I was sent this photograph of a lady’s gold neck chain she was wearing, taken with a Canon DSLR camera fitted with an infrared filter. Had the chain been placed on a table and photographed in the same way, it would have produced a pretty uninteresting more or less blank picture. But because the gold is being excited by the electromagnetic field produced by the wearer it is emitting infrared radiation that is being picked up by the camera. This is exactly what happens when gold is buried and excited by the Earth’s electromagnetic field, which is a lot stronger.
A graduate scientist explained this process fairly simply to me. Gold, as all substances, is made up of atoms. Atoms consist of a dense positively charged nucleus surrounded by negatively charged electrons, all being held together by electromagnetic force. Under the influence of an electromagnetic field the electrons are excited into an orbit further from the nucleus and then spontaneously return to their normal orbit releasing energy in the form of infrared radiation.