Are there any historical examples of Gold mines being closed?
You cannot go from there... If something did not happen in History, it does not mean that it may not have happened in an alternate reality.
The Portuguese when they had the opportunity, they flooded Europe (and especially the Papal States) with Gold from Brazil. The prices of gold fell, but still, there was so much gold coming from America that no one here in Portugal seemed to care if prices went down. But then, it happened, there was no more gold to mine. Portugal went through a huge crisis, bla, bla,bla.
But imagine that the gold did not ran out. The gold price would keep going down, until the point it was as common that a simple peasant had a golden necklace and a golden bracelet, because it was sou cheap. Remember, Supply-Demand Law.
Portugal is not known for it's ability to think ahead or in the future, but some other countries are. Now imagine that instead of a full exploration of gold, the Portuguese would extract a little bit at a time, the prices would still go up, no inflation, and in the long term, well, it would be better for the country.