I might have a maybe-too-easy idea for these "higher" metals (i.e. noble): you can add some filtering of water. As I recall, one can get gold out of water, but it will take huge amounts so as far as I know, it's an academic possibility. Those, you can add the metals in advance without the proper ore, but later, one will then go to the ore source for this.
My thinking would be that the 'gold' ore should be really thinned out, so maybe hard to get (far in the tech tree or far away from home), but you still have some backstop with the water filtering, because water is somewhat abundantly available.
I might have a maybe-too-easy idea for these "higher" metals (i.e. noble): you can add some filtering of water. As I recall, one can get gold out of water, but it will take huge amounts so as far as I know, it's an academic possibility. Those, you can add the metals in advance without the proper ore, but later, one will then go to the ore source for this.
My thinking would be that the 'gold' ore should be really thinned out, so maybe hard to get (far in the tech tree or far away from home), but you still have some backstop with the water filtering, because water is somewhat abundantly available.
(Source: lookingat)