[en] A new high sensitivity gamma logging tool for better insight in to the characterization of subsurface rock formations and lithological correlation in the exploration for uranium, developed by Atomic Minerals Directorate (AMD) for Exploration and Research has been used in rock/sediment characterization and to determine the average uranium content at low levels (ppm) in Vindhyan sediments in Banda district, Uttar Pradesh. The design of the logging tool is shown. Interpretation of the variation of natural gamma-ray in borewell logging is applied successfully for lithological description of the borewells in the area. This work aims at accurately determining and interpretation of total gamma intensity at low levels in the borewells and characterization of the lithological units traversed by them. The average U₃O₈ (μg g^-1) content of different lithounits, which is a direct function of their typical mineralogy, is obtained. The attempt gains significance because these borewells are drilled for the purpose of irrigation and no core/sludge is available for visual determination of lithologies traversed and hence is proved to be immensely helpful in using extra departmental borewells while optimizing the core drilling thus inducing cost effectiveness in planning the future exploration programme in these areas in a broader sense. The average U₃O₈ content of Kaimur and Semri sediments and basement granite are 5.2, 13.1 and 6.3 μgg^-1, U₃O₈ with respective confidence levels of 7.7%, 4.8% and 7% respectively. The methodology used here appears to be a powerful tool for rapid interpretation of gamma-ray logging data to identify low level radioactive anomalies and determining the lithological boundaries even when the layers have small thickness. It is therefore possible to identify subtle variations in the subsurface lithologies penetrated by the borehole using this new high sensitivity logging tool. (author)

[en] High resolution heliborne geophysical survey data with magnetic, time domain electromagnetic and gamma-ray spectrometric sensors over Alwar sub-basin of North Delhi Fold Belt from north of Jaipur to north of Alwar are interpreted. Metasediments of basin are predominantly non-magnetic manifesting low amplitude and low frequency magnetic signature except basic volcanics of Raialo, magnetite quartizite-phyllite of Alwar and Ajabgarh Groups and later intrusives that impart higher amplitude magnetic anomalies. NNE-SSW to N-S trending concealed fold axes and parallel shears and NW-SE to E-W lineaments/ faults related to younger structure have been identified. Exposed intrusive granite of Bairat, Barodia, Dadikar and Harsora with higher radioelement concentration and feldspathic quartzite of Alwar Group with higher concentration of potassium are very well discernable through radiometric data. Borewell water showing radioactivity above threshold at a few locations in the northeastern part of the basin indicate possible presence of radioelement concentration. Lenses and thick pile of carbonaceous phyllite of Raialo and Ajabgarh Groups are delineated from conductivity image of Time domain electromagnetic data. Airborne Inductive Induced Polarisation effect near Khoh, Agar-Bhaonta, Bansur, Sirawas and other places indicate presence of polarizable materials. Integrated study including geological interpretation of the datasets led to demarcation of target areas for further exploration for uranium mineralisation. (author)

[en] The South Khetri sub-basin (KSB) in North Delhi Fold Belt (NDFB) along Narsinghpuri-Khandela-Rohil tract exposes Ajabgarh Group of metasediments of Delhi Supergroup. The Ajabgarh Group comprises impure carbonate sequence with volcanics in the lower part and psammopelitic assemblage with minor lenses of carbonate and siliceous rocks in the middle and upper part. The NNE-SSW trending wide spread zone of albitisation in KSB forms a mega lineament, which can be traced from north of Sior-Siswali to south of Kishangarh, covering approximately 170 km length along strike with 6-10 km width. Integrated exploration approach by AMD has led to the establishment of sizeable uranium deposit at Rohil, Sikar district, Rajasthan; thereby NDFB has now been established as uranium potential province. The study area is mostly soil covered baring N-S to NNE-SSW trending quartzite ridge exposed in the northwestern part of Rohil village