Remote mapping of lineaments and hydrothermal alteration zones related to unconformity-related uranium deposits in the Badami Group of the western Kaladgi basin, India

Abstract

In mineral exploration, identifying geophysical, geochemical and mineralogical indicators is crucial and many techniques have been employed to discover the occurrence of mineralization and the associated host rock alterations. In the case of unconformity-related uranium deposits that are spatially-linked to major faults and unconformities between basement rocks and overlying basinal rocks, extensive alteration zones produced by hydrothermal fluid-rock interactions which are used to target mineralization and are therefore vital tools for uranium exploration. The synoptic capability of remote sensing enables precise geological mapping by delineating structural features (faults, folds, shear zones), lithology and mineralogy, addressing field investigation constraints. The present study uses digital elevation model and satellite-borne multispectral data to map major lineaments and hydrothermal alteration zones associated with unconformity-related uranium deposits in the Badami Group of the western Kaladgi basin, India. Geologically, the study area comprises relatively undeformed arenites and conglomerates of the Neoproterozoic Badami Group that unconformably overlie an Archean basement (Peninsular gneiss). A few unconformity-related uranium prospects hosted by the Badami conglomerates and basal arenite have been identified by the Atomic Minerals Directorate in the study area. Conjunctive analysis of SRTM DEM and ASTER VNIR-SWIR data were used to map structures and lithological units. Band ratios, colour composite, least square fitting, principal component analysis and spectral angle mapper methods were further applied to ASTER VNIR-SWIR data to map the hydrothermal alteration zones. Follow-up ground checks were carried out to validate the results of the remote sensing analysis and interpretation. The results reveal that NE-SW and E-W trending lineaments are the major structural features and argillic (kaolinite) and phyllic (illite) are the dominant alteration types present in the study area. There is a strong intercorrelation between lineaments and hydrothermal alteration zones. Field surveys and laboratory analysis including petrographic studies and XRD analysis confirmed the occurrences of such alteration zones. The spatial association of hydrothermal alteration zones with structures indicates that these major lineaments and unconformable contact between the basement and the basinal sandstone could have provided major pathways for uranium-rich fluids and zones of low redox potential may have facilitated uranium precipitation. Several potential exploration targets were demarcated based on the juxtaposition of alteration zones, unconformity surface, major lineaments and cross-cutting structures. The identified targets correlate well with known uranium mineralization. This investigation demonstrates that integrating STRM with ASTER data is a valuable tool that can improve the efficiency of uranium exploration. This study narrows down the area for further exploration activities and provides a low-cost approach for prospecting unconformity-related uranium deposits in the Badami Group of the western Kaladgi basin and in similar areas elsewhere.