So I've what i can see that resource (ore) spawn in any biomes. Would be maybe better (and will add some difficultly) if only iron/copper spawn in all biomes while other ones in different (eg, gold, silver in snow).
It might be that other biomes would have small (rare) chance to spawn other ores (than iron/copper) in every biome.
Also, I'm playing on low-ores settings (to not have too easy) but on many occasions I'm finding patches that are 2-3 voxels (due to setting). Would be possible to add (as setting) more rare but dense/bigger deposits?
This could be mixed with above idea, so more hash (like snow) biome will have bigger deposits.