That (a) subject to the conditions and provisions of this Act and to any valid intervening rights acquired under the laws of the United States, any mining claim located under the mining laws of the United States subsequent to July 31, 1939, and prior to February 10, 1954, on lands of the United States, which at the time of location were—

(1) Included in a permit or lease issued under the mineral leasing laws; or

(2) Covered by an application or offer for a permit or lease which had been filed under the mineral leasing laws; or

(3) Known to be valuable for minerals subject to disposition under the mineral leasing laws, shall be effective to the same extent in all respects as if such lands at the time of location, and at all times thereafter, had not been so included or covered or known: Provided, however, That, in order to be entitled to the benefits of this act, the owner of any such mining claim located prior to January 1, 1953, must have posted and filed for record, within the time allowed by the provisions of the Act of August 12, 1953 (67 Stat. 539) [not later than December 10, 1953.] an amended notice of location as to such mining claim, stating that such notice was filed pursuant to the provisions of said Act of August 12, 1953, and for the purpose of obtaining the benefits thereof: And provided further, That, in order to obtain the benefits of this act, the owner of any such mining claim located subsequent to December 31, 1952, and prior to February 10, 1954, not later than one hundred and twenty days after the date of enactment of this act, must post on such claim in the manner required for posting notice of location of mining claims and file for record in the office where the notice or certificate of location of such claim is of record an amended notice of location for such claim, stating that such notice is filed pursuant to the provisions of this act, and for the purpose of obtaining the benefits thereof and, within said one hundred and twenty day period, if such owner shall have filed a uranium lease application as to the tract covered by such mining claim, must file with the Atomic Energy Commission a withdrawal of such uranium lease application or, if a uranium lease shall have issued pursuant thereto, a release of such lease, and must record a notice of the filing of such withdrawal or release in the county office wherein such notice or certificate of location shall have been filed for record.