Alchemy in it’s purest form?.......Reaction yes, fusion, NO.
If (big if) nickel is being changed into copper then nuclear fusion is taking place. That isn't just a chemical reaction. Give me a few megawatts of power and a particle accelerator and I can do that, so the fact that it can happen isn't alchemy, magic or a chemical reaction. Since both copper and nickel have atomic numbers less than iron the conversion from nickel and hydrogen to copper will convert matter to energy. Now the only question is can it happen at a low temperature and can be done efficiently enough where the amount I put in is less than the amount I can harvest.
I don't know if cold fusion works, but having more copper when you finish than you started with points to something nuclear happening. The next thing to check is impurities higher up the list to see if the copper is coming as the decay product of another heavier isotope.