30 U.S.C. § 501: Mining claims located between July 31, 1939 , and January 1, 1953

included in a permit or lease issued under the mineral leasing laws; or covered by an application or offer for a permit or lease which had been filed under the mineral leasing laws; or known to be valuable for minerals subject to disposition under the mineral leasing laws; Labor performed or improvements made upon or for the benefit of such mining claims after the original location thereof shall be recognized as applicable thereto for all purposes to the same extent as labor performed and improvements made upon or for the benefit of mining claims which are not affected by this chapter. Any withdrawal or reservation made after the original location of such mining claim affecting land covered by such mining claim is modified and amended so that the effect thereof upon such mining claim shall be the same as if such mining claim had been located upon lands of the United States, which, subsequent to July 31, 1939 , and prior to the date of such withdrawal, were subject to location under the mining laws of the United States.