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

G. R. Gangadharan ¹, K. K. Achar ¹, K. Umamaheswar ¹, Mary K. Kumar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Nagarabhavi, Bangalore-560 072, IN

Abstract

No Abstract.

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R. Dhana Raju ¹, R. N. Prasad ², D. D. Pande ², A. Panneer Selvam ¹, Mary K. Kumar ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Bangalore-560 072, IN
2 Atomic Minerals Division, Department of Atomic Energy, Hyderabad-500 016, IN

Abstract

This study shows δ³⁴S values for the study of co-existing baryte and galena, respectively, are in the ranges of +6.9 to 8.0% and -6.0 to - 9.8%0. Such narrow ranges make biogenic sedimentary source for sulphur less likely and suggest magmatic source. Sulphur isotope values indicate a hydrothermal system with a T of ∼440°C, pH 5±1 and Log f0₂ of -34 to -37.

Keywords

Economic Geology, Sulphur Isotopes, Baryte, Galena, Tamil Nadu.

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Mary K. Kumar ¹, D. Veera Baskar ², Mithilesh Sharma ³, T. Chabria ⁴, R. Dhanar Raju ³

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Bangalore - 560 072, IN
2 Atomic Minerals Division, Department of Atomic Energy, Nagpur - 440 001, IN
3 Atomic Minerals Division, Department of Atomic Energy, Bangalore - 560 072, IN
4 Atomic Minerals Division, Department of Atomic Energy, Hyderabad - 500 016, IN

Abstract

Sulphur-isotopic dataon fifteen samples of baryte from the quartz-baryte rock occurring along a shear zone east of the Elagiri Syenite pluton at Andiyappanur, Tamil Nadu have shown a narrow range of +5.1‰ to +9.5‰, with an average of +6.70‰, for δ³⁴S_CDT. The data, in conjunction with the field and petromineralogical characteristics, indicate hydrothermal-type mineralisation of baryte. Association of relatively earlier formed sulphides like pyrite, molybdenite and galena, and later formed sulphates like baryte and jarosite in this quartz-baryte rock is attributed to dual behaviour of sulphur in the magmatichydrothermal system, with formation of sulphides at depth under reducing conditions and of sulphates in the shallower oxidised zones.

Keywords

Baryte, Geochemistry, Andiyappanur, Tamil Nadu.

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Mary K. Kumar ¹, D. Veera Bhaskar ², Y. Lakshmi Narayana ¹, R. Dhana Raju ¹

Affiliations
1 Atomic Minerals Division, Departntent of Atomic Energy, Bangalore-560 072, IN
2 Atomic Minerals Division, Departntent of Atomic Energy, Nagpur-440 001, IN

Abstract

Radiometric survey along the Goddaru Vanka stream near Rangampeta of North Arcot district, TamilNadu has brought to light an appreciable concenuation of rare-earths (RE)- and yttrium-minerals (allanite, monazite and xenotime) in the stream sands with feed samples assaying 0.034-0.35% CeO, and 0.003-0.34% Y₂, O₃, and their non-magnetic tabIe concentrates (1-10 wt% of feed) assaying 1.13-10.30% CeO₂ and 0.25-1.37% Y₂O₃. Of the different heavy minerals, magnetite shows positive correlation (r = 0.93 to 0.99) with allanite, xenotime, total RE- and Y-minerals, total heavy minerals, CeO₂, and Y₂,O₃, of the feed samples. The results also confirm the effectiveness of radiometric and magnetic surveys in delimiting RE- and Y-minerals in the stream sands.

Keywords

Re- and Y-Minerals, Stream Sands, Rangampeta, Tamil Nadu.

