The Secretary of the Interior, upon such terms and under such regulations as he may deem proper, may permit responsible persons or associations to use and occupy, for the erection of bathhouses, hotels, or other improvements for the accommodation of the public, suitable spaces or tracts of land near or adjacent to mineral, medicinal, or other springs which are located upon unreserved public lands or public lands which have been withdrawn for the protection of such springs: Provided, That permits or leases hereunder shall be for periods not exceeding twenty years.