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S. Mukherjee ¹, B. K. Bandyopadhyay ¹

Affiliations
1 Department of Geology, Calcutta University, Calcutta, IN

Abstract

The presence of a Gonditic rock unit is reported from Manbazar, Purulia district, West Bengal. It occurs as a distinct band cofolded with the associated metapelites into an isoclinal antiform followed to the west by a complimentary synform with granitic rocks occupying the antiformal core. The metasediments including the gonditic unit were metamorphosed under Upper Greenschist Facies conditions of regional metamorphism. Mineralogically it is composed mainly of quartz, spessartite, piedmontite, braunite, magnetite, specularite and ilmenite. The minerology and textural relationships indicate moderately high temperature and high oxygen fugacity under which the original sediments were metamorphosed.

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B. K. Bandyopadhyay ¹, Abhinaba Roy ¹

Affiliations
1 Geological Survey of India, AMSE Wing, Nagpur, IN

Abstract

Occurrence of thin but persistent horizons of banded garnet-amphibole-rock (BGA) is reported from the Proterozoic Bijawar or Mahakoshal Group in Sidhi district, Madhya Pradesh. The physical appearance, mineralogy and chemistry of the rock are closely comparable to some metamorphosed manganiferous iron-formations. The rock occurs in association with a sequence of low-grade metasediments, mainly comprising wacke and argillites together with subordinate quartz arenite, banded magnetite quartzite, limestone, tuffs and basic volcanics, which bear similarity with the sediment-hosted Algoma type iron formation. Although there is a broad similarity in the composition of the Bijawar BGA rocks with the known B1F of the world, the former showsan appreciable enrichment in A1₂O₃, MnO, MgO, CaO, Ba, Zn, Co, Ti, Y and V compared to the latter.

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Abhinaba Roy ¹, B. K. Bandyopadhyay ¹

Affiliations
1 Geological Survey of India, Nagpur 440022, IN

Abstract

Serpentinised ultramafic bodies of peridotite-dunite composition occur as solid state intrusions in the Bijawar volcano-sedimentary sequence around Tal in Sidhi district, Madhya Pradesh. The associated basic volcanics and gabbros are predominantly tholeiitic in composition, although a slight enrichment in Na is recognised locally. However, apart from their juxtaposition, there is no petrological or chemical evidence to suggest that the uhramafic and gabbroic rocks were derived from a common magma. The ultramafics represent olivine-pyroxene cumulates, crystallised at depth and subsequently emplaced as crystalline mush (? diapiric intrusion) during the pre- to early-kinematic stage of basin development. This suggests the possible role of a mantle-derived magma to initiate basin depression. Near the cratonic margin of the basin, shelf sediments (orthoquartzite, carbonate-pelletal chert etc.) were deposited over the gneissic basement while the distal facies was mainly a turbidite. The rocks underwent polyphase deformation and low-grade greenschist facies metamorphism. The closing stage of Bijawar was marked by the emplacement of post-tectonic granite and occasional gabbroic diorite near the peripheral zones of the belt.

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B. K. Bandyopadhyay ¹, Anupendu Gupta ¹

Affiliations
1 Geological Survey of India, IN

Abstract

The rocks in the basin range in age from Early Ordovician to Devonian. Proximal sedimentation began with the deposition of an orthoquartzite-conglomerate lithofacies of the Nake Chu Formation. Rapid sedimentation coupled with quicker subsidence initiated a period of instability that led to the deposition of the distal facies sediments of the Mane Ting Formation characterised essentially by interbanded quartz wacke and shale with an input of andesite. A number of conformable interbedded para-conglomerate beds, identified as submarine debris flow deposits, occur within this Mane Ting Formation.

Lithic fragments ranging in size from 1 mm to 2 m and upwards constitute one modal class and are of diverse types, including quartz wacke, shale, quartzite and chert and limonitised clasts. Monocrystalline quartz, muscovite, siderite and feldspar in combination with the matrix define the second mode with size ranging from 1/4 to l/200 mm. The bimodality is interpreted to be due to mixing of the coarse sand and gravel component with the matrix.

