Per the IRS Instructions for Form 8924 Excise Tax on Certain Transfers of Qualifying Geothermal or Mineral Interests:

An eligible entity who subsequently transfers ownership or possession (by sale, exchange, or lease) of a qualifying mineral or geothermal interest must file Form 8924 for each transfer of an interest acquired, directly or indirectly:

• in a conservation sale in which the previous transferor excluded 25% of the qualifying gain, or
• transfer in which the previous transferor was relieved of liability for the Form 8924 tax

A 25% exclusion from gross income is allowed for long-term capital gain from certain conservation sales of qualifying mineral and geothermal interests located on eligible federal land. The sale must be to an eligible entity and occur after December 19, 2006. An excise tax may be imposed if an eligible entity fails to take steps consistent with the protection of conservation purposes. 

For details, including the geographical location of eligible federal land, see section 403 of Title IV, Division C, of the Tax Relief and Health Care Act of 2006.