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

D. K. Sinha ¹, Sohail Fahmi ¹, A. K. Bhatt ¹, Govind Singh ¹, Rajendra Singh ²

Affiliations
1 Department of Atomic Energy, C-31, Devnagar, Tonk Road, Jaipur-302018, IN
2 Department of Atomic Energy, AMD Complex, Begumpet, Hyderabad-560016, IN

Abstract

Albitite and albitised banded gneissic country rock from the Ladera-Sakhun area, situated about 80km southwest of Jaipur, show several evidences for soda metasomatism. Megascopic evidences include reddening of outcrops due to aventurisation, gradational contacts between albitite and gneisses, development of metasomatic minerals, dequartzification, epidotization and cataclasitisation. Microscopic evidences include relict microcline in the newly formed albite grain, poor and discontinuous development of twin lamellae in albite giving step-like appearance, ubiquitous sweeping extinction in albite due to cataclasitisation, occasional mortar texture in albitite, tapering of twin lamellae within the grain, twin lamellae forming in chequered fashion, development of aventurine albite containing dusty Fe-oxide inclusions, development of albite along twin/cfeavage plane of microcline, formation of new albite in plagioclase, destruction of sericite in plagioclase of albitised granite, formation of myrmekite of intergranular, intragranular and rim types, development of epidote corona around clinopyroxene in pyroxenite, partial to complete dequartzification and filling up of voids by calcite. Petrochemical evidences of increased characteristic values of Na₂O from 3.17 to 7.00 wt%, K₂O and Si₂O from -0.03 to -6.00 wt% and -0.76 to -10.55 wt% in the unalbitised to albitised rocks respectively, provide further support for soda metasomatism. Albitisation at Ladera-Sakhun area extends over a considerable distance into Haryana in the NE and beyond Tal in the SW, attesting to its regional significance and its potential for mineralisation.

Keywords

Petrology, Metasomatism, Albitite, Ladera-Sakhun, Rajasthan.

Full Text

     

Rajan B. Jain ¹, O. P. Yadav ¹, M. Rahman ¹, S. Thippeswamy ², S. Fahmi ¹, D. K. Sharma ¹, Govind Singh ¹

Affiliations
1 Atomic Minerals Division, J.L.N. Marg, Uniara Garden, Jaipur - 302 004, IN
2 Atomic Minerals Division, Nagarabhavi, Bangalore, IN

Abstract

A partly concealed radioactive alibitized pegmatoid/quartz albitite body (1200 m x 0.5 to 20 m) containing 0.010 to 0.190% U₃O₈ and 0.007 to 0.076% ThO₂ and about 20 brick red coloured albitite lenses varying in dimension from 13 m x 7 m to 220 m x 12-30 m and containing 0.022 to 3.50% U₃O₈ and 2 are described at Banjaron Ki Dhani, new Maonda in north Rajasthan. Davidite, brannerite, rutile, anatase, zircon, monazite and traces of uraninite have been identified in the albitites. A metasomatic origin for the albitites is suggested. The distribution of albitites along NE-SW to NW-SE and E-W trending weak structural planes and the coincidence of 'Albitite Line' with Kaliguman lineament, demonstrates the tectonic control of albitization.

Keywords

Geochemistry, Albitite, Soda Metasomatism, Radioactivity, Rajasthan.

Full Text

     

G. R. Narayan Das ¹, D. K. Sharma ¹, Govind Singh ¹, Rajendra Singh ¹

Affiliations
1 Atomic Minerals Division, Department of Atomic Energy, New Delhi-110022, IN

Abstract

Uranium mineralisation of segregated type consisting mostly of uraninite and less commonly of brannerite has been noted in the pink quartzo-feldspathic or aplitic emplacements along shear zones in Rohil-Ghateshwar-Khandela-Diara and Saladipura area in Sikar district of Rajasthan. Ilmenite, molybdenite, pyrrhotite, chalcopyrite and pyrite are noted along with uraninite.

Mineralisation is controlled by structure and generally occurs along linear shears that are parallel to the main tectonic lineament. In Ghateshwar area, the mineralised quartzo-feldspathic emplacements have undergone refolding along with the rest of the formations. Uranium mineralisation is near to the main tectonic lineament that passes through the axis of the Ajabgarh synclinorium. Integrated radiometric and hydrogeochemical surveys have indicated continuity of the uranium bearing quartzo-feldspatbic emplacements along a 16 km belt.

The Salwari fluorite occurrence 10 km NE of Khandela is a post feldspathic emplacement and probably formed during the final phases of mineralisation.

Full Text