Pardon if I'm off base with the mechanics, jorb/loftar take this with a grain of salt if I'm wrong, but with 4 villages worth of mining experiences I think I've got an idea. Ores come in fields now, so one area will have many veins of one ore type. The issue here is that trade over metal while realistic doesn't work with haven's mechanics. Metal is a basic resource here, lacking any of the basic tin/copper/iron (or at least either only having tin or copper, or lacking iron/quality iron ore) makes you incredibly poor trade wise, and incredibly frustrated. Having a precious ore deposit can make one random village very rich, but you get too much of it. Like an insane amount. The impacts here are twofold. The first is that village placement is a lottery as to whether or not you're dirt poor in metal or hit it big. Alternatively, villages need to expand much further in the underground just to meet their basic metal needs. To the tune of 40x40 minimaps if my region is indicative but I'm sure that varies by luck.
While realistic, I don't think this is healthy for gameplay. I miss the old system of intermixed ore deposits significantly, and I'm not particularly screwed by this system as I have ore regions for the basics. I think the old random ore deposists is better because it means a village is rewarded with mining resources by elbow grease and a bit of luck instead of mostly where you placed your village luck.