Collateralization

The use of gold as collateral for foreign exchange loans was pioneered between Italy and Germany in 1974 to tide the former over a massive balance of payments deficit. That collateralization was between their respective central banks but this practice has evolved into more complex swap operations between a central bank and one or more commercial banks.
Such deals are particularly useful in a short-term foreign exchange crisis, where the sudden outright sale of the metal might undermine the price. It also enables producer countries, such as South Africa, to hold gold off the market when the price is weak.

While terms vary from deal to deal, on most straightforward collateralization the central bank would receive close to 100 per cent of the market price of the gold when the arrangement was made and would be liable for margin calls if the price fell.