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Sukantadey ¹, R. Gajapathi Rao ¹, R. A. Gorikhan ¹, D. Veerabhaskar ¹, Sunil Kumar ¹, Mary K. Kumar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Bangalore - 560 072, IN

Abstract

The late Archaean Closepet Granite of the Gudur-Guledagudda area consists of equigranular pink and grey biotite granites, and porphyntic pink biotite granodionte to quartz-monzodionte. The granitoids exhibit intrusive relation with the Hungund-Kushtagi schist belt at places. The equigranular granites show limited range of major oxide compositions and compared to the porphyntic granodionte and quartz-monzodionte, are enriched in Si0₂, K₂0 and Rb but depleted in Al₂0₃, FeO, Fe₂0₃, CaO, MgO, P₂0₅, Sr, Ba, Y, Nb and REE. The granitoids fall near the boundary between peraluminous and metaluminous granitoids with the A/CNK ratios around one Fractionated LREE and flat HREE patterns and a negative Eu anomaly characterize all the samples Field evidences indicate mainly post-kinematic nature of the granitoids. The equigranular granites appear to be minimum melt derived from anatexis of Peninsular Gneiss without fractional crystallization. The porphyntic granodionte and quartz-monzodionte represent non-minimum melt derived from a different source enriched in REE Geochemical signatures indicate that the Closepet Granite of Gudur-Guledagudda area is the product of melting at shallower level compared to the southern Closepet Granite.

Keywords

Petrography, Geochemistry, Northern Closepet Granite, Gudur-Guledagudda Area, Karnataka.

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R. Dhana Raju ¹, Mary K. Kumar ², E. V. S. S. K. Babu ¹, S. A. Pandit ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Hyderabad - 500 01 6, IN
2 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Bangalore - 560 072, IN

Abstract

Uranium mineralisation in the Neoproterozoic Bhima basin todate has been found near Ukinal and at Gogi. U-mineralised phosphatic horizon near Ukinal includes the lithounits of phosphatic micritic limestonelchert and siliceous, calcareous phosphorite, some of which are manganiferous and glauconite-bearing. Uranium in these phosphatic rocks, correlatable with P₂O₅content (r>0.9), occurs mostly in collophanc and is difficult to extract. This mineralisation is sedimentary-diagenetic.

Mineralisation at Gogi is more promising. This occurs within the major E-W trending Gogi-Kurlagere fault, near to its intersection with a NE-SW trending fault and is hosted by both brecciated, siliceous limestone and deformed basement rock represented by low-Ca biotite granite-granodiorite. Over 80% of the mineralisation at Gogi occurs as veins, veinlets and fracture-fills, composed of coffinite, lesser pitchblende, accessory U-Ti-Si complex (only in granitoid), associated intimately with reductants like sulphides and organic matter, and also clays (illite, smectite). Pitchblende is of two generations, both replaced by and replacing coffinite, and these two U-minerals, in turn, arc replaced by U-Ti-Si complex. The U-minerals occurring in limestone are Th-poor and are characterised by variable contents of U, Pb, Si and lanthanides (LREE>HREE), and as compared to those in granitoid are marked by higher contents of U, Pb, Fe and lower contents of Si and lanthanides. Amongst the sulphides, pyrite is predominant and occurs in three modes, viz., coarse euhedral-subhedral, framboidal and reticulate. The rest comprise marcasitc, chalcopyrite and galena in accessory to minor amount. These sulphides carry notable contents of Co, Ni, Se As, Ag and Au, with enrichment of Ag, Co, Ni in chalcopyrite followed by pyrite (more in framboidal type), Se in galena and Au more in sulphides from the granitoid. These high-value metals can be recovered as by-products during extraction of U. The organic n~atteris heterogenous and contains U, Si, Ca, Al, Pb and Fe, with the one rich in U is also high in the other elements. Radioactive clay contains U, P and REE. Both radioactive organic matter and clay are almost free of Th and Zr, with LREE>HREE. Paragenetically, the uranium minerals were formed later than the sulphides and organic matter. U-mineralisation at Gogi is poly-phase and poly-metallic, hydrothermal vein type with an Eh of -0.2 to -0.3V, pH of 7 to 8, and temperature of <200°C. The controls for this U-mineralisation are: (a) fertile granitoid as source, (b) structurally weak and permeable zones of faults, folds, brittle-ductile deformation and unconformity, along basin margin, (c) presence of strong reductants of organic matter and sulphides, (d) impervious and reactive cover rock of limestone and (e) dyke activity in the basement which may have acted as heat source and created necessary geothermal gradient for remobilisation and precipitation of U. These can be taken as guides for U-exploration in similar geologic set-up.

Keywords

U-Mineralisation, Hydrothermal, Neoproterozoic, Bhima Basin, Gogi, Ukinal, Karnataka.

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