This came about from thinking about ore distribution. In vanilla metal ores always occur in massive quanitities. If you set mineral frequencies to high you will have massive quantities of almost every ore, if you set it lower you still have ridiculous quantities of the ores you do have, you just have fewer different ores. What I wanted was an embark where you have a lot of different metal ores, but in small quantities and with a higher effort to get them.
I only changed to of the object files, first in the 'inorganic_stone_mineral.txt' I divided all the ore frequencies by 10. Ie for hematite change the line [METAL_ORE:IRON:100] to [METAL_ORE:IRON:10] and similar for all other minerals. Second, in the 'reaction_smelter.txt' I changed all alloy reactions from ores from say [PRODUCT:100:8:BAR:NO_SUBTYPE:METAL:BRASS] to
[PRODUCT:10:8:BAR:NO_SUBTYPE:METAL:BRASS] and I adjusted the returns for making coke from bitumous coal and lignite down to 3 coke and 2 coke respectivly.
Combine this with a mineral frequency of 'everywhere' in world generation (less if you are a masochist) and you get a version of df where finding a hematite vein and mining it out completly will give you maybe 10 bars of iron. So a single vein is enough to make a weapons and maybe helms for a squad of 6 dwarfs but not enough to immediately equip the entire squad with a full set of armor.
Note you can still cheat by making rock crafts out of say gold nuggets instead of smelting the gold ore first but you would have to actively set that up.
I didn't post the modded files because the changes are so simple but I can do so if there is interest.