The Secretary of the Interior is authorized to accept, as a donation, the relinquishment of all right, title, and interest of the Minnesota Chippewa Tribe and the Grand Portage Band of Chippewa Indians, Minnesota, in and to any of the lands described in section 450oo of this title which is now held in trust by the United States of America for the said tribe or band; the executive committee of the Minnesota Chippewa Tribe and the tribal council of the Grand Portage Band of Chippewa Indians, Minnesota, are authorized to execute such instruments of relinquishment in favor of the United States; and acceptance of the relinquishment by the Secretary shall operate as a transfer of custody, control and administration of such properties for administration and as a part of the Grand Portage National Monument: Provided, That upon the acceptance of any donated lands and interests therein the Secretary shall recognize, honor, and respect, in accordance with the terms thereof, any existing life assignments on such properties.