Subject to the conditions and provisions of this chapter and to any valid intervening rights acquired under the laws of the United States, public lands of the United States classified as or known to be valuable for coal subject to disposition under the mineral leasing laws and which are open to location and entry subject to the conditions and provisions of chapter
of this title, unless embraced within a coal prospecting permit or lease, shall also be open to location and entry under the mining laws of the United States upon the discovery of a valuable source material occurring within any seam, bed, or deposit of lignite in such lands: Provided, That a copy of the notice of any mining location made for source material occurring in any such bed, seam, or deposit, shall be filed for record in the land office of the Bureau of Land Management for the State in which the claim is situated within ninety days after the date of its location: Provided further, That the claimant to any such mining location shall report annually to the Mining Supervisor of the Geological Survey the amount of lignite mined or stripped in the recovery of such valuable source material during each calendar year and tender payment to him of 10 cents per ton thereon. Any mineral patents issued hereunder shall be made subject to the recording and payment requirements of this section and shall contain a reservation to the United States of all Leasing Act minerals owned by the United States other than lignite containing valuable source material and lignite necessary to be stripped or mined in the recovery of such material. Mining claims located and mineral patents issued under the provisions of this chapter shall not include rights to lignite not containing valuable source material except to the extent it may be necessary to mine or strip such lignite in order to mine the source material and, with respect to lode claims, shall not include extralateral rights. For all purposes of this chapter “source material” and “lignite” shall have the meanings given in section
of this title.