Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

A. V. Jeyagopal ¹, R. V. Singh ¹, P. Nageswara Rao ¹, V. P. Saxena ¹, R. M. Sinha ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad - 500 0 16, IN

Abstract

Recent geological studies have brought out the presence of hitherto unknown Cumbum shale/Phyllite in the Julakallu-Pinneli area, Guntur district, Andhra Pradesh within the Palnad Sub-Basin of the Cuddapah basin. Cumbum shale/Phyllite and quarzite was found to rest above the Narji Limestone at southeast of Petasannigandla. This has necessitated northward shift of thrust boundary separating the Cumbum Formation and Narji Limestone from earlier known location. Subsurface data have confirmed larger thickness of the Narji Limestone than that reported in the literature. Geochemical characteristics of the Cumbum shale/Phyllite have indicated its deposition as first cycle of sediments in a tectonically active setting. This is supported by the depletion of immobile oxide Al₂O₃ and enrichment of mobile oxide CaO in the Cumbum shale. The A-CN-K plot indicates that provenance for shale/Phyllite could be granodiorite to granite in composition, which is also supported by petrological observations. The field, petrological and geochemical interpretations have brought out much new information on this part of the basin, which necessitates, revision of the geology of area.

Keywords

Cumbum Formation, Narji Limestone, Thrust Boundary, Cuddapah Basin, Julakallu, Andhra Pradesh.

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S. Niranjan Kumar ¹, G. Nagendra Babu ¹, A. V. Jeyagopal ¹, P. B. Maithani ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Hyderabad - 500 016, IN

Abstract

Reconnaissance radiometric surveys in the northwestern parts of the western Pakhal belt in the Pranhita-Godavari Basin (PG basm), have led to the location of uranium anomalies for the first time in the environs of P-G Basin exclusively in the "older sheared fuchsite bearing quartzite'' overlain by the Neo-Proterozoic Penganga sediments in the proxmity of their unconformity contact at Mysemgutta, Kaddam, district Adilabad, A. P. Surface mineralisation is manifested in the form of secondary uranium minerals associated mainly along the fractures in the fault zones. The quartzite assayed up to 0.23% U₃O₈ with negligible thorium (2). Follow up petrological and XRD studies of the rocks revealed the presence of primary uranium mineral uraninite (UO₂) in addition to secondary U-Minerats in the form of lanthinite [U₆O₇(OH)₂O], metatorbernite [Cu(UO₂)₂(P0₄)₂ 8H₂O] and phosphuranylite [Ca(UO₂)₄(PO₄)₂(OH)₄ 7H₂O], besides U+Ti phases/brannerite [U,Ca,Ce)(Ti,Fe)₂0₆ Other ore minerals associated are chromite, pynte, pyrrhotite and rutile. The discovery has opened up new vistas for seeking Proterozoic unconformity related uranium mineralisation at the base of Neo-Proterozoic Penganga sediments in the PG Basin, Andhra Pradesh.

Keywords

PG Basin, Penganga, Fuchsite Quartzite, Unconformity, Kaddam, Mysemgutta, Andhra Pradesh.

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A. V. Jeyagopal ¹, R. Dhana Raju ², P. B. Maithani ¹, Anjan Chaki ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, 6-3-124, Hastinapuri, Secundarabad - 500 094, IN

Abstract

The Mesoproterozoic Papaghni Group in the Cuddapah basin of southern Andhra Pradesh comprises mainly arenaceous, argillaceous and calcareous sediments. These sediments occur in sequences that are mappable on large scale (15000) and the sequences are idenified by unconfornities which are recognised by conglomerate/breccia beds in Vempalle Formation (Papaghni Group). Each sequence starts with near shore arenaceous and argillaceous sediments and ends up with relatively deeper marine chemical precipitate, viz dolomitic sediment, with these three constituting one cycle of sediments. The thickness of each cycle ranges from about twenty meters to hundreds of meters and three such cycles of sedimentation are identified. On the basis of the identification of cyclic sedimentation and bounding unconfornuties it is proposed that the Vempalle Formation of Papaghni Group may be classified into Lower, Middle and Upper members, which denote recurrence of similar depositional settings during the Vempalle sedimentation.

Keywords

Cyclic Sedimentation, Papaghni Group, Cuddapah Basin, Andhra Pradesh.

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Anjan Som ¹, M. Sai Baba ², A. V. Jeyagopal ¹, K. Shobhita ¹, R. Mohanty ², P. B. Maithani ¹

Affiliations
1 Atomic Mineral Directorate for Exploration and Research, Begumpet, Hyderabad - 560 629, IN
2 Atomic Mineral Directorate for Exploration and Research, North Eastern Region, Shillong - 793 011, IN

Abstract

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.

Keywords

Uraninite, Karimnagar Granulite Terrain, Metasediment, Peddur, Kottur, Andhra Pradesh.

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R. Dhana Raju ¹, R. N. Prasad ², D. D. Pandey ², A. V. Jeyagopal ², R. D. Deshmukh ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Bangalore - 560072, IN
2 Atomic Minerals Division, Department of Atomic Energy, Hyderabad - 500016, IN

Abstract

Baryte at Vemula near to the southwestern margin of Cudapah Basin occurs as a vein-type deposit discordant to both the carbonate rocks of Vempalle formation and its intrusive dolerite. S-isotopic data on the baryte have a range of δ³⁴S_CDT between +16.2‰ and +23.3‰ whereas the coexisting chalcopyrite has a restricted range between +10.9‰ and +11.4‰. The average value of δ³⁴S of Vemula baryte (+20.8‰) differs much from that of magmatic rocks (0‰ to +2.5‰), metamorphic rocks (+3‰) and sediments of continental margins, platform areas and geosynclines (-12.5‰ -17,1‰), but is similar to that of sea water (+20‰) which appears to be the source for sulphur. The narrow range of δ³⁴S of baryte and chalcopyrite points to a uniform source with their sulphur possibly derived from sea water sulphate by bacteriogenic reduction.

Keywords

Economic Geology, Baryte, Sulphur Isotope, Cuddapah Basin, Andhra Pradesh.

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