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

S. K. Das ¹, S. Mukherji ²

Affiliations
1 Regional Research Laboratory, Bhubaneswar 751 013, IN
2 Department of Geology, Utkal University, Bhubaneswar 751 004, IN

Abstract

Electron probe data arc presented for coexisting ilmeno-magnetite and hemoilmenite for three samples along with the two published analytical results. The Mol % ulv and hem are plotted in T-fo₂ diagram and compared with the results of DubJabera and Skaergaard. The oxides of the five samples equilibrated at 710°C to 1050°C with fo₂ ranging between 10^-9.2 to 10^-17.5 atm. The lower temperature of formation indicated by three samples is probably due to external granule exsolution process and high water content of the magma which is responsible for widespread deuteric and hydrothermal alteration of the genetically associated rock types.

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B. C. Acharya ¹, S. K. Das ¹, R. K. Sahoo ¹, B. C. Patnaik ², N. K. Das ³

Affiliations
1 Regional Research Laboratory, Bhubaneswar 751 013, IN
2 Directorate of Mines, Govt. of Orissa, Bhubaneswar, IN
3 Orissa Remote Sensing Application Centre, Bhubaneswar, IN

Abstract

Tin along with Nb and Ta occurs both as primary mineral in pegmatites and as detrital mineral in the colluvial, eluvial and alluvial placers in Matili-Mundaguda area of Koraput District, Orissa. Cassiterite is commonly associated with soda plagioclase, microcline, perthite, quartz and muscovite, and it invariably contains inclusions of columbite-tantaIite, tapiolite, pyrochlore and fergusonite varying from 0.4 to 18% by volume and 3 to 400 microns in size. Minerals, like ilmenite, magnetite, lepidolite, pyrite, chalcopyrite and sphalerite are also associated with cassiterite. Nb and Ta is present in cassiterite both in solid solution as well as separate mineral phases.

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S. K. Das ¹, R. K. Sahoo ¹, J. Muralidhar ¹, B. K. Nayak ¹

Affiliations
1 Regional Research Laboratory, Bhubaneswar-751013, Orissa, IN

Abstract

In the Sukinda ultramafic belt of Orissa, significant deposits of nickeliferous laterite have formed by weathering of large chromiferous dunite-peridotite suite of rocks. Two typical laterite profiles obtained by drilling (BH-1 = 50 m and BH-2 = 46 m) from Kansa sector of Sukinda belt were studied in order to establish petrochemical relationships between supergene Ni-laterites and the parent rock. In BH-1, ferruginous layers comprise the profile where goethite is intimately admixed with quartz, kaolinite and gibbsite at various depths. In BH-2, a complete laterite profile from bed rock (altered dunite) to top pisolitic laterite with transitional clay-serpentinite zone is encountered. The altered dunite is essentially composed of olivine (FO_93.8 ≅ 35% vol.) and serpentine. The clay-serpentinite zone consists of varying proportions of smectite clay (nontronite) and antigorite with minor amount of chromite, goethite and quartz. This zone is enriched in Ni with a maximum value of 1.09% Ni. In the ochreous ferruginous zone overlying clay-serpentinite zone, serpentine and nontronite disappear completely and goethite constitutes the principal mineral with varying proportions of secondary quartz. This zone is rich in Fe, Ni, Co, Mn, Al and Cr and is formed by residual concentration of stable oxides. Mass-balance equation assuming Cr₂O₃ as constant chemical constituent reveals that nickel is strongly accumulated in the clay-serpentinite zone. A second maximum in nickel concentration is found in ochreous ferruginous zone with almost complete removal of magnesium. Normalised major and trace element data generated on the bore hole samples have been processed, by using R-mode factor analysis of correlation matrix to understand the natural process of weathering. Leaching studies of the samples suggest that nickel occurs in adsorbed state within amorphous hydrated iron oxide and in weakly bonded and lattice bound states within gaethite and secondary silicates.

Keywords

Economic Geology, Geochemistry, Nickeliferous Laterite, Leaching, Sukinda, Orissa.

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S. K. Das ¹, R. K. Sahoo ¹, A. K. Paul ², G. Friedrich ³

Affiliations
1 Regional Research Laboratory, Bhubaneswar - 751 013, IN
2 Department of Geology, Utkal Universty, Bhubaneswar - 751 004, IN
3 Institut fuer Mineralogie und Lagerstattenlehre der RWTH, Aachen, DE

Abstract

Minor amount of Mn oxides occur as veins and fracture fillings in some of the chromite ore samples of D-Quarry of South Kaliapani, Sukinda. Microscopic, XRD and EPMA studies indicate that the Mn oxide minerals are lithiophorite and chalcophanite. These minerals are enriched in Ni and Co and were formed by lateritic weathering of ultramafic rocks.

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S. K. Das ¹, S. Mukherji ²

Affiliations
1 Regional Research Laboratory, Bhubaneswar - 751 013, IN
2 Department of Geology, Utkal University, Bhubaneswar - 751 004, IN

Abstract

The basic igneous complex of Mayurbhanj is a differentiated suite composed of harzburgite, gabbronorite, leucogabbronorite and anorthosite. EPMA of the coexisting oxides in the rock samples reveal that magnetite-ilmenite have re-equilibrated between 770°C and less than 500°C and fo₂, of 10_-16 to less than 10_-25. Ilmenite granules and thick lamellae have identical composition and approach pure FeTiO₃. The chrominn spinel-olivine geothermometry in harzburgite suggests a temperature of 1263°C. The pyroxene geothermometric data in gabbroic rocks indicate equilibration temperature range of 819° C to 1071° C. The thermometric data indicate that the magnetite and ilmenite equilibrated at lower temperature than the coexisting pyroxenes for a particular rock sample.

Keywords

Igneous Petrology, Basic Igneous Complex, P-T Conditions, Oxygen Fugacity, Orissa.

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S. K. Das ¹

Affiliations
1 Institute of Minerals and Materials Technology, Bhubaneswar - 751 013, IN

Abstract

No Abstract.

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S. K. Das ¹, B. K. Nayak ¹, P. Chattopadhyay ¹, J. Muralidhar ¹, B. B. Nayak ¹, A. K. Singh ², R. K. Sahoo ³

Affiliations
1 Regional Research Laboratory, Bhubaneswar - 751 013, IN
2 2N3/278, IRC Village, Bhubaneswar - 751 015, IN
3 137, Jagganath Vihar, Bhubaneswar - 751 003, IN

Abstract

At Gopur, Onssa, auriferous quartz veins with stringers and rich disseminations of sulphides occur in the latcntes derived by tropical weathering of metabasaltic rocks. Minute to coarse irregular gold grains were hand picked from the panned heavies obtained by washing the excavated wall rock materials of the quartz veins which are composed of powdery latente ± kaolinite ± quartz. The gold grains display pitted, fractured, striated, wavy surface and occasional smooth contour pattern. The gold content of the quartz veins and latentic wall rocks vanes widely from < 1 ppm to 9 ppm SEM-EDS and microprobe analytical results of four gold grains reveal contrasting chemical characters. One gold gram exhibits nmward increase in fineness value indicating that silver has been preferentially leached out by supergene fluid. This grain possibly represents the residually concentrated hypogene gold. The other gold grains do not show chemical gradients within the domain of individual gram and formed by precipitation from supergene fluids.

Keywords

Gold, Supergene Mineralisation, Vein Quartz, Latentcs Fineness, Gopur, Orissa.

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Kalachand Sain ¹, Maheswar Ojha ¹, Nittala Satyavani ¹, G. A. Ramadass ², T. Ramprasad ³, S. K. Das ⁴, Harsh Gupta ¹

Affiliations
1 CSIR - National Geophysical Research Institute, Uppal Road, Hyderabad - 500 007, IN
2 National Institute of Ocean Technology, Velachery-Tambaram Main Road, Chennai - 600 100, IN
3 CSIR-National Institute of Oceanography, Dona Paula, Goa - 403 004, IN
4 Ministry of Earth Sciences, Prithvi Bhavan, Lodhi Road, New Delhi - 110 003, IN

Abstract

Gas-hydrates are crystalline substances consisting of mainly methane and water, and occur in shallow sediments of outer continental margins and permafrost regions. They are formed at high pressure and low temperature regime when supply of methane gas exceeds the solubility limit. Unlike natural gas, oil and minerals, gas-hydrates are not stable at standard temperature and pressure (STP). One volume of gas-hydrates, when dissociated, releases 164 volumes of methane at STP. Since methane is the lowest molecular weight hydrocarbon, use of gas-hydrates as fuel will cause less pollution to the environment. These have attracted the global attention due to their natural occurrences in abundance and huge energy potential. The methane locked as gas-hydrates is envisaged as 1-120 x 10¹⁵ m³ (Boswell and Collett, 2011). Only 15% recovery from this gigantic reserve may be sufficient to meet the global energy requirement for about 200 years (Makogon et al. 2007). Thus, gas-hydrates seem to be a viable major energy resource of future, and have been identified globally either by geophysical, geochemical and geological surveys or by drilling and coring (Boswell and Saeki, 2011; Ruppel, 2011; Sain and Gupta, 2012). Besides having the energy potential, the study of gas-hydrates is also important from natural hazards point of view related to seafloor subsidence, slumps and slides (Gupta and Sain, 2011).

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