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

K. L. Chakraborty ¹, A. K. Mallik ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

Pockets of 'sack-form' chromite deposit occur at the intersection of dykes of olivine gabbro near Moulabhanja hills in the Dhenkanal district of Orissa. The dykes intruded the Precambrian granite-gneiss belonging to the Eastern Ghat orogenic belt. Chromite also occurs as minor accessory in olivine gabbro; and in this respect differs in its mode of occurrence from chromite deposits associated with the dunite-peridotite of the Iron ore orogenic cycle. The close association of chromite with olivine gabbro, the paragenetic sequence of the minerals in the rock, and the mineralogy, texture and chemical nature of the ore, suggest that the chromite melt was separated from the basic (olivine gabbro) magma as an immiscible liquid fraction and crystallized earlier than the silicate minerals.

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K. L. Chakraborty ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

No Abstract.

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K. L. Chakraborty ¹, Tapan Lal Chakraborty ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

Nickeliferous limonite occurs over a wide area above tbe serpentinized ultramafic rocks of Sukinda Valley (85°45'E: 21°4'N - 85°52'E: 21°4'N), Orissa, India. It is overlain by a thin mantle of laterite, and is itself underlain successively by silicified ultramafics and serpentinites with layers of chrornitite, followed by unaltered or partly altered dunite-peridotite. Nickeliferous limonite profile extends from 1.22 metres up to 7.0 metres on an average below the laterite cover. NiO content in limonite varies from 0.32 to 1.17 per cent; in the primary ultramafic rocks (e.g., dunite-peridotite) from 0.44 to 0.75 per cent, and in the chromitite from 0.13 to 0.40 per cent. Thin laminations of the chromite layers are preserved in the limonite on the hanging and foot-wall sides, indicating its formation in situ. No separate nickel mineral was identified.

It is concluded that nickel was fixed in the lattice positions of olivine and chromite in dunite-peridotite and chromitite respectively. The element was released during breakdown of these minerals by residual weathering, and was precipitated in the limonite profile at the base of the laterite mantle in an acid environment.

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K. L. Chakraborty ¹, Tapan Baidya ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta-700032, IN

Abstract

The chromitite lodes are emplaced in serpentinites as banded layers, lenses or clots. The ores are high alumina chromite with RO:R₂O₃ ranging from 0.92 to 1.08 and formed by magmatic segregation.

Hydrothermal alteration has produced different chrome-bearing silicates like kammererite, uvarovite, chrome-amphibole, and chrome-bearing chalcedony, which occur either as transgressing veinlets in chromitites or in the interspaces between chromite grains. The primary dunite-peridotite has been altered to massive and compact serpentinite.

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K. L. Chakraborty ¹, T. L. Chakraborty ¹, Tapan Majumder ²

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 700032, IN
2 Department of Applied Geology, Indian School of Mines, Dhanbad 826004, IN

Abstract

The Sukinda Valley of Orissa is underlain by the banded iron formation (BlF) and chromite-bearing ultramafic rocks of Precambrian age. Besides these, local exposure of a quartz-arenite bed with basal conglomerate is correlated with the Kolhans. A basal quartzite horizon is conformably overlain by the BIF. lhe quartz-arenite (Kolhans?) with a conglomerate at the base lies with a local disconformity over the BIF. Chromitebearing ultramafites are pre-kinematic intrusives into the iron formation and have been co-folded with the older sediments. Orthopyroxenite and granitic rocks are intrusive into the chromiferous ultramafites. Occasional intrusive dolerite dykes in the valley may be correlated with the Newer Dolerites of Singhbhum.

The regional structure of the Precambrian rocks of the Sukinda Valley, as established by the present authors, is a cross-folded doubly plunging syncline with the culminated fold axis striking ENE-WSW which is parallel to the main fold axis of the Eastern Ghats Orogenic belt. The plunge of the main fold axis is towards NE and wsw. The cross-folded axis, lying between Tungaisuni and Champajhar villages, trends NNW-SSE and is subparallel to the cross-folded axes of the Eastern Ghat Orogenic belt.

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K. L. Chakraborty ¹, A. Bhattacharyya ¹, B. Roy ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 700032, IN

Abstract

Study on the field-relations, petrography and chemical composition of gabbroanorthosite-granophyre-leucogranite suite supports a co-magmatic origin of these rocks.

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K. L. Chakraborty ¹, Tapan Majumder ²

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 32, IN
2 Department of Applied Geology, Indian School of Mines, Dhanbad, Bihar, IN

Abstract

The metamorphic age (2.55-3.07 Ga) of BIF of Tomka-Daiteri belt has been established from Sm/Nd data which seemingly indicates that the sedimentation age of BIF is older than Singhbhum granite (3.12±0.OI Ga). Intrusive evidences of Singhbhum granite into BIF have been documented. An older age of the GorumahisaniBadampahar- Tomka·Daiteri-Malayagiri BIF with respect to that of Jamda-Koira Valley is supported.

The BIF, consisting predominantly of magnetite-chert, magnetite-jasper (BMJ) hematite-jasper (BHJ) or martite-quartz (BMtQ}form part of a sedimentary succession, underlain by quartz-arenite or lithic wacke and interlayered with altered volcanic tuff (shale ?). Magnetite, hematite and chert were primary precipitates in the BIF. No primary carbonate, silicate or sulphide have been noticed to occur in these rocks excepting sporadic occurrence of carbonate pseudomorphs in the underlying quartz-arenite.

Primary sedimentary structures like current ripples, syneresis cracks, penecontemporaneous deformation structures (e.g. folds, faults, micro-brecciation, pods, etc.) and diagenetic recrystallization features are described.

Similar to other world deposits of Precambrian and Archaean age, the BIF of Bihar and Orissa are also deficient in major, trace (TE) and rare earth elements (REE). Mineralogical composition and geochemistry suggest that they belong to the oxide facies iron-formation, Low concentration of Al₂0₃, CaO, MgO. MnO and of Zr, Cr, Ti, V, Ni and Cu in the BIF with respect to their abundance in. the interlayered pyroclastics presumably suggests a non-volcanogenic source of iron and silica. Eu/Sm ratio (0.541.01) indicates an Archaean age for the BJF. A shallow water marine environment is predicted for the deposition of BIF.

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K. L. Chakraborty ¹, Jishu Roy ¹, Tapan Majumder ²

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta 32, IN
2 Department of Applied Geology, Indian School of Mines, Dhanbad, Bihar, IN

Abstract

Various types of exsolution and replacement structures and textures uf the vanadium-bearing titano-magnetite ores have been described from the titano-magnetite deposits occurring in the gabbro-anorthosite complexes of Orissa, India. Attempt has been made to correlate different textures to various oxidation stages. The ores were formed within the temperature range of 600°-800°C and average fO₂ = 18.4.

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Tapan Majumder ¹, K. L. Chakraborty ²

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad 826 004, IN
2 Department of Geological Sciences, Jadavpur University, Calcutta 700 032, IN

Abstract

Electron microprobe study of low temperature zoned magnetite grains of primary sedimentary origin from the Precambrian banded iron formation (BIF) of Eastern India revealed alternate micro-bands rich in silica and iron, while minor concentration of magnesium is also found in silica-rich bands. X-ray data indicate a normal type of magnetite structure and trace element values support its primary sedimentary origin. Origin of the zoning in magnetite is attributed to enrichment of Si and Fe in alternate bands on a microscale simulating the alternate silica and iron rich bands of the host-rock-banded iron formation.

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K. L. Chakraborty ¹, A. K. Mallik ¹

Affiliations
1 Department of Geological Sciences, Jadavpur University, Calcutta, IN

Abstract

The Moulabhanja hills and the adjoining areas are underlain by Precambrian granite gneiss which is intersected by a variety of gabbroic dykes and stocks. Mineral assemblages and textural relationships point recognition of four types of gabbroic rocks which also represent critical stages of fractional crystallization, e,g., (i) olivine gabbro with essential olivine, pigeonite augite and bytownite (ii) hypersthene gabbro with essential hypersthene, augite and labradorite (iii) doleritic gabbro with essential augite and labradorite, and (iv) normal gabbro with augite and less calcic labradorite.

The chemical and normative mineral composition of the basic magma is tholeiitic. The magma seemingly differentiated into different types of gabbroic rocks by fractional crystallization and gradual enrichment in iron. Two analyses of the olivine gabbro lie on the transitional zone between tholeiitic and calc-alkali suite. The closing temperature ofcrystallization of the basic magma and the corresponding oxygen fugacity are estimated to be 600°C and 18.4 (-Log₁₀ FO₂) respectively.

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