They call them hand held X-Ray Flourescence analyzers, XRF for short.

They give a low precision range and are not very good for low grade gold or other precious or rare earth metals, the more costly ones are better at the lower grades. They can cost $50,000 or more??. They are good for fast ballparking of grab samples in the field and fast indications on core.

this link will take you to a search where you can read up more details.

http://tinyurl.com/63jjqk2