[en] Abnormally radioactive granitoids are targets of uranium exploration because they can be the source for uranium deposits as well as the hosts. Significant uranium mineralization is known to occur northwest of Suryamalai granite batholith at Kullampatti situated 40 km southwest of Salem. This paper embodies the geophysical exploration for uranium, using results of magnetic and radiometric methods. The investigations revealed that uranium mineralization is structurally controlled and such structures have magnetic expression. Incidentally, correlation of anomalous content of W with U is also brought to light. (author)

[en] Regional emanometric survey using the closed circuit technique was carried our for measurement of radon and thoron concentration in the soil covered areas of Mogarra and Bijepar, Bhandara district, Maharashtra. The aim of the survey was to delineate potential areas for subsurface uranium bearing horizons to be taken up for detailed investigations. The radon and thoron values obtained from the survey were correlated with the soil samples analysis data by the method of class intervals and cumulative frequency analysis. Anomalous zones holding promise for subsurface uranium occurrences have been identified, substantiated by statistical treatment and recommended for detailed investigations (author). 11 refs., 5 figs

[en] The role of geophysical methods in lithostructural mapping of thickly soil covered areas has been well recognized by geoscientists for a long time. The present paper highlights the effectiveness of magnetic and induced polarisation (IP) techniques in mapping poorly exposed rock units and also deciphering structures favourable for uranium mineralization at Jhamankela-Bhalulata areas (Long. 84 deg 30': Lat. 22 deg 19') of Gangpur basin, Sundargarh district, Orissa. Magnetic intensity data indicate three linear features representing basic intrusives (amphibolites) which are folded and faulted at places. Besides, three oval shaped and weakly magnetised bodies have been interpreted indicating presence of deep-seated granitic intrusives. Based on the results of IP surveys, scantily exposed carbon phyllites, considered to be marker beds in Gangpur Formation and showing major and minor/secondary folds are delineated. The inferred features like secondary folds, faults, and granitic intrusives are the suggested targets for uranium mineralization. (author). 8 refs., 6 figs

[en] Recent studies on airborne radiometric data followed by surface radiometric checking reported a wide radioactive zone near Ukinal (Lat.16045'45'N, Long.76039'59E), Gulbarga district, Karnataka which extends intermittently all along the major EW trending Gogi-Kurlagere fault over a stretch of 15 kms proximal to the southern margin of Bhima basin. In course of detailed ground checking all along this faulted margin, occurrence of significant uranium mineralisation hosted by both fractured granites and brecciated limestone at Gogi (Lat.16045'N, Long.76045'E) evoked considerable interest among the geoscientists due to its richer grade and shallow depth environment. Targeting this mineralized host in a complex structural set-up under soil cover turned out to be a challenging task and prime objective of the geophysical investigation at Gogi. (author)

[en] The application of non-radiometric geophysical methods like magnetic, electrical resistivity, induced polarisation, electromagnetic and seismic for uranium exploration has been discussed by many workers. In thispaper it has been demonstrated that the self-potential technique which is simple, fast and cheap can also be effectively and meaningfully employed. For this purpose, a case study from Arbail (Lat 14⁰, 50' 40'', Long 74⁰ 38' 25''), India where uranium mineralisation is known to occur in association with sulphides, is presented. The method of downward continuation is used to estimate the depth to the top of the target and the results thus obtained are correlated with the data obtained from subsequent borehole drilling. (author)

[en] An integrated geophysical approach was attempted for uranium exploration in Jamiri area, Arunachal Pradesh, using the techniques of magnetic, self-potential (SP) and resistivity profiling, coupled with solid state nuclear track detection (SSNTD), to delineate favourable structures controlling uranium mineralisation in phyllitic quartzites and quartzites of the Precambrian Daling formation. Three promising zones of uranium mineralisation were recognised based on integrated results from these surveys. Magnetic survey identified lithologic contacts and faults in the area. A high-order SP anomaly of -900 millivolts was observed near the contact of phyllites in the east and phyllitic quartzites in the west. A very low resistivity of 1.0 ohm.m and high SSNTD values of 120 tracks/mm² over a background of 20 to 30 tracks/mm² were also recorded near this contact. These anomalies are characteristic of a fault that channelises radon and gives low resistivities. The SP anomaly may indicate sulphide mineralisation, and hence, uranium mineralisation in this contact zone may be associated with sulphides. The phyllitic quartzites west of this contact are characterised by magnetic highs ranging from 540 to 900 gammas. Here, SP anomalies are also small closures of -80 to -100 mV. The SSNTD values range between 100 and 120 tracks/mm². This rock unit (phyllitic quartzite) appears to host uranium mineralisation along with sulphides at some places where radon anomalies are high. A fault in the western portion of the area interpreted from the magnetic map separates phyllitic quartzites in the east and quartzites to its west. The faulted contact is characterised by a high SP gradient and SSNTD anomalies of 100 to 140 tracks/mm². This contact may also be promising for uranium mineralisation at depth. (author). 10 refs., 8 figs

[en] Geophysical investigations comprising gravity, magnetic, resistivity and induced polarization methods were carried out at Garumal, Panchmahals district, Gujarat, where uranium mineralisation occurs in Champaner group of rocks as fracture controlled veins along the axial zone of a WNW-ESE plunging fold. The distinct break in the Bouguer gravity contour map signifies a lineament within the Champaner group of rocks and this probably represents a mega-fracture. Sharp magnetic anomalies forming a ring and the associated high resistivity characterize an acidic intrusive body, the probable source for the uranium mineralisation occurring in this area. Resistivity contour map delineates the lithic boundaries distinctly. The linear magnetic feature observed over a strike length of 2.5 km represents a small scale skarn-type iron ore deposit. (author)

[en] The variations of radon concentration in well waters have been used as a precursor of an oncoming earthquake. A closed circuit technique of radon measurement is used to monitor radon in water from a bore well at Pyntheromukrah, Shillong. The variation of 35 to 210 alpha counts per 50 seconds of the radon concentration in the water has been correlated to the local earthquake monitored by the Indian meteorological Department at Upper Shillong and to the meteorological variations which might have affected it. Though no major event has taken place during the period of two years of observation, a fair degree of correlation is observed with earthquakes of medium magnitude taking place even at large distances. The importance of this paper is restricted to a large extent on the development of the technology of radon monitoring for earthquake prediction. 7 refs., 4 figures, 1 table. (author)

[en] Geophysical methods have been extensively used for delineation of structural features such as fractures and shear zones which often control and host economic mineralisation. Numerous fractures hosting uranium mineralisation and confined to younger intrusives and leucogranites occur within basement gneissic complex on the southwestern margin of the Mesoproterozoic Cuddapah basin. The geophysical signatures of one such mineralised fracture zone near Mulapalle are discussed. Mineralised fractures are mostly confined to a zone of cataclastic rocks characterised by widely varying magnetic character with respect to the surroundings. A strong redox barrier associated with the mineralisation is revealed by self-potential data. The mineralised zone is also indicated by a higher order resistivity attributable to the enrichment of silica in the fracture zone. (author)