Thesis

Dissertation Report 2010

CHAPTER-I

Department of Studies in Geology, University Of Mysore 1


1.1 INTRODUCTION

The study of Proterozoic basins has become important as it gives much

insight about the crustal evolution in that part of earth. Beside academic

interest, from the mineral economics point of view these basins are equally

important as most of the world’s high grade, large tonnage uranium deposits

are located within it. One-third of world’s uranium comes from Proterozoic

basins where is occur as unconformity related deposits. The Proterozoic basins

are exposed in several isolated patches, found throughout India unconformably

overlying the crystalline Achaean or Palaeoproterozoic basements. The rocks

are mainly shallow marine, platform type, undisturbed and undeformed

sediments developed in shelf environment, proximal to cratonic margins. The

only deformation these rocks have undergone is local metamorphism and

penecontemporaneous faults. Presently these basins are prime target of

ongoing uranium exploration programme in the country. The small,

Neoproterozoic Bhima Basin located in the northern part of Karnataka and

western part of Andhra Pradesh, India is one such basin. The basin is

characterized by long linear basement related faults and the present disposition

of Bhima sediments is largely attributed to these faults. With the discovery of

uranium mineralisation at Ukinal and Gogi along Gogi – Kurlagere fault (1995-

96) which subsequently lead to the establishment of a high grade low tonnage

uranium deposit, richest grade in India, at Gogi, the whole of Bhima basin has

become prime target for uranium exploration. The work carried out by Atomic



Minerals Directorate for Exploration and Research (AMD) in subsequent years

(1997-2010) lead to the discovery of several uraniferous anomalies in the basin.

Uranium mineralization in the basin is only metallic resource in Bhima

basin. The non metallic resource found in Bhima basin is cement- grade

limestone estimates to 1000-1500 million tons (Venkoba Rao et al., 1967).

Uranium mineralization so far known in the basin is typically associated with

the tectonised zones closer to the sediment-basement boundary. Mainly

mineralization occurs in phosphatic limestone, non –phosphatic limestone,

Shale and in basement granitoids, and migmatites and shear zones. The

phosphatic limestone type of occurrence is confined to altered phosphatic

portions of limestone in the immediate vicinity of fault/fracture zone. The

mineralized rock is identified as micritic, siliceous limestone and siliceous

phosphorite. This type of occurrence is predominantly seen in the following

two areas; Along Kurlagere-Gogi fault, Along Wadi-Ramthirth-Bhimanahalli

fault.

The non-phosphatic limestone type of mineralization is structurally

related, epigenetic, vein- type. The main phases of uranium are pitchblende and

coffinite. They occur in close association with pyrite and carbonaceous matter.

Uranium mineralization at Gogi, Halbhavi and Halkal are a few example of

which Gogi occurrence in type locality.

The Shale type of uranium mineralization is in shales that immediately

overlie the basement crystalline rocks. In the Gogi area, moderate to feeble

radioactivity is recorded in the shales that immediately overlie granites.



Kasturipalle uranium occurrence is the only example of outcrop showing shale-

hosted uranium mineralization.

Uranium mineralization in the basement granitoids and migmatites

along shear zone is recorded over considerable extent. Granitic rocks rimming

the Bhima basin south of Hunsigi, Wajhal and other areas are a few such

examples. Tirth-Thintini fault is one more example of this type. In the Gogi

area biotite granitic rocks lying within the tectonised zone of the cross fault

contain several fracture filled with pitchblende and coffinite.



CHAPTER-II



2.1 AIM AND SCOPE OF THE INVESTIGATION

A low tonnage high grade uranium deposit has already been established

at Gogi area along Gogi-Kurlagere-Gundahalli fault. Gogi-Kurlagere-

Gundahalli fault is an E-W trending 40 km long fault along the southern

margin of Bhima basin. Gogi is located at the center of the east-west trending

Gogi- Kurlagere fault. The fault zone takes NW-SE and NE-SW swing at Gogi

due to cross faulting. Kurlagere – Gogi fault is further traced eastwards

through Hulkal – Halbhavi – Madnal and further beyond Dornahalli to

Gundahalli where it continues in the basement crystallines for a distance of

nearly 20 km. The fault zone is marked by steep dipping of the limestone beds

towards the basement and brecciation. Clasts and fragments of granite, basic

rock, limestone, shale and quartzite are embedded in grey blocky / massive

limestone characterizing the breccia zone. The mineralization at Gogi is

structurally controlled, vein type. The present area of investigation lies in the

eastern part of Gogi-Kurlagere-Gundahalli fault between Madnal and

Doornahalli in south and up to Sirwal in north (between Latitude 16°43’00”N

to 16°48’30”N and the Longitude 76°51’00”E to 76°58’00”E). In the eastern

part, most of the area is soil cover was not mapped in detailed and radiometric

survey data was meager. To understand the geological/structural behavior of

rocks and find out any possible extension of uranium mineralization of Gogi

area in eastern part this investigation was taken up. This investigation aims at

detailed radiometric survey, geological cum structural mapping on 1:25000



scale, in addition to characterized the rocks petrographically, to understand

nature of rock and associated mineralisation.



