Trying to create an Enchantment

Hello! I'm trying to make an Armour enchantment called Prospecting. it will have 5 levels, and each single level of prospecting you are wearing, will give +1% chance to drop double drops when you mine an ore, (for example, if your helmet has Prospecting III and your chestplate has Prospecting II, overall you will have a 5% chance to drop double drops). the only problem with this is I have literally no clue how to code that in using procedures. I have the actual enchantment in, and it works, but i honestly have no clue where to even start with the procedure. it will also need to check if an ore is placed by a player, or if it was placed naturally, as if the enchantment worked on player placed blocks, that would introduce an exploit of just placing and mining ore blocks with silk touch. if anyone can help me with this,  I will greatly appreciate it!