The Secretary of the Interior is authorized to lease to any applicant qualified under this chapter, through advertisement, competitive bidding, or such other methods as he may by general regulations adopt, any phosphate deposits of the United States, and lands containing such deposits, including associated and related minerals, when in his judgment the public interest will be best served thereby. The lands shall be leased under such terms and conditions as are herein specified, in units reasonably compact in form of not to exceed two thousand five hundred and sixty acres.