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Dissertation Report 2010
CHAPTER-I
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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
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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.
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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.
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CHAPTER-II
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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
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scale, in addition to characterized the rocks petrographically, to understand
nature of rock and associated mineralisation.
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CHAPTER-III
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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.
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Fig: 1 Location Map of Study areas.
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Fig: 2 Political Map of India showing the location of Karnataka.
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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-
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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.
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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
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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
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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
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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.
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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
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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-
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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
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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.
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Fig: 4 Geological Map of Karnataka showing the location of Bhima basin.
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Fig: 5 Geological map of Bhima basin and location of Study area in basin.
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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.
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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.
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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
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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.
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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
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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.
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CHAPTER-IV
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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.
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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.
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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
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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.
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CHAPTER-V
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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.
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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
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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.
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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
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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
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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.
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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
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Fig: 17 altered Feldspar under TLXN 20X
Fig: 18 Recrystallised Quartz TLXN 5X
Fig: 19 Showing sphene under TLXN 10X
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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
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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
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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.
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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
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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
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Fig: 28 Pyrite 20X RLON Fig: 29 Titanomagnetite 20X RLON
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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
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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’
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Fig: 31 Chert and Gluconite
showing under TLXN 20X
Fig: 32 Chert and Gluconite showing
under TLXN 20X
Dissertation Report 2010
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
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Fig: 33 Micritic Limestone with
Sparry calcite veins TLXN 10X
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CHAPTER-VI
6.1 CONCLUSION
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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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