TL;DR
Alter ore generation to allow for patches that are large but not dense, as well as small, dense patches, then align with terrain types to encourage player exploration and resource transport.What ?
Add additional sliders to map generation: resource variation and resource alignment. Ore density would also affect resource mining.Resource variation takes the existing frequency/size/richness and adds more randomness to them. You may get very large, low-density resources, and then very rich areas that are small in size. Adding in frequency variation, you might get lots of small patches (in a way that standard mining blueprints don't work, then another area is one large patch.
With resource alignment, the resources would be more likely to be found in a specific terrain type. High resource alignment might put oil in just the arid biome. Copper and iron could be in areas more likely to have trees and cliffs. Moderate moisture/temp areas might have few/no resources to make them more suitable for building.
Ore density could also affect mining rate, much like oil pumps are affected.
Expert players might even like the starting area to be affected by these new sliders.
Why ?
Admittedly, these are definitely expert player oriented, but even average players building their mini-mega-bases would be encouraged to play a little differently and think how to best utilize their resources while more are built.Ore generation is pretty consistent, you select the frequency, size, and density (richness), for each ore type. You find them consistently across the map, and you can go in any direction and get whatever resource you're looking for more of and you'll also have the other resources right at hand when you're ready, and they always get bigger the further you get from the starting point. With resource variation, the player might need to decide how they exploit resources. Do they want to try and mine a huge patch of low-density ore, consuming a lot of miners and belts and needing to build more defenses, or go further out for something more usable, but harder to protect. Or do they mine a lot of smaller patches (even just 2-6 squares each, spread out so that existing blueprints just don't work) and work their assemblers in-between to add to the spaghetti.
If we look at global resources, oil is more likely to be found in certain regions (arid regions is most obvious, but that is not the rule), and ores tend to be found in more mountainous regions (analogous to trees+cliffs). Using resource alignment, players would have to spread out to explore more deserts in search of ore, getting further away from home, but then have to travel in a very different direction to get more copper or iron.
Adding in ore density affecting mining rate multiplies the sliders above as a small very rich "vein" could be far more useful at certain times. It's also "consistent" with real-world consumption. We tend to go for easier resources first, then develop technologies to get the harder ones. This could result in a research element to it (you can only mine x density or higher, research for better).
I think this would encourage more exploration, train usage, and interaction with the locals.