||3,96,000 sq km
||Andhra Pradesh(South of 15° N latitude), Karnataka and Maharashtra (South of 17° N latitude), Goa, Kerala, Tamil Nadu and Pondicherry
||Regional Centre for Exploration and Research (RCER),Nagarabhavi, Bangalore – 560 072
||D. K. Choudhury, Regional Director
Ph : 080-23210246
Fax : 080- 23211511
e-mail : email@example.com
This Region was set up in 1956 in a rented accommodation at Patan Bhavan, Bangalore. AMD’s own office/ laboratories and residential quarters were established in 1986 in Nagarabhavi, Bangalore.
Broad Geological features
The following are the broad geological domains of the Southern Region.
(i) Archaean Basement Rocks (>2500 Ma) :The basement rocks comprise of Archaean granulite facies containing quartzites, garnet-sillimanite gneiss, marble, alciphyres, amphibolites and charnockites in Tamil Nadu, Kerala, Andhra Pradesh,Karnataka and Goa.The peninsular gneisses, which are mainly composed of migmatites and banded grey granites are fairly homogeneous and are exposed over large tracts in these states.
(ii) Late Archaean Dharwar Supergroup rocks : They comprise piles of volcano-sedimentary sequence broadly divisible into a lower Bababudan and an upper Chitradurga Group.The Bababudan Group is characterized by platformal sediments with quartz pebble conglomerates, pebbly quartzite and fuchsite quartzite and banded magnetite quartzites which were followed by sub-aerial mafic volcanics. The Chitradurga Group is typified by geosynclinal sediments with subordinate volcanics and well developed linear tracts of limestone, manganese and associated iron formations. They occur mostly in Karnataka and parts of Andhra Pradesh.
(iii) Lower Proterozoic Closepet Granites : Granites of this age extend in a north-south direction as a 50 km wide narrow belt. This belt of younger potassic granite is believed to mark a major geo-suture separating two distinct crustal blocks of Archaean age. The western block is characterized by a number of well developed low grade granite-greenstone belts with their iron-manganese ores and the eastern block is marked mainly by younger gneisses of granitic and granodioritic composition enclosing within them a number of narrow, linear bands of auriferous schist belts.
(iv) Middle to Upper Proterozoic Cuddapah Supergroup rocks and their equivalents such as Bhima Group & Kaladgi Group of rocks: These are the most significant geological domains of Indian geology.The Cuddapah basin comprises a sedimentary thickness of 12 km and volcanic sequences in the form of sills and dykes, which are resting on the Archaean peninsular gneissic complex marked by a pronounced Eparchaean unconformity. This basin comprises of rocks of Cuddapah Supergroup which includes Kurnool Group.
The Kaladgi and Bhima basins occur in the northern parts and extend below the Deccan Traps. These basins comprise of rocks of clastic/chemogenic origin.
(v) Deccan trap of Mesozoic-Tertiary age : These formations spread over very small parts of the Region and overlie the northern extensions of the Dharwar craton.
(vi) Younger basins(Mesozoic - Tertiary) :These sediments include Gondwanas of Palar basin, Cretaceous rocks of Tiruchinapally, Cuddalore Sandstone, Warkala beds,Quilon beds etc.
(vii) Beach and Inland Placers : They are part of Quaternary group of rocks. The beach and inland placers of Tamil Nadu and Kerala host some of the richest deposits of ilmenite, monazite, rutile, garnet, zircon and sillimanite.
Present Thrust areas of Investigations
The present thrust on uranium exploration is on Proterozoic unconformities with the basement rocks. As such the three basins viz. Kaladgi-Badami and the Bhima basin in Karnataka and the Cuddapah basin in Andhra Pradesh are under active exploration.
