Commands:
Step 1: Diamond Structure
Throw some exp and x64 re-named diamonds (e.g. “diamondz“) into a 1×1 area of a structure block and save the structure as “loot:diamond“.

Step 2: Add & Remove Tags
/tag @p add Fortune (enables fortune 1000 for the closest player)
/tag @p remove Fortune (disables fortune 1000 for the closest player)

Step 3: Fortune 1000 Commands
1) /enchant @a[tag=Fortune] fortune 1
2) /execute @e[type=item,name="diamond"] ~~~ structure load loot:diamond ~ ~ ~
3) /execute @e[type=item,name="diamond"] ~~~ kill @s

Please Note: With this method, you will randomly receive 1 – 3 stacks of diamonds each time that you mine diamond ore.