expenditures paid or incurred for the development of a mine or other natural deposit (other than an oil or gas well) if paid or incurred after the existence of ores or minerals in commercially marketable quantities has been disclosed shall be allowed as a deduction ratably over the 84-month period beginning on the date that such expenditure was paid or incurred. (b) Mid-Month convention For purposes of subsection (a), any expenditures paid or incurred during any month shall be treated as paid or incurred on the mid-point of such month. (c) Exclusive method Except as provided in this section, no depreciation or amortization deduction shall be allowed with respect to expenditures described in subsection (a). (d) Treatment upon abandonment If any property with respect to which expenditures described in subsection (a) are paid or incurred is retired or abandoned during the 84-month period described in such subsection, no deduction shall be allowed on account of such retirement or abandonment and the amortization deduction under this section shall continue with respect to such payment. . (b) Conforming amendments (1) The item relating to section 616 in the table of sections for part I of subchapter I of chapter 1 of the Internal Revenue Code of 1986 is amended to read as follows: Sec. 616. Amortization of development expenditures. . (2) Section 56(a)(2)(A) of such Code is amended by striking 616(a) or . (3) Section 59(e) of such Code is amended— (A) in paragraph (2)— (i) in subparagraph (C), by inserting or at the end, (ii) by striking subparagraph (D), and (iii) by redesignating subparagraph (E) as subparagraph (D), and (B) in paragraph (5)(A), by striking , 616(a), . (4) Section 263(a)(1) of such Code is amended by striking subparagraph (A). (5) Section 263A(c)(3) of such Code is amended by striking 616, . (6) Section 291(b) of such Code is amended— (A) in paragraph (1)(B), by striking 616(a) or , (B) in paragraph (2), by striking , 616(a), , and (C) in paragraph (3), by striking , 616(a), . (7) Section