CHAPTER-III



3.1 LOCATION ACCESSIBILITY

Gogi-Kurlagere-Gundahalli fault is located in Shahpur Taluq of Yadgir

district of Karnataka, India. It is located about 210km southwest of Hyderabad,

525 km north of Bangalore, 625 km southeast of Mumbai and 450 km east of

Panaji, Goa. As the area is criss crossed by major railway line and roadways it

is easily accessible. This area being an important region for agriculture, cement

and associated industries, the infrastructural are well developed. Nearest

railway station is situated at Yadgir which is about 20km away from present

area of study.



Fig: 1 Location Map of Study areas.



Fig: 2 Political Map of India showing the location of Karnataka.



3.2 CLIMATE

The study area experiences a monsoon type climate as it is situated in

the central part of the peninsular India. The area experiences three seasons

namely summer, winter and rainy season. March to May is summer months and

temperature may go up to 450C in some places and December is the coldest

month with temperature going down as 8 - 100C. Summer month is best suited

to take up a geological field work in the area as vegetation cover will be scarce

and streams will be dry.

3.3 GEOMORPHOLOGY

The land forms developed in and around Gogi-Kurlagere-Gundahalli

fault is mainly plain to undulating topography with most of the area under

cultivation. The ground level varies from +367m to +449 m above MSL.

There are clear indications at several places that once the Deccan plateau

basalts have covered the entire basin, even overlapped the Peninsular Gneissic

complex and presently have receded due to erosion leaving behind “mesas” and

“buttes” capped by basalt. Hence the present plain topography has developed

over exhumed Bhima sediments during post-Eocene times.

River Bhima drains the area. The area is characterized by medium

dendritic drainage pattern with several ephemeral streams –water courses. Soil

has poorly developed over argillites and silicieous limestone. The soil profile

thickness, range from nil at higher elevation capped by flaggy limestone to 2-



4m at lower level and 4-5m along the banks of rivers with combination of

alluvium and soil. But blanket of black to deep black soil with calcrete and

occasionally gypsum occurs over both the rock types with a sharp contact,

except along weak zones. Much of the soils over the Bhima formations appear

to be transported with its source from Deccan Trap area.

Three types of land use pattern have been observed i.e. settlements,

agricultural and mining. Groundwater condition is poor over the horizontally

disposed sediments. Few fault zones and fractures near the proximity of

perennial and few seasonal major streams are being trapped for irrigation. Due

to the irrigation projects (Upper Krishna Project) which irrigates vast area and

supports the agriculture. The black cotton soil supports cultivation of Cotton,

groundnut, chilies, rice, sugarcane, wheat, pulses, sunflower, hybrid varieties of

jowar and kusube (for oil).

3.4 PREVIOUS WORKS

The first description about unmetamorphosed sediments lying

unconformably over the basement granite in the region was given by Captain

Newbold (1842-45). He compared this formation to Kurnool and identified the

flaggy limestone near Talikota and red sand band at Muddhebihal. It was in

1872 William King who mapped the basin but his work was restricted to

erstwhile Madras presidency. He named the sediments as ‘Bhima series’ which

is deposited on the either side of river Bhima a tributary of river Krishna.



William King did not cover significant areas around Shahbad which was then

part of erstwhile Maratha and erstwhile Hyderabad.

Bruce Foote (1876) studied nearly all the areas of the basin and

proposed a two fold classification based on the importance of the coarse clastic

component. The lower Bhima constituting mainly of conglomerate, sandstone

and shale, the upper Bhima comprising of shale and Limestone. He correlated

Bhima sediments with Kurnools of the Cuddapah basin.

Mahadevan (1947) revised the stratigraphy of Bhima basin based on

depositional history and Paleo-geographic considerations. He proposed a three

fold classification division comprising Lower-mechanically derived sediments

represented by conglomerate, sandstone, flaggy limestone, green and purple

shale. Middle-Chemically precipitate marked by limestone of different colour.

Upper-consisting of mechanically derived sediments like sandstone, buff,

purple and red shale and flaggy limestone. Janardhan Rao et. al. (1975) adopted

the morden code of stratigraphic nomenclature and gave the Bhima series a

status of “Group” and adopted a five fold classification with formational status

given to the different units having distinct composition. He divided the upper

Bhima into three formations, while retaining the middle and lower Bhima as

separate formations. Mahadevan’s lower and middle series was renamed as

Rabanpalle and Shahbad formations while the upper series was split in to

Hulkal shale, Katamadevarahalli limestone and Harwal shale formations.

