A18 is unforgiving. Mining doesn’t really make fun anymore, especially because veins are rare to find without the corresponding resourceblocks above. Claymore decided to simply port over the harvests from A17 to 18. With this 7 Days to Die mod, resource stones are giving iron, potassium, lead, coal and stone, and terrestrial stone is also giving some iron. Like he said: Same like A17.
The forum topic of the mod is here.