As used in this chapter “mineral leasing laws” shall mean the Act of October 20, 1914 (38 Stat. 741); the Act of February 25, 1920 (41 Stat. 437) [30 U.S.C. 181 et seq.]; the Act of April 17, 1926 (44 Stat. 301) [30 U.S.C. 271 et seq.]; the Act of February 7, 1927 (44 Stat. 1057) [30 U.S.C. 281 et seq.] and all Acts heretofore or hereafter enacted which are amendatory of or supplementary to any of the foregoing Acts.