Exploration for concealed fracture controlled uranium mineralization: A case from Shivaramapuram-Nutankalva tract in basement granitoids, south of Cuddapah basin, Andhra Pradesh, India

Abstract

The application of hydro geochemical exploration for sub-surface uranium mineralization is becoming significant due to the geochemical properties of uranium. The oxygen in natural water enhances the mobility of uranium by the complexing action of carbonates and bicarbonates with oxidized uranyl ions. The uranium and its decay products (i.e., radium group) can be used as good tracers for pinpointing uranium mineralization.The basement complex in the south of Cuddapah basin comprises granite, gneiss-migmatites and patches of greenstone belts. There are different generation of fractures and mafic dykes trending E–W, NS, NW-SE and NE–SW directions. The NNE–SSW to NE–SW trending fractures are youngest and often show higher uranium values in water along the same trend indicating possible mineralization. The fractures are often intruded by younger basic intrusive rocks and quartz reefs which often show high uranium content. Several NE–SW to NNE–SSW trending fracture zones with uranium mineralization are observed in the areas around Shivaramapuram-Nutankalva, Kamaguttapalle and T. Sundupalle villages. These sympathetic fracture zones are important for further sub-surface exploration.The present focus is given on a NE-SW fracture zone along Sivaramapuram–Nutanakalva tract extends over a strike length of ~15 km with a plan width of ~1 to 1.5 km. The tract is mostly soil covered and rock outcrops are scanty. Radioactive anomalies are located at small outcrops in fractured basic dyke, fractured and altered granite, deformed quartz vein, sludge samples collected from private village drilling sites, Pincha river channel sands and soils (U3O8 values up to 0.19% (β/γ); n = 44;). Hydrogeochemical exploration along this fracture zone has indicated anomalous concentration of uranium in water samples ranging from 100 to 19,434 ppb U (n = 110). Selective borewells have been monitored for 8 months to check the seasonal variation. The data remain persistent and indicated encouraging outcome. This NE–SW fracture zone has affected the Nagari quartzite of Cuddapah Supergroup, thus indicate Post Nallamalai Mesoproterozoic Grenville orogeny, which is metallogenically favourable epoch for fracture controlled uranium mineralization.The surface anomalies vis-a-vis the hydro uranium anomalies and suitable geochemical condition along the NE-SW trending fracture make this zone a potential target for further sub-surface exploration.