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The Fed has three ways to add a buffer to the treasury.
1. It can sell from its holdings some of the older treasury bills that have high interest rates. The profit would then appear on the Fed books and could be repatriated to the treasury.
2. The Fed can transfer in advance the interest profits on the securities it holds. Profits sent to the treasury before they show up on the Fed's books are covered because the securities are clearly going to provide the stream of income. This is like a payday loan.
3. If the Treasury gets permission to demonetize gold, it can take back the gold certificates it gave the Fed based on a $42/oz price by paying the Fed $11 billion. Treasury then has clear title to the gold and could sell off some of the 260 million ounces it holds at market prices. Gold's price would fall but it's a long way from $1600 to $42.
The Zero Hedge author thinks the total could be up to $500 billion.