MAPPING RADIOACTIVITY IN CONTINENTAL TERMINAL 3 (CT3) FORMATIONS: THE CASE OF THE THREE SISTERS, NIAMEY REGION (EASTERN EDGE OF THE WEST AFRICAN CRATON, ILLUMMEDEN BASIN)

The Continental Terminal 3 (Ct³) formations, which rest in major unconformity on the Birimian basement of the West African Craton, correspond to the last filling deposits of the Iullemmeden basin in the Niamey region (West, Niger). The general objective of this study is to produce a surface radiometric map of the Niamey Three Sisters Hills area. The methodology used included field and laboratory work, with radiometric data processed using Surfer software. Radioactivity values in the Three Sisters area ranged from 5 to 25 shocks per second (C/s). High radioactivity values (15 to 25 c/s) are recorded in the upper terms, corresponding to the breastplates. Low values of radioactivity (5 to 15 c/s) are measured in the basal layers, corresponding to clays and alluvium. This radioactivity is thought to be due to trace amounts of uranium in these outcrops.