Mathur (1977) suggested modification in this scheme by renaming the Shahbad

formation as the Kurkunta and Gogi formations respectively. 1n 1987 Mishra



et.al. sub divided the Bhima group into Andola sub group comprising of

Harwal-Gogi shale, Katamadevarahalli limestone and Hulkal shale formation

and Sedam sub group comprising Shahbad limestone and Rabanpalle

formation. The break in sedimentation between the Sedam and Andola sub

group, recognized on the basis of the arenite at Hulkal has been interpreted to

be a paraconformity. Kale et. al. (1995) came into a conclusion that the Sedam

and Andola group are nothing but lateral change in facies of one another and

the entire sedimentation in the Bhima basin is a product of a singular short

lived transgressive event. He grouped the entire clastic as Rabanpalle clastic

formation and the carbonate sediment as Shahbad limestone formations. The

latest litho stratigraphic succession was proposed by Jayaprakesh A.V. (1999)

of G.S.I. where he dropped the nomenclature of two sub-groups and put them

in one Bhima group with five formations.

In late 1980’s radiometric survey in the Bhima basin by P.S. Naidu

had led to identification of a number of spot activities in granities in the

Yadgir-Wadi tract, however a few were also recorded within the basin also.

During 1995 radioactive anomalies were reported for the first time in Bhima

basin near Ukinal, in the vicinity of Gogi-Kuralgere fault, by ASRS Group,

AMD (1995–96). Subsequent to this discovery preliminary radiometric survey

carried out at Ukinal has led to the identification of interesting radioactive

anomaly over a strike length of about 600mts intermittently at the

limestone/shale contact (Natarajan. V. 1995). Since the discovery of uranium



mineralization along Gogi-Kurlagere fault in 1997 extensive exploration

activity is going on.

3.5 GEOLOGY OF BHIMA BASIN

The Karnataka craton is broadly divided into two tectonic stratigraphic

blocks, separated by the Chitradurga boundary fault close to western margin of

the linear Closepet granite (Swaminathan et. al. 1976, Swaminathan and

Ramakrishanan 1981).

The two blocks

The western block comprises tonalite-trondhjemite-grandiorite (TTG)

gneisses with enclaves of the sargur complex intrusive granititoids and a

thick cover of the Dharwar supracrustal belt.

The eastern block comprising TTG with enclaves of Sargur complex,

volumetrically large proportion of intrusive granitoids in comparison

with the western block and a series of sub parallel belts of greenstone

The Bhima basin is located on the northern edge of the eastern block,

NE-SW trending linear basin sandwiched between the Archaen granite

greenstone terrain of the eastern Dharwar craton in the south and the Deccan

trap volcanic province in the north.

The Bhima basin (named by W King 1872) receives its name after

‘Bhima River’ a major tributary to River ‘Krishna’ flowing through basin. It is



smallest (in term of area) and youngest (in terms of chronology) of Proterozoic

basins spreading over 5300 Sq. Km in Peninsular India in parts of Gulbarga,

Yadgir, Bijapur Districts of Karnataka and Mahaboobnagar and Rangareddy

districts of Andhra Pradesh,India. It lays between Latitude 16°20’00”N to

17°40’30”N and the Longitude 75°30’00”E to 77°30’00”E in the Surveys of

India topo sheet Nos. 56C, D, G and H. Bhima basin is having a North East –

South West trending, epicratonic, extensional basin, formed due to gravity

faulting (Dhana Raju et.al. 2002). The ‘S’ shape of the basin is attributed to the

large scale fault systems that dissects the Bhima in to different segments.

The total thickness of sediments is about 300mts. Fine to coarse grained

arenite unit ranging from few centimeters up to 5 mts forms the basal portion

immediately overlaying the Archaean granite green stone terrain with a marked

unconformity. Glauconite shale, grading in to purple colored, fissible

ferruginous shale ranging in thickness from less than a meter up to about 30

mts makes the next sedimentary unit. Grey to dark colored micritic limestone

locally cherty ranging thickness up to about 200 mts from the uppermost

sedimentary unit characterizing the basin. The Stratigraphy of Bhima basin was

first proposed by Bruce Foote (1876) since then it has been studied by many

works. The latest litho Stratigraphic succession was proposed by Jayaprakesh

A.V. (1999) of G.S.I.



Jayaprakash A.V. (1999) Kale V.S (1995)GROUP FORMATION MEMBER LITHOLOGY

B) Shahabad Limestone Formation

** Grey micritic impure limestone.

** Dark blue – grey massive limestone.

** Variegated, siliceous and cherty limestones

** Flaggy impure (cherty/argillaceous) limestones

-Gradational and transitional

----- Facies changes---

A) Rabanpalli Clastics FormationB) Ekmai Shale Member (ferruginous & calcareous shales)C) Kasturpalli Glauconitic MemberD) Kundrapalli Quatz- Arenite Membera) Adki Hill Conglomerate Member.

