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Southern Region of AMD, which is headquartered at Bengaluru, is carrying out an intensive exploration programme for uranium and other atomic minerals by planning and implementing systematic phase-wise exploration programme in various geological domains of Southern India. The important geological domains in Southern Region include Mesoarchaean-Cambrian Southern Granulite Terrain, Proterozoic Basins such as Cudappah, Bhima and Kaladgi, Cretaceous-Tertiary Deccan Traps and Recent sediments. The unique geological set-up provides several target areas for exploration of uranium, rare-metals and rare-earth minerals. Additionally, the long coastal stretch along the western and eastern margin of Southern Region contains rich concentration of beach sand minerals including monazite and exploration is continuing for these minerals in various parts of the coastal stretches. Southern Region hosts the largest uranium deposit in the country at Tummalapalle, YSR District Andhra Pradesh as well as the richest grade uranium deposit in the country at Gogi, Yadgiri dirstict, Karnataka.
The following are the broad geological domains of the Southern Region.
(i) Archaean Dharwar Craton: Dharwar Craton comprises a western part (Western Dharwar Craton-WDC) underlain by Peninsular Gneiss (2900-3300 Ma), an ensemble of orthogneisses and granodiorites interspersed with older tracts of metasedimentary and metamorphosed igneous suit (Sargur Group). This association forms the basement to volcano-sedimentary schist belts of the low-grade Late Archean Dharwar Supergroup. The WDC is intruded by Late Archean granite plutons. The eastern part of the craton (Eastern Dharwar Craton - EDC) is dominated by Late Archean calc-alkaline complex of anatectic granites, granodiorites, monzonites and diorites. They are interspersed with schist belts, which are lithologically similar to Dharwar Supergroup in the west. The plutonic complex is named Dharwar batholith on account of the close lithological similarity, structural coherence and emplacement of its principal components in the period ca. 2750-2510 Ma. High-grade metamorphism leading to formation of charnockite took place to the south of the batholith. The WDC and EDC are separated by a linear tract of granites and gneisses referred as Closepet Granite trending N-S or NW-SE close to the western boundary of the batholith.
(ii) Late Archaean Dharwar Supergroup: The rocks of Dharwar Supergroup consist of volcano-sedimentary sequences that can be broadly divided into the Lower Bababudan Group and the Upper Chitradurga Group. Bababudan Group is characterised by platformal sediments with quartz pebble conglomerate, pebbly quartzite, fuchsite quartzite and banded magnetite quartzite. It is followed by sub-aerial mafic volcanics. Chitradurga Group is typified by geosynclinal sediments with subordinate volcanics and well-developed linear tracts of limestone, manganese and associated iron formations. These rocks are mostly found in Karnataka and parts of Andhra Pradesh.
(iii) Neo-Archean to Palaeoproterozoic Closepet Granite: Closepet Granite extends in a north-south direction as a 50 km wide narrow belt. It marks a major geo-suture separating two distinct crustal blocks of Archaean age. The Western Block is characterized by well-developed low-grade granite-greenstone belts with iron-manganese ores. The Eastern Block is represented by younger gneisses of granitic and granodioritic composition enclosing a number of narrow, linear bands of auriferous schist belts.
(iv) Middle to Upper Proterozoic Cuddapah Supergroup: Cuddapah Supergroup and its equivalents, such as Bhima Group & Kaladgi Group of rocks, are the most significant geological domains in Indian geology. Cuddapah Basin comprises a sedimentary sequence of approximately 12 km thickness and volcanic rocks in the form of sills and dykes. These rocks overlie Archaean Peninsular Gneissic Complex along a pronounced Eparchaean unconformity.
(v) The Kaladgi and Bhima Basins: These basins occur in the northern parts and extend below the Deccan Traps. These basins comprise rocks of clastic/chemogenic origin.
(vi) The Deccan Trap of Mesozoic-Tertiary age : These overlie the northern extensions of the Dharwar craton.
(vii) The Younger (Mesozoic - Tertiary): These sediments include Gondwanas of Palar Basin, Cretaceous rocks of Tiruchinapally, Cuddalore Sandstone, Warkala Beds, Quilon Beds etc.
(viii) The Beach and Inland Placers: These are part of Quaternary Group of rocks. The beach and inland placers of Tamil Nadu and Kerala host some of the richest deposits of monazite, ilmenite, rutile, leucoxene, garnet, zircon and sillimanite.
Cuddapah Basin:
The Cuddapah Basin in Southern Indian Shield is an established uranium province. The basin hosts different types of uranium mineralization of varying age, including Granite-related Mullapalle and Gandi-Madyalabodu, Carbonate type (Tummalapalle Group), and Proterozoic Unconformity type (Chitrial, Peddagattu and Lambapur).
Tummalapalle Group uranium deposit is located in the YSR (Kadapa) district, Andhra Pradesh in Toposheet no. 57J/7. The deposit and its extension areas are falls in the south-western part of the Proterozoic Cuddapah basin from Gidankivaripalle village in the east to Motnutalapalle in the west.
The association of uranium with impure phosphatic dolostone in the Vempalle Formation was first reported by the Geological Survey of India in 1986. Subsequently, surface and subsurface investigations by AMD in two phases, from 1986 to 1995 and 2007 till date, have revealed substantial uranium resources. Uranium mineralization here occurs in the form of a strata-bound, dolostone (Vempalle Formation) hosted carbonate deposit, in the western margin of the Papaghni Sub-basin. It extends from Reddipalle in the northwest to Maddimadugu in the southeast over a belt of 160 km. The Vempalle Formation, which is approximately 1900 m thick, overlies the Gulcheru Formation with a transitional boundary. Studies on the complete sequence of Vempalle Formation in the explored areas reveal that the carbonate facies commence with massive dolostone, followed by a thin band of conglomerate, uraniferous phosphatic dolostone, red shale, and cherty dolostone. Ultrafine pitchblende and uraninite are the main uranium minerals, while coffinite, U-Si-Ti complex, and U in adsorbed form with collophane have been identified as minor U mineral phases. The associated ore minerals are mainly pyrite, molybdenite, chalcopyrite, bornite, and covellite.
Uranium mineralization in the Tummalapalle area was confirmed over a strike length of 6.6 km and a dip length of 1.2 km, ranging from a depth of 15 m to 250 m. Uranium mineralization occurs as two bands: the hangwall and footwall bands, with a vertical separation of 1 m to 3 m. Both bands exhibit isotropic characteristics along and across the strike in terms of grade and thickness.
A total of approximately 2,48,759 tonnes of U3O8 have been established in the deposit. Currently, the dip continuity of the stratabound uranium mineralization has been proven up to 1000 meters depth. The strike and dip continuity of the correlatable stratabound mineralization is observed over 26.0 km x 4.5 km.
Investigations in Cuddapah basement fracture zones:
The basement complex of the Cuddapah Basin comprises an Archaean greenstone-granitoid association with profuse mafic (doleritic) dykes and felsic (quartzo-feldspathic reef/veins) intrusions along reactivated fracture zones. Geological and radiometric investigations of the crystalline basement initiated in the 1980s by AMD led to the location of a number of thorium-free uraniferous fracture zones, ranging from Nagari-Kurvapalle area in the east to Bimunipalle area near Gooty in the west. These fracture zones show varying trends ranging from NNE-SSW (Sanipaya-T.Sundupalle), ENE-WSW (Mulapalle), and NW-SE (Lakshmipuram). Mineralization is associated with cataclasite and mylonite along fault/shear zones. Alterations such as chloritisation, haematitisation, phosphatisation and silicification have been observed in association with the uranium mineralisation related to the granite.
First phase of exploratory drilling commenced in 1989 which established a lean mineralised zone over a 500 m strike length at the Sanipaya-T. Sundupalle fracture zone, over 700 m strike length at Mulapalle fracture zone, and 1.3km along strike length at Varikuntapalle fracture zone. Apart from these, six (06) other fracture zones namely Chenchalapalle, Burjupalle, Timmareddigaripalle, Payalopalle (N), Mulapalle-II and Gollapalle were tested by drilling.
Second phase of exploration started during 2015-16 along 15 km long N20oE-S20oW Kamaguttapalle fracture zone where detailed surface investigations were carried out in the 1990s and was established for 320m with vertical depth impact of 250m. Subsequently, Pincha-Sivaramapuram fracture zone and Reddivaripalle fracture zone were also explored.
Presently sub surface exploration commenced in 2022 in Katimayakunta Block in the central part of 27 km long NE-SW BR Palle fracture zone where significant uranium mineralisation has been proved over a strike length of 285 m.
Bhima Basin is one of the smallest Proterozoic Basins of Peninsular India, with an aerial extent of 5,200 sq km situated at the north-western fringe of Eastern Dharwar Craton (EDC). The Basin is characterized by a number of regional, E-W trending basin margin faults affecting both basement and the cover sediments of Bhima Group.
An integrated exploration programme comprising satellite image analysis, litho-structural mapping, radiometrics, heliborne time domain electromagnetic (TDEM), gamma ray spectrometry and magnetic survey, geochemical survey and gamma ray logging of bore-wells were carried out in the basin, which lead to the identification of number of surface uranium anomalies and occurrences along Kurlegere-Gundahalli (KG), Farhatabad and Wadi fault zones. The most prominent and significant uranium anomalies like those in Malla, Ukinal, Darshanapur, Gogi, Kanchankayi and Halbhavi.
Sub-surface exploration commenced at Gogi in 1997. The KG Fault exhibits reverse nature up to 2 km east of Halbhavi and is transacted by several NW-SE and NE-SW cross faults. In Gogi area, uranium mineralisation is hosted by deformed limestone, shale and basement granite and continues up to a depth of 270m to 290m below the surface.
Gogi uranium deposit is located 12 km west of Shahapur and 75 km south of Kalaburagi. Extensive sub-surface exploration at Gogi established a uranium deposit (4,200 tonnes U3O8) hosted in brecciated limestone and granite. Exploratory mining at Gogi commenced in 2007 to study the ore body characteristics and to obtain bulk ore for process studies was carried out.
In Kanchankayi Block, sub-surface exploration established approximately 2,100 tonnes U3O8 hosted in brecciated limestone. In Hulkal Block, in the eastern extension of Kanchankayi deposit,integrated geological and geophysical studies have demarcated the continuity of the fault zone over another ~3.5 km from Kanchankayi Block. Sub-surface exploration established approximately 800 tonnes U3O8 hosted by brecciated limestone and granite. Further exploration along KG fault in the eastern part is in progress. Pitchblende and coffinite are the main uranium minerals, which associated with pyrite and organic matter. The ore contains anomalous concentration of Pb, Cu, Co, Ni, Zn, Cr, Mo, V and Ba and elevated concentration of REE, Ag and Au.
Further, geological favourability of Bhima Basin for uranium mineralisation has prompted exploration for uranium along other E-W trending regional faults especially Tirth-Tintini, Wajhal- Hunsagi and Farhatabad-Sedam Faults besides NE-SW trending Wadi Fault.
Kaladgi Basin covers an area of approximately 8,300 sq km.  It occupies the northwestern fringes of the western Dharwar craton, in parts of Karnataka, Maharashtra, and Goa. The northern and western extensions of the basin are covered by Deccan Trap. The basin exposes sediments of older Bagalkot Group and younger Badami Group of Kaladgi Supergroup. Bagalkot Group consists of 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. Archaean Peninsular Gneiss, Chitradurga Schist of Dharwar Supergroup, 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.
Reconnaissance drilling was carried out around Tugunshi, Siddankola, Murdi, Hulikeri, Khanapur, and Deshnur to locate unconformity-type mineralization. Significant uranium mineralization was located in 2005 near Deshnur, which is about 30 km east of Belagavi, in unconformity surface below the feldspathic conglomerate and arenite of Badami Group. Correlatable mineralization has been established over a strike length of 360 m hosted by highly altered, fractured, sulphide-bearing feldspathic Lower Conglomerate along NE-SW direction. Pitchblende and coffinite are identified as the main uranium minerals. Bravoite, arsenopyrite, chalcopyrite, covellite, bornite, sphalerite and galena are the sulphide phases associated with mineralization.
A systematic multipronged approach resulted in identifying uranium mineralisation in Gujanal-Ankalgi Block. Exploration targeted along NE-SW trending fault zone intercepted correlatable mineralization over 700 m, hosted by sulphide-bearing feldspathic conglomerate/arenite and basement chlorite schist in fracture zone.
Present thrust areas:
Presently, uranium exploration in Southern Region is focused on Proterozoic unconformity type, carbonate type and granite-related types. As a result, the Kaladgi-Badami and Bhima Basins in Karnataka and the Cuddapah Basin in Andhra Pradesh along with basement rocks are under active exploration.
The Region is equipped with various facilities in different laboratories such as:
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