Informatics Publishing Limited

N. Krishna Rao ¹, G. V. U. Rao ¹

Affiliations
1 Metallurgy Division, Bhabha Atomic Research Centre, Trombay, IN

Abstract

This paper incorporates results of textural and mineratogical study of phosphorites from Mussourie and Maldeota in Uttar Pradesh, and Kanpur, Maton and Birmania in Rajasthan. In Uttar Pradesh phosphorites, the phosphatic mineral collophane occurs in pelletal, interstitial and massive form. Different types of pellets - ovulitic, oolitic, encased, nucleated and polynucleated, are encountered. Most of the collophane is isotropic, rarely cryptocrystalline or microcryptocrystalline. Calcite, muscovite-sericite, clay, quartz and chert are the principal gangue associates. In phosphorite from Kanpur collophane lacks pelletal arrangement and occurs in the form of irregular bands in limestone. Maton phosphorites consist of nodules and large pellets of micro- and cryptocrystalline collophane enclosed in a matrix of chert and calcite, while in Birmania collophane occurs both in the form of dispersed pellets and bands in limestone.

Infra-red spectra of pure collophane samples from each of the localities show the presence of structural (OH) and (CO₃) groups. This coupled with the chemical analysis shows that the samples from Maldeota and Birmania can be called carbonate-hydroxyl-fluorapatite, while those from Kanpur and Maton fall in the range of fluoiapatite. Calculation of ionic composition of the collophanes shows that C replaces P, further the direct relationship observed between H₂O⁺ and Ca/P+C ratio indicates the possibility of PO«^*(OH)₄ substitution. The unit cell dimensions fall in between those of fluorapatite, hydroxylapatite and francolite. Substitution of C for P reduces slightly the average refractive indices.

It is interesting to note that collophane from Maton and Kanpur areas which occur in precambrian formations approach fluorapatite in composition while those from later horizons (Birmania - late Palaeozoic, Mussourie and Maldeota - Mezozoic) are carbonate-hydroxyl-fluorapatites.

Full Text

     

N. K. Rao ¹, G. V. U. Rao ¹

Affiliations
1 Metallurgy Division, Atomic Energy Establishment, Trombay, IN

Abstract

Prismatic sections of stibnite obtained from-Punjab, India, show various types of twinning, whose nature indicates deformation origin of the twinning . The twinning is simple or repeated or polysynthetic; in the latter case the twin lamellae may be parallel, wedge-, lens- or spindle-shaped, twisted and sinuous.

The disposition of the twinning lamellae and their relation to the (010) cleavage indicate that twin gliding has taken place in the plane (001) along [010]. This is probably due to the least coherence along [010]. The various patterns of twin lamellae are due to (a) trans­ lation gliding (010) [001] (b) bending about [100] and © twisting about [001] subsequent to the twinning. The simple types of twins are either due to accumulation of localised stresses during alteration or due to grinding and polishing, and the complex ones are due to shearing movements during or after deposition of stibnite.

Full Text

     

N. P. Subrahmanyam ¹, G. V. U. Rao ¹

Affiliations
1 Metallurgy Division, Bhabha Atomic Research Centre, Trombay, IN

Abstract

Lenticular veins of carbonatite are located in the pheripheral Erinpura granites E of Alkalic Mer pluton in Mundwara igneous complex, Sirohi District, Rajasthan. These veins vary in length from 20' to 200' and are composed of discontinuous lenses arranged en echelon. Calcite is the principal mineral of these veins and the associated accessory minerals are ankerite, hematite, magnetite, aegirine, apatite, feldspar, quartz and baryte. Frothy and fluidal textures as well as chilled marginal and fenitisation effects are observed in these veins. Martitised magnetite and chalcedony indicate low temperature of formation whereas the vesicular nature of these veins indicates low confining pressures (may be as low as I bar). These veins.are having high Sr, Ba and RE contents. The calcites from these are enriched in Sr, Ba, RE, Mo, Mg and P compared to their sedimentary counterparts. Thus, these veins are alvikites formed under pneumatolytic-hydrothermal conditions.

Lenticular veins are not reported by earlier workers and the Mundwara veins seem to be unique in this respect.

Full Text

     

N. Krishna Rao ¹, S. K. Aggarwal ², G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, 3rd floor, Chandralok, 111, Sarojini Devi Road, Secunderabad 500003 (A.P.), IN
2 Radiochemistry Division, B.A.R.C. Trombay, Bombay 400085, IN

Abstract

The lead isotopic ratios of four samples of uraninites from different parts of Singhbhum Shear Zone, Bihar, gave discordant ages in the sequence ²⁰⁷pb/²⁰⁶pb age > ²⁰⁷Pb ²³⁵U age > ²⁰⁶Pb/²³⁸U age. However, the ²⁰⁷pb/²⁰⁶pb ages of all the four samples gave fairly concordant values. Those from Bhatin, Rakha and Surda gave 1478 ± 14 m. years and that From Narwapahar 1580 m. years. The discordant ratios gave a concordia age of 1580 m. years, which can be taken as the age of original deposition of uraninite in the shear zone.

