USGS simply uses letter codes for natural resources, with the presentation indicating the level of exploitation at a particular site.
USGS Minerals Information: Mineral Map Symbols and Legend
The Adobe Carta font may have other symbols that are useful. I know for sure it has the typical mine symbol (crossed pickaxes).
I used some alchemical symbols for silver and copper on a map once, but I had to custom make the brushes from images. I unfortunately lost the source files for that map in a hard drive crash a while back, though. Obviously, that one required a detailed legend to interpret the symbols.