Definitely rarer. We have lead everywhere, practically tripping over it. Same with iron. Nitrate I rarely see in the snow biom (maybe 2 sightings) but we have about 9 marked off in the forest biom. Maybe they are just really really hard to spot in snow. The coal deposits in the burning lands are almost rare but we get quite a few of them bunched up around the coal plants, which is kinda cool and makes it easier to find.
Wasteland needs its own mineral to mine honestly, besides land mines.