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

Chanchal Sarbajna ¹, P. Krishnamurthy ¹, A. K. Paul ¹, D. C. Banerjee ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN

Abstract

Detailed mineralogical and chemical studies by EPMA on the Nb-Ta minerals from the rare metal pegmatites of southern Karnataka have revealed wide compositional variations, and the presence of some new minerals like tapiolite and microlite, hitherto unreported from these pegmatites. Back scattered electron (BSE) images have indicated complex zoning patterns such as oscillatory, patchy and/or their combinations, associated with replacement of columbite-tantalite by microlite, manifested by the variations of Nb₂O₅, Ta₂O₅, FeO and MnO. Such features, although known from a few rare meral pegmatites of the world, are being recorded here for the first time in India. Oscillatory zones in columbite-tantalites are manifested as alternating dark and light grey coloured bands, of which darker bands are Nb-rich (30-300 μM thick) and lighter bands are Ta-rich (125-450 μm thick). The wider zones may, in turn, consist of a group of very fine sub-zones (1-50 μm) of slightly varying composition: Patchy zoned crystals exhibit corroded remnants of early formed columbite-tantalite (with 39.73-44.02% Ta₂O₅), surrounded by later formed zones which are enriched in Ta₂O₅ (up to 50.99 %) in columbite-tantalite leading to the formation of microlite containing up to 73.4% Ta₂O₅. The zoning of the columbite-tantalites has been attributed to periodic changes in the composition of the major components such as Nb, Ta, Fe and Mn in the pegmatite fluid system, apparently influenced by the late stage fractionation of volatiles. This ultimately generated fluids rich in Ta and Na, resulting in resorption and replacement with patchy zoning of early formed, zoned columbite-tantalites.

Keywords

Columbite-Tantalite, Rare Metal Pegmatite, Zoning, Ore Mineralogy, Southern Karnataka.

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U. K. Pandey ¹, Tikam Chabria ¹, P. Krishnamurthy ¹, R. Viswanathan ¹, B. Kumar ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN
2 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Carbon isotope studies on calcite - graphite system yield narrow Δ Cat - Gr values, varying from 3.9 to 4.3, indicating equilibrium between coexisting calcite and graphite. Calcite - graphite geothermometry has assigned temperatures ranging from 630° to 700°C for the calc - granulites found to the NE of Usilampatti area. The inferred temperatures correspond to the retrograde temperatures obtained by cation exchange thermometry on the granulites from other areas in the Madurai Block. These temperatures may correspond to the late isobaric cooling event. X-ray diffraction studies indicate well ordered nature of these graphites and corroborate the findings of isotope geothermometric inferences.

Keywords

Geothermometry, Calc-Granulite, Calcite-Graphite, Carbon-Oxygen Isotopes, X-Ray Diffraction, Usilampatti, Tamil Nadu.

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Chanchal Sarbajna ¹, R. P. Sinha ¹, P. Krishnamurthy ¹, K. V. G. Krishna ², R. Viswanathan ¹, D. C. Banerjee ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Nagarbhavi, Bangalore - 560072, IN

Abstract

White coloured alkali beryl from the pegmatites of Mariagalla-Allapatna in Mandya district, Karnataka contains distinctly higher alkali elements (Na, Li, Rb, Ca) and relatively low beryllium oxide (c. 11 % BeO) compared to normal beryl. Beryl occurs mostly between graphic intermediate zone and quartz core in the complexly zoned, spodumene-bearing Li-Cs-Ta (LCT) type pegmatites in this area. The average value (n = 7) for alkali beryl from this area are Na₂O 1.26%, Li₂O 0.6%, Cs₂O, 0.74%, K₂O 0.07 and Rb₂O 0.08%. Cs content in some of the beryls are higher than Na and hence such beryls may be termed as a new Na-Li-Cs type X-ray powder diffraction data for the beryl (a_o = 9.2765-9.339 Å, c_o = 9.2079-9.2487 Å) reveal differences in crystal structure with respect to normal beryls from Royalstone, Massachusetts, USA (a_o = 9.215Å, c_o = 9.192Å) and compares well with the reported alkali beryl from Arizona, USA (a_o = 9.30Å, c_o = 9.20Å) Their refractive index (N_ω) ranges from 1.588 to 1.592 and the specific gravity varies from 2.74 to 2.79.

Keywords

Economic Geology, Geochemistry, Mineralogy, Rare Metal Pegmatites, Beryl, Marlagalla, Karnataka.

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P. Krishnamurthy ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, Hyderabad 16, IN

Abstract

The major and trace element compositions of the Sevattur carbonatites are broadly comparable with the 'typical carbonatite abundance' values compiled by Gold (1966). The mean values for the Sevattur carbonatites are as follows (in weight per cent): SiO₂-2.60, Al₂O₃-2.49, TiO₂-0.46, Fe₂O₃ + FeO-9.64, MnO-0.52, MgO-10.14, CaO-32.84, Na₂O-0.85, K₂O-0.49, P₂O₅-3.48, CO₂-36.15, H₂O±0.32, with trace elements in parts per million as: Ba-1663, Sr-6427, Zr-763, Rb-2, La-271, Ce-641, Y -41, Nb-78, Ta-34, SC-16, Zn-69, Cu-78, Ni-18, Pb-27.

There is an enrichment of total iron, MgO, MnO, P₂O₅ and Na₂O with successively younger phases within the main carbonatite body and such a feature is comparable with the liquid lines of descent, observed in synthetic carbonatite systems. Fenitisation of the country rocks (granitic gneisses) along the southern border of the carbonatite body is indicated from the enrichment of K₂O, Na₂O, Al₂O₃ and impoverishment in SiO2, total iron and MgO in the fenites when compared with the country rocks.

Sr (4109-9375 ppm, mean 6427) exceeds Ba (1000-2420 ppm, mean 1663) in all the types of carbonatites by a factor of 2 to 5. The lighter rare earths such as La and Ce are enriched in the calcitic types (La + Ce, 892-1351 ppm) when compared to the beforsites (647-920 ppm). In general, the beforsites are richer in Ba, Nb, Ta and Sc.

Among the carbonatitic minerals, early calcites are much enriched in Sr (5500-6200 ppm) in comparison with Ba (1230-1700) by a factor of 3 to 5. Sr with successively younger fractions of the carbonatite, seems to show a preference to the dolomites (3500-4000 ppm in the early phases and 9000-11000 ppm in the later phases) rather than to the apatites (6200 ppm). No systematic variation has been found in the Sr content of the different carbonatitic minerals within a particular carbonatite type.

The study emphasizes the importance of chemical data as one of the essential parameters in identifying carbonatite complexes from doubtful occurrences and also in elucidating their evolution. The study confirms the earlier observation that the carbonatites of Sevattur belong to the apatite-magnetite type.

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P. Krishnamurthy ¹

Affiliations
1 Atomic Minerals Division, Begumpet, Hyderabad, IN

Abstract

In Sung Valley, (Lat : 25°31' -25°36'N : Long; 92°05' -92°10'E) the Shillong Series rocks comprising mainly quartzites and phyllites are intruded by a N-S trending, roughly oval shaped body of pyroxenite covering an area of about 35 km² and into which the following genetically related rock types have been emplaced in order of decreasing age and abundance. Peridotites (stock-like bodies), ijolites (ring dyke and plug like), carbonatites (incomplete cone sheets) and syenites (sheets, dykes and veins). Minor dykes and veins of magnetite-serpentine rock, ijolite and melilite-bearing types with a rough radial disposition are also present. Fenitization, due to both ijolites and carbonatites, has affected older rocks resulting in wollastonite-rich aegirine-augite bearing rocks, K-feldspar-aegirine-augite veins and oversaturated potassic syenites.

Carbonatites are mainly sovites with minor beforsite and types rich in magnetite and apatite are present. Average abundances of trace elements (values in ppm) characterizing carbonatites such as Bu (549), Sr (3134), La (50-100), Ce (489), Y (50), Nb (372), Zr (179) and P₂O₅ (5.7) wt% are comparable to those found in reported intrusive carbonatites. The weathered mantle of the carbonatites and the contact zones between carbonatites and pyroxenites have resulted in soils rich in pyrochlore, apatite and magnetite. It is postulated that the carbonatites may be differentiates of an ijolitic magma, in turn derived (liquid immiscibility?) from a parental mela-nephelinite or alkali picritic magma. The ultramafic suite could represent the cumulates from such a picritic source.

