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Kumar I.,Atomic Mineral Directorate for Exploration and Research | Kumar S.V.,Atomic Mineral Directorate for Exploration and Research | Babu V.R.,Atomic Mineral Directorate for Exploration and Research | Kumar B.V.L.,Atomic Mineral Directorate for Exploration and Research | And 2 more authors.
Journal of the Geological Society of India | Year: 2017

Cuddapah basin is known for hosting unconformity proximal uranium deposits viz., Lambapur, Peddagattu, Chitirial and Koppunuru along the northern margin of the basin. It is well known that these deposits are mostly associated with basement granitoids in Srisailam Sub-basin, and with cover sediments in Palnad subbasin where basement topography and fault/fracture system influence the fluid flow causing basement alteration and ore deposition. Geological setup, surface manifestation of uranium anomalies and association of the hydro-uranium anomalies near Durgi area in southern part of the Palnad sub-basin, have prompted detail investigation by geophysical methods to probe greater depths. Controlled Source Audio Magneto Telluric (CSAMT) survey conducted over five decades of frequency (0.1-9600 Hz) delineated the various lithounits of Kurnool and Nallamalai Groups along with their thicknesses as there exist an appreciable resistivity contrast. Interpretation of CSAMT sounding data are constrained by resistivity logs and litholog data obtained from the boreholes drilled within the basin indicated three to four layered structure. Sub-surface 2-D and 3-D geo-electrical models are simulated by stitching 1-D layered inverted resistivity earth models. Stitched 1-D inverted resistivity sections revealed the unconformity between the Kurnool Group and Nallamalai Group along with basement undulations. The faults/fractures delineated from the CSAMT data corroborated well with the results of gravity data acquired over the same area. Simulated 3-D voxel resistivity model helped in visualising the faults/fractures, their depth extent, thickness of the Banganapalle quartzite and basement configuration. Integrated interpretation of CSAMT, gravity and borehole data facilitated in delineating the unconformity and the structural features favourable for uranium mineralisation in deeper parts of the Palnad sub-basin. © 2017, Geological Society of India.

Bhoopathi V.,Osmania University | Niranjan Kumar S.,Atomic Mineral Directorate for Exploration and Research | Sastry R.S.N.,Osmania University | Srinivas B.,Osmania University
Chinese Journal of Geochemistry | Year: 2015

Surface radioactive survey has been carried with portable gamma ray spectrometer (PGRS) about the 45 km2 around the Srisailam sub basin, the surface radioactive anomalies were found at Chennakesavula gutta in the Srisailam sub basin of Cuddapah basin in the age of meso-neo proterozoic, India. The integrated geochemical and radiometric surveys were conducted as part of research work in the Srisailam basin, it has resulted the locating of surface radioactive anomalies near the Chennakesavula gutta. Secondary uranium minerals are observed along with the fracture planes in the Archean basement granite in the proximity of unconformity contact of Srisailam quartzite. The granite underlies the Srisailam formation and forms the source for possible unconformity related uranium mineralisation in the Srisailam sub-basin evidence by the significant radioactive anomalies. The radioactivity recorded by PGRS reflected uraniferous nature of the radioactivity (Average total counts = 195 ppm; U = 202 ppm; Th = 22 ppm; %K = 4.1, n = 15). © 2015, Science Press, Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg.

Pandey U.K.,Atomic Mineral Directorate for Exploration and Research | Sastry D.V.L.N.,Atomic Mineral Directorate for Exploration and Research | Pandey B.K.,Atomic Mineral Directorate for Exploration and Research | Roy M.,Atomic Mineral Directorate for Exploration and Research | And 3 more authors.
Journal of the Geological Society of India | Year: 2012

