He does not say, just leave it untouched. He is saying if it is protected in its mine, from solidifying.Just in the copper thing ... what he said was that if is left untouched, in a pure state it would change to gold, on it's own. Of course any scientist could set that up, contain it for 70 years. So why aren't scientists trying this? I know that if I believed it, I'g get a bunch of copper, and leave it to charity, to be opened in 70 years, and cashed in as gold. Why not?
His statement seems to suggest, that if copper in the mine is not solid, but remains in state of liquid copper for 70 years, then under certain conditions converts to gold. Perhaps, it means, if copper remains molten in its mine, and protected for 70 years. We do not know, exactly the conditions. Bahaullah is not revealing all details here.
But in many copper mines, some gold is also found together with copper.
Originally, when big bang happened, and the earth, was yet molten, different metals formed on earth after cooling. It requires much knowledge of geology, which I do not have.