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B. V. Oleinikov ¹, A. F. Korobeinikov ¹, O. V. Koroleva ¹, P. Krishnamurthy ², Anil Kumar ³, K. Gopalan ³

Affiliations
1 Yakut Institute of Geological Sciences, Siberian Branch, Russian Academy of Science, Yakutsk - 677 891, RU
2 Atomic Minerals Division, Hyderabad-500 016, IN
3 National Geophysical Research Institute, Hyderabad-500 007, IN

Abstract

Sixty nine (69) samples of Deccan basalt flows from the Western Ghats representing the Wai, Lonavala and Kalsubai subgroups average 3.7 ppb of gold. Gold content shows limited variation from 3.0 to 5.8 ppb in 62 samples whereas they range from 1.4 to 2.7 ppb in 7 samples. Flows of the Wai subgroup show the maximum variation in gold abundances (1.4 - 5.8 ppb) and which may be related to the presence of primitive uncontaminated basalts (Ambenali)- lowest value-crust-contaminated basalts (Poladpur) and basalts derived from enriched-mantle sources (Mahabaleshwar). Gold appears to be insensitive to crystal fractionation or differentiation as basalts of different types such as the picritic, porphyritic, aphyric and giant plagioclase-bearing types found within a subgroup or formation have similar avcrages (3.6-3.8 ppb).

Deccan Tholciitic basalts contain higher amounts of gold than dome of the occean island (Hawaii) tholciitic basalts island are (Kurile-Kamchatka) tholciites, but contain values similar to those found in the Columbia River basalt province.

Keywords

Gold, Deccan Basalts, Western Ghats, Economic Geology.

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R. Murari ¹, P. Krishnamurthy ², K. S. Gopalan ¹, G. V. Nesterekno ³, P. I. Tihonenko ⁴

Affiliations
1 National Geophysical Research Institute, Hyderabad 500007, IN
2 Atornic Minerals Division, Hyderabad-500016, IN
3 Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow-117075, RU
4 Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow-117075, IN

Abstract

Electron probe microanalysis (EPMA) and preliminary x- ray diffraction studies on a basalt flow from Mt.Sundook have revealed the presence of rare high-alumina hypersthene in the groundmass. The basalt occurs at the base of a 800 m flow sequence (Ivakinsky and Syverminsky suite) that unconformably overlies a Permo-Carboniferous sedimentary sequences. It is postulated that besides normal processes of fractionation, assimilation-fractional Crystallization (AFC) processes involving the parental magma and crustal components (pelitic sedinientary rocks) were responsible for the formation of hypersthene in the basalt. The presence of a complex feldspar and pyroxene assemblage may also be an additional evidence for the operation of such an AFC process.

Keywords

High-Alumina Hypersthene, Basalt, Siberian Traps, Mt. Sundook, Russia.

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Chanchal Sarbajna ¹, P. Krishnamurthy ¹

Affiliations
1 Atomic Minerals Division, Hyderabad - 500 016, IN

Abstract

The Allapatna granite has been found to be a low-calcic (CaO-0.85%), peraluminous (A/C+N+K ratio = 1.04) and potassic type (K₂O=4.75%), enriched in Rb(362), Ga(25), Cs(3), Nb( 19), U(l3), Ta(18), Th(38), Pb(55) and strongly depleted in Ba(333). Such abundances together with low K/Rb ( 118.9), Ba/Rb (0.92) and Th/U (2.92), and high Rb/Sr (3.45) ratios than normal granite indicate their highly fractionated and fertile character and strongly suggests that the Li-Cs-Ta (LeT) rich rare metal bearing pegmatites of Marlagalla and nearby areas may have been derived from such a parental granitic magma.

Keywords

Granite, Pegmatites, Rare Metals, Allapatna, Karnataka.

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P. Krishnamurthy ¹

Affiliations
1 Atomic Minerals Division Begumpet Hyderabad - 500 016, IN

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No Abstract.

