No mortgage or other encumbrance of the said lands, or any part thereof, shall be valid in favor of any person or for any purpose or under any circumstances whatsoever. Said lands shall not be sold or leased, in whole or in part, except to the highest and best bidder at a public auction to be held at the county seat of the county wherein the lands to be affected, or the major portion thereof, shall lie, notice of which public auction shall first have been duly given by advertisement, which shall set forth the nature, time and place of the transaction to be had, with a full description of the lands to be offered, and be published once each week for not less than ten successive weeks in a newspaper of general circulation published regularly at the state capital, and in that newspaper of like circulation which shall then be regularly published nearest to the location of the lands so offered; nor shall any sale or contract for the sale of any timber or other natural product of such lands be made, save at the place, in the manner, and after the notice by publication provided for sales and leases of the lands themselves. Nothing herein, or elsewhere in article X contained, shall prevent:

1. 1. The leasing of any of the lands referred to in this article in such manner as the legislature may prescribe, for grazing, agricultural, commercial and homesite purposes, for a term of ten years or less, without advertisement;
2. 2. The leasing of any of said lands, in such manner as the legislature may prescribe, whether or not also leased for grazing and agricultural purposes, for mineral purposes, other than for the exploration, development, and production of oil, gas and other hydrocarbon substances, for a term of twenty years or less, without advertisement, or,
3. 3. The leasing of any of said lands, whether or not also leased for other purposes, for the exploration, development, and production of oil, gas and other hydrocarbon substances on, in or under said lands for an initial term of twenty (20) years or less and as long thereafter as oil, gas or other hydrocarbon substance may be procured therefrom in paying quantities, the leases to be made in any manner, with or without advertisement, bidding, or appraisement, and under such terms and provisions, as the legislature may prescribe, the terms and provisions to include a reservation of a royalty to the state of not less than twelve and one-half per cent of production.