DECCAN TRAP

Basic flows with intertrappean sediments

BHIMA GROUP

Total Aggregate Thickness 297m

HarwalBrown, pink to vermellion shale (45)

KatamaDevarahalli

Deep grey, occasionally stylolitic flaggy limestone (40)

Hulkal

Grey, blackish buff, dull and pale pink shale, occasionally with fine grained thin silty beds at the base (30)

Shahabad

Mulkod Limestone

Deep grey to black flaggy limestone (100)

Gudur Limestone

Akin to Wadi limestone, yet slightly inferior in chemical composition (20)

Sedam Limestone

Variegated medium to thickly bedded siliceous limestone (60)

Wadi Limestone

Thickly bedded, stylolitic, relatively superior cement grade limestone (15)

Ravoor Limestone

Flaggy limestone with prominent fissility (Shahabad slabs) (10)

Rabanpalli

Korla shale

Fine silty base, grades into green shale, followed by chocolate brown shale with prominent parting (50)

Kundrapalle Sandstone

Fine grained quartz arenite, subfelspathic arenite, ferruginous cemented medium grained quartz arenite (15)

MuddebihalConglomerate

Pebbly orthoconglomerate, locally or at the top matrix supported and also granular (2)

~~~~~~~~~~~~~~~~~~~~~~~~~Unconformity ~~~~~~~~~~~~~~~~~~~~~~BASEMENT

CRYSTALLINESYounger Granites, Eastern Block Greenstone Belts, Peninsular Gneisses.

(Figures in bracket indicates the thickness in meters)

Fig: 3 Stratigraphic sucession of Bhima basin



The outcrops of the basin is exposed between “Tandur” in the North

East and “Muddebihal” in the South West for a stretch of 160 Km across with a

maximum width of 40 Km across “Sedam”. The Northern and Northwestern

extensions are concealed under Deccan traps. The southern and Eastern

margins of the basin mark the ‘unconformity contact’ with granitic gneisses

and younger granites of the Dharwar Craton. It exhibits a gentle northerly dip

of about 5° except along fault zones where sediments are steeply dipping and

brecciated locally. A number of fault zones have been identified in the basin

displaying trends varying between East-West (Kulagere-Gogi-Gundahalli,

Farthatabad, Tirth-Tintini and Rabanpalle faults), North-West to South-East

(Wadi-Bhimanahalli and Shahabad). Few minor North-South (Mullamari and

Nirgund) trending faults are also identified. Primary sedimentary structures are

well preserved in the Bhima sediments in tectonically undisturbed area.

The Bhima basin is devoid of fossils, though the constituent beds are

well suited to the preservation of organic remains. The Kaladgi lie to their west

but no where come in contact with them, the nearest out crop is 50 Kms away.

The lithology, horizontal disposition and unmetamorphosed nature of the

Bhima indicate their equivalence to Kurnool formation.

The present outcrop pattern and supported by palaeocurrent evidences,

the depositional trend was in NE-SW direction. Sedimentation took place all

along the southern boundary. In general deposition took place in an undisturbed

quiet sea. The clastic members of the lower Bhima’s show evidences of having

been deposited in a shallow marine environment either along beaches or intra-



tidal zone grading on to deeper tidal flat or sub-tidal environment. The

overlaying Shahabad limestone, which is famous for its ability to split into thin

slabs of a pleasing blue-grey colour, was obviously deposited in a quiet

protected tidal flat environment. The purple colour of the sandstone and shale

especially in the upper beds are indicative of an oxidizing environment. The

Bhima sediments are separated from the underlying schistose and granitic rocks

of Archaean age by a profound unconformity –‘the Great Eparchaean

Unconformity’.

Sediments of the Bhima Group are structurally least disturbed and

preserve their horizontal bedded character originally impressed at the time of

deposition. Dip of strata rarely exceeds 5°. Deformation is observed only in the

neighborhood faults. The primary structures like current bedding and ripple

marks in the quartzite rocks are recorded. Other structures like joints and

stylolites are also present. A number of dykes (mostly basics in composition)

traverse the crystalline terrain in the environs of Bhima basin. No radiometric

dating has been done on Bhima sediments. The resemblance of Bhima

sediments with Kurnool Group sediments rules out the possibility of the Bhima

Group sediments transgressing in to the Cambrian. The upper age limit may,

therefore, be not less than 600 Ma. Salujha and Rehman (1973) recorded the

occurrence of planktons from limestone quarries in different areas of Bhima

basin. Out of the planktons described some plankton like Archaeofavosina and

Trematosphalsindium are restricted to late Precambrian age. From the

palynological assemblages (by Venkatachala and Rawat 1973) assigned late



Cambrian age to the Bhima Group of sediments. It is, however, significant to

stress that the total lack of deformational evidences points to a distinct post-

cratonic age for the Bhima. It is, therefore, likely than an age assignment of

uppermost Proterozoic (or just over 600 Ma) in the geological time scale could

be adjudged as the best approximation for the Bhima Group deduced from

biota and litho-Stratigraphy as vendian / Neo-Proterozoic age, i.e., older than

550 Ma but younger than 625 Ma. One of the most striking features is the

absence of stromatolites in the Bhima Group, which are present in adjacent

