2.05 X 10 exp 9 years Age of the Oklo Uranium Deposit

摘要

U and Pb isotopic data on samples (10 to 100 gram) 2 to 10 m away from the borders of the Oklo reactor zones indicate a primary age of 2.05 x 10 exp 9 years for the Oklo deposit and a secondary age of 0.375 x 10 exp 9 years. All samples show effects of Pb loss; the average loss is 50 percent. Both the U--Pb and Pb isotopic data are consistent with a model of a primary 2.05 x 10 exp 9 year age of the deposit, continuous volume diffusion of Pb from uraninite, and either continuous or recent loss of this Pb. In this case the 0.375 x 10 exp 9 year age is an artifact without time significance. Using an average value of D/a exp 2 3.5 x 10 exp -11 a exp -1 (Cowan, this conference) this model explains the apparent 1.8 x 10 exp 9 year Pb age observed by other workers. From the exp 208 Pb/ exp 206 Pb data the average U/Th value calculated for the Oklo deposit is approximately 100. (ERA citation 03:032780)