Full Text

   

D. Narasimhan ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, BARC, Chandralok, 3rd Floor, 111, S.D. Road, Secunderabad 500003, IN

Abstract

Parkerite, a rare nickel bismuth sulphide has been identified from Rakha copper deposit of Singhbhum shear zone. The mineral is associated with chalcopyrite, pentlandite bismuthinite and native bismuth. EPMA indicated the composition to be Ni_3.17. Bi_2.06 S₂. The mineral has low indentation hardness (VHN 119 Kg/mm²) and the reflectivity ranges from 41.0% (470 nm) to 49.0% (589 nm).

Full Text

   

N. Krishna Rao ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, 111, S. D. Road, Secunderabad 500 003, IN

Abstract

Uraninite is the main uranium mineral in the uranium deposits of Singhbhum Shear Zone, Bihar. The uraninite from different deposits have compositions varying between UO_2.30 to UO_2.44 which is typical of vein uraninites. They contain < 1 % ThO₂, but have appreciable rare earths C≃5%). They also contain 12-15% PbO, which is all radiogenic. Among the rare earths the heavy lanthanides predominate. In addition uraninite from Narwapahar shows an enrichment in Eu. The unit cell edge of uraninite from different deposits varies between 5.420 Å and 5.453 Å. The uraninite from the copper deposits of Rakha and Surda, and Narwapahar have decidedly higher cell edge (5.45 Å) than those from Bhatin and Jaduguda (5.42 Å). On annealing at 1000°C in an inert atmosphere the cell edge decreased to a near constant value of 5.428 Å, the contraction varying between 0.01 Å to 0.03 Å.

D. T.A. and T.G.A. curves of Narwapahar and Bhatin uraninite indicate that these differ considerably from those of pure UO₂. There are also significant differences between the two. These differences are attributed to crystallinity and degree of disorder in the uraninite lattice. The variations in the composition, cell edge, annealing and oxidation characteristics of uraninite from different uranium deposits reflect different temperature conditions during their formation.

Full Text

     

N. P. Subrahmanyam ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, 1-10-153/156, Begumpet, Hyderabad 500016, IN

Abstract

Rutile concentrate produced by the Indian Rare Earths Limited from Kerala beach sands analyses 1.5% Nb₂O₅ and 0.13% Ta₂O₅. Incident light microscopy and scanning electron microscopy have revealed that niobium and tantalum are camouflaging Ti in this rutile. Exsolved acicular inclusions of tapiolite are observed in a few grains. Preliminary experiments to obtain Nb-Ta rich fraction from this rutile by physical methods have not given encouraging results, but it is observed that these elements get relatively enriched in the residual titanium dust, which accumulates as a waste product in the titanium pilot plant at Nuclear Fuel Complex, Hyderabad. Concentrates containing up to 31% Nb₂O₅ and 3.8% Ta₂O₅ could be obtained from this residual dust after elimination of carbon.

Full Text

   

N. P. Subrahmanyam ¹, N. K. Rao ¹, D. Narasimhan ¹, G. V. U. Rao ¹, N. K. Jaggi ², K. R. P. M. Rao ²

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hyderabad - 500 016, IN
2 Nuclear Physics Division, B. A. R. C., Bombay - 400085, IN

Abstract

The study shows that the alteration of ilmenite has taken place according to the two stage model proposed by Grey and Reid (1975). Identification of the intermediate altered compound, pseudorutile, was found difficult in earlier studies by optical and X-ray diffraction methods, because of the occurrence of this phase in altered ilmenite in very fine grain size (30 Å), its poor crystallinity and coincidence of many of the diffraction lines with those of other phases. The present study has shown that the Mossbauer technique is more suitable in the identification and estimation of this phase.

The relative amount of pseudorutile increases progressively in the magnetic fractions in the following order: 0.30 - 0.35 amps (5%), 0.25 - 0.30 amps (40%), 0-0.25 amps (75%) and 0.35 - 0.50amps (95%), indicating that the magnetic susceptibility of the grains is increasing initially with progressive pseudorutile formation, and decreasing in the later stages of alteration. Reflectivity and hardness are also increasing up to the stage of pseudorutile formation and decreasing in the later stages.