basins. This significant feature has been attributed to the emergence of

Metazoa, which scavenged the stromatolite – producing algal biota in shallow

marine environment (Awarmik, 1990). For this, Moitra et al., (1999) refer to

Groetziner (1990), who points to three principle periods of decline of

stromatolites in the earth’s stratigraphic record, with one of them

corresponding to the base of Cambrian i.e., Vendian – Neoproterozoic.

The carbonate rocks of Bhima basins were deposited in marine

environment during Neo Proterozoic period. The 13 C enrichment associated

with carbonates indicates increased burial of organic carbon in response to

global tectonic processes at around 0.6 Ga.



Fig: 4 Geological Map of Karnataka showing the location of Bhima basin.



Fig: 5 Geological map of Bhima basin and location of Study area in basin.



LITHOLOGY

Basement rocks

The late Achaean continental crustal crystalline rocks form the basement

of the Bhima Basin. It shows a gently undulating peneplained topography,

punctuated by isolated tors. Before the deposition of Bhima sediments the

Archaean rocks subjected to the action of erosional forces in a continental

environment. This unconformity is termed as Eparchaean unconformity. This

forms the undulating terrain interspersed with hill ranges cinsisting schist belts

and granitoids. These undifferentiated crystalline rocks include a variety of

tonalitic and trondjhemetic gneisses (PGC), amphibolites, and schists of

Eastern Block Green Stone Belts and other intrusive younger granitic rocks,

equivalent to Closepet granite. From the gravity data, it is interpreted that a low

density body, extending up to the depth of 6-7 Km below the Bhima sediments

as emplacement of granite along weak/shear zone. The Bhima sediments are

overlaying on basement crystallines on angular and erosional unconformity.

The late Archaean granitoids are rich in accessory minerals which as sphene,

allanite, apatite and zircon, which are the main carriers of uranium and

thorium. Insitu gamma-ray spectrometric analysis reveals that these granitoids

have higher abundances of Th, U, and K relative to granitoids occurring farther

away from the basin. Thus, they belong to the class of fertile granitoids from

the point of uranium mineralization.



Rabanpalli Formation

It is the first sedimentation of Bhima basin composed of Conglomerates,

Arenite, and Shale separated from the Archaean basement with a profound

Eparchaean Unconformity. The base of the Rabanpalli Formation is made up of

a matrix supported conglomerate comprising of quartz and feldspar and few

rock fragments. The clasts in general are sub rounded. The conglomerate

grades upward to coarse sand, fine sand or arenite, siltstone and shale. At

places sandstone and siltstones directly overlie the basement. The matrix

supported pebbly conglomerate comprising clast of Quartz and Feldspar and a

few rock fragments constitute Muddebihal conglomerate. It is followed by the

deposition of quartzarenite, feldspathic arenite and medium grained

Quartzarenite cemented by ferruginous matrix called the Kundrapalle

Sandstone. The fine silty particles grade into Green Shale, followed by the

deposition of Brown Shale called Korla shale. The sandstone comprises of

quartz, feldspar (10-30%) and few rock fragments. The sandstone is thick to

thin bedded and the siltstone- shale thinly bedded to laminated. A variety of

sedimentary structures occur in the formation. Gold occurs in the

conglomerates of the formation in the Balashetehal area as heavy detrital

grains.



Shahabad Formation

The limestone of Shahabad Formation gradationally overlies the

siltstone- shale in the upper part of the Rabanpalli Formation. The transitional

zone is about 5 m thick. At This formation composed of different types of

Limestones, it having thickness approximately 210m. Each types of Limestone

deposition constituting as a member. Flaggy Limestone, Cement grade

Limestone, Medium grade Siliceous Limestone, Limestone which has slight

difference in chemical composition, deep grey Limestone are called Ravoor

Limestone, Wadi Limestone, sedam Limestone, Gudur Limestone and Mulkod

Limestone Respectively. Near to fault zones the limestone resting on granite

has clasts of granite and schistose rocks. Cross bedding, scour and fill

structures and stylolites are the sedimentary structures present in the limestone.

Glauconite occurs in the limestone and especially in the sand lenses.

Hulkal Formation

The Grey Blackish buff and pale colored shale with thin silty beds are

called Hulkal Formation. The limestone of Shahabad is gradationally overlain

by the siltstone- shale of Hulkal Formation. The transitional contact is exposed

in the Bhima river section between Ferozabad and Kolkur, and is about 4 m

thick. The lower part of the formation has thin phosphorite bands and the upper

part has minor occurrence of barite. Glauconite is present in the entire upper



part of the formation; indicate local change in depositional environment during

the late stages of deposition.

Katamadevarahalli Formation

The 40 Km thick deep grey Limestone of Katamadevarahalli Formation

gradationally overlies the Halkal Formation. The transitional zone is up to 4 m

thick and is well exposed in the Katamadevarahalli and Kokur areas. The basal

