I'm attempt to create a similar game to I guess Minecraft and what I'm wanting to do is place a bunch of different types of ores randomly throughout my map based on how deep they are underground. I've not attempted to do this yet to be honest as I wanted to get an idea of how I should even approach this first as I have no idea. Is it going to be as simple as creating another noies map for the ores or is there a better technique?

It depends on what you want from the ore distribution, but I can't think of any particular reason why you can't use a noise map for ores given that you are using one for terrain.