In all cases where it shall appear that a double allotment of land has been wrongfully or erroneously made by the Secretary of the Interior to any Indian by an assumed name or otherwise, or where a mistake has been made in the description of the land inserted in any patent, said Secretary is authorized and directed, during the time that the United States may hold the title to the land in trust for any such Indian, and for which a conditional patent may have been issued, to rectify and correct such mistakes and cancel any patent which may have been thus erroneously and wrongfully issued whenever in his opinion the same ought to be canceled for error in the issue thereof, and if possession of the original patent cannot be obtained, such cancellation shall be effective if made upon the records of the Bureau of Land Management; and no proclamation shall be necessary to open to settlement the lands to which such an erroneous allotment patent has been canceled, provided such lands would otherwise be subject to entry: And provided, That such lands shall not be open to settlement for sixty days after such cancellation: And further provided, That no conditional patent that has been or that may be executed in favor of any Indian allottee, excepting in cases hereinbefore authorized, and excepting in cases where the conditional patent is relinquished by the patentee or his heirs to take another allotment, shall be subject to cancellation without authority of Congress.