part of the formation has occasional small lenses and crystals of barite.

Ferruginous concretions, chert nodules and pyrite occur in the limestone.

Harwal Formation

The Katamadevarahalli Formation is conformably overlain by siltstone-

shale of Harwal Formation (pink coloured shales). The siltstone-shale is thinly

bedded to laminated.

Hotpet Formation

In the Gogi-Hotpet area, a locally developed arenaceous unit occurs

uncomfortably resting over both the Shahabad and Halkal Formations. This

formation has a chert pebble conglomerate at the base followed upward by

medium grained well sorted sandstone.



Gulbarga Infra-trappean formation

The hiatus between the Hotpet formation and the overlying Deccan traps

represents nearly 400 Ma. It is rather difficult to conceive that nothing notable

resulted during this period and one has to probe into this period of so called

“Geological Silence”. At least it would be logical to believe some Pre trappean

topography evolved resulting in undulating terrain. Depressions in this

undulating topography might have supported some sedimentation. This is

evidenced by the present disposition of Deccan traps of different elevations.

Kale (1990) lists a few localities with elevations above the present day MSL

(Mean Sea Level) of the base of the Deccan Traps. Just above the Bhima

Group, impersistant, disconnected thin horizons of sediments termed

“Infratrappeans” are known since long (Foote 1876; Pascoe 1965).

Deccan Traps

Deccan traps, essentially simple basaltic flows, are mostly fine-grained,

compact but some of them are typically amygdaloidal. These traps, considered

to be of Cretaceous to Eocene in age, are seen as outliers and are also present

directly overlying the Archaean basement complex much to the south of Bhima

basin. This clearly indicates that the traps were far more extensive than their

present limits. It may not be completely wrong, if it is said that the entire

Bhima basin at one point of time in the geological history was concealed under



Deccan traps. Extension of Bhima basin below the traps is illustrated along the

erosional valley along the Mullamari fault south of Chincholi. Road section

between Kembhavi and Hunasgi exposes a small outlier of Deccan traps.

Development of reddish, ferruginous “boles” is clearly seen.



CHAPTER-IV



4.1 METHODOLOGY

In order to achieve the defined objective the following methodology was

adopted.

Literature Survey

Published literature on geology and uranium mineralization of Bhima

basin in general and along the Gogi-Kurlagere-Gundahalli fault area in

particular was carried out by referring in journals and internet.

Geological Mapping

Geological mapping is the fundamental task on the basis of which all

quantitative and qualitative geological studies are carried out leading to

understanding of evolution of the area under study, with respect to space and

time. It is a two dimensional representation of spatial and temporal relation

among different geological features in a given terrain.



4.2 PROCEDURE

A toposheet of Survey of India (56/D/13SW, SE and 56/D/14NW, NE)

in the scale 1:25000 was chosen as the base map. A Field investigation was

taken up for 30 days. During the investigation eighteen traverses across the

strike of the formation was made this enabled to mark the lithological contacts

precisely and to understand the field relationship of various lithological units.

While taking traverses to find precise location of geological features, outcrops,

sample location a Global Positioning System (GPS) Garmin 76CSx (using Map

Datum-Indian Bangladesh) was used, and around 300 points were taken in

GPS. In order to find the attitude of beds (Strike, Dip and Dip amount) a

brunton compass was used. These data was later plotted on base map back in

field camp to prepare a detail geological map of study area.

Along with this a radiometric survey was also carried out using a

scintillometer. A Scintillometer is used to detect radiation energy released in

the form of alpha and beta particles and gamma rays during the breakdown

(decay) of radioactive minerals. The radiation values given by scintillometer

were recorded in terms of milliroentgens per hours (mr/hr). From 170 locations

radiation values were recorded and these values were used to prepare an isorad

contour map. An Isorad contour is an imaginary line connecting parts of equal

radiation. Thus, isorad map is one which shows variation in radiation from ore

body by means of isorad contours. Isorad map helps in deciphering the richer

ore shoots in an area and helps in guiding in subsequent exploration program.



Scintillometer

The scintillation counter is superior to the Geiger counter in terms of

efficiency and sensitivity and hence, more suitable for the detection and

measurement of gamma rays. The instrument makes use of one of the several

substance called Scintillators which, when struck by a single particle, converts

some of the energy received in the process of collision into a tiny flash of

visible light, known scintillation. Scintillation is caused by ionization and

excitation produced in the scintillators by the incident nuclear radiation. It is

possible to watch a scintillator and count the light flashes to light. Usually,

however, a photomultiplier connected to the scintillator converts the light

