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

S. Mohantay ¹, A. K. Mohanty ¹, P. K. Nayak ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad 826004, IN

Abstract

Detailed mapping of the Sausar Group around Kandri Mines, Nagpur district, Maharashtra, shows that the rocks of the area have been involved in folding of three generations. The metasedimentary bands in the Kandri Mines and the surrounding area show an arcuate outcrop that closes northwest. The bedding and schistosity strike ∼ E-W in the northern part of the mine. The orientation gradually changes from E-W through NE-SW to N-S in the central put and NW-SE to NE-SW in the southern part of the mine. This variation defines a synformal fold of second (F₂) generation (syncline near Kandri Mines), with WNW-ESE axial trace. The axial trace of the regional F₂ fold of the Kandri area coincides with that of the Ramtek area when extrapolated over the soil cover. The terminations of the manganese-ore bands of the Kandri Mines and Mansar Mines are the result of original sedimentary facies change.

Keywords

Structural Geology, Superposed Deformation, Structural Analysis, Sausar Group, Manganese Ore, Maharashtra.

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P. K. Banerji ¹, A. K. Mohanty ¹, S. P. Mahakud ¹

Affiliations
1 Geological Survey of India, IN

Abstract

Host rocks are kyanite-quartzite at Kesarpur and uralitised garnet-diopside granulite (± scapolite) at Adash. Primary sulphides include chalcopyrite, pyrite and pyrrhotite with small but variable amounts of bornite. The ore bodies are lenticular and carry variable trace constituents of Ag. Au, Ni and Co. Supergene minerals occur only in thin stretches and include covellite, marcasite and violarite. No discrete zone of supergene enrichment is noted in the boreholes. Oxidised zones at the top are 15-45m. thick and analyse in Adash up to 2.27% Cu plus 0.4% Zn over 3-4 m width. Goethite, haematite, malachite, azurite and chrysocolla are the constituent minerals.

Feeble to strong anomalies are present in pedogenetic laterites over orc bodies. but spurious anomalies locally with 1 % Mn are common. Laterites in Adash are polycyclic and anomaly values are locally erratic. Over groundwater laterites of Kesarpur. very feeble secondary anomalies are confined to only 100 m from the ore zone.

Stream sediment signals are confined to first order seasonal drainge courses and are traceable for only 2-3 km from the source down stream. Such limited anomaly dispersion is due to differential block movements in this area.

Landforms developing under this dynamic system have not given rise to widespread and strong stream sediment dispersion patterns of chalcophile elements. Systematic search for small ore bodies in such tracts has, therefore, to be hased only on sampling the sediments of first order drainage courses.

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A. K. Mohanty ¹, S. Mohanty ¹

Affiliations
1 Department of Applied Geology, Indian School of Mines, Dhanbad - 826 004, IN

Abstract

The Precambrian rocks of the Mansar area, Nagpur district, Maharashtra, belong to the Sausar Group and the Tirodi Gneiss. Both these lithological units show an unconformable relation in the area, marked by a conglomerate at the base of the Sausar Group. The metasediments of the Sausar Group bear imprints of polyphase deformation. The folds of the first generation (F₁) are isoclinal with high amplitude to wavelength ratios and pervasive axial planar cleavage (S₁). The structures of the second generation are represented by WNW-ESE trending upright isoclinal folds (F₂) and axial planar crenulation cleavage (S₂). Gentle upright folds with NE-SW striking axial planes represent structures of the third generation (F₃) Superposition of F₂ folds on F₁ folds is marked by mushroom shaped interference pattern in small-scale. Because of upright isoclinal nature of F₂ folds on WNW-ESE striking axial planes, the metasedimentary bands extend in E-W direction. Slight arcuate geometry of the metasedimentary bands is the result of superposition of F₃ folds on F₁/F₂ folds.

Keywords

Structural Geology, Sausar Group, Unconformity, Nagpur Dist., Maharashtra.

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K. Sashidharan ¹, A. K. Mohanty ¹, Anupendu Gupta ¹

Affiliations
1 Geological Survey of India, Seminary Hills, Nagpur - 440 006, IN

Abstract

Incidence of diamond is reported from the highly deformed polymictic conglomerates of suspected Early Proterozoic age from Wairagarh area, Garhchiroli District, Maharashtra. The gem quality diamond recovered during the ongoing search for kimberlite-lamproite rocks in western Bastar craton is an octahedral crystal with a light greenish tint and weighs 0.029g (0.15 carat). Reports of diamond mining in Wairagarh date back to as early as 15^th century (Ball, 1884; Satyanarayana, 2000). Mining activity continued till 19^th century (Streeter, 1882). These records provide information about richness of the mines and quality of the diamonds won. Despite intensive search by local people, there are no records of diamond recovery for over a century. The present find is first of its kind during the modern times and has opened up new vistas of diamond search in similar geological milieu in the western part of Bastar craton.

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