Laws of Minnesota 1963, Chapter 81, relating to the taxation of taconite and semi-taconite, and facilities for the mining, production and beneficiation thereof shall not be repealed, modified or amended, nor shall any laws in conflict therewith be valid until November 4, 1989. Laws may be enacted fixing or limiting for a period not extending beyond the year 1990, the tax to be imposed on persons engaged in (1) the mining, production or beneficiation of copper, (2) the mining, production or beneficiation of copper-nickel, or (3) the mining, production or beneficiation of nickel. Taxes imposed on the mining or quarrying of taconite or semi-taconite and on the production of iron ore concentrates therefrom, which are in lieu of a tax on real or personal property, shall not be considered to be occupation, royalty, or excise taxes within the meaning of this amendment.