The new "Top Hat" Gold Magnet is a plunger-type black sands magnet with smoother action and a more powerful magnet than past designs.
Black sand is heavy, and can make panning a chore, but much of the black sands you run into while prospecting is magnetite, a ferrous mineral that can be removed with a magnet. This is where the Gold Magnet comes in.
Depress the plunger with your thumb and move the magnet around in your pan to pick up the magnetics. Once you've collected the unwanted magnetite and other iron based minerals on your magnet, move the magnet away and release the plunger to drop the black sands.
Some prospectors save these sands for later processing, as they will often contain small amounts of gold, while others write off the small loss for the increased speed and efficiency in panning.