Full Text

     

N. Krishna Rao ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hyderabad 500016, IN

Abstract

On the basis of an analysis of the various characteristics of the uranium deposits of the Singhbhum Shear Zone, a new sequence of events has been postulated to explain the origin of mineralization. The main events are:

(i) The Singhbhum Granite is the geochemical source of uranium, (ii) The metavolcanic rocks closely associated with the Chaibasa Formation rocks along the shear zone are the geochemical source of base metals, (iii) Uranium was first syngenetically deposited in the sediments of the Chaibasa Formation, (iv) This uranium was mobilized during metamorphic-metasomatic process, accompanied by shearing, leading to syntectonic granitization and extensive feldspathization. During this episode a part of the geochemical stock of uranium was incorporated in the metasomatic refractory uranium minerals, and the rest in (a) deuteric uraninite, (b) tiny crystals of uraninite included in metasomatic minerals and (c) molecular and ionic desserninations occluded in crystals and inter-granular fluids in the metasomatised rocks, (v) uranium was remobilized again by tectonically heated waters during further extensive shearing and redeposited as uraninite in suitable structural traps, (vi) emplacement of basic sills at Jaduguda aided this remobilization and exerted a geochemical control in precipitating uranium along with other metals such as Cu and Ni, (vii) in some parts of western sector (eg. Narwapahar) exogenic remobilization also played a part, (viii) the sooty pitchblende, secondary uranium minerals and supergene uraniferous iron oxides are due to subsequent local remobilization and deposition.

Thus, uranium mineralization in the Singhbhum Shear Zone is the result of a series of overalapping geological processes.

Full Text

     

N. Krishna Rao ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Engineering Hall, 1-10-153/156, Begumpet, Hyderabad 500 016, IN

Abstract

Uraniferous apatite-magnetite veins occur in several parts of the Singhbhum Shear Zone, Bihar. Besides these veins, apatite and magnetite are ubiquitous minerals in the uranium ore deposits of the zone, with which too uranium values are associated.

Both primary and secondary uranium occur in the apatite-magnetite veins, though the latter is more abundant. Diadochic uranium in apatite lattice, inclusions of uraninite in apatite and uranium-bearing accessory minerals such as allanite, sphene, xenotime and rare monazite are the source of primary uramium. Secondary uranium is in the form of minerals like autunite, potassium autunite, uranophane and torbernite, uraniferous iron oxides and rare interstitial uraninite/pitchblende.

The relationship between uranium-bearing minerals and magnetite indicates that magnetite has played a role in the precipitation of uranium, not only in the apatite-magnetite veins, but also in the mineralised schists of the shear zone. Oxidation of Fe²⁺ to Fe³⁺ with the concomitant reduction and precipitation of uranium is the probable mechanism. This can take place both at elevated temperatures leading to coprecipitation of uraninite and hematite, and supergene and low temperature conditions which favour the formation of uraniferous iron oxides and fine-grained pitchblende.

Full Text

     

N. Krishna Rao ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hyderabad 500016, IN

Abstract

More than fifty ore minerals have been identified in the uranium and copper deposits of the zone. Uranium occurs in several forms-uraninite, sooty pitchblende, refractory uranium-bearing minerals like allanite, davidite. sphene, xenotime, etc., secondary uranium minerals and uraniferous iron oxides. Other ore minerals include sulphides of Cu, Ni, Mo and Fe, tellurides of Bi and Ni and native metals Bi, Au, Ag and Te.

The structure, texture and paragenetic association of uranium minerals in the different sectors of the shear zone differ considerably, indicating varying physicochemical conditions of their formation. The study also shows that more than one episode of mineralization has taken place.

Full Text

     

N. Krishna Rao ¹, G. V. U. Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hyderabad 500 016, IN

Abstract

Composite grain-aggregates of titanium and uranium oxide phases resemble, both in texture and composition, those described as 'brannerite' grains occurring in quartz-pebble conglomerate-type uranium deposits such as those of Witwatersrand in South Africa and Blind River in Canada. The grain-aggregates contain variable amounts of quartz, rutile, anatase, uraninite, brannerite (s.s), pyrite, galena and hematite. Intimate inter-growths of uranium-rich and titanium-rich phases are observed. 'Brannerite' grains are secondary in origin, both detrital and metamorphic ilmenite being the antecedent mineral. They have been formed by the action of uranium-bearing solutions on ilmenite under conditions which favoured (i) alteration of ilmenite to titania by removal of iron (ii) simultaneous precipitation of uranium from solutions as uraninite and (iii) adsorption of uranium by titania. This can take place under both reducing and oxidizing conditions.

Full Text