Uranium Exploration in Bhima Basin
Uranium exploration programme in Bhima basin was taken up in 1995 in analogy to other Proterozoic basins in India and abroad. An integrated exploration programme was launched viz., satellite image analysis and litho-structural mapping, 2100 line km Car borne radiometrics, 16330 line km airborne gamma ray spectrometry and magnetics, 7000 sq km hydro-geochemistry, ground radiometrics, gamma ray logging of domestic borewells and sub-surface core and non-core drilling. All these led to identify a number of surface uranium occurrences along Gogi-Kurlagere and Wadi fault zones besides a number of potential target zones delineated by hydro-geochemical survey. Heliborne time domain electromagnetic (TDEM), magnetic and gamma ray spectrometry was also completed recently.
Extensive sub-surface drilling (55000m) at Gogi has established uranium mineralisation hosted in limestone and granite. It is one of the complex structurally controlled epigenetic hydrothermal type uranium mineralisation which necessitated close spaced drilling. Pitchblende and coffinite are the main uranium minerals. The ore is having anomalous concentration of REE, Pb, Ag, and Au. Gogi uranium deposit is located 12km west of Shahapur, the Taluk town and 75km south of Gulbarga the district town. The nearest rail head is Yadgir about 40km to the east.
Exploratory mining is under progress to study the ore body nature and to obtain bulk ore for process studies. Sub-surface exploration is continuing in the extension areas of Gogi uranium deposit e.g., Darshanapur and Halbhavi areas. Apart from Gogi –Kurlagere and Wadi fault zones, many other prominent faults in Bhima basin are also under various stages of investigations, especially the significant hydro-uranium anomalous zones of Kamarwadi, Sedam, Santi and Farhatabad fault zone. Bhima basin has got immense potential for discovering more uranium deposits.
Uranium Exploration in Kaladgi Basin
The meso to neo-Proterozoic Kaladgi Basin, covering an area of 8500 km2 occupies the northwestern fringes of the western Dharwar craton, in parts of Karnataka, Maharashtra and Goa. The northern and western extension of the basin is covered by Deccan Trap. The basin exposes sediments of older Bagalkot and younger Badami groups of Kaladgi Super Group. The Bagalkot group consists of ortho-quartzite, shale, dolomite and limestone, which are highly deformed. Conglomerate, arenite, shale and limestone constitute the main rock types of Badami group, which are undeformed. Achaean Peninsular gneisses, Chitradurga schists of Dharwar super group and intrusive Closepet granite and its equivalents form the basement rocks for these sediments. E-W, NE-SW and NW-SE trending faults and fractures have affected both basement rocks and the sediments.
Uranium exploration was initiated in the sixties with a multipronged strategy. An area of 6600 km2 has been covered by Airborne Gamma ray Spectrometric and Magnetic surveys in the eastern and western parts of the basin, along the basin margin during 1984. Interpretation of Litho-structural map based on LANDSAT imagery and aero-radiometric data of 3000 km2 indicated that eastern part of the basin is a favourable for uranium mineralisation. Hydro-uranium anomalous zones around Deshnur, Yadwad, Chipalkatti, Hulikeri and Tugunshi areas were delineated by regional geochemical survey, carried over an area of 7500 km2. Uranium, thorium and mixed anomalies were located in basement granite, conglomerate and arenite at Tugunshi, Siddankola, Hulikeri, Khanapur and Almatti in the eastern part and Deshnur, Khangaon and Hanbarhatti in the western part of the basin as a result of extensive ground radiometric survey carried out over an area of 8000 km2. Ground geophysical survey viz., resistivity, magnetic and electro-magnetic surveys were also carried out along favourable zones, covering an area of 20 km2, around Deshnur and 7 km2 around Hulihatti.
