||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.
The following are the broad geological domains of the Southern Region.
(i) Archaean Basement Rocks (>2500 Ma) :The basement rocks comprise Archaean granulite facies containing quartzites, garnet-sillimanite gneiss, marble, 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, 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 sedimentary sequence of ~12 km thickness 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 : 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 ilmenite, monazite, rutile, garnet, zircon and sillimanite.
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 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, 2,100 line km Car borne radiometrics, 16,330 line km airborne gamma ray spectrometry and magnetics, 7,000 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 number of surface uranium occurrences along Gogi-Kurlagere (KG) and Wadi fault zones besides number of potential target zones delineated by hydro-geochemical survey, heliborne time domain electromagnetic (TDEM), magnetic and gamma ray spectrometric surveys.
Extensive sub-surface exploration (55,600m) at Gogi has established uranium mineralisation hosted in limestone and granite. It is a granite related deposit, which is structurally complex. Pitchblende and coffinite are the main uranium minerals. The ore contains anomalous concentration of REE, Pb, Ag and Au. Gogi uranium deposit is located 12 km west of Shahapur, the Taluk town and 75 km south of Kalaburgi. The nearest rail head is Yadgir about 40 km to the east, which is also the district headquarter.
Exploratory mining to study the ore body characteristics and to obtain bulk ore for process studies was carried out earlier. Sub-surface exploration in the extension areas of Gogi uranium deposit, along tectonic contact between the basement granitoid and sediments of Bhima Group defined by KG fault resulted in establishing another uranium deposit with a strike length of 2,000m with 20-90m width in Kanchankiyi-Hulkal area hosted by brecciated limestone having carbonaceous matter. The northeastern trend of the subsidiary arm of the KG fault associated with uranium mineralisation in Kanchankiyi-Hulkal continues eastward and is under active exploration. Bhima basin has got immense potential for discovering more uranium deposits.
The meso to neo-Proterozoic Kaladgi basin, covering an area of 8,300 sq km 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 and younger Badami Groups of Kaladgi Supergroup. 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. 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.
Uranium exploration was initiated in the sixties with a multipronged strategy. An area of 6,600 sq km has been covered by Airborne Gamma Ray Spectrometric (AGRS) 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 3,000 sq km indicated that eastern part of the basin is 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 7,500 sq km. 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 8,000 sq km. Ground geophysical survey viz., resistivity, magnetic and electro-magnetic surveys were also carried out along favourable zones, covering an area of 20 sq km, around Deshnur and 7 sq km around Hulihatti.
Reconnoitory drilling (25,000m) 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 were recorded in Badami arenite in boreholes around Tugunshi area whose thickness varies from 0.50 to 1.70m. Significant uranium mineralisation has been located in the year 2005 near Deshnur, which is about 30 km east of Belgavi. 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 mineralisation has been established over a strike length of 360m hosted by highly altered, fractured, sulphide bearing feldspathic lower conglomerate 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.
Systematic multipronged approach resulted in identifying uranium mineralised zone in Gujanal block. A total of 102 boreholes were completed in Gujanal with a cumulative drilling of 34,052.40m. In the first phase of exploration, significant uranium mineralisation of 0.020 - 0.16% eU3O8 x 0.20 - 6.50m over 1800 m strike length with the width of 40 to 360m was intercepted in sulphide bearing feldspathic conglomerate / arenite intercalated clay bands, mainly confined along bedding planes. In the second phase, exploration targeted along NE - SW trending fault zone intercepted high order correlatable mineralisation of 0.012 - 0.075% eU3O8 x 0.20 to 22.70m over 700m, hosted by sulphide bearing feldspathic conglomerate / arenite and basement chlorite schist in fracture zone. Pitchblende, traces of coffinite, uraninite along with pyrite, bravoite, galena, bornite and sphalerite are identified by petrography.
Active exploration is being continued and Kaladgi basin offers an ideal geological setting for hosting typical unconformity type uranium deposit.
Cuddapah Basin a Uranium Province
Tummalapalle Uranium Deposit: Cuddapah basin in South Indian Shield is an established uranium province. Different types of uranium mineralisation of varying age are reported here viz. Granite-related (Granite hosted: Mullapalle), Granite-related (Gulcheru quartzite hosted : Gandi-Madyalabodu), Carbonate deposit (Strata-bound, dolostone hosted: Tummalapalle) and Proterozoic Unconformity deposits (Stratiform structure-controlled deposits, between basement granite and Srisailam quartzite: Chitrial and Lambapur).
Tummalapalle uranium deposit situated in YSR (Kadapa) 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 Bengaluru (220 km), Hyderabad (400 km) and Tirupathi 250km. This deposit and its extension areas are located at the south-western part of Proterozoic Cuddapah basin over an area of 21 km x 2 km from Gidankivaripalle village in east to Motnutalapalle in west.
Association of uranium with the impure phosphatic dolostone in Vempalle Formation was first reported by Geological Survey of India in 1986. Subsequently, surface and sub surface investigation by AMD in two phases i.e. from 1986 to 1995 and 2007 till date have proved substantial uranium resources. Here uranium mineralisation is in the form of strata-bound, dolostone (Vempalle Formation) hosted carbonate deposit, 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 reveals that the carbonate facies commences with massive dolostone, followed by 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 some U in the adsorbed form with collophane 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 6.6 km along strike length and 1.2 km along dip from 15 m to 250 m depth. Uranium mineralisation occurs as two bands, hangwall and footwall bands with a vertical separation of 1m to 3m. Both the bands show isotropic character along and across the strike in terms of grade and thickness. Average thicknesses of these bands are 2.3m and 1.75m for hangwall and footwall respectively with average grade of 0.05% eU3O8 at 0.02% cut off. During this phase 37,635m was drilled in 264 boreholes and about 14,600te of U3O8 proved. Investigation in this area was suspended in 1993 due to hydrometallurgical constraints and shift in priority areas of AMD.
Considering the demand of uranium for the ongoing Indian Nuclear programme and after successfully overcoming the constraints of hydrometallurgical process, commercial mining of Tummalapalle uranium deposit commenced. Foundation was laid for mining and processing plant of Tummalapalle deposit on November 19 - 20, 2007. The mining of the footwall band of the deposit was first taken up for exploitation. As a part of target expansion programme (second phase), exploratory drilling in the extension areas of Tummalapalle was initiated during the 2007-08.
During second phase of exploration programme, about 4,46,500 m of drilling has been completed in 1,437 boreholes and about 1,78,300 te of U3O8 has been added in Tummalapalle deposit and its extension areas as on October 2020. Tummalapalle Mill was inaugurated on April 20, 2012. Sub-surface exploration in the area is in progress.
Investigations in Cuddapah basement fracture zones:
The basement complex of crescent–shaped Cuddapah basin in the eastern Dharwar craton comprises 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 1980s by AMD led to location of number of thorium free uraniferous fracture zones right from Nagari - Kurvapalle area in the east to Bimunipalle area near Gooty in the west. These fracture zones show varying trend ranging from NNE-SSW (Sanipaya - T.Sundupalle), ENE-WSW (Mulapalle) and NW-SE (Lakshmipuram). Among these, ENE-WSW trend is predominant and shows significant mineralisation. The mineralised fracture zones show strike extent ranging from 250 m to 16 kms (intermittently) with a width of <1 m to 5 m. Mineralisation is associated with cataclsite and mylonites along fault/shear zone. Though the fracture zones are widespread, mineralised fracture zones are confined to fertile granites of Closepet affinity.
Alterations like chloritisation, haematitisation, phosphatisation and silicification associated with the granite related uranium mineralisation have been observed. Three types of granitoids namely Peninsular Gneiss, K-rich Closepet Granite and Na rich microgranites are reported in the terrain. About 68 fracture zones associated with uranium mineralisation are reported in the southwestern margin of Cuddapah basin.
Exploratory drilling commenced in 1989 at Sanipaya-T Sundupalle fracture zone, where 33 boreholes (3,454.95m) were drilled. A lean mineralised zone over 500 m strike length was established in the area. Subsequently, emphasis was shifted to Mulapalle fracture zone, which was also located during, 1987-88 and detailed investigations were carried out during 1989-90 and 1991-92. Exploratory drilling in Mulapalle commenced in May 1993. This fracture zone was under active exploration till September 1998 and has given the most promising results of all the fracture zones. A total of 38 boreholes were drilled (6,479.85 m) in this area covering a total strike length of 500m. Mineralisation in the form of three different lenses was delineated in the area. Exploratory drilling was carried out during the period 1995-98 in six other fracture zones such as Chenchalapalle, Burjupalle, Timmareddigaripalle, Payalopalle (N), Mulapalle-II and Varikuntapalle.
In Kamagutapalle area, surface uranium mineralisation was traced for about 3 km along fracture trending N20°E-S20°W in the 90’s. Shielded probe logging revealed 9 lenses distributed over a length of 710m in the southern part of the fracture zone. Based on further rechecking during 2014-15, encouraging result lead to reopening the Kamaguttapalle area for subsurface exploration by contract drilling in 2015-16. Currently, sub surface exploration is in progress, which has resulted in proving uranium mineralisation over a strike length of 320 m in Kamaguttapalle Main block.
The Region is equipped with various facilities in different laboratories such as: