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

S. Subramanian ¹, C. G. K. Ramanujam ², R. S. Patil ¹

Affiliations
1 Geological Survey of India, Hyderabad, IN
2 Saifabad Science College, Osmania University, Hyderabad, IN

Abstract

This paper highlights the geomorphic and palynological significance of the carbonaceous shale horizon subcropping 3 m below surface in the pits dug in the Korttalaiyar river section near Kondakarai, north of Madras. The carbonaceous shale underlies recent alluvial sand and appears to overlie Cuddalore Sandstones which are exposed to the west.

The palynological assemblage recovered consists of fungal spores, pteridophytic spores and angiospermic pollen grains. The pteridophytic spores are referable to Polypodiaceae, Cyatheaceae, Dicksoniaceae and Parkeriaceae, of which the Polypodiaceae represents the predominant taxon. The angiospermic pollen grains are referable to monocotyledonous and dicotyledonous taxa. The pollen grains of the following families have been recognised., viz., Palmae, Rhizophoraceae, Verbenaceae, Chenopodiaceae, Lecythidaceae, Caryophyllaceae and Leguminosae. Of these, the pollen grains of Rhizophoraceae and Verbenaceae are the most abundant. The spore and pollen assemblage indicates a Neogene-Quaternary age and points towards the presence of brackish water mangrove vegetation.

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Jayasree Thomas ¹, M. S. Riyazulla ¹, S. Subramanian ², V. N. Vasudev ³, C. S. Gundewar ⁴

Affiliations
1 Indian Bureau of Mines, G G Palaya, Bangalore-560022, IN
2 Department of Metallurgy, Indian Institute of Science, Bangalore-560012, IN
3 Australian Indian Resources, SBI Colony,7th Main, 111 Block, Bangalore-560034, IN
4 Indian Bureau of Mines, Indira Bhavan, Civil lines, Nagpur-400001, IN

Abstract

Cobalt mineralisation in the Kalyadi copper-Cobalt deposit in the Hassan district, Karnataka, is mostly in sulphidic banded, feldspathic cherty quartzite. Electron microprobe study conducted on sulphide concentrates from this deposit revealed that cobalt up to 3.21 wt% is present exclusively in pyrite grains, whereas it is absent in chalcopyrite and arsenopyrite. From this, it infers that pyrite crystallized first, followed by chalcopyrite and arsenopyrite with most cobalt present in the mineralizing system replacing Fe in the paragenetically early-Formed pyrite,thereby rendering the system deficient in cobalt during later crystallization of chalcopyrite and arsenopyrite.

Keywords

Pyrite, Cobalt, Electron Microprobe Study, Kalyadi, Karnataka.

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P. Periakali ¹, S. Eswaramoorthi ¹, S. Subramanian ¹, P. Jaisankar ¹

Affiliations
1 Climate Change Research Unit, Department of Applied Geology University of Madras, Guindy Campus, Chennai 600 025, IN

Abstract

Fourteen sediment samples collected from Pichavararn mangrove were analysed for grain size, organic carbon, sedimentary sulphur, calcium carbonate, Fe, Mn, Al, Cu, and Hg. Factor analysis was carried out to infer the mechanisms controlling the behaviour of metals. Four factors accounted for around 75% variance. Fe, Mn, and Hg are associated with organic carbon and fine fraction content of the sediments and loaded onto factor I whlch accounted for 33.6% variance. This is due to the complexation of Fe, Mn, and Hg with organic matter and the adsorption of these organo-metallic compounds onto the finer sediments due to their high surface/volume ratio and presence of surface charge. Factor 2 accounted for 18.6% variance and is loaded with CaCO₃, finer fraction, Al and Cu, implying contribution of Al and Cu from detritai clay minerals. The association of CaCO₃, with this factor is not clearly understood. Factor 3 is loaded with organic carbon and coarse fraction of the sediments and it accounted for 13.3% variance. The association of organic carbon with coarse fraction of the sediments could be either due to the Ca²⁺ and Mg²⁺ ions induced adsorption of organic matter onto mineral grains, or due to the presence of coarse vegetal debris. The fourth factor accounted for 9.8% variance and is loaded with sedimentary sulphur; no metal is associated with this factor. This explains that though sulphate reduction occurs in the surface sediments, it could not result in the burial of Fe, Cu, and Hg as their respective sulphides. This could be due to their back oxidation by Mn oxides present in the sediments where upon FeS is converted to Fe hydrous oxide, and Cu and Hg are released to the water column.

Keywords

Geochemistry, Sediments, Pichavaram Mangroves, Trace Metals, East Coast of India.

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P. Periakali ¹, S. Eswaramoorthi ¹, S. Subramanian ¹

Affiliations
1 Climate Change Research Unit, Department of Applied Geology, University of Madras, Guindy Campus, Madras- 600025, IN

Abstract

The sequential extraction of core sediment samples of Pulicat lake for the determination of exchangeable, carbonate-bound. Fe-Mn oxides-bound, and organic-bound fractions of Fe and Mn were carried out to study the remineralization of organic matter in the sediments. Iron and manganese oxides are highly depleted in the upper portion (0-18 cm) of the core due to their reduction during organic matter oxidation. The model calculations based on the solid phase organic carbon depth profile indicate an average accumulation rate for organic carbon in the Pulicat lake sediments to be 13.5 gC/m².yr. The average remineralization rate is 12gC/m².yr. This is around 89% of the organic carbon deposited in thc sediments. The remineralization of organic carbon in this lake sediment could release 16 x 10³ tonnes of CO₂ /yr.

Keywords

Organic Geochemistry, Carbon, Sequential Extraction, Trace Metals, Core Sediments, Pulicat Lake, Tamil Nadu.

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