Quantitative appraisal of Heliborne and ground-based Time Domain Electromagnetic surveys for uranium exploration ? A case study from Rajasthan, India

Abstract

Soda-metasomatised and metasediments hosted uranium deposits constitute 18% of the world?s uranium resources. In India, such deposits are identified along the albitite line in the environs of North Delhi Fold Belts in the state of Rajasthan. These are structurally controlled with association of albitisation and pyroxenisation of metasediments, metallic sulphides and carbonaceous phyllites. Uraninite is the dominant mineral phase along with copper, molybdenum and sulphides. The low resistivity of the fractures associated with metallic minerals produces a significant contrast with the host rock, which can be located with electromagnetic methods. High-resolution heliborne geophysical surveys comprising of VTEM, magnetic and gamma-ray spectrometric were conducted to identify uranium deposits in the vicinity of albitite zone. This paper demonstrates the results of heliborne and ground followup geophysical surveys to prioritize targets for uranium exploration. For the first time in India, a ground based Time Domain Electromagnetic survey employing Geonics EM37 system was conducted over one of the target areas delineated based on the VTEM surveys. Interpreted results from ground data correlate well with the spatial locations of the EM conductors delineated from heliborne surveys. Additionally modelling of heliborne and ground data produces comparable physical parameters. The results obtained are extremely useful in planning the boreholes in ongoing exploration programme.