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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.

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D. Narasimhan ¹, T. S. Sunilkumar ¹, E. V. S. S. K. Babu ², N. Krishna Rao ¹

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hyderabad - 500 016, IN
2 Department of Earth Sciences, University of Cambridge, GB

Abstract

Palladian melonite, containing upto 7% palladium is reported for the first time from the uranium ores, Jaduguda Mines.

Keywords

Mineralogy, Palladian Melonite, Uranium, Singhbhum, Bihar.

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T. S. Sunil Kumar ¹, N. Krishna Rao ¹, M. M. Palrecha ², R. Parthasarathy ², V. L. Shah ³, K. K. Sinha ⁴

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Hyderabad 500 016, IN
2 Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, IN
3 Atomic Minerals Division, Begumpet, Hyderabad 500 016, IN
4 Prem Mandir, Anugrah Narayan Road, Kadamkuan, Patna 800 003, IN

Abstract

he basal quartz-pebble conglomerate of Dhanjori Group of Singhbhum-Orissa craton is characterised by a distinct heavy mineral assemblage of pink zircon, chromite, pyrite, monazite and rutile-silicate intergrowth. Statistical analysis of morphometric features of zircons shows that they are significantly different from those found in Older Metamorphic Group and Older Metamorphic Tonalite Gneiss, but they have resemblance to those found in Singhbhum Granite. The trace and REE characteristics of the conglomerates, and the morphology and chemistry of zircon, identify the Singhbhum Granite Complex as the predominant source rock. At the same time, abundant detrital chromite, the positive trend of Cr-Ni and Cr-Co plots, and high Cr/Th ratios of the QPCs suggest a mixed provenance with an ultramafic component ofkomatiitic affinity (older greenstones) in the granite complex. The relative proportion of older greenstones was higher towards western and southern margins of the Dhanjori basin.

Keywords

Mineralogy, Geochemistry, Quartz-Pebble Conglomerate, Dhanjori Group, Singhbhum-Orissa Craton.

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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.

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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.

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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.

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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.

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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.

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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.

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N. Krishna Rao ¹, T. S. Sunilkumar ¹, D. Narasimhan ¹

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

Abstract

Uranium in the sandstone-hosted uranium deposit at Domiasiat, Meghalaya is mainly associated with organic matter (OM), which is also enriched in several trace elements, viz. Zn, Pb, Ni, V, Co, Ba, Sn, Mo, Cr, Ag, P etc. This paper is an attempt to characterize and discuss the origin of the OM and the associated uranium.

The OM occurs in several forms - lumps, layers, veins, dispersions, fracture fillings, coatings and impregnations. Based on structural features and optical properties, seven types of OM are identified. The structural and compositional features indicate that the OM is type II kerogen with macerals mainly belonging to liptinite group. Some of the primary structures have acted as loci of deposition of uraninite and other inorganic minerals like pyrite, marcasite, sphaleri'te and apatite, thereby giving rise to certain interesting textural features. Development of asecondary granular structure and bIades of secondary OM are features related to maturation. Uranium occurs in the form of uraninite of three generations, minor coffinite and a distinct organo-uranyl complex.

Both the South Khasi granite batholith and the tuffaceous matter related to Sylhet Trap episode appear to be the source for various inorganic elements enriched in the OM. From structures and association it appears that uranium fixation in the OM has taken pIace both due to anaerobic reduction by bacterial H₂S and complexation to form organo-uranyl complexes. The latter, on maturation, was reduced to form fine precipitates of uraninite dispersed in the OM. It is suggested that the maturity of OM, extending up to semi-anthracitic stage, has taken place due to radiolysis and radiogenic heat.

Keywords

Organic Matter, Uranium Ore, Sandstone, Domiasiat, Meghalaya.

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D. Narasimhan ¹, N. Krishna Rao ¹, V. Panchapakesan ², K. C. Sahu ²

Affiliations
1 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hydembad - 500016, IN
2 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay - 400076, IN

Abstract

Fluid inclusion study has indicated two distinct stages of mineralisation: one with higher T_H and lower salinity (greisens) and the other with lower T_H and slightly higher salinity (quartz vein) conditions. These mark the formation conditions of wolframite and scheelite respectively.

