Royalties will be required as follows, subject to the approval of the President, in accordance with the act of June 28, 1906 (34 Stat. 543):

(a) For gold, silver, or copper lessee shall pay quarterly a royalty of 10 percent to be computed on the gross value of the ores as shown by reduction returns after deducting freight and treatment charges. Duplicate reduction returns shall be filed by the lessee with the officer in charge within 20 days after the reduction of the ores.

(b) For coal the lessee shall pay a royalty of 10 cents per ton of 2,000 pounds on mine run or coal as taken from the mines, including what is commonly called “slack.”

(c) For asphaltum and allied substances, the lessee shall pay quarterly a royalty of 10 cents per ton of 2,000 pounds on crude material, and 60 cents per ton on refined substances.

(d) For substances other than gold, silver, copper, lead, zinc, coal, and asphaltum the lessee shall pay quarterly a royalty of 10 percent of the value at the nearest shipping point of all ores, metals, or minerals marketed.

(e) The royalties to be paid for lead and zinc shall be computed for each mineral at the same rate that the amount of the concentrates of such mineral bears to the total amount of dirt or rock actually mined, except as stipulated in this section. The royalty so determined shall be increased by adding 1 percent for each increase of $10 in the selling price per ton thereof over and above the following, which shall be the agreed base or standard:

but in no case shall the rate of royalty be less than 5 percent or more than 20 percent. The percentage of recovery shall be computed as nearly as practicable upon the ore included in each sale, but where it is impracticable so to do the officer in charge and the lessee shall agree upon some other method of computation which will produce substantially the same result: Provided, That in case of their disagreement the Commissioner of Indian Affairs shall prescribe a rule of computation to be followed in such cases.