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

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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J. K. Mohanty ¹, S. K. Misra ¹, B. B. Nayak ¹

Affiliations
1 Regional Research Laboratory, Bhubaneswar - 751 013, Orissa, IN

Abstract

The extent of vaporisation and subsequent condensation of many trace elements during coal combustion is largely dependent upon the mode of occurrence of the trace elements, besides many other parameters. Mode of occurrence of a few important trace elements in coals from Talcher coalfield representing low and high ash type from Karharbari and Barakar Formations is studied by sequential leaching experiments. It is observed that in both the coal samples, Cr and Mn exhibit more affinity towards organic matrix and/or insoluble oxide phases. Pb and Cd are mostly associated with soluble sulphide and oxide minerals. Co is mostly bonded with silicate phases in the coal samples. No definite mode of occurrence is visualised for Ni from the present study, as it is associated more with the residue indicating its association with either organic matrix or insoluble oxide.

Keywords

Mode of Occurrence, Trace Elements, Leaching, Coal, Talcher Coalfield, Orissa.

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