Find Minerals ?Follow

You don't - the minimap shows all minerals present. What Blizzard means when they say only one will be shown is one type of detector - herbs, minerals, undead, animals, humanoids, treasure, etc. If you have minerals showing, you will see all the minerals present.

However, the minerals track with the level of the zone you are in - if you see mobs < level 15 or so, you won't find anything but copper.

Not that copper veins aren't useful, but the rare hits won't come that often. I manage to get something like a shadowgem, or tigerseye, or malachite in something like 1/10 points, with 2-4 tries per spot before they disappear.