I grew up in the middle of the "Mother Lode Gpld Belt" in an 1849 gold rush town! The general rule of thumb there,- is that if you don't have lots of "black sand" (which is iron pyrites)-- the iron is "rusted" or more closely blued from water minerals! Now in that area, you wanted to find lots of white quartz too!.... Seems as though when lots of minerals came to surface,- gold, lead, and iron seem to like to show up at same places,--- sometimes silver too! But you don't often find gold and silver in like amounts in west coast gold mines etc!