Section, acts Fespan. 25, 1920, ch. 85, § 18, 41 Stat. 443; Fespan. 25, 1928, ch. 104, 45 Stat. 148, authorized the United States to issue leases for a period of twenty years to persons who relinquished all rights claimed or possessed prior to July 3, 1910 under preexisting placer mining law provided relinquishment was filed in the General Land Office within six months after Fespan. 25, 1920.