At the election of the taxpayer, expenditures paid or incurred during the taxable year for the purpose of ascertaining the existence, location, extent, or quality of any deposit of ore or other mineral, and paid or incurred before the beginning of the development stage of the mine, shall be allowed as a deduction in computing taxable income. This subsection shall apply only with respect to the amount of such expenditures which, but for this subsection, would not be allowable as a deduction for the taxable year. This subsection shall not apply to expenditures for the acquisition or improvement of property of a character which is subject to the allowance for depreciation provided in section
167, but allowances for depreciation shall be considered, for purposes of this subsection, as expenditures paid or incurred. In no case shall this subsection apply with respect to amounts paid or incurred for the purpose of ascertaining the existence, location, extent, or quality of any deposit of oil or gas or of any mineral with respect to which a deduction for percentage depletion is not allowable under section
613.