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

M. K. Devarajan ¹, M. Hanuma Prasad ¹, A. V. Keshava Prasad ¹, M. K. Soni ¹

Affiliations
1 Operation M.P. II, Geological Survey of India, P.O. Garha, Jabalpur-482003, IN

Abstract

Gold Mineralization in the eastern part of the Late Archaean Mahakoshal Belt is observed in sulphidic chert associated with banded ferruginous chert (BFC) and in quartz-carbonate-sulphide veins and quartz-carbonate veins emplaced into argillites, greywackes, carbonaceous phyllite and BFC. In the western part of the Mahakoshal belt gold mineralization is noticed in quartz-carbonate veins intruded along the lithological contacts between metabasalts and dolomitic limestone, and in quartz veins/quartz porphyry dykes within dolomitic limestone. Bulk of the gold mineralization is associated with quartzcarbonate and quartz-carbonate-sulphide veins, emplaced during the initial phase of deformation of the Mahakoshal Belt.

Keywords

Economic Geology, Gold, Mahakoshal Belt, Son-Narmada Lineament, Madhya Pradesh.

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S. D. Pimprikar ¹, M. k. Devarajan ²

Affiliations
1 Geological Survey of India, Operation M. P. -II, P.O. Garha, Jabalpur - 482 003, IN
2 Geological Survey of India, Earthquake Geology Division, Central Region, PO.Seminary Hills, Nagpur - 440 006, IN

Abstract

No Abstract.

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Abhinaba Roy ¹, M. K. Devarajan ¹, M. Hanuma Prasad ¹

Affiliations
1 Geological Survey of India, Central Region, PO. Seminary Hills, Nagpur - 440 006, IN

Abstract

A prominent E-W trending, sub-vertical to steep south dipping, ductile shear zone occurs along the southern margin of the Palaeoproterozoic Mahakoshal supracrustal belt of Central India. Shear zone structures have been documented from the supracrustal rocks as well as from the intrusive granites (s.l.) from an area near Singrauli. The supracrustal belt away from the shear zone displays a set of subhorizontal upright folds on E-W to ENE-WSW striking axial planes. The intensity of deformation increases southward; the folds become tight to isoclinal with slight overturning towards the north while the fold hinges arc rotated from the subhorizontal position to sub-vertical or down-dip reclined attitude. Mylonitic foliation within the shear zone is sub-parallel to the axial plane schistosity of the dominant fold-set outside the shear zone. The granitic rocks show both magmatic and solid-state fabrics which are part of a continuum of emplacement and deformation in the shear zone. In the initial stages of solid-state deformation, which gave rise to protomylonites, coarse K-feldspar porphyroclasts behavcd in a brittle manner in an overall bulk ductile deformation in the matrix. With increase in intensity of deformation accompanied by the introduction of fluids, the deformation mechanism in feldspar changed from brittle to ductile. Mylonitic foliation is invariably associated with a pervasive stretching lineation. Shear-sense indicators suggest oblique-slip movement with a large reverse-slip component and a small sinistral strike-slip component. The geometry of the folds and their sequence of development are similar in the rocks within and outside the shear zone. Concordance between the granite plutons and the supracrustal rocks is due to syntectonic emplacement. Low pressure-medium temperature metamorphism in the Mahakoshal supracrustal belt contemporaneous with granite intrusion suggests depth of emplacement about 10- 12 km. The bulk kinematic model involves N-S to NNESSW subhorizontal compression over which was superimposed in the southern part a sinistral shearing movement during progressive transpressional deformation.

Keywords

Ductile Shear Zone, Mylonites, Syntectonic Granite, Shear-Sense Indicators, Mahakoshal Group, Palaeoproterozoic, Central India.

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