Every person engaged in the business of mining or producing iron ore or other ores in this state shall pay to the state an occupation tax on the valuation of all ores mined or produced, which tax shall be in addition to all other taxes provided by law. The tax is due on the first day of May in the calendar year next following the mining or producing. The valuation of ore for the purpose of determining the amount of tax shall be ascertained as provided by law. Funds derived from the tax shall be used as follows: 50 percent to the state general revenue fund, 40 percent for the support of elementary and secondary schools and ten percent for the general support of the university.