Informatics Publishing Limited

G. S. Sharma ¹, R. K. Purohit ¹, Minati Roy ¹, B. Sengupta ¹, Jagmer Singh ²

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, New Delhi-110066, IN
2 Atomic Minerals Division, Department of Atomic Energy, Hyderabad-500016, IN

Abstract

Radioactive alkali feldspar granite (alaskite) occurs as dykes within the Proterozoic granite gneiss around Dhanota. Samples have assayed 0.011 to 0.16% U₃O₈ and 0.005 to 0.16% ThO₂. Yttrium values range from 250 to 800 ppm. Uranothorite occurs in association with zircon, xenotime, magnetite, hematite, sphene and goethite. The U-Th-Y mineralisation in alaskites of Dhanota is disseminated syn-magmatic intrusive type.

Keywords

Economic Geology, Geochemistry, Petrography, Alaskite Dyke, Xenotime, Uranothorite, Dhanota, Haryana.

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R. Dhana Raju ¹, Minati Roy ¹, Madhuparna Roy ¹, S. G. Vasudeva ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Bangalore 560072, IN

Abstract

Two types of uranium mineralisation occur in the south-western part of Cuddapah basin, viz., stratabound type hosted by impure dolostone of the Vempalle Formation of the Papaghni Group and structuralIy-controlled type hosted by deformed basement grani toid. The carbonate-hosted type occurs over a 140 km-long belt from Reddipalle in the west to Maddimadugu in the east with promising mineralisation at Tummalapalle, Rachakuntapalle and Gadankipalle. It is sandwiched between a Iower massive limestone and upper shale and cherty limestone. The rnineralised carbonate rock is a stromatolite-bearing 'siliceous, calcitic doIostone ' (SCD+phosphate) associated with other impure dolostones, quartzite, chert, phyllite, conglomerate, and intrusive dolerite a nd basalt. Uranium mineralisation occurs along the bedding plane, carbonate-phosphate conlact, micro-stylolites, grain boundaries of clasts and within pelioids, mainly in the form ultrafine pitchblende, in intimate association with pyrite and as disseminations in cellophane-rich parts, besides as minor phases ot'coffi~itea nd U-Ti compIex. The associated ore minerats include pyrite, molybdenite, chalcopyrite, bornite, digenite and covellite. The fertile basement granite fs.1.) is the source of uranium and the mineralisation, which appears to be polygenetic(syn-, dia- and epi-genetic), is controIled by impure nature of dotostone and organic activity. The mineralisation in the southern part of the belt in Cuddapa h district is typically molybdenum-rich, whereas the northern portion, in parts of Anantapur district, is characterised by high content of copper. The rnineralised SCD in the S/SE parts is also marked by high content of P, V and Pb, in addition to Mo. There is a good positive correlation of U with Pand V (r : 0.98 and more).

The structurally-controlled uranium mineralisation occurs around Rayachoti (outside the SW margin of Cuddapah basin) along a number of fracture zones within the basement granitoid, and is hosted by mylonites and cataclasites indicative of intense dislocation metamorphism. Of many such zones, the one between T. Sundupalle and Sanipaya is promising and has a strike extension of about 16 km. This mineralisation is epigenetic hydrothermal vein-type, mainly represented by coffinite, pitchblende, U-Ti. complex and secondary uranium minerals.

Keywords

Uranium Mineralisation, Stratabound Deposit, Hydrothermaltype, Cuddapah Basin, Andhra Pradesh.

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Minati Roy ¹, R. Dhana Raju ²

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy Hyderabad-500016, IN
2 Atomic Minerals Division, Department of Atomic Energy, Bangalore-560 072, IN

Abstract

The phosphatic siliceous dolostone (PSD) predominantly comprises ferroan dolomite that occurs as (a) micritic mosaic within the groundmass, intraclasts, peloids and ooids; (b) fibrous dolomite coating (a); and (c) clear dolomite filling cavities, and is secondary in nature formed due to dolomitisation of precursor high-Mg calcite. Stratigraphic position, sedimentary structures, structures of dolomite, process of dolomitisation and association with collophane and silicate clasts indicate a shallow marine intertidal depositional environment for PSD.

Keywords

Petrography, Sedimentology, Uranium, Vempalle Formation, Cuddapah Basin Andhra Pradesh.

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Minati Roy ¹, Madhuparna Roy ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, New Delhi - 110 066, IN

Abstract

Uraninite contains primarily UO₂ besides a few other oxides, viz radiogenic PbO, ThO₂ and minor amount of (RE)₂O₃in varying proportions. The environment and process of uraninite formation control its variation in chemical composition and optical properties. Uraninites generally form in high temperature magmatic granites and pegmatites, with repeated remobilization of uranium lead to its economic concentration, by hydrothermal/metasomatic activity, metamorphic, sedimentary phenomena or conjunction of one or more of these processes spread in space and time. Petrology and mineral chemistry of uraninites help in inferring the processes of uranium mineralisation, which have important bearing on exploration and ore beneficiation.

