Several counties have enacted mineral severance taxes by private act.  Private acts on this subject are no longer authorized, but private acts on this subject enacted prior to June 5, 1984, remain in effect, except that the rate cannot exceed 15 cents per ton. T.C.A. §§ 67-7-209, 67-7-212. The minerals subject to the tax are delineated in each county's private act, along with provisions regarding rate, collection and distribution of the tax proceeds. Currently, the following counties have a mineral severance tax levied by private act:  Benton, Carroll, Carter, Decatur, Giles, Humphreys, Roane, Rutherford, Unicoi, Weakley, White, and Williamson.