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P. Krishnamurthy ¹

Affiliations
1 A.M.D., Hyderabad, IN

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Rajeev Bidwai ¹, P. Krishnamurthy ¹

Affiliations
1 Atomic Minerals Division, Begumpet, Hyderabad, IN

Abstract

Lava propagating systems comprising channels and tubes from the Siwana caldera sequence of the Malani Igneous Suite are reported at Sain Ki Beri and Dhiran. Their location near the periphery of the ring dyke suggests that these channels may have been fed by the volcanic vents or cones, that were part of the ring which collapsed later.

Keywords

Petrology, Malani Igneous Suite, Lava Channels, Caldera, Rajasthan.

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P. Krishnamurthy ¹, Chanchal Sarbajna ¹

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

Abstract

A ring-like structure is defined by a late Archaean granite around Chandra. It is a fertile granite with a parental status akin to the rare metal pegmatite-hosted deposits of Li-Be-Nb and Ta around Allapatna-Marlagalla. This observation has important implications for new exploration targets for rare metal pegmatites in southern Karnataka and also geological evolution of the terrain as a whole.

Keywords

Petrology, Ring Structure, Fertile Granite, Karnataka.

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P. Krishnamurthy ¹

Affiliations
1 Geological Society of India, Bangalore - 560 019, IN

Abstract

No abstract.

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P. Krishnamurthy ¹

Affiliations
1 Management Training Centre UCIL, Narwapahar, Singhbhum East Jharkhand - 832 107, IN

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U. K. Pandey ¹, B. K. Pandey ², P. Krishnamurthy ³

Affiliations
1 Atomic Minerals Directorate Geochronology Lab , Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate, Pratap Nagar, Sanganer, Jaipur - 303 906, IN
3 Atomic Minerals Directorate, Khasmahal, Tatanagar - 831 002, Jharkhand, IN

Abstract

Rb-Sr, Sm-Nd and Pb-Pb systematics on mafic granulites, intermediate-charnockites, charnockites, calcgranulites, orthogneisses, leptynites, granites and two (2) mineral samples (microcline and muscovite) from pegmatite have been studied Sm-Nd model ages (T_DM) for most of the rocks cluster around 2 1 Ga Calc-Granulites gave Rb-Sr whole rock isochron age of 1339 ± 110 Ma with initial ⁸⁷sr/⁸⁶sr ratio(I R ) = 0 709 Mesoproterozoic age for the Metasedimentary. Group of rocks (calc-granulites) has been inferred based on their ⁸⁷sr/⁸⁶sr ratio also. Granites and leptynites have yielded Rb-Sr whole rock isochron ages of 823 ± 38 Ma, with I R = 0 713 and 894 ± 82 Ma, with I R = 0 708 respectively which are younger than the calc-Granulites. Microcline and muscovite from pegmatite gave Rb-Sr model ages as 532 and 491 Ma respectively. Granites, leptynites and calc-Granulites are derived from the crustal source as indicated by their high initial ⁸⁷sr/⁸⁶sr ratios. Most probably the protolith of the granitic and granulitic rocks is of Palaeoproterozoic age in this part of the Madurai Block. The minimum age of granulite grade of metamorphism has been inferred at c 850 Ma, indirectly on the basis of Rb-Sr ages of leptynites, which normally form during the evolution of granulite facies assemblages. Both granulite facies metamorphism and granitic magmatism probably took place during Neoproterozoic period correlatable to the early phase of Pan-African orogeny. Later decompression, causing mineral scale resetting of the Rb-Sr and Sm-Nd systematics, around 450-550 Ma, may correspond to the final exhumation, which brought the middle to lower crustal granulites to upper crustal levels, during the last phase of Pan-African activity. As per ages obtained on various lithounits in the present study the Metasedimentary Group of rocks (Mesoproterozoic) are younger than the Charnockite Group of rocks (Palaeoproterozoic) followed by the rocks belonging to the Migmatite Complex (Neoproterozoic).

Keywords

Rb-Sr, Sm-Nd, Pb-Pb Geochronology, Proterozoic, Granulites, Age, Lithounits Usilampatti, Madurai, Tamil Nadu.

