The severance tax is imposed at the following rates on the taxable value determined under Section 7-26-4 N.M. Stat. Ann. of the following natural resources:

A.    potash                                                                                                     2 1/2% B.    copper                                                                                                     1/2% C.    timber                                                                                                     1/8% D.    pumice, gypsum, sand, gravel, clay, fluorspar and other nonmetallic minerals E.    lead, zinc, thorium, molybdenum, manganese, rare earth and other metals 1/8% 1/8% F.    gold and silver                                                                                         1/5%