Radioactive Disequilibrium Studies in Uranium Series of Core Samples of Koppunuru Area, Guntur District, Andhra Pradesh, India

Disequilibrium studies were attempted on mineralised core samples (n=870) from Koppunuru uranium deposit located in south-western part of Palnad sub-basin, Guntur district, Andhra Pradesh, India. The area exposes Banganapalle quartzites unconformably deposited over altered biotite granite (basement). Uranium mineralisation in Koppunuru deposit is hosted by Banganapalle quartzites well above the unconformity, and grit/basement granite close to the unconformity contact. For disequilibrium studies, the core samples were broadly divided in two groups, (a) quartzite hosted (above unconformity) and (b) basement granite hosted mineralisation (below unconformity). Average disequilibrium factor of 41% has been recorded in favour of parent uranium in both types of core samples. It shows significant enrichment of uranium in the system as evident from 41% of disequilibrium in favour of parent uranium. This is probably due to significant migration of some of the daughter radio nuclides due to dissolution of minerals by groundwater action. Besides, the escape of radioactive radon might have accentuated the disequilibrium factor thus increasing the grade of uranium mineralization. The presence of fractures and faults in the study area are the probable conduits for radon migration/escape. Linear regression coefficient between uranium and radium is 0.98 indicates invariability of disequilibrium irrespective of grade.