Subject to valid existing rights, the minerals in public lands within the Copper River addition to the Chugach National Forest, are hereby withdrawn from location, entry, and patent under the United States mining laws. With respect to such areas, the Secretary, under such reasonable regulations as he deems appropriate, may permit the removal of non­leasable minerals from the lands in the manner prescribed by Reorganization Plan Numbered 3 of 1946 and section 520 of this title