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Mitra, Sachinath
- Sukinda Sandstone - A Kolhan
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 14, No 2 (1973), Pagination: 184-185Abstract
No Abstract.- Low Ca Low Al Orthopyroxenes from Chromite-Bearing Area of Sukinda and their Significance
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 15, No 3 (1974), Pagination: 327-329Abstract
No Abstract.- Compositional Variations in Chromites from Sukinda Orissa, India
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 17, No 2 (1976), Pagination: 224-235Abstract
The chromite-bearing ultramafic pluton in Sukinda, Orissa, was emplaced in two horizons in the Iron Ore Series rocks which were subjected to shearing deformation and hydrothermal activity, followed by silicification. These processes in most cases completely transformed the early silicates to chlorites and produced, in some cases, compositional zoning in the periphery of chromite grains. The chromite grains and samples from different horizons show variations in composition, reflectivity and latticeparameter. Eight analyses of separated chromite samples are presented along with spot microprobe analyses for Cr, Mg, Fe and Al; these reveal not only marked compositional differences among discrete grains but also show distinct compositional zoning in individual grains.- Distribution and Textural Characteristics of the Heavy Minerals in the Beach and Dune Sands of Cox's Bazar, Bangladesh
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta 700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 1 (1990), Pagination: 54-66Abstract
The beach and coastal dune sands of Cox's Bazar constitute the most important source of metallic minerals in Bangladesh. The sands are fine, well-sorted, negatively skewed and leptokurtic in their grain-size distributions. Plots of different size parameters suggest that (a) the finer the grain-size the better is the sorting; (b) the sediments are more negatively skewed as the grain-size decreases; and (c) sorting improves as the skewness changes from nearly symmetrical to negative. The dune sands are finer, better sorted and more negatively skewed than beach sands. The percentage of heavy minerals increases from 2 φ (250 μ m) to 3.5 φ (88 μ m) fraction. The light fraction consists predominantly of quartz (about 90 %), while amphibole, ilmenite, garnet, epidote, mica, pyroxene, magnetite. kyanite, tourmaline, staurolite, zircon, rutile and monazite constitute the heavy minerals. The distribution of the heavies in the dunes and beaches depend on their respective shape. The equant ones are predominant in the former than in the latter. The predominance of unstable minerals and their shapes suggest that the major source of the sediment may be in the easterly highlands of Chittagong-Arakan hills.Keywords
Sedimentology, Beach and Dune Sands, Cox's Bazar, Bangladesh.- William Lawrence Bragg (1890-1971)
Authors
1 Jadavpur University, Calcutta 700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 36, No 6 (1990), Pagination: 560-563Abstract
No Abstract.- Ilmenites from Cox's Bazar Beach Sands, Bangladesh : Their Intergrowths
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta - 700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 40, No 1 (1992), Pagination: 29-41Abstract
About 52% of the samples of Cox's Bazar beach contain six textural types of hematite-ilmenite exsolutions,the commonest (∼83%) being the seriate type. Hemo-ilmenite with greater ilmenite contnet exsolves in a process of continuous exsolution mechanism, whereas more hematiterich phases (very common) exsolve discontinuously. The hemo-ilmenites (IIm45 Hem55 to IIm75 Hem25) are ferrimagnetic in nature. Modal analysis has indicated the percentages of pure ilmenite (exsolved + unexsolved type) and hematite (exsolved, both host and guest) to be 73.74% and 26.26% respectively. This result also corroborates with X-ray, Mossbauer and chemical analyses.Keywords
Cox's Bazar Beach Sand, Bangladesh, Exsolution Textures, Mossbauer Spectroscopy, X - ray Diffraction, Petrography.- Distribution of Iron Cations in Natural Chromites at Different Stages of Oxidatio - A57Fe Mossbauer Investigation
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta- 700032, IN
2 Department of Geology, Yonsei University, Seoul, KR
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 1 (1994), Pagination: 53-64Abstract
57Fe Mossbauer spectroscopic investigation of natural chromites from two chromite deposits of India (Sukinda and Byrapur) documents partly inverse spinel structure arising out of oxidation. The spectral fitting was based on allowing a disordering distribution of Fe2+ and Fe3+ ions at tetrahedral (A) and octahedral (B) sites. Mossbauer investigation of the samples taken from the physico-chemically distinct two horizons of Sukinda viz. brown are and grey ores, and Byrapur area revealed three types of iron ion distribution as: Fe2+(A), Fe3+(A) and Fe2+(B) (GC-group); (b) Fe3+(A1), Fe3+(A2) and Fe2+(B) (BC-2 group), and (c) Fe3+(A1), Fe3+(A2) and Fe3+(B) (BC-1 group).
The distribution pattern of iron cations at A and B sites was linked to the degree of oxidation. The stages of oxidation could be modelled from normal to inverse fonn. A model suggesting 'electron localisation' at the B-sites makes the intermediate stage. Iron site occupancy determined by Mossbauer spectroscopy of the presently studied samples indicates that these fall under three groups of oxidation stages. An early stage of oxidation is shown by samples of group GC, intermediate stage by group BC-2 and final stage by BC-1 group of chromite samples. The imprint of progressive oxidation manifested by Fe cation site occupancy has been correlated with the Fe2+/Σ:Fe ratios, obtained for each group of samples.
Keywords
Chromites, Mineralogy, Sukinda, Orissa, Byrapur, Karnataka, Mossbauer Spectroscopy.- 57Fe Mossbauer Study of Low Aluminous (Low Ca) Orthopyroxene from Sukinda, Orissa (India) and its Petrogenetic Implication
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta-700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 43, No 1 (1994), Pagination: 41-50Abstract
A low Al, low Ca enstatite from within an orthopyroxenite dyke rock in the Sukinda chromite field was physico-chemically investigated by use of 57Fe Mossbauer spectroscopy XRF and XRD. The parameters of the fitted 57Fe Mossbauer spectra show the presence of Fe3+ in the octahedral M1 site of pyroxene structure.
The room temperature Mossbauer results show three doublets corresponding to Fe2+ (Ml), Fe2+ (M2) and Fe3+ (M1) sites. The QS values in two samples are found to be 2.80 and 2.96 mm/s for Fe2+ , (M1), and 1.89 and 2.08 mm/s for Fe2+ (M2) doublets. In both samples Fe3+-(M1) gives IS values 0.38 and 0.56 mm/s and QS values 0.48 and 0.49 mm/s. From their dependence on XFe21M1and XFe21M2 distributions the bond distances of tetrahedral and octahedral sites have been measured.
In the present case Fe3+ in the orthopyroxene structure is presumed to have been formed primarily at the stage of its crystallisation from a melt having requisitely high fO2. The temperature recorded by the Sukinda orthopyroxenile body has been estimatcd as 800°C from the distribution of Fe2+ - Mg over Ml and M2 sites. From the Fe3+/Fe2+ ratio the oxygen fugacity has been calculated as log fO2 = -6.189, which suggests that crystallisation of Sukinda orthopyroxene took place in the lower crustal regions rather than in the mantle.
Keywords
Mineralogy, Pyroxenes, Sukinda, Orissa.- Rutile Exsolution in Fe3+-chromites: A Case Study from Layered Granulitic Complex of Sittampundi, S. India
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta-700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 47, No 1 (1996), Pagination: 75-82Abstract
The presence of Fe3+ at both tetrahedral (A) and octahedral (B) sites (-45% of total iron). from Mossbauer spectroscopic data of Sittampundi chromite, strongly suggests that high fO2(10-7.30 to 10-7.34) conditions were prevalent during its formation. This Cr-spinel was formed with enough of Ti and Al (at its B-site) in its initial structure, attained while in the primary melt at high P-T field (>10.6 kbar, >950°C). The high fO2 in the crystallizing environment did not allow iron to remain as "free" Fe2+ ion to be stabilized into ilmenite structure. In chromite lattice, Ti4+ gets stabilized at Bsite only by coupled occupancy with bivalent cations, strongly with Fe2+. Inadequacy of Fe2+ content to charge-balance Ti4+ at B-site due to further oxidation of iron to Fe3+ caused an expulsion of Ti4+ from the chromite lattice. The released free Ti4+ ion readily combines with oxygen alone to form rutile (or its ilk) which comes out as acicular exsolution bodies within chromite, often following its crystallographic planes [along (111)].Keywords
Chromite, Mineral Chemistry, Rutile Exsolution, Sittampundi Complex, Tamil Nadu.- Mineralogy and Geochemistry Of Detrital Magnetites from the Beach Sands of Cox's Bazar, Bangladesh and their Petrogenetic Implications
Authors
1 Department of Geological Sciences, Jadavpur University, Calcutta-700 032, IN
2 Department of Geology and Mining, Rajshahi University, Bangladesh, BD