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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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E. V. S. S. K. Babu ¹, S. Nayak ¹, A. K. Rai ², P. Krishnamurthy ³, S. N. Kak 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, Department of Atomic Energy, Shillong, Meghalaya, IN
3 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Tatanagar, Jamshedpur, IN

Abstract

Occurrences of discrete selenide phases in the geological environment are rather rare and are confined to a few sulphide deposits and sandstone-type uranium deposits such as those of the Colorado plateau, USA. The occurrence of discrete selenide phases viz., clausthalite (PbSe), ferroselite (FeSe₂) and Co-penroseite (CoNiCuSe₂) are reported for the first time from the Uraniferous Mahadek sandstones of Domiasiat and Wahkyn South, West Khasi Hills District, Meghalaya. The selenide phases are associated with pyritiferous organic matter, pitchblende and other ore minerals such as marcasite and sphalerite.

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P. Senthil kumar ¹, G. Parthasarathy ¹, S. Das Sharma ¹, R. Srinivasan ¹, P. Krishnamurthy ²

Affiliations
1 National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, IN
2 Atomic Minerals Directorate for Exploration and Research, AMD Complex, Begumpet, Hyderabad-500 01 6, IN

Abstract

Carbonate veins up to few metres thick have been recognised in the E-W striking Salem-Attur deep fault zone which represents the eastern extention of the Moyar fault in the southern granulite terrane of India. X-ray diffraction, FTIR spectroscopy and chemical analyses show calcite, ankerite, siderite and benstonite as dominant minerals besides minor apatite and green biotite. Whole rock compositions show enrichment of light REE, Ba, Sr and Nb. C and 0 isotopic data determined for calcite (δ¹³C= -4.9 to -5.1%0 V-PDB and δ¹⁸0 = 9 to 9.2%0 V-SMOW) points to a mantle origin. The chemical characteristics therefore suggest that the carbonate veins have carbonatitic affinity. The FTIR spectra provide evidence for presence of H₂0 and CH₄ in addition to CO₂ in the carbonate minerals of these veins.

Keywords

Ferrocarbonatites, Benstonite, FTIR Spectroscopy, X-Ray Diffraction, Geochemistry, Isotopes, Tamil Nadu.

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P. Krishnamurthy ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research Jamshedpur - 831 002, IN

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P. Krishnamurthy

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P. Krishnamurthy

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P. Krishnamurthy ¹

Affiliations
1 Bangalore, IN

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P. Krishnamurthy ¹

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1 Geolgoical Society of India, Bangalore, IN

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P. Krishnamurthy

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R. H. Sawkar ¹, P. Krishnamurthy ¹

Affiliations
1 Geological Society of India, Bangalore - 560 019, IN

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P. Krishnamurthy

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P. Krishnamurthy ¹

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1 Bangalore, IN

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P. Krishnamurthy

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P. Krishnamurthy ¹

Affiliations
1 Geological Society of India, Bangalore, IN

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P. Krishnamurthy ¹, R. H. Sawkar ¹

Affiliations
1 Geological Society of India, Bangalore - 560 019, IN

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P. Krishnamurthy , R. H. Sawkar

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P. Krishnamurthy

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P. Krishnamurthy

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P. Krishnamurthy

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R. H. Sawkar ¹, P. Krishnamurthy ¹

Affiliations
1 Geological Society of India, Bangalore - 560 019, IN

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P. Krishnamurthy

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P. Krishnamurthy , G. V. Hegde

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P. Krishnamurthy , R. H. Sawkar

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P. Krishnamurthy , R. H. Sawkar

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P. Krishnamurthy ¹

Affiliations
1 Department of Atomic Energy Begumpet, Hyderabad - 500 016, IN

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P. Krishnamurthy

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P. Krishnamurthy

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P. Krishnamurthy

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These two books by Rabindra Nath Hota, Utkal University, Bhubaneshwar, Orissa, under review, are a welcome, low cost editions to students of geology besides others who want to understand practical aspects on these subjects. Classification of crystals, stereographic projections of crystals, determination of axial ratios and problems related to zonal laws are covered lucidly besides physical and determinative aspects on minerals using different instruments for specific gravity and the optical properties using the petrological microscope is well laid out with tabulated material for ready reference. Computation of mineral formulae from a given chemical analysis of minerals is also provided with examples.

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P. Krishnamurthy , K. S. Godhavari

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