1.621-1—Payments to encourage exploration, development, and mining for defense purposes.

(a) General rule. (1) Under section 621, a taxpayer shall exclude from gross income amounts which are paid to him:
(i) By the United States or by an agency or instrumentality of the United States,
(ii) As a grant, gift, bounty, bonus, premium, incentive, subsidy, loan, or advance,
(iii) For the encouragement of exploration for, or development or mining of, a critical and strategic mineral or metal,
(iv) Pursuant to or in connection with an undertaking by the taxpayer to explore for, or develop or produce, such mineral or metal and to expend or use any amounts so received for the purpose and in accordance with the terms and conditions upon which such amounts are paid, which undertaking has been approved by the United States or by an agency or instrumentality of the United States, and
(v) For which the taxpayer has accounted, or is required to account, to an appropriate agency of the United States Government for the expenditure or use thereof for the purpose and in accordance with the terms and conditions upon which such amounts are paid

Code of Federal Regulations

In order for section 621 to apply, such amount must qualify under each of the foregoing subdivisions of this paragraph. Under section 621, there shall also be excluded from gross income any income attributable to the forgiveness or discharge of any indebtedness arising from amounts to which such section applies.
(2) Section 621 is applicable whether or not the payee is obligated to repay to the United States any portion or all of the amount so received. However, such section is not applicable to any loan or advance for the repayment of which the borrower's liability is unconditional and legally enforceable.
(3) Except as provided in paragraph (e) of this section any expenditure attributable to an amount received by a taxpayer to which section 621 applies shall not be deductible by the taxpayer as an expense under subtitle A of the Code, nor shall any such expenditure increase the basis of the taxpayer's property either for determining gain or loss on sale, exchange, or other disposition, or for computing depletion or depreciation (including amortization under section 168 ).
(b) Allowance as part of purchase price. (1) Section 621 is not applicable to any part of the purchase price of a critical and strategic mineral or metal which amount is received, whether before, on, or after delivery from the United States or any agency or instrumentality thereof, and irrespective of whether such purchase price is below, at, or above the currently prevailing market price.
(2) However, a payment of a separate and specific amount for the encouragement of exploration for, or development or mining of, a critical and strategic mineral or metal shall not be considered to be a part of the purchase price of such mineral or metal merely because such payment is added to, or included with, the payment of such purchase price.
(c) Payments for expenditures previously deducted or capitalized. (1) Where amounts described in section 621 and this section are paid to a taxpayer in reimbursement for expenditures previously allowed as a deduction, the taxpayer shall include in gross income that portion of such amounts which is equivalent to the deduction for such expenditures allowed to the taxpayer and which deduction resulted in a reduction for any taxable year of the taxpayer's taxes under subtitle A of the Code (other than chapter 2, relating to tax on self-employment income), or prior income, war-profits, or excess-profits tax laws.
(2) Where amounts described in section 621 and this section are paid to the taxpayer in reimbursement for expenditures which have been deferred under sections 615 and 616 (relating to exploration and development expenditures) the taxpayer shall include in gross income that portion of such amounts which is equivalent to any deduction for such expenditures allowed to the taxpayer and which deduction resulted in a reduction for any taxable year of the taxpayer's taxes under subtitle A of the Code (other than chapter 2, relating to tax on self-employment income), or prior income, war-profits, or excess-profits tax laws. The portion of such amounts, equivalent to expenditures which are reflected in the adjusted basis of the assets to which charged, shall be excluded from gross income, and such adjusted basis shall be decreased by the amount of such exclusion.
(3) Where amounts described in section 621 and this section are paid to the taxpayer in reimbursement for expenditures which have been charged to capital account (either to a depletable or depreciable account), there shall be included in the taxpayer's gross income that portion of such amounts which is equivalent to such capital expenditures that have been recovered through cost depletion or depreciation deductions and which deductions have resulted in a reduction of the taxpayer's taxes for any taxable year under subtitle A of the Code (other than chapter 2, relating to tax on self-employment income), or prior income, war-profits, or excess-profits tax laws. The portion of such amounts which is equivalent to the expenditures which are reflected in the adjusted basis of the asset to which charged shall be excluded from gross income. The adjusted basis of such assets shall be reduced by the amount of such exclusion from gross income.
(4) Where amounts described in section 621 and this section are paid to the taxpayer in reimbursement for expenditures which have been charged to a depletable capital account, such amounts shall be excluded to the extent such expenditures are recovered through depletion deductions computed under section 613 (relating to percentage depletion).
(5) The amount of reimbursed expenditures charged to an account (depletable or depreciable) and recovered through depletion or depreciation deductions for any taxable year shall be that proportion of the total deductions allowed with respect to such account that such reimbursed expenditures bear to the total amount in the account. For example, in 1956 A incurs exploration expenditures of $12,000 which he charges to a depletable capital account. This brings the total amount in this account to $36,000 which is the adjusted basis of the property on January 1, 1957. In 1957, A is allowed a deduction for cost depletion of $9,000 which resulted in a reduction of A's income taxes. One-third of this deduction is attributable to the $12,000 of exploration expenditures since they were a third of the total in the capital account on January 1, 1957. Therefore, on January 1, 1958, these exploration expenditures make up $9,000 of the remaining $27,000 in the account. If on January 1, 1958, A receives $12,000, which qualifies under section 621, in reimbursement for these exploration expenditures, he must report $3,000 as income and reduce the capital account by $9,000.
(d) Definition. As used in section 621 and this section, the term critical and strategic minerals or metals means minerals and metals which are considered by those departments, agencies, and instrumentalities of the United States charged with the encouragement of exploration for, and development and mining of, critical and strategic minerals and metals, to constitute critical and strategic minerals and metals for defense purposes. See, for example, 30 CFR 301.3 (Regulations for Obtaining Federal Assistance in Financing Explorations for Mineral Reserves, Excluding Organic Fuels, in the United States, its Territories and Possessions).
(e) Repayments of amounts excluded under Upon the repayment by the taxpayer of any portion of any amount to which section 621 applies and which portion has been expended for the purpose and in accordance with the terms and conditions upon which it was paid to the taxpayer, any expenditures attributable to such amount made by the taxpayer shall be treated as if such expenditures had been made at the time of such repayment. Such expenditures shall to the extent of the repayment be expensed or capitalized, as the case may be, in the order in which they were actually made or in such other manner as may be adopted by the taxpayer with the approval of the Commissioner.