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

D. C. Pal ¹, M. K. Panigrahi ¹, B. Mishra ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721 302, IN

Abstract

Stanniferous pegmatites of Malkangiri occur both in metabasics and metasediments showing signatures of deformation but very little wall rock alteration. Fluid inclusion microthermometric studies in pegmatitic quartz and quartz from quartz veins reveal the following three types of inclusions: aqueous biphase, metastable (?) monophase aqueous inclusions which do not show any thermal response, and rare halite-bearing inclusions. The CO₂-free nature of the inclusions is noteworthy. Isochores of halitebearing inclusions (where T_{s Nacl} > T_h) intersect at P-T values of 2.65 kb and 337°C, implying preservation of the magmatic fluid that separated during the late stage of felsic magmatism in the area. Additionally, the above P-T values compare reasonably well with those obtained from the intersection of halite liquidi with the corresponding isochores.

Tin-bearing pegmatites in metabasics are characterized by their low temperature of homogenization and isothermal variation in salinity. This is explained by mixing of a Sn-bearing, granite affiliated, presumably reduced fluid with a heated, less evolved oxygenated meteoric water that led to cassiterite precipitation. Interestingly, inclusions in cassiterite-bearing pegmatites within metasediments record a low temperature comparable with those from within metabasics. In contrast, barren pegmatites within the schistose metasediments preserve high temperature signature and indicate a simple cooling trend. The study reveals different styles of evolution of stanniferous and barren pegmatites at Malkangiri.

Keywords

Economic Geology, Pegmatites, Tin, Fluid Inclusion, Malkangiri, Orissa.

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B. Mishra ¹, K. L. Pruseth ¹, S. Sarkar ¹

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, IN

Abstract

Acanthite (Ag₂S), Stibnite (Sb₂S₃) and Boumonite (CuPbSbS₃) were synthesized by the evacuated silica tube method under dry conditions. Boumonite was synthesized both from its elemental composition and from the component sulfides. All the products were characterized by the optical and XRD methods and were found to be pure, homogeneous and direct semiconductors.

Diffuse reflectance studies were undertaken on these synthetic mineral phases. The forbidden energy gap (E_g) was calculated by α² vs. hν plots and linear extrapolation to α² = zero. E_g was also deduced by calculating the Kubelka - Munk remission function, and plotting it against the photon energy. The E_g values obtained were: acanthite 0.98, 1.0 eV; stibnite 1.50, 1.55 eV and boumonite 1.15, 1.23 eV. Possible industrial application of these syntheti∼ semiconducting mineral phases are discussed.

Keywords

Mineral Synthesis, Acanthite, Stibnite, Boumonite, Reflectance Spectroscopy.

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M. K. Panigrahi ¹, B. Mishra ¹, A. Mookherjee ¹

Affiliations
1 Department of Geology and Geophysics Indian Institute of Technology, Kharagpur 721302, IN

Abstract

Textural and paragenetic study of primary minerals (chalcopyrite, pyrite, magnetite, hematite, sphalerite, bornite, chalcocite and molybdenite) reveal intermittent fracturing, precipitation and dissolution phenomena with at least two recognizable stages: magnetite(I) - pyritc(I) - molybdenite (?) followed by pyrite(II) - chalcopyrite - sphalerite - magnetite(II) - hematite - bornite - chalcocite. Oxidation and supergene enrichment effects producing cuprite-malachite-native copper and chalcocite-covellite are moderate. Difference in the mineralogy of the oxidation zone and restricted occurrence of supergene enrichment are due to the variation in the primaty mineralogy of the ore.

The ranges of fluid inclusion homogenization temperature (maxima 160°-180°C) and fluid densities in the reef quartz and ore bearing vein quartz are more or less the same, with a wider range of salinity in the vein quartz ores. However, mixed aqueous carbonic inclusions are restricted to the vein quartz ores and hence points towards a difference in the fluid regime. T_h vs. salinity and T_h vs. density plottings rule out simple cooling and/or mixing processes in the evolution of the fluid but rather hint at immiscible two-fluid phase separation. The suspected presence of low temperature Iss-phases and the results of fluid inclusion microthermometty point towards an unexpectedly low temperature environment of ore deposition. The paragenetic sequence is suggestive of an increase in the Cuffe ratio and fluctuating f_O2 conditions in the fluid during the main stage of mineralization.

Keywords

Ore Mineralogy, Fluid Inclusion Study, Malanjkhand, Copper, Madhya Pradesh

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P. C. Mishra ¹, B. Mishra ², M. W. Y. Khan ³

Affiliations
1 South Zone, Berhampur - 760 010, IN
2 PG Dept of Geology, Khallikote Autonomous College, Berhampur - 760 001, IN
3 School of Studies in Geology and Water Resources, Pt R S University, Raipur - 492 010, IN

Abstract

Marine marginal zones are most susceptible to geomorphic modifications. Study of sequential datasets enables clear understanding of the changes that an area has undergone. Systematic study of the datasets of Bahuda estuary region revealed that the mouth of the river is oscillating during the past seven decades. The morphology of the estuary is also modified due to combined action of fluvial, fluviomarine, marine and aeohan action. The tidal influence together with the fluvial regime is responsible for modification of the coastal landforms and tidal swamps located inland. The channel bars and mouth bars are under constant influence of the physical processes and are adjusting to the dominant processes, which control their existence and geometry. The Bahuda estuary region can be considered as one of the most attractive sites along the coast of Orissa due to panoramic view and unique geomorphological set up in the context of tourist potential.

Keywords

Marine Marginal Zone, Bahuda Estuary, Spit, Tidal Energy, Ambaghai Nadi, Tidal Swamp, Ganju Tampara, Fluviomarine Processes, Morphological Changes, Orissa.

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Mihir Deb ¹, R. Shankar ², M. Jayananda ³, B. Mishra ⁴

Affiliations
1 Geology Department, University of Delhi Delhi - 110 007, IN
2 Department of Marine Geology, Mangalore University, Mangalagangotri - 574 199, IN
3 Department of Geology, Bangalore University, Bangalore - 560 056, IN
4 P.G. Department of Geology, Khallikote Autonomous College, Berhampur - 760 001, Orissa, IN

Abstract

No Abstract.

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B. Mishra ¹

Affiliations
1 Indian Institute of Technology, Dept of Geology and Geophysics, Kharagpur - 721 302, IN

Abstract

No Abstract.

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B. Mishra ¹

Affiliations
1 P.G. Department of Geology, Khallikote Autonomous College Berhampur - 760 001, Orissa, IN

Abstract

No Abstract.

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B. Mishra ¹, N. Pal ¹, S. Ghosh ²

Affiliations
1 Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur - 721 302, IN
2 EASC, 8888 University Drive, Simon Fraser University, Burnabay, B.C., Canada V5A156, CA

Abstract

Fluid inclusions in quartz from the mineralized quartz veins from the Mosabani and Rakha copper deposits were investigated. On the basis of petrography, two distinct types of primary inclusions were identified. These are low saline aqueous biphase inclusions and high saline halite-bearing polyphase inclusions. The halite-bearing inclusions mostly homogenized by halite dissolution; barring instances where homogenization was manifest by disappearance of the vapour bubble. Minimum entrapment pressure values were eslimated by intersection of the halite liquid with the corresponding incIusion isochores. The ranges in P-T at the ternpcratures of halite dissolution are: 2.6 kb / 370°C - 0.8 kb / 263°C for Mosabani and 2.1 kb 1 270°C - 0.65kb / 217°C for Rakha. Temperature-salinity plots fot both the deposits is suggestive of restricted mixing (and simple cooling) of a hot saline magmatic fluid with cooler low saline meteoric water that caused precipitatin of sulphide minerals. Stable isotope data (δ¹⁸O and D) from Changkakoti et al. (1987) are re-interpreted in the present study, leading to the conclusion that the main fluid component for Mosabani mineralization was either of magmatic/metasomatic parentage or an evolved meteoric water at a low water/rock ratio, after its interaction with a granitic pluton. The observed high saline nature of fluids in both the deposits compels us to choose an initial magmatic/metasomatic fluid that evolved by restricted mixing and simple cooling.

Keywords

Fluid inclusions, Microthermornetry, Copper Ores, Mosabani, Rakha, Singhbhum, Jharkhand.

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Kalyan Chakrabarti ¹, N. R. R. Ecka ¹, B. Mishra ¹, P. V. Ramesh Babu ², P. S. Parihar ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Jamshedpur - 831 002, IN
2 Atomic Minerals Directorate for Exploration and Research, Hyderabad - 500 016, IN

Abstract

Ground Radiometric survey of Paleoproterozoic pyritiferous quartz-pebble conglomerate (QPC) occurring to the north of Pallahara area led to the discovery of a QPC type uranium mineralisation near Mankarhachua village. Significant radioactivity is recorded in three sub-parallel uraniferous QPC horizons with metamorphosed pebbly to medium grained recrystallised massive sandstones. Detrital grains of uranothorite, thorite, radioactive allanite, monazite, zircon, minute uraninite grains in carbonaceous matter and thucolite contributes to the radioactive phases present in QPC matrix. Adsorbed U on limonite and goethite, secondary uranyl minerals in matrix, along bedding planes and fractures are commonly observed. This discovery has opened up a new horizon for future exploration for QPC type uranium mineralization in the area. The paper presents observations on geology, radioactivity, petrological and geochemical nature of the uraniferous QPC horizons.

Keywords

Conglomerate, Uranium Mineralization, Orissa.

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