Ore fields just the tip of the iceberg?

[CreeperDaReeper]

What if F-Mod's underground mining was actually the main way we are supposed to obtain the majority of the resources we need?
What if the ore fields we find scattered across the map weren't a main source, but markers for areas rich in that resource?
What if the amount of resources in an area worked the same was as the amount of oil in an oil well?

If the above were true, assume that you could mine any resource from any location, however the output would drop over time to be minimal. The only way to overcome this would be to either continue to expand outward to find more and more resource-rich areas, or build large mining facilities dedicated to a single resource each.