The Prospecting skill allows the current ore stack(which contains bonus drops) to be placed in the world, thus the ores can be mined again and benefit from Prospecting repeatedly, leading to an effect similar to duping.
Tested on MC eternal, at max prospecting level, there is a 100% chance to drop bonus, so the dupe is viable.

Potential cause and solution:

note that in the original Level-Up mod, the author adds a NBTtag with a "NoPlacing" key to the ore stack containing the bonus drop to prevent placing the stack.

I don't seem to notice similar implementation in this repo. Apologies beforehand if I am wrong.