In the case of the disposal of coal (including lignite), or iron ore mined in the United States, held for more than 1 year before such disposal, by the owner thereof under any form of contract by virtue of which such owner retains an economic interest in such coal or iron ore, the difference between the amount realized from the disposal of such coal or iron ore and the adjusted depletion basis thereof plus the deductions disallowed for the taxable year under section 272 shall be considered as though it were a gain or loss, as the case may be, on the sale of such coal or iron ore. If for the taxable year of such gain or loss the maximum rate of tax imposed by this chapter on any net capital gain is less than such maximum rate for ordinary income, such owner shall not be entitled to the allowance for percentage depletion provided in section 613 with respect to such coal or iron ore. This subsection shall not apply to income realized by any owner as a co-adventurer, partner, or principal in the mining of such coal or iron ore, and the word “owner” means any person who owns an economic interest in coal or iron ore in place, including a sublessor. The date of disposal of such coal or iron ore shall be deemed to be the date such coal or iron ore is mined. In determining the gross income, the adjusted gross income, or the taxable income of the lessee, the deductions allowable with respect to rents and royalties shall be determined without regard to the provisions of this subsection. This subsection shall have no application, for purposes of applying subchapter G, relating to corporations used to avoid income tax on shareholders (including the determinations of the amount of the deductions under section 535(b)(6) or section 545(b)(5)). This subsection shall not apply to any disposal of iron ore or coal—