Keywords

Economic Geology, Fluid Inclusions, Tungsten, Wolframite, Maharashtra.

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N. Krishna Rao ¹, T. S. Sunilkumar ¹, D. Narasimhan ¹

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

Abstract

Native gold, etectrum with a wide spectrum of compositional variations between gold and silver, and native silver are identified based on ore microscopic and scanning electron microscopic studies in the copper ores of Khetri-Kolihan, Rajasthan and probable mode of origin is discussed.

Keywords

Economic Geology, Gold, Silver, Copper, Rajasthan.

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N. Krishna Rao ¹, T. S. Sunilkumar ², D. Narasimhan ²

Affiliations
1 B-41, Taxila Apartments, Sardar Patel Road, Secunderabad 500 003, IN
2 Ore Dressing Section, Bhabha Atomic Research Centre, Begumpet, Hyderabad 500 016, IN

Abstract

Nature of occurrence of native gold in the uranium ore from Jaduguda and copper ore from Mosabani in the Singhbhum Shear Zone, Bihar, is described. Preliminary data on the gold contents of different ore deposits along the shear zone, and their beneficiation products, are also reported. The native gold particles appear to be of detrital origin.

Keywords

Economic Geology, Gold, Detrital Origin, U-Cu Ores, Singhbhum Shear Zone, Bihar.

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K. K. Sinha ¹, N. Krishna Rao ², V. L. Shah ³, T. S. Sunilkumar ²

Affiliations
1 Prem Mandir, Anugrah Narayan Road, Kadamkuan, Patna - 800 003, IN
2 Ore Dressing Section, Bhabha Atomic Research Centre, Hyderabad - 500 016, IN
3 Atomic Minerals Division, Begumpet, Hyderabad - 500 016, IN

Abstract

Though the stratigraphic succession in the Precambrian of Singbhum-Orissa region of the Indian shield given by Saba et al. is widely accepted, there are several contentious issues whieh have been hotly debated over the years. The occurrence of uraninite and pyrite bearing quartz-pebble conglomerate at the base of Iron Ore Group (lOG) as well as the Dhanjori Group has indicated the necessity for a revision in the stratigraphic succession in view of the temporal significance of such conglomerate the world over.

The conglomerate contains a significant population of zircon, chromite and shows a typical minor and trace element composition. The zircon has morphometric properties similar to those found in several members of the Singhbhum Granite Complex. The presence of detrital chromite and high Cr content indicate the occurrence of older mafics/ultramafics in the provenance along with the Singhbhum Granite Complex. It is suggested that some mafic and ultramafic members presently grouped within the IOG may represent such "older greenstones". The IOG as well as the Dhanjori Group with basal QPC horizon lie over a basement of Singhbhum Granite-Greenstone Complex. From available evidences it is surmised that both IOG sensu stricto (the BIF sequence and associated ferruginous cherts. greywackes and acid-intennediate volcanics) and the Dhanjori Group represent late Archaean (2500-3000 Ma) supracrustals and hence are nearly coeval. The Singhbhum Group north of the shear zone represents early Proterozoic supracrustals.

Keywords

Stratigraphy, Quartz-Pebble Conglomerate, Detrital Zircon, Singhbhum Craton, Bihar.

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T. S. Sunilkumar ¹, D. Narasimhan ¹, N. Krishna Rao ¹

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

Abstract

The occurrence of authigenic apatite with uraninite, pyrite, sphalerite and galena within organic matter is a characteristic feature of the sandstone-type uranium deposit at Domiasiat, Meghalaya. Apatite occurs in the form of thin hexagonal basal plates and its identification is confirmed by x-ray diffraction. The authigenic apatite in this specific association points towards diagenesis in euxenic conditions of marine affinity.

Keywords

Mineralogy, Economic Geology, Apatite, Uranium, Organic Matter, Meghalaya.

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