When Credit Miners end, they pay a fee for the number of days that the Genius Credit was loaned for Genius Shares. This fee remains in the Collateral Vault, and the proportions of Collateral to Genius Credit change in a way that mostly raises the GENI value redeemable from the Collateral Vault. This mechanic is a big part to Genius enforcing a constantly rising value for the GENI token.