Helium geological setting
Helium is a decay product of Uranium, but the decay is slow and only certain crystalline basement rocks or suitable organic rich Protozoic and older sediments with a sufficient volume will generate enough helium to be of interest.
This only generates helium in low concentrations and to accumulate it into commercial quantities requires a trap, a robust seal and a migration mechanism.
Such combinations of geological circumstances over space and time are extremely rare, but they do occur and have been recorded.
Most of the UK's helium is supplied from accumulations associated with the North American craton, some is supplied as a by-product from LNG production in Qatar.
Both of these suffer from political and other issues creating a real need to explore for commercial helium, especially in the UK.