The present study of uraninites from some important uraniferous/thoriferous horizons in parts of India shows that they are controlled by temperature of formation. These uraninites may be classified as high- and low-temperature types. The high temperature type occurs in magmatic rocks, high temperature hydrothermal veins, migmatites and high temperature metasomatites. The typical high temperature magmatic/migmatic type uraninites occurring in granite, pegmatites and migmatites, are coarse, euhedral to subhedral grains, of high reflectivity and high micro hardness, and occur as inclusions within gangue minerals and also are associated with oxides, sulphides, rare earth and rare metal minerals. Chemically, such uraninites are marked by higher concentration of ThO₂, (RE)₂O₃, Y₂O₃ and lower content of SiO₂, CaO and TiO₂.

The low temperature type found in sedimentary uraninites is invariably fine grained, anhedral with lower reflectivity and hardness, distributed along weak planes and associated with sulphides with or without organic matter. In such uraninites, the concentration of ThO₂, (RE)₂O₃, Y₂O₃ is relatively lower and they have substantial amount of SiO₂ CaO and TiO₂.

The high temperature uraninites formed by fluid activity in veins and metasomatites are anhedral to euhedral grains, coarse to fine in grain size and are associated with both opaque oxides, sulphides and occasionally with organic matter. These uraninites contain variable amount of ThO₂, moderate to high (RE)₂O₃ and high Y₂O₃ and low SiO₂, CaO and TiO₂.

Keywords

Uraninite, High- and Low-Temperature Types, India.

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Minati Roy ¹, A. K. Roy ², P. S. Parihar ³

Affiliations
1 AMD, Department of Atomic Energy, Northern Region, New Delhi-110066, IN
2 AMD, Department of Atomic Energy, F-1149, Chittaranjan Park, New Delhi (Ex AMD, NR, New Delhi), IN
3 AMD, Department of Atomic Energy, Head Quarter, Hyderabad-500016, IN

Abstract

Radioactive carbonaceous matter, possibly of organic origin, with coffinite inclusions {U(SiO₄)_{1_x}(OH)_4x} are reported for the first time in the fractures within the core samples of highly deformed Bundelkhand granitoids in the Gwalior Basin. Intense hydrothermal alterations along these fractures are manifested in the form of silicification, argillic alteration (clay formation), chlontisation, ferruginisation and by sulphide formation. The globular radioactive carbonaceous matter is of organic origin and generally associated with silica rich veins. Globular nature of this carbonaceous matter indicates their formation from coagulation of smaller colloids in a low temperature hydrotherm. Mixing of descending oxidizing hydrotherm derived from basinal fluid rich in heavy metals, uranium, organic matter and ascending reducing fluid (hydrotherm) rich in H₂S and Si in these fracture zones has resulted in the precipitation of sulphides, secondary quartz, carbonaceous material and coffinite.

Keywords

Radioactive Material, Bundelkhand Granite, Gwalior Basin, Madhya Pradesh.

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Minati Roy ¹, A. K. Bagchi ², E. V. S. S. K. Babu ³, Brindaban Mishra ¹, P. Krishnamurthy ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, New Delhi, IN
2 Atomic Minerals Directorate for Exploration and Research, Jamshedpur, IN
3 Atomic Minerals Directorate for Exploration and Research, Hyderabad, IN

Abstract

Bituminous shale of the Sonrai Formation of the Bijawar Group hosts uranium mineralisation in Sonrai, Lalitpur dist., U.P. Mineragraphy of radioactive mineral phases viz. pitchblende and U-Si complex indicate that the pitchblende, apparently the first formed uranium phase, occurs as dispersed phase in the bitumen. Multistage remobilisation of uranium due to thermal gradient provided by basic and acid magmatic activity have resulted in the concentration of pitchblende along the fractures. EMP based mineral chemistry of pitchblende has shown negligible amount of Th0₂ and small amounts of RE₂0₃(0.78 to 0.90%) indicating its low-temperature formation. Chemistry of U-Si complex, a precursor phase of coffinite-like phase, suggests its formation from U-Zr-Y-REE-P-rich and Th-depleted hydrothermal fluid. High variability of PbO content in pitchblende and U-Si complex and resultant large range in their chemical ages suggest high degree of mobility and remobilization of Pb. Pyrite and chalcopyrite besides bitumen, are indicative of reducing environment necessary for the precipitation of pitchblende. Three major episodes of U-mineralisation based on the chemical ages of pitchblende (within bitumen: 413 Ma and as fracture fill: 51 Ma) and U-Si complex (1 to 13 Ma) have been inferred from this area.

Keywords

Petromineragraphy, Mineral Chemistry, Pitchblende, Uranium Mineralisation, Sonrai, Uttar Pradesh.

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S. K. Bhattacharya ¹, M. M. Sarin ¹, Minati Roy ², R. Dhana Raju ³

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN
2 Atomic Minerals Division, Dept. of Atomic Energy, Hyderabad - 500 016, IN
3 Atomic Minerals Division, Dept. of Atomic Energy, Bangalore 560 072, IN

Abstract

The dolostones show a narrOw range of δ¹³C values but a large range of δ¹³O values. The small spread of δ¹³C from 0.1‰ to -0.9‰ is typical of marine carbonates, whereas the large range of δ¹³O from -7‰ to -14‰ represents characteristic Proterozoic marine carbonates some of which were exposed to alteration by fresh continental waters. A diagenetic environment of mixed marine and fresh water for the dolostone alteration is also supported by earlier studies in sedimentary structures and petrography. The ²³⁴U/²³⁸U activity ratio of 0.7 in some of the mineralised samples shows the effect of ongoing chemical leaching of uranium from discrete uranium minerals like pitchblende and coffinite.

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