A fracture-controlled uranium deposit was identified in Proterozoic Ajabgarh metasediments of the North Delhi Fold Belt within the Khetri subbasin at Rohil, Sikar district, Rajasthan, India. Uranium mineralization in the area is associated with geologic structures, albitization, and pyroxenization of metasediments and conductors such as metallic sulfides and carbonaceous phyllites/graphitic schists. To locate uranium mineralization akin to Rohil in nearby thick soil covered areas, this association was targeted through heliborne geophysical surveys. High-resolution heliborne magnetic and time domain electromagnetic (TEM) surveys were conducted around Rohil. The survey delineated several targets with favorable geologic structures and conductors such as graphitic schist for further uranium exploration. One favorable target near Chappar village was taken up for follow-up exploration work. The EM conductor mapped from heliborne survey was subsequently validated through ground time-domain electromagnetic surveys and subsurface exploration. Modeling of heliborne and ground-based electromagnetic data revealed the presence of subsurface conducting bodies with comparable model parameters. Drilling established the presence of a subsurface conductor up to a depth of 300 m, which was attributed to the presence of graphite and sulfides (pyrrhotite) along foliation plane of carbon phyllite/graphitic schist/quartz-biotite schist and calc-silicate rock. Further detailed laboratory investigations (petrology/X-ray diffraction) of selected core samples from the conductive zones confirmed the presence of pyrrhotite and graphite responsible for EM signature. This study, carried out by using multiparameter data sets, proved the efficacy of heliborne surveys in locating favorable targets for uranium exploration in Ajabgarh group of rocks.
We show the effectiveness of forward and inversion modelling of high‐resolution magnetic data in deciphering the geological framework in a polydeformed Proterozoic Kaladgi basin. The Meso to Neo Proterozoic Kaladgi basin exposes platformal sediments in the northern margin of Dharwar Craton, Peninsular India. The study of high‐resolution magnetic data over Deshnur locality suggests two prominent trends NW–SE and NE–SW, followed by two minor trends of E–W and N–S. Analysis of the magnetic anomalies aided in understanding the succession of deformation events and their impact over sedimentation. The NW–SE trending Nalur shear zone marks the western contact between the Chitradurga Schist belt and Peninsular gneisses that are traced beneath the Badami sediments. The forward model suggests that the NE–SW trending block faulting resulted in generating a series of Horst and Graben structures. Three‐dimensional compact inversion of circular features bearing remanent magnetisation indicates elliptical‐shaped pipe‐like bodies. The three‐dimensional inversion of magnetic data implied thicker sediments within these Graben structures. The basement configuration depicted as elevation of magnetic basement corroborates these three‐dimensional inversion results. The derived results are validated by drill holes, and the intercepts substantiate the inferred structural setup over the study area. Available drill hole and magnetic data interpretation are combined with field information to reconstruct the tectonostratigraphy and the architecture of the Kaladgi basin around Deshnur locality.
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