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

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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R. Parthasarathy ¹, M. Sankar Das ¹

Affiliations
1 Bhabha Atomic Research Centre, Bombay, IN

Abstract

A number of zircon separates from-various localities of India were analysed for their uranium, thorium and lead contents. Uranium and thorium were analysed by neutron activation, and lead by anodic stripping methods respectively. Thorium, uranium and lead were found to vary between 60-250, 60-900, 8-90 ppm, respectively. The Th/U ratios are found to be in conformity with the accepted values for granitic or pegmatiticzircon. The elemental abundances have been used to calculate their chemical ages and the values compared with those reported in literature. The ages obtained in this study range from 400-800 m.y. These ages are comparable with the previous reported values.

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R. Parthasarathy ¹, A. V. Murali ¹, M. Sankar Das ¹, A. M. Nair ², Narayanaswamy ²

Affiliations
1 Analytical Chemistry Division, BARC, Bombay 400085, IN
2 Geosciences Division, Centre for Earth Science Studies, Trivandrum, Kerala 695010, IN

Abstract

Zircon separates from a few whole rocks and sediments along with the parent sources have been analysed for Zr, Hf, Se, REE, Th and U concentrations by the neutron activation analysis technique. The major, minor and trace analyses of rock samples and their modal analyses are also presented. The chondritic normalised REE patterns of rock samples show positive Eu anomalies, while the zircon samples show negative Eu anomalies. The data have been used to explain the genetical relationship among the rocks under study. This study supports the hypothesis proposed from this laboratory that the detrital zircons of Kerala beach are time integrated cumulates from the whole-rocks of this region. The scandium data indicate the paragenetic sequence of crystallization of zircons in relation to cpx and magnetite.

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R. Parthasarathy ¹, M. M. Palrecha ¹, M. Sankar Das ¹

Affiliations
1 Analytical Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay 400 085, IN

Abstract

Seven zircon separates from different geological environments have been analysed for U, Th and Pb contents. U and Th are determined by Neutron Activation Analysis (NAA) and Pb by Differential Pulse Anodic Stripping Analysis (DPASV). The.elemental abundances have been utilised to calculate the chemical ages of zircons,

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Tapan K. Baidya ¹, S. K. Mondal ², V. Balaram ³, R. Parthasarathy ⁴, R. Verma ⁴, P. K. Mathur ⁴

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 700 032, IN
2 Refractory Division, Central Glass & Ceramic Research Institute, Calcutta 700 032, IN
3 Geochemistry Group, National Geophysical Research Institute, Hyderabad 500 007, IN
4 Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, IN

Abstract

The Precambrian ultramafic-mafic plutonic complex of Nuasahi, Orissa in the Eastern Indian Shield represents at least three suites of magmatic intrusion: (i) an interlayered sequence of enstatitite, websterite (± olivine), dunite, chromitite, harzburgite and orthopyroxenite; (ii) massive gabbroic suite with minor bodies of norite, anorthosite and bands of titaniferous magnetite and (iii) dykes and sills of dolerite and clinopyroxenite. A prominent breccia zone is developed near the interface of the first and second magmatic suites in the eastern part of the complex including the Shankar chromite lode and the ultramafic host of the first suite, and the gabbro-noritic rocks of the second suite. This breccia zone is enriched in Cu-Fe-Ni sulphides and has become the principal site for concentration of PGE, gold and silver. On a whole, Pd dominates over Pt in the sulphide-bearing Shankar chromite lode and the adjacent orthopyroxenite as well as gabbro in this breccia zone. The chromite-sulphide association is the most enriched part for PGE, gold and silver. Ag is positively correlated with Pd. The breccia zone which was developed prior to the gabbroic emplacement into the chromiferous ultramafics. represents a sulphide-rich metasomatic zone leading to maximum concentrations of PGE, Au, Ag in this zone alongwith formation of various sulphides, oxides and silicates. Both Pt and Pd are considerably higher and Ir is lower in the present area than in chromite-sulphide associations from ophiolitic complexes and Alpine-type massifs. Rather, Pt, Pd and Ir values compare better with the chromite-sulphide associations from layered intrusions.

Keywords

Economic Geology, Ultramafic-Mafic Complex, Breccia Zone, Chromite-Sulphide Assemblage, PGE-Ag-Au, Nuasahi, Orissa.

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T. K. Biswal ¹, K. C. Gyani ², R. Parthasarathy ³, D. R. Pant ³

Affiliations
1 Dept. of Earth Sciences, Indian Institute of Technology, Powai, Mumbai, 400 076, IN
2 Department of Geology, MLS University, Udaipur, IN
3 Analytical Chemistry Division, BARC, Bombay, IN

Abstract

The granulitic terrain of Proterozoic Delhi Supergroup exposed between Balaram and Mawal in Gujarat carries a suite of plutonic basic intrusive rocks consisting of gabbro, norite and basic granulites. Chronologically the suite is younger than metabasic rocks of north and central Rajasthan and occurs as melt intrusion within the host of pelitic granulites, calc granulites and granite gneisses. The suite ranges in chemical composition from alkaline to tholeiite through calc alkaline with characteristic major elemental distribution. Rare earth element chemistry shows Eu anomaly with LREE and LILE enrichment over HREE and HFSE. On the basis of the above enrichment it is invoked that the rocks are possibly derived from an enriched mantle beneath a subduction zone. Further, the Hf / 3-Th-Ta and Th / Yb-Ta / Yb systematics reflect a compositional match with calc alkaline basalt of present arc setting. These lead to suggest that the gabbro-norite-basic granulite suite signifies continental are magmatism in Delhi Supergroup and the Aravalli mountain had been evolved through continental collision and subduction during upper Proterozoic time.

Keywords

Geochemistry, Proterozoic, Tectonic Setting, Basic Granulites, Delhi Supergroup, Rajasthan.

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