Any permit, lease, occupation, or use permitted under this chapter shall reserve to the Secretary of the Interior the right to permit upon such terms as he may determine to be just, for joint or several use, such easements or rights-of-way, including easements in tunnels upon, through, or in the lands leased, occupied, or used as may be necessary or appropriate to the working of the same, or of other lands containing the deposits described in this chapter, and the treatment and shipment of the products thereof by or under authority of the Government, its lessees, or permittees, and for other public purposes. The Secretary of the Interior, in his discretion, in making any lease under this chapter, may reserve to the United States the right to lease, sell, or otherwise dispose of the surface of the lands embraced within such lease under existing law or laws hereafter enacted, insofar as said surface is not necessary for use of the lessee in extracting and removing the deposits therein. If such reservation is made it shall be so determined before the offering of such lease. The said Secretary, during the life of the lease, is authorized to issue such permits for easements herein provided to be reserved.