36 CFR 228.66: Refunds.

Upon termination of any contract, payments in excess of $10 may be refunded, less the costs incurred by the United States, under any of the following conditions:

(a) Payment in excess of value. If the total payment exceeds the value of the mineral material removed, unless it is the minimum annual payment in lieu of production;

(b) Insufficiency of material. If insufficient mineral material existed in the sale area to provide the quantity of material estimated to have been available;

(c) Cancellation. (1) If the contract is cancelled by the authorized officer for reasons which are beyond the purchaser's control; or

(2) If the contract is cancelled by mutual agreement. This refund provision is not a warranty that a specific quantity of material exists in the sale area.