC which overlies

Singhbhum and Nilgiri granites, IOG and Singhbhum Group of metasediments.

Simlipal complex is composed mainly of basal quartz arenite and locally

conglomerate followed by spilitic lava and tuffs in three successive sequence

separated by two thick inter-trappean quartz arenite beds. This sequence is intruded

by Mayurbhanj granite.

The other two prominent undeformed basic volcanics are present along western and

south-western part of SOC known as Malangtoli lava and Jagannathpur lava which

are post- Singhbhum granite in age and overlain by undeformed Kolhan Group or

equivalent sediments showing low grade metamorphism (Saha, 1994). Both are

mostly basaltic andesite in composition (Bose, 2000).

The whole rock Pb-Pb five point isochron data for Dhanjori volcanic is 2794± 210

Ma. A much improved three point Pb-Pb isochron age data was obtained 2858±17

Ma with A five point isochron gives a Sm-Nd age of 2787± 270 Ma for Dhanjori

volcanics(Mishra and Johnson, 2005). Therefore a radiometric age of about 2.8Ga

indicated by both methods has been considered as the formation age of the Dhanjori

volcanic. The whole rock Pb-Pb four point isochron indicated 2250±81 Ma age for

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Jagannathpur volcanic. Since this volcanic rock is nearly un-metamorphosed, this age

can be considered as the formation age for Jaganathpur volcanic and stratigraphically

equivalent Malangtoli volcanics (Mishra and Johnson, 2005).

According to Saha (1994), Bonai granite Phase-I is the basement for IOG quartzite

and Bonai granite phase-II is intrusive within IOG quartzite. Further NW, IOG–

metabasic sequence are overlain unconformably by Archaean sediments and meta-

sediments known as Darjing Group (Mahalik, 1987) which in turn, is overlain

conformably by more calcareous and carbonaceous formations of Gangpur Group of

rocks whose sedimentation age is around 1600 to 1700 based on Pb age of galena

from Sargipalli (Viswakarma and Ulabhaje,1991). The upper part of Birtola Fm

which is the lowest Formation of Darjing Group is intruded by a granitic rock

termed as Tamperkola granite having age of 2.809 Ga (Bandopadhayay, 2001).

Darjing Group : The upper most Darjing Group along the western margin of Bonai

granite is intruded by the 800-900 Ma old Itma and Ekma granite (AMD,1982),

which is the youngest granitic activity recorded in the western part of entire

Singhbhum-Orissa Craton. Based on above field and geochronological data, the age

of QPC-IOG-Metabasic sequence developed along western margin of second phase

of Bonai granite ranges from 3.3Ga to 3.16 Ga and age of the lower most formation

of Darjing Group i.e. Birtola has been placed between 3.16 Ga to 2.8 Ga (Saha,2004).

Another smaller basin further west of Tamperkola granite has been named as Kunjar

Basin after the village name Kunjar located in the basin (Iyenger and Murthy, 1982)

(Fig. 4.1b). This is the youngest sedimentary basin in this region which has been

correlated with Kolhan and Gangpur basin. The general straigraphy of SOC ( after

Saha ,1988) is given in Table 4.1 and chronostratigraphy (after Saha, 1994 and Auge

et al., 2003 in Mondal et al., 2006) is given in Table 4.2.

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Fig.4.1a. Geology of the Singhbhum Craton, India showing locations of Iron Ore Group (IOG) basins with respect to Singhbhum granite (after Saha,1994;Sengupta et al.,1997). Inset map shows generalized geology of the Indian shield with location of Singhbhum Craton ( Mondal et al., 2006).

Fig.4.1b. Redrawn and Modified from Simplified geological map of Singhbhum-Orissa Craton showing different lithounits (after Saha, 1994, Mukhopadhayay et al., 1990) and modified ages of formation( after Misra,2006). Some modifications on distribution of location of Singhbhum Granite-1(SBG-1) is indicated after Ghosh et al., 1996). BG- Bonai granite, DNV- Dhanjori volcanic, IOG- Iron Ore Group, JPV- Jagannathpur volcanic, MBG- Mayurbhanj Granite, MTV- Malantoli volcanic, OMG- Older Metamorphic Group, OMTG- Older Metamorphic Tonalite Gneiss, SBG-1- Singhbum Granite, Phase-I, SBG-II, Singhbhum Granite,Phase-II, SBG-III- Singhbhum Granite, phase-III, SPLV- Simplipal volcano-sedimentary basin.

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Fig.4.2. Generalised stratigraphic column of Singhbhum –Orissa Craton (after Ramakrishnan and Vaidyanathan, 2008 in Meert et al., 2010). Not to scale. Paleoprot. --- Paleoproterozoic.

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Table 4.1: Generalised Chronostratigraphic Succession of the Singhbhum- Orissa

Craton (after Saha et al., 1988) Newer Dolerite dykes and sills C.1600-950 Ma Mayurbhanj Granite C.2100 Ma Gabbro - anorthosite - ultrabasics ~~~~~~~~~~~~~~~~~~~~~~~~ Unconformity ~~~~~~~~~~~~~~~~~~~~~~~~~ Jagannathpur lava Dhanjori - Simlipal lava Dhanjori Group Quartzite conglomerate ~~~~~~~~~~~~~~~~~~~~~~~~~~Unconformity~~~~~~~~~~~~~~~~~~~~~~~~~~~ Singhbhum Granite C. 3100 Ma Mafic lava, tuff, acidic volcanics, Tuffaceous shales, BHJ and BHQ with Iron Ore Group Iron Ores, ferrugenous chert, local dolomite, Quartzite and Sandstone ~~~~~~~~~~~~~~~~~~~~~~~~~~Unconformity ~~~~~~~~~~~~~~~~~~~~~~~~~~ Nilgiri Granite Singhbhum Granite Bonai Granite ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Folding and metamorphism of OMG and OMTG C.3400 - 3500 Ma Older metamorphic tonalite gneiss (OMTG) C.3775 Ma Older metamorphic group (OMG): Pelitic Schist, Quartzite, Para-amphibolite, Ortho-amphibolite C.4000 Ma