Intact load structures and convolute folds in rip-up clasts and rafts, very poor sorting with high mud matrix, angularity of the constituent fragments. chaotic and often vertical orientation of the platy clasts and the presence of mud balls, armoured sand grains and shale-coated clasts strongly suggest transportation within a high density, cohesive debris-flow.

Keywords

Sedimentology, Debris-Flow Deposils, Ordovician, Himalaya, Bhutan.

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P. R. Golani ¹, M. L. Dora ¹, B. K. Bandyopadhyay ¹

Affiliations
1 Geological Survey of Indra, Project Thematic Mapping, Op Maharashtra, Seminary Hills, Nagpur - 440 006, IN

Abstract

The southeastern part of the Proterozoic Betul Belt exposes a Felsic-Dominated sequence around Bhuyari in the Kanhan river sector. The felsic volcanic rocks, identified as rhyolite occur in the form of two mappable bands in a milieu of biotite ± hornblende bearing Quartzo-Feldspathic rocks of subvolcanic affinity. A very well developed zone of hydrothermal alteration is recognized in rhyolite that occurs to the immediate south of Bhuyan village. The hydrothermal facies mapped in the alteration zone include sericite - muscovite-bearing rhyolite, phlogopite± spessartite biotite schist and trernolite (± actinolite) - rich rock with serpentine, talc, epidote and dolomitic carbonates. Discrete grains of fluorite and REE bearing flour carbonates form part of the hydrothermal mineral assemblage. Apart from the magnesian enrichment, the occurrence of spessartite garnet, epidote and sporadic development of staurolite indicate significant fluxes of manganese, calcium and alumina in the zone of hydrothermal alteration. The alteration is attendant with polymetallic base metal mieralisation which is invariably Zinc-Dominated. Bedrock samples and selected channel sampling indicate that the Tremolite-Rich facies is intensely mineralized, followed by phlogopite ± garnet biotite schist. Primary sulphides observed in a dug well section are pyrite, sphalerite galena and chalcopyrite which occur as disseminations and also as several millimeter thick semiconformable veins Rare quartz Phenocryst-Groundmass relationship in the mineralized host rock from the dug well provide incontrovertible evidence for the volcanic affinity of the base metal mineralisation.

Keywords

Base Metal Mineralisation, Hydrothermal Alteration, Volcanic Rocks, Chhrndwara District, Madhya Pradesh.

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S. K. Tripathy ¹, D. S. Jeere ², B. K. Bandyopadhyay ³

Affiliations
1 Geological Survey of India, Marine wing, Salt Lake, Kolkata - 700 091, IN
2 Geological Survey of India, Central Region, Alandi Road, Pune, IN
3 Geological Survey of India, Operation Orissa, Bhubaneswar, IN

Abstract

Geological mapping (1,25,000) and stream sediment sampling (1 km x 1 km grid) were carried out simultaneously in parts of Sindhudurg district, Maharashtra during the year 2001-02. The area is occupied by gneisses, granites, and low-grade supracrustals of possible Late Archaean age, Neo-Proterozoic Badami sediments, Deccan Trap basalts and extensive laterites.

This paper deals with the spatial distribution patterns of selected major oxides (Fe₂O₃, Al₂O₃, P₂O₅, MnO and MgO) and trace elements (Co, Ni, Cr, Zr, Sr, Rb and Ba) in stream sediments in relation to the underlying rock outcrops. The study area has neither Large-Scale anthropogenic activities nor any reported mineral occurrence. In such terrains, the study reveals that the spatial elemental distribution in stream sediments is mainly guided by the bedrock geology and chemistry. A gabbroic body in the central part of the area is reflected remarkably well in the high value stream-sediment contours of Co, Ni&Cr and matches fairly well with elevated values of Fe₂O₃, MgO and MnO Stream sediment samples over younger granites are rich in Zr, Ba and Sr. The elemental concentrations in stream sediments over gneissic rocks show moderately high values of Ba, Sr, Zr, Al₂O₃ and low values of remaining elements.

Cluster analysis of the data set reveals three groups within the elements discussed above, viz Group I (Cr-Co-Ni- Mg-Mn), Group II (Ba-Sr-Zr-Rb) and Group III (Al-Fe-P) Group-I elements are concentrated and depleted in ultramaficmafic rocks and acid rocks respectively while Group II elements are depleted in mafic rocks but ennched in acid and alkaline rocks Group-Ill elements show minor affinity towards both acid and basic rocks.

Therefore, in a terrain occupied by vaned rock units, stream sediment sampling is required to be dense enough to represent the changing lithology. A gneissic terrain requires a much denser sampling programme compared to an area occupied by Deccan Traps.

Keywords

Geochemical Map, Stream Sediment, Geochemical Anomaly, Trace Elements. Statistical Analysis, Sindhudurg, Maharashtra.

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Anupam Chattopadhyay ¹, A. S. Khan ¹, A. K. Huin ¹, B. K. Bandyopadhyay ¹

Affiliations
1 Geological Survey of India, Seminary Hills, Nagpur 440 006, IN

Abstract

Geological mapping and structural analysis of the manganese-bearing Sausar Group and associated rocks in Ramtek-Mansar-Kandri area, Maharashtra, have led to reinterpretation of stratigraphy and structure. A local stratigraphic succession for the Sausar supracrustal rocks, giving due weightage to lithologic critena and structural considerations, has been proposed which is different from the existing divergent lithostratigraphic successions suggested by different workers at different times. The lithologic unit interpreted as a conglomerate horizon by some earlier workers, near the contact of the granite gneiss and the Sausar Group in Mansar-Kandri area, has been reintmpreted to be of tectonic origin, Sausar Group preserves evidence of four generations of folding (F₁ to F₄). The map pattern is controlled by F₂ and F₄ whereas F₁ and F₃ have developed only on hand specimen to outcrop scale Ramtek synform, the major structural feature in the area, is a polyharmonic, second-generation fold with shallow southeasterly plunge and a steep to subvertical, WNW-ESE striking axial plane. It is not a large scale non-plane, non-cylindrical superposed fold (F₂ on F₁), as interpreted earlier. Regional metamorphism of pelitic-psammopelitic rocks possibly reached amphlbolite facies with peak metamorphic condition post-dating D₁ deformation.

Keywords

Sausar Group, Structure, Stratigraphy, Folding, Metamorphism, Maharashtra, Central India.

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Abhinaba Roy ¹, B. K. Bandyopadhyay ¹, A. K. Huin ¹

Affiliations
1 Geological Survey of India, Central Region, Nagpur - 440006, IN

Abstract

The Mafic volcanic suite exposed mainly in the eastern part of the Sakoli schist belt comprises the lower part of the Sakoli sequence. The samples are tholeiitic in composilion having moderate M-values (45-62) and lower abundances of Ni, Co and Cr indicative of evolved nature of the magma. Certain major and trace element characteristics and LREE enriched REE patterns suggest magma derivation by low degrees of partial melting of komatiite-like sources.

Keywords

Sakoli Schist Belt, Geochemistry, Komatiites, Maharashtra.

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A. C. Saha ¹, B. K. Bandyopadhyay ¹

Affiliations
1 Department of Physics, Hooghly Mohsiu College Chimsiirnh, Hooghly, West Bengal, IN

Abstract

A precise search for the fireball type of interactions has been made iisin^g photo-eniulsin plates exposed to 70 GeV Proton beam at Serpukhov Accelerator at Dnbna, USSR (erstwhile). It is observed that the frequency of occurrence of fireballs at this primary energy is very small, Pions produced through this particular type of interactions are very nearly isotropic regarding the Duller-Walker distribution and also the differential angular distribution. The authors have further arrived at the conclusion that (he angular distribution of the pions in Fireball Rest System (FRS) comes out to be a Gaussian. As regards the energy distribution of the pions in FRS it is observed that the distribution closely resembles Planck's distribution of Photons. Furthermore this study reveals that Maxwell-Blotzmann distribution deviates enough from the experimental data. It is lastly concluded that the pions are emitted with the invarient transverse momentum equal to (0.544 ± .02) GcV/c and the average energy equal to (0.740 ± .02) GeV in FRS.

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