flashes into electrical pulses, which may then be recorded electromechanically.

Fig: 6 Parts of the Scintillation counter: 1. Scintillator: 2. Photo-Cathode; 3.

emitters (dynodes) 4. Collector (anode) 5. Photo-multiplier tube



Fig: 7 Schematic diagram of a simple scintillation counting system

As shown in the diagram the in-coming nuclear radiation produces a

flash of light in the scintillator. By means of the light pipe and reflector, a large

fraction of the light is transmitted to the photocathode of a photomultiplier

tube, which converts the light flashes into electrical pulses proportional to the

light energy. The amplifer amplifies the pulses to an amplitude suitable for the

discriminator and pulse sharper, after which the pulses are counted by the

electronic counter. The electronic counter would be replaced by a differential

pulse height analyser (single- or multi-channel) for spectrometric work. A high

voltage supply is required for the photomultiplier tube, for its electron

multiplying device to produce a stable output.

Radiation readings recorded from various locations are given below.



CHAPTER-V



5.1 LOCAL GEOLOGY

Geological mapping and reconnaissance radiometric survey was carried

out in 100 sq. Km area, laying between Latitude 16°43’00” to 16°48’30” and

the Longitude 76°51’00” to 76°58’00”E in the Surveys of India topo sheet No.

56 D, 13 & 14. The area surveyed exposes basement crystallines comprising

mainly pink granite (grey granite, gneisses also seen) and Bhima sediments

consisting predominantly of limestone and shale.

Granite

Basement granite are mainly exposed in south of Madnal and

Doranahalli. It is also found in areas around bidrani and Ibrahimpur. The pink

granite variety belonging to younger granites occurs widely in study area.

Granite quarries are found in eastern part mainly on the way to Ibrahimpur and

in North of it also. In southern part it is mainly soil cover and exposures are

very less. Fine to medium grained variety of pink granite is mostly found. In

granite quarries it is clearly visible that in upper part it is coarse grained and in

depth it is fine grained. Few anomalies have been spotted in granitic terrain.

Near to fault zones veins of quartz are seen especially near to Doranahalli and

Hurasagundigi area. Occurrence of granite as clasts in limestone widely seen in

east of Doranahalli on the either side of Shahpur-Yadgir road and in Madnal

also.. Few outcrops of grey granite can be seen near to Ibrahimpur area.



Fig: 8 Fig: 9

Fig: 10 Fig: 11

Fig: 8 Xenolith seen is pink granite near Ibrahimpur

Fig: 9 Kankak type of Limestone seen near Madnal

Fig: 10 Lithological contact near Gogi fault showing granite, arenite and

siltstone near Dornahalli

Fig: 11 Massive Limestone having clast of granite seen near Dornahalli



Basic Dykes

Dark green to brown colour basic dykes are seen having North East-

South West trend can be seen in Doranahalli and Hurasagundigi. These

Dolerite dykes have caused shearing of in basement granites.

Arenites

Arenite belonging to Rabanhalli formation is seen in study area. It is

mainly exposured in fault zones between Madnal and Doranahalli. It has sand

size grains, having buff colour.

Silt stone

Silt stone belonging to Rabanhalli formation is seen in study area.

Exposures are found in fault zones north of Doranahalli. Its colour varies from

purple to green, Individual grains are not visible and have thin lamination. The

attitude of the siltstone varies from place to place, it mainly bed depends on

faulting.



Fig: 12 Fig: 13

Fig: 14 Fig: 15

Fig: 12 an hand specimen of purple limestone with granite clast seen near

Dornahalli

Fig: 13 an hand specimen

Fig: 14 Granite quarry near Ibrahimpur

Fig: 15 Limestone quarry located in Sirwal



Shale

Shale belonging to Rabanhalli formation is seen in study area. It is

mainly exposed along fault zones, wide exposures are found in north of

Doranahalli. Normally purple variety is found, and green shale is also seen.

Attitude of shale bed depends on strike, varying from east-west to north-south.

Dip varies from 150 to 650.

Limestone

Limestone is mainly exposed in northern and central regions of the study

area. The limestone varieties like flaggy limestone, cherty limestone, and

massive limestone are seen. They belong to shahbad formation. Near to contact

purple limestone is seen. In places like north of Madnal, east of Doranahalli

and along the Yadgir-Shahpur road we can see the granite clasts with in

limestone, indicating the fault zone. Near to fault zone limestone is criss

crossed by calcite veins of various sizes. Very few occurrence of khaki

limestone is seen, mainly between Dornahalli and Bidrani. In south central part

limestone is having east-west strike, near to Dornahalli it is having north west-

south east strike. The dips in the limestone are mainly due to faulting and

thrusts, these are entirely local. There was no significant radioactive anomaly

seen in limestone area. Normally limestone is having a light grey colour it is

having a bluish tinge, buff to khaki (khaki limestone) colour also seen. The



flaggy limestone is widely quarried for building and other purposes. The

limestone beds have dip of 30-50.

Stratigraphy

Shahbad formation (Limestone)

Shale

Rabanhalli formation Siltstone

Arenites

