ABSTRACT
An attempt is made to understand uranium series disequilibrium in unconformity proximal related uranium mineralisation in Chenchu colony area, Guntur district, Andhra Pradesh, India. The uranium mineralization in Chenchu colony is the western continuity of the Koppunuru uranium deposit and predominantly hosted by gritty quartzite/conglomerate, which occasionally transgresses to underlying basement granite/basic rock. Disequilibrium studies are based on borehole core samples (35 boreholes, No. of samples=634) broadly divided in two groups of cover rocks of Banganapalle formation (above unconformity) and basement granites (below unconformity). Linear regression coefficient between uranium and radium is 0.95, which reflects excellent correlation and significant enrichment of parent uranium. Disequilibrium studies have indicated predominant disequilibrium in favour of parent uranium (35%), which is probably due to the weathering process causing migration of some of the radionuclides while dissolution of minerals due to groundwater action might have also played a significant role. Further, escape of radon might have accentuated the disequilibrium factor resulting in an increase in the grade of the mineralization. This is well corroborated by the presence of fractures and faults in the study area providing channels for radon migration/escape.