Uranium mineralisation in Daida–Gottimukkala area of Palnad sub-basin, Guntur district, Andhra Pradesh: An integrated exploration approach Banerjee Rahul*, Singh R.V., Verma M.B., Nanda L.K. Atomic Minerals Directorate for Exploration and Research, 1-10-153/156, AMD Complex, Begumpet, Hyderabad *Email: rahulbnrg@gmail.com
Online published on 13 February, 2019. Abstract Daida–Gottimukkala area, Guntur district, Andhra Pradesh is located in the central part of Palnad Sub-basin, where NNE–SSW and ESE–WNW trending faults have brought up the basement granite and the overlying sub-horizontal beds of Banganapalle sediments as an inlier within calcareous country (Narji Formation). An upthrown faulted block near Gottimukkala in the Krishna River section exposes sheared and fractured granite profusely traversed by mafic intrusives. High resolution aeromagnetic data has confirmed the presence of a few N–S to NE–SW trending faults, while the ternary radiometric image has confirmed upliftment of the basement around Daida due to a N–S trending fault. Furthermore, the presence of conducting shale as indicated by EM signals and hydrouranium anomaly (10–31ppb, av. 19ppb; n=5) has indicated uranium potential of the study area, where initial subsurface exploration for rapid assessment has been done by 25 non-coring boreholes over an area of 1.84 sq km. These boreholes have intercepted a 75 to 88m thick column of Banganapalle quartzite and shale sequence underlain by basement granites. Unconformity proximal uranium mineralisation (0.010–0.061% eU3O8 x 0.30–3.50m) was recorded in 20 boreholes. Sub-surface databased, basement configuration contours show a gentle southerly slope while the superimposed accumulation factor (Grade x Thickness) contour indicates possible westward continuity of mineralisation. This is further substantiated by sub-surface exploration in southern and western extensions (3 sq km; 12 coring boreholes), where continuation of mineralisation (0.010–0.028% eU3O8 x 0.30–1.80m) is recorded in 8 boreholes. Radiometric assay of representative core samples (n=36) have confirmed uranium mineralisation (0.010–0.039% U3O8with <0.005% ThO2) and exhibits 10–77.7% disequilibrium in favour of parent uranium. The mineralised cores have indicated preferential concentration of radioactive minerals along fractures, cavities, grain boundaries and as thin veins. Thus the study area has high potential for fracture-controlled,epigenetic type of mineralisation in an unconformity proximal setup. This also exhibits the successful application of integrated field geological, radiometric, aeromagnetic, EM and hydrogeochemical studies, which has not only corroborated the surface litho-structural setup but also has given an insight into the possible sub-surface features that are significant for uranium exploration in this terrain, as evidenced by correlatable mineralised intercepts recorded during non-core and diamond core drilling. Top Keywords Uranium mineralisation, Integrated exploration, Drilling, Hydrogeochemistry, Palnad Sub-basin, Daida–Gottimukkala area, Guntur district. Top |