~~~~~~~~~~~~~~~Unconformity~~~~~~~~~~~~~~~~

Younger Granites, Eastern Block Greenstone Belts, Peninsular Gneisses.



5.2 PETROGRAPHY

Specimen number: A1

Location: N160 48.750’ E760 55.710’

Megascopic studies: It is having equigranular texture, medium to coarse

grained light pinkish in colour.

Microscopic studies: Under microscope it is showing Quartz, feldspar,

microcline. The quartz grains shows anhedral shape this is due to deformation

recrystallised it is showing undulation twinning and coarse to medium grain

sizes. Accessory minerals like sphene are also identified. Opaques are also

present.

Deformation and Alteration: It is moderately deformed, alteration of feldspar is

seen. Flame perthite is also a signature of deformation.

Rock Nomenclature: Pink Granite.

Fig: 16 Flame Perthite under TLXN 20X


Fig: 17 altered Feldspar under TLXN 20X

Fig: 18 Recrystallised Quartz TLXN 5X

Fig: 19 Showing sphene under TLXN 10X


Specimen number: A3

Location: N160 43.917 E760 55.363

Megascopic studies: The rock is greenish in colour, it is compact, medium

grained.

Microscopic studies: Under microscope it is showing ophitic to sub ophitic

texture. Major minerals observed in thin section are feldspar, pyroxene,

Olivine. Euhedral to Subhedral grains of pyroxenes are seen. Opaques are

present.

Deformation and Alteration: Feldspar is altered to clay and pyroxene is altered

to chlorite.

Rock Nomenclature: Dolerite


Fig: 21 Ophitic texture under TLXN 5X

Fig: 20 Alteration of Feldspar to clay under TLXN 10X

Fig: 22 Pyroxene(Augite) under TLXN 10X

Fig: 23 Pyroxene(Augite) under TLXN 5X


Specimen number: A4

Location: N160 44.340 E760 57.342

Megascopic studies: It is having Hypidiomorphic texture, fine to medium

grained light pinkish in colour.

Microscopic studies: Under microscope quartz, Plagioclase, microcline and

orthoclase are identified. Minor minerals like biotite were identified. Opaques

are present.


Fig: 25 Biotite alteration to clay

under TLON 20X

Fig: 24 Biotite alteration to chlorite

under TLON 20X

Fig: 26 Alteration of feldspar to

sericite under TLXN 10X

Fig: 27 Ilmenite 50X RLON


Deformation and Alteration: It is less deformed, alteration of feldspar to

sericite is seen. Biotite is altered to clay and chlorite.

Ore Microscopy: In ore microscopic studies llmenite, Pyrite, Titanomagnetite

were identified.

Rock Nomenclature: Pink Granite

The Radiometric assay of rock sample A4 was carried out and which gave the

results as U3O8 = 0.01% and Th = <0.005.

Specimen number: A7


Fig: 28 Pyrite 20X RLON Fig: 29 Titanomagnetite 20X RLON


Location: N160 44.878 E760 51.800

Megascopic studies: It is Purple in colour, induivdial grains are not identifiable.

The sample gives effervescences with dilute HCL.

Microscopic studies: Under microscope quartz and calite is seen. The grains

are very small to identify. Anhedral quartz is set in groundmass of clay and

calcite.

Rock Nomenclature: Shale

Fig: 30 Calcite and quartz in shale

20X TLXN

Specimen number: A10



Location: N160 44.988’ E760 53.627’

Megascopic studies: It is dark redish in colour, very hard and compact.

Microscopic studies: This rock is composed of chert, chalcedony, gluconite,

chlorite and ferruginous matter. Chalcedony is present around gluconite

material, calcite is present as vein, and ferruginous materials are redish in

colour and are seen around the grain bountry. Biotite, Chlorite and quartz are

scattered or dispersed.

Rock Nomenclature: Chert Glauconitic rich rock

Specimen number: A2

Location: N160 43.840’ E760 55.471’


Fig: 31 Chert and Gluconite

showing under TLXN 20X

Fig: 32 Chert and Gluconite showing

under TLXN 20X


Megascopic studies: It is gray in colour, fine grained and compact. White to

buff colored Calcite veins are criss crossing it. The sample gives effervescences

with dilute HCL.

Microscopic studies: In thin section one portion is composed of micritic

limestone. The grains are very small to identify. The other portion shows sparry

calcite it is having rhombohedral cleavage. Calcite veins are also seen in thin

section.

Rock Nomenclature: Micritic Limestone


Fig: 33 Micritic Limestone with

Sparry calcite veins TLXN 10X


CHAPTER-VI

6.1 CONCLUSION



In general the granite shows higher background radioactivity due to

high content of radioactive elements. The only radioactive anomaly is located

in granitic terrain only. A sample collected from this location on analysis by

radiometric assay showed 100pm of U3O8, so the granite is the main source for

uranium in Bhima sediments. Several faulting has taken place in the vicinity of

Bhima basin in the investigated area. Due to which Dextral movement has

taken place along Gogi-Kurlagere-Gundahalli fault which is visible in the form

of a caught up patch of limestone with in granite. A major constrain to

radiometric survey in the studied area has been lack of exposures of outcrops. It

is quiet likely that if mineralization is present it has been offsetted by fault.



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Thesis

Documents

gogi kurlagere fault

kurlageregogi fault

kurlagere gogi fault

gogi occurrence

fault zone

worlds uranium

gundahalli fault

long fault