(a) In leases offered for sale at public auction under the regulations in this part the royalty to be paid by the lessee shall be stipulated at a fixed percent of the gross proceeds of all lead and zinc ores and concentrates extracted from the leased premises, the royalty to be computed and based upon each sale of ore or concentrates separately, the rate of royalty to be determined and fixed by the Secretary of the Interior in the case of each lease prior to the offering of such lease for sale. Subject to the right of the Secretary of the Interior to reject any and all bids, leases offered for sale at public auction shall be awarded in each case to the responsible bidder submitting the highest bonus offer.

(b) In leases not offered for sale at public auction but otherwise made and entered into under the provisions of the regulations in this part the royalty stipulated and fixed therein shall be such as may be determined by the Secretary of the Interior or as may be agreed upon in each case, subject to the approval of the Secretary of the Interior.

(c) It shall be further provided, however, that said sale-price basis for the determination of the rates and amount of royalty shall not be less than the highest and best obtainable market price of the lead and zinc ores and concentrates at the usual and customary place of disposing of such ores and concentrates at the time of sale: Provided, however, That the right is reserved to the Secretary of the Interior to determine and declare such market price if it is deemed necessary for him to do so for the protection of the interests of the Indian lessor: And provided further, That the right is reserved to the Secretary of the Interior on behalf of the Indian lessors to reserve at any time it shall be deemed to be to the best interests of the Indian lessors and upon due notice to the lessee, the royalty share of the gross production of the ore and concentrates and upon such notice that the royalty share of such production shall be stored and not sold, the lessee shall be required to store, free of charge to the Indian lessors in the ore bins of said lessee, said royalty shares of the gross production of ore and concentrates, provided that the lessee may not be required to store ore or concentrates for the lessor in amounts greater than one-third of his bin capacity or for a period longer than 6 months.