(1) For income tax years commencing on or after January 1, 1989, but prior to January 1, 2005, there shall be allowed, as a credit against any taxes imposed on income by this part 3, an amount equal to one dollar per ton for each ton of Colorado coal purchased by and delivered to the taxpayer in excess of the number of tons of Colorado coal purchased by and delivered to the taxpayer in the income tax year commencing on or after January 1, 1988. If the amount of the tax credit allowed by this section exceeds the amount of income tax due for the taxable year, the excess amount may be carried forward as a credit against subsequent years' income tax liability for a period not exceeding three years and shall be applied first to the earliest income tax years possible. For purposes of this section, "Colorado coal" means coal mined in Colorado, as certified by the producer of such coal.

(2)

(a) Any public or private corporate purchaser who is not liable for or subject to state income tax during the year the coal is purchased and who is otherwise eligible for the credit allowed by subsection (1) of this section may by written agreement transfer such credit to the producer of the coal. Said producer shall be allowed, as a credit against any taxes imposed on income by this part 3, an amount equal to the amount of credit for which the purchaser would otherwise have been eligible pursuant to subsection (1) of this section. Any such credit shall be subject to any limitations established in subsection (1) of this section. Said producer shall reduce the purchase price of said coal to such corporate purchaser by the amount of the credit so transferred.

(b) The corporate purchaser shall file a copy of the written agreement with the department of revenue. The agreement shall contain, but shall not be limited to, terms stipulating the number of tons of Colorado coal purchased by the corporate purchaser in the 1988 base income tax year and the number of tons of Colorado coal over and above that base amount which is being purchased pursuant to the agreement.