If there isn't any known natural placer gold deposits or veins in this area, then the gold signal must be a man made gold object. Unless of course, they got some mined gold from another location, but it still would have to be a cache. But if, the map is from a natural gold producing location, then it might be really hard to tell the difference betweee gold nuggets and a gold cache.
You can expect the light green marked spots to contain either man made objects and/or altered stones. Same with the red areas, except those are more likely to have some metallic targets you can metal detect.