Determining uranium concentration in boreholes using wireline logging techniques: Comparison of gamma logging with prompt fission neutron technology (PFN)

The continuous movement of ground water in sandstone hosted uranium deposits renders them subject to disequilibrium between uranium and its daughter products. This is important when wireline gamma logging alone is used to quantify the presence of uranium which can be over- or under-estimated by a significant percentage. The problem can be overcome by logging using the prompt fission neutron (PFN) tool which directly measures the presence of uranium through neutron activation. PFN technology is also superior to core drilling and assay as it provides a larger sample, is less expensive and is instantaneous, allowing drilling programs to proceed uninterrupted. Examples are presented from uranium deposits in Australia and the USA demonstrating disequilibrium, and the use of PFN to map uranium throughout a deposit and to set the screens in in situ leach mining.