The Dargawan gabbros intrusive into the Moli Subgroup of Bijawar Group, yielded Rb-Sr whole rock isochron age of 1967 ± 140 Ma. Based on the oldest age from overlying Lower Vindhyan (1.6Ga) and the underlying youngest basement ages (2.2 Ga), the time range of Bijawar sedimentation may be assigned as 2.1-1.6 Ga (Paleoproterozoic). Sm-Nd Model ages (T DM), obtained, for Dargawan gabbros, is c. 2876 - 3145 Ma. High initial 87Sr/ 86Sr ratio of 0.70451 (higher than the contemporary mantle) and negative ε Ndi (at 1.9 Ga) value of -1.5 to - 4.5, indicate assimilation of Archaean lower crustal component by the enriched mantle source magma at the time of gabbroic intrusion. The dolerite, from Damdama area, which is intrusive into the basement and overlying sediments of Chandrapur Group in the central Indian craton, yielded Rb-Sr internal isochron age of 1641 ± 120 Ma. The high initial 87Sr/ 86Sr ratio of 0.7098 and εNdi value of -3.5 to -3.7 (at 1.6 Ga) is due to contamination of the mantle source magma with the overlying sediments. These dolerites have younger Sm-Nd Model ages (T DM) than Dargawan gabbros as c. 2462 - 2675 Ma, which is similar to the age of the Sambalpur granite, from which probably sediments to this part of Chattisgarh basin are derived. Hence mixing of sediments with the Damdama dyke during its emplacement, gives rise to high initial 87Sr/ 86Sr and low initial 143Nd/ 144 ratios for these dykes. The c. 1600 Ma age indicates minimum age of onset of the sedimentation in the Chandrapur Group of Chattisgarh basin. Both the above mafic intrusions might have taken place in an intracratonic rift related (anorogenic) tectonic setting. This study is the first reliable age report on the onset of sedimentation in the Chandrapur Group. The total minimum time span of Chandrapur and Raipur Group may be 1.6 Ga to 1.0 Ga (Mesoproterozoic). The unconformably underlying Shingora Group of rocks of Chhattisgarh Supergroup thus indicates Paleoproterozoic age (older than 1.6 Ga). Most part of the recently classified Chattisgarh Supergroup and Bijawar- Vindhyan sequence are of Mesoproterozoic-Paleoproterozoic age and not of Neoproterozoic-Mesoproterozoic age as considered earlier. Petrographic study of basic dykes from Damdama area (eastern margin of Chattisgarh Supergroup) indicated presence of primary uranium mineral brannerite associated with goethite. This is the evidence of mafic intrusive providing geotherm and helping in scavenging the uranium from the surrounding and later alterations causing remobilisation and reconcentration of pre-existing uranium in host rocks as well as in mafic dyke itself otherwise mafic rocks are poor source of uranium and can not have primary uranium minerals initially. It can be concluded that mafic dykes have role in uranium mineralisation although indirectly. © Geol. Soc. India.

Jha S.K.,University of Delhi | Shrivastava J.P.,University of Delhi | Bhairam C.L.,Atomic Mineral Directorate for Exploration and Research
Journal of the Geological Society of India | Year: 2012

Clays associated with the Precambrian unconformity-related (sensu lato) uranium mineralization that occur along fractures of Rohini carbonate, Bandai sandstone and clay-organic rich black carbonaceous Gorakalan shale of the Sonrai Formation from Bijawar Group is significant. Nature and structural complexity of these clays have been studied to understand depositional mechanism and palaeoenvironmental conditions responsible for the restricted enrichment of uranium in the Sonrai basin. Clays (<2 μm fraction) separated from indurate sedimentary rocks by disaggregation, chemical treatment and centrifugation were examined using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Presence of tv-1M type illite is inferred from the Rohini and Bandai Members of the Sonrai Formation, indicative of high fluid/rock interaction and super-saturation state of the fluids available in proximity with the uranium mineralization. It is observed that the Sonrai Formation is characterized by kaolinite > chlorite > illite > smectite mineral assemblages, whereas, Solda Formation contains kaolinite > illite > chlorite clays. It has been found that the former mineral assemblage resulted from the alteration process is associated with the uranium mineralization and follow progressive reaction series, indicating palaeoenvironmental (cycles of tropical humid to semi-arid/arid) changes prevailed during maturation of the Sonrai basin. The hydrothermal activity possibly associated with Kurrat volcanics is accountable for the clay mineral alterations. © 2012 Geological Society of India.

Som A.,Atomic Mineral Directorate for Exploration and Research | Sai Baba M.,Atomic Mineral Directorate for Exploration and Research | Jeyagopal A.V.,Atomic Mineral Directorate for Exploration and Research | Shobhita K.,Atomic Mineral Directorate for Exploration and Research | And 2 more authors.
Journal of the Geological Society of India | Year: 2010

Several radioactive anomalies due to uranium and thorium, associated with the mesedimentary enclaves (Archaean) within granite (Archaean to Early-Proterozoic) have been recorded in parts of Karimnagar Granulite Terrain, Karimnagar Dist. At Peddur and Kottur, Uraninite has been identified in the samples of metasediments. The metasediment from these two places have been subjected to granulite facies of metamorphism and host high values of uranium with negligible thorium. In Peddur, samples of metasediments have assayed as high as 1.96% U3O8 with negligible thorium, and in Kottur up to 0.059% U3O8. Leaching studies on these samples have indicated that most of the U3O8 present is leachable. This discovery has opened up the possibility of finding uranium mineralisation in Archaean metasediments and thus provides a thrust for uranium exploration in similar geological environs in India. Further, the basement granite along with the metasedimentary enclaves has the potential to act as a provenance for a possible unconformity type or sandstone type U-deposit in the rocks of overlying Pakhal and Gondwana Supergroup, in Pranhita-Godavari Basin, situated to the east of this area. © 2010 Geological Society of India.

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