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

P. K. Boruah ¹, S. K. Dutta ¹

Affiliations
1 Applied Geology Department, Dibrugarh University, Dibrugarh - 786 004, Assam, IN

Abstract

The Laitrengew-Cherrapunji area of East Khasi Hills, Meghalaya exposes a complete Palaeocehe sequence of sedimentary rocks. The coal-bearing sandstone around Laitrengew-Cherrapunji area is regarded as Lakadong Sandstone Member of the Sylhet Formation. The Lakadong sandstones are quartz dominated, fine to medium grained, well to very well sorted, and have not been subjected to significant alteration. The intensive solution effect lowers the packing index values for the underlying Therria Formation around Laitrengew. The quartz arenite type of Therria and Lakadong sandstones is indicative of intense paleoweathering processes under humid climate and low relief. The sediments were derived from the exposed shield areas of plutonic rocks and low to medium grade metasedimentary rocks. The structural, textural as well as compositional attributes of the Therria and Lakadong sandstones indicate that the sediments were deposited in a slowly subsiding, stable depositional area in which the sediments were subjected to higher hydraulic energy winnowing processes. During the period, the paleoclimate was humid and tropical. The intermittent subaerial exposure of the depositional surface and development of shallow swampy lagoons in the coastal environment was supported by the palyontological evidences such as trace fossils and pollen grains of Arecaceue family.

Keywords

Mineralogy, Texture, Palaeocene, Sandstone, East Khasi Hills, Meghalaya.

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M. S. Pandian ¹, S. K. Dutta ²

Affiliations
1 Department of Earth Sciences, Pondicherry University, Pondicherry - 605 014, IN
2 State Remote Sensing Application Centre, Vivek Vihar, Itanagar - 791 113, IN

Abstract

In Sewariya-Alniawas-Govindgarh areas of central Rajasthan, the Delhi metasediments are intruded by an older, biotite granite (Sewariya granite) which is equivalent to Erinpura granite occurring further south, and an younger, tourmaline leucogranite (Govindgarh granite) which is geochemically specialised. Sewariya granite hosts wolframite bearing quartz veins along its sheared contact with mica schist of Barotiya Group. Govindgarh granite occurs in the form of small intrusive bodies within rocks of Barotiya Group, essentially along a major ductile shear zone at the western margin of South Delhi fold belt. Our study reveals that leucogranite magmatism yielded tungsten mineralisation in Sewariya area.

Keywords

Economic Geology, Leucogranite, Tungsten, Tourmaline, Aravalli Craton, Rajasthan.

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