Reconnaitary drilling ( 25000m) was carried out around Tugunshi, Siddankola, Murdi, Hulikeri, Khanapur and Deshnur to locate unconformity type of mineralisation. Uranium values ranging from 0.010% to 0.034% U3O8 was recorded in Badami arenite in boreholes around Tugunshi area (16°02’41”:75°43’20”), whose thickness varies from 0.50 to 1.70m. Significant uranium mineralisation has been located near Deshnur, which is located at 30 km east of Belgaum (15°54’50”:74°43’50”) in the year 2005. The mineralisation is confined to the unconformity surface in feldspathic conglomerate and arenite of Badami group. The grade and thickness varies from 0.015% to 0.13% U3O8 and 2.50 to 63.20m, respectively. Correlatable mineralization has been established over a strike length of 360m along NE-SW direction. Pitchblende and coffinite are identified as main uranium minerals. Bravoite, arsenopyrite, chalcopyrite, covellite, bornite, sphalerite and galena are the sulphide phases associated with mineralisation. Kaladgi Basin offers an ideal geological setting to host typical unconformity type uranium deposit.
Cuddapah Basin a Uranium Province-Tummalapalle Uranium Deposit: Cuddapah Basin in South Indian Shield is an established Uranium Province. Five types of Uranium mineralisation of varying age are reported here. They are i) Basement granite hosted Fracture controlled type (Mullapalle); ii) Gulcheru quartzite hosted Structurally controlled type; iii) Dolostone (Vempalle formation) hosted Stratabound type (Tummalapalle); iv) Shear controlled type in Eastern margin (Kasturigattu), v) Unconformity type between basement granite and Srisailam quartzite (Lambapur).
Tummalapalle uranium deposit (14019’45”N; 14020’4”N: 78015’17”E, 78016’67”E) is situated in Cuddapah district of Andhra Pradesh, falls in toposheet no. 57J/7. Pulivendla is the nearest town at a distance of 12 km from mine site. This town is linked by road with major cities such as Bangalore (220km), Hyderabad (400km), and Tirupathi 250km. Geologically this deposit and its extension areas are located at the south-western part of Proterozoic Cuddapah basin over an area of 15km x 2km from Rachakuntapalle village in east to Motnutalapalle in west.
Uranium concentration in dolostone near Tummlapalle was first discovered in 1986 during the investigation carried out by GSI for phosphates. Subsequently, surface and sub surface investigation by AMD in two phases i.e. from 1987 to 1993 and 2007 to till date have proved substantial uranium reserves. Here uranium mineralisation is of strata-bound , associated with the dolostone in Vempalle Formation, in the western margin of Papaghni Sub-basin. It extends from Reddipalle in the northwest to Maddimadugu in the southeast over a belt of 160 km. Vempalle Formation overlies the Gulcheru Formation with transitional boundary. Vempalle Formation is around 1900m thick and study of the complete sequence of Vempalle Formation in the explored areas shows that the carbonate facies commences with massive limestone, followed by thin band of conglomerate, uraniferous -phosphatic dolostone, purple shale and cherty limestone. Ultrafine pitchblende and uraninite are the main uranium minerals while coffenite, U – Si-Ti complex as well as little U in the adsorbed form with callophane have been identified as minor U – mineral phases. The associated ore minerals are mainly pyrite, molybdenite, chalcopyrite, bornite, digenite and covellite.
During first phase of investigation, uranium mineralisation in Tummalapalle area was proved over 6.6km in strike length and 1.2km along dip from 15m to 250m depth. Uranium mineralisation occurs along the bedding planes with dip of 150 to 170 due N220E and as two bands, hangwall and footwall band with a vertical separation of 1m to 5m Both the bands show isotropic character along and across the strike in terms of grade and thickness. Average thickness of these bands are 2.3m and 1.75m for hangwall and footwall respectively and average grade 0.05 % eU3O8 at 0.02 cut off. During this phase 37635m. in 264 boreholes have been drilled and 14687te of U3O8 have been proved. Investigation in this area was suspended in 1993 due to leaching constraints and shifts in priority areas of AMD in Cuddapah basin.
