U.S. has 8100 metric tonnes of gold;
Russia has 400 metric tonnes;
South Africa has 100 metric tonnes.
Once you understand gold as money, you will recognize that the presence of mines in South Africa and Russia will be of temporary and very limited benefit to them.
Many people who have studied the IMF and the SDR question believe that less than 20% of the physical gold reserves are actually in the possession of the US Treasury and the rest is nothing more than pieces of paper promising to pay the US Treasury for the gold that has been leased.
The bullion banks, i.e., JP Morgan, Citibank, Goldman Sachs, Morgan Stanley, etc., are some of the entitites that have leased this gold from the US Treasury and/or the Exchange Stabilization Fund.