IVZ - General Discussion, page-1007

"The presence of uranium and thorium would also explain the helium content in our gas sample."

The concentrations of U, Th and U within clay minerals is very low and would be a very minor source of helium. Most of the helium trapped in the east African Rift System is most likely sourced from older igenous rocks within the deeper basement of the rift basins and also associated with volcanism within the rift system. Granitic igenous rocks are high in Potassium Feldspar.....the presence of high amounts of K40 is the reason wireline GR readings shoot up when you log over a granite.