What Verba is trying to tell you is that the "Gold Detectors" that you see advertised for sale are just ordinary metal detectors with sensitiviy enhancements. They use different frequencies, sense coil sizes, and pulsed signal techniques to allow detection of small metallic objects against a background of metallic oxide sand, or other naturally interferring objects.
Gold is a non-ferrous metal. A metal detector can "see" it because any conductor in a moving magnetic field will have a current induced in it. The moving field can be created by physically moving the search coil, or by driving the search coil with a shaped current pulse. The change in magnetic flux around the search coil can be detected and amplified.
The reason that people with "gold detectors" find gold is they go to where there is likely to be affluvial or effluvial gold. When their detector sees metal in a likely location, it may be gold - they have to dig it up to be sure. There's nothing special about the detector that ensures finding gold. People using such detectors find nails, cans, iron ore, and other metal objects. Once in a while, they get lucky and it's the real stuff.