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Table 4.2. Chronostratigraphy of Singhbhum Craton (after Saha, 1994 and Auge et al., 2003 in Mondal et al., 2006).

a Saha et al.(1988), b Roy et al.(2005), C Roy et al.(2002), d Mishra et al.(1999),e auge et al.(2003),f Sharma et al. (1994)

Generalized sequence

Zircon Methods

Other Methods

Kolhan Group 2100-2200Maa

Unconformity Dolerite dyke swarm Newer dolerite suite 950-2500 Maa,b

Dhanjori- Dalma-Simlipal-Jagnathpur-Malangtoli belt: PMB igneous suites and PMB sedimentary sequence

Proterozoic Mobile Belts

(PMB)

2072Mac

Metasediments with mafic sills

Singhbhum Group

2300-2400Maa

Unconformity

Mayurbhanj Granite SBG-B 3.1Ga d

Singhbhum Granite Type-B SBG-B 3.1Ga a

Iron Ore Group igneous and sedimentary sequence: IOG igneous suites(Ultramafic-mafic plutonic suites eg. Nuasahi-Sukinda-Jojuhatu–ultramafic suites;gabbro-anorthosite-diorite mafic suite; ultramafic-mafix volcanic suite;eg. Komatiitatites and high Mg-basalts in Gorumahisani-Badampahar, Tomka-Daitari and Jamda-Koira belts, Felsic igneous suites) IOG sedimentary sequence

Iron Ore Group(IOG)

3121±3Mae age of zircon from gabbro suites ,Nuasahi breecia zone

3205± 280 Mae Sm-Nd age of gabbroic suites from Nuasahi massif.

Singhbhum Granite TypeA SBG A 3328±7Ma d 3.3Ga a Older Metamorphic Tonalite Gneiss

OMTG Age clustering at 3.4 and 3.2Gad

3288±35Maf Sm-Nd isochron age with OMG

Older Metamorphic Group OMG Age clustering at 3.55, 3.4 and 3.2Ga d

3305±60 Maf Sm-Nd isochron age.

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4.3. Iron Ore Group (IOG)

The Iron Ore Group (IOG), consisting of banded iron formation (BIF) and

metasedimentary and metavolcanic rocks, occurs in the western, eastern, and

southern flanks of the Singhbum Granite massif. The BIF’s are inter-banded with

lavas and pyroclastics, and even basic volcanics inter-bedded with rhyodacite and

trachytic volcaniclastics (Banerjee, 1982). Along the eastern border zone of the

Singhbhum Granite the BIF is intruded by a group of un-metamorphosed gabbro,

norite, and anorthosite. The IOG rocks in the Singhbhum Craton occur either as

linear narrow intra- cratonic belts or as more extensive peripheral bodies. Recently

iron-ore characterization from Jilling and Joda area in Koira- Noamundi iron ore

basin has been described by Roy et al. (2007) and Upadhayay et al. (2010)

respectively. Eriksson et al., 2006 (Meert et al., 2010) has divided IOG into an Older

and a Younger section, with similar compositions but differing ages. The Older IOG

is comprised of clastic sedimentary rocks formed in a shallow marine setting along

with syn-depositional volcanic rocks that together suggest large scale rifting.

The Older IOG formed prior to the intrusion of the Singhbhum Granite and was

thought to have an age range between 3.3 and 3.1 Ga, based solely on associations to

nearby rocks and available ages for related rocks (Eriksson et al., 2006; Mondal et al.,

2007 in Meert et al., 2010). A recent geochronologic study of the IOG yielded an age

of 3506.8 ± 2.3 Ma for a dacitic lava (Mukhopadhyay et al., 2008) and confirms that

the IOG formed just prior to, or slightly before the earliest Singhbhum Granites.

Detrital zircons found in the TTG suite may have been derived from the IOG.

The Younger Iron Ore Group formed after the Singhbhum Granite cratonization

event and has a suggested depositional age >2.55 and <3.0 Ga. It is comprised of

shallow or shelf marine greenstone deposits with banded iron formation (Eriksson et

al., 2006 in Meert et al., 2010). The IOG is believed to have deposited on the OMG.

Three major basins of IOG are recognized along the fringes of the ACCR. These are:

(1) Gorumhasani-Badampahar basin in the eastern part, (2) the Tomka-Daiteri

basin along the southern part, and (3) the West Singhbhum-Keonjhar basin or the

Jamda-Koira basin in the western flank of the SOC. The basin (3) contains the most

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spectacular occurrence of the BIF in the Jamda-Koira valley to the west, where its

outcrop define a major horse-shoe shaped syncline.

Sarkar and Saha (1983) place these three Archaean basins in one stratigraphic group,

termed the IOG, as interconnected basin, while Iyengar and Murthy (1982) believe

that the Gorumahisani basin belongs to much older orogenic cycle during which the

IOG- (3) welded to the Archaean Craton. Banerji (1974) also suggests that the

Noamundi basin of IOG- (3) is stratigraphically distinct. He recognized two cycles of

iron formations, an older Gorumahisani Group and a younger Iron-ore Group,

separated by the Jagannathpur volcanic flows (Banerji, 1974). Dating of the intrusive

granite phase-III (3.17 ± 0.1 Ga; Saha, 1994) of the Singhbhum Granite into the IOG

suggests that the IOG are older than 3.1 Ga.