Second phase of exploration for Tummlapalle type of uranium deposit was initiated in 2007. The main reasons for again initiating exploration activity for strata bound carbonate hosted uranium mineralisation in Vempalle Formation, in the Papaghni sub-basin are (a) Significant improvement in leaching process (b) demand for uranium in Indian nuclear programme (c) large geological domain of hosting significant uranium deposit (d) high level of confidence in lateral and down dip continuity of uranium mineralisation both in terms of grade and thickness (e) Very low ratio of drilling metres to tonnage and (f) forest free - ground accessibility and suitability for executing drilling progrmme.
During second phase of exploration programme, about 68000.00m of drilling have been completed and approximately 31500te of U3O8 has been added in Tummalapalle deposit and its extension areas. Sub surface drilling in the area is still continued.
Uranium Investigations in Tamilnadu : The state of Tamil Nadu with an area of 1,30,0528 sq.km is situated in the South –eastern part of Indian peninsula between latitudes 08° 00’ and 13°30’ and longitudes 76°15’ and 80°18’. Geologically, Tamil Nadu forms a part of Pandian Mobile Belt (PMB) in the southern granulite terrain which covers Tamil Nadu, Kerala and marginal parts of Karnataka. About 80% of the area is occupied by the crystalline rocks mainly comprised of granulites, charnockite, gneisses, migmatites, Khondalite, layered mafic and ultra mafic, basic, ultrabasic, alkaline and granite suit of rocks of Archaean to Palaeozoic age (3200-390 Ma). It includes the southern extension of Kolar Schist Belt of Karnataka and Andhra Pradesh comprising of greenstone rocks designated as Kolar Group (2700-2900 Ma) which extends as dismembered lenses and linear patches within the Peninsular Gneiss in the northern part of Tamil Nadu. The phanerozoic sedimentary rocks ranging in age from Lower Permian to Mio-Pliocene and covered with quarternary sediments of Pleistocene to Recent are exposed in the coastal region.
Tectonically, it is affected by many prominent lineaments, the major being E-W trending Palaghat-Cauvery and Moyar-Bhavani-Attur lineaments. The area to the north of PCL exhibits NNE to NE-SSW to SW trending fracture /lineaments, the major being Dharmapuri rift zone which extends from Bhavani in the west and Gudiyattham in the east. The area to the south of Palaghat-Cauvery lineament (PCL) is called Pandian Mobile Belt (PMB) and the NW-SE trending Achankoil lineament is developed at the southern most fringe of PMB.
The survey and exploration for atomic minerals was initiated in Tami Nadu during 1948 by the Madras Party of then Rare Minerals Survey Unit (RMSU). In the earlier stages of investigations (1950-55), emphasis was given to locate beryle bearing pegmatites occurring within the crystallines. Radioactivity due to thorium was reported in general and a few uranium anomalies were reported in (a) granite and pegmatites in the western margin of Suryamalai batholiths at the contact of hornblende biotite gneiss in Kullampatti (1955-56), Kodamedu and Serandampalayam (1981-82) areas in Salem district; (b) carbonaceous clay overlying the lignite in Neyveli area in Cuddalore district (1962-63); (c) quartz veins occurring within the migmatite and gneiss in Narlapalli and Pungurthi (1971-72) areas in Dharmapuri district (d) alkali syenites in Rasimalai hill (1992-93) and quartz barite veins in Andyapanur-Ponmalai-Narasingapuram tract (1989-90) and Pungulam area (2006-07) which are emplaced within the quartzo-feldspathic epidote bearing hornblende gneiss in the northern part of Dharmapuri rift zone in parts of Vellore district. Besides, several uranium –thorium –REE-Nb-Ta anomalies were reported in the carbonatites and quartz-barite veins associated with the alkaline complexes occurring within the Dharmapuri Rift Zone in the northern parts of Tamil Nadu. Those associated with carbonatite are reported in Sevathur and Pakkanadu and Mulakkadu (1972-73) areas and some of them associated with pegmatites are in Kurumbatti area of Srinivasa Mica mines (1950-51), Suliapatti (1966-67) and Manaparai (1969-70) areas.
Other facilities available at Southern Region
The Region is equipped with various facilities in different laboratories such as: