If I understand this correctly (and I may very well not), the U.S. gold reserves are priced at about $40/ounce for accounting purposes - a holdover from the old gold standard days. I believe Lummis' proposal is to sell gold IOUs to the Federal Reserve for dollars at the market rate (currently about $2600/ounce). That way, the gold doesn't actually move anywhere, the Federal Reserve balance sheet stays balanced, and the government suddenly has a huge stockpile of USD they can spend on Bitcoin.