The major, “West Singhbhum-Keonjhar” basin is exposed on the western flank of

SBG, extending from Chakradharpur to Malangtoli known as the “Noamundi-Jamda-

Koira” valley which extends to a strike length of 100 km in NNE-SSW direction with

widths varying from 20 to 30 km. The eastern “Gorumahisani-Badampahar” basin

along the eastern border of SBG, extending from Jamshedpur to Nausahi. The

southern “Daitari Palahara” basin in southern fringes of the Craton also known as

“Sukinda Valley” (Fig.4.1b). In all the three principal basins, the supracrustal

sequence starts with sandstone-conglomerate at the base followed upward by

ferruginous shales, tuffs, lavas and Banded Iron Formation (BIF) (Murthy and

Acharyya, 1975; Chakraborty and Majumder, 1986). A major controversial issue is

whether the BIFs in the different basins are of the same age or not. According to

Dunn and Dey (1942) and Sarkar and Saha (1977), all the iron formations of

Jharkhand and Orissa belong to one group. The BIFs belong to different age groups, a

view supported by Iyenger and Murthy (1982), Banerji (1977), Banerjee (1982) and

Acharyya (1984). Acharyya (1984) is of the view that the BIFs belong to three

different sequences. The BIF of the first sequence extends from Gorumahisani-

Badampahar southwards to Nausahi and Sukinda and then continues eastward to

Malayagiri.

BIF of the second sequence is exposed in the Tomka Daitari region, while the BIF of

the Noamundi- Jamda- Koira valley belongs to the youngest as the third sequence.

The BIF of second sequence is in turn unconformably overlain by gritty quartzite in

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the Tomka- Daitari belt; the latter underlies the BIF of third sequence. However, field

relations do not prove the above relations (Sarkar et al., 1990). There are some

differences in the mineralogy, geochemistry and lithlogical association of the BIFs in

the three different belts (Acharyya, 1984). Details of west Singhbhum IOG basin is

the area of present research work. The area of study is confined to west of main Koira

IOG basin along western margin of Bonai granite pluton.

Table 4.3: Ages of different rocks in Singhbhum-Orissa Craton, Eastern India

Itma and Ekma granite(intrusive within Gangpur Group)

800-900 Ma AMD, 1982

Sushina nepheline syenite body ages from the SG complex

922.4 ± 10.4 Ma, (SHRIMP) Reddy et al., 2008 in Meert et al. 2010

Gangpur Group sedimentation age

1600 to 1700 based on Pb age of galena from Sargipalli

Viswakarma and Ulabhaje, 1991

Soda granite 1677±11 Ma ; 1633±6Ma The five point whole rock Rb-Sr age considered as the reset age of soda granite due to shearing along Singhbhum shear zone and associated metamorphism

Sarkar et al., 1985

Jagannathpur and equivalent Malangtoli volcanic

2250 ± 81 WR Pb-Pb four point isochron

Mishra and Johnson, 2005

Bamra granite (SE of Bamra 2738±28Ma Chaki et al., 2005 Tamperkola granite

2809 Ma 2746 ±144 Ma

Bandopadhayay, 2001 Chaki et al., 2005

Rengali-Raimal charnockites in Palla-Lhara region

2.74Rb-Sr WR isochron age Sarkar et. al., 2000

Dhanjori Gp (Phuljari Fm.) detrital zircon grains from QPC

chemical ages between 3.044 to 3.09 Ga

Sunil Kumar et al., 1996

Mayurbhanj granite (Ph-1 and II)

3080±8 Ma and 3092±5 Ma (in-situ Pb-Pb zircon ages)

Misra et al., 1999 in Mishra and Johnson, 2005.

Bonai granite, Phase-II 3163±126Ma, Pb-Pb WR Sengupta et al., 1991,1996

Bonai granite, Phase-I 3369±57Ma, Pb-Pb WR Sengupta et al.,1991,1996

SBG phase-II intrusive into the IOG

3.17 ± 0.1 Ga Saha, 1994

SBG phase-II 3298 ± 63 Ma Pb-Pb whole rock isochron date

Ghosh et al., 1996.

SBG phase-I 3442 ± 26 Ma Pb-Pb whole rock isochron date

Ghosh et al., 1996.

OMTG 3378±98Ma, Pb-Pb date Moorbath et al., 1986

OMTG 3280±130Ma, Rb-Sr whole-rock isochron date

Moorbath et al., 1986.

OMTG 3448± 19 Ma and 3527± 17Ma, U-Pb age, zircon grain separate

Acharyya et al., 2010a).

Daitari-Tomka IOG basins 3507+ 2.3Ma, SHRIMP age of zircon

Mukhopadhayay et al., 2008

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4.4. Geological Setting and Stratigraphy of Study Area

The study area forms a part of Survey of India toposheet no. 73C/13 which is located

between Rourkela in north and Bonaigarh in South in parts of Sundargarh district of

Orissa, eastern India (Fig.4.3 & 4.4). Geologically, it is bounded in South by Bonai

granite and in north by Gangpur Group of rocks. Review of literature indicates that

not much work has been done in this sector of Precambrian rocks. The area lying

south of Gangpur were mapped first and named as Iron Ore Series by Jones (1934)

and later by Krishnan (1937). Murty (1955) who first mapped the area in Toposheet

No. 73C/13 and parts of 73C/14 distinguished three groups of sedimentaries, viz. Iron

Ore Series, Dhanjori Series and Kolhan Series. Prasada Rao et al. (1964) mapped this

area and grouped them into sequence I to VI. Prasada Rao et al. (1964), Kanungo and

Mahalik (1967) considered these meta-sedimentary sequence different from Iron Ore

Group. Sarkar, Saha and Miller (1969) correlated these metasediments with the

Dhalbhum Formation of Singhbhum Group.

Iynegar and Murthy (1980) classified these rocks along with the Iron Formation of

Koira area under Koira Group. Krishnan (1937) considered the Raghunathpali

conglomerate as the southern limit of “Gangpur Series” and was of the opinion that

the rocks lying south of Raghunathpali conglomerate were younger to Gangpur

series.

Fig.4.3.Geological map of Singhbum –Orissa Craton showing different IOG basins. Redrawn from Saha, 1994.

Fig.4.4.Geological map of Bonai granite pluton showing enclaves of Bonai granite phase-I and radioactive QPC along its margin. Bracket area indicate study area along its western margin. Redrawn from (Sengupta et al. 1991).

99

Kanungo and Mahalik (1967) classified Gangpur structure as a regional re-folded

antiform plunging east. Palaeocurrent data analysis by Kanungo and Mahalik (1970)

revealed sedimentary transport for Gangpur basin from the South. Ramachandran and

Raju (1982) worked on structure and stratigraphy of the rocks in the southern

Gangpur- Bonaigarh region and identified four group of rocks and classified them

Group-I, II,III and IV. Group I and II are equivalent to sequence I and V of Prasada

Rao et al. (1964) while Group III includes the sequence VI of Prasada Rao et al.

(1964) and the rocks south of Raghunathpali conglomerate under Iron-Ore Series of

Krishnan (1937).Group-IV refers to Gangpur Group.

Ramachandran and Raju (1982) named these groups as the basal Iron-Ore Group

(Group-I), the middle Dhanjori Group ( Group-II) and uppermost Gangpur Group

which includes lower carbon bearing phyllite, quartzite and garnet-staurolite schist

(Group-III) and upper Raghunathpalli conglomerate, carbon-phyllite and quartzite

and dolomite-limestone-marble (Group-IV)( Table. 4.4).

IOG rocks are intruded by Bonai granite whereas the overlying Dhanjori Group of

rocks are intruded by Tamperkola granite. According to Ramachandran and Raju

(1982),the IOG rocks along western margin of Bonai granite are represented by

fuchsite quartzite, mica-schist, chlorite schist and associated metavolcanics and

ultrabasic/basic intrusive having general NE-SW strike. The IOG quartzites are found

as enclaves within Bonai granite south of Darjing village. The western margin of

Bonai granite near Darjing is faulted.

IOG rocks are overlain unconformably by arenaceous facies whose unconformity is

defined by a polymictic conglomerate having boulders of biotite and hornblende

granite similar to Bonai granite and pebbles of hematite jasper and fuchsite quartzite,

thus confirming the younger age of Group-II rocks compared to Group-I, IOG rocks

and Bonai granite. Tamperkola granite is intrusive within both IOG rocks and

overlying Dhanjori Group of rocks (Ramachandran and Raju, 1982). Recent work by

Mahalik (1987) classified the unclassified rocks lying between Bonai granite and Iron

Ore Group in South and Gangpur Group in North into Darjing Group comprising of

three well defined Formations namely basal Birtola Formation, middle Kumakela

Formation and upper Jalda Formation.

100

The youngest units of Darjing Group are overlain by the Raghunathpali conglomerate

which is the basal part of the Gangpur Group. The rocks of Darjing Group are akin to

that of Gangpur Group but are different from rocks of Iron-Ore Group (Table. 4.4).

Later, Sarkar and Saha (1992) carried out aerial-photo-interpretation of Bonai granite

and associated supracrustals in the area and concluded that IOG rocks are intruded by

porphyritic variety of Bonai granite of phase-II and thus IOG are older than phase II

of Bonai granite but younger than Bonai granite-phase-I.

The stratigraphic sequence of the area worked out by Sarkar and Saha (1992) is given

in Table. 4.5. Naik (2001) revised the stratigraphy of the supracrustals lying western

part of Bonai granite and eastern part of Tamperkola granite and classified them

under “Chandiposh Group”. Naik (2001) has divided the entire rock sequence

developed along western margin of Bonai granite into six formations, the lowermost

Lahunipara Formation which occurs as enclave within grey granite Phase-I of Bonai

granite complex (BGC) of Bonai granite.

The other formations are lower Gurundia Formation followed by Nalghati Formation,

Birtola Formation, Madhupur Formation, Soldega Formation and uppermost

Bhaliyadihi Formation which is intruded by 3163± 126 Ma old grey granite of BGC

and Tamperkola granite of 2809± 12 Ma age and other ultrabasic and dolerite dykes.

The stratigraphic succession of Chandiposh Group is given in Table.4.6.

The whole Chandiposh Group is unconformably overlain by Tamra Formation of

Gangpur Group of 1664 Ma age. Based on available age data of basal Bonai granite-

ph-I and intrusive Tamperkola granite, the Chandiposh Group range in age from 3300

Ma to 2809 Ma age window i.e. Late Archean to Mid-Proterozoic age.

Recently Saha et al. (2004) has given an account of geochemical and petrological

aspects and Nd-isotopic analysis of Archean sandstones from Western margin of

Bonai granite forming part of Birtola Formation. The work by Saha et al. (2004)

indicated that the sandstones of Birtola were derived from amphibolites and tonalities

of Eastern Indian Craton. The Nb-Ta depletion in sandstones were noted due to the

presence of protolith of amphibolite and tonalities. Ce/Pb ratio less than 4.0 in Birtola

sandstone, the present day value in continental crust has been explained due to

richness of Archaean crust in Pb having a much lower Ce/Pb ratio than present day

101

mantle. Sm-Nd model ages of the sandstones with respect to the depleted

mantle(TDM) range from 3.6 to 4.0Ga clustering around higher than 3.3 Ga old

crystallisation ages of the tonalities and amphibolites. These higher model ages

suggest the presence of an older 4.0 Ga crustal component in the Craton.

The basement in the study area is represented by Archean Bonai granite. It occupies a

triangular area covering over 700Sq.Km in the extreme west of the Singhbhum-

Orissa Iron-Ore craton (Saha, 1994). It is bordered on the NW and North by IOG

quartzites, metalavas and low grade schists, to the east by the IOG rocks of western

flank of famous Jamda-Koira horse-shoe synclinorium. According to Sarkar and Saha

(1992), IOG rocks are older than the main porphyritic phase of Bonai granite

complex but may be younger than the tonalitic migmatite. It is possible that the IOG

rocks were deposited on an older tonalite-amphibolite basement. The Bonai granite is

separated from the main Singhbhum Granite batholith by a belt of IOG supracrustals

(Jamda-Koira horse-shoe synclinorium) (Sengupta et al., 1991; Saha, 1994).

4.5. Review of Geochronology Data from Western Wargin of Bonai Granite Very little work has been done in this part of Orissa. The available geochronological

data along western margin of Bonai granite are meagre. Bonai granite has been dated

by Sengupta et al.(1991) However, Pb isotopic data for porphyritic and equigranular

suites of Bonai granite indicates isochron ages of 3163±126 Ma The xenolithic

tonalities within Bonai granite gave isochron age of 3369±57 Ma The xenolithic

tonalite has fairly close resemblance with the OMTG. The 3369 Ma Pb-Pb age of the

highly deformed xenolithic tonalite component of Bonai granite is also likely to

represent the age of metamorphism (Sengupta et al., 1991).

Thus the age of Bonai granite ranges from 3369±57 Ma to 3163±126 Ma respectively

for phase-I and phase-II. The age of Tamperkola granite occurring west of Bonai

granite and also west of IOG sequence has yielded 2809 ± 12 Ma by in situ zircon 207Pb/206Pb ages (Bandyopadhyay et al., 2001)and 2746±46 Ma by Rb-Sr whole rock

age (Chaki et al. 2005).

A regional granite magmatic event has been active during about 2.8 Ga along the

periphery of the Singhbhum Craton (Acharyya et al., 2010a). Detrital zircons from

QPC belonging to the Phuljhari Formation in Dhanjori basin have yielded oldest

102

chemical ages of 3.09–3.04 Ga thus fixing the upper age limit of the formation

(Acharyya et al., 2010b).

According to Acharyya et al. (2010b), detrital Au–U-pyrite bearing quartz-pebble-

conglomerate in the Phuljhari Formation in Dhanjori Group appears to mark the

Neoarchean sedimentation at the margin of the peneplained craton. Similarly, the

basement nature of Bonai granite phase-II of 3.16Ga for Birtola Formation and

intrusive nature of Tamperkola granite in upper part of Birtola puts Birtola Formation

age between 3.16 Ga and 2.8 Ga. If we consider intrusive nature of Bonai granite

phase-II in IOG sequence and basement nature of Bonai granite phase-I for IOG, the

age of QPC-IOG sequence can be considered between 3.3Ga and 3.16Ga.

Table 4.4: Straigraphic succession along western margin of Bonai granite (after

Ramachandran and Raju, 1982).

SN GROUP LITHOUNITS GROUP-III AND IV GANGPUR Dolomite-Marble

Carbon-Phyllite Raghunathpalli conglomerate

garnet-staurolite schist Carbon phyllite and quartzite,

-------- UNCONFORMITY-------- vein quartz

Tamperkola granite Ferruginous shale, lava flows and tuffs

Conglomeratic quartzite Meta lava and chlorite schist

quartzite and quartz-sericite schist Chloritic conglomerate

Sericite-chlorite phyllite, greywacke and grit

Conglomerate ------------UNCONFORMITY-----------

Quartz reef Bonai granite

Volcanic lava flows Chlorite-schist and amphibolite

Fuchsite quartzite, quartz-schist and mica-schist

Base not seen

GROUP-II

DHANJHORI

GROUP-I IRON-ORE (IOG)

103

Table 4.5: Regional Stratigraphic Succession of the area (after Mahalik, 1987)

Table 4.6: Stratigraphic sequence along Western Margin of Bonai granite (Sarkar and Saha, 1992)

GROUPS FORMATIONS ROCK TYPES

GANGPUR GROUP

Raghunathpalli

conglomerate

------------Disconformity-----

Calcareous and carbonaceous rocks Conglomerate and Quartzites

DARJING GROUP Quartz vein Basic and Ultrabasic dykes Jalda Formation

Kumakela Formation

Birtola Formation

Disconformity

Garnet and staurolite bearing schists and minor quartzite Carbonaceous quartzite, phyllite

and schist

Feldspathic quartzites and

conglomerates

Greenschist conglomerate and

greenish quartzites

Basal conglomerates and quartzites

BONAI GRANITE-II Intrusive in IOG quartzite Biotite Granites

IRON ORE GROUP (IOG) (Noamundi/ Koira group)

Metabasic Gurundia Quartzite

Metabasic Fuchsite Quartzites

BONAI GRANITE-I Basement Migmatitic as enclave in Granite-II

Group Formation Litology

Feldspathic quartzites and conglomerates

Green-schist conglomerate and greenish quartzites

Darjing Group Birtola Quartzites. Basal polymictic conglomerates

-----------------------unconformity---------------------

Iron Ore Group(IOG)

Dolerite dykes, basic sills, ultrabasics, aplite and pegmatitic veins.

Bonai Granite, Phase-II

Quartzite and metabasic lavas.

Basement Bonai Granite I (Migmatitic tonalite)

Mafic crust (folded and migmatised amphibolite enclaves)

104

Table 4.7: The stratigraphic sequence along Western Margin of Bonai granite (after Naik, 2001)

AGE (Ma) GROUP FORMATIONS LITHOUNITS

1664 GANGPUR TAMRA Carbon-phyllite ( Kumakela) -------Un-----------

↓ 2809±12

Ma

3163±126

Ma MID TO LATE

ARCHEAN AGE

↑

CHANDIPOSH

GROUP

Ultrabasic,dolerite dykes, Tamperkola granite Grey granite of BGC ( intrusive)

BHALIYADIHI Grey tuffite,schist,Milky wite quartzite and chert Amygdaloidal and massive volcanics BHJ and BHQ pebble bearing conglomerate

SOLDEGA Thick bedded quartzite with pebbly horizon Argillaceous schist Thick bedded quartzite with pebbly horizon with cross-bedding

MADHUPUR Purple tuffite and volcanic,Quartzite with ripple marks and cross-bedding Beds and lenses of green schist quartzite and conglomerate

BIRTOLA Brown colour quartzite and argillite Lodhani massive and giant cross-bedded quartzite Pink phyllite Oligomictic Siyalkudar conglomerate

NALGHATI Khandamuni schist and quartzite Bagiyabahal boulder oligomictic conglomerate

GURUNDIA Cross-bedded Sinkrikhol / Bagiyabahal greenish quartzite Baratangra quartzite oligomictic conglomerate at base

LAHUNIPARA OCCURS AS ENCLAVE WITHIN GREY GRANITE OF BGC (PHASE-II)

Different types of quartzite(feldspathic, chloritic and cross-bedded quartzite) and biotite and chlorite schist

3300 Ma BONAI GRANITE

PHASE-I OF BGC

105

4.6. Metamorphism in the Study Area According to Ramachandran and Raju, 1982, the rocks belonging to Gp-I and Gp-II

have undergone low grade of regional metamorphism, i.e. Greenschist facies

metamorphism. In Gp-III, the grade of metamorphism is Greenschist facies in the

basal part as indicated by the presence of rocks like slates and phyllites containing

chlorite and sericite minerals. In the upper part, metamorphic grade increases to

Almandine-amphibolite facies as indicated by presence of assemblages like quartz-

almandine-biotite-muscovite in mica schist and quartz-calcite-tremolite-actinolite-

diopside- scapolite- sphene in the marbles.

According to Mahalik (1987), the rocks lying between Gangpur and Bonai granite

have undergone different variety of metamorphism, very weakly metamorphosed in

the southern basal part to the medium grade in the upper horizons. This effect is well

observed in the northern part in Jalda formation where the rocks have been

metamorphosed upto staurolite grade.

106

Table 4.8: Stratigraphic Succession along Western Margin of Bonai Granite

(modified after Sarkar and Saha,1992)

Gangpur Group -------------------------------------------------Disconformity-----------------------------------

Darjing Group

------Polymictic conglomerate--------

Bonai Granite, Phase-II (Porphyritic)

IOG fuchsite quartzite

Quartz-pebble conglomerate (QPC)

--------------------- Faulted and sheared contact---------------

Bonai Granite , Phase-I (Migmatitic)

107

4.7 Geophysical data of Singhbhum-Orissa Craton:

The Digitized Gravity Model (DGM) of the Bouguer anomaly map of Singhbhum –

Orissa Craton and its surroundings have been done by Pal et al., (2006) using GIS

techniques. Their study brought to light several gravity highs and lows which bear a

strong correlation with the surface geology. Eight (H1-H8) gravitional highs in the

present study have been identified (Figs. 4.5 and 4.6). Details of gravity highs over

the study area, area covering gravity high, Magnitude near Gravity High (mgal) and

their Geological Attribution are given in Table.4.8. Aspect lineaments superimposed

over DGM and geology of the study area is shown in Fig.4.7.

Table. 4.9: Details of gravity highs over the study area Pal et al., (2006).

Gravity High

Area covering gravity high

Magnitude (milligal)

Geological Attributes

H-1 1255 -2.6007 IOG sediments

H-2 1098 3.6767 Singhbhum Group of rocks

H-3 1562 -1.3085 Rocks of Dalma volcanics

H-4 188 -7.0602 Pelitic enclaves and Prophyritic member of CGG

H-5 842 -4.3413 Rocks of Mayurbanj granite and Dhanjori-Simlipal-Jagannathpur lavas

H-6 714 -0.9967 Simlipal Basin consisting of volcanics, quartzite, and conglomerates in analternating sequence

H-7 898 -0.6683 Nilgiri Granite, IOG and Alluvium

tertiaries

H-8 2043 -4.5329 Pala Lahara Gneiss and IOG

sediments

108

Fig.4.5. Digital Gravity Model (DGM) generated from Bouguer gravity anomaly (after Verma, Sharma and Mukhopadhyay, 1984) over SSZ and its surroundings.

Fig. 4.6. 3D perspective view of Bouguer gravity field as generated from DGM using ARCGIS system (after Verma, Sharma and Mukhopadhyay, 1984)

109

4.8. Revised Stratigraphy and Position of QPC

In Sundargarh district of Orissa also, not much work have been carried out for

uranium exploration. Considering the similarities in geological setting between

Karnataka and Singhbhum Cratons and the time bound and spatial characters of such

rock types, surveys were taken up to examine the basal members of the Early

Precambrian supracrustals of the Singhbhum-North Orissa craton of Eastern India.

These efforts led to the discovery of uranium mineralization in the quartz-pebble

conglomerates of Iron Ore Group (IOG), Gorumahisani- Badampahar and Dhanjori

Basins. Reconnaissance radiometric surveys during 1985-1998 in the Late Archean

Koira-Noamundi Iron Ore Basin in Sundergarh district, Orissa helped in the

discovery of radioactive QPC occurrences at Okharshila, Bolanda, Sayamba and

Taladihi, along the eastern margin of BGP and near Baratangra and Balisura on the

Fig. 4.7. Aspect lineaments superimposed over DGM and geology of the study area.

110

western margin of BGP. The second phase of exploration commenced in the field

season 2004-05 by AMD.

Semi- detailed and later on detailed investigation in 2005-06 by Kumar et al.(2006)

brought to light new radioactive QPC occurrences at Birtola, Phuljhori Pahar and

Bagiyabahal on the western margin of the BGP in Sundargarh district of Orissa. This

is the area where research work is under progress to characterise these QPC

occurrences in parts of Sundargarh district of Orissa in Eastern India.

With a view to characterize these QPC occurrences, detailed mapping on 1:1000

scales followed by sampling of QPC and associated quartzites and their chemical

analysis have been taken up in the area. Geochemical work like major and minor

elemental analysis, REE analysis, mineral analysis, SEM-EDS and economic

potential of QPC-quartzite sequence from U-Th-Au-Ag-REE–PGE are lacking.

Although geochronological data on BGP is available, whole rock dating as well as

mineral dating of QPC- quartzite sequence are not available.

Although several workers (Prasada Rao et. at.1964, Ramachandran and Raju, 1982,

Mahalik, 1987 and Naik, 2001) have workout the stratigraphic sequence of the area

between Bonai granite and Gangpur Group, but none have described the presence of

Quartz-pebble conglomerates. Presence of two QPC occurrences and their radioactive

nature, one from Baratangra and other from north of Balisura village in Phuljhori

Pahar has been dealt by Saxena et.al (1994) from western margin of Bonai granite.

Naik (2001) has described the presence of oligomictic conglomerate from Baratangra

area but has not given the exact position of this conglomerate whether it is

intraformational or basal. Later work by Kumar and Birua, 2005 and Kumar and

Pande, 2006 helped in the delineation of several new QPC occurrences NE of

Baratangra near Bagiyabahal, near Birtola village and atop of Phuljori Pahar located

north of Darjing; all located between Baratangra and Balisura over a strike length of

about 8 to 10 km. intermittently along western margin of Bonai granite.

Closer examination of these QPC and their detailed mapping on 1:1000 scale

indicated that all these QPC occurrences are near basal to interbedded in character,

111

generally located at the base of IOG rocks represented along western margin by green

coloured fuchsitic quartzite and associated metabasic.

Although, Saha (1994) in the stratigraphic sequence along western margin has shown

that the quartzites in the area are older than second phase of Bonai granite but

younger than first phase migmatitic variety of Bonai granite. Further Saha (1994),

Raju and Ramachandran (1992) have also shown that the second phase of Bonai

granite is intrusive into IOG sequence. But during the field traverses nowhere

intrusive nature of Bonai granite into IOG rocks along western margin of Bonai

granite could be seen.

Field traverses along Baratangra, right bank of Brahmni River near Bagiyabahal

village and also about 1km north of Balisura in Phuljhori Pahar have indicated that

QPCs are overlain by quartzites and metabasic and underlain by thick soil cover. But

at a distance of hardly 50 m south of QPC exposures, Bonai granites are exposed. No

other rock types were noted in the soil covered zone between Bonai granite and QPC-

quartzite sequence, thus indicating the basement nature of Bonai granite in the area

above which QPC-quartzite sequences have been deposited.

However, in order to prove the basement nature of Bonai granite phase II for QPC-

quartzite sequence with certainty, geochronological data on detrital grains in both

QPC and quartzites are required. The comparative petrographic and geochemical

studies of quartzites occurring as enclave within Bonai granite phase-II and quartzites

along western margin of BGP phase-II can reveal the real picture of the status of the

both quartzites.

Thus, the stratigraphy of the area can be revised as follow (Table.4.9). Thus, from the

field observations, it is clear that IOG equivalent rocks were deposited over the Bonai

granite phase-I. QPC-IOG quartzites show faulted and sheared contact with Bonai

granite of phase-II. IOG rocks along western margin of Bonai granite are represented

here by QPC-quartzite and metabasic sequence and not only by quartzites- metabasic

as shown by earlier workers (Saha, 1994; Raju and Ramachandran, 1982, Naik,

2001).

112

Sarkar and Saha (1992) classified arenaceous and metavolcanic units along the

margin of Bonai granite in Koira-Noamundi basin into the lowermost part of IOG

and opine that they form a northeasterly plunging anticline in southwest. They also

noted many enclaves of these rocks in the BGP. In the arenaceous units, oligomictic

uraniferous quartz-pebble conglomerates (QPC) bands are reported (Mishra et al.,

1997). In the study area, lowermost part of IOG rocks are present as lenses and thin

bands consisting of lower fuchsite quartzites, quartz-schists and QPC and an upper

metavolcanics at places. These rocks are referred either as IOG, Gurundia quartzites

or equivalents of Badampahar Group. All the workers favour the view that these

constitute the oldest rock sequence in the area. QPC are noted at Balisura area in

these units (Bhattacharya, 1995 in Chaki et al., 2005).The geology of the area right

from basal BGP to QPC-IOG quartzite sequence along western margin of BGP is

discussed below:

Table 4.10: Local Stratigraphic sequence (modified after Sarkar and Saha, 1994; Kumar et al., 2011).

FORMATION/GROUP LITHOUNITS

DARJING GROUP

(BIRTOLA

FORMATION)

Feldspathic quartzites and conglomerates

Greenschist conglomerate and greenish quartzites

Basal polymictic conglomerates and quartzites.

-----------------UNCONFORMITY-----------------------------

IRON ORE GROUP

( IOG)

Quartzite and metabasic lavas.

Quartz-Pebble Conglomerate (QPC)

-----------------Faulted and sheared-----------------------------

BONAI GRANITE Dolerite dykes, basic sills, ultrabasics, aplite and pegmatitic

veins.

Bonai Granite II (Potassic porphyritic granite)

Older quartzites as enclave in granite-II

Bonai Granite,phase- I (Migmatitic tonalite) as enclave in

Bonai granite-II

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Fig.4.9. Geological map of study area between Gurundia and Phuljhori Pahar, Sundargarh district, Orissa (Kumar et al., 2009).

Fig.4.10.E-W trending Phuljhori Pahar having QPC and quartzite. Soil covered area is Bonai granite east of Darjing. NH-23 passes from this area.

Fig. 4.8. Satellite imagery of a part of western margin of Bonai Granite Pluton (from Google).

Phuljhori Pahar Brahmni R.

Bagiyabahal

Bonai granite with basic/ intrusive

Birtola

Bonai granite (Soil covered)

Phuljhori Pahar

NH-23

To Rourkela

To Bonai

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The different lithounits encountered in the study area are described below:

4.8.1. Bonai granite

Bonai granite forms the basement of the overlying metasedimentary sequence along

its western margin from Bonaigarh in the south to Gangpur in the north in parts of

Sundargarh district of Orissa. Bonai granite is a complex body and have been

grouped into two based on its age by Sengupta et al, 1996. The older phase of Bonai

granite-I is occurring as enclave within Bonai granite-II. Phase-I granite is migmatitic

in nature with bands of dark colour minerals and light colour minerals (Fig.4.11).

Most of the part in the area is occupied by Bonai granite of phase-II which is

generally biotite rich in nature (Fig.4.12). They are generally pink to grey coloured,

medium grained, equigranular to porphyritic and comprising mainly quartz, potash

feldspar, plagioclase and biotite and minor muscovite.

They are best exposed south of Darjing village, in river section near Birtola village,

1km north of Balisura village, near Bhaludungri village and south of Baratangra

village in a nala cutting, west of Bagiyabahal village along right bank of Brahmni

river and eastern most part of Bagiyabahal near Tikiyatpalli in toposheet no. 73 C/13.

The Bonai granite phase-II is traversed by basic/ ultrabasic bodies and also by

pegmatitic body at number of places which is clearly visible in satellite imagery

(Fig.4.8). Phase-I is the basement for QPC-quartzite sequence in the area.

4.8.2. IRON ORE GROUP (IOG) QUARTZITE:

IOG quartzites are well exposed in series of hills south of Gurundia and also north

and south-east of Darjing village. The quartzites are greenish to whitish, hard and

compact, well foliated having NE-SW to E-W trend similar to quartzites exposed in

the main IOG Koira basin. Based on the tectonic trend, the quartzite in the area has

been correlated with quartzites of main IOG basin of Koira-Noamundi area (Saha,

1994). These quartzites are locally named as Gurundia quartzites. The quartzites are

generally sheared, folded and show small-scale cross-bedding at places (Fig.4.13,

4.14, 4.15, 4.16). Colour banding is also noted in the quartzites near Birtola village.

The bedding shows variation in strike from NE-SW to E-W with 53°-85° northwest

to northerly dips. Quartzites are overlain by metabasic.

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Fig.4.13.Cross-bedding in IOG quartzite, near Birtola village, Sundergarh dist, Orissa.

Fig.4.14. Steep dips in IOG quartzite, Birtola, near Birtola village, Sundergarh dist, Orissa.

Fig.4.15. Colour banding and folding in IOG quartzite, Birtola, near Birtola village, Sundergarh dist, Orissa.

Fig.4.11. Bonai granite, phase-I (Migmatite), Bonaigarh, Sundergarh district,Orissa.

Fig.4.12.Bonai Granite, phase-II (Porphyritic), 50m south of Bagiyabahal village, Sundergarh district, Orissa.

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At places, conglomerate lenses are also noted interbedded with these quartzites, but

most of the places, the sequence starts with conglomerate.

4.8.3. Quartz-Pebble Conglomerates (QPC)

Geological mapping and radiometric investigations helped in identification and

delineation of several Quartz-pebble conglomerate (QPC) occurrences nearby

Bagiyabahal, Birtola and Phuljhori Pahar of varying dimensions from SW to NE

along western margin of Bonai granite. The sequence of IOG rocks starts with

conglomerate at the base followed by quartzites and metabasics along western margin

of Bonai granite complex. These conglomerates occur as lensoidal body with variable

dimensions either as basal just above Bonai granite or as interbedded with IOG

quartzites. The conglomerate are oligomictic in nature and contains only pebbles of

white vein quartz and few ash grey colour smoky quartz, hence named as quartz-

pebble conglomerates. They are well exposed near Baratangra, Bagiyabahal village

and its environs, near Birtola village and 500m east of Birtola village in hill top in

Phuljhori Pahar (Fig.4.14). The best development of QPC has been noted in the

central part of Bagiyabahal. The field photos of a these QPC occurrences are given in

Fig.4.16, 4.17, 4.18 & 4.19. The details of different QPC occurrences have been dealt

in chapter-V.

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Fig.4.17. QPC with large pebbles of quartz is overlain by fine grained pebbly horizon and finally by steeply dipping IOG quartzites in the central part of Bagiyabahal area, western margin of Bonai granite, Sundergarh district, Orissa.

Fig.4.16. QPC with stains of iron-oxides on surface along right bank of Brahmni river west of Bagiyabahal, western margin of Bonai granite, Sundergarh district, Orissa. Note the presence of ash grey coloured smoky quartz as pebbles.

Fig.4.19.Radioactive QPC, near Birtola village, Sundergarh dist, Orissa.

Fig.4.18. QPC with coarse grained white quartz as pebbles near Bagiyabahal.

Iron-stains

SQ Iron-stains

Iron-stains

Iron-stains Coarse grained QPC

Fine grained QPC

Fine grained IOG Quartzite