But rather than test the radioactive decay using just one method, the researchers used three, involving the elements lead, samarium and neodymium.

Most famously, uranium-238 decays into lead-206 with a half life of 4.5 billion years, though radioactive rubidium and samarium are also useful for dating things billions of years old.

Lead isotope research shows that lead in ores of Mujiazhuang copper deposit and near ore country rocks is characterized by being rich in radioactive lead.