Copper tool better enchantability BUT it requires diamonds? A problem!

Enchanting tables need diamonds therefore coppertools are not that useful by the time you get enchanting going and its enchantablity is wasted therefore:

Copper should get some unique enchant(s) related to its patina, maybe using the grindstone (another use for this item as well) will reset the protective patina and the copper tool rusting would quickly regenerate durability if it is enchanted with the unique enchant (would be faster when raining or the player holding the tool is submerged in water), the opposite would be true in deserts and similar biomes. Maybe also raise the mining level with patina and consider adding a tooltipp for mining level so that no accidents happen while mining valuable ores.

Because of the higher enchantability it could be a good alternative to iron and maybe early, unenchanted diamond tools.