25 C.F.R. § 151.3
Land not held in trust or restricted status may only be acquired for an individual Indian or a tribe in trust status when such acquisition is authorized by an act of Congress. No acquisition of land in trust status, including a transfer of land already held in trust or restricted status, shall be valid unless the acquisition is approved by the Secretary.
(a) Subject to the provisions contained in the acts of Congress which authorize land acquisitions, land may be acquired for a tribe in trust status:
(b) Subject to the provisions contained in the acts of Congress which authorize land acquisitions or holding land in trust or restricted status, land may be acquired for an individual Indian in trust status: