you don't understand reusable proof of work. If it didn't take energy to get more gold what do you imagine would happen to the price?
The cost of mining gold and silver is obviously not the same.
Since silver is often the byproduct of mining gold, the energy price should be pretty close, I'd think...
Crypto-bros reinventing the (train-wreck of) labour theory of value is my favorite genre of HN comments.