There are three general types of resources: food, industry, and luxury.
I believe that the game currently abstracts food well enough that additional resources of that type may just clutter the game. As such they may be able to be done without.
As Frogboy suggested there should be a small amount of these resources automatically generated by any settlement. This is justified in my mind in that the "quality" of mineral or material deposits can vary greatly. There are many examples of this. Like the difference in the ease of production of pig iron by the iron ores of Hematite vs Siderite, the usefulness of shale vs granite for construction, and lastly, the difference between Maple and Cedar for ship building.
These lesser sources of the final resource will get you what you need but you will need to process the source more to achieve similar results. i.e. It would take longer to produce a particular structure or item...
Some industrial resources that may be included are as follows:
- Tin -----> Considering the technology level I believe that tin should be included b/c of its requirement in bronze for weapons and durable goods which were very common...
- Marble -----> Give a prestige bonus for construction with the resource or something...
- Some hair bearing animal. Considering the fantasy nature of this game "sheep" may be a bit mundane....
- some animal for mobility i.e. horses...
These should be resources that increase happiness of populace or prestige of country. These resources should not be generated automaticaly. Either you have them or you don't...
Some luxury resources that may be included are as follows:
This all would be unnecessarily mundane for a fantasy game so I propose that there exists a special building, "Alchemy Lab?", that allows resources to be imbued with differing types/combinations of mana for differing effects. This way if a player wants to make Mithrialian Longswords they wouldn't be mining "Mithril" but rather take, for example, Iron, Silver, Air Mana, and Earth Mana and combine to make the mentioned material.
It would be great to be able to make these materials fully customizable by the player but I fear that would greatly complicate trading b/c two players could make the same material and call it different things or how would the AI value such combinations.
Overall, I think this method for handling special materials would add strategic depth and lend to the uniqness of each kingdoms units, structures, and overall game play.