Although it does not appear until almost the end of this article in the Financial Times, BIS Gold Swaps Mystery Unravelled, the source of the gold provided in the dollar swaps with BIS is coming from customers of about 10 European banks who are holding their gold at the banks in ‘unallocated accounts.’
“The gold used in the swaps came mainly from investors’ deposit accounts at the European commercial banks. Some investors prefer to deposit their gold in so-called “allocated accounts”, which restrict the custodian banks’ ability to use the gold in their market operations by assigning them specific bullion bars. But other investors prefer cheaper “unallocated accounts”, which